No

Calcium imaging has been used as a promising technique to monitor the dynamic activity of neuronal populations. However, the calcium trace is temporally smeared which restricts the extraction of quantities of interest such as spike trains of individual neurons. To address this issue, spike reconstruction algorithms have been introduced. One limitation of such reconstructions is that the underlying models are not informed about the biophysics of spike and burst generations. Such existing prior knowledge might be useful for constraining the possible solutions of spikes. Here we describe, in a novel Bayesian approach, how principled knowledge about neuronal dynamics can be employed to infer biophysical variables and parameters from fluorescence traces. By using both synthetic and in vitro recorded fluorescence traces, we demonstrate that the new approach is able to reconstruct different repetitive spiking and/or bursting patterns with accurate single spike resolution. Furthermore, we show that the high inference precision of the new approach is preserved even if the fluorescence trace is rather noisy or if the fluorescence transients show slow rise kinetics lasting several hundred milliseconds, and inhomogeneous rise and decay times. In addition, we discuss the use of the new approach for inferring parameter changes, e.g. due to a pharmacological intervention, as well as for inferring complex characteristics of immature neuronal circuits.

Le canal calcique de type-L CaV1.2 participe au couplage excitation-contraction des cardiomyocytes. Cav1.2 est composé d’une sous-unité principale CaVα1, associée aux sous-unités auxiliaires CaVβ et CaVα2δ1. Lorsque présente à la membrane, c’est CaVα2δ1 qui est responsable de moduler la densité du courant calcique. Elle ne possède qu’un seul segment transmembranaire présent du côté C-terminal, au niveau de la protéine δ, ce qui en fait une protéine transmembranaire de type I. Certaines protéines qui appartiennent à cette famille doivent être clivées au niveau du site dit « omega », une modification post-traductionnelle nécessaire à leur fonction. Une fois clivées, ces protéines sont retenues à la membrane plasmique par une ancre glycosyl-phosphatidyl-inositol (GPI). Nos études en microscopie confocale montrent que la protéine sauvage est sensible à l’action de la phospholipase C qui clive de manière spécifique les groupements phosphoinositol, ce qui est compatible avec la présence d’une ancre GPI fonctionnelle. De plus, la mutation des résidus formant le site « omega » en isoleucine au niveau des sites G1060 et G1061 prévient l’adressage membranaire de CaVα2δ1 estimé par cytométrie en flux et imagerie confocale, et réduit la modulation des courants calciques mesurés par la méthode du « patch-clamp ». Les mutants G1060I et G1061I sont aussi associés à un changement dans le patron de migration de la partie C-terminale, suggérant un processus protéolytique défecteueux. Les mutations simples des glycines en alanines préservent les propriétés de la protéine mais le double mutant G1060A/G1061A réduit significativement l’expression de CaVα2δ1 à la surface de la cellule et sa modulation sur le canal CaV1.2. Ces données suggèrent fortement que le clivage requiert spécifiquement un résidu Glycine en position 1060 ou 1061 pour produire le clivage protéolytique dominant chez CaVα2δ1, et que cet ancrage GPI est essentiel à la fonction du canal. / Voltage-gated calcium channels CaV1.2 play an essential role in the regulation of cardiac excitability. Functional channels are formed by the CaVα1 subunit and the intracellular CaVβ and the extracellular CaVα2δ1 subunits. CaVα2δ1 are type I transmembrane proteins that undergo a posttranslational modification producing their association at the plasma membrane through a glycosylphosphatidylinositol (GPI) anchor. The molecular determinants required for the proteolytic cleavage of the recombinant CaVα2δ1 protein were studied using biochemical, immunocytochemical, fluorescence, and electrophysiological methods. Enzymatic treatment with a phospholipase C specific for the cleavage of phosphatidyl inositol lipids abolished the colocalisation of CaVα2δ1 with a plasma membrane marker as shown using live-cell confocal imaging. Single point mutations G1060I or G1061I in the predicted transmembrane CaVδ domain was shown to significantly reduce the cell surface fluorescence of CaVα2δ1 as characterized by two-color flow cytometry assays and confocal imaging, and to prevent the CaVα2δ1-mediated increase in the peak current density and voltage-dependent gating of CaV1.2 currents. The isoleucine mutations were also associated with a change in the migration pattern of the C-terminal fragments suggesting that proteolytic processing was altered. Single glycine to alanine mutations preserved the protein properties but the double mutant G1060A/G1061A significantly impaired cell surface expression of CaVα2δ1 and its functional regulation of CaV1.2. Altogether our data support a model where one Glycine residue at position 1060 or 1061 is required to produce the dominant proteolytic cleavage of CaVα2δ1 and further suggest that the GPI-anchored form of CaVα2δ1 is essential for channel function.

