Hypoglycemia promotes inner blood-retinal barrier breakdown and retinal vascular leakage in diabetic mice

The blood-retinal barrier (BRB) serves as a physiological boundary regulating the passage of nutrients, waste, ions, proteins, and water to and from the retina. In patients with diabetic retinopathy, breakdown of the inner BRB (iBRB) results in damage to the neurovascular unit and is a principal cause of vision loss in the diabetic population. Here, we demonstrate that hypoglycemia, a common consequence of tight glycemic control and high glycemic variability, results in accumulation of the transcription factors hypoxia-inducible factor-1α (HIF-1α) and HIF-2α and the expression of dozens of HIF-dependent vasoactive mediators in the mouse retina. In diabetic mice, this modest increase in HIF-dependent hyperpermeability factors was sufficient to promote vesicular transcytosis, breakdown of the iBRB, and retinal vascular permeability. Genetic inhibition of either HIF-1α or HIF-2α resulted in an incomplete inhibition of the broad increase in HIF-regulated vasoactive gene expression in response to hypoglycemia. We therefore evaluated a pharmacologic dual HIF-1 and HIF-2 inhibitor, 32-134D, as a therapeutic approach to prevent hypoglycemia-induced HIF-dependent vasoactive gene expression. 32-134D effectively inhibited HIF-1α accumulation and HIF-regulated gene expression in human retinal tissue. In diabetic mice, intravitreal administration of 32-134D prevented the increase in expression of HIF-regulated vasoactive genes after transient episodes of hypoglycemia, blocking both breakdown of the iBRB and the promotion of retinal vascular hyperpermeability. Collectively, these observations help explain why patients with diabetes initiating tight glycemic control have worsening of their diabetic retinopathy and provide the foundation for clinical studies assessing HIF inhibition with 32-134D for its prevention.