Reciprocal regulation of tissue-type and urokinase-type plasminogen activators in the differentiation of murine preadipocyte line 3T3-L1 and the hormonal regulation of fibrinolytic factors in the mature adipocytes

Adipose tissue expresses a variety of genes including tumor necrosis factor alpha and type-1 plasminogen activator inhibitor (PAI-1); and these factor s, produced by adipocytes, may be associated with the risk of coronary even ts in obesity. In this study, we characterized the production of fibrinolyt ic factors including tissue-type plasminogen activator (tPA), urokinase-typ e PA (uPA), and PAI-1 in the differentiation of preadipocytes, and examined the hormonal regulation of these fibrinolytic factors in mature adipocytes . Mouse 3T3-L1 preadipocytes were employed as a model of adipocytes. Adipoc yte differentiation was induced by insulin, dexamethasone, and 3-isobutyl-1 -methyl xanthine (IBMX). alpha -Glycerophosphate dehydrogenase (GPDH) activ ity and glucose transporter 4 (GLUT4) mRNA, indices for adipocyte maturatio n, were induced on Day 4, and gradually increased. GPDH activity reached it s maximum level on Day 14. The level of tPA, a major PA in preadipocytes, d ramatically decreased with differentiation. On the other hand, that of uPA reciprocally increased. PAI-1 production was also dramatically induced conc omitant with differentiation. In mature adipocytes, uPA production was domi nant (25 mug/ml/24 h vs. 0.8 mug/ml/24 h for tPA). Total PA activity in the mature adipocytes was reduced by insulin or clexamethasone, but not by glu cagon. Insulin, IBMX, and clexamethasone significantly decreased both uPA a nd tPA production, and increased PAI-1 production. Glucagon had no effect o n the production of these fibrinolytic factors. Our results reveal that uPA is one of the markers for the differentiation of 3T3-L1 cells and that ins ulin, IBMX, and clexamethasone are potent regulators of the fibrinolytic. a ctivity in differentiated 3T3-L1 cells, reciprocally affecting PA and PAM l evels in them. J. Cell. Physiol. 189: 72-78, 2001. (C) 2001 Wiley-Liss, Inc .