ADIPOSE TISSUES FROM VARIOUS ANATOMICAL SITES ARE CHARACTERIZED BY DIFFERENT PATTERNS OF GENE-EXPRESSION AND REGULATION

We have shown previously the presence of brown adipocytes among white fat pads, and proposed the existence of a spectrum of adipose depots a ccording to the abundance of brown fat cells [Cousin, Cinti, Morroni, Raimbault, Ricquier, Penicaud and Casteilla (1992) J. Cell Sci. 103, 9 31-942]. In this study, we tried to characterize this spectrum better. We determined in several adipose depots (i) the richness of pre-adipo se cells, as assessed by A2COL6 mRNA levels; (ii) whether a fat pad wa s characterized by a pattern of mRNA expression; (iii) whether this pa ttern was close related to abundance of brown adipocytes, and (iv) whe ther the regulation of this pattern by catecholamines under cold expos ure or beta-agonist treatment was similar in the different pads. This was achieved by studying proteins involved in glucose and lipid metabo lism such as insulin-sensitive glucose transporter (GLUT4), fatty acid synthase, lipoprotein lipase and fatty acid binding protein aP2, as w ell as beta3-adrenergic-receptor expression. Among white adipose depot s, the periovarian fat pad was characterized by the highest content of pre-adipocytes and of brown adipocytes, and inguinal fat by the highe st lipogenic activity potential. There was no close correlation betwee n beta3-adrenergic-receptor expression and brown adipocyte content in the tissues, as measured by the degree of uncoupling protein (UCP) gen e expression. However, in pads expressing UCP mRNA, mRNA levels of bet a3-adrenergic receptor and other markers were increased in parallel. U nder cold exposure or beta3-agonist treatment, a specific up-regulatio n of GLUT4 expression was observed in interscapular brown adipose tiss ue. The regional difference described in this study, could participate in preferential fat-pad growth under physiological conditions as well as in pathological situations.