The emerging role for metabolism in fueling neutrophilic inflammation

Antibody-Fab and -Fc features promote Mycobacterium tuberculosis restriction

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), a leading cause of death by an infectious disease globally, has no efficacious vaccine. Antibodies are implicated in M. tuberculosis control, but the mechanisms of action remain poorly understood. We assembled a library of monoclonal antibodies (mAb) and screened for M. tuberculosis-restrictive activity in mice, identifying protective antibodies targeting diverse antigens. To dissect the mechanism of mAb-mediated M. tuberculosis restriction, we optimized a protective lipoarabinomannan-specific mAb, generating Fc variants. In vivo analysis of these Fc variants revealed a role for Fc-effector function in M. tuberculosis restriction. Restrictive Fc variants altered distribution of M. tuberculosis across innate immune cells. Single-cell transcriptomics highlighted distinctly activated pathways within innate immune cell subpopulations, identifying early activation of neutrophils as a key signature of mAb-mediated M. tuberculosis restriction. Therefore, antibody-mediated restriction of M. tuberculosis is associated with reorganization of the tissue-level immune response to infection and depends on the collaboration of antibody Fab and Fc.

De novo DUOX2 expression in neutrophil subsets shapes the pathogenesis of intestinal disease

Infiltrating neutrophils are key effector cells in inflammatory bowel disease (IBD) while providing antimicrobial defense and tissue restitution in the intestine. The complexity of neutrophil functions in local environments underscores our limited understanding of how their adaptation in tissues influences disease progression. Here, we demonstrate that neutrophils recruited in murine colitis and infection models, idiopathic IBD, and chronic granulomatous disease-associated IBD undergo extensive transcriptional reprogramming, resulting in the emergence of neutrophil populations that feature unique DUOX2 NADPH oxidase expression. Functional studies utilizing mice with myeloid and neutrophil specific DUOX2 inactivation reveal a vital and dichotomous role for this NADPH oxidase in both colitis and intestinal infection. Niche-directed reprogramming promoted a DUOX2-dependent chemokine and cytokine-rich intestinal environment that amplified and prolonged inflammatory responses, suggesting that selectively suppressing DUOX2 may constitute an anti-inflammatory strategy for IBD treatment. Altering spatiotemporal redox signaling by de novo expression of a ROS-generating enzyme represents an important feature for functional neutrophil diversification in disease, with implications for other neutrophil-driven diseases in specialized niches.

Oxidant-Based Cytotoxic Agents During Aging: From Disturbed Energy Metabolism to Chronic Inflammation and Disease Progression

In humans, aging is an inevitable consequence of diminished growth processes after reaching maturity. The high order of biomolecules in cells and tissues is continuously disturbed by numerous physical and chemical destructive impacts. Host-derived oxidant-based cytotoxic agents (reactive species, transition free metal ions, and free heme) contribute considerably to this damage. These agents are under the control of immediately acting antagonizing principles, which are important to ensure cell and tissue homeostasis. In this review, I apply the concept of host-derived cytotoxic agents and their interplay with antagonizing principles to the aging process. During aging, energy metabolism and the supply of tissues with dioxygen and nutrients are increasingly disturbed. In addition, a chronic inflammatory state develops, a condition known as inflammaging. The balance between oxidant-based cytotoxic agents and protective mechanisms is analyzed depending on age-based physiological alterations in ATP production. Disturbances in this balance are associated with the development of age-related diseases and comorbidities. An enhanced production of reactive species from dysfunctional mitochondria, alterations in cellular redox homeostasis, and adaptations to hypoxia are highlighted. Examples of how disturbances between oxidant-based cytotoxic agents and antagonizing principles contribute to the pathogenesis of diseases in persons of advanced age are given.

