Document Detail

Gene therapy in animal models of autosomal dominant retinitis pigmentosa.
Jump to Full Text
MedLine Citation:
PMID:  23077406     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Gene therapy for dominantly inherited genetic disease is more difficult than gene-based therapy for recessive disorders, which can be treated with gene supplementation. Treatment of dominant disease may require gene supplementation partnered with suppression of the expression of the mutant gene either at the DNA level, by gene repair, or at the RNA level by RNA interference or transcriptional repression. In this review, we examine some of the gene delivery approaches used to treat animal models of autosomal dominant retinitis pigmentosa, focusing on those models associated with mutations in the gene for rhodopsin. We conclude that combinatorial approaches have the greatest promise for success.
Authors:
Brian Rossmiller; Haoyu Mao; Alfred S Lewin
Related Documents :
22969786 - Syntenic gene analysis between brassica rapa and other brassicaceae species.
24023886 - Evolutionary history of chordate pax genes: dynamics of change in a complex gene family.
23761406 - Targeted mutations in a highly conserved motif of nsp1beta protein impair interferon an...
25048176 - Identification and validation of quantitative real-time reverse transcription pcr refer...
19998056 - Pseudovirions as vehicles for the delivery of sirna.
11078556 - Adult with an interstitial deletion of chromosome 10 [del(10)(q25. 1q25.3)]: overlap wi...
Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't; Review     Date:  2012-10-06
Journal Detail:
Title:  Molecular vision     Volume:  18     ISSN:  1090-0535     ISO Abbreviation:  Mol. Vis.     Publication Date:  2012  
Date Detail:
Created Date:  2012-10-18     Completed Date:  2013-01-29     Revised Date:  2013-07-11    
Medline Journal Info:
Nlm Unique ID:  9605351     Medline TA:  Mol Vis     Country:  United States    
Other Details:
Languages:  eng     Pagination:  2479-96     Citation Subset:  IM    
Affiliation:
Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, FL 32611, USA.
Export Citation:
APA/MLA Format     Download EndNote     Download BibTex
MeSH Terms
Descriptor/Qualifier:
Adenoviridae / genetics
Animals
Disease Models, Animal
Gene Expression
Gene Transfer Techniques
Genes, Dominant
Genetic Therapy*
Genetic Vectors
Humans
Mice
Mutation
RNA Interference
Retinitis Pigmentosa / genetics*,  pathology,  therapy*
Rhodopsin / genetics*
Transcription, Genetic
Grant Support
ID/Acronym/Agency:
T32 EY007132/EY/NEI NIH HHS
Chemical
Reg. No./Substance:
9009-81-8/Rhodopsin
Comments/Corrections

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

Full Text
Journal Information
Journal ID (nlm-ta): Mol Vis
Journal ID (iso-abbrev): Mol. Vis
Journal ID (publisher-id): MV
ISSN: 1090-0535
Publisher: Molecular Vision
Article Information
Download PDF
Copyright © 2012 Molecular Vision.
open-access:
Received Day: 07 Month: 2 Year: 2012
Accepted Day: 04 Month: 10 Year: 2012
collection publication date: Year: 2012
Electronic publication date: Day: 06 Month: 10 Year: 2012
Volume: 18First Page: 2479 Last Page: 2496
PubMed Id: 23077406
ID: 3472929
Publisher Id: 260
Publisher Id: 2012MOLVIS0064

Gene therapy in animal models of autosomal dominant retinitis pigmentosa
Brian Rossmiller
Haoyu Mao
Alfred S. Lewin
Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, FL
Correspondence: Correspondence to: Alfred S. Lewin, Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, FL 32611; Phone: (352) 392-2617; FAX: (352) 273-6269; email: lewin@ufl.edu

Introduction

Vision is one of our most valuable senses, allowing for the detection of a single photon at night and high acuity perception in the day. Thus, retinal degenerative diseases can have a large impact on the quality of life. One such disease, retinitis pigmentosa (RP), is responsible for vision loss in 1 in 4,000 people worldwide [1]. As retinitis pigmentosa is initially a disease of the rod photoreceptors, vision loss is first perceived in the periphery and at night. In retinal images, dark pigmentary deposits termed “bone spicules” are observed [2,3]. As the rods continue to die, a paling of the optic nerve, spreading of pigmentary deposits, thinning of retinal vessels, and decrease in electroretinogram (ERG) response are observed [2,3]. Only after the loss of rods do the cones of the macula begin to die, causing near total blindness in afflicted individuals [2,3].

Retinitis pigmentosa is transmitted in autosomal dominant, autosomal recessive, sex-linked dominant, and sex-linked recessive modes of inheritance [3]. More than 30 genes and many different mutations, over 100 mutations in rhodopsin alone, have been associated with retinitis pigmentosa [4,5]. This genetic heterogeneity is associated with differences in rate and the extent of the degeneration. Accounting for 30%–40% of all cases of retinitis pigmentosa, autosomal dominant retinitis pigmentosa (ADRP) is the most common mode of inheritance and is the consequence of mutations in 24 known genes (Table 1) [6].

Currently, there are no effective treatments for ADRP. Nutritional therapy featuring vitamin A or vitamin A plus docosahexaenoic acid reduces the rate of degeneration in some patients [7]. Retinal analogs and pharmaceuticals functioning as chaperones show some progress in protecting the retina in animal models [8-11], and several antioxidant studies have shown lipophilic antioxidant taurousodeoxycholic acid (TUDCA), metallocomplex zinc desferrioxamine, N-acetyl-cysteine, and a mixture of antioxidants slow retinal degeneration in rodent rd1, rd10, and Q344ter models [12-15]. Although TUDCA is in clinical trials for other indications, it has not been tested in patients with retinal disease. A clinical trial is under way to test the efficacy of the protein deacetylase inhibitor valproic acid as a treatment for retinitis pigmentosa (Clinicaltrials). Valproic acid blocks T-type calcium channels and voltage-gated sodium channels [16], and is associated with significant side effects such as hearing loss and diarrhea. Therefore, the use of valproic acid as a treatment for retinitis pigmentosa has been questioned [17,18].

Rhodopsin mutations

Despite the range of genes responsible for ADRP, approximately 30% of ADRP arises from mutations in the rhodopsin gene [19], and therefore, we focus our attention on treatment of mutations affecting the rhodopsin gene (RHO in humans and Rho in mice). Numerous alterations in RHO cause ADRP (Figure 1; RetNet). These mutations do not localize to any specific regions of the protein, suggesting that functional and stable rhodopsin tolerates few amino acid changes. In fact, human rhodopsin protein differs at only 13 positions from the rabbit, 17 positions from the cat, and 18 positions from the mouse. The maximum sequence identity is ≥95% among all of these organisms. The consequences of particular mutations have been analyzed in transfected cells and animal models, sometimes with conflicting results [20]. Rods are also highly susceptible to changes in rhodopsin expression and translocation to the outer segment of photoreceptors, as rhodopsin composes greater than 90% of the outer segment protein [1,5,21-23].

ADRP mutations in rhodopsin have been placed into categories based on the mutations’ impact on protein folding and trafficking. Class I mutations result in normal rhodopsin folding, but the protein is not efficiently transported to the outer segment and has constitutive activation or an increased transducin activation rate [24]. Mutations affecting the C-terminus of rhodopsin, such as P347S, fall into this class. Class II mutations result in opsin that folds improperly, is retained in the endoplasmic reticulum (ER), and does not reconstitute with the 11-cis-retinal chromophore [24,25]. Rhodopsin folding and function can be affected by alterations in post-translation modification sites for glycosylation and disulfide bond formation [21,26]. Mutations affecting glycosylation at N2 and N15 and the disulfide bond between C110 and C187 are known causes of ADRP [26-28]. The T17M mutation results in rapid degeneration especially evident in the inferior retina. In some cases, degeneration from this class can be slowed with restricted light exposure [29,30]. The most common class II mutation in RHO in North America is P23H. P23H has been shown to be a target of the endoplasmic reticulum associated protein degradation (ERAD) effector valosin containing protein (VCP), a chaperone responsible for removing misfolded proteins from the ER for proteasomal degradation. In a rat model of ADRP, P23H rhodopsin stimulates the unfolded protein response [31,32]. Other mutations in RHO have been classified based on the stability of the protein or by the constitutive activation of the visual transduction pathway [24]. G90D, for example, leads to constitutive activation of transducin and causes congenital stationary night blindness.

Although ADRP mutations affect rod photoreceptors directly, they ultimately result in the death of cone photoreceptors and the loss of central vision. The mechanism by which RHO mutations cause cone cell death is not known, but several mechanisms have been proposed. These include (i) release of endotoxins, (ii) loss of rod trophic factors, (iii) loss of contact with the retinal pigment epithelium (RPE), (iv) activation of Müller glial cells, (v) increased oxygen toxicity, and/or increased metabolic load [5,33].

Animal models of autosomal dominant retinitis pigmentosa

The need for an effective therapy for ADRP has led to the creation of several mammalian models, and the use of these models has aided in the ongoing development of treatments focusing on neurotrophic factors, gene suppression, and gene replacement using viral or non-viral delivery. Due to the high degree of sequence homology in rhodopsin, mutations affecting human families can often be studied in animals. Because of their genetic malleability, mice and rats provide the most common models with rhodopsin mutations, including P23H, T17M, P347S, and S334X, present on transgenes, leading to retinal degeneration at varying rates. Chemical mutagenesis has led to the isolation of mouse lines bearing other mutations at the Rho locus, and Sakami et al. have produced a line bearing P23H Rho knocked into the endogenous locus [34,35]. The canine model of ADRP has provided insight into the risks of clinical illumination and the benefits of neurotrophic factors as potential treatments [36-39]. Porcine models of ADRP are also available. The size of the pig eye has lent it to testing of surgical treatments for ADRP such as retinal sheet transplants [40,41], but the large size of domestic swine make them difficult to work with as adults. Ross et al. have recently described an inbred line of miniature pigs bearing a human P23H transgene, and these may prove to be a tractable model [42].

Preclinical outcome measurements

Assessing the course of retinal degeneration and the success of treatment in rodent models of retinal disease employs some of the same technologies used to evaluate patients with retinitis pigmentosa: ERG, spectral domain optical coherence tomography (SD-OCT), and digital fundus imaging. In addition, light and electron microscopy on fixed tissue can be used to measure histopathology in animal models of ADRP.

Full-field ERG is typically used to assess retinal function in mouse and rat models of ADRP [22,43-46]. Because the retinas of these nocturnal rodents are rod-rich, dark-adapted (scotopic) ERG measurements are recorded, though light-adapted (photopic) ERG amplitudes may be affected in models of cone-rod dystrophy or late in the course of RP models. Results are typically presented as a-wave and b-wave maximum amplitudes as a function of flash intensity or as a-wave and b-wave amplitudes as a function of time at a single flash intensity. Because the full-field ERG recordings measure the response of the whole retina, local improvements in retinal function resulting from localized gene delivery may be difficult to accurately measure. Because ERG responses from both eyes are typically recorded simultaneously, a sham-treated contralateral eye can be used as the control for eyes treated with gene therapy.

Visual function can also be evaluated with behavioral analysis [47]. Although the Morris water maze can be used in dim light to measure the recovery of rod function after gene therapy [48], optokinetic (OptoMotry ™ CerebralMechanics, Lethbridge, AB, Canada) analysis has been used to measure visual acuity and contrast sensitivity in mice following gene therapy or cell transplantation therapy for retinal degeneration [49-51]. Since optokinetic measurements are performed in a lit room, they are primarily useful for measuring photopic function.

