Paediatric sepsis survivors are resistant to sepsis-induced long-term immune dysfunction

BACKGROUND AND PURPOSE

Sepsis-surviving adult individuals commonly develop immunosuppression and increased susceptibility to secondary infections, an outcome mediated by the axis IL-33/ILC2s/M2 macrophages/Tregs. Nonetheless, the long-term immune consequences of paediatric sepsis are indeterminate. We sought to investigate the role of age in the genesis of immunosuppression following sepsis.

EXPERIMENTAL APPROACH

Here, we compared the frequency of Tregs, the activation of the IL-33/ILC2s axis in M2 macrophages and the DNA methylation of epithelial lung cells from post-septic infant and adult mice. Likewise, sepsis-surviving mice were inoculated intranasally with Pseudomonas aeruginosa or by subcutaneous inoculation of the B16 melanoma cell line. Finally, blood samples from sepsis-surviving patients were collected and the concentration of IL-33 and Tregs frequency were assessed.

KEY RESULTS

In contrast to 6-week-old mice, 2-week-old mice were resistant to secondary infection and did not show impairment in tumour controls upon melanoma challenge. Mechanistically, increased IL-33 levels, Tregs expansion, and activation of ILC2s and M2-macrophages were observed in 6-week-old but not 2-week-old post-septic mice. Moreover, impaired IL-33 production in 2-week-old post-septic mice was associated with increased DNA methylation in lung epithelial cells. Notably, IL-33 treatment boosted the expansion of Tregs and induced immunosuppression in 2-week-old mice. Clinically, adults but not paediatric post-septic patients exhibited higher counts of Tregs and seral IL-33 levels.

CONCLUSION AND IMPLICATIONS

These findings demonstrate a crucial and age-dependent role for IL-33 in post-sepsis immunosuppression. Thus, a better understanding of this process may lead to differential treatments for adult and paediatric sepsis.

Platelets exacerbate cardiovascular inflammation in a murine model of Kawasaki disease vasculitis

Kawasaki disease (KD) is the leading cause of acquired heart disease among children. Increased platelet counts and activation are observed during the course of KD, and elevated platelet counts are associated with higher risks of developing intravenous immunoglobulin resistance and coronary artery aneurysms. However, the role of platelets in KD pathogenesis remains unclear. Here, we analyzed transcriptomics data generated from the whole blood of patients with KD and discovered changes in the expression of platelet-related genes during acute KD. In the Lactobacillus casei cell wall extract (LCWE) murine model of KD vasculitis, LCWE injection increased platelet counts and the formation of monocyte-platelet aggregates (MPAs), upregulated the concentration of soluble P-selectin, and increased circulating thrombopoietin and interleukin 6 (IL-6). Furthermore, platelet counts correlated with the severity of cardiovascular inflammation. Genetic depletion of platelets (Mpl-/- mice) or treatment with an anti-CD42b antibody significantly reduced LCWE-induced cardiovascular lesions. Furthermore, in the mouse model, platelets promoted vascular inflammation via the formation of MPAs, which likely amplified IL-1B production. Altogether, our results indicate that platelet activation exacerbates the development of cardiovascular lesions in a murine model of KD vasculitis. These findings enhance our understanding of KD vasculitis pathogenesis and highlight MPAs, which are known to enhance IL-1B production, as a potential therapeutic target for this disorder.

Measuring NLR Oligomerization II: Detection of ASC Speck Formation by Confocal Microscopy and Immunofluorescence

Inflammasomes are crucial sentinels of the innate immune system that sense clues of infection, cellular stress, or metabolic imbalances. Upon activation, the inflammasome sensor (e.g., NLRP3) recruits the adaptor protein apoptosis-associated speck-like protein containing a CARD (ASC). ASC rapidly oligomerizes to form a micron-sized structure termed "ASC speck." These are crucial for the activation of caspase-1 and downstream inflammatory signals released following a specific form of lytic cell death called pyroptosis. Hence, due to their considerably large size, ASC specks can be easily visualized by microscopy as a simple upstream readout for inflammasome activation. Here, we provide three detailed protocols for imaging ASC specks: (1) live-cell imaging of macrophage cell lines expressing a fluorescent protein fusion form of ASC, (2) imaging of human primary cells using immunofluorescence staining of endogenous ASC, and (3) visualization and quantification of specks on a single-cell level using imaging flow cytometry.

Nanobodies dismantle post-pyroptotic ASC specks and counteract inflammation in vivo

Inflammasomes sense intracellular clues of infection, damage, or metabolic imbalances. Activated inflammasome sensors polymerize the adaptor ASC into micron‐sized “specks” to maximize caspase‐1 activation and the maturation of IL‐1 cytokines. Caspase‐1 also drives pyroptosis, a lytic cell death characterized by leakage of intracellular content to the extracellular space. ASC specks are released among cytosolic content, and accumulate in tissues of patients with chronic inflammation. However, if extracellular ASC specks contribute to disease, or are merely inert remnants of cell death remains unknown. Here, we show that camelid‐derived nanobodies against ASC (VHH_ASC) target and disassemble post‐pyroptotic inflammasomes, neutralizing their prionoid, and inflammatory functions. Notably, pyroptosis‐driven membrane perforation and exposure of ASC specks to the extracellular environment allowed VHH_ASC to target inflammasomes while preserving pre‐pyroptotic IL‐1β release, essential to host defense. Systemically administrated mouse‐specific VHH_ASC attenuated inflammation and clinical gout, and antigen‐induced arthritis disease. Hence, VHH_ASC neutralized post‐pyroptotic inflammasomes revealing a previously unappreciated role for these complexes in disease. VHH_ASC are the first biologicals that disassemble pre‐formed inflammasomes while preserving their functions in host defense.

