Activin A: an autocrine inhibitor of initiation of DNA synthesis in rat hepatocytes

Molecular Pathways Governing the Termination of Liver Regeneration

The liver has the unique capacity to regenerate, and up to 70% of the liver can be removed without detrimental consequences to the organism. Liver regeneration is a complex process involving multiple signaling networks and organs. Liver regeneration proceeds through three phases: the initiation phase, the growth phase, and the termination phase. Termination of liver regeneration occurs when the liver reaches a liver-to-body weight that is required for homeostasis, the so-called "hepatostat." The initiation and growth phases have been the subject of many studies. The molecular pathways that govern the termination phase, however, remain to be fully elucidated. This review summarizes the pathways and molecules that signal the cessation of liver regrowth after partial hepatectomy and answers the question, "What factors drive the hepatostat?" SIGNIFICANCE STATEMENT: Unraveling the pathways underlying the cessation of liver regeneration enables the identification of druggable targets that will allow us to gain pharmacological control over liver regeneration. For these purposes, it would be useful to understand why the regenerative capacity of the liver is hampered under certain pathological circumstances so as to artificially modulate the regenerative processes (e.g., by blocking the cessation pathways) to improve clinical outcomes and safeguard the patient's life.

Antagonizing Activin A/p15INK4b Signaling as Therapeutic Strategy for Liver Disease

BACKGROUND/AIM

Activin A is involved in the pathogenesis of human liver diseases, but its therapeutic targeting is not fully explored. Here, we tested the effect of novel, highly specific small-molecule-based activin A antagonists (NUCC-474/555) in improving liver regeneration following partial hepatectomy and halting fibrosis progression in models of chronic liver diseases (CLDs).

METHODS

Cell toxicity of antagonists was determined in rat hepatocytes and Huh-7 cells using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay. Hepatocytes and hepatic stellate cells (HSCs) were treated with activin A and NUCC-555 and analyzed by reverse transcription-polymerase chain reaction and immunohistochemistry. Partial hepatectomized Fisher (F)344 rats were treated with NUCC-555, and bromodeoxyuridine (BrdU) incorporation was determined at 18/24/36/120/240 h. NUCC-555 was administered into thioacetamide- or carbon tetrachloride-treated F344 rats or C57BL/6 mice, and the fibrosis progression was studied.

RESULTS

NUCC-474 showed higher cytotoxicity in cultured hepatic cells; therefore, NUCC-555 was used in subsequent studies. Activin A-stimulated overexpression of cell cycle-/senescence-related genes (e.g., p15INK4b, DEC1, Glb1) was near-completely reversed by NUCC-555 in hepatocytes. Activin A-mediated HSC activation was blocked by NUCC-555. In partial hepatectomized rats, antagonizing activin A signaling resulted in a 1.9-fold and 2.3-fold increase in BrdU+ cells at 18 and 24 h, respectively. Administration of NUCC-555 in rats and mice with progressing fibrosis significantly reduced collagen accumulation (7.9-fold), HSC activation indicated by reduced alpha smooth muscle actin+ and vimentin+ cells, and serum aminotransferase activity.

CONCLUSIONS

Our studies demonstrate that activin A antagonist NUCC-555 promotes liver regeneration and halts fibrosis progression in CLD models, suggesting that blocking activin A signaling may represent a new approach to treating people with CLD.

"Small Hepatocytes" in the Liver

Mature hepatocytes (MHs) in an adult rodent liver are categorized into the following three subpopulations based on their proliferative capability: type I cells (MH-I), which are committed progenitor cells that possess a high growth capability and basal hepatocytic functions; type II cells (MH-II), which possess a limited proliferative capability; and type III cells (MH-III), which lose the ability to divide (replicative senescence) and reach the final differentiated state. These subpopulations may explain the liver's development and growth after birth. Generally, small-sized hepatocytes emerge in mammal livers. The cells are characterized by being morphologically identical to hepatocytes except for their size, which is substantially smaller than that of ordinary MHs. We initially discovered small hepatocytes (SHs) in the primary culture of rat hepatocytes. We believe that SHs are derived from MH-I and play a role as hepatocytic progenitors to supply MHs. The population of MH-I (SHs) is distributed in the whole lobules, a part of which possesses a self-renewal capability, and decreases with age. Conversely, injured livers of experimental models and clinical cases showed the emergence of SHs. Studies demonstrate the involvement of SHs in liver regeneration. SHs that appeared in the injured livers are not a pure population but a mixture of two distinct origins, MH-derived and hepatic-stem-cell-derived cells. The predominant cell-derived SHs depend on the proliferative capability of the remaining MHs after the injury. This review will focus on the SHs that appeared in the liver and discuss the significance of SHs in liver regeneration.

Gastrointestinal pharmacology activins in liver health and disease

Activins are a subgroup of the TGFβ superfamily of growth and differentiation factors, dimeric in nature and consisting of two inhibin beta subunits linked via a disulfide bridge. Canonical activin signaling occurs through Smad2/3, with negative feedback initiated by Smad6/7 following signal transduction, which binds activin type I receptor preventing phosphorylation of Smad2/3 and activation of downstream signaling. In addition to Smad6/7, other inhibitors of activin signaling have been identified as well, including inhibins (dimers of an inhibin alpha and beta subunit), BAMBI, Cripto, follistatin, and follistatin-like 3 (fstl3). To date, activins A, B, AB, C, and E have been identified and isolated in mammals, with activin A and B having the most characterization of biological activity. Activin A has been implicated as a regulator of several important functions of liver biology, including hepatocyte proliferation and apoptosis, ECM production, and liver regeneration; the role of other subunits of activin in liver physiology are less understood. There is mounting data to suggest a link between dysregulation of activins contributing to various hepatic diseases such as inflammation, fibrosis, and hepatocellular carcinoma, and emerging studies demonstrating the protective and regenerative effects of inhibiting activins in mouse models of liver disease. Due to their importance in liver biology, activins demonstrate utility as a therapeutic target for the treatment of hepatic diseases such as cirrhosis, NASH, NAFLD, and HCC; further research regarding activins may provide diagnostic or therapeutic opportunity for those suffering from various liver diseases.

The pharmacology and mechanisms of traditional Chinese medicine in promoting liver regeneration: A new therapeutic option

BACKGROUND

The liver is renowned for its remarkable regenerative capacity to restore its structure, size and function after various types of liver injury. However, in patients with end-stage liver disease, the regenerative capacity is inhibited and liver transplantation is the only option. Considering the limitations of liver transplantation, promoting liver regeneration is suggested as a new therapeutic strategy for liver disease. Traditional Chinese medicine (TCM) has a long history of preventing and treating various liver diseases, and some of them have been proven to be effective in promoting liver regeneration, suggesting the therapeutic potential in liver diseases.

PURPOSE

This review aims to summarize the molecular mechanisms of liver regeneration and the pro-regenerative activity and mechanism of TCM formulas, extracts and active ingredients.

METHODS

We conducted a systematic search in PubMed, Web of Science and the Cochrane Library databases using "TCM", "liver regeneration" or their synonyms as keywords, and classified and summarized the retrieved literature. The PRISMA guidelines were followed.

RESULTS

Forty-one research articles met the themes of this review and previous critical studies were also reviewed to provide essential background information. Current evidences indicate that various TCM formulas, extracts and active ingredients have the effect on stimulating liver regeneration through modulating JAK/STAT, Hippo, PI3K/Akt and other signaling pathways. Besides, the mechanisms of liver regeneration, the limitation of existing studies and the application prospect of TCM to promote liver regeneration are also outlined and discussed in this review.

CONCLUSION

This review supports TCM as new potential therapeutic options for promoting liver regeneration and repair of the failing liver, although extensive pharmacokinetic and toxicological studies, as well as elaborate clinical trials, are still needed to demonstrate safety and efficacy.

