Background—Collagen cross-linking is mediated by lysyl oxidase (LOX) enzyme in the extracellular matrix (ECM) of mitral valve leaflets. Alterations in collagen content and LOX protein expression in the ECM of degenerative mitral valve may enhance leaflet expansion and disease severity.

Methods—Twenty posterior degenerative mitral valve leaflets from patients with severe mitral regurgitation were obtained at surgery. Five normal posterior mitral valve leaflets procured during autopsy served as controls. Valvular interstitial cells (VICs) density was quantified by immunohistochemistry, collagen types I and III by picro-sirius red staining and immunohistochemistry, and proteoglycans by alcian blue staining. Protein expression of LOX and its mediator TGFβ1 were quantified by immunofluorescence and gene expression by PCR.

Results—VICs density was increased, structural type I collagen density was reduced, while reparative type III collagen and proteoglycan densities were increased (p < 0.0001) with an increase in spongiosa layer thickness in myxomatous valves. These changes were associated with a reduction in LOX (p < 0.0001) and increase in TGFβ1 protein expression (p < 0.0001). However, no significant change was seen in gene expression. Linear regression analysis identified a correlation between type I collagen density and LOX grade (R2 = 0.855; p < 0.0001).

Conclusions—Reduced type I collagen density with a simultaneous increase in type III collagen and proteoglycan densities possibly contributes to spongiosa layer expansion resulting in incompetent mitral valve leaflets. Observed changes in type I and III collagen densities in DMVD may be secondary to alterations in LOX protein expression, contributing to disorganization of ECM and disease severity.

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Published in Cardiovascular Pathology, v. 29, p. 11-18.

© 2017 Elsevier Inc. All rights reserved.

This manuscript version is made available under the CC‐BY‐NC‐ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/.

The document available for download is the author's post-peer-review final draft of the article.

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The authors acknowledge funding from the Zena and Michael A. Weiner Cardiovascular Institute, Department of Cardiovascular Surgery, Icahn School of Medicine at Mount Sinai, New York and from National Institutes of Health (NIH)/NHLBI through grant K01HL133424 (to ICT).