Smad phosphoisoform signals in acute and chronic liver injury: similarities and differences between epithelial and mesenchymal cells

Response to retention hypothesis as a source of targets for arterial wall-directed therapies to prevent atherosclerosis: A critical review

The subendothelial retention of circulating lipoproteins on extracellular matrix proteins and proteoglycans is one of the earliest events in the development of atherosclerosis. Multiple factors, including the size, type, composition, surrounding pH, and chemical modifications to lipoproteins, influence the electrostatic interactions between relevant moieties of the apolipoproteins on lipoproteins and the glycosaminoglycans of proteoglycans. The length and chemical composition of glycosaminoglycan chains attached to proteoglycan core proteins determine the extent of initial lipoprotein binding and retention in the artery wall. The phenomena of hyperelongation of glycosaminoglycan chains is associated with initial lipid retention and later atherosclerotic plaque formation. This review includes a summary of the current literature surrounding cellular mechanisms leading to GAG chain modification and lipid retention and discusses potential therapeutic strategies to target lipoprotein:proteoglycan interactions to prevent the development and progression of atherosclerosis.

Hepatitis B virus X protein and TGF-β: partners in the carcinogenic journey of hepatocellular carcinoma

Hepatitis B infection is substantially associated with the development of liver cancer globally, with the prevalence of hepatocellular carcinoma (HCC) cases exceeding 50%. Hepatitis B virus (HBV) encodes the Hepatitis B virus X (HBx) protein, a pleiotropic regulatory protein necessary for the transcription of the HBV covalently closed circular DNA (cccDNA) microchromosome. In previous studies, HBV-associated HCC was revealed to be affected by HBx in multiple signaling pathways, resulting in genetic mutations and epigenetic modifications in proto-oncogenes and tumor suppressor genes. In addition, transforming growth factor-β (TGF-β) has dichotomous potentials at various phases of malignancy as it is a crucial signaling pathway that regulates multiple cellular and physiological processes. In early HCC, TGF-β has a significant antitumor effect, whereas in advanced HCC, it promotes malignant progression. TGF-β interacts with the HBx protein in HCC, regulating the pathogenesis of HCC. This review summarizes the respective and combined functions of HBx and TGB-β in HCC occurrence and development.

TGF-β downstream of Smad3 and MAPK signaling antagonistically regulate the viability and partial epithelial-mesenchymal transition of liver progenitor cells

BACKGROUND

Liver progenitor cells (LPCs) are a subpopulation of cells that contribute to liver regeneration, fibrosis and liver cancer initiation under different circumstances.

RESULTS

By performing adenoviral-mediated transfection, CCK-8 analyses, F-actin staining, transwell analyses, luciferase reporter analyses and Western blotting, we observed that TGF-β promoted cytostasis and partial epithelial-mesenchymal transition (EMT) in LPCs. In addition, we confirmed that TGF-β activated the Smad and MAPK pathways, including the Erk, JNK and p38 MAPK signaling pathways, and revealed that TGFβ-Smad signaling induced growth inhibition and partial EMT, whereas TGFβ-MAPK signaling had the opposite effects on LPCs. We further found that the activity of Smad and MAPK signaling downstream of TGF-β was mutually restricted in LPCs. Mechanistically, we found that TGF-β activated Smad signaling through serine phosphorylation of both the C-terminal and linker regions of Smad2 and 3 in LPCs. Additionally, TGFβ-MAPK signaling inhibited the phosphorylation of Smad3 but not Smad2 at the C-terminus, and it reinforced the linker phosphorylation of Smad3 at T179 and S213. We then found that overexpression of mutated Smad3 at linker phosphorylation sites intensifies TGF-β-induced cytostasis and EMT, mimicking the effects of MAPK inhibition in LPCs, whereas mutation of Smad3 at the C-terminus caused LPCs to blunt TGF-β-induced cytostasis and partial EMT.

CONCLUSION

These results suggested that TGF-β downstream of Smad3 and MAPK signaling were mutually antagonistic in regulating the viability and partial EMT of LPCs. This antagonism may help LPCs overcome the cytostatic effect of TGF-β under fibrotic conditions and maintain partial EMT and progenitor phenotypes.

Prognostic significance and relationship of SMAD3 phospho-isoforms and VEGFR-1 in gastric cancer: A clinicopathological study

BACKGROUND

The TGF-β/SMAD3 and VEGFR-1 signaling pathways play important roles in gastric cancer metastasis. SMAD3 phosphorylation is a crucial prognostic marker in gastric cancer.

AIM

To determine the prognostic value and relationship of SMAD3 phospho-isoforms and VEGFR-1 in gastric cancer.

METHODS

This was a single-center observational study which enrolled 98 gastric cancer patients and 82 adjacent normal gastric tissues from patients aged 32-84 years (median age 65) between July 2006 and April 2007. Patients were followed up until death or the study ended (median follow-up duration of 28.5 mo). The samples were used to generate tissue microarrays (TMAs) for immunohistochemical (IHC) staining. The expressions of TGF-β1, pSMAD3C(S423/425), pSMAD3L(S204), and VEGFR-1 in gastric cancer (GC) tumor tissue and normal tissue were measured by IHC staining using TMAs obtained from 98 GC patients. Prognosis and survival information of the patients was recorded by Outdo Biotech from May 2007 to July 2015. The relationship between TGF-β1, pSMAD3C(S423/425), pSMAD3L(S204), and VEGFR-1 protein expression levels was analyzed using Pearson's correlation coefficient. The relationship between protein expression levels and clinicopathological parameters was analyzed using the Chi-squared test. A survival curve was generated using the Kaplan-Meier survival analysis.

RESULTS

TGFβ-1 and VEGFR-1 expression was significantly upregulated in gastric cancer tissue compared to adjacent non-cancerous tissue. The positive expression of phosphorylated isoforms of Smad3 varied depending on the phosphorylation site [pSMAD3C(S423/425): 51.0% and pSMAD3L(S204): 31.6%]. High expression of pSMAD3L(S204) was significantly correlated with larger tumors (P = 0.038) and later N stages (P = 0.035). Additionally, high expression of VEGFR-1 was closely correlated with tumor size (P = 0.015) and pathological grading (P = 0.013). High expression of both pSMAD3L(S204) and VEGFR-1 was associated with unfavorable outcomes in terms of overall survival (OS). Multivariate analysis indicated that high expression of pSMAD3L(S204) and VEGFR-1 were independent risk factors for prognosis in GC patients. VEGFR-1 protein expression was correlated with TGF-β1 (r = 0.220, P = 0.029), pSMAD3C(S423/425) (r = 0.302, P = 0.002), and pSMAD3L(S204) (r = 0.201, P = 0.047), respectively. Simultaneous overexpression of pSMAD3L(S204) and VEGFR-1 was associated with poor OS in gastric cancer patients.

CONCLUSION

Co-upregulation of pSMAD3L(S204) and VEGFR-1 can serve as a predictive marker for poor gastric cancer prognosis, and pSMAD3L(204) may be involved in enhanced gastric cancer metastasis in a VEGFR-1-dependent manner.

Experimental Models for Studying Structural and Functional State of the Pathological Liver (Review)

Liver pathologies remain one of the leading causes of mortality worldwide. Despite a high prevalence of liver diseases, the possibilities of diagnosing, prognosing, and treating non-alcoholic and alcoholic liver diseases still have a number of limitations and require the development of new methods and approaches. In laboratory studies, various models are used to reconstitute the pathological conditions of the liver, including cell cultures, spheroids, organoids, microfluidic systems, tissue slices. We reviewed the most commonly used in vivo, in vitro, and ex vivo models for studying non-alcoholic fatty liver disease and alcoholic liver disease, toxic liver injury, and fibrosis, described their advantages, limitations, and prospects for use. Great emphasis was placed on the mechanisms of development of pathological conditions in each model, as well as the assessment of the possibility of reconstructing various key aspects of pathogenesis for all these pathologies. There is currently no consensus on the choice of the most adequate model for studying liver pathology. The choice of a certain effective research model is determined by the specific purpose and objectives of the experiment.

Cardiac Hepatopathy: New Perspectives on Old Problems through a Prism of Endogenous Metabolic Regulations by Hepatokines

Cardiac hepatopathy refers to acute or chronic liver damage caused by cardiac dysfunction in the absence of any other possible causative reasons of liver injury. There is a large number of evidence of the fact that cardiac hepatopathy is associated with poor clinical outcomes in patients with acute or actually decompensated heart failure (HF). However, the currently dominated pathophysiological background does not explain a role of metabolic regulative proteins secreted by hepatocytes in progression of HF, including adverse cardiac remodeling, kidney injury, skeletal muscle dysfunction, osteopenia, sarcopenia and cardiac cachexia. The aim of this narrative review was to accumulate knowledge of hepatokines (adropin; fetuin-A, selenoprotein P, fibroblast growth factor-21, and alpha-1-microglobulin) as adaptive regulators of metabolic homeostasis in patients with HF. It is suggested that hepatokines play a crucial, causative role in inter-organ interactions and mediate tissue protective effects counteracting oxidative stress, inflammation, mitochondrial dysfunction, apoptosis and necrosis. The discriminative potencies of hepatokines for HF and damage of target organs in patients with known HF is under on-going scientific discussion and requires more investigations in the future.

Roles of TGF-β in cancer hallmarks and emerging onco-therapeutic design

Transforming growth factor-beta (TGF-β) is a double-edged sword in cancer treatment because of its pivotal yet complex and roles played during cancer initiation/development. Current anti-cancer strategies involving TGF-β largely view TGF-β as an onco-therapeutic target that not only substantially hinders its full utilisation for cancer control, but also considerably restricts innovations in this field. Thereby, how to take advantages of therapeutically favourable properties of TGF-β for cancer management represents an interesting and less investigated problem. Here, by categorising cancer hallmarks into four critical transition events and one enabling characteristic controlling cancer initiation and progression, and delineating TGF-β complexities according to these cancer traits, we identify the suppressive role of TGF-β in tumour initiation and early-stage progression and its promotive functionalities in cancer metastasis as well as other cancer hallmarks. We also propose the feasibility and possible scenarios of combining cold atmospheric plasma (CAP) with onco-therapeutics utilising TGF-β for cancer control given the intrinsic properties of CAP against cancer hallmarks.

Free radicals, antioxidants, nuclear factor-E2-related factor-2 and liver damage

The liver performs various biochemical and molecular functions. Its location as a portal to blood arriving from the intestines makes it susceptible to several insults, leading to diverse pathologies, including alcoholic liver disease, viral infections, nonalcoholic steatohepatitis, and hepatocellular carcinoma, which are causes of death worldwide. Illuminating the molecular mechanism underlying hepatic injury will provide targets to develop new therapeutic strategies to fight liver maladies. In this regard, reactive oxygen species (ROS) are well-recognized mediators of liver damage. ROS induce nuclear factor-κB and the nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 inflammasome, which are the main proinflammatory signaling pathways that upregulate several proinflammatory and profibrogenic mediators. Additionally, oxygen-derived free radicals induce hepatic stellate cell activation to produce exacerbated quantities of extracellular matrix proteins, leading to fibrosis, cirrhosis and eventually hepatocellular carcinoma. Exogenous and endogenous antioxidants counteract the harmful effects of ROS, preventing liver necroinflammation and fibrogenesis. Therefore, several researchers have demonstrated that the administration of antioxidants, mainly derived from plants, affords beneficial effects on the liver. Notably, nuclear factor-E2-related factor-2 (Nrf2) is a major factor against oxidative stress in the liver. Increasing evidence has demonstrated that Nrf2 plays an important role in liver necroinflammation and fibrogenesis via the induction of antioxidant response element genes. The use of Nrf2 inducers seems to be an interesting approach to prevent/attenuate hepatic disorders, particularly under conditions where ROS play a causative role.

The upregulation of stromal antigen 3 expression suppresses the phenotypic hallmarks of hepatocellular carcinoma through the Smad3-CDK4/CDK6-cyclin D1 and CXCR4/RhoA pathways

Background

The stromal antigen 3 (STAG3) gene encodes an adhesion complex subunit that can regulate sister chromatid cohesion during cell division. Chromosome instability caused by STAG3 gene mutation may potentially promote tumor progression, but the effect of STAG3 on hepatocellular carcinoma (HCC) and the related molecular mechanism are not reported in the literature. The mechanism of the occurrence and development of HCC is not adequately understood. Therefore, the biological role of STAG3 in HCC remains to be studied, and whether STAG3 might be a sensitive therapeutic target in HCC remains to be determined.

Methods

The expression and clinical significance of STAG3 in HCC tissues and cell lines were determined by RT–qPCR and immunohistochemistry analyses. The biological functions of STAG3 in HCC were determined through in vitro and in vivo cell function tests. The molecular mechanism of STAG3 in HCC cells was then investigated by western blot assay.

Results

The mRNA expression of STAG3 was lower in most HCC cells than in normal cells. Subsequently, an immunohistochemical analysis of STAG3 was performed with 126 samples, and lower STAG3 expression was associated with worse overall survival in HCC patients. Moreover, cytofunctional tests revealed that the lentivirus-mediated overexpression of STAG3 in HCC cells inhibited cell proliferation, migration, and invasion; promoted apoptosis; induced G1/S phase arrest in vitro; and inhibited tumor growth in vivo. Furthermore, studies of the molecular mechanism suggested that the overexpression of STAG3 increased Smad3 expression and decreased CDK4, CDK6, cyclin D1, CXCR4 and RhoA expression.

Conclusion

STAG3 exhibits anticancer effects against HCC, and these effects involve the Smad3-CDK4/CDK6-cyclin D1 and CXCR4/RhoA pathways. STAG3 is a tumor-suppressor gene that may serve as a potential target for molecular therapy, which provides a new idea for the treatment of HCC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12876-022-02400-z.

Smad3 Phospho-Isoform Signaling in Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis with insulin resistance, oxidative stress, lipotoxicity, adipokine secretion by fat cells, endotoxins (lipopolysaccharides) released by gut microbiota, and endoplasmic reticulum stress. Together, these factors promote NAFLD progression from steatosis to nonalcoholic steatohepatitis (NASH), fibrosis, and eventually end-stage liver diseases in a proportion of cases. Hepatic fibrosis and carcinogenesis often progress together, sharing inflammatory pathways. However, NASH can lead to hepatocarcinogenesis with minimal inflammation or fibrosis. In such instances, insulin resistance, oxidative stress, and lipotoxicity can directly lead to liver carcinogenesis through genetic and epigenetic alterations. Transforming growth factor (TGF)-β signaling is implicated in hepatic fibrogenesis and carcinogenesis. TGF-β type I receptor (TβRI) and activated-Ras/c-Jun-N-terminal kinase (JNK) differentially phosphorylate the mediator Smad3 to create two phospho-isoforms: C-terminally phosphorylated Smad3 (pSmad3C) and linker-phosphorylated Smad3 (pSmad3L). TβRI/pSmad3C signaling terminates cell proliferation, while constitutive Ras activation and JNK-mediated pSmad3L promote hepatocyte proliferation and carcinogenesis. The pSmad3L signaling pathway also antagonizes cytostatic pSmad3C signaling. This review addresses TGF-β/Smad signaling in hepatic carcinogenesis complicating NASH. We also discuss Smad phospho-isoforms as biomarkers predicting HCC in NASH patients with or without cirrhosis.

Expression of IL-37 Correlates With Immune Cell Infiltrate and Fibrosis in Pediatric Autoimmune Liver Diseases

OBJECTIVES

The activation of innate immune mechanisms is key for chronic liver injury. Interleukin-37 (IL-37) is a profound inhibitor of innate and adaptive immune responses, and its overexpression protects mice from liver inflammation and fibrosis. Here, we characterize the hepatic inflammatory infiltrate and expression of IL-37 in children with autoimmune liver diseases.

METHODS

We compared the inflammatory microenvironment of the liver in a retrospective cohort of children with primary sclerosing cholangitis (PSC), autoimmune sclerosing cholangitis (ASC) and autoimmune hepatitis (AIH) by immunohistochemistry. The expression of IL-37 was quantified in liver parenchyma and portal tracts. Double immunofluorescence was used for detection of IL-37 in specific cell types and colocalization with Smad3.

RESULTS

AIH is characterized by a dense lymphoplasmacytic infiltrate whereas ASC shows high numbers of granulocytes in portal tracts. IL-37 expression correlates positively with liver inflammation and fibrosis, the number of infiltrating immune cells and serum markers for hepatic inflammation. IL-37 is mainly expressed in hepatocytes, cholangiocytes and infiltrating immune cells. Double staining revealed IL-37 positivity in T helper and regulatory T cells (Treg), Kupffer (KC) and hepatic stellate cells (HSC). IL-37 colocalizes with intranuclear pSmad3L in areas of liver inflammation.

CONCLUSIONS

Pediatric ASC separates from PSC and AIH by a granulocyte-rich portal infiltrate. Upregulation of IL-37 with liver injury, the expression in Treg as well as KC and HSC and the colocalization of IL-37 with pSmad3L in cholangiocytes and hepatocytes suggest a modulating role to limit hepatic inflammation and fibrosis in pediatric autoimmune liver diseases.

Caffeine mitigates experimental nonalcoholic steatohepatitis and the progression of thioacetamide-induced liver fibrosis by blocking the MAPK and TGF-β/Smad3 signaling pathways

INTRODUCTION AND OBJECTIVES

Caffeine consumption is associated with beneficial effects on hepatic disorders. The objectives of this study were to evaluate the antifibrotic effects of caffeine on experimental nonalcoholic steatohepatitis (NASH) induced with a high-fat, high-sucrose, high-cholesterol diet (HFSCD), as well as to evaluate the ability of caffeine to prevent the progression of experimental liver fibrosis induced by the administration of thioacetamide (TAA) in rats and explore the mechanisms of action.

