Autocrine regulation of human preadipocyte migration by plasminogen activator inhibitor-1

One of the initial stages of adipogenesis is migration of preadipocytes of mesenchymal origin into cell clusters to form primitive fat organs. The ser ine protease inhibitor plasminogen activator inhibitor-1 (PAI-1) is synthes ized and released from human adipose tissue ex vivo and regulates smooth mu scle and endothelial cell migration in vitro, but its role in adipose tissu e is not known. We investigated the role of PAI-1 in cultures of human prea dipocytes from men and women of various ages and body mass indexes. Human p readipocytes expressed the messenger ribonucleic acid for PAI-1 and release d significant quantities of PAI-1 protein into the medium. As PAI-1 regulat es motility through the interaction of vitronectin with its receptor, the i ntegrin alpha(v)beta(3) we identified this receptor in human preadipocytes. Flow cytometric analysis indicated that human preadipocytes express the vi tronectin receptor alpha(v)beta(3), in a similar pattern as human umbilical vein endothelial cells. Functional studies indicated that active, but not latent, PAI-1 inhibited preadipocyte attachment to vitronectin with an IC50 of 13.3 nmol/L, and preincubation of vitronectin-coated Transwells with ac tive PAI-1 prevented preadipocyte migration. Vitronectin was identified in homogenates of the stromal-vascular fraction of human adipose tissue, but w as absent from human adipocytes and cultured preadipocytes. These data indi cate that human preadipocyte migration is regulated through the endogenous expression of PAI-1 and alpha(v)beta(3) integrin, a novel autocrine mechani sm for potentially regulating cell cluster formation in adipogenesis.