Calcium Oscillations In Astrocytes Research Articles

Modulation of Type 5 Metabotropic Glutamate Receptor-Mediated Intracellular Calcium Mobilization by Regulator of G Protein Signaling 4 (RGS4) in Cultured Astrocytes.

Acting as GTPase activating proteins promoting the silencing of activated G-proteins, regulators of G protein signaling (RGSs) are generally considered negative modulators of cell signaling. In the CNS, the expression of RGS4 is altered in diverse pathologies and its upregulation was reported in astrocytes exposed to an inflammatory environment. In a model of cultured cortical astrocytes, we herein investigate the influence of RGS4 on intracellular calcium signaling mediated by type 5 metabotropic glutamate receptor (mGluR5), which is known to support the bidirectional communication between neurons and glial cells. RGS4 activity was manipulated by exposure to the inhibitor CCG 63802 or by infecting the cells with lentiviruses designed to achieve the silencing or overexpression of RGS4. The pharmacological inhibition or silencing of RGS4 resulted in a decrease in the percentage of cells responding to the mGluR5 agonist DHPG and in the proportion of cells showing typical calcium oscillations. Conversely, RGS4-lentivirus infection increased the percentage of cells showing calcium oscillations. While the physiological implication of cytosolic calcium oscillations in astrocytes is still under investigation, the fine-tuning of calcium signaling likely determines the coding of diverse biological events. Indirect signaling modulators such as RGS4 inhibitors, used in combination with receptor ligands, could pave the way for new therapeutic approaches for diverse neurological disorders with improved efficacy and selectivity.

Emergent dynamics in an astrocyte-neuronal network coupled via nitric oxide

In the brain, both neurons and glial cells work in conjunction with each other during information processing. Stimulation of neurons can induce calcium oscillations in astrocytes which in turn can affect neuronal calcium dynamics. The ‘glissandi’ effect is one such phenomenon, associated with a decrease in infraslow fluctuations, in which synchronized calcium oscillations propagate as a wave in hundreds of astrocytes. Nitric oxide molecules released from the astrocytes contribute to synaptic functions based on the underlying astrocyte–neuron interaction network. In this study, by defining an astrocyte–neuronal (A–N) calcium unit as an integrated circuit of one neuron and one astrocyte, we developed a minimal model of neuronal stimulus-dependent and NO-mediated emergence of calcium waves in astrocytes. Incorporating inter-unit communication via NO molecules, a coupled network of 1000 such A–N calcium units is developed in which multiple stable regimes were found to emerge in astrocytes. We examined the ranges of neuronal stimulus strength and the coupling strength between A–N calcium units that give rise to such dynamical behaviors. We also report that there exists a range of coupling strength, wherein units not receiving stimulus also start showing oscillations and become synchronized. Our results support the hypothesis that glissandi-like phenomena exhibiting synchronized calcium oscillations in astrocytes help in efficient synaptic transmission by reducing the energy demand of the process.

Cholesterol-load evokes robust calcium response in macrophages: An early event toward cholesterol-induced macrophage death

Macrophages in atherosclerotic lesions accumulate large amounts of unesterified cholesterol. Excess cholesterol load leads to cell death of macrophages, which is associated with the progression of atherosclerotic lesions. Calcium depletion in the endoplasmic reticulum (ER) and subsequent pro-apoptotic aberrant calcium signaling are key events in cholesterol-induced macrophage death. Although these concepts imply cytoplasmic calcium events in cholesterol-loaded macrophages, the mechanisms linking cholesterol accumulation to cytoplasmic calcium response have been poorly investigated. Based on our previous finding that extracellularly applied cholesterol evoked robust calcium oscillations in astrocytes, a type of glial cells in the brain, we hypothesized that cholesterol accumulation in macrophages triggers cytoplasmic calcium elevation. Here, we showed that cholesterol application induces calcium transients in THP-1-derived and peritoneal macrophages. Inhibition of inositol 1,4,5-trisphosphate receptors (IP3Rs) and l-type calcium channels (LTCCs) prevented cholesterol-induced calcium transients and ameliorated cholesterol-induced macrophage death. These results suggest that cholesterol-induced calcium transients through IP3Rs and LTCCs are crucial mechanisms underlying cholesterol-induced cell death of macrophages.

