Impact of caspase-8 and PKA in regulating neutrophil-derived microparticle generation

Granulocyte microvesicles with a high plasmin generation capacity promote clot lysis and improve outcome in septic shock

Microvesicles (MVs) have previously been shown to exert profibrinolytic capacity, which is increased in patients with septic shock (SS) with a favorable outcome. We, therefore, hypothesized that the plasmin generation capacity (PGC) could confer to MVs a protective effect supported by their capacity to lyse a thrombus, and we investigated the mechanisms involved. Using an MV-PGC kinetic assay, ELISA, and flow cytometry, we found that granulocyte MVs (Gran-MVs) from SS patients display a heterogeneous PGC profile driven by the uPA (urokinase)/uPAR system. In vitro, these MVs lyse a thrombus according to their MV-PGC levels in a uPA/uPAR-dependent manner, as shown in a fluorescent clot lysis test and a lysis front retraction assay. Fibrinolytic activators conveyed by MVs contribute to approximately 30% of the plasma plasminogenolytic capacity of SS patients. In a murine model of SS, the injection of high PGC Gran-MVs significantly improved mouse survival and reduced the number of thrombi in vital organs. This was associated with a modification of the mouse coagulation and fibrinolysis properties toward a more fibrinolytic profile. Interestingly, mouse survival was not improved when soluble uPA was injected. Finally, using a multiplex array on plasma from SS patients, we found that neutrophil elastase correlates with the effect of high-PGC-capacity plasma and modulates the Gran-MV plasmin generation capacity by cleaving uPA-PAI-1 complexes. In conclusion, we show that the high PGC level displayed by Gran-MVs reduces thrombus formation and improves survival, conferring to Gran-MVs a protective role in a murine model of sepsis.

Extracellular vesicles in toxicological studies: key roles in communication between environmental stress and adverse outcomes

External stressors, especially environmental toxicants can disturb biological homeostasis and thus lead to adverse health effects. However, there is limited understanding of how cells directly exposed to stressors transmit the signals to cells indirectly in contact with stressors. Extracellular vesicles (EVs) are receiving increasing attention as signal transductors between various types of cells in organisms. Cargo in EVs, including RNAs, proteins, lipids, and other signal molecules can be transferred between cells and become critical determining factors of intercellular communication. EVs can be a powerful mediator of environmental stimuli. It has been shown that external stressors reshape the secretion of EVs, modify the composition of EVs, and thus influence the mediating function of EVs. These abnormal EVs can lead to dysfunction of recipient cells, and even the pathogenesis of diseases. In this review, we first summarized current knowledge about the responses of EVs to external stimuli, including chemicals and chemical mixtures. Then we explained how these altered EVs regulate signal pathways in recipient cells, thus mediating physio-pathological responses in detail. The most up-to-date evidence from molecular, cellular, animal and human levels was synthesized to systematically address the mediating roles of EVs. EVs can be regarded as a bridge to link external stressors and internal response. Further toxicological and molecular epidemiological studies are expected to provide further insight into the roles of EVs in toxicology. The gaps in the engulfment of toxicants into EVs are listed as the priority to be solved in future studies.

Lung injury, oxidative stress and fibrosis in mice following exposure to nitrogen mustard

Nitrogen mustard (NM) is a cytotoxic vesicant known to cause acute lung injury which progresses to fibrosis. Herein, we developed a murine model of NM-induced pulmonary toxicity with the goal of assessing inflammatory mechanisms of injury. C57BL/6J mice were euthanized 1-28 d following intratracheal exposure to NM (0.08 mg/kg) or PBS control. NM caused progressive alveolar epithelial thickening, perivascular inflammation, bronchiolar epithelial hyperplasia, interstitial fibroplasia and fibrosis, peaking 14 d post exposure. Enlarged foamy macrophages were also observed in the lung 14 d post NM, along with increased numbers of microparticles in bronchoalveolar lavage fluid (BAL). Following NM exposure, rapid and prolonged increases in BAL cells, protein, total phospholipids and surfactant protein (SP)-D were also detected. Flow cytometric analysis showed that CD11b⁺Ly6G^-F4/80⁺Ly6C^hi proinflammatory macrophages accumulated in the lung after NM, peaking at 3 d. This was associated with macrophage expression of HMGB1 and TNFα in histologic sections. CD11b⁺Ly6G^-F4/80⁺Ly6C^lo anti-inflammatory/pro-fibrotic macrophages also increased in the lung after NM peaking at 14 d, a time coordinate with increases in TGFβ expression and fibrosis. NM exposure also resulted in alterations in pulmonary mechanics including increases in tissue elastance and decreases in compliance and static compliance, most prominently at 14 d. These findings demonstrate that NM induces structural and inflammatory changes in the lung that correlate with aberrations in pulmonary function. This mouse model will be useful for mechanistic studies of mustard lung injury and for assessing potential countermeasures.

