Autophagy and acute pancreatitis: a novel autophagy theory for trypsinogen activation

Autodigestion of the pancreas by its own prematurely activated digestive proteases is thought to be an important event in the onset of acute pancreatitis. Although lysosomal hydrolases, such as cathepsin B, play a key role in intrapancreatic trypsinogen activation, it remains unclear where and how trypsinogen meets these lysosomal enzymes. Autophagy is an intracellular bulk degradation system in which cytoplasmic components are directed to the lysosome/vacuole by a membrane-mediated process. To analyze the role of autophagy in acute pancreatitis, we produced a conditional knockout mouse that lacks the autophagy-related (Atg) gene Atg5 in the pancreatic acinar cells. The severity of acute pancreatitis induced by cerulein is greatly reduced in these mice. In addition, Atg5-deficient acinar cells show a significantly decreased level of trypsinogen activation. These data suggest that autophagy exerts a detrimental effect in pancreatic acinar cells by activation of trypsinogen to trypsin. We propose a theory in which autophagy accelerates trypsinogen activation by lysosomal hydrolases under acidic conditions, thus triggering acute pancreatitis in its early stage.     

Acute pancreatitis: proteinase-activated receptor-2 as Dr. Jekyll and Mr. Hyde

"Proteinase-activated" receptor-2 (PAR-2) is a G protein-coupled transmembrane receptor with seven transmembrane domains activated by trypsin. It has been shown in the pancreatic tissue that PAR-2 is involved in duct/acinary cells secretion, arterial tonus regulation and capillary liquid content turnover under physiological conditions. These above mentioned structures play an important role during the development of acute pancreatitis and are profoundly influenced by a high concentration of trypsin enzyme after its secretion into the interstitial tissue from the basolateral aspect of acinar cells. Among the other factors, it is the increase of interstitial trypsin concentration followed rapidly by PAR-2 action on pancreatic vascular smooth muscle cells that initiates ischemic changes in pancreatic parenchyma and that finally leads to necrosis of the pancreas. Consequent reperfusion perpetuates changes leading to the acute pancreatitis development. On the contrary, PAR-2 action on both exocrine and duct structures seems to play locally a protective role during acute pancreatitis development. Moreover, PAR-2 action is not confined to the pancreas but it contributes to the systemic vascular endothelium and immune cell activation that triggers the systemic inflammatory response syndrome (SIRS) contributing to an early high mortality rate in severe disease.     

PAR2 exerts local protection against acute pancreatitis via modulation of MAP kinase and MAP kinase phosphatase signaling

During acute pancreatitis, protease-activated receptor 2 (PAR2) can be activated by interstitially released trypsin. In the mild form of pancreatitis, PAR2 activation exerts local protection against intrapancreatic damage, whereas, in the severe form of pancreatitis, PAR2 activation mediates some systemic complications. This study aimed to identify the molecular mechanisms of PAR2-mediated protective effects against intrapancreatic damage. A mild form of acute pancreatitis was induced by an intraperitoneal injection of caerulein (40 microg/kg) in rats. Effects of PAR2 activation on intrapancreatic damage and on mitogen-activated protein (MAP) kinase signaling were assessed. Caerulein treatment activated extracellular signal-regulated kinase (ERK) and c-Jun NH(2)-terminal kinase (JNK) within 15 min and maintained phosphorylation of ERK and JNK for 2 h in the rat pancreas. Although PAR2 activation by the pretreatment with PAR2-activating peptide (AP) itself increased ERK phosphorylation in rat pancreas, the same treatment remarkably decreased caerulein-induced activation of ERK and JNK principally by accelerating their dephosphorylation. Inhibition of ERK and JNK phosphorylation by the pretreatment with MAP/ERK kinase (MEK) or JNK inhibitors decreased caerulein-induced pancreatic damage that was similar to the effect induced by PAR2-AP. Notably, in caerulein-treated rats, PAR2-AP cotreatment highly increased the expression of a group of MAP kinase phosphatases (MKPs) that deactivate ERK and JNK. The above results imply that downregulation of MAP kinase signaling by MKP induction is a key mechanism involved in the protective effects of PAR2 activation on caerulein-induced intrapancreatic damage.     