Effects of store-operated and receptor-operated calcium channels on synchronization of calcium oscillations in astrocytes

Intercellular calcium signaling allows cells to communicate with each other and to interact with adjacent cells. Gap junction is the most common and important way for cellular communication. Recently, mathematical models have been widely used to gain a precise and quantitative understanding of the dynamics of intracellular calcium ions (Ca2＋). In this paper, we establish a mathematical model considering the gap junction permeable to Ca2＋ and to IP3 for describing the calcium oscillations in coupled astrocytes. Store-operated calcium entry (SOCE) is viewed as the main process which controls the non-excitable cells, hence, we focus on the effect of store-operated calcium channel (SOCC) and receptor-operated calcium channel (ROCC) on the intercellular synchronization, respectively. By employing bifurcation analysis on this model, the dynamic behaviors of the coupled system with different physiological state cells is obtained with changes in the maximum capacity of the SOCC and the ROCC. The synchronization boundaries for different conditions are gained in the two parameters space of the channel parameters and the coupling strength. The results suggest that the variation of the maximum flow for different calcium channels determines the stable oscillations of the coupled system, as well as for the frequency and amplitude of oscillations. The SOCC has an expected effect on the change of the oscillatory interval while the ROCC demonstrated the influence on the amplitude modulation. Furthermore, the coupling strength and channel parameters could induce 1:1 locking of intercellular Ca2＋ oscillations and the synchronization region like Arnol’d tongue is found.

Bifurcation analysis on the effect of store-operated and receptor-operated calcium channels for calcium oscillations in astrocytes

Experimental evidence has proved that calcium ions ( $$\mathrm {Ca^{2+}}$$ ) play an important role in cellular physiological processes via calcium oscillations. The entry rate of $$\mathrm {Ca^{2+}}$$ into cells through plasma membrane cells is a major modulator of intracellular $$\mathrm {Ca^{2+}}$$ dynamics, including the voltage-gated $$\mathrm {Ca^{2+}}$$ channel, the store-operated $$\mathrm {Ca^{2+}}$$ channel (SOCC) and the receptor-operated $$\mathrm {Ca^{2+}}$$ channel (ROCC). In this paper, we modify an established four-dimensional dynamical model, which contains the SOCC and ROCC, and carry out a bifurcation analysis to study dynamics of the model. In particular, Hopf bifurcation is identified with the maximum flow of the SOCC chosen as the bifurcation parameter, and normal form theory is applied to consider the stability of bifurcating limit cycles. Bifurcation of multiple limit cycles arising from generalized Hopf bifurcation is also discussed, which may yield complex dynamical behaviors. Further, it is shown that the variation of the maximum flows for different calcium channels determines the parameter range for stable oscillations, as well as for the frequency and amplitude of oscillations. The results indicate that Hopf bifurcation is the main source to generate oscillating behaviors, yielding a different bistable phenomenon which involves stable limit cycle and stable equilibrium. Moreover, it is shown that partially blocking the SOCC or the ROCC can change the parameter region of stable calcium oscillations, and the ROCC has more impact than the SOCC on amplitude or frequency of calcium oscillations.

Temperature Impacts on Transient Receptor Potential Channel Mediated Calcium Oscillations in Astrocytes**Supported by the National Natural Science Foundation of China under Grant Nos 11175055 and 11547013, and the Natural Science Foundation of Hebei Province under Grant No A2015202268.

We computationally study the possible effects of thermosensitive transient receptor potential (TRP) channels on the spontaneous calcium oscillations in astrocytes at various temperatures. Based on the previous model and the result of thermosensitive TRP channels’ open probabilities, some meaningful conclusions are obtained. It is shown that the occurrence of calcium oscillations depends on temperature and the molar heat capacity difference between the closed and open channels (). The data indicate that calcium oscillations in astrocytes occurred in the ranges of 7 °C–11 °C and 27 °C–30 °C when is , and calcium oscillations only occur in the range of 27 °C–30 °C when is . In this study, the frequency decreases rapidly at temperatures ranging from 7 °C to 11 °C, and there is a contrary result in the range of 27 °C–30 °C.

