Effects of oxidative and nitrosative stress in brain on p53 proapoptotic protein in amnestic mild cognitive impairment and Alzheimer disease

Many studies reported that oxidative and nitrosative stress might be important for the pathogenesis of Alzheimer's disease (AD) beginning with arguably the earliest stage of AD, i.e., as mild cognitive impairment (MCI). p53 is a proapoptotic protein that plays an important role in neuronal death, a process involved in many neurodegenerative disorders. Moreover, p53 plays a key role in the oxidative stress-dependent apoptosis. We demonstrated previously that p53 levels in brain were significantly higher in MCI and AD IPL (inferior parietal lobule) compared to control brains. In addition, we showed that in AD IPL, but not in MCI, HNE, a lipid peroxidation product, was significantly bound to p53 protein. In this report, we studied by means of immunoprecipitation analysis, the levels of markers of protein oxidation, 3-nitrotyrosine (3-NT) and protein carbonyls, in p53 in a specific region of the cerebral cortex, namely the inferior parietal lobule, in MCI and AD compared to control brains. The focus of these studies was to measure the oxidation and nitration status of this important proapoptotic protein, consistent with the hypothesis that oxidative modification of p53 could be involved in the neuronal loss observed in neurodegenerative conditions.     

Oxidatively Modified GST and MRP1 in Alzheimer’s Disease Brain: Implications for Accumulation of Reactive Lipid Peroxidation Products

Alzheimer disease (AD) is a neurodegenerative disorder characterized pathologically by intracellular inclusions including neurofibrillary tangles (NFT) and senile plaques. Several lines of evidence implicate oxidative stress with the progression of AD. 4-hydroxy-2-trans-nonenal (HNE), an aldehydic product of membrane lipid peroxidation, is increased in AD brain. The alpha class of glutathione S-transferase (GST) can detoxify HNE and plays an important role in cellular protection against oxidative stress. The export of the glutathione conjugate of HNE is required to fully potentiate the GST-mediated protection. The multidrug resistance protein-1 (MRP1) and GST proteins may act in synergy to confer cellular protection. In the present study, we studied oxidative modification of GST and MRP1 in AD brain by immunoprecipitation of GST and MRP1 proteins followed by Western blot analysis using anti-HNE antibody. The results suggested that HNE is covalently bound to GST and MRP1 proteins in excess in AD brain. Collectively, the data suggest that HNE may be an important mediator of oxidative stress-induced impairment of this detoxifying system and may thereby play a role in promoting neuronal cell death. The results from this study also imply that augmenting endogenous oxidative defense capacity through dietary or pharmacological intake of antioxidants may slow down the progression of neurodegenerative processes in AD.     

Involvements of the lipid peroxidation product,HNE, in the pathogenesis and progression of Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder. A number of hypotheses have been proposed to explain AD pathogenesis. One such hypothesis proposed to explain AD pathogenesis is the oxidative stress hypothesis. Increased levels of oxidative stress markers including the markers of lipid peroxidation such as acrolein, 4-hydroxy-2-trans-nonenal (HNE), malondialdehyde, etc. are found in brains of AD subjects. In this review, we focus principally on research conducted in the area of HNE in the central nervous system (CNS) of AD and mild cognitive impairment (MCI), and further, we discuss likely consequences of lipid peroxidation with respect to AD pathogenesis and progression. Based on the research conducted so far in the area of lipid peroxidation, it is suggested that lipid accessible antioxidant molecules could be a promising therapeutic approach to treat or slow progression of MCI and AD.     

