Computer-assisted analysis of endothelial cell migration and proliferation
Doctor of Philosophy
This work presents some important results from experimental studies aimed at elucidating the fundamental mechanisms of endothelial cell migration and proliferation. To continuously monitor populations of migrating and proliferating cells, we used video microscopy coupled with a novel computer-automated digital time-lapse recording technique. Migrating cells were identified and their positions at each time instant were obtained using digital image processing. We also developed a modified nearest neighbor tracking algorithm to reconstruct approximations to the cell trajectories. Our experimental studies on the locomotion of bovine pulmonary artery endothelial (BPAE) cells have shown that these cells execute persistent random walks in culture. Cells change their direction of migration either in response to some intracellular signal or because they collide with other cells. Cells slow down as they approach other cells and then turn and move away from each other with increasing speeds. The temporal evolution of population-average speed of locomotion reveals that increases in cell density due to proliferation are immediately accompanied by a decrease in the average cell speed. Markov chain analysis on cell trajectories has shown that the enhanced motility of the BPAE cells cultured with basic fibroblast growth factor (bFGF) seems to be derived not only from fewer visits to the stationary state, but also from a decrease in the waiting time for each visit to the stationary state. BPAE cells execute persistent random walks when they are cultured without or with added bFGF, although the addition of bFGF does make them more motile. An independent set of cell proliferation experiments indicates that bFGF concentrations that increase cell motility also increase cell proliferation rates. A model based on a cellular automaton was developed to describe the proliferation of migrating cells. Our cellular automaton models asynchronous proliferation of cells executing persistent random walks and accounts for changes in the direction of movement when two cells collide. The simulation results reveal that cell motility reduces the adverse effects of contact inhibition on cell proliferation rates. Excellent agreement between model predictions and experimental data was observed indicating that this discrete model can accurately describe the dynamics of populations of migrating and proliferating cells.