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

Activation of TGR5 Increases Urine Concentration by Inducing AQP2 and AQP3 Expression in Renal Medullary Collecting Ducts

Introduction

G protein-coupled bile acid receptor (TGR5), the first G protein-coupled receptor for bile acids identified, is capable of activating a variety of intracellular signaling pathways after interacting with bile acids. TGR5 plays an important role in multiple physiological processes and is considered to be a potential target for the treatment of various metabolic diseases, including type 2 diabetes. Evidence has emerged that genetic deletion of TGR5 results in an increase in basal urine output, suggesting that it may play a critical role in renal water and salt reabsorption. The present study aims to elucidate the effect and mechanism of TGR5 activation on urine concentration.

Methods

Mice were treated with TGR5 agonists (LCA and INT-777) for 3 days. The 24-h urine of mice was collected and analyzed for urine biochemical parameters. The mRNA expressions were detected by real-time PCR, and the protein expressions were detected by western blot. Immunohistochemistry and immunofluorescence were performed to examine the cellular location of proteins. The cultured primary medullary collecting duct cells were pretreated with H89 (a PKA inhibitor) for 1 h, followed by 12-h treatment of LCA and INT-777. Luciferase reporter assays were used to detect the effect of CREB on the gene transcription of AQPs. Gel electrophoretic mobility shift assays were used to analyze DNA-protein interactions.

Results

Treatment of mice with the TGR5 agonist LCA and INT-777 markedly reduced urine output and increased urine osmolality, accompanied by a marked increase in AQP2 and AQP3 protein expression and membrane translocation. In cultured primary medullary collecting duct cells, LCA and INT-777 dose-dependently upregulated AQP2 and AQP3 expression in a cAMP/PKA-dependent manner. Mechanistically, both AQP2 and AQP3 gene promoter contains a putative CREB-binding site, which can be bound and activated by CREB as assessed by both gene promoter-driven luciferase and gel shift assays.

Conclusion

Collectively, our findings demonstrate that activation of TGR5 can promote urine concentration by upregulation of AQP2 and AQP3 expression in renal collecting ducts. TGR5 may represent an attractive target for the treatment of patients with urine concentration defect.

Human liver organoids: From generation to applications

In the last decade, research into human hepatology has been revolutionized by the development of mini human livers in a dish. These liver organoids are formed by self-organizing stem cells and resemble their native counterparts in cellular content, multicellular architecture, and functional features. Liver organoids can be derived from the liver tissue or pluripotent stem cells generated from a skin biopsy, blood cells, or renal epithelial cells present in urine. With the development of liver organoids, a large part of previous hurdles in modeling the human liver is likely to be solved, enabling possibilities to better model liver disease, improve (personalized) drug testing, and advance bioengineering options. In this review, we address strategies to generate and use organoids in human liver disease modeling, followed by a discussion of their potential application in drug development and therapeutics, as well as their strengths and limitations.

Update on the development of TGR5 agonists for human diseases

The G protein-coupled bile acid receptor 1 (GPBAR1) or TGR5 is widely distributed across organs, including the small intestine, stomach, liver, spleen, and gallbladder. Many studies have established strong correlations between TGR5 and glucose homeostasis, energy metabolism, immune-inflammatory responses, and gastrointestinal functions. These results indicate that TGR5 has a significant impact on the progression of tumor development and metabolic disorders such as diabetes mellitus and obesity. Targeting TGR5 represents an encouraging therapeutic approach for treating associated human ailments. Notably, the GLP-1 receptor has shown exceptional efficacy in clinical settings for diabetes management and weight loss promotion. Currently, numerous TGR5 agonists have been identified through natural product-based approaches and virtual screening methods, with some successfully progressing to clinical trials. This review summarizes the intricate relationships between TGR5 and various diseases emphasizing recent advancements in research on TGR5 agonists, including their structural characteristics, design tactics, and biological activities. We anticipate that this meticulous review could facilitate the expedited discovery and optimization of novel TGR5 agonists.

Bile acids and coronavirus disease 2019

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been significantly alleviated. However, long-term health effects and prevention strategy remain unresolved. Thus, it is essential to explore the pathophysiological mechanisms and intervention for SARS-CoV-2 infection. Emerging research indicates a link between COVID-19 and bile acids, traditionally known for facilitating dietary fat absorption. The bile acid ursodeoxycholic acid potentially protects against SARS-CoV-2 infection by inhibiting the farnesoid X receptor, a bile acid nuclear receptor. The activation of G-protein-coupled bile acid receptor, another membrane receptor for bile acids, has also been found to regulate the expression of angiotensin-converting enzyme 2, the receptor through which the virus enters human cells. Here, we review the latest basic and clinical evidence linking bile acids to SARS-CoV-2, and reveal their complicated pathophysiological mechanisms.

Single-cell, single-nucleus, and spatial transcriptomics characterization of the immunological landscape in the healthy and PSC human liver

BACKGROUND & AIMS

Primary sclerosing cholangitis (PSC) is an immune-mediated cholestatic liver disease for which there is an unmet need to understand the cellular composition of the affected liver and how it underlies disease pathogenesis. We aimed to generate a comprehensive atlas of the PSC liver using multi-omic modalities and protein-based functional validation.

METHODS

We employed single-cell and single-nucleus RNA sequencing (47,156 cells and 23,000 nuclei) and spatial transcriptomics (one sample by 10x Visium and five samples with Nanostring GeoMx DSP) to profile the cellular ecosystem in 10 PSC livers. Transcriptomic profiles were compared to 24 neurologically deceased donor livers (107,542 cells) and spatial transcriptomics controls, as well as 18,240 cells and 20,202 nuclei from three PBC livers. Flow cytometry was performed to validate PSC-specific differences in immune cell phenotype and function.

RESULTS

PSC explants with parenchymal cirrhosis and prominent periductal fibrosis contained a population of cholangiocyte-like hepatocytes that were surrounded by diverse immune cell populations. PSC-associated biliary, mesenchymal, and endothelial populations expressed chemokine and cytokine transcripts involved in immune cell recruitment. Additionally, expanded CD4+ T cells and recruited myeloid populations in the PSC liver expressed the corresponding receptors to these chemokines and cytokines, suggesting potential recruitment. Tissue-resident macrophages, by contrast, were reduced in number and exhibited a dysfunctional and downregulated inflammatory response to lipopolysaccharide and interferon-γ stimulation.

CONCLUSIONS

We present a comprehensive atlas of the PSC liver and demonstrate an exhaustion-like phenotype of myeloid cells and markers of chronic cytokine expression in late-stage PSC lesions. This atlas expands our understanding of the cellular complexity of PSC and has potential to guide the development of novel treatments.

IMPACT AND IMPLICATIONS

Primary sclerosing cholangitis (PSC) is a rare liver disease characterized by chronic inflammation and irreparable damage to the bile ducts, which eventually results in liver failure. Due to a limited understanding of the underlying pathogenesis of disease, treatment options are limited. To address this, we sequenced healthy and diseased livers to compare the activity, interactions, and localization of immune and non-immune cells. This revealed that hepatocytes lining PSC scar regions co-express cholangiocyte markers, whereas immune cells infiltrate the scar lesions. Of these cells, macrophages, which typically contribute to tissue repair, were enriched in immunoregulatory genes and demonstrated a lack of responsiveness to stimulation. These cells may be involved in maintaining hepatic inflammation and could be a target for novel therapies.

