Elastin Layer in Bruch's Membrane as a Target for Immunization or Tolerization to Modulate Pathology in the Mouse Model of Smoke-Induced Ocular Injury.

Age-related macular degeneration (AMD) is associated with an overactive complement system and an increase in circulating antibodies. Our search for potential neoantigens that can trigger complement activation in disease has led us to investigate elastin. A loss of the elastin layer (EL) of Bruch's membrane (BrM) has been reported in aging and AMD together with an increase of serum elastin-derived peptides and α-elastin antibodies. In the mouse model of cigarette smoke exposure (CSE), damage in BrM, loss of the EL, and vision loss are dependent on complement activation. We have examined the hypothesis that CSE generates immunogenic elastin neoepitopes that trigger an increase in α-elastin IgG and IgM antibodies, which can then bind to the neoepitopes in the target cells or membranes, triggering complement activation. Specifically, we showed that immunization with elastin peptide oxidatively modified by cigarette smoke (ox-elastin) exacerbated ocular pathology and vision loss in CSE mice. In contrast, mice receiving peptide immunotherapy (PIT) with ox-elastin did not lose vision over the smoking period and exhibited a more preserved BrM. Immunization and PIT correlated with humoral immunity and complement activation and IgG/IgM deposition in the RPE/BrM/choroid. Finally, PIT modulated immune markers IFNγ and IL-4. The data further support the hypothesis that complement activation, triggered by immune complex formation in target tissues, plays a role in ocular damage in the CSE model. As PIT with ox-elastin peptides reduces damage, we discuss the possibility that AMD progression might be preventable.

Peptide-based immunotherapy against oxidized elastin ameliorates pathology in mouse model of smoke-induced ocular injury.

PURPOSE: Age-related macular degeneration (AMD), the leading cause of blindness in western populations, is associated with an overactive complement system, and an increase in circulating antibodies against certain epitopes, including elastin. As loss of the elastin layer of Bruch's membrane (BrM) has been reported in aging and AMD, we previously showed that immunization with elastin peptide oxidatively modified by cigarette smoke (ox-elastin), exacerbated ocular pathology in the smoke-induced ocular pathology (SIOP) model. Here we asked whether ox-elastin peptide-based immunotherapy (PIT) ameliorates damage. METHODS: C57BL/6J mice were injected with ox-elastin peptide at two doses via weekly subcutaneous administration, while exposed to cigarette smoke for 6 months. FcγR-/- and uninjected C57BL/6J mice served as controls. Retinal morphology was assessed by electron microscopy, and complement activation, antibody deposition and mechanisms of immunological tolerance were assessed by Western blotting and ELISA. RESULTS: Elimination of Fcγ receptors, preventing antigen/antibody-dependent cytotoxicity, protected against SIOP. Mice receiving PIT with low dose ox-elastin (LD-PIT) exhibited reduced humoral immunity, reduced complement activation and IgG/IgM deposition in the RPE/choroid, and largely a preserved BrM. While there is no direct evidence of ox-elastin pathogenicity, LD-PIT reduced IFNγ and increased IL-4 within RPE/choroid. High dose PIT was not protective. CONCLUSIONS: These data further support ox-elastin role in ocular damage in part via elastin-specific antibodies, and support the corollary that PIT with ox-elastin attenuates ocular pathology. Overall, damage is associated with complement activation, antibody-dependent cell-mediated cytotoxicity, and altered cytokine signature.

Conditional Loss of the Exocyst Component Exoc5 in Retinal Pigment Epithelium (RPE) Results in RPE Dysfunction, Photoreceptor Cell Degeneration, and Decreased Visual Function.

