Citrullinated Histone H3 as a Therapeutic Target for Endotoxic Shock in Mice

Sunlight Exposure and Phototherapy: Perspectives for Healthy Aging in an Era of COVID-19

Most humans depend on sunlight exposure to satisfy their requirements for vitamin D₃. However, the destruction of the ozone layer in the past few decades has increased the risk of skin aging and wrinkling caused by excessive exposure to ultraviolet (UV) radiation, which may also promote the risk of skin cancer development. The promotion of public health recommendations to avoid sunlight exposure would reduce the risk of skin cancer, but it would also enhance the risk of vitamin D₃ insufficiency/deficiency, which may cause disease development and progression. In addition, the ongoing global COVID-19 pandemic may further reduce sunlight exposure due to stay-at-home policies, resulting in difficulty in active and healthy aging. In this review article, we performed a literature search in PubMed and provided an overview of basic and clinical data regarding the impact of sunlight exposure and vitamin D₃ on public health. We also discuss the potential mechanisms and clinical value of phototherapy with a full-spectrum light (notably blue, red, and near-infrared light) as an alternative to sunlight exposure, which may contribute to combating COVID-19 and promoting active and healthy aging in current aged/superaged societies.

Involvement of Neutrophil Extracellular Traps in Cerebral Arteriovenous Malformations

BACKGROUND

Cerebral arteriovenous malformations (cAVMs) represent tangles of abnormal vasculature without intervening capillaries. High-pressure vascular channels due to abnormal arterial and venous shunts can lead to rupture. Multiple pathways are involved in the pathobiology of cAVMs including inflammation and genetic factors such as KRAS mutations. Neutrophil release of nuclear chromatin, known as neutrophil extracellular traps (NETs), plays a multifunctional role in infection, inflammation, thrombosis, intracranial aneurysms, and tumor progression. However, the relationship between NETs and the pathobiology of cAVMs remains unknown. We tested whether NETs play a role in the pathobiology of cAVMs.

METHODS

We analyzed samples from patients who had undergone surgery for cAVM and immunohistochemically investigated expression of citrullinated histone H3 (CitH3) as a marker of NETs. CitH3 expression was compared among samples from cAVM patients, epilepsy patients, and normal human brain tissue. Expressions of thrombotic and inflammatory markers were also examined immunohistochemically in samples from cAVM patients.

RESULTS

Expression of CitH3 derived from neutrophils was observed intravascularly in all cAVM samples but not other samples. Nidi of AVMs showed migration of many Iba-I-positive cells adjacent to the endothelium and endothelial COX2 expression, accompanied by expression of IL-6 and IL-8 in the endothelium and intravascular neutrophils. Unexpectedly, expression of CitH3 was not necessarily localized to the vascular wall and thrombus.

CONCLUSIONS

Our results offer the first evidence of intravascular expression of NETs, which might be associated with vascular inflammation in cAVMs.

Kynurenic Acid and Its Synthetic Derivatives Protect Against Sepsis-Associated Neutrophil Activation and Brain Mitochondrial Dysfunction in Rats

Background and Aims

The systemic host response in sepsis is frequently accompanied by central nervous system (CNS) dysfunction. Evidence suggests that excessive formation of neutrophil extracellular traps (NETs) can increase the permeability of the blood–brain barrier (BBB) and that the evolving mitochondrial damage may contribute to the pathogenesis of sepsis-associated encephalopathy. Kynurenic acid (KYNA), a metabolite of tryptophan catabolism, exerts pleiotropic cell-protective effects under pro-inflammatory conditions. Our aim was to investigate whether exogenous KYNA or its synthetic analogues SZR-72 and SZR-104 affect BBB permeability secondary to NET formation and influence cerebral mitochondrial disturbances in a clinically relevant rodent model of intraabdominal sepsis.

