Defective hepatocyte aquaporin-8 expression and reduced canalicular membrane water permeability in estrogen-induced cholestasis

2007 ◽  
Vol 292 (3) ◽  
pp. G905-G912 ◽  
Author(s):  
Flavia I. Carreras ◽  
Guillermo L. Lehmann ◽  
Domenico Ferri ◽  
Mariana F. Tioni ◽  
Giuseppe Calamita ◽  
...  
Keyword(s):  
Water Permeability ◽  
Protein Level ◽  
Intrahepatic Cholestasis ◽  
Rat Hepatocytes ◽  
Functional Expression ◽  
Bile Secretion ◽  
Northern Blotting ◽  
Bile Formation ◽  
Canalicular Membrane ◽  
Lysosomal Protease

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 17α-ethinylestradiol administration (5 mg·kg body wt−1·day−1 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 ∼70% in plasma (canalicular) and intracellular (vesicular) liver membranes. However, 17α-ethinylestradiol-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 μm/s) 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 posttranscriptional mechanism of protein level reduction. Accordingly, studies in primary cultured rat hepatocytes indicated that the lysosomal protease inhibitor leupeptin prevented the estrogen-induced AQP8 downregulation. In conclusion, hepatocyte AQP8 protein expression is downregulated in estrogen-induced intrahepatic cholestasis, presumably by lysosomal-mediated degradation. Reduced canalicular membrane AQP8 expression is associated with 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.

Knockdown of hepatocyte aquaporin-8 by RNA interference induces defective bile canalicular water transport

2009 ◽  
Vol 296 (1) ◽  
pp. G93-G100 ◽  
Author(s):  
M. Cecilia Larocca ◽  
Leandro R. Soria ◽  
M. Victoria Espelt ◽  
Guillermo L. Lehmann ◽  
Raúl A. Marinelli
Keyword(s):  
Rna Interference ◽  
Water Transport ◽  
Hepg2 Cells ◽  
Water Movement ◽  
Rat Hepatocytes ◽  
Conclusive Evidence ◽  
Osmotic Gradient ◽  
Bile Formation ◽  
Canalicular Membrane ◽  
Water Secretion

Aquaporin-8 (AQP8) water channels, which are expressed in rat hepatocyte bile canalicular membranes, are involved in water transport during bile formation. Nevertheless, there is no conclusive evidence that AQP8 mediates water secretion into the bile canaliculus. In this study, we directly evaluated whether AQP8 gene silencing by RNA interference inhibits canalicular water secretion in the human hepatocyte-derived cell line, HepG2. By RT-PCR and immunoblotting we found that HepG2 cells express AQP8 and by confocal immunofluorescence microscopy that it is localized intracellularly and on the canalicular membrane, as described in rat hepatocytes. We also verified the expression of AQP8 in normal human liver. Forty-eight hours after transfection of HepG2 cells with RNA duplexes targeting two different regions of human AQP8 molecule, the levels of AQP8 protein specifically decreased by 60–70%. We found that AQP8 knockdown cells showed a significant decline in the canalicular volume of ∼70% ( P < 0.01), suggesting an impairment in the basal (nonstimulated) canalicular water movement. We also found that the decreased AQP8 expression inhibited the canalicular water transport in response either to an inward osmotic gradient (−65%, P < 0.05) or to the bile secretory agonist dibutyryl cAMP (−80%, P < 0.05). Our data suggest that AQP8 plays a major role in water transport across canalicular membrane of HepG2 cells and support the notion that defective expression of AQP8 causes bile secretory dysfunction in human hepatocytes.

scholarly journals The Water Channel Aquaporin-8 Is Mainly Intracellular in Rat Hepatocytes, and Its Plasma Membrane Insertion Is Stimulated by Cyclic AMP

2001 ◽  
Vol 276 (15) ◽  
pp. 12147-12152 ◽  
Author(s):  
Fabiana Garcı́a ◽  
Arlinet Kierbel ◽  
M. Cecilia Larocca ◽  
Sergio A. Gradilone ◽  
Patrick Splinter ◽  
...  
Keyword(s):  
Water Transport ◽  
Water Permeability ◽  
Plasma Membranes ◽  
Water Channel ◽  
Rat Hepatocytes ◽  
Immunoblot Analysis ◽  
Subcellular Fractionation ◽  
Bile Secretion ◽  
Confocal Immunofluorescence Microscopy ◽  
Microsomal Membranes

