La régulation du calcium intracellulaire et son rôle dans la signalisation des phagocytes

Le contrôle des fonctions des neutrophiles humains dépend de plusieurs voies de signalisation où la signalisation calcique joue un rôle prépondérant. Celle-ci est basée sur une entrée de calcium extracellulaire consécutive à une déplétion des réservoirs calciques intracellulaires (SOCE). Ces entrées calciques dites capacitives sont régulées par des canaux ioniques (SOC) qui constituent des cibles thérapeutiques potentielles. Un nouvel inhibiteur des influx calciques a été développé chez les lymphocytes: le BTP2 (3,5-bistrifluomethyle pyrazole). Nous avons cherché à savoir si le BTP2 agissait sur des cellules HL60 différenciées et sur des neutrophiles humains. Nos résultats montrent que le BTP2 réduit significativement les entrées SOCE. De plus, le BTP2 inhibe l'exocytose d'enzymes microbicides, ainsi que la libération d'espèces oxygénées réactives (ROS). Par contre, le BTP2 n'affecte pas significativement les fonctions bactéricides importantes des granulocytes : la production intra-phagosomale de ROS, la phagocytose et la destruction de bactéries Pseudomonas aeruginosa. Certaines études suggèrent que le BTP2 agirait sur les canaux SOC constitués en particulier de protéines TRPC. Nous avons donc étudié chez les granulocytes l'expression des ARNm des protéines TRPC. Une expression différentielle a pu être corrélée à des changements de sensibilité au BTP2. Ce dernier est donc un nouvel outil qui pourrait permettre de mettre en évidence le rôle de la signalisation calcique chez les granulocytes afin de développer de nouvelles stratégies thérapeutiques dans le cadre de maladies inflammatoires chroniques.Store operated calcium entry (SOCE) is a key regulator in the activation of leukocytes. This calcium entry is regulated by SOC channels. A new inhibitor of SOCE, the BTP2 (3,5-bistrifluoromethyl pyrazole) has been identified in T lymphocytes. We therefore investigated the effect of BTP2 on calcium homeostasis and functional responses of human neutrophils. BTP2 significantly inhibited the calcium influx after stimulation with thapsigargin or fMLF. BTP2 reduced microbicidal enzyme release and superoxide anion production. On the contrary, phagocytosis, intraphagosomal radical production and bacterial killing by neutrophils were not significantly reduced. We studied TRPC mRNA expression during granulocyte differentiation; their presence changes during myelocyte differentiation. We also investigated whether these changes of gene expression are correlated with a change of BTP2 impact on store operated calcium influx. Our results suggest that differentiated HL60 cells and neutrophils are more sensitive to BTP2 than undifferentiated HL60 cells. This work suggests that BTP2 could become an important tool to characterize calcium signaling in neutrophils. Furthermore, BTP2 or related compounds could constitute a new approach to the down regulation of neutrophils in chronic inflammatory disease without compromising antibacterial host defense.NANCY1-SCD Sciences & Techniques (545782101) / SudocSudocFranceF

An essential role of STIM1, Orai1, and S100A8-A9 proteins for Ca2+ signaling and FcγR-mediated phagosomal oxidative activity

Phagocytosis is a process of innate immunity that allows for the enclosure of pathogens within the phagosome and their subsequent destruction through the production of reactive oxygen species (ROS). Although these processes have been associated with increases of intracellular Ca(2+) concentrations, the mechanisms by which Ca(2+) could regulate the different phases of phagocytosis remain unknown. The aim of this study was to investigate the Ca(2+) signaling pathways involved in the regulation of FcγRs-induced phagocytosis. Our work focuses on IgG-opsonized zymosan internalization and phagosomal ROS production in DMSO-differentiated HL-60 cells and neutrophils. We found that chelation of intracellular Ca(2+) by BAPTA or emptying of the intracellular Ca(2+) store by thapsigargin reduced the efficiency of zymosan internalization. Using an small interfering RNA strategy, our data establish that the observed Ca(2+) release occurs through two isoforms of inositol 1,4,5-triphosphate receptors, ITPR1 and ITPR3. In addition, we provide evidence that phagosomal ROS production is dependent on extracellular Ca(2+) entry. We demonstrate that the observed Ca(2+) influx is supported by ORAI calcium release-activated calcium modulator 1 (Orai1) and stromal interaction molecule 1 (STIM1). This result suggests that extracellular Ca(2+) entry, which is required for ROS production, is mediated by a store-operated Ca(2+) mechanism. Finally, our data identify the complex formed by S100A8 and S100A9 (S100 calcium-binding protein A8 and A9 complex), two Ca(2+)-binding proteins, as the site of interplay between extracellular Ca(2+) entry and intraphagosomal ROS production. Thus, we demonstrate that FcγR-mediated phagocytosis requires intracellular Ca(2+) store depletion for the internalization phase. Then phagosomal ROS production requires extracellular Ca(2+) entry mediated by Orai1/STIM1 and relayed by S100A8-A9 as Ca(2+) sensor

