Pancreatitis and calcium signalling: report of an international workshop

Calcium, mitochondria and the initiation of acute pancreatitis

Acute pancreatitis is characterized by necrosis of its parenchymal cells and influx and activation of inflammatory cells that further promote injury and necrosis. This review is intended to discuss the central role of disorders of calcium metabolism and mitochondrial dysfunction in the mechanism of pancreatitis development. The disorders are placed in context of calcium and mitochondria in physiologic function of the pancreas. Moreover, we discuss potential therapeutics for preventing pathologic calcium signals that injure mitochondria and interventions that promote the removal of injured mitochondria and regenerate new and heathy populations of mitochondria.

Acute Pancreatitis: Genetic Risk and Clinical Implications

Acute pancreatitis (AP) is one of the most common gastroenterological indications for emergency admittance and hospitalization. Gallstones, alcohol consumption or the presence of additional initiating factors give rise to a disease with a diverse clinical appearance and a hard-to predict course of progression. One major challenge in the treatment of AP patients is the early identification of patients at risk for the development of systemic complications and organ failure. In addition, 20%-30% of patients with a first episode of AP later experience progress to recurrent or chronic disease. Complex gene-environment interactions have been identified to play a role in the pathogenesis of pancreatitis, but so far no predictive genetic biomarkers could be implemented into the routine clinical care of AP patients. The current review explains common and rare etiologies of acute pancreatitis with emphasis on underlying genetic aberrations and ensuing clinical management.

Melatonin induces reactive oxygen species generation and changes in glutathione levels and reduces viability in human pancreatic stellate cells

In this study, the effects of pharmacological concentrations of melatonin (1 μM-1 mM) on human pancreatic stellate cells (HPSCs) have been examined. Cell type-specific markers and expression of melatonin receptors were analyzed by western blot analysis. Changes in intracellular free Ca2+ concentration were followed by fluorimetric analysis of fura-2-loaded cells. Reduced glutathione (GSH) and oxidized glutathione (GSSG) levels were determined by fluorescence techniques. Production of reactive oxygen species (ROS) was monitored following 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate acetyl ester and MitoSOX™ Red-derived fluorescence. Cell viability was studied using the AlamarBlue® test. Cultured cells expressed markers typical of stellate cells. However, cell membrane receptors for melatonin could not be detected. Thapsigargin, bradykinin, or melatonin induced changes in intracellular free Ca2+ concentration. In the presence of the indole, a decrease in the GSH/GSSG ratio was observed that depended on the concentration of melatonin used. Furthermore, the indole evoked a concentration-dependent increase in ROS production in the mitochondria and in the cytosol. Finally, melatonin decreased HPSC viability in a time and concentration-dependent manner. We conclude that melatonin, at pharmacological concentrations, induces changes in the oxidative state of HPSC. This might regulate cellular viability and could not involve specific plasma membrane receptors.

The Orai Ca2+ channel inhibitor CM4620 targets both parenchymal and immune cells to reduce inflammation in experimental acute pancreatitis

KEY POINTS

This work confirms previous reports that CM4620, a small molecule inhibitor of Ca2+ entry via store operated Ca2+ entry (SOCE) channels formed by stromal interaction molecule 1 (STIM1)/Orai complexes, attenuates acinar cell pathology and acute pancreatitis in mouse experimental models. Here we report that intravenous administration of CM4620 reduces the severity of acute pancreatitis in the rat, a hitherto untested species. Using CM4620, we probe further the mechanisms whereby SOCE via STIM1/Orai complexes contributes to the disease in pancreatic acinar cells, supporting a role for endoplasmic reticulum stress/cell death pathways in these cells. Using CM4620, we show that SOCE via STIM1/Orai complexes promotes neutrophil oxidative burst and inflammatory gene expression during acute pancreatitis, including in immune cells which may be either circulating or invading the pancreas. Using CM4620, we show that SOCE via STIM1/Orai complexes promotes activation and fibroinflammatory gene expression within pancreatic stellate cells.

ABSTRACT

Key features of acute pancreatitis include excess cellular Ca2+ entry driven by Ca2+ depletion from the endoplasmic reticulum (ER) and subsequent activation of store-operated Ca2+ entry (SOCE) channels in the plasma membrane. In several cell types, including pancreatic acinar, stellate cells (PaSCs) and immune cells, SOCE is mediated via channels composed primarily of Orai1 and stromal interaction molecule 1 (STIM1). CM4620, a selective Orai1 inhibitor, prevents Ca2+ entry in acinar cells. This study investigates the effects of CM4620 in preventing or reducing acute pancreatitis features and severity. We tested the effects of CM4620 on SOCE, trypsinogen activation, acinar cell death, activation of NFAT and NF-κB, and inflammatory responses in ex vivo and in vivo rodent models of acute pancreatitis and human pancreatic acini. We also examined whether CM4620 inhibited cytokine release in immune cells, fibro-inflammatory responses in PaSCs, and oxidative burst in neutrophils, all cell types participating in pancreatitis. CM4620 administration to rats by i.v. infusion starting 30 min after induction of pancreatitis significantly diminished pancreatitis features including pancreatic oedema, acinar cell vacuolization, intrapancreatic trypsin activity, cell death signalling and acinar cell death. CM4620 also decreased myeloperoxidase activity and inflammatory cytokine expression in pancreas and lung tissues, fMLF peptide-induced oxidative burst in human neutrophils, and cytokine production in human peripheral blood mononuclear cells (PBMCs) and rodent PaSCs, indicating that Orai1/STIM1 channels participate in the inflammatory responses of these cell types during acute pancreatitis. These findings support pathological Ca2+ entry-mediated cell death and proinflammatory signalling as central mechanisms in acute pancreatitis pathobiology.

Serum calcium as an indicator of persistent organ failure in acute pancreatitis

AIM

Decreased level of serum calcium was commonly seen in critical illness. Hypocalcemia was significantly more frequent in patients with severe form of acute pancreatitis (AP), and a negative correlation was observed between endotoxemia and serum calcium in AP. AP patients with persistent organ failure (POF) show an extremely high mortality. The association underlying calcium and POF in AP has not been characterized.

METHODS

We conducted a retrospective cohort study of adult patients who presented within 72hours from symptom onset of AP at our center between January 2014 and May 2015. Demographic parameters on admission, organ failure assessment, laboratory data and in-hospital mortality were compared between patients with and without POF. Uni-and multi-variate logistic regression analyses were utilized to evaluated the predictive ability of serum calcium.

RESULTS

A total of 128 consecutive AP patients, including 29 with POF, were included. Compared to patients without POF, patients with POF showed a significantly lower value of serum calcium on admission (2.11±0.46 vs. 1.55±0.36mmol/L, P<0.001). After multivariate logistic analysis, serum calcium remained an independent risk factor for POF (Hazard ratio 0.21, 95% confident interval: 0.08-0.58; P=0.002). A calcium value of 1.97mmol/L predicted POF with an area under the curve (AUC) of 0.888, a sensitivity with 89.7% and specificity with 74.8%, respectively.

CONCLUSION

Our results indicate that serum calcium on admission is independently associated with POF in AP and may serve as a potential prognostic factor.

Acute pancreatitis

Acute pancreatitis, an inflammatory disorder of the pancreas, is the leading cause of admission to hospital for gastrointestinal disorders in the USA and many other countries. Gallstones and alcohol misuse are long-established risk factors, but several new causes have emerged that, together with new aspects of pathophysiology, improve understanding of the disorder. As incidence (and admission rates) of acute pancreatitis increase, so does the demand for effective management. We review how to manage patients with acute pancreatitis, paying attention to diagnosis, differential diagnosis, complications, prognostic factors, treatment, and prevention of second attacks, and the possible transition from acute to chronic pancreatitis.

Pancreatic adaptive responses in alcohol abuse: Role of the unfolded protein response

The majority of those who drink excessive amounts of alcohol do not develop pancreatic disease. One overarching hypothesis is that alcohol abuse requires additional risk factors, either environmental or genetic, for disease to occur. However, another reason be a result of alcohol-induced activation of adaptive systems that protect the pancreas from the toxic effects of alcohol. We show that mechanisms within the unfolded protein response (UPR) of the endoplasmic reticulum (ER) that can lead to protection of the pancreas from pancreatic diseases with alcohol abuse. The remarkable ability of the pancreas to adapt its machinery to alcohol abuse using UPR systems and continue functioning is the likely reason that pancreatitis from alcohol abuse does not occur in the majority of heavy drinkers. These findings indicate that methods to enhance the protective responses of the UPR can provide opportunities for prevention and treatment of pancreatic diseases.

