Inhibition of lethal inflammatory responses through the targeting of membrane-associated Toll-like receptor 4 signaling complexes with a Smad6-derived peptide

Pellino-1, a therapeutic target for control of SARS-CoV-2 infection and disease severity

Enhanced expression of Pellino-1 (Peli1), a ubiquitin ligase is known to be associated with COVID-19 susceptibility. The underlying mechanisms are not known. Here, we report that mice deficient in Peli1 (Peli1-/-) had reduced viral load and attenuated inflammatory immune responses and tissue damage in the lung following SARS-CoV-2 infection. Overexpressing Peli1 in 293 T cells increased SARS-CoV-2 infection via promoting virus replication and transcription, without affecting virus attachment and entry into the cells. Smaducin-6 treatment which is known to disrupt Peli1-mediated NF-KB activation, attenuated inflammatory immune responses in human lung epithelial cells as well as in the lung of K18-hACE2 mice following SARS-CoV-2 infection, though it had minimal effects on SARS-CoV-2 infection in human nasal epithelial cells. Overall, our findings suggest that Peli1 contributes to SARS-CoV-2 pathogenesis by promoting virus replication and positively regulating virus-induced inflammatory responses in lung epithelial cells. Peli1 is a therapeutic target to control SARS-CoV-2 -induced disease severity.

Biology of Pellino1: a potential therapeutic target for inflammation in diseases and cancers

Pellino1 (Peli1) is a highly conserved E3 Ub ligase that exerts its biological functions by mediating target protein ubiquitination. Extensive evidence has demonstrated the crucial role of Peli1 in regulating inflammation by modulating various receptor signaling pathways, including interleukin-1 receptors, Toll-like receptors, nuclear factor-κB, mitogen-activated protein kinase, and phosphoinositide 3-kinase/AKT pathways. Peli1 has been implicated in the development of several diseases by influencing inflammation, apoptosis, necrosis, pyroptosis, autophagy, DNA damage repair, and glycolysis. Peli1 is a risk factor for most cancers, including breast cancer, lung cancer, and lymphoma. Conversely, Peli1 protects against herpes simplex virus infection, systemic lupus erythematosus, esophageal cancer, and toxic epidermolysis bullosa. Therefore, Peli1 is a potential therapeutic target that warrants further investigation. This comprehensive review summarizes the target proteins of Peli1, delineates their involvement in major signaling pathways and biological processes, explores their role in diseases, and discusses the potential clinical applications of Peli1-targeted therapy, highlighting the therapeutic prospects of Peli1 in various diseases.

Pellino 3 promotes the colitis-associated colorectal cancer through suppression of IRF4-mediated negative regulation of TLR4 signalling

The incidence of colitis-associated colorectal cancer (CAC) has increased due to a high-nutrient diet, increased environmental stimuli and inherited gene mutations. To adequately treat CAC, drugs should be developed by identifying novel therapeutic targets. E3 ubiquitin-protein ligase pellino homolog 3 (pellino 3; Peli3) is a RING-type E3 ubiquitin ligase involved in inflammatory signalling; however, its role in the development and progression of CAC has not been elucidated. In this study, we studied Peli3-deficient mice in an azoxymethane/dextran sulphate sodium-induced CAC model. We observed that Peli3 promotes colorectal carcinogenesis with increased tumour burden and oncogenic signalling pathways. Ablation of Peli3 reduced inflammatory signalling activation at the early stage of carcinogenesis. Mechanistic studies indicate that Peli3 enhances toll-like receptor 4 (TLR4)-mediated inflammation through ubiquitination-dependent degradation of interferon regulatory factor 4, a negative regulator of TLR4 in macrophages. Our study suggests an important molecular link between Peli3 and colonic inflammation-mediated carcinogenesis. Furthermore, Peli3 can be a therapeutic target in the prevention and treatment of CAC.

Effect of plant polysaccharides (Poria cocos and Astragalus polysaccharides) on immune responses and intestinal microbiota of Dabry's sturgeons

Searching for non-toxic and harmless feed ingredients that can improve growth performance and host immunity has always been the focus of attention in the protected areas for artificially bred Dabry's sturgeons. The present study explored the effect of dietary Poria cocos and Astragalus polysaccharides on the antioxidant status, expression of immune related genes, and composition and putative functions of gut bacterial communities in Dabry's sturgeons for the first time. In this study, Dabry's sturgeons were randomly divided into 3 groups and fed diets of normal, P. cocos polysaccharide-added (200 mg/kg), and Astragalus polysaccharide-added (200 mg/kg) food for 14 days. The results indicated that dietary Astragalus polysaccharide can increase the final body weight of Dabry's sturgeon. Compared with normal breeding individuals, feeding diets containing the P. cocos and Astragalus polysaccharides up-regulated the activity of superoxide dismutase, lysozyme, catalase, and glutathione peroxidase while also decreasing the levels of malondialdehyde. In addition, the Astragalus polysaccharide group had higher gene expression of two inflammatory cytokines, tumor necrosis factor alpha and immunoglobulin M, than the control group. Analysis of intestinal microbiota revealed that the dietary Astragalus polysaccharide improved the richness and diversity of major gut microbiota in Dabry's sturgeons, while the structure in the P. cocos polysaccharide group was clearly distinguished from that of the control group. Our results preliminarily indicated that dietary supplementation of P. cocos and Astragalus polysaccharides may contribute to better performance in growth, development, and inflammatory response for Dabry's sturgeons, and they provide basic guidance for plant polysaccharide additives in artificial breeding of sturgeons.