Comprehensive Profiling of Blood Coagulation and Fibrinolysis Marker Reveals Elevated Plasmin-Antiplasmin Complexes in Parkinson's Disease

Parkinson's disease (PD) is the second most common age-related neurodegenerative disease. Accumulating evidence demonstrates that alpha-synuclein (α-Syn), an apparently predominant neuronal protein, is a major contributor to PD pathology. As α-Syn is also highly abundant in blood, particularly in red blood cells (RBCs) and platelets, this in turn raises the question on the function of presumably dysfunctional α-Syn in "peripheral" cells and its putative effect on the other enclosed constituents. Herein, we detected the internal variance in erythrocytes of PD patients by Raman spectroscopy, but no measurable amount of erythrocytic behavioural change (eryptosis) or any haemoglobin variation was noticed. An elevated level of plasmin-antiplasmin complexes (PAP) was observed in the plasma of PD patients, indicating activation of the fibrinolytic system, but platelet activation after thrombin stimulation was not altered. Sex-specific patterns were noticed for blood coagulation factor XIII and factor XII activity in PD patients. Additionally, the alterations in homocysteine levels which have often been observed in PD patients were found to be independent from L-DOPA usage and PAP levels. Furthermore, a selective gene expression analysis identified subsets of genes related to different blood-associated compartments (RBCs, platelets, coagulation-fibrinolysis) also involved in PD-related pathways.

Necroptosis, pyroptosis and apoptosis: an intricate game of cell death

Cell death is a fundamental physiological process in all living organisms. Its roles extend from embryonic development, organ maintenance, and aging to the coordination of immune responses and autoimmunity. In recent years, our understanding of the mechanisms orchestrating cellular death and its consequences on immunity and homeostasis has increased substantially. Different modalities of what has become known as 'programmed cell death' have been described, and some key players in these processes have been identified. We have learned more about the intricacies that fine tune the activity of common players and ultimately shape the different types of cell death. These studies have highlighted the complex mechanisms tipping the balance between different cell fates. Here, we summarize the latest discoveries in the three most well understood modalities of cell death, namely, apoptosis, necroptosis, and pyroptosis, highlighting common and unique pathways and their effect on the surrounding cells and the organism as a whole.

The Interface Between Inflammatory Mediators and MicroRNAs in Plasmodium vivax Severe Thrombocytopenia

Severe thrombocytopenia can be a determinant factor in the morbidity of Plasmodium vivax, the most widespread human malaria parasite. Although immune mechanisms may drive P. vivax-induced severe thrombocytopenia (PvST), the current data on the cytokine landscape in PvST is scarce and often conflicting. Here, we hypothesized that the analysis of the bidirectional circuit of inflammatory mediators and their regulatory miRNAs would lead to a better understanding of the mechanisms underlying PvST. For that, we combined Luminex proteomics, NanoString miRNA quantification, and machine learning to evaluate an extensive array of plasma mediators in uncomplicated P. vivax patients with different degrees of thrombocytopenia. Unsupervised clustering analysis identified a set of PvST-linked inflammatory (CXCL10, CCL4, and IL-18) and regulatory (IL-10, IL-1Ra, HGF) mediators. Among the mediators associated with PvST, IL-6 and IL-8 were critical to discriminate P. vivax subgroups, while CCL2 and IFN-γ from healthy controls. Supervised machine learning spotlighted IL-10 in P. vivax-mediated thrombocytopenia and provided evidence for a potential signaling route involving IL-8 and HGF. Finally, we identified a set of miRNAs capable of modulating these signaling pathways. In conclusion, the results place IL-10 and IL-8/HGF in the center of PvST and propose investigating these signaling pathways across the spectrum of malaria infections.

Molecular basis of carrageenan-induced cytokines production in macrophages

BACKGROUND

Low molecular weight carrageenan (Cg) is a seaweed-derived sulfated polysaccharide widely used as inflammatory stimulus in preclinical studies. However, the molecular mechanisms of Cg-induced inflammation are not fully elucidated. The present study aimed to investigate the molecular basis involved in Cg-induced macrophages activation and cytokines production.

METHODS

Primary culture of mouse peritoneal macrophages were stimulated with Kappa Cg. The supernatant and cell lysate were used for ELISA, western blotting, immunofluorescence. Cg-induced mouse colitis was also developed.

RESULTS

Here we show that Cg activates peritoneal macrophages to produce pro-inflammatory cytokines such as TNF and IL-1β. While Cg-induced TNF production/secretion depends on TLR4/MyD88 signaling, the production of pro-IL-1β relies on TLR4/TRIF/SYK/reactive oxygen species (ROS) signaling pathway. The maturation of pro-IL1β into IL-1β is dependent on canonical NLRP3 inflammasome activation via Pannexin-1/P2X7/K+ efflux signaling. In vivo, Cg-induced colitis was reduced in mice in the absence of NLRP3 inflammasome components.

CONCLUSIONS

In conclusion, we unravel a critical role of the NLRP3 inflammasome in Cg-induced pro-inflammatory cytokines production and colitis, which is an important discovery on the pro-inflammatory properties of this sulfated polysaccharide for pre-clinical studies. Video abstract Carrageenan (Cg) is one the most used flogistic stimulus in preclinical studies. Nevertheless, the molecular basis of Cg-induced inflammation is not totally elucidated. Herein, Lopes et al. unraveled the molecular basis for Cg-induced macrophages production of biological active IL-1β. The Cg-stimulated macrophages produces pro-IL-1β depends on TLR4/TRIF/Syk/ROS, whereas its processing into mature IL-1β is dependent on the canonical NLRP3 inflammasome.