Neutrophil Heterogeneity in Wound Healing

Neutrophils are the most abundant type of immune cells and also the most underestimated cell defenders in the human body. In fact, their lifespan has also been extensively revised in recent years, going from a half-life of 8-10 h to a longer lifespan of up to 5.4 days in humans; it has been discovered that their mechanisms of defense are multiple and finely modulated, and it has been suggested that the heterogeneity of neutrophils occurs as well as in other immune cells. Neutrophils also play a critical role in the wound healing process, and their involvement is not limited to the initial stages of defense against pathogens, but extends to the inflammatory phase of tissue reconstruction. Neutrophil heterogeneity has recently been reported at the presence of distinct subtypes expressing different functional states, which contribute uniquely to the different phases of innate immunity and wound healing. This heterogeneity can be induced by the local microenvironment, by the presence of specific cytokines and by the type of injury. The different functional states of neutrophils enable a finely tuned response to injury and stress, which is essential for effective healing. Understanding the functional heterogeneity of neutrophils in wound healing can unveil potential pathological profiles and therapeutic targets. Moreover, the understanding of neutrophil heterogeneity dynamics could help in designing strategies to manage excessive inflammation or impaired healing processes. This review highlights the complexity of neutrophil heterogeneity and its critical roles throughout the phases of wound healing.

Neutrophils Display Novel Partners of Cytosolic Proliferating Cell Nuclear Antigen Involved in Interferon Response in COVID-19 Patients

INTRODUCTION

Neutrophils are key players in the hyperinflammatory response during SARS-CoV-2 infection. The cytosolic proliferating cell nuclear antigen (PCNA) is a scaffolding protein highly dependent on the microenvironment status and known to interact with numerous proteins that regulate neutrophil functions. This study aimed to examine the cytosolic protein content and PCNA interactome in neutrophils from COVID-19 patients.

METHODS

Proteomic analyses were performed on neutrophil cytosols from healthy donors and patients with severe or critical COVID-19. In vitro approaches were used to explore the biological significance of the COVID-19-specific PCNA interactome.

RESULTS

Neutrophil cytosol analysis revealed a strong interferon (IFN) protein signature, with variations according to disease severity. Interactome analysis identified associations of PCNA with proteins involved in interferon signaling, cytoskeletal organization, and neutrophil extracellular trap (NET) formation, such as protein arginine deiminase type-4 (PADI4) and histone H3, particularly in critical patients. Functional studies of interferon signaling showed that T2AA, a PCNA scaffold inhibitor, downregulated IFN-related genes, including STAT1, MX1, IFIT1, and IFIT2 in neutrophils. Additionally, T2AA specifically inhibited the secretion of CXCL10, an IFN-dependent cytokine. PCNA was also found to interact with key effector proteins implicated in NET formation, such as histone H3, especially in critical COVID-19 cases.

CONCLUSION

The analysis of the PCNA interactome has unveiled new protein partners that enhance the interferon pathway, thereby modulating immune responses and contributing to hyperinflammation in COVID-19. These findings provide valuable insights into interferon dysregulation in other immune-related conditions.

INTRODUCTION

Neutrophils are key players in the hyperinflammatory response during SARS-CoV-2 infection. The cytosolic proliferating cell nuclear antigen (PCNA) is a scaffolding protein highly dependent on the microenvironment status and known to interact with numerous proteins that regulate neutrophil functions. This study aimed to examine the cytosolic protein content and PCNA interactome in neutrophils from COVID-19 patients.

METHODS

Proteomic analyses were performed on neutrophil cytosols from healthy donors and patients with severe or critical COVID-19. In vitro approaches were used to explore the biological significance of the COVID-19-specific PCNA interactome.

RESULTS

Neutrophil cytosol analysis revealed a strong interferon (IFN) protein signature, with variations according to disease severity. Interactome analysis identified associations of PCNA with proteins involved in interferon signaling, cytoskeletal organization, and neutrophil extracellular trap (NET) formation, such as protein arginine deiminase type-4 (PADI4) and histone H3, particularly in critical patients. Functional studies of interferon signaling showed that T2AA, a PCNA scaffold inhibitor, downregulated IFN-related genes, including STAT1, MX1, IFIT1, and IFIT2 in neutrophils. Additionally, T2AA specifically inhibited the secretion of CXCL10, an IFN-dependent cytokine. PCNA was also found to interact with key effector proteins implicated in NET formation, such as histone H3, especially in critical COVID-19 cases.

