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A significant fraction of the glycerophospholipids in the human body is composed of plasmalogens, particularly in the brain, cardiac, and immune cell membranes. A decline in these lipids has been observed in such diseases as Alzheimer’s and chronic obstructive pulmonary disease. Plasmalogens contain a characteristic 1-O-alk-1′-enyl ether (vinyl ether) double bond that confers special biophysical, biochemical, and chemical properties to these lipids. However, the genetics of their biosynthesis is not fully understood, since no gene has been identified that encodes plasmanylethanolamine desaturase (E.C. 1.14.99.19), the enzyme introducing the crucial alk-1′-enyl ether double bond. The present work identifies this gene as transmembrane protein 189 (TMEM189). Inactivation of the TMEM189 gene in human HAP1 cells led to a total loss of plasmanylethanolamine desaturase activity, strongly decreased plasmalogen levels, and accumulation of plasmanylethanolamine substrates and resulted in an inability of these cells to form labeled plasmalogens from labeled alkylglycerols. Transient expression of TMEM189 protein, but not of other selected desaturases, recovered this deficit. TMEM189 proteins contain a conserved protein motif (pfam10520) with eight conserved histidines that is shared by an alternative type of plant desaturase but not by other mammalian proteins. Each of these histidines is essential for plasmanylethanolamine desaturase activity. Mice homozygous for an inactivated Tmem189 gene lacked plasmanylethanolamine desaturase activity and had dramatically lowered plasmalogen levels in their tissues. These results assign the TMEM189 gene to plasmanylethanolamine desaturase and suggest that the previously characterized phenotype of Tmem189-deficient mice may be caused by a lack of plasmalogens. [ABSTRACT FROM AUTHOR]

Current strategies used to quantitatively describe the biological diversity of lipids by mass spectrometry are often limited in assessing the exact structural variability of individual molecular species in detail. A major challenge is represented by the extensive isobaric overlap present among lipids' hampering their accurate identification. This is especially true for cardiolipins, a mitochondria-specific class of phospholipids, which are functionally involved in many cellular functions, including energy metabolism, cristae structure, and apoptosis. Substituted with four fatty acyl side chains, cardiolipins offer a particularly high potential to achieve complex mixtures of molecular species. Here, we demonstrate how systematically generated high-performance liquid chromatography-mass spectral data can be utilized in a mathematical structural modeling approach, to comprehensively analyze and characterize the molecular diversity of mitochondrial cardio-lipin compositions in cell culture and disease models, cardiolipin modulation experiments, and a broad variety of frequently studied model organisms. [ABSTRACT FROM AUTHOR]

Tetrahydrobiopterin is a cofactor synthesized from GTP with well-known roles in enzymatic nitric oxide synthesis and aromatic amino acid hydroxylation. It is used to treat mild forms of phenylketonuria. Less is known about the role of tetrahydrobiopterin in lipid metabolism, although it is essential for irreversible ether lipid cleavage by alkylglycerol monooxygenase. Here we found intracellular alkylglycerol monooxygenase activity to be an important regulator of alkylglycerol metabolism in intact murine RAW264.7 macrophage-like cells. Alkylglycerol monooxygenase was expressed and active also in primary mouse bone marrowderived monocytes and "alternatively activated" M2 macrophages obtained by interleukin 4 treatment, but almost missing in M1 macrophages obtained by IFN-γ and lipopolysaccharide treatment. The cellular lipidome of RAW264.7 was markedly changed in a parallel way by modulation of alkylglycerol monooxygenase expression and of tetrahydrobiopterin biosynthesis affecting not only various ether lipid species upstream of alkylglycerol monooxygenase but also other more complex lipids including glycosylated ceramides and cardiolipins, which have no direct connection to ether lipid pathways. Alkylglycerol monooxygenase activity manipulation modulated the IFN-γ/lipopolysaccharide-induced expression of inducible nitric oxide synthase, interleukin-1β, and interleukin 1 receptor antagonist but not transforming growth factor β1, suggesting that alkylglycerolmonooxygenase activity affects IFN-γ/lipopolysaccharide signaling. Our results demonstrate a central role of tetrahydrobiopterin and alkylglycerol monooxygenase in ether lipid metabolism of murine macrophages and reveal that alteration of alkylglycerol monooxygenase activity has a profound impact on the lipidome also beyond the class of ether lipids. [ABSTRACT FROM AUTHOR]