46-OR: The Transcriptional Coregulator Ldb1 Directly Regulates Brown Adipose Thermogenic Function

Abstract

Brown adipose tissue (BAT) is critical for mammalian thermogenesis. BAT utilizes fatty acids and glucose for heat production via mitochondrial uncoupling and is thus an attractive therapeutic target for combatting obesity. Exploiting the energy uncoupling capacity of this tissue will require a greater understanding of underlying BAT transcriptional mechanisms. Our prior work using a global deficiency model supported a novel role for the LIM domain-binding protein 1 (Ldb1) transcriptional co-regulator in regulating BAT function. However, direct roles for Ldb1 expressed in brown adipocytes has not been tested. Ldb1 acts as a scaffold to promote the assembly of transcriptional complexes and is important for the development and function of several metabolic tissues. We hypothesized that Ldb1 maintains BAT thermogenic function through direct regulation of thermogenic genes, like Ucp1. Loss of Ldb1 in primary brown adipocytes resulted in reduced expression of BAT-selective genes including Ucp1 and Elovl3 and the inability to induce Ucp1 expression upon Beta-3 adrenergic receptor agonism. This result was replicated using a siLdb1-transfected Ucp1-expressing cell line. To test Ldb1 roles on systemic thermogenesis, we developed a mouse model, termed Ldb1ΔBAT, where Ldb1 was reduced in thermogenic adipocytes using a Ucp1-driven Cre recombinase. Similar to our in vitro observations, Ldb1ΔBAT mice had reduced mRNAs of key BAT genes, including Ucp1 and Cidea. Through indirect calorimetry and a cold challenge, we uncovered significant impairments in energy expenditure and cold intolerance in Ldb1ΔBAT mice. To assess the transcriptional mechanisms underlying Ldb1 impacts on BAT thermogenesis, we conducted chromatin immunoprecipitation and found Ldb1 occupied upstream regulatory domains of Ucp1 in chromatin prepared from a BAT cell line and primary tissue. Overall, this work supports that Ldb1 is required for the thermogenic function of brown adipocytes. Disclosure J. Kepple: None. Y. Liu: None. T. Kim: None. K.M. Habegger: Consultant; Self; Glyscend, Inc. Research Support; Self; Daiichi Sankyo, Novo Nordisk Inc. M. Young: None. C.S. Hunter: None. Funding National Institutes of Health (R01DK111483, F31DK121414, T32GM109780)