Folic acid supplementation prevents high body fat-induced bone loss through TGR5 signaling pathways

Osteoporosis caused by bone loss is one of the serious global public health problems. Folic acid is a B vitamin with multiple physiological functions such as lipid regulation and antioxidant capacity, and its potential to improve bone loss has attracted our attention. Through NHANES database analysis, we found that folic acid intake was significantly correlated with whole-body bone mineral density (BMD) in people aged 20-60 years, and the association may be mediated by the body fat rate. Male C57Bl/6 mice were fed either a normal diet or a high-fat diet, and folic acid was added to drinking water for supplementation. Our results indicated that mice with high body fat showed bone microstructure damage and bone loss, while folic acid supplementation improved bone quality. At the same time, we found that mice with high body fat exhibited abnormal blood lipids, dysregulation of intestinal flora, and metabolic disorders. Folic acid supplementation improved these phenomena. Through the network analysis of intestinal flora and metabolites, we found that LCA and TGR5 may play important roles. The results showed that folic acid promoted the expression of LCA and TGR5 in mice, increased the phosphorylation of AMPK, and decreased the phosphorylation of NF-κB and ERK, thereby reducing bone loss. In summary, folic acid intake is closely related to BMD, and folic acid supplementation can prevent high body fat-induced bone loss. Our study provides new ideas and an experimental basis for preventing bone loss and osteoporosis.

Deletion of Tgm2 suppresses BMP-mediated hepatocyte-to-cholangiocyte metaplasia in ductular reaction

Transglutaminase 2 (Tgm2) plays an essential role in hepatic repair following prolonged toxic injury. During cholestatic liver injury, the intrahepatic cholangiocytes undergo dynamic tissue expansion and remodelling, referred to as ductular reaction (DR), which is crucial for liver regeneration. However, the molecular mechanisms governing the dynamics of active cells in DR are still largely unclear. Here, we generated Tgm2-knockout mice (Tgm2-/-) and Tgm2-CreERT2-Rosa26-mTmG flox/flox (Tgm2CreERT2-R26T/Gf/f) mice and performed a three-dimensional (3D) collagen gel culture of mouse hepatocytes to demonstrate how Tgm2 signalling is involved in DR to remodel intrahepatic cholangiocytes. Our results showed that the deletion of Tgm2 adversely affected the functionality and maturity of the proliferative cholangiocytes in DR, thus leading to more severe cholestasis during DDC-induced liver injury. Additionally, Tgm2 hepatocytes played a crucial role in the regulation of DR through metaplasia. We unveiled that Tgm2 regulated H3K4me3Q5ser via serotonin to promote BMP signalling activation to participate in DR. Besides, we revealed that the activation or inhibition of BMP signalling could promote or suppress the development and maturation of cholangiocytes in DDC-induced DR. Furthermore, our 3D collagen gel culture assay indicated that Tgm2 was vital for the development of cholangiocytes in vitro. Our results uncovered a considerable role of BMP signalling in controlling metaplasia of Tgm2 hepatocytes in DR and revealed the phenotypic plasticity of mature hepatocytes.

Understanding the role of ursodeoxycholic acid and gut microbiome in non-alcoholic fatty liver disease: current evidence and perspectives

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease, resulting in a huge medical burden worldwide. Accumulating evidence suggests that the gut microbiome and bile acids play pivotal roles during the development of NAFLD. Patients with NAFLD exhibit unique signatures of the intestinal microbiome marked by the priority of Gram-negative bacteria, decreased ratio of Firmicutes/Bacteroidetes (F/B), and increased Prevotella and Lachnospiraceae. The intestinal microbiota is involved in the metabolism of bile acids. Ursodeoxycholic acid (UDCA) is a key determinant in maintaining the dynamic communication between the host and gut microbiota. It generally shows surprising therapeutic potential in NAFLD with several mechanisms, such as improving cellular autophagy, apoptosis, and mitochondrial functions. This action is based on its direct or indirect effect, targeting the farnesoid X receptor (FXR) and various other nuclear receptors. This review aims to discuss the current studies on the involvement of the microbiome-UDCA interface in NAFLD therapy and provide prospective insights into future preventative and therapeutic approaches for NAFLD.

Antagonistic effects of the cytotoxic molecules granzyme B and TRAIL in the immunopathogenesis of sclerosing cholangitis

BACKGROUND AND AIMS

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease characterized by biliary inflammation and fibrosis. We showed an elevated interferon γ response in patients with primary sclerosing cholangitis and in multidrug resistance protein 2-deficient ( Mdr2-/- ) mice developing sclerosing cholangitis. Interferon γ induced expression of the cytotoxic molecules granzyme B (GzmB) and TRAIL in hepatic lymphocytes and mediated liver fibrosis in sclerosing cholangitis.

APPROACH AND RESULTS

In patient samples and Mdr2-/- mice, we identified lymphocyte clusters with a cytotoxic gene expression profile using single-cell RNA-seq and cellular indexing of transcriptomes and epitopes by sequencing analyses combined with multi-parameter flow cytometry. CD8 + T cells and NK cells showed increased expression of GzmB and TRAIL in sclerosing cholangitis. Depletion of CD8 + T cells ameliorated disease severity in Mdr2-/- mice. By using Mdr2-/- × Gzmb-/- and Mdr2-/- × Tnfsf10-/- mice, we investigated the significance of GzmB and TRAIL for disease progression in sclerosing cholangitis. Interestingly, the lack of GzmB resulted in reduced cholangiocyte apoptosis, liver injury, and fibrosis. In contrast, sclerosing cholangitis was aggravated in the absence of TRAIL. This correlated with elevated GzmB and interferon γ expression by CD8 + T cells and NK cells enhanced T-cell survival, and increased apoptosis and expansion of cholangiocytes.

CONCLUSIONS

GzmB induces apoptosis and fibrosis in sclerosing cholangitis, whereas TRAIL regulates inflammatory and cytotoxic immune responses, subsequently leading to reduced liver injury and fibrosis.

Targeting bile salt homeostasis in biliary diseases

PURPOSE OF REVIEW

Advances in the understanding of bile salt synthesis, transport and signalling show the potential of modulating bile salt homeostasis as a therapeutic strategy in cholestatic liver diseases. Here, recent developments in (pre)clinical research in this field is summarized and discussed.

RECENT FINDINGS

Inhibition of the apical sodium-dependent bile salt transporter (ASBT) and Na + -taurocholate cotransporting polypeptide (NTCP) seems effective against cholestatic liver diseases, as well as Farnesoid X receptor (FXR) agonism or a combination of both. While approved for the treatment of primary biliary cholangitis (PBC) and intrahepatic cholestasis of pregnancy (ICP), ursodeoxycholic acid (UDCA) has retrospectively shown carefully promising results in primary sclerosing cholangitis (PSC). The side chain shortened derivate norUDCA is of further therapeutic interest since its mechanisms of action are independent of the bile salt transport machinery. In the pathogenesis of sclerosing cholangiopathies, a skewed T-cell response with alterations in gut microbiota and bile salt pool compositions are observed. In PSC pathogenesis, the bile salt receptor Takeda G-protein-coupled receptor 5 (TGR5) in cholangiocytes is implicated, whilst in immunoglobulin G4-related cholangitis the autoantigens annexin A11 and laminin 511-E8 are involved in protecting cholangiocytes.

SUMMARY

Modulating bile salt homeostasis has proven a promising treatment strategy in models of cholestasis and are continuously being further developed. Confirmatory clinical studies are needed in order to assess the proposed treatment strategies in patients allowing for a broader therapeutic arsenal in the future.

