Mitochondria dysfunction of Alzheimer's disease cybrids enhances Abeta toxicity

Blockage of GSK3β-mediated Drp1 phosphorylation provides neuroprotection in neuronal and mouse models of Alzheimer's disease

It is well established that mitochondrial fragmentation plays a key role in the pathogenesis of Alzheimer's disease (AD). Mitochondrial fission is mediated by dynamin-related protein 1 (Drp1), which is highly expressed in nervous system and regulated by various posttranslational modifications including phosphorylation. We identified glycogen synthase kinase (GSK)3β-dependent Drp1 phosphorylation at Ser(40) and Ser(44), which increases Drp1 GTPase activity and its mitochondrial distribution and could induce mitochondrial fragmentation. Moreover, neurons transfected with Ser(40)Ser(44) phosphomimic Drp1 showed increased mitochondria fragmentation and were more vulnerable to amyloid-β (Aβ)-induced apoptosis. Therefore, blocking GSK3β-induced Drp1 phosphorylation may be an effective way to protect neurons from Aβ toxicity. To address this, we designed and synthesized an artificial polypeptide named TAT-Drp1-SpS, which could specifically block GSK3β-induced Drp1 phosphorylation. Our results demonstrated that TAT-Drp1-SpS treatment could significantly reduce Aβ-induced neuronal apoptosis in cultured neurons. Notably, TAT-Drp1-SpS administration in hippocampus Cornu Ammonis 1 (CA1) region significantly reduced Aβ burden and rescued the memory deficits in AD transgenic mice. Although Aβ has multiple targets to exert its neurotoxicity, our findings suggested that GSK3β-induced mitochondrial fragmentation was, at least partially, mediated by Aβ toxicity and contribute to the pathogenesis of AD. Taken together, GSK3β-induced Drp1 phosphorylation provides a novel mechanism for mitochondrial fragmentation in AD, and our findings suggested a novel therapeutic strategy for AD.

Mo polyoxometalate nanoclusters capable of inhibiting the aggregation of Aβ-peptide associated with Alzheimer's disease

A neuropathological hallmark of Alzheimer's disease (AD) is aggregation of a forty-residue peptide known as amyloid beta forty (Aβ40). While past work has indicated that blocking Aβ40 aggregation could be an effective strategy for the treatment of AD, developing therapies with this goal has been met with limited success. Polyoxometalates (POMs) have been previously investigated for their anti-viral and anti-tumoral properties and we report here that three representative POM nanoclusters have been synthesized for use against Aβ40 aggregation. Through the use of thioflavin T fluorescence, turbidity, circular dichroism spectroscopy, and transmission electron microscopy (TEM), we found that all three POM complexes can significantly inhibit both natural Aβ40 self-aggregation and metal-ion induced Aβ40 aggregation. We also evaluated the protective effect of POM complexes on Aβ40-induced neurotoxicity in cultured PC12 cells and found that treatment with POM complexes can elevate cell viability, decrease levels of intracellular reactive oxygen species, and stabilize mitochondrial membrane potential. These findings indicate that all three representative POM complexes are capable of inhibiting Aβ40 aggregation and subsequent neurotoxicity. While a complete mechanistic understanding remains to be elucidated, the synthesized POM complexes may work through a synergistic interaction with metal ions and Aβ40. These data indicate that POM complexes have high therapeutic potential for use against one of the primary neuropathological features of AD.

Memory decline in Down syndrome and its relationship to iPF2alpha, a urinary marker of oxidative stress

BACKGROUND

Lipid peroxidation may be a marker of free-radical-mediated injury associated with Alzheimer's disease (AD). We aimed to investigate whether changes in lipid peroxidation is associated with cognitive decline in individuals with Down syndrome over a 4-year period.

METHODS

Thirty-two adults with DS participated in a longitudinal study with urinary isoprostane 8,12-iso-iPF2alpha (iPF2alpha) assays at baseline and four years follow-up. Informants rated their functional ability and memory function and the adults with DS attempted assessments of language skills and memory. Twenty-six individuals completed assessments of memory (Modified Memory Object Task, MOMT), adaptive behavior (ABAS), and receptive vocabulary (British Picture vocabulary, BPVS) at both time-points.

RESULTS

Overall change in iPF2alpha level was negatively correlated with change in the MOMT score (Spearman's Rho =  -0.576, p = 0.006), i.e., increased lipid peroxidation was correlated with worse memory functioning over time. An increase of ≥ 0.02 ng/mg creatinine iPF2α had good sensitivity (85.7%), positive predictive value (75%,), specificity (85.7%) and negative predictive value (92.3%) for memory decline.

CONCLUSION

Change in iPF2alpha over time may have potential as a biomarker for memory decline in Down syndrome and potentially also help to track progression of MCI to AD in the general population.

AlphaLISA-based high-throughput screening assay to measure levels of soluble amyloid precursor protein α

Activation of nonamyloidogenic processing of amyloid precursor protein (APP) has been hypothesized to be a viable approach for Alzheimer's disease drug discovery. However, until recently, the lack of HTS-compatible assay technologies precluded large scale screening efforts to discover molecules that potentiate nonamyloidogenic pathways. We have developed an HTS-compatible assay based on AlphaLISA technology that quantitatively detects soluble APPα (sAPPα), a marker of nonamyloidogenic processing of APP, released from live cells in low volume, 384-well plates. The assay exhibited good QC parameters (Z'>0.5, S/B>2). A pilot screen of 801 compounds yielded a novel chemotype that increased the release of sAPPα 2-fold at 5μM. These results suggest that the AlphaLISA-based HTS assay is robust and sensitive and can be used to screen large compound collections to discover molecules that potentiate the release of sAPPα. Additionally, we demonstrated that increase of APP processing by nonamyloidogenic pathways will result in decrease of release of amyloidogenic Aβ40 fragments.

