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Defects in gallbladder emptying and bile Acid homeostasis in mice with cystic fibrosis transmembrane conductance regulator deficiencies.

ABSTRACT: Patients with cystic fibrosis (CF) have poorly defined defects in biliary function. We evaluated the effects of cystic fibrosis transmembrane conductance regulator (CFTR) deficiency on the enterohepatic disposition of bile acids (BAs).Bile secretion and BA homeostasis were investigated in Cftr(tm1Unc) (Cftr-/-) and Cftr?F508 (?F508) mice.Cftr-/- and ?F508 mice did not grow to normal size, but did not have liver abnormalities. The gallbladders of Cftr-/- mice were enlarged and had defects in emptying, based on (99m)technetium-mebrofenin scintigraphy or post-prandial variations in gallbladder volume; gallbladder contraction in response to cholecystokinin-8 was normal. Cftr-/- mice had abnormal gallbladder bile and duodenal acidity, and overexpressed the vasoactive intestinal peptide-a myorelaxant factor for the gallbladder. The BA pool was larger in Cftr-/- than wild-type mice, although there were no differences in fecal loss of BAs. Amounts of secondary BAs in portal blood, liver, and bile of Cftr-/- mice were much lower than normal. Expression of genes that are induced by BAs, including fibroblast growth factor-15 and BA transporters, was lower in the ileum but higher in the gallbladders of Cftr-/- mice, compared with wild-type mice, whereas enzymes that synthesize BA were down-regulated in livers of Cftr-/- mice. This indicates that BAs underwent a cholecystohepatic shunt, which was confirmed using cholyl-(Ne-NBD)-lysine as a tracer. In Cftr-/- mice, cholecystectomy reversed most changes in gene expression and partially restored circulating levels of secondary BAs. The ?F508 mice overexpressed vasoactive intestinal peptide and had defects in gallbladder emptying and in levels of secondary BAs, but these features were less severe than in Cftr-/- mice.Cftr-/- and Cftr?F508 mice have defects in gallbladder emptying that disrupt enterohepatic circulation of BAs. These defects create a shunt pathway that restricts the amount of toxic secondary BAs that enter the liver.

SUBMITTER: Debray D

PROVIDER: S-EPMC3579557 | biostudies-literature | 2012 Jun

REPOSITORIES: biostudies-literature

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Defects in gallbladder emptying and bile Acid homeostasis in mice with cystic fibrosis transmembrane conductance regulator deficiencies.

Debray Dominique D Rainteau Dominique D Barbu Véronique V Rouahi Myriam M El Mourabit Haquima H Lerondel Stéphanie S Rey Colette C Humbert Lydie L Wendum Dominique D Cottart Charles-Henry CH Dawson Paul P Chignard Nicolas N Housset Chantal C

Gastroenterology 20120224 7

<h4>Background & aims</h4>Patients with cystic fibrosis (CF) have poorly defined defects in biliary function. We evaluated the effects of cystic fibrosis transmembrane conductance regulator (CFTR) deficiency on the enterohepatic disposition of bile acids (BAs).<h4>Methods</h4>Bile secretion and BA homeostasis were investigated in Cftr(tm1Unc) (Cftr-/-) and CftrΔF508 (ΔF508) mice.<h4>Results</h4>Cftr-/- and ΔF508 mice did not grow to normal size, but did not have liver abnormalities. The gallblad ...[more]

PMID: 22370478

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Project description:Background: Most cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene that lead to protein misfolding and degradation by the ubiquitin–proteasome system. Previous studies demonstrated that PIAS4 facilitates the modification of wild-type (WT) and F508del CFTR by small ubiquitin-like modifier (SUMO)-1, enhancing CFTR biogenesis by slowing immature CFTR degradation and producing increased immature CFTR band B. Methods: We evaluated two correction strategies using misfolding mutants, including the common variant, F508del. We examined the effects on mutant expression of co-expression with PIAS4 (E3 SUMO ligase), and/or the corrector, C18. To study the impact of these correction conditions, we transfected CFBE410- cells, a bronchial epithelial cell line, with a CFTR mutant plus: (1) empty vector, (2) empty vector plus overnight 5 μM C18, (3) PIAS4, and (4) PIAS4 plus C18. We assessed expression at steady state by immunoblot of CFTR band B, and if present, band C, and the corresponding C:B band ratio. The large PIAS4-induced increase in band B expression allowed us to ask whether C18 could act on the now abundant immature protein to enhance correction above the control level, as reported by the C:B ratio. Results: The data fell into three mutant CFTR categories as follows: (1) intransigent: no observable band C under any condition (i.e., C:B = 0); (2) throughput responsive: a C:B ratio less than control, but suggesting that the increased band C resulted from PIAS4-induced increases in band B production; and (3) folding responsive: a C:B ratio greater than control, reflecting C18-induced folding greater than that expected from increased throughput due to the PIAS4-induced band B level. Conclusion: These results suggest that the immature forms of CFTR folding intermediates occupy different loci within the energetic/kinetic folding landscape of CFTR. The evaluation of their properties could assist in the development of correctors that can target the more difficult-to-fold mutant conformations that occupy different sites within the CFTR folding pathway.

Dataset Information

Defects in gallbladder emptying and bile Acid homeostasis in mice with cystic fibrosis transmembrane conductance regulator deficiencies.

Publications

Defects in gallbladder emptying and bile Acid homeostasis in mice with cystic fibrosis transmembrane conductance regulator deficiencies.

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