The phosphatidylethanolamine N-methyltransferase pathway is quantitatively not essential for biliary phosphatidylcholine secretion. 2007

Henkjan J Verkade, and Rick Havinga, and David J Shields, and Henk Wolters, and Vincent W Bloks, and Folkert Kuipers, and Dennis E Vance, and Luis B Agellon
Pediatric Gastroenterology/Research Laboratory Pediatrics, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands. h.j.verkade@med.umcg.nl

The phosphatidylethanolamine N-methyltransferase (PEMT) pathway of phosphatidylcholine (PC) biosynthesis is not essential for the highly specific acyl chain composition of biliary PC. We evaluated whether the PEMT pathway is quantitatively important for biliary PC secretion in mice under various experimental conditions. Biliary bile salt and PC secretion were determined in mice in which the gene encoding PEMT was inactivated (Pemt(-/-)) and in wild-type mice under basal conditions, during acute metabolic stress (intravenous infusion of the bile salt tauroursodeoxycholate), and during chronic metabolic stress (feeding a taurocholate-containing diet for 1 week). The activity of CTP:phosphocholine cytidylyltransferase, the rate-limiting enzyme of PC biosynthesis via the CDP-choline pathway, and the abundance of multi-drug-resistant protein 2 (Mdr2; encoded by the Abcb4 gene), the canalicular membrane flippase essential for biliary PC secretion, were determined. Under basal conditions, Pemt(-/-) and wild-type mice exhibited similar biliary secretion rates of bile salt and PC ( approximately 145 and approximately 28 nmol/min/100 g body weight, respectively). During acute or chronic bile salt administration, the biliary PC secretion rates increased similarly in Pemt(-/-) and control mice. Mdr2 mRNA and protein abundance did not differ between Pemt(-/-) and wild-type mice. The cytidylyltransferase activity in hepatic lysates was increased by 20% in Pemt(-/-) mice fed the basal (bile salt-free) diet (P < 0.05). We conclude that the biosynthesis of PC via the PEMT pathway is not quantitatively essential for biliary PC secretion under acute or chronic bile salt administration.

UI MeSH Term Description Entries
D008099 Liver A large lobed glandular organ in the abdomen of vertebrates that is responsible for detoxification, metabolism, synthesis and storage of various substances. Livers
D010713 Phosphatidylcholines Derivatives of PHOSPHATIDIC ACIDS in which the phosphoric acid is bound in ester linkage to a CHOLINE moiety. Choline Phosphoglycerides,Choline Glycerophospholipids,Phosphatidyl Choline,Phosphatidyl Cholines,Phosphatidylcholine,Choline, Phosphatidyl,Cholines, Phosphatidyl,Glycerophospholipids, Choline,Phosphoglycerides, Choline
D002796 Choline Deficiency A condition produced by a deficiency of CHOLINE in animals. Choline is known as a lipotropic agent because it has been shown to promote the transport of excess fat from the liver under certain conditions in laboratory animals. Combined deficiency of choline (included in the B vitamin complex) and all other methyl group donors causes liver cirrhosis in some animals. Unlike compounds normally considered as vitamins, choline does not serve as a cofactor in enzymatic reactions. (From Saunders Dictionary & Encyclopedia of Laboratory Medicine and Technology, 1984) Deficiency, Choline,Choline Deficiencies,Deficiencies, Choline
D000097202 ATP-Binding Cassette Sub-Family B Member 4 An ATP-binding cassette, sub-family B protein that functions in translocating PHOSPHATIDYLCHOLINES from the inner to the outer leaflet of the canalicular membrane of the HEPATOCYTES. MDR2 Protein,Multidrug Resistance Protein 2,P-Glycoprotein 2,Pgp2 protein,Phosphatidylcholine Translocator ABCB4,2, P-Glycoprotein,ABCB4, Phosphatidylcholine Translocator,ATP Binding Cassette Sub Family B Member 4,P Glycoprotein 2,Translocator ABCB4, Phosphatidylcholine,protein, Pgp2
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D001646 Bile An emulsifying agent produced in the LIVER and secreted into the DUODENUM. Its composition includes BILE ACIDS AND SALTS; CHOLESTEROL; and ELECTROLYTES. It aids DIGESTION of fats in the duodenum. Biliary Sludge,Sludge, Biliary
D050918 Phosphatidylethanolamine N-Methyltransferase An enzyme that catalyses three sequential METHYLATION reactions for conversion of phosphatidylethanolamine to PHOSPHATIDYLCHOLINE. Cephalin N-Methyltransferase,PHET Methyltransferase II,Phosphatidylethanolamine Methyltransferase,Phosphatidylethanolamine N-Methyltransferase-2,Phosphatidylethanolamine-Methyltransferase II,Phosphatidylethanolamine-Phosphatidylcholine N-Methyltransferase,Phospholipid Methyltransferase II,S-Adenosylmethionine Phosphatidylethanolamine N-Methyltransferase,Cephalin N Methyltransferase,Methyltransferase II, PHET,Methyltransferase II, Phospholipid,Methyltransferase, Phosphatidylethanolamine,N-Methyltransferase, Cephalin,N-Methyltransferase, Phosphatidylethanolamine,N-Methyltransferase, Phosphatidylethanolamine-Phosphatidylcholine,N-Methyltransferase, S-Adenosylmethionine Phosphatidylethanolamine,N-Methyltransferase-2, Phosphatidylethanolamine,Phosphatidylethanolamine Methyltransferase II,Phosphatidylethanolamine N Methyltransferase,Phosphatidylethanolamine N Methyltransferase 2,Phosphatidylethanolamine N-Methyltransferase, S-Adenosylmethionine,Phosphatidylethanolamine Phosphatidylcholine N Methyltransferase,S Adenosylmethionine Phosphatidylethanolamine N Methyltransferase
D051379 Mice The common name for the genus Mus. Mice, House,Mus,Mus musculus,Mice, Laboratory,Mouse,Mouse, House,Mouse, Laboratory,Mouse, Swiss,Mus domesticus,Mus musculus domesticus,Swiss Mice,House Mice,House Mouse,Laboratory Mice,Laboratory Mouse,Mice, Swiss,Swiss Mouse,domesticus, Mus musculus
D053858 Metabolic Networks and Pathways Complex sets of enzymatic reactions connected to each other via their product and substrate metabolites. Metabolic Networks,Metabolic Pathways,Metabolic Network,Metabolic Pathway,Network, Metabolic,Networks, Metabolic,Pathway, Metabolic,Pathways, Metabolic
D018435 ATP Binding Cassette Transporter, Subfamily B A subfamily of transmembrane proteins from the superfamily of ATP-BINDING CASSETTE TRANSPORTERS that are closely related in sequence to ATP BINDING CASSETTE TRANSPORTER, SUBFAMILY B, MEMBER 1. When overexpressed, they function as ATP-dependent efflux pumps able to extrude lipophilic drugs (especially ANTINEOPLASTIC AGENTS) from cells, causing multidrug resistance (DRUG RESISTANCE, MULTIPLE). Although ATP BINDING CASSETTE TRANSPORTER, SUBFAMILY B share functional similarities to MULTIDRUG RESISTANCE-ASSOCIATED PROTEINS they are two distinct subclasses of ATP-BINDING CASSETTE TRANSPORTERS, and have little sequence homology. Multidrug Resistance Proteins,P-Glycoproteins,ATP Binding Cassette Transporter, Sub-Family B,ATP-Binding Cassette, Sub-Family B Proteins,ATP Binding Cassette Transporter, Sub Family B,ATP Binding Cassette, Sub Family B Proteins,P Glycoproteins

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