Polarized calcium signaling in exocrine gland cells

CRAC channel activity pulsates during cytosolic Ca2+ oscillations

Intracellular Ca2+ ions are used as second messengers throughout the phylogenetic tree. They are indispensable for diverse biological processes ranging from fertilization to cell death. In Metazoans, signaling information is conveyed via the amplitude, frequency and spatial profile of cytosolic Ca2+ oscillations. In non-excitable cells, these oscillations generally arise from regenerative release of Ca2+ from inositol 1,4,5-trisphosphate (InsP3)-sensitive intracellular stores, which are refilled by entry of Ca2+ through Ca2+ release-activated Ca2+ (CRAC) channels in the plasma membrane. However, the precise contribution of these store-operated CRAC channels to Ca2+ oscillations has remained controversial for decades. One view proposes that CRAC channels remain open throughout stimulation, functioning as the pacemaker in setting Ca2+ oscillation frequency. An alternative hypothesis is that channel activity oscillates in parallel with InsP3-driven regenerative Ca2+ release. Here, by tethering a genetically encoded Ca2+ indicator to the pore- forming subunit of the CRAC channel, Orai1, we distinguish between these hypotheses and demonstrate that CRAC channel activity fluctuates in phase with cytosolic Ca2+ oscillations during physiological levels of stimulation. We also find that spatially distinct CRAC channel clusters fire in a coordinated manner, revealing that CRAC channels are not independent units but might function in a synchronized manner to provide pulses of Ca2+ signal at the same time.

Redox signaling in the pancreas in health and disease

This review addresses oxidative stress and redox signaling in the pancreas under healthy physiological conditions as well as in acute pancreatitis, chronic pancreatitis, pancreatic cancer, and diabetes. Physiological redox homeodynamics is maintained mainly by NRF2/KEAP1, NF-κB, protein tyrosine phosphatases, peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α), and normal autophagy. Depletion of reduced glutathione (GSH) in the pancreas is a hallmark of acute pancreatitis and is initially accompanied by disulfide stress, which is characterized by protein cysteinylation without increased glutathione oxidation. A cross talk between oxidative stress, MAPKs, and NF-κB amplifies the inflammatory cascade, with PP2A and PGC1α as key redox regulatory nodes. In acute pancreatitis, nitration of cystathionine-β synthase causes blockade of the transsulfuration pathway leading to increased homocysteine levels, whereas p53 triggers necroptosis in the pancreas through downregulation of sulfiredoxin, PGC1α, and peroxiredoxin 3. Chronic pancreatitis exhibits oxidative distress mediated by NADPH oxidase 1 and/or CYP2E1, which promotes cell death, fibrosis, and inflammation. Oxidative stress cooperates with mutant KRAS to initiate and promote pancreatic adenocarcinoma. Mutant KRAS increases mitochondrial reactive oxygen species (ROS), which trigger acinar-to-ductal metaplasia and progression to pancreatic intraepithelial neoplasia (PanIN). ROS are maintained at a sufficient level to promote cell proliferation, while avoiding cell death or senescence through formation of NADPH and GSH and activation of NRF2, HIF-1/2α, and CREB. Redox signaling also plays a fundamental role in differentiation, proliferation, and insulin secretion of β-cells. However, ROS overproduction promotes β-cell dysfunction and apoptosis in type 1 and type 2 diabetes.

Ca2+ tunneling architecture and function are important for secretion

Ca2+ tunneling requires both store-operated Ca2+ entry (SOCE) and Ca2+ release from the endoplasmic reticulum (ER). Tunneling expands the SOCE microdomain through Ca2+ uptake by SERCA into the ER lumen where it diffuses and is released via IP3 receptors. In this study, using high-resolution imaging, we outline the spatial remodeling of the tunneling machinery (IP3R1; SERCA; PMCA; and Ano1 as an effector) relative to STIM1 in response to store depletion. We show that these modulators redistribute to distinct subdomains laterally at the plasma membrane (PM) and axially within the cortical ER. To functionally define the role of Ca2+ tunneling, we engineered a Ca2+ tunneling attenuator (CaTAr) that blocks tunneling without affecting Ca2+ release or SOCE. CaTAr inhibits Cl- secretion in sweat gland cells and reduces sweating in vivo in mice, showing that Ca2+ tunneling is important physiologically. Collectively our findings argue that Ca2+ tunneling is a fundamental Ca2+ signaling modality.

Diagnostic and Prognostic Markers for Pancreatitis and Pancreatic Ductal Adenocarcinoma

Diagnostic markers are desperately needed for the early detection of pancreatic ductal adenocarcinoma (PDA). We describe sets of markers expressed in temporal order in mouse models during pancreatitis, PDA initiation and progression. Cell type specificity and the differential expression of PDA markers were identified by screening single cell (sc) RNAseq from tumor samples of a mouse model for PDA (KIC) at early and late stages of PDA progression compared to that of a normal pancreas. Candidate genes were identified from three sources: (1) an unsupervised screening of the genes preferentially expressed in mouse PDA tumors; (2) signaling pathways that drive PDA, including the Ras pathway, calcium signaling, and known cancer genes, or genes encoding proteins that were identified by differential mass spectrometry (MS) of mouse tumors and conditioned media from human cancer cell lines; and (3) genes whose expression is associated with poor or better prognoses (PAAD, oncolnc.org). The developmental progression of PDA was detected in the temporal order of gene expression in the cancer cells of the KIC mice. The earliest diagnostic markers were expressed in epithelial cancer cells in early-stage, but not late-stage, PDA tumors. Other early markers were expressed in the epithelium of both early- and late-state PDA tumors. Markers that were expressed somewhat later were first elevated in the epithelial cancer cells of the late-stage tumors, then in both epithelial and mesenchymal cells, or only in mesenchymal cells. Stromal markers were differentially expressed in early- and/or late-stage PDA neoplasia in fibroblast and hematopoietic cells (lymphocytes and/or macrophages) or broadly expressed in cancer and many stromal cell types. Pancreatitis is a risk factor for PDA in humans. Mouse models of pancreatitis, including caerulein treatment and the acinar-specific homozygous deletion of differentiation transcription factors (dTFs), were screened for the early expression of all PDA markers identified in the KIC neoplasia. Prognostic markers associated with a more rapid decline were identified and showed differential and cell-type-specific expression in PDA, predominately in late-stage epithelial and/or mesenchymal cancer cells. Select markers were validated by immunohistochemistry in mouse and human samples of a normal pancreas and those with early- and late-stage PDA. In total, we present 2165 individual diagnostic and prognostic markers for disease progression to be tested in humans from pancreatitis to late-stage PDA.

PFKFB3 controls acinar IP3R-mediated Ca2+ overload to regulate acute pancreatitis severity

Acute pancreatitis (AP) is among the most common hospital gastrointestinal diagnoses; understanding the mechanisms underlying the severity of AP is critical for development of new treatment options for this disease. Here, we evaluate the biological function of phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) in AP pathogenesis in 2 independent genetically engineered mouse models of AP. PFKFB3 was elevated in AP and severe AP (SAP), and KO of Pfkfb3 abrogated the severity of alcoholic SAP (FAEE-SAP). Using a combination of genetic, pharmacological, and molecular studies, we defined the interaction of PFKFB3 with inositol 1,4,5-trisphosphate receptor (IP3R) as a key event mediating this phenomenon. Further analysis demonstrated that the interaction between PFKFB3 and IP3R promotes FAEE-SAP severity by altering intracellular calcium homeostasis in acinar cells. Together, our results support a PFKFB3-driven mechanism controlling AP pathobiology and define this enzyme as a therapeutic target to ameliorate the severity of this condition.

