TGFbeta1 autocrine growth control in isolated pancreatic fibroblastoid cells/stellate cells in vitro

Activation of Pancreatic Stellate Cells Is Beneficial for Exocrine but Not Endocrine Cell Differentiation in the Developing Human Pancreas

Pancreatic stellate cells (PaSCs) are non-endocrine, mesenchymal-like cells that reside within the peri-pancreatic tissue of the rodent and human pancreas. PaSCs regulate extracellular matrix (ECM) turnover in maintaining the integrity of pancreatic tissue architecture. Although there is evidence indicating that PaSCs are involved in islet cell survival and function, its role in islet cell differentiation during human pancreatic development remains unclear. The present study examines the expression pattern and functional role of PaSCs in islet cell differentiation of the developing human pancreas from late 1st to 2nd trimester of pregnancy. The presence of PaSCs in human pancreata (8–22 weeks of fetal age) was characterized by ultrastructural, immunohistological, quantitative RT-PCR and western blotting approaches. Using human fetal PaSCs derived from pancreata at 14–16 weeks, freshly isolated human fetal islet-epithelial cell clusters (hIECCs) were co-cultured with active or inactive PaSCs in vitro. Ultrastructural and immunofluorescence analysis demonstrated a population of PaSCs near ducts and newly formed islets that appeared to make complex cell-cell dendritic-like contacts. A small subset of PaSCs co-localized with pancreatic progenitor-associated transcription factors (PDX1, SOX9, and NKX6-1). PaSCs were highly proliferative, with significantly higher mRNA and protein levels of PaSC markers (desmin, αSMA) during the 1st trimester of pregnancy compared to the 2nd trimester. Isolated human fetal PaSCs were identified by expression of stellate cell markers and ECM. Suppression of PaSC activation, using all-trans retinoic acid (ATRA), resulted in reduced PaSC proliferation and ECM proteins. Co-culture of hIECCs, directly on PaSCs or indirectly using Millicell^® Inserts or using PaSC-conditioned medium, resulted in a reduction the number of insulin⁺ cells but a significant increase in the number of amylase⁺ cells. Suppression of PaSC activation or Notch activity during the co-culture resulted in an increase in beta-cell differentiation. This study determined that PaSCs, abundant during the 1st trimester of pancreatic development but decreased in the 2nd trimester, are located near ductal and islet structures. Direct and indirect co-cultures of hIECCs with PaSCs suggest that activation of PaSCs has opposing effects on beta-cell and exocrine cell differentiation during human fetal pancreas development, and that these effects may be dependent on Notch signaling.

Molecular mechanisms of pancreatic myofibroblast activation in chronic pancreatitis and pancreatic ductal adenocarcinoma

Pancreatic fibrosis (PF) is an essential component of the pathobiology of chronic pancreatitis (CP) and pancreatic ductal adenocarcinoma (PDAC). Activated pancreatic myofibroblasts (PMFs) are crucial for the deposition of the extracellular matrix, and fibrotic reaction in response to sustained signaling. Consequently, understanding of the molecular mechanisms of PMF activation is not only critical for understanding CP and PDAC biology but is also a fertile area of research for the development of novel therapeutic strategies for pancreatic pathologies. This review analyzes the key signaling events that drive PMF activation including, initiating signals from transforming growth factor-β1, platelet derived growth factor, as well as other microenvironmental cues, like hypoxia and extracellular matrix rigidity. Further, we discussed the intracellular signal events contributing to PMF activation, and crosstalk with different components of tumor microenvironment. Additionally, association of epidemiologically established risk factors for CP and PDAC, like alcohol intake, tobacco exposure, and metabolic factors with PMF activation, is discussed to comprehend the role of lifestyle factors on pancreatic pathologies. Overall, this analysis provides insight into the biology of PMF activation and highlights salient features of this process, which offer promising therapeutic targets.

Orai1 Channel Regulates Human-Activated Pancreatic Stellate Cell Proliferation and TGFβ1 Secretion through the AKT Signaling Pathway

Simple Summary

Activated pancreatic stellate cells (aPSCs), the main source of cancer-associated fibroblasts in pancreatic ductal adenocarcinoma (PDAC), are well known as the key actor of the abundant fibrotic stroma development surrounding the tumor cells. In permanent communication with the tumor cells, they enhance PDAC early spreading and limit the drug delivery. However, the understanding of PSC activation mechanisms and the associated signaling pathways is still incomplete. In this study, we aimed to evaluate the role of Ca²⁺, and Orai1 Ca²⁺ channels, in two main PSC activation processes: cell proliferation and cytokine secretion. Indeed, Ca²⁺ is a versatile second messenger implicated in the regulation of numerous biological processes. We believe that a better comprehension of PSC Ca²⁺ -dependent activation mechanisms will bring up new crucial PDAC early prognostic markers or new targeting approaches in PDAC treatment.

Abstract

Activated pancreatic stellate cells (aPSCs), the crucial mediator of pancreatic desmoplasia, are characterized, among others, by high proliferative potential and abundant transforming growth factor _β1 (TGF_β1) secretion. Over the past years, the involvement of Ca²⁺ channels in PSC pathophysiology has attracted great interest in pancreatic cancer research. We, thus, aimed to investigate the role of the Orai1 Ca²⁺ channel in these two PSC activation processes. Using the siRNA approach, we invalided Orai1 expression and assessed the channel functionality by Ca²⁺ imaging, the effect on aPSC proliferation, and TGF_β1 secretion. We demonstrated the functional expression of the Orai1 channel in human aPSCs and its implication in the store-operated Ca²⁺ entry (SOCE). Orai1 silencing led to a decrease in aPSC proliferation, TGF_β1 secretion, and AKT activation. Interestingly, TGF_β1 induced a higher SOCE response by increasing Orai1 mRNAs and proteins and promoted both AKT phosphorylation and cell proliferation, abolished by Orai1 silencing. Together, our results highlight the role of Orai1-mediated Ca²⁺ entry in human aPSC pathophysiology by controlling cell proliferation and TGF_β1 secretion through the AKT signaling pathway. Moreover, we showed a TGF_β1-induced autocrine positive feedback loop by promoting the Orai1/AKT-dependent proliferation via the stimulation of Orai1 expression and function.

Antioxidants for Pancreatic Functions in Chronic Pancreatitis: A Double-blind Randomized Placebo-controlled Pilot Study

BACKGROUND

Antioxidants (AO) supplementation in chronic pancreatitis (CP) has been evaluated for pain. But it is not clear whether AO in CP have an effect on pancreatic functions and other clinical outcomes. We evaluated effect of AO on endocrine function in CP.

MATERIALS AND METHODS

Double-blind placebo (PL)-controlled randomized pilot study on 107 patients with CP assigned to receive daily combined AO or PL for 6 months. Primary outcome was: improvement in endocrine function (Homeostasis Model Assessment-Insulin Resistance). Secondary outcome measures were: improvement in C-peptide, Qualitative Insulin Sensitivity Check Index, exocrine pancreatic function (fecal elastase), surrogate markers of fibrosis (platelet-derived growth factor BB, transforming growth factor-β1, α-smooth muscle actin), quality of life (QOL), pain, nutritional status, markers of oxidative stress (OS), AO status, and inflammation.

RESULTS

There was an increase in levels of serum selenium (107.2±26.9 to 109.7±26.9 vs. 104.1±28.6 to 124.0±33.6 μg/L, P=0.022) and serum vitamin E [0.58 (range, 0.27-3.22) to 0.66 (range, 0.34-1.98) vs. 0.63 (range, 0.28-1.73) to 1.09 (range, 0.25-2.91) mg/dL, P=0.001] in the AO than the PL group. However, no significant differences were observed between groups in any of the primary or secondary outcome measures.

CONCLUSIONS

Supplementation with AO to patients with CP causes a sustained increase in blood levels of AO; however, it has no addition benefit over PL on endocrine and exocrine functions, markers of fibrosis, OS and inflammation, nutritional status, pain and QOL. Further larger studies with adequate sample size are required.

Transforming growth factor-β in pancreatic diseases: Mechanisms and therapeutic potential

Pancreatic diseases, such as acute pancreatitis, chronic pancreatitis, and pancreatic cancer, are common gastrointestinal diseases resulting in the development of local and systemic complications with a high risk of death. Numerous studies have examined pancreatic diseases over the past few decades; however, the pathogenesis remains unclear, and there is a lack of effective treatment options. Recently, emerging evidence has suggested that transforming growth factor beta (TGF-β) exerts controversial functions in apoptosis, inflammatory responses, and carcinogenesis, indicating its complex role in the pathogenesis of pancreas-associated disease. Therefore, a further understanding of relevant TGF-β signalling will provide new ideas and potential therapeutic targets for preventing disease progression. This is the first systematic review of recent data from animal and human clinical studies focusing on TGF-β signalling in pancreas damage and diseases. This information may aid in the development of therapeutic agents for regulating TGF-β in this pathology to prevent or treat pancreatic diseases.

