title: Effects of phosphatidylethanolamine N-methyltransferase on phospholipid composition, microvillus formation and bile salt resistance in LLC-PK1 cells.
abstract: Bile salts are potent detergents and can disrupt cellular membranes, which causes cholestasis and hepatocellular injury. However, the mechanism for the resistance of the canalicular membrane against bile salts is not clear. Phosphatidylethanolamine (PE) is converted to phosphatidylcholine (PC) in the liver by phosphatidylethanolamine N-methyltransferase (PEMT). In this study, to investigate the effect of PEMT expression on the resistance to bile salts, we established an LLC-PK1 cell line stably expressing PEMT. By using enzymatic assays, we showed that the expression of PEMT increased the cellular PC content, lowered the PE content, but had no effect on the sphingomyelin content. Consequently, PEMT expression led to reductions in PE/PC and sphingomyelin/PC ratios. Mass spectrometry demonstrated that PEMT expression increased the levels of PC species containing longer acyl chains and almost all ether-linked PC species. PEMT expression enhanced the resistance to duramycin and lysenin, suggesting decreased ratios of PE and sphingomyelin in the apical membrane, respectively. In addition, SEM revealed that PEMT expression increased the diameter of microvilli. The expression of PEMT resulted in reduced resistance to unconjugated bile salts, but surprisingly in increased resistance to conjugated bile salts, which might be attributable to modifications of the phospholipid composition and/or structure in the apical membrane. Because most bile salts exist as conjugated forms in the bile canaliculi, PEMT may be important in the protection of hepatocytes from bile salts and in cholestatic liver injury.
authors.affiliation: Department of Pharmacy, Shiga University of Medical Science Hospital, Otsu City, Shiga, Japan. smorita@belle.shiga-med.ac.jp
authors.forename: Shin-ya
authors.initials: SY
authors.lastname: Morita
authors.forename: Noriaki
authors.initials: N
authors.lastname: Ikeda
authors.forename: Manami
authors.initials: M
authors.lastname: Horikami
authors.forename: Kuriko
authors.initials: K
authors.lastname: Soda
authors.forename: Kosuke
authors.initials: K
authors.lastname: Ishihara
authors.forename: Reiko
authors.initials: R
authors.lastname: Teraoka
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Terada
authors.forename: Shuji
authors.initials: S
authors.lastname: Kitagawa
mesh_terms: D000818:Animals; D001430:Bacteriocins / Q000494:pharmacology; D001647:Bile Acids and Salts / Q000494:pharmacology*; D001648:Bile Canaliculi / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects; D003603:Cytotoxins / Q000494:pharmacology; D004351:Drug Resistance; D018374:LLC-PK1 Cells; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology; D010713:Phosphatidylcholines / Q000096:biosynthesis; D050918:Phosphatidylethanolamine N-Methyltransferase / Q000096:biosynthesis / Q000378:metabolism*; D010714:Phosphatidylethanolamines / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D013109:Sphingomyelins / Q000378:metabolism*; D013552:Swine
chemical_list: D001430:Bacteriocins; D001647:Bile Acids and Salts; D003603:Cytotoxins; D010455:Peptides; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010743:Phospholipids; D013109:Sphingomyelins; C040522:duramycin; D050918:Phosphatidylethanolamine N-Methyltransferase