Intestine-specific expression of Apobec-1 rescues apolipoprotein B RNA editing and alters chylomicron production in Apobec1 mice

Valerie Blanc,Nicholas O Davidson,Susan Kennedy,Jianyang Luo,Yan Xie

doi:10.1194/jlr.m030494

Abstract

Intestinal apolipoprotein B (apoB) mRNA undergoes C-to-U editing, mediated by the catalytic deaminase apobec-1, which results in translation of apoB48. Apobec1(-/-) mice produce only apoB100 and secrete larger chylomicron particles than those observed in wild-type (WT) mice. Here we show that transgenic rescue of intestinal apobec-1 expression (Apobec1(Int/O)) restores C-to-U RNA editing of apoB mRNA in vivo, including the canonical site at position 6666 and also at approximately 20 other newly identified downstream sites present in WT mice. The small intestine of Apobec1(Int/O) mice produces only apoB48, and the liver produces only apoB100. Serum chylomicron particles were smaller in Apobec1(Int/O) mice compared with those from Apobec1(-/-) mice, and the predominant fraction of serum apoB48 in Apobec1(Int/O) mice migrated in lipoproteins smaller than chylomicrons, even when these mice were fed a high-fat diet. Because apoB48 arises exclusively from the intestine in Apobec1(Int/O) mice and intestinal apoB48 synthesis and secretion rates were comparable to WT mice, we were able to infer the major sites of origin of serum apoB48 in WT mice. Our findings imply that less than 25% of serum apoB48 in WT mice arises from the intestine, with the majority originating from the liver.

Highlights

Intestinal apolipoprotein B mRNA undergoes C-to-U editing, mediated by the catalytic deaminase apobec-1, which results in translation of apoB48
For the purposes of this report, we focused on two lines in which human apobec-1 was expressed homogeneously in the small intestine at either a relatively high or low level when compared with endogenous murine apobec-1
Relative expression levels of the GFP-apobec-1 fusion protein in extracts from these lines of mice (Fig. 1C) indicated ‫ف‬8-fold higher levels in the high-expressor line compared with the low-expressor line (Fig. 1D), which was more in line with the semiquantitative RT-PCR data

Summary

Introduction

Intestinal apolipoprotein B (apoB) mRNA undergoes C-to-U editing, mediated by the catalytic deaminase apobec-1, which results in translation of apoB48. We show that transgenic rescue of intestinal apobec-1 expression (Apobec1Int/O) restores C-to-U RNA editing of apoB mRNA in vivo, including the canonical site at position 6666 and at approximately 20 other newly identified downstream sites present in WT mice. Because apoB48 arises exclusively from the intestine in Apobec1Int/O mice and intestinal apoB48 synthesis and secretion rates were comparable to WT mice, we were able to infer the major sites of origin of serum apoB48 in WT mice. Our findings imply that less than 25% of serum apoB48 in WT mice arises from the intestine, with the majority originating from the liver.—Blanc, V., Y. Intestine-specific expression of Apobec-1 rescues apolipoprotein B RNA editing and alters chylomicron production in Apobec1Ϫ/Ϫ mice.

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Conclusion