Involvement of calcineurin in the neurotoxic effects induced by amyloid-beta and prion peptides

Blockade of adenosine A(2A) receptors prevents staurosporine-induced apoptosis of rat hippocampal neurons

Since adenosine A(2A) receptor (A(2A)Rs) blockade protects against noxious brain insults involving apoptosis, we directly tested if A(2A)R blockade prevents apoptosis induced by staurosporine (STS). Exposure of rat hippocampal neurons to STS (30 nM, 24 h) decreased neuronal viability while increasing the number apoptotic-like neurons and de-localizing mitochondria and cytochrome c immunoreactivities. This was prevented by the selective A(2A)R antagonists, SCH58261 and ZM241385 (50 nM). Shorter incubation periods (6 h) with STS caused no neuronal loss but decreased synaptophysin and MAP-2 immunoreactivities, which was prevented by SCH58261. Furthermore, STS (100 nM) decreased MTT reduction and increased caspase-3 activity in rat hippocampal nerve terminals, which was prevented by SCH58261. These results show that A(2A)R blockade inhibits STS-induced apoptotic-like neuronal cell death. This begins with an apoptotic-like synaptotoxicity, which later evolved into an overt neurotoxicity, and A(2A)Rs effectively control this initial synaptotoxicity, in agreement with their predominant synaptic localization in the hippocampus.

Acute inhibition of calcineurin restores associative learning and memory in Tg2576 APP transgenic mice

Misfolded amyloid beta peptide (Abeta) is a pathological hallmark of Alzheimer's disease (AD), a neurodegenerative illness characterized by cognitive deficits and neuronal loss. Transgenic mouse models of Abeta over-production indicate that Abeta-induced cognitive deficits occur in the absence of overt neuronal death, suggesting that while extensive neuronal death may be associated with later stages of the human disease, subtle physiological changes may underlie initial cognitive deficits. Therefore, identifying signaling elements involved in those Abeta-induced cognitive impairments that occur prior to loss of neurons may reveal new potential pharmacological targets. Here, we report that the enzymatic activity of calcineurin, a key protein phosphatase involved in phosphorylation-dependent kinase activity crucial for synaptic plasticity and memory function, is upregulated in the CNS of the Tg2576 animal model for Abeta over-production. Furthermore, acute treatment of Tg2576 mice with the calcineurin inhibitor FK506 (10mg/kg i.p.) improves memory function. These results indicate that calcineurin may mediate some of the cognitive effects of excess Abeta such that inhibition of calcineurin shall be further explored as a potential treatment to reverse cognitive impairments in AD.

Mechanisms of noise-induced hearing loss indicate multiple methods of prevention

Recent research has shown the essential role of reduced blood flow and free radical formation in the cochlea in noise-induced hearing loss (NIHL). The amount, distribution, and time course of free radical formation have been defined, including a clinically significant late formation 7-10 days following noise exposure, and one mechanism underlying noise-induced reduction in cochlear blood flow has finally been identified. These new insights have led to the formulation of new hypotheses regarding the molecular mechanisms of NIHL; and, from these, we have identified interventions that prevent NIHL, even with treatment onset delayed up to 3 days post-noise. It is essential to now assess the additive effects of agents intervening at different points in the cell death pathway to optimize treatment efficacy. Finding safe and effective interventions that attenuate NIHL will provide a compelling scientific rationale to justify human trials to eliminate this single major cause of acquired hearing loss.

Estrogen regulates Bcl-w and Bim expression: role in protection against beta-amyloid peptide-induced neuronal death

