Native and modified LDL activate extracellular signal-regulated kinases inmesangial cells

Glycation and/or oddation of LDL may promote diabetic nephropathy. The mito gen-activated protein kinase (MAPK) cascade, which includes extracellular s ignal-regulated protein kinases (ERKs), modulates cell function. Therefore, we examined the effects of LDL on ERR phosphorylation in cultured rat mesa ngial cells. In cells exposed to 100 mug/ml native LDL or LDL modified by g lycation, and/or mild or marked (copper-mediated) oxidation, ERK activation peaked at 5 min. Five minutes of exposure to 10-100 mug/ml native or modif ied LDL produced a concentration-dependent (up to sevenfold) increase in ER K activity. Also, 10 mug/ml native LDL and mildly modified LDL (glycated an d/or mildly oxidized) produced significantly greater ERR activation than th at induced by copper-oxidized LDL +/- glycation (P < 0.05). Pretreatment of cells with Src kinase and MAPK kinase inhibitors blocked ERK activation by 50-80% (P < 0.05). Native and mildly modified LDL, which are recognized by the native LDL receptor, induced a transient spike of intracellular calciu m. Copper-oxidized (+/- glycation) LDL, recognized by the scavenger recepto r, induced a sustained rise in intracellular calcium. The intracellular cal cium chelator (EGTA/AM) further increased ERK activation by native and mild ly modified LDL (P < 0.05). These findings demonstrate that native and modi fied LDL activate ERKs 1 and 2, an early mitogenic signal, in mesangial cel ls and provide evidence for a potential link between modified LDL and the d evelopment of glomerular injury in diabetes.