TGF-beta1 modulates matrix metalloproteinase-13 expression in hepatic stellate cells by complex mechanisms involving p38MAPK, PI3-kinase, AKT, and p70S6k

Association between single nucleotide polymorphisms, TGF-β1 promoter methylation, and polycystic ovary syndrome

BACKGROUND

Polycystic ovarian syndrome (PCOS) is a common endocrine and metabolic disease in women. Hyperandrogenaemia (HA) and insulin resistance (IR) are the basic pathophysiological characteristics of PCOS. The aetiology of PCOS has not been fully identified and is generally believed to be related to the combined effects of genetic, metabolic, internal, and external factors. Current studies have not screened for PCOS susceptibility genes in a large population. Here, we aimed to study the effect of TGF-β1 methylation on the clinical PCOS phenotype.

METHODS

In this study, three generations of family members with PCOS with IR as the main characteristic were selected as research subjects. Through whole exome sequencing and bioinformatic analysis, TGF-β1 was screened as the PCOS susceptibility gene in this family. The epigenetic DNA methylation level of TGF-β1 in peripheral blood was detected by heavy sulfite sequencing in patients with PCOS clinically characterised by IR, and the correlation between the DNA methylation level of the TGF-β1 gene and IR was analysed. We explored whether the degree of methylation of this gene affects IR and whether it participates in the occurrence and development of PCOS.

RESULTS

The results of this study suggest that the hypomethylation of the CpG4 and CpG7 sites in the TGF-β1 gene promoter may be involved in the pathogenesis of PCOS IR by affecting the expression of the TGF-β1 gene.

CONCLUSIONS

This study provides new insights into the aetiology and pathogenesis of PCOS.

Down-Regulation of CXXC5 De-Represses MYCL1 to Promote Hepatic Stellate Cell Activation

Liver fibrosis is mediated by myofibroblasts, a specialized cell type involved in wound healing and extracellular matrix production. Hepatic stellate cells (HSC) are the major source of myofibroblasts in the fibrotic livers. In the present study we investigated the involvement of CXXC-type zinc-finger protein 5 (CXXC5) in HSC activation and the underlying mechanism. Down-regulation of CXXC5 was observed in activated HSCs compared to quiescent HSCs both in vivo and in vitro. In accordance, over-expression of CXXC5 suppressed HSC activation. RNA-seq analysis revealed that CXXC5 influenced multiple signaling pathways to regulate HSC activation. The proto-oncogene MYCL1 was identified as a novel target for CXXC5. CXXC5 bound to the proximal MYCL1 promoter to repress MYCL1 transcription in quiescent HSCs. Loss of CXXC5 expression during HSC activation led to the removal of CpG methylation and acquisition of acetylated histone H3K9/H3K27 on the MYCL1 promoter resulting in MYCL1 trans-activation. Finally, MYCL1 knockdown attenuated HSC activation whereas MYCL1 over-expression partially relieved the blockade of HSC activation by CXXC5. In conclusion, our data unveil a novel transcriptional mechanism contributing to HSC activation and liver fibrosis.

TGF beta -1, -2 and -3 in the modulation of fibrosis in the cornea and other organs

The TGF beta-1, -2 and -3 isoforms are transcribed from different genes but bind to the same receptors and signal through the same canonical and non-canonical signal transduction pathways. There are numerous regulatory mechanisms controlling the action of each isoform that include the organ-specific cells producing latent TGF beta growth factors, multiple effectors that activate the isoforms, ECM-associated SLRPs and basement membrane components that modulate the activity and localization of the isoforms, other interactive cytokine-growth factor receptor systems, such as PDGF and CTGF, TGF beta receptor expression on target cells, including myofibroblast precursors, receptor binding competition, positive and negative signal transduction effectors, and transcription and translational regulatory mechanisms. While there has long been the view that TGF beta-1and TGF beta-2 are pro-fibrotic, while TGF beta-3 is anti-fibrotic, this review suggests that view is too simplistic, at least in adult tissues, since TGF beta-3 shares far more similarities in its modulation of fibrotic gene expression with TGF beta-1 and TGF beta-2, than it does differences, and often the differences are subtle. Rather, TGF beta-3 should be seen as a fibro-modulatory partner to the other two isoforms that modulates a nuanced and better controlled response to injury. The complex interplay between the three isoforms and numerous interactive proteins, in the context of the cellular milieu, controls regenerative non-fibrotic vs. fibrotic healing in a response to injury in a particular organ, as well as the resolution of fibrosis, when that occurs.

Dual Pharmacological Targeting of HDACs and PDE5 Inhibits Liver Disease Progression in a Mouse Model of Biliary Inflammation and Fibrosis

Simple Summary

Chronic liver injury and inflammation leads to excessive deposition of extracellular matrix, known as liver fibrosis, and the distortion of the hepatic parenchyma. Liver fibrosis may progress to cirrhosis, a condition in which hepatic function is impaired and most cases of liver tumors occur. Currently, there are no effective therapies to inhibit and reverse the progression of liver fibrosis, and therefore, chronic liver disease remains a global health problem. In this study we have tested the efficacy of a new class of molecules that simultaneously target two molecular pathways known to be involved in the pathogenesis of hepatic fibrosis. In a clinically relevant mouse model of liver injury and inflammation we show that the combined inhibition of histones deacetylases and the cyclic guanosine monophosphate (cGMP) phosphodiesterase phosphodiesterase 5 (PDE5) results in potent anti-inflammatory and anti-fibrotic effects. Our findings open new avenues for the treatment of liver fibrosis and therefore, the prevention of hepatic carcinogenesis.

Abstract

Liver fibrosis, a common hallmark of chronic liver disease (CLD), is characterized by the accumulation of extracellular matrix secreted by activated hepatic fibroblasts and stellate cells (HSC). Fibrogenesis involves multiple cellular and molecular processes and is intimately linked to chronic hepatic inflammation. Importantly, it has been shown to promote the loss of liver function and liver carcinogenesis. No effective therapies for liver fibrosis are currently available. We examined the anti-fibrogenic potential of a new drug (CM414) that simultaneously inhibits histone deacetylases (HDACs), more precisely HDAC1, 2, and 3 (Class I) and HDAC6 (Class II) and stimulates the cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG) pathway activity through phosphodiesterase 5 (PDE5) inhibition, two mechanisms independently involved in liver fibrosis. To this end, we treated Mdr2-KO mice, a clinically relevant model of liver inflammation and fibrosis, with our dual HDAC/PDE5 inhibitor CM414. We observed a decrease in the expression of fibrogenic markers and collagen deposition, together with a marked reduction in inflammation. No signs of hepatic or systemic toxicity were recorded. Mechanistic studies in cultured human HSC and cholangiocytes (LX2 and H69 cell lines, respectively) demonstrated that CM414 inhibited pro-fibrogenic and inflammatory responses, including those triggered by transforming growth factor β (TGFβ). Our study supports the notion that simultaneous targeting of pro-inflammatory and fibrogenic mechanisms controlled by HDACs and PDE5 with a single molecule, such as CM414, can be a new disease-modifying strategy.

Targeting Follistatin like 1 ameliorates liver fibrosis induced by carbon tetrachloride through TGF-β1-miR29a in mice

Background

Hepatic fibrosis is a pathological response of the liver to a variety of chronic stimuli. Hepatic stellate cells (HSCs) are the major source of myofibroblasts in the liver. Follistatin like 1 (Fstl1) is a secreted glycoprotein induced by transforming growth factor-β1 (TGF-β1). However, the precise functions and regulation mechanisms of Fstl1 in liver fibrogenesis remains unclear.

Methods

Hepatic stellate cell (HSC) line LX-2 stimulated by TGF-β1, primary culture of mouse HSCs and a model of liver fibrosis induced by CCl4 in mice was used to assess the effect of Fstl1 in vitro and in vivo.

Results

Here, we found that Fstl1 was significantly up regulated in human and mouse fibrotic livers, as well as activated HSCs. Haplodeficiency of Fstl1 or blockage of Fstl1 with a neutralizing antibody 22B6 attenuated CCl₄-induced liver fibrosis in vivo. Fstl1 modulates TGF-β1 classic Samd2 and non-classic JNK signaling pathways. Knockdown of Fstl1 in HSCs significantly ameliorated cell activation, cell migration, chemokines C-C Motif Chemokine Ligand 2 (CCL2) and C-X-C Motif Chemokine Ligand 8 (CXCL8) secretion and extracellular matrix (ECM) production, and also modulated microRNA-29a (miR29a) expression. Furthermore, we identified that Fstl1 was a target gene of miR29a. And TGF-β1 induction of Fstl1 expression was partially through down regulation of miR29a in HSCs.

