Role of oxidative stress and JNK pathway in apoptotic death induced by potassium deprivation and staurosporine in cerebellar granule neurons

Txnip expression promotes JNK-mediated neuronal death in response to reactive oxygen species

TXNIP is a protein sensitive to oxidant conditions whose expression is related to the progression of death in cancer, diabetes, ischemia, and neurodegenerative diseases, among others. Because of this, many studies propose TXNIP as a therapeutic target in several diseases. Exposure of cerebellar granule neurons to staurosporine or low potassium leads to apoptotic death. Both conditions generate an early production of reactive oxygen species (ROS) that induces the activation of the ASK1 pathway and the apoptotic machinery. In these models, it has been shown an increase in TXNIP protein mediated by ROS. Here, we evaluated the molecular mechanisms involved in the regulation of the Txnip expression during neuronal death, as well as the role of the protein in the progression of cell death induced by these two apoptotic conditions. In cultured cerebellar granule neurons, we observed that low potassium and staurosporine induced an early increase in ROS that correlated with an increase in Txnip mRNA. When we evaluated the promoter of the gene, we found that the JASPAR-reported FOXO1/3 transcription factor motifs are close to the transcription start site (TSS). We then verified through the Chromatin immunoprecipitation technique (ChIP) that FOXO3 interacts with the Txnip promoter after 1 h of low potassium treatment. We also detected FOXO3 nuclear translocation by low potassium and staurosporine treatments. Finally, by using shRNA in the neuroblastoma MSN cell line, we found that Txnip downregulation decreased neuronal death induced by staurosporine stimulus. Together, these results suggest that ROS promotes the expression of Txnip through the activation of the FOXO3 transcription factor mediated by Akt inhibition. We also demonstrated that TXNIP is necessary for neuronal death progression.

An Open Question: Is Non-Ionizing Radiation a Tool for Controlling Apoptosis-Induced Proliferation?

Non-ionizing radiation is commonly used in the clinical setting, despite its known ability to trigger oxidative stress and apoptosis, which can lead to damage and cell death. Although induction of cell death is typically considered harmful, apoptosis can also be beneficial in the right context. For example, cell death can serve as the signal for new tissue growth, such as in apoptosis-induced proliferation. Recent data has shown that exposure to non-ionizing radiation (such as weak static magnetic fields, weak radiofrequency magnetic fields, and weak electromagnetic fields) is able to modulate proliferation, both in cell culture and in living organisms (for example during tissue regeneration). This occurs via in vivo changes in the levels of reactive oxygen species (ROS), which are canonical activators of apoptosis. This review will describe the literature that highlights the tantalizing possibility that non-ionizing radiation could be used to manipulate apoptosis-induced proliferation to either promote growth (for regenerative medicine) or inhibit it (for cancer therapies). However, as uncontrolled growth can lead to tumorigenesis, much more research into this exciting and developing area is needed in order to realize its promise.

Differential ROS-Mediated Phosphorylation of Drp1 in Mitochondrial Fragmentation Induced by Distinct Cell Death Conditions in Cerebellar Granule Neurons

Reactive oxygen species (ROS) production has been associated with neuronal death. ROS are also involved in mitochondrial fission, which is mediated by Dynamin-related protein 1 (Drp1). The regulation of mitochondrial fragmentation mediated by Drp1 and its relationship to mitochondrial ROS (mtROS) in neuronal death have not been completely clarified. The aim of this study is to evaluate the role of mtROS in cell death and their involvement in the activation of Drp1 and mitochondrial fission in a model of cell death of cultured cerebellar granule neurons (CGN). Neuronal death of CGN induced by potassium deprivation (K5) and staurosporine (ST) triggers mitochondrial ROS production and mitochondrial fragmentation. K5 condition evoked an increase of Drp1 phosphorylation at Ser616, but ST treatment led to a decrease of Drp1 phosphorylation. Moreover, the death of CGN induced by both K5 and ST was markedly reduced in the presence of MitoTEMPO; however, mitochondrial morphology was not recovered. Here, we show that the mitochondria are the initial source of ROS involved in the neuronal death of CGN and that mitochondrial fragmentation is a common event in cell death; however, this process is not mediated by Drp1 phosphorylation at Ser616.

