Murine Neutrophils Research Articles

Chondroprotective functions of neutrophil-derived extracellular vesicles by promoting the production of secreted frizzled-related protein 5 in cartilage

BackgroundOsteoarthritis (OA) is the most common degenerative joint disease characterized by cartilage degradation and various degrees of inflammation in the synovium. Growing evidence highlights that neutrophil extracellular vesicles (EVs) play a protective role in arthritic joints by promoting the resolution of inflammation and the synthesis of proteoglycans in cartilage. However, this homeostatic function is dependent on the activation state of neutrophils and the surrounding environment/tissues. Hence, we explored the chondroprotective functions of neutrophil-derived EVs under different stimulation conditions and the underlying molecular mechanism.MethodsHuman blood-derived neutrophils, murine bone marrow-derived neutrophils, C-28I2 cells and primary chondrocytes were used. Neutrophils were stimulated with different cytokines, and their EVs were isolated for chondrocyte stimulation and further subjected to RNA-sequencing analysis. Two experimental murine OA models were used, and the treatment was performed by intraarticular injections.ResultsConditioned medium from neutrophils stimulated with TGF-β (N-β) had the greatest inhibitory effect on the expression of catabolic factors in stimulated chondrocytes. These protective effects were not impaired when conditioned medium of N-β from AnxA1-deficient mice was used. Consistent with these results, EVs isolated from N-β significantly reduced the expression of catabolic factors in stimulated chondrocytes. Bulk RNA-seq analysis revealed that secreted frizzled-related protein 5 (SFRP5) is upregulated in N-β-EV-stimulated chondrocytes. Furthermore, recombinant SFRP5 treatment significantly reduced the expression of catabolic factors in vitro and catabolic process in experimental murine OA models.ConclusionsThe current study emphasizes the potential therapeutic application of neutrophils in OA and provides new knowledge on the molecular mechanisms underlying their function.

BTK and MMP9 regulate NLRP3 inflammasome-dependent cytokine and NET responses in primary neutrophils.

BackgroundInflammation is a double-edged state of immune activation required to resolve threats harmful to the host but can also cause severe collateral damage. Polymorphonuclear neutrophils (PMN) the primary leukocyte population in humans, mediate inflammation through the release of cytokines and neutrophil extracellular traps (NETs). Whilst the pathophysiological importance of NETs is unequivocal, the multiple molecular pathways driving NET release are not fully defined. Recently, NET release was linked to the NLRP3 inflammasome which is regulated by Bruton’s tyrosine kinase in macrophages. ObjectiveAs NLRP3 inflammasome regulation by BTK has not been studied in neutrophils, we here explored a potential regulatory role of BTK in primary murine and human neutrophils and matched monocytes or macrophages from Btk-deficient vs WT mice or healthy donors (HD) vs BTK-deficient X-linked agammaglobulinemia (XLA) patients, respectively. MethodsCytokine, MPO and MMP-9 release were quantified by ELISA, NET release and inflammasome formation by immunofluorescence microscopy. ResultsSurprisingly, in both mouse and human primary neutrophils, we observed a significant increase in NLRP3 inflammasome-dependent IL-1β and NETs when BTK was absent or inhibited, whereas IL-1β release was decreased in corresponding primary mouse macrophages or human PBMC, respectively. This suggests a novel negative regulatory role of BTK in terms of neutrophil NLRP3 activation. Both IL-1β and NET release in mouse and human primary neutrophils were strictly dependent of NLRP3, caspase-1 and, surprisingly, MMP-9. ConclusionThis highlights BTK and MMP-9 as novel and versatile inflammasome regulators and may have implications for the clinical use of BTK inhibitors.

Tbp and Hprt1 Are Appropriate Reference Genes for Splenic Neutrophils Isolated from Healthy or Tumor-Bearing Mice.

