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

Chronic Morphine Modulates PDGFR-β and PDGF-B Expression and Distribution in Dorsal Root Ganglia and Spinal Cord in Male Rats

The analgesic effect of opioids decreases over time due to the development of analgesic tolerance. We have shown that inhibition of the platelet-derived growth factor beta (PDGFR-β) signaling eliminates morphine analgesic tolerance in rats. Although the PDGFR-β and its ligand, the platelet-derived growth factor type B (PDGF-B), are expressed in the substantia gelatinosa of the spinal cord (SG) and in the dorsal root ganglia (DRG), their precise distribution within different cell types of these structures is unknown. Additionally, the impact of a tolerance-mediating chronic morphine treatment, on the expression and distribution of PDGF-B and PDGFR-β has not yet been studied. Using immunohistochemistry (IHC), we found that in the spinal cord, PDGFR-β and PDGF-B were expressed in neurons and oligodendrocytes and co-localized with the mu-opioid receptor (MOPr) in opioid naïve rats. PDGF-B was also found in microglia and astrocytes. Both PDGFR-β and PDGF-B were detected in DRG neurons but not in spinal primary afferent terminals. Chronic morphine exposure did not change the cellular distribution of PDGFR-β or PDGF-B. However, PDGFR-β expression was downregulated in the SG and upregulated in the DRG. Consistent with our previous finding that morphine caused tolerance by inducing PDGF-B release, PDGF-B was upregulated in the spinal cord. We also found that chronic morphine exposure caused a spinal proliferation of oligodendrocytes. The changes in PDGFR-β and PDGF-B expression induced by chronic morphine treatment suggest potential mechanistic substrates underlying opioid tolerance.

Gomisin D alleviates liver fibrosis through targeting PDGFRβ in hepatic stellate cells

Platelet-derived growth factor receptor β (PDGFRβ) plays an important role in hepatic fibrosis and is closely associated with hepatic stellate cells (HSCs) activation. Previously, by modeling PDGFRβ affinity chromatography, we found that gomisin D can target PDGFRβ. However, whether gomisin D has anti-fibrosis effects through targeting PDGFRβ remained unclear. In this study, the effect of gomisin D on hepatic fibrosis was evaluated in vivo and vitro. HSC cell lines and primary HSC were cultured and functionally we found that gomisin D promotes HSC apoptosis, inhibits HSCs activation and proliferation. A male BALB/c mouse liver fibrosis model was established to comfirm gomisin D (especially in 50 mg/kg) could improve liver fibrosis by inhibiting HSCs activation. In addition, gomisin D had a good binding ability with PDGFRβ (KD = 3.3e^-5 M). Mechanically, gomisin D regulated PDGF-BB/PDGFRβ signaling pathway by targeting PDGFRβ, further more inhibited HSC activation, subsequently inhibited inflammatory factors, ultimately improved CCl₄-induced liver fibrosis. Overall, gomisin D could inhibit HSC proliferation and activation, promote HSC apoptosis, and alleviate CCl₄-induced hepatic fibrosis by targeting PDGFRβ and regulating PDGF-BB/PDGFRβ signaling pathway. This study provides a new drug for anti-liver firbosis therapy, and elucidates the deeper mechanism of gomisin D against HSCs activation by targeting PDGFRβ.

Yinchenhao decoction suppresses rat liver fibrosis involved in an apoptosis regulation mechanism based on network pharmacology and transcriptomic analysis

Yinchenhao decoction (YCHD) is a classical Traditional Chinese Medicine (TCM) formula that has been widely used in the treatment of liver fibrosis caused by chronic hepatitis B and jaundice for more than 1800 years. The purpose of this study was to investigate the apoptosis regulation mechanisms of YCHD and its active components suppresses liver fibrosis. The active components and putative targets of YCHD were predicted by network pharmacology approach. Functional and pathway enrichment analysis were presented in the present study by using clusterProfiler. Further, experimental validation was done by using terminal deoxynucleotidyl transferase (TDT) dUTP nick end labelling (TUNEL) assay and western blotting in dimethylnitrosamine (DMN)-induced liver fibrosis rats, and cell proliferation assay, apoptosis assay, and western blotting in human hepatic L02 cells and LX2 cells. 45 active compounds in YCHD formula, 592 potential target proteins and 1191 liver fibrosis-related human genes were identified. Functional and pathway enrichment analysis indicated that YCHD obviously influenced TNF, PI3K-Akt signaling pathways. Further, In vivo experiment indicated that YCHD treatment not only attenuated the symptoms of liver fibrosis, but also decrease the apoptosis of hepatic parenchyma cells. Moreover, in vitro experiments showed that rhein, kaempferol and quercetin treatments remarkably decreased the protein levels of cleaved caspase-3 and increased p-ERK1/2, PI3K and Bcl-XL protein expression in TNF-α-stimulated L02 cells. On the contrary, rhein, kaempferol, aloe-emodin and quercetin inhibited the proliferation of LX2 cells and up-regulated the protein levels of Bax and cleaved caspase-8. In conclusion, 45 active components and 296 potential targets of YCHD against liver fibrosis were identified by the analysis of network pharmacology and transcriptomics combination. The mechanisms of YCHD against liver fibrosis were involved in the regulation of multiple targets, especially affecting the apoptosis-related signaling pathways.

