Estrogen inhibits vascular calcification via vascular RANKL system: common mechanism of osteoporosis and vascular calcification.
BACKGROUND
Arterial calcification and osteoporosis are associated in postmenopausal women. RANK (the receptor activator of nuclear factor kappaB), RANKL (RANK ligand), and osteoprotegerin are key proteins in bone metabolism and have been found at the site of aortic calcification. The role of these proteins in vasculature, as well as the contribution of estrogen to vascular calcification, is poorly understood.


OBJECTIVE
To clarify the mechanism of RANKL system to vascular calcification in the context of estrogen deficiency.


RESULTS
RANKL induced the calcification inducer bone morphogenetic protein-2 by human aortic endothelial cells (HAECs) and decreased the calcification inhibitor matrix Gla protein (MGP) in human aortic smooth muscle cells (HASMCs), as quantified by real-time PCR and Western blot analysis. RANKL also induced bone-related gene mRNA expression and calcium deposition (Alizarin red staining) followed by the osteogenic differentiation of HASMCs. Estrogen inhibited RANKL signaling in HAECs and HASMCs mainly through estrogen receptor alpha. Apolipoprotein E-deficient mice fed with Western high-fat diet for 3 months presented atherosclerotic calcification (Oil red and Alizarin red staining) and osteoporosis (microcomputed tomographic analysis) after ovariectomy and increased expression of RANKL, RANK, and osteopontin in atherosclerotic lesion, as detected by in situ hybridization. Estrogen replacement inhibited osteoporosis and the bone morphogenetic protein osteogenic pathway in aorta by decreasing phosphorylation of smad-1/5/8 and increasing MGP mRNA expression.


CONCLUSIONS
RANKL contributes to vascular calcification by regulating bone morphogenetic protein-2 and MGP expression, as well as bone-related proteins, and is counteracted by estrogen in a receptor-dependent manner.
Osako
Mariana Kiomy
MK
Division of Clinical Gene Therapy, Department of Geriatric Medicine, Graduate School of Medicine, Osaka University, Japan.
Nakagami
Hironori
H
Koibuchi
Nobutaka
N
Shimizu
Hideo
H
Nakagami
Futoshi
F
Koriyama
Hiroshi
H
Shimamura
Munehisa
M
Miyake
Takashi
T
Rakugi
Hiromi
H
Morishita
Ryuichi
R
D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000096:biosynthesis; D002114:Calcinosis / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D002478:Cells, Cultured; D004967:Estrogens / Q000502:physiology* / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D010024:Osteoporosis / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D053245:RANK Ligand / Q000037:antagonists & inhibitors / Q000502:physiology*; D014652:Vascular Diseases / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*
C525718:BMP2 protein, human; D055396:Bone Morphogenetic Protein 2; D004967:Estrogens; D053245:RANK Ligand