Myeloid-specific deficiency of group VIA calcium-independent phospholipase A2 preconditions myeloid cells for injury resolution after acetaminophen exposure

Abstract

Genetic PLA2G6 variants are associated with C-reactive protein in humans. Myeloid-specific PLA2G6-deficient (Pla2g6^M-/-) mice show increased hepatic myeloperoxidase and recruitment of granulocytes in response to lipopolysaccharide (LPS). We hypothesized that Pla2g6^M-/- mice could be protected from acetaminophen (APAP) hepatotoxicity whereby neutrophils, eosinophils, and alternatively activated macrophages are reportedly protective. Herein, Pla2g6^M-/- mice treated with 300 mg/kg APAP for 24 h showed attenuated hepatic necrosis and plasma cytokines, and with elevated levels of Ly6C^lo in peripheral blood mononuclear cells and plasma lipoxin A4. Remarkably, bone-marrow-derived macrophages (BMDMs) from untreated Pla2g6^M-/- mice exhibited elevated baseline expression of cPLA2α, NOX2, Rac1, Arg-1, phospho-MLKL, and iNOS protein, which was exacerbated by LPS in vitro. APAP administration preconditioned Pla2g6^M-/- BMDMs for further activation of enzymes involving in phagocytosis (Rac1 and phospho-MLKL) and eicosanoids (COX2 and A15LOXB). Pla2g6^M-/- BMDMs showed an increased release of pro-resolution lipid mediators lipoxin A4, PGE2, and 15d-PGJ2, which was further elevated by LPS in vitro or APAP in vivo. Phagocytic gene signatures (myeloperoxidase and NOX2) were also upregulated in livers of untreated and APAP-treated Pla2g6^M-/- mice. APAP protection in Pla2g6^M-/- mice was associated with increased proportion of neutrophils (Ly6G), eosinophils (eosinophilic cationic protein), and M2 macrophages (CD206) in/at the portal tract and central vein as determined by immunohistochemistry. Thus, myeloid-specific PLA2G6 deficiency preconditioned macrophages for eicosanoid and phagocytic pathways rendering protection against APAP hepatotoxicity. Our results may be applicable to patients with PLA2G6 mutations, and PLA2G6 inhibition specifically in myeloid cells may represent a new strategy to alleviate APAP poisoning.