Hepatic encephalopathy (HE) is a common complication of liver cirrhosis, associated with high morbidity and mortality, for which no brain-targeted therapies exist at present. The interplay between hyperammonemia and inflammation is thought to drive HE development. As such, astrocytes, the most important ammonia-metabolizing cells in the brain, and microglia, the main immunomodulatory cells in the brain, have been heavily implicated in HE development. As insight into cellular perturbations driving brain pathology remains largely elusive, we aimed to investigate cell-type specific transcriptomic changes in the HE brain. In the recently established mouse bile duct ligation (BDL) model of HE, we performed RNA-Seq of sorted astrocytes and microglia at 14 and 28 days after induction. This revealed a marked transcriptional response in both cell types which was most pronounced in microglia. In both cell types, pathways related to inflammation and hypoxia, mechanisms commonly implicated in HE, were enriched. Additionally, astrocytes exhibited increased corticoid receptor and oxidative stress signaling, whereas microglial transcriptome changes were linked to immune cell attraction. Accordingly, both monocytes and neutrophils accumulated in the BDL mouse brain. Time-dependent changes were limited in both cell types, suggesting early establishment of a pathological phenotype. While HE is often considered a unique form of encephalopathy, astrocytic and microglial transcriptomes showed significant overlap with previously established gene expression signatures in other neuroinflammatory diseases like septic encephalopathy and stroke, suggesting common pathophysiological mechanisms. Our dataset identifies key molecular mechanisms involved in preclinical HE and provides a valuable resource for development of novel glial-directed therapeutic strategies. Graphical Abstract

Background Inflammatory bowel diseases (IBD) are often associated with psychological comorbidities such as fatigue. Up to 47% of patients reports fatigue despite disease remission. The aim of the current study was to assess neurobehavioural changes in a mouse model of extinguished chronic colitis and to explore associated changes along the gut-brain axis. Methods Repeated administration of 2% dextran sulphate sodium (DSS) was used to induce chronic colitis in C57BL/6 mice, followed by a recovery period of 3 weeks to mimic quiescent IBD (Figure 1). Behavioural testing was performed at baseline and after the recovery period and compared with control mice. RNA sequencing was performed of the distal colon and choroid plexus and weighted correlation network analysis (WGCNA) was applied. Next, quantitative polymerase chain reaction (qPCR) was used for the confirmation of the expression levels of genes identified in the WGCNA analysis. The number of microglia and their morphology were assessed by Iba1 immunofluorescence in a second experiment, also including acute colitis (aDSS), which was induced by 1 week of 2% DSS, with sampling at day 7. Results Chronic DSS (cDSS) treatment resulted in chronic inflammation with minimal residual intestinal symptoms (control: median disease activity index (DAI) of 0 IQR [0-0], cDSS: median DAI of 0.5 [0.5-0.88], P <0.0001) after 3 weeks of recovery, which mimics quiescent IBD. At the time of sampling, the mean weight and haematological parameters (including red and white blood cells) in cDSS were comparable to those in control mice. cDSS mice exhibited significantly reduced spontaneous activity compared with their baseline behaviour (P = 0.0084) and with the controls (P = 0.0186). WGCNA on the colon and the choroid plexus expression data revealed a consensus module of 123 co-expressed genes that differed significantly between the control and cDSS mice (P = 0.00001721). These genes were implied in pathways of neutrophil and complement activation and qPCR on different brain regions (frontal cortex, hippocampus and choroid plexus) confirmed upregulation of inflammatory genes Lcn2, TNFa, S100A8 and S100A9 (Figure 2). Acute colitis was associated with activation of microglia in the prefrontal cortex and hippocampus, persisting in the prefrontal cortex of mice that recovered from chronic colitis (Figures 3 and 4). Conclusion In this mouse model of chronic extinguished colitis reduced spontaneous activity was seen, indicating fatigue-like behaviour as observed in patients with IBD. Moreover, mice that recovered from colitis exhibited persisting neuroinflammation.