To characterize the mechanisms by which the highly conserved exocyst trafficking complex regulates eye physiology in zebrafish and mice, we focused on Exoc5 (also known as sec10), a central exocyst component. We analyzed both exoc5 zebrafish mutants and retinal pigmented epithelium (RPE)-specific Exoc5 knockout mice. Exoc5 is present in both the non-pigmented epithelium of the ciliary body and in the RPE. In this study, we set out to establish an animal model to study the mechanisms underlying the ocular phenotype and to establish if loss of visual function is induced by postnatal RPE Exoc5-deficiency. Exoc5-/- zebrafish had smaller eyes, with decreased number of melanocytes in the RPE and shorter photoreceptor outer segments. At 3.5 days post-fertilization, loss of rod and cone opsins were observed in zebrafish exoc5 mutants. Mice with postnatal RPE-specific loss of Exoc5 showed retinal thinning associated with compromised visual function and loss of visual photoreceptor pigments. Abnormal levels of RPE65 together with a reduced c-wave amplitude indicate a dysfunctional RPE. The retinal phenotype in Exoc5-/- mice was present at 20 weeks, but was more pronounced at 27 weeks, indicating progressive disease phenotype. We previously showed that the exocyst is necessary for photoreceptor ciliogenesis and retinal development. Here, we report that exoc5 mutant zebrafish and mice with RPE-specific genetic ablation of Exoc5 develop abnormal RPE pigmentation, resulting in retinal cell dystrophy and loss of visual pigments associated with compromised vision. Together, these data suggest that exocyst-mediated signaling in the RPE is required for RPE structure and function, indirectly leading to photoreceptor degeneration.

The exocyst is required for photoreceptor ciliogenesis and retinal development.

We previously have shown that the highly conserved eight-protein exocyst trafficking complex is required for ciliogenesis in kidney tubule cells. We hypothesized here that ciliogenic programs are conserved across organs and species. To determine whether renal primary ciliogenic programs are conserved in the eye, and to characterize the function and mechanisms by which the exocyst regulates eye development in zebrafish, we focused on exoc5, a central component of the exocyst complex, by analyzing both exoc5 zebrafish mutants, and photoreceptor-specific Exoc5 knock-out mice. Two separate exoc5 mutant zebrafish lines phenocopied exoc5 morphants and, strikingly, exhibited a virtual absence of photoreceptors, along with abnormal retinal development and cell death. Because the zebrafish mutant was a global knockout, we also observed defects in several ciliated organs, including the brain (hydrocephalus), heart (cardiac edema), and kidney (disordered and shorter cilia). exoc5 knockout increased phosphorylation of the regulatory protein Mob1, consistent with Hippo pathway activation. exoc5 mutant zebrafish rescue with human EXOC5 mRNA completely reversed the mutant phenotype. We accomplished photoreceptor-specific knockout of Exoc5 with our Exoc5 fl/fl mouse line crossed with a rhodopsin-Cre driver line. In Exoc5 photoreceptor-specific knock-out mice, the photoreceptor outer segment structure was severely impaired at 4 weeks of age, although a full-field electroretinogram indicated a visual response was still present. However, by 6 weeks, visual responses were eliminated. In summary, we show that ciliogenesis programs are conserved in the kidneys and eyes of zebrafish and mice and that the exocyst is necessary for photoreceptor ciliogenesis and retinal development, most likely by trafficking cilia and outer-segment proteins.

Inhibition of HDAC1 and 3 in the Presence of Systemic Inflammation Reduces Retinal Degeneration in a Model of Dry Age-Related Macular Degeneration.

