Cell-Type-Specific Complement Profiling in the ABCA4−/− Mouse Model of Stargardt Disease

Stargardt macular degeneration is an inherited retinal disease caused by mutations in the ATP-binding cassette subfamily A member 4 (ABCA4) gene. Here, we characterized the complement expression profile in ABCA4(-/-) retinae and aligned these findings with morphological markers of retinal degeneration. We found an enhanced retinal pigment epithelium (RPE) autofluorescence, cell loss in the inner retina of ABCA4(-/-) mice and demonstrated age-related differences in complement expression in various retinal cell types irrespective of the genotype. However, 24-week-old ABCA4(-/-) mice expressed more c3 in the RPE and fewer cfi transcripts in the microglia compared to controls. At the protein level, the decrease of complement inhibitors (complement factor I, CFI) in retinae, as well as an increased C3b/C3 ratio in the RPE/choroid and retinae of ABCA4(-/-), mice was confirmed. We showed a corresponding increase of the C3d/C3 ratio in the serum of ABCA4(-/-) mice, while no changes were observed for CFI. Our findings suggest an overactive complement cascade in the ABCA4(-/-) retinae that possibly contributes to pathological alterations, including microglial activation and neurodegeneration. Overall, this underpins the importance of well-balanced complement homeostasis to maintain retinal integrity

PDGF Receptor Alpha Signaling Is Key for Muller Cell Homeostasis Functions

Muller cells, the major retinal macroglia, are key to maintaining vascular integrity as well as retinal fluid and ion homeostasis. Although platelet derived growth factor (PDGF) receptor expression in Muller glia has been reported earlier, their actual role for Muller cell function and intimate interaction with cells of the retinal neurovascular unit remains unclear. To close this gap of knowledge, Muller cell-specific PDGF receptor alpha (PDGFR alpha) knockout (KO) mice were generated, characterized, and subjected to a model of choroidal neovascularization (CNV). PDGFR alpha-deficient Muller cells could not counterbalance hypoosmotic stress as efficiently as their wildtype counterparts. In wildtypes, the PDGFR alpha ligand PDGF-BB prevented Muller cell swelling induced by the administration of barium ions. This effect could be blocked by the PDGFR family inhibitor AC710. PDGF-BB could not restore the capability of an efficient volume regulation in PDGFR alpha KO Muller cells. Additionally, PDGFR alpha KO mice displayed reduced rod and cone-driven light responses. Altogether, these findings suggest that Muller glial PDGFR alpha is central for retinal functions under physiological conditions. In contrast, Muller cell-specific PDGFR alpha KO resulted in less vascular leakage and smaller lesion areas in the CNV model. Of note, the effect size was comparable to pharmacological blockade of PDGF signaling alone or in combination with anti-vascular endothelial growth factor (VEGF) therapy-a treatment regimen currently being tested in clinical trials. These data imply that targeting PDGF to treat retinal neovascular diseases may have short-term beneficial effects, but may elicit unwarranted side effects given the putative negative effects on Muller cell homeostatic functions potentially interfering with a long-term positive outcome

Pharmacological blockade of the P2X7 receptor reverses retinal damage in a rat model of type 1 diabetes

Aims: Retinopathy is a leading cause of vision impairment in diabetes. Its pathogenesis involves inflammation, pathological angiogenesis, neuronal and glial dysfunction. The purinergic P2X7 receptor (P2X7R) has a leading role in inflammation and angiogenesis. Potent and selective P2X7R blockers have been synthesized and tested in Phase I/II clinical studies. We hypothesize that P2X7R blockade will ameliorate diabetes-related pathological retinal changes. Methods: Streptozotocin (STZ)-treated rats were intraperitoneally inoculated with either of two small molecule P2X7R receptor inhibitors, A740003 and AZ10606120, and after blood glucose levels increased to above 400 mg/dL, retinae were analyzed for P2X7R expression, vascular permeability, VEGF, and IL-6 expression. Results: STZ administration caused a near fourfold increase in blood glucose, a large increase in retinal microvasculature permeability, as well as in retinal P2X7R, VEGF, and IL-6 expression. P2X7R blockade fully reversed retinal vascular permeability increase, VEGF accumulation, and IL-6 expression, with no effect on blood glucose. Conclusion: P2X7R blockade might be promising strategy for the treatment of microvascular changes observed in the early phases of diabetic retinopathy