THE SHORT-TERM AND LONG-TERM EFFECTS OF TUMOR-NECROSIS-FACTOR-ALPHA AND BRL-49653 ON PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR (PPAR)GAMMA-2 GENE-EXPRESSION AND OTHER ADIPOCYTE GENES

Expression of turner necrosis factor-alpha (TNF alpha) in adipocytes h as been reported to correlate with insulin resistance associated with obesity, The thiazolidinediones such as BRL 49653 have been reported t o improve insulin sensitivity in obese animals and humans. Although it s exact mechanism of action is not known, BRL 49653 has been shown to antagonize some of the inhibitory actions of TNF alpha. BRL 49653 bind s and activates the peroxisome proliferator-activated receptor (PPAR g amma 2), an important nuclear transcription factor in adipocyte differ entiation; however, its regulation of PPAR gamma 2 in differentiated a dipocytes is unknown. In this paper, we find that BRL 49653 blocked th e ability of TNF alpha to down-regulate the expression and transcripti on of several adipocyte genes, but BRL 49653 did not prevent TNF alpha from down-regulating PPAR gamma 2. Moreover, BRL 49653 alone initiall y decreased the expression of PPAR gamma 2 mRNA and protein greatly. A fter 24 h of treatment in 3T3-L1 adipocytes, BRL 49653 down-regulated PPAR gamma 2 by greater than 90% and potentiated the decrease of PPAR gamma 2 mRNA by TNF alpha at this time. These unexpected results promp ted us to repeat the experiments for a longer time to determine whethe r BRL 49653 would continue to down-regulate PPAR gamma 2. With prolong ed BRL 49653 treatment, PPAR gamma 2 mRNA expression was not decreased as greatly, and the protein levels were decreased 20-30% below contro l at 72 h compared Po 90% at 24 h. Although BRL 49653 continued to pre vent the inhibitory effects of TNF alpha on perilipin and aP2 mRNA, by 72 h, BRL 49653 was not as potent an inhibitor of TNF alpha's down-re gulation of perilipin protein. Since PPAR gamma 2 protein was more abu ndant at this time, these results suggest that the level of PPAR gamma 2 protein is not the sole factor that regulates the transcriptional c ontrol by BRL 49653.