Glutamate excitotoxicity activates the MAPK/ERK signaling pathway and induces the survival of rat hippocampal neurons in vivo

Current knowledge concerning the molecular mechanisms of the cellular response to excitotoxic insults in neurodegenerative diseases is insufficient. Although glutamate (Glu) has been widely studied as the main excitatory neurotransmitter and principal excitotoxic agent, the neuroprotective response enacted by neurons is not yet completely understood. Some of the molecular participants have been revealed, but the signaling pathways involved in this protective response are just beginning to be identified. Here, we demonstrate in vivo that, in response to the cell damage and death induced by Glu excitotoxicity, neurons orchestrate a survival response through the extracellular signal-regulated kinase (ERK) signaling pathway by increasing ERK expression in the rat hippocampal (CA1) region, allowing increased neuronal survival. In addition, this protective response is specifically reversed by U0126, an ERK inhibitor, which promotes cell death only when it is administered together with Glu. Our findings demonstrate that the ERK signaling pathway has a neuroprotective role in the response to Glu-induced excitotoxicity in hippocampal neurons. Therefore, the ERK signaling pathway may be activated as a cellular response to excitotoxic injury to prevent damage and neural loss, representing a novel therapeutic target in the treatment of neurodegenerative diseases.

Wnt pathway regulation by long-term moderate exercise in rat hippocampus

An active lifestyle involving regular exercise reduces the deleterious effects of the aging process. At the cerebral level, both synaptic plasticity and neurogenesis are modulated by exercise, although the molecular mechanisms underlying these effects are not clearly understood. In the mature nervous system, the canonical Wnt (Wnt/β-catenin) signaling pathway is implicated in neuroprotection and synaptic plasticity. Here, we examined whether the Wnt pathway could be modulated in adult male rat hippocampus by long-term moderate exercise (treadmill running) or enrichment (handling/environmental stimulation). Sedentary animals showed higher protein levels of the Wnt antagonist, Dkk-1, the lowest levels being found in the exercised group. Although there was no evidence of any changes in activation of the LRP6 receptor, the total levels of LRP6 were higher in exercised and enriched animals. Analysis of some of the components implicated in the phosphorylation of β-catenin, which leads ultimately to its proteasomal degradation, revealed higher levels and activation of Axin1 and GSK-3α/β respectively in sedentary animals. However neither different phosphorylated forms nor total β-catenin protein levels differed between the experimental groups. Higher protein levels of Axin2 and the antiapoptotic protein, Bcl-2, were found with exercise and handling, whereas the proapototic, Bax, was unaffected. Thus, our results suggest activation of the Wnt pathway not only with moderate exercise, but also with the handling of the animals.

Long-term exercise modulates hippocampal gene expression in senescent female mice

The senescence-accelerated SAMP8 mouse is considered a useful non-transgenic model for studying aspects of progressive cognitive decline and Alzheimer's disease (AD). Using SAMR1 mice as controls, here we explored the effects of 6 months of voluntary wheel running in 10-month-old female SAMP8 mice. Exercise in SAMP8 mice improved phenotypic features associated with premature aging (i.e., skin color and body tremor) and enhanced vascularization and BDNF gene expression in the hippocampus compared with controls. With the aim of identifying genes involved in brain aging responsive to long-term exercise, we performed whole genome microarray studies in hippocampus from sedentary SAMP8 (P8sed), SAMR1 (R1sed), and exercised SAMP8 (P8run) mice. The genes differentially expressed in P8sed versus R1sed were considered as putative aging markers (i) and those differentially expressed in P8run versus P8sed were considered as genes modulated by exercise (ii). Genes differentially expressed in both comparisons (i and ii) were considered as putative aging genes responsive to physical exercise. We identified 34 genes which met both criteria. Gene ontology analysis revealed that they are mainly involved in functions related to extracellular matrix maintenance. Selected genes were validated by real-time quantitative PCR assays, i.e., collagen type 1 alpha 1 (col1a1), collagen type 1 alpha 2 (col1a2), fibromodulin (fmod), prostaglandin D(2) synthase (ptgds), and aldehyde dehydrogenase (Aldh1a2). As a whole, our study suggests that exercise training during adulthood may prevent or delay gene expression alterations and processes associated with hippocampal aging in at-risk subjects.