Methods

Sprague–Dawley rats were subjected to fecal peritonitis (0.6 g kg^-1 ip) or a sham operation. Septic animals were treated with saline or KYNA, SZR-72 or SZR-104 (160 µmol kg^-1 each ip) 16h and 22h after induction. Invasive monitoring was performed on anesthetized animals to evaluate respiratory, cardiovascular, renal, hepatic and metabolic parameters to calculate rat organ failure assessment (ROFA) scores. NET components (citrullinated histone H3 (CitH3); myeloperoxidase (MPO)) and the NET inducer IL-1β, as well as IL-6 and a brain injury marker (S100B) were detected from plasma samples. After 24h, leukocyte infiltration (tissue MPO) and mitochondrial complex I- and II-linked (CI–CII) oxidative phosphorylation (OXPHOS) were evaluated. In a separate series, Evans Blue extravasation and the edema index were used to assess BBB permeability in the same regions.

Results

Sepsis was characterized by significantly elevated ROFA scores, while the increased BBB permeability and plasma S100B levels demonstrated brain damage. Plasma levels of CitH3, MPO and IL-1β were elevated in sepsis but were ameliorated by KYNA and its synthetic analogues. The sepsis-induced deterioration in tissue CI–CII-linked OXPHOS and BBB parameters as well as the increase in tissue MPO content were positively affected by KYNA/KYNA analogues.

Conclusion

This study is the first to report that KYNA and KYNA analogues are potential neuroprotective agents in experimental sepsis. The proposed mechanistic steps involve reduced peripheral NET formation, lowered BBB permeability changes and alleviation of mitochondrial dysfunction in the CNS.

Protectin D1 protects against lipopolysaccharide-induced acute lung injury through inhibition of neutrophil infiltration and the formation of neutrophil extracellular traps in lung tissue

Protectin D1 (PD1), a DHA-derived lipid mediator, has recently been shown to possess anti-inflammatory and pro-resolving properties. To date, little is known about the effect of PD1 on lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice. The aim of the present study was to investigate the therapeutic effects of PD1 on LPS-induced ALI and its potential mechanisms of action. ALI was induced via an intraperitoneal injection of LPS, where PD1 (2 ng/mouse) was administered intravenously 30 min after LPS challenge. Mice were sacrificed 24 h after modeling. Lung histopathological changes were assessed using hematoxylin and eosin staining and myeloperoxidase (MPO) activity was tested using immunohistochemistry. Tumor necrosis-α and interleukin-6 levels in the bronchoalveolar lavage fluid (BALF) and serum were measured using ELISA. To detect neutrophil extracellular traps produced by infiltrated neutrophils in the lung tissue, immunofluorescence staining was performed using anti-MPO and anti-histone H3 antibodies. The results indicated that PD1 significantly attenuated histological damage and neutrophil infiltration in lung tissue, reduced the lung wet/dry weight ratio, protein concentration and proinflammatory cytokine levels in BALF and decreased proinflammatory cytokine levels in serum. Moreover, neutrophil citrullinated histone H3 (CitH3) expression was also reduced after PD1 administration. In conclusion, PD1 attenuated LPS-induced ALI in mice via inhibition of neutrophil extracellular trap formation in lung tissue. Therefore, PD1 administration may serve to be a new strategy for treating ALI.

A Fragile Balance: Does Neutrophil Extracellular Trap Formation Drive Pulmonary Disease Progression?

Neutrophils act as the first line of defense during infection and inflammation. Once activated, they are able to fulfil numerous tasks to fight inflammatory insults while keeping a balanced immune response. Besides well-known functions, such as phagocytosis and degranulation, neutrophils are also able to release "neutrophil extracellular traps" (NETs). In response to most stimuli, the neutrophils release decondensed chromatin in a NADPH oxidase-dependent manner decorated with histones and granule proteins, such as neutrophil elastase, myeloperoxidase, and cathelicidins. Although primarily supposed to prevent microbial dissemination and fight infections, there is increasing evidence that an overwhelming NET response correlates with poor outcome in many diseases. Lung-related diseases especially, such as bacterial pneumonia, cystic fibrosis, chronic obstructive pulmonary disease, aspergillosis, influenza, and COVID-19, are often affected by massive NET formation. Highly vascularized areas as in the lung are susceptible to immunothrombotic events promoted by chromatin fibers. Keeping this fragile equilibrium seems to be the key for an appropriate immune response. Therapies targeting dysregulated NET formation might positively influence many disease progressions. This review highlights recent findings on the pathophysiological influence of NET formation in different bacterial, viral, and non-infectious lung diseases and summarizes medical treatment strategies.

