Nuclear factor-κB activation by reactive oxygen species mediates voltage-gated K+ current enhancement by neurotoxic β-amyloid peptides in nerve growth factor-differentiated PC-12 cells and hippocampal neurones

Cerium-Doped Self-Assembling Nanoparticles as a Novel Anti-Oxidant Delivery System Preserving Mitochondrial Function in Cortical Neurons Exposed to Ischemia-like Conditions

Neurodegenerative diseases are characterized by mitochondrial dysfunction leading to abnormal levels of reactive oxygen species (ROS), making the use of ROS-scavenging nanomaterials a promising therapeutic approach. Here, we combined the unique ROS-scavenging properties of cerium-based nanomaterials with the lipid self-assembling nanoparticles (SANP) technology. We optimized the preparation of cerium-doped SANP (Ce-SANP) and characterized the formulations in terms of both physiochemical and biological properties. Ce-SANP exhibited good colloidal properties and were able to mimic the activity of two ROS-scavenging enzymes, namely peroxidase and super oxide dismutase. Under ischemia-like conditions, Ce-SANP could rescue neuronal cells from mitochondrial suffering by reducing ROS production and preventing ATP level reduction. Furthermore, Ce-SANP prevented mitochondrial Ca²⁺ homeostasis dysfunction, partially restoring mitochondrial Ca²⁺ handling. Taken together, these results highlight the potential of the anti-oxidant Ce-SANP platform technology to manage ROS levels and mitochondrial function for the treatment of neurodegenerative diseases.

Increased KV2.1 Channel Clustering Underlies the Reduction of Delayed Rectifier K+ Currents in Hippocampal Neurons of the Tg2576 Alzheimer's Disease Mouse

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the progressive deterioration of cognitive functions. Cortical and hippocampal hyperexcitability intervenes in the pathological derangement of brain activity leading to cognitive decline. As key regulators of neuronal excitability, the voltage-gated K⁺ channels (K_V) might play a crucial role in the AD pathophysiology. Among them, the K_V2.1 channel, the main α subunit mediating the delayed rectifier K⁺ currents (I_DR) and controlling the intrinsic excitability of pyramidal neurons, has been poorly examined in AD. In the present study, we investigated the K_V2.1 protein expression and activity in hippocampal neurons from the Tg2576 mouse, a widely used transgenic model of AD. To this aim we performed whole-cell patch-clamp recordings, Western blotting, and immunofluorescence analyses. Our Western blotting results reveal that K_V2.1 was overexpressed in the hippocampus of 3-month-old Tg2576 mice and in primary hippocampal neurons from Tg2576 mouse embryos compared with the WT counterparts. Electrophysiological experiments unveiled that the whole I_DR were reduced in the Tg2576 primary neurons compared with the WT neurons, and that this reduction was due to the loss of the K_V2.1 current component. Moreover, we found that the reduction of the K_V2.1-mediated currents was due to increased channel clustering, and that glutamate, a stimulus inducing K_V2.1 declustering, was able to restore the I_DR to levels comparable to those of the WT neurons. These findings add new information about the dysregulation of ionic homeostasis in the Tg2576 AD mouse model and identify K_V2.1 as a possible player in the AD-related alterations of neuronal excitability.

Na+/Ca2+ exchanger isoform 1 (NCX1) and canonical transient receptor potential channel 6 (TRPC6) are recruited by STIM1 to mediate Store-Operated Calcium Entry in primary cortical neurons

Excessive calcium (Ca²⁺) release from the endoplasmic reticulum (ER) represents an important hallmark of several neurodegenerative diseases. ER is recharged from Ca²⁺ through the so-called Store-Operated Calcium Entry (SOCE) thus providing Ca²⁺ signals to regulate critical cell functions. Single transmembrane-spanning domain protein stromal interacting molecule 1 (STIM1), mainly residing in the ER, and plasmalemmal channel Orai1 represent the SOCE key components at neuronal level. However, many other proteins participate to ER Ca²⁺ refilling including the Na⁺/Ca²⁺ exchanger isoform 1 (NCX1), whose regulation by ER remains unknown. In this study, we tested the possibility that neuronal NCX1 may take part to SOCE through the interaction with STIM1. In rat primary cortical neurons and in nerve growth factor (NGF)-differentiated PC12 cells NCX1 knocking down by siRNA strategy significantly prevented SOCE as well as SOCE pharmacological inhibition by SKF-96365 and 2-APB. A significant reduction of SOCE was recorded also in synaptosomes from ncx1^-/^- mice brain compared with ncx1⁺/⁺ mice. Double labeling confocal experiments showed a large co-localization between NCX1 and STIM1 in rat primary cortical neurons. Accordingly, NCX1 and STIM1 co-immunoprecipitated and functionally interacted each other during ischemic preconditioning, a phenomenon inducing ischemic tolerance. However, STIM1 knocking down reduced NCX1 activity recorded by either patch-clamp electrophysiology or Fura-2 single-cell microfluorimetry. Furthermore, canonical transient receptor potential channel 6 (TRPC6) was identified as the mechanism mediating local increase of sodium (Na⁺) useful to drive NCX1 reverse mode and, therefore, NCX1-mediated Ca²⁺ refilling. In fact, TRPC6 not only interacted with STIM1, as shown by the co-localization and co-immunoprecipitation with the ER Ca²⁺ sensor, but it also mediated 1,3-Benzenedicarboxylic acid, 4,4'-[1,4,10-trioxa-7,13-diazacyclopentadecane-7,13-diylbis(5-methoxy-6,12-benzofurandiyl)]bis-, tetrakis[(acetyloxy)methyl] ester (SBFI)-monitored Na⁺ increase elicited by thapsigargin in primary cortical neurons. Accordingly, efficient TRPC6 knockdown prevented thapsigargin-induced intracellular Na⁺ elevation and SOCE. Collectively, we identify NCX1 as a new partner of STIM1 in mediating SOCE, whose activation in the reverse mode may be facilitated by the local increase of Na⁺ concentration due to the interaction between STIM1 and TRPC6 in primary cortical neurons.

The Antioxidant Activity of Limonene Counteracts Neurotoxicity Triggered byAβ1-42 Oligomers in Primary Cortical Neurons

Many natural-derived compounds, including the essential oils from plants, are investigated to find new potential protective agents in several neurodegenerative disorders such as Alzheimer's disease (AD). In the present study, we tested the neuroprotective effect of limonene, one of the main components of the genus Citrus, against the neurotoxicity elicited by Aβ_1-42 oligomers, currently considered a triggering factor in AD. To this aim, we assessed the acetylcholinesterase activity by Ellman's colorimetric method, the mitochondrial dehydrogenase activity by MTT assay, the nuclear morphology by Hoechst 33258, the generation of reactive oxygen species (ROS) by DCFH-DA fluorescent dye, and the electrophysiological activity of K_V3.4 potassium channel subunits by patch-clamp electrophysiology. Interestingly, the monoterpene limonene showed a specific activity against acetylcholinesterase with an IC₅₀ almost comparable to that of galantamine, used as positive control. Moreover, at the concentration of 10 µg/mL, limonene counteracted the increase of ROS production triggered by Aβ_1-42 oligomers, thus preventing the upregulation of K_V3.4 activity. This, in turn, prevented cell death in primary cortical neurons, showing an interesting neuroprotective profile against Aβ_1-42-induced toxicity. Collectively, the present results showed that the antioxidant properties of the main component of the genus Citrus, limonene, may be useful to prevent neuronal suffering induced by Aβ_1-42 oligomers preventing the hyperactivity of K_V3.4.