Melatonin suppresses nitric oxide production in glial cultures by pro-inflammatory cytokines through p38 MAPK inhibition

Melatonin has been shown to down-regulate inflammatory responses and provide neuroprotection. However, the mechanisms underlying the anti-inflammatory properties of melatonin are poorly understood. In the present work, we studied the modulatory effect of melatonin against pro-inflammatory cytokines in glial cell cultures. Treatment with pro-inflammatory cytokines mainly tumor necrosis factor-alpha, interleukin 1-beta, and interferon-gamma induces an increase in inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production. Pre-treatment with melatonin produced an inhibitory effect on iNOS expression and NO production. The biochemical studies revealed that cytokine treatment favors the activation of several pathways, such as mitogen-activated protein kinases (MAPKs), STAT1, and STAT3; however, the anti-inflammatory effect of melatonin was accompanied only by a decrease in p38 MAPK activity. Likewise, SB203580 a p38 kinase inhibitor inhibits NO production. These data indicate that the anti-inflammatory action of melatonin in glial cells after stimulation with pro-inflammatory cytokines may be in part, attributable to p38 inhibition which down-regulates iNOS expression and NO production.

Cell-surface Expression of Heat Shock proteins in Dog Neutrophils after Oxidative Stress

The effect of oxidative stress induced by different concentrations of hydrogen peroxide on dog neutrophils was studied. This effect was measured using dichlorofluorescein-diacetate (DCFH-DA) and by the cell surface membrane expression of heat shock protein (HSP) 27kDa, HSP 72kDa and HSP 90kDa families. Hydrogen peroxide induced a concentration-dependent increase in DCFH oxidation (from 10(-6)mto 10(-4)m), and an increase in the cell surface expression of HSPs families. At a concentration of 10(-4)m, the percentage of positive cells that showed an oxidation of DCFH was 94.7%+/-5.2 (n=3). Only vitamin E (but not vitamin C) at a concentration of 0.5mm was able to inhibit the intracellular oxidative stress induced by hydrogen peroxide. The percentage of positive cells that express these proteins after the treatment with hydrogen peroxide (10(-4)m) was: 74%+/-3.5 for HSP 27, 72%+/-2.6 for HSP 72 and 73%+/-1.2 for HSP 90 (n=3). This cell surface expression was not abolished by either vitamin C or vitamin E. Localization of HSPs in plasma membrane is of immunological interest because they have been implicated in autoimmune diseases.

Lack of Jun-N-terminal kinase 3 (JNK3) does not protect against neurodegeneration induced by 3-nitropropionic acid

AIMS

3-Nitropropionic acid (3-NP) is a toxin that replicates most of the clinical and pathophysiological symptoms of Huntington's disease, inducing neurodegeneration in the striatum due to the inhibition of mitochondrial succinate dehydrogenase. Different pathways have been implicated in the cell death induced by 3-NP in rodents. One of them is the Jun-N-terminal kinase (JNK) pathway, which may play a role in the neurodegenerative process in different diseases. Moreover, the lack of one isoform of JNK (JNK3) has been associated with neuroprotection in different experimental models of neurodegeneration. Therefore, in the present study the role of JNK3 in the experimental Huntington's model induced by 3-NP administration was evaluated.

METHODS

3-NP was intraperitoneally administered once a day for 3 days to wild-type and Jnk3-null mice. Coronal brain sections were used to determine cell death and astrogliosis in striatum. Western blots were performed to determine the involvement of different pathways in both wild-type and Jnk3-null mice.

RESULTS

Although JNK activation was observed following 3-NP administration, the results indicate that the lack of JNK3 does not confer neuroprotection against 3-NP toxicity. Thus, other pathways must be involved in the neurodegeneration induced in this model. One of the possible pathways towards 3-NP-induced apoptosis could involve the calpains, as their activity was increased in wild-type and Jnk3-null mice.

CONCLUSION

Although JNK3 is a key protein involved in cell death in different neurodegenerative diseases, the present study demonstrates that the lack of JNK3 does not confer neuroprotection against 3-NP-induced neuronal death.

Long-term treadmill exercise induces neuroprotective molecular changes in rat brain

Exercise enhances general health. However, its effects on neurodegeneration are controversial, and the molecular pathways in the brain involved in this enhancement are poorly understood. Here, we examined the effect of long-term moderate treadmill training on adult male rat cortex and hippocampus to identify the cellular mechanisms behind the effects of exercise. We compared three animal groups: exercised (30 min/day, 12 m/min, 5 days/wk, 36 wk), handled but nonexercised (treadmill handling procedure, 0 m/min), and sedentary (nonhandled and nonexercised). Moderate long-term exercise induced an increase in IGF-1 levels and also in energy parameters, such as PGC-1α and the OXPHOS system. Moreover, the sirtuin 1 pathway was activated in both the exercised and nonexercised groups but not in sedentary rats. This induction could be a consequence of exercise as well as the handling procedure. To determine whether the long-term moderate treadmill training had neuroprotective effects, we studied tau hyperphosphorylation and GSK3β activation. Our results showed reduced levels of phospho-tau and GSK3β activation mainly in the hippocampus of the exercised animals. In conclusion, in our rodent model, exercise improved several major brain parameters, especially in the hippocampus. These improvements induced the upregulation of sirtuin 1, a protein that extends life, the stimulation of mitochondrial biogenesis, the activation of AMPK, and the prevention of signs of neurodegeneration. These findings are consistent with other reports showing that physical exercise has positive effects on hormesis.

[Effects of melatonin in the brain of the senescence-accelerated mice-prone 8 (SAMP8) model]

Senescence-accelerated mice (SAM) represent an aging model establish by selective inbreeding of the AKR/J strain. SAMP8 is a suitable model to study the genetics or proteics fundamental mechanisms of aging, in physiological or pathological conditions, because SAMP8 develop neuropathological markers also found in neurodegenerative diseases like Alzheimer. Melatonin is known as sleep hormone because its action controlling the sleep/awake circadian rhythm. Moreover, melatonin has antioxidant properties and may have an important anti-aging role. The chronic treatment with melatonin in the SAMP8 model was able to reduce oxidative stress and the neurodegenerative calpain/Cdk5 pathway and primed phosphorylation of GSK3beta and tau hiperphosphorylation markers of cerebral aging and neurodegeneration in SAMP8 brains, indicating the neuroprotective and anti-aging effect of melatonin.

Regulation of GSK-3beta by calpain in the 3-nitropropionic acid model

Glycogen synthase kinase-3beta (GSK-3beta) is a crucial component in the cascade of events that culminate in a range of neurodegenerative diseases. It is controlled by several pathways, including calpain-mediated cleavage. Calpain mediates in cell death induced by 3-nitropropionic acid (3-NP), but GSK-3beta regulation has not been demonstrated. Here we studied changes in total GSK-3beta protein levels and GSK-3beta phosphorylation at Ser-9 in this model. The 3-NP treatment induced GSK-3beta truncation. This regulation was dependent on calpain activation, since addition of calpeptin to the medium prevented this cleavage. While calpain inhibition prevented 3-NP-induced neuronal loss, inhibition of GSK-3beta by SB-415286 did not. Furthermore, inhibition of cdk5, a known target of calpain involved in 3-NP-induced cell death, also failed to rescue neurons in our model. Our results point to a new target of calpain and indicate possible cross-talk between calpain and GSK-3beta in the 3-NP toxicity pathway. On the basis of our findings, we propose that calpain may modulate 3-NP-induced neuronal loss.

Proton MR spectroscopy provides relevant prognostic information in high-grade astrocytomas

BACKGROUND AND PURPOSE

There is a large range of survival times in patients with HGA that can only be partially explained by histologic grade and clinical aspects. This study aims to retrospectively assess the predictive value of single-voxel (1)H-MRS regarding survival in HGA.

MATERIALS AND METHODS

Pretreatment (1)H-MRS in 187 patients with HGA produced 180 spectra at STE (30 ms) and 182 at LTE (136 ms). Patients were dichotomized into 2 groups according to survival better or worse than the median. The spectra of the 2 groups were compared using the Mann-Whitney U test. The points on the spectrum with the most significant differences were selected for discriminating patients with good and poor prognosis. Thresholds were defined with ROC curves, and survival was analyzed by using the Kaplan-Meier method and the Cox proportional hazards model.

RESULTS

Four points on the spectrum showed the most significant differences: 0.98 and 3.67 ppm at STE; and 0.98 and 1.25 ppm at LTE (P between <.001 and .011). These points were useful for stratifying 2 prognostic groups (P between <.001 and .003, Kaplan-Meier). The Cox forward stepwise model selected 3 spectroscopic variables: the intensity values of the points 3.67 ppm at STE (hazard ratio, 2.132; 95% CI, 1.504-3.023), 0.98 ppm at LTE (hazard ratio, 0.499; 95% CI, 0.339-0.736), and 1.25 ppm at LTE (hazard ratio, 0.574; 95% CI, 0.368-0.897).

CONCLUSIONS

(1)H-MRS is of value in predicting the length of survival in patients with HGA and could be used to stratify prognostic groups.

Neuroprotective role of intermittent fasting in senescence-accelerated mice P8 (SAMP8)

Dietary interventions have been proposed as a way to increase lifespan and improve health. The senescence-accelerated prone 8 (SAMP8) mice have a shorter lifespan and show alterations in the central nervous system. Moreover, this mouse strain shows decreased sirtuin 1 protein expression and elevated expression of the acetylated targets NFkappaB and FoxO1, which are implicated in transcriptional control of key genes in cell proliferation and cell survival, in reference to control strain, SAMR1. After eight weeks of intermittent fasting, sirtuin 1 protein expression was recovered in SAMP8. This recovery was accompanied by a reduction in the two acetylated targets. Furthermore, SAMP8 showed a lower protein expression of BDNF and HSP70 while intermittent fasting re-established normal values. The activation of JNK and FoxO1 was also reduced in SAMP8 mice subjected to an IF regimen, compared with control SAMP8. Our findings provide new insights into the participation of sirtuin 1 in ageing and point to a potential novel application of this enzyme to prevent frailty due to ageing processes in the brain.

Taurine treatment inhibits CaMKII activity and modulates the presence of calbindin D28k, calretinin, and parvalbumin in the brain

Taurine, 2-aminoethanesulfonic acid, is present at high concentrations in many invertebrate and vertebrate systems and has several biological functions. In addition, it has been related to a neuroprotective role against several diseases such as epilepsy. In the present work, we treated mice with taurine and examined its effects on the expression of proteins in the hippocampus associated with calcium regulation. Taurine treatment alters the presence of calbindin-D28k, calretinin, and parvalbumin in the brain, mainly in the hippocampus. It also reduced CaMKII activity, indicating that taurine could alter calcium signaling pathways. However, the activity of calpain, a protease related to apoptosis induced by calcium signalling, did not change. The concentration of taurine in the hippocampus was also unaffected by the treatment. These results provide new insight into the role of taurine in calcium homeostasis.

Anti-aging properties of melatonin in an in vitro murine senescence model: involvement of the sirtuin 1 pathway

Sirtuin 1 is a member of the sirtuin family of protein deacetylases, which have attracted considerable attention as mediators of lifespan extension in several model organisms. Induction of sirtuin 1 expression also attenuates neuronal degeneration and death in animal models of Alzheimer's disease and Huntington's disease. In this study, an in vitro model of neuronal aging was used to test in several ways whether melatonin acts as a sirtuin 1 inducer and if this effect could be neuroprotective. It is shown that melatonin is able to increase the level of this deacetylase in young primary neurons, as well as in aged neurons. We also observed an increase in the deacetylation of several substrates of sirtuin 1, such as p53, PGC-1alpha, FoxO1, ADAM10 and NFkappaB. In addition, there was a reduction in its nuclear translocation and, subsequently, an improvement in transcriptional activity. Sirtinol, a sirtuin 1 inhibitor, was used to correlate these effects with sirtuin. It is shown that sirtinol reduces sirtuin 1 expression and impairs the beneficial action of melatonin on cell viability and apoptosis prevention. Moreover, some of the sirtuin 1 substrates studied also reversed the melatonin effect when sirtinol is added to the cells, mainly p53. Globally, these results add weight to the findings of previous reports, indicating a new role for melatonin in improving cell function gated to an increased neuroprotective role for the sirtuin 1 pathway.

Prevention of epilepsy by taurine treatments in mice experimental model

An experimental model based on kainic acid (KA) injections replicates many phenomenological features of human temporal lobe epilepsy, the most common type of epilepsy in adults. Taurine, 2-aminoethanesulfonic acid, present in high concentrations in many invertebrate and vertebrate systems, is believed to serve several important biological functions. In addition, it is believed to have a neuroprotective role against several diseases. In the present study, an experimental mouse model based on taurine pretreatment prior to KA administration has been improved to study whether taurine has a neuroprotective effect against KA-induced behavior and cell damage. Under different treatments tested, taurine's most neuroprotective effects were observed with intraperitoneal taurine injection (150 mg/kg dosage) 12 hr before KA administration. Thus, a reduction in or total absence of seizures, together with a reduction in or even disappearance of cellular and molecular KA-derived effects, was detected in mice pretreated with taurine compared with those treated only with KA. Moreover, the use of tritiated taurine revealed taurine entry into the brain, suggesting possible changes in intracellular:extracellular taurine ratios and the triggering of pathways related to neuroprotective effects.

Age-related expression of adenosine receptors in brain from the senescence-accelerated mouse

Senescence-accelerated mice (SAM) are used as a model of aging and age-associated diseases. SAMP8 are prone strains that show shortened life span and deficits in learning and memory processes, while SAMR1 are strains of accelerated senescence-resistant, long-lived mice. Due to their abnormal APP (amyloid precursor protein) metabolism in brain, SAMP8 may be an Alzheimer-type model. Adenosine receptors are G-protein coupled receptors which are altered in brain from Alzheimer disease (AD) cases. The analysis of adenosine receptors in brain from young (21 days old) and middle-aged (180 days old) SAMP8 as compared with SAMR1 mice revealed differences between these strains associated with age. The age-related increase in mRNA coding A1 and A2B receptors observed in SAMR1 was absent in SAMP8. A1 receptors were significantly decreased with age in SAMR1, while no differences were observed in SAMP8. However, the levels of A1 receptors in young SAMP8 were even lower than those obtained in middle-aged SAMR1. In addition, A2A receptors were significantly increased only in aged SAMR1. A similar age-related decrease in A1 receptors level was also observed in brain from male Wistar rats. These results suggest different age-related effects on adenosine receptors in SAMR1 and SAMP8 strains. Since A1 receptors are mainly neuroprotective, their important loss in very young SAMP8 strain suggests the involvement of these receptors in the pathogenesis of neurodegenerative diseases associated with aging.

