Molecular mechanisms underlying the inhibitory effect of uniaxial cyclic stretch on endothelial cell migration

Vascular endothelial cells in large arteries are constantly subjected to uniaxial cyclic stretch in vivo as a result of blood pressure's pulsatile nature. This thesis research aimed to understand the molecular mechanisms underlying the inhibitory effect of uniaxial cyclic stretch on endothelial cell migration in a wound healing scenario and with different wound directionalities. Our results showed that cyclic stretch decreased the migration speed in wounds with both long axes perpendicular and parallel to the stretch direction. This decrease in migration speed was significantly greater in perpendicular wounds than in parallel wounds, a finding that explains the potential importance of selective surgical incision directionalities to promote faster vascular wound healing.;In order to understand the possible mechanisms leading to the decrease of migration under cyclic stretch, the effects of uniaxial cyclic stretch on cell morphology and cytoskeletal remodeling, as well as the production of the pro-wound healing transcription factor ETS-1 and anti-wound healing excessive reactive oxygen species (ROS), were investigated. It was found that stretch did not affect cell area, which increased as the cells migrated into and covered a denuded region, thereby preventing the exposure of the thrombogenic vascular wall tissue to blood. However, stretch promoted the elongation and preferential alignment of cells perpendicular to the stretch direction. For subconfluent cells (e.g., such as those in a denuded area), the effect of stretch on elongation and alignment was affected by the shape (i.e., the spatial boundary condition) of the denuded area. It was also found that stretch changed the focal adhesion dynamics (specifically, enhanced focal adhesions for adhesion and against migration) and decreased the amount of ETS-1. Both mechanisms may explain the decrease of migration under cyclic stretch. Although cyclic stretch induced the amount of intracellular ROS, ROS inhibitory studies, incorporating ROS scavengers and ROS generating enzyme inhibitors, showed neither reagent ameliorated recovery in cell migration.;Results from the hyperglycemia wound healing studies showed that hyperglycemia and cyclic stretch had additive effects on inhibiting endothelial cell migration through different mechanisms. Hyperglycemia hindered the increase in cell area in the wound zone, and ROS scavengers blocked the inhibitive effect of hyperglycemia on migration. These findings were the opposite of those in stretch experiments with normal glycemia as described above. Overall, the results explain the prolonged vascular injury and delayed wound healing in patients of hypertension (i.e., as approximated here by stretch) and hyperglycemia as well as suggest potential targets for developing new treatment to promote endothelial cell migration and wound healing in these diseased conditions.