Alzheimer disease: DNA fragmentation indicates increased neuronal vulnerability, but not apoptosis

Regulated cell death and its role in Alzheimer's disease and amyotrophic lateral sclerosis

Despite considerable research efforts, it is still not clear which mechanisms underlie neuronal cell death in neurodegenerative diseases. During the last 20 years, multiple pathways have been identified that can execute regulated cell death (RCD). Among these RCD pathways, apoptosis, necroptosis, pyroptosis, ferroptosis, autophagy-related cell death, and lysosome-dependent cell death have been intensively investigated. Although RCD consists of numerous individual pathways, multiple common proteins have been identified that allow shifting from one cell death pathway to another. Another layer of complexity is added by mechanisms such as the endosomal machinery, able to regulate the activation of some RCD pathways, preventing cell death. In addition, restricted axonal degeneration and synaptic pruning can occur as a result of RCD activation without loss of the cell body. RCD plays a complex role in neurodegenerative processes, varying across different disorders. It has been shown that RCD is differentially involved in Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), among the most common neurodegenerative diseases. In AD, neuronal loss is associated with the activation of not only necroptosis, but also pyroptosis. In ALS, on the other hand, motor neuron death is not linked to canonical necroptosis, whereas pyroptosis pathway activation is seen in white matter microglia. Despite these differences in the activation of RCD pathways in AD and ALS, the accumulation of protein aggregates immunoreactive for p62/SQSTM1 (sequestosome 1) is a common event in both diseases and many other neurodegenerative disorders. In this review, we describe the major RCD pathways with clear activation in AD and ALS, the main interactions between these pathways, as well as their differential and similar involvement in these disorders. Finally, we will discuss targeting RCD as an innovative therapeutic concept for neurodegenerative diseases, such as AD and ALS. Considering that the execution of RCD or "cellular suicide" represents the final stage in neurodegeneration, it seems crucial to prevent neuronal death in patients by targeting RCD. This would offer valuable time to address upstream events in the pathological cascade by keeping the neurons alive.

NcRNAs: A synergistically antiapoptosis therapeutic tool in Alzheimer's disease

AIMS

The aim of this review is to systematically summarize and analyze the noncoding RNAs (ncRNAs), especially microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs), in the cell apoptosis among Alzheimer's disease (AD) in recent years to demonstrate their value in the diagnosis and treatment of AD.

METHODS

We systematically summarized in vitro and in vivo studies focusing on the ncRNAs in the regulation of cell apoptosis among AD in PubMed, ScienceDirect, and Google Scholar.

RESULTS

We discover three patterns of ncRNAs (including 'miRNA-mRNA', 'lncRNA-miRNA-mRNA', and 'circRNA-miRNA-mRNA') form the ncRNA-based regulatory networks in regulating cell apoptosis in AD.

CONCLUSIONS

This review provides a future diagnosis and treatment strategy for AD patients based on ncRNAs.

Roles of Oxidative Stress in Synaptic Dysfunction and Neuronal Cell Death in Alzheimer's Disease

Alzheimer's disease (AD) is a brain disorder that progressively undermines memory and thinking skills by affecting the hippocampus and entorhinal cortex. The main histopathological hallmarks of AD are the presence of abnormal protein aggregates (Aβ and tau), synaptic dysfunction, aberrant proteostasis, cytoskeletal abnormalities, altered energy homeostasis, DNA and RNA defects, inflammation, and neuronal cell death. However, oxidative stress or oxidative damage is also evident and commonly overlooked or considered a consequence of the advancement of dementia symptoms. The control or onset of oxidative stress is linked to the activity of the amyloid-β peptide, which may serve as both antioxidant and pro-oxidant molecules. Furthermore, oxidative stress is correlated with oxidative damage to proteins, nucleic acids, and lipids in vulnerable cell populations, which ultimately lead to neuronal death through different molecular mechanisms. By recognizing oxidative stress as an integral feature of AD, alternative therapeutic or preventive interventions are developed and tested as potential or complementary therapies for this devastating neurodegenerative disease.

Sting and p53 DNA repair pathways are compromised in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia. A common finding in AD is DNA damage. Double-strand DNA breaks (DSBs) are particularly hazardous to neurons because their post-mitotic state forces neurons to rely on error-prone and potentially mutagenic mechanisms to repair DNA breaks. However, it remains unclear whether DNA damage results from increased DNA damage or failure of DNA repair. Oligomerization of the tumor suppressor protein p53 is an essential part of DSB repair, and p53 phosphorylated on S15 is an indicator of DNA damage. We report that the monomer:dimer ratio of phosphorylated (S15) p53 is increased by 2.86-fold in temporal lobes of AD patients compared to age-matched controls, indicating that p53 oligomerization is compromised in AD. In vitro oxidation of p53 with 100 nM H2O2 produced a similar shift in the monomer:dimer ratio. A COMET test showed a higher level of DNA degradation in AD consistent with double-strand DNA damage or inhibition of repair. Protein carbonylation was also elevated (190% of control), indicating elevated oxidative stress in AD patients. Levels of the DNA repair support protein 14-3-3σ, γ-H2AX, a phosphorylated histone marking double strand DNA breaks, and phosphorylated ataxia telangiectasia mutated (ATM) protein were all increased. cGAS-STING-interferon signaling was impaired in AD and was accompanied by a depletion of STING protein from Golgi and a failure to elevate interferon despite the presence of DSBs. The results suggest that oxidation of p53 by ROS could inhibit the DDR and decrease its ability to orchestrate DSB repair by altering the oligomerization state of p53. The failure of immune-stimulated DNA repair may contribute to cell loss in AD and suggests new therapeutic targets for AD.

How neurons die in Alzheimer's disease: Implications for neuroinflammation

Despite the long-standing observation of vast neuronal loss in Alzheimer's disease (AD) our understanding of how and when neurons are eliminated is incomplete. While previous investigation has focused on apoptosis, several novel forms of cell death (i.e. necroptosis, parthanatos, ferroptosis, cuproptosis) have emerged that require further investigation. This review aims to collect evidence for different modes of neuronal cell death in AD and to also discuss how these different forms of cell death may impact the neuroinflammatory environment that prevails in the AD brain. Improved understanding of how neurons die may help to delineate disease pathogenesis, provide insights toward treatment, and aid in the development of improved animal models of AD.

The influence of vinpocetine alone or in combination with Epigallocatechin-3-gallate, Coenzyme COQ10, Vitamin E and Selenium as a potential neuroprotective combination against aluminium-induced Alzheimer's disease in Wistar Albino Rats

Alzheimer's disease (AD) is one of such diseases that represent the most prominent cause of dementia in elderly people. To explore the possible neuroprotective effect as well as mechanism of action of Vinpocetine either alone or in combination with EGCG, CoQ10, or VE & Se in ameliorating aluminum chloride-induced AD in rats. Rats were received AlCl₃ (70 mg/kg) intraperitoneal daily dose for 30 days along with EGCG (10 mg/kg, I.P), CoQ10 (200 mg/kg, P.O), VE (100 mg/kg, P.O) & Se (1 mg/kg, P.O) as well as Vinpocetine (20 mg/kg, P.O) either alone or in combination. Results revealed that the combination of Vinpocetine with EGCG showed the best neuroprotection. This protection in the brain was indicated by the significant decrease in Aβ and ACHE. The same pattern of results were shown in the levels of monoamines and BDNF. In addition, the combination of Vinpocetine with EGCG showed more pronounced anti-inflammatory (TNF-α, IL-1β) and antioxidant (MDA, SOD, TAC) effects in comparison to other combinations. These results were confirmed using histopathological examinations as well as DNA fragmentation assays. Vinpocetine with EGCG showed pronounced protection on neurons against AD induced by AlCl₃ in rats.

