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Journal of Lipid Research, Vol. 49, 2013-2022, September 2008
Copyright © 2008 by American Society for Biochemistry and Molecular Biology

ApoB100 is required for increased VLDL-triglyceride secretion by microsomal triglyceride transfer protein in ob/ob mice^*

Zhouji Chen^1,*, Elizabeth P. Newberry, Jin Y. Norris^*, Yan Xie, Jianyang Luo, Susan M. Kennedy and Nicholas O. Davidson^1,

^* Center for Human Nutrition, Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110
Division of Gastroentrology, Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110

^* This work was supported by NIH grants DK-56260, HL-38180, and Digestive Diseases Research Core Center (DK-52574) (to N.O.D) and HL-73939 (to Z.C). This work was also supported, in part, by the Clinical Nutrition Research Unit (DK-56341) of Washington University.

Published, JLR Papers in Press, June 2, 2008.

¹ To whom communication should be addressed: e-mail: nod{at}wustl.edu (N.O.D); zchen23{at}wustl.edu (Z.C)

Microsomal triglyceride transfer protein (Mttp) is a key player in the assembly and secretion of hepatic very low density lipoproteins (VLDL). Here we determined the effects of Mttp overexpression on hepatic triglyceride (TG) and VLDL secretion in leptin-deficient (ob/ob) mice, specifically in relation to apolipoproteinB (apoB) isoforms. We crossed Apobec1^–/– mice with congenic ob/ob mice to generate apoB100-only ob/ob mice (A-ob/ob). The obesity phenotype in both genotypes was similar, but A-ob/ob mice had greater hepatic TG content. Administration of recombinant adenovirus expressing murine Mttp cDNA (Ad-mMTP) increased hepatic Mttp content and activity and increased hepatic VLDL-TG secretion in A-ob/ob mice. However, despite equivalent overexpression of Mttp, there was no change in VLDL-TG secretion in ob/ob mice in a wild-type Apobec1 background. Metabolic labeling studies in primary hepatocytes from A-ob/ob mice demonstrated that Ad-mMTP increased triglyceride secretion without changing the synthesis and secretion of apoB100, suggesting greater incorporation of TG into existing VLDL particles rather than increased particle number. Ad-mMTP administration failed to increase hepatic VLDL secretion in lean Apobec1^–/– mice or controls. By contrast, VLDL secretion increased and hepatic TG content decreased following Ad-mMTP administration to human APOB transgenic mice crossed into the Apobec1^–/– line. These findings demonstrate that Ad-mMTP increases murine hepatic VLDL-TG secretion only in the apoB100 background, and even then only in situations with either increased hepatic TG accumulation or increased apoB100 expression.

Supplementary key words hepatic steatosis • VLDL secretion • apoB mRNA editing • apobec1

Abbreviations: ALT, alanine aminotransferase; ApoB, apolipoprotein B; apobec1, apolipoprotein B mRNA editing catalytic polypeptide 1; GFP, green fluorescent protein; Mttp, microsomal triglyceride transfer protein; TG, triglyceride; VLDL, very low density lipoprotein

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