Vascular Endothelial Cells Perform Distinct Sensing and Signaling of Laminar and Disturbed Flows across Plasma Membranes and Mitochondria

BACKGROUNDVascular endothelial cells (ECs) experience two different blood flow patterns: laminar and disturbed flows. Their responses to laminar flow contribute to vascular homeostasis, whereas their responses to disturbed flow result in EC dysfunction and vascular diseases. However, it remains unclear how ECs differentially sense laminar and disturbed flows and trigger signalings that elicit different EC responses. We aimed to investigate EC flow-sensing and signaling mechanisms, focusing on the role of the plasma membrane and mitochondria. METHODSWe exposed cultured human aortic ECs to laminar flow and disturbed flow in flow-loading devices and used real-time imaging with optical probes to examine changes in the lipid order of the plasma and mitochondria membranes and the mitochondrial adenosine triphosphate (ATP) production and hydrogen peroxide (H2O2) release. RESULTSThe lipid order of EC plasma membranes immediately decreased in response to laminar flow, while it increased in response to disturbed flow. Laminar flow also decreased the lipid order of mitochondrial membranes and increased mitochondrial ATP production. In contrast, disturbed flow increased the lipid order of mitochondrial membranes and increased the release of H2O2 from mitochondria. Addition of cholesterol to the cells increased the lipid order of both membranes and abrogated the laminar flow-induced ATP production, while treatment of the cells with a cholesterol-depleting reagent, methyl-{beta} cyclodextrin, decreased the lipid order of both membranes and abolished the disturbed flow-induced H2O2 release, indicating that the changes in the membrane lipid order are closely linked to the flow-induced changes in the mitochondrial functions. CONCLUSIONSECs differentially sense laminar and disturbed flows by altering the lipid order of their plasma and mitochondrial membranes in opposite directions, which result in distinct changes in the mitochondrial functions, namely, increased ATP production for laminar flow and increased H2O2 release for disturbed flow, leading to ATP- and H2O2-mediated signalings, respectively.