Transcriptional Remodeling in Primary Hippocampal Astrocytes from an Alzheimer's Disease Mouse Model.

BACKGROUND: It is well known that alterations in astrocytes occur in Alzheimer's disease and reactive astrogliosis is one of the hallmarks of the disease. Recently, data has emerged that suggests that alterations in astrocytes may also occur early in the pathogenesis of the disease. OBJECTIVE: The aim of present work was to characterize the transcriptional alterations occurring in cultured astrocytes from 3xTg-AD mouse pups compared to control non-transgenic mice. Furthermore, we also compared these changes to those reported by others in astrocytes from symptomatic AD mice. METHOD: We conducted a whole-genome microarray study on primary cultured astrocytes from the hippocampus of 3xTg-AD and non-transgenic mouse newborn pups. We used cross-platform normalization and an unsupervised hierarchical clustering algorithm to compare our results with other datasets of cultured or freshly isolated astrocytes, including those isolated from plaque-stage APPswe/PS1dE9 AD mice. RESULTS: We found a set of 993 genes differentially expressed in 3xTg-AD as compared with non-Tg astrocytes. Over-represented gene ontology terms were related to calcium, cell-cell communication, mitochondria, transcription, nucleotide binding and phosphorylation. Of note, no genes related to inflammation were found in cultured 3xTg-AD astrocytes. Comparison with astrocytes isolated from plaque stage APPswe/PS1dE9 showed that 882 out of 993 genes were selectively changed in primary 3xTg-AD astrocytes while 50 genes were co-regulated and 61 were anti-regulated (regulated in the opposite direction in the datasets). CONCLUSION: Our data show that in cultured astrocytes from an AD mouse model, transcriptional changes occur and are different from those reported in models mimicking later stages of the disease.

SiO2 nanoparticles modulate the electrical activity of neuroendocrine cells without exerting genomic effects.

Engineered silica nanoparticles (NPs) have attracted increasing interest in several applications, and particularly in the field of nanomedicine, thanks to the high biocompatibility of this material. For their optimal and controlled use, the understanding of the mechanisms elicited by their interaction with the biological target is a prerequisite, especially when dealing with cells particularly vulnerable to environmental stimuli like neurons. Here we have combined different electrophysiological approaches (both at the single cell and at the population level) with a genomic screening in order to analyze, in GT1-7 neuroendocrine cells, the impact of SiO2 NPs (50 ± 3 nm in diameter) on electrical activity and gene expression, providing a detailed analysis of the impact of a nanoparticle on neuronal excitability. We find that 20 µg mL-1 NPs induce depolarization of the membrane potential, with a modulation of the firing of action potentials. Recordings of electrical activity with multielectrode arrays provide further evidence that the NPs evoke a temporary increase in firing frequency, without affecting the functional behavior on a time scale of hours. Finally, NPs incubation up to 24 hours does not induce any change in gene expression.

Calcium signaling in neuronal motility: pharmacological tools for investigating specific pathways.

Migration of neurons and neuronal precursors from the site of origin to their final location is a key process in the development of the nervous system and in the correct organization of neuronal structures and circuits. Different modes of migration (mainly radial and tangential) have been described in the last 40 years; for these, as for motility processes involving other cellular types, calcium signaling plays a key role, with influx from the extracellular medium representing the main mechanism, and a more delimited but specific role played by release from intracellular stores. Deciphering the involvement of the different calcium influx pathways has been a major task for cellular neurobiologists, and the availability - or lack - of reliable and selective pharmacological tools has represented the main limiting factor. This review addresses the strategies employed to investigate the role of voltage-dependent calcium channels and of neurotransmitter activated channels, either calcium permeable or not, that directly or indirectly can elicit cytosolic calcium increases; in addition, reference to recent findings on the involvement of other families of calcium permeable channels (such as the transient receptor potential superfamily) is presented. Finally, a brief description of the present - and limited - knowledge of the perturbations of calcium signaling involved in neuronal migration pathologies is provided.

Hydrophilic/hydrophobic features of TiO2 nanoparticles as a function of crystal phase, surface area and coating, in relation to their potential toxicity in peripheral nervous system.

