Activity and expression of ecto-5'-nucleotidase/CD73 are increased during phenotype conversion of a hepatic stellate cell line

Mesenchymal "stem" cells, or facilitators for the development of regenerative macrophages? Pericytes at the interface of wound healing

Cultured mesenchymal stromal cells are among the most used cells in clinical trials. Currently, their potential benefits include provision of mature cell types through differentiation, and secretion of various types of paracrine signaling molecules. Even though research on these cells has spanned some decades now, surprisingly, their therapeutic potential has not been fully translated into clinical practice yet, which calls for further understanding of their intrinsic nature and modes of action. In this review, after discussing pieces of evidence that suggest that some perivascular cells may exhibit mesenchymal stem cell characteristics in vivo, we examine the possibility that subpopulations of perivascular and/or adventitial cells activated after tissue injury behave as MSCs and contribute to the resolution of tissue injury by providing cues for the development of regenerative macrophages at injured sites. Under this perspective, an important contribution of cultured MSCs (or their acellular products, such as extracellular vesicles) used in cell therapies would be to instigate the development of M2-like macrophages that support the tissue repair process.

TNAP is a novel regulator of cardiac fibrosis after myocardial infarction by mediating TGF-β/Smads and ERK1/2 signaling pathways

BACKGROUND

Cardiac fibrosis is the most important pathogenesis leading to cardiac remodeling and heart failure after myocardial infarction (MI). Tissue nonspecific alkaline phosphatase (TNAP) has recently been recognized as a potential prognostic factor for MI. Nevertheless, the role of TNAP in cardiac fibrosis after MI has not been explicitly delineated.

METHODS

A systematic review and meta-analysis was conducted to assess the effect of serum TNAP levels on mortality in patients with ischemic heart disease (IHD). A correlation analysis was performed to investigate the relationship between serum levels of TNAP and biomarkers of fibrosis. Heart biopsies from patients with MI and a mouse model of MI were used to detect the expression and distribution of TNAP. Furthermore, we established adenovirus-mediated knockdown and overexpression of TNAP, using a combination of in vivo and in vitro studies in mice, to determine the role and mechanism of TNAP in cardiac fibrosis after MI. In the in vitro studies, cardiac fibroblasts were cultured on soft plates.

FINDINGS

After searching the main databases and performing a detailed assessment of the full-text articles, eight studies with 14,816 individuals were included in the quantitative analysis. We found that a high serum TNAP level was associated with an increased risk of mortality in patients with IHD and MI. The correlation analysis revealed a positive correlation between serum TNAP levels and the concentration of fibrosis biomarkers (PICP/PIIINP). The expression of TNAP was upregulated in the myocardium of patients with MI and in a mouse model of MI, accompanied by fibroblast activation and the deposition of collagen fibers. In the in vivo study, TNAP knockdown ameliorated cardiac fibrosis and improved cardiac function in mice. TNAP overexpression aggravated cardiac fibrosis and worsened cardiac function. In the in vitro study, TNAP promoted cardiac fibroblast differentiation, migration and proliferation. Mechanistically, the pro-fibrotic effect of TNAP on cardiac fibroblasts was at least partially achieved by activating the TGF-β1/Smads and ERK1/2 signaling pathways.

INTERPRETATION

Based on these findings, TNAP plays an important pro-fibrotic role in cardiac fibrosis after MI by activating TGF-β/Smads and ERK1/2 signaling, indicating that it functions as a potential regulator of and therapeutic target in cardiac fibrosis.

FUNDING

This work was supported by the National Natural Science Foundation of China.

Purinergic Signaling in Liver Pathophysiology

Extracellular nucleosides and nucleotides activate a group of G protein-coupled receptors (GPCRs) known as purinergic receptors, comprising adenosine and P2Y receptors. Furthermore, purinergic P2X ion channels are activated by ATP. These receptors are expressed in liver resident cells and play a critical role in maintaining liver function. In the normal physiology, these receptors regulate hepatic metabolic processes such as insulin responsiveness, glycogen and lipid metabolism, and bile secretion. In disease states, ATP and other nucleotides serve as danger signals and modulate purinergic responses in the cells. Recent studies have demonstrated that purinergic receptors play a significant role in the development of metabolic syndrome associated non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), fibrosis, hepatocellular carcinoma (HCC) and liver inflammation. In this concise review, we dissect the role of purinergic signaling in different liver resident cells involved in maintaining healthy liver function and in the development of the above-mentioned liver pathologies. Moreover, we discuss potential therapeutic strategies for liver diseases by targeting adenosine, P2Y and P2X receptors.

