NETs promote ALI/ARDS inflammation by regulating alveolar macrophage polarization

Immunotherapy strategies and prospects for acute lung injury: Focus on immune cells and cytokines

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a disastrous condition, which can be caused by a wide range of diseases, such as pneumonia, sepsis, traumas, and the most recent, COVID-19. Even though we have gained an improved understanding of acute lung injury/acute respiratory distress syndrome pathogenesis and treatment mechanism, there is still no effective treatment for acute lung injury/acute respiratory distress syndrome, which is partly responsible for the unacceptable mortality rate. In the pathogenesis of acute lung injury, the inflammatory storm is the main pathological feature. More and more evidences show that immune cells and cytokines secreted by immune cells play an irreplaceable role in the pathogenesis of acute lung injury. Therefore, here we mainly reviewed the role of various immune cells in acute lung injury from the perspective of immunotherapy, and elaborated the crosstalk of immune cells and cytokines, aiming to provide novel ideas and targets for the treatment of acute 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.

The role of lung macrophages in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is an acute and diffuse inflammatory lung injury in a short time, one of the common severe manifestations of the respiratory system that endangers human life and health. As an innate immune cell, macrophages play a key role in the inflammatory response. For a long time, the role of pulmonary macrophages in ARDS has tended to revolve around the polarization of M1/M2. However, with the development of single-cell RNA sequencing, fate mapping, metabolomics, and other new technologies, a deeper understanding of the development process, classification, and function of macrophages in the lung are acquired. Here, we discuss the function of pulmonary macrophages in ARDS from the two dimensions of anatomical location and cell origin and describe the effects of cell metabolism and intercellular interaction on the function of macrophages. Besides, we explore the treatments for targeting macrophages, such as enhancing macrophage phagocytosis, regulating macrophage recruitment, and macrophage death. Considering the differences in responsiveness of different research groups to these treatments and the tremendous dynamic changes in the gene expression of monocyte/macrophage, we discussed the possibility of characterizing the gene expression of monocyte/macrophage as the biomarkers. We hope that this review will provide new insight into pulmonary macrophage function and therapeutic targets of ARDS.

Quercetin alleviates ferroptosis accompanied by reducing M1 macrophage polarization during neutrophilic airway inflammation

Ferroptosis is a kind of regulated cell death, supporting the pathological process of lung inflammation, including asthma. Quercetin (QCT), a kind of natural dietary flavonoid, exerts anti-inflammatory and anti-ferroptosis effects in various diseases. However, the role of QCT in ferroptosis-associated airway inflammation of neutrophilic asthma remains to be described. Our study aimed to investigate the therapeutic effects of QCT on neutrophilic airway inflammation of asthma. Ferrostatin-1 (Fer-1), as a kind of ferroptosis inhibitor, was used to demonstrate whether neutrophilic airway inflammation of asthma relied on ferroptosis. In our study, the alleviation effect of QCT on neutrophilic airway inflammation was similar to Fer-1. Moreover, the significantly decreased levels of ferroptosis anti-oxidant protein (GPX4 and SLC7A11), increased malondialdehyde (MDA) levels, upregulated levels of 4-hydroxynonenal (4-HNE) expression by immunohistochemistry, and distorted mitochondria morphological changes in the lung tissues suggested lung ferroptosis in neutrophilic airway inflammation, which could be reversed by QCT treatment. In vitro experiments showed that QCT reduced LPS-induced ferroptosis through upregulating cell viability and levels of ferroptosis anti-oxidant protein (SLC7A11 and GPX4), reducing inflammatory cytokines, and decreasing the levels of MDA. Furthermore, ferroptosis was accompanied by enhancing M1 phenotype in neutrophilic airway inflammation, and QCT suppressed ferroptosis by inhibiting the pro-inflammatory M1 profile in vitro and in vivo, just as Fer-1 did. In conclusion, our study found that QCT ameliorated ferroptosis-associated neutrophilic airway inflammation accompanied by inhibiting M1 macrophage polarization. QCT may be a promising ferroptosis inhibitor for neutrophilic airway inflammation.

Multiple Death Pathways of Neutrophils Regulate Alveolar Macrophage Proliferation

Alveolar macrophage (AM) proliferation and self-renewal play an important role in the lung tissue microenvironment. However, the impact of immune cells, especially the neutrophils, on AM homeostasis or function is not well characterized. In this study, we induced in vivo migration of neutrophils into bronchoalveolar lavage (BAL) fluid and lung using CXCL1, and then co-cultured these with AMs in vitro. Neutrophils in the BAL (BAL-neutrophils), rather than neutrophils of bone marrow (BM-neutrophils), were found to inhibit AM proliferation. Analysis of publicly available data showed high heterogeneity of lung neutrophils with distinct molecular signatures of BM- and blood-neutrophils. Unexpectedly, BAL-neutrophils from influenza virus PR8-infected mice (PR8-neutrophils) did not inhibit the proliferation of AMs. Bulk RNA sequencing further revealed that co-culture of AMs with PR8-neutrophils induced IFN-α and -γ responses and inflammatory response, and AMs co-cultured with BAL-neutrophils showed higher expression of metabolism- and ROS-associated genes; in addition, BAL-neutrophils from PR8-infected mice modulated AM polarization and phagocytosis. BAL-neutrophil-mediated suppression of AM proliferation was abrogated by a combination of inhibitors of different neutrophil death pathways. Collectively, our findings suggest that multiple cell death pathways of neutrophils regulate the proliferation of AMs. Targeting neutrophil death may represent a potential therapeutic strategy for improving AM homeostasis during respiratory diseases.

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.

Ferret acute lung injury model induced by repeated nebulized lipopolysaccharide administration

Inflammatory lung diseases affect millions of people worldwide. These diseases are caused by a number of factors such as pneumonia, sepsis, trauma, and inhalation of toxins. Pulmonary function testing (PFT) is a valuable functional methodology for better understanding mechanisms of lung disease, measuring disease progression, clinical diagnosis, and evaluating therapeutic interventions. Animal models of inflammatory lung diseases are needed that accurately recapitulate disease manifestations observed in human patients and provide an accurate prediction of clinical outcomes using clinically relevant pulmonary disease parameters. In this study, we evaluated a ferret lung inflammation model that closely represents multiple clinical manifestations of acute lung inflammation and injury observed in human patients. Lipopolysaccharide (LPS) from Pseudomonas aeruginosa was nebulized into ferrets for 7 repeated daily doses. Repeated exposure to nebulized LPS resulted in a restrictive pulmonary injury characterized using Buxco forced maneuver PFT system custom developed for ferrets. This is the first study to report repeated forced maneuver PFT in ferrets, establishing lung function measurements pre- and post-injury in live animals. Bronchoalveolar lavage and histological analysis confirmed that LPS exposure elicited pulmonary neutrophilic inflammation and structural damage to the alveoli. We believe this ferret model of lung inflammation, with clinically relevant disease manifestations and parameters for functional evaluation, is a useful pre-clinical model for understanding human inflammatory lung disease and for the evaluation of potential therapies.

Jian-Ti-Kang-Yi decoction alleviates poly(I:C)-induced pneumonia by inhibiting inflammatory response, reducing oxidative stress, and modulating host metabolism

Jian-Ti-Kang-Yi decoction (JTKY) is widely used in the treatment of COVID-19. However, the protective mechanisms of JTKY against pneumonia remain unknown. In this study, polyinosinic-polycytidylic acid (poly(I:C)), a mimic of viral dsRNA, was used to induce pneumonia in mice; the therapeutic effects of JTKY on poly(I:C)-induced pneumonia model mice were evaluated. In addition, the anti-inflammatory and anti-oxidative potentials of JTKY were also investigated. Lastly, the metabolic regulatory effects of JTKY in poly(I:C)-induced pneumonia model mice were studied using untargeted metabolomics. Our results showed that JTKY treatment decreased the wet-to-dry ratio in the lung tissue, total protein concentration, and total cell count of the bronchoalveolar lavage fluid (BALF). Hematoxylin and Eosin (HE) and Masson staining indicated that the JTKY treatment alleviated the pathological changes and decreased the fibrotic contents in the lungs. JTKY treatment also decreased the expression of pro-inflammatory cytokines [interleukin (IL)-1β, IL-6, and tumor necrosis factor-alpha (TNF-α)] and increased the levels of immunomodulatory cytokines (IL-4 and IL-10) in the BALF and serum. Flow cytometry analysis showed that the JTKY treatment lowered the ratio of CD86+/CD206+ macrophages in the BALF, decreased inducible nitric oxide synthase (iNOS) level, and increased arginase 1 (Arg-1) level in lung. JTKY also lowered CD11b+Ly6G+ neutrophils in BALF and decreased myeloperoxidase (MPO) activity in lung. Moreover, it also elevated superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities and decreased methane dicarboxylic aldehyde (MDA) level in lung. Untargeted metabolomic analysis showed that the JTKY treatment could affect 19 metabolites in lung, such as L-adrenaline, L-asparagine, ornithine, and alpha-ketoglutaric acid. These metabolites are associated with the synthesis and degradation of ketone bodies, butanoate, alanine, aspartate, and glutamate metabolism, and tricarboxylic acid (TCA) cycle processes. In conclusion, our study demonstrated that treatment with JTKY ameliorated poly(I:C)-induced pneumonia. The mechanism of action of JTKY may be associated with the inhibition of the inflammatory response, the reduction of oxidative stress, and the regulation of the synthesis and degradation of ketone bodies, TCA cycle, and metabolism of alanine, aspartate, glutamate, and butanoate processes in lung.