SD-OCT instruments have become widely used for assessing retinal degeneration in animal models in the past few years [49,52-55]. OCT is an interferometer-based imaging technology providing cross-sectional images of tissues transparent to infrared illumination. Instruments from Heidelberg Engineering or Bioptigen permit measurement of retinal thickness and of the thickness of the outer nuclear layer (ONL), which is often used to assess the survival of photoreceptor cells. The ONL is measured between highly reflective bands corresponding to the outer plexiform layer and the external limiting layer of the retina. SD-OCT permits the same cohort of animals to be followed longitudinally over the course of retinal degeneration and response to treatment. An added value of SD-OCT for preclinical gene therapy testing is that retinal detachment resulting from subretinal injections is readily detected, allowing these animals to be removed from the analysis.

Fundus imaging using film, and, more recently, digital imaging, has long been used to qualitatively monitor the course of retinal degeneration in patients and in research animals [56], and many of the mouse models of retinal degeneration were first recognized by fundus phenotype [57]. Some instruments used for SD-OCT are also capable of digital fundus imaging, and this is useful because both image modalities can be used in the same session of anesthesia. Unlike RP in humans, which is recognized by pigment deposition, mouse models of retinal degeneration are characterized by hypopigmented regions or spots. These regions may become larger during the course of retinal degeneration, and this progression may be arrested with successful gene therapy [58].

Although SD-OCT provides a measurement of ONL thickness, SD-OCT does so only in the central 30% of the retina, so that light microscopy is necessary to assess retinal structure in the periphery. In addition, the photoreceptor outer and inner segments are not well resolved by SD-OCT, so that the structure and thickness of these layers must be measured by microscopy and morphometry. Typically, eyes are fixed in glutaraldehyde and paraformaldehyde, dehydrated, and then embedded in plastic or in paraffin. Sections are made along the vertical meridian through the optic nerve head, and the thickness of the retinal layers is measured at regular distances from the optic nerve head in the superior and the inferior retina [59].

Therapeutic approach: neurotrophic factors

Neurotrophic factors (NTFs) play a large role in the development and maintenance central nervous system including the retina. One RPE cell, for instance, contacts 40 cones and rods and secretes NTFs both to the choroid and the photoreceptors [6]. Rods also produce a neurotrophic factor, rod derived cone viability factor (RdCVF), a thioredoxin-like protein lacking the oxoreductase activity, that influences cone survival [60,61]. The injection of RdCVF protein in P23H rats increased cone density 19% [62]. RdCVF also increased the survival of retinal explants from rd1 mice, an effect that could be blocked if RdCVF was immunodepleted [60]. Basic fibroblast growth factor (bFGF) comprises 22 types, but only bFGF2 has been shown to preserve photoreceptors in RCS rats for approximately two months [59]. Application of acidic fibroblast growth factor (aFGF) and bFGF in the subretinal space and the vitreous preserved ONL thickness in RCS rats with diminished RPE engulfment of photoreceptor outer segments [59]. Brain derived neurotrophic factor (BDNF) is expressed in many locations, including the brain, motor neurons, and the retina. When administered with other NTFs, including ciliary-derived neurotrophic factor (CNTF) and glial-derived neurotrophic factor (GDNF), BDNF increased photoreceptor preservation but caused the cells to revert to a more primitive state and reduced synthesis of rhodopsin [63,64]. Pigment epithelium derived factor (PEDF) is being studied for treatment of age-related macular degeneration and is known to be secreted by Müller glial cells and the RPE [65,66]. PEDF protects cells from glutamate toxicity and photoreceptors from excessive light. PEDF also slows degeneration in rd1 mice. Two of the more promising NTFs, CNTF, and GDNF, have been delivered by gene transfer. These factors could promote cell survival in different forms of ADRP and thus prolong useful vision and the window for therapeutic treatment.

Ciliary-derived neurotrophic factor

CNTF is a member of the interleukin-6 (IL-6) family of cytokines [67]. Its effectiveness is limited by a short half-life of 120–400 min, which rules out bolus injections [68]. Research has instead focused on a virally delivered CNTF gene or on mammalian cell lines encapsulated in an implantable device, NT-501 [67,68]. Mice transgenic for a dominant negative mutant (P216L) of rds/peripherin (Prph2) showed photoreceptor protection, but reduced ERG and decreased photoreceptor gene expression when injected with an adeno-associated virus (AAV) expressing a secreted form of CNTF in the subretinal space [69]. Loss of retinal function in Prph2 mutant mice was also reported by Schlichtenbrede et al. [70]. CNTF delivered as a protein was beneficial in maintaining ONL thickness in rats bearing the S334X mutation of rhodopsin [71]. CNTF was even shown to cause regeneration of cone outer segments (OS). Liang and colleagues, also working with rats transgenic for S334X or P23H RHO and Prph2rd2/rd2 mice, had similar results, showing a preservation of retinal histology months after the photoreceptors began to degenerate [72]. A reduction in the ERG a-wave and b-wave responses and an increase in Müller glial cell activation were also noted. Similar results were also seen, using NT-501 during human phase I clinical trials [67].

Glial-derived neurotrophic factor

The benefits of GDNF, a member of the transforming growth factor-beta family, to the central and peripheral nervous system have been studied for years: GDNF prolongs dopaminergic neuron and dorsal root ganglion cell survival. GDNF and its receptors are naturally expressed in the retina [40]. AAV expression of GDNF, driven by a CMV enhancer/chicken beta-actin (CBA) promoter, slowed photoreceptor degeneration and maintained ONL thickness and ERG response in rats bearing a transgene containing an ADRP RHO mutation (S334X) [73]. There are several possible mechanisms for the protective effects of GDNF. First, GDNF may elicit effects through increases in the levels of other NTFs, including BDNF and fibroblast growth factor-2 [74,75]. Second, GDNF could protect the metabolically active retina from reactive oxygen species, already shown in kainate injected pyramidal neurons [76]. Since GDNF receptors are expressed on Müller glial cells but not in photoreceptors, GDNF probably protects photoreceptors indirectly, acting through Müller cells [40].

Retinas of rats treated with AAV-GDNF had no indication of inflammatory cell infiltration, no decrease in retinal ganglion cells, and no statistical effect on ERG response after 1 year of expression [77]. GDNF not only increased retinal cell survival in vivo but also enhanced the survival of axotomized retinal ganglion cells and light response of transplanted retinal sheets [78,79]. Using the Prph2rd2/rd2 mouse model and the RCS rat model of retinal degeneration, Buch et al. showed that AAV-CBA-GDNF led to significant functional improvement based on ERG amplitudes and preservation of the ONL especially when combined with gene supplementation [80].

Neurotrophic factor disadvantages

Neurotrophic factors have the disadvantage of non-specific action. CNTF in the vitreous has demonstrated effects on retinal ganglion cells, Müller glial cells, astrocytes, and cone and rod photoreceptor cells [81-83]. CNTF has been shown to cause regeneration of cone outer segments but at the expense of rod function [83]. The knockdown of photoreceptor gene expression by CNTF is transient, and normal gene expression is detected when CNTF is no longer present. GDNF is also known to affect various cell types and possibly dose-dependent toxicity [84]. Application of neurotrophic factors as proteins could allow degeneration to be slowed until a long-term treatment has been administered.

Therapeutic approach: gene suppression and replacement

Although neurotrophic factors are aimed at preserving the photoreceptors without addressing the underlying mutation, more direct treatments including gene suppression or replacement are also being tested. Photoreceptors are sensitive to changes in rhodopsin levels, and overabundance of this protein can lead to retinal degeneration in mouse models [23,85]. In a transgenic mouse line, an excess of rhodopsin of only 23% was enough to cause RP-like retinal degeneration [86]. However, heterozygous null mutations in the mouse Rho gene result in a relatively normal retina at birth, with the length of rod outer segments approximately 60% that of Rho+/+ mice [87]. Similar to humans bearing heterozygous null mutations, Rho+/− show a reduced response to light flash. Rhodopsin mutations, acting in a dominant negative manner, may be treatable simply through a DNA cassette expressing wild-type RHO [88,89]. With a single injection of AAV-transferred normal rhodopsin, 90% of the ERG response in a- and b-wave amplitudes can be preserved in P23H mice compared with P23H mice without treatment (Figure 2) [89]. Other mutations, however, may require suppression of the mutant gene plus provision of a wild-type replacement gene, especially since overexpression of rhodopsin can be toxic [86]. The methods for suppressing endogenous expression begin at the either the RNA or DNA level. RNA interference or ribozymes achieve suppression at the RNA level while advances in zinc finger transcription factors and endonucleases and transcription activator-like (TAL) effector nucleases could correct the mutations at the DNA level.

Short interfering RNA

Therapeutic RNA interference (RNAi) employs three types of small RNA molecules: microRNA (miRNA), short hairpin RNA (shRNA), and short interfering RNA (siRNA). RNA interference with siRNA usually takes the form of direct treatment with modified double-stranded RNA (dsRNA) molecules, and requires repeated administration [90]. Therefore, this approach is not optimal for treating a chronic genetic disease, such as ADRP, though siRNAs are in clinical trials for age-related macular degeneration. Several groups are developing the use of RNAi for therapy for ADRP [91-97]. RNA interference was shown effective at knocking down the mutant mRNA and aiding in replacement with the wild-type gene [91,98] (Figure 3C).

Short hairpin RNA

Stably expressed shRNAs can be used to selectively suppress expression of mutant RHO if there is sufficient nucleotide difference with the wild-type gene. A more generally applicable approach, however, is to use RNAi to suppress the production endogenous rhodopsin and allow expression of a sequence-altered RHO gene that is resistant to the shRNA [97-99]. Millington-Ward and colleagues used a two-vector approach to treat a mouse model of ADRP: one virus to deliver the shRNA and one to deliver the replacement rhodopsin cRNA. They reported retention of an average b-wave response of 60 microvolts at 20 weeks post injection in treated eyes, compared to a baseline response in control treated eyes. We have used a single AAV delivery vector to deliver a RHO-specific shRNA under the control of the H1 promoter and a resistant Rho gene under the control of the mouse opsin proximal promoter. We observed sustained protection of the retina (80% of the normal ERG response) up to 9 months post treatment with the combination vector [46].

MicroRNA

The limitations of shRNAs and siRNA have led to the utilization of artificial miRNAs, which are derived from a natural pre-miRNA backbone such as miR-30 or miR-155 (101–106). Artificial miRNAs, avoid toxicity even when longer dsRNA regions are employed [100-102]. The natural antisense sequence, found in the miRNA, is removed and replaced with the siRNA sequence of interest [103]. Several structural properties are also necessary for potency: these include appropriate 3′ and 5′ flanking regions and a mismatch bulge at positions +1 and +11–12 [104]. Unlike shRNAs, artificial miRNAs allow for expression from Pol II promoters and from within natural or artificial introns [105,106]. This allows for greater temporal and spatial expression and incorporation of the artificial miRNA into an mRNA coding sequence. Multiple artificial miRNAs strung together may target several genes or multiple sites of the same gene [106,107]. Tested in cell and mouse lines, artificial miRNAs had fewer toxic effects and greater knockdown even when encoding the same siRNA as an equivalent shRNA when both were expressed from the U6 promoter [108-111]. Their effectiveness has also been studied in gene therapy and several disease models including HIV and cancer [111-114]. Mueller and colleagues recently demonstrated long-term prevention of the liver disease associated with a dominant mutation of α-1-antitrypsin using AAV delivery of a combination of concatenated artificial miRNAs and a resistant AAT cDNA [115].

