Identification, culture, and characterization of pancreatic stellate cells in rats and humans

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.

Desmoplastic reaction in pancreatic cancer: role of pancreatic stellate cells

OBJECTIVES

Pancreatic cancer has a very poor prognosis, largely due to its propensity for early local and distant spread. Histopathologically, most pancreatic cancers are characterized by a prominent stromal/fibrous reaction in and around tumor tissue. The aims of this study were to determine whether (1) the cells responsible for the formation of the stromal reaction in human pancreatic cancers are activated pancreatic stellate cells (PSCs) and (2) an interaction exists between pancreatic cancer cells and PSCs that may facilitate local and distant invasion of tumor.

METHODS

Serial sections of human pancreatic cancer tissue were stained for desmin and glial fibrillary acidic protein (stellate cell selective markers) and alpha-smooth muscle actin (alphaSMA), a marker of activated PSC activation, by immunohistochemistry, and for collagen using Sirius Red. Correlation between the extent of positive staining for collagen and alphaSMA was assessed by morphometry. The cellular source of collagen in stromal areas was identified using dual staining methodology, ie, immunostaining for alphaSMA and in situ hybridization for procollagen alpha1I mRNA. The possible interaction between pancreatic cancer cells and PSCs was assessed in vitro by exposing cultured rat PSCs to control medium or conditioned medium from 2 pancreatic cancer cell lines (PANC-1 and MiaPaCa-2) for 24 hours. PSC activation was assessed by cell proliferation and alphaSMA expression.

RESULTS

Stromal areas of human pancreatic cancer stained strongly positive for the stellate cell selective markers desmin and GFAP (indicating the presence of PSCs), for alphaSMA (suggesting that the PSCs were in their activated state) and for collagen. Morphometric analysis demonstrated a close correlation (r = 0.77; P < 0.04; 8 paired sections) between the extent of PSC activation and collagen deposition. Procollagen mRNA expression was localized to alphaSMA-positive cells in stromal areas indicating that activated PSCs were the predominant source of collagen in stromal areas. Exposure of PSCs to pancreatic cancer cell secretions in vitro resulted in PSC activation as indicated by significantly increased cell proliferation and alphaSMA expression.

CONCLUSIONS

Activated PSCs are present in the stromal reaction in pancreatic cancers and are responsible for the production of stromal collagen. PSC function is influenced by pancreatic cancer cells. Interactions between tumor cells and stromal cells (PSCs) may play an important role in the pathobiology of pancreatic cancer.

4-hydroxy-2, 3-nonenal activates activator protein-1 and mitogen-activated protein kinases in rat pancreatic stellate cells

AIM: Activated pancreatic stellate cells (PSCs) are implicated in the pathogenesis of pancreatic inflammation and fibrosis, where oxidative stress is thought to play a key role. 4-hydroxy-2,3-nonenal (HNE) is generated endogenously during the process of lipid peroxidation, and has been accepted as a mediator of oxidative stress. The aim of this study was to clarify the effects of HNE on the activation of signal transduction pathways and cellular functions in PSCs.

METHODS: PSCs were isolated from the pancreas of male Wistar rats after perfusion with collagenase P, and used in their culture-activated, myofibroblast-like phenotype unless otherwise stated. PSCs were treated with physiologically relevant and non-cytotoxic concentrations (up to 5 μmol/L) of HNE. Activation of transcription factors was examined by electrophoretic mobility shift assay and luciferase assay. Activation of mitogen-activated protein (MAP) kinases was assessed by Western blotting using anti-phosphospecific antibodies. Cell proliferation was assessed by measuring the incorporation of 5-bromo-2’-deoxyuridine. Production of type I collagen and monocyte chemoattractant protein-1 was determined by enzyme-linked immunosorbent assay. The effect of HNE on the transformation of freshly isolated PSCs in culture was also assessed.

RESULTS: HNE activated activator protein-1, but not nuclear factor κB. In addition, HNE activated three classes of MAP kinases: extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38 MAP kinase. HNE increased type I collagen production through the activation of p38 MAP kinase and c-Jun N-terminal kinase. HNE did not alter the proliferation, or monocyte chemoattractant protein-1 production. HNE did not initiate the transformation of freshly isolated PSCs to myofibroblast-like phenotype.

CONCLUSION: Specific activation of these signal transduction pathways and altered cell functions such as collagen production by HNE may play a role in the pathogenesis of pancreatic disorders.

Induction of myofibroblast MMP-9 transcription in three-dimensional collagen I gel cultures: regulation by NF-kappaB, AP-1 and Sp1

Chronic liver injury leads to a progressive wound healing response that eventually results in hepatic fibrosis characterised by net deposition of fibrillar extracellular matrix (ECM) and a qualitative shift from type IV to type I/III collagen. The pivotal cellular event underlying this response is hepatic stellate cell (HSC) activation towards a myofibroblast-like phenotype. Activated HSC contribute to ECM remodelling via secretion of type I/III collagens and matrix metalloproteinases (MMPs). Previous studies showed that three-dimensional (3D) contact of activated HSC with type I collagen further stimulates the ECM remodelling properties of HSC by inducing the type IV gelatinase, MMP-9. The aim of the current study was to confirm transcriptional activation of the MMP-9 gene and identify transcription factors regulating this response. Gelatin zymography and Northern blotting were used to confirm induction of MMP-9 protein and mRNA expression in primary rat HSC cultured in a three-dimensional collagen I gel lattice. MMP-9 promoter studies in transfected HSC and electrophoretic mobility shift assay (EMSA) were employed to study transcriptional events. Both NF-kappaB and AP-1 DNA were induced in HSC cultured in 3D collagen I gels and binding sites for these factors in the MMP-9 promoter were crucial for induction of transcription. By contrast removal of an Sp1 site in the promoter enhanced transcription, while over-expression of either Sp1 or Sp3 repressed transcription. It is concluded that 3D contact of activated HSC with collagen I stimulates MMP-9 expression by elevating NF-kappaB and AP-1 activities which are able to overcome the repressive influence of Sp1/Sp3 on MMP-9 gene transcription.

A c-Jun NH2-terminal kinase inhibitor SP600125 (anthra[1,9-cd]pyrazole-6 (2H)-one) blocks activation of pancreatic stellate cells

In response to pancreatic injury and in cell culture, pancreatic stellate cells (PSCs) are transformed ("activated") into highly proliferative myofibroblast-like cells that express alpha-smooth muscle actin and produce extracellular matrix components. Activated PSCs are implicated in the pathogenesis of pancreatic fibrosis and inflammation. We here evaluated the effects of SP600125 (anthra[1,9-cd]pyrazole-6 (2H)-one), an inhibitor of c-Jun NH(2)-terminal kinase (JNK), on the activation of PSCs. PSCs were isolated from rat pancreas tissue and used in their culture-activated, myofibroblast-like phenotype unless otherwise stated. Activation of JNK was determined by Western blotting using anti-phosphospecific JNK and c-Jun antibodies. Activation of transcription factors was determined by electrophoretic mobility shift assay. The effects of SP600125 on the key parameters of activation (chemokine production, collagen production, and proliferation) were examined. The effect of SP600125 on the activation of freshly isolated PSCs in culture also was examined. Interleukin-1beta activated both 46- and 54-kDa JNK, whereas platelet-derived growth factor-BB activated only 46-kDa JNK. SP600125 inhibited interleukin-1beta-induced JNK activity and activator protein-1 activation, but it did not affect the activation of extracellular-regulated kinase, p38 mitogen-activated protein kinase, and nuclear factor-kappaB. SP600125 inhibited platelet-derived growth factor-induced proliferation, inducible monocyte chemoattractant protein-1 production, and serum-induced type I collagen production. Although SP600125 did not inhibit the transformation, it attenuated the proliferation of freshly isolated PSCs in culture. Collectively, our results suggest a role of JNK in the activation of PSCs, and a potential application of JNK inhibitors for the treatment of pancreatic fibrosis and inflammation.