Neutrophil extracellular traps impair intestinal barrier functions in sepsis by regulating TLR9-mediated endoplasmic reticulum stress pathway

Increased neutrophil extracellular traps (NETs) formation has been found to be associated with intestinal inflammation, and it has been reported that NETs may drive the progression of gut dysregulation in sepsis. However, the biological function and regulation of NETs in sepsis-induced intestinal barrier dysfunction are not yet fully understood. First, we found that both circulating biomarkers of NETs and local NETs infiltration in the intestine were significantly increased and had positive correlations with markers of enterocyte injury in abdominal sepsis patients. Moreover, the levels of local citrullinated histone 3 (Cit H3) expression were associated with the levels of BIP expression. To further confirm the role of NETs in sepsis-induced intestinal injury, we compared peptidylarginine deiminase 4 (PAD4)-deficient mice and wild-type (WT) mice in a lethal septic shock model. In WT mice, the Cit H3-DNA complex was markedly increased, and elevated intestinal inflammation and endoplasmic reticulum (ER) stress activation were also found. Furthermore, PAD4 deficiency alleviated intestinal barrier disruption and decreased ER stress activation. Notably, NETs treatment induced intestinal epithelial monolayer barrier disruption and ER stress activation in a dose-dependent manner in vitro, and ER stress inhibition markedly attenuated intestinal apoptosis and tight junction injury. Finally, TLR9 antagonist administration significantly abrogated NETs-induced intestinal epithelial cell death through ER stress inhibition. Our results indicated that NETs could contribute to sepsis-induced intestinal barrier dysfunction by promoting inflammation and apoptosis. Suppression of the TLR9-ER stress signaling pathway can ameliorate NETs-induced intestinal epithelial cell death.

TNFAIP8L2/TIPE2 impairs autolysosome reformation via modulating the RAC1-MTORC1 axis

Macroautophagy/autophagy is an evolutionarily conserved process that involves the selective degradation of cytoplasmic components within lysosomes in response to starvation. Autophagy is an ancient defense mechanism that has been closely integrated with the immune system and has multiple effects on innate and adaptive immunity. The pro-inflammatory and anti-inflammatory cytokines can activate and inhibit autophagy, respectively. TNFAIP8L2/TIPE2 (tumor necrosis factor, alpha-induced protein 8-like 2) is a newly identified immune negative regulator of innate and adaptive immunity that plays an important role in immune homeostasis. However, whether and how TNFAIP8L2 controls autophagy is still unknown. Murine TNFAIP8L2 can directly bind to and block the RAC1 GTPase activity to regulate innate immunity. RAC1 can also bind to MTOR and regulate MTORC1 cellular localization and activity. Here, we find that TNFAIP8L2 can compete with MTOR for binding to the GTP-bound state of RAC1 and negatively regulate MTORC1 activity. Interestingly, TNFAIP8L2 overexpression fails to induce autophagy flux by the suppression of the MTOR activity under glutamine and serum starvation. Instead, TNFAIP8L2 appears to impair autophagic lysosome reformation (ALR) during prolonged starvation. Finally, we demonstrate that TNFAIP8L2 overexpression leads to a defect in MTOR reactivation and disrupts autophagy flux, thereby leading to cell death. Furthermore, TNFAIP8L2 deficiency can exacerbate the inflammatory response and lung injury by controlling the MTOR activity in an LPS-induced mouse endotoxemia model. Our study reveals a novel role of TNFAIP8L2 in autophagy by regulating the RAC1-MTORC1 axis that supports its potential as a target for therapeutic treatment.Abbreviations: ALR: autophagic lysosome reformation; BafA1: bafilomycin A1; BMDMs: bone marrow-derived macrophages; Co-IP: Co-Immunoprecipitation; LAMP1: lysosomal associated membrane protein 1; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MTORC1: mechanistic target of rapamycin kinase complex 1; RAPA: rapamycin; RPS6: ribosomal protein S6; SQSTM1/p62: sequestosome 1; Starv: Starvation; TNFAIP8L2/TIPE2: tumor necrosis factor-alpha-induced protein-8 like-2.

