Platelet-derived growth factor receptor tyrosine kinase inhibitor AG1295 attenuates rat hepatic stellate cell growth

Therapeutic Potential of Benzimidazoisoquinoline Derivatives in Alleviating Murine Hepatic Fibrosis

Short Title: Benzimidazoisoquinoline derivatives as potent antifibrotics Hepatic fibrosis is a pathological condition of liver disease with an increasing number of cases worldwide. Therapeutic strategies are warranted to target the activated hepatic stellate cells (HSCs), the collagen-producing cells, an effective strategy for controlling the disease progression. Benzimidazoisoquinoline derivatives were synthesized as hybrid molecules by the combination of benzimidazoles and isoquinolines to evaluate their anti-fibrotic potential using an in-vitro and in-vivo model of hepatic fibrosis. A small library of benzimidazoisoquinoline derivatives (1-17 and 18-21) was synthesized from 2-aryl benzimidazole and acetylene functionalities through C-H and N-H activation. Compounds (10 and its recently synthesized derivatives 18-21) depicted a significant decrease in PDGF-BB and/or TGFβ-induced proliferation (1.7-1.9 -fold), migration (3.5-5.0 -fold), and fibrosis-related gene expressions in HSCs. These compounds could revert the hepatic damage caused by chronic exposure to hepatotoxicants, ethanol, and/or carbon tetrachloride as evident from the histological, biochemical, and molecular analysis. Anti-fibrotic effect of the compounds was supported by the decrease in the malondialdehyde level, collagen deposition, and gene expression levels of fibrosis-related markers such as α-SMA, COL1α1, PDGFRβ, and TGFRIIβ in the preclinical models of hepatic fibrosis. In conclusion, the synthesized benzimidazoisoquinoline derivatives (compounds 18, 19, 20, and 21) possess anti-fibrotic therapeutic potential against liver fibrosis.

Tetrahydroquinoxalines induce a lethal evisceration phenotype in Haemonchus contortus in vitro

In the present study, the anthelmintic activity of a human tyrosine kinase inhibitor, AG-1295, and 14 related tetrahydroquinoxaline analogues against Haemonchus contortus was explored. These compounds were screened against parasitic larvae - exsheathed third-stage (xL3) and fourth-stage (L4) - using a whole-organism screening assay. All compounds were shown to have inhibitory effects on larval motility, development and growth, and induced evisceration through the excretory pore in xL3s. The estimated IC₅₀ values ranged from 3.5 to 52.0 μM for inhibition of larval motility or development. Cytotoxicity IC₅₀ against human MCF10A cells was generally higher than 50 μM. Microscopic studies revealed that this eviscerated (Evi) phenotype occurs rapidly (<20 min) and relates to a protrusion of internal tissues and organs (evisceration) through the excretory pore in xL3s; severe pathological damage in L4s as well as a suppression of larval growth in both stages were also observed. Using a relatively low concentration (12.5 μM) of compound m10, it was established that the inhibitor has to be present for a relatively short time (between 30 h and 42 h) during in vitro development from xL3 to L4, to induce the Evi phenotype. Increasing external osmotic pressure prevented evisceration and moulting, and xL3s remained unaffected by the test compound. These results point to a mode of action involving a dysregulation of morphogenetic processes during a critical time-frame, in agreement with the expected behaviour of a tyrosine kinase inhibitor, and suggest potential for development of this compound class as nematocidal drugs.

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Tetrahydroquinoxalines kill Haemonchus contortus larvae in vitro.

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Compounds induce a lethal evisceration phenotype (Evi).

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The Evi phenotype is associated with the timing of ecdysis.

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These compounds might be developable as nematocidal drugs.

PDGF signaling pathway in hepatic fibrosis pathogenesis and therapeutics (Review)

The platelet‑derived growth factor (PDFG) signaling pathway exerts persistent activation in response to a variety of stimuli and facilitates the progression of hepatic fibrosis. Since this pathway modulates a broad spectrum of cellular processes, including cell growth, differentiation, inflammation and carcinogenesis, it has emerged as a therapeutic target for hepatic fibrosis and liver‑associated disorders. The present review exhibits the current knowledge of the role of the PDGF signaling pathway and its pathological profiles in hepatic fibrosis, and assesses the potential of inhibitors which have been investigated in the experimental hepatic fibrosis model, in addition to the clinical challenges associated with these inhibitors.

Screening of the 'Stasis Box' identifies two kinase inhibitors under pharmaceutical development with activity against Haemonchus contortus

Background

In partnership with the Medicines for Malaria Venture (MMV), we screened a collection (‘Stasis Box’) of 400 compounds (which have been in clinical development but have not been approved for illnesses other than neglected infectious diseases) for inhibitory activity against Haemonchus contortus, in order to attempt to repurpose some of the compounds to parasitic nematodes.

Methods

We assessed the inhibition of compounds on the motility and/or development of exsheathed third-stage (xL3s) and fourth-stage (L4) larvae of H. contortus using a whole-organism screening assay.

