Thyroid Hormone Receptor α Modulates Lipopolysaccharide-Induced Changes in Peripheral Thyroid Hormone Metabolism

Acute inflammation is characterized by low serum T3 and T4 levels accompanied by changes in liver type 1 deiodinase (D1), liver D3, muscle D2, and muscle D3 expression. It is unknown at present whether thyroid hormone receptor α (TRα) plays a role in altered peripheral thyroid hormone metabolism during acute illness in vivo. We induced acute illness in TRα-deficient (TRα0/0) mice by administration of a sublethal dose of LPS. Compared with wild-type, TRα0/0 mice have lower basal serum T4 and lower liver D1 activity and muscle D3 mRNA expression, whereas liver D3 activity is higher. These changes are gender specific. The inflammatory response to LPS was similar in WT and TRα0/0 mice. The decrease in serum thyroid hormones and liver D1 was attenuated in TRα0/0 mice, whereas the LPS induced fall in liver D3 mRNA was more pronounced in TRα0/0 mice. Muscle D2 mRNA increased similarly in both strains, whereas muscle D3 mRNA decreased less pronounced in TRα0/0 mice. We conclude that alterations in peripheral thyroid hormone metabolism induced by LPS administration are partly regulated via TRα. Illness-induced decrease of serum T4, liver D1, and muscle D3 is partly regulated via Trα, whereas TRβ is involved in liver D3 decrease during illness.