Peli3 ablation ameliorates acetaminophen-induced liver injury through inhibition of GSK3β phosphorylation and mitochondrial translocation

The signaling pathways governing acetaminophen (APAP)-induced liver injury have been extensively studied. However, little is known about the ubiquitin-modifying enzymes needed for the regulation of APAP-induced liver injury. Here, we examined whether the Pellino3 protein, which has E3 ligase activity, is needed for APAP-induced liver injury and subsequently explored its molecular mechanism. Whole-body Peli3-/- knockout (KO) and adenovirus-mediated Peli3 knockdown (KD) mice showed reduced levels of centrilobular cell death, infiltration of immune cells, and biomarkers of liver injury, such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST), upon APAP treatment compared to wild-type (WT) mice. Peli3 deficiency in primary hepatocytes decreased mitochondrial and lysosomal damage and reduced the mitochondrial reactive oxygen species (ROS) levels. In addition, the levels of phosphorylation at serine 9 in the cytoplasm and mitochondrial translocation of GSK3β were decreased in primary hepatocytes obtained from Peli3-/- KO mice, and these reductions were accompanied by decreases in JNK phosphorylation and mitochondrial translocation. Pellino3 bound more strongly to GSK3β compared with JNK1 and JNK2 and induced the lysine 63 (K63)-mediated polyubiquitination of GSK3β. In rescue experiments, the ectopic expression of wild-type Pellino3 in Peli3-/- KO hepatocytes restored the mitochondrial translocation of GSK3β, but this restoration was not obtained with expression of a catalytically inactive mutant of Pellino3. These findings are the first to suggest a mechanistic link between Pellino3 and APAP-induced liver injury through the modulation of GSK3β polyubiquitination.

SMAD6 transduces endothelial cell flow responses required for blood vessel homeostasis

Fluid shear stress provided by blood flow instigates a transition from active blood vessel network expansion during development, to vascular homeostasis and quiescence that is important for mature blood vessel function. Here we show that SMAD6 is required for endothelial cell flow-mediated responses leading to maintenance of vascular homeostasis. Concomitant manipulation of the mechanosensor Notch1 pathway and SMAD6 expression levels revealed that SMAD6 functions downstream of ligand-induced Notch signaling and transcription regulation. Mechanistically, full-length SMAD6 protein was needed to rescue Notch loss-induced flow misalignment. Endothelial cells depleted for SMAD6 had defective barrier function accompanied by upregulation of proliferation-associated genes and down regulation of junction-associated genes. The vascular protocadherin PCDH12 was upregulated by SMAD6 and required for proper flow-mediated endothelial cell alignment, placing it downstream of SMAD6. Thus, SMAD6 is a required transducer of flow-mediated signaling inputs downstream of Notch1 and upstream of PCDH12, as vessels transition from an angiogenic phenotype to maintenance of a homeostatic phenotype.

Identification of miR-4793-3p as a potential biomarker for bacterial infection in patients with hepatitis B virus-related liver cirrhosis: A pilot study

Hepatitis B virus-related liver cirrhosis (HBV-LC) is susceptible to bacterial infections, which could lead to adverse prognosis in patients. MicroRNAs (miRs/miRNAs) are easily detected in peripheral blood and are involved in multiple liver diseases. The present pilot study aimed to investigate differentially expressed (DE) miRNAs in the serum of patients with HBV-LC and bacterial infection, and to identify potential biomarkers. The first batch of clinical samples was collected, including four patients with HBV-LC and infection, four patients with HBV-LC without infection, four patients with chronic hepatitis B (CHB) and four healthy controls. miRNA expression was analyzed by Affymetrix GeneChip miRNA 4.0 Array. A total of 385 DE miRNAs (upregulated, 160; downregulated, 225) were detected in patients with HBV-LC and infection compared with patients with HBV-LC without infection. miR-4793-3p was significantly upregulated in patients with HBV-LC and infection compared with its levels in the other three groups: HBV-LC without infection [log-transformed fold change (logFC)=7.96; P=0.0458), CHB (logFC=34.53; P=0.0003) and healthy controls (logFC=3.34; P=0.0219)]. Reverse transcription-quantitative PCR (RT-qPCR) was performed to validate miR-4793-3p expression in another batch of clinical samples. RT-qPCR showed that miR-4793-3p was highly expressed in patients with HBV-LC and infection compared with its levels in patients with HBV-LC without infection (P<0.05). The non-parametric random forest regression model was built to access the diagnostic value of miR-4793-3p, and the receiver operating characteristic curve demonstrated that the area under the curve was 92.2%. Target gene analysis with bioinformatics tools and Gene Expression Omnibus data (GSE46955) showed that miR-4793-3p could participate in the TGF-β signaling pathway. Functional experiments revealed that overexpressed miR-4793-3p could impair TGF-β function by downregulating Gremlin-1. The present pilot study suggests that miR-4793-3p could be a feasible indicator for bacterial infection in patients with HBV-LC, and it would be valuable for further research.