Electroacupuncture pretreatment protects septic rats from acute lung injury by relieving inflammation and regulating macrophage polarization

BACKGROUND

Macrophage polarization toward the M2 phenotype may attenuate inflammation and have a therapeutic effect in acute lung injury (ALI).

OBJECTIVE

To investigate the role of electroacupuncture (EA) pretreatment on the inflammatory response and macrophage polarization in a septic rat model of lipopolysaccharide (LPS)-induced ALI.

METHODS

Male Sprague Dawley rats (n = 24) were randomly divided into three groups (n = 8 each): control (Ctrl), ALI (LPS) and pre-EA (LPS + EA pretreatment). ALI and pre-EA rats were injected with LPS via the caudal vein. Pulmonary edema was assessed by left upper pulmonary lobe wet-to-dry (W/D) ratios. Lung injury scores were obtained from paraffin-embedded and hematoxylin and eosin-stained sections of the left lower pulmonary lobe. Inflammatory activation was quantified using serum tumor necrosis factor (TNF)-α, interleukin (IL)-1β, transforming growth factor (TGF)-β and IL-10 levels measured by enzyme linked immunosorbent assay (ELISA). Macrophage phenotype was determined by real-time quantitative polymerase chain reaction (RT-qPCR) and Western blotting.

RESULTS

Mean lung W/D ratio was significantly lower and serum IL-1β levels were decreased in pre-EA rats compared to ALI rats (P < 0.05). TNF-α mRNA expression was decreased and mannose receptor (MR) and Arg1 mRNA expression was increased in the lung tissues of pre-EA rats compared to ALI rats (P < 0.01). Arg1 protein expression was similarly increased in the lung tissues of pre-EA rats compared to ALI rats (P < 0.05).

CONCLUSION

EA pretreatment may play a protective role by promoting macrophage polarization to the M2 phenotype in a septic rat model of LPS-induced ALI.

Role of released mitochondrial DNA in acute lung injury

Acute lung injury(ALI)/acute respiratory distress syndrome(ARDS) is a form of acute-onset hypoxemic respiratory failure characterised by an acute, diffuse, inflammatory lung injury, and increased alveolar-capillary permeability, which is caused by a variety of pulmonary or nonpulmonary insults. Recently, aberrant mitochondria and mitochondrial DNA(mtDNA) level are associated with the development of ALI/ARDS, and plasma mtDNA level shows the potential to be a promising biomarker for clinical diagnosis and evaluation of lung injury severity. In mechanism, the mtDNA and its oxidised form, which are released from impaired mitochondria, play a crucial role in the inflammatory response and histopathological changes in the lung. In this review, we discuss mitochondrial outer membrane permeabilisation (MOMP), mitochondrial permeability transition pore(mPTP), extracellular vesicles (EVs), extracellular traps (ETs), and passive release as the principal mechanisms for the release of mitochondrial DNA into the cytoplasm and extracellular compartments respectively. Further, we explain how the released mtDNA and its oxidised form can induce inflammatory cytokine production and aggravate lung injury through the Toll-like receptor 9(TLR9) signalling, cytosolic cGAS-stimulator of interferon genes (STING) signalling (cGAS-STING) pathway, and inflammasomes activation. Additionally, we propose targeting mtDNA-mediated inflammatory pathways as a novel therapeutic approach for treating ALI/ARDS.

Dysregulation of neutrophil death in sepsis

Sepsis is a prevalent disease that has alarmingly high mortality rates and, for several survivors, long-term morbidity. The modern definition of sepsis is an aberrant host response to infection followed by a life-threatening organ dysfunction. Sepsis has a complicated pathophysiology and involves multiple immune and non-immune mediators. It is now believed that in the initial stages of sepsis, excessive immune system activation and cascading inflammation are usually accompanied by immunosuppression. During the pathophysiology of severe sepsis, neutrophils are crucial. Recent researches have demonstrated a clear link between the process of neutrophil cell death and the emergence of organ dysfunction in sepsis. During sepsis, spontaneous apoptosis of neutrophils is inhibited and neutrophils may undergo some other types of cell death. In this review, we describe various types of neutrophil cell death, including necrosis, apoptosis, necroptosis, pyroptosis, NETosis, and autophagy, to reveal their known effects in the development and progression of sepsis. However, the exact role and mechanisms of neutrophil cell death in sepsis have not been fully elucidated, and this remains a major challenge for future neutrophil research. We hope that this review will provide hints for researches regarding neutrophil cell death in sepsis and provide insights for clinical practitioners.

The emerging role of neutrophil extracellular traps in fungal infection

Fungal infections are global public health problems and can lead to substantial human morbidity and mortality. Current antifungal therapy is not satisfactory, especially for invasive, life-threatening fungal infections. Modulating the antifungal capacity of the host immune system is a feasible way to combat fungal infections. Neutrophils are key components of the innate immune system that resist fungal pathogens by releasing reticular extracellular structures called neutrophil extracellular traps (NETs). When compared with phagocytosis and oxidative burst, NETs show better capability in terms of trapping large pathogens, such as fungi. This review will summarize interactions between fungal pathogens and NETs. Molecular mechanisms of fungi-induced NETs formation and defensive strategies used by fungi are also discussed.

Advances in mesenchymal stromal cell therapy for acute lung injury/acute respiratory distress syndrome

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) develops rapidly and has high mortality. ALI/ARDS is mainly manifested as acute or progressive hypoxic respiratory failure. At present, there is no effective clinical intervention for the treatment of ALI/ARDS. Mesenchymal stromal cells (MSCs) show promise for ALI/ARDS treatment due to their biological characteristics, easy cultivation, low immunogenicity, and abundant sources. The therapeutic mechanisms of MSCs in diseases are related to their homing capability, multidirectional differentiation, anti-inflammatory effect, paracrine signaling, macrophage polarization, the polarization of the MSCs themselves, and MSCs-derived exosomes. In this review, we discuss the pathogenesis of ALI/ARDS along with the biological characteristics and mechanisms of MSCs in the treatment of ALI/ARDS.

Xiao-Chai-Hu Decoction Ameliorates Poly (I:C)-Induced Viral Pneumonia through Inhibiting Inflammatory Response and Modulating Serum Metabolism

Viral pneumonia is widespread, progresses rapidly, and has a high mortality rate. Developing safe and effective therapies to treat viral pneumonia can minimize risks to public health and alleviate pressures on the associated health systems. Xiao-Chai-Hu (XCH) decoction can be used in the treatment of viral pneumonia. However, the mechanisms of XCH on viral pneumonia remain unclear. In this study, poly (I:C) was used to establish a mouse model of viral pneumonia, and the therapeutic effects of XCH on viral pneumonia were assessed. Furthermore, we evaluated the effects of XCH on inflammatory response. Lastly, untargeted metabolomics were used to study the metabolic regulatory mechanisms of XCH on viral pneumonia model mice. Our results showed that XCH treatment decreased the wet/dry ratio in lung tissue, total protein concentration, and total cell count in bronchoalveolar lavage fluid (BALF). H&E staining indicated that XCH treatment alleviated the pathological changes in lung. Moreover, XCH treatment decreased the levels of proinflammatory cytokines (IL-1β, IL-6, and TNF-α) and lowered the ratio of CD86⁺/CD206⁺ macrophages and CD11b⁺LY6G⁺ neutrophils in BALF. XCH treatment also decreased the myeloperoxidase (MPO) and reduced the phosphorylations of PI3K, AKT, and NF-κB p65 in lung. Serum untargeted metabolomics analysis showed that XCH treatment could affect 18 metabolites in serum such as creatine, hydroxyproline, cortisone, hydrocortisone, corticosterone, hypotaurine, and taurine. These metabolites were associated with arginine and proline metabolism, steroid hormone biosynthesis, and taurine and hypotaurine metabolism processes. In conclusion, our study demonstrated that treatment with XCH can ameliorate viral pneumonia and reduce inflammatory response in viral pneumonia. The mechanism of action of XCH in the treatment of viral pneumonia may be associated with inhibiting the activation of PI3K/AKT/NF-κB signaling pathway in lung and regulating arginine and proline metabolism, steroid hormone biosynthesis, and taurine and hypotaurine metabolism in serum.

