Synthesis and secretion of plasminogen activator inhibitor-1 by human preadipocytes

To further investigate the role of plasminogen activator inhibitor-1 (PAI-1 ) in adipose tissue physiology, the production and regulation of PAI-1 was determined in primary cultures of human preadipocytes. When expressed as pr oduction per cell and cultured under identical conditions, human preadipocy tes from both visceral (omental) and sc depots of lean and obese individual s released significant, yet similar, amounts of PAI-1 protein into the cond itioned medium. High steady-state PAI-1 messenger RNA (mRNA) concentrations were observed in visceral and sc preadipocytes, with the relative level of expression equivalent to beta-actin mRNA. Tumor necrosis factor alpha sign ificantly decreased PAI-1 production in a concentration-dependent manner in both visceral and sc cultures, whereas transforming growth factor beta sig nificantly elevated PAI-1 production, but only in se preadipocytes from obe se individuals. Addition of insulin had no effect on antigen levels in cond itioned medium of preadipocyte cultures. Stimulation of the preadipocyte cu ltures with a defined medium resulted in differentiation to the adipocyte p henotype, as determined by flow cytometric analysis, verifying the cultures as human preadipocyte. These studies are the first to observe significant PAI-1 mRNA expression and protein production in primary cultures of a human adipose tissue cellular component, and they suggest that nascent adipocyte s contribute significantly to the elevated plasma PAI-1 observed in obesity .