T cell numbers correlate with neuronal loss rather than with seizure activity in medial temporal lobe epilepsy

OBJECTIVE

Medial temporal lobe epilepsy (MTLE) is a drug-resistant focal epilepsy that can be caused by a broad spectrum of different inciting events, including tumors, febrile seizures, and viral infections. In human epilepsy surgical resections as well as in animal models, an involvement of the adaptive immune system was observed. We here analyzed the presence of T cells in various subgroups of MTLE. We aimed to answer the question of how much inflammation was present and whether the presence of T cells was associated with seizures or associated with hippocampal neurodegeneration.

METHODS

We quantified the numbers of CD3⁺ T cells and CD8⁺ cytotoxic T cells in the hippocampus of patients with gangliogliomas (GGs; intrahippocampal and extrahippocampal, with and without sclerosis), febrile seizures, and postinfectious encephalitic epilepsy and compared this with Rasmussen encephalitis, Alzheimer disease, and normal controls.

RESULTS

We could show that T cell numbers were significantly elevated in MTLE compared to healthy controls. CD3⁺ as well as CD8⁺ T cell numbers, however, varied highly among MTLE subgroups. By comparing GG patients with and without hippocampal sclerosis (HS), we were able to show that T-cell numbers were increased in extrahippocampal GG patients with hippocampal neuronal loss and HS, whereas extrahippocampal GG cases without hippocampal neuronal loss (i.e., absence of HS) did not differ from healthy controls. Importantly, T cell numbers in MTLE correlated with the degree of neuronal loss, whereas no correlation with seizure frequency or disease duration was found. Finally, we found that in nearly all MTLE groups, T cell numbers remained elevated even years after the inciting event.

SIGNIFICANCE

We here provide a detailed histopathological investigation of the involvement of T cells in various subgroups of MTLE, which suggests that T cell influx correlates to neuronal loss rather than seizure activity.

Amyloids: The History of Toxicity and Functionality

Proteins can perform their specific function due to their molecular structure. Partial or complete unfolding of the polypeptide chain may lead to the misfolding and aggregation of proteins in turn, resulting in the formation of different structures such as amyloid aggregates. Amyloids are rigid protein aggregates with the cross-β structure, resistant to most solvents and proteases. Because of their resistance to proteolysis, amyloid aggregates formed in the organism accumulate in tissues, promoting the development of various diseases called amyloidosis, for instance Alzheimer's diseases (AD). According to the main hypothesis, it is considered that the cause of AD is the formation and accumulation of amyloid plaques of Aβ. That is why Aβ-amyloid is the most studied representative of amyloids. Therefore, in this review, special attention is paid to the history of Aβ-amyloid toxicity. We note the main problems with anti-amyloid therapy and write about new views on amyloids that can play positive roles in the different organisms including humans.

Tau and DNA Damage in Neurodegeneration

Neurodegenerative disorders are a family of incurable conditions. Among them, Alzheimer's disease and tauopathies are the most common. Pathological features of these two disorders are synaptic loss, neuronal cell death and increased DNA damage. A key pathological protein for the onset and progression of the conditions is the protein tau, a microtubule-binding protein highly expressed in neurons and encoded by the MAPT (microtubule-associated protein tau) gene. Tau is predominantly a cytosolic protein that interacts with numerous other proteins and molecules. Recent findings, however, have highlighted new and unexpected roles for tau in the nucleus of neuronal cells. This review summarizes the functions of tau in the metabolism of DNA, describing them in the context of the disorders.

Sulfur-containing Secondary Metabolites as Neuroprotective Agents

Sulfur-containing secondary metabolites are a relatively small group of substances of plant origin. The present review is focused on their neuroprotective properties. The results obtained in a series of in vitro and in vivo studies are reported. Among glucosinolates, the wide class of compounds in the sulfur-containing metabolites, glucoraphanin, sulforaphane and isothiocyanates proved to be the more studied in this context and showed interesting properties as modulators of several systems involved in the pathogenesis of neurologic diseases such as oxidative stress, inflammation and apoptosis. Allium sativum L. (garlic) is widely known for its sulfur-containing components endowed with health-promoting activities and its medicinal properties are known from ancient times. In recent studies, garlic components proved active in neuroprotection due to the direct and indirect antioxidant properties, modulation of apoptosis mediators and inhibiting the formation of amyloid protein. Dihydroasparagusic acid, the first dimercaptanic compound isolated from a natural source, effectively inhibited inflammatory and oxidative processes that are important factors for the etiopathogenesis of neurodegenerative diseases, not only for its antioxidant and radical scavenging properties but also because it may down-regulate the expression of several microglial-derived inflammatory mediators. Serofendic acid represents a rare case of sulfur-containing animal-derived secondary metabolite isolated from fetal calf serum extract. It proved effective in the suppression of ROS generation and in the expression of several inflammatory and apoptosis mediators and showed a cytotrophic property in astrocytes, promoting the stellation process. Lastly, the properties of hydrogen sulfide were also reported since in recent times it has been recognized as a signaling molecule and as a mediator in regulating neuron death or survival. It may be produced endogenously from cysteine but may also be released by sulfur-containing secondary metabolites, mainly from those present in garlic.

Naringenin protects AlCl3/D-galactose induced neurotoxicity in rat model of AD via attenuation of acetylcholinesterase levels and inhibition of oxidative stress

Currently prescribed medications for the treatment of Alzheimer's disease (AD) that are based on acetylcholinesterase inhibition only offer symptomatic relief but do not provide protection against neurodegeneration. There appear to be an intense need for the development of therapeutic strategies that not only improve brain functions but also prevent neurodegeneration. The oxidative stress is one of the main causative factors of AD. Various antioxidants are being investigated to prevent neurodegeneration in AD. The objective of this study was to investigate the neuroprotective effects of naringenin (NAR) against AlCl3+D-gal induced AD-like symptoms in an animal model. Rats were orally pre-treated with NAR (50 mg/kg) for two weeks and then exposed to AlCl3+D-gal (150 mg/kg + 300 mg/kg) intraperitoneally for one week to develop AD-like symptoms. The standard drug, donepezil (DPZ) was used as a stimulator of cholinergic activity. Our results showed that NAR pre-treatment significantly protected AD-like behavioral disturbances in rats. In DPZ group, rats showed improved cognitive and cholinergic functions but the neuropsychiatric functions were not completely improved and showed marked histopathological alterations. However, NAR not only prevented AlCl3+D-gal induced AD-like symptoms but also significantly prevented neuropsychiatric dysfunctions in rats. Results of present study suggest that NAR may play a role in enhancing neuroprotective and cognition functions and it can potentially be considered as a neuroprotective compound for therapeutic management of AD in the future.

