Age-related differences in messenger ribonucleic acid expression of key proteins involved in adipose cell differentiation and metabolism

This study was performed to compare the expression of key proteins [lipopro tein lipase (LPL), hormone-sensitive lipase (HSL), complement 3 (C3), and p eroxisome proliferator-stimulated receptor-gamma (PPAR gamma)] involved in sc abdominal adipose tissue (AT) metabolism of young (n = 13) vs. middle-ag ed (n = 16) men. The sc abdominal AT-LPL activity as well as fat cell lipol ysis were also measured in both groups of men. Young and middle-aged men di splayed similar body weight and sc abdominal fat accumulation, measured by computed tomography. However, middle-aged men were characterized by a highe r percent body fat (28 +/- 5% us. 22 +/- 7%; P < 0.05) than young subjects. No difference between groups was observed in sc abdominal adipose tissue L PL activity. On the other hand, maximal lipolytic responses of sc abdominal adipocytes to isoproterenol (<beta>-adrenergic agonist) or to postadrenoce ptor agents such as dibutyryl cAMP, forskolin, and theophylline were lower in middle-aged than in young men (P < 0.05). AT-LPL messenger ribonucleic a cid (mRNA) levels were similar regardless of the subject's age. However, HS L, C3, and PPAR<gamma> mRNA levels were higher in middle-aged than in young individuals (P < 0.01-0.05). After correction for percent body fat, only H SL and C3 mRNA levels remained significantly different between groups (P < 0.05). Taken together, these results suggest that aging has an effect on th e up-regulation of HSL and C3 mRNA levels, whereas PPAR gamma expression se ems to be related mainly to increased adiposity.