Calcium-mediated transductive systems and functionally active gap junctions in astrocyte-like GL15 cells

The Volume-Regulated Anion Channel in Glioblastoma

Malignancy of glioblastoma multiforme (GBM), the most common and aggressive form of human brain tumor, strongly depends on its enhanced cell invasion and death evasion which make surgery and accompanying therapies highly ineffective. Several ion channels that regulate membrane potential, cytosolic Ca²⁺ concentration and cell volume in GBM cells play significant roles in sustaining these processes. Among them, the volume-regulated anion channel (VRAC), which mediates the swelling-activated chloride current (IClswell) and is highly expressed in GBM cells, arguably plays a major role. VRAC is primarily involved in reestablishing the original cell volume that may be lost under several physiopathological conditions, but also in sustaining the shape and cell volume changes needed for cell migration and proliferation. While experimentally VRAC is activated by exposing cells to hypotonic solutions that cause the increase of cell volume, in vivo it is thought to be controlled by several different stimuli and modulators. In this review we focus on our recent work showing that two conditions normally occurring in pathological GBM tissues, namely high serum levels and severe hypoxia, were both able to activate VRAC, and their activation was found to promote cell migration and resistance to cell death, both features enhancing GBM malignancy. Also, the fact that the signal transduction pathway leading to VRAC activation appears to involve GBM specific intracellular components, such as diacylglicerol kinase and phosphatidic acid, reportedly not involved in the activation of VRAC in healthy tissues, is a relevant finding. Based on these observations and the impact of VRAC in the physiopathology of GBM, targeting this channel or its intracellular regulators may represent an effective strategy to contrast this lethal tumor.

RCCS bioreactor-based modelled microgravity induces significant changes on in vitro 3D neuroglial cell cultures

We propose a human-derived neuro-/glial cell three-dimensional in vitro model to investigate the effects of microgravity on cell-cell interactions. A rotary cell-culture system (RCCS) bioreactor was used to generate a modelled microgravity environment, and morphofunctional features of glial-like GL15 and neuronal-like SH-SY5Y cells in three-dimensional individual cultures (monotypic aggregates) and cocultures (heterotypic aggregates) were analysed. Cell survival was maintained within all cell aggregates over 2 weeks of culture. Moreover, compared to cells as traditional static monolayers, cell aggregates cultured under modelled microgravity showed increased expression of specific differentiation markers (e.g., GL15 cells: GFAP, S100B; SH-SY5Y cells: GAP43) and modulation of functional cell-cell interactions (e.g., N-CAM and Cx43 expression and localisation). In conclusion, this culture model opens a wide range of specific investigations at the molecular, biochemical, and morphological levels, and it represents an important tool for in vitro studies into dynamic interactions and responses of nervous system cell components to microgravity environmental conditions.

Identification of differentially expressed genes regulated by transcription factors in glioblastomas by bioinformatics analysis

The present study aimed to identify differentially expressed genes (DEGs) regulated by transcription factors (TFs) in glioblastoma, by conducting a bioinformatics analysis. The results of the present study may provide potential therapeutic targets that are involved in the development of glioblastoma. The GSE4290 raw data set was downloaded from the Gene Expression Omnibus database, and consisted of 23 non‑tumor samples and 77 glioblastoma (grade 4) tumor samples. Robust Multichip Averaging was used to identify DEGs between the glioblastoma and non‑tumor samples. Functional enrichment analysis of the DEGs was also performed. Based on the TRANSFAC® database, TFs associated with the glioblastoma gene expression profile were used to construct a regulatory network. Furthermore, trimmed subnets were identified according to calculated Z‑scores. A total of 676 DEGs were identified, of which 190 were upregulated and 496 were downregulated. Gene Ontology analysis demonstrated that the majority of these DEGs were functionally enriched in synaptic transmission, regulation of vesicle‑mediated transport and ion‑gated channel activity. In addition, the enriched Kyoto Encyclopedia of Genes and Genomes pathway included neuroactive ligand‑receptor interaction, calcium signaling pathway, p53 signaling pathway and cell cycle. Based on the TRANSFAC® database, transcriptional regulatory networks with 2,246 nodes and 4,515 regulatory pairs were constructed. According to the Z‑scores, the following candidate TFs were identified: TP53, SP1, JUN, STAT3 and SPI1; alongside their downstream DEGs. TP53 was the only differentially expressed TF. These candidate TFs and their downstream DEGs may have important roles in the progression of glioblastoma, and could be potential biomarkers for clinical treatment.

