Induction of TGF-beta 1 by the matricellular protein SPARC in a rat model of glomerulonephritis

Background. SPARC has been implicated as a counteradhesive and antiprolifer ative protein associated with deposits of extracellular matrix in renal dis ease. Method. We have examined the effect of recombinant SPARC containing a C-ter minal His tag (rSPARC) in an acute model of mesangial cell injury that is i nduced 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. Results. rSPARC was localized to the renal glomeruli of rats treated with a nti-Thy1 antibody. Type I collagen and fibronectin, as well as transforming growth factor-beta 1 (TGF-beta 1), were increased at day 5 in rats treated with rSPARC (N = 4, P < 0.05 vs. delivery buffer), but only minimal effect s were seen on mesangial cell and endothelial cell proliferation. In primar y cultures of rat mesangial cells, infusion of rSPARC was associated with i ncreases in TGF-beta 1 mRNA and in total, secreted TGF-beta 1 protein. Conclusions. rSPARC stimulates expression of TGF-beta 1 both in vitro and i n vivo. Given the closely regulated expression of SPARC, TGF-beta 1, and ty pe I collagen in several animal models of glomerulonephritis, we propose th at SPARC could be one of the major mediators of the induction of TGF-beta 1 in renal disease.