To investigate the effect of protein kinase C (PKC)-zeta inhibition on vascular leakage in diabetic retinopathy, streptozotocin-induced diabetic mice were intravitreously injected with siPKC-zeta. According to the fluorescein angiography of the retinal vessels, suppression of PKC-zeta effectively attenuated vascular leakage in diabetic retina. Further evaluation on the retina with western blot analysis and immunohistochemistry revealed accompanying restoration of tight junction proteins on retinal vessels. As two major contributors to vascular leakage in diabetic retinopathy, vascular endothelial growth factor (VEGF) and advanced glycation end products (AGES) were investigated on the tight junction protein expression in endothelial cells. Inhibition of PlKC-zeta attenuated VEGF-induced decrease of tight junction proteins and accompanying hyperpermeability in human retinal microvascular endothelial cells (HRMECs). PKC-zeta inhibition also attenuated AGE-induced decrease of tight junction proteins in HRMECs. Our findings suggest that inhibition of PKC-zeta could be an alternative treatment option for compromised blood-retinal barrier in diabetic retinopathy. (C) 2014 Elsevier Inc. All rights reserved.