Phospholipase D Activity Underlies Very-Low-Density Lipoprotein (VLDL)-induced Aldosterone Production in Adrenal Glomerulosa Cells

Abstract

Aldosterone is the mineralocorticoid responsible for sodium retention, thus increased blood volume and pressure. Excessive production of aldosterone results in high blood pressure as well as renal disease, stroke, and visual loss via both direct effects and effects on blood pressure. Weight gain is often associated with increased blood pressure, but it remains unclear how obesity increases blood pressure. Obese patients typically have higher lipoprotein levels; moreover, some studies have suggested that aldosterone levels are also elevated and represent a link between obesity and hypertension. Very-low-density lipoprotein (VLDL) functions to transport triglycerides from the liver to peripheral tissues. Although previous studies have demonstrated that VLDL can stimulate aldosterone production, the mechanisms underlying this effect are largely unclear. Here we show for the first time that phospholipase D (PLD) is involved in VLDL-induced aldosterone production in both a human adrenocortical cell line (HAC15) and primary cultures of bovine zona glomerulosa cells. Our data also reveal that PLD mediates steroidogenic acute regulatory (StAR) protein and aldosterone synthase (CYP11B2) expression via increasing the phosphorylation (activation) of their regulatory transcription factors. Finally, by using selective PLD inhibitors, our studies suggest that both PLD1 and PLD2 isoforms play an important role in VLDL-induced aldosterone production.

Obesity, hypertension and aldosterone: is leptin the link?

“…In recent studies, we showed in primary cultures of human adrenocortical and bovine glomerulosa cells, as well as the adrenocortical cell line, H295R, and its clone the HAC15 cell line, that VLDL significantly increases aldosterone synthesis in these various models of zona glomerulosa cells (Xing et al 2012, Tsai et al 2014). This stimulation occurs at physiological VLDL levels of 30-100 µg protein/mL and is largely due to VLDL's stimulation of the expression of steroidogenic acute regulatory protein and CYP11B2 (Xing et al 2012).…”

“…This stimulation occurs at physiological VLDL levels of 30-100 µg protein/mL and is largely due to VLDL's stimulation of the expression of steroidogenic acute regulatory protein and CYP11B2 (Xing et al 2012). In the H295R cell line, the effects of VLDL on CYP11B2 transcript levels are not additive with high AngII or elevated extracellular potassium levels, but are additive with the cAMP-elevating agents ACTH and forskolin (Xing et al 2012) and are not altered by exposure to an AT1R antagonist (Tsai et al 2014). The effect of VLDL on aldosterone and CYP11B2 involves the calcium signaling pathway, as the changes can be inhibited by antagonists 230:1 of voltage-dependent L-type calcium channels and calcium/calmodulin-dependent protein kinases (Xing et al 2012).…”

“…The effect of VLDL on aldosterone and CYP11B2 involves the calcium signaling pathway, as the changes can be inhibited by antagonists 230:1 of voltage-dependent L-type calcium channels and calcium/calmodulin-dependent protein kinases (Xing et al 2012). Phospholipase D has also been found to mediate aldosterone production and CYP11B2 expression in response to VLDL (Tsai et al 2014), similarly to its role in AngII-induced steroidogenesis. Finally, we also showed that rats on a chow and liquid-sucrose diet that induces obesity and insulin resistance exhibit increased aldosterone synthase levels correlating with elevated triglyceride levels (a measure of VLDL levels in fasted animals) in vivo (Xing et al 2012).…”

Very low-density lipoprotein (VLDL)-induced signals mediating aldosterone production

“…In collaboration, we showed that VLDL stimulates aldosterone production in multiple zona glomerulosa cell models, including primary cultures of bovine adrenal glomerulosa cells and human adrenocortical cells as well as the human adrenocortical carcinoma cell line, H295R cells (Xing et al 2012). In subsequent studies, we also showed a similar effect in the HAC15 cell line (Tsai et al 2014), a clone of H295R, which shows good responses to AngII and ACTH . The ability of VLDL to enhance CYP11B2 expression is not additive with a near-maximal concentration of angiotensin II (10 nM) but VLDL enhances the stimulatory effect of the cAMP pathway agonist forskolin, even at a high dose (10 µM) that causes a large increase in cAMP levels and aldosterone production in H295R cells (Fassnacht et al 1998).…”

“…In further studies, a key role of phospholipase D (PLD) in the VLDL response was also demonstrated (Tsai et al 2014), similar to the involvement of this lipid-metabolizing enzyme in AngII-and sphingosine 1-phosphate-induced aldosterone secretion (e.g., Brizuela et al 2006, Qin et al 2010and reviewed in Bollag 2016. Thus, PLD inhibitors reduce VLDL-induced CYP11B2 expression and aldosterone secretion, as does overexpression of lipase-inactive mutants of either PLD1 or PLD2 (Tsai et al 2014).…”