NETosis in the pathogenesis of acute lung injury following cutaneous chemical burns

Guardians Turned Culprits: NETosis and Its Influence on Pulmonary Fibrosis Development

Idiopathic pulmonary fibrosis (IPF) is a debilitating, life-threatening irreversible lung disease characterized by the excessive accumulation of fibrotic tissue in the lungs, impairing their function. The exact mechanisms underlying Pulmonary fibrosis (PF) are multifaceted and not yet fully understood. Reports show that during COVID-19 pandemic, PF was dramatically increased due to the hyperactivation of the immune system. Neutrophils and macrophages are the patrolling immune cells that keep the microenvironment balanced. Neutrophil extracellular traps (NETs) are a normal protective mechanism of neutrophils. The chief components of the NETs include DNA, citrullinated histones, and anti-microbial peptides which are released by the activated neutrophils. However, it is becoming increasingly evident that hyperactivation of immune cells can also turn into criminals when it comes to pathological state. Dysregulated NETosis may contribute to sustained inflammation, overactivation of fibroblasts, and ultimately promoting collagen deposition which is the characteristic feature of PF. The role of NETs along with inflammation is attaining greater attention. However, seldom researches are related to the relationship between NETs causing PF. This review highlights the cellular mechanism of NETs-induced pulmonary fibrosis, which could give a better understanding of molecular targets which may be helpful for treating NETs-induced PF.

PAD4 inhibition impacts immune responses in SARS-CoV-2 infection

Protein arginine deiminase 4 (PAD4) has emerged as a potential therapeutic target for various diseases due to its role in promoting neutrophil extracellular trap (NET) formation. NETs, composed of DNA and antimicrobial proteins, serve as a defense mechanism against pathogens but can also drive lung injury, particularly in SARS-CoV-2 infection. In this study, we examined the effects of PAD4 inhibition on clinical outcomes and adaptive immunity within the context of SARS-CoV-2 infection. Our results show that PAD4 pharmacological inhibition reduced lung NET concentration and improved clinical outcomes, similar to treatment with recombinant human DNase (rhDNase), which degrades NET structure. However, in contrast to rhDNase, PAD4 targeting diminished virus-specific T cell responses by impairing dendritic cell antigen presentation and reducing IL-2 signaling by affecting its production by T cells. In line with these observations, PAD4 pharmacological inhibition diminished antigen-specific T cell responses in a model of lung inflammation. These findings highlight the importance of carefully evaluating PAD4 as a therapeutic target in COVID-19, given its potential to compromise adaptive immune responses crucial for fighting the virus.

Persistent neutrophilic inflammation is associated with delayed toxicity of phenylarsine oxide in lungs

Phenyl arsine oxide (PAO) is a vesicant, similar to Lewisite, a potential chemical warfare agent and an environmental contaminant. PAO-induced skin burns can trigger acute organ injury, including lungs. We have recently demonstrated that PAO burns can have delayed toxicity, although the specific mechanism/s remain to be determined. A single cutaneous exposure to PAO resulted in inflammatory acute lung injury at 6 and 24 h. While acute injury subsiding by 1 week, we observed a significant airway remodeling at 10 weeks post-PAO exposure. The mechanism of prolonged PAO toxicity was associated with the influx of neutrophils that produced harmful neutrophil extracellular traps (NETs). We demonstrated that the crosstalk between NET deployments and expression of IL-33, a pro-remodeling mediator was associated with the development of peribronchial fibrosis. In summary, these results suggest that a single cutaneous exposure to PAO causes the acute inflammatory phase followed by NETs/IL-33 feed forward signaling implicated for the persistent neutrophil influx and NETs formation resulting in airway remodeling.

Persistent Neutrophilic Inflammation is Associated with Delayed Toxicity of Phenylarsine Oxide in Lungs

Phenyl arsine oxide (PAO) is a vesicant, similar to Lewisite, a potential chemical warfare agent and an environmental contaminant. PAO-induced skin burns can trigger acute organ injury, including lungs. We have recently demonstrated that PAO burns can also has a delayed toxicity, although the specific mechanism/s remain to be determined. A single cutaneous exposure to PAO resulted in inflammatory acute lung injury at 6 and 24 hours. While acute injury subsiding by 1 week, we observed a significant airway remodeling at 10 weeks post-PAO exposure. The mechanism of prolonged PAO toxicity was associated with the influx of neutrophils that produced harmful neutrophil extracellular traps (NETs). We demonstrated that the crosstalk between NET deployments and expression of IL-33, a pro-remodeling mediator was associated with the development of peribronchial fibrosis. In summary, these results suggest that a single cutaneous exposure to PAO causes the acute inflammatory phase followed by NETs/IL-33 feed forward signaling implicated for the persistent neutrophil influx and NETs formation resulting in airway remodeling.

Sorafenib-induced macrophage extracellular traps via ARHGDIG/IL4/PADI4 axis confer drug resistance through inhibiting ferroptosis in hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most common as well as leading causes of mortality worldwide, and sorafenib is the first-line treatment in HCC patients. Unfortunately, drug resistance to sorafenib often develops. However, the underlying mechanism remains unclear. Here, we reveal the important role of macrophage extracellular traps (METs)-mediated crosstalk between macrophages and tumor cells in sorafenib resistance.

