A CD36-Binding Peptide from Thrombospondin-1 Can Stimulate Resorption by Osteoclasts in Vitro

Thrombospondin-1 (TSP-1), purified from platelets, stimulates resorption by avian osteoclasts in an in vitro resorption assay. TSP-1 binds to a number of different cellular receptors via different domains of the molecule and several short receptor-binding sequences have been identified within the TSP-1 molecule. In this study, we have used synthetic peptides representing these various sequences in order to identify the cellular receptor and TSP domain responsible for stimulation of resorption. We show that one peptide CSVTCG, which represents the CD36-binding region of TSP-1, stimulates resorption in a fashion similar to the intact molecule, while the peptides RGDS, RFYVVMWK, and RFYVVM, representing other cell-binding domains of TSP, have no effect on resorption. Using RT-PCR and immunoblotting, we further demonstrate expression of CD36 in human osteoclastoma (giant cell tumour), primary human bone derived cells, and clonal osteoblastic cells. These studies suggest that CD36 is involved in regulation of resorption by osteoclasts and is the receptor responsible for the resorption-promoting effects of TSP-1.