Suppression of ROS Production by Exendin-4 in PSC Attenuates the High Glucose-Induced Islet Fibrosis

Pancreatic stellate cells (PSCs) play a major role to fibrotic islet destruction observed in diabetic patients and animal model of diabetes. Exendin-4 (Ex-4) is a potent insulinotropic agent and has been approved for the treatment of type 2 diabetes. However, there have been no reports demonstrating the effects of Ex-4 on pancreatic islet fibrosis. In this study, Ex-4 treatment clearly attenuated fibrotic islet destruction and improved glucose tolerance and islet survival. GLP-1 receptor expression was upregulated during activation and proliferation of PSCs by hyperglycemia. The activation of PKA pathway by Ex-4 plays a role in ROS production and angiotensin II (Ang II) production. Exposure to high glucose stimulated ERK activation and Ang II-TGF- β1 production in PSCs. Interestingly, Ex-4 significantly reduced Ang II and TGF-β1 production by inhibition of ROS production but not ERK phosphorylation. Ex-4 may be useful not only as an anti-diabetic agent but also as an anti-fibrotic agent in type 2 diabetes due to its ability to inhibit PSC activation and proliferation and improve islet fibrosis in OLETF rats.

Periostin induces pancreatic regeneration

We found that the secreted protein periostin (Postn) is highly induced after partial pancreatectomy in regenerating areas containing mesenchymal stroma and tubular complexes. Importantly, after partial pancreatectomy, Postn-deficient mice exhibit impaired mesenchymal formation and reduced regeneration specifically within the pancreatic β-cell compartment. Furthermore, Postn-deficient mice demonstrate an increased sensitivity to streptozotocin. Notably, injection of Postn directly into the pancreas stimulated proliferation of vimentin-expressing cells within 24 hours, and by 3 days, a mesenchymal stroma was present containing proliferating duct-like cells expressing the progenitor markers Ngn3 and Pdx1. Intraperitoneal injection of Postn resulted in increased numbers of islets and long-term glucoregulatory benefits with no adverse effects found in other tissues. Delivery of Postn throughout the pancreas via the common bile duct resulted in increased numbers of small insulin-expressing clusters and a significant improvement in glucose tolerance. Therefore, Postn is novel molecule capable of potentiating pancreatic β-cell regeneration.

Effect of antioxidant supplementation on surrogate markers of fibrosis in chronic pancreatitis: a randomized, placebo-controlled trial

OBJECTIVES

This study aimed to determine the effect of antioxidant (AO) supplementation on surrogate markers of fibrosis in patients with chronic pancreatitis (CP).

METHODS

In a randomized, placebo (PL)-controlled trial, patients with CP were randomized to groups that were given PL or AO for 3 months. Outcome measures were change in serum levels of transforming growth factor β1 and platelet-derived growth factor AA (PDGF-AA) (primary outcome) as well as blood markers of oxidative stress (thiobarbituric acid-reactive substances) and AO status (ferric-reducing ability of plasma) (secondary outcome). Pain relief and analgesic requirement was also recorded.

RESULTS

Patients (n = 61; mean [SD] age, 35.2 [10.0]; male patients, 43) were assigned to AO (n = 31) and PL (n = 30) groups. The median (range) percent reduction from baseline to 3 months in levels of PDGF-AA (17.1% [-25.3% to 88.7%] vs 2.8% [-243.1% to 30.2%]; P = 0.001), transforming growth factor β1 (P = 0.573), and thiobarbituric acid-reactive substances (P = 0.207) as well as percent increment from baseline to 3 months in ferric-reducing ability of plasma (P = 0.003) were higher in the AO group compared with the PL group. Proportion of patients who had both reduced PDGF-AA and reduced pain was greater in AO as compared with PL group (17/31 vs 9/30, P = 0.05)

CONCLUSIONS

Reduction in markers of fibrosis (PDGF-AA) translated into clinical outcome (reduction in pain and analgesic requirements) in those supplemented with AOs in CP (trial registration, CTRI/2011/05/001747).

miR-15b and miR-16 induce the apoptosis of rat activated pancreatic stellate cells by targeting Bcl-2 in vitro

OBJECTIVES

Activated pancreatic stellate cells (PSCs) play a pivotal role in the development of pancreatic diseases, especially chronic pancreatitis and pancreatic cancer. MicroRNAs have become a focal point of interest as post-transcriptional regulators of gene expression via their interaction with the 3' untranslated region of target mRNAs, which results in gene silencing. We examined the relative expression of microRNAs (miR-15b and miR-16) and their target gene, Bcl-2, during activation of rat PSCs, and determined their effects on apoptosis of rat PSCs in vitro.

METHODS

miR-15b and miR-16 expression levels were analyzed in quiescent and activated PSCs by stem-loop RT-PCR. In addition, the effects of miR-15b and miR-16 on apoptosis of activated PSCs were investigated by immunofluorescence microscopy with Hoechst 33342 staining, and flow cytometry with annexin-V/propidium (PI) co-labeling. Bcl-2 and Bcl-xl were also analyzed by real-time RT-PCR and Western blotting.

RESULTS

During activation of PSCs, from the quiescent stage to activated stage, miR-15b and miR_16 were downregulated, while Bcl-2 expression was upregulated. Restoring intracellular miRNA levels by miR-15b and miR-16 administration greatly reduced Bcl-2 protein levels, and significantly induced apoptosis in activated PSCs.

CONCLUSIONS

miR-15b and miR-16 could induce apoptosis of rat PSCs by targeting Bcl-2.

L-cysteine administration attenuates pancreatic fibrosis induced by TNBS in rats by inhibiting the activation of pancreatic stellate cell

BACKGROUND AND AIMS

Recent studies have shown that activated pancreatic stellate cells (PSCs) play a major role in pancreatic fibrogenesis. We aimed to study the effect of L-cysteine administration on fibrosis in chronic pancreatitis (CP) induced by trinitrobenzene sulfonic acid (TNBS) in rats and on the function of cultured PSCs.

METHODS

CP was induced by TNBS infusion into rat pancreatic ducts. L-cysteine was administrated for the duration of the experiment. Histological analysis and the contents of hydroxyproline were used to evaluate pancreatic damage and fibrosis. Immunohistochemical analysis of α-SMA in the pancreas was performed to detect the activation of PSCs in vivo. The collagen deposition related proteins and cytokines were determined by western blot analysis. DNA synthesis of cultured PSCs was evaluated by BrdU incorporation. We also evaluated the effect of L-cysteine on the cell cycle and cell activation by flow cytometry and immunocytochemistry. The expression of PDGFRβ, TGFβRII, collagen 1α1 and α-SMA of PSCs treated with different concentrations of L-cysteine was determined by western blot. Parameters of oxidant stress were evaluated in vitro and in vivo. Nrf2, NQO1, HO-1, IL-1β expression were evaluated in pancreas tissues by qRT-PCR.

RESULTS

The inhibition of pancreatic fibrosis by L-cysteine was confirmed by histological observation and hydroxyproline assay. α-SMA, TIMP1, IL-1β and TGF-β1 production decreased compared with the untreated group along with an increase in MMP2 production. L-cysteine suppressed the proliferation and extracellular matrix production of PSCs through down-regulating of PDGFRβ and TGFβRII. Concentrations of MDA+4-HNE were decreased by L-cysteine administration along with an increase in GSH levels both in tissues and cells. In addition, L-cysteine increased the mRNA expression of Nrf2, NQO1 and HO-1 and reduced the expression of IL-1β in L-cysteine treated group when compared with control group.

CONCLUSION

L-cysteine treatment attenuated pancreatic fibrosis in chronic pancreatitis in rats.