The role of Ca2+ influx in endocytic vacuole formation in pancreatic acinar cells

The inducers of acute pancreatitis trigger a prolonged increase in the cytosolic Ca(2+) concentration ([Ca(2+)]c), which is responsible for the damage to and eventual death of pancreatic acinar cells. Vacuolization is an important indicator of pancreatic acinar cell damage. Furthermore, activation of trypsinogen occurs in the endocytic vacuoles; therefore the vacuoles can be considered as 'initiating' organelles in the development of the cell injury. In the present study, we investigated the relationship between the formation of endocytic vacuoles and Ca(2+) influx developed in response to the inducers of acute pancreatitis [bile acid taurolithocholic acid 3-sulfate (TLC-S) and supramaximal concentration of cholecystokinin-8 (CCK)]. We found that the inhibitor of STIM (stromal interaction molecule)/Orai channels, GSK-7975A, effectively suppressed both the Ca(2+) influx (stimulated by inducers of pancreatitis) and the formation of endocytic vacuoles. Cell death induced by TLC-S or CCK was also inhibited by GSK-7975A. We documented the formation of endocytic vacuoles in response to store-operated Ca(2+) entry (SOCE) induced by thapsigargin [TG; inhibitor of sarcoplasmic/endoplasmic reticulum (ER) Ca(2+) pumps] and observed strong inhibition of TG-induced vacuole formation by GSK-7975A. Finally, we found that structurally-unrelated inhibitors of calpain suppress formation of endocytic vacuoles, suggesting that this Ca2+-dependent protease is a mediator between Ca(2+) elevation and endocytic vacuole formation.

Melatonin induces calcium mobilization and influences cell proliferation independently of MT1/MT2 receptor activation in rat pancreatic stellate cells

Melatonin, the product of the pineal gland, possesses antioxidant, anti-inflammatory, and antitumor properties in different tissues, in addition to its role as regulator of biological rhythms. In this study, the effects of pharmacological concentrations of melatonin (1 μM-1 mM) on pancreatic stellate cells (PSCs) have been examined. Cell viability was studied using AlamarBlue® test. Cell-type specific markers and total amylase content were analyzed by immunocytochemistry and colorimetric methods, respectively. Changes in intracellular free Ca(2+) concentration were followed by fluorimetric analysis of fura-2-loaded cells. The cellular red-ox state was monitored following CM-H2DCFDA-derived fluorescence. Determination of the activation of p44/42 mitogen-activated protein kinase (MAPK), SAPK/JNK and p38 was measured by Western blot analysis. Our results show that PSCs viability decreased in the presence of 100 μM or 1 mM melatonin. However, in the presence of 1 or 10 μM melatonin, no changes in cell viability were observed. Melatonin MT1 and MT2 receptors could not be detected. Melatonin induced Ca(2+) mobilization from intracellular pools. In the presence of melatonin, activation of crucial components of MAPKs pathway was noticed. Finally, the indole did not change the oxidative state of PSCs, but exerted a protective effect against H2O2-induced oxidation. We conclude that melatonin, at pharmacological concentrations, might regulate cellular proliferation of PSCs independently of specific plasma membrane receptors.

Novel lipophilic probe for detecting near-membrane reactive oxygen species responses and its application for studies of pancreatic acinar cells: effects of pyocyanin and L-ornithine

AIMS

The aim of this study was to develop a fluorescent reactive oxygen species (ROS) probe, which is preferentially localized in cellular membranes and displays a strong change in fluorescence upon oxidation. We also aimed to test the performance of this probe for detecting pathophysiologically relevant ROS responses in isolated cells.

RESULTS

We introduced a novel lipophilic ROS probe dihydrorhodamine B octadecyl ester (H2RB-C18). We then applied the new probe to characterize the ROS changes triggered by inducers of acute pancreatitis in pancreatic acinar cells. We resolved ROS changes produced by L-ornithine, L-arginine, cholecystokinin-8, acetylcholine, taurolithocholic acid 3-sulfate, palmitoleic acid ethyl ester, and the bacterial toxin pyocyanin. Particularly prominent ROS responses were induced by pyocyanin and L-ornithine. These ROS responses were accompanied by changes in cytosolic Ca(2+)concentration ([Ca(2+)]i), mitochondrial membrane potential (ΔΨ), and NAD(P)H concentration.