Formation and Developmental Specification of the Odontogenic and Osteogenic Mesenchymes

Within the mandible, the odontogenic and osteogenic mesenchymes develop in a close proximity and form at about the same time. They both originate from the cranial neural crest. These two condensing ecto-mesenchymes are soon separated from each other by a very loose interstitial mesenchyme, whose cells do not express markers suggesting a neural crest origin. The two condensations give rise to mineralized tissues while the loose interstitial mesenchyme, remains as a soft tissue. This is crucial for proper anchorage of mammalian teeth. The situation in all three regions of the mesenchyme was compared with regard to cell heterogeneity. As the development progresses, the early phenotypic differences and the complexity in cell heterogeneity increases. The differences reported here and their evolution during development progressively specifies each of the three compartments. The aim of this review was to discuss the mechanisms underlying condensation in both the odontogenic and osteogenic compartments as well as the progressive differentiation of all three mesenchymes during development. Very early, they show physical and structural differences including cell density, shape and organization as well as the secretion of three distinct matrices, two of which will mineralize. Based on these data, this review highlights the consecutive differences in cell-cell and cell-matrix interactions, which support the cohesion as well as mechanosensing and mechanotransduction. These are involved in the conversion of mechanical energy into biochemical signals, cytoskeletal rearrangements cell differentiation, or collective cell behavior.

The role of the CD39-CD73-adenosine pathway in liver disease

Extracellular adenosine triphosphate (ATP) is a danger signal released by dying and damaged cells, and it functions as an immunostimulatory signal that promotes inflammation. The ectonucleotidases CD39/ectonucleoside triphosphate diphosphohydrolase-1 and CD73/ecto-5'-nucleotidase are cell-surface enzymes that breakdown extracellular ATP into adenosine. This drives a shift from an ATP-driven proinflammatory environment to an anti-inflammatory milieu induced by adenosine. The CD39-CD73-adenosine pathway changes dynamically with the pathophysiological context in which it is embedded. Accumulating evidence suggests that CD39 and CD73 play important roles in liver disease as critical components of the extracellular adenosinergic pathway. Recent studies have shown that the modification of the CD39-CD73-adenosine pathway alters the liver's response to injury. Moreover, adenosine exerts different effects on the pathophysiology of the liver through different receptors. In this review, we aim to describe the role of the CD39-CD73-adenosine pathway and adenosine receptors in liver disease, highlighting potential therapeutic targets in this pathway, which will facilitate the development of therapeutic strategies for the treatment of liver disease.

An Elf2-like transcription factor acts as repressor of the mouse ecto-5'-nucleotidase gene expression in hepatic myofibroblasts

Hepatic fibrosis represents a pathological wound healing and tissue repair process triggered in response to chronic liver injury. A heterogeneous population of activated non-parenchymal liver cells, known as liver myofibroblasts, functions as the effector cells in hepatic fibrosis. Upon activation, liver myofibroblasts become fibrogenic, acquiring contractile properties and increasing collagen production capacity, while developing enhanced sensitivity to endogenous molecules and factors released in the local microenvironment. Hepatic extracellular adenosine is a bioactive small molecule, increasingly recognized as an important regulator of liver myofibroblast functions, and an important mediator in the pathogenesis of liver fibrosis overall. Remarkably, ecto-5'-nucleotidase/Nt5e/Cd73 enzyme, which accounts for the dominant adenosine-generating activity in the extracellular medium, is expressed by activated liver myofibroblasts. However, the molecular signals regulating Nt5e gene expression in liver myofibroblasts remain poorly understood. Here, we show that activated mouse liver myofibroblasts express Nt5e gene products and characterize the putative Nt5e minimal promoter in the mouse species. We describe the existence of an enhancer sequence upstream of the mouse Nt5e minimal promoter and establish that the mouse Nt5e minimal promoter transcriptional activity is negatively regulated by an Elf2-like Ets-related transcription factor in activated mouse liver myofibroblasts.

