国立情報学研究所で電子化したコンテンツを使用している。

Die Calcineurin/NFAT-Signalkaskade spielt eine wichtige Rolle bei der Entwicklung einer kardialen Hypertrophie. Im Zytoplasma von Kardiomyozyten wird die Phosphatase Calcineurin nach Stimulierung der Zellen, z. B. durch Dehnungsreize, Angiotensin II (Ang II) oder Endothelin I (ET-1), und einen daraus folgenden intrazellulären Ca2+-Strom aktiviert. Dies führt zur Dephosphorylierung von NFAT und zu dessen nukleärer Translokation. In früheren Arbeiten von Ritter et al. wurden sowohl eine nukleäre Lokalisationssequenz (NLS) als auch eine nukleäre Exportsequenz (NES) innerhalb von Calcineurin identifiziert, die den Transport von Calcineurin zwischen dem Zytoplasma und dem Nukleus ermöglichen. Basierend auf diesen Ergebnissen wurde das Import Blocking Peptid (IBP) entwickelt. Dieses Peptid entspricht der NLS von Calcineurin und blockiert die Calcineurin-Bindungsstellen des Shuttleproteins (Karyopherins) Importin β1. So wird die Translokation von Calcineurin in den Nukleus unterbunden und die Signalkaskade zur Aktivierung von Hypertrophie-Genen in Kardiomyozyten unterbrochen. Dabei blieb die Phosphatase-Aktivität von Calcineurin unbeeinflusst. Eines der Ziele dieser Arbeit war, IBP weiter zu optimieren und den „proof of principle“ auch in vivo zu führen. Hierfür wurden u. a. ein geeignetes Lösungsmittel bestimmt (biokompatibel und an die Peptidcharakteristika angepasst), die Peptidstruktur modifiziert (Erhöhung der Spezifität/Wirksamkeit) und die erforderliche Dosis weiter eingegrenzt (Belastungs- und Kostenreduktion). Unter Verwendung einer TAMRA-markierten Wirkstoffvariante konnten der Weg des Peptids in Mäusen nachverfolgt und die Ausscheidung quantifiziert werden. Aufbauend auf den Ergebnissen von Burkard et al., die die Entstehung einer konstitutiv-aktiven und nukleären Calcineurin-Isoform nach proteolytischer Spaltung durch Calpain nachwiesen, wurde die Rolle von Calcineurin im Zellkern genauer untersucht. Außerdem sollte die Frage beantwortet werden, wie (über Calcineurin?) die Herzmuskelzelle zwischen Calciumschwankungen im Zuge der Exzitations-Kontraktions-Kopplung (ECC) und vergleichsweise schwachen Calciumsignalen zur Transkriptionsteuerung unterscheidet. Mit Hilfe von nukleären Calcineurin-Mutanten, die einen Defekt in der Ca2+-Bindung aufwiesen, konnte die Bedeutung von Calcineurin als Calciumsensor für die NFAT-abhängige Transkription nachgewiesen werden. Im Mausmodell waren unter Hypertrophie-Bedingungen die Ca2+-Transienten in der nukleären Mikrodomäne signifikant stärker als im Zytosol, wodurch die Hypothese, dass die Aktivierung der Calcineurin/NFAT-Signalkaskade unabhängig von zytosolischem Ca2+ erfolgt, gestützt wird. Messungen von nukleären und zytosolischen Ca2+-Transienten in IP3-Sponge-Mäusen zeigten im Vergleich zu Wildtyp-Mäusen keine Erhöhung des Ca2+-Spiegels während der Diastole, was auf eine Rolle von Inositoltrisphosphat (IP3) in der Signalkaskade deutet. Außerdem zeigten isolierte Zellkerne ventrikulärer adulter Kardiomyozyten eine erhöhte Expression des IP3-Rezeptors 2 (IP3R2) nach Ang II-Stimulierung. Diese gesteigerte Expression war abhängig von der Calcineurin/NFAT-Kaskade und bestand sogar 3 Wochen nach Entfernung des Ang II-Stimulus fort. Zusammenfassend lässt sich sagen, dass nukleäres Calcineurin als ein Ca2+-Sensor agiert, dass die lokale Ca2+-Freisetzung im Kern über IP3-Rezeptoren detektiert wird und dass dies im Zusammenspiel mit NFAT die Transkription von Hypertrophiegenen initiiert. / The Calcineurin/NFAT signaling pathway plays an important role in the development of cardiac hypertrophy. Calcineurin is activated in the cytoplasm of cardiac myocytes by the interaction of different factors, e.g. Ang II or ET-1, with structures of the cell surface, this leads to the desphosphorylation of NFAT and its translocation into the nucleus. Previous works by the working group led to the detection of a nuclear localization sequence (NLS) and a nuclear export signal (NES) within the Calcineurin domains. They are required for the transport of Calcineurin through the nuclear membrane. Supported by these findings the import blocking peptide (IBP) was conceived. IBP mimics the NLS of Calcineurin and binds to the shuttle protein Importin β1, thereby blocking