Effect of cyclic mechanical strain on glycosaminoglycan and proteoglycan synthesis by heart valve cells

Heart valves are presumed to remodel their extracellular matrix upon application of mechanical strains. In this study, we investigated the effect of cyclic tensile strain on valvular interstitial cells’ synthesis of glycosaminoglycans (GAGs) and proteoglycans (PGs), which are altered during myxomatous degeneration. Interstitial cells were isolated from mitral valve leaflets and chordate, and seeded separately within three-dimensional collagen gels. Cell-seeded collagen gels were then subjected to cyclic strains of 2%, 5% or 10% at 1.16 Hz for 48 h using a custom-built stretching device. The application of cyclic strains reduced the total GAGs retained within collagen gels in a magnitude-dependent manner for both leaflet and chordal cells. With increasing strain magnitude, however, secretion of total GAGs into the medium was reduced for leaflet cells and elevated for chordal cells. Retention of 4-sulfated GAGs increased with increasing strain magnitude for both cell types; for the chordal samples, retention of 6-sulfated GAGs was reduced at higher strain magnitudes. Compared to statically constrained or unconstrained conditions, the application of cyclic strain reduced the secretion of 6-sulfated GAGs by both cell types, and elevated secretion of 4-sulfated GAGs by leaflet cells only. Retention of the PG biglycan and secretion of the PG decorin was significantly reduced at 10% strain compared to 2% strain. In addition, there were numerous differences in the strain-dependent retention and secretion of GAGs and PGS within the leaflet and chordal groups. These results demonstrate that GAG and PG synthesis by VICs is regulated by cyclic stretching conditions.