Role of TRAF6 from obscure puffer (Takifugu obscurus) in immune response against Edwardsiella tarda infection

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is a vital molecule of inflammatory signaling pathways in innate immune response against pathogens. To elucidate its role in defense against Edwardsiella tarda infection in teleost fish, TRAF6 homologue was identified from obscure puffer (Takifugu obscurus) and functionally analyzed in this study. The obscure puffer TRAF6 (ToTRAF6) is a protein of 565 amino acids containing conserved RING domain, zinc finger-TRAF and MATH_TRAF6 domain. ToTRAF6 mRNA distributed in various healthy tissues of obscure puffer and was upregulated in the immune related tissues after E. tarda infection. ToTRAF6 protein was localized in the cytoplasm and aggregate as dots around the nuclei in FHM cells. The overexpression of ToTRAF6 in FHM cells decreased the quantity of E. tarda and induced the significant upregulation of downstream MAPK signaling pathway genes. These data suggest that ToTRAF6 is a key molecule of MAPK signaling pathway in defense against E. tarda infection.

Associations of Gastrointestinal Tract Tumor Necrosis Factor Receptor-Associated Factor 6 Expression with Clinical Features and Prognosis of Eosinophilic Gastroenteritis

BACKGROUND

Few studies have been conducted to explore the expression of tumor necrosis factor receptor-associated factor 6 in eosinophilic gastroenteritis patients. Therefore, the expression profile of tumor necrosis factor receptor-associated factor 6 in the gastrointestinal tract of eosinophilic gastroenteritis patients and its associations with clinical features were explored in this study.

METHODS

Thirty-four eosinophilic gastroenteritis patients who presented in Ruijin Hospital from December 2012 to May 2019 and had accepted gastrointestinal endoscopic examinations were recruited. Medical records and endoscopic biopsies were collected, and the prognosis was followed up by telephone. Healthy persons were selected as the control group. Hematoxylin and eosin and immunohistochemical staining were performed in both eosinophilic gastroenteritis patients and healthy persons. The final results were analyzed by skilled pathologists, and mean optical density values of tumor necrosis factor receptor-associated factor 6 were calculated by Image J software. Final results were analyzed by Statistical Package for the Social Sciences software 22.0.

RESULTS

Thirty-four patients (mean age: 25.56 ± 21.14 years, 61.76% males) were recruited for this study. There was no significant difference in tumor necrosis factor receptor-associated factor 6 mean optical density values of gastric tissues in eosinophilic gastroenteritis patients and healthy people (0.22 ± 0.16 vs. 0.14 ± 0.05, P > .05). Eosinophilic gastroenteritis patients had a significantly lower level of intestinal tumor necrosis factor receptor-associated factor 6 mean optical density values than that of healthy people (0.16 ± 0.05 vs. 0.23 ± 0.06, P < .05). Intestinal tumor necrosis factor receptor-associated factor 6 mean optical density values negatively linearly correlated with serum interleukin-10 level (r = -0.618, P = .043 < .05). There were no differences between eosinophilic gastroenteritis patients with or without relapse regarding the expression level of intestinal tumor necrosis factor receptor-associated factor 6 (P = .227 > .05).

CONCLUSION

Patients with eosinophilic gastroenteritis might have a deficiency of intestinal tumor necrosis factor receptor-associated factor 6 compared to healthy controls.

An enriched environment reduces hippocampal inflammatory response and improves cognitive function in a mouse model of stroke

An enriched environment is used as a behavioral intervention therapy that applies sensory, motor, and social stimulation, and has been used in basic and clinical research of various neurological diseases. In this study, we established mouse models of photothrombotic stroke and, 24 hours later, raised them in a standard, enriched, or isolated environment for 4 weeks. Compared with the mice raised in a standard environment, the cognitive function of mice raised in an enriched environment was better and the pathological damage in the hippocampal CA1 region was remarkably alleviated. Furthermore, protein expression levels of tumor necrosis factor receptor-associated factor 6, nuclear factor κB p65, interleukin-6, and tumor necrosis factor α, and the mRNA expression level of tumor necrosis factor receptor-associated factor 6 were greatly lower, while the expression level of miR-146a-5p was higher. Compared with the mice raised in a standard environment, changes in these indices in mice raised in an isolated environment were opposite to mice raised in an enriched environment. These findings suggest that different living environments affect the hippocampal inflammatory response and cognitive function in a mouse model of stroke. An enriched environment can improve cognitive function following stroke through up-regulation of miR-146a-5p expression and a reduction in the inflammatory response.

Resveratrol Enhances Wound Healing in Type 1 Diabetes Mellitus by Promoting the Expression of Extracellular Vesicle-Carried MicroRNA-129 Derived from Mesenchymal Stem Cells

Recent studies have shown the promotive effect of resveratrol on wound healing. This study aims to explore the underlying molecular mechanism of resveratrol in type 1 diabetes mellitus (T1DM) through microRNA (miR)-129-containing extracellular vesicles (EVs) derived from mesenchymal stem cells (MSCs) based on in silico analysis. The rat model of T1DM was established by intraperitoneal injection of sodium citrate containing streptozotocin, and the wound was made around the deep fascia. Rat MSCs were isolated and treated with resveratrol (SRT501), and the corresponding EVs (SRT501-EVs) were isolated, where the expression of miR-129 was determined. By performing function experiments, the effect of SRT501-EVs and miR-129 on the biological functions of human umbilical vein endothelial cells (HUVECs) was determined. Finally, the binding relationship between miR-129 and tumor necrosis factor receptor-associated factor 6 (TRAF6) was also determined by the dual-luciferase reporter gene assay. miR-129 was shown as a candidate related to both resveratrol and wound healing in T1DM. SRT501-EVs promoted the skin wound healing of T1DM rats and also further improved the proliferative, migratory, and tube formation potentials of HUVECs. Resveratrol inhibited the expression of TRAF6 in HUVECs stimulated by MSC-conditioned medium and promoted the transfer of miR-129 via EVs, while TRAF6 was confirmed as a target gene of miR-129. Furthermore, inhibition of miR-129 attenuated the proangiogenic effect of resveratrol on HUVECs. Resveratrol exerts promotive role in wound healing in T1DM through downregulation of TRAF6 via MSC-EV-carried miR-129, suggesting a regulatory network involved in the wound healing process in T1DM.

MicroRNA-602 prevents the development of inflammatory bowel diseases in a microbiota-dependent manner

Inflammatory bowel diseases (IBD) are a group of chronic disorders occurring in the intestinal tract. Previous studies demonstrated that genetics and microbiota play critical roles in the pathogenesis of IBD. Discoveries of genes that may regulate the homeostasis of gut microbiota and pathogenesis of IBD have the potential to provide new therapeutic targets for IBD treatment. The results suggested that the expression level of microRNA (miR)-602 is negatively related to the development of IBD, and that miR-602 overexpression in mice may prevent inflammation and intestinal barrier injuries in dextran sulfate sodium (DSS)-induced IBD mice. It was also found that the microbiota is important for miR-602-mediated prevention of IBD, as the inhibitory effect of miR-602 was lost when the microbiota was depleted using antibiotics. Furthermore, co-housing or adoptive transfer of microbiota from miR-602 could attenuate the pathogenesis of IBD. In addition, it was demonstrated that miR-602 could target tumor necrosis factor receptor-associated factor 6 (TRAF6) in intestinal epithelial cells. Collectively, the present results suggest that miR-602 plays a protective role in DSS-induced IBD by targeting TRAF6 in a microbiota-dependent manner.

