3,5 Diiodo-l-Thyronine (T2) 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.