Mechanotransduction of substrate stiffness in endothelial cell collective migration

Abstract

Endothelial damage during life-saving percutaneous angioplasty contributes to re-stenosis rates of nearly 20% within 5 years. Re-endothelialization, the collective endothelial cell migration over exposed extracellular matrix (ECM) and stent struts, can restore a continuous, functional endothelium. During atherosclerotic disease, vascular ECM becomes stiffer. ECM stiffness affects epithelial cell collective migration in other pathogenic contexts. However, substrate stiffness effects on endothelial cell collective migration have yet to be explored. We developed quantitative computational image processing algorithms for assessing collective migration. We then used these image analysis techniques to measure the effect of substrate stiffness on critical aspects of porcine aortic endothelial cell (PAEC) two-dimensional collective migration: (1) migration distance, (2) directedness, and (3) togetherness. PAEC were seeded on collagen-coated polyacrylamide hydrogels (4-50 kPa) in a 5 mm cloning ring and then allowed to migrate outwards. We found that migration distance increased with substrate stiffness and that there was a concomitant increase in PAEC alignment. We found that decreased togetherness on stiffer substrates led to enhanced proliferation at the migratory interface. We used the specific Rho kinase (ROCK) inhibitor Y27632 to show that ROCK-mediated contractility limited endothelial cell collective migration on soft substrates. We observed that PAEC secrete and remodel fibronectin on collagen-coated substrates. Interestingly, α5 integrin, but not fibronectin, was important for directed collective migration on stiff substrates. These findings provide insight into how substrate stiffness affects endothelial cell collective migration. This work will inform how the mechanical properties of tissue and tissue engineered construct could be designed to promote a functional endothelium.%%%%Ph.D., Biomedical Engineering – Drexel University, 2015