RXR-alpha 在敗血症鼠合併肝內膽汁淤積中所扮演的角色

Abstract

sepsis is an illness after infecting and the death rate is to achieve 40% ~ 60%. Multiple organs failure continues to be the primary cause of death after sepsis. The liver is thought to be one of the major organs responsible for the initiation of multiple organ failure because of its central role in metabolism. Hepatic dysfunction in sepsis is characterized by apoptosis、mitochondria Damage 、hyperbilirumia (Kim et al., 2000) 、impaired uptake and secretion of hepatocyte transport of bile acids and organic anions 、increased GOT, GPT and intra-hepatic cholestasis. The nuclear receptor RXRα(retinoid X receptor) has three family members (RXRα, RXRβ,?z RXRγ ) and RXRα is highly expressed in liver. There is substantial evidence that RXRα virtually participates in all aspects of hepatic function including metabolism of cholesterol, fatty acid, carbohydrate, bile acid and transporter activities. Heterodimer of RXRα with special nuclear receptor (CAR, FXR, LXR, PPAR, or PXR) controls the expression of?n proteins which involve in bile acid metabolism , such as bile acid synthesis enzyme(CYP7A1、rBAT) and bile salt transporters (BSEP、NTCP、MRP2、OATP1).[10].Through suppression subtractive hybridization (SSH) technique, we have been identified that two genes, 3α-HSD and BAT, were down regulated in late septic liver. Both 3α-HSD and rBAT are the key enzymes in bile acid synthesis and metabolism.We find that decreased rBAT expression was a specific character in sepsis-associated intra-cholestasis and RXRα was the key transcription factor. In primary hepatocyte culture, RXRα agonist dexamethasone (Dexa) can increase the protein content of RXRα and binding activity of IR-1(Shock aceepted). It is interesting for us to know the roles of RXRα in the regulation of bile acid metabolism during sepsis, in vivo. In this study, we identified the best treated time and dose of Dexamethason which can improve the survival rate of CLP-induced septic rats. The volume of bile flow and concentration of bile salt were analyzed. Tissue extract (nuclear, cytosolic, and membrane)、Western blot (protein expression)、Real-time PCR (mRNA expression)、EMSA(protein and DNA binding activity) 、siRNA transfection techniques were used .The results showed that: Dexamethason (0.01mg/Kg) improves the survival rates of CLP-induced septic rat. Dexamethason can increase the expression of RXRα protein in CLP-induced septic rat. Dexamethason treated can increase the volume of bile flow and the concentration of bile salt in bile duct of septic rats. The protein and mRNA expressions of bile acid synthesis enzymes (CYP7A1、rBAT) were decreased during sepsis and Dexa can improve the expression of rBAT but not CYP7A1. Both BSEP and OATP1 were unaffected by sepsis and Dexa treated. The mRNA, but not protein, expression of NTCP and MRP2 were decreased during sepsis. The protein and mRNA expression of rBat was significantly enhanced while RXRα protein increased, but not BSEP、NTCP、MRP2、OATP1 and CYP7A1 in septic rats. DNA binding activity of RXRα/FXR to IR-1 was also increased in septic rats after Dexa treatment. RXRα and rBAT protein expression showed downregulation after RXRα siRNA transfection. Take all the results together, both rBAT and RXRα decreased during sepsis and the expression of rBAT was significantly enhanced while RXRα protein increased after Dexamethason treated. It is suggested that rBAT and RXRα might be developed as a diagnostic and prognostic markers of sepsis