METHODS

NASH and fibrosis were induced in rats by the administration of an HFSCD for 15 weeks, and liver fibrosis was induced by intraperitoneal administration of 200 mg/kg TAA 3 times per week, for 6 weeks. Caffeine was administered at a dose of 50 mg/kg body weight. The effects of diet, TAA, and caffeine on fibrosis were evaluated by biochemical and histological examinations. The profibrotic pathways were analyzed by western blotting and immunohistochemistry.

RESULTS

Rats exhibited liver fibrosis after HFSCD feeding and the administration of TAA. Caffeine could reduce the hepatic level of collagen and the fibrotic area in the liver. Caffeine prevented the progression of liver fibrosis by decreasing transforming growth factor-beta (TGF-β), connective tissue growth factor (CTGF), and alpha-smooth muscle actin (α-SMA) expression and by inhibiting the activation of mitogen-activated protein kinases (MAPKs) and Smad3 phosphorylation.

CONCLUSIONS

Caffeine attenuates NASH and the progression of liver fibrosis due to its antifibrotic effects and modulating the MAPK and TGF-β pathways. Therefore, caffeine could be a suitable candidate for treating liver diseases associated with fibrosis.

Low-dose paclitaxel modulates the cross talk between the JNK and Smad signaling in primary biliary fibroblasts

OBJECTIVE

The objective of this study was to explore the molecular mechanism underlying the occurrence of benign bile duct stricture and the target of low-dose paclitaxel in the prevention of benign bile duct stricture.

METHODS

Under the stimulation of transforming growth factor beta 1, the expression of collagen type I and connective tissue growth factor were detected on isolated primary fibroblasts. The phosphorylation levels of JNK and Smad2L were detected using Western blot. The effect of low-dose paclitaxel on the transforming growth factor beta 1-induced inhibition of type I collagen and connective tissue growth factor expression and JNK and Smad2L phosphorylation was also observed.

RESULTS

Transforming growth factor beta 1 induced the secretion of type I collagen and connective tissue growth factor as well as JNK phosphorylation in biliary fibroblasts. The JNK inhibitor or siRNA-Smad2 inhibited the transforming growth factor beta 1-induced secretion of type I collagen and connective tissue growth factor. Low-dose paclitaxel inhibited the expression of type I collagen induced by transforming growth factor beta 1 and may inhibit the secretion of collagen in biliary fibroblasts.

CONCLUSION

The activation of JNK/Smad2L induced by transforming growth factor beta 1 is involved in the occurrence of benign bile duct stricture that is mediated by the overexpression of type I collagen and connective tissue growth factor, and low-dose paclitaxel may inhibit the phosphorylation of JNK/Smad2L.

Role of Circulating Hematopoietic Fibrocytes in Chronic Hepatitis C Patients Induced Liver Fibrosis

Background: Bone marrow derived fibrocytes may play an important role in pathogenesis and resolution of liver fibrosis. These cells may offer new approaches for better understanding the pathogenesis of liver fibrosis. Aim of the work: To define the proportion of circulating fibrocytes with hematopoietic progenitor origin as defined by CD45 and CD34 positivity and to assess whether they are increased in patients with chronic C hepatitis in correlation to the degree of liver fibrosis. Subjects and Methods: Sixty HCV patients were classified according to METAVIR score into 4 stages of liver fibrosis, 15 age and sex-matched controls were included. Flowcytometric analysis for circulating levels of fibrocytes CD34+ve cells, CD45+ve cells, collagen type I+ve cells and CXCR4+ve cells was carried out using monoclonal antibodies (anti-CD34, CD45, collagen type I and CD184). GM-CSF, TGF-β and α-SMA were assessed using ELISA. Results and Conclusions: A significant increase in the circulating levels of GM-CSF, TGF- β and α-SMA, with a significant increase in the percentage of cells express CXCR4and in the co expression of CD34, CD45 and collagen type I positive cells in different groups of patients compared to control group, denoting the presence of an increased proportion of circulating fibrocytes in peripheral blood of these patients. The percentage of fibrocytes that positively expression CD34, CD45, collagen type I and CXCR4, were increased in step wise fashion in conjunction with worsening severity of liver disease. Liver fibrosis is associated with increased levels of circulating TGF-β1 and lipopolysaccharide, activation of myofibroblasts, and extensive deposition of extracellular matrix, mostly collagen Type I. TGF-β and LPS play a critical role in fibrogenesis and trigger fibrocyte recruitment to the injured liver promoting their differentiation into collagen type I producing myofibroblast, supporting that fibrocytes may become a novel target for anti fibrotic therapy.

A cytokine in turmoil: Transforming growth factor beta in cancer

Cancer remains one of the debilitating health threats to mankind in view of its incurable nature. Many factors are complicit in the initiation, progression and establishment of cancers. Early detection of cancer is the only window of hope that allows for appreciable management and possible limited survival. However, understanding of cancer biology and knowledge of the key factors that interplay at multi-level in the initiation and progression of cancer may hold possible avenues for cancer treatment and management. In particular, dysregulation of growth factor signaling such as that of transforming growth factor beta (TGF-β) and its downstream mediators play key roles in various cancer subtypes. Expanded understanding of the context/cell type-dependent roles of TGF-β and its downstream signaling mediators in cancer may provide leads for cancer pharmacotherapy. Reliable information contained in original articles, reviews, mini-reviews and expert opinions on TGF-β, cancer and the specific roles of TGF-β signaling in various cancer subtypes were retrieved from major scientific data bases including PubMed, Scopus, Medline, Web of Science core collections just to mention but a sample by using the following search terms: TGF-β in cancer, TGF-β and colorectal cancer, TGF-β and brain cancer, TGF-β in cancer initiation, TGF-β and cell proliferation, TGF-β and cell invasion, and TGF-β-based cancer therapy. Retrieved information and reports were carefully examined, contextualized and synchronized into a coherent scientific content to highlight the multiple roles of TGF-β signaling in normal and cancerous cells. From a conceptual standpoint, development of pharmacologically active agents that exert non-specific inhibitory effects on TGF-β signaling on various cell types will undoubtedly lead to a plethora of serious side effects in view of the multi-functionality and pleiotropic nature of TGF-β. Such non-specific targeting of TGF-β could derail any beneficial therapeutic intention associated with TGF-β-based therapy. However, development of pharmacologically active agents designed specifically to target TGF-β signaling in cancer cells may improve cancer pharmacotherapy. Similarly, specific targeting of downstream mediators of TGF-β such as TGF-β type 1 and II receptors (TβRI and TβRII), receptor-mediated Smads, mitogen activated protein kinase (MAPK) and importing proteins in cancer cells may be crucial for cancer pharmacotherapy.

Hepatic stellate cells - from past till present: morphology, human markers, human cell lines, behavior in normal and liver pathology

Hepatic stellate cell (HSC), initially analyzed by von Kupffer, in 1876, revealed to be an extraordinary mesenchymal cell, essential for both hepatocellular function and lesions, being the hallmark of hepatic fibrogenesis and carcinogenesis. Apart from their implications in hepatic injury, HSCs play a vital role in liver development and regeneration, xenobiotic response, intermediate metabolism, and regulation of immune response. In this review, we discuss the current state of knowledge regarding HSCs morphology, human HSCs markers and human HSC cell lines. We also summarize the latest findings concerning their roles in normal and liver pathology, focusing on their impact in fibrogenesis, chronic viral hepatitis and liver tumors.

Salvianolic acid B protects against acute and chronic liver injury by inhibiting Smad2C/L phosphorylation

Salvianolic acid B (Sal B) has strong antioxidant and anti-fibrosis effects, which are related to the transforming growth factor β/Smad signaling pathway. However, how Sal B affects this antioxidant pathway and the phosphorylation (p-) of Smad2 at both the COOH-terminal (pSmad2C) and linker region (pSmad2L) are unknown. The aims of the present study were to investigate the underlying mechanisms of Sal B on acute and chronic liver injury induced by CCl₄ and H₂O₂, and its effects on p-Smad2C/L. In in vivo experiments, acute and chronic liver injury models were induced by CCl₄, and the oxidative damage cell model was established in vitro with H₂O₂. Liver histopathology was assessed using hematoxylin and eosin and Van Gieson's staining. Moreover, serum biochemical indicators were analyzed using specific assay kits. Furthermore, the present study evaluated the oxidant/antioxidant status in acute and chronic liver injury models by oxidative stress parameters such as malondialdehyde, glutathione and superoxide dismutase. In addition, western blot analysis was performed to analyze the protein expression levels of pSmad2C, pSmad2L, nuclear factor erythroid-2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1). It was found that Sal B improved liver histology, decreased the levels of aminotransferase and attenuated oxidative stress in acute and chronic liver injury models. Additionally, the protein expression levels of pSmad2C and pSmad2L were decreased, but Nrf2 and HO-1 expression levels were increased both in vivo and in vitro. Collectively, the present results suggested that Sal B may protect against acute and chronic liver injury via inhibition of Smad2C/L phosphorylation, and the Nrf2/HO-1 signaling pathway may play an important role in this process.