Tau acetylates and stabilizes β-catenin thereby promoting cell survival

Overexpressing Tau counteracts apoptosis and increases dephosphorylated β-catenin levels, but the underlying mechanisms are elusive. Here, we show that Tau can directly and robustly acetylate β-catenin at K49 in a concentration-, time-, and pH-dependent manner. β-catenin K49 acetylation inhibits its phosphorylation and its ubiquitination-associated proteolysis, thus increasing β-catenin protein levels. K49 acetylation further promotes nuclear translocation and the transcriptional activity of β-catenin, and increases the expression of survival-promoting genes (bcl2 and survivin), counteracting apoptosis. Mutation of Tau's acetyltransferase domain or co-expressing non-acetylatable β-catenin-K49R prevents increased β-catenin signaling and abolishes the anti-apoptotic function of Tau. Our data reveal that Tau preserves β-catenin by acetylating K49, and upregulated β-catenin/survival signaling in turn mediates the anti-apoptotic effect of Tau.

Microglia damage precedes major myelin breakdown in X-linked adrenoleukodystrophy and metachromatic leukodystrophy

X-linked adrenoleukodystrophy (X-ALD) and metachromatic leukodystrophy (MLD) are two relatively common examples of hereditary demyelinating diseases caused by a dysfunction of peroxisomal or lysosomal lipid degradation. In both conditions, accumulation of nondegraded lipids leads to the destruction of cerebral white matter. Because of their high lipid content, oligodendrocytes are considered key to the pathophysiology of these leukodystrophies. However, the response to allogeneic stem cell transplantation points to the relevance of cells related to the hematopoietic lineage. In the present study, we aimed to better characterize the pathogenetic role of microglia in the above-mentioned diseases. Applying recently established microglia markers to human autopsy cases of X-ALD and MLD we were able to delineate distinct lesion stages in evolving demyelinating lesions. The immune-phenotype of microglia was altered already early in lesion evolution, and microglia loss preceded full-blown myelin degeneration both in X-ALD and MLD. DNA fragmentation indicating phagocyte death was observed in areas showing microglia loss. The morphology and dynamics of phagocyte decay differed between the diseases and between lesion stages, hinting at distinct pathways of programmed cell death. In summary, the present study shows an early and severe damage to microglia in the pathogenesis of X-ALD and MLD. This hints at a central pathophysiologic role of these cells in the diseases and provides evidence for an ongoing transfer of toxic substrates primarily enriched in myelinating cells to microglia.

Neuronal Cell Death

Neuronal cell death occurs extensively during development and pathology, where it is especially important because of the limited capacity of adult neurons to proliferate or be replaced. The concept of cell death used to be simple as there were just two or three types, so we just had to work out which type was involved in our particular pathology and then block it. However, we now know that there are at least a dozen ways for neurons to die, that blocking a particular mechanism of cell death may not prevent the cell from dying, and that non-neuronal cells also contribute to neuronal death. We review here the mechanisms of neuronal death by intrinsic and extrinsic apoptosis, oncosis, necroptosis, parthanatos, ferroptosis, sarmoptosis, autophagic cell death, autosis, autolysis, paraptosis, pyroptosis, phagoptosis, and mitochondrial permeability transition. We next explore the mechanisms of neuronal death during development, and those induced by axotomy, aberrant cell-cycle reentry, glutamate (excitoxicity and oxytosis), loss of connected neurons, aggregated proteins and the unfolded protein response, oxidants, inflammation, and microglia. We then reassess which forms of cell death occur in stroke and Alzheimer's disease, two of the most important pathologies involving neuronal cell death. We also discuss why it has been so difficult to pinpoint the type of neuronal death involved, if and why the mechanism of neuronal death matters, the molecular overlap and interplay between death subroutines, and the therapeutic implications of these multiple overlapping forms of neuronal death.

U1 snRNP Alteration and Neuronal Cell Cycle Reentry in Alzheimer Disease

The aberrancy of U1 small nuclear ribonucleoprotein (snRNP) complex and RNA splicing has been demonstrated in Alzheimer’s disease (AD). Importantly, the U1 proteopathy is AD-specific, widespread and early-occurring, thus providing a very unique clue to the AD pathogenesis. The prominent feature of U1 histopathology is its nuclear depletion and redistribution in the neuronal cytoplasm. According to the preliminary data, the initial U1 cytoplasmic distribution pattern is similar to the subcellular translocation of the spliceosome in cells undergoing mitosis. This implies that the U1 mislocalization might reflect the neuronal cell cycle-reentry (CCR) which has been extensively evidenced in AD brains. The CCR phenomenon explains the major molecular and cellular events in AD brains, such as Tau and amyloid precursor protein (APP) phosphorylation, and the possible neuronal death through mitotic catastrophe (MC). Furthermore, the CCR might be mechanistically linked to inflammation, a critical factor in the AD etiology according to the genetic evidence. Therefore, the discovery of U1 aberrancy might strengthen the involvement of CCR in the AD neuronal degeneration.

Necroptosis activation in Alzheimer's disease

Alzheimer's disease (AD) is characterized by severe neuronal loss; however, the mechanisms by which neurons die remain elusive. Necroptosis, a programmed form of necrosis, is executed by the mixed lineage kinase domain-like (MLKL) protein, which is triggered by receptor-interactive protein kinases (RIPK) 1 and 3. We found that necroptosis was activated in postmortem human AD brains, positively correlated with Braak stage, and inversely correlated with brain weight and cognitive scores. In addition, we found that the set of genes regulated by RIPK1 overlapped significantly with multiple independent AD transcriptomic signatures, indicating that RIPK1 activity could explain a substantial portion of transcriptomic changes in AD. Furthermore, we observed that lowering necroptosis activation reduced cell loss in a mouse model of AD. We anticipate that our findings will spur a new area of research in the AD field focused on developing new therapeutic strategies aimed at blocking its activation.

Neuroprotective effect of the Chinese medicine Tiantai No. 1 and its molecular mechanism in the senescence-accelerated mouse prone 8

Tiantai No. 1, a Chinese medicine predominantly composed of powdered Rhizoma Gastrodiae, Radix Ginseng, and Ginkgo leaf at a ratio of 2:1:2 and dissolved in pure water, is neuroprotective in animal models of various cognitive disorders, but its molecular mechanism remains unclear. We administered Tiantai No. 1 intragastrically to senescence-accelerated mouse prone 8 (SAMP8) mice (a model of Alzheimer's disease) at doses of 50, 100 or 150 mg/kg per day for 8 weeks and evaluated their behavior in the Morris water maze and expression of Alzheimer's disease-related proteins in the brain. Tiantai No. 1 shortened the escape latency in the water maze training trials, and increased swimming time in the target quadrant during the spatial probe test, indicating that Tiantai No. 1 improved learning and memory in SAMP8 mice. Immunohistochemistry revealed that Tiantai No. 1 restored the proliferation potential of Ki67-positive cells in the hippocampus. In addition, mice that had received Tiantai No. 1 had fewer astrocytes, and less accumulation of amyloid-beta and phosphorylated tau. These results suggest that Tiantai No. 1 is neuroprotective in the SAMP8 mouse model of Alzheimer's disease and acts by restoring neuronal number and proliferation potential in the hippocampus, decreasing astrocyte infiltration, and reducing the accumulation of amyloid-beta and phosphorylated tau.

