The mitochondrial redistribution of eNOS is involved in lipopolysaccharide induced inflammasome activation during acute lung injury

The mitochondrial redistribution of ENOS is regulated by AKT1 and dimer status

Previously, we have shown that endothelial nitric-oxide synthase (eNOS) dimer levels directly correlate with the interaction of eNOS with hsp90 (heat shock protein 90). Further, the disruption of eNOS dimerization correlates with its redistribution to the mitochondria. However, the causal link between these events has yet to be investigated and was the focus of this study. Our data demonstrates that simvastatin, which decreases the mitochondrial redistribution of eNOS, increased eNOS-hsp90 interactions and enhanced eNOS dimerization in cultured pulmonary arterial endothelial cells (PAEC) from a lamb model of pulmonary hypertension (PH). Our data also show that the dimerization of a monomeric fraction of human recombinant eNOS was stimulated in the presence of hsp90 and ATP. The over-expression of a dominant negative mutant of hsp90 (DNHsp90) decreased eNOS dimer levels and enhanced its mitochondrial redistribution. We also found that the peroxynitrite donor3-morpholinosydnonimine (SIN-1) increased the mitochondrial redistribution of eNOS in PAEC and this was again associated with decreased eNOS dimer levels. Our data also show in COS-7 cells, the SIN-1 mediated mitochondrial redistribution of wildtype eNOS (WT-eNOS) is significantly higher than a dimer stable eNOS mutant protein (C94R/C99R-eNOS). Conversely, the mitochondrial redistribution of a monomeric eNOS mutant protein (C96A-eNOS) was enhanced. Finally, we linked the SIN-1-mediated mitochondrial redistribution of eNOS to the Akt1-mediated phosphorylation of eNOS at Serine(S)617 and showed that the accessibility of this residue to phosphorylation is regulated by dimerization status. Thus, our data reveal a novel mechanism of pulmonary endothelial dysfunction mediated by mitochondrial redistribution of eNOS, regulated by dimerization status and the phosphorylation of S617.

Linoleic Acid Promotes Mitochondrial Biogenesis and Alleviates Acute Lung Injury

INTRODUCTION

Acute lung injury (ALI) is a critical and lethal medical condition. This syndrome is characterized by an imbalance in the body's oxidation stress and inflammation. Linoleic acid (LA), a polyunsaturated fatty acid, has been extensively studied for its potential health benefits, including anti-inflammatory and antioxidant activities. However, the therapeutic effects of LA on ALI remain unexplored.

METHODS

Lipopolysaccharide (LPS), found in gram-negative bacteria's outer membrane, was intraperitoneally injected to induce ALI in mice. In vitro model was established by LPS stimulation of mouse lung epithelial 12 (MLE-12) cells.

RESULTS

LA treatment demonstrated a significant amelioration in LPS-induced hypothermia, poor state, and pulmonary injury in mice. LA treatment resulted in a reduction in the concentration of bronchoalveolar lavage fluid (BALF) protein and an increase in myeloperoxidase (MPO) activity in LPS-induced mice. LA treatment reduced the generation of white blood cells. LA treatment reduced cell-free (cfDNA) release and promote adenosine triphosphate (ATP) production. LA increased the levels of superoxide dismutase (SOD) and glutathione (GSH) but decreased the production of malondialdehyde (MDA). LA treatment enhanced mitochondrial membrane potential. LA attenuated LPS-induced elevations of inflammatory cytokines in both mice and cells. Additionally, LA exerted its protective effect against LPS-induced damage through activation of the peroxisome proliferator-activated receptor γ coactivator l alpha (PGC-1α)/nuclear respiratory factor 1 (NRF1)/transcription factor A of the mitochondrion (TFAM) pathway.

CONCLUSION

LA may reduce inflammation and stimulate mitochondrial biogenesis in ALI mice and MLE-12 cells.

Inflammatory lung injury is associated with endothelial cell mitochondrial fission and requires the nitration of RhoA and cytoskeletal remodeling

Higher levels of extracellular nicotinamide phosphoribosyltransferase (eNAMPT), a TLR4 agonist, are associated with poor clinical outcomes in sepsis-induced acute lung injury (ALI). Little is known regarding the mechanisms by which eNAMPT is involved in ALI. Our recent work has identified a crucial role for mitochondrial dysfunction in ALI. Thus, this study aimed to determine if eNAMPT-mediated inflammatory injury is associated with the loss of mitochondrial function. Our data show that eNAMPT disrupted mitochondrial bioenergetics. This was associated with cytoskeleton remodeling and the loss of endothelial barrier integrity. These changes were associated with enhanced mitochondrial fission and blocked when Rho-kinase (ROCK) was inhibited. The increases in mitochondrial fission were also associated with the nitration-mediated activation of the small GTPase activator of ROCK, RhoA. Blocking RhoA nitration decreased eNAMPT-mediated mitochondrial fission and endothelial barrier dysfunction. The increase in fission was linked to a RhoA-ROCK mediated increase in Drp1 (dynamin-related protein 1) at serine(S)616. Another TLR4 agonist, lipopolysaccharide (LPS), also increased mitochondrial fission in a Drp1 and RhoA-ROCK-dependent manner. To validate our findings in vivo, we challenged C57BL/6 mice with eNAMPT in the presence and absence of the Drp1 inhibitor, Mdivi-1. Mdivi-1 treatment protected against eNAMPT-induced lung inflammation, edema, and lung injury. These studies demonstrate that mitochondrial fission-dependent disruption of mitochondrial function is essential in TLR4-mediated inflammatory lung injury and identify a key role for RhoA-ROCK signaling. Reducing mitochondrial fission could be a potential therapeutic strategy to improve ARDS outcomes.