Therapeutic Cell Repopulation of the Liver: From Fetal Rat Cells to Synthetic Human Tissues

Progenitor cells isolated from the fetal liver can provide a unique cell source to generate new healthy tissue mass. Almost 20 years ago, it was demonstrated that rat fetal liver cells repopulate the normal host liver environment via a mechanism akin to cell competition. Activin A, which is produced by hepatocytes, was identified as an important player during cell competition. Because of reduced activin receptor expression, highly proliferative fetal liver stem/progenitor cells are resistant to activin A and therefore exhibit a growth advantage compared to hepatocytes. As a result, transplanted fetal liver cells are capable of repopulating normal livers. Important for cell-based therapies, hepatic stem/progenitor cells containing repopulation potential can be separated from fetal hematopoietic cells using the cell surface marker δ-like 1 (Dlk-1). In livers with advanced fibrosis, fetal epithelial stem/progenitor cells differentiate into functional hepatic cells and out-compete injured endogenous hepatocytes, which cause anti-fibrotic effects. Although fetal liver cells efficiently repopulate the liver, they will likely not be used for human cell transplantation. Thus, utilizing the underlying mechanism of repopulation and developed methods to produce similar growth-advantaged cells in vitro, e.g., human induced pluripotent stem cells (iPSCs), this approach has great potential for developing novel cell-based therapies in patients with liver disease. The present review gives a brief overview of the classic cell transplantation models and various cell sources studied as donor cell candidates. The advantages of fetal liver-derived stem/progenitor cells are discussed, as well as the mechanism of liver repopulation. Moreover, this article reviews the potential of in vitro developed synthetic human fetal livers from iPSCs and their therapeutic benefits.

Activin A specifically suppresses the expression of annexin A5 mRNA and augments gonadotropin-releasing hormone stimulation of A1 expression in LβT2 gonadotrope cells

Recently, we reported that gonadotropin-releasing hormone (GnRH) stimulates annexin A1 (Anxa1) and A5 (Anxa5) mRNA expression through the GnRH-receptor-mitogen-activated protein kinase cascade in LβT2 cells. As LβT2 cells respond to activin, we examined the effect of activin A on Anxa1 and a5 expression in LβT2 cells. Activin A (0.4 and 4 ng/mL) treatment decreased Anxa5 mRNA levels in a dose-dependent manner, but did not affect Anxa1 mRNA levels at concentrations up to 40 ng/mL. After activin A treatment (4 ng/mL), Anxa5 mRNA levels significantly decreased at 6 h, gradually declined until 24 h, and remained low until 48 h, whereas Anxa1 mRNA levels did not significantly change following treatment. Pretreatment with activin A for 24 h increased GnRH agonist (GnRHa)-induced Anxa1 increase by approximately 7-fold compared with GnRHa stimulation alone, but Anxa5 was not affected. As previously reported, these activin A treatments increased gonadotropin β subunit and GnRH receptor mRNA levels and slightly decreased common α-glycoprotein subunit mRNA levels. Furthermore, we examined the effect of activin A on Nr4a3, which is repressed by ANXA5 and which reduces Fshb expression, and found that activin A augmented Nr4a3 expression and slightly decreased the GnRHa-induced increase in Nr4a3. These results suggest that in gonadotrope cells, the mechanism regulating Anxa1 and a5 expression is differentially coupled with activin A signal transduction. Activin A suppresses Anxa5 expression under increased Nr4a3 expression, whereas activin A and GnRH synergistically stimulate Anxa1 expression. These GnRH-inducible annexins may have different specific functions in gonadotropes.

Activin B promotes the initiation and progression of liver fibrosis

The role of activin B, a transforming growth factor β (TGFβ) superfamily cytokine, in liver health and disease is largely unknown. We aimed to investigate whether activin B modulates liver fibrogenesis. Liver and serum activin B, along with its analog activin A, were analyzed in patients with liver fibrosis from different etiologies and in mouse acute and chronic liver injury models. Activin B, activin A, or both was immunologically neutralized in mice with progressive or established carbon tetrachloride (CCl₄ )-induced liver fibrosis. Hepatic and circulating activin B was increased in human patients with liver fibrosis caused by several liver diseases. In mice, hepatic and circulating activin B exhibited persistent elevation following the onset of several types of liver injury, whereas activin A displayed transient increases. The results revealed a close correlation of activin B with liver injury regardless of etiology and species. Injured hepatocytes produced excessive activin B. Neutralizing activin B largely prevented, as well as improved, CCl₄ -induced liver fibrosis, which was augmented by co-neutralizing activin A. Mechanistically, activin B mediated the activation of c-Jun-N-terminal kinase (JNK), the induction of inducible nitric oxide synthase (iNOS) expression, and the maintenance of poly (ADP-ribose) polymerase 1 (PARP1) expression in injured livers. Moreover, activin B directly induced a profibrotic expression profile in hepatic stellate cells (HSCs) and stimulated these cells to form a septa structure. Conclusions: We demonstrate that activin B, cooperating with activin A, mediates the activation or expression of JNK, iNOS, and PARP1 and the activation of HSCs, driving the initiation and progression of liver fibrosis.

Changes in the expressions of annexin A1, annexin A5, inhibin/activin subunits, and vitamin D receptor mRNAs in pituitary glands of female rats during the estrous cycle: correlation analyses among these factors

Pituitary gonadotropin secretion is regulated by several pituitary factors as well as GnRH and ovarian hormones. To elucidate the regulatory mechanisms of pituitary gonadotropin secretions, we observed changes in the mRNA levels of pituitary factors, namely annexin A1 (Anxa1) and Anxa5, inhibin/activin subunits, follistatin (Fst), and vitamin D receptor (Vdr), in female rat pituitary glands during the estrous cycle. Additionally, levels of LHβ subunit (Lhb), FSHβ subunit (Fshb), and GnRH receptor (Gnrh-r) mRNA were examined. During proestrus, Anxa1, Anxa5, Vdr, and inhibin α-subunit (Inha) exhibited the lowest levels, while during estrus, activin βB-subunit (Actbb), Lhb, and Gnrh-r were the lowest. Moreover, Fshb exhibited the highest value during metestrus, whereas Fst did not differ significantly. Correlation analyses revealed 16 statistically significant gene combinations. In particular, four combinations, namely Anxa5 and Inha, Anxa5 and Actbb, Inha and Vdr, and Inha and Actbb, were highly significant (P<0.0001), while four combinations, Anxa1 and Anxa5, Anxa1 and Vdr, Anxa5 and Vdr, and Lhb and Gnrh-r, were moderately significant (P<0.001). The remaining eight combinations that exhibited statistical significance were Anxa1 and Inha, Anxa1 and Actbb, Vdr and Actbb, Anxa1 and Fshb, Inha and Lhb, Actbb and Fshb, Actbb and Lhb, and Fst and Fshb (P<0.05). These results highlight strong correlations among Anxa1, Anxa5, Vdr, Inha, and Actbb, thereby suggesting that an interaction among ANXA1, ANXA5, and VDR may lead to further communications with inhibin and/or activin in the pituitary gland.

