Downregulation of TGR5 (GPBAR1) in biliary epithelial cells contributes to the pathogenesis of sclerosing cholangitis

BACKGROUND & AIMS

Primary sclerosing cholangitis (PSC) is characterized by chronic inflammation and progressive fibrosis of the biliary tree. The bile acid receptor TGR5 (GPBAR1) is found on biliary epithelial cells (BECs), where it promotes secretion, proliferation and tight junction integrity. Thus, we speculated that changes in TGR5-expression in BECs may contribute to PSC pathogenesis.

METHODS

TGR5-expression and -localization were analyzed in PSC livers and liver tissue, isolated bile ducts and BECs from Abcb4^-/-, Abcb4^-/-/Tgr5^Tg and ursodeoxycholic acid (UDCA)- or 24-norursodeoxycholic acid (norUDCA)-fed Abcb4^-/- mice. The effects of IL8/IL8 homologues on TGR5 mRNA and protein levels were studied. BEC gene expression was analyzed by single-cell transcriptomics (scRNA-seq) from distinct mouse models.

RESULTS

TGR5 mRNA expression and immunofluorescence staining intensity were reduced in BECs of PSC and Abcb4^-/- livers, in Abcb4^-/- extrahepatic bile ducts, but not in intrahepatic macrophages. No changes in TGR5 BEC fluorescence intensity were detected in liver tissue of other liver diseases, including primary biliary cholangitis. Incubation of BECs with IL8/IL8 homologues, but not with other cytokines, reduced TGR5 mRNA and protein levels. BECs from Abcb4^-/- mice had lower levels of phosphorylated Erk and higher expression levels of Icam1, Vcam1 and Tgfβ2. Overexpression of Tgr5 abolished the activated inflammatory phenotype characteristic of Abcb4^-/- BECs. NorUDCA-feeding restored TGR5-expression levels in BECs in Abcb4^-/- livers.

CONCLUSIONS

Reduced TGR5 levels in BECs from patients with PSC and Abcb4^-/- mice promote development of a reactive BEC phenotype, aggravate biliary injury and thus contribute to the pathogenesis of sclerosing cholangitis. Restoration of biliary TGR5-expression levels represents a previously unknown mechanism of action of norUDCA.

LAY SUMMARY

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease-associated with progressive inflammation of the bile duct, leading to fibrosis and end-stage liver disease. Bile acid (BA) toxicity may contribute to the development and disease progression of PSC. TGR5 is a membrane-bound receptor for BAs, which is found on bile ducts and protects bile ducts from BA toxicity. In this study, we show that TGR5 levels were reduced in bile ducts from PSC livers and in bile ducts from a genetic mouse model of PSC. Our investigations indicate that lower levels of TGR5 in bile ducts may contribute to PSC development and progression. Furthermore, treatment with norUDCA, a drug currently being tested in a phase III trial for PSC, restored TGR5 levels in biliary epithelial cells.

Therapeutic inhibition of TRF1 impairs the growth of p53-deficient K-RasG12V-induced lung cancer by induction of telomeric DNA damage

Telomeres are considered anti-cancer targets, as telomere maintenance above a minimum length is necessary for cancer growth. Telomerase abrogation in cancer-prone mouse models, however, only decreased tumor growth after several mouse generations when telomeres reach a critically short length, and this effect was lost upon p53 mutation. Here, we address whether induction of telomere uncapping by inhibition of the TRF1 shelterin protein can effectively block cancer growth independently of telomere length. We show that genetic Trf1 ablation impairs the growth of p53-null K-Ras^G12V-induced lung carcinomas and increases mouse survival independently of telomere length. This is accompanied by induction of telomeric DNA damage, apoptosis, decreased proliferation, and G2 arrest. Long-term whole-body Trf1 deletion in adult mice did not impact on mouse survival and viability, although some mice showed a moderately decreased cellularity in bone marrow and blood. Importantly, inhibition of TRF1 binding to telomeres by small molecules blocks the growth of already established lung carcinomas without affecting mouse survival or tissue function. Thus, induction of acute telomere uncapping emerges as a potential new therapeutic target for lung cancer.

Combined hepatocellular-cholangiocarcinoma derives from liver progenitor cells and depends on senescence and IL-6 trans-signaling

BACKGROUND & AIMS

Primary liver cancers include hepatocellular carcinoma (HCC), intrahepatic cholangiocarcinoma (CCA) and combined HCC-CCA tumors (cHCC-CCA). It has been suggested, but not unequivocally proven, that hepatic progenitor cells (HPCs) can contribute to hepatocarcinogenesis. We aimed to determine whether HPCs contribute to HCC, cHCC-CCA or both types of tumors.

METHODS

To trace progenitor cells during hepatocarcinogenesis, we generated Mdr2-KO mice that harbor a yellow fluorescent protein (YFP) reporter gene driven by the Foxl1 promoter which is expressed specifically in progenitor cells. These mice (Mdr2-KO^{Foxl1-CRE;RosaYFP}) develop chronic inflammation and HCCs by the age of 14-16 months, followed by cHCC-CCA tumors at the age of 18 months.

