title: Biglycan induces the expression of osteogenic factors in human aortic valve interstitial cells via Toll-like receptor-2.
abstract: OBJECTIVE
  Although biglycan (BGN) and oxidized low-density lipoprotein (oxLDL) accumulation has been observed in calcific, stenotic aortic valves, their role in the pathogenesis of calcific aortic valve disease is poorly understood. We hypothesized that soluble BGN induces the osteogenic response in human aortic valve interstitial cells via Toll-like receptor (TLR) 2 and TLR4 and mediates the proosteogenic effect of oxLDL.
  
  
  RESULTS
  Aortic valve interstitial cells of stenotic valves express higher levels of BGN. Stimulation of cells from normal valves with BGN increased the expression of bone morphogenetic protein-2 (BMP-2) and alkaline phosphatase (ALP) among the chondrogenic/osteogenic markers examined and caused accumulation of calcium deposits. TLR2 silencing, but not TLR4 silencing, reduced BMP-2 and ALP levels after BGN stimulation although coimmunoprecipitation revealed that BGN interacts with both TLR2 and TLR4. BGN induced the phosphorylation of extracellular signal-regulated protein kinase-1/2, p38 mitogen-activated protein kinase and nuclear factor-κB. Inhibition of extracellular-regulated kinase-1/2 markedly reduced the upregulation of BMP-2 and ALP expression by BGN whereas inhibition of p38 mitogen-activated protein kinase or nuclear factor-κB had a moderate effect. Stimulation of aortic valve interstitial cells with oxLDL upregulated BGN expression and release. Knockdown and neutralization of BGN reduced the effect of oxLDL on BMP-2 and ALP expression.
  
  
  CONCLUSIONS
  Extracellular soluble BGN induces the expression of BMP-2 and ALP in human aortic valve interstitial cells primarily via TLR2 and contributes to the proosteogenic effect of oxLDL. These findings highlight the potential role of soluble BGN and oxLDL in the development of calcific aortic valve disease.
authors.affiliation: Department of Surgery, University of Colorado Denver, Aurora, CO 80045, USA.
authors.forename: Rui
authors.initials: R
authors.lastname: Song
authors.forename: Qingchun
authors.initials: Q
authors.lastname: Zeng
authors.forename: Lihua
authors.initials: L
authors.lastname: Ao
authors.forename: Jessica A
authors.initials: JA
authors.lastname: Yu
authors.forename: Joseph C
authors.initials: JC
authors.lastname: Cleveland
authors.forename: Ke-Seng
authors.initials: KS
authors.lastname: Zhao
authors.forename: David A
authors.initials: DA
authors.lastname: Fullerton
authors.forename: Xianzhong
authors.initials: X
authors.lastname: Meng
mesh_terms: D000328:Adult; D000368:Aged; D000469:Alkaline Phosphatase / Q000378:metabolism; D001021:Aortic Valve / Q000378:metabolism* / Q000473:pathology; D001024:Aortic Valve Stenosis / Q000378:metabolism* / Q000473:pathology; D058578:Biglycan / Q000235:genetics / Q000378:metabolism*; D015415:Biomarkers / Q000378:metabolism; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism; D002114:Calcinosis / Q000378:metabolism* / Q000473:pathology; D016022:Case-Control Studies; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D010012:Osteogenesis; D010766:Phosphorylation; D034622:RNA Interference; D015398:Signal Transduction; D013997:Time Factors; D051195:Toll-Like Receptor 2 / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: C546884:BGN protein, human; C525718:BMP2 protein, human; D058578:Biglycan; D015415:Biomarkers; D055396:Bone Morphogenetic Protein 2; D008077:Lipoproteins, LDL; D016328:NF-kappa B; C495342:TLR2 protein, human; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; C099252:oxidized low density lipoprotein; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D000469:Alkaline Phosphatase