Les canaux calciques de type L CaV1.2 sont principalement responsables de l’entrée des ions calcium pendant la phase plateau du potentiel d’action des cardiomyocytes ventriculaires. Cet influx calcique est requis pour initier la contraction du muscle cardiaque. Le canal CaV1.2 est un complexe oligomérique qui est composé de la sous-unité principale CaVα1 et des sous-unités auxiliaires CaVβ et CaVα2δ1. CaVβ joue un rôle déterminant dans l’adressage membranaire de la sous-unité CaVα1. CaVα2δ1 stabilise l’état ouvert du canal mais le mécanisme moléculaire responsable de cette modulation n’a pas été encore identifié. Nous avons récemment montré que cette modulation requiert une expression membranaire significative de CaVα2δ1 (Bourdin et al. 2015). CaVα2δ1 est une glycoprotéine qui possède 16 sites potentiels de glycosylation de type N. Nous avons donc évalué le rôle de la glycosylation de type-N dans l’adressage membranaire et la stabilité de CaVα2δ1. Nous avons d’abord confirmé que la protéine CaVα2δ1 recombinante, telle la protéine endogène, est significativement glycosylée puisque le traitement à la PNGase F se traduit par une diminution de 50 kDa de sa masse moléculaire, ce qui est compatible avec la présence de 16 sites Asn. Il s’est avéré par ailleurs que la mutation simultanée de 6/16 sites (6xNQ) est suffisante pour 1) réduire significativement la densité de surface de! CaVα2δ1 telle que mesurée par cytométrie en flux et par imagerie confocale 2) accélérer les cinétiques de dégradation telle qu’estimée après arrêt de la synthèse protéique et 3) diminuer la modulation fonctionnelle des courants générés par CaV1.2 telle qu’évaluée par la méthode du « patch-clamp ». Les effets les plus importants ont toutefois été obtenus avec les mutants N663Q, et les doubles mutants N348Q/N468Q, N348Q/N812Q, N468Q/N812Q. Ensemble, ces résultats montrent que Asn663 et à un moindre degré Asn348, Asn468 et Asn812 contribuent à la biogenèse et la stabilité de CaVα2δ1 et confirment que la glycosylation de type N de CaVα2δ1 est nécessaire à la fonction du canal calcique cardiaque de type L. / L-type CaV1.2 channels play a key role in the excitation-contraction coupling in the heart. They are formed of a pore-forming CaVα1 subunit in complex with the intracellular CaVβ and the disulfur-linked CaVα2δ accessory subunits. CaVα2δ significantly increases peak current densities of CaV1.2. The mechanism underlying this effect is still under study but requires that CaVα2δ be trafficked at the cell surface. CaVα2δ contains 16 putative N-glycosylation sites. A study was carried out to identify the role of N-glycosylation in the trafficking and protein stability of the subunit CaVα2δ. Herein we show that enzymatic removal of N-glycans produced a 50 kDa shift in the mobility of cardiac and recombinant CaVα2δ1 proteins. Simultaneous mutation of the 16 Asn sites was required to fully account for this change in protein mobility. Nonetheless, the mutation of only 6/16 sites was sufficient to 1) significantly reduce the steady-state cell surface fluorescence of CaVα2δ1 as characterized by two-color flow cytometry assays and confocal imaging; 2) accelerate the degradation kinetics estimated from cycloheximide chase assays; and 3) prevent the CaVα2δ1-mediated increase in peak current density and voltage-dependent gating of CaV1.2. Reversing the N348Q and N812Q mutations in the non-operational 6 Asn mutant functionally rescued CaVα2δ1. Single mutation N663Q and double mutations N348Q/ N468Q, N348Q/ N812Q, N468Q/N812Q decreased protein stability/synthesis and abolished steady-state cell surface density as well as upregulation of L-type currents. These results demonstrate that Asn663, and to a lesser extent Asn348, Asn468, and Asn812 contribute to the stability of CaVα2δ1 function and furthermore that N- glycosylation of CaVα2δ1 is essential to produce functional L-type Ca2+ channels.

Receptores purinérgicos e canais de cálcio voltagem-dependentes estão envolvidos em diversos processos biológicos como na gastrulação, durante o desenvolvimento embrionário, e na diferenciação neural. Quando ativados, canais de cálcio voltagem-dependentes e receptores purinérgicos do tipo P2, ativados por nucleotídeos, desencadeiam transientes de cálcio intracelulares controlando diversos processos biológicos. Neste trabalho, nós estudamos a participação de canais de cálcio voltagem-dependentes e receptores do tipo P2 na geração de transientes de cálcio espontâneos e sua regulação na expressão de fatores de transcrição relacionados com a neurogênese utilizando como modelo células tronco (CTE) induzidas à diferenciação em células tronco neurais (NSC) com ácido retinóico. Descrevemos que CTE indiferenciadas podem ter a proliferação acelerada pela ativação de receptores P2X7, enquanto que a expressão e a atividade desse receptor precisam ser inibidas para o progresso da diferenciação em neuroblasto. Além disso, ao longo da diferenciação neural, por análise em tempo real dos níveis de cálcio intracelular livre identificamos 3 padrões de oscilações espontâneas de cálcio (onda, pico e unique), e mostramos que ondas e picos tiveram a frequência e amplitude aumentadas conforme o andamento da diferenciação. Células tratadas com o inibidor do receptor de inositol 1,4,5-trifosfato (IP3R), Xestospongin C, apresentaram picos mas não ondas, indicando que ondas dependem exclusivamente de cálcio oriundo do retículo endoplasmático pela ativação de IP3R. NSC de telencéfalo de embrião de camundongos transgênicos ou pré-diferenciadas de CTE tratadas com Bz-ATP, o agonista do receptor P2X7, e com 2SUTP, agonista de P2Y2 e P2Y4, aumentaram a frequência e a amplitude das oscilações espontâneas de cálcio do tipo pico. Dados, obtidos por microscopia de luminescência, da expressão em tempo real de gene repórter luciferase fusionado à Mash1 e Ngn2 revelou que a