P4145Endothelial NLRP3-Inflammasome impairs vascular function via microparticles

Background

In recent years inflammation has emerged to the centre of attention of cardiovascular research. One of its key figures is the NLRP3-inflammasome a multimeric protein complex that stimulates inflammatory responses in atherogenesis through proinflammatory cytokines like caspases IL-1β and -18. It is activated by danger signals such as cholesterol crystals, oxidized LDL, ATP or uric acids. Microparticles (MP) are extracellular vesicles that are released by activated or apoptotic cells. They are known as a vector for the intercellular transfer of biological information. The body of evidence indicates that endothelial microparticles contribute to the development and complications in atherosclerosis. With this study we sought to elucidate the effects microparticles, that are discharged by inflammasome activated endothelial cells, exert on arterial vascular cells.

Methods and results

RTPCR experiments showed that activation of human coronary artery endothelial cells (HCAEC) with LPS and Nigericin leads to NLRP3-inflammasome-specific upregulation of NLRP3 and IL1β. Analysis of the supernatant of aforementioned cells via westernblot revealed release of cleaved caspase-1 while donorcells undergo pyroptosis. FACS and electronmicroscopy experiments revealed time dependent release of endothelial microparticles (EMP) by inflammasome activated HCAEC, while western blot demonstrated that EMP enclose active caspase-1. Fluorescence microscopic imaging illustrated time dependent incorporation of EMP by HCAEC. Stimulation of HCAEC with EMP revealed detrimental biological effects on recipient cells as viability assay and scratch assay showed decreased viability and proliferation/ migration, cytotoxity assay showed increased cytotoxity and RT-PCR experiments showed increased expression of NALP3, IL-1b, VCAM and ICAM. The fact that treatment of recipient cells with the NLRP3-Inhibitor isoliquiritigenin (ILG), heat-inactivation of EMP and rupturing the EMP-membrane by freezing is able to diminish harmful effects EMP exert on recipient cells shown by viability assay, scratch assay and microscopic imaging underlines detrimental effects being exerted by EMP-encapsuled inflamasome-components.

Conclusion

Our findings verify that MP released from inflammasome-activated endothelial cells are incorporated by vascular cells which in turn sustain a reduction of cell viability, migration and proliferation. EMP effectuate activation of the NLRP3-inflammasme in their target cells. The cytotoxic effects of EMP are suppressed by inhibitors of the NLRP3-inflammasome and affection of EMP-membrane. Our results emphasize the immunological role of endothelial cells and indicate that inflammasome activation is transferable through microparticle-associated communication. This in turn facilitates cell death and possibly initiates a vicious cycle of inflammation suggesting a role in the advancement of atherosclerosis.

Acknowledgement/Funding

Else Kröner Scholarship

Regulation of Innate Immune Responses by Platelets

The role of platelets has been extensively studied in the context of coagulation and vascular integrity. Their hemostatic imbalance can lead to known conditions as atherosclerotic plaques, thrombosis, and ischemia. Nevertheless, the knowledge regarding the regulation of different cell types by platelets has been growing exponentially in the past years. Among these biological systems, the innate immune response is remarkably affected by the crosstalk with platelets. This interaction can come from the formation of platelet-leukocyte aggregates, signaling by direct contact between membrane surface molecules or by the stimulation of immune cells by soluble factors and active microparticles secreted by platelets. These ubiquitous blood components are able to sense and react to danger signals, guiding leukocytes to an injury site and providing a scaffold for the formation of extracellular traps for efficient microbial killing and clearance. Using several different mechanisms, platelets have an important task as they regulate the release of different cytokines and chemokines upon sterile or infectious damage, the expression of cell markers and regulation of cell death and survival. Therefore, platelets are more than clotting agents, but critical players within the fine inflammatory equilibrium for the host. In this review, we present pointers to a better understanding about how platelets control and modulate innate immune cells, as well as a summary of the outcome of this interaction, providing an important step for therapeutic opportunities and guidance for future research on infectious and autoimmune diseases.

Charcot-Leyden Crystals Activate the NLRP3 Inflammasome and Cause IL-1β Inflammation in Human Macrophages

Charcot-Leyden crystals (CLCs) are Galectin-10 protein crystals that can form after eosinophils degranulate. CLCs can appear and persist in tissues from patients with eosinophilic disorders, such as asthma, allergic reactions, and fungal and helminthic infections. Despite abundant reports of their occurrence in human disease, the inflammatory potential of CLCs has remained unknown. In this article, we show that CLCs induce the release of the proinflammatory cytokine IL-1β upon their phagocytosis by primary human macrophages in vitro. Chemical inhibition and small interfering RNA knockdown of NLRP3 in primary human macrophages abrogated their IL-1β response to CLCs. Using C57BL/6 ASC-mCitrine transgenic inflammasome reporter mice, we showed that the instillation of CLCs into the lungs promoted the assembly of ASC complexes in infiltrating immune cells (neutrophils and inflammatory monocytes) and resulted in IL-1β accumulation into the bronchoalveolar lavage fluid. Our findings reveal that CLCs are recognized by the NLRP3 inflammasome, which may sustain inflammation that follows eosinophilic inflammatory processes.

Detection of ASC Speck Formation by Flow Cytometry and Chemical Cross-linking

Assembly of a relatively large protein aggregate or "speck" formed by the adaptor protein ASC is a common downstream step in the activation of most inflammasomes. This unique feature of ASC allows its visualization by several imaging techniques and constitutes a reliable and feasible readout for inflammasome activation in cells and tissues. We have previously described step-by-step protocols to generate immortalized cell lines stably expressing ASC fused to a fluorescent protein for measuring inflammasome activation by confocal microscopy, and immunofluorescence of endogenous ASC in primary cells. Here, we present two more methods to detect ASC speck formation: (1) Assessment of ASC speck formation by flow cytometry; and (2) Chemical cross-linking of ASC followed by immunoblotting. These methods allow for the discrimination of inflammasome-activated versus non-activated cells, the identification of lineage-specific inflammasome activation in complex cell mixtures, and sorting of inflammasome-activated cells for further analysis.