OCaR1 endows exocytic vesicles with autoregulatory competence by preventing uncontrolled Ca2+ release, exocytosis, and pancreatic tissue damage

Regulated exocytosis is initiated by increased Ca2+ concentrations in close spatial proximity to secretory granules, which is effectively prevented when the cell is at rest. Here we showed that exocytosis of zymogen granules in acinar cells was driven by Ca2+ directly released from acidic Ca2+ stores including secretory granules through NAADP-activated two-pore channels (TPCs). We identified OCaR1 (encoded by Tmem63a) as an organellar Ca2+ regulator protein integral to the membrane of secretory granules that controlled Ca2+ release via inhibition of TPC1 and TPC2 currents. Deletion of OCaR1 led to extensive Ca2+ release from NAADP-responsive granules under basal conditions as well as upon stimulation of GPCR receptors. Moreover, OCaR1 deletion exacerbated the disease phenotype in murine models of severe and chronic pancreatitis. Our findings showed OCaR1 as a gatekeeper of Ca2+ release that endows NAADP-sensitive secretory granules with an autoregulatory mechanism preventing uncontrolled exocytosis and pancreatic tissue damage.

Western diet-induced ultrastructural changes in mouse pancreatic acinar cells

Mouse models of diet-induced type 2 diabetes mellitus provide powerful tools for studying the structural and physiological changes that are related to the disease progression. In this study, diabetic-like glucose dysregulation was induced in mice by feeding them a western diet, and light and transmission electron microscopy were used to study the ultrastructural changes in the pancreatic acinar cells. Acinar necrosis and vacuolization of the cytoplasm were the most prominent features. Furthermore, we observed intracellular and extracellular accumulation of lipid compounds in the form of lipid droplets, structural enlargement of the cisternae of the rough endoplasmic reticulum (RER), and altered mitochondrial morphology, with mitochondria lacking the typical organization of the inner membrane. Last, autophagic structures, i.e., autophagosomes, autolysosomes, and residual bodies, were abundant within the acinar cells of western diet-fed mice, and the autolysosomes contained lipids and material of varying electron density. While diets inducing obesity and type 2 diabetes are clearly associated with structural changes and dysfunction of the endocrine pancreas, we here demonstrate the strong effect of dietary intervention on the structure of acinar cells in the exocrine part of the organ before detectable changes in plasma amylase activity, which may help us better understand the development of non-alcoholic fatty pancreas disease and its association with endo- and exocrine dysfunction.

Pacing intracellular Ca2+ signals in exocrine acinar cells

An increase in intracellular [Ca2+ ] in exocrine acinar cells resident in the salivary glands or pancreas is a fundamental event that drives fluid secretion and exocytosis of proteins. Stimulation with secretagogues initiates Ca2+ signals with precise spatiotemporal properties thought to be important for driving physiological output. Both in vitro, in acutely isolated acini, and in vivo, in animals expressing genetically encoded indicators, individual cells appear specialized to initiate Ca2+ signals upon stimulation. Furthermore, these signals appear to spread to neighbouring cells. These properties are present in the absence of a conventional pacemaker mechanism dependent on the cyclical activation of Ca2+ -dependent or Ca2+ -conducting plasma membrane ion channels. In this article, we propose a model for 'pacing' intracellular Ca2+ signals in acinar cells based on the enhanced sensitivity of a subpopulation of individual cells and the intercellular diffusion through gap junctions of inositol 1,4,5-trisphosphate and Ca2+ to neighbouring cells.

Pancreatitis in RYR1-related disorders

Mutations in RYR1 encoding the ryanodine receptor (RyR) skeletal muscle isoform (RyR1) are a common cause of inherited neuromuscular disorders. Despite its expression in a wide range of tissues, non-skeletal muscle manifestations associated with RYR1 mutations have only been rarely reported. Here, we report three patients with a diagnosis of Central Core Disease (CCD), King-Denborough Syndrome (KDS) and Malignant Hyperthermia Susceptibility (MHS), respectively, who in addition to their (putative) RYR1-related disorder also developed symptoms and signs of acute pancreatitis. In two patients, episodes were recurrent, with severe multisystem involvement and sequelae. RyR1-mediated calcium signalling plays an important role in normal pancreatic function but has also been critically implicated in the pathophysiology of acute pancreatitis, particularly in bile acid- and ethanol-induced forms. Findings from relevant animal models indicate that pancreatic damage in these conditions may be ameliorated through administration of the specific RyR1 antagonist dantrolene and other compounds modifying pancreatic metabolism including calcium signalling. These observations suggest that patients with RYR1 gain-of-function variants may be at increased risk of developing acute pancreatitis, a condition which should therefore be considered in the health surveillance of such individuals.

MSCs Deliver Hypoxia-Treated Mitochondria Reprogramming Acinar Metabolism to Alleviate Severe Acute Pancreatitis Injury

Mitochondrial function impairment due to abnormal opening of the mitochondrial permeability transition pore (MPTP) is considered the central event in acute pancreatitis; however, therapeutic choices for this condition remain controversial. Mesenchymal stem cells (MSCs) are a family member of stem cells with immunomodulatory and anti-inflammatory capabilities that can mitigate damage in experimental pancreatitis. Here, it is shown that MSCs deliver hypoxia-treated functional mitochondria to damaged pancreatic acinar cells (PACs) via extracellular vesicles (EVs), which reverse the metabolic function of PACs, maintain ATP supply, and exhibit an excellent injury-inhibiting effect. Mechanistically, hypoxia inhibits superoxide accumulation in the mitochondria of MSCs and upregulates the membrane potential, which is internalized into PACs via EVs, thus, remodeling the metabolic state. In addition, cargocytes constructed via stem cell denucleation as mitochondrial vectors are shown to exert similar therapeutic effects to MSCs. These findings reveal an important mechanism underlying the role of mitochondria in MSC therapy and offer the possibility of applying mitochondrial therapy to patients with severe acute pancreatitis.

Endogenous Amyloid-formed Ca2+-permeable Channels in Aged 3xTg AD Mice

Alzheimer's disease (AD), the leading cause of dementia, is characterized by the accumulation of beta-amyloid peptides (Aβ). However, whether Aβ itself is a key toxic agent in AD pathogenesis and the precise mechanism of Aβ-elicited neurotoxicity are still debated. Emerging evidence demonstrates that the Aβ channel/pore hypothesis could explain Aβ toxicity, because Aβ oligomers are able to disrupt membranes and cause edge-conductivity pores that may disrupt cell Ca2+ homeostasis and drive neurotoxicity in AD. However, all available data to support this hypothesis have been collected from "in vitro" experiments using high concentrations of exogenous Aβ. It is still unknown whether Aβ channels can be formed by endogenous Aβ in AD animal models. Here, we report an unexpected finding of the spontaneous Ca2+ oscillations in aged 3xTg AD mice but not in age-matched wild-type mice. These spontaneous Ca2+ oscillations are sensitive to extracellular Ca2+, ZnCl2, and the Aβ channel blocker Anle138b, suggesting that these spontaneous Ca2+ oscillations in aged 3xTg AD mice are mediated by endogenous Aβ-formed channels.

