S1PR3 inhibition protects against LPS-induced ARDS by inhibiting NF-κB and improving mitochondrial oxidative phosphorylation.

BACKGROUND: Inflammation and endothelial barrier dysfunction are the major pathophysiological changes in acute respiratory distress syndrome (ARDS). Sphingosine-1-phosphate receptor 3 (S1PR3), a G protein-coupled receptor, has been found to mediate inflammation and endothelial cell (EC) integrity. However, the function of S1PR3 in ARDS has not been fully elucidated. METHODS: We used a murine lipopolysaccharide (LPS)-induced ARDS model and an LPS- stimulated ECs model to investigate the role of S1PR3 in anti-inflammatory effects and endothelial barrier protection during ARDS. RESULTS: We found that S1PR3 expression was increased in the lung tissues of mice with LPS-induced ARDS. TY-52156, a selective S1PR3 inhibitor, effectively attenuated LPS-induced inflammation by suppressing the expression of proinflammatory cytokines and restored the endothelial barrier by repairing adherens junctions and reducing vascular leakage. S1PR3 inhibition was achieved by an adeno-associated virus in vivo and a small interfering RNA in vitro. Both the in vivo and in vitro studies demonstrated that pharmacological or genetic inhibition of S1PR3 protected against ARDS by inhibiting the NF-κB pathway and improving mitochondrial oxidative phosphorylation. CONCLUSIONS: S1PR3 inhibition protects against LPS-induced ARDS via suppression of pulmonary inflammation and promotion of the endothelial barrier by inhibiting NF-κB and improving mitochondrial oxidative phosphorylation, indicating that S1PR3 is a potential therapeutic target for ARDS.

PLD2 deficiency alleviates endothelial glycocalyx degradation in LPS-induced ARDS/ALI.

- Acute respiratory distress syndrome (ARDS)/acute lung injury (ALI) is a life-threatening condition marked by severe lung inflammation and increased lung endothelial barrier permeability. Endothelial glycocalyx deterioration is the primary factor of vascular permeability changes in ARDS/ALI. Although previous studies have shown that phospholipase D2 (PLD2) is closely related to the onset and progression of ARDS/ALI, its role and mechanism in the damage of endothelial cell glycocalyx remains unclear. We used LPS-induced ARDS/ALI mice (in vivo) and LPS-stimulated injury models of EA.hy926 endothelial cells (in vitro). We employed C57BL/6 mice, including wild-type and PLD2 knockout (PLD2-/-) mice, to establish the ARDS/ALI model. We applied immunofluorescence and ELISA to examine changes in syndecan-1 (SDC-1), matrix metalloproteinase-9 (MMP9), inflammatory cytokines (TNF-α, IL-6, and IL-1ß) levels and the effect of external factors, such as phosphatidic acid (PA), 1-butanol (a PLD inhibitor), on SDC-1 and MMP9 expression levels. We found that PLD2 deficiency inhibits SDC-1 degradation and MMP9 expression in LPS-induced ARDS/ALI. Externally added PA decreases SDC-1 levels and increases MMP9 in endothelial cells, hence underlining PA's role in SDC-1 degradation. Additionally, PLD2 deficiency decreases the production of inflammatory cytokines (TNF-α, IL-6, and IL-1ß) in LPS-induced ARDS/ALI. In summary, these findings suggest that PLD2 deficiency plays a role in inhibiting the inflammatory process and protecting against endothelial glycocalyx injury in LPS-induced ARDS/ALI.

Endothelial cell-derived extracellular vesicles modulate the therapeutic efficacy of mesenchymal stem cells through IDH2/TET pathway in ARDS.