Abstract PR470

Background & Objectives: Reveal the mechanism of general anesthesia induced loss of consciousness is crucial in the study of anesthetic effect[1-2]. Study found that neuronal activity and synaptic transmission can be regulated by a variety of neural active substance released from astrocytes, which participating in the brain information integration[3-4]. Astrocytes may take part in the general anesthesia induced loss of consciousness, however, there is no related report. Materials & Methods: This study chose the rats cortical astrocytes as the main object of observation, utilizing the brain slice patch clamp technique and calcium imaging to investigate the effects of three intravenous anesthetics (propofol, dexmedetomidine and ketamine) on astrocytes calcium ion excitatory and the information exchange between astrocytes and neurons. Results: Among three kinds of anesthetics, only ketamine inhibits ADP-induced calcium oscillations in astrocytes in a concentration dependent manner. Ketamine (220μM) inhibits astrocyte-induced slow inward current in rat cortical neuron.Conclusion: Our data provided experimental evidence proving astrocyte-related mechanism of central effects of ketamine.

Ectonucleotidase activity and immunosuppression in astrocyte-CD4 T cell bidirectional signaling.

Astrocytes play a crucial role in neuroinflammation as part of the glia limitans, which regulates infiltration of the brain parenchyma by leukocytes. The signaling pathways and molecular events, which result from the interaction of activated T cells with astrocytes are poorly defined. Here we show that astrocytes promote the expression and enzymatic activity of CD39 and CD73 ectonucleotidases in recently activated CD4 cells by a contact dependent mechanism that is independent of T cell receptor interaction with class II major histocompatibility complex (MHC). Transforming growth factor-β (TGF-β) is robustly upregulated and sufficient to promote ectonucleotidases expression. T cell adhesion to astrocyte results in differentiation to an immunosuppressive phenotype defined by expression of the transcription factor Rorγt, which characterizes the CD4 T helper 17 subset. CD39 activity in T cells in turn inhibits spontaneous calcium oscillations in astrocytes that correlated with enhanced and reduced transcription of CCL2 chemokine and Sonic hedgehog (Shh), respectively. We hypothesize this TCR-independent interaction promote an immunosuppressive program in T cells to control possible brain injury by deregulated T cell activation during neuroinflammation. On the other hand, the increased secretion of CCL2 with concomitant reduction of Shh might promote leukocytes extravasation into the brain parenchyma.

Long-term facilitation of spontaneous calcium oscillations in astrocytes with endogenous adenosine in hippocampal slice cultures

It is well established that astrocytes release gliotransmitters and moderate neuronal activity in the central nervous system via intracellular Ca2+ dynamics. Astrocytic Ca2+ oscillations are one type of spontaneous Ca2+ mobilization that occurs in astrocytes. However, the modulation of spontaneous astrocytic Ca2+ oscillations, especially in pathophysiological conditions, is not yet fully understood. Here, we demonstrate that activation of adenosine receptors induces a long-lasting increase in the frequency of astrocytic Ca2+ oscillations in rat hippocampal slice cultures. The long-term facilitation of the frequency of Ca2+ oscillations was mediated by endogenous adenosine generated via breakdown of extracellular ATP by ecto-ATPase. We also demonstrate that local tissue injury with ultraviolet irradiation can cause this long-term facilitation of Ca2+ oscillations via endogenous adenosine. Our data suggest that endogenous adenosine is one of the modulators of spontaneous astrocytic Ca2+ oscillations in the rat hippocampus, and may play a significant role in altered Ca2+ dynamics in astrocytes observed during pathophysiological conditions.