The hydrophilic/hydrophobic properties of a variety of commercial TiO(2) nanoparticles (NP), to be employed as inorganic filters in sunscreen lotions, were investigated both as such (dry powders) and dispersed in aqueous media. Water uptake and the related interaction energy have been determined by means of adsorption microcalorimetry of H(2)O vapor, whereas dispersion features in aqueous solutions were investigated by dynamic light scattering and electrokinetic measurements (zeta potential). The optimized dispersions in cell culture medium were employed to assess the possible in vitro neuro-toxicological effect on dorsal root ganglion (DRG) cells upon exposure to TiO(2)-NP, as a function of crystal phase, surface area and coating. All investigated materials, with the only exception of the uncoated rutile, were found to induce apoptosis on DRG cells; the inorganic/organic surface coating was found not to protect against the TiO(2)-induced apoptosis. The risk profile for DRG cells, which varies for the uncoated samples in the same sequence as the photo-catalytic activity of the different polymorphs: anatase-rutile>anatase>>rutile, was found not to be correlated with the surface hydrophilicity of the uncoated/coated specimens. Aggregates/agglomerates hydrodynamic diameter was comprised in the ~200-400 nm range, compatible with the internalization within DRG cells.

Calcium signals: analysis in time and frequency domains.

Cytosolic calcium signals play important roles in processes such as cell growth and motility, synaptic communication and formation of neural circuitry. These signals have complex time courses and their quantitative analysis is not easily accomplished; in particular it may be difficult to evidence subtle differences in their temporal patterns. In this paper, we use wavelet analysis to extract information on the structure of [Formula: see text] oscillations. To this aim we have derived a set of indices by which different [Formula: see text] oscillatory patterns and their change in time can be extracted and quantitatively evaluated. This approach has been validated with examples of experimental recordings showing changes in oscillatory behavior in cells stimulated with a calcium-releasing agonist.

Calcineurin primes immature gonadotropin-releasing hormone-secreting neuroendocrine cells for migration.

During development, many neurons display calcium-dependent migration, but the role of this messenger in regulating gene expression leading to this event has not yet been elucidated. Among the decoders of calcium signals is calcineurin, a Ca(2+)/calmodulin serine/threonine phosphatase that has been involved in both short-term and long-term cellular changes. By using immortalized GnRH-secreting neurons, we now show that, in vitro, Ca(2+)-dependent gene expression, proceeding via calcineurin and the transcription factor nuclear factor of activated T cells, is a key player controlling the chemomigratory potential of developing GnRH-secreting neurons. Furthermore, our data highlight the switch nature of this phosphatase, whose activation or inactivation guides cells to proceed from one genetic program to the next.

A transport mechanism for NAADP in a rat basophilic cell line.

NAADP is a second messenger that releases Ca2+ from intracellular stores. Surprisingly, it has been recently shown that extracellular application of NAADP is capable of inducing intracellular Ca2+ release. This is particularly important since the only mammalian enzymes known to catalyze the synthesis of this second messenger are located extracellularly. In the present manuscript, we have investigated whether mammalian cells possess a transport system capable of transporting this highly charged molecule into cells. Indeed, in RBL-2H3 cells, a rat basophilic cell line, and in SK-N-BE cells, a neuroblastoma cell line, [32P]NAADP is efficiently transported inside cells. NAADP transport is Na+ and Ca2+ dependent, is partially blocked by dipyridamole, but is unaffected by nitrobenzylthioinosine. RBL-2H3 cells also transport [32P]cADPR, but the differences in the pharmacological profile suggest that NAADP transport proceeds by a novel mechanism. Lastly, extracellular application of NAADP, but not NADP, induced a raise in intracellular Ca2+. This is the first demonstration that NAADP is transported into cells and highlights the possibility that, alongside a second messenger, NAADP might also act as an autocrine/paracrine signal.

A simple method to study cellular migration.

We describe here a simple and fast method for the characterisation of cell motion. By projecting on a single plane different positions of the cell a ribbon is generated, whose characteristics can be related to the type of motion. The proposed method allows both to determine, very quickly, the motility of a population of cells and to investigate and characterise properties of a single cell's motion. The methodology presented here can be applied to a large range of cell movement and also adapted and extended to other problems involving biological motion.

In vitro identification of dividing neuronal precursors from chick embryonic ciliary ganglion.

In chick parasympathetic ciliary ganglion the neuronal birthdate is well defined, between 2.5 and 5.5 days of embryonic development, and neuronal precursor cells that are able to differentiate into neurons in vitro can be isolated from E4.5 ganglia. In this report, using bromodeoxyuridine incorporation and Maplb immunostaining, we demonstrate that these cells can be isolated from E7-E8 chick embryos as well, suggesting that neuronal precursor cells are still present in the ciliary ganglion after the end of the in vivo neurogenesis. These precursor cells retain the ability to divide and generate newly differentiated neurons in vitro when cultured in a chemically defined medium. Such a capacity is highly stimulated by bFGF but not by CNTF.

Neuronal survival and calcium influx induced by basic fibroblast growth factor in chick ciliary ganglion neurons.

Basic fibroblast growth factor (bFGF/FGF2) exhibits widespread biological activities in the nervous system. However, little is known about the cascade of intracellular events that links the activation of its tyrosine kinase receptors to these effects. Here we report that, in ciliary ganglion neurons from chick embryo, this trophic factor significantly enhanced neuronal survival. The percentage of surviving neurons was reduced when intracellular calcium was chelated by adding a membrane-permeable BAPTA ester to the culture medium, while antagonists of L- and N-type voltage-dependent calcium channels were ineffective. The ionic signals in response to bFGF stimulation have been studied using cytofluorimetric and patch-clamp techniques. In single-cell Fura-2 measurements, bFGF elicited a long lasting rise of the cytosolic calcium concentration that was dependent on [Ca2+]o. In whole-cell experiments, we observed a reversible depolarization of the membrane resting potential and an inward cationic current. Single channel experiments, performed in the cell-attached configuration, provide evidence for the activation of two families of Ca2+-permeable cationic channels. Moreover, inositol 1,4,5-trisphosphate opens channels with similar properties, suggesting that this cytosolic messenger can be responsible for the calcium influx induced by bFGF.

Arachidonic acid mediates calcium influx induced by basic fibroblast growth factor in Balb-c 3T3 fibroblasts.

Basic fibroblast growth factor (bFGF), a peptide acting as a mitogen in different cell types, is able to induce a long lasting non capacitative calcium influx from the extracellular medium in Balb-c 3T3 mouse fibroblasts. This effect is mediated by the tyrosine kinase activity of bFGF receptors and the opening of voltage independent, agonist activated calcium channels. In this paper we investigate the signal transduction steps involved in this process using single cell calcium fluorimetry and electrophysiological techniques. One of the pathways initiated by the binding of growth factors to their tyrosine kinase receptors is the activation of cytosolic phospholipase A2 (cPLA2) and the release of arachidonic acid (AA) from the plasma membrane with the subsequent production of eicosanoids. We show here that, in our preparation, this pathway is involved in the opening of the bFGF-activated calcium permeable channels, through the activation of mitogen activated protein kinase (MAPK) and cPLA2. Evidence for direct involvement of AA is given by the finding that: (i) bFGF induces AA release from Balb-c 3T3 cells; (ii) blockers of AA metabolism are not effective; and (iii) the application of either arachidonic acid or its non metabolizable analogue 5,8,11,14-eicosatetraynoic acid (ETYA) reproduces the responses described for bFGF. Finally, single channel analysis indicates that bFGF, AA and ETYA can activate the same calcium permeable channel.

Sustained calcium influx activated by basic fibroblast growth factor in Balb-c 3T3 fibroblasts.

1. We have investigated the ionic events elicited in Balb-c 3T3 fibroblasts by basic fibroblast growth factor (bFGF), a peptide that binds to membrane receptors with tyrosine kinase activity and has a mitogenic action on many cell types. The peptide (0.2-100 ng ml-1) caused the appearance of an inward current, as observed in whole-cell patch-clamp experiments at a holding potential of -50 mV, that could last for tens of minutes and had a peak density of 4.6 +/- 2.6 pA pF-1. The reversal potential was 18.8 +/- 16.7 mV. 2. The current was reversibly abolished by removal of bFGF from the external bath. Inhibition of low-affinity FGF receptors had no effect on the activation of the inward current; it was completely abolished when cells were pre-incubated with tyrphostin or 5'-methylthioadenosine (MTA), two inhibitors of the tyrosine kinase activity of the high-affinity FGF receptors. The inward current was not activated by the emptying of internal calcium stores, as tested with 200 nM thapsigargin. 3. Values of peak current density comparable to control ones were obtained when either all Na+ ions or all Ca2+ ions were removed from the external solution; when both ions were completely removed, no inward current could be observed. The inward current was not affected by 2 microM nifedipine, and was reversibly blocked by the imidazole derivative SK&F 96365-A. 4. Measurements of free intracellular calcium concentration ([Ca2+]i) with the dye fura-2 showed that bFGF elicited sustained increases in [Ca2+]i that were completely dependent on external calcium and on the presence of the agonist and could last more than 1 h. 5. Single channel currents (conductance 7.9 pS) in response to bFGF stimulation could be recorded in the cell-attached configuration with 100 mM CaCl2 in the pipette. When the resting potential was brought near to 0 mV by external perfusion in a high-K+ solution, Vrev was about 0 mV. 6. We conclude that in Balb-c 3T3 cells bFGF induces an inward current that is carried at least partially by Ca2+ ions; this current in turn causes a long-lasting increase in intracellular Ca2+ concentration. The amplitude and time course of these bFGF-activated ionic events are compatible with their involvement in the control of cell proliferation.

Basic fibroblast growth factor opens calcium-permeable channels in quail mesencephalic neural crest neurons.

In order to investigate the action of basic fibroblast growth factor (bFGF) in the nervous system, we have studied the ionic signals elicited by this peptide in cultured quail mesencephalic neural crest neurons using patch-clamp and cytofluorimetric techniques. In this preparation stimulation with bFGF induced, with a delay of some tens of seconds, an inward cationic current. Single-channel experiments provided evidence for the activation of a calcium-permeable channel. In single-cell cytofluorimetric measurements, a sustained rise in [Ca2+]i was observed, which was dependent on the presence of external calcium. These events may play a role in the developmental effects of bFGF.

Single-channel current simulation and recording using a photodiode as current generator.

A device which can generate rectangular currents in the picoampere range is described. The current generator is a photodiode connected to the head stage of a single-channel recording amplifier. The photodiode is activated by a light-emitting diode controlled by a computer or any other current source. The device can transmit signals corresponding to simulated single-channel behaviour. Since the kinetic parameters of the simulation are known, the user can test the data acquisition and analysis system under conditions similar to those prevailing during recording from a biological membrane. This current generator can also be used for the tuning of patch-clamp amplifiers; rectangular currents generated by the photodiode allow the frequency response of the amplifier to be properly adjusted.

Potassium channels in mouse neonate dorsal root ganglion cells: a patch-clamp study.

Isolated neurons from mouse neonate dorsal root ganglia were analyzed using both whole-cell clamp and single-channel recording techniques and presented a complex repertoire of potassium (K) channels. Different types of potassium channels have been found: calcium-activated K channel presenting a large unit conductance of 260 pS in symmetrical K; voltage-dependent K channels of 130 pS without calcium-dependence; two types of inward rectifying K channels (90 and 120 pS in symmetrical K); low probability K channels; delayed rectifier channels and non-selective cationic channels.

Development of ionic channels during mouse neuronal differentiation.

Using a mouse embryonal teratocarcinoma (E.C.) cell line, it was possible to follow the sequence of development of ionic channels during neuronal differentiation, with patch-clamp techniques. 1003 E.C. cells were induced to differentiate into neurons by culturing them in defined medium without foetal calf serum (DARMON et al., 1981). Non-differentiated cells were not excitable and presented mainly 2 types of K+ channels: a Ca2+ activated K+ channel (220 pS in symmetrical K+) and a delayed rectifier (30 pS in symmetrical K+). When the cells start to grow neurites, a low threshold calcium current can be recorded, only if the cell is held at hyperpolarized potentials (-70 to -80 mV). Fully differentiated cells with long neurites presented a complete repertoire of ionic channels: voltage dependent Na+ and Ca2+ channels, Ca2+ activated K+ channel and K+ delayed rectifier.