Nedd8 modification of Cullin-5 regulates lipopolysaccharide-induced acute lung injury

MLN4924 alleviates autoimmune myocarditis by promoting Act1 degradation and blocking Act1-mediated mRNA stability

BACKGROUND

Prolonged exposure to interleukin-17A (IL-17A) can induce autoimmune myocarditis, and MLN4924, an inhibitor of NEDD8 activating enzyme (NAE), has been reported to effectively suppress various inflammatory reactions. However, the effects of MLN4924 in IL-17A-mediated inflammation associated with autoimmune myocarditis remain uncertain.

METHODS

An experimental autoimmune myocarditis (EAM) model was established and treated with MLN4924. The inflammation degree of heart tissues was assessed histopathologically. The expression levels of inflammatory cytokines and chemokines were measured using ELISA and RT-qPCR, respectively. Additionally, the interaction of biomacromolecules was detected through co-immunoprecipitation (Co-IP) and RNA immunoprecipitation (RIP).

RESULTS

MLN4924 could attenuate IL-17A-induced inflammation. In the in vivo studies, MLN4924 treatment improved inflammatory responses, diminished immune cell infiltration and tissue fibrosis, and reduced the secretion of various inflammatory cytokines in serum, including IL-1β, IL-6, TNF-α, and MCP-1. In vitro experiments further corroborated these findings, showing that MLN4924 treatment reduced the secretion and transcription of pro-inflammatory factors, particularly MCP-1. Mechanistically, we confirmed that MLN4924 promoted Act1 ubiquitination degradation and disrupted Act1's interaction with IL-17R, thereby impeding the formation of the IL-17R/Act1/TRAF6 complex and subsequent activation of TAK1, c-Jun, and p65. Moreover, MLN4924 interfered with Act1's binding to mRNA, resulting in mRNA instability.

CONCLUSIONS

In conclusion, MLN4924 effectively alleviated inflammatory symptoms in EAM by disrupting the interaction between IL and 17R and Act1, thereby reducing Act1-mediated mRNA stability and resulting in decreased expression of pro-inflammatory factors.

Protein neddylation and its role in health and diseases

NEDD8 (Neural precursor cell expressed developmentally downregulated protein 8) is an ubiquitin-like protein that is covalently attached to a lysine residue of a protein substrate through a process known as neddylation, catalyzed by the enzyme cascade, namely NEDD8 activating enzyme (E1), NEDD8 conjugating enzyme (E2), and NEDD8 ligase (E3). The substrates of neddylation are categorized into cullins and non-cullin proteins. Neddylation of cullins activates CRLs (cullin RING ligases), the largest family of E3 ligases, whereas neddylation of non-cullin substrates alters their stability and activity, as well as subcellular localization. Significantly, the neddylation pathway and/or many neddylation substrates are abnormally activated or over-expressed in various human diseases, such as metabolic disorders, liver dysfunction, neurodegenerative disorders, and cancers, among others. Thus, targeting neddylation becomes an attractive strategy for the treatment of these diseases. In this review, we first provide a general introduction on the neddylation cascade, its biochemical process and regulation, and the crystal structures of neddylation enzymes in complex with cullin substrates; then discuss how neddylation governs various key biological processes via the modification of cullins and non-cullin substrates. We further review the literature data on dysregulated neddylation in several human diseases, particularly cancer, followed by an outline of current efforts in the discovery of small molecule inhibitors of neddylation as a promising therapeutic approach. Finally, few perspectives were proposed for extensive future investigations.