Mycobacterium tuberculosis Rv2626c-derived peptide as a therapeutic agent for sepsis

The Rv2626c protein of Mycobacterium tuberculosis is a promising vaccine candidate owing to its strong serum antibody response in patients with tuberculosis. However, there is limited information regarding the intracellular response induced by Rv2626c in macrophages. In this study, we demonstrated that Rv2626c interacts with the RING domain of TRAF6 and inhibits lysine (K) 63‐linked polyubiquitination of TRAF6 (E3 ubiquitin ligase activity); this results in the suppression of TLR4 inflammatory signaling in macrophages. Furthermore, we showed that the C‐terminal 123–131‐amino acid Rv2626c motif promotes macrophage recruitment, phagocytosis, M2 macrophage polarization, and subsequent bacterial clearance. We developed rRv2626c‐CA, a conjugated peptide containing the C‐terminal 123–131‐amino acid Rv2626c that targets macrophages, penetrates the cell membrane, and has demonstrated significant therapeutic effects in a mouse model of cecal ligation and puncture‐induced sepsis. This multifunctional rRv2626c‐CA has considerably improved potency, with an IC₅₀ that is 250‐fold (in vitro) or 1,000‐fold (in vivo) lower than that of rRv2626c‐WT. We provide evidence for new peptide‐based drugs with anti‐inflammatory and antibacterial properties for the treatment of sepsis.

Peli1 signaling blockade attenuates congenital zika syndrome

Zika virus (ZIKV) infects pregnant women and causes devastating congenital zika syndrome (CZS). How the virus is vertically transmitted to the fetus and induces neuronal loss remains unclear. We previously reported that Pellino (Peli)1, an E3 ubiquitin ligase, promotes p38MAPK activation in microglia and induction of lethal encephalitis by facilitating the replication of West Nile virus (WNV), a closely related flavivirus. Here, we found that Peli1 expression was induced on ZIKV-infected human monocytic cells, peripheral blood mononuclear cells, human first-trimester placental trophoblasts, and neural stem cell (hNSC)s. Peli1 mediates ZIKV cell attachment, entry and viral translation and its expression is confined to the endoplasmic reticulum. Moreover, Peli1 mediated inflammatory cytokine and chemokine responses and induced cell death in placental trophoblasts and hNSCs. ZIKV-infected pregnant mice lacking Peli1 signaling had reduced placental inflammation and tissue damage, which resulted in attenuated congenital abnormalities. Smaducin-6, a membrane-tethered Smad6-derived peptide, blocked Peli1-mediated NF-κB activation but did not have direct effects on ZIKV infection. Smaducin-6 reduced inflammatory responses and cell death in placental trophoblasts and hNSCs, and diminished placental inflammation and damage, leading to attenuated congenital malformations in mice. Collectively, our results reveal a novel role of Peli1 in flavivirus pathogenesis and suggest that Peli1 promotes ZIKV vertical transmission and neuronal loss by mediating inflammatory cytokine responses and induction of cell death. Our results also identify Smaducin-6 as a potential therapeutic candidate for treatment of CZS.

We previously reported that Pellino (Peli)1, an E3 ubiquitin ligase mediates p38MAPK activation in microglia and induces lethal encephalitis by facilitating replication of a mosquito -borne flavivirus, West Nile virus (WNV). Zika virus (ZIKV), a closely related flavivirus, causes devastating congenital zika syndrome (CZS) in pregnant women. How ZIKV is vertically transmitted to the fetus and induces neuronal loss remains unclear. Here, we found that Peli1 expression was enhanced in human monocytic cells, peripheral blood mononuclear cells, first-trimester placental trophoblasts and neural stem cell (hNSC)s following ZIKV infection. Peli1 expression colocalized with the endoplasmic reticulum and double-stranded RNA in ZIKV-infected cells and was required for ZIKV cell attachment and replication. Peli1 knockdown in placental trophoblasts inhibited ZIKV replication and decreased inflammatory cytokine responses and cell death. ZIKV-infected pregnant mice lacking Peli1 signaling showed reduced placental inflammation and tissue damage, which resulted in attenuated congenital abnormalities. Furthermore, Smaducin-6, a membrane-tethered Smad6-derived peptide, blocked Peli1-mediated NF-κB activation, but not ZIKV replication. Smaducin 6 inhibited Peli1-mediated inflammatory cytokine responses and cell death in placental trophoblasts and hNSCs, and attenuated congenital malformations in mice. Collectively, our results reveal a novel role of Peli1 in flavivirus pathogenesis and suggest that Peli1 promotes ZIKV vertical transmission and neuronal loss by mediating inflammatory cytokine responses and induction of cell death.

