P: 61 Attenuation of Neurological Symptoms of Type C Hepatic Encephalopathy by Selective Ablation of Neuronal FXR Expression

Abstract

BACKGROUND: Hepatic encephalopathy (HE) describes the neurological deficits that result from liver impairment. Liver disease is associated with an increase of circulating bile acids that can cross the blood brain barrier and activate FXR receptors in neurons. We have previously demonstrated that aberrant bile acid signaling via activation of neuronal FXR contributes to HE pathogenesis in rodent models of acute liver failure. However, a role for FXR-mediated bile acid signaling in HE due to chronic liver cirrhosis is undefined. METHODS: Neuron-specific FXR knockout mice were generated by crossing Floxed FXR mice (FXRfl) with SNAP-25 cre recombinase mice. The resulting mice were designated FXRΔneu. C57Bl/6 (WT), FXRfl, and FXRΔneu were treated with carbon tetrachloride (CCl4; 1 ml/kg) by oral gavage twice per week for 12 weeks. Neurobehavioral indices and neuromuscular deficits were assessed by open field test, rotarod, grip strength test and gait analysis. After 12 weeks, tissue was collected and liver damage was assessed by serum chemistry and H&E staining. Total bile acid content was assessed in the cortex and cerebellum using colorimetric assays. The expression of ASBT, FXR, and its downstream effector SHP was assessed by qPCR and immunofluorescence. Microglia activation was assessed by Iba1 immunofluorescence. The expression of proinflammatory cytokines were assessed by qPCR and EIA. In parallel, total bile acids, ASBT and FXR expression were assessed in brain tissue from cirrhotic patients with HE, compared to cirrhotics without HE and age- and gender-matched controls that had been collected and banked by the Australian Brain Bank Network. RESULTS: Total bile acid content was elevated in the cortex and cerebellum in CCl4-treated WT mice and in cirrhotic patients with HE, compared to cirrhotics without HE and non-liver impaired controls. Furthermore, ASBT, FXR and SHP expression were increased in the frontal cortex of mice and humans with HE, but not in non-HE control samples. WT and FXRfl mice treated with CCl4 had significant deficits observed in every neurobehavioral and neuromuscular test performed, as well as marked microglia activation and increased proinflammatory cytokine expression compared to vehicle-treated mice. These neurological deficits and neuroinflammation were attenuated in FXRΔneu mice after CCl4 treatment, even though liver damage was comparable in all genotypes of mice used. CONCLUSIONS: These data indicate that neuronal expression of FXR plays an important role in the development of HE. Specific targeting of FXR activation in the brain may be a potential therapeutic target for the management of HE.