Intermediate Filaments as a Target of Signaling Mechanisms in Neurotoxicity

In this chapter, we deal with the current knowledge and important results on the cytoskeletal proteins and their differential regulation by kinases/phosphatases and Ca2+‐mediated mechanisms in developmental rat brain. We focus on the misregulation of the phosphorylating system associated with intermediate filament proteins of neural cells and its relevance to cell and tissue dysfunction. Taking into account our findings, we propose that intermediate‐filament proteins are dynamic structures whose regulation is crucial for proper neural cell function. Given their relevance, they must be regulated in response to extracellular and intracellular signals. The complexity and connection between signaling pathways regulating intermediate‐filament dynamics remain obscure. In this chapter, we get light into some kinase/phosphatase cascades downstream of membrane receptors disrupting the dynamics of intermediate filaments and its association with neural dysfunction. However, intermediate filaments do not act individually into the neural cells. Our results evidence the importance of misregulated cytoskeletal crosstalk in disrupting cytoskeletal dynamics and cell morphology underlying neural dysfunction in experimental conditions mimicking metabolic diseases and nongenomic actions of thyroid hormones and as an end point in the neurotoxicity of organic tellurium

Signaling Mechanisms and Disrupted Cytoskeleton in the Diphenyl Ditelluride Neurotoxicity

Evidence from our group supports that diphenyl ditelluride (PhTe)2 neurotoxicity depends on modulation of signaling pathways initiated at the plasma membrane. The (PhTe)2-evoked signal is transduced downstream of voltage-dependent Ca2+ channels (VDCC), N-methyl-D-aspartate receptors (NMDA), or metabotropic glutamate receptors activation via different kinase pathways (protein kinase A, phospholipase C/protein kinase C, mitogen-activated protein kinases (MAPKs), and Akt signaling pathway). Among the most relevant cues of misregulated signaling mechanisms evoked by (PhTe)2 is the cytoskeleton of neural cells. The in vivo and in vitro exposure to (PhTe)2 induce hyperphosphorylation/hypophosphorylation of neuronal and glial intermediate filament (IF) proteins (neurofilaments and glial fibrillary acidic protein, resp.) in different brain structures of young rats. Phosphorylation of IFs at specific sites modulates their association/disassociation and interferes with important physiological roles, such as axonal transport. Disrupted cytoskeleton is a crucial marker of neurodegeneration and is associated with reactive astrogliosis and apoptotic cell death. This review focuses the current knowledge and important results on the mechanisms of (PhTe)2 neurotoxicity with special emphasis on the cytoskeletal proteins and their differential regulation by kinases/phosphatases and Ca2+-mediated mechanisms in developmental rat brain. We propose that the disrupted cytoskeletal homeostasis could support brain damage provoked by this neurotoxicant

Exposure of young rats to diphenyl ditelluride during lactation affects the homeostasis of the cytoskeleton in neural cells from striatum and cerebellum

AbstractIn the present report we examined the effect of maternal exposure to diphenyl ditelluride (PhTe)2 (0.01mg/kg body weight) during the first 14 days of lactational period on the activity of some protein kinases targeting the cytoskeleton of striatum and cerebellum of their offspring. We analyzed the phosphorylating system associated with glial fibrillary acidic protein (GFAP), and neurofilament of low, medium and high molecular weight (NF-L, NF-M and NF-H, respectively) of pups on PND 15, 21, 30 and 45. We found that (PhTe)2 induced hyperphosphorylation of all the proteins studied on PND 15 and 21, recovering control values on PND 30 and 45. The immunocontent of GFAP, NF-L, NF-M and NF-H in the cerebellum of 15-day-old pups was increased. Western blot assays showed activation/phosphorylation of Erk1/2 on PND 21 and activation/phosphorylation of JNK on PND 15. Otherwise, p38MAPK was not activated in the striatum of (PhTe)2 exposed pups. On the other hand, the cerebellum of pups exposed to (PhTe)2 presented activated/phosphorylated Erk1/2 on PND 15 and 21 as well as activated/phosphorylated p38MAPK on PND 21, while JNK was not activated. Western blot assays showed that both in the striatum and in the cerebellum of (PhTe)2 exposed pups, the immunocontent of the catalytic subunit of PKA (PKAcα) was increased on PND 15. Western blot showed that the phosphorylation level of NF-L Ser55 and NF-M/NF-H KSP repeats was increased in the striatum and cerebellum of both 15- and 21-day-old pups exposed to (PhTe)2. Diphenyl diselenide (PhSe)2, the selenium analog of (PhTe)2, prevented (PhTe)2-induced hyperphosphorylation of striatal intermediate filament (IF) proteins but it failed to prevent the action of (PhTe)2 in cerebellum. Western blot assay showed that the (PhSe)2 prevented activation/phosphorylation of Erk1/2, JNK and PKAcα but did not prevent the stimulatory effect of (PhTe)2 on p38MAPK in cerebellum at PND 21. In conclusion, this study demonstrated that dam exposure to low doses of (PhTe)2 can alter cellular signaling targeting the cytoskeleton of striatum and cerebellum in the offspring in a spatiotemporal manner, which can be related to the neurotoxic effects of (PhTe)2

Dual action of chronic ethanol treatment on LPS-induced response in C6 glioma cells

AbstractIn this study we investigated the anti-inflammatory effects of chronic ethanol (EtOH) treatment on lipopolysaccharide (LPS)-stimulated C6 glioma cells. The cells were chronically treated with 200mM EtOH; coincubation with LPS and EtOH was obtained upon addition of 2μg/ml LPS to the incubation medium in the last 24h of EtOH exposure. We found that EtOH prevented the LPS-induced production of tumor necrosis factor α (TNFα) without decreasing cell viability. Either LPS treated or EtOH plus LPS treated cells presented upregulated glial fibrillary acidic protein (GFAP) and downregulated vimentin levels characterizing a program of reactive astrogliosis. Also, EtOH plus LPS stimulation greatly increased the oxidative stress generation evaluated by DCF-DA measurement, while either EtOH alone or LPS alone was unable to induce oxidative stress. Western blot analysis indicated that either EtOH, LPS or EtOH plus LPS treatments are unable to affect Akt/GSK3β signaling pathway. However, LPS alone and EtOH plus LPS co-treatment inhibited Erk phosphorylation. A dramatic loss of stress fibers was found in EtOH exposed cells, evaluated by cytochemistry using phalloidin-fluorescein. However, LPS alone was not able to disrupt actin organization. Furthermore, cells co-incubated with LPS and EtOH presented reversion of the disrupted stress fibers provoked by EtOH. Supporting this action, RhoA and vinculin immunocontent were upregulated in response to EtOH plus LPS. Interestingly, EtOH suppresses the inflammatory cascade (TNFα production) in response to LPS. Concomitantly it sustains Erk inhibition, increases oxidative stress generation and induces reactive astrogliosis in the presence of LPS, conditions associated with neurotoxicity. The effects observed were not supported by actin reorganization. Altogether, these findings suggest that Erk signaling inhibition could play a role in both suppressing TNFα production and inducing oxidative stress generation and astrogliosis, therefore modulating a dual action of EtOH plus LPS in glial cells

Quantificação de neurofilamentos de hipocampo de ratos submetidos à isquemia cerebral transitória

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Efeito dos ácidos propiônico e metilmalônico sobre os níveis de AMPc em córtex cerebral de ratos jovens

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Efeito da desnutrição proteica sobre o citoesqueleto de cerebro de rato

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