Purpose: Previously, we identified increased retinal degeneration and cytokine response in a mouse model of dry age-related macular degeneration (AMD) in the presence of systemic inflammation from rheumatoid arthritis (RA). Histone deacetylases (HDACs) regulate cytokine production by reducing acetylation and are found to be dysregulated in inflammatory diseases, including RA and AMD. Therefore, this current study investigates the effect of HDAC inhibition on AMD progression in the presence of systemic inflammation. Methods: Collagen induced arthritis (CIA) was induced in C57BL6J mice, followed by sodium iodate (NaIO3)-induced retinal degeneration. Mice were treated with a selective HDAC class I inhibitor, MS-275, and retinal structure [optical coherence tomography (OCT)], function (electroretinography), and molecular changes quantitative real-time polymerase chain reaction (RT-qPCR, Western Blot) were assessed. Results: NaIO3 retinal damage was diminished in CIA mice treated with MS-275 (P ≤ 0.05). While no significant difference was observed in retinal pigment epithelium (RPE) function, a trend in increased c-wave amplitude was detected in CIA + NaIO3 mice treated with MS-275. Finally, we identified decreased Hdac1, Hdac3, and Cxcl9 expression in CIA + NaIO3 mouse RPE/choroid when treated with MS-275 (P ≤ 0.05). Conclusions: Our data demonstrate that HDAC inhibition can reduce the additive effect of NaIO3-induced retinal degeneration in the presence of systemic inflammation by CIA as measured by OCT analysis. In addition, HDAC inhibition in CIA + NaIO3 treated mice resulted in reduced cytokine production. These findings are highly innovative and provide additional support to the therapeutic potential of HDAC inhibitors for dry AMD treatment.

Evaluation of a connexin-based peptide for the treatment of age-related macular degeneration.

A critical target in age-related macular degeneration (AMD) is the retinal pigment epithelium (RPE), which forms the outer blood-retina barrier (BRB). RPE-barrier dysfunction might result from the disruption of intercellular tight junctions (TJs). A Connexin43 (Cx43)-based peptide, aCT1, has been shown to prevent VEGF-induced loss of transepithelial resistance, choroidal neovascularization (CNV) and RPE-cell damage via the stabilization of TJs. Here, we probe the relative efficacies of aCT1 alone, anti-VEGF alone, and aCT1 with anti-VEGF in treating AMD pathologies. aCT1 monotherapy administered as topical eye drops with and without a VEGF blocking antibody administered systemically was tested in a mouse model of laser-induced CNV. The CNV mouse is the standard neovascular AMD model, reproducing hallmarks of its pathology. CNV lesion size and fluid accumulation were assessed using optical coherence tomography. During the angiogenesis phase of CNV lesion development, single applications of anti-VEGF or aCT1 reduced lesion and fluid dome size equally. The combinatorial aCT1/anti-VEGF strategy demonstrated lack of additive effects in this model. These data suggest that TJ stabilization by aCT1 is effective in ameliorating RPE dysfunction in a model of AMD-like angiogenesis, and that this strategy is as effective as the current clinical standard of care, anti-VEGF therapy. Critically, aCT1 holds potential as a new neovascular AMD treatment that can be administered using eye drops, which is preferable to the intravitreal injections required for standard anti-VEGF therapy.

Dabigatran and Wet AMD, Results From Retinal Pigment Epithelial Cell Monolayers, the Mouse Model of Choroidal Neovascularization, and Patients From the Medicare Data Base.

Background: Age-related macular degeneration (AMD), the leading cause of irreversible blindness in elderly Caucasian populations, includes destruction of the blood-retina barrier (BRB) generated by the retinal pigment epithelium-Bruch's membrane complex (RPE/BrM), and complement activation. Thrombin is likely to get access to those structures upon BRB integrity loss. Here we investigate the potential role of thrombin in AMD by analyzing effects of the thrombin inhibitor dabigatran. Material and Methods: MarketScan data for patients aged ≥65 years on Medicare was used to identify association between AMD and dabigatran use. ARPE-19 cells grown as mature monolayers were analyzed for thrombin effects on barrier function (transepithelial resistance; TER) and downstream signaling (complement activation, expression of connective tissue growth factor (CTGF), and secretion of vascular endothelial growth factor (VEGF)). Laser-induced choroidal neovascularization (CNV) in mouse is used to test the identified downstream signaling. Results: Risk of new wet AMD diagnosis was reduced in dabigatran users. In RPE monolayers, thrombin reduced TER, generated unique complement C3 and C5 cleavage products, led to C3d/MAC deposition on cell surfaces, and increased CTGF expression via PAR1-receptor activation and VEGF secretion. CNV lesion repair was accelerated by dabigatran, and molecular readouts suggest that downstream effects of thrombin include CTGF and VEGF, but not the complement system. Conclusions: This study provides evidence of association between dabigatran use and reduced exudative AMD diagnosis. Based on the cell- and animal-based studies, we suggest that thrombin modulates wound healing and CTGF and VEGF expression, making dabigatran a potential novel treatment option in AMD.