Oocyte-specific deletion of eukaryotic translation initiation factor 5 causes apoptosis of mouse oocytes within the early-growing follicles by mitochondrial fission defect-reactive oxygen species-DNA damage

BACKGROUND

Mutations in several translation initiation factors are closely associated with premature ovarian insufficiency (POI), but the underlying pathogenesis remains largely unknown.

METHODS AND RESULTS

We generated eukaryotic translation initiation factor 5 (Eif5) conditional knockout mice aiming to investigate the function of eIF5 during oocyte growth and follicle development. Here, we demonstrated that Eif5 deletion in mouse primordial and growing oocytes both resulted in the apoptosis of oocytes within the early-growing follicles. Further studies revealed that Eif5 deletion in oocytes downregulated the levels of mitochondrial fission-related proteins (p-DRP1, FIS1, MFF and MTFR) and upregulated the levels of the integrated stress response-related proteins (AARS1, SHMT2 and SLC7A1) and genes (Atf4, Ddit3 and Fgf21). Consistent with this, Eif5 deletion in oocytes resulted in mitochondrial dysfunction characterized by elongated form, aggregated distribution beneath the oocyte membrane, decreased adenosine triphosphate content and mtDNA copy numbers, and excessive accumulation of reactive oxygen species (ROS) and mitochondrial superoxide. Meanwhile, Eif5 deletion in oocytes led to a significant increase in the levels of DNA damage response proteins (γH2AX, p-CHK2 and p-p53) and proapoptotic proteins (PUMA and BAX), as well as a significant decrease in the levels of anti-apoptotic protein BCL-xL.

CONCLUSION

These findings indicate that Eif5 deletion in mouse oocytes results in the apoptosis of oocytes within the early-growing follicles via mitochondrial fission defects, excessive ROS accumulation and DNA damage. This study provides new insights into pathogenesis, genetic diagnosis and potential therapeutic targets for POI.

KEY POINTS

Eif5 deletion in oocytes leads to arrest in oocyte growth and follicle development. Eif5 deletion in oocytes impairs the translation of mitochondrial fission-related proteins, followed by mitochondrial dysfunction. Depletion of Eif5 causes oocyte apoptosis via ROS accumulation and DNA damage response pathway.

The Role of Pericytes in Lipopolysaccharide-Induced Murine Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a heterogeneous clinical syndrome that is most commonly triggered by infection-related inflammation. Lung pericytes can respond to infection and act as immune and proangiogenic cells; moreover, these cells can differentiate into myofibroblasts in nonresolving ARDS and contribute to the development of pulmonary fibrosis. Here, we aimed to characterize the role of lung cells, which present characteristics of pericytes, such as peri-endothelial location and expression of a panel of specific markers. A murine model of lipopolysaccharide (LPS)-induced resolving ARDS was used to study their role in ARDS. The development of ARDS was confirmed after LPS instillation, which was resolved 14 days after onset. Immunofluorescence and flow cytometry showed early expansion of neural-glial antigen 2+ β-type platelet-derived growth factor receptor+ pericytes in murine lungs with loss of CD31+ β-type platelet-derived growth factor receptor+ endothelial cells. These changes were accompanied by specific changes in lung structure and loss of vascular integrity. On day 14 after ARDS onset, the composition of pericytes and endothelial cells returned to baseline values. LPS-induced ARDS activated NOTCH signaling in lung pericytes, the inhibition of which during LPS stimulation reduced the expression of its downstream target genes, pericyte markers, and angiogenic factors. Together, these data indicate that lung pericytes in response to inflammatory injury activate NOTCH signaling that supports their maintenance and in turn can contribute to recovery of the microvascular endothelium.

Acute Lung Injury and the NLRP3 Inflammasome

Acute lung injury (ALI) manifests through harm to the capillary endothelium and alveolar epithelial cells, arising from a multitude of factors, leading to scattered interstitial alterations, pulmonary edema, and subsequent acute hypoxic respiratory insufficiency. Acute lung injury (ALI), along with its more serious counterpart, acute respiratory distress syndrome (ARDS), carry a fatality rate that hovers around 30-40%. Its principal pathological characteristic lies in the unchecked inflammatory reaction. Currently, the main strategies for treating ALI are alleviation of inflammation and prevention of respiratory failure. Concerning the etiology of ALI, NLRP3 Inflammasome is essential to the body's innate immune response. The composition of this inflammasome complex includes NLRP3, the pyroptosis mediator ASC, and pro-caspase-1. Recent research has reported that the inflammatory response centered on NLRP3 inflammasomes plays a key part in inflammation in ALI, and may hence be a prospective candidate for therapeutic intervention. In the review, we present an overview of the ailment characteristics of acute lung injury along with the constitution and operation of the NLRP3 inflammasome within this framework. We also explore therapeutic strategies targeting the NLRP3 inflammasome to combat acute lung injury.