Delayed neutrophil apoptosis may enhance NET formation in ARDS

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a neutrophil-associated disease. Delayed neutrophil apoptosis and increased levels of neutrophil extracellular traps (NETs) have been described in ARDS. We aimed to investigate the relationship between these phenomena and their potential as inflammation drivers. We hypothesized that delayed neutrophil apoptosis might enhance NET formation in ARDS.

METHOD

Our research was carried out in three aspects: clinical research, animal experiments, and in vitro experiments. First, we compared the difference between neutrophil apoptosis and NET levels in healthy controls and patients with ARDS and analyzed the correlation between neutrophil apoptosis and NET levels in ARDS. Then, we conducted animal experiments to verify the effect of neutrophil apoptosis on NET formation in Lipopolysaccharide-induced acute lung injury (LPS-ALI) mice. Furthermore, this study explored the relationship between neutrophil apoptosis and NETs at the cellular level. Apoptosis was assessed using morphological analysis, flow cytometry, and western blotting. NET formation was determined using immunofluorescence, PicoGreen assay, SYTOX Green staining, and western blotting.

RESULTS

ARDS neutrophils lived longer because of delayed apoptosis, and the cyclin-dependent kinase inhibitor, AT7519, reversed this phenomenon both in ARDS neutrophils and neutrophils in bronchoalveolar lavage fluid (BALF) of LPS-ALI mice. Neutrophils in a medium containing pro-survival factors (LPS or GM-CSF) form more NETs, which can also be reversed by AT7519. Tissue damage can be reduced by promoting neutrophil apoptosis.

CONCLUSIONS

Neutrophils with extended lifespan in ARDS usually enhance NET formation, which aggravates inflammation. Enhancing neutrophil apoptosis in ARDS can reduce the formation of NETs, inhibit inflammation, and consequently alleviate ARDS.

Atherosclerosis is a side effect of cellular senescence

Atherosclerosis is a systemic autoimmune disease of the arterial wall characterized by chronic inflammation, high blood pressure, oxidative stress, and progressive loss of cell and organ function with aging. An imbalance of macrophage polarization is associated with many aging diseases, including atherosclerosis. The polarization toward the pro-inflammatory M1 macrophage is a major promoter of the atheroma formation. It is known that efferocytosis, or ingestion of apoptotic cells, is stimulated by M2 macrophage polarization. A failure of efferocytosis leads to the prolongation of chronic pathology in tissue. In addition, fat-laden macrophages contribute to the plague progression by transforming into foam cells in response to excess lipid deposition in arteries. In spite of the generally accepted theory that macrophages capture oxidized low-density lipoprotein by phagocytosis and become foam cells, we postulate that the main source of lipid accumulation in foam cells are senescent erythrocytes. Senescent erythrocytes lose their plasticity, which affects the rheological blood properties. It is known that their membrane contains high levels of cholesterol. There is evidence that senescent erythrocytes play a pathogenic role in the atheroma formation after breaking down during flowing through an artery bifurcation. Here we review the current knowledge on the impact of age-associated immune cells and red blood cells modifications on atherogenesis.

Graphical abstract:

Macrophage-Targeted Nanomedicines for ARDS/ALI: Promise and Potential

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are characterized by progressive lung impairment typically triggered by inflammatory processes. The mortality toll for ARDS/ALI yet remains high because of the poor prognosis, lack of disease-specific inflammation management therapies, and prolonged hospitalizations. The urgency for the development of new effective therapeutic strategies has become acutely evident for patients with coronavirus disease 2019 (COVID-19) who are highly susceptible to ARDS/ALI. We propose that the lack of target specificity in ARDS/ALI of current treatments is one of the reasons for poor patient outcomes. Unlike traditional therapeutics, nanomedicine offers precise drug targeting to inflamed tissues, the capacity to surmount pulmonary barriers, enhanced interactions with lung epithelium, and the potential to reduce off-target and systemic adverse effects. In this article, we focus on the key cellular drivers of inflammation in ARDS/ALI: macrophages. We propose that as macrophages are involved in the etiology of ARDS/ALI and regulate inflammatory cascades, they are a promising target for new therapeutic development. In this review, we offer a survey of multiple nanomedicines that are currently being investigated with promising macrophage targeting potential and strategies for pulmonary delivery. Specifically, we will focus on nanomedicines that have shown engagement with proinflammatory macrophage targets and have the potential to reduce inflammation and reverse tissue damage in ARDS/ALI.

The "Self-Sacrifice" of ImmuneCells in Sepsis

Sepsis is a life-threatening organ dysfunction caused by the host’s malfunctioning response to infection. Due to its high mortality rate and medical cost, sepsis remains one of the world’s most intractable diseases. In the early stage of sepsis, the over-activated immune system and a cascade of inflammation are usually accompanied by immunosuppression. The core pathogenesis of sepsis is the maladjustment of the host’s innate and adaptive immune response. Many immune cells are involved in this process, including neutrophils, mononuclear/macrophages and lymphocytes. The immune cells recognize pathogens, devour pathogens and release cytokines to recruit or activate other cells in direct or indirect manner. Pyroptosis, immune cell-extracellular traps formation and autophagy are several novel forms of cell death that are different from apoptosis, which play essential roles in the progress of sepsis. Immune cells can initiate “self-sacrifice” through the above three forms of cell death to protect or kill pathogens. However, the exact roles and mechanisms of the self-sacrifice in the immune cells in sepsis are not fully elucidated. This paper mainly analyzes the self-sacrifice of several representative immune cells in the forms of pyroptosis, immune cell-extracellular traps formation and autophagy to reveal the specific roles they play in the occurrence and progression of sepsis, also to provide inspiration and references for further investigation of the roles and mechanisms of self-sacrifice of immune cells in the sepsis in the future, meanwhile, through this work, we hope to bring inspiration to clinical work.

Endothelial Dysfunction Induced by Extracellular Neutrophil Traps Plays Important Role in the Occurrence and Treatment of Extracellular Neutrophil Traps-Related Disease

Many articles have demonstrated that extracellular neutrophil traps (NETs) are often described as part of the antibacterial function. However, since the components of NETs are non-specific, excessive NETs usually cause inflammation and tissue damage. Endothelial dysfunction (ED) caused by NETs is the major focus of tissue damage, which is highly related to many inflammatory diseases. Therefore, this review summarizes the latest advances in the primary and secondary mechanisms between NETs and ED regarding inflammation as a mediator. Moreover, the detailed molecular mechanisms with emphasis on the disadvantages from NETs are elaborated: NETs can use its own enzymes, release particles as damage-associated molecular patterns (DAMPs) and activate the complement system to interact with endothelial cells (ECs), drive ECs damage and eventually aggravate inflammation. In view of the role of NETs-induced ED in different diseases, we also discussed possible molecular mechanisms and the treatments of NETs-related diseases.

The role of neutrophil elastase in aortic valve calcification

Background

Calcific aortic valve disease (CAVD) is the most commonly valvular disease in the western countries initiated by inflammation and abnormal calcium deposition. Currently, there is no clinical drug for CAVD. Neutrophil elastase (NE) plays a causal role in inflammation and participates actively in cardiovascular diseases. However, the effect of NE on valve calcification remains unclear. So we next explore whether it is involved in valve calcification and the molecular mechanisms involved.