RNA interference disadvantages

Overexpressed shRNAs have been shown to be toxic in the central nervous system and the liver [116]. This is possibly due to the saturation of exportin 5 and obstruction of the normal miRNA maturation process. These instances of shRNA-associated toxicity required a duplex region of greater than 20 bp, and shorter duplexes appear to be safe [117]. Ambati and colleagues have reported that administering siRNAs greater than 21 bp can actually lead to retinal degeneration in animal models, through Toll-like receptor-3 (TLR3), but TLR7 and TLR8 are more commonly accepted as mediating the innate immune response to dsRNA [118,119]. Other potential problems of shRNAs and artificial miRNAs arise from “off target” effects [100-102]. These can arise from base pairing to the coding region or within the 3′ UTR of an unintended target mRNA. Fifteen consecutive base pairs can stimulate the RNAi response (mRNA digestion), but as few as seven base pairs in the 3′ UTR can inhibit translation via the miRNA pathway [120,121]. Double-stranded RNA such as siRNAs can also kindle non-specific antiviral defense mechanisms, leading to cell death [122].

Ribozymes

Ribozyme technology for gene therapy arose in the early 1990s but has not advanced as rapidly as RNAi, and no commercial ribozyme has been marketed despite considerable effort. Nevertheless, small ribozymes such as hammerheads and hairpins are relatively easy to engineer and can be effective RNA knockdown agents in cells and in tissues (Figure 3D). The cleavage site for a hammerhead ribozyme has only moderate requirements, targeting NUX, where N is any nucleotide and X is any base except G [123-125]. There are differences in activity based on the target triplet, with AUC being the best followed by GUC and UUC [123-125]. Specificity is typically achieved through 12–15 base pairs with the target RNA [123,124]. The target for a hairpin ribozyme is BNGUC, where B is any nucleotide but adenosine. Because base pairing of the ribozyme is not assisted by a protein complex, experimental verification of the availability of targets within the folded RNA is important [126,127]. Since base pairing for either hammerheads or hairpins occurs in two distinct regions, there are no long contiguous regions of dsRNA in either ribozyme, minimizing their potential to stimulate the interferon pathway, though cleavage of an unintended RNA is still a problem. Regions of base pairing with the target mRNA are short, and it is relatively easy to use silent base changes to produce a cleavage-resistant mRNA: one mismatch is sometimes sufficient. The potential of ribozymes in treating ADRP has already been demonstrated in tissue culture and in animal models [91,92,96,128-130]. Ribozyme delivery with AAV led to reduced cleavage of a “hardened” (i.e., resistant) RHO transgene, preservation of ERG a- and b-wave amplitudes, and preservation of retinal structure based on histology.

Zinc finger transcription factors

Zinc fingers (ZFs) are DNA-binding domains present in many transcription factors. A single zinc finger domain is composed of 30 amino acids forming a ββα fold and recognizes a three to four base pair target [131,132]. The targets can overlap at the fourth position, as the fourth base is bound on the opposite DNA strand. To ensure specificity, at least 16–18 base pairs or six ZF modules are needed [132,133]. The zinc finger modules can then be linked to transcriptional regulatory domains, typically repressors, or to endonucleases.

ZFs linked to transcriptional regulators are termed zinc finger artificial transcription factors (ZF-ATFs; Figure 3A). With repressor domains, ZF-ATFs have been effective at suppressing endogenous rhodopsin expression from wild-type and mutant Rho in a P347S transgenic mouse model of ADRP [134]. Mussolino et al. used a Krüppel-associated box repressor domain to silence both alleles (mutant and wild-type) of Rho [135]. Although this method reduced the rate of photoreceptor loss, this technique should be coupled to a gene replacement for full therapeutic results. In this case, base changes in the promoter driving expression of RHO could be introduced to prevent recognition by the ZF-repressor. A convenient way to do this would be to use the RHO promoter from another species, e.g., mouse promoter driving human RHO.

Zinc finger nucleases

Zinc finger nucleases (ZFNs) provide a powerful tool capable of permanently and specifically altering the genomic DNA (Figure 3B). They are constructed using the DNA binding domains of two zinc finger modules dimerizing two subunits of the endonuclease domain of the nuclease FokI (or similar nuclease that cleaves downstream of its recognition domain) [133]. Each ZFN has a target sequence of about nine base pairs for a total recognition sequence of 18 bp. Cleavage of the target gene can lead to non-homologous end-joining to repair the chromosome or can lead to correction of the mutated sequence either through homologous recombination with the sister chromosome or through recombination with an ectopically administered DNA fragment with the corrected (wild-type) sequence. Recombination was increased to 17% using ZFN in a human P23H RHO expressing cell line [136].

Transcription activator-like effector nucleases

Transcription activator-like effector nucleases, or TALENs, are reportedly easier to engineer than ZFNs and may supplant them in the molecular toolkit of gene therapists [137-139]. TALENs are produced by bacteria of the genus Xanthomonas. These proteins contain as many as 30 tandem repeats of a 33- to 35-amino-acid-sequence motif, but a pair of residues in each repeat allows for single nucleotide specificity. As with ZFNs, engineered TALENs include a FokI endonuclease domain to introduce a double-strand break in the target gene. The use of TALENs in targeted gene suppression has already been demonstrated by Wood and et al. in C. elegans [140].

Zinc finger and TALEN disadvantages

Before ZFNs or TALENs are used in humans, the potential side effects need to be addressed. First, ZFNs are not completely specific and can induce toxic nonspecific cleavage [141]. The lack of specificity is largely due to one of the ZFNs binding and forming a homodimer. To overcome the formation of homodimers in ZFNs, small amino acid changes have been made with complementary changes on the other ZFN [142]. These changes destabilize homodimers while not affecting heterodimers. Another research group has attached destabilizing moieties, such as ubiquitin and FKBP12 [143]. These adducts allow control of protein levels and stability through the use of protease inhibitors nor a small ligand that stabilizes FKBP12 [141,143]. TALENs exhibited neither toxicity or non-specific mutagenesis in yeast grown on glucose medium, though no test of genotoxicity has been reported in mammalian cells [138]. Optimization of these techniques as well as increased screening and redesigning of ZFNs or TALENS before clinical use will likely provide a powerful tool for future retinal gene therapy [131,133].

Additional pathways

Additional pathways to increase retinal survival include modification of the mammalian target of rapamycin (mTOR) pathway and delivery of molecular chaperones. The mTOR is a protein kinase regulated by various upstream signaling pathways. The level mTOR is upregulated in cones in some RP models, suggesting starvation for amino acids and/or glucose [144,145]. Administration of insulin to rd1 mice led to a 50% increase in survival of cone photoreceptors [144].

Grp78 or Bip is an ER resident chaperone of the Hsp70 family. Although increased production of Bip is taken as a sign of ER stress, AAV delivery of Bip relieved ER stress and protected photoreceptors in a P23H RHO transgenic model of ADRP [32]. Misfolded rhodopsin can also be cleared from the endoplasmic reticulum by the so-called ERAD pathway and VCP, a molecular chaperone involved in that pathway, may have therapeutic potential for treating ADRP [146]. As an alternative to gene therapy, pharmacologic chaperones have great as treatment for diseases such as ADRP that are associated with misfolded proteins [12,147].

Therapeutic delivery
Viral mediated delivery

ADRP gene therapy has relied heavily on viral mediated delivery [148]. Lentivirus, adenovirus and AAV vectors have proven effective at delivering genes to the retina and RPE for ocular gene therapy [149]. Lentivirus delivers genes efficiently to the RPE, but AAV is probably the most versatile vector due to its wide range of host cells, DNA-based genome, no known pathogenicity, and many serotypes with differing tissue specificity [6,150-152]. Several methods have already been created for large-scale production of recombinant AAV (rAAV), and it is already in clinical trials for Leber congenital amaurosis (LCA) associated with mutations in RPE65 [153-158]. Due to these advantages, AAV has been used to develop treatments for many forms of retinal degeneration, including achromatopsia, retinoschisis, X-linked RP, recessive RP, and dominant RP [6,49,159-167]. AAV, however, can accommodate only a 4.7 kb insert. This limitation does not preclude most ADRP genes, neurotrophic factors, or small shRNA and miRNA [6]. Recombination between rAAV genomes in cells infected with two viruses can increase the delivery capacity of AAV, albeit at reduced efficiency [168]. For larger genes and promoters, lentiviral vectors can be used, as they offer the greater carrying capacity at 8 kb [1,148,169,170]. Helper-dependent adenoviral vectors have little remaining genetic material between the terminal repeats and therefore have a high capacity for inserts (about 35 kb) [48]. Vector production requires helper viruses that cannot be completely removed, so safety may be an issue. Another significant problem is that neither lentiviral vectors nor adenoviral vectors transduce photoreceptors efficiently, thus limiting the vectors’ utility for treating ADRP. Modifying the lentiviral pseudotype has not improved photoreceptor transduction substantially [171,172]. Deletion of the RGD sequence in the penton base of Ad5 improved infection of photoreceptors, but transduction efficiency lags behind that of AAV5 or AAV8 [173]. A recently developed “gutted” version of Sendai virus has been used for RPE transduction in mice and rats, and this RNA virus may be particularly useful for rapid onset delivery of siRNA [174].

Disadvantages of viral delivery

Despite the clear advantages to viral vectors, all viruses have size limitations, differing degrees of immune response mediated by Müller cell activation, and inflammation [149,170,175]. The humoral response to viral infection can prevent readministration of the same virus serotype following intravitreal injection [176]. In addition, neutralizing antibodies to AAV resulting from current or previous infections may attenuate gene transfer and should preclude participation in a clinical trial. Due to the size of the particles and the blood–retinal barrier, ocular injections are used for retinal gene transfer. However, in neonatal mice systemic injection of AAV9 transduces the retina, though systemic injections are likely to elicit an immune response and to transfer genes to the spleen, lung, and liver. For these reasons, alternatives to viral vectors are being investigated [177].

Non-viral delivery

Gene transfer to photoreceptors with liposomes has been inefficient in animal models. In contrast, DNA delivery using several types of nanoparticles has had more success. Nanoparticles may circumvent many of the disadvantages to viral vectors including limited carrying capacity and the immunogenic response to viral capsid proteins. Gene and siRNA delivery has been shown in intestinal cells with the use of orally administered nanoparticles [178]. Additional success with nanoparticles has been demonstrated in the lungs and central nervous system [1,179]. Delivery of the nanoparticles may be aided by gene gun or electrotransfer, which have proven useful for ciliary muscles and the cornea; however, the gene gun is not suitable for gene transfer to the retina [149]. Electroporation produced lasting expression of GDNF and GFP in the retina [149,180]. Additionally, electroporation has been effective in cultured retinal cells and retinal explants, and electroporation has been used in animals for plasmid and siRNA delivery to the retina [93,181,182].

CK30-PEG nanoparticles have shown promise in mouse models of ADRP [183,184]. CK30-PEG nanoparticles are composed of poly-L-lysine coated with polyethylene glycol (PEG) moieties [183,184]. Together, these neutralize the negative charge of DNA, allowing for DNA compaction. PEG groups prolong circulation by preventing protein attachment and slow DNA degradation [183]. The carrying capacity has been tested up to 20 kb, four times larger than AAV, and provided robust gene expression [183]. Moreover, the gene activation was within hours, while AAV requires a minimum of 2 days. The size is only 8–20 nm, allowing passage through the tight junctions in the retina [183]. Injections of nanoparticles containing wild-type rds/peripherin (Perph2) in Perph2+/− mice at postnatal day 5 mice led to protection of the retina as demonstrated by IRBP and opsin expression out to 15 months [183]. Using either the IRBP promoter or the chicken beta actin promoter to drive rds/peripherin expression, Perph2+/− mice showed increased ERG response and improved retinal structure [185]. Additional studies measured onset of luciferase and LacZ expression following retina and corneal nanoparticle delivery [186]. CK30-PEG showed no signs of an immunogenic response or of toxicity [1,187].