Characterization of Endo-Lysosomal Cation Channels Using Calcium Imaging

Endo-lysosomes are membrane-bound acidic organelles that are involved in endocytosis, recycling, and degradation of extracellular and intracellular material. The membranes of endo-lysosomes express several Ca²⁺-permeable cation ion channels, including two-pore channels (TPC1-3) and transient receptor potential mucolipin channels (TRPML1-3). In this chapter, we will describe four different state-of-the-art Ca²⁺ imaging approaches, which are well-suited to investigate the function of endo-lysosomal cation channels. These techniques include (1) global cytosolic Ca²⁺ measurements, (2) peri-endo-lysosomal Ca²⁺ imaging using genetically encoded Ca²⁺ sensors that are directed to the cytosolic endo-lysosomal membrane surface, (3) Ca²⁺ imaging of endo-lysosomal cation channels, which are engineered in order to redirect them to the plasma membrane in combination with approaches 1 and 2, and (4) Ca²⁺ imaging by directing Ca²⁺ indicators to the endo-lysosomal lumen. Moreover, we will review useful small molecules, which can be used as valuable tools for endo-lysosomal Ca²⁺ imaging. Rather than providing complete protocols, we will discuss specific methodological issues related to endo-lysosomal Ca²⁺ imaging.

Mitochondrial form and function in hair cells

Hair cells (HCs) are specialised sensory receptors residing in the neurosensory epithelia of inner ear sense organs. The precise morphological and physiological properties of HCs allow us to perceive sound and interact with the world around us. Mitochondria play a significant role in normal HC function and are also intricately involved in HC death. They generate ATP essential for sustaining the activity of ion pumps, Ca²⁺ transporters and the integrity of the stereociliary bundle during transduction as well as regulating cytosolic calcium homoeostasis during synaptic transmission. Advances in imaging techniques have allowed us to study mitochondrial populations throughout the HC, and how they interact with other organelles. These analyses have identified distinct mitochondrial populations between the apical and basolateral portions of the HC, in which mitochondrial morphology appears determined by the physiological processes in the different cellular compartments. Studies in HCs across species show that ototoxic agents, ageing and noise damage directly impact mitochondrial structure and function resulting in HC death. Deciphering the molecular mechanisms underlying this mitochondrial sensitivity, and how their morphology relates to their function during HC death, requires that we first understand this relationship in the context of normal HC function.

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.

Plasma Membrane Ca2+ ATPase Activity Enables Sustained Store-operated Ca2+ Entry in the Absence of a Bulk Cytosolic Ca2+ Rise

In many cell types, the rise in cytosolic Ca2+ due to opening of Ca2+ release-activated Ca2+ (CRAC) channels drives a plethora of responses, including secretion, motility, energy production, and gene expression. The amplitude and time course of the cytosolic Ca2+ rise is shaped by the rates of Ca2+ entry into and removal from the cytosol. However, an extended bulk Ca2+ rise is toxic to cells. Here, we show that the plasma membrane Ca2+ ATPase (PMCA) pump plays a major role in preventing a prolonged cytosolic Ca2+ signal following CRAC channel activation. Ca2+ entry through CRAC channels leads to a sustained sub-plasmalemmal Ca2+ rise but bulk Ca2+ is kept low by the activity of PMCA4b. Despite the low cytosolic Ca2+, membrane permeability to Ca2+ is still elevated and Ca2+ continues to enter through CRAC channels. Ca2+-dependent NFAT activation, driven by Ca2+ nanodomains near the open channels, is maintained despite the return of bulk Ca2+ to near pre-stimulation levels. Our data reveal a central role for PMCA4b in determining the pattern of a functional Ca2+ signal and in sharpening local Ca2+ gradients near CRAC channels, whilst protecting cells from a toxic Ca2+ overload.

Autophagy, Acute Pancreatitis and the Metamorphoses of a Trypsinogen-Activating Organelle

Recent studies have highlighted the importance of autophagy and particularly non-canonical autophagy in the development and progression of acute pancreatitis (a frequent disease with considerable morbidity and significant mortality). An important early event in the development of acute pancreatitis is the intrapancreatic activation of trypsinogen, (i.e., formation of trypsin) leading to the autodigestion of the organ. Another prominent phenomenon associated with the initiation of this disease is vacuolisation and specifically the formation of giant endocytic vacuoles in pancreatic acinar cells. These organelles develop in acinar cells exposed to several inducers of acute pancreatitis (including taurolithocholic acid and high concentrations of secretagogues cholecystokinin and acetylcholine). Notably, early trypsinogen activation occurs in the endocytic vacuoles. These trypsinogen-activating organelles undergo activation, long-distance trafficking, and non-canonical autophagy. In this review, we will discuss the role of autophagy in acute pancreatitis and particularly focus on the recently discovered LAP-like non-canonical autophagy (LNCA) of endocytic vacuoles.

Damage associated molecular patterns and neutrophil extracellular traps in acute pancreatitis

Previous researches have emphasized a trypsin-centered theory of acute pancreatitis (AP) for more than a century. With additional studies into the pathogenesis of AP, new mechanisms have been explored. Among them, the role of immune response bears great importance. Pro-inflammatory substances, especially damage-associated molecular patterns (DAMPs), play an essential role in activating, signaling, and steering inflammation. Meanwhile, activated neutrophils attach great importance to the immune defense by forming neutrophil extracellular traps (NETs), which cause ductal obstruction, premature trypsinogen activation, and modulate inflammation. In this review, we discuss the latest advances in understanding the pathological role of DAMPs and NETs in AP and shed light on the flexible crosstalk between these vital inflammatory mediators. We, then highlight the potentially promising treatment for AP targeting DAMPs and NETs, with a focus on novel insights into the mechanism, diagnosis, and management of AP.

Calcium imaging in intact mouse acinar cells in acute pancreas tissue slices

The physiology and pathophysiology of the exocrine pancreas are in close connection to changes in intra-cellular Ca²⁺ concentration. Most of our knowledge is based on in vitro experiments on acinar cells or acini enzymatically isolated from their surroundings, which can alter their structure, physiology, and limit our understanding. Due to these limitations, the acute pancreas tissue slice technique was introduced almost two decades ago as a complementary approach to assess the morphology and physiology of both the endocrine and exocrine pancreas in a more conserved in situ setting. In this study, we extend previous work to functional multicellular calcium imaging on acinar cells in tissue slices. The viability and morphological characteristics of acinar cells within the tissue slice were assessed using the LIVE/DEAD assay, transmission electron microscopy, and immunofluorescence imaging. The main aim of our study was to characterize the responses of acinar cells to stimulation with acetylcholine and compare them with responses to cerulein in pancreatic tissue slices, with special emphasis on inter-cellular and inter-acinar heterogeneity and coupling. To this end, calcium imaging was performed employing confocal microscopy during stimulation with a wide range of acetylcholine concentrations and selected concentrations of cerulein. We show that various calcium oscillation parameters depend monotonically on the stimulus concentration and that the activity is rather well synchronized within acini, but not between acini. The acute pancreas tissue slice represents a viable and reliable experimental approach for the evaluation of both intra- and inter-cellular signaling characteristics of acinar cell calcium dynamics. It can be utilized to assess many cells simultaneously with a high spatiotemporal resolution, thus providing an efficient and high-yield platform for future studies of normal acinar cell biology, pathophysiology, and screening pharmacological substances.

Science CommuniCa2+tion Developing Scientific Literacy on Calcium: The Involvement of CRAC Currents in Human Health and Disease

All human life starts with a calcium (Ca2+) wave. This ion regulates a plethora of cellular functions ranging from fertilisation and birth to development and cell death. A sophisticated system is responsible for maintaining the essential, tight concentration of calcium within cells. Intricate components of this Ca2+ network are store-operated calcium channels in the cells' membrane. The best-characterised store-operated channel is the Ca2+ release-activated Ca2+ (CRAC) channel. Currents through CRAC channels are critically dependent on the correct function of two proteins: STIM1 and Orai1. A disruption of the precise mechanism of Ca2+ entry through CRAC channels can lead to defects and in turn to severe impacts on our health. Mutations in either STIM1 or Orai1 proteins can have consequences on our immune cells, the cardiac and nervous system, the hormonal balance, muscle function, and many more. There is solid evidence that altered Ca2+ signalling through CRAC channels is involved in the hallmarks of cancer development: uncontrolled cell growth, resistance to cell death, migration, invasion, and metastasis. In this work we highlight the importance of Ca2+ and its role in human health and disease with focus on CRAC channels.

New insights into the etiology, risk factors, and pathogenesis of pancreatitis in dogs: Potential impacts on clinical practice

While most cases of pancreatitis in dogs are thought to be idiopathic, potential risk factors are identified. In this article we provide a state‐of‐the‐art overview of suspected risk factors for pancreatitis in dogs, allowing for improved awareness and detection of potential dog‐specific risk factors, which might guide the development of disease prevention strategies. Additionally, we review important advances in our understanding of the pathophysiology of pancreatitis and potential areas for therapeutic manipulation based thereof. The outcome of pathophysiologic mechanisms and the development of clinical disease is dependent on the balance between stressors and protective mechanisms, which can be evaluated using the critical threshold theory.

A microRNA checkpoint for Ca2+ signaling and overload in acute pancreatitis

Acute pancreatitis (AP) is a common digestive disease without specific treatment, and its pathogenesis features multiple deleterious amplification loops dependent on translation, triggered by cytosolic Ca2+ ([Ca2+]i) overload; however, the underlying mechanisms in Ca2+ overload of AP remains incompletely understood. Here we show that microRNA-26a (miR-26a) inhibits pancreatic acinar cell (PAC) store-operated Ca2+ entry (SOCE) channel expression, Ca2+ overload, and AP. We find that major SOCE channels are post-transcriptionally induced in PACs during AP, whereas miR-26a expression is reduced in experimental and human AP and correlated with AP severity. Mechanistically, miR-26a simultaneously targets Trpc3 and Trpc6 SOCE channels and attenuates physiological oscillations and pathological elevations of [Ca2+]i in PACs. MiR-26a deficiency increases SOCE channel expression and [Ca2+]i overload, and significantly exacerbates AP. Conversely, global or PAC-specific overexpression of miR-26a in mice ameliorates pancreatic edema, neutrophil infiltration, acinar necrosis, and systemic inflammation, accompanied with remarkable improvements on pathological determinants related with [Ca2+]i overload. Moreover, pancreatic or systemic administration of an miR-26a mimic to mice significantly alleviates experimental AP. These findings reveal a previously unknown mechanism underlying AP pathogenesis, establish a critical role for miR-26a in Ca2+ signaling in the exocrine pancreas, and identify a potential target for the treatment of AP.

Assessment of exocrine pancreatic function in children and adolescents with direct and indirect testing

The exocrine pancreas plays an important role in digestion. Understanding of the physiology and regulation of exocrine function provides insight into disease processes and basis of functional testing. Specifically, exocrine pancreatic insufficiency (EPI) can cause maldigestion and thus a proper assessment of exocrine pancreatic function is important. There are indirect and direct methods for evaluating pancreatic function. Indirect methods are varied and include stool, serum, urine, and breath tests. Fecal elastase is a commonly used indirect test today. Direct methods involve stimulated release of pancreatic fluid that is collected from the duodenum and analyzed for enzyme activity. The most used direct test today is the endoscopic pancreatic function test. Indirect pancreatic function testing is limited in identifying cases of mild to moderate EPI, and as such in these cases, direct testing has higher sensitivity and specificity in diagnosing EPI. This review provides a comprehensive guide to indirect and direct pancreatic function tests as well as an in-depth look at exocrine pancreatic function including anatomy, physiology, and regulatory mechanisms.

Regulation of pancreatic exocrine in ruminants and the related mechanism: The signal transduction and more

The unique structure of the stomach, including the rumen, reticulum, omasum, and abomasum, indicates the differences between the ruminant and monogastric animals in the digestion of nutrients. This difference is reflected in the majority of dietary nutrients that may be fermented in the rumen. Significant proteins and a certain amount of starch can flow to the small intestine apart from rumen. The initial phase of small intestinal digestion requires pancreatic digestive enzymes. In theory, the enzymatic digestion and utilization efficiency of starch in the small intestine are considerably higher than that in the rumen, but the starch digestibility in the small intestine is quite low in ruminants. Therefore, improving the digestion of nutrients, especially starch in the small intestine is more urgent for high-yield ruminants. Although the pancreas plays a central role in nutrient digestion, the progress of research investigating pancreatic exocrine regulation in the ruminant is slow due to some factors, such as the complex structure of the pancreas, the selection of experimental model and duration, and internal (hormones or ages) and external (diet) influences. The present review is based on the research findings of pancreatic exocrine regulation of dairy animals and expounded from the physiological structure of the ruminant pancreas, the factors affecting the digestion and exocrine processing of carbohydrates, and the regulatory mechanism governing this process. The review aims to better understand the characteristics of enzymatic digestion, thereby advancing pancreatic exocrine research and improving the digestion and utilization of nutrients in ruminants. Additionally, this review provides the theoretical basis for improving nutrient utilization efficiency, reducing wastage of feed resources, and promoting the efficient development of the dairy industry.

Effects of calcium‑permeable ion channels on various digestive diseases in the regulation of autophagy (Review)

Autophagy is a process of degradation and catabolism in cells. By removing damaged or dysfunctional organelles, autophagy interacts with the ubiquitin‑proteasome degradation system to jointly regulate cell function and energy homeostasis. Since autophagy plays a key role in physiology, disorders of the autophagy mechanism are associated with various diseases. Therefore, thorough understanding of the autophagy regulatory mechanism are crucially important in the diagnosis and treatment of diseases. To date, ion channels may affect the development and treatment of diseases by regulating autophagy, especially calcium‑permeable ion channels, in the process of digestive system diseases. However, the mechanism by which calcium ions and their channels regulate autophagy is still poorly understood, thus emphasizing the need for further research in this field. The present review intends to discuss the association, mechanism and application of calcium ions, their channels and autophagy in the occurrence and development of digestive system diseases.

Dual Mode of Action of Acetylcholine on Cytosolic Calcium Oscillations in Pancreatic Beta and Acinar Cells In Situ

Cholinergic innervation in the pancreas controls both the release of digestive enzymes to support the intestinal digestion and absorption, as well as insulin release to promote nutrient use in the cells of the body. The effects of muscarinic receptor stimulation are described in detail for endocrine beta cells and exocrine acinar cells separately. Here we describe morphological and functional criteria to separate these two cell types in situ in tissue slices and simultaneously measure their response to ACh stimulation on cytosolic Ca2+ oscillations [Ca2+]c in stimulatory glucose conditions. Our results show that both cell types respond to glucose directly in the concentration range compatible with the glucose transporters they express. The physiological ACh concentration increases the frequency of glucose stimulated [Ca2+]c oscillations in both cell types and synchronizes [Ca2+]c oscillations in acinar cells. The supraphysiological ACh concentration further increases the oscillation frequency on the level of individual beta cells, inhibits the synchronization between these cells, and abolishes oscillatory activity in acinar cells. We discuss possible mechanisms leading to the observed phenomena.

