OR26-5 Musashi-2 Regulatory Interactions Promote Adrenal Steroidogenesis

Abstract The adrenal gland is the site of steroid hormone synthesis. These hormones regulate many physiological processes including metabolism, blood pressure and volume, and sexual characteristic development. While signaling pathways, steroidogenic enzymes, and transcription factors have all been well characterized, little is known about the contribution of RNA-binding proteins (RBPs) in regulating steroidogenesis. We recently demonstrated that regulated RNA decay controls the timing of the steroidogenic gene expression response and identified 9 RBPs that regulate aldosterone production in an immortalized human cell line model for steroidogenesis, H295R. One of the RBPs we identified was Musashi-2 (MSI2), which is required for development of other steroidogenic tissues such as ovary and testis in mice. We found that MSI2 mRNA is enriched in human adrenal glands relative to other tissues, positively correlates in expression with mRNAs encoding steroidogenic enzymes, and abundantly expressed in H295R cells. Staining of normal human adrenal gland sections demonstrated that MSI2 protein is expressed in all three layers of the human adrenal cortex. Taken together, we hypothesized that MSI2 promotes steroidogenesis through regulating expression of target mRNAs encoding. Using the selective MSI2 inhibitor Ro-08-2750 (Ro) we found that aldosterone and cortisol production is decreased in a dosage dependent manner in H295R cells, which is consistent with siRNA knockdown of MSI2. We performed RNA-immunoprecipitation and sequencing and identified 1428 mRNA targets of MSI2 in H295R cells. A target of interest was Stearoyl-CoA Desaturase (SCD), which functions to convert saturated fatty acids to unsaturated fatty acids that promote formation of lipid droplets. Cholesterol esters in lipid droplets are a source of cholesterol used to produce all steroid hormones. Ro treatment of H295R cells resulted in a suppression of SCD mRNA and protein induction. Furthermore, inhibition of SCD with A939572 caused a dosage dependent decrease in aldosterone production. These data suggest that potentiation of stimulation dependent SCD induction is one mechanism by which MSI2 promotes steroidogenesis. It will be important to determine if and how MSI2 promotes steroidogenesis in primary human adrenal cells and mouse models. Since it is possible to deliver oligonucleotides to the adrenal cortex, disruption of MSI2-SCD mRNA regulatory interactions may open new therapeutic avenues for modulate aldosterone production. Presentation: Monday, June 13, 2022 12:00 p.m. - 12:15 p.m.