R-spondin2 activates hepatic stellate cells and promotes liver fibrosis

The biological functions and related signaling pathways of SPON2

Spondin-2 (SPON2), also referred to as M-spondin or DIL-1, is a member of the extracellular matrix protein family known as Mindin-F-spondin (FS). SPON2 can be used as a broad-spectrum tumor marker for more than a dozen tumors, mainly prostate cancer. Meanwhile, SPON2 is also a potential biomarker for the diagnosis of certain non-tumor diseases. Additionally, SPON2 plays a pivotal role in regulating tumor metastasis and progression. In normal tissues, SPON2 has a variety of biological functions represented by promoting growth and development and cell proliferation. This paper presents a comprehensive overview of the regulatory mechanisms, diagnostic potential as a broad-spectrum biomarker, diverse biological functions, involvement in various signaling pathways, and clinical applications of SPON2.

The RSPO-LGR4/5-ZNRF3/RNF43 module in liver homeostasis, regeneration, and disease

WNT/β-catenin signaling plays pivotal roles during liver development, homeostasis, and regeneration. Likewise, its deregulation disturbs metabolic liver zonation and is responsible for the development of a large number of hepatic tumors. Liver fibrosis, which has become a major health burden for society and a hallmark of NASH, can also be promoted by WNT/β-catenin signaling. Upstream regulatory mechanisms controlling hepatic WNT/β-catenin activity may constitute targets for the development of novel therapies addressing these life-threatening conditions. The R-spondin (RSPO)-leucine-rich repeat-containing G protein-coupled receptor (LGR) 4/5-zinc and ring finger (ZNRF) 3/ring finger 43 (RNF43) module is fine-tuning WNT/β-catenin signaling in several tissues and is essential for hepatic WNT/β-catenin activity. In this review article, we recapitulate the role of the RSPO-LGR4/5-ZNRF3/RNF43 module during liver development, homeostasis, metabolic zonation, regeneration, and disease. We further discuss the controversy around LGR5 as a liver stem cell marker.

The role of roof plate-specific spondins in liver homeostasis and disease

As evolutionarily conserved signals, roof plate-specific spondins (R-spondins; RSPOs) are a family with four members (RSPO1-4) exerting distinctly different functions. RSPOs have five receptors and correlate with different signaling pathways through these receptors and then perform various functions. Moreover, their best-known molecular function is the capacity to enhance WNT signaling pathways, which play critical roles in several processes. A recent study shows that RSPOs not only potentiate the WNT/beta (β)-catenin signaling pathway but are also involved in the WNT/planar cell polarity signaling pathway. RSPOs influence liver homeostasis and the development of multiple liver diseases. RSPO1 increases cell proliferation, protects hepatocytes from injury, improves liver regenerative potential, and affects liver metabolic zonation. RSPO2 not only regulates proliferation-associated genes and promotes differentiation in the liver but also participates in liver fibrosis through the WNT/β-catenin signaling pathway. RSPO3 is a key determinant of proper liver function, such as promoting hepatocyte regeneration and maintaining liver zonation. RSPO3 is upregulated in liver fibrosis and livers of patients with non-alcoholic steatohepatitis. Besides, RSPO2 and RSPO3 are confirmed as oncogenes and involved in the occurrence of liver cancer. The role of RSPO4 in the liver remains unclear. In this review, the structural and biochemical properties of RSPOs and their receptors and their roles in liver homeostasis and disease are summarized.

Targeting the Wnt Signaling Pathway in Liver Fibrosis for Drug Options: An Update

