Activation of Nuclear Factor-κB Induced by Diabetes and High Glucose Regulates a Proapoptotic Program in Retinal Pericytes

To reconstruct the events that may contribute to the accelerated death of retinal vascular cells in diabetes, we investigated in situ and in vitro the activation of nuclear factor-kappaB (NF-kappaB), which is triggered by cellular stress and controls several programs of gene expression. The retinal capillaries of diabetic eye donors showed an increased number of pericyte nuclei positive for NF-kappaB, when compared with nondiabetic donors, whereas endothelial cells were negative. Microvascular cell apoptosis and acellular capillaries were increased only in the diabetic donors with numerous NF-kappaB-positive pericytes. Likewise, high glucose in vitro activated NF-kappaB in retinal pericytes but not in endothelial cells, and increased apoptosis only in pericytes. Studies with NF-kappaB inhibitors suggested that in pericytes, basal NF-kappaB has prosurvival functions, whereas NF-kappaB activation induced by high glucose is proapoptotic. Pericytes exposed to high glucose showed increased expression of Bax and of tumor necrosis factor-alpha, which were prevented by the NF-kappaB inhibitors and mimicked by transfection with the p65 subunit of NF-kappaB, and failed to increase the levels of the NF-kappaB-dependent inhibitors of apoptosis. Colocalization of activated NF-kappaB and Bax overexpression was observed in the retinal pericytes of diabetic donors. A proapoptotic program triggered by NF-kappaB selectively in retinal pericytes in response to hyperglycemia is a possible mechanism for the early demise of pericytes in diabetic retinopathy.