The Anemonia sulcata Toxin BDS-I Protects Astrocytes Exposed to Aβ1-42 Oligomers by Restoring [Ca2+]i Transients and ER Ca2+ Signaling

Intracellular calcium concentration ([Ca2+]i) transients in astrocytes represent a highly plastic signaling pathway underlying the communication between neurons and glial cells. However, how this important phenomenon may be compromised in Alzheimer's disease (AD) remains unexplored. Moreover, the involvement of several K+ channels, including KV3.4 underlying the fast-inactivating currents, has been demonstrated in several AD models. Here, the effect of KV3.4 modulation by the marine toxin blood depressing substance-I (BDS-I) extracted from Anemonia sulcata has been studied on [Ca2+]i transients in rat primary cortical astrocytes exposed to Aβ1-42 oligomers. We showed that: (1) primary cortical astrocytes expressing KV3.4 channels displayed [Ca2+]i transients depending on the occurrence of membrane potential spikes, (2) BDS-I restored, in a dose-dependent way, [Ca2+]i transients in astrocytes exposed to Aβ1-42 oligomers (5 µM/48 h) by inhibiting hyperfunctional KV3.4 channels, (3) BDS-I counteracted Ca2+ overload into the endoplasmic reticulum (ER) induced by Aβ1-42 oligomers, (4) BDS-I prevented the expression of the ER stress markers including active caspase 12 and GRP78/BiP in astrocytes treated with Aβ1-42 oligomers, and (5) BDS-I prevented Aβ1-42-induced reactive oxygen species (ROS) production and cell suffering measured as mitochondrial activity and lactate dehydrogenase (LDH) release. Collectively, we proposed that the marine toxin BDS-I, by inhibiting the hyperfunctional KV3.4 channels and restoring [Ca2+]i oscillation frequency, prevented Aβ1-42-induced ER stress and cell suffering in astrocytes.

TNFAIP1 Is Upregulated in APP/PS1 Mice and Promotes Apoptosis in SH-SY5Y Cells by Binding to RhoB

Alzheimer's disease (AD) poses a significant threat to human life and health. The intraneuronal accumulation of β-amyloid (Aβ) plaques in the brains of AD patients results in neuronal cell death, which is a key factor that triggers multiple changes in the pathogenesis of AD. The inhibition of Aβ-induced neuronal cell death may potentially help in the intervention and treatment of AD. Our previous study reported that tumor necrosis factor α-induced protein 1 (TNFAIP1) is induced by and promotes Aβ_25-35-induced neurotoxicity in mouse neuronal cells, but the roles and regulatory mechanisms of TNFAIP1 are still largely unknown. In this study, our experimental results show that TNFAIP1 and p-TNFAIP1 (phosphorylation of TNFAIP1 at Ser280) are overexpressed in the neurons of the cortex and hippocampus in the brains of APP/PS1 mice, and the transcription factor NF-κB is involved in the Aβ-induced upregulation of TNFAIP1. Moreover, our results suggest that TNFAIP1 contributes to the Aβ-induced reactive oxygen species (ROS) production, decreased mitochondrial membrane potential (∆Ψm), and neuronal cell death in human SH-SY5Y cells. We further revealed that Aβ increases the binding of TNFAIP1 to RhoB, and knockdown of RhoB attenuates the TNFAIP1-induced apoptosis of human SH-SY5Y cells. These data suggest that TNFAIP1 is closely associated with AD pathogenesis, and overexpression of TNFAIP1 in the neurons of the brains of AD patients plays a role in apoptosis, at least in part, via RhoB signaling.

Lavender and coriander essential oils and their main component linalool exert a protective effect against amyloid-β neurotoxicity

Alzheimer's disease (AD) is a neurodegenerative disorder leading to cognitive deficits and cognitive decline. Since no cure or preventing therapy is currently available to counteract AD, natural-derived compounds are investigated to find new potential neuroprotective agents for its treatment. In the present study, we tested the neuroprotective effect of lavender and coriander essential oils (EOs) and their main active constituent linalool, against the neurotoxicity elicited by Aβ_1-42 oligomers, a key molecular factor in the neurodegeneration of AD. Importantly, our findings on neuronally differentiated PC12 cells exposed to Aβ_1-42 oligomers are in accordance with previous in vivo studies reporting the neuroprotective potential of lavender and coriander EOs and linalool. We found that lavender and coriander EOs at the concentration of 10 μg/mL as well as linalool at the same concentration were able to improve viability and to reduce nuclear morphological abnormalities in cells treated with Aβ_1-42 oligomers for 24 hours. Lavender and coriander EOs and linalool also showed to counteract the increase of intracellular reactive oxygen species production and the activation of the pro-apoptotic enzyme caspase-3 induced by Aβ_1-42 oligomers. Our findings provide further evidence that these EOs and their main constituent linalool could be natural agents of therapeutic interest against Aβ_1-42 -induced neurotoxicity.

The Na+/Ca2+exchanger in Alzheimer's disease

As a pivotal player in regulating sodium (Na⁺) and calcium (Ca²⁺) homeostasis and signalling in excitable cells, the Na⁺/Ca²⁺ exchanger (NCX) is involved in many neurodegenerative disorders in which an imbalance of intracellular Ca²⁺ and/or Na⁺ concentrations occurs, including Alzheimer's disease (AD). Although NCX has been mainly implicated in neuroprotective mechanisms counteracting Ca²⁺ dysregulation, several studies highlighted its role in the neuronal responses to intracellular Na⁺ elevation occurring in several pathophysiological conditions. Since the alteration of Na⁺ and Ca²⁺ homeostasis significantly contributes to synaptic dysfunction and neuronal loss in AD, it is of crucial importance to analyze the contribution of NCX isoforms in the homeostatic responses at neuronal and synaptic levels. Some studies found that an increase of NCX activity in brains of AD patients was correlated with neuronal survival, while other research groups found that protein levels of two NCX subtypes, NCX2 and NCX3, were modulated in parietal cortex of late stage AD brains. In particular, NCX2 positive synaptic terminals were increased in AD cohort while the number of NCX3 positive terminals were reduced. In addition, NCX1, NCX2 and NCX3 isoforms were up-regulated in those synaptic terminals accumulating amyloid-beta (Aβ), the neurotoxic peptide responsible for AD neurodegeneration. More recently, the hyperfunction of a specific NCX subtype, NCX3, has been shown to delay endoplasmic reticulum stress and apoptotic neuronal death in hippocampal neurons exposed to Aβ insult. Despite some issues about the functional role of NCX in synaptic failure and neuronal loss require further studies, these findings highlight the putative neuroprotective role of NCX in AD and open new strategies to develop new druggable targets for AD therapy.