Subretinal Rather Than Intravitreal Adeno-Associated Virus-Mediated Delivery of a Complement Alternative Pathway Inhibitor Is Effective in a Mouse Model of RPE Damage.

Purpose: The risk for age-related macular degeneration has been tied to an overactive complement system. Despite combined attempts by academia and industry to develop therapeutics that modulate the complement response, particularly in the late geographic atrophy form of advanced AMD, to date, there is no effective treatment. We have previously demonstrated that pathology in the smoke-induced ocular pathology (SIOP) model, a model with similarities to dry AMD, is dependent on activation of the alternative complement pathway and that a novel complement activation site targeted inhibitor of the alternative pathway can be delivered to ocular tissues via an adeno-associated virus (AAV). Methods: Two different viral vectors for specific tissue targeting were compared: AAV5-VMD2-CR2-fH for delivery to the retinal pigment epithelium (RPE) and AAV2YF-smCBA-CR2-fH for delivery to retinal ganglion cells (RGCs). Efficacy was tested in SIOP (6 months of passive smoke inhalation), assessing visual function (optokinetic responses), retinal structure (optical coherence tomography), and integrity of the RPE and Bruch's membrane (electron microscopy). Protein chemistry was used to assess complement activation, CR2-fH tissue distribution, and CR2-fH transport across the RPE. Results: RPE- but not RGC-mediated secretion of CR2-fH was found to reduce SIOP and complement activation in RPE/choroid. Bioavailability of CR2-fH in RPE/choroid could be confirmed only after AAV5-VMD2-CR2-fH treatment, and inefficient, adenosine triphosphate-dependent transport of CR2-fH across the RPE was identified. Conclusions: Our results suggest that complement inhibition for AMD-like pathology is required basal to the RPE and argues in favor of AAV vector delivery to the RPE or outside the blood-retina barrier.

Systemic Inflammation by Collagen-Induced Arthritis Affects the Progression of Age-Related Macular Degeneration Differently in Two Mouse Models of the Disease.

Purpose: Age-related macular degeneration (AMD) shares similar risk factors and inflammatory responses with rheumatoid arthritis (RA). Previously, we identified increased risk for dry AMD among patients with RA compared to control subjects, using retrospective data analysis. In this current study, we investigate the role of systemic inflammation triggered in a murine model of arthritis on choroidal neovascularization and retinal pigment epithelium (RPE) degeneration mouse models. Methods: Collagen-induced arthritis (CIA) was induced in C57BL/6J mice prior to laser-induced choroidal neovascularization (CNV; wet AMD model) or sodium iodate-induced retinal degeneration (NaIO3; dry AMD model). CNV lesion size and retinal thickness were quantified by optical coherence photography (OCT), visual function was analyzed using optokinetic response and electroretinography, RPE morphology was examined by immunohistochemistry, and inflammatory gene expression was analyzed by quantitative PCR. Results: CIA mice demonstrated decreased spatial acuity and contrast sensitivity, whereas no difference was observed in the RPE-generated c-wave. CNV lesion size was decreased in CIA mice. NaIO3 decreased c-wave amplitude, as well as retinal thickness, which was augmented by CIA. NaIO3 treatment resulted in loss of normal RPE hexagonal shape, which was further aggravated by CIA. Increased Cxcl9 expression was observed in the presence of CIA and CIA combined with AMD. Disease severity differences were observed between sexes. Conclusions: Our data suggest systemic inflammation by CIA results in increased pathology in a dry AMD model, whereas it reduces lesions in a wet AMD model. These findings highlight the need for additional investigation into the role of secondary inflammation and sex-based differences on AMD.