TGR5 signalling in heart and brain injuries: focus on metabolic and ischaemic mechanisms

The heart and brain are the core organs of the circulation and central nervous system, respectively, and play an important role in maintaining normal physiological functions. Early neuronal and cardiac damage affects organ function. The relationship between the heart and brain is being continuously investigated. Evidence-based medicine has revealed the concept of the "heart- brain axis," which may provide new therapeutic strategies for certain diseases. Takeda protein-coupled receptor 5 (TGR5) is a metabolic regulator involved in energy homeostasis, bile acid homeostasis, and glucose and lipid metabolism. Inflammation is critical for the development and regeneration of the heart and brain during metabolic diseases. Herein, we discuss the role of TGR5 as a metabolic regulator of heart and brain development and injury to facilitate new therapeutic strategies for metabolic and ischemic diseases of the heart and brain.

A novel model to study mechanisms of cholestasis in human cholangiocytes reveals a role for the SIPR2 pathway

BACKGROUND

Ductular reactivity is central to the pathophysiology of cholangiopathies. Mechanisms underlying the reactive phenotype activation by exogenous inflammatory mediators and bile acids are poorly understood.

METHODS

Using human extrahepatic cholangiocyte organoids (ECOs) we developed an injury model emulating the cholestatic microenvironment with exposure to inflammatory mediators and various pathogenic bile acids. Moreover, we explored roles for the bile acid activated Sphingosine-1-phosphate receptor 2 (S1PR2) and potential beneficial effects of therapeutic bile acids UDCA and norUDCA.

RESULTS

Synergistic exposure to bile acids (taurocholic acid, glycocholic acid, glycochenodeoxycholic acid) and TNF-α for 24 hours induced a reactive state as measured by ECO diameter, proliferation, lactate dehydrogenase activity and reactive phenotype markers. While NorUDCA and UDCA treatments given 8 hours after injury induction both suppressed reactive phenotype activation and most injury parameters, proliferation was improved by NorUDCA only. Extrahepatic cholangiocyte organoid stimulation with S1PR2 agonist sphingosine-1-phosphate reproduced the cholangiocyte reactive state and upregulated S1PR2 downstream mediators; these effects were suppressed by S1PR2 antagonist JET-013 (JET), downstream mediator extracellular signal-regulated kinase 1/2 inhibitor, and by norUDCA or UDCA treatments. JET also partially suppressed reactive phenotype after bile acid injury.

CONCLUSIONS

We developed a novel model to study the reactive cholangiocyte state in response to pathological stimuli in cholestasis and demonstrated a contributory role of S1PR2 signaling in both injury and NorUDCA/UDCA treatments. This model is a valuable tool to further explore the pathophysiology of human cholangiopathies.

A bidirectional two-sample Mendelian randomization using the gut microbiota to reveal potential therapeutic targets for primary sclerosing cholangitis

BACKGROUND

Previous studies indicate that gut microbiota correlates to primary sclerosing cholangitis (PSC), but the causation is still unclear. We sought to reveal the causal relationship between gut microbiota and PSC with a bidirectional two-sample Mendelian randomization (MR) analysis.

METHODS

The large-scale genome-wide association study (GWAS) summary statistics and a bidirectional two-sample MR study were used to assess the causality between gut microbiota and PSC. Multiple sensitivity analyses were used to identify the robustness of our results.

RESULTS

Three microbial taxa causally correlated to PSC. Genus Ruminococcaceae UCG002 (OR: 1.855, 95% CI: 1.068-3.220, P = 0.028) increased the risk of PSC. Class Betaproteobacteria (OR: 0.360, 95% CI: 0.171-0.758, P = 0.007), and genus Ruminiclostridium6 (OR: 0.474, 95% CI: 0.219-0.820, P = 0.011) had protective effects on PSC. In addition, we found the causal relationship of PSC with higher abundance of genus Dialister (beta: 0.059, 95% CI: 0.017-0.102, P = 0.006), genus Veillonella (beta: 0.065, 95% CI: 0.016-0.113, P = 0.009), class Melainabacteria (beta: 0.073, 95% CI: 0.012-0.133, P = 0.019), and order Gastranaerophilales (beta: 0.072, 95% CI: 0.011-0.113, P = 0.133).

CONCLUSION

Our study reveals the causality between gut microbiota and PSC, providing new insights into the pathological mechanisms of PSC and facilitating the development of novel biomarkers and disease-modifying therapeutics for PSC from the perspective of gut microbiota.

Increased expression of TNFRSF14 and LIGHT in biliary epithelial cells of patients with primary sclerosing cholangitis

BACKGROUND AND AIMS

There is a lack of biliary epithelial molecular markers for primary sclerosing cholangitis (PSC). We analyzed candidates from disease susceptibility genes identified in recent genome-wide association studies (GWAS).

METHODS

Expression levels of GWAS genes were analyzed in archival liver tissues of patients with PSC and controls. Immunohistochemical analysis was performed to evaluate expression levels in the biliary epithelia of PSC (N = 45) and controls (N = 12). Samples from patients with primary biliary cholangitis (PBC) were used as disease controls (N = 20).

RESULTS

Hepatic expression levels of ATXN2, HHEX, PRDX5, MST1, and TNFRSF14 were significantly altered in the PSC group. We focused on the immune-related receptor, TNFRSF14. Immunohistochemistry revealed that high expression of TNFRSF14 in biliary epithelial cells was observed only in the PSC group. In addition, the expression of LIGHT, which encodes a TNFRSF14-activating ligand, was increased in PSC liver. Immunohistochemistry showed that high expression of LIGHT was more common in PSC biliary epithelia (53%) than in the PBC (15%) or control (0%) groups; moreover, it was positively associated with fibrotic progression, although it was not an independent prognostic factor.

CONCLUSIONS

TNFRSF14 and LIGHT are promising candidate markers for PSC.

Microbial Players in Primary Sclerosing Cholangitis: Current Evidence and Concepts

Primary sclerosing cholangitis (PSC) is a rare cholestatic liver disease with progressive biliary inflammation, destruction of the biliary tract, and fibrosis, resulting in liver cirrhosis and end-stage liver disease. To date, liver transplantation is the only definitive treatment option for PSC. The precise etiology of PSC remains elusive, but it is widely accepted to involve a complex interplay between genetic predisposition, immunologic dysfunction, and environmental influence. In recent years, the gut-liver axis has emerged as a crucial pathway contributing to the pathogenesis of PSC, with particular focus on the role of gut microbiota. However, the role of the fungal microbiome or mycobiome has been overlooked for years, resulting in a lack of comprehensive studies on its involvement in PSC. In this review, we clarify the present clinical and mechanistic data and concepts concerning the gut bacterial and fungal microbiota in the context of PSC. This review sheds light on the role of specific microbes and elucidates the dynamics of bacterial and fungal populations. Moreover, we discuss the latest insights into microbe-altering therapeutic approaches involving the gut-liver axis and bile acid metabolism.

PGC1α deficiency reverses cholestasis-induced liver injury via attenuating hepatic inflammation and promoting bile duct remodeling

OBJECTIVES

Cholestatic liver diseases are characterized by hepatocellular damage, cholangiocyte proliferation, and progressive fibrosis. Bile duct ligation (BDL) is widely used to resemble liver injuries induced by cholestasis. Peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC1α) was reported to play a critical role in multiple biological responses. Nevertheless, whether PGC1α is involved in bile acid metabolism and biliary disorders remains unclear. This study aimed to investigate the effect of PGC1α on hepatic responses after cholestatic injury.