CONCLUSION

The analysis of the PCNA interactome has unveiled new protein partners that enhance the interferon pathway, thereby modulating immune responses and contributing to hyperinflammation in COVID-19. These findings provide valuable insights into interferon dysregulation in other immune-related conditions.

Carbohydrate metabolism in supporting and regulating neutrophil effector functions

Neutrophils, the first responders of the innate immune system, can turn on a range of effector functions upon activation. Emerging research shows activated neutrophils undergo highly dynamic metabolic rewiring. This metabolic rewiring provides energy and reducing power to fuel effector functions and modulate signaling molecules to regulate neutrophil functions. Here, we review the current understanding of the specific metabolic requirements and regulators of neutrophil migration, neutrophil extracellular traps release, and pathogen killing. Particularly, we discuss how major carbohydrate metabolic pathways, including glycolysis, glycogen cycling, pentose phosphate pathway, and TCA cycle, are rewired upon neutrophil activation to support these functions. Continued investigation into the metabolic regulators of neutrophil functions can lead to therapeutic opportunities in various diseases.

Single cell autofluorescence imaging reveals immediate metabolic shifts of neutrophils with activation across biological systems

Neutrophils, the most abundant leukocytes in human peripheral circulation, are crucial for the innate immune response. They are typically quiescent but rapidly activate in response to infection and inflammation, performing diverse functions such as oxidative burst, phagocytosis, and NETosis, which require significant metabolic adaptation. Deeper insights into such metabolic changes will help identify regulation of neutrophil functions in health and diseases. Due to their short lifespan and associated technical challenges, the metabolic processes of neutrophils are not completely understood. This study uses optical metabolic imaging (OMI), which entails optical redox ratio and fluorescence lifetime imaging microscopy of intrinsic metabolic coenzymes NAD(P)H and FAD to assess the metabolic state of single neutrophils. Primary human neutrophils were imaged in vitro under a variety of activation conditions and metabolic pathway inhibitors, while metabolic and functional changes were confirmed with mass spectrometry, oxidative burst, and NETosis measurements. Our findings show that neutrophils undergo rapid metabolic remodeling to a reduced redox state indicated by changes in NAD(P)H lifetime and optical redox ratio, with a shift to an oxidized redox state during activation. Additionally, single cell OMI analysis reveals a heterogeneous metabolic response across neutrophils and human donors to live pathogen infection ( Pseudomonas aeruginosa and Toxoplasma gondii ). Finally, consistent OMI changes with activation were confirmed between in vitro human and in vivo zebrafish larvae neutrophils. This study demonstrates the potential of OMI as a versatile tool for studying neutrophil metabolism and underscores its use across different biological systems, offering insights into neutrophil metabolic activity and function at a single cell level.

Metabolic pathways fueling the suppressive activity of myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSC) are considered an aberrant population of immature myeloid cells that have attracted considerable attention in recent years due to their potent immunosuppressive activity. These cells are typically absent or present in very low numbers in healthy individuals but become abundant under pathological conditions such as chronic infection, chronic inflammation and cancer. The immunosuppressive activity of MDSC helps to control excessive immune responses that might otherwise lead to tissue damage. This same immunosuppressive activity can be detrimental, particularly in cancer and chronic infection. In the cancer setting, tumors can secrete factors that promote the expansion and recruitment of MDSC, thereby creating a local environment that favors tumor progression by inhibiting the effective immune responses against cancer cells. This has made MDSC a target of interest in cancer therapy, with researchers exploring strategies to inhibit their function or reduce their numbers to improve the efficacy of cancer immunotherapies. In the context of chronic infections, MDSC can lead to persistent infections by suppressing protective immune responses thereby preventing the clearance of pathogens. Therefore, targeting MDSC may provide a novel approach to improve pathogen clearance during chronic infections. Ongoing research on MDSC aims to elucidate the exact processes behind their expansion, recruitment, activation and suppressive mechanisms. In this context, it is becoming increasingly clear that the metabolism of MDSC is closely linked to their immunosuppressive function. For example, MDSC exhibit high rates of glycolysis, which not only provides energy but also generates metabolites that facilitate their immunosuppressive activity. In addition, fatty acid metabolic pathways, such as fatty acid oxidation (FAO), have been implicated in the regulation of MDSC suppressive activity. Furthermore, amino acid metabolism, particularly arginine metabolism mediated by enzymes such as arginase-1, plays a critical role in MDSC-mediated immunosuppression. In this review, we discuss the metabolic signature of MDSC and highlight the therapeutic implications of targeting MDSC metabolism as a novel approach to modulate their immunosuppressive functions.

