Effect of Thyroid hormone on Lipogenesis in Rat White and Brown Adipocytes Culture System

Thyroid hormone(T3) stimulates hepatic lipogenesis by increasing expression of genes, indluding acetyl-CoA carboxylase and fatty acid synthase. S14 protein, which is thougth to be involved in lipid metabolism , appears to respond in parallel . Effect of T3 on lipogenesis in white and brown adipose tissue are less clear, and may be complicated by indirect effects of the hormone. We developed an adipocytes system where the indirect effects of thyroid hormone are abolished and direct effects of T3 on lipogenesis could be tested. Fat accumulation was mesured by Oil-Red O staining. Insulin clearly enhanced fat accumulation by 2-fold . Isobutylemethylxanthie(IBMX) apeared to inhibit insulin -stimulated fat accumulation. Dexamethasone increased insulin-stimulatedfat accumulation about 1.3-fold. confluent adipocytes were cultured in serum-free medium or medium containing 10% fetal calf serum or 10% fetal calf serum stripped of thyroid hormone and lipogenesis, assessed by the incorporation of 3H2O , was measured. Medium without serum or supplemented with T3-depleted serum did not amplify the stimulatory effect of T3 on lipogenesis compared to medium containing 10% fetal calf seru. Dexamethasone alone led to a decrease inlopogenesis of about 50 % in white adipocytes and 25% in brown adipocytes. However, dexamethasone amplified the lipogenic respnse to T3 by about 30% in whit eadipocytes and 60% in brown adipocytes. T3(1$\mu$M) stimulated lipogenesis and acetyl-CoA carboxylase and fatty acid syntase mRNA levels up to 2 -fold in both types of adipocytes. It seems that these adipocytes systems are as useful model to study the effects of hormones on lipogenic gene expression as well as lipogenesis.