Cyclic strain effects on human monocyte interactions with endothelial cells and extracellular matrix proteins

Human vascular endothelial cells (ECs) are exposed to various levels of hemodynamic forces, cyclic strain, and shear stress in vivo. Here, we examined the in vitro effects of the various levels (0-6%, 7-16%, and 17- 25%) of strain at 60, 30, and 15 cycles per minute (cpm) on human monocyte adherence to endothelial cells and extracellular matrix protein preadsorbed surfaces. Monocyte adhesion to endothelial cells under cyclic strain significantly increased. At both 30 and 60 cpm, ECs under strains of 7-16% and 17-25% showed >52% and >117% higher monocyte adhesion than endothelial cells under static condition when monocytes were added for 0.5 h. This increase in monocyte adhesion to ECs under cyclic strain remained significantly higher even after 24 h of incubation. Human monocyte adhesion to extracellular matrix protein preadsorbed surfaces differed depending on the specific extracellular matrix protein. Monocytes adhered to collagen type I and fibronectin preadsorbed surfaces >50% under 0-6% strain, >23% under 7- 16% strain, and >52% under 17-25% strain at 15 and 30 cpm compared to the collagen type V preadsorbed surface. However, when extracellular protein preadsorbed surfaces under cyclic strain were compared to the control static condition, monocyte adhesion did not significantly change on most of other surfaces. These results suggest that cyclic strain may play a role in the regulation of monocyte-endothelial cells/extracellular matrix interactions in vivo.