Synthesis and Pharmacological Evaluation of a Novel Peptide Based on Anemonia sulcata BDS-I Toxin as a New KV3.4 Inhibitor Exerting a Neuroprotective Effect Against Amyloid-β Peptide

There is increasing evidence that the fast-inactivating potassium current I_A, encoded by K_V3. 4 channels, plays an important role in Alzheimer's Disease (AD), since the neurotoxic β-amyloid peptide1-42 (Aβ_1-42) increases the I_A current triggering apoptotic processes. The specific inhibition of K_V3.4 by the marine toxin extracted from Anemonia sulcata, named blood depressing substance-I (BDS-I), reverts the Aβ peptide-induced cell death. The aim of the present study was to identify the smallest fragments of BDS-I, obtained by peptide synthesis, able to inhibit K_V3.4 currents. For this purpose, whole-cell patch clamp technique was used to evaluate the effects of BDS-I fragments on K_V3.4 currents in CHO cells heterologously expressing K_V3.4. We found that BDS-I[1-8] fragment, containing the N-terminal octapeptide sequence of full length BDS-I, was able to inhibit K_V3.4 currents in a concentration dependent manner, whereas the scrambled sequence of BDS-I[1-8] and all the other fragments obtained from BDS-I full length were ineffective. As we demonstrated in a previous study, BDS-I full length is able to counteract Aβ_1-42-induced enhancement of K_V3.4 activity, preventing Aβ_1-42-induced caspase-3 activation and the abnormal nuclear morphology in NGF-differentiated PC-12 cells. Similarly to BDS-I, we found that BDS-I[1-8] blocking K_V3.4 currents prevented Aβ_1-42-induced caspase-3 activation and apoptotic processes. Collectively, these results suggest that BDS-I[1-8] could represent a lead compound to be developed as a new drug targeting K_V3.4 channels.

Kv3 Channels: Enablers of Rapid Firing, Neurotransmitter Release, and Neuronal Endurance

The intrinsic electrical characteristics of different types of neurons are shaped by the K+ channels they express. From among the more than 70 different K+ channel genes expressed in neurons, Kv3 family voltage-dependent K+ channels are uniquely associated with the ability of certain neurons to fire action potentials and to release neurotransmitter at high rates of up to 1,000 Hz. In general, the four Kv3 channels Kv3.1-Kv3.4 share the property of activating and deactivating rapidly at potentials more positive than other channels. Each Kv3 channel gene can generate multiple protein isoforms, which contribute to the high-frequency firing of neurons such as auditory brain stem neurons, fast-spiking GABAergic interneurons, and Purkinje cells of the cerebellum, and to regulation of neurotransmitter release at the terminals of many neurons. The different Kv3 channels have unique expression patterns and biophysical properties and are regulated in different ways by protein kinases. In this review, we cover the function, localization, and modulation of Kv3 channels and describe how levels and properties of the channels are altered by changes in ongoing neuronal activity. We also cover how the protein-protein interaction of these channels with other proteins affects neuronal functions, and how mutations or abnormal regulation of Kv3 channels are associated with neurological disorders such as ataxias, epilepsies, schizophrenia, and Alzheimer's disease.

The expression and activity of KV3.4 channel subunits are precociously upregulated in astrocytes exposed to Aβ oligomers and in astrocytes of Alzheimer's disease Tg2576 mice

Astrocyte dysfunction emerges early in Alzheimer's disease (AD) and may contribute to its pathology and progression. Recently, the voltage gated potassium channel K_V3.4 subunit, which underlies the fast-inactivating K⁺ currents, has been recognized to be relevant for AD pathogenesis and is emerging as a new target candidate for AD. In the present study, we investigated both in in vitro and in vivo models of AD the expression and functional activity of K_V3.4 potassium channel subunits in astrocytes. In primary astrocytes our biochemical, immunohistochemical, and electrophysiological studies demonstrated a time-dependent upregulation of K_V3.4 expression and functional activity after exposure to amyloid-β (Aβ) oligomers. Consistently, astrocytic K_V3.4 expression was upregulated in the cerebral cortex, hippocampus, and cerebellum of 6-month-old Tg2576 mice. Further, confocal triple labeling studies revealed that in 6-month-old Tg2576 mice, K_V3.4 was intensely coexpressed with Aβ in nonplaque associated astrocytes. Interestingly, in the cortical and hippocampal regions of 12-month-old Tg2576 mice, plaque-associated astrocytes much more intensely expressed K_V3.4 subunits, but not Aβ. More important, we evidenced that the selective knockdown of K_V3.4 expression significantly downregulated both glial fibrillary acidic protein levels and Aβ trimers in the brain of 6-month-old Tg2576 mice. Collectively, our results demonstrate that the expression and function of K_V3.4 channel subunits are precociously upregulated in cultured astrocytes exposed to Aβ oligomers and in reactive astrocytes of AD Tg2576 mice.

Role of TGFβ signaling in the pathogenesis of Alzheimer's disease

Aging is the main risk factor for Alzheimer’s disease (AD); being associated with conspicuous changes on microglia activation. Aged microglia exhibit an increased expression of cytokines, exacerbated reactivity to various stimuli, oxidative stress, and reduced phagocytosis of β-amyloid (Aβ). Whereas normal inflammation is protective, it becomes dysregulated in the presence of a persistent stimulus, or in the context of an inflammatory environment, as observed in aging. Thus, neuroinflammation can be a self-perpetuating deleterious response, becoming a source of additional injury to host cells in neurodegenerative diseases. In aged individuals, although transforming growth factor β (TGFβ) is upregulated, its canonical Smad3 signaling is greatly reduced and neuroinflammation persists. This age-related Smad3 impairment reduces protective activation while facilitating cytotoxic activation of microglia through several cellular mechanisms, potentiating microglia-mediated neurodegeneration. Here, we critically discuss the role of TGFβ-Smad signaling on the cytotoxic activation of microglia and its relevance in the pathogenesis of AD. Other protective functions, such as phagocytosis, although observed in aged animals, are not further induced by inflammatory stimuli and TGFβ1. Analysis in silico revealed that increased expression of receptor scavenger receptor (SR)-A, involved in Aβ uptake and cell activation, by microglia exposed to TGFβ, through a Smad3-dependent mechanism could be mediated by transcriptional co-factors Smad2/3 over the MSR1 gene. We discuss that changes of TGFβ-mediated regulation could at least partially mediate age-associated microglia changes, and, together with other changes on inflammatory response, could result in the reduction of protective activation and the potentiation of cytotoxicity of microglia, resulting in the promotion of neurodegenerative diseases.

Resveratrol via sirtuin-1 downregulates RE1-silencing transcription factor (REST) expression preventing PCB-95-induced neuronal cell death

Resveratrol (3,5,4'-trihydroxystilbene) (RSV), a polyphenol widely present in plants, exerts a neuroprotective function in several neurological conditions; it is an activator of class III histone deacetylase sirtuin1 (SIRT1), a crucial regulator in the pathophysiology of neurodegenerative diseases. By contrast, the RE1-silencing transcription factor (REST) is involved in the neurotoxic effects following exposure to polychlorinated biphenyl (PCB) mixture A1254. The present study investigated the effects of RSV-induced activation of SIRT1 on REST expression in SH-SY5Y cells. Further, we investigated the possible relationship between the non-dioxin-like (NDL) PCB-95 and REST through SIRT1 to regulate neuronal death in rat cortical neurons. Our results revealed that RSV significantly decreased REST gene and protein levels in a dose- and time-dependent manner. Interestingly, overexpression of SIRT1 reduced REST expression, whereas EX-527, an inhibitor of SIRT1, increased REST expression and blocked RSV-induced REST downregulation. These results suggest that RSV downregulates REST through SIRT1. In addition, RSV enhanced activator protein 1 (AP-1) transcription factor c-Jun expression and its binding to the REST promoter gene. Indeed, c-Jun knockdown reverted RSV-induced REST downregulation. Intriguingly, in SH-SY5Y cells and rat cortical neurons the NDL PCB-95 induced necrotic cell death in a concentration-dependent manner by increasing REST mRNA and protein expression. In addition, SIRT1 knockdown blocked RSV-induced neuroprotection in rat cortical neurons treated with PCB-95. Collectively, these results indicate that RSV via SIRT1 activates c-Jun, thereby reducing REST expression in SH-SY5Y cells under physiological conditions and blocks PCB-95-induced neuronal cell death by activating the same SIRT1/c-Jun/REST pathway.

