Regulation of alveolar macrophage death in acute lung inflammation

Exosomes derived from adipose-derived stem cells alleviate cigarette smoke-induced lung inflammation and injury by inhibiting alveolar macrophages pyroptosis

Background

Chronic obstructive pulmonary disease (COPD) is a frequently encountered disease condition in clinical practice mainly caused by cigarette smoke (CS). The aim of this study was to investigate the protective roles of human adipose-derived stem cells-derived exosomes (ADSCs-Exo) in CS-induced lung inflammation and injury and explore the underlying mechanism by discovering the effects of ADSCs-Exo on alveolar macrophages (AMs) pyroptosis.

Methods

ADSCs were isolated from human adipose tissues harvested from three healthy donors, and then ADSCs-Exo were isolated. In vivo, 24 age-matched male C57BL/6 mice were exposed to CS for 4 weeks, followed by intratracheal administration of ADSCs-Exo or phosphate buffered saline. In vitro, MH-S cells, derived from mouse AMs, were stimulated by 2% CS extract (CSE) for 24 h, followed by the treatment of ADSCs-Exo or phosphate buffered saline. Pulmonary inflammation was analyzed by detecting pro-inflammatory cells and mediators in the bronchoalveolar lavage fluid. Lung histology was assessed by hematoxylin and eosin staining. Mucus production was determined by Alcian blue-periodic acid-Schiff staining. The profile of AMs pyroptosis was evaluated by detecting the levels of pyroptosis-indicated proteins. The inflammatory response in AMs and the phagocytic activity of AMs were also investigated.

Results

In mice exposed to CS, the levels of pro-inflammatory cells and mediators were significantly increased, mucus production was markedly increased and lung architecture was obviously disrupted. AMs pyroptosis was elevated and AMs phagocytosis was inhibited. However, the administration of ADSCs-Exo greatly reversed these alterations caused by CS exposure. Consistently, in MH-S cells with CSE-induced properties modelling those found in COPD, the cellular inflammatory response was elevated, the pyroptotic activity was upregulated while the phagocytosis was decreased. Nonetheless, these abnormalities were remarkably alleviated by the treatment of ADSCs-Exo.

Conclusions

ADSCs-Exo effectively attenuate CS-induced airway mucus overproduction, lung inflammation and injury by inhibiting AMs pyroptosis. Therefore, hADSCs-Exo may be a promising cell-free therapeutic candidate for CS-induced lung inflammation and injury.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-01926-w.

GPA Peptide Attenuates Sepsis-Induced Acute Lung Injury in Mice via Inhibiting Oxidative Stress and Pyroptosis of Alveolar Macrophage

Acute lung injury (ALI) has been known to be a devastating form of respiratory infection and an important contributor to mortality in intensive care, due to its lacking of effective treatment. Inflammation, oxidative stress, and pyroptosis are associated with multiple kinds of inflammatory diseases such as ALI. It is commonly accepted that Gly-Pro-Ala (GPA) peptide regulates oxidative stress and pyroptosis in different kinds of inflammatory diseases. Our study is aimed at exploring the regulatory function and protective effects of GPA peptides on ALI. In the current study, the cecal ligation and puncture (CLP) technique was used to evoke sepsis in mice, and GPA peptide was administered intraperitoneally with different concentrations (50, 100, and 150 mg/kg) after CLP. Histopathological changes and the ratio of wet-to-dry in lung were recorded and analyzed. We also investigated the level of oxidative stress, inflammation, and pyroptosis. Results showed that GPA peptide significantly ameliorated CLP-stimulated lung tissue injury, impeded proinflammatory cytokine release, and reduced inflammatory cell infiltration. Additionally, GPA peptide suppressed oxidative stress and caspase-1-dependent pyroptosis in alveolar macrophages. Furthermore, our study showed that the GPA peptide prevents alveolar macrophage from undergoing pyroptosis by attenuating ROS. In conclusion, results demonstrated that GPA peptide has protective effects in CLP-stimulated ALI by inhibiting oxidative stress as well as pyroptosis of alveolar macrophage.

Identification of Immune Infiltration and Effective Immune Biomarkers in Acute Lung Injury by Bioinformatics Analysis

Acute lung injury (ALI) is a serious complication in clinical settings. This study aimed to elucidate the immune molecular mechanisms underlying ALI by bioinformatics analysis. Human ALI and six ALI mouse model datasets were collected. Immune cell infiltration between the ALI samples and non-ALI controls was estimated using the ssGSEA algorithm. Least absolute shrinkage and selection operator (LASSO) regression analysis and Wilcoxon test were performed to obtain the significantly different immune cell infiltration types. Immune feature genes were screened by differential analysis and the weighted correlation network analysis (WGCNA) algorithm. Functional enrichment was then performed and candidate hub biomarkers were identified. Finally, the receiver operator characteristic curve (ROC) analysis was used to predict their diagnostic performances. Three significantly different immune cell types (B cells, CD4 T cells, and CD8 T cells) were identified between the ALI samples and controls. A total of 13 immune feature genes were obtained by WGCNA and differential analysis and found to be significantly associated with immune functions and lung diseases. Four hub genes, including CD180, CD4, CD74, and MCL1 were identified using cytoHubba and were shown to have good specificity and sensitivity for the diagnosis of ALI. Correlation analysis suggested that CD4 was positively associated with T cells, whereas MCL1 was negatively correlated with B and T cells. We found that CD180, CD4, CD74, and MCL1 can serve as specific immune biomarkers for ALI. MCL1-B cell, MCL1-T cell, and CD4-T cell axes may be involved in the progression of ALI.

GHS-R1a deficiency mitigates lipopolysaccharide-induced lung injury in mice via the downregulation of macrophage activity

Acute respiratory distress syndrome (ARDS) is a critical illness syndrome characterized by dysregulated pulmonary inflammation. Currently, effective pharmacological treatments for ARDS are unavailable. Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor type 1a (GHS-R1a), has a pivotal role in regulating energy metabolism and immunomodulation. The role of endogenous ghrelin in ARDS remains unresolved. Herein, we investigated the role of endogenous ghrelin signaling by using GHS-R1a-null (ghsr^-/-) mice and lipopolysaccharide (LPS)-induced ARDS model. Ghsr^-/- mice survived longer than controls after LPS-induced lung injury. Ghsr^-/- mice showed lower levels of pro-inflammatory cytokines and higher oxygenation levels after lung injury. The peritoneal macrophages isolated from ghsr^-/- mice exhibited lower levels of cytokines production and oxygen consumption rate after LPS stimulation. Our results indicated that endogenous ghrelin plays a pivotal role in initiation and continuation in acute inflammatory response in LPS-induced ARDS model by modulating macrophage activity, and highlighted endogenous GHS-R1a signaling in macrophage as a potential therapeutic target in this relentless disease.

Ethyl ferulate protects against lipopolysaccharide-induced acute lung injury by activating AMPK/Nrf2 signaling pathway

Ethyl ferulate (EF) is abundant in Rhizoma Chuanxiong and grains (e.g., rice and maize) and possesses antioxidative, antiapoptotic, antirheumatic, and anti-inflammatory properties. However, its effect on lipopolysaccharide (LPS)-induced acute lung injury (ALI) is still unknown. In the present study, we found that EF significantly alleviated LPS-induced pathological damage and neutrophil infiltration and inhibited the gene expression of proinflammatory cytokines (TNF-α, IL-1β, and IL-6) in murine lung tissues. Moreover, EF reduced the gene expression of TNF-α, IL-1β, IL-6, and iNOS and decreased the production of NO in LPS-stimulated RAW264.7 cells and BMDMs. Mechanistic experiments revealed that EF prominently activated the AMPK/Nrf2 pathway and promoted Nrf2 nuclear translocation. AMPK inhibition (Compound C) and Nrf2 inhibition (ML385) abolished the beneficial effect of EF on the inflammatory response. Furthermore, the protective effect of EF on LPS-induced ALI was not observed in Nrf2 knockout mice. Taken together, the results of our study suggest that EF ameliorates LPS-induced ALI in an AMPK/Nrf2-dependent manner. These findings provide a foundation for developing EF as a new anti-inflammatory agent for LPS-induced ALI/ARDS therapy.

Memantine Alleviates Acute Lung Injury Via Inhibiting Macrophage Pyroptosis

ABSTRACT

Acute lung injury (ALI) is caused by direct pulmonary insults and indirect systemic inflammatory responses that result from conditions such as sepsis and trauma. Alveolar macrophages are the main and critical leukocytes in the airspace, and through the synthesis and release of various inflammatory mediators critically influence the development of ALI following infection and non-infectious stimuli. There is increasing recognition that inflammation and cell death reciprocally affect each other, which forms an auto-amplification loop of these two factors, and in turn, exaggerates inflammation. Therefore, pharmacological manipulation of alveolar macrophage death signals may serve as a logical therapeutic strategy for ALI. In this study, we demonstrate that memantine, a N-methyl-D-aspartic acid receptor (NMDAR) antagonist, through suppressing Ca2+ influx and subsequent ASC oligomerization inhibits macrophage Nlrp3 inflammasome activation and pyroptosis, therefore, alleviates ALI in septic mice. This finding explores a novel application of memantine, an FDA already approved medication, in the treatment of ALI, which is currently lacking effective therapy.

