CHOLESTATIC LIVER DISEASE AND BRAIN DYSFUNCTION: ROLE OF THE ARYL HYDROCARBON RECEPTOR

Abstract

BackgroundCholestatic liver disease is associated with immune‐mediated inflammatory liver injury and tissue damage. This disorder is also associated with brain dysfunction and behavioural changes, notably fatigue, depression and social withdrawal. The mechanisms leading to these central nervous system abnormalities are unknown, however, they are associated with neuroinflammation in the brain. Microglia and astrocytes are two glial cell populations that play key roles in neuroinflammation. Activated glia display morphological changes, secrete cytokines, and mediate electrophysiological changes, altering the normal functioning of the brain. The aryl hydrocarbon receptor (AhR) is a transcription factor involved in the immune response. AhR is present on glia and its’ activation has been shown to reduce CNS inflammation. The role of the AhR in cholestatic liver disease has yet to examined.AimsTo study the function of the AhR and its ligands in an extensively characterized model of cholestic liver disease. We will test the hypothesis that activation of AhR in the brain will reduce neuroinflammation and associated behavioral deficits observed in cholestatic mice.MethodsMale C57Bl/6J mice had cholestasis induced by bile duct ligation (BDL); comparisons were made to sham‐operated controls. Mice were tested for social interaction with a 4‐week old juvenile male in their home cage and the number of social interaction attempts quantified. After this behavioral assay, mice were euthanized, brains were removed and processed for immunofluorescence analysis. Brain sections were stained for markers of microglia (IBA‐1) and astrocytes (GFAP). Microglia were counted and astrocyte activation was qualitatively assessed as higher GFAP immunofluorescence. PCR was used to quantify relative gene expression of AhR and its downstream gene targets (eg. CYP1A1) in mice that recived treatment with beta‐napthoflavone (BNF), a potent AhR agonist, or in vehicle treated controls.ResultsBDL mice made significantly fewer attempts to interact with the juvenile as compared to controls (P<0.05). We also observed a significant increase in IBA‐1 immunoreactive cell numbers in both the CA1 region of the hippocampus and the hypothalamic paraventricular nucleus (PVN, P<0.05). BDL mice also displayed marked increases in GFAP+ staining in the PVN, but not the CA1 region of hippocampus, in contrast to sham controls. Lastly, we found that BNF significantly upregulated CYP1A1 (P<0.05) in the liver and brain prefrontal cortex of mice. We are currently examining whether BNF can downregulate neuroinflammation and improve decreased social interaction behaviors in cholestatic mice.ConclusionCholestatic liver damage was associated with impaired social behavior. Further, glial activation, an indicator of neuroinflammation was significantly increased in components of the brain limbic system associated with the response to stress, learning, and memory. Future experiments will address whether activation of the AhR will ameliorate neuroinflammation and behavioral changes observed in mice with cholestatic liver injury.Support or Funding InformationCanadian Institutes of Health Research