Effect of platelet-derived transforming growth factor (TGF) type β1 on murine inflammatory mononuclear phagocytes: Increased fibronectin production

Abstract

The effect of transforming growth factor type β1 (TGF-β1) on mononuclear phagocytes (macrophages), cells which play an important role in the inflammatory response resulting from tissue wounding, was investigated. We found that fibronectin production by murine inflammatory macrophages is significantly enhanced by highly purified human TGF-β1 in a time- and dosedependent manner. Specifically, 2 p M TGF-β1 was sufficient to cause significant elevation of fibronectin levels, which peaked between 24 and 48 hr of incubation. Both TGF-β1-induced and basal levels of fibronectin were completely abolished by cycloheximide, suggesting that protein synthesis was required. Furthermore, fibronectin mRNA levels were significantly enhanced in TGF-β1-treated macrophages. The inductive capacity of TGF-β1 appeared specific since other agents such as phorbol myristate acetate and endotoxin failed to induce fibronectin production. Since macrophages have been recently shown to secrete an inactive form of TGF-β1, the ability of this precursor molecule to induce fibronectin production was tested. It was found that partially purified human platelet latent TGF-β1 could not induce fibronectin synthesis, whereas acid treatment of the same preparation which releases mature TGF-β1 enhanced fibronectin production. Taken together, results presented here suggest that inflammatory macrophages can directly contribute to the formation of extracellular matrix upon interaction with TGF-β1 and that these cells lack the ability to augment fibronectin production in response to a platelet-derived latent form of TGF-β1.