Therapeutic ACPA inhibits NET formation: a potential therapy for neutrophil-mediated inflammatory diseases

Excessive release of neutrophil extracellular traps (NETs) is associated with disease severity and contributes to tissue injury, followed by severe organ damage. Pharmacological or genetic inhibition of NET release reduces pathology in multiple inflammatory disease models, indicating that NETs are potential therapeutic targets. Here, we demonstrate using a preclinical basket approach that our therapeutic anti-citrullinated protein antibody (tACPA) has broad therapeutic potential. Treatment with tACPA prevents disease symptoms in various mouse models with plausible NET-mediated pathology, including inflammatory arthritis (IA), pulmonary fibrosis, inflammatory bowel disease and sepsis. We show that citrulline residues in the N-termini of histones 2A and 4 are specific targets for therapeutic intervention, whereas antibodies against other N-terminal post-translational histone modifications have no therapeutic effects. Because citrullinated histones are generated during NET release, we investigated the ability of tACPA to inhibit NET formation. tACPA suppressed NET release from human neutrophils triggered with physiologically relevant human disease-related stimuli. Moreover, tACPA diminished NET release and potentially initiated NET uptake by macrophages in vivo, which was associated with reduced tissue damage in the joints of a chronic arthritis mouse model of IA. To our knowledge, we are the first to describe an antibody with NET-inhibiting properties and thereby propose tACPA as a drug candidate for NET-mediated inflammatory diseases, as it eliminates the noxious triggers that lead to continued inflammation and tissue damage in a multidimensional manner.

The Crosstalk Between Cancer Cells and Neutrophils Enhances Hepatocellular Carcinoma Metastasis via Neutrophil Extracellular Traps-Associated Cathepsin G Component: A Potential Therapeutic Target

Background

Emerging evidences have highlighted the roles of neutrophils, as the major host microenvironment component, in the development of hepatocellular carcinoma (HCC). Neutrophils extracellular traps (NETs) produced in the infection can strengthen the behavior of cancer metastasis. Here, we investigated the roles of NETs in HCC metastasis and further explore the underlying mechanism of how NETs interact with cancer.

Methods

The neutrophils were isolated from whole blood of HCC patients and used to evaluate the formation of NETs. NET markers were detected in tissue samples, plasma and cell climbing slice. Mouse models were used to evaluate the roles of NETs in HCC metastasis in vivo, and the corresponding mechanisms were explored using in vivo and in vitro assays.

Results

An increase in the release of NETs in patients with HCC, particularly those with portal vein tumor thrombosis (PVTT). The presence of NETs in HCC tumor tissues closely correlated with a poor prognosis. Functionally, the invasion ability of HCC cells was enhanced by co-culture with HCC neutrophils, through NETs formation, while the neutrophils from a healthy donor (HD) exhibited the inhibition of the invasion ability. Furthermore, we observed an enhanced ability of forming NETs in neutrophils from HCC patients in vitro, especially patients with PVTT or extra-hepatic metastasis. An in-vivo animal study demonstrated that neutrophils of HCC facilitated the metastatic behavior towards the lung. The further mechanistic investigation unveiled that HCC cells-derived cytokine IL-8 triggered NETs formation in an NADPH oxidase-dependent manner, and NETs-associated cathepsin G (cG) promoted HCC metastasis in vitro as well as vivo. Clinically, the expression of the cG protein in tumor tissues displayed a close correlation with the disease prognosis of HCC patients.

