Angiotensin II type 1 receptor expression is increased via 12-lipoxygenase in high glucose-stimulated glomerular cells and type 2 diabetic glomeruli

Background. Angiotensin II type 1 receptor (AT1) plays an important role in the development of diabetic nephropathy (DN). However, the roles played by 12-lipoxygenase (12-LO) in the AT1 expression in glomerular cells exposed to high glucose (HG) and diabetic glomeruli remain unclear. Our objective in the present study was to investigate the role of 12-LO in the AT1 expression in glomerular cells and glomeruli under diabetic conditions. Methods. Mesangial cells (MCs), podocytes and glomeruli isolated from rats were used in this study. The rats fed a high fat diet received low-dose streptozotocin to make type 2 diabetes. The 12-LO product 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE] was infused to rats by osmotic mini-pump. Morphometric measurement for glomerular volume, competitive reverse transcription polymerase chain reaction for mRNA expression, western blot and immunohistochemistry for protein expression were performed, respectively. Results. Both the 12(S)-HETE and HG increased AT1 protein expression in MCs and podocytes. Furthermore, the levels of the AT1 were significantly higher in glomeruli derived from 12(S)-HETE-treated rats compared with control rats. In addition, HG-induced AT1 expression was significantly reduced by the 12-LO inhibitor cinnamyl-3,4-dihydroxy-alpha-cynanocinnamate (CDC). Compared with the non-diabetic controls, DN rats showed significant glomerular hypertrophy and albuminuria. This was associated with significant increases in AT1 protein expression. These abnormalities were prevented by treatment of the CDC. Conclusions. These results indicate that AT1 expression is enhanced, at least in part, by 12-LO in the type 2 diabetic glomeruli, and 12-LO inhibition can ameliorate DN progression through downregulation of AT1 expression.