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.

Hepatic Fibrosis in Dogs

Hepatic fibrosis is commonly diagnosed in dogs, often as a sequela to chronic hepatitis (CH). The development of fibrosis is a crucial event in the progression of hepatic disease that is of prognostic value. The pathophysiology of hepatic fibrosis in human patients and rodent models has been studied extensively. Although less is known about this process in dogs, evidence suggests that fibrogenic mechanisms are similar between species and that activation of hepatic stellate cells is a key step. Diagnosis and staging of hepatic fibrosis in dogs requires histopathological examination of a liver biopsy specimen. However, performing a liver biopsy is invasive and assessment of fibrotic stage is complicated by the absence of a universally accepted staging scheme in veterinary medicine. Serum biomarkers that can discriminate among different fibrosis stages are used in human patients, but such markers must be more completely evaluated in dogs before clinical use. When successful treatment of its underlying cause is feasible, reversal of hepatic fibrosis has been shown to be possible in rodent models and human patients. Reversal of fibrosis has not been well documented in dogs, but successful treatment of CH is possible. In human medicine, better understanding of the pathomechanisms of hepatic fibrosis is leading to the development of novel treatment strategies. In time, these may be applied to dogs. This article comparatively reviews the pathogenesis of hepatic fibrosis, its diagnosis, and its treatment in dogs.

Interaction between autophagy and senescence is required for dihydroartemisinin to alleviate liver fibrosis

Autophagy and cellular senescence are stress responses essential for homeostasis. Therefore, they may represent new pharmacologic targets for drug development to treat diseases. In this study, we sought to evaluate the effect of dihydroartemisinin (DHA) on senescence of activated hepatic stellate cells (HSCs), and to further elucidate the underlying mechanisms. We found that DHA treatment induced the accumulation of senescent activated HSCs in rat fibrotic liver, and promoted the expression of senescence markers p53, p16, p21 and Hmga1 in cell model. Importantly, our study identified the transcription factor GATA6 as an upstream molecule in the facilitation of DHA-induced HSC senescence. GATA6 accumulation promoted DHA-induced p53 and p16 upregulation, and contributed to HSC senescence. By contrast, siRNA-mediated knockdown of GATA6 dramatically abolished DHA-induced upregulation of p53 and p16, and in turn inhibited HSC senescence. Interestingly, DHA also appeared to increase autophagosome generation and autophagic flux in activated HSCs, which was underlying mechanism for DHA-induced GATA6 accumulation. Autophagy depletion impaired GATA6 accumulation, while autophagy induction showed a synergistic effect with DHA. Attractively, p62 was found to act as a negative regulator of GATA6 accumulation. Treatment of cultured HSCs with various autophagy inhibitors, led to an inhibition of DHA-induced p62 degradation, and in turn, prevented DHA-induced GATA6 accumulation and HSC senescence. Overall, these results provide novel implications to reveal the molecular mechanism of DHA-induced senescence, by which points to the possibility of using DHA based proautophagic drugs for the treatment of liver fibrosis.

Ubiquitin C-terminal hydrolase 1: A novel functional marker for liver myofibroblasts and a therapeutic target in chronic liver disease

BACKGROUND & AIMS

Ubiquitination is a reversible protein modification involved in the major cellular processes that define cell phenotype and behaviour. Ubiquitin modifications are removed by a large family of proteases named deubiquitinases. The role of deubiquitinases in hepatic stellate cell (HSC) activation and their contribution to fibrogenesis are poorly defined. We have identified that the deubiquitinase ubiquitin C-terminal hydrolase 1 (UCHL1) is highly induced following HSC activation, determined its function in activated HSC and its potential as a therapeutic target for fibrosis.

METHODS

Deubiquitinase expression was determined in day 0 and day 10 HSC. Increased UCHL1 expression was confirmed in human HSC and in an alcoholic liver disease (ALD) patient liver. The importance of UCHL1 in hepatic fibrosis was investigated in CCl4 and bile duct ligation injured mice using a pharmacological inhibitor (LDN 57444). The effects of UCHL1 inhibition on HSC proliferation were confirmed by Western blot and 3H thymidine incorporation.

