Oxidative Stress Drives Hyperglycemia-Induced Retinal Neurodegeneration Independently of Microvascular Leakage

Diabetic retinopathy (DR) is a metabolic disease of the neurovascular unit, in which retinal microvascular dysfunction and neurodegeneration are interconnected processes that contribute to disease progression. Oxidative stress is a major pathogenic driver of DR; however, whether reactive oxygen species (ROS)-mediated microvascular leakage directly contributes to retinal neurodegeneration remains unclear. Here, we investigated whether targeting ROS-mediated microvascular leakage through inhibition of the ROS–transglutaminase 2 (TGase2) pathway can ameliorate hyperglycemia-induced retinal neurodegeneration in human retinal endothelial cells (HRECs) and diabetic mice. In HRECs, ROS-dependent activation of TGase2 was required for endothelial hyperpermeability. In diabetic mouse retinas, hyperglycemia induced TGase2 activation, stress fiber formation, vascular endothelial-cadherin disassembly, and microvascular leakage, all of which were effectively suppressed by pharmacological inhibition of the ROS-TGase2 pathway or TGase2-specific siRNA. Consistently, diabetic TGase2-null mice exhibited complete protection against retinal microvascular leakage. In contrast, pharmacological inhibition or genetic deletion of TGase2 failed to suppress hyperglycemia-induced inflammatory responses, reactive gliosis, retinal ganglion cell apoptosis, or retinal thinning in diabetic mice. These findings reveal that oxidative stress induces distinct downstream responses in the retinal vasculature and neural retina. TGase2 is a critical effector of ROS-dependent microvascular leakage but is dispensable for hyperglycemia-induced retinal neurodegeneration. Thus, suppression of ROS–TGase2-mediated microvascular dysfunction alone is insufficient to prevent retinal neurodegeneration, indicating that vascular leakage and neurodegeneration are mechanistically dissociable consequences of oxidative stress in DR.