Background/Objectives: Neutrophils have recently gained significant attention due to their heterogeneity in tumor settings. The gene expression profiles of neutrophils from different tumor types are of great interest. Murine splenic neutrophils reflect the immune status of the organism and could be a source of tumor-associated neutrophils in tumor-bearing mice. However, information about appropriate reference genes for RT-qPCR analysis of murine neutrophils in the literature is lacking. The aim of this study was to identify stably expressed reference genes in murine splenic neutrophils. Methods: Bone marrow- and spleen-derived neutrophils were isolated from healthy C57Bl/6 and CBA/LacSto mice. Spleen-derived neutrophils were isolated from mice with Lewis lung carcinoma (LLC) and drug-resistant lymphosarcoma (RLS40). RNA was isolated and used for RT-qPCR analysis of 10 selected reference genes. Analysis of reference gene stability was performed using four different algorithms (BestKeeper, NormFinder, geNorm, ΔCt method), and comprehensive ranking was constructed using RefFinder. Results: The Ct values for the reference genes were in the range of 16.73-30.83 with the highest expression levels observed for B2m and the lowest for Sdha. Differences in the stability ranking performed by different algorithms were observed; however, the overall ranking of the studied reference genes was as follows, from most to least stably expressed: Tbp, Hprt1, Ywhaz, B2m, Gapdh, Actb, Sdha, Eef2, Rack1, and Rpl13a. Using Tbp or Rpl13a for RT-qPCR data normalization significantly affected the interpretation of target gene expression. Conclusions: Tbp and Hprt1 are recommended reference genes for murine splenic neutrophils regardless of their activation status.

Glutamine modulates neutrophil recruitment and effector functions during sterile inflammation.

During sterile inflammation, tissue damage induces excessive activation and infiltration of neutrophils into tissues, where they critically contribute to organ dysfunction. Tight regulation of neutrophil migration and their effector functions is crucial to prevent overshooting immune responses. Neutrophils utilize more glutamine, the most abundant free α-amino acid in the human blood, than other leukocytes. However, under inflammatory conditions, the body's requirements exceed its ability to produce sufficient amounts of glutamine. This study investigates the impact of glutamine on neutrophil recruitment and their key effector functions. Glutamine treatment effectively reduced neutrophil activation by modulating β2-integrin activity and chemotaxis in vitro. In a murine in vivo model of sterile inflammation induced by renal ischemia-reperfusion injury, glutamine administration significantly attenuated neutrophil recruitment into injured kidneys. Transcriptomic analysis revealed, glutamine induces transcriptomic reprogramming in murine neutrophils, thus improving mitochondrial functionality and glutathione metabolism. Further, glutamine influenced key neutrophil effector functions, leading to decreased production of reactive oxygen species and formation of neutrophil extracellular traps. Mechanistically, we used a transglutaminase 2 inhibitor to identify transglutaminase 2 as a downstream mediator of glutamine effects on neutrophils. In conclusion, our findings suggest that glutamine diminishes activation and recruitment of neutrophils and thus identify glutamine as a potent means to curb overshooting neutrophil responses during sterile inflammation.

Protocols for circulating neutrophil depletion in neonatal C57Bl/6 mice.

Dual antibody-based neutrophil depletion effectively induces circulating neutrophil clearance in neonatal mice.

Proteomic Characterization of 1000 Human and Murine Neutrophils Freshly Isolated From Blood and Sites of Sterile Inflammation

Neutrophils are indispensable for defense against pathogens. Injured tissue-infiltrated neutrophils can establish a niche of chronic inflammation and promote degeneration. Studies investigated transcriptome of single-infiltrated neutrophils which could misinterpret molecular states of these post mitotic cells. However, neutrophil proteome characterization has been challenging due to low harvests from affected tissues. Here, we present a workflow to obtain proteome of 1,000 murine and human tissue-infiltrated neutrophils. We generated spectral libraries containing ∼6,200 mouse and ∼5,300 human proteins from circulating neutrophils. 4,800 mouse and 3,400 human proteins were recovered from 1,000 cells with 102-108 copies/cell. Neutrophils from stroke-affected mouse brains adapted to the glucose-deprived environment with increased mitochondrial activity and ROS-production while cells invading inflamed human oral cavities increased phagocytosis and granule release. We provide an extensive protein repository for resting human and mouse neutrophils, identify proteins lost in low input samples, thus enabling the proteomic characterization of limited tissue infiltrated neutrophils.

