AIM: We have previously demonstrated that cholangiocytes, the epithelial cells lining intrahepatic bile ducts,encode two functional bile acid transporters via alternative splicing of a single gene to facilitate bile a...AIM: We have previously demonstrated that cholangiocytes, the epithelial cells lining intrahepatic bile ducts,encode two functional bile acid transporters via alternative splicing of a single gene to facilitate bile acid vectorial transport. Cholangiocytes possess ASBT,an apical sodium-dependent bile acid transporter to take up bile acids,and t-ASBT,a basolateral alternatively spliced and truncated form of ASBT to efflux bile acids.Though hepatocyte and ileal bile acid transporters are in part regulated by the flux of bile acids, the effect of alterations in bile acid flux on the expression of t-ASBT in terminal ileocytes remains undear.Thus,we tested the hypothesis that expression of ASBT and t-ASBT in cholangiocytes and ileocytes was regulated by bile acid flux. METHODS: Expression of ASBT and t-ASBT message and protein in cholangiocytes and ileocytes isolated from pair- fed rats given control (C) and 1% taurocholate (TCA) or 5% cholestyramine (CY) enriched diets,were assessed by both quantitative RNase protection assays and quantitative immunoblotting.The data obtained from each of the control groups were pooled to reflect the changes observed following TCA and CY treatments with respect to the control diets. Cholangiocyte taurocholate uptake was determined using a novel microperfusion technique on intrahepatic bile duct units (IBDUs) derived from C,TCA and CY fed rats. RESULTS: In cholangiocytes,both ASBT and t-ASBT message RNA and protein were significantly decreased in response to TCA feeding compared to C diet.In contrast, message and protein of both bile acid transporters significantly increased following CY feeding compared to C diet.In the ileum,TCA feeding significantly up-regulated both ASBT and t-ASBT message and protein compared to C diet,while CY feeding significantly down-regulated message and protein of both bile acid transporters compared to C diet.As anticipated from alterations in cholangiocyte ASBT expression,the uptake of taurocholate in microperfused IBDUs derived from rats on TCA diet decreased 2.7-fold,whereas it increased 1.7-fold in those on CY diet compared to C diet fed groups. CONCLUSION: These data demonstrate that expression of ASBT and t-ASBT in cholangiocytes is regulated by a negative feedback loop while the expression of these transporters in terminal ileum is modified via positive feedback.Thus, while transcriptional regulatory mechanisms in response to alterations in bile acid pool size are operative in both cholangiocytes and ileocytes,each cell type responds differently to bile acid supplementation and depletion.展开更多
Th1-response plays a crucial role in determining pathogenesis of organ-specific autoimmune diseases. It is believed that both IL-12 and INF-alpha are initiators to regulate Th1-response. In our experimental autoimmune...Th1-response plays a crucial role in determining pathogenesis of organ-specific autoimmune diseases. It is believed that both IL-12 and INF-alpha are initiators to regulate Th1-response. In our experimental autoimmune uveitis (EAU) model, both Lewis and Fischer 344 rats share the same MHC class II molecules, while Lewis rat is EAU susceptible and Fischer 344 rat is EAU resistant. However, under the same condition of immunization, if pertussis toxin (PTX) was injected intraperitoneally as an additional adjuvant, Fischer 344 rat can develop EAU. In this study we investigate which mechanisms are involved in the induction of EAU in CFA+R16+PTX-treated (CRP-treated) Fischer 344 rats. In vivo and in vitro data demonstrated that Th1-cytokine, IFN-gamma mRNA expression was significantly increased in disease target tissue-eyes and in draining lymph node cells of CRP-treated Fischer 344 rat. When IL-12 and IFN-alpha mRNA expression were compared in the experimental groups, only IFN-alpha mRNA expression was associated with EAU development. To distinguish the sources of IFN-alpha producing cells, it was observed that IFN-alpha expression was mainly produced by macrophages. It was further confirmed that normal macrophage from Fischer 344 rat was able to produce significant IFN-alpha in the presence of PTX. The data strongly suggested that IFN-alpha might be involved in initiating Th1-cell differentiation and in turn contribute to the induction of EAU. High IFN-alpha expression induced by PTX may represent a novel pathway to initiate Th1 response in Fischer 344 rat.展开更多