Impaired mitochondrial energy metabolism in Alzheimer's disease: Impact on pathogenesis via disturbed epigenetic regulation of chromatin landscape

The amyloid cascade hypothesis for the pathogenesis of Alzheimer's disease (AD) was proposed over twenty years ago. However, the mechanisms of neurodegeneration and synaptic loss have remained elusive delaying the effective drug discovery. Recent studies have revealed that amyloid-β peptides as well as phosphorylated and fragmented tau proteins accumulate within mitochondria. This process triggers mitochondrial fission (fragmentation) and disturbs Krebs cycle function e.g. by inhibiting the activity of 2-oxoglutarate dehydrogenase. Oxidative stress, hypoxia and calcium imbalance also disrupt the function of Krebs cycle in AD brains. Recent studies on epigenetic regulation have revealed that Krebs cycle intermediates control DNA and histone methylation as well as histone acetylation and thus they have fundamental roles in gene expression. DNA demethylases (TET1-3) and histone lysine demethylases (KDM2-7) are included in the family of 2-oxoglutarate-dependent oxygenases (2-OGDO). Interestingly, 2-oxoglutarate is the obligatory substrate of 2-OGDO enzymes, whereas succinate and fumarate are the inhibitors of these enzymes. Moreover, citrate can stimulate histone acetylation via acetyl-CoA production. Epigenetic studies have revealed that AD is associated with changes in DNA methylation and histone acetylation patterns. However, the epigenetic results of different studies are inconsistent but one possibility is that they represent both coordinated adaptive responses and uncontrolled stochastic changes, which provoke pathogenesis in affected neurons. Here, we will review the changes observed in mitochondrial dynamics and Krebs cycle function associated with AD, and then clarify the mechanisms through which mitochondrial metabolites can control the epigenetic landscape of chromatin and induce pathological changes in AD.

Mechanisms of chemotherapy-induced behavioral toxicities

While chemotherapeutic agents have yielded relative success in the treatment of cancer, patients are often plagued with unwanted and even debilitating side-effects from the treatment which can lead to dose reduction or even cessation of treatment. Common side effects (symptoms) of chemotherapy include (i) cognitive deficiencies such as problems with attention, memory and executive functioning; (ii) fatigue and motivational deficit; and (iii) neuropathy. These symptoms often develop during treatment but can remain even after cessation of chemotherapy, severely impacting long-term quality of life. Little is known about the underlying mechanisms responsible for the development of these behavioral toxicities, however, neuroinflammation is widely considered to be one of the major mechanisms responsible for chemotherapy-induced symptoms. Here, we critically assess what is known in regards to the role of neuroinflammation in chemotherapy-induced symptoms. We also argue that, based on the available evidence, neuroinflammation is unlikely the only mechanism involved in the pathogenesis of chemotherapy-induced behavioral toxicities. We evaluate two other putative candidate mechanisms. To this end we discuss the mediating role of damage-associated molecular patterns (DAMPs) activated in response to chemotherapy-induced cellular damage. We also review the literature with respect to possible alternative mechanisms such as a chemotherapy-induced change in the bioenergetic status of the tissue involving changes in mitochondrial function in relation to chemotherapy-induced behavioral toxicities. Understanding the mechanisms that underlie the emergence of fatigue, neuropathy, and cognitive difficulties is vital to better treatment and long-term survival of cancer patients.

Undifferentiated and differentiated PC12 cells protected by huprines against injury induced by hydrogen peroxide

Oxidative stress is implicated in the pathogenesis of neurodegenerative disorders and hydrogen peroxide (H₂O₂) plays a central role in the stress. Huprines, a group of potent acetylcholinesterase inhibitors (AChEIs), have shown a broad cholinergic pharmacological profile. Recently, it has been observed that huprine X (HX) improves cognition in non transgenic middle aged mice and shows a neuroprotective activity (increased synaptophysin expression) in 3xTg-AD mice. Consequently, in the present experiments the potential neuroprotective effect of huprines (HX, HY, HZ) has been analyzed in two different in vitro conditions: undifferentiated and NGF-differentiated PC12 cells. Cells were subjected to oxidative insult (H₂O₂, 200 µM) and the protective effects of HX, HY and HZ (0.01 µM–1 µM) were analyzed after a pre-incubation period of 24 and 48 hours. All huprines showed protective effects in both undifferentiated and NGF-differentiated cells, however only in differentiated cells the effect was dependent on cholinergic receptors as atropine (muscarinic antagonist, 0.1 µM) and mecamylamine (nicotinic antagonist, 100 µM) reverted the neuroprotection action of huprines. The decrease in SOD activity observed after oxidative insult was overcome in the presence of huprines and this effect was not mediated by muscarinic or nicotinic receptors. In conclusion, huprines displayed neuroprotective properties as previously observed in in vivo studies. In addition, these effects were mediated by cholinergic receptors only in differentiated cells. However, a non-cholinergic mechanism, probably through an increase in SOD activity, seems to be also involved in the neuroprotective effects of huprines.

A transgenic Alzheimer rat with plaques, tau pathology, behavioral impairment, oligomeric aβ, and frank neuronal loss. J Neurosci. 2013;33:6245-6256. [PMID: 23575824 DOI: 10.1523/jneurosci.3672-12.2013]

Alzheimer's disease (AD) is hallmarked by amyloid plaques, neurofibrillary tangles, and widespread cortical neuronal loss (Selkoe, 2001). The "amyloid cascade hypothesis" posits that cerebral amyloid sets neurotoxic events into motion that precipitate Alzheimer dementia (Hardy and Allsop, 1991). Yet, faithful recapitulation of all AD features in widely used transgenic (Tg) mice engineered to overproduce Aβ peptides has been elusive. We have developed a Tg rat model (line TgF344-AD) expressing mutant human amyloid precursor protein (APPsw) and presenilin 1 (PS1ΔE9) genes, each independent causes of early-onset familial AD. TgF344-AD rats manifest age-dependent cerebral amyloidosis that precedes tauopathy, gliosis, apoptotic loss of neurons in the cerebral cortex and hippocampus, and cognitive disturbance. These results demonstrate progressive neurodegeneration of the Alzheimer type in these animals. The TgF344-AD rat fills a critical need for a next-generation animal model to enable basic and translational AD research.

Global analysis of phosphorylation of tau by the checkpoint kinases Chk1 and Chk2 in vitro

Hyperphosphorylation of microtubule-associated protein tau is thought to contribute to Alzheimer's disease (AD) pathogenesis. We previously showed that DNA damage-activated cell cycle checkpoint kinases Chk1 and Chk2 phosphorylate tau at an AD-related site and enhance tau toxicity, suggesting potential roles of these kinases in AD. The purpose of this study is to systematically identify which sites in tau are directly phosphorylated by Chk1 and Chk2. Using recombinant human tau phosphorylated by Chk1 and Chk2 in vitro, we first analyzed tau phosphorylation at the AD-related sites by Western blot with phospho-tau-specific antibodies. Second, to globally identify phosphorylated sites in tau, liquid chromatography-tandem mass spectrometry (LC-MS(3)) was employed. These systematic analyses identified a total of 27 Ser/Thr residues as Chk1- or Chk2- target sites. None of them were proline-directed kinase targets. Many of these sites are located within the microtubule-binding domain and C-terminal domain, whose phosphorylation has been shown to reduce tau binding to microtubules and/or has been implicated in tau toxicity. Among these 27 sites, 13 sites have been identified to be phosphorylated in AD brains. Since DNA damage is accumulated in diseased brains, Chk1 and Chk2 may be involved in tau phosphorylation and toxicity in AD pathogenesis.