the binding sites for Calcineurin and inhibiting the transport of Calcineurin to the nucleus. One characteristic of the peptide is that it does not affect the phosphatase activity of Calcineurin. The aim of this project was to improve the peptide and to investigate its efficacy in vivo. We identified the optimal solvent and were able to significantly improve the solubility of IBP. We developed new isoforms of IBP with higher specificity. We were able to identify the minimal effective dose and studied the degradation and excretion of the substance in vivo. As shown by Burkard et al., Calcineurin is proteolytically cleaved by calpain, which leads to a constitutively active Calcineurin form. We investigated the role of this isoform in the nucleus. Furthermore, we investigated how Calcineurin is able to differentiate between Ca2+ fluctuations in the course of excitation contraction coupling (ECC) and Ca2+ signals for a hypertrophic response. Nuclear Calcineurin mutants defective for Ca2+ binding failed to activate NFAT-dependent transcription. Under hypertrophic conditions Ca2+ transients in the nuclear microdomain were significantly higher than in the cytosol providing a basis for sustained Calcineurin/NFAT mediated signaling uncoupled from cytosolic Ca2+. Measurements of nuclear and cytosolic Ca2+ transients in IP3 sponge mice showed no increase of Ca2+ levels during diastole as we detected in wildtype mice. Nuclei, isolated from ventricular myocytes of mice after chronic Ang II treatment, showed an elevation of IP3R2 expression which was dependent from calcineurin/NFAT signaling and persisted for 3 weeks after removal of the Ang II stimulus. Thus, we demonstrate that nuclear calcineurin was able to act as a nuclear Ca2+ sensor detecting local Ca2+ release from the nuclear envelope via IP3R.

Cyclosporine is a commonly used immunosuppressive drug in dogs, but dosing is often empirical and based primarily on clinical response. Pharmacokinetic monitoring of blood drug concentrations can be performed, but target blood concentrations for various disease states in dogs are not well described. Pharmacodynamic assays measuring the effects of cyclosporine on target cells are being used to evaluate immunosuppressive effectiveness in humans, but have been minimally explored in veterinary medicine. This dissertation describes the development of pharmacodynamic assays for measuring the effects of cyclosporine on canine T cell cytokine production and surface antigen expression. Incubation with cyclosporine in vitro caused significant suppression of activated T cell production of interleukin-2 (IL-2), IL-4, interferon-gamma (IFN-gamma), CD25, and CD95 measured in peripheral blood mononuclear cells using flow cytometry. IL-2 and IFN-gamma were then evaluated using flow cytometry and quantitative reverse transcription polymerase chain reaction (qRT-PCR) in whole blood incubated with cyclosporine and dexamethasone in vitro. Cyclosporine caused concentration-dependent inhibition of both cytokines, and a greater degree of suppression was noted with qRT-PCR than flow cytometry. Dexamethasone caused concentration-dependent inhibition of IFN-gamma with both methods, but IL-2 reduction was only significant for qRT-PCR. Both methods were then used to evaluate IL-2 and IFN-gamma after administration of high dose oral cyclosporine to dogs. Both qRT-PCR and flow cytometry identified marked cytokine suppression after cyclosporine dosing, but qRT-PCR was uniformly suppressed across the 12-hour dosing interval, while flow cytometry results were significantly higher at trough blood drug concentrations than at peak blood concentrations and subsequent post-dosing time points. Both flow cytometry and qRT-PCR are valid methods for evaluation of T cell cytokine expression in dogs. Further study at lower drug doses is needed to correlate pharmacodynamic results with pharmacokinetic drug concentrations, and to confirm the best method for cytokine monitoring. Studies in clinic patients are also needed to determine the level of cytokine suppression associated with clinical effectiveness in different disease states. Pharmacodynamic evaluation of cyclosporine’s effects shows promise, and may allow for more individualized dosing of cyclosporine in dogs.