BACKGROUND: Acute respiratory distress syndrome (ARDS) is a severe and fatal disease. Although mesenchymal stem cell (MSC)-based therapy has shown remarkable efficacy in treating ARDS in animal experiments, clinical outcomes have been unsatisfactory, which may be attributed to the influence of the lung microenvironment during MSC administration. Extracellular vesicles (EVs) derived from endothelial cells (EC-EVs) are important components of the lung microenvironment and play a crucial role in ARDS. However, the effect of EC-EVs on MSC therapy is still unclear. In this study, we established lipopolysaccharide (LPS) - induced acute lung injury model to evaluate the impact of EC-EVs on the reparative effects of bone marrow-derived MSC (BM-MSC) transplantation on lung injury and to unravel the underlying mechanisms. METHODS: EVs were isolated from bronchoalveolar lavage fluid of mice with LPS - induced acute lung injury and patients with ARDS using ultracentrifugation. and the changes of EC-EVs were analysed using nanoflow cytometry analysis. In vitro assays were performed to establish the impact of EC-EVs on MSC functions, including cell viability and migration, while in vivo studies were performed to validate the therapeutic effect of EC-EVs on MSCs. RNA-Seq analysis, small interfering RNA (siRNA), and a recombinant lentivirus were used to investigate the underlying mechanisms. RESULTS: Compared with that in non-ARDS patients, the quantity of EC-EVs in the lung microenvironment was significantly greater in patients with ARDS. EVs derived from lipopolysaccharide-stimulated endothelial cells (LPS-EVs) significantly decreased the viability and migration of BM-MSCs. Furthermore, engrafting BM-MSCs pretreated with LPS-EVs promoted the release of inflammatory cytokines and increased pulmonary microvascular permeability, aggravating lung injury. Mechanistically, LPS-EVs reduced the expression level of isocitrate dehydrogenase 2 (IDH2), which catalyses the formation of α-ketoglutarate (α-KG), an intermediate product of the tricarboxylic acid (TCA) cycle, in BM-MSCs. α-KG is a cofactor for ten-eleven translocation (TET) enzymes, which catalyse DNA hydroxymethylation in BM-MSCs. CONCLUSIONS: This study revealed that EC-EVs in the lung microenvironment during ARDS can affect the therapeutic efficacy of BM-MSCs through the IDH2/TET pathway, providing potential strategies for improving the therapeutic efficacy of MSC-based therapy in the clinic.

Identification and genetic validation of leukemia inhibitory factor super-enhancers in acute respiratory distress syndrome and lung cancer.

Super-enhancers play prominent roles in driving robust pathological gene expression, but they are hidden in human genome at noncoding regions, making them difficult to explore. Leukemia inhibitory factor (LIF) is a multifunctional cytokine crucially involved in acute respiratory distress syndrome (ARDS) and lung cancer progression. However, the mechanisms governing LIF regulation in disease contexts remain largely unexplored. In this study, we observed elevated levels of LIF in the bronchoalveolar lavage fluid (BALF) of patients with sepsis-related ARDS compared to those with nonsepsis-related ARDS. Furthermore, both basal and LPS-induced LIF expression were under the control of super-enhancers. Through analysis of H3K27Ac ChIP-seq data, we pinpointed three potential super-enhancers (LIF-SE1, LIF-SE2, and LIF-SE3) located proximal to the LIF gene in cells. Notably, genetic deletion of any of these three super-enhancers using CRISPR-Cas9 technology led to a significant reduction in LIF expression. Moreover, in cells lacking these super-enhancers, both cell growth and invasion capabilities were substantially impaired. Our findings highlight the critical role of three specific super-enhancers in regulating LIF expression and offer new insights into the transcriptional regulation of LIF in ARDS and lung cancer.

Indole-3-carbinol attenuates lipopolysaccharide-induced acute respiratory distress syndrome through activation of AhR: role of CCR2+ monocyte activation and recruitment in the regulation of CXCR2+ neutrophils in the lungs.

Introduction: Indole-3-carbinol (I3C) is found in cruciferous vegetables and used as a dietary supplement. It is known to act as a ligand for aryl hydrocarbon receptor (AhR). In the current study, we investigated the role of AhR and the ability of I3C to attenuate LPS-induced Acute Respiratory Distress Syndrome (ARDS). Methods: To that end, we induced ARDS in wild-type C57BL/6 mice, Ccr2gfp/gfp KI/KO mice (mice deficient in the CCR2 receptor), and LyZcreAhRfl/fl mice (mice deficient in the AhR on myeloid linage cells). Additionally, mice were treated with I3C (65 mg/kg) or vehicle to investigate its efficacy to treat ARDS. Results: I3C decreased the neutrophils expressing CXCR2, a receptor associated with neutrophil recruitment in the lungs. In addition, LPS-exposed mice treated with I3C revealed downregulation of CCR2+ monocytes in the lungs and lowered CCL2 (MCP-1) protein levels in serum and bronchoalveolar lavage fluid. Loss of CCR2 on monocytes blocked the recruitment of CXCR2+ neutrophils and decreased the total number of immune cells in the lungs during ARDS. In addition, loss of the AhR on myeloid linage cells ablated I3C-mediated attenuation of CXCR2+ neutrophils and CCR2+ monocytes in the lungs from ARDS animals. Interestingly, scRNASeq showed that in macrophage/monocyte cell clusters of LPS-exposed mice, I3C reduced the expression of CXCL2 and CXCL3, which bind to CXCR2 and are involved in neutrophil recruitment to the disease site. Discussion: These findings suggest that CCR2+ monocytes are involved in the migration and recruitment of CXCR2+ neutrophils during ARDS, and the AhR ligand, I3C, can suppress ARDS through the regulation of immune cell trafficking.

