Hypobetalipoproteinemic mice with a targeted apolipoprotein (Apo) B-27.6-specifying mutation: in vivo evidence for an important role of amino acids 1254-1744 of ApoB in lipid transport and metabolism of the apoB-containing lipoprotein.
Carboxyl-terminal deletion of apoB-100 may impair its triglyceride (TG)-transporting capability and alter its catabolism. Here, we compare our newly generated apoB gene (Apob)-targeted apoB-27.6-bearing mice to our previously reported apoB-38.9 mice to understand further the relationship between the size of a truncated apoB variant and its function/metabolism in vivo. The apoB-27.6-specifying mutation produces a premature stop codon six amino acids (aa) downstream of the last codon of mouse Apob exon 24 (corresponding to aa 1254 of human apoB-100). ApoB-27.6 transcripts were 3- and 5-fold more abundant than apoB wild type and apoB-38.9 transcripts in the liver. Likewise, hepatic secretion rates of apoB-27.6 were 7-fold higher than those of apoB-48 and apoB-38.9. In contrast, apoB-27.6 heterozygotes (Apob(27.6/+)) had lower hepatic TG secretion rates and higher liver TG contents than both apoB-38.9 heterozygotes (Apob(38.9/+)) and apoB wild type mice (Apob(+/+)). ApoB-27.6 was secreted by Apob(27.6/+) hepatocytes as dense high density lipoprotein particles. Moreover, despite its high secretion rates, apoB-27.6 was barely detectable in plasma. Disruption of apoE gene in Apob(38.9/+) and Apob(27.6/+) dramatically increased plasma levels of apoB-38.9 as well as apoB-48 but caused no change in plasma apoB-27.6 concentrations. Finally, the birth rate of apoB-27.6 homozygotes (Apob(27.6/27.6)) from intercrosses of Apob(27.6/+) was 7-fold lower than that of Apob(38.9/38.9) from Apob(38.9/+) intercrosses (1.8% versus 12%). Crossbreeding of Apob(27.6/27.6) and Apob(38.9/38.9) produced viable Apob(27.6/38.9) offspring, but Apob(27.6/27.6) intercrosses produced no offspring. Together, these results demonstrate in vivo that the apoB-27.6-apoB-38.9 peptide segment (aa 1254-1744) plays a critical role, not only in supporting hepatic TG-secretion and in modulating catabolism of apoB-containing lipoproteins, but also in normal mouse embryonic development.
Chen
Zhouji
Z
Division of Atherosclerosis, Nutrition and Lipid Research, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA. zchen@im.wustl.edu
Fitzgerald
Robin L
RL
Schonfeld
Gustav
G
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D001055:Apolipoproteins B / Q000235:genetics*; D001483:Base Sequence; D001692:Biological Transport; D015152:Blotting, Northern; D015153:Blotting, Western; D002784:Cholesterol / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D005838:Genotype; D022781:Hepatocytes / Q000378:metabolism; D006995:Hypobetalipoproteinemias / Q000235:genetics*; D050356:Lipid Metabolism; D008074:Lipoproteins / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D011233:Precipitin Tests; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors
D000596:Amino Acids; D001055:Apolipoproteins B; D008074:Lipoproteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D012313:RNA; D002784:Cholesterol