4-hydroxynonenal and neurodegenerative diseases

The development of oxidative stress, in which production of highly reactive oxygen species (ROS) overwhelms antioxidant defenses, is a feature of many neurological diseases: ischemic, inflammatory, metabolic and degenerative. Oxidative stress is increasingly implicated in a number of neurodegenerative disorders characterized by abnormal filament accumulation or deposition of abnormal forms of specific proteins in affected neurons, like Alzheimer's disease (AD), Pick's disease, Lewy bodies related diseases, amyotrophic lateral sclerosis (ALS), and Huntington disease. Causes of neuronal death in neurodegenerative diseases are multifactorial. In some familiar cases of ALS mutation in the gene for Cu/Zn superoxide dismutase (SOD1) can be identified. In other neurodegenerative diseases ROS have some, usually not clear, role in early pathogenesis or implications on neuronal death in advanced stages of illness. The effects of oxidative stress on "post-mitotic cells", such as neurons may be cumulative, hence, it is often unclear whether oxidative damage is a cause or consequence of neurodegeneration. Peroxidation of cellular membrane lipids, or circulating lipoprotein molecules generates highly reactive aldehydes among which one of most important is 4-hydroxynonenal (HNE). The presence of HNE is increased in brain tissue and cerebrospinal fluid of AD patients, and in spinal cord of ALS patients. Immunohistochemical studies show presence of HNE in neurofibrilary tangles and in senile plaques in AD, in the cytoplasm of the residual motor neurons in sporadic ALS, in Lewy bodies in neocortical and brain stem neurons in Parkinson's disease (PD) and in diffuse Lewy bodies disease (DLBD). Thus, increased levels of HNE in neurodegenerative disorders and immunohistochemical distribution of HNE in brain tissue indicate pathophysiological role of oxidative stress in these diseases, and especially HNE in formation of abnormal filament deposites.     

Proteomic identification of oxidatively modified proteins in Alzheimer's disease brain. Part II: dihydropyrimidinase-related protein 2, alpha-enolase and heat shock cognate 71

Alzheimer's disease (AD) is a neurodegenerative disorder in which oxidative stress has been implicated as an important event in the progression of the pathology. In particular, it has been shown that protein modification by reactive oxygen species (ROS) occurs to a greater extent in AD than in control brain, suggesting a possible role for oxidation-related decrease in protein function in the process of neurodegeneration. Oxidative damage to proteins, assessed by measuring the protein carbonyl content, is involved in several events such as loss in specific protein function, abnormal protein clearance, depletion of the cellular redox-balance and interference with the cell cycle, and, ultimately, neuronal death. The present investigation represents a further step in understanding the relationship between oxidative modification of protein and neuronal death in AD. Previously, we used our proteomics approach, which successfully substitutes for labor-intensive immunochemical analysis, to detect proteins and identified creatine kinase, glutamine synthase and ubiquitin carboxy-terminal hydrolase L-1 as specifically oxidized proteins in AD brain. In this report we again applied our proteomics approach to identify new targets of protein oxidation in AD inferior parietal lobe (IPL). The dihydropyrimidinase related protein 2 (DRP-2), which is involved in the axonal growth and guidance, showed significantly increased level in protein carbonyls in AD brain, suggesting a role for impaired mechanism of neural network formation in AD. Additionally, the cytosolic enzyme alpha-enolase was identified as a target of protein oxidation and is involved the glycolytic pathway in the pathological events of AD. Finally, the heat shock cognate 71 (HSC-71) revealed increased, but not significant, oxidation in AD brain. These results are discussed with reference to potential involvement of these oxidatively modified proteins in neurodegeneration in AD brain.     

Cocoa procyanidins attenuate 4-hydroxynonenal-induced apoptosis of PC12 cells by directly inhibiting mitogen-activated protein kinase kinase 4 activity

Neurodegenerative disorders such as Alzheimer's disease (AD) are associated with oxidative stress, and it has been suggested that apoptosis is a crucial pathway in neuronal cell death in AD patients. 4-Hydroxynonenal (HNE), one of the aldehydic products of membrane lipid peroxidation, is reported to be elevated in the brains of AD patients and mediates the induction of neuronal apoptosis in the presence of oxidative stress. In this study, we investigated the HNE-induced apoptosis mechanism and the protective effects of the cocoa procyanidin fraction (CPF) and its major antioxidant procyanidin B2 against the apoptosis induced by HNE in rat pheochromocytoma (PC12) cells. HNE-induced nuclear condensation and increased sub-G1 fraction, both of which are markers of apoptotic cell death, were inhibited by CPF and procyanidin B2. Intracellular reactive oxygen species (ROS) accumulation was attenuated by pretreatment with CPF and procyanidin B2. CPF and procyanidin B2 also prevented HNE-induced poly(ADP-ribose) polymerase cleavage, antiapoptotic protein (Bcl-2 and Bcl-X_L) down-regulation, and caspase-3 activation. Activation of c-Jun N-terminal protein kinase (JNK) and mitogen-activated protein kinase kinase 4 (MKK4) was attenuated by CPF and procyanidin B2. Moreover, CPF and procyanidin B2 bound directly to MKK4 and inhibited its activity. Data obtained with SP600125, a selective inhibitor of JNK, revealed that JNK is involved in HNE-induced apoptosis through the inhibition of PARP cleavage and caspase-3 activation in PC12 cells. Collectively, these results indicate that CPF and procyanidin B2 protect PC12 cells against HNE-induced apoptosis by blocking MKK4 activity as well as ROS accumulation.     

