Age-related macular degeneration (AMD) is the leading cause of vision loss in the western world. Recent evidence suggests that RPE and photoreceptors have an interconnected metabolism and that mitochondrial damage in RPE is a trigger for degeneration in both RPE and photoreceptors in AMD. To test this hypothesis, this study was designed to induce mitochondrial damage in RPE in mice to determine whether this is sufficient to cause RPE and photoreceptor damage characteristic of AMD. In this study, we conditionally deleted the gene encoding the mitochondrial antioxidant enzyme, manganese superoxide dismutase (MnSOD encoded by Sod2 ) in the retinal pigment epithelium (RPE) of albino BALB/cJ mice. VMD2-Cre;Sod2 flox/flox BALB/cJ mice were housed in either 12-h dark, 12-h 200 lux white lighting (normal light), or 12-h dark, 12-h <10 lux red lighting (dim light). Electroretinography (ERG) and spectral-domain optical coherence tomography (SD-OCT) were performed to assess retinal function and morphology. Immunofluorescence was used to examine protein expression; quantitative RT-PCR was used to measure gene expression. Sod2 knockout (KO) mice had reduced RPE function with age and increased oxidative stress compared to wild type (WT) controls as expected by the cell-specific deletion of Sod2. This was associated with alterations in RPE morphology and the structure and function of RPE mitochondria. In addition, data show a compensatory increase in RPE glycolytic metabolism. The metabolic shift in RPE correlated with severe disruption of photoreceptor mitochondria including a reduction in TOMM20 expression, mitochondrial fragmentation, and reduced COXIII/β-actin levels. These findings demonstrate that mitochondrial oxidative stress can lead to RPE dysfunction and metabolic reprogramming of RPE. Secondary to these changes, photoreceptors also undergo metabolic stress with increased mitochondrial damage. These data are consistent with the hypothesis of a linked metabolism between RPE and photoreceptors and suggest a mechanism of retinal degeneration in dry AMD.

Viruses are widely used as a platform for the production of therapeutics. Vaccines containing live, dead and components of viruses, gene therapy vectors and oncolytic viruses are key examples of clinically-approved therapeutic uses for viruses. Despite this, the use of virus-derived proteins as natural sources for immune modulators remains in the early stages of development. Viruses have evolved complex, highly effective approaches for immune evasion. Originally developed for protection against host immune responses, viral immune-modulating proteins are extraordinarily potent, often functioning at picomolar concentrations. These complex viral intracellular parasites have “performed the R&D”, developing highly effective immune evasive strategies over millions of years. These proteins provide a new and natural source for immune-modulating therapeutics, similar in many ways to penicillin being developed from mold or streptokinase from bacteria. Virus-derived serine proteinase inhibitors (serpins), chemokine modulating proteins, complement control, inflammasome inhibition, growth factors (e.g., viral vascular endothelial growth factor) and cytokine mimics (e.g., viral interleukin 10) and/or inhibitors (e.g., tumor necrosis factor) have now been identified that target central immunological response pathways. We review here current development of virus-derived immune-modulating biologics with efficacy demonstrated in pre-clinical or clinical studies, focusing on pox and herpesviruses-derived immune-modulating therapeutics.

Chronic oxidative stress contributes to age related diseases including age related macular degeneration (AMD). Earlier work showed that the 5-hydroxy-tryptophan 1a (5HT1a) receptor agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) protects retinal pigment epithelium (RPE) cells from hydrogen peroxide treatment and mouse retinas from oxidative insults including light injury. In our current experiments, RPE derived cells subjected to mitochondrial oxidative stress were protected from cell death by the up-regulation of anti-oxidant enzymes and of the metal ion chaperon metallothionein. Differentiated RPE cells were resistant to oxidative stress, and the expression of genes for protective proteins was highly increased by oxidative stress plus drug treatment. In mice treated with 8-OH-DPAT, the same genes (MT1, HO1, NqO1, Cat, Sod1) were induced in the neural retina, but the drug did not affect the expression of Sod2, the gene for manganese superoxide dismutase. We used a mouse strain deleted for Sod2 in the RPE to accelerate age-related oxidative stress in the retina and to test the impact of 8-OH-DPAT on the photoreceptor and RPE degeneration developed in these mice. Treatment of mice with daily injections of the drug led to increased electroretinogram (ERG) amplitudes in dark-adapted mice and to a slight improvement in visual acuity. Most strikingly, in mice treated with a high dose of the drug (5 mg/kg) the structure of the RPE and Bruch's membrane and the normal architecture of photoreceptor outer segments were preserved. These results suggest that systemic treatment with this class of drugs may be useful in preventing geographic atrophy, the advanced form of dry AMD, which is characterized by RPE degeneration.

The eye is an immuno-privileged organ. However, certain diseases such as uveitis are intrinsically linked to inflammation. In several retinal degenerative diseases, there is a unique damage at the onset of the disease, but evidence suggests that chronic and low-grade inflammatory processes play an important role in their progression. Studies have identified similar signaling pathways and changes in resident immune cells within the retina among these diseases. Herein, we will discuss some of these studies and propose how understanding this inflammatory response could aid in the development of therapies.