Results

In the primary screen, we identified compound MMV690767 (also known as SNS-032) that inhibited xL3 motility by ~70% at a concentration of 20 μM after 72 h as well as compound MMV079840 (also known as AG-1295), which induced a coiled xL3 phenotype, with ~50% inhibition on xL3 motility. Subsequently, we showed that SNS-032 (IC₅₀ = 12.4 μM) and AG-1295 (IC₅₀ = 9.92 ± 1.86 μM) had a similar potency to inhibit xL3 motility. Although neither SNS-032 nor AG-1295 had a detectable inhibitory activity on L4 motility, both compounds inhibited L4 development (IC₅₀ values = 41.24 μM and 7.75 ± 0.94 μM for SNS-032 and AG-1295, respectively). The assessment of the two compounds for toxic effects on normal human breast epithelial (MCF10A) cells revealed that AG-1295 had limited cytotoxicity (IC₅₀ > 100 μM), whereas SNS-032 was quite toxic to the epithelial cells (IC₅₀ = 1.27 μM).

Conclusions

Although the two kinase inhibitors, SNS-032 and AG-1295, had moderate inhibitory activity on the motility or development of xL3s or L4s of H. contortus in vitro, further work needs to be undertaken to chemically alter these entities to achieve the potency and selectivity required for them to become nematocidal or nematostatic candidates.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2246-x) contains supplementary material, which is available to authorized users.

The Role of Embryonic Stem Cell-expressed RAS (ERAS) in the Maintenance of Quiescent Hepatic Stellate Cells

Hepatic stellate cells (HSCs) were recently identified as liver-resident mesenchymal stem cells. HSCs are activated after liver injury and involved in pivotal processes, such as liver development, immunoregulation, regeneration, and also fibrogenesis. To date, several studies have reported candidate pathways that regulate the plasticity of HSCs during physiological and pathophysiological processes. Here we analyzed the expression changes and activity of the RAS family GTPases and thereby investigated the signaling networks of quiescent HSCs versus activated HSCs. For the first time, we report that embryonic stem cell-expressed RAS (ERAS) is specifically expressed in quiescent HSCs and down-regulated during HSC activation via promoter DNA methylation. Notably, in quiescent HSCs, the high level of ERAS protein correlates with the activation of AKT, STAT3, mTORC2, and HIPPO signaling pathways and inactivation of FOXO1 and YAP. Our data strongly indicate that in quiescent HSCs, ERAS targets AKT via two distinct pathways driven by PI3Kα/δ and mTORC2, whereas in activated HSCs, RAS signaling shifts to RAF-MEK-ERK. Thus, in contrast to the reported role of ERAS in tumor cells associated with cell proliferation, our findings indicate that ERAS is important to maintain quiescence in HSCs.

Role of retinoic acid and platelet-derived growth factor receptor cross talk in the regulation of neonatal gonocyte and embryonal carcinoma cell differentiation

Neonatal gonocytes are direct precursors of spermatogonial stem cells, the cell pool that supports spermatogenesis. Although unipotent in vivo, gonocytes express pluripotency genes common with embryonic stem cells. Previously, we found that all-trans retinoic acid (RA) induced the expression of differentiation markers and a truncated form of platelet-derived growth factor receptor (PDGFR)β in rat gonocytes, as well as in F9 mouse embryonal carcinoma cells, an embryonic stem cell-surrogate that expresses somatic lineage markers in response to RA. The present study is focused on identifying the signaling pathways involved in RA-induced gonocyte and F9 cell differentiation. Mitogen-activated protein kinase kinase (MEK) 1/2 activation was required during F9 cell differentiation towards somatic lineage, whereas its inhibition potentiated RA-induced Stra8 expression, suggesting that MEK1/2 acts as a lineage specification switch in F9 cells. In both cell types, RA increased the expression of the spermatogonial/premeiotic marker Stra8, which is in line with F9 cells being at a stage before somatic-germline lineage specification. Inhibiting PDGFR kinase activity reduced RA-induced Stra8 expression. Interestingly, RA increased the expression of PDGFRα variant forms in both cell types. Together, these results suggest a potential cross talk between RA and PDGFR signaling pathways in cell differentiation. RA receptor-α inhibition partially reduced RA effects on Stra8 in gonocytes, indicating that RA acts in part via RA receptor-α. RA-induced gonocyte differentiation was significantly reduced by inhibiting SRC (v-src avian sarcoma [Schmidt-Ruppin A-2] viral oncogene) and JAK2/STAT5 (Janus kinase 2/signal transducer and activator of transcription 5) activities, implying that these signaling molecules play a role in gonocyte differentiation. These results suggest that gonocyte and F9 cell differentiation is regulated via cross talk between RA and PDGFRs using different downstream pathways.

HBV promotes the proliferation of hepatic stellate cells via the PDGF-B/PDGFR-β signaling pathway in vitro

The activation of hepatic stellate cells (HSCs) is closely associated with liver fibrosis in chronic hepatitis B virus (HBV) infection. However, the molecular mechanisms leading to HSC activation remain unclear. It has been reported that the platelet-derived growth factor-B (PDGF-B)/PDGF receptor-β (PDGFR-β) signaling pathway is involved in this process. Thus, we investigated whether HBV and its protein contribute to HSC proliferation by the PDGF-B/PDGFR-β signaling pathway. HBV particles were purified from the supernatant of HepG2.2.15 cells by ultracentrifugation and the cell lines carrying HBV preS, e, c or x genes were obtained. After incubation with HBV particles or co-cultured with the cell lines expressed in the viral protein, the proliferation of LX-2 cells, an HSC cell line, were detected by flow cyto-metry and real-time PCR and the expression of molecules related to the PDGF-B/PDGFR-β signaling pathway were further measured. Our results indicated that HBV particles, c and x proteins promoted LX-2 proliferation and increased the mRNA levels of PDGF-B, PDGFR-β, collagen-I and α-smooth muscle actin (α-SMA), as well as the phosphorylation of PDGFR-β; however, the expression protein levels of PDGF-B and PDGFR-β remained unchanged. In conclusion, HBV particles and HBV c and x proteins promote HSC proliferation and fibrogenesis in vitro and the PDGF-B/PDGFR-β signaling pathway is important in this process.

