Regulation of Angiotensin II Binding in Renal Proximal Tubule Cells by High Glucose : II.Involvement of PKC, MAPK, and PLA2

Park, Soo Hyun; Han, Ho Jae

Abstract

Renin-angiotensin system is associated with development of diabetic nephropathy. Hyperglycemia is known as a primary etiologic factor about it. Thus, we investigated the effect of high glucose on angiotensin II(ANG II) binding in the primary cultured rabbit renal proximal tubule cells(PTCs). 25 mM glucose(48 hr incubation) induces inhibition of ANG II binding. The high glucose-induced inhibition of ANG II binding was recovered by the removal of glucose, suggesting the role of glucose specificity. High glucose-induced inhibition of ANG II binding was blocked by mepacrine and AACOCF3, phospholipase A2(PLA2) inhibitors. Indomethacin, a cyclooxygenase inhibitor, significantly prevented high glucose-induced inhibition of ANG II binding. However, nordihydroguaiareic acid(NDGA), a lipoxygenase inhibitor, and econazole, a cytochrome P450 epoxygenase inhibitor, did not block the effect of high glucose. This result suggest that cyclooxygenase metabolites of arachidonic acid(AA) released by high glucose are involved in the high glucose-induced inhibition of ANG II binding. Next, we examined the involvement of PKC in the effect of high glucose. Staurosporine, bisindolylmaleimide I, protein kinase C(PKC) inhibitors, and PD 98059, a p44/42 mitogen activated protein kinase(MAPK) inhibitor, significantly blocked high glucose- induced increase of [3H]-AA release and inhibition of ANG II binding. Indeed, 25 mM glucose increased PKC activity from cytosolic to particulate fraction and phosphorylation of p44/42 MAPK. In addition, high glucose increased phosphorylation of p44/42 MAPK and its activation was significantly blocked by PKC inhibitor. In conclusion, high glucose partially inhibits ANG II binding via PKC-MAPK-PLA2 signal pathway in the PTCs.