Strain magnitude-dependent calcific marker expression in valvular and vascular cells

Aortic valve disease and atherosclerosis tend to coexist in most patients with cardiovascular disease; however, the causes and mechanisms of disease development in heart valves are still not clearly understood. To understand the contributions of the magnitude of cyclic strain (5% hypotension, 10% physiological, and 15% hypertension) in calcification, we used a model system of tissue-engineered collagen gels containing human aortic smooth muscle cells and human aortic valvular interstitial cells, both isolated from noncalcific heart transplant tissue. The compacted collagen gels were cultured in osteogenic media for 3 weeks in a custom-designed bioreactor and all assessments were performed at the end of the culture period. The major finding of this study is that bone morphogenic protein (BMP)-2 and BMP-4 and transforming growth factor-β1 mRNA expression significantly changed in response to the magnitude of applied strain in valvular cells, while the lowest expression was observed for the representative physiological strain. On the other hand, mRNA expression in vascular cells did not vary in response to the magnitude of strain. Regarding BMP-2 and BMP-4 protein expression determined by immunostaining, trends were similar to mRNA expression in vascular and valvular cells, where only valvular cells showed a varied protein expression depending on the magnitude of the strain applied. Our results suggest that cellular differences exist between vascular and valvular cells in their response to altered levels of cyclic strain during calcification.