Stretch-induced mesangial cell ERK1/ERK2 activation is enhanced in high glucose by decreased dephosphorylation

Glomerular hypertension and hyperglycemia are major determinants of diabeti c nephropathy. We sought to identify the mechanisms whereby stretch-induced activation of mesangial cell extracellular signal-regulated kinase 1 and 2 (ERK1/ERK2) is enhanced in high glucose (HG). Mesangial cells cultured on fibronectin Flex I plates in normal glucose (NG; 5.6 mM) or HG (30 mM), wer e stretched by 15% elongation at 60 cycles/ min for up to 60 min. In HG, a 5-min stretch increased ERK1/ERK2 phosphorylation by 6.4 +/- 0.4/4.3 +/- 0. 3-fold (P < 0.05 vs. NG stretch). In constrast, p38 phosphorylation was inc reased identically by stretch in NG and HG. Unlike many effects of HG, augm entation of ERK activity by HG was not dependent on protein kinase C (PKC) as indicated by downregulation of PKC with 24-h phorbol ester or inhibition with bisindolylmaleimide IV. In both NG and HG, pretreatment with arginine -glycine-aspartic acid peptide (0.5 mg/ml) to inhibit integrin binding or w ith cytochalasin D (100 ng/ml) to disassemble filamentous (F) actin, signif icantly reduced phosphorylation of ERK1/ERK2 and p38. To determine whether the rate of mitogen-activated protein kinase dephosphorylation is affected by HG, cellular kinase activity was inhibited by depleting ATP. Post-ATP de pletion, phosphorylation of ERK1/ERK2 was reduced to 36 +/- 9/51 +/- 14% vs . 9 +/- 5/7 +/- 6% in NG (P < 0.05, n = 5). Thus stretch-induced ERK1/ERK2 and p38 activation in both NG and HG is beta(1)-integrin and F-actin depend ent. Stretch-induced ERK1/ERK2 is enhanced in high glucose by diminished de phosphorylation, suggesting reduced phosphatase activity in the diabetic mi lieu. Enhanced mesangial cell ERK1/ERK2 signaling in response to the combin ed effects of mechanical stretch and HG may contribute to the pathogenesis of diabetic nephropathy.