Die Ca2+/Calmodulin-aktivierte Serin/Threonin-Phosphatase Calcineurin ist ein Schlüsselmolekül des T-Zell-Rezeptorabhängigen Signalnetzwerkes. Calcineurin aktiviert die Transkriptionsfaktoren der NFATc-Familie durch Dephosphorylierung und reguliert darüber die Expression wichtiger Zytokine und Oberflächenproteine. Die Aktivität von Calcineurin wird durch zahlreiche endogene Proteine moduliert und ist Angriffspunkt der immunsuppressiven Substanzen Cyclosporin A und FK506. In dieser Arbeit wurde der alternative niedermolekulare Calcineurin-NFATc-Inhibitor NCI3 hinsichtlich seiner Effekte auf T-Zell-Rezeptor-abhängige Signalwege charakterisiert. Die Ergebnisse zeigen, daß das Pyrazolopyrimidinderivat NCI3 nichttoxisch und zellmembranpermeabel ist. In T-Zell-Rezeptor-stimulierten primären humanen TH-Zellen unterdrückt NCI3 die Proliferation und IL-2-Produktion (IC50-Wert ~4 µM), da die Dephosphorylierung von NFATc und die anschließende nukleäre Translokation gehemmt wird. NCI3 inhibiert die calcineurinabhängige NFAT- und NF-κB-, aber nicht die AP-1-kontrollierte Reprtergenexpression, in mikromolaren Konzentrationen (IC50-Werte 2 bzw. 7 µM). Im Gegensatz zu Cyclosporin A stört NCI3 nicht die Phosphataseaktivität von Calcineurin, sondern interferiert mit der Calcineurin-NFATc-Bindung. Ein wichtiges endogenes Modulatorprotein für die Calcineurinaktivität ist RCAN1, das vermutlich den Calcineurin-NFATc-Signalweg über einen negativen Rückkopplungsmechanismus reguliert. Hier wurde gezeigt, daß RCAN1 in humanen TH-Zellen exprimiert wird. Die Spleißvariante RCAN1-1 ist in ruhenden T-Zellen basal exprimiert und wird nicht durch T-Zell-Rezeptor-Stimulierung in seiner Expression verändert. RCAN1-4 dagegen ist in ruhenden Zellen kaum zu detektieren und wird stimulierungsabhängig induziert. Durch die Verwendung Calcineurin-NFATc-spezifischer Inhibitoren wie NCI3 wurde gezeigt, daß die RCAN1-4-Induktion durch diesen Signalweg limitiert ist. Die in dieser Arbeit gewonnenen Daten und Erkenntnisse tragen dazu bei, das Verständnis der Funktion und Regulation von Calcineurin in T-Zellen zu vertiefen. / The Ca2+/calmodulin dependent serine/threonine phosphatase calcineurin is a key molecule in the T cell receptor dependent signalling network. Calcineurin dephosphorylates and thereby activates the transcription factors of the NFATc family that, among others, control the expression of important cytokines and cell surface molecules. The activity of Calcineurin is modulated by several endogenous proteins and is inhibited by the immunosuppressants cyclosporine A and FK506. Here, the novel low molecular weight inhibitor NCI3 was characterized in respect to its effects on T cell receptor dependent signalling. The results of this work show, that the pyrazolopyrimidine derivate NCI3 is nontoxic and permeates the cell membrane. Upon TCR stimulation NCI3 suppresses T cell proliferation and IL-2 production of primary human TH cells with IC50 values of ~4 µM by blocking the dephosphorylation and subsequent nuclear translocation of NFATc. NCI3 conse-quently inhibits calcineurin dependent NFAT- and NF-κB-, but not AP-1-controlled reporter gene expression, in micromolar concentrations (IC50 values 2 and 7 µM, respectively). In opposite to cyclosporine A and FK506, NCI3 does not interfere with the phosphatase activity of calcineurin but rather disturbs the calcineurin-NFATc interaction. A major endogenous modulator of calcineurin is the protein RCAN1, which is supposed to regulate calcineurin-NFATc signalling in a negative feedback loop. The presented data show that RCAN1 is expressed in human TH cells. The splice variant RCAN1-1 is basally expressed in resting T cells, and its expression levels are not changed by T cell receptor stimulation. Expression of RCAN1-4, on the other hand, is nearly undetectable in resting TH cells and is induced upon cell stimulation. By using calcineurin-NFATc specific inhibitors such as NCI3 it could be shown that RCAN1-4 induction is limited by this pathway. This work provides a comprehensive characterization of the novel inhibitor NCI3 and insights into the regulation of calcineurin by RCAN1 in human TH cells.