Purification and characterization of decorin from the culture media of MRC-5 cells

Myofibroblasts play an important role in fibrogenesis. Myofibroblasts secrete several components of the extracellular matrix, including decorin. To clarify the properties of decorin synthesized by myofibroblasts, we have purified and characterized decorin secreted into culture medium by the myofibroblast cell line MRC-5. Decorin was purified by successive chromatography steps using Hitrap Q and Superdex 200. Purified decorin showed a broad band on SDS-polyacrylamide gel electrophoresis, which was resolved into two smaller molecular weight bands after digestion with chondroitinase ABC. Further digestion with N-glycanase resolved these two bands into a single band, indicating that the N-glycation pattern of decorin is heterogeneous. The N-terminal amino acid sequence analysis of the purified protein and its reactivity towards an antibody raised against a C-terminal peptide of decorin indicate that MRC-5 cells secrete full-length decorin into the culture medium. To characterize the glycosaminoglycan chains attached to decorin, glycosaminoglycans from the purified protein were treated with chondroitinase ACI, chondroitinase ACII, chondroitinase ABC and chondroitinase B. The resulting disaccharides were analyzed by chromatography, which indicated that decorin secreted by MRC-5 cells is a dermatan sulfate proteoglycan. In conclusion, the decorin secreted by MRC-5 cells has similar characteristics to the decorin expressed in several tissues. Thus, culturing MRC-5 cells may be highly useful for studying the role of decorin and myofibroblasts in fibrosis.

Angiotensin II type 1 receptor interaction is an important regulator for the development of pancreatic fibrosis in mice

The renin-angiotensin system (RAS) plays important roles in various pathophysiological processes. However, the role of the RAS in pancreatic fibrosis has not been established. We investigated the role of angiotensin II (ANG II)-ANG II type 1 (AT(1)) receptor pathway in the development of pancreatic fibrosis with AT(1a) receptor-deficient [AT(1a)(-/-)] mice. To induce pancreatic fibrosis, AT(1a)(-/-) and wild-type (WT) mice were submitted to three episodes of acute pancreatitis induced by six intraperitoneal injections of 50 microg/kg body wt cerulein at hourly intervals, per week, for four consecutive weeks. Pancreatic fibrosis was assessed by histology and hydroxyproline content. Pancreatic stellate cell (PSC) activation and the localization of AT(1) receptors were assessed by Western blot analysis for alpha-smooth muscle actin and immunostaining. Transforming growth factor-beta(1) (TGF-beta(1)) mRNA expression in the pancreas was assessed by RT-PCR. Six intraperitoneal injections of cerulein induced acute pancreatitis in both AT(1a)(-/-) and WT mice. There were no significant differences between two groups with regard to serum amylase and histological changes. Pancreatic fibrosis induced by repeated episodes of acute pancreatitis was significantly attenuated in AT(1a)(-/-) mice compared with that in WT mice. This finding was accompanied by a reduction of activated PSCs. Dual-immunofluorescence staining in WT mice revealed that activated PSCs express AT(1) receptors. The level of TGF-beta(1) mRNA was lower in AT(1a)(-/-) mice than in WT mice. Our results demonstrate that the ANG II-AT(1) receptor pathway is not essential for the local pancreatic injury in acute pancreatitis but plays an important role in the development of pancreatic fibrosis through PSC activation and proliferation.

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.

Pancreatic stellate cell migration: role of the phosphatidylinositol 3-kinase(PI3-kinase) pathway

Pancreatic stellate cells (PSCs) are implicated as key mediators of pancreatic fibrogenesis and are found in increased numbers in areas of pancreatic injury. This increase in number may be due to increased local proliferation and/or migration of PSCs to affected areas from surrounding tissue. We have recently shown that PSCs can migrate and that this migration is stimulated by PDGF in a predominantly chemotactic manner [Gut 52 (2003) 677]. However, the signalling mechanisms responsible for PDGF-induced PSC migration are not known.

AIMS

(i) To determine whether PDGF-induced PSC migration is mediated by the PI3-kinase pathway. (ii) To investigate whether cell migration is influenced by cell proliferation and whether an interaction exists between the PI3-kinase pathway and the ERK1/2 pathway (known to mediate cell proliferation) in PSCs exposed to PDGF.

METHODS

(i) PI3-kinase activity was assessed by measuring the activation (phosphorylation) of its downstream substrate Akt in rat PSCs incubated with PDGF (10ng/mL) for 5min, 15min, 60min, and 24hr in the presence or absence of the specific PI3-kinase inhibitor wortmannin. (ii) The role of the PI3-kinase pathway in PSC migration was examined by assessing PSC migration through a porous membrane after exposure to PDGF in the presence and absence of wortmannin for 24hr. (iii) The relationship between migration and proliferation was assessed by examining migration of PSCs exposed to PDGF in the presence and absence of mitomycin C, an inhibitor of cell proliferation. (iv) The interaction between PI3-kinase and ERK1/2 was examined by incubation of PSCs with PDGF in the presence and absence of wortmannin, followed by assessment of ERK1/2 activation by western blot.

RESULTS

PDGF increased Akt activation in PSCs as early as at 5min of incubation and this increase was sustained for 24hr. Inhibition of PI3-kinase by wortmannin decreased basal as well as PDGF-induced migration and also inhibited ERK1/2 activation. Inhibition of PSC proliferation with mitomycin C significantly reduced (but did not abolish) basal and PDGF-induced PSC migration.

CONCLUSIONS

(i) The PI3-kinase pathway is induced in PSCs after exposure to PDGF and this induction is sustained for at least 24hr. (ii) The PI3-kinase pathway plays a role in PDGF-induced PSC migration and is partially involved in mediating ERK1/2 activation. (iii) PSC migration is dependent, at least in part, on cell proliferation.

Effects of angiotensin II on rat pancreatic stellate cells

The aim of the study was to identify pancreatic stellate cells (PSCs) as a potential target of angiotensin II (ATII) action because recently a local renin-angiotensin system (RAS) has been described in the pancreas. PSCs were isolated from male Wistar rats and investigated for ATII receptor expression and ATII-induced calcium transients, contractions, proliferation, and alpha-smooth muscle actin expression. Quiescent and activated PSCs expressed the ATII receptor subtype AT1 but not AT2. Addition of ATII led to a rapid elevation of intracellular calcium ([Ca]i). The sensitivity toward ATII with respect to calcium transients did not change during the transdifferentiation process. In activated PSCs, ATII dose dependently induced PSC cell contraction. Furthermore, ATII induced an activation of the c-Jun-N-terminal kinase (JNK) and extracellular regulated kinase (Erk), which was inhibited after intracellular calcium chelation by BAPTA-AM. The p38 mitogen-activated protein kinase (p38) was also activated by ATII. BAPTA-AM itself induced p38 activation, which was not further enhanced by ATII. ATII stimulated PSC proliferation, while PSC transdifferentiation, as indicated by alpha-smooth muscle actin expression and collagen type I secretion, was not enhanced. The data suggest that PSCs are targets of ATII action with potential pathophysiological relevance.