Estrogen is neuroprotective against a variety of insults, including beta-amyloid peptide (Abeta); however, the underlying mechanism(s) is not fully understood. Here, we report that 17beta-estradiol (E2) selectively regulates neuronal expression of the Bcl-2 family (bcl-2, bcl-x, bcl-w, bax, bak, bad, bik, bnip3, bid, and bim). In primary cerebrocortical neuron cultures under basal conditions, we observe that E2 upregulates expression of antiapoptotic Bcl-w and downregulates expression of proapoptotic Bim in an estrogen receptor (ER)-dependent manner. In the presence of toxic levels of Abeta, we observe that E2 attenuates indices of neuronal apoptosis: c-Jun N-terminal kinase (JNK)-dependent downregulation of Bcl-w and upregulation of Bim, mitochondrial release of cytochrome c and Smac, and cell death. These neuroprotective effects of E2 against Abeta-induced apoptosis are mimicked by the JNK inhibitor SP600125 (anthra[1,9-cd]pyrazol-6(2H)-one). In addition, E2 attenuates Abeta-induced JNK phosphorylation in an ER-dependent manner, but does not affect basal levels of JNK phosphorylation. These results suggest that E2 may reduce Abeta-induced neuronal apoptosis at least in part by two complementary pathways: (1) ER-dependent, JNK-independent upregulation of Bcl-w and downregulation of Bim under basal conditions, and (2) ER-dependent inhibition of Abeta-induced JNK activation and subsequent JNK-dependent downregulation of Bcl-w and upregulation of Bim, resulting in mitochondrial release of cytochrome c and Smac and eventual cell death. These data provide new understanding into the mechanisms contributing to estrogen neuroprotection, a neural function with potential therapeutic relevance to Alzheimer's disease.

Evidence for a role for the group I metabotropic glutamate receptor in the inhibitory effect of tumor necrosis factor-α on long-term potentiation

Pro-inflammatory cytokines are known to be elevated in several neuropathological states that are associated with learning and memory. We have previously demonstrated in our laboratory that the inhibition of long-term potentiation (LTP) in the dentate gyrus region of the rat hippocampus, by tumor necrosis factor (TNF)-alpha, represents a biphasic response, an early phase dependent on p38 mitogen activated protein kinase (MAPK) activation and a later phase, possible dependent on protein synthesis. Many of the factors involved in the early modulation of LTP by TNF-alpha have yet to be elucidated. This study investigated if metabotropic glutamate receptors (mGluRs) are functionally linked to the inhibitory effect of TNF-alpha on LTP in the rat dentate gyrus in vitro. We report that the impairment of early-LTP by TNF-alpha is significantly attenuated by prior application of the group I/II mGluR antagonist MCPG and more specifically the mGluR5 antagonist MPEP. Since TNF-alpha is now known to cause transient increases in intracellular Ca(2+) levels from ryanodine-sensitive stores, we explored the possibility that disruption of intracellular Ca(2+) homeostasis could be involved. Ryanodine was found to significantly reverse the inhibition of LTP by TNF-alpha. From these studies we propose that the TNF-alpha inhibition of LTP is dependent upon the activation of TNFR1 and mGlu5-receptors. Importantly this study provides the first proof of the involvement of ryanodine-sensitive intracellular Ca(2+) stores in TNF-alpha mediated inhibition of LTP.

Susceptibility of hippocampal neurons to Abeta peptide toxicity is associated with perturbation of Ca2+ homeostasis

Neuritic dystrophy, loss of synapses and neuronal death in the cerebral cortex and hippocampus are hallmarks of Alzheimer's disease. The aim of the present study was to investigate the differential susceptibility of cortical and hippocampal neurons to amyloid-beta (Abeta)-induced toxicity. For that, we have used primary neuronal cultures prepared from rat brain cortex and hippocampus which were treated with the synthetic peptides Abeta25-35 or Abeta1-40. Abeta-induced apoptotic cell death was analyzed by determining caspase-3-like activity. Neuritic dystrophy was evaluated by cobalt staining and MAP2 immunoreactivity. Perturbation of Ca(2+) homeostasis caused by exposure to Abeta was evaluated by determining basal cytosolic calcium levels in the whole neuronal population and by single cell calcium imaging under basal and KCl-depolarization conditions. Finally, levels of GluR2 subunit of glutamate AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionate) receptors were quantified by western blotting. Our results demonstrated that hippocampal neurons in culture are more susceptible than cortical neurons to Abeta-induced apoptosis and also that this mechanism involves the perturbation of Ca(2+) homeostasis. Accordingly, the exposure of hippocampal neurons to Abeta peptides decreases the protein levels of the GluR2 subunit of glutamate AMPA receptors that may be associated with a significant rise of cytosolic Ca(2+) concentration, leading to dendritic dystrophy and activation of apoptotic neuronal death.

