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Expression of inositol 1,4,5-trisphosphate receptor isoforms in rat cirrhosis
J F Dufour1, M Lüthi, M Forestier
1Department of Clinical Pharmacology, University of Bern, Switzerland. jf.dufour@ikp.unibe.ch
Abstract:
Ca(2+) signals mediate the hepatic effects of numerous hormones and growth factors. Hepatic Ca(2+) signals are elicited by the inositol trisphosphate receptor, an intracellular Ca(2+) channel. Three isoforms of this receptor have been identified; they are expressed and regulated differently. We investigated the effect of liver fibrosis and cirrhosis on the hepatic expression of the inositol trisphosphate receptor isoforms. Two different rat models were used: bile duct ligation (fibrosis) and chronic exposure to CCl(4)/phenobarbital (cirrhosis). Messenger RNA levels were determined by ribonuclease protection assay (RPA), competitive polymerase chain reaction (PCR) followed by Southern blotting, and real-time quantitative PCR. Protein expression was assessed by Western blotting; tissue distribution was assessed by immunohistology. In control animals, isoform 2 was the predominant isoform, isoform 1 represented less than one third, and isoform 3 less than 1%. After bile duct ligation, expression of types 1 and 3 increased 1.9- and 5.7-fold, and expression of type 2 decreased 2. 5-fold at the protein level. After exposure to CCl(4)/phenobarbital, expression of types 1, 2, and 3 were 2.4-, 0.9-, and 4.2-fold their expression in control animals. Type 2 was localized to the apical domain of hepatocytes, consistent with a role for Ca(2+) signals in canalicular function. Type 3 was detectable in intrahepatic bile duct epithelial cells and not in hepatocytes, suggesting that Ca(2+) signals may be regulated differently in these cells. Signaling through inositol trisphosphate receptor participates in the pathogenesis of cirrhosis, because this process affects the expression of its isoforms.
Insights
Liver fibrosis and cirrhosis alter the expression of inositol trisphosphate receptor isoforms, crucial for calcium signaling in liver cells. These changes suggest the receptor
Area of Science:
- Hepatology and molecular biology
- Cellular signaling pathways
- Calcium ion (Ca2+) regulation
Background:
- Calcium (Ca2+) signals are vital for liver function, mediated by the inositol trisphosphate receptor (IP3R), an intracellular Ca2+ channel.
- Three IP3R isoforms exist, with distinct expression and regulation patterns.
- Understanding IP3R isoform changes in liver disease is crucial for elucidating disease mechanisms.
Purpose of the Study:
- To investigate the impact of liver fibrosis and cirrhosis on the expression of IP3R isoforms in rat livers.
- To determine the cellular localization of IP3R isoforms in healthy and diseased liver tissue.
Main Methods:
- Utilized two rat models: bile duct ligation for fibrosis and chronic CCl4/phenobarbital for cirrhosis.
- Quantified messenger RNA (mRNA) levels using ribonuclease protection assay (RPA), competitive polymerase chain reaction (PCR), and real-time quantitative PCR.
- Assessed protein expression via Western blotting and tissue distribution through immunohistology.
Main Results:
- In control rats, IP3R isoform 2 was predominant, with isoform 1 at less than one third and isoform 3 at less than 1%.
- Bile duct ligation (fibrosis) led to increased protein expression of IP3R types 1 (1.9-fold) and 3 (5.7-fold), and decreased expression of type 2 (2.5-fold).
- CCl4/phenobarbital exposure (cirrhosis) resulted in altered expression: IP3R types 1 (2.4-fold), 2 (0.9-fold), and 3 (4.2-fold) compared to controls. IP3R type 2 localized to the apical hepatocyte domain, while type 3 was found in bile duct epithelial cells, not hepatocytes.
Conclusions:
- Liver fibrosis and cirrhosis significantly alter the expression patterns of inositol trisphosphate receptor isoforms.
- IP3R isoform changes during liver disease suggest their involvement in the pathogenesis of cirrhosis.
- Differential localization of IP3R isoforms indicates distinct roles and regulation of calcium signaling in hepatocytes versus bile duct epithelial cells.