Conclusion

Our findings implicated that the induction of NETs by HCC cells is a critical metastasis-supporting cancer–host interaction and that NETs may serve as an immune-based potential therapeutic target against HCC progression.

Cl-Amidine Improves Survival and Attenuates Kidney Injury in a Rabbit Model of Endotoxic Shock

Objective: Sepsis causes millions of deaths on a global scale annually. Activation of peptidylarginine deiminase (PAD) enzymes in sepsis causes citrullination of histones, which results in neutrophil extracellular trap formation and sepsis progression. This study evaluates pan-PAD inhibitor, Cl-amidine, in a model of lipopolysaccharide (LPS)-induced endotoxic shock in rabbits. We hypothesized that Cl-amidine would improve survival and attenuate kidney injury. Methods: In the survival model, rabbits were injected injected intravenously with 1 mg/kg of LPS, and then randomly assigned either to receive dimethyl sulfoxide (DMSO; 1 mcL/g) or Cl-amidine (10 mg/kg diluted in 1 mcL/g DMSO). They were then monitored for 14 days to evaluate survival. In the non-survival experiment, the same insult and treatment were administered, however; the animals were euthanized 12 hours after LPS injection for kidney harvest. Acute kidney injury (AKI) scoring was performed by a histopathologist who was blinded to the group assignment. Serial blood samples were also collected and compared. Results: Rabbits that received Cl-amidine had a higher survival (72%) compared with the rabbits that received DMSO (14%; p < 0.05). Cl-amidine-treated rabbits had lower (p < 0.05) histopathologic AKI scores, as well as plasma creatinine and blood urea nitrogen (BUN) levels 12 hours after insult. Conclusions: Pan-PAD inhibitor Cl-amidine improves survival and attenuates kidney injury in LPS-induced endotoxic shock in rabbits.

Circulating Histones in Sepsis: Potential Outcome Predictors and Therapeutic Targets

Sepsis is defined as a life-threatening organ dysfunction caused by a dysregulated host response to infection and is associated with high morbidity and mortality. Circulating histones (CHs), a group of damage-associated molecular pattern molecules mainly derived from neutrophil extracellular traps, play a crucial role in sepsis by mediating inflammation response, organ injury and death through Toll-like receptors or inflammasome pathways. Herein, we first elucidate the molecular mechanisms of histone-induced inflammation amplification, endothelium injury and cascade coagulation activation, and discuss the close correlation between elevated level of CHs and disease severity as well as mortality in patients with sepsis. Furthermore, current state-of-the-art on anti-histone therapy with antibodies, histone-binding proteins (namely recombinant thrombomodulin and activated protein C), and heparin is summarized to propose promising approaches for sepsis treatment.

Circulating Markers of Neutrophil Extracellular Traps Are of Prognostic Value in Patients With COVID-19

OBJECTIVE

The full spectrum of coronavirus disease 2019 (COVID-19) infection ranges from asymptomatic to acute respiratory distress syndrome, characterized by hyperinflammation and thrombotic microangiopathy. The pathogenic mechanisms are poorly understood, but emerging evidence suggest that excessive neutrophil extracellular trap (NET) formation plays a key role in COVID-19 disease progression. Here, we evaluate if circulating markers of NETs are associated with COVID-19 disease severity and clinical outcome, as well as to markers of inflammation and in vivo coagulation and fibrinolysis. Approach and Results: One hundred six patients with COVID-19 with moderate to severe disease were enrolled shortly after hospital admission and followed for 4 months. Acute and convalescent plasma samples as well as plasma samples from 30 healthy individuals were assessed for markers of NET formation: citrullinated histone H3, cell-free DNA, NE (neutrophil elastase). We found that all plasma levels of NET markers were elevated in patients with COVID-19 relative to healthy controls, that they were associated with respiratory support requirement and short-term mortality, and declined to those found in healthy individuals 4 months post-infection. The levels of the NET markers also correlated with white blood cells, neutrophils, inflammatory cytokines, and C-reactive protein, as well as to markers of in vivo coagulation, fibrinolysis, and endothelial damage.