How Do ROS Induce NETosis? Oxidative DNA Damage, DNA Repair, and Chromatin Decondensation

Neutrophil extracellular traps (NETs) are intricate, DNA-based, web-like structures adorned with cytotoxic proteins. They play a crucial role in antimicrobial defense but are also implicated in autoimmune diseases and tissue injury. The process of NET formation, known as NETosis, is a regulated cell death mechanism that involves the release of these structures and is unique to neutrophils. NETosis is heavily dependent on the production of reactive oxygen species (ROS), which can be generated either through NADPH oxidase (NOX) or mitochondrial pathways, leading to NOX-dependent or NOX-independent NETosis, respectively. Recent research has revealed an intricate interplay between ROS production, DNA repair, and NET formation in different contexts. UV radiation can trigger a combined process of NETosis and apoptosis, known as apoNETosis, driven by mitochondrial ROS and DNA repair. Similarly, in calcium ionophore-induced NETosis, both ROS and DNA repair are key components, but only play a partial role. In the case of bacterial infections, the early stages of DNA repair are pivotal. Interestingly, in serum-free conditions, spontaneous NETosis occurs through NOX-derived ROS, with early-stage DNA repair inhibition halting the process, while late-stage inhibition increases it. The intricate balance between DNA repair processes and ROS production appears to be a critical factor in regulating NET formation, with different pathways being activated depending on the nature of the stimulus. These findings not only deepen our understanding of the mechanisms behind NETosis but also suggest potential therapeutic targets for conditions where NETs contribute to disease pathology.

Antibody-Fab and -Fc features promote Mycobacterium tuberculosis restriction

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is a leading cause of death by an infectious disease globally, with no efficacious vaccine. Antibodies are implicated in Mtb control, but the mechanisms of antibody action remain poorly understood. We assembled a library of TB monoclonal antibodies (mAb) and screened for the ability to restrict Mtb in mice, identifying protective antibodies targeting known and novel antigens. To dissect the mechanism of mAb-mediated Mtb restriction, we optimized a protective lipoarabinomannan-specific mAb through Fc-swapping. In vivo analysis of these Fc-variants revealed a critical role for Fc-effector function in Mtb restriction. Restrictive Fc-variants altered distribution of Mtb across innate immune cells. Single-cell transcriptomics highlighted distinctly activated molecular circuitry within innate immune cell subpopulations, highlighting early activation of neutrophils as a key signature of mAb-mediated Mtb restriction. Therefore, improved antibody-mediated restriction of Mtb is associated with reorganization of the tissue-level immune response to infection and depends on the collaboration of antibody Fab and Fc.

Catching the Big Fish in Big Data: A Meta-Analysis of Zebrafish Kidney scRNA-Seq Datasets Highlights Conserved Molecular Profiles of Macrophages and Neutrophils in Vertebrates

The innate immune system (IIS) is an ancient and essential defense mechanism that protects animals against a wide range of pathogens and diseases. Although extensively studied in mammals, our understanding of the IIS in other taxa remains limited. The zebrafish (Danio rerio) serves as a promising model organism for investigating IIS-related processes, yet the immunogenetics of fish are not fully elucidated. To address this gap, we conducted a meta-analysis of single-cell RNA sequencing (scRNA-seq) datasets from zebrafish kidney marrow, encompassing approximately 250,000 immune cells. Our analysis confirms the presence of key genetic pathways in zebrafish innate immune cells that are similar to those identified in mammals. Zebrafish macrophages specifically express genes encoding cathepsins, major histocompatibility complex class II proteins, integral membrane proteins, and the V-ATPase complex and demonstrate the enrichment of oxidative phosphorylation ferroptosis processes. Neutrophils are characterized by the significant expression of genes encoding actins, cytoskeleton organizing proteins, the Arp2/3 complex, and glycolysis enzymes and have demonstrated their involvement in GnRH and CLR signaling pathways, adherents, and tight junctions. Both macrophages and neutrophils highly express genes of NOD-like receptors, phagosomes, and lysosome pathways and genes involved in apoptosis. Our findings reinforce the idea about the existence of a wide spectrum of immune cell phenotypes in fish since we found only a small number of cells with clear pro- or anti-inflammatory signatures.