Linking aβ42-induced hyperexcitability to neurodegeneration, learning and motor deficits, and a shorter lifespan in an Alzheimer's model

Alzheimer's disease (AD) is the most prevalent form of dementia in the elderly. β-amyloid (Aβ) accumulation in the brain is thought to be a primary event leading to eventual cognitive and motor dysfunction in AD. Aβ has been shown to promote neuronal hyperactivity, which is consistent with enhanced seizure activity in mouse models and AD patients. Little, however, is known about whether, and how, increased excitability contributes to downstream pathologies of AD. Here, we show that overexpression of human Aβ42 in a Drosophila model indeed induces increased neuronal activity. We found that the underlying mechanism involves the selective degradation of the A-type K+ channel, Kv4. An age-dependent loss of Kv4 leads to an increased probability of AP firing. Interestingly, we find that loss of Kv4 alone results in learning and locomotion defects, as well as a shortened lifespan. To test whether the Aβ42-induced increase in neuronal excitability contributes to, or exacerbates, downstream pathologies, we transgenically over-expressed Kv4 to near wild-type levels in Aβ42-expressing animals. We show that restoration of Kv4 attenuated age-dependent learning and locomotor deficits, slowed the onset of neurodegeneration, and partially rescued premature death seen in Aβ42-expressing animals. We conclude that Aβ42-induced hyperactivity plays a critical role in the age-dependent cognitive and motor decline of this Aβ42-Drosophila model, and possibly in AD.

Early growth response 2 (Egr-2) expression is triggered by NF-κB activation

Transcription factors are known to play multiple roles in cellular function. Investigators report that factors such as early growth response (Egr) protein and nuclear factor kappa B (NF-κB) are activated in the brain during cancer, brain injury, inflammation, and/or memory. To explore NF-κB activity further, we investigated the transcriptomes of hippocampal slices following electrical stimulation of NF-κB p50 subunit knockout mice (p50-/-) versus their controls (p50+/+). We found that the early growth response gene Egr-2 was upregulated by NF-κB activation, but only in p50+/+ hippocampal slices. We then stimulated HeLa cells and primary cortical neurons with tumor necrosis factor alpha (TNFα) to activate NF-κB and increase the expression of Egr-2. The Egr-2 promoter sequence was analyzed for NF-κB binding sites and chromatin immunoprecipitation (ChIP) assays were performed to confirm promoter occupancy in vivo. We discovered that NF-κB specifically binds to an NF-κB consensus binding site within the proximal promoter region of Egr-2. Luciferase assay demonstrated that p50 was able to transactivate the Egr-2 promoter in vitro. Small interfering RNA (siRNA)-mediated p50 knockdown corroborated other Egr-2 expression studies. We show for the first time a novel link between NF-κB activation and Egr-2 expression with Egr-2 expression directly controlled by the transcriptional activity of NF-κB.

Curcumin a potent cancer preventive agent: Mechanisms of cancer cell killing

There is no doubt that diet could effectively improve health and halt cancers. Dietary phytochemical compounds and their derivatives represent a cornucopia of effectively anticancer compounds. This review discusses existing data on the anticancer activities of curcumin, and then offers possible explanations for and mechanisms of its cancer-preventive action. This review also offers insights into the molecular mechanism and targets through which curcumin modulates cell cycle, apoptotic signals, anti-apoptotic proteins, miRNAs, Wnt/beta-catenin signaling, protein kinases, nuclear factor-κB, proteasome activation, epigenetic regulation including DNA methylation and histone modification. Finally, this review provides explanations for how curcumin reverses the multi-drug resistance (MDR) of cancer cells.

Attenuation of Aβ25-35-induced parallel autophagic and apoptotic cell death by gypenoside XVII through the estrogen receptor-dependent activation of Nrf2/ARE pathways

Amyloid-beta (Aβ) has a pivotal function in the pathogenesis of Alzheimer's disease. To investigate Aβ neurotoxicity, we used an in vitro model that involves Aβ25-35-induced cell death in the nerve growth factor-induced differentiation of PC12 cells. Aβ25-35 (20μM) treatment for 24h caused apoptotic cell death, as evidenced by significant cell viability reduction, LDH release, phosphatidylserine externalization, mitochondrial membrane potential disruption, cytochrome c release, caspase-3 activation, PARP cleavage, and DNA fragmentation in PC12 cells. Aβ25-35 treatment led to autophagic cell death, as evidenced by augmented GFP-LC3 puncta, conversion of LC3-I to LC3-II, and increased LC3-II/LC3-I ratio. Aβ25-35 treatment induced oxidative stress, as evidenced by intracellular ROS accumulation and increased production of mitochondrial superoxide, malondialdehyde, protein carbonyl, and 8-OHdG. Phytoestrogens have been proved to be protective against Aβ-induced neurotoxicity and regarded as relatively safe targets for AD drug development. Gypenoside XVII (GP-17) is a novel phytoestrogen isolated from Gynostemma pentaphyllum or Panax notoginseng. Pretreatment with GP-17 (10μM) for 12h increased estrogen response element reporter activity, activated PI3K/Akt pathways, inhibited GSK-3β, induced Nrf2 nuclear translocation, augmented antioxidant responsive element enhancer activity, upregulated heme oxygenase 1 (HO-1) expression and activity, and provided protective effects against Aβ25-35-induced neurotoxicity, including oxidative stress, apoptosis, and autophagic cell death. In conclusion, GP-17 conferred protection against Aβ25-35-induced neurotoxicity through estrogen receptor-dependent activation of PI3K/Akt pathways, inactivation of GSK-3β and activation of Nrf2/ARE/HO-1 pathways. This finding might provide novel insights into understanding the mechanism for neuroprotective effects of phytoestrogens or gypenosides.

Voltage-gated potassium channels at the crossroads of neuronal function, ischemic tolerance, and neurodegeneration

Voltage-gated potassium (Kv) channels are widely expressed in the central and peripheral nervous system and are crucial mediators of neuronal excitability. Importantly, these channels also actively participate in cellular and molecular signaling pathways that regulate the life and death of neurons. Injury-mediated increased K(+) efflux through Kv2.1 channels promotes neuronal apoptosis, contributing to widespread neuronal loss in neurodegenerative disorders such as Alzheimer's disease and stroke. In contrast, some forms of neuronal activity can dramatically alter Kv2.1 channel phosphorylation levels and influence their localization. These changes are normally accompanied by modifications in channel voltage dependence, which may be neuroprotective within the context of ischemic injury. Kv1 and Kv7 channel dysfunction leads to neuronal hyperexcitability that critically contributes to the pathophysiology of human clinical disorders such as episodic ataxia and epilepsy. This review summarizes the neurotoxic, neuroprotective, and neuroregulatory roles of Kv channels and highlights the consequences of Kv channel dysfunction on neuronal physiology. The studies described in this review thus underscore the importance of normal Kv channel function in neurons and emphasize the therapeutic potential of targeting Kv channels in the treatment of a wide range of neurological diseases.