Endothelial cell dynamics in sepsis-induced acute lung injury and acute respiratory distress syndrome: pathogenesis and therapeutic implications

Sepsis, a prevalent critical condition in clinics, continues to be the leading cause of death from infections and a global healthcare issue. Among the organs susceptible to the harmful effects of sepsis, the lungs are notably the most frequently affected. Consequently, patients with sepsis are predisposed to developing acute lung injury (ALI), and in severe cases, acute respiratory distress syndrome (ARDS). Nevertheless, the precise mechanisms associated with the onset of ALI/ARDS remain elusive. In recent years, there has been a growing emphasis on the role of endothelial cells (ECs), a cell type integral to lung barrier function, and their interactions with various stromal cells in sepsis-induced ALI/ARDS. In this comprehensive review, we summarize the involvement of endothelial cells and their intricate interplay with immune cells and stromal cells, including pulmonary epithelial cells and fibroblasts, in the pathogenesis of sepsis-induced ALI/ARDS, with particular emphasis placed on discussing the several pivotal pathways implicated in this process. Furthermore, we discuss the potential therapeutic interventions for modulating the functions of endothelial cells, their interactions with immune cells and stromal cells, and relevant pathways associated with ALI/ARDS to present a potential therapeutic strategy for managing sepsis and sepsis-induced ALI/ARDS.

Protective effects of Prussian blue nanozyme against sepsis-induced acute lung injury by activating HO-1

Sepsis is a life-threatening condition involving dysfunctional organ responses stemming from dysregulated host immune reactions to various infections. The lungs are most prone to failure during sepsis, resulting in acute lung injury (ALI). ALI is associated with oxidative stress and inflammation, and current therapeutic strategies are limited. To develop a more specific treatment, this study aimed to synthesise Prussian blue nanozyme (PBzyme), which can reduce oxidative stress and inflammation, to alleviate ALI. PBzyme with good biosafety was synthesised using a modified hydrothermal method. PBzyme was revealed to be an activator of haem oxygenase-1 (HO-1), improving survival rate and ameliorating lung injury in mice. Zinc protoporphyrin, an inhibitor of HO-1, inhibited the prophylactic therapeutic efficacy of PBzyme on ALI, and affected the nuclear factor-κB signaling pathway and activity of HO-1. This study demonstrates that PBzyme can alleviate oxidative stress and inflammation through HO-1 and has a prophylactic therapeutic effect on ALI. This provides a new strategy and direction for the clinical treatment of sepsis-induced ALI.

Mitochondrial network dynamics in pulmonary disease: Bridging the gap between inflammation, oxidative stress, and bioenergetics

Once thought of in terms of bioenergetics, mitochondria are now widely accepted as both the orchestrator of cellular health and the gatekeeper of cell death. The pulmonary disease field has performed extensive efforts to explore the role of mitochondria in regulating inflammation, cellular metabolism, apoptosis, and oxidative stress. However, a critical component of these processes needs to be more studied: mitochondrial network dynamics. Mitochondria morphologically change in response to their environment to regulate these processes through fusion, fission, and mitophagy. This allows mitochondria to adapt their function to respond to cellular requirements, a critical component in maintaining cellular homeostasis. For that reason, mitochondrial network dynamics can be considered a bridge that brings multiple cellular processes together, revealing a potential pathway for therapeutic intervention. In this review, we discuss the critical modulators of mitochondrial dynamics and how they are affected in pulmonary diseases, including chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), acute lung injury (ALI), and pulmonary arterial hypertension (PAH). A dysregulated mitochondrial network plays a crucial role in lung disease pathobiology, and aberrant fission/fusion/mitophagy pathways are druggable processes that warrant further exploration. Thus, we also discuss the candidates for lung disease therapeutics that regulate mitochondrial network dynamics.

The DNA-dependent protein kinase catalytic subunit exacerbates endotoxemia-induced myocardial microvascular injury by disrupting the MOTS-c/JNK pathway and inducing profilin-mediated lamellipodia degradation

Rationale: The DNA-dependent protein kinase catalytic subunit (DNA-PKcs) promotes pathological mitochondrial fission during septic acute kidney injury. The mitochondrial open reading frame of the 12S rRNA type-c (MOTS-c) is a mitochondria-derived peptide that exhibits anti-inflammatory properties during cardiovascular illnesses. We explored whether endotoxemia-induced myocardial microvascular injury involved DNA-PKcs and MOTS-c dysregulation. Methods: To induce endotoxemia in vivo, endothelial cell-specific DNA-PKcs-knockout mice were injected intraperitoneally with a single dose of lipopolysaccharide (10 mg/kg) and evaluated after 72 h. Results: Lipopolysaccharide exposure increased DNA-PKcs activity in cardiac microvascular endothelial cells, while pharmacological inhibition or endothelial cell-specific genetic ablation of DNA-PKcs reduced lipopolysaccharide-induced myocardial microvascular dysfunction. Proteomic analyses showed that endothelial DNA-PKcs ablation primarily altered mitochondrial protein expression. Verification assays confirmed that DNA-PKcs drastically repressed MOTS-c transcription by inducing mtDNA breaks via pathological mitochondrial fission. Inhibiting MOTS-c neutralized the endothelial protective effects of DNA-PKcs ablation, whereas MOTS-c supplementation enhanced endothelial barrier function and myocardial microvascular homeostasis under lipopolysaccharide stress. In molecular studies, MOTS-c downregulation disinhibited c-Jun N-terminal kinase (JNK), allowing JNK to phosphorylate profilin-S173. Inhibiting JNK or transfecting cells with a profilin phosphorylation-defective mutant improved endothelial barrier function by preventing F-actin depolymerization and lamellipodial degradation following lipopolysaccharide treatment. Conclusions: DNA-PKcs inactivation during endotoxemia could be a worthwhile therapeutic strategy to restore MOTS-c expression, prevent JNK-induced profilin phosphorylation, improve F-actin polymerization, and enhance lamellipodial integrity, ultimately ameliorating endothelial barrier function and reducing myocardial microvascular injury.

