Effects of protein kinase C inhibition and activation on proliferation and apoptosis of bovine retinal pericytes

Abstract

Aims/hypothesis. Drop-out of capillary pericytes occurs early and selectively in diabetic retinopathy. High glucose concentrations decrease replication and increase apoptosis of cultured pericytes. Since glucose activates protein kinase C, we investigated the effects of modulating this intracellular mediator on replication, cell cycle and apoptosis of cultured bovine retinal pericytes. Methods. Pericytes cultured in 5.6 or 28 mmol/l glucose were exposed to a protein kinase C activator (phorbol 12-myristate 13-acetate) and/or a selective inhibitor of its β2 isoform (LY379196). Cells were counted after 7 days. Proliferation by the tetrazolium to formazan assay and DNA synthesis by 5-bromo-2′-deoxyuridine incorporation were measured at day 4. Cell cycle by flow cytometry and apoptosis by ELISA were assessed at day 2. Results. High glucose reduced pericyte replication and increased apoptosis. Protein kinase C activation increased proliferation, while inhibition of its β2 isoform decreased it. Cell cycle was accelerated by protein kinase C activation and delayed by inhibition. Apoptosis was enhanced by protein kinase C inhibition and reduced by activation. Conclusions/interpretation. Protein kinase C inhibition amplifies the anti-proliferative and pro-apoptotic effects of high glucose on cultured pericytes, whereas stimulation reduces apoptosis and promotes proliferation both in physiological glucose and high glucose. Protein kinase C inhibition, proposed for the treatment of diabetic macular edema and proliferative retinopathy, might accelerate pericyte dropout in earlier stages when these cells are still present in retinal capillaries. [Diabetologia (2003) 46:416-419]

Towards Newer Molecular Targets for Chronic Diabetic Complications

“…PKC-mediated activation of numerous substrate proteins is important in regulating vascular cell function. PKC may mediate endothelial cell permeability, pericyte loss, and expression of various angiogenic factors, which are implicated in diabetic retinopathy [74][75][76][77]. In addition, PKC may affect the activation of vasoactive factors such as ET-1 and NO [76,78], leading to blood flow alteration.…”

Pericytes and Their Role in Microvasculature Homeostasis

“…Inhibition of PKC in pericytes grown in high glucose conditions increased apoptosis and activation of PKC decreased apoptosis [35].…”

Antibody-Mediated Retinal Pericyte Injury: Implications for Diabetic Retinopathy

“…2,3 Pericytes begin to die relatively early in the course of diabetic retinopathy, and are considered to be integrally involved in the pathogenesis of the retinopathy. 4 A variety of mechanisms, including oxidative stress, 5 formation of advanced glycation end-products, 6 and upregulation of protein kinase C, 7 have been implicated in pericyte death in diabetes, but the possible contributions of autoantibodies and complement in such cell loss in diabetic retinopathy has not been studied.…”