Decreased expression of cholesterol 7alpha-hydroxylase and altered bile acid metabolism in Apobec-1-/- mice lead to increased gallstone susceptibility.
Quantitative trait mapping in mice identified a susceptibility locus for gallstones (Lith6) spanning the Apobec-1 locus, the structural gene encoding the RNA-specific cytidine deaminase responsible for production of apolipoprotein B48 in mammalian small intestine and rodent liver. This observation prompted us to compare dietary gallstone susceptibility in Apobec-1(-/-) mice and congenic C57BL/6 wild type controls. When fed a lithogenic diet (LD) for 2 weeks, 90% Apobec-1(-/-) mice developed solid gallstones in comparison with 16% wild type controls. LD-fed Apobec-1(-/-) mice demonstrated increased biliary cholesterol secretion as well as increased cholesterol saturation and bile acid hydrophobicity indices. These changes occurred despite a relative decrease in cholesterol absorption in LD-fed Apobec-1(-/-) mice. Among the possible mechanisms to account for this phenotype, expression of Cyp7a1 mRNA and protein were significantly decreased in chow-fed Apobec-1(-/-) mice, decreasing further in LD-fed animals. Cyp7a1 transcription in hepatocyte nuclei, however, was unchanged in Apobec-1(-/-) mice, excluding transcriptional repression as a potential mechanism for decreased Cyp7a1 expression. We demonstrated that APOBEC-1 binds to AU-rich regions of the 3'-untranslated region of the Cyp7a1 transcript, containing the UUUN(A/U)U consensus motif, using both UV cross-linking to recombinant APOBEC-1 and in vivo RNA co-immunoprecipitation. In vivo Apobec-1-dependent modulation of Cyp7a1 expression was further confirmed following adenovirus-Apobec-1 administration to chow-fed Apobec-1(-/-) mice, which rescued Cyp7a1 gene expression. Taken together, the findings suggest that the AU-rich RNA binding-protein Apobec-1 mediates post-transcriptional regulation of murine Cyp7a1 expression and influences susceptibility to diet-induced gallstone formation.
Xie
Yan
Y
From the Departments of Medicine, St. Louis, Missouri 63110.
Blanc
Valerie
V
From the Departments of Medicine, St. Louis, Missouri 63110.
Kerr
Thomas A
TA
From the Departments of Medicine, St. Louis, Missouri 63110.
Kennedy
Susan
S
From the Departments of Medicine, St. Louis, Missouri 63110.
Luo
Jianyang
J
From the Departments of Medicine, St. Louis, Missouri 63110.
Newberry
Elizabeth P
EP
From the Departments of Medicine, St. Louis, Missouri 63110.
Davidson
Nicholas O
NO
From the Departments of Medicine, St. Louis, Missouri 63110; Pharmacology and Developmental Biology, Washington University School of Medicine, St. Louis, Missouri 63110. Electronic address: nod@wustl.edu.
D020413:3' Untranslated Regions; D000071479:APOBEC-1 Deaminase; D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D001647:Bile Acids and Salts / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D002784:Cholesterol / Q000378:metabolism; D002790:Cholesterol 7-alpha-Hydroxylase / Q000235:genetics* / Q000378:metabolism*; D003564:Cytidine Deaminase / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D004032:Diet / Q000009:adverse effects; D042882:Gallstones / Q000209:etiology* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D022781:Hepatocytes / Q000378:metabolism; D008297:Male; D051379:Mice; D020297:Mice, Congenic; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010641:Phenotype; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection
D020413:3' Untranslated Regions; D001647:Bile Acids and Salts; D012333:RNA, Messenger; D011994:Recombinant Proteins; D002784:Cholesterol; D002790:Cholesterol 7-alpha-Hydroxylase; D000071479:APOBEC-1 Deaminase; C000605090:Apobec1 protein, mouse; D003564:Cytidine Deaminase