Baicalein suppresses lipopolysaccharide-induced acute lung injury by regulating Drp1-dependent mitochondrial fission of macrophages

Acute lung injury (ALI) and its serious form, the acute respiratory distress syndrome (ARDS) are devastating diseases without effective chemotherapy. Exuberant or uncontrolled proinflammation responses in the lung, also known as "cytokine storms", is one of the main culprits in the pathogenesis of organ failure, and anti-inflammatory therapy is essential to alleviate ALI/ARDS-associated injuries. Emerging evidence suggests that baicalein has potent anti-inflammatory and antioxidant properties. However, the underlined mechanism of baicalein to mitigate inflammation in ALI remains unclear. Herein, we demonstrated a critical role for baicalein in suppressing the inflammatory response of LPS-activated macrophages. We found that mitochondria function was restored in the condition of baicalein. Interestingly, results showed that mitochondrial dysfunction positively correlates with inflammatory cytokine generation at each corresponding baicalein concentration. Further mRNA analysis revealed that baicalein mitigates mitochondrial defects via attenuation of dynamin-related protein 1 (Drp1) expression. These reprogrammed mitochondria prevent their function shift from the ATP synthesis to reactive oxygen species (ROS) production after the LPS challenge, thereby dampening NF-κB-dependent inflammatory cytokine transcription. Baicalein reduces the production of inflammatory mediators TNF-α, MIP-1, IL-6, and diminishes neutrophil influx and severity of endotoxin-mediated ALI. Taken together, our results show that baicalein may serve as a new clinical therapeutic strategy in ALI by modulating Drp1-induced mitochondrial impairment, restraining inflammatory responses, and reducing the severity of lung injury.

Impact of injection buffer volume to perform bronchoalveolar lavage fluid collection for isolating alveolar macrophages to investigate fine particle-induced IL-1α secretion

The importance of alveolar macrophages has been reported in many toxicology/immunology studies. Alveolar macrophages release interleukin (IL)-1α as a damage-associated molecular pattern (DAMP) when stimulated by fine particles. However, it is unclear whether cell isolation procedures affect ex vivo particle-induced responses in primary mouse alveolar macrophages (mAM). In this study, effects of injection buffer volume used to perform bronchoalveolar lavage fluid (BALF) collection to isolate mAM for use in ex vivo particle-induced responses were assessed. Among the mAM obtained from BALF collected using a 0.55 or 0.75 ml, but not a 1.0 ml buffer injection volume, decreased cell viability and IL-1α release were observed when cells were stimulated ex vivo with silica crystal or aluminum salt. Injected buffer composition did not affect the IL-1α release. On the other hand, IL-6 secretion induced by lipopolysaccharide (LPS) did not differ among mAM obtained from BALF collected using the different volumes. Expression levels of cell surface markers like CD11c, SiglecF, and CD64 did not differ among mAM obtained from BALF collected using the different injection buffer volumes. IL-1α release (and also necroptosis) induced by ex vivoparticle stimulation was suppressed by RIPK3 inhibitor or cytochalasin D co-treatment. Decreases in RIPK3 phosphorylation were noted in mAM obtained in BALF collected using the 1.0 ml injection volume compared with mAM obtained in BALF using 0.55 or 0.75 ml buffer. These observations illustrate that larger volumes of buffer used to collect BALF from mice can affect sensitivity of the isolated mAM to ex vivo particle-induced responses by inhibiting their functions.

Inflammatory alveolar macrophage-derived microvesicles damage lung epithelial cells and induce lung injury

Emerging evidence has demonstrated that several microvesicles (MVs) are secreted in bronchoalveolar lavage fluid (BALF) during the pathogenesis of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). However, the impact of alveolar macrophage (AM)-derived MVs on epithelial cells and their in vivo effects on ALI/ARDS require further exploration. In this study, MVs were isolated from BALF of mice or mouse alveolar macrophage (MHS) cells by sequential centrifugation and then delivered to epithelial cells or mice. Enzyme-linked immunosorbent assay revealed that BALF-derived MVs (BALF-MVs) and MHS-derived MVs (AM-MVs) were rich in tumor necrosis factor-α (TNF-α) at the early stage of lung injury. In vitro, both inflammatory BALF-MVs and AM-MVs decreased the expression of α subunit of epithelial sodium channel (α-ENaC), γ-ENaC, and Na⁺,K⁺-ATPase α1 and β1 in lung epithelial cells. However, antibodies against TNF-α inhibited the effects of inflammatory AM-MVs in epithelial cells. In vivo, the inflammatory AM-MVs, delivered intratracheally to mice, impaired lung tissues and increased the injury score. They also resulted in decreased alveolar fluid clearance and increased lung wet weight/dry weight ratio. Furthermore, inflammatory AM-MVs downregulated the α-ENaC, γ-ENaC, and Na⁺,K⁺-ATPase α1 and β1 levels in lung tissues. According to our results, inflammatory AM-derived MVs may potentially contribute to lung injury and pulmonary edema, thereby indicating a potential novel therapeutic approach against ALI/ARDS based on AM-MVs.

Inflammasome activation at the crux of severe COVID-19

The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), results in life-threatening disease in a minority of patients, especially elderly people and those with co-morbidities such as obesity and diabetes. Severe disease is characterized by dysregulated cytokine release, pneumonia and acute lung injury, which can rapidly progress to acute respiratory distress syndrome, disseminated intravascular coagulation, multisystem failure and death. However, a mechanistic understanding of COVID-19 progression remains unclear. Here we review evidence that SARS-CoV-2 directly or indirectly activates inflammasomes, which are large multiprotein assemblies that are broadly responsive to pathogen-associated and stress-associated cellular insults, leading to secretion of the pleiotropic IL-1 family cytokines (IL-1β and IL-18), and pyroptosis, an inflammatory form of cell death. We further discuss potential mechanisms of inflammasome activation and clinical efforts currently under way to suppress inflammation to prevent or ameliorate severe COVID-19.

The Protective Activity of Penehyclidine Hydrochloride against Renal Ischemia/Reperfusion-Mediated NLRP3 Inflammasome Activation is Induced by SIRT1

Background: The activation of alveolar macrophages (AMs) modulated via leucine-rich repeat (NLR) pyrin domain containing 3 (NLRP3) inflammasome activation is key to the progression of renal ischemia/reperfusion (rI/R)-mediated acute lung injury (ALI). Sirtuin-1 (SIRT1) can attenuate NLRP3 inflammasome activation during I/R stress and may be an important mechanism underlying ALI pathogenesis. Penehyclidine hydrochloride (PHC), an anticholinergic drug, exerts protective effects against rI/R-mediated ALI. This study aimed to decipher the effects of PHC on SIRT1 activation and the underlying mechanism of the protective activity of PHC against rI/R-mediated ALI.Materials and methods: We used an ALI rat model and the rat AMs cell line NR8383 to assess the degree of lung injury in vivo and in vitro.Results: The results show that PHC attenuates rI/R-mediated lung injury indices, myeloperoxidase, and apoptosis in vivo. It decreases the rI/R-mediated release of prostaglandin E2 and nitric oxide, mitochondrial reactive oxygen species production, and the activity of NADPH oxidase-4 in vitro. PHC ameliorates the rI/R-induced activation of the thioredoxin-interacting protein, caspase 1 (P10 unit), and NLRP3 inflammasome, along with reduced activation of interleukin-1β and interleukin-18 in vitro. We show that PHC alleviates the rI/R-induced reduction of SIRT1 and the depletion of SIRT1 eliminates the ameliorating activity of PHC on the NLRP3 inflammasome activation in vitro. Conclusions: In summary, the findings suggest that PHC ameliorates the rI/R-mediated ALI through the SIRT1-mediated NLRP3 inflammasome activation.

Necroptosis in Pulmonary Diseases: A New Therapeutic Target

In the past decades, apoptosis has been the most well-studied regulated cell death (RCD) that has essential functions in tissue homeostasis throughout life. However, a novel form of RCD called necroptosis, which requires receptor-interacting protein kinase-3 (RIPK3) and mixed-lineage kinase domain-like pseudokinase (MLKL), has recently been receiving increasing scientific attention. The phosphorylation of RIPK3 enables the recruitment and phosphorylation of MLKL, which oligomerizes and translocates to the plasma membranes, ultimately leading to plasma membrane rupture and cell death. Although apoptosis elicits no inflammatory responses, necroptosis triggers inflammation or causes an innate immune response to protect the body through the release of damage-associated molecular patterns (DAMPs). Increasing evidence now suggests that necroptosis is implicated in the pathogenesis of several human diseases such as systemic inflammation, respiratory diseases, cardiovascular diseases, neurodegenerative diseases, neurological diseases, and cancer. This review summarizes the emerging insights of necroptosis and its contribution toward the pathogenesis of lung diseases.

Overexpressing long non-coding RNA OIP5-AS1 ameliorates sepsis-induced lung injury in a rat model via regulating the miR-128-3p/Sirtuin-1 pathway

Sepsis, resulting from infections, is a systemic inflammatory response syndrome with a high fatality rate. The present study revolves around probing into the function and molecular mechanism of long non-coding RNA OIP5 antisense RNA 1 (lncRNA OIP5-AS1) in modulating acute lung injury (ALI) mediated by sepsis. Here, a sepsis model was constructed using cecal ligation and puncture (CLP) surgery in vivo. The alveolar macrophage cell line NR8383 and the alveolar type II cell line RLE-6TN were dealt with lipopolysaccharide (LPS) for in-vitro experiments. We discovered that OIP5-AS1 and Sirtuin1 (SIRT1) were markedly down-regulated in sepsis models elicited by CLP or LPS, while miR-128-3p experienced a dramatic up-regulation. OIP5-AS1 overexpression attenuated NR8383 and RLE-6TN cell apoptosis triggered by LPS and suppressed the expressions of nuclear factor kappa B (NF-κB), inducible nitric oxide synthase (iNOS), interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in NR8383 and RLE-6TN cells, whereas miR-128-3p overexpression resulted in the opposite phenomenon. Moreover, OIP5-AS1 overexpression relieved lung edema, lung epithelial cell apoptosis, infiltration of myeloperoxidase (MPO)-labeled polymorphonuclear neutrophils (PMN), inflammatory responses triggered by CLP in vivo. Mechanistically, miR-128-3p, which targeted SIRT1, was hobbled by OIP5-AS1. All in all, OIP5-AS1 overexpression enhanced sepsis-induced ALI by modulating the miR-128-3p/SIRT1 pathway, which helps create new insights into sepsis treatment.