MATERIALS AND METHODS

Wild-type mice were subjected to BDL or sham surgery for 14 days and human liver specimens from patients with primary biliary cholangitis (PBC) were collected to detect the expression of PGC1α. Hepatic-specific PGC1α knockout mice (HKO) were constructed and subjected to BDL, in which the effects of PGC1α on cholestatic liver injury were demonstrated by biochemical and histopathological assessments, immunoblotting, and metabolomics.

RESULTS

The expression of PGC1α was upregulated in the liver of PBC patients and murine models. Both in vivo and in vitro experiments supported the protective effects of PGC1α on cholestasis-induced hepatocyte injury. Infiltrated inflammatory cells after BDL were decreased in HKO mice. Inhibited Wnt/β-Catenin pathway and enhanced Notch signaling promoted transdifferentiation of hepatic progenitor cells (HPC)/ hepatocytes into cholangiocytes, leading to the greater ductular reaction observed in the HKO mice. But bile acids metabolism and mitochondrial function were not affected due to hepatic PGC1α deficiency in cholestasis.

CONCLUSIONS

Hepatic-specific deletion of PGC1α regulated liver regeneration by promoting ductular reactions, thereby exerting protective effects against BDL-induced liver injury, which could be a new potential therapeutic target.

IgG4-related cholangitis - a mimicker of fibrosing and malignant cholangiopathies

IgG4-related cholangitis (IRC) is the major hepatobiliary manifestation of IgG4-related disease (IgG4-RD), a systemic fibroinflammatory disorder. The pathogenesis of IgG4-RD and IRC is currently viewed as multifactorial, as there is evidence of a genetic predisposition while environmental factors, such as blue-collar work, are major risk factors. Various autoantigens have been described in IgG4-RD, including annexin A11 and laminin 511-E8, proteins which may exert a partially protective function in cholangiocytes by enhancing secretion and barrier function, respectively. For the other recently described autoantigens, galectin-3 and prohibitin 1, a distinct role in cholangiocytes appears less apparent. In relation to these autoantigens, oligoclonal expansions of IgG4+ plasmablasts are present in patients with IRC and disappear upon successful treatment. More recently, specific T-cell subtypes including regulatory T cells, follicular T helper 2 cells, peripheral T helper cells and cytotoxic CD8+ and CD4+ SLAMF7+ T cells have been implicated in the pathogenesis of IgG4-RD. The clinical presentation of IRC often mimics other biliary diseases such as primary sclerosing cholangitis or cholangiocarcinoma, which may lead to inappropriate medical and potentially invalidating surgical interventions. As specific biomarkers are lacking, diagnosis is made according to the HISORt criteria comprising histopathology, imaging, serology, other organ manifestations and response to therapy. Treatment of IRC aims to prevent or alleviate organ damage and to improve symptoms and consists of (i) remission induction, (ii) remission maintenance and (iii) long-term management. Glucocorticosteroids are highly effective for remission induction, after which immunomodulators can be introduced for maintenance of remission as glucocorticosteroid-sparing alternatives. Increased insight into the pathogenesis of IRC will lead to improved diagnosis and novel therapeutic strategies in the future.

Bile acid receptors and renal regulation of water homeostasis

The kidney is the key organ responsible for maintaining the body's water and electrolyte homeostasis. About 99% of the primary urine filtered from the Bowman's capsule is reabsorbed along various renal tubules every day, with only 1-2 L of urine excreted. Aquaporins (AQPs) play a vital role in water reabsorption in the kidney. Currently, a variety of molecules are found to be involved in the process of urine concentration by regulating the expression or activity of AQPs, such as antidiuretic hormone, renin-angiotensin-aldosterone system (RAAS), prostaglandin, and several nuclear receptors. As the main bile acid receptors, farnesoid X receptor (FXR) and membrane G protein-coupled bile acid receptor 1 (TGR5) play important roles in bile acid, glucose, lipid, and energy metabolism. In the kidney, FXR and TGR5 exhibit broad expression across all segments of renal tubules, and their activation holds significant therapeutic potential for numerous acute and chronic kidney diseases through alleviating renal lipid accumulation, inflammation, oxidative stress, and fibrosis. Emerging evidence has demonstrated that the genetic deletion of FXR or TGR5 exhibits increased basal urine output, suggesting that bile acid receptors play a critical role in urine concentration. Here, we briefly summarize the function of bile acid receptors in renal water reabsorption and urine concentration.

Current Therapeutics in Primary Sclerosing Cholangitis

Primary sclerosing cholangitis (PSC) is an orphan, cholestatic liver disease that is characterized by inflammatory biliary strictures with variable progression to end-stage liver disease. Its pathophysiology is poorly understood. Chronic biliary inflammation is likely driven by immune dysregulation, gut dysbiosis, and environmental exposures resulting in gut-liver crosstalk and bile acid metabolism disturbances. There is no proven medical therapy that alters disease progression in PSC, with the commonly prescribed ursodeoxycholic acid being shown to improve liver biochemistry at low-moderate doses (15-23 mg/kg/day) but not alter transplant-free survival or liver-related outcomes. Liver transplantation is the only option for patients who develop end-stage liver disease or refractory complications of PSC. Immunosuppressive and antifibrotic agents have not proven to be effective, but there is promise for manipulation of the gut microbiome with fecal microbiota transplantation and antibiotics. Bile acid manipulation via alternate synthetic bile acids such as norursodeoxycholic acid, or interaction at a transcriptional level via nuclear receptor agonists and fibrates have shown potential in phase II trials in PSC with several leading to larger phase III trials. In view of the enhanced malignancy risk, statins, and aspirin show potential for reducing the risk of colorectal cancer and cholangiocarcinoma in PSC patients. For patients who develop clinically relevant strictures with cholestatic symptoms and worsening liver function, balloon dilatation is safer compared with biliary stent insertion with equivalent clinical efficacy.

Human vascularized bile duct-on-a chip: a multi-cellular micro-physiological system for studying cholestatic liver disease

Exploring the pathogenesis of and developing therapies for cholestatic liver diseases such as primary sclerosing cholangitis (PSC) remains challenging, partly due to a paucity ofin vitromodels that capture the complex environments contributing to disease progression and partly due to difficulty in obtaining cholangiocytes. Here we report the development of a human vascularized bile duct-on-a-chip (VBDOC) that uses cholangiocyte organoids derived from normal bile duct tissue and human vascular endothelial cells to model bile ducts and blood vessels structurally and functionally in three dimensions. Cholangiocytes in the duct polarized, formed mature tight junctions and had permeability properties comparable to those measured inex vivosystems. The flow of blood and bile was modeled by perfusion of the cell-lined channels, and cholangiocytes and endothelial cells displayed differential responses to flow. We also showed that the device can be constructed with biliary organoids from cells isolated from both bile duct tissue and the bile of PSC patients. Cholangiocytes in the duct became more inflammatory under the stimulation of IL-17A, which induced peripheral blood mononuclear cells and differentiated Th17 cells to transmigrate across the vascular channel. In sum, this human VBDOC recapitulated the vascular-biliary interface structurally and functionally and represents a novel multicellular platform to study inflammatory and fibrotic cholestatic liver diseases.