No description available.

<p>Calcineurin is both necessary and sufficient to induce cardiac hypertrophy, an independent risk factor for arrhythmia, dilated cardiomyopathy, heart failure, and sudden cardiac death. However, current knowledge of the downstream effectors of calcineurin is limited. My study utilizes <italic>Drosophila melanogaster</italic> to 1) establish a reliable model for discovering novel modifiers of calcineurin-induced cardiomyopathy; and 2) discover and characterize novel modifiers of calcineurin-induced cardiomyopathy.</p><p>In this study, I generated sensitized <italic>Drosophila</italic> lines expressing constitutively active calcineurin (CanA<super>act</super>) that was either fused to yellow fluorescent protein (YFP) or a Flag epitope (Flag-tagged) specifically in the heart using the cardiac-specific tinC driver (<italic>tinC-CanA<super>act</super></italic>). These sensitized lines displayed significant cardiac enlargement as assayed via optical coherence tomography (OCT), histology, and confocal microscopy. The feasibility of this method was established by testing <italic>Drosophila</italic> expressing deficiency of a known calcineurin modifier, Mef2. </p><p>Employing a targeted deficiency screen informed by calcineurin modifier screens in the eye and mesoderm, Galactokinase (<italic>Galk</italic>) was discovered as a novel modifier of calcineurin-induced cardiomyopathy in the fly through 1) genetic deficiencies, transposable elements, and RNAi disrupting <italic>Galk</italic> expression rescued <italic>tinC-CanA<super>act</super></italic>-induced cardiomyopathy; and 2) transposable element in <italic>Galk</italic> rescued <italic>tinC-CanA<super>act</super></italic>-induced decreased life span. Further characterization identified that the genetic disruption of <italic>Galk</italic> rescued CanA<super>act</super>-induced phenotypes driven in the posterior wing, but not ectodermaly, mesodermaly, or ubiquitously driven phenotypes. In a separate region, genetic disruption of the galactoside-binding lectin, galectin, was also found to rescue <italic>tinC-CanA<super>act</super></italic>-induced cardiac enlargement.</p><p>Together, these results characterize <italic>tinC-CanA<super>act</super></italic>-induced cardiac enlargement in the fly, establish that the <italic>tinC-CanA<super>act</super></italic> sensitized line is a reliable model for discovering novel calcineurin regulators and suggest that galactokinase and galectin-regulated glycosylation is important for calcineurin-induced cardiomyopathy. These results have the potential to provide insight into new treatments for cardiac hypertrophy.</p> / Dissertation

Traumatic brain injury is a leading cause of death and disability in the United States. The injury is often composed of two processes: the primary injury, which can involve irreversible loss of tissue, and the secondary injury, which involves a cascade of reactive processes such as excitotoxicity that occur in the hours and days after the initial insult. Excitotoxic stimulation of neuronal circuits can lead to cellular dysfunction and modulation of neuronal sensitivity. One mechanism of dysfunction involves the calcium-regulated phosphatase, calcineurin. Calcineurin has been shown to be involved in the modulation of the neuronal post-synaptic structures known as dendritic spines. One means by which CaN regulates spine structure is through the dephosphorylation of the down-stream effector proteins such as, cofilin. This study tracks the changes in CaN activity levels as well as the phosphorylation state of cofilin in the cortex and hippocampus in each hemisphere of the laterally injured brain. We report that the lateral brain injury causes an increase in CaN activity in the hippocampus with a corresponding dephosphorylation of cofilin. Trauma-induced changes in CaN follow a slightly different time course in cortical tissue, as there is a biphasic modulation of cofilin that begins with an increased phosphorylation which is followed by an extended dephosphorylation. This dephosphorylation is partially prevented by a single post-injury injection of FK506, a calcineurin inhibitor. Since dephosphorylation of cofilin is a rate-limiting step in dendritic spine collapse, the results of this study demonstrate a potential cellular mechanism through which traumatic brain injury results in altered neuronal function.