Deletion of KLF10 Leads to Stress-Induced Liver Fibrosis upon High Sucrose Feeding

Liver fibrosis is a consequence of chronic liver injury associated with chronic viral infection, alcohol abuse, and nonalcoholic fatty liver. The evidence from clinical and animal studies indicates that transforming growth factor-β (TGF-β) signaling is associated with the development of liver fibrosis. Krüppel-like factor 10 (KLF10) is a transcription factor that plays a significant role in TGF-β-mediated cell growth, apoptosis, and differentiation. In recent studies, it has been reported to be associated with glucose homeostasis and insulin resistance. In the present study, we investigated the role of KLF10 in the progression of liver disease upon a high-sucrose diet (HSD) in mice. Wild type (WT) and Klf10 knockout (KO) mice were fed either a control chow diet or HSD (50% sucrose) for eight weeks. Klf10 KO mice exhibited significant hepatic steatosis, inflammation, and liver injury upon HSD feeding, whereas the WT mice exhibited mild hepatic steatosis with no apparent liver injury. The livers of HSD-fed Klf10 KO mice demonstrated significantly increased endoplasmic reticulum stress, oxidative stress, and proinflammatory cytokines. Klf10 deletion led to the development of sucrose-induced hepatocyte cell death both in vivo and in vitro. Moreover, it significantly increased fibrogenic gene expression and collagen accumulation in the liver. Increased liver fibrosis was accompanied by increased phosphorylation and nuclear localization of Smad3. Here, we demonstrate that HSD-fed mice develop a severe liver injury in the absence of KLF10 due to the hyperactivation of the endoplasmic reticulum stress response and CCAAT/enhance-binding protein homologous protein (CHOP)-mediated apoptosis of hepatocytes. The current study suggests that KLF10 plays a protective role against the progression of hepatic steatosis into liver fibrosis in a lipogenic state.

Activation of Nrf2/AREs-mediated antioxidant signalling, and suppression of profibrotic TGF-β1/Smad3 pathway: a promising therapeutic strategy for hepatic fibrosis - A review

Hepatic fibrosis (HF) is a wound-healing response that occurs during chronic liver injury and features by an excessive accumulation of extracellular matrix (ECM) components. Activation of hepatic stellate cell (HSC), the leading effector in HF, is responsible for overproduction of ECM. It has been documented that transforming growth factor-β1 (TGF-β1) stimulates superfluous accumulation of ECM and triggers HSCs activation mainly via canonical Smad-dependent pathway. Also, the pro-fibrogenic TGF-β1 is correlated with generation of reactive oxygen species (ROS) and inhibition of antioxidant mechanisms. Moreover, involvement of oxidative stress (OS) can be clearly elucidated as a fundamental event in liver fibrogenesis. Nuclear factor erythroid 2-related factor 2-antioxidant response elements (Nrf2-AREs) pathway, a group of OS-mediated transcription factors with diverse downstream targets, is associated with the induction of diverse detoxifying enzymes and the most pivotal endogenous antioxidative system. More specifically, Nrf2-AREs pathway has recently assigned as a new therapeutic target for cure of HF. The overall goal of this review will focus on recent findings about activation of Nrf2-AREs-mediated antioxidant and suppression of profibrotic TGF-β1/Smad3 pathway in the liver, providing an overview of recent advances in transcriptional repressors that dislocated during HF formation, and highlighting possible novel therapeutic targets for liver fibrosis.

Smad Phospho-Isoforms for Hepatocellular Carcinoma Risk Assessment in Patients with Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH)-related hepatocellular carcinoma (HCC) sometimes occurs in mildly fibrotic livers, while HCC incidence in NASH-related cirrhosis is lower than and less predictable than in hepatitis C virus (HCV)-related cirrhosis. Transforming growth factor (TGF)-β signaling in hepatocytic nuclei is implicated in fibrosis and carcinogenesis. TGF-βtype I receptor (TβRI) and c-Jun N-terminal kinase (JNK) differentially phosphorylate the mediator Smad3, resulting in 2 distinct phospho-isoforms: C-terminally phosphorylated Smad3 (pSmad3C) and linker-phosphorylated Smad3 (pSmad3L). In mature hepatocytes, oncogenic signaling via the JNK/pSmad3L pathway antagonizes signaling via the tumor-suppressive TβRI/pSmad3C pathway. We immunohistochemically examined domain-specific Smad3 phosphorylation in liver biopsy specimens from 30 NASH patients representing different fibrotic stages and 20 chronically infected hepatitis C patients as controls, correlating Smad3 phosphorylation with clinical course. HCC occurred during follow-up in 11 of 12 NASH patients with abundant pSmad3L and limited pSmad3C but in only 2 of 18 with limited pSmad3L. In contrast, HCC developed in 12 of 15 NASH patients with limited pSmad3C but only 1 of 15 with abundant pSmad3C. Two of fourteen NASH patients with mild fibrosis developed HCC, their hepatocytic nuclei showed abundant pSmad3L and limited pSmad3C. Five of sixteen patients with severe fibrosis did not develop HCC, their hepatocytic nuclei showed limited pSmad3L and abundant pSmad3C. Smad phospho-isoforms may represent important biomarkers predicting HCC in NASH and potential therapeutic targets for preventing NASH-related HCC.

Rebaudioside A administration prevents experimental liver fibrosis: an in vivo and in vitro study of the mechanisms of action involved

Rebaudioside A (Reb A) is a diterpenoid isolated from the leaves of Stevia rebaudiana (Bertoni) that has been shown to possess pharmacological activity, including anti-inflammatory and antioxidant properties. However, the ability of Reb A to prevent liver injury has not been evaluated. Therefore, we aimed to study the potential of Reb A (20 mg/kg; two times daily intraperitoneally) to prevent liver injury induced by thioacetamide (TAA) administration (200 mg/kg; three times per week intraperitoneally). In addition, cocultures were incubated with either lipopolysaccharide or ethanol. Antifibrotic, antioxidant and immunological responses were evaluated. Chronic TAA administration produced considerable liver damage and distorted the liver parenchyma with the presence of prominent thick bands of collagen. In addition, TAA upregulated the expression of α-smooth muscle actin, transforming growth factor-β1, metalloproteinases 9, 2 and 13, and nuclear factor kappaB and downregulated nuclear erythroid factor 2. Reb A administration prevented all of these changes. In cocultured cells, Reb A prevented the upregulation of genes implicated in fibrotic and inflammatory processes when cells were exposed to ethanol and lipopolysaccharide. Altogether, our results suggest that Reb A prevents liver damage by blocking oxidative processes via upregulation of nuclear erythroid factor 2, exerts immunomodulatory effects by downregulating the nuclear factor-κB system and acts as an antifibrotic agent by maintaining collagen content.

Stevia prevents experimental cirrhosis by reducing hepatic myofibroblasts and modulating molecular profibrotic pathways

AIM

The aims of the present study were to investigate the capacity of stevia leaves to prevent experimental cirrhosis induced by chronic administration of carbon tetrachloride (CCl₄ ) in rats and to explore the action mechanism involved.

METHODS

Liver cirrhosis was established by CCl₄ treatment (400 mg/kg i.p. three times a week for 12 weeks); stevia powder was administered (100 mg/kg by gavage daily) during the CCl₄ treatment. Serum markers of liver damage and hydroxyproline were evaluated and histopathological analyses were carried out. The profibrotic pathways were analyzed by western blot and immunohistochemistry.

RESULTS

We found for the first time that stevia cotreatment prevented the elevation of serum markers of necrosis and cholestasis and the occurrence of liver fibrosis. It is worth noting that stevia downregulated several profibrogenic pathways, including the reduction of hepatic myofibroblasts and decreased matrix metalloproteinase (MMP)2 and MMP13 expression, thereby blocking the liberation of transforming growth factor-β from the extracellular matrix. Notably, stevia reduced the phosphorylation of pSmad3L, the most profibrogenic and mitogenic Smad, by inhibiting the activation of c-Jun N-terminal kinase and extracellular signal-regulated kinase. Interestingly, Smad7, an important antifibrotic molecule, was upregulated by stevia treatment in cirrhotic rats. These multitarget mechanisms led to the prevention of experimental cirrhosis.

CONCLUSIONS

Because stevia possesses a reasonable safety profile, our results indicate that it could be useful in the clinical setting to treat chronic liver diseases.