We previously found that water transport across hepatocyte plasma membranes occurs mainly via a non-channel mediated pathway. Recently, it has been reported that mRNA for the water channel, aquaporin-8 (AQP8), is present in hepatocytes. To further explore this issue, we studied protein expression, subcellular localization, and regulation of AQP8 in rat hepatocytes. By subcellular fractionation and immunoblot analysis, we detected anN-glycosylated band of ∼34 kDa corresponding to AQP8 in hepatocyte plasma and intracellular microsomal membranes. Confocal immunofluorescence microscopy for AQP8 in cultured hepatocytes showed a predominant intracellular vesicular localization. Dibutyryl cAMP (Bt2cAMP) stimulated the redistribution of AQP8 to plasma membranes. Bt2cAMP also significantly increased hepatocyte membrane water permeability, an effect that was prevented by the water channel blocker dimethyl sulfoxide. The microtubule blocker colchicine but not its inactive analog lumicolchicine inhibited the Bt2cAMP effect on both AQP8 redistribution to cell surface and hepatocyte membrane water permeability. Our data suggest that in rat hepatocytes AQP8 is localized largely in intracellular vesicles and can be redistributed to plasma membranes via a microtubule-depending, cAMP-stimulated mechanism. These studies also suggest that aquaporins contribute to water transport in cAMP-stimulated hepatocytes, a process that could be relevant to regulated hepatocyte bile secretion.

LPS induces the TNF-α-mediated downregulation of rat liver aquaporin-8: role in sepsis-associated cholestasis

2008 ◽  
Vol 294 (2) ◽  
pp. G567-G575 ◽  
Author(s):  
Guillermo L. Lehmann ◽  
Flavia I. Carreras ◽  
Leandro R. Soria ◽  
Sergio A. Gradilone ◽  
Raúl A. Marinelli
Keyword(s):  
Molecular Mechanisms ◽  
Water Movement ◽  
Primary Cultures ◽  
Proteasome Inhibitors ◽  
Functional Expression ◽  
Subcellular Fractionation ◽  
Bile Formation ◽  
Lysosomal Protease ◽  
Osmotic Water ◽  
Tnf Α

Although bacterial lipopolysaccharides (LPS) are known to cause cholestasis in sepsis, the molecular mechanisms accounting for this effect are only partially known. Because aquaporin-8 (AQP8) seems to facilitate the canalicular osmotic water movement during hepatocyte bile formation, we studied its gene and functional expression in LPS-induced cholestasis. By subcellular fractionation and immunoblotting analysis, we found that 34-kDa AQP8 was significantly decreased by 70% in plasma (canalicular) and intracellular (vesicular) liver membranes. However, expression and subcellular localization of hepatocyte sinusoidal AQP9 were unaffected. Immunohistochemistry for liver AQPs confirmed these observations. Osmotic water permeability ( Pf) of canalicular membranes, measured by stopped-flow spectrophotometry, was significantly reduced (65 ± 1 vs. 49 ± 1 μm/s) by LPS, consistent with defective canalicular AQP8 functional expression. By Northern blot analysis, we found that 1.5-kb AQP8 mRNA expression was increased by 80%, suggesting a posttranscriptional mechanism of protein reduction. The tumor necrosis factor-α (TNF-α) receptor fusion protein TNFp75:Fc prevented the LPS-induced impairment of AQP8 expression and bile flow, suggesting the cytokine TNF-α as a major mediator of LPS effect. Accordingly, studies in hepatocyte primary cultures indicated that recombinant TNF-α downregulated AQP8. The effect of TNF-α was prevented by the lysosomal protease inhibitors leupeptin or chloroquine or by the proteasome inhibitors MG132 or lactacystin, suggesting a cytokine-induced AQP8 proteolysis. In conclusion, our data suggest that LPS induces the TNF-α-mediated posttranscriptional downregulation of AQP8 functional expression in hepatocytes, a mechanism potentially relevant to the molecular pathogenesis of sepsis-associated cholestasis.