METHODS

METs in HCC tumor tissues were detected using immunofluorescence. The concentrations of MPO-DNA, elastase and cytokines were measured using ELISA. The mRNA expression levels of genes were confirmed by qRT-PCR. The siRNAs were conducted to knock ARHGDIG in Hepa1-6 and Hep3B cells. Western Blot assay was performed to determine protein expression of Rho GDP dissociation inhibitor gamma (ARHGDIG, or RHOGDI-3), PADI2, and PADI4. Cell viability and migration were evaluated by CCK-8 assay and transwell assay, respectively. Cell ferroptosis was assessed by measurement of Fe2+ concentration, flow cytometry assay of lipid ROS, and western blot assay of GPX4. The functions of sorafenib, DNase I, IL4 neutralization antibody and GPX4 in tumor growth were explored through in vivo experiments.

RESULTS

Sorafenib induced MET formation in M2 macrophages rather than M1 macrophages derived from both human and mice. In Hepa1-6 HCC mice, METs clearance by DNase I improved response to sorafenib therapy, detected by tumor weight, tumor growth curve, tumor volume, and survival. By screening candidate cytokines that affect macrophage function, we found that sorafenib-promoting IL4 secretion by HCC cells plays a crucial role in sorafenib-induced MET formation. Understanding the critical role of IL4 in sorafenib-induced MET formation led us to find that IL4 neutralization significantly improved the efficiency of sorafenib in HCC models. Mechanistically, we discovered that sorafenib increased the expression of ARHGDIG in HCC cells, which led to the release of IL4. In M2 macrophages, IL4 triggered MET formation by elevating the mRNA and protein expression of peptidyl arginine deiminase 4 (PADI4) rather than PADI2. In HCC models, GSK484 inhibition of PADI4 could consistently weaken sorafenib resistance and improve sorafenib efficiency. Importantly, we discovered that METs contribute to sorafenib resistance by inhibiting the ferroptosis of HCC cells. Meanwhile, PADI4 inhibition or DNase I could reverse the sorafenib resistance caused by METs-inhibiting ferroptosis of HCC cells.

CONCLUSION

Our study concludes that sorafenib-induced METs inhibit the ferroptosis of tumor cells, suggesting that targeting the IL4/PADI4/METs axis in HCC could reduce or prevent sorafenib resistance.

Recombinant thrombomodulin and recombinant antithrombin attenuate pulmonary endothelial glycocalyx degradation and neutrophil extracellular trap formation in ventilator-induced lung injury in the context of endotoxemia

BACKGROUND

Vascular endothelial damage is involved in the development and exacerbation of ventilator-induced lung injury (VILI). Pulmonary endothelial glycocalyx and neutrophil extracellular traps (NETs) are endothelial protective and damaging factors, respectively; however, their dynamics in VILI and the effects of recombinant thrombomodulin and antithrombin on these dynamics remain unclear. We hypothesized that glycocalyx degradation and NETs are induced by VILI and suppressed by recombinant thrombomodulin, recombinant antithrombin, or their combination.

METHODS

VILI was induced in male C57BL/6J mice by intraperitoneal lipopolysaccharide injection (20 mg/kg) and high tidal volume ventilation (20 mL/kg). In the intervention groups, recombinant thrombomodulin, recombinant antithrombin, or their combination was administered at the start of mechanical ventilation. Glycocalyx degradation was quantified by measuring serum syndecan-1, fluorescence-labeled lectin intensity, and glycocalyx-occupied area in the pulmonary vascular lumen. Double-stranded DNA in the bronchoalveolar fluid and fluorescent areas of citrullinated histone H3 and myeloperoxidase were quantified as NET formation.

RESULTS

Serum syndecan-1 increased, and lectin fluorescence intensity decreased in VILI. Electron microscopy revealed decreases in glycocalyx-occupied areas within pulmonary microvessels in VILI. Double-stranded DNA levels in the bronchoalveolar lavage fluid and the fluorescent area of citrullinated histone H3 and myeloperoxidase in lung tissues increased in VILI. Recombinant thrombomodulin, recombinant antithrombin, and their combination reduced glycocalyx injury and NET marker levels. There was little difference in glycocalyx injury and NET makers between the intervention groups.

CONCLUSION

VILI induced glycocalyx degradation and NET formation. Recombinant thrombomodulin and recombinant antithrombin attenuated glycocalyx degradation and NETs in our VILI model. The effect of their combination did not differ from that of either drug alone. Recombinant thrombomodulin and antithrombin have the potential to be therapeutic agents for biotrauma in VILI.

Neutrophil extracellular traps trigger alveolar epithelial cell necroptosis through the cGAS-STING pathway during acute lung injury in mice

Extensive loss of alveolar epithelial cells (AECs) undergoing necroptosis is a crucial mechanism of acute lung injury (ALI), but its triggering mechanism needs to be thoroughly investigated. Neutrophil extracellular traps (NETs) play a significant role in ALI. However, the effect of NETs on AECs' death has not been clarified. Our study found that intratracheal instillation of NETs disrupted lung tissue structure, suggesting that NETs could induce ALI in mice. Moreover, we observed that NETs could trigger necroptosis of AECs in vivo and in vitro. The phosphorylation levels of RIPK3 and MLKL were increased in MLE12 cells after NETs treatment (P < 0.05). Mechanistically, NETs taken up by AECs through endocytosis activated the cGAS-STING pathway and triggered AECs necroptosis. The expression of cGAS, STING, TBK1 and IRF3 were increased in MLE12 cells treated with NETs (P < 0.05). Furthermore, the cGAS inhibitor RU.521 inhibited NETs-triggered AECs necroptosis and alleviated the pulmonary damage induced by NETs in mice. In conclusion, our study demonstrates that NETs taken up by AECs via endocytosis can activate the cGAS-STING pathway and trigger AECs necroptosis to promote ALI in mice. Our findings indicate that targeting the NETs/cGAS-STING/necroptosis pathway in AECs is an effective strategy for treating ALI.