The intra- and extracellular functions of ASC specks

Inflammasomes are the central signaling hubs of the inflammatory response. They process cytosolic evidence of infection, cell damage, or metabolic disturbances, and elicit a pro-inflammatory response mediated by members of the interleukin-1 family of cytokines and pyroptotoic cell death. On the molecular level, this is accomplished by the sensor-nucleated recruitment and oligomerization of the adapter protein ASC. Once a tunable threshold is reached, cooperative assembly of ASC into linear filaments and their condensation into macromolecular ASC specks promotes an all-or-none response. These structures are highly regulated and provide a unique signaling platform or compartment to control the activity of caspase-1 and likely other effectors. Emerging evidence indicates that ASC specks are also released from inflammasome-activated cells and accumulate in inflamed tissues, where they can continue to mature cytokines or be internalized by surrounding cells to further nucleate ASC specks in their cytosol. Little is known about the mechanisms governing ASC speck release, uptake, and endosomal escape, as well as its contribution to inflammation and disease. Here, we describe the different outcomes of inflammasome activation and discuss the potential function of extracellular ASC specks. We highlight gaps in our understanding of this central process of inflammation, which may have direct consequences on the modulation of host responses and chronic inflammation.

PD-L1 is expressed on human platelets and is affected by immune checkpoint therapy

Cancer immunotherapy has been revolutionised by drugs that enhance the ability of the immune system to detect and fight tumors. Immune checkpoint therapies that target the programmed death-1 receptor (PD-1), or its ligand (PD-L1) have shown unprecedented rates of durable clinical responses in patients with various cancer types. However, there is still a large fraction of patients that do not respond to checkpoint inhibitors, and the challenge remains to find cellular and molecular cues that could predict which patients would benefit from these therapies. Using a series of qualitative and quantitative methods we show here that PBMCs and platelets from smokers and patients with head and neck squamous cell carcinoma (HNSCC) or lung cancer express and up-regulate PD-L1 independently of tumor stage. Furthermore, treatment with Atezolizumab, a fully humanised monoclonal antibody against PD-L1, in 4 patients with lung cancer caused a decrease in PD-L1 expression in platelets, which was restored over 20 days. Altogether, our findings reveal the expression of the main therapeutic target in current checkpoint therapies in human platelets and highlight their potential as biomarkers to predict successful therapeutic outcomes.

Evidence of inflammasome activation and formation of monocyte-derived ASC specks in HIV-1 positive patients

OBJECTIVE

The formation of large intracellular protein aggregates of the inflammasome adaptor protein ASC (apoptosis-associated speck-like protein containing a caspase-recruitment domain; also know as PYCARD) is a hallmark of inflammasome activation. ASC speck-forming cells release the highly proinflammatory cytokine IL-1β in addition to ASC specks into the extracellular space during pyroptotic cell death. There ASC specks can propagate inflammation to other nonactivated cells or tissues. HIV-1 retroviral infection triggers inflammasome activation of abortively infected CD4⁺ T cells in secondary lymphatic tissues. However, if pyroptosis occurs in other peripheral blood mononuclear cells (PBMCs) of HIV-1-infected patients is currently unknown. We investigated if ASC speck positive cells are present in the circulation of HIV-1-infected patients.

DESIGN AND METHODS

PBMCs or plasma of HIV-1 infected, antiretroviral therapy-naive patients were analyzed for the presence of ASC speck⁺ cells or extracellular ASC and compared with healthy controls. Intracellular staining for ASC was employed to detect ASC speck⁺ cells within PBMCs by flow cytometry, and ELISA to detect free ASC in the plasma. ASC multimerization was confirmed by immunoblot.

RESULTS

Peripheral blood CD14⁺⁺CD16⁻ monocytes were ASC speck⁺ in HIV patients, but not in healthy controls. In the subgroup analysis, HIV patients with lower CD4⁺ T-cell counts and higher viral load had significantly more ASC speck⁺ monocytes. ASC speck formation did not correlate with Gag expression, coinfection, lactate dehydrogenase or C-reactive protein.

CONCLUSION

Our findings suggest that pyroptotic CD14⁺⁺CD16⁻ classical monocytes of HIV-1-infected patients release ASC specks into the blood stream, a phenomenon that may contribute to HIV-1 induced inflammation and immune activation.

Molecular Integration of Incretin and Glucocorticoid Action Reverses Immunometabolic Dysfunction and Obesity

Chronic inflammation has been proposed to contribute to the pathogenesis of diet-induced obesity. However, scarce therapeutic options are available to treat obesity and the associated immunometabolic complications. Glucocorticoids are routinely employed for the management of inflammatory diseases, but their pleiotropic nature leads to detrimental metabolic side effects. We developed a glucagon-like peptide-1 (GLP-1)-dexamethasone co-agonist in which GLP-1 selectively delivers dexamethasone to GLP-1 receptor-expressing cells. GLP-1-dexamethasone lowers body weight up to 25% in obese mice by targeting the hypothalamic control of feeding and by increasing energy expenditure. This strategy reverses hypothalamic and systemic inflammation while improving glucose tolerance and insulin sensitivity. The selective preference for GLP-1 receptor bypasses deleterious effects of dexamethasone on glucose handling, bone integrity, and hypothalamus-pituitary-adrenal axis activity. Thus, GLP-1-directed glucocorticoid pharmacology represents a safe and efficacious therapy option for diet-induced immunometabolic derangements and the resulting obesity.