The Deubiquitinating Enzyme USP20 Regulates the TNFα-Induced NF-κB Signaling Pathway through Stabilization of p62

p62/sequestosome-1 is a scaffolding protein involved in diverse cellular processes such as autophagy, oxidative stress, cell survival and death. It has been identified to interact with atypical protein kinase Cs (aPKCs), linking these kinases to NF-κB activation by tumor necrosis factor α (TNFα). The diverse functions of p62 are regulated through post-translational modifications of several domains within p62. Among the enzymes that mediate these post-translational modifications, little is known about the deubiquitinating enzymes (DUBs) that remove ubiquitin chains from p62, compared to the E3 ligases involved in p62 ubiquitination. In this study, we first demonstrate a role of ubiquitin-specific protease USP20 in regulating p62 stability in TNFα-mediated NF-κB activation. USP20 specifically binds to p62 and acts as a positive regulator for NF-κB activation by TNFα through deubiquitinating lysine 48 (K48)-linked polyubiquitination, eventually contributing to cell survival. Furthermore, depletion of USP20 disrupts formation of the atypical PKCζ-RIPK1-p62 complex required for TNFα-mediated NF-κB activation and significantly increases the apoptosis induced by TNFα plus cycloheximide or TNFα plus TAK1 inhibitor. These findings strongly suggest that the USP20-p62 axis plays an essential role in NF-κB-mediated cell survival induced by the TNFα-atypical PKCζ signaling pathway.

MiR-32-5p aggravates intestinal epithelial cell injury in pediatric enteritis induced by Helicobacter pylori

BACKGROUND

Pediatric enteritis is one of the infectious diseases in the digestive system that causes a variety of digestive problems, including diarrhea, vomiting, and bellyache in children. Clinically, Helicobacter pylori (H. pylori) infection is one of the common factors to cause pediatric enteritis. It has been demonstrated that aberrant expression of microRNAs (miRNAs) is found in gastrointestinal diseases caused by H. pylori, and we discovered a significant increase of miR-32-5p in H. pylori-related pediatric enteritis. However, the exact role of miR-32-5p in it is still unknown.

AIM

To investigate the role of aberrant miR-32-5p in pediatric enteritis induced by H. pylori.

METHODS

MiR-32-5p expression was detected by quantitative real time-polymerase chain reaction. The biological role of miR-32-5p in H. pylori-treated intestinal epithelial cells was evaluated by Cell Counting Kit-8 assay and flow cytometry. The potential target of miR-32-5p was predicted with TargetScanHuman and verified by luciferase assay. The downstream mechanism of miR-32-5p was explored by using molecular biology methods.

RESULTS

We found that miR-32-5p was overexpressed in serum of H. pylori-induced pediatric enteritis. Further investigation revealed that H. pylori infection promoted the death of intestinal epithelial cells, and increased miR-32-5p expression. Moreover, miR-32-5p mimic further facilitated apoptosis and inflammatory cytokine secretion of intestinal epithelial cells. Further exploration revealed that SMAD family member 6 (SMAD6) was the direct target of miR-32-5p, and SMAD6 overexpression partially rescued cell damage induced by H. pylori. The following experiments showed that miR-32-5p/SMAD6 participated in the apoptosis of intestinal epithelial cells induced by transforming growth factor-β-activated kinase 1 (TAK1)-p38 activation under H. pylori infection.

CONCLUSION

Our work uncovered the crucial role of aberrant expression of miR-32-5p in H. pylori-related pediatric enteritis, and suggested that the TAK1-p38 pathway is involved in it.

Kinesin family member KIF18A is a critical cellular factor that regulates the differentiation and activation of dendritic cells

BACKGROUND

KIF18A is a kinesin family member that is involved in various cellular processes including cell division, cell transformation, and carcinogenesis. However, its possible role in the regulation of host immunity has not been examined.

OBJECTIVE

The aim of this study is to investigate the functional role of KIF18A in the differentiation and activation of dendritic cells (DCs) that are the most efficient antigen-presenting cells.

METHODS

A bioinformatic analysis of the KIF18A gene family was performed to understand its sequence variability and evolutionary history. To inhibit KIF18A activity, a highly specific small molecule inhibitor for KIF18A, BTB-1 was used. DCs were differentiated from mouse bone marrow (BM) cells from 6 to 7 week old C57BL/6 mice with recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF). Expression of KIF18A was measured by Western blotting. The surface expression of differentiation and activation markers on DCs were analyzed by flow cytometry.

RESULTS

The phylogenetic analysis revealed that the KIF18A gene family is remarkably conserved across vertebrates. Interestingly, the expression of KIF18A was increased as BM precursor cells differentiated into DCs. BTB-1 treatment strongly inhibited the differentiation of BM cells into DCs in a dose-dependent manner. Furthermore, treatment of immature DCs with BTB-1 significantly impaired the expression of activation markers on DCs including MHC class I, CD80, and CD86 upon TLR4 or TLR7 treatment.

CONCLUSION

Our results reveal that KIF18A is a critical DC differentiation and activation regulator. Therefore, KIF18A could be a potential therapeutic target for immune-mediated disorders.

Pellino-1 Regulates Immune Responses to Haemophilus influenzae in Models of Inflammatory Lung Disease

Non-typeable Haemophilus influenzae (NTHi) is a frequent cause of lower respiratory tract infection in people with chronic obstructive pulmonary disease (COPD). Pellino proteins are a family of E3 ubiquitin ligases that are critical regulators of TLR signaling and inflammation. The aim of this study was to identify a role for Pellino-1 in airway defense against NTHi in the context of COPD. Pellino-1 is rapidly upregulated by LPS and NTHi in monocyte-derived macrophages (MDMs) isolated from individuals with COPD and healthy control subjects, in a TLR4 dependent manner. C57BL/6 Peli1^−/− and wild-type (WT) mice were subjected to acute (single LPS challenge) or chronic (repeated LPS and elastase challenge) airway inflammation followed by NTHi infection. Both WT and Peli1^−/− mice develop airway inflammation in acute and chronic airway inflammation models. Peli1^−/− animals recruit significantly more neutrophils to the airway following NTHi infection which is associated with an increase in the neutrophil chemokine, KC, in bronchoalveolar lavage fluid as well as enhanced clearance of NTHi from the lung. These data suggest that therapeutic inhibition of Pellino-1 may augment immune responses in the airway and enhance bacterial clearance in individuals with COPD.

Linear and Rationally Designed Stapled Peptides Abrogate TLR4 Pathway and Relieve Inflammatory Symptoms in Rheumatoid Arthritis Rat Model

A mounting evidence exists for the despicable role of the aberrant immune response in the pathogenesis of rheumatoid arthritis (RA), where toll-like receptor 4 (TLR4) can activate synovial fibroblasts that lead to the chronic inflammation and joint destruction, thus making TLR4 a potent drug target in RA. We report that novel TLR4-antagonizing peptide, PIP2, inhibits the induction of inflammatory biomarkers in vitro as well as in vivo. Systemically, PIP2 inhibits the lipopolysaccharide (LPS)-elicited TNF-α, IL-6, and IL-12p40 in a mouse model. The rationally designed cyclic derivative, cPIP2, is capable of inhibiting LPS-induced proinflammatory cytokines at significantly lower concentration as compared to PIP2 (PIP2 IC₅₀ = 20 μM, cPIP2 IC₅₀ = 5 μM). Finally, cPIP2 was able to relieve the inflammatory symptoms and synovial tissue destruction in the RA rat model. Cumulatively, these data suggest that PIP2 and cPIP2 hold strong promise for the development of peptide-based immunotherapeutics that could be of great value in curbing TLR-related immune complications including RA.

Peli1 facilitates virus replication and promotes neuroinflammation during West Nile virus infection

The E3 ubiquitin ligase Pellino 1 (Peli1) is a microglia-specific mediator of autoimmune encephalomyelitis. Its role in neurotropic flavivirus infection is largely unknown. Here, we report that mice deficient in Peli1 (Peli1-/-) were more resistant to lethal West Nile virus (WNV) infection and exhibited reduced viral loads in tissues and attenuated brain inflammation. Peli1 mediates chemokine and proinflammatory cytokine production in microglia and promotes T cell and macrophage infiltration into the CNS. Unexpectedly, Peli1 was required for WNV entry and replication in mouse macrophages and mouse and human neurons and microglia. It was also highly expressed on WNV-infected neurons and adjacent inflammatory cells from postmortem patients who died of acute WNV encephalitis. WNV passaged in Peli1-/- macrophages or neurons induced a lower viral load and impaired activation in WT microglia and thereby reduced lethality in mice. Smaducin-6, which blocks interactions between Peli1 and IRAK1, RIP1, and IKKε, did not inhibit WNV-triggered microglia activation. Collectively, our findings suggest a nonimmune regulatory role for Peli1 in promoting microglia activation during WNV infection and identify a potentially novel host factor for flavivirus cell entry and replication.

Nuclear Smad6 promotes gliomagenesis by negatively regulating PIAS3-mediated STAT3 inhibition

To date, the molecular mechanism underlying constitutive signal transducer and activator of transcription 3 (STAT3) activation in gliomas is largely unclear. In this study, we report that Smad6 is overexpressed in nuclei of glioma cells, which correlates with poor patient survival and regulates STAT3 activity via negatively regulating the Protein Inhibitors of Activated STAT3 (PIAS3). Mechanically, Smad6 interacts directly with PIAS3, and this interaction is mediated through the Mad homology 2 (MH2) domain of Smad6 and the Ring domain of PIAS3. Smad6 recruits Smurf1 to facilitate PIAS3 ubiquitination and degradation, which also depends on the MH2 domain and the PY motif of Smad6. Consequently, Smad6 reduces PIAS3-mediated STAT3 inhibition and promotes glioma cell growth and stem-like cell initiation. Moreover, the Smad6 MH2 transducible protein restores PIAS3 expression and subsequently reduces gliomagenesis. Collectively, we conclude that nuclear-Smad6 enhances glioma development by inducing PIAS3 degradation and subsequent STAT3 activity upregulation.