RESULTS

In this Mdr2-KO^{Foxl1-CRE;RosaYFP} mouse model, liver progenitor cells are the source of cHCC-CCA tumors, but not the source of HCC. Ablating the progenitors, caused reduction of cHCC-CCA tumors but did not affect HCCs. RNA-sequencing revealed enrichment of the IL-6 signaling pathway in cHCC-CCA tumors compared to HCC tumors. Single-cell RNA-sequencing (scRNA-seq) analysis revealed that IL-6 is expressed by immune and parenchymal cells during senescence, and that IL-6 is part of the senescence-associated secretory phenotype. Administration of an anti-IL-6 antibody to Mdr2-KO^{Foxl1-CRE;RosaYFP} mice inhibited the development of cHCC-CCA tumors. Blocking IL-6 trans-signaling led to a decrease in the number and size of cHCC-CCA tumors, indicating their dependence on this pathway. Furthermore, the administration of a senolytic agent inhibited IL-6 and the development of cHCC-CCA tumors.

CONCLUSION

Our results demonstrate that cHCC-CCA, but not HCC tumors, originate from HPCs, and that IL-6, which derives in part from cells in senescence, plays an important role in this process via IL-6 trans-signaling. These findings could be applied to develop new therapeutic approaches for cHCC-CCA tumors.

LAY SUMMARY

Combined hepatocellular carcinoma-cholangiocarcinoma is the third most prevalent type of primary liver cancer (i.e. a cancer that originates in the liver). Herein, we show that this type of cancer originates in stem cells in the liver and that it depends on inflammatory signaling. Specifically, we identify a cytokine called IL-6 that appears to be important in the development of these tumors. Our results could be used for the development of novel treatments for these aggressive tumors.

Nuclear Translocation of RELB Is Increased in Diseased Human Liver and Promotes Ductular Reaction and Biliary Fibrosis in Mice

BACKGROUND & AIMS

Cholangiocyte proliferation and ductular reaction contribute to the onset and progression of liver diseases. Little is known about the role of the transcription factor nuclear factor-κB (NF-κB) in this process. We investigated the activities of the RELB proto-oncogene NF-κB subunit in human cholangiocytes and in mouse models of liver disease characterized by a ductular reaction.

METHODS

We obtained liver tissue samples from patients with primary sclerosing cholangitis, primary biliary cholangitis, hepatitis B or C virus infection, autoimmune hepatitis, alcoholic liver disease, or without these diseases (controls) from a tissue bank in Germany. Tissues were analyzed by immunohistochemistry for levels of RELB and lymphotoxin β (LTB). We studied mice with liver parenchymal cell (LPC)-specific disruption of the cylindromatosis (CYLD) lysine 63 deubiquitinase gene (Cyld), with or without disruption of Relb (Cyld^ΔLPC mice and Cyld/Relb^ΔLPC mice) and compared them with C57BL/6 mice (controls). Mice were fed 5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) or standard chow diets to induce biliary injury or were given injections of CCl₄ to induce non-cholestatic liver fibrosis. Liver tissues were analyzed by histology, immunohistochemistry, immunoblots, in situ hybridization, and quantitative real-time polymerase chain reaction. Cholangiocytes were isolated from normal human liver, incubated with LTB receptor agonist, and transfected with small interfering RNAs to knock down RELB.

RESULTS

In liver tissues from patients with primary sclerosing cholangitis, primary biliary cholangitis, chronic infection with hepatitis B or C virus, autoimmune hepatitis, or alcoholic liver disease, we detected increased nuclear translocation of RELB and increased levels of LTB in cholangiocytes that formed reactive bile ducts compared with control liver tissues. Human cholangiocytes, but not those with RELB knockdown, proliferated with exposure to LTB. The phenotype of Cyld^ΔLPC mice, which included ductular reaction, oval cell activation, and biliary fibrosis, was completely lost from Cyld/Relb^ΔLPC mice. Compared with livers from control mice, livers from Cyld^ΔLPC mice (but not Cyld/Relb^ΔLPC mice) had increased levels of mRNAs encoding cytokines (LTB; CD40; and tumor necrosis factor superfamily [TNFSF] members TNFSF11 [RANKL], TNFSF13B [BAFF], and TNFSF14 [LIGHT]) produced by reactive cholangiocytes. However, these strains of mice developed similar levels of liver fibrosis in response to CCl₄ exposure. Cyld^ΔLPC mice and Cyld/Relb^ΔLPC mice had improved liver function on the DDC diet compared with control mice fed the DDC diet.

CONCLUSION

Reactive bile ducts in patients with chronic liver diseases have increased levels of LTB and nuclear translocation of RELB. RELB is required for the ductular reaction and development of biliary fibrosis in Cyld^ΔLPC mice. Deletion of RELB and CYLD from LPCs protects mice from DDC-induced cholestatic liver fibrosis.