NLRP3 inflammasome assembly is regulated by phosphorylation of the pyrin domain

NLRP3 is an innate immune receptor that needs to be tightly regulated to prevent overshooting immune responses. Stutz et al. demonstrate that NLRP3 is phosphorylated as a safeguard against accidental activation, and that dephosphorylation involving PP2A activity is required for NLRP3 activation.

NLRP3 is a cytosolic pattern recognition receptor that senses microbes and endogenous danger signals. Upon activation, NLRP3 forms an inflammasome with the adapter ASC, resulting in caspase-1 activation, release of proinflammatory cytokines and cell death. How NLRP3 activation is regulated by transcriptional and posttranslational mechanisms to prevent aberrant activation remains incompletely understood. Here, we identify three conserved phosphorylation sites in NLRP3 and demonstrate that NLRP3 activation is controlled by phosphorylation of its pyrin domain (PYD). Phosphomimetic residues in NLRP3 PYD abrogate inflammasome activation and structural modeling indicates that phosphorylation of the PYD regulates charge–charge interaction between two PYDs that are essential for NLRP3 activation. Phosphatase 2A (PP2A) inhibition or knock-down drastically reduces NLRP3 activation, showing that PP2A can license inflammasome assembly via dephosphorylating NLRP3 PYD. These results propose that the balance between kinases and phosphatases acting on the NLRP3 PYD is critical for NLRP3 activation.

Intercellular transfer of miR-126-3p by endothelial microparticles reduces vascular smooth muscle cell proliferation and limits neointima formation by inhibiting LRP6

BACKGROUND

Vascular smooth muscle cell (VSMC) proliferation is of importance in the pathogenesis of vascular diseases such as restenosis or atherosclerosis. Endothelial microparticles (EMPs) regulate function and phenotype of target endothelial cells (ECs), but their influence on VSMC biology is unknown. We aim to investigate the role of EMPs in the regulation of vascular smooth muscle cell (VSMC) proliferation and vascular remodeling.

METHODS AND RESULTS

Systemic treatment of mice with EMPs after vascular injury reduced neointima formation in vivo. In vitro, EMP uptake in VSMCs diminished VSMC proliferation and migration, both pivotal steps in neointima formation. To explore the underlying mechanisms, Taqman microRNA-array was performed and miR-126-3p was identified as the predominantly expressed miR in EMPs. Confocal microscopy revealed an EMP-mediated miR-126 transfer into recipient VSMCs. Expression of miR-126 target protein LRP6, regulating VSMC proliferation, was reduced in VSMCs after EMP treatment. Importantly, genetic regulation of miR-126 in EMPs showed a miR-126-dependent inhibition of LRP6 expression, VSMC proliferation and neointima formation in vitro and in vivo, suggesting a crucial role of miR-126 in EMP-mediated neointima formation reduction. Finally, analysis of miR-126 expression in circulating MPs in 176 patients with coronary artery disease revealed a reduced PCI rate in patients with high miR-126 expression level, supporting a central role for MP-incorporated miR-126 in vascular remodelling.

CONCLUSION

EMPs reduce VSMC proliferation, migration and subsequent neointima formation by delivering functional miR-126 into recipient VSMCs.

Statins improve NASH via inhibition of RhoA and Ras

Nonalcoholic steatohepatitis (NASH), especially as part of the metabolic syndrome (MS), is an increasing burden in Western countries. Statins are already used in MS and seem to be beneficial in liver diseases. The aim of this study was to investigate the molecular mechanisms underlying pleiotropic effects on small GTPases of statins in NASH. NASH within MS was induced in 12-wk-old apoE^-/- mice after 7 wk of Western diet (NASH mice). Small GTPases were inhibited by activated simvastatin (SMV), NSC23766 (NSC), or Clostridium sordellii lethal toxin (LT) by using subcutaneous osmotic minipumps. Hepatic steatosis, inflammation, and fibrosis were assessed by histology, Western blot, and RT-PCR measurements of cholesterol and hydroxyproline content. SMV treatment significantly decreased hepatic inflammation and fibrosis, but had no significant effect on steatosis and hepatic cholesterol content in NASH. SMV blunted fibrosis due to inhibition of both RhoA/Rho kinase and Ras/ERK pathways. Interestingly, inhibition of RAC1 and Ras (by LT) failed to decrease fibrosis to the same extent. Inhibition of RAC1 (by NSC) showed no significant effect at all. Inhibition of RhoA and Ras downstream signaling by statins is responsible for the beneficial hepatic effects in NASH.

Abstract 564: Inflammasome-induced Endothelial Microparticles Exert Detrimental Effects on Recipient Vascular Cells

Background: The inflammasome, a multi-protein signaling platform, is an important mediator of vascular inflammation resulting in atherosclerosis. Microparticles (MPs) are small membrane vesicles, specifically packaged and released from apoptotic cells for intercellular communication. Endothelial cell derived MPs have recently been linked to atherogenesis. Whether inflammasome activation in endothelial cells mediates MP release and thereby exert biological effects on recipient vascular cells is unknown.

Methods and results: Human coronary artery endothelial cells (HCAEC) were primed with 1μg/ml LPS and subsequently stimulated with 20μM Nigericin leading to a specific inflammasome activation as detected by significant upregulation of Caspase-1 mRNA in RT-PCR and protein in Westernblots (Figure1). Inflammasome activation in vascular cells lead to formation of endothelial microparticles (EMP) in a time- and dosis-dependend manner (Figure 2). Comparison of EMP with beads of known size using flow cytometric and electron microscopic imaging could point out an EMP-size between 0,1 – 1 μm (Figure 3). EMP-uptake by recipient vascular cells could be illustrated by fluorescence-microscopic imaging of PKH26 labeled EMP (Figure 4). Viability assay and scratch assay showed detrimental effects of EMPs from inflammasome activated cells on recipient vascular cells. Viability, proliferation and migration were reduced significantly 4h after treatment (Figure 5).