Conclusions

Our data suggests TGF-β1-miR29a-Fstl1 regulatory circuit plays a key role in regulation the HSC activation and ECM production, and targeting Fstl1 may be a strategy for the treatment of liver fibrosis.

Myricetin Possesses Anthelmintic Activity and Attenuates Hepatic Fibrosis via Modulating TGFβ1 and Akt Signaling and Shifting Th1/Th2 Balance in Schistosoma japonicum-Infected Mice

Schistosomiasis is a zoonotic and debilitating parasitic disease caused by Schistosoma japonicum. Praziquantel remains the choice for treating schistosomiasis, but its efficacy could be hampered by emergence of resistance. In this study, using large-scale drug screening, we selected out myricetin, a natural flavonol compound, having a good anti-schistosome effect. We found that myricetin exhibited dose and time-dependent insecticidal effect on S. japonicum in vitro, with an LC₅₀ of 600 μM for 24 h, and inhibited female spawning. The drug mainly destroyed the body structure of the worms and induced apoptosis of the worm cells, which in turn led to death. In addition, oral administration of myricetin in mice infected with S. japonicum showed a deworming effect in vivo, as evidenced by a significant reduction in the liver egg load. H&E staining, quantitative RT-PCR, and Western blotting assays showed that myricetin significantly alleviated liver fibrosis in mice infected with S. japonicum. Myricetin also effectively inhibited the expression of TGFβ1, Smad2, phospho-Smad2, Smad3, phospho-Smad3, ERK, phospho-ERK, Akt, and phospho-Akt in the liver of infected mice, suggesting that myricetin attenuated liver fibrosis in mice via modulating TGFβ1 and Akt signaling. Flow cytometric analysis of Th subtypes (Th1/Th2/Th17/Treg) in the mouse spleen further revealed that myricetin significantly increased the percentage Th1 cells in infected mice and reduced the proportion of Th2 cells and Th17 cells. Immunology multiplex assay further showed that myricetin attenuated S. japonicum-induced rise in the plasma levels of IL-4, IL-5, IL-10, IL-13, and IL-17A in infected mice while increasing the plasma contents of IFN-γ, IL-12, and IL-7. In conclusion, our study provides the first direct evidence that myricin possesses potent anti-schistosome activities in vitro and in vivo, and offers new insights into the mechanisms of action by myricetin. The present findings suggest that myricetin could be further explored as a therapeutic agent for S. japonicum.

Fluorofenidone affects hepatic stellate cell activation in hepatic fibrosis by targeting the TGF-β1/Smad and MAPK signaling pathways

The aim of the present research was to study the therapeutic impacts of fluorofenidone (AKF-PD) on pig serum (PS)-induced liver fibrosis in rats and the complex molecular mechanisms of its effects on hepatic stellate cells (HSCs). Wistar rats were randomly divided into normal control, PS and PS/AKF-PD treatment groups. The activated human HSC LX-2 cell line was also treated with AKF-PD. The expression of collagen I and III, and α-smooth muscle actin (α-SMA) was determined by immunohistochemical staining and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Western blotting and/or RT-qPCR analyses were used to determine the expression of transforming growth factor (TGF)-β1, α-SMA, collagen I, mothers against decapentaplegic homolog (Smad)-3, extracellular signal-regulated kinase (ERK)1/2, p38 mitogen-activated protein kinase (p38 MAPK) and c-Jun N-terminal kinase (JNK). AKF-PD attenuated the degree of hepatic fibrosis and liver injury in vivo, which was associated with the downregulation of collagen I and III, and α-SMA at the mRNA and protein levels. In vitro, AKF-PD treatment significantly reduced the TGF-β1-induced activation of HSCs, as determined by the reduction in collagen I and α-SMA protein expression. The TGF-β1-induced upregulation of the phosphorylation of Smad 3, ERK1/2, p38 and JNK was attenuated by AKF-PD treatment. These findings suggested that AKF-PD attenuated the progression of hepatic fibrosis by suppressing HSCs activation via the TGF-β1/Smad and MAPK signaling pathways, and therefore that AKF-PD may be suitable for use as a novel therapeutic agent against liver fibrosis.

Thymosin β4 inhibits PDGF-BB induced activation, proliferation, and migration of human hepatic stellate cells via its actin-binding domain

OBJECTIVES

Hepatic stellate cells (HSC) trans-differentiation is central to the development of liver fibrosis, marked by the expression of pro-fibrogenic genes and the proliferation and migration of activated HSC. Therefore, preventing and/or reverting the activation, proliferation, and migration of HSC may lead to new therapies for treating fibrosis/cirrhosis. Thymosin β4 (Tβ4) inhibits PDGF-BB-induced fibrogenesis, proliferation and migration of HSC by blocking Akt phosphorylation. Here, we utilized Tβ4-derived peptides: amino-terminal-Ac-SDKPDMAEIEKFDKS (1-15aa) and actin-binding-LKKTETQ (17-23aa) to investigate the molecular mechanisms in the anti-fibrogenic actions of Tβ4.

METHODS

We used RT-PCR, Western blot, and proliferation and migration assays in early passages of human HSC cultures treated with PDGF-BB and/or Tβ4 peptides.

RESULTS

We showed that 17-23aa but not 1-15aa inhibited PDGF-BB-dependent up-regulation of PDGFβ receptor, α-SMA, and collagen 1. It also blunted the phosphorylation of Akt at T 308 and S473, resulting in the inhibition of phosphorylation of PRAS40, and HSC proliferation and migration. Interestingly, 1-15aa blocked Akt phosphorylation at S473, but not T308 by inhibiting mTOR phosphorylation, thus, it did not have any effect on HSC proliferation and migration.

CONCLUSION

These findings suggest that while 1-15aa has a minor effect on Akt phosphorylation, the anti-fibrogenic actions of Tβ4 are exerted via 17-23aa.

The STAT3 inhibitor S3I-201 suppresses fibrogenesis and angiogenesis in liver fibrosis

Liver fibrosis is a common pathological response to chronic hepatic injury. STAT3 is actively involved in the fibrogenesis and angiogenesis seen in liver fibrosis. S3I-201 (NSC 74859) is a chemical inhibitor of STAT3 activity, which blocks the dimerization of STAT3, STAT3-DNA binding and transcription activity. This study evaluated the effects of S3I-201 against liver fibrosis. S3I-201 inhibited the proliferation, migration, and actin filament formation in primary human hepatic stellate cells (HSCs), as well as the expression of α-SMA, collagen I and TIMP1 in both primary HSC and in a CCl₄-induced fibrosis mouse model. S3I-201 induced both apoptosis and cell cycle arrest in the HSC cell line (LX-2). S3I-201 inhibited the expression of fibrogenesis factors TGFβ1 and TGFβRII, as well as the downstream phosphorylation of Smad2, Smad3, Akt and ERK induced by TGFβ1. In addition to fibrogenesis, both in vitro and in vivo assays showed that S3I-201 inhibited angiogenesis through expression suppression of VEGF and VEGFR2. Moreover, S3I-201 also had a synergistic effect with sorafenib, an FDA approved liver cancer drug, in the proliferation, apoptosis, angiogenesis and fibrogenesis of HSC. S3I-201 suppressed liver fibrosis through multiple mechanisms, and combined with sorafenib, S3I-201 could be a potentially effective antifibrotic agent.