RESULTS

Here we report that pharmacological inhibition of UCHL1 blocks progression of established fibrosis in CCl4 injured mice. UCHL1 siRNA knockdown, LDN 57444 treatment, or HSC isolated from UCHL1(-/-) mice show attenuated proliferation in response to the mitogen, platelet-derived growth factor. Additionally, we observed changes in the phosphorylation of the cell cycle regulator retinoblastoma protein (Rb) in the absence of UCHL1 highlighting a potential mechanism for the reduced proliferative response.

CONCLUSIONS

UCHL1 expression is highly upregulated upon HSC activation and is involved in the regulation of HSC proliferation. This study highlights therapeutic opportunities for pharmacological targeting of UCHL1 in chronic liver disease.

NIM811 downregulates transforming growth factor‑β signal transduction in vivo and in vitro

Liver fibrosis is the common histological feature of a number of chronic liver diseases, and leads to cirrhosis and hepatocellular carcinoma (HCC). It has been demonstrated that N‑methyl‑4‑isoleucine cyclosporine (NIM811) attenuates CCl4‑induced liver fibrosis and inflammation in rats. The present study investigated whether NIM811 downregulated transforming growth factor (TGF)‑β signaling in rats with CCl4‑induced liver fibrosis and in HSC‑T6 cells. Liver tissues were obtained from rats with CCl4‑induced liver fibrosis, with or without NIM811 treatment. HSC‑T6 cells were cultured with or without NIM811 for 18 h under serum‑free conditions. Expression of collagen I, α‑smooth muscle actin (α‑SMA), TGF‑β1, TGF‑β receptor I (TβR‑I) and TGF‑β pathway downstream signaling molecules were measured by reverse transcription‑quantitative polymerase chain reaction and/or western blotting. Collagen I and TGF‑β1 content in the cell supernatant was measured by ELISA. NIM811 profoundly inhibited collagen I, α‑SMA, TGF‑β1 and TβR‑I expression in the liver of CCl4‑treated rats. Phosphorylation of Smad2, 3 and 1/5/8 was decreased in the liver of NIM811‑treated groups, accompanied by increased In addition, Smad7 expression compared with the CCl4‑treated rats. NIM811 inhibited collagen I, TGF‑β1 and TβR‑I expression in HSC‑T6 cells. Smad1 mRNA and phospho‑Smad1/5/8 protein levels decreased following NIM811 treatment, accompanied by increased Smad7 expression in HSC‑T6 cells compared with normal controls. Furthermore, NIM811 also inhibited collagen I mRNA expression in the liver of rats with CCl4‑induced liver fibrosis and in HSC‑T6 cells. The results suggest that the antifibrotic effect of NIM811 was due to the inhibition of TGF‑β1 and its downstream signaling molecules.

Cellular and molecular mechanisms in the pathogenesis of liver fibrosis: An update

There have been considerable recent advances towards a better understanding of the complex cellular and molecular network underlying liver fibrogenesis. Recent data indicate that the termination of fibrogenic processes and the restoration of deficient fibrolytic pathways may allow the reversal of advanced fibrosis and even cirrhosis. Therefore, efforts have been made to better clarify the cellular and molecular mechanisms that are involved in liver fibrosis. Activation of hepatic stellate cells (HSCs) remains a central event in fibrosis, complemented by other sources of matrix-producing cells, including portal fibroblasts, fibrocytes and bone marrow-derived myofibroblasts. These cells converge in a complex interaction with neighboring cells to provoke scarring in response to persistent injury. Defining the interaction of different cell types, revealing the effects of cytokines on these cells and characterizing the regulatory mechanisms that control gene expression in activated HSCs will enable the discovery of new therapeutic targets. Moreover, the characterization of different pathways associated with different etiologies aid in the development of disease-specific therapies. This article outlines recent advances regarding the cellular and molecular mechanisms involved in liver fibrosis that may be translated into future therapies. The pathogenesis of liver fibrosis associated with alcoholic liver disease, non-alcoholic fatty liver disease and viral hepatitis are also discussed to emphasize the various mechanisms involved in liver fibrosis.

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.

Hepatitis B virus directly promotes collagen I expression of LX-2 cells without infection in vitro

AIM

  To investigate direct effects of hepatitis B virus (HBV) on collagen type I in vitro.

METHODS

  Collagen type I were measured after LX-2 cell cultured with purified or serum HBV for 12, 24 and 48 h. Furthermore, evidence of HBV infection to LX-2 were detected, and different inhibitors were used to identify pathways regulating collagen I expression.