CONCLUSIONS

Our findings suggest a role of NETs in COVID-19 disease progression, implicating their contribution to an immunothrombotic state. Further, we observed an association between circulating markers of NET formation and clinical outcome, demonstrating a potential role of NET markers in clinical decision-making, as well as for NETs as targets for novel therapeutic interventions in COVID-19.

Advances in sepsis diagnosis and management: a paradigm shift towards nanotechnology

Sepsis, a dysregulated immune response due to life-threatening organ dysfunction, caused by drug-resistant pathogens, is a major global health threat contributing to high disease burden. Clinical outcomes in sepsis depend on timely diagnosis and appropriate early therapeutic intervention. There is a growing interest in the evaluation of nanotechnology-based solutions for sepsis management due to the inherent and unique properties of these nano-sized systems. This review presents recent advancements in nanotechnology-based solutions for sepsis diagnosis and management. Development of nanosensors based on electrochemical, immunological or magnetic principals provide highly sensitive, selective and rapid detection of sepsis biomarkers such as procalcitonin and C-reactive protein and are reviewed extensively. Nanoparticle-based drug delivery of antibiotics in sepsis models have shown promising results in combating drug resistance. Surface functionalization with antimicrobial peptides further enhances efficacy by targeting pathogens or specific microenvironments. Various strategies in nanoformulations have demonstrated the ability to deliver antibiotics and anti-inflammatory agents, simultaneously, have been reviewed. The critical role of nanoformulations of other adjuvant therapies including antioxidant, antitoxins and extracorporeal blood purification in sepsis management are also highlighted. Nanodiagnostics and nanotherapeutics in sepsis have enormous potential and provide new perspectives in sepsis management, supported by promising future biomedical applications included in the review.

Extracellular histones in lung dysfunction: a new biomarker and therapeutic target?

Extracellular histones released from injured or dying cells following trauma and other severe insults can act as potent damage-associated molecular patterns. In fact, elevated levels of histones are present in human circulation in hyperinflammatory states such as acute respiratory distress syndrome and sepsis. The molecular mechanisms owing to histone-induced pathologies are at the very beginning of elucidating. However, neutralization of histones with antibodies, histone-binding or histone-degrading proteins, and heparan sulfates have shown promising therapeutic effects in pre-clinical acute respiratory distress syndrome and sepsis models. Various cell types undergoing necrosis and apoptosis or activated neutrophils forming neutrophil extracellular traps have been implicated in excessive release of histones which further augments tissue injury and may culminate in multiple organ failure. At the molecular level, an uncontrolled inflammatory cascade has been considered as the major event; however, histone-activated coagulation and thrombosis represent additional pathologic events reflecting coagulopathy. Furthermore, epigenetic regulation and chemical modifications of circulating histones appear to be critically important in their biological functions as evidenced by increased cytotoxicity associated with citrullinated histone. Herein, we will briefly review the current knowledge on the role of histones in acute respiratory distress syndrome and sepsis, and discuss the future potential of anti-histone therapy for treatment of these life-threatening disorders.

Immunohistochemical detection of citrullinated histone H3-positive neutrophils is useful for identifying active glomerular and interstitial lesions in antineutrophil cytoplasmic antibody-associated vasculitis

AIMS

Activated neutrophils release neutrophil extracellular traps (NETs), resulting in a form of cell death called NETosis. NET formation is reportedly involved in the onset of systemic lupus erythematosus and antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Citrullination of histones is a key step in NET formation, and the presence of citrullinated histones in neutrophils may be associated with disease induction and activity. The aim of this study was to investigate the relationship between infiltrating citrullinated histone H3 (H3Cit)-positive neutrophils and disease specificity and activity in various glomerulonephritides.

