Intestinal B cells license metabolic T-cell activation in NASH microbiota/antigen-independently and contribute to fibrosis by IgA-FcR signalling.

BACKGROUND & AIMS: The progression of non-alcoholic steatohepatitis (NASH) to fibrosis and hepatocellular carcinoma (HCC) is aggravated by auto-aggressive T cells. The gut-liver axis contributes to NASH, but the mechanisms involved and the consequences for NASH-induced fibrosis and liver cancer remain unknown. We investigated the role of gastrointestinal B cells in the development of NASH, fibrosis and NASH-induced HCC. METHODS: C57BL/6J wild-type (WT), B cell-deficient and different immunoglobulin-deficient or transgenic mice were fed distinct NASH-inducing diets or standard chow for 6 or 12 months, whereafter NASH, fibrosis, and NASH-induced HCC were assessed and analysed. Specific pathogen-free/germ-free WT and µMT mice (containing B cells only in the gastrointestinal tract) were fed a choline-deficient high-fat diet, and treated with an anti-CD20 antibody, whereafter NASH and fibrosis were assessed. Tissue biopsy samples from patients with simple steatosis, NASH and cirrhosis were analysed to correlate the secretion of immunoglobulins to clinicopathological features. Flow cytometry, immunohistochemistry and single-cell RNA-sequencing analysis were performed in liver and gastrointestinal tissue to characterise immune cells in mice and humans. RESULTS: Activated intestinal B cells were increased in mouse and human NASH samples and licensed metabolic T-cell activation to induce NASH independently of antigen specificity and gut microbiota. Genetic or therapeutic depletion of systemic or gastrointestinal B cells prevented or reverted NASH and liver fibrosis. IgA secretion was necessary for fibrosis induction by activating CD11b+CCR2+F4/80+CD11c-FCGR1+ hepatic myeloid cells through an IgA-FcR signalling axis. Similarly, patients with NASH had increased numbers of activated intestinal B cells; additionally, we observed a positive correlation between IgA levels and activated FcRg+ hepatic myeloid cells, as well the extent of liver fibrosis. CONCLUSIONS: Intestinal B cells and the IgA-FcR signalling axis represent potential therapeutic targets for the treatment of NASH. IMPACT AND IMPLICATIONS: There is currently no effective treatment for non-alcoholic steatohepatitis (NASH), which is associated with a substantial healthcare burden and is a growing risk factor for hepatocellular carcinoma (HCC). We have previously shown that NASH is an auto-aggressive condition aggravated, amongst others, by T cells. Therefore, we hypothesized that B cells might have a role in disease induction and progression. Our present work highlights that B cells have a dual role in NASH pathogenesis, being implicated in the activation of auto-aggressive T cells and the development of fibrosis via activation of monocyte-derived macrophages by secreted immunoglobulins (e.g., IgA). Furthermore, we show that the absence of B cells prevented HCC development. B cell-intrinsic signalling pathways, secreted immunoglobulins, and interactions of B cells with other immune cells are potential targets for combinatorial NASH therapies against inflammation and fibrosis.

Role of immune responses in the development of NAFLD-associated liver cancer and prospects for therapeutic modulation.

The liver is the central metabolic organ of the body, regulating energy and lipid metabolism, while also having potent immunological functions. Overwhelming the metabolic capacity of the liver via obesity and a sedentary lifestyle leads to hepatic lipid accumulation, chronic necro-inflammation, enhanced mitochondrial/endoplasmic reticulum stress and development of non-alcoholic fatty liver disease (NAFLD), and its more severe form non-alcoholic steatohepatitis (NASH). Based on an improved understanding of pathophysiological mechanisms, specifically targeting metabolic pathways to prevent or slow down the progression of NAFLD to liver cancer will become possible. Genetic/environmental factors are also known to contribute to the development of NASH and progression to liver cancer. The complex pathophysiology of NAFLD-NASH is reflected by environmental factors, particularly the gut microbiome and its metabolic products. NAFLD-associated HCC most often occurs in the context of a chronically inflamed and cirrhotic liver. Recognition of environmental alarmins or metabolites derived from the gut microbiota and the metabolically injured liver create a strong inflammatory milieu supported by innate and adaptive immunity. Several recent studies indicate that chronic steatosis induces auto-aggressive CD8+CXCR6+PD1+ T cells that eliminate parenchymal and non-parenchymal cells in an antigen-independent manner. This promotes chronic liver damage and a pro-tumorigenic environment. CD8+CXCR6+PD1+ T cells possess an exhausted, hyperactivated, resident phenotype; they trigger the NASH to HCC transition and might be responsible for weaker responses to immune checkpoint inhibitors - in particular atezolizumab/bevacizumab. Here, we provide an overview of NASH-related inflammation/pathogenesis, focusing on new discoveries on the role of T cells. This review discusses preventive measures to halt disease progression to liver cancer and therapeutic strategies to manage patients with NASH-HCC.