IL-13 promotes the proliferation of rat pancreatic stellate cells through the suppression of NF-kappaB/TGF-beta1 pathway

In chronic pancreatitis, pancreatic stellate cells (PSCs) play a central role in tissue fibrogenesis. Transforming growth factor beta(1) (TGF-beta(1)) and the Th2 lymphokines such as interleukin (IL)-13 are major profibrogenic cytokines in many organs. Activated PSCs produce various inflammatory cytokines including TGF-beta(1). In this study, we investigated whether IL-13 affects pancreatic fibrogenesis by modulating the functions of PSCs. IL-13 promoted PSCs proliferation without activation through the suppression of autocrine TGF-beta(1). IL-13 enhanced Stat6 phosphorylation in PSCs but Stat6 was not involved in the suppression of TGF-beta(1). IL-13 inhibited the transcriptional activity of NF-kappaB, and the expression of mutant I-kappaB reproduced the suppression of autocrine TGF-beta(1) and promoted PSCs proliferation. Taken together, we demonstrated that IL-13 promotes PSCs proliferation through the suppression of the transcriptional activity of NF-kappaB, resulting in the decrease of autocrine TGF-beta(1). This finding provides an unequivocal evidence of IL-13 participation in pancreatic fibrosis, illustrating a new strategy for chronic pancreatitis.

Mathematical modelling of interferon-gamma signalling in pancreatic stellate cells reflects and predicts the dynamics of STAT1 pathway activity

Signal transducer and activator of transcription (STAT) 1 is essentially involved in the mediation of antifibrotic interferon-gamma (IFN gamma) effects in pancreatic stellate cells (PSC). Here, we have further analysed the activation of the STAT1 pathway in a PSC line by combining quantitative data generation with mathematical modelling. At saturating concentrations of IFN gamma, a triphasic pattern of STAT1 activation was observed. An initial, rapid induction of phospho-STAT1 was followed by a plateau phase and another, long-lasting phase of further increase. The late increase occurred despite enhanced expression of the feedback inhibitor (SOCS1), and corresponded to increased levels of total STAT1 protein. If IFN gamma was applied at non-saturating concentrations, phospho-STAT1 and SOCS1 levels peaked and declined again over a 12 hour period, while STAT1 protein levels remained high. The mathematical model, based on a system of ordinary differential equations, describes temporal changes of the network components as a function of interactions and transport processes. The model reproduced activation profiles of all components of the STAT1 pathway that were experimentally analysed. Furthermore, it successfully predicted the dynamics of network components in additional experimental studies. Based on experimental findings and the results obtained from modelling, we suggest exhaustion of applied IFN gamma and STAT1 dephosphorylation by tyrosine phosphatases as limiting factors of STAT1 activation in PSC. In contrast, we did not obtain compelling evidence that SOCS1 acts as an efficient feedback inhibitor in our experimental system. We believe that further investigations into mathematical modelling of the STAT1 pathway will improve the understanding of the antifibrotic interferon action.

Mechanisms of pancreatic fibrosis and applications to the treatment of chronic pancreatitis

Pancreatic stellate cells (PSCs) play a crucial role in pancreatic fibrogenesis in chronic pancreatitis and in the desmoplastic reaction of pancreatic cancer. When PSCs are stimulated by oxidative stress, ethanol and its metabolite acetaldehyde, and cytokines, the phenotype of quiescent fat-storing cells converts to myofibroblastlike activated PSCs, which then produce extracellular matrix, adhesion molecules, and various chemokines in response to cytokines and growth factors. Recent data suggest that PSCs have a phagocytic function. Plateletderived growth factor is a potent stimulator of PSC proliferation. Transforming growth factor beta, activin A, and connective tissue growth factor also play a role in PSC-mediated pancreatic fibrogenesis through autocrine and paracrine loops. Following pancreatic damage, pathophysiological processes that occur in the pancreas, including pancreas tissue pressure, hyperglycemia, intracellular reactive oxygen species production, activation of protease-activated receptor 2, induction of cyclooxygenase 2, and bacterial infection play a role in sustaining pancreatic fibrosis through increased PSC proliferation and collagen production by PSCs. Targeting PSCs might be an effective therapeutic approach in chronic pancreatitis. Various substances including vitamin A, vitamin E, polyphenols, peroxisome proliferator-activated receptor gamma ligands, and inhibitors of the renin-angiotensin system show great promise of being useful in the treatment of chronic pancreatitis.

Synergistic growth inhibitory effects of the dual endothelin-1 receptor antagonist bosentan on pancreatic stellate and cancer cells

Pancreatic stellate cells (PSC) play a key role in pancreatic fibrosis. Activation of PSC occurs in response to pro-fibrogenic stimuli and is maintained by autocrine loops of mediators, such as endothelin (ET)-1. Here, we have evaluated effects of the dual ET receptor antagonist bosentan in models of pancreatic fibrogenesis and cancer. Cell culture studies revealed that PSC and DSL6A pancreatic cancer cells expressed both ET-1 and ET receptors. Bosentan efficiently inhibited proliferation of both cell types and collagen synthesis in PSC. Expression of the myofibroblastic marker alpha-smooth muscle actin, connective tissue growth factor, and ET-1 itself in PSC was reduced, while expression of matrix metalloproteinase-9 was enhanced. Like PSC, DSL6A cells secrete less ET-1 when cultured with bosentan. In a rat model of pancreatic fibrosis, chronic pancreatitis induced by dibutyltin dichloride, a tendency towards a diminished disease progression was observed in a subgroup of rats with less severe disease. Together, our results indicate that bosentan exerts antifibrotic and antitumor effects in vitro. Its efficiency in vivo warrants further investigation.

Crucial role of fibrogenesis in pancreatic diseases

Chronic pancreatitis and pancreatic cancer are characterised by a progressive fibrosis. Accumulation of extracellular matrix not only accompanies both diseases but is directly involved in their progression, suggesting inhibition of fibrogenesis as a potential therapeutic strategy. Pancreatic stellate cells (PSC) are the main extracellular matrix-producing cell type in the diseased pancreas. In response to pro-fibrogenic mediators including cytokines and ethanol metabolites, PSC undergo phenotypic changes termed activation, resulting in the exhibition of a myofibroblast-like phenotype. In the perpetuation of PSC activation, autocrine loops of mediators such as transforming growth factor beta play an important role. Most recently signal transduction pathways in PSC that are associated with the process of activation were characterised, facilitating identification of potential intracellular targets for an anti-fibrotic therapy. While some putative inhibitors of fibrogenesis have been tested in animal models of pancreatic fibrosis for their in vivo efficiency, clinical studies still remain to be performed.

TGF-beta-induced fibrosis and SMAD signaling: oligo decoys as natural therapeutics for inhibition of tissue fibrosis and scarring

Transforming-growth factor-beta (TGF-beta) is a pleiotrophic growth factor that is synthesized by many cells in the body. This growth factor is chemotactic for fibroblasts, stimulates fibroblast proliferation, and increases the synthesis of a number of extracellular matrix proteins including collagens. The TGF-beta activator protein is a transacting factor, which binds to the TGF-beta element in the distal promoter of the COL1A1 collagen gene and induces transcription of this gene. Although transient TGF-beta 1 activity participates in repair and regeneration of tissues, persistent TGF-beta 1 function affects excessive fibrosis and ultimately scarring of both skin and internal organs. Scarring of internal organ (e.g., liver and lung) results in a loss of function and ultimately death may occur. The central issue of this review is that phosphorothioate double-stranded decoys or other decoys decrease procollagen gene expression, procollagen synthesis, and collagen during fibrogenesis. The rationale is that the decoys containing the TGF-beta element or other gene transcription regulatory CIS-elements bind the transacting proteins preventing the latter from binding to the CIS-element in the 5'-flanking region of the natural gene resulting in transcription inhibition. We will, in part, focus on aspects involved in TGF-beta 1-induced fibrosis that occur during fibrogenesis and the use of the dsTGF-beta element containing oligodeoxynucleotide decoys to control excessive collagen synthesis, and deposition resulting from persistent TGF-beta. In our model of regulation of collagen synthesis, these double-stranded oligo decoys act as promoter competitors, binding to the activator protein either in the cytoplasm or in the nucleus. The significance of the proposed studies is that these novel natural antifibrotics will mimic the effect of glucocorticoids on collagen synthesis during fibrogenesis without the unwanted side effects of these steroids. Based on our previous studies on the molecular mechanisms by which glucocorticoids selectively decrease collagen synthesis, designed phosphorothioate oligodeoxynucleotides resistant to nuclease action will mimic the effects of glucocorticoids at the molecular, cellular, and in vivo levels of collagen synthesis. However, the glucocorticoids significantly inhibit noncollagen protein synthesis. Both the single-stranded and double-stranded oligodeoxynucleotide specifically decrease collagen synthesis without an inhibitory effect on noncollagen protein synthesis. In this review, we will specifically ask if TGF-beta-induced collagen synthesis is inhibited in cell culture and in vivo by using the double-stranded oligodeoxynucleotide decoys, will this inhibit fibrogenesis and ultimately scarring?

