Age-dependent response of endothelial cells to mechanical deformation

The number one killer of older Americans is atherosclerosis. The second most prevalent cause of death in the population at large, and the number one cause of death in juveniles is injury. In both cases, the etiology has been strongly linked to injury on the cellular level which may result from mechanical deformation. Furthermore, the cellular response may be directly effected by the cell age due to the functional and morphological differences which exist between young and old cells. In this dissertation, loads are applied to bovine aortic endothelial cells at different in vitro ages (population doubling levels). Mechanical deformation is measured in individual cells, along with concomitant changes in the intracellular calcium concentration. A system was designed and assembled which enables one to examine the magnitude and spatial distribution of strains produced within individual cells in response to changes in the hydrostatic environment of the cell. Strain contour maps of individual cells were assembled which illustrate the inhomogeneity of strains distributed across the cell. These data were compared for young and old cells, and it was shown that older cells have multiple areas of high strain concentration, while young cells usually only have one area of high strain. In either case, the highest strains were generally in the perinuclear regions of the cell. The cellular response to different magnitudes of strain was examined by monitoring changes in the intracellular calcium concentration using Fura-2 calcium binding dye. This technique demonstrated that cells are much more likely to respond to high strain rate deformation than low strain rate deformation. It was also shown that senescent cells generally exhibit a prolonged and delayed response which is usually not seen in younger cells. Explanations for the differences which exist between young and old cells are explored in a mathematical diffusion model of the cell. In conclusion, this dissertation provides detailed measurements of the changes in intracellular calcium concentration in individual cells at different population doubling levels, as a result of measured levels of strain and strain rate