Inhibition of the alternative complement pathway accelerates repair processes in the murine model of choroidal neovascularization.

Age-related macular degeneration (AMD) is the leading cause of blindness in the US. Polymorphisms in complement components are associated with increased AMD risk, and it has been hypothesized that an overactive complement system is partially responsible for AMD pathology. Choroidal neovascularization (CNV) has two phases, injury/angiogenesis and repair/fibrosis. Complement activation has been shown to be involved in the angiogenesis phase of murine CNV, but has not been investigated during repair. Anaphylatoxin (C3a and C5a) signaling in particular has been shown to be involved in both tissue injury and repair in other models. CNV was triggered by laser-induced photocoagulation in C57BL/6 J mice, and lesion sizes measured by optical coherence tomography. Alternative pathway (AP) activation or C3a-receptor (C3aR) and C5a-receptor (C5aR) engagement was inhibited during the repair phase only of CNV with the AP-inhibitor CR2-fH, a C3aR antagonist (N2-[(2,2-diphenylethoxy)acetyl]-l-arginine, TFA), or a C5a blocking antibody (CLS026), respectively. Repair after CNV was also investigated in C3aR/C5aR double knockout mice. CR2-fH treatment normalized anaphylatoxin levels in the eye and accelerated regression of CNV lesions. In contrast, blockade of anaphylatoxin-receptor signaling pharmacologically or genetically did not significantly alter the course of lesion repair. These results suggest that continued complement activation prevents fibrotic scar resolution, and emphasizes the importance of reducing anaphylatoxins to homeostatic levels. This duality of complement, playing a role in injury and repair, will need to be considered when selecting a complement inhibitory strategy for AMD.

Delivery of CR2-fH Using AAV Vector Therapy as Treatment Strategy in the Mouse Model of Choroidal Neovascularization.

Complement activation plays a significant role in age-related macular degeneration (AMD) pathogenesis, and polymorphisms interfering with factor H (fH) function, a complement alternative pathway (AP) inhibitor, are associated with increased AMD risk. We have previously validated an AP inhibitor, a fusion protein consisting of a complement receptor 2 fragment linked to the inhibitory domain of fH (CR2-fH) as an efficacious treatment for choroidal neovascularization (CNV) when delivered intravenously. Here we tested an alternative approach of AAV-mediated delivery (AAV5-VMD2-CR2-fH or AAV5-VMD2-mCherry) using subretinal delivery in C57BL/6J mice. Secretion of CR2-fH was confirmed in polarized retinal pigment epithelium (RPE) cells. A safe concentration of AAV5-VMD2-CR2-fH was identified using electroretinography, optical coherence tomography (OCT), RPE morphology, and antibody profiling. One month after gene delivery, CNV was induced using argon laser photocoagulation. OCT assessment demonstrated reduced CNV with AAV5-VMD2-CR2-fH administration. Bioavailability studies revealed that gene-therapy delivered similar levels of CR2-fH to the RPE/choroid as treatment by intravenous injections, and C3a ELISA verified reduced CNV-associated ocular C3a production. These results contribute to existing data illustrating the importance of the AP of complement in CNV development and its potential role in AMD treatment. Demonstration of AAV-vector efficacy opens new avenues for the development of treatment strategies.

Recombinant Manganese Peroxidase Reduces A2E Burden in Age-Related and Stargardt's Macular Degeneration Models.

Macular degeneration is hallmarked by retinal accumulation of toxic retinoid species (e.g., A2E) for which there is no endogenous mechanism to eliminate it. This ultimately results in progressive dysfunction and loss of vision either in advanced age for genetically normal patients (age-related macular degeneration) or in adolescence for those with inherited genetic mutations (Stargardt's disease). In this article, we present a proof-of-concept study for an enzyme-based therapy to remove these retinoids, modeled on traditional enzyme replacement therapy. Recombinant manganese peroxidase (rMnP) is produced in Pichia pastoris. In vitro, we demonstrate that rMnP breaks down A2E and other lipofuscin fluorophores with limited cellular toxicity, and as this enzyme is mannosylated, it can be taken up into cells through mannose receptor-dependent endocytosis. In vivo, we demonstrate that rMnP can significantly reduce the A2E burden when administered by intravitreal injections. Together, these data provide encouraging results toward the development of an enzyme-based therapy for macular degeneration and indicate the need for additional work to characterize the molecular mechanism of A2E breakdown and to improve the pharmacological parameters of the enzyme.