Proteomic identification of nitrated brain proteins in amnestic mild cognitive impairment: a regional study

Oxidative stress is an imbalance between the level of antioxidants and oxidants in a cell. Oxidative stress has been shown in brain of subjects with mild cognitive impairment (MCI) as well Alzheimer's disease (AD). MCI is considered as a transition phase between control and AD. The focus of the current study was to identify nitrated proteins in the hippocampus and inferior parietal lobule (IPL) brain regions of subjects with amnestic MCI using proteomics. The identified nitrated proteins in MCI brain were compared to those previously reported to be nitrated and oxidatively modified in AD brain, a comparison that might provide an invaluable insight into the progression of the disease.     

Oxidative stress impairs glutamate uptake in fibroblasts from patients with Alzheimer's disease

Oxidative stress has been demonstrated in Alzheimer's disease (AD) brain and may affect glutamate transport (GT), thereby leading to excitotoxic neuronal death. Since oxidative stress markers have been shown also in peripheral tissues, we investigated possible GT alterations in fibroblast cultures obtained from 18 patients with AD and 15 control patients and analyzed the effects of the lipoperoxidation product 4-hydroxynonenal (4-HNE) and antioxidants. Basal GT was decreased by 60% in fibroblasts from patients with AD versus control patients. Exposure to HNE did not affect GT in control patients, but it reduced GT by 50% in patients with AD, without any concomitant change in cell viability; conversely, HNE exposure induced a larger increase in ROS intracellular levels in AD than in control fibroblasts. Glutathione and N-acetylcysteine completely blocked 4-HNE effects and also increased basal uptake in AD cells. Moreover, inhibition of glutathione synthesis in control fibroblasts by pretreatment with buthionine sulfoximine resulted in GT reduction (40%) and an increase in ROS levels after exposure to 4-HNE. Nevertheless, since there are no differences between GSH basal level in controls and patients with AD, the alteration of other antioxidant systems cannot be excluded. Our study supports the hypothesis of a systemic impairment of GT in AD, possibly linked to oxidative stress and to reduced antioxidant defenses, which may be partially reversed by antioxidant treatment. Therefore, we suggest fibroblast cultures as a tool for exploring pathogenetic mechanisms and possible therapeutic strategies in patients with AD.     

Multifunctional roles of enolase in Alzheimer's disease brain: beyond altered glucose metabolism

Enolase enzymes are abundantly expressed, cytosolic carbon-oxygen lyases known for their role in glucose metabolism. Recently, enolase has been shown to possess a variety of different regulatory functions, beyond glycolysis and gluconeogenesis, associated with hypoxia, ischemia, and Alzheimer's disease (AD). AD is an age-associated neurodegenerative disorder characterized pathologically by elevated oxidative stress and subsequent damage to proteins, lipids, and nucleic acids, appearance of neurofibrillary tangles and senile plaques, and loss of synapse and neuronal cells. It is unclear if development of a hypometabolic environment is a consequence of or contributes to AD pathology, as there is not only a significant decline in brain glucose levels in AD, but also there is an increase in proteomics identified oxidatively modified glycolytic enzymes that are rendered inactive, including enolase. Previously, our laboratory identified α-enolase as one the most frequently up-regulated and oxidatively modified proteins in amnestic mild cognitive impairment (MCI), early-onset AD, and AD. However, the glycolytic conversion of 2-phosphoglycerate to phosphoenolpyruvate catalyzed by enolase does not directly produce ATP or NADH; therefore it is surprising that, among all glycolytic enzymes, α-enolase was one of only two glycolytic enzymes consistently up-regulated from MCI to AD. These findings suggest enolase is involved with more than glucose metabolism in AD brain, but may possess other functions, normally necessary to preserve brain function. This review examines potential altered function(s) of brain enolase in MCI, early-onset AD, and AD, alterations that may contribute to the biochemical, pathological, clinical characteristics, and progression of this dementing disorder.     