Increased A20-E3 ubiquitin ligase interactions in bid-deficient glia attenuate TLR3- and TLR4-induced inflammation

Background

Chronic pro-inflammatory signaling propagates damage to neural tissue and affects the rate of disease progression. Increased activation of Toll-like receptors (TLRs), master regulators of the innate immune response, is implicated in the etiology of several neuropathologies including amyotrophic lateral sclerosis, Alzheimer’s disease, and Parkinson’s disease. Previously, we identified that the Bcl-2 family protein BH3-interacting domain death agonist (Bid) potentiates the TLR4-NF-κB pro-inflammatory response in glia, and specifically characterized an interaction between Bid and TNF receptor associated factor 6 (TRAF6) in microglia in response to TLR4 activation.

Methods

We assessed the activation of mitogen-activated protein kinase (MAPK) and interferon regulatory factor 3 (IRF3) inflammatory pathways in response to TLR3 and TLR4 agonists in wild-type (wt) and bid-deficient microglia and macrophages, using Western blot and qPCR, focusing on the response of the E3 ubiquitin ligases Pellino 1 (Peli1) and TRAF3 in the absence of microglial and astrocytic Bid. Additionally, by Western blot, we investigated the Bid-dependent turnover of Peli1 and TRAF3 in wt and bid^−/− microglia using the proteasome inhibitor Bortezomib. Interactions between the de-ubiquitinating Smad6-A20 and the E3 ubiquitin ligases, TRAF3 and TRAF6, were determined by FLAG pull-down in TRAF6-FLAG or Smad6-FLAG overexpressing wt and bid-deficient mixed glia.

Results

We elucidated a positive role of Bid in both TIR-domain-containing adapter-inducing interferon-β (TRIF)- and myeloid differentiation primary response 88 (MyD88)-dependent pathways downstream of TLR4, concurrently implicating TLR3-induced inflammation. We identified that Peli1 mRNA levels were significantly reduced in PolyI:C- and lipopolysaccharide (LPS)-stimulated bid-deficient microglia, suggesting disturbed IRF3 activation. Differential regulation of TRAF3 and Peli1, both essential E3 ubiquitin ligases facilitating TRIF-dependent signaling, was observed between wt and bid^−/− microglia and astrocytes. bid deficiency resulted in increased A20-E3 ubiquitin ligase protein interactions in glia, specifically A20-TRAF6 and A20-TRAF3, implicating enhanced de-ubiquitination as the mechanism of action by which E3 ligase activity is perturbed. Furthermore, Smad6-facilitated recruitment of the de-ubiquitinase A20 to E3-ligases occurred in a bid-dependent manner.

Conclusions

This study demonstrates that Bid promotes E3 ubiquitin ligase-mediated signaling downstream of TLR3 and TLR4 and provides further evidence for the potential of Bid inhibition as a therapeutic for the attenuation of the robust pro-inflammatory response culminating in TLR activation.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1143-3) contains supplementary material, which is available to authorized users.

Smad6 Methylation Represses NFκB Activation and Periodontal Inflammation

The balance between pro- and anti-inflammatory signals maintains tissue homeostasis and defines the outcome of chronic inflammatory diseases such as periodontitis, a condition that afflicts the tooth-supporting tissues and exerts an impact on systemic health. The induction of tissue inflammation relies heavily on Toll-like receptor (TLR) signaling, which drives a proinflammatory pathway through recruiting myeloid differentiation primary response gene 88 (MyD88) and activating nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB). TLR-induced production of proinflammatory cytokines and chemokines is reined in by anti-inflammatory cytokines, including the transforming growth factor β (TGFβ) family of cytokines. Although Smad6 is a key mediator of TGFβ-induced anti-inflammatory signaling, the exact mechanism by which TGFβ regulates TLR proinflammatory signaling in the periodontal tissue has not been addressed to date. In this study, we demonstrate for the first time that the ability of TGFβ to inhibit TLR-NFκB signaling is mediated by protein arginine methyltransferase 1 (PRMT1)-induced Smad6 methylation. Upon methylation, Smad6 recruited MyD88 and promoted MyD88 degradation, thereby inhibiting NFκB activation. Most important, Smad6 is expressed and methylated in the gingival epithelium, and PRMT1-Smad6 signaling promotes tissue homeostasis by limiting inflammation. Consistent with this, disturbance of Smad6 methylation exacerbates inflammation and bone loss in experimental periodontitis. The dissected mechanism is therapeutically important, as it highlights the manipulation of PRMT1-Smad6 signaling as a novel promising strategy to modulate the host immune response in periodontitis.