Stevioside inhibits experimental fibrosis by down-regulating profibrotic Smad pathways and blocking hepatic stellate cell activation

Liver cirrhosis is associated with increased morbidity and mortality with important health and social consequences; however, an effective treatment has not been found yet. Previous reports have shown some beneficial effects of stevioside (SVT) in different diseases, but the ability of SVT to inhibit liver cirrhosis has not been reported. Therefore, we studied the potential of this diterpenoid to inhibit liver cirrhosis induced by thioacetamide, a model that shares many similarities with the human disease, and investigated the possible underlying molecular mechanism using in vivo and in vitro approaches. Cirrhosis was induced in male Wistar rats by chronic thioacetamide administration (200 mg/kg) intraperitoneally three times per week. Rats received saline or SVT (20 mg/kg) two times daily intraperitoneally. In addition, co-cultures were incubated with either lipopolysaccharide or ethanol. Liver fibrosis, hepatic stellate cells activation, metalloproteinases activity, canonical and non-canonical Smads pathway and expression of several profibrogenic genes were evaluated. Thioacetamide activated hepatic stellate cells and distorted the liver parenchyma with the presence of abundant thick bands of collagen. In addition, thioacetamide up-regulated the protein expression of α-smooth muscle actin, transforming growth factor-β1, metalloproteinases-9,-2 and -13 and overstimulate the canonical and non-canonical Smad pathways. SVT administration inhibited all of these changes. In vitro, SVT inhibited the up-regulation of several genes implicated in cirrhosis when cells were exposed to lipopolysaccharides or ethanol. We conclude that SVT inhibited liver damage by blocking hepatic stellate cells activation, down-regulating canonical and non-canonical profibrotic Smad pathways.

Role of Endothelial Cells in Renal Fibrosis

Renal fibrosis has been regarded as the common pathway of end-stage renal failure. Understanding the fundamental mechanism that leads to renal fibrosis is essential for developing better therapeutic options for chronic kidney diseases. So far, the main abstractions are on the injury of tubular epithelial cells, activation of interstitial cells, expression of chemotactic factor and adhesion molecule, infiltration of inflammatory cells and homeostasis of ECM. However, emerging studies revealed that endothelial cells (ECs) might happen to endothelial-to-mesenchymal transition (EndMT) dependent and/or independent endothelial dysfunction, which were supposed to accelerate renal fibrosis and are identified as new mechanisms for the proliferation of myofibroblasts as well. In this chapter, we are about to interpret the role of ECs in renal fibrosis and analyze the related molecules and pathways of both EndMT and EndMT independent endothelial dysfunction.

Antifibrotic Effect of Smad Decoy Oligodeoxynucleotide in a CCl₄-Induced Hepatic Fibrosis Animal Model

Hepatic fibrosis is the wound-healing process of chronic hepatic disease that leads to the end-stage of hepatocellular carcinoma and demolition of hepatic structures. Epithelial–mesenchymal transition (EMT) has been identified to phenotypic conversion of the epithelium to mesenchymal phenotype that occurred during fibrosis. Smad decoy oligodeoxynucleotide (ODN) is a synthetic DNA fragment containing a complementary sequence of Smad transcription factor. Thus, this study evaluated the antifibrotic effects of Smad decoy ODN on carbon tetrachloride (CCl₄)-induced hepatic fibrosis in mice. As shown in histological results, CCl₄ treatment triggered hepatic fibrosis and increased Smad expression. On the contrary, Smad decoy ODN administration suppressed fibrogenesis and EMT process. The expression of Smad signaling and EMT-associated protein was markedly decreased in Smad decoy ODN-treated mice compared with CCl₄-injured mice. In conclusion, these data indicate the practicability of Smad decoy ODN administration for preventing hepatic fibrosis and EMT processes.

Clinico-Pathological Importance of TGF-β/Phospho-Smad Signaling during Human Hepatic Fibrocarcinogenesis

Chronic viral hepatitis is a global public health problem, with approximately 570 million persons chronically infected. Hepatitis B and C viruses increase the risk of morbidity and mortality from liver cirrhosis, hepatocellular carcinoma (HCC), and extrahepatic complications that develop. Hepatitis virus infection induces transforming growth factor (TGF)-β, which influences microenvironments within the infected liver. TGF-β promotes liver fibrosis by up-regulating extracellular matrix production by hepatic stellate cells. TGF-β is also up-regulated in patients with HCC, in whom it contributes importantly to bringing about a favorable microenvironment for tumor growth. Thus, TGF-β is thought to be a major factor regulating liver fibrosis and carcinogenesis. Since TGF-β carries out regulatory signaling by influencing the phosphorylation of Smads, we have generated several kinds of phospho-specific antibodies to Smad2/3. Using these, we have identified three types of phospohorylated forms: COOH-terminally phosphorylated Smad2/3 (pSmad2C and pSmad3C), linker phosphorylated Smad2/3 (pSmad2L and pSmad3L), and dually phosphorylated Smad3 (pSmad2L/C and pSmad3L/C). TGF-β-mediated pSmad2/3C signaling terminates cell proliferation; on the other hand, cytokine-induced pSmad3L signaling accelerates cell proliferation and promotes fibrogenesis. This review addresses TGF-β/Smad signal transduction in chronic liver injuries and carcinogenic processes. We also discuss the reversibility of Smad signaling after antiviral therapy.

Dysregulation of fibrosis related genes in HCV induced liver disease

BACKGROUND

Liver fibrosis results from a wound healing response to chronic injury, which leads to excessive matrix deposition. Genome wide association studies have showen transcriptional dysregulation in mild and severe liver fibrosis. Recent studies suggested that genetic markers may be able to define the exact stage of liver fibrosis.

AIM

To define genes or genetic pathways that could serve as markers for staging or as therapeutic targets to halt progression of liver fibrosis.

METHODS

The study was performed on 105 treatment naïve HCV genotype 4 infected patients [F0-F2, n = 56; F3-F4, n = 49] and 16 healthy subjects. The study included PCR array on 84 fibrosis related genes followed by customization of a smaller array consisting of 11 genes that were designed on the bases of results obtained from the larger array. Genes that displayed significant dysregulation at mRNA levels were validated at protein levels.

RESULTS AND DISCUSSION

Two major pathways exhibited high dysregulation in early fibrosis as compared with controls or when compared with late fibrosis, these were the TGFβ - related pathway genes and Matrix - deposition associated genes. Hepatic stellate cell (HSC) activators i.e. TGFβ pathway genes [TGFβ1, 2 and 3, their receptors TGFβR1 and 2, signaling molecules SMAD genes and PDGF growth factors] were considerably over-expressed at transcriptional levels as early as F0, whereas expression of their inhibitor TGIF1 was simultaneously down regulated. Matrix proteins including collagen and MMPs were upregulated in early fibrosis whereas tissue inhibitors TIMPs 1 and 2 began over expression in late fibrosis. Expression at protein levels was concordant with RNA data excluding dysregulation at post transcriptional levels.

CONCLUSION

Since these 2 gene sets are closely interrelated regarding HSC activation and proliferation, we assume that the current findings suggest that they are favorable targets to further search for stage specific markers.

Protective effect of dihydromyricetin on LPS-induced acute lung injury

Dihydromyricetin (DHM), a bioactive flavonoid component isolated from Ampelopsis grossedentata, is known to have anti-inflammatory effect, but the effect of DHM on acute lung injury (ALI) is largely unknown. Here, we investigated the effect of DHM on ALI and the underlying mechanism by bioinformatic analyses and animal experiments. We found that pretreatment with DHM ameliorated lung pathological changes and suppressed the inflammation response in lung tissues after LPS challenge. The potential targets of DHM were predicted by DDI-CPI and DRAR-CPI tools and analyzed using the STRING server to predict the functionally related signaling pathways, such as MAPK signaling. Molecular docking calculations indicated that DHM could be embedded tightly into the binding pocket of ERK, JNK, and p38. Furthermore, the activation of MAPK signaling induced by LPS was inhibited by DHM. In conclusion, these findings suggest that DHM may exert its protective effect on ALI by inhibiting MAPK signaling. The present study supports a potential clinical application for DHM in treating ALI and provides a novel design that combines in silico methods with in vivo experiments for drug research.

Imidazoline I2 receptor inhibitor idazoxan regulates the progression of hepatic fibrosis via Akt-Nrf2-Smad2/3 signaling pathway

Liver fibrosis is a global health problem and its relationship with imidazoline I₂ receptor has not been reported. This study aimed to investigate the effects and underlying mechanisms of imidazoline I₂ receptor (I₂R) inhibitor idazoxan (IDA) on carbon tetrachloride (CCl₄)-induced liver fibrosis. In vivo liver fibrosis in mice was induced by intraperitoneally injections of CCl₄ for eight weeks, and in vitro studies were performed on activated LX2 cells treated with transforming growth factor-β (TGF-β). Our results showed that IDA significantly improved liver inflammation, ameliorated hepatic stellate cells activation and reduced collagen accumulation by suppressing the pro-fibrogenic signaling of TGF-β/Smad. Further investigation showed that IDA significantly balanced oxidative stress through improving the expressions and activities of anti-oxidant and detoxifying enzymes and activating Nrf2-the key defender against oxidative stress with anti-fibrotic potentials. Even more impressively, knock out of Nrf2 or suppression of Akt by perifosine (PE) eliminated the anti-oxidant and anti-fibrotic effects of IDA in vivo and in vitro, suggesting that Akt/Nrf2 constitutes a critical component of IDA's protective functions. Taken together, IDA exhibits potent effects against liver fibrosis via Akt-Nrf2-Smad2/3 signaling pathway, which suggests that specifically targeting I₂R may be a potentially useful therapeutic strategy for liver fibrosis.