Extracellular vesicles derived from M2-like macrophages alleviate acute lung injury in a miR-709-mediated manner.

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is characterised by an uncontrolled inflammatory response, and current treatment strategies have limited efficacy. Although the protective effect of M2-like macrophages (M2φ) and their extracellular vesicles (EVs) has been well-documented in other inflammatory diseases, the role of M2φ-derived EVs (M2φ-EVs) in the pathogenesis of ALI/ARDS remains poorly understood. The present study utilised a mouse model of lipopolysaccharide-induced ALI to first demonstrate a decrease in endogenous M2-like alveolar macrophage-derived EVs. And then, intratracheal instillation of exogenous M2φ-EVs from the mouse alveolar macrophage cell line (MH-S) primarily led to a take up by alveolar macrophages, resulting in reduced lung inflammation and injury. Mechanistically, the M2φ-EVs effectively suppressed the pyroptosis of alveolar macrophages and inhibited the release of excessive cytokines such as IL-6, TNF-α and IL-1ß both in vivo and in vitro, which were closely related to NF-κB/NLRP3 signalling pathway inhibition. Of note, the protective effect of M2φ-EVs was partly mediated by miR-709, as evidenced by the inhibition of miR-709 expression in M2φ-EVs mitigated their protective effect against lipopolysaccharide-induced ALI in mice. In addition, we found that the expression of miR-709 in EVs derived from bronchoalveolar lavage fluid was correlated negatively with disease severity in ARDS patients, indicating its potential as a marker for ARDS severity. Altogether, our study revealed that M2φ-EVs played a protective role in the pathogenesis of ALI/ARDS, partly mediated by miR-709, offering a potential strategy for assessing disease severity and treating ALI/ARDS.

Inhibition of GBP5 activates autophagy to alleviate inflammatory response in LPS-induced lung injury in mice.

BACKGROUND: Pulmonary emphysema is a condition that causes damage to the lung tissue over time. GBP5, as part of the guanylate-binding protein family, is dysregulated in mouse pulmonary emphysema. However, the role of GBP5 in lung inflammation in ARDS remains unveiled. METHODS: To investigate whether GBP5 regulates lung inflammation and autophagy regulation, the study employed a mouse ARDS model and MLE-12 cell culture. Vector transfection was performed for the genetic manipulation of GBP5. Then, RT-qPCR, WB and IHC staining were conducted to assess its transcriptional and expression levels. Histological features of the lung tissue were observed through HE staining. Moreover, ELISA was conducted to evaluate the secretion of inflammatory cytokines, autophagy was assessed by immunofluorescent staining, and MPO activity was determined using a commercial kit. RESULTS: Our study revealed that GBP5 expression was altered in mouse ARDS and LPS-induced MLE-12 cell models. Moreover, the suppression of GBP5 reduced lung inflammation induced by LPS in mice. Conversely, overexpression of GBP5 diminished the inhibitory impact of LPS on ARDS during autophagy, leading to increased inflammation. In the cell line of MLE-12, GBP5 exacerbates LPS-induced inflammation by blocking autophagy. CONCLUSION: The study suggests that GBP5 facilitates lung inflammation and autophagy regulation. Thus, GBP5 could be a potential therapeutic approach for improving ARDS treatment outcomes, but further research is required to validate these findings.

Elk1 enhances inflammatory cell infiltration and exacerbates acute lung injury/acute respiratory distress syndrome by suppressing Fcgr2b transcription.