Nigral neurons are likely to die of a mechanism other than classical apoptosis in Parkinson's disease

The finding of apoptosis in Parkinson's disease (PD) represents a contentious issue. In fact, there is increasing evidence that an alternative mechanism of cell death is at work in the parkinsonian substantia nigra, which we tentatively term aposklesis. Unlike apoptosis, aposklesis ("withering") lacks the morphological signs of apoptosis and takes a slow course which is in agreement with the predicted rate of dopaminergic cell death in PD. Cells undergoing aposklesis may stain positive in the TUNEL reaction and show a reticular nuclear labeling but lack any significant chromatin condensation and the formation of apoptotic bodies. Not only neurons but also glial cells appear to undergo this form of cell death, which represents a relatively common finding in degenerative diseases of the CNS.

Mitochondrial- and endoplasmic reticulum-associated oxidative stress in Alzheimer's disease: from pathogenesis to biomarkers

Alzheimer's disease (AD) is the most common cause of dementia in the elderly, affecting several million of people worldwide. Pathological changes in the AD brain include the presence of amyloid plaques, neurofibrillary tangles, loss of neurons and synapses, and oxidative damage. These changes strongly associate with mitochondrial dysfunction and stress of the endoplasmic reticulum (ER). Mitochondrial dysfunction is intimately linked to the production of reactive oxygen species (ROS) and mitochondrial-driven apoptosis, which appear to be aggravated in the brain of AD patients. Concomitantly, mitochondria are closely associated with ER, and the deleterious crosstalk between both organelles has been shown to be involved in neuronal degeneration in AD. Stimuli that enhance expression of normal and/or folding-defective proteins activate an adaptive unfolded protein response (UPR) that, if unresolved, can cause apoptotic cell death. ER stress also induces the generation of ROS that, together with mitochondrial ROS and decreased activity of several antioxidant defenses, promotes chronic oxidative stress. In this paper we discuss the critical role of mitochondrial and ER dysfunction in oxidative injury in AD cellular and animal models, as well as in biological fluids from AD patients. Progress in developing peripheral and cerebrospinal fluid biomarkers related to oxidative stress will also be summarized.

Sublethal doses of β-amyloid peptide abrogate DNA-dependent protein kinase activity

Accumulation of DNA damage and deficiency in DNA repair potentially contribute to the progressive neuronal loss in neurodegenerative disorders, including Alzheimer disease (AD). In multicellular eukaryotes, double strand breaks (DSBs), the most lethal form of DNA damage, are mainly repaired by the nonhomologous end joining pathway, which relies on DNA-PK complex activity. Both the presence of DSBs and a decreased end joining activity have been reported in AD brains, but the molecular player causing DNA repair dysfunction is still undetermined. β-Amyloid (Aβ), a potential proximate effector of neurotoxicity in AD, might exert cytotoxic effects by reactive oxygen species generation and oxidative stress induction, which may then cause DNA damage. Here, we show that in PC12 cells sublethal concentrations of aggregated Aβ(25-35) inhibit DNA-PK kinase activity, compromising DSB repair and sensitizing cells to nonlethal oxidative injury. The inhibition of DNA-PK activity is associated with down-regulation of the catalytic subunit DNA-PK (DNA-PKcs) protein levels, caused by oxidative stress and reversed by antioxidant treatment. Moreover, we show that sublethal doses of Aβ(1-42) oligomers enter the nucleus of PC12 cells, accumulate as insoluble oligomeric species, and reduce DNA-PK kinase activity, although in the absence of oxidative stress. Overall, these findings suggest that Aβ mediates inhibition of the DNA-PK-dependent nonhomologous end joining pathway contributing to the accumulation of DSBs that, if not efficiently repaired, may lead to the neuronal loss observed in AD.

Dopamine D3 receptor specifically modulates motor and sensory symptoms in iron-deficient mice

Restless legs syndrome (RLS) is a common neurological disorder whose exact pathophysiological mechanism remains unclear despite the successful use of dopaminergic treatment and recent discovery of predisposing genetic factors. As iron deficiency has been associated with RLS for some patients and there is evidence for decreased spinal dopamine D(3)-receptor (D3R) signaling in RLS, we aimed at establishing whether D3R activity and iron deficiency share common pathways within the pathophysiology of RLS sensory and motor symptoms. Using a combined mouse model of iron deficiency and dopamine D(3)-receptor deficiency (D3R-/-), circadian motor symptoms were evaluated by continuous recording of spontaneous wheel running activity. Testing the acute and persistent pain responses with the hot-plate test and formalin test, respectively, assessed sensory symptoms. A 15 week iron-deficient (ID) diet alone increased acute and persistent pain responses as compared to control diet. As compared to C57BL/6 (WT), homozygous D3R-/- mice already exhibited elevated responses to acute and persistent pain stimuli, where the latter was further elevated by concurrent iron deficiency. ID changed the circadian activity pattern toward an increased running wheel usage before the resting period, which resembled the RLS symptom of restlessness before sleep. Interestingly, D3R-/- shifted this effect of iron deficiency to a time point 3-4 h earlier. The results confirm the ability of iron deficiency and D3R-/- to evoke sensory and motor symptoms in mice resembling those observed in RLS patients. Furthermore this study suggests an increase of ID-related sensory symptoms and modification of ID-related motor symptoms by D3R-/-.

Tau Ser262 phosphorylation is critical for Abeta42-induced tau toxicity in a transgenic Drosophila model of Alzheimer's disease

The amyloid-beta 42 (Abeta42) peptide has been suggested to promote tau phosphorylation and toxicity in Alzheimer's disease (AD) pathogenesis; however, the underlying mechanisms are not fully understood. Using transgenic Drosophila expressing both human Abeta42 and tau, we show here that tau phosphorylation at Ser262 plays a critical role in Abeta42-induced tau toxicity. Co-expression of Abeta42 increased tau phosphorylation at AD-related sites including Ser262, and enhanced tau-induced neurodegeneration. In contrast, formation of either sarkosyl-insoluble tau or paired helical filaments was not induced by Abeta42. Co-expression of Abeta42 and tau carrying the non-phosphorylatable Ser262Ala mutation did not cause neurodegeneration, suggesting that the Ser262 phosphorylation site is required for the pathogenic interaction between Abeta42 and tau. We have recently reported that the DNA damage-activated Checkpoint kinase 2 (Chk2) phosphorylates tau at Ser262 and enhances tau toxicity in a transgenic Drosophila model. We detected that expression of Chk2, as well as a number of genes involved in DNA repair pathways, was increased in the Abeta42 fly brains. The induction of a DNA repair response is protective against Abeta42 toxicity, since blocking the function of the tumor suppressor p53, a key transcription factor for the induction of DNA repair genes, in neurons exacerbated Abeta42-induced neuronal dysfunction. Our results demonstrate that tau phosphorylation at Ser262 is crucial for Abeta42-induced tau toxicity in vivo, and suggest a new model of AD progression in which activation of DNA repair pathways is protective against Abeta42 toxicity but may trigger tau phosphorylation and toxicity in AD pathogenesis.

