TNF-α induces a pro-inflammatory phenotypic shift in monocytes through ACSL1: Relevance to metabolic inflammation

Abstract Background TNF-α mediated proinflammatory phenotypic change in monocytes is known to be implicated in the pathogenesis of metabolic inflammation and insulin resistance. However, the mechanism by which TNF-α induces inflammatory phenotypic shift in monocytes is poorly understood. Since long-chain acyl-CoA synthetase 1 (ACSL1) is associated with inflammatory monocytes/macrophages, we investigated the role of ACSL1 in the TNF- α driven inflammatory phenotypic shift in the monocytes. Methods Monocytes (Human monocytic THP-1 cells) were stimulated with TNF-α. Inflammatory phenotypic markers (CD16, CD11b, CD11c and HLA-DR) expression was determined with real time RT-PCR and flow cytometry. IL-1b and MCP-1 were determined by ELISA. Signaling pathways were identified by using ACSL1 inhibitor, ACSL1 siRNA and NF-kB reporter monocytic cells. Phosphorylation of NF-kB was analyzed by western blotting and flow cytometry. Results Our data show that TNF-α induced significant increase in the expression of CD16, CD11b, CD11c and HLA-DR. Inhibition of ACSL1 activity in the cells with triacsin C significantly suppressed the expression of these inflammatory markers. Using ACSL-1 siRNA, we further demonstrate that TNF-α induced inflammatory markers expression in monocytic cells requires ACSL1. In addition, IL-1b and MCP-1 production by TNF-α activated monocytic cells was significantly blocked by the inhibition of ACSL-1 activity. Interestingly, elevated NF-κB activity resulting from TNF-α stimulation was attenuated in ACSL1 deficient cells. Conclusion Our findings provide an evidence that TNF-α associated inflammatory polarization in monocytes is an ACSL1 dependent, which indicates its central role in metabolic inflammation.