MicroRNA-181a and its target Smad 7 as potential biomarkers for tracking child acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most common pediatric hematologic tumor. MiR-181a was expected to have a role in the development of hematological malignancies; it might act as tumor suppressor or oncogene. Smad7 was selected as miR-181a target pair. It is a negative regulator for the TGF-β1 signaling pathway. In this study, relative expression levels of miR-181a by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), both Smad 7 and TGF-β1 proteins levels by enzyme linked immunosorbent assay (ELISA) were all measured in serum of 60 child, 30 with ALL and 30 age and sex matched healthy child as control group. MiR-181a expression showed highly significant decrease; plus a significant increase and decrease of Smad7 and TGF-β1 protein levels respectively, in serum samples of ALL as compared to control group. MiR-181a expression achieved a highly significant positive and a significant negative correlation with TGF-β1 and Smad7 respectively. Furthermore, the levels of Smad7 and TGF-β1 were negatively correlated with each other (p<0.05). Although, positivity rate of both Smad7 and TGF-β1 in ALL group increased with presence of hepatosplenomegaly, still there was no statistical significance. In conclusion, miR-181a could act as a tumor suppressor in pediatric ALL with over expression of its target pair, Smad7. Smad7 regulates TGF-β1 signaling via a negative feedback loop and mediates the interaction between TGF-β1 and other signaling pathways; suggesting that Smad7 over expression may have therapeutic potential in ALL.

ERK pathway activation contributes to the tumor-promoting effects of hepatic stellate cells in hepatocellular carcinoma

BACKGROUND

Activated hepatic stellate cell (aHSC) play a critical role in hepatocellular carcinoma (HCC) progression crosstalking with cancer cell via various signaling pathways. The aim of our study is to explore the tumor-promoting effects of aHSCs on HCC via ERK pathway.

METHODS

α-SMA, p-ERK and p-JNK expression levels in tumoral and peritumoral tissues of HCC were assessed by immunohistochemical and western blotting. The protein and mRNA expression levels in human hepatoma cell treated with aHSC conditioned medium (CM) were determined by western blotting and real-time quantitative PCR, respectively. Cell migration and invasion abilities were assessed using transwell assays. The proliferation ability of HCC cells induced by aHSCs-CM was detected by CCK-8 assay and cell cycle analysis.

RESULTS

We found that aHSC number was positively correlated with p-ERK expression levels in tumoral tissues and aHSC-CM could time-dependently promote PCNA, p-ERK expression in HCC cells. Moreover, aHSC-CM enhanced HCC cells proliferation via ERK. Additionally, aHSC upregulated c-jun and cyclinD1 expression levels, accelerating the transition from G1 to the S phase of HCC cells, and this effect could be arrested by inhibiting ERK pathway. Furthermore, aHSC-CM promoted migration and invasion of HCC cells via ERK. Epithelial-mesenchymal transitions (EMT) phenomenon could be reversed by ERK suppression.

CONCLUSION

High expression of p-ERK and aHSCs may be associated with the aggressive behavior of HCC cells. Secretions from aHSCs could promote proliferation and EMT of HCC cells via ERK1/2/c-jun/cyclinD1 axis or ERK pathway.

Phenylethanol Glycosides from Cistanche tubulosa Suppress Hepatic Stellate Cell Activation and Block the Conduction of Signaling Pathways in TGF-β1/smad as Potential Anti-Hepatic Fibrosis Agents

Cistanche tubulosa is a traditional Chinese herbal medicine widely used for regulating immunity and phenylethanol glycosides (CPhGs) are among the primary components responsible for this activity. Previous studies have indicated the preventive and therapeutic effects of CPhGs on bovine serum albumin (BSA)-induced hepatic fibrosis in rats. The aim of the study was to evaluate the anti-hepatic fibrosis effect of CPhGs and the monomers echinacoside and acteoside by inhibiting hepatic stellate cell (HSC) activation, blocking the conduction of signaling pathways in transforming growth factor-β1 (TGF-β1)/smad, and determine their in vitro hepatoprotective activity. HSC proliferation was obviously inhibited after treatment with CPhGs (100, 50 μg/mL)/echinacoside (500, 250, 125 μg/mL)/acteoside (6, 3 μg/mL), with IC50 values of 119.125, 520.345 and 6.999 μg/mL, respectively, in the MTT assay. Different concentrations of CPhGs/echinacoside/acteoside did not affect the cellular toxicity on HSC according to lactate dehydrogenase (LDH) measurements. Different concentrations of CPhGs/echinacoside/acteoside increased the mRNA level and protein expression of smad7, and decreased the mRNA levels of smad2, smad3 and the protein expression of smad2, phospho-smad2 (p-smad2), smad3, phospho-smad3 (p-smad3) in HSC. In summary, these results demonstrate that CPhGs/echinacoside/acteoside can block the conduction of the signaling pathways in TGF-β1/smad, and inhibit the activation of HSC, suggesting that C. tubulosa may thus be a potential herbal medicine for the treatment of liver fibrosis.

Reversible Human TGF-β Signal Shifting between Tumor Suppression and Fibro-Carcinogenesis: Implications of Smad Phospho-Isoforms for Hepatic Epithelial-Mesenchymal Transitions

Epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are observed during both physiological liver wound healing and the pathological fibrotic/carcinogenic (fibro-carcinogenetic) process. TGF-β and pro-inflammatory cytokine are considered to be the major factors accelerating liver fibrosis and promoting liver carcinogenesis. Smads, consisting of intermediate linker regions connecting Mad homology domains, act as the intracellular mediators of the TGF-β signal transduction pathway. As the TGF-β receptors, c-Jun N-terminal kinase and cyclin-dependent kinase, differentially phosphorylate Smad2/3, we have generated numerous antibodies against linker (L) and C-terminal (C) phosphorylation sites in Smad2/3 and identified four types of phosphorylated forms: cytostatic COOH-terminally-phosphorylated Smad3 (pSmad3C), mitogenic pSmad3L (Ser-213) signaling, fibrogenic pSmad2L (Ser-245/250/255)/C signaling and migratory pSmad2/3L (Thr-220/179)/C signaling. After acute liver injury, TGF-β upregulates pSmad3C signaling and terminates pSmad3L (Ser-213)-mediated hepatocyte proliferation. TGF-β and pro-inflammatory cytokines cooperatively enhance collagen synthesis by upregulating pSmad2L (Thr-220)/C and pSmad3L (Thr-179)/C pathways in activated hepatic stellate cells. During chronic liver injuries, hepatocytes persistently affected by TGF-β and pro-inflammatory cytokines eventually become pre-neoplastic hepatocytes. Both myofibroblasts and pre-neoplastic hepatocyte exhibit the same carcinogenic (mitogenic) pSmad3L (Ser-213) and fibrogenic pSmad2L (Ser-245/250/255)/C signaling, with acquisition of fibro-carcinogenic properties and increasing risk of hepatocellular carcinoma (HCC). Firstly, we review phospho-Smad-isoform signalings in epithelial and mesenchymal cells in physiological and pathological conditions and then consider Smad linker phosphorylation as a potential target for pathological EMT during human fibro-carcinogenesis, because human Smad phospho-isoform signals can reverse from fibro-carcinogenesis to tumor-suppression in a process of MET after therapy.

Metabolic derivatives of alcohol and the molecular culprits of fibro-hepatocarcinogenesis: Allies or enemies?

Chronic intake of alcohol undoubtedly overwhelms the structural and functional capacity of the liver by initiating complex pathological events characterized by steatosis, steatohepatitis, hepatic fibrosis and cirrhosis. Subsequently, these initial pathological events are sustained and ushered into a more complex and progressive liver disease, increasing the risk of fibro-hepatocarcinogenesis. These coordinated pathological events mainly result from buildup of toxic metabolic derivatives of alcohol including but not limited to acetaldehyde (AA), malondialdehyde (MDA), CYP2E1-generated reactive oxygen species, alcohol-induced gut-derived lipopolysaccharide, AA/MDA protein and DNA adducts. The metabolic derivatives of alcohol together with other comorbidity factors, including hepatitis B and C viral infections, dysregulated iron metabolism, abuse of antibiotics, schistosomiasis, toxic drug metabolites, autoimmune disease and other non-specific factors, have been shown to underlie liver diseases. In view of the multiple etiology of liver diseases, attempts to delineate the mechanism by which each etiological factor causes liver disease has always proved cumbersome if not impossible. In the case of alcoholic liver disease (ALD), it is even more cumbersome and complicated as a result of the many toxic metabolic derivatives of alcohol with their varying liver-specific toxicities. In spite of all these hurdles, researchers and experts in hepatology have strived to expand knowledge and scientific discourse, particularly on ALD and its associated complications through the medium of scientific research, reviews and commentaries. Nonetheless, the molecular mechanisms underpinning ALD, particularly those underlying toxic effects of metabolic derivatives of alcohol on parenchymal and non-parenchymal hepatic cells leading to increased risk of alcohol-induced fibro-hepatocarcinogenesis, are still incompletely elucidated. In this review, we examined published scientific findings on how alcohol and its metabolic derivatives mount cellular attack on each hepatic cell and the underlying molecular mechanisms leading to disruption of core hepatic homeostatic functions which probably set the stage for the initiation and progression of ALD to fibro-hepatocarcinogenesis. We also brought to sharp focus, the complex and integrative role of transforming growth factor beta/small mothers against decapentaplegic/plasminogen activator inhibitor-1 and the mitogen activated protein kinase signaling nexus as well as their cross-signaling with toll-like receptor-mediated gut-dependent signaling pathways implicated in ALD and fibro-hepatocarcinogenesis. Looking into the future, it is hoped that these deliberations may stimulate new research directions on this topic and shape not only therapeutic approaches but also models for studying ALD and fibro-hepatocarcinogenesis.