Calcineurin mediates acetylcholinesterase expression during calcium ionophore A23187-induced HeLa cell apoptosis

We previously reported that acetylcholinesterase plays a critical role in apoptosis and its expression is regulated by Ca(2+) mobilization. In the present study, we show that activated calpain, a cytosolic calcium-activated cysteine protease, and calcineurin, a calcium-dependent protein phosphatase, regulate acetylcholinesterase expression during A23187-induced apoptosis. The calpain inhibitor, calpeptin, and the calcineurin inhibitors, FK506 and cyclosporine A, inhibited acetylcholinesterase expression at both mRNA and protein levels and suppressed the activity of the human acetylcholinesterase promoter. In contrast, overexpression of constitutively active calcineurin significantly activated the acetylcholinesterase promoter. Furthermore, we identify a role for the transcription factor NFAT (nuclear factor of activated T cells), a calcineurin target, in regulating the acetylcholinesterase promoter during ionophore-induced apoptosis. Overexpression of human NFATc3 and NFATc4 greatly increased the acetylcholinesterase promoter activity in HeLa cells treated with A23187. Overexpression of constitutive nuclear NFATc4 activated the acetylcholinesterase promoter independent of A23187, whereas overexpression of dominant-negative NFAT blocked A23187-induced acetylcholinesterase promoter activation. These results indicate that calcineurin mediates acetylcholinesterase expression during apoptosis.

Prion Protein Aggregation and Neurotoxicity in Cortical Neurons

Prion diseases are degenerative disorders of the central nervous system characterized by cerebral protein aggregation and deposition. A cellular glycoprotein, PrP(C) is converted in an altered isoform, PrP(Sc), that accumulates in the brain, and is believed to be responsible for the neuronal loss observed in prion diseases. The synthetic peptide PrP(106-126) shares many characteristics with PrP(Sc) and is largely used to explore the toxic mechanisms underlying prion diseases. In this article we analyzed the neurotoxic effects of PrP(106-126) in primary rat brain cortical neurons, correlating these results with the presence of amyloid plaques in cultures. Incubation of cells with PrP(106-126), 25 muM, for 2 days did not significantly decrease neuronal viability, although we have observed an increase of basal intracellular calcium levels, reactive oxygen species (ROS) formation, and lipid peroxidation. The presence of congophylic and thioflavin S-amyloid-positive plaques in cortical cultures was only observed after a 5-day-treatment period, correlating with a significant decrease of neuronal viability, as assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and lactate dehydrogenase (LDH) leakage. The data obtained support the idea that PrP(106-126) aggregates in vitro and that the aggregation state is important for its neurotoxicity but also suggest that this synthetic peptide, even when is not aggregated in vitro, can compromise cell homeostasis.

Cardosins: A new and efficient plant enzymatic tool to dissociate neuronal cells for the establishment of cell cultures

In the present work, we examined the feasibility of using cardosins, plant aspartic-proteinases from Cynara cardunculus L., to isolate cells from rat embryonic brain. Using morphological and functional assays, we compared cell cultures obtained with cardosins with those prepared with a well-established trypsin protocol. Cardosins and trypsin dissociation produced cells with similar yield, viability, and GABA release in response to a depolarizing stimulus. However, cardosins-dissociated cells appeared to recover faster in culture, as assessed by the MTT-test and by the number and length of neurtites, suggesting that cardosins are less aggressive to neurons than trypsin. This feature might be helpful for research and medical purposes requiring fast manipulations of cells.

Prion-derived copper-binding peptide fragments catalyze the generation of superoxide anion in the presence of aromatic monoamines

OBJECTIVES

Studies have proposed two opposing roles for copper-bound forms of prion protein (PrP) as an anti-oxidant supporting the neuronal functions and as a pro-oxidant leading to neurodegenerative process involving the generation of reactive oxygen species. The aim of this study is to test the hypothesis in which putative copper-binding peptides derived from PrP function as possible catalysts for monoamine-dependent conversion of hydrogen peroxide to superoxide in vitro.

