Molecular mechanisms regulating secretory organelles and endosomes in neutrophils and their implications for inflammation

Neutrophils in glioma microenvironment: from immune function to immunotherapy

Glioma is a malignant tumor of the central nervous system (CNS). Currently, effective treatment options for gliomas are still lacking. Neutrophils, as an important member of the tumor microenvironment (TME), are widely distributed in circulation. Recently, the discovery of cranial-meningeal channels and intracranial lymphatic vessels has provided new insights into the origins of neutrophils in the CNS. Neutrophils in the brain may originate more from the skull and adjacent vertebral bone marrow. They cross the blood-brain barrier (BBB) under the action of chemokines and enter the brain parenchyma, subsequently migrating to the glioma TME and undergoing phenotypic changes upon contact with tumor cells. Under glycolytic metabolism model, neutrophils show complex and dual functions in different stages of cancer progression, including participation in the malignant progression, immune suppression, and anti-tumor effects of gliomas. Additionally, neutrophils in the TME interact with other immune cells, playing a crucial role in cancer immunotherapy. Targeting neutrophils may be a novel generation of immunotherapy and improve the efficacy of cancer treatments. This article reviews the molecular mechanisms of neutrophils infiltrating the central nervous system from the external environment, detailing the origin, functions, classifications, and targeted therapies of neutrophils in the context of glioma.

Neutrophils and Anesthetic Drugs: Implications in Onco-Anesthesia

Apart from being a significant line of defense in the host defense system, neutrophils have many immunological functions. Although there are not many publications that accurately present the functions of neutrophils in relation to oncological pathology, their activity and implications have been studied a lot recently. This review aims to extensively describe neutrophils functions'; their clinical implications, especially in tumor pathology; the value of clinical markers related to neutrophils; and the implications of neutrophils in onco-anesthesia. This review also aims to describe current evidence on the influence of anesthetic drugs on neutrophils' functions and their potential influence on perioperative outcomes.

Gene editing of hematopoietic stem cells restores T-cell response in familial hemophagocytic lymphohistiocytosis

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory disorder characterized by a life-threatening cytokine storm and immunopathology. Familial HLH type 3 (FHL3) accounts for approximately 30% of all inborn HLH cases worldwide. It is caused by mutations in the UNC13D gene that result in impaired degranulation of cytotoxic vesicles and hence compromised T-cell- and natural killer-cell-mediated killing. Current treatment protocols, including allogeneic hematopoietic stem cell (HSC) transplantation, still show high mortality.

OBJECTIVE

We sought to develop and evaluate a curative genome editing strategy in the preclinical FHL3 Jinx mouse model. Jinx mice harbor a cryptic splice donor site in Unc13d intron 26 and develop clinical symptoms of human FHL3 upon infection with lymphocytic choriomeningitis virus (LCMV).

METHODS

We employed clustered regularly interspaced short palindromic repeats (CRISPR)-Cas technology to delete the disease-causing mutation in HSCs and transplanted Unc13d-edited stem cells into busulfan-conditioned Jinx recipient mice. Safety studies included extensive genotyping and chromosomal aberrations analysis by single targeted linker-mediated PCR sequencing (CAST-Seq)-based off-target analyses. Cure from HLH predisposition was assessed by LCMV infection.

RESULTS

Hematopoietic cells isolated from transplanted mice revealed efficient gene editing (>95%), polyclonality of the T-cell receptor repertoire, and neither signs of off-target effects nor leukemogenesis. Unc13d transcription levels of edited and wild-type cells were comparable. While LCMV challenge resulted in acute HLH in Jinx mice transplanted with mock-edited HSCs, Jinx mice grafted with Unc13d-edited cells showed rapid virus clearance and protection from HLH.

CONCLUSIONS

Our study demonstrates that transplantation of CRISPR-Cas edited HSCs supports the development of a functional polyclonal T-cell response in the absence of genotoxicity-associated clonal outgrowth.

A potential therapeutic target: The role of neutrophils in the central nervous system

Neutrophils play a critical role in immune defense as the first recruited and most abundant leukocytes in the innate immune system. As such, regulation of neutrophil effector functions have strong implications on immunity. These cells display a wide heterogeneity of function, including both inflammatory and immunomodulatory roles. Neutrophils commonly infiltrate the central nervous system (CNS) in response to varied pathological conditions. There is still little understanding of the role these cells play in the CNS in such conditions. In the present review, we will summarize what is known of neutrophil's role in cancer and Alzheimer's disease (AD), with a focus on highlighting the gaps in our understanding.

Role of Mitochondria in the Regulation of Effector Functions of Granulocytes

Granulocytes (neutrophils, eosinophils, and basophils) are the most abundant circulating cells in the innate immune system. Circulating granulocytes, primarily neutrophils, can cross the endothelial barrier and activate various effector mechanisms to combat invasive pathogens. Eosinophils and basophils also play an important role in allergic reactions and antiparasitic defense. Granulocytes also regulate the immune response, wound healing, and tissue repair by releasing of various cytokines and lipid mediators. The effector mechanisms of granulocytes include the production of reactive oxygen species (ROS), degranulation, phagocytosis, and the formation of DNA-containing extracellular traps. Although all granulocytes are primarily glycolytic and have only a small number of mitochondria, a growing body of evidence suggests that mitochondria are involved in all effector functions as well as in the production of cytokines and lipid mediators and in apoptosis. It has been shown that the production of mitochondrial ROS controls signaling pathways that mediate the activation of granulocytes by various stimuli. In this review, we will briefly discuss the data on the role of mitochondria in the regulation of effector and other functions of granulocytes.

The role of neutrophils in chorioamnionitis

Chorioamnionitis, commonly referred to as intrauterine infection or inflammation, is pathologically defined by neutrophil infiltration and inflammation at the maternal-fetal interface. Chorioamnionitis is the common complication during late pregnancy, which lead to a series of serious consequences, such as preterm labor, preterm premature rupture of the fetal membranes, and fetal inflammatory response syndrome. During infection, a large number of neutrophils migrate to the chorio-decidua in response to chemokines. Although neutrophils, a crucial part of innate immune cells, have strong anti-inflammatory properties, over-activating them can harm the body while also eliminating pathogens. This review concentrated on the latest studies on chorioamnionitis-related consequences as well as the function and malfunction of neutrophils. The release of neutrophil extracellular traps, production of reactive oxygen species, and degranulation from neutrophils during intrauterine infection, as well as their pathological roles in complications related to chorioamnionitis, were discussed in detail, offering fresh perspectives on the treatment of chorioamnionitis.

Cytoplasmic dynein1 intermediate-chain2 regulates cellular trafficking and physiopathological development in Magnaporthe oryzae

The cytoplasmic dynein 1, a minus end-directed motor protein, is an essential microtubule-based molecular motor that mediates the movement of molecules to intracellular destinations in eukaryotes. However, the role of dynein in the pathogenesis of Magnaporthe oryzae is unknown. Here, we identified cytoplasmic dynein 1 intermediate-chain 2 genes in M. oryzae and functionally characterized it using genetic manipulations, and biochemical approaches. We observed that targeted the deletion of MoDYNC1I2 caused significant vegetative growth defects, abolished conidiation, and rendered the ΔModync1I2 strains non-pathogenic. Microscopic examinations revealed significant defects in microtubule network organization, nuclear positioning, and endocytosis ΔModync1I2 strains. MoDync1I2 is localized exclusively to microtubules during fungal developmental stages but co-localizes with the histone OsHis1 in plant nuclei upon infection. The exogenous expression of a histone gene, MoHis1, restored the homeostatic phenotypes of ΔModync1I2 strains but not pathogenicity. These findings could facilitate the development of dynein-directed remedies for managing the rice blast disease.

The Obligate Intracellular Bacterial Pathogen Anaplasma phagocytophilum Exploits Host Cell Multivesicular Body Biogenesis for Proliferation and Dissemination

Anaplasma phagocytophilum is the etiologic agent of the emerging infection, granulocytic anaplasmosis. This obligate intracellular bacterium lives in a host cell-derived vacuole that receives membrane traffic from multiple organelles to fuel its proliferation and from which it must ultimately exit to disseminate infection. Understanding of these essential pathogenic mechanisms has remained poor. Multivesicular bodies (MVBs) are late endosomal compartments that receive biomolecules from other organelles and encapsulate them into intralumenal vesicles (ILVs) using endosomal sorting complexes required for transport (ESCRT) machinery and ESCRT-independent machinery. Association of the ESCRT-independent protein, ALIX, directs MVBs to the plasma membrane where they release ILVs as exosomes. We report that the A. phagocytophilum vacuole (ApV) is acidified and enriched in lysobisphosphatidic acid, a lipid that is abundant in MVBs. ESCRT-0 and ESCRT-III components along with ALIX localize to the ApV membrane. siRNA-mediated inactivation of ESCRT-0 and ALIX together impairs A. phagocytophilum proliferation and infectious progeny production. RNA silencing of ESCRT-III, which regulates ILV scission, pronouncedly reduces ILV formation in ApVs and halts infection by arresting bacterial growth. Rab27a and its effector Munc13-4, which drive MVB trafficking to the plasma membrane and subsequent exosome release, localize to the ApV. Treatment with Nexinhib20, a small molecule inhibitor that specifically targets Rab27a to block MVB exocytosis, abrogates A. phagocytophilum infectious progeny release. Thus, A. phagocytophilum exploits MVB biogenesis and exosome release to benefit each major stage of its intracellular infection cycle: intravacuolar growth, conversion to the infectious form, and exit from the host cell. IMPORTANCE Anaplasma phagocytophilum causes granulocytic anaplasmosis, a globally emerging zoonosis that can be severe, even fatal, and for which antibiotic treatment options are limited. A. phagocytophilum lives in an endosomal-like compartment that interfaces with multiple organelles and from which it must ultimately exit to spread within the host. How the bacterium accomplishes these tasks is poorly understood. Multivesicular bodies (MVBs) are intermediates in the endolysosomal pathway that package biomolecular cargo from other organelles as intralumenal vesicles for release at the plasma membrane as exosomes. We discovered that A. phagocytophilum exploits MVB biogenesis and trafficking to benefit all aspects of its intracellular infection cycle: proliferation, conversion to its infectious form, and release of infectious progeny. The ability of a small molecule inhibitor of MVB exocytosis to impede A. phagocytophilum dissemination indicates the potential of this pathway as a novel host-directed therapeutic target for granulocytic anaplasmosis.

The Olfactomedin-4-Defined Human Neutrophil Subsets Differ in Proteomic Profile in Healthy Individuals and Patients with Septic Shock

The specific granule glycoprotein olfactomedin-4 (Olfm4) marks a subset (1-70%) of human neutrophils and the Olfm4-high (Olfm4-H) proportion has been found to correlate with septic shock severity. The aim of this study was to decipher proteomic differences between the subsets in healthy individuals, hypothesizing that Olfm4-H neutrophils have a proteomic profile distinct from that of Olfm4 low (Olfm4-L) neutrophils. We then extended the investigation to septic shock. A novel protocol for the preparation of fixed, antibody-stained, and sorted neutrophils for LC-MS/MS was developed. In healthy individuals, 39 proteins showed increased abundance in Olfm4-H, including the small GTPases Rab3d and Rab11a. In Olfm4-L, 52 proteins including neutrophil defensin alpha 4, CXCR1, Rab3a, and S100-A7 were more abundant. The data suggest differences in important neutrophil proteins that might impact immunological processes. However, in vitro experiments revealed no apparent difference in the ability to control bacteria nor produce oxygen radicals. In subsets isolated from patients with septic shock, 24 proteins including cytochrome b-245 chaperone 1 had significantly higher abundance in Olfm4-H and 30 in Olfm4-L, including Fc receptor proteins. There was no correlation between Olfm4-H proportion and septic shock severity, but plasma Olfm4 concentration was elevated in septic shock. Thus, the Olfm4-H and Olfm4-L neutrophils have different proteomic profiles, but there was no evident functional significance of the differences in septic shock.

Differential dysregulation of granule subsets in WASH-deficient neutrophil leukocytes resulting in inflammation

Dysregulated secretion in neutrophil leukocytes associates with human inflammatory disease. The exocytosis response to triggering stimuli is sequential; gelatinase granules modulate the initiation of the innate immune response, followed by the release of pro-inflammatory azurophilic granules, requiring stronger stimulation. Exocytosis requires actin depolymerization which is actively counteracted under non-stimulatory conditions. Here we show that the actin nucleator, WASH, is necessary to maintain azurophilic granules in their refractory state by granule actin entrapment and interference with the Rab27a-JFC1 exocytic machinery. On the contrary, gelatinase granules of WASH-deficient neutrophil leukocytes are characterized by decreased Rac1, shortened granule-associated actin comets and impaired exocytosis. Rac1 activation restores exocytosis of these granules. In vivo, WASH deficiency induces exacerbated azurophilic granule exocytosis, inflammation, and decreased survival. WASH deficiency thus differentially impacts neutrophil granule subtypes, impairing exocytosis of granules that mediate the initiation of the neutrophil innate response while exacerbating pro-inflammatory granule secretion.

Recent advances in conventional and unconventional vesicular secretion pathways in the tumor microenvironment

All cells in the changing tumor microenvironment (TME) need a class of checkpoints to regulate the balance among exocytosis, endocytosis, recycling and degradation. The vesicular trafficking and secretion pathways regulated by the small Rab GTPases and their effectors convey cell growth and migration signals and function as meditators of intercellular communication and molecular transfer. Recent advances suggest that Rab proteins govern conventional and unconventional vesicular secretion pathways by trafficking widely diverse cargoes and substrates in remodeling TME. The mechanisms underlying the regulation of conventional and unconventional vesicular secretion pathways, their action modes and impacts on the cancer and stromal cells have been the focus of much attention for the past two decades. In this review, we discuss the current understanding of vesicular secretion pathways in TME. We begin with an overview of the structure, regulation, substrate recognition and subcellular localization of vesicular secretion pathways. We then systematically discuss how the three fundamental vesicular secretion processes respond to extracellular cues in TME. These processes are the conventional protein secretion via the endoplasmic reticulum-Golgi apparatus route and two types of unconventional protein secretion via extracellular vesicles and secretory autophagy. The latest advances and future directions in vesicular secretion-involved interplays between tumor cells, stromal cell and host immunity are also described.