OBJECTIVE: Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are associated with significant mortality rates. The role of Fcgr2b in the pathogenesis of ALI/ARDS is not fully elucidated. This study aimed to investigate the functions of Fcgr2b in ALI/ARDS and explore its underlying mechanisms. METHODS: Methods: In this study, rat models of ARDS and pulmonary microvascular endothelial cell (PMVEC) injury models were established through the administration of lipopolysaccharide (LPS). The expression levels of Fcgr2b and Elk1 were quantified in both LPS-induced ARDS rats and PMVECs. Subsequent gain- and loss-of-function experiments were conducted, followed by comprehensive assessments of lung tissue for pathomorphological changes, edema, glycogen storage, fibrosis, and infiltration of inflammatory cells. Additionally, bronchoalveolar lavage fluid was analyzed for T-helper 17 (Th17) cell infiltration, inflammatory response, and microvascular permeability to evaluate lung injury severity in ARDS models. Furthermore, the activity, cytotoxicity, apoptosis, and angiogenic potential of PMVECs were assessed to gauge cell injury. The interaction between Elk1 and Fcgr2b was also examined to confirm their regulatory relationship. RESULTS: In the context of LPS-induced ARDS and PMVEC injury, Fcgr2b expression was markedly reduced, whereas Elk1 expression was elevated. Overexpression of Fcgr2b led to a decrease in Th17 cell infiltration and mitigated lung tissue damage in ARDS models, in addition to reducing LPS-induced injury in PMVECs. Elk1 was found to suppress Fcgr2b transcription through the recruitment of histone 3 lysine 9 trimethylation (H3K9me3). Knockdown of Elk1 diminished Th17 cell infiltration and lung tissue damage in ARDS models, and alleviated LPS-induced injury in PMVECs, effects that were reversed upon Fcgr2b upregulation. CONCLUSION: Elk1 negatively regulates Fcgr2b transcription, thereby augmenting the inflammatory response and exacerbating lung injury in LPS-induced ALI/ARDS.

Therapeutic potential of proteases in acute lung injury and respiratory distress syndrome via TLR4/Nrf2/NF-kB signaling modulation.

The COVID-19 pandemic has drawn attention to acute lung injury and respiratory distress syndrome as major causes of death, underscoring the urgent need for effective treatments. Protease enzymes possess a wide range of beneficial effects, including antioxidant, anti-inflammatory, antifibrotic, and fibrinolytic effects. This study aimed to evaluate the potential therapeutic effects of bacterial protease and chymotrypsin in rats in mitigating acute lung injury induced by lipopolysaccharide. Molecular docking was employed to investigate the inhibitory effect of bacterial protease and chymotrypsin on TLR-4, the receptor for lipopolysaccharide. Bacterial protease restored TLR-4, Nrf2, p38 MAPK, NF-kB, and IKK-ß levels to normal levels, while chymotrypsin normalized TLR-4, IKK-ß, IL-6, and IL-17 levels. The expression of TGF-ß, caspase-3, and VEGF in the bacterial protease- and chymotrypsin-treated groups was markedly reduced. Our results suggest that both therapies ameliorate LPS-induced acute lung injury and modulate the TLR4/Nrf2/NF-k signaling pathway. Each protease exhibited distinct mechanisms, with bacterial protease showing a better response to oxidative stress, edema, and fibrosis, whereas chymotrypsin provided a better response in the acute phase and innate immunity. These findings highlight the potential of each protease as a promising therapeutic option for acute lung injury and respiratory distress syndrome.

Endothelial cell-derived extracellular vesicles expressing surface VCAM1 promote sepsis-related acute lung injury by targeting and reprogramming monocytes.