Estrogen receptor‑β‑dependent effects of saikosaponin‑d on the suppression of oxidative stress‑induced rat hepatic stellate cell activation

Saikosaponin-d (SSd) is one of the major triterpenoid saponins derived from Bupleurum falcatum L., which has been reported to possess antifibrotic activity. At present, there is little information regarding the potential target of SSd in hepatic stellate cells (HSCs), which serve an important role in excessive extracellular matrix (ECM) deposition during the pathogenesis of hepatic fibrosis. Our recent study indicated that SSd may be considered a novel type of phytoestrogen with estrogen-like actions. Therefore, the present study aimed to investigate the effects of SSd on the proliferation and activation of HSCs, and the underlying mechanisms associated with estrogen receptors. In the present study, a rat HSC line (HSC-T6) was used and cultured with dimethyl sulfoxide, SSd, or estradiol (E₂; positive control), in the presence or absence of three estrogen receptor (ER) antagonists [ICI-182780, methylpiperidinopyrazole (MPP) or (R,R)-tetrahydrochrysene (THC)], for 24 h as pretreatment. Oxidative stress was induced by exposure to hydrogen peroxide for 4 h. Cell proliferation was assessed by MTT growth assay. Malondialdehyde (MDA), CuZn-superoxide dismutase (CuZn-SOD), tissue inhibitor of metalloproteinases-1 (TIMP- 1), matrix metalloproteinase-1 (MMP-1), transforming growth factor-β1 (TGF-β1), hydroxyproline (Hyp) and collagen-1 (COL1) levels in cell culture supernatants were determined by ELISA. Reactive oxygen species (ROS) was detected by flow cytometry. Total and phosphorylated mitogen-activated protein kinases (MAPKs) and α-smooth muscle actin (α-SMA) were examined by western blot analysis. TGF-β1 mRNA expression was determined by RT-quantitative (q)PCR. SSd and E₂ were able to significantly suppress oxidative stress-induced proliferation and activation of HSC-T6 cells. Furthermore, SSd and E₂ were able to reduce ECM deposition, as demonstrated by the decrease in transforming growth factor-β1, hydroxyproline, collagen-1 and tissue inhibitor of metalloproteinases-1, and by the increase in matrix metalloproteinase-1. These results suggested that the possible molecular mechanism could involve downregulation of the reactive oxygen species/mitogen-activated protein kinases signaling pathway. Finally, the effects of SSd and E₂ could be blocked by co-incubation with ICI-182780 or THC, but not MPP, thus indicating that ERβ may be the potential target of SSd in HSC-T6 cells. In conclusion, these findings suggested that SSd may suppress oxidative stress-induced activation of HSCs, which relied on modulation of ERβ.

Signaling Cross Talk between TGF-β/Smad and Other Signaling Pathways

Cytokines of the transforming growth factor β (TGF-β) family, including TGF-βs, bone morphogenic proteins (BMPs), activins, and Nodal, play crucial roles in embryonic development and adult tissue homeostasis by regulating cell proliferation, survival, and differentiation, as well as stem-cell self-renewal and lineage-specific differentiation. Smad proteins are critical downstream mediators of these signaling activities. In addition to regulating the transcription of direct target genes of TGF-β, BMP, activin, or Nodal, Smad proteins also participate in extensive cross talk with other signaling pathways, often in a cell-type- or developmental stage-specific manner. These combinatorial signals often produce context-, time-, and location-dependent biological outcomes that are critical for development. This review discusses recent progress in our understanding of the cross talk between Smad proteins and signaling pathways of Wnt, Notch, Hippo, Hedgehog (Hh), mitogen-activated protein (MAP), kinase, phosphoinositide 3-kinase (PI3K)-Akt, nuclear factor κB (NF-κB), and Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathways.

Signaling Cross Talk between TGF-β/Smad and Other Signaling Pathways

Cytokines of the transforming growth factor β (TGF-β) family, including TGF-βs, bone morphogenic proteins (BMPs), activins, and Nodal, play crucial roles in embryonic development and adult tissue homeostasis by regulating cell proliferation, survival, and differentiation, as well as stem-cell self-renewal and lineage-specific differentiation. Smad proteins are critical downstream mediators of these signaling activities. In addition to regulating the transcription of direct target genes of TGF-β, BMP, activin, or Nodal, Smad proteins also participate in extensive cross talk with other signaling pathways, often in a cell-type- or developmental stage-specific manner. These combinatorial signals often produce context-, time-, and location-dependent biological outcomes that are critical for development. This review discusses recent progress in our understanding of the cross talk between Smad proteins and signaling pathways of Wnt, Notch, Hippo, Hedgehog (Hh), mitogen-activated protein (MAP), kinase, phosphoinositide 3-kinase (PI3K)-Akt, nuclear factor κB (NF-κB), and Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathways.

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

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

Hypoxia reduces placental mTOR activation in a hypoxia-induced model of intrauterine growth restriction (IUGR)

Mammalian target of rapamycin (mTOR) is a protein that regulates cell growth in response to altered nutrient and growth factor availability. Our objective was to assess activated mTOR and its intracellular intermediates p70, and 4EBP1 in placental and invasive trophoblast cells in a hypoxia‐induced model of intrauterine growth restriction (IUGR) in rats. Rats were treated with hypoxia (9%) for 4 days. Placental and fetal weights, as well as conceptus numbers were recorded at the time of necropsy. Immunohistochemistry was used to determine the level of trophoblast invasion and apoptosis. Western blots were used to determine the activation of mTOR, p70, and 4EBP1 in the placenta and the uterine mesometrial compartment. We observed (1) decreased placental (21%) and fetal (24%) weights (P < 0.05); (2) decreased trophoblast invasion; (3) significantly increased active 4EBP1 (28%; P < 0.05) in invasive trophoblast cells yet no changes in the activation of mTOR and p70 proteins; and (4) a significant decrease in the activation of mTOR (48%; P < 0.05) with no differences in p70 or 4EBP1 activation in the placenta. We conclude that the development of IUGR is correlated with decreased activation of the mTOR protein in the placenta and increased 4EBP1 activity in the invading trophoblast. These results provide important insight into the physiological relevance of these pathways. Furthermore, modification of these and other related targets during gestation may alleviate IUGR severity.

Thalidomide Accelerates the Degradation of Extracellular Matrix in Rat Hepatic Cirrhosis via Down-Regulation of Transforming Growth Factor-β1

PURPOSE

The degradation of the extracellular matrix has been shown to play an important role in the treatment of hepatic cirrhosis. In this study, the effect of thalidomide on the degradation of extracellular matrix was evaluated in a rat model of hepatic cirrhosis.

MATERIALS AND METHODS

Cirrhosis was induced in Wistar rats by intraperitoneal injection of carbon tetrachloride (CCl₄) three times weekly for 8 weeks. Then CCl₄ was discontinued and thalidomide (100 mg/kg) or its vehicle was administered daily by gavage for 6 weeks. Serum hyaluronic acid, laminin, procollagen type III, and collagen type IV were examined by using a radioimmunoassay. Matrix metalloproteinase-13 (MMP-13), tissue inhibitor of metalloproteinase-1 (TIMP-1), and α-smooth muscle actin (α-SMA) protein in the liver, transforming growth factor β1 (TGF-β1) protein in cytoplasm by using immunohistochemistry and Western blot analysis, and MMP-13, TIMP-1, and TGF-β1 mRNA levels in the liver were studied using reverse transcriptase polymerase chain reaction.

RESULTS

Liver histopathology was significantly better in rats given thalidomide than in the untreated model group. The levels of TIMP-1 and TGF-β1 mRNA and protein expressions were decreased significantly and MMP-13 mRNA and protein in the liver were significantly elevated in the thalidomide-treated group.

CONCLUSION

Thalidomide may exert its effects on the regulation of MMP-13 and TIMP-1 via inhibition of the TGF-β1 signaling pathway, which enhances the degradation of extracellular matrix and accelerates the regression of hepatic cirrhosis in rats.

Osteopontin induces ductular reaction contributing to liver fibrosis

OBJECTIVE

In human chronic liver disease, there is association between ductular reaction (DR) and fibrosis; yet, the mechanism triggering its onset and its role in scar formation remains unknown. Since we previously showed that osteopontin (OPN) is highly induced during drug-induced liver fibrosis, we hypothesised that OPN could drive oval cells (OC) expansion and DR and signal to hepatic stellate cells (HSC) to promote scarring.

RESULTS

In vivo studies demonstrated increased OPN expression in biliary epithelial cells (BEC) and in OC in thioacetamide (TAA)-treated mice. OPN ablation protected mice from TAA and bile duct ligation-induced liver injury, DR and scarring. This was associated with greater hepatocyte proliferation, lower OC expansion and DR along with less fibrosis, suggesting that OPN could activate the OC compartment to differentiate into BEC, which could then signal to HSC to enhance scarring. Since TAA-treated wild-type mice and cirrhotic patients showed TGF-β(+) BEC, which were lacking in TAA-treated Opn(-/-) mice and in healthy human explants, this suggested that OPN could regulate TGF-β, a profibrogenic factor. In vitro experiments confirmed that recombinant OPN (rOPN) decreases hepatocyte proliferation and increases OC and BEC proliferation. To evaluate how BEC regulate collagen-I production in HSC, co-cultures were established. Co-cultured BEC upregulated OPN and TGF-β expression and enhanced collagen-I synthesis by HSC. Lastly, recombinant TGF-β (rTGFβ) and rOPN promoted BEC proliferation and neutralisation of OPN and TGF-β reduced collagen-I expression in co-cultured HSC.