Modulation of hepatic stellate cells and reversibility of hepatic fibrosis

Hepatic fibrosis (HF) is the pathological component of a variety of chronic liver diseases. Hepatic stellate cells (HSC) are the main collagen-producing cells in the liver and their activation promotes HF. If HSC activation and proliferation can be inhibited, HF occurrence and development can theoretically be reduced and even reversed. Over the past ten years, a number of studies have addressed this process, and here we present a review of HSC modulation and HF reversal.

Purinergic signalling in the liver in health and disease

Purinergic signalling is involved in both the physiology and pathophysiology of the liver. Hepatocytes, Kupffer cells, vascular endothelial cells and smooth muscle cells, stellate cells and cholangiocytes all express purinoceptor subtypes activated by adenosine, adenosine 5'-triphosphate, adenosine diphosphate, uridine 5'-triphosphate or UDP. Purinoceptors mediate bile secretion, glycogen and lipid metabolism and indirectly release of insulin. Mechanical stress results in release of ATP from hepatocytes and Kupffer cells and ATP is also released as a cotransmitter with noradrenaline from sympathetic nerves supplying the liver. Ecto-nucleotidases play important roles in the signalling process. Changes in purinergic signalling occur in vascular injury, inflammation, insulin resistance, hepatic fibrosis, cirrhosis, diabetes, hepatitis, liver regeneration following injury or transplantation and cancer. Purinergic therapeutic strategies for the treatment of these pathologies are being explored.

Platelet-derived adenosine 5'-triphosphate suppresses activation of human hepatic stellate cell: In vitro study

AIM

  Activated hepatic stellate cells (HSC) play a critical role in liver fibrosis. Suppressing abnormal function of HSC or reversion from activated to quiescent form is a hopeful treatment for liver cirrhosis. The interaction between platelets and HSC remains unknown although platelets go through hepatic sinusoids surrounded by HSC. This study aimed at clarifying the hypothesis that platelets control activation of HSC.

METHODS

  We used human platelets, platelet extracts, and primary or immortalized human HSC. We examined the effect of platelets on the activation, DNA synthesis, type I collagen production, and fibrosis-relating gene expressions of HSC. We investigated what suppressed activation of HSC within platelets and examined the mechanism of controlling activation in vitro.

RESULTS

  Platelets and platelet extracts suppressed activation of HSC. Platelets decreased type I collagen production without affecting DNA synthesis. Platelets increased the expression of matrix metallopeptidase 1. As platelet extracts co-cultured with an enzyme of degrading adenosine 5'-triphosphate (ATP) suppressed activation, we detected adenine nucleotides within platelets or on their surfaces and confirmed the degradation of adenine nucleotides by HSC and the production of adenosine. Adenosine and platelets increased the intracellular cyclic adenosine 5'-monophosphate (cAMP), which is important in quiescent HSC. A great amount of adenosine and ATP also suppressed activation of HSC.

CONCLUSION

  Activation of human HSC is suppressed by human platelets or platelet-derived ATP via adenosine-cAMP signaling pathway in vitro. Therefore, platelets have the possibility to be used in the treatment of liver cirrhosis.

Ecto-5'-nucleotidase/CD73 knockdown increases cell migration and mRNA level of collagen I in a hepatic stellate cell line

Ecto-5'-nucleotidase (eNT/CD73, E.C.3.1.3.5) is a glycosyl phosphatidylinositol (GPI)-linked cell-surface protein with several functions, including the local generation of adenosine from AMP, with the consequent activation of adenosine receptors and the salvaging of extracellular nucleotides. It also apparently functions independently of this activity, e.g., in the mediation of cell-cell adhesion. Liver fibrosis can be considered as a dynamic and integrated cellular response to chronic liver injury and the activation of hepatic stellate cells (HSCs) plays a role in the fibrogenic process. eNT/CD73 and adenosine are reported to play an important role in hepatic fibrosis in murine models. Knockdown of eNT/CD73 leads to an increase in mRNA expression of tissue non-specific alkaline phosphatase (TNALP), another AMP-degrading enzyme and thus no alteration is seen in the total ecto-AMPase activity of the cell. eNT/CD73 knockdown also leads to changes in the expression of collagen I and a clear alteration of cell migration. We suggest that eNT/CD73 protein expression controls cell migration and collagen expression in a mechanism independent of changes in nucleotide metabolism.