Ultramicronized Palmitoylethanolamide Inhibits NLRP3 Inflammasome Expression and Pro-Inflammatory Response Activated by SARS-CoV-2 Spike Protein in Cultured Murine Alveolar Macrophages

Despite its possible therapeutic potential against COVID-19, the exact mechanism(s) by which palmitoylethanolamide (PEA) exerts its beneficial activity is still unclear. PEA has demonstrated analgesic, anti-allergic, and anti-inflammatory activities. Most of the anti-inflammatory properties of PEA arise from its ability to antagonize nuclear factor-κB (NF-κB) signalling pathway via the selective activation of the PPARα receptors. Acting at this site, PEA can downstream several genes involved in the inflammatory response, including cytokines (TNF-α, Il-1β) and other signal mediators, such as inducible nitric oxide synthase (iNOS) and COX2. To shed light on this, we tested the anti-inflammatory and immunomodulatory activity of ultramicronized(um)-PEA, both alone and in the presence of specific peroxisome proliferator-activated receptor alpha (PPAR-α) antagonist MK886, in primary cultures of murine alveolar macrophages exposed to SARS-CoV-2 spike glycoprotein (SP). SP challenge caused a significant concentration-dependent increase in proinflammatory markers (TLR4, p-p38 MAPK, NF-κB) paralleled to a marked upregulation of inflammasome-dependent inflammatory pathways (NLRP3, Caspase-1) with IL-6, IL-1β, TNF-α over-release, compared to vehicle group. We also observed a significant concentration-dependent increase in angiotensin-converting enzyme-2 (ACE-2) following SP challenge. um-PEA concentration-dependently reduced all the analyzed proinflammatory markers fostering a parallel downregulation of ACE-2. Our data show for the first time that um-PEA, via PPAR-α, markedly inhibits the SP induced NLRP3 signalling pathway outlining a novel mechanism of action of this lipid against COVID-19.

Therapeutic Effects and Molecular Mechanisms of Bioactive Compounds Against Respiratory Diseases: Traditional Chinese Medicine Theory and High-Frequency Use

Respiratory diseases, especially the pandemic of respiratory infectious diseases and refractory chronic lung diseases, remain a key clinical issue and research hot spot due to their high prevalence rates and poor prognosis. In this review, we aimed to summarize the recent advances in the therapeutic effects and molecular mechanisms of key common bioactive compounds from Chinese herbal medicine. Based on the theories of traditional Chinese medicine related to lung diseases, we searched several electronic databases to determine the high-frequency Chinese medicines in clinical application. The active compounds and metabolites from the selected medicines were identified using the Traditional Chinese Medicine Systems Pharmacology Database (TCMSP) by analyzing oral bioavailability and drug similarity index. Then, the pharmacological effects and molecular mechanisms of the selected bioactive compounds in the viral and bacterial infections, inflammation, acute lung injury (ALI), chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, asthma, and lung cancer were summarized. We found that 31 bioactive compounds from the selected 10 common Chinese herbs, such as epigallocatechin-3-gallate (EGCG), kaempferol, isorhamnetin, quercetin, and β-sitosterol, can mainly regulate NF-κB, Nrf2/HO-1, NLRP3, TGF-β/Smad, MAPK, and PI3K/Akt/mTOR pathways to inhibit infection, inflammation, extracellular matrix deposition, and tumor growth in a series of lung-related diseases. This review provides novel perspectives on the preclinical study and clinical application of Chinese herbal medicines and their bioactive compounds against respiratory diseases.

Fine particulate matter-induced lung inflammation is mediated by pyroptosis in mice

BACKGROUND

Exposure to ambient air-borne fine particulate matter (PM_2.5) increases respiratory morbidity and mortality. The mechanisms underlying PM_2.5-induced adverse effects remain unclear. This study aimed to uncover the molecular mechanisms of PM_2.5-induced lung toxicity using a mouse model.

METHODS

Scanning electron microscopy and inductively coupled plasma mass spectrometry were used to examine and analyze PM_2.5 morphology and element compositions, respectively. Twenty four male mice were randomly divided into three groups: control (PBS), PM_2.5 (4.0 mg/kg b.w.), and PM_2.5 + Z-YVAD-FMK. In the latter group, the pan-caspase inhibitor (Z-YVAD-FMK) was intraperitoneally injected into mice at a dose of 12.5 mg/kg body weight prior to intratracheal instillation of PM_2.5 (4.0 mg/kg b.w.) every other day for a total of 3 times (n = 8 in each group). Bronchoalveolar lavage fluids (BALFs) were collected 24 h after the last instillation of PM_2.5. Levels of total proteins (TP), lactate dehydrogenase (LDH), IL-1β and IL-18 were analyzed for biomarkers of cell injury and inflammation. Additionally, histological alterations of lung tissues were assessed by hematoxylin-eosin staining. mRNA and protein expression of Caspase1, NLRP3 and GSDMD were examined by real-time fluorescent quantitative PCR and immunohistochemical staining.

RESULTS

Exposure to PM_2.5 increased levels of TP, LDH, IL-1β, IL-18 and inflammatory cell counts in lung. The mRNA and protein expression of Caspase1, NLRP3 and GSDMD were increased. Inhibition of the NALRP3/Caspase-1 signaling pathway ameliorated PM_2.5-induced lung injury and inflammation, partially through suppressing pyroptosis in lung.

CONCLUSION

PM_2.5 exposure induces lung injury and inflammation, which is mediated by the NALRP3/Caspase-1 signaling pathway.

The effect of environmental diesel exhaust pollution on SARS-CoV-2 infection: The mechanism of pulmonary ground glass opacity

Diesel exhaust particles (DEP) are the major components of atmospheric particulate matter (PM) and chronic exposure is recognized to enhance respiratory system complications. Although the spread of SARS-CoV-2 was found to be associated with the PMs, the mechanism by which exposure to DEP increases the risk of SARS-CoV-2 infection is still under discussion. However, diesel fine PM (dPM) elevate the probability of SARS-CoV-2 infection, as it coincides with the increase in the number of ACE2 receptors. Expression of ACE2 and its colocalized activator, transmembrane protease serine 2 (TMPRSS2) facilitate the entry of SARS-CoV-2 into the alveolar epithelial cells exposed to dPM. Thus, the coexistence of PM and SARS-CoV-2 in the environment augments inflammation and exacerbates lung damage. Increased TGF-β1 expression due to DEP accompanies the proliferation of the extracellular matrix. In this case, "multifocal ground-glass opacity" (GGO) in a CT scan is an indication of a cytokine storm and severe pneumonia in COVID-19.

Pulmonary Macrophage Cell Death in Lung Health and Disease

Over the last several decades, our understanding of regulated-cell-death (RCD) pathways has increased dramatically. In addition to apoptosis and accidental cell death (primary necrosis), a diverse spectrum of RCD pathways has been delineated. In the lung, airway macrophages are critical for maintaining the functionality of airways via the clearance of inhaled particles, cell debris, and infectious agents. Exposure of these cells to pathogenic organisms or particles can induce a variety of RCD pathways that promote the release of danger signals into the lung. These responses have evolved to trigger the innate and adaptive arms of the immune system and thus offer protection against pathogens; yet they can also contribute to the development of lung injury and pathogenic immune responses. In this review, we discuss recent studies that suggest a critical role for airway-macrophage RCD pathways in promoting the release of pulmonary danger signals in health and disease.

Evidence for reprogramming of monocytes into reparative alveolar macrophages in vivo by targeting PDE4b

Increased lung vascular permeability and neutrophilic inflammation are hallmarks of acute lung injury. Alveolar macrophages (AMϕ), the predominant sentinel cell type in the airspace, die in massive numbers while fending off pathogens. Recent studies indicate that the AMϕ pool is replenished by airspace-recruited monocytes, but the mechanisms instructing the conversion of recruited monocytes into reparative AMϕ remain elusive. Cyclic AMP (cAMP) is a vascular barrier protective and immunosuppressive second messenger in the lung. Here, we subjected mice expressing GFP under the control of the Lysozyme-M promoter (LysM-GFP mice) to the LPS model of rapidly resolving lung injury to address the impact of mechanisms determining cAMP levels in AMϕ and regulation of mobilization of the reparative AMϕ-pool. RNA-seq analysis of flow-sorted Mϕ identified phosphodiesterase 4b (PDE4b) as the top LPS-responsive cAMP-regulating gene. We observed that PDE4b expression markedly increased at the time of peak injury (4 h) and then decreased to below the basal level during the resolution phase (24 h). Activation of transcription factor NFATc2 was required for transcription of PDE4b in Mϕ. Inhibition of PDE4 activity at the time of peak injury, using i.t. rolipram, increased cAMP levels, augmented the reparative AMϕ pool, and resolved lung injury. This response was not seen following conditional depletion of monocytes, thus establishing airspace-recruited PDE4b-sensitive monocytes as the source of reparative AMϕ. Interestingly, adoptive transfer of rolipram-educated AMϕ into injured mice resolved lung edema. We propose suppression of PDE4b as an effective approach to promote reparative AMϕ generation from monocytes for lung repair.

