Gene Therapy for Autosomal Dominant Disorders of Keratin

Dominant mutations that interfere with the assembly of keratin filaments cause painful and disfiguring epidermal diseases like pachyonychia congenita and epidermolysis bullosa simplex. Genetic therapies for such diseases must either suppress the production of the toxic proteins or correct the genetic defect in the chromosome. Because epidermal skin cells may be genetically modified in tissue culture or in situ, gene correction is a legitimate goal for keratin diseases. In addition, recent innovations, such as RNA interference in animals, make an RNA knockdown approach plausible in the near future. Although agents of RNA reduction (small interfering RNA, ribozymes, triplex oligonucleotides, or antisense DNA) can be delivered as nucleotides, the impermeability of the skin to large charged molecules presents a serious impediment. Using viral vectors to deliver genes for selective inhibitors of gene expression presents an attractive alternative for long-term treatment of genetic disease in the skin

Delivery of Antioxidant Enzyme Genes to Protect against Ischemia/Reperfusion-Induced Injury to Retinal Microvasculature

PURPOSE. Retinal ischemia/reperfusion (I/R) injury results in the generation of reactive oxygen species (ROS). The aim of this study was to investigate whether delivery of the manganese superoxide dismutase gene (SOD2) or the catalase gene (CAT) could rescue the retinal vascular damage induced by I/R in mice. METHODS. I/R injury to the retina was induced in mice by elevating intraocular pressure for 2 hours, and reperfusion was established immediately afterward. One eye of each mouse was pretreated with plasmids encoding manganese superoxide dismutase or catalase complexed with cationic liposomes and delivered by intravitreous injection 48 hours before initiation of the procedure. Superoxide ion, hydrogen peroxide, and 4-hydroxynonenal (4-HNE) protein modifications were measured by fluorescence staining, immunohistochemistry, and Western blot analysis 1 day after the I/R injury. At 7 days after injury, retinal vascular cell apoptosis and acellular capillaries were quantitated. RESULTS. Superoxide ion, hydrogen peroxide, and 4-HNE protein modifications increased at 24 hours after I/R injury. Administration of plasmids encoding SOD2 or CAT significantly reduced levels of superoxide ion, hydrogen peroxide, and 4-HNE. Retinal vascular cell apoptosis and acellular capillary numbers increased greatly by 7 days after the injury. Ϫ in retinal I/R injury was proven either directly by electron paramagnetic resonance or indirectly by showing diminished damage after administration of antioxidant drugs such as EGB 761 extracted from Ginkgo biloba, vitamin E, mannitol, catalase, and several other compounds. 2-6 The importance of ⅐ O 2 Ϫ is also indicated by the fact that a manganese superoxide dismutase mimetic and transgenic manganese superoxide dismutase inhibited I/R-induced retinal injury and diabetes-induced oxidative stress. 6 -8 Superoxide dismutase catalyzes the dismutation of ⅐ O 2 Ϫ to O 2 and the less reactive species, H 2 O 2 . Catalase is a potent scavenger of H 2 O 2 and provides another means of inhibiting oxidant stress. It prevents the formation of the more toxic hydroxyl radical (HO ⅐ ) resulting from the reaction of H 2 O 2 and ferrous ions. Thus, the production of catalase provides additional antioxidative protection during I/R. The delivery of SOD and catalase proteins has successfully prevented retinal I/R injury in rabbits. 8 A recent report showed that retinal ischemia and reperfusion cause capillary degeneration similar to diabetes. 6,10 demonstrated that transgenic mice that express elevated levels of manganese superoxide dismutase have higher antioxidant capacity and are protected from damage to the retinal vasculature (formation of acellular blood vessels) as a result of streptozotocin-induced diabetes. Berkowitz et al. 11 have recently shown that transgenic expression of SOD1, which encodes the cytoplasmic Cu/Zn superoxide dismutase, also protects retinal vasculature in the same diabetes model. However, overexpression of Cu/Zn superoxide dismutase caused retinal degeneration independent of diabetes. 11 The purpose of the present study was to assess the efficacy of manganese superoxide dismutase and catalase gene transfer on I/R-induced retinal capillary injury in mice. We investigated the effect of I/R injury on superoxide and hydrogen peroxide levels, apoptosis of retinal vascular cells, number of acellular capillaries, and levels of 4-hydroxynonenal (4-HNE) protein modifications. We also determined whether increased expression of superoxide dismutase and catalase protected against capillary injury. Our studies show that in this model there is an increase in capillary degeneration, superoxide radical and hydrogen peroxide production and 4-HNE in the retinas. Transfer of superoxide dismutase or catalase genes protected the retinal capillaries from ROS elevation and from I/R-induced injury