Mutations in amyloid precursor protein and presenilin-1 genes increase the basal oxidative stress in murine neuronal cells and lead to increased sensitivity to oxidative stress mediated by amyloid beta-peptide (1-42), HO and kainic acid: implications for Alzheimer's disease

Oxidative stress is observed in Alzheimer's disease (AD) brain, including protein oxidation and lipid peroxidation. One of the major pathological hallmarks of AD is the brain deposition of amyloid beta-peptide (Abeta). This 42-mer peptide is derived from the beta-amyloid precursor protein (APP) and is associated with oxidative stress in vitro and in vivo. Mutations in the PS-1 and APP genes, which increase production of the highly amyloidogenic amyloid beta-peptide (Abeta42), are the major causes of early onset familial AD. Several lines of evidence suggest that enhanced oxidative stress, inflammation, and apoptosis play important roles in the pathogenesis of AD. In the present study, primary neuronal cultures from knock-in mice expressing mutant human PS-1 and APP were compared with those from wild-type mice, in the presence or absence of various oxidizing agents, viz, Abeta(1-42), H2O2 and kainic acid (KA). APP/PS-1 double mutant neurons displayed a significant basal increase in oxidative stress as measured by protein oxidation, lipid peroxidation, and 3-nitrotyrosine when compared with the wild-type neurons (p < 0.0005). Elevated levels of human APP, PS-1 and Abeta(1-42) were found in APP/PS-1 cultures compared with wild-type neurons. APP/PS-1 double mutant neuron cultures exhibited increased vulnerability to oxidative stress, mitochondrial dysfunction and apoptosis induced by Abeta(1-42), H2O2 and KA compared with wild-type neuronal cultures. The results are consonant with the hypothesis that Abeta(1-42)-associated oxidative stress and increased vulnerability to oxidative stress may contribute significantly to neuronal apoptosis and death in familial early onset AD.     

Oxidatively modified,mitochondria-relevant brain proteins in subjects with Alzheimer disease and mild cognitive impairment

Alzheimer disease (AD) is an age-related neurodegenerative disorder, characterized histopathologically by the presence of senile plaques (SP), neurofibrillary tangles and synapse loss in selected brain regions. Positron emission tomography (PET) studies of glucose metabolism revealed decreased energetics in brain of subjects with AD and arguably its earliest form, mild cognitive impairment (MCI), and this decrease correlated with brain structural studies using MRI. The main component of senile plaques is amyloid beta-peptide (Aβ), a 40–42 amino acid peptide that as oligomers is capable of inducing oxidative stress under both in vitro and in vivo conditions and is neurotoxic. In the mitochondria isolated from AD brain, Aβ oligomers that correlated with the reported increased oxidative stress markers in AD have been reported. The markers of oxidative stress have been localized in the brain regions of AD and MCI that show pathological hallmarks of this disease, suggesting the possible role of Aβ in the initiation of the free-radical mediated process and consequently to the build up oxidative stress and AD pathogenesis. Using redox proteomics our laboratory found a number of oxidatively modified brain proteins that are directly in or are associated with the mitochondrial proteome, consistent with a possible involvement of the mitochondrial targeted oxidatively modified proteins in AD progression or pathogenesis. The precise mechanistic link between mitochondrial oxidative damage and role of oligomeric Aβ has not been explicated. In this review, we discuss the role of the oxidation of mitochondria-relevant brain proteins to the pathogenesis and progression of AD.     