Vitamin A distribution and content in tissues of the lamprey,Lampetra japonica

Vitamin A (retinol and retinyl ester) distribution and content in tissues of a lamprey (Lampetra japonica) were analyzed by morphological methods, namely, gold chloride staining, fluorescence microscopy to detect specific vitamin A autofluorescence, and electron microscopy, as well as high-performance liquid chromatography (HPLC). Hepatic stellate cells showed an abundance of vitamin A stored in lipid droplets in their cytoplasm. Similar cells storing vitamin A were present in the intestine, kidney, gill, and heart in both female and male lampreys. Morphological data obtained by gold chloride staining method, fluorescence microscopy, transmission electron microscopy, and HPLC quantification of retinol were consistent. The highest level of total retinol measured by HPLC was found in the intestine. The second and third highest concentrations of vitamin A were found in the liver and the kidney, respectively. These vitamin A-storing cells were not epithelial cells, but mesoderm-derived cells. We propose as a hypothesis that these cells belong to the stellate cell system (family) that stores vitamin A and regulates homeostasis of the vitamin in the whole body in the lamprey. Fibroblastic cells in the skin and somatic muscle stored little vitamin A. These results indicate that there is difference in the vitamin A-storing capacity between the splanchnic and intermediate mesoderm-derived cells (stellate cells) and somatic and dorsal mesoderm-derived cells (fibroblasts) in the lamprey. Stellate cells derived from the splanchnic and intermediate mesoderm have high capacity and fibroblasts derived from the somatic and dorsal mesoderm have low capacity for the storage of vitamin A in the lamprey.

Analysis of tumor necrosis factor-alpha, transforming growth factor-beta 1, interleukin-10, and interferon-gamma polymorphisms in patients with alcoholic chronic pancreatitis

The pathophysiologic mechanisms underlying alcoholic chronic pancreatitis are poorly understood. Cytokines participate in the immunologic progression of acute and chronic pancreatitis and may play an important role in the development of pancreatic fibrosis. Functional polymorphisms in cytokine genes have been identified that alter cytokine production. The aims of the current investigation were to determine whether functional polymorphisms in the tumor necrosis factor-alpha (TNF-alpha) gene at positions -308 and -238; in the transforming growth factor-beta 1 (TGF-beta(1)) gene at positions -509, +869 (codon 10), and +915 (codon 25); in the interleukin-10 (IL-10) gene at position -1082; and in the intron 1 of the interferon-gamma (IFN-gamma) gene at position +874 are associated with alcoholic chronic pancreatitis. We investigated 42 patients with alcoholic chronic pancreatitis. We studied 94 control subjects for the TNF-alpha polymorphisms and 73 control subjects for the remaining polymorphisms. Mutation analysis was performed by direct DNA sequencing or by amplification refractory mutation system-polymerase chain reaction (ARMS-PCR). The genotype frequencies were similar between patients and control subjects for all investigated cytokine polymorphisms (P>.05). We did not find an association between the different genotypes and the clinical course of the disease. Therefore, we assume that these genetic variants do not play a dominant role in alcoholic chronic pancreatitis.

Cytoglobin/STAP, its unique localization in splanchnic fibroblast-like cells and function in organ fibrogenesis

Cytoglobin/stellate cell activation-associated protein (Cygb/STAP) consists of a new class of hexacoordinate globin superfamily, which was recently discovered by a proteome analysis on the rat hepatic stellate cells. Unlike haemoglobin, myoglobin, and neuroglobin, Cygb/STAP is ubiquitously expressed in several organs, although its detailed localization has not been clarified. Immunohistochemistry and immunoelectron microscopy revealed that Cygb/STAP is uniquely localized in fibroblast-like cells in splanchnic organs, namely the vitamin A-storing cell lineage, but neither in epithelial cells, endothelial cells, muscle cells, blood cells, macrophages, nor dermal fibroblasts. The expression of Cygb/STAP was upregulated in fibrotic lesions of the pancreas and kidney in which activated fibroblast-like cells or myofibroblasts are known to increase in number. In cultured hepatic stellate cells, Cygb/STAP expression was augmented by the stimulation with sera, platelet-derived growth factor-BB, and transforming growth factor-beta 1. Overexpression of Cygb/STAP in NIH 3T3 cells induced the cells to lessen migratory activities and increase the expression of collagen alpha1(I) mRNA. These results indicate that Cygb/STAP is a tissue globin uniquely localized in splanchnic fibroblastic cell lineage and may play a role in fibrotic organ disorder.

Mechanisms of pancreatic fibrosis

Pancreatic fibrosis, a characteristic histopathological feature of chronic pancreatitis, is no longer considered an epiphenomenon of chronic injury, but an active process that may be reversible in the early stages. The identification and characterization of pancreatic stellate cells (PSCs) in recent years has had a significant impact on research into pancreatic fibrogenesis. Accumulating evidence from both in vivo studies (using human pancreatic sections and experimental models of pancreatic fibrosis) and in vitro studies (using cultured pancreatic stellate cells) indicates a key role for activated PSCs in the fibrotic process. These cells are now known to be activated by ethanol and its metabolites and by several factors that are upregulated during pancreatic injury including growth factors, cytokines and oxidant stress. Based on this knowledge, potential antifibrotic strategies such as antioxidants and cytokine inhibition have been assessed in experimental models. Studies are also underway to characterise the signaling pathways/molecules responsible for mediating PSC activation, in order to identify potential therapeutic targets for the inhibition of PSC activation, thereby preventing or reversing the development of pancreatic fibrosis.

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.

Establishment and characterization of a rat pancreatic stellate cell line by spontaneous immortalization

AIM: Activated pancreatic stellate cells (PSCs) have been implicated in the pathogenesis of pancreatic fibrosis and inflammation. Primary PSCs can be subcultured only several times because of their limited growth potential. A continuous cell line may therefore be valuable in studying molecular mechanisms of these pancreatic disorders. The aim of this study was to establish a cell line of rat PSCs by spontaneous immortalization.

METHODS: PSCs were isolated from the pancreas of male Wistar rats, and conventional subcultivation was performed repeatedly. Telomerase activity was measured using the telomere repeat amplification protocol. Activation of transcription factors was assessed by electrophoretic mobility shift assay. Activation of mitogen-activated protein (MAP) kinases was examined by Western blotting using anti-phosphospecific antibodies. Expression of cytokine-induced neutrophil chemoattractant-1 was determined by enzyme immunoassay.

RESULTS: Conventional subcultivation yielded actively growing cells. One clone was obtained after limiting dilution, and designated as SIPS. This cell line has been passaged repeatedly more than 2 years, and is thus likely immortalized. SIPS cells retained morphological characteristics of primary, culture-activated PSCs. SIPS expressed α-smooth muscle actin, glial acidic fibrillary protein, vimentin, desmin, type I collagen, fibronectin, and prolyl hydroxylases. Telomerase activity and p53 expression were negative. Proliferation of SIPS cells was serum-dependent, and stimulated with platelet-derived growth factor-BB through the activation of extracellular signal-regulated kinase. Interleukin-1β activated nuclear factor-κB, activator protein-1, and MAP kinases. Interleukin-1β induced cytokine-induced neutrophil chemoattractant-1 expression through the activation of nuclear factor-κB and MAP kinases.

CONCLUSION: SIPS cells can be useful for in vitro studies of cell biology and signal transduction of PSCs.

Nonoxidative ethanol metabolites alter extracellular matrix protein content in rat pancreas

BACKGROUND & AIMS

The mechanisms involved in ethanol-induced pancreas fibrosis are poorly understood. Here we show that fatty acid ethyl esters (FAEEs), nonoxidative ethanol metabolites, increase extracellular matrix (ECM) protein levels in pancreas.

METHODS

Rat pancreatic acini were incubated for 1-4 hours with FAEEs or acetaldehyde. In another set of experiments, rats received an intravenous infusion of FAEEs for 6 hours. Collagens were assessed by a hydroxyproline assay. Laminin and fibronectin were analyzed by Western blotting. Gene expression of ECM proteins was measured by conventional and real-time reverse-transcription polymerase chain reaction (RT-PCR). Matrix metalloproteinase (MMP), plasmin, and urokinase-type plasminogen activator (uPA) activities were determined by zymography and fluorogenic assays.

