Lung Immune Regulation by Vectorial Transport of Endothelial Mitochondria

Abstract

The mitochondrial regulation of lung immunity and repair remains unclear. Here, we consider the role of vectorial mitochondrial transport in endothelial cells (EC) of alveolar capillaries. In axons, which have high length‐diameter ratios, the mitochondrial Rho‐GTPase, Miro determines microtubule‐guided, vectorial mitochondrial transport. Cytosolic Ca2+ elevation increases Ca2+ binding to Miro, causing mitochondrial transport arrest. To determine whether similar mechanisms occur in lung ECs in situ, which are linearized cells with 30–50 μm long cytoplasmic extensions, we viewed live capillaries by confocal microscopy of isolated, blood‐perfused mouse lungs. To visualize EC mitochondria, we microinfused the capillaries with the fluorescent dye, mitotracker green (MTG) that specifically localizes to mitochondria. By vascular transfection, we induced EC expression of a Miro mutant, Mirokk, which does not cause Ca2+‐dependent mitochondrial transport arrest. EC mitochondria were evident as distinct, fluorescent spots of diameter 2–3 um, each representing a cluster of 1–3 mitochondria, that distributed linearly along the cell length. Time‐dependent imaging revealed that the clusters were in continuous motion at 1 um/min, such that a single cluster traversed the distance from the nucleus to the cell periphery in ~40 min. Vascular microinfusion of tumor necrosis factor‐alpha (TNFα) elevated EC cytosolic Ca2+, arrested mitochondrial transport and induced peri‐nuclear mitochondrial clustering. By contrast, Mirokk expression inhibited the transport arrest, while decreasing lung inflammation, as reflected in leukocyte counts in the broncho‐alveolar lavage, and mouse mortality. We show for the first time, that vectorial mitochondrial transport occurs along the cytoplasmic length of capillary EC. We report a novel, Miro‐dependent mechanism of lung immune regulation in which agonist‐induced cytosolic Ca2+ elevation blocks the mitochondrial transport, promoting lung inflammation and injury. Miro may be a therapeutic target for lung repair (support HL122730).Support or Funding Informationsupport HL122730 to JB and AHA Grand‐in‐Aid to MNIThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.