Effect of Thrombospondin-4 on Pro-inflammatory Phenotype Differentiation and Apoptosis in Macrophages.

Abstract

Thrombospondin-4 (TSP4) attracted a lot of attention recently as a result of new functions identified for this matricellular protein in cardiovascular, muscular, and nervous systems. We have previously reported that TSP4 promotes local vascular inflammation in mouse atherosclerosis model. A common variant of TSP4, P387-TSP4, was associated with increased cardiovascular disease risk in human population studies. In a mouse atherosclerosis model, TSP4 had profound effect on accumulation of macrophages in lesions, which prompted us to examine its effects on macrophages, more in detail in this report.\n\nWe examined the effects of A387-TSP-4 and P387-TSP-4 on mouse macrophages in cell culture and in vivo in the model of LPS-induced peritonitis. In tissues and in cell culture, TSP4 expression was associated with inflammation: TSP4 expression was upregulated in peritoneal tissues in LPS-induced peritonitis, and pro-inflammatory signals, INF{gamma}, GM-CSF, and LPS, induced TSP4 expression in macrophages in vivo and in cell culture. Deficiency in TSP-4 in macrophages from Thbs4-/- mice reduced the expression of pro-inflammatory macrophage markers, suggesting that TSP-4 facilitates macrophage differentiation into pro-inflammatory phenotype. Expression of TSP4, especially more active P387-TSP4, was associated with higher cellular apoptosis. Cultured macrophages displayed increased adhesion to TSP4 and reduced migration in presence of TSP4, and these responses were further increased with P387 variant.\n\nWe concluded that TSP4 expression in tissue macrophages and in cultured macrophages increases their accumulation in tissues during the acute inflammatory process and supports macrophage differentiation into a pro-inflammatory phenotype. In a model of acute inflammation, TSP4 supports pro-inflammatory macrophage apoptosis, a response that is closely related to their pro-inflammatory activity and release of pro-inflammatory signals. P387-TSP4 was found to be more active form of TSP4 in all examined functions.