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a common life-threatening syndrome with no effective pharmacotherapy. Sepsis-related ARDS is the main type of ARDS and is more fatal than other types. Extracellular vesicles (EVs) are considered novel mediators in the development of inflammatory diseases. Our previous research suggested that endothelial cell-derived EVs (EC-EVs) play a crucial role in ALI/ARDS development, but the mechanism remains largely unknown. Here, we demonstrated that the number of circulating EC-EVs was increased in sepsis, exacerbating lung injury by targeting monocytes and reprogramming them towards proinflammatory macrophages. Bioinformatics analysis and further mechanistic studies revealed that vascular cell adhesion molecule 1 (VCAM1), overexpressed on EC-EVs during sepsis, activated the NF-κB pathway by interacting with integrin subunit alpha 4 (ITGA4) on the monocyte surface, rather than the tissue resident macrophage surface, thereby regulating monocyte differentiation. This effect could be attenuated by decreasing VCAM1 levels in EC-EVs or blocking ITGA4 on monocytes. Furthermore, the number of VCAM1+ EC-EVs was significantly increased in patients with sepsis-related ARDS. These findings not only shed light on a previously unidentified mechanism underling sepsis-related ALI/ARDS, but also provide potential novel targets and strategies for its precise treatment.

Inhibition the ubiquitination of ENaC and Na,K-ATPase with erythropoietin promotes alveolar fluid clearance in sepsis-induced acute respiratory distress syndrome.

Sepsis-induced acute respiratory distress syndrome (ARDS) causes significant fatalities worldwide and lacks pharmacological intervention. Alveolar fluid clearance (AFC) plays a pivotal role in the remission of ARDS and is markedly impaired in the pathogenesis of ARDS. Here, we demonstrated that erythropoietin could effectively ameliorate lung injury manifestations and lethality, restore lung function and promote AFC in a rat model of lipopolysaccharide (LPS)-induced ARDS. Moreover, it was proven that EPO-induced restoration of AFC occurs through triggering the total protein expression of ENaC and Na,K-ATPase channels, enhancing their protein abundance in the membrane, and suppressing their ubiquitination for degeneration. Mechanistically, the data indicated the possible involvement of EPOR/JAK2/STAT3/SGK1/Nedd4-2 signaling in this process, and the pharmacological inhibition of the pathway markedly eliminated the stimulating effects of EPO on ENaC and Na,K-ATPase, and subsequently reversed the augmentation of AFC by EPO. Consistently, in vitro studies of alveolar epithelial cells paralleled with that EPO upregulated the expression of ENaC and Na,K-ATPase, and patch-clamp studies further demonstrated that EPO substantially strengthened sodium ion currents. Collectively, EPO could effectively promote AFC by improving ENaC and Na,K-ATPase protein expression and abundance in the membrane, dependent on inhibition of ENaC and Na,K-ATPase ubiquitination, and resulting in diminishing LPS-associated lung injuries.

Functional roles of CD26/DPP4 in lipopolysaccharide-induced lung injury.

Acute respiratory distress syndrome (ARDS) is characterized by dysregulated inflammation and increased permeability of lung microvascular cells. CD26/dipeptidyl peptidase-4 (DPP4) is a type II membrane protein that is expressed in several cell types and mediates multiple pleiotropic effects. We previously reported that DPP4 inhibition by sitagliptin attenuates lipopolysaccharide (LPS)-induced lung injury in mice. The current study characterized the functional role of CD26/DPP4 expression in LPS-induced lung injury in mice, isolated alveolar macrophages, and cultured lung endothelial cells. In LPS-induced lung injury, inflammatory responses [bronchoalveolar lavage fluid (BALF) neutrophil numbers and several proinflammatory cytokine levels] were attenuated in Dpp4 knockout (Dpp4 KO) mice. However, multiple assays of alveolar capillary permeability were similar between the Dpp4 KO and wild-type mice. TNF-α and IL-6 production was suppressed in alveolar macrophages isolated from Dpp4 KO mice. In contrast, in cultured mouse lung microvascular endothelial cells (MLMVECs), reduction in CD26/DPP4 expression by siRNA resulted in greater ICAM-1 and IL-6 expression after LPS stimulation. Moreover, the LPS-induced vascular monolayer permeability in vitro was higher in MLMVECs treated with Dpp4 siRNA, suggesting that CD26/DPP4 plays a protective role in endothelial barrier function. In summary, this study demonstrated that genetic deficiency of Dpp4 attenuates inflammatory responses but not permeability in LPS-induced lung injury in mice, potentially through differential functional roles of CD26/DPP4 expression in resident cellular components of the lung. CD26/DPP4 may be a potential therapeutic target for ARDS and warrants further exploration to precisely identify the multiple functional effects of CD26/DPP4 in ARDS pathophysiology.NEW & NOTEWORTHY We aimed to clarify the functional roles of CD26/DPP4 in ARDS pathophysiology using Dpp4-deficient mice and siRNA reduction techniques in cultured lung cells. Our results suggest that CD26/DPP4 expression plays a proinflammatory role in alveolar macrophages while also playing a protective role in the endothelial barrier. Dpp4 genetic deficiency attenuates inflammatory responses but not permeability in LPS-induced lung injury in mice, potentially through differential roles of CD26/DPP4 expression in the resident cellular components of the lung.