Caspase-3 Activation Correlates With the Initial Mitochondrial Membrane Depolarization in Neonatal Cerebellar Granule Neurons

In this study we evaluated the effect of the reduction in the endoplasmic reticulum calcium concentration ([Ca²⁺]_ER), changes in the cytoplasmic calcium concentration ([Ca²⁺]_i), alteration of the mitochondrial membrane potential, and the ER stress in the activation of caspase-3 in neonatal cerebellar granule cells (CGN). The cells were loaded with Fura-2 to detect changes in the [Ca²⁺]_i and with Mag-fluo-4 to measure variations in the [Ca²⁺]_ER or with TMRE to follow modifications in the mitochondrial membrane potential in response to five different inducers of CGN cell death. These inducers were staurosporine, thapsigargin, tunicamycin, nifedipine and plasma membrane repolarization by switching culture medium from 25 mM KCl (K25) to 5 mM KCl (K5). Additionally, different markers of ER stress were determined and all these parameters were correlated with the activation of caspase-3. The different inducers of cell death in CGN resulted in three different levels of activation of caspase-3. The highest caspase-3 activity occurred in response to K5. At the same time, staurosporine, nifedipine, and tunicamycin elicited an intermediate activation of caspase-3. Importantly, thapsigargin did not activate caspase-3 at any time. Both K5 and nifedipine rapidly decreased the [Ca²⁺]_i, but only K5 immediately reduced the [Ca²⁺]_ER and the mitochondrial membrane potential. Staurosporine and tunicamycin increased the [Ca²⁺]_i and they decreased both the [Ca²⁺]_ER and mitochondrial membrane potential, but at a much lower rate than K5. Thapsigargin strongly increased the [Ca²⁺]_i, but it took 10 min to observe any decrease in the mitochondrial membrane potential. Three cell death inducers -K5, staurosporine, and thapsigargin- elicited ER stress, but they took 30 min to have any effect. Thapsigargin, as expected, displayed the highest efficacy activating PERK. Moreover, a specific PERK inhibitor did not have any impact on cell death triggered by these cell death inducers. Our data suggest that voltage-gated Ca²⁺ channels, that are not dihydropyridine-sensitive, load the ER with Ca²⁺ and this Ca²⁺ flux plays a critical role in keeping the mitochondrial membrane potential polarized. A rapid decrease in the [Ca²⁺]_ER resulted in rapid mitochondrial membrane depolarization and strong activation of caspase-3 without the intervention of the ER stress in CGN.

Oxidative Stress-Induced DNA Damage and Apoptosis in Clove Buds-Treated MCF-7 Cells

In recent decades, several spices have been studied for their potential in the prevention and treatment of cancer. It is documented that spices have antioxidant, anti-inflammatory, immunomodulatory, and anticancer effects. The main mechanisms of spices action included apoptosis induction, proliferation, migration and invasion of tumour inhibition, and sensitization of tumours to radiotherapy and chemotherapy. In this study, the ability of clove buds extract (CBE) to induce oxidative stress, DNA damage, and stress/survival/apoptotic pathways modulation were analysed in MCF-7 cells. We demonstrated that CBE treatment induced intrinsic caspase-dependent cell death associated with increased oxidative stress mediated by oxygen and nitrogen radicals. We showed also the CBE-mediated release of mitochondrial pro-apoptotic factors, signalling of oxidative stress-mediated DNA damage with modulation of cell antioxidant SOD (superoxide dismutase) system, and modulation activity of the Akt, p38 MAPK, JNK and Erk 1/2 pathways.

