title: Reciprocal interactions between mitral valve endothelial and interstitial cells reduce endothelial-to-mesenchymal transition and myofibroblastic activation.
abstract: Thickening of mitral leaflets, endothelial-to-mesenchymal transition (EndMT), and activated myofibroblast-like interstitial cells have been observed in ischemic mitral valve regurgitation. We set out to determine if interactions between mitral valve endothelial cells (VECs) and interstitial cells (VICs) might affect these alterations. We used in vitro co-culture in Transwell™ inserts to test the hypothesis that VICs secrete factors that inhibit EndMT and conversely, that VECs secrete factors that mitigate the activation of VICs to a myofibroblast-like, activated phenotype. Primary cultures and clonal populations of ovine mitral VICs and VECs were used. Western blot, quantitative reverse transcriptase PCR (qPCR) and functional assays were used to assess changes in cell phenotype and behavior. VICs or conditioned media from VICs inhibited transforming growth factor β (TGFβ)-induced EndMT in VECs, as indicated by reduced expression of EndMT markers α-smooth muscle actin (α-SMA), Slug, Snai1 and MMP-2 and maintained the ability of VECs to mediate leukocyte adhesion, an important endothelial function. VECs or conditioned media from VECs reversed the spontaneous cell culture-induced change in VICs to an activated phenotype, as indicated by reduced expression of α-SMA and type I collagen, increased expression chondromodulin-1 (Chm1), and reduced contractile activity. These results demonstrate that mitral VECs and VICs secrete soluble factors that can reduce VIC activation and inhibit TGFβ-driven EndMT, respectively. These findings suggest that the endothelium of the mitral valve is critical for the maintenance of a quiescent VIC phenotype and that, in turn, VICs prevent EndMT. We speculate that the disturbance of the ongoing reciprocal interactions between VECs and VICs in vivo may contribute to the thickened and fibrotic leaflets observed in ischemic mitral regurgitation, and in other types of valve disease.
authors: Vascular Biology Program, Department of Surgery, Boston Children's Hospital, Harvard Medical School, USA; Biomedical Engineering Department, Boston University, Boston, MA, USA; Department of Cardiothoracic Surgery, Boston Children's Hospital, Harvard Medical School, USA.
authors: Kayle
authors: K
authors: Shapero
authors: Vascular Biology Program, Department of Surgery, Boston Children's Hospital, Harvard Medical School, USA.
authors: Jill
authors: J
authors: Wylie-Sears
authors: Cardiac Ultrasound Laboratory, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
authors: Robert A
authors: RA
authors: Levine
authors: Department of Cardiothoracic Surgery, Boston Children's Hospital, Harvard Medical School, USA.
authors: John E
authors: JE
authors: Mayer
authors: Vascular Biology Program, Department of Surgery, Boston Children's Hospital, Harvard Medical School, USA. Electronic address: joyce.bischoff@childrens.harvard.edu.
authors: Joyce
authors: J
authors: Bischoff
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002450:Cell Communication; D054338:Cell Transdifferentiation / Q000187:drug effects; D002478:Cells, Cultured; D018920:Coculture Techniques; D042783:Endothelial Cells / Q000378:metabolism*; D016130:Immunophenotyping; D008943:Mitral Valve / Q000166:cytology; D058628:Myofibroblasts / Q000378:metabolism*; D010641:Phenotype; D012756:Sheep; D053773:Transforming Growth Factor beta1 / Q000378:metabolism / Q000494:pharmacology
chemical_list: D015415:Biomarkers; D053773:Transforming Growth Factor beta1
keywords: Endothelial cells; Endothelial-to-mesenchymal transition; Mitral valve; Valve interstitial cells
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