RESULTS

  The 3 × 10(5)  IU/mL purified/serum HBV increased collagen type I mRNA expression by 2.2-/3.2- and 1.3-/1.5-fold at 24 and 48 h, respectively. Collagen type I protein in the supernatant of purified/serum HBV group also increased compared to the control group (408.0 ± 8.0/384.4 ± 6.8 vs 262.7 ± 15.7 ng/mL, P < 0.05). However, the 3 × 10(7)  IU/mL purified/serum HBV increased collagen type I expression similar to that of 3 × 10(5)  IU/mL, while 3 × 10(3)  IU/mL group showed no effect. Human HBV immunoglobulin alleviated HBV-induced collagen I expression, but no evidence of HBV infection was found. Neutralization of transforming growth factor beta, tumor necrosis factor alpha, platelet-derived growth factor, extracellular signal-regulated kinase and TGF-β receptor had no obvious inhibitory effects; only inhibition of p38 mitogen-activated protein kinase decreased collagen type I mRNA expression by 0.5-/0.4- and 0.4-/0.3-fold at 24 and 48 h, respectively. It reduced collagen type I protein in the purified/serum HBV group for 48 h (252.1 ± 14.1/251.7 ± 18.8 vs 403.9 ± 4.9/385.0 ± 4.2 ng/mL, P < 0.05).

CONCLUSION

  HBV directly promotes collagen type I expression of LX-2 cells without infection in vitro.

Synthesis and biological characterization of protease-activated prodrugs of doxazolidine

Doxazolidine (doxaz) is a new anthracycline anticancer agent. While structurally similar to doxorubicin (dox), doxaz acts via a distinct mechanism to selectively enhance anticancer activity over cardiotoxicity, the most significant clinical impediment to successful anthracycline treatment. Here, we describe the synthesis and characterization of a prodrug platform designed for doxaz release mediated by secreted proteolytic activity, a common association with invasiveness and poor prognosis in cancer patients. GaFK-Doxaz is hydrolyzable by the proteases plasmin and cathepsin B, both strongly linked with cancer progression, as well as trypsin. We demonstrate that activation of GaFK-Doxaz releases highly potent doxaz that powerfully inhibits the growth of a wide variety of cancer cells (average IC(50) of 8 nM). GaFK-Doxaz is stable in human plasma and is poorly membrane permeable, thereby limiting activation to locally secreted proteolytic activity and reducing the likelihood of severe side effects.

Anti-fibrotic activity and enhanced interleukin-6 production by hepatic stellate cells in response to imatinib mesylate

OBJECTIVE

To examine imatinib mesylate's effects on stellate cell responses in vivo and in vitro. The hepatic stellate cell (HSC) is a key target of anti-fibrotic therapies. Imatinib mesylate is a small molecule receptor tyrosine kinase inhibitor indicated for treatment of chronic myelogenous leukaemia and GI stromal tumours.

DESIGN

Because imatinib inhibits β-PDGFR signalling, which stimulates HSC proliferation, we assessed its activity in culture and in vivo, and examined downstream targets in a human stellate cell line (LX-2) using cDNA microarray.

METHODS AND RESULTS

Imatinib inhibited proliferation of LX-2 cells (0.5-10 mM) but not primary human stellate cells, with no effect on viability, associated with attenuated β-PDGFR phosphorylation. Mitochondrial activity and superoxide anion production were decreased in response to imatinib. cDNA microarray uncovered up-regulation of 29 genes in response to imatinib, including interleukin-6 (IL-6) mRNA, which was correlated with progressive IL-6 secretion. Imatinib also decreased gene expression of collagen α(1) (I), alpha smooth muscle actin, β-PDGFR, transforming growth factor β receptor type 1, matrix metalloproteinase 2 and tissue inhibitor of metalloproteinase 2. In vivo, imatinib administered to rats beginning 4 weeks after starting thioacetamide (TAA) led to reduced collagen content, with significant reductions in portal pressure and down-regulation of fibrogenic genes in whole liver. Importantly, hepatic IL-6 mRNA levels were significantly increased in TAA-treated animals receiving imatinib.

CONCLUSIONS

These findings reinforce the anti-fibrotic activity of imatinib and uncover an unexpected link between inhibition of HSC activation by imatinib and enhanced secretion of IL-6, a regenerative cytokine.

