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TNF-? in Combination with Palmitate Enhances IL-8 Production via The MyD88- Independent TLR4 Signaling Pathway: Potential Relevance to Metabolic Inflammation.

ABSTRACT: Elevated levels of IL-8 (CXCL8) in obesity have been linked with insulin resistance and type 2 diabetes (T2D). The mechanisms that lead to the profound production of IL-8 in obesity remains to be understood. TNF-? and saturated free fatty acids (FFAs) are increased in obese humans and correlate with insulin resistance. Hence, we sought to investigate whether the cooccurrence of TNF-? and FFAs led to increase the production of IL-8 by human monocytes. We found that co-stimulation of human monocytes with palmitate and TNF-? led to increased IL-8 production as compared to those stimulated with palmitate or TNF-? alone. The synergistic production of IL-8 by TNF-?/palmitate was suppressed by neutralizing anti- Toll like receptor 4 (TLR4) antibody and by genetic silencing of TLR4. Both MyD88-deficient and MyD88-competent cells responded comparably to TNF-?/Palmitate. However, TIR-domain-containing adapter-inducing interferon (TRIF) inhibition or interferon regulatory transcription factor 3 (IRF3) knockdown partly blocked the synergistic production of IL-8. Our human data show that increased adipose tissue TNF-? expression correlated positively with IL-8 expression (r = 0.49, P = 0.001). IL-8 and TNF-? correlated positively with macrophage markers including CD68, CD163 and CD86 in adipose tissue. These findings suggest that the signaling cross-talk between saturated fatty acid palmitate and TNF-? may be a key driver in obesity-associated chronic inflammation via an excessive production of IL-8.

SUBMITTER: Hasan A

PROVIDER: S-EPMC6747275 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature

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TNF-α in Combination with Palmitate Enhances IL-8 Production via The MyD88- Independent TLR4 Signaling Pathway: Potential Relevance to Metabolic Inflammation.

Hasan Amal A Akhter Nadeem N Al-Roub Areej A Thomas Reeby R Kochumon Shihab S Wilson Ajit A Koshy Merin M Al-Ozairi Ebaa E Al-Mulla Fahd F Ahmad Rasheed R

International journal of molecular sciences 20190823 17

Elevated levels of IL-8 (CXCL8) in obesity have been linked with insulin resistance and type 2 diabetes (T2D). The mechanisms that lead to the profound production of IL-8 in obesity remains to be understood. TNF-α and saturated free fatty acids (FFAs) are increased in obese humans and correlate with insulin resistance. Hence, we sought to investigate whether the cooccurrence of TNF-α and FFAs led to increase the production of IL-8 by human monocytes. We found that co-stimulation of human monocyt ...[more]

PMID: 31443599

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Project description:IntroductionToll-like receptor (TLR)4 promotes joint inflammation in mice. Despite that several studies report a functional link between TLR4 and interleukin-(IL-)1? in arthritis, TLR4-mediated regulation of the complicated cytokine network in arthritis is poorly understood. To address this, we investigated the mechanisms by which TLR4 regulates the cytokine network in antibody-induced arthritis.MethodsTo induce arthritis, we injected mice with K/BxN serum. TLR4-mediated pathogenesis in antibody-induced arthritis was explored by measuring joint inflammation, cytokine levels and histological alteration.ResultsCompared to wild type (WT) mice, TLR4-/- mice showed attenuated arthritis and low interferon (IFN)-?, IL-12p35 and IL-1? transcript levels in the joints, but high transforming growth factor (TGF)-? expression. Injection of lipopolysaccharide (LPS) enhanced arthritis and exaggerated joint cytokine alterations in WT, but not TLR4-/- or IL-12p35-/- mice. Moreover, STAT4 phosphorylation in joint cells and intracellular IL-12p35 expression in macrophages, mast cells and Gr-1+ cells were detected in WT mice with arthritis and enhanced by LPS injection. Therefore, IL-12p35 appears to act downstream of TLR4 in antibody-induced arthritis. TLR4-mediated IL-12 production enhanced IFN-? and IL-1? production via T-bet and pro-IL-1? production. Recombinant IL-12, IFN-? and IL-1? administration restored arthritis, but reduced joint TGF-? levels in TLR4-/- mice. Moreover, a TGF-? blockade restored arthritis in TLR4-/- mice. Adoptive transfer of TLR4-deficient macrophages and mast cells minimally altered joint inflammation and cytokine levels in macrophage- and mast cell-depleted WT mice, respectively, whereas transfer of WT macrophages or mast cells restored joint inflammation and cytokine expression. Gr-1+ cell-depleted splenocytes partially restored arthritis in TLR4-/- mice.ConclusionTLR4-mediated IL-12 production by joint macrophages, mast cells and Gr-1+ cells enhances IFN-? and IL-1? production, which suppresses TGF-? production, thereby promoting antibody-induced arthritis.