Comprehensive Approach to Analyzing Rare Genetic Variants

Recent findings suggest that rare variants play an important role in both monogenic and common diseases. Due to their rarity, however, it remains unclear how to appropriately analyze the association between such variants and disease. A common approach entails combining rare variants together based on a priori information and analyzing them as a single group. Here one must make some assumptions about what to aggregate. Instead, we propose two approaches to empirically determine the most efficient grouping of rare variants. The first considers multiple possible groupings using existing information. The second is an agnostic “step-up” approach that determines an optimal grouping of rare variants analytically and does not rely on prior information. To evaluate these approaches, we undertook a simulation study using sequence data from genes in the one-carbon folate metabolic pathway. Our results show that using prior information to group rare variants is advantageous only when information is quite accurate, but the step-up approach works well across a broad range of plausible scenarios. This agnostic approach allows one to efficiently analyze the association between rare variants and disease while avoiding assumptions required by other approaches for grouping such variants

Room temperature shipment does not affect the biological activity of pluripotent stem cell-derived retinal organoids

The generation of laminated and light responsive retinal organoids from induced pluripotent stem cells (iPSCs) provides a powerful tool for the study of retinal diseases and drug discovery and a robust platform for cell-based therapies. The aim of this study is to investigate whether retinal organoids can retain their morphological and functional characteristics upon storage at room temperature (RT) conditions and shipment by air using a commercially available container that maintains the environment at ambient temperature. Morphological analysis and measurements of neuroepithelial thickness revealed no differences between control, RT incubated and shipped organoids. Similarly immunohistochemical analysis showed no differences in cell type composition and position within the laminated retinal structure. All groups showed a similar response to light, suggesting that the biological function of retinal organoids was not affected by RT storage or shipment. These findings provide an advance in transport of ready-made retinal organoids, increasing their availability to many research and pharma labs worldwide and facilitating cross-collaborative research

Rapid, widespread transduction of the murine myocardium using self-complementary Adeno-associated virus

Adeno-associated virus (AAV) has shown great promise as a gene transfer vector. However, the incubation time needed to attain significant levels of gene expression is often too long for some clinical applications. Self-complementary AAV (scAAV) enters the cell as double stranded DNA, eliminating the step of second-strand synthesis, proven to be the rate-limiting step for gene expression of single-stranded AAV (ssAAV). The aim of this study was to compare the efficiency of these two types of AAV vectors in the murine myocardium. Four day old CD-1 mice were injected with either of the two AAV constructs, both expressing GFP and packaged into the AAV1 capsid. The animals were held for 4, 6, 11 or 21 days, after which they were euthanized and their hearts were excised. Serial sections of the myocardial tissue were used for real-time PCR quantification of AAV genome copies and for confocal microscopy. Although we observed similar numbers of AAV genomes at each of the different time points present in both the scAAV and the ssAAV infected hearts, microscopic analysis showed expression of GFP as early as 4 days in animals injected with the scAAV, while little or no expression was observed with the ssAAV constructs until day 11. AAV transduction of murine myocardium is therefore significantly enhanced using scAAV constructs

Systemic Injection of RPE65-Programmed Bone Marrow-Derived Cells Prevents Progression of Chronic Retinal Degeneration

Bone marrow stem and progenitor cells can differentiate into a range of non-hematopoietic cell types, including retinal pigment epithelium (RPE)-like cells. In this study, we programmed bone marrow-derived cells (BMDCs) ex vivo by inserting a stable RPE65 transgene using a lentiviral vector. We tested the efficacy of systemically administered RPE65-programmed BMDCs to prevent visual loss in the superoxide dismutase 2 knockdown (Sod2 KD) mouse model of age-related macular degeneration. Here, we present evidence that these RPE65-programmed BMDCs are recruited to the subretinal space, where they repopulate the RPE layer, preserve the photoreceptor layer, retain the thickness of the neural retina, reduce lipofuscin granule formation, and suppress microgliosis. Importantly, electroretinography and optokinetic response tests confirmed that visual function was significantly improved. Mice treated with non-modified BMDCs or BMDCs pre-programmed with LacZ did not exhibit significant improvement in visual deficit. RPE65-BMDC administration was most effective in early disease, when visual function and retinal morphology returned to near normal, and less effective in late-stage disease. This experimental paradigm offers a minimally invasive cellular therapy that can be given systemically overcoming the need for invasive ocular surgery and offering the potential to arrest progression in early AMD and other RPE-based diseases

