Liver-specific inactivation of the abetalipoproteinemia gene completely abrogates very low density lipoprotein/low density lipoprotein production in a viable conditional knockout mouse.
Conventional knockout of the microsomal triglyceride transfer protein large subunit (lMTP) gene is embryonic lethal in the homozygous state in mice. We have produced a conditional lMTP knockout mouse by inserting loxP sequences flanking exons 5 and 6 by gene targeting. Homozygous floxed mice were born live with normal plasma lipids. Intravenous injection of an adenovirus harboring Cre recombinase (AdCre1) produced deletion of exons 5 and 6 and disappearance of lMTP mRNA and immunoreactive protein in a liver-specific manner. There was also disappearance of plasma apolipoprotein (apo) B-100 and marked reduction in apoB-48 levels. Wild-type mice showed no response, and heterozygous mice, an intermediate response, to AdCre1. Wild-type mice doubled their plasma cholesterol level following a high cholesterol diet. This hypercholesterolemia was abolished in AdCre1-treated lMTP-/- mice, the result of a complete absence of very low/intermediate/low density lipoproteins and a slight reduction in high density lipoprotein. Heterozygous mice showed an intermediate lipoprotein phenotype. The rate of accumulation of plasma triglyceride following Triton WR1339 treatment in lMTP-/- mice was <10% that in wild-type animals, indicating a failure of triglyceride-rich lipoprotein production. Pulse-chase experiments using hepatocytes isolated from wild-type and lMTP-/- mice revealed a failure of apoB secretion in lMTP-/- animals. Therefore, the liver-specific inactivation of the lMTP gene completely abrogates apoB-100 and very low/intermediate/low density lipoprotein production. These conditional knockout mice are a useful in vivo model for studying the role of MTP in apoB biosynthesis and the biogenesis of apoB-containing lipoproteins.
Chang
B H
BH
Departments of Cell Biology and Medicine, Baylor College of Medicine, Houston, Texas 77030, USA.
Liao
W
W
Li
L
L
Nakamuta
M
M
Mack
D
D
Chan
L
L
D000012:Abetalipoproteinemia / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D001055:Apolipoproteins B / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics*; D004195:Disease Models, Animal; D008077:Lipoproteins, LDL / Q000096:biosynthesis* / Q000235:genetics; D008079:Lipoproteins, VLDL / Q000096:biosynthesis* / Q000235:genetics; D008099:Liver / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout
D001055:Apolipoproteins B; D002352:Carrier Proteins; D008077:Lipoproteins, LDL; D008079:Lipoproteins, VLDL; C106092:microsomal triglyceride transfer protein