Abnormal expression of anion exchanger genes in primary biliary cirrhosis

Prìeto, Jesús; Qian, Cheng; Garcı́a, Nicolás; Dı́ez, Javier; Medina, Juan F.

doi:10.1016/0016-5085(93)90735-u

Cited by 131 publications

(99 citation statements)

References 28 publications

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“…[17][18][19][20]39,43 Our data may provide a missing pathophysiologic link in the pathogenesis of PBC, which, in our view, is based on the interplay between genetic, exogenous, and endogenous predisposing factors. [17][18][19][20]39,43 Future therapeutic approaches might, therefore, aim to further strengthen the weakened biliary HCO À 3 umbrella in PBC. 7 Advances have been made in understanding the mechanisms and sites of action of ursodeoxycholic acid (UDCA) in the therapy of chronic cholangiopathies.…”

Section: Discussionmentioning

confidence: 78%

“…23 Ischemia-type biliary lesions and nonanastomotic bile duct strictures after liver transplantation with denervation in man 42 may be a consequence of disrupted vagal acetylcholine signaling, a physiologic driving force of biliary HCO À Our data may have particular impact on the understanding of the pathogenesis and treatment of PBC. [17][18][19][20]39,43 Increasing evidence supports the view that cholangiocyte apoptosis is a driving force in the pathogenesis of PBC: It has long been demonstrated that cholangiocyte apoptosis is associated with ductular inflammation in PBC, but not PSC. 44 Furthermore, cholangiocytes of small bile ducts expose immunologically reactive PDC-E2 or PDC-E2-like protein during apoptosis, 16 which might explain, in part, the organ specificity of the immune reaction in PBC.…”

Section: Discussionmentioning

confidence: 93%

“…15,16 By altering sensitivity toward bile salt toxicity and increasing frequency of apoptotic events in cholangiocytes, genetic and acquired defects disrupting the biliary HCO À 3 umbrella may be a common pathogenetic factor in various cholangiopathies. Genetic variants of key modulators of the biliary HCO À 3 umbrella 7 have been associated with the manifestation or progression of chronic cholestasis, as demonstrated for anion exchanger 2 (AE2) in PBC, [17][18][19][20] TGR5 in primary sclerosing cholangitis (PSC), 21 or cystic fibrosis transmembrane conductance regulator (CFTR) 22,23 in cystic-fibrosis-associated liver disease.…”

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confidence: 99%

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A biliary HCO₃⁻umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

et al. 2011

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Human cholangiocytes are continuously exposed to millimolar levels of hydrophobic bile salt monomers. We recently hypothesized that an apical biliary HCO À 3 umbrella might prevent the protonation of biliary glycine-conjugated bile salts and uncontrolled cell entry of the corresponding bile acids, and that defects in this biliary HCO À 3 umbrella might predispose to chronic cholangiopathies. Here, we tested in vitro whether human cholangiocyte integrity in the presence of millimolar bile salt monomers is dependent on (1) pH, (2) adequate expression of the key HCO À 3 exporter, anion exchanger 2 (AE2), and (3) an intact cholangiocyte glycocalyx. To address these questions, human immortalized cholangiocytes and cholangiocarcinoma cells were exposed to chenodeoxycholate and its glycine/taurine conjugates at different pH levels. Bile acid uptake was determined radiochemically. Cell viability and apoptosis were measured enzymatically. AE2 was knocked down by lentiviral short hairpin RNA. A cholangiocyte glycocalyx was identified by electron microscopy, was enzymatically desialylated, and sialylation was quantified by flow cytometry. We found that bile acid uptake and toxicity in human immortalized cholangiocytes and cholangiocarcinoma cell lines in vitro were pH and AE2 dependent, with the highest rates at low pH and when AE2 expression was defective. An apical glycocalyx was identified on cholangiocytes in vitro by electron microscopic techniques. Desialylation of this protective layer increased cholangiocellular vulnerability in a pH-dependent manner. Conclusion: A biliary HCO À 3 umbrella protects human cholangiocytes against damage by bile acid monomers. An intact glycocalyx and adequate AE2 expression are crucial in this process. Defects of the biliary HCO À 3 umbrella may lead to the development of chronic cholangiopathies.