Pancreatic carcinoma cells stimulate proliferation and matrix synthesis of hepatic stellate cells

BACKGROUND/AIMS

Pancreatic ductal carcinoma cells induce fibrosis by stimulating pancreatic stellate cells to proliferate and synthesize matrix. Desmoplastic reaction has also been observed in liver metastases of pancreatic carcinoma. Hepatic stellate cells are similar to pancreatic stellate cells and may contribute to the desmoplasia associated with liver metastases of pancreatic cancer. The aim of this study was to determine the role of hepatic stellate cells in metastasis.

METHODS

Markers of the desmoplastic reaction in tumors induced in nude mice (n=6) by subcutaneously injecting pancreatic carcinoma cells with and without hepatic stellate cells were monitored immunohistochemically. Paracrine stimulation was studied by measuring matrix synthesis (collagen type I and c-fibronectin protein) and cell proliferation.

RESULTS

Supernatants of pancreatic carcinoma cells stimulated proliferation of cultured hepatic stellate cells and synthesis of collagen I and c-fibronectin. Preincubation of the supernatants with neutralizing antibodies against fibroblast growth factor 2, transforming growth factor-beta1, and platelet-derived growth factor significantly reduced these stimulatory effects. Subcutaneous injection of hepatic stellate cells induced earlier onset and faster-growth of subcutaneous fibrotic pancreatic tumors in nude mice.

CONCLUSIONS

Hepatic stellate cells enhance tumor growth in nude mouse and may play an important role in metastasis formation.

Effects of plumbago zeylanica on the proliferation, apoptosis and cell cycle of HSC-T6

AIM: To observe the effects of the plumbago -containing serum on proliferation, apoptosis and cell cycle of the rat hepatic stellate cells (HSC-T6) so as to explore the plumbago's anti-hepatic fibrosis effects and its mechanism.

METHODS: Plumbago-containing serum was obtained by intragastric administration to the SD rats with plumbago decoction. HSC-T6 was incubated at different concentrations of the plumbago -containing serum. The colchicine and Fufang compound biejia containing serum were used as positive control group. MTT were applied to measure the HSC-T6 proliferation and flow cytometry to measure the cell apoptosis, and the percentage of DNA content in different groups.

RESULTS: Compared with blank group, all the plumbago-containing serum groups had a significantly higher proliferation inhibition rate and apoptosis rate (P < 0.01). When the plumbago-containing serum concentration was increased, proliferation inhibition rate and apoptosis rate to HSC-T6 reached the highest. Its action intensity was the same as compound biejia but stronger than that of Colchicine's. Cell percentage in G₂/M phase had no significant change in each group. Compared with blank control group, the cell percentage in G₀/G₁ phase was significantly increased and significantly decreased in S phase in all plumbago -containing serum groups, (55.23% ± 2.83%, 52.60% ± 2.26%, 48.75% ± 1.37% vs 44.08% ± 1.41%, all P < 0.01; 31.47% ± 1.26%, 34.14% ± 1.17%, 40.28% ± 1.62% vs 47.36% ± 1.35%, all P < 0.01). When the plumbago-containing serum concentration was decreased, the cell percentage was significantly decreased in G₀/G₁ phase and significantly decreased in S phase. Compared with colchicine group at the same serum concentration, the cell percentage was significantly increased in G₀/G₁ phase and significantly decreased in S phase in all plumbago-containing serum groups, compared with compound biejia group, but there was no significant difference.

CONCLUSION: The plumbago-containing serum can inhibit the proliferation and induce apoptosis to HSC-T6, in a dose-dependent manner. Its action intensity is the same as compound biejia but stronger than that of Colchicine's. The possible mechanism to inhibit the proliferation of HSC-T6 may be related with HSC-T6's stagnation in G₀/G₁ phase due to plumbago's action to prevent HSC-T6 to pass G₁/S checkpoint.

RNA interference targeting the platelet-derived growth factor receptor beta subunit ameliorates experimental hepatic fibrosis in rats

BACKGROUND/AIMS

Platelet-derived growth factor (PDGF) is the strongest stimulator of the proliferation of hepatic stellate cells (HSCs). PDGF receptor beta subunit (PDGFR-beta) is acquired on HSCs proliferation induced by PDGF. In this study, we aim to investigate the effect of PDGFR-beta small interference RNA (siRNA) on experimental hepatic fibrosis.

METHODS

We constructed a PDGFR-beta siRNA expression plasmid and investigated its effect on the activation of HSCs. Bromodeoxyuridine incorporation was performed to investigate the effect of PDGFR-beta siRNA on HSCs proliferation. A hydrodynamics-based transfection method was used to deliver PDGFR-beta siRNA to rats with hepatic fibrosis. The distribution of transgenes in the liver was observed by immunofluorescence. The antifibrogenic effect of PDGFR-beta siRNA was investigated pathologically.