Disadvantages of non-viral delivery

Currently, nanoparticles have several disadvantages. Nanoparticles are typically degraded quickly in endosomes, and delivered genes may have a shorter duration of expression than viral vectors [186]. Long-term gene delivery has been reported using CK30-PEG nanoparticles [183-185], but these results must be replicated in other laboratories. Because the outer retina is not well perfused, nanoparticles may have a long residence time, and formulations containing gold or iron that may be suitable for gene delivery in larger organs may prove toxic in the retina [188]. In addition, some nanoparticles may induce light damage to the retina [189].

Future directions

The future of ocular gene therapy may not lie in any one treatment discussed above but in the combination of treatments. NTFs are effective at retarding photoreceptor loss, but the degeneration is only slowed, and a more permanent gene-directed treatment may be needed. NTFs could be used as an initial treatment to protect and slow photoreceptor loss. This approach would prove most useful in rapidly degenerating forms of ADRP. Second, a combination of ribozymes, miRNA, and/or shRNAs could be used to ensure sufficient suppression of the mutant allele. Third, advancements in ZFNs or TALENs to reduce toxic off-site cleavage will make these powerful tools for permanently correcting the mutant allele at the DNA level. This technology partnered with stem cell–based regenerative medicine may permit repair of a patient’s own stem cells for replacing defective photoreceptors or RPE.

The use of self-complementary AAV and capsid modifications will improve AAV-mediated gene delivery [161,190,191]. Gene therapy using self-complementary AAV permits delivery of double-stranded DNA to shorten the onset of gene expression and increases transduction efficiency [192-197]. Capsid modification of AAV has also yielded improvements in transduction [177,190,198,199]. Because phosphorylation of surface tyrosine residues leads to degradation of AAV particles after infection, mutating certain tyrosines to phenylalanine increases productive infection. Although AAV serotypes 5 and 8 have been the vectors of choice for photoreceptors, the modified AAV8 (Y733F) has increased transduction efficiency [6,190,191,200].

Finally, nanoparticles hold a great potential for treating not just the eyes but also the entire central nervous system, as these particles have the ability to pass through the blood/central nervous system barriers, have low immunogenicity, and allow for large insert sizes. Although further research is needed, advances in nanoparticles may allow for topical or systemically delivered gene therapies to the retina.


Acknowledgments

The authors acknowledge support by the Foundation Fighting Blindness, the Shaler Richardson endowment and by NIH grant T32 EY007132.