Hermansky-Pudlak Syndrome: Identification of Novel Variants in the Genes HPS3, HPS5, and DTNBP1 (HPS-7)

Hermansky-Pudlak syndrome (HPS), a rare heterogeneous autosomal recessive disorder, is characterized by oculocutaneous albinism (OCA) and a bleeding diathesis due to a defect regarding melanosomes and platelet delta (δ)-granule secretion. Interestingly, patients with HPS type 2 (HPS-2) or HPS type 10 (HPS-10) present additionally with an immunological defect. We investigated three patients (IP1, IP2, and IP3) who suffer from a bleeding diathesis. Platelet aggregometry showed impaired platelet function and flow cytometry revealed a severely reduced platelet CD63 expression hinting to either a defect of platelet delta granule secretion or a decreased number of delta granules in these patients. However, only IP3 presents with an apparent OCA. We performed panel sequencing and identified a homozygous deletion of exon 6 in DTNBP1 for IP3. Western analysis confirmed the absence of the encoded protein dysbindin confirming the diagnosis of HPS-7. Interestingly, this patient reported additionally recurrent bacterial infections. Analysis of lymphocyte cytotoxicity showed a slightly reduced NK-degranulation previously documented in a more severe form in patients with HPS-2 or HPS-10. IP1 is carrier of two compound heterozygous variants in the HPS3 gene (c.65C > G and c.1193G > A). A homozygous variant in HPS5 (c.760G > T) was identified in IP2. The novel missense variants were classified as VUS (variant of uncertain significance) according to ACMG guidelines. For IP1 with the compound heterozygous variants in HPS3 a specialized ophthalmological examination showed ocular albinism. HPS3 and HPS5 encode subunits of the BLOC-2 complex and patients with HPS-3 or HPS-5 are known to present with variable/mild hypopigmentation.

Mechanism of Hip Arthropathy in Ankylosing Spondylitis: Abnormal Myeloperoxidase and Phagosome

Background

The pathogenesis of Ankylosing spondylitis (AS) has not been elucidated, especially involving hip joint disease. The purpose of this study was to analyze the proteome of diseased hip in AS and to identify key protein biomarkers.

Material and Methods

We used label-free quantification combined with liquid chromatography mass spectrometry (LC–MS/MS) to screen for differentially expressed proteins in hip ligament samples between AS and No-AS groups. Key protein was screened by Bioinformatics methods. and verified by in vitro experiments.

Results

There were 3,755 identified proteins, of which 92.916% were quantified. A total of 193 DEPs (49 upregulated proteins and 144 downregulated proteins) were identified according to P < 0.01 and Log|FC| > 1. DEPs were mainly involved in cell compartment, including the vacuolar lumen, azurophil granule, primary lysosome, etc. The main KEGG pathway included Phagosome, Glycerophospholipid metabolism, Lysine degradation, Pentose phosphate pathway. Myeloperoxidase (MPO) was identified as a key protein involved in Phagosome pathway. The experiment of siRNA interfering with cells further confirmed that the upregulated MPO may promote the inflammatory response of fibroblasts.

Conclusions

The overexpression of MPO may contribute to the autoimmune inflammatory response of AS-affected hip joint through the phagosome pathway.

The atypical small GTPase GEM/Kir is a negative regulator of the NADPH oxidase and NETs production through macroautophagy

Despite the important function of neutrophils in the eradication of infections and induction of inflammation, the molecular mechanisms regulating the activation and termination of the neutrophil immune response is not well understood. Here, the function of the small GTPase from the RGK family, Gem, is characterized as a negative regulator of the NADPH oxidase through autophagy regulation. Gem knockout (Gem KO) neutrophils show increased NADPH oxidase activation and increased production of extracellular and intracellular reactive oxygen species (ROS). Enhanced ROS production in Gem KO neutrophils was associated with increased NADPH oxidase complex-assembly as determined by quantitative super-resolution microscopy, but normal exocytosis of gelatinase and azurophilic granules. Gem-deficiency was associated with increased basal autophagosomes and autolysosome numbers but decreased autophagic flux under phorbol ester-induced conditions. Neutrophil stimulation triggered the localization of the NADPH oxidase subunits p22phox and p47phox at LC3-positive structures suggesting that the assembled NADPH oxidase complex is recruited to autophagosomes, which was significantly increased in Gem KO neutrophils. Prevention of new autophagosome formation by treatment with SAR405 increased ROS production while induction of autophagy by Torin-1 decreased ROS production in Gem KO neutrophils, and also in wild-type neutrophils, suggesting that macroautophagy contributes to the termination of NADPH oxidase activity. Autophagy inhibition decreased NETs formation independently of enhanced ROS production. NETs production, which was significantly increased in Gem-deficient neutrophils, was decreased by inhibition of both autophagy and calmodulin, a known GEM interactor. Intracellular ROS production was increased in Gem KO neutrophils challenged with live Gram-negative bacteria Pseudomonas aeruginosa or Salmonella Typhimurium, but phagocytosis was not affected in Gem-deficient cells. In vivo analysis in a model of Salmonella Typhimurium infection indicates that Gem-deficiency provides a genetic advantage manifested as a moderate increased in survival to infections. Altogether, the data suggest that Gem-deficiency leads to the enhancement of the neutrophil innate immune response by increasing NADPH oxidase assembly and NETs production and that macroautophagy differentially regulates ROS and NETs in neutrophils.

Neutrophils as Regulators and Biomarkers of Cardiovascular Inflammation in the Context of Abdominal Aortic Aneurysms

Neutrophils represent up to 70% of circulating leukocytes in healthy humans and combat infection mostly by phagocytosis, degranulation and NETosis. It has been reported that neutrophils are centrally involved in abdominal aortic aneurysm (AAA) pathogenesis. The natural course of AAA is growth and rupture, if left undiagnosed or untreated. The rupture of AAA has a very high mortality and is currently among the leading causes of death worldwide. The use of noninvasive cardiovascular imaging techniques for patient screening, surveillance and postoperative follow-up is well established and recommended by the current guidelines. Neutrophil-derived biomarkers may offer clinical value to the monitoring and prognosis of AAA patients, allowing for potential early therapeutic intervention. Numerous promising biomarkers have been studied. In this review, we discuss neutrophils and neutrophil-derived molecules as regulators and biomarkers of AAA, and our aim was to specifically highlight diagnostic and prognostic markers. Neutrophil-derived biomarkers may potentially, in the future, assist in determining AAA presence, predict size, expansion rate, rupture risk, and postoperative outcome once validated in highly warranted future prospective clinical studies.

