Real-time electrical measurement of L929 cellular spontaneous and synchronous oscillation

Nonexcitable cell types, fibroblasts of heart muscle or astrocytes, are well known for their spontaneous Ca2+ oscillations. On the other hand, murine fibroblast (L929) cells are known to be deficient in cell–cell adhesive proteins and therefore lack gap junctions for cellular communication. However, these cells exhibit a unique property of collectively synchronized and spontaneous oscillation, as revealed by real-time monitoring of cells cultured on a 250-μm diameter microelectrode for more than 3 days using an electrical cell-substrate impedance-sensing system (ECIS). Live-cell imaging is a widely used technique for oscillation detection, but it has limitations relating to cellular physiological environment maintenance for microscopic analysis and for prolonged periods of study. The present research emphasizes an electrical-sensing technique (ECIS) capable of overcoming the most important issues inherent in live-cell imaging systems for the detection of L929 cellular spontaneous and synchronized oscillation in real-time for longer periods. Possible mechanisms involved in L929 oscillation were elucidated to be periodic extension/contraction of lamellipodia continued as blebbing, which is produced by signals from the actomyosin complex initiated by connexin hemichannel opening and adenosine triphosphate (ATP) release. By applying the connexin hemichannel inhibitor, flufenamic acid, the hindrance of ATP release and calcium transients were analyzed to elucidate this hypothesis

A role of ATP in modulating vasomotion during hypoxia in umbilical cord blood vessels

Previous studies have associated intracellular calcium ([Ca2+]i) oscillations in vascular smooth muscle cells (SMC) with vasomotion in multiple species. In normal and pre-eclamptic pregnancies, there is strong evidence to suggest that the intrauterine environment is hypoxic. The aim of this study was to investigate whether ATP and [Ca2+]i oscillations play a role in modulating vasomotion during hypoxia in human umbilical blood vessels. The results obtained from in vitro studies using firefly luciferase assay and quinacrine staining indicated that human umbilical artery and vein endothelial cell (HUAEC, HUVEC respectively) constitutively released ATP and, in HUVEC at least, the release was accentuated by hypoxia (7.6 mmHg O2, 30 min). This release is dependent on the PI3K/ROCK pathway, and on normal vesicular transport. Further, application of ATP to human umbilical artery SMC induced dose-dependent [Ca2+]i oscillations, which was mediated by P2Y4 receptor. Moreover, ex vivo data from freshly isolated umbilical artery rings showed that acute hypoxia increased the frequency of vasomotion. It is therefore proposed that the findings of the present study is important in the understanding of the behaviour of human umbilical vessels in normal pregnancy, but may also have implications in the pathophysiology of complicated pregnancy such as pre-eclampsia

Steady-State Regulation of Secretory Cargo Export and ER Homeostasis by Inositol Trisphosphate Receptors and Penta-EF-Hand Proteins

Constant protein degradation and turnover necessitates constitutive secretion that delivers the correct mix of nascent proteins to their appropriate subcellular destinations. Cells thus exhibit steady-state secretion and the additional ability to adjust secretory flux, though we lack a clear understanding of this critical process. During secretion, the COPII coat is responsible for providing a balance of actively and passively selected ER cargos to enter the secretory pathway. Furthermore, Ca2+ -binding proteins have been implicated in regulating this process in response to Ca2+ signals. In Chapter 1, we review the secretory pathway and vesicular trafficking, with a focus on ER-to-Golgi transport. We then examine the known roles of Ca2+ in ER proteostasis and trafficking with a particular emphasis on the Inositol 1,4,5-Trisphosphate Receptors (IP3Rs) and the Penta-EF-Hand (PEF) proteins ALG-2 and Peflin. Chapter 2 describes experimental procedures while Chapter 3 examines the roles of Ca2+ and the PEF proteins in determining steady-state trafficking flux. We find that in Normal Rat Kidney (NRK) epithelial cells, depletion of the IP3R-3 isoform augments Ca2+ signaling, including spontaneous Ca2+ oscillations. This shift in Ca2+ signaling drove an ‘activated’ ALG-2 phenotype in which ER-to-Golgi transport of the model cargo VSV-G is accelerated. Additionally, we find that ALG-2 activation augments COPII cargo sorting stringency, concentrating COPII client cargo at ER Exit Sites (ERES) at the expense of bulk flow cargos. These findings suggest that the steady-state transport and cargo sorting capacity of a given cell may be influenced by its spontaneous Ca2+ signaling characteristics via ALG-2 regulation of COPII function. Chapter 4 details a set of preliminary experiments exploring the role that IP3R-3 and Mitochondria-ER Contact Sites (MERCs or MAMs) may play in the maintenance of ER proteostasis. Depletion of IP3R-1 from NRK cells–a condition which favors function of the IP3R-3 channel–causes partial depletion of ER Ca2+, yet cells are protected from ER stress. This is of interest since Ca2+ is traditionally thought of as a rate-limiting component for protein folding in the ER. Since IP3R-3 is known to be the IP3R at MAMs, this data highlights the protective effects of MAMs on ER proteostasis

Modélisation des réponses calciques de réseaux d'astrocytes : Relations entre topologie et dynamiques