Pancreatic stellate cells: new target in the treatment of chronic pancreatitis

Chronic pancreatitis (CP) is characterized by progressive fibrosis, pain and/or loss of exocrine and endocrine functions. Recent in vitro and in vivo experiments have proven objectively the role of activated pancreatic stellate cells (PSC) in fibrogenesis in CP. Molecular mediators shown to regulate the pathogenesis include transforming growth factor beta (TGF-beta), platelet-derived growth factor (PDGF), and pro-inflammatory cytokines such as IL-1, IL-6 and TNF-alpha. Furthermore, molecular pathways involving mitogen-activated protein kinases (MAPK), phosphatidyl inositol 3-kinase (PI3K), Ras superfamily G proteins, serine threonine protein kinase Raf-1 and peroxisome proliferator activated receptor gamma (PPAR-gamma) have been elucidated. Understanding of the pathogenesis has led to identification of novel molecular targets and development of potential newer therapeutic agents. Those found to retard the progression of experimental CP and fibrosis in animal models include interferon (IFN) beta and IFN-gamma; a Japanese herbal medicine called Saiko-keishi-to (TJ-10); curcumin; PPAR-gamma ligand (troglitazone); antioxidants (vitamin A, vitamin E, DA 9601 and epigallocatechin-3-gallate); a protease inhibitor (camostat mesilate) and hydroxymethylglutaryl-CoA inhibitor (lovastatin). This review summarizes the current literature addressing the role of different pharmacological agents aimed at reducing or preventing inflammation and the consequent fibrogenesis in CP.

Antifibrogenic effects of histone deacetylase inhibitors on pancreatic stellate cells

Pancreatic stellate cells (PSCs) are essentially involved in pancreatic fibrogenesis and considered as a target for antifibrotic therapies. Here, we have analyzed the effects of three histone deacetylase inhibitors (HDACIs), sodium butyrate, sodium valproate (VPA) and trichostatin A (TSA), on profibrogenic activities of PSC and elucidated molecular targets of HDACI action. Therefore, cultured PSCs were exposed to HDACI. Cell proliferation and viability were assessed by 5-bromo-2'-deoxyuridine (BrdU) incorporation and trypan blue staining assays. Exhibition of the myofibroblastic PSC phenotype was monitored by immunofluorescence analysis of alpha-smooth muscle actin (alpha-SMA) expression. [(3)H]-proline incorporation into acetic acid-soluble proteins was measured to quantify collagen synthesis. Levels of mRNA were determined by quantitative reverse transcriptase real-time PCR. Protein expression, phosphorylation and acetylation were analyzed by immunoblotting, and gel shift assays were performed to study DNA binding of nuclear proteins. HDACI enhanced histone H3 acetylation in a dose-dependent manner. In the same dose range, they strongly inhibited cell proliferation, alpha-SMA expression and collagen synthesis. A significantly increased rate of cell death was observed in response to TSA at 1 microM. While all three HDACI inhibited mRNA expression of endothelin-1, only VPA significantly reduced expression of transforming growth factor-beta1. Both mediators exert autocrine profibrogenic effects on PSC. Furthermore, HDACI-treated PSC displayed a diminished DNA binding of AP-1, a key transcription factor in profibrogenic signaling. Together, the results suggest that HDACI exert antifibrogenic effects on PSC. Interruption of AP-1 signaling and autocrine loops enhancing PSC activation might be key mechanisms of HDACI action.

Effects of epigallocatechin gallate on diethyldithiocarbamate-induced pancreatic fibrosis in rats

Epigallocatechin gallate (EGCG), a major component of green tea extracts, is known to have anti-fibrotic properties in many organs. The aim of present study was to investigate effects of EGCG on rat pancreatic fibrosis induced by diethyldithiocarbamate (DDC). Oral gavages of different dose of EGCG (50, 100 and 200 mg/kg daily for 8 weeks) ameliorated histological changes and significantly suppressed collagen deposition in a dose-dependent manner. Meanwhile, administration of EGCG inhibited overexpression of TGF-beta1 and alpha-smooth muscle actin (a symbol of activation of pancreatic stellate cells). Moreover, EGCG has a potent influence on expression of Smads (downstream transcription factor of TGF-beta1). EGCG suppressed the expression of Smad3 and enhanced the expression of Smad7. In conclusion, our results demonstrated that EGCG attenuated rat pancreatic fibrosis induced by DDC and therefore may be an anti-fibrogenic candidate in the pancreatic fibrosis.

Transforming Growth Factor β Is a Critical Regulator of Adult Human Islet Plasticity

Tissue plasticity is well documented in the context of pancreatic regeneration and carcinogenesis, with recent reports implicating dedifferentiated islet cells both as endocrine progenitors and as the cell(s) of origin in pancreatic adenocarcinoma. Accordingly, it is noteworthy that accumulating evidence suggests that TGFβ signaling is essential to pancreatic endocrine development and maintenance, whereas its loss is associated with the progression to pancreatic adenocarcinoma. The aim of this study was to examine the role of TGFβ in an in vitro model of islet morphogenetic plasticity. Human islets were embedded in a collagen gel and cultured under conditions that induced transformation into duct-like epithelial structures (DLS). Addition of TGFβ caused a dose-dependent decrease in DLS formation. Although it was demonstrated that collagen-embedded islets secrete low levels of TGFβ, antibody-mediated neutralization of this endogenously released TGFβ improved DLS formation rates, suggesting local TGFβ concentrations may in fact be higher. Time course studies indicated that TGFβ signaling was associated with an increase in ERK and p38 MAPK phosphorylation, although inhibitor-based studies were consistent with an islet endocrine-stabilizing effect mediated by p38 alone. Localization of TGFβ signaling molecules suggested that the action of TGFβ is directly on the β-cell to inhibit apoptosis and thus stabilize endocrine phenotype.

Adenovirus-mediated gene transfer of interleukin-4 into pancreatic stellate cells promotes interleukin-10 expression

Pancreatic stellate cells (PSC) are crucially involved in the development of fibrosis, a hallmark of chronic pancreatitis. Therefore, PSC represent an attractive target for the modulation of cellular functions providing the prerequisite for the establishment of novel therapeutic strategies like transfer of genetic material to the cells. Based on recent studies suggesting that the chronic course of pancreatitis is associated with immune deviation towards a Th1 cytokine profile, we have investigated the applicability of primary PSC to an adenovirus-mediated transfer of the cDNA encoding the Th2 cytokine interleukin (IL) 4 and the autocrine-acting effects of IL 4 on the cells in vitro. The trans-duction of primary PSC with a replication-incompetent adenovirus type 5 vector carrying the cDNA encoding rat IL-4 resulted in a distinct expression of the cytokine on mRNA and protein level for two weeks. Similar to recombinant IL 4, effects of the endogenously synthesized cytokine were mediated by the signal transducer and activator of transcription (STAT)6. Interestingly, beside the increase of PSC proliferation, IL 4 transduction was accompanied by an up-regulation in the endogenous expression of the anti-inflammatory cytokine IL 10. In summary, our data suggest that PSC are suitable targets for gene therapy modulating cellular interactions in the pancreas.

Inhibitory effects of interferon-gamma on activation of rat pancreatic stellate cells are mediated by STAT1 and involve down-regulation of CTGF expression

Pancreatic stellate cells (PSCs) are the main source of extracellular matrix proteins in pancreatic fibrosis, a pathological feature of chronic pancreatitis and pancreatic cancer. Interferon-gamma (IFN-gamma) is an antifibrotic cytokine, but how precisely it exerts its effects on PSCs is largely unknown. Here, we have focussed on the role of STAT1 as well as target genes of IFN-gamma signalling. Our data indicate that IFN-gamma regulates the expression of two autocrine mediators of PSC activation, connective tissue growth factor and endothelin-1, in a transforming growth factor-beta1-antagonistic manner. STAT1 overexpression under the control of a tetracycline-dependent promoter revealed a close correlation between STAT1 expression and activation, the biological effects of IFN-gamma (growth inhibition, induction of apoptosis), and target gene expression. Our data further support the hypothesis that IFN-gamma interferes with stellate cell activation in the pancreas and suggest activated STAT1 as an inductor of a quiescent PSC phenotype.

