Ischaemia-induced retinal neovascularisation and diabetic retinopathy in mice with conditional knockout of hypoxia-inducible factor-1 in retinal Muller cells

Retinal Muller cells are known to produce inflammatory and angiogenic cytokines, which play important roles in diabetic retinopathy. Hypoxia-inducible factor (HIF)-1 has been shown to play a crucial role in retinal inflammation and neovascularisation. We sought to determine the role of Muller cell-derived HIF-1 in oxygen-induced retinopathy (OIR) and diabetic retinopathy using conditional Hif-1 alpha (also known as Hif1a) knockout (KO) mice. Conditional Hif-1 alpha KO mice were generated by crossing mice expressing cyclisation recombinase (cre, also known as P1_gp003) in Muller cells with floxed Hif-1 alpha mice and used for OIR and streptozotocin-induced diabetes to induce retinal neovascularisation and inflammation, respectively. Abundance of HIF-1 alpha and pro-angiogenic and pro-inflammatory factors was measured by immunoblotting and immunohistochemistry. Retinal neovascularisation was visualised by angiography and quantified by counting pre-retinal nuclei. Retinal inflammation was evaluated by leucostasis and vascular leakage. While the Hif-1 alpha KO mice showed significantly decreased HIF-1 alpha levels in the retina, they exhibited no apparent histological or visual functional abnormalities under normal conditions. Compared with wild-type counterparts, Hif-1 alpha KO mice with OIR demonstrated attenuated overproduction of vascular endothelial growth factor (VEGF) and intercellular adhesion molecule (ICAM)-1, reduced vascular leakage and alleviated neovascularisation in the retina. Under diabetes conditions, disruption of Hif-1 alpha in Muller cells attenuated the increases of retinal vascular leakage and adherent leucocytes, as well as the overproduction of VEGF and ICAM-1. Muller cell-derived HIF-1 alpha is a key mediator of retinal neovascularisation, vascular leakage and inflammation, the major pathological changes in diabetic retinopathy. Muller cell-derived HIF-1 alpha is therefore a promising therapeutic target for diabetic retinopathy.