title: Increased calcification in osteoprotegerin-deficient smooth muscle cells: Dependence on receptor activator of NF-κB ligand and interleukin 6.
abstract: OBJECTIVE
  Vascular calcification is highly correlated with cardiovascular disease morbidity and mortality. Osteoprotegerin (OPG) is a secreted decoy receptor for receptor activator of NF-κB ligand (RANKL). Inactivation of OPG in apolipoprotein E-deficient (ApoE-/-) mice increases lesion size and calcification. The mechanism(s) by which OPG is atheroprotective and anticalcific have not been entirely determined. We investigated whether OPG-deficient vascular smooth muscle cells (VSMCs) are more susceptible to mineralization and whether RANKL mediates this process.
  
  
  RESULTS
  Lesion-free aortas from 12-week-old ApoE-/-OPG-/- mice had spotty calcification, an appearance of osteochondrogenic factors and a decrease of smooth muscle markers when compared to ApoE-/-OPG+/+ aortas. In osteogenic conditions, VSMCs isolated from ApoE-/-OPG-/- (KO-VSMC) mice deposited more calcium than VSMCs isolated from ApoE-/-OPG+/+ (WT-VSMC) mice. Gene expression and biochemical analysis indicated accelerated osteochondrogenic differentiation. Ablation of RANKL signaling in KO-VSMCs rescued the accelerated calcification. While WT-VSMCs did not respond to RANKL treatment, KO-VSMCs responded with enhanced calcification and the upregulation of osteochondrogenic genes. RANKL strongly induced interleukin 6 (IL-6), which partially mediated RANKL-dependent calcification and gene expression in KO-VSMCs.
  
  
  CONCLUSIONS
  OPG inhibits vascular calcification by regulating the procalcific effects of RANKL on VSMCs and is thus a possible target for therapeutic intervention.
authors.affiliation: Department of Bioengineering, University of Washington, Seattle, Wash., USA.
authors.forename: Andrea
authors.initials: A
authors.lastname: Callegari
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Coons
authors.forename: Jerry L
authors.initials: JL
authors.lastname: Ricks
authors.forename: Michael E
authors.initials: ME
authors.lastname: Rosenfeld
authors.forename: Marta
authors.initials: M
authors.lastname: Scatena
mesh_terms: D000818:Animals; D001057:Apolipoproteins E / Q000172:deficiency* / Q000235:genetics; D002454:Cell Differentiation; D002478:Cells, Cultured; D020219:Chondrogenesis; D005838:Genotype; D015850:Interleukin-6 / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009131:Muscle, Smooth, Vascular / Q000378:metabolism* / Q000473:pathology; D032389:Myocytes, Smooth Muscle / Q000378:metabolism* / Q000473:pathology; D010012:Osteogenesis; D053244:Osteoprotegerin / Q000172:deficiency* / Q000235:genetics; D010641:Phenotype; D053245:RANK Ligand / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D015398:Signal Transduction; D014161:Transduction, Genetic; D061205:Vascular Calcification / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000517:prevention & control
chemical_list: D001057:Apolipoproteins E; D015850:Interleukin-6; D053244:Osteoprotegerin; D053245:RANK Ligand; C506031:Tnfrsf11b protein, mouse; C505689:Tnfsf11 protein, mouse; C577686:interleukin-6, mouse