ERK-dependent signaling pathway and transcriptional factor Ets-1 regulate matrix metalloproteinase-9 production in transforming growth factor-beta 1 stimulated glomerular podocytes

The unregulated synthesis of glomerular basement membrane (GBM) components, extracelluar matrix (ECM) proteins, or the secretion of ECM-degradation enzymes, matrix metalloproteinases ( MMPs), by podocytes under pathological conditions might be major factors in GBM damage. The present study examined the effects and the underlying molecular mechanism of transforming growth factor beta 1 (TGF beta 1) on the production of gelatinase in cultured murine podocytes. Our results showed that TGF beta 1 is the most potent inducer of MMP-9 secretion in both a dose- and time-dependent manner, but has very little effect on MMP-2 secretion. TGF beta 1 upregulated MMP-9 mRNA levels, but did not affect the expression of matrix mettaloproteinases TIMP-1 mRNA. TGF beta 1 induced activation of both Smad2 and extracellular signal-regulated kinases (ERK1/2). However, blockade of Smad2 signaling pathway by Staurosporine did not affect the TGF beta 1-stimulated secretion of MMP-9, whereas inhibition of activation of ERK1/2 by PD98059 abolished TGF beta 1-stimulated secretion of MMP-9 and expression of MMP-9 mRNA. Protein levels of the transcriptional factor Ets-1 increased and were sustained for 12 h by TGF beta 1-stimulation. Our data also showed that blockage of ERK1/2 activation by PD98059 led to a reduction in the level of Ets-1 protein and to a consequent decrease in MMP-9 mRNA levels. These results demonstrate that TGF beta 1 can induce the production of MMP-9 in podocytes through the ERK1/2 MAPK pathway, and suggested that an increase in MMP-9 enzymatic activities may be involved in the damage of the GBM in response to inflammatory factors, ultimately leading to glomerulosclerosis.