Forced expression of Hnf4a induces hepatic gene activation through directed differentiation.

Embryonic stem (ES) cells are capable of unlimited self-renewal and have a diverse differentiation potential. These unique features make ES cells as an attractive source for developmental biology studies. Having the mature hepatocyte in the lab with functional activities is valuable in drug discovery studies. Overexpression of hepatocyte lineage-specific transcription factors (TFs) becomes a promising approach in pluripotent cell differentiation toward liver cells. Many studies generate transgenic ES cell lines to examine the effects of specific TFs overexpression in cell differentiation. In the present report, we have addressed whether a suspension or adherent model of differentiation is an appropriate way to study the role of Hnf4a overexpression. We generated ES cells that carried a doxycycline (Dox)-inducible Hnf4a using lentiviral vectors. The transduced cells were subjected to induced Hnf4a overexpression through both spontaneous and directed differentiation methods. Gene expression analysis showed substantially increased expression of hepatic gene markers, particularly Ttr and endogenous Hnf4a, in transduced cells differentiated by the directed approach. These results demonstrated that forced expression of TFs during directed differentiation would be an appropriate way to study relevant gene activation and the effects of overexpression in the context of hepatic differentiation.

Forced expression of Hnf1b/Foxa3 promotes hepatic fate of embryonic stem cells.

Embryonic stem (ES) cell-derived hepatocytes have the potential to be used for basic research, regenerative medicine, and drug discovery. Recent reports demonstrated that in addition to conventional differentiation inducers such as chemical compounds and cytokines, overexpression of lineage-specific transcription factors could induce ES cells to differentiate to a hepatic fate. Here, we hypothesized that lentivirus-mediated inducible expression of hepatic lineage transcription factors could enhance mouse ES cells to hepatocyte-like cells. We screened the effects of candidate transcription factors Hnf1b, Hnf1a, Hnf4a, Foxa1, Foxa3 and Hex, and determined that the combination of Hnf1b/Foxa3 promoted expression of several hepatic lineage-specific markers and proteins, in addition to glycogen storage, ICG uptake, and secretion of albumin and urea. The differentiated cells were engraftable and expressed albumin when transplanted into a carbon tetrachloride-injured mouse model. These results demonstrated the crucial role of Hnf1b and Foxa3 in hepatogenesis in vitro and provided a valuable tool for the efficient differentiation of HLCs from ES cells.

Mutations in the E2 and NS5A regions in patients infected with hepatitis C virus genotype 1a and their correlation with response to treatment.

Heterogeneity of subgenomic regions of hepatitis C virus (HCV) may be associated with response to interferon (IFN) therapy. The amino acid sequences of the PKR/eIF-2α phosphorylation homology domain (pePHD), IFN sensitivity determining region (ISDR), PKR binding domain (PKRBD), and variable region 3 (V3) were studied in 19 patients before and after 4 weeks of treatment. All patients were infected with HCV genotype 1a and were treated with pegylated-IFN and ribavirin. Thirteen patients achieved sustained viral response (responders) and six failed to clear viral RNA (nonresponders). The amino acid sequences in the pePHD and ISDR were identical in responders and nonresponders. However, amino acid substitution at position 2252 of PKRBD was significantly different between responders and nonresponders (P = 0.044). A larger number of mutations were observed in the V3 region of responders (P < 0.001). In this region, the amino acid in position 2364 differed between responders and nonresponders (responders: aspartic acid and serine, nonresponders: asparagine, P = 0.018). The amino acid sequences in the regions which were studied did not change after 4 weeks of treatment. It is concluded that the presence of specific amino acids in position 2252 of PKRBD and position 2364 of V3 might be associated with clinical response to IFN.