Reduced Sox9 Function Promotes Heart Valve Calcification Phenotypes In Vivo

Abstract

Rationale: Calcification of heart valve structures is the most common form of valvular disease and is characterized by the appearance of bone-like phenotypes within affected structures. Despite the clinical significance, the underlying etiology of disease onset and progression is largely unknown and valve replacement remains the most effective treatment. The SRY-related transcription factor Sox9 is expressed in developing and mature heart valves, and its function is required for expression of cartilage-associated proteins, similar to its role in chondrogenesis. In addition to cartilage-associated defects, mice with reduced sox9 function develop skeletal bone prematurely; however, the ability of sox9 deficiency to promote ectopic osteogenic phenotypes in heart valves has not been examined. Objective: This study aims to determine the role of Sox9 in maintaining connective tissue homeostasis in mature heart valves using in vivo and in vitro approaches. Methods and Results: Using histological and molecular analyses, we report that, from 3 months of age, Sox9 fl/؉ ;Col2a1-cre mice develop calcific lesions in heart valve leaflets associated with increased expression of bone-related genes and activation of inflammation and matrix remodeling processes. Consistently, ectopic calcification is also observed following direct knockdown of Sox9 in heart valves in vitro. Furthermore, we show that retinoic acid treatment in mature heart valves is sufficient to promote calcific processes in vitro, which can be attenuated by Sox9 overexpression. Conclusions: This study provides insight into the molecular mechanisms of heart valve calcification and identifies reduced Sox9 function as a potential genetic basis for calcific valvular disease. (Circ Res. 2010;106:712-719.)Key Words: heart valves Ⅲ calcification Ⅲ Sox9 Ⅲ extracellular matrix Ⅲ mouse model C alcification of heart valve structures affects more than 27% of the US population over 65 years of age and is the major contributor of heart valve malfunction. 1 Despite the clinical significance, little is known about the mechanisms that underlie this multifactorial disease. Treatment options for valve calcification are limited, and no known therapies prevent disease progression. 2 Normal heart valve function requires organization of differentiated cell types and specialized extracellular matrix (ECM) within the valve leaflet is arranged according to blood flow. 3 This defined tissue architecture provides the mechanical resilience and compressibility required to open and close the valve orifices effectively during the cardiac cycle. 4 In diseased heart valves, loss of ECM organization is associated with changes in mechanical properties, ultimately leading to dysfunction. 5,6 One of the most striking alterations in valve ECM homeostasis is ectopic bone-like matrix mineralization observed in calcific valve disease. 7,8 At the functional level, this histopathologic alteration results in stiffened leaflets, narrowing of the valve opening, and impaired blood flow. 9 The mechanis...

Low-level overexpression of p53 promotes warfarin-induced calcification of porcine aortic valve interstitial cells by activating Slug gene transcription

“…In human osteoblasts and mesenchymal stem cells, Slug is recruited to the Runx2 promoter and upregulates Runx2. Silencing of Slug has been shown to promote expression of the chondrogenic marker Sox9 (29,32), which protects AVICs from calcification (33). We found that slug is transcriptionally regulated by p53 in pAVICs concomitant with increased Runx2 expression.…”

Abnormal muscle mechanosignaling triggers cardiomyopathy in mice with Marfan syndrome

“…Both collagen IV-producing (BM-producing) cardiomyocytes and collagen I-producing (interstitial matrixproducing) cardiac fibroblasts secrete fibrillin 1 and thus cooperate in assembling the interconnected meshwork of myocardial microfibrils (5,7). Lacking suitable fibroblast-specific Cre-driving transgenes, we assessed the role of fibrillin 1 in the myocardium by selectively targeting Fbn1 gene expression in cardiomyocytes using the αMHC-Cre transgenic mouse (Supplemental Figure 2A 36,37). Since an aorta with no fibrillin 1 ruptures soon after birth (38), we interbred hypomorphic Fbn1 Lox/mgR mice with Wnt1-Cre transgenic mice so as to decrease rather than eliminate fibrillin 1 deposition in the aortic media.…”

Regulation of Human Chondrocyte Function through Direct Inhibition of Cartilage Master Regulator SOX9 by MicroRNA-145 (miRNA-145)

“…However, miR-145 has been shown to be expressed in various mouse tissues (although cartilage was not tested), being highly abundant in fat and the aorta, and loss of miR-145 induced structural modifications specifically in the proximal aorta, where the aorta emerges from the heart (15). This is intriguing because the aortic valves in the heart express Sox9, which when deleted in the mouse leads to calcification of the aortic valves, the most prominent form of valvular disease (32). Significantly increased expression of Runx2 and other osteogenic markers was detected in these Sox9-deficient aortic valves.…”