Activation of extracellular-signal regulated kinase by platelet-derived growth factor is potentiated by phenylephrine in primary cultures of adult rat hepatocytes

We investigated the effects of the α(1)-adrenergic agonist phenylephrine on platelet-derived growth factor (PDGF)-stimulated extracellular signal-regulated kinase (ERK) in primary cultures of adult rat hepatocytes. Hepatocytes were isolated and cultured with PDGF (10 ng/ml) and/or α-adrenergic agonist. Phosphorylated ERK isoforms (ERK1 and ERK2) were detected by Western blotting analysis using anti-phospho mitogen-activated protein kinase (MAPK) antibody. PDGF stimulated phosphorylation of ERK2 (42 kDa MAPK) by 2.0-fold within 3-5 min. The PDGF-induced ERK activation was abolished by AG1296 (10(-7) M) or LY294002 (10(-7) M) treatment. MAPK kinase inhibitor, PD98059 (10(-6) M), completely inhibited the PDGF-induced increase in ERK activity. In addition, PDGF-induced mammalian target of rapamycin activity was completely inhibited by AG1296, LY294002, PD98059, or rapamycin treatment. Phenylephrine alone showed no effects on ERKs, but significantly increased phosphorylation of ERK2 induced by PDGF. Moreover, a synthetic analog of diacylglycerol (DG), phorbol 12-myristate 13 acetate (TPA; 10(-7) M), potentiated PDGF-induced ERK2 phosphorylation, while ionomycin had no effect (10(-6) M). The effects of phenylephrine and TPA were antagonized by the phospholipase C (PLC) inhibitor U73122 (10(-7) M), and the protein kinase C (PKC) inhibitor GF109203X (10(-7) M), respectively. Accordingly, PDGF-induced DNA synthesis and proliferation in the presence or absence of phenylephrine or TPA were completely inhibited by AG1296, LY294002, PD98059, or rapamycin treatment. These results suggest that activation of PLC/PKC by phenylephrine represent an indirect positive regulatory mechanism for stimulating ERK induced by 10 ng/ml PDGF.

Thymosin-β4 (Tβ4) blunts PDGF-dependent phosphorylation and binding of AKT to actin in hepatic stellate cells

Hepatic stellate cell transdifferentiation is a key event in the fibrogenic cascade. Therefore, attempts to prevent and/or revert the myofibroblastic phenotype could result in novel therapeutic approaches to treat liver cirrhosis. The expression of platelet-derived growth factor (PDGF)-β receptor and the proliferative response to platelet-derived growth factor-ββ (PDGF-ββ) are hallmarks of the transdifferentiation of hepatic stellate cells (HSC). In this communication, we investigated whether thymosin-β4 (Tβ4), a chemokine expressed by HSC could prevent PDGF-BB-mediated proliferation and migration of cultured HSC. Using early passages of human HSC, we showed that Tβ4 inhibited cell proliferation and migration and prevented the expression of PDGF-β receptor (PDGF-βr), α-smooth muscle actin and α1(I) collagen mRNAs. Tβ4 also inhibited the reappearance of PDGF-βr after its PDGF-BB-dependent degradation. These PDGF-dependent events were associated with the inhibition of AKT phosphorylation at both T308 and S473 amino acid residues. The lack of AKT phosphorylation was not due to the inhibition of PDGF-βr phosphorylation, the activation of phosphoinositide 3-kinase (PI3K), pyruvate dehydrogenase kinase isozyme 1 (PDK1), and mammalian target of rapamycin (mTOR). We found that PDGF-BB induced AKT binding to actin, and that Tβ4 prevented this effect. Tβ4 also prevented the activation of freshly isolated HSC cultured in the presence of Dulbecco's modified Eagle's medium or Dulbecco's minimal essential medium containing 10% fetal bovine serum. In conclusion, overall, our findings suggest that Tβ4 by sequestering actin prevents binding of AKT, thus inhibiting its phosphorylation. Therefore, Tβ4 has the potential to be an antifibrogenic agent.

Suppression of hepatic stellate cell activation by microRNA-29b

MicroRNAs (miRNAs) participate in the regulation of cellular functions including proliferation, apoptosis, and migration. It has been previously shown that the miR-29 family is involved in regulating type I collagen expression by interacting with the 3'UTR of its mRNA. Here, we investigated the roles of miR-29b in the activation of mouse primary-cultured hepatic stellate cells (HSCs), a principal collagen-producing cell in the liver. Expression of miR-29b was found to be down-regulated during HSC activation in primary culture. Transfection of a miR-29b precursor markedly attenuated the expression of Col1a1 and Col1a2 mRNAs and additionally blunted the increased expression of α-SMA, DDR2, FN1, ITGB1, and PDGFR-β, which are key genes involved in the activation of HSCs. Further, overexpression of miR-29b led HSCs to remain in a quiescent state, as evidenced by their quiescent star-like cell morphology. Although phosphorylation of FAK, ERK, and Akt, and the mRNA expression of c-jun was unaffected, miR-29b overexpression suppressed the expression of c-fos mRNA. These results suggested that miR-29b is involved in the activation of HSCs and could be a candidate molecule for suppressing their activation and consequent liver fibrosis.