RESULTS

FAEEs increased collagen, laminin, and fibronectin levels in pancreatic acini without affecting messenger RNA (mRNA) expression for these proteins. Actinomycin D, a transcriptional inhibitor, did not block the increase in ECM proteins induced by FAEEs. FAEEs reduced the activity of the serine protease, plasmin, and that of the uPA. Consistent with these results, the serine protease inhibitor aprotinin reproduced the effects of FAEEs and prevented the further increase in ECM proteins induced by FAEEs. In vivo administration of FAEEs reduced plasmin and uPA activities and increased ECM protein levels in pancreas. Acetaldehyde had minor effects on ECM protein levels and did not affect plasmin activity.

CONCLUSIONS

FAEEs increase ECM protein levels in pancreas. The results suggest that this effect is caused primarily by an inhibition in ECM degradation via serine proteases including the plasminogen system.

Pancreatic duct obstruction itself induces expression of alpha smooth muscle actin in pancreatic stellate cells

BACKGROUND

Pancreatic stellate cells (PSCs) are thought to be responsible for pancreatic fibrosis. Although fibrosis is a major characteristic of chronic pancreatitis (CP) induced by pancreatic duct obstruction, it is unclear whether pancreatic duct obstruction itself activates PSCs.

METHODS

To test the hypothesis that pancreatic duct obstruction activates PSCs, clinical and experimental analyses were performed using alpha smooth muscle actin (alpha-SMA) as a marker of their activation. In clinical analysis, surgical specimens from the patients with pancreatic cancer or cancer of the papilla Vater were classified into two groups with or without duct obstruction. alpha-SMA expression was examined on these specimens, and the difference between two groups was evaluated. In animal experiment, duct ligation-induced pancreatitis was developed in rats by ligating the secondary pancreatic duct in duodenal segment, and the expression of alpha-SMA was examined.

RESULTS

In clinical analysis, the specimens from the pancreas with duct obstruction (14 cases) expressed alpha-SMA significantly stronger than those from the pancreas without duct obstruction (7 cases). All specimens in the former expressed alpha-SMA, but 4 specimens from the latter did not at all (P < 0.05). In animal experiment, alpha-SMA expression was detected 7 days after the ligation and was increased on the 10th day.

CONCLUSIONS

We can assume that pancreatic duct obstruction itself activates PSCs. This mechanism may play roles in the development of CP from multiple origins.

Stellate cell activation in alcoholic pancreatitis

The pathogenesis of pancreatic fibrosis, a characteristic feature of alcohol-induced chronic pancreatitis, has received increasing attention over the past few years, largely due to the identification and characterization of stellate cells in the pancreas. These cells are morphologically similar to hepatic stellate cells, the principal effector cells in liver fibrosis. The role of pancreatic stellate cells (PSCs) in alcoholic pancreatic fibrosis has been studied using 2 approaches: (i) in vivo studies using pancreatic tissue from patients with alcohol-induced chronic pancreatitis and from animal models of experimental pancreatitis and (ii) in vitro studies using cultured PSCs. These studies indicate that PSCs are activated early in the course of pancreatic injury and are the predominant source of collagen in the fibrotic pancreas. Several factors that may be responsible for mediating PSC activation during chronic alcohol exposure have also been identified. From the findings to date, it may be speculated that the pathogenesis of alcoholic pancreatic fibrosis may involve 2 pathways: (i) a necroinflammatory pathway involving cytokine release and PSC activation and (ii) a nonnecroinflammatory pathway involving direct activation of PSCs by ethanol via its metabolism to acetaldehyde and the generation of oxidant stress.

Role of PGE2 in the development of pancreatic injury induced by chronic alcohol feeding in rats

BACKGROUND

Eicosanoids are known to modulate inflammation. Moreover, some studies report that endogenous prostaglandin E(2) (PGE(2)) protects the pancreas against injury. Therefore, we investigated its role in a rat model of chronic alcohol consumption.

METHODS

Rats were fed with 20% ethanol and a corn oil-supplemented diet using the interrupted alcohol feeding regimen (EI). Controls received water instead of ethanol (WI) or uninterruptedly ethanol (EU). After 13 mo, pancreas tissue was investigated morphologically, immunohistochemically and biochemically.

RESULTS

Pancreatic tissue was more severely injured in EI than in WI and EU (p < 0.05). Fibrogenesis (alpha-smooth muscle actin-positive cells, collagen types I and III) was increased in EI compared to WI (p < 0.05). In EI, mast cell numbers were increased, compared to WI, but decreased, compared to EU (p < 0.05). EI showed decreased PGE(2) and malondialdehyde contents compared to EU (p < 0.05) and decreased glutathione concentrations compared to WI (p < 0.05). PGE(2) content and fibrogenesis were inversely correlated in EU. The same correlation was detectable as a trend in all alcohol-fed rats.

CONCLUSION

The decrease in PGE(2) together with the increase in tissue damage and the inverse correlation between PGE(2) and fibrogenesis led us to suggest that endogenous PGE(2) plays a protective role in alcohol-induced injury in the pancreas.

Pathogenesis of pain in chronic pancreatitis: ongoing enigma

The pathogenesis of pain in chronic pancreatitis remains an enigma. The cause of pain is almost certainly multifactorial and may vary at different stages of the disease process. These factors may include the release of excessive oxygen-derived free radicals, tissue hypoxia and acidosis, inflammatory infiltration with influx of pain transmittent substances into damaged nerve ends, and the development of pancreatic ductal and tissue fluid hypertension due to morphological changes of the pancreas. Investigations into the causes of pain have been limited by changes in the dynamics with the progression of the disease process, limitations in studying functional and morphological changes of the pancreas in the clinical setting, and the psychosomatic profile of patients. Many of these patients are addicted to alcohol, and suffer from personality disorders. The difficulty in quantifying pain, which is at best subjective, further compounds the issue, especially when assessing the efficacy of treatment.

Rho kinase inhibitors block activation of pancreatic stellate cells

1. In response to pancreatic injury and in cell culture, pancreatic stellate cells (PSCs) are transformed ('activated') into highly proliferative myofibroblast-like cells, which express alpha-smooth muscle actin (alpha-SMA), and produce type I collagen and other extracellular matrix components. There is accumulating evidence that activated PSCs play important roles in pancreatic fibrosis and inflammation. 2. The small GTP-binding protein Rho has emerged as an important regulator of the actin cytoskeleton and cell morphology through the downstream effector Rho kinase (ROCK). But, the roles of Rho-ROCK pathway in PSCs are unknown. Here, we examined the effects of (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide (Y-27632) and HA-1077 (fasudil), specific inhibitors of ROCK, on the activation of PSCs. 3. PSCs were isolated from the pancreas of male Wistar rats after perfusion with collagenase P. The actin cytoskeleton was analyzed by phalloidin staining. Expression of RhoA and ROCK was examined by immunostaining and Western blotting. Effects of Y-27632 and HA-1077 on alpha-SMA expression, platelet-derived growth factor-induced proliferation and chemotaxis, and collagen production were assessed. 4. Culture-activated PSCs developed a well-spread cell shape, with extended stress fiber formation. PSCs expressed RhoA, ROCK-1, and ROCK-2. 5. Y-27632 caused disassembly of stress fibers. Y-27632 and HA-1077 inhibited alpha-SMA expression, proliferation, chemotaxis, and type I collagen production in culture-activated PSCs. 6. In addition, Y-27632 and HA-1077 inhibited spontaneous activation of freshly isolated PSCs in culture on plastic. 7. These findings suggest a role of Rho-ROCK pathway in the activation process of PSCs by regulating the actin cytoskeleton, and a potential application of Rho-ROCK pathway inhibitors for the treatment of pancreatic inflammation and fibrosis.