Ribozyme Knockdown of the ␥-Subunit of Rod cGMP Phosphodiesterase Alters the ERG and Retinal Morphology in Wild-Type Mice

PURPOSE. To generate an animal model of retinal degeneration by using AAV-mediated ribozyme knockdown of the ␥-subunit of the rod cGMP phosphodiesterase (PDE␥) mRNA in the retina of wild-type mice. METHODS. Two hammerhead ribozymes, HRz35 and HRz42, were designed to target the PDE␥ gene in wild-type C57BL/6 mice. The efficiency and specificity of the ribozyme cleavage was tested in vitro against three different types of target: short synthetic RNA oligomers, longer targets transcribed from clones, and full-length mRNA from total retinal RNA extracts. After in vitro validation, the ribozymes were cloned and packaged in a recombinant adenoassociated virus (rAAV) containing a proximal 472-bp murine rod opsin promoter (MOPS) to drive ribozyme synthesis. Three-week-old wild-type C57BL/6 mice were injected subretinally with the vectors. For treated versus partner control retinas, responses to light were measured by full-field electroretinography (ERG), and retinal tissues were examined by light microscopy. Messenger RNA and protein levels of PDE␥ gene were monitored by reverse transcription-polymerase chain reaction (RT-PCR) and Western immunoblot assay. RESULTS. The ribozymes had comparable in vitro kinetic properties in multiple turnover kinetic analyses. Ribozyme HRz35 exhibited a K cat of 0.48 minute Ϫ1 and a K m of 980 nM, and HRz42 showed a K cat of 0.17 minute Ϫ1 and a K m of 971 nM. Both ribozymes cleaved at accessible sites in the RNA, as they digested long transcripts transcribed from clones and fulllength mRNA from total retinal RNA extracts in vitro. At increasing intervals after subretinal injection with either AAV ribozyme, a 30% to 90% reduction in a-and b-wave amplitudes was observed compared with those in contralateral control eyes that were not injected. Retinal tissue analysis showed that loss of the photoreceptor cells and PDE␥ mRNA and protein paralleled the ERG results. CONCLUSIONS. Ribozyme-mediated somatic knockdown of wildtype PDE␥ mRNA in vivo can efficiently reduce the target RNA leading to a loss in rod photoreceptors and in rod-mediated ERG amplitudes, thus generating an animal model of retinal degeneration resembling human RP in an essentially normal adult retina. This vector ribozyme technique should be applicable to other genes associated with RP and perhaps also to mRNAs of phototransduction genes not yet associated with RP. Application of this approach may be age and species independent. (Invest Ophthalmol Vis Sci. 2005;46: 3836 -3844

rAAV2/5 Gene-Targeting to Rods: Dose-Dependent Efficiency and Complications Associated With Different Promoters

A prerequisite for using corrective gene therapy to treat humans with inherited retinal degenerative diseases that primarily affect rods is to develop viral vectors that target specifically this population of photoreceptors. The delivery of a viral vector with photoreceptor tropism coupled with a rod-specific promoter is likely to be the safest and most efficient approach to target expression of the therapeutic gene to rods. Three promoters that included a fragment of the proximal mouse opsin promoter (mOP), the human G-protein-coupled receptor protein kinase 1 promoter (hGRK1), or the cytomegalovirus immediate early enhancer combined with the chicken β actin proximal promoter CBA were evaluated for their specificity and robustness in driving GFP reporter gene expression in rods, when packaged in a recombinant adeno-associated viral vector of serotype 2/5 (AAV2/5), and delivered via subretinal injection to the normal canine retina. Photoreceptor-specific promoters (mOP, hGRK1) targeted robust GFP expression to rods, whereas the ubiquitously expressed CBA promoter led to transgene expression in the retinal pigment epithelium, rods, cones and rare Müller, horizontal and ganglion cells. Late onset inflammation was frequently observed both clinically and histologically with all three constructs when the highest viral titers were injected. Cone loss in the injected regions of the retinas that received the highest titers occurred with both the hGRK1 and CBA promoters. Efficient and specific rod transduction, together with preservation of retinal structure was achieved with both mOP and hGRK1 promoters when viral titers in the order of 1011 vg ml–1 were used