Dietary magnesium deficiency impaired intestinal structural integrity in grass carp (Ctenopharyngodon idella)

Grass carp (223.85–757.33 g) were fed diets supplemented with magnesium (73.54–1054.53 mg/kg) for 60 days to explore the impacts of magnesium deficiency on the growth and intestinal structural integrity of the fish. The results demonstrated that magnesium deficiency suppressed the growth and damaged the intestinal structural integrity of the fish. We first demonstrated that magnesium is partly involved in (1) attenuating antioxidant ability by suppressing Nrf2 signalling to decrease antioxidant enzyme mRNA levels and activities (except CuZnSOD mRNA levels and activities); (2) aggravating apoptosis by activating JNK (not p38MAPK) signalling to upregulate proapoptotic protein (Apaf-1, Bax and FasL) and caspase-2, -3, -7, -8 and -9 gene expression but downregulate antiapoptotic protein (Bcl-2, IAP and Mcl-1b) gene expression; (3) weakening the function of tight junctional complexes (TJs) by promoting myosin light chain kinase (MLCK) signalling to downregulate TJ gene expression [except claudin-7, ZO-2b and claudin-15 gene expression]. Additionally, based on percent weight gain (PWG), against reactive oxygen species (ROS), against caspase-9 and claudin-3c in grass carp, the optimal dietary magnesium levels were calculated to be 770.38, 839.86, 856.79 and 811.49 mg/kg, respectively.

Reactive Oxygen Species Evoked by Potassium Deprivation and Staurosporine Inactivate Akt and Induce the Expression of TXNIP in Cerebellar Granule Neurons

The reactive oxygen species (ROS) play a critical role in neuronal apoptosis; however, the mechanisms are not well understood. It has been shown that thioredoxin-interacting protein (TXNIP) overexpression renders cells more susceptible to oxidative stress and promotes apoptosis and that the activation of PI3K/Akt pathway leads to a downregulation of TXNIP. Here, we evaluated the role of ROS in the regulation of Akt activity and the subsequent regulation of the TXNIP expression in a model of apoptotic death of cerebellar granule neurons (CGN). We observed that two apoptotic conditions that generate ROS at short times led to an increase in the expression of TXNIP in a time-dependent manner; antioxidants significantly reduced this expression. Also, H₂O₂ caused an increase in TXNIP expression. Moreover, apoptotic conditions induced inactivation of Akt in a time-dependent manner similar to TXNIP expression and H₂O₂ treatment led to Akt inactivation. Besides, the pharmacological inhibition of Akt increases TXNIP expression and induces CGN cell death. Together, these results suggest that ROS promote neuronal apoptosis through the Akt-TXNIP signaling pathway, supporting the idea that the PI3K/Akt pathway regulates the TXNIP expression. This study highlights the potential importance of this mechanism in neuronal death.

Peroxynitrite is Involved in the Apoptotic Death of Cultured Cerebellar Granule Neurons Induced by Staurosporine, but not by Potassium Deprivation

Nitric oxide (NO) regulates numerous physiological process and is the main source of reactive nitrogen species (RNS). NO promotes cell survival, but it also induces apoptotic death having been involved in the pathogenesis of several neurodegenerative diseases. NO and superoxide anion react to form peroxynitrite, which accounts for most of the deleterious effects of NO. The mechanisms by which these molecules regulate the apoptotic process are not well understood. In this study, we evaluated the role of NO and peroxynitrite in the apoptotic death of cultured cerebellar granule neurons (CGN), which are known to experience apoptosis by staurosporine (St) or potassium deprivation (K5). We found that CGN treated with the peroxynitrite catalyst, FeTTPs were completely rescued from St-induced death, but not from K5-induced death. On the other hand, the inhibition of the inducible nitric oxide synthase partially protected cell viability in CGN treated with K5, but not with St, while the inhibitor L-NAME further reduced the cell viability in St, but it did not affect K5. Finally, an inhibitor of the soluble guanylate cyclase (sGC) diminished the cell viability in K5, but not in St. Altogether, these results shows that NO promotes cell survival in K5 through sGC-cGMP and promotes cell death by other mechanisms, while in St NO promotes cell survival independently of cGMP and peroxynitrite results critical for St-induced death. Our results suggest that RNS are differentially handled by CGN during cell death depending on the death-inducing conditions.

Glutathione administration reduces mitochondrial damage and shifts cell death from necrosis to apoptosis in ageing diabetic mice hearts during exercise

BACKGROUND AND PURPOSE

The effect of antioxidants on ageing type 2 diabetic (T2D) hearts during exercise is unclear. We hypothesized that GSH therapy during exercise reduces mitochondrial oxidative stress (mOXS) and cell death in ageing db/db mice hearts.

EXPERIMENTAL APPROACH

The effect of GSH on cardiac mOXS and cell death was evaluated both in vivo and in vitro.

KEY RESULTS

During exercise, GSH treatment protected db/db hearts from exaggerated mOXS without reducing total cell death. Despite similar cell death, investigations on apoptosis-specific single-stranded DNA breaks and necrosis-specific damage provided the first in vivo evidence of a shift from necrosis to apoptosis, with reduced fibrosis following GSH administration in exercised db/db hearts. Further support for a GSH-regulated 'switch' in death phenotypes came from NIH-3T3 fibroblasts and H9c2 cardiomyocytes treated with H2 O2 , a reactive oxygen species (ROS). Similar to in vivo findings, augmenting GSH by overexpressing glutamyl cysteine ligase (GCLc) protected fibroblasts and cardiomyocytes from necrosis induced by H2 O2 , but elevated caspase-3 and apoptosis instead. Similar to in vivo findings, where GSH therapy in normoglycaemic mice suppressed endogenous antioxidants and augmented caspase-3 activity, GCLc overexpression during staurosporine-induced death, which was not characterized by ROS, increased GSH efflux and aggravated death in fibroblasts and cardiomyocytes, confirming that oxidative stress is required for GSH-mediated cytoprotection.

CONCLUSIONS AND IMPLICATIONS

While GSH treatment is useful for reducing mOXS and attenuating necrosis and fibrosis in ageing T2D hearts during exercise, such antioxidant treatment could be counterproductive in the healthy heart during exercise.

ROS produced by NOX2 control in vitro development of cerebellar granule neurons development

Reactive oxygen species (ROS) act as signaling molecules that regulate nervous system physiology. ROS have been related to neural differentiation, neuritogenesis, and programmed cell death. Nevertheless, little is known about the mechanisms involved in the regulation of ROS during neuronal development. In this study, we evaluated the mechanisms by which ROS are regulated during neuronal development and the implications of these molecules in this process. Primary cultures of cerebellar granule neurons (CGN) were used to address these issues. Our results show that during the first 3 days of CGN development in vitro (days in vitro; DIV), the levels of ROS increased, reaching a peak at 2 and 3 DIV under depolarizing (25 mM KCl) and nondepolarizing (5 mM KCl) conditions. Subsequently, under depolarizing conditions, the ROS levels markedly decreased, but in nondepolarizing conditions, the ROS levels increased gradually. This correlated with the extent of CGN maturation. Also, antioxidants and NADPH-oxidases (NOX) inhibitors reduced the expression of Tau and MAP2. On the other hand, the levels of glutathione markedly increased at 1 DIV. We inferred that the ROS increase at this time is critical for cell survival because glutathione depletion leads to axonal degeneration and CGN death only at 2 DIV. During the first 3 DIV, NOX2 was upregulated and expressed in filopodia and growth cones, which correlated with the hydrogen peroxide (H2O2) distribution in the cell. Finally, NOX2 KO CGN showed shorter neurites than wild-type CGN. Taken together, these results suggest that the regulation of ROS is critical during the early stages of CGN development.

Sub-chronic agmatine treatment modulates hippocampal neuroplasticity and cell survival signaling pathways in mice

Agmatine is an endogenous neuromodulator which, based on animal and human studies, is a putative novel antidepressant drug. In this study, we investigated the ability of sub-chronic (21 days) p.o. agmatine administration to produce an antidepressant-like effect in the tail suspension test and examined the hippocampal cell signaling pathways implicated in such an effect. Agmatine at doses of 0.01 and 0.1 mg/kg (p.o.) produced a significant antidepressant-like effect in the tail suspension test and no effect in the open-field test. Additionally, agmatine (0.001-0.1 mg/kg, p.o.) increased the phosphorylation of protein kinase A substrates (237-258% of control), protein kinase B/Akt (Ser(473)) (116-127% of control), glycogen synthase kinase-3β (Ser(9)) (110-113% of control), extracellular signal-regulated kinases 1/2 (119-137% and 121-138% of control, respectively) and cAMP response elements (Ser(133)) (127-152% of control), and brain-derived-neurotrophic factor (137-175% of control) immunocontent in a dose-dependent manner in the hippocampus. Agmatine (0.001-0.1 mg/kg, p.o.) also reduced the c-jun N-terminal kinase 1/2 phosphorylation (77-71% and 65-51% of control, respectively). Neither protein kinase C nor p38(MAPK) phosphorylation was altered under any experimental conditions. Taken together, the present study extends the available data on the mechanisms that underlie the antidepressant action of agmatine by showing an antidepressant-like effect following sub-chronic administration. In addition, our results are the first to demonstrate the ability of agmatine to elicit the activation of cellular signaling pathways associated with neuroplasticity/cell survival and the inhibition of signaling pathways associated with cell death in the hippocampus.