Neutrophil trapping and nexocytosis, mast cell-mediated processes for inflammatory signal relay

Neutrophils are sentinel immune cells with essential roles for antimicrobial defense. Most of our knowledge on neutrophil tissue navigation derived from wounding and infection models, whereas allergic conditions remained largely neglected. Here, we analyzed allergen-challenged mouse tissues and discovered that degranulating mast cells (MCs) trap living neutrophils inside them. MCs release the attractant leukotriene B4 to re-route neutrophils toward them, thus exploiting a chemotactic system that neutrophils normally use for intercellular communication. After MC intracellular trap (MIT) formation, neutrophils die, but their undigested material remains inside MC vacuoles over days. MCs benefit from MIT formation, increasing their functional and metabolic fitness. Additionally, they are more pro-inflammatory and can exocytose active neutrophilic compounds with a time delay (nexocytosis), eliciting a type 1 interferon response in surrounding macrophages. Together, our study highlights neutrophil trapping and nexocytosis as MC-mediated processes, which may relay neutrophilic features over the course of chronic allergic inflammation.

Not just sugar: metabolic control of neutrophil development and effector functions

The mammalian immune system is constantly surveying our tissues to clear pathogens and maintain tissue homeostasis. In order to fulfill these tasks, immune cells take up nutrients to supply energy for survival and for directly regulating effector functions via their cellular metabolism, a process now known as immunometabolism. Neutrophilic granulocytes, the most abundant leukocytes in the human body, have a short half-life and are permanently needed in the defense against pathogens. According to a long-standing view, neutrophils were thought to primarily fuel their metabolic demands via glycolysis. Yet, this view has been challenged, as other metabolic pathways recently emerged to contribute to neutrophil homeostasis and effector functions. In particular during neutrophilic development, the pentose phosphate pathway, glycogen synthesis, oxidative phosphorylation, and fatty acid oxidation crucially promote neutrophil maturation. At steady state, both glucose and lipid metabolism sustain neutrophil survival and maintain the intracellular redox balance. This review aims to comprehensively discuss how neutrophilic metabolism adapts during development, which metabolic pathways fuel their functionality, and how these processes are reconfigured in case of various diseases. We provide several examples of hereditary diseases, in which mutations in metabolic enzymes validate their critical role for neutrophil function.

Metabolic regulation of neutrophil functions in homeostasis and diseases

Neutrophils are the most abundant leukocytes in humans and play a role in the innate immune response by being the first cells attracted to the site of infection. While early studies presented neutrophils as almost exclusively glycolytic cells, recent advances show that these cells use several metabolic pathways other than glycolysis, such as the pentose phosphate pathway, oxidative phosphorylation, fatty acid oxidation, and glutaminolysis, which they modulate to perform their functions. Metabolism shifts from fatty acid oxidation-mediated mitochondrial respiration in immature neutrophils to glycolysis in mature neutrophils. Tissue environments largely influence neutrophil metabolism according to nutrient sources, inflammatory mediators, and oxygen availability. Inhibition of metabolic pathways in neutrophils results in impairment of certain effector functions, such as NETosis, chemotaxis, degranulation, and reactive oxygen species generation. Alteration of these neutrophil functions is implicated in certain human diseases, such as antiphospholipid syndrome, coronavirus disease 2019, and bronchiectasis. Metabolic regulators such as AMPK, HIF-1α, mTOR, and Arf6 are linked to neutrophil metabolism and function and could potentially be targeted for the treatment of diseases associated with neutrophil dysfunction. This review details the effects of alterations in neutrophil metabolism on the effector functions of these cells.

