Regulation of expression of leptin mRNA and secretion of leptin by thyroid hormone in 3T3-L1 adipocytes.

Leptin, the obese gene product, is secreted exclusively by adipocytes and regulates energy balance. We examined the effects of thyroid hormones on the regulation of leptin in 3T3-L1 adipocytes. Fully differentiated adipocytes were incubated with thyroid hormones, and the expression of leptin mRNA was measured by quantitative reverse transcription-polymerase chain reaction. After a 24-h incubation, triiodothyronine (T3) at 10-1000 nmol/l significantly increased the expression of leptin mRNA (237-337%). These stimulatory effects were not observed in preadipocytes. By contrast, thyroxine (T4) at 1-1000 nmol/l did not affect leptin mRNA expression in adipocytes. We also measured the levels of secreted leptin in conditioned media using radioimmunoassay. T3 at 10 and 1000 nmol/l significantly increased the levels of secreted leptin (132% and 126%, respectively) after a 24-h incubation. Our present data suggest that thyroid hormone is a novel regulator of leptin mRNA expression and protein secretion in 3T3-L1 adipocytes.