Pathogenesis of liver fibrosis

Liver fibrosis is a major cause of morbidity and mortality worldwide due to chronic viral hepatitis and, more recently, from fatty liver disease associated with obesity. Hepatic stellate cell activation represents a critical event in fibrosis because these cells become the primary source of extracellular matrix in liver upon injury. Use of cell-culture and animal models has expanded our understanding of the mechanisms underlying stellate cell activation and has shed new light on genetic regulation, the contribution of immune signaling, and the potential reversibility of the disease. As pathways of fibrogenesis are increasingly clarified, the key challenge will be translating new advances into the development of antifibrotic therapies for patients with chronic liver disease.

Epithelial-mesenchymal interactions in biliary diseases

In most cholangiopathies, liver diseases of different etiologies in which the biliary epithelium is the primary target in the pathogenic sequence, the central mechanism involves inflammation. Inflammation, characterized by pleomorphic peribiliary infiltrate containing fibroblasts, macrophages, lymphocytes, as well as endothelial cells and pericytes, is associated to the emergence of "reactive cholangiocytes." These biliary cells do not possess bile secretory functions, are in contiguity with terminal cholangioles, and are of a less-differentiated phenotype. They have acquired several mesenchymal properties, including motility and ability to secrete a vast number of proinflammatory chemo/cytokines and growth factors along with de novo expression of a rich receptor machinery. These functional properties enable reactive cholangiocytes to establish intimate contacts and to mutually exchange a variety of paracrine signals with the different mesenchymal cell types populating the portal infiltrate. The extensive crosstalk between the epithelial and mesenchymal compartments is the driver of liver repair mechanisms in cholangiopathies, ultimately evolving toward portal fibrosis. Herein, the authors first review the properties of the different cell types involved in their interaction, and then analyze the underlying molecular mechanisms as they relate to liver repair in cholangiopathies.

Liver fibrosis: pathogenesis and clinical diagnosis

Hepatic fibrosis represents a wound healing response to liver injury due to various causes. Cirrhosis is the most advanced stage of fibrosis and, along with its complications, constitutes one of the major causes of morbidity and mortality worldwide. Past decades have witnessed tremendous progress in understanding the mechanisms of hepatic fibrosis. Activation of hepatic stellate cells is a key event in fibrosis, while a wide range of cytokines and their receptors and inflammatory cell subsets participate in the dynamic regulation of fibrosis progression. In terms of the diagnosis of hepatic fibrosis, novel serum markers and transient elastography have helped a lot in the assessment of liver fibrosis in addition to traditional liver biopsy. These findings both in the mechanism of liver fibrosis and the diagnosis of fibrosis are important for the implementation of rationally based approaches to limit fibrosis, accelerate repair and enhance liver regeneration in patients with chronic liver disease.

Paediatric cholestatic liver disease: Diagnosis, assessment of disease progression and mechanisms of fibrogenesis

Cholestatic liver disease causes significant morbidity and mortality in children. The diagnosis and management of these diseases can be complicated by an inability to detect early stages of fibrosis and a lack of adequate interventional therapy. There is no single gold standard test that accurately reflects the presence of liver disease, or that can be used to monitor fibrosis progression, particularly in conditions such as cystic fibrosis. This has lead to controversy over how suspected liver disease in children is detected and diagnosed. This review discusses the challenges in using commonly available methods to diagnose hepatic fibrosis and monitor disease progression in children with cholestatic liver disease. In addition, the review examines the mechanisms hypothesised to be involved in the development of hepatic fibrogenesis in paediatric cholestatic liver injury which may ultimately aid in identifying new modalities to assist in both disease detection and therapeutic intervention.

Proanthocyanidin derived from the leaves of Vaccinium virgatum suppresses platelet-derived growth factor-induced proliferation of the human hepatic stellate cell line LI90

AIM

Hepatic stellate cell (HSC) proliferation plays a pivotal role in liver fibrogenesis, and agents that suppress HSC activation, including platelet-derived growth factor (PDGF)-induced HSC proliferation, are good candidates for antifibrogenic therapies. In this report, we use the LI90 HSC line to elucidate the antifibrogenic effects of proanthocyanidin derived from the leaves of Vaccinium virgatum.

METHODS

Proanthocyanidin (PAC) was extracted from the leaves of blueberry V. virgatum (BB-PAC), grape seeds (GS-PAC) and Croton lechleri (CL-PAC). These extracts were examined for their effects on PDGF-BB-induced LI90 cell proliferation and DNA synthesis. Extracellular signal-regulated kinase (ERK) and Akt phosphorylation and PDGF receptor-beta (PDGFR-beta) expression were evaluated by western blot analysis.