INNOVATION

The study describes a novel sensitive lipophilic ROS probe. The probe is particularly suitable for detecting ROS in near-membrane regions and therefore for reporting the ROS environment of plasma membrane channels and pumps.

CONCLUSIONS

In our experimental conditions, the novel probe was more sensitive than 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein (CM-H2DCF) and dihydrorhodamine123 (H2R123) and allowed us to resolve ROS responses to secretagogues, pyocyanin, and L-ornithine. Changes in the fluorescence of the new probe were particularly prominent in the peripheral plasma membrane-associated regions. Our findings suggest that the new probe will be a useful tool in studies of the contribution of ROS to the pathophysiology of exocrine pancreas and other organs/tissues.

Hypothermia slows sequential and parallel steps initiated during caerulein pancreatitis

BACKGROUND AND OBJECTIVES

Multiple deleterious signaling cascades are simultaneously activated in acute pancreatitis (AP), which may limit the success of pharmacologic approaches targeting a single step. We explored whether cooling acinar cells slows distinct steps initiated from a stimulus causing pancreatitis simultaneously, and the temperature range over which inhibition of such deleterious signaling occurs.

METHODS

Caerulein (100 nM) induced trypsinogen activation (TGA), CXCL1, CXCL2 mRNA levels, cell injury were studied at 37 °C, 34 °C, 31 °C, 29 °C and 25 °C in acinar cells. Trypsin, cathepsin B activities and cathepsin B mediated TGA were studied at 37 °C, 23 °C and 4 °C.

RESULTS

There was >80% reduction in TGA, CXCL1 and CXCL2 mRNA levels at 29 °C, and in cell injury at 34 °C, compared to those at 37 °C. Trypsin activity, cathepsin B activity and cathepsin B mediated TGA at 23 °C were respectively, 53%, 64% and 26% of that at 37 °C. Acinar cooling to 31 °C reduced LDH leakage even when cooling was initiated an hour after caerulein stimulation at 37 °C.

CONCLUSIONS

Hypothermia synergistically and simultaneously slows parallel and distinct signaling steps initiated by caerulein, thereby reducing TGA, upregulation of inflammatory mediators and acinar injury.

Characterization of store-operated Ca2+ channels in pancreatic duct epithelia

Store-operated Ca2+ channels (SOCs) are activated by depletion of intracellular Ca2+ stores following agonist-mediated Ca2+ release. Previously we demonstrated that Ca2+ influx through SOCs elicits exocytosis efficiently in pancreatic duct epithelial cells (PDEC). Here we describe the biophysical, pharmacological, and molecular properties of the duct epithelial SOCs using Ca2+ imaging, whole-cell patch-clamp, and molecular biology. In PDEC, agonists of purinergic, muscarinic, and adrenergic receptors coupled to phospholipase C activated SOC-mediated Ca2+ influx as Ca2+ was released from intracellular stores. Direct measurement of [Ca2+] in the ER showed that SOCs greatly slowed depletion of the ER. Using IP3 or thapsigargin in the patch pipette elicited inwardly rectifying SOC currents. The currents increased ∼8-fold after removal of extracellular divalent cations, suggesting competitive permeation between mono- and divalent cations. The current was completely blocked by high doses of La3+ and 2-aminoethoxydiphenyl borate (2-APB) but only partially depressed by SKF-96365. In polarized PDEC, SOCs were localized specifically to the basolateral membrane. RT-PCR screening revealed the expression of both STIM and Orai proteins for the formation of SOCs in PDEC. By expression of fluorescent STIM1 and Orai1 proteins in PDEC, we confirmed that colocalization of the two proteins increases after store depletion. In conclusion, basolateral Ca2+ entry through SOCs fills internal Ca2+ stores depleted by external stimuli and will facilitate cellular processes dependent on cytoplasmic Ca2+ such as salt and mucin secretion from the exocrine pancreatic ducts.

Urinary trypsinogen-2 for diagnosing acute pancreatitis: a meta-analysis

BACKGROUND

Currently, serum amylase and lipase are the most popular laboratory markers for early diagnosis of acute pancreatitis with reasonable sensitivity and specificity. Urinary trypsinogen-2 (UT-2) has been increasingly used but its clinical value for the diagnosis of acute pancreatitis and post-endoscopic retrograde cholangiopancreatography (ERCP) pancreatitis has not yet been systematically assessed.