Pretreatment with Coenzyme Q10 Combined with Aescin Protects against Sepsis-Induced Acute Lung Injury

Sepsis-associated acute lung injury (ALI) is a critical condition characterized by severe inflammatory response and mitochondrial dysfunction. Coenzyme Q10 (CoQ10) and aescin (AES) are well-known for their anti-inflammatory activities. However, their effects on lipopolysaccharide (LPS)-induced lung injury have not been explored yet. Here, we asked whether combined pretreatment with CoQ10 and AES synergistically prevents LPS-induced lung injury. Fifty male rats were randomized into 5 groups: (1) control; (2) LPS-treated, rats received a single i.p. injection of LPS (8 mg/kg); (3) CoQ10-pretreated, (4) AES-pretreated, or (5) combined-pretreated; animals received CoQ10 (100 mg/kg), AES (5 mg/kg), or both orally for 7 days before LPS injection. Combined CoQ10 and AES pretreatment significantly reduced lung injury markers; 52.42% reduction in serum C-reactive protein (CRP), 53.69% in alkaline phosphatase (ALKP) and 60.26% in lactate dehydrogenase (LDH) activities versus 44.58, 37.38, and 48.6% in CoQ10 and 33.81, 34.43, and 39.29% in AES-pretreated groups, respectively. Meanwhile, combination therapy significantly reduced interleukin (IL)-1β and tumor necrosis factor (TNF)-α expressions compared to monotherapy (p < 0.05). Additionally, combination therapy prevented LPS-induced histological and mitochondrial abnormalities greater than separate drugs. Western blotting indicated that combination therapy significantly suppressed nucleotide-binding oligomerization domain (NOD)-like receptors-3 (NLRP-3) inflammasome compared to separate drugs (p < 0.05). Further, combination therapy significantly decreased the expression of signaling cascades, p38 mitogen-activated protein kinases (p38 MAPK), nuclear factor kappa B (NF-κB)-p65, and extracellular-regulated kinases 1/2 (ERK1/2) versus monotherapy (p < 0.05). Interestingly, combined pretreatment significantly downregulated high mobility group box-1 (HMGB1) by 72.93%, and toll-like receptor 4 (TLR4) by -0.93-fold versus 61.92%, -0.83-fold in CoQ10 and 38.67%, -0.70-fold in AES pretreatment, respectively. Our results showed for the first time that the enhanced anti-inflammatory effect of combined CoQ10 and AES pretreatment prevented LPS-induced ALI via suppression of NLRP-3 inflammasome through regulation of HMGB1/TLR4 signaling pathway and mitochondrial stabilization.

Protective effect of taurine on sepsis‑induced lung injury via inhibiting the p38/MAPK signaling pathway

Sepsis, a leading cause of acute lung injury (ALI), is characterized by an overwhelming systemic inflammatory response and widespread organ injury, particularly in the lungs. Taurine, an intracellular free amino acid, has been used for the treatment of various diseases, including lung injury; however, the underlying mechanisms are unclear. The present study aimed to investigate the protective effect of taurine on septic ALI and the underlying mechanism. A septic ALI model was established by performing cecal ligation and puncture (CLP) surgery on Sprague Dawley rats. Following successful model establishment, rats were treated with taurine. The results of hematoxylin and eosin, respiratory function detection, malondialdehyde level and superoxide dismutase activity determination and ELSIA demonstrated that taurine significantly alleviated lung injury, restored respiratory function, reduced oxidation and decreased the concentrations of inflammatory factors in CLP‑induced septic ALI model rats. In addition, compared with that in the ALI group, western blotting results indicated that taurine ameliorated lung epithelial injury by significantly increasing the expression levels of lung epithelial markers, E‑cadherin and occludin. The western blotting results demonstrated that, compared with the control group, the p38/MAPK and NF‑κB signaling pathways were significantly activated in CLP‑induced septic ALI model rats, but taurine significantly suppressed ALI‑mediated signaling pathway activation. To investigate the mechanism underlying taurine in the treatment of septic ALI, CLP‑induced septic ALI model rats were treated with an antagonist of the p38/MAPK signaling pathway (SB203580). The effects of SB203580 on CLP‑induced septic ALI model rats were similar to those of taurine. SB203580 significantly attenuated sepsis‑induced lung injury and increases in IL‑1β and TNF‑α concentrations in the lung tissue. In addition, SB203580 promoted restoration of the injured lung tissue and respiratory function in CLP‑induced septic ALI model rats. The western blotting results indicated that SB203580 significantly decreased the ratios of phosphorylated (p)‑p38/p38 and p‑p65/065, and increased the protein expression levels of E‑cadherin and occludin compared with those in the ALI group. In summary, the present study demonstrated that taurine alleviated sepsis‑induced lung injury, which was associated with suppression of the inflammatory response and oxidative stress via inhibiting the p38/MAPK signaling pathway. Therefore, the p38/MAPK signaling pathway may serve as a potential therapeutic target for the treatment of sepsis‑induced ALI.

Butorphanol Promotes Macrophage Phenotypic Transition to Inhibit Inflammatory Lung Injury via κ Receptors

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is characterized by diffuse inflammation of the lung parenchyma and refractory hypoxemia. Butorphanol is commonly used clinically for perioperative pain relief, but whether butorphanol can regulate LPS-induced alveolar macrophage polarization is unclear. In this study, we observed that butorphanol markedly attenuated sepsis-induced lung tissue injury and mortality in mice. Moreover, butorphanol also decreased the expression of M1 phenotype markers (TNF-α, IL-6, IL-1β and iNOS) and enhanced the expression of M2 marker (CD206) in alveolar macrophages in the bronchoalveolar lavage fluid (BALF) of LPS-stimulated mice. Butorphanol administration reduced LPS-induced numbers of proinflammatory (M1) macrophages and increased numbers of anti-inflammatory (M2) macrophages in the lungs of mice. Furthermore, we found that butorphanol-mediated suppression of the LPS-induced increases in M1 phenotype marker expression (TNF-α, IL-6, IL-1β and iNOS) in bone marrow-derived macrophages (BMDMs), and this effect was reversed by κ-opioid receptor (KOR) antagonists. Moreover, butorphanol inhibited the interaction of TLR4 with MyD88 and further suppressed NF-κB and MAPKs activation. In addition, butorphanol prevented the Toll/IL-1 receptor domain-containing adaptor inducing IFN-β (TRIF)-mediated IFN signaling pathway. These effects were ameliorated by KOR antagonists. Thus, butorphanol may promote macrophage polarization from a proinflammatory to an anti-inflammatory phenotype secondary to the inhibition of NF-κB, MAPKs, and the TRIF-mediated IFN signaling pathway through κ receptors.

BMSC-Derived Exosomes Ameliorate LPS-Induced Acute Lung Injury by miR-384-5p-Controlled Alveolar Macrophage Autophagy

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are common critical diseases. Bone marrow mesenchymal stem cell (BMSC) transplantation is previously shown to effectively rescue injured lung tissues. The therapeutic mechanism of BMSC-derived exosomes is not fully understood. Here, we investigated the BMSC-derived exosomal microRNAs (miRNAs) on effecting lipopolysaccharide- (LPS-) induced ALI and its mechanism. In vitro, rat alveolar macrophages were treated with or without exosomes in the presence of 10 μg/ml LPS for 24 h. Cell viability was determined with Cell Counting Kit-8 assay. Apoptotic ratio was determined with TUNEL and Annexin V-FITC/PI double staining. The levels of miR-384-5p and autophagy-associated genes were measured by RT-qPCR and western blot. Autophagy was observed by TEM and assessed by means of the mRFP-GFP-LC3 adenovirus transfection assay. In vivo, we constructed LPS-induced ALI rat models. Exosomes were injected into rats via the caudal vein or trachea 4 h later after LPS treatment. The lung histological pathology was determined by H&E staining. Pulmonary vascular permeability was assessed by wet-to-dry weight ratio and Evans blue dye leakage assay, and inflammatory cytokines in serum and BALF were measured by ELISA. Furthermore, the therapeutic mechanism involved in miR-384-5p and Beclin-1 was determined. The results showed that BMSC-derived exosomes were taken up by the alveolar macrophages and attenuated LPS-induced alveolar macrophage viability loss and apoptosis. Exosomes effectively improved the survival rate of ALI rats within 7 days, which was associated with alleviating lung pathological changes and pulmonary vascular permeability and attenuating inflammatory response. Furthermore, this study for the first time found that miR-384-5p was enriched in BMSC-derived exosomes, and exosomal miR-384-5p resulted in relieving LPS-injured autophagy disorder in alveolar macrophages by targeting Beclin-1. Therefore, exosomal miR-384-5p could be demonstrated as a promising therapeutic strategy for ALI/ARDS.