ABCB4/MDR3 in health and disease – at the crossroads of biochemistry and medicine

2019 ◽  
Vol 400 (10) ◽  
pp. 1245-1259 ◽  
Author(s):  
Martin Prescher ◽  
Tim Kroll ◽  
Lutz Schmitt
Keyword(s):  
Intrahepatic Cholestasis ◽  
Bile Salts ◽  
Biliary Tree ◽  
Drug Induced ◽  
Bile Formation ◽  
Canalicular Membrane ◽  
Outer Leaflet ◽  
Separate Step ◽  
Type 3

Abstract Several ABC transporters of the human liver are responsible for the secretion of bile salts, lipids and cholesterol. Their interplay protects the biliary tree from the harsh detergent activity of bile salts. Among these transporters, ABCB4 is essential for the translocation of phosphatidylcholine (PC) lipids from the inner to the outer leaflet of the canalicular membrane of hepatocytes. ABCB4 deficiency can result in altered PC to bile salt ratios, which led to intrahepatic cholestasis of pregnancy, low phospholipid associated cholelithiasis, drug induced liver injury or even progressive familial intrahepatic cholestasis type 3. Although PC lipids only account for 30–40% of the lipids in the canalicular membrane, 95% of all phospholipids in bile are PC lipids. We discuss this discrepancy in the light of PC synthesis and bile salts favoring certain lipids. Nevertheless, the in vivo extraction of PC lipids from the outer leaflet of the canalicular membrane by bile salts should be considered as a separate step in bile formation. Therefore, methods to characterize disease causing ABCB4 mutations should be considered carefully, but such an analysis represents a crucial point in understanding the currently unknown transport mechanism of this ABC transporter.

scholarly journals MRP3, a new ATP-binding cassette protein localized to the canalicular domain of the hepatocyte

1999 ◽  
Vol 276 (6) ◽  
pp. G1493-G1500 ◽  
Author(s):  
Daniel F. Ortiz ◽  
Shaohua Li ◽  
Ramachandran Iyer ◽  
Xingming Zhang ◽  
Phyllis Novikoff ◽  
...  
Keyword(s):  
Multidrug Resistance ◽  
Sequence Similarity ◽  
Immunoblot Analysis ◽  
Bile Secretion ◽  
Membrane Topology ◽  
Atp Binding ◽  
Sprague Dawley ◽  
Bile Formation ◽  
Canalicular Membrane ◽  
Atp Binding Cassette

Bile secretion in liver is driven in large part by ATP-binding cassette (ABC)-type proteins that reside in the canalicular membrane and effect ATP-dependent transport of bile acids, phospholipids, and non-bile acid organic anions. Canalicular ABC-type proteins can be classified into two subfamilies based on membrane topology and sequence identity: MDR1, MDR3, and SPGP resemble the multidrug resistance (MDR) P-glycoprotein, whereas MRP2 is similar in structure and sequence to the multidrug resistance protein MRP1 and transports similar substrates. We now report the isolation of the rMRP3 gene from rat liver, which codes for a protein 1522 amino acids in length that exhibits extensive sequence similarity with MRP1 and MRP2. Northern blot analyses indicate that rMRP3 is expressed in lung and intestine of Sprague-Dawley rats as well as in liver of Eisai hyperbilirubinemic rats and TR− mutant rats, which are deficient in MRP2 expression. rMRP3 expression is also transiently induced in liver shortly after birth and during obstructive cholestasis. Antibodies raised against MRP3 recognize a polypeptide of 190–200 kDa, which is reduced in size to 155–165 kDa after treatment with endoglycosidases. Immunoblot analysis and immunoconfocal microscopy indicate that rMRP3 is present in the canalicular membrane, suggesting that it may play a role in bile formation.

scholarly journals Combination of Novel c.3484G> T/p.Glu162Ter Variant in ABCB11 and c.208G> A/p.Asp70Asn Variant in ATP8B1 Are Associated with Severe Symptoms in Progressive Family Intrahepatic Cholestasis

2020 ◽  
Vol 09 (04) ◽  
pp. 285-288
Author(s):  
Mervan Bekdas ◽  
Guray Can ◽  
Recep Eroz ◽  
Selma Erdogan Duzcu
Keyword(s):  
Intrahepatic Cholestasis ◽  
Autosomal Recessive ◽  
Autosomal Recessive Disease ◽  
Bile Secretion ◽  
Peripheral Blood Sample ◽  
Portal Fibrosis ◽  
Traditional Treatment ◽  
Pathogenic Variants ◽  
Chronic Cholestasis ◽  
Whole Exome

AbstractProgressive family intrahepatic cholestasis (PFIC) is an autosomal recessive disease that causes chronic cholestasis. It is associated with pathogenic variants in genes that encode proteins involved in bile secretion to canaliculus from hepatocytes. In this study, we present a 16-year-old boy who presented with severe pruritus and cholestatic jaundice. All possible infectious etiologies were negative. A liver biopsy was consistent with intrahepatic cholestasis and portal fibrosis. DNA was isolated from a peripheral blood sample, and whole exome sequencing was performed. A novel c.3484G > T/p.Glu162Ter variant in the ABCB11 gene and a c.208G> A/p.Asp70Asn variant in the ATP8B1 gene were detected. Despite traditional treatment, the patient's recurrent severe symptoms did not improve. The patient was referred for a liver transplantation. This novel c.3484G > T/p.Glu162Ter variant is associated with a severe and recurrent presentation, and the two compound variants could explain the severity of PFIC.

