Shear stress induces immunomodulatory signaling in bone marrow mesenchymal stromal cells (MSCs)

Bone marrow mesenchymal stromal cells (MSCs) regulate homeostasis and trafficking of cells of the blood lineage. In response to traumatic injury or infection, MSCs are believed to mobilize from the bone marrow, but it is largely unknown how egress into circulation impacts MSC function. Here we show that biomechanical forces associated with trafficking of MSCs from the bone marrow into the vasculature contribute uniquely to genetic signaling that reinforces MSC repression of immune cell activation. Laminar wall shear stress (LSS) typical of fluid frictional forces present on the lumen of arterioles stimulates increases in antioxidant and anti-inflammatory mediators, as well as an array of chemokines capable of immune cell recruitment. Importantly, LSS promotes a signaling cascade through COX2 that elevates prostaglandin E2 (PGE2) biosynthesis, permitting MSCs to suppress immune cell activation in the presence of inflammatory cues. Pharmacological inhibition of COX2 depleted PGE2 and impaired the ability of MSCs to block tumor necrosis factor- (TNF-) production, supporting a key role for PGE2 in the MSC immunomodulatory response to LSS. Preconditioning of MSCs by LSS ex vivo was an effective means of enhancing therapeutic efficacy in a rat model of traumatic brain injury, as evidenced by decreased numbers of apoptotic and M1-type activated microglia in the hippocampus and by retention of endogenous MSCs in the bone marrow. We conclude that biomechanical forces provide critical cues to MSCs residing at the vascular interface which influence MSC immunomodulatory and paracrine functions, thus providing unique opportunities for functional enhancement of MSCs used in therapeutic applications.

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Diaz MF, Vaidya AB, Evans SM, Lee HJ, Aertker BM, Alexander AJ, Price KM, Ozuna JA, Liao GP, Aroom KR, Xue H, Gu L, Omichi R, Bedi S, Olson SD, Cox CS Jr, Wenzel PL