Autophagy and acute pancreatitis: A novel autophagy theory for trypsinogen activation

Auto-digestion of the pancreas by its own prematurely activated digestive proteases is thought to be an important event in the onset of acute pancreatitis. Although lysosomal hydrolases, such as cathepsin B, play a key role in intrapancreatic trypsinogen activation, it remains unclear where and how trypsinogen meets these lysosomal enzymes. Autophagy is an intracellular bulk degradation system in which cytoplasmic components are directed to the lysosome/vacuole by a membrane-mediated process. To analyze the role of autophagy in acute pancreatitis, we produced a conditional knockout mouse that lacks the autophagy-related (Atg) gene Atg5 in the pancreatic acinar cells. The severity of acute pancreatitis induced by cerulein is greatly reduced in these mice. In addition, Atg5-deficient acinar cells show a significantly decreased level of trypsinogen activation. These data suggest that autophagy exerts a detrimental effect in pancreatic acinar cells by activation of trypsinogen to trypsin. We propose a theory in which autophagy accelerates trypsinogen activation by lysosomal hydrolases under acidic conditions, thus triggering acute pancreatitis in its early stage.

Addendum to: Hashimoto D, Ohmuraya M, Hirota M, Yamamoto A, Suyama K, Ida S, Okumura Y, Takahashi E, Kido H, Araki K, Baba H, Mizushima N, Yamamura K. Involvement of autophagy in trypsinogen activation within the pancreatic acinar cells. J Cell Biol 2008; 181:1065-72.     

Chymotrypsin C (caldecrin) stimulates autoactivation of human cationic trypsinogen

Trypsin-mediated trypsinogen activation (autoactivation) facilitates digestive zymogen activation in the duodenum but may precipitate pancreatitis if it occurs prematurely in the pancreas. Autoactivation of human cationic trypsinogen is inhibited by a repulsive electrostatic interaction between the unique Asp218 on the surface of cationic trypsin and the conserved tetra-aspartate (Asp19-22) motif in the trypsinogen activation peptide (Nemoda, Z., and Sahin-Tóth, M. (2005) J. Biol. Chem. 280, 29645-29652). Here we describe that this interaction is regulated by chymotrypsin C (caldecrin), which can specifically cleave the Phe18-Asp19 peptide bond in the trypsinogen activation peptide and remove the N-terminal tripeptide. In contrast, chymotrypsin B, elastase 2A, or elastase 3A (proteinase E) are ineffective. Autoactivation of N-terminally truncated cationic trypsinogen is stimulated approximately 3-fold, and this effect is dependent on the presence of Asp218. Because chymotrypsinogen C is activated by trypsin, and chymotrypsin C stimulates trypsinogen activation, these reactions establish a positive feedback mechanism in the digestive enzyme cascade of humans. Furthermore, inappropriate activation of chymotrypsinogen C in the pancreas may contribute to the development of pancreatitis. Consistent with this notion, the pancreatitis-associated mutation A16V in cationic trypsinogen increases the rate of chymotrypsin C-mediated processing of the activation peptide 4-fold and causes accelerated trypsinogen activation in vitro.     