Liver fibrosis is a life-threatening disease, with challenging morbidity and mortality for healthcare systems worldwide. It imparts an enormous economic burden to societies, making continuous research and informational updates about its pathogenesis and treatment crucial. This review's focus is on the current knowledge about the Wnt signaling pathway, serving as an important pathway in liver fibrosis development and activation of hepatic stellate cells (HSCs). Two types of Wnt pathways are distinguished, namely the ß-catenin-dependent canonical and non-canonical Ca2+ or planar cell polarity (PCP)-dependent pathway. The dynamic balance of physiologically healthy liver and hepatocytes is disturbed by repeated liver injuries. Activation of the ß-catenin Wnt pathway prevents the regeneration of hepatocytes by the replacement of extracellular matrix (ECM), leading to the appearance of scar tissue and the formation of regenerated nodular hepatocytes, lacking the original function of healthy hepatocytes. Therefore, liver function is reduced due to the severely advanced disease. Selective inhibition of ß-catenin inhibits inflammatory processes (since chemokines and pro-inflammatory cytokines are produced during Wnt activation), reduces growth of activated HSCs and reduces collagen synthesis and angiogenesis, thereby reducing the progression of liver fibrosis in vivo. While the canonical Wnt pathway is usually inactive in a physiologically healthy liver, it shows activity during cell regeneration or renewal and in certain pathophysiological conditions, such as liver diseases and cancer. Targeted blocking of some of the basic components of the Wnt pathway is a therapeutic approach. These include the frizzled transmembrane receptor (Fz) receptors using the secreted frizzled-related protein family (sFRP), Fz-coreceptors low-density LRP 5/6 through dickkopf-related protein 1 (DKK1) or niclosamide, glycogen kinase-3 beta (GSK-3β) using SB-216763, cyclic-AMP response element-binding protein (CBP) using PRI-724 and ICG-001, the lymphoid enhancer binding factor (LEF)/T cell-specific transcription factor (TCF) system as well as Wnt inhibitory factor 1 (WIF1) and miR-17-5p using pinostilbene hydrate (PSH). Significant progress has been made in inhibiting Wnt and thus stopping the progression of liver fibrosis by diminishing key components for its action. Comprehending the role of the Wnt signaling pathway in liver fibrosis may lead to discovery of novel targets in liver fibrosis therapeutic strategies' development.

Beneficial effects of LRP6-CRISPR on prevention of alcohol-related liver injury surpassed fecal microbiota transplant in a rat model

Alcohol intake can modify gut microbiota composition, increase gut permeability, and promote liver fibrogenesis. LRP6 is a signal transmembrane protein and a co-receptor for the canonical Wnt signaling pathway. This study compared the curative effect of LRP6-CRISPR on alcohol-related liver injury with that of traditional fecal microbiota transplant (FMT) and investigated the alteration of the gut microbiome following the treatment. A rat model of alcohol-related liver injury was established and injected with lentiviral vectors expressing LRP6-CRISPR or administered with fecal filtrate from healthy rats, with healthy rat served as the control. Liver tissues of rats were examined by HE staining, Sirius staining, and Oil red O staining, respectively. The expression of LRP6 and fibrosis biomarkers were tested by PCR. The fecal sample of rats was collected and examined by 16S rRNA sequencing. Our data indicated that LRP6-CRISPR was more efficient in the prevention of alcohol-related liver injury than FMT. Microbiome analysis showed that alcohol-related liver injury related to gut microbiota dysbiosis, while treatment with LRP6-CRISPR or FMT increased gut microflora diversity and improved gut symbiosis. Further, bacteria specific to the disease stages were identified. Genera Romboutsia, Escherichia-Shigella, Pseudomonas, Turicibacter, and Helicobacter were prevalent in the intestine of rats with alcohol-related liver injury, while the domination of Lactobacillus was found in rats treated with LRP6-CRISPR or FMT. Besides, Lactobacillus and genera belonging to family Lachnospiraceae, Bacteroidales S24-7 group, and Ruminococcaceae were enriched in healthy rats. LRP6-CRISPR and FMT have beneficial effects on the prevention of alcohol-related liver injury, and correspondently, both treatments altered the disrupted gut microflora to a healthy one.