ativação dos receptores P2Y2/P2Y4 aumentou a expressão estável de Mash1 enquanto que ativação do receptor P2X7 levou ao aumento de Ngn2. Além disso, células na presença do quelante de cálcio extracelular (EGTA) ou do depletor dos estoques intracelulares de cálcio do retículo endoplasmático (thapsigargin) apresentaram redução na expressão de Mash1 e Ngn2, indicando que ambos são regulados pela sinalização de cálcio. A investigação dos canais de cálcio voltagem-dependentes demonstrou que o influxo de cálcio gerado por despolarização da membrana de NSC diferenciadas de CTE é decorrente da ativação de canais de cálcio voltagem-dependentes do tipo L. Além disso, esse influxo pode controlar o destino celular por estabilizar expressão de Mash1 e induzir a diferenciação neuronal por fosforilação e translocação do fator de transcrição CREB. Esses dados sugerem que os receptores P2X7, P2Y2, P2Y4 e canais de cálcio voltagem-dependentes do tipo L podem modular as oscilações espontâneas de cálcio durante a diferenciação neural e consequentemente alteram o padrão de expressão de Mash1 e Ngn2 favorecendo a decisão do destino celular neuronal. / Purinergic receptors and voltage gated Ca2+ channels have been attributed with developmental functions including gastrulation and neural differentiation. Upon activation, nucleotide-activated P2 purinergic receptor and voltage-gated Ca2+ channel subtypes trigger intracellular calcium transients controlling cellular processes. Here, we studied the participation of voltage-gated calcium channels and P2 receptor activity in spontaneous calcium transients and consequent regulation expression of transcription factors related to retinoic acid-induced neurogenesis of mouse neural stem and embryonic stem cells (ESC). In embryonic pluripotent stem cells, proliferation is accelerated by P2X7 receptor activation, while receptor expression / activity needs to be down-regulated for the progress of neuroblast differentiation. Moreover, along neural differentiation time lapse imaging with means of a cytosolic calcium-sensitive fluorescent probe provided different patterns of spontaneous calcium transients (waves and spikes) showing that both, frequency and amplitude increased along differentiation. Cells treated with the inositol 1,4,5-trisphosphate receptor (IP3R) inhibitor Xestospongin C showed spikes but not waves, indicating that waves exclusively depended on calcium release from endoplasmic reticulum by IP3R activation. Cells treated with the P2X7 receptor subtype agonist Bz-ATP and the P2Y2 and P2Y4 receptor 2-S-UTP increased frequency and amplitudes of calcium transients, mainly spikes, in embryonic telencephalon neural stem cells (NSC) and NSC pre-differentiated from ESC. Data obtained by luminescence time lapse imaging of stable transfected cells with Mash1 or Ngn2 promoter-protein fusion to luciferase reporter construct revealed increased Mash1 expression due to activation of P2Y2/P2Y4 receptor subtypes, while increased expression of Ngn2 was observed following P2X7 receptor activation. In addition, cells imaged in presence of the extracellular calcium chelator EGTA or following endoplasmic reticulum calcium store depletion by thapsigargin showed a decrease in Mash1 and Ngn2 expression, indicating that both are regulated by calcium signaling. Investigation of the roles of voltage gated Ca2+ channels in neural differentiation showed that Ca2+ influx in NSC pre-differentiated from ESC is due to membrane depolarization and L-type voltage gated Ca2+ channel activation, thereby controlling cell fate decision, by stabilizing the expression of MASH1 and inducing differentiation, by phosphorylation of the transcription factor CREB. Altogether these data suggest that P2X7, P2Y2, P2Y4 receptors and L-type voltage gated Ca2+ channels can modulate spontaneous calcium oscillations during neural differentiation and consequently change the Mash1 and Ngn2 expression patterns, thus favoring the cell fate decision to the neuronal phenotype.

Kar Wing To. / Thesis submitted in: December 1999. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 200-223). / Abstracts in English and Chinese. / Acknowledgements --- p.i / List of Abbreviations --- p.ii / Abstract --- p.v / 撮要 --- p.viii / List of Tables --- p.x / List of Figures --- p.xi / Contents --- p.xv / Chapter CHAPTER 1 --- INTRODUCTION / Chapter 1.1 --- The General Characteristics of Glial Cells --- p.1 / Chapter 1.1.1 --- Astrocytes --- p.1 / Chapter 1.1.2 --- Oligodendrocytes --- p.5 / Chapter 1.1.3 --- Microglial --- p.6 / Chapter 1.2 --- Brain Injury and Astrocyte Proliferation --- p.6 / Chapter 1.3 --- Reactive Astrogliosis and Glial Scar Formation --- p.9 / Chapter 1.4 --- Astrocytes and Immune Response --- p.10 / Chapter 1.5 --- Cytokines --- p.10 / Chapter 1.5.1 --- Cytokines and the Central Nervous System (CNS) --- p.12 / Chapter 1.5.2 --- Cytokines and brain injury --- p.13 / Chapter 1.5.3 --- Cytokines-activated astrocytes in brain injury --- p.13 / Chapter 1.5.4 --- Tumour Necrosis Factor-a --- p.14 / Chapter 1.5.4.1 --- Types of TNF-α receptor and their sturctures --- p.16 / Chapter 1.5.4.2 --- Binding to TNF-α --- p.17 / Chapter 1.5.4.3 --- Different Roles of the TNF-a Receptor Subtypes --- p.17 / Chapter 1.5.4.4 --- Role of TNF-α and Brain Injury --- p.19 / Chapter 1.5.4.5 --- TNF-α Stimulates Proliferation of Astrocytes and C6 Glioma Cells --- p.23 / Chapter 1.5.5 --- Interleukin-1 (IL-1) --- p.26 / Chapter 1.5.5.1 --- Interleukin-1 and Brain Injury --- p.27 / Chapter 1.5.6 --- Interleukin-6 (IL-6) --- p.28 / Chapter 1.5.6.1 --- Interleukin-6 and brain injury --- p.29 / Chapter 1.5.7 --- γ-Interferon (γ-IFN) --- p.30 / Chapter 1.5.7.1 --- γ-Interferon and Brain Injury --- p.30 / Chapter 1.6 --- Ion Channels and Astrocytes --- p.31 / Chapter 1.6.1 --- Roles of Sodium Channels in Astrocytes --- p.33 / Chapter 1.6.2 --- Role of Potassium Channels in Astrocytes --- p.33 / Chapter 1.6.3 --- Importance of Calcium Ion Channels in Astrocytes --- p.34 / Chapter 1.6.3.1 --- Function of Cellular and Nuclear Calcium --- p.34 / Chapter 1.6.3.2 --- Nuclear Calcium in Cell Proliferation --- p.36 / Chapter 1.6.3.3 --- Nuclear Calcium in Gene Transcription --- p.36 / Chapter 1.6.3.4 --- Nuclear Calcium in Apoptosis --- p.38 / Chapter 1.6.3.5 --- Spatial and Temporal Changes of Calcium-Calcium Oscillation --- p.39 / Chapter 1.6.3.6 --- Calcium Signalling in Glial Cells --- p.39 / Chapter 1.6.3.7 --- Calcium Channels in Astrocytes --- p.41 / Chapter 1.6.3.8 --- Relationship Between [Ca2+]i and Brain Injury --- p.43 / Chapter 1.6.3.9 --- TNF-α and Astrocyte [Ca2+]i --- p.45 / Chapter 1.6.3.10 --- Calcium-Sensing Receptor (CaSR) --- p.46 / Chapter 1.7 --- Protein Kinase C (PKC) Pathways --- p.49 / Chapter 1.7.1 --- PKC and Brain Injury --- p.50 / Chapter 1.7.2 --- Role of Protein Kinase C Activity in TNF-α Gene Expression in Astrocytes --- p.51 / Chapter 1.7.3 --- PKC and Calcium in Astrocytes --- p.52 / Chapter 1.8 --- Intermediate Early Gene (IEGs) --- p.54 / Chapter 1.8.1 --- IEGs Expression and Brain Injury --- p.54 / Chapter 1.8.2 --- IEGs Expression and Calcium --- p.55 / Chapter 1.9 --- The Rat C6 Clioma Cells --- p.56 / Chapter 1.10 --- The Aim of This Project --- p.58 / Chapter CHAPTER 2 --- MATERIALS AND METHODS / Chapter 2.1 --- Materials --- p.61 / Chapter 2.1.1 --- Sources of the Chemicals --- p.61 / Chapter 2.1.2 --- Materials Preparation --- p.65 / Chapter 2.1.2.1 --- Rat C6 Glioma Cell Line --- p.65 / Chapter 2.1.2.2 --- C6 Glioma Cell Culture --- p.65 / Chapter 2.1.2.2.1 --- Complete Dulbecco's Modified Eagle Medium (CDMEM) --- p.65 / Chapter 2.1.2.2.2 --- Serum-free Dulbecco's Modified Eagle Medium --- p.66 / Chapter 2.1.2.3 --- Phosphate Buffered Saline (PBS) --- p.66 / Chapter 2.1.2.4 --- Recombinant Cytokines --- p.67 / Chapter 2.1.2.5 --- Antibodies --- p.67 / Chapter 2.1.2.5.1 --- Anti-TNF-Receptor 1 (TNF-R1) Antibody --- p.67 / Chapter 2.1.2.5.2 --- Anti-TNF-Receptor 2 (TNF-R2) Antibody --- p.67 / Chapter 2.1.2.6 --- Chemicals for Signal Transduction Study --- p.68 / Chapter 2.1.2.6.1 --- Calcium Ionophore and Calcium Channel Blocker --- p.68 / Chapter 2.1.2.6.2 --- Calcium-Inducing Agents --- p.68 / Chapter 2.1.2.6.3 --- Modulators of Protein Kinase C (PKC) --- p.69 / Chapter 2.1.2.7 --- Reagents for Cell Proliferation --- p.69 / Chapter 2.1.2.8 --- Reagents for Calcium Level Measurement --- p.70 / Chapter 2.1.2.9 --- Reagents for RNA Extraction and Reverse Transcription-Polymerase Chain Reaction (RT-PCR) --- p.71 / Chapter 2.1.2.10 --- Sense and Antisense Used --- p.72 / Chapter 2.1.2.11 --- Reagents for Electrophoresis --- p.74 / Chapter 2.2 --- Methods --- p.74 / Chapter 2.2.1 --- Maintenance of the C6 Cell Line --- p.74 / Chapter 2.2.2 --- Cell Preparation for Assays --- p.75 / Chapter 2.2.3 --- Determination of Cell Proliferation --- p.76 / Chapter 2.2.3.1 --- Determination of Cell Proliferation by [3H]- Thymidine Incorporation --- p.76 / Chapter 2.2.3.2 --- Measurement of Cell Viability Using Neutral Red Assay --- p.77 / Chapter 2.2.3.3 --- Measurement of Cell Proliferation by MTT Assay --- p.77 / Chapter 2.2.3.4 --- Protein Assay --- p.78 / Chapter 2.2.3.5 --- Data Analysis --- p.79 / Chapter 2.2.3.5.1 --- The Measurement of Cell Proliferation by [3H]- Thymidine Incorporation --- p.79 / Chapter 2.2.3.5.2 --- The Measurement of Cell growth in Neutral Red and MTT Assays --- p.79 / Chapter 2.2.3.5.3 --- The Measurement of Cell Proliferationin Protein Assay --- p.79 / Chapter 2.2.4 --- Determination of Intracellular Calcium Changes --- p.80 / Chapter 2.2.4.1 --- Confocal Microscopy --- p.80 / Chapter 2.2.4.1.1 --- Procedures for Detecting Cell Activity by CLSM --- p.81 / Chapter 2.2.4.1.2 --- Precautions of CLSM --- p.82 / Chapter 2.2.5 --- Determination of Gene Expression by Reverse- Transcription Polymerase Chain Reaction (RT-PCR) --- p.83 / Chapter 2.2.5.1 --- RNA Preparation --- p.83 / Chapter 2.2.5.1.1 --- RNA Extraction --- p.83 / Chapter 2.2.5.1.2 --- Measurement of RNA Yield --- p.84 / Chapter 2.2.5.2 --- Reverse Transcription (RT) --- p.84 / Chapter 2.2.5.3 --- Polymerase Chain Reaction (PCR) --- p.85 / Chapter 2.2.5.4 --- Separation of PCR Products by Agarose Gel Electrophoresis --- p.85 / Chapter 2.2.5.5 --- Quantification of Band Density --- p.86 / Chapter CHAPTER 3 --- RESULTS / Chapter 3.1 --- Effects of Different Drugs on C6 Cell Proliferation --- p.87 / Chapter 3.1.1 --- Effects of Cytokines on C6 Cell Proliferation --- p.87 / Chapter 3.1.1.1 --- Effect of TNF-α on C6 Proliferation --- p.88 / Chapter 3.1.1.2 --- Effects of Other Cytokines on C6 Cell Proliferation --- p.92 / Chapter 3.1.2 --- The Signalling Pathway of TNF-α induced C6 Cell Proliferation --- p.92 / Chapter 3.1.2.1 --- The Involvement of Calcium Ions in TNF-α-induced C6Cell Proliferation --- p.95 / Chapter 3.1.2.2 --- The Involvement of Protein Kinase C in TNF-α- induced C6 Cell Proliferation --- p.96 / Chapter 3.1.3 --- Effects of Anti-TNF Receptor Subtype Antibodies on C6 Cell Proliferation --- p.102 / Chapter 3.2 --- The Effect of in Tumour Necrosis Factor-α on Changesin Intracellular Calcium Concentration --- p.102 / Chapter 3.2.1 --- Release of Intracellular Calcium in TNF-α-Treated C6 Cells --- p.104 / Chapter 3.2.2 --- Effects of Calcium Ionophore and Calcium Channel Blocker on TNF-α-induced [Ca2+]i Release --- p.107 / Chapter 3.2.3 --- Effects of Other Cytokines on the Change in [Ca2+]i --- p.109 / Chapter 3.2.4 --- The Role of PKC in [Ca2+]i release in C6 Glioma Cells --- p.109 / Chapter 3.2.4.1 --- Effects of PKC Activators and Inhibitors on the Changes in [Ca2+]i --- p.114 / Chapter 3.3 --- Determination of Gene Expression by RT-PCR --- p.114 / Chapter 3.3.1 --- Studies on TNF Receptors Gene