title: Acylglycerophosphate acyltransferase 4 (AGPAT4) is a mitochondrial lysophosphatidic acid acyltransferase that regulates brain phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol levels.
abstract: The acylglycerophosphate acyltransferase/lysophosphatidic acid acyltransferase (AGPAT/LPAAT) family is a group of homologous acyl-CoA-dependent lysophospholipid acyltransferases. We performed studies to better understand the subcellular localization, activity, and in vivo function of AGPAT4/LPAATδ, which we found is expressed in multiple mouse brain regions. Endogenous brain AGPAT4 and AGPAT4 overexpressed in HEK293 or Sf9 insect cells localizes to mitochondria and is resident on the outer mitochondrial membrane. Further fractionation showed that AGPAT4 is present specifically in the mitochondria and not in the mitochondria-associated endoplasmic reticulum membrane (i.e. MAM). Lysates from Sf9 cells infected with baculoviral Agpat4 were tested with eight lysophospholipid species but showed an increased activity only with lysophosphatidic acid as an acyl acceptor. Analysis of Sf9 phospholipid species, however, indicated a significant 72% increase in phosphatidylinositol (PI) content. We examined the content of major phospholipid species in brains of Agpat4(-/-) mice and found also a >50% decrease in total levels of PI relative to wildtype mice, as well as significant decreases in phosphatidylcholine (PC) and phosphatidylethanolamine (PE), but no significant differences in phosphatidylserine, phosphatidylglycerol, cardiolipin, or phosphatidic acid (PA). A compensatory upregulation of Agpats 1, 2, 3, 5, and 9 may help to explain the lack of difference in PA. Our findings indicate that AGPAT4 is a mitochondrial AGPAT/LPAAT that specifically supports synthesis of brain PI, PC, and PE. This understanding may help to explain apparent redundancies in the AGPAT/LPAAT family.
authors.affiliation: University of Waterloo, Department of Kinesiology, Faculty of Applied Health Sciences, 200 University Avenue W., BMH1110, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Bradley
authors.affiliation: University of Waterloo, Department of Kinesiology, Faculty of Applied Health Sciences, 200 University Avenue W., BMH1110, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Phillip M
authors.initials: PM
authors.lastname: Marvyn
authors.affiliation: University of Waterloo, Department of Kinesiology, Faculty of Applied Health Sciences, 200 University Avenue W., BMH1110, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Aristizabal Henao
authors.affiliation: University of Waterloo, Department of Kinesiology, Faculty of Applied Health Sciences, 200 University Avenue W., BMH1110, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Emily B
authors.initials: EB
authors.lastname: Mardian
authors.affiliation: University of Waterloo, Department of Chemical Engineering, Faculty of Engineering, 200 University Avenue W., E5, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Steve
authors.initials: S
authors.lastname: George
authors.affiliation: University of Waterloo, Department of Chemical Engineering, Faculty of Engineering, 200 University Avenue W., E5, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Marc G
authors.initials: MG
authors.lastname: Aucoin
authors.affiliation: University of Waterloo, Department of Kinesiology, Faculty of Applied Health Sciences, 200 University Avenue W., BMH1110, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Ken D
authors.initials: KD
authors.lastname: Stark
authors.affiliation: University of Waterloo, Department of Kinesiology, Faculty of Applied Health Sciences, 200 University Avenue W., BMH1110, Waterloo, Ontario N2L 3G1, Canada. Electronic address: reduncan@uwaterloo.ca.
authors.forename: Robin E
authors.initials: RE
authors.lastname: Duncan
mesh_terms: D000818:Animals; D001921:Brain / Q000166:cytology / Q000378:metabolism*; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D005992:Glycerol-3-Phosphate O-Acyltransferase / Q000096:biosynthesis* / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D024101:Mitochondrial Proteins / Q000096:biosynthesis* / Q000235:genetics; D010713:Phosphatidylcholines / Q000096:biosynthesis* / Q000235:genetics; D010714:Phosphatidylethanolamines / Q000096:biosynthesis* / Q000235:genetics; D010716:Phosphatidylinositols / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D024101:Mitochondrial Proteins; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010716:Phosphatidylinositols; C483858:phosphatidylethanolamine; D005992:Glycerol-3-Phosphate O-Acyltransferase
keywords: Acylglycerophosphate acyltransferase 4 (AGPAT4)/lysophosphatidic acid acyltransferase delta (LPAAT4); Brain metabolism; Gene knockout; Kennedy pathway; Land's pathway; Mitochondria; Phosphatidic acid; Phosphatidylinositol; Phospholipid metabolism