STIM1 and STIM2 cooperatively regulate mouse neutrophil store-operated calcium entry and cytokine production

Neutrophil PPIF exacerbates lung ischemia-reperfusion injury after lung transplantation by promoting calcium overload-induced neutrophil extracellular traps formation

Lung ischemia-reperfusion (I/R) injury is the main risk factor for primary graft dysfunction and patient death after lung transplantation (LTx). It is widely accepted that the main pathological mechanism of lung I/R injury are calcium overload, oxygen free radical explosion and neutrophil-mediated damage, which leading to the lack of effective treatment options. The aim of this study was to further explore the mechanisms of lung I/R injury after LTx and to provide potential therapeutic strategies. Our bioinformatics analysis revealed that the neutrophil extracellular traps (NETs) formation was closely involved in lung I/R injury after LTx, which was accompanied by up-regulation of peptidylprolyl isomerase F (PPIF) and peptidyl arginine deiminase 4 (PADI4). We further established an orthotopic LTx mouse model to simulate lung I/R injury in vivo, and found that PPIF and PADI4 inhibitors effectively reduced neutrophil infiltration, NETs formation, inflammatory response, and lung I/R injury. In the neutrophil model induced by HL-60 cell line in vitro, we found that PPIF inhibitor cyclosporin A (Cys A) better alleviated calcium overload induced inflammatory response, reactive oxygen species content and NETs formation. Further study demonstrated that interfering with neutrophil PPIF protected mitochondrial function by alleviating store-operated calcium entry (SOCE) during calcium overload and played the above positive role. On this basis, we found that the reduction of calcium content in neutrophils was accompanied by the inhibition of calcineurin (CN) and nuclear factor of activated T cells (NFAT). In conclusion, our findings suggested that neutrophil PPIF could serve as a novel biomarker and potential therapeutic target of lung I/R injury after LTx, which provided new clues for its treatment by inhibiting calcium overload-induced NETs formation.

STIM1 promotes acquired resistance to sorafenib by attenuating ferroptosis in hepatocellular carcinoma

Dysregulated calcium (Ca2+) signaling pathways are associated with tumor cell death and drug resistance. In non-excitable cells, such as hepatocellular carcinoma (HCC) cells, the primary pathway for Ca2+ influx is through stromal interaction molecule 1 (STIM1)-mediated store-operated calcium entry (SOCE). Previous studies have demonstrated the involvement of STIM1-mediated SOCE in processes such as genesis, metastasis, and stem cell self-renewal of HCC. However, it remains unclear whether STIM1-mediated SOCE plays a role in developing acquired resistance to sorafenib in HCC patients. In this study, we established acquired sorafenib-resistant (SR) HCC cell lines by intermittently exposing them to increasing concentrations of sorafenib. Our results showed higher levels of STIM1 and stronger SOCE in SR cells compared with parental cells. Deleting STIM1 significantly enhanced sensitivity to sorafenib in SR cells, while overexpressing STIM1 promoted SR by activating SOCE. Mechanistically, STIM1 increased the transcription of SLC7A11 through the SOCE-CaN-NFAT pathway. Subsequently, up-regulated SLC7A11 increased glutathione synthesis, resulting in ferroptosis insensitivity and SR. Furthermore, combining the SOCE inhibitor SKF96365 with sorafenib significantly improved the sensitivity of SR cells to sorafenib both in vitro and in vivo. These findings suggest a potential strategy to overcome acquired resistance to sorafenib in HCC cells.

New insights into the stromal interaction molecule 2 function and its impact on the immunomodulation of tumor microenvironment

Immune cells-enhanced immunotherapy exhibits unprecedented overall survival-prolongation even curable in some cancer patients. Although so, most of the patients show no response. Tumor microenvironment (TME) where immune cells settle down has multi-faceted influences, but usually creates an immunosuppressive niche that facilitating tumor cells escape from immune attack. The metabolites and malnutrition of TME exert enormous effects on the resident immune cells, but the underlying mechanism is largely unknown. The stromal interaction molecules 2 (STIM2) is an endoplasmic reticulum (ER) calcium (Ca2+) sensor to maintain Ca2+ homeostasis. Notably, the cytosol STIM2 C-terminus is long with various domains that are available for the combination or/and molecular modification. This distinct structure endows STIM2 with a high susceptibility to numerous permeable physico-chemical molecules or protein interactions. STIM2 and its variants are extensively expressed in various immune cells, especially in T immune cells. STIM2 was reported closely correlated with the function of immune cells via regulating Ca2+ signaling, energy metabolism and cell fitness. Herein, we sum the latest findings on the STIM2 structure, focusing on its distinct characteristics and profound effect on the regulation of Ca2+ homeostasis and multi-talented functionality. We also outline the advancements on the underlying mechanism how STIM2 anomalies influence the function of immune cells and on the turbulent expression or/and amenably modification of STIM2 within the tumor niches. Then we discuss the translation of these researches into antitumor approaches, emphasizing the potential of STIM2 as a therapeutic target for direct inhibition of tumor cells or more activation towards immune cells driving to flare TME. This review is an update on STIM2, aiming to rationalize the potential of STIM2 as a therapeutic target for immunomodulation, engaging immune cells to exert the utmost anti-tumor effect.

STIM2 Suppression Blocks Glial Activation to Alleviate Brain Ischemia Reperfusion Injury via Inhibition of Inflammation and Pyroptosis

Cerebral ischemia/reperfusion injury (CIRI) involves various pathogenic mechanisms, including cytotoxicity, apoptosis, inflammation, and pyroptosis. Stromal interactive molecule 2 (STIM2) is implicated in cerebral ischemia. Consequently, this study investigates the biological functions of STIM2 and its related mechanisms in CIRI progression. Middle cerebral artery occlusion/reperfusion (MCAO/R) mouse models and oxygen-glucose deprivation/reoxygenation (OGD/R) cellular models were established. STIM2 level was upregulated in experimental CIRI models, as shown by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), western blotting and immunofluorescence staining. Brain infarction and edema were attenuated by STIM2 knockdown, as 2,3,5-triphenyltetrazolium chloride (TTC) staining and brain water content evaluation revealed. STIM2 knockdown relieved neuronal apoptosis, microglia activation, inflammation and pyroptosis in MCAO/R mice, as detected by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining, enzyme-linked immunosorbent assay (ELISA) and western blotting. Results of flow cytometry, ELISA, western blotting and cell counting kit-8 (CCK-8) assays also showed that STIM2 knockdown inhibited inflammation, apoptosis and pyroptosis in OGD/R-treated BV2 cells. Moreover, STIM2 knockdown inhibited apoptosis and pyroptosis in PC12 cells incubated with conditioned medium collected from OGD/R-exposed BV2 cells. Mechanistically, lncRNA Malat1 (metastasis associated lung adenocarcinoma transcript 1) positively regulated STIM2 expression by sponging miR-30d-5p. Their binding relationship was confirmed by luciferase reporter assays. Finally, lncRNA Malat1 elevation or miR-30d-5p knockdown abolished the sh-STIM2-induced inhibition in cell damage. In conclusion, STIM2 knockdown in microglia alleviates CIRI by inhibiting microglial activation, inflammation, apoptosis, and pyroptosis.

Anandamide modulation of monocyte-derived Langerhans cells: implications for immune homeostasis and skin inflammation

Introduction

The endocannabinoid system (ECS), named after the chemical compounds found in the cannabis plant, is a regulatory network of neurotransmitters, receptors, and enzymes that plays crucial roles in skin health and disease. Endogenous ligands of the ECS, called endocannabinoids, have proven to be important regulators of immune responses. One of the most prevalent endocannabinoids, arachidonoylethanolamide (also known as anandamide), is known for its anti-inflammatory effects. Langerhans cells (LCs) are the sole antigen-presenting cells present in the human epidermis. They serve as the first line of defense against pathogens and are essential for the skin's specific immune responses and play a critical role in maintaining tissue homeostasis; however, little is known about the effect of endocannabinoids on these cells. Our research aimed to provide the connection between monocyte-derived Langerhans cells (moLCs) and the ECS, shedding light on their collaborative roles in immune homeostasis and inflammation.

Methods

Human monocytes were differentiated into moLCs using established protocols. Anandamide was applied during the differentiation process to test its effect on the viability, marker expression, and cytokine production of the cells, as well as in short term treatments for intracellular calcium measurement. TLR ligands applied after the differentiation protocol were used to activate moLCs. The impact of anandamide on the functionality of moLCs was further assessed using differential gene expression analysis of bulk RNA-Seq data, moLC-T cell cocultures, while ELISpot was employed to determine polarization of T cells activated in the aforementioned cocultures.