Cullin5 drives experimental asthma exacerbations by modulating alveolar macrophage antiviral immunity

Asthma exacerbations caused by respiratory viral infections are a serious global health problem. Impaired antiviral immunity is thought to contribute to the pathogenesis, but the underlying mechanisms remain understudied. Here using mouse models we find that Cullin5 (CUL5), a key component of Cullin-RING E3 ubiquitin ligase 5, is upregulated and associated with increased neutrophil count and influenza-induced exacerbations of house dust mite-induced asthma. By contrast, CUL5 deficiency mitigates neutrophilic lung inflammation and asthma exacerbations by augmenting IFN-β production. Mechanistically, following thymic stromal lymphopoietin stimulation, CUL5 interacts with O-GlcNAc transferase (OGT) and induces Lys48-linked polyubiquitination of OGT, blocking the effect of OGT on mitochondrial antiviral-signaling protein O-GlcNAcylation and RIG-I signaling activation. Our results thus suggest that, in mouse models, pre-existing allergic injury induces CUL5 expression, impairing antiviral immunity and promoting neutrophilic inflammation for asthma exacerbations. Targeting of the CUL5/IFN-β signaling axis may thereby serve as a possible therapy for treating asthma exacerbations.

Neddylation Regulation of Immune Responses

Neddylation plays a vital role in post-translational modification, intricately shaping the regulation of diverse biological processes, including those related to cellular immune responses. In fact, neddylation exerts control over both innate and adaptive immune systems via various mechanisms. Specifically, neddylation influences the function and survival of innate immune cells, activation of pattern recognition receptors and GMP-AMP synthase-stimulator of interferon genes pathways, as well as the release of various cytokines in innate immune reactions. Moreover, neddylation also governs the function and survival of antigen-presenting cells, which are crucial for initiating adaptive immune reactions. In addition, neddylation regulates T cell activation, proliferation, differentiation, survival, and their effector functions, thereby ensuring an appropriate adaptive immune response. In this review, we summarize the most recent findings in these aspects and delve into the connection between dysregulated neddylation events and immunological disorders, especially inflammatory diseases. Lastly, we propose future directions and potential treatments for these diseases by targeting neddylation.

Cullin 5 aggravates hypoxic pulmonary hypertension by activating TRAF6/NF-κB/HIF-1α/VEGF

Hypoxic pulmonary hypertension (HPH) lacks effective pharmacologic treatments. Microarray-based gene expression indicates the crucial role of Cullin 5 (Cul 5) in HPH. This study showed that Cul 5 was upregulated in HPH patients and a murine model of HPH. In vitro, Cul 5 promoted the angiogenesis and adhesion capacity of human pulmonary artery endothelial cells (PAECs), which could be mitigated by Cul 5 inactivation mediated by pevonedistat or NEDD8 silence. In vivo, silencing of Cul 5 in the endothelium and Cul 5 inactivation by pevonedistat could also alleviate hypoxic vascular remodeling. Mechanistic research showed that Cul 5 participated in HPH pathogenesis via the TRAF6/NF-κB/HIF-1α/VEGF pathway. Inhibition of the TRAF6/NF-κB/HIF-1α/VEGF pathway could reverse Cul 5-induced human PAEC dysfunction. These findings demonstrate that Cul 5 is an important mediator of HPH via the TRAF6/NF-κB/HIF-1α/VEGF pathway firstly, and could be considered as a potential therapeutic target in the clinical treatment of HPH.

Staphylococcal virulence factor HlgB targets the endoplasmic-reticulum-resident E3 ubiquitin ligase AMFR to promote pneumonia

Staphylococcus aureus invades cells and persists intracellularly, causing persistent inflammation that is notoriously difficult to treat. Here we investigated host-pathogen interactions underlying intracellular S. aureus infection in macrophages and discovered that the endoplasmic reticulum (ER) is an important cellular compartment for intracellular S. aureus infection. Using CRISPR-Cas9 guide RNA library screening, we determined that the autocrine motility factor receptor (AMFR), an ER-resident E3 ubiquitin ligase, played an essential role in mediating intracellular S. aureus-induced inflammation. AMFR directly interacted with TAK1-binding protein 3 (TAB3) in the ER, inducing K27-linked polyubiquitination of TAB3 on lysine 649 and promoting TAK1 activation. Moreover, the virulence factor γ-haemolysin B (HIgB) of S. aureus bound to the AMFR and regulated TAB3. Our findings highlight an unknown role of AMFR in intracellular S. aureus infection-induced pneumonia and suggest that pharmacological interruption of AMFR-mediated TAB3 signalling cascades and HIgB targeting may prevent invasive staphylococci-mediated pneumonia.

BP5 alleviates endotoxemia-induced acute lung injury by activating Nrf2 via dual regulation of the Keap1-Nrf2 interaction and the Akt (Ser473)/GSK3β (Ser9)/Fyn pathway

Oxidative stress and inflammation play a crucial role in the pathogenesis of acute lung injury (ALI). Previously, pentapeptide bursopentin (BP5, Cys-Lys-Arg-Val-Tyr) was reported to possess significant antioxidant activity and inhibit lipopolysaccharides (LPS)-induced NF-κB activation in vitro, whereas little is known about its effects in vivo. In this study, we explored the effects of BP5 on endotoxemia-induced ALI in mice and the underlying molecular mechanisms. Our studies revealed that BP5 markedly improved survival and effectively alleviated lung injury by reducing overoxidation and excessive inflammatory response in endotoxemia mice. In LPS-stimulated mouse primary macrophages and RAW 264.7 cells, BP5 also exhibited antioxidant and anti-inflammatory properties by enhancing Nrf2 activation. Importantly, these beneficial effects were abolished by Nrf2 knockdown. To further elucidate the underlying mechanisms, we performed localized surface plasmon resonance (LSPR) assays, molecular docking, together with cell-based studies, and found that BP5 inhibited the Keap1-Nrf2 interaction to promote Nrf2 nuclear translocation and activation. Moreover, BP5-induced Nrf2 activation was shown to be accompanied by an increase in the phosphorylation of Akt (at Ser473) and GSK3β (at Ser9), and a decrease in Fyn nuclear accumulation both in vitro and in vivo. Pharmacologically inhibiting phosphorylation of Akt and GSK3β obviously enhanced Fyn nuclear accumulation in RAW 264.7 cells, which partially attenuated the promoting effect of BP5 on Nrf2 nuclear accumulation and activation. Furthermore, In Nrf2^-/- mice, the protective effects of BP5 on the endotoxemia-induced ALI in WT mice were largely vanished. Our findings indicated that BP5 effectively protected endotoxemia-induced ALI against oxidative stress and inflammatory response, which are largely dependent on activation of the Nrf2 pathway. Underlying mechanisms include dual regulation of the Keap-Nrf2 interaction and the Akt (Ser473)/GSK3β (Ser9)/Fyn pathway.

AMFR drives allergic asthma development by promoting alveolar macrophage-derived GM-CSF production

Alveolar macrophages (AMs) are specialized tissue-resident macrophages that orchestrate the immune response in allergic inflammation and asthma. However, what signals direct AMs to cross talk with other immune cells remains unclear. Here, we report that autocrine motility factor receptor (AMFR), an endoplasmic reticulum-resident E3 ubiquitin ligase, is upregulated in AMs of asthma and is critical for this condition. AMFR deficiency significantly decreased allergy-induced T helper 2 (Th2) and eosinophilic inflammation, with less granulocyte-macrophage colony-stimulating factor (GM-CSF) production in AMs. Mechanistically, following thymic stromal lymphopoietin (TSLP) stimulation, AMFR associated directly with cytokine-inducible SH2-containing protein (CIS), induced the ubiquitination of Lys48-linked polyubiquitination of CIS, and consequently blocked the inhibitory effect of CIS on signal transducer and activator of transcription 5 (STAT5) phosphorylation and the downstream pathway activation in AMs. In conclusion, our results demonstrate that AMFR serves a crucial role in promoting inflammation in asthma through regulating AM function, and may emerge as a new potential drug target for asthma therapy.

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.

Neddylation Regulates Macrophages and Implications for Cancer Therapy

Tumor-associated macrophages (TAMs) promote cancer progression via stimulating angiogenesis, invasion/metastasis, and suppressing anti-cancer immunity. Targeting TAMs is a potential promising cancer therapeutic strategy. Neddylation adds the ubiquitin-like protein NEDD8 to substrates, and thereby regulates diverse biological processes in multiple cell types, including macrophages. By controlling cellular responses, the neddylation pathway regulates the function, migration, survival, and polarization of macrophages. In the present review we summarized how the neddylation pathway modulates Macrophages and its implications for cancer therapy.