Primary Sclerosing Cholangitis-Associated Cholangiocarcinoma: From Pathogenesis to Diagnostic and Surveillance Strategies

Cholangiocarcinoma (CCA) is the most common malignancy in patients with primary sclerosing cholangitis (PSC), accounting for 2-8% of cases and being the leading cause of death in these patients. The majority of PSC-associated CCAs (PSC-CCA) develop within the first few years after PSC diagnosis. Older age and male sex, as well as concomitant inflammatory bowel disease (IBD) or high-grade biliary stenosis, are some of the most relevant risk factors. A complex combination of molecular mechanisms involving inflammatory pathways, direct cytopathic damage, and epigenetic and genetic alterations are involved in cholangiocytes carcinogenesis. The insidious clinical presentation makes early detection difficult, and the integration of biochemical, radiological, and histological features does not always lead to a definitive diagnosis of PSC-CCA. Surveillance is mandatory, but current guideline strategies failed to improve early detection and consequently a higher patient survival rate. MicroRNAs (miRNAs), gene methylation, proteomic and metabolomic profile, and extracellular vesicle components are some of the novel biomarkers recently applied in PSC-CCA detection with promising results. The integration of these new molecular approaches in PSC diagnosis and monitoring could contribute to new diagnostic and surveillance strategies.

Estrogen deficiency induces bone loss through the gut microbiota

Postmenopausal osteoporosis is a common bone metabolic disease, and gut microbiota (GM) imbalance plays an important role in the development of metabolic bone disease. Here, we show that ovariectomized mice had high levels of lipopolysaccharide in serum and gut microbiota dysbiosis through increases in luminal Firmicutes:Bacteroidetes ratio. We depleted the GM through antibiotic treatment and observed improvements in bone mass, bone microstructure, and bone strength in ovariectomized mice. Conversely, transplantation of GM adapted to ovariectomy induced bone loss. However, GM depletion reversed ovariectomy-induced gene expression in the tibia and increased periosteal bone formation. Furthermore, bioinformatics analysis revealed that the G-protein-coupled bile acid receptor (TGR5) and systemic inflammatory factors play key roles in bone metabolism. Silencing TGR5 expression through small interfering RNA (siRNA) in the local tibia and knockout of TGR5 attenuated the effects of GM depletion in ovariectomized mice, confirming these findings. Thus, this study highlights the critical role of the GM in inducing bone loss in ovariectomized mice and suggests that targeting TGR5 within the GM may have therapeutic potential for postmenopausal osteoporosis.

Human Placental Mesenchymal Stem Cells Relieve Primary Sclerosing Cholangitis via Upregulation of TGR5 in Mdr2-/- Mice and Human Intrahepatic Cholangiocyte Organoid Models

Primary sclerosing cholangitis (PSC) is a biliary disease accompanied by chronic inflammation of the liver and biliary stricture. Mesenchymal stem cells (MSCs) are used to treat liver diseases because of their immune regulation and regeneration-promoting functions. This study was performed to explore the therapeutic potential of human placental MSCs (hP-MSCs) in PSC through the Takeda G protein-coupled receptor 5 (TGR5) receptor pathway. Liver tissues were collected from patients with PSC and healthy donors (n = 4) for RNA sequencing and intrahepatic cholangiocyte organoid construction. hP-MSCs were injected via the tail vein into Mdr2-/-, bile duct ligation (BDL), and 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) mouse models or co-cultured with organoids to confirm their therapeutic effect on biliary cholangitis. Changes in bile acid metabolic profile were analyzed by liquid chromatography/tandem mass spectrometry (LC-MS/MS). Compared with healthy controls, liver tissues and intrahepatic cholangiocyte organoids from PSC patients were characterized by inflammation and cholestasis, and marked downregulation of bile acid receptor TGR5 expression. hP-MSC treatment apparently reduced the inflammation, cholestasis, and fibrosis in Mdr2-/-, BDL, and DDC model mice. By activating the phosphatidylinositol 3 kinase/extracellular signal-regulated protein kinase pathway, hP-MSC treatment promoted the proliferation of cholangiocytes, and affected the transcription of downstream nuclear factor κB through regulation of the binding of TGR5 and Pellino3, thereby affecting the cholangiocyte inflammatory phenotype.

Primary sclerosing cholangitis (PSC) and inflammatory bowel disease (IBD): a condition exemplifying the crosstalk of the gut-liver axis

The close relationship between primary sclerosing cholangitis (PSC) and inflammatory bowel disease (IBD) provides a good opportunity to comprehend the gut-liver axis. The gut and the liver have reciprocal interactions, including how gut inflammation influences the liver through immune cells and the microbiota and how the microbiota in the gut modifies bile acids, which are produced and secreted from the liver. PSC-IBD shows distinct clinical findings from classical IBD. In addition, a distinct genetic predisposition and unique microbiota composition suggest that PSC-IBD is an independent disease entity. Understanding the pathogenesis of PSC-IBD helps to develop novel and effective therapeutic agents. Given the high risk of malignancies associated with PSC-IBD, it is critical to identify patients at high risk and implement appropriate surveillance and monitoring strategies. In this review, we provide an overview of PSC-IBD, which exemplifies the gut-liver axis.

WITHDRAWN: RNA binding protein Musashi2 regulates dairy cows' mastitis by activating the TGFβ signaling pathway

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Organoids: The current status and biomedical applications

Organoids are three-dimensional (3D) miniaturized versions of organs or tissues that are derived from cells with stem potential and can self-organize and differentiate into 3D cell masses, recapitulating the morphology and functions of their in vivo counterparts. Organoid culture is an emerging 3D culture technology, and organoids derived from various organs and tissues, such as the brain, lung, heart, liver, and kidney, have been generated. Compared with traditional bidimensional culture, organoid culture systems have the unique advantage of conserving parental gene expression and mutation characteristics, as well as long-term maintenance of the function and biological characteristics of the parental cells in vitro. All these features of organoids open up new opportunities for drug discovery, large-scale drug screening, and precision medicine. Another major application of organoids is disease modeling, and especially various hereditary diseases that are difficult to model in vitro have been modeled with organoids by combining genome editing technologies. Herein, we introduce the development and current advances in the organoid technology field. We focus on the applications of organoids in basic biology and clinical research, and also highlight their limitations and future perspectives. We hope that this review can provide a valuable reference for the developments and applications of organoids.

Crosstalk between Gut Microbiota and Bile Acids in Cholestatic Liver Disease

Emerging evidence suggests the complex interactions between gut microbiota and bile acids, which are crucial end products of cholesterol metabolism. Cholestatic liver disease is characterized by dysfunction of bile production, secretion, and excretion, as well as excessive accumulation of potentially toxic bile acids. Given the importance of bile acid homeostasis, the complex mechanism of the bile acid-microbial network in cholestatic liver disease requires a thorough understanding. It is urgent to summarize the recent research progress in this field. In this review, we highlight how gut microbiota regulates bile acid metabolism, how bile acid pool shapes the bacterial community, and how their interactions contribute to the pathogenesis of cholestatic liver disease. These advances might provide a novel perspective for the development of potential therapeutic strategies that target the bile acid pathway.