ABSTRACT MOLECULAR MECHANISMS AND GENE SIGNATURES INVOVLED IN CALCINEURIN INHIBITOR NEPHROTOXICITY IN KIDNEY ALLOGRAFT By Huong Le Diem Nguyen, M.S. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Physiology at Virginia Commonwealth University. Virginia Commonwealth University, 2011. Major Director: Valeria Mas, Ph.D. Associate Professor, Department of Surgery and Pathology Director of Molecular Transplant Research Laboratory, Division of Transplant Calcineurin inhibitors (CNI), cyclosporin A and tacrolimus, are potent immunosuppressive agents but induce toxicities causing damages and graft dysfunction, and have been suggested to contribute to late-term loss of graft in kidney transplant recipients. Even though insights on mechanism of CNI nephrotoxicity have been uncovered, prevention and treatment of these toxicities remain a major challenge in the clinical administration of CNI due to low dose-toxicity correlation, difficulty in establishing a differential patho-histological diagnosis, and varying individual susceptibility. We hypothesize that CNI nephrotoxicity follows distinct disease pathways and is characterized by significant gene signatures that differentiate it from other conditions such as acute rejection and chronic allograft dysfunction. Moreover, we postulate that CNI-induced toxicity profiles contribute to the IF/TA signatures. Microarray analysis and gene annotation were done on the study database included of tissues diagnosed with CNI nephrotoxicity (n = 9), interstitial fibrosis/tubular atrophy (IF/TA, n=10), and normal allografts (NA, n = 8). All samples were histologically classified based on the revised Banff ‘07 criteria for renal allograft pathology. Top-scored biological networks in CNI tissues were related to metabolic disease, cellular development, renal necrosis, apoptosis cell-death, immunological disease, inflammatory disease, and many others. Canonical pathway analysis emphasized oxidative stress response mediated by NRF2 and various cell-death signaling pathways including 14-3-3 signaling pathway, p53 signaling pathway, and TGF-β signaling pathway. Profiling of differentially expressed genes was done based on their statistical significance and biological relevance to the unique pathology of CNI nephrotoxicity. Among these, three genes RGS1, CXCR4, and TGIF1 were further quantitatively evaluated using real time-PCR. Between CNI group and normal allograft, t-test results showed only RGS1 gene expression level was statistically significant. Between IF/TA group in normal allograft, both RGS1 and CXCR4 showed statistical significance. The calculated relative fold changes revealed an up-regulated pattern of RGS1 and CXCR4 expression in association with pathological groups (CNI and IF/TA). We did not, however, find any association between the expression of TGIF1 in either CNI group or IF/TA group.

