Transient low shear-stress preconditioning influences long-term endothelial traction and alignment under high shear flow

Abstract

Endothelial cells (ECs) within the vascular system encounter fluid shear stress (FSS). High, laminar FSS promotes vasodilation and anti-inflammatory responses, while low or disturbed FSS induces dysfunction and inflammation. However, the adaptation of ECs to dynamically changing FSS patterns remains underexplored. Here, by combining traction force microscopy with a custom flow chamber, we examined human umbilical vein endothelial cells adapting their traction during transitions from short-term low shear to long-term high shear stress. We discovered that the initial low FSS elevates the traction by only half of the amount by direct high FSS even after flow changes to high FSS. However, in the long term under high FSS, the flow started with low FSS triggers a substantial second rise in traction, for over 10 hours. In contrast, direct high FSS exposure results in a quick traction surge followed by a huge reduction below the baseline traction. Importantly, we find that the orientation of traction vectors is steered by initial shear exposure. Using Granger Causality analysis, we show that the traction that aligns in the flow direction under direct high FSS functionally causes cell alignment. Similarly, EC traction that orients perpendicular to the flow that starts with temporary low FSS functionally causes cell orientation perpendicular to the flow. Taken together, our findings elucidate the significant influence of initial short-term low FSS on lasting changes in endothelial traction that induces EC alignment.