Liver regeneration biology: Implications for liver tumour therapies

The liver has remarkable regenerative potential, with the capacity to regenerate after 75% hepatectomy in humans and up to 90% hepatectomy in some rodent models, enabling it to meet the challenge of diverse injury types, including physical trauma, infection, inflammatory processes, direct toxicity, and immunological insults. Current understanding of liver regeneration is based largely on animal research, historically in large animals, and more recently in rodents and zebrafish, which provide powerful genetic manipulation experimental tools. Whilst immensely valuable, these models have limitations in extrapolation to the human situation. In vitro models have evolved from 2-dimensional culture to complex 3 dimensional organoids, but also have shortcomings in replicating the complex hepatic micro-anatomical and physiological milieu. The process of liver regeneration is only partially understood and characterized by layers of complexity. Liver regeneration is triggered and controlled by a multitude of mitogens acting in autocrine, paracrine, and endocrine ways, with much redundancy and cross-talk between biochemical pathways. The regenerative response is variable, involving both hypertrophy and true proliferative hyperplasia, which is itself variable, including both cellular phenotypic fidelity and cellular trans-differentiation, according to the type of injury. Complex interactions occur between parenchymal and non-parenchymal cells, and regeneration is affected by the status of the liver parenchyma, with differences between healthy and diseased liver. Finally, the process of termination of liver regeneration is even less well understood than its triggers. The complexity of liver regeneration biology combined with limited understanding has restricted specific clinical interventions to enhance liver regeneration. Moreover, manipulating the fundamental biochemical pathways involved would require cautious assessment, for fear of unintended consequences. Nevertheless, current knowledge provides guiding principles for strategies to optimise liver regeneration potential.

4-Methylcatechol stimulates apoptosis and reduces insulin secretion by decreasing betacellulin and inhibin beta-A in INS-1 beta-cells

Insulinoma INS-1 cell line is a pancreatic beta cell tumor which is characterized with high insulin content and secretion in response to increasing glucose levels. 4-Methylcatechol (4-MC) is a metabolite of quercetin, which is known as a potential drug for inhibition of tumorigenesis. The aim of this study was to determine the applying doses of 4-methylcatechol (4-MC) for triggening cell death and decreasing the cell function of rat insulinoma INS-1 beta cells. The rate of apoptosis and the amount of insulin in the cell and the secretions were determined by the ELISA method. Betacellulin (BTC) and inhibin beta-A amounts in both the cell and the glucose induced secretion were investigated by Western blotting. Furthermore, BTC, Inhibin beta-A, Ins1, Ins2, and GLUT2 gene expression levels were determined by the by the real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) method. We noted a significant decrease in cell viability, while an increase in apoptotic cell death by 4-MC treatment. It caused a decrease in the secretion of BTC, expressions of both BTC and inhibin beta-A. We showed a decrease in the expressions of Ins1 and GLUT2, while there is no alteration in the level of insulin protein. Insulin secretion levels increased in INS-1 cells given 4-MC by basal glucose concentration while they did not response to high concentration of glucose, which indicates that 4-MC disrupts the functionality of INS-1 cells. These results revealed that 4-MC induces apoptosis and decreases insulin secretion by reducing BTC and inhibin beta-A in insulinoma INS-1 cells. Thus, 4-MC may be offered as a potential molecule for treatment of insulinoma.

Activin A is a prominent autocrine regulator of hepatocyte growth arrest

Activin A, a multifunctional cytokine, plays an important role in hepatocyte growth suppression and is involved in liver size control. The present study was aimed to determine the cell location of activin A in the normal rat liver microenvironment and the contribution of activin A signaling to the hepatocyte phenotype to obtain insight into molecular mechanisms. Immunohistochemical and in situ hybridization analyses identified hepatocytes as the major activin A‐positive cell population in normal liver and identified mast cells as an additional activin A source. To investigate paracrine and autocrine activin A‐stimulated effects, hepatocytes were cocultured with engineered activin A‐secreting cell lines (RF1, TL8) or transduced with an adeno‐associated virus vector encoding activin βA, which led to strikingly altered expression of cell cycle‐related genes (Ki‐67, E2F transcription factor 1 [E2F1], minichromosome maintenance complex component 2 [Mcm2], forkhead box M1 [FoxM1]) and senescence‐related genes (cyclin‐dependent kinase inhibitor 2B [p15^INK4b/CDKN2B], differentiated embryo‐chondrocyte expressed gene 1 [DEC1]) and reduced proliferation and induction of senescence. Microarray analyses identified 453 differentially expressed genes, many of which were not yet recognized as activin A downstream targets (e.g., ADAM metallopeptidase domain 12 [Adam12], semaphorin 7A [Sema7a], LIM and cysteine‐rich domains‐1 [Lmcd1], DAB2, clathrin adaptor protein [Dab2]). Among the main activin A‐mediated molecular/cellular functions are cellular growth/proliferation and movement, molecular transport, and metabolic processes containing highly down‐regulated genes, such as cytochrome P450, subfamily 2, polypeptide 11 (Cyp2C11), sulfotransferase family 1A, member 1 (Sult1a1), glycine‐N‐acyltransferase (Glyat), and bile acid‐CoA:amino acid N‐acyltransferase (Baat). Moreover, Ingenuity Pathway Analyses identified particular gene networks regulated by hepatocyte nuclear factor (HNF)‐4α and peroxisome proliferator‐activated receptor gamma (PPARγ) as key targets of activin A signaling. Conclusion: Our in vitro models demonstrated that activin A‐stimulated growth inhibition and cellular senescence is mediated through p15^INK4b/CDKN2B and is associated with up‐ and down‐regulation of numerous target genes involved in multiple biological processes performed by hepatocytes, suggesting that activin A fulfills a critical role in normal liver function. (Hepatology Communications 2017;1:852‐870)

Proliferation‑inhibiting pathways in liver regeneration (Review)

Liver regeneration, an orchestrated process, is the primary compensatory mechanism following liver injury caused by various factors. The process of liver regeneration consists of three stages: Initiation, proliferation and termination. Proliferation‑promoting factors, which stimulate the recovery of mitosis in quiescent hepatocytes, are essential in the initiation and proliferation steps of liver regeneration. Proliferation‑promoting factors act as the 'motor' of liver regeneration, whereas proliferation inhibitors arrest cell proliferation when the remnant liver reaches a suitable size. Certain proliferation inhibitors are also expressed and activated in the first two steps of liver regeneration. Anti‑proliferation factors, acting as a 'brake', control the speed of proliferation and determine the terminal point of liver regeneration. Furthermore, anti‑proliferation factors function as a 'steering‑wheel', ensuring that the regeneration process proceeds in the right direction by preventing proliferation in the wrong direction, as occurs in oncogenesis. Therefore, proliferation inhibitors to ensure safe and stable liver regeneration are as important as proliferation‑promoting factors. Cytokines, including transforming growth factor‑β and interleukin‑1, and tumor suppressor genes, including p53 and p21, are important members of the proliferation inhibitor family in liver regeneration. Certain anti‑proliferation factors are involved in the process of gene expression and protein modification. The suppression of liver regeneration led by metabolism, hormone activity and pathological performance have been reviewed previously. However, less is known regarding the proliferation inhibitors of liver regeneration and further investigations are required. Detailed information regarding the majority of known anti‑proliferation signaling pathways also remains fragmented. The present review aimed to understand the signalling pathways that inhbit proliferation in the process of liver regeneration.

Effects of the Activin A-Follistatin System on Myocardial Cell Apoptosis through the Endoplasmic Reticulum Stress Pathway in Heart Failure

BACKGROUND

A previous study suggested that activin A inhibited myocardial cell apoptosis. This study thus aimed to explore the effects of the activin A-follistatin system on myocardial cell apoptosis in heart failure (HF) rats in order to determine whether or not the mechanism operates through the endoplasmic reticulum stress (ERS) pathway.

METHODS

Myocardial infarction (MI) by vascular deprivation was used to induce HF. The enzyme-linked immunosorbent assay was used to detect activin A, follistatin and brain natriuretic peptide (BNP) contents in serum. Immunohistochemical staining for activin A, follistatin, CCAAT-enhancer-binding protein (C/EBP) homologous protein (CHOP) and caspase-3 was performed on the myocardial tissue. The activin A-stimulated apoptosis of H9c2 cells was tested by flow cytometry. Western blot was used to detect the expression levels of activin A, follistatin and ERS-related proteins.