Pneumocystis murina promotes inflammasome formation and NETosis during Pneumocystis pneumonia

Pneumocystis jirovecii pneumonia (PjP) poses a serious risk to individuals with compromised immune systems, such as individuals with HIV/AIDS or undergoing immunosuppressive therapies for cancer or solid organ transplants. Severe PjP triggers excessive lung inflammation, resulting in lung function decline and consequential alveolar damage, potentially culminating in acute respiratory distress syndrome. Non-HIV patients face a 30%-60% mortality rate, emphasizing the need for a deeper understanding of inflammatory responses in PjP. Prior research emphasized macrophages in Pneumocystis infections, neglecting neutrophils' role in tissue damage. Consequently, the overemphasis on macrophages led to an incomplete understanding of the role of neutrophils and inflammatory responses. In the current investigation, our RNAseq studies on a murine surrogate model of PjP revealed heightened activation of the NLRP3 inflammasome and NETosis cell death pathways in their lungs. Immunofluorescence staining confirmed neutrophil extracellular trap (NET) presence in the lungs of the P. murina-infected mice, validating our findings. Moreover, isolated neutrophils exhibited NETosis when directly stimulated with P. murina. Isolated NETs compromised P. murina viability in vitro, highlighting the potential role of neutrophils in controlling fungal growth and promoting inflammation during P. murina pneumonia through NLRP3 inflammasome assembly and NETosis. These pathways, essential for inflammation and pathogen elimination, bear the risk of uncontrolled activation leading to excessive tissue damage and persistent inflammation. This pioneering study is the first to identify the formation of NETs and inflammasomes during Pneumocystis infection, paving the way for comprehensive investigations into treatments aimed at mitigating lung damage and augmenting survival rates for individuals with PjP.IMPORTANCEPneumocystis jirovecii pneumonia (PjP) affects individuals with weakened immunity, such as HIV/AIDS, cancer, and organ transplant patients. Severe PjP triggers lung inflammation, impairing function and potentially causing acute respiratory distress syndrome. Non-HIV individuals face a 30%-60% mortality rate, underscoring the need for deeper insight into PjP's inflammatory responses. Past research focused on macrophages in managing Pneumocystis infection and its inflammation, while the role of neutrophils was generally overlooked. In contrast, our findings in P. murina-infected mouse lungs showed neutrophil involvement during inflammation and increased expression of NLRP3 inflammasome and NETosis pathways. Detection of neutrophil extracellular traps further indicated their involvement in the inflammatory process. Although beneficial in combating infection, unregulated neutrophil activation poses a potential threat to lung tissues. Understanding the behavior of neutrophils in Pneumocystis infections is crucial for controlling detrimental reactions and formulating treatments to reduce lung damage, ultimately improving the survival rates of individuals with PjP.

Epigenetic regulation of pulmonary inflammation

Pulmonary disease such as chronic obstructive pulmonary disease (COPD), asthma, pulmonary fibrosis and pulmonary hypertension are the leading cause of deaths. More importantly, lung diseases are on the rise and environmental factors induced epigenetic modifications are major players on this increased prevalence. It has been reported that dysregulation of genes involved in epigenetic regulation such as the histone deacetylase (HDACs) and histone acetyltransferase (HATs) play important role in lung health and pulmonary disease pathogenesis. Inflammation is an essential component of respiratory diseases. Injury and inflammation trigger release of extracellular vesicles that can act as epigenetic modifiers through transfer of epigenetic regulators such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), proteins and lipids, from one cell to another. The immune dysregulations caused by the cargo contents are important contributors of respiratory disease pathogenesis. N6 methylation of RNA is also emerging to be a critical mechanism of epigenetic alteration and upregulation of immune responses to environmental stressors. Epigenetic changes such as DNA methylation are stable and often long term and cause onset of chronic lung conditions. These epigenetic pathways are also being utilized for therapeutic intervention in several lung conditions.

Reduced Bioactive Microbial Products (Pathogen-Associated Molecular Patterns) Contribute to Dysregulated Immune Responses and Impaired Healing in Infected Wounds in Mice with Diabetes

Diabetic chronic ulcers are plagued with persistent nonresolving inflammation. However, diabetic wound environment early after injury suffers from inadequate inflammatory responses due to reductions in proinflammatory cytokines levels. Diabetic neutrophils have known impairments in bactericidal functions. We hypothesized that reduced bacterial killing by diabetic neutrophils, due to their bactericidal functional impairments, results in reduced bioactive bacterial products, known as pathogen-associated molecular patterns, which in turn contribute to reduced signaling through toll-like receptors, leading to inadequate production of proinflammatory cytokines in infected diabetic wound early after injury. We tested our hypothesis in db/db type 2 obese diabetic mouse wound infection model with Pseudomonas aeruginosa. Our data indicate that despite substantially higher levels of infection, toll-like receptor 4-mediated signaling is reduced in diabetic wounds early after injury owing to reduced bioactive levels of lipopolysaccharide. We further demonstrate that topical treatment with lipopolysaccharide enhances toll-like receptor 4 signaling, increases proinflammatory cytokine production, restores leukocyte trafficking, reduces infection burden, and stimulates healing in diabetic wounds. We posit that lipopolysaccharide may be a viable therapeutic option for the treatment of diabetic foot ulcers if it is applied topically after the surgical debridement process, which is intended to reset chronic ulcers into acute fresh wounds.

