Journal
CELLS
Volume 9, Issue 8, Pages -Publisher
MDPI
DOI: 10.3390/cells9081799
Keywords
palmitate; TNF-alpha; oxidative stress; ROS; MIP-1 alpha; TLR4; IRF3; metabolic inflammation
Categories
Funding
- Kuwait Foundation for the Advancement of Sciences (KFAS) [RA-2014-016, RA AH 2016-007, RA 2015-027]
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Metabolic inflammation is associated with increased expression of saturated free fatty acids, proinflammatory cytokines, chemokines, and adipose oxidative stress. Macrophage inflammatory protein (MIP)-1 alpha recruits the inflammatory cells such as monocytes, macrophages, and neutrophils in the adipose tissue; however, the mechanisms promoting the MIP-1 alpha expression remain unclear. We hypothesized that MIP-1 alpha co-induced by palmitate and tumor necrosis factor (TNF)-alpha 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-alpha and mRNA and protein levels of MIP-1 alpha 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 alpha gene/protein expression was upregulated in cells co-stimulated with palmitate/TNF-alpha compared to those stimulated with either palmitate or TNF-alpha (P< 0.05). Further, TLR4-IRF3 pathway was implicated in the cooperative induction of MIP-1 alpha in THP-1 cells, and this cooperativity between palmitate and TNF-alpha was clathrin-dependent and also required signaling through c-Jun and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappa B). Notably, ROS itself induced MIP-1 alpha and could further promote MIP-1 alpha secretion together with palmitate and TNF-alpha. In conclusion, palmitate and TNF-alpha co-induce MIP-1 alpha in human monocytic cells via the TLR4-IRF3 pathway and signaling involving c-Jun/NF-kappa B. Importantly, oxidative stress leads to ROS-driven MIP-1 alpha amplification, which may have significance for metabolic inflammation.
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