Neddylation pathway alleviates chronic pancreatitis by reducing HIF1α-CCL5-dependent macrophage infiltration

Chronic pancreatitis (CP) is characterized by a wide range of irreversible fibro-inflammatory diseases with largely ambiguous pathogenesis. Although neddylation pathway has been implicated in regulating immune responses, whether the dysregulation of neddylation is involved in the progression of CP and how neddylation regulates the inflammatory microenvironment of CP have not yet been reported. Here, we demonstrate that global inactivation of neddylation pathway by MLN4924 significantly exacerbates chronic pancreatitis. The increased M2 macrophage infiltration, mediated by the upregulated chemokine (C-C motif) ligand 5 (CCL5), is responsible for the enhanced pancreatitis-promoting activity of MLN4924. Both CCL5 blockade and macrophage depletion contribute to alleviating pancreatic fibrosis and inflammation in MLN4924-treated CP mice. Mechanistic investigation identifies that inactivation of Cullin-RING ligases (CRLs) stabilizes cellular levels of hypoxia-inducible factor 1α (HIF-1α), which increases CCL5 expression by promoting CCL5 transactivation. Clinically, UBE2M expression remarkably decreases in human CP tissues compared with normal specimens and the levels of CCL5 and M2 marker CD163 are negatively correlated with UBE2M intensity, suggesting that neddylation is involved in the pathogenesis of pancreatitis. Hence, our studies reveal a neddylation-associated immunopathogenesis of chronic pancreatitis and provide new ideas for the disease treatment.

Sophoricoside attenuates lipopolysaccharide-induced acute lung injury by activating the AMPK/Nrf2 signaling axis

Sophoricoside (SOP), an isoflavone glycoside isolated from seed of Sophora japonica L., has been reported to have various pharmacological activities, including anti-cancer, anti-allergy and anti-inflammation. However, the effect of SOP on lipopolysaccharides (LPS)-acute lung injury (ALI) is completely unclear. Here, we found that SOP pretreatment significantly ameliorated LPS-induced pathological damage, tissue permeability, neutrophil infiltration and the production of pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) in a murine model of ALI. Besides, SOP reduced the production of pro-inflammatory mediators such as iNOS, NO and inflammatory cytokines including TNF-α, IL-1β and IL-6 in LPS-stimulated RAW264.7 cells and bone marrow derived macrophages. Interestingly, treatment with SOP exhibited no effect on the activation of NF-κB and MAPKs in macrophages but prominently accelerated the expression and nuclear translocation of Nrf2. By using ML385, a specific Nrf2 inhibitor, we found that inhibition of Nrf2 abolished the inhibitory effect of SOP on LPS-induced iNOS expression, NO production as well as pro-inflammatory cytokine generation. SOP also activated AMPK, an upstream protein of Nrf2, under LPS stimuli. Furthermore, we demonstrated that the accelerated expression of Nrf2 induced by SOP was reversed by interference with the AMPK inhibitor Compound C. Taken together, our results suggested that SOP attenuated LPS-induced ALI in AMPK/Nrf2 dependent manner and indicated that SOP might be a potential therapeutic candidate for treating ALI/ARDS.

Diverse and pivotal roles of neddylation in metabolism and immunity

Neddylation is one type of protein post-translational modification by conjugating a ubiquitin-like protein neural precursor cell-expressed developmentally downregulated protein 8 to substrate proteins via a cascade involving E1, E2, and E3 enzymes. The best-characterized substrates of neddylation are cullins, essential components of cullin-RING E3 ubiquitin-ligase complexes. The discovery of noncullin neddylation targets indicates that neddylation may have diverse biological functions. Indeed, neddylation has been implicated in various cellular processes including cell cycle progression, metabolism, immunity, and tumorigenesis. Here, we summarized the reported neddylation substrates and also discuss the functions of neddylation in the immune system and metabolism.

