A TSP-1 functional fragment inhibits activation of latent transforming growth factor-β1 derived from rat alveolar macrophage after bleomycin treatment

The antineoplastic antibiotic, bleomycin, is known to induce a well-recognized model of lung fibrosis. Active transforming growth factor-β1 (TGF-β1) plays a key role in lung fibrosis induced by bleomycin, TSP-1 (thrombospondin-1) being critical to the activation of L (latent)-TGF-β1 by virtue of an association of the TSP-1/L-TGF-β1 complex with CD36, involving the sequence CSVTCG of the TSP-1 functional fragment. To observe the inhibitory effects of TSP-1 functional fragments, critical for CD36 binding, on the activation of L-TGF-β1, we isolated alveolar macrophages from Wistar rat lungs 7 days after bleomycin administration (5 mg/kg body weight) and cultured the cells with or without TSP-1 functional or control fragments. We observed a cell surface association of TGF-β1 with CD36 by immunofluorescence and quantified the active and total TGF-β1 by ELISA. The co-localization of CD36 with TGF-β1, shown by a yellow fluorescence deriving from a mixture of the green and red of the two components, for the TSP-1 functional fragment groups was clearly less than that of the TSP-1 control fragment groups. The quantities and the percentages of active TGF-β1 in the TSP-1 functional fragment groups were lower than those in the TSP-1 control fragment groups (P<0.05 or P<0.01). These findings suggest that TSP-1 functional fragments could inhibit the activation of L-TGF-β1 secreted by activated alveolar macrophages through blocking the binding of TSP-1 to CD36.