Cytoplasmic hybrid (cybrid) cell lines as a practical model for mitochondriopathies

Cytoplasmic hybrid (cybrid) cell lines can incorporate human subject mitochondria and perpetuate its mitochondrial DNA (mtDNA)-encoded components. Since the nuclear background of different cybrid lines can be kept constant, this technique allows investigators to study the influence of mtDNA on cell function. Prior use of cybrids has elucidated the contribution of mtDNA to a variety of biochemical parameters, including electron transport chain activities, bioenergetic fluxes, and free radical production. While the interpretation of data generated from cybrid cell lines has technical limitations, cybrids have contributed valuable insight into the relationship between mtDNA and phenotype alterations. This review discusses the creation of the cybrid technique and subsequent data obtained from cybrid applications.

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The cytoplasmic hybrid (cybrid) model can be used to determine mitochondrial DNA (mtDNA) contributions to phenotypic alterations.

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Cybrids are used to study mitochondriopathies such as Parkinson’s disease and Alzheimer’s disease.

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mtDNA heteroplasmy threshold and nuclear DNA-mtDNA compatibility can be determined using cybrid models.

Aβ and tau toxicities in Alzheimer's are linked via oxidative stress-induced p38 activation: protective role of vitamin E

Oxidative stress is a hallmark of Alzheimer's disease (AD). We propose that rather than causing damage because of the action of free radicals, oxidative stress deranges signaling pathways leading to tau hyperphosphorylation, a hallmark of the disease. Indeed, incubation of neurons in culture with 5 µM beta-amyloid peptide (Aβ) causes an activation of p38 MAPK (p38) that leads to tau hyperphosphorylation. Inhibition of p38 prevents Aβ-induced tau phosphorylation. Aβ-induced effects are prevented when neurons are co-incubated with trolox (the water-soluble analog of vitamin E). We have confirmed these results in vivo, in APP/PS1 double transgenic mice of AD. We have found that APP/PS1 transgenic mice exhibit a high level of P-p38 in the hippocampus but not in cortex and this is prevented by feeding animals with a diet supplemented with vitamin E. Our results underpin the role of oxidative stress in the altered cell signaling in AD pathology and suggest that antioxidant prevention may be useful in AD therapeutics.

Identification of human presequence protease (hPreP) agonists for the treatment of Alzheimer's disease

Amyloid-β (Aβ), a neurotoxic peptide, is linked to the onset of Alzheimer's disease (AD). Increased Aβ content within neuronal cell mitochondria is a pathological feature in both human and mouse models with AD. This accumulation of Aβ within the mitochondrial landscape perpetuates increased free radical production and activation of the apoptotic pathway. Human Presequence Protease (hPreP) is responsible for the degradation of mitochondrial amyloid-β peptide in human neuronal cells, and is thus an attractive target to increase the proteolysis of Aβ. Therefore, it offers a potential target for Alzheimer's drug design, by identifying potential activators of hPreP. We applied structure-based drug design, combined with experimental methodologies to investigate the ability of various compounds to enhance hPreP proteolytic activity. Compounds 3c &4c enhanced hPreP-mediated proteolysis of Aβ (1-42), pF₁β (2-54) and fluorogenic-substrate V. These results suggest that activation of hPreP by small benzimidazole derivatives provide a promising avenue for AD treatment.

Latrepirdine: molecular mechanisms underlying potential therapeutic roles in Alzheimer's and other neurodegenerative diseases

Latrepirdine (Dimebon(TM)) was originally marketed as a non-selective antihistamine in Russia. It was repurposed as an effective treatment for patients suffering from Alzheimer's disease (AD) and Huntington's disease (HD) following preliminary reports showing its neuroprotective functions and ability to enhance cognition in AD and HD models. However, latrepirdine failed to show efficacy in phase III trials in AD and HD patients following encouraging phase II trials. The failure of latrepirdine in the clinical trials has highlighted the importance of understanding the precise mechanism underlying its cognitive benefits in neurodegenerative diseases before clinical evaluation. Latrepirdine has shown to affect a number of cellular functions including multireceptor activity, mitochondrial function, calcium influx and intracellular catabolic pathways; however, it is unclear how these properties contribute to its clinical benefits. Here, we review the studies investigating latrepirdine in cellular and animal models to provide a complete evaluation of its mechanisms of action in the central nervous system. In addition, we review recent studies that demonstrate neuroprotective functions for latrepirdine-related class of molecules including the β-carbolines and aminopropyl carbazoles in AD, Parkinson's disease and amyotrophic lateral sclerosis models. Assessment of their neuroprotective effects and underlying biological functions presents obvious value for developing structural analogues of latrepirdine for dementia treatment.

Inhibition of ERK-DLP1 signaling and mitochondrial division alleviates mitochondrial dysfunction in Alzheimer's disease cybrid cell

Mitochondrial dysfunction is an early pathological feature of Alzheimer's disease (AD). The underlying mechanisms and strategies to repair it remain unclear. Here, we demonstrate for the first time the direct consequences and potential mechanisms of mitochondrial functional defects associated with abnormal mitochondrial dynamics in AD. Using cytoplasmic hybrid (cybrid) neurons with incorporated platelet mitochondria from AD and age-matched non-AD human subjects into mitochondrial DNA (mtDNA)-depleted neuronal cells, we observed that AD cybrid cells had significant changes in morphology and function; such changes associate with altered expression and distribution of dynamin-like protein (DLP1) and mitofusin 2 (Mfn2). Treatment with antioxidant protects against AD mitochondria-induced extracellular signal-regulated kinase (ERK) activation and mitochondrial fission-fusion imbalances. Notably, inhibition of ERK activation not only attenuates aberrant mitochondrial morphology and function but also restores the mitochondrial fission and fusion balance. These effects suggest a role of oxidative stress-mediated ERK signal transduction in modulation of mitochondrial fission and fusion events. Further, blockade of the mitochondrial fission protein DLP1 by a genetic manipulation with a dominant negative DLP1 (DLP1(K38A)), its expression with siRNA-DLP1, or inhibition of mitochondrial division with mdivi-1 attenuates mitochondrial functional defects observed in AD cybrid cells. Our results provide new insights into mitochondrial dysfunction resulting from changes in the ERK-fission/fusion (DLP1) machinery and signaling pathway. The protective effect of mdivi-1 and inhibition of ERK signaling on maintenance of normal mitochondrial structure and function holds promise as a potential novel therapeutic strategy for AD.

Mitochondrial diseases of the brain

Neurodegenerative disorders are debilitating diseases of the brain, characterized by behavioral, motor and cognitive impairments. Ample evidence underpins mitochondrial dysfunction as a central causal factor in the pathogenesis of neurodegenerative disorders including Parkinson's disease, Huntington's disease, Alzheimer's disease, Amyotrophic lateral sclerosis, Friedreich's ataxia and Charcot-Marie-Tooth disease. In this review, we discuss the role of mitochondrial dysfunction such as bioenergetics defects, mitochondrial DNA mutations, gene mutations, altered mitochondrial dynamics (mitochondrial fusion/fission, morphology, size, transport/trafficking, and movement), impaired transcription and the association of mutated proteins with mitochondria in these diseases. We highlight the therapeutic role of mitochondrial bioenergetic agents in toxin and in cellular and genetic animal models of neurodegenerative disorders. We also discuss clinical trials of bioenergetics agents in neurodegenerative disorders. Lastly, we shed light on PGC-1α, TORC-1, AMP kinase, Nrf2-ARE, and Sirtuins as novel therapeutic targets for neurodegenerative disorders.

Mitochondrial haplotypes associated with biomarkers for Alzheimer's disease

Various studies have suggested that the mitochondrial genome plays a role in late-onset Alzheimer's disease, although results are mixed. We used an endophenotype-based approach to further characterize mitochondrial genetic variation and its relationship to risk markers for Alzheimer's disease. We analyzed longitudinal data from non-demented, mild cognitive impairment, and late-onset Alzheimer's disease participants in the Alzheimer's Disease Neuroimaging Initiative with genetic, brain imaging, and behavioral data. We assessed the relationship of structural MRI and cognitive biomarkers with mitochondrial genome variation using TreeScanning, a haplotype-based approach that concentrates statistical power by analyzing evolutionarily meaningful groups (or clades) of haplotypes together for association with a phenotype. Four clades were associated with three different endophenotypes: whole brain volume, percent change in temporal pole thickness, and left hippocampal atrophy over two years. This is the first study of its kind to identify mitochondrial variation associated with brain imaging endophenotypes of Alzheimer's disease. Our results provide additional evidence that the mitochondrial genome plays a role in risk for Alzheimer's disease.

Bioenergetic flux, mitochondrial mass and mitochondrial morphology dynamics in AD and MCI cybrid cell lines

Bioenergetic dysfunction occurs in Alzheimer's disease (AD) and mild cognitive impairment (MCI), a clinical syndrome that frequently precedes symptomatic AD. In this study, we modeled AD and MCI bioenergetic dysfunction by transferring mitochondria from MCI, AD and control subject platelets to mtDNA-depleted SH-SY5Y cells. Bioenergetic fluxes and bioenergetics-related infrastructures were characterized in the resulting cytoplasmic hybrid (cybrid) cell lines. Relative to control cybrids, AD and MCI cybrids showed changes in oxygen consumption, respiratory coupling and glucose utilization. AD and MCI cybrids had higher ADP/ATP and lower NAD+/NADH ratios. AD and MCI cybrids exhibited differences in proteins that monitor, respond to or regulate cell bioenergetic fluxes including HIF1α, PGC1α, SIRT1, AMPK, p38 MAPK and mTOR. Several endpoints suggested mitochondrial mass increased in the AD cybrid group and probably to a lesser extent in the MCI cybrid group, and that the mitochondrial fission-fusion balance shifted towards increased fission in the AD and MCI cybrids. As many of the changes we observed in AD and MCI cybrid models are also seen in AD subject brains, we conclude reduced bioenergetic function is present during very early AD, is not brain-limited and induces protean retrograde responses that likely have both adaptive and mal-adaptive consequences.

Maternal family history is associated with Alzheimer's disease biomarkers

A family history of Alzheimer's disease (AD) increases one's risk of developing late-onset AD (LOAD), and a maternal family history of LOAD influences risk more than a paternal family history. Accumulating evidence suggests that a family history of dementia associates with AD-typical biomarker changes. We analyzed cross-sectional data from non-demented, mild cognitive impairment (MCI), and LOAD participants in the Alzheimer's Disease Neuroimaging Initiative (ADNI) with PET imaging using Pittsburgh Compound B (PiB, n = 99) and cerebrospinal fluid (CSF) analysis (n = 403) for amyloid-β peptide (Aβ) and total tau. We assessed the relationship of CSF and PiB biomarkers and family history of dementia, as well as parent gender effects. In the larger analysis of CSF biomarkers, we assessed diagnosis groups individually. In the overall sample, CSF Aβ, tau/Aβ ratio, and global PiB uptake were significantly different between family history positive and negative groups, with markers of increased AD burden associated with a positive maternal family history of dementia. Moreover, a maternal family history of dementia was associated with significantly greater PiB Aβ load in the brain in the parietal cortex, precuneus, and sensorimotor cortex. Individuals with MCI positive for a maternal family history of dementia had significantly more markers of AD pathophysiology than individuals with no family history of dementia. A family history of dementia is associated with AD-typical biomarker changes. These biomarker associations are most robust in individuals with a maternal family history, suggesting that a maternally inherited factor influences AD risk.

Long-term Aβ exposure augments mCa2+-independent mROS-mediated depletion of cardiolipin for the shift of a lethal transient mitochondrial permeability transition to its permanent mode in NARP cybrids: a protective targeting of melatonin

Mitochondrial dysfunction is a hallmark of amyloid β-peptide (Aβ)-induced neurodegeneration of Alzheimer's disease (AD). This study investigated whether mtDNA T8993G mutation-induced complex V inhibition, clinically associated with neurological muscle weakness, ataxia, and retinitis pigmentosa (NARP), is a potential risk factor for AD and the pathological link for long-term exposure of Aβ-induced mitochondrial toxicity and apoptosis in NARP cybrids. Using noninvasive fluorescence probe-coupled laser scanning imaging microscopy and NARP cybrids harboring 98% mutant genes along with its parental 143B osteosarcoma cells, we demonstrated that Aβ-augmented mitochondrial Ca(2+) (mCa(2+))-independent mitochondrial reactive oxygen species (mROS) formation for a cardiolipin (CL, a major mitochondrial protective phospholipid)-dependent lethal modulation of the mitochondrial permeability transition (MPT). Aβ augmented not only the amount but also the propagation rate of mROS-induced mROS formation to significantly depolarize mitochondrial membrane potential (∆Ψ(m)) and reduce mCa(2+) stress. Aβ-augmented mROS oxidized and depleted CL, thereby enhances mitochondrial fission and movement retardation, which promoted the NARP-augmented lethal transient-MPT (t-MPT) to switch to its irreversible mode of permanent-MPT (p-MPT). Interestingly, melatonin, a multiple mitochondrial protector, markedly reduced Aβ-augmented mROS formation and therefore significantly reduced mROS-mediated depolarization of ∆Ψ(m), fission of mitochondria and retardation of mitochondrial movement to stabilize CL and hence the MPT. In the presence of melatonin, Aβ-promoted p-MPT was reversed to a protective t-MPT, which preserved ∆Ψ(m) and lowered elevated mCa(2+) to sublethal levels for an enhanced mCa(2+)-dependent O(2) consumption. Thus, melatonin may potentially rescue AD patients associated with NARP symptoms.

Reduced mitochondria cytochrome oxidase activity in adult children of mothers with Alzheimer's disease

Biomarker studies demonstrate inheritance of glucose hypometabolism and increased amyloid-β deposition in adult offspring of mothers, but not fathers, affected by late-onset Alzheimer's disease (LOAD). The underlying genetic mechanisms are unknown. We investigated whether cognitively normal (NL) individuals with a maternal history of LOAD (MH) have reduced platelet mitochondrial cytochrome oxidase activity (COX, electron transport chain complex IV) compared to those with paternal (PH) or negative family history (NH). Thirty-six consecutive NL individuals (age 55 ± 15 y, range 27-71 y, 56% female, CDR = 0, MMSE ≥28, 28% APOE-4 carriers), including 12 NH, 12 PH, and 12 MH, received a blood draw to measure platelet mitochondrial COX activity. Citrate synthase activity (CS) was measured as a reference. Groups were comparable for clinical and neuropsychological measures. We found that after correcting for CS, COX activity was reduced by 29% in MH compared to NH, and by 30% in MH compared to PH (p ≤ 0.006). Results remained significant controlling for age, gender, education, and APOE. No differences were found between PH and NH. COX measures discriminated MH from the other groups with accuracy ≥75%, and relative risk ≥3 (p ≤ 0.005). Among NL with LOAD-parents, only those with MH showed reduced COX activity in platelet mitochondria compared to PH and NH. The association between maternal history of LOAD and systemic COX reductions suggests transmission via mitochondrial DNA, which is exclusively maternally inherited in humans.

Swedish Alzheimer mutation induces mitochondrial dysfunction mediated by HSP60 mislocalization of amyloid precursor protein (APP) and beta-amyloid

Alzheimer disease (AD) is a complex disorder that involves numerous cellular and subcellular alterations including impairments in mitochondrial homeostasis. To better understand the role of mitochondrial dysfunction in the pathogenesis of AD, we analyzed brains from clinically well-characterized human subjects and from the 3xTg-AD mouse model of AD. We find Aβ and critical components of the γ-secretase complex, presenilin-1, -2, and nicastrin, accumulate in the mitochondria. We used a proteomics approach to identify binding partners and show that heat shock protein 60 (HSP60), a molecular chaperone localized to mitochondria and the plasma membrane, specifically associates with APP. We next generated stable neural cell lines expressing human wild-type or Swedish APP, and provide corroborating in vitro evidence that HSP60 mediates translocation of APP to the mitochondria. Viral-mediated shRNA knockdown of HSP60 attenuates APP and Aβ mislocalization to the mitochondria. Our findings identify a novel interaction between APP and HSP60, which accounts for its translocation to the mitochondria.

S-52, a novel nootropic compound, protects against β-amyloid induced neuronal injury by attenuating mitochondrial dysfunction

Accumulating evidence suggests that β-amyloid (Aβ)-induced oxidative DNA damage and mitochondrial dysfunction may initiate and contribute to the progression of Alzheimer's disease (AD). This study evaluated the neuroprotective effects of S-52, a novel nootropic compound, on Aβ-induced mitochondrial failure. In an established paradigm of moderate cellular injury induced by Aβ, S-52 was observed to attenuate the toxicity of Aβ to energy metabolism, mitochondrial membrane structure, and key enzymes in the electron transport chain and tricarboxylic acid cycle. In addition, S-52 also effectively inhibited reactive oxygen species accumulation dose dependently not only in Aβ-harmed cells but also in unharmed, normal cells. The role of S-52 as a scavenger of free radicals is involved in the antioxidative effect of this compound. The beneficial effects on mitochondria and oxidative stress extend the neuroprotective effects of S-52. The present study provides crucial information for better understanding the beneficial profiles of this compound and discovering novel potential drug candidates for AD therapy.

Mitochondria and cell bioenergetics: increasingly recognized components and a possible etiologic cause of Alzheimer's disease

SIGNIFICANCE

Mitochondria and brain bioenergetics are increasingly thought to play an important role in Alzheimer's disease (AD).

RECENT ADVANCES

Data that support this view are discussed from the perspective of the amyloid cascade hypothesis, which assumes beta-amyloid perturbs mitochondrial function, and from an opposite perspective that assumes mitochondrial dysfunction promotes brain amyloidosis. A detailed review of cytoplasmic hybrid (cybrid) studies, which argue mitochondrial DNA (mtDNA) contributes to sporadic AD, is provided. Recent AD endophenotype data that further suggest an mtDNA contribution are also summarized.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Biochemical, molecular, cybrid, biomarker, and clinical data pertinent to the mitochondria-bioenergetics-AD nexus are synthesized and the mitochondrial cascade hypothesis, which represents a mitochondria-centric attempt to conceptualize sporadic AD, is discussed.

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.

New insights in the amyloid-Beta interaction with mitochondria

Biochemical and morphological alterations of mitochondria may play an important role in the pathogenesis of Alzheimer's disease (AD). Particularly, mitochondrial dysfunction is a hallmark of amyloid-beta-induced neuronal toxicity in Alzheimer's disease. The recent emphasis on the intracellular biology of amyloid-beta and its precursor protein (APP) has led researchers to consider the possibility that mitochondria-associated and mitochondrial amyloid-beta may directly cause neurotoxicity. Both proteins are known to localize to mitochondrial membranes, block the transport of nuclear-encoded mitochondrial proteins to mitochondria, interact with mitochondrial proteins, disrupt the electron transport chain, increase reactive oxygen species production, cause mitochondrial damage, and prevent neurons from functioning normally. In this paper, we will outline current knowledge of the intracellular localization of amyloid-beta. Moreover, we summarize evidence from AD postmortem brain as well as animal AD models showing that amyloid-beta triggers mitochondrial dysfunction through a number of pathways such as impairment of oxidative phosphorylation, elevation of reactive oxygen species production, alteration of mitochondrial dynamics, and interaction with mitochondrial proteins. Thus, this paper supports the Alzheimer cascade mitochondrial hypothesis such as the most important early events in this disease, and probably one of the future strategies on the therapy of this neurodegenerative disease.

Targeting mitochondrial bioenergetics for Alzheimer's prevention and treatment

Alzheimer's is a neurodegenerative disease with a complex and progressive pathological phenotype characterized first by hypometabolism and impaired mitochondrial bioenergetics followed by pathological burden. The progressive and multifaceted degenerative phenotype of Alzheimer's suggests that successful treatment strategies necessarily will be equally multi-faceted and disease stage specific. Traditional therapeutic strategies based on the pathological aspect of the disease have achieved success in preclinical models which has not translated into clinical therapeutic efficacy. Meanwhile, increasing evidence indicates an antecedent and potentially causal role of mitochondrial bioenergetic deficits and brain hypometabolism coupled with increased mitochondrial oxidative stress in AD pathogenesis. The essential role of mitochondrial bioenergetics and the unique trajectory of alterations in brain metabolic capacity enable a bioenergetic- centric strategy that targets disease-stage specific pattern of brain metabolism for disease prevention and treatment. A combination of nutraceutical and pharmaceutical intervention that enhances glucose-driven metabolic activity and potentiates mitochondrial bioenergetic function could prevent the antecedent decline in brain glucose metabolism, promote healthy aging and prevent AD. Alternatively, during the prodromal incipient phase of AD, sustained activation of ketogenic metabolic pathways coupled with supplement of the alternative fuel source, ketone bodies, could sustain mitochondrial bioenergetic function to prevent or delay further progression of the disease.

Insulin in central nervous system: more than just a peripheral hormone

Insulin signaling in central nervous system (CNS) has emerged as a novel field of research since decreased brain insulin levels and/or signaling were associated to impaired learning, memory, and age-related neurodegenerative diseases. Thus, besides its well-known role in longevity, insulin may constitute a promising therapy against diabetes- and age-related neurodegenerative disorders. More interestingly, insulin has been also faced as the potential missing link between diabetes and aging in CNS, with Alzheimer's disease (AD) considered as the "brain-type diabetes." In fact, brain insulin has been shown to regulate both peripheral and central glucose metabolism, neurotransmission, learning, and memory and to be neuroprotective. And a future challenge will be to unravel the complex interactions between aging and diabetes, which, we believe, will allow the development of efficient preventive and therapeutic strategies to overcome age-related diseases and to prolong human "healthy" longevity. Herewith, we aim to integrate the metabolic, neuromodulatory, and neuroprotective roles of insulin in two age-related pathologies: diabetes and AD, both in terms of intracellular signaling and potential therapeutic approach.

Houttuyniae Herba protects rat primary cortical cells from Aβ(25-35)-induced neurotoxicity via regulation of calcium influx and mitochondria-mediated apoptosis

Amyloid beta (Aβ) fibrils are believed to play a major role in the pathogenesis of Alzheimer's disease. Although the mechanisms underlying Aβ toxicity remain largely unknown, Aβ fibrils disrupt calcium homeostasis and generate free radicals, resulting in oxidative stress, mitochondrial dysfunction, and apoptotic cell death. Houttuyniae Herba, the aerial part of Houttuynia cordata Thunb. (Saururaceae), is a commonly used herb in traditional Asian medicine. It has been reported to have various bioactivities, including antioxidant effects. In the present study, we investigated the protective effect of standardised Houttuyniae Herba water extract (HCW) against Aβ(25-35)-induced neurotoxicity and its possible mechanisms in rat primary cortical cells. Pretreatment with HCW attenuated the cell damage caused by 8 μM Aβ(25-35) exposure, as evidenced by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, a lactate dehydrogenase assay, and microtubule-associated protein 2 immunostaining. Moreover, HCW inhibited the Aβ(25-35)-induced elevation of the intracellular calcium level, reactive oxygen species overproduction, mitochondrial membrane potential disruption, and caspase 3 activation. These results indicate that HCW protects rat primary cortical neurons against Aβ(25-35)-induced toxicity via the regulation of calcium and the inhibition of mitochondria-mediated apoptosis.

Role of mitochondrial homeostasis and dynamics in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that affects a staggering percentage of the aging population and causes memory loss and cognitive decline. Mitochondrial abnormalities can be observed systemically and in brains of patients suffering from AD, and may account for part of the disease phenotype. In this review, we summarize some of the key findings that indicate mitochondrial dysfunction is present in AD-affected subjects, including cytochrome oxidase deficiency, endophenotype data, and altered mitochondrial morphology. Special attention is given to recently described perturbations in mitochondrial autophagy, fission-fusion dynamics, and biogenesis. We also briefly discuss how mitochondrial dysfunction may influence amyloidosis in Alzheimer's disease, why mitochondria are a valid therapeutic target, and strategies for addressing AD-specific mitochondrial dysfunction.

Estrogen regulation of mitochondrial bioenergetics: implications for prevention of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease with a complex and progressive pathological phenotype characterized first by hypometabolism and impaired mitochondrial bioenergetics followed by pathological burden. Increasing evidence indicates an antecedent and potentially causal role of mitochondrial bioenergetic deficits and brain hypometabolism coupled with increased mitochondrial oxidative stress in AD pathogenesis. Compromised aerobic glycolysis pathway coupled with oxidative stress is first accompanied by a shift toward a ketogenic pathway that eventually progresses into fatty acid oxidation (FAO) pathways and leads to white matter degeneration and overproduction and mitochondrial accumulation of β-amyloid. Estrogen-induced signaling pathways converge upon the mitochondria to enhance mitochondrial function and to sustain aerobic glycolysis coupled with citric acid cycle-driven oxidative phosphorylation to potentiate ATP (Adenosine triphosphate) generation. In addition to potentiated mitochondrial bioenergetics, estrogen also enhances neural survival and health through maintenance of calcium homeostasis, promotion of antioxidant defense against free radicals, efficient cholesterol trafficking, and beta amyloid clearance. Significantly, the convergence of E2 mechanisms of action onto mitochondria is also a potential point of vulnerability when activated in diseased neurons that exacerbates degeneration through increased load on dysregulated calcium homeostasis. The "healthy cell bias of estrogen action" hypothesis examines the role that regulating mitochondrial function and bioenergetics play in promoting neural health and the mechanistic crossroads that lead to divergent outcomes following estrogen exposure. As the continuum of neurological health progresses from healthy to unhealthy, so too do the benefits of estrogen or hormone therapy.

Mitochondria in neurodegeneration

Many neurodegenerative diseases demonstrate abnormal mitochondrial morphology and biochemical dysfunction. Alterations are often systemic rather than brain-limited. Mitochondrial dysfunction may arise as a consequence of abnormal mitochondrial DNA, mutated nuclear proteins that interact directly or indirectly with mitochondria, or through unknown causes. In most cases it is unclear where mitochondria sit in relation to the overall disease cascades that ultimately causes neuronal dysfunction and death, and there is still controversy regarding the question of whether mitochondrial dysfunction is a necessary step in neurodegeneration. In this chapter we highlight and catalogue mitochondrial perturbations in some of the major neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD). We consider data that suggest mitochondria may be critically involved in neurodegenerative disease neurodegeneration cascades.

Mitochondrial and metabolic-based protective strategies in Huntington's disease: the case of creatine and coenzyme Q

Huntington's disease (HD) is a neurodegenerative genetic disorder caused by an expansion of CAG repeats in the HD gene encoding for huntingtin (Htt), resulting in progressive death of striatal neurons, with clinical symptoms of chorea, dementia and dramatic weight loss. Metabolic and mitochondrial dysfunction caused by the expanded polyglutamine sequence have been described along with other mechanisms of neurodegeneration previously described in human tissues and animal models of HD. In this review, we focus on mitochondrial and metabolic disturbances affecting both the central nervous system and peripheral cells, including mitochondrial DNA damage, mitochondrial complexes defects, loss of calcium homeostasis and transcriptional deregulation. Glucose abnormalities have also been described in peripheral tissues of HD patients and in HD animal and cellular models. Moreover, there are no effective neuroprotective treatments available in HD. Thus, we briefly discuss the role of creatine and coenzyme Q10 that target mitochondrial dysfunction and impaired bioenergetics and have been previously used in HD clinical trials.

Mitochondrial dysfunction and accumulation of the β-secretase-cleaved C-terminal fragment of APP in Alzheimer's disease transgenic mice

Mitochondrial dysfunction is an early feature of Alzheimer's disease (AD) and may play an important role in the pathogenesis of disease. Emerging evidence indicates that amyloid-β (Aβ) peptides enter mitochondria and may thereby disrupt mitochondrial function in brains of AD patients and transgenic model mice. However, it remains to be determined whether the β-cleaved C-terminal fragment (C99), another neurotoxic fragment of amyloid precursor protein (APP), may accumulate in mitochondria of neurons affected by AD. Using immunoblotting, digitonin fractionation and immunofluorescence labeling techniques, we found that C99 is targeted to mitochondria, in particular, to the mitoplast (i.e., inner membrane and matrix compartments) in brains of AD transgenic mice (5XFAD model). Furthermore, full-length APP (fl-APP) was also identified in mitochondrial fractions of 5XFAD mice. Remarkably, partial deletion of the β-site APP-cleaving enzyme 1 (BACE1(+/-)) almost completely abolished mitochondrial targeting of C99 and fl-APP in 5XFAD mice at 6 months of age. However, substantial amounts of C99 and fl-APP accumulation remained in mitochondria of 12-month-old BACE1(+/-)·5XFAD mouse brains. Consistent with these changes in mitochondrial C99/fl-APP levels, BACE1(+/-) deletion age-dependently rescued mitochondrial dysfunction in 5XFAD mice, as assessed by cytochrome c release from mitochondria, reduced redox or complex activities and oxidative DNA damage. Moreover, BACE1(+/-) deletion also improved memory deficits as tested by the spontaneous alternation Y-maze task in 5XFAD mice at 6 months but not at 12 months of age. Taken together, our findings suggest that mitochondrial accumulation of C99 and fl-APP may occur through BACE1-dependent mechanisms and contribute to inducing mitochondrial dysfunction and cognitive impairments associated with AD.

Mitochondrial therapeutics in Alzheimer's disease and Parkinson's disease

In neurons, mitochondria serve a wide variety of processes that are integral to their function and survival. It is, therefore, not surprising that evidence of mitochondrial dysfunction is observed across numerous neurodegenerative diseases. Alzheimer's disease and Parkinson's disease are two such diseases in which aberrant mitochondrial activity is proposed to contribute to pathogenesis. Current therapies for each disease target various mechanisms, but few, if any, directly target improved mitochondrial function. Recent discoveries pertaining to mitochondrial dynamics reveal that regulation of mitochondrial fission and fusion may play a key role in the pathogenesis of these diseases and consequently could be novel future therapeutic targets.

Amyloid β-induced ER stress is enhanced under mitochondrial dysfunction conditions

Previously we reported that endoplasmic reticulum (ER)-mitochondria crosstalk is involved in amyloid-β (Aβ)-induced apoptosis. Now we show that mitochondrial dysfunction affects the ER stress response triggered by Aβ using cybrids that recreate the defect in mitochondrial cytochrome c oxidase (COX) activity detected in platelets from Alzheimer's disease (AD) patients. AD and control cybrids were treated with Aβ or classical ER stressors and the ER stress-mediated apoptotic cell death pathway was accessed. Upon treatment, we found increased glucose-regulated protein 78 (GRP78) levels and caspase-4 activation (ER stress markers) which were more pronounced in AD cybrids. Treated AD cybrids also exhibited decreased cell survival as well as increased caspase-3-like activity, poli-ADP-ribose-polymerase (PARP) levels and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive apoptotic cells. Finally, we showed that Aβ-induced caspase-3 activation in both cybrid cell lines was prevented by dantrolene, thus implicating ER Ca(2+) release in ER stress-mediated apoptosis. Our results demonstrate that mitochondrial dysfunction occurring in AD patients due to COX inhibition potentiates cell susceptibility to Aβ-induced ER stress. This study further supports the close communication between ER and mitochondria during apoptosis in AD.

The concept of FDG-PET endophenotype in Alzheimer's disease

Often viewed as a potential tool for preclinical diagnosis in early asymptomatic stages of Alzheimer's disease (AD), the term "endophenotype" has acquired a recent popularity in the field. In this review, we analyze the construct of endophenotype-originally designed to discover genes, and examine the literature on potential endophenotypes for the late-onset form of AD (LOAD). We focus on the [18F]-fluoro-2-deoxyglucose (FDG) PET technique, which shows a characteristic pattern of hypometabolism in AD-related regions in asymptomatic carriers of the ApoE E4 allele and in children of AD mothers. We discuss the pathophysiological significance and the positive predictive accuracy of an FDG-endophenotype for LOAD in asymptomatic subjects, and discuss several applications of this endophenotype in the identification of both promoting and protective factors. Finally, we suggest that the term "endophenotype" should be reserved to the study of risk factors, and not to the preclinical diagnosis of LOAD.

Mitochondrial dysfunction and Alzheimer's disease

To date, one of the most discussed hypotheses for Alzheimer's disease (AD) etiology implicates mitochondrial dysfunction and oxidative stress as one of the primary events in the course of AD. In this review we focus on the role of mitochondria and mitochondrial DNA (mtDNA) variation in AD and discuss the rationale for the involvement of mitochondrial abnormalities in AD pathology. We summarize the current data regarding the proteins involved in mitochondrial function and pathology observed in AD, and discuss the role of somatic mutations and mitochondrial haplogroups in AD development.

Amyloid-Beta interaction with mitochondria

Mitochondrial dysfunction is a hallmark of amyloid-beta(Aβ)-induced neuronal toxicity in Alzheimer's disease (AD). The recent emphasis on the intracellular biology of Aβ and its precursor protein (AβPP) has led researchers to consider the possibility that mitochondria-associated and/or intramitochondrial Aβ may directly cause neurotoxicity. In this paper, we will outline current knowledge of the intracellular localization of both Aβ and AβPP addressing the question of how Aβ can access mitochondria. Moreover, we summarize evidence from AD postmortem brain as well as cellular and animal AD models showing that Aβ triggers mitochondrial dysfunction through a number of pathways such as impairment of oxidative phosphorylation, elevation of reactive oxygen species (ROS) production, alteration of mitochondrial dynamics, and interaction with mitochondrial proteins. In particular, we focus on Aβ interaction with different mitochondrial targets including the outer mitochondrial membrane, intermembrane space, inner mitochondrial membrane, and the matrix. Thus, this paper establishes a modified model of the Alzheimer cascade mitochondrial hypothesis.

Cyclophilin D deficiency improves mitochondrial function and learning/memory in aging Alzheimer disease mouse model

Mitochondrial stress is one of the early features of Alzheimer disease (AD). Mitochondrial Aβ has been linked to mitochondrial toxicity. Our recent study demonstrated that cyclophilin D (CypD) mediated mitochondrial permeability transition pore (mPTP) is an important mechanism for neuronal and synaptic stress induced by both Aβ and oxidative stress. In transgenic AD-type mice overexpressing mutant amyloid precursor protein (APP) and Aβ (mAPP), CypD deficiency improves mitochondrial and synaptic function and learning/memory up to 12 months old. Here we provide evidence of the protective effects of CypD deficiency in aged AD mice (22-24 months). Cyp D deficient mAPP mice demonstrate less calcium-induced mitochondrial swelling, increased mitochondrial calcium uptake capacity, preserved mitochondrial respiratory function and improved spatial learning/memory even in old age (known to be the age for late stage AD pathology and synaptic dysfunction). These data demonstrate that abrogation of CypD results in persistent life-long protection against Aβ toxicity in an Alzheimer's disease mouse model, thereby suggesting that blockade of CypD may be of benefit for Alzheimer disease treatment.

Role and treatment of mitochondrial DNA-related mitochondrial dysfunction in sporadic neurodegenerative diseases

Several sporadic neurodegenerative diseases display phenomena that directly or indirectly relate to mitochondrial function. Data suggesting altered mitochondrial function in these diseases could arise from mitochondrial DNA (mtDNA) are reviewed. Approaches for manipulating mitochondrial function and minimizing the downstream consequences of mitochondrial dysfunction are discussed.

Oxidative stress and amyloid-beta pathology in normal individuals with a maternal history of Alzheimer's

BACKGROUND

Epidemiology and imaging studies showed that cognitively normal (NL) individuals with a maternal history (MH) of late-onset Alzheimer's disease (LOAD) might be at increased risk for Alzheimer's disease (AD) compared with NL with a paternal history (PH) and NL with a negative family history of LOAD (NH). With a panel of cerebrospinal fluid (CSF) markers, this study examined whether NL MH showed evidence for AD pathology compared with PH and NH.

METHODS

Fifty-nine 40-80-year-old NL subjects were examined, including 23 MH and 14 PH whose parents had a clinician-certified diagnosis of LOAD and 22 NH. All subjects completed clinical neuropsychological examinations and a lumbar puncture to measure CSF levels of amyloid-beta (Aβ(40), Aβ(42), Aβ(42/40)), total and hyperphosphorylated tau (T-Tau and P-Tau(231); markers of axonal degeneration and neurofibrillary tangles, respectively), and F₂-isoprostanes (IsoP) (a marker of oxidative stress).

RESULTS

Groups were comparable for demographic and neuropsychological measures. The MH subjects showed higher IsoP and reduced Aβ(42/40) CSF levels compared with NH and with PH (p values ≤ .05), whereas no differences were found between NH and PH. No group differences were found for P-Tau(231) and T-Tau. The IsoP and Aβ(42/40) levels were correlated only within the MH group (R² = .32, p = .005) and discriminated MH from the other subjects with 70% accuracy (relative risk = 3.7%, 95% confidence interval = 1.6-9.7, p < .001). Results remained significant controlling for age, gender, education, and apolipoprotein E genotype.

CONCLUSIONS

Adult children of LOAD-affected mothers express a pathobiological phenotype characterized by Aβ-associated oxidative stress consistent with AD, which might reflect increased risk for developing the disease.

Early deficits in synaptic mitochondria in an Alzheimer's disease mouse model

Synaptic dysfunction and the loss of synapses are early pathological features of Alzheimer's disease (AD). Synapses are sites of high energy demand and extensive calcium fluctuations; accordingly, synaptic transmission requires high levels of ATP and constant calcium fluctuation. Thus, synaptic mitochondria are vital for maintenance of synaptic function and transmission through normal mitochondrial energy metabolism, distribution and trafficking, and through synaptic calcium modulation. To date, there has been no extensive analysis of alterations in synaptic mitochondria associated with amyloid pathology in an amyloid β (Aβ)-rich milieu. Here, we identified differences in mitochondrial properties and function of synaptic vs. nonsynaptic mitochondrial populations in the transgenic mouse brain, which overexpresses the human mutant form of amyloid precursor protein and Aβ. Compared with nonsynaptic mitochondria, synaptic mitochondria showed a greater degree of age-dependent accumulation of Aβ and mitochondrial alterations. The synaptic mitochondrial pool of Aβ was detected at an age as young as 4 mo, well before the onset of nonsynaptic mitochondrial and extensive extracellular Aβ accumulation. Aβ-insulted synaptic mitochondria revealed early deficits in mitochondrial function, as shown by increased mitochondrial permeability transition, decline in both respiratory function and activity of cytochrome c oxidase, and increased mitochondrial oxidative stress. Furthermore, a low concentration of Aβ (200 nM) significantly interfered with mitochondrial distribution and trafficking in axons. These results demonstrate that synaptic mitochondria, especially Aβ-rich synaptic mitochondria, are more susceptible to Aβ-induced damage, highlighting the central importance of synaptic mitochondrial dysfunction relevant to the development of synaptic degeneration in AD.