Ferroptosis and Necroptosis in the Kidney

In the last decade, the role of apoptosis in the pathophysiology of acute kidney injury (AKI) and AKI to chronic kidney disease (CKD) progression has been revisited as our understanding of ferroptosis and necroptosis has emerged. A growing body of evidence, reviewed here, ascribes a central pathophysiological role for ferroptosis and necroptosis to AKI, nephron loss, and acute tubular necrosis. We will introduce concepts to the non-cell-autonomous manner of kidney tubular injury during ferroptosis, a phenomenon that we refer to as a "wave of death." We hypothesize that necroptosis might initiate cell death propagation through ferroptosis. The remaining necrotic debris requires effective removal processes to prevent a secondary inflammatory response, referred to as necroinflammation. Open questions include the differences in the immunogenicity of ferroptosis and necroptosis, and the specificity of necrostatins and ferrostatins to therapeutically target these processes to prevent AKI-to-CKD progression and end-stage renal disease.

Nur77 Attenuates Inflammasome Activation by Inhibiting Caspase-1 Expression in Pulmonary Vascular Endothelial Cells

Inflammasomes are intracellular multiprotein complexes that help trigger and maintain the inflammatory response as part of the innate immune system. Recently, it has been increasingly recognized that aberrant inflammasome activation is critically involved endothelial dysfunction in a variety of human diseases, such as atherosclerosis, acute lung injury (ALI), and type 2 diabetes. The molecular mechanisms underlying endothelial inflammasome activation, however, are not completely elucidated. In the present study, we identified orphan nuclear receptor Nur77 as a novel regulator in controlling inflammasome activation in vascular endothelial cells (ECs). We demonstrated that LPS-induced inflammasome activation was significantly inhibited by ectopic overexpression of Nur77, predominantly through transcriptionally suppression of caspase-1 expression in vascular ECs. Consistent with this observation, we found that LPS-induced inflammasome activation was significantly augmented in lung ECs isolated from Nur77 knockout (KO) mice. Mechanistically, we showed that Nur77-induced inhibition of caspase-1 expression was due to an inhibition of Interferon Regulatory Factor 1 (IRF1) expression and its subsequent binding to the caspase-1 promoter. Importantly, in a mouse model of LPS-induced acute lung injury (ALI), Nur77 KO led to a marked activation of caspase-1 in the lung, increased alveolar and circulating IL-1β levels, and exacerbated ALI, all of which were substantially inhibited by administration of caspase-1 inhibitor. Together, our results support an important role for Nur77 in controlling inflammasome activation in vascular ECs and suggest that Nur77 could be a novel therapeutic target for the treatment of human diseases associated with aberrant inflammasome activation, such as ALI and atherosclerosis.

Cirsilineol attenuates LPS-induced inflammation in both in vivo and in vitro models via inhibiting TLR-4/NFkB/IKK signaling pathway

The anti-inflammatory activity of cirsilineol in in vivo condition was assessed by measuring the relative organ weight, lung dry/wet weight ratio, protein concentration, and infiltration of inflammatory cells in bronchoalveolar lavage fluid. We estimated the myeloperoxidase activity and levels of cytokines, chemokines, and inflammatory markers to analyze the efficacy of cirsilineol against lipopolysaccharide (LPS)-induced lung inflammation. Furthermore, we quantified the gene expression of NFkB/IKK signaling molecules in cirsilineol-treated and untreated acute lung injury mice to confirm the anti-inflammatory property of cirsilineol. The lung histology was assessed with hematoxylin and eosin staining. Apart from in vivo experiments, in vitro tests with LPS-stimulated RAW 264.7 macrophages were also performed. Cell viability assay was performed in the presence and absence of LPS in RAW 264.7 macrophages to determine the cytotoxic effect of cirsilineol against macrophages. Reverse-transcription polymerase chain reaction (RT-PCR) analysis was done to analyze the gene expression of inflammatory markers in LPS-treated RAW 264.7 macrophages to prove that cirsilineol effectively inhibits inflammation in vitro. The results of our study prove that cirsilineol effectively inhibits inflammation in both in vivo and in vitro conditions. RT-PCR analysis results of NFkB/IKK signaling molecules clearly illustrate that cirsilineol inhibited the expression of NFkB/IKK signaling protein and thereby prevented inflammation in in vivo condition, and it is further confirmed with the results of inflammatory protein expression in vitro model. The lung histopathological studies authentically confirm that cirsilineol potentially prevented the mice from LPS-induced lung inflammation.

M1 Macrophages Are More Susceptible to Necroptosis

Macrophages play a crucial role in host innate immune defense against infection and tissue injury. Although macrophage activation and polarization has been well studied, we know less regarding the role of macrophage activation/polarization in inflammation-associated necrotic cell death. By using bone marrow-derived macrophages, we have recently demonstrated that M1 macrophages are much more susceptible than M0 and M2 subtypes of macrophages to necrotic cell death. Moreover, we showed that the enhanced necroptosis in M1 macrophages is dependent on the kinase activity of receptor-interacting protein kinase-3 (RIPK3) and may involve the upregulation of key necroptosis signaling molecules including RIPK3, mixed lineage kinase domain-like protein, and Z-DNA/ RNA binding protein 1. Our findings provide novel insights into the mechanisms of M1 macrophage engagement in inflammation and tissue injury.

Construction of mannose-modified polyethyleneimine-block-polycaprolactone cationic polymer micelles and its application in acute lung injury

This study evaluated the D-mannose modified polyethyleneimine-block-polycaprolactone biomacromolecule copolymer micelles (PCL-PEI-mannose) as a targeted delivery of the glucocorticoid dexamethasone (DXM) to lung inflammation tissues and enhances the vehicle for its anti-inflammatory effects. Dexamethasone was encapsulated in the hydrophobic core of cationic polymer micelles by solvent evaporation. The polymeric micelles exhibited sustained-release within 48 h, good blood compatibility, and colloidal stability in vitro. The cellular uptake of mannose-modified micelles was higher compared with the non-modified micelles. And drug-loaded targeted micelles could inhibit the production of inflammatory factors in activated RAW264.7 cells. The distribution results indicated that drug-loaded targeted micelles highly improved the lung targeting ability, reduced the wet/dry ratio of injured lung tissue, and relieved the lung inflammation, accompanied by the decrease of inflammatory cell infiltration, myeloperoxidase activity, and inflammatory mediator levels in bronchoalveolar lavage fluid. These findings suggested that PCL-PEI-mannose delivery system could facilitate the lung-specific delivery and inhibit the inflammatory response. Collectively, PCL-PEI-mannose polymer micelles could be used as a potential delivery system for the treatment of acute lung injury (ALI).

Emodin Alleviates Severe Acute Pancreatitis-Associated Acute Lung Injury by Inhibiting the Cold-Inducible RNA-Binding Protein (CIRP)-Mediated Activation of the NLRP3/IL-1β/CXCL1 Signaling

Objective: Severe acute pancreatitis (SAP) can lead to acute lung injury (ALI). This study investigated the therapeutic effect of emodin and its molecular mechanisms in a rat model of SAP-ALI.

Methods: Forty male Sprague-Dawley rats were randomly divided into the groups: Control (CON), SAP (SAP), emodin (EMO), and C23 (C23). The latter three groups of rats were induced for SAP-ALI by retrograde injection of 5% sodium taurocholate into the biliary-pancreatic duct and were treated with vehicle, emodin or C23, respectively. One day post induction, their pancreatic and lung injury was assessed by histology and arterial blood gas analysis. In vitro, rat alveolar macrophages (NR8383 cells) were treated with recombinant rat CIRP in the presence or absence of TAK242 (a TLR4 inhibitor), C23 or emodin. The CIRP-mediated activation of the NLRP3/IL-1β/CXCL1 signaling in rat lungs and NR8383 cells was determined. Similarly, the role of IL-1β in the CIRP-induced CXCL1 expression was investigated.

Results: Emodin treatment significantly reduced inflammation and tissue damages in the pancreatic and lung tissues in rats with SAP-ALI, accompanied by decreasing serum amylase, CIRP and IL-1β levels and improving lung function. Furthermore, emodin significantly mitigated the SAP-up-regulated CIRP expression in the pancreatic islets and lung tissues, and attenuated the SAP-activated NF-κB signaling, NLRP3 inflammasome formation and CXCL1 expression in lung resident macrophages as well as neutrophil infiltration in the lungs of rats. In addition, treatment with CIRP significantly activated the NF-κB signaling and NLRP3 inflammasome formation and induced IL-1β and CXCL1 expression and pyroptosis in NR8383 cells, which were abrogated by TAK242 and significantly mitigated by C23 or emodin. Moreover, CIRP only induced very lower levels of CXCL1 expression in IL-1β-silencing NR8383 cells and treatment with IL-1β induced CXCL1 expression in NR8383 cells in a dose and time-dependent manner.

Conclusion: Emodin may inhibit the CIRP-activated NLRP3/IL-1β/CXCL1signaling to decrease neutrophil infiltration and ameliorate the SAP-ALI in rats.