Existence of autocrine loop between interleukin-6 and transforming growth factor-beta1 in activated rat pancreatic stellate cells

Interleukin (IL)-6 is a proinflammatory cytokine assumed to participate in pancreatic fibrosis by activating pancreatic stellate cells (PSCs). Autocrine TGF-beta1 is to central in PSC functional regulation. In this study, we examined IL-6 secretion from culture-activated rat PSCs and its regulatory mechanism. Activated PSCs express and secrete IL-6. When anti-TGF-beta1 neutralizing antibody was added in the culture medium, IL-6 secretion from activated PSCs was inhibited, whereas exogenous TGF-beta1 added in the culture medium enhanced IL-6 expression and secretion by PSCs in a dose dependent manner. Infection of PSCs with an adenovirus expressing dominant-negative Smad2/3 attenuated basal and TGF-beta1-stimulated IL-6 expression and secretion of PSCs. We also demonstrated the reciprocal effect of PSCs-secreted IL-6 on autocrine TGF-beta1. Anti-IL-6 neutralizing antibody inhibited TGF-beta1 secretion from PSCs. Preincubation of cells with 10 nM PD98059, an extracellular signal-regulated kinase (ERK)-dependent pathway inhibitor, attenuated IL-6-enhanced TGF-beta1 expression and secretion of PSCs. In addition, IL-6 activated ERK in PSCs. These data indicate the existence of autocrine loop between IL-6 and TGF-beta1 through ERK- and Smad2/3-dependent pathways in activated PSCs.

Cigarette smoke-induced differential expression of the genes involved in exocrine function of the rat pancreas

OBJECTIVE

Little is known about the molecular and biological aspects of the epidemiological association between smoking and pancreatic pathology, such as chronic pancreatitis and pancreatic cancer. Recently, we reported that tobacco smoke exposure induced morphological alterations in the rat pancreas. Here, we have investigated the alterations in the expression of genes associated with exocrine pancreatic function and cellular differentiation upon exposure to cigarette smoke.

METHODS

Female rats were exposed to environmental smoke inhalation for 2 d/wk (70 min/d) for 12 weeks. The expression profiles of trypsinogen, pancreas-specific trypsin inhibitor, cholecystokinin A receptor, cystic fibrosis transmembrane conductance regulator (CFTR), carbonic anhydrase, and Muc1 and Muc4 mucins transcripts were analyzed by RNA slot blot analysis. Muc4 expression was also examined by immunohistochemistry.

RESULTS

Our data revealed that the ratio of trypsinogen to that of the protective pancreas-specific trypsin inhibitor was elevated upon cigarette smoke exposure. The expression of carbonic anhydrase and CFTR remained unaltered when inflammatory signs were not detected in histological examinations. On the other hand, when pancreatic inflammation was present, the levels of CFTR and carbonic anhydrase were increased, indicating ductal and/or centroacinar cell involvement. No changes in the expression of Muc1 and Muc4 mucins were observed.

CONCLUSIONS

Our data show that cigarette smoke exposure leads to an increased vulnerability to pancreatic self-digestion. Moreover, the concomitant involvement of pancreatic ducts occurs only when focal pancreatic inflammation is present.

High glucose increases extracellular matrix production in pancreatic stellate cells by activating the renin-angiotensin system

Pancreatic stellate cells (PSCs) are involved in pancreatic inflammation and fibrosis. Recent studies have shown that blocking the renin-angiotensin system (RAS) attenuates pancreatic inflammation and fibrosis. However, there are few data about the direct effects of high glucose on extracellular matrix (ECM) protein synthesis and angiotensin II (Ang II) induction in PSCs. PSCs were isolated from male Sprague-Dawley rats and cultured in medium containing 5.5 mM (LG group) or 27 mM D-glucose (HG group). Levels of Ang II and transforming growth factor-beta (TGF-beta) in culture media were measured and Ang II-positive cells were counted. We used real-time polymerase chain reaction (PCR) to detect Ang II receptor expression and Western blot analysis for the expression of ECM proteins such as connective-tissue growth factor (CTGF) and collagen type IV. Cells were also treated with an Ang II-receptor antagonist (candesartan, 10 microM) or angiotensin-converting enzyme (ACE) inhibitor (ramiprilat, 100 nM). Thymidine uptake by PSCs increased fourfold with high glucose treatment. Ang II levels and the proportion of Ang II-positive PSCs were significantly increased after 6 h under high-glucose conditions. TGF-beta concentrations also increased significantly with high glucose. After 72 h, the expression of CTGF and collagen type IV proteins in high-glucose cultures increased significantly and this increase was effectively attenuated by the candesartan or the ramiprilat. All together, high glucose induced PSCs proliferation and ECM protein synthesis, and these effects were attenuated by an Ang II-receptor antagonist. The data suggest that pancreatic inflammation and fibrosis aggravated by hyperglycemia, and Ang II play an important role in this pathogenesis.

Chronic pancreatitis: evolving paradigms

Chronic pancreatitis (CP) is characterized by progressive fibrosis, pain and/or loss of exocrine and endocrine functions. With the identification and characterization of pancreatic stellate cells (PSCs), the pathogenesis of CP and pancreatic fibrosis is now better understood. Molecular mediators shown to regulate the pathogenesis include transforming growth factor-beta, platelet-derived growth factor, and proinflammatory cytokines such as interleukin (IL)-1, IL-6 and tumor necrosis factor-alpha. Besides these, the roles of cyclooxygenase (COX)-2 and apoptosis-related proteins have also been implicated in the pathogenesis. Furthermore, molecular pathways involving mitogen-activated protein kinases, phosphatidylinositol 3-kinase, Ras superfamily G proteins, serine threonine protein kinase Raf-1 and peroxisome proliferator-activated receptor-gamma (PPAR-gamma) have been elucidated. Newer pathobiologic concepts concerning pain generation have also been put forward. Understanding the pathogenesis has led to the identification of novel molecular targets and the development of newer potential therapeutic agents. Those found to retard the progression of experimental CP and fibrosis in animal models include antioxidants, a Japanese herbal medicine called Saiko-keisi-to (TJ 10), the PPAR-gamma ligand troglitazone, the protease inhibitor Camostat mesilate, and Lovastatin.

Cyclooxygenase-2 is required for activated pancreatic stellate cells to respond to proinflammatory cytokines

Cyclooxygenase-2 (COX-2) mediates various inflammatory responses and is expressed in pancreatic tissue from patients with chronic pancreatitis. To examine the role of COX-2 in chronic pancreatitis, we investigated its participation in regulating functions of pancreatic stellate cells (PSCs), using isolated rat PSCs. COX-2 was expressed in culture-activated PSCs but not in freshly isolated quiescent PSCs. TGF-beta1, IL-1beta, and IL-6 enhanced COX-2 expression in activated PSCs, concomitantly increasing the expression of alpha-smooth muscle actin (alpha-SMA), a parameter of PSC activation. The COX-2 inhibitor NS-398 blocked culture activation of freshly isolated quiescent PSCs. NS-398 also inhibited the enhancement of alpha-SMA expression by TGF-beta1, IL-1beta, and IL-6 in activated PSCs. These data indicate that COX-2 is required for the initiation and promotion of PSC activation. We further investigated the mechanism by which cytokines enhance COX-2 expression in PSCs. Adenovirus-mediated expression of dominant negative Smad2/3 inhibited the increase in expression of COX-2, alpha-SMA, and collagen-1 mediated by TGF-beta1 in activated PSCs. Moreover, dominant negative Smad2/3 expression attenuated the expression of COX-2 and alpha-SMA enhanced by IL-1beta and IL-6. Anti-TGF-beta neutralizing antibody also attenuated the increase in COX-2 and alpha-SMA expression caused by IL-1beta and IL-6. IL-6 as well as IL-1beta enhanced TGF-beta1 secretion from PSCs. These data indicate that Smad2/3-dependent pathway plays a central role in COX-2 induction by TGF-beta1, IL-1beta, and IL-6. Furthermore, IL-1beta and IL-6 promote PSC activation by enhancing COX-2 expression indirectly through Smad2/3-dependent pathway by increasing TGF-beta1 secretion from PSCs.

Inhibitory effects of interferons on pancreatic stellate cell activation

AIM: To analyze and to compare the effects of interferon (IFN)-α, IFN-β, and IFN-γ on pancreatic stellate cell (PSC) activation in vitro and to elucidate the molecular basis of IFN action.