Regulation of TGF-β Family Signaling by Inhibitory Smads

Inhibitory Smads (I-Smads) have conserved carboxy-terminal MH2 domains but highly divergent amino-terminal regions when compared with receptor-regulated Smads (R-Smads) and common-partner Smads (co-Smads). Smad6 preferentially inhibits Smad signaling initiated by the bone morphogenetic protein (BMP) type I receptors ALK-3 and ALK-6, whereas Smad7 inhibits both transforming growth factor β (TGF-β)- and BMP-induced Smad signaling. I-Smads also regulate some non-Smad signaling pathways. Here, we discuss the vertebrate I-Smads, their roles as inhibitors of Smad activation and regulators of receptor stability, as scaffolds for non-Smad signaling, and their possible roles in the nucleus. We also discuss the posttranslational modification of I-Smads, including phosphorylation, ubiquitylation, acetylation, and methylation.

Regulation of TGF-β Family Signaling by Inhibitory Smads

Inhibitory Smads (I-Smads) have conserved carboxy-terminal MH2 domains but highly divergent amino-terminal regions when compared with receptor-regulated Smads (R-Smads) and common-partner Smads (co-Smads). Smad6 preferentially inhibits Smad signaling initiated by the bone morphogenetic protein (BMP) type I receptors ALK-3 and ALK-6, whereas Smad7 inhibits both transforming growth factor β (TGF-β)- and BMP-induced Smad signaling. I-Smads also regulate some non-Smad signaling pathways. Here, we discuss the vertebrate I-Smads, their roles as inhibitors of Smad activation and regulators of receptor stability, as scaffolds for non-Smad signaling, and their possible roles in the nucleus. We also discuss the posttranslational modification of I-Smads, including phosphorylation, ubiquitylation, acetylation, and methylation.

Differential modulation of Helicobacter pylori lipopolysaccharide-mediated TLR2 signaling by individual Pellino proteins

BACKGROUND

Eradication rates for current H. pylori therapies have fallen in recent years, in line with the emergence of antibiotic resistant infections. The development of therapeutic alternatives to antibiotics, such as immunomodulatory therapy and vaccines, requires a more lucid understanding of host-pathogen interactions, including the relationships between the organism and the innate immune response. Pellino proteins are emerging as key regulators of immune signaling, including the Toll-like receptor pathways known to be regulated by H. pylori. The aim of this study was to characterize the role of Pellino proteins in the innate immune response to H. pylori lipopolysaccharide.

MATERIALS AND METHODS

Gain-of-function and loss-of-function approaches were utilized to elucidate the role of individual Pellino proteins in the Toll-like receptor 2-mediated response to H. pylori LPS by monitoring NF-ĸB activation and the induction of proinflammatory chemokines. Expression of Pellino family members was investigated in gastric epithelial cells and gastric tissue biopsy material.

RESULTS

Pellino1 and Pellino2 positively regulated Toll-like receptor 2-driven responses to H. pylori LPS, whereas Pellino3 exerted a negative modulatory role. Expression of Pellino1 was significantly higher than Pellino3 in gastric epithelial cells and gastric tissue. Furthermore, Pellino1 expression was further augmented in gastric epithelial cells in response to infection with H. pylori or stimulation with H. pylori LPS.

CONCLUSIONS

The combination of low Pellino3 levels together with high and inducible Pellino1 expression may be an important determinant of the degree of inflammation triggered upon Toll-like receptor 2 engagement by H. pylori and/or its components, contributing to H. pylori-associated pathogenesis by directing the incoming signal toward an NF-kB-mediated proinflammatory response.

Bone Morphogenetic Protein 9 Enhances Lipopolysaccharide-Induced Leukocyte Recruitment to the Vascular Endothelium

Bone morphogenetic protein (BMP)9 is a circulating growth factor that is part of the TGF-β superfamily and is an essential regulator of vascular endothelial homeostasis. Previous studies have suggested a role for BMP9 signaling in leukocyte recruitment to the endothelium, but the directionality of this effect and underlying mechanisms have not been elucidated. In this study, we report that BMP9 upregulates TLR4 expression in human endothelial cells and that BMP9 pretreatment synergistically increases human neutrophil recruitment to LPS-stimulated human endothelial monolayers in an in vitro flow adhesion assay. BMP9 alone did not induce neutrophil recruitment to the endothelium. We also show that E-selectin and VCAM-1, but not ICAM-1, are upregulated in response to BMP9 in LPS-stimulated human endothelial cells. Small interfering RNA knockdown of activin receptor-like kinase 1 inhibited the BMP9-induced expression of TLR4 and VCAM-1 and inhibited BMP9-induced human neutrophil recruitment to LPS-stimulated human endothelial cells. BMP9 treatment also increased leukocyte recruitment within the pulmonary circulation in a mouse acute endotoxemia model. These results demonstrate that although BMP9 alone does not influence leukocyte recruitment, it primes the vascular endothelium to mount a more intense response when challenged with LPS through an increase in TLR4, E-selectin, and VCAM-1 and ultimately through enhanced leukocyte recruitment.