Results

Anandamide did not significantly affect the viability of moLCs up to 10 µM. When applied during the differentiation process it had only a negligible effect on CD207 expression, the prototypic marker of LCs; however, there was an observed reduction in CD1a expression by moLCs. Anandamide had no significant effects on the maturation status of moLCs, nor did it affect the maturation induced by TLR3 and TLR7/8 agonists. MoLCs differentiated in the presence of anandamide did however show decreased production of CXCL8, IL-6, IL-10 and IL-12 cytokines induced by TLR3 and TLR7/8 activation. Anandamide-treated moLCs showed an increased capability to activate naïve T cells; however, not to the level seen with combined TLR agonism. RNA sequencing analysis of moLCs differentiated with anandamide showed modest changes compared to control cells but did reveal an inhibitory effect on oxidative phosphorylation specifically in activated moLCs. Anandamide also promoted the polarization of naïve T cells towards a Th1 phenotype.

Discussion

Our results show that anandamide has nuanced effects on the differentiation, maturation, cytokine secretion, metabolism and function of activated moLCs. Among these changes the decrease in CD1a expression on moLCs holds promise to selectively dampen inflammation induced by CD1a restricted T cells, which have been implicated as drivers of inflammation in common inflammatory skin conditions such as psoriasis, atopic dermatitis and contact dermatitis.

STIM1 Mediates Methamphetamine-Induced Neuronal Autophagy and Apoptosis

Methamphetamine (METH) is a widely abused amphetamine-type psychoactive drug that causes serious health problems. Previous studies have demonstrated that METH can induce neuron autophagy and apoptosis in vivo and in vitro. However, the molecular mechanisms underlying METH-induced neuron autophagy and apoptosis remain poorly understood. Stromal interacting molecule 1 (STIM1) was hypothesized to be involved in METH-induced neuron autophagy and apoptosis. Therefore, the expression of STIM1 protein was measured and the effect of blocking STIM1 expression with siRNA was investigated in cultured neuronal cells, and the hippocampus and striatum of mice exposed to METH. Furthermore, intracellular calcium concentration and endoplasmic reticulum (ER) stress-related proteins were determined in vitro and in vivo in cells treated with METH. The results suggested that STIM1 mediates METH-induced neuron autophagy by activating the p-Akt/p-mTOR pathway. METH exposure also resulted in increased expression of Orai1, which was reversed after STIM1 silencing. Moreover, the disruption of intracellular calcium homeostasis induced ER stress and up-regulated the expression of pro-apoptotic protein CCAAT/enhancer-binding protein homologous protein (CHOP), resulting in classic mitochondria apoptosis. METH exposure can cause neuronal autophagy and apoptosis by increasing the expression of STIM1 protein; thus, STIM1 may be a potential gene target for therapeutics in METH-caused neurotoxicity.

STIM2 is involved in the regulation of apoptosis and the cell cycle in normal and malignant monocytic cells

Calcium is a ubiquitous messenger that regulates a wide range of cellular functions, but its involvement in the pathophysiology of acute myeloid leukemia (AML) is not widely investigated. Here, we identified, from an analysis of The Cancer Genome Atlas and genotype-tissue expression databases, stromal interaction molecule 2 (STIM2) as being highly expressed in AML with monocytic differentiation and negatively correlated with overall survival. This was confirmed on a validation cohort of 407 AML patients. We then investigated the role of STIM2 in cell proliferation, differentiation, and survival in two leukemic cell lines with monocytic potential and in normal hematopoietic stem cells. STIM2 expression increased at the RNA and protein levels upon monocyte differentiation. Phenotypically, STIM2 knockdown drastically inhibited cell proliferation and induced genomic stress with DNA double-strand breaks, as shown by increased levels of phosphorylate histone H2AXγ (p-H2AXγ), followed by activation of the cellular tumor antigen p53 pathway, decreased expression of cell cycle regulators such as cyclin-dependent kinase 1 (CDK1)-cyclin B1 and M-phase inducer phosphatase 3 (CDC25c), and a decreased apoptosis threshold with a low antiapoptotic/proapoptotic protein ratio. Our study reports STIM2 as a new actor regulating genomic stability and p53 response in terms of cell cycle and apoptosis of human normal and malignant monocytic cells.

miRNA-132-5p mediates a negative feedback regulation of IL-8 secretion through S100A8/A9 downregulation in neutrophil-like HL-60 cells

Background

Neutrophils are an important source of pro-inflammatory and immunomodulatory cytokines. This makes neutrophils efficient drivers of interactions with immune and non-immune cells to maintain homeostasis and modulate the inflammatory process by notably regulating the release of cytokines. Ca2+-dependent regulatory mechanism encompassing cytokine secretion by neutrophils are not still identified. In this context, we propose to define new insights on the role of Ca2+-binding proteins S100A8/A9 and on the regulatory role of miRNA-132-5p, which was identified as a regulator of S100A8/A9 expression, on IL-8 secretion.

Methods

Differentiated HL-60 cells, a human promyelocytic leukemia cell line that can be induced to differentiate into neutrophil-like cells, were used as a model of human neutrophils and treated with N- formyl-methionyl-leucyl-phenylalanine (fMLF), a bacterial peptide that activates neutrophils. shRNA knockdown was used to define the role of selected targets (S100A8/A9 and miRNA-132-5p) on IL-8 secretion.

Results and discussion

Different types of cytokines engage different signaling pathways in the secretion process. IL-8 release is tightly regulated by Ca2+ binding proteins S100A8/A9. miRNA-132-5p is up-regulated over time upon fMLF stimulation and decreases S100A8/A9 expression and IL-8 secretion.

Conclusion

These findings reveal a novel regulatory loop involving S100A8/A9 and miRNA-132-5p that modulates IL-8 secretion by neutrophils in inflammatory conditions. This loop could be a potential target for therapeutic intervention in inflammatory diseases.

Staphylococcus aureus α-toxin impairs early neutrophil localization via electrogenic disruption of store-operated calcium entry

The pore-forming S. aureus α-toxin (Hla) contributes to virulence and disease pathogenesis. While high concentrations of toxin induce cell death, neutrophils exhibit relative resistance to lysis, suggesting that the action of Hla may not be solely conferred by lytic susceptibility. Using intravital microscopy, we observed that Hla disrupts neutrophil localization and clustering early in infection. Hla forms a narrow, ion-selective pore, suggesting that Hla may dysregulate calcium or other ions to impair neutrophil function. We found that sub-lytic Hla did not permit calcium influx but caused rapid membrane depolarization. Depolarization decreases the electrogenic driving force for calcium, and concordantly, Hla suppressed calcium signaling in vitro and in vivo and calcium-dependent leukotriene B4 (LTB4) production, a key mediator of neutrophil clustering. Thus, Hla disrupts the early patterning of the neutrophil response to infection, in part through direct impairment of neutrophil calcium signaling. This early mis-localization of neutrophils may contribute to establishment of infection.

STIM1 in tumor cell death: angel or devil?

Stromal interaction molecule 1 (STIM1) is involved in mediating the store-operated Ca2+ entry (SOCE), driving the influx of the intracellular second messenger calcium ion (Ca2+), which is closely associated with tumor cell proliferation, metastasis, apoptosis, autophagy, metabolism and immune processes. STIM1 is not only regulated at the transcriptional level by NF-κB and HIF-1, but also post-transcriptionally modified by miRNAs and degraded by ubiquitination. Recent studies have shown that STIM1 or Ca2+ signaling can regulate apoptosis, autophagy, pyroptosis, and ferroptosis in tumor cells and act discrepantly in different cancers. Furthermore, STIM1 contributes to resistance against antitumor therapy by influencing tumor cell death. Further investigation into the mechanisms through which STIM1 controls other forms of tumor cell death could aid in the discovery of novel therapeutic targets. Moreover, STIM1 has the ability to regulate immune cells within the tumor microenvironment. Here, we review the basic structure, function and regulation of STIM1, summarize the signaling pathways through which STIM1 regulates tumor cell death, and propose the prospects of antitumor therapy by targeting STIM1.