Novel humanized anti-PcrV monoclonal antibody COT-143 protects mice from lethal Pseudomonas aeruginosa infection via inhibition of toxin translocation by the type III secretion system.

Treatment of Pseudomonas aeruginosa infection is challenging due to its intrinsic and acquired antibiotic resistance. As the number of current therapeutic options for P. aeruginosa infections is limited, developing novel treatments against the pathogen is an urgent clinical priority. The suppression of virulence of P. aeruginosa could be a new therapeutic option, and the type III secretion system (T3SS), which enables the bacteria to translocate various kinds of toxins into host cells and inhibits cellular functions, is considered as one possible target. In this report, we examined T3SS inhibition by COT-143/INFEX702, a humanized monoclonal antibody against PcrV, T3SS component, and present the crystal structure of the antibody-PcrV complex. COT-143 inhibited T3SS-dependent cytotoxicity and protected mice from the mortality caused by P. aeruginosa infection. The inhibition of cytotoxicity coincided with inhibition of translocon formation in a host cell membrane, which is necessary for T3SS intoxication. COT-143 protected murine neutrophils and facilitated phagocytosis of P. aeruginosa. These results suggest that COT-143 facilitates P. aeruginosa clearance by protecting neutrophil via inhibition of T3SS-dependent toxin translocation. This is the first report to show that an anti-PcrV antibody directly interferes with translocon formation to inhibit intoxication of host cells.

An essential role for the Hv1 voltage-gated proton channel in Pseudomonas aeruginosa corneal infection.

Assembly of NADPH oxidase 2 (NOX2) proteins in neutrophils plays an essential role in controlling microbial infections by producing high levels of reactive oxygen species (ROS). In contrast, the role of the Hv1 voltage-gated proton channel that is required for sustained NOX2 activity is less well characterized. We examined the role of Hv1 in a murine model of blinding Pseudomonas aeruginosa corneal infection and found that in contrast to C57BL/6 mice, Hvcn1 -/- mice exhibit an impaired ability to kill bacteria and regulate disease severity. In vitro, we used a novel Hv1 Inhibitor Flexible (HIF) to block ROS production by human and murine neutrophils and found that HIF inhibits ROS production in a dose-dependent manner following stimulation with PMA or infection with P. aeruginosa. Collectively, these findings demonstrate an important role for Hv1 on controlling bacterial growth in a clinically relevant bacterial infection model.

Immune-enhancing neutrophils reprogrammed by subclinical low-dose endotoxin in cancer treatment

Despite the re-emergence of the pioneering “Coley’s toxin” concept in anti-cancer immune therapies highlighted by check-point inhibitors and CAR-T approaches, fundamental mechanisms responsible for the immune-enhancing efficacy of low-dose “Coley’s toxin” remain poorly understood. This study examines the novel reprogramming of immune-enhancing neutrophils by super-low dose endotoxin conducive for anti-cancer therapies. Through integrated analyses including scRNAseq and functional characterizations, we examined the efficacy of reprogrammed neutrophils in treating experimental cancer. We observed that neutrophils trained by super-low dose endotoxin adopt a potent immune-enhancing phenotype characterized by CD177loCD11bloCD80hiCD40hiDectin2hi. Both murine and human neutrophils trained by super-low dose endotoxin exhibit relieved suppression of adaptive T cells as compared to un-trained neutrophils. Functionally, neutrophils trained by super-low dose endotoxin can potently reduce tumor burden when transfused into recipient tumor-bearing mice. Mechanistically, Super-low dose endotoxin enables the generation of immune-enhancing neutrophils through activating STAT5 and reducing innate suppressor IRAK-M. Together, our data clarify the long-held mystery of “Coley’s toxin” in rejuvenating anti-tumor immune defense, and provide a proof-of-concept in developing innate neutrophil-based anti-tumor therapeutics.

