Shear Stress Induces a Pro-Inflammatory Phenotype in Human Monocyte-Derived Macrophages

Abstract

AbstractMacrophages are innate immune cells that are known for their diverse phenotypes and plasticity. They switch between pro-inflammatory (M1) and anti-inflammatory/pro-fibrotic (M2) phenotypes depending on surrounding microenvironmental cues, which have been implicated in disease outcomes. Although considerable research has been focused on macrophage response to biochemical cues and mechanical signals, there is a scarcity of knowledge surrounding their behavior in response to shear stress. Animal studies have shown that shear stress modulates macrophage activation; however it is difficult to determine the specific signals that macrophages release in response to shearin vivo, due to the challenge of isolating shear stress as a variable. This necessitates a more controlled environment using anin vitromodel. We achieved this by applying varying magnitudes of shear stress on human monocyte-derived macrophages (MDMs) using a cone-and-plate viscometer and evaluating changes in morphology, gene expression, protein expression, and cytokine secretion over time. MDMs exposed to shear stress exhibited a rounder morphology compared to statically-cultured controls. RT-qPCR results showed significant upregulation of TNF-α, and analysis of cytokine release revealed increased secretion of TNF-α, IL-18, fractalkine, and other chemokines. The upregulation of pro-inflammatory factors was evident with both increasing magnitudes of shear and time. Taken together, these results indicate that prolonged shear exposure induced a pro-inflammatory M1 phenotype. These findings have implications for medical technology development, such asin situvascular graft design wherein macrophages are exposed to shear and have been shown to affect graft resorption, and in delineating disease pathophysiology, for example to further illuminate the role of macrophages in atherosclerosis where shear is directly related to disease outcome.