Peptide inhibition of p22phox and Rubicon interaction as a therapeutic strategy for septic shock

Sepsis is a clinical syndrome that complicates severe infection and is characterized by the systemic inflammatory response syndrome (SIRS), is a life threatening disease characterized by inflammation of the entire body. Upon microbial infection, p22phox-gp91phox NADPH oxidase (NOX) complexes produce reactive oxygen species (ROS) that are critical for the elimination of invading microbes. However, excess production of ROS represents a key element in the cascade of deleterious processes in sepsis. We have previously reported direct crosstalk between autophagy and phagocytosis machineries by demonstrating that the Rubicon protein interacts with p22phox upon microbial infection, facilitating phagosomal trafficking of the p22phox-gp91phox NOX complex to induce a ROS burst, inflammatory cytokine production, and thereby, potent anti-microbial activities. Here, we showed N8 peptide, an N-terminal 8-amino acid peptide derived from p22phox, was sufficient for Rubicon interaction and thus, capable of robustly blocking the Rubicon-p22phox interaction and profoundly suppressing ROS and inflammatory cytokine production. Consequently, treatment with the Tat-N8 peptide or a N8 peptide-mimetic small-molecule dramatically reduced the mortality associated with Cecal-Ligation-and-Puncture-induced polymicrobial sepsis in mice. This study demonstrates a new anti-sepsis therapeutic strategy by blocking the crosstalk between autophagy and phagocytosis innate immunity machineries, representing a potential paradigm shift for urgently needed therapeutic intervention against this life-threatening SIRS.

IL-27 enhances innate immunity of human pulmonary fibroblasts and epithelial cells through upregulation of TLR4 expression

Lung tissue cells play an active role in the pathogenesis of pulmonary inflammatory diseases by releasing a variety of cytokines and chemokines. However, how lung tissue cells respond to microbial stimuli during pulmonary infections remains unclear. In this study, we found that patients with community-acquired pneumonia displayed increased IL-27 levels in bronchoalveolar lavage fluid and serum. We subsequently examined the immunopathological mechanisms for the activation of primary human lung fibroblasts and bronchial epithelial cells by IL-27. We demonstrated that IL-27 priming enhanced LPS-induced production of IL-6 and IL-8 from lung fibroblasts and bronchial epithelia cells via upregulating Toll-like receptor-4 (TLR4) expression. IL-27 upregulated TLR4 expression in lung fibroblasts through activation of Janus-activated kinase (JAK) and Jun NH2-terminal kinase (JNK) signaling pathways, and inhibition of the JAK pathway could partially decrease IL-27-induced TLR4 expression, while inhibition of JNK pathway could completely suppress IL-27-induced TLR4 expression. Our data suggest that IL-27 modulates innate immunity of lung tissue cells through upregulating TLR4 expression during pulmonary infections.

Pellino-1 Positively Regulates Toll-like Receptor (TLR) 2 and TLR4 Signaling and Is Suppressed upon Induction of Endotoxin Tolerance

Endotoxin tolerance reprograms Toll-like receptor (TLR) 4-mediated macrophage responses by attenuating induction of proinflammatory cytokines while retaining expression of anti-inflammatory and antimicrobial mediators. We previously demonstrated deficient TLR4-induced activation of IL-1 receptor-associated kinase (IRAK) 4, IRAK1, and TANK-binding kinase (TBK) 1 as critical hallmarks of endotoxin tolerance, but mechanisms remain unclear. In this study, we examined the role of the E3 ubiquitin ligase Pellino-1 in endotoxin tolerance and TLR signaling. LPS stimulation increased Pellino-1 mRNA and protein expression in macrophages from mice injected with saline and in medium-pretreated human monocytes, THP-1, and MonoMac-6 cells, whereas endotoxin tolerization abrogated LPS inducibility of Pellino-1. Overexpression of Pellino-1 in 293/TLR2 and 293/TLR4/MD2 cells enhanced TLR2- and TLR4-induced nuclear factor κB (NF-κB) and expression of IL-8 mRNA, whereas Pellino-1 knockdown reduced these responses. Pellino-1 ablation in THP-1 cells impaired induction of myeloid differentiation primary response protein (MyD88), and Toll-IL-1R domain-containing adapter inducing IFN-β (TRIF)-dependent cytokine genes in response to TLR4 and TLR2 agonists and heat-killed Escherichia coli and Staphylococcus aureus, whereas only weakly affecting phagocytosis of heat-killed bacteria. Co-expressed Pellino-1 potentiated NF-κB activation driven by transfected MyD88, TRIF, IRAK1, TBK1, TGF-β-activated kinase (TAK) 1, and TNFR-associated factor 6, whereas not affecting p65-induced responses. Mechanistically, Pellino-1 increased LPS-driven K63-linked polyubiquitination of IRAK1, TBK1, TAK1, and phosphorylation of TBK1 and IFN regulatory factor 3. These results reveal a novel mechanism by which endotoxin tolerance re-programs TLR4 signaling via suppression of Pellino-1, a positive regulator of MyD88- and TRIF-dependent signaling that promotes K63-linked polyubiquitination of IRAK1, TBK1, and TAK1.