RESULTS

It was found that the high expression of activin A could cause activin A-follistatin system imbalance, inducing myocardial cell apoptosis via ERS in vivo. When HF developed to a certain stage, the expression of follistatin was upregulated to antagonize the expression of activin A. Activin A inhibited cardiomyocyte apoptosis with a low concentration and promoted apoptosis with a high concentration in vitro, also via ERS.

CONCLUSION

Activin A-follistatin system participated in ERS-mediated myocardial cell apoptosis in HF.

Clinical and Therapeutic Implications of Follistatin in Solid Tumours

Follistatin (FST), as a single-chain glycosylated protein, has two major isoforms, FST288 and FST315. The FST315 isoform is the predominant form whilst the FST288 variant accounts for less than 5% of the encoded mRNA. FST is differentially expressed in human tissues and aberrant expression has been observed in a variety of solid tumours, including gonadal, gastric and lung cancer, hepatocellular carcinoma, basal cell carcinoma and melanoma. Based on the current evidence, FST is an antagonist of transforming growth factor beta family members, such as activin and bone morphogenetic proteins (BMPs). FST plays a role in tumourigenesis, metastasis and angiogenesis of solid tumours through its interaction with activin and BMPs, thus resulting in pathophysiological function. In terms of diagnosis, prognosis and therapy, FST has shown strong promise. Through a better understanding of its biological functions, potential clinical applications may yet emerge.

Activins and Follistatin in Chronic Hepatitis C and Its Treatment with Pegylated-Interferon-α Based Therapy

Pegylated-interferon-α based therapy for the treatment of chronic hepatitis C (CHC) is considered suboptimal as not all patients respond to the treatment and it is associated with several side effects that could lead to dose reduction and/or termination of therapy. The currently used markers to monitor the response to treatment are based on viral kinetics and their performance in the prediction of treatment outcome is moderate and does not combine accuracy and their values have several limitations. Hence, the development of new sensitive and specific predictor markers could provide a useful tool for the clinicians and healthcare providers, especially in the new era of interferon-free therapy, for the classification of patients according to their response to the standard therapy and only subscribing the novel directly acting antiviral drugs to those who are anticipated not to respond to the conventional therapy and/or have absolute contraindications for its use. The importance of activins and follistatin in the regulation of immune system, liver biology, and pathology has recently emerged. This review appraises the up-to-date knowledge regarding the role of activins and follistatin in liver biology and immune system and their role in the pathophysiology of CHC.

Activin A prevents neuron-like PC12 cell apoptosis after oxygen-glucose deprivation

In this study, PC12 cells were induced to differentiate into neuron-like cells using nerve growth factor, and were subjected to oxygen-glucose deprivation. Cells were treated with 0, 10, 20, 30, 50, 100 ng/mL exogenous Activin A. The 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide assay and Hoechst 33324 staining showed that the survival percentage of PC12 cells significantly decreased and the rate of apoptosis significantly increased after oxygen-glucose deprivation. Exogenous Activin A significantly increased the survival percentage of PC12 cells in a dose-dependent manner. Reverse transcription-PCR results revealed a significant increase in Activin receptor IIA, Smad3 and Smad4 mRNA levels, which are key sites in the Activin A/Smads signaling pathway, in neuron-like cells subjected to oxygen-glucose deprivation, while mRNA expression of the apoptosis-regulation gene caspase-3 decreased. Our experimental findings indicate that exogenous Activin A plays an anti-apoptotic role and protects neurons by means of activating the Activin A/Smads signaling pathway.

Conophylline suppresses hepatic stellate cells and attenuates thioacetamide-induced liver fibrosis in rats

BACKGROUND & AIMS

Conophylline (CnP) is a vinca alkaloid purified from a tropical plant and inhibits activation of pancreatic stellate cells. We investigated the effect of CnP on hepatic stellate cells (HSC) in vitro. We also examined whether CnP attenuates hepatic fibrosis in vivo.

METHOD

We examined the effect of CnP on the expression of α-smooth muscle actin (α-SMA) and collagen-1, DNA synthesis and apoptosis in rat HSC and Lx-2 cells. We also examined the effect of CnP on hepatic fibrosis induced by thioacetamide (TAA).

RESULTS

In rat HSC and Lx-2 cells, CnP reduced the expression of α-SMA and collagen-1. CnP inhibited DNA synthesis induced by serum. CnP also promoted activation of caspase-3 and induced apoptosis as assessed by DNA ladder formation and TUNEL assay. In contrast, CnP did not induce apoptosis in AML12 cells. We then examined the effect of CnP on TAA-induced cirrhosis. In TAA-treated rats, the surface of the liver was irregular and multiple nodules were observed. Histologically, formation of pseudolobules surrounded by massive fibrous tissues was observed. When CnP was administered together with TAA, the surface of the liver was smooth and liver fibrosis was markedly inhibited. Collagen content was significantly reduced in CnP-treated liver.

CONCLUSION

Conophylline suppresses HSC and induces apoptosis in vitro. CnP also attenuates formation of the liver fibrosis induced by TAA in vivo.

The effect of activin A on signal transduction pathways in PC12 cells subjected to oxygen and glucose deprivation

The processes and mechanisms underlying brain injuries due to ischemia and anoxia have yet to be determined. Additionally, few clinical treatements are currently available. Activins have a protective role in the restoration, differentiation, and survival of injured cells, including Activin A (ActA), which acts as a neuroprotectant. However, its exact mechanism of action remains to be determined. ActA has been shown to protect neurons following ischemic brain injury. In this study, PC12 cells were differentiated into neuron-like cells after stimulation with nerve growth factor to prepare an oxygen/glucose deprivation (OGD) model in neurons. The differentiated PC12 cells, subjected to the OGD model, were exposed to ActA. Results showed that the PC12 survival rate decreased after OGD, leading to an increase in caspase-3 expression in these cells. Pretreatment with ActA was able to partially prevent OGD-induced apoptosis, likely through the downregulation of caspase-3. Futhermore, ActA pretreatment increased the expression of key proteins in the ActA/Smads signal transduction pathway, which may promote neuroprotection after OGD. Therefore, exogenous ActA may function as a neuroprotectant and provide a novel therapeutic treatment for ischemic brain injury.

Activin receptor antagonists for cancer-related anemia and bone disease

INTRODUCTION

Antagonists of activin receptor signaling may be beneficial for cancer-related anemia and bone disease caused by malignancies such as multiple myeloma and solid tumors.

AREAS COVERED

We review evidence of dysregulated signaling by activin receptor pathways in anemia, myeloma-associated osteolysis, and metastatic bone disease, as well as potential involvement in carcinogenesis. We then review properties of activin receptor antagonists in clinical development.

EXPERT OPINION

Sotatercept is a novel receptor fusion protein that functions as a soluble trap to sequester ligands of activin receptor type IIA (ActRIIA). Preclinically, the murine version of sotatercept increased red blood cells (RBC) in a model of chemotherapy-induced anemia, inhibited tumor growth and metastasis, and exerted anabolic effects on bone in diverse models of multiple myeloma. Clinically, sotatercept increases RBC markedly in healthy volunteers and patients with multiple myeloma. With a rapid onset of action differing from erythropoietin, sotatercept is in clinical development as a potential first-in-class therapeutic for cancer-related anemia, including those characterized by ineffective erythropoiesis as in myelodysplastic syndromes. Anabolic bone activity in early clinical studies and potential antitumor effects make sotatercept a promising therapeutic candidate for multiple myeloma and malignant bone diseases. Antitumor activity has been observed preclinically with small-molecule inhibitors of transforming growth factor-β receptor type I (ALK5) that also antagonize the closely related activin receptors ALK4 and ALK7. LY-2157299, the first such inhibitor to enter clinical studies, has shown an acceptable safety profile so far in patients with advanced cancer. Together, these data identify activin receptor antagonists as attractive therapeutic candidates for multiple diseases.