Activation of TGF-β1-CD147 positive feedback loop in hepatic stellate cells promotes liver fibrosis

Activation of hepatic stellate cells (HSCs) by transforming growth factor-β1 (TGF-β1) initiates HBV-associated fibrogenesis. The mechanism of TGF-β1 modulating HSC activation is not fully uncovered. We hypothesized a positive feedback signaling loop of TGF-β1-CD147 promoting liver fibrogenesis by activation of HSCs. Human HSC cell line LX-2 and spontaneous liver fibrosis model derived from HBV transgenic mice were used to evaluate the activation of molecules in the signaling loop. Wound healing and cell contraction assay were performed to detect the CD147-overexpressed HSC migration and contraction. The transcriptional regulation of CD147 by TGF-β1/Smad4 was determined using dual-luciferase reporter assay and chromatin immunoprecipitation. We found that a positive reciprocal regulation between TGF-β1 and CD147 mediated HSC activation. CD147 over-expression promoted HSC migration and accelerated TGF-β1-induced cell contraction. Phosphorylation of Smad2 and Smad3 in cooperation with Smad4 mediated the TGF-β1-regulated CD147 expression. Smad4 activated the transcription by direct interaction with CD147 promoter. Meanwhile, CD147 modulated the activated phenotype of HSCs through the ERK1/2 and Sp1 which up-regulated α-SMA, collagen I, and TGF-β1 synthesis. These findings indicate that TGF-β1-CD147 loop plays a key role in regulating the HSC activation and combination of TGF-β receptor inhibitor and anti-CD147 antibody might be promised to reverse fibrogenesis.

Compound Astragalus and Salvia miltiorrhiza extracts modulate MAPK-regulated TGF-β/Smad signaling in hepatocellular carcinoma by multi-target mechanism

ETHNOPHARMACOLOGICAL RELEVANCE

Astragalus membranaceus Bunge (Leguminosae) and Salvia miltiorrhiza Bunge (Lamiaceae) are two important Chinese herbs with a long history of extensive ethnobotanical usage in the treatment of liver-related diseases over many centuries. Presently, these two herbs are being used either as a single herbal formulation or a composite formula for the treatment of liver related conditions. In response, recent studies on these two herbs have focused on elucidating their mechanisms of action, particularly with regards to their anti-hepatocarcinogenic effects. Previously, we have reported that Compound Astragalus and Salvia miltiorrhiza extract (CASE), a synergized composite extract from Astragalus membranaceus and Salvia miltiorrhiza ameliorates liver fibrosis and hepatocellular carcinoma (HCC) by modulating the TGF-β/Smad pathway. Meanwhile, MAPK activation and MAPK-dependent linker phosphorylation of Smad2/3 and their preferential nuclear import are crucial for overall oncogenic role of TGF-β/Smad signaling in HCC. To elucidate further, we studied the effect of CASE on the MAPK pathway and how it affects MAPK-dependent regulation of TGF-β/Smad signaling using both cell and animal models of HCC.

MATERIALS AND METHODS

We used immunofluorescence and western blot techniques to monitor effect of CASE on the activation of the MAPKs (pERK, pJNK and pp38) in TGF-β1-stimulated hepatic stellate cells (HSCs), HepG2 cells and also diethylnitrosamine (DEN)-induced HCC in rats. Also phosphorylation and subcellular distribution of pSmad2/3, Smad4 and Imp7/8 in TGF-β1-stimulated HSC and HepG2 cells were monitored. The expression of pERK, pJNK, pp38 and PAI-1 gene were monitored by using western blot technique. The effect of CASE on domain-specific phosphorylation of Smad2/3 and their subcellular distribution, and the expression of Smad4 and its subcellular distribution in TGF-β1-stimulated HSCs and HepG2 cells were evaluated by using immunofluorescence technique. And the expression of Imp7/8 and their subcellular distribution were assessed by both immunofluorescence and western blot techniques, while PAI-1 gene expression was assessed by western blot

RESULTS

In vitro, CASE in a concentration-dependent manner increased the expression of pp38 but decreased the expression of pERK and pJNK; however, in vivo, CASE in a dose dependent manner decreased the expression of pERK, pJNK as well as pp38. Also, CASE concentration dependently inhibited pSmad2C/L, pSmad3L, Smad4, Imp7/8 and their nuclear import; it had no effect on pSmad3C in HepG2 cells; significantly decreased PAI-1 gene expression in both in vitro and in vivo.

CONCLUSIONS

CASE blocked MAPK activation, MAPK-dependent linker phosphorylation of Smad2/3, Smad4 expression, Imp7 expression and their nuclear import leading to significant down-regulation of PAI-1 gene expression; further highlighting the multi-target anti-HCC effect of CASE and its potential drug candidature.

Hepatic stellate cells: central modulators of hepatic carcinogenesis

Hepatocellular carcinoma (HCC) represents the second most common cause of cancer-related death worldwide, and is increasing in incidence. Currently, our therapeutic repertoire for the treatment of HCC is severely limited, and therefore effective new therapies are urgently required. Recently, there has been increasing interest focusing on the cellular and molecular interactions between cancer cells and their microenvironment. HCC represents a unique opportunity to study the relationship between a diseased stroma and promotion of carcinogenesis, as 90 % of HCCs arise in a cirrhotic liver. Hepatic stellate cells (HSC) are the major source of extracellular proteins during fibrogenesis, and may directly, or via secreted products, contribute to tumour initiation and progression. In this review we explore the complex cellular and molecular interplay between HSC biology and hepatocarcinogenesis. We focus on the molecular mechanisms by which HSC modulate HCC growth, immune cell evasion and angiogenesis. This is followed by a discussion of recent progress in the field in understanding the mechanistic crosstalk between HSC and HCC, and the pathways that are potentially amenable to therapeutic intervention. Furthermore, we summarise the exciting recent developments in strategies to target HSC specifically, and novel techniques to deliver pharmaceutical agents directly to HSC, potentially allowing tailored, cell-specific therapy for HCC.

Actin-cytoskeleton polymerization differentially controls the stability of Ski and SnoN co-repressors in normal but not in transformed hepatocytes

BACKGROUND

Ski and SnoN proteins function as transcriptional co-repressors in the TGF-β pathway. They regulate cell proliferation and differentiation, and their aberrant expression results in altered TGF-β signalling, malignant transformation, and alterations in cell proliferation.

METHODS

We carried out a comparative characterization of the endogenous Ski and SnoN protein regulation by TGF-β, cell adhesion disruption and actin-cytoskeleton rearrangements between normal and transformed hepatocytes; we also analyzed Ski and SnoN protein stability, subcellular localization, and how their protein levels impact the TGF-β/Smad-driven gene transcription.

RESULTS

Ski and SnoN protein levels are lower in normal hepatocytes than in hepatoma cells. They exhibit a very short half-life and a nuclear/cytoplasmic distribution in normal hepatocytes opposed to a high stability and restricted nuclear localization in hepatoma cells. Interestingly, while normal cells exhibit a transient TGF-β-induced gene expression, the hepatoma cells are characterized by a strong and sustained TGF-β-induced gene expression. A novel finding is that Ski and SnoN stability is differentially regulated by cell adhesion and cytoskeleton rearrangements in the normal hepatocytes. The inhibition of protein turnover down-regulated both Ski and SnoN co-repressors impacting the kinetic of expression of TGF-β-target genes.

CONCLUSION

Normal regulatory mechanisms controlling Ski and SnoN stability, subcellular localization and expression are altered in hepatocarcinoma cells.

GENERAL SIGNIFICANCE

This work provides evidence that Ski and SnoN protein regulation is far more complex in normal than in transformed cells, since many of the normal regulatory mechanisms are lost in transformed cells.

