Abstract 14623: “Estrogen Prevents Aortic Calcification by inducing MGP Expression and Inhibiting BMP Expression in an Estrogen Receptor alpha Dependent Way
Background: Unopposed RANKL (receptor activator of NFkB ligand) activation causes osteoporosis and vascular calcification in mice, and both phenotypes coincide in women with estrogen deficiency. RANKL inhibition by human monoclonal antibody (denosumab) ameliorates osteoporosis in postmenopausal women, and decreases calcium deposition in mice. Estrogen is also effective to treat osteoporosis, and clinical trials show its benefitial effect in vascular calcification. In this study we assessed the hypothesis that under estrogen deficiency, RANKL system may regulate both osteoporosis and vascular calcification, and we propose the molecular mechanism underpinning vascular calcification under RANKL activation.
Methods and Results: RANKL increased the expression of the calcification inducer bone morphogenetic protein (BMP) in human aortic endothelial cells (HAEC), and decreased the inhibitor matrix Gla protein (MGP) in human aortic smooth muscle cells (HASMC), which may support the paracrine function of BMP, as quantified by real-time PCR and western blot analysis. RANKL increased calcium deposition (Alizarin Red staining) followed by the osteogenic differentiation of HASMC. Using specific estrogen receptor (ER) agonists, we found that estrogen inhibited RANKL signaling in HAEC and HASMC via ER alpha. ApoE-deficient mice fed with western diet for 3 months presented atherosclerotic calcification (Oil Red and Alizarin Red staining) and osteoporosis (micro computed tomography analysis) after ovariectomy, and increased expression of RANKL, RANK and osteopontin in atherosclerotic lesion as detected by in situ hybridization. Estrogen (20 ug/kg/day 17beta-estradiol) inhibited osteoporosis and BMP osteogenic pathway in aorta by decreasing phosphorylation of smad-1/5/8 and increasing MGP mRNA expression.
Conclusions: RANKL leads to an imbalance of pro- and anti-calcification factors, and contributes to vascular calcification by regulating BMP and MGP, as well as bone-related protein expression. Estrogen decreases BMP signaling, and counteracts the effect of RANKL towards calcification by inducing MGP expression in HASMC and inhibiting RANKL-induced BMP expression in HAEC in an ER alpha dependent way.
- © 2010 by American Heart Association, Inc.