Micah Foster
Pronouns: he/him
Research Mentor(s): Gary Hammer
Research Mentor School/College/Department: Internal Medicine MEND / Medicine
Program:
Authors: Micah Foster, Typhanie Dumontet, Christopher LaPensee, Gary D. Hammer
Session: Session 3 11:00 – 12:50 a.m. Hussey Room
Poster:
Abstract
Sex hormones influence the transcription of many genes, causing sexual dimorphism in organisms. Upon the investigation of Hhex (hematopoietically-expressed homeobox), an essential gene in defining adrenal gland cells and regulating adrenal cholesterol homeostasis, sexual dimorphism was observed. Specifically, HHEX knockout in mouse models presented with lipid depletion in the adrenal zona fasciculata of male but not female mice. Further, gonadectomy of HHEX knockout male mice rescued lipid droplets, revealing that HHEX is a mediator to androgen-induced lipid depletion of the adrenal zona fasciculata. To understand the mechanism HHEX uses to suppress androgen-induced lipid depletion, two processes of lipid catabolism, lipolysis and lipophagy, were investigated. Lipolysis refers to the breakdown cholesterol ester by the enzyme HSL (Hormone-sensitive lipase), while lipophagy refers to the targeted degradation of lipid droplets by autophagy machinery. SF1-Cre mice were crossed with Hhex floxed mice to generate wild-type (WT) and HHEX knockout (Hhex KO) mice. To evaluate lipolysis, levels of phosphorylated (active) hormone-sensitive lipase were compared between Hhex KO and WT mice using Western Blot. To assess lipophagy, levels of p62 were compared between Hhex KO and WT mice using immunohistochemistry. Experimental results revealed no increase in phospho-HSL levels between WT and Hhex KO mice. On the contrary, decreased levels of p62 were observed in the inner adrenal cortex of Hhex KO mice compared to WT, revealing the upregulation of lipophagy in Hhex KO. Further, upon gonadectomy, p62 levels were rescued in Hhex KO male mice, implying androgens as the driving force for increased lipophagy in Hhex KO. To confirm that the activation of lipophagy was responsible for the lipid depletion observed in male Hhex KO, we administered Hydroxychloroquine (HCQ) via drinking water to inhibit the fusion of autophagosomes with lysosomes, therefore preventing lipophagy in vivo. After 2 weeks of treatment, we performed immunohistochemistry for Plin1 to stain the adrenal lipid droplets and observed a partial rescue in HCQ-treated Hhex KO mice compared to Vehicle-treated. The experimental results suggested that HHEX prevents androgen-induced lipid depletion of the adrenal zona fasciculata by suppressing lipophagy. Taken together, these results imply that disrupting HHEX signaling could decrease cholesterol stores in the adrenal cortex which could ultimately lead to dysfunction of zona fasciculata and glucocorticoid production. Therefore, a better understanding of genetic programs and regulatory factors orchestrating the adrenal cortex function and sexual dimorphism have important implications for providing better care and new therapeutic options for patients suffering from adrenal diseases.