Sodium arsenite induces heat shock protein 70 expression and protects against secretagogue-induced trypsinogen and NF-kappaB activation

Heat shock proteins (HSPs), induced by a variety of stresses, are known to protect against cellular injury. Recent studies have demonstrated that prior beta-adrenergic stimulation as well as thermal or culture stress induces HSP70 expression and protects against cerulein-induced pancreatitis. The goal of our current studies was to determine whether or not a non-thermal, chemical stressor like sodium arsenite also upregulates HSP70 expression in the pancreas and prevents secretagogue-induced trypsinogen and NF-kappaB activation. We examined the effects of sodium arsenite preadministration on the parameters of cerulein-induced pancreatitis in rats and then monitored the effects of preincubating pancreatic acini with sodium arsenite in vitro. Our results showed that sodium arsenite pretreatment induced HSP70 expression both in vitro and in vivo and significantly ameliorated the severity of cerulein-induced pancreatitis, as evidenced by the markedly reduced degree of hyperamylasemia, pancreatic edema, and acinar cell necrosis. Sodium arsenite pretreatment not only inhibited trypsinogen activation and the subcellular redistribution of cathepsin B, but also prevented NF-kappaB translocation to the nucleus by inhibiting the IkappaBalpha degradation both in vivo and in vitro. We also examined the effect of sodium arsenite pretreatment in a more severe model of pancreatitis induced by L-arginine and found a similarly protective effect. Based on our observations we conclude that, like thermal stress, chemical stressors such as sodium arsenite also induce HSP70 expression in the pancreas and protect against acute pancreatitis. Thus, non-thermal pharmacologically induced stress can help prevent or treat pancreatitis.     

Serum complex of trypsin 2 and alpha 1 antitrypsin as diagnostic and prognostic marker of acute pancreatitis: clinical study in consecutive patients.

OBJECTIVE--To estimate the usefulness of serum concentrations of the complex of trypsin 2 and alpha 1 antitrypsin in diagnosing and assessing the severity of acute pancreatitis in comparison with serum C reactive protein, amylase, and trypsinogen 2 concentrations (reference markers). DESIGN--Markers were measured in consecutive patients admitted with acute abdominal pain that was either due to pancreatitis or to other disease unrelated to the pancreas (controls). SETTING--Department of surgery of a teaching hospital in Helsinki. SUBJECTS--110 patients with acute pancreatitis and 66 with acute abdominal diseases of extrapancreatic origin. On the basis of the clinical course, acute pancreatitis was classified as mild (82 patients) or severe (28 patients). MAIN OUTCOME MEASURES--Clinical diagnosis of acute pancreatitis and severity of the disease. RESULTS--At admission all patients with acute pancreatitis had clearly raised concentrations of trypsin 2-alpha 1 antitrypsin complex (32 micrograms/l), whereas only three of the controls had such values. Of the markers studied, trypsin 2-alpha 1 antitrypsin complex had the largest area under the receiver operating curve, both in differentiating acute pancreatitis from extrapancreatic disease and in differentiating mild from severe disease. CONCLUSIONS--Of the markers studied, trypsin 2-alpha 1 antitrypsin complex was the most accurate in differentiating between acute pancreatitis and extrapancreatic disease and in predicting a severe course for acute pancreatitis.     

Autocrine Extra-Pancreatic Trypsin 3 Secretion Promotes Cell Proliferation and Survival in Esophageal Adenocarcinoma

Trypsin or Tumor associated trypsin (TAT) activation of Protease-activated receptor 2 (PAR-2) promotes tumor cell proliferation in gastrointestinal cancers. The role of the trypsin/PAR-2 network in esophageal adenocarcinoma (EA) development has not yet been investigated. The aim of this study is to investigate the role of trypsin/PAR-2 activation in EA tumorogenesis and therapy. We found that esophageal adenocarcinoma cells (EACs) and Barrett’s Metaplasia (BART) expressed high levels of type 3 extra-pancreatic trypsinogen (PRSS3), a novel type of TAT. Activity of secreted trypsin was detected in cultured media from EA OE19 and OE33 cultures but not from BART culture. Surface PAR-2 expression in BART and EACs was confirmed by both flow cytometry and immunofluorescence. Trypsin induced cell proliferation (∼ 2 fold; P<0.01) in all tested cell lines at a concentration of 10 nM. Inhibition of PAR-2 activity in EACs via the PAR-2 antagonist ENMD (500 µM), anti-PAR2 antibody SAM-11 (2 µg/ml), or siRNA PAR-2 knockdown, reduced cell proliferation and increased apoptosis by up to 4 fold (P<0.01). Trypsin stimulation led to phosphorylation of ERK1/2, suggesting involvement of MAPK pathway in PAR-2 signal transduction. Inhibition of PAR-2 activation or siRNA PAR-2 knockdown in EACs prior to treatment with 5 FU reduced cell viability of EACs by an additional 30% (P<0.01) compared to chemotherapy alone. Our data suggest that extra-pancreatic trypsinogen 3 is produced by EACs and activates PAR-2 in an autocrine manner. PAR-2 activation increases cancer cell proliferation, and promotes cancer cell survival. Targeting the trypsin activated PAR-2 pathway in conjunction with current chemotherapeutic agents may be a viable therapeutic strategy in EA.     