Pro-inflammatory cytokine-induced matrix metalloproteinase-1 (MMP-1) secretion in human pancreatic periacinar myofibroblasts

Matrix metalloproteinases (MMPs) are the proteases involved in the degradation of the extracellular matrix. MMP-1 is thought to be one of the key enzymes in fibrolysis, a process closely related to tissue remodeling. In the present study, we investigated MMP-1 secretion from human pancreatic periacinar myofibroblasts in response to pro-inflammatory cytokines IL-1beta and TNF-alpha. We also attempted to clarify the intracellular signaling pathways mediating the cytokine-induced MMP-1 secretion. MMP-1 secretion was measured by an enzyme-linked immunosorbent assay. MMP-1 molecules were analyzed by Western blotting. MMP-1 mRNA expression was evaluated by Northern blotting. IL-1l and TNF-alpha stimulated the MMP-1 secretion in a dose- and time-dependent manner. Ninety percent of MMP-1 was secreted as inactive form (pro-MMP-1). The effects of IL-1beta and TNF-alpha were significantly inhibited by PD98059 MEK/ERK inhibitor). In contrast, SB203580 (p38 MAPK inhibitor), GF109203X (PKC inhibitor), and PDTC (NF-kappaB inhibitor) did not alter the MMP-1 secretion induced by IL-1beta and TNF-alpha. These effects were also observed at them RNA level. In conclusion, in human pancreatic periacinar myofibroblasts, MMP-1 secretion was regulated by the pro-inflammatory cytokines via the MEK/ERK cascade. Thus, human pancreatic periacinar myofibroblasts may play an important role in the remodeling of damaged pancreatic tissue in chronic pancreatitis via MMP-1 secretion.

TGFbeta-induced fibrogenesis of the pancreas

The biological cause of fibrosis is the accumulation of excessive amounts of extracellular matrix (ECM) which leads to tissue dysfunction and organ failure. A strong correlation can be found between pancreatic diseases and fibrotic processes, in particular chronic pancreatitis and pancreatic cancer. There is growing evidence that pancreatic fibrosis represents a dysregulation of the normal repair processes after injury. This concept is based on the findings that fibrosis and tissue repair involve similar biological reactions regulated by the same group of molecules. The best characterized example for these regulatory molecules are the members of the transforming growth factor beta family (TGFbeta). TGFbeta1 represents the prototype of this family of highly similar growth factors, with the unique ability to stimulate the expression and deposition of extracellular matrix and to inhibit its degradation. Growth factor-induced fibrotic events are targeted by a myofibroblast-like cell called pancreatic stellate cell (PSC). These cells show enhanced expression of all-important ECM proteins after TGFbeta stimulation including collagen, fibronectin and proteoglycans. At the same time TGFbeta inhibits the degradation of ECM by blocking the secretion of proteases and stimulating the production of naturally occurring protease inhibitors.

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.

Genetic polymorphisms in alcoholic pancreatitis

Chronic, excessive alcohol consumption is clearly associated with acute and chronic pancreatitis. However, both clinical and laboratory studies have demonstrated that alcohol consumption alone does not directly cause pancreatitis. Growing evidence suggests that environmental and possibly genetic cofactors must also be present before the mechanisms protecting the pancreas from pancreatitis are circumvented and pancreatitis develops. The discovery that mutations in the cationic trypsinogen gene (R122H, N29I) predisposed to acute and chronic pancreatitis focused attention on possible genetic predispositions. Mutations in the cationic trypsinogen gene, however, are rarely associated with alcoholic chronic pancreatitis. Mutations in the SPINK1 gene (e.g. N34S) provide a threefold increased risk, and cystic fibrosis transmembrane conductance regulator (CFTR) mutations continue to be investigated. However, the major cofactor associated with alcoholic chronic pancreatitis is yet to be identified.

Alcohol-induced pancreatic injury

Alcoholic pancreatitis is a major complication of alcohol abuse. Until recently, it was generally accepted that alcoholic pancreatitis was a chronic disease from the outset. However, evidence is now emerging in support of the 'necrosis-fibrosis' hypothesis that alcoholic pancreatitis begins as an acute process and that repeated episodes of acute injury lead to the changes of chronic pancreatitis (acinar atrophy and fibrosis) resulting in exocrine and endocrine dysfunction. The treatment of acute pancreatitis follows the regimen of bed rest, nasogastric suction, analgesia and intravenous support. The role of additional therapeutic measures such as prophylactic antibiotics, antioxidants and enteral nutrition in severe cases has not yet been precisely defined. The treatment of chronic pancreatitis involves attention to its three cardinal features: pain, maldigestion and diabetes. With respect to the pathogenesis of alcoholic pancreatitis, the focus of research over the past 30 years has shifted from the sphincter of Oddi and ductular abnormalities to the acinar cell itself. It has now been established that the acinar cell is capable of metabolizing alcohol and that direct toxic effects of alcohol and/or its metabolites on acinar cells may predispose the gland to injury in the presence of an appropriate trigger factor. A significant recent development relates to the characterization of pancreatic stellate cells, increasingly implicated in alcoholic pancreatic fibrosis. This chapter summarizes the natural history, clinical features, current trends in treatment as well as recent advances in our understanding of the pathogenesis of alcoholic pancreatitis.

Pancreatic stellate cell activation by ethanol and acetaldehyde: is it mediated by the mitogen-activated protein kinase signaling pathway?

BACKGROUND

Pancreatic fibrosis is a characteristic feature of alcoholic chronic pancreatitis. Recent studies suggest that activated pancreatic stellate cells (PSCs) are the major cell-type involved in pancreatic fibrogenesis. Cultured PSCs become activated when exposed to ethanol or its metabolite acetaldehyde (as indicated by increased alpha-smooth muscle actin [alpha-SMA] expression and increased collagen synthesis). However the intracellular signaling mechanisms responsible for ethanol- or acetaldehyde-induced PSC activation remain to be fully elucidated. One of the major signaling pathways known to regulate protein synthesis in mammalian cells is the mitogen-activated protein kinase (MARK) pathway.

AIMS

To examine the effects of ethanol and acetaldehyde on the MAPK pathway (by assessing the activities of the 3 major subfamilies (extracellular-regulated kinases 1 and 2 [ERK 1/2], JNK and p38 kinase) in PSCs and to examine the role of p38 kinase in mediating the ethanol- and acetaldehyde-induced increase in alpha-SMA expression in activated rat PSCs.

METHODS

Rat PSCs were incubated with ethanol (50 mM) or acetaldehyde (200 microM) for 15 min, 30 min, 60 min, and 24 h; and activities of ERK 1/2, JNK, and p38 kinase were assessed in cell lysates using kinase assays and Western blot. In addition, rat PSCs were treated with the specific p38 MAPK inhibitor SB203580 in the presence or absence of ethanol or acetaldehyde for 24h, and activation of the downstream protein kinase MAPKAP kinase-2 (an indicator of p38 MAPK activity) was assessed by Western blot. Specific inhibitors were also used to inhibit the activity of ERK 1/2 and JNK. Following inhibition of the above signaling pathways, alpha-SMA expression by PSCs was assessed by Western blot.

RESULTS

Ethanol and acetaldehyde increased the activation of all 3 subfamilies (ERK 1/2, JNK and p38 kinase) of the MAPK pathway in PSCs. Treatment of PSCs with SB203580 abolished the ethanol- and acetaldehyde-induced increase in p38 MAPK activity and also prevented the induction of alpha-SMA expression in PSCs. However, inhibition of ERK 1/2 and JNK had no effect on ethanoland acetaldehyde-induced alpha-SMA expression in PSCs.

CONCLUSIONS

(1) The MAP kinase pathway is induced in PSCs after exposure to ethanol or acetaldehyde and this induction is sustained for at least 24h. (2) The p38 MAPK pathway mediates the activation (as indicated by increased alpha-SMA expression) of PSCs by ethanol or acetaldehyde.

