title: Calcification by valve interstitial cells is regulated by the stiffness of the extracellular matrix.
abstract: OBJECTIVE
  Extensive remodeling of the valve ECM in calcific aortic valve sclerosis alters its mechanical properties, but little is known about the impact of matrix mechanics on the cells within the valve interstitium. In this study, the influence of matrix stiffness in modulating calcification by valve interstitial cells (VICs), and their differentiation to pathological phenotypes was assessed.
  
  
  RESULTS
  Primary porcine aortic VICs were cultured in standard media or calcifying media on constrained type I fibrillar collagen gels. Matrix stiffness was altered by changing only the thickness of the gels. Calcification did not occur in standard media, regardless of matrix stiffness. However, when VICs were grown in calcifying media on relatively compliant matrices with stiffness similar to that of normal tissue, they readily formed calcified aggregates of viable cells that expressed osteoblast-related transcripts and proteins. In contrast, VICs cultured in calcifying media on stiffer matrices (similar to stenotic tissue) differentiated to myofibroblasts and formed calcified aggregates that contained apoptotic cells. Actin depolymerization reduced aggregation on stiff, but not compliant, matrices. TGF-beta1 potentiated aggregate formation on stiff matrices by enhancing alpha-smooth muscle actin expression and cellular contractility, but not on compliant matrices attributable to downregulation of TGF-beta receptor I. Cell contraction by VICs inhibited Akt activation and enhanced apoptosis-dependent calcification on stiff matrices.
  
  
  CONCLUSIONS
  Differentiation of VICs to pathological phenotypes in response to biochemical cues is modulated by matrix stiffness. Although osteogenic or myofibrogenic differentiation of VICs can result in calcification, the processes are distinct.
authors.affiliation: Institute of Biomaterials and Biomedical Engineering, University of Toronto, ON, Canada.
authors.forename: Cindy Ying Yin
authors.initials: CY
authors.lastname: Yip
authors.forename: Jan-Hung
authors.initials: JH
authors.lastname: Chen
authors.forename: Ruogang
authors.initials: R
authors.lastname: Zhao
authors.forename: Craig A
authors.initials: CA
authors.lastname: Simmons
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D001021:Aortic Valve / Q000378:metabolism / Q000473:pathology*; D017209:Apoptosis; D002114:Calcinosis / Q000378:metabolism / Q000473:pathology*; D049109:Cell Proliferation; D048430:Cell Shape; D054338:Cell Transdifferentiation; D002478:Cells, Cultured; D024042:Collagen Type I / Q000378:metabolism; D004548:Elasticity; D005109:Extracellular Matrix / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology*; D010006:Osteoblasts / Q000378:metabolism / Q000473:pathology*; D010641:Phenotype; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D012598:Sclerosis; D013552:Swine; D013997:Time Factors; D053773:Transforming Growth Factor beta1 / Q000378:metabolism
chemical_list: D000199:Actins; D024042:Collagen Type I; D018125:Receptors, Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D000077293:Receptor, Transforming Growth Factor-beta Type I