oa Investigating the Contribution of Pathological Levels of Cyclic Strain on Vascular and Valvular Calcification

Aortic stenosis and atherosclerosis tend to coexist in most patients with cardiovascular disease; however, the causes and mechanisms of calcification are still not clearly understood. To understand the contributions of physiological (10%) and pathological (5%, 15%) levels of cyclic strain in calcification, we used a model system of tissue-engineered collagen gels containing human aortic smooth muscle cells (HASMC) and human aortic valvular interstitial cells (HAVIC), both isolated from non-calcific heart transplant tissues. The tissue engineered collagen gels were cultured in standard osteogenic media for three weeks in a custom designed bioreactor and all assessments were performed at the end of the culture period. The major finding of this study was that bone morphogenic protein (BMP) -2, -4 and transforming growth factor (TGF)-β1 mRNA expression significantly changed in response to the magnitude of strain in valvular cells, while the least expression was observed for the representative 10% physiological strain. On the other hand, these mRNA expressions in vascular cells responded to strain, but did not vary due to the magnitude (5% versus 10% versus 15%) of strain. When the BMP-2 and BMP-4 protein expression was detected using immunostaining, we observed that only valvular cells showed greater BMP-2 expression for 5% and 15% strain when compared to 10% strain within the same cell type. Our results suggest that cell mediated differences exist between vascular and valvular cells in their response to different levels of cyclic strain.