CONCLUSIONS

OPN emerges as a key matricellular protein driving DR and contributing to scarring and liver fibrosis via TGF-β.

TGF-β1 up-regulates the expression of PDGF-β receptor mRNA and induces a delayed PI3K-, AKT-, and p70(S6K) -dependent proliferative response in activated hepatic stellate cells

BACKGROUND

Transforming growth factor beta 1 (TGF-β1) is a pleiotropic cytokine that activates hepatic stellate cell (HSC) proliferation, but inhibits parenchymal cell proliferation. Therefore, we hypothesize that TGF-β1 regulates HSC proliferation and elucidated its molecular action.

METHODS

In order to elucidate the molecular mechanism whereby TGF-β1 up-regulates platelet derived growth factor beta (PDGF-β) receptor mRNA and induces a delayed proliferation of HSC, we used proliferation and apoptosis assays as well as RT-PCR, Western blot analysis, immunostaining, and flow cytometry in mouse and rat HSC.

RESULTS

We show that TGF-β1 markedly induces the proliferation of mouse HSC in culture with concomitant 2.1-fold (p < 0.001) stimulation in [(3) H]-thymidine incorporation into cellular DNA. This induction is maximal between 24 and 36 hours postcytokine exposure that is triggered by 7.6-fold (p < 0.001) up-regulation of PDGF-β receptor mRNA and associated increase in PDGF-β receptor protein after 48 hours. TGF-β1-dependent HSC proliferation is mimicked by H2 O2 that is inhibited by catalase, implying that TGF-β1 action is mediated via reactive oxygen species. HSC proliferation is blunted by PDGF-β receptor-neutralizing antibody as well as by specific inhibitors of PI3 kinase (PI3K), AKT, and p70(S6K) , indicating that the action of TGF-β1 involves the activation of PDGF-β receptor via the PI3K/AKT/p70(S6K) signaling pathway. TGF-β1 also induces a reorganization of actin and myosin filaments and cell morphology leading to the formation of palisades although their myosin and actin contents remained constant. These findings suggest that TGF-β1-mediated oxidative stress causes the transdifferentiation of HSC and primes them for extracellular matrix (ECM) deposition and scar contraction.

CONCLUSIONS

We conclude that liver injury up-regulates TGF-β1 that inhibits parenchymal cell proliferation, but stimulates HSC proliferation leading to the production of ECM and type I collagen resulting in fibrosis.

A histone deacetylase inhibitor, largazole, decreases liver fibrosis and angiogenesis by inhibiting transforming growth factor-β and vascular endothelial growth factor signalling

BACKGROUND & AIMS

Largazole is a novel histone deacetylase (HDAC) inhibitor. This study investigated the effects of largazole against liver fibrosis.

METHODS

The in vitro effects of largazole were examined using hepatic stellate cells (HSCs). In vivo effects of largazole were studied using a mouse liver fibrotic model induced by CCl4 .

RESULTS

Largazole augmented acetylation of histone H3 (H3) and histone H4 (H4) in HSCs. It directly inhibited the activation of HSCs owing to HDAC inhibitory activity as the antifibrotic effect of largazole was significantly decreased in cells with HDAC1, HDAC2 and HDAC3 knockdown. Largazole also induced apoptosis of HSCs. Largazole not only inhibited the expression of TGFβR2, but also reduced phosphorylation of Smad2 and Akt induced by TGF-β1. Largazole also inhibited the expression of vascular endothelial growth factor (VEGF) and its receptor. VEGF-induced proliferation of HSCs and activation of Akt and p38MAPK were also suppressed by largazole. In vivo, largazole reduced the expression of collagen I, α-smooth muscle actin and tissue inhibitor of metalloproteinase-1 in CCl4 -induced fibrosis, and these antifibrotic effects were associated with increased acetylation of H3 and H4. Largazole also induced HSCs to undergo apoptosis in vivo, which was correlated with downregulation of bcl-2 and bcl-xL. Furthermore, largazole inhibited angiogenesis in vivo as evidenced by reduced expression of CD34, VEGF and VEGFR. In addition to its antifibrotic activity, the drug reduced inflammatory activity in CCl4 -induced liver fibrosis.

CONCLUSIONS

Our findings revealed a novel role of largazole in the treatment of liver fibrosis. Through multiple mechanisms, largazole could be a potentially effective antifibrotic agent.

Nilotinib induces apoptosis and autophagic cell death of activated hepatic stellate cells via inhibition of histone deacetylases

Increasing hepatic stellate cell (HSC) death is a very attractive approach for limiting liver fibrosis. Tyrosine kinase inhibitors have been shown to have anti-fibrotic properties, but the mechanisms are poorly understood. Here, we identified the mechanism of action of the second-generation tyrosine kinase inhibitor nilotinib in inducing HSC death. Human HSC line (LX-2) and rat HSCs were treated with nilotinib and its predecessor, imatinib, in the absence or presence of various blockers, known to interfere with death signaling pathways. Nilotinib, but not imatinib, induced progressive cell death of activated, but not quiescent, HSCs in a dose-dependent manner. Activated HSCs died through apoptosis, as denoted by increased DNA fragmentation and caspase activation, and through autophagy, as indicated by the accumulation of autophagic markers, light chain (LC)3A-II and LC3B-II. Although inhibition of caspases with Z-VAD-FMK suppressed nilotinib-induced HSCs' apoptosis, there was no increase in HSCs' survival, because autophagy was exacerbated. However, blocking the mitochondrial permeability transition pore (mPTP) opening with cyclosporin A completely abolished both apoptosis and autophagy due to nilotinib. Moreover, nilotinib treatment decreased the protein expression of histone deacetylases 1, 2 and 4. Interestingly, pretreament with C646, a selective p300/CBP histone acetyl transferase inhibitor, resulted in diverting nilotinib-induced apoptosis and autophagy towards necrosis. In conclusion, the identification of mPTP as a target of nilotinib in activated HSCs suggests coordination with histone deacetylases inhibition to induce apoptosis and autophagy. Thus, our study provides novel insights into the anti-fibrotic effects of nilotinib.

Collagenolytic potential of rat liver myofibroblasts

Rat liver myofibroblasts (MFB) were isolated by repeated passaging of nonparenchymal liver cell fraction. They were cultured on polystyrene Petri dishes, on fibrin or on type I collagen gels for 5 days. Quantitative RT-PCR, Western blotting, zymography and immunocytochemistry were used to study differences in cell morphology and protein expression. MFB were large and spread on plastic substrate, with prominent alpha-smooth muscle (alpha-SMA) fibres. They turned much smaller and elongated on collagen which was accompanied by the rearrangement of the cytoskeleton and a decrease in alpha-SMA and beta-actin content. Collagen gel induced the expression of a group of metalloproteinases (MMP-2, -3, -9, -13), on mRNA and protein level which resulted in the degradation of the gel. This response was accompanied by changes in the mRNA expression of cytokines of TGF-beta family, CTGF and interleukin-6, as well as of osteopontin and thrombospondin-2 that are involved in metalloproteinases (MMPs) regulation. The expression of MMPs substrates, collagen types I, IV and XII did not change or decreased. The effects of fibrin gels on MFB were milder than those of collagen. MFB assumed to deposit collagen and other ECM components in fibrotic liver, besides hepatic stellate cells, also possess a great collagenolytic potential.

NOX-mediated MAPK and PI3K/Akt signaling pathways and liver fibrosis

Hepatic satellite cells (HSCs) are the main cell type involved in the development of liver fibrosis and have been recognized as the important cellular source of extracellular matrix (ECM). NADPH oxidase (NOX) catalyzes the generation of reactive oxygen species (ROS), regulates signal transduction in HSCs, and thereby plays a key role in the pathogenesis of hepatic fibrosis. ROS generated by NOX promotes proliferation and inhibits apoptosis of HSCs by activation of mitogen-activated protein kinase and phosphatidylinositol-3 kinase/Akt signaling pathways, thus contributing to the development of liver fibrosis. Inhibition of NOX activation to generate ROS and NOX-mediated signal transduction induces HSC apoptosis. Therefore, drugs that target specific NOX can be expected to be useful in arresting the progression of liver fibrosis.