Vitamin K2 (MK-7) attenuates LPS-induced acute lung injury via inhibiting inflammation, apoptosis, and ferroptosis

Acute lung injury (ALI) is a life-threatening disease that has received considerable critical attention in the field of intensive care. This study aimed to explore the role and mechanism of vitamin K2 (VK2) in ALI. Intraperitoneal injection of 7 mg/kg LPS was used to induce ALI in mice, and VK2 injection was intragastrically administered with the dose of 0.2 and 15 mg/kg. We found that VK2 improved the pulmonary pathology, reduced myeloperoxidase (MPO) activity and levels of TNF-α and IL-6, and boosted the level of IL-10 of mice with ALI. Moreover, VK2 played a significant part in apoptosis by downregulating and upregulating Caspase-3 and Bcl-2 expressions, respectively. As for further mechanism exploration, we found that VK2 inhibited P38 MAPK signaling. Our results also showed that VK2 inhibited ferroptosis, which manifested by reducing malondialdehyde (MDA) and iron levels, increasing glutathione (GSH) level, and upregulated and downregulated glutathione peroxidase 4 (GPX4) and heme oxygenase-1 (HO-1) expressions, respectively. In addition, VK2 also inhibited elastin degradation by reducing levels of uncarboxylated matrix Gla protein (uc-MGP) and desmosine (DES). Overall, VK2 robustly alleviated ALI by inhibiting LPS-induced inflammation, apoptosis, ferroptosis, and elastin degradation, making it a potential novel therapeutic candidate for ALI.

TRPC6 Deletion Enhances eNOS Expression and Reduces LPS-Induced Acute Lung Injury

Acute lung injury (ALI) is characterized by endothelial barrier disruption and associated inflammatory responses, and transient receptor potential cation channel 6 (TRPC6)-mediated Ca2+ influx is critical for endothelial hyperpermeability. In this study, we investigated the role of TRPC6 in LPS-induced ALI, analyzed gene expression in WT and TRPC6-/- lungs using RNA sequencing, and explored the effects of TRPC6 in the LPS-induced hyperpermeability in human umbilical vein endothelial cells (HUVECs) to elucidate the underlying mechanisms. Intratracheal instillation of LPS caused edema in the mouse lungs. Deletion of TRPC6 reduced LPS-induced lung edema and decreased cell infiltration. RNA sequencing analysis suggested that downregulated cell adhesion molecules in TRPC6-/- lungs may be responsible for their resistance to LPS-induced injury. In addition, downregulation of TRPC6 significantly alleviated the LPS-induced decrease in eNOS expression in lung tissue as well as in HUVECs. Moreover, inhibition of TRPC6 with the channel antagonist larixyl led to a decrease in LPS-induced hyperpermeability and ROS production in HUVECs, which could be reversed by blocking eNOS. Our findings suggest that inhibition of TRPC6 ameliorates LPS-induced ALI, which may be achieved by acting on the cell adhesion molecule signaling pathway and participating in the regulation of eNOS levels in endothelial cells.

Reactive Oxygen Species and Strategies for Antioxidant Intervention in Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a life-threatening pulmonary condition characterized by the sudden onset of respiratory failure, pulmonary edema, dysfunction of endothelial and epithelial barriers, and the activation of inflammatory cascades. Despite the increasing number of deaths attributed to ARDS, a comprehensive therapeutic approach for managing patients with ARDS remains elusive. To elucidate the pathological mechanisms underlying ARDS, numerous studies have employed various preclinical models, often utilizing lipopolysaccharide as the ARDS inducer. Accumulating evidence emphasizes the pivotal role of reactive oxygen species (ROS) in the pathophysiology of ARDS. Both preclinical and clinical investigations have asserted the potential of antioxidants in ameliorating ARDS. This review focuses on various sources of ROS, including NADPH oxidase, uncoupled endothelial nitric oxide synthase, cytochrome P450, and xanthine oxidase, and provides a comprehensive overview of their roles in ARDS. Additionally, we discuss the potential of using antioxidants as a strategy for treating ARDS.

The potential mechanism of Choulingdan mixture in improving acute lung injury based on HPLC-Q-TOF-MS, network pharmacology and in vivo experiments

Choulingdan mixture (CLDM) is an empirical clinical prescription for the adjuvant treatment of acute lung injury (ALI). CLDM has been used for almost 30 years in the clinic. However, its mechanism for improving ALI still needs to be investigated. In this study, high-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry (HPLC-Q-TOF-MS/MS) was applied to characterize the overall chemical composition of CLDM. A total of 93 ingredients were characterized, including 25 flavonoids, 20 organic acids, 11 saponins, nine terpenoids, seven tannins and 21 other compounds. Then network pharmacology was applied to predict the potential bioactive components, target genes and signaling pathways of CLDM in improving ALI. Additionally, molecular docking was performed to demonstrate the interaction between the active ingredients and the disease targets. Finally, animal experiments further confirmed that CLDM significantly inhibits pulmonary inflammation, pulmonary edema and oxidative stress in lipopolysaccharide-induced ALI mice by inhibiting the PI3K-AKT signaling pathway. This study enhanced the amount and accuracy of compounds of CLDM and provided new insights into CLDM preventing and treating ALI.

MEGF6 prevents sepsis-induced acute lung injury in mice

OBJECTIVE

Acute lung injury (ALI) is featured as excessive inflammatory response and oxidative damage, and results in high death rate of septic patients. This research intends to determine the function of multiple EGF like domains 6 (MEGF6) in sepsis-induced ALI.

