Differential expression of protein kinase C isoforms in streptozotocin- induced diabetic rats

Abstract

Background. The cellular effects of hyperglycemia are mediated by protein kinase C (PKC). However, PKC consists of several distinct isoforms, and their contribution to the pathogenesis of diabetic complications in different organs is not clear. We investigated the expression and translocation of PKC isoforms α, βI, βII, δ, ε, and ζ in kidney, heart, and aorta from diabetic rats. Methods. Hyperglycemia was induced with streptozotocin (70 mg/kg) in the rat. After four weeks, PKC isoform expression was assessed by Western blot after tissue fractionation and by immunohistochemistry. Results. Streptozotocin increased blood glucose from 117.0 3.6 to 510.0 ± 19.4 mg/dl (N = 8, P < 0.01) and induced albuminuria. PKC isoforms α, β, δ, ε, and ζ were all detected in control animals. Western blot showed increased PKC α expression in kidney and heart (160% and 170%, respectively). PKC βI, βII, and δ expression was not influenced by hyperglycemia. PKC ζ was decreased in diabetic animals in both tissues by 60%. The membrane association of PKC α and PKC was increased: however, the relative amount of PKC in the particulate fraction was not influenced by hyperglycemia. Immunohistochemistry revealed a marked increase in PKC α immunoreactivity in renal glomeruli and interstitial capillaries, cardiac capillaries, and skeletal muscle, as well as in the endothelial cells of larger arteries. PKC β showed a small decrease in the glomeruli. PKC ε was increased in renal tubules in diabetic rats but was decreased in the myocardium. PKC ζ was expressed in both myocardial and glomerular cells but was decreased during hyperglycemia. Our results demonstrate that PKC isoforms are differentially regulated in kidney and heart in diabetes. High glucose increases PKC α expression, whereas PKC ζ is down-regulated. The finding that PKC α is mostly increased in endothelial cells supports a role for PKC α in functional endothelial disturbances observed in diabetes.