Requirement of the phosphatidylinositol 3-kinase/Akt signaling pathway for the effect of nicotine on interleukin-1beta-induced chondrocyte apoptosis in a rat model of osteoarthritis

Chondrocyte apoptosis is mainly responsible for the progressive degeneration of cartilage in osteoarthritis (OA). Interleukin-1beta (IL-1β) was widely used as a modulating and chondrocyte apoptosis-inducing agent. Nicotine is able to confer resistance to apoptosis and promote cell survival in some cell lines, but its regulatory mechanism is ambiguous. We aimed to investigate the effect of nicotine on IL-1β-induced chondrocyte apoptosis and the mechanism underlying how nicotine antagonizes IL-1β-induced apoptosis of rat chondrocytes. Chondrocytes isolated from newborn rat joints were exposed to IL-1β. The cell viability was analyzed by the MTT (3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide) assay, and the apoptotic cells were counted with DAPI staining. The levels of Akt, phosphorylated-Akt (p-Akt) and downstream protein targets of Akt were detected by western blotting. The results showed that nicotine neutralized the effect of IL-1β on chondrocytes by activating PI3K/Akt signaling pathways, including the PI3K/Akt/Bcl-2 pathway, to block IL-1β-induced cell apoptosis and the PI3K/Akt/p70S6K (p70S6 kinase)/S6 pathway for promoting protein synthesis, modulating its downstream effectors such as TIMP-1 and MMP-13. Activation of the PI3K/Akt pathway is, in part, required for the effect of nicotine on IL-1β-induced chondrocyte apoptosis in a rat model of osteoarthritis.

Inhibition of PDGF, TGF-β, and Abl signaling and reduction of liver fibrosis by the small molecule Bcr-Abl tyrosine kinase antagonist Nilotinib

BACKGROUND & AIMS

Nilotinib is a novel tyrosine kinase inhibitor of Bcr-Abl and other kinases. In this study, we have examined its activity as an anti-fibrotic agent.

METHODS

The in vitro effect of Nilotinib on rat and human HSCs was assessed using proliferation assays and Western blotting. The in vivo antifibrotic efficacy of Nilotinib was assessed in mice with liver fibrosis induced by CCl(4) and bile duct ligation (BDL).

RESULTS

Nilotinib inhibited proliferation, migration, and actin filament formation, as well as the expression of α-SMA and collagen in activated HSCs. Nilotinib induced apoptosis of HSCs, which was correlated with reduced bcl-2 expression, increased p53 expression, cleavage of PARP, as well as increased expression of PPARγ and TRAIL-R. Nilotinib also induced cell cycle arrest, accompanied by increased expression of p27 and downregulation of cyclin D1. Interestingly, Nilotinib not only inhibited activation of PDGFR, but also TGFRII through Src. Nilotinib significantly inhibited PDGF and TGFβ-simulated phosphorylation of ERK and Akt. Furthermore, PDGF- and TGFβ-activated phosphorylated form(s) of Abl in human HSCs were inhibited by Nilotinib. In vivo, Nilotinib reduced collagen deposition and α-SMA expression in CCl(4) and BDL-induced fibrosis. These beneficial effects were associated with suppressed expression of procollagen-(I), TIMP-1, CD31, CD34, VEGF, and VEGFR. Nilotinib could induce HSC undergoing apoptosis in vivo, which was correlated with downregulation of bcl-2. We also observed reduced expression of phosphorylated ERK, Akt, and Abl in the Nilotinib-treated CCl(4) and BDL livers. In addition to its antifibrotic activity, the drug was hepatoprotective and reduced the elevations of ALT and AST after CCl(4) and BDL.

CONCLUSIONS

These studies uncover a novel role of Bcr-Abl activity in treatment of liver fibrosis through multiple mechanisms and indicate that Nilotinib represents a potentially effective antifibrotic agent.

Effect of salvianolic-acid B on inhibiting MAPK signaling induced by transforming growth factor-β1 in activated rat hepatic stellate cells

AIM OF THE STUDY

Salvianolic-acid B (SA-B) is an effective component of Radix Salviae miltiorrhizae for anti-hepatic fibrotic herbs. MAPK signaling pathway has been implicated in hepatic stellate cells (HSC) stimulated by TGF-(1. We have investigated the effect of SA-B on MAPK pathway in rat HSC.

MATERIALS AND METHODS

To observe the pharmacological effect of SA-B on HSC, SA-B was added into the medium of primary HSC. TGF-(1 was added during last 2h, and PD98059 (ERK inhibitor) and SB203580 (p38 inhibitor) were added just 30 min before adding TGF-(1. MEF2 and Col. I were measured by luciferase reporter gene assay and Western blot. (-SMA, MEF2, Raf, ERK, p-ERK, MEK, p-MEK, p38, p-p38, MKK3 and p-MKK3/6 were assayed by Western blot. Activity of MMP-2 and MMP-9 was analyzed by zymography. Each experiment was repeated for three times.

RESULTS

The expression of (-SMA and Col. I in HSC was inhibited by SA-B. There was no effect of SA-B on the activity of MMP-2 or MMP-9 in the media of cultured HSC. Phosphorylation of ERK1/2 in HSC stimulated with or without TGF-(1 was inhibited by SA-B. Specifically, phosphorylation of MEK (upstream kinase of ERK pathway) was inhibited by SA-B. SA-B also inhibited phosphorylation of MKK3/6 (upstream kinases of p38 pathway) and inhibited the synthesis of MEF2.

CONCLUSIONS

SA-B performs anti-hepatic fibrosis through inhibiting ERK and p38 MAPK pathway in HSC. SA-B inhibits ERK pathway via inhibiting phosphorylation of MEK and inhibits p38 MAPK pathway via blocking phosphorylation of MKK3/6 and inhibiting expression of MEF2 in HSC with or without TGF-(1 stimulation.

Chloramphenicol causes mitochondrial stress, decreases ATP biosynthesis, induces matrix metalloproteinase-13 expression, and solid-tumor cell invasion

Overuse and abuse of antibiotics can increase the risk of cancer. Chloramphenicol can inhibit both bacterial and mitochondrial protein synthesis, causing mitochondrial stress and decreased ATP biosynthesis. Chloramphenicol can accelerate cancer progression; however, the underlying mechanisms of chloramphenicol in carcinogenesis and cancer progression are still unclear. We found that chloramphenicol can induce matrix metalloproteinase (MMP)-13 expression and increase MMP-13 protein in conditioned medium, resulting in an increase in cancer cell invasion. Chloramphenicol also activated c-Jun N-terminal kinases (JNK) and phosphatidylinositol 3-kinase (PI-3K)/Akt signaling, leading to c-Jun protein phosphorylation. The activated c-Jun protein has been proven to activate binding to the MMP-13 promoter and also upregulate the amount of MMP-13. Both the SP 600125 (JNK inhibitor) and LY 294002 (PI-3K/Akt inhibitor) can inhibit chloramphenicol-induced c-Jun phosphorylation, MMP-13 expression, and cell invasion. Overexpression of the dominant-negative JNK and PI-3K p85 subunit also negate chloramphenicol-induced responses. Other antibiotics that cause mitochondrial stress and a decrease in ATP biosynthesis also induce MMP-13 expression. These findings suggest that chloramphenicol-induced PI-3K/Akt, JNK phosphorylation, and activator protein 1 activation might function as a novel mitochondrial stress signal that result in an increase of MMP-13 expression and MMP-13-associated cancer cell invasion. The findings of this study confirms that chloramphenicol, and other 70S ribosomal inhibitors, should be administered with caution, especially during cancer therapy.

