IFISE   05411
INSTITUTO DE FISIOLOGIA EXPERIMENTAL
Unidad Ejecutora - UE
artículos
Título:
Defective hepatocyte aquaporin-8 expression and reduced canalicular membrane water permeability in estrogen-induced cholestasis
Autor/es:
CARRERAS FI; LEHMANN GL; FERRI D; TIONI MF; CALAMITA G; MARINELLI RA
Revista:
AMERICAN JOURNAL OF PHYSIOLOGY-GASTROINTESTINAL AND LIVER PHYSIOLOGY
Referencias:
Año: 2007 vol. 292 p. 905 - 912
ISSN:
0193-1857
Resumen:
Our previous work
supports a role for aquaporin-8 (AQP8) water channels in rat hepatocyte bile
formation mainly by facilitating the osmotically driven canalicular secretion
of water. In this study, we tested
whether a condition with compromised canalicular bile secretion, i.e. the
estrogen-induced intrahepatic cholestasis, displays defective hepatocyte AQP8
functional expression. After EE administration (5 mg/kg b.w./day for 5 days) to
rats, the bile flow was reduced by 58% (P<
0.05). By subcellular fractionation and immunoblotting analysis, we found that
34 kDa AQP8 was significantly decreased by about 70% in plasma (canalicular)
and intracellular (vesicular) liver membranes. However, EE-induced cholestasis did not significantly affect the protein level or
the subcellular localization of sinusoidal AQP9. Immunohistochemistry for liver
AQPs confirmed these observations. Osmotic water permeability (Pf) of canalicular membranes, measured by
stopped-flow spectrophotometry, was significantly reduced (73 ± 1 vs. 57 ± 2 mm.sec-1) in cholestasis, consistent with defective
canalicular AQP8 functional expression. By Northern blotting, we found that AQP8 mRNA expression was increased by 115% in cholestasis, suggesting
a post-transcriptional mechanism of protein level reduction. Accordingly,
studies in primary cultured rat hepatocytes indicated that the lysosomal
protease inhibitor leupeptin prevented the estrogen-induced AQP8 down-regulation.
In conclusion, hepatocyte AQP8 protein expression is down-regulated in
estrogen-induced intrahepatic cholestasis presumably by lysosomal-mediated
degradation. Reduced canalicular membrane AQP8 expression is associated to
impaired osmotic membrane water permeability. Our data support the novel notion
that a defective expression of canalicular AQP8 contributes as a mechanism for
bile secretory dysfunction of cholestatic
hepatocytes.