Methods

NE expression and activity in calcific aortic valve stenosis (CAVD) patients (n = 58) and healthy patients (n = 30) were measured by enzyme-linked immunosorbent assay (ELISA), western blot and immunohistochemistry (IHC). Porcine aortic valve interstitial cells (pVICs) were isolated and used in vitro expriments. The effects of NE on pVICs inflammation, apoptosis and calcification were detected by TUNEL assay, MTT assay, reverse transcription polymerase chain reaction (RT-PCR) and western blot. The effects of NE knockdown and NE activity inhibitor Alvelestat on pVICs inflammation, apoptosis and calcification under osteogenic medium induction were also detected by RT-PCR, western blot, alkaline phosphatase staining and alizarin red staining. Changes of Intracellular signaling pathways after NE treatment were measured by western blot. Apolipoprotein E⁻/⁻ (APOE⁻/⁻) mice were employed in this study to establish the important role of Alvelestat in valve calcification. HE was used to detected the thickness of valve. IHC was used to detected the NE and α-SMA expression in APOE⁻/⁻ mice. Echocardiography was employed to assess the heat function of APOE⁻/⁻ mice.

Results

The level and activity of NE were evaluated in patients with CAVD and calcified valve tissues. NE promoted inflammation, apoptosis and phenotype transition in pVICs in the presence or absence of osteogenic medium. Under osteogenic medium induction, NE silencing or NE inhibitor Alvelestat both suppressed the osteogenic differentiation of pVICs. Mechanically, NE played its role in promoting osteogenic differentiation of pVICs by activating the NF-κB and AKT signaling pathway. Alvelestat alleviated valve thickening and decreased the expression of NE and α-SMA in western diet-induced APOE⁻/⁻ mice. Alvelestat also reduced NE activity and partially improved the heart function of APOE⁻/⁻mice.

Conclusions

Collectively, NE is highly involved in the pathogenesis of valve calcification. Targeting NE such as Alvelestat may be a potential treatment for CAVD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03363-1.

Anisodamine enhances macrophage M2 polarization through suppressing G9a-mediated IRF4 silencing to alleviate LPS-induced acute lung injury

Acute lung injury (ALI) is a serious inflammatory lung disease. Imbalances in the polarization of classically activated (M1) and alternatively activated (M2) macrophages are closely related to ALI. Anisodamine has a promising therapeutic effect for septic shock. Nevertheless, the role of Anisodamine in progression of ALI remains to be investigated. Our results showed that Anisodamine significantly reduced lung damage, myeloperoxidase (MPO) activity, lung wet/dry ratio, total cell number and protein concentrations in bronchoalveolar lavage fluid (BALF), and decreased IL-6 level and the levels of M1 phenotypic markers, while increased IL-10 level and the levels of M2 phenotypic markers in mice with a nasal instillation of lipopolysaccharide (LPS). Bone marrow-derived macrophages (BMDMs) were stimulated or transfected with LPS plus Anisodamine or LPS plus G9a shRNA. Anisodamine and downregulation of G9a both promoted BMDM M2 polarization caused by IL-4 treatment and inhibited M1 polarization resulted from LPS treatment. ChIP assay revealed that Anisodamine inhibited G9a-mediated methylation and expression suppression on IRF4. Overexpression of G9a or silence of IRF4 reversed the improvement effect of Anisodamine on lung tissue injury, evidencing by an increase of MPO activity and the restoration of LPS-induced alterations of M1 and M2 polarization. In conclusion, Anisodamine protected against LPS-induced ALI, during which Anisodamine suppressed the LPS-stimulated alterations of macrophage M1 and M2 polarization through inhibiting G9a mediated methylation of IRF4, suggesting that Anisodamine was a potential therapeutic drug to alleviate ALI. Significance Statement Anisodamine treatment was able to attenuate lung injury and pulmonary edema after the stimulation of LPS, and the specific mechanism was through reversing the LPS-induced alterations of M1 and M2 polarization by inhibiting G9a mediated silencing of IRF4, which suggests the Anisodamine has the potential to alleviate ALI.

Pan-Cancer Analysis Reveals a Distinct Neutrophil Extracellular Trap-Associated Regulatory Pattern

Background

Neutrophils form extracellular net-like structures called neutrophil extracellular traps (NETs). Emerging evidence has shown that cancer can induce NET formation; however, it is not fully understood how NETs influence cancer biology, and no consensus has been reached on their pro- or antitumor effects. A comprehensive analysis of the global NET-associated gene regulatory network is currently unavailable and is urgently needed.

Methods

We systematically explored and discussed NET enrichment, NET-associated gene regulatory patterns, and the prognostic implications of NETs in approximately 8,000 patients across 22 major human cancer types. We identified NET-associated regulatory gene sets that we then screened for NET-associated regulatory patterns that might affect patient survival. We functionally annotated the NET-associated regulatory patterns to compare the biological differences between NET-related survival subgroups.

Results

A gene set variation analysis (GSVA) based on 23 major component genes was used to calculate a metric called the NET score. We found that the NET score was closely associated with many important cancer hallmarks, particularly inflammatory responses and epithelial-to-mesenchymal transition (EMT)-induced metastasis. Higher NET scores were related to poor immunotherapy response. Survival analysis revealed that NETs had diverse prognostic impacts among various cancer types. The NET-associated regulatory patterns linked to shorter or longer cancer patient survival were distinct from each other. Functional analysis revealed that more of the NET-associated regulatory genes linked to poor cancer survival were associated with extracellular matrix (ECM) remodeling and pan-cancerous risk factors. SPP1 was found to be highly expressed and correlated with NET formation in cancers with poor survival. We also found that the co-upregulation of NET formation and SPP1 expression was closely linked to increased EMT and poor survival, that SPP1 influenced NET-induced malignant capacity, and that SPP1 overproduction induced a robust formation of metastatic-promoting NETs.

Conclusion

NETs were common across cancers but displayed a diverse regulatory pattern and outcome readouts in different cancer types. SPP1 is potentially the key to NET-related poor outcomes.

A roadmap to pulmonary delivery strategies for the treatment of infectious lung diseases

Pulmonary drug delivery is a highly attractive topic for the treatment of infectious lung diseases. Drug delivery via the pulmonary route offers unique advantages of no first-pass effect and high bioavailability, which provides an important means to deliver therapeutics directly to lung lesions. Starting from the structural characteristics of the lungs and the biological barriers for achieving efficient delivery, we aim to review literatures in the past decade regarding the pulmonary delivery strategies used to treat infectious lung diseases. Hopefully, this review article offers new insights into the future development of therapeutic strategies against pulmonary infectious diseases from a delivery point of view.

Infiltration of inflammatory macrophages and neutrophils and widespread pyroptosis in lung drive influenza lethality in nonhuman primates

Severe influenza kills tens of thousands of individuals each year, yet the mechanisms driving lethality in humans are poorly understood. Here we used a unique translational model of lethal H5N1 influenza in cynomolgus macaques that utilizes inhalation of small-particle virus aerosols to define mechanisms driving lethal disease. RNA sequencing of lung tissue revealed an intense interferon response within two days of infection that resulted in widespread expression of interferon-stimulated genes, including inflammatory cytokines and chemokines. Macaques with lethal disease had rapid and profound loss of alveolar macrophages (AMs) and infiltration of activated CCR2⁺ CX3CR1⁺ interstitial macrophages (IMs) and neutrophils into lungs. Parallel changes of AMs and neutrophils in bronchoalveolar lavage (BAL) correlated with virus load when compared to macaques with mild influenza. Both AMs and IMs in lethal influenza were M1-type inflammatory macrophages which expressed neutrophil chemotactic factors, while neutrophils expressed genes associated with activation and generation of neutrophil extracellular traps (NETs). NETs were prominent in lung and were found in alveolar spaces as well as lung parenchyma. Genes associated with pyroptosis but not apoptosis were increased in lung, and activated inflammatory caspases, IL-1β and cleaved gasdermin D (GSDMD) were present in bronchoalveolar lavage fluid and lung homogenates. Cleaved GSDMD was expressed by lung macrophages and alveolar epithelial cells which were present in large numbers in alveolar spaces, consistent with loss of epithelial integrity. Cleaved GSDMD colocalized with viral NP-expressing cells in alveoli, reflecting pyroptosis of infected cells. These novel findings reveal that a potent interferon and inflammatory cascade in lung associated with infiltration of inflammatory macrophages and neutrophils, elaboration of NETs and cell death by pyroptosis mediates lethal H5N1 influenza in nonhuman primates, and by extension humans. These innate pathways represent promising therapeutic targets to prevent severe influenza and potentially other primary viral pneumonias in humans.

