Thyroid hormone receptor α in skeletal muscle is essential for T3-mediated increase in energy expenditure

Thyroid hormones are important for homeostatic control of energy metabolism and body temperature. Although skeletal muscle is considered a key site for thyroid action, the contribution of thyroid hormone receptor signaling in muscle to whole-body energy metabolism and body temperature has not been resolved. Here, we show that T3-induced increase in energy expenditure requires thyroid hormone receptor alpha 1 (TRα₁ ) in skeletal muscle, but that T3-mediated elevation in body temperature is achieved in the absence of muscle-TRα₁ . In slow-twitch soleus muscle, loss-of-function of TRα₁ (TRα^HSACre ) alters the fiber-type composition toward a more oxidative phenotype. The change in fiber-type composition, however, does not influence the running capacity or motivation to run. RNA-sequencing of soleus muscle from WT mice and TRα^HSACre mice revealed differentiated transcriptional regulation of genes associated with muscle thermogenesis, such as sarcolipin and UCP3, providing molecular clues pertaining to the mechanistic underpinnings of TRα₁ -linked control of whole-body metabolic rate. Together, this work establishes a fundamental role for skeletal muscle in T3-stimulated increase in whole-body energy expenditure.