Project description:BACKGROUND:Previous studies indicate that soyasaponins may reduce inflammation via modulating toll-like receptor 4 (TLR4)/myeloid differentiation factor 88 (MyD88) signaling. However, its underlying mechanisms are still not fully understood. METHODS:Lipopolysaccharide (LPS)-challenged inflamed male ICR mice were intervened by intragastrical administration with 10 and 20??mol/kg·BW of soyasaponin A1, A2 or I for 8?weeks. The serum inflammatory markers were determined by commercial kits and the expression of molecules in TLR4/MyD88 signaling pathway in liver by real-time PCR and western blotting. The recruitments of TLR4 and MyD88 into lipid rafts of live tissue lysates were detected by sucrose gradient ultracentrifugation and western blotting. LPS-stimulated RAW264.7 macrophages were treated with 10, 20 and 40??mol/L of soyasaponin A1, A2 or I for 2?h. MyD88-overexpressed HEK293T cells were treated with 20 and 40??mol/L of soyasaponins (A1, A2 or I) or 20??mol/L of ST2825 (a MyD88 inhibitor) for 6?h. The expression of molecules in TLR4/MyD88 signaling pathway were determined by western blotting. Data were analyzed by using one way analysis of variance or t-test by SPSS 20.0 statistical software. RESULTS:Soyasaponins A1, A2 or I significantly reduced the levels of tumor necrosis factor alpha (TNF?), interleukin (IL)-6 and nitric oxide (NO) in serum (p?<?0.05), and decreased the mRNA levels of TNF?, IL-6, IL-1?, cyclooxygenase 2 (COX-2) and inducible nitric oxide synthase (iNOS) (p?<?0.05), the protein levels of myeloid differentiation protein 2 (MD-2), TLR4, MyD88, toll-interleukin1 receptor domain containing adaptor protein (TIRAP), phosphorylated interleukin-1 receptor-associated kinase 4 (p-IRAK-4), phosphorylated interleukin-1 receptor-associated kinase 1 (p-IRAK-1) and TNF receptor associated factor 6 (TRAF6) (p?<?0.05), and the recruitments of TLR4 and MyD88 into lipid rafts in liver (p?<?0.05). In LPS-stimulated macrophages, soyasaponins A2 or I significantly decreased MyD88 (p?<?0.05), soyasaponins A1, A2 or I reduced p-IRAK-4 and p-IRAK-1 (p?<?0.05), and soyasaponin I decreased TRAF6 (p?<?0.05). In MyD88-overexpressed HEK293T cells, soyasaponins (A1, A2 or I) and ST2825 significantly decreased MyD88 and TRAF6 (p?<?0.05). CONCLUSION:Soyasaponins can reduce inflammation by downregulating MyD88 expression and suppressing the recruitments of TLR4 and MyD88 into lipid rafts. This study provides novel understanding about the anti-inflammatory mechanism of soyasaponins.

Project description:Background: In spinal cord injury (SCI), systemic inflammation and the death of nerve cells in the spinal cord are life threatening. The connection between gut microbiota and signaling pathways has been a hot research topic in recent years. The Toll-like receptor 4/Myeloid differentiation factor 88 (TLR4/MyD88) signaling pathway is closely related to the inflammatory response. This study explored whether the gut microbiota imbalance could affect the TLR4/MyD88 signaling pathway to regulate SCI to provide a new basis for SCI research and treatment. Methods: An SCI model was constructed to study the influence on the injury of gut microbiota. 16S amplicon sequencing was used to identify the diversity and abundance of gut microbes. Fecal microbiota transplantation was performed in mice with SCI. ELISA was used to detect the serum levels of pro-inflammatory and anti-inflammatory factors in mice. Hematoxylin and eosin staining was used to observe SCI in mice. Immunofluorescence was used to detect the rates of loss glial fibrillary acidic protein (GFAP), neuronal nuclear protein (NeuN), and ionized calcium-binding adapter molecule 1 (IBA1) in the spinal cord as indicators of apoptosis. The expression of the TLR4/MyD88 signaling pathway was detected by qRT-PCR and western blotting. Results: Significant differences were observed in the gut microbiota of SCI mice and normal mice. The gut microbiota of SCI mice was imbalanced. The levels of pro-inflammatory cytokines tumor necrosis factor-α, interleukin (IL)-1β, and IL-6 in SCI mice were increased, as was the level of the toxic induced nitric oxide synthase. The levels of anti-inflammatory factors IL-4, transforming growth factor-β, and IL-10 were decreased, as was the level of arginase-1. The apoptosis rates of GFAP, NeuN, and IBA1 were increased. The TLR4/MyD88 signaling pathway was activated. In the SCI group, inflammation increased after fecal transplantation, apoptosis of GFAP, NeuN, and IBA1 increased, and SCI was more serious. Conclusion: The TLR4/MyD88 signaling pathway promotes the death of nerve cells by inducing inflammation. Gut microbiota dysregulation can lead to aggravated SCI by activating the TLR4/MyD88 signaling pathway.

Dataset Information

TNF-? in Combination with Palmitate Enhances IL-8 Production via The MyD88- Independent TLR4 Signaling Pathway: Potential Relevance to Metabolic Inflammation.

Publications

TNF-α in Combination with Palmitate Enhances IL-8 Production via The MyD88- Independent TLR4 Signaling Pathway: Potential Relevance to Metabolic Inflammation.

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