Auranofin-Mediated NRF2 Induction Attenuates Interleukin 1 Beta Expression in Alveolar Macrophages

Background: Alveolar macrophages (AMs) are resident inflammatory cells in the lung that serve as early sentinels of infection or injury. We have identified thioredoxin reductase 1 inhibition by gold compounds increases activation of nuclear factor erythroid 2-related factor 2 (NRF2)-dependent pathways to attenuate inflammatory responses. The present studies utilized murine alveolar macrophages (MH-S) to test the hypothesis that the gold compound, auranofin (AFN), decreases interleukin (IL)-1β expression through NRF2-mediated interactions with nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway genes and/or increases in glutathione synthesis. Methods: MH-S cells were treated with AFN and lipopolysaccharide (LPS) and analyzed at 6 and 24 h. The Il1b promoter was analyzed by chromatin immunoprecipitation for direct interaction with NRF2. Results: Expression of IL-1β, p-IκBα, p-p65 NF-kB, and NOD-, LRR-, and pyrin domain-containing protein 3 were elevated by LPS exposure, but only IL-1β expression was suppressed by AFN treatment. Both AFN and LPS treatments increased cellular glutathione levels, but attenuation of glutathione synthesis by buthionine sulfoximine (BSO) did not alter expression of Il-1β. Analysis revealed direct NRF2 binding to the Il1b promoter which was enhanced by AFN and inhibited the transcriptional activity of DNA polymerase II. Conclusions: Our data demonstrate that AFN-induced NRF2 activation directly suppresses IL-1β synthesis independent of NFκB and glutathione-mediated antioxidant mechanisms. NRF2 binding to the promoter region of IL1β directly inhibits transcription of the IL1β gene. Collectively, our research suggests that gold compounds elicit NRF2-dependent pulmonary protection by suppressing macrophage-mediated inflammation.

Extracellular histones aggravate inflammation in ARDS by promoting alveolar macrophage pyroptosis

Extracellular histones have been discovered to play a pathogenic role in ARDS, but the underlying mechanisms are yet to be fully defined. Alveolar macrophage (AM) is essential for the initiation and progression of lung inflammation; of note, AM pyroptosis has been suggested contributing to ARDS-associated inflammation. Here we aimed to investigate whether extracellular histones promote ARDS by triggering AM pyroptosis. The BALF samples of ARDS patients were collected and AMs were further isolated. Extracellular histones, AM pyroptosis, and pyroptosis-associated mediators were measured. Furthermore, the effects of extracellular histones on AM pyroptosis and the underlying mechanisms were investigated. It showed that extracellular histones were markedly elevated in the BALF of ARDS patients and correlated with the increased AM pyroptosis. ARDS patient's BALF induced pronounced pyroptosis in cultured human monocytes, which could be prevented by neutralizing extracellular histones with heparin. In addition, exogenous histones induced pyroptosis of MH-S cells in a dose- and time-dependent manner, which acted through the NLRP3 inflammasome signaling pathway. Inhibition of NLRP3 inflammasome signaling substantially reduced cell pyroptosis. In a murine model of LPS-induced ARDS, extracellular histones were increased in the BALF and its increase was associated with enhanced AM pyroptosis and exaggerated lung inflammation. Blockade of extracellular histones or NLPR3 inflammasome equally inhibited macrophage pyroptosis, whereas targeting histones appeared more effective in alleviating lung inflammation. This study suggested that extracellular histones promote AM pyroptosis through NLRP3 inflammasome pathway, which in turn aggravates lung inflammation in ARDS. Pharmacological manipulation of extracellular histones or AM pyroptosis may become promising strategies for the treatment of ARDS.

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.

Nuclear factor-kappaB regulates the transcription of NADPH oxidase 1 in human alveolar epithelial cells

Objective

Acute lung injury (ALI) is characterized by inflammation and oxidative stress. Nuclear factor-kappaB (NF-κB) mediates the expression of various inflammation-related genes, including the NADPH oxidase family. This study aimed to identify the potential regulatory role of NF-κB on NADPH oxidases in tumor necrosis factor-α (TNF-α)-induced oxidative stress in human alveolar epithelial cells.

Methods

A549 cells were treated with TNF-α for 24 h to establish ALI cell models. RT-PCR, western blot, assessment of oxidative stress, Alibaba 2.1 online analysis, electrophoretic mobility shift assays and luciferase reporter analysis were employed to identify the potential regulatory role of NF-κB on NADPH oxidases in TNF-α-induced oxidative stress in human alveolar epithelial cells.

Results

The expression of NF-κB/p65 was notably upregulated in TNF-α-stimulated A549 cells. NF-κB knockdown by siRNA significantly inhibited the TNF-α-induced oxidative stress. Moreover, NF-κB/p65 siRNA could inhibit the activation of NOX1, NOX2 and NOX4 mRNA and protein expression in TNF-α-stimulated A549 cells. The next study demonstrated that NF-κB activated the transcription of NOX1 by binding to the -261 to -252 bp (NOX1/κB2, TAAAAATCCC) region of NOX1 promoter in TNF-α-stimulated A549 cells.

Conclusion

Our data demonstrated that NF-κB can aggravate TNF-α-induced ALI by regulating the oxidative stress response and the expression of NOX1, NOX2 and NOX4. Moreover, NF-κB could promote the NOX1 transcriptional activity via binding its promoter in TNF-α-stimulated A549 cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-021-01464-z.

Cerium oxide nanoparticle delivery of microRNA-146a for local treatment of acute lung injury

Acute respiratory distress syndrome (ARDS) is a devastating pulmonary disease with significant in-hospital mortality and is the leading cause of death in COVID-19 patients. Excessive leukocyte recruitment, unregulated inflammation, and resultant fibrosis contribute to poor ARDS outcomes. Nanoparticle technology with cerium oxide nanoparticles (CNP) offers a mechanism by which unstable therapeutics such as the anti-inflammatory microRNA-146a can be locally delivered to the injured lung without systemic uptake. In this study, we evaluated the potential of the radical scavenging CNP conjugated to microRNA-146a (termed CNP-miR146a) in preventing acute lung injury (ALI) following exposure to bleomycin. We have found that intratracheal delivery of CNP-miR146a increases pulmonary levels of miR146a without systemic increases, and prevents ALI by altering leukocyte recruitment, reducing inflammation and oxidative stress, and decreasing collagen deposition, ultimately improving pulmonary biomechanics.

Fungal-Induced Programmed Cell Death

Fungal infections are a cause of morbidity in humans, and despite the availability of a range of antifungal treatments, the mortality rate remains unacceptably high. Although our knowledge of the interactions between pathogenic fungi and the host continues to grow, further research is still required to fully understand the mechanism underpinning fungal pathogenicity, which may provide new insights for the treatment of fungal disease. There is great interest regarding how microbes induce programmed cell death and what this means in terms of the immune response and resolution of infection as well as microbe-specific mechanisms that influence cell death pathways to aid in their survival and continued infection. Here, we discuss how programmed cell death is induced by fungi that commonly cause opportunistic infections, including Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans, the role of programmed cell death in fungal immunity, and how fungi manipulate these pathways.

Involvement of TFAP2A in the activation of GSDMD gene promoter in hyperoxia-induced ALI

Oxygen therapy is a common treatment in neonatal intensive care units, but long-term continuous hyperoxia ventilation may induce acute lung injury (ALI). Gasdermin D (GSDMD)-mediated pyroptosis participates in various diseases including ALI, but the role of GSDMD in hyperoxia-induced ALI is yet understood. Here, we showed a significant increase in GSDMD after exposure to high oxygen. To elucidate the molecular mechanisms involved in GSDMD regulation, we identified the core promoter of GSDMD, -98 ~ -12 bp relative to the transcriptional start site (TSS). The results of mutational analysis, overexpression or siRNA interference, EMSA and ChIP demonstrated that E2F4 and TFAP2A positively regulate the transcriptional activity of the GSDMD by binding to its promoter. However, only TFAP2A showed a regulatory effect on the expression of GSDMD. Moreover, TFAP2A was increased in the lung tissues of rats exposed to hyperoxia and showed a strong linear correlation with GSDMD. Our results indicated that TFAP2A positively regulates the GSDMD expression via binding to the promoter region of GSDMD.

Cell-Cell Interaction Mechanisms in Acute Lung Injury

ABSTRACT

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are caused by an exaggerated inflammatory response arising from a wide variety of pulmonary and systemic insults. Lung tissue is composed of a variety of cell populations, including parenchymal and immune cells. Emerging evidence has revealed that multiple cell populations in the lung work in concert to regulate lung inflammation in response to both direct and indirect stimulations. To date, the question of how different types of pulmonary cells communicate with each other and subsequently regulate or modulate inflammatory cascades remains to be fully addressed. In this review, we provide an overview of current advancements in understanding the role of cell-cell interaction in the development of ALI and depict molecular mechanisms by which cell-cell interactions regulate lung inflammation, focusing on inter-cellular activities and signaling pathways that point to possible therapeutic opportunities for ALI/ARDS.

Vimentin regulation of autophagy activation in lung fibroblasts in response to lipopolysaccharide exposure in vitro

Background

The activation and assembly of the NLRP3 inflammasome is dependent on the interaction between NLRP3 and the intermediate filament protein vimentin in an acute respiratory distress syndrome (ARDS) model. We investigated the role of vimentin in this process using human fetal lung (HFL-1) fibroblasts with vimentin transfer genes or gene knockdown and lipopolysaccharide (LPS) intervention.

Methods

HFL-1 cells [con-vector + LPS, vimentin-pCMV3 (VIM-pCMV3), con-siRNA, and vimentin siRNA (VIM-siRNA)] were treated with LPS. An oxidative stress damage assessment, apoptosis analysis, and quantification of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, and IL-10 by enzyme linked immunosorbent assay (ELISA) were performed. Immunoblotting was used to reveal the autophagy pathway.

Results

We demonstrated that in response to LPS vimentin expression was lower in the HFL-1 cells with the vimentin gene knocked down. Specifically, an increase in oxidative stress, a decrease in mitochondrial membrane potential, or an increase in calcium ion permeability resulted in an increase in the fibroblast apoptosis rate. In addition, the inflammatory response after vimentin gene knockout was upregulated, as indicated by higher levels of TNF-a, IL-1β, IL-6, and IL-10. Importantly, the mechanism of suppression of vimentin in the lung fibroblasts was caused by a decrease in autophagy, an increase in mitochondrial membrane protein, and a decrease in mitochondrial function, which may contribute to the augmented cellular injury generated during the response to LPS.