Pancreas: healing response in critical illness

OBJECTIVE

The pathophysiology of acute pancreatitis represents a diverse mix of congenital, hereditary, and acquired problems associated with or causing acute pancreatic inflammation. Acute pancreatitis is characterized by acinar cell injury that may involve regional and systemic inflammatory responses. The systemic manifestations of acute pancreatitis are responsible for the majority of pancreatitis-associated morbidity and are due to the actions of specific inflammatory cytokines. This report summarizes this pancreatic injury, the role of cytokines in the pathogenesis of acute pancreatitis, and the pancreatic healing response that follows.

DESIGN

A comprehensive literature review of experimental pancreatitis as well as reports of cytokine involvement and healing response during clinical pancreatitis was performed.

RESULTS

Histamine release, bradykinin generation, and cytokine release play a significant role during acute pancreatic inflammation. Following an experimental insult, there is rapid expression of tumor necrosis factor-alpha, interleukin-6, interleukin-1, and chemokines by pancreatic acinar cells and/or transmigrated leukocytes. Preventing the action of these mediators has a profound beneficial effect in experimental animals. Pancreatic fibrosis is a central histologic response after pancreatitis. Transient collagen deposition with acinar necrosis occurs in acute pancreatitis; in chronic pancreatitis, permanent and disorganized pancreatic fibrosis and parenchymal cell atrophy occur.

CONCLUSIONS

Inflammatory mediators are responsible for the systemic manifestations of acute pancreatitis and the associated distant organ dysfunction. After the acute injury, regeneration or pancreatic repair is characterized by decreased release of proinflammatory mediators and decreased infiltrating inflammatory cells. Differentiation and proliferation of pancreatic myofibroblasts or "stellate" cells may be responsible for increased extracellular matrix production. The predictable nature in which the inflammation and fibrosis are produced may stimulate novel approaches to disease treatment.

Production and effects of endothelin-1 in rat pancreatic stellate cells

INTRODUCTION

Proliferation and matrix synthesis of activated pancreatic stellate cells (PSCs) participate in the development of chronic pancreatitis. Besides other substances, endothelin-1 (ET-1) may influence the activation process of PSCs. Until now, ET-1 has not been studied in this particular cell type.

AIMS

To characterize PSCs in rat pancreas with respect to expression of ET(A)-receptors, production of ET-1, and physiological effects induced by ET-1 during PSC activation.

METHODOLOGY

Immunocytochemical and ELISA techniques and cDNA microarray analysis were used. Physiologic effects were characterized by single cell measurements of free cytosolic Ca2+-concentration and of PSC contractility on collagen lattices.

RESULTS

Activation of PSCs in vitro, as assessed by alpha-smooth muscle actin expression, was accompanied by the de novo expression of ET(A)-receptors and synthesis of ET-1 mRNA and protein. Cytosolic Ca2+-concentration was increased upon ET-1 stimulation in activated but not in quiescent PSCs. Contractility of activated PSCs was significantly reduced by the selective ET(A)-receptor antagonist BQ123 but not by the ET(B)-receptor antagonist IRL-1038.

CONCLUSIONS

The results suggest that ET-1 may act as a paracrine and autocrine factor for activated PSCs and may mediate contractions of activated, but not quiescent, PSCs.

Chemosensitivity testing and test-directed chemotherapy in human pancreatic cancer

Human pancreatic cancer is a devastating disease with poor prognosis. In many cases it is diagnosed at stages in which a complete resection is not possible. However, even after complete resection most tumors recur. Therefore, several chemotherapeutic strategies have been developed, so far, with little impact on the clinical outcome. Because one of the hallmarks of human pancreatic cancer is its general resistance to chemotherapeutic agents, it seems important to develop strategies to individualize chemotherapy and to render cells more sensitive to chemotherapeutic agents. In this summary we describe our methods of in vitro chemosensitivity testing using the human tumor colony-forming assay for pancreatic cancer in comparison with other solid tumors and describe how the in vitro results influence chemotherapy. Furthermore, we point out new developments of mRNA quantitation of chemoresistance target enzymes based on real-time PCR, which may help in the future to individualize chemotherapy of pancreatic cancer. Finally, we present results of studies of cyclin D1 inhibition. Suppression of cyclin D1 by cyclin D1 antisense mRNA expression was associated with growth inhibition and an increase in chemosensitivity to fluoropyrimidines and platinum compounds. Because human pancreatic cancers are relatively chemoresistant and material for chemosensitivity testing with the human tumor colony-forming assay (HTCA) is in most cases difficult to obtain, future investigations should aim at the development of methods requiring only very small samples to analyzemarkers of chemosensitivity. Our results further suggest that chemotherapy in combination with strategies to increase chemosensitivity may be a reasonable regimen for the treatment of human pancreatic cancer in the future.

Acute experimental pancreatitis and NF-kappaB/Rel activation

Acute pancreatitis is a serious disease with a high morbidity and an overall mortality rate of about 10%. However, in its most severe form, which is characterized by pancreatic necrosis, 20-30% of the patients die. Death is often the result of multiorgan dysfunction, including acute respiratory, kidney, and hepatic failure as well as generalized diffuse capillary leak water retention, hypoxia, and acid/base disturbance. The mechanisms by which distant organ systems are involved still remain obscure, but several lines of evidence suggest the participation of cytokines (IL-1, IL-6, and TNF-alpha) as a response to local tissue damage. A series of studies have now shed new light on the pivotal pathogenic role of the transcription factor NF-kappaB/Rel that binds to the promoter regions of many proinflammatory genes and regulates their transcription.

In chronic pancreatitis, widespread emergence of TRAIL receptors in epithelia coincides with neoexpression of TRAIL by pancreatic stellate cells of early fibrotic areas

TRAIL (TNF-related apoptosis-inducing ligand) induces apoptosis by cross-linking of the two TRAIL receptors that contain a death domain, TRAIL-R1 and TRAIL-R2. TRAIL-R3 and TRAIL-R4 are receptors that do not transmit an apoptotic signal. Our aim was to determine the expression of TRAIL and its receptors in normal pancreas and chronic pancreatitis. We applied real-time PCR, immunohisto(cyto)chemistry, and nick-end labeling of apoptosis. In normal pancreas, a minor subset of acinar cells coexpressed TRAIL-R2 and TRAIL-R4, whereas ductular epithelium and interstitial fibroblast-like cells (FLC) expressed TRAIL-R4. TRAIL-R1 and TRAIL-R3 were not detected in normal pancreas. In chronic pancreatitis, the exocrine epithelium strongly expressed TRAIL-R1, -R2, -R4, and, to a lesser extent, TRAIL-R3. Islets focally neoexpressed TRAIL-R1 and -R2 and intensely expressed TRAIL-R4. Changes in TRAIL receptor expression were most pronounced in areas of inflammatory infiltration and active fibrosis. In normal pancreas, expression of TRAIL was low on the mRNA level and undetectable on the protein level. In chronic pancreatitis, FLC in areas of active fibrosis expressed TRAIL. In addition, apoptosis were most numerous in these areas. We show that these FLC are pancreatic stellate cells. Pancreatic stellate cells express TRAIL in vivo and in vitro, and TRAIL expression is enhanced by IFN-gamma. Our findings indicate that the TRAIL/TRAIL receptor system is likely to be involved in chronic pancreatitis and suggest that pancreatic stellate cells may directly contribute to acinar regression by inducing apoptosis of parenchymal cells in a TRAIL-dependent manner.

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.

Overexpression of heparin-binding EGF-like growth factor in mouse pancreas results in fibrosis and epithelial metaplasia

BACKGROUND & AIMS

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is expressed in both normal pancreatic islets and in pancreatic cancers, but its role in pancreatic physiology and disease is not known. This report examines the effects of HB-EGF overexpression in mouse pancreas.

METHODS

Transgenic mice were established using a tissue-specific promoter to express an HB-EGF complementary DNA in pancreatic beta cells, effectively elevating HB-EGF protein 3-fold over endogenous levels.

