Leptin–thyroid hormone axis affects energy use in muscle

Thyroid hormones have a wide range of functions, including regulating energy metabolism. In a study published in Cell Metabolism, a group of researchers show that leptin is involved in thyroid hormone activation, which results in an increased metabolic rate in the context of obesity.

In mice, leptin injection increased the expression of type 2 deiodinase mRNA. Of note, this effect was not seen in db/db mice, which lack the leptin receptor. Leptin injection also increased intramuscular levels of triiodothyronine in wild-type mice, but not in db/db mice. Systemic levels of thyroid hormones were not changed following leptin injection, which indicates that the hypothalamus–pituitary–thyroid axis was not affected by leptin treatment. The authors also demonstrated that leptin alters type 2 deiodinase expression via a mechanism that is dependent on STAT3 and α-MSH.