Mesenchymal stem cells alleviate LPS-induced acute lung injury by inhibiting the proinflammatory function of Ly6C+ CD8+ T cells

Systemic inflammatory processes, including alveolar injury, cytokine induction, and neutrophil accumulation, play key roles in the pathophysiology of acute lung injury (ALI). The immunomodulatory effects of mesenchymal stem cells (MSCs) can contribute to the treatment of inflammatory disorders. In previous studies, the focus was on innate immune cells and the effects of MSCs on ALI through CD8⁺ T cells remain unclear. In the present study, lipopolysaccharide (LPS) was used to induce ALI in mice. ALI mice were treated with MSCs via intratracheal instillation. Survival rate, histopathological changes, protein levels, total cell count, cytokine levels, and chemokine levels in alveolar lavage fluid were used to determine the efficacy of MSCs. Mass cytometry and single-cell RNA sequencing (scRNA-seq) were used to characterize the CD8⁺ T cells in the lungs. Ly6C^- CD8⁺ T cells are prevalent in normal mice, whereas a specialized effector phenotype expressing a high level of Ly6C is predominant in advanced disease. MSCs significantly mitigated ALI and improved survival. MSCs decreased the infiltration of CD8⁺ T cells, especially Ly6C⁺ CD8⁺ T cells into the lungs. Mass cytometry revealed that CD8⁺ T cells expressing high Ly6C and CXCR3 levels caused tissue damage in the lungs of ALI mice, which was alleviated by MSCs. The scRNA-seq showed that Ly6C⁺ CD8⁺ T cells exhibited a more activated phenotype and decreased expression of proinflammatory factors that were enriched the most in immune chemotaxis after treatment with MSCs. We showed that CD8⁺ T cells play an important role in MSC-mediated ALI remission, and both infiltration quantity and proinflammatory function were inhibited by MSCs, indicating a potential mechanism for therapeutic intervention.

The pivotal roles of neddylation pathway in immunoregulation

Introduction

Protein neddylation, one of the most important posttranslational modifications that tagging neuronal precursor cell‐expressed developmentally downregulated protein 8 onto substrate proteins, plays fundamental roles in the process of many cellular functions. A number of studies have demonstrated the critical roles of neddylation modification in multiple pathophysiological processes, but its regulatory role in the immune system has only been finitely unveiled.

Methods

In this review, the latest advances in the field of neddylation modification in regulating the immune responses are succinctly discussed.

Results

Neddylation modification acts as a crucial modulator of innate immune cells (neutrophils, macrophages, and dendritic cells) and lymphocytes. Dysregulation of neddylation alters characteristics and functions of those cells due to abnormal degradation of key signaling molecules involved in immunoregulation. Furthermore, the ectopic immune responses caused by the abnormal neddylation play pivotal roles in a variety of immune‐related diseases, such as infection, inflammation, and cancer.

Conclusions

The pivotal roles of neddylation pathway in immunoregulation are attracted more and more attention, which may provide new insights into the pathogenesis of a variety of immune‐related diseases and help to indicate new therapeutic targets and potential treatment strategies.

Cullin-RING Ligase 5: Functional characterization and its role in human cancers

Cullin-RING ligase 5 (CRL5) is a multi-protein complex and consists of a scaffold protien cullin 5, a RING protein RBX2 (also known as ROC2 or SAG), adaptor proteins Elongin B/C, and a substrate receptor protein SOCS. Through targeting a variety of substrates for proteasomal degradation or modulating various protein-protein interactions, CRL5 is involved in regulation of many biological processes, such as cytokine signal transduction, inflammation, viral infection, and oncogenesis. As many substrates of CRL5 are well-known oncoproteins or tumor suppressors, abnormal regulation of CRL5 is commonly found in human cancers. In this review, we first briefly introduce each of CRL5 components, and then discuss the biological processes regulated by four members of SOCS-box-containing substrate receptor family through substrate degradation. We next describe how CRL5 is hijacked by a variety of viral proteins to degrade host anti-viral proteins, which facilitates virus infection. We further discuss the regulation of CUL5 and its various roles in human cancers, acting as either a tumor suppressor or an oncoprotein in a context-dependent manner. Finally, we propose novel insights for future perspectives on the validation of cullin5 and other CRL5 components as potential targets, and possible targeting strategies to discover CRL5 inhibitors for anti-cancer and anti-virus therapies.