文摘AIM: We have previously demonstrated that cholangiocytes, the epithelial cells lining intrahepatic bile ducts,encode two functional bile acid transporters via alternative splicing of a single gene to facilitate bile acid vectorial transport. Cholangiocytes possess ASBT,an apical sodium-dependent bile acid transporter to take up bile acids,and t-ASBT,a basolateral alternatively spliced and truncated form of ASBT to efflux bile acids.Though hepatocyte and ileal bile acid transporters are in part regulated by the flux of bile acids, the effect of alterations in bile acid flux on the expression of t-ASBT in terminal ileocytes remains undear.Thus,we tested the hypothesis that expression of ASBT and t-ASBT in cholangiocytes and ileocytes was regulated by bile acid flux. METHODS: Expression of ASBT and t-ASBT message and protein in cholangiocytes and ileocytes isolated from pair- fed rats given control (C) and 1% taurocholate (TCA) or 5% cholestyramine (CY) enriched diets,were assessed by both quantitative RNase protection assays and quantitative immunoblotting.The data obtained from each of the control groups were pooled to reflect the changes observed following TCA and CY treatments with respect to the control diets. Cholangiocyte taurocholate uptake was determined using a novel microperfusion technique on intrahepatic bile duct units (IBDUs) derived from C,TCA and CY fed rats. RESULTS: In cholangiocytes,both ASBT and t-ASBT message RNA and protein were significantly decreased in response to TCA feeding compared to C diet.In contrast, message and protein of both bile acid transporters significantly increased following CY feeding compared to C diet.In the ileum,TCA feeding significantly up-regulated both ASBT and t-ASBT message and protein compared to C diet,while CY feeding significantly down-regulated message and protein of both bile acid transporters compared to C diet.As anticipated from alterations in cholangiocyte ASBT expression,the uptake of taurocholate in microperfused IBDUs derived from rats on TCA diet decreased 2.7-fold,whereas it increased 1.7-fold in those on CY diet compared to C diet fed groups. CONCLUSION: These data demonstrate that expression of ASBT and t-ASBT in cholangiocytes is regulated by a negative feedback loop while the expression of these transporters in terminal ileum is modified via positive feedback.Thus, while transcriptional regulatory mechanisms in response to alterations in bile acid pool size are operative in both cholangiocytes and ileocytes,each cell type responds differently to bile acid supplementation and depletion.
文摘Th1-response plays a crucial role in determining pathogenesis of organ-specific autoimmune diseases. It is believed that both IL-12 and INF-alpha are initiators to regulate Th1-response. In our experimental autoimmune uveitis (EAU) model, both Lewis and Fischer 344 rats share the same MHC class II molecules, while Lewis rat is EAU susceptible and Fischer 344 rat is EAU resistant. However, under the same condition of immunization, if pertussis toxin (PTX) was injected intraperitoneally as an additional adjuvant, Fischer 344 rat can develop EAU. In this study we investigate which mechanisms are involved in the induction of EAU in CFA+R16+PTX-treated (CRP-treated) Fischer 344 rats. In vivo and in vitro data demonstrated that Th1-cytokine, IFN-gamma mRNA expression was significantly increased in disease target tissue-eyes and in draining lymph node cells of CRP-treated Fischer 344 rat. When IL-12 and IFN-alpha mRNA expression were compared in the experimental groups, only IFN-alpha mRNA expression was associated with EAU development. To distinguish the sources of IFN-alpha producing cells, it was observed that IFN-alpha expression was mainly produced by macrophages. It was further confirmed that normal macrophage from Fischer 344 rat was able to produce significant IFN-alpha in the presence of PTX. The data strongly suggested that IFN-alpha might be involved in initiating Th1-cell differentiation and in turn contribute to the induction of EAU. High IFN-alpha expression induced by PTX may represent a novel pathway to initiate Th1 response in Fischer 344 rat.