Redox proteomics identification of oxidatively modified proteins in Alzheimer's disease brain and in vivo and in vitro models of AD centered around Abeta(1-42)

Alzheimer's disease is a progressive neurodegenerative disease associated with loss of memory and cognition. One hallmark of AD is the accumulation of amyloid beta-peptide (Abeta), which invokes a cascade of oxidative damage to neurons that can eventually result in neuronal death. Several markers of oxidative stress have been identified in AD brain, thus providing greater understanding into potential mechanisms involved in the disease pathogenesis and progression. In the present article, we review the application of redox proteomics to the identification of oxidized proteins in AD brain and also our recent findings on amyloid beta-peptide (Abeta)-associated in vivo and in vitro models of AD. Our redox proteomics approach has made possible the identification of specifically oxidized proteins in Alzheimer's disease (AD) brain, providing for the first time evidence on how oxidative stress plays a crucial role in AD-related neurodegeneration. The information obtained has great potential to aid in determining the molecular pathogenesis in and detecting disease markers of AD, as well as identifying potential targets for drug therapy in AD. Application of redox proteomics to study cellular events, especially related to disease dysfunction, may provide an efficient tool to understand the main mechanisms involved in the pathogenesis and progression of oxidative stress-related neurodegenerative disorders.     

Lymphocyte mitochondria: toward identification of peripheral biomarkers in the progression of Alzheimer disease

Alzheimer disease (AD) is an age-related neurodegenerative condition. AD is histopathologically characterized by the presence of three main hallmarks: senile plaques (rich in amyloid-β peptide), neuronal fibrillary tangles (rich in phosphorylated tau protein), and synapse loss. However, definitive biomarkers for this devastating disease in living people are still lacking. In this study, we show that levels of oxidative stress markers are significantly increased in the mitochondria isolated from lymphocytes of subjects with mild cognitive impairment (MCI) compared to cognitively normal individuals. Further, an increase in mitochondrial oxidative stress in MCI is associated with MMSE score, vitamin E components, and β-carotene. Further, a proteomics approach showed that alterations in the levels of thioredoxin-dependent peroxide reductase, myosin light polypeptide 6, and ATP synthase subunit β might be important in the progression and pathogenesis of AD. Increased understanding of oxidative stress and protein alterations in easily obtainable peripheral tissues will be helpful in developing biomarkers to combat this devastating disorder.     

Involvement of PI3K/PKG/ERK1/2 signaling pathways in cortical neurons to trigger protection by cotreatment of acetyl-L-carnitine and alpha-lipoic acid against HNE-mediated oxidative stress and neurotoxicity: implications for Alzheimer's disease

Oxidative stress has been shown to underlie neuropathological aspects of Alzheimer's disease (AD). 4-Hydroxy-2-nonenal (HNE) is a highly reactive product of lipid peroxidation of unsaturated lipids. HNE-induced oxidative toxicity is a well-described model of oxidative stress-induced neurodegeneration. GSH plays a key role in antioxidant defense, and HNE exposure causes an initial depletion of GSH that leads to gradual toxic accumulation of reactive oxygen species. In the current study, we investigated whether pretreatment of cortical neurons with acetyl-L-carnitine (ALCAR) and alpha-lipoic acid (LA) plays a protective role in cortical neuronal cells against HNE-mediated oxidative stress and neurotoxicity. Decreased cell survival of neurons treated with HNE correlated with increased protein oxidation (protein carbonyl, 3-nitrotyrosine) and lipid peroxidation (HNE) accumulation. Pretreatment of primary cortical neuronal cultures with ALCAR and LA significantly attenuated HNE-induced cytotoxicity, protein oxidation, lipid peroxidation, and apoptosis in a dose-dependent manner. Additionally, pretreatment of ALCAR and LA also led to elevated cellular GSH and heat shock protein (HSP) levels compared to untreated control cells. We have also determined that pretreatment of neurons with ALCAR and LA leads to the activation of phosphoinositol-3 kinase (PI3K), PKG, and ERK1/2 pathways, which play essential roles in neuronal cell survival. Thus, this study demonstrates a cross talk among the PI3K, PKG, and ERK1/2 pathways in cortical neuronal cultures that contributes to ALCAR and LA-mediated prosurvival signaling mechanisms. This evidence supports the pharmacological potential of cotreatment of ALCAR and LA in the management of neurodegenerative disorders associated with HNE-induced oxidative stress and neurotoxicity, including AD.     

