Hyperhomocysteinemia selectively alters expression and stoichiometry of intermediate filament and induces glutamate‐ and calcium‐mediated mechanisms in rat brain during development

Cytotoxic and genotoxic effects of epoxiconazole on F98 glioma cells

Epoxiconazole (EPX) is a very effective fungicide of the triazole family. Given its wide spectrum of use, the increased application of this pesticide may represent a serious risk on human health. Previous studies have found that EPX is cytotoxic to cells, although the exact mechanism remains elusive. In particular, the effect on the nervous system is poorly elucidated. Here we evaluated the implication of oxidative stress in the neurotoxicity and studied its apoptotic mechanism of action. We demonstrated that the treatment by EPX reduces the viability of cells in a dose dependent manner with an IC50 of 50 μM. It also provokes the reduction of cell proliferation. EPX could trigger arrest in G1/S phase of cell cycle with low doses, however with IC50, it induced an accumulation of F98 cells in G2/M phase. Moreover, EPX induced cytoskeleton disruption as evidenced by immunocytochemical analysis. It provoked also DNA fragmentation in a concentration dependent manner. The EPX induced apoptosis, which was observed by morphological changes and by positive Annexin V FITC-PI staining concurrent with a depolarization of mitochondria. Furthermore, the cell mortality provoked by EPX was significantly reduced by pretreatment with Z-VAD-FMK, a caspase inhibitor. Moreover, N-acetylcysteine (NAC) strongly restores cell viability that has been inhibited by EPX. The results of these findings highlight the implication of ROS generation in the neurotoxicity induced by EPX, indicating that the production of ROS is the main cause of the induction of apoptosis probably via the mitochondrial pathway.

Neurofilament proteins in axonal regeneration and neurodegenerative diseases

Neurofilament protein is a component of the mature neuronal cytoskeleton, and it interacts with the zygosome, which is mediated by neurofilament-related proteins. Neurofilament protein regulates enzyme function and the structure of linker proteins. In addition, neurofilament gene expression plays an important role in nervous system development. Previous studies have shown that neurofilament gene transcriptional regulation is crucial for neurofilament protein expression, especially in axonal regeneration and degenerative diseases. Post-transcriptional regulation increased neurofilament protein gene transcription during axonal regeneration, ultimately resulting in a pattern of neurofilament protein expression. An expression imbalance of post-transcriptional regulatory proteins and other disorders could lead to amyotrophic lateral sclerosis or other neurodegenerative diseases. These findings indicated that after transcription, neurofilament protein regulated expression of related proteins and promoted regeneration of damaged axons, suggesting that regulation disorders could lead to neurodegenerative diseases.

Signaling mechanisms downstream of quinolinic acid targeting the cytoskeleton of rat striatal neurons and astrocytes

The studies of signaling mechanisms involved in the disruption of the cytoskeleton homeostasis were performed in a model of quinolinic acid (QUIN) neurotoxicity in vitro. This investigation focused on the phosphorylation level of intermediate filament (IF) subunits of astrocytes (glial fibrillary acidic protein - GFAP) and neurons (low, medium and high molecular weight neurofilament subunits - NFL, NFM and NFH, respectively). The activity of the phosphorylating system associated with the IFs was investigated in striatal slices of rat exposed to QUIN or treated simultaneously with QUIN plus glutamate receptor antagonists, calcium channel blockers or kinase inhibitors. Results showed that in astrocytes, the action of 100 μM QUIN was mainly due to increased Ca(2+) influx through NMDA and L-type voltage-dependent Ca(2+) channels (L-VDCC). In neuronal cells QUIN acted through metabotropic glutamate receptor (mGluR) activation and influx of Ca(2+) through NMDA receptors and L-VDCC, as well as Ca(2+) release from intracellular stores. These mechanisms then set off a cascade of events including activation of PKA, PKCaMII and PKC, which phosphorylate head domain sites on GFAP and NFL. Also, Cdk5 was activated downstream of mGluR5, phosphorylating the KSP repeats on NFM and NFH. mGluR1 was upstream of phospholipase C (PLC) which, in turn, produced diacylglycerol (DAG) and inositol 3,4,5 triphosphate (IP3). DAG is important to activate PKC and phosphorylate NFL, while IP(3) contributed to Ca(2+) release from internal stores promoting hyperphosphorylation of KSP repeats on the tail domain of NFM and NFH. The present study supports the concept of glutamate and Ca(2+) contribution in excitotoxic neuronal damage provoked by QUIN associated to dysfunction of the cytoskeleton homeostasis and highlights the differential signaling mechanisms elicited in striatal astrocytes and neurons.

Acute ethanol exposure disrupts actin cytoskeleton and generates reactive oxygen species in c6 cells

Central nervous system dysfunctions are among the most significant effects of exposure to ethanol and the glial cells that play an important role in maintaining neuronal function, are extremely involved with these effects. The actin cytoskeleton plays a crucial role in a wide variety of cellular functions, especially when there is some injury. Therefore the aim of the present study was to analyze the short-term effects of ethanol (50, 100 and 200 mM) on the cytoskeleton of C6 glioma cells. Here we report that acute ethanol exposure profoundly disrupts the actin cytoskeleton in C6 cells decreasing stress fiber formation and downregulating RhoA and vinculin immunocontent. In contrast, microtubule and GFAP networks were not altered. We further demonstrate that anti-oxidants prevent ethanol-induced actin alterations, suggesting that the actions of ethanol on the actin cytoskeleton are related with generation of reactive oxygen species (ROS) in these cells. Our results show that ethanol at concentrations described to be toxic to the central nervous system was able to target the cytoskeleton of C6 cells and this effect could be related with increased ROS generation. Therefore, we propose that the dynamic restructuring of the cytoskeleton of glial cells might contribute to the response to the injury provoked by binge-like ethanol exposure in brain.

Homocysteine induces hypophosphorylation of intermediate filaments and reorganization of actin cytoskeleton in C6 glioma cells

In this study, we investigated the actions of high homocysteine (Hcy) levels (100 and 500 microM) on the cytoskeleton of C6 glioma cells. Results showed that the predominant cytoskeletal response was massive formation of actin-containing filopodia at the cell surface that could be related with Cdc42 activation and increased vinculin immunocontent. In cells treated with 100 microM Hcy, folic acid, trolox, and ascorbic acid, totally prevented filopodia formation, while filopodia induced by 500 microM Hcy were prevented by ascorbic acid and attenuated by folic acid and trolox. Moreover, competitive NMDA ionotropic antagonist DL-AP5 totally prevented the formation of filopodia in both 100 and 500 microM Hcy treated cells, while the metabotropic non-selective group I/II antagonist MCPG prevented the effect of 100 microM Hcy but only slightly attenuated the effect induced by of 500 microM Hcy on actin cytoskeleton. The competitive non-NMDA ionotropic antagonist CNQX was not able to prevent the effects of Hcy on the reorganization of actin cytoskeleton in the two concentrations used. Also, Hcy-induced hypophosphorylation of vimentin and glial fibrillary acidic protein (GFAP) and this effect was prevented by DL-AP5, MCPG, and CNQX. In conclusion, our results show that Hcy target the cytoskeleton of C6 cells probably by excitoxicity and/or oxidative stress mechanisms. Therefore, we could propose that the dynamic restructuring of the actin cytoskeleton of glial cells might contribute to the response to the injury provoked by elevated Hcy levels in brain.