Thyroid hormones (THs) play a crucial role in regulating energy metabolism and interact with other endocrine and metabolic factors. Leptin, in particular, has been shown to enhance hypothalamic control over TH synthesis, acting as an adaptive response to regulate body weight. Caterina Miro's study revealed that TH signaling is heightened in overweight individuals but is diminished in those with obesity. In mice, both systemic and intracerebroventricular leptin injections lead to an increase in the expression of type 2 deiodinase (D2), an enzyme that activates TH, in skeletal muscle. Mechanistically, leptin boosts D2 transcription via a STAT3- and α-melanocyte-stimulating hormone (α-MSH)/cyclic AMP (cAMP)-dependent pathway. Importantly, mice that lack D2 or have a mutation in the TH receptor do not exhibit the metabolic effects of leptin, such as improved insulin sensitivity and increased oxygen consumption. This suggests that leptin’s peripheral metabolic effects in skeletal muscle are mediated by TH. These findings highlight leptin’s vital role in coordinating TH-driven metabolic activation, while also contributing to appetite suppression in response to perceived fat stores.
Mechanism:
Leptin enhances the expression of type 2 deiodinase (D2) in muscle tissue, an enzyme that converts the inactive thyroid hormone (T4) into its active form (T3).
Impact on metabolism:
The increased activation of thyroid hormones within muscle cells boosts metabolic activity, leading to higher energy expenditure and improved glucose uptake.
Relevance to energy balance:
By driving muscle metabolism through thyroid hormone activation, leptin helps regulate overall energy balance, signaling satiety when fat stores are sufficient.