METHODS: PSCs were isolated from rat’s pancreatic tissue, cultured and stimulated with recombinant rat IFNs. Cell proliferation and collagen synthesis were assessed by measuring the incorporation of 5-bromo-2’-deoxyuridine (BrdU) into DNA and [³H]-proline into acetic acid-soluble proteins, respectively. Apoptotic cells were determined by FACS analysis (sub-G₁ peak method). Exhibition of the myofibroblastic PSC phenotype was monitored by immunoblot analysis of α-smooth muscle actin (α-SMA) expression. To assess the activation of signal transducer and activator of transcription (STAT), Western blots using phospho-STAT-specific antibodies were performed. In studies on STAT1 function, expression of the protein was inhibited by siRNA.

RESULTS: IFN-β and IFN-γ, but not IFN-α significantly diminished PSC proliferation and collagen synthesis. IFN-γ was the only IFN that clearly inhibited α-SMA expression. Under the experimental conditions used, no enhanced rate of apoptotic cell death was observed in response to any IFN treatment. IFN-β and IFN-γ induced a strong increase of STAT1 and STAT3 tyrosine phosphorylation, while the effect of IFN-α was much weaker. Inhibition of STAT1 expression with siRNA was associated with a significantly reduced growth-inhibitory effect of IFN-γ.

CONCLUSION: IFN-β and particularly IFN-γ display inhibitory effects on PSC activation in vitro and should be tested regarding their in vitro efficiency. Growth inhibition by IFN-γ action requires STAT1.

Autocrine loop between TGF-beta1 and IL-1beta through Smad3- and ERK-dependent pathways in rat pancreatic stellate cells

Pancreatic stellate cells (PSCs) are activated during pancreatitis and promote pancreatic fibrosis by producing and secreting ECMs such as collagen and fibronectin. IL-1beta has been assumed to participate in pancreatic fibrosis by activating PSCs. Activated PSCs secrete various cytokines that regulate PSC function. In this study, we have examined IL-1beta secretion from culture-activated PSCs as well as its regulatory mechanism. RT-PCR and ELISA have demonstrated that PSCs express IL-1beta mRNA and secrete IL-1beta peptide. Inhibition of TGF-beta(1) activity secreted from PSCs by TGF-beta(1)-neutralizing antibody attenuated IL-1beta secretion from PSCs. Exogenous TGF-beta(1) increased IL-1beta expression and secretion by PSCs in a dose-dependent manner. Adenovirus-mediated expression of dominant-negative (dn)Smad2/3 expression reduced both basal and TGF-beta(1)-stimulated IL-1beta expression and secretion by PSCs. Coexpression of Smad3 with dnSmad2/3 restored IL-1beta expression and secretion by PSCs, which were attenuated by dnSmad2/3 expression. In contrast, coexpression of Smad2 with dnSmad2/3 did not alter them. Furthermore, inhibition of IL-1beta activity secreted from PSCs by IL-1beta-neutralizing antibody attenuated TGF-beta(1) secretion from PSCs. Exogenous IL-1beta enhanced TGF-beta(1) expression and secretion by PSCs. IL-1beta activated ERK, and PD-98059, a MEK1 inhibitor, blocked IL-1beta enhancement of TGF-beta(1) expression and secretion by PSCs. We propose that an autocrine loop exists between TGF-beta(1) and IL-1beta in activated PSCs through Smad3- and ERK-dependent pathways.

Angiotensin II promotes the proliferation of activated pancreatic stellate cells by Smad7 induction through a protein kinase C pathway

Activated pancreatic stellate cells (PSCs) play major roles in promoting pancreatic fibrosis. We previously reported that angiotensin II (Ang II) enhances activated PSC proliferation through EGF receptor transactivation. In the present study, we elucidated a novel intracellular mechanism by which Ang II stimulates cellular proliferation. TGF-beta1 inhibits activated PSC proliferation via a Smad3 and Smad4-dependent pathway in an autocrine manner. We demonstrated that Ang II inhibited TGF-beta1-induced nuclear accumulation of Smad3 and Smad4. Furthermore, Ang II rapidly induced inhibitory Smad7 mRNA expression. Adenovirus-mediated Smad7 overexpression inhibited TGF-beta1-induced nuclear accumulation of Smad3 and Smad4, and potentiated activated PSC proliferation. PKC inhibitor Go6983 blocked the induction of Smad7 mRNA expression by Ang II. In addition, 12-O-tetradecanoyl-phorbol 13-acetate, a PKC activator, increased Smad7 mRNA expression. These results suggest that Ang II enhances activated PSC proliferation by blocking autocrine TGF-beta1-mediated growth inhibition by inducing Smad7 expression via a PKC-dependent pathway.

Inhibition of lymphocyte apoptosis by pancreatic stellate cells: impact of interleukin-15

There is growing evidence that pancreatic stellate cells (PSCs) produce cytokines and take part in the regulation of inflammatory processes in the pancreas. IL-15 inhibits apoptosis of various cell populations. This study was performed to investigate whether PSCs produce IL-15 and thereby can affect lymphocytes. Primary PSCs were isolated from the rat pancreas using density gradient centrifugation. mRNA expression of IL-15 was demonstrated by RT-PCR, and IL-15 protein was analyzed by immunoblotting. Lymphocytes obtained from rat mesenterial lymph nodes were cocultured with in vitro activated PSCs. Apoptosis has been quantified by the binding of annexin V-FITC with a flow cytometer. Proliferation was monitored using [3H]thymidine incorporation. PSCs express two splice variants of IL-15. The protein was detectable only in cell lysates but not in the cell culture supernatant. Cocultivation of lymphocytes with PSCs and IL-15 inhibited spontaneous lymphocyte apoptosis, and this effect was reduced by an anti-IL-15 antibody. Lymphocytes induced vice versa the proliferation and collagen production of PSCs. The inhibition of spontaneous lymphocyte apoptosis in cocultures with PSCs was at least partially mediated by cell-bound IL-15. This effect and the stimulation of PSCs by lymphocytes may lead to a circulus vitiosus, resulting in the persistence of inflammatory processes and the development of fibrosis during chronic pancreatitis.

Parenchymal regression in chronic pancreatitis spares islets reprogrammed for the expression of NFkappaB and IAPs

In advanced chronic pancreatitis (CP), islets are preserved even in the midst of scarring. We recently showed in CP local production of interferon (IFN)gamma, transforming growth factor (TGF)beta and death receptor ligand TRAIL (tumor necrosis factor-related apoptosis-inducing ligand), along with functional death receptor neoexpression and apoptosis in exocrine but not in endocrine cells. However, islets are strongly induced for TRAIL-receptor (R)-4 lacking the functional death domain. TRAIL-R4 signaling in T cells induces NFkappaB, which activates antiapoptotic programs. Here, we demonstrate that in insulinoma cells CM, TGFbeta/IFNgamma/TRAIL in combination induced TRAIL-R4 surface expression. TRAIL/IFNgamma upregulated NFkappaB subunits and its target gene survivin while downmodulating IkappaB alpha mRNA. RelA transcriptional activity increased upon stimulation with IFNgamma and IFNgamma/TRAIL. In situ, normal pancreatic epithelia had low mRNA levels of NFkappaB subunits. These were higher in parenchymal areas of CP with severe fibrosis and highest in islets. NFkappaB-regulated proteins IkappaB alpha, survivin and another apoptosis inhibitor, cIAP1, were found in corresponding sites, again at highest levels in islets surrounded by fibrosis. In conclusion, islets in CP not only evade immune attack by nonexposure of functional death receptors in the presence of TRAIL-R4 but also additionally neoexpress NFkappaB and its target genes, survivin and cIAP1, to protect themselves from apoptosis.

Amelioration of pancreatic fibrosis in mice with defective TGF-beta signaling

OBJECTIVES

Pancreatic fibrosis is a characteristic feature of chronic pancreatic injury, which is a result of the imbalance between synthesis and degradation of extracellular matrix (ECM) proteins. Transforming growth factor-beta (TGF-beta) plays a central role in biosynthesis and turnover of the ECM. In this study, we evaluated the role of TGF-beta signaling in pancreatic fibrosis induced by repetitive acute pancreatic injuries with mice of dominant-negative mutant of TGF-beta receptor II selectively in pancreas.

METHODS

TGF-beta signaling was inactivated by overexpressing a dominant-negative mutant form of TGF-beta type II receptor (pS2-dnR II) only in the pancreas under control of pS2/TFF1 promoter. Pancreatic fibrosis was induced by repeated intraperitoneal injections of 40 microg/kg cerulein for 5 or 10 weeks.