Molecular regulation of neutrophil swarming in health and disease: Lessons from the phagocyte oxidase

Neutrophil swarming is a complex coordinated process in which neutrophils sensing pathogen or damage signals are rapidly recruited to sites of infections or injuries. This process involves cooperation between neutrophils where autocrine and paracrine positive-feedback loops, mediated by receptor/ligand pairs including lipid chemoattractants and chemokines, amplify localized recruitment of neutrophils. This review will provide an overview of key pathways involved in neutrophil swarming and then discuss the cell intrinsic and systemic mechanisms by which NADPH oxidase 2 (NOX2) regulates swarming, including modulation of calcium signaling, inflammatory mediators, and the mobilization and production of neutrophils. We will also discuss mechanisms by which altered neutrophil swarming in disease may contribute to deficient control of infections and/or exuberant inflammation. Deeper understanding of underlying mechanisms controlling neutrophil swarming and how neutrophil cooperative behavior can be perturbed in the setting of disease may help to guide development of tools for diagnosis and precision medicine.

Complement dependent TNFα production in neutrophil-like HL60 cells

Neutrophils develop in the bone marrow (BM) from hematopoietic stem cells (HSCs) through a series of progenitor cells and mature neutrophils play a critical role in the human immune system. Previous studies revealed that tumor necrosis factor α (TNFα) produced by immature neutrophils contributes to HSCs development and vascular regeneration in the BM niche. However, the precise mechanism of TNFα production in immature neutrophils remains unclear. This study aims to assess the relationship between complement C3 activation and TNFα production from immature neutrophils. We investigated the regulatory mechanism of TNFα production by complement components in neutrophil-like HL60 cells. Flow cytometric analysis showed that C3a receptor (C3aR) and C3bi receptor (CR3, Mac-1, CD11b/CD18, integrin αMβ2) are expressed on the surface of neutrophil-like HL60 cells. We found that zymosan-treated human serum leads to TNFα production in neutrophil-like HL60 cells, but not in human polymorphonuclear cells (PMNs). A C3-convertase inhibitor, compstatin suppresses TNFα production. These data suggest that the TNFα production is mediated by complement C3 activation. Furthermore, the TNFα production is enhanced by Ca²⁺ elevating agents, thapsigargin (TG), but is suppressed by treatment with Ca²⁺ chelators, EGTA, or BAPTA-AM. In addition, the soluble TNFα production is suppressed by treatment with immobilized-fibrinogen or -fibronectin. Thus, the TNFα production is enhanced by intracellular Ca²⁺ elevation and is negatively regulated by the interaction between the neutrophil-like HL60 cells and fibrinogen or fibronectin.

A Critical Role for ERO1α in Arterial Thrombosis and Ischemic Stroke

BACKGROUND

Platelet adhesion and aggregation play a crucial role in arterial thrombosis and ischemic stroke. Here, we identify platelet ERO1α (endoplasmic reticulum oxidoreductase 1α) as a novel regulator of Ca2+ signaling and a potential pharmacological target for treating thrombotic diseases.

METHODS

Intravital microscopy, animal disease models, and a wide range of cell biological studies were utilized to demonstrate the pathophysiological role of ERO1α in arteriolar and arterial thrombosis and to prove the importance of platelet ERO1α in platelet activation and aggregation. Mass spectrometry, electron microscopy, and biochemical studies were used to investigate the molecular mechanism. We used novel blocking antibodies and small-molecule inhibitors to study whether ERO1α can be targeted to attenuate thrombotic conditions.

RESULTS

Megakaryocyte-specific or global deletion of Ero1α in mice similarly reduced platelet thrombus formation in arteriolar and arterial thrombosis without affecting tail bleeding times and blood loss following vascular injury. We observed that platelet ERO1α localized exclusively in the dense tubular system and promoted Ca2+ mobilization, platelet activation, and aggregation. Platelet ERO1α directly interacted with STIM1 (stromal interaction molecule 1) and SERCA2 (sarco/endoplasmic reticulum Ca2+-ATPase 2) and regulated their functions. Such interactions were impaired in mutant STIM1-Cys49/56Ser and mutant SERCA2-Cys875/887Ser. We found that ERO1α modified an allosteric Cys49-Cys56 disulfide bond in STIM1 and a Cys875-Cys887 disulfide bond in SERCA2, contributing to Ca2+ store content and increasing cytosolic Ca2+ levels during platelet activation. Inhibition of Ero1α with small-molecule inhibitors but not blocking antibodies attenuated arteriolar and arterial thrombosis and reduced infarct volume following focal brain ischemia in mice.

CONCLUSIONS

Our results suggest that ERO1α acts as a thiol oxidase for Ca2+ signaling molecules, STIM1 and SERCA2, and enhances cytosolic Ca2+ levels, promoting platelet activation and aggregation. Our study provides evidence that ERO1α may be a potential target to reduce thrombotic events.

Deep genomic characterization highlights complexities and prognostic markers of pediatric acute myeloid leukemia

Pediatric acute myeloid leukemia (AML) is an uncommon but aggressive hematological malignancy. The poor outcome is attributed to inadequate prognostic classification and limited treatment options. A thorough understanding on the genetic basis of pediatric AML is important for the development of effective approaches to improve outcomes. Here, by comprehensively profiling fusion genes as well as mutations and copy number changes of 141 myeloid-related genes in 147 pediatric AML patients with subsequent variant functional characterization, we unveil complex mutational patterns of biological relevance and disease mechanisms including MYC deregulation. Also, our findings highlight TP53 alterations as strong adverse prognostic markers in pediatric AML and suggest the core spindle checkpoint kinase BUB1B as a selective dependency in this aggressive subgroup. Collectively, our present study provides detailed genomic characterization revealing not only complexities and mechanistic insights into pediatric AML but also significant risk stratification and therapeutic strategies to tackle the disease.

Stromal Interaction Molecule 1 (STIM1) is a Potential Prognostic Biomarker and Correlates with Immune Infiltrates in Solid Tumors

Increasing evidence has shown that stromal interaction molecule 1 (STIM1), a key subunit of store-operated Ca2+ entry (SOCE), is closely associated with tumor growth, development, and metastasis. However, there is no report of a comprehensive assessment of STIM1 in pan-cancer. This study aimed to perform a general analysis of STIM1 in human tumors, including its molecular characteristics, functional mechanisms, clinical significance, and immune infiltrates correlation based on pan-cancer data from The Cancer Genome Atlas (TCGA). Gene expression analysis was investigated using TCGA RNA-seq data, the Tumor Immune Estimation Resource (TIMER). Phosphorylation analysis was undertaken using the Clinical Proteomic Tumor Analysis Consortium (CP-TAC) and the PhosphoNET database. Genetic alterations of STIM1 were analyzed using cBioPortal. Prognostic analysis was via the R package "survival" function and the Kaplan-Meier plotter. Functional enrichment analysis was via by the R package "cluster Profiler" function. The association between STIM1 and tumor-infiltrating immune cells and immune markers was by the R package "GSVA" function and TIMER. STIM1 was differentially expressed and associated with distinct clinical stages in multiple tumors. The phosphorylation of STIM1 at S673 is highly expressed in clear cell renal carcinoma and lung adenocarcinoma tumors compared to normal tissues. STIM1 genetic alterations correlate with poor prognosis in several tumors, including ovarian cancer and lung squamous cell carcinomas. High STIM1 expression is associated with good or poor prognosis across diverse tumors. Overall survival (OS) analysis indicated that STIM1 is a favorable prognostic factor for patients with BRCA, KIRC, LIHC, LUAD, OV, SARC, and UCEC, and is a risk prognostic factor for BLCA, KIRP, STAD, and UVM. There is a close correlation between STIM1 expression and immune cell infiltration, immune-regulated genes, chemokines, and immune checkpoints in a variety of tumors. STIM1 functions differently in diverse tumors, playing an oncogenic or antitumor role. Moreover, It may serve as a prognostic biomarker and an immunotherapy target across multiple tumors.