MATERIALS AND METHODS

Four peptides corresponding to the copper (II)-binding motifs in PrP were synthesized and used for analysis of peptide-catalyzed generation of superoxide in the presence of Cu (II) and other factors naturally present in the neuronal tissues.

RESULTS

Among the Cu-binding peptides tested, the amino acid sequence corresponding to the Cu-binding site in the helical region was shown to be the most active for superoxide generation in the presence of Cu(II), hydrogen peroxide and aromatic monoamines, known precursors or intermediates of neurotransmitters. Among monoamines tested, three compounds namely phenylethylamine, tyramine and benzylamine were shown to be good substrates for superoxide-generating reactions by the Cu-bound helical peptide.

CONCLUSIONS

Possible roles for these reactions in development of prion disease were suggested.

An endoplasmic-reticulum-specific apoptotic pathway is involved in prion and amyloid-beta peptides neurotoxicity

Prion (PrP) and amyloid-beta (Abeta) peptides are involved in the neuronal loss that occurs in Prion disorders (PrD) and Alzheimer's disease (AD), respectively, partially due to Ca(2+) dysregulation. Besides, the endoplasmic reticulum (ER) stress has an active role in the neurotoxic mechanisms that lead to these pathologies. Here, we analyzed whether the ER-mediated apoptotic pathway is involved in the toxic effect of synthetic PrP and Abeta peptides. In PrP106-126- and Abeta1-40-treated cortical neurons, the release of Ca(2+) through ER ryanodine (RyR) and inositol 1,4,5-trisphosphate (IP(3)R) receptors induces ER stress and leads to increased cytosolic Ca(2+) and reactive oxygen species (ROS) levels and subsequently to apoptotic death involving mitochondrial cytochrome c release and caspases activation. These results demonstrate that the early PrP- and Abeta-induced perturbation of ER Ca(2+) homeostasis is a death message that leads to neuronal loss, suggesting that the regulation of ER Ca(2+) levels may be a potential therapeutical target for PrD and AD.

Huperzine A attenuates mitochondrial dysfunction in beta-amyloid-treated PC12 cells by reducing oxygen free radicals accumulation and improving mitochondrial energy metabolism

We observed previously that huperzine A (HupA), a selective acetylcholinesterase inhibitor, can counteract neuronal apoptosis and cell damage induced by several neurotoxic substances, and that this neuroprotective action somehow involves the mitochondria. We investigated the ability of HupA to reduce mitochondrial dysfunction in neuron-like rat pheochromocytoma (PC12) cells exposed in culture to the amyloid beta-peptide fragment 25-35 (Abeta(25-35)). After exposure to 1 microM Abeta(25-35) for various periods, cells exhibited a rapid decline of ATP levels and obvious disruption of mitochondrial membrane homeostasis and integrity as determined by characteristic morphologic alterations, reduced membrane potential, and decreased activity of ion transport proteins. In addition, Abeta(25-35) treatment also led to inhibition of key enzyme activities in the electron transport chain and the tricarboxylic acid cycle, as well as an increase of intracellular reactive oxygen species (ROS). Pre-incubation with HupA for 2 hr not only attenuated these signs of cellular stress caused by Abeta, but also enhanced ATP concentration and decreased ROS accumulation in unharmed normal cells. Those results indicate that HupA protects mitochondria against Abeta-induced damages, at least in part by inhibiting oxidative stress and improving energy metabolism, and that these protective effects reduce the apoptosis of neuronal cells exposed to this toxic peptide.