The Effect of miR-361-3p Targeting TRAF6 on Apoptosis of Multiple Myeloma Cells

microRNA-361-3p (miR-361-3p) is involved in the carcinogenesis of oral cancer and pancreatic catheter adenocarcinoma, and has anti-carcinogenic effects on non-small cell lung cancer (NSCLC). However, its effect on multiple myeloma (MM) is less reported. Here, we found that upregulating the expression of miR-361-3p inhibited MM cell viability and promoted MM apoptosis. We measured expressions of tumor necrosis factor receptor-associated factor 6 (TRAF6) and miR-361-3p in MM cells and detected the viability, colony formation rate, and apoptosis of MM cells. In addition, we measured expressions of apoptosis-related genes Bcl-2, Bax, and Cleaved caspase-3 (C caspase-3). The binding site between miR-361-3p and TRAF6 was predicted by TargetScan. Our results showed that miR-361-3p was low expressed in the plasma of MM patients and cell lines, while its overexpression inhibited viability and colony formation of MM cells and increased the cell apoptosis. Furthermore, TRAF6, which was predicted to be a target gene of miR-361-3p, was highexpressed in the plasma of patients and cell lines with MM. Rescue experiments demonstrated that the effect of TRAF6 on MM cells was opposite to that of miR-361-3p. Upregulation of miR-361-3p induced apoptosis and inhibited the proliferation of MM cells through targeting TRAF6, suggesting that miR-361-3p might be a potential target for MM therapy.

Targeting spinal TRAF6 expression attenuates chronic visceral pain in adult rats with neonatal colonic inflammation

Background

Irritable bowel syndrome is one of the most common gastrointestinal disorders. It is featured by abdominal pain in conjunction with altered bowel habits. However, the pathophysiology of the syndrome remains largely unknown. Tumor necrosis factor receptor-associated factor 6 (TRAF6) has been reported to be involved in neuropathic pain. The aim of this study was to investigate roles and mechanisms of TRAF6 in the chronic visceral hypersensitivity.

Methods

Visceral hypersensitivity was induced by neonatal colonic inflammation and was identified by colorectal distention. The protein level, RNA level, and cellular distribution of TRAF6 and its related molecules were detected with Western blot, quantitative polymerase chain reaction, and immunofluorescence. In vitro spinal cord slice recording technique was performed to determine the synaptic transmission activities.

Results

Neonatal colonic inflammation rats displayed visceral hypersensitivity at the age of six weeks. The expression of TRAF6 was obviously upregulated in spinal cord dorsal horn of neonatal colonic inflammation rats at the age of six weeks. Immunofluorescence study showed that TRAF6 was dominantly expressed in spinal astrocytes. Intrathecal injection of TRAF6 small interfering RNA (siRNA) significantly reduced the amplitude of spontaneous excitatory postsynaptic currents at the spinal dorsal horn level. Furthermore, knockdown of TRAF6 led to a significant downregulation of cystathionine β synthetase expression in the spinal dorsal horn of neonatal colonic inflammation rats. Importantly, intrathecal injection of TRAF6 siRNA remarkably alleviated visceral hypersensitivity of neonatal colonic inflammation rats.

Conclusions

Our results suggested that the upregulation of TRAF6 contributed to visceral pain hypersensitivity, which is likely mediated by regulating cystathionine β synthetase expression in the spinal dorsal horn. Our findings suggest that TRAF6 might act as a potential target for the treatment of chronic visceral pain in irritable bowel syndrome patients.

NOD-like receptor X1, tumor necrosis factor receptor-associated factor 6 and NF-κB are associated with clinicopathological characteristics in gastric cancer