METHODS

Mice were intratracheally treated with adenovirus to knock down or overexpress MEGF6 in lung tissues, and then were subjected to cecum ligation and puncture (CLP) operation to induce ALI. Primary peritoneal macrophages were isolated, and were knocked down or overexpressed with MEGF6, and then, were stimulated with lipopolysaccharide (LPS) to confirm its role in vitro.

RESULTS

Serum and lung MEGF6 levels were significantly elevated in septic mice. MEGF6 knockdown exacerbated, while MEGF6 overexpression prevented inflammation, oxidative damage and ALI in CLP mice. Meanwhile, LPS-elicited inflammatory response and oxidative damage in primary macrophages were reduced by MEGF6 overexpression, but were further aggravated by MEGF6 knockdown. Mechanistic studies revealed that MEGF6 reduced cluster of differentiation 38 (CD38) expression and subsequently elevated intracellular nicotinamide adenine dinucleotide levels, thereby activating sirtuin 1 (SIRT1) without affecting the protein expression. SIRT1 suppression or CD38 overexpression with either genetic or pharmacologic methods remarkably blunted the lung protective effects of MEGF6 in CLP mice.

CONCLUSION

MEGF6 prevents CLP-induced ALI through CD38/SIRT1 pathway, and it might be a valuable therapeutic candidate for the management of sepsis-induced ALI.

Metabolic reprogramming, oxidative stress, and pulmonary hypertension

Mitochondria are highly dynamic organelles essential for cell metabolism, growth, and function. It is becoming increasingly clear that endothelial cell dysfunction significantly contributes to the pathogenesis and vascular remodeling of various lung diseases, including pulmonary arterial hypertension (PAH), and that mitochondria are at the center of this dysfunction. The more we uncover the role mitochondria play in pulmonary vascular disease, the more apparent it becomes that multiple pathways are involved. To achieve effective treatments, we must understand how these pathways are dysregulated to be able to intervene therapeutically. We know that nitric oxide signaling, glucose metabolism, fatty acid oxidation, and the TCA cycle are abnormal in PAH, along with alterations in the mitochondrial membrane potential, proliferation, and apoptosis. However, these pathways are incompletely characterized in PAH, especially in endothelial cells, highlighting the urgent need for further research. This review summarizes what is currently known about how mitochondrial metabolism facilitates a metabolic shift in endothelial cells that induces vascular remodeling during PAH.

Targeting CXCR1 alleviates hyperoxia-induced lung injury through promoting glutamine metabolism

Although increasing evidence suggests potential iatrogenic injury from supplemental oxygen therapy, significant exposure to hyperoxia in critically ill patients is inevitable. This study shows that hyperoxia causes lung injury in a time- and dose-dependent manner. In addition, prolonged inspiration of oxygen at concentrations higher than 80% is found to cause redox imbalance and impair alveolar microvascular structure. Knockout of C-X-C motif chemokine receptor 1 (Cxcr1) inhibits the release of reactive oxygen species (ROS) from neutrophils and synergistically enhances the ability of endothelial cells to eliminate ROS. We also combine transcriptome, proteome, and metabolome analysis and find that CXCR1 knockdown promotes glutamine metabolism and leads to reduced glutathione by upregulating the expression of malic enzyme 1. This preclinical evidence suggests that a conservative oxygen strategy should be recommended and indicates that targeting CXCR1 has the potential to restore redox homeostasis by reducing oxygen toxicity when inspiratory hyperoxia treatment is necessary.

Pathophysiology and pathogenic mechanisms of pulmonary hypertension: role of membrane receptors, ion channels, and Ca2+ signaling

The pulmonary circulation is a low-resistance, low-pressure, and high-compliance system that allows the lungs to receive the entire cardiac output. Pulmonary arterial pressure is a function of cardiac output and pulmonary vascular resistance, and pulmonary vascular resistance is inversely proportional to the fourth power of the intraluminal radius of the pulmonary artery. Therefore, a very small decrease of the pulmonary vascular lumen diameter results in a significant increase in pulmonary vascular resistance and pulmonary arterial pressure. Pulmonary arterial hypertension is a fatal and progressive disease with poor prognosis. Regardless of the initial pathogenic triggers, sustained pulmonary vasoconstriction, concentric vascular remodeling, occlusive intimal lesions, in situ thrombosis, and vascular wall stiffening are the major and direct causes for elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension and other forms of precapillary pulmonary hypertension. In this review, we aim to discuss the basic principles and physiological mechanisms involved in the regulation of lung vascular hemodynamics and pulmonary vascular function, the changes in the pulmonary vasculature that contribute to the increased vascular resistance and arterial pressure, and the pathogenic mechanisms involved in the development and progression of pulmonary hypertension. We focus on reviewing the pathogenic roles of membrane receptors, ion channels, and intracellular Ca2+ signaling in pulmonary vascular smooth muscle cells in the development and progression of pulmonary hypertension.

Nitration-mediated activation of the small GTPase RhoA stimulates cellular glycolysis through enhanced mitochondrial fission

Mitochondrial fission and a Warburg phenotype of increased cellular glycolysis are involved in the pathogenesis of pulmonary hypertension (PH). The purpose of this study was to determine whether increases in mitochondrial fission are involved in a glycolytic switch in pulmonary arterial endothelial cells (PAECs). Mitochondrial fission is increased in PAEC isolated from a sheep model of PH induced by pulmonary overcirculation (Shunt PAEC). In Shunt PAEC we identified increases in the S616 phosphorylation responsible for dynamin-related protein 1 (Drp1) activation, the mitochondrial redistribution of Drp1, and increased cellular glycolysis. Reducing mitochondrial fission attenuated cellular glycolysis in Shunt PAEC. In addition, we observed nitration-mediated activation of the small GTPase RhoA in Shunt PAEC, and utilizing a nitration-shielding peptide, NipR1 attenuated RhoA nitration and reversed the Warburg phenotype. Thus, our data identify a novel link between RhoA, mitochondrial fission, and cellular glycolysis and suggest that targeting RhoA nitration could have therapeutic benefits for treating PH.