METHODS AND RESULTS

We selected 32 kidney biopsies with glomerulonephritides, including AAV, lupus nephritis (LN), Henoch-Schönlein purpura nephritis (HSPN), and poststreptococcal acute glomerulonephritis (PSAGN). We examined the presence of H3Cit in infiltrating neutrophils and their association with necrotising, crescentic lesions and tubulointerstitial lesions. In PSAGN and HSPN, we found many myeloperoxidase (MPO)+ neutrophils in glomeruli; however, only a few were H3Cit+. In LN, MPO+ neutrophils mainly existed in the margins of glomerular tufts forming wire-loop lesions, and some of these were noted to be H3Cit+ neutrophils. In contrast, we found a significantly higher frequency of H3Cit+ neutrophils, despite the small number of MPO+ neutrophils, in microscopic polyangiitis in AAV. In particular, H3Cit+ neutrophils were prominent in necrotising lesions along the glomerular capillaries. Moreover, we also found H3Cit+ neutrophils in the interstitium, with marked peritubular capillaritis in AAV.

CONCLUSIONS

H3Cit immunostaining is a useful tool for identifying activated neutrophils. The frequency of H3Cit+ neutrophils is not only a disease-specific marker but also a potential marker for disease activity in AAV.

Peptidylarginine deiminase 2 has potential as both a biomarker and therapeutic target of sepsis

Peptidylarginine deiminases (PADs) are a family of calcium-dependent enzymes that are involved in a variety of human disorders, including cancer and autoimmune diseases. Although targeting PAD4 has shown no benefit in sepsis, the role of PAD2 remains unknown. Here, we report that PAD2 is engaged in sepsis and sepsis-induced acute lung injury in both human patients and mice. Pad2^–/– or selective inhibition of PAD2 by a small molecule inhibitor increased survival and improved overall outcomes in mouse models of sepsis. Pad2 deficiency decreased neutrophil extracellular trap (NET) formation. Importantly, Pad2 deficiency inhibited Caspase-11–dependent pyroptosis in vivo and in vitro. Suppression of PAD2 expression reduced inflammation and increased macrophage bactericidal activity. In contrast to Pad2^–/–, Pad4 deficiency enhanced activation of Caspase-11–dependent pyroptosis in BM-derived macrophages and displayed no survival improvement in a mouse sepsis model. Collectively, our findings highlight the potential of PAD2 as an indicative marker and therapeutic target for sepsis.

Peptidylarginine deiminases 2 (PAD2) regulates neutrophil extracellular trap (NET) formation in sepsis and sepsis-induced acute lung injury.

Serum citrullinated histone H3 concentrations differentiate patients with septic verses non-septic shock and correlate with disease severity

Purpose

Microbial infection stimulates neutrophil/macrophage/monocyte extracellular trap formation, which leads to the release of citrullinated histone H3 (CitH3) catalyzed by peptidylarginine deiminase (PAD) 2 and 4. Understanding these molecular mechanisms in the pathogenesis of septic shock will be an important next step for developing novel diagnostic and treatment modalities. We sought to determine the expression of CitH3 in patients with septic shock, and to correlate CitH3 levels with PAD2/PAD4 and clinically relevant outcomes.

Methods

Levels of CitH3 were measured in serum samples of 160 critically ill patients with septic and non-septic shock, and healthy volunteers. Analyses of clinical and laboratory characteristics of patients were conducted.

Results

Levels of circulating CitH3 at enrollment were significantly increased in septic shock patients (n = 102) compared to patients hospitalized with non-infectious shock (NIC) (n = 32, p < 0.0001). The area under the curve (95% CI) for distinguishing septic shock from NIC using CitH3 was 0.76 (0.65–0.86). CitH3 was positively correlated with PAD2 and PAD4 concentrations and Sequential Organ Failure Assessment Scores [total score (r = 0.36, p < 0.0001)]. The serum levels of CitH3 at 24 h (p < 0.01) and 48 h (p < 0.05) were significantly higher in the septic patients that did not survive.