HSP90, a Common Therapeutic Target for Suppressing Skin Injury Caused by Exposure to Chemically Diverse Classes of Blistering Agents

Vesicants such as arsenicals and mustards produce highly painful cutaneous inflammatory and blistering responses, hence developed as chemical weapons during World War I/II. Here, using lewisite and sulfur mustard surrogates, namely phenylarsine oxide (PAO) and 2-chloroethyl ethyl sulfide (CEES), respectively, we defined a common underlying mechanism of toxic action by these two distinct classes of vesicants. Murine skin exposure to these chemicals causes tissue destruction characterized by increase in skin bifold thickness, Draize score, infiltration of inflammatory cells, and apoptosis of epidermal and dermal cells. RNA sequencing analysis identified ∼346 inflammatory genes that were commonly altered by both PAO and CEES, along with the identification of cytokine signaling activation as the top canonical pathway. Activation of several proinflammatory genes and pathways is associated with phosphorylation-dependent activation of heat shock protein 90α (p-HSP90α). Topical treatment with known HSP90 inhibitors SNX-5422 and IPI-504 post PAO or CEES skin challenge significantly attenuated skin damage including reduction in overall skin injury and clinical scores. In addition, highly upregulated inflammatory genes Saa3, Cxcl1, Ccl7, IL-6, Nlrp3, Csf3, Chil3, etc. by both PAO and CEES were significantly diminished by treatment with HSP90 inhibitors. These drugs not only reduced PAO- or CEES-induced p-HSP90α expression but also its client proteins NLRP3 and pP38 and the expression of their target inflammatory genes. Our data confirm a critical role of HSP90 as a shared underlying molecular target of toxicity by these two distinct vesicants and provide an effective and novel medical countermeasure to suppress vesicant-induced skin injury. SIGNIFICANCE STATEMENT: Development of effective and novel mechanism-based antidotes that can simultaneously block cutaneous toxic manifestations of distinct vesicants is important and urgently needed. Due to difficulties in determining the exact nature of onsite chemical exposure, a potent drug that can suppress widespread cutaneous damage may find great utility. Thus, this study identified HSP90 as a common molecular regulator of cutaneous inflammation and injury by two distinct warfare vesicants, arsenicals and mustards, and HSP90 inhibitors afford significant protection against skin damage.

A Murine Model of Vesicant-Induced Acute Lung Injury

Burn injuries including those caused by chemicals can result in systemic effects and acute lung injury (ALI). Cutaneous exposure to Lewisite, a warfare and chemical burn agent, also causes ALI. To overcome the limitations in conducting direct research on Lewisite-induced ALI in a laboratory setting, an animal model was developed using phenylarsine oxide (PAO) as a surrogate for Lewisite. Due to lack of a reliable animal model mimicking the effects of such exposures, development of effective therapies to treat such injuries is challenging. We demonstrated that a single cutaneous exposure to PAO resulted in disruption of the alveolar-capillary barrier as evidenced by elevated protein levels in the bronchoalveolar lavage fluid (BALF). BALF supernatant of PAO-exposed animals had increased levels of high mobility group box 1, a damage associated molecular pattern molecule. Arterial blood-gas measurements showed decreased pH, increased PaCO2, and decreased partial pressure of arterial O2, indicative of respiratory acidosis, hypercapnia, and hypoxemia. Increased protein levels of interleukin (IL)-6, CXCL-1, CXCL-2, CXCL-5, granulocyte-macrophage colony-stimulating factor, CXCL-10, leukemia inhibitory factor, leptin, IL-18, CCL-2, CCL-3, and CCL-7 were observed in the lung of PAO-exposed mice. Further, vascular endothelial growth factor levels were reduced in the lung. Pulmonary function evaluated using a flexiVent showed a downward shift in the pressure-volume loop, decreases in static compliance and inspiratory capacity, increases in respiratory elastance and tissue elastance. These changes are consistent with an ALI phenotype. These results demonstrate that cutaneous PAO exposure leads to ALI and that the model can be used as an effective surrogate to investigate vesicant-induced ALI. SIGNIFICANCE STATEMENT: This study presents a robust model for studying ALI resulting from cutaneous exposure to PAO, a surrogate for the toxic vesicating agent Lewisite. The findings in this study mimic the effects of cutaneous Lewisite exposure, providing a reliable model for investigating mechanisms underlying toxicity. The model can also be used to develop medical countermeasures to mitigate ALI associated with cutaneous Lewisite exposure.

