Insights into the role of CTP:phosphocholine cytidylyltransferase-alpha in hepatic lipid metabolism and cellular integrity

• Author / Creator

  Niebergall, Lorissa J

• Lower levels of hepatic phosphatidylcholine (PC) are suggested to play a role in the pathogenesis of non-alcoholic steatohepatitis (NASH). Mice lacking hepatic CTP:phosphocholine cytidylyltransferase-α (LCTα-/-), the regulatory enzyme in the CDP-choline pathway for PC biosynthesis, were fed a high fat diet to investigate the role of impaired PC biosynthesis in the pathogenesis of NASH. CTα-deficient livers developed moderate NASH within one week of high fat feeding. In addition, LCTα deficiency caused a 2-fold increase in hepatic levels of ceramide, and a 20% decrease in hepatic PC mass. Although stimulation of PC biosynthesis prevented hepatic steatosis, normalization of hepatic PC did not prevent either hepatic ceramide accumulation, or the development of NASH. These data indicate that impaired PC biosynthesis does not play a direct role in the transition from steatosis to NASH. Although reduced cellular PC induces apoptosis, a lower PC to phosphatidylethanolamine (PE) ratio has been demonstrated to influence membrane integrity, causing NASH. To investigate whether a reduced PC:PE ratio, rather than reduced cellular PC, influences membrane integrity, we utilized mutant 58 (MT58) Chinese hamster ovary cells. After incubation at the restrictive temperature, MT58 cells showed a 2-fold reduction in cellular PC and in the PC:PE ratio, leading to cellular death. In an attempt to normalize the PC:PE ratio and stabilize cellular membranes, MT58 cells were treated with silencing RNA to inhibit PE biosynthesis. However, inhibition of PE biosynthesis caused a 30% reduction in cellular PE and PC masses, and therefore, did not normalize the PC:PE ratio. Moreover, MT58 cells showed a further loss of membrane integrity after knockdown of PE biosynthesis. Treatment of MT58 cells with lysophosphatidylcholine normalized cellular PC mass and prevented cellular death. However, lysophosphatidylcholine treatment caused an increase in PE mass, and therefore, did not normalize the PC:PE ratio. These data show that manipulation of the PC:PE ratio will not rescue MT58 cells from cell death since cellular growth and integrity are influenced by the total amount of cellular PC and PE, and not by the PC:PE ratio. In summary, these studies outline the importance of CTα in maintaining cellular integrity and hepatic lipid metabolism.

• Subjects / Keywords

  • Phosphatidylethanolamine
  • Non-alcoholic steatohepatitis
  • Ceramide
  • Apoptosis
  • CTP:phosphocholine cytidylyltransferase
  • Phosphatidylcholine
  • ChoK1

• Graduation date

  Fall 2011

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R36060

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.