Influenza can cause acute lung injury and death, but the mechanisms resulting in lethal influenza in humans are not well understood. We used a novel model of lethal influenza in nonhuman primates caused by aerosol infection with highly pathogenic avian influenza virus that closely resembles human disease to define how the virus causes severe pneumonia. We found that a potent innate immune response starting with high-level production of interferons and inflammatory factors in the lung drives severe disease. Inflammatory cells including macrophages and neutrophils were recruited into lung because of this early response, which in turn led to release of neutrophil extracellular traps that blocked lung alveoli. In addition, a particularly inflammatory form of cell death known as pyroptosis occurred in lungs during lethal influenza. These new findings show that an intense interferon response leading to an inflammatory cascade of macrophages and neutrophils, release of neutrophil extracellular traps, and cell death by pyroptosis is responsible for acute lung injury in lethal influenza. These innate pathways could be targeted by drugs to prevent lung injury in critically ill influenza patients.

H2 Inhibits the Formation of Neutrophil Extracellular Traps

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NETs have been implicated as therapeutic targets to address inflammation and thrombotic tissue damage in conditions such as sepsis, acute respiratory disease syndrome, COVID-19, and CVDs.

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H₂ has been clinically and experimentally proven to ameliorate inflammation; however, the underlying molecular mechanisms remain elusive.

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Compared with control neutrophils, PMA-stimulated human neutrophils exposed to H₂ exhibited reduced citrullination of histones and release of NET components; mechanistically, H₂-mediated neutralization of HOCl produced during oxidative bursts suppresses DNA damage.

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Inhalation of H₂ inhibited the formation and release of NET components in the blood and BAL of the LPS-induced sepsis in mice and aged mini pigs.

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H₂ therapy is potentially a new therapeutic strategy for inflammatory diseases involving NETs associated with excessive neutrophil activation.

Neutrophil extracellular traps (NETs) contribute to inflammatory pathogenesis in numerous conditions, including infectious and cardiovascular diseases, and have attracted attention as potential therapeutic targets. H₂ acts as an antioxidant and has been clinically and experimentally proven to ameliorate inflammation. This study was performed to investigate whether H₂ could inhibit NET formation and excessive neutrophil activation. Neutrophils isolated from the blood of healthy volunteers were stimulated with phorbol-12-myristate-13-acetate (PMA) or the calcium ionophore A23187 in H₂-exposed or control media. Compared with control neutrophils, PMA- or A23187-stimulated human neutrophils exposed to H₂ exhibited reduced neutrophil aggregation, citrullination of histones, membrane disruption by chromatin complexes, and release of NET components. CXCR4^high neutrophils are highly prone to NETs, and H₂ suppressed Ser-139 phosphorylation in H2AX, a marker of DNA damage, thereby suppressing the induction of CXCR4 expression. H₂ suppressed both myeloperoxidase chlorination activity and production of reactive oxygen species to the same degree as N-acetylcysteine and ascorbic acid, while showing a more potent ability to inhibit NET formation than these antioxidants do in PMA-stimulated neutrophils. Although A23187 formed NETs in a reactive oxygen species–independent manner, H₂ inhibited A23187-induced NET formation, probably via direct inhibition of peptidyl arginine deiminase 4-mediated histone citrullination. Inhalation of H₂ inhibited the formation and release of NET components in the blood and bronchoalveolar lavage fluid in animal models of lipopolysaccharide-induced sepsis (mice and aged mini pigs). Thus, H₂ therapy can be a novel therapeutic strategy for NETs associated with excessive neutrophil activation.

Xuanfei Baidu Decoction reduces acute lung injury by regulating infiltration of neutrophils and macrophages via PD-1/IL17A pathway

The pathogenic hyper-inflammatory response has been revealed as the major cause of the severity and death of the Corona Virus Disease 2019 (COVID-19). Xuanfei Baidu Decoction (XFBD) as one of the "three medicines and three prescriptions" for the clinically effective treatment of COVID-19 in China, shows unique advantages in the control of symptomatic transition from moderate to severe disease states. However, the roles of XFBD to against hyper-inflammatory response and its mechanism remain unclear. Here, we established acute lung injury (ALI) model induced by lipopolysaccharide (LPS), presenting a hyperinflammatory process to explore the pharmacodynamic effect and molecular mechanism of XFBD on ALI. The in vitro experiments demonstrated that XFBD inhibited the secretion of IL-6 and TNF-α and iNOS activity in LPS-stimulated RAW264.7 macrophages. In vivo, we confirmed that XFBD improved pulmonary injury via down-regulating the expression of proinflammatory cytokines such as IL-6, TNF-α and IL1-β as well as macrophages and neutrophils infiltration in LPS-induced ALI mice. Mechanically, we revealed that XFBD treated LPS-induced acute lung injury through PD-1/IL17A pathway which regulates the infiltration of neutrophils and macrophages. Additionally, one major compound from XFBD, i.e. glycyrrhizic acid, shows a high binding affinity with IL17A. In conclusion, we demonstrated the therapeutic effects of XFBD, which provides the immune foundations of XFBD and fatherly support its clinical applications.

Neutrophil Extracellular Traps Facilitate A549 Cell Invasion and Migration in a Macrophage-Maintained Inflammatory Microenvironment

Introduction

The biological functions of neutrophil extracellular traps (NETs) in tumorigenesis have drawn an increasing amount of attention. This study explored the relationship between NETs and the inflammatory microenvironment in lung cancer cell invasion and metastasis.

Methods

NETs were quantified using myeloperoxidase (MPO–DNA) and immunofluorescence staining. Cytokine levels were measured using ELISA kits. THP-1 and A549 cells were used for in vitro experiments. Transwell and Matrigel assays were used to assess the invasion and migration abilities of the cells.

Results

Neutrophil infiltration and NET formation were observed in the lung cancer tissues. Compared with healthy controls, the level of MPO–DNA complexes in lung cancer patients increased remarkably and was positively correlated with peripheral blood neutrophil counts, smoking status, and poor prognosis. Increased circulating NET levels were also positively correlated with the levels of inflammatory cytokines, including IL-1β, IL-6, IL-18, and TNF-α. Neutrophils isolated from patients with lung cancer are more prone to NET release. NETs can promote the invasion and migration ability of THP-1 and A549 cell in coculture systems, while pretreatment with NET inhibitors can effectively reduce NET-induced invasion and metastasis. The ability of NETs to promote invasion and metastasis is partly dependent on macrophages.

Conclusion

Taken together, our study demonstrated that NETs facilitate A549 cell invasion and migration in a macrophage-maintained inflammatory microenvironment.

Extracellular CIRP-Impaired Rab26 Restrains EPOR-Mediated Macrophage Polarization in Acute Lung Injury

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a condition with an imbalanced inflammatory response and delayed resolution of inflammation. Macrophage polarization plays an important role in inflammation and resolution. However, the mechanism of macrophage polarization in ALI/ARDS is not fully understood. We found that mice with lipopolysaccharide administration developed lung injury with the accumulation of extracellular cold-inducible RNA-binding protein (eCIRP) in the lungs. eCIRP, as a damage-associated molecular pattern (DAMP), inhibited M2 macrophage polarization, thereby tipping the balance toward inflammation rather than resolution. Anti-CIRP antibodies reversed such phenotypes. The levels of macrophage erythropoietin (EPO) receptor (EPOR) were reduced after eCIRP treatment. Myeloid-specific EPOR-deficient mice displayed restrained M2 macrophage polarization and impaired inflammation resolution. Mechanistically, eCIRP impaired Rab26, a member of Ras superfamilies of small G proteins, and reduced the transportation of surface EPOR, which resulted in macrophage polarization toward the M1 phenotype. Moreover, EPO treatment hardly promotes M2 polarization in Rab26 knockout (KO) macrophages through EPOR. Collectively, macrophage EPOR signaling is impaired by eCIRP through Rab26 during ALI/ARDS, leading to the restrained M2 macrophage polarization and delayed inflammation resolution. These findings identify a mechanism of persistent inflammation and a potential therapy during ALI/ARDS.