RESULTS

Platelet-derived growth factor receptor-beta subunit siRNA could significantly downregulate PDGFR-beta expression, suppress HSCs activation, block the mitogen-activated protein kinase signalling pathway and inhibit HSCs proliferation in vitro. PDGFR-beta siRNA expression plasmid could be delivered into activated HSCs by the hydrodynamics-based transfection method, and remarkably improve the liver function of the rat model induced by dimethylnitrosamine and bile duct ligation. Furthermore, the progression of fibrosis in the liver was significantly suppressed by PDGFR-beta siRNA in both animal models.

CONCLUSIONS

Platelet-derived growth factor receptor-beta subunit siRNA may be presented as an effective antifibrogenic gene therapeutic method for hepatic fibrosis.

Targeted inhibition of platelet-derived growth factor receptor-beta subunit in hepatic stellate cells ameliorates hepatic fibrosis in rats

The activation of hepatic stellate cells (HSCs) is the key event of the pathogenesis of hepatic fibrosis. Platelet-derived growth factor (PDGF) is the most potent mitogen for HSCs, and PDGF receptor-beta subunit (PDGFR-beta) is required for the proliferation of HSCs induced by PDGF. In this study, a high gene-silencing-efficacy PDGFR-beta small interference RNA (siRNA) was synthesized that could suppress the PDGFR-beta expression and inhibit the activation and proliferation but could not induce the apoptosis of HSCs in vitro. To avoid the side effect of nonspecific interference of PDGFR-beta, we constructed an HSCs-specific short hairpin RNA (shRNA) expression plasmid in which PDGFR-beta shRNA was driven by a glial fibrillary acidic protein (GFAP) promoter. The double-staining immunofluorescence examination indicated that GFAP promoter could target the transgene expression into HSCs in carbon tetrachloride induced acute injured rat's liver and bile duct ligation (BDL)-induced chronic injured rat's liver. Furthermore, HSCs-specific PDGFR-beta shRNA could relieve liver injury and hepatic fibrosis in the rat's model induced by BDL. This study demonstrates that PDGFR-beta siRNA may be presented as an antifibrogenic agent. The application of HSCs-specific RNA interference induced by the GFAP promoter might supply a new powerful tool for cell-specific gene therapy of hepatic fibrogenesis.

Platelet-derived growth factor signals play critical roles in differentiation of longitudinal smooth muscle cells in mouse embryonic gut

In the development of mouse gut, longitudinal smooth muscle cells (LMC) and interstitial cells of Cajal (ICC) originate from common precursor cells expressing c-Kit. Recently, some gastrointestinal stromal tumours, which develop from smooth muscle layers of the gut and have gain-of-function mutations of c-kit, have been reported to have gain-of-function mutations of platelet-derived growth factor (PDGF) receptor alpha gene. These data raise the possibility that PDGF signalling might be involved in the development of LMC. Therefore, we examined the expression pattern of the PDGF signal family of embryonic gut by immunohistochemistry and in situ hybridization, and investigated the role of PDGF signals in the development of smooth muscle layers in mouse gut using a new organ culture system. During embryonic development, the circular muscle layer expressed PDGF-A, enteric neurons expressed PDGF-B and common precursor cells of LMC and ICC expressed both PDGF receptor alpha and beta. The selective PDGF receptor inhibitor AG1295 suppressed the differentiation of LMC in gut explants. We conclude that PDGF signals play critical roles in the differentiation of LMC in mouse embryonic gut.

Genistein modifies liver fibrosis and improves liver function by inducing uPA expression and proteolytic activity in CCl4-treated rats

AIM

To evaluate the effect of genistein on the fibrosis and matrix degradation caused by experimentally induced fibrosis in rats.

METHODS

Hepatic fibrosis was brought about by chronic administration of carbon tetrachloride to rats. To evaluate the effect of genistein on liver fibrosis and function, total collagen content and proteolytic activity in the liver were quantified. Urokinase-type plasminogen activator (uPA) expression during experimental fibrosis was localized by immunohistochemistry. Histopathological changes were evaluated using light and electron microscopy.

RESULTS

Animals with fibrosis and treated with genistein showed an important reduction (73%) in hepatic collagen content as well as an improvement in liver function (p < 0.001). Genistein increased the capacity of the liver to degrade type I collagen and Matrigel (3.1- and 3.7-fold, respectively; p < 0.001) in animals with liver fibrosis. Genistein increased the number of uPA-immunoreactive cells. The increase in the uPA expression correlated with an increase in proteolytic activity. Histological analysis revealed a reduction in the number of fiber septa in pericentral and perisinusoidal areas. Transmission electron micrographs of livers from animals with fibrosis and treated with genistein showed a reduction in the number of hepatic stellate cells activated and a smaller number of collagen fibers.

CONCLUSION

Genistein is able to improve the liver after injury and fibrosis induced by chronic administration of carbon tetrachloride. This finding suggests that genistein has antifibrogenic potential and could therefore be useful for treating chronic liver disease.