Gastric cancer (GC) is a common cancer worldwide and its precise mechanism is largely unknown. The aim of the present study was to evaluate the expression levels of NOD-like receptor X1 (NLRX1), tumor necrosis factor receptor-associated factor 6 (TRAF6) and NF-κB in GC and normal gastric tissue samples to determine the association with the clinicopathological features of GC. GC and adjacent normal gastric tissues from 60 patients with GC were analyzed using immunohistochemistry and western blotting analysis. In addition, the association between NLRX1, TRAF6 and NF-κB expression levels were investigated by Spearman's correlation analysis. The results revealed that NLRX1 protein expression levels were downregulated in the GC tissues compared with the normal gastric tissues (P<0.05). Conversely, TRAF6 and NF-κB protein expression levels were upregulated in the GC tissues compared with the normal gastric tissues (P<0.05). A significant difference was identified between GC patients with high and low expression levels of each protein in the tumor size, vascular invasion, neural invasion, lymph node metastasis, differentiation, gross stage and clinical stage. In addition, a negative correlation was observed between NLRX1 and TRAF6, and NLRX1 and NF-κB expression levels, while a positive correlation was observed between TRAF6 and NF-κB expression levels. In conclusion, NLRX1 expression levels were discovered to be downregulated in GC tissues. The expression levels of NLRX1, TRAF6 and NF-κB were also significantly associated with the clinicopathological characteristics of GC, and the aforementioned results indicated that NLRX1 may be a biomarker in assessing GC.

P22077 inhibits LPS-induced inflammatory response by promoting K48-linked ubiquitination and degradation of TRAF6

Inflammation is a biological process associated with multiple human disorders such as autoimmune diseases and metabolic diseases. Therefore, alleviation of inflammation is important for disease prevention or treatment. Recently, deubiquitinating enzymes (DUBs), especially ubiquitin specific protease-7 (USP7) attracts increasing attention as a potential drug target for inflammation. As an inhibitor of USP7, P22077 has been used to study the roles of USP7 in inflammatory response and neuroblastoma growth. However, the role and precise mechanism of P22077 in anti-inflammatory is still indistinct. In this study, we demonstrated that P22077 could attenuate the release of pro-inflammatory factors including TNF-α, IL-1β, IL-6 and NO, suppress mRNA expression of COX-2 and iNOS, and inhibit activation of NF-κB and MAPKs signaling pathways in Raw264.7 cells and mouse peritoneal macrophages after LPS stimulation. In vivo study showed that P22077 could relieve inflammatory response and reduce the lung injury in C57BL/6 mice with LPS-induced endotoxemia. Mechanically, P22077 might play an anti-inflammatory role by promoting tumor necrosis factor receptor-associated factor 6 (TRAF6) degradation via K48-linked polyubiquitination. These findings provide a rationale for the role of the P22077 in anti-inflammatory pathway and the promising clinical application of P22077 to treat inflammatory diseases.

Effect of TLR4 on the growth of SiHa human cervical cancer cells via the MyD88-TRAF6-TAK1 and NF-κB-cyclin D1-STAT3 signaling pathways

The present study aimed to investigate the effect of Toll-like receptor 4 (TLR4) on SiHa human cervical cancer cells and its potential molecular biological mechanisms. The expression of TLR4 following treatment with lipopolysaccharide (LPS) in in SiHa cervical cancer cells was detected by quantitative polymerase chain reaction (qPCR). LPS-induced cell proliferation and apoptosis were detected by MTT assay as well as staining with propidium iodide (PI) and Annexin V/PI double staining. qPCR was performed to analyze the expression levels of tumor necrosis factor receptor-associated factor 6 (TRAF6) and transforming growth factor-activated kinase 1 (TAK1) genes. Western blot analysis was performed to analyze the expression of myeloid differentiation 88 (MyD88), nuclear factor-κB (NF-κB), cyclin D1 and signal transducer and activator of transcription 3 (STAT3) proteins. In the present study, it was revealed that TLR4 expression in SiHa cervical cancer cells may be upregulated by LPS. Additionally, LPS was able to increase the proliferation of SiHa cells. However, LPS treatment did not have an effect on apoptosis of the cells. In addition, the MyD88-TRAF6-TAK1 and NF-κB-cyclin D1-STAT3 signaling pathways were induced in SiHa cells by LPS. These results suggested the effect of LPS and TLR4 on proliferation of SiHa human cervical cancer cells via the MyD88-TRAF6-TAK1 and NF-κB-cyclin D1-STAT3 signaling pathways.