Phenylarsine oxide induced corneal injury involves oxidative stress mediated unfolded protein response and ferroptotic cell death: Amelioration by NAC

Phenylarsine oxide (PAO), an analog of lewisite, is a highly toxic trivalent arsenical and a potential chemical warfare agent. PAO-induced toxicity has been studied in lung, liver, and skin tissues. Nevertheless, very few studies have been published to comprehend the impact of PAO-induced toxicity on ocular tissues, even though eyes are uniquely vulnerable to injury by vesicants. Notably, arsenical vesicants such as lewisite have been shown to cause edema of eyelids, inflammation, massive corneal necrosis, and blindness. Accordingly, human corneal epithelial cells were used to study the effects of PAO exposure. PAO (100 and 200 nM) induced significant oxidative stress in corneal epithelial cells. Simultaneous treatment with N-acetyl-l-cysteine (NAC), an FDA-approved antioxidant, reversed the PAO-induced toxicity in human corneal epithelial cells. Furthermore, oxidative stress induction by PAO was accompanied by unfolded protein response (UPR) signaling activation and ferroptotic cell death. Further, to validate the findings of our in vitro studies, we optimized injury biomarkers and developed an ex vivo rabbit corneal culture model of PAO exposure. Investigations using PAO in ex vivo rabbit corneas revealed similar results. PAO (5 or 10 μg) for 3, 5, and 10 min caused moderate to extensive corneal epithelial layer degradation and reduced the epithelial layer thickness in a concentration- and time-dependent manner. Similar to human corneal cells, injuries by PAO in ex vivo cultured rabbit corneas were also associated with elevated oxidative stress, UPR signaling, and ferroptosis induction. NAC mitigated PAO-induced corneal injuries in rabbit ex vivo cornea culture as well. The reversal of PAO toxicity upon NAC treatment observed in our studies could be attributed to its antioxidant properties. These findings suggest that PAO exposure can cause significant corneal injury and highlight the need for further mechanistic studies to better understand the pathobiology of different arsenical vesicants, including PAO and lewisite.

The role of neutrophil extracellular traps in sepsis and sepsis-related acute lung injury

Neutrophils release neutrophil extracellular traps (NETs) to trap pathogenic microorganisms. NETs are involved in the inflammatory response and bacterial killing and clearance. However, their excessive activation can lead to an inflammatory storm in the body, which may damage tissues and cause organ dysfunction. Organ dysfunction is the main pathophysiological cause of sepsis and also a cause of the high mortality rate in sepsis. Acute lung injury caused by sepsis accounts for the highest proportion of organ damage in sepsis. NET formation can lead to the development of sepsis because by promoting the release of interleukin-1 beta, interleukin-8, and tumor necrosis factor-alpha, thereby accelerating acute lung injury. In this review, we describe the critical role of NETs in sepsis-associated acute lung injury and review the current knowledge and novel therapeutic approaches.

Cutaneous Exposure to Arsenicals Is Associated with Development of Constrictive Bronchiolitis in Mice

Organoarsenicals, such as lewisite and related chloroarsine, diphenylchloroarsine (DPCA), are chemical warfare agents developed during World War I. Stockpiles in Eastern Europe remain a threat to humans. The well-documented effects of cutaneous exposure to these organoarsenicals include skin blisters, painful burns, and life-threatening conditions such as acute respiratory distress syndrome. In survivors, long-term effects such as the development of respiratory ailments are reported for the organoarsenical sulfur mustard; however, no long-term pulmonary effects are documented for lewisite and DPCA. No animal models exist to explore the relationship between skin exposure to vesicants and constrictive bronchiolitis. We developed and characterized a mouse model to study the long-term effects of cutaneous exposure on the lungs after exposure to a sublethal dose of organoarsenicals. We exposed mice to lewisite, DPCA, or a less toxic surrogate organoarsenic chemical, phenyl arsine oxide, on the skin. The surviving mice were followed for 20 weeks after skin exposure to arsenicals. Lung microcomputed tomography, lung function, and histology demonstrated increased airway resistance, increased thickness of the smooth muscle layer, increased collagen deposition in the subepithelium, and peribronchial lymphocyte infiltration in mice exposed to arsenical on skin.

ROLE OF PEPTIDYLARGININE DEIMINASE AND NEUTROPHIL EXTRACELLULAR TRAPS IN INJURIES: FUTURE NOVEL DIAGNOSTICS AND THERAPEUTIC TARGETS

ABSTRACT

Injuries lead to an early systemic inflammatory state with innate immune system activation. Neutrophil extracellular traps (NETs) are a complex of chromatin and proteins released from the activated neutrophils. Although initially described as a response to bacterial infections, NETs have also been identified in the sterile postinjury inflammatory state. Peptidylarginine deiminases (PADs) are a group of isoenzymes that catalyze the conversion of arginine to citrulline, termed citrullination or deimination. PAD2 and PAD4 have been demonstrated to play a role in NET formation through citrullinated histone 3. PAD2 and PAD4 have a variety of substrates with variable organ distribution. Preclinical and clinical studies have evaluated the role of PADs and NETs in major trauma, hemorrhage, burns, and traumatic brain injury. Neutrophil extracellular trap formation and PAD activation have been shown to contribute to the postinjury inflammatory state leading to a detrimental effect on organ systems. This review describes our current understanding of the role of PAD and NET formation following injury and burn. This is a new field of study, and the emerging data appear promising for the future development of targeted biomarkers and therapies in trauma.

Neutrophils drive pulmonary vascular leakage in MHV-1 infection of susceptible A/J mice

Background

Lung inflammation, neutrophil infiltration, and pulmonary vascular leakage are pathological hallmarks of acute respiratory distress syndrome (ARDS) which can lethally complicate respiratory viral infections. Despite similar comorbidities, however, infections in some patients may be asymptomatic while others develop ARDS as seen with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections for example.