Conclusions: We show for the first time that Nigericin, an established inflammasome activator, leads to inflammasome activation and release of microparticles by endothelial cells. Furthermore, that these microparticles are taken up by recipient vascular cells and thereby cause cell death accompanied with reduced cell migration and proliferation.

Measuring NLR Oligomerization II: Detection of ASC Speck Formation by Confocal Microscopy and Immunofluorescence

Inflammasome assembly results in the formation of a large intracellular protein scaffold driven by the oligomerization of the adaptor protein apoptosis-associated speck-like protein containing a CARD (ASC). Following inflammasome activation, ASC polymerizes to form a large singular structure termed the ASC "speck," which is crucial for recruitment of caspase-1 and its inflammatory activity. Hence, due to the considerably large size of these structures, ASC specks can be easily visualized by microscopy as a simple upstream readout for inflammasome activation. Here, we provide two detailed protocols for imaging ASC specks: by (1) live-cell imaging of monocyte/macrophage cell lines expressing a fluorescently tagged version of ASC and (2) immunofluorescence of endogenous ASC in cell lines and human immune cells. In addition, we outline a protocol for increasing the specificity of ASC antibodies for use in immunofluorescence.

The inflammasomes and autoinflammatory syndromes

Inflammation, a vital response of the immune system to infection and damage to tissues, can be initiated by various germline-encoded innate immune-signaling receptors. Among these, the inflammasomes are critical for activation of the potent proinflammatory interleukin-1 cytokine family. Additionally, inflammasomes can trigger and maintain inflammatory responses aimed toward excess nutrients and the numerous danger signals that appear in a variety of chronic inflammatory diseases. We discuss our understanding of how inflammasomes assemble to trigger caspase-1 activation and subsequent cytokine release, describe how genetic mutations in inflammasome-related genes lead to autoinflammatory syndromes, and review the contribution of inflammasome activation to various pathologies arising from metabolic dysfunction. Insights into the mechanisms that govern inflammasome activation will help in the development of novel therapeutic strategies, not only for managing genetic diseases associated with overactive inflammasomes, but also for treating common metabolic diseases for which effective therapies are currently lacking.

MicroRNA expression in circulating microvesicles predicts cardiovascular events in patients with coronary artery disease

Background

Circulating microRNAs (miRNAs) are differentially regulated and selectively packaged in microvesicles (MVs). We evaluated whether circulating vascular and endothelial miRNAs in patients with stable coronary artery disease have prognostic value for the occurrence of cardiovascular (CV) events.

Methods and Results

Ten miRNAs involved in the regulation of vascular performance—miR‐126, miR‐222, miR‐let7d, miR‐21, miR‐20a, miR‐27a, miR‐92a, miR‐17, miR‐130, and miR‐199a—were quantified in plasma and circulating MVs by reverse transcription polymerase chain reaction in 181 patients with stable coronary artery disease. The median duration of follow‐up for major adverse CV event–free survival was 6.1 years (range: 6.0–6.4 years). Events occurred in 55 patients (31.3%). There was no significant association between CV events and plasma level of the selected miRNAs. In contrast, increased expression of miR‐126 and miR‐199a in circulating MVs was significantly associated with a lower major adverse CV event rate. In univariate analysis, above‐median levels of miR‐126 in circulating MVs were predictors of major adverse CV event–free survival (hazard ratio: 0.485 [95% CI: 0.278 to 0.846]; P=0.007) and percutaneous coronary interventions (hazard ratio: 0.458 [95% CI: 0.222 to 0.945]; P=0.03). Likewise, an increased level of miR‐199a in circulating MVs was associated with a reduced risk of major adverse CV events (hazard ratio: 0.518 [95% CI: 0.299 to 0.898]; P=0.01) and revascularization (hazard ratio: 0.439 [95% CI: 0.232 to 0.832]; P=0.01) in univariate analysis. miRNA expression analysis in plasma compartments revealed that miR‐126 and miR‐199a are present mainly in circulating MVs. MV‐sorting experiments showed that endothelial cells and platelets were found to be the major cell sources of MVs containing miR‐126 and miR‐199a, respectively.

Conclusion

MVs containing miR‐126 and miR‐199a but not freely circulating miRNA expression predict the occurrence of CV events in patients with stable coronary artery disease.

The adaptor ASC has extracellular and 'prionoid' activities that propagate inflammation

Microbes or danger signals trigger inflammasome sensors, which induce polymerization of the adaptor ASC and the assembly of ASC specks. ASC specks recruit and activate caspase-1, which induces maturation of the cytokine interleukin 1β (IL-1β) and pyroptotic cell death. Here we found that after pyroptosis, ASC specks accumulated in the extracellular space, where they promoted further maturation of IL-1β. In addition, phagocytosis of ASC specks by macrophages induced lysosomal damage and nucleation of soluble ASC, as well as activation of IL-1β in recipient cells. ASC specks appeared in bodily fluids from inflamed tissues, and autoantibodies to ASC specks developed in patients and mice with autoimmune pathologies. Together these findings reveal extracellular functions of ASC specks and a previously unknown form of cell-to-cell communication.