Platelet-derived growth factor receptor beta-mediated phosphorylation of MUC1 enhances invasiveness in pancreatic adenocarcinoma cells

MUC1 is a heterodimeric transmembrane glycoprotein that is overexpressed and aberrantly glycosylated in ductal adenocarcinomas. Differential phosphorylation of the MUC1 cytoplasmic tail (MUC1CT) has been associated with signaling events that influence the proliferation and metastasis of cancer cells. We identified a novel tyrosine phosphorylation site (HGRYVPP) in the MUC1CT by mass spectrometric analysis of MUC1 from human pancreatic adenocarcinoma cell lines. Analyses in vitro and in vivo showed that platelet-derived growth factor receptor beta (PDGFRbeta) catalyzed phosphorylation of this site and of tyrosine in the RDTYHPM site. Stimulation of S2-013.MUC1F cells with PDGF-BB increased nuclear colocalization of MUC1CT and beta-catenin. PDGF-BB stimulation had no significant effect on cell proliferation rate; however, it enhanced invasion in vitro through Matrigel and in vivo tumor growth and metastases. Invasive properties of the cells were significantly altered on expression of phosphorylation-abrogating or phosphorylation-mimicking mutations at these sites. We propose that interactions of MUC1 and PDGFRbeta induce signal transduction events that influence the metastatic properties of pancreatic adenocarcinoma.

Liver fibrosis induced by hepatic overexpression of PDGF-B in transgenic mice

BACKGROUND/AIMS

In hepatic fibrogenesis, stellate cells are activated leading to production and deposition of extracellular matrix. To clarify the role of PDGF-B in liver fibrogenesis, we overexpressed PDGF-B in the liver of transgenic mice.

METHODS

Transgenic mice for the conditional overexpression of PDGF-B in the liver under control of an albumin promoter were generated utilising the Cre/loxP system. Constitutive PDGF-B expression was achieved after breeding with mice expressing Cre-recombinase under actin promoter control. Tamoxifen inducible expression was achieved after breeding with mice expressing Cre under transthyretin receptor promoter control. Levels of fibrosis were assessed and the expression of regulators of matrix remodelling was measured.

RESULTS

PDGF-B expression caused hepatic stellate cell and myofibroblast activation marked by alpha-smooth muscle actin and PDGFR-beta expression. Liver fibrosis was verified macroscopically, histologically and by collagen I mRNA quantification in 4-6 week-old animals. MMP-2, MMP-9 and TIMP-1 were upregulated whereas TGF-beta expression was unchanged.

CONCLUSIONS

We identified PDGF-B as a proliferative and profibrogenic stimulus and potential inducer of stellate cell transdifferentiation in vivo. PDGF-B overexpression causes liver fibrosis without significantly upregulating TGF-beta1, suggesting a TGF-beta-independent mechanism. The established model provides a tool for testing anti-PDGF-B therapeutic strategies in liver fibrosis in vivo.

Involvement of phosphatidylinositol 3-kinase and extracellular-regulated kinase in hepatic stellate cell antioxidant response and myofibroblastic transdifferentiation

Liver fibrogenesis is dependent upon transdifferentiation of hepatic stellate cells to a profibrogenic phenotype. Prooxidant stress purportedly stimulates both an antioxidant response and myofibroblastic transdifferentiation with fibrogenic gene expression; however, mechanisms by which oxidative stress mediates stellate cell activation remain unclear. To this end, stellate cells were treated with tert-butylhydroquinone (tBHQ), a known inducer of antioxidant response genes. As anticipated, tBHQ induced expression of antioxidant response element (ARE)-regulated genes via the transcription factor Nrf2. Further, tBHQ promoted transdifferentiation of quiescent stellate cells cultured on Engelbreth-Holm-Swarm extracellular matrix. Pretreatment of cultured stellate cells with a phosphatidylinositol 3-kinase (PI3K) inhibitor blocked tBHQ-mediated ARE-dependent gene induction as well as stellate cell transdifferentiation. In contrast, extracellular signal-regulated kinase, which was demonstrated to be prominently phosphorylated following tBHQ treatment, was not found to affect either induction of the antioxidant response nor stellate cell transdifferentiation. These data implicate involvement of PI3K pathways in tBHQ-mediated stellate cell activation and demonstrate a requirement for PI3K in the antioxidant response of hepatic stellate cells.

Oral imatinib treatment reduces early fibrogenesis but does not prevent progression in the long term

BACKGROUND/AIMS

Transactivated hepatic stellate cells (HSCs) represent the key source of extra cellular matrix (ECM) in fibrotic liver. Imatinib, a potent inhibitor of the PDGF receptor tyrosine kinase, reduces HSC proliferation and fibrogenesis when treatment is initiated before fibrosis has developed. We tested the antifibrotic potential of imatinib in ongoing liver injury and in established fibrosis.

METHODS

BDL-rats were gavage fed with 20 mg/kg/d imatinib either early (days 0-21) or late (days 22-35) after BDL. Untreated BDL-rats served as controls. ECM and activated HSCs were quantified by morphometry. Tissue activity of MMP-2 was determined by gelatin zymography. mRNA expression of TIMP-1 and procollagen alpha1(I) were measured by RT-PCR. Liver tissue concentration of imatinib was measured by tandem mass spectrometry.

RESULTS

Early imatinib reduced ECM formation by 30% (P=0.0455) but left numbers of activated HSCs and procollagen I expression unchanged. MMP-2 activity and TIMP-1 expression were reduced by 50%. Late imatinib treatment did not alter histological or molecular markers of fibrogenesis despite high imatinib tissue levels.

CONCLUSIONS

The antifibrotic effectiveness of imatinib is limited to the early phase of fibrogenesis. In ongoing liver injury other mediators most likely compensate for the inhibited PDGF effect.

