Differentielle Regulation organischer Anionentransporter der Oatp-Familie bei Ethinylöstradiol-induzierter Cholestase der Ratte

Estrogen-mediated cholestasis is an important clinical entity, but its molecular pathophysiology is still not fully understood. The phenomenon of intrahepatic cholestasis under estrogen influence can occur during pregnancy or by taking estrogens for oral anticonception and hormone substitution. Impaired sodium-dependent uptake of bile acids has been associated with diminished expression of the basolateral Natrium/bile acid cotransporter (Ntcp), whereas sodium-independent uptake is maintained despite a down-regulation of the organic anion transporter Oatp1. Thus, expression of the two other rat Oatps (Oatp2 and Oatp4) was determined in estrogen-induced cholestasis. In Addition, known transactivators of Oatp2 and Ntcp were studied to further characterize transcriptional regulation of these transporter genes. Hepatic protein and mRNA expression of various Oatps in comparison to Ntcp and canalicular transporters bile salt export pump (Bsep) und multidrug resistance protein 2 (Mrp2) were analyzed after 0.5, 1,3 and 5 days of ethinylestradiol treatment (5mg/kg) in rats. Regulation in mRNA and Protein levels were determined by northern and westernblotting. Binding activities of Oatp2 and Ntcp transactivators were assessed by electrophoretic mobility shift assays. As results all basolateral Oatps (1, 2 and 4) were specifically down-regulated at the protein levels. In contrast to unaltered Oatp4 mRNA levels, which is most likely regulated posttranscriptionally, Oatp1 and Oatp2 mRNAs were reduced to various extends. Binding activity of known transactivators of Ntcp and Oatp2 such as HNF-1, C/EBP and PXR:RXR were also diminished during the time of cholestasis and might lead to the reduction of mRNA expression of Ntcp, Oatp1 and Oatp2. The mRNA and protein levels of the canalicular bile salt export pump, as the best maintained transporter, remains stabile, whereas Mrp2 expression is only reduced at the protein level. This might be due to posttranscriptional mechanisms. This study gives deep inside in the pathophysiology in estrogen-induced cholestasis with detailed information of the expression and regulation of all organic anion transporters

Differentielle Regulation organischer Anionentransporter der Oatp-Familie bei Ethinylöstradiol-induzierter Cholestase der Ratte

Estrogen-mediated cholestasis is an important clinical entity, but its molecular pathophysiology is still not fully understood. The phenomenon of intrahepatic cholestasis under estrogen influence can occur during pregnancy or by taking estrogens for oral anticonception and hormone substitution. Impaired sodium-dependent uptake of bile acids has been associated with diminished expression of the basolateral Natrium/bile acid cotransporter (Ntcp), whereas sodium-independent uptake is maintained despite a down-regulation of the organic anion transporter Oatp1. Thus, expression of the two other rat Oatps (Oatp2 and Oatp4) was determined in estrogen-induced cholestasis. In Addition, known transactivators of Oatp2 and Ntcp were studied to further characterize transcriptional regulation of these transporter genes. Hepatic protein and mRNA expression of various Oatps in comparison to Ntcp and canalicular transporters bile salt export pump (Bsep) und multidrug resistance protein 2 (Mrp2) were analyzed after 0.5, 1,3 and 5 days of ethinylestradiol treatment (5mg/kg) in rats. Regulation in mRNA and Protein levels were determined by northern and westernblotting. Binding activities of Oatp2 and Ntcp transactivators were assessed by electrophoretic mobility shift assays. As results all basolateral Oatps (1, 2 and 4) were specifically down-regulated at the protein levels. In contrast to unaltered Oatp4 mRNA levels, which is most likely regulated posttranscriptionally, Oatp1 and Oatp2 mRNAs were reduced to various extends. Binding activity of known transactivators of Ntcp and Oatp2 such as HNF-1, C/EBP and PXR:RXR were also diminished during the time of cholestasis and might lead to the reduction of mRNA expression of Ntcp, Oatp1 and Oatp2. The mRNA and protein levels of the canalicular bile salt export pump, as the best maintained transporter, remains stabile, whereas Mrp2 expression is only reduced at the protein level. This might be due to posttranscriptional mechanisms. This study gives deep inside in the pathophysiology in estrogen-induced cholestasis with detailed information of the expression and regulation of all organic anion transporters