The roles of calcium and ATP in the physiology and pathology of the exocrine pancreas

This review deals with the roles of calcium ions and ATP in the control of the normal functions of the different cell types in the exocrine pancreas as well as the roles of these molecules in the pathophysiology of acute pancreatitis. Repetitive rises in the local cytosolic calcium ion concentration in the apical part of the acinar cells not only activate exocytosis but also, via an increase in the intramitochondrial calcium ion concentration, stimulate the ATP formation that is needed to fuel the energy-requiring secretion process. However, intracellular calcium overload, resulting in a global sustained elevation of the cytosolic calcium ion concentration, has the opposite effect of decreasing mitochondrial ATP production, and this initiates processes that lead to necrosis. In the last few years it has become possible to image calcium signaling events simultaneously in acinar, stellate, and immune cells in intact lobules of the exocrine pancreas. This has disclosed processes by which these cells interact with each other, particularly in relation to the initiation and development of acute pancreatitis. By unraveling the molecular mechanisms underlying this disease, several promising therapeutic intervention sites have been identified. This provides hope that we may soon be able to effectively treat this often fatal disease.

PAR-2-activated secretion by airway gland serous cells: role for CFTR and inhibition by Pseudomonas aeruginosa

Airway submucosal gland serous cells are important sites of fluid secretion in conducting airways. Serous cells also express the cystic fibrosis (CF) transmembrane conductance regulator (CFTR). Protease-activated receptor 2 (PAR-2) is a G protein-coupled receptor that activates secretion from intact airway glands. We tested if and how human nasal serous cells secrete fluid in response to PAR-2 stimulation using Ca²⁺ imaging and simultaneous differential interference contrast imaging to track isosmotic cell shrinking and swelling reflecting activation of solute efflux and influx pathways, respectively. During stimulation of PAR-2, serous cells exhibited dose-dependent increases in intracellular Ca²⁺. At stimulation levels >EC₅₀ for Ca²⁺, serous cells simultaneously shrank ∼20% over ∼90 s due to KCl efflux reflecting Ca²⁺-activated Cl^- channel (CaCC, likely TMEM16A)-dependent secretion. At lower levels of PAR-2 stimulation (<EC₅₀ for Ca²⁺), shrinkage was not evident due to failure to activate CaCC. Low levels of cAMP-elevating VIP receptor (VIPR) stimulation, also insufficient to activate secretion alone, synergized with low-level PAR-2 stimulation to elicit fluid secretion dependent on both cAMP and Ca²⁺ to activate CFTR and K⁺ channels, respectively. Polarized cultures of primary serous cells also exhibited synergistic fluid secretion. Pre-exposure to Pseudomonas aeruginosa conditioned media inhibited PAR-2 activation by proteases but not peptide agonists in primary nasal serous cells, Calu-3 bronchial cells, and primary nasal ciliated cells. Disruption of synergistic CFTR-dependent PAR-2/VIPR secretion may contribute to reduced airway surface liquid in CF. Further disruption of the CFTR-independent component of PAR-2-activated secretion by P. aeruginosa may also be important to CF pathophysiology.

Mechanisms and functions of calcium microdomains produced by ORAI channels, d-myo-inositol 1,4,5-trisphosphate receptors, or ryanodine receptors

With the discovery of local Ca²⁺ signals in the 1990s the concept of 'elementary Ca²⁺ signals' and 'fundamental Ca²⁺ signals' was developed. While 'elementary Ca²⁺signals' relate to optical signals gained by activity of small clusters of Ca²⁺channels, 'fundamental signals' describe such optical signals that arise from opening of single Ca²⁺channels. In this review, we discuss (i) concepts of local Ca²⁺ signals and Ca²⁺ microdomains, (ii) molecular mechanisms underlying Ca²⁺ microdomains, (iii) functions of Ca²⁺ microdomains, and (iv) mathematical modelling of Ca²⁺ microdomains. We focus on Ca²⁺ microdomains produced by ORAI channels, D-myo-inositol 1,4,5-trisphosphate receptors, or ryanodine receptors. In summary, research on local Ca²⁺ signals in different cell models aims to better understand how cells use the Ca²⁺ toolkit to produce Ca²⁺ microdomains as relevant signals for specific cellular responses, but also how local Ca²⁺ signals as building blocks merge into global Ca²⁺ signaling.

Ion Channel Signature in Healthy Pancreas and Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the fourth most common cause of cancer-related deaths in United States and Europe. It is predicted that PDAC will become the second leading cause of cancer-related deaths during the next decades. The development of PDAC is not well understood, however, studies have shown that dysregulated exocrine pancreatic fluid secretion can contribute to pathologies of exocrine pancreas, including PDAC. The major roles of healthy exocrine pancreatic tissue are secretion of enzymes and bicarbonate rich fluid, where ion channels participate to fine-tune these biological processes. It is well known that ion channels located in the plasma membrane regulate multiple cellular functions and are involved in the communication between extracellular events and intracellular signaling pathways and can function as signal transducers themselves. Hereby, they contribute to maintain resting membrane potential, electrical signaling in excitable cells, and ion homeostasis. Despite their contribution to basic cellular processes, ion channels are also involved in the malignant transformation from a normal to a malignant phenotype. Aberrant expression and activity of ion channels have an impact on essentially all hallmarks of cancer defined as; uncontrolled proliferation, evasion of apoptosis, sustained angiogenesis and promotion of invasion and migration. Research indicates that certain ion channels are involved in the aberrant tumor growth and metastatic processes of PDAC. The purpose of this review is to summarize the important expression, localization, and function of ion channels in normal exocrine pancreatic tissue and how they are involved in PDAC progression and development. As ion channels are suggested to be potential targets of treatment they are furthermore suggested to be biomarkers of different cancers. Therefore, we describe the importance of ion channels in PDAC as markers of diagnosis and clinical factors.

Calcium Signaling in Pancreatic Immune Cells In situ

Immune cells were identified in intact live mouse pancreatic lobules and their Ca²⁺ signals, evoked by various agents, characterized and compared with the simultaneously recorded Ca²⁺ signals in neighboring acinar and stellate cells. Immunochemistry in the live lobules indicated that the pancreatic immune cells most likely are macrophages. In the normal pancreas the density of these cells is very low, but induction of acute pancreatitis (AP), by a combination of ethanol and fatty acids, markedly increased the number of the immune cells. The principal agent eliciting Ca²⁺ signals in the pancreatic immune cells was ATP, but these cells also frequently produced Ca²⁺ signals in response to acetylcholine and to high concentrations of bradykinin. Pharmacological studies, using specific purinergic agonists and antagonists, indicated that the ATP-elicited Ca²⁺ signals were mediated by both P2Y1 and P2Y13 receptors. The pancreatic immune cells were not electrically excitable and the Ca²⁺ signals generated by ATP were primarily due to release of Ca²⁺ from internal stores followed by store-operated Ca²⁺ entry through Ca²⁺ release-activated Ca²⁺ channels. The ATP-induced intracellular Ca²⁺ liberation was dependent on both IP₃ generation and IP₃ receptors. We propose that the ATP-elicited Ca²⁺ signal generation in the pancreatic immune cells is likely to play an important role in the severe inflammatory response to the primary injury of the acinar cells that occurs in AP.