Comparative study of microglia activation induced by amyloid-beta and prion peptides: Role in neurodegeneration

The inflammatory responses in Alzheimer's disease (AD) and prion-related encephalopathies (PRE) are dominated by microglia activation. Several studies have reported that the amyloid-beta (Abeta) peptides, which are associated with AD, and the pathogenic isoform of prion protein (PrPSc) have a crucial role in neuronal death and gliosis that occur in both of these disorders. In this study, we investigate whether Abeta and PrPSc cause microglia activation per se and whether these amyloidogenic peptides differentially affect these immunoeffector cells. In addition, we also determined whether substances released by Abeta- and PrP-activated microglia induce neuronal death. Cultures of rat brain microglia cells were treated with the synthetic peptides Abeta1-40, Abeta1-42 and PrP106-126 for different time periods. The lipopolysaccharide was used as a positive control of microglia activation. Our results show that Abeta1-40 and PrP106-126 caused similar morphological changes in microglia and increased the production of nitric oxide and hydroperoxides. An increase on inducible nitric oxide synthase expression was also observed in microglia treated with Abeta1-40 or PrP106. However, these peptides affected in a different manner the secretion of interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) secretion. In cocultures of microglia-neurons, it was observed that microglia treated with Abeta1-40 or PrP106-126 induced a comparable extent of neuronal death. The neutralizing antibody for IL-6 significantly reduced the neuronal death induced by Abeta- or PrP-activated microglia. Taken together, the data indicate that Abeta and PrP peptides caused microglia activation and differentially affected cytokine secretion. The IL-6 released by reactive microglia caused neuronal injury.

Calcium-regulated signaling pathways: role in amyloid beta-induced synaptic dysfunction

Amyloid beta (Abeta) peptides have been shown to impair synaptic function, especially long-term synaptic plasticity, in transgenic mouse models of Alzheimer's disease (AD) and in acute hippocampal preparations. In the transgenic mice overexpressing mutant forms of human amyloid precursor protein (APP), the deficits in hippocampal long-term potentiation (LTP) occur prior to synaptic loss and cell death, suggesting early functional changes at these synapses. Recent studies demonstrate that Abeta-induced synaptic dysfunction is linked with altered Ca2+ signaling in hippocampal neurons. While reducing Ca2+ influx through NMDA receptors, Abeta peptides elevate intracellular Ca2+ concentration by enhancing Ca2+ influx from voltage-gated Ca2+ channels or nonselective cation channels, or by stimulating Ca2+ release from intracellular stores. Interestingly, acute application of Abeta or APP overexpression inhibits activity-dependent regulation of several protein kinase pathways that require Ca2+ influx via NMDA receptors for activation, including Ca2+/calmodulin-dependent protein kinase II, protein kinase A, and extracellular regulated kinases (Erk). On the other hand, activation of Ca2+-dependent protein phosphatase 2B (calcineurin) is implicated in Abeta inhibition of LTP. Thus, multiple Ca2+-regulated signaling pathways are involved in the synaptic action of Abeta, and malfunction of these pathways may underlie the synaptic dysfunction in early AD.

Different roles of adenosine A1, A2A and A3 receptors in controlling kainate-induced toxicity in cortical cultured neurons

Adenosine is a neuromodulator that can control brain damage through activation of A(1), A(2A) and A(3) receptors, which are located in both neurons and other brain cells. We took advantage of cultured neurons to investigate the role of neuronal adenosine receptors in the control of neurotoxicity caused by kainate and cyclothiazide. Both A(1), A(2A) and A(3) receptors were immunocytochemically identified in cortical neurons. Activation of A(1) receptors with 100 nM CPA did not modify the extent of neuronal death whereas the A(1) receptor antagonist, DPCPX (50 nM), attenuated neurotoxicity by 28 +/- 5%, and effect similar to that resulting from the removal of endogenous adenosine with 2U/ml of adenosine deaminase (27 +/- 3% attenuation of neurotoxicity). In the presence of adenosine deaminase, DPCPX had no further effect and CPA now exacerbated neurotoxicity by 42 +/- 4%. Activation of A(2A) receptor with 30 nM CGS21680 attenuated neurotoxicity by 40 +/- 8%, an effect prevented by the A(2A) receptor antagonists, SCH58261 (50 nM) or ZM241385 (50 nM), which by themselves were devoid of effect. Finally, neither A(3) receptor activation with Cl-IB-MECA (100-500 nM) nor blockade with MRS1191 (5 microM) modified neurotoxicity. These results show that A(1) receptor activation enhances and A(2A) receptor activation attenuates neurotoxicity in cultured cortical neurons, indicating that these two neuronal adenosine receptors directly control neurodegeneration. Interestingly, the control by adenosine of neurotoxicity in cultured neurons is similar to that observed in vivo in newborn animals and is the opposite of what is observed in adult brain preparations where A(1) receptor activation and A(2A) receptor blockade are neuroprotective.