References
1. Sung CH,Chuang JZ. The cell biology of vision.J Cell BiolYear: 20101909536320855501
2. Hamel CP. Cone rod dystrophies.Orphanet J Rare DisYear: 20072717270046
3. Hamel C. Retinitis pigmentosa.Orphanet J Rare DisYear: 200614017032466
4. Rakoczy EP,Kiel C,McKeone R,Stricher F,Serrano L. Analysis of disease-linked rhodopsin mutations based on structure, function, and protein stability calculations.J Mol BiolYear: 201140558460621094163
5. Bramall AN,Wright AF,Jacobson SG,McInnes RR. The genomic, biochemical, and cellular responses of the retina in inherited photoreceptor degenerations and prospects for the treatment of these disorders.Annu Rev NeurosciYear: 2010334417220572772
6. Dinculescu A,Glushakova L,Min SH,Hauswirth WW. Adeno-associated virus-vectored gene therapy for retinal disease.Hum Gene TherYear: 2005166496315960597
7. Berson EL,Rosner B,Sandberg MA,Weigel-DiFranco C,Moser A,Brockhurst RJ,Hayes KC,Johnson CA,Anderson EJ,Gaudio AR,Willett WC,Schaefer EJ. Clinical trial of docosahexaenoic acid in patients with retinitis pigmentosa receiving vitamin A treatment.Arch OphthalmolYear: 2004122129730515364708
8. Krebs MP,Holden DC,Joshi P,Clark CL 3rd,Lee AH,Kaushal S. Molecular mechanisms of rhodopsin retinitis pigmentosa and the efficacy of pharmacological rescue.J Mol BiolYear: 201039510637819913029
9. Tam LC,Kiang AS,Campbell M,Keaney J,Farrar GJ,Humphries MM,Kenna PF,Humphries P. Prevention of autosomal dominant retinitis pigmentosa by systemic drug therapy targeting heat shock protein 90 (Hsp90).Hum Mol GenetYear: 20101944213620817636
10. Ohgane K,Dodo K,Hashimoto Y. Retinobenzaldehydes as proper-trafficking inducers of folding-defective P23H rhodopsin mutant responsible for retinitis pigmentosa.Bioorg Med ChemYear: 2010187022820805032
11. Maeda T,Maeda A,Leahy P,Saperstein DA,Palczewski K. Effects of long-term administration of 9-cis-retinyl acetate on visual function in mice.Invest Ophthalmol Vis SciYear: 2009503223318708622
12. Mendes HF,Zaccarini R,Cheetham ME. Pharmacological manipulation of rhodopsin retinitis pigmentosa.Adv Exp Med BiolYear: 20106643172320238031
13. Lee SY,Usui S,Zafar AB,Oveson BC,Jo YJ,Lu L,Masoudi S,Campochiaro PA. N-Acetylcysteine promotes long-term survival of cones in a model of retinitis pigmentosa.J Cell PhysiolYear: 20112261843921506115
14. Komeima K,Rogers BS,Campochiaro PA. Antioxidants slow photoreceptor cell death in mouse models of retinitis pigmentosa.J Cell PhysiolYear: 20072138091517520694
15. Obolensky A,Berenshtein E,Lederman M,Bulvik B,Alper-Pinus R,Yaul R,Deleon E,Chowers I,Chevion M,Banin E. Zinc-desferrioxamine attenuates retinal degeneration in the rd10 mouse model of retinitis pigmentosa.Free Radic Biol MedYear: 20115114829121824515
16. Löscher W. Basic pharmacology of valproate: a review after 35 years of clinical use for the treatment of epilepsy.CNS DrugsYear: 2002166699412269861
17. Sisk RA. Valproic acid treatment may be harmful in non-dominant forms of retinitis pigmentosa.Br J OphthalmolYear: 2012961154522581401
18. Sandberg MA,Rosner B,Weigel-DiFranco C,Berson EL. Lack of scientific rationale for use of valproic acid for retinitis pigmentosa.Br J OphthalmolYear: 20119574421131379
19. Roof DJ,Adamian M,Hayes A. Rhodopsin accumulation at abnormal sites in retinas of mice with a human P23H rhodopsin transgene.Invest Ophthalmol Vis SciYear: 1994354049627960587
20. Chen YF,Wang IJ,Lin LL,Chen MS. Examining rhodopsin retention in endoplasmic reticulum and intracellular localization in vitro and in vivo by using truncated rhodopsin fragments.J Cell BiochemYear: 20111125203021268073
21. Murray AR,Fliesler SJ,Al-Ubaidi MR. Rhodopsin: the functional significance of asn-linked glycosylation and other post-translational modifications.Ophthalmic GenetYear: 2009301092019941415
22. Frederick JM,Krasnoperova NV,Hoffmann K,Church-Kopish J,Ruther K,Howes K,Lem J,Baehr W. Mutant rhodopsin transgene expression on a null background.Invest Ophthalmol Vis SciYear: 2001428263311222546
23. Wen XH,Shen L,Brush RS,Michaud N,Al-Ubaidi MR,Gurevich VV,Hamm HE,Lem J,Dibenedetto E,Anderson RE,Makino CL. Overexpression of rhodopsin alters the structure and photoresponse of rod photoreceptors.Biophys JYear: 2009969395019186132
24. Mendes HF,van der Spuy J,Chapple JP,Cheetham ME. Mechanisms of cell death in rhodopsin retinitis pigmentosa: implications for therapy.Trends Mol MedYear: 2005111778515823756
25. Kang MJ,Ryoo HD. Suppression of retinal degeneration in Drosophila by stimulation of ER-associated degradation.Proc Natl Acad Sci USAYear: 200910617043819805114
26. Kaushal S,Ridge KD,Khorana HG. Structure and function in rhodopsin: the role of asparagine-linked glycosylation.Proc Natl Acad Sci USAYear: 199491402488171029
27. Sakami S,Maeda T,Bereta G,Okano K,Golczak M,Sumaroka A,Roman AJ,Cideciyan AV,Jacobson SG,Palczewski K. Probing mechanisms of photoreceptor degeneration in a new mouse model of the common form of autosomal dominant retinitis pigmentosa due to P23H opsin mutations.J Biol ChemYear: 2011286105516721224384
28. Kaushal S,Khorana HG. Structure and function in rhodopsin. 7. Point mutations associated with autosomal dominant retinitis pigmentosa.BiochemistryYear: 199433612188193125
29. Tam BM,Moritz OL. Dark rearing rescues P23H rhodopsin-induced retinal degeneration in a transgenic Xenopus laevis model of retinitis pigmentosa: a chromophore-dependent mechanism characterized by production of N-terminally truncated mutant rhodopsin.J NeurosciYear: 20072790435317715341
30. White DA,Fritz JJ,Hauswirth WW,Kaushal S,Lewin AS. Increased sensitivity to light-induced damage in a mouse model of autosomal dominant retinal disease.Invest Ophthalmol Vis SciYear: 20074819425117460245
31. Lin JH,Li H,Yasumura D,Cohen HR,Zhang C,Panning B,Shokat KM,Lavail MM,Walter P. IRE1 signaling affects cell fate during the unfolded protein response.ScienceYear: 2007318944917991856
32. Gorbatyuk MS, Knox T, LaVail MM, Gorbatyuk OS, Noorwez SM, Hauswirth WW, Lin JH, Muzyczka N, Lewin AS. Restoration of visual function in P23H rhodopsin transgenic rats by gene delivery of BiP/Grp78. Proceedings of the National Academy of Sciences of the United States of America.107:5961–6.
33. Fletcher EL. Mechanisms of photoreceptor death during retinal degeneration.Optom Vis SciYear: 2010872697520019644
34. Tam BM,Moritz OL. The role of rhodopsin glycosylation in protein folding, trafficking, and light-sensitive retinal degeneration.J NeurosciYear: 200929151455419955366
35. Liu H,Wang M,Xia CH,Du X,Flannery JG,Ridge KD,Beutler B,Gong X. Severe retinal degeneration caused by a novel rhodopsin mutation.Invest Ophthalmol Vis SciYear: 20105110596519741247
36. Zhu L,Jang GF,Jastrzebska B,Filipek S,Pearce-Kelling SE,Aguirre GD,Stenkamp RE,Acland GM,Palczewski K. A naturally occurring mutation of the opsin gene (T4R) in dogs affects glycosylation and stability of the G protein-coupled receptor.J Biol ChemYear: 2004279538283915459196
37. Komáromy AM,Acland GM,Aguirre GD. Operating in the dark: a night-vision system for surgery in retinas susceptible to light damage.Arch OphthalmolYear: 2008126714718474785
38. Zeiss CJ,Allore HG,Towle V,Tao W. CNTF induces dose-dependent alterations in retinal morphology in normal and rcd-1 canine retina.Exp Eye ResYear: 20068239540416143329
39. Cideciyan AV,Jacobson SG,Aleman TS,Gu D,Pearce-Kelling SE,Sumaroka A,Acland GM,Aguirre GD. In vivo dynamics of retinal injury and repair in the rhodopsin mutant dog model of human retinitis pigmentosa.Proc Natl Acad Sci USAYear: 20051025233815784735
40. Hauck SM,Kinkl N,Deeg CA,Swiatek-de Lange M,Schoffmann S,Ueffing M. GDNF family ligands trigger indirect neuroprotective signaling in retinal glial cells.Mol Cell BiolYear: 20062627465716537917
41. Ghosh F,Engelsberg K,English RV,Petters RM. Long-term neuroretinal full-thickness transplants in a large animal model of severe retinitis pigmentosa. Graefe's archive for clinical and experimental ophthalmologyAlbrecht Von Graefes Arch Klin Exp OphthalmolYear: 200724583546
42. Ross JW,Fernandez de Castro JP,Zhao J,Samuel M,Walters E,Rios C,Bray-Ward P,Jones BW,Marc RE,Wang W,Zhou L,Noel JM,McCall MA,DeMarco PJ,Prather RS,Kaplan HJ. Generation of an inbred miniature pig model of retinitis pigmentosa.Invest Ophthalmol Vis SciYear: 201253501722247487
43. Goto Y,Peachey NS,Ripps H,Naash MI. Functional abnormalities in transgenic mice expressing a mutant rhodopsin gene.Invest Ophthalmol Vis SciYear: 19953662717822160
44. Peachey NS,Ridder WH 3rd,Seeliger MW. Electrophysiologic assessment of the mouse visual system.Doc OphthalmolYear: 200711512517823836
45. Chadderton N,Millington-Ward S,Palfi A,O'Reilly M,Tuohy G,Humphries MM,Li T,Humphries P,Kenna PF,Farrar GJ. Improved retinal function in a mouse model of dominant retinitis pigmentosa following AAV-delivered gene therapy.Mol TherYear: 200917593919174761
46. Mao H,Gorbatyuk MS,Rossmiller B,Hauswirth WW,Lewin AS. Long-term rescue of retinal structure and function by rhodopsin RNA replacement with a single adeno-associated viral vector in P23H RHO transgenic mice.Hum Gene TherYear: 2012233566622289036
47. Prusky GT,Alam NM,Beekman S,Douglas RM. Rapid quantification of adult and developing mouse spatial vision using a virtual optomotor system.Invest Ophthalmol Vis SciYear: 2004454611615557474
48. Kumar-Singh R,Chamberlain JS. Encapsidated adenovirus minichromosomes allow delivery and expression of a 14 kb dystrophin cDNA to muscle cells.Hum Mol GenetYear: 19965913218817325
49. Pang JJ,Dai X,Boye SE,Barone I,Boye SL,Mao S,Everhart D,Dinculescu A,Liu L,Umino Y,Lei B,Chang B,Barlow R,Strettoi E,Hauswirth WW. Long-term retinal function and structure rescue using capsid mutant AAV8 vector in the rd10 mouse, a model of recessive retinitis pigmentosa.Mol TherYear: 2011192344221139570
50. Alexander JJ,Umino Y,Everhart D,Chang B,Min SH,Li Q,Timmers AM,Hawes NL,Pang JJ,Barlow RB,Hauswirth WW. Restoration of cone vision in a mouse model of achromatopsia.Nat MedYear: 200713685717515894
51. Pearson RA,Barber AC,Rizzi M,Hippert C,Xue T,West EL,Duran Y,Smith AJ,Chuang JZ,Azam SA,Luhmann UF,Benucci A,Sung CH,Bainbridge JW,Carandini M,Yau KW,Sowden JC,Ali RR. Restoration of vision after transplantation of photoreceptors.NatureYear: 20124859910322522934
52. Ruggeri M,Wehbe H,Jiao S,Gregori G,Jockovich ME,Hackam A,Duan Y,Puliafito CA. In vivo three-dimensional high-resolution imaging of rodent retina with spectral-domain optical coherence tomography.Invest Ophthalmol Vis SciYear: 20074818081417389515
53. Gabriele ML,Ishikawa H,Schuman JS,Bilonick RA,Kim J,Kagemann L,Wollstein G. Reproducibility of spectral-domain optical coherence tomography total retinal thickness measurements in mice.Invest Ophthalmol Vis SciYear: 20105165192320574022
54. Huber G,Beck SC,Grimm C,Sahaboglu-Tekgoz A,Paquet-Durand F,Wenzel A,Humphries P,Redmond TM,Seeliger MW,Fischer MD. Spectral domain optical coherence tomography in mouse models of retinal degeneration.Invest Ophthalmol Vis SciYear: 20095058889519661229
55. Wang R,Jiang C,Ma J,Young MJ. Monitoring morphological changes in the retina of rhodopsin−/− mice with spectral domain optical coherence tomography.Invest Ophthalmol Vis SciYear: 20125339677222618589
56. Hawes NL,Smith RS,Chang B,Davisson M,Heckenlively JR,John SW. Mouse fundus photography and angiography: a catalogue of normal and mutant phenotypes.Mol VisYear: 199952210493779
57. Chang B,Hawes NL,Hurd RE,Wang J,Howell D,Davisson MT,Roderick TH,Nusinowitz S,Heckenlively JR. Mouse models of ocular diseases.Vis NeurosciYear: 2005225879316332269
58. Pang JJ,Chang B,Kumar A,Nusinowitz S,Noorwez SM,Li J,Rani A,Foster TC,Chiodo VA,Doyle T,Li H,Malhotra R,Teusner JT,McDowell JH,Min SH,Li Q,Kaushal S,Hauswirth WW. Gene therapy restores vision-dependent behavior as well as retinal structure and function in a mouse model of RPE65 Leber congenital amaurosis.Mol TherYear: 2006135657216223604
59. Faktorovich EG,Steinberg RH,Yasumura D,Matthes MT,LaVail MM. Photoreceptor degeneration in inherited retinal dystrophy delayed by basic fibroblast growth factor.NatureYear: 19903478362168521
60. Léveillard T,Mohand-Said S,Lorentz O,Hicks D,Fintz AC,Clerin E,Simonutti M,Forster V,Cavusoglu N,Chalmel F,Dolle P,Poch O,Lambrou G,Sahel JA. Identification and characterization of rod-derived cone viability factor.Nat GenetYear: 200436755915220920
61. Léveillard T,Mohand-Said S,Fintz AC,Lambrou G,Sahel JA. The search for rod-dependent cone viability factors, secreted factors promoting cone viability.Novartis Found SympYear: 20042551172714750600
62. Yang Y,Mohand-Said S,Danan A,Simonutti M,Fontaine V,Clerin E,Picaud S,Léveillard T,Sahel JA. Functional cone rescue by RdCVF protein in a dominant model of retinitis pigmentosa.Mol TherYear: 2009177879519277021
63. Caffé AR,Soderpalm AK,Holmqvist I,van Veen T. A combination of CNTF and BDNF rescues rd photoreceptors but changes rod differentiation in the presence of RPE in retinal explants.Invest Ophthalmol Vis SciYear: 2001422758211133879
64. Yang PB,Seiler MJ,Aramant RB,Yan F,Mahoney MJ,Kitzes LM,Keirstead HS. Trophic factors GDNF and BDNF improve function of retinal sheet transplants.Exp Eye ResYear: 2010917273820804751
65. Tombran-Tink J,Shivaram SM,Chader GJ,Johnson LV,Bok D. Expression, secretion, and age-related downregulation of pigment epithelium-derived factor, a serpin with neurotrophic activity.J NeurosciYear: 199515499250037623128
66. Sugita Y,Becerra SP,Chader GJ,Schwartz JP. Pigment epithelium-derived factor (PEDF) has direct effects on the metabolism and proliferation of microglia and indirect effects on astrocytes.J Neurosci ResYear: 19974971089335258
67. Sieving PA,Caruso RC,Tao W,Coleman HR,Thompson DJ,Fullmer KR,Bush RA. Ciliary neurotrophic factor (CNTF) for human retinal degeneration: phase I trial of CNTF delivered by encapsulated cell intraocular implants.Proc Natl Acad Sci USAYear: 2006103389690116505355
68. Thanos CG,Bell WJ,O'Rourke P,Kauper K,Sherman S,Stabila P,Tao W. Sustained secretion of ciliary neurotrophic factor to the vitreous, using the encapsulated cell therapy-based NT-501 intraocular device.Tissue EngYear: 20041016172215684670