Increased serum activin-A differentiates alcoholic from cirrhosis of other aetiologies

BACKGROUND

Activin-A is a molecule of the TGF superfamily, implicated in liver fibrosis, regeneration and stem cell differentiation. However, data on activins in liver diseases are few. We therefore studied serum levels of activin-A in chronic liver diseases. To identify the origin of activin-A, levels in the hepatic vein were also estimated.

MATERIALS AND METHODS

Nineteen controls and 162 patients participated in the study: 39 with hepatocellular carcinoma (HCC: 19 viral associated and 20 alcohol associated), 18 with chronic hepatitis C (CHC), 47 with primary biliary cirrhosis (26 PBC stage I-II and 21 stage IV), 22 with alcoholic cirrhosis (AC, hepatic vein blood available in 16), 20 with HCV cirrhosis (hepatic vein blood available in 18) and 16 patients with alcoholic fatty liver with mild to moderate fibrosis but no cirrhosis.

RESULTS

Activin-A levels were significantly increased (P < 0·001) in serum of patients with AC (median 673 pg/mL, range 449-3279), compared with either controls (149 pg/mL, 91-193) or patients with viral cirrhosis (189 pg/mL, 81-480), CHC (142 pg/mL, 65-559) PBC stage I-II (100 pg/mL, 59-597) and PBC stage IV (104 pg/mL, 81-579). Only patients with AC-associated HCC had significantly increased levels of activin-A (2403 pg/mL, 1561-7220 pg/mL). Activin-A serum levels could accurately discriminate AC from cirrhosis of other aetiologies and noncirrhotic alcoholic fatty liver with fibrosis.

CONCLUSIONS

Increased serum levels of activin-A only in patients with alcohol-related cirrhosis or HCC suggest a possible role of this molecule in the pathophysiology of AC. Further research is warranted to elucidate its role during the profibrotic process and its possible clinical applications.

Novel developmental biology-based protocol of embryonic stem cell differentiation to morphologically sound and functional yet immature hepatocytes

BACKGROUND/AIMS

Liver diseases are common in the United States and often require liver transplantation; however, donated organs are limited and thus alternative sources for liver cells are in high demand. Embryonic stem cells (ESC) can provide a continuous and readily available source of liver cells. ESC differentiation to liver cells is yet to be fully understood and comprehensive differentiation protocols are yet to be defined. Here, we aimed to achieve human (h)ESC differentiation into mature hepatocytes using defined recombinant differentiation factors and metabolites.

METHODS

Embryonic stem cell H1 line was sub-cultured on feeder layer. We induced hESCs into endodermal differentiation succeeded by early/late hepatic specification and finally into hepatocyte maturation using step combinations of Activin A and fibroblast growth factor (FGF)-2 for 7 days; followed by FGF-4 and bone morphogenic protein 2 (BMP2) for 7 days, succeeded by FGF-10 + hepatocyte growth factor 4 + epidermal growth factor for 14 days. Specific inhibitors/stimulators were added sequentially throughout differentiation. Cells were analysed by PCR, flow cytometry, microscopy or functional assays.

RESULTS

Our hESC differentiation protocol resulted in viable cells with hepatocyte shape and morphology. We observed gradual changes in cell transcriptome, including up-regulation of differentiation-promoting GATA4, GATA6, POU5F1 and HNF4 transcription factors, steady levels of stemness-promoting SOX-2 and low levels of Nanog, as defined by PCR. The hESC-derived hepatocytes expressed alpha-antitrypsin, CD81, cytokeratin 8 and low density lipoprotein (LDL) receptor. The levels of alpha-fetoprotein and proliferation marker Ki-67 in hESC-derived hepatocytes remained elevated. Unlike stem cells, the hESC-derived hepatocytes performed LDL uptake, produced albumin and alanine aminotransferase and had functional alcohol dehydrogenase.

CONCLUSION

We report a novel protocol for hESC differentiation into morphological and functional yet immature hepatocytes as an alternative method for hepatocyte generation.

Proliferation of rat small hepatocytes requires follistatin expression

Small hepatocytes (SHs) are a subpopulation of hepatocytes that have high growth potential in culture and can differentiate into mature hepatocytes (MHs). The activin (Act)/follistatin (Fst) system critically contributes to homeostasis of cell growth in the normal liver. ActA and ActB consist of two disulfide-linked Inhibin (Inh)β subunits, InhβA and InhβB, respectively. Fst binds to Act and blocks its bioactivity. In the present study we carried out the experiments to clarify how Fst regulates the proliferation of SHs. The gene expression was analyzed using DNA microarray analysis, reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR, and protein expression was examined by western blots, immunocytochemistry, and enzyme-linked immunosorbent assay. RT-PCR showed that Fst expression was high in SHs and low in MHs. Although the ActA expression was opposite to that of Fst, ActB expression was high in SHs and low in MHs and increased with time in culture. Fst protein was detected in the cytoplasm of SHs and secreted into the culture medium. ActB protein was also secreted into the medium. Although the exogenous administration of ActA and ActB apparently suppressed the proliferation of SHs, apoptosis of SHs was not induced by treatment with ActA or ActB. On the other hand, Fst treatment did not affect the colony formation of SHs but prevented the inhibitory effect of ActA. Neutralization by the anti-Fst antibody resulted in the suppression of DNA synthesis in SHs, and small hairpin RNA against Fst suppressed the expansion of SH colonies. In conclusion, Fst expression is necessary for the proliferation of SHs.

TGF-β in progression of liver disease

Transforming growth factor-β (TGF-β) is a central regulator in chronic liver disease contributing to all stages of disease progression from initial liver injury through inflammation and fibrosis to cirrhosis and hepatocellular carcinoma. Liver-damage-induced levels of active TGF-β enhance hepatocyte destruction and mediate hepatic stellate cell and fibroblast activation resulting in a wound-healing response, including myofibroblast generation and extracellular matrix deposition. Being recognised as a major profibrogenic cytokine, the targeting of the TGF-β signalling pathway has been explored with respect to the inhibition of liver disease progression. Whereas interference with TGF-β signalling in various short-term animal models has provided promising results, liver disease progression in humans is a process of decades with different phases in which TGF-β or its targeting might have both beneficial and adverse outcomes. Based on recent literature, we summarise the cell-type-directed double-edged role of TGF-β in various liver disease stages. We emphasise that, in order to achieve therapeutic effects, we need to target TGF-β signalling in the right cell type at the right time.

The regulation and functions of activin and follistatin in inflammation and immunity

The activins are members of the transforming growth factor β superfamily with broad and complex effects on cell growth and differentiation. Activin A has long been known to be a critical regulator of inflammation and immunity, and similar roles are now emerging for activin B, with which it shares 65% sequence homology. These molecules and their binding protein, follistatin, are widely expressed, and their production is increased in many acute and chronic inflammatory conditions. Synthesis and release of the activins are stimulated by inflammatory cytokines, Toll-like receptor ligands, and oxidative stress. The activins interact with heterodimeric serine/threonine kinase receptor complexes to activate SMAD transcription factors and the MAP kinase signaling pathways, which mediate inflammation, stress, and immunity. Follistatin binds to the activins with high affinity, thereby obstructing the activin receptor binding site, and targets them to cell surface proteoglycans and lysosomal degradation. Studies on transgenic mice and those with gene knockouts, together with blocking studies using exogenous follistatin, have established that activin A plays critical roles in the onset of cachexia, acute and chronic inflammatory responses such as septicemia, colitis and asthma, and fibrosis. However, activin A also directs the development of monocyte/macrophages, myeloid dendritic cells, and T cell subsets to promote type 2 and regulatory immune responses. The ability of both endogenous and exogenous follistatin to block the proinflammatory and profibrotic actions of activin A has led to interest in this binding protein as a potential therapeutic for limiting the severity of disease and to improve subsequent damage associated with inflammation and fibrosis. However, the ability of activin A to sculpt the subsequent immune response as well means that the full range of effects that might arise from blocking activin bioactivity will need to be considered in any therapeutic applications.