Expression --- p.117 / Chapter 3.3.1.1 --- Effect of TNF-α on TNF Receptors Expression --- p.117 / Chapter 3.3.1.2 --- Effects of Other Cytokines on the TNF Receptors Expression --- p.119 / Chapter 3.3.1.3 --- Effects of Anti-TNF Receptor Subtype Antibodies on the TNF-a-induced Receptors Expression --- p.121 / Chapter 3.3.1.4 --- Effect of Calcium Ions on TNF Receptors Expression --- p.121 / Chapter 3.3.1.4.1 --- Effect of Calcium Ionophore on TNF Receptors Expression --- p.126 / Chapter 3.3.1.4.2 --- Effect of TNF-α Combination with A23187 on the Expression of TNF Receptors --- p.128 / Chapter 3.3.1.4.3 --- Effects of Calcium Ionophore and Channel Blocker on TNF Receptors Expression --- p.130 / Chapter 3.3.1.4.4 --- Effects of Calcium-Inducing Agents on TNF Receptors Gene Expressions --- p.130 / Chapter 3.3.1.5 --- Effects of PKC Activator and Inhibitor on TNF-α- induced TNF Receptors Expressions --- p.135 / Chapter 3.3.1.6 --- Effect of PKC and Ro31-8220 on IL-l-induced TNF Receptors Expressions --- p.138 / Chapter 3.3.2 --- Expression of Calcium-sensing Receptor upon Different Drug Treatments --- p.138 / Chapter 3.3.2.1 --- Effect of TNF-α on the Calcium-sensing Receptor Expression --- p.141 / Chapter 3.3.2.2 --- Effects of Other Cytokines on CaSR Expression --- p.143 / Chapter 3.3.2.3 --- Effect of A23187 on CaSR Expression --- p.143 / Chapter 3.3.2.4 --- Effect of TNF-α and A23187 Combined Treatment on CaSR Expression --- p.146 / Chapter 3.3.2.5 --- Effects of Calcium-inducing Agents on CaSR Expression --- p.149 / Chapter 3.3.2.6 --- Effects of PKC Activator and PKC Inhibitor on CaSR Expression --- p.149 / Chapter 3.3.3 --- Expression of PKC Isoforms upon Treatment with Different Drugs --- p.153 / Chapter 3.3.3.1 --- Effect of TNF-α on the PKC Isoforms Expression --- p.155 / Chapter 3.3.3.2 --- Effect of A23187 on the PKC Isoforms Expression --- p.155 / Chapter 3.3.3.3 --- Effect of TNF-α and Calcium Ionophore Combined Treatment on PKC Isoforms Expression --- p.157 / Chapter 3.3.3.4 --- Effects of Calcium-inducing Agents on PKC Isoforms Expression --- p.159 / Chapter 3.3.4 --- Expression of the Transcription Factors c-fos and c-junin Drug Treatments --- p.161 / Chapter 3.3.4.1 --- Effect of TNF-a on c-fos and c-jun Expression --- p.163 / Chapter 3.3.4.2 --- Effect of A23187 on c-fos and c-jun Expression --- p.163 / Chapter 3.3.4.3 --- Effect of TNF-a in Combination with A23187 on c- fos and c-jun Expression --- p.165 / Chapter 3.3.4.4 --- Effects of Calcium-inducing Agents on c-fos and c- jun Expression --- p.167 / Chapter 3.3.5 --- Effects of Different Drugs on Endogenous TNF-α Expression --- p.167 / Chapter 3.3.5.1 --- Effect of TNF-α on Endogenous TNF-α Expression --- p.169 / Chapter 3.3.5.2 --- Effect of A23187 on Endogenous TNF-α Expression --- p.169 / Chapter 3.3.5.3 --- Effect of TNF-α in Combination with A23187 on the Expression of Endogenous TNF-α --- p.172 / Chapter 3.3.5.4 --- Effects of Calcium-inducing Agents on Endogenous TNF-α Expression --- p.172 / Chapter 3.3.6 --- Effect of Different Drugs on LL-1 Expression --- p.175 / Chapter 3.3.6.1 --- Effect of TNF-a on IL-lα Expression --- p.177 / Chapter 3.3.6.2 --- Effect of A23187 on the IL-lα Expression --- p.177 / Chapter 3.3.6.3 --- Effect of Calcium Ionophore and TNF-α Combined Treatment on IL-1α Expression --- p.179 / Chapter 3.3.6.4 --- Effects of Calcium-inducing Agents on IL-lα Expression --- p.179 / Chapter 3.3.6.5 --- Effect of PKC Activator on the IL-1α Expression --- p.181 / Chapter CHAPTER 4 --- DISCUSSIONS AND CONCLUSIONS / Chapter 4.1 --- "Effects of Cytokines, Ca2+ and PKC and Anti-TNF-α Antibodies on C6 Glioma Cells Proliferation" --- p.184 / Chapter 4.2 --- The Role of Calcium in TNF-α-induced Signal Transduction Pathways --- p.186 / Chapter 4.3 --- Gene Expressions in C6 Cells after TNF-a Stimulation --- p.187 / Chapter 4.3.1 --- "Expression of TNF-α, TNF-Receptors and IL-1" --- p.187 / Chapter 4.3.2 --- CaSR Expression --- p.190 / Chapter 4.3.3 --- PKC Isoforms Expressions --- p.192 / Chapter 4.3.4 --- Expression of c-fos and c-jun --- p.193 / Chapter 4.4 --- Conclusion --- p.194 / REFERENCES --- p.200

Cerebral ischaemia is a leading cause of disability and death world-wide. The only effective treatments are thrombolytic therapy (plasminogen activator; tPA) and hypothermia (33?C). However, tPA has limited clinical application due to its short therapeutic time window and its specific application in thrombo-embolic stroke. Moderate hypothermia (33?C) is only being used following cardiac arrest in comatose survivors. Hence more treatments are urgently required. The first step in developing new treatments is the identification and characterisation of a potential therapeutic target. Since brain damage following cerebral ischaemia is associated with disturbances in intracellular calcium homeostasis, the sodium-calcium exchanger (NCX) is a potential therapeutic target due to its ability to regulate intracellular calcium. Currently, however there is uncertainty as to whether the plasma membrane NCX has a neuroprotective or neurodamaging role following cerebral ischemia. To address this issue I compared hippocampal neuronal injury in NCX3 knockout mice (Ncx3-/-) and wild-type mice (Ncx3+/+) following global cerebral ischaemia. In order to perform this study I first established a bilateral common carotid occlusion (BCCAO) model of global ischaemia in wild-type C57/BlHsnD mice using controlled ventilation. After trials of several ischaemic time points, 17 minutes was established as the optimum duration of ischaemia to produce selective hippocampal CA1 neuronal loss in the wild-type mice. I then subjected NCX3 knockout and wild-type mice to 17 minutes of ischaemia. Following the 17 minute period of ischaemia, wild-type mice exhibited 80% CA1 neuronal loss and 40% CA2 neuronal loss. In contrast, NCX3 