PDGF receptor kinase inhibitors for the treatment of PDGF driven diseases

PDGF and its receptors are involved in a variety of diseases: cancers, atherosclerosis, balloon injury induced restenosis, pulmonary fibrosis and more. In all cases enhanced signaling of the receptor is the hallmark. In some cases, like chronic monomyelocytic leukemia (CMML), the persistent PDGFR signaling is essential for the survival of the cancer cell. These findings induced the research community as well as the pharmaceutical industry to develop agents that block PDGFR signaling. The possible utilization of PDGFR kinase inhibitors as anti-restenosis agents is likely to move ahead of the utilization of these agents to treat human malignancies.

Dominant-negative soluble PDGF-beta receptor inhibits hepatic stellate cell activation and attenuates liver fibrosis

Hepatic fibrogenesis is a consequence of hepatic stellate cells that become activated and transdifferentiate into a myofibroblastic phenotype with the ability to proliferate and synthesize large quantities of extracellular matrix components. In this process, platelet-derived growth factor (PDGF) is the most potent stimulus for hepatic stellate cell proliferation and migration, and is overexpressed during active hepatic fibrogenesis. This cytokine binds to the PDGF receptor type beta, activates Ras and sequentially propagates the stimulatory signal sequentially via phosphorylation of Raf-1, MEK and the extracellular-signal regulated kinases ERK1/ERK2. Hepatic injury is associated with both increased autocrine PDGF signaling and upregulation of PDGF receptor. In this study, we report that a dominant-negative soluble PDGF-beta receptor consisting of a chimeric IgG containing the extracellular portion of the PDGF receptor type beta blocks HSC activation and attenuates fibrogenesis induced by ligation of the common bile duct in rats. In culture-activated hepatic stellate cells, the soluble receptor blocks phosphorylation of endogenous PDGF receptor, phosphorylation of the ERK1/EKR2 signal and reduces proliferative activities of HSC. In vivo, both the delivery of the purified soluble PDGF antagonist and the administration of adenoviruses expressing the artificial transgene were able to reduce significantly the expression of collagen and alpha-smooth muscle actin. Our results demonstrate that PDGF plays a critical role in the progression and initiation of experimental liver fibrogenesis, and suggest that early anti-PDGF intervention should have a therapeutical impact on the treatment of liver fibrogenesis.

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Chinese herbs Kangxian ruangan keli inhibits expression of MEK-1 and c-fos in hepatic stellate cell indused by PDGF

AIM: To investigate the effect of Kangxian ruangan keli (KXR) on the expression of MEK-1 and c-fos in hepatic stellate cell (HSC) indused by PDGF.

METHODS: In a serum-free culture system, HSC was treated with a KXR preparation for 24 hours, followed by stimulation with PDGF-BB for 24 hours. Then the cells were incubated again in the medium containing KXR for 3 hours stimulated with PDGF-BB for 5 minutes, and collected. The proliferation of HSC was examined using an MTT assay. MEK-1 was detected with Western blotting and visualized by the enhenced chemiluminescent (ECL) method. The expression of c-fos mRNA was analyzed with in situ hybridization.

RESULTS: The A values for the HSC growing in the media without and with addition of PDGF were 0.170±0.060 and 0.820±0.050, respectively. The PDGF-induced increase was hindered remarkably by KXR preparation in a dose-dependent manner. Reaction values for the systems with 5 g/L and 1.25 g/L of KXR were 0.280±0.030 and 0.430±0.040 respectively, lower significantly than that in the culture free of KXR (0.820±0.050, P < 0.01). In addition, values for MEK-1 in HSC treated with 5 mg/mL and 1.25 mg/mL of KXR were 0.143±0.013, and 0.170±0.007, respectively, being lower than that in the cells treated only with PDGF-BB (0.186±0.010, P < 0.01). The expression level of c-fos mRNA was 0.152±0.010 and 0.163±0.005, respectively, also lower than that of the PDGF group (0.183±0.014, P < 0.01).

CONCLUSION: Within the dose range used in the present study, KXR preparation shows an inhibitory effect on HSC proliferation induced by PDGF. The mechanism of this process may involve interference with Ras-MEK-MAPK singal transduction mediated by PDGF.

Kangxian ruangan keli inhibits hepatic stellate cell proliferation mediated by PDGF

AIM: To investigate the effect of Kangxian ruangan keli (KXR) on hepatic stellate cell (HSC) proliferation mediated by platelet-derived growth factor (PDGF) and the underlying mechanism.

METHODS: In a serum-free culture system, HSCs were treated with a KXR preparation for 24 h, followed by stimulation with PDGF-BB for 24 h. Then the cells were incubated again in the medium containing KXR for 3 h stimulated with PDGF-BB for 5 minutes, and collected. The proliferation of HSC was examined using an MTT assay and flow cytometry. Tyrosine phosphorylation was detected with Western blotting and visualized by the enhenced chemiluminescent (ECL) method.