Systemic administration of substance P recovers beta amyloid-induced cognitive deficits in rat: involvement of Kv potassium channels

Reduced levels of Substance P (SP), an endogenous neuropeptide endowed with neuroprotective and anti-apoptotic properties, have been found in brain and spinal fluid of Alzheimer's disease (AD) patients. Potassium (K(+)) channel dysfunction is implicated in AD development and the amyloid-β (Aβ)-induced up-regulation of voltage-gated potassium channel subunits could be considered a significant step in Aβ brain toxicity. The aim of this study was to evaluate whether SP could reduce, in vivo, Aβ-induced overexpression of Kv subunits. Rats were intracerebroventricularly infused with amyloid-β 25-35 (Aβ25-35, 20 µg) peptide. SP (50 µg/Kg, i.p.) was daily administered, for 7 days starting from the day of the surgery. Here we demonstrate that the Aβ infused rats showed impairment in cognitive performances in the Morris water maze task 4 weeks after Aβ25-35 infusion and that this impairing effect was prevented by SP administration. Kv1.4, Kv2.1 and Kv4.2 subunit levels were quantified in hippocampus and in cerebral cortex by Western blot analysis and immunofluorescence. Interestingly, SP reduced Kv1.4 levels overexpressed by Aβ, both in hippocampus and cerebral cortex. Our findings provide in vivo evidence for a neuroprotective activity of systemic administration of SP in a rat model of AD and suggest a possible mechanism underlying this effect.

A new concept: Aβ1-42 generates a hyperfunctional proteolytic NCX3 fragment that delays caspase-12 activation and neuronal death

Although the amyloid-β(1-42) (Aβ(1-42)) peptide involved in Alzheimer's disease is known to cause a dysregulation of intracellular Ca(2+) homeostasis, its molecular mechanisms still remain unclear. We report that the extracellular-dependent early increase (30 min) in intracellular calcium concentration ([Ca(2+)](i)), following Aβ(1-42) exposure, caused the activation of calpain that in turn elicited a cleavage of the Na(+)/Ca(2+) exchanger isoform NCX3. This cleavage generated a hyperfunctional form of the antiporter and increased NCX currents (I(NCX)) in the reverse mode of operation. Interestingly, this NCX3 calpain-dependent cleavage was essential for the Aβ(1-42)-dependent I(NCX) increase. Indeed, the calpain inhibitor calpeptin and the removal of the calpain-cleavage recognition sequence, via site-directed mutagenesis, abolished this effect. Moreover, the enhanced NCX3 activity was paralleled by an increased Ca(2+) content in the endoplasmic reticulum (ER) stores. Remarkably, the silencing in PC-12 cells or the knocking-out in mice of the ncx3 gene prevented the enhancement of both I(NCX) and Ca(2+) content in ER stores, suggesting that NCX3 was involved in the increase of ER Ca(2+) content stimulated by Aβ(1-42). By contrast, in the late phase (72 h), when the NCX3 proteolytic cleavage abruptly ceased, the occurrence of a parallel reduction in ER Ca(2+) content triggered ER stress, as revealed by caspase-12 activation. Concomitantly, the late increase in [Ca(2+)](i) coincided with neuronal death. Interestingly, NCX3 silencing caused an earlier activation of Aβ(1-42)-induced caspase-12. Indeed, in NCX3-silenced neurons, Aβ(1-42) exposure hastened caspase-dependent apoptosis, thus reinforcing neuronal cell death. These results suggest that Aβ(1-42), through Ca(2+)-dependent calpain activation, generates a hyperfunctional form of NCX3 that, by increasing Ca(2+) content into ER, delays caspase-12 activation and thus neuronal death.

Alzheimer's disease: redox dysregulation as a common denominator for diverse pathogenic mechanisms

Alzheimer's disease (AD) is the most common cause of dementia and a progressive neurodegeneration that appears to result from multiple pathogenic mechanisms (including protein misfolding/aggregation, involved in both amyloid β-dependent senile plaques and tau-dependent neurofibrillary tangles), metabolic and mitochondrial dysfunction, excitoxicity, calcium handling impairment, glial cell dysfunction, neuroinflammation, and oxidative stress. Oxidative stress, which could be secondary to several of the other pathophysiological mechanisms, appears to be a major determinant of the pathogenesis and progression of AD. The identification of oxidized proteins common for mild cognitive impairment and AD suggests that key oxidation pathways are triggered early and are involved in the initial progression of the neurodegenerative process. Abundant data support that oxidative stress, also considered as a main factor for aging, the major risk factor for AD, can be a common key element capable of articulating the divergent nature of the proposed pathogenic factors. Pathogenic mechanisms influence each other at different levels. Evidence suggests that it will be difficult to define a single-target therapy resulting in the arrest of progression or the improvement of AD deterioration. Since oxidative stress is present from early stages of disease, it appears as one of the main targets to be included in a clinical trial. Exploring the articulation of AD pathogenic mechanisms by oxidative stress will provide clues for better understanding the pathogenesis and progression of this dementing disorder and for the development of effective therapies to treat this disease.

Effect of synthetic aβ peptide oligomers and fluorinated solvents on Kv1.3 channel properties and membrane conductance

The impact of synthetic amyloid β (1–42) (Aβ_1–42) oligomers on biophysical properties of voltage-gated potassium channels Kv 1.3 and lipid bilayer membranes (BLMs) was quantified for protocols using hexafluoroisopropanol (HFIP) or sodium hydroxide (NaOH) as solvents prior to initiating the oligomer formation. Regardless of the solvent used Aβ_1–42 samples contained oligomers that reacted with the conformation-specific antibodies A11 and OC and had similar size distributions as determined by dynamic light scattering. Patch-clamp recordings of the potassium currents showed that synthetic Aβ_1–42 oligomers accelerate the activation and inactivation kinetics of Kv 1.3 current with no significant effect on current amplitude. In contrast to oligomeric samples, freshly prepared, presumably monomeric, Aβ_1–42 solutions had no effect on Kv 1.3 channel properties. Aβ_1–42 oligomers had no effect on the steady-state current (at −80 mV) recorded from Kv 1.3-expressing cells but increased the conductance of artificial BLMs in a dose-dependent fashion. Formation of amyloid channels, however, was not observed due to conditions of the experiments. To exclude the effects of HFIP (used to dissolve lyophilized Aβ_1–42 peptide), and trifluoroacetic acid (TFA) (used during Aβ_1–42 synthesis), we determined concentrations of these fluorinated compounds in the stock Aβ_1–42 solutions by ¹⁹F NMR. After extensive evaporation, the concentration of HFIP in the 100× stock Aβ_1–42 solutions was ∼1.7 μM. The concentration of residual TFA in the 70× stock Aβ_1–42 solutions was ∼20 μM. Even at the stock concentrations neither HFIP nor TFA alone had any effect on potassium currents or BLMs. The Aβ_1–42 oligomers prepared with HFIP as solvent, however, were more potent in the electrophysiological tests, suggesting that fluorinated compounds, such as HFIP or structurally-related inhalational anesthetics, may affect Aβ_1–42 aggregation and potentially enhance ability of oligomers to modulate voltage-gated ion channels and biological membrane properties.

Prolonged Abeta treatment leads to impairment in the ability of primary cortical neurons to maintain K+ and Ca2+ homeostasis

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disease, characterised by the formation of insoluble amyloidogenic plaques and neurofibrillary tangles. Beta amyloid (Abeta) peptide is one of the main constituents in Abeta plaques, and is thought to be a primary causative agent in AD. Neurons are likely to be exposed to chronic, sublethal doses of Abeta over an extended time during the pathogenesis of AD, however most studies published to date using in vitro models have focussed on acute studies. To experimentally model the progressive pathogenesis of AD, we exposed primary cortical neurons daily to 1 muM of Abeta1-40 over 7 days and compared their survival with age-similar untreated cells. We also investigated whether chronic Abeta exposure affects neuronal susceptibility to the subsequent acute excitotoxicity induced by 10 muM glutamate and assessed how Ca2+ and K+ homeostasis were affected by either treatment.