Early events of target deprivation/axotomy-induced neuronal apoptosis in vivo: oxidative stress,DNA damage,p53 phosphorylation and subcellular redistribution of death proteins

The mechanisms of injury- and disease-associated apoptosis of neurons within the CNS are not understood. We used a model of cortical injury in rat and mouse to induce retrograde neuronal apoptosis in thalamus. In this animal model, unilateral ablation of the occipital cortex induces apoptosis of corticopetal projection neurons in the dorsal lateral geniculate nucleus (LGN), by 7 days post-lesion, that is p53 modulated and Bax dependent. We tested the hypothesis that this degenerative process is initiated by oxidative stress and early formation of DNA damage and is accompanied by changes in the levels of pro-apoptotic mediators of cell death. Immunoblotting revealed that the protein profiles of Bax, Bak and Bad were different during the progression of neuronal apoptosis in the LGN. Bax underwent a subcellular redistribution by 1 day post-lesion, while Bak increased later. Bad showed an early sustained increase. Cleaved caspase-3 was elevated maximally at 5 and 6 days. Active caspase-3 underwent a subcellular translocation to the nucleus. A dramatic phosphorylation of p53 was detected at 4 days post-lesion. DNA damage was assessed immunocytochemically as hydroxyl radical adducts (8-hydroxy-2-deoxyguanosine) and single-stranded DNA. Both forms of DNA damage accumulated early in target-deprived LGN neurons. Transgenic overexpression of superoxide dismutase-1 provided significant protection against the apoptosis but antioxidant pharmacotreatments with trolox and ascorbate were ineffective. We conclude that overlapping and sequential signaling pathways are involved in the apoptosis of adult brain neurons and that DNA damage generated by superoxide derivatives is an upstream mechanism for p53-regulated, Bax-dependent apoptosis of target-deprived neurons.     

Multiple signaling events in amyloid beta-induced,oxidative stress-dependent neuronal apoptosis

Current evidence suggests that amyloid beta peptides (Abeta) may play a major role in the pathogenesis of Alzheimer's disease by eliciting oxidative stress and neuronal apoptosis. In this study we have used differentiated SK-N-BE neurons to investigate molecular mechanisms and regulatory pathways underlying apoptotic neuronal cell death elicited by Abeta(1-40) and Abeta(1-42) peptides as well as the relationships between apoptosis and oxidative stress. Abeta peptides, used at concentrations able to induce oxidative stress, elicit a classic type of neuronal apoptosis involving mitochondrial regulatory proteins and pathways (i.e. affecting Bax and Bcl-2 protein levels as well as release of cytochrome c in the cytosol), poly-ADP rybose polymerase cleavage and activation of caspase 3. This pattern of neuronal apoptosis, that is significantly prevented by alpha-tocopherol and N-acetylcysteine and completely abolished by specific inhibitors of stress-activated protein kinases (SAPK) such as JNKs and p38(MAPK), involved early elevation of p53 protein levels. Pretreatment of neurons with alpha-pifithrin, a specific p53 inhibitor, resulted in a 50-60% prevention of Abeta induced apoptosis. These results suggest that oxidative stress - mediated neuronal apoptosis induced by amyloid beta operates by eliciting a SAPK-dependent multiple regulation of pro-apoptotic mitochondrial pathways involving both p53 and bcl-2.     

The glial glutamate transporter, GLT-1, is oxidatively modified by 4-hydroxy-2-nonenal in the Alzheimer's disease brain: the role of Aβ1–42