Zymogen activation in a reconstituted pancreatic acinar cell system

Pathological activation of digestive zymogens within the pancreatic acinar cell initiates acute pancreatitis. Cytosolic events regulate this activation within intracellular compartments of unclear identity. In an in vivo model of acute pancreatitis, zymogen activation was detected in both zymogen granule-enriched and microsomal cellular fractions. To examine the mechanism of this activation in vitro, a reconstituted system was developed using pancreatic cytosol, a zymogen granule-enriched fraction, and a microsomal fraction. Addition of cytosol to either particulate fraction resulted in a prominent increase in both trypsin and chymotrypsin activities. The percentage of the pool of trypsinogen and chymotrypsinogen activated was about twofold and sixfold greater, respectively, in the microsomal than in the zymogen granule-enriched fraction. Activation of chymotrypsinogen but not trypsinogen was significantly enhanced by ATP (5 mM) but not by the inactive ATP analog AMP-PNP. The processing of procarboxypeptidase B to its mature form also demonstrated a requirement for ATP and cytosol. E64d, an inhibitor of cathepsin B, a thiol protease that can activate trypsin, completely inhibited trypsin activity but did not affect chymotrypsin activity or carboxypeptidase B generation. These studies demonstrate that both zymogen granule-enriched and microsomal fractions from the pancreas can support cytosol-dependent zymogen activation. A component of the activation of some zymogens, such as chymotrypsinogen and procarboxypeptidase, may depend on ATP but not on trypsin or cathepsin B.     

Human mesotrypsin is a unique digestive protease specialized for the degradation of trypsin inhibitors

Mesotrypsin is an enigmatic minor human trypsin isoform, which has been recognized for its peculiar resistance to natural trypsin inhibitors such as soybean trypsin inhibitor (SBTI) or human pancreatic secretory trypsin inhibitor (SPINK1). In search of a biological function, two conflicting theories proposed that due to its inhibitor-resistant activity mesotrypsin could prematurely activate or degrade pancreatic zymogens and thus play a pathogenic or protective role in human pancreatitis. In the present study we ruled out both theories by demonstrating that mesotrypsin was grossly defective not only in inhibitor binding, but also in the activation or degradation of pancreatic zymogens. We found that the restricted ability of mesotrypsin to bind inhibitors or to hydrolyze protein substrates was solely due to a single evolutionary mutation, which changed the serine-protease signature glycine 198 residue to arginine. Remarkably, the same mutation endowed mesotrypsin with a novel and unique function: mesotrypsin rapidly hydrolyzed the reactive-site peptide bond of the Kunitz-type trypsin inhibitor SBTI, and irreversibly degraded the Kazal-type temporary inhibitor SPINK1. The observations suggest that the biological function of human mesotrypsin is digestive degradation of trypsin inhibitors. This mechanism can facilitate the digestion of foods rich in natural trypsin inhibitors. Furthermore, the findings raise the possibility that inappropriate activation of mesotrypsinogen in the pancreas might lower protective SPINK1 levels and contribute to the development of human pancreatitis. In this regard, it is noteworthy that the well known pathological trypsinogen activator cathepsin B exhibited a preference for the activation of mesotrypsinogen of all three human trypsinogen isoforms, suggesting a biochemical mechanism for mesotrypsinogen activation in pancreatic acinar cells.     

