MIP-1? Expression Induced by Co-Stimulation of Human Monocytic Cells with Palmitate and TNF-? Involves the TLR4-IRF3 Pathway and Is Amplified by Oxidative Stress.

ABSTRACT: Metabolic inflammation is associated with increased expression of saturated free fatty acids, proinflammatory cytokines, chemokines, and adipose oxidative stress. Macrophage inflammatory protein (MIP)-1? recruits the inflammatory cells such as monocytes, macrophages, and neutrophils in the adipose tissue; however, the mechanisms promoting the MIP-1? expression remain unclear. We hypothesized that MIP-1? co-induced by palmitate and tumor necrosis factor (TNF)-? in monocytic cells/macrophages could be further enhanced in the presence of reactive oxygen species (ROS)-mediated oxidative stress. To investigate this, THP-1 monocytic cells and primary human macrophages were co-stimulated with palmitate and TNF-? and mRNA and protein levels of MIP-1? were measured by using quantitative reverse transcription, polymerase chain reaction (qRT-PCR) and commercial enzyme-linked immunosorbent assays (ELISA), respectively. The cognate receptor of palmitate, toll-like receptor (TLR)-4, was blunted by genetic ablation, neutralization, and chemical inhibition. The involvement of TLR4-downstream pathways, interferon regulatory factor (IRF)-3 or myeloid differentiation (MyD)-88 factor, was determined using IRF3-siRNA or MyD88-deficient cells. Oxidative stress was induced in cells by hydrogen peroxide (H2O2) treatment and ROS induction was measured by dichloro-dihydro-fluorescein diacetate (DCFH-DA) assay. The data show that MIP-1? gene/protein expression was upregulated in cells co-stimulated with palmitate/TNF-? compared to those stimulated with either palmitate or TNF-? (P < 0.05). Further, TLR4-IRF3 pathway was implicated in the cooperative induction of MIP-1? in THP-1 cells, and this cooperativity between palmitate and TNF-? was clathrin-dependent and also required signaling through c-Jun and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-?B). Notably, ROS itself induced MIP-1? and could further promote MIP-1? secretion together with palmitate and TNF-?. In conclusion, palmitate and TNF-? co-induce MIP-1? in human monocytic cells via the TLR4-IRF3 pathway and signaling involving c-Jun/NF-?B. Importantly, oxidative stress leads to ROS-driven MIP-1? amplification, which may have significance for metabolic inflammation.

SUBMITTER: Sindhu S 

PROVIDER: S-EPMC7465096 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature