TGF-beta1 pathway activation and adherens junction molecular pattern in nonsyndromic mitral valve prolapse.
OBJECTIVE
Dysregulation of the transforming growth factor beta (TGF-β) 1 pathway has been associated with either syndromic or isolated mitral valve (MV) prolapse due to myxoid degeneration (floppy MV). The activation of Smad receptor-mediated intracellular TGF-β pathway and its effect on adherens junction (AJ) molecular pattern of activated valvular interstitial cells (VICs) in MV prolapse are herein investigated.


METHODS
Floppy MV leaflets were obtained from 30 patients (24 males, mean age 55.5±12.7 years) who underwent surgical repair, and 10 age- and sex-matched Homograft Tissue Bank samples served as controls. MV leaflet cellular and extracellular matrix composition, including collagen I and III, was evaluated by histology and transmission electron microscopy. Smad2 active phosphorylated form (p-Smad2), α-smooth muscle actin (α-SMA), and junctional proteins (N-cadherin, cadherin-11, β-catenin, plakoglobin, plakophilin-2) in VICs were assessed by immunohistochemistry and immunofluorescence and confirmed by immunoblotting. Quantitative real-time polymerase chain reaction was carried out for components of TGF-β pathway cascade and filamin A (FLN-A).


RESULTS
Floppy MV leaflets were thicker (P<.001) and had higher α-SMA+ cell density (P=.002) and collagen III expression (P<.001) than controls. Enhanced p-Smad2 nuclear immunoreactivity (P<.001) and TGF-β1 gene (P=.045), TIMP1 (P=.020), and CTGF (P=.047) expression but no differences in FLN-A and total Smad2 gene expression levels were found between floppy MV and controls. Higher expression of cadherin-11, either exclusively or in colocalization with N-cadherin, and aberrant presence of plakophilin-2 at the AJ were found in floppy MV vs.


CONCLUSIONS
TGF-β1 pathway activation in nonsyndromic MV prolapse induces VICs differentiation into contractile myofibroblasts and is associated with changes in the molecular pattern of the AJ, with increased cadherin-11 and aberrant plakophilin-2 expression. AJ reinforcement might promote latent TGF-β1 activation leading to extracellular matrix remodeling in floppy MV.
Cardiovascular Pathology Unit, Department of Cardiac, Thoracic and Vascular Sciences, University of Padua Medical School, Padua, Italy. Electronic address: stefania.rizzo75@gmail.com.
Stefania
S
Rizzo
Cardiovascular Pathology Unit, Department of Cardiac, Thoracic and Vascular Sciences, University of Padua Medical School, Padua, Italy. Electronic address: cristina.basso@unipd.it.
Cristina
C
Basso
Cardiovascular Pathology Unit, Department of Cardiac, Thoracic and Vascular Sciences, University of Padua Medical School, Padua, Italy. Electronic address: elisabetta.lazzarini@studenti.unipd.it.
Elisabetta
E
Lazzarini
Cardiovascular Pathology Unit, Department of Cardiac, Thoracic and Vascular Sciences, University of Padua Medical School, Padua, Italy. Electronic address: rudy.celeghin@gmail.com.
Rudy
R
Celeghin
Tissue Bank of Veneto Region, Civil Hospital, Treviso, Italy. Electronic address: apaolin@fbtv-treviso.org.
Adolfo
A
Paolin
Cardiac Surgery Unit, Department of Cardiac, Thoracic and Vascular Sciences, University of Padua Medical School, Italy. Electronic address: gino.gerosa@unipd.it.
Gino
G
Gerosa
Pathological Anatomy, Department of Cardiac, Thoracic and Vascular Sciences, University of Padua Medical School, Padua, Italy. Electronic address: marialuisa.valente@unipd.it.
Marialuisa
M
Valente
Cardiovascular Pathology Unit, Department of Cardiac, Thoracic and Vascular Sciences, University of Padua Medical School, Padua, Italy. Electronic address: gaetano.thiene@unipd.it.
Gaetano
G
Thiene
Cardiovascular Pathology Unit, Department of Cardiac, Thoracic and Vascular Sciences, University of Padua Medical School, Padua, Italy. Electronic address: kalliopi.pilichou@unipd.it.
Kalliopi
K
Pilichou
D000199:Actins / Q000032:analysis; D022005:Adherens Junctions / Q000737:chemistry* / Q000648:ultrastructure; D000328:Adult; D000368:Aged; D015820:Cadherins / Q000032:analysis; D016022:Case-Control Studies; D054338:Cell Transdifferentiation; D024042:Collagen Type I / Q000032:analysis; D024061:Collagen Type III / Q000032:analysis; D051180:Desmoplakins / Q000032:analysis; D005109:Extracellular Matrix / Q000737:chemistry; D005260:Female; D064448:Filamins / Q000235:genetics; D006801:Humans; D008297:Male; D008875:Middle Aged; D008943:Mitral Valve / Q000737:chemistry* / Q000601:surgery / Q000648:ultrastructure; D008945:Mitral Valve Prolapse / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000601:surgery; D058628:Myofibroblasts / Q000737:chemistry* / Q000648:ultrastructure; D010641:Phenotype; D010766:Phosphorylation; D051191:Plakophilins / Q000032:analysis; D015398:Signal Transduction; D051899:Smad2 Protein / Q000032:analysis; D053773:Transforming Growth Factor beta1 / Q000032:analysis* / Q000235:genetics; D051176:beta Catenin / Q000032:analysis; D051185:gamma Catenin
C541116:ACTA2 protein, human; D000199:Actins; C495270:CTNNB1 protein, human; D015820:Cadherins; D024042:Collagen Type I; D024061:Collagen Type III; D051180:Desmoplakins; C578663:FLNA protein, human; D064448:Filamins; C495292:JUP protein, human; C495337:PKP2 protein, human; D051191:Plakophilins; C497782:SMAD2 protein, human; D051899:Smad2 Protein; C508960:TGFB1 protein, human; D053773:Transforming Growth Factor beta1; D051176:beta Catenin; D051185:gamma Catenin
Adherens junction; Mitral valve prolapse; TGF-β activation; Valvular interstitial cell