Apoptotic Activity in Valvular Interstitial Cell Aggregates Corresponds to Low Cell Stress

Calcific aortic valve disease (CAVD) is the most prevalent valvular disorder in the developed world wherein calcific lesions form on the valve leaflets causing stenosis and regurgitation. The role of valvular interstitial... [ view full abstract ]

Calcific aortic valve disease (CAVD) is the most prevalent valvular disorder in the developed world wherein calcific lesions form on the valve leaflets causing stenosis and regurgitation. The role of valvular interstitial cells (VICs) in CAVD is increasingly being recognized but not fully understood. Dystrophic calcification can be replicated in vitro from monolayers of cells which spontaneously form aggregates, undergo programmed cell death, and calcify, yet factors that apoptosis have not been elucidated. We hypothesize that low cell tension in the center of the aggregates initiates apoptosis. In this study, VIC aggregates were created by micro-contact printing collagen islands on polyacrylamide gels; aggregate geometry was varied from a circle to ellipses of increasing elongation. A computational model simulating contraction was created to determine the theoretical distribution of stresses within the aggregates. Contraction was simulated in two steps: first, the 10 micron thick lab was pre-strained 10%, then the lower surface of the sample was fixed and the resulting stresses calculated. Experimentally, apoptosis was evaluated using caspase 3/7 detection reagent on days 1, 2, 4, and 7. Apoptotic activity followed areas of low principal stress predicted by the model. Together, these results indicate that apoptosis and subsequent calcium accumulation may be a result of the inability of the central cells to generate sufficient forces due to the geometric constraint imposed by aggregation.