Ubiquitin-Specific Protease 14 Negatively Regulates Toll-Like Receptor 4-Mediated Signaling and Autophagy Induction by Inhibiting Ubiquitination of TAK1-Binding Protein 2 and Beclin 1

Ubiquitin-specific protease 14 (USP14), one of three proteasome-associated deubiquitinating enzymes, has multifunctional roles in cellular context. Here, we report a novel molecular mechanism and function of USP14 in regulating autophagy induction and nuclear factor-kappa B (NF-κB) activation induced by toll-like receptor (TLR) 4 (TLR4). USP14 interacted with tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6) and interrupted the association of Beclin 1 with TRAF6, leading to inhibition of TRAF6-mediated ubiquitination of Beclin 1. Reduced expression of USP14 in USP14-knockdown (USP14^KD) THP-1 cells enhanced autophagy induction upon TLR4 stimulation as shown by the increased conversion of cytosolic LC3-I to membrane-bound LC3-II. Moreover, USP14^KD human breast carcinoma MDA-MB-231 cells and USP14^KD human hepatic adenocarcinoma SK-HEP-1 cells showed increased cell migration and invasion, indicating that USP14 is negatively implicated in the cancer progression by the inhibition of autophagy induction. Furthermore, we found that USP14 interacted with TAK1-binding protein (TAB) 2 protein and induced deubiquitination of TAB 2, a key factor in the activation of NF-κB. Functionally, overexpression of USP14 suppressed TLR4-induced activation of NF-κB. In contrast, USP14^KD THP-1 cells showed enhanced activation of NF-κB, NF-κB-dependent gene expression, and production of pro-inflammatory cytokines such as IL-6, IL-1β, and tumor necrosis factor-α. Taken together, our data demonstrate that USP14 can negatively regulate autophagy induction by inhibiting Beclin 1 ubiquitination, interrupting association between TRAF6 and Beclin 1, and affecting TLR4-induced activation of NF-κB through deubiquitination of TAB 2 protein.

Blockade of 146b-5p promotes inflammation in atherosclerosis-associated foam cell formation by targeting TRAF6

Atherosclerosis (AS) is a chronic inflammation in response to lipid accumulation. Increasing evidence has demonstrated that numerous microRNAs (miRs) have critical roles in inflammatory responses. A previous study suggested that miR-146b-5p is possibly associated with AS; however, its exact role has remained largely elusive. The present study aimed to investigate the potential role of miR-146b-5p in AS and to explore the underlying mechanism. Fist, the levels of miR-146b-5p were determined in foam cells and clinical specimens from patients with AS by reverse-transcription quantitative PCR. The role of miR-146b-5p in AS was then investigated by using miR-146b-5p inhibitor. The results demonstrated that the expression levels of miR-146b-5p were elevated in the lesions of patients with AS. In addition, the levels of miR-146b-5p in THP-1 cells stimulated with phorbol 12-myristate 13-acetate (100 nM) to induce their differentiation into macrophages were dose- and time-dependently elevated by oxidized low-density lipoprotein treatment applied for inducing foam cell formation. miR-146b-5p was also revealed to directly target tumor necrosis factor receptor-associated factor 6 (TRAF6), which functions as a signal transducer in the nuclear factor-κB (NF-κB) pathway. Furthermore, the present study reported for the first time that miR-146b-5p inhibition promotes the inflammatory response and enhances lipid uptake during foam cell formation. In conclusion, miR-146b-5p inhibition promoted chronic inflammation and had a detrimental role during AS-associated foam cell formation by targeting TRAF6.