Small extracellular vesicle-mediated bidirectional crosstalk between neutrophils and tumor cells

Neutrophils are the first line of defense against tissue injury and play an important role in tumor progression. Tumor-associated neutrophils (TANs) mediate pro-tumor immunosuppressive activity and their infiltration into tumors is associated with poor outcome in a variety of malignant diseases. The tumor cell-neutrophil crosstalk is mediated by small extracellular vesicles (sEVs) also referred to as exosomes which represent a major mechanism for intercellular communication. This review will address the role of neutrophil-derived sEVs (NEX) in reprogramming the TME and on mechanisms that regulate the dual potential of NEX to promote tumor progression on one hand and suppress tumor growth on the other. Emerging data suggest that both, NEX and tumor-derived sEVs (TEX) carry complex molecular cargos which upon delivery to recipient cells in the tumor microenvironment (TME) modulate their behavior and reprogram them to mediate pro-inflammatory or immunosuppressive responses. Although it remains unknown how the balance between the often conflicting signaling of TEX and NEX is regulated, this review is an attempt to provide insights into mechanisms that underpin this complex bidirectional crosstalk. A better understanding of the signals NEX process or deliver in the TME might lead to the development of novel approaches to the control of tumor progression in the future.

Neutrophil and Nanoparticles Delivery to Tumor: Is It Going to Carry That Weight?

The application of cell carriers for transporting nanodrugs to the tumor draws much attention as the alternative to the passive drug delivery. In this concept, the neutrophil (NΦ) is of special interest as this cell is able to uptake nanoparticles (NPs) and cross the vascular barrier in response to tumor signaling. There is a growing body of literature describing NP-NΦ interactions in vitro and in vivo that demonstrates the opportunity of using these cells to improve the efficacy of cancer therapy. However, a number of conceptual and technical issues need to be resolved for translating the technology into clinics. The current review summarizes the recent advances and challenges associated with NP-NΦ interactions, with the special focus on the complex interplay between the NP internalization pathways and the modulation of NΦ activity, and its potential consequences for nanodrug delivery.

For Better or for Worse: A Look Into Neutrophils in Traumatic Spinal Cord Injury

Neutrophils are short-lived cells of the innate immune system and the first line of defense at the site of an infection and tissue injury. Pattern recognition receptors on neutrophils recognize pathogen-associated molecular patterns or danger-associated molecular patterns, which recruit them to the destined site. Neutrophils are professional phagocytes with efficient granular constituents that aid in the neutralization of pathogens. In addition to phagocytosis and degranulation, neutrophils are proficient in creating neutrophil extracellular traps (NETs) that immobilize pathogens to prevent their spread. Because of the cytotoxicity of the associated granular proteins within NETs, the microbes can be directly killed once immobilized by the NETs. The role of neutrophils in infection is well studied; however, there is less emphasis placed on the role of neutrophils in tissue injury, such as traumatic spinal cord injury. Upon the initial mechanical injury, the innate immune system is activated in response to the molecules produced by the resident cells of the injured spinal cord initiating the inflammatory cascade. This review provides an overview of the essential role of neutrophils and explores the contribution of neutrophils to the pathologic changes in the injured spinal cord.

Cytoskeletal Transport, Reorganization, and Fusion Regulation in Mast Cell-Stimulus Secretion Coupling

Mast cells are well known for their role in allergies and many chronic inflammatory diseases. They release upon stimulation, e.g., via the IgE receptor, numerous bioactive compounds from cytoplasmic secretory granules. The regulation of granule secretion and its interaction with the cytoskeleton and transport mechanisms has only recently begun to be understood. These studies have provided new insight into the interaction between the secretory machinery and cytoskeletal elements in the regulation of the degranulation process. They suggest a tight coupling of these two systems, implying a series of specific signaling effectors and adaptor molecules. Here we review recent knowledge describing the signaling events regulating cytoskeletal reorganization and secretory granule transport machinery in conjunction with the membrane fusion machinery that occur during mast cell degranulation. The new insight into MC biology offers novel strategies to treat human allergic and inflammatory diseases targeting the late steps that affect harmful release from granular stores leaving regulatory cytokine secretion intact.

Roles of neutrophil granule proteins in orchestrating inflammation and immunity

Neutrophil granulocytes form the first line of host defense against invading pathogens and tissue injury. They are rapidly recruited from the blood to the affected sites, where they deploy an impressive arsenal of effectors to eliminate invading microbes and damaged cells. This capacity is endowed in part by readily mobilizable proteins acquired during granulopoiesis and stored in multiple types of cytosolic granules with each granule type containing a unique cargo. Once released, granule proteins contribute to killing bacteria within the phagosome or the extracellular milieu, but are also capable of inflicting collateral tissue damage. Neutrophil-driven inflammation underlies many common diseases. Research over the last decade has documented neutrophil heterogeneity and functional versatility far beyond their antimicrobial function. Emerging evidence indicates that neutrophils utilize granule proteins to interact with innate and adaptive immune cells and orchestrate the inflammatory response. Granule proteins have been identified as important modulators of neutrophil trafficking, reverse transendothelial migration, phagocytosis, neutrophil life span, neutrophil extracellular trap formation, efferocytosis, cytokine activity, and autoimmunity. Hence, defining their roles within the inflammatory locus is critical for minimizing damage to the neighboring tissue and return to homeostasis. Here, we provide an overview of recent advances in the regulation of degranulation, granule protein functions, and signaling in modulating neutrophil-mediated immunity. We also discuss how targeting granule proteins and/or signaling could be harnessed for therapeutic benefits.

Orchestration of Neutrophil Extracellular Traps (Nets), a Unique Innate Immune Function during Chronic Obstructive Pulmonary Disease (COPD) Development

Morbidity, mortality and economic burden caused by chronic obstructive pulmonary disease (COPD) is a significant global concern. Surprisingly, COPD is already the third leading cause of death worldwide, something that WHO had not predicted to occur until 2030. It is characterized by persistent respiratory symptoms and airway limitation due to airway and/or alveolar abnormalities usually caused by significant exposure to noxious particles of gases. Neutrophil is one of the key infiltrated innate immune cells in the lung during the pathogenesis of COPD. Neutrophils during pathogenic attack or injury decide to undergo for a suicidal death by releasing decondensed chromatin entangled with antimicrobial peptides to trap and ensnare pathogens. Casting neutrophil extracellular traps (NETs) has been widely demonstrated to be an effective mechanism against invading microorganisms thus controlling overwhelming infections. However, aberrant and massive NETs formation has been reported in several pulmonary diseases, including chronic obstructive pulmonary disease. Moreover, NETs can directly induce epithelial and endothelial cell death resulting in impairing pulmonary function and accelerating the progression of the disease. Therefore, understanding the regulatory mechanism of NET formation is the need of the hour in order to use NETs for beneficial purpose and controlling their involvement in disease exacerbation. For example, DNA neutralization of NET proteins using protease inhibitors and disintegration with recombinant human DNase would be helpful in controlling excess NETs. Targeting CXC chemokine receptor 2 (CXCR2) would also reduce neutrophilic inflammation, mucus production and neutrophil-proteinase mediated tissue destruction in lung. In this review, we discuss the interplay of NETs in the development and pathophysiology of COPD and how these NETs associated therapies could be leveraged to disrupt NETopathic inflammation as observed in COPD, for better management of the disease.