Hydrogen alleviates impaired lung epithelial barrier in acute respiratory distress syndrome via inhibiting Drp1-mediated mitochondrial fission through the Trx1 pathway.

Acute respiratory distress syndrome (ARDS) is an acute and severe clinical complication lacking effective therapeutic interventions. The disruption of the lung epithelial barrier plays a crucial role in ARDS pathogenesis. Recent studies have proposed the involvement of abnormal mitochondrial dynamics mediated by dynamin-related protein 1 (Drp1) in the mechanism of impaired epithelial barrier in ARDS. Hydrogen is an anti-oxidative stress molecule that regulates mitochondrial function via multiple signaling pathways. Our previous study confirmed that hydrogen modulated oxidative stress and attenuated acute pulmonary edema in ARDS by upregulating thioredoxin 1 (Trx1) expression, but the exact mechanism remains unclear. This study aimed to investigate the effects of hydrogen on mitochondrial dynamics both in vivo and in vitro. Our study revealed that hydrogen inhibited lipopolysaccharide (LPS)-induced phosphorylation of Drp1 (at Ser616), suppressed Drp1-mediated mitochondrial fission, alleviated epithelial tight junction damage and cell apoptosis, and improved the integrity of the epithelial barrier. This process was associated with the upregulation of Trx1 in lung epithelial tissues of ARDS mice by hydrogen. In addition, hydrogen treatment reduced the production of reactive oxygen species in LPS-induced airway epithelial cells (AECs) and increased the mitochondrial membrane potential, indicating that the mitochondrial dysfunction was restored. Then, the expression of tight junction proteins occludin and zonula occludens 1 was upregulated, and apoptosis in AECs was alleviated. Remarkably, the protective effects of hydrogen on the mitochondrial and epithelial barrier were eliminated after applying the Trx1 inhibitor PX-12. The results showed that hydrogen significantly inhibited the cell apoptosis and the disruption of epithelial tight junctions, maintaining the integrity of the epithelial barrier in mice of ARDS. This might be related to the inhibition of Drp1-mediated mitochondrial fission through the Trx1 pathway. The findings of this study provided a new theoretical basis for the application of hydrogen in the clinical treatment of ARDS.

Metabolic signatures of acute respiratory distress syndrome: COVID versus non-COVID.

Acute respiratory distress syndrome (ARDS) is a fatal pulmonary disorder characterized by severe hypoxia and inflammation. ARDS is commonly triggered by systemic and pulmonary infections, with bacteria and viruses. Notable pathogens include Pseudomonas aeruginosa, Streptococcus aureus, Enterobacter species, coronaviruses, influenza viruses, and herpesviruses. COVID-19 ARDS represents the latest etiological phenotype of the disease. The pathogenesis of ARDS caused by bacteria and viruses exhibits variations in host immune responses and lung mesenchymal injury. We postulate that the systemic and pulmonary metabolomics profiles of ARDS induced by COVID-19 pathogens may exhibit distinctions compared with those induced by other infectious agents. This review aims to compare metabolic signatures in blood and lung specimens specifically within the context of ARDS. Both prevalent and phenotype-specific metabolomic signatures, including but not limited to glycolysis, ketone body production, lipid oxidation, and dysregulation of the kynurenine pathways, were thoroughly examined in this review. The distinctions in metabolic signatures between COVID-19 and non-COVID ARDS have the potential to reveal new biomarkers, elucidate pathogenic mechanisms, identify druggable targets, and facilitate differential diagnosis in the future.

Ficolin-A/2 Aggravates Severe Lung Injury through Neutrophil Extracellular Traps Mediated by Gasdermin D-Induced Pyroptosis.

