High levels of glucose stimulate angiotensinogen gene expression via the p38 mitogen-activated protein kinase pathway in rat kidney proximal tubular cells

The present studies investigated whether the effect of high levels of gluco se on angiotensinogen (ANG) secretion and gene expression in kidney proxima l tubular cells is mediated at least in part via the activation of p38 mito gen-activated protein kinase (p38 MAPK). Rat immortalized renal proximal tu bular cells (IRPTCs) were cultured in monolayer. The levels of immunoreacti ve rat ANG (IR-rANG) secreted into the medium and the levels of cellular AN G messenger RNA were determined by a specific RIA for rat ANG and a RT-PCR assay, respectively. Phosphorylation of cellular p38 MAPK was determined by Western blot analysis using the Phospho Plus p38 MAPK antibody kit. High l evels of glucose (i.e. 25 mM) and phorbol 12-myristate 13-acetate (PMA; 10( -7) M) increased the secretion of IR-rANG and cellular ANG messenger RNA as well as phosphorylation of p38 MAPK in IRPTCs. This stimulatory effect of high levels of glucose and PMA was blocked by SE 203580 (a specific inhibit or of p38 MAPK), but not by SE 202474 (a negative control of SE 203580). Hi gh levels of D-sorbitol or 2-deoxy-D-glucose (i.e. greater than or equal to 35 mM) also stimulated the phosphorylation of p38 MAPK, but did not stimul ate ANG secretion or gene expression. GF 109203X (an inhibitor of protein k inase C) blocked the stimulatory effect of high levels of glucose and PMA o n ANG gene expression, whereas it did not block the effect of high levels o f glucose, sorbitol, or 2-deoxy-D-glucose on p38 MAPK phosphorylation in IR PTCs. These studies demonstrate that the stimulatory effect of a high level of glucose (25 mM) on ANG gene expression in IRPTCS may be mediated at lea st in part via activation of p38 MAPK signal transduction pathway and is pr otein kinase C independent.