Methods

In this study, we infected resistant C57BL/6 and susceptible A/J strains of mice with pulmonary administration of murine hepatitis virus strain 1 (MHV-1) to determine mechanisms underlying susceptibility to pulmonary vascular leakage in a respiratory coronavirus infection model.

Results

A/J animals displayed increased lung injury parameters, pulmonary neutrophil influx, and deficient recruitment of other leukocytes early in the infection. Moreover, under basal conditions, A/J neutrophils overexpressed primary granule protein genes for myeloperoxidase and multiple serine proteases. During infection, myeloperoxidase and elastase protein were released in the bronchoalveolar spaces at higher concentrations compared to C57BL/6 mice. In contrast, genes from other granule types were not differentially expressed between these 2 strains. We found that depletion of neutrophils led to mitigation of lung injury in infected A/J mice while having no effect in the C57BL/6 mice, demonstrating that an altered neutrophil phenotype and recruitment profile is a major driver of lung immunopathology in susceptible mice.

Conclusions

These results suggest that host susceptibility to pulmonary coronaviral infections may be governed in part by underlying differences in neutrophil phenotypes, which can vary between mice strains, through mechanisms involving primary granule proteins as mediators of neutrophil-driven lung injury.

Role of neutrophil extracellular traps in inflammatory evolution in severe acute pancreatitis

ABSTRACT

Severe acute pancreatitis (SAP) is a life-threatening acute abdominal disease with two peaks of death: the first in the early stage, characterized by systemic inflammatory response-associated organ failure; and the second in the late stage, characterized by infectious complications. Neutrophils are the main immune cells participating in the whole process of SAP. In addition to the traditional recognition of neutrophils as the origination of chemokine and cytokine cascades or phagocytosis and degranulation of pathogens, neutrophil extracellular traps (NETs) also play an important roles in inflammatory reactions. We reviewed the role of NETs in the occurrence and development of SAP and its fatal complications, including multiple organs injury, infected pancreatic necrosis, and thrombosis. This review provides novel insights into the involvement of NETs throughout the entire process of SAP, showing that targeting NETs might be a promising strategy in SAP treatment. However, precision therapeutic options targeting NETs in different situations require further investigation.

Extracellular vesicles in the pathogenesis and treatment of acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are common life-threatening lung diseases associated with acute and severe inflammation. Both have high mortality rates, and despite decades of research on clinical ALI/ARDS, there are no effective therapeutic strategies. Disruption of alveolar-capillary barrier integrity or activation of inflammatory responses leads to lung inflammation and injury. Recently, studies on the role of extracellular vesicles (EVs) in regulating normal and pathophysiologic cell activities, including inflammation and injury responses, have attracted attention. Injured and dysfunctional cells often secrete EVs into serum or bronchoalveolar lavage fluid with altered cargoes, which can be used to diagnose and predict the development of ALI/ARDS. EVs secreted by mesenchymal stem cells can also attenuate inflammatory reactions associated with cell dysfunction and injury to preserve or restore cell function, and thereby promote cell proliferation and tissue regeneration. This review focuses on the roles of EVs in the pathogenesis of pulmonary inflammation, particularly ALI/ARDS.

Advances in molecular pathogenesis of hidradenitis suppurativa: Dysregulated keratins and ECM signaling

Hidradenitis suppurativa (HS) is characterized by deep-seated, highly inflamed, and painful lumps/abscesses, fistulae, and sinus tracts that grow extensively deep in the dermis and are highly immunogenic in nature. In about one-third of the HS patients there is strong evidence for the role of γ-secretase mutations along with dysregulated Notch signaling. However, the contribution of dysregulated Notch signaling in HS pathogenesis in relation to hair follicle alterations and hyper-activation of the immune system remains undefined. A genome-wide association study (GWAS), proteomic data and functional investigations of identified sequence variants in HS pathology are not fully revealing. The disease initiation or progression may involve bacterial infection besides intrinsic functional defects in keratinocytes, which may be key to further exacerbate immune cell infiltration and cytokine production in and around the lesional tissue. The absence of a suitable animal model that could fully recapitulate the pathogenesis of HS is a major impediment for proper understanding the underlying mechanisms and development of effective treatments. The presence of extracellular matrix (ECM) degradation products along with dysregulation in keratinocytes and, dermal fibroblasts ultimately affect immune regulation and are various components of HS pathogenesis. Bacterial infection further exacerbates the complexity of the disease progression. While anti-TNFα therapy shows partial efficacy, treatment to cure HS is absent. Multiple clinical trials targeting various cytokines, complement C5a and ECM products are in progress. This review provides state-of-the-art information on these aspects with a focus on dysregulated keratinocyte and immune cells; and role of ECM, and Keratin functions in this regard.