Melatonin alters cell death processes in response to age-related oxidative stress in the brain of senescence-accelerated mice

We studied the effect of age and melatonin on cell death processes in brain aging. Senescence-accelerated prone mice 8 (SAMP8) and senescence-accelerated resistant mice (SAMR1) at 5 and 10 months of age were used as models of the study. Melatonin (10 mg/kg) or its vehicle (ethanol at 0.066%) was administered in the drinking water from 1 to 9 months of age. Neurodegeneration, previously shown in the aged brain of SAMP8 and SAMR1 at 10 months of age, may be due to a drop in age-related proteolytic activities (cathepsin D, calpains, and caspase-3). Likewise, lack of apoptotic and macroautophagic processes were found, without apparent modification by melatonin. However, the caspase-independent cell death, owing to high p53 and apoptosis-inducing factor (AIF) levels, might be an alternative pathway of cell death in the aged brain. The main effects of melatonin treatment were observed in the aged SAMR1 mice; in this strain we observed a marked increase in antioxidant activity (catalase and superoxide dismutase). Likewise, a key antioxidant role of apoptosis-related proteins, Bcl-2 and AIF, was suggested in the aged brain of SAM mice, which was clearly influenced by melatonin. Moreover, the age-related increase of lysosomal activity of cathepsin B and a lysosomal membrane-associated protein 2 supports the possibility of the maintenance of lysosomal viability in addition to age-related impairments of the proteolytic or macroautophagic activities. The effectiveness of melatonin against the oxidative stress-related impairments and apoptosis during the aging process is, once more, corroborated in this article.

Favorable effects of a prolonged treatment with melatonin on the level of oxidative damage and neurodegeneration in senescence-accelerated mice

Senescence-accelerated mice (SAMP8) and senescence-accelerated resistant mice (SAMR1) were studied at 5 and 10 months of age, respectively. In the animals, neurodegenerative processes and how they were influenced by melatonin were examined. Melatonin (10 mg/kg) or vehicle (ethanol at 0.066%) treatments were administrated from the age of 1 to 9 months in the drinking water. Differences in the neurodegenerative markers examined were found between the two strains with a more damaged protein, phosphorylated Tau at Ser392, increased neurofibrillary tangles (NT) and higher alpha-synuclein expression in SAMP8 versus SAMR1 mice overall, when the mice were 10 months of age. Changes in density of receptors and oxidative stress-related signaling with age were found in the brains of SAM strains at 10 months as shown by a marked decrease in the level of MT-1 melatonin receptor and retinoic acid receptor-related orphan receptor (ROR)-alpha1. This diminution was earlier and more pronounced in SAMP8 mice. Likewise, the levels of nuclear factor-kappa B (NF-kB) transcriptional factor were higher in SAMP8 mice compared with SAMR1 mice regardless of age confirming the direct role of oxidative stress in the aging process. Treatment with melatonin in SAMP8 and SAMR1 mice reduced the neurodegenerative changes with an increase of ROR-alpha1 levels without an apparent influence in the levels of MT-1 receptor. However, different melatonin effects on NF-kB signaling were observed suggesting that NF-kB could trigger inflammatory processes in a different way, being SAM strain-dependent and associated with age-related oxidative stress levels. The effectiveness of melatonin in improving age-related neural impairments is corroborated.

Apoptotic mechanisms involved in neurodegenerative diseases: experimental and therapeutic approaches

Alzheimer's disease (AD) and Parkinson's disease (PD) are two of the most significant neurodegenerative disorders in the developed world. However, although these diseases were described almost a century ago, the molecular mechanisms that lead to the neuronal cell death associated with these diseases are not yet clear, and vigorous research efforts have failed to identify effective treatment options. In the present review, we evaluate the potential mechanisms underlying apoptosis and neuronal death in neurodegenerative disorders. A role for mitochondria in the release of proapoptotic proteins, such as cytochrome c and apoptosis-inducing factor (AIF) etc., is discussed along with key processes involving oxidative stress and activation of glutamate receptors. We also deliberate the implication of DNA damage, primarily p53 induction and reentry in the cell cycle. Finally, we postulate that multitargeting therapies comprising antioxidants, cell cycle inhibitors and modulating agents of COX-2 or c-JUN kinase pathways could be suitable strategies to prevent or delay the process of neuronal cell death in neurodegenerative disorders. Thus, the aim of this review is to discuss the pathways involved in the pathogenesis of neurodegenerative diseases such as AD, PD and Huntington's disease (HD). Furthermore, current and future pharmacotherapeutics will be considered.