Neutrophil extracellular traps (NETs) and pyroptosis are critical events in lung injury. This study investigated whether ficolin-A influenced NET formation through pyroptosis to exacerbate lipopolysaccharide (LPS)-induced lung injury. The expression of ficolin-A/2, NETs, and pyroptosis-related molecules was investigated in animal and cell models. Knockout and knockdown (recombinant protein) methods were used to elucidate regulatory mechanisms. The Pearson correlation coefficient was used to analyze the correlation between ficolins and pyroptosis- and NET-related markers in clinical samples. In this study, ficolin-2 (similar to ficolin-A) showed significant overexpression in patients with acute respiratory distress syndrome. In vivo, knockout of Fcna, but not Fcnb, attenuated lung inflammation and inhibited NET formation in the LPS-induced mouse model. DNase I further alleviated lung inflammation and NET formation in Fcna knockout mice. In vitro, neutrophils derived from Fcna-/- mice showed less pyroptosis and necroptosis than those from the control group after LPS stimulation. Additionally, GSDMD knockdown or Nod-like receptor protein 3 inhibitor reduced NET formation. Addition of recombinant ficolin-2 protein to human peripheral blood neutrophils promoted NET formation and pyroptosis after LPS stimulation, whereas Fcn2 knockdown had the opposite effect. Acute respiratory distress syndrome patients showed increased levels of pyroptosis- and NET-related markers, which were correlated positively with ficolin-2 levels. In conclusion, these results suggested that ficolin-A/2 exacerbated NET formation and LPS-induced lung injury via gasdermin D-mediated pyroptosis.

Semaphorin 7A coordinates neutrophil response during pulmonary inflammation and sepsis.

ABSTRACT: Pulmonary defense mechanisms are critical for host integrity during pneumonia and sepsis. This defense is fundamentally dependent on the activation of neutrophils during the innate immune response. Recent work has shown that semaphorin 7A (Sema7A) holds significant impact on platelet function, yet its role on neutrophil function within the lung is not well understood. This study aimed to identify the role of Sema7A during pulmonary inflammation and sepsis. In patients with acute respiratory distress syndrome (ARDS), we were able to show a correlation between Sema7A and oxygenation levels. During subsequent workup, we found that Sema7A binds to the neutrophil PlexinC1 receptor, increasing integrins, and L-selectin on neutrophils. Sema7A prompted neutrophil chemotaxis in vitro and the formation of platelet-neutrophil complexes in vivo. We also observed altered adhesion and transmigration of neutrophils in Sema7A-/-animals in the lung during pulmonary inflammation. This effect resulted in increased number of neutrophils in the interstitial space of Sema7A-/- animals but reduced numbers of neutrophils in the alveolar space during pulmonary sepsis. This finding was associated with significantly worse outcome of Sema7A-/- animals in a model of pulmonary sepsis. Sema7A has an immunomodulatory effect in the lung, affecting pulmonary sepsis and ARDS. This effect influences the response of neutrophils to external aggression and might influence patient outcome. This trial was registered at www.ClinicalTrials.gov as #NCT02692118.

In Vivo Cellular Phosphatidylcholine Kinetics of CD15+ Leucocytes and CD3+ T-Lymphocytes in Adults with Acute Respiratory Distress Syndrome.

Mammalian cell membranes composed of a mixture of glycerophospholipids, the relative composition of individual phospholipids and the dynamic flux vary between cells. In addition to their structural role, membrane phospholipids are involved in cellular signalling and immunomodulatory functions. In this study, we investigate the molecular membrane composition and dynamic flux of phosphatidylcholines in CD15+ leucocytes and CD3+ lymphocytes extracted from patients with acute respiratory distress syndrome (ARDS). We identified compositional variations between these cell types, where CD15+ cells had relatively higher quantities of alkyl-acyl PC species and CD3+ cells contained more arachidonoyl-PC species. There was a significant loss of arachidonoyl-PC in CD3+ cells in ARDS patients. Moreover, there were significant changes in PC composition and the methyl-D9 enrichment of individual molecular species in CD15+ cells from ARDS patients. This is the first study to perform an in vivo assessment of membrane composition and dynamic changes in immunological cells from ARDS patients.

A Narrative Review: The Role of NETs in Acute Respiratory Distress Syndrome/Acute Lung Injury.