Analysis of gene expression changes in a cellular model of Parkinson disease

We employed Serial Analysis of Gene Expression to identify transcriptional changes in a cellular model of Parkinson Disease (PD). The model consisted of neuronally differentiated PC12 cells compared before and after 8 hours' exposure to 6-hydroxydopamine. Approximately 1200 transcripts were significantly induced by 6-OHDA and approximately 500 of these are currently matched to known genes. Here, we categorize the regulated genes according to known functional activities and discuss their potential roles in neuron death and survival and in PD. We find induction of multiple death-associated genes as well as many with the capacity for neuroprotection. This suggests that survival or death of individual neurons in PD may reflect an integrated response to both protective and destructive gene changes. Our findings identify a number of regulated genes as candidates for involvement in PD and therefore as potential targets for therapeutic intervention. Such intervention may include both inhibiting the induction/activity of death-promoting genes and enhancing those with neuroprotective activity.

Amidation and structure relaxation abolish the neurotoxicity of the prion peptide PrP106-126 in vivo and in vitro

One of the major pathological hallmarks of transmissible spongiform encephalopathies (TSEs) is the accumulation of a pathogenic (scrapie) isoform (PrP(Sc)) of the cellular prion protein (PrP(C)) primarily in the central nervous system. The synthetic prion peptide PrP106-126 shares many characteristics with PrP(Sc) in that it shows PrP(C)-dependent neurotoxicity both in vivo and in vitro. Moreover, PrP106-126 in vitro neurotoxicity has been closely associated with the ability to form fibrils. Here, we studied the in vivo neurotoxicity of molecular variants of PrP106-126 toward retinal neurons using electroretinographic recordings in mice after intraocular injections of the peptides. We found that amidation and structure relaxation of PrP106-126 significantly reduced the neurotoxicity in vivo. This was also found in vitro in primary neuronal cultures from mouse and rat brain. Thioflavin T binding studies showed that amidation and structure relaxation significantly reduced the ability of PrP106-126 to attain fibrillar structures in physiological salt solutions. This study hence supports the assumption that the neurotoxic potential of PrP106-126 is closely related to its ability to attain secondary structure.

Neuroprotective effect of tacrolimus (FK506) on ischemic brain damage following permanent focal cerebral ischemia in the rat

We investigated the neuroprotective effect of tacrolimus (FK506) on the ischemic cell death with respect to cytochrome c translocation and DNA fragmentation, which are pivotal events in the necrotic and apoptotic signaling pathway, using permanent focal cerebral ischemia in rats. Immunohistochemically, cytochrome c was observed in the cytoplasm as early as 1 h after middle cerebral artery (MCA) occlusion in the infarcted hemisphere. Cytosolic release of cytochrome c after MCA occlusion was also confirmed by Western blot analysis and enzyme immunoassay. Terminal deoxynucleotidyl transferase mediated dUTP nick-end labeling (TUNEL) showed DNA fragmentation evolving in the ipsilateral cortex and the caudate putamen after 3 and 6 h, respectively, following MCA occlusion. Tacrolimus (1 mg/kg, i.v.), administered immediately after MCA occlusion, significantly attenuated the release of cytochrome c in the ischemic region, the number of TUNEL-positive cells in the ischemic penumbra zone, and the size of cortical ischemic lesions. This study demonstrated that tacrolimus ameliorated the accumulation of cytochrome c in the cytosol and the increase of TUNEL-positive cells induced by cerebral ischemia, indicating that the neuroprotective action of tacrolimus on ischemic brain injury caused by permanent focal cerebral ischemia could partially be attributed to the attenuation of the activation of the apoptotic execution machinery.

