Effect Of Nuclear Receptor FXR On Copper Accumulation And Liver Function In TX Mice

Objective:Hepatolenticular degeneration(HLD)is an autosomal recessive disorder caused by mutations in the ATP7 B gene.It is caused by a mutation in the ATP7 B gene in the hepatocytes of the patient,which leads to a decrease in copper cyanidin synthesis and impaired biliary excretion of copper,resulting in abnormal accumulation of copper in the body and severe damage to the liver,kidneys,brain and other tissues and organs.Bile secretion is an important factor in copper accumulation in the liver,and bile secretion is closely related to bile acid transport proteins in the hepatocyte membrane.The representative nuclear receptor Farnesoid X Repoter(FXR)plays an important role in bile circulation and excretion,and has become a promising therapeutic target for fatty liver and cholestasis diseases.In order to explore the role of Farosine X Receptor in HLD disease,the HLD transgenic animal model TX mice were used as the research object to investigate the effects of agonist/inhibit nuclear receptor FXR on copper accumulation and liver function in TX mice,and to explore the role and mechanism of nuclear receptor FXR in HLD disease.This study provides a basis for exploring the nuclear receptor FXR as an intervention target for HLD diseases.Methods:TX mice were used as the study subjects,and DL mice of the same strain were used as the reference,and the FXR agonist Obeticholic Acid(OCA)and FXR inhibitor Guggulsterone(GS)were selected for group administration.The effects of FXR on copper excretion in TX mice were investigated by measuring copper levels in liver,brain,kidney,urine and feces using Atomic Absorption Spectroscopy(AAS).H&E and Sirius red staining were used to observe the histopathological changes and liver fibrosis in each group of mice to investigate the extent of liver injury and the effect of FXR intervention on nuclear receptors in TX mice.The levels of Alanine Aminotransferase(ALT),Aspartate Aminotrasferase(AST)and Total Bile Acid(TBA)were measured to investigate the effects of FXR on liver injury in mice.Using FXR agonist OCA and FXR inhibitor GS,the expression levels of FXR,BSEP and NTCP in each group were measured by Western blot technique to further investigate the regulation mechanism of nuclear receptor FXR in TX mice.Results:1.Activation of FXR promoted copper excretion and reduced copper accumulation in TX miceThe AAS results showed that the hepatic,brain and kidney copper contents of TX mice in the model group were significantly higher than those in the control group(P <0.01),with the liver copper accumulation being the most serious,about 24 times higher than that in the control group;the copper contents in urine and feces were significantly lower than those in the control group(P <0.01).The FXR agonist OCA significantly decreased the copper content in the liver,brain and kidney of TX mice(P <0.05 or P<0.01)and significantly promoted their fecal copper excretion(P <0.01),while it had no significant effect on their urinary copper content.The FXR inhibitor GS significantly increased the copper content in the liver,brain and kidney of TX mice(P <0.05),and significantly decreased their fecal copper content(P <0.05),but had no significant effect on their urinary copper content.These results suggest that copper metabolism is impaired in TX mice and that agitation of FXR improves copper accumulation in TX mice,whereas inhibition of FXR worsens their copper accumulation.2.Activation of FXR protected liver function in TX miceThe results of H&E staining showed that the FXR agonist OCA significantly improved the liver injury and protected the tissue and cell structure of TX mice,while the FXR inhibitor GS aggravated the liver lesions and tissue deterioration of TX mice;the results of Sirius red staining showed that OCA significantly improved the liver fibrosis of TX mice,while GS significantly aggravated the liver fibrosis.The results of biochemical indexes showed that the plasma ALT,AST and TBA levels of TX mice in the model group were significantly higher than those of mice in the control group(P <0.01),and the liver indexes were significantly reduced after the FXR agonist OCA intervention(P <0.01),but the levels of ALT,AST and TBA were significantly increased when the FXR inhibitor GS was intervened compared with the model group(P <0.05 or P <0.01),which indicated that agonizing FXR could significantly improve the liver function of TX mice,while inhibition of FXR aggravated their liver injury.3.The mechanism of FXR receptor activation in liver protectionThe results of Western blot showed that the expression levels of FXR,Bile Saltexport Pump(BSEP)and Sodium Taurocholate Cotransporting Polypeptide(NTCP)were significantly lower in TX mice than in normal mice(P <0.01).The FXR agonist OCA significantly promoted the expression of FXR and BSEP in TX mice(P <0.01)and significantly inhibited the expression of NTCP(P <0.01);the FXR inhibitor GS significantly reduced the levels of FXR and BSEP in TX mice(P <0.05)and increased the levels of NTCP(P <0.01).This suggests that activation of FXR receptors exerts hepatoprotective effects in relation to the promotion of FXR and BSEP and inhibition of NTCP protein expression levels.Conclusion:Copper metabolism is impaired and liver damage exists in TX mice,and agonizing FXR improves copper accumulation and liver function in TX mice,while inhibiting FXR makes their copper accumulation and liver damage more severe,and the mechanism by which agonism of FXR exerts hepatoprotective effects in TX mice is related to upregulation of FXR and BSEP and downregulation of NTCP protein expression.