Cyclic strain regulates pro-inflammatory protein expression in porcine aortic valve endothelial cells

Background and aim of the study: The endothelium of diseased heart valves is known to express the adhesion molecules VCAM-1, ICAM-1 and E-selectin, while healthy valves lack these pro-inflammatory proteins. The study aim was to determine if mechanical forces were responsible for the pro-inflammatory reaction in aortic valve endothelial cells. Methods: Isolated porcine aortic valve endothelial cells (PAVEC) were cultured and seeded onto BioFlex™ culture plates. The cells were exposed to equibiaxial cyclic strains of 5,10 and 20% for 24 h in a Flexcell FX-4000T™ Tension Plus system at 1 Hz. Pro-inflammatory protein expression was detected through the use of monoclonal antibodies via fluorescence-assisted cell sorting (FACS) and confocal laser scanning microscopy (CLSM). Results: Pro-inflammatory protein expression was evident at cyclic strains of 5 and 20%, while a 10% strain did not elicit an inflammatory response. Confocal images indicated a disrupted endothelial monolayer, evidence of significant cell death, and the presence of all adhesion molecules at 5% strain. PAVEC exposed to 10% cyclic strain failed to express any of the pro-inflammatory proteins, while the cellular monolayer appeared near-confluent and characteristically similar to cellular images captured prior to cyclic stretching. CLSM images of PAVEC cyclically stretched by 20% demonstrated a similar proinflammatory reaction to those with 5% strain, while the cellular environment also showed decreased monolayer integrity. FACS data showed a significant up-regulation of the membrane-bound VCAM-1-, ICAM-1- and E-selectin-positive cells at 5% and 20% strain, compared to 10% strain and controls. Conclusion: The finding that equibiaxial cyclic strain regulates the pro-inflammatory response in PAVEC suggests that alterations in the mechanical environment of heart valves may contribute to valve pathogenesis.