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

Hepatocellular carcinoma (HCC) usually arises from hepatic fibrosis caused by chronic inflammation. In chronic liver damage, hepatic stellate cells undergo progressive activation to myofibroblasts (MFB), which are important extracellular-matrix-producing mesenchymal cells. Concomitantly, perturbation of transforming growth factor (TGF)-β signaling by pro-inflammatory cytokines in the epithelial cells of the liver (hepatocytes) promotes both fibrogenesis and carcinogenesis (fibro-carcinogenesis). Insights into fibro-carcinogenic effects on chronically damaged hepatocytes have come from recent detailed analyses of the TGF-β signaling process. Smad proteins, which convey signals from TGF-β receptors to the nucleus, have intermediate linker regions between conserved Mad homology (MH) 1 and MH2 domains. TGF-β type I receptor and pro-inflammatory cytokine-activated kinases differentially phosphorylate Smad2 and Smad3 to create phosphoisoforms phosphorylated at the COOH-terminal, linker, or both (L/C) regions. After acute liver injury, TGF-β-mediated pSmad3C signaling terminates hepatocytic proliferation induced by the pro-inflammatory cytokine-mediated mitogenic pSmad3L pathway; TGF-β and pro-inflammatory cytokines synergistically enhance collagen synthesis by activated hepatic stellate cells via pSmad2L/C and pSmad3L/C pathways. During chronic liver disease progression, pre-neoplastic hepatocytes persistently affected by TGF-β together with pro-inflammatory cytokines come to exhibit the same carcinogenic (mitogenic) pSmad3L and fibrogenic pSmad2L/C signaling as do MFB, thereby accelerating liver fibrosis while increasing risk of HCC. This review of Smad phosphoisoform-mediated signals examines similarities and differences between epithelial and mesenchymal cells in acute and chronic liver injuries and considers Smad linker phosphorylation as a potential target for the chemoprevention of fibro-carcinogenesis.

Beneficial effects of follistatin in hepatic ischemia-reperfusion injuries in rats

BACKGROUND

Ischemia-reperfusion injury has been demonstrated in a variety of clinical settings. The morbidity associated with liver transplantation and major hepatic resections is partly a result of ischemia-reperfusion injury. Follistatin, an activin-binding protein, binds to activins and subsequently blocks their action. It was reported that blockade of the action of activin with administration of follistatin accelerates recovery from ischemia renal injury. This study was conducted to investigate the involvement of the activin-follistatin system in hepatic ischemia-reperfusion injury.

METHODS

Total hepatic ischemia for 30 min was performed followed by reperfusion in a rat model. Rats were divided into two groups: a follistatin group and a control group. Follistatin (1 μg/body), which is an activin-binding protein, was administered at the time of reperfusion.

RESULTS

Though 80% of animals survived in the follistatin group, four of five animals died in the control group within 3 days after reperfusion (p<0.05). AST was significantly lower at 3 h after reperfusion in the follistatin group (p<0.05). LDH was also lower at 6 h after reperfusion in the follistatin group (p<0.05). Follistatin inhibited the mRNA expression of the βA subunit of activin. Moreover, the expression of IL-6, which is an inflammatory cytokine, was suppressed at 6 h after reperfusion in the follistatin group (p<0.05).

CONCLUSIONS

The present study demonstrated that treatment with follistatin reduced the expression of IL-6 and activin resulting in beneficial support for hepatic ischemia-reperfusion injuries.

Inhibin/activin expression in human and rodent liver: subunits α and βB as new players in human hepatocellular carcinoma?

Background:

Activins and inhibins belong to the TGFβ-superfamily, which controls cell proliferation and differentiation in many organs. Activin A, the dimer of inhibin βA subunit, acts strongly anti-proliferative in hepatocytes. Little is known on the other activin/inhibin subunits in human liver and hepatocellular carcinoma (HCC).

Methods:

We studied the expression of the complete inhibin family α, βA, βB, βC, βE in normal liver, tumour-adjacent and HCC tissue, 12 additional organs and rodent liver. A total of 16 HCC and 10 disease-free livers were analysed. Expression of inhibin subunits was determined by qRT–PCR, normalised to RNA input and by geNorm algorithm, and confirmed by immunohistochemistry.

Results:

Remarkably, βA expression was not decreased in HCC. Similarly, βC and βE exhibited no major changes. In contrast, inhibin α, barely detectable in normal liver, was strongly increased in tumour-adjacent liver and dramatically enhanced in HCC. βB was strongly enhanced in some HCC. At variance with human liver, rodent liver showed higher inhibin α and βC expression, but βA was somewhat, and βB dramatically lower.

Conclusions:

Upregulation of inhibin α – and possibly of βB – may shield HCC cells from anti-proliferative effects of activin A. Dramatic variations between humans and rodents may reflect different functions of some inhibins/activins.

Activin A, p15INK4b signaling, and cell competition promote stem/progenitor cell repopulation of livers in aging rats

BACKGROUND & AIMS

Highly proliferative fetal liver stem/progenitor cells (FLSPCs) repopulate livers of normal recipients by cell competition. We investigated the mechanisms by which FLSPCs repopulate livers of older compared with younger rats.

METHODS

Fetal liver cells were transplanted from DPPIV(+) F344 rats into DPPIV(-) rats of different ages (2, 6, 14, or 18 months); liver tissues were analyzed 6 months later. Cultured cells and liver tissues were analyzed by reverse transcription polymerase chain reaction, immunoblot, histochemistry, laser-capture microscopy, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling analyses.

RESULTS

We observed 4- to 5-fold increases in liver repopulation when FLSPCs were transplanted into older compared with younger rats. Messenger RNA levels of cyclin-dependent kinase inhibitors increased progressively in livers of older rats; hepatocytes from 20-month-old rats had 6.1-fold higher expression of p15INK4b and were less proliferative in vitro than hepatocytes from 2-month-old rats. Expression of p15INK4b in cultured hepatocytes was up-regulated by activin A, which increased in liver during aging. Activin A inhibited proliferation of adult hepatocytes, whereas FLSPCs were unresponsive because they had reduced expression of activin receptors (eg, ALK-4). In vivo, expanding cell clusters derived from transplanted FLSPCs had lower levels of ALK-4 and p15INK4b and increased levels of Ki-67 compared with the host parenchyma. Liver tissue of older rats had 3-fold more apoptotic cells than that of younger rats.

CONCLUSIONS

FLSPCs, resistant to activin A signaling, repopulate livers of older rats; hepatocytes in older rats have less proliferation because of increased activin A and p15INK4b levels and increased apoptosis than younger rats. These factors and cell types might be manipulated to improve liver cell transplantation strategies in patients with liver diseases in which activin A levels are increased.

