Memet Emin

Mitochondrial transfer from bone-marrow–derived stromal cells to pulmonary alveoli protects against acute lung injury

Bone marrow–derived stromal cells (BMSCs) protect against acute lung injury (ALI). To determine the role of BMSC mitochondria in this protection, we airway-instilled mice first with lipopolysaccharide (LPS) and then with either mouse BMSCs (mBMSCs) or human BMSCs (hBMSCs). Live optical studies revealed that the mBMSCs formed connexin 43 (Cx43)-containing gap junctional channels (GJCs) with the alveolar epithelia in these mice, releasing mitochondria-containing microvesicles that the epithelia engulfed. The presence of BMSC-derived mitochondria in the epithelia was evident optically, as well as by the presence of human mitochondrial DNA in mouse lungs instilled with hBMSCs. The mitochondrial transfer resulted in increased alveolar ATP concentrations. LPS-induced ALI, as indicated by alveolar leukocytosis and protein leak, inhibition of surfactant secretion and high mortality, was markedly abrogated by the instillation of wild-type mBMSCs but not of mutant, GJC-incompetent mBMSCs or mBMSCs with dysfunctional mitochondria. This is the first evidence, to our knowledge, that BMSCs protect against ALI by restituting alveolar bioenergetics through Cx43-dependent alveolar attachment and mitochondrial transfer.

Activation of TNFR1 ectodomain shedding by mitochondrial Ca2+ determines the severity of inflammation in mouse lung microvessels.

Shedding of the extracellular domain of cytokine receptors allows the diffusion of soluble receptors into the extracellular space; these then bind and neutralize their cytokine ligands, thus dampening inflammatory responses. The molecular mechanisms that control this process, and the extent to which shedding regulates cytokine-induced microvascular inflammation, are not well defined. Here, we used real-time confocal microscopy of mouse lung microvascular endothelium to demonstrate that mitochondria are key regulators of this process. The proinflammatory cytokine soluble TNF-α (sTNF-α) increased mitochondrial Ca2+, and the purinergic receptor P2Y2 prolonged the response. Concomitantly, the proinflammatory receptor TNF-α receptor-1 (TNFR1) was shed from the endothelial surface. Inhibiting the mitochondrial Ca2+ increase blocked the shedding and augmented inflammation, as denoted by increases in endothelial expression of the leukocyte adhesion receptor E-selectin and in microvascular leukocyte recruitment. The shedding was also blocked in microvessels after knockdown of a complex III component and after mitochondria-targeted catalase overexpression. Endothelial deletion of the TNF-α converting enzyme (TACE) prevented the TNF-α receptor shedding response, which suggests that exposure of microvascular endothelium to sTNF-α induced a Ca2+-dependent increase of mitochondrial H2O2 that caused TNFR1 shedding through TACE activation. These findings provide what we believe to be the first evidence that endothelial mitochondria regulate TNFR1 shedding and thereby determine the severity of sTNF-α-induced microvascular inflammation.

Secondhand Smoking Is Associated With Vascular Inflammation

BACKGROUND The relative risk for cardiovascular diseases in passive smokers is similar to that of active smokers despite almost a 100-fold lower dose of inhaled cigarette smoke. However, the mechanisms underlying the surprising susceptibility of the vascular tissue to the toxins in secondhand smoke (SHS) have not been directly investigated. The aim of this study was to investigate directly vascular endothelial cell function in passive smokers. METHODS Using a minimally invasive method of endothelial biopsy, we investigated directly the vascular endothelium in 23 healthy passive smokers, 25 healthy active smokers, and 23 healthy control subjects who had never smoked and had no regular exposure to SHS. Endothelial nitric oxide synthase (eNOS) function (expression of basal eNOS and activated eNOS [phosphorylated eNOS at serine1177 (P-eNOS)]) and expression of markers of inflammation (nuclear factor-κB [NF-κB]) and oxidative stress (nitrotyrosine) were assessed in freshly harvested venous endothelial cells by quantitative immunofluorescence. RESULTS Expression of eNOS and P-eNOS was similarly reduced and expression of NF-κB was similarly increased in passive and active smokers compared with control subjects. Expression of nitrotyrosine was greater in active smokers than control subjects and similar in passive and active smokers. Brachial artery flow-mediated dilation was similarly reduced in passive and active smokers compared with control subjects, consistent with reduced endothelial NO bioavailability. CONCLUSIONS Secondhand smoking increases vascular endothelial inflammation and reduces active eNOS to a similar extent as active cigarette smoking, indicating direct toxic effects of SHS on the vasculature.