RESULTS

Mice overexpressing HB-EGF in pancreatic islets showed both endocrine and exocrine pancreatic defects. Initially, islets from transgenic mice failed to segregate alpha, beta, delta, and PP cells appropriately within islets, and had impaired separation from ducts and acini. Increased stroma was detected within transgenic islets, expanding with age to cause fibrosis of both endocrine and exocrine compartments. In addition to these structural abnormalities, subsets of transgenic mice developed profound hyperglycemia and/or proliferation of metaplastic ductal epithelium. Both conditions were associated with severe stromal expansion, suggesting a role for islet/stromal interaction in the onset of the pancreatic disease initiated by HB-EGF. Supporting this conclusion, primary mouse fibroblasts adhered to transgenic islets when the 2 tissues were cocultured in vitro, but did not interact with nontransgenic islets.

CONCLUSIONS

An elevation in HB-EGF protein in pancreatic islets led to altered interactions among islet cells and among islets, stromal tissues, and ductal epithelium. Many of the observed phenotypes appeared to involve altered cell adhesion. These data support a role for islet factors in the development of both endocrine and exocrine disease.

Immunocytes and activated stellate cells in pancreatic fibrogenesis

INTRODUCTION AND AIMS

Chronic pancreatitis is a progressive chronic inflammatory disease characterized by irreversible destruction of exocrine pancreatic tissue and extensive fibrosis. Excessive alcohol consumption has been identified as the main etiologic factor of this disease in the Western world. Idiopathic pancreatitis accounts for approximately 30% of cases. An autoimmune mechanism may be involved in some patients, but this concept has not been generally accepted as a new clinical entity. The purpose of this work was to investigate the pathogenesis of pancreatic fibrosis and to establish the role of immunocytes and activated stellate cells in chronic pancreatitis, which was categorized into three groups: chronic alcoholic pancreatitis (AP), chronic idiopathic pancreatitis (IP), and chronic pancreatitis in the presence of pancreatic cancer (CA).

METHODOLOGY

Fifty-one pancreatic tissue samples were studied histopathologically and immunohistochemically (AP, 16 samples; IP, 12; CA, 12; and samples of tissue with apparently normal pancreatic histology, 11). The following immunohistochemical stains were used: alpha-smooth muscle antibody, desmin, and synaptophysin, as markers of activated stellate cells; and laminin, fibronectin, and collagen IV, as markers of extracellular matrix (ECM) proteins. Immunocytes were stained with antibody to LCA, CD68 antibody (macrophages), and CD8 antibody (natural killer T cell subset), and mast cells were examined using the Giemsa method. Positively stained macrophages, lymphocytes, and mast cells were counted in three high-power fields of a light microscope. The immunoreactivity of activated stellate cells and ECM proteins was assessed by a semiquantitative method (0, lack of positive staining; 5, numerous cells with strong positive immunostaining). Results were assessed statistically.

RESULTS

We found no statistical differences between cases of AP, IP, and CA in terms of total lymphocyte count (mean numbers: 416, 418, and 407 per three high-power fields, respectively). The percentage of CD8+ T cells in IP was statistically higher than that in AP. The macrophage count was significantly higher in the IP group than in the AP and CA groups. The mast cell count was markedly higher in the IP group than in the other groups. The stellate cell markers alpha-smooth muscle antibody and desmin showed slightly higher immunoreactivity in IP. The immunopositivity for synaptophysin was also higher in the IP group. There was a positive correlation between alpha-smooth muscle antibody, desmin, and synaptophysin expression and the degree of fibrosis. ECM protein markers showed no statistically significant differences between the three groups.

CONCLUSION

Results of this work show that a significant number of IP cases might have an autoimmune etiology. There was a positive correlation between activated stellate cell marker expression and the degree of fibrosis.

Bezafibrate, a peroxisome proliferator-activated receptor (PPAR)-alpha activator, prevents pancreatic degeneration in obese and diabetic rats

INTRODUCTION

Damage to the exocrine pancreas has been observed in patients and animals with hyperlipidemia and hyperglycemia. Bezafibrate, a peroxisome proliferator-activated receptor (PPAR)-alpha activator, has been shown to improve lipid and glucose metabolism, and to interfere with the inflammatory response.

AIM

To examine the effects of bezafibrate on exocrine pancreas in hyperlipidemic obese and diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats that have no cholecystokinin-1 receptor gene expression.

METHODOLOGY

One group of rats (n = 8) received a bezafibrate-rich diet (150 mg/100 g normal chow) from 12 weeks of age until 30 weeks of age, whereas a control group (n = 8) received standard rat chow.

RESULTS

Bezafibrate treatment significantly reduced serum triglyceride, total cholesterol, and free fatty acids levels and significantly increased the pancreatic wet weight (1,145 +/- 54 vs 874 +/- 33 mg/rat, p < 0.01), and protein (169 +/- 7 vs 128 +/- 11 mg/pancreas p < 0.01) and enzyme contents in the pancreas compared with those in untreated control rats. Immunohistochemical studies of the pancreas showed that expression of proinflammatory cytokines such as tumor necrosis factor-alpha, interleukin-1beta and interleukin-6, and alpha-smooth muscle actin in bezafibrate-treated rats was greatly suppressed compared with that in the untreated control rats. The histopathologic changes such as vacuolar degeneration and tubular complexes observed in the control rat pancreas were markedly improved in bezafibrate-treated rats.

CONCLUSIONS

Our results suggest that bezafibrate reduces hyperlipidemia, inhibits pancreatic inflammation, and prevents pancreatic degeneration in obese and diabetic OLETF rats.

Oleic acid-induced pancreatitis alters expression of transforming growth factor-beta1 and extracellular matrix components in rats

INTRODUCTION AND AIMS

Extracellular matrix (ECM) components participate in the process of tissue repair and development of fibrosis in the pancreas. We studied the production kinetics of ECM components and transforming growth factor (TGF)-beta1 and identified their production sites in the pancreas following pancreatitis.

METHODOLOGY

Pancreatitis was induced in rats by a single intraductal infusion of oleic acid. Gene expression of TGF-betas and ECM components was studied by northern blotting. Pancreatic stellate cell activation was assessed by immunostaining for alpha-smooth muscle actin (alphaSMA) and desmin.

RESULTS

Gene expression of TGF-betas and ECM components was increased in association with pancreatic fibrosis after 1-2 weeks and remained higher than the control levels for the ensuing 12 weeks. Both alphaSMA and desmin were strongly immunostained around small vessels and faintly stained in mesenchymal cells and tubular complexes at 1 week. The combination of staining for alphaSMA plus in situ hybridization for procollagen type III mRNA revealed that procollagen type III mRNA was expressed in both alphaSMA-positive and alphaSMA-negative cells in the mesenchyma.

CONCLUSIONS

Our findings demonstrate that expression of genes for both TGF-betas and ECM components was increased and that both alphaSMA-positive myofibroblasts and mesenchymal cells are the major sources of ECM components after pancreatitis.

Differential roles of signaling pathways for proliferation and migration of rat pancreatic stellate cells

Activated pancreatic stellate cells (PSCs) have recently been implicated in the pathogenesis of pancreatic fibrosis and inflammation. Accumulation of PSCs is a fundamental feature of pancreatic fibrosis, and platelet-derived growth factor (PDGF)-BB is the most potent mitogen for PSCs. But, the molecular mechanisms responsible for PDGF's actions in PSCs are largely unknown. In hepatic stellate cells, it has been established that activation of both phosphatidylinositol (PI) 3-kinase and extracellular-signal regulated kinase (ERK) pathways is required for PDGF-BB-induced proliferation and migration. The aim of this study was to elucidate the signaling pathways mediating PDGF-BB's actions in PSCs. PSCs were isolated from rat pancreas tissue and used in their culture-activated, myofibroblast-like phenotype. Culture-activated PSCs expressed PDGF alpha- and beta-receptors. PDGF-BB induced autophosphorylation of its receptor, followed by the activation of PI 3-kinase, Akt, and ERK pathways. Activation of PI 3-kinase was not required for PDGF-BB-induced ERK activation. PDGF-BB induced approximately five-fold increase in proliferation and chemotaxis of PSCs. Inhibition of ERK pathway with PD98059 completely blocked proliferation, whereas PD98059 had a modest inhibitory effect on cell migration (approximately 50%). On the other hand, inhibition of PI 3-kinase pathway with wortmannin or LY294002 almost completely inhibited migration, but did not affect proliferation of PSCs. In conclusion, our results suggest that ERK pathway regulates proliferation and migration in response to PDGF-BB, whereas PI 3-kinase mediates cellular migration, but not proliferation of PSCs.