PurposeTo investigate whether antioxidant gene therapy protects the structure and function of retina in a murine model of RPE atrophy, and to determine whether antioxidant gene therapy can prevent degeneration once it has begun.MethodsWe induced mitochondrial oxidative stress in RPE by conditional deletion of Sod2, the gene for manganese superoxide dismutase (MnSOD). These mice exhibited localized atrophy of the RPE and overlying photoreceptors. We restored Sod2 to the RPE of one eye using adeno-associated virus (AAV) by subretinal injection at an early (6 weeks) and a late stage (6 months), injecting the other eye with an AAV vector expressing green fluorescent protein (GFP). Retinal degeneration was monitored over a period of 9 months by electroretinography (ERG) and spectral-domain optical coherence tomography (SD-OCT). Immunohistochemical and histologic analyses were conducted to measure oxidative stress markers and to visualize retinal structure.ResultsOne month after delivery, the AAV-Sod2 injection resulted in production of MnSod in the RPE and negligible expression in the neural retina. Electroretinography and OCT suggested no adverse effects due to increased expression of MnSOD or subretinal injection. Decrease in the ERG response and thinning retinal thickness was significantly delayed in eyes with early treatment with the Sod2 vector, but treatment at 6 months of age did not affect the ERG decline seen in these mice.ConclusionsWe conclude that antioxidant gene therapy may be effective in preventing the detrimental effects of oxidative stress, but may not be beneficial once substantial tissue damage has occurred.

PurposeOxidative stress has been linked to several ocular diseases, initiating an inflammatory response that increases tissue injury. The Nrf2 transcription factor regulates expression of antioxidant genes and is tightly regulated by Kelch-Like ECH-Associated Protein 1 (Keap-1). We evaluate the antioxidant and anti-inflammatory properties of an adeno-associated virus (AAV) vector delivering an Nrf2-derived peptide that binds Keap-1.MethodsThe sequence of the Nrf2 peptide was fused to a cell-penetrating peptide (Tat-peptide) sequence (TatNrf2mer). The effects of lentiviral-delivered TatNrf2mer were studied in vitro. Transcript (quantitative [q] RT-PCR) and protein levels (ELISA and immunofluorescence) were quantified. Cell viability was measured by MTT and Cell Titer assays. The AAV vectors were packaged with the TatNrf2mer fused to secretable green fluorescent protein (GFP) under the control of the small chicken β actin promoter. The protective effects of this vector were evaluated in a model of RPE oxidative injury and in a mouse model of uveitis after intravitreal injection.ResultsExpression of TatNrf2mer peptide induced antioxidant gene expression, blocked IL-1β secretion, and protected cells from oxidative injury. In mice, TatNrf2mer expression partially protected photoreceptor function based on ERG responses and optical coherence tomography measurements in the sodium iodate (NaIO3) model. Furthermore, sGFP-TatNrf2mer expression decreased IL-1β and IL-6 in the NaIO3-treated mice, and resulted in a 54% decrease in the number of inflammatory cells in the vitreous body of the endotoxin-induced uveitis mouse model.ConclusionsThe intravitreally delivered AAV-TatNrf2mer has antioxidant and anti-inflammatory effects in widely-used models of ocular injury, suggesting it also could be useful in ocular diseases associated with oxidative stress and inflammasome activation.

PurposeThe I307N rhodopsin (Rho) mouse is a light-inducible model of autosomal dominant retinitis pigmentosa (adRP) that may be useful in testing therapies. We investigated the time-course of retinal changes of the I307N Rho mouse with spectral-domain optical coherence tomography (SD-OCT).MethodsSD-OCT was performed up to day 30 after light damage; electroretinography (ERG) was employed to evaluate photoreceptor function. We utilized ImageJ to analyze reflectivity of the retina. We used light and electron microscopy to assess retinal organization. We stained synaptophysin and zonula occludins-1 with immunohistochemistry to determine injury to the plexiform layers and retinal pigment epithelium (RPE). We performed lectin staining to evaluate retinal blood vessels.ResultsRetinal degeneration increased with longer exposures to light. An increase in retinal thickness was detected by SD-OCT on day 1 after light challenge followed by loss of the outer nuclear layer (ONL) by day 8. Degeneration was most severe in the nasal and inferior retina. Hyper-reflectivity on SD-OCT developed as early as 1 day after light exposure. Disorganization of the ONL, condensation of photoreceptor chromatin, disruption of the outer limiting membrane, and disarray of outer segments were associated with the hyper-reflectivity. Retraction of the outer plexiform synapses and resorption of the subretinal detachment contributed to retinal thinning. The RPE remained intact, whereas atrophied major retinal vessels were evident after light damage.ConclusionsOur time-course analysis of retinal degeneration in the I307N Rho mouse with SD-OCT and other outcome measures should enable the use of the mouse model in preclinical efficacy studies and mechanistic studies.

Inflammation of the retina is a contributing factor in ocular diseases such as uveitis, diabetic retinopathy, and age-related macular degeneration (AMD). The M013 immunomodulatory protein from myxoma virus has been shown to interfere with the proinflammatory signaling pathways involving both the NLRP3 inflammasome and NF-κB. We have developed and characterized an adeno-associated viral (AAV) vector that delivers a secretable and cell-penetrating form of the M013 protein (TatM013). The expressed TatM013 protein was secreted and blocked the endotoxin-induced secretion of interleukin (IL)-1β in monocyte-derived cells and the reactive aldehyde-induced secretion of IL-1β in retinal pigment epithelium cells. The local anti-inflammatory effects of AAV-delivered TatM013 were evaluated in an endotoxin-induced uveitis (EIU) mouse model after intravitreal injection of mice with an AAV2-based vector carrying either TatM013 fused to a secreted green fluorescent protein (GFP) tag (sGFP-TatM013) or GFP. Expression of the sGFP-TatM013 transgene was demonstrated by fluorescence funduscopy in living mice. In EIU, the number of infiltrating cells and the concentration of IL-1β in the vitreous body were significantly lower in the eyes injected with AAV-sGFP-TatM013 compared with the eyes injected with control AAV-GFP. These results suggest that a virus-derived inhibitor of the innate immune response, when delivered via AAV, could be a generalized therapy for various inflammatory diseases of the eye.