Deletion of pyruvate dehydrogenase kinases reduces susceptibility to deep vein thrombosis in mice

ABSTRACT

Neutrophils contribute to deep vein thrombosis (DVT) by releasing prothrombotic neutrophil extracellular traps (NETs). NET formation (known as NETosis) is an energy-intensive process that requires an increased rate of aerobic glycolysis. The metabolic enzymes pyruvate dehydrogenase kinases (PDKs) inhibit the pyruvate dehydrogenase complex to divert the pyruvate flux from oxidative phosphorylation toward aerobic glycolysis. Herein, we identified that the combined deletion of PDK2 and PDK4 (PDK2/4-/-) renders mice less susceptible to DVT (measured by thrombus incidence, weight, and length) in the inferior vena cava-stenosis model at day 2 after surgery. Compared with wild-type (WT) mice, the venous thrombus obtained from PDK2/4-/- mice exhibited reduced citrullinated histone content, a known marker of NETs. In line with in vivo observations, phorbol 12-myristate 13-acetate (PMA)-stimulated PDK2/4-/- neutrophils displayed reduced NETosis and secretion of cathepsin G and elastase compared with PMA-stimulated WT neutrophils. The formation of platelet aggregates mediated by PMA-stimulated PDK2/4-/- neutrophils were significantly reduced compared with PMA-stimulated WT neutrophils. Finally, PDK2/4-/- neutrophils exhibited reduced levels of intracellular Ca2+ concentration, extracellular signal-regulated kinase 1/2 (Erk1/2) phosphorylation, and glycolytic proton efflux rate (a measure of aerobic glycolysis), known to facilitate NETosis. Together, these findings elucidate, to our knowledge, for the first time, the fundamental role of PDK2/4 in regulating NETosis and acute DVT.

Metabolic features of neutrophilic differentiation of HL-60 cells in hyperglycemic environments

INTRODUCTION

Chronic hyperglycemia affects neutrophil functions, leading to reduced pathogen killing and increased morbidity. This impairment has been directly linked to increased glycemia, however, how this specifically affects neutrophils metabolism and their differentiation in the bone marrow is unclear and difficult to study.

RESEARCH DESIGN AND METHODS

We used high-resolution respirometry to investigate the metabolism of resting and activated donor neutrophils, and flow cytometry to measure surface CD15 and CD11b expression. We then used HL-60 cells differentiated towards neutrophil-like cells in standard media and investigated the effect of doubling glucose concentration on differentiation metabolism. We measured the oxygen consumption rate (OCR), and the enzymatic activity of carnitine palmitoyl transferase 1 (CPT1) and citrate synthase during neutrophil-like differentiation. We compared the surface phenotype, functions, and OCR of neutrophil-like cells differentiated under both glucose concentrations.

RESULTS

Donor neutrophils showed significant instability of CD11b and OCR after phorbol 12-myristate 13-acetate stimulation at 3 hours post-enrichment. During HL-60 neutrophil-like cell differentiation, there was a significant increase in surface CD15 and CD11b expression together with the loss of mitochondrial mass. Differentiated neutrophil-like cells also exhibited higher CD11b expression and were significantly more phagocytic. In higher glucose media, we measured a decrease in citrate synthase and CPT1 activities during neutrophil-like differentiation.

CONCLUSIONS

HL-60 neutrophil-like differentiation recapitulated known molecular and metabolic features of human neutrophil differentiation. Increased glucose concentrations correlated with features described in hyperglycemic donor neutrophils including increased CD11b and phagocytosis. We used this model to describe metabolic features of neutrophil-like cell differentiation in hyperglycemia and show for the first time the downregulation of CPT1 and citrate synthase activity, independently of mitochondrial mass.