Acute ethanol exposure disrupts actin cytoskeleton and generates reactive oxygen species in c6 cells

Central nervous system dysfunctions are among the most significant effects of exposure to ethanol and the glial cells that play an important role in maintaining neuronal function, are extremely involved with these effects. The actin cytoskeleton plays a crucial role in a wide variety of cellular functions, especially when there is some injury. Therefore the aim of the present study was to analyze the short-term effects of ethanol (50, 100 and 200 mM) on the cytoskeleton of C6 glioma cells. Here we report that acute ethanol exposure profoundly disrupts the actin cytoskeleton in C6 cells decreasing stress fiber formation and downregulating RhoA and vinculin immunocontent. In contrast, microtubule and GFAP networks were not altered. We further demonstrate that anti-oxidants prevent ethanol-induced actin alterations, suggesting that the actions of ethanol on the actin cytoskeleton are related with generation of reactive oxygen species (ROS) in these cells. Our results show that ethanol at concentrations described to be toxic to the central nervous system was able to target the cytoskeleton of C6 cells and this effect could be related with increased ROS generation. Therefore, we propose that the dynamic restructuring of the cytoskeleton of glial cells might contribute to the response to the injury provoked by binge-like ethanol exposure in brain.

Characterization of ATP-induced cell death in the GL261 mouse glioma

Gliomas have one of the worst prognosis among cancers. Their resistance to cell death induced by endogenous neurotoxic agents, such as extracellular ATP, seems to play an important role in their pathobiology since alterations in the degradation rate of extracellular ATP drastically affects glioma growth in rats. In the present work we characterized the mechanisms of cell death induced by extracellular ATP in a murine glioma cell line, GL261. ATP and BzATP, a P2X7 agonist, induced cell death at concentrations that are described to activate the P2X7 receptor in mouse. oATP, an antagonist of P2X7, blocked the ATP-induced cell death. Agonists of purinergic receptors expressed in GL261 such as adenosine, ADP, UTP did not cause any cell death, even at mM concentrations. A sub-population of cells more sensitive to ATP expressed more P2X7 when compared to a less sensitive subpopulation. Accordingly, RNA interference of the P2X7 receptor drastically reduced ATP-induced cell death, suggesting that this receptor is necessary for this effect. The mechanism of ATP-induced cell death is predominantly necrotic, since cells presented shrinkage accompanied by membrane permeabilization, but not apoptotic, since no phosphatidylserine externalization or caspase activity was observed. These data show the importance of P2X7 in ATP-induced cell death and shed light on the importance of ATP-induced cell death in glioma development.

Biochemical characterization of the binding of cyclic RGDyK to hepatic stellate cells

Activated hepatic stellate cells (HSCs) play a crucial role in the development of liver fibrosis. Noninvasive monitoring of the activation of HSCs has been challenging due to the lack of specific receptors or motifs on the cells. The present study provides the evidence that integrin alpha v beta 3 expressed on HSCs is a biomarker reflecting the activation of HSCs. Solid-phase synthesis of cRGDyK (Arg-Gly-Asp-(D)Tyr-Lys) peptide and FAM-conjugated peptide were employed for binding to integrin alpha v beta 3. The increased expression of integrin alpha v and beta 3 at mRNA and protein levels was detected during HSC activation. The affinity of cRGDyK to integrin alpha v beta 3 was examined by both radioligand binding assay and FAM-conjugated peptide binding measurements. Quantitative RT-PCR and Western blotting showed a less dramatic, but significant increase in alpha v and beta 3 integrin mRNA and protein expression following activation of rat HSCs. Radioiodinated cRGDyK binds to both purified and membrane-bound integrin alpha v beta 3 with high affinity in a dissociable manner. FAM-conjugated cRGDyK was coupled to activated HSCs in a time- and dose-dependent, receptor-mediated manner. Activated HSCs express sufficient number of integrin alpha v beta 3 receptor. cRGDyK peptide binds to both purified and membrane-bound integrin alpha v beta 3 with high affinity in a reversible fashion. Thus, the cRGDyK peptide represented a new agent potentially useful for the diagnosis of liver fibrosis.

