Role of strain direction in endothelial cell remodeling and signal transduction

The response of arterial endothelial cells (ECs) to pulsatile strain due to pressure changes in the cardiac cycle may play a significant role in vascular function in health and disease. The purpose of this dissertation was to study the molecular basis of the remodeling of cultured endothelial cells (ECs) in response to pulsatile uniaxial strain and the relation of this remodeling to the strain-activation of c-Jun N-terminal kinase (JNK) signaling, with special attention to actin filaments, Rho small GTPase and myosin light chain kinase (NECK).; Uniaxial strain caused ECs and their actin filaments to orient perpendicular to the direction of strain. Inhibition of Rho or effectors downstream of Rho (Rho-kinase and mDia) caused ECs and their actin filaments to orient parallel to the direction of the uniaxial strain Inhibition of NECK blocked strain-induced cell and actin orientation, without causing parallel or perpendicular alignment. Augmenting Rho activity enhanced cell and actin orientation perpendicular to the direction of strain, and this was blocked by the inhibition of Rho-kinase, but not NECK.; The roles of cell and actin remodeling in JNK activation were assessed by comparing EC responses to uniaxial and equibiaxial strains. In contrast to the directional remodeling and transient JNK activation induced by uniaxial strain, equibiaxial strain did not induce directional remodeling and the resulting JNK activation was sustained. After the subsidence of JNK activation following uniaxial strain, changing the direction of the uniaxial strain by 90° resulted in reorientation of cells and actin perpendicular to the new strain direction and another round of transient activation of JNK. When the directional remodeling in response to uniaxial pulsatile strain was blocked by the inhibition of Rho-kinase activity or actin polymerization, JNK activation in response to uniaxial strain became sustained.; My results suggest that the orientation of cells and actin filaments perpendicular to the direction of uniaxial strain is an adaptive response that requires Rho-signaling and that such remodeling is accompanied by a subsidence of JNK activation. When cells are unable to orient perpendicular to the direction of strain, then JNK is not down-regulated and its activation becomes maintained.