Abstract 2082: Neutrophil Programming In Atherosclerosis

Emerging evidence suggest the involvement of neutrophils during the progression of human atherosclerosis through secreting inflammatory mediators and causing damages to endothelial vasculature. However, compared to other well-recognized immune cells such as monocytes/macrophages, mechanisms underlying the regulation of neutrophils during atherosclerosis are relatively less studied and understood. This presents a major impediment in our thorough understanding of the pathogenesis of atherosclerosis. In this study, we reported that both murine and human neutrophil population possesses a minor homeostatic resolving subset characterized by reduced expression of inflammatory mediators (LTB4, elastase), elevated expression of anti-inflammatory resolving mediators (RvD1, CD200R), correlated with reduced expression of inflammatory signaling adaptor TRAM. We observed that TRAM deficient neutrophils are effectively reprogrammed into the resolving state, and can potently improve vascular integrity and suppress atherosclerosis pathogenesis when adoptively transfused into recipient atherosclerotic animals. Mechanistically, TRAM deficiency reduces the expression of LOX5AP, dislodges nuclear localization of LOX5, and favors the generation of RvD1 instead of LTB4. We also observed that human TRAM-low neutrophils are less inflammatory, as reflected in reduced swarming and reduced induction of LTB4/elastase. TRAM serves as a stress sensor of oxLDL and/or free cholesterol, triggers inflammatory signaling processes that facilitate elastase release. Our data defines a novel resolving neutrophil subset due to reduced TRAM expression which may hold therapeutic potential for reducing inflammation and treating atherosclerosis.

Gram-negative anaerobes elicit a robust keratinocytes immune response with potential insights into HS pathogenesis.

Hidradenitis Suppurativa (HS) is a chronic autoinflammatory skin disease with activated keratinocytes, tunnel formation and a complex immune infiltrate in tissue. The HS microbiome is polymicrobial with an abundance of commensal gram-positive facultative (GPs) Staphylococcus species and gram-negative anaerobic (GNA) bacteria like Prevotella, Fusobacterium and Porphyromonas with increasing predominance of GNAs with disease severity. We sought to define the keratinocyte response to bacteria commonly isolated from HS lesions to probe pathogenic relationships between HS and the microbiome. Type strains of Prevotella nigrescens, Prevotella melaninogenica, Prevotella intermedia, Prevotella asaccharolytica, Fusobacterium nucleatum, as well as Staphylococcus aureus and the normal skin commensal Staphylococcus epidermidis were heat-killed and co-incubated with normal human keratinocytes. RNA was collected and analysed using RNAseq and RT-qPCR. The supernatant was collected from cell culture for protein quantification. Transcriptomic profiles between HS clinical samples and stimulated keratinocytes were compared. Co-staining of patient HS frozen sections was used to localize bacteria in lesions. A mouse intradermal injection model was used to investigate early immune recruitment. TLR4 and JAK inhibitors were used to investigate mechanistic avenues of bacterial response inhibition. GNAs, especially F. nucleatum, stimulated vastly higher CXCL8, IL17C, CCL20, IL6, TNF and IL36γ transcription in normal skin keratinocytes than the GPs S. epidermidis and S. aureus. Using RNAseq, we found that F. nucleatum (and Prevotella) strongly induced the IL-17 pathway in keratinocytes and overlapped with transcriptome profiles of HS patient clinical samples. Bacteria were juxtaposed to activated keratinocytes invivo, and F. nucleatum strongly recruited murine neutrophil and macrophage migration. Both the TLR4 and pan-JAK inhibitors reduced cytokine production. Detailed transcriptomic profiling of healthy skin keratinocytes exposed to GNAs prevalent in HS revealed a potent, extensive inflammatory response vastly stronger than GPs. GNAs stimulated HS-relevant genes, including many genes in the IL-17 response pathway, and were significantly associated with HS tissue transcriptomes. The close association of activated keratinocytes with bacteria in HS lesions and innate infiltration in murine skin cemented GNA pathogenic potential. These novel mechanistic insights could drive future targeted therapies.