Changes in E-NTPDase 3 expression and extracellular nucleotide hydrolysis during the myofibroblast/lipocyte differentiation

Hepatic stellate cells (HSC) play a critical role in the development and maintenance of liver fibrosis. HSC are lipocytes that displayed the capacity to develop into myofibroblast-like cells. Ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases) regulate the concentration of extracellular nucleotides, signaling molecules that play a role in the pathogenesis of hepatic fibrosis. In the present study, we identified and compared the expressions of E-NTPDase family members in two different phenotypes of the mouse hepatic stellate cell line (GRX) and evaluated the nucleotide hydrolysis by these cells. We show that both phenotypes of GRX cell line expressed NTPDase 3 and 5. However, only activated cells expressed NTPDase 6. In quiescent-like cells, the hydrolysis of triphosphonucleosides was significantly higher, and was related to an increase in Entpd3 mRNA expression. The diphosphonucleosides were hydrolyzed at a similar rate by two phenotypes of GRX cells. We suggest that up-regulation of Entpd3 mRNA expression modulates the extracellular concentration of nucleotides/nucleosides and affect P2-receptor signaling differently in quiescent-like cells and may play a role in the regulation of HSC functions.

A contradictory role of A1 adenosine receptor in carbon tetrachloride- and bile duct ligation-induced liver fibrosis in mice

Mice lacking A(1) adenosine receptors (A(1)AR) were thought to be protected from developing fatty liver; however, the contribution of A(1)AR to hepatic fibrosis has not been explored. Here we found that the expression of A(1)AR was decreased in fibrotic liver induced by chronic carbon tetrachloride (CCl(4)) but increased in that induced by bile duct ligation (BDL). Therefore, we examined whether A(1)AR contributes to hepatic fibrosis in CCl(4) and BDL animal models using A(1)AR knockout mice. Compared with wild-type (WT) mice, hepatic fibrosis resulting from chronic CCl(4) exposure was attenuated in A(1)AR(-/-) mice with markedly decreased collagen deposition and reduced hepatic stellate cell activation, whereas bile duct-ligated A(1)AR(-/-) mice displayed a significant increase in hepatic fibrosis. Hepatocyte damage was reduced in A(1)AR(-/-) mice after a single injection of CCl(4), with down-regulation of CYP2E1 and UCP2 gene expression in livers, which resulted in impaired liver sensitivity to CCl(4). However, BDL caused severe bile infarcts in livers of A(1)AR(-/-) mice, with significantly elevated levels of bile acid compared with those in WT mice. CCl(4) and BDL resulted in different expression patterns of genes involved in fibrogenesis in A(1)AR(-/-) mice. These results indicate that A(1)AR participates in the pathogenesis of hepatic fibrosis with a complex mechanism, and the effect of targeting adenosine and its receptors in the prevention of hepatic fibrosis should be cautiously evaluated.

Activity and expression of ecto-nucleotide pyrophosphate/phosphodiesterases in a hepatic stellate cell line

Nucleotides and nucleosides represent an important and ubiquitous class of molecules that interact with specific receptors, regulate a variety of activities within the liver, and play a role in the pathogenesis of hepatic fibrosis. Ecto-nucleotide pyrophosphatase/phosphodiesterases (E-NPPs) are ecto-enzymes that are located on the cell surface. NPP1, NPP2, and NPP3 (abbreviated as NPP1-3 hereafter) have been implicated in the hydrolysis of nucleotides; together with other ecto-nucleotidases, they control the events induced by extracellular nucleotides. We have identified and compared the expression of E-NPP family members in two different phenotypes of the mouse hepatic stellate cell line (GRX). In quiescent-like hepatic stellate cells (HSCs), E-NPP activity was significantly higher, NPP2 mRNA expression decreased and NPP3 mRNA increased. The differential NPP activity and expression in two phenotypes of GRX cells suggests that they are involved in the regulation of extracellular nucleotide metabolism in HSCs. However, the role of E-NPPs in the liver remains to be clarified.