Roles of Acyl-CoA:Diacylglycerol Acyltransferases 1 and 2 in Triacylglycerol Synthesis and Secretion in Hepatocytes

  • Author / Creator
    Li, Chen
  • Triacylglycerol (TG) metabolism with its high-energy potential is stringently regulated. Unbalanced TG regulation, either too much TG that overwhelms cellular storage capacity or too little TG due to defects in adipogenesis, is associated with various metabolic disorders. TG can be exported from liver in very-low density lipoprotein (VLDL). Although compelling evidence suggests that the majority of TG in VLDL is derived from re-esterification of lipolytic products released by endoplasmic reticulum-associated lipases, little is known about the roles of enzymes that catalyze the re-esterification reaction, acyl-CoA:diacylglycerol acyltransferases (DGATs). In mammals, two DGAT enzymes (DGAT1 and DGAT2) with no homology in primary amino acid sequences are encoded by genes belonging to distinct gene families and perform non-redundant physiological functions. The research goal was to investigate the contribution of DGAT1 and DGAT2 to lipid metabolism and lipoprotein secretion in primary mouse and human hepatocytes. Highly selective small-molecule inhibitors of DGAT1 and DGAT2 were used to track storage and secretion of lipids synthesized de novo from [3H]acetic acid and from exogenously supplied [3H]oleic acid. Inactivation of an individual DGAT did not affect incorporation of either radiolabeled precursor into intracellular TG, whereas combined inactivation of both DGATs severely attenuated TG synthesis. However, inhibition of DGAT2 augmented fatty acid oxidation, whereas inhibition of DGAT1 increased TG secretion, suggesting preferential channeling of separate DGAT-derived TG pools to distinct metabolic pathways. Inactivation of DGAT2 impaired cytosolic lipid droplet expansion, whereas DGAT1 inactivation promoted large lipid droplet formation. Moreover, ii inactivation of DGAT2 attenuated expression of lipogenic genes. Finally, TG secretion was significantly reduced upon DGAT2 inhibition without altering extracellular apoB levels. The data suggest that DGAT1 and DGAT2 can compensate for each other to synthesize TG, but TG synthesized by DGAT1 is preferentially channeled to oxidation, while DGAT2 synthesizes TG destined for VLDL assembly.

  • Subjects / Keywords
  • Graduation date
    Fall 2015
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • 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.