Complete phenotypic characterization of apobec-1 knockout mice with a wild-type genetic background and a human apolipoprotein B transgenic background, and restoration of apolipoprotein B mRNA editing by somatic gene transfer of Apobec-1.
We have produced gene knockout mice by targeted disruption of the apobec-1 gene. As recently reported by Hirano et al. (Hirano, K.-I., Young, S. G., Farese, R. V., Jr., Ng, J., Sande, E., Warburton, C., Powell-Braxton, L. M., and Davidson, N. O. (1996) J. Biol. Chem. 271, 9887-9890), these animals do not edit apolipoprotein (apo) B mRNA or produce apoB-48. In this study we have performed a detailed analysis of the lipoprotein phenotypic effects of apobec-1 gene disruption that were not examined in the previous study. We first analyzed the plasma lipoproteins in knockout animals with a wild-type genetic background. Although there was no difference in plasma cholesterol between apobec-1(-/-), +/-, or +/+ mice, there was a marked (176%) increase in plasma apoB-100, from 1.8 +/- 1.2 mg/dl in apobec-1(+/+) mice to 2.7 +/- 0.6 mg/dl in apobec-1(+/-) and 5.0 +/- 1.4 mg/dl in apobec-1(-/-) mice. Plasma apoE was similar in these animals. By fast protein liquid chromatography (FPLC) analysis, there was a significant decrease in plasma high density lipoprotein (HDL) cholesterol in apobec-1(-/-) mice. We further fractionated the plasma lipoproteins into d < 1.006, 1.006-1.02, 1.02-1.05, 1.05-1.08, 1.08-1.10, and 1.10-1.21 g/ml classes, and found a marked (30-40%) reduction in the cholesterol and protein content in the (d 1.08-1.10 and 1.10-1.21) HDL fractions, corroborating the FPLC data. SDS-gel analysis revealed an absence of apoB-48, an increase in apoB-100 in the very low density lipoprotein (VLDL) and low density lipoprotein (LDL) fractions, and a small decrease in apoA-I in the HDL fractions in the apobec-1(-/-) samples. We next raised the basal plasma apoB levels in the apobec-1(-/-) animals by cross-breeding them with human apoB transgenic (TgB) mice. The plasma apoB-100 was 3-fold higher in apobec-1(-/-)/TgB+/- mice (26.6 +/- 18.3 mg/dl) than in apobec-1(+/+)/TgB+/- mice (9.8 +/- 3.9 mg/dl, p < 0.05). The apobec-1(-/-)/TgB+/- mice had a plasma cholesterol levels of 170 +/- 28 mg/dl and triglyceride levels of 106 +/- 31 mg/dl, which are 80% and 58% higher, respectively, than the corresponding values of 94 +/- 21 mg/dl and 67 +/- 11 mg/dl in apobec+/+/TgB+/- mice. By FPLC, the apobec-1(-/-)/TgB+/- animals developed markedly elevated plasma LDL cholesterol (518.5 +/- 329.5 microg/ml) that is 373% that of apobec1(+/+)/TgB+/- mice (139.0 +/- 87.0 microg/ml) (p < 0.05). The elevated plasma triglyceride was accounted for mainly by a 97% increase in VLDL triglyceride in the apobec1(-/-)/TgB+/- mice. We conclude that apobec-1(-/-) animals have a distinctive lipoprotein phenotype characterized by significant hyperapoB-100 and HDL deficiency in mice with a wild-type genetic background. Furthermore, the abolition of apoB mRNA editing elevates plasma total cholesterol and LDL cholesterol in apobec-1(-/-) animals with a TgB background. Finally, to exclude the possibility that absence of apoB mRNA editing was a secondary effect of chronic Apobec-1 deficiency, we treated apobec-1(-/-) mice with a replication-defective mouse Apobec-1 adenoviral vector and found that we could acutely restore apoB mRNA editing in the liver. These experiments indicate that Apobec-1 is an essential component of the apoB mRNA editing machinery and absence of editing in the knockout animals is a direct consequence of the absence of functional Apobec-1.
Nakamuta
M
M
Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030-3498, USA.
Chang
B H
BH
Zsigmond
E
E
Kobayashi
K
K
Lei
H
H
Ishida
B Y
BY
Oka
K
K
Li
E
E
Chan
L
L
D000071479:APOBEC-1 Deaminase; D000256:Adenoviridae; D000818:Animals; D053299:Apolipoprotein B-100; D001055:Apolipoproteins B / Q000097:blood / Q000235:genetics*; D001057:Apolipoproteins E / Q000097:blood; D002874:Chromosome Mapping; D003564:Cytidine Deaminase / Q000235:genetics*; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D018014:Gene Transfer Techniques; D006801:Humans; D008055:Lipids / Q000097:blood; D008077:Lipoproteins, LDL / Q000097:blood; D008079:Lipoproteins, VLDL / Q000097:blood; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D010641:Phenotype; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000378:metabolism*; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
D053299:Apolipoprotein B-100; D001055:Apolipoproteins B; D001057:Apolipoproteins E; D008055:Lipids; D008077:Lipoproteins, LDL; D008079:Lipoproteins, VLDL; D012333:RNA, Messenger; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D000071479:APOBEC-1 Deaminase; C000605089:APOBEC1 protein, human; C000605090:Apobec1 protein, mouse; D003564:Cytidine Deaminase