Calcium Oscillatory Patterns and Oocyte Activation During Fertilization: a Possible Mechanism for Total Fertilization Failure (TFF) in Human In Vitro Fertilization?

This paper reviews the effects of calcium oscillatory patterns in oocytes and early embryo development. Total fertilization failure (TFF) is the failure of fertilization in all oocytes in a human IVF cycle, even after treatment with intracytoplasmic sperm injection (ICSI). It is not well understood and currently attributed to oocyte activation deficiency. Calcium signaling is important in oocyte activation events. Calcium oscillations, in particular, have been reported in animal and human oocytes after fertilization. Abnormal calcium oscillations after fertilization may be the principal mechanism for TFF. While studies also establish strong associations between abnormal calcium oscillatory patterns and suboptimal developmental outcomes, critical basic parameters and their mechanism of action have yet to be identified. Empirical use of artificial oocyte activation (AOA) methods has shown initial success in helping patients overcome TFF. The AOA methods attempt to raise calcium levels after fertilization, but the efficacy and safety of these AOA methods are still in early stages of addressing TFF. Additional information about calcium oscillatory patterns and the effects of AOA in human ART may allow the prevention of TFF or allow treatment of TFF patients effectively and safely.

Heparanase in Acute Pancreatitis

Acute pancreatitis (AP) is one of the most common diseases in gastroenterology, affecting 2% of all hospitalized patients. Nevertheless, neither the etiology nor the pathophysiology of the disease is fully characterized, and no specific or effective treatment has been developed. Heparanase (Hpa) is an endoglycosidase that cleaves heparan sulfate (HS) side chains of heparan sulfate proteoglycans (HSPGs) into shorter oligosaccharides, activity that is highly implicated in cell invasion associated with cancer metastasis and inflammation. Given that AP is a typical inflammatory disease, we investigated whether Hpa plays a role in AP. Our results provide keen evidence that Hpa expression and activity are significantly increased following cerulein-induced AP in wild type mice. In parallel to the classic manifestations of AP, namely elevation of amylase and lipase levels, pancreas edema and inflammation as well as induction of cytokines and signaling molecules, have been detected in this experimental model of the disease. Noteworthy, these features were far more profound in transgenic mice overexpressing heparanase (Hpa-Tg), suggesting that these mice can be utilized as a model system to reveal the molecular mechanism by which Hpa functions in AP. Further support for the involvement of Hpa in the pathogenesis of AP emerged from our observation that treatment of experimental AP with PG545 or SST0001(= Ronepastat), two potent Hpa inhibitors, markedly attenuated the biochemical, histological and immunological manifestations of the disease. Hpa, therefore, emerges as a potential new target in AP, and Hpa inhibitors are hoped to prove beneficial in AP along with their promising efficacy as anti-cancer compounds.

LAP-like non-canonical autophagy and evolution of endocytic vacuoles in pancreatic acinar cells

Activation of trypsinogen (formation of trypsin) inside the pancreas is an early pathological event in the development of acute pancreatitis. In our previous studies we identified the activation of trypsinogen within endocytic vacuoles (EVs), cellular organelles that appear in pancreatic acinar cells treated with the inducers of acute pancreatitis. EVs are formed as a result of aberrant compound exocytosis and subsequent internalization of post-exocytic structures. These organelles can be up to 12 μm in diameter and can be actinated (i.e. coated with F-actin). Notably, EVs can undergo intracellular rupture and fusion with the plasma membrane, providing trypsin with access to cytoplasmic and extracellular targets. Unraveling the mechanisms involved in cellular processing of EVs is an interesting cell biological challenge with potential benefits for understanding acute pancreatitis. In this study we have investigated autophagy of EVs and discovered that it involves a non-canonical LC3-conjugation mechanism, reminiscent in its properties to LC3-associated phagocytosis (LAP); in both processes LC3 was recruited to single, outer organellar membranes. Trypsinogen activation peptide was observed in approximately 55% of LC3-coated EVs indicating the relevance of the described process to the early cellular events of acute pancreatitis. We also investigated relationships between actination and non-canonical autophagy of EVs and concluded that these processes represent sequential steps in the evolution of EVs. Our study expands the known roles of LAP and indicates that, in addition to its well-established functions in phagocytosis and macropinocytosis, LAP is also involved in the processing of post-exocytic organelles in exocrine secretory cells.

ABBREVIATIONS

AP: acute pancreatitis; CCK: cholecystokinin; CLEM: correlative light and electron microscopy; DPI: diphenyleneiodonium; EV: endocytic vacuole; LAP: LC3-associate phagocytosis; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; PACs: pancreatic acinar cells; PFA: paraformaldehyde; PtdIns3K: phosphatidylinositol 3-kinase; PtdIns3P: phosphatidylinositol 3-phosphate; Res: resveratrol; TAP: trypsinogen activation peptide; TEM: transmission electron microscopy; TLC-S: taurolithocholic acid 3-sulfate; TRD: Dextran Texas Red 3000 MW Neutral; ZGs: zymogen granules.

Knockout of the Mitochondrial Calcium Uniporter Strongly Suppresses Stimulus-Metabolism Coupling in Pancreatic Acinar Cells but Does Not Reduce Severity of Experimental Acute Pancreatitis

Acute pancreatitis is a frequent disease that lacks specific drug treatment. Unravelling the molecular mechanisms of acute pancreatitis is essential for the development of new therapeutics. Several inducers of acute pancreatitis trigger sustained Ca²⁺ increases in the cytosol and mitochondria of pancreatic acinar cells. The mitochondrial calcium uniporter (MCU) mediates mitochondrial Ca²⁺ uptake that regulates bioenergetics and plays an important role in cell survival, damage and death. Aberrant Ca²⁺ signaling and mitochondrial damage in pancreatic acinar cells have been implicated in the initiation of acute pancreatitis. The primary aim of this study was to assess the involvement of the MCU in experimental acute pancreatitis. We found that pancreatic acinar cells from MCU^-/- mice display dramatically reduced mitochondrial Ca²⁺ uptake. This is consistent with the drastic changes of stimulus-metabolism coupling, manifested by the reduction of mitochondrial NADH/FAD⁺ responses to cholecystokinin and in the decrease of cholecystokinin-stimulated oxygen consumption. However, in three experimental models of acute pancreatitis (induced by caerulein, taurolithocholic acid 3-sulfate or palmitoleic acid plus ethanol), MCU knockout failed to reduce the biochemical and histological changes characterizing the severity of local and systemic damage. A possible explanation of this surprising finding is the redundancy of damaging mechanisms activated by the inducers of acute pancreatitis.