Targeting the Wnt signaling pathway through R-spondin 3 identifies an anti-fibrosis treatment strategy for multiple organs

The Wnt/β-catenin signaling pathway has been implicated in human proliferative diseases such as cancer and fibrosis. The functions of β-catenin and several other components of this pathway have been investigated in fibrosis. However, the potential role of R-spondin proteins (RSPOs), enhancers of the Wnt/β-catenin signaling, has not been described. A specific interventional strategy targeting this pathway for fibrosis remains to be defined. We developed monoclonal antibodies against members of the RSPO family (RSPO1, 2, and 3) and probed their potential function in fibrosis in vivo. We demonstrated that RSPO3 plays a critical role in the development of fibrosis in multiple organs. Specifically, an anti-RSPO3 antibody, OMP-131R10, when dosed therapeutically, attenuated fibrosis in carbon tetrachloride (CCl₄)-induced liver fibrosis, bleomycin-induced pulmonary and skin fibrosis models. Mechanistically, we showed that RSPO3 induces multiple pro-fibrotic chemokines and cytokines in Kupffer cells and hepatocytes. We found that the anti-fibrotic activity of OMP-131R10 is associated with its inhibition of β-catenin activation in vivo. Finally, RSPO3 was found to be highly elevated in the active lesions of fibrotic tissues in mouse models of fibrosis and in patients with idiopathic pulmonary fibrosis (IPF) and nonalcoholic steatohepatitis (NASH). Together these data provide an anti-fibrotic strategy for targeting the Wnt/β-catenin pathway through RSPO3 blockade and support that OMP-131R10 could be an important therapeutic agent for fibrosis.

Insulin-Like Growth Factor Binding Protein-Related Protein 1 Activates Primary Hepatic Stellate Cells via Autophagy Regulated by the PI3K/Akt/mTOR Signaling Pathway

BACKGROUND

Autophagy is a self-degrading process. Previously, we showed that insulin-like growth factor binding protein-related protein 1 (IGFBPrP1) is a novel transforming growth factor β1 (TGFβ1)-interacting factor in liver fibrosis; the role of TGFβ1-mediated autophagy in hepatic stellate cells (HSCs) activation has been investigated. However, whether autophagy is regulated by IGFBPrP1 remains unknown.

AIMS

We investigated the interactions among IGFBPrP1, autophagy, and activation of primary rat HSCs.

METHODS

Primary HSCs were separated from Sprague Dawley rats by two-step enzymatic digestion, and then, we overexpressed or inhibited IGFBPrP1 expression in HSCs under serum-starved condition. Autophagy inducer rapamycin or inhibitor 3-methyladenine (3MA) was used to assess the relationship between autophagy and HSCs activation.

RESULTS

We observed the expression of activation marker α-SMA and autophagy markers such as LC3B and Beclin1, which were significantly increased in HSCs treated with adenovirus vector harboring the IGFBPrP1 gene (AdIGFBPrP1) compared to cells cultured under serum-starved. In comparison, HSCs treated with shIGFBPrP1 showed opposite results. Furthermore, HSCs activation and autophagy increased when cells were treated with rapamycin, whereas opposite results were obtained when cells were treated with 3MA. AdIGFBPrP1 treatment downregulated the phosphorylation of Akt and mTOR.

CONCLUSION

Autophagy was induced in IGFBPrP1-treated primary HSCs, and IGFBPrP1-induced autophagy promoted the activation of HSCs and extracellular matrix expression, the underlying mechanism of which may involve the phosphatidylinositide 3-kinase/Akt/mTOR signaling pathway.

Elimination of Wnt Secretion From Stellate Cells Is Dispensable for Zonation and Development of Liver Fibrosis Following Hepatobiliary Injury

Alterations in the Wnt signaling pathway including those impacting hepatic stellate cells (HSCs) have been implicated in liver fibrosis. In the current study, we first examined the expression of Wnt genes in human HSC (HHSCs) after treatment with a profibrogenic factor TGF-β1. Next, we generated HSC-specific Wntless (Wls) knockout (KO) using the Lrat-cre and Wls-floxed mice. KO and littermate controls (CON) were characterized for any basal phenotype and subjected to two liver fibrosis protocols. In vitro, TGF-β1 induced expression of Wnt2, 5a and 9a while decreasing Wnt2b, 3a, 4, and 11 in HHSC. In vivo, KO and CON mice were born at normal Mendelian ratio and lacked any overt phenotype. Loss of Wnt secretion from HSCs had no effect on liver weight and did not impact β-catenin activation in the pericentral hepatocytes. After 7 days of bile duct ligation (BDL), KO and CON showed comparable levels of serum alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, total and direct bilirubin. Comparable histology, Sirius red staining, and immunohistochemistry for α-SMA, desmin, Ki-67, F4/80, and CD45 indicated similar proliferation, inflammation, and portal fibrosis in both groups. Biweekly administration of carbon tetrachloride for 4 or 8 weeks also led to comparable serum biochemistry, inflammation, and fibrosis in KO and CON. Specific Wnt genes were altered in HHSCs in response to TGF-β1; however, eliminating Wnt secretion from HSC did not impact basal β-catenin activation in normal liver nor did it alter the injury-repair response during development of liver fibrosis.

