Background and aim of the study: Aortic valve ectopic calcification occurs exclusively on the fibrosa surface. This may be due to the distinct mechanical environments on either side of the valve, or to the existence of unique, side-specific endothelial sub-phenotypes. The study aim was to determine if side-specific endothelial cells (ECs) would differentially express cell-cell and cell-matrix adhesion molecules in response to elevated levels of equibiaxial tensile strain.
Methods: Side-specific porcine aortic valve ECs were isolated and strained at 10% or 20% using a Flexcell 4000T for 24 h, and compared to static controls. The quantity and pattern of distribution of adhesion proteins was then assessed using ELISA and fluorescence microscopy, respectively. The adhesion proteins of interest were platelet endothelial cell adhesion molecule-1 (PECAM-1), beta1-integrin, VE-cadherin, and vinculin.
Results: Overall, ventricular ECs were more reactive to changes in cyclic strain, with significant increases in VE-cadherin and vinculin at 20% strain. However, the expression of beta1-integrin was significantly increased at 20% strain in fibrosa ECs. Expression of PECAM-1 was not significantly changed at all strain levels for both sub-populations of ECs.
Conclusion: Endothelial cells isolated from the fibrosa and ventricularis surfaces of porcine aortic valves showed significantly different expression profiles of cell-cell and cell-extracellular matrix adhesion molecules under elevated tensile strain. These differences in response to cyclic strain suggest that different endothelial sub-phenotypes exist on the fibrosa and ventricularis surfaces of the aortic valve.