Therapeutic targeting of the PDGF and TGF-beta-signaling pathways in hepatic stellate cells by PTK787/ZK22258

Stimulation of hepatic stellate cells (HSCs) by platelet-derived growth factor (PDGF) and transforming growth factor-beta1 (TGF-beta1) is an essential pathway of proliferation and fibrogenesis, respectively, in liver fibrosis. We provide evidence that PTK787/ZK222584 (PTK/ZK), a potent tyrosine kinase inhibitor that blocks vascular endothelial growth factor receptor (VEGFR), significantly inhibits PDGF receptor expression, as well as PDGF-simulated HSC proliferation, migration and phosphorylation of ERK1/2, Akt and p70S6 kinase. Interestingly, PTK/ZK also antagonizes the TGF-beta1-induced expression of VEGF and VEGFR1. Furthermore, PTK/ZK downregulates TGF-beta receptor expression, which is associated with reduced Akt, ERK and p38MAPK phosphorylation. Furthermore, PDGF-induced TGF-beta1 expression is inhibited by PTK/ZK. These findings provide evidence that PTK/ZK targets multiple essential pathways of stellate cell activation that provoke proliferation and fibrogenesis. Our study underscores the potential use of PTK/ZK as an antifibrotic drug in chronic liver disease.

Experimental mouse models for hepatocellular carcinoma research

Every year almost 500,000 new patients are diagnosed with hepatocellular carcinoma (HCC), a primary malignancy of the liver that is associated with a poor prognosis. Numerous experimental models have been developed to define the pathogenesis of HCC and to test novel drug candidates. This review analyses several mouse models useful for HCC research and points out their advantages and weaknesses. Chemically induced HCC mice models mimic the injury-fibrosis-malignancy cycle by administration of a genotoxic compound alone or, if necessary, followed by a promoting agent. Xenograft models develop HCC by implanting hepatoma cell lines in mice, either ectopically or orthotopically; these models are suitable for drug screening, although extrapolation should be considered with caution as multiple cell lines must always be used. The hollow fibre assay offers a solution for limiting the number of test animals in xenograft research because of the ability for implanting multiple cell lines in one mouse. There is also a broad range of genetically modified mice engineered to investigate the pathophysiology of HCC. Transgenic mice expressing viral genes, oncogenes and/or growth factors allow the identification of pathways involved in hepatocarcinogenesis.

Age-dependent increases in interstitial collagenase and MAP Kinase levels are exacerbated by superoxide dismutase deficiencies

Many age-associated degenerative diseases commonly involve degradation of the extracellular matrix and aberrant matrix metalloproteinase-1 (MMP-1) expression. In diverse cell lines MMP-1 or interstitial collagenase (CL) expression is tightly regulated through a network of signals involving reactive oxygen species (ROS). However, whether the in vivo age-associated increase in CL expression is also sensitive to ROS-mediated signaling has not been established. To evaluate the contribution of ROS to the age-dependent increase in CL we monitored the levels of murine CL in two well-established models of oxidant stress. Analysis of murine CL levels in mice deficient in either of the intracellular superoxide dismutases (Sod2(+/-) or Sod1(-/-)) revealed its age- and redox-dependent expression relative to WT controls. Both age- and redox-dependent increases in murine CL expression were associated with elevations in phosphorylation of the MAP Kinases, Erk, JNK and p38. CL expression was highest in renal and skeletal muscle tissue from the aged Sod1(-/-) mice and was associated with a decrease in collagen staining. These findings suggest that MAPK signaling and CL production are both age- and redox-responsive. The redox sensitivity of age-associated CL expression suggests that degenerative disease associated with aberrant matrix remodeling and oxidant stress may be amenable to antioxidant-based therapies.

Regulatory T cells and viral liver disease

Important questions remain on the role of T cells in progression of hepatitis virus-mediated liver pathogenesis: are T cells 'Good or Bad'? How could one maintain a beneficial balance, in which regulatory T-cell (Treg) populations might play an important role? Treg are a heterogeneous population of cells, including the classical CD4+CD25+ subset expressing the transcription factor Foxp3, CD4 T cells secreting IL-10 (Tr1) or TGF-beta (Th3), but also some CD8 T cells, double negative T cells and gammadelta T cells. The role of Treg in viral hepatitis, particularly HBV and HCV, seems to range from suppressing T-cell responses directed against hepatitis viruses to down-regulating the immune responses causing the liver damage. Questions also remain unresolved on which Treg populations are important and how to establish a beneficial balance, mostly due to the difficulties in studying the heterogeneous Treg populations but also due to the problem accessing liver, the principal target of hepatitis viruses. Here, we will review progress to date on understanding Treg populations in regard to viral hepatitis.

TGF-[beta]1 limits plaque growth, stabilizes plaque structure, and prevents aortic dilation in apolipoprotein E-null mice

OBJECTIVE

Impairment of transforming growth factor (TGF)-beta1 signaling accelerates atherosclerosis in experimental mice. However, it is uncertain whether increased TGF-beta1 expression would retard atherosclerosis. The role of TGF-beta1 in aneurysm formation is also controversial. We tested whether overexpression of active TGF-beta1 in hyperlipidemic mice affects atherogenesis and aortic dilation.

METHODS AND RESULTS

We generated apolipoprotein E-null mice with transgenes that allow regulated overexpression of active TGF-beta1 in their hearts. Compared to littermate controls, these mice had elevated cardiac and plasma TGF-beta1, less aortic root atherosclerosis (P< or =0.002), fewer lesions in the thoracic and abdominal aortae (P< or =0.01), less aortic root dilation (P<0.001), and fewer pseudoaneurysms (P=0.02). Mechanistic studies revealed no effect of TGF-beta1 overexpression on plasma lipids or cytokines, or on peripheral lymphoid organ cells. However, aortae of TGF-beta1-overexpressing mice had fewer T-lymphocytes, more collagen, less lipid, lower expression of inflammatory cytokines and matrix metalloproteinase-13, and higher expression of tissue inhibitor of metalloproteinase-2.

CONCLUSIONS

When overexpressed in the heart and plasma, TGF-beta1 is an antiatherogenic, vasculoprotective cytokine that limits atherosclerosis and prevents aortic dilation. These actions are associated with significant changes in cellularity, collagen and lipid accumulation, and gene expression in the artery wall.

Effects of rhubarb on migration of rat hepatic stellate cells

BACKGROUND AND AIMS

In chronic liver injury, hepatic stellate cells (HSCs) acquire an activated phenotype, migrate to the injured region in response to chemotactic factors, and produce extracellular matrix proteins including collagen. In this study, we investigated the effects of rhubarb (Rheum palmatum L.) on transforming growth factor (TGF)-beta1-induced expressions of alpha-smooth-muscle actin (SMA) and collagen, and the migration of HSCs.

METHODS

HSC-T6, a cell line of rat HSCs, was used in the in vitro experiments. An enzyme-linked immunosorbent assay and Sircol red assay were used to detect the expressions of alpha-SMA and collagen, respectively. HSC-T6 migration was assayed with a transwell apparatus. Phosphorylations of Smad2/3 and mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinase (ERK) 1/2, p38, and c-jun N-terminal kinase (JNK), were analyzed with Western blotting. Matrix metalloproteinase (MMP)-2 activity was examined by gelatin zymography.

RESULTS

The results revealed that a rhubarb extract concentration-dependently attenuated TGF-beta1-induced alpha-SMA and collagen expressions and migration of HSCs. The inhibitory effect of rhubarb was associated with (i) down-regulation of the phosphorylation of Smad2/3 and JNK, and (ii) attenuation of MMP-2 activity. Within the working concentrations used, the rhubarb extract did not affect cell viability of HSCs.

CONCLUSION

The results suggest that rhubarb attenuated TGF-beta1-mediated migration of HSCs possibly by interfering with Smad2/3 phosphorylation, the MAPK pathway, and MMP-2 activity.