RESULTS

We show that continuous exposure to 1 muM Abeta1-40 for seven days decreased survival of cultured cortical neurons by 20%. This decrease in survival correlated with increased K+ efflux from the cells. One day treatment with 1 muM Abeta followed by glutamate led to a substantially higher K+ efflux than in the age-similar untreated control. This difference further increased with the duration of the treatment. K+ efflux also remained higher in Abeta treated cells 20 min after glutamate application leading to 2.8-fold higher total K+ effluxed from the cells compared to controls. Ca2+ uptake was significantly higher only after prolonged Abeta treatment with 2.5-fold increase in total Ca2+ uptake over 20 min post glutamate application after six days of Abeta treatment or longer (P < 0.05).

CONCLUSIONS

Our data suggest that long term exposure to Abeta is detrimental because it reduces the ability of cortical neurons to maintain K+ and Ca2+ homeostasis in response to glutamate challenge, a response that might underlie the early symptoms of AD. The observed inability to maintain K+ homeostasis might furthermore be useful in future studies as an early indicator of pathological changes in response to Abeta.

l-Theanine, an amino acid in green tea, attenuates beta-amyloid-induced cognitive dysfunction and neurotoxicity: reduction in oxidative damage and inactivation of ERK/p38 kinase and NF-kappaB pathways

Amyloid beta (Abeta)-induced neurotoxicity is a major pathological mechanism of Alzheimer disease (AD). In this study, we investigated the inhibitory effect of l-theanine, a component of green tea (Camellia sinensis), on Abeta(1-42)-induced neuronal cell death and memory impairment. Oral treatment of l-theanine (2 and 4 mg/kg) for 5 weeks in the drinking water of mice, followed by injection of Abeta(1-42) (2 microg/mouse, icv), significantly attenuated Abeta(1-42)-induced memory impairment. Furthermore, l-theanine reduced Abeta(1-42) levels and the accompanying Abeta(1-42)-induced neuronal cell death in the cortex and hippocampus of the brain. Moreover, l-theanine inhibited Abeta(1-42)-induced extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase as well as the activity of nuclear factor kappaB (NF-kappaB). l-Theanine also significantly reduced oxidative protein and lipid damage and the elevation of glutathione levels in the brain. These data suggest that the positive effects of l-theanine on memory may be mediated by suppression of ERK/p38 and NF-kappaB as well as the reduction of macromolecular oxidative damage. Thus, l-theanine may be useful in the prevention and treatment of AD.

SP protects cerebellar granule cells against beta-amyloid-induced apoptosis by down-regulation and reduced activity of Kv4 potassium channels

The tachykinin endecapeptide substance P (SP) has been demonstrated to exert a functional role in neurodegenerative disorders, including Alzheimer's disease (AD). Aim of the present study was to evaluate the SP neuroprotective potential against apoptosis induced by the neurotoxic beta-amyloid peptide (A beta) in cultured rat cerebellar granule cells (CGCs). We found that SP protects CGCs against both A beta(25-35)- and A beta(1-42)-induced apoptotic CGCs death as revealed by live/dead cell assay, Hoechst staining and caspase(s)-induced PARP-1 cleavage, through an Akt-dependent mechanism. Since in CGCs the fast inactivating or A-type K(+) current (I(KA)) was potentiated by A beta treatment through up-regulation of Kv4 subunits, we investigated whether I(KA) and the related potassium channel subunits could be involved in the SP anti-apoptotic activity. Patch-clamp experiments showed that the A beta-induced increase of I(KA) current amplitude was reversed by SP treatment. In addition, as revealed by Western blot analysis and immunofluorescence studies, SP prevented the up-regulation of Kv4.2 and Kv4.3 channel subunits expression. These results indicate that SP plays a role in the regulation of voltage-gated potassium channels in A beta-mediated neuronal death and may represent a new approach in the understanding and treatment of AD.

Post-ischemic brain damage: NF-kappaB dimer heterogeneity as a molecular determinant of neuron vulnerability

Nuclear factor-kappaB (NF-kappaB) has been proposed to serve a dual function as a regulator of neuron survival in pathological conditions associated with neurodegeneration. NF-kappaB is a transcription family of factors comprising five different proteins, namely p50, RelA/p65, c-Rel, RelB and p52, which can combine differently to form active dimers in response to external stimuli. Recent research shows that diverse NF-kappaB dimers lead to cell death or cell survival in neurons exposed to ischemic injury. While the p50/p65 dimer participates in the pathogenesis of post-ischemic injury by inducing pro-apoptotic gene expression, c-Rel-containing dimers increase neuron resistance to ischemia by inducing anti-apoptotic gene transcription. We present, in this report, the latest findings and consider the therapeutic potential of targeting different NF-kappaB dimers to limit ischemia-associated neurodegeneration.

NF-kappaB dimers in the regulation of neuronal survival

Nuclear factor-kappaB (NF-kappaB) is a dimeric transcription factor composed of five members, p50, RelA/p65, c-Rel, RelB, and p52 that can diversely combine to form the active transcriptional dimer. NF-kappaB controls the expression of genes that regulate a broad range of biological processes in the central nervous system such as synaptic plasticity, neurogenesis, and differentiation. Although NF-kappaB is essential for neuron survival and its activation may protect neurons against oxidative-stresses or ischemia-induced neurodegeneration, NF-kappaB activation can contribute to inflammatory reactions and apoptotic cell death after brain injury and stroke. It was proposed that the death or survival of neurons might depend on the cell type and the timing of NF-kappaB activation. We here discuss recent evidence suggesting that within the same neuronal cell, activation of diverse NF-kappaB dimers drives opposite effects on neuronal survival. Unbalanced activation of NF-kappaB p50/RelA dimer over c-Rel-containing complexes contributes to cell death secondary to the ischemic insult. While p50/RelA acts as transcriptional inducer of Bcl-2 family proapoptotic Bim and Noxa genes, c-Rel dimers specifically promote transcription of antiapototic Bcl-xL gene. Changes in the nuclear content of c-Rel dimers strongly affect the threshold of neuron vulnerability to ischemic insult and agents, likewise leptin, activating a NF-kappaB/c-Rel-dependent transcription elicit neuroprotection in animal models of brain ischemia.

NOX enzymes as novel targets for drug development

The members of the NOX/DUOX family of NADPH oxidases mediate such physiologic functions as host defense, cell signaling, and thyroid hormone biosynthesis through the generation of reactive oxygen species (ROS), including superoxide anion and hydrogen peroxide. Moreover, ROS are involved in a broad range of fundamental biochemical and cellular processes, and data accumulated in recent years indicate that the NOX enzymes comprise one of the most important biological sources of ROS. Given the high biochemical reactivity of ROS, it is not surprising that they have been implicated in a wide variety of pathologies and diseases. Prominent among the settings that feature ROS-mediated tissue injury are disorders associated with inflammation, aging, and progressive degenerative changes in cells and organ systems, and it appears that essentially no organ system is exempt. Among the disorders currently believed to be mediated at least in part by NOX-derived ROS are hypertension, aortic aneurysm, myocardial infarction (and other ischemia-reperfusion disorders), pulmonary fibrosis and hypertension, amyotropic lateral sclerosis, Alzheimer's disease, Parkinson's disease, ischemic stroke, diabetic nephropathy, and renal cell carcinoma. Several small-molecule and peptide inhibitors of the NOX enzymes have been useful in experimental studies, but issues of specificity, potency, and toxicity militate against any of the existing published compounds as candidates for drug development. Given the broad array of disease targets documented in recent work, the time is here for vigorous efforts to develop clinically useful inhibitors of the NOX enzymes. As most (though not all) NOX-related diseases appear to be mediated by a single member of the NOX family, agents with isoform specificity will be preferred, although broadly active NOX inhibitors may prove to be useful in some settings.

