Adipose tissue and skeletal muscle expression of genes associated with thyroid hormone action in obesity and insulin resistance.

BACKGROUND Thyroid hormone (TH) regulates metabolic pathways which may interfere with insulin action. There is limited knowledge on adipose tissue (AT) and skeletal muscle (SM) expression of genes associated with TH action in relation to insulin sensitivity. The aim of this study was to analyze AT and SM expression of the genes associated with TH action in subjects with different degree of insulin sensitivity and the regulation of these genes by insulin and free fatty acids (FFA). METHODS The study group comprised 72 euthyroid male subjects, 36 normal-weight and 36 overweight/obese. Two-hour hyperinsulinemic-euglycemic clamp and tissue biopsies were performed. In the subgroup of 20 subjects, 9 normal-weight and 11 overweight/obese, clamp was prolonged to 6h and another clamp with Intralipid/heparin infusion was performed after 1 week. Tissue biopsies were performed before and after each clamp. RESULTS Overweight/obese subjects had higher AT DIO2, DIO3, NCOR1, lower AT THRA and PPARGC1A, higher SM NCOR1 and lower SM DIO2, DIO3, PPARGC1A and ATP2A2 expression. In AT, DIO2 and PPARGC1A increased whereas NCOR1 and FOXO1 decreased after the clamp only in normal-weight individuals. DIO3 decreased in both groups. In SM, NCOR1 decreased whereas PPARGC1A and ATP2A2 increased after the clamp only in normal-weight individuals. Tissue THRA and THRB decreased in both groups. Intralipid/heparin abolished these effects. CONCLUSIONS Alterations in AT and SM expression of TH-related gene indicate a decreased tissue TH action in obesity. Inability to increase TH-related gene expression in obesity and during FFA oversupply may contribute to the aggravation of lipotoxicity.