Glutamate transporters are involved in the maintenance of synaptic glutamate concentrations. Because of its potential neurotoxicity, clearance of glutamate from the synaptic cleft may be critical for neuronal survival. Inhibition of glutamate uptake from the synapse has been implicated in several neurodegenerative disorders. In particular, glutamate uptake is inhibited in Alzheimer's disease (AD); however, the mechanism of decreased transporter activity is unknown. Oxidative damage in brain is implicated in models of neurodegeneration, as well as in AD. Glutamate transporters are inhibited by oxidative damage from reactive oxygen species and lipid peroxidation products such as 4-hydroxy-2-nonenal (HNE). Therefore, we have investigated a possible connection between the oxidative damage and the decreased glutamate uptake known to occur in AD brain. Western blots of immunoprecipitated HNE-immunoreactive proteins from the inferior parietal lobule of AD and control brains suggest that HNE is conjugated to GLT-1 to a greater extent in the AD brain. A similar analysis of beta amyloid (Abeta)-treated synaptosomes shows for the first time that Abeta1-42 also increases HNE conjugation to the glutamate transporter. Together, our data provide a possible link between the oxidative damage and neurodegeneration in AD, and supports the role of excitotoxicity in the pathogenesis of this disorder. Furthermore, our data suggests that Abeta may be a possible causative agent in this cascade.     

Phosphoproteomics of Alzheimer disease brain: Insights into altered brain protein regulation of critical neuronal functions and their contributions to subsequent cognitive loss

Alzheimer disease (AD) is the major locus of dementia worldwide. In the USA there are nearly 6 million persons with this disorder, and estimates of 13–20 million AD cases in the next three decades. The molecular bases for AD remain unknown, though processes involving amyloid beta-peptide as small oligomeric forms are gaining attention as known agents to both lead to oxidative stress and synaptic dysfunction associated with cognitive dysfunction in AD and its earlier forms, including amnestic mild cognitive impairment (MCI) and possibly preclinical Alzheimer disease (PCAD).Altered brain protein phosphorylation is a hallmark of AD, and phosphoproteomics offers an opportunity to identify these altered phosphoproteins in order to gain more insights into molecular mechanisms of neuronal dysfunction and death that lead to cognitive loss. This paper reviews what, to this author, are believed to be the known phosphoproteomics studies related to in vitro and in vivo models of AD as well as phosphoproteomics studies of brains from subjects with AD, and in at least one case in MCI and PCAD as well. The results of this review are discussed with relevance to new insights into AD brain protein dysregulation in critical neuronal functions and to potential therapeutic targets to slow, or in favorable cases, halt progression of this dementing disorder that affects millions of persons and their families worldwide.     

Alteration of mTOR signaling occurs early in the progression of Alzheimer disease (AD): analysis of brain from subjects with pre‐clinical AD,amnestic mild cognitive impairment and late‐stage AD

The clinical symptoms of Alzheimer disease (AD) include a gradual memory loss and subsequent dementia, and neuropathological deposition of senile plaques and neurofibrillary tangles. At the molecular level, AD subjects present overt amyloid β (Aβ) production and tau hyperphosphorylation. Aβ species have been proposed to overactivate the phosphoinositide3‐kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) axis, which plays a central role in proteostasis. The current study investigated the status of the PI3K/Akt/mTOR pathway in post‐mortem tissue from the inferior parietal lobule (IPL) at three different stages of AD: late AD, amnestic mild cognitive impairment (MCI) and pre‐clinical AD (PCAD). Our findings suggest that the alteration of mTOR signaling and autophagy occurs at early stages of AD. We found a significant increase in Aβ (1–42) levels, associated with reduction in autophagy (Beclin‐1 and LC‐3) observed in PCAD, MCI, and AD subjects. Related to the autophagy impairment, we found a hyperactivation of PI3K/Akt/mTOR pathway in IPL of MCI and AD subjects, but not in PCAD, along with a significant decrease in phosphatase and tensin homolog. An increase in two mTOR downstream targets, p70S6K and 4EBP1, occurred in AD and MCI subjects. Both AD and MCI subjects showed increased, insulin receptor substrate 1, a candidate biomarker of brain insulin resistance, and GSK‐3β, a kinase targeting tau phosphorylation. Nevertheless, tau phosphorylation was increased in the clinical groups. The results hint at a link between Aβ and the PI3K/Akt/mTOR axis and provide further insights into the relationship between AD pathology and insulin resistance. In addition, we speculate that the alteration of mTOR signaling in the IPL of AD and MCI subjects, but not in PCAD, is due to the lack of substantial increase in oxidative stress.