R-Spondin-2 Is Upregulated in Idiopathic Pulmonary Fibrosis and Affects Fibroblast Behavior

Idiopathic pulmonary fibrosis (IPF) is characterized by the expansion of the myofibroblast population, excessive extracellular matrix accumulation, and destruction of the lung parenchyma. The R-spondin family (RSPO) comprises a group of proteins essential for development. Among them, RSPO2 is expressed primarily in the lungs, and its mutations cause severe defects in the respiratory tract. Interestingly, RSPO2 participates in the canonical Wingless/int1 pathway, a critical route in the pathogenesis of IPF. Thus, the aim of this study was to examine the expression and putative role of RSPO2 in this disease. We found that RSPO2 and its receptor leucine-rich G protein-coupled receptor 6 were upregulated in IPF lungs, where they localized primarily in fibroblasts and epithelial cells. Stimulation of IPF and normal lung fibroblasts with recombinant human RSPO2 resulted in the deregulation of numerous genes, although the transcriptional response was essentially distinct. In IPF fibroblasts, RSPO2 stimulation induced the up- or downregulation of several genes involved in the Wingless/int1 pathway (mainly from noncanonical signaling). In both normal and IPF fibroblasts, RSPO2 modifies the expression of genes implicated in several pathways, including the cell cycle and apoptosis. In accordance with gene expression, the stimulation of normal and IPF fibroblasts with RSPO2 significantly reduced cell proliferation and induced cell death. RSPO2 also inhibited collagen production and increased the expression of matrix metalloproteinase 1. Silencing RSPO2 with shRNA induced the opposite effects. Our findings demonstrate, for the first time to our knowledge, that RSPO2 is upregulated in IPF, where it appears to have an antifibrotic role.

Emerging role and therapeutic implication of Wnt signaling pathways in liver fibrosis

Activation of hepatic stellate cells (HSCs) is a pivotal cellular event in liver fibrosis. Therefore, improving our understanding of the molecular pathways that are involved in these processes is essential to generate new therapies for liver fibrosis. Greater knowledge of the role of the Wnt signaling pathway in liver fibrosis could improve understanding of the liver fibrosis pathogenesis. The aim of this review is to describe the present knowledge about the Wnt signaling pathway, which significantly participates in liver fibrosis and HSC activation, and look ahead on new perspectives of Wnt signaling pathway research. Moreover, we will discuss the different interactions with Wnt signaling pathway-regulated liver fibrosis. The Wnt signaling pathway modulates several important aspects of function, including cell proliferation, activation and differentiation. Targeting the Wnt signaling pathway can be a promising direction in liver fibrosis treatment. We discuss new perspectives of Wnt signaling pathway activation in liver fibrosis. For example, antagonist to Wnt and Wnt ligands could inhibit liver fibrosis by regulating Wnt/β-catenin signaling pathway. These findings identify the Wnt signaling pathway as a potentially important for therapeutic targets in liver fibrosis. Future studies are needed in order to find safer and more effective Wnt-based drugs.