Nowadays, acute respiratory distress syndrome (ARDS) still has a high mortality rate, and the alleviation and treatment of ARDS remains a major research focus. There are various causes of ARDS, among which pneumonia and non-pulmonary sepsis are the most common. Trauma and blood transfusion can also cause ARDS. In ARDS, the aggregation and infiltration of neutrophils in the lungs have a great influence on the development of the disease. Neutrophils regulate inflammatory responses through various pathways, and the release of neutrophils through neutrophil extracellular traps (NETs) is considered to be one of the most important mechanisms. NETs are mainly composed of DNA, histones, and granuloproteins, all of which can mediate downstream signaling pathways that can activate inflammatory responses, generate immune clots, and cause damage to surrounding tissues. At the same time, the components of NETs can also promote the formation and release of NETs, thus forming a vicious cycle that continuously aggravates the progression of the disease. NETs are also associated with cytokine storms and immune balance. Since DNA is the main component of NETs, DNase I is considered a viable drug for removing NETs. Other therapeutic methods to inhibit the formation of NETs are also worthy of further exploration. This review discusses the formation and mechanism of NETs in ARDS. Understanding the association between NETs and ARDS may help to develop new perspectives on the treatment of ARDS.

Sulfasalazine ameliorates lipopolysaccharide-induced acute lung injury by inhibiting oxidative stress and nuclear factor-kappaB pathways.

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) has a high mortality rate and incidence of complications. The pathophysiology of ALI/ARDS is still not fully understood. The lipopolysaccharide (LPS)-induced mouse model of ALI has been widely used to study human ALI/ARDS. Sulfasalazine (SASP) has antibacterial and anti-inflammatory effects and is used for treating inflammatory bowel and rheumatic diseases. However, the effect of SASP on LPS-induced ALI in mice has not yet been reported. Therefore, we aimed to investigate the effect of SASP on LPS-induced ALI in mice. Mice were intraperitoneally injected with SASP 2 h before or 4 h after LPS modeling. Pulmonary pathological damage was measured based on inflammatory factor expression (malondialdehyde and superoxide dismutase levels) in the lung tissue homogenate and alveolar lavage fluid. The production of inflammatory cytokines and occurrence of oxidative stress in the lungs induced by LPS were significantly mitigated after the prophylactic and long-term therapeutic administration of SASP, which ameliorated ALI caused by LPS. SASP reduced both the production of inflammatory cytokines and occurrence of oxidative stress in RAW264.7 cells, which respond to LPS. Moreover, its mechanism contributed to the suppression of NF-κB and nuclear translocation. In summary, SASP treatment ameliorates LPS-induced ALI by mediating anti-inflammatory and antioxidant effects, which may be attributed to the inhibition of NF-κB activation and promotion of antioxidant defenses. Thus, SASP may be a promising pharmacologic agent for ALI therapy.

Engineered Biomimetic Nanovesicles Based on Neutrophils for Hierarchical Targeting Therapy of Acute Respiratory Distress Syndrome.

Acute Respiratory Distress Syndrome (ARDS) is a clinically severe respiratory disease that causes severe medical and economic burden. To improve therapeutic efficacy, effectively targeting delivery to the inflamed lungs and inflamed cells remains an ongoing challenge. Herein, we designed engineered biomimetic nanovesicles (DHA@ANeu-DDAB) by fusion of lung-targeting functional lipid, neutrophil membrane containing activated ß2 integrins, and the therapeutic lipid, docosahexaenoic acid (DHA). By the advantage of lung targeting lipid and ß2 integrin targeting adhesion, DHA@ANeu-DDAB can first target lung tissue and further target inflammatory vascular endothelial cells, to achieve "tissue first, cell second" hierarchical delivery. In addition, the ß2 integrins in DHA@ANeu-DDAB could bind to the intercellular cell adhesion molecule-1/2 (ICAM-1/2) ligand on the endothelium in the inflamed blood vessels, thus inhibiting neutrophils' infiltration in the blood circulation. DHA administration to inflamed lungs could effectively regulate macrophage phenotype and promote its anti-inflammatory activity via enhanced biosynthesis of specialized pro-resolving mediators. In the lipopolysaccharide-induced ARDS mouse model, DHA@ANeu-DDAB afforded a comprehensive and efficient inhibition of lung inflammation and promoted acute lung damage repair. Through mimicking physiological processes, these engineered biomimetic vesicles as a delivery system possess good potential in targeting therapy for ARDS.