Triacylglycerol/phospholipid molecular species profiling of fatty livers and regenerated non-fatty livers in cystathionine beta-synthase-deficient mice, an animal model for homocysteinemia/homocystinuria
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Fatty liver is one of the typical manifestations in homocysteinemia/homocystinuria patients and their genetic animal model, mice lacking cystathionine β-synthase (Cbs −/−). The vast majority of Cbs −/− die within 4 weeks after birth via yet unknown mechanisms, whereas a small portion survive to adulthood, escaping fatty degeneration of the liver during lactation periods, through regeneration. To investigate the molecular basis of such fatty changes, we analyzed lipid components in fatty livers of 2-week-old Cbs −/− and regenerated non-fatty livers of 8-week-old Cbs −/− survivors using a chip-based nanoESI (electrospray ionization)-MS system, which allows quantitative detection of triacylglycerol/phospholipid molecular species. Hepatic levels of all major triacylglycerol species were much higher in Cbs −/− than in wild-type mice at 2 weeks, although not at 8 weeks. Levels of some phospholipid species were either up- or downregulated in 2-week-old Cbs −/−; e.g. saturated (16:0 and 18:0) or mono-unsaturated (16:1 and 18:1) fatty acids-containing phosphatidylcholine/phosphatidylethanolamine species were upregulated, while poly-unsaturated fatty acids-containing phosphatidylcholine (18:2–18:2 and 18:2–20:5), phosphatidylethanolamine (18:1–20:4), and phosphatidylinositol (18:0–20:4) were downregulated. Capillary electrophoresis-MS analysis identified high-level accumulation of S-adenosylmethionine and S-adenosylhomocysteine in fatty livers of 2-week-old Cbs −/− but much less in non-fatty livers of 8-week-old Cbs −/−. Although hepatic S-adenosylmethionine/S-adenosylhomocysteine ratios were comparable between 2-week-old Cbs −/− and wild-type, global protein arginine methylation was disturbed in fatty livers of Cbs −/−. Our results suggest that cellular signaling mediated by altered phospholipid contents might be involved in pathogenesis of fatty liver in Cbs −/–.
KeywordsCapillary electrophoresis Hepatic steatosis Methylation NanoESI-MS Neutral loss scanning Precursor ion scanning
This work was supported by Grants-in-Aid for Scientific Research (no. 22590292 to I.I. and no. 22790219 to N.A.) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan; research grants for Core Research for Evolutional Science and Technology (CREST) Program (to R.T.) and ERATO Suematsu Gas Biology Project (to M.S.) from JST; and research grants from Keio University (to I.I.). CE-MS analysis was supported by Research and Development of the Next-Generation Integrated Simulation of Living Matter, a part of the Development and Use of the Next-Generation Supercomputer Project of the MEXT.
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