Relationship between NF-kappaB and trypsinogen activation in rat pancreas after supramaximal caerulein stimulation

Intra-acinar cell nuclear factor-kappaB (NF-kappaB) and trypsinogen activation are early events in secretagogue-induced acute pancreatitis. We have studied the relationship between NF-kappaB and trypsinogen activation in rat pancreas. CCK analogue caerulein induces early (within 15 min) parallel activation of both NF-kappaB and trypsinogen in pancreas in vivo as well as in pancreatic acini in vitro. However, NF-kappaB activation can be induced without trypsinogen activation by lipopolysaccharide in pancreas in vivo and by phorbol ester in pancreatic acini in vitro. Stimulation of acini with caerulein after 6 h of culture results in NF-kappaB but not trypsinogen activation. Protease inhibitors (AEBSF, TLCK, and E64d) inhibit both intracellular trypsin activity and NF-kappaB activation in caerulein stimulated acini. A chymotrypsin inhibitor (TPCK) inhibits NF-kappaB activation but not trypsin activity. The proteasome inhibitor MG-132 prevents caerulein-induced NF-kappaB activation but does not prevent trypsinogen activation. These findings indicate that although caerulein-induced NF-kappaB and trypsinogen activation are temporally closely related, they are independent events in pancreatic acinar cells. NF-kappaB activation per se is not required for the development of early acinar cell injury by supramaximal secretagogue stimulation.     

Cathepsin B inhibition prevents trypsinogen activation and reduces pancreatitis severity

Intrapancreatic activation of trypsinogen is believed to play a critical role in the initiation of acute pancreatitis, but mechanisms responsible for intrapancreatic trypsinogen activation during pancreatitis have not been clearly defined. In previous in vitro studies, we have shown that intra-acinar cell activation of trypsinogen and acinar cell injury in response to supramaximal secretagogue stimulation could be prevented by the cell permeant cathepsin B inhibitor E64d (Saluja A, Donovan EA, Yamanaka K, Yamaguchi Y, Hofbauer B, and Steer ML. Gastroenterology 113: 304-310, 1997). The present studies evaluated the role of intrapancreatic trypsinogen activation, this time under in vivo conditions, in two models of pancreatitis by using another highly soluble cell permeant cathepsin B inhibitor, L-3-trans-(propylcarbamoyl)oxirane-2-carbonyl-L-isoleucyl-L-proline methyl ester (CA-074me). Intravenous administration of CA-074me (10 mg/kg) before induction of either secretagogue-elicited pancreatitis in mice or duct infusion-elicited pancreatitis in rats markedly reduced the extent of intrapancreatic trypsinogen activation and substantially reduced the severity of both pancreatitis models. These observations support the hypothesis that, during the early stages of pancreatitis, trypsinogen activation in the pancreas is mediated by the lysosomal enzyme cathepsin B. Our findings also suggest that pharmacological interventions that inhibit cathepsin B may prove useful in preventing acute pancreatitis or reducing its severity.     

Constitutive protease-activated receptor-2-mediated migration of MDA MB-231 breast cancer cells requires both beta-arrestin-1 and -2