Neutrophil extracellular traps modulate inflammatory markers and uptake of oxidized LDL by human and murine macrophages

Neutrophil extracellular traps (NETs) are web-like structures, which are released upon neutrophil activation. It has previously been demonstrated that NETs are present in atherosclerotic lesions of both humans and animal models thus playing a decisive role in atherosclerosis. Besides, macrophages have a crucial role in disease progression, whereby classically activated M1 macrophages sustain inflammation and alternatively activated M2 macrophages display anti-inflammatory effects. Although NETs and macrophages were found to colocalize in atherosclerotic lesions, the impact of NETs on macrophage function is not fully understood. In the present study, we aimed to investigate the effect of NETs on human and murine macrophages in respect to the expression of pro-inflammatory cytokines, matrix metalloproteinases (MMPs) and uptake of oxidized LDL (oxLDL) in vitro. Human THP-1 and murine bone marrow-derived macrophages were cultured under M1 (LPS + IFN-γ)- and M2a (IL-4)-polarizing culture conditions and treated with NETs. To mimic intraplaque regions, cells were additionally cultured under hypoxic conditions. NETs significantly increased the expression of IL-1β, TNF-α and IL-6 in THP-M1 macrophages under normoxia but suppressed their expression in murine M1 macrophages under hypoxic conditions. Notably, NETs increased the number of oxLDL-positive M1 and M2 human and murine macrophages under normoxia, but did not influence formation of murine foam cells under hypoxia. However, oxLDL uptake did not strongly correlate with the expression of the LDL receptor CD36. Besides, upregulated MMP-9 expression and secretion by macrophages was detected in the presence of NETs. Again, hypoxic culture conditions dampened NETs effects. These results suggest that NETs may favor foam cell formation and plaque vulnerability, but exert opposite effects in respect to the inflammatory response of human and murine M1 macrophages. Moreover, effects of NETs on macrophages’ phenotype are altered under hypoxia.

A hitchhiker's guide through the COVID-19 galaxy

Numerous reviews have summarized the epidemiology, pathophysiology and the various therapeutic aspects of Coronavirus disease 2019 (COVID-19), but a practical guide on "how to treat whom with what and when" based on an understanding of the immunological background of the disease stages remains missing. This review attempts to combine the current knowledge about the immunopathology of COVID-19 with published evidence of available and emerging treatment options. We recognize that the information about COVID-19 and its treatment is rapidly changing, but hope that this guide offers those on the frontline of this pandemic an understanding of the host response in COVID-19 patients and supports their ongoing efforts to select the best treatments tailored to their patient's clinical status.

Pulmonary fibrosis from molecular mechanisms to therapeutic interventions: lessons from post-COVID-19 patients

Pulmonary fibrosis (PF) is characterised by several grades of chronic inflammation and collagen deposition in the interalveolar space and is a hallmark of interstitial lung diseases (ILDs). Recently, infectious agents have emerged as driving causes for PF development; however, the role of viral/bacterial infections in the initiation and propagation of PF is still debated. In this context, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for the current coronavirus disease 2019 (COVID-19) pandemic, has been associated with acute respiratory distress syndrome (ARDS) and PF development. Although the infection by SARS-CoV-2 can be eradicated in most cases, the development of fibrotic lesions cannot be precluded; furthermore, whether these lesions are stable or progressive fibrotic events is still unknown. Herein, an overview of the main molecular mechanisms driving the fibrotic process together with the currently approved and newly proposed therapeutic solutions was given. Then, the most recent data that emerged from post-COVID-19 patients was discussed, in order to compare PF and COVID-19-dependent PF, highlighting shared and specific mechanisms. A better understanding of PF aetiology is certainly needed, also to develop effective therapeutic strategies and COVID-19 pathology is offering one more chance to do it. Overall, the work reported here could help to define new approaches for therapeutic intervention in the diversity of the ILD spectrum.

Inflammation-modulating nanoparticles for pneumonia therapy

Pneumonia is a common but serious infectious disease, and is the sixth leading cause for death. The foreign pathogens such as viruses, fungi, and bacteria establish an inflammation response after interaction with lung, leading to the filling of bronchioles and alveoli with fluids. Although the pharmacotherapies have shown their great effectiveness to combat pathogens, advanced methods are under developing to treat complicated cases such as virus-infection and lung inflammation or acute lung injury (ALI). The inflammation modulation nanoparticles (NPs) can effectively suppress immune cells and inhibit inflammatory molecules in the lung site, and thereby alleviate pneumonia and ALI. In this review, the pathological inflammatory microenvironments in pneumonia, which are instructive for the design of biomaterials therapy, are summarized. The focus is then paid to the inflammation-modulating NPs that modulate the inflammatory cells, cytokines and chemokines, and microenvironments of pneumonia for better therapeutic effects. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Respiratory Disease.

Norisoboldine Attenuates Sepsis-Induced Acute Lung Injury by Modulating Macrophage Polarization via PKM2/HIF-1α/PGC-1α Pathway

This study aimed to investigate the effect of norisopoldine (NOR) on acute lung injury in septic mice. Lipopolysaccharide (LPS) was used to establish sepsis induced acute lung injury (ALI) in mice. The dry and wet weight of mice lung was detected, and the pathological changes of lung were observed by hematoxylin and eosin (H&E) staining. Bronchoalveolar lavage fluid (BALF) was detected. Inflammatory factors in BALF were detected by enzyme-linked immunosorbent assay (ELISA). The polarization of macrophages in lung tissue was detected by flow cytometry. The markers of M1 and M2 macrophages were detected by RT-PCR. LPS induced RAW264.7 cells were treated with NOR. Inflammatory response, macrophage polarization, glycolysis, and M2 pyruvate kinase (PKM2)/hypoxia inducible factor-1α (HIF-1α)/peroxisome proliferator activated receptor-γ co-activator 1-α (PGC-1α) signaling pathway were detected. NOR could effectively alleviate sepsis induced ALI, and reduce the number of total cells, total protein concentration, neutrophils, macrophages in BALF. NOR decreased the level of inflammatory factors and promoted macrophages from M1 to M2 type in vivo and vitro. Moreover, NOR could activated PKM2, and inhibited PKM2 from cytoplasm to nuclear, attenuated HIF-1α expression, and increased PGC-1α and peroxisome proliferator-activated receptor (PPAR)-γ expression. In addition, NOR inhibited glycolysis and promoted oxidative phosphorylation in RAW264.7 cells. Furthermore, PKM2 inhibitors could reverse the effect of NOR on PKM2/HIF-1α/PGC-1α signaling pathway in RAW264.7 cells. NOR alleviated sepsis induced AIL in mice, inhibited the inflammatory response, promote M2 polarization of macrophages through regulating PKM2/HIF-1α/PGC-1α signaling pathway.

Neutrophil Extracellular Traps in Fatal COVID-19-Associated Lung Injury

An excess formation of neutrophil extracellular traps (NETs), previously shown to be strongly associated with cytokine storm and acute respiratory distress syndrome (ARDS) with prevalent endothelial dysfunction and thrombosis, has been postulated to be a central factor influencing the pathophysiology and clinical presentation of severe COVID-19. A growing number of serological and morphological evidence has added to this assumption, also in regard to potential treatment options. In this study, we used immunohistochemistry and histochemistry to trace NETs and their molecular markers in autopsy lung tissue from seven COVID-19 patients. Quantification of key immunomorphological features enabled comparison with non-COVID-19 diffuse alveolar damage. Our results strengthen and extend recent findings, confirming that NETs are abundantly present in seriously damaged COVID-19 lung tissue, especially in association with microthrombi of the alveolar capillaries. In addition, we provide evidence that low-density neutrophils (LDNs), which are especially prone to NETosis, contribute substantially to COVID-19-associated lung damage in general and vascular blockages in particular.

Long non-coding RNA OIP5-AS1 aggravates acute lung injury by promoting inflammation and cell apoptosis via regulating the miR-26a-5p/TLR4 axis

Background

Acute lung injury (ALI) is a pulmonary disorder that leads to acute respiration failure and thereby results in a high mortality worldwide. Increasing studies have indicated that toll-like receptor 4 (TLR4) is a promoter in ALI, and we aimed to explore the underlying upstream mechanism of TLR4 in ALI.

Methods

We used lipopolysaccharide (LPS) to induce an acute inflammatory response in vitro model and a murine mouse model. A wide range of experiments including reverse transcription quantitative polymerase chain reaction, western blot, enzyme linked immunosorbent assay, flow cytometry, hematoxylin–eosin staining, RNA immunoprecipitation, luciferase activity and caspase-3 activity detection assays were conducted to figure out the expression status, specific role and potential upstream mechanism of TLR4 in ALI.

