Cyclic Strain–Mediated Regulation of Vascular Endothelial Occludin and ZO-1

Abstract

Objective— The vascular endothelium constitutes a highly effective fluid/solute barrier through the regulated apposition of intercellular tight junction complexes. Because endothelium-mediated functions and pathology are driven by hemodynamic forces (cyclic strain and shear stress), we hypothesized a dynamic regulatory link between endothelial tight junction assembly/function and hemodynamic stimuli. We, therefore, examined the effects of cyclic strain on the expression, modification, and function of 2 pivotal endothelial tight junction components, occludin and ZO-1. Methods and Results— For these studies, bovine aortic endothelial cells were subjected to physiological levels of equibiaxial cyclic strain (5% strain, 60 cycles/min, 24 hours). In response to strain, both occludin and ZO-1 protein expression increased by 2.3±0.1-fold and 2.0±0.3-fold, respectively, concomitant with a strain-dependent increase in occludin (but not ZO-1) mRNA levels. These changes were accompanied by reduced occludin tyrosine phosphorylation (75.7±8%) and increased ZO-1 serine/threonine phosphorylation (51.7±9% and 82.7±25%, respectively), modifications that could be completely blocked with tyrosine phosphatase and protein kinase C inhibitors (dephostatin and rottlerin, respectively). In addition, there was a significant strain-dependent increase in endothelial occludin/ZO-1 association (2.0±0.1-fold) in parallel with increased localization of both occludin and ZO-1 to the cell–cell border. These events could be completely blocked by dephostatin and rottlerin, and they correlated with a strain-dependent reduction in transendothelial permeability to FITC-dextran. Conclusions— Overall, these findings indicate that cyclic strain modulates both the expression and phosphorylation state of occludin and ZO-1 in vascular endothelial cells, with putative consequences for endothelial tight junction assembly and barrier integrity.