A DNA damage-activated checkpoint kinase phosphorylates tau and enhances tau-induced neurodegeneration

Hyperphosphorylation of the microtubule associated protein tau is detected in the brains of individuals with a range of neurodegenerative diseases including Alzheimer's disease (AD). An imbalance in phosphorylation and/or dephosphorylation of tau at disease-related sites has been suggested to initiate the abnormal metabolism and toxicity of tau in disease pathogenesis. However, the mechanisms underlying abnormal phosphorylation of tau in AD are not fully understood. Here, we show that the DNA damage-activated Checkpoint kinase 2 (Chk2) is a novel tau kinase and enhances tau toxicity in a transgenic Drosophila model. Overexpression of Drosophila Chk2 increases tau phosphorylation at Ser262 and enhances tau-induced neurodegeneration in transgenic flies expressing human tau. The non-phosphorylatable Ser262Ala mutation abolishes Chk2-induced enhancement of tau toxicity, suggesting that the Ser262 phosphorylation site is involved in the enhancement of tau toxicity by Chk2. In vitro kinase assays revealed that human Chk2 and a closely related checkpoint kinase 1 (Chk1) directly phosphorylate human tau at Ser262. We also demonstrate that Drosophila Chk2 does not modulate the activity of the fly homolog of microtubule affinity regulating kinase, which has been shown to be a physiological tau Ser262 kinase. Since accumulation of DNA damage has been detected in the brains of AD patients, our results suggest that the DNA damage-activated kinases Chk1 and Chk2 may be involved in tau phosphorylation and toxicity in the pathogenesis of AD.

Iron-deficiency sensitizes mice to acute pain stimuli and formalin-induced nociception

Iron deficiency has been described as a risk factor in secondary restless legs syndrome (RLS), although it has not been investigated whether iron deficiency induces sensory symptoms in RLS patients. In this study, we established a mouse model of iron deficiency by administering a purified iron-deficient (ID) diet (<8 mg/kg iron) or nonpurified standard diet [normal diet (ND)] (<179 mg/kg iron) to male C57Bl/6 mice from postnatal d 28 for 1, 4, or 15 wk. The level of iron deficiency was assessed by the plasma iron concentration. After varying durations of iron deficiency, both acute and chronic sensory components of pain were measured using hot-plate and formalin tests, which preferentially assess Adelta- and C-fibers, respectively. Based on hot-plate reaction time, ID mice had a lower acute pain threshold than the ND mice after 4 and 15 wk but not after 1 wk. In addition, ID mice had an increased chronic pain response compared with the ND mice only in the late phase of the formalin-test after 1, 4, and 15 wk of iron deficiency. This increased pain response was accompanied by an elevated expression of c-Fos immunoreactive cells at the ipsilateral dorsal horn, suggesting that iron deficiency indirectly increases cell activity at the spinal cord level. These results demonstrate that iron deficiency increases acute and chronic pain responses in mice and may cause similar alterations to the acute pain threshold and sensitivity to C-fiber-mediated chronic pain in ID RLS patients.

Biomarkers of oxidative and nitrosative damage in Alzheimer's disease and mild cognitive impairment

Alzheimer's disease (AD) is the most common type of dementia in the elderly. Products of oxidative and nitrosative stress (OS and NS, respectively) accumulate with aging, which is the main risk factor for AD. This provides the basis for the involvement of OS and NS in AD pathogenesis. OS and NS occur in biological systems due to the dysregulation of the redox balance, caused by a deficiency of antioxidants and/or the overproduction of free radicals. Free radical attack against lipids, proteins, sugars and nucleic acids leads to the formation of bioproducts whose detection in fluids and tissues represents the currently available method for assessing oxidative/nitrosative damage. Post-mortem and in-vivo studies have demonstrated an accumulation of products of free radical damage in the central nervous system and in the peripheral tissues of subjects with AD or mild cognitive impairment (MCI). In addition to their individual role, biomarkers for OS and NS in AD are associated with altered bioenergetics and amyloid-beta (Abeta) metabolism. In this review we discuss the main results obtained in the field of biomarkers of oxidative/nitrosative stress in AD and MCI in humans, in addition to their potential role as a tool for diagnosis, prognosis and treatment efficacy in AD.

Classification and basic pathology of Alzheimer disease

The lesions of Alzheimer disease include accumulation of proteins, losses of neurons and synapses, and alterations related to reactive processes. Extracellular Abeta accumulation occurs in the parenchyma as diffuse, focal or stellate deposits. It may involve the vessel walls of arteries, veins and capillaries. The cases in which the capillary vessel walls are affected have a higher probability of having one or two apoepsilon 4 alleles. Parenchymal as well as vascular Abeta deposition follows a stepwise progression. Tau accumulation, probably the best histopathological correlate of the clinical symptoms, takes three aspects: in the cell body of the neuron as neurofibrillary tangle, in the dendrites as neuropil threads, and in the axons forming the senile plaque neuritic corona. The progression of tau pathology is stepwise and stereotyped from the entorhinal cortex, through the hippocampus, to the isocortex. The neuronal loss is heterogeneous and area-specific. Its mechanism is still discussed. The timing of the synaptic loss, probably linked to Abeta peptide itself, maybe as oligomers, is also controversial. Various clinico-pathological types of Alzheimer disease have been described, according to the type of the lesions (plaque only and tangle predominant), the type of onset (focal onset), the cause (genetic or sporadic) and the associated lesions (Lewy bodies, vascular lesions, hippocampal sclerosis, TDP-43 inclusions and argyrophilic grain disease).

Misfolded tau protein and disease modifying pathways in transgenic rodent models of human tauopathies

Human tauopathies represent a heterogeneous group of neurodegenerative disorders such as Alzheimer's disease (AD) that are characterized by the presence of intracellular accumulations of abnormal filaments of protein tau. Presently, AD poses an increasing public health concern, because it affects nearly 2% of the population in industrialized countries and the number of patients is expected to increase threefold within the next 50 years. Therefore, the identification of disease modifying pathways that will lead to the development of novel therapeutic approaches targeting downstream molecular events of the tauopathy is of paramount importance. In order to identify factors that may exacerbate or inhibit the disease phenotype a number of genetically modified rodent models reproducing key clinical, histopathological and molecular hallmarks of human tauopathies were developed. Current tau transgenic rodent models express as a transgene either an individual or all six human wild-type tau isoforms, mutant tau linked to FTDP-17, or structurally modified tau species derived from AD. In this review we will provide an up-to-date account of various facets of the tau neurodegenerative cascade with a special emphasis on the evolution of neurofibrillary tangles, neuronal death and neuroinflammation.