R-spondin 2 promotes proliferation and migration via the Wnt/β-catenin pathway in human hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a leading cause of malignant disease-associated mortality, particularly in China. The RSPO2 (R-spondin 2) gene is evolutionarily conserved in vertebrates and is involved in developmental and physiological processes. Importantly, RSPO2 has been reported to be associated with colon cancer and potentiate the Wnt/β-catenin signaling pathway. In the present study, enhanced expression of RSPO2 in HCC was observed using tissue microarray. Similarly, the expression level of RSPO2 was higher in HepG2, Huh7 and Hep3B cells but lower in Bel7404 and QGY7703 cells compared with human normal QSG7701 liver cells. Subsequently, gain-of-function studies indicated that RSPO2 promotes the proliferation and migration of QGY7703 cells based on lentivirus-based gene delivery. Furthermore, it was revealed that p21 and leptin, rather than vascular endothelial growth factor-A, are involved in the function of RSPO2 in QGY7703 cells. Particularly, the signal transducer and activator of transcription 3 (STAT3) and Wnt/β-catenin signaling pathways are involved in this process. Overexpression of RSPO2 resulted in the elevated expression of phosphorylated STAT3, β-catenin and c-Myc. Therefore, the present study is beneficial to the understanding of RSPO2-involved liver cancer transformation and drug discovery.

Immunohistochemical Analysis of the Stem Cell Marker LGR5 in Pediatric Liver Disease

Aims In regenerating liver, hepatic progenitor cells (HPCs) are recruited in response to injury; however, few highly specific human HPC markers exist for the hepatocyte lineage. Leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5), a Wnt-associated stem cell marker, has been extensively studied in intestinal stem cells, but little is known about its expression in human liver. We hypothesized that LGR5+ HPCs are induced in the regenerative response to pediatric liver injury. Methods and results Immunohistochemistry was used to characterize LGR5 expression in pediatric liver explants (n = 36). We found cytoplasmic LGR5 expression in all cases; although, much less was observed in acute hepatic necrosis compared to chronic liver diseases. In the latter cases, >50% of hepatocytes were LGR5+, signifying a robust regenerative response mainly in the periphery of regenerative nodules. Only weak LGR5 staining was noted in bile ducts, suggesting hepatocyte-specific expression at the interface. Conclusions Although we observed some degree of regenerative response in all cases, LGR5 was highly expressed in chronic liver disease, possibly due to alternate regeneration and reprogramming pathways. LGR5 is predominant in peri-septal hepatocytes rather than epithelial cell adhesion molecule (EpCAM) positive ductular reactions in chronic pediatric liver diseases and may represent a transitional HPC phenotype for the hepatocyte lineage. These studies are the first to support a unique role for LGR5 in human hepatocyte regeneration and as a potential predictive biomarker for recovery of liver function in children. Future work will also investigate the molecular mechanisms behind LGR5 expression.

Effect of Yinshao powder on expression of transforming growth factor-β1 and β-catenin in hepatic fibrosis in rats

AIM: To investigate the effect of traditional Chinese medicine Yinshao powder on the expression of transforming growth factor-β1 (TGF-β1) and β-catenin in hepatic fibrosis in rats to clarify the molecular mechanism of clearing heat, expelling damp and promoting blood circulation.

METHODS: Sixty adult male Wistar rats were divided randomly into six groups: a normal control group, a model group, low-, medium- and high-dose Yinshao powder groups and a colchicine group. Hepatic fibrosis was induced by giving subcutaneous injection of carbon tetrachloride, a high-fat diet and 30 mL/L alcohol for 16 wk. At the fifth week, Yinshao powder or colchicine was intragastrically administered. After 12 wk of treatment, the rats were sacrificed to measure serum levels of hyaluronidase (HA), type Ⅳ collagen, procollagen type Ⅲ (PCⅢ), and laminin (LN), observe hepatic pathological changes by HE staining and Masson staining, and determine the mRNA and protein expression levels of TGF-β1 and β-catenin by RT-PCR and Western blot.

RESULTS: Compared with the colchicine group and model group, serum levels of HA, type Ⅳ collagen, PCⅢ, and LN declined significantly in the other groups. The degree of hepatic fibrosis in the Yinshao powder groups was less than that in the colchicine group and model group. The mRNA and protein expression levels of TGF-β1 and β-catenin were significantly lower in the Yinshao powder groups than in the model group and colchicine group.

CONCLUSION: Clearing heat, expelling damp and promoting blood circulation with Yinshao powder for intervention of hepatic fibrosis may be via molecular mechanisms associated with inhibiting or down-regulating the expression of TGF-β1 and β-catenin and blocking the activation of TGF-β1 signaling pathway and Wnt/β-catenin signaling pathway.