TGF-beta1 pathway activation and adherens junction molecular pattern in nonsyndromic mitral valve prolapse

Aims: Dysregulation of the transforming growth factor beta (TGF-beta) 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-beta pathway and its effect on adherens junction (AJ) molecular pattern of activated valvular interstitial cells (VICs) in MV prolapse are herein investigated. Methods: FloppyMVleafletswere obtained from30 patients (24males, 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 extracellularmatrix composition, including collagen I and III, was evaluated by histology and transmission electron microscopy. Smad2 active phosphorylated form (p-Smad2), alpha-smooth muscle actin (alpha-SMA), and junctional proteins (N-cadherin, cadherin-11, beta-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-beta pathway cascade and filamin A (FLN-A). Results: Floppy MV leaflets were thicker (Pb. 001) and had higher alpha-SMA + cell density (P=.002) and collagen III expression (Pb. 001) than controls. Enhanced p-Smad2 nuclear immunoreactivity (Pb. 001) and TGF-beta 1 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 colocalizationwith N-cadherin, and aberrant presence of plakophilin-2 at the AJ were found in floppyMVvs. controls. Conclusions: TGF-beta 1 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-beta 1 activation leading to extracellular matrix remodeling in floppy MV. (C) 2015 Elsevier Inc. All rights reserved.