Treatment of hepatic fibrosis: almost there

Hepatic fibrosis is the scarring response of the liver to chronic liver injury; when fibrosis progresses to cirrhosis, morbid complications can develop. Available therapies for many chronic liver diseases are ineffective, with liver transplantation as the only option, though the supply of donor organs is inadequate to meet the growing demand. Novel approaches that attack the scarring response are therefore urgently needed. Optimism in this effort is fueled by major insights into the pathogenesis of fibrosis and by accumulating evidence that even cirrhosis is reversible in many patients. Most evolving antifibrotic therapies will be aimed at inhibiting the activated hepatic stellate cell, which is responsible for the fibrotic response to injury. This review describes the ways in which insights into the cellular basis of hepatic fibrosis are leading to realistic strategies for antifibrotic treatment that may revolutionize the management of patients with chronic liver disease.

Inhibition of p38 mitogen-activated protein kinase blocks activation of rat pancreatic stellate cells

Activated pancreatic stellate cells (PSCs) have recently been implicated in the pathogenesis of pancreatic fibrosis and inflammation. However, the signal transduction pathways in PSCs remain largely unknown. We examined the role of p38 mitogen-activated protein (MAP) kinase in the activation of PSCs. PSCs were isolated from rat pancreas tissue and used in their culture-activated, myofibroblast-like phenotype. Activation of p38 MAP kinase was determined by Western blotting using anti-phosphospecific antibody. The effects of two p38 MAP kinase inhibitors, 4-(4-flurophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)imidazole (SB203580) and 4-(4-flurophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)1H-imidazole (SB202190), on the parameters of PSC activation, including proliferation, expression of alpha-smooth muscle actin, alpha1(I) procollagen, and prolyl 4-hydroxylase (alpha) genes, and monocyte chemoattractant protein-1 production were evaluated. Interleukin-1beta and platelet-derived growth factor-BB activated p38 MAP kinase. Platelet-derived growth factor-induced PSC proliferation was inhibited by SB203580 and SB202190. These reagents decreased alpha-smooth muscle actin protein expression, and alpha1(I) procollagen and prolyl 4-hydroxylase (alpha) mRNA levels. Treatment with these p38 MAP kinase inhibitors also resulted in inhibition of monocyte chemoattractant protein-1 expression. In addition, SB203580 inhibited spontaneous activation of freshly isolated PSCs in culture on plastic. Thus, inhibition of p38 MAP kinase modulated profibrogenic and proinflammatory actions in PSCs, implying a potential application of p38 MAP kinase inhibitors for the treatment of pancreatic fibrosis and inflammation.

Minute pancreatic adenocarcinoma presenting with stenosis of the main pancreatic duct

We describe a case of minute pancreatic ductal adenocarcinoma featuring stenosis of the main pancreatic duct (MPD) and associated with histological findings of periductal elastosis and fibroblast proliferation. A 53-year-old Japanese man with preoperative radiological evidence of MPD stricture and dilation of the distal MPD, and suspected of having pancreatic cancer, underwent successful resection. Neither radiological nor macroscopic examination directly disclosed any tumorous lesions, and a small focus of carcinoma (8 x 8 mm) was only revealed on microscopic examination. The tumor was a poorly differentiated, invasive ductal adenocarcinoma that had invaded the intrapancreatic nerves and veins. Interestingly, the MPD located at the edges of the tumor had not been destroyed by the carcinoma, but its wall had been thickened by elastic tissue and fibroblast proliferation, resulting in stenosis. The peripheral pancreas exhibited secondary obstructive pancreatitis. To date, the detection of small pancreatic tumor masses using imaging procedures remains difficult, and most patients are diagnosed on the basis of pancreatic ductal changes. However, the published work on small pancreatic cancers contains little information about the histological features of the affected MPD. The present findings suggest that MPD strictures are not always provoked by destruction or filling with cancer cells, and that they can be caused by periductal elastosis and fibroblast proliferation in a minute carcinoma. Such changes in the MPD may therefore be of clinical importance in the detection of early stage cancers.

Establishment and characterization of a simian virus 40-immortalized rat pancreatic stellate cell line

Activated pancreatic stellate cells (PSCs) have recently been implicated in the pathogenesis of pancreatic fibrosis and inflammation. Primary PSCs can be subcultured only several times because of their limited growth potential. A continuous cell line would be valuable in studying molecular mechanisms of these pancreatic disorders. The aim of this study was to establish an immortalized cell line of rat PSCs. PSCs were isolated from the pancreas of male Wistar rats, and the simian virus 40 T antigen was introduced to PSCs by retrovirus-mediated gene transfer. This procedure yielded an actively growing cell line, designated as SAM-K. This cell line has been passaged repeatedly for almost 2 years, and is thus likely immortalized. SAM-K cells retained morphological characteristics of primary PSCs, and expressed alpha-smooth muscle actin, glial fibrillary acidic protein, type I collagen, fibronectin, and prolyl hydroxylases. The level of p53 expression was very high in SAM-K cells. Proliferation of SAM-K cells was stimulated by serum and platelet-derived growth factor-BB. Interleukin-1beta (IL-1beta) activated nuclear factor-kappaB, activator protein-1, and three classes of mitogen-activated protein (MAP) kinases: extracellular signal-regulated kinase1/2, c-Jun N-terminal kinase, and p38 MAP kinase. IL-1beta induced expression of intercellular adhesion molecule-1 and monocyte chemoattractant protein-1, both of which were abolished in the presence of pyrrolidine dithiocarbamate, a specific inhibitor of nuclear factor-kappaB activation. IL-1beta-induced monocyte chemoattractant protein-1 was partially inhibited by specific inhibitors of MAP kinase kinase (U0126) and of p38 MAP kinase (SB203580) whereas intercellular adhesion molecule-1 expression was not altered by the inhibitors. Thus, SAM-K would be useful for in vitro studies of cell biology and signal transduction of PSCs.

Conservative treatment of chronic pancreatitis

Chronic pancreatitis has been difficult to treat because the origin, pathophysiologic mechanisms and causes of unrelenting pain are so poorly understood. Furthermore, the pharmacologic agents often employed in other diseases with pain appear to be ineffective in many cases. The conservative management of chronic pancreatitis aims at (1) limiting progression and complications of the disease; (2) replacing lost exocrine and endocrine function; and (3) pain control. Thus, life style changes such as cessation of alcohol consumption and tobacco smoking, trials of pancreatic enzymes, treatment of duct obstruction and pseudocysts, and surgical therapies are currently employed. The good news is that the understanding of the underlying pathophysiological mechanisms is now advancing rapidly, and hopefully patient-specific and highly effective therapies will become available in the near future.

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.

From acinar cell damage to systemic inflammatory response: current concepts in pancreatitis

Acute pancreatitis represents a local inflammatory disorder with severe systemic consequences. Significant progress in understanding the pathophysiology of acute pancreatitis has been achieved in recent years. However, there is no clear concept about initialization and propagation of the disease both in experimental models and in humans. Furthermore, reliable strategies to evaluate prognosis and perform therapy are still missing. The review focuses on mechanisms originating from acinar cells leading to a systemic inflammatory response in experimental pancreatitis.