Protease-activated receptor-2 (PAR-2) is activated by trypsin-like serine proteases and can promote cell migration through an ERK1/2-dependent pathway, involving formation of a scaffolding complex at the leading edge of the cell. Previous studies also showed that expression of a dominant negative fragment of beta-arrestin-1 reduces PAR-2-stimulated internalization, ERK1/2 activation, and cell migration; however, this reagent may block association of many proteins, including beta-arrestin-2 with clathrin-coated pits. Here we investigate the role of PAR-2 in the constitutive migration of a metastatic breast cancer cell line, MDA MB-231, and use small interfering RNA to determine the contribution of each beta-arrestin to this process. We demonstrate that a trypsin-like protease secreted from MDA MB-231 cells can promote cell migration through autocrine activation of PAR-2 and this correlates with constitutive localization of PAR-2, beta-arrestin-2, and activated ERK1/2 to pseudopodia. Addition of MEK-1 inhibitors, trypsin inhibitors, a scrambled PAR-2 peptide, and silencing of beta-arrestins with small interfering RNA also reduce base-line migration of MDA MB-231 cells. In contrast, a less metastatic PAR-2 expressing breast cancer cell line does not exhibit constitutive migration, pseudopodia formation, or trypsin secretion; in these cells PAR-2 is more uniformly distributed around the cell periphery. These data demonstrate a requirement for both beta-arrestins in PAR-2-mediated motility and suggest that autocrine activation of PAR-2 by secreted proteases may contribute to the migration of metastatic tumor cells through beta-arrestin-dependent ERK1/2 activation.     

Gain-of-function mutations associated with hereditary pancreatitis enhance autoactivation of human cationic trypsinogen

Hereditary pancreatitis (HP), an autosomal dominant disorder, has been associated with mutations in the cationic trypsinogen gene. Here we demonstrate that the two most frequent HP mutations, Arg117 --> His and Asn21 --> Ile, significantly enhance autoactivation of human cationic trypsinogen in vitro, in a manner that correlates with the severity of clinical symptoms in HP. In addition, mutation Arg117 --> His inhibits autocatalytic inactivation of trypsin, while mutation Asn21 --> Ile has no such effect. The findings strongly argue that increased trypsinogen activation in the pancreas is the common initiating step in both forms of HP, whereas trypsin stabilization might also contribute to HP associated with the Arg117 --> His mutation.     

Protection from pancreatitis by the zymogen granule membrane protein integral membrane-associated protein-1

Pancreatitis is a common disease with substantial morbidity and mortality. To better understand the mechanisms conferring sensitivity or resistance to pancreatitis, we have initiated the analysis of novel acinar cell proteins. Integral membrane-associated protein-1 (Itmap1) is a CUB (complement subcomponents C1r/C1s, sea urchin Uegf protein, bone morphogenetic protein-1) and zona pellucida (ZP) domain-containing protein we find prominently expressed in pancreatic acinar cells. Within the acinar cell, Itmap1 localizes to zymogen granule membranes. Although roles in epithelial polarity, granule assembly, and mucosal protection have been postulated for CUB/ZP proteins, in vivo functions for these molecules have not been proven. To determine the function of Itmap1, we generated Itmap1-deficient mice. Itmap1(-/-) mice demonstrate increased severity of secretagogue- and diet-induced pancreatitis in comparison to Itmap1(+/+) mice. In contrast to previous animal models exhibiting altered severity of pancreatitis, Itmap1 deficiency results in impaired activation of trypsin, an enzyme believed critical for initiating a cascade of digestive zymogen activation during pancreatitis. Itmap1 deficiency does not alter zymogen granule size, appearance, or the composition of zymogen granule contents. Our results demonstrate that Itmap1 plays an essential role in trypsinogen activation and that both impaired and augmented trypsinogen activation can be associated with increased severity of pancreatitis.     

Interleukin-22 ameliorates cerulein-induced pancreatitis in mice by inhibiting the autophagic pathway

Pancreatitis occurs when digestive enzymes are activated in the pancreas. Severe pancreatitis has a 10-30% mortality rate. No specific treatments for pancreatitis exist now. Here, we discovered that interleukin-22 (IL-22) may have therapeutic potential in treating acute and chronic pancreatitis. Wild-type and IL-22 knockout mice were equally susceptible to cerulein-induced acute and chronic pancreatitis, whereas liver-specific IL-22 transgenic mice were completely resistant to cerulein-induced elevation of serum digestive enzymes, pancreatic necrosis and apoptosis, and inflammatory cell infiltration. Treatment of wild-type mice with recombinant IL-22 or adenovirus IL-22 markedly attenuated the severity of cerulein-induced acute and chronic pancreatitis. Mechanistically, we show that the protective effect of IL-22 on pancreatitis was mediated via the induction of Bcl-2 and Bcl-X(L), which bind to Beclin-1 and subsequently inhibit autophagosome formation to ameliorate pancreatitis. In conclusion, IL-22 ameliorates cerulein-induced pancreatitis by inhibiting the autophagic pathway. IL-22 could be a promising therapeutic drug to treat pancreatitis.     

Expression and functional analysis of rat P23, a gut hormone-inducible isoform of trypsin,reveals its resistance to proteinaceous trypsin inhibitors

Rat P23 is an isoform of trypsin (ogens) synthesized by rat acinar cells. Expression of P23 is stimulated strongly by caerulein, an analogue of cholecystokinin (CCK). However, the physiological relevance of rat P23 in healthy and pathological conditions such as caerulein-induced pancreatitis is largely unknown. Using recombinant P23 trypsinogen and reconstitution analysis of zymogen autoactivation, unique inhibitor-resistance characteristics of P23 were elucidated. P23 cDNA was expressed in Escherichia coli periplasm, yielding recombinant P23 trypsinogen. Autoactivation of zymogen granule contents from caerulein-induced rat pancreas was also studied. Activation kinetics of P23 by enterokinase was similar to those of rat anionic trypsinogen, which is a major isoform of trypsinogen. Interestingly, rat pancreatic secretory trypsin inhibitor (PSTI), which protects against deleterious activation of trypsinogens in zymogen granules, failed to inhibit P23 trypsin even with four-fold molar excess, at which concentration it effectively inhibited rat anionic trypsin to almost 100%. P23 trypsin also showed marked resistance to proteinaceous trypsin inhibitors such as soybean trypsin inhibitor and aprotinin. P23 trypsin activated by enterokinase dramatically accelerated the cascade of autoactivation of anionic trypsinogen even in the presence of PSTI. Taken together with a previous observation that P23 is specifically upregulated 14-fold by 24-h caerulein infusion, these results suggest that elevated levels of P23 should be taken into consideration in the mechanism of trypsinogens within the pancreas in pathological conditions.     

Phenotypic changes in mouse pancreatic stellate cell Ca2+ signaling events following activation in culture and in a disease model of pancreatitis

The specific characteristics of intracellular Ca 2+ signaling and the downstream consequences of these events were investigated in mouse pancreatic stellate cells (PSC) in culture and in situ using multiphoton microscopy in pancreatic lobules. PSC undergo a phenotypic transformation from a quiescent state to a myofibroblast-like phenotype in culture. This is believed to parallel the induction of an activated state observed in pancreatic disease such as chronic pancreatitis and pancreatic cancer. By day 7 in culture, the complement of cell surface receptors coupled to intracellular Ca 2+ signaling was shown to be markedly altered. Specifically, protease-activated receptors (PAR) 1 and 2, responsive to thrombin and trypsin, respectively, and platelet-derived growth factor (PDGF) receptors were expressed only in activated PSC (aPSC). PAR-1, ATP, and PDGF receptor activation resulted in prominent nuclear Ca 2+ signals. Nuclear Ca 2+ signals and aPSC proliferation were abolished by expression of parvalbumin targeted to the nucleus. In pancreatic lobules, PSC responded to agonists consistent with the presence of only quiescent PSC. aPSC were observed following induction of experimental pancreatitis. In contrast, in a mouse model of pancreatic disease harboring elevated K-Ras activity in acinar cells, aPSC were present under control conditions and their number greatly increased following induction of pancreatitis. These data are consistent with nuclear Ca 2+ signaling generated by agents such as trypsin and thrombin, likely present in the pancreas in disease states, resulting in proliferation of "primed" aPSC to contribute to the severity of pancreatic disease.