TLR4/MyD88 -mediated CCL2 production by lipopolysaccharide (endotoxin): Implications for metabolic inflammation
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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.
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.
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.
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.
American Type Culture Collection
Chemokine (C-C motif) ligand −2
Enzyme-linked immunosorbent assay
Mitogen-activated protein kinase
Myeloid differentiation factor 88
Peripheral blood mononuclear cells
Polymerase chain reaction
Secreted embryonic alkaline phosphatase
A human monocytic cell line
Tumor necrosis factor-alpha
This study was financially supported by Kuwait Foundation for the Advancement of Sciences (KFAS). Grant # RC14016001 (RA-AM-2017-007).
NA performed experiments, analyzed the data and participated in writing the paper. AW, SS, and SK participated in performing experiments. AH contributed in scientific discussions and critically reviewed/edited the manuscript. SA participated in arranging data and preparing graphs. JT critically reviewed and commented the manuscript. SS participated in designing experiments. RA conceived the idea, designed the experiments, analyzed the data, and wrote the manuscript.
Compliance with ethical standards
The authors declare that they have no competing interests.
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