Abstract P250: Sphingosine-1-phosphate Receptor Agonist And Very Low-density Lipoprotein Regulate Aldosterone Production Via Lipin-1 In Human Adrenocortical Cells

Abstract

Aldosterone is considered to be a link between hypertension and obesity; obese individuals have high serum levels of both sphingosine-1-phosphate (S1P) and very low-density lipoprotein (VLDL). S1P has been reported to be a novel stimulator of aldosterone secretion and phospholipase D (PLD) activity. VLDL has also been shown to stimulate aldosterone production in multiple zona glomerulosa cell models via PLD. PLD is an enzyme that hydrolyzes phosphatidylcholine to phosphatidic acid (PA) which can then be converted to diacylglycerol (DAG) by lipin-1. However, it is unclear which of the two lipid signals, PA or DAG, underlies PLD’s mediation of aldosterone production. We hypothesized that the S1P1 receptor (S1PR1) agonist, SEW2871, (and VLDL) induces steroidogenesis and therefore aldosterone production via lipin-1-mediated metabolism of PA to DAG, with our hypothesis focusing on DAG as the key lipid signal produced by PLD (indirectly). In HAC15 cells, lipin-1 was overexpressed using an adenovirus or inhibited using propranolol followed by treatment with or without SEW2871 (or VLDL) for 24 h. Steroidogenic gene expression and aldosterone levels were monitored by qRT-PCR and radioimmunoassay, respectively. We demonstrated that lipin-1 overexpression (OE) enhanced the SEW2871-stimulated 109-fold increase in CYP11B2 expression by 26% while lipin-1 inhibition decreased the SEW2871-stimulated 56-fold increase in CYP11B2 expression by 74%. While lipin-1 OE had no further effect, propranolol reduced SEW2871-stimulated increases in NR4A1 (2-fold) and NR4A2 (9-fold) mRNA levels by 22% and 52% respectively. The SEW2871-stimulated increase in aldosterone production was inhibited by propranolol (53%), although it was not enhanced by lipin-1 OE. Similar results were obtained with VLDL. Our results are, therefore, suggestive of DAG being the key lipid signal since regulating lipin-1 affects S1PR1 agonist- and VLDL-stimulated steroidogenic gene expression and ultimately, aldosterone production. Our study warrants further investigation into these steroidogenic signaling pathways which can lead to the identification of novel therapeutic targets such as lipin-1, or its downstream pathways, to potentially treat obesity-associated hypertension.