Conclusions

This study provides insights into whether vimentin may interfere with the inflammatory cascade by activating the autophagy pathway of mitochondrial lung fibroblasts in the early stage of acute lung injury (ALI).

Targeting MALAT1 and miRNA-181a-5p for the intervention of acute lung injury/acute respiratory distress syndrome

BACKGROUND

ALI/ARDS is a severe lung injury leading to refractory respiratory failure, accounting for high morbidity and mortality. However, therapeutic approaches are rather limited. Targeting long non-coding RNA MALAT1 and microRNA miR-181a-5p might be potential option for ALI/ARDS intervention.

OBJECTIVE

We aimed to investigate the role of MALAT and miR-181a-5p in the pathogenesis of ALI/ARDS, and test the therapeutic effects of targeting MALAT and miR-181a-5p for ALI/ARDS intervention in vitro.

METHODS

MALAT1 and miR-181a-5p levels were measured in plasma from ALI/ARDS patients. In vitro human pulmonary microvascular endothelial cell (HPMEC) injury was induced by LPS treatment, and molecular targets of MALAT1 and miR-181a-5p were explored by molecular biology approaches, mainly focusing on cell apoptosis and vascular inflammation. Interaction between MALAT1 and miR-181a-5p was also detected. Finally, the effects of targeting MALAT1 and miR-181a-5p for ALI/ARDS intervention were validated in a rat ALI/ARDS model.

RESULTS

MALAT1 upregulation and miR-181a-5p downregulation were observed in ALI/ARDS patients. Transfection of mimic miR-181a-5p into HPMECs revealed decreased Fas and apoptosis, along with reduced inflammatory factors. Fas was proved to be a direct target of miR-181a-5p. Similar effects were also present upon MALAT1 knockdown. As for the interaction between MALAT1 and miR-181a-5p, MALAT1 knockdown increased miR-181a-5p expression. Knocking down of MALAT1 and miR-181a-5p could both improve the outcome in ALI/ARDS rats.

CONCLUSION

MALAT1 antagonism or miR-181a-5p could both be potential therapeutic strategies for ALI/ARDS. Mechanistically, miR-181a-5p directly inhibits Fas and apoptosis, along with reduced inflammation. MALAT1 negatively regulates miR-181a-5p.

Preventing the development of severe COVID-19 by modifying immunothrombosis

BACKGROUND

COVID-19-associated acute respiratory distress syndrome (ARDS) is associated with significant morbidity and high levels of mortality. This paper describes the processes involved in the pathophysiology of COVID-19 from the initial infection and subsequent destruction of type II alveolar epithelial cells by SARS-CoV-2 and culminating in the development of ARDS.

MAIN BODY

The activation of alveolar cells and alveolar macrophages leads to the release of large quantities of proinflammatory cytokines and chemokines and their translocation into the pulmonary vasculature. The presence of these inflammatory mediators in the vascular compartment leads to the activation of vascular endothelial cells platelets and neutrophils and the subsequent formation of platelet neutrophil complexes. These complexes in concert with activated endothelial cells interact to create a state of immunothrombosis. The consequence of immunothrombosis include hypercoagulation, accelerating inflammation, fibrin deposition, migration of neutrophil extracellular traps (NETs) producing neutrophils into the alveolar apace, activation of the NLRP3 inflammazome, increased alveolar macrophage destruction and massive tissue damage by pyroptosis and necroptosis Therapeutic combinations aimed at ameliorating immunothrombosis and preventing the development of severe COVID-19 are discussed in detail.

Celastrol alleviates LPS-induced inflammation in BMDMs and acute lung injury in mice via inhibition of p-38 MAPK/MK2 signaling

Objective:

Celastrol is a compound extracted from a medicinal plant Tripterygium wilfordii which has a broad-spectrum anti-inflammatory effect in traditional medicine. However, the effect of celastrol on acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) is still unknown.

Methods:

We reported that celastrol alleviated LPS-induced acute lung injury by H&E staining, MPO activity and the expression of cytokines in broncho-alveolar lavage fluid. The effect of celastrol on bone marrow-derived macrophages (BMDMs) after LPS treatment was measured by ELISA and Western blotting.

Results:

In vivo, celastrol reduced the LPS-induced lung edema and MPO activity of lung tissue. Furthermore, the production of inflammatory cytokines IL-6, TNF-α, and KC in bronchoalveolar lavage was reduced. In vitro, upon treatment of LPS, celastrol dose-dependently inhibited the expression of iNOS in BMDMs. Meanwhile, the expression of IL-6, TNF-α, and KC in BMDMs were also inhibited by celastrol treatment. Furthermore, we found that celastrol attenuated the phosphorylation of p38 MAPK and MK2, and inhibited the interaction between p38 MAPK and MK2.

Conclusion:

Our data indicate that celastrol has an anti-inflammatory effect on LPS-induced inflammatory response in vivo and in vitro, suggesting celastrol is a promising compound for the treatment of ALI and ARDS.

Respiratory epithelium: Place of entry and / or defense against SARS-CoV-2 virus

Coronavirus Disease (COVID-19) is caused by the RNA virus SARS-CoV-2. The primary receptor for the virus is most likely Angiotensin-converting enzyme 2 (ACE2), and the virus enters the body by infecting epithelial cells of the respiratory tract. Through the activation of Toll Like Receptors (TLRs), epithelial cells begin to synthesize various biologically active molecules. The pathophysiology of the COVID 19 is primarily attributed to the hyperactivation of host's immune system due to direct damage to the cells, with consequent release of proinflammatory substances, but also due to the activation of the innate immune response through the activation of alveolar macrophages and dendrite cells (DC). A strong proinflammatory reaction causes damage to alveolar epithelial cells and vascular endothelium. Respiratory epithelial cells, alveolar macrophages and DC are likely to be the most important cells involved in the innate immune response to the virus, since prolonged and excessive SARS-CoV-2-induced activation of these cells leads to the secretion of cytokines and chemokines that massively attract leukocytes and monocytes to the lungs and cause lung damage.

α2A-adrenoceptor deficiency attenuates lipopolysaccharide-induced lung injury by increasing norepinephrine levels and inhibiting alveolar macrophage activation in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a severe condition with high morbidity and mortality and few interventions. The role of sympathetic stress in the pathogenesis of ARDS has attracted recent research attention. Blockade of α-2 or α2A-adrenoceptor (α2A-AR) has been shown to attenuate lung injury induced by lipopolysaccharide (LPS) in rats. However, the mechanism is unclear. We confirmed the role of α2A-AR in ARDS using knockout mice and alveolar macrophages following LPS stimulation to assess the underlying mechanisms. We found that α2A-AR deficiency decreased the permeability of the alveolar capillary barrier in ARDS mice and suppressed lung inflammation by reducing inflammatory cell infiltration and the production of TNF-α, interleukin (IL)-6, and CXCL2/MIP-2. LPS stimulation decreased NF-κB activation in lung tissues of α2A-AR deficient mice and increased norepinephrine concentrations. In vitro, we found that norepinephrine inhibited the production of TNF-α, IL-6, and CXCL2/MIP-2 and promoted the secretion of IL-10 from LPS-stimulated murine alveolar macrophages. Blockade of α2A-AR by a specific antagonist further inhibited the production of TNF-α, IL-6, and IL-10. Furthermore, norepinephrine down-regulated NF-κB activation in stimulated alveolar macrophages. Altogether, these results suggest that α2A-AR deficiency ameliorates lung injury by increasing norepinephrine concentrations in lung tissues and inhibiting the activation of alveolar macrophages.

Can endolysosomal deacidification and inhibition of autophagy prevent severe COVID-19?

The possibility is examined that immunomodulatory pharmacotherapy may be clinically useful in managing the pandemic coronavirus disease 2019 (COVID-19), known to result from infection by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a positive-sense single-stranded RNA virus. The dominant route of cell entry of the coronavirus is via phagocytosis, with ensconcement in endosomes thereafter proceeding via the endosomal pathway, involving transfer from early (EEs) to late endosomes (LEs) and ultimately into lysosomes via endolysosomal fusion. EE to LE transportation is a rate-limiting step for coronaviruses. Hence inhibition or dysregulation of endosomal trafficking could potentially inhibit SARS-CoV-2 replication. Furthermore, the acidic luminal pH of the endolysosomal system is critical for the activity of numerous pH-sensitive hydrolytic enzymes. Golgi sub-compartments and Golgi-derived secretory vesicles also depend on being mildly acidic for optimal function and structure. Activation of endosomal toll-like receptors by viral RNA can upregulate inflammatory mediators and contribute to a systemic inflammatory cytokine storm, associated with a worsened clinical outcome in COVID-19. Such endosomal toll-like receptors could be inhibited by the use of pharmacological agents which increase endosomal pH, thereby reducing the activity of acid-dependent endosomal proteases required for their activity and/or assembly, leading to suppression of antigen-presenting cell activity, decreased autoantibody secretion, decreased nuclear factor-kappa B activity and decreased pro-inflammatory cytokine production. It is also noteworthy that SARS-CoV-2 inhibits autophagy, predisposing infected cells to apoptosis. It is therefore also suggested that further pharmacological inhibition of autophagy might encourage the apoptotic clearance of SARS-CoV-2-infected cells.