Expression of pro- and anti-angiogenic isoforms of VEGF is differentially regulated by splicing and growth factors

Vascular endothelial growth factor A (VEGFA; hereafter referred to as VEGF) is a key regulator of physiological and pathological angiogenesis. Two families of VEGF isoforms are generated by alternate splice-site selection in the terminal exon. Proximal splice-site selection (PSS) in exon 8 results in pro-angiogenic VEGFxxx isoforms (xxx is the number of amino acids), whereas distal splice-site selection (DSS) results in anti-angiogenic VEGFxxxb isoforms. To investigate control of PSS and DSS, we investigated the regulation of isoform expression by extracellular growth factor administration and intracellular splicing factors. In primary epithelial cells VEGFxxxb formed the majority of VEGF isoforms (74%). IGF1, and TNFalpha treatment favoured PSS (increasing VEGFxxx) whereas TGFbeta1 favoured DSS, increasing VEGFxxxb levels. TGFbeta1 induced DSS selection was prevented by inhibition of p38 MAPK and the Clk/sty (CDC-like kinase, CLK1) splicing factor kinase family, but not ERK1/2. Clk phosphorylates SR protein splicing factors ASF/SF2, SRp40 and SRp55. To determine whether SR splicing factors alter VEGF splicing, they were overexpressed in epithelial cells, and VEGF isoform production assessed. ASF/SF2, and SRp40 both favoured PSS, whereas SRp55 upregulated VEGFxxxb (DSS) isoforms relative to VEGFxxx. SRp55 knockdown reduced expression of VEGF165b. Moreover, SRp55 bound to a 35 nucleotide region of the 3'UTR immediately downstream of the stop codon in exon 8b. These results identify regulation of splicing by growth and splice factors as a key event in determining the relative pro-versus anti-angiogenic expression of VEGF isoforms, and suggest that p38 MAPK-Clk/sty kinases are responsible for the TGFbeta1-induced DSS selection, and identify SRp55 as a key regulatory splice factor.

P38 mitogen-activated protein kinase signal pathway and hepatic stellate cells

Mitogen-activated protein kinases (MAPKs) play a pivotal role in the transduction of extracellular signals to the nucleus, which results in numerous cellular responses, including proliferation, differentiation, and regulation of specific metabilic pathways. P38 MAPK is one of the MAPK-family groups. Hepatic stellate cells (HSCs) are the main effector cells in the occurrence of liver fibrosis, so this review describes P38 MAPK signal pathway and its role in HSCs.

Oxidative and nitrosative stress and fibrogenic response

Uncontrolled production of collagen I is the main feature of liver fibrosis. Following a fibrogenic stimulus such as alcohol, hepatic stellate cells (HSC) transform into an activated collagen-producing cell. In alcoholic liver disease, numerous changes in gene expression are associated with HSC activation, including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses for understanding the molecular basis of the collagen I gene regulation have revealed a complex process involving reactive oxygen species (ROS) as key mediators. Less is known, however, about the contribution of reactive nitrogen species (RNS). In addition, a series of cytokines, growth factors, and chemokines, which activate extracellular matrix (ECM)-producing cells through paracrine and autocrine loops, contribute to the fibrogenic response.

Leptin stimulates alpha1(I) collagen expression in human hepatic stellate cells via the phosphatidylinositol 3-kinase/Akt signalling pathway

BACKGROUND/AIMS

Leptin has been recognized as a profibrogenic hormone in the liver and is involved in collagen type I formation by activated hepatic stellate cells (HSCs) in response to fibrogenic substances, but the molecular signal mechanisms by which leptin promotes liver fibrogenesis through upregulation of collagen type I expression is not clear. We investigated whether leptin-induced collagen type I is mediated by the Janus kinase-phosphatidylinositol 3-kinase-Akt (JAKs-PI3K-Akt) pathway in a human HSC cell line, LX-2.

METHODS

LX-2 cells were treated with or without various inhibitors in the presence of leptin.

RESULTS

Leptin increased alpha1(I) collagen mRNA and protein. JAK1, PI3K and Akt were activated after leptin stimulation. AG490, a JAK inhibitor, blocked JAK1 phosphorylation accompanied by inhibition of PI3K and Akt activation as well as alpha1(I) collagen mRNA expression, indicating a JAK1-dependent mechanism. Wortmannin, a PI3K inhibitor, prevented PI3K and Akt activation and resulted in suppression of alpha1(I) collagen mRNA expression, suggesting a PI3K-mediated process. These changes were reproduced by overexpression of the dominant-negative p85alpha mutant. A443654.3, an Akt inhibitor, opposed Akt activation, leading to downregulation of alpha1(I) collagen mRNA. Overexpression of the dominant-negative Akt mutant led to similar alterations.

CONCLUSION

Leptin has a direct action on liver fibrogenesis by stimulating alpha1(I) collagen production in activated HSC. The process appears to be mediated by the PI3K/Akt pathway through activated JAK1.

Expression of MMPs and TIMPs in liver fibrosis - a systematic review with special emphasis on anti-fibrotic strategies

In liver tissue matrix metalloproteinases (MMPs) and their specific inhibitors (tissue inhibitors of metalloproteinases, TIMPs) play a pivotal role in both, fibrogenesis and fibrolysis. The current knowledge of the pathophysiology of liver fibrogenesis with special emphasis on MMPs and TIMPs is presented. A systematic literature search was conducted. All experimental models of liver fibrosis that evaluated a defined anti-fibrotic intervention in vivo or in vitro considering MMPs and TIMPs were selected. The methodological quality of all these publications has been critically appraised using an objective scoring system and the content has been summarized in a table.

Transforming growth factor-beta1 stimulates heme oxygenase-1 expression via the PI3K/Akt and NF-kappaB pathways in human lung epithelial cells

A previous report showed that transforming growth factor-beta1 (TGF-beta1) can induce heme oxygenase-1 (HO-1) expression, attenuate cellular injury, and maintain tissue homeostasis. In this study, we investigated the involvement of phosphoinositide-3-OH-kinase (PI3K)/Akt and the nuclear factor-kappaB (NF-kappaB) signaling pathway in TGF-beta1-induced HO-1 expression in human lung epithelial cells (A549). Treatment of A549 cells with TGF-beta1 caused HO-1 to be expressed in a concentration- and time-dependent manner. Treatment of A549 cells with LY 294002 (2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one, a PI3K inhibitor), an Akt inhibitor, and the dominant negative mutant of Akt (Akt DN) inhibited TGF-beta1-induced HO-1 expression and HO-1-luciferase activity. Stimulation of cells with TGF-beta1 caused an increase in Akt phosphorylation in a time-dependent manner, which was inhibited by wortmannin and LY 294002 (PI3K inhibitors). In addition, treatment of A549 cells with Bay 117082 ((E)-3-[4-methylphenylsulfonyl]-2-propenenitrile, an IkappaB phosphorylation inhibitor), pyrrolidine dithiocarbamate (PDTC, an NF-kappaB inhibitor), and the dominant negative mutant of IkappaBalpha (IkappaBalphaM) inhibited TGF-beta1-induced HO-1 expression and HO-1-luciferase activity. Treatment of A549 cells with TGF-beta1-induced IkappaB kinase alpha/beta (IKKalpha/beta) phosphorylation, IkappaBalpha phosphorylation, IkappaBalpha degradation, p65 Ser536 phosphorylation, and kappaB-luciferase activity. The TGF-beta1-mediated increases in IKKalpha/beta phosphorylation, p65 Ser536 phosphorylation, and kappaB-luciferase activity were inhibited by LY 294002, an Akt inhibitor, and Akt DN. Taken together, these results suggest that the PI3K/Akt dependent IKKalpha/beta/NF-kappaB signaling pathway plays an important role in TGF-beta1-induced HO-1 expression in A549 cells.

PI3K is involved in PDGF-beta receptor upregulation post-PDGF-BB treatment in mouse HSC

Increased expression of PDGF-beta receptors is a landmark of hepatic stellate cell activation and transdifferentiation into myofibroblasts. However, the molecular mechanisms that regulate the fate of the receptor are lacking. Recent studies suggested that N-acetylcysteine enhances the extracellular degradation of PDGF-beta receptor by cathepsin B, thus suggesting that the absence of PDGF-beta receptors in quiescent cells is due to an active process of elimination and not to a lack of expression. In this communication we investigated further molecular mechanisms involved in PDGF-beta receptor elimination and reappearance after incubation with PDGF-BB. We showed that in culture-activated hepatic stellate cells there is no internal protein pool of receptor, that the protein is maximally phosphorylated by 5 min and completely degraded after 1 h by a lysosomal-dependent mechanism. Inhibition of receptor autophosphorylation by tyrphostin 1296 prevented its degradation, but several proteasomal inhibitors had no effect. We also showed that receptor reappearance is time and dose dependent, being more delayed in cells treated with 50 ng/ml (48 h) compared with 10 ng/ml (24 h).

