SUN-746 Thyroid Hormone Receptor Alpha Sumoylation Is Important for the Development of Adipose Tissue

Thyroid hormone (TH) plays an essential role in normal development. TH action requires binding to its receptor. There are two types of thyroid hormone receptor, alpha (THRA) and beta (THRB). THRB is important for regulation of the Hypothalamic-Pituitary-Thyroid axis and regulating cholesterol metabolism. THRA is involved in the development and the function of brain, adipose tissue, small intestine, bone and heart. Both THRA and THRB are post-translationally modified by small ubiquitin-like modifier (SUMO). Previously, we showed in an in vitro model that mutation of a THRA sumoylation motif impairs proliferation and differentiation of human primary white adipocytes. This is due to interference of the desumolyated THRA in the cell cycle at G1/S phase and disruption of PPAR signaling. To determine the in vivo effects of a desumoylated THRA, we generated a mouse model carrying a mutation of the THRA gene, which eliminates SUMO conjugation at lysine (K) 283. At 12 weeks of age, there was no difference in body composition (body weight, fat mass, and lean mass) in THRA mutant mice compared to wild-type (WT). From 12 weeks onward mutant mice and WT did not have significant change body weight compared to Wt mice. However, THRA sumoylation mutant mice had much lower percent body fat. Dissected WAT fat pads from mutant mice were significantly smaller compared to WT mice. Histological analysis showed that the cell size of white adipose tissue in mutant mice was significantly smaller than that in Wt mice as well. Serum leptin levels in the mutant mice were significantly lower than that in mice, consistent with reduced fat mass. We isolated fat stem cells from stromal vesicular fraction of 6 week old mice and found that the number of fat stem cells was significant less in mutant mice compared to those in WT mice. This data suggest that de-sumoylated THRA is associated with reduced fat stem cells at a young age, resulting in reduced adipose tissue mass in adult. THRA sumoylation is important for thyroid hormone modulation of fat mass. Reference: (1) Yan-Yun Liu et al, JBC 2012 (2) Yan-Yun Liu et al., JBC 2015