Potent inhibition of store-operated Ca2+ influx and superoxide production in HL60 cells and polymorphonuclear neutrophils by the pyrazole derivative BTP2.: BTP2 inhibits calcium influx in neutrophils

International audienceStore-operated calcium entry (SOCE) is a key regulator in the activation of leukocytes. 3,5-Bistrifluoromethyl pyrazole (BTP) derivatives have been identified recently as inhibitors of T lymphocyte activation. The inhibitory effect of one of these compounds, N-(4-[3,5-bis(trifluoromethyl)-1H-pyrazol-1-yl]phenyl)-4-methyl-1,2,3-thiadiazole-5-carboxamide (BTP2), appears to be a result of inhibition of SOC influx. Polymorphonuclear neutrophils provide effective protection against bacterial infection, but they are also involved in tissue damage during chronic inflammation. As for T lymphocytes, their activation relies on SOCE. We therefore investigated the effect of BTP2 on calcium homeostasis and functional responses of human neutrophils. BTP2 significantly inhibited the calcium influx after stimulation with thapsigargin or fMLF. This inhibition was seen after 5 min of incubation with 10 microM BTP2 and after 24 h with lower concentrations. With 24 h incubation, the effect appeared irreversible, as the removal of BTP2 3 h before the experiment did not reduce this inhibition in granulocyte-differentiated HL60 cells. In human neutrophils, BTP2 reduced superoxide anion production by 82% after 24 h of incubation. On the contrary, phagocytosis, intraphagosomal radical production, and bacterial killing by neutrophils were not reduced significantly, even after 24 h treatment with 10 microM BTP2. This work suggests that BTP2 could become an important tool to characterize calcium signaling in neutrophils. Furthermore, BTP2 or related compounds could constitute a new approach to the down-regulation of neutrophils in chronic inflammatory disease without compromising antibacterial host defense

The functions of store-operated calcium channels

Store-operated calcium channels provide calcium signals to the cytoplasm of a wide variety of cell types. The basic components of this signaling mechanism include a mechanism for discharging Ca stores (commonly but not exclusively phospholipase C and inositol 1,4,5-trisphosphate), a sensor in the endoplasmic reticulum that also serves as an activator of the plasma membrane channel (STIM1 and STIM2), and the store-operated channel (Orai1, 2 or 3). The advent of mice genetically altered to reduce store-operated calcium entry globally or in specific cell types has provided important tools to understand the functions of these widely encountered channels in specific and clinically important physiological systems. This review briefly discusses the history and cellular properties of store-operated calcium channels, and summarizes selected studies of their physiological functions in specific physiological or pathological contexts. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech

Essential role of Orai1 store-operated calcium channels in lactation

The nourishment of neonates by nursing is the defining characteristic of mammals. However, despite considerable research into the neural control of lactation, an understanding of the signaling mechanisms underlying the production and expulsion of milk by mammary epithelial cells during lactation remains largely unknown. Here we demonstrate that a store-operated Ca2+ channel subunit, Orai1, is required for both optimal Ca2+ transport into milk and for milk ejection. Using a novel, 3D imaging strategy, we visualized live oxytocin-induced alveolar unit contractions in the mammary gland, and we demonstrated that in this model milk is ejected by way of pulsatile contractions of these alveolar units. In mammary glands of Orai1 knockout mice, these contractions are infrequent and poorly coordinated. We reveal that oxytocin also induces a large transient release of stored Ca2+ in mammary myoepithelial cells followed by slow, irregular Ca2+ oscillations. These oscillations, and not the initial Ca2+ transient, are mediated exclusively by Orai1 and are absolutely required for milk ejection and pup survival, an observation that redefines the signaling processes responsible for milk ejection. These findings clearly demonstrate that Ca2+ is not just a substrate for nutritional enrichment in mammals but is also a master regulator of the spatiotemporal signaling events underpinning mammary alveolar unit contraction. Orai1-dependent Ca2+ oscillations may represent a conserved language in myoepithelial cells of other secretory epithelia, such as sweat glands, potentially shedding light on other Orai1 channelopathies, including anhidrosis (an inability to sweat)