PS-B12-6: OXIDIZED LDL ENHANCES AT1-GQ SIGNALING MEDIATED BY ANGIOTENSIN II THROUGH LOX-1-AT1 COMPLEX IN ADRENAL CELLS.

Abstract

Objectives: Previous clinical studies have implied that dyslipidemia is associated with increase of blood pressure (BP) or the incidence of hypertension. Oxidized LDL (oxLDL), which is increased in dyslipidemia, binds to lectin-like oxLDL receptor (LOX-1), while angiotensin II (AII), which is involved in the development of hypertension, binds to AII type 1 receptor (AT1), a G protein-coupled receptor. Using vascular endothelial cells, we have shown that LOX-1 and AT1 form a complex on the plasma membrane and oxLDL activates AT1. Notably, the activation of G protein by oxLDL is partial as shown by the results that it activates Gai but not Gaq (Gq), the latter of which mediates the AII-induced BP elevation by mechanisms including the promotion of adrenal aldosterone synthesis. However, we recently found that additional treatment with oxLDL enhanced AT1-Gq signaling compared to AII alone in genetically engineered-Chinese hamster ovary cells expressing both AT1 and LOX-1. In the present study, we examined whether oxLDL enhances AII-Gq signaling in aldosterone-producing adrenal cells, in order to strengthen the hypothesis that oxLDL potentiates AII-induced aldosterone production. Design and Methods: H295R, human adrenal gland carcinoma cell line were treated with oxLDL, AII, or both. Gq-dependent activation of phospholipase C was quantified by measurement of inositol monophosphate (IP1) using the IP-One assay kit. When necessary, cells were pretreated with YM-254890, a Gq inhibitor or siRNA of AT1 or LOX-1. Gq-dependent activation of Ca2+ influx was quantified by measurement of intracellular Ca2+ concentrations using the Fura-2 Ca assay kit. Results: The IP1 assay showed that oxLDL additively increases AII-mediated IP1 production compared to AII alone. Pretreatment of Gq inhibitor or siRNA of AT1 completely abolished and siRNA of LOX-1 partially abolished the activation of AT1-Gq signaling by the combination of oxLDL and AII. In the Fura-2 Ca assay, although AII at concentrations as low as 10–11 M and oxLDL alone did not activate Ca influx, the combination of oxLDL and AII vigorously induced the phenomenon. Conclusions: These results suggest that oxLDL potentiates AII-Gq signaling via a pathway depending on the LOX-1-AT1 interaction in adrenal cells. Further investigation will be required to elucidate if this phenomenon contributes to enhanced production of aldosterone both in vitro and in vivo.