USP9X promotes lipopolysaccharide-stimulated acute lung injury by deubiquitination of NLRP3

Alveolar epithelial cells (AECs) function as a vital defense barrier avoiding the invasion of exogenous agents and preserving the functional and structural integrity of lung tissues, while damage/breakdown of this airway epithelial barrier is frequently associated with the pathogenesis of acute lung injury (ALI). NOD-like receptor family, pyrindomain-containing 3 (NLRP3) inflammasome activation-associated pyroptosis is involved in the development of ALI. Yet, how the activity of NLRP3 inflammasome is regulated in the context of ALI remains unknown. Herein we hypothesized that USP9X, an important deubiquitinase, participates in modulating the activation of NLRP3 inflammasome, thereby affecting the phenotypes in a lipopolysaccharide (LPS)-stimulated AEC model. Human pulmonary AECs were subjected to LPS/adenosine triphosphate (ATP) treatment to induce NLRP3 inflammasome activation and cell pyroptosis. Knockdown and overexpression of USP9X were applied to validate the function of USP9X. Inhibitors of proteinase and protein synthesis, as well as approach of co-immunoprecipitation coupled with Western blot, were utilized to explore the molecular mechanism. LPS/ATP challenge resulted in pronouncedly increased pyroptosis of AECs, activation of NLRP3 inflammasome and release of interleukin (IL)-1β and IL-18 cytokines, while downregulation of USP9X could reverse these alterations. USP9X was found to have marked impact on NLRP3 protein instead of mRNA level. Furthermore, increased ubiquitination of NLRP3 was observed upon downregulating USP9X. Additionally, the inhibitory effect of USP9X downregulation was reversed by NLRP3 overexpression, while the promoting impact of USP9X overexpression was dampened by NLRP3 inhibitor in terms of cell pyroptosis and cytokine secretion. USP9X modulated the activity of NLRP3 inflammasome and pyroptosis of AECs via its deubiquitination function.

Growth Differentiation Factor 7 Prevents Sepsis-Induced Acute Lung Injury in Mice

Objective

Acute lung injury (ALI) is a life-threatening complication during sepsis and contributes to multiple organ failure and high mortality for septic patients. The present study aims to investigate the role and molecular basis of growth differentiation factor 7 (GDF7) in sepsis-induced ALI.

Methods

Mice were subcutaneously injected with recombinant mouse GDF7 Protein (rmGDF7) and then intratracheally injected with lipopolysaccharide (LPS) to generate sepsis-induced ALI. Primary peritoneal macrophages were isolated to further evaluate the role and underlying mechanism of GDF7 in vitro.

Results

GDF7 was downregulated in LPS-stimulated lung tissues, and rmGDF7 treatment significantly inhibited inflammation and oxidative stress in ALI mice, thereby preventing LPS-induced pulmonary injury and dysfunction. Mechanistically, we found that rmGDF7 activated AMP-activated protein kinase (AMPK), and AMPK inhibition significantly blocked the anti-inflammatory and antioxidant effects of rmGDF7 during LPS-induced ALI. Further findings revealed that rmGDF7 activated AMPK through a downregulated stimulator of interferon gene (STING) in vivo and in vitro.

Conclusion

GDF7 prevents LPS-induced inflammatory response, oxidative stress, and ALI by regulating the STING/AMPK pathway. Our findings for the first time identify GDF7 as a potential agent for the treatment of sepsis-induced ALI.

Loss of SOX18/CLAUDIN5 disrupts the pulmonary endothelial barrier in ventilator-induced lung injury

Mechanical strain contributes to ventilator-induced lung injury (VILI) through multi-factorial and complex mechanisms that remain unresolved. Prevailing evidence suggests that the loss of pulmonary endothelial tight junctions (TJs) plays a critical role. TJs are dynamically regulated by physiologic and hemodynamic forces to stabilize the endothelial barrier. The transcription factor sex-determining region Y-box (SOX)-18 is important in regulating blood vessel development and vascular permeability through its ability to regulate the transcription of Claudin-5, an endothelial TJ protein. Previously, we demonstrated that SOX18 expression is increased by shear stress in the pulmonary endothelium. Therefore, in this study, we investigated how mechanical strain mediated through cyclic stretch affects the SOX18/Claudin-5 regulatory axis. Our data demonstrate that SOX18 and Claudin-5 are downregulated in human lung microvascular endothelial cells (HLMVEC) exposed to cyclic stretch and the mouse lung exposed to high tidal mechanical ventilation. Overexpression of SOX18 reduced the loss of Claudin-5 expression in HLMVEC with cyclic stretch and preserved endothelial barrier function. Additionally, overexpression of Claudin-5 in HLMVEC ameliorated barrier dysfunction in HLMVEC exposed to cyclic stretch, although SOX18 expression was not enhanced. Finally, we found that the targeted overexpression of SOX18 in the pulmonary vasculature preserved Claudin-5 expression in the lungs of mice exposed to HTV. This, in turn reduced lung vascular leak, attenuated inflammatory lung injury, and preserved lung function. Together, these data suggest that enhancing SOX18 expression may prove a useful therapy to treat patients with ventilator-induced lung injury.