Caspase activation in Alzheimer's disease: early to rise and late to bed

It has been almost 15 years since the first report of apoptosis as a major mechanism of cell death associated with Alzheimer's disease (AD). Presently, whether neurons die through apoptosis or some other pathway is still a hotly debated issue. However, mounting evidence suggests a role for the activation of caspases and cleavage of critical cellular proteins during the progression of AD. The activation of apoptotic pathways may represent a protracted battle due to the presence of various anti-apoptotic molecules such as Bcl-2 whereby neurons do not immediately execute the apoptotic program but caspase activation occurs discretely at some low level. During this time, caspase cleavage of the amyloid precursor protein (APP), the adaptor protein GGA3 involved with beta-amyloid production, and tau may promote the formation of beta-amyloid (A beta) and neurofibrillary tangles (NFTs). Thus, not only may activation of caspases represent a terminal event associated with AD (i.e. cell death), but also a proximal event that promotes the pathology underlying this disease. Therefore, therapeutics aimed at preventing the activation and execution of apoptosis may provide an effective means of treating AD.

The relation between inflammation and neurodegeneration in multiple sclerosis brains

Some recent studies suggest that in progressive multiple sclerosis, neurodegeneration may occur independently from inflammation. The aim of our study was to analyse the interdependence of inflammation, neurodegeneration and disease progression in various multiple sclerosis stages in relation to lesional activity and clinical course, with a particular focus on progressive multiple sclerosis. The study is based on detailed quantification of different inflammatory cells in relation to axonal injury in 67 multiple sclerosis autopsies from different disease stages and 28 controls without neurological disease or brain lesions. We found that pronounced inflammation in the brain is not only present in acute and relapsing multiple sclerosis but also in the secondary and primary progressive disease. T- and B-cell infiltrates correlated with the activity of demyelinating lesions, while plasma cell infiltrates were most pronounced in patients with secondary progressive multiple sclerosis (SPMS) and primary progressive multiple sclerosis (PPMS) and even persisted, when T- and B-cell infiltrates declined to levels seen in age matched controls. A highly significant association between inflammation and axonal injury was seen in the global multiple sclerosis population as well as in progressive multiple sclerosis alone. In older patients (median 76 years) with long-disease duration (median 372 months), inflammatory infiltrates declined to levels similar to those found in age-matched controls and the extent of axonal injury, too, was comparable with that in age-matched controls. Ongoing neurodegeneration in these patients, which exceeded the extent found in normal controls, could be attributed to confounding pathologies such as Alzheimer's or vascular disease. Our study suggests a close association between inflammation and neurodegeneration in all lesions and disease stages of multiple sclerosis. It further indicates that the disease processes of multiple sclerosis may die out in aged patients with long-standing disease.

Senescence-accelerated mouse (SAM) with special references to neurodegeneration models, SAMP8 and SAMP10 mice

The SAM strains, a group of related inbred strains consisting of senescence-prone inbred strains (SAMP) and senescence-resistant inbred strains (SAMR), have been successfully developed by selective inbreeding of the AKR/J strain of mice donated by the Jackson laboratory in 1968. The characteristic feature of aging common to the SAMP and SAMR is accelerated senescence and normal aging, respectively. Furthermore, SAMP and SAMR strains of mice manifest various pathobiological phenotypes spontaneously. Among SAMP strains, SAMP8 and SAMP10 mice show age-related behavioral deterioration such as deficits in learning and memory, emotional disorders (reduced anxiety-like behavior and depressive behavior) and altered circadian rhythm associated with certain pathological, biochemical and pharmacological changes. Here, the previous and recent literature on SAM mice are reviewed with an emphasis on SAMP8 and SAMP10 mice. A spontaneous model like SAM with distinct advantages over the gene-modified model is hoped by investigators to be used more widely as a biogerontological resource to explore the etiopathogenesis of accelerated senescence and neurodegenerative disorders.

TrkA pathway activation induced by amyloid-beta (Abeta)

Amyloid-beta (Abeta), a cytotoxic fragment of Amyloid Precursor Protein (APP), has been implicated in the etiopathogenesis of Alzheimer's disease (AD). Since several neurotrophins signalling pathways may be activated in response to toxic insults, we investigated whether a similar response is triggered also by Abeta. After Abeta (25-35) peptide administration to cultured rat hippocampal neurons, the nerve growth factor (NGF) and its receptor (TrkA) mRNA expression is up-regulated. Moreover, we observe an increased cellular TrkA expression (4.5 fold) and NGF release in the culture medium (5-fold). Concomitantly, TrkA, Akt and glycogen synthase kinase 3beta (Gsk3beta) phosphorylation significantly increase. Interestingly, when cells were treated with Abeta (25-35) in the presence of blocking antibody against NGF, only a partial TrkA activation (2-fold) was observed. These results have been confirmed by using pathophysiological Abeta (1-42) oligomers. Our data provide the evidence that Abeta induces the TrkA pathway activation directly by itself and indirectly promoting NGF secretion.

Neurofibrillary degeneration in Alzheimer's disease: from molecular mechanisms to identification of drug targets

PURPOSE OF REVIEW

Great progress has been made in understanding the pathogenesis of neurofibrillary degeneration in Alzheimer's disease brains in the last two decades. In this review we summarize how neurons are degenerated in Alzheimer's disease brains and highlight the evidence of using kinases such as glycogen synthase kinase 3 and p70 S6 kinase and phosphatases such as protein phosphatase 2A as drug targets to prohibit the formation of neurofibrillary degeneration of Alzheimer's disease.

RECENT FINDINGS

In general there are two types of neuronal degeneration in Alzheimer's disease brains: neurofibrillary formation and apoptosis. The microtubule-associated protein tau that stabilizes neuronal microtubules under normal physiological conditions is abnormally hyperphosphorylated in Alzheimer's disease brains, resulting in the generation of aberrant aggregates that are toxic to neurons. The processes of tau hyperphosphorylation and the formation of neurofibrillary tangles are caused by the imbalance of the activities of protein kinases and protein phosphatases in Alzheimer's disease brains. Recent findings from our and other groups have suggested glycogen synthase kinase 3 and p70 S6 kinase as main tau kinases and protein phosphatase 2A as the main tau phosphatase involved in the formation of these processes. Activities of these targets are implicated by Abeta peptide, the major component of another hallmark in Alzheimer's disease brains, senile plaques.

SUMMARY

To prevent the clinical progression of neurodegeneration, a combination strategy is suggested to target both senile plaques with immunization and neurofibrillary tangles with drugs to prevent the synthesis and phosphorylation of tau.

Molecular changes in white matter adjacent to an active demyelinating lesion in early multiple sclerosis

A stereotactic biopsy of a 17-year-old woman revealed an active inflammatory demyelinating lesion compatible with pattern III multiple sclerosis (MS) according to Lucchinetti et al. The biopsy included a white matter region distant from the active inflammatory demyelinating lesion with abnormal MRI signal, lacking histopathological signs of demyelination and/or oligodendrocyte apoptosis. Expression analysis of this area revealed a strong up-regulation of neuronal nitric oxide synthase (nNOS). Furthermore, detection of nitrotyrosine provided evidence for reactive nitrogen species (RNS)-mediated damage to oligodendrocytes. Concomitantly, genes involved in neuroprotection against oxidative stress such as heme oxygenase 1 were up-regulated. Even though a single case report, this study shows earliest molecular changes in white matter surrounding an actively demyelinating lesion during the first manifestation of MS, pointing toward a more widespread pathological process. Therapeutic targeting of the identified mechanisms of tissue injury might be crucial to prevent further lesion formation or secondary tissue damage.