Over the last 20 years, astrocytes, a hitherto under-investigated type of brain cells, have gradually rose to prominence owing to multiple experimental discoveries. In contrast with neurons, these cells do not propagate electrical signals but communicate instead through changes in their intracellular calcium concentration. Recent discoveries indicate that, far from being isolated cells, astrocytes respond to neuronal activity and, although this is still controversial, seem to modulate synaptic transmission through the release of `gliotransmitter' molecules (in reference to neurotransmitters). Like neurons, astrocyte are organized in networks and communicate their calcium activity by intercellular diffusion of second messengers, forming intercellular calcium waves. Two networks, one of neurons and the other of astrocytes, thus coexist in the brain; while neuronal networks have been the subject of intense experimental and theoretical investigations, astrocyte networks have been much less investigated. Notably, it was only discovered recently that astrocyte network topology could be more complex than what the hitherto dominant view held (astrocytes organized in a syncytium deprived of any topological specificities). The work presented in this thesis is mainly related to the effect that different network topologies could have on astrocyte calcium signaling. The mechanisms that drive calcium signaling in astrocytes are, at both subcellular and intercellular levels, still not completely understood. Even in the best documented case of astrocyte somatic response to neuronal stimulation, the precise characteristic required from the stimulation to elicit an astrocytic response are still unknown. Similarly, the mechanisms governing intercellular calcium wave propagation in astrocyte networks are not fully known; notably, the effects of the recently documented network heterogeneity on calcium wave propagation have not been investigated. Finally, at the subcellular level, astrocytes display an extremely ramified and complex morphology that also hosts calcium activity. The work presented in this thesis make use of modeling and simulation in order to determine the possible effects of astrocyte network organization on their calcium signaling. We propose that astrocyte network topology: (1) controls single-cell responses to neuronal stimulation; (2) drives the propagation of intercellular calcium waves by favoring it when networks are weakly coupled; (3) can determine the appearance of stochastic resonance phenomena; (4) can be modulated by neuronal activity.Pendant les 20 dernières années, les astrocytes, un type de cellules cérébrales ayant été jusque là relativement ignoré des neuroscientifiques, ont peu à peu gagné en notoriété grâce à de multiples découvertes. Contrairement aux neurones, ces cellules ne transmettent pas de signaux électriques mais communiquent par des changements intracellulaires de leurs concentrations en calcium. Des découvertes récentes semblent indiquer que, loin d'agir en autarcie, les astrocytes répondent à l'activité neuronale et sembleraient, bien que cela soit plus débattu, moduler la transmission synaptique par le relargage de molécules spécifiques appelées `gliotransmetteurs' (en référence aux neurotransmetteurs). Comme les neurones, les astrocytes forment des réseaux et communiquent leur activité calcique par diffusion d'un astrocyte à l'autre, formant ainsi de véritables vagues de calcium intercellulaires. Deux réseaux, de neuronnes et d'astrocytes, cohabitent ainsi dans le cerveau ; mais, alors que les réseaux de neuronnes ont fait l'objet de recherches expérimentales et théoriques, les réseaux d'astrocytes restent encore mal connus. Ainsi, il n'a été découvert que très récement que la topologie de ces réseaux pourrait s'averer plus complexe que la vision qui dominait jusqu'alors : celle d'un syncitium astrocytaire dépourvu de spécificités topologiques. Les travaux présentés dans cette thèse portent principalement sur l'effet que ces différentes topologies pourraient avoir sur la signalisation calcique astrocytaire. En effet, autant au niveau subcellulaire qu'inter-cellulaire, les mécanismes gouvernant l'activité calcique des astrocytes restent mals connus. Même dans le cas le plus documenté de la réponse somatique des astrocytes à une stimulation neuronale, les caractéristiques précises que la stimulation doit avoir pour évoquer une réponse des astrocytes sont inconnues. Il en est de même pour la transmission de vagues de calcium dans des réseaux d'astrocytes : on ignore encore les possibles effets de la complexité récemment documentée des réseaux d'astrocytes sur la propagation de ces vagues. Enfin, au niveau subcelulaire, les astrocytes possèdent une morphologie ramifiée extrèmement complexe qui possède elle-même une activité calcique. Les travaux présentés dans cette thèse utilisent des outils de modélisation et de simulation afin de déterminer les répercussions que l'organisation en réseaux des astrocytes pourrait avoir sur leurs dynamiques calciques. En résumé, nous proposons que la topologie des réseaux d'astrocytes a (1) des répercussion au niveau cellulaire, modulant la réponse des astrocytes à des stimulations neuronales ; (2) contrôle la propagation de vagues de calcium inter-astrocytaire en la favorisant lorsque les réseau sont peu couplés ; (3) joue un rôle important dans l’apparition de phénomènes de résonance stochastique

Removal of antagonistic spindle forces can rescue metaphase spindle length and reduce chromosome segregation defects