Mutant NADH dehydrogenase subunit 4 gene delivery to mitochondria by targeting sequence-modified adeno-associated virus induces visual loss and optic atrophy in mice

Although mutated G11778A NADH ubiquinone oxidoreductase subunit 4 (ND4) mitochondrial DNA (mtDNA) is firmly linked to the blindness of Leber hereditary optic neuropathy (LHON), a bona fide animal model system with mutated mtDNA complex I subunits that would enable probing the pathogenesis of optic neuropathy and testing potential avenues for therapy has yet to be developed. The mutant human ND4 gene with a guanine to adenine transition at position 11778 with an attached FLAG epitope under control of the mitochondrial heavy strand promoter (HSP) was inserted into a modified self-complementary (sc) adeno-associated virus (AAV) backbone. The HSP-ND4FLAG was directed toward the mitochondria by adding the 23 amino acid cytochrome oxidase subunit 8 (COX8) presequence fused in frame to the N-terminus of green fluorescent protein (GFP) into the AAV2 capsid open reading frame. The packaged scAAV-HSP mutant ND4 was injected into the vitreous cavity of normal mice (OD). Contralateral eyes received scAAV-GFP (OS). Translocation and integration of mutant human ND4 in mouse mitochondria were assessed with PCR, reverse transcription-polymerase chain reaction (RT-PCR), sequencing, immunoblotting, and immunohistochemistry. Visual function was monitored with serial pattern electroretinography (PERG) and in vivo structure with spectral domain optical coherence tomography (OCT). Animals were euthanized at 1 year and processed for light and transmission electron microscopy. The PCR products of the mitochondrial and nuclear DNA extracted from infected retinas and optic nerves gave the expected 500 base pair bands. RT-PCR confirmed transcription of the mutant human ND4 DNA in mice. DNA sequencing confirmed that the PCR and RT-PCR products were mutant human ND4 (OD only). Immunoblotting revealed the expression of mutant ND4FLAG (OD only). Pattern electroretinograms showed a significant decrement in retinal ganglion cell function OD relative to OS at 1 month and 6 months after AAV injections. Spectral domain optical coherence tomography showed optic disc edema starting at 1 month post injection followed by optic nerve head atrophy with marked thinning of the inner retina at 1 year. Histopathology of optic nerve cross sections revealed reductions in the optic nerve diameters of OD versus OS where transmission electron microscopy revealed significant loss of optic nerve axons in mutant ND4 injected eyes where some remaining axons were still in various stages of irreversible degeneration with electron dense aggregation. Electron lucent mitochondria accumulated in swollen axons where fusion of mitochondria was also evident. Due to the UGA codon at amino acid 16, mutant G11778A ND4 was translated only in the mitochondria where its expression led to significant loss of visual function, loss of retinal ganglion cells, and optic nerve degeneration recapitulating the hallmarks of human LHON

Successful Arrest of Photoreceptor and Vision Loss Expands the Therapeutic Window of Retinal Gene Therapy to Later Stages of Disease

Inherited retinal degenerations cause progressive loss of photoreceptor neurons with eventual blindness. Corrective or neuroprotective gene therapies under development could be delivered at a predegeneration stage to prevent the onset of disease, as well as at intermediate-degeneration stages to slow the rate of progression. Most preclinical gene therapy successes to date have been as predegeneration interventions. In many animal models, as well as in human studies, to date, retinal gene therapy administered well after the onset of degeneration was not able to modify the rate of progression even when successfully reversing dysfunction. We evaluated consequences of gene therapy delivered at intermediate stages of disease in a canine model of X-linked retinitis pigmentosa (XLRP) caused by a mutation in the Retinitis Pigmentosa GTPase Regulator (RPGR) gene. Spatiotemporal natural history of disease was defined and therapeutic dose selected based on predegeneration results. Then interventions were timed at earlier and later phases of intermediate-stage disease, and photoreceptor degeneration monitored with noninvasive imaging, electrophysiological function, and visual behavior for more than 2 y. All parameters showed substantial and significant arrest of the progressive time course of disease with treatment, which resulted in long-term improved retinal function and visual behavior compared with control eyes. Histology confirmed that the human RPGR transgene was stably expressed in photoreceptors and associated with improved structural preservation of rods, cones, and ON bipolar cells together with correction of opsin mislocalization. These findings in a clinically relevant large animal model demonstrate the long-term efficacy of RPGR gene augmentation and substantially broaden the therapeutic window for intervention in patients with RPGR-XLRP