The effect of marrow stromal cells on TRAF6 expression levels in myeloma cells

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is an important E3 ubiquitin ligase, which is key to immunity. TRAF6 has been implicated in the invasive growth and metastasis of various types of cancer, including squamous cell carcinoma, gastric cancer, myelodysplastic syndromes and acute myeloid leukemia. In the present study, associations between multiple myeloma (MM) and TRAF6, its downstream component nuclear factor-κB (NF-κB) and bone marrow stromal cells (MSC) were investigated. The TRAF6 protein expression levels of 18 patients were positively correlated with the protein levels of β-2 microglobulin (r²=0.3472; P=0.01) and negatively correlated with albumin protein levels (r²=0.5494; P=0.0004). In vitro expression of the TRAF6 protein, phosphorylated transcription factor p65 and phosphorylated p100 in myeloma cell lines was induced by MSCs from patients with MM. In addition, the in vitro expression of TRAF6 was associated with an enhanced proliferation rate of myeloma cells, which was blocked by silencing TRAF6 using small interfering RNA. Due to the association between the TRAF6-NF-κB signaling pathway in myeloma cells and MSCs, this signaling pathway may be a useful prognostic and therapeutic target in myeloma.

TRAF6 regulates the effects of polarized maturation of tolerability: Marrow-derived dendritic cells on collagen-induced arthritis in mice

The study aimed to investigate the relationship between tumor necrosis factor receptor-associated factor 6 (TRAF6) and a differentially mature dendritic cell (mDC) in collagen-induced arthritis (CIA) mice and to determine whether or not TRAF6 regulates the activation of an immature dendritic cell (iDC) and inhibits iDC maturation to induce immune tolerance. The mouse bone marrow stem cells were induced with recombinant granulocyte-macrophage colony-stimulating factor (rmGM-CSF) and recombinant interleukin-4 (rmIL-4) to differentiate immature dendritic cells (DCs), which were divided into four groups with different maturation states: rmGM-CSF, rmIL-4; TNF-α; LPS; and FK506 group. The levels of the cell surfaces of CD80, CD86, and MHI-II were analyzed by flow cytometry to prove DCs at different levels of maturity. The expression of IL-12 in DCs at different maturation states was detected by enzyme-linked immunosorbent assay (ELISA). The expression of TRAF6 mRNA and protein in each group of DCs was detected by a reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis. The results revealed that the differentiation of bone marrow cells into iDCs was significantly induced by cytokines (rmGM-CSF, IL-4). CD80, CD86, MHC-II were expressed in the four groups, and the difference between them was statistically significant (P<0.05). A higher degree of DC differentiation led to a gradual increase of IL-12 secretion in the four groups. The difference was statistically significant (P<0.05) for this secretion (group D, 10,620.73±276.73 pg/ml). The expression levels of TRAF6 mRNA were significantly higher in group D than those in the other three groups (P<0.01). Although there was no significant difference in the expression levels of TRAF6 mRNA between groups B and C, the expression levels of TRAF6 mRNA between groups B and C were higher than those of the control group. The TRAF6 protein expression was higher in group D than that in the other three groups (P<0.01), and the difference was statistically significant. There was a statistically significant difference in the TRAF6 protein expression between group A and groups B and C, but the expression in group C was higher than that in group B (P<0.01). In conclusion, the expression of co-stimulatory molecules gradually increased in the DCs of different maturation states, and the expression of IL-12, TRAF6 mRNA, and TRAF6 protein positively correlated with the degree of DC maturation. TRAF6 is important in iDC polarity and maturation.