Dusp6 deficiency attenuates neutrophil-mediated cardiac damage in the acute inflammatory phase of myocardial infarction

Dual-specificity phosphatase 6 (DUSP6) serves a specific and conserved function on the dephosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2). We previously identified Dusp6 as a regenerative repressor during zebrafish heart regeneration, therefore we propose to investigate the role of this repressor in mammalian cardiac repair. Utilizing a rat strain harboring Dusp6 nonsense mutation, rat neutrophil-cardiomyocyte co-culture, bone marrow transplanted rats and neutrophil-specific Dusp6 knockout mice, we find that Dusp6 deficiency improves cardiac outcomes by predominantly attenuating neutrophil-mediated myocardial damage in acute inflammatory phase after myocardial infarction. Mechanistically, Dusp6 is transcriptionally activated by p38-C/EBPβ signaling and acts as an effector for maintaining p-p38 activity by down-regulating pERK and p38-targeting phosphatases DUSP1/DUSP16. Our findings provide robust animal models and novel insights for neutrophil-mediated cardiac damage and demonstrate the potential of DUSP6 as a therapeutic target for post-MI cardiac remodeling and other relevant inflammatory diseases.

Intravital calcium imaging in myeloid leukocytes identifies calcium frequency spectra as indicators of functional states

The assessment of leukocyte activation in vivo is mainly based on surrogate parameters, such as cell shape changes and migration patterns. Consequently, additional parameters are required to dissect the complex spatiotemporal activation of leukocytes during inflammation. Here, we showed that intravital microscopy of myeloid leukocyte Ca²⁺ signals with Ca²⁺ reporter mouse strains combined with bioinformatic signal analysis provided a tool to assess their activation in vivo. We demonstrated by two-photon microscopy that tissue-resident macrophages reacted to sterile inflammation in the cremaster muscle with Ca²⁺ transients in a distinct spatiotemporal pattern. Moreover, through high-resolution, intravital spinning disk confocal microscopy, we identified the intracellular Ca²⁺ signaling patterns of neutrophils during the migration cascade in vivo. These patterns were modulated by the Ca²⁺ channel Orai1 and Gα_i-coupled GPCRs, whose effects were evident through analysis of the range of frequencies of the Ca²⁺ signal (frequency spectra), which provided insights into the complex patterns of leukocyte Ca²⁺ oscillations. Together, these findings establish Ca²⁺ frequency spectra as an additional dimension to assess leukocyte activation and migration during inflammation in vivo.

Spatiotemporal dynamics of calcium signals during neutrophil cluster formation

Neutrophils form cellular clusters or swarms in response to injury or pathogen intrusion. Yet, intracellular signaling events favoring this coordinated response remain to be fully characterized. Here, we show that calcium signals play a critical role during mouse neutrophil clustering around particles of zymosan, a structural fungal component. Pioneer neutrophils recognizing zymosan or live Candida albicans displayed elevated calcium levels. Subsequently, a transient wave of calcium signals in neighboring cells was observed followed by the attraction of neutrophils that exhibited more persistent calcium signals as they reached zymosan particles. Calcium signals promoted LTB4 production while the blocking of extracellular calcium entry or LTB4 signaling abrogated cluster formation. Finally, using optogenetics to manipulate calcium influx in primary neutrophils, we show that calcium signals could initiate recruitment of neighboring neutrophils in an LTB4-dependent manner. Thus, sustained calcium responses at the center of the cluster are necessary and sufficient for the generation of chemoattractive gradients that attract neutrophils in a self-reinforcing process.

Immune Cell Plasticity in Inflammation: Insights into Description and Regulation of Immune Cell Phenotypes

Inflammation is a life-saving immune reaction occurring in response to invading pathogens. Nonetheless, inflammation can also occur in an uncontrolled, unrestricted manner, leading to chronic disease and organ damage. Mechanisms triggering an inflammatory response, hindering such a response, or leading to its resolution are well-studied but so far insufficiently elucidated with regard to precise therapeutic interventions. Notably, as an immune reaction evolves, requirements and environments for immune cells change, and thus cellular phenotypes adapt and shift, leading to the appearance of distinct cellular subpopulations with new functional features. In this article, we aim to highlight properties of, and overarching regulatory factors involved in, the occurrence of immune cell phenotypes with a special focus on neutrophils, macrophages and platelets. Additionally, we point out implications for both diagnostics and therapeutics in inflammation research.

Neutrophils in acute inflammation: current concepts and translational implications

Modulation of neutrophil recruitment and function is crucial for targeting inflammatory cells to sites of infection to combat invading pathogens while, at the same time, limiting host tissue injury or autoimmunity. The underlying mechanisms regulating recruitment of neutrophils, 1 of the most abundant inflammatory cells, have gained increasing interest over the years. The previously described classical recruitment cascade of leukocytes has been extended to include capturing, rolling, adhesion, crawling, and transmigration, as well as a reverse-transmigration step that is crucial for balancing immune defense and control of remote organ endothelial leakage. Current developments in the field emphasize the importance of cellular interplay, tissue environmental cues, circadian rhythmicity, detection of neutrophil phenotypes, differential chemokine sensing, and contribution of distinct signaling components to receptor activation and integrin conformations. The use of therapeutics modulating neutrophil activation responses, as well as mutations causing dysfunctional neutrophil receptors and impaired signaling cascades, have been defined in translational animal models. Human correlates of such mutations result in increased susceptibility to infections or organ damage. This review focuses on current advances in the understanding of the regulation of neutrophil recruitment and functionality and translational implications of current discoveries in the field with a focus on acute inflammation and sepsis.

Single-Cell RNA-Seq Reveals the Promoting Role of Ferroptosis Tendency During Lung Adenocarcinoma EMT Progression

Epithelial-mesenchymal transition (EMT) and ferroptosis are two important processes in biology. In tumor cells, they are intimately linked. We used single-cell RNA sequencing to investigate the regulatory connection between EMT and ferroptosis tendency in LUAD epithelial cells. We used Seurat to construct the expression matrix using the GEO dataset GSE131907 and extract epithelial cells. We found a positive correlation between the trends of EMT and ferroptosis tendency. Then we used SCENIC to analyze differentially activated transcription factors and constructed a molecular regulatory directed network by causal inference. Some ferroptosis markers (GPX4, SCP2, CAV1) were found to have strong regulatory effects on EMT. Cell communication networks were constructed by iTALK and implied that Ferro_High_EMT_High cells have a higher expression of SDC1, SDC4, and activation of LGALS9-HARVCR2 pathways. By deconvolution of bulk sequencing, the results of CIBERSORTx showed that the co-occurrence of ferroptosis tendency and EMT may lead to tumor metastasis and non-response to immunotherapy. Our findings showed there is a strong correlation between ferroptosis tendency and EMT. Ferroptosis may have a promotive effect on EMT. High propensities of ferroptosis and EMT may lead to poor prognosis and non-response to immunotherapy.

Clinical value of serum calcium in elderly patients with sepsis

PURPOSE

To explore the clinical value of serum calcium (Ca) in elderly patients with sepsis.

MATERIALS AND METHODS

The clinical data and laboratory data of elderly patients with sepsis (n = 165) and elderly population for physical examination (n = 67) in a tertiary hospital from January 2020 to November 2020 were collected. We analyzed serum Ca levels in sepsis and septic shock firstly, and then continued to investigate them in the survival group and the death group. Meanwhile, we also assessed the correlation between serum Ca and PCT.

RESULTS

The serum Ca levels of the elderly patients with sepsis were lower than that of the control group (median 1.98 vs 2.31 mmol/L, P < 0.001), and the more severe the sepsis, the lower the serum Ca levels. Sepsis patients with decreased serum Ca had higher shock rate and mortality. There was a negative correlation between serum Ca and PCT (r = -0.2957, P < 0.001).

CONCLUSION

Serum Ca has a certain value for the early recognition of elderly patients with sepsis and the judgment of the severity of the disease.

Role of S100A8/A9 for Cytokine Secretion, Revealed in Neutrophils Derived from ER-Hoxb8 Progenitors

S100A9, a Ca²⁺-binding protein, is tightly associated to neutrophil pro-inflammatory functions when forming a heterodimer with its S100A8 partner. Upon secretion into the extracellular environment, these proteins behave like damage-associated molecular pattern molecules, which actively participate in the amplification of the inflammation process by recruitment and activation of pro-inflammatory cells. Intracellular functions have also been attributed to the S100A8/A9 complex, notably its ability to regulate nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation. However, the complete functional spectrum of S100A8/A9 at the intracellular level is far from being understood. In this context, we here investigated the possibility that the absence of intracellular S100A8/A9 is involved in cytokine secretion. To overcome the difficulty of genetically modifying neutrophils, we used murine neutrophils derived from wild-type and S100A9^−/− Hoxb8 immortalized myeloid progenitors. After confirming that differentiated Hoxb8 neutrophil-like cells are a suitable model to study neutrophil functions, our data show that absence of S100A8/A9 led to a dysregulation of cytokine secretion after lipopolysaccharide (LPS) stimulation. Furthermore, we demonstrate that S100A8/A9-induced cytokine secretion was regulated by the nuclear factor kappa B (NF-κB) pathway. These results were confirmed in human differentiated HL-60 cells, in which S100A9 was inhibited by shRNAs. Finally, our results indicate that the degranulation process could be involved in the regulation of cytokine secretion by S100A8/A9.