Metabolic predictors of COVID-19 mortality and severity: a survival analysis

Introduction

The global healthcare burden of COVID-19 pandemic has been unprecedented with a high mortality. Metabolomics, a powerful technique, has been increasingly utilized to study the host response to infections and to understand the progression of multi-system disorders such as COVID-19. Analysis of the host metabolites in response to SARS-CoV-2 infection can provide a snapshot of the endogenous metabolic landscape of the host and its role in shaping the interaction with SARS-CoV-2. Disease severity and consequently the clinical outcomes may be associated with a metabolic imbalance related to amino acids, lipids, and energy-generating pathways. Hence, the host metabolome can help predict potential clinical risks and outcomes.

Methods

In this prospective study, using a targeted metabolomics approach, we studied the metabolic signature in 154 COVID-19 patients (males=138, age range 48-69 yrs) and related it to disease severity and mortality. Blood plasma concentrations of metabolites were quantified through LC-MS using MxP Quant 500 kit, which has a coverage of 630 metabolites from 26 biochemical classes including distinct classes of lipids and small organic molecules. We then employed Kaplan-Meier survival analysis to investigate the correlation between various metabolic markers, disease severity and patient outcomes.

Results

A comparison of survival outcomes between individuals with high levels of various metabolites (amino acids, tryptophan, kynurenine, serotonin, creatine, SDMA, ADMA, 1-MH and carnitine palmitoyltransferase 1 and 2 enzymes) and those with low levels revealed statistically significant differences in survival outcomes. We further used four key metabolic markers (tryptophan, kynurenine, asymmetric dimethylarginine, and 1-Methylhistidine) to develop a COVID-19 mortality risk model through the application of multiple machine-learning methods.

Conclusions

Metabolomics analysis revealed distinct metabolic signatures among different severity groups, reflecting discernible alterations in amino acid levels and perturbations in tryptophan metabolism. Notably, critical patients exhibited higher levels of short chain acylcarnitines, concomitant with higher concentrations of SDMA, ADMA, and 1-MH in severe cases and non-survivors. Conversely, levels of 3-methylhistidine were lower in this context.

Stress hyperglycaemia following trauma - a survival benefit or an outcome detriment?

PURPOSE OF REVIEW

Stress hyperglycaemia occur often in critically injured patients. To gain new consideration about it, this review compile current as well as known immunological and biochemical findings about causes and emergence.

RECENT FINDINGS

Glucose is the preferred energy substrate for fending immune cells, reparative tissue and the cardiovascular system following trauma. To fulfil these energy needs, the liver is metabolically reprogrammed to rebuild glucose from lactate and glucogenic amino acids (hepatic insulin resistance) at the expenses of muscles mass and - to a less extent - fat tissue (proteolysis, lipolysis, peripheral insulin resistance). This inevitably leads to stress hyperglycaemia, which is evolutionary preserved and seems to be an essential and beneficial survival response. It is initiated by damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs), intensified by immune cells itself and mainly ruled by tumour necrosis factor (TNF)α and catecholamines with lactate and hypoxia inducible factor (HIF)-1α as intracellular signals and lactate as an energy shuttle. Important biochemical mechanisms involved in this response are the Warburg effect as an efficient metabolic shortcut and the extended Cori cycle.

SUMMARY

Stress hyperglycaemia is beneficial in an acute life-threatening situation, but further research is necessary, to prevent trauma patients from the detrimental effects of persisting hyperglycaemia.

Dinner date: Neisseria gonorrhoeae central carbon metabolism and pathogenesis

Neisseria gonorrhoeae, the causative agent of the sexually transmitted infection gonorrhea, is a human-adapted pathogen that does not productively infect other organisms. The ongoing relationship between N. gonorrhoeae and the human host is facilitated by the exchange of nutrient resources that allow for N. gonorrhoeae growth in the human genital tract. What N. gonorrhoeae 'eats' and the pathways used to consume these nutrients have been a topic of investigation over the last 50 years. More recent investigations are uncovering the impact of N. gonorrhoeae metabolism on infection and inflammatory responses, the environmental influences driving N. gonorrhoeae metabolism, and the metabolic adaptations enabling antimicrobial resistance. This mini-review is an introduction to the field of N. gonorrhoeae central carbon metabolism in the context of pathogenesis. It summarizes the foundational work used to characterize N. gonorrhoeae central metabolic pathways and the effects of these pathways on disease outcomes, and highlights some of the most recent advances and themes under current investigation. This review ends with a brief description of the current outlook and technologies under development to increase understanding of how the pathogenic potential of N. gonorrhoeae is enabled by metabolic adaptation.

