Myocardial contraction and hyaluronic acid mechanotransduction in epithelial-to-mesenchymal transformation of endocardial cells

Abstract

Epithelial-to-mesenchymal transition (EMT) of endocardial cells is a critical initial step in the formation of heart valves. The collagen gel in vitro model has provided significant information on the role of growth factors regulating EMT but has not permitted investigation of mechanical factors. Therefore we sought to develop a system to probe the effects of mechanical inputs on endocardial EMT by incorporating hyaluronic acid (HA), the primary component of endocardial cushions in developing heart valves, into the gel assay. This was achieved using a combination collagen and crosslinkable methacrylated HA hydrogel (Coll-MeHA). Avian atrioventricular canal explants on Coll-MeHA gels showed increased numbers of transformed cells. Analysis of the mechanical properties of Coll-MeHA gels show that stiffness does not directly affect EMT. Hydrogel deformation from the beating myocardium of explants directly led to higher levels of regional gel deformation and larger average strain magnitudes associated with invaded cells on Coll-MeHA gels. Inhibition of this contraction reduced EMT on all gel types, although to a lesser extent on Coll-MeHA gels. Using the system we have developed, which permits the manipulation of mechanical factors, we have demonstrated that active mechanical forces play a role in the regulation of endocardial EMT.

Endothelial to mesenchymal transformation is induced by altered extracellular matrix in aortic valve endothelial cells

“…Cushion explants plated onto collagen‐HA and collagen‐CS gels showed increased invasion into the matrix, and electron micrographs of these in vitro models suggested that the increase in migration was due to increased disruption of intercellular junctions by the GAGs . Sewell‐Loftin et al . similarly found that collagen+HA gels enhance endocardial cell transformation.…”

In vitro models of aortic valve calcification: solidifying a system

“…These EMT-related events are likely directly mediated by the mechanical forces present in the valve. In a recent study using chick explanted atrioventricular canals, EMT was found to occur preferentially in higher regions of strain [37]. This developmental process is likely recapitulated in an unregulated fashion during CAVD progression.…”

Cardiac valve cells and their microenvironment—insights from in vitro studies

“…For example, VECs can secrete paracrine molecules and undergo EMT to become a mesenchymal type cell that mediates tissue repair. 6,64,65 The EMT triggered in VECs by pathogenic biochemical factors has common molecular features with cardiac valve development (such as expression of mesenchymal markers and activation of NF-κB); 64,66 however, further characterization is needed to identify the precise mechanism by which this occurs. In addition, VICs secrete fibrous matrix proteins, matrix metalloproteinases (such as MMP1 and MMP2), biochemical factors, and can differentiate into myofibroblasts or osteoblast-like cells or undergo cell death-mediated calcification 7,25,67 …”