OR19-1 Ncor1 Regulates the Expression of Dhcr24, which Controls de novo Cholesterol Synthesis in the Adrenal Gland Inner Cortex

Abstract

Abstract In many types of cells and tissues, the nuclear receptor corepressor 1 (Ncor1) is known as a main corepressor that interacts with thyroid hormone receptors (i.e., TRα, TRβ1, and TRβ2). In the absence of thyroid hormone (T3), NCOR1 is recruited by TRs to inhibit gene transcription. In the liver, the deletion of Ncor1 increases hepatic triglyceride levels. However, the detailed mechanism of how NCOR1 is involved in thyroid hormone signaling in different types of tissues is not fully understood. Our previous study showed that TRβ1 is expressed in the adrenal gland inner cortex and T3 treatment leads to the hypertrophy of this area. To determine the role of NCOR1 in the regulation of thyroid hormone signaling in adrenocortical cells, we generated the mice with a conditional deletion of Ncor1 in the adrenal cortex by crossing the Ncor1 floxed mice with the steroidogenic factor 1 (SF1) Cre mice. The RNA-seq data showed that only 76 genes were differentially expressed in adrenal glands due to the deletion of Ncor1 in adrenocortical cells. Gene ontology (GO) analysis revealed that 'cholesterol synthesis’ was the top GO term associated with these 76 genes. Interestingly, 24-dehydrocholesterol reductase (Dhcr24), the key enzyme for cholesterol synthesis, was upregulated in knockout mice adrenal glands in both sexes. This phenotype fits the results in our previous studies that (1) Dhcr24 is significantly increased under T3 treatment in wild-type mice adrenal glands and (2) the DHCR24-expressing zone in the inner cortex is the primary responsive adrenal cortical layer under T3 treatment which leads to increased lipid accumulation in this area. To further study how DHCR24 is involved in this T3-induced lipid accumulation in the adrenal gland inner cortex, we generated Dhcr24 conditional knockout mice. We found that the T3-induced lipid accumulation in the adrenal gland inner cortex was sharply decreased in the Dhcr24;Sf1-Cre mice. In summary, with the Ncor1 conditional knockout mice, we found that the regulation of the cholesterol synthesis through DHCR24 is the primary function of NCOR1 in the adrenal gland inner cortex; by using the Dhcr24 conditional knockout mice, we further confirmed that the T3-induced lipid accumulation in the adrenal inner cortex can be blocked by the deletion of DHCR24. This study used genetic mouse models to decipher the connection between nuclear receptor corepressor Ncor1, the cholesterol synthesis enzyme Dhcr24, and how they control de novo cholesterol synthesis in the adrenal gland inner cortex. Presentation: Monday, June 13, 2022 11:00 a.m. - 11:15 a.m.