Anti-Fibrotic Effects of Neferine on Carbon Tetrachloride-Induced Hepatic Fibrosis in Mice

The effects of neferine, a bisbenzylisoquinline alkaloid extracted from the seed embryo of the Chinese traditional medicine Nelumbo nucifera Gaertn, on carbon tetrachloride ( CCl 4)-induced hepatic fibrosis in mice were evaluated. Adult male Kunming mice were administered with CCl 4 1 ml/kg via intraperitoneal injection twice a week for 8 weeks. At the beginning of the 9th week, mice were treated with normal saline, colchicine (0.1 mg/kg), and neferine (5, 10, 20 mg/kg) via intraperitoneal injection once a day for 2 weeks. The liver index and histological examination, plasma ALT/AST levels, hydroxyproline and TGF-β1 content of liver tissue were examined. In the model group, the liver index, the hydroxyproline content of liver tissue and plasma ALT/AST levels were increased, and a high expression of TGF-β1 was observed. The abnormal changes could be improved by neferine in a dose-dependent manner. Our data showed that neferine had an antifibrosis effect on CCl 4-induced hepatic fibrosis in mice, possibly partly due to the decreased expression of TGF-β1 in the liver.

Acute toxicity of CCl4 but not of paracetamol induces a transcriptomic signature of fibrosis in precision-cut liver slices

In rat in vivo, both paracetamol (APAP) and carbon tetrachloride (CCl4) induce liver necrosis, but long-term treatment with CCl4, in contrast to paracetamol, causes liver fibrosis. The aim of this study was to perform transcriptomic analysis to compare the early changes in mRNA expression profiles induced by APAP and CCl4 in the rat precision-cut liver slice model (PCLS) and to identify early markers that could predict fibrosis-inducing potential. Microarray data of rat PCLS exposed to APAP andCCl4was generated using a toxic dose based on decrease in ATP levels. Toxicity pathway analysis using a custom made fibrosis-related gene list showed fibrosis as one of the predominant toxic endpoints in CCl4-treated, but not in APAP-treated PCLS. Moreover, genes which have a role in fibrosis such as alpha-B crystallin, jun proto-oncogene, mitogen-activated protein kinase 6, serpin peptidase inhibitor and also the transcription factor Kruppel-like-factor-6 were up-regulated by CCl4, but not by APAP. Predicted activation or inhibition of several upstream regulators due to CCl4 is in accordance with their role in fibrosis. In conclusion, transcriptomic analysis of PCLS successfully identified the fibrotic potential of CCl4 as opposed to APAP. The application of PCLS as an ex vivo model to identify early biomarkers to predict the fibrogenic potential of toxic compounds should be further explored.

Effects of 18α-glycyrrhizin on TGF-β1/Smad signaling pathway in rats with carbon tetrachloride-induced liver fibrosis

BACKGROUND

Glycyrrhizin has various pharmacological effects including hepato-protection. This study aimed to investigate the potential mechanism underlying the protective effects of 18α-glycyrrhizin (18α-GL) in rats with carbon tetrachloride (CCl4) induced liver fibrosis.

METHODS

Male Sprague-Dawley (SD) rats were randomly divided into control group, fibrosis group, 25 mg/kg 18α-GL group and 12.5 mg/kg 18α-GL group. Rats in experimental groups were subcutaneously injected with 40% CCl4 twice weekly for 8 weeks. Immunohistochemical examination was carried out to detect the protein expressions of collagen I, collagen III, TGF-β1, p-Smad2, p-Smad3, Smad 7 and SP-1, in the liver, and the mRNA and protein expressions of these genes were determined in the liver by real time PCR and Western blot assay, respectively.

RESULTS

18α-GL ameliorated histological changes and significantly suppressed collagen deposition. 18α-GL significantly decreased the mRNA expressions of TGF-β1, Smad2, Smad3 and SP-1 in the liver. Immunohistochemical staining revealed that TGF-β1, p-Smad2, p-Smad3 and SP-1 expressions reduced following 18α-GL therapy. Western blot assay showed p-Smad2, p-Smad3, smad2 and smad3 expressions decreased after 18α-GL treatment. The mRNA and protein expression of Smad7 remained unchanged.

CONCLUSION

18α-GL is able to attenuate CCl4 induced liver fibrosis in rat.

MAPK inhibitors differently modulate TGF-β/Smad signaling in HepG2 cells

The aim of this study was to investigate the mitogen-activated protein kinase (MAPK) pathway, which crosstalk with TGF-β/Smad signaling via linker phosphorylation of Smad2/3 to promote hepatocarcinogenesis. After DEN-induced hepatocellular carcinoma (HCC) in rats showed increased phosphorylation of JNK1/2, p38, and ERK1/2, we next antagonized TGF-β1-induced phosphorylation of JNK1/2, p38, ERK1/2, Smad2/3 signaling in HepG2 cells using SP600125, SB203580, and PD98059, respectively. Cell proliferation and invasion were assessed by MTT assay and transwell invasion chambers, respectively. Smad2/3, Smad4, and Smad7 expressions and PAI-1 messenger RNA (mRNA) transcription were measured by using immuno-precipitation/immuno-blotting and real-time RT-PCR, respectively. All the MAPK-specific inhibitors suppressed cell invasion, while all but PD98059 suppressed cell proliferation. Both SP600125 and SB203580 blocked pSmad2C/L and oncogenic pSmad3L. PD98059 blocked pSmad2L but had no effect on elevated pSmad2C and oncogenic pSmad3L. All but PD98059 blocked Smad2/3/4 complex formation and restored Smad7 expression, while all the three MAPK-Specific inhibitors repressed PAI-1 mRNA transcription. Both SP600125 and SB203580 inhibited HepG2 cells' proliferation and invasion by blocking oncogenic pSmad3L and Smad2/3/4 complex formation. PD98059 repressed PAI-1 mRNA by an unknown mechanism.

PDGFRα in liver pathophysiology: emerging roles in development, regeneration, fibrosis, and cancer

Platelet-derived growth factor receptor α (PDGFRα) is an isoform of the PDGFR family of tyrosine kinase receptors involved in cell proliferation, survival, differentiation, and growth. In this review, we highlight the role of PDGFRα and the current evidence of its expression and activities in liver development, regeneration, and pathology-including fibrosis, cirrhosis, and liver cancer. Studies elucidating PDGFRα signaling in processes ranging from profibrotic signaling, angiogenesis, and oxidative stress to epithelial-to-mesenchymal transition point toward PDGFRα as a potential therapeutic target in various hepatic pathologies, including hepatic fibrosis and liver cancer. Furthermore, PDGFRα localization and modulation during liver development and regeneration may lend insight into its potential roles in various pathologic states. We will also briefly discuss some of the current targeted treatments for PDGFRα, including multi receptor tyrosine kinase inhibitors and PDGFRα-specific inhibitors.

Linker phosphorylation of Smad3 promotes fibro-carcinogenesis in chronic viral hepatitis of hepatocellular carcinoma

Epidemiological and clinical data point to a close association between chronic hepatitis B virus infection or chronic hepatitis C virus infection and development of hepatocellular carcinoma (HCC). HCC develops over several decades and is associated with fibrosis. This sequence suggests that persistent viral infection and chronic inflammation can synergistically induce liver fibrosis and hepatocarcinogenesis. The transforming growth factor-β (TGF-β) signaling pathway plays a pivotal role in diverse cellular processes and contributes to hepatic fibro-carcinogenesis under inflammatory microenvironments during chronic liver diseases. The biological activities of TGF-β are initiated by the binding of the ligand to TGF-β receptors, which phosphorylate Smad proteins. TGF-β type I receptor activates Smad3 to create COOH-terminally phosphorylated Smad3 (pSmad3C), while pro-inflammatory cytokine-activated kinases phosphorylates Smad3 to create the linker phosphorylated Smad3 (pSmad3L). During chronic liver disease progression, virus components, together with pro-inflammatory cytokines and somatic mutations, convert the Smad3 signal from tumor-suppressive pSmad3C to fibro-carcinogenic pSmad3L pathways, accelerating liver fibrosis and increasing the risk of HCC. The understanding of Smad3 phosphorylation profiles may provide new opportunities for effective chemoprevention and personalized therapy for patients with hepatitis virus-related HCC in the future.

Smad3 phospho-isoform signaling in hepatitis C virus-related chronic liver diseases

The risk of hepatocellular carcinoma (HCC) development increases as hepatitis virus C (HCV)-related liver diseases progress, especially in patients with active inflammation. Insight into hepatic carcinogenesis have emerged from recent detailed analyses of transforming growth factor-β and c-Jun-N-terminal kinase signaling processes directed by multiple phosphorylated (phospho)-isoforms of a Smad3 mediator. In the course of HCV-related chronic liver diseases, chronic inflammation and host genetic/epigenetic alterations additively shift the hepatocytic Smad3 phospho-isoform signaling from tumor suppression to carcinogenesis, increasing the risk of HCC. Chronic inflammation represents an early carcinogenic step that provides a nonmutagenic tumor-promoting stimulus. After undergoing successful antiviral therapy, patients with chronic hepatitis C could experience a lower risk of HCC as Smad3 phospho-isoform signaling reverses from potential carcinogenesis to tumor suppression. Even after HCV clearance, however, patients with cirrhosis could still develop HCC because of sustained, intense carcinogenic Smad3 phospho-isoform signaling that is possibly caused by genetic or epigenetic alterations. Smad3 phospho-isoforms should assist with evaluating the effectiveness of interventions aimed at reducing human HCC.