Down-regulation of miR-23b may contribute to activation of the TGF-β1/Smad3 signalling pathway during the termination stage of liver regeneration

MicroRNAs (miRNAs) are known to play important roles in liver regeneration, although the role of miRNAs associated with the termination of liver regeneration is not as well studied. Here we reported the down-regulation of miR-23b in the termination stage of liver regeneration in rats. In addition, Smad3 was identified as a target of miR-23b during liver regeneration. Up-regulation of miR-23b promoted BRL-3A cell proliferation and partially inhibited transforming growth factor (TGF)-β1-induced apoptosis. Furthermore, TGF-β1 transcriptionally inhibited miR-23b expression. We conclude that down-regulation of miR-23b may contribute to activation of the TGF-β1/Smad3 signalling pathway during the termination stage of liver regeneration.

Activins and follistatins: Emerging roles in liver physiology and cancer

Activins are secreted proteins belonging to the TGF-β family of signaling molecules. Activin signals are crucial for differentiation and regulation of cell proliferation and apoptosis in multiple tissues. Signal transduction by activins relies mainly on the Smad pathway, although the importance of crosstalk with additional pathways is increasingly being recognized. Activin signals are kept in balance by antagonists at multiple levels of the signaling cascade. Among these, follistatin and FLRG, two members of the emerging family of follistatin-like proteins, can bind secreted activins with high affinity, thereby blocking their access to cell surface-anchored activin receptors. In the liver, activin A is a major negative regulator of hepatocyte proliferation and can induce apoptosis. The functions of other activins expressed by hepatocytes have yet to be more clearly defined. Deregulated expression of activins and follistatin has been implicated in hepatic diseases including inflammation, fibrosis, liver failure and primary cancer. In particular, increased follistatin levels have been found in the circulation and in the tumor tissue of patients suffering from hepatocellular carcinoma as well as in animal models of liver cancer. It has been argued that up-regulation of follistatin protects neoplastic hepatocytes from activin-mediated growth inhibition and apoptosis. The use of follistatin as biomarker for liver tumor development is impeded, however, due to the presence of elevated follistatin levels already during preceding stages of liver disease. The current article summarizes our evolving understanding of the multi-faceted activities of activins and follistatins in liver physiology and cancer.

Identification of proteomic changes during human liver development by 2D-DIGE and mass spectrometry

BACKGROUND/AIMS

The aim of this study was to identify human liver proteins that are associated with different stages of liver development.

METHODS

We collected liver samples from 14 fetuses between 14 and 41 weeks of development, one child and four adults. Proteins which exhibited consistent and significant variations during development by two-dimensional differential in gel electrophoresis (2D-DIGE) were subjected to peptide mass fingerprint analysis by MALDI-TOF mass spectrometry. Real-time PCR analysis confirmed, at the transcriptional level, the data obtained by the proteomic approach.

RESULTS

Among a total of 80 protein spots showing differential expression, we identified 42 different proteins or polypeptide chains, of which 26 were upregulated and 16 downregulated in developing in comparison to adult liver. These proteins could be classified in specific groups according to their function. By comparing their temporal expression profiles, we identified protein groups that were associated with different developmental stages of human fetal liver and suggest that the changes in protein expression observed during the 20- to 36-week time window play a pivotal role in liver development.

CONCLUSIONS

The identification of these proteins may represent good markers of human liver and stem cells differentiation.

Upregulated INHBA expression may promote cell proliferation and is associated with poor survival in lung adenocarcinoma

INTRODUCTION

The expression, mechanisms of regulation, and functional impact of INHBA (activin A) in lung adenocarcinoma (AD) have not been fully elucidated.

METHODS

INHBA expression was examined in 96 lung samples (86 ADs, 10 normal lung) using oligonucleotide microarrays and 187 lung samples (164 ADs, 6 bronchioalveolar carcinomas, and 17 normal lung) using immunohistochemistry. The proliferation of AD cell lines H460 and SKLU1 was examined with WST-1 assays after treatment with recombinant activin A, follistatin, and INHBA-targeting small-interfering RNA. Cells were also treated with 5-aza-2' deoxycytidine and trichostatin A to investigate the role of epigenetic regulation in INHBA expression.

RESULTS

Primary ADs expressed 3.1 times more INHBA mRNA than normal lung. In stage I AD patients, high levels of primary tumor INHBA transcripts were associated with worse prognosis. Immunohistochemistry confirmed higher inhibin betaA protein expression in ADs (78.7%) and bronchioalveolar carcinomas (66.7%) compared with normal lung (11.8%). H460 and SKLU1 demonstrated increased proliferation when treated with exogenous activin A and reduced proliferation when treated with follistatin or INHBA-targeting small-interfering RNA. INHBA mRNA expression in H460 cells was upregulated after treatment with trichostatin A and 5-aza-2' deoxycytidine.

CONCLUSIONS

INHBA is overexpressed in AD relative to controls. Inhibin betaA may promote cell proliferation, and its overexpression is associated with worse survival in stage I AD patients. In addition, overexpression of INHBA may be affected by promoter methylation and histone acetylation in a subset of lung ADs.

Identification of differentially expressed genes during proliferative response of the liver induced by follistatin

The liver mass is controlled strictly and maintained constant in normal and pathological situations. An exception is observed after an administration of follistatin, which induces proliferation in intact liver. In the present study, we identified genes differentially expressed in proliferating liver caused by overexpression of follistatin-288. Adenovirus vector encoding follistatin-288 (Ad-FS) or green fluorescent protein was injected intraperitoneally in rats. Changes in the liver weight, expression of follistatin and nuclear bromodeoxyuridine labeling were measured. Samples taken on day 5 and day 7 were used to prepare RNA for microarray analysis. The expression of the genes was confirmed by quantitative reverse transcriptase PCR. After the injection of Ad-FS follistatin mRNA peaked on day 3, which was followed by progressive increase in the protein expression. A peak in bromodeoxyuridine labeling was observed on day 7. Microarray data from day 5 and day 7 samples showed that follistatin modified the expression of 907 genes, of which 575 were overexpressed and 332 were downregulated taking into consideration a two fold change reference compared to control rats. In particular, significant increases and time related changes in gene expression after the Ad-FS injection were found in nine genes including growth differentiation factor 15 and fibroblast growth factor 21. This study confirmed that follistatin induced proliferation in intact liver, and identified candidate genes involved in follistatin-induced liver cell growth.

Activin, TGF-beta and menin in pituitary tumorigenesis

Pituitary adenomas are common monoclonal neoplasms accounting for approximately one-fifth of primary intracranial tumors. Prolactin-secreting pituitary adenomas (prolactinomas) are the most common form of pituitary tumors in humans. They are associated with excessive release of the hormone prolactin and increased tumor growth, giving rise to severe endocrine disorders and serious clinical concerns for the patients. Recent studies indicated that the activin/TGF-beta family of growth factors plays a prominent role in regulating pituitary tumor growth and prolactin secretion from anterior pituitary lactotrope cells. Furthermore, these studies highlighted the tumor suppressor menin and the protein Smads as central regulators of these biological processes in the pituitary. Alterations in the activin/TGF-beta downstream signaling pathways are critical steps towards tumor formation and progression. This chapter will review the role and intracellular molecular mechanisms of action by which activin, TGF-beta, Smads and menin act in concert to prevent pituitary tumor cell growth and control hormonal synthesis by the anterior pituitary.

