Nonbiased Molecular Screening Identifies Novel Molecular Regulators of Fibrogenic and Proliferative Signaling in Myxomatous Mitral Valve Disease

Circ Cardiovasc Genet. 2015 Jun;8(3):516-28. doi: 10.1161/CIRCGENETICS.114.000921. Epub 2015 Mar 26.

Abstract

Background: Pathological processes underlying myxomatous mitral valve degeneration (MMVD) remain poorly understood. We sought to identify novel mechanisms contributing to the development of this condition.

Methods and results: Microarrays were used to measure gene expression in 11 myxomatous and 11 nonmyxomatous human mitral valves. Differential gene expression (thresholds P<0.05; fold-change >1.5) and pathway activation (Ingenuity) were confirmed using quantitative reverse transcriptase polymerase chain reaction and immunohistochemistry. Contributions of bone morphogenetic protein 4 and transforming growth factor (TGF)-β2 to differential gene expression were evaluated in vitro. Contributions of angiotensin II to differential pathway activation were examined in mice in vivo. A total of 2602 genes were differentially expressed between myxomatous and nonmyxomatous valves. Canonical TGF-β signaling was increased in MMVD because of increased ligand expression and derepression of SMA mothers against decapentaplegic 2/3 signaling and was confirmed with quantitative reverse transcriptase polymerase chain reaction and immunohistochemistry. Myxomatous valves demonstrated activation of canonical bone morphogenetic protein and Wnt/β-catenin signaling and upregulation of their common target runt-related transcription factor 2. Our data set provided transcriptional and immunohistochemical evidence for activated immune cell infiltration. In vitro treatment of mitral valve interstitial cells with TGF-β2 increased β-catenin signaling at mRNA and protein levels, suggesting interactions between TGF-β2 and Wnt signaling. In vivo infusion of mice with angiotensin II recaptured several changes in signaling pathways characteristic of human MMVD.

Conclusions: These data support a new disease framework whereby activation of TGF-β2, bone morphogenetic protein 4, Wnt/β-catenin, or immune signaling plays major roles in the pathogenesis of MMVD. We propose these pathways act in a context-dependent manner to drive phenotypic changes that fundamentally differ from those observed in aortic valve disease and open novel avenues guiding future research into the pathogenesis of MMVD.

Keywords: general surgery; mitral valve; molecular biology; pathology.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Angiotensin II / pharmacology
  • Animals
  • Aortic Valve / metabolism
  • Aortic Valve / pathology
  • Bicuspid Aortic Valve Disease
  • Bone Morphogenetic Protein 4 / genetics
  • Bone Morphogenetic Protein 4 / metabolism
  • Cells, Cultured
  • Cytokines / metabolism
  • Echocardiography
  • Gene Expression Regulation
  • Heart Defects, Congenital / metabolism
  • Heart Defects, Congenital / pathology*
  • Heart Valve Diseases / metabolism
  • Heart Valve Diseases / pathology*
  • Humans
  • Immunohistochemistry
  • Mice
  • Mice, Inbred C57BL
  • Mitral Valve / cytology
  • Mitral Valve / drug effects
  • Mitral Valve / metabolism*
  • Real-Time Polymerase Chain Reaction
  • Signal Transduction / genetics*
  • Transforming Growth Factor beta2 / genetics
  • Transforming Growth Factor beta2 / metabolism
  • Wnt Proteins / metabolism
  • beta Catenin / genetics
  • beta Catenin / metabolism

Substances

  • Bone Morphogenetic Protein 4
  • Cytokines
  • Transforming Growth Factor beta2
  • Wnt Proteins
  • beta Catenin
  • Angiotensin II