Malaria-induced NLRP12/NLRP3-dependent caspase-1 activation mediates inflammation and hypersensitivity to bacterial superinfection

Cyclic paroxysm and high fever are hallmarks of malaria and are associated with high levels of pyrogenic cytokines, including IL-1β. In this report, we describe a signature for the expression of inflammasome-related genes and caspase-1 activation in malaria. Indeed, when we infected mice, Plasmodium infection was sufficient to promote MyD88-mediated caspase-1 activation, dependent on IFN-γ-priming and the expression of inflammasome components ASC, P2X7R, NLRP3 and/or NLRP12. Pro-IL-1β expression required a second stimulation with LPS and was also dependent on IFN-γ-priming and functional TNFR1. As a consequence of Plasmodium-induced caspase-1 activation, mice produced extremely high levels of IL-1β upon a second microbial stimulus, and became hypersensitive to septic shock. Therapeutic intervention with IL-1 receptor antagonist prevented bacterial-induced lethality in rodents. Similar to mice, we observed a significantly increased frequency of circulating CD14⁺CD16⁻Caspase-1⁺ and CD14^dimCD16⁺Caspase-1⁺ monocytes in peripheral blood mononuclear cells from febrile malaria patients. These cells readily produced large amounts of IL-1β after stimulation with LPS. Furthermore, we observed the presence of inflammasome complexes in monocytes from malaria patients containing either NLRP3 or NLRP12 pyroptosomes. We conclude that NLRP12/NLRP3-dependent activation of caspase-1 is likely to be a key event in mediating systemic production of IL-1β and hypersensitivity to secondary bacterial infection during malaria.

Together Plasmodium falciparum and P. vivax infect approximately 250 million individuals, reaping life of near one million children every year. Extensive research on malaria pathogenesis has funneled into the consensus that the clinical manifestations are often a consequence of the systemic inflammation. Importantly, secondary bacterial and viral infections potentiate this inflammatory reaction being important co-factors for the development of severe disease. One of the hallmarks of malaria syndrome is the paroxysm, which is characterized by high fever associated with peak of parasitemia. In this study we dissected the mechanisms of induction and the importance of the pyrogenic cytokine, IL-1β in the pathogenesis of malaria. Our results demonstrate the critical role of the innate immune receptors named Toll-Like Receptors and inflammasome on induction, processing and release of active form of IL-1β during malaria. Importantly, we provide evidences that bacterial superinfection further potentiates the Plasmodium-induced systemic inflammation, leading to the release of bulk amounts of IL-1β and severe disease. Hence, this study uncovers new checkpoints that could be targeted for preventing systemic inflammation and severe malaria.

Endothelial microparticle-mediated transfer of MicroRNA-126 promotes vascular endothelial cell repair via SPRED1 and is abrogated in glucose-damaged endothelial microparticles

BACKGROUND

Repair of the endothelium after vascular injury is crucial for preserving endothelial integrity and preventing the development of vascular disease. The underlying mechanisms of endothelial cell repair are largely unknown. We sought to investigate whether endothelial microparticles (EMPs), released from apoptotic endothelial cells (ECs), influence EC repair.

METHODS AND RESULTS

Systemic treatment of mice with EMPs after electric denudation of the endothelium accelerated reendothelialization in vivo. In vitro experiments revealed that EMP uptake in ECs promotes EC migration and proliferation, both critical steps in endothelial repair. To dissect the underlying mechanisms, Taqman microRNA array was performed, and microRNA (miR)-126 was identified as the predominantly expressed miR in EMPs. The following experiments demonstrated that miR-126 was transported into recipient human coronary artery endothelial cells by EMPs and functionally regulated the target protein sprouty-related, EVH1 domain-containing protein 1 (SPRED1). Knockdown of miR-126 in EMPs abrogated EMP-mediated effects on human coronary artery endothelial cell migration and proliferation in vitro and reendothelialization in vivo. Interestingly, after simulating diabetic conditions, EMPs derived from glucose-treated ECs contained significantly lower amounts of miR-126 and showed reduced endothelial repair capacity in vitro and in vivo. Finally, expression analysis of miR-126 in circulating microparticles from 176 patients with stable coronary artery disease with and without diabetes mellitus revealed a significantly reduced miR-126 expression in circulating microparticles from diabetic patients.

CONCLUSIONS

Endothelial microparticles promote vascular endothelial repair by delivering functional miR-126 into recipient cells. In pathological hyperglycemic conditions, EMP-mediated miR-126-induced EC repair is altered.

Endothelial Microparticle Uptake in Target Cells Is Annexin I/Phosphatidylserine Receptor Dependent and Prevents Apoptosis

Objective—

Endothelial microparticles (EMP) are released from activated or apoptotic cells, but their effect on target cells and the exact way of incorporation are largely unknown. We sought to determine the uptake mechanism and the biological effect of EMP on endothelial and endothelial-regenerating cells.

Methods and Results—

EMP were generated from starved endothelial cells and isolated by ultracentrifugation. Caspase 3 activity assay and terminal deoxynucleotidyl transferase dUTP nick end labeling assay showed that EMP protect target endothelial cells against apoptosis in a dose-dependent manner. Proteomic analysis was performed to identify molecules contained in EMP, which might be involved in EMP uptake. Expression of annexin I in EMP was found and confirmed by Western blot, whereas the corresponding receptor phosphatidylserine receptor was present on endothelial target cells. Silencing either annexin I on EMP or phosphatidylserine receptor on target cells using small interfering RNA showed that the uptake of EMP by human coronary artery endothelial cells is annexin I/phosphatidylserine receptor dependent. Annexin I–downregulated EMP abrogated the EMP-mediated protection against apoptosis of endothelial target cells. p38 activation was found to mediate camptothecin-induced apoptosis. Finally, human coronary artery endothelial cells pretreated with EMP inhibited camptothecin-induced p38 activation.

Conclusion—

EMP are incorporated by endothelial cells in an annexin I/phosphatidylserine receptor–dependent manner and protect target cells against apoptosis. Inhibition of p38 activity is involved in EMP-mediated protection against apoptosis.

Plasma circulating nucleic acids levels increase according to the morbidity of Plasmodium vivax malaria

BACKGROUND

Given the increasing evidence of Plasmodium vivax infections associated with severe and fatal disease, the identification of sensitive and reliable markers for vivax severity is crucial to improve patient care. Circulating nucleic acids (CNAs) have been increasingly recognized as powerful diagnostic and prognostic tools for various inflammatory diseases and tumors as their plasma concentrations increase according to malignancy. Given the marked inflammatory status of P. vivax infection, we investigated here the usefulness of CNAs as biomarkers for malaria morbidity.

