[HTML][HTML] The cooperative induction of CCL4 in human monocytic cells by TNF-α and palmitate requires MyD88 and involves MAPK/NF-κB signaling pathways

S Sindhu, S Kochumon, S Shenouda, A Wilson… - International journal of …, 2019 - mdpi.com
S Sindhu, S Kochumon, S Shenouda, A Wilson, F Al-Mulla, R Ahmad
International journal of molecular sciences, 2019mdpi.com
Chronic low-grade inflammation, also known as metabolic inflammation, is a hallmark of
obesity and parallels with the presence of elevated circulatory levels of free fatty acids and
inflammatory cytokines/chemokines. CCL4/MIP-1β chemokine plays a key role in the
adipose tissue monocyte recruitment. Increased circulatory levels of TNF-α, palmitate and
CCL4 are co-expressed in obesity. We asked if the TNF-α/palmitate could interact
cooperatively to augment the CCL4 production in human monocytic cells and macrophages …
Chronic low-grade inflammation, also known as metabolic inflammation, is a hallmark of obesity and parallels with the presence of elevated circulatory levels of free fatty acids and inflammatory cytokines/chemokines. CCL4/MIP-1β chemokine plays a key role in the adipose tissue monocyte recruitment. Increased circulatory levels of TNF-α, palmitate and CCL4 are co-expressed in obesity. We asked if the TNF-α/palmitate could interact cooperatively to augment the CCL4 production in human monocytic cells and macrophages. THP-1 cells/primary macrophages were co-treated with TNF-α/palmitate and CCL4 mRNA/protein expression was assessed using qRT-PCR/ELISA. TLR4 siRNA, a TLR4 receptor-blocking antibody, XBlue™-defMyD cells and pathway inhibitors were used to decipher the signaling mechanisms. We found that TNF-α/palmitate co-stimulation augmented the CCL4 expression in monocytic cells and macrophages compared to controls (p < 0.05). TLR4 suppression or neutralization abrogated the CCL4 expression in monocytic cells. Notably, CCL4 cooperative induction in monocytic cells was: (1) Markedly less in MyD88-deficient cells, (2) IRF3 independent, (3) clathrin dependent and (4) associated with the signaling mechanism involving ERK1/2, c-Jun, JNK and NF-κB. In conclusion, TNF-α/palmitate co-stimulation promotes the CCL4 expression in human monocytic cells through the mechanism involving a TLR4-MyD88 axis and MAPK/NF-κB pathways. These findings unravel a novel mechanism of the cooperative induction of CCL4 by TNF-α and palmitate which could be relevant to metabolic inflammation.
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