Super-Resolution Microscopy and Particle-Tracking Approaches for the Study of Vesicular Trafficking in Primary Neutrophils

Neutrophils are short-lived cells after isolation. The analysis of neutrophil vesicular trafficking requires rapid and gentle handling. Recently developed super-resolution microscopy technologies have generated unparalleled opportunities to help understand the molecular mechanisms regulating neutrophil vesicular trafficking, exocytosis, and associated functions at the molecular level. Here, we describe super-resolution and total internal reflection fluorescence (TIRF) microscopy approaches for the analysis of vesicular trafficking and associated functions of primary neutrophils.

The journey of Ca2+ through the cell - pulsing through the network of ER membrane contact sites

Calcium is the third most abundant metal on earth, and the fundaments of its homeostasis date back to pre-eukaryotic life forms. In higher organisms, Ca²⁺ serves as a cofactor for a wide array of (enzymatic) interactions in diverse cellular contexts and constitutes the most important signaling entity in excitable cells. To enable responsive behavior, cytosolic Ca²⁺ concentrations are kept low through sequestration into organellar stores, particularly the endoplasmic reticulum (ER), but also mitochondria and lysosomes. Specific triggers are then used to instigate a local release of Ca²⁺ on demand. Here, communication between organelles comes into play, which is accomplished through intimate yet dynamic contacts, termed membrane contact sites (MCSs). The field of MCS biology in relation to cellular Ca²⁺ homeostasis has exploded in recent years. Taking advantage of this new wealth of knowledge, in this Review, we invite the reader on a journey of Ca²⁺ flux through the ER and its associated MCSs. New mechanistic insights and technological advances inform the narrative on Ca²⁺ acquisition and mobilization at these sites of communication between organelles, and guide the discussion of their consequences for cellular physiology.

Rab27a Contributes to the Processing of Inflammatory Pain in Mice

Tissue injury and inflammation may result in chronic pain, a severe debilitating disease that is associated with great impairment of quality of life. An increasing body of evidence indicates that members of the Rab family of small GTPases contribute to pain processing; however, their specific functions remain poorly understood. Here, we found using immunofluorescence staining and in situ hybridization that the small GTPase Rab27a is highly expressed in sensory neurons and in the superficial dorsal horn of the spinal cord of mice. Rab27a mutant mice, which carry a single-nucleotide missense mutation of Rab27a leading to the expression of a nonfunctional protein, show reduced mechanical hyperalgesia and spontaneous pain behavior in inflammatory pain models, while their responses to acute noxious mechanical and thermal stimuli is not affected. Our study uncovers a previously unrecognized function of Rab27a in the processing of persistent inflammatory pain in mice.

The Progression of Acute Myeloid Leukemia from First Diagnosis to Chemoresistant Relapse: A Comparison of Proteomic and Phosphoproteomic Profiles

Acute myeloid leukemia (AML) is an aggressive hematological malignancy. Nearly 50% of the patients who receive the most intensive treatment develop chemoresistant leukemia relapse. Although the leukemogenic events leading to relapse seem to differ between patients (i.e., regrowth from a clone detected at first diagnosis, progression from the original leukemic or preleukemic stem cells), a common characteristic of relapsed AML is increased chemoresistance. The aim of the present study was to investigate at the proteomic level whether leukemic cells from relapsed patients present overlapping molecular mechanisms that contribute to this chemoresistance. We used liquid chromatography–tandem mass spectrometry (LC–MS/MS) to compare the proteomic and phosphoproteomic profiles of AML cells derived from seven patients at the time of first diagnosis and at first relapse. At the time of first relapse, AML cells were characterized by increased levels of proteins important for various mitochondrial functions, such as mitochondrial ribosomal subunit proteins (MRPL21, MRPS37) and proteins for RNA processing (DHX37, RNA helicase; RPP40, ribonuclease P component), DNA repair (ERCC3, DNA repair factor IIH helicase; GTF2F1, general transcription factor), and cyclin-dependent kinase (CDK) activity. The levels of several cytoskeletal proteins (MYH14/MYL6/MYL12A, myosin chains; VCL, vinculin) as well as of proteins involved in vesicular trafficking/secretion and cell adhesion (ITGAX, integrin alpha-X; CD36, platelet glycoprotein 4; SLC2A3, solute carrier family 2) were decreased in relapsed cells. Our study introduces new targetable proteins that might direct therapeutic strategies to decrease chemoresistance in relapsed AML.

Redundant and Cooperative Roles for Yersinia pestis Yop Effectors in the Inhibition of Human Neutrophil Exocytic Responses Revealed by Gain-of-Function Approach

Yersinia pestis causes a rapid, lethal disease referred to as plague. Y. pestis actively inhibits the innate immune system to generate a noninflammatory environment during early stages of infection to promote colonization. The ability of Y. pestis to create this early noninflammatory environment is in part due to the action of seven Yop effector proteins that are directly injected into host cells via a type 3 secretion system (T3SS). While each Yop effector interacts with specific host proteins to inhibit their function, several Yop effectors either target the same host protein or inhibit converging signaling pathways, leading to functional redundancy. Previous work established that Y. pestis uses the T3SS to inhibit neutrophil respiratory burst, phagocytosis, and release of inflammatory cytokines. Here, we show that Y. pestis also inhibits release of granules in a T3SS-dependent manner. Moreover, using a gain-of-function approach, we discovered previously hidden contributions of YpkA and YopJ to inhibition and that cooperative actions by multiple Yop effectors are required to effectively inhibit degranulation. Independent from degranulation, we also show that multiple Yop effectors can inhibit synthesis of leukotriene B₄ (LTB₄), a potent lipid mediator released by neutrophils early during infection to promote inflammation. Together, inhibition of these two arms of the neutrophil response likely contributes to the noninflammatory environment needed for Y. pestis colonization and proliferation.

The Impact of Hypoxia on Neutrophil Degranulation and Consequences for the Host

Neutrophils are key effector cells of innate immunity, rapidly recruited to defend the host against invading pathogens. Neutrophils may kill pathogens intracellularly, following phagocytosis, or extracellularly, by degranulation and the release of neutrophil extracellular traps; all of these microbicidal strategies require the deployment of cytotoxic proteins and proteases, packaged during neutrophil development within cytoplasmic granules. Neutrophils operate in infected and inflamed tissues, which can be profoundly hypoxic. Neutrophilic infiltration of hypoxic tissues characterises a myriad of acute and chronic infectious and inflammatory diseases, and as well as potentially protecting the host from pathogens, neutrophil granule products have been implicated in causing collateral tissue damage in these scenarios. This review discusses the evidence for the enhanced secretion of destructive neutrophil granule contents observed in hypoxic environments and the potential mechanisms for this heightened granule exocytosis, highlighting implications for the host. Understanding the dichotomy of the beneficial and detrimental consequences of neutrophil degranulation in hypoxic environments is crucial to inform potential neutrophil-directed therapeutics in order to limit persistent, excessive, or inappropriate inflammation.