Extracellular Vesicles as Markers and Mediators in Sepsis

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. It remains a highly lethal condition in which current tools for early diagnosis and therapeutic decision-making are far from ideal. Extracellular vesicles (EVs), 30 nm to several micrometers in size, are released from cells upon activation and apoptosis and express membrane epitopes specific for their parental cells. Since their discovery two decades ago, their role as biomarkers and mediators in various diseases has been intensively studied. However, their potential importance in the sepsis syndrome has gained attention only recently. Sepsis and EVs are both complex fields in which standardization has long been overdue. In this review, several topics are discussed. First, we review current studies on EVs in septic patients with emphasis on their variable quality and clinical utility. Second, we discuss the diagnostic and therapeutic potential of EVs as well as their role as facilitators of cell communication via micro RNA and the relevance of micro-organism-derived EVs. Third, we give an overview over the potential beneficial but also detrimental roles of EVs in sepsis. Finally, we focus on the role of EVs in selected intensive care scenarios such as coagulopathy, mechanical ventilation and blood transfusion. Overall, the prospect for EV use in septic patients is bright, ranging from rapid and precise (point-of-care) diagnostics, prevention of harmful iatrogenic interventions, to using EVs as guides of individualized therapy. Before the above is achieved, however, the EV research field requires reliable standardization of the current methods and development of new analytical procedures that can close the existing technological gaps.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Bronchoalveolar Lavage Microvesicles Protect Burn-Injured Mice from Pulmonary Infection

BACKGROUND

Pseudomonas aeruginosa is a major cause of morbidity and mortality among burn patients, despite antibiotic therapy. There is a need to identify innate immune defenses that prevent P aeruginosa infection in injured adults in an effort to find therapeutic alternatives to antibiotics. Here, we tested our hypothesis that microvesicles (MVs) in bronchoalveolar (BAL) fluid have a role in the immunity of the lung in response to pathogens.

STUDY DESIGN

Microvesicles were isolated from murine BAL fluid, quantified using Nanoparticle Tracking Analysis, and injected into burn-injured mice before P aeruginosa infection. Survival was assessed and BAL bacterial loads enumerated. Neutrophil number and interleukin 6 activity were determined. Lungs were harvested and sphingosine (SPH) content analyzed via immunohistochemistry. Antimicrobial effects of MVs and SPH-enriched MVs were assessed in an in vitro assay.

RESULTS

Burn-injured mice have reduced BAL MV number and SPH content compared with sham. When BAL MVs from healthy mice are administered to injured mice, survival and bacterial clearance are improved robustly. We also observed that intranasal administration of MVs restores SPH levels after burn injury, MVs kill bacteria directly, and this bacterial killing is increased when the MVs are supplemented with SPH.

CONCLUSIONS

Using a preclinical model, BAL MVs are reduced after scald injury and BAL MV restoration to injured mice improves survival and bacterial clearance. The antimicrobial mechanisms leading to improved survival include the quantity and SPH content of BAL MVs.

Mitochondrial DNA-enriched microparticles promote acute-on-chronic alcoholic neutrophilia and hepatotoxicity

Over the last several years, one of the major advances in the field of alcoholic liver disease research was the discovery that binge alcohol consumption induced neutrophilia and hepatic neutrophil infiltration in chronically ethanol-fed mice and human subjects with excessive alcohol use (EAU); however, the underlying mechanisms remain obscure. Here, we demonstrated that chronic EAU patients with a history of recent excessive drinking (EAU + RD) had higher serum levels of mitochondrial DNA (mtDNA)-enriched microparticles (MPs) than EAU without recent drinking (EAU - RD) and healthy controls, which correlated positively with circulating neutrophils. Similarly, mice with chronic-plus-binge (E10d + 1B) ethanol feeding also had markedly elevated serum levels of mtDNA-enriched MPs, with activation of hepatic ER stress and inflammatory responses. Inhibition of ER stress by gene KO or inhibitors attenuated ethanol-induced elevation of mtDNA-enriched MPs, neutrophilia, and liver injury. The data from the study of hepatocyte-specific deletion of the protein kinase RNA-like ER kinase (Perk) gene in mice and of cultured hepatocytes demonstrated that hepatocytes were the main source of mtDNA-enriched MPs after ethanol feeding. Finally, administration of mtDNA-enriched MPs isolated from E10d+1B-fed mice caused neutrophilia in mice. In conclusion, E10d + 1B ethanol consumption activates hepatic ER stress-dependent mtDNA-enriched MP release, leading to neutrophilia and liver injury.