Regulation of ICAM-1 in human neutrophils

Abstract Intercellular cell adhesion molecule 1 (ICAM-1) is a cell surface glycoprotein with a vital role in the immune response to pathogens. The expression pattern of ICAM-1 is wide ranging, encompassing endothelial cells, epithelial cells, and neutrophils. Recent work has characterized the role of ICAM-1 in murine neutrophils, but the function of human neutrophil ICAM-1 is incompletely understood. Herein, we investigated the expression and role of ICAMs in human neutrophils in vitro and in vivo. Our findings show clear expression of ICAM-1, -3, and -4 on peripheral blood–derived neutrophils and demonstrate that the pathogen-associated molecular pattern lipoteichoic acid is an inducer of ICAM-1 expression in vitro. In vivo, neutrophils obtained from the pleural cavity of patients with a parapneumonic effusion display enhanced expression of ICAM-1 compared with peripheral blood– and oral cavity–derived neutrophils. Moreover, migration of peripheral blood–derived neutrophils across endothelial cells can upregulate neutrophil ICAM-1 expression. These findings indicate that pathogen-associated molecular patterns and/or cytokines, alongside transmigration, enhance neutrophil ICAM-1 expression at sites of inflammation. Mechanistically, we observed that ICAM-1high neutrophils display elevated S. aureus phagocytic capacity. However, unlike murine neutrophils, ICAM-1 intracellular signaling in human neutrophils was not essential for phagocytosis of Staphylococcus aureus and reactive oxygen species generation. Taken together, these results have important implications for the regulation of neutrophil-mediated pathogen clearance.

Peripheral priming induces plastic transcriptomic and proteomic responses in circulating neutrophils required for pathogen containment.

Neutrophils rapidly respond to inflammation and infection, but to which degree their functional trajectories after mobilization from the bone marrow are shaped within the circulation remains vague. Experimental limitations have so far hampered neutrophil research in human disease. Here, using innovative fixation and single-cell-based toolsets, we profile human and murine neutrophil transcriptomes and proteomes during steady state and bacterial infection. We find that peripheral priming of circulating neutrophils leads to dynamic shifts dominated by conserved up-regulation of antimicrobial genes across neutrophil substates, facilitating pathogen containment. We show the TLR4/NF-κB signaling-dependent up-regulation of canonical neutrophil activation markers like CD177/NB-1 during acute inflammation, resulting in functional shifts in vivo. Blocking de novo RNA synthesis in circulating neutrophils abrogates these plastic shifts and prevents the adaptation of antibacterial neutrophil programs by up-regulation of distinct effector molecules upon infection. These data underline transcriptional plasticity as a relevant mechanism of functional neutrophil reprogramming during acute infection to foster bacterial containment within the circulation.

How murine neutrophils are hijacked within the microenvironment of pancreatic cancer.

Discoveries made in the past decades have brought out that, in addition to their classical primary defensive functions against infections, polymorphonuclear neutrophils play key effector roles not only in chronic inflammatory and immune-mediated diseases but also in cancer. In addition, depending on their differentiation/activation status and/or on the physiological or pathological microenvironment in which they reside, neutrophils have been shown to behave as highly plastic cells, able to acquire new phenotypes/functional states. All these features are well manifested in cancer and modulated during tumor progression. Herein, we discuss intriguing data by Lai Ng's group that have shed light on the origin and development of terminally differentiated, proangiogenic, tumor-associated neutrophils, facilitating tumor growth in a murine orthotopic model of pancreatic ductal adenocarcinoma. These findings help to progress toward the ambitious goal of selectively targeting only the skewed pathological neutrophil populations present within the tumor microenvironment.

Cell surface RNAs control neutrophil recruitment

RNAs localizing to the outer cell surface have been recently identified in mammalian cells, including RNAs with glycan modifications known as glycoRNAs. However, the functional significance of cell surface RNAs and their production are poorly known. We report that cell surface RNAs are critical for neutrophil recruitment and that the mammalian homologs of the sid-1 RNA transporter are required for glycoRNA expression. Cell surface RNAs can be readily detected in murine neutrophils, the elimination of which substantially impairs neutrophil recruitment to inflammatory sites invivo and reduces neutrophils' adhesion to and migration through endothelial cells. Neutrophil glycoRNAs are predominantly on cell surface, important for neutrophil-endothelial interactions, and can be recognized by P-selectin (Selp). Knockdown of the murine Sidt genes abolishes neutrophil glycoRNAs and functionally mimics the loss of cell surface RNAs. Our data demonstrate the biological importance of cell surface glycoRNAs and highlight a noncanonical dimension of RNA-mediated cellular functions.