knockout mice displayed > 95% CA1 neuronal loss and 95% CA2 neuronal loss. Following experiments using a 17 minute duration of global ischaemia, a 15 minute duration of ischaemia was also evaluated. Wild-type mice exposed to a 15 minute period of ischaemia, did not exhibit any significant hippocampal neuronal loss. In contrast, NCX3 knockout mice displayed 45% CA1 neuronal loss and 25% CA2 neuronal loss. The results clearly demonstrate that mice deficient for the NCX3 protein are more susceptible to global cerebral ischaemia than wild-type mice. My findings showing a neuroprotective role for NCX3 following ischaemia, suggest that the exchanger has a positive role in maintaining neuronal intracellular calcium homeostasis. When this function is disrupted, neurons are more susceptible to calcium deregulation, with resultant cell death via calcium mediated pathways. Therefore, improving NCX activity following cerebral ischaemia may provide a therapeutic strategy to reduce neuronal death.

Compromised calcium homeostasis in the central nervous system (CNS) is implicated as a major contributor in the pathology of neurodegeneration. Dysregulation of Ca2+ homeostasis initiates downstream Ca2+–dependent events that lead to apoptotic and/or necrotic cell death. Increases in the intracellular free calcium concentration ([Ca2+]i) may be the result of Ca2+ influx from the extracellular environment or Ca2+ release from intracellular Ca2+ stores such as the endoplasmic reticulum (ER). Influx from the extracellular environment is controlled predominantly by voltage gated calcium channels (VGCC), such as L–type calcium channels (LTCC) and ionotropic glutamate receptors, such as the N–methyl–D–aspartate (NMDA) receptors. Ca2+ release from the ER occurs through the inositol–1,4,5–triphosphate receptors (IP3Rs) or ryanodine receptors (RyRs) via IP3–induced or Ca2+–induced mechanisms. Mitigation of Ca2+ overload through these Ca2+ channels offers an opportunity for pharmacological interventions that may protect against neuronal death. In the present study the ability of a novel series of polycyclic compounds, both the pentacycloundecylamines and triquinylamines, to regulate calcium influx through LTCC was evaluated in PC12 cells using calcium imaging with Fura–2/AM in a fluorescence microplate reader. We were also able for the first time to determine IC50 values for these compounds as LTCC blockers. In addition, selected compounds were evaluated for their ability to offer protection in apoptosis–identifying assays such as the lactate dehydrogenase release assay (LDH–assay), trypan blue staining assay and immunohistochemistry utilizing the Annexin V–FITC stain for apoptosis. We were also able to obtain single crystal structures for the tricyclo[6.3.0.02,6]undecane–4,9–dien–3,11–dione (9) and tricyclo[6.3.0.02,6]undecane–3,11–dione (10) scaffolds as well as a derivative, N–(3–methoxybenzyl)–3,11–azatricyclo[6.3.0.02,6]undecane (14f). We also evaluated the possibility that the polycyclic compounds might be able to modulate Ca2+ flux through intracellular Ca2+ channels. Computational methods were utilized to accurately predicted IC50 values and develop a QSAR model with marginal error. The linear regression model delivered r2 = 0.83, which indicated a favorable correlation between the predicted and experimental IC50 values. This model could thus serve as valuable predictor for future structural design and optimization efforts. Data obtained from the crystallographic analysis confirmed the NMR–data based structural assignments done for these compounds in previous studies. Obtaining structural information gave valuable insight into the differences in size and geometric constrains, which are key features for the LTCC activity of these compounds. vii In conclusion, we found that all of the compounds evaluated were able to attenuate Ca2+ influx through the LTCC, with some compounds having IC50 values comparable with known LTCC blockers such as nimodipine. Representative compounds were evaluated for their ability to afford protection against apoptosis induced by 200 ?M H2O2. With the exception of compound 14c (the most potent LTCC blocker in the series, IC50 = 0.398 ?M), most compounds were able to afford protection at two or more concentrations evaluated. Compound 14c displayed inherent toxicity at the highest concentrations evaluated (100 ?M). We concluded that compounds representing both types of structures (pentacycloudecylamines and triquinylamines) have the ability to attenuate excessive Ca2+ influx through the LTCC. In general the aza–pentacycloundecylamines (8a–c) were the most potent LTCC blocker which also had the ability to offer protection in the cell viability assays. However, NGP1–01 (7a) had the most favorable pharmacological profile overall with good activity as an LTCC blocker (IC50 = 86 ?M) and the ability to significantly attenuate cell death in the cell viability assays, exhibiting no toxicity. In addition to their ability to modulate Ca2+ influx from the extracellular environment, these compounds also displayed the ability to modulate Ca2+ flux through intracellular Ca2+ channels. The mechanisms by which they act on intracellular Ca2+ channels still remains unclear, but from this preliminary study it would appear that these compounds are able to partially inhibiting Ca2+–ATPase activity whilst possibly simultaneously inhibiting the IP3R. In the absence of extracellular Ca2+ these compounds showed the ability in inhibit voltage–induced Ca2+ release (VICaR), possibly by modulating the gating charge of the voltage sensor being the dihydropyridine receptors. In future studies it might be worthwhile to do an expanded QSAR study and evaluate the aza–pentacycloundecylamines. To clarify the mechanisms by which the polycyclic compounds interact with intracellular Ca2+ channels we should examine the direct interaction with the individual Ca2+ channels independently. The polycyclic compounds evaluated in this study demonstrate potential as multifunctional drugs due to their ability to broadly regulate calcium homeostasis through multiple pathways of Ca2+ entry. This may prove to be more effective in diseases where perturbed Ca2+ homeostasis have devastating effects eventually leading to excitotoxicity and cell death. / Thesis (Ph.D. (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2012.

