Diferentially expressed adenylyl cyclase isoforms mediate secretory functions in cholangiocyte subpopulation

Authors

  • Mario Strazzabosco,

    Corresponding author
    1. Section of Digestive Diseases, Department of Internal Medicine, Yale University School of Medicine and Liver Center, New Haven CT
    2. Center for Liver Research (CeliveR), Ospedali Riuniti, Bergamo, Italy
    3. Department of Clinical Medicine, University of Milano-Bicocca, Milan, Italy
    • Section of Digestive Diseases, Department of Internal Medicine, Yale University School of Medicine, 333 Cedar Street LMP 1080, New Haven, CT 06520
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    • fax: 203-785-7273.

  • Romina Fiorotto,

    1. Section of Digestive Diseases, Department of Internal Medicine, Yale University School of Medicine and Liver Center, New Haven CT
    2. Department of Gastroenterological and Surgical Sciences “P.G. Cevese,” Università di Padova, Padova, Italy
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  • Saida Melero,

    1. Center for Liver Research (CeliveR), Ospedali Riuniti, Bergamo, Italy
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  • Shannon Glaser,

    1. Division of Research and Education, Department of Medicine, Scott & White/Texas A&M Health Science Center, College of Medicine, Temple, TX
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  • Heather Francis,

    1. Division of Research and Education, Department of Medicine, Scott & White/Texas A&M Health Science Center, College of Medicine, Temple, TX
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  • Carlo Spirli,

    1. Section of Digestive Diseases, Department of Internal Medicine, Yale University School of Medicine and Liver Center, New Haven CT
    2. Center for Liver Research (CeliveR), Ospedali Riuniti, Bergamo, Italy
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    • C. S. is a recipient of an American Liver Foundation/American Association for the Study of Liver Diseases Liver Scholar Award.

  • Gianfranco Alpini

    1. Division of Research and Education, Department of Medicine, Scott & White/Texas A&M Health Science Center, College of Medicine, Temple, TX
    2. Central Texas Veterans Health Care System, Temple, TX
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  • Potential conflict of interest: Nothing to report.

Abstract

Cyclic adenosine monophosphate (cAMP) is generated by adenylyl cyclases (ACs), a group of enzymes with different tissue specificity and regulation. We hypothesized that AC isoforms are heterogeneously expressed along the biliary tree, are associated with specific secretory stimuli, and are differentially modulated in cholestasis. Small duct and large duct cholangiocytes were isolated from controls and from lipopolysaccharide-treated or α-naphthylisothiocyanate–treated rats. AC isoform expression was assessed via real-time polymerase chain reaction. Secretion and cAMP levels were measured in intrahepatic bile duct units after stimulation with secretin, forskolin, HCO3/CO2, cholinergic agonists, and β-adrenergic agonists, with or without selected inhibitors or after silencing of AC8 or soluble adenylyl cyclase (sAC) with small interfering RNA. Gene expression of the Ca2+-insensitive isoforms (AC4, AC7) was higher in small duct cholangiocytes, whereas that of the Ca2+-inhibitable (AC5, AC6, AC9), the Ca2+/calmodulin-stimulated AC8, and the soluble sAC was higher in large duct cholangiocytes. Ca2+/calmodulin inhibitors and AC8 gene silencing inhibited choleresis and cAMP production stimulated by secretin and acetylcholine, but not by forskolin. Secretion stimulated by isoproterenol and calcineurin inibitors was cAMP-dependent and γ-aminobutyric acid–inhibitable, consistent with activation of AC9. Cholangiocyte secretion stimulated by isohydric changes in [HCO3]i was cAMP-dependent and inhibited by sAC inhibitor and sAC gene silencing. Treatment with lipopolysaccharide or α-naphthylisothiocyanate increased expression of AC7 and sAC but decreased expression of the other ACs. Conclusion: These studies demonstrate a previously unrecognized role of ACs in biliary pathophysiology. In fact: (1) AC isoforms are differentially expressed in cholangiocyte subpopulations; (2) AC8, AC9, and sAC mediate cholangiocyte secretion in response to secretin, β-adrenergic agonists, or changes in [HCO3]i, respectively; and (3) AC gene expression is modulated in experimental cholestasis. (HEPATOLOGY 2009)

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