Karina Pires Reis

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.

Methylglyoxal-induced cytotoxicity in neonatal rat brain: a role for oxidative stress and MAP kinases

Carbonyl compounds such as methylglyoxal (MGO) seem to play an important role in complications resulting from diabetes mellitus, in aging and neurodegenerative disorders. In this study, we are showing, that MGO is able to suppress cell viability and induce apoptosis in the cerebral cortex and hippocampus of neonatal rats ex-vivo. These effects are partially related with ROS production, evaluated by DCFH-DA assay. Coincubation of MGO and reduced glutathione (GSH) or Trolox (vitamin E) totally prevented ROS production but only partially prevented the MGO-induced decreased cell viability in the two brain structures, as evaluated by the MTT assay. Otherwise, L-NAME, a nitric oxide (NO) inhibitor, partially prevented ROS production in the two structures but partially prevented cytotoxicity in the hippocampus. Pharmacological inhibition of Erk, has totally attenuated MGO-induced ROS production and cytotoxicity, suggesting that MEK/Erk pathway could be upstream of ROS generation and cell survival. Otherwise, p38MAPK and JNK failed to prevent ROS generation but induced decreased cell survival consistent with ROS-independent mechanisms. We can propose that Erk, p38MAPK and JNK are involved in the cytotoxicity induced by MGO through different signaling pathways. While Erk could be an upstream effector of ROS generation, p38MAPK and JNK seem to be associated with ROS-independent cytotoxicity in neonatal rat brain. The cytotoxic damage progressed to apoptotic cell death at MGO concentration higher than those described for adult brain, suggesting that the neonatal brain is resistant to MGO-induced cell death. The consequences of MGO-induced brain damage early in life, remains to be clarified. However, it is feasible that high MGO levels during cortical and hippocampal development could be, at least in part, responsible for the impairment of cognitive functions in adulthood.

Advantages and challenges offered by biofunctional core–shell fiber systems for tissue engineering and drug delivery

Whereas highly porous scaffolds composed of electrospun nanofibers can mimick major features of the extracellular matrix in tissue engineering, they lack the ability to incorporate and release biocompounds (drugs, growth factors) safely in a controlled way. Here, electrospun core-shell fibers (core made from water and aqueous solutions of hydrophilic polymers and the shell from materials with well-defined release mechanisms) offer unique advantages in comparison with those that have helped make porous nanofibrillar scaffolds highly successful in tissue engineering. This review considers the preparation and biofunctionalization of such core-shell fibers as well as applications in various areas, including neural, vascular, cardiac, cartilage and bone tissue engineering, and touches on the topic of clinical trials.

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.

Cross-talk among intracellular signaling pathways mediates the diphenyl ditelluride actions on the hippocampal cytoskeleton of young rats.

In the present report, we showed that diphenyl ditelluride (PhTe)(2) induced in vitro hyperphosphorylation of glial fibrillary acidic protein (GFAP), vimentin and neurofilament (NF) subunits in hippocampus of 21 day-old rats. Hyperphosphorylation was dependent on L-voltage dependent Ca(2+) channels (L-VDCC), N-methyl-d-aspartate (NMDA) and metabotropic glutamate receptors, as demonstrated by the specific inhibitors verapamil, DL-AP5 and MCPG, respectively. Also, dantrolene, a ryanodine channel blocker, EGTA and Bapta-AM, extra and intracellular Ca(2+) chelators respectively, totally prevented this effect. Activation of metabotropic glutamate receptors by (PhTe)(2) upregulates phospholipase C (PLC), producing inositol 1, 4, 5-trisphosphate (IP(3)) and diacylglycerol (DAG). Therefore, high Ca(2+) levels and DAG directly activate Ca(2+)/calmodulin-dependent protein kinase (PKCaMII) and protein kinase C (PCK), resulting in the hyperphosphorylation of Ser-57 in the carboxyl-terminal tail domain of the low molecular weight NF subunit (NF-L). Also, the activation of Erk1/2, and p38MAPK resulted in hyperphosphorylation of KSP repeats of the medium molecular weight NF subunit (NF-M). It is noteworthy that PKCaMII and PKC inhibitors prevented (PhTe)(2)-induced Erk1/2MAPK and p38MAPK activation as well as hyperphosphorylation of KSP repeats on NF-M, suggesting that PKCaMII and PKC could be upstream of this activation. Taken together, our results highlight the role of Ca(2+) as a mediator of the (PhTe)(2)-elicited signaling targeting specific phosphorylation sites on IF proteins of neural cells of rat hippocampus. Interestingly, this action shows a significant cross-talk among signaling pathways elicited by (PhTe)(2), connecting glutamate metabotropic cascade with activation of Ca(2+) channels. The extensively phosphorylated amino- and carboxyl- terminal sites could explain, at least in part, the neural dysfunction associated with (PhTe)(2) exposure.