Targeting ETosis by miR-155 inhibition mitigates mixed granulocytic asthmatic lung inflammation

Asthma is phenotypically heterogeneous with several distinctive pathological mechanistic pathways. Previous studies indicate that neutrophilic asthma has a poor response to standard asthma treatments comprising inhaled corticosteroids. Therefore, it is important to identify critical factors that contribute to increased numbers of neutrophils in asthma patients whose symptoms are poorly controlled by conventional therapy. Leukocytes release chromatin fibers, referred to as extracellular traps (ETs) consisting of double-stranded (ds) DNA, histones, and granule contents. Excessive components of ETs contribute to the pathophysiology of asthma; however, it is unclear how ETs drive asthma phenotypes and whether they could be a potential therapeutic target. We employed a mouse model of severe asthma that recapitulates the intricate immune responses of neutrophilic and eosinophilic airway inflammation identified in patients with severe asthma. We used both a pharmacologic approach using miR-155 inhibitor-laden exosomes and genetic approaches using miR-155 knockout mice. Our data show that ETs are present in the bronchoalveolar lavage fluid of patients with mild asthma subjected to experimental subsegmental bronchoprovocation to an allergen and a severe asthma mouse model, which resembles the complex immune responses identified in severe human asthma. Furthermore, we show that miR-155 contributes to the extracellular release of dsDNA, which exacerbates allergic lung inflammation, and the inhibition of miR-155 results in therapeutic benefit in severe asthma mice. Our findings show that targeting dsDNA release represents an attractive therapeutic target for mitigating neutrophilic asthma phenotype, which is clinically refractory to standard care.

Multicenter analysis of neutrophil extracellular trap dysregulation in adult and pediatric COVID-19

Dysregulation in neutrophil extracellular trap (NET) formation and degradation may play a role in the pathogenesis and severity of COVID-19; however, its role in the pediatric manifestations of this disease, including multisystem inflammatory syndrome in children (MIS-C) and chilblain-like lesions (CLLs), otherwise known as “COVID toes,” remains unclear. Studying multinational cohorts, we found that, in CLLs, NETs were significantly increased in serum and skin. There was geographic variability in the prevalence of increased NETs in MIS-C, in association with disease severity. MIS-C and CLL serum samples displayed decreased NET degradation ability, in association with C1q and G-actin or anti-NET antibodies, respectively, but not with genetic variants of DNases. In adult COVID-19, persistent elevations in NETs after disease diagnosis were detected but did not occur in asymptomatic infection. COVID-19–affected adults displayed significant prevalence of impaired NET degradation, in association with anti-DNase1L3, G-actin, and specific disease manifestations, but not with genetic variants of DNases. NETs were detected in many organs of adult patients who died from COVID-19 complications. Infection with the Omicron variant was associated with decreased NET levels when compared with other SARS-CoV-2 strains. These data support a role for NETs in the pathogenesis and severity of COVID-19 in pediatric and adult patients.

Development of BRD4 inhibitors as anti-inflammatory agents and antidotes for arsenicals

Arsenicals belong to the class of chemical warfare agents known as vesicants, which are highly reactive, toxic and cause robust inflammatory response. Cutaneous exposure to arsenicals causes a wide range of systemic organ damage, beginning with cutaneous injuries, and later manifest multi-organ damage and death. Thus, the development of suitable antidotes that can effectively block injury following exposure to these agents is of great importance. Bromodomain 4 (BRD4), a member of the bromodomain and extra terminal domain (BET) family, plays crucial role in regulating transcription of inflammatory, proliferation and cell cycle genes. In this context, the development of potent small molecule inhibitors of BRD4 could serve as potential antidotes for arsenicals. Herein, we describe the synthesis and biological evaluation of a series of compounds.

Pathophysiological Role of Vimentin Intermediate Filaments in Lung Diseases

Vimentin intermediate filaments, a type III intermediate filament, are among the most widely studied IFs and are found abundantly in mesenchymal cells. Vimentin intermediate filaments localize primarily in the cytoplasm but can also be found on the cell surface and extracellular space. The cytoplasmic vimentin is well-recognized for its role in providing mechanical strength and regulating cell migration, adhesion, and division. The post-translationally modified forms of Vimentin intermediate filaments have several implications in host-pathogen interactions, cancers, and non-malignant lung diseases. This review will analyze the role of vimentin beyond just the epithelial to mesenchymal transition (EMT) marker highlighting its role as a regulator of host-pathogen interactions and signaling pathways for the pathophysiology of various lung diseases. In addition, we will also examine the clinically relevant anti-vimentin compounds and antibodies that could potentially interfere with the pathogenic role of Vimentin intermediate filaments in lung disease.

Neutrophils Contribute to ER Stress in Lung Epithelial Cells in the Pristane-Induced Diffuse Alveolar Hemorrhage Mouse Model

Diffuse alveolar hemorrhage (DAH), although rare, is a life-threatening complication of systemic lupus erythematosus (SLE). Little is known about the pathophysiology of DAH in humans, although increasingly neutrophils, NETosis and inflammatory monocytes have been shown to play an important role in the pristane-induced model of SLE which develops lung hemorrhage and recapitulates many of the pathologic features of human DAH. Using this experimental model, we asked whether endoplasmic reticulum (ER) stress played a role in driving the pathology of pulmonary hemorrhage and what role infiltrating neutrophils had in this process. Analysis of lung tissue from pristane-treated mice showed genes associated with ER stress and NETosis were increased in a time-dependent manner and reflected the timing of CD11b⁺Ly6G⁺ neutrophil accumulation in the lung. Using precision cut lung slices from untreated mice we observed that neutrophils isolated from the peritoneal cavity of pristane-treated mice could directly induce the expression of genes associated with ER stress, namely Chop and Bip. Mice which had myeloid-specific deletion of PAD4 were generated and treated with pristane to assess the involvement of PAD4 and PAD4-dependent NET formation in pristane-induced lung inflammation. Specific deletion of PAD4 in myeloid cells resulted in decreased expression of ER stress genes in the pristane model, with accompanying reduction in IFN-driven genes and pathology. Lastly, coculture experiments of human neutrophils and human lung epithelial cell line (BEAS-2b) showed neutrophils from SLE patients induced significantly more ER stress and interferon-stimulated genes in epithelial cells compared to healthy control neutrophils. These results support a pathogenic role of neutrophils and NETs in lung injury during pristane-induced DAH through the induction of ER stress response and suggest that overactivation of neutrophils in SLE and NETosis may underlie development of DAH.