DATA SOURCES

A comprehensive search was carried out using PubMed (MEDLINE), Embase, and Web of Science for clinical trials, which studied the usefulness of UT-2 as a diagnostic marker for acute pancreatitis. Sensitivity, specificity and the diagnostic odds ratios (DORs) with 95% confidence interval (CI) were calculated for each study and were compared with serum amylase and lipase. Summary receiver-operating curves were conducted and the area under the curve (AUC) was evaluated.

RESULTS

A total of 18 studies were included. The pooled sensitivity and specificity of UT-2 for the diagnosis of acute pancreatitis were 80% and 92%, respectively (AUC=0.96, DOR=65.63, 95% CI: 31.65-139.09). The diagnostic value of UT-2 was comparable to serum amylase but was weaker than serum lipase. The pooled sensitivity and specificity for the diagnosis of post-ERCP pancreatitis were 86% and 94%, respectively (AUC=0.92, DOR=77.68, 95% CI: 24.99-241.48).

CONCLUSIONS

UT-2 as a rapid test could be potentially used for the diagnosis of post-ERCP pancreatitis and to an extent, acute pancreatitis. Further studies are warranted to confirm these results.

The role of calcium in acute pancreatitis

Until recently, it was unclear whether calcium is more than a bystander in the development of acute pancreatitis. Now important evidence has been accumulated supporting a pivotal role of intracellular levels of calcium in the early pathogenesis of the disease. A sustained increase of cytosolic calcium concentrations, as observed in various models of acute pancreatitis, was identified as sabotaging crucial cellular defense mechanisms and initiating premature trypsinogen activation. These processes lead the acinar cell to necrosis, with spillage of activated proteases into the interstitial space, affecting surrounding acinar cells and initiating a vicious circle that ends in macroscopic acute pancreatitis and systemic inflammatory response syndrome. Comprehensive knowledge of the pathobiology of cytosolic calcium in the pancreatic acinar cell is leading to the understanding of coherent molecular pathways of early events in the pathogenesis of acute pancreatitis and is opening horizons for research into directly targeted therapeutic agents.

The association of primary hyperparathyroidism with pancreatitis

The association between primary hyperparathyroidism (PHPT) and acute or chronic pancreatitis is controversial. For this reason, we conducted a review of the literature over the past 30 years to explore the relationship between these 2 disorders. Ten retrospective studies each with >50 patients diagnosed with PHPT were identified. With the notable exception of 2 studies, the rate of pancreatitis among patients with PHPT was higher than that reported in general among hospitalized patients without PHPT. A higher serum calcium level may contribute to pancreatitis in these cases, along with additional genetic or environmental insults. Hypercalcemia may predispose the pancreatic acinar cell to abnormal, sustained calcium levels, lead to premature pancreatic protease activation, and pancreatitis. Although there was only short-term follow-up, most reports cited that definitive treatment of PHPT by parathyroidectomy led to the resolution of pancreatitis attacks. The published cohorts of patients with PHPT and pancreatitis are subject to bias, because serum calcium screening was not universally performed among all control nonpancreatitis patients to evaluate for PHPT. However, the pooled clinical and experimental data suggest an association between PHPT and pancreatitis and implicate hypercalcemia. For clinicians, it is important to recognize pancreatitis in patients with PHPT and, conversely, to consider PHPT by checking serum calcium levels in patients, who present with an unexplained pancreatitis.

Mitochondrial calcium in the life and death of exocrine secretory cells

The remarkable recent discoveries of the proteins mediating mitochondrial Ca(2+) transport (reviewed in this issue) provide an exciting opportunity to utilise this new knowledge to improve our fundamental understanding of relationships between Ca(2+) signalling and bioenergetics and, importantly, to improve the understanding of diseases in which Ca(2+) toxicity and mitochondrial malfunction play a crucial role. Ca(2+) is an important activator of exocrine secretion, a regulator of the bioenergetics of exocrine cells and a contributor to exocrine cell damage. Exocrine secretory cells, exocrine tissues and diseases affecting exocrine glands (like Sjögren's syndrome and acute pancreatitis) will, therefore, provide worthy research areas for the application of this new knowledge of the Ca(2+) transport mechanisms in mitochondria.