Macrophage Sprouty4 deficiency diminishes sepsis-induced acute lung injury in mice

OBJECTIVE

Inflammation and oxidative stress play critical roles in sepsis-induced acute lung injury (ALI). Sprout4 (Spry4) is involved in regulating inflammation and tissue injury; however, its role and mechanism in sepsis-induced ALI remain elusive.

METHODS

Macrophage-specific Spry4 knockout (Spry4^MKO), transgenic (Spry4^MTG) mice and matched control littermates were generated and exposed to cecum ligation and puncture (CLP) surgery to establish bacterial sepsis-induced ALI. Bone marrow-derived macrophages (BMDMs) from Spry4^MKO or Spry4^MTG mice were isolated and subjected to lipopolysaccharide (LPS) stimulation to further validate the role of Spry4 in vitro. To verify the necessity of AMP-activated protein kinase (AMPK), Spry4 and AMPK double knockout mice and compound C were used in vivo and in vitro. BMDMs were treated with STO-609 to inhibit calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2).

RESULTS

We found that macrophage Spry4 was increased in CLP mice and positively correlated with sepsis-induced ALI. Macrophage Spry4 deficiency prevented, while macrophage Spry4 overexpression exacerbated sepsis-induced inflammation, oxidative stress and ALI in mice and BMDMs. Mechanistic studies revealed that macrophage Spry4 deficiency alleviated sepsis-induced ALI through activating CaMKK2/AMPK pathway.

CONCLUSION

Our study identify macrophage Spry4 as a promising predictive and therapeutic target of sepsis-induced ALI.

The protective effect of natural medicines against excessive inflammation and oxidative stress in acute lung injury by regulating the Nrf2 signaling pathway

Acute lung injury (ALI) is a common critical disease of the respiratory system that progresses into acute respiratory distress syndrome (ARDS), with high mortality, mainly related to pulmonary oxidative stress imbalance and severe inflammation. However, there are no clear and effective treatment strategies at present. Nuclear factor erythroid 2-related factor 2(Nrf2) is a transcription factor that interacts with multiple signaling pathways and regulates the activity of multiple oxidases (NOX, NOS, XO, CYP) related to inflammation and apoptosis, and exhibits antioxidant and anti-inflammatory roles in ALI. Recently, several studies have reported that the active ingredients of natural medicines show protective effects on ALI via the Nrf2 signaling pathway. In addition, they are cheap, naturally available, and possess minimal toxicity, thereby having good clinical research and application value. Herein, we summarized various studies on the protective effects of natural pharmaceutical components such as polyphenols, flavonoids, terpenoids, alkaloids, and polysaccharides on ALI through the Nrf2 signaling pathway and demonstrated existing gaps as well as future perspectives.

Salvianolactone acid A isolated from Salvia miltiorrhiza ameliorates lipopolysaccharide-induced acute lung injury in mice by regulating PPAR-γ

BACKGROUND

Severe inflammation of the lungs results from acute lung injury (ALI), a common life-threatening lung disease with a high mortality rate. The ligand-activated transcription factor peroxisome proliferator-activated receptor (PPAR) γ plays essential roles in diverse biological processes including inflammation, metabolism, development, and immune response. Salvianolactone acid A (SA) is a terpenoid derived from the herb Salvia miltiorrhiza. However, there is a scarcity of experimental evidence indicating whether the effect of SA on ALI occurs via PPAR-γ.

METHODS

SA (20 or 40 mg/kg, i.g., 1 time/day) was administered to mice for 3 d, followed by the induction of ALI by intranasal lipopolysaccharide (LPS, 10 mg/kg). The lung function and levels of inflammation, reactive oxygen species (ROS), immune cells, apoptosis, and PPAR-γ were examined. The antagonistic activity of GW9662 (GW, 1 µM, specific PPAR-γ blocker) and PPAR-γ transfection silencing against SA (10 μM) in BEAS-2B cells induced by LPS (10 μg/ml, 24 h) was also investigated to assess whether the observed effects caused by SA were mediated by PPAR-γ.

RESULTS

The results showed that lung histopathological injury, the B-line, the fluorescence intensity of live small animal, and the biomarkers in BALF or lung in the treatment of SA could regulate significantly. In addition, SA obviously decreased the levels of ROS and apoptosis in the primary lung cells, and MDA, increased the levels of GSH-Px and SOD. SA reduced levels of macrophages and neutrophils. Furthermore, SA reduced the protein levels of Keap-1, Cleaved-caspase-3, Cleaved-caspase-9, p-p65/p65, NLRP3, IL-1β, and upregulated the levels of p-Nrf2/Nrf2, HO-1, Bcl-2/Bax, PPAR-γ, p-AMPK/AMPK in lung tissue. In addition, silencing and inhibition of PPAR-γ effectively decreased the protective effects of SA in BEAS-2B cells induced by LPS, which might indicate that the active molecules of SA regulate ALI via mediation by PPAR-γ, which exhibited that the effect of SA related to PPAR-γ.

CONCLUSIONS

The anti-ALI effects of SA were partially mediated through PPAR-γ signaling. These data provide the molecular justification for the usage of SA in treating ALI and can assist in increasing the comprehensive utilization rate of Salvia miltiorrhiza.