RESULTS: The OD values for the HSCs growing in the media without and with addition of PDGF were 0.17 ± 0.06 and 0.82 ± 0.05, respectively. The PDGF-induced increase was hindered remarkably by KXR preparation in a dose-dependent manner. The reaction values for the systems with 5 mg/mL, 2.5 mg/mL and 1.25 mg/mL of KXR were 0.28 ± 0.03, 0.37 ± 0.02 and 0.43 ± 0.04, respectively. Moreover, the percentages of S-phase cells in these KXR-containing culture systems were 10.95 ± 1.35, 32.76 ± 1.07 and 43.19 ± 1.09, respectively, all of which were significantly lower than that in the culture free of KXR (68.24 ± 2.72). In addition, the values for tyrosine-phosphorylated protein in HSCs treated with 5 mg/mL and 1.25 mg/mL of KXR were 0.1349 ± 0.0072 and 0.1658 ± 0.0025, respectively, which were smaller than that in the cells treated only with PDGF-BB (0.1813 ± 0.0117).

CONCLUSION: Within the dose range used in the present study, KXR preparation shows an inhibitory effect on HSC proliferation induced by PDGF. The mechanism of this process may involve interference with tyrosine phosphorylation mediated by PDGF.

Effects of PD98059 on proliferation of rat cultured hepatic stellate cells stimulated by acetaldehyde

AIM

To study the effects of PD98059, the specific blocking agent of MEK1, on the proliferation of hepatic stellate cells and expression of Proliferating Cell Nuclear Antigen in rat hepatic stellate cells (HSC).

METHODS

HSC stimulated by acetaldehyde were cultured. The cell growth was evaluated by MTT colorimetric assay. Proliferating cell nuclear antigen (PCNA) was examined by immunocytochemical staining.

RESULTS

PD98059 of 20 μmol/L had an inhibitory effect on proliferation of HSC (P<0.05, 0.109±0.020 vs 0.146±0.030), which was more obvious when cells exposed to PD98059 at 50 and 100 μmol /L (P<0.05, 0.081±0.010, 0.056±0.020 vs 0.146±0.030), and the expression of PCNA also showed a descending tendency with the increase of PD98059 concentration (P<0.05, 0.62±0.09, 0.47±0.04, 0.34±0.04 vs 0.740.05)

CONCLUSION

PD98059 inhibits proliferation of HSC and expression of PCNA, which is correlated with the decreased activity of PCNA.

Requirement of Gbetagamma and c-Src in D2 dopamine receptor-mediated nuclear factor-kappaB activation

The D2 dopamine receptor (D2R) was examined for its ability to mediate nuclear factor-kappaB (NF-kappaB) activation through G proteins. Stimulation of D2R-transfected HeLa cells with its agonist quinpirole induced the expression of a NF-kappaB luciferase reporter and formation of NF-kappaB-DNA complex. This response was blocked by pertussis toxin, and by the Gbetagamma scavengers transducin and beta-adrenergic receptor kinase 1 carboxyl-terminal fragment. Unlike Gi-coupled chemoattractant receptors, D2R activated NF-kappaB without an increase in phospholipase C-beta activity, and the response was only slightly affected by the phosphoinositide 3-kinase inhibitor 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002). In contrast, treatment with genistein and 4-amino-1-tert-butyl-3-(p-methylphenyl)pyrazolo[3,4-d] pyrimidine abolished the induced NF-kappaB activation, suggesting involvement of protein tyrosine kinases. Activation of D2R led to phosphorylation of c-Src at Tyr-418, and expression of a kinase-deficient c-Src inhibited D2R-mediated NF-kappaB activation. The D2R-mediated NF-kappaB activation was not dependent on epidermal growth factor (EGF) receptor transactivation since 4-(3'-chloroanilino)-6,7-dimethoxyquinazoline (AG1478), an EGF receptor-selective tyrphostin used at 1 microM, blocked EGF-induced NF-kappaB activation but not the quinpirole-induced response. In addition, the D2R-mediated NF-kappaB activation was enhanced by over-expression of beta-arrestin 1. These results suggest that D2R-mediated NF-kappaB activation requires Gbetagamma and c-Src, and possibly involves beta-arrestin 1.

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Extracellular signal-regulated kinase in liver fibrogenesis of rat

AIM

To explore the role of ERK signal transduction pathway in the pathogenesis of liver fibrosis via investigating the expression and distribution of ERK1 in rats with liver fibrosis.

METHODS

Liver fibrosis model of rats were made by subcutaneously injecting with CCl4. Thirty-two male SD rats (weight 250-300 g) were randomly scarified at 1, 4 and 8 weeks after injection of CCl4 respectively, and their liver were used to detect ERK1 expression by immunohistochemical staining.

RESULTS

The expression of ERK1 in rats after injection with CCl4 were found chiefly in hepatic stellate cells(HSC)and all significantly higher than those in normal rats(P<0.05). Moreover, it presented with a progressive tendency for the expression of ERK1 in rats respectively at 1st, 4th and 8th week after injection with CCl4 (P<0.05).

CONCLUSION

The activation of ERK signal transduction pathway enhances HSC proliferation, and it may play an important role in liver fibrogenesis in rat.