The Retinol Binding Protein Receptor 2 (Rbpr2) is required for Photoreceptor Outer Segment Morphogenesis and Visual Function in Zebrafish.

Vitamin A (all-trans retinol) plays critical roles in mammalian development and vision. Since vitamin A is food-derived, tissue-specific uptake and storage mechanism are needed. In the eye, uptake of RBP4-retinol is mediated by the receptor Stra6, whereas the receptor mediating RBP4 binding and retinol transport into the liver has just recently been discovered. Here we examined the role of zebrafish retinol binding protein receptor 2 (Rbpr2) for RBP4-retinol uptake in developing embryos, using eye development and vision as sensitive readouts. In cultured cells, Rbpr2 localized to membranes and promoted RBP4-retinol uptake. In larvae, Rbpr2 expression was detected in developing intestinal enterocytes and liver hepatocytes. Two rbpr2 mutant zebrafish lines, each resulting in Rbpr2 deficiency, exhibit a small eye defect, and systemic malformations including hydrocephaly and cardiac edema, phenotypes associated with vitamin A deficiency. In the retina, Rbpr2 loss resulted in shorter photoreceptor outer segments, mislocalization and decrease in visual pigments, decreased expression of retinoic acid-responsive genes and photoreceptor cell loss, overall leading to a reduction of visual function. Together, these results demonstrate that Rbpr2-mediated RBP4-retinol uptake in developing liver and intestine is necessary to provide sufficient substrate for ocular retinoid production required for photoreceptor cell maintenance and visual function.

Targeting the tight junction protein, zonula occludens-1, with the connexin43 mimetic peptide, αCT1, reduces VEGF-dependent RPE pathophysiology.

A critical target tissue in age-related macular degeneration (AMD) is the retinal pigment epithelium (RPE), which forms the outer blood-retina barrier (BRB). RPE-barrier dysfunction might result from attenuation/disruption of intercellular tight junctions. Zonula occludens-1 (ZO-1) is a major structural protein of intercellular junctions. A connexin43-based peptide mimetic, αCT1, was developed to competitively block interactions at the PDZ2 domain of ZO-1, thereby inhibiting ligands that selectively bind to this domain. We hypothesized that targeting ZO-1 signaling using αCT1 would maintain BRB integrity and reduce RPE pathophysiology by stabilizing gap- and/or tight-junctions. RPE-cell barrier dysfunction was generated in mice using laser photocoagulation triggering choroidal neovascularization (CNV) or bright light exposure leading to morphological damage. αCT1 was delivered via eye drops. αCT1 treatment reduced CNV development and fluid leakage as determined by optical coherence tomography, and damage was correlated with disruption in cellular integrity of surrounding RPE cells. Light damage significantly disrupted RPE cell morphology as determined by ZO-1 and occludin staining and tiling pattern analysis, which was prevented by αCT1 pre-treatment. In vitro experiments using RPE and MDCK monolayers indicated that αCT1 stabilizes tight junctions, independent of its effects on Cx43. Taken together, stabilization of intercellular junctions by αCT1 was effective in ameliorating RPE dysfunction in models of AMD-like pathology. KEY MESSAGE: The connexin43 mimetic αCT1 accumulates in the mouse retinal pigment epithelium following topical delivery via eye drops. αCT1 eye drops prevented RPE-cell barrier dysfunction in two mouse models. αCT1 stabilizes intercellular tight junctions. Stabilization of cellular junctions via αCT1 may serve as a novel therapeutic approach for both wet and dry age-related macular degeneration.