RESULTS

BB-PAC potently suppressed PDGF-BB-induced proliferation and DNA synthesis of LI90 cells. BB-PAC also suppressed PDGF-BB-induced DNA synthesis in primary cultured rat HSC. Moreover, GS-PAC and CL-PAC suppressed PDGF-BB-induced DNA synthesis in LI90 cells. In contrast, the monomeric PAC catechin and epicatechin and dimeric PAC procyanidin B2 only slightly suppressed PDGF-BB-induced DNA synthesis. Western blot analysis showed that BB-PAC completely or partially inhibited PDGF-BB-induced ERK and Akt phosphorylation, respectively. In addition, BB-PAC partially inhibited the PDGF-BB-induced degradation of PDGFR-beta.

CONCLUSION

Our results suggest that BB-PAC suppresses activated HSC by inhibiting the PDGF signaling pathway. In addition, these results provide novel findings that may facilitate the development of antifibrogenic agents.

Advances in research on the signaling pathways involved in activation and phenotypic transformation of hepatic stellate cells and their inhibitors

Liver fibrosis is a progressive pathologic process that involves deposition of excess extracellular matrix leading to distorted architecture and culminating in cirrhosis. It is believed that activation and phenotypic transformation of hepatic stellate cells (HSCs) play a central role in the development and resolution of liver fibrosis. Many cytokines and related signaling pathways are involved in the phenotypic transformation and proliferation of HSCs. In recent years, great advances have been made in the study of these signaling pathways and their specific inhibitors, thereby providing a new avenue for clinical therapy of liver fibrosis. However, as the mechanisms underlying the roles of these signaling pathways are very complicated, further intensive studies are still essential. In this article, we will review the advances in research on the signaling pathways involved in activation and phenotypic transformation of hepatic stellate cells and their inhibitors.

Advances in antifibrotic therapy

Sustained progress in defining the molecular pathophysiology of hepatic fibrosis has led to a comprehensive framework for developing antifibrotic therapies. Indeed, the single greatest limitation in bringing new drugs to the clinical setting is a lack of clarity regarding clinical trial and treatment end points, not a lack of promising agents. A range of treatments, including those developed for other indications, as well as those specifically developed for hepatic fibrosis, are nearing or in clinical trials. Most are focused on attacking features of either hepatic injury and/or activated stellate cells and myofibroblasts, which are the primary sources of extracellular matrix (scar) proteins. Thus, features of injury and stellate cell activation provide a useful template for classifying these emerging agents and point to a new class of therapies for patients with fibrosing liver disease.

Platelet-derived growth factor-B gene delivery sustains gingival fibroblast signal transduction

BACKGROUND AND OBJECTIVE

Platelet-derived growth factor-BB is a potent mediator of tooth-supporting periodontal tissue repair and regeneration. A limitation of the effects of topical platelet-derived growth factor-BB application is its short half-life in vivo. Gene therapy has shown strong promise for the long-term delivery of platelet-derived growth factor in both skin ulcer healing and periodontal tissue engineering. However, little is known regarding the extended effects of platelet-derived growth factor-B on cell signaling via gene delivery, especially at the level of phosphorylation of intracellular kinases. This study sought to evaluate the effect of gene transfer by Ad-PDGF-B on human gingival fibroblasts (HGFs) and the subsequent regulation of genes and cell-surface proteins associated with cellular signaling.

MATERIAL AND METHODS

HGFs from human subjects were treated by adenoviral PDGF-B, PDGF-1308 (a dominant negative mutant of PDGF) and recombinant human platelet-derived growth factor-BB, and then incubated in serum-free conditions for various time points and harvested at 1, 6, 12, 24, 48, 72 and 96 h. Exogenous PDGF-B was measured by RT-PCR and Western blot. Cell proliferation was evaluated by [methyl-3H]thymidine incorporation assay. We used proteomic arrays to explore phosphorylation patterns of 23 different intracellular kinases after PDGF-B gene transfer. The expression of alpha and beta PDGFR and Akt were measured by Western blot analysis.

RESULTS

Sustained in vitro expression of PDGF-B in HGFs by Ad-PDGF-B transduction was seen at both the mRNA and protein levels. Compared to rhPDGF-BB and Ad-PDGF-1308, Ad-PDGF-B maintained cell growth in serum-free conditions, with robust increases in DNA synthesis. Gene delivery of PDGF-B also prolonged downregulation of the growth arrest specific gene (gas) PDGF alpha R. Of the 23 intracellular kinases that we tested in proteomic arrays, Akt revealed the most notable long-term cell signaling effect as a result of the over-expression of Ad-PDGF-B, compared with pulse recombinant human platelet-derived growth factor BB. Prolonged Akt phosphorylation was induced by treatment with Ad-PDGF-B, for at least up to 96 h.

