Circulating endothelial microparticles (EMPs) are emerging as biomarkers of chronic obstructive pulmonary disease (COPD) in individuals exposed to cigarette smoke (CS), but their mechanism of release and function remain unknown. We assessed biochemical and functional characteristics of EMPs and circulating microparticles (cMPs) released by CS. CS exposure was sufficient to increase microparticle levels in plasma of humans and mice, and in supernatants of primary human lung microvascular endothelial cells. CS-released EMPs contained predominantly exosomes that were significantly enriched in let-7d, miR-191; miR-126; and miR125a, microRNAs that reciprocally decreased intracellular in CS-exposed endothelium. CS-released EMPs and cMPs were ceramide-rich and required the ceramide-synthesis enzyme acid sphingomyelinase (aSMase) for their release, an enzyme which was found to exhibit significantly higher activity in plasma of COPD patients or of CS-exposed mice. The ex vivo or in vivo engulfment of EMPs or cMPs by peripheral blood monocytes-derived macrophages was associated with significant inhibition of efferocytosis. Our results indicate that CS, via aSMase, releases circulating EMPs with distinct microRNA cargo and that EMPs affect the clearance of apoptotic cells by specialized macrophages. These targetable effects may be important in the pathogenesis of diseases linked to endothelial injury and inflammation in smokers.

BackgroundSeveral inflammatory lung diseases display abundant presence of hyaluronic acid (HA) bound to heavy chains (HC) of serum protein inter-alpha-inhibitor (IαI) in the extracellular matrix. The HC-HA modification is critical to neutrophil sequestration in liver sinusoids and to survival during experimental lipopolysaccharide (LPS)-induced sepsis. Therefore, the covalent HC-HA binding, which is exclusively mediated by tumor necrosis factor α (TNFα)-stimulated-gene-6 (TSG-6), may play an important role in the onset or the resolution of lung inflammation in acute lung injury (ALI) induced by respiratory infection.MethodsReversible ALI was induced by a single intratracheal instillation of LPS or Pseudomonas aeruginosa in mice and outcomes were studied for up to six days. We measured in the lung or the bronchoalveolar fluid HC-HA formation, HA immunostaining localization and roughness, HA fragment abundance, and markers of lung inflammation and lung injury. We also assessed TSG-6 secretion by TNFα- or LPS-stimulated human alveolar macrophages, lung fibroblast Wi38, and bronchial epithelial BEAS-2B cells.ResultsExtensive HC-modification of lung HA, localized predominantly in the peri-broncho-vascular extracellular matrix, was notable early during the onset of inflammation and was markedly decreased during its resolution. Whereas human alveolar macrophages secreted functional TSG-6 following both TNFα and LPS stimulation, fibroblasts and bronchial epithelial cells responded to only TNFα. Compared to wild type, TSG-6-KO mice, which lacked HC-modified HA, exhibited modest increases in inflammatory cells in the lung, but no significant differences in markers of lung inflammation or injury, including histopathological lung injury scores.ConclusionsRespiratory infection induces rapid HC modification of HA followed by fragmentation and clearance, with kinetics that parallel the onset and resolution phase of ALI, respectively. Alveolar macrophages may be an important source of pulmonary TSG-6 required for HA remodeling. The formation of HC-modified HA had a minor role in the onset, severity, or resolution of experimental reversible ALI induced by respiratory infection with gram-negative bacteria.Electronic supplementary materialThe online version of this article (10.1186/s12931-018-0812-1) contains supplementary material, which is available to authorized users.

A better understanding of the pathogenesis of distinct chronic obstructive pulmonary disease (COPD) phenotypes will improve diagnostic and therapeutic options for this common disease. We present evidence that sphingolipids such as ceramides are involved in the emphysema pathogenesis. Whereas distinct ceramide species cause cell death by apoptosis and necroptosis, cell adaptation leads to accumulation of other sphingolipid metabolites that extend cell survival by triggering autophagy. Cigarette smoke-released sphingolipids have been involved in both the initiation and persistence of lung injury via intracellular signaling and paracrine effects mediated via exosomes and plasma membrane-bound microparticles. Strategies to control sphingolipid metabolite production may promote cellular repair and maintenance to treat COPD.

Objective: MicroRNA-126-3p (miR-126) is required for angiogenesis during organismal development or the repair of injured arterial vasculature. The role of miR-126 in lung microvascular endothelial cells, which are essential for gas exchange and for lung injury repair and regeneration, remains poorly understood. Considering the significant heterogeneity of endothelial cells from different vascular beds, we aimed to determine the role of miR-126 in regulating lung microvascular endothelial cell function and to elucidate its downstream signaling pathways. Approach and Results: Overexpression and knockdown of miR-126 in primary human lung microvascular endothelial cells (HLMVEC) were achieved via transfections of miR-126 mimics and antisense inhibitors. Increasing miR-126 levels in HLMVEC reduced cell proliferation, weakened tube formation, and increased cell apoptosis, whereas decreased miR-126 levels stimulated cell proliferation and tube formation. Whole-genome RNA sequencing revealed that miR-126 was associated with an antiangiogenic and proapoptotic transcriptomic profile. Using validation assays and knockdown approaches, we identified that the effect of miR-126 on HLMVEC angiogenesis was mediated by the LAT1 (L-type amino acid transporter 1), via regulation of mTOR (mammalian target of rapamycin) signaling. Furthermore, downregulation of miR-126 in HLMVEC inhibited cell apoptosis and improved endothelial tube formation during exposure to environmental insults such as cigarette smoke. Conclusions: miR-126 inhibits HLMVEC angiogenic function by targeting the LAT1-mTOR signaling axis, suggesting that miR-126 inhibition may be useful for conditions associated with microvascular loss, whereas miR-126 augmentation may help control unwanted microvascular angiogenesis.