Involvement of endoplasmic reticulum Ca2+ release through ryanodine and inositol 1,4,5-triphosphate receptors in the neurotoxic effects induced by the amyloid-beta peptide

Studies with in-vitro-cultured neurons treated with amyloid-beta (A beta) peptides demonstrated neuronal loss by apoptosis that is due, at least in part, to the perturbation of intracellular Ca(2+) homeostasis. In addition, it was shown that an endoplasmic reticulum (ER)-specific apoptotic pathway mediated by caspase-12, which is activated upon the perturbation of ER Ca(2+) homeostasis, may contribute to A beta toxicity. To elucidate the involvement of deregulation of ER Ca(2+) homeostasis in neuronal death induced by A beta peptides, we have performed a comparative study using the synthetic peptides A beta(25-35) or A beta(1-40) and thapsigargin, a selective inhibitor of Ca(2+) uptake into the ER. Incubation of cortical neurons with thapsigargin (2.5 microM) increased the intracellular Ca(2+) levels and activated caspase-3, leading to a significant increase in the number of apoptotic cells. Similarly, upon incubation of cortical cultures with the A beta peptides (A beta(25-35), 25 microM; A beta(1-40), 0.5 microM), we observed a significant increase in [Ca(2+)](i), in caspase-3-like activity, and in number of neurons exhibiting apoptotic morphology. The role of ER Ca(2+) release through ryanodine receptors (RyR) or inositol 1,4,5-trisphosphate receptors (IP(3)R) in A beta neurotoxicity has been also investigated. Dantrolene and xestospongin C, inhibitors of ER Ca(2+) release through RyR or IP(3)R, were able to prevent the increase in [Ca(2+)](i) and the activation of caspase-3 and to protect partially against apoptosis induced by treatment with A beta(25-35) or A beta(1-40). In conclusion, our results demonstrate that the release of Ca(2+) from the ER, mediated by both RyR and IP(3)R, is involved in A beta toxicity and can contribute, together with the activation of other intracellular neurotoxic mechanisms, to A beta-induced neuronal death. This study suggests that A beta accumulation may have a key role in the pathogenesis of AD as a result of deregulation of ER Ca(2+) homeostasis.

Neuroprotective effect of H. perforatum extracts on beta-amyloid-induced neurotoxicity

In the present study we assessed the neuroprotective role of a Hypericum perforatum ethanolic extract and obtained fractions in amyloid-beta peptide (Abeta)((25-35))-induced cell death in rat cultured hippocampal neurons. Lipid peroxidation was used as a marker of oxidative stress by following the formation of TBARS in rat cortical synaptosomes, after incubation with ascorbate/Fe2+, alone or in the presence of EC97 effective concentrations of H. perforatum fractions. Induced lipid peroxidation was significantly inhibited by fractions containing flavonol glycosides, flavonol and biflavone aglycones, and by a fraction containing several phenols, mainly chlorogenic acid-type phenolics (21%, 77% and 98%, respectively). Lipid peroxidation evaluated after incubation with 25 microM Abeta(25-35), was significantly inhibited by H. perforatum extract. Cell viability was assessed by use of the Syto-13/PI assay. The total ethanolic extract (TE) and fractions containing flavonol glycosides, flavonol and biflavone aglycones, reduced Abeta(25-35)-induced cell death (65%, 58% and 59%, respectively). These results were further supported by morphological analysis of cells stained with cresyl violet. Peptide beta-amyloid(25-35) induced a decrease in cell volume, chromatin condensation and nuclear fragmentation, alterations not evident in the presence of the TE and fractions containing hypericins (hypericin concentration = 11.02 microM), or fractions containing flavonoids (quercetin concentration = 21.13 microM). Dendritic lesion, an evidence of neurodegeneration, was observed by neuronal staining with cobalt following insult with Abeta(25-35), but prevented after exposure to the peptide plus the fractions referred above. The results of the present paper suggest that H. perforatum extracts may be endowed with neuroprotective compounds able to prevent Abeta(25-35)-induced toxicity.