PDGF and FGF2 regulate oligodendrocyte progenitor responses to demyelination

Acute demyelination of adult CNS, resulting from trauma or disease, is initially followed by remyelination. However, chronic lesions with subsequent functional impairment result from eventual failure of the remyelination process, as seen in multiple sclerosis. Studies using animal models of successful remyelination delineate a progression of events facilitating remyelination. A universal feature of this repair process is extensive proliferation of oligodendrocyte progenitor cells (OPs) in response to demyelination. To investigate signals that regulate OP proliferation in response to demyelination we used murine hepatitis virus-A59 (MHV-A59) infection of adult mice to induce focal demyelination throughout the spinal cord followed by spontaneous remyelination. We cultured glial cells directly from demyelinating and remyelinating spinal cords using conditions that maintain the dramatically enhanced OP proliferative response prior to CNS remyelination. We identify PDGF and FGF2 as significant mitogens regulating this proliferative response. Furthermore, we demonstrate endogenous PDGF and FGF2 activity in these glial cultures isolated from demyelinated CNS tissue. These findings correlate well with our previous demonstration of increased in vivo expression of PDGF and FGF2 ligand and corresponding receptors in MHV-A59 lesions. Together these studies support the potential of these pathways to function in vivo as critical factors in regulating remyelination.

Platelet-derived growth factor up-regulates the expression of transcription factors NF-E2, GATA-1 and c-Fos in megakaryocytic cell lines

Platelet-derived growth factor (PDGF) is a platelet alpha-granule protein. In previous reports, we demonstrated the expression of PDGF receptors on platelets and megakaryocytic cells and that PDGF enhanced the proliferation of megakaryocytic progenitor cells. In this study, we investigated the effects of PDGF on mRNA and protein expressions of megakaryocyte-associated transcription factors, c-Fos, GATA-1, NF-E2 and PU.1, in two human megakaryocytic cell lines CHRF-288-11 and DAMI. RT-PCR/Southern blot analysis and Real-time PCR demonstrated that PDGF increased the mRNA expression of c-Fos, GATA-1 and NF-E2, but not PU.1 in a dose- and time-dependent manner. The activation was confirmed at the protein level by Western blot analysis of both total cell and nuclear lysates. The addition of increasing concentrations of Tyrphostin AG1295, an inhibitor of PDGF receptor kinase, blocked the stimulatory effect of PDGF on the mRNA and protein expressions of these transcription factors. The up-regulation of c-Fos, GATA-1 and NF-E2 protein by PDGF was inhibited by actinomycin D and cycloheximide, suggesting that mRNA and protein synthesis might be involved in the mechanism. Our data suggest a direct stimulatory effect of PDGF on c-Fos, GATA-1 and NF-E2 expressions and we speculate that these transcription factors might be involved in the signal transduction of PDGF on the regulation of megakaryocytopoiesis.

Effects of the tyrosine protein kinase inhibitor genistein on the proliferation, activation of cultured rat hepatic stellate cells

AIM: Hepatic stellate cell (HSC) plays a pivotal role in liver fibrosis and is considered as the therapeutic target for the treatment of hepatic fibrosis. Tyrosine protein kinase plays an important role in the proliferation, activation of HSC. The purpose of the study is to investigate the effects of the tyrosine protein kinase inhibitor genistein on the proliferation and activation of cultured rat HSC.

METHODS: Rat HSC were isolated from Wistar rats by in situ perfusion of collagenase and pronase and single-step density Nycodenz gradient. Culture-activated HSC were serum-starved and incubated with 10^-9 to 10^-5 mol/L concentration of genistein for 24, 48 or 72 h. In PDGF-induced HSC proliferation, HSC were stimulated with 10 μg·L^-1 PDGF-BB for 15 min, and then treated with genistein for the same time. Cell proliferation was measured by MTT assay and based on flow cytometric analysis of cell cycle. The α-smooth muscle actin (α-SMA) expression in HSC was studied with confocal laser microscopy and flow cytometry. c-fos, c-jun and cyclin D1 expression in HSC was also detected by flow cytometry.

RESULTS: Genistein inhibited basal and PDGF-induced proliferation of HSC at the concentration of 10^-8 to 10^-5 mol/L, and treatment with 10^-7 mol/L concentration of genistein for 48 h inhibited the HSC proliferation significantly (the inhibition rate was 70.3%, P < 0.05). Immunofluorescence detected by confocal laser microscopy and flow cytometry showed that treatment with 10^-7 mol/L genistein for 48 h suppressed the expression of α-SMA significantly in HSC (the specific fluorescence intensity were 60.2 ± 21.5 vs 35.3 ± 11.6 and 12.8 ± 10.4 vs 9.54 ± 6.39, respectively, both P < 0.05). The intensity of c-fos, c-jun and cyclin D1 expression of HSCs treated with 10^-7 mol/L genistein for 48 h was also significantly decreased compared with the controls.

CONCLUSION: Genistein influences proliferation of HSC, suppresses the expression of α-SMA in HSC and t inhibits the intensity of c-fos, c-jun and cyclin D1 expression of HSCs. Genistein has therapeutic potential against liver fibrosis.

The Raf/MEK/ERK signal transduction cascade as a target for chemotherapeutic intervention in leukemia

The Raf/MEK/ERK (MAPK) signal transduction cascade is a vital mediator of a number of cellular fates including growth, proliferation and survival, among others. The focus of this review centers on the MAPK signal transduction pathway, its mechanisms of activation, downstream mediators of signaling, and the transcription factors that ultimately alter gene expression. Furthermore, negative regulators of this cascade, including phosphatases, are discussed with an emphasis placed upon chemotherapeutic intervention at various points along the pathway. In addition, mounting evidence suggests that the PI3K/Akt pathway may play a role in the effects elicited via MAPK signaling; as such, potential interactions and their possible cellular ramifications are discussed.