METHODS AND FINDINGS

CNAs levels in plasma from twenty-one acute P. vivax malaria patients from the Brazilian Amazon and 14 malaria non-exposed healthy donors were quantified by two different methodologies: amplification of the human telomerase reverse transcriptase (hTERT) genomic sequence by quantitative real time PCR (qPCR), and the fluorometric dsDNA quantification by Pico Green. CNAs levels were significantly increased in plasma from P. vivax patients as compared to healthy donors (p<0.0001). Importantly, plasma CNAs levels were strongly associated with vivax morbidity (p<0.0001), including a drop in platelet counts (p = 0.0021). These findings were further sustained when we assessed CNAS levels in plasma samples from 14 additional P. vivax patients of a different endemic area in Brazil, in which CNAS levels strongly correlated with thrombocytopenia (p = 0.0072). We further show that plasma CNAs levels decrease and reach physiological levels after antimalarial treatment. Although we found both host and parasite specific genomic sequences circulating in plasma, only host CNAs clearly reflected the clinical spectrum of P. vivax malaria.

CONCLUSIONS

Here, we provide the first evidence of increased plasma CNAs levels in malaria patients and reveal their potential as sensitive biomarkers for vivax malaria morbidity.

Augmented plasma microparticles during acute Plasmodium vivax infection

Background

In the last few years, the study of microparticles (MPs) - submicron vesicles released from cells upon activation or apoptosis - has gained growing interest in the field of inflammation and in infectious diseases. Their role in the human malaria parasite Plasmodium vivax remains unexplored. Because acute vivax malaria has been related to pro-inflammatory responses, the main hypothesis investigated in this study was that Plasmodium vivax infection is associated with elevated levels of circulating MPs, which may play a role during acute disease in non-immune patients.

Methods

Plasma MPs were analysed among thirty-seven uncomplicated P. vivax infections from an area of unstable malaria transmission in the Brazilian Amazon. The MP phenotype was analysed by flow cytometry using the classical MP marker, annexin, and fluorochrome-labeled monoclonal antibodies against specific cell surface markers. The frequencies of plasma MPs in P. vivax patients (n = 37) were further compared to malaria-unexposed controls (n = 15) and ovarian carcinoma patients (n = 12), a known MPs-inducing disease non-related to malaria.

Results

The frequencies of plasma circulating MPs were markedly increased in P. vivax patients, as compared to healthy age-matched malaria-unexposed controls. Although platelets, erythrocytes and leukocytes were the main cellular sources of MPs during vivax malaria, platelet derived-MPs (PMPs) increased in a linear fashion with the presence of fever at the time of blood collection (β = 0.06, p < 0.0001) and length of acute symptoms (β = 0.36, p < 0.0001). Finally, the results suggest that plasma levels of PMPs diminish as patient experience more episodes of clinical malaria (β = 0.07, p < 0.003).

Conclusions

Abundant circulating MPs are present during acute P. vivax infection, and platelet derived-MPs may play a role on the acute inflammatory symptoms of malaria vivax.

MyD88-dependent activation of dendritic cells and CD4(+) T lymphocytes mediates symptoms, but is not required for the immunological control of parasites during rodent malaria

We investigated the role of different TLRs and MyD88 in host resistance to infection and malaria pathogenesis. TLR2(-/-), TLR4(-/-), TLR6(-/-), TLR9(-/-) or CD14(-/-) mice showed no change in phenotypes (parasitemia, body weight and temperature) when infected with Plasmodium chabaudi chabaudi (AS). MyD88(-/-) mice displayed comparable ability to wild type animals in controlling and clearing parasitemia. Importantly, MyD88(-/-) mice exhibited impaired production of TNF-alpha and IFN-gamma as well as attenuated symptoms, as indicated by changes in body weight and temperature during parasitemia. Consistently, CD11b(+) monocytes and CD11c(+) dendritic cells from infected MyD88(-/-) mice were shown impaired for production of pro-inflammatory cytokines, and in initiating CD4(+) T cell responses. Importantly, the inhibition of T cell activation with anti-CD134L, mostly inhibited IFN-gamma, partially inhibited TNF-alpha production, and protected the animals from malaria symptoms. Our findings suggest that MyD88 and possibly its associated TLRs expressed by dendritic cells play an important role in pro-inflammatory responses, T cell activation, and pathogenesis of malaria, but are not critical for the immunological control of the erythrocytic stage of P. chabaudi.

Effect of the Aedes fluviatilis saliva on the development of Plasmodium gallinaceum infection in Gallus (gallus) domesticus

Effect of Aedes fluviatilis saliva on the development of Plasmodium gallinaceum experimental infection in Gallus (gallus) domesticus was studied in distinct aspects. Chickens subcutaneously infected with sporozoites in the presence of the mosquito salivary gland homogenates (SGH) showed higher levels of parasitaemia when compared to those ones that received only the sporozoites. However, the parasitaemia levels were lower among chickens previously immunized by SGH or non-infected mosquito bites compared to the controls, which did not receive saliva. High levels of anti-saliva antibodies were observed in those immunized chickens. Moreover, 53 and 102 kDa saliva proteins were recognized by sera from immunized chickens. After the sporozoite challenge, the chickens also showed significant levels of anti-sporozoite antibodies. However, the ability to generate anti-sporozoites antibodies was not correlated to the saliva immunization. Our results suggest that mosquito saliva components enhance P. gallinaceum parasite development in naive chickens. However, the prior exposure of chickens to salivary components controls the parasitemia levels in infected individuals.