RESULTS

Repeated administration of cerulein induced significant pancreatic fibrosis, but of which fibrosis was remarkably attenuated in pS2-dnR II mice compared with wild-type littermates (P < 0.01). The ameliorated fibrosis was due to the reduction of synthesis of ECM proteins such as collagen type I, fibronectin, and ICAM-1. DNA binding activity of transcriptional factors including nuclear factor (NF)-kappaB and AP-1, responsible for the induction of immediate early genes of inflammatory responses, were significantly decreased in pS2-dnR II mice. While TGF-beta1 treatment in isolated pancreatic stellate cells (PSCs) stimulated the expression of alpha-SMA and fibronectin, PSCs transfected with TGF-beta dnRII showed attenuation of the ECM components.

CONCLUSION

Conditional loss of TGF-beta signaling selectively in the pancreas led to a failure in fibrogenic responses of repeated injections of cerulein, signifying that the modulation of TGF-beta signaling could be the therapeutic target for the prevention of chronic fibrosing pancreatitis.

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Galectin-1 is an inductor of pancreatic stellate cell activation

Pancreatic stellate cells (PSCs) play a key role in the development of pancreatic fibrosis, a pathological feature of chronic pancreatitis and pancreatic cancer. Here, we show that activation of rat PSCs in vitro is associated with increased expression of galectin-1 (gal-1) and that gal-1 modulates PSC function. Expression of the lectin was stimulated by fetal calf serum and platelet-derived growth factor. PSCs exposed to exogenous gal-1 proliferated at a higher rate and synthesised more collagen than controls. Gal-1-dependent collagen synthesis was blocked by lactose but not by cellobiose, suggesting that gal-1 acts on PSCs through targeting beta-galactoside-containing glycoconjugates. Analysis of gal-1 signalling in PSCs revealed an activation of the extracellular signal-regulated kinases 1 and 2 and enhanced DNA binding of AP-1 transcription factors. Together, our data implicate gal-1 in PSC activation and suggest further studies to analyse the role of endogenous lectins in the development of pancreatic fibrosis in vivo.

Pressure activates rat pancreatic stellate cells

Pancreatic stellate cells (PSCs) play a central role in development of pancreatic fibrosis. In chronic pancreatitis, pancreatic tissue pressure is higher than that of the normal pancreas. We here evaluate the effects of pressure on the activation of rat PSCs. PSCs were isolated from the pancreas of Wistar rat using collagenase digestion and centrifugation with Nycodenz gradient. Pressure was applied to cultured rat PSCs by adding compressed helium gas into the pressure-loading apparatus to raise the internal pressure. Cell proliferation rate was assessed by 5-bromo-2'-deoxyuridine (BrdU) incorporation. MAPK protein levels and alpha-smooth muscle actin (alpha-SMA) expression were evaluated by Western blot analysis. Concentration of activated transforming growth factor-beta1 (TGF-beta1) secreted from PSCs into culture medium was determined by ELISA. Collagen type I mRNA expression and collagen secretion were assessed by quantitative PCR and Sirius red dye binding assay, respectively. Application of pressure significantly increased BrdU incorporation and alpha-SMA expression. In addition, pressure rapidly increased the phosphorylation of p44/42 and p38 MAPK. Treatment of PSCs with an MEK inhibitor and p38 MAPK inhibitor suppressed pressure-induced cell proliferation and alpha-SMA expression, respectively. Moreover, pressure significantly promoted activated TGF-beta1 secretion, collagen type I mRNA expression, and collagen secretion. Our results demonstrate that pressure itself activates rat PSCs and suggest that increased pancreatic tissue pressure may accelerate the development of pancreatic fibrosis in chronic pancreatitis.

Molecular regulation of pancreatic stellate cell function

Until now, no specific therapies are available to inhibit pancreatic fibrosis, a constant pathological feature of chronic pancreatitis and pancreatic cancer. One major reason is the incomplete knowledge of the molecular principles underlying fibrogenesis in the pancreas. In the past few years, evidence has been accumulated that activated pancreatic stellate cells (PSCs) are the predominant source of extracellular matrix (ECM) proteins in the diseased organ. PSCs are vitamin A-storing, fibroblast-like cells with close morphological and biochemical similarities to hepatic stellate cells (also known as Ito-cells). In response to profibrogenic mediators such as various cytokines, PSCs undergo an activation process that involves proliferation, exhibition of a myofibroblastic phenotype and enhanced production of ECM proteins. The intracellular mediators of activation signals, and their antagonists, are only partially known so far. Recent data suggest an important role of enzymes of the mitogen-activated protein kinase family in PSC activation. On the other hand, ligands of the nuclear receptor PPARγ (peroxisome proliferator-activated receptor γ) stimulate maintenance of a quiescent PSC phenotype. In the future, targeting regulators of the PSC activation process might become a promising approach for the treatment of pancreatic fibrosis.

Generation and characterization of immortalized rat pancreatic stellate cells

Pancreatic stellate cells (PSCs) are involved in, among other things, the pathogenesis of pancreatic fibrosis. Here, we present the generation of immortalized PSCs 7 and 14 days after isolation by retroviral gene transfer of the SV40 large T antigen encoding region. Propagated cell lines [large T immortalized cells (LTC)-7, LTC-14] retained characteristics of primary cells in terms of morphology, responsiveness to mediators regulating cellular functions such as proliferation, and expression profile of a number of investigated genes. Whereas LTC-14 kept the morphological features of the differentiation status of the primary cells they were made of, LTC-7 appeared similar to an earlier stage. Thus the established cell lines represent a versatile tool to investigate various aspects of PSC biology.

Angiotensin II stimulates DNA synthesis of rat pancreatic stellate cells by activating ERK through EGF receptor transactivation

Although angiotensin II (Ang II) is known to participate in pancreatic fibrosis, little is known as to the mechanism by which Ang II promotes pancreatic fibrosis. To elucidate the mechanism, we examined the action of Ang II on the proliferation of rat pancreatic stellate cells (PSCs) that play central roles in pancreatic fibrosis. Immunocytochemistry and Western blotting demonstrated that both Ang II type 1 and type 2 receptors were expressed in PSCs. [3H]Thymidine incorporation assay revealed that Ang II enhanced DNA synthesis in PSCs, which was blocked by Ang II type 1 receptor antagonist losartan. Western blotting using anti-phospho-epidermal growth factor (EGF) receptor and anti-phospho-extracellular signal regulated kinase (ERK) antibodies showed that Ang II-activated EGF receptor and ERK. Both EGF receptor kinase inhibitor AG1478 and MEK1 inhibitor PD98059 attenuated ERK activation and DNA synthesis enhanced by Ang II. These results indicate that Ang II stimulates PSC proliferation through EGF receptor transactivation-ERK activation pathway.

Distinct roles of Smad2-, Smad3-, and ERK-dependent pathways in transforming growth factor-beta1 regulation of pancreatic stellate cellular functions

Pancreatic stellate cells (PSCs) play a major role in promoting pancreatic fibrosis. Transforming growth factor-beta(1) (TGF-beta(1)) regulates PSC activation and proliferation in an autocrine manner. The intracellular signaling pathways of the regulation were examined in this study. Immunoprecipitation and immunocytochemistry revealed that Smad2, Smad3, and Smad4 were functionally expressed in PSCs. Adenovirus-mediated expression of Smad2, Smad3, or dominant-negative Smad2/3 did not alter TGF-beta(1) mRNA expression level or the amount of autocrine TGF-beta(1) peptide. However, expression of dominant-negative Smad2/3 inhibited PSC activation and enhanced their proliferation. Co-expression of Smad2 with dominant-negative Smad2/3 restored PSC activation inhibited by dominant-negative Smad2/3 expression without changing their proliferation. By contrast, co-expression of Smad3 with dominant-negative Smad2/3 attenuated PSC proliferation enhanced by dominant-negative Smad2/3 expression without altering their activation. Exogenous TGF-beta(1) increased TGFbeta(1) mRNA expression in PSCs. However, PD98059, a specific inhibitor of mitogen-activated protein kinase kinase (MEK1), inhibited ERK activation by TGF-beta(1), and consequently attenuated TGF-beta(1) enhancement of its own mRNA expression in PSCs. We propose that TGF-beta(1) differentially regulates PSC activation, proliferation, and TGF-beta(1) mRNA expression through Smad2-, Smad3-, and ERK-dependent pathways, respectively.

