Induction of endothelin-1 expression by glucose - An effect of protein kinase C activation

Enhanced actions or levels of endothelin-1 (ET-1), a potent vasoconstrictor , have been associated with decreased blood flow in the retina and peripher al nerves of diabetic animals and may be related to the development of path ologies in these tissues. Hyperglycemia has been postulated to increase ET- 1 secretion in endothelial cells. We have characterized the mechanism by wh ich elevation of glucose is increasing ET-1 mRNA expression in capillary bo vine retinal endothelial cells (BREC) and bovine retinal pericytes (BRPC). Elevation of glucose, but not mannitol, from 5.5 to 25 mmol/l for 3 days in creased membranous protein kinase C (PKC) activities and ET-1 mRNA in paral lel levels by 2-fold in BREC and BRPC. These effects were reversed by decre asing glucose levels to 5.5 mmol/l for an additional 2 days. Glucose-induce d ET-1 overexpression was inhibited by a general PKC inhibitor, GF109203X, and a mitogen-activated protein kinase kinase inhibitor, PD98059, but not b y wortmannin, a phosphatidylinositol 3-kinase inhibitor By immunoblot analy sis, PKC-beta 2 and -delta isoforms in BREC were significantly increased re lative to other isoforms in the membranous fractions when glucose level was increased. Overexpression of PKC-beta 1 and -delta isoforms but not PKC-ze ta isoform by adenovirus vectors containing the respective cDNA enhanced in parallel PKC activities, proteins, and basal and glucose-induced ET-1 mRNA expression by at least 2-fold. These results showed that enhanced ET-1 exp ression induced by hyperglycemia in diabetes is partly due to activation of PKC-beta and -delta isoforms, suggesting that inhibition of these PKC isof orms may prevent early changes in diabetic retinopathy and neuropathy.