HMGB1-Mediated Neutrophil Extracellular Trap Formation Exacerbates Intestinal Ischemia/Reperfusion-Induced Acute Lung Injury

Influx of activated neutrophils into the lungs is the histopathologic hallmark of acute lung injury (ALI) after intestinal ischemia/reperfusion (I/R). Neutrophils can release DNA and granular proteins to form cytotoxic neutrophil extracellular traps (NETs), which promotes bystander tissue injury. However, whether NETs are responsible for the remote ALI after intestinal I/R and the mechanisms underlying the dissemination of harmful gut-derived mediators to the lungs are unknown. In the C57BL/6J mouse intestinal I/R model, DNase I-mediated degradation and protein arginine deiminase 4 (PAD4) inhibitor-mediated inhibition of NET treatments reduced NET formation, tissue inflammation, and pathological injury in the lung. High-mobility group protein B1 (HMGB1) blocking prevented NET formation and protected against tissue inflammation, as well as reduced cell apoptosis and improved survival rate. Moreover, recombinant human HMGB1 administration further drives NETs and concurrent tissue toxic injury, which in turn can be reversed by neutrophil deletion via anti-Ly6G Ab i.p. injection. Furthermore, global MyD88 deficiency regulated NET formation and alleviated the development of ALI induced by intestinal I/R. Thus, HMGB1 released from necroptotic enterocytes caused ALI after intestinal I/R by inducing NET formation. Targeting NETosis and the HMGB1 pathway might extend effective therapeutic strategies to minimize intestinal I/R-induced ALI.

Citrullination in the pathology of inflammatory and autoimmune disorders: recent advances and future perspectives

Numerous post-translational modifications (PTMs) govern the collective metabolism of a cell through altering the structure and functions of proteins. The action of the most prevalent PTMs, encompassing phosphorylation, methylation, acylations, ubiquitination and glycosylation is well documented. A less explored protein PTM, conversion of peptidylarginine to citrulline, is the subject of this review. The process of citrullination is catalysed by peptidylarginine deiminases (PADs), a family of conserved enzymes expressed in a variety of human tissues. Accumulating evidence suggest that citrullination plays a significant role in regulating cellular metabolism and gene expression by affecting a multitude of pathways and modulating the chromatin status. Here, we will discuss the biochemical nature of arginine citrullination, the enzymatic machinery behind it and also provide information on the pathological consequences of citrullination in the development of inflammatory diseases (rheumatoid arthritis, multiple sclerosis, psoriasis, systemic lupus erythematosus, periodontitis and COVID-19), cancer and thromboembolism. Finally, developments on inhibitors against protein citrullination and recent clinical trials providing a promising therapeutic approach to inflammatory disease by targeting citrullination are discussed.

The role of neutrophil extracellular traps in acute lung injury

Acute lung injury (ALI) is a heterogeneous inflammatory condition associated with high morbidity and mortality. Neutrophils play a key role in the development of different forms of ALI, and the release of neutrophil extracellular traps (NETs) is emerging as a common pathogenic mechanism. NETs are essential in controlling pathogens, and their defective release or increased degradation leads to a higher risk of infection. However, NETs also contain several pro-inflammatory and cytotoxic molecules than can exacerbate thromboinflammation and lung tissue injury. To reduce NET-mediated lung damage and inflammation, DNase is frequently used in preclinical models of ALI due to its capability of digesting NET DNA scaffold. Moreover, recent advances in neutrophil biology led to the development of selective NET inhibitors, which also appear to reduce ALI in experimental models. Here we provide an overview of the role of NETs in different forms of ALI discussing existing gaps in our knowledge and novel therapeutic approaches to modulate their impact on lung injury.

Extracellular Vesicles and Alveolar Epithelial-Capillary Barrier Disruption in Acute Respiratory Distress Syndrome: Pathophysiological Role and Therapeutic Potential

Extracellular vesicles (EVs) mediate intercellular communication by transferring genetic material, proteins and organelles between different cells types in both health and disease. Recent evidence suggests that these vesicles, more than simply diagnostic markers, are key mediators of the pathophysiology of acute respiratory distress syndrome (ARDS) and other lung diseases. In this review, we will discuss the contribution of EVs released by pulmonary structural cells (alveolar epithelial and endothelial cells) and immune cells in these diseases, with particular attention to their ability to modulate inflammation and alveolar-capillary barrier disruption, a hallmark of ARDS. EVs also offer a unique opportunity to develop new therapeutics for the treatment of ARDS. Evidences supporting the ability of stem cell-derived EVs to attenuate the lung injury and ongoing strategies to improve their therapeutic potential are also discussed.