Neuroprotective properties of Valeriana officinalis extracts

Valeriana officinalis have been used in traditional medicine for its sedative, hypnotic, and anticonvulsant effects. There are several reports in the literature supporting a GABAergic mechanism of action for valerian. The rationale of the present work is based on the concept that by decreasing neuronal network excitability valerian consumption may contribute to neuroprotection. The aim of our investigation was to evaluate the neuroprotective effects of V. officinalis against the toxicity induced by amyloid beta peptide 25-35 Abeta(25-35). Cultured rat hippocampal neurons were exposed to Abeta(25-35) (25 microM) for 24-48 h, after which morphological and biochemical properties were evaluated. The neuronal injury evoked by Abeta, which includes a decrease in cell reducing capacity and associated neuronal degeneration, was prevented by valerian extract. Analysis of intracellular free calcium (Ca(2+)i) indicated that the neuroprotective mechanisms may involve the inhibition of excess influx of Ca2+ following neuronal injury. Moreover, membrane peroxidation in rat hippocampal synaptosomes was evaluated, and our data indicate that valerian extract partially inhibited ascorbate/iron-induced peroxidation. In conclusion we show evidence that the signalling pathways involving Ca(2+)i and the redox state of the cells may play a central role in the neuroprotective properties of V. officinalis extract against Abeta toxicity. The novelty of the findings of the present work, indicating neuroprotective properties of valerian against Abeta toxicity may, at the long-term, contribute to introduction of a new relevant use of valerian alcoholic extract to prevent neuronal degeneration in aging or neurodegenerative disorders.

Reduction of calcium release from the endoplasmic reticulum could only provide partial neuroprotection against beta-amyloid peptide toxicity

Beta-amyloid (Abeta) peptide has been suggested to play important roles in the pathogenesis of Alzheimer's disease (AD). Abeta peptide neurotoxicity was shown to induce disturbance of cellular calcium homeostasis. However, whether modulation of calcium release from the endoplasmic reticulum (ER) can protect neurons from Abeta toxicity is not clearly defined. In the present study, Abeta peptide-triggered ER calcium release in primary cortical neurons in culture is modulated by Xestospongin C, 2-aminoethoxydiphenyl borate or FK506. Our results showed that reduction of ER calcium release can partially attenuate Abeta peptide neurotoxicity evaluated by LDH release, caspase-3 activity and quantification of apoptotic cells. While stress signals associated with perturbations of ER functions such as up-regulation of GRP78 was significantly attenuated, other signaling machinery such as activation of caspase-7 transmitting death signals from ER to other organelles could not be altered. We further provide evidence that molecular signaling in mitochondria play also a significant role in determining neuronal apoptosis because Abeta peptide-triggered activation of caspase-9 was not significantly reduced by attenuating ER calcium release. Our results suggest that neuroprotective strategies aiming at reducing Abeta toxicity should include molecular targets linked to ER perturbations associated with ER calcium release as well as mitochondrial stress.

Selective prion protein binding to synaptic components is modulated by oxidative and nitrosative changes induced by copper(II) and peroxynitrite in cholinergic synaptosomes, unveiling a role for calcineurin B and thioredoxin

Choline acetyltransferase (ChAT) and choline transport are decreased after nitrosative stress. ChAT activity is altered in scrapie-infected neurons, where oxidative stress develops. Cellular prion protein (PrPc) may play a neuroprotective function in participating in the redox control of neuronal environment and regulation of copper metabolism, a role impaired when PrPc is transformed into PrPSc in prion pathologies. The complex cross-talk between PrPc and cholinergic neurons was analyzed in vitro using peroxynitrite and Cu2+ treatments on nerve endings isolated from Torpedo marmorata, a model of the motoneuron pre-synaptic element. Specific interactions between solubilized synaptic components and recombinant ovine prion protein (PrPrec) could be demonstrated by Biacore technology. Peroxynitrite abolished this interaction in a concentration-dependent way and induced significant alterations of neuronal targets. Interaction was restored by prior addition of peroxynitrite trapping agents. Cu2+ (in the form of CuSO4) treatment of synaptosomes triggered a milder oxidative effect leading to a bell-shaped increase of PrPrec binding to synaptosomal components, counteracted by the natural thiol agents, glutathione and thioredoxin. Copper(II)-induced modifications of thiols in several neuronal proteins. A positive correlation was observed between PrPrec binding and immunoreactive changes for calcineurin B and its partners, suggesting a synergy between calcineurin complex and PrP for copper regulation.