Activation of Phosphoinositide 3-kinase in Response to High Glucose Leads to Regulation of Reactive Oxygen Species- Related Nuclear Factor- B Activation and Cyclooxygenase-2 Expression in Mesangial Cells

Hyperglycemia causes glomerular mesangial cell proliferation and increases matrix synthesis, contributing to early diabetic glomerulopathy. Immunohistochemical and functional correlations of renal cyclooxygenase-2 in experimental diabetes have been identified. However, the role of cyclooxygenase-2 in early diabetes-induced mesangial cell proliferation remains unknown. The authors tested the hypothesis that hyperglycemia modulates an intrarenal cyclooxygenase-2 expression, which might mediate the mesangial cell proliferation via a possible phosphoinositide 3-kinase/Akt pathway. Expression of cyclooxygenase-2, but not cyclooxygenase-1, could be induced in mesangial cells cultured under high glucose. Antioxidants (pyrrolidine dithiocarbamate and N-acetyl-L-cysteine) and phosphoinositide 3-kinase inhibitors [2-(4-morpholinyl)-8phenyl-1(4H)-benzopyran-4-one hydrochloride (LY294002) and wortmannin] effectively inhibited this high glucose-induced response. Moreover, high glucose markedly triggered the activation of phosphoinositide 3-kinase and Akt in mesangial cells, suggesting that a phosphoinositide 3-kinase/Akt pathway is involved in the high glucose-induced responses. Phosphoinositide 3-kinase inhibitors could also effectively attenuate the high glucose-triggered intracellular reactive oxygen species generation and nuclear factorB activation. Likewise, blocking the phosphoinositide 3-kinase or Akt activity with the dominant-negative vectors DN-p85 or DN-Akt, respectively, also greatly diminished the high glucosetriggered reactive oxygen species generation and nuclear factorB activation. Treatment of mesangial cells with LY294002 and cyclooxygenase-2 inhibitors [N-[2-(cyclohexyloxyl)-4-nitrophenyl]-methane sulfonamide (NS398) and aspirin] effectively inhibited the high glucose-induced mesangial cell proliferation. These results suggest that high glucose may trigger the reactive oxygen species-regulated nuclear factorB activation and cyclooxygenase-2 expression and cell proliferation in mesangial cells through a phosphoinositide 3-kinase-dependent pathway. Hyperglycemia is a well recognized pathogenic factor of long-term complications in diabetes mellitus. Altered growth of renal cells is one of the early abnormalities detected after the onset of diabetes (Shankland and Wolf, 2000). Cell culture studies whereby renal cells are exposed to high glucose concentrations have provided a considerable amount of insight into mechanisms of altered growth. Early streptozotocin (STZ) diabetes studies showed that rats exhibit a 15% increase of whole kidney weight within 72 h of induction with STZ (Osterby and Gundersen, 1975; Phillips et al., 1999). More detailed studies showed that glomerular enlargement was accompanied by glomerular cell proliferation, which predominantly involved the mesangial cells, in the early phase of diabetes (Flyvbjerg et al., 1995; Young et al., 1995). However, the specific factor(s) and the natural mechanism(s) that initiate the progression of diabetic glomerulopathy remains