Genetic and pharmacologic inhibition of the Ca2+ influx channel TRPC3 protects secretory epithelia from Ca2+-dependent toxicity

BACKGROUND & AIMS

Excessive Ca2+ influx mediates many cytotoxic processes, including those associated with autoimmune inflammatory diseases such as acute pancreatitis and Sjögren syndrome. Transient receptor potential (canonical) channel (TRPC) 3 is a major Ca2+ influx channel in pancreatic and salivary gland cells. We investigated whether genetic or pharmacologic inhibition of TRPC3 protects pancreas and salivary glands from Ca2+-dependent damage.

METHODS

We developed a Ca2+-dependent model of cell damage for salivary gland acini. Acute pancreatitis was induced by injection of cerulein into wild-type and Trpc3-/- mice. Mice were also given the Trpc3-selective inhibitor pyrazole 3 (Pyr3).

RESULTS

Salivary glands and pancreas of Trpc3-/- mice were protected from Ca2+-mediated cell toxicity. Analysis of Ca2+ signaling in wild-type and Trpc3-/- acini showed that Pyr3 is a highly specific inhibitor of Tprc3; it protected salivary glands and pancreas cells from Ca2+-mediated toxicity by inhibiting the Trpc3-mediated component of Ca2+ influx.

CONCLUSIONS

TRPC3-mediated Ca2+ influx mediates damage to pancreas and salivary glands. Pharmacologic inhibition of TRPC3 with the highly selective TRPC3 inhibitor Pyr3 might be developed for treatment of patients with acute pancreatitis and Sjögren syndrome.

Environmental and genetic stressors and the unfolded protein response in exocrine pancreatic function - a hypothesis

The exocrine pancreas has the greatest protein synthetic capacity of any mammalian organ and is challenged with the synthesis, processing and transporting a large load of digestive enzymes. Based on recent findings we present a hypothesis proposing that mutations in the digestive enzymes and environmental risks impacting the pancreas (i.e., alcohol abuse, smoking, metabolic disorders, and drugs) cause endoplasmic reticulum (ER) stress. We review recent findings showing that in normal pancreas the ER stress resulting from alcohol abuse leads to an adaptive unfolded protein response (UPR) allowing for maintenance of protein synthesis, processing, and transport. However, when key pathways necessary for the adaptive UPR are altered, the exocrine cell of the pancreas is unable to maintain these processes and cellular pathology results. These findings may explain why some individuals with alcohol abuse disorders develop organ injury and disease while most do not. Further, the findings allow us to hypothesize that the UPR in the exocrine pancreas adapts the protein synthetic machinery of the ER stress resulting from mutational and environmental stressors. When the ability of the UPR to adapt to the stressors is exceeded, pathologic pathways and disease develop.

Pediatric brain tumor cancer stem cells: cell cycle dynamics, DNA repair, and etoposide extrusion

Reliable model systems are needed to elucidate the role cancer stem cells (CSCs) play in pediatric brain tumor drug resistance. The majority of studies to date have focused on clinically distinct adult tumors and restricted tumor types. Here, the CSC component of 7 newly established primary pediatric cell lines (2 ependymomas, 2 medulloblastomas, 2 gliomas, and a CNS primitive neuroectodermal tumor) was thoroughly characterized. Comparison of DNA copy number with the original corresponding tumor demonstrated that genomic changes present in the original tumor, typical of that particular tumor type, were retained in culture. In each case, the CSC component was approximately 3-4-fold enriched in neurosphere culture compared with monolayer culture, and a higher capacity for multilineage differentiation was observed for neurosphere-derived cells. DNA content profiles of neurosphere-derived cells expressing the CSC marker nestin demonstrated the presence of cells in all phases of the cell cycle, indicating that not all CSCs are quiescent. Furthermore, neurosphere-derived cells demonstrated an increased resistance to etoposide compared with monolayer-derived cells, having lower initial DNA damage, potentially due to a combination of increased drug extrusion by ATP-binding cassette multidrug transporters and enhanced rates of DNA repair. Finally, orthotopic xenograft models reflecting the tumor of origin were established from these cell lines. In summary, these cell lines and the approach taken provide a robust model system that can be used to develop our understanding of the biology of CSCs in pediatric brain tumors and other cancer types and to preclinically test therapeutic agents.