CONCLUSION

These findings further demonstrate that gene delivery of PDGF-B displays sustained signal transduction effects in human gingival fibroblasts that are higher than those conveyed by treatment with recombinant human platelet-derived growth factor-BB protein. These data on platelet-derived growth factor gene delivery contribute to an improved understanding of these pathways that are likely to play a role in the control of clinical outcomes of periodontal regenerative therapy.

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.

Cytokines and renin-angiotensin system signaling in hepatic fibrosis

Hepatic fibrosis is the result of a complex interplay between resident hepatic cells, infiltrating inflammatory cells, and a number of locally acting peptides called cytokines. Key mediators include transforming growth factor b1, vasoactive substances, adipokines, inflammatory cytokines and chemokines. Angiotensin II, the main effector of the renin-angiotensin system, is a true cytokine that plays a major role in liver fibrosis. Angiotensin II is locally synthesized in the injured liver and induces profibrogenic actions in hepatic stellate cells. Drugs blocking the renin-angiotensin system are promising antifibrotic agents. There are multiple signal transduction pathways involved in cytokine signaling. Drugs interfering intracellular pathways involved in increased collagen production are potential therapies for liver fibrosis.

Hepatic fibrosis -- overview

The study of hepatic fibrosis, or scarring in response to chronic liver injury, has witnessed tremendous progress in the past two decades. Clarification of the cellular sources of scar, and emergence of hepatic stellate cells not only as a fibrogenic cell type, but also as a critical immunomodulatory and homeostatic regulator are among the most salient advances. Activation of hepatic stellate cells remains a central event in fibrosis, complemented by evidence of additional sources of matrix-producing cells including bone marrow, portal fibroblasts, and epithelial-mesenchymal transition from both hepatocytes and cholangiocytes. A growing range of cytokines and their receptors and inflammatory cell subsets have further expanded our knowledge about this dynamic process. Collectively, these findings have laid the foundation for continued elucidation of underlying mechanisms, and more importantly for the implementation of rationally based approaches to limit fibrosis, accelerate repair and enhance liver regeneration in patients with chronic liver disease.

Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver

The hepatic stellate cell has surprised and engaged physiologists, pathologists, and hepatologists for over 130 years, yet clear evidence of its role in hepatic injury and fibrosis only emerged following the refinement of methods for its isolation and characterization. The paradigm in liver injury of activation of quiescent vitamin A-rich stellate cells into proliferative, contractile, and fibrogenic myofibroblasts has launched an era of astonishing progress in understanding the mechanistic basis of hepatic fibrosis progression and regression. But this simple paradigm has now yielded to a remarkably broad appreciation of the cell's functions not only in liver injury, but also in hepatic development, regeneration, xenobiotic responses, intermediary metabolism, and immunoregulation. Among the most exciting prospects is that stellate cells are essential for hepatic progenitor cell amplification and differentiation. Equally intriguing is the remarkable plasticity of stellate cells, not only in their variable intermediate filament phenotype, but also in their functions. Stellate cells can be viewed as the nexus in a complex sinusoidal milieu that requires tightly regulated autocrine and paracrine cross-talk, rapid responses to evolving extracellular matrix content, and exquisite responsiveness to the metabolic needs imposed by liver growth and repair. Moreover, roles vital to systemic homeostasis include their storage and mobilization of retinoids, their emerging capacity for antigen presentation and induction of tolerance, as well as their emerging relationship to bone marrow-derived cells. As interest in this cell type intensifies, more surprises and mysteries are sure to unfold that will ultimately benefit our understanding of liver physiology and the diagnosis and treatment of liver disease.

Thymosin beta4 upregulates the expression of hepatocyte growth factor and downregulates the expression of PDGF-beta receptor in human hepatic stellate cells

Hepatic stellate cells (HSCs) are the main producers of type I collagen in the liver, and therefore are responsible, in part, for the fibrous scar observed in cirrhotic livers. Although there is no approved treatment for this deadly disease, drugs inducing HSC apoptosis in animals (gliotoxin) and hepatocyte regeneration in man (hepatocyte growth factor [HGF]), have been used successfully in ameliorating liver fibrosis. In this communication we investigated whether thymosin beta(4) (Tbeta(4)), an actin-sequestering peptide that prevents scarring of the heart after a myocardial infarction and that prevents kidney fibrosis in animals, has the potential to be used to treat liver fibrosis. To this end we studied whether the administration of Tbeta(4) to HSCs could alter the expression of genes encoding for extracellular matrix components, as well as those required for differentiation of HSCs. Our preliminary findings show that Tbeta(4) had no effect on the expression of alpha2 (I) collagen, tissue inhibitor of metalloproteinases-1, and matrix metalloproteinase-2 mRNAs. However, it upregulated the expression of HGF and downregulated the expression of platelet-derived growth factor-beta receptor mRNAs in these cells. Overall, these findings suggest that Tbeta(4) has antifibrogenic potential.