Compromised calcium homeostasis in the central nervous system (CNS) is implicated as a major contributor in the pathology of neurodegeneration. Dysregulation of Ca2+ homeostasis initiates downstream Ca2+–dependent events that lead to apoptotic and/or necrotic cell death. Increases in the intracellular free calcium concentration ([Ca2+]i) may be the result of Ca2+ influx from the extracellular environment or Ca2+ release from intracellular Ca2+ stores such as the endoplasmic reticulum (ER). Influx from the extracellular environment is controlled predominantly by voltage gated calcium channels (VGCC), such as L–type calcium channels (LTCC) and ionotropic glutamate receptors, such as the N–methyl–D–aspartate (NMDA) receptors. Ca2+ release from the ER occurs through the inositol–1,4,5–triphosphate receptors (IP3Rs) or ryanodine receptors (RyRs) via IP3–induced or Ca2+–induced mechanisms. Mitigation of Ca2+ overload through these Ca2+ channels offers an opportunity for pharmacological interventions that may protect against neuronal death. In the present study the ability of a novel series of polycyclic compounds, both the pentacycloundecylamines and triquinylamines, to regulate calcium influx through LTCC was evaluated in PC12 cells using calcium imaging with Fura–2/AM in a fluorescence microplate reader. We were also able for the first time to determine IC50 values for these compounds as LTCC blockers. In addition, selected compounds were evaluated for their ability to offer protection in apoptosis–identifying assays such as the lactate dehydrogenase release assay (LDH–assay), trypan blue staining assay and immunohistochemistry utilizing the Annexin V–FITC stain for apoptosis. We were also able to obtain single crystal structures for the tricyclo[6.3.0.02,6]undecane–4,9–dien–3,11–dione (9) and tricyclo[6.3.0.02,6]undecane–3,11–dione (10) scaffolds as well as a derivative, N–(3–methoxybenzyl)–3,11–azatricyclo[6.3.0.02,6]undecane (14f). We also evaluated the possibility that the polycyclic compounds might be able to modulate Ca2+ flux through intracellular Ca2+ channels. Computational methods were utilized to accurately predicted IC50 values and develop a QSAR model with marginal error. The linear regression model delivered r2 = 0.83, which indicated a favorable correlation between the predicted and experimental IC50 values. This model could thus serve as valuable predictor for future structural design and optimization efforts. Data obtained from the crystallographic analysis confirmed the NMR–data based structural assignments done for these compounds in previous studies. Obtaining structural information gave valuable insight into the differences in size and geometric constrains, which are key features for the LTCC activity of these compounds. vii In conclusion, we found that all of the compounds evaluated were able to attenuate Ca2+ influx through the LTCC, with some compounds having IC50 values comparable with known LTCC blockers such as nimodipine. Representative compounds were evaluated for their ability to afford protection against apoptosis induced by 200 ?M H2O2. With the exception of compound 14c (the most potent LTCC blocker in the series, IC50 = 0.398 ?M), most compounds were able to afford protection at two or more concentrations evaluated. Compound 14c displayed inherent toxicity at the highest concentrations evaluated (100 ?M). We concluded that compounds representing both types of structures (pentacycloudecylamines and triquinylamines) have the ability to attenuate excessive Ca2+ influx through the LTCC. In general the aza–pentacycloundecylamines (8a–c) were the most potent LTCC blocker which also had the ability to offer protection in the cell viability assays. However, NGP1–01 (7a) had the most favorable pharmacological profile overall with good activity as an LTCC blocker (IC50 = 86 ?M) and the ability to significantly attenuate cell death in the cell viability assays, exhibiting no toxicity. In addition to their ability to modulate Ca2+ influx from the extracellular environment, these compounds also displayed the ability to modulate Ca2+ flux through intracellular Ca2+ channels. The mechanisms by which they act on intracellular Ca2+ channels still remains unclear, but from this preliminary study it would appear that these compounds are able to partially inhibiting Ca2+–ATPase activity whilst possibly simultaneously inhibiting the IP3R. In the absence of extracellular Ca2+ these compounds showed the ability in inhibit voltage–induced Ca2+ release (VICaR), possibly by modulating the gating charge of the voltage sensor being the dihydropyridine receptors. In future studies it might be worthwhile to do an expanded QSAR study and evaluate the aza–pentacycloundecylamines. To clarify the mechanisms by which the polycyclic compounds interact with intracellular Ca2+ channels we should examine the direct interaction with the individual Ca2+ channels independently. The polycyclic compounds evaluated in this study demonstrate potential as multifunctional drugs due to their ability to broadly regulate calcium homeostasis through multiple pathways of Ca2+ entry. This may prove to be more effective in diseases where perturbed Ca2+ homeostasis have devastating effects eventually leading to excitotoxicity and cell death. / Thesis (Ph.D. (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2012.

