Flow Mechanotransduction Response in Endothelial Cell Monolayers and Platelets

Abstract

Blood flow through the cardiovascular system forms many spatiotemporally dynamic flow fields. This is due to the naturally pulsatile motion of the cardiac cycle, the inherent elastic behavior of arteries and the collapsibility of veins, and changes in activity levels throughout the day leading to changes in flow rate. Shear stress forces from the complex blood flow interact with the cells that comprise blood vessels and blood-borne cells such as platelets. Forces sensed by these cells can cause signaling to occur internally that modify and regulate morphology and cell-to-cell interactions. In this research we investigate endothelial cell monolayers and platelet response to shear stresses, while examining cytoskeletal forces, intercellular forces and complexes, and cell-to-cell protein structures. Aim 1: A bioreactor device was designed and fabricated to simulate physiologically relevant shear profiles across endothelial cells grown as quasi-monolayers on micropost force sensors. The design allowed for the application of both laminar and disturbed shear regimes over time. Aim 2: Laminar shear was found to reinforce the natural barrier function by increasing the presence of adherens and tight junctions, while also strengthening and aligning traction forces and intercellular forces. Conversely, static and disturbed flow had lower traction and intercellular forces and lower markers of healthy cell boundary structures. Aim 3: Platelets also interact with shear forces, and a microfluidic device was created to expose separated platelets and platelets in whole blood to various shear rates in an effort to study clot contractility development under shear. Aim 4: Results demonstrated that platelets adhered to high shear gradient regimes and that increasing shear led to enhanced platelet adhesion and aggregation. Microposts placed behind shear concentration features allowed for the measurement of contractile forces, with higher shears also leading to quicker contractility onset and faster force development. Inhibition of myosin and surface integrins also revealed the critical roles that myosin-II, glycoprotein Ib, integrin AlphaIIb-Beta3, and ADP receptor P2Y12 have in platelet clot dynamics.