Calcineurin is a Ser/Thr phosphatase whose function is implicated in critical physiological processes such as immune system activation, fetal heart development, and long-term depression in neurons. Calcineurin has been implicated in the progression of Alzheimer’s disease and cardiac hypertrophy. It is not well understood how calcineurin is activated on a molecular level by Ca2+ and its activating protein calmodulin. Previous data from our lab show that calmodulin interaction induces the folding of the intrinsically disordered regulatory domain of calcineurin in two discrete and distant regions into α-helical conformations and that this folding is critical for complete activation of calcineurin. It was also discovered that one of the helical elements which we call the “distal helix” was unstable at a human body temperature of 37°C in dilute buffer. This raises the question; how can a structure critical for the complete activation of calcineurin be unstable at average human body temperature? Proteins do not exist in solutions of the dilute buffer, but rather in a crowded cosmos that ranges between 200 and 400 g/L of macromolecules such as proteins, DNA, and other cellular components. We show here that phenomenon known as macromolecular crowding can stabilize the distal helix and that stabilization increases the activity of calcineurin at human body temperature. Much about intrinsically disordered proteins (IDPs) remains a mystery, especially what influences the rate at which they interact with their target molecules. IDPs lack any sort of stable three-dimensional structure because of their lack of sufficient hydrophobic or aromatic amino acids while having a large proportion of polar and charged amino acids. Because of the high degree of charged amino acids, electrostatic forces play a significant role in their interaction other proteins. This is known to be the case for calmodulin which is net negatively charged protein that has over 300 binding targets of which are usually basic amphipathic alpha-helices. The calmodulin-binding site located in the intrinsically disordered regulatory domain of calcineurin is net positively charged, and, interestingly, is flanked by acidic patches on either side. These acidic patches might perturb attractive electrostatic forces between the calmodulin-binding site and calmodulin. Using fluorescence spectroscopy in conjunction with a stopped-flow apparatus to measure the kinetics between calmodulin and calcineurin we seek to characterize the influence of the steric and electrostatic forces between the two proteins. Also, we present data on RCAN1-4 (Regulator of Calcineurin Isoform 1-4) which has been shown to be an inhibitor in some contexts and an activator of calcineurin in other. RCAN1-4 is expressed in the heart and its upregulation has been shown to prevent calcineurin-mediated pathological cardiac hypertrophy suggesting that it plays an inhibitory role in this context. The work shown demonstrates that RCAN1-4 is a competitive inhibitor of calcineurin and whose binding affinity is modulated by Ca2+/calmodulin. These data unveil a binding site utilized by RCAN1-4 which is commonly used among other calcineurin substrates.

Mitochondria are dynamic organelles that constantly undergo opposing fission and fusion events which impact many aspects of mitochondrial and cellular homeostasis including bioenergetic activity, calcium buffering and organelle transport. The large GTPase dynamin-related protein 1 (Drp1) acts as a mechanoenzyme to catalyze fission of mitochondria. Drp1 activity is regulated through a series of reversible posttranslational modifications. Phosphorylation of the conserved serine residue, S656, by cAMP dependent protein kinase A (PKA) acts as a master regulator of Drp1 activity. Two phosphatases oppose PKA by dephosporylating Drp1 S656, a mitochondrial isoform of protein phosphatase 2A and the calcium-calmodulin dependent phosphatase calcineurin (CaN). Here I report the characterization of a conserved CaN docking site on Drp1, an LxVP motif, just upstream of the Drp1 S656 site. Mutational modification of the Drp1 LxVP motif resulted in selective bidirectional modulation of formation of the CaN:Drp1 complex. Stability of the CaN:Drp1 LxVP motif mutant complexes was qualitatively described by affinity purification and quantitatively described by isothermal titration calorimetry. Stability of the CaN:Drp1 complex was found to directly correlate with Drp1 S656 dephosphorylation kinetics as demonstrated by studies conducted in vitro and in intact cells. Further, the CaN:Drp1 signaling axis was shown to shape basal mitochondrial morphology in a heterologous cell line system and in primary hippocampal neurons. Finally, disruption of the CaN:Drp1 signaling axis was found to protect neurons from oxygen-glucose deprivation, an in vitro model of ischemic injury. While these results suggest that the CaN:Drp1 signaling axis may be a potential target for neuroprotective therapeutic exploitation, the mechanism by which disruption of the CaN:Drp1 signaling axis specifically and mitochondrial elongation generally results in resistance to ischemic injury remains unknown. Additional studies reported here demonstrate that mitochondrial fragmentation remains a prominent feature of injured neurons regardless of the fidelity of the CaN:Drp1 signaling axis. Mitochondrial fragmentation at the time of injury was found to occur in a Drp1-independent manner. Chronic mitochondrial elongation was also found to leave unaltered the ability of neurons to detoxify reactive oxygen species, buffer intracellular calcium and supply ATP for homeostatic function.