Expression of thyrotropin and thyroid hormone receptors in adipose tissue of patients with morbid obesity and/or type 2 diabetes: effects of weight loss

Abstract

Increased thyroid-stimulating hormone (TSH) and FT₃ levels are often found in clinically euthyroid obese individuals. Information on thyroid gene expression in human adipose tissue is scarce. The objective of this study was to measure the expression of the TSH receptor (TSHR) and the thyroid hormone receptor (TRα1) genes in subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) in obese individuals and to test the effect of weight loss on these genes. This study is a prospective study involving 107 obese (body mass index (BMI)=46±8 kg m⁻², 52 with type 2 diabetes or impaired glucose tolerance) and 12 lean nondiabetic participants. A total of 27 obese patients were restudied 1 year after gastric bypass surgery. Total RNA was extracted from SAT and VAT obtained at baseline from all participants, and from SAT in obese patients post surgery. Circulating TSH and FT₃ levels were 170 and 36%, respectively, higher in obese patients than in controls. In SAT, TSHR and TRα1 were reduced in the obese by 67 and 33%, respectively, regardless of glucose tolerance. A similar trend was found in VAT. Post surgery, a BMI decrease of 33% was associated with a decrease in TSH and FT₃ levels and with a 150 and 70% increase in SAT of TSHR and TRα1, respectively. In both subcutaneous and visceral fat, the thyroid gene expression (especially TSHR) is reduced in obesity. The reversal of these changes with major weight loss and the reciprocal changes in plasma TSH and FT₃ levels suggest a role for adipocytes in the regulation of TSH and thyroid hormones.