Effect of staurosporine in the morphology and viability of cerebellar astrocytes: role of reactive oxygen species and NADPH oxidase

Cell death implies morphological changes that may contribute to the progression of this process. In astrocytes, the mechanisms involving the cytoskeletal changes during cell death are not well explored. Although NADPH oxidase (NOX) has been described as being a critical factor in the production of ROS, not much information is available about the participation of NOX-derived ROS in the cell death of astrocytes and their role in the alterations of the cytoskeleton during the death of astrocytes. In this study, we have evaluated the participation of ROS in the death of cultured cerebellar astrocytes using staurosporine (St) as death inductor. We found that astrocytes express NOX1, NOX2, and NOX4. Also, St induced an early ROS production and NOX activation that participate in the death of astrocytes. These findings suggest that ROS produced by St is generated through NOX1 and NOX4. Finally, we showed that the reorganization of tubulin and actin induced by St is ROS independent and that St did not change the level of expression of these cytoskeletal proteins. We conclude that ROS produced by a NOX is required for cell death in astrocytes, but not for the morphological alterations induced by St.

Substantial neuroprotection against K+ deprivation-induced apoptosis in primary cerebellar granule neurons by novel dimer bis(propyl)-cognitin via the activation of VEGFR-2 signaling pathway

BACKGROUND

Neuronal loss via apoptosis in CNS is the fundamental mechanism underlying various neurodegenerative diseases. Compounds with antiapoptotic property might have therapeutic effects for these diseases. In this study, bis(propyl)-cognitin (B3C), a novel dimer that possesses anti-AChE and anti-N-methyl-d-aspartate receptor activities, was investigated for its neuroprotective effect on K(+) deprivation-induced apoptosis in cerebellar granule neurons (CGNs).

METHODS

Cerebellar granule neurons were switched to K(+) deprived medium with or without B3C. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium assay, fluorescein diacetate (FDA)/propidium iodide (PI) staining, Hoechst staining, and DNA laddering assays were applied to detect cytotoxicity and apoptosis. Additionally, the expression of p-VEGFR-2, p-Akt, p-glycogen synthase kinase 3β (GSK3β), and p-extracellular signal-regulated kinase (ERK) was examined in CGNs.

RESULTS

Switching CGNs to K(+) deprived medium resulted in remarkable apoptosis, which could be substantially blocked by B3C treatment (IC50 , 0.37 μM). Moreover, a rapid decrease in p-Tyr1054-VEGFR-2 was observed after the switch. B3C significantly reversed the inhibition of p-Tyr1054-VEGFR-2 as well as Akt and ERK pathways. VEGFR-2 inhibitor PTK787/ZK222584, as well as PI3-K inhibitor LY294002 and MEK inhibitor PD98059, each abolished the neuroprotective effect of B3C.

CONCLUSIONS

Our results demonstrate that B3C blocks K(+) deprivation-induced apoptosis in CGNs through regulating VEGFR-2/Akt/GSK3β and VEGFR-2/ERK signaling pathways, providing a molecular insight into the therapeutic potential of B3C for the treatment of neurodegenerative diseases.

