Induction of TGF-β1 by the matricellular protein SPARC in a rat model of glomerulonephritis

Induction of TGF-β1 by the matricellular protein SPARC in a rat model of glomerulonephritis.BackgroundSPARC has been implicated as a counteradhesive and antiproliferative protein associated with deposits of extracellular matrix in renal disease.MethodWe have examined the effect of recombinant SPARC containing a C-terminal His tag (rSPARC) in an acute model of mesangial cell injury that is induced in the rat by an antibody against the Thy1 antigen on the mesangial cell membrane. The recombinant protein was administered 24 hours after the induction of nephritis and was infused through day 4.ResultsrSPARC was localized to the renal glomeruli of rats treated with anti-Thy1 antibody. Type I collagen and fibronectin, as well as transforming growth factor-β1 (TGF-β1), were increased at day 5 in rats treated with rSPARC (N = 4, P < 0.05 vs. delivery buffer), but only minimal effects were seen on mesangial cell and endothelial cell proliferation. In primary cultures of rat mesangial cells, infusion of rSPARC was associated with increases in TGF-β1 mRNA and in total, secreted TGF-β1 protein.ConclusionsrSPARC stimulates expression of TGF-β1 both in vitro and in vivo. Given the closely regulated expression of SPARC, TGF-β1, and type I collagen in several animal models of glomerulonephritis, we propose that SPARC could be one of the major mediators of the induction of TGF-β1 in renal disease.