Result

TLR4 expression was upregulated in ALI mice and LPS-treated primary bronchial/tracheal epithelial cells. Moreover, miR-26a-5p was confirmed to target TLR4 according to results of luciferase reporter assay. In addition, miR-26a-5p overexpression decreased the contents of proinflammatory factors and inhibited cell apoptosis, while upregulation of TLR4 reversed these effects of miR-26a-5p mimics, implying that miR-26a-5p alleviated ALI by regulating TLR4. Afterwards, OPA interacting protein 5 antisense RNA 1 (OIP5-AS1) was identified to bind with miR-26a-5p. Functionally, OIP5-AS1 upregulation promoted the inflammation and miR-26a-5p overexpression counteracted the influence of OIP5-AS1 upregulation on cell inflammatory response and apoptosis.

Conclusion

OIP5-AS1 promotes ALI by regulating the miR-26a-5p/TLR4 axis in ALI mice and LPS-treated cells, which indicates a promising insight into diagnostics and therapeutics in ALI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-021-01589-1.

SSRIs: Applications in inflammatory lung disease and implications for COVID-19

Selective serotonin reuptake inhibitors (SSRIs) have anti-inflammatory properties that may have clinical utility in treating severe pulmonary manifestations of COVID-19. SSRIs exert anti-inflammatory effects at three mechanistic levels: (a) inhibition of proinflammatory transcription factor activity, including NF-κB and STAT3; (b) downregulation of lung tissue damage and proinflammatory cell recruitment via inhibition of cytokines, including IL-6, IL-8, TNF-α, and IL-1β; and (c) direct suppression inflammatory cells, including T cells, macrophages, and platelets. These pathways are implicated in the pathogenesis of COVID-19. In this review, we will compare the pathogenesis of lung inflammation in pulmonary diseases including COVID-19, ARDS, and chronic obstructive pulmonary disease (COPD), describe the anti-inflammatory properties of SSRIs, and discuss the applications of SSRIS in treating COVID-19-associated inflammatory lung disease.

Effects of Ultrashort Wave Therapy on Inflammation and Macrophage Polarization after Acute Lung Injury in Rats

Acute lung injury (ALI) features dysregulated pulmonary inflammation. Ultrashort waves (USWs) exert anti-inflammatory effects but no studies have evaluated their activity in ALI. Herein, we used an in vivo lipopolysaccharide (LPS)-induced ALI model to investigate whether the anti-inflammatory activity of USWs is mediated by altering the polarization of M1 to M2 macrophages. Twenty-four male Sprague-Dawley rats were randomly divided into control, untreated ALI, and ALI treated with USW groups (n = 8 in each group). ALI was induced by intratracheal LPS instillation. Rats in the USW group were treated for 15 min at 0, 4, and 8 h after a single LPS intratracheal instillation. Histopathologic examination, wet/dry lung weight ratio, enzyme-linked immunosorbent assay, quantitative real-time polymerase chain reaction, and western blot analyses were performed to evaluate the degree of lung injury and to determine macrophage phenotypes. Histopathologic examination disclosed attenuation of ALI, with reduced alveolar hemorrhage and neutrophilic infiltration in the USW group. Serum levels of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were significantly decreased after USW therapy. Moreover, the messenger RNA (mRNA) expressions of TNF-α and IL-1β were significantly decreased in the USW group, whereas the mRNA expression of Arginase 1 (Arg1) and the protein expression of mannose receptor significantly increased in comparison with the untreated ALI group. We conclude that USW therapy may attenuate inflammation in LPS-induced ALI through the modulation of macrophage polarization. © 2021 Bioelectromagnetics Society.

Development and Functions of Alveolar Macrophages

Macrophages residing in various tissue types are unique in terms of their anatomical locations, ontogenies, developmental pathways, gene expression patterns, and immunological functions. Alveolar macrophages (AMs) reside in the alveolar lumen of the lungs and serve as the first line of defense for the respiratory tract. The immunological functions of AMs are implicated in the pathogenesis of various pulmonary diseases such as allergic asthma, chronic obstructive pulmonary disorder (COPD), pulmonary alveolar proteinosis (PAP), viral infection, and bacterial infection. Thus, the molecular mechanisms driving the development and function of AMs have been extensively investigated. In this review article, we discuss the roles of granulocyte-macrophage colony-stimulating factor (GM-CSF) and transforming growth factor (TGF)-β in AM development, and provide an overview of the anti-inflammatory and proinflammatory functions of AMs in various contexts. Notably, we examine the relationships between the metabolic status of AMs and their development processes and functions. We hope that this review will provide new information and insight into AM development and function.

Bongkrekic acid induced neutrophil extracellular traps via p38, ERK, PAD4, and P2X1-mediated signaling

Bongkrekic acid (BKA) produced by pseudomonas cocovenenans is a deadly toxin, and is mainly found in spoiled or fermented foods. However, less is known on its immunotoxicity. Neutrophil extracellular traps (NETs) are a novel effector mechanism of neutrophils against invading pathogens, but excessive NETs also contribute to tissue damage. This study aimed to investigate NET formation triggered by BKA in murine neutrophils, and describe its characteristics and potential mechanisms. Our results showed that BKA triggered NET formation via co-localization of DNA and histone or MPO by immunostaining. Moreover, BKA-triggered NET formation was dose- and time-dependent via NET quantification based on Picogreen-derived fluorescence intensities. Furthermore, BKA increased ROS production in neutrophils. Pharmacological inhibition indicated that BKA-triggered NET formation was associated with ROS-p38 and -ERK signaling pathways, but independent on NADPH oxidase. Besides, PAD4 and P2X1 receptor also mediated BKA-triggered NET formation. To our knowledge, all these findings provide for the first time an initial understanding of BKA on innate immunity, which might be helpful for further investigation on BKA immunotoxicity.

The Role of Macrophages in the Pathogenesis of SARS-CoV-2-Associated Acute Respiratory Distress Syndrome

Macrophages are cells that mediate both innate and adaptive immunity reactions, playing a major role in both physiological and pathological processes. Systemic SARS-CoV-2-associated complications include acute respiratory distress syndrome (ARDS), disseminated intravascular coagulation syndrome, edema, and pneumonia. These are predominantly effects of massive macrophage activation that collectively can be defined as macrophage activation syndrome. In this review we focus on the role of macrophages in COVID-19, as pathogenesis of the new coronavirus infection, especially in cases complicated by ARDS, largely depends on macrophage phenotypes and functionalities. We describe participation of monocytes, monocyte-derived and resident lung macrophages in SARS-CoV-2-associated ARDS and discuss possible utility of cell therapies for its treatment, notably the use of reprogrammed macrophages with stable pro- or anti-inflammatory phenotypes.

Immunothrombosis in COVID-19: Implications of Neutrophil Extracellular Traps

SARS-CoV-2 is a member of the family of coronaviruses associated with severe outbreaks of respiratory diseases in recent decades and is the causative agent of the COVID-19 pandemic. The recognition by and activation of the innate immune response recruits neutrophils, which, through their different mechanisms of action, form extracellular neutrophil traps, playing a role in infection control and trapping viral, bacterial, and fungal etiological agents. However, in patients with COVID-19, activation at the vascular level, combined with other cells and inflammatory mediators, leads to thrombotic events and disseminated intravascular coagulation, thus leading to a series of clinical manifestations in cerebrovascular, cardiac, pulmonary, and kidney disease while promoting severe disease and mortality. Previous studies of hospitalized patients with COVID-19 have shown that elevated levels of markers specific for NETs, such as free DNA, MPO, and H3Cit, are strongly associated with the total neutrophil count; with acute phase reactants that include CRP, D-dimer, lactate dehydrogenase, and interleukin secretion; and with an increased risk of severe COVID-19. This study analyzed the interactions between NETs and the activation pathways involved in immunothrombotic processes in patients with COVID-19.

Vascular Inflammation Is Associated with Loss of Aquaporin 1 Expression on Endothelial Cells and Increased Fluid Leakage in SARS-CoV-2 Infected Golden Syrian Hamsters

Vascular changes represent a characteristic feature of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection leading to a breakdown of the vascular barrier and subsequent edema formation. The aim of this study was to provide a detailed characterization of the vascular alterations during SARS-CoV-2 infection and to evaluate the impaired vascular integrity. Groups of ten golden Syrian hamsters were infected intranasally with SARS-CoV-2 or phosphate-buffered saline (mock infection). Necropsies were performed at 1, 3, 6, and 14 days post-infection (dpi). Lung samples were investigated using hematoxylin and eosin, alcian blue, immunohistochemistry targeting aquaporin 1, CD3, CD204, CD31, laminin, myeloperoxidase, SARS-CoV-2 nucleoprotein, and transmission electron microscopy. SARS-CoV-2 infected animals showed endothelial hypertrophy, endothelialitis, and vasculitis. Inflammation mainly consisted of macrophages and lower numbers of T-lymphocytes and neutrophils/heterophils infiltrating the vascular walls as well as the perivascular region at 3 and 6 dpi. Affected vessels showed edema formation in association with loss of aquaporin 1 on endothelial cells. In addition, an ultrastructural investigation revealed disruption of the endothelium. Summarized, the presented findings indicate that loss of aquaporin 1 entails the loss of intercellular junctions resulting in paracellular leakage of edema as a key pathogenic mechanism in SARS-CoV-2 triggered pulmonary lesions.

