SAT263 Osteocalcin Promotes Cortisol Production In Human Adrenal Cells

Abstract

Abstract Disclosure: R. Scheske: None. D. van Rooyen: None. W.E. Rainey: None. Background: Osteocalcin (OCN) is a peptide exclusively produced by osteoblasts in bone. In an uncarboxylated form, OCN has been shown to function as a hormone affecting physiological processes such as reproduction and energy metabolism in mice and humans. Murine studies have shown that uncarboxylated OCN upregulates fetal mouse glucocorticoid production through a unique regulatory axis between osteoblasts and adrenal cortex cells. The increase in adrenal steroid production has been attributed to OCN heightening adrenocorticotropic hormone (ACTH). The influence of adrenal glucocorticoids on glucose metabolism and bone composition is well studied but the effect of OCN on human adrenal steroidogenesis remains unknown. Herein, we hypothesized OCN would stimulate cortisol production in human adrenal cells. Methods: OCN’s effect on adrenal glucocorticoid production was investigated using primary cultures of human adrenal cells (PAC). Cells were treated for 24h with 1000 nM OCN with/without cAMP/protein kinase A (PKA) signaling pathway agonists (ACTH, forskolin, 8-bromo cAMP (8Br-cAMP), and dibutyryl cyclic AMP (dbcAMP)). Cortisol levels were quantified using an enzyme-linked immunosorbent assay. RNA was isolated and assessed by quantitative real-time PCR (RT-qPCR) to identify changes in transcript levels of enzymes catalyzing glucocorticoid production: cholesterol side-chain cleavage enzyme (CYP11A1), 17α-hydroxylase/17,20-lyase (CYP17A1), and 11β-hydroxylase (CYP11B1). Results: Cortisol production in PAC were significantly induced by all tested agonists; ACTH (22-fold), forskolin (27-fold), 8Br-cAMP (26-fold), and dbcAMP (30-fold) relative to basal. Although OCN, alone, did not significantly increase cortisol in this cell model, co-treatment with ACTH increased cortisol levels 1.4-fold (40.1 ng/mL; p<0.0001) compared to ACTH (28.2 ng/mL). Similarly, co-treatment with forskolin or 8Br-cAMP increased cortisol, relative to the respective agonists, by 1.3-fold (p<0.001) and dbcAMP by 1.2-fold (p<0.01). RT-qPCR analysis showed no changes in CYP11A1 or CYP17A1 transcript levels in co-treatments with OCN and ACTH relative to ACTH. However, CYP11B1 mRNA levels, relative to the respective controls, were increased in samples co-treated with OCN and ACTH/-agonist. OCN co-treatments with ACTH, forskolin, 8Br-cAMP and dbcAMP increased CYP11B1 levels by 1.8-, 1.4-, 1.3-, and 1.2-fold, respectively. Conclusion: Data presented in this study show stimulatory effect of OCN on human adrenal cells. OCN, in the presence of ACTH and other PKA agonists, increased cortisol production via upregulating CYP11B1 transcript levels. Defining the mechanism and receptor interaction through which OCN functions in human adrenal cells remain to be determined. Presentation: Saturday, June 17, 2023