3,5 Diiodo-l-Thyronine (T(2)) Promotes the Browning of White Adipose Tissue in High-Fat Diet-Induced Overweight Male Rats Housed at Thermoneutrality

The conversion of white adipose cells into beige adipose cells is known as browning, a process affecting energy metabolism. It has been shown that 3,5 diiodo-l-thyronine (T(2)), an endogenous metabolite of thyroid hormones, stimulates energy expenditure and a reduction in fat mass. In light of the above, the purpose of this study was to test whether in an animal model of fat accumulation, T(2) has the potential to activate a browning process and to explore the underlying mechanism. Three groups of rats were used: (i) receiving a standard diet for 14 weeks; (ii) receiving a high-fat diet (HFD) for 14 weeks; and (iii) receiving a high fat diet for 10 weeks and being subsequently treated for four weeks with an HFD together with the administration of T(2). We showed that T(2) was able to induce a browning in the white adipose tissue of T(2)-treated rats. We also showed that some miRNA (miR133a and miR196a) and MAP kinase 6 were involved in this process. These results indicate that, among others, the browning may be another cellular/molecular mechanism by which T(2) exerts its beneficial effects of contrast to overweight and of reduction of fat mass in rats subjected to HFD.