Activin C antagonizes activin A in vitro and overexpression leads to pathologies in vivo

Activin A is a potent growth and differentiation factor whose synthesis and bioactivity are tightly regulated. Both follistatin binding and inhibin subunit heterodimerization block access to the activin receptor and/or receptor activation. We postulated that the activin-beta(C) subunit provides another mechanism regulating activin bioactivity. To test our hypothesis, we examined the biological effects of activin C and produced mice that overexpress activin-beta(C). Activin C reduced activin A bioactivity in vitro; in LNCaP cells, activin C abrogated both activin A-induced Smad signaling and growth inhibition, and in LbetaT2 cells, activin C antagonized activin A-mediated activity of an follicle-stimulating hormone-beta promoter. Transgenic mice that overexpress activin-betaC exhibited disease in testis, liver, and prostate. Male infertility was caused by both reduced sperm production and impaired sperm motility. The livers of the transgenic mice were enlarged because of an imbalance between hepatocyte proliferation and apoptosis. Transgenic prostates showed evidence of hypertrophy and epithelial cell hyperplasia. Additionally, there was decreased evidence of nuclear Smad-2 localization in the testis, liver, and prostate, indicating that overexpression of activin-beta(C) antagonized Smad signaling in vivo. Underlying the significance of these findings, human testis, liver, and prostate cancers expressed increased activin-betaC immunoreactivity. This study provides evidence that activin-beta(C) is an antagonist of activin A and supplies an impetus to examine its role in development and disease.

Advances in research of activins C and E

Activins, which consist of two disulfide-linked β subunits, are members of the transforming growth factor β (TGF-β) superfamily of growth factors. Four mammalian activin β subunits, termed as βA, βB, βC, and βE respectively, have been identified. Activin A, the homodimer of two βA subunits, is a pleiotropic cytokine and is expressed in many tissues and cells. There has been compelling evidence that activin A is involved in the regulation of reproductive biology, embryonic development, erythroid differentiation, systemic inflammation, induced apoptosis, tissue repair, fibrogenesis and so on, through classic activin signaling pathway. βC and βE subunits, which are almost exclusively expressed in the liver, are still quite incompletely understood. In this review, we summarize and discuss the function of βC and βE subunits in liver. Further research should be made to understand the biological role of the βC and βE subunits.

Liver regeneration and tumor stimulation--a review of cytokine and angiogenic factors

Liver resection for metastatic (colorectal carcinoma) tumors is often followed by a significant incidence of tumor recurrence. Cellular and molecular changes resulting from hepatectomy and the subsequent liver regeneration process may influence the kinetics of tumor growth and contribute to recurrence. Clinical and experimental evidence suggests that factors involved in liver regeneration may also stimulate the growth of occult tumors and the reactivation of dormant micrometastases. An understanding of the underlying changes may enable alternative strategies to minimize tumor recurrence and improve patient survival after hepatectomy.

Liver regeneration and tumor stimulation--a review of cytokine and angiogenic factors

Liver resection for metastatic (colorectal carcinoma) tumors is often followed by a significant incidence of tumor recurrence. Cellular and molecular changes resulting from hepatectomy and the subsequent liver regeneration process may influence the kinetics of tumor growth and contribute to recurrence. Clinical and experimental evidence suggests that factors involved in liver regeneration may also stimulate the growth of occult tumors and the reactivation of dormant micrometastases. An understanding of the underlying changes may enable alternative strategies to minimize tumor recurrence and improve patient survival after hepatectomy.

Activins and activin antagonists in hepatocellular carcinoma

In many parts of the world hepatocellular carcinoma (HCC) is among the leading causes of cancer-related mortality but the underlying molecular pathology is still insufficiently understood. There is increasing evidence that activins, which are members of the transforming growth factor β (TGFβ) superfamily of growth and differentiation factors, could play important roles in liver carcinogenesis. Activins are disulphide-linked homo- or heterodimers formed from four different β subunits termed βA, βB, βC, and βE, respectively. Activin A, the dimer of two βA subunits, is critically involved in the regulation of cell growth, apoptosis, and tissue architecture in the liver, while the hepatic function of other activins is largely unexplored so far. Negative regulators of activin signals include antagonists in the extracellular space like the binding proteins follistatin and FLRG, and at the cell membrane antagonistic co-receptors like Cripto or BAMBI. Additionally, in the intracellular space inhibitory Smads can modulate and control activin activity. Accumulating data suggest that deregulation of activin signals contributes to pathologic conditions such as chronic inflammation, fibrosis and development of cancer. The current article reviews the alterations in components of the activin signaling pathway that have been observed in HCC and discusses their potential significance for liver tumorigenesis.

Homogeneous differentiation of hepatocyte-like cells from embryonic stem cells: applications for the treatment of liver failure

One of the major hurdles of cellular therapies for the treatment of liver failure is the low availability of functional human hepatocytes. While embryonic stem (ES) cells represent a potential cell source for therapy, current methods for differentiation result in mixed cell populations or low yields of the cells of interest. Here we describe a rapid, direct differentiation method that yields a homogeneous population of endoderm-like cells with 95% purity. Mouse ES cells cultured on top of collagen-sandwiched hepatocytes differentiated and proliferated into a uniform and homogeneous cell population of endoderm-like cells. The endoderm-like cell population was positive for Foxa2, Sox17, and AFP and could be further differentiated into hepatocyte-like cells, demonstrating hepatic morphology, functionality, and gene and protein expression. Incorporating the hepatocyte-like cells into a bioartificial liver device to treat fulminant hepatic failure improved animal survival, thereby underscoring the therapeutic potential of these cells.

Microarray analysis of gene expression of mouse hepatocytes of different ploidy

Polyploidisation in hepatocytes has been associated with many physiologic and pathologic processes such as proliferation, metabolism, regeneration, aging, and cancer. We studied gene expression patterns in hepatocytes of different ploidy. Primary hepatocytes were obtained from mice of different ages: young (4-6 weeks old), adult (8-10 weeks old), and older (22-24 weeks old). Diploid (2N), tetraploid (4N), and octoploid (8N) hepatocytes were isolated for studies using a high-density mouse genome microarray. No major changes of gene expression patterns between hepatocytes of different ploidy were found. Fifty genes were identified as differentially expressed in the diploid and tetraploid populations, but the changes were less than twofold either way. Four genes (Gas2, Igfbp2, Nr1i3, and Ccne2) were differentially expressed in tetraploid and octoploid cells. This was confirmed in two age groups, "adult" and "older," but once again the factors were less than twofold and the expressions of Gas2 and Igfbp2 were more different between age groups than between ploidy classes. Our results show that polyploid hepatocytes are stable and "normal" without aberrant gene expression, unlike what is thought for cancer cells. By contrast to megakaryocytes, hepatocyte polyploidisation is not a differentiation step associated with major changes in gene expression. Our data support the hypothesis that hepatocyte polyploidisation is a protective mechanism against oxidative stress that occurs via a controlled process throughout growth and aging where binucleation is important.

Deregulation of the activin/follistatin system in hepatocarcinogenesis

BACKGROUND/AIMS

Activins A and E negatively regulate hepatic cell number by inhibiting cell replication and inducing apoptosis. Follistatin and follistatin-like 3 bind activins and antagonise their biological activities. Aim of our study was to investigate, whether activins and follistatins may play a role in hepatocarcinogenesis.

METHODS

Expression levels of follistatin, follistatin-like 3, and activin subunits beta(A) as well as beta(E) were investigated in chemically induced rat and human liver tumours by real-time PCR and immunohistochemistry. In addition, the effects of follistatin and activin A on DNA synthesis of normal as well as preneoplastic hepatocytes and hepatoma cells were analysed.

RESULTS

Follistatin was overexpressed while both activin subunits were downregulated in the majority of rat and human liver tumours. Follistatin-like 3 expression was low in normal but enhanced in malignant rat liver. In human normal liver, in contrast, it was abundantly expressed but downregulated in liver cancer. Administration of follistatin to normal and preneoplastic hepatocytes stimulated DNA synthesis preferentially in preneoplastic rat hepatocytes, whereas activin A repressed it.

CONCLUSIONS

The balanced expression of follistatins and activins becomes deregulated during hepatocarcinogenesis. The sensitivity of preneoplastic hepatocytes to activin signals suggests the activin/follistatin system as promising target for therapeutic intervention.