Role of reactive oxygen species and NADPH-oxidase in the development of rat cerebellum

Experimental evidence suggests that reactive oxygen species (ROS) could participate in the regulation of some physiological conditions. In the nervous system, ROS have been suggested to act as signaling molecules involved in several developmental processes including cell differentiation, proliferation and programmed of cell death. Although ROS can be generated by several sources, it has been suggested that NADPH oxidase (NOX) could be critical in the production of ROS acting as a signal in some of these events. It has been reported that ROS production by NOX enzymes participate in neuronal maturation and differentiation during brain development. In the present study, we found that during rat cerebellar development there was a differential ROS generation at different ages and areas of the cerebellum. We also found a differential expression of NOX homologues during rat cerebellar development. When we treated developing rats with an antioxidant or with apocynin, an inhibitor of NOX, we found a marked decrease of the ROS levels in all the cerebellar layers at all the ages tested. Both treatments also induced a significant change in the cerebellar foliation as well as an alteration in motor behavior. These results suggest that both ROS and NOX have a critical role during cerebellar development.

PI3 k/akt inhibition induces apoptosis through p38 activation in neurons

Accumulating evidence suggests that the PI3K/AKT pathway is a pro-survival signalling system in neurons. Therefore, the inhibition of this pathway may be implicated in the degeneration of neurons in Parkinson's disease (PD), Alzheimer's disease (AD), and other neurological disorders. Here we study the participation of the mitogen-activated protein kinase (MAPK) pathway on apoptosis induced by PI3K/AKT inhibition in cultured cerebellar granule cells (CGCs). LY294002, a specific PI3K/AKT inhibitor, selectively activated the p38 MAPK kinase pathway and enhanced c-Jun phosphorylation, but did not activate JNK. The pharmacological inhibitors SB203580 (p38 inhibitor) and SP600125 (a JNK inhibitor) protected primary cultures of rat CGCs from LY294002-induced apoptosis. Furthermore, both compounds decreased the phosphorylation of c-Jun and lowered mRNA levels of the pro-apoptotic gene dp5, a direct target of c-Jun. Taken together, our data demonstrate that PI3K/AKT inhibition induces neuronal apoptosis, a process that is mediated by the activation of p38 MAPK/c-Jun/dp5.

PCSK9 regulates neuronal apoptosis by adjusting ApoER2 levels and signaling

The secreted protease proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to low-density lipid (LDL) receptor family members LDLR, very low density lipoprotein receptor (VLDLR) and apolipoprotein receptor 2 (ApoER2), and promotes their degradation in intracellular acidic compartments. In the liver, LDLR is a major controller of blood LDL levels, whereas VLDLR and ApoER2 in the brain mediate Reelin signaling, a critical pathway for proper development of the nervous system. Expression level of PCSK9 in the brain is highest in the cerebellum during perinatal development, but is also increased in the adult brain after ischemia. The mechanism of PCSK9 function and its involvement in neuronal apoptosis is poorly understood. We show here that RNAi-mediated knockdown of PCSK9 significantly reduced the death of potassium-deprived cerebellar granule neurons (CGN), as shown by reduced levels of nuclear phosphorylated c-Jun and activated caspase-3, as well as condensed apoptotic nuclei. ApoER2 protein levels were increased in PCSK9 RNAi cells. Knockdown of ApoER2 but not of VLDLR was sufficient to reverse the protection provided by PCSK9 RNAi, suggesting that proapoptotic signaling of PCSK9 is mediated by altered ApoER2 function. Pharmacological inhibition of signaling pathways associated with lipoprotein receptors suggested that PCSK9 regulates neuronal apoptosis independently of NMDA receptor function but in concert with ERK and JNK signaling pathways. PCSK9 RNAi also reduced staurosporine-induced CGN apoptosis and axonal degeneration in the nerve growth factor-deprived dorsal root ganglion neurons. We conclude that PCSK9 potentiates neuronal apoptosis via modulation of ApoER2 levels and related anti-apoptotic signaling pathways.

Increased phagocyte-like NADPH oxidase and ROS generation in type 2 diabetic ZDF rat and human islets: role of Rac1-JNK1/2 signaling pathway in mitochondrial dysregulation in the diabetic islet

OBJECTIVE

To determine the subunit expression and functional activation of phagocyte-like NADPH oxidase (Nox), reactive oxygen species (ROS) generation and caspase-3 activation in the Zucker diabetic fatty (ZDF) rat and diabetic human islets.

RESEARCH DESIGN AND METHODS

Expression of core components of Nox was quantitated by Western blotting and densitometry. ROS levels were quantitated by the 2',7'-dichlorofluorescein diacetate method. Rac1 activation was quantitated using the gold-labeled immunosorbent assay kit.

RESULTS

Levels of phosphorylated p47(phox), active Rac1, Nox activity, ROS generation, Jun NH(2)-terminal kinase (JNK) 1/2 phosphorylation, and caspase-3 activity were significantly higher in the ZDF islets than the lean control rat islets. Chronic exposure of INS 832/13 cells to glucolipotoxic conditions resulted in increased JNK1/2 phosphorylation and caspase-3 activity; such effects were largely reversed by SP600125, a selective inhibitor of JNK. Incubation of normal human islets with high glucose also increased the activation of Rac1 and Nox. Lastly, in a manner akin to the ZDF diabetic rat islets, Rac1 expression, JNK1/2, and caspase-3 activation were also significantly increased in diabetic human islets.

CONCLUSIONS

We provide the first in vitro and in vivo evidence in support of an accelerated Rac1-Nox-ROS-JNK1/2 signaling pathway in the islet β-cell leading to the onset of mitochondrial dysregulation in diabetes.

Caspase-3 is a target gene of c-Jun:ATF2 heterodimers during apoptosis induced by activity deprivation in cerebellar granule neurons

Caspase-3, a key executor of neuronal apoptosis, is up-regulated and activated during apoptosis induced by activity deprivation in cerebellar granule neurons (CGNs). However, the transcriptional mechanism regulating caspase-3 during CGN apoptosis remains unknown. Here, we show that the caspase-3 gene is transactivated and its induction is preceded by c-Jun NH(2)-terminal kinase (JNK)/c-Jun:ATF2 pathway activation following activity deprivation in CGNs. We observed that caspase-3 induction is abolished by pharmacological inhibition of the JNK/c-Jun:ATF2 pathway. Destroying c-Jun:ATF2 heterodimers with dominant negative mutants of c-Jun and ATF2 or knockdown by small RNA interference reduced caspase-3 promoter activity and mRNA level. Furthermore, chromatin immunoprecipitation showed increased binding of c-Jun:ATF2 heterodimers to the caspase-3 promoter in response to activity deprivation in vivo. Site-directed mutagenesis of the caspase-3 promoter revealed that caspase-3 transcriptional activation depends primarily on an ATF site -233 to -225 nucleotides upstream of the start site. Taken together, these data demonstrate that caspase-3 is a target gene of c-Jun:ATF2 heterodimers during apoptosis induced by activity deprivation in CGNs.

Reactive oxygen species are related to ionic fluxes and volume decrease in apoptotic cerebellar granule neurons: role of NOX enzymes

Reactive oxygen species (ROS) are produced early during apoptosis of cerebellar granule neurons induced by low potassium (K5) and staurosporine (Sts). In addition, K5 and Sts activate NADPH oxidases (NOX). Recently, we described that K5 and Sts induce apoptotic volume decrease (AVD) at a time when ROS generation and NOX activity occur. In the present study, we evaluated the relationship between ROS generation and ionic fluxes during AVD. Here, we showed that K5- and Sts-induced AVD was inhibited by antioxidants and that direct ROS production induced AVD. Moreover, NOX inhibitors eliminated AVD induced by both K5 and Sts. Sts, but not K5, failed to induce AVD in cerebellar granule neurons from NOX2 knockout mice. These findings suggest that K5- and Sts-induced AVD is largely mediated by ROS produced by NOX. On the other hand, we also found that the blockage of ionic fluxes involved in AVD inhibited both ROS generation and NOX activity. These findings suggest that ROS generation and NOX activity are involved in ionic fluxes activation, which in turn could maintain ROS generation by activating NOX, leading to a self-amplifying cycle.

Posttranslational regulation of BCL2 levels in cerebellar granule cells: A mechanism of neuronal survival

Apoptosis can be modulated by K(+) and Ca(2+) inside the cell and/or in the extracellular milieu. In murine organotypic cultures, membrane potential-regulated Ca(2+) signaling through calcineurin phosphatase has a pivotal role in development and maturation of cerebellar granule cells (CGCs). P8 cultures were used to analyze the levels of expression of B cell lymphoma 2 (BCL2) protein, and, after particle-mediated gene transfer in CGCs, to study the posttranslational modifications of BCL2 fused to a fluorescent tag in response to a perturbation of K(+)/Ca(2+) homeostasis. There are no changes in Bcl2 mRNA after real time PCR, whereas the levels of the fusion protein (monitored by calculating the density of transfected CGCs under the fluorescence microscope) and of BCL2 (inWestern blotting) are increased. After using a series of agonists/antagonists for ion channels at the cell membrane or the endoplasmic reticulum (ER), and drugs affecting protein synthesis/degradation, accumulation of BCL2 was related to a reduction in posttranslational cleavage by macroautophagy. The ER functionally links the [K(+)](e) and [Ca(2+)](i) to the BCL2 content in CGCs along two different pathways. The first, triggered by elevated [K(+)](e) under conditions of immaturity, is independent of extracellular Ca(2+) and operates via IP3 channels. The second leads to influx of extracellular Ca(2+) following activation of ryanodine channels in the presence of physiological [K(+)](e), when CGCs are maintained in mature status. This study identifies novel mechanisms of neuroprotection in immature and mature CGCs involving the posttranslational regulation of BCL2.

Differential activation of mitogen-activated protein kinases and brain-derived neurotrophic factor after temporary or permanent damage to a sensory system

Functional and morphological differences between temporary (TTS) and permanent (PTS) hearing loss induced by acoustic trauma are well characterized whereas molecular differences remain to be elucidated. A comparative analysis of the expression of the phosphorylated forms of extracellular signal-regulated kinase (ERK1/2), c-jun-N-terminal kinases 1/2 (JNK1/2) and p38 in the mouse cochlea after acoustic trauma resulting in either a temporary or permanent damage is presented. In the acute phase of PTS an upregulation of phosphorylated p38, JNK1/2, and ERK1/2 was found while in the acute phase of TTS a downregulation of phospho-p38 occurred and no immediate change of pJNK1/2 and pERK1/2 was noted. After a 24 h recovery from TTS JNK1/2 and ERK1/2 was activated while the expression of phospho-p38 was downregulated. In contrast PTS group showed complete recovery to control values for all three MAPKs by 24 h post. The level of brain-derived neurotrophic factor (BDNF), a potent otoprotective agent, was elevated after both types of acoustic trauma but the elevation after permanent trauma was of a longer duration. The expression of BDNF receptor's TrkB (truncated form) was downregulated only after permanent hearing loss. Thus, temporary and permanent hearing loss demonstrate different expression patterns and temporal aspects of MAPK, BDNF and TrkB in the cochlea. The results of this study will help reveal the cellular mechanisms underlying hearing loss induced by acoustic trauma.

Oxidative stress in rat hippocampus caused by pilocarpine-induced seizures is reversed by buspirone

Temporal lobe epilepsy is the most common form of epilepsy in humans. Oxidative stress is a mechanism of cell death induced by seizures. Buspirone presents anxyolitic and antidepressant effects due to their ability to stimulate 5-HT(1A) receptor. We studied the buspirone effects on oxidative stress in rat hippocampus after seizures and status epilepticus (SE) induced by pilocarpine. In pilocarpine group there was a significant increase in lipid peroxidation and nitrite levels. However, no alteration was observed in superoxide dismutase and catalase activities. Buspirone pretreatment produces significantly reduction of the lipid peroxidation level (60%) and nitrite content (44%) as well as increased the superoxide dismutase (47%) and catalase (40%) activities in rat hippocampus after seizures, when compared with the pilocarpine group. The intraperitoneal injection of buspirone prior to pilocarpine suppressed the behavioral seizure occurrence. According to our results, the oxidative stress is present during seizures. Buspirone exerted anticonvulsant effects associated with the inhibition of the development of oxidative stress. These results suggest a therapeutic use potential of buspirone in epilepsy treatment.