69. Bok D,Yasumura D,Matthes MT,Ruiz A,Duncan JL,Chappelow AV,Zolutukhin S,Hauswirth W,LaVail MM. Effects of adeno-associated virus-vectored ciliary neurotrophic factor on retinal structure and function in mice with a P216L rds/peripherin mutation.Exp Eye ResYear: 2002747193512126945
70. Schlichtenbrede FC,MacNeil A,Bainbridge JW,Tschernutter M,Thrasher AJ,Smith AJ,Ali RR. Intraocular gene delivery of ciliary neurotrophic factor results in significant loss of retinal function in normal mice and in the Prph2Rd2/Rd2 model of retinal degeneration.Gene TherYear: 200310523712621456
71. Li Y,Tao W,Luo L,Huang D,Kauper K,Stabila P,Lavail MM,Laties AM,Wen R. CNTF induces regeneration of cone outer segments in a rat model of retinal degeneration.PLoS ONEYear: 20105e949520209167
72. Liang FQ,Aleman TS,Dejneka NS,Dudus L,Fisher KJ,Maguire AM,Jacobson SG,Bennett J. Long-term protection of retinal structure but not function using RAAV.CNTF in animal models of retinitis pigmentosa.Mol TherYear: 200144617211708883
73. McGee Sanftner LH,Abel H,Hauswirth WW,Flannery JG. Glial cell line derived neurotrophic factor delays photoreceptor degeneration in a transgenic rat model of retinitis pigmentosa.Mol TherYear: 20014622911735347
74. Frasson M,Picaud S,Leveillard T,Simonutti M,Mohand-Said S,Dreyfus H,Hicks D,Sabel J. Glial cell line-derived neurotrophic factor induces histologic and functional protection of rod photoreceptors in the rd/rd mouse.Invest Ophthalmol Vis SciYear: 19994027243410509671
75. Koeberle PD,Ball AK. Effects of GDNF on retinal ganglion cell survival following axotomy.Vision ResYear: 1998381505159667015
76. Cheng H,Fu YS,Guo JW. Ability of GDNF to diminish free radical production leads to protection against kainate-induced excitotoxicity in hippocampus.HippocampusYear: 200414778615058485
77. Wu WC,Lai CC,Chen SL,Sun MH,Xiao X,Chen TL,Lin KK,Kuo SW,Tsao YP. Long-term safety of GDNF gene delivery in the retina.Curr Eye ResYear: 2005307152216109652
78. Yang PB,Seiler MJ,Aramant RB,Yan F,Mahoney MJ,Kitzes LM,Keirstead HS. Trophic factors GDNF and BDNF improve function of retinal sheet transplants.Exp Eye ResYear: 2010917273820804751
79. Yan Q,Wang J,Matheson CR,Urich JL. Glial cell line-derived neurotrophic factor (GDNF) promotes the survival of axotomized retinal ganglion cells in adult rats: comparison to and combination with brain-derived neurotrophic factor (BDNF).J NeurobiolYear: 1999383829010022580
80. Buch PK,MacLaren RE,Durán Y,Balaggan KS,MacNeil A,Schlichtenbrede FC,Smith AJ,Ali RR. In contrast to AAV-mediated Cntf expression, AAV-mediated Gdnf expression enhances gene replacement therapy in rodent models of retinal degeneration.Mol TherYear: 200614700916872907
81. Rodger J,Drummond ES,Hellstrom M,Robertson D,Harvey AR. Long-term gene therapy causes transgene-specific changes in the morphology of regenerating retinal ganglion cells.PLoS ONEYear: 20127e3106122347429
82. Xue W,Cojocaru RI,Dudley VJ,Brooks M,Swaroop A,Sarthy VP. Ciliary neurotrophic factor induces genes associated with inflammation and gliosis in the retina: a gene profiling study of flow-sorted, Muller cells.PLoS ONEYear: 20116e2032621637858
83. Wen R,Tao W,Li Y,Sieving PA. CNTF and retina.Prog Retin Eye ResYear: 2012311365122182585
84. Touchard E,Heiduschka P,Berdugo M,Kowalczuk L,Bigey P,Chahory S,Gandolphe C,Jeanny JC,Behar-Cohen F. Non-viral gene therapy for GDNF production in RCS rat: the crucial role of the plasmid dose.Gene TherYear: 2012198869821993171
85. Olsson JE,Gordon JW,Pawlyk BS,Roof D,Hayes A,Molday RS,Mukai S,Cowley GS,Berson EL,Dryja TP. Transgenic mice with a rhodopsin mutation (Pro23His): a mouse model of autosomal dominant retinitis pigmentosa.NeuronYear: 19929815301418997
86. Tan E,Wang Q,Quiambao AB,Xu X,Qtaishat NM,Peachey NS,Lem J,Fliesler SJ,Pepperberg DR,Naash MI,Al-Ubaidi MR. The relationship between opsin overexpression and photoreceptor degeneration.Invest Ophthalmol Vis SciYear: 20014258960011222515
87. Lem J,Krasnoperova NV,Calvert PD,Kosaras B,Cameron DA,Nicolo M,Makino CL,Sidman RL. Morphological, physiological, and biochemical changes in rhodopsin knockout mice.Proc Natl Acad Sci USAYear: 199996736419892703
88. Wilson JH,Wensel TG. The nature of dominant mutations of rhodopsin and implications for gene therapy.Mol NeurobiolYear: 2003281495814576453
89. Mao H,James T Jr,Schwein A,Shabashvili AE,Hauswirth WW,Gorbatyuk MS,Lewin AS. AAV delivery of wild-type rhodopsin preserves retinal function in a mouse model of autosomal dominant retinitis pigmentosa.Hum Gene TherYear: 2011225677521126223
90. Lares MR,Rossi JJ,Ouellet DL. RNAi and small interfering RNAs in human disease therapeutic applications.Trends BiotechnolYear: 201028570920833440
91. Gorbatyuk M,Justilien V,Liu J,Hauswirth WW,Lewin AS. Suppression of mouse rhodopsin expression in vivo by AAV mediated siRNA delivery.Vision ResYear: 2007471202817292939
92. Gorbatyuk M,Justilien V,Liu J,Hauswirth WW,Lewin AS. Preservation of photoreceptor morphology and function in P23H rats using an allele independent ribozyme.Exp Eye ResYear: 200784445217083931
93. Kiang AS,Palfi A,Ader M,Kenna PF,Millington-Ward S,Clark G,Kennan A,O'reilly M,Tam LC,Aherne A,McNally N,Humphries P,Farrar GJ. Toward a gene therapy for dominant disease: validation of an RNA interference-based mutation-independent approach.Mol TherYear: 2005125556115967729
94. Cashman SM,Binkley EA,Kumar-Singh R. Towards mutation-independent silencing of genes involved in retinal degeneration by RNA interference.Gene TherYear: 2005121223815877050
95. Smith AJ,Bainbridge JW,Ali RR. Prospects for retinal gene replacement therapy. Trends in geneticsTIGYear: 2009251566519303164
96. Sullivan JM,Pietras KM,Shin BJ,Misasi JN. Hammerhead ribozymes designed to cleave all human rod opsin mRNAs which cause autosomal dominant retinitis pigmentosa.Mol VisYear: 200281021311961505
97. Millington-Ward S,Chadderton N,O'Reilly M,Palfi A,Goldmann T,Kilty C,Humphries M,Wolfrum U,Bennett J,Humphries P,Kenna PF,Farrar GJ. Suppression and replacement gene therapy for autosomal dominant disease in a murine model of dominant retinitis pigmentosa.Mol TherYear: 201119642921224835
98. Li C,Xiao P,Gray SJ,Weinberg MS,Samulski RJ. Combination therapy utilizing shRNA knockdown and an optimized resistant transgene for rescue of diseases caused by misfolded proteins.Proc Natl Acad Sci USAYear: 2011108142586321844342
99. O'Reilly M,Palfi A,Chadderton N,Millington-Ward S,Ader M,Cronin T,Tuohy T,Auricchio A,Hildinger M,Tivnan A,McNally N,Humphries MM,Kiang AS,Humphries P,Kenna PF,Farrar GJ. RNA interference-mediated suppression and replacement of human rhodopsin in vivo.Am J Hum GenetYear: 2007811273517564969
100. Boudreau RL,Monteys AM,Davidson BL. Minimizing variables among hairpin-based RNAi vectors reveals the potency of shRNAs.RNAYear: 20081418344418697922
101. McBride JL,Boudreau RL,Harper SQ,Staber PD,Monteys AM,Martins I,Gilmore BL,Burstein H,Peluso RW,Polisky B,Carter BJ,Davidson BL. Artificial miRNAs mitigate shRNA-mediated toxicity in the brain: implications for the therapeutic development of RNAi.Proc Natl Acad Sci USAYear: 200810558687318398004
102. Beer S,Bellovin DI,Lee JS,Komatsubara K,Wang LS,Koh H,Börner K,Storm TA,Davis CR,Kay MA,Felsher DW,Grimm D. Low-level shRNA cytotoxicity can contribute to MYC-induced hepatocellular carcinoma in adult mice.Mol TherYear: 2010181617019844192
103. Zeng Y,Wagner EJ,Cullen BR. Both natural and designed micro RNAs can inhibit the expression of cognate mRNAs when expressed in human cells.Mol CellYear: 2002913273312086629
104. Sin O,Mabiala P,Liu Y,Sun Y,Hu T,Liu Q,Guo D. Gene silencing efficiency and INF-β induction effects of splicing miRNA 155-based artificial miRNA with pre-miRNA stem-loop structures.Biochem GenetYear: 2012501122122119863
105. Liu Z,Sall A,Yang D. MicroRNA: An emerging therapeutic target and intervention tool.Int J Mol SciYear: 200899789919325841
106. Chung KH,Hart CC,Al-Bassam S,Avery A,Taylor J,Patel PD,Vojtek AB,Turner DL. Polycistronic RNA polymerase II expression vectors for RNA interference based on BIC/miR-155.Nucleic Acids ResYear: 200634e5316614444
107. Chen SC,Stern P,Guo Z,Chen J. Expression of multiple artificial microRNAs from a chicken miRNA126-based lentiviral vector.PLoS ONEYear: 20116e2243721789258
108. Borel F,van Logtenstein R,Koornneef A,Maczuga P,Ritsema T,Petry H,van Deventer SJ,Jansen PL,Konstantinova P. In vivo knock-down of multidrug resistance transporters ABCC1 and ABCC2 by AAV-delivered shRNAs and by artificial miRNAs.J RNAi Gene Silencing.Year: 201174344221769296
109. Shan Z,Lin Q,Deng C,Li X,Huang W,Tan H,Fu Y,Yang M,Yu XY. An efficient method to enhance gene silencing by using precursor microRNA designed small hairpin RNAs.Mol Biol RepYear: 2009361483918758992
110. Furukawa N,Sakurai F,Katayama K,Seki N,Kawabata K,Mizuguchi H. Optimization of a microRNA expression vector for function analysis of microRNA.J Control ReleaseYear: 20111509410121146569
111. Boden D,Pusch O,Silbermann R,Lee F,Tucker L,Ramratnam B. Enhanced gene silencing of HIV-1 specific siRNA using microRNA designed hairpins.Nucleic Acids ResYear: 2004321154814966264
112. Hu T,Fu Q,Chen P,Ma L,Sin O,Guo D. Construction of an artificial MicroRNA expression vector for simultaneous inhibition of multiple genes in mammalian cells.Int J Mol SciYear: 20091021586819564946
113. Chen S,Ni M,Yu B,Lv T,Lu M,Gong F. Construction and identification of a human liver specific microRNA eukaryotic expression vector.Cell Mol ImmunolYear: 20074473718163960
114. Stegmeier F,Hu G,Rickles RJ,Hannon GJ,Elledge SJ. A lentiviral microRNA-based system for single-copy polymerase II-regulated RNA interference in mammalian cells.Proc Natl Acad Sci USAYear: 200510213212716141338
115. Mueller C,Tang Q,Gruntman A,Blomenkamp K,Teckman J,Song L,Zamore PD,Flotte TR. Sustained miRNA-mediated knockdown of mutant AAT with simultaneous augmentation of wild-type AAT has minimal effect on global liver miRNA profiles.Mol TherYear: 20122059060022252449
116. Martin JN,Wolken N,Brown T,Dauer WT,Ehrlich ME,Gonzalez-Alegre P. Lethal toxicity caused by expression of shRNA in the mouse striatum: implications for therapeutic design.Gene TherYear: 2011186667321368900
117. Grimm D,Streetz KL,Jopling CL,Storm TA,Pandey K,Davis CR,Marion P,Salazar F,Kay MA. Fatality in mice due to oversaturation of cellular microRNA/short hairpin RNA pathways.NatureYear: 20064415374116724069
118. Kleinman ME,Kaneko H,Cho WG,Dridi S,Fowler BJ,Blandford AD,Albuquerque RJ,Hirano Y,Terasaki H,Kondo M,Fujita T,Ambati BK,Tarallo V,Gelfand BD,Bogdanovich S,Baffi JZ,Ambati J. Short-interfering RNAs induce retinal degeneration via TLR3 and IRF3.Mol TherYear: 201220101821988875
119. Sioud M. RNA interference and innate immunity.Adv Drug Deliv RevYear: 2007591536317459518
120. Birmingham A,Anderson EM,Reynolds A,Ilsley-Tyree D,Leake D,Fedorov Y,Baskerville S,Maksimova E,Robinson K,Karpilow J,Marshall WS,Khvorova A. 3′ UTR seed matches, but not overall identity, are associated with RNAi off-targets.Nat MethodsYear: 2006319920416489337
121. Grimm D,Kay MA. Therapeutic application of RNAi: is mRNA targeting finally ready for prime time?J Clin InvestYear: 200711736334118060021
122. Robbins M,Judge A,Ambegia E,Choi C,Yaworski E,Palmer L,McClintock K,MacLachlan I. Misinterpreting the therapeutic effects of small interfering RNA caused by immune stimulation.Hum Gene TherYear: 200819991918713023
123. Hauswirth WW,Lewin AS. Ribozyme uses in retinal gene therapy.Prog Retin Eye ResYear: 20001968971011029552
124. Amarzguioui M,Prydz H. Hammerhead ribozyme design and application.Cell Mol Life SciYear: 19985411752029849614
125. Norris JS,Hoel B,Voeks D,Maggouta F,Dahm M,Pan W,Clawson G. Design and testing of ribozymes for cancer gene therapy.Adv Exp Med BiolYear: 200046529330110810634
126. Abdelmaksoud HE,Yau EH,Zuker M,Sullivan JM. Development of lead hammerhead ribozyme candidates against human rod opsin mRNA for retinal degeneration therapy.Exp Eye ResYear: 2009888597919094986
127. Sullivan JM,Yau EH,Taggart RT,Butler MC,Kolniak TA. Bottlenecks in development of retinal therapeutic post-transcriptional gene silencing agents.Vision ResYear: 2008484536917976683
128. Lewin AS,Drenser KA,Hauswirth WW,Nishikawa S,Yasumura D,Flannery JG,LaVail MM. Ribozyme rescue of photoreceptor cells in a transgenic rat model of autosomal dominant retinitis pigmentosa.Nat MedYear: 19984967719701253
129. Chakraborty D,Whalen P,Lewin AS,Naash MI. In vitro analysis of ribozyme-mediated knockdown of an ADRP associated rhodopsin mutation.Adv Exp Med BiolYear: 20086139710618188933
130. O'Neill B,Millington-Ward S,O'Reilly M,Tuohy G,Kiang AS,Kenna PF,Humphries P,Farrar GJ. Ribozyme-based therapeutic approaches for autosomal dominant retinitis pigmentosa.Invest Ophthalmol Vis SciYear: 2000412863910967039
131. Cornu TI,Cathomen T. Quantification of zinc finger nuclease-associated toxicity.Methods Mol BiolYear: 20106492374520680838
132. Mussolino C,Sanges D,Marrocco E,Bonetti C,Di Vicino U,Marigo V,Auricchio A,Meroni G,Surace EM. Zinc-finger-based transcriptional repression of rhodopsin in a model of dominant retinitis pigmentosa.EMBO Mol Med.Year: 201131182821268285
133. Cradick TJ,Ambrosini G,Iseli C,Bucher P,McCaffrey AP. ZFN-site searches genomes for zinc finger nuclease target sites and off-target sites.BMC BioinformaticsYear: 20111215221569489
134. Mussolino C,Sanges D,Marrocco E,Bonetti C,Di Vicino U,Marigo V,Auricchio A,Meroni G,Surace EM. Zinc-finger-based transcriptional repression of rhodopsin in a model of dominant retinitis pigmentosa.EMBO Mol Med.Year: 201131182821268285
135. Otteson DC,Lai H,Liu Y,Zack DJ. Zinc-finger domains of the transcriptional repressor KLF15 bind multiple sites in rhodopsin and IRBP promoters including the CRS-1 and G-rich repressor elements.BMC Mol BiolYear: 200561515963234
136. Greenwald DL,Cashman SM,Kumar-Singh R. Engineered zinc finger nuclease-mediated homologous recombination of the human rhodopsin gene.Invest Ophthalmol Vis SciYear: 20105163748020671268
137. Christian M,Cermak T,Doyle EL,Schmidt C,Zhang F,Hummel A,Bogdanove AJ,Voytas DF. Targeting DNA double-strand breaks with TAL effector nucleases.GeneticsYear: 20101867576120660643