Bile acid-mediated signaling in cholestatic liver diseases

Chronic cholestatic liver diseases, such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), are associated with bile stasis and gradually progress to fibrosis, cirrhosis, and liver failure, which requires liver transplantation. Although ursodeoxycholic acid is effective in slowing the disease progression of PBC, it has limited efficacy in PSC patients. It is challenging to develop effective therapeutic agents due to the limited understanding of disease pathogenesis. During the last decade, numerous studies have demonstrated that disruption of bile acid (BA) metabolism and intrahepatic circulation promotes the progression of cholestatic liver diseases. BAs not only play an essential role in nutrition absorption as detergents but also play an important role in regulating hepatic metabolism and modulating immune responses as key signaling molecules. Several excellent papers have recently reviewed the role of BAs in metabolic liver diseases. This review focuses on BA-mediated signaling in cholestatic liver disease.

Liver organoids: established tools for disease modeling and drug development

In the past decade, liver organoids have evolved rapidly as valuable research tools, providing novel insights into almost all types of liver diseases, including monogenic liver diseases, alcohol-associated liver disease, metabolic-associated fatty liver disease, various types of (viral) hepatitis, and liver cancers. Liver organoids in part mimic the microphysiology of the human liver and fill a gap in high-fidelity liver disease models to a certain extent. They hold great promise to elucidate the pathogenic mechanism of a diversity of liver diseases and play a crucial role in drug development. Moreover, it is challenging but opportunistic to apply liver organoids for tailored therapies of various liver diseases. The establishment, applications, and challenges of different types of liver organoids, for example, derived from embryonic, adult, or induced pluripotent stem cells, to model different liver diseases, are presented in this review.

Capsaicin receptor TRPV1 maintains quiescence of hepatic stellate cells in the liver via recruitment of SARM1

BACKGROUND & AIMS

Capsaicin receptor, also known as transient receptor potential vanilloid 1 (TRPV1), is involved in pain physiology and neurogenic inflammation. Herein, we discovered the presence of TRPV1 in hepatic stellate cells (HSCs) and aimed to delineate its function in this cell type and liver fibrosis.

METHODS

TRPV1 expression was examined in liver biopsies from patients with liver fibrosis using quantitative real-time PCR and immunostaining. Its contribution to liver fibrosis was examined in Trpv1^-/- mice, upon lentiviral delivery of the TRPV1 gene, and in human and mouse primary HSCs, using patch clamp, intracellular Ca²⁺ mobilization determination, FACS analyses and gain/loss of function experiments. Binding of sterile alpha and Toll/interleukin-1 receptor motif-containing protein 1 (SARM1) to TRPV1 was determined using mass spectrometry, co-immunoprecipitation, surface plasmon resonance, bioluminescence resonance energy transfer, and NanoBiT.

RESULTS

TRPV1 mRNA levels are significantly downregulated in patients with liver fibrosis and mouse models, showing a negative correlation with F stage and α-smooth muscle actin expression, a marker of HSC activation. TRPV1 expression and function decrease during HSC activation in fibrotic livers in vivo or during culture. Genetic and pharmacological inhibition of TRPV1 in quiescent HSCs leads to NF-κB activation and pro-inflammatory cytokine production. TRPV1 requires binding of its N-terminal ankyrin repeat domain to the TIR-His583 (Toll/interleukin-1 receptor) domain of SARM1 to prevent HSCs from pro-inflammatory activation. Trpv1^-/- mice display increased HSC activation and more severe liver fibrosis, whereas TRPV1 overexpression is antifibrotic in various disease models.

CONCLUSION

The antifibrotic properties of TRPV1 are attributed to the prevention of HSC activation via the recruitment of SARM1, which could be an attractive therapeutic strategy against liver fibrosis.

IMPACT AND IMPLICATIONS

We identified the neuronal channel protein TRPV1 as a gatekeeper of quiescence in hepatic stellate cells, a key driver of liver fibrogenesis and chronic liver disease. Physiologically expressed in healthy liver and consistently downregulated during liver fibrosis development, its therapeutic re-expression is expected to have few side effects, making it an attractive target diagnostic tool and drug candidate for industry and clinicians.

The microbiota and the gut-liver axis in primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) offers unique opportunities to explore the gut-liver axis owing to the close association between liver disease and colonic inflammation. It is well established that the gut microbiota in people with PSC differs from that of healthy individuals, but details of the microbial factors that demarcate PSC from inflammatory bowel disease (IBD) without PSC are poorly understood. In this Review, we aim to provide an overview of the latest literature on the gut microbiome in PSC and PSC with IBD, critically examining hypotheses on how microorganisms could contribute to the pathogenesis of PSC. A particular emphasis will be put on pathogenic features of the gut microbiota that might explain the occurrence of bile duct inflammation and liver disease in the context of IBD, and we postulate the potential existence of a specific yet unknown factor related to the gut-liver axis as causative in PSC. Available data are scrutinized in the perspective of therapeutic approaches related to the gut-liver axis.

A novel lipid metabolism gene signature for clear cell renal cell carcinoma using integrated bioinformatics analysis

Background: Clear cell renal cell carcinoma (ccRCC), which is the most prevalent type of renal cell carcinoma, has a high mortality rate. Lipid metabolism reprogramming is a hallmark of ccRCC progression, but its specific mechanism remains unclear. Here, the relationship between dysregulated lipid metabolism genes (LMGs) and ccRCC progression was investigated. Methods: The ccRCC transcriptome data and patients' clinical traits were obtained from several databases. A list of LMGs was selected, differentially expressed gene screening performed to detect differential LMGs, survival analysis performed, a prognostic model established, and immune landscape evaluated using the CIBERSORT algorithm. Gene Set Variation Analysis and Gene set enrichment analysis were conducted to explore the mechanism by which LMGs affect ccRCC progression. Single-cell RNA-sequencing data were obtained from relevant datasets. Immunohistochemistry and RT-PCR were used to validate the expression of prognostic LMGs. Results: Seventy-one differential LMGs were identified between ccRCC and control samples, and a novel risk score model established comprising 11 LMGs (ABCB4, DPEP1, IL4I1, ENO2, PLD4, CEL, HSD11B2, ACADSB, ELOVL2, LPA, and PIK3R6); this risk model could predict ccRCC survival. The high-risk group had worse prognoses and higher immune pathway activation and cancer development. Conclusion: Our results showed that this prognostic model can affect ccRCC progression.

Cholestasis: exploring the triangular relationship of gut microbiota-bile acid-cholestasis and the potential probiotic strategies

Cholestasis is a condition characterized by the abnormal production or excretion of bile, and it can be induced by a variety of causes, the factors of which are extremely complex. Although great progress has been made in understanding cholestasis pathogenesis, the specific mechanisms remain unclear. Therefore, it is important to understand and distinguish cholestasis from different etiologies, which will also provide indispensable theoretical support for the development of corresponding therapeutic drugs. At present, the treatment of cholestasis mainly involves several bile acids (BAs) and their derivatives, most of which are in the clinical stage of development. Multiple lines of evidence indicate that ecological disorders of the gut microbiota are strongly related to the occurrence of cholestasis, in which BAs also play a pivotal role. Recent studies indicate that probiotics seem to have certain effects on cholestasis, but further confirmation from clinical trials is required. This paper reviews the etiology of and therapeutic strategies for cholestasis; summarizes the similarities and differences in inducement, symptoms, and mechanisms of related diseases; and provides information about the latest pharmacological therapies currently available and those under research for cholestasis. We also reviewed the highly intertwined relationship between gut microbiota-BA-cholestasis, revealing the potential role and possible mechanism of probiotics in the treatment of cholestasis.