A Robust In Vitro Co-culture Model for Studying the Intercellular Communication of Neutrophils.

Communication among neutrophils plays critical roles during various phases of inflammatory responses, with clinical relevance to both acute and chronic inflammatory diseases. Despite its significance, underlying mechanisms are not well understood, due to the lack of an effective in vitro system to properly address this important question. Here we report a robust in vitro method to culture primary murine neutrophils derived from bone marrow, amenable for well-controlled studies of both neutrophil activation and intercellular communication among co-cultured neutrophils. This protocol can generate primary neutrophils with high purity and survival for an extended culture period, suitable for further phenotypic and functional analyses.

A Comparative Study of Different Protocols for Isolation of Murine Neutrophils from Bone Marrow and Spleen.

Neutrophils are considered as the main player in innate immunity. In the last few years, it has been shown that they are involved in different physiological conditions and diseases. However, progress in the field of neutrophil biology is relatively slow due to existing difficulties in neutrophil isolation and maintenance in culture. Here we compare four protocols based on density-gradient and immunomagnetic methods for isolation of murine neutrophils from bone marrow and spleen. Neutrophil isolation was performed using Ficoll 1.077/1.119 g/mL density gradient, Ficoll 1.083/1.090/1.110 g/mL density gradient and immunomagnetic method of negative and positive selection. The different protocols were compared with respect to sample purity, cell viability, yield, and cost. The functionality of isolated neutrophils was checked by NETosis analysis and neutrophil oxidative burst test. Obtained data revealed that given purity/yield/viability/cost ratio the protocol based on cell centrifugation on Ficoll 1.077/1.119 g/mL density gradient is recommended for isolation of neutrophils from bone marrow, whereas immunomagnetic method of positive selection using Dynabeads is recommended for isolation of splenic neutrophils.

Cell Surface RNAs Control Neutrophil Function

Recently, RNAs localizing to the outer cell surface have been reported in mammalian cells, with such RNAs containing glycan modifications (referred to as GlycoRNAs). However, the function of cell surface RNAs are poorly known. In this study, we investigated whether cell surface RNAs exist in neutrophils, what their functions are, and the mechanism by which they function. We first determined that neutrophils express cell surface GlycoRNAs. We utilized two strategies to assess cell surface GlycoRNAs. First, we utilized a sialic acid homologue to metabolically label glycans inside cells. Labeled glycans can be readily detected in purified total RNAs from primary murine neutrophils. The GlycoRNAs signals were depleted upon RNase digestion but not digestion by proteinase or DNase, supporting the existence of GlycoRNAs in neutrophils. Importantly, treating live neutrophils with RNase extracellularly removed over 90% of GlycoRNA signals, supporting that the majority of GlycoRNAs were located on the surface of neutrophils. Second, we directly visualized cell surface RNAs by labeling cellular RNAs with the nucleoside homologue 5'-bromouridine (BrU) and detecting live cells with an anti-BrU antibody applied extracellularly. These data support the existence of cell surface GlycoRNAs on neutrophils. We next revealed that cell surface GlycoRNAs play important functions in neutrophils to mediate transendothelial migration both in vivo and in vitro. We utilized an acute peritonitis model in which primarily neutrophils with cell surface GlycoRNAs removed by extracellular RNase were injected into circulation in mice that were treated with thioglycolate, and the migration of these neutrophils into the peritoneal cavity was quantified and compared to mock treated cells in vivo. We observed a 9-fold decrease of migration by neutrophils treated with extracellular RNase. To determine the in vitro function of cell surface RNAs, we tested the ability of neutrophils to migrate toward a chemoattractant in a trans-well assay. While neutrophils treated with extracellular RNase were viable and migrated similarly as control neutrophils, we observed a substantial defect in migration by extracellular-RNase-treated neutrophils when an endothelial layer was present on the tanswell membrane. A similar defect was observed when assaying neutrophil attachment to endothelial cells in vitro. This defect can be replicated using control neutrophils but by pre-blocking endothelial cells with purified neutrophil GlycoRNAs or the glycan fraction of GlycoRNAs. The defect in neutrophil endothelial interaction in vivo was observed by intravital confocal microscopy. These data support the function of neutrophil cell surface GlycoRNAs in helping transendothelial migration. Lastly, we found that neutrophil GlycoRNAs are bona fide ligands for P-selectin on endothelial surface. Removal of neutrophil surface RNAs with extracellular RNase treatment did not significantly change cell surface integrin levels or reactivity, but reduced recombinant P-selectin binding. Furthermore, recombinant P-selectin, but not recombinant E-selectin, can detect glycoRNAs in purified neutrophil total RNAs. Additionally, blocking endothelial cells with an antibody against P-selectin led to a significant reduction in GlycoRNA binding. These data support that GlycoRNA-P-selectin interaction, at least in part, mediate neutrophil transendothelial migration. Our data demonstrate a critical role of cell surface RNAs in neutrophils, and reveal a new dimension that regulate the function of hematopoietic cells.

