Phosphatidylethanolamine-esterified Eicosanoids in the Mouse

Abstract

In this study, murine peritoneal macrophages from naïve lavage were found to generate four phospholipids that contain 12-hydroxyeicosatetraenoic acid (12-HETE). They comprise three plasmalogen and one diacyl phosphatidylethanolamines (PEs) (16:0p, 18:1p, 18:0p, and 18:0a at sn-1) and are absent in macrophages from 12/15-lipoxygenase (12/15-LOX)-deficient mice. They are generated acutely in response to calcium mobilization, are primarily cell-associated, and are detected on the outside of the plasma membrane. Levels of 12-HETE-PEs in naïve lavage are in a similar range to those of free 12-HETE (5.5 ± 0.2 ng or 18.5 ± 1.03 ng/lavage for esterified versus free, respectively). In healthy mice, 12/15-LOX-derived 12-HETE-PEs are found in the peritoneal cavity, peritoneal membrane, lymph node, and intestine, with a similar distribution to 12/15-LOX-derived 12-HETE. In vivo generation of 12-HETE-PEs occurs in a Th2-dependent model of murine lung inflammation associated with interleukin-4/interleukin-13 expression. In contrast, in Toll receptor-dependent peritonitis mediated either by live bacteria or bacterial products, 12-HETE-PEs are rapidly cleared during the acute phase then reappear during resolution. The human homolog, 18:0a/15-HETE-PE inhibited human monocyte generation of cytokines in response to lipopolysaccharide. In summary, a new family of lipid mediators generated by murine macrophages during Th2 inflammation are identified and structurally characterized. The studies suggest a new paradigm for lipids generated by 12/15-LOX in inflammation involving formation of esterified eicosanoids.

Platelet Lipidomics

“…We have also found that LOX isoforms in other innate immune cells including neutrophils and monocytes/macrophages generate analogous lipids on activation, indicating that this is a common theme of likely importance in acute response to injury 33, 129-131 . All these cell types undergo significant changes to the plasma membrane compartment on activation, including shape change, vesiculation, phagocytosis and microvilli generation.…”

12/15-Lipoxygenase Orchestrates the Clearance of Apoptotic Cells and Maintains Immunologic Tolerance

“…Although this enzyme can participate in the generation of different classes of eicosanoids, 12/15-LO was recently shown to preferentially oxygenate esterified fatty acids in the form of membrane-bound phosphatidylethanolamine (PE), although the biological consequence of this oxidation process remains largely elusive (Maskrey et al, 2007;Morgan et al, 2009). Analysis of phospholipids in resMF by mass spectrometry confirmed the presence of 12/15-LO-specific PE oxidation products in this macrophage subpopulation.…”

“…Even single oxPE species such as PAPE-OH (PAPE reflects around 20%-30% of total PE) are detected in mM concentrations within resMF. Moreover, oxPE is enriched in the outer membrane leaflet in a 12/15-LO-dependent manner (Morgan et al, 2009), which might yield even higher local concentrations.…”

“…Quantification of PAPE-OH by mass spectrometry showed an increased production of PAPE-OH during later phases of the peritonitis in vivo coinciding with the resolution phase of inflammation ( Figure 3E). 12/15-LO was shown to oxidize PAPE directly within the plasma membrane (Morgan et al, 2009). Concentrations of cell-associated PAPE hydro(pero)xides were calculated to reach 0.3 to 1.5 mmol/l within the resMF assuming a cellular volume of 460 fl (Nibbering et al, 1990).…”

“…Upon 12/15-LO-mediated oxidation, PE was shown to translocate to the outer leaflet of the plasma membrane in resMF (Morgan et al, 2009). We therefore determined binding of recombinant MFG-E8 to the plasma membrane of resMF.…”