Mycobacterium tuberculosis Lipoarabinomannan Activates Human Neutrophils via a TLR2/1 Mechanism Distinct from Pam3CSK4

Neutrophils, polymorphonuclear (PMN) leukocytes, play an important role in the early innate immune response to Mycobacterium tuberculosis infection in the lung. Interactions between PMN and mycobacterial lipids impact the activation state of these migrated cells with consequences for the surrounding tissue in terms of resolution versus ongoing inflammation. We hypothesized that lipoarabinomannan from M. tuberculosis (Mtb LAM) would prime human PMN in a TLR2-dependent manner and investigated this with specific comparison with the purified synthetic TLR2 agonists, Pam₃CSK₄ and FSL-1. In contrast to Pam₃CSK₄ and FSL-1, we found Mtb LAM did not induce any of the classical PMN priming phenotypes, including enhancement of NADPH oxidase activity, shedding of l-selectin, or mobilization of CD11b. However, exposure of PMN to Mtb LAM did elicit pro- and anti-inflammatory cytokine production and release in a TLR2/1-dependent manner, using the TLR1 single-nucleotide polymorphism rs5743618 (1805G/T) as a marker for TLR2/1 specificity. Moreover, Mtb LAM did not elicit p38 MAPK phosphorylation or endocytosis, although these processes occurred with Pam₃CSK₄ stimulation, and were necessary for the early priming events to occur. Interestingly, Mtb LAM did not abrogate priming responses elicited by Pam₃CSK₄ Notably, subfractionation of light membranes from Pam₃CSK₄ versus Mtb LAM-stimulated cells demonstrated differential patterns of exocytosis. In summary, Mtb LAM activates PMN via TLR2/1, resulting in the production of cytokines but does not elicit early PMN priming responses, as seen with Pam₃CSK₄ We speculate that the inability of Mtb LAM to prime PMN may be due to differential localization of TLR2/1 signaling.

Inhibition of Neutrophil Primary Granule Release during Yersinia pestis Pulmonary Infection

Inhalation of Yersinia pestis causes primary pneumonic plague, the most severe manifestation of plague that is characterized by a dramatic neutrophil influx to the lungs. Neutrophils are ineffective during primary pneumonic plague, failing to control Y. pestis growth in the airways. However, the mechanisms by which Y. pestis resists neutrophil killing are incompletely understood. Here, we show that Y. pestis inhibits neutrophil degranulation, an important line of host innate immune defense. We observed that neutrophils from the lungs of mice infected intranasally with Y. pestis fail to release primary granules throughout the course of disease. Using a type III secretion system (T3SS) injection reporter strain, we determined that Y. pestis directly inhibits neutrophil granule release by a T3SS-dependent mechanism. Combinatorial mutant analysis revealed that a Y. pestis strain lacking both effectors YopE and YopH did not inhibit primary granule release and is killed by neutrophils both in vivo and in vitro Similarly, Y. pestis strains injecting only YopE or YopH are able to inhibit the majority of primary granule release from human neutrophils. We determined that YopE and YopH block Rac2 activation and calcium flux, respectively, to inhibit neutrophil primary granule release in isolated human neutrophils. These results demonstrate that Y. pestis coordinates the inhibition of neutrophil primary granule release through the activities of two distinct effectors, and this inhibition promotes Y. pestis survival during primary pneumonic plague.IMPORTANCEYersinia pestis is the causative agent of plague and is one of the deadliest human pathogens. The pneumonic form of Y. pestis infection has played a critical role in the severity of both historical and modern plague outbreaks, yet the host-pathogen interactions that govern the lethality of Yersinia pestis pulmonary infections are incompletely understood. Here, we report that Yersinia pestis inhibits neutrophil degranulation during infection, rendering neutrophils ineffective and allowing unrestricted growth of Y. pestis in the lungs. This coordinated inhibition of granule release not only demonstrates the pathogenic benefit of "silencing" lung neutrophils but also reveals specific host processes and pathways that could be manipulated to reduce the severity of primary pneumonic plague.

Cell intrinsic functions of neutrophils and their manipulation by pathogens

Neutrophils are a crucial first line of defense against infection, migrating rapidly into tissues where they deploy granule components and toxic oxidants for efficient phagocytosis and microbe killing. Subsequent apoptosis and clearance of dying neutrophils are essential for control of infection and resolution of the inflammatory response. A subset of microbial pathogens survive exposure to neutrophils by manipulating phagocytosis, phagosome-granule fusion, oxidant production, and lifespan. Elucidating how they accomplish this unusual feat provides new insights into normal neutrophil function. In this review, we highlight recent discoveries about the ways in which neutrophils use cell-intrinsic mechanisms to control infection, and how these defenses are subverted by pathogens.

The trafficking protein JFC1 regulates Rac1-GTP localization at the uropod controlling neutrophil chemotaxis and in vivo migration

Neutrophil chemotaxis is essential in responses to infection and underlies inflammation. In neutrophils, the small GTPase Rac1 has discrete functions at both the leading edge and in the retraction of the trailing structure at the cell's rear (uropod), but how Rac1 is regulated at the uropod is unknown. Here, we identified a mechanism mediated by the trafficking protein synaptotagmin-like 1 (SYTL1 or JFC1) that controls Rac1-GTP recycling from the uropod and promotes directional migration of neutrophils. JFC1-null neutrophils displayed defective polarization and impaired directional migration to N-formyl-methionine-leucyl-phenylalanine in vitro, but chemoattractant-induced actin remodeling, calcium signaling and Erk activation were normal in these cells. Defective chemotaxis was not explained by impaired azurophilic granule exocytosis associated with JFC1 deficiency. Mechanistically, we show that active Rac1 localizes at dynamic vesicles where endogenous JFC1 colocalizes with Rac1-GTP. Super-resolution microscopy (STORM) analysis shows adjacent distribution of JFC1 and Rac1-GTP, which increases upon activation. JFC1 interacts with Rac1-GTP in a Rab27a-independent manner to regulate Rac1-GTP trafficking. JFC1-null cells exhibited Rac1-GTP accumulation at the uropod and increased tail length, and Rac1-GTP uropod accumulation was recapitulated by inhibition of ROCK or by interference with microtubule remodeling. In vivo, neutrophil dynamic studies in mixed bone marrow chimeric mice show that JFC1^-/- neutrophils are unable to move directionally toward the source of the chemoattractant, supporting the notion that JFC1 deficiency results in defective neutrophil migration. Our results suggest that defective Rac1-GTP recycling from the uropod affects directionality and highlight JFC1-mediated Rac1 trafficking as a potential target to regulate chemotaxis in inflammation and immunity.

The Nrf2/HO-1 axis can be a prognostic factor in clear cell renal cell carcinoma

Objective

To study the protein expression level of Nrf2/HO-1 in clear cell renal cell carcinoma (ccRCC) and adjacent normal tissue and to explore its relationship with clinicopathological characteristics and prognosis in ccRCC patients.

Materials and methods

In total, 152 ccRCC patients with available follow-up and clinical data were enrolled, and sample microarrays were prepared for immunohistochemistry studies. The human ccRCC cell lines 786-O, OS-RC-2, A498, and ACHN were cultured for immunofluorescence. The protein concentrations of five ccRCC patients’ tumor and adjacent normal renal tissues were prepared for Western blotting. Chi-squared tests, Fisher’s exact test, Kaplan–Meier analyses, log-rank tests, and Cox regression were performed for statistical analyses.

Results

The immunoreactivity results showed that the Nrf2 and HO-1 proteins were found in consistent locations in vitro and were expressed both in ccRCC and adjacent normal tissues. The two proteins were localized in the cytoplasm and nucleus of RCC tumor cells and in adjacent normal tissue cells. The expression levels of Nrf2 and HO-1 were significantly higher in ccRCC tissues than in the adjacent normal tissues. The Nrf2 protein level was found to be significantly correlated with the tumor size. Additionally, higher protein expression levels of Nrf2 and HO-1 were also correlated with worse overall survival outcomes and could potentially be used to predict the prognosis of ccRCC patients.

Conclusion

Our study provides an important theoretical basis for evaluating the clinical prognosis of ccRCC patients, which implies that the Nrf2/HO-1 axis can be a prognostic factor in ccRCC.

An Integrated, High-Throughput Strategy for Multiomic Systems Level Analysis

Proteomics, metabolomics, and transcriptomics generate comprehensive data sets, and current biocomputational capabilities allow their efficient integration for systems biology analysis. Published multiomics studies cover methodological advances as well as applications to biological questions. However, few studies have focused on the development of a high-throughput, unified sample preparation approach to complement high-throughput omic analytics. This report details the automation, benchmarking, and application of a strategy for transcriptomic, proteomic, and metabolomic analyses from a common sample. The approach, sample preparation for multi-omics technologies (SPOT), provides equivalent performance to typical individual omic preparation methods but greatly enhances throughput and minimizes the resources required for multiomic experiments. SPOT was applied to a multiomics time course experiment for zinc-treated HL-60 cells. The data reveal Zn effects on NRF2 antioxidant and NFkappaB signaling. High-throughput approaches such as these are critical for the acquisition of temporally resolved, multicondition, large multiomic data sets such as those necessary to assess complex clinical and biological concerns. Ultimately, this type of approach will provide an expanded understanding of challenging scientific questions across many fields.

Noncanonical Hippo Signalling in the Regulation of Leukocyte Function

The mammalian sterile 20-like (MST) kinases are central constituents of the evolutionary ancient canonical Hippo pathway regulating cell proliferation and survival. However, perhaps surprisingly, MST1 deficiency in human patients leads to a severe combined immunodeficiency syndrome with features of autoimmune disease. In line with this, Mst1-deficient mice exhibit severe defects in lymphocyte and neutrophil functions as well as disturbed intracellular vesicle transport. These findings spurred research on the noncanonical functions of MST1 in leukocytes. Here, we summarise the latest findings on this topic and discuss MST1 as a critical regulator of various leukocyte functions.

The Neutrophil's Choice: Phagocytose vs Make Neutrophil Extracellular Traps

Neutrophils recognize particulate substrates of microbial or endogenous origin and react by sequestering the cargo via phagocytosis or by releasing neutrophil extracellular traps (NETs) outside the cell, thus modifying and alerting the environment and bystander leukocytes. The signals that determine the choice between phagocytosis and the generation of NETs are still poorly characterized. Neutrophils that had phagocytosed bulky particulate substrates, such as apoptotic cells and activated platelets, appear to be “poised” in an unresponsive state. Environmental conditions, the metabolic, adhesive and activation state of the phagocyte, and the size of and signals associated with the tethered phagocytic cargo influence the choice of the neutrophils, prompting either phagocytic clearance or the generation of NETs. The choice is dichotomic and apparently irreversible. Defects in phagocytosis may foster the intravascular generation of NETs, thus promoting vascular inflammation and morbidities associated with diseases characterized by defective phagocytic clearance, such as systemic lupus erythematosus. There is a strong potential for novel treatments based on new knowledge of the events determining the inflammatory and pro-thrombotic function of inflammatory leukocytes.

Autophagy Mediates Interleukin-1β Secretion in Human Neutrophils

Interleukin-1β (IL-1β), a major pro-inflammatory cytokine, is a leaderless cytosolic protein whose secretion does not follow the classical endoplasmic reticulum-to-Golgi pathway, and for which a canonical mechanism of secretion remains to be established. Neutrophils are essential players against bacterial and fungi infections. These cells are rapidly and massively recruited from the circulation into infected tissues and, beyond of displaying an impressive arsenal of toxic weapons effective to kill pathogens, are also an important source of IL-1β in infectious conditions. Here, we analyzed if an unconventional secretory autophagy mechanism is involved in the exportation of IL-1β by these cells. Our findings indicated that inhibition of autophagy with 3-methyladenine and Wortmannin markedly reduced IL-1β secretion induced by LPS + ATP, as did the disruption of the autophagic flux with Bafilomycin A1 and E64d. These compounds did not noticeable affect neutrophil viability ruling out that the effects on IL-1β secretion were due to cell death. Furthermore, VPS34IN-1, a specific autophagy inhibitor, was still able to reduce IL-1β secretion when added after it was synthesized. Moreover, siRNA-mediated knockdown of ATG5 markedly reduced IL-1β secretion in neutrophil-differentiated PLB985 cells. Upon LPS + ATP stimulation, IL-1β was incorporated to an autophagic compartment, as was revealed by its colocalization with LC3B by confocal microscopy. Overlapping of IL-1β-LC3B in a vesicular compartment peaked before IL-1β increased in culture supernatants. On the other hand, stimulation of autophagy by cell starvation augmented the colocalization of IL-1β and LC3B and then promoted neutrophil IL-1β secretion. In addition, specific ELISAs indicated that although both IL-1β and pro-IL-1β are released to culture supernatants upon neutrophil stimulation, autophagy only promotes IL-1β secretion. Furthermore, the serine proteases inhibitor AEBSF reduced IL-1β secretion. Moreover, IL-1β could be also found colocalizing with elastase, suggesting both some vesicles containing IL-1β intersect azurophil granules content and that serine proteases also regulate IL-1β secretion. Altogether, our findings indicate that an unconventional autophagy-mediated secretory pathway mediates IL-1β secretion in human neutrophils.

Gene transfer into hematopoietic stem cells reduces HLH manifestations in a murine model of Munc13-4 deficiency

Patients with mutations in the UNC13D gene (coding for Munc13-4 protein) suffer from familial hemophagocytic lymphohistiocytosis type 3 (FHL3), a life-threatening immune and hyperinflammatory disorder. The only curative treatment is allogeneic hematopoietic stem cell (HSC) transplantation, although the posttreatment survival rate is not satisfactory. Here, we demonstrate the curative potential of UNC13D gene correction of HSCs in a murine model of FHL3. We generated a self-inactivating lentiviral vector, used it to complement HSCs from Unc13d-deficient (Jinx) mice, and transplanted the cells back into the irradiated Jinx recipients. This procedure led to complete reconstitution of the immune system (ie, to wild-type levels). The recipients were then challenged with lymphocytic choriomeningitis virus to induce hemophagocytic lymphohistiocytosis (HLH)-like manifestations. All the clinical and biological signs of HLH were significantly reduced in mice having undergone HSC UNC13D gene correction than in nontreated animals. This beneficial effect was evidenced by the correction of blood cytopenia, body weight gain, normalization of the body temperature, decreased serum interferon-γ level, recovery of liver damage, and decreased viral load. These improvements can be explained by the restoration of the CD8⁺ T lymphocytes' cytotoxic function (as demonstrated here in an in vitro degranulation assay). Overall, our results demonstrate the efficacy of HSC gene therapy in an FHL-like setting of immune dysregulation.

