HPLC-Based Mass Spectrometry Characterizes the Phospholipid Alterations in Ether-Linked Lipid Deficiency Models Following Oxidative Stress

Abstract

Despite the fact that the discovery of ether-linked phospholipids occurred nearly a century ago, many unanswered questions remain concerning these unique lipids. Here, we characterize the ether-linked lipids of the nematode with HPLC-MS/MS and find that more than half of the phosphoethanolamine-containing lipids are ether-linked, a distribution similar to that found in mammalian membranes. To explore the biological role of ether lipids in vivo, we target fatty acyl-CoA reductase (fard-1), an essential enzyme in ether lipid synthesis, with two distinct RNAi strategies. First, when fard-1 RNAi is initiated at the start of development, the treated animals have severely reduced ether lipid abundance, resulting in a shift in the phosphatidylethanolamine lipid population to include more saturated fatty acid chains. Thus, the absence of ether lipids during development drives a significant remodeling of the membrane landscape. A later initiation of fard-1 RNAi in adulthood results in a dramatic reduction of new ether lipid synthesis as quantified with 15N-tracers; however, there is only a slight decrease in total ether lipid abundance with this adult-only fard-1 RNAi. The two RNAi strategies permit the examination of synthesis and ether lipid abundance to reveal a relationship between the amount of ether lipids and stress survival. We tested whether these species function as sacrificial antioxidants by directly examining the phospholipid population with HPLC-MS/MS after oxidative stress treatment. While there are significant changes in other phospholipids, including polyunsaturated fatty acid-containing species, we did not find any change in ether-linked lipids, suggesting that the role of ether lipids in stress resistance is not through their general consumption as free radical sinks. Our work shows that the nematode will be a useful model for future interrogation of ether lipid biosynthesis and the characterization of phospholipid changes in various stress conditions.

Potential Role of Plasmalogens in the Modulation of Biomembrane Morphology

“…In addition to KO mice models and human neuronal cell culture, a nematode, C. elegans , has lately been established as a model for plasmalogen deficiency ( Drechsler et al, 2016 ; Shi et al, 2016 ). Unlike murine KO mutants, which are often infertile, the ether lipid mutants C elegans are viable and fertile, which offers a valuable model to study severe forms of plasmalogen deficiencies.…”

From peroxisomal disorders to common neurodegenerative diseases – the role of ether phospholipids in the nervous system

“…Animal models of isolated ether lipid deficiency have been largely restricted to mice. Purely ether lipid‐deficient variants of Caenorhabditis elegans have been reported but, so far, no information has been provided on the potential role of ether lipids in their nervous system. Strikingly, the capability of ether lipid‐deficient worms to develop into adults differs remarkably between studies.…”

Plasmalogen homeostasis – regulation of plasmalogen biosynthesis and its physiological consequence in mammals

“…Similarly, complementation of PlsEtn with AG by culturing CHO cell mutants defective in peroxisome assembly and plasmalogen‐deficient murine cells derived from RAW 264.7 recovers the impaired resistance against reactive oxygen species . Recent studies using the plasmalogen‐deficient mouse and Caenorhabditis elegans are less supportive of the protective function of PlsEtn as a scavenger of reactive oxygen species . Moreover, plasmalogen deficiency causes an impaired high‐density lipoprotein‐mediated cholesterol efflux in murine macrophage‐like cells , the delayed transport of internalized cholesterol to the ER and reduced cholesterol synthesis .…”