TLR4/MyD88 -mediated CCL2 production by lipopolysaccharide (endotoxin): Implications for metabolic inflammation

Abstract

Background Obese human and mice were reported to have higher circularity endotoxin (LPS) levels as compared to their lean counter parts. The current study was aimed to reveal the molecular mechanisms underlying the LPS mediated induction of CCL2 in human monocytes/macrophages. Methods Human monocytic cell line THP-1, THP-1 cells derived macrophages and primary macrophages were treated with LPS and TNF-α (positive control). CCL2 expression was determined with real-time RT-PCR and ELISA. THP-1-XBlue™ cells, THP-1-XBlue™-defMyD cells, TLR4 neutralization antibody, TLR4 siRNA and inhibitors for NF-kB and MAPK were used to study the signaling pathways. Phosphorylation of NF-kB and c-Jun was analyzed by ELISA. Results LPS upregulates CCL2 expression at both mRNA (THP-1: 23.40 ± .071 Fold, P < 0.0001; THP-1-derived macrophages: 103 ± 0.56 Fold, < 0.0001; Primary macrophages: 48 ± 1.41 Fold, P < 0.0005) and protein (THP1 monocytes:1048 ± 5.67 pg/ml, P < 0.0001; THP-1-derived macrophages; 2014 ± 2.12, P = 0.0001; Primary macrophages: 859.5 ± 3.54, P < 0.0001) levels in human monocytic cells/macrophages. Neutralization of TLR4 blocked LPS-induced CCL-2 secretion ( P < 0.0001). Silencing of TLR4 by siRNA also significantly reduced LPS-induced CCL-2 production. Furthermore, MyD88-Knockout cells treated with LPS did not produce CCL-2. NF-kB and c-Jun phosphorylation was noted in LPS treated cells. Conclusion Overall, our data reveal that LPS induces CCL-2 in monocytes/macrophages via TLR4/MyD88 signaling which leads to the activation of NF-kB/AP-1 transcription factors.

Polygonatum sibiricum polysaccharides prevent LPS‑induced acute lung injury by inhibiting inflammation via the TLR4/Myd88/NF‑κB pathway

“…In theory, regarding the underlying dynamics of inflammatory effects upon ALI, LPS enters the body and is recognized by lipopolysaccharide-binding protein (LBP), and then binds to cluster of differentiation 14 (CD14) to form the LPS/LBP/CD14 complex, which can induce inflammation through multiple signal transduction pathways to ultimately release a large amount of inflammation factors. This release causes lung damage, of which TLR4/Myd88/NF-κB is one of the most critical pathways (31,32). Our results also indicated that PSPs decreased LPS-induced increases in mRNA expression of inflammatory factors, and of TLR4, Myd88, p-IKB-α/IKB-α and p-p65/p65 proteins in lung tissue.…”

Transcriptional re-programming in rat central nervous system two weeks after burn trauma: the impact of nephrilin treatment on the expression of oxidative stress-related genes

“…Some genes whose transcripts were elevated by burn injury in this study have been shown to cluster into well-characterised regulons. The TLR4/MyD88 regulon is known to regulate production of ROS, immunosuppression and chronic inflammation in response to lipopolysaccharide challenge via NOX4, ARG1 and CCL2, 50 – 52 three genes whose burn trauma-induced elevations were not reversed by nephrilin in the current study. One possible line of investigation suggested by this result is co-treatment of thermal insult with both nephrilin and a modifier of TLR4 signalling such as fenofibric acid.…”

Anti-inflammatory activities of puerarin in high-fat diet-fed rats with streptozotocin-induced gestational diabetes mellitus

“…TLR4 is known to trigger the inflammatory response by activating the NF-κB pathway, which leads to the production of inflammatory mediators [ 34 – 36 ]. Activated TLR4 subsequently transmits inflammatory signals through the adaptor protein MyD88 [ 37 , 38 ]. The MyD88-dependent signalling pathway activated NF-κB to induce the inflammatory cytokine TNF-α [ 39 ].…”