Inhibition of the outgrowth and elongation of neurites from pheochromocytoma cells by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and preventive effects of dimethylsulfoniopropionate in the presence of nerve growth factor

The combined effects of dimethylsulfoniopropionate (DMSP) (10(-3), 10(-4) and 10(-5) M) with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (5 ng/mL) and the nerve growth factor (NGF) (5 ng/mL) on the outgrowth and elongation of neurites from pheochromocytoma (PC12) cells were examined on RPMI medium containing fetal bovine serum and horse serum with penicillin and streptomycin in collagen-coated dishes for 5 d. The growth was higher in increasing order of the DMSP (10(-3) M), MPTP and NGF, the DMSP (10(-5) M), MPTP and NGF, the MPTP and NGF group and the control group up to 3 d, but not in the NGF and the DMSP (10(-4) M), MPTP and NGF groups. The growth in all the experimental groups showed plateaus from days 4 to 5. The appearance of neurites from the cells in all the groups showed maxima on the 3rd day. The administration of NGF significantly stimulated the outgrowth of neurites from the cells, while the supplementation of MPTP noticeably inhibited the appearance of neurites even in the presence of NGF up to 5 d. However, the addition of DMSP (10(-3 )and 10(-4) M) to the latter group completely prevented the inhibition of the MPTP. These facts were significantly supported by the photographs of neurite-bearing cells on the 3rd day and also by the photometric analyses examining the reaction of MPTP to DMSP, NGF or Collagen IV.

A critical role for the potassium-dependent sodium-calcium exchanger NCKX2 in protection against focal ischemic brain damage

The superfamily of cation/Ca2+ plasma-membrane exchangers contains two branches, the K+-independent Na+-Ca2+ exchangers (NCXs) and the K+-dependent Na+-Ca2+ exchangers (NCKXs), widely expressed in mammals. NCKX2 is the major neuronally expressed isoform among NCKX members. Despite its importance in maintaining Na+, Ca2+, and K+ homeostasis in the CNS, the role of NCKX2 during cerebral ischemia, a condition characterized by an alteration of ionic concentrations, has not yet been investigated. The present study examines NCKX2 role in the development of ischemic brain damage in permanent middle cerebral artery occlusion (pMCAO) and transient middle cerebral artery occlusion. Furthermore, to evaluate the effect of nckx2 ablation on neuronal survival, nckx2-/- primary cortical neurons were subjected to oxygen glucose deprivation plus reoxygenation. NCKX2 mRNA and protein expression was evaluated in the ischemic core and surrounding ipsilesional areas, at different time points after pMCAO in rats. In ischemic core and in periinfarctual area, NCKX2 mRNA and protein expression were downregulated. In addition, NCKX2 knock-down by antisense oligodeoxynucleotide and NCKX2 knock-out by genetic disruption dramatically increased infarct volume. Accordingly, nckx2-/- primary cortical neurons displayed a higher vulnerability and a greater [Ca2+]i increase under hypoxic conditions, compared with nckx2+/+ neurons. In addition, NCKX currents both in the forward and reverse mode of operation were significantly reduced in nckx2-/- neurons compared with nckx2+/+ cells. Overall, these results indicate that NCKX2 is involved in brain ischemia, and it may represent a new potential target to be investigated in the study of the molecular mechanisms involved in cerebral ischemia.

Targeting IKK2 by pharmacological inhibitor AS602868 prevents excitotoxic injury to neurons and oligodendrocytes

Among the diverse mechanisms involved in the pathophysiology of post-ischemic and post-traumatic injuries, excitotoxicity and nuclear factor-kappaB (NF-kappaB) activation through induction of IkappaB kinase (IKK) complex have a primary role. We investigated the effects of the selective inhibitor of the IKK2 subunit, the anilinopyrimidine derivative AS602868, on excitotoxic injury produced in rat organotypic hippocampal slices and cerebellar primary neurons. Brief exposure to N-methyl-D-aspartate (NMDA) induces astrocyte reactivity, neuron cell death and oligodendrocyte degeneration in hippocampal slices. Application of AS602868 elicited a long-lasting protection of both neurons and oligodendrocytes. Maximal effect was observed with prolonged application of the compound after NMDA exposure. Neuroprotection was also evident in primary cultures of cerebellar granule cells starting from 20 nM concentration. AS602868-elicited neuroprotection correlated with inhibition of NF-kappaB activity. Our results suggest that AS602868 may prove to be a valuable approach in treating neurodegeneration and demyelination associated with cerebral trauma and ischemia.

Effects of nerve growth factor and dimethylsulfoniopropionate in green sea algae on the outgrowth of neurites from pheochromocytoma cells

The effects of various concentrations of the nerve growth factor (NGF) and of dimethylsulfoniopropionate (DMSP) on the outgrowth of neurites from pheochromocytoma (PC12) cells were examined singly or in combination on an RPMI 1640 medium containing 10% horse serum, 5% fetal bovine serum, penicillin and streptomycin in collagen-coated Petri dishes by increasing the incubation times up to 4 d. The results indicated that NGF significantly accelerated the number of neurite-bearing cells, which reached a maximum at concentrations of more than 0.5 ng/mL among the various concentrations of NGF on the 4th day. The combined effects of the various concentrations (10(-6)-10(-3) M) of DMSP with NGF (5 ng/mL) on the growth and the number of neurite-bearing cells were then examined, which demonstrated that all the concentrations of DMSP restricted the growth of the cells to various extents but that the concentration of DMSP at 10(-4) M with the NGF more highly accelerated the number of neurite-bearing cells than did the NGF alone during the experimental period.

Carnosine protects against Abeta42-induced neurotoxicity in differentiated rat PC12 cells

(1) The present study was designed to investigate whether histamine is involved in the protective effect of carnosine on Abeta42-induced impairment in differentiated PC12 cells. (2) PC12 cells were exposed to Abeta42 (5 muM) for 24 h after carnosine (5 mM) applied for 18 h. Histamine receptor antagonists (diphenhydramine, zolantidine, thioperamide, clobenpropit) or histidine decarboxylase inhibitor (alpha-fluoromethylhistidine) were added 15 min before carnosine. Cell viability, glutamate release or cell surface expression of NMDA receptor was examined. (3) Abeta42 caused a concentration-dependent reduction of viability in PC12 cells and pretreatment with carnosine ameliorated this impairment. This amelioration was reversed by the H(3) receptor antagonists thioperamide and clobenpropit, but not by either the H(1) receptor antagonist diphenhydramine or the H(2) receptor antagonist zolantidine. Further, alpha-fluoromethylhistidine, an irreversible inhibitor of histidine decarboxylase, also had no effect. In the presence of Abeta42, carnosine significantly decreased glutamate release and carnosine increased the surface expression of NMDA receptor. (4) These results indicate that the mechanism by which carnosine attenuates Abeta42-induced neurotoxicity is independent of the carnosine-histidine-histamine pathway, but may act through regulation of glutamate release and NMDA receptor trafficking.