Regulation of pancreatic stellate cell function in vitro: biological and molecular effects of all-trans retinoic acid

Pancreatic stellate cells (PSCs) are essentially involved in the development of pancreatic fibrosis, a constant feature of chronic pancreatitis and pancreatic cancer. Profibrogenic mediators, such as ethanol metabolites and cytokines, induce a PSC activation process that involves proliferation, enhanced production of extracellular matrix proteins and a phenotypic transition towards myofibroblasts which includes a loss of the characteristic retinoid-containing fat droplets. Here, we have analysed how exogenous all-trans retinoic acid (ATRA) affects activation of rat PSCs induced by sustained culture. Bromodeoxyuridine-incorporation assays indicated an ATRA-dependent inhibition of DNA synthesis. In contrast, ATRA did not affect expression of alpha-smooth muscle actin, a protein typical for myofibroblasts. Quantification of [3H]proline incorporation revealed a diminished collagen production in ATRA-treated PSCs. Furthermore, zymography experiments showed that supernatants of ATRA-exposed PSC cultures contained higher levels of matrix metalloproteinase-9 but not of matrix metalloproteinase-2 than untreated controls. At the level of intracellular signalling, ATRA had no effect on extracellular signal-regulated kinase activation after incubation of PSCs with the mitogen platelet-derived growth factor (PDGF). In addition, PDGF-induced DNA binding of activator protein-1 (AP-1) transcription factors was not inhibited by ATRA treatment. Luciferase reporter gene assays, however, revealed an ATRA-dependent transrepression of AP-1 in PDGF-stimulated PSCs. Together, the results indicate that exogenous ATRA displays inhibitory effects on PSC proliferation and collagen synthesis but does not block phenotypic transition towards myofibroblasts. We hypothesise that inhibition of AP-1 signalling may be involved in the mediation of biological effects of ATRA on PSCs.

Inhibition of pancreatic stellate cell activation by the hydroxymethylglutaryl coenzyme A reductase inhibitor lovastatin

Pancreatic stellate cells (PSCs) play a key role in pancreatic fibrosis, a constant feature of chronic pancreatitis. PSC activation occurs in response to profibrogenic mediators such as cytokines and involves proliferation, transition towards a myofibroblastic phenotype and enhanced production of extracellular matrix proteins. Previously, we have shown that PSC activation correlates with the activity of the Ras-Raf-ERK (extracellular signal-regulated kinase) signalling cascade [Gut 51 (2002) 579]. Using a rat culture model of PSCs, we have now evaluated the effects of lovastatin, a hydroxymethylglutaryl coenzyme A reductase inhibitor that interferes with protein isoprenylation, on PSC viability and activation as well as on signalling through Ras proteins. Apoptotic cells were detected applying the TUNEL assay. Proliferation of PSCs was quantitated using the bromodeoxyuridine DNA incorporation assay. Expression of alpha-smooth muscle actin (an indicator of the myofibroblastic phenotype), ERK activation and membrane translocation of the Ras superfamily member RhoA were analysed by immunoblotting. Lovastatin inhibited serum- and platelet-derived growth factor-stimulated PSC proliferation in a dose-dependent manner. At drug concentrations above the level required for growth inhibition, a strong increase of apoptotic cells was observed. Furthermore, lovastatin inhibited induction of alpha-smooth muscle actin expression in the course of primary culture. Immunoblot experiments indicated that lovastatin suppressed both Ras-mediated ERK 1/2 activation and platelet-derived growth factor-induced membrane translocation of RhoA. Together, our data suggest that lovastatin, through the interruption of Ras signalling, interferes with PSC activation. The antifibrotic efficiency of statins should be tested in animal models of chronic pancreatitis.

Apoptosis in activated rat pancreatic stellate cells

Proliferation and matrix synthesis by activated pancreatic stellate cells (PSC) participate in the development of chronic pancreatitis. Apoptosis of PSC may terminate this process but has not yet been studied in this particular cell type and was the aim of the present study. PSC were isolated from rat pancreas and characterized for expression of glial fibrillary acidic protein, alpha-smooth muscle actin, CD95, and tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL) receptors. Apoptosis was determined by TdT-UTP nick end-labeling reaction, annexin V binding, and caspase-8 activation. Both CD95L and TRAIL induced apoptosis in PSC. The apoptotic response was minor in PSC cultured for 7 days but increased markedly thereafter. Sensitization of PSC with culture duration was accompanied by increased expression of CD95 and TRAIL receptor 2 and no alterations of Flip expression or protein kinase B phosphorylation but was paralleled by the appearance of a COOH-terminal cleavage product of receptor-interacting protein. PSC apoptosis was also induced by PK-11195, a ligand of the peripheral benzodiazepine receptor. PSC apoptosis may be important in terminating the wound-healing response after pancreas injury and exhibits features distinct from apoptosis induction in hepatic stellate cells.

Expression of transforming growth factor-beta 1 by pancreatic stellate cells and its implications for matrix secretion and turnover in chronic pancreatitis

Pancreatic stellate cells mediate fibrosis in chronic pancreatitis. Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs)-1 and -2 are crucial modulators of fibrosis. Transforming growth factor-beta (TGF-beta) is a key regulator of extracellular matrix production and myofibroblast proliferation. We have examined MMP and TIMP synthesis by transformed cultured pancreatic stellate cells and their regulation by TGF-beta 1. By Northern analysis they expressed mRNAs for procollagen 1, TIMP-1, TIMP-2, and MMP-2. Expression of membrane type-1 MMP was confirmed by Western blotting. By immunohistochemistry these enzymes localized to fibrotic areas in human chronic pancreatitis. Active TGF-beta 1 constitutes 2 to 5% of total TGF-beta 1 secreted by pancreatic stellate cells; they express TGF-beta receptors I and II. Exogenous TGF-beta 1 (10 ng/ml) significantly increased procollagen-1 mRNA by 69% and collagen protein synthesis by 34%. Similarly TGF-beta 1 at 0.1, 1, and 10 ng/ml significantly reduced cellular proliferation rate by 37%, 44%, and 44%, respectively, whereas pan-TGF-beta-neutralizing antibody increased proliferation by 40%. TGF-beta1 (10 ng/ml) down-regulated MMP-9 by 54% and MMP-3 by 34% whereas TGF-beta 1-neutralizing antibody increased MMP-9 expression by 39%. Pancreatic stellate cells express both mediators of matrix remodeling and the regulatory cytokine TGF-beta 1 that, by autocrine inhibition of MMP-3 and MMP-9, may enhance fibrogenesis by reducing collagen degradation.

Isolation, long-term culture, and characterization of rat pancreatic fibroblastoid/stellate cells

Investigation of pancreatic interstitial fibroblasts has proven difficult in situ. We have established a method for the isolation of pancreatic fibroblastoid/stellate cells by outgrowth from pancreatic tissue explanted into culture dishes. This technique gives a high yield of viable cells from small tissue samples. Outgrown fibroblastoid cells were established as a primary cell line and characterized during long-term culture. We investigated the development of stellate cell markers, i.e. fat storage, expression of desmin, and alpha-smooth muscle actin (alphaSMA), over weeks in culture. AlphaSMA, investigated by indirect immunofluorescence staining and Western blot analysis, revealed a constant rise in expression during routine culture. After 13 passages. approximately 100% of cells were positive for alphaSMA expression, indicating a myofibroblast type of differentiation in vitro.

Proteomics -- the protein expression technology to study connective tissue biology

During the formation of peribronchial fibrosis in asthma, remodeling of connective tissue is due to an increase in deposition of extracellular matrix components like that of specific types of collagens and proteoglycans. By taking bronchial biopsies, we were able to isolate cell cultures derived from asthmatic patients and healthy volunteers, which provides a good model system to study differences regarding cell morphology and key connective tissue proteins in the remodeling process. Proteomics, utilizing two-dimensional electrophoresis and modern image analysis systems have made it possible to study protein expression and regulation of proteins in biological systems. By using this powerful tool, it is possible to quantitatively study protein regulation and to obtain increased knowledge about the mechanism behind the inflammatory process and formation of peribronchial fibrosis. We have optimized a proteomic protocol enabling detailed investigation of the protein expression pattern in human lung cells. An increased expression pattern was obtained, whereby 20 protein spots could be detected by image analysis in the <45 kDa region. Out of these, specific regulations of four spots were found by quantitative image analysis and spots of interest were identified by MALDI TOF-MS. This protocol enables us to study 1000--2000 proteins simultaneously and the possibility to correlate protein expression to the physiological status of the cell culture investigated. We have found that two proteins, actin and tropomyosin, are increased in expression due to transforming growth factor-beta stimulation. These proteins are correlated to the transformation of normal fibroblasts to myofibroblasts which are involved in the remodeling processes observed in asthma.