Microvesicles in vascular homeostasis and diseases. Position Paper of the European Society of Cardiology (ESC) Working Group on Atherosclerosis and Vascular Biology

Microvesicles are members of the family of extracellular vesicles shed from the plasma membrane of activated or apoptotic cells. Microvesicles were initially characterised by their pro-coagulant activity and described as "microparticles". There is mounting evidence revealing a role for microvesicles in intercellular communication, with particular relevance to hemostasis and vascular biology. Coupled with this, the potential of microvesicles as meaningful biomarkers is under intense investigation. This Position Paper will summarise the current knowledge on the mechanisms of formation and composition of microvesicles of endothelial, platelet, red blood cell and leukocyte origin. This paper will also review and discuss the different methods used for their analysis and quantification, will underline the potential biological roles of these vesicles with respect to vascular homeostasis and thrombosis and define important themes for future research.

Neutrophil derived microparticles increase mortality and the counter-inflammatory response in a murine model of sepsis

Although advances in medical care have significantly improved sepsis survival, sepsis remains the leading cause of death in the ICU. This is likely due to a lack of complete understanding of the pathophysiologic mechanisms that lead to dysfunctional immunity. Neutrophil derived microparticles (NDMPs) have been shown to be the predominant microparticle present at infectious and inflamed foci in human models, however their effect on the immune response to inflammation and infection is sepsis has not been fully elucidated. As NDMPs may be a potential diagnostic and therapeutic target, we sought to determine the impact NDMPs on the immune response to a murine polymicrobial sepsis. We found that peritoneal neutrophil numbers, bacterial loads, and NDMPs were increased in our abdominal sepsis model. When NDMPs were injected into septic mice, we observed increased bacterial load, decreased neutrophil recruitment, increased expression of IL-10 and worsened mortality. Furthermore, the NDMPs express phosphatidylserine and are ingested by F4/80 macrophages via a Tim-4 and MFG-E8 dependent mechanism. Finally, upon treatment, NDMPs decrease macrophage activation, increase IL-10 release and decrease macrophage numbers. Altogether, these data suggest that NDMPs enhance immune dysfunction in sepsis by blunting the function of neutrophils and macrophages, two key cell populations involved in the early immune response to infection. This article is part of a Special Issue entitled: Immune and Metabolic Alterations in Trauma and Sepsis edited by Dr. Raghavan Raju.

Activation of Endothelial Pro-resolving Anti-Inflammatory Pathways by Circulating Microvesicles from Non-muscular Myosin Light Chain Kinase-Deficient Mice

Microvesicles, small membrane vesicles released from cells, have beneficial and/or deleterious effects in sepsis. We previously reported that non-muscle myosin light chain kinase (nmMLCK) deletion protects mice against endotoxic shock by reducing inflammation. Here, we have evaluated the consequences of nmMLCK deletion on microvesicle phenotypes and their effects on mouse aortic endothelial cells in association with vascular inflammation and endothelial dysfunction during endotoxic shock induced by lipopolysaccharide in mice. Treatment with lipopolysaccharide induced an increase in levels of circulating microvesicles in wild type but not in nmMLCK-deficient mice. Microvesicles from nmMLCK-deficient mice (MVs^nmMLCK-/-) prevented the inflammatory effects of lipopolysaccharide with concomitant increase of anti- inflammatory and reduction of pro-inflammatory secretome in mouse aortic endothelial cells. In addition, MVs^nmMLCK-/- reduced the efficacy of lipopolysaccharide to increase aortic oxidative and nitrosative stresses as well as macrophage infiltration in the aorta. Moreover, MVs^nmMLCK-/- prevented ex vivo endothelial dysfunction, vascular hyporeactivity, and in vivo overproduction of nitric oxide in heart and liver in response to lipopolysaccharide. Altogether, these findings provide evidence that nmMLCK deletion generates circulating microvesicles displaying protective effects by activating endothelial pro-resolving anti-inflammatory pathways allowing the effective down-regulation of oxidative and nitrative stresses associated with endotoxic shock. Thus, nmMLCK plays a pivotal role in susceptibility to sepsis via the control of cellular activation and release of circulating microvesicles.