Nucleic acid oxidation in Alzheimer disease

Increasing evidence suggests that oxidative stress is intimately associated with Alzheimer disease pathophysiology. Nucleic acids (nuclear DNA, mitochondrial DNA, and RNA) are one of the several cellular macromolecules damaged by reactive oxygen species, particularly the hydroxyl radical. Because neurons are irreplaceable and survive as long as the organism does, they need elaborate defense mechanisms to ensure their longevity. In Alzheimer disease, however, an accumulation of nucleic acid oxidation is observed, indicating an increased level of oxidative stress and/or a decreased capacity to repair the nucleic acid damage. In this review, we present data supporting the notion that mitochondrial and metal abnormalities are key sources of oxidative stress in Alzheimer disease. Furthermore, we outline the mechanisms of nucleic acid oxidation and repair. Finally, evidence showing the occurrence of nucleic acid oxidation in Alzheimer disease will be discussed.

Differential nigral expression of bcl-2 protein family in the pure and common forms of Dementia with Lewy bodies: relevance for dopaminergic neuronal vulnerability

We investigated whether bcl-2 protein family is involved in the pathogenesis of the dopaminergic neurodegeneration that occurs in Dementia with Lewy bodies (DLB). The expression of the proapoptotic protein bax and the antiapoptotic proteins bcl-2 and bcl-xL was investigated by Western blot in the pars compacta of the substantia nigra of pure and common DLB forms. No changes in the nigral expression levels of bax, bcl-2 and bcl-xL proteins were found between control and DLB pure cases. In the common DLB forms, nigral bcl-xL and bcl-2 proteins levels were significantly decreased in the DLB cases associated with a concomitant severe AD pathology (p < 0.05). An increase in nigral bcl-2 protein expression was observed in the DLB cases with a mild AD-associated pathology (p < 0.05). The present results are in agreement with previous observations indicating that DLB cases with severe AD pathology tend to show severe Lewy pathology suggesting that AD pathology might exacerbate Lewy pathology.

Expression of Bcl-2, Bax and Caspase-3 in nerve tissues of rats chronically exposed to 2,5-hexanedione

Occupational exposure and experimental intoxication with n-hexane or its metabolite 2,5-hexanedione (HD) produce a central-peripheral neuropathy. However, the mechanism remains unknown. We hypothesized that HD affected the expression of Bcl-2, Bax and Caspase-3 in the central nervous system (CNS) and the peripheral nervous system (PNS). Male adult Wistar rats were administered by intraperitoneal injection at a dosage of 200 or 400 mg/kg HD, five days per week for 8 weeks. Samples of the cerebral cortex, cerebellum, spinal cord and sciatic nerves were collected and examined for Bcl-2, Bax and Caspase-3 expression using Western blotting. Subchronic exposure to HD resulted in significantly increased expression of both anti-apoptotic protein Bcl-2 and pro-apoptotic protein Bax and Caspase-3 in cerebral cortex and cerebellum, which exhibited a dose-dependent pattern. Though little change was detected in spinal cord, our results showed that the expression of Bcl-2, Bax and Caspase-3 was markedly enhanced in the sciatic nerves. These findings suggested that the changes of apoptosis-related protein level in rat nerve tissues were associated with the intoxication of HD, which might be involved in early molecular regulatory mechanism of apoptosis in the HD-induced neuropathy.

Oxidative stress: A bridge between Down's syndrome and Alzheimer's disease

Besides the genetic, biochemical and neuropathological analogies between Down's syndrome (DS) and Alzheimer's disease (AD), there is ample evidence of the involvement of oxidative stress (OS) in the pathogenesis of both disorders. The present paper reviews the publications on DS and AD in the past 10 years in light of the "gene dosage" and "two-hit" hypotheses, with regard to the alterations caused by OS in both the central nervous system and the periphery, and the main pipeline of antioxidant therapeutic strategies. OS occurs decades prior to the signature pathology and manifests as lipid, protein and DNA oxidation, and mitochondrial abnormalities. In clinical settings, the assessment of OS has traditionally been hampered by the use of assays that suffer from inherent problems related to specificity and/or sensitivity, which explains some of the conflicting results presented in this work. For DS, no scientifically proven diet or drug is yet available, and AD trials have not provided a satisfactory approach for the prevention of and therapy against OS, although most of them still need evidence-based confirmation. In the future, a balanced up-regulation of endogenous antioxidants, together with multiple exogenous antioxidant supplementation, may be expected to be one of the most promising treatment methods.

Nitric Oxide Synthase 3-Mediated Neurodegeneration After Intracerebral Gene Delivery

In Alzheimer disease (AD), increased nitric oxide synthase 3 (NOS3) expression correlates with apoptosis in cortical neurons and colocalizes with amyloid precursor protein (APP)-amyloid beta (Abeta) deposits in the brain. In the present study we examined the potential role of NOS3 in relation to AD-type neurodegeneration using an in vivo model of gene delivery. Long Evans rat pups were given a single intracerebral injection of recombinant plasmid DNA containing the human NOS3 cDNA (p-hNOS3) or the luciferase (p-Luc) gene as a negative control, and complexed with polyamine reagent. Overexpression of NOS3 in the brain increased the levels of APP, APP-Abeta, p53, Tau, glial fibrillary acidic protein, and peroxisome proliferator activated receptors (PPAR) delta and gamma and decreased the levels of Hu (neuronal marker) mRNA, phosphorylated glycogen synthase kinase 3beta, ATP synthase, and choline acetyltransferase expression as demonstrated by real-time quantitative reverse-transcribed polymerase chain reaction, Western blot analysis, or immunohistochemical staining. These effects of NOS3 overexpression were accompanied by increased single-stranded DNA immunoreactivity, reflecting DNA damage. The results suggest that increased cerebral expression of NOS3 causes several molecular abnormalities related to AD-type neurodegeneration, including oxidative stress, mitochondrial dysfunction, and impaired acetylcholine homeostasis. The coexisting increases in PPAR-delta and -gamma expression suggest that the adverse effects of NOS3 overexpression may be abated by PPAR agonist treatment.

Comparison of three methods to assess enteric neuronal apoptosis in patients with slow transit constipation

BACKGROUND

The pathophysiological basis of slow transit constipation are scarcely understood. Some recent evidence suggests that increased apoptotic phenomena in the colonic enteric neurons may play a role. However, the best method to assess these phenomena has not been evaluated.

AIMS

To compare three different methods to detect enteric neuronal apoptosis in these patients.

METHODS

Serial colonic tissue sections obtained in 10 patients with intractable slow transit constipation were evaluated with immunohistochemical methods aimed at evaluating apoptotic phenomena: the formamide-MAb method, the TUNEL, and the caspase-3.

RESULTS

The highest yield of apoptotic neurons was obtained by means of the formamide-MAb method, compared to the other two, whereas the lowest yield was observed with the caspase-3.

CONCLUSIONS

The formamide-MAb method, which is able to distinguish apoptosis from necrosis and is not influenced by DNA breaks, may prove useful to assess neuronal apoptotic phenomena in the human enteric nervous system. This represents a relevant method to detect enteric neuronal apoptosis.