Abstract PO026: Bile acid signaling remodels the iCCA immune microenvironment

Intrahepatic cholangiocarcinoma (iCCA) primarily arises from the transformation of cholangiocytes (epithelial cells of the bile ducts), is diagnosed at late stage and has a dismal prognosis (average 5-year survival after resection is 32%). An alarming increase in its incidence over the past decades and the scarce treatment options available urges for the development of novel therapeutic strategies to tackle this malignancy. Immunotherapy has had limited success in iCCA. Possible explanations are that iCCA immune microenvironment is poor in CD8+ T cells and rich in immunosuppressive innate immune cells. The immune landscape of iCCA is determined by the aetiology of the liver insult (e.g. viral, cholestatic) and these different iCCA immune landscapes have not yet been characterized. Therefore, in depth studies on the immunobiology of iCCA are essential to develop new immunotherapy strategies where innate immune cells play a prominent role. We hypothesized that bile acids (BA) are a potential, valid therapeutic target for iCCA, as they strongly influence liver immune microenvironment and proliferation. This idea is supported by the fact that BA have an immunomodulatory role through inhibition of NF-KB and reduction of macrophage production of pro-inflammatory cytokines, suppressing cholangiocyte transformation in iCCA. Since BA and derivatives have recently been approved for the treatment of human chronic cholestatic diseases and primary sclerosis cholangitis, but have not yet been tested to treat iCCA, the proposed project might directly offer evidence for a second use of these drugs in patients with iCCA. Using novel preclinical mouse models of iCCA and human iCCA samples, our objective is to develop new therapeutic strategies for iCCA treatment based on BA signalling, that would impair tumour growth and foster the immune response against the tumour. In order to investigate the effects that BA can exert in tumour initiation and development, we adopted a iCCA mouse model based on the hydrodynamic tail-vein delivery of genetic elements specifically in hepatocytes, which differentiate into cholangiocytes and ultimately leads to the development of iCCA, while conserving a competent immune system. We found that by feeding the animals with an endogenous BA-enriched diet (BA diet), we reduced the overall tumor burden and strikingly increased overall survival. The positive response to the BA diet was associated to an inhibition of tumor proliferation and a robust increase in the abundance and activation of inflammatory monocytes and T cells. Our preliminary results indicate that mimicking the effect of BA could represent a novel immunotherapeutic strategy for iCCA. We will present these data as well as ongoing studies including fluorescence-activated cell sorting and single-cell RNA seq sequencing, focused on understanding the cooperation between different immune cell types that foster response against the tumor.

Citation Format: María García-Beccaria, Mirian Fernández-Vaquero, Maria Reich, Dominik Pfister, Diran Herebian, Benjamin Goeppert, Darjus Felix Tschaharganeh, Verena Keitel, Mathias Heikenwälder. Bile acid signaling remodels the iCCA immune microenvironment [abstract]. In: Proceedings of the AACR Special Conference: Advances in the Pathogenesis and Molecular Therapies of Liver Cancer; 2022 May 5-8; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(17_Suppl):Abstract nr PO026.

Lymphotoxin beta-activated LTBR/NIK/RELB axis drives proliferation in cholangiocarcinoma

BACKGROUND AND AIMS

Cholangiocarcinoma (CCA) is an aggressive malignancy arising from the intrahepatic (iCCA) or extrahepatic (eCCA) bile ducts with poor prognosis and limited treatment options. Prior evidence highlighted a significant contribution of the non-canonical NF-κB signalling pathway in initiation and aggressiveness of different tumour types. Lymphotoxin-β (LTβ) stimulates the NF-κB-inducing kinase (NIK), resulting in the activation of the transcription factor RelB. However, the functional contribution of the non-canonical NF-κB signalling pathway via the LTβ/NIK/RelB axis in CCA carcinogenesis and progression has not been established.

METHODS

Human CCA-derived cell lines and organoids were examined to determine the expression of NF-κB pathway components upon activation or inhibition. Proliferation and cell death were analysed using real-time impedance measurement and flow cytometry. Immunoblot, qRT-PCR, RNA sequencing and in situ hybridization were employed to analyse gene and protein expression. Four in vivo models of iCCA were used to probe the activation and regulation of the non-canonical NF-κB pathway.

RESULTS

Exposure to LTα1/β2 activates the LTβ/NIK/RelB axis and promotes proliferation in CCA. Inhibition of NIK with the small molecule inhibitor B022 efficiently suppresses RelB expression in patient-derived CCA organoids and nuclear co-translocation of RelB and p52 stimulated by LTα1/β2 in CCA cell lines. In murine CCA, RelB expression is significantly increased and LTβ is the predominant ligand of the non-canonical NF-κB signalling pathway.

CONCLUSIONS

Our study confirms that the non-canonical NF-κB axis LTβ/NIK/RelB drives cholangiocarcinogenesis and represents a candidate therapeutic target.