Hypoxia inducible factors inhibit respiratory syncytial virus infection by modulation of nucleolin expression

Respiratory syncytial virus (RSV) is a global healthcare problem, causing respiratory illness in young children and elderly individuals. Our knowledge of the host pathways that define susceptibility to infection and disease severity are limited. Hypoxia inducible factors (HIFs) define metabolic responses to low oxygen and regulate inflammatory responses in the lower respiratory tract. We demonstrate a role for HIFs to suppress RSV entry and RNA replication. We show that hypoxia and HIF prolyl-hydroxylase inhibitors reduce the expression of the RSV entry receptor nucleolin and inhibit viral cell-cell fusion. We identify a HIF regulated microRNA, miR-494, that regulates nucleolin expression. In RSV-infected mice, treatment with the clinically approved HIF prolyl-hydroxylase inhibitor, Daprodustat, reduced the level of infectious virus and infiltrating monocytes and neutrophils in the lung. This study highlights a role for HIF-signalling to limit multiple aspects of RSV infection and associated inflammation and informs future therapeutic approaches for this respiratory pathogen.

PCNA at the crossroads of human neutrophil activation, metabolism, and survival

The proliferating cell nuclear antigen scaffold differentially binds hexokinase, procaspase-9, and p47phox to regulate neutrophil metabolism, viability and activation state.

G-CSF reshapes the cytosolic PCNA scaffold and modulates glycolysis in neutrophils

Cytosolic proliferating cell nuclear antigen (PCNA) is involved in neutrophil survival and function, in which it acts as a scaffold and associates with proteins involved in apoptosis, NADPH oxidase activation, cytoskeletal dynamics, and metabolism. While the PCNA interactome has been characterized in neutrophils under homeostatic conditions, less is known about neutrophil PCNA in pathophysiological contexts. Granulocyte colony-stimulating factor (G-CSF) is a cytokine produced in response to inflammatory stimuli that regulates many aspects of neutrophil biology. Here, we used isolated normal-density neutrophils from G-CSF-treated haemopoietic stem cell donors (GDs) as a model to understand the role of PCNA during inflammation. Proteomic analysis of the neutrophil cytosol revealed significant differences between GDs and healthy donors (HDs). PCNA was one of the most upregulated proteins in GDs, and the PCNA interactome was significantly different in GDs compared with HDs. Importantly, while PCNA associated with almost all enzymes involved in glycolysis in HDs, these associations were decreased in GDs. Functionally, neutrophils from GDs had a significant increase in glycolysis compared with HDs. Using p21 competitor peptides, we showed that PCNA negatively regulates neutrophil glycolysis in HDs but had no effect on GD neutrophils. These data demonstrate that G-CSF alters the PCNA scaffold, affecting interactions with key glycolytic enzymes, and thus regulates glycolysis, the main energy pathway utilized by neutrophils. By this selective control of glycolysis, PCNA can organize neutrophils functionality in parallel with other PCNA mechanisms of prolonged survival. PCNA may therefore be instrumental in the reprogramming that neutrophils undergo in inflammatory or tumoral settings.

The emerging role for neutrophil mitochondrial metabolism in lung inflammation

Recent advances shed light on the importance of mitochondrial metabolism in supporting essential neutrophil functions such as trafficking, NETosis, bacterial killing, and modulating inflammatory responses. Mitochondrial metabolism is now recognized to contribute to a number of lung diseases marked by neutrophilic inflammation, including bacterial pneumonia, acute lung injury, and chronic obstructive pulmonary disease. In this mini review, we provide an overview of neutrophil metabolism focusing on the role of mitochondrial programs, discuss select neutrophil effector functions that are directly influenced by mitochondrial metabolism, and present what is known about the role for mitochondrial metabolism in lung diseases marked by neutrophilic inflammation.