Human Lung Macrophages Challenged to Oxidants ex vivo: Lysosomal Membrane Sensitization is Associated with Inflammation and Chronic Airflow Limitation

Background

The lung macrophage (LM) is involved in most inflammatory processes of the human lung by clearance of dying cells and by wound repair. Upon cellular stress by oxidant challenge in vivo lysosomes may rupture in LMs and leakage of cellular content and cell debris may trigger airway inflammation and fibrosis, which may lead to chronic airflow limitation (CAL).

Objective

The aim of this study was to determine whether lysosomal membrane permeabilization (LMP) in LMs challenged to oxidants ex vivo is associated with airway inflammation and CAL, the latter assessed as the reduced forced expiratory volume in one second (FEV₁) expressed as % of predicted.

Materials and Methods

Twenty-eight subjects were investigated; 13 lung-healthy subjects and 15 subjects with a variety of inflammatory disorders, demonstrating CAL on dynamic spirometry (defined as an FEV₁/FVC ratio < 0.70). LMs were harvested by broncho-alveolar lavage (BAL) and challenged ex vivo by oxidants. LMP in oxidant-exposed LMs was assessed as the emitted acridine orange (AO) green fluorescence from oxidant-exposed LMs (using macrophage-like murine J774 cells as positive controls). Inflammatory cells in BAL were counted and lung volumes were recorded.

Results

Oxidant-induced LMP in LMs was significantly greater among subjects with CAL and particularly among those with ongoing inflammation. Previous tobacco history did not influence LMP. Among subjects with CAL, oxidant-induced LMP correlated negatively with FEV₁% of predicted.

Conclusion

Lysosomes of LMs harvested from patients with CAL demonstrate an increased sensitivity to oxidants, which may trigger mechanisms behind CAL, eg, chronic airway inflammation and fibrotic re-modelling. The study suggests a mechanistic role for LMP in LMs on airway inflammation, suggesting an anti-inflammatory effect by drugs that prevent increased LMP.

Targeting MALAT1 and miRNA-181a-5p for the intervention of acute lung injury/acute respiratory distress syndrome

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal).

This article has been retracted at the request of the authors due to a reported lack of agreement among the authors. The usage of the image in E-b part of Figure 7 had not received permission from the co-author. In order to resolve the issue, the authors agreed to retract the article.

Cyclic helix B peptide alleviates sepsis-induced acute lung injury by downregulating NLRP3 inflammasome activation in alveolar macrophages

Acute lung injury (ALI) exhibits high clinical morbidity and mortality rates. Our previous study has indicated that the novel proteolysis-resistant cyclic helix B peptide (CHBP) exerts an anti-inflammatory effect in mice with AKI. In the present study, we evaluated the effect of CHBP in an in vivo sepsis-induced ALI model and in vitro using lipopolysaccharide (LPS) and ATP stimulated bone marrow-derived macrophages (BMDMs). For in vivo experiments, mice were randomly divided into three groups: 1) sham; 2) LPS; and 3) LPS + CHBP (n = 6). All relevant data were collected after 18 h. Following CHBP treatment, the lung function of the mice was significantly improved compared to the LPS group. CHBP administration inhibited interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α production at both the protein and mRNA levels. Additionally, following CHBP treatment, the population of pulmonary macrophages decreased. Simultaneously, the proportion of caspase-1-activated alveolar macrophages was also decreased after CHBP treatment. The protein levels of NLRP3 and cleaved caspase-1 were attenuated in the lung tissue following CHBP treatment. In in vitro experiments, CHBP treatment decreased NLRP3 inflammasome expression and downstream IL-1β secretion, consistent with the in vivo results. In addition, CHBP reversed nuclear factor (NF)-κB and I-κB phosphorylation with a significant dose-dependent effect. Therefore, these findings suggest the potential of CHBP as a therapeutic agent in sepsis-induced ALI owing to inhibition of the NLRP3 inflammasome via the NF-κB pathway in macrophages.

Salviplenoid A from Salvia plebeia attenuates acute lung inflammation via modulating NF-κB and Nrf2 signaling pathways

Acute lung injury (ALI) involves series of inflammatory pathologies and cause high morbidity. Salviplenoid A (SA) was a new sesquiterpenoid from the traditional inflammatory herb Salvia plebeia. In our previous study, SA exhibited antiinflammatory activity in RAW264.7 cells. However, the extensive effects of SA in human cells and in vivo and the active mechanisms are unclear. Thus, in this study, we sought to access its effects in vitro and in vivo and to investigate its mechanisms. SA was proved to inhibit the induction of proinflammatory cytokines in human cell types, including pulmonary epithelial cells and endothetial cells. It also depressed monocyte adhesion. Moreover, SA potently attenuated the acute lung inflammation in the LPS-induced mouse model shown by down-regulation of proinflammatory mediators, inhibition of polymorphonuclear neutrophil infiltration, and alleviation of related symptoms like alveolar congestion and mucus secretion. Further evaluation confirmed that SA regulated NF-κB pathway by inhibiting the IκB-α phosphorylation. And it markedly mediated Nrf2/HO-1 pathway by activating the Nrf2/HO-1 expression and promoting Nrf2 nuclear translocation. Therefore, SA could attenuate acute lung inflammation via suppressing NF-κB and activating Nrf2, which provide a theoretical basis for the potential application of SA in clinic.

Omega-3 Docosahexaenoic Acid (DHA) Impedes Silica-Induced Macrophage Corpse Accumulation by Attenuating Cell Death and Potentiating Efferocytosis

Airway exposure of lupus-prone NZBWF1 mice to crystalline silica (cSiO₂), a known trigger of human autoimmune disease, elicits sterile inflammation and alveolar macrophage death in the lung that, in turn, induces early autoimmune onset and accelerates lupus progression to fatal glomerulonephritis. Dietary supplementation with docosahexaenoic acid (DHA), a marine ω-3 polyunsaturated fatty acid (PUFA), markedly ameliorates cSiO₂-triggered pulmonary, systemic, and renal manifestations of lupus. Here, we tested the hypothesis that DHA influences both cSiO₂-induced death and efferocytotic clearance of resultant cell corpses using three murine macrophage models: (i) primary alveolar macrophages (AM) isolated from NZBWF1 mice; (ii) self-renewing AM-like Max Planck Institute (MPI) cells isolated from fetuses of C57BL/6 mice, and (iii) RAW 264.7 murine macrophages, a virus-transformed cell line derived from BALB/c mice stably transfected with the inflammasome adaptor protein ASC (RAW-ASC). Incubation with cSiO₂ at 25 and 50 μg/ml for 6 h was found to dose-dependently induce cell death (p < 0.05) in all three models as determined by both acridine orange/propidium iodide staining and release of lactate dehydrogenase into cell culture supernatant. Pre-incubation with DHA at a physiologically relevant concentration (25 μM) significantly reduced cSiO₂-induced death (p < 0.05) in all three models. Cell death induction by cSiO₂ alone and its suppression by DHA were primarily associated with caspase-3/7 activation, suggestive of apoptosis, in AM, MPI, and RAW-ASC cells. Fluorescence microscopy revealed that all three macrophage models were similarly capable of efferocytosing RAW-ASC target cell corpses. Furthermore, MPI effector cells could likewise engulf RAW-ASC target cell corpses elicited by treatment with staurosporine (apoptosis), LPS, and nigericin (pyroptosis), or cSiO₂. Pre-incubation of RAW-ASC target cells with 25 μM DHA prior to death induced by these agents significantly enhanced their efferocytosis (p < 0.05) by MPI effector cells. In contrast, pre-incubating MPI effector cells with DHA did not affect engulfment of RAW-ASC target cells pre-incubated with vehicle. Taken together, these findings indicate that DHA at a physiologically relevant concentration was capable of attenuating macrophage death and could potentiate efferocytosis, with the net effect of reducing accumulation of cell corpses capable of eliciting autoimmunity.

The pathophysiology of SARS-CoV-2: A suggested model and therapeutic approach

In this paper, a model is proposed of the pathophysiological processes of COVID-19 starting from the infection of human type II alveolar epithelial cells (pneumocytes) by SARS-CoV-2 and culminating in the development of ARDS. The innate immune response to infection of type II alveolar epithelial cells leads both to their death by apoptosis and pyroptosis and to alveolar macrophage activation. Activated macrophages secrete proinflammatory cytokines and chemokines and tend to polarise into the inflammatory M1 phenotype. These changes are associated with activation of vascular endothelial cells and thence the recruitment of highly toxic neutrophils and inflammatory activated platelets into the alveolar space. Activated vascular endothelial cells become a source of proinflammatory cytokines and reactive oxygen species (ROS) and contribute to the development of coagulopathy, systemic sepsis, a cytokine storm and ARDS. Pulmonary activated platelets are also an important source of proinflammatory cytokines and ROS, as well as exacerbating pulmonary neutrophil-mediated inflammatory responses and contributing to systemic sepsis by binding to neutrophils to form platelet-neutrophil complexes (PNCs). PNC formation increases neutrophil recruitment, activation priming and extraversion of these immune cells into inflamed pulmonary tissue, thereby contributing to ARDS. Sequestered PNCs cause the development of a procoagulant and proinflammatory environment. The contribution to ARDS of increased extracellular histone levels, circulating mitochondrial DNA, the chromatin protein HMGB1, decreased neutrophil apoptosis, impaired macrophage efferocytosis, the cytokine storm, the toll-like receptor radical cycle, pyroptosis, necroinflammation, lymphopenia and a high Th17 to regulatory T lymphocyte ratio are detailed.