Pain signaling involves transmission of nociceptive stimuli in the spinal cord where a critical balance between excitatory and inhibitory inputs determines the response to noxious stimuli. The neuropeptide, substance P (SP), mediates transmission of pain in part by binding to the tachykinin receptor (NK-1R) in the dorsal horn (DH) of the spinal cord. One of SP’s downstream effects is to modulate N-type Ca2+(N-) channels. While phospholipid breakdown is a part of the inflammatory process that accompanies tissue damage, the role of this metabolic pathway has not been completely described with respect to N-channel modulation during pain signaling. Despite the incomplete understanding of this modulation, pharmacological antagonists of both NK-1R and N-channels have been used to treat pain. In Chapter II, using whole-cell patch clamp recording techniques, the SP signaling cascade that mediates inhibition of recombinant N-channel activity was characterized. By adopting a pharmacological approach, I show that this pathway resembles the slow pathway that was earlier described for modulation of N-current by the M1 muscarinic receptor (M1R). M1R couples to Gq to stimulate phospholipid breakdown. Together with previous observations, the data presented in this chapter provide evidence for involvement of the extracellular receptor kinase (ERK1/2), phospholipase A2 and release of phospholipid metabolites in the modulation of N-current by SP. Overall, this chapter shows that phospholipid metabolism involved in modulation of N-currents is not specific to M1Rs but that other Gq-coupled receptors may also modulate N-currents via the same signal transduction pathway. In Chapter III, enhancement of N-current by SP was studied as part of a collaborative project to understand current enhancement that occurs when a palmitoylated accessory CaVβ2a subunit is co-expressed with the pore-forming subunit CaV2.2 and the accessory subunit α2δ-1. When CaVβ3 is present, SP inhibits N-current as described in Chapter II. However, when palmitoylated CaVβ2a is co-expressed with CaV2.2 (and α2δ-1), current enhancement is observed at negative test potentials, demonstrating that both M1Rs and NK-1Rs exhibit the same profile of N-current modulation. This change in modulation by muscarinic agonists is not observed in the presence of a depalmitoylated CaVβ2a. However a chimeric CaVβ2aβ1b subunit that contains the palmitoylated N-terminus from CaVβ2a confers enhancement. Normally expression of the β1b subunit resulted in current inhibition. These findings indicated that the palmitoylated CaVβ2a participates in enhancement of current. Our data support a model where inhibition dominates over enhancement; when inhibition is blocked, enhancement may be observed. Lastly, we show that N-current inhibition by SP is minimized when exogenous palmitic acid is applied to cells co-expressing CaVβ3 subunits with N-channels. These results indicate that the presence of palmitic acid can prevent N-current inhibition when SP is applied most likely by interacting with CaV2.2. We propose a model where palmitic acid occupies the inhibitory site and serves to antagonize inhibition by a lipid metabolite, which is most likely arachidonic acid. The CaVβ2a protein seems to have a role in positioning the palmitoyl groups near CaV2.2. This chapter provides a new role for protein palmitoylation where the palmitoyl groups of CaVβ2a are both necessary and sufficient to block inhibition of another protein: CaV2.2. In Chapter IV, I probe the role of the relative orientation of CaVβ2a and the pore-forming subunit of the N-channel in N-current modulation. Evidence is presented that shows that not just the presence of a palmitoylated CaVβ2a is necessary, but the relative orientation of CaVβ2a to CaV2.2 is critical for blocking inhibition. Using N-channel mutants that cause a change in the orientation of CaVβ2a relative to CaV2.2, I show that the block of inhibition is disrupted; inhibition by the slow pathway is rescued. These findings further support my model that the palmitoyl groups of CaVβ2a normally reside in a specific location that overlaps with the slow pathway inhibitory site on CaV2.2. Lastly I present data showing that the enhancement of N-current, observed when palmitoylated CaVβ2a is present, occurs via the slow pathway. In Chapter V the effect of CaVβ’s orientation on N-channel modulation by the dopamine D2 receptor is tested. In this form of modulation, inhibition is rapid and voltage-dependent. The signaling pathway is membrane-delimited since Gβγ, released after receptor stimulation, directly interacts with the N-channel at a site that overlaps with a high affinity binding site for CaVβs. While N-currents are modulated by this pathway, the deletion mutants show aberrant membrane-delimited modulation. The findings in this chapter further underscore the importance of proper positioning of CaVβ to CaV2.2 for eliciting proper N-current modulation after GPCR stimulation. Overall, the data presented in this dissertation provides a mechanistic approach into examining modulation of N-current by different GPCRs via two different signaling pathways as well as the role CaVβ subunits serve in each modulatory pathway.