T cell exosome-derived miR-142-3p impairs glandular cell function in Sjögren's syndrome

Sjögren's syndrome (SS) is a systemic autoimmune disease that mainly affects exocrine salivary and lacrimal glands. Local inflammation in the glands is thought to trigger glandular dysfunction and symptoms of dryness. However, the mechanisms underlying these processes are incompletely understood. Our work suggests T cell exosome-derived miR-142-3p as a pathogenic driver of immunopathology in SS. We first document miR-142-3p expression in the salivary glands of patients with SS, both in epithelial gland cells and within T cells of the inflammatory infiltrate, but not in healthy volunteers. Next, we show that activated T cells secreted exosomes containing miR-142-3p, which transferred into glandular cells. Finally, we uncover a functional role of miR-142-3p-containing exosomes in glandular cell dysfunction. We find that miR-142-3p targets key elements of intracellular Ca2+ signaling and cAMP production - sarco(endo)plasmic reticulum Ca2+ ATPase 2b (SERCA2B), ryanodine receptor 2 (RyR2), and adenylate cyclase 9 (AC9) - leading to restricted cAMP production, altered calcium signaling, and decreased protein production from salivary gland cells. Our work provides evidence for a functional role of the miR-142-3p in SS pathogenesis and promotes the concept that T cell activation may directly impair epithelial cell function through secretion of miRNA-containing exosomes.

Pancreatic Cancer and Its Microenvironment-Recent Advances and Current Controversies

Pancreatic ductal adenocarcinoma (PDAC) causes annually well over 400,000 deaths world-wide and remains one of the major unresolved health problems. This exocrine pancreatic cancer originates from the mutated epithelial cells: acinar and ductal cells. However, the epithelia-derived cancer component forms only a relatively small fraction of the tumor mass. The majority of the tumor consists of acellular fibrous stroma and diverse populations of the non-neoplastic cancer-associated cells. Importantly, the tumor microenvironment is maintained by dynamic cell-cell and cell-matrix interactions. In this article, we aim to review the most common drivers of PDAC. Then we summarize the current knowledge on PDAC microenvironment, particularly in relation to pancreatic cancer therapy. The focus is placed on the acellular stroma as well as cell populations that inhabit the matrix. We also describe the altered metabolism of PDAC and characterize cellular signaling in this cancer.

TRPV4 channel opening mediates pressure-induced pancreatitis initiated by Piezo1 activation

Elevated pressure in the pancreatic gland is the central cause of pancreatitis following abdominal trauma, surgery, endoscopic retrograde cholangiopancreatography, and gallstones. In the pancreas, excessive intracellular calcium causes mitochondrial dysfunction, premature zymogen activation, and necrosis, ultimately leading to pancreatitis. Although stimulation of the mechanically activated, calcium-permeable ion channel Piezo1 in the pancreatic acinar cell is the initial step in pressure-induced pancreatitis, activation of Piezo1 produces only transient elevation in intracellular calcium that is insufficient to cause pancreatitis. Therefore, how pressure produces a prolonged calcium elevation necessary to induce pancreatitis is unknown. We demonstrate that Piezo1 activation in pancreatic acinar cells caused a prolonged elevation in intracellular calcium levels, mitochondrial depolarization, intracellular trypsin activation, and cell death. Notably, these effects were dependent on the degree and duration of force applied to the cell. Low or transient force was insufficient to activate these pathological changes, whereas higher and prolonged application of force triggered sustained elevation in intracellular calcium, leading to enzyme activation and cell death. All of these pathological events were rescued in acinar cells treated with a Piezo1 antagonist and in acinar cells from mice with genetic deletion of Piezo1. We discovered that Piezo1 stimulation triggered transient receptor potential vanilloid subfamily 4 (TRPV4) channel opening, which was responsible for the sustained elevation in intracellular calcium that caused intracellular organelle dysfunction. Moreover, TRPV4 gene-KO mice were protected from Piezo1 agonist- and pressure-induced pancreatitis. These studies unveil a calcium signaling pathway in which a Piezo1-induced TRPV4 channel opening causes pancreatitis.

Influence of spatially segregated IP3-producing pathways on spike generation and transmitter release in Purkinje cell axons

It has been known for a long time that inositol-trisphosphate (IP₃) receptors are present in the axon of certain types of mammalian neurons, but their functional role has remained unexplored. Here we show that localized photolysis of IP₃ induces spatially constrained calcium rises in Purkinje cell axons. Confocal immunohistology reveals that the axon initial segment (AIS), as well as terminals onto deep cerebellar cells, express specific subtypes of Gα/q and phospholipase C (PLC) molecules, together with the upstream purinergic receptor P2Y1. By contrast, intermediate parts of the axon express another set of Gα/q and PLC molecules, indicating two spatially segregated signaling cascades linked to IP₃ generation. This prompted a search for distinct actions of IP₃ in different parts of Purkinje cell axons. In the AIS, we found that local applications of the specific P2Y1R agonist MRS2365 led to calcium elevation, and that IP₃ photolysis led to inhibition of action potential firing. In synaptic terminals on deep cerebellar nuclei neurons, we found that photolysis of both IP₃ and ATP led to GABA release. We propose that axonal IP₃ receptors can inhibit action potential firing and increase neurotransmitter release, and that these effects are likely controlled by purinergic receptors. Altogether our results suggest a rich and diverse functional role of IP₃ receptors in axons of mammalian neurons.

Ca2+ Signaling in Exocrine Cells

Calcium (Ca²⁺) and cyclic AMP (cAMP) signaling cross talk and synergize to stimulate the cardinal functions of exocrine cells, regulated exocytosis, and fluid and electrolyte secretion. This physiological process requires the organization of the two signaling pathways into complexes at defined cellular domains and close placement. Such domains are formed by membrane contact sites (MCS). This review discusses the basic properties of Ca²⁺ signaling in exocrine cells, the role of MCS in the organization of cell signaling and in cross talk and synergism between the Ca²⁺ and cAMP signaling pathways and, finally, the mechanism by which the Ca²⁺ and cAMP pathways synergize to stimulate epithelial fluid and electrolyte secretion.

Signaling in the Physiology and Pathophysiology of Pancreatic Stellate Cells - a Brief Review of Recent Advances

The interest in pancreatic stellate cells (PSCs) has been steadily growing over the past two decades due mainly to the central role these cells have in the desmoplastic reaction associated with diseases of the pancreas, such as pancreatitis or pancreatic cancer. In recent years, the scientific community has devoted substantial efforts to understanding the signaling pathways that govern PSC activation and interactions with neoplastic cells. This mini review aims to summarize some very recent findings on signaling in PSCs and highlight their impact to the field.

The Endoplasmic Reticulum-Plasma Membrane Junction: A Hub for Agonist Regulation of Ca2+ Entry

Stimulation of cell-surface receptors induces cytosolic Ca²⁺ ([Ca²⁺]_i) increases that are detected and transduced by effector proteins for regulation of cell function. Intracellular Ca²⁺ release, via endoplasmic reticulum (ER) proteins inositol 1,4,5-trisphosphate receptors (IP₃R) and ryanodine receptors (RyR), and Ca²⁺ influx, via store-operated Ca²⁺ entry (SOCE), contribute to the increase in [Ca²⁺]_i The amplitude, frequency, and spatial characteristics of the [Ca²⁺]_i increases are controlled by the compartmentalization of proteins into signaling complexes such as receptor-signaling complexes and SOCE complexes. Both complexes include protein and lipid components, located in the plasma membrane (PM) and ER. Receptor signaling initiates in the PM via phospholipase C (PLC)-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP₂), and culminates with the activation of IP₃R in the ER. Conversely, SOCE is initiated in the ER by Ca²⁺-sensing stromal interaction molecule (STIM) proteins, which then interact with PM channels Orai1 and TRPC1 to activate Ca²⁺ entry. This review will address how ER-PM junctions serve a central role in agonist regulation of SOCE.