Leucine stimulates procollagen alpha1(I) translation on hepatic stellate cells through ERK and PI3K/Akt/mTOR activation

The essential amino acid leucine has been described to specifically activate signaling pathways leading to the activation of the translational machinery and the increase of total protein synthesis. Regulation of type I collagen production by hepatic stellate cells (HSC) is a multistep process involving transcriptional and post-transcriptional mechanisms. In the present work we studied the effect of leucine on translation regulation of collagen alpha1(I) production in HSC and the signaling pathways involved. Treatment of HSC with 5 mM leucine did not alter half-life or steady state levels of procollagen alpha1(I) mRNA, but caused an increase in procollagen alpha1(I) protein that correlated with changes of components involved in translational regulation, like enhanced 4E-BP1, Mnk-1, and eIF4E phosphorylation. Leucine also induced mTOR, ERK, and Akt phosphorylation in HSC, without affecting p38 and JNK activation. Pre-treatment of HSC with PD098059, wortmannin, or rapamycin prevented the profibrogenic action of leucine due to the inhibition of different molecular mechanisms. These results suggest leucine is a profibrogenic agent for HSC, activating signaling pathways that lead to an enhancement of collagen alpha1(I) production through translational regulation.

Loss of MMP 13 attenuates murine hepatic injury and fibrosis during cholestasis

Cholestasis occurs in a variety of clinical settings and often results in liver injury and secondary biliary fibrosis. Several matrix metalloproteinases (MMPs) are upregulated in the liver during cholestasis. The function of the major interstitial collagenase, MMP-13, in the initial phase of liver fibrosis is unknown. The aim of this study was to evaluate the role of MMP-13 during the development of cholestasis-induced liver fibrosis by comparing wild-type and MMP-13-deficient mice. Cholestasis was induced by bile duct ligation (BDL) for 5 days or 3 weeks. Activation and proliferation of hepatic stellate cells (HSCs) were detected by immunohistochemistry. Expression of MMP-13 mRNA increased significantly in BDL livers of WT mice. After BDL for 3 weeks liver fibrosis was suppressed in MMP-13-deficient mice versus WT animals. Activation and proliferation of HSCs were also suppressed in livers of MMP-13-deficient mice after BDL. To clarify the mechanism of this suppression, samples from 5-day BDL mice were used for evaluation of liver injury. Compared with those in WT animals, serum ALT and the number of hepatic neutrophils were reduced in MMP-13-deficient mice. Increased expression of the mRNA of inflammatory mediators such as tumor necrosis factor-alpha (TNF-alpha) was significantly suppressed in livers of MMP-13-deficient mice. Upregulation of fibrogenic markers, for example, transforming growth factor beta1 (TGF-beta1), was also significantly suppressed in livers of MMP-13-deficient mice versus in WT mice. In conclusion, distinct from the known function of interstitial collagenase to reduce liver fibrosis by degrading the extracellular matrix, MMP-13 contributes to accelerating fibrogenesis in cholestatic livers by mediating the initial inflammation of the liver.

Confirmation of a linkage between H-Ras and MMP-13 expression as well as MMP-9 by chemical genomic approach

As farnesylation of the Ras protein by farnesyl transferase is a critical step for the Ras functional activity, the farnesyl transferase inhibitor could affect H-Ras functions and the inhibitors such as arteminolide, SCH66336 and LB42908 completely inhibited Ras-farnesylation. However, they did not induce apoptosis of H-Ras-transformed cells with concentration for blocking H-Ras farnesylation. To determine the antitumor effects of the inhibitors, it was analyzed through the expression profile of genes, regulated by activated H-Ras or FTIs by using cDNA microarray. On the basis of the results, the relationship between H-Ras and MMPs expression was confirmed by RT-PCR, Western bolt, zymographic analysis and angiogenesis assay. Our results suggested that activation of MMP-13 as well as MMP-9 induced by H-Ras is involved in angiogenesis and with farnesyl transferase inhibitors, in part, exerts their anticancer effects. We confirmed that MMP-13 is a critical H-Ras target gene through chemical genomic approaches with farnesyl transferase inhibitors.

Involvement of the serine/threonine p70S6 kinase in TGF-beta1-induced ADAM12 expression in cultured human hepatic stellate cells

BACKGROUND/AIMS

In chronic liver injury, quiescent hepatic stellate cells change into proliferative myofibroblast-like cells, which are a main source of fibrosis. We have recently reported that these cells synthesize ADAM12, a disintegrin and metalloprotease whose expression is up-regulated by TGF-beta1 in liver cancers. Here, we studied the role of the serine/threonine p70S6 kinase (p70S6K) in regulating TGF-beta1-induced ADAM12 expression.

RESULTS

The phophatidylinositol 3-kinase (PI3K) inhibitor LY294002 and the mitogen-activated protein kinase inhibitor, UO126, decreased the TGF-beta1-dependent ADAM12 expression and prevented the phosphorylation of p70S6K. In addition, TGF-beta1-induced ADAM12 up-regulation was blocked by the Frap/mTOR inhibitor rapamycin, which abrogated the phosphorylation of p70S6K. In untreated cells, LY294002 but not rapamycin diminished the basal ADAM12 expression related to inhibition of Akt and the glycogen synthase kinase-3 phosphorylation.

CONCLUSIONS

The data suggest that TGF-beta1 induces ADAM12 gene expression through both the PI3K/Frap-mTOR/p70S6K and MEK/ERK pathways. In addition, activation of the PI3 pathway might be involved in the basal ADAM12 expression in cultured hepatic stellate cells. The involvement of PI3K in ADAM12 expression, similar to that previously observed for collagen I and fibronectin, suggests common pathways for gene up-regulation in hepatic stellate cells that occur during liver fibrogenesis and contribute to tumor progression.

Mechanisms of liver fibrosis

Liver fibrosis represents a significant health problem worldwide of which no acceptable therapy exists. The most characteristic feature of liver fibrosis is excess deposition of type I collagen. A great deal of research has been performed to understand the molecular mechanisms responsible for the development of liver fibrosis. The activated hepatic stellate cell (HSC) is the primary cell type responsible for the excess production of collagen. Following a fibrogenic stimulus, HSCs change from a quiescent to an activated, collagen-producing cell. Numerous changes in gene expression are associated with HSC activation including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses in understanding the molecular basis of collagen gene regulation have revealed a complex process offering the opportunity for multiple potential therapeutic strategies. However, further research is still needed to gain a better understanding of HSC activation and how this cell maintains its fibrogenic nature. In this review we describe many of the molecular events that occur following HSC activation and collagen gene regulation that contribute to the fibrogenic nature of these cells and provide a review of therapeutic strategies to treat this disease.

MKK3/6-p38 MAPK negatively regulates murine MMP-13 gene expression induced by IL-1beta and TNF-alpha in immortalized periodontal ligament fibroblasts

Matrix metalloprotease-13 (MMP-13) or collagenase-3 is involved in a number of pathologic processes such as tumor metastasis and angiogenesis, osteoarthritis, rheumatoid arthritis and periodontal diseases. These conditions are associated with extensive degradation of both connective tissue and bone. This report examines gene regulation mechanisms and signal transduction pathways involved in Mmp-13 expression induced by proinflammatory cytokines in periodontal ligament (PDL) fibroblasts. Mmp-13 mRNA expression was increased 10.7 and 9.5 fold after stimulation with IL-1beta (5 ng/mL) and TNF-alpha (10 ng/mL), respectively. However, inhibition of p38 MAPKinase with SB203580 resulted in significant (p<0.001) induction (23.2 and 18.1 fold, respectively) of Mmp-13 mRNA as assessed by real time PCR. Negative regulation of IL-1beta induced Mmp-13 expression was confirmed by inhibiting p38 MAPK gene expression with siRNA. Transient transfection of dominant negative forms of MKK3 and MKK6 also resulted in increased levels of Mmp-13 mRNA after IL-1beta stimulation. Mmp-13 mRNA expression induced by TNF-alpha was decreased by JNK and ERK inhibition. Western blot and zymogram analysis indicated that Mmp-13 protein expression induced by the proinflammatory cytokines were also upregulated by inhibition of p38 MAPK. Reporter gene experiments using stable cell lines harboring 660-bp sequence of the murine Mmp-13 proximal promoter indicated that transcriptional mechanisms were at least partially involved in this negative regulation of Mmp-13 expression by p38 MAPK and upstream MKK3/6. These results suggest a negative transcriptional regulatory mechanism mediated by p38 MAPK and upstream MKK3/6 on Mmp-13 expression induced by proinflammatory cytokines in PDL fibroblasts.