Recent advances in dead cell clearance during acute lung injury and repair

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are clinical syndromes that cause significant mortality in clinical settings and morbidity among survivors accompanied by huge healthcare costs. Lung-resident cell dysfunction/death and neutrophil alveolitis accompanied by proteinous edema are the main pathological features of ALI/ARDS. While understanding of the mechanisms underlying ALI/ARDS pathogenesis is progressing and potential treatments such as statin therapy, nutritional strategies, and mesenchymal cell therapy are emerging, poor clinical outcomes in ALI/ARDS patients persist. Thus, a better understanding of lung-resident cell death and neutrophil alveolitis and their mitigation and clearance mechanisms may provide new therapeutic strategies to accelerate lung repair and improve outcomes in critically ill patients. Macrophages are required for normal tissue development and homeostasis as well as regulating tissue injury and repair through modulation of inflammation and other cellular processes. While macrophages mediate various functions, here we review recent dead cell clearance (efferocytosis) mechanisms mediated by these immune cells for maintaining tissue homeostasis after infectious and non-infectious lung injury.

NETosis in Wound Healing: When Enough Is Enough

The neutrophils extracellular traps (NETs) are a meshwork of chromatin, histonic and non-histonic proteins, and microbicidal agents spread outside the cell by a series of nuclear and cytoplasmic events, collectively called NETosis. NETosis, initially only considered a defensive/apoptotic mechanism, is now considered an extreme defensive solution, which in particular situations induces strong negative effects on tissue physiology, causing or exacerbating pathologies as recently shown in NETs-mediated organ damage in COVID-19 patients. The positive effects of NETs on wound healing have been linked to their antimicrobial activity, while the negative effects appear to be more common in a plethora of pathological conditions (such as diabetes) and linked to a NETosis upregulation. Recent evidence suggests there are other positive physiological NETs effects on wound healing that are worthy of a broader research effort.

Iridin Prevented Against Lipopolysaccharide-Induced Inflammatory Responses of Macrophages via Inactivation of PKM2-Mediated Glycolytic Pathways

Purpose

Abnormal glycolysis of immune cells contributed to the development of inflammatory response. Inhibition of this Warburg phenotype could be a promising strategy for preventing various inflammatory diseases. Iridin (IRD) is a natural isoflavone, and exerts anticancer, antioxidant, and anti-inflammatory effects. However, the underlying mechanism of IRD on acute inflammation remains unknown. In this study, the protective effects of IRD against lipopolysaccharide (LPS)-induced inflammation were investigated in murine macrophage RAW264.7 cells and in mice.

Methods

The inhibition of IRD on NO production in culture medium was detected by Griess assay while the levels of TNF-α, IL-1β, and MCP-1 were detected by ELISA assay. The effects of IRD on OCR and ECAR levels in LPS-treated macrophages were monitored by using Seahorse Analyzer. The apoptosis rate as well as the release of ROS and NO of RAW264.7 cells were analyzed by flow cytometric assay. The protective effects of IRD were investigated on LPS-induced inflammation in mice. The expressions of PKM2 and its downstream (p-JAK1, p-STAT1, p-STAT3, p-p65, iNOS, and COX2) in cells and in lung tissues were detected by Western blotting analysis.

Results

IRD treatment at the concentrations of 12.5-50 μM significantly inhibited the productions of TNF-α, IL-1β, MCP-1, and ROS, and suppressed the levels of glucose uptake and lactic acid in LPS-treated RAW264.7 cells. Oral administration with IRD (20-80 mg/kg) inhibited LPS-induced acute lung injury as well as inflammatory cytokine production in mice. Moreover, IRD targeted pyruvate kinase isozyme type M2 (PKM2) and suppressed its downstream p-JAK1, p-STAT1, p-STAT3, p-p65, iNOS, and COX2, which could be abolished by PKM2 agonist DASA-58 and antioxidant N-acetyl-L-cysteine, but partly be reversed by NF-κB activator CUT129 and JAK1 activator RO8191.

Conclusion

IRD alleviated LPS-induced inflammation through suppressing PKM2-mediated pathways, and could be a potential candidate for the prevention of inflammatory diseases.

Hypoxia, HIF-1α, and COVID-19: from pathogenic factors to potential therapeutic targets

The pandemic of coronavirus disease 2019 (COVID-19) and its pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have become the greatest current threat to global public health. The highly infectious SARS-CoV-2 virus primarily attacks pulmonary tissues and impairs gas exchange leading to acute respiratory distress syndrome (ARDS) and systemic hypoxia. The current pharmacotherapies for COVID-19 largely rely on supportive and anti-thrombi treatment and the repurposing of antimalarial and antiviral drugs such as hydroxychloroquine and remdesivir. For a better mechanistic understanding of COVID-19, our present review focuses on its primary pathophysiologic features: hypoxia and cytokine storm, which are a prelude to multiple organ failure and lethality. We discussed a possible link between the activation of hypoxia inducible factor 1α (HIF-1α) and cell entry of SARS-CoV-2, since HIF-1α is shown to suppress the angiotensin-converting enzyme 2 (ACE2) receptor and transmembrane protease serine 2 (TMPRSS2) and upregulate disintegrin and metalloproteinase domain-containing protein 17 (ADAM17). In addition, the protein targets of HIF-1α are involved with the activation of pro-inflammatory cytokine expression and the subsequent inflammatory process. Furthermore, we hypothesized a potential utility of so-called "hypoxic conditioning" to activate HIF-1α-induced cytoprotective signaling for reduction of illness severity and improvement of vital organ function in patients with COVID-19. Taken together, we would propose further investigations into the hypoxia-related molecular mechanisms, from which novel targeted therapies can be developed for the improved management of COVID-19.

Differential type I interferon response and primary airway neutrophil extracellular trap release in children with acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a heterogeneous condition characterized by the recruitment of large numbers of neutrophils into the lungs. Neutrophils isolated from the blood of adults with ARDS have elevated expression of interferon (IFN) stimulated genes (ISGs) associated with decreased capacity of neutrophils to kill Staphylococcus aureus and worse clinical outcomes. Neutrophil extracellular traps (NETs) are elevated in adults with ARDS. Whether pediatric ARDS (PARDS) is similarly associated with altered neutrophil expression of ISGs and neutrophil extracellular trap release is not known. Tracheal aspirate fluid and cells were collected within 72 h from seventy-seven intubated children. Primary airway neutrophils were analyzed for differential ISG expression by PCR, STAT1 phosphorylation and markers of degranulation and activation by flow cytometry. Airway fluid was analyzed for the release of NETs by myeloperoxidase-DNA complexes using an ELISA. Higher STAT1 phosphorylation, markers of neutrophil degranulation, activation and NET release were found in children with versus without PARDS. Higher NETs were detected in the airways of children with ventilator-free days less than 20 days. Increased airway cell IFN signaling, neutrophil activation, and NET production is associated with PARDS. Higher levels of airway NETs are associated with fewer ventilator-free days.

Neutrophil extracellular traps increased by hyperglycemia exacerbate ischemic brain damage

Hyperglycemia is common and associated with poor outcome in acute ischemic stroke patients. Neutrophil extracellular traps (NETs) are increased either in diabetes or ischemic stroke. We aimed to determine the role of NETs in acute ischemic stroke with hyperglycemia as it has not been clarified. NETs were observed in thrombi retrieved from ischemic stroke patients undergoing endovascular treatment. Citrullinated histone H3 was much more abundant in thrombi from hyperglycemic patients than in those from normoglycemic patients. BKS-db/db and wild-type mice injected with glucose were used to establish the permanent middle cerebral artery occlusion model with hyperglycemia. NETs induced by hyperglycemia were detected in the peri-ischemic brain tissue. Inhibition of NET formation decreased the infarction volume both in db/db and wild-type mice with hyperglycemia. Neurological function deficits were alleviated by blocking NET formation. These findings suggest that NETs increased by hyperglycemia play a role in exacerbation of ischemic brain damage.