Cloning and functional expression of an MIP (AQP0) homolog from killifish (Fundulus heteroclitus) lens

2001 ◽  
Vol 281 (6) ◽  
pp. R1994-R2003 ◽  
Author(s):  
Leila V. Virkki ◽  
Gordon J. Cooper ◽  
Walter F. Boron
Keyword(s):  
Water Permeability ◽  
Fundulus Heteroclitus ◽  
Water Channel ◽  
Fold Increase ◽  
Functional Expression ◽  
Xenopus Laevis Oocytes ◽  
Lens Fiber ◽  
Fiber Cells ◽  
Aqp1 Expression ◽  
Very High

The major intrinsic protein (MIP) of lens fiber cells is a member of the aquaporin (AQP) water channel family. The protein is expressed at very high levels in lens fiber cells, but its physiological function is unclear. By homology to known AQPs, we have cloned a full-length cDNA encoding an MIP from the lens of killifish ( Fundulus heteroclitus). The predicted protein (263 amino acids; GenBank accession no. AF191906 ) shows 77% identity to amphibian MIPs, 70% identity to mammalian MIPs, and 46% identity to mammalian AQP1. Expression of MIPfun in Xenopus laevis oocytes causes an ∼40-fold increase in oocyte water permeability. This stimulation is comparable to that seen with AQP1 and substantially larger than that seen with other MIPs. The mercurials HgCl2 and p-chloromercuribenzenesulfonate inhibit the water permeability of MIPfun by ∼25%. MIPfun is not permeable to glycerol, urea, or formic acid but is weakly permeable to CO2.

scholarly journals Sepsis as a cause of intrahepatic cholestasis

2009 ◽  
Vol 137 (5-6) ◽  
pp. 278-281
Author(s):  
Jelena Rudic ◽  
Rada Jesic ◽  
Djordje Culafic ◽  
Radmila Sarenac-Kovac ◽  
Vladislava Bulat ◽  
...  
Keyword(s):  
Antibiotic Treatment ◽  
Intrahepatic Cholestasis ◽  
Liver Function Tests ◽  
Biliary Cirrhosis ◽  
Abdominal Ultrasonography ◽  
Laboratory Findings ◽  
Bile Formation ◽  
Normocytic Normochromic Anaemia ◽  
Inflammatory Syndrome ◽  
Possible Cause

Introduction. The causes of intrahepatic cholestasis include cholestatic viral hepatitis, primary biliary cirrhosis, benign recurrent cholestasis, primary sclerosing cholangitis and sepsis. During sepsis, proinflammatory cytokines and nitric oxide cause cholestasis by impairing hepatocellular and ductal bile formation. Case Outline. We report a 48-year-old woman who was admitted to hospital due to malaise, jaundice, fever and pain in the neck. Physical examination revealed jaundice, tachycardia (pulse rate was 120/min), hypotension 90/60 mm Hg. Laboratory findings showed normocytic normochromic anaemia, inflammatory syndrome and abnormal liver function tests indicating cholestasis and hepatocellular necrosis. Abdominal ultrasonography detected hepatosplenomegaly. Chest computed tomography showed bronchopneumonic infiltrates. Percutaneous liver biopsy was performed using a Menghini needle of 1.4 mm. Pathohystological analysis of the liver tissue confirmed reactive, intrahepatic cholestasis. Blood cultures isolated Staphylococcus aureus. After the diagnosis was established the treatment with broad-spectrum antibiotics was carried out, resulting in the improvement of general condition of the patient, regression of inflammatory syndrome, disappearance of cholestasis and regression of pulmonary infiltrates. Abdominal ultrasonography after antibiotic treatment did not show hepatosplenomegaly. Conclusion. Concerning patients with cholestasis of uncertain origin, we should always think of sepsis as a possible cause in order to start antibiotic treatment in time.

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