Characterization of 2‐Chlorofatty Acid Signaling Pathways

Abstract

Monocytes and macrophages are key inflammatory cell mediators in the response to infection and tissue injury. Monocytes and macrophages produce a respiratory burst, resulting in the release of reactive oxygen species. Upon activation of these leukocytes, myeloperoxidase (MPO) is released. MPO catalyzes the conversion of hydrogen peroxide into hypochlorous acid (HOCl). HOCl then is able to target the vinyl ether bond of plasmalogens, an abundant class of phospholipids. This results in the production of a novel class of chlorinated lipids, including 2‐chlorofatty aldehyde (2‐ClFALD) and its oxidation product, 2‐chlorofatty acid (2‐ClFA). 2‐Chlorofatty acids have been shown to accumulate in activated human neutrophils and monocytes, as well as the plasma of rats subjected to lipopolysaccharide treatment or the cecal ligation and puncture sepsis model. The present study is designed to identify signaling mechanisms mediated by 2‐ClFA. Initial studies used dynamic mass redistribution (DMR) assays, which is a label‐free functional cell‐based technology that measures whole cell response to ligands. DMR analyses demonstrated that the 2‐ClFA, 2‐chloropalmitic acid, selectively stimulates THP‐1 cells and not HEK293 cells. Furthermore, the dose‐response for 2‐chloropalmitic acid was striking compared to the lack of response to equimolar concentrations of the non‐chlorinated fatty acid, palmitic acid. CCAAT/enhancer‐binding protein homologous protein (CHOP) mRNA increases selectively in response to 2‐chloropalmitic acid compared to palmitic acid in both RAW 264.7 and THP‐1 cells. CHOP mRNA expression in RAW 264.7 cells is inhibited by Bisindolylmaleimide, SB203580, and U0126 indicating 2‐ClFA elicited CHOP expression is PKC, p38 and MEK1/2 dependent. Thus, THP‐1 and RAW 264.7 cells are ideal cells to use for expression analysis and DMR to further elucidate the mechanisms and receptor by which 2‐ClFA elicits cell responses.Support or Funding InformationNational Institutes of Health Grant GM115553