Influence of random and oriented electrospun fibrous poly(lactic-co-glycolic acid) scaffolds on neural differentiation of mouse embryonic stem cells

Engineering neural tissue by combining biodegradable materials, cells and growth factors is a promising strategy for the treatment of central and peripheral nervous system injuries. In this study, neural differentiation of mouse embryonic stem cells (mESCs) was investigated in combination with three dimensional (3D) electrospun nanofibers as a substitute for the extracellular matrix (ECM). Nano/microfibrous poly(lactic-co-glycolic acid) (PLGA) 3D scaffolds were fabricated through electrospinning and characterized. The scaffolds consisted of either a randomly oriented or an aligned structure of PLGA fibers. The mESCs were induced to differentiate into neuronal lineage and the effect of the polymer and fiber orientation on cell survival, morphology and differentiation efficiency was studied. The neural progenitors derived from the mESCs could survive and migrate onto the fibrous scaffolds. Aligned fibers provided more contact guidance with the neurites preferentially extending along the long axis of fiber. The mESCs differentiated into neural lineages expressing neural markers as seen by the immunocytochemistry. The nestin and beta3-tubulin expression was enhanced on the PLGA aligned fibers in comparison with the other groups, as seen by the quantitative analysis. Taken together, a combination of electrospun fiber scaffolds and mESC derived neural progenitor cells could provide valuable information about the effects of topology on neural differentiation and axonal regeneration.

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

In the present report we examined the effect of maternal exposure to diphenyl ditelluride (PhTe)(2) (0.01 mg/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).

High postnatal susceptibility of hippocampal cytoskeleton in response to ethanol exposure during pregnancy and lactation

Ethanol exposure to offspring during pregnancy and lactation leads to developmental disorders, including central nervous system dysfunction. In the present work, we have studied the effect of chronic ethanol exposure during pregnancy and lactation on the phosphorylating system associated with the astrocytic and neuronal intermediate filament (IF) proteins: glial fibrillary acidic protein (GFAP), and neurofilament (NF) subunits of low, medium, and high molecular weight (NFL, NFM, and NFH, respectively) in 9- and 21-day-old pups. Female rats were fed with 20% ethanol in their drinking water during pregnancy and lactation. The homeostasis of the IF phosphorylation was not altered in the cerebral cortex, cerebellum, or hippocampus of 9-day-old pups. However, GFAP, NFL, and NFM were hyperphosphorylated in the hippocampus of 21-day-old pups. PKA had been activated in the hippocampus, and Ser55 in the N-terminal region of NFL was hyperphosphorylated. In addition, JNK/MAPK was activated and KSP repeats in the C-terminal region of NFM were hyperphosphorylated in the hippocampus of 21-day-old pups. Decreased NFH immunocontent but an unaltered total NFH/phosphoNFH ratio suggested altered stoichiometry of NFs in the hippocampus of ethanol-exposed 21-day-old pups. In contrast to the high susceptibility of hippocampal cytoskeleton in developing rats, the homeostasis of the cytoskeleton of ethanol-fed adult females was not altered. Disruption of the cytoskeletal homeostasis in neural cells supports the view that regions of the brain are differentially vulnerable to alcohol insult during pregnancy and lactation, suggesting that modulation of JNK/MAPK and PKA signaling cascades target the hippocampal cytoskeleton in a window of vulnerability in 21-day-old pups. Our findings are relevant, since disruption of the cytoskeleton in immature hippocampus could contribute to later hippocampal damage associated with ethanol toxicity.