TLR4 inhibitor alleviates sepsis-induced organ failure by inhibiting platelet mtROS production, autophagy, and GPIIb/IIIa expression

Thrombocytopenia and impaired platelet function are associated with sepsis-induced organ failure. Numerous studies have shown that mitochondrial ROS (mtROS) and autophagy are related to organ injury in sepsis. However, the relationships between platelet mtROS, autophagy and sepsis organ failure remain unclear. Herein, we explored whether toll like receptor 4 (TLR4) inhibitor alleviates sepsis organ failure by inhibiting platelet mtROS production, autophagy, and GPIIb/IIIa expression.Mice were administrated with LPS, LPS + TAK242 or vehicle. The lungs and kidneys were harvested and analyzed using hematoxylin and eosin staining assay. Platelet rich plasma (PRP) was isolated from blood and platelets aggregation and TLR4 expression were analyzed using flow cytometer and western blot. PRP from healthy volunteers was treated with saline, LPS, or LPS + TAK242, and then mitoSOX and calcium were detected using flow cytometer, and NOX2 and LC3B were tested using western blot.Results showed that TAK242 effectively alleviated LPS-induced acute kidney and lung injury in mice, and decreased CD41 expression more significantly than CD62P. In vitro, by inhibiting TLR4, TAK242 suppressed Ca²⁺, mitoSOX fluorescence, NOX2 expression and LC3BII/LC3BI ratio in LPS treated platelets.TLR4 inhibitor TAK242 may effectively alleviate mouse lung and kidney injury by inhibition of mouse platelet GPIIb/IIIa, and reduce LPS-induced mtROS generation related to Ca²⁺ influx, thus reducing platelet activation.

Agonists for Bitter Taste Receptors T2R10 and T2R38 Attenuate LPS-Induced Permeability of the Pulmonary Endothelium in vitro

One of the hallmarks of acute respiratory distress syndrome (ARDS) is an excessive increase in pulmonary vascular permeability. In settings of ARDS, the loss of barrier integrity is mediated by cell-cell contact disassembly and actin remodelling. Studies into molecular mechanisms responsible for improving microvascular barrier function are therefore vital in the development of therapeutic targets for reducing vascular permeability seen in ARDS. Bitter taste receptors (T2Rs) belong to the superfamily of G-protein-coupled receptors found in several extraoral systems, including lung epithelial and smooth muscle cells. In the present study, we show for the first time that several T2Rs are expressed in human pulmonary arterial endothelial cells (HPAECs). Our results focus on those which are highly expressed as: T2R10, T2R14 and T2R38. Agonists for T2R10 (denatonium) and T2R38 (phenylthiourea), but not T2R14 (noscapine), significantly attenuated lipopolysaccharide (LPS)-induced permeability and VE-cadherin internalisation in HPAECs. In T2R10- or T2R38-siRNA knockdown cells, these endothelial-protective effects were abolished, indicating a direct effect of agonists in regulating barrier integrity. Our further findings indicate that T2R10 and T2R38 exert their barrier-protective function through cAMP but via Rac1-dependent and independent pathways, respectively. However, using an in vivo model of ARDS, the T2R38 agonist, phenylthiourea, was not able to protect against pulmonary edema formation. Taken together, these studies identify bitter taste sensing in the pulmonary endothelium to regulate barrier integrity in vitro through cAMP-Rac1 signalling.

Berberine Ameliorates Inflammation in Acute Lung Injury via NF-κB/Nlrp3 Signaling Pathway

The inflammatory response is the key pathophysiological character of acute lung injury (ALI). Berberine (BBR), a natural quaternary ammonium alkaloid, plays a functional role in anti-inflammation both in vitro and in vivo. However, the underlying mechanism between BBR and ALI has not been expounded. Here, we found that BBR improved the permeability of pulmonary and repressed the inflammatory factors in the lipopolysaccharides (LPSs)-induced ALI model. We demonstrated that BBR could suppress the expression of phosphorylated nuclear factor-kappa B (NF-κB) and further restrain the downstream gene nucleotide-binding domain and leucine-rich repeat protein-3 (Nlrp3). Moreover, we also revealed that BBR could directly interact with Nlrp3 protein. After knocked down of Nlrp3 by using siRNA, the protective role of BBR was abrogated in vitro. The expression of IL-1β and IL-18 was downregulated by BBR via the two signaling pathways. Notably, in Nlrp3 deficient mice, the protective effect of BBR was abolished. These findings demonstrate that BBR has a depressant effect on inflammatory response caused by LPS via regulating NF-κB/Nlrp3 signaling pathway, providing a potential therapeutic strategy in ALI.

Methionine Restriction Prevents Lipopolysaccharide-Induced Acute Lung Injury via Modulating CSE/H2S Pathway

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) result in high mortality, whereas effective treatments are limited. Methionine restriction (MR) has been reported to offer various benefits against multiple pathological processes of organ injuries. However, it remains unknown whether MR has any potential therapeutic value for ALI/ARDS. The current study was set to investigate the therapeutic potential of MR on lipopolysaccharide (LPS)-induced ALI and its underlying mechanisms. We found that MR attenuated LPS-induced pulmonary edema, hemorrhage, atelectasis, and alveolar epithelial cell injuries in mice. MR upregulated cystathionine-gamma-lyase (CSE) expression and enhanced the production of hydrogen sulfide (H2S). MR also inhibited the activation of Toll-like receptors 4 (TLR4)/NF-κB/NOD-like receptor protein 3 (NLRP3), then reduced IL-1β, IL-6, and TNF-α release and immune cell infiltration. Moreover, the protective effects of MR on LPS-induced ALI were abrogated by inhibiting CSE, whereas exogenous H2S treatment alone mimicked the protective effects of MR in Cse-/- mice after LPS administration. In conclusion, our findings showed that MR attenuated LPS-induced lung injury through CSE and H2S modulation. This work suggests that developing MR towards clinical use for ALI/ARDS patients may be a valuable strategy.