MicroRNA-351 inhibits denervation-induced muscle atrophy by targeting TRAF6

MicroRNAs (miRs) have been observed to be involved in the modulation of various physiopathological processes. However, the impacts of miRNAs on muscle atrophy have not been fully investigated. In the present study, the results demonstrated that miR-351 was differentially expressed in the tibialis anterior (TA) muscle at various times following sciatic nerve transection, and the time-dependent expression profile of miR-351 was inversely correlated with that of tumor necrosis factor receptor-associated factor 6 (TRAF6) at the mRNA and protein levels. The dual luciferase reporter assay indicated that miR-351 was able to significantly downregulate the expression levels of TRAF6 by directly targeting the 3'-untranslated region of TRAF6. Overexpression of miR-351 inhibited a significant decrease in the wet weight ratio or cross-sectional area of the TA muscle following sciatic nerve transection. Western blot analysis indicated that the protein expression levels of TRAF6, muscle ring-finger protein 1 (MuRF1) and muscle atrophy F-box (MAFBx) in denervated TA muscles were suppressed by overexpression of miR-351. These results demonstrate that miR-351 inhibits denervation-induced atrophy of TA muscles following sciatic nerve transection at least partially through negative regulation of TRAF6 as well as MuRF1 and MAFBx, the two downstream signaling molecules of TRAF6.

Tumor Necrosis Factor Receptor-associated Factor 6 Plays a Role in the Inflammatory Responses of Human Periodontal Ligament Fibroblasts to Enterococcus faecalis

INTRODUCTION

Enterococcus faecalis is a frequently isolated microorganism in persistent periapical lesion or secondary infection. However, no evidence has demonstrated that E. faecalis induced inflammation directly in the apical area. This study aimed to explore the mechanism of the inflammatory responses of human periodontal ligament fibroblasts (PDLs) to E. faecalis.

METHODS

PDLs were stimulated with heat-killed E. faecalis (HKEF) or lipoteichoic acid from E. faecalis (LTA) with or without silencing of tumor necrosis factor receptor-associated factor 6 (TRAF6). The expressions of toll-like receptor 2/4, nucleotide-binding oligomerization domain 1/2, and TRAF6 were detected by using quantitative real-time polymerase chain reaction and Western blot. The secretions of proinflammatory cytokines, including interleukin-1β, interleukin-6, interleukin-8, and tumor necrosis factor-α, were determined in the cell supernatants with enzyme-linked immunosorbent assay.

RESULTS

Both HKEF and LTA stimulated the expression of toll-like receptor 2 and TRAF6 in a time-dependent manner. The secretions of proinflammatory cytokines were also increased. After silencing TRAF6, the upregulations of proinflammatory cytokines induced by HKEF or LTA were attenuated.

CONCLUSIONS

TRAF6 plays a pivotal role in inflammation induced by E. faecalis or its LTA in PDLs.

TRAF6-Mediated SM22α K21 Ubiquitination Promotes G6PD Activation and NADPH Production, Contributing to GSH Homeostasis and VSMC Survival In Vitro and In Vivo

RATIONALE

Vascular smooth muscle cell (VSMC) survival under stressful conditions is integral to promoting vascular repair, but facilitates plaque stability during the development of atherosclerosis. The cytoskeleton-associated smooth muscle (SM) 22α protein is involved in the regulation of VSMC phenotypes, whereas the pentose phosphate pathway plays an essential role in cell proliferation through the production of dihydronicotinamide adenine dinucleotide phosphate.

OBJECTIVE

To identify the relationship between dihydronicotinamide adenine dinucleotide phosphate production and SM22α activity in the development and progression of vascular diseases.

METHODS AND RESULTS

We showed that the expression and activity of glucose-6-phosphate dehydrogenase (G6PD) are promoted in platelet-derived growth factor (PDGF)-BB-induced proliferative VSMCs. PDGF-BB induced G6PD membrane translocation and activation in an SM22α K21 ubiquitination-dependent manner. Specifically, the ubiquitinated SM22α interacted with G6PD and mediated G6PD membrane translocation. Furthermore, we found that tumor necrosis factor receptor-associated factor (TRAF) 6 mediated SM22α K21 ubiquitination in a K63-linked manner on PDGF-BB stimulation. Knockdown of TRAF6 decreased the membrane translocation and activity of G6PD, in parallel with reduced SM22α K21 ubiquitination. Elevated levels of activated G6PD consequent to PDGF-BB induction led to increased dihydronicotinamide adenine dinucleotide phosphate generation through stimulation of the pentose phosphate pathway, which enhanced VSMC viability and reduced apoptosis in vivo and in vitro via glutathione homeostasis.

