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

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.

Isolated porcine aortic valve endothelial cells (PAVEC) were cultured and seeded onto BioFlexTM 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).

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.

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.