Bile acids and their receptors: modulators and therapeutic targets in liver inflammation

Bile acids participate in the intestinal emulsion, digestion, and absorption of lipids and fat-soluble vitamins. When present in high concentrations, as in cholestatic liver diseases, bile acids can damage cells and cause inflammation. After the discovery of bile acids receptors about two decades ago, bile acids are considered signaling molecules. Besides regulating bile acid, xenobiotic, and nutrient metabolism, bile acids and their receptors have shown immunomodulatory properties and have been proposed as therapeutic targets for inflammatory diseases of the liver. This review focuses on bile acid-related signaling pathways that affect inflammation in the liver and provides an overview of the preclinical and clinical applications of modulators of these pathways for the treatment of cholestatic and autoimmune liver diseases.

Discovery of farnesoid X receptor and its role in bile acid metabolism

In 1995, the nuclear hormone orphan receptor farnesoid X receptor (FXR, NR1H4) was identified as a farnesol receptor expressed mainly in liver, kidney, and adrenal gland of rats. In 1999, bile acids were identified as endogenous FXR ligands. Subsequently, FXR target genes involved in the regulation of hepatic bile acid synthesis, secretion, and intestinal re-absorption were identified. FXR signaling was proposed as a mechanism of feedback regulation of the rate-limiting enzyme for bile acid synthesis, cholesterol 7⍺-hydroxylase (CYP7A1). The primary bile acids synthesized in the liver are transformed to secondary bile acids by the gut microbiota. The gut-to-liver axis plays a critical role in the regulation of bile acid synthesis, composition and circulating bile acid pool size, which in turn regulates glucose, lipid, and energy metabolism. Dysregulation of bile acid metabolism and FXR signaling in the gut-to-liver axis contributes to metabolic diseases including obesity, diabetes, and non-alcoholic fatty liver disease. This review will cover the discovery of FXR as a bile acid sensor in the regulation of bile acid metabolism and as a metabolic regulator of lipid, glucose, and energy homeostasis. It will also provide an update of FXR functions in the gut-to-liver axis and the drug therapies targeting bile acids and FXR for the treatment of liver metabolic diseases.

Mucosal immunity in primary sclerosing cholangitis: from the bowel to bile ducts and back again

PURPOSE OF REVIEW

In this article, we provide a contemporary overview on PSC pathogenesis, with a specific focus on the role of mucosal immunity.

RECENT FINDINGS

The extent of enteric dysbiosis in PSC has been extensively quantified, with evidence of reduced bacterial diversity and enrichment of species capable of driving lymphocyte recruitment from the gut to the liver. Integrative pathway-based analysis and metagenomic sequencing indicate a reduction in butyrate-producing species, near absence of bacteria that activate the nuclear bile acid receptor FXR, and depletion of species that regulate the synthesis of vitamin B6 and branched-chain amino acids. Immunotyping of the cellular inflammatory infiltrate has identified a population of intrahepatic naive T cells, with tendency to acquire a Th17 polarisation state, paralleled by heightened responses to pathogen stimulation. Moreover, the search for antigen specificity has revealed the presence of overlapping nucleotide clonotypes across the gut and liver, highlighting the ability to recognize a common pool of epitopes bearing structural similarities across afflicted sites.

SUMMARY

Understanding the complex mechanisms that underpin mucosal immune responses between the liver and gut will help identify new druggable targets in PSC, centring on gut microbial manipulation, bile acid therapies, and restoration of immune homeostasis.

Macrophages in cholangiopathies

PURPOSE OF REVIEW

Cholangiopathies are a heterogeneous class of liver diseases where cholangiocytes are the main targets of liver injury. Although available and emerging therapies mainly target bile acids (ursodeoxycholic acid/UDCA, 24-Norursodeoxycholic acid/norUDCA) and related signaling pathways (obeticholic acid, fibrates, FXR, and PPAR agonists), the mechanisms underlying inflammation, ductular reaction and fibrosis in cholestatic liver diseases remain poorly understood.

RECENT FINDINGS

Data from patients with cholestatic diseases, such as primary biliary cholangitis (PBC) or primary sclerosing cholangitis (PSC) as well as mouse models of biliary injury emphasize the role of immune cells in the pathogenesis of cholestatic disorders and indicate diverse functions of hepatic macrophages. Their versatile polarization phenotypes and their capacity to interact with other cell types (e.g. cholangiocytes, other immune cells) make macrophages central actors in the progression of cholangiopathies.

SUMMARY

In this review, we summarize recent findings on the response of hepatic macrophages to cholestasis and biliary injury and their involvement in the progression of cholangiopathies. Furthermore, we discuss how recent discoveries may foster the development of innovative therapies to treat patients suffering from cholestatic liver diseases, in particular, treatments targeting macrophages to limit hepatic inflammation.

Role of the IgG4-related cholangitis autoantigen annexin A11 in cholangiocyte protection

BACKGROUND & AIMS

Annexin A11 was identified as autoantigen in IgG4-related cholangitis (IRC), a B-cell driven disease. Annexin A11 modulates calcium-dependent exocytosis, a crucial mechanism for insertion of proteins into their target membranes. Human cholangiocytes form an apical 'biliary bicarbonate umbrella' regarded as defense against harmful hydrophobic bile acid influx. The bicarbonate secretory machinery comprises the chloride/bicarbonate exchanger AE2 and the chloride channel ANO1. We aimed to investigate the expression and function of annexin A11 in human cholangiocytes and a potential role of IgG1/IgG4-mediated autoreactivity against annexin A11 in the pathogenesis of IRC.

METHODS

Expression of annexin A11 in human liver was studied by immunohistochemistry and immunofluorescence. In human control and ANXA11 knockdown H69 cholangiocytes, intracellular pH, AE2 and ANO1 surface expression, and bile acid influx were examined using ratio microspectrofluorometry, cell surface biotinylation, and 22,23-3H-glycochenodeoxycholic acid permeation, respectively. The localization of annexin A11-mEmerald and ANO1-mCherry was investigated by live-cell microscopy in H69 cholangiocytes after incubation with IRC patient serum containing anti-annexin A11 IgG1/IgG4-autoantibodies or disease control serum.

RESULTS

Annexin A11 was strongly expressed in human cholangiocytes, but not hepatocytes. Knockdown of ANXA11 led to reduced plasma membrane expression of ANO1, but not AE2, alkalization of intracellular pH and uncontrolled bile acid influx. High intracellular calcium conditions led to annexin A11 membrane shift and colocalization with ANO1. Incubation with IRC patient serum inhibited annexin A11 membrane shift and reduced ANO1 surface expression.

CONCLUSION

Cholangiocellular annexin A11 mediates apical membrane abundance of the chloride channel ANO1, thereby supporting biliary bicarbonate secretion. Insertion is inhibited by IRC patient serum containing anti-annexin A11 IgG1/IgG4-autoantibodies. Anti-annexin A11 autoantibodies may contribute to the pathogenesis of IRC by weakening the 'biliary bicarbonate umbrella'.

LAY SUMMARY

We previously identified annexin A11 as a specific autoantigen in immunoglobulin G4-related cholangitis (IRC), a B-cell driven disease affecting the bile ducts. Human cholangiocytes are protected against harmful hydrophobic bile acid influx by a defense mechanism referred to as the 'biliary bicarbonate umbrella'. We found that annexin A11 is required for the formation of a robust bicarbonate umbrella. Binding of patient-derived annexin A11 autoantibodies inhibits annexin A11 function, possibly contributing to bile duct damage by weakening the biliary bicarbonate umbrella in patients with IRC.

