TSH effects on thermogenesis in rat brown adipocytes

Abstract

Brown adipose tissue (BAT) thermogenesis increases under cold exposure due to UCP1 activation. T3 stimulates UCP1 adrenergic stimulation and is required for BAT thermogenesis. D2 produces T3 under adrenergic stimulation. The TSH receptor (TSHR) is present in BAT and cold exposure down-regulates it. In brown adipocytes basal UCP1 and D2 activity and mRNA increase using high TSH doses (10-100 mU/ml). The function of TSH in adipose tissue remains to be clarified. [Objectives]: To examine the effect of TSH on TSHR, UCP1, D2 and leptin mRNAs in rat brown adipocytes, under T3, NE, T3+NE treatment, analyzing TSH signalling pathways, and to check the TSH effect on O2 consumption. [Methods]: Primary cultures of rat brown adipocytes were used. TSHR, UCP1, D2, leptin mRNAs were analyzed by qRTPCR using Taqman probes. D2 activities were determined using 2 nM T4. O2 consumption was measured in Seahorse plates. [Results]: TSHR increased during adipocyte differentiation and with insulin and decreased with NE, T3 or both. TSH increased basal and T3-stimulated UCP1 mRNA (100- and 1000-fold), but did not improve the adrenergic induction of UCP1. TSH increased (6-fold) basal and T3-stimulated D2 mRNA only at the highest dose. TSH added to NE-treated cells decreased D2 mRNA by 15-25%. TSH had no effect on basal D2 activities but increased D2 activity in T3-treated cells. TSH added to T3+NE decreased D2 activity in a dose-dependent manner to 50%. NE and TSH (1-10 mU/ml) increased O2 consumption by 20-40% and these effects were maintained 2 h and after overnight treatment. T3 had no effect. TSH inhibited leptin mRNA. [Conclusions]: TSHR increases by insulin and during differentiation of brown adipocytes, while T3 and NE down-regulate it. TSH increases basal and T3-stimulated UCP1 and D2 mRNA. TSH regulates UCP1 and D2, thermogenic markers of BAT and increases O2 consumption.