Neutrophils in Tumorigenesis: Missing Targets for Successful Next Generation Cancer Therapies?

Neutrophils—once considered as simple killers of pathogens and unexciting for cancer research—are now acknowledged for their role in the process of tumorigenesis. Neutrophils are recruited to the tumor microenvironment where they turn into tumor-associated neutrophils (TANs), and are able to initiate and promote tumor progression and metastasis. Conversely, anti-tumorigenic properties of neutrophils have been documented, highlighting the versatile nature and high pleiotropic plasticity of these polymorphonuclear leukocytes (PMN-L). Here, we dissect the ambivalent roles of TANs in cancer and focus on selected functional aspects that could be therapeutic targets. Indeed, the critical point of targeting TAN functions lies in the fact that an immunosuppressive state could be induced, resulting in unwanted side effects. A deeper knowledge of the mechanisms linked to diverse TAN functions in different cancer types is necessary to define appropriate therapeutic strategies that are able to induce and maintain an anti-tumor microenvironment.

A sustained type I IFN-neutrophil-IL-18 axis drives pathology during mucosal viral infection

Neutrophil responses against pathogens must be balanced between protection and immunopathology. Factors that determine these outcomes are not well-understood. In a mouse model of genital herpes simplex virus-2 (HSV-2) infection, which results in severe genital inflammation, antibody-mediated neutrophil depletion reduced disease. Comparative single-cell RNA-sequencing analysis of vaginal cells against a model of genital HSV-1 infection, which results in mild inflammation, demonstrated sustained expression of interferon-stimulated genes (ISGs) only after HSV-2 infection primarily within the neutrophil population. Both therapeutic blockade of IFNα/β receptor 1 (IFNAR1) and genetic deletion of IFNAR1 in neutrophils concomitantly decreased HSV-2 genital disease severity and vaginal IL-18 levels. Therapeutic neutralization of IL-18 also diminished genital inflammation, indicating an important role for this cytokine in promoting neutrophil-dependent immunopathology. Our study reveals that sustained type I interferon (IFN) signaling is a driver of pathogenic neutrophil responses and identifies IL-18 as a novel component of disease during genital HSV-2 infection.

Ion and Water Transport in Neutrophil Granulocytes and Its Impairment during Sepsis

Neutrophil granulocytes are the vanguard of innate immunity in response to numerous pathogens. Their activity drives the clearance of microbe- and damage-associated molecular patterns, thereby contributing substantially to the resolution of inflammation. However, excessive stimulation during sepsis leads to cellular unresponsiveness, immunological dysfunction, bacterial expansion, and subsequent multiple organ dysfunction. During the short lifespan of neutrophils, they can become significantly activated by complement factors, cytokines, and other inflammatory mediators. Following stimulation, the cells respond with a defined (electro-)physiological pattern, including depolarization, calcium influx, and alkalization as well as with increased metabolic activity and polarization of the actin cytoskeleton. Activity of ion transport proteins and aquaporins is critical for multiple cellular functions of innate immune cells, including chemotaxis, generation of reactive oxygen species, and phagocytosis of both pathogens and tissue debris. In this review, we first describe the ion transport proteins and aquaporins involved in the neutrophil ion-water fluxes in response to chemoattractants. We then relate ion and water flux to cellular functions with a focus on danger sensing, chemotaxis, phagocytosis, and oxidative burst and approach the role of altered ion transport protein expression and activity in impaired cellular functions and cell death during systemic inflammation as in sepsis.

The coordinated outcome of STIM1-Orai1 and superoxide signalling is crucial for headkidney macrophage apoptosis and clearance of Mycobacterium fortuitum

The mechanisms underlying M. fortuitum-induced pathogenesis remains elusive. Using headkidney macrophages (HKM) from Clarias gariepinus, we report that TLR-2-mediated internalization of M. fortuitum is imperative to the induction of pathogenic effects. Inhibiting TLR-2 signalling alleviated HKM apoptosis, thereby favouring bacterial survival. Additionally, TLR-2-mediated cytosolic calcium (Ca²⁺)_c elevation was instrumental for eliciting ER-stress in infected HKM. ER-stress triggered the activation of membrane-proximal calcium entry channels comprising stromal interaction molecule 1 (STIM1) and calcium-release activated calcium channel 1 (Orai1). RNAi studies suggested STIM1-Orai1 signalling initiate calpain-mediated cleavage of nitric oxide synthase interacting protein, prompting the release of pro-apoptotic nitric oxide. Inhibiting STIM1-Orai1 signalling attenuated superoxide production (O₂^•-) and vice versa. We conclude, TLR-2-induced ER-stress triggers STIM1/Orai1 expression and that the reciprocal association between STIM1-Orai1 signalling and oxidative stress is critical for sustaining (Ca²⁺)_c level, thereby prolonging ER-stress and maintenance of pro-oxidant rich environment to induce HKM apoptosis and bacterial clearance.

Oxidative Stress-Induced STIM2 Cysteine Modifications Suppress Store-Operated Calcium Entry

Store-operated calcium entry (SOCE) through STIM-gated ORAI channels governs vital cellular functions. In this context, SOCE controls cellular redox signaling and is itself regulated by redox modifications. However, the molecular mechanisms underlying this calcium-redox interplay and the functional outcomes are not fully understood. Here, we examine the role of STIM2 in SOCE redox regulation. Redox proteomics identify cysteine 313 as the main redox sensor of STIM2 in vitro and in vivo. Oxidative stress suppresses SOCE and calcium currents in cells overexpressing STIM2 and ORAI1, an effect that is abolished by mutation of cysteine 313. FLIM and FRET microscopy, together with MD simulations, indicate that oxidative modifications of cysteine 313 alter STIM2 activation dynamics and thereby hinder STIM2-mediated gating of ORAI1. In summary, this study establishes STIM2-controlled redox regulation of SOCE as a mechanism that affects several calcium-regulated physiological processes, as well as stress-induced pathologies.

ORAI1 and ORAI2 modulate murine neutrophil calcium signaling, cellular activation, and host defense

Calcium signals are initiated in immune cells by the process of store-operated calcium entry (SOCE), where receptor activation triggers transient calcium release from the endoplasmic reticulum, followed by opening of plasma-membrane calcium-release activated calcium (CRAC) channels. ORAI1, ORAI2, and ORAI3 are known to comprise the CRAC channel; however, the contributions of individual isoforms to neutrophil function are not well understood. Here, we show that loss of ORAI1 partially decreases calcium influx, while loss of both ORAI1 and ORAI2 completely abolishes SOCE. In other immune-cell types, loss of ORAI2 enhances SOCE. In contrast, we find that ORAI2-deficient neutrophils display decreased calcium influx, which is correlated with measurable differences in the regulation of neutrophil membrane potential via KCa3.1. Decreased SOCE in ORAI1-, ORAI2-, and ORAI1/2-deficient neutrophils impairs multiple neutrophil functions, including phagocytosis, degranulation, leukotriene, and reactive oxygen species (ROS) production, rendering ORAI1/2-deficient mice highly susceptible to staphylococcal infection. This study demonstrates that ORAI1 and ORAI2 are the primary components of the neutrophil CRAC channel and identifies subpopulations of neutrophils where cell-membrane potential functions as a rheostat to modulate the SOCE response. These findings have implications for mechanisms that modulate neutrophil function during infection, acute and chronic inflammatory conditions, and cancer.

The Ubiquitin-Modifying Enzyme A20 Terminates C-Type Lectin Receptor Signals and Is a Suppressor of Host Defense against Systemic Fungal Infection

C-type lectin receptors (CLRs) play key roles in antifungal defense. CLR-induced NF-κB is central to CLR functions in immunity, and thus, molecules that control the amplitude of CLR-induced NF-κB could profoundly influence host defense against fungal pathogens. However, little is known about the mechanisms that negatively regulate CLR-induced NF-κB, and molecules which act on the CLR family broadly and which directly regulate acute CLR-signaling cascades remain unidentified. Here, we identify the ubiquitin-editing enzyme A20 as a negative regulator of acute NF-κB activation downstream of multiple CLR pathways. Absence of A20 suppression results in exaggerated CLR responses in cells which are A20 deficient and also cells which are A20 haplosufficient, including multiple primary immune cells. Loss of a single allele of A20 results in enhanced defense against systemic Candida albicans infection and prolonged host survival. Thus, A20 restricts CLR-induced innate immune responses in vivo and is a suppressor of host defense against systemic fungal infection.