Regular Abstracts - Tuesday Poster Presentations: no. 1925Metaphase describes a phase of mitosis where chromosomes are attached and oriented on the bipolar spindle for subsequent segregation at anaphase. In diverse cell types, the metaphase spindle is maintained at a relatively constant length. Metaphase spindle length is proposed to be regulated by a balance of pushing and pulling forces generated by distinct sets of spindle microtubules and their interactions with motors and microtubule-associated proteins (MAPs). Spindle length appears important for chromosome segregation fidelity, as cells with shorter or longer than normal metaphase spindles, generated through deletion or inhibition of individual mitotic motors or MAPs, showed chromosome segregation defects. To test the force balance model of spindle length control and its effect on chromosome segregation, we applied fast microfluidic temperature-control with live-cell imaging to monitor the effect of switching off different combinations of antagonistic forces in the fission yeast metaphase spindle. We show that spindle midzone proteins kinesin-5 cut7p and microtubule bundler ase1p contribute to outward pushing forces, and spindle kinetochore proteins kinesin-8 klp5/6p and dam1p contribute to inward pulling forces. Removing these proteins individually led to aberrant metaphase spindle length and chromosome segregation defects. Removing these proteins in antagonistic combination rescued the defective spindle length and, in some combinations, also partially rescued chromosome segregation defects. Our results stress the importance of proper chromosome-to-microtubule attachment over spindle length regulation for proper chromosome segregation.postprin

Psr1p interacts with SUN/sad1p and EB1/mal3p to establish the bipolar spindle

Regular Abstracts - Sunday Poster Presentations: no. 382During mitosis, interpolar microtubules from two spindle pole bodies (SPBs) interdigitate to create an antiparallel microtubule array for accommodating numerous regulatory proteins. Among these proteins, the kinesin-5 cut7p/Eg5 is the key player responsible for sliding apart antiparallel microtubules and thus helps in establishing the bipolar spindle. At the onset of mitosis, two SPBs are adjacent to one another with most microtubules running nearly parallel toward the nuclear envelope, creating an unfavorable microtubule configuration for the kinesin-5 kinesins. Therefore, how the cell organizes the antiparallel microtubule array in the first place at mitotic onset remains enigmatic. Here, we show that a novel protein psrp1p localizes to the SPB and plays a key role in organizing the antiparallel microtubule array. The absence of psr1+ leads to a transient monopolar spindle and massive chromosome loss. Further functional characterization demonstrates that psr1p is recruited to the SPB through interaction with the conserved SUN protein sad1p and that psr1p physically interacts with the conserved microtubule plus tip protein mal3p/EB1. These results suggest a model that psr1p serves as a linking protein between sad1p/SUN and mal3p/EB1 to allow microtubule plus ends to be coupled to the SPBs for organization of an antiparallel microtubule array. Thus, we conclude that psr1p is involved in organizing the antiparallel microtubule array in the first place at mitosis onset by interaction with SUN/sad1p and EB1/mal3p, thereby establishing the bipolar spindle.postprin

Sinalização purinérgica

Embora existam diversos grupos brasileiros de pesquisa da sinalização purinérgica, o conhecimento sobre o tema tem sido amplamente difundido em língua inglesa em periódicos internacionais. Em língua portuguesa, os estudos, de um modo geral, constituem dissertações e teses. Todos os colaboradores do livro são pesquisadores brasileiros que estudam alguma situação fisiológica ou patológica envolvendo o sistema purinérgico. O livro trata do funcionamento da sinalização purinérgica em condições fisiológicas gerais e sobre a história das enzimas e dos receptores purinérgicos. Aborda situações fisiológicas, como a modulação do sistema purinérgico pelo exercício físico e por moléculas nutracêuticas. E dedica alguns capítulos para a relação da sinalização purinérgica em condições patológicas: diversos tipos de câncer; doenças endócrinas, como diabetes e disfunções da glândula tireoide; doença renal; hipertensão arterial sistêmica; doenças degenerativas, como doença de Alzheimer e doença macular relacionada à idade; doenças parasitárias e virais, dentre outras

Possible involvement of ATP-purinoceptor signalling in the intercellular synchronization of intracellular Ca2+ oscillation in cultured cardiac myocytes.

Isolated and cultured neonatal cardiac myocytes contract spontaneously and cyclically. The contraction rhythms of two isolated cardiac myocytes, each of which beats at different frequencies at first, become synchronized after the establishment of mutual contacts, suggesting that mutual entrainment occurs due to electrical and/or mechanical interactions between two myocytes. The intracellular concentration of free Ca2+ also changes rhythmically in association with the rhythmic contraction of myocytes (Ca2+ oscillation), and such a Ca2+ oscillation was also synchronized among cultured cardiac myocytes. In this study, we investigated whether intercellular communication other than via gap junctions was involved in the intercellular synchronization of intracellular Ca2+ oscillation in spontaneously beating cultured cardiac myocytes. Treatment with either blockers of gap junction channels or an un-coupler of E–C coupling did not affect the intercellular synchronization of Ca2+ oscillation. In contrast, treatment with a blocker of P2 purinoceptors resulted in the asynchronization of Ca2+ oscillatory rhythms among cardiac myocytes. The present study suggested that the extracellular ATP-purinoceptor system was responsible for the intercellular synchronization of Ca2+ oscillation among cardiac myocytes