Conclusion

CitH3 is increased in patients with septic shock. Its serum concentrations correlate with disease severity and prognosis, which may yield vital insights into the pathophysiology of sepsis.

Electronic supplementary material

The online version of this article (10.1007/s15010-020-01528-y) contains supplementary material, which is available to authorized users.

Citrullination of extracellular histone H3.1 reduces antibacterial activity and exacerbates its proteolytic degradation

BACKGROUND

Cystic fibrosis (CF), involves excessive airway accumulation of neutrophils, often in parallel with severe infection caused by Pseudomonas aeruginosa. Free histones are known to possess bactericidal properties, but the degree of antibacterial activity exerted on specific lung-based pathogens is largely unknown. Neutrophils have a high content of peptidyl deiminase 4 (PADI4), which citrullinate cationic peptidyl-arginines. In histone H3.1, several positions in the NH₂-terminal tail are subject to citrullination.

METHODS

Full-length and segmented histone subunit H3.1 was investigated for bactericidal activity towards P. aeruginosa (strain PAO1). PADI4-induced citrullination of histone H3.1 was assessed for antibacterial activity towards P. aeruginosa. Next, the effect of neutrophil elastase (NE)-mediated proteolysis of histone H3.1 was investigated. Finally, PADI4, H3.1, and citrullinated H3.1 were examined in healthy control and CF patient lung tissues.

RESULTS

Full-length histone H3.1 and sections of the histone H3.1 tail, displayed bactericidal activity towards P. aeruginosa. These antibacterial effects were reduced following citrullination by PADI4 or proteolysis by NE. Interestingly, citrullination of histone H3.1 exacerbated NE-mediated degradation. In CF lung tissue, citrullinated histone H3.1 and PADI4 immunoreactivity was abundant. Degraded histone H3.1 was detected in the sputum of CF patients but was absent in the sputum of healthy controls.

CONCLUSIONS

Citrullination impairs the antibacterial activity of histone H3.1 and exacerbates its proteolytic degradation by NE. Citrullination is likely to play an important role during resolution of acute inflammation. However, in chronic inflammation akin to CF, citrullination may dampen host defense and promote pathogen survival, as exemplified by P. aeruginosa.

Neuroinflammation and histone H3 citrullination are increased in X-linked Dystonia Parkinsonism post-mortem prefrontal cortex

Neuroinflammation plays a pathogenic role in neurodegenerative diseases and recent findings suggest that it may also be involved in X-linked Dystonia-Parkinsonism (XDP) pathogenesis. Previously, fibroblasts and neuronal stem cells derived from XDP patients demonstrated hypersensitivity to TNF-α, dysregulation in NFκB signaling, and an increase in several pro-inflammatory markers. However, the role of inflammatory processes in XDP patient brain remains unknown. Here we demonstrate that there is a significant increase in astrogliosis and microgliosis in human post-mortem XDP prefrontal cortex (PFC) compared to control. Furthermore, there is a significant increase in histone H3 citrullination (H3R2R8R17cit₃) with a concomitant increase in peptidylarginine deaminase 2 (PAD2) and 4 (PAD4), the enzymes catalyzing citrullination, in XDP post-mortem PFC. While there is a significant increase in myeloperoxidase (MPO) levels in XDP PFC, neutrophil elastase (NE) levels are not altered, suggesting that MPO may be released by activated microglia or reactive astrocytes in the brain. Similarly, there was an increase in H3R2R8R17cit₃, PAD2 and PAD4 levels in XDP-derived fibroblasts. Importantly, treatment of fibroblasts with Cl-amidine, a pan inhibitor of PAD enzymes, reduced histone H3 citrullination and pro-inflammatory chemokine expression, without affecting cell survival. Taken together, our results demonstrate that inflammation is increased in XDP post-mortem brain and fibroblasts and unveil a new epigenetic potential therapeutic target.