CRAC Channels and Calcium Signaling in T Cell-Mediated Immunity

Calcium (Ca²⁺) signals play fundamental roles in immune cell function. The main sources of Ca²⁺ influx in mammalian lymphocytes following antigen receptor stimulation are Ca²⁺ release-activated Ca²⁺ (CRAC) channels. These are formed by ORAI proteins in the plasma membrane and are activated by stromal interaction molecules (STIM) located in the endoplasmic reticulum (ER). Human loss-of-function (LOF) mutations in ORAI1 and STIM1 that abolish Ca²⁺ influx cause a unique disease syndrome called CRAC channelopathy that is characterized by immunodeficiency autoimmunity and non-immunological symptoms. Studies in mice lacking Stim and Orai genes have illuminated many cellular and molecular mechanisms by which these molecules control lymphocyte function. CRAC channels are required for the differentiation and function of several T lymphocyte subsets that provide immunity to infection, mediate inflammation and prevent autoimmunity. This review examines new insights into how CRAC channels control T cell-mediated immunity.

Modulation of Cerebral Store-operated Calcium Entry-regulatory Factor (SARAF) and Peripheral Orai1 Following Focal Cerebral Ischemia and Preconditioning in Mice

Store-operated Ca²⁺ entry (SOCE) contributes to Ca²⁺ refilling of endoplasmic reticulum (ER), but also provides Ca²⁺ influx involved in physiological and pathological signalling functions. Upon depletion of Ca²⁺ store, the sensor protein stromal interaction molecule (STIM) activates Orai1, forming an ion-conducting pore highly selective for Ca²⁺. SOCE-associated regulatory factor (SARAF) associates with STIM1 to facilitate a slow form of Ca²⁺-dependent inactivation of SOCE or interacts with Orai1 to stimulate SOCE in STIM1-independent manner. We have investigated whether cerebral ischemic damage and neuroprotection conferred by ischemic preconditioning (PC) in mouse are associated with changes in the expression of the molecular components of SOCE. Ischemic PC induced by 15-min occlusion of the middle cerebral artery (MCAo) resulted in significant amelioration of histological and functional outcomes produced, 72 h later, by a more severe ischemia (1 h MCAo). Neither ischemia, nor PC affected the expression of Orai1 in the frontoparietal cortex. However, the number of Orai1-immunopositive cells, mostly corresponding to Ly-6G+ neutrophils, was significantly elevated in the blood after the ischemic insult, regardless of previous PC. The expression of Stim1 and SARAF, mainly localised in NeuN-immunopositive neurons, was reduced in the ischemic cortex. Interestingly, neuroprotection by ischemic PC prevented the reduction of SARAF expression in the lesioned cortex and this could be interpreted as a compensatory mechanism to restore ER Ca²⁺ refilling in neurons in the absence of STIM1. Thus, preventing SARAF downregulation may represent a pivotal mechanism implicated in neuroprotection provided by ischemic PC and should be exploited as an original target for novel stroke therapies.

NADPH oxidase controls pulmonary neutrophil infiltration in the response to fungal cell walls by limiting LTB4

Leukocyte reduced NADP (NADPH) oxidase plays a key role in host defense and immune regulation. Genetic defects in NADPH oxidase result in chronic granulomatous disease (CGD), characterized by recurrent bacterial and fungal infections and aberrant inflammation. Key drivers of hyperinflammation induced by fungal cell walls in CGD are still incompletely defined. In this study, we found that CGD (CYBB-) neutrophils produced higher amounts of leukotriene B4 (LTB4) in vitro after activation with zymosan or immune complexes, compared with wild-type (WT) neutrophils. This finding correlated with increased calcium influx in CGD neutrophils, which was restrained in WT neutrophils by the electrogenic activity of NADPH oxidase. Increased LTB4 generation by CGD neutrophils was also augmented by paracrine cross talk with the LTB4 receptor BLT1. CGD neutrophils formed more numerous and larger clusters in the presence of zymosan in vitro compared with WT cells, and the effect was also LTB4- and BLT1-dependent. In zymosan-induced lung inflammation, focal neutrophil infiltrates were increased in CGD compared with WT mice and associated with higher LTB4 levels. Inhibiting LTB4 synthesis or antagonizing the BLT1 receptor after zymosan challenge reduced lung neutrophil recruitment in CGD to WT levels. Thus, LTB4 was the major driver of excessive neutrophilic lung inflammation in CGD mice in the early response to fungal cell walls, likely by a dysregulated feed-forward loop involving amplified neutrophil production of LTB4. This study identifies neutrophil LTB4 generation as a target of NADPH oxidase regulation, which could potentially be exploited therapeutically to reduce excessive inflammation in CGD.

Molecular Mechanisms of Calcium Signaling During Phagocytosis

Calcium (Ca²⁺) is a ubiquitous second messenger involved in the regulation of numerous cellular functions including vesicular trafficking, cytoskeletal rearrangements and gene transcription. Both global as well as localized Ca²⁺ signals occur during phagocytosis, although their functional impact on the phagocytic process has been debated. After nearly 40 years of research, a consensus may now be reached that although not strictly required, Ca²⁺ signals render phagocytic ingestion and phagosome maturation more efficient, and their manipulation make an attractive avenue for therapeutic interventions. In the last decade many efforts have been made to identify the channels and regulators involved in generating and shaping phagocytic Ca²⁺ signals. While molecules involved in store-operated calcium entry (SOCE) of the STIM and ORAI family have taken center stage, members of the canonical, melastatin, mucolipin and vanilloid transient receptor potential (TRP), as well as purinergic P2X receptor families are now recognized to play significant roles. In this chapter, we review the recent literature on research that has linked specific Ca²⁺-permeable channels and regulators to phagocytic function. We highlight the fact that lipid mediators are emerging as important regulators of channel gating and that phagosomal ionic homeostasis and Ca²⁺ release also play essential parts. We predict that improved methodologies for measuring these factors will be critical for future advances in dissecting the intricate biology of this fascinating immune process.

Calcium signaling and regulation of neutrophil functions: Still a long way to go

Neutrophils are the most abundant leukocytes in blood and disruption in their functions often results in an increased risk of serious infections and inflammatory autoimmune diseases. Following recent discoveries in their influence over disease progression, a resurgence of interest for neutrophil biology has taken place. The multitude of signaling pathways activated by the engagement of numerous types of receptors, with which neutrophils are endowed, reflects the functional complexity of these cells. It is therefore not surprising that there remains a huge lack in the understanding of molecular mechanisms underlining neutrophil functions. Moreover, studies on neutrophils are undoubtedly limited by the difficulty to efficiently edit the cell's genome. Over the past 30 years, compelling evidence has clearly highlighted that Ca²⁺ -signaling is governing the key processes associated with neutrophil functions. The confirmation of the role of an elevation of intracellular Ca²⁺ concentration has come from studies on NADPH oxidase activation and phagocytosis. In this review, we give an overview and update of our current knowledge on the role of Ca²⁺ mobilization in the regulation of pro-inflammatory functions of neutrophils. In particular, we stress the importance of Ca²⁺ in the formation of NETs and cytokine secretion in the light of newest findings. This will allow us to embrace how much further we have to go to understand the complex dynamics of Ca²⁺ -dependent mechanisms in order to gain more insights into the role of neutrophils in the pathogenesis of inflammatory diseases. The potential for therapeutics to regulate the neutrophil functions, such as Ca²⁺ influx inhibitors to prevent autoimmune and chronic inflammatory diseases, has been discussed in the last part of the review.