138. Li T,Huang S,Zhao X,Wright DA,Carpenter S,Spalding MH,Weeks DP,Yang B. Modularly assembled designer TAL effector nucleases for targeted gene knockout and gene replacement in eukaryotes.Nucleic Acids ResYear: 20113963152521459844
139. Cermak T,Doyle EL,Christian M,Wang L,Zhang Y,Schmidt C,Baller JA,Somia NV,Bogdanove AJ,Voytas DF. Efficient design and assembly of custom TALEN and other TAL effector-based constructs for DNA targeting.Nucleic Acids ResYear: 201139e8221493687
140. Wood AJ,Lo TW,Zeitler B,Pickle CS,Ralston EJ,Lee AH,Amora R,Miller JC,Leung E,Meng X,Zhang L,Rebar EJ,Gregory PD,Urnov FD,Meyer BJ. Targeted genome editing across species using ZFNs and TALENs.ScienceYear: 201133330721700836
141. Carroll D. Progress and prospects: zinc-finger nucleases as gene therapy agents.Gene TherYear: 2008151463818784746
142. Miller JC,Holmes MC,Wang J,Guschin DY,Lee YL,Rupniewski I,Beausejour CM,Waite AJ,Wang NS,Kim KA,Gregory PD,Pabo CO,Rebar EJ. An improved zinc-finger nuclease architecture for highly specific genome editing.Nat BiotechnolYear: 2007257788517603475
143. Pruett-Miller SM,Reading DW,Porter SN,Porteus MH. Attenuation of zinc finger nuclease toxicity by small-molecule regulation of protein levels.PLoS GenetYear: 20095e100037619214211
144. Punzo C,Kornacker K,Cepko CL. Stimulation of the insulin/mTOR pathway delays cone death in a mouse model of retinitis pigmentosa.Nat NeurosciYear: 200912445219060896
145. Zhao C,Yasumura D,Li X,Matthes M,Lloyd M,Nielsen G,Ahern K,Snyder M,Bok D,Dunaief JL,LaVail MM,Vollrath D. mTOR-mediated dedifferentiation of the retinal pigment epithelium initiates photoreceptor degeneration in mice.J Clin InvestYear: 20111213698321135502
146. Griciuc A,Aron L,Piccoli G,Ueffing M. Clearance of Rhodopsin(P23H) aggregates requires the ERAD effector VCP.Biochim Biophys ActaYear: 201018034243420097236
147. Noorwez SM,Ostrov DA,McDowell JH,Krebs MP,Kaushal S. A high-throughput screening method for small-molecule pharmacologic chaperones of misfolded rhodopsin.Invest Ophthalmol Vis SciYear: 20084932243018378578
148. Han Z,Conley SM,Naash MI. AAV and compacted DNA nanoparticles for the treatment of retinal disorders: challenges and future prospects.Invest Ophthalmol Vis SciYear: 2011523051921558483
149. Bloquel C,Bourges JL,Touchard E,Berdugo M,BenEzra D,Behar-Cohen F. Non-viral ocular gene therapy: potential ocular therapeutic avenues.Adv Drug Deliv RevYear: 20065812244217095114
150. Rabinowitz JE,Rolling F,Li C,Conrath H,Xiao W,Xiao X,Samulski RJ. Cross-packaging of a single adeno-associated virus (AAV) type 2 vector genome into multiple AAV serotypes enables transduction with broad specificity.J VirolYear: 20027679180111752169
151. Doi K,Hargitai J,Kong J,Tsang SH,Wheatley M,Chang S,Goff S,Gouras P. Lentiviral transduction of green fluorescent protein in retinal epithelium: evidence of rejection.Vision ResYear: 200242551811853772
152. van Adel BA,Kostic C,Deglon N,Ball AK,Arsenijevic Y. Delivery of ciliary neurotrophic factor via lentiviral-mediated transfer protects axotomized retinal ganglion cells for an extended period of time.Hum Gene TherYear: 2003141031512614562
153. Muzyczka N. Use of adeno-associated virus as a general transduction vector for mammalian cells.Curr Top Microbiol ImmunolYear: 1992158971291316261
154. Grimm D,Kay MA,Kleinschmidt JA. Helper virus-free, optically controllable, and two-plasmid-based production of adeno-associated virus vectors of serotypes 1 to 6.Mol TherYear: 200378395012788658
155. Peden CS,Burger C,Muzyczka N,Mandel RJ. Circulating anti-wild-type adeno-associated virus type 2 (AAV2) antibodies inhibit recombinant AAV2 (rAAV2)-mediated, but not rAAV5-mediated, gene transfer in the brain.J VirolYear: 20047863445915163728
156. Burger C,Gorbatyuk OS,Velardo MJ,Peden CS,Williams P,Zolotukhin S,Reier PJ,Mandel RJ,Muzyczka N. Recombinant AAV viral vectors pseudotyped with viral capsids from serotypes 1, 2, and 5 display differential efficiency and cell tropism after delivery to different regions of the central nervous system.Mol TherYear: 2004103021715294177
157. Stieger K,Lorenz B. Gene therapy for vision loss–recent developments.Discov MedYear: 2010104253321122474
158. Cideciyan AV,Hauswirth WW,Aleman TS,Kaushal S,Schwartz SB,Boye SL,Windsor EA,Conlon TJ,Sumaroka A,Pang JJ,Roman AJ,Byrne BJ,Jacobson SG. Human RPE65 gene therapy for Leber congenital amaurosis: persistence of early visual improvements and safety at 1 year.Hum Gene TherYear: 200920999100419583479
159. Sun X,Pawlyk B,Xu X,Liu X,Bulgakov OV,Adamian M,Sandberg MA,Khani SC,Tan MH,Smith AJ,Ali RR,Li T. Gene therapy with a promoter targeting both rods and cones rescues retinal degeneration caused by AIPL1 mutations.Gene TherYear: 2010171173119710705
160. Dinculescu A,Estreicher J,Zenteno JC,Aleman TS,Schwartz SB,Huang WC,Roman AJ,Sumaroka A,Li Q,Deng WT,Min SH,Chiodo VA,Neeley A,Liu X,Shu X,Matias-Florentino M,Buentello-Volante B,Boye SL,Cideciyan AV,Hauswirth WW,Jacobson SG. Gene therapy for retinitis pigmentosa caused by MFRP mutations: human phenotype and preliminary proof of concept.Hum Gene TherYear: 2012233677622142163
161. Mussolino C,della Corte M,Rossi S,Viola F,Di Vicino U,Marrocco E,Neglia S,Doria M,Testa F,Giovannoni R,Crasta M,Giunti M,Villani E,Lavitrano M,Bacci ML,Ratiglia R,Simonelli F,Auricchio A,Surace EM. AAV-mediated photoreceptor transduction of the pig cone-enriched retina.Gene TherYear: 2011186374521412286
162. Bainbridge JW,Smith AJ,Barker SS,Robbie S,Henderson R,Balaggan K,Viswanathan A,Holder GE,Stockman A,Tyler N,Petersen-Jones S,Bhattacharya SS,Thrasher AJ,Fitzke FW,Carter BJ,Rubin GS,Moore AT,Ali RR. Effect of gene therapy on visual function in Leber's congenital amaurosis.N Engl J MedYear: 20083582231918441371
163. Cideciyan AV,Aleman TS,Boye SL,Schwartz SB,Kaushal S,Roman AJ,Pang JJ,Sumaroka A,Windsor EA,Wilson JM,Flotte TR,Fishman GA,Heon E,Stone EM,Byrne BJ,Jacobson SG,Hauswirth WW. Human gene therapy for RPE65 isomerase deficiency activates the retinoid cycle of vision but with slow rod kinetics.Proc Natl Acad Sci USAYear: 200810515112718809924
164. Cideciyan AV,Hauswirth WW,Aleman TS,Kaushal S,Schwartz SB,Boye SL,Windsor EA,Conlon TJ,Sumaroka A,Roman AJ,Byrne BJ,Jacobson SG. Vision 1 year after gene therapy for Leber's congenital amaurosis.N Engl J MedYear: 2009361725719675341
165. Dejneka NS,Surace EM,Aleman TS,Cideciyan AV,Lyubarsky A,Savchenko A,Redmond TM,Tang W,Wei Z,Rex TS,Glover E,Maguire AM,Pugh EN Jr,Jacobson SG,Bennett J. In utero gene therapy rescues vision in a murine model of congenital blindness.Mol TherYear: 20049182814759802
166. Komáromy AM,Alexander JJ,Cooper AE,Chiodo VA,Glushakova LG,Acland GM,Hauswirth WW,Aguirre GD. Targeting gene expression to cones with human cone opsin promoters in recombinant AAV.Gene TherYear: 20081510495518337838
167. Park TK,Wu Z,Kjellstrom S,Zeng Y,Bush RA,Sieving PA,Colosi P. Intravitreal delivery of AAV8 retinoschisin results in cell type-specific gene expression and retinal rescue in the Rs1-KO mouse.Gene TherYear: 2009169162619458650
168. Lai Y,Yue Y,Duan D. Evidence for the failure of adeno-associated virus serotype 5 to package a viral genome > or = 8.2 kb.Mol TherYear: 20101875919904238
169. Tosi J,Sancho-Pelluz J,Davis RJ,Hsu CW,Wolpert KV,Sengillo JD,Lin CS,Tsang SH. Lentivirus-mediated expression of cDNA and shRNA slows degeneration in retinitis pigmentosa.Exp Biol Med (Maywood)Year: 20112361211721885480
170. Kay MA. State-of-the-art gene-based therapies: the road ahead.Nat Rev GenetYear: 2011123162821468099
171. Auricchio A,Kobinger G,Anand V,Hildinger M,O'Connor E,Maguire AM,Wilson JM,Bennett J. Exchange of surface proteins impacts on viral vector cellular specificity and transduction characteristics: the retina as a model.Hum Mol GenetYear: 20011030758111751689
172. Balaggan KS,Binley K,Esapa M,Iqball S,Askham Z,Kan O,Tschernutter M,Bainbridge JW,Naylor S,Ali RR. Stable and efficient intraocular gene transfer using pseudotyped EIAV lentiviral vectors.J Gene MedYear: 200682758516299834
173. Sweigard JH,Cashman SM,Kumar-Singh R. Adenovirus vectors targeting distinct cell types in the retina.Invest Ophthalmol Vis SciYear: 20105122192819892875
174. Murakami Y,Ikeda Y,Yonemitsu Y,Tanaka S,Kondo H,Okano S,Kohno R,Miyazaki M,Inoue M,Hasegawa M,Ishibashi T,Sueishi K. Newly-developed Sendai virus vector for retinal gene transfer: reduction of innate immune response via deletion of all envelope-related genes.J Gene MedYear: 2008101657618074401
175. Lowenstein PR,Mandel RJ,Xiong WD,Kroeger K,Castro MG. Immune responses to adenovirus and adeno-associated vectors used for gene therapy of brain diseases: the role of immunological synapses in understanding the cell biology of neuroimmune interactions.Curr Gene TherYear: 200773476017979681
176. Li Q,Miller R,Han PY,Pang J,Dinculescu A,Chiodo V,Hauswirth WW. Intraocular route of AAV2 vector administration defines humoral immune response and therapeutic potential.Mol VisYear: 2008141760918836574
177. Dalkara D,Byrne LC,Lee T,Hoffmann NV,Schaffer DV,Flannery JG. Enhanced gene delivery to the neonatal retina through systemic administration of tyrosine-mutated AAV9.Gene TherYear: 2012191768122011645
178. Xu J,Ganesh S,Amiji M. Non-condensing polymeric nanoparticles for targeted gene and siRNA delivery.Int J PharmYear: 2012427213421621597
179. Yurek DM,Fletcher AM,Smith GM,Seroogy KB,Ziady AG,Molter J,Kowalczyk TH,Padegimas L,Cooper MJ. Long-term transgene expression in the central nervous system using DNA nanoparticles.Mol TherYear: 2009176415019223866
180. Ishikawa H,Takano M,Matsumoto N,Sawada H,Ide C,Mimura O,Dezawa M. Effect of GDNF gene transfer into axotomized retinal ganglion cells using in vivo electroporation with a contact lens-type electrode.Gene TherYear: 2005122899815616607
181. Matsuda T,Cepko CL. Electroporation and RNA interference in the rodent retina in vivo and in vitro.Proc Natl Acad Sci USAYear: 2004101162214603031
182. Sanuki R,Onishi A,Koike C,Muramatsu R,Watanabe S,Muranishi Y,Irie S,Uneo S,Koyasu T,Matsui R,Cherasse Y,Urade Y,Watanabe D,Kondo M,Yamashita T,Furukawa T. miR-124a is required for hippocampal axogenesis and retinal cone survival through Lhx2 suppression.Nat NeurosciYear: 20111411253421857657
183. Conley SM,Naash MI. Nanoparticles for retinal gene therapy.Prog Retin Eye ResYear: 2010293769720452457
184. Kimura T,Nibe Y,Funamoto S,Okada M,Furuzono T,Ono T,Yoshizawa H,Fujisato T,Nam K,Kishida A. Preparation of a Nanoscaled Poly(vinyl alcohol)/Hydroxyapatite/DNA Complex Using High Hydrostatic Pressure Technology for In Vitro and In Vivo Gene Delivery.J Drug DelivYear: 2011201196274321773048
185. Cai X,Nash Z,Conley SM,Fliesler SJ,Cooper MJ,Naash MI. A partial structural and functional rescue of a retinitis pigmentosa model with compacted DNA nanoparticles.PLoS ONEYear: 20094e529019390689
186. Binder C,Read SP,Cashman SM,Kumar-Singh R. Nuclear targeted delivery of macromolecules to retina and cornea.J Gene MedYear: 2011131587021344542
187. Ding XQ,Quiambao AB,Fitzgerald JB,Cooper MJ,Conley SM,Naash MI. Ocular delivery of compacted DNA-nanoparticles does not elicit toxicity in the mouse retina.PLoS ONEYear: 20094e741019823583
188. Jo DH,Lee TG,Kim JH. Nanotechnology and nanotoxicology in retinopathy.Int J Mol SciYear: 201112828830122174664
189. Wielgus AR,Roberts JE. Retinal Photodamage by Endogenous and Xenobiotic AgentsPhotochem PhotobiolYear: 2012xxxxxx22582903
190. Li M,Jayandharan GR,Li B,Ling C,Ma W,Srivastava A,Zhong L. High-efficiency transduction of fibroblasts and mesenchymal stem cells by tyrosine-mutant AAV2 vectors for their potential use in cellular therapy.Hum Gene TherYear: 20102115274320507237
191. Surace EM,Auricchio A. Versatility of AAV vectors for retinal gene transfer.Vision ResYear: 200848353917923143
192. McCarty DM. Self-complementary AAV vectors; advances and applications.Mol TherYear: 20081616485618682697
193. Pang J,Boye SE,Lei B,Boye SL,Everhart D,Ryals R,Umino Y,Rohrer B,Alexander J,Li J,Dai X,Li Q,Chang B,Barlow R,Hauswirth WW. Self-complementary AAV-mediated gene therapy restores cone function and prevents cone degeneration in two models of Rpe65 deficiency.Gene TherYear: 2010178152620237510
194. Kong F,Li W,Li X,Zheng Q,Dai X,Zhou X,Boye SL,Hauswirth WW,Qu J,Pang JJ. Self-complementary AAV5 vector facilitates quicker transgene expression in photoreceptor and retinal pigment epithelial cells of normal mouse.Exp Eye ResYear: 2010905465420138034
195. Koilkonda RD,Hauswirth WW,Guy J. Efficient expression of self-complementary AAV in ganglion cells of the ex vivo primate retina.Mol VisYear: 200915279680220019878
196. Gray SJ,Foti SB,Schwartz JW,Bachaboina L,Taylor-Blake B,Coleman J,Ehlers MD,Zylka MJ,McCown TJ,Samulski RJ. Optimizing promoters for recombinant adeno-associated virus-mediated gene expression in the peripheral and central nervous system using self-complementary vectors.Hum Gene TherYear: 20112211435321476867
197. Simons DL,Boye SL,Hauswirth WW,Wu SM. Gene therapy prevents photoreceptor death and preserves retinal function in a Bardet-Biedl syndrome mouse model.Proc Natl Acad Sci USAYear: 201110862768121444805
198. Zhong L,Li B,Mah CS,Govindasamy L,Agbandje-McKenna M,Cooper M,Herzog RW,Zolotukhin I,Warrington KH Jr,Weigel-Van Aken KA,Hobbs JA,Zolotukhin S,Muzyczka N,Srivastava A. Next generation of adeno-associated virus 2 vectors: point mutations in tyrosines lead to high-efficiency transduction at lower doses.Proc Natl Acad Sci USAYear: 200810578273218511559
199. Zhong L,Li B,Jayandharan G,Mah CS,Govindasamy L,Agbandje-McKenna M,Herzog RW,Weigel-Van Aken KA,Hobbs JA,Zolotukhin S,Muzyczka N,Srivastava A. Tyrosine-phosphorylation of AAV2 vectors and its consequences on viral intracellular trafficking and transgene expression.VirologyYear: 200838119420218834608
200. Vandenberghe LH,Bell P,Maguire AM,Cearley CN,Xiao R,Calcedo R,Wang L,Castle MJ,Maguire AC,Grant R,Wolfe JH,Wilson JM,Bennett J. Dosage thresholds for AAV2 and AAV8 photoreceptor gene therapy in monkey.Sci Transl MedYear: 2011388ra5421697530