Gum arabic reduces inflammation, oxidative, and nitrosative stress in the gastrointestinal tract of mice with chronic kidney disease

The aim of this study was to investigate some biochemical indices of inflammation and oxidative and nitrosative stresses in the gastrointestinal tract of mice with experimental chronic kidney disease (CKD) and treated with gum arabic (GA). Male CD1 mice (n = 28) were randomly distributed into four groups and treated for four consecutive weeks: group 1: Control: received the same diet without treatment until the end of the study; group 2: Adenine: switched to a powder diet containing adenine (0.2% w/w in feed); group 3: Gum acacia (GA): given normal feed and GA in drinking water at a concentration of 15% w/v; and group 4: Adenine + GA: given adenine in the feed as in the second group plus GA in the drinking water at concentration of 15% w/v. CKD was induced to mice by adenine feeding and concomitantly treated with the prebiotic dietary fiber gum acacia, GA (15% in drinking water). Duodenal mucosa from CKD mice had significantly higher concentrations of TNF-alfa, IL- 6, and TGF-beta-1 and lipid peroxidation. Moreover, low concentrations of IL-10, some antioxidants (catalase, glutathione reductase, total antioxidant capacity, and superoxide dismutase), and nuclear factor erythroid 2-related factor 2 were found in the duodenum. The levels of nitrosative stress (nitrite, nitrate, and total nitrate) were significantly increased by CKD, as well as the concentrations of ammonia and urea creatinine in the cecal content. Concomitant GA treatment significantly mitigated these harmful effects. Taken together, GA reduces inflammation and duodenal oxidative and nitrosative stress in the gastrointestinal tract of mice with CKD.

Increase in circulating ACE-positive endothelial microparticles during acute lung injury

Circulating endothelial microparticles (EMPs) are considered to be markers of endothelial injury, and lung microvascular endothelial cells express higher levels of angiotensin-converting enzyme (ACE). The aim of this study is to examine whether the number of ACE⁺ microvascular EMPs could be a prognostic marker for the development of acute respiratory distress syndrome (ARDS) in septic patients.The numbers of EMPs and ACE⁺ EMPs in the culture supernatant from human microvascular endothelial cells, as well as in the blood of mouse lung injury models and septic patients (n=82), were examined using flow cytometry.ACE⁺ EMPs in the culture supernatant from pulmonary microvascular endothelial cells increased after exposure to an inflammatory stimulus. In the mouse lung injury models, the circulating ACE⁺ EMPs and ACE⁺ EMP/EMP ratio were higher than in the controls (p<0.001). The ACE⁺ EMP/EMP ratio was correlated with the wet/dry lung ratio (r_s=0.775, p<0.001). The circulating ACE⁺ EMPs and ACE⁺ EMP/EMP ratio on admission were significantly increased in septic patients who developed ARDS compared with septic patients who did not (p<0.001).Therefore, circulating ACE⁺ EMPs may be a prognostic marker for the development of ARDS in the septic patients.

MLN4924 protects against interleukin-17A-induced pulmonary inflammation by disrupting ACT1-mediated signaling

An excessive inflammatory response in terminal airways, alveoli, and the lung interstitium eventually leads to pulmonary hypertension and chronic obstructive pulmonary disease. Proinflammatory cytokine interleukin-17A (IL-17A) has been implicated in the pathogenesis of pulmonary inflammatory diseases. MLN4924, an inhibitor of NEDD8-activating enzyme (NAE), is associated with the treatment of various types of cancers, but its role in the IL-17A-mediated inflammatory response has not been identified. Here, we report that MLN4924 can markedly reduce the expression of proinflammatory cytokines and chemokines such as IL-1β, IL-6, and CXCL-1 and neutrophilia in a mouse model of IL-17A adenovirus-induced pulmonary inflammation. MLN4924 significantly inhibited IL-17A-induced stabilization of mRNA of proinflammatory cytokines and chemokines in vitro. Mechanistically, MLN4924 significantly blocked the activation of MAPK and NF-κB pathways and interfered with the interaction between ACT1 and tumor necrosis factor receptor-associated factor proteins (TRAFs), thereby inhibiting TRAF6 ubiquitination. Taken together, our data uncover a previously uncharacterized inhibitory effect of MLN4924 on the IL-17A-mediated inflammatory response; this phenomenon may facilitate the development of MLN4924 into an effective small-molecule drug for the treatment of pulmonary inflammatory diseases.