PVB exerts anti-inflammatory effects by inhibiting the activation of MAPK and NF-κB signaling pathways and ROS generation in neutrophils

Pinaverium bromide (PVB) has been shown to protect mice against sepsis, which is predominantly attributed to PVB-mediated anti-inflammatory effects by inhibiting primed neutrophils to produce proinflammatory cytokines. However, the underlying mechanism(s) by which PVB affects neutrophils remains unknown. In this study, we report that treatment with PVB either before or after LPS stimulation attenuated IL-1β and TNF-α expression at both mRNA and protein levels in LPS-activated murine neutrophils. Further experiments revealed that PVB inhibited the phosphorylation of ERK, JNK, and IκBα in LPS-stimulated murine neutrophils. Moreover, PVB reduced reactive oxygen species (ROS) levels via regulating NADPH oxidase 2 (NOX2) activity, as represented by inhibiting p47phox translocation from the cytoplasm to the cellular membrane. Importantly, PVB significantly attenuated IL-1β, TNF-α, IL-6, CXCL1 production in both LPS-stimulated low density neutrophils (LDNs) and normal density neutrophils (NDNs) isolated from septic patients. Collectively, we demonstrated that PVB exerts anti-inflammatory effect by attenuating ROS generation and suppressing the activation of MAPK and NF-κB signaling pathways, suggesting that PVB may act as a potential therapeutic agent for sepsis by inhibiting neutrophil priming and activation.

Neutrophil-specific ORAI1 Calcium Channel Inhibition Reduces Pancreatitis-associated Acute Lung Injury.

Acute pancreatitis is initiated within pancreatic exocrine cells and sustained by dysregulated systemic inflammatory responses mediated by neutrophils. Store-operated Ca2+ entry (SOCE) through ORAI1 channels in pancreatic acinar cells triggers acute pancreatitis, and ORAI1 inhibitors ameliorate experimental acute pancreatitis, but the role of ORAI1 in pancreatitis-associated acute lung injury has not been determined. Here, we showed mice with pancreas-specific deletion of Orai1 (Orai1ΔPdx1, ∼70% reduction in the expression of Orai1) are protected against pancreatic tissue damage and immune cell infiltration, but not pancreatitis-associated acute lung injury, suggesting the involvement of unknown cells that may cause such injury through SOCE via ORAI1. Genetic (Orai1ΔMRP8) or pharmacological inhibition of ORAI1 in murine and human neutrophils decreased Ca2+ influx and impaired chemotaxis, reactive oxygen species production, and neutrophil extracellular trap formation. Unlike pancreas-specific Orai1 deletion, mice with neutrophil-specific deletion of Orai1 (Orai1ΔMRP8) were protected against pancreatitis- and sepsis-associated lung cytokine release and injury, but not pancreatic injury in experimental acute pancreatitis. These results define critical differences between contributions from different cell types to either pancreatic or systemic organ injury in acute pancreatitis. Our findings suggest that any therapy for acute pancreatitis that targets multiple rather than single cell types is more likely to be effective.