Calcium Signaling in Astrocytes: Modeling Fura-2AM Measurements

Event Abstract Back to Event Calcium Signaling in Astrocytes: Modeling Fura-2AM Measurements Eeva Toivari1, Tiina Manninen1*, Amit K. Nahata2, Tuula O. Jalonen3 and Marja-Leena Linne1 1 Tampere University of Technology, Finland 2 Kidney Care Center at DCI, United States 3 School of Medicine, St. Georges University, Department of Physiology and Neuroscience, Grenada Purpose: In addition to wet lab and clinical studies, mathematical models can be used to better understand and verify the hypothesis concerning complex molecular level interactions, including the role of intracellular calcium stores such as endoplasmic reticulum, in cellular functions. Ionic equilibrium in astrocytes can be disturbed by transmitters, for example by serotonin and Alzheimer's disease related amyloid plaques forming amyloid-ß peptides (Aß). We studied the effects of small amounts of Aß fragments on the neurotransmitter-induced calcium signals in astrocytes by doing Fura-2-acetoxymethyl ester (Fura-2AM) measurements and computer modeling based on calcium-induced kinetic reactions. Method: Fura-2AM measurements were done to study the effects of transmitters, such as serotonin and glutamate, on the cytosolic concentration of calcium in astrocytes separately and together with neurotoxic Aß25-35. Fura-2AM is a membrane penetrating derivative of the radiometric calcium indicator Fura-2 used in biochemistry to measure intracellular calcium concentrations by fluorescence. Aß25-35 is a synthetic derivative of the longer peptide Aß42 which predominates in the neuritic plaques. A computational model, introduced by Di Garbo et al. (2007), was adjusted to mimic the calcium signals measured with the calcium imaging technique. The model includes kinetic reaction equations, for example, the effect of both metabotropic and ionotropic receptors, the flux of calcium from/to extracellular matrix, the pumping of calcium from cytosol to the endoplasmic reticulum and the leak back to cytosol, and the release of calcium from the endoplasmic reticulum via inositol 1,4,5-trisphosphate receptors. Results: Though serotonin and glutamate have earlier been shown to induce calcium release in astrocytes (Jalonen et al. 1997, Kimelberg et al. 1997), it is shown in this study how serotonin and Aß25-35, when added together, clearly increase the amplitudes of the calcium signal. Thus, even small amounts of neurotoxic Aß25-35 can have a severe effect on the intracellular ionic equilibrium. In the modeling part of this study, different experimental setups were computationally simulated using different values of the model parameters and/or different inputs. The model presented by Di Garbo et al. (2007) was found to sufficiently explain the results measured by us using the Fura-2AM technique. For example, phenomena related to unfilled intracellular calcium stores were observed both by calcium imaging and computer simulations. Thus, model simulations support the hypothesis about the importance of intracellular calcium stores, such as endoplasmic reticulum, to calcium signaling in astrocytes. Conclusions: We conclude that the experimental results on astrocytic calcium oscillations can be reproduced with the computational model originally proposed by Di Garbo et al. (2007). Modeling the mechanisms of intracellular calcium oscillations in astrocytes is important, as astrocytes have an essential role in regulating the central nervous system microenvironment.

Anti-phase calcium oscillations in astrocytes via inositol (1, 4, 5)-trisphosphate regeneration

Observations in cultured mouse astrocytes suggest anti-phase synchronization of cytosolic calcium concentrations in nearest neighbor cells that are coupled through gap junctions. A mathematical model is used to investigate physiologic conditions under which diffusion of the second messenger inositol (1, 4, 5)-trisphosphate (IP 3) through gap junctions can facilitate synchronized anti-phase Ca 2+ oscillations. Our model predicts anti-phase oscillations in both cytosolic calcium and IP 3 concentrations if (a) the gap junction permeability is within a window of values and (b) IP 3 is regenerated in the astrocytes via, e.g. phospholipase C δ. This result sheds new light on the current dispute on the mechanism of intercellular calcium signaling. It provides indirect evidence for a partially regenerative mechanism as the model excludes anti-phase synchrony in the absence of IP 3 regeneration.

Intracellular Calcium Oscillations in Astrocytes: A Highly Plastic, Bidirectional Form of Communication between Neurons and AstrocytesIn Situ

The spatial-temporal characteristics of intracellular calcium ([Ca2+]i) changes elicited in neurons and astrocytes by various types of stimuli were investigated by means of confocal fluorescent microscopy in acute rat brain slices loaded with the Ca2+ indicator indo-1. Neurons and astrocytes from the visual cortex and CA1 hippocampal region were identified in situ on the basis of their morphological, electrophysiological, and pharmacological features. We show here that stimulation of neuronal afferents triggered periodic [Ca2+]i oscillations in astrocytes. The frequency of these oscillations was under a dynamic control by neuronal activity as it changed according to the pattern of stimulation. After repetitive episodes of neuronal stimulation as well as repetitive stimulation with a metabotropic glutamate receptor agonist, astrocytes displayed a long-lasting increase in [Ca2+]i oscillation frequency. Oscillating astrocytes were accompanied by repetitive [Ca2+]i elevations in adjacent neurons, most likely because of the release of glutamate via a tetanus toxin-resistant process. These results reveal that [Ca2+]i oscillations in astrocytes represent a highly plastic signaling system that underlies the reciprocal communication between neurons and astrocytes.