A review of reagents for fluorescence microscopy of cellular compartments and structures, Part III: reagents for actin, tubulin, cellular membranes, and whole cell and cytoplasm

Non-antibody commercial fluorescent reagents for imaging of cytoskeletal structures have been limited primarily to tubulin and actin, with the main factor in choice based mainly on whether cells are live or fixed and permeabilized. A wider range of options exist for cell membrane dyes, and the choice of reagent primarily depends on the preferred localization in the cell (i.e., all membranes or only the plasma membrane) and usage (i.e., whether the protocol involves fixation and permeabilization). For whole-cell or cytoplasmic imaging, the choice of reagent is determined mostly by the length of time that the cells need to be visualized (hours or days) and by fixation status. Presented here is a discussion on choosing commercially available reagents for these cellular structures, with an emphasis on use for microscopic imaging, with a featured reagent for each structure, a recommended protocol, troubleshooting guide, and example image.

Identification of key signaling molecules involved in the activation of the swelling-activated chloride current in human glioblastoma cells

The swelling-activated chloride current (I Cl,Vol) is abundantly expressed in glioblastoma (GBM) cells, where it controls cell volume and invasive migration. The transduction pathway mediating I Cl,Vol activation in GBM cells is, however, poorly understood. By means of pharmacological and electrophysiological approaches, on GL-15 human GBM cells we found that I Cl,Vol activation by hypotonic swelling required the activity of a U73122-sensitive phospholipase C (PLC). I Cl,Vol activation could also be induced by the membrane-permeable diacylglycerol (DAG) analog OAG. In contrast, neither calcium (Ca(2+)) chelation by BAPTA-AM nor changes in PKC activity were able to affect I Cl,Vol activation by hypotonic swelling. We further found that R59022, an inhibitor of diacylglycerol kinase (DGK), reverted I Cl,Vol activation, suggesting the involvement of phosphatidic acid. In addition, I Cl,Vol activation required the activity of a EHT1864-sensitive Rac1 small GTPase and the resulting actin polymerization, as I Cl,Vol activation was prevented by cytochalasin B. We finally show that I Cl,Vol can be activated by the promigratory fetal calf serum in a PLC- and DGK-dependent manner. This observation is potentially relevant because blood serum can likely come in contact with glioblastoma cells in vivo as a result of the tumor-related partial breakdown of the blood-brain barrier. Given the relevance of I Cl,Vol in GBM cell volume regulation and invasiveness, the several key signaling molecules found in this study to be involved in the activation of the I Cl,Vol may represent potential therapeutic targets against this lethal cancer.

Serum-activated K and Cl currents underlay U87-MG glioblastoma cell migration

Glioblastoma cells in vivo are exposed to a variety of promigratory signals, including undefined serum components that infiltrate into high grade gliomas as result of blood-brain barrier breakdown. Glioblastoma cell migration has been further shown to depend heavily on ion channels activity. We have then investigated the modulatory effects of fetal calf serum (FCS) on ion channels, and their involvement in U87-MG cells migration. Using the perforated patch-clamp technique we have found that, in a subpopulation of cells (42%), FCS induced: (1) an oscillatory activity of TRAM-34 sensitive, intermediate-conductance calcium-activated K (IK(Ca) ) channels, mediated by calcium oscillations previously shown to be induced by FCS in this cell line; (2) a stable activation of a DIDS- and NPPB-sensitive Cl current displaying an outward rectifying instantaneous current-voltage relationship and a slow, voltage-dependent inactivation. By contrast, in another subpopulation of cells (32%) FCS induced a single, transient IK(Ca) current activation, always accompanied by a stable activation of the Cl current. The remaining cells did not respond to FCS. In order to understand whether the FCS-induced ion channel activities are instrumental to promoting cell migration, we tested the effects of TRAM-34 and DIDS on the FCS-induced U87-MG cell migration using transwell migration assays. We found that these inhibitors were able to markedly reduce U87-MG cell migration in the presence of FCS, and that their co-application resulted in an almost complete arrest of migration. It is concluded that the modulation of K and Cl ion fluxes is essential for the FCS-induced glioblastoma cell migration.

Organ-specific manganese toxicity: a comparative in vitro study on five cellular models exposed to MnCl2

Manganese (Mn) is both an essential nutrient and a toxicant, with specific effects on liver and kidney (acute exposure) and on central nervous system (CNS) (chronic exposure). Mn neurotoxicity includes neurobehavioral disorders and extra-pyramidal motor dysfunctions (manganism), possibly due to focal injuries to the basal ganglia. Even if widely investigated, the molecular mechanisms responsible for Mn toxicity remain to be clarified. Aim of this study was to identify suitable in vitro models to investigate these molecular pathways. To this purpose we compared the effect of manganese chloride on four cell lines, representative of the main target organs of Mn toxicity in vivo. HepG2 and MDCK cell lines were selected for liver and kidney, respectively; glial GL15 and neuronal SHSY5Y cells were used as models of CNS components. To complete the "motor system" model, skeletal muscle C2C12 cells were also included. Our results demonstrate that hepatic, renal, glial and neuronal cell types differently react to Mn, mirroring the specific in vivo response of the tissue they represent. This confirms their value as suitable in vitro models to study Mn-related toxic events. Interestingly, also muscle C2C12 cells showed a noticeable sensitivity to Mn, preferential targets being differentiated myotubes.