Neutrophil β-defensin gene expression of postpartum dairy cows is altered by prepartum dietary cation-anion difference

The objective of this study was to evaluate expression of a cluster of genes encoding β-defensin antimicrobial peptides in neutrophils of postpartum cows in relation to prepartum dietary cation-anion difference (DCAD), vitamin D, and postpartum disease. Pregnant dry Holstein cows (28 nulliparous and 51 parous) at 255 d gestation were blocked by parity and randomly assigned to 4 prepartum diets of positive (+130 mEq/kg) or negative (-130 mEq/kg) DCAD and either 3 mg vitamin D₃ or 3 mg of 25-hydroxyvitamin D₃ per 11 kg of dry matter/d. Treatment diets were fed from 255 d of gestation until calving. Peripheral blood neutrophils of 35 parous cows were collected at 0 and 3 d after calving and stimulated with 0 or 100 ng/mL of lipopolysaccharide (LPS). Furthermore, serum Ca and incidences of postpartum diseases were recorded for all cows. The mRNA transcripts of β-defensin genes were quantified by real-time PCR, and data were analyzed with a general linear mixed model to test for fixed effects and interactions of day, level of DCAD, source of vitamin D, and incidence of disease. Effects of DCAD and vitamin D on neutrophil oxidative burst and phagocytosis were previously reported but were analyzed for effects of disease in the present study. Transcripts for DEFB1, DEFB3, DEFB4, DEFB5, DEFB7, DEFB10, and lingual antimicrobial peptide (LAP) in neutrophils were upregulated by LPS at 0 d but not at 3 d. Transcripts for DEFB4 and DEFB7 in LPS-stimulated neutrophils were greater in cows fed negative DCAD diets compared with positive DCAD. Source of vitamin D (vitamin D₃ vs. 25-hydroxyvitamin D₃) did not affect expression of β-defensins in neutrophils. Cows with postpartum subclinical hypocalcemia (serum Ca <2.0 mM) had decreased DEFB3, DEFB4, DEFB6, DEFB7, DEFB10, and LAP expression in LPS-stimulated neutrophils compared with cows that did not experience subclinical hypocalcemia. Likewise, DEFB4, DEFB6, DEFB7, DEFB10, and LAP in LPS-stimulated neutrophils at 3 d postpartum were positively associated with serum Ca at 0 d postpartum. Transcripts for DEFB7, DEFB10 and LAP also were less abundant in neutrophils from cows with metritis compared with healthy cows. In conclusion, feeding a prepartum negative DCAD to improve postpartum serum Ca resulted in greater neutrophil β-defensin expression, and greater neutrophil β-defensin expression was positively associated with postpartum health.

Leucine-rich repeat kinase 2 regulates mouse dendritic cell migration by ORAI2

The leucine-rich repeat kinase 2 (LRRK2) is expressed in various immune cells and involved in regulating inflammatory processes. LRRK2 facilitates calcium extrusion exchanger and sodium-calcium exchanger activity and hence influences intracellular Ca²⁺ concentration in dendritic cells (DCs). DC maturation and migration are governed by the intracellular Ca²⁺ concentration, but the related mechanisms whereby LRRK2 regulates DC function and involved Ca²⁺ channels are still under investigation. In the previous study, we found that LRRK2^-/- DCs exhibited higher store-operated Ca²⁺ entry (SOCE) activity than LRRK2^+/+ DCs. Herein, we ascertained the exact SOCE components by using genetic, pharmacological, and fluorescent approaches. Ca²⁺ imaging showed that LRRK2 kinase activity negatively modulated SOCE activity. Moreover, LRRK2 deficiency resulted in an enhanced migration capacity of DCs but had little effect on the maturation process. SOCE is widely known to regulate DC functions; we wanted to dissect the reason why LRRK2 specifically influenced DC migration and therefore silenced ORAI1, ORAI2, and ORAI3, respectively. Transwell assays showed that both ORAI1 and ORAI2 silencing markedly decreased the migration of DCs, but only ORAI1 deficiency influenced the expression of maturation markers CD11c, CD86, and major histocompatibility complex class II. Of note, LRRK2 deficiency increased ORAI2 expression but not that of ORAI1 and ORAI3. Thus, we suggest that LRRK2 modulates DC migration by interfering with ORAI2.-Yan, J., Zhao, W., Gao, C., Liu, X., Zhao, X., Wei, T., Gao, Z. Leucine-rich repeat kinase 2 regulates mouse dendritic cell migration by ORAI2.

The Orai Ca2+ channel inhibitor CM4620 targets both parenchymal and immune cells to reduce inflammation in experimental acute pancreatitis

KEY POINTS

This work confirms previous reports that CM4620, a small molecule inhibitor of Ca2+ entry via store operated Ca2+ entry (SOCE) channels formed by stromal interaction molecule 1 (STIM1)/Orai complexes, attenuates acinar cell pathology and acute pancreatitis in mouse experimental models. Here we report that intravenous administration of CM4620 reduces the severity of acute pancreatitis in the rat, a hitherto untested species. Using CM4620, we probe further the mechanisms whereby SOCE via STIM1/Orai complexes contributes to the disease in pancreatic acinar cells, supporting a role for endoplasmic reticulum stress/cell death pathways in these cells. Using CM4620, we show that SOCE via STIM1/Orai complexes promotes neutrophil oxidative burst and inflammatory gene expression during acute pancreatitis, including in immune cells which may be either circulating or invading the pancreas. Using CM4620, we show that SOCE via STIM1/Orai complexes promotes activation and fibroinflammatory gene expression within pancreatic stellate cells.

ABSTRACT

Key features of acute pancreatitis include excess cellular Ca2+ entry driven by Ca2+ depletion from the endoplasmic reticulum (ER) and subsequent activation of store-operated Ca2+ entry (SOCE) channels in the plasma membrane. In several cell types, including pancreatic acinar, stellate cells (PaSCs) and immune cells, SOCE is mediated via channels composed primarily of Orai1 and stromal interaction molecule 1 (STIM1). CM4620, a selective Orai1 inhibitor, prevents Ca2+ entry in acinar cells. This study investigates the effects of CM4620 in preventing or reducing acute pancreatitis features and severity. We tested the effects of CM4620 on SOCE, trypsinogen activation, acinar cell death, activation of NFAT and NF-κB, and inflammatory responses in ex vivo and in vivo rodent models of acute pancreatitis and human pancreatic acini. We also examined whether CM4620 inhibited cytokine release in immune cells, fibro-inflammatory responses in PaSCs, and oxidative burst in neutrophils, all cell types participating in pancreatitis. CM4620 administration to rats by i.v. infusion starting 30 min after induction of pancreatitis significantly diminished pancreatitis features including pancreatic oedema, acinar cell vacuolization, intrapancreatic trypsin activity, cell death signalling and acinar cell death. CM4620 also decreased myeloperoxidase activity and inflammatory cytokine expression in pancreas and lung tissues, fMLF peptide-induced oxidative burst in human neutrophils, and cytokine production in human peripheral blood mononuclear cells (PBMCs) and rodent PaSCs, indicating that Orai1/STIM1 channels participate in the inflammatory responses of these cell types during acute pancreatitis. These findings support pathological Ca2+ entry-mediated cell death and proinflammatory signalling as central mechanisms in acute pancreatitis pathobiology.

Tmem178 negatively regulates store-operated calcium entry in myeloid cells via association with STIM1

Store-operated calcium entry (SOCE) modulates cytosolic calcium in multiple cells. Endoplasmic reticulum (ER)-localized STIM1 and plasma membrane (PM)-localized ORAI1 are two main components of SOCE. STIM1:ORAI1 association requires STIM1 oligomerization, its re-distribution to ER-PM junctions, and puncta formation. However, little is known about the negative regulation of these steps to prevent calcium overload. Here, we identified Tmem178 as a negative modulator of STIM1 puncta formation in myeloid cells. Using site-directed mutagenesis, co-immunoprecipitation assays and FRET imaging, we determined that Tmem178:STIM1 association occurs via their transmembrane motifs. Mutants that increase Tmem178:STIM1 association reduce STIM1 puncta formation, SOCE activation, impair inflammatory cytokine production in macrophages and osteoclastogenesis. Mutants that reduce Tmem178:STIM1 association reverse these effects. Furthermore, exposure to plasma from arthritic patients decreases Tmem178 expression, enhances SOCE activation and cytoplasmic calcium. In conclusion, Tmem178 modulates the rate-limiting step of STIM1 puncta formation and therefore controls SOCE in inflammatory conditions.

