The effect of line patterns on intracellular ATP concentration in vascular endothelial cells

The migration of endothelial cells (ECs) is critical for various processes including vascular wound healing, tumor angiogenesis, and the development of viable endovascular implants. EC migration is regulated by intracellular ATP; thus, elucidating the dynamics of intracellular ATP concentration is important. Recent observations (time-lapse imaging over 12-hr periods) in our laboratory on ECs cultured on line patterns - surfaces where cellular adhesion is limited to 15 ?m-wide lines that physically confine the cells - have demonstrated very different migration behavior from cells on control unpatterned surfaces. Specifically, while ECs on unpatterned surfaces exhibit random motion in the absence of flow and persistent directed motion under flow, cells on line patterns both in the presence and absence of flow exhibit three distinct migration phenotypes (Fig. 1): a) running - cells are polarized and migrate continuously and persistently on the adhesive lines with possible directional changes, b) undecided - cells are elongated and exhibit periodic changes in the direction of their polarization and minimal net migration, and c) tumbling-like - cells migrate persistently for a certain amount of time but then stop and round up for a few hours before spreading again and resuming migration. We hypothesize that the three migration phenotypes on line patterns reflect differences in intracellular ATP profiles. Specifically, we propose that running ECs have sufficiently high ATP concentrations at all time in order to elongate, polarize, and migrate. In contrast, we suggest that undecided ECs have an intermediate level of ATP concentration that is sufficiently high for cell spreading but not for sustained polarization and migration. Finally, tumbling-like cells are thought to have low levels of intracellular ATP during the rounding-up phase but manage to "recharge their batteries" so that ATP levels recover sufficiently for the cells to eventually elongate, polarize, and migrate. To test this hypothesis, we have developed a mathematical model that describes the time evolution of intracellular ATP concentration.