Figures

[Figure ID: f1]
Figure 1 

Human rhodopsin illustrating sites of known mutations or deletions. This figure is based on an illustration at RetNet.



[Figure ID: f2]
Figure 2 

Improvement of electroretinography (ERG) response by single AAV injection of normal mouse rhodopsin cDNA (WT Rho) in P23H transgenic mice [89]. Bars represent the average of five scotopic ERG scans at 0 dB (2.6 cd (cd)-s/m2) a-wave response. A: and b-wave response. B: at 1 month and 6 months post injection. ERG amplitudes of 1 month uninjected P23H eyes were set as 100%. A: Compared with that of corresponding contralateral eyes, injection of AAV-Rho demonstrated a significant increase in a-wave amplitudes at both 1 month (122%) and 6 months (90%) time points. (*p<0.05, n=6). B: Compared with contralateral eyes, injection of WT Rho demonstrated the same significant increase in b-wave amplitudes as that of a-wave response at both 1 month (122%) and 6 months (90%) time points. (*p<0.05, ** p<0.005, n=6). Although injection injury can induce protective cytokines such as CNTF, this effect peaks within a few days of injection and is complete before the first measurements were made.



[Figure ID: f3]
Figure 3 

Gene suppression. A: Zinc finger artificial transcription factors (ZF-ATF) use suppressor transcription factors to silence gene transcription. B: Zinc finger nucleases (ZFN) causes a double-stranded break leading to correction of the mutation through recombination. C: miRNA and shRNA degrade the endogenous target transcript while sparing the introduced resistant mRNA (hardened) with an altered sequence. D: Ribozymes catalytically cleave the target transcript, but insertion of a guanosine at the target site dramatically reduces cleavage of the hardened target.



Tables
[TableWrap ID: t1] Table 1  Genes and loci associated with ADRP.
Protein Gene Location
Bestrophin-1
BEST1
11q13
Carbonic anhydrase IV
CA4, RP17
17q23.2
Cone-Rod Homeobox
CRX
19q13.32
Fascin homolog 2
FSCN2, RP30
17q25.3
Guanylate cyclase activator 1B
GUCA1B, RP48
6q21.1
Inosine monophosphate dehydrogenase 1
IMPDH1, RP10
7q32.1
kelch-like protein 7
KLHL7, RP42
7p15.3
Nuclear receptor subfamily 2 group E member 3
NR2E3

Neural retina leucine zipper
NRL, RP27
14q11.2
OSBP-related protein 1
ORP1, DCDC4A, RP1
8q12.1
pre-mRNA processing factor 3
PRPF3, RP18
1q21.2
pre-mRNA processing factor 31 homolog
PRPF31
19q13.342
pre-mRNA processing factor 6
PRPF6,rp60
20q13.33
pre-mRNA processing factor 8
PRPF8
17.13.3
Peripherin 2
PRPH2, RDS, RP7
6q21.1
Rhodopsin
RHO
3q22.1
Retinal outer segment membrane protein 1
ROM1
11q12.3
Retinitis pigmentosa 1 protein
RP1, L1
8q23.1
Unknown
RP63
6q23
Retinitis pigmentosa 9 protein
RP9
7p14.3
Retinal pigment epithelium-specific protein
RPE65, RP20
1p31.2
Semiphorin
SEMA4A, RP35
1q22
Proto-oncogene tyrosine-protein kinase MER
MERTK, RP33
2q11.2
Topoisomerase I-binding arginine/serine-rich protein TOPORS 9q21.1

Known gene and loci locations for ADRP causing mutations and associated proteins or loci names. References are at RetNet.



Article Categories:
  • Review


Previous Document:  A model for the easy assessment of pressure-dependent damage to retinal ganglion cells using cyan fl...
Next Document:  Participation of the histamine receptor encoded by the gene hclB (HCLB) in visual sensitivity contro...