CONCLUSIONS

We provide evidence that TRAF6-induced SM22α ubiquitination maintains VSMC survival through increased G6PD activity and dihydronicotinamide adenine dinucleotide phosphate production. The TRAF6-SM22α-G6PD pathway is a novel mechanism underlying the association between glucose metabolism and VSMC survival, which is beneficial for vascular repair after injury but facilitates atherosclerotic plaque stability.

TGF-β1 inhibits the production of IFN in response to CpG DNA via ubiquitination of TNF receptor-associated factor (TRAF) 6

The effect of TGF-β1 on CpG DNA-induced type I IFN production was examined by reconstituting a series of signaling molecules in TLR 3 signaling. TGF-β1 inhibited CpG DNA-induced IFN-α4 productivity in HeLa cells. Transfection of IFN regulatory factor (IRF)7 but not TNF receptor-associated factor (TRAF)6 and TRAF3 into cells triggered IFN-α4 productivity, and TGF-β1 inhibited IRF7-mediated type I IFN production in the presence of TRAF6. TGF-β1 induced ubiquitination of TRAF6, although CpG DNA did not induce it. Moreover, TGF-β1 accelerated the ubiquitination of TRAF6 in the presence of CpG DNA. TGF-β1 ubiquitinated TRAF6 at K63 but not K48. TGF-β1 also induced ubiquitination of IRF7. Further, TGF-β1 did not impair the interaction of IRF7 and TRAF6. CpG DNA induced the phosphorylation of IRF7 in the presence of TRAF6, whereas TGF-β1 inhibited the IRF7 phosphorylation. Blocking of TRAF6 ubiquitination abolished the inhibition of CpG DNA-induced type I IFN production by TGF-β. Taken together, TGF-β was suggested to inhibit CpG DNA-induced type I IFN production transcriptionally via ubiquitination of TRAF6.

The role of miR-146a in dorsal root ganglia neurons of experimental diabetic peripheral neuropathy

Sensory neurons mediate diabetic peripheral neuropathy. Using a mouse model of diabetic peripheral neuropathy (BKS.Cg-m+/+Lepr(db)/J (db/db) mice) and cultured dorsal root ganglion (DRG) neurons, the present study showed that hyperglycemia downregulated miR-146a expression and elevated interleukin-1 receptor-activated kinase (IRAK1) and tumor necrosis factor receptor-associated factor 6 (TRAF6) levels in DRG neurons. In vitro, elevation of miR-146a by miR-146a mimics in DRG neurons increased neuronal survival under high-glucose conditions. Downregulation and elevation of miR-146a in DRG neurons, respectively, were inversely related to IRAK1 and TRAF6 levels. Treatment of diabetic peripheral neuropathy with sildenafil, a phosphodiesterase type 5 inhibitor, augmented miR-146a expression and decreased levels of IRAK1 and TRAF6 in the DRG neurons. In vitro, blockage of miR-146a in DRG neurons abolished the effect of sildenafil on DRG neuron protection and downregulation of IRAK1 and TRAF6 proteins under hyperglycemia. Our data provide the first evidence showing that miR-146a plays an important role in mediating DRG neuron apoptosis under hyperglycemic conditions.

Unique features of chicken Toll-like receptors

Toll-like receptors (TLRs) are a major class of innate immune pattern recognition receptors that have a key role in immune homeostasis and the defense against infections. The research explosion that followed the discovery of TLRs more than a decade ago has boosted fundamental knowledge on the function of the immune system and the resistance against disease, providing a rational for clinical modulation of the immune response. In addition, the conserved nature of the ancient TLR system throughout the animal kingdom has enabled a comparative biology approach to understand the evolution, structural architecture, and function of TLRs. In the present review we focus on TLR biology in the avian species, and, especially, on the unique functional properties of the chicken TLR repertoire.