Insulin increases gelatinase activity in rat glomerular mesangial cells via ERK- and PI-3 kinase-dependent signalling.

Diabetic nephropathy is associated with increased accumulation of the extracellular matrix (ECM) in the kidney, which ultimately leads to kidney failure. This may occur due to excessive synthesis of ECM components or reduced degradation, a process primarily mediated by matrix metalloproteinases (MMPs). The direct effect of insulin on ECM synthesis and degradation in glomerular mesangial cells (GMCs) is unclear. Here, we show an increased gelatinase activity in conditioned media from insulin-treated rat GMCs, determined by gelatin zymography. Furthermore, we show using the specific inhibitors LY294002 and PD98059 that insulin induced increased gelatinase activity via an intracellular signalling mechanism involving phosphatidylinositol-3 kinase (PI-3K) and the extracellular signal-regulated kinase 1/2 (ERK1/2) mitogen-activated protein kinases (MAPKs) respectively. In addition, we demonstrate that PI-3 kinase and ERK1/2 MAPK are activated by insulin in GMCs. The appearance of protease activity at approximately 72 kDa suggested that MMP-2 activity may be induced by insulin, however, we did not detect an increase in MMP-2 expression by Western blotting. In summary, our results suggest that insulin can induce gelatinase activity in GMCs, and it is possible that loss of this input in insulin-resistant type 2 diabetic individuals may contribute to ECM accumulation and the development of nephropathy.

Leptin induces rat glomerular mesangial cell hypertrophy, but does not regulate hyperplasia or apoptosis.

OBJECTIVE: There is an increased incidence of renal glomerulosclerosis in obese individuals. One of the major structural changes observed in nephropathy is the increase in kidney size, which may occur due to hypertrophy or changes in the rate of hyperplasia or apoptosis. Here we investigated whether leptin, the product of the obese (ob) gene which is found at high plasma levels in obese and diabetic individuals, alters any of these parameters. RESULTS: We show that leptin increased hypertrophy of these cells. This was indicated by an approximately 33% increase in cell size and 40% increase in leucine incorporation. Furthermore, we show that the hypertrophic effect of leptin was mediated via PI 3-kinase and ERK1/2 by using the inhibitors LY294002 and PD98059, respectively. We also confirm that leptin activates both PI 3-kinase and ERK1/2 in these cells. We show that hyperplasia was not affected by leptin by measuring rat glomerular mesangial cell number and by assessing bromodeoxyuridine uptake. Leptin also did not alter caspase 3-like activity under control conditions or upon induction of apoptosis by ultraviolet light, suggesting that apoptosis was not regulated by leptin in these cells. CONCLUSION: Our results show that leptin induced glomerular mesangial cell hypertrophy via PI 3-kinase and ERK1/2, and that hyperplasia and apoptosis were not altered by leptin. The hypertrophic effect of leptin may play a role in the pathophysiology of nephropathy associated with obesity.