Inhibition of NKCC1 Modulates Alveolar Fluid Clearance and Inflammation in Ischemia-Reperfusion Lung Injury via TRAF6-Mediated Pathways

Background: The expression of Na-K-2Cl cotransporter 1 (NKCC1) in the alveolar epithelium is responsible for fluid homeostasis in acute lung injury (ALI). Increasing evidence suggests that NKCC1 is associated with inflammation in ALI. We hypothesized that inhibiting NKCC1 would attenuate ALI after ischemia-reperfusion (IR) by modulating pathways that are mediated by tumor necrosis-associated factor 6 (TRAF6).

Methods: IR-ALI was induced by producing 30 min of ischemia followed by 90 min of reperfusion in situ in an isolated and perfused rat lung model. The rats were randomly allotted into four groups comprising two control groups and two IR groups with and without bumetanide. Alveolar fluid clearance (AFC) was measured for each group. Mouse alveolar MLE-12 cells were cultured in control and hypoxia-reoxygenation (HR) conditions with or without bumetanide. Flow cytometry and transwell monolayer permeability assay were carried out for each group.

Results: Bumetanide attenuated the activation of p-NKCC1 and lung edema after IR. In the HR model, bumetanide decreased the cellular volume and increased the transwell permeability. In contrast, bumetanide increased the expression of epithelial sodium channel (ENaC) via p38 mitogen-activated protein kinase (p38 MAPK), which attenuated the reduction of AFC after IR. Bumetanide also modulated lung inflammation via nuclear factor-κB (NF-κB). TRAF6, which is upstream of p38 MAPK and NF-κB, was attenuated by bumetanide after IR and HR.

Conclusions: Inhibition of NKCC1 by bumetanide reciprocally modulated epithelial p38 MAPK and NF-κB via TRAF6 in IR-ALI. This interaction attenuated the reduction of AFC via upregulating ENaC expression and reduced lung inflammation.

MK2 mediates macrophage activation and acute lung injury by regulating let-7e miRNA

MAPK-activated protein kinase 2 (MK2) plays a critical role in the development of inflammation. However, the modulatory mechanisms in macrophage activation and acute lung injury (ALI) have not been completely defined. Here, we reported that MK2-deficient mice (MK2^-/-) protected against sepsis-induced ALI. In response to lipopolysaccharide (LPS) challenge, MK2^-/- mice and myeloid cell-specific MK2 conditional knockout mice (MK2^Lyz2-KO) exhibited attenuated inflammatory response, especially producing fewer amounts of tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and macrophage inflammatory protein 2 (MIP-2). LPS treatment in vitro resulted in reduced cytokine expression in MK2^-/- bone marrow-derived macrophages (BMDMs). Furthermore, we found that LPS-induced microRNA lethal-7e ( let-7e) expression was significantly increased in MK2^-/- macrophages. Transfection of let-7e antagomirs into MK2^-/- BMDM rescued LPS-induced expression of TNF-α, IL-6, and MIP-2. In contrast, transfection of let-7e mimics into MK2^+/+BMDM decreased cytokine expression. Meanwhile, LPS-induced phosphorylation of cAMP response element-binding (CREB) protein, a substrate of MK2, was downregulated in MK2^-/- BMDMs. Lin28, an inhibitory molecule of let-7, was significantly reduced in MK2^-/- macrophages. Our results suggested that MK2 boosts LPS-induced macrophage activation and ALI via increasing activation of CREB and consequently, the expression of Lin28 and downregulation of let-7e.