Erythrocytes induce proinflammatory endothelial activation in hypoxia.

Although exposure to ambient hypoxia is known to cause proinflammatory vascular responses, the mechanisms initiating these responses are not understood. We tested the hypothesis that in systemic hypoxia, erythrocyte-derived H(2)O(2) induces proinflammatory gene transcription in vascular endothelium. We exposed mice or isolated, perfused murine lungs to 4 hours of hypoxia (8% O(2)). Leukocyte counts increased in the bronchoalveolar lavage. The expression of leukocyte adhesion receptors, reactive oxygen species, and protein tyrosine phosphorylation increased in freshly recovered lung endothelial cells (FLECs). These effects were inhibited by extracellular catalase and by the removal of erythrocytes, indicating that the responses were attributable to erythrocyte-derived H(2)O(2). Concomitant nuclear translocation of the p65 subunit of NF-κB and hypoxia-inducible factor-1α stabilization in FLECs occurred only in the presence of erythrocytes. Hemoglobin binding to the erythrocyte membrane protein, band 3, induced the release of H(2)O(2) from erythrocytes and the p65 translocation in FLECs. These data indicate for the first time, to our knowledge, that erythrocytes are responsible for endothelial transcriptional responses in hypoxia.

Increased internalization of complement inhibitor CD59 may contribute to endothelial inflammation in obstructive sleep apnea

Reduced protection against complement attack mediates endothelial inflammation in obstructive sleep apnea. Sleep tight, don’t let the complement bite Obstructive sleep apnea is a common medical condition characterized by intermittent cessation of breathing during sleep, which results in intermittent hypoxia. It greatly increases patients’ risk of cardiovascular disease, and now Emin et al. provide a mechanism, which helps to explain this correlation. The authors discovered that intermittent hypoxia causes internalization of CD59, a protein that is normally found on the membrane of endothelial cells and protects them from being injured by circulating complement. After internalization, CD59 could no longer protect the cells, resulting in damage to the vascular walls. In contrast, statins stabilized CD59 on the endothelial cell surface and protected them from injury, revealing yet another mechanism by which these versatile drugs protect against cardiovascular disease. Obstructive sleep apnea (OSA), characterized by intermittent hypoxia (IH) during transient cessation of breathing, triples the risk for cardiovascular diseases. We used a phage display peptide library as an unbiased approach to investigate whether IH, which is specific to OSA, activates endothelial cells (ECs) in a distinctive manner. The target of a differentially bound peptide on ECs collected from OSA patients was identified as CD59, a major complement inhibitor that protects ECs from the membrane attack complex (MAC). A decreased proportion of CD59 is located on the EC surface in OSA patients compared with controls, suggesting reduced protection against complement attack. In vitro, IH promoted endothelial inflammation predominantly via augmented internalization of CD59 and consequent MAC deposition. Increased internalization of endothelial CD59 in IH appeared to be cholesterol-dependent and was reversed by statins in a CD59-dependent manner. These studies suggest that reduced complement inhibition may mediate endothelial inflammation and increase vascular risk in OSA patients.

Platelets induce endothelial tissue factor expression in a mouse model of acid-induced lung injury

Although the lung expresses procoagulant proteins under inflammatory conditions, underlying mechanisms remain unclear. Here, we addressed lung endothelial expression of tissue factor (TF), which initiates the coagulation cascade and expression of which signifies development of a procoagulant phenotype in the vasculature. To establish the model of acid-induced acute lung injury (ALI), we intranasally instilled anesthetized mice with saline or acid. Then 2 h later, we isolated pulmonary vascular cells for flow cytometry and confocal microscopy to detect the leukocyte antigen, CD45 and the endothelial markers VE-cadherin and von Willebrand factor (vWf). Acid increased both the number of vWf-expressing cells as well as TF and P-selectin expressions on these cells. All of these effects were markedly inhibited by treating mice with antiplatelet serum, suggesting the involvement of platelets. The increased expressions of TF, vWf, and P-selectin in response to acid also occurred in platelets. Moreover, the effects were replicated in endothelial cells derived from isolated, blood-perfused lungs. However, the effect was inhibited completely in lungs perfused with platelet-depleted and, to a lesser extent, with leukocyte-depleted blood. Acid injury increased endothelial expressions of the platelet proteins, CD41 and CD42b, providing evidence that platelet proteins were transferred to the vascular surface. Reactive oxygen species (ROS) were implicated in these responses, in that the endothelial and platelet protein expressions were inhibited. We conclude that acid-induced ALI causes NOX2-mediated ROS generation that activates platelets, which then generate a procoagulant endothelial surface.