An Update on Novel Pharmacological Agents for Primary Sclerosing Cholangitis

INTRODUCTION

: Primary sclerosing cholangitis (PSC) is a rare chronic cholestatic liver disease with heterogeneous phenotypes that may lead to liver transplantation and/or end-stage liver disease. Its multifactorial etiopathogenesis remains uncertain, but gut-liver axis and bile composition and excretion are widely demonstrated to influence the immune-mediated fibrogenic reactive cascade.

AREAS COVERED

: Different experimental therapeutic options are under investigation, mainly aiming at modulating bile acids excretion, limiting inflammatory-cascade reactions, and changing intestinal microbiota composition; none of them yet demonstrated to prolong transplant free survival.

This review provides a comprehensive description of the experimental drugs recently tested and/or currently under investigation. A bibliographical search was performed in Pubmed, MEDLINE, EMBASE, OVID and clinicaltrial.gov until July 2021.

EXPERT OPINION

: The heterogeneity and poor prevalence of PSC, its uncertain pathophysiology, and the lack of surrogate endpoints are the major challenges in drug discovery. Strategies that synergistically target microbiota, bile acids, and liver fibrosis are needed. In parallel, we must enhance biomarker discovery to develop surrogate endpoints, as biochemical markers' fluctuations over the time hamper their effectiveness. Magnetic resonance cholangiopancreatography tools that accurately measure bile duct changes represent a potential, novel marker for disease monitoring. A collaboration between academia, research consortia, patient's associations and industry is required.

Novel therapeutic targets for cholestatic and fatty liver disease

Cholestatic and non-alcoholic fatty liver disease (NAFLD) share several key pathophysiological mechanisms which can be targeted by novel therapeutic concepts that are currently developed for both areas. Nuclear receptors (NRs) are ligand-activated transcriptional regulators of key metabolic processes including hepatic lipid and glucose metabolism, energy expenditure and bile acid (BA) homoeostasis, as well as inflammation, fibrosis and cellular proliferation. Dysregulation of these processes contributes to the pathogenesis and progression of cholestatic as well as fatty liver disease, placing NRs at the forefront of novel therapeutic approaches. This includes BA and fatty acid activated NRs such as farnesoid-X receptor (FXR) and peroxisome proliferator-activated receptors, respectively, for which high affinity therapeutic ligands targeting specific or multiple isoforms have been developed. Moreover, novel liver-specific ligands for thyroid hormone receptor beta 1 complete the spectrum of currently available NR-targeted drugs. Apart from FXR ligands, BA signalling can be targeted by mimetics of FXR-activated fibroblast growth factor 19, modulation of their enterohepatic circulation through uptake inhibitors in hepatocytes and enterocytes, as well as novel BA derivatives undergoing cholehepatic shunting (instead of enterohepatic circulation). Other therapeutic approaches more directly target inflammation and/or fibrosis as critical events of disease progression. Combination strategies synergistically targeting metabolic disturbances, inflammation and fibrosis may be ultimately necessary for successful treatment of these complex and multifactorial disorders.

Bryodulcosigenin a natural cucurbitane-type triterpenoid attenuates dextran sulfate sodium (DSS)-induced colitis in mice

BACKGROUND

Bryodulcosigenin (BDG) a cucurbitane-type triterpenoid has been isolated from the roots of Bryonia dioca and possesses marked anti-inflammatory effects, although its beneficial effect against intestinal disorders remains unclear.

PURPOSE

To explore the underlying mechanism of BDG on the dysbiosis of chronic ulcerative colitis (UC) and its associated side-effects on lung tissues.

METHODS

A chronic UC model was established using 2.5% dextran sulfate sodium (DSS) in mice treated for 64 days and diagnostic assessments, western blot analysis and quantitative real time-PCR were employed to determine the protective mechanism of BDG.

RESULTS

Oral administration of BDG (10 mg/kg/day) significantly improved colon length, disease activity index, and alleviated colonic histopathological damage in the DSS-induced colitis  mice. BDG not only reversed the TNF-α-induced degradation of tight junction proteins (occludin and ZO-1) but also suppressed the elevated apoptosis seen in intestinal epithelial cells (NCM460). In addition, BDG significantly attenuated damage in alveolar epithelial cells (MLE-12) co-cultured with NCM460 cells under inflammatory conditions. Furthermore, BDG in vivo significantly prevented the symptoms of respiratory disorders and repressed alveolar inflammation by regulating DSS-induced chronic colitis in mice.

CONCLUSION

BDG effectively inhibited the apoptosis of intestinal epithelial cells and suppressed the activation of the NLRP3 inflammasome which resulted in the restoration of the intestinal barrier. Therefore, the enhanced integrity of intestinal epithelial cells produced by BDG intervention contributed to its anti-colitis effects, indicating its great potential as an inhibitor of UC and lung injury. Therefore, restoring intestinal integrity may represent a promising strategy in the prevention of pulmonary disease.

Molecular and Cellular Mediators of the Gut-Liver Axis in the Progression of Liver Diseases

The gut-liver axis covers the bidirectional communication between the gut and the liver, and thus includes signals from liver-to-gut (e.g., bile acids, immunoglobulins) and from gut-to-liver (e.g., nutrients, microbiota-derived products, and recirculating bile acids). In a healthy individual, liver homeostasis is tightly controlled by the mostly tolerogenic liver resident macrophages, the Kupffer cells, capturing the gut-derived antigens from the blood circulation. However, disturbances of the gut-liver axis have been associated to the progression of varying chronic liver diseases, such as non-alcoholic fatty liver disease, non-alcoholic steatohepatitis, and primary sclerosing cholangitis. Notably, changes of the gut microbiome, or intestinal dysbiosis, combined with increased intestinal permeability, leads to the translocation of gut-derived bacteria or their metabolites into the portal vein. In the context of concomitant or subsequent liver inflammation, the liver is then infiltrated by responsive immune cells (e.g., monocytes, neutrophils, lymphoid, or dendritic cells), and microbiota-derived products may provoke or exacerbate innate immune responses, hence perpetuating liver inflammation and fibrosis, and potentiating the risks of developing cirrhosis. Similarly, food derived antigens, bile acids, danger-, and pathogen-associated molecular patterns are able to reshape the liver immune microenvironment. Immune cell intracellular signaling components, such as inflammasome activation, toll-like receptor or nucleotide-binding oligomerization domain-like receptors signaling, are potent targets of interest for the modulation of the immune response. This review describes the current understanding of the cellular landscape and molecular pathways involved in the gut-liver axis and implicated in chronic liver disease progression. We also provide an overview of innovative therapeutic approaches and current clinical trials aiming at targeting the gut-liver axis for the treatment of patients with chronic liver and/or intestinal diseases.

The many facets of bile acids in the physiology and pathophysiology of the human liver

Bile acids perform vital functions in the human liver and are the essential component of bile. It is therefore not surprising that the biology of bile acids is extremely complex, regulated on different levels, and involves soluble and membrane receptors as well as transporters. Hereditary disorders of these proteins manifest in different pathophysiological processes that result in liver diseases of varying severity. In this review, we summarize our current knowledge of the physiology and pathophysiology of bile acids with an emphasis on recently established analytical approaches as well as the molecular mechanisms that underlie signaling and transport of bile acids. In this review, we will focus on ABC transporters of the canalicular membrane and their associated diseases. As the G protein-coupled receptor, TGR5, receives increasing attention, we have included aspects of this receptor and its interaction with bile acids.