Thrombospondin peptides are potent inhibitors of mesangial and glomerular endothelial cell proliferation in vitro and in vivo

Background. Thrombospondin 1 (TSP1), a multifunctional, matricellular glyco protein, is expressed de novo in many inflammatory disease processes, inclu ding glomerular disease. Short peptide fragments derived from the type I pr operdin repeats of the TSP1 molecule mimic anti-angiogenic and/or transform ing growth factor-p (TGF-P)-activating properties of the whole TSP1. glycop rotein. We investigated the effects of D-reverse peptides derived from the type I domain of TSP1 in experimental mesangial proliferative glomeruloneph ritis in the rat (anti-Thy1 model), as well as their effects on cultured me sangial and glomerular endothelial cells. Methods. Effects of TSP peptides on proliferation of mesangial or glomerula r endothelial cells in culture after growth arrest or growth factor stimula tion (fibroblast growth factor-2, platelet-derived growth factor-BE, 10% fe tal calf serum) were measured by [H-3]thymidine incorporation assay. Adhesi on of rat mesangial cells (MCs) to a TSP-peptide matrix was assayed using a n attachment-hexosaminidase assay. TSP peptides were intraperitoneally inje cted daily in rats that had received an intravenous injection of polyclonal anti-Thy1 antibody to induce mesangial proliferative glomerulonephritis. O n biopsies from days 2, 5, and 8 of anti-Thy1 disease, mesangial and glomer ular endothelial proliferation, matrix expansion, mesangial activation, and microaneurysm formation were assessed. Functional parameters such as blood pressure and proteinuria were also measured. Results. An 18-amino acid peptide (type I peptide) with antiangiogenic and TGF-P-activating sequences decreased mesangial and glomerular endothelial c ell proliferation in vitro and in vivo and reduced microaneurysm formation and proteinuria in experimental glomerulonephritis. Analogues lacking the T GF-P-activating sequence mimicked most effects of the type I peptide. The m echanism of action of these peptides may include antagonism of fibroblast g rowth factor-2 and alteration of MC adhesion. The TGF-P-activating sequence alone did not have significant effects on mesangial or glomerular endothel ial cells in vitro or in experimental kidney disease in vivo. Conclusion. Peptides from TSP1 may be promising therapeutics in treating gl omerular disease with mesangial and endothelial cell injury.