Regulation of Membrane Calcium Transport Proteins by the Surrounding Lipid Environment

Calcium ions (Ca2+) are major messengers in cell signaling, impacting nearly every aspect of cellular life. Those signals are generated within a wide spatial and temporal range through a large variety of Ca2+ channels, pumps, and exchangers. More and more evidences suggest that Ca2+ exchanges are regulated by their surrounding lipid environment. In this review, we point out the technical challenges that are currently being overcome and those that still need to be defeated to analyze the Ca2+ transport protein-lipid interactions. We then provide evidences for the modulation of Ca2+ transport proteins by lipids, including cholesterol, acidic phospholipids, sphingolipids, and their metabolites. We also integrate documented mechanisms involved in the regulation of Ca2+ transport proteins by the lipid environment. Those include: (i) Direct interaction inside the protein with non-annular lipids; (ii) close interaction with the first shell of annular lipids; (iii) regulation of membrane biophysical properties (e.g., membrane lipid packing, thickness, and curvature) directly around the protein through annular lipids; and (iv) gathering and downstream signaling of several proteins inside lipid domains. We finally discuss recent reports supporting the related alteration of Ca2+ and lipids in different pathophysiological events and the possibility to target lipids in Ca2+-related diseases.

Evaluation of the Relative Performance of Pancreas-Specific MicroRNAs in Rat Plasma as Biomarkers of Pancreas Injury

Drug-induced pancreatic injury (DIPI) has become linked in recent years to many commonly prescribed medications from several pharmacological classes. Diagnosis is currently most often focused on identification of acute pancreatitis and generally based on subjective clinical assessment and serum amylase and lipase enzymatic activity, which have been criticized as being insufficiently sensitive and specific. The lack of novel noninvasive biomarkers of DIPI can impede the advancement of drug candidates through nonclinical development and translation into clinical settings. Pancreas-specific microRNAs (miRNAs) are currently being evaluated as biomarkers of DIPI that may outperform and/or add value to the interpretation of amylase and lipase. To assess the relative performance of these novel miRNAs, a comprehensive evaluation was conducted to determine the sensitivity and specificity of detecting DIPI in rats. Four miRNAs were evaluated (miR-216a-5p, miR-216b-5p, miR-217-5p, and miR-375-3p) in plasma from 10 studies in which rats were treated with known pancreatic toxicants to assess sensitivity, and from 10 different studies in which toxicity was evident in tissues other than pancreas to assess specificity. The candidate miRNA biomarker performance was compared with amylase and lipase, and receiver operator characteristics (ROC) were determined. Analysis of ROCs demonstrated that all four miRNAs outperformed amylase and lipase in monitoring acute pancreatic injury defined as acinar cell degeneration/necrosis. Specifically, miR-217-5p had the highest performance among all biomarkers assessed. The increased sensitivity and specificity of these miRNAs support their use as biomarkers of DIPI, thereby adding value to the interpretation of amylase and lipase measurements in nonclinical studies. The potential for miRNAs to serve as translational biomarkers in the clinic for the monitoring of DIPI is also supported by this investigation.

Selective recruitment of different Ca2+-dependent transcription factors by STIM1-Orai1 channel clusters

Store-operated Ca2+ entry, involving endoplasmic reticulum Ca2+ sensing STIM proteins and plasma membrane Orai1 channels, is a widespread and evolutionary conserved Ca2+ influx pathway. This form of Ca2+ influx occurs at discrete loci where peripheral endoplasmic reticulum juxtaposes the plasma membrane. Stimulation evokes numerous STIM1-Orai1 clusters but whether distinct signal transduction pathways require different cluster numbers is unknown. Here, we show that two Ca2+-dependent transcription factors, NFAT1 and c-fos, have different requirements for the number of STIM1-Orai1 clusters and on the Ca2+ flux through them. NFAT activation requires fewer clusters and is more robustly activated than c-fos by low concentrations of agonist. For similar cluster numbers, transcription factor recruitment occurs sequentially, arising from intrinsic differences in Ca2+ sensitivities. Variations in the number of STIM1-Orai1 clusters and Ca2+ flux through them regulate the robustness of signalling to the nucleus whilst imparting a mechanism for selective recruitment of different Ca2+-dependent transcription factors.

Study on PREP localization in mouse seminal vesicles and its possible involvement during regulated exocytosis

SummaryProlyl endopeptidase (PREP) is a post-proline cleaving enzyme. It is involved in the regulation of multiple inositol polyphosphate phosphatase activity implicated in the pathway of inositol 1,4,5-trisphosphate, resulting in the modulation of cytosolic Ca2+ levels. Besides its peptidase activity, PREP was identified as a binding partner of tubulin, suggesting that it may participate in microtubule-associate processes. In this paper, we evaluated the expression of PREP mRNA and protein by polymerase chain reaction and western blot analyses and its co-localization with tubulin by immunofluorescence in adult mouse seminal vesicles. We showed that both proteins are cytoplasmic: tubulin is localized at the apical half part of the cell, while PREP has a more diffuse localization, showing a prominent distribution at the apical cytoplasm. These findings support our hypothesis of a specific role for PREP in cytoskeletal rearrangement that occurs during the exocytosis of secretory vesicles, and in particular its association with tubulin filaments. Moreover, it may regulate Ca2+ levels, and promote the final step of vesicular exocytosis, namely the fusion of the vesicles with the plasma membrane. These results strongly suggest that there is a pivotal role for PREP in vesicle exocytosis, as well as in the physiology of mouse seminal vesicles.

Associations between gastrointestinal humoral factors and pancreatic proteolytic enzymes in alcohol-related versus non-alcohol-related pancreatitis

BACKGROUND

Alcohol-related pancreatitis is common and the gastrointestinal tract plays an important role in the regulation of pancreatic exocrine function. While the relationship between pancreatic proteolytic enzymes and insulin (as well as other pancreatic hormones) has been investigated in detail, little is known about the relationship between pancreatic proteolytic enzymes and gastrointestinal humoral factors. The aim of this study was to study the associations between trypsin, chymotrypsin, and a panel of gastrointestinal humoral factors in patients after an episode of alcohol-related versus non-alcohol-related pancreatitis.

METHODS

Fasting venous blood samples were analyzed for trypsin, chymotrypsin, cholecystokinin, gastrin, ghrelin, gastrin-related peptide, neuropeptide Y, peptide YY, secretin, and vasoactive intestinal peptide. Linear regression analysis was used in three statistical models, adjusting for covariates (age, sex, ethnicity, smoking, exercise, body mass index, dysglycemia, recurrence of pancreatitis, duration of pancreatitis, and severity of pancreatitis).

RESULTS

The study included 21 patients with alcohol-related pancreatitis and 72 with non-alcohol-related pancreatitis. Gastrin, cholecystokinin, and vasoactive intestinal peptide were significantly associated with chymotrypsin in all three statistical models and resulted in a 1.06, 1.98, and 2.74 times higher chymotrypsin level in alcohol-related pancreatitis, respectively. Ghrelin was significantly associated with trypsin in all three statistical models and resulted in a 2.64 times higher trypsin level in alcohol-related pancreatitis. Other associations did not demonstrate a consistent significant pattern.

CONCLUSION

In alcohol-related pancreatitis, several gut-related peptides are significantly associated with pancreatic exocrine function. Further studies to investigate the effect of alcohol on the interaction between cholecystokinin (as well as gastrin, ghrelin, and vasoactive intestinal peptide) and pancreatic exocrine function are warranted.