Mycobacterium tuberculosis secretory proteins CFP‐10, ESAT‐6 and the CFP10:ESAT6 complex inhibit lipopolysaccharide‐induced NF‐κB transactivation by downregulation of reactive oxidative species (ROS) production

Mycobacterium tuberculosis (Mtb) causes death of 2-3 million people annually and is considered one of the most successful intracellular pathogens to persist inside the host macrophage. Recent studies have implicated the role of RD-1 region of Mtb genome in the mycobacterial pathogenesis. The role of RD-1-encoded secretory proteins of Mtb in modulation of macrophage function has not been investigated in detail. Here we show that RD-1 encoded two major secretory proteins, namely, culture filtrate protein-10 kDa (CFP-10) and early secreted antigenic target-6 kDa (ESAT-6), and their 1:1 CFP-10:ESAT6 complex inhibit production of reactive oxidative species (ROS) in RAW264.7 cells. These proteins also downregulated the bacterial lipopolysaccharide (LPS)-induced ROS production, which, in turn, downregulated LPS-induced nuclear factor-kappaB (NF-kappaB) p65 DNA-binding activity, as well as inhibited the NF-kappaB-dependent reporter gene (chloramphenicol acetyl transferase) expression in the treated macrophages. Moreover, addition of N-acetyl cysteine, which is a scavenger of ROS, also inhibited LPS-induced reporter gene expression by scavenging the ROS, thereby preventing NF-kappaB transactivation. These studies indicate that the secretory proteins CFP-10, ESAT-6 and the CFP10:ESAT6 complex of Mtb can inhibit LPS-induced NF-kappaB-dependent gene expression via downregulation of ROS production.

Nox enzymes, ROS, and chronic disease: an example of antagonistic pleiotropy

Reactive oxygen species (ROS) are considered to be chemically reactive with and damaging to biomolecules including DNA, protein, and lipid, and excessive exposure to ROS induces oxidative stress and causes genetic mutations. However, the recently described family of Nox and Duox enzymes generates ROS in a variety of tissues as part of normal physiological functions, which include innate immunity, signal transduction, and biochemical reactions, e.g., to produce thyroid hormone. Nature's "choice" of ROS to carry out these biological functions seems odd indeed, given its predisposition to cause molecular damage. This review describes normal biological roles of Nox enzymes as well as pathological conditions that are associated with ROS production by Nox enzymes. By far the most common conditions associated with Nox-derived ROS are chronic diseases that tend to appear late in life, including atherosclerosis, hypertension, diabetic nephropathy, lung fibrosis, cancer, Alzheimer's disease, and others. In almost all cases, with the exception of a few rare inherited conditions (e.g., related to innate immunity, gravity perception, and hypothyroidism), diseases are associated with overproduction of ROS by Nox enzymes; this results in oxidative stress that damages tissues over time. I propose that these pathological roles of Nox enzymes can be understood in terms of antagonistic pleiotropy: genes that confer a reproductive advantage early in life can have harmful effects late in life. Such genes are retained during evolution despite their harmful effects, because the force of natural selection declines with advanced age. This review discusses some of the proposed physiologic roles of Nox enzymes, and emphasizes the role of Nox enzymes in disease and the likely beneficial effects of drugs that target Nox enzymes, particularly in chronic diseases associated with an aging population.

Up-regulation and increased activity of KV3.4 channels and their accessory subunit MinK-related peptide 2 induced by amyloid peptide are involved in apoptotic neuronal death

The aim of the present study was to investigate whether K(V)3.4 channel subunits are involved in neuronal death induced by neurotoxic beta-amyloid peptides (Abeta). In particular, to test this hypothesis, three main questions were addressed: 1) whether the Abeta peptide can up-regulate both the transcription/translation and activity of K(V)3.4 channel subunit and its accessory subunit, MinK-related peptide 2 (MIRP2); 2) whether the increase in K(V)3.4 expression and activity can be mediated by the nuclear factor-kappaB (NF-kappaB) family of transcriptional factors; and 3) whether the specific inhibition of K(V)3.4 channel subunit reverts the Abeta peptide-induced neurodegeneration in hippocampal neurons and nerve growth factor (NGF)-differentiated PC-12 cells. We found that Abeta(1-42) treatment induced an increase in K(V)3.4 and MIRP2 transcripts and proteins, detected by reverse transcription-polymerase chain reaction and Western blot analysis, respectively, in NGF-differentiated PC-12 cells and hippocampal neurons. Patch-clamp experiments performed in whole-cell configuration revealed that the Abeta peptide caused an increase in I(A) current amplitude carried by K(V)3.4 channel subunits, as revealed by their specific blockade with blood depressing substance-I (BDS-I) in both hippocampal neurons and NGF-differentiated PC-12 cells. The inhibition of NF-kappaB nuclear translocation with the cell membrane-permeable peptide SN-50 prevented the increase in K(V)3.4 protein and transcript expression. In addition, the SN-50 peptide was able to block Abeta(1-42)-induced increase in K(V)3.4 K(+) currents and to prevent cell death caused by Abeta(1-42) exposure. Finally, BDS-I produced a similar neuroprotective effect by inhibiting the increase in K(V)3.4 expression. As a whole, our data indicate that K(V)3.4 channels could be a novel target for Alzheimer's disease pharmacological therapy.

Distinct roles of diverse nuclear factor-kappaB complexes in neuropathological mechanisms

The nuclear transcription factors kappaB (NF-kappaB) function as key regulators of physiological processes in the central nervous system. Aberrant regulation of NF-kappaB can underlie neurological disorders associated with neurodegeneration. A large number of studies have reported a dual role of NF-kappaB in regulating neuron survival in pathological conditions. A recent progress in understanding the mechanisms responsible for opposite effects elicited by NF-kappaB in brain dysfunctions arises from the identification of diverse NF-kappaB complexes specifically involved in the mechanism of neuronal cell death or cell survival. We here discuss the latest findings and consider the therapeutic potential of targeting distinct NF-kappaB complexes for the treatment of neurodegenerative disorders and memory dysfunctions.

Nitric oxide induces [Ca2+]i oscillations in pituitary GH3 cells: involvement of IDR and ERG K+ currents

The role of nitric oxide (NO) in the occurrence of intracellular Ca2+ concentration ([Ca2+]i) oscillations in pituitary GH3 cells was evaluated by studying the effect of increasing or decreasing endogenous NO synthesis with L-arginine and nitro-L-arginine methyl ester (L-NAME), respectively. When NO synthesis was blocked with L-NAME (1 mM) [Ca2+]i, oscillations disappeared in 68% of spontaneously active cells, whereas 41% of the quiescent cells showed [Ca2+]i oscillations in response to the NO synthase (NOS) substrate L-arginine (10 mM). This effect was reproduced by the NO donors NOC-18 and S-nitroso-N-acetylpenicillamine (SNAP). NOC-18 was ineffective in the presence of the L-type voltage-dependent Ca2+ channels (VDCC) blocker nimodipine (1 microM) or in Ca2+-free medium. Conversely, its effect was preserved when Ca2+ release from intracellular Ca2+ stores was inhibited either with the ryanodine-receptor blocker ryanodine (500 microM) or with the inositol 1,4,5-trisphosphate receptor blocker xestospongin C (3 microM). These results suggest that NO induces the appearance of [Ca2+]i oscillations by determining Ca2+ influx. Patch-clamp experiments excluded that NO acted directly on VDCC but suggested that NO determined membrane depolarization because of the inhibition of voltage-gated K+ channels. NOC-18 and SNAP caused a decrease in the amplitude of slow-inactivating (IDR) and ether-à-go-go-related gene (ERG) hyperpolarization-evoked, deactivating K+ currents. Similar results were obtained when GH3 cells were treated with L-arginine. The present study suggests that in GH3 cells, endogenous NO plays a permissive role for the occurrence of spontaneous [Ca2+]i oscillations through an inhibitory effect on IDR and on IERG.