Mitochondria-targeted antioxidants protect against amyloid-beta toxicity in Alzheimer's disease neurons

Mitochondrial division ensures the survival of postmitotic neurons by suppressing oxidative damage

Mitochondria divide and fuse continuously, and the balance between these two processes regulates mitochondrial shape. Alterations in mitochondrial dynamics are associated with neurodegenerative diseases. Here we investigate the physiological and cellular functions of mitochondrial division in postmitotic neurons using in vivo and in vitro gene knockout for the mitochondrial division protein Drp1. When mouse Drp1 was deleted in postmitotic Purkinje cells in the cerebellum, mitochondrial tubules elongated due to excess fusion, became large spheres due to oxidative damage, accumulated ubiquitin and mitophagy markers, and lost respiratory function, leading to neurodegeneration. Ubiquitination of mitochondria was independent of the E3 ubiquitin ligase parkin in Purkinje cells lacking Drp1. Treatment with antioxidants rescued mitochondrial swelling and cell death in Drp1KO Purkinje cells. Moreover, hydrogen peroxide converted elongated tubules into large spheres in Drp1KO fibroblasts. Our findings suggest that mitochondrial division serves as a quality control mechanism to suppress oxidative damage and thus promote neuronal survival.

Where the endoplasmic reticulum and the mitochondrion tie the knot: the mitochondria-associated membrane (MAM)

More than a billion years ago, bacterial precursors of mitochondria became endosymbionts in what we call eukaryotic cells today. The true significance of the word "endosymbiont" has only become clear to cell biologists with the discovery that the endoplasmic reticulum (ER) superorganelle dedicates a special domain for the metabolic interaction with mitochondria. This domain, identified in all eukaryotic cell systems from yeast to man and called the mitochondria-associated membrane (MAM), has a distinct proteome, specific tethers on the cytosolic face and regulatory proteins in the ER lumen of the ER. The MAM has distinct biochemical properties and appears as ER tubules closely apposed to mitochondria on electron micrographs. The functions of the MAM range from lipid metabolism and calcium signaling to inflammasome formation. Consistent with these functions, the MAM is enriched in lipid metabolism enzymes and calcium handling proteins. During cellular stress situations, like an altered cellular redox state, the MAM alters its set of regulatory proteins and thus alters MAM functions. Notably, this set prominently comprises ER chaperones and oxidoreductases that connect protein synthesis and folding inside the ER to mitochondrial metabolism. Moreover, ER membranes associated with mitochondria also accommodate parts of the machinery that determines mitochondrial membrane dynamics and connect mitochondria to the cytoskeleton. Together, these exciting findings demonstrate that the physiological interactions between the ER and mitochondria are so bilateral that we are tempted to compare their relationship to the one of a married couple: distinct, but inseparable and certainly dependent on each other. In this paradigm, the MAM stands for the intracellular location where the two organelles tie the knot. Resembling "real life", the happy marriage between the two organelles prevents the onset of diseases that are characterized by disrupted metabolism and decreased lifespan, including neurodegeneration and cancer. This article is part of a Special Issue entitled: Mitochondrial dynamics and physiology.

The bad, the good, and the ugly about oxidative stress

Alzheimer's disease (AD), Parkinson's disease (PD), and cancer (e.g., leukemia) are the most devastating disorders affecting millions of people worldwide. Except for some kind of cancers, no effective and/or definitive therapeutic treatment aimed to reduce or to retard the clinic and pathologic symptoms induced by AD and PD is presently available. Therefore, it is urgently needed to understand the molecular basis of these disorders. Since oxidative stress (OS) is an important etiologic factor of the pathologic process of AD, PD, and cancer, understanding how intracellular signaling pathways respond to OS will have a significant implication in the therapy of these diseases. Here, we propose a model of minimal completeness of cell death signaling induced by OS as a mechanistic explanation of neuronal and cancer cell demise. This mechanism might provide the basis for therapeutic design strategies. Finally, we will attempt to associate PD, cancer, and OS. This paper critically analyzes the evidence that support the “oxidative stress model” in neurodegeneration and cancer.

Mitochondria-specific accumulation of amyloid β induces mitochondrial dysfunction leading to apoptotic cell death

Mitochondria are best known as the essential intracellular organelles that host the homeostasis required for cellular survival, but they also have relevance in diverse disease-related conditions, including Alzheimer's disease (AD). Amyloid β (Aβ) peptide is the key molecule in AD pathogenesis, and has been highlighted in the implication of mitochondrial abnormality during the disease progress. Neuronal exposure to Aβ impairs mitochondrial dynamics and function. Furthermore, mitochondrial Aβ accumulation has been detected in the AD brain. However, the underlying mechanism of how Aβ affects mitochondrial function remains uncertain, and it is questionable whether mitochondrial Aβ accumulation followed by mitochondrial dysfunction leads directly to neuronal toxicity. This study demonstrated that an exogenous Aβ_1–42 treatment, when applied to the hippocampal cell line of mice (specifically HT22 cells), caused a deleterious alteration in mitochondria in both morphology and function. A clathrin-mediated endocytosis blocker rescued the exogenous Aβ_1–42-mediated mitochondrial dysfunction. Furthermore, the mitochondria-targeted accumulation of Aβ_1–42 in HT22 cells using Aβ_1–42 with a mitochondria-targeting sequence induced the identical morphological alteration of mitochondria as that observed in the APP/PS AD mouse model and exogenous Aβ_1–42-treated HT22 cells. In addition, subsequent mitochondrial dysfunctions were demonstrated in the mitochondria-specific Aβ_1–42 accumulation model, which proved indistinguishable from the mitochondrial impairment induced by exogenous Aβ_1–42-treated HT22 cells. Finally, cellular toxicity was directly induced by mitochondria-targeted Aβ_1–42 accumulation, which mimics the apoptosis process in exogenous Aβ_1–42-treated HT22 cells. Taken together, these results indicate that mitochondria-targeted Aβ_1–42 accumulation is the necessary and sufficient condition for Aβ-mediated mitochondria impairments, and leads directly to cellular death rather than along with other Aβ-mediated signaling alterations.

Mitochondria-targeted catalase reduces abnormal APP processing, amyloid β production and BACE1 in a mouse model of Alzheimer's disease: implications for neuroprotection and lifespan extension

The purpose of this study was to investigate the protective effects of the mitochondria-targeted antioxidant catalase (MCAT) and lifespan extension in mice that express amyloid beta (Aβ). Using immunoblotting and immunostaining analyses, we measured the production of full-length amyloid precursor protein (APP), soluble APPα, C-terminal fragments CTF99 and CTF83, monomeric and oligomeric Aβ, Aβ deposits and beta site amyloid precursor protein cleaving enzyme 1 (BACE1), in different stages of disease progression in MCAