The effects of laminar and oscillatory fluid shear stress on microvascular endothelial cells

Abstract

Cardiovascular disease (CVD) is one of the most prevalent causes of death in the United States, being responsible for nearly one in every three deaths. Cellular mechanics related to CVD are often studied using human umbilical cord vein endothelial cells (HUVECs) and bovine aortic endothelial cells (BAECs). These studies have led to the understanding that atherosclerotic plaques prevalent in CVD are found in areas of low, disturbed shear stress where cells do not align to a direction of flow. This is the common assumption for endothelial cells across the cardiovascular system, although new research has shown this may not be the case. This study showcases the effects of fluid shear stress on human microvascular endothelial cells (HMEC-1s) originating in the dermis, those found in the vascular system measuring >100 μm in diameter. Utilizing the Ibidi fluidic pump system we cultured cells under laminar and oscillatory fluid shear conditions at a range of fluid shear values (5-15 dyne/cm2) over a time period of 24-72 hours. Images of the nuclei in each sample were stained with Hoechst 33258 and sampled at various time points throughout the studies. These images were segmented in ImageJ and analyzed for morphological changes in the area, perimeter, aspect ratio, major and minor axis, and angle of alignment. Results showed that over the course of 72-hours, there were no significant changes in nuclear morphology or alignment. Additionally, there was significant cell loss under oscillatory flow conditions that was not seen in the laminar study. From these results it may be concluded that these microvascular cells have developed an adaptation to resist morphological change due to exposure to fluid shear stress. While these results are preliminary, with one sample of each flow type, they are consistent with other literature regarding the effects of shear on brain microvascular cells. Future studies will analyze how chromatin structure is reorganized due to the fluid shear and how the cytoskeleton responds to fluid shear stress.