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Anti-VEGF drugs are first-line treatments for retinal neovascular diseases, but these anti-angiogenic agents may also aggravate retinal damage by inducing hypoxia. Mitophagy can protect against hypoxia by maintaining mitochondrial quality, thereby sustaining metabolic homeostasis and reducing reactive oxygen species (ROS) generation. Here we report that the anti-VEGF agent bevacizumab upregulated the hypoxic cell marker HIF-1α in photoreceptors, Müller cells, and vascular endothelial cells of oxygen-induced retinopathy (OIR) model mice, as well as in hypoxic cultured 661W photoreceptors, MIO-MI Müller cells, and human vascular endothelial cells. Bevacizumab also increased expression of mitophagy-related proteins, and mitophagosome formation both in vivo and in vitro, but did not influence cellular ROS production or apoptosis rate. The HIF-1α inhibitor LW6 blocked mitophagy, augmented ROS production, and triggered apoptosis. Induction of HIF-1α and mitophagy were associated with upregulation of BCL2/adenovirus E1B 19-kDa protein-interacting protein 3 (BNIP3) and FUN14 domain containing 1 (FUNDC1), and overexpression of these proteins in culture reversed the effects of HIF-1α inhibition. These findings suggest that bevacizumab does induce retinal hypoxia, but that concomitant activation of the HIF-1α-BNIP3/FUNDC1 signaling pathway also induces mitophagy, which can mitigate the deleterious effects by reducing oxidative stress secondary. Promoting HIF-1α-BNIP3/FUNDC1-mediated mitophagy may enhance the safety of anti-VEGF therapy for retinal neovascular diseases and indicate new explanation and possible new target of the anti-VEGF therapy with suboptimal effect.

Retinal ischemia is a common pathological event that can result in retinal ganglion cell (RGC) death and irreversible vision loss. The pathogenic mechanisms linking retinal ischemia to RGC loss and visual deficits are uncertain, which has greatly hampered the development of effective treatments. It is increasingly recognized that pyroptosis of microglia contributes to the indirect inflammatory death of RGCs. In this study, we report a regulatory NOD-like receptor, NOD-, LRR- and CARD-containing 5 (NLRC5), as a key regulator on microglial pyroptosis and the retinal ischemia process. Through an in-depth analysis of our recently published transcriptome data, we found that NLRC5 was significantly up-regulated in retina during ischemia–reperfusion injury, which were further confirmed by subsequent detection of mRNA and protein level. We further found that NLRC5 was upregulated in retinal microglia during ischemia, while NLRC5 knockdown significantly ameliorated retinal ischemic damage and RGC death. Mechanistically, we revealed that knockdown of NLRC5 markedly suppressed gasdermin D (GSDMD) cleavage and activation of interleukin-1β (IL-1β) and caspase-3, indicating that NLRC5 promotes both microglial pyroptosis and apoptosis. Notably, we found that NLRC5 directly bound to NLRP3 and NLRC4 in inflammasomes to cooperatively drive microglial pyroptosis and apoptosis mediating retinal ischemic damage. Overall, these findings reveal a previously unidentified key contribution of NLRC5 signaling to microglial pyroptosis under ischemia or hypoxia conditions. This NLRC5-dependent pathway may be a novel therapeutic target for treatment of ischemic retinopathy.