RF21 | PSAT77 ROLE OF THE TRANSCRIPTION FACTOR HHEX IN INNER ADRENAL CORTEX HOMEOSTASIS AND RESPONSE TO PROGESTERONE SIGNALING

Congenital adrenal hyperplasia (CAH) is a set of defects in cortisol synthesis due to mutations in genes encoding steroidogenic enzymes. Consequently, the loss of glucocorticoid-mediated negative feedback on the HPA axis leads to chronically elevated ACTH (Adrenocorticotropin Hormone) secretion. The sustained ACTH elevation, in turn, stimulates proliferation and hypertrophy of the adrenal cortex and leads to overproduction of androgens. To study the complexity of the ACTH-responsive cell population in the adrenal cortex, we performed single-cell RNA sequencing of the steroidogenic lineage in the adult mouse adrenal. We identified the transcription factor HHEX as a gene with restricted expression in the ACTH-responsive zona fasciculata. Although the role of HHEX in adrenal biology is completely unknown, a meta-analysis identified a germ-line variant of uncertain significance near the gene HHEX associated with increased DHEAS (adrenal-specific androgen) in human serum samples, which led us to hypothesize that HHEX contributes to the unique function of the ACTH-responsive inner cortex. To investigate the mechanisms by which HHEX controls adrenal differentiation and homeostasis, we generated genetically modified mice harboring a deletion of the Hhex gene in the adrenal cortex. Hhex KO mice exhibited progressive adrenomegaly by 15 weeks of age, accompanied by hypertrophy prominent in the inner cortex and disruption of the endothelial organization. Expression of the transcription factor Nr5a1/Sf-1 and steroidogenic enzymes involved in corticosterone production were significantly upregulated at 6 weeks old, prior to adenomegaly, suggesting a precocious increase in cell production of glucocorticoids. For insights into the signaling pathways controlled by HHEX, we analyzed global transcriptional changes during loss of Hhex and found dramatic downregulation of members of the membranous progesterone receptor family (PAQR). PAQR signaling has been implicated in the downregulation of cAMP, a primary mediator of ACTH signaling, and thereby could, in part, drive the increase in steroidogenesis in Hhex KO mice. These findings suggest that the inner cortex contains a progesterone-responsive cell population in which HHEX provides additional fine-tuning of ACTH-driven cAMP signaling by progesterone and derivatives. Since we observed an increase in Hhex expression in a mouse model of CAH, experiments are now ongoing to assess the implication of HHEX and autocrine progesterone signaling in contributing to the hypertrophy and steroidogenic phenotype observed in CAH. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m., Sunday, June 12, 2022 12:54 p.m. - 12:59 p.m.