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Section: Discussionmentioning

confidence: 78%

Section: Discussionmentioning

confidence: 93%

mentioning

confidence: 99%

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A biliary HCO₃⁻umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

et al. 2011

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“…In human liver, the expression of the AE2 message has been shown by reverse transcription-polymerase chain reaction on total RNA (Prieto et al 1993). Immunocytochemical studies on human liver, using a monoclonal antibody against a synthetic AE2 peptide, have shown that immunoreactivity is restricted to the canicular membrane of hepatocytes and to the luminal surfaces of intrahepatic bile ducts (Martínez-Ansó et al 1994).…”

Section: Introductionmentioning

confidence: 99%

In situ detection of AE2 anion-exchanger mRNA in the human liver

García

Montuenga

Medina

et al. 1998

Cell and Tissue Research

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Na + -independent anion exchangers, a family of membrane proteins that mediate electroneutral exchanges of chloride and bicarbonate ions across the cell membrane, are considered to be involved in intracellular pH regulation as well as in transepithelial acid/base transport. Previous immunohistochemical data have shown that anion-exchanger-2 (AE2) protein is expressed in the liver parenchyma, localizing at both the canaliculi and the luminal surfaces of intrahepatic bile ducts, where it may have a role in the biliary secretion of bicarbonate. In the present study, we have carried out in situ hybridization experiments on biopsies of human liver using three overlapping antisense anion-exchanger-2 riboprobes. Anion-exchanger-2 mRNA signals were localized mainly in the cytoplasm of terminal and interlobular bile-duct cells, whereas weaker signals were observed in bile-duct cells of larger intrahepatic ducts. Furthermore, some hepatocytes, mostly periportal, contained detectable anion-exchanger-2 mRNA signals in their cytoplasm. No hybridization signals were observed in controls with sense riboprobes, with omission of the antisense probe, or with treatment of the sections with RNase before hybridizations. Finally, intense anion-exchanger-2 hybridization signals were observed in lymphomononuclear cells in sinusoids and in portal infiltrates. Immunocytochemical data from reverse-phase sections suggest that these cells correspond to some of the CD45R+ (UCHL1+) T lymphocytes resident in the liver.

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“…Thus, the first 17 amino acid triplets of AE2a are replaced by 3 triplets for residues MTQ in AE2b 1 and by 8 triplets for residues MDFLLRPQ in AE2b 2 . In addition to the mRNA level [9][10][11], liver expression of the human AE2 gene has been substantiated at the protein level by using a monoclonal antibody against an AE2 peptide common to all three AE2 isoforms [12]. This study showed AE2 immunoreactivity restricted to the lumenal surface of the hepatobiliary tree [12].…”

mentioning

confidence: 96%

Shared apical sorting of anion exchanger isoforms AE2a, AE2b1, and AE2b2 in primary hepatocytes

Aranda

Martı́nez

Melero

et al. 2004

Biochemical and Biophysical Research Communications

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AE2 (SLC4A2) is the member of the Na þ -independent anion exchanger (AE) family putatively involved in the secretion of bicarbonate to bile. In humans, three variants of AE2 mRNA have been described: the full-length transcript AE2a (expressed from the upstream promoter in most tissues), and alternative transcripts AE2b 1 and AE2b 2 (driven from alternate promoter sequences in a tissue-restricted manner, mainly in liver and kidney). These transcripts would result in AE protein isoforms with short N-terminal differences. To ascertain their translation, functionality, and membrane sorting, we constructed expression vectors encoding each AE2 isoform fused to GFP at the C-terminus. Transfected HEK293 cells showed expression of functional GFP-tagged AE2 proteins, all three isoforms displaying comparable AE activities. Primary rat hepatocytes transfected with expression vectors and repolarized in a collagen-sandwich configuration showed a microtubule-dependent apical sorting of each AE2 isoform. This shared apical sorting is liver-cell specific, as sorting of AE2 isoforms was basolateral in control experiments on polarized kidney MDCK cells. Hepatocytic apical targeting of AE2 isoforms suggests that they all may participate in the canalicular secretion of bicarbonate to bile.

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Abnormal expression of anion exchanger genes in primary biliary cirrhosis

Cited by 131 publications

References 28 publications

A biliary HCO₃⁻umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

A biliary HCO₃⁻umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

In situ detection of AE2 anion-exchanger mRNA in the human liver

Shared apical sorting of anion exchanger isoforms AE2a, AE2b1, and AE2b2 in primary hepatocytes

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Abnormal expression of anion exchanger genes in primary biliary cirrhosis

Cited by 131 publications

References 28 publications

A biliary HCO3−umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

A biliary HCO3−umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

In situ detection of AE2 anion-exchanger mRNA in the human liver

Shared apical sorting of anion exchanger isoforms AE2a, AE2b1, and AE2b2 in primary hepatocytes

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A biliary HCO₃⁻umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

A biliary HCO₃⁻umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes