Active Rap1-mediated inhibition of choroidal neovascularization requires interactions with IQGAP1 in choroidal endothelial cells

Oxidative stress and epigenetics in ocular vascular aging: an updated review

Vascular aging is an inevitable process with advancing age, which plays a crucial role in the pathogenesis of cardiovascular and microvascular diseases. Diabetic retinopathy (DR) and age-related macular degeneration (AMD), characterized by microvascular dysfunction, are the common causes of irreversible blindness worldwide, however there is still a lack of effective therapeutic strategies for rescuing the visual function. In order to develop novel treatments, it is essential to illuminate the pathological mechanisms underlying the vascular aging during DR and AMD progression. In this review, we have summarized the recent discoveries of the effects of oxidative stress and epigenetics on microvascular degeneration, which could provide potential therapeutic targets for DR and AMD.

Role of Erythropoietin Receptor Signaling in Macrophages or Choroidal Endothelial Cells in Choroidal Neovascularization

Erythropoietin (EPO) has been proposed to reduce the progression of atrophic age-related macular degeneration (AMD) due to its potential role in neuroprotection. However, overactive EPO receptor (EPOR) signaling increased laser-induced choroidal neovascularization (CNV) and choroidal macrophage number in non-lasered mice, which raised the question of whether EPOR signaling increased CNV through the recruitment of macrophages to the choroid that released pro-angiogenic factors or through direct angiogenic effects on endothelial cells. In this study, we addressed the hypothesis that EPOR signaling increased CNV by direct effects on macrophages or endothelial cells. We used tamoxifen-inducible macrophage-specific or endothelial cell-specific EPOR knockout mice in the laser-induced CNV model, and cultured choroidal endothelial cells isolated from adult human donors. We found that macrophage-specific knockout of EPOR influenced laser-induced CNV in females only, whereas endothelial-specific knockout of EPOR reduced laser-induced CNV in male mice only. In cultured human choroidal endothelial cells, knockdown of EPOR reduced EPO-induced signal transducer and activator of transcription 3 (STAT3) activation. Taken together, our findings suggest that EPOR signaling in macrophages or choroidal endothelial cells regulates the development of CNV in a sex-dependent manner. Further studies regarding the role of EPO-induced signaling are required to assess EPO safety and to select or develop appropriate therapeutic approaches.

Regulation of Rac1 Activation in Choroidal Endothelial Cells: Insights into Mechanisms in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is one of the leading causes of blindness worldwide. Vision loss from the neovascular form is associated with the invasion of choroidal endothelial cells into the neural retina to form vision-threatening macular neovascularization (MNV). Anti-angiogenic agents are the current standard of care but are effective in only ~50% of AMD cases. The molecular mechanisms involved in invasive MNV point to the importance of regulating signaling pathways that lead to pathologic biologic outcomes. In studies testing the effects of AMD-related stresses, activation of the Rho GTPase, Rac1, was found to be important for the choroidal endothelial cell invasion into the neural retina. However, current approaches to prevent Rac1 activation are inefficient and less effective. We summarize active Rac1-mediated mechanisms that regulate choroidal endothelial cell migration. Specifically, we discuss our work regarding the role of a multidomain protein, IQ motif containing GTPase activating protein 1 (IQGAP1), in sustaining pathologic Rac1 activation and a mechanism by which active Rap1, a Ras-like GTPase, may prevent active Rac1-mediated choroidal endothelial cell migration.