Increased Neutrophil Secretion Induced by NLRP3 Mutation Links the Inflammasome to Azurophilic Granule Exocytosis

Heterozygous mutations in the NLRP3 gene in patients with cryopyrin associated periodic syndrome (CAPS) lead to hyper-responsive inflammasome function. CAPS is a systemic auto-inflammatory syndrome characterized by the activation of the innate immune system induced by elevated pro-inflammatory cytokines, but the involvement of selective innate immune cells in this process is not fully understood. Neutrophil secretion and the toxic components of their granules are mediators of inflammation associated with several human diseases and inflammatory conditions. Here, using the Nlrp3^A350V inducible mouse model (MWS CreT) that recapitulates human patients with the A352V mutation in NLRP3 observed in the Muckle-Wells sub-phenotype of CAPS, we studied the relationship between hyper-activation of the inflammasome and neutrophil exocytosis. Using a flow cytometry approach, we show that Nlrp3^A350V (MWS) neutrophils express normal basal levels of CD11b at the plasma membrane and that the upregulation of CD11b from secretory vesicles in response to several plasma membrane or endocytic agonist including the bacterial-derived mimetic peptide formyl-Leu-Met-Phe (fMLF) and the unmethylated oligonucleotide CpG is normal in MWS neutrophils. Significant but modest CD11b upregulation in MWS neutrophils compared to wild type was only observed in response to GM-CSF and CpG. The same pattern was observed for the secretion of matrix metalloproteinase-9 (MMP-9) from gelatinase granules in that MMP-9 secretion in MWS neutrophils was not different from that observed in wild-type neutrophils except when stimulated with GM-CSF and CpG. In contrast, azurophilic granule secretion, whose cargoes constitute the most toxic secretory and pro-inflammatory factors of the neutrophil, was markedly dysregulated in MWS neutrophils under both basal and stimulated conditions. This could not be attributed to paracrine effects of secretory cytokines because IL-1β secretion by neutrophils was undetectable under these experimental conditions. The increased azurophilic granule exocytosis in MWS neutrophils was attenuated by treatment with the neutrophil exocytosis inhibitor Nexinhib20. In agreement with a possible neutrophil contribution to systemic inflammation in CAPS, the levels of neutrophil secretory proteins were significantly elevated in the plasma from Nlrp3^A350V mice. Altogether, our data indicates an azurophilic granule-selective dysregulation of neutrophil exocytosis in CAPS.

Role of Translocator 18 KDa Ligands in the Activation of Leukotriene B4 Activated G-Protein Coupled Receptor and Toll Like Receptor-4 Pathways in Neutrophils

TSPO (Translocator 18 KDa; tryptophan-rich sensory protein oxygen sensor) is a constitutive outer mitochondrial membrane protein overexpressed in inflammatory cells during local or systemic processes. Despite its expression is characterized, role of TSPO in inflammation remains elusive. For this study, we investigated the role of TSPO ligands on neutrophil functions elicited by two different inflammatory pathways. Peritoneal neutrophils were isolated from male Balb-C mice, treated with TSPO ligand diazepam, Ro5-4864 or PK11195 (1,100 or 1000 nM; 2 h) and further stimulated with lipopolysaccharide from Escherichia coli (LPS), a binding for Toll-Like Receptor-4 (TLR4), or leukotriene B4 (LTB4), a G-protein coupled receptor (GPCR) ligand. LPS treatment did not lead to overexpression of TSPO on neutrophils, and pre-treatment with any TSPO ligand did not alter cytokine expression, adhesion molecule expression, or the production of reactive oxygen and nitrogen species caused by LPS stimulation. Conversely, all TSPO ligands impaired LTB4’s actions, as visualized by reductions in L-selectin shedding, β2 integrin overexpression, neutrophil chemotaxis, and actin filament assembly. TSPO ligands showed distinct intracellular effects on LTB4-induced neutrophil locomotion, with diazepam enhancing cofilin but not modifying Arp2/3 expression, and Ro5-4864 and PK11195 reducing both cofilin and Arp2/3 expression. Taken together, our data exclude a direct role of TSPO ligands in TLR4-elicited pathways, and indicate that TSPO activation inhibits GPCR inflammatory pathways in neutrophils, with a relevant role in neutrophil influx into inflammatory sites.

Neutrophil programming dynamics and its disease relevance

Neutrophils are traditionally considered as first responders to infection and provide antimicrobial host defense. However, recent advances indicate that neutrophils are also critically involved in the modulation of host immune environments by dynamically adopting distinct functional states. Functionally diverse neutrophil subsets are increasingly recognized as critical components mediating host pathophysiology. Despite its emerging significance, molecular mechanisms as well as functional relevance of dynamically programmed neutrophils remain to be better defined. The increasing complexity of neutrophil functions may require integrative studies that address programming dynamics of neutrophils and their pathophysiological relevance. This review aims to provide an update on the emerging topics of neutrophil programming dynamics as well as their functional relevance in diseases.

Rab GTPases in Immunity and Inflammation

Strict spatiotemporal control of trafficking events between organelles is critical for maintaining homeostasis and directing cellular responses. This regulation is particularly important in immune cells for mounting specialized immune defenses. By controlling the formation, transport and fusion of intracellular organelles, Rab GTPases serve as master regulators of membrane trafficking. In this review, we discuss the cellular and molecular mechanisms by which Rab GTPases regulate immunity and inflammation.

Peptoanaerobacter stomatis Primes Human Neutrophils and Induces Granule Exocytosis

Peptoanaerobacter stomatis is a newly appreciated taxon associated with periodontal diseases; however, little is known about the organism's pathogenic potential or its interaction with the host immune response. Neutrophils are the most abundant innate immune cell present in the gingival tissue and function to constrain the oral microbial challenge. However, some periodontal pathogens have developed strategies to evade phagocytosis and killing by neutrophils. Therefore, to begin to understand the role of P. stomatis in periodontitis, we studied its interactions with human neutrophils. Our data showed that after 30 min of incubation, neutrophils failed to engulf P. stomatis efficiently; however, when P. stomatis was internalized, it was promptly eradicated. P. stomatis challenge induced a robust intracellular respiratory burst; however, this response did not contribute to bacterial killing. Minimal superoxide release was observed by direct bacterial challenge; however, P. stomatis significantly increased N-formyl-methionyl-leucyl phenylalanine (fMLF)-stimulated superoxide release to an extent similar to that of cells primed with tumor necrosis factor alpha (TNF-α). When neutrophils were challenged with P. stomatis, 52% of the bacterium-containing phagosomes were enriched for the specific granule marker lactoferrin and 82% with the azurophil granule marker elastase. P. stomatis challenge stimulated exocytosis of the four neutrophil granule subtypes. Moreover, P. stomatis susceptibility to extracellular killing could be attributed to the exocytosis of antimicrobial components present in neutrophil granules. Priming neutrophils for an enhanced respiratory burst together with promoting granule content release could contribute to the chronic inflammation and tissue destruction that characterize periodontal diseases.