Knockout of A-Crystallin Inhibits Ocular Neovascularization

Abstract

The present study aimed to investigate the effects of αA-crystallin on pathologic ocular neovascularization. Human umbilical vein endothelial cells (HUVECs) were used for the in vitro study, and αA-crystallin-knockout (CRYAA[-/-]) mice were used for the in vivo study. αA-crystallin was knocked down in HUVECs by using a specific small interfering RNA (siRNA), and the effects of αA-crystallin knockdown on proliferation, migration, tube formation, and apoptosis were evaluated. Enzyme-linked immunosorbent assays were performed to investigate extracellular concentrations of vascular endothelial growth factor (VEGF). In vivo mouse models of oxygen-induced retinopathy (OIR) and laser-induced choroidal neovascularization (CNV) were generated by using CRYAA(-/-) mice. The nonperfused area in the OIR model was measured in flat-mounted retinas, and angiogenesis resulting in CNV was evaluated in retinal sections. Western blot analysis was performed to investigate the phosphorylation status of vascular endothelial growth factor receptor 2 (VEGFR2, high affinity receptor for VEGF), AKT, PLCγ1, FAK, Src, p42/p44MAPK, p38MAPK, caspase-3, and caspase-9 in cultured HUVECs, as well as in the OIR and CNV models. The CRYAA siRNA not only induced HUVEC apoptosis but also inhibited exogenous and endogenous VEGF-induced cell activities, including proliferation, migration, and tube formation. Pathologic neovascularization was attenuated in the CRYAA(-/-) murine OIR and CNV models. Both in vitro and in vivo, the inhibition of angiogenesis was mediated by the suppression of VEGF secretion and the inhibition of the VEGFR2 signaling pathway; VEGFR2, AKT, PLCγ1, FAK, Src, p42/p44 MAPK, and p38 MAPK all showed reduced phosphorylation levels. In addition, CRYAA knockout led to increased levels of cleaved caspase-9 and caspase-3. Knockout of αA-crystallin inhibited pathologic neovascularization through the VEGF and VEGFR2 signaling pathways both in vitro and in vivo. These results suggest that αA-crystallin could be a novel pharmaceutical target for the prevention of ocular neovascularization.