Pivotal role of STIM2, but not STIM1, in IL-4 production by IL-3-stimulated murine basophils

Basophils have nonredundant roles in various immune responses that require Ca²⁺ influx. Here, we examined the role of two Ca²⁺ sensors, stromal interaction molecule 1 and 2 (STIM1 and STIM2), in basophil activation. We found that loss of STIM1, but not STIM2, impaired basophil IL-4 production after stimulation with immunoglobulin E (IgE)-containing immune complexes. In contrast, when basophils were stimulated with IL-3, loss of STIM2, but not STIM1, reduced basophil IL-4 production. This difference in STIM proteins was associated with distinct time courses of Ca²⁺ influx and transcription of the Il4 gene that were elicited by each stimulus. Similarly, basophil-specific STIM1 expression was required for IgE-driven chronic allergic inflammation in vivo, whereas STIM2 was required for IL-4 production after combined IL-3 and IL-33 treatment in mice. These data indicate that STIM1 and STIM2 have differential roles in the production of IL-4, which are stimulus dependent. Furthermore, these results illustrate the vital role of STIM2 in basophils, which is often considered to be less important than STIM1.

Mechanical features of endothelium regulate cell adhesive molecule-induced calcium response in neutrophils

Atherosclerosis is caused by chronic inflammation associated with the adhesion of neutrophils and endothelial cells (ECs) that is mediated by their respective cellular adhesive molecules to stiffened blood vessel walls. However, the stiffness dependence of calcium flux on neutrophils remains unclear yet. Here, the effect of substrate stiffness by ECs on neutrophils' calcium spike was quantified when the individual neutrophils that adhered to the human umbilical vascular endothelial cell (HUVEC) monolayer were pre-placed onto a stiffness-varied polyacrylamide substrate (5 or 34.88 kPa) or glass surface. Our data indicated that E-/P-selectins and intercellular adhesion molecule 1 (ICAM-1) on HUVECs and β₂-integrins, P-selectin glycoprotein ligand 1 (PSGL-1), and CD44s on neutrophils were all involved in mediating neutrophil calcium spike in a stiffness-dependent manner, in which the increase in substrate stiffness enhanced the calcium intensity and the oscillation frequency (spike number). Such stiffness-dependent calcium response is associated with the induced selectin related to β₂-integrin activation through the Syk/Src signaling pathway, and F-actin/myosin II are also involved in this. Moreover, tension-activated calcium ion channels displayed critical roles in initiating stiffness-dependent calcium spike. These results provide an insight into understanding how the stiffening of vascular walls could regulate the calcium flux of adhered neutrophils, and thus the immune responses in atherosclerosis.

CRAC channel regulation of innate immune cells in health and disease

Calcium is a major intracellular signaling messenger in innate immune cells. Similar to other immune cell subsets, the majority of calcium entry into innate immune cells is induced by cell surface receptors that stimulate store-operated calcium entry through calcium-release activated calcium (CRAC) channels. Since the molecular description of the STIM family of calcium sensors and the ORAI family of CRAC channel proteins, the majority of studies support a dominant role for these proteins in calcium signaling in innate cells. In reviewing the literature on CRAC channel function in innate cells, several general themes emerge. All innate cells express multiple members of the STIM and ORAI family members, however the ratio and relative contribution of individual isoforms changes depending on the cell type and activation state of the cell. It is evident that study of functional roles for STIM molecules is clearly ahead of studies of specific ORAI family members in all innate cell types, and that studies of CRAC channels in innate cells are not nearly as advanced as studies in lymphocytes. However, taken together, evidence from both STIM calcium sensors and ORAI channels in innate cells indicates that deficiency of STIM and ORAI proteins tends not to affect the development of any innate cell lineage, but certainly affects their function, in particular activation of the neutrophil oxidase and mast cell activation via IgE receptors. Furthermore, there are clearly hints that therapeutic targeting of CRAC channels in innate cells offers a new approach to various inflammatory and allergic diseases.

Expression of calcium release-activated and voltage-gated calcium channels genes in peripheral blood mononuclear cells is altered in pregnancy and in type 1 diabetes

Calcium (Ca2+) is an important ion in physiology and is found both outside and inside cells. The intracellular concentration of Ca2+ is tightly regulated as it is an intracellular signal molecule and can affect a variety of cellular processes. In immune cells Ca2+ has been shown to regulate e.g. gene transcription, cytokine secretion, proliferation and migration. Ca2+ can enter the cytoplasm either from intracellular stores or from outside the cells when Ca2+ permeable ion channels in the plasma membrane open. The Ca2+ release-activated (CRAC) channel is the most prominent Ca2+ ion channel in the plasma membrane. It is formed by ORAI1-3 and the channel is opened by the endoplasmic reticulum Ca2+ sensor proteins stromal interaction molecules (STIM) 1 and 2. Another group of Ca2+ channels in the plasma membrane are the voltage-gated Ca2+ (CaV) channels. We examined if a change in immunological tolerance is accompanied by altered ORAI, STIM and CaV gene expression in peripheral blood mononuclear cells (PBMCs) in pregnant women and in type 1 diabetic individuals. Our results show that in pregnancy and type 1 diabetes ORAI1-3 are up-regulated whereas STIM1 and 2 are down-regulated in pregnancy but only STIM2 in type 1 diabetes. Expression of L-, P/Q-, R- and T-type voltage-gated Ca2+ channels was detected in the PBMCs where the CaV2.3 gene was up-regulated in pregnancy and type 1 diabetes whereas the CaV 2.1 and CaV3.2 genes were up-regulated only in pregnancy and the CaV1.3 gene in type 1 diabetes. The results are consistent with that expression of ORAI, STIM and CaV genes correlate with a shift in immunological status of the individual in health, as during pregnancy, and in the autoimmune disease type 1 diabetes. Whether the changes are in general protective or in type 1 diabetes include some pathogenic components remains to be clarified.

Store-operated calcium entry in thrombosis and thrombo-inflammation

Cytosolic free calcium (Ca²⁺) is a second messenger regulating a wide variety of functions in blood cells, including adhesion, activation, proliferation and migration. Store-operated Ca²⁺ entry (SOCE), triggered by depletion of Ca²⁺ from the endoplasmic reticulum, provides a main mechanism of regulated Ca²⁺ influx in blood cells. SOCE is mediated and regulated by isoforms of the ion channel proteins ORAI and TRP, and the transmembrane Ca²⁺ sensors stromal interaction molecules (STIMs), respectively. This report provides an overview of the (patho)physiological importance of SOCE in blood cells implicated in thrombosis and thrombo-inflammation, i.e. platelets and immune cells. We also discuss the physiological consequences of dysregulated SOCE in platelets and immune cells and the potential of SOCE inhibition as a therapeutic option to prevent or treat arterial thrombosis as well as thrombo-inflammatory disease states such as ischemic stroke.

Calcium signalling and related ion channels in neutrophil recruitment and function

The recruitment of neutrophils to sites of inflammation, their battle against invading microorganisms through phagocytosis and the release of antimicrobial agents is a highly coordinated and tightly regulated process that involves the interplay of many different receptors, ion channels and signalling pathways. Changes in intracellular calcium levels, caused by cytosolic Ca2+ store depletion and the influx of extracellular Ca2+ via ion channels, play a critical role in synchronizing neutrophil activation and function. In this review, we provide an overview of how Ca2+ signalling is initiated in neutrophils and how changes in intracellular Ca2+ levels modulate neutrophil function.

Ion Channels and Transporters in Inflammation: Special Focus on TRP Channels and TRPC6

Allergy and autoimmune diseases are characterised by a multifactorial pathogenic background. Several genes involved in the control of innate and adaptive immunity have been associated with diseases and variably combine with each other as well as with environmental factors and epigenetic processes to shape the characteristics of individual manifestations. Systemic or local perturbations in salt/water balance and in ion exchanges between the intra- and extracellular spaces or among tissues play a role. In this field, usually referred to as elementary immunology, novel evidence has been recently acquired on the role of members of the transient potential receptor (TRP) channel family in several cellular mechanisms of potential significance for the pathophysiology of the immune response. TRP canonical channel 6 (TRPC6) is emerging as a functional element for the control of calcium currents in immune-committed cells and target tissues. In fact, TRPC6 influences leukocytes’ tasks such as transendothelial migration, chemotaxis, phagocytosis and cytokine release. TRPC6 also modulates the sensitivity of immune cells to apoptosis and influences tissue susceptibility to ischemia-reperfusion injury and excitotoxicity. Here, we provide a view of the interactions between ion exchanges and inflammation with a focus on the pathogenesis of immune-mediated diseases and potential future therapeutic implications.