Inhibitors of Bcl-2 protein family deplete ER Ca2+ stores in pancreatic acinar cells

Physiological stimulation of pancreatic acinar cells by cholecystokinin and acetylcholine activate a spatial-temporal pattern of cytosolic [Ca⁺²] changes that are regulated by a coordinated response of inositol 1,4,5-trisphosphate receptors (IP₃Rs), ryanodine receptors (RyRs) and calcium-induced calcium release (CICR). For the present study, we designed experiments to determine the potential role of Bcl-2 proteins in these patterns of cytosolic [Ca⁺²] responses. We used small molecule inhibitors that disrupt the interactions between prosurvival Bcl-2 proteins (i.e. Bcl-2 and Bcl-xl) and proapoptotic Bcl-2 proteins (i.e. Bax) and fluorescence microfluorimetry techniques to measure both cytosolic [Ca⁺²] and endoplasmic reticulum [Ca⁺²]. We found that the inhibitors of Bcl-2 protein interactions caused a slow and complete release of intracellular agonist-sensitive stores of calcium. The release was attenuated by inhibitors of IP₃Rs and RyRs and substantially reduced by strong [Ca²⁺] buffering. Inhibition of IP₃Rs and RyRs also dramatically reduced activation of apoptosis by BH3I-2′. CICR induced by different doses of BH3I-2′ in Bcl-2 overexpressing cells was markedly decreased compared with control. The results suggest that Bcl-2 proteins regulate calcium release from the intracellular stores and suggest that the spatial-temporal patterns of agonist-stimulated cytosolic [Ca⁺²] changes are regulated by differential cellular distribution of interacting pairs of prosurvival and proapoptotic Bcl-2 proteins.

Deletion of TRPC3 in mice reduces store-operated Ca2+ influx and the severity of acute pancreatitis

BACKGROUND & AIMS

Receptor-stimulated Ca(2+) influx is a critical component of the Ca(2+) signal and mediates all cellular functions regulated by Ca(2+). However, excessive Ca(2+) influx is highly toxic, resulting in cell death, which is the nodal point in all forms of pancreatitis. Ca(2+) influx is mediated by store-operated channels (SOCs). The identity and function of the native SOCs in most cells is unknown.

METHODS

Here, we determined the role of deletion of Trpc3 in mice on Ca(2+) signaling, exocytosis, intracellular trypsin activation, and pancreatitis.

RESULTS

Deletion of TRPC3 reduced the receptor-stimulated and SOC-mediated Ca(2+) influx by about 50%, indicating that TRPC3 functions as an SOC in vivo. The reduced Ca(2+) influx in TRPC3(-/-) acini resulted in reduced frequency of the physiologic Ca(2+) oscillations and of the pathologic sustained increase in cytosolic Ca(2+) levels caused by supramaximal stimulation and by the toxins bile acids and palmitoleic acid ethyl ester. Consequently, deletion of TRPC3 shifted the dose response for receptor-stimulated exocytosis and prevented the pathologic inhibition of digestive enzyme secretion at supramaximal agonist concentrations. Accordingly, deletion of TRPC3 markedly reduced intracellular trypsin activation and excessive actin depolymerization in vitro and the severity of pancreatitis in vivo.

CONCLUSIONS

These findings establish the native TRPC3 as an SOC in vivo and a role for TRPC3-mediated Ca(2+) influx in the pathogenesis of acute pancreatitis and suggest that TRPC3 should be considered a target for prevention of pancreatic damage in acute pancreatitis.

Is CD133 a marker of metastatic colon cancer stem cells?

The concept of the so-called cancer stem cell (CSC) holds that only a minority of cells within a tumor have the ability to generate a new tumor. Over the last decade, a large body of literature has implicated the protein CD133 as a marker of organ-specific adult stem cells and in some cancers as a bona fide CSC marker. In this issue of the JCI, Shmelkov et al. challenge the view that CD133 is a marker of CSCs in colon cancer (see the related article beginning on page 2111). CD133 was thought previously to have a very restricted distribution within tissues; the authors have used genetic knock-in models to demonstrate that CD133 in fact is expressed on a wide range of differentiated epithelial cells in adult mouse tissues and on spontaneous primary colon tumors in mice. In primary human colon tumors, all of the epithelial cells also expressed CD133, whereas metastatic colon cancers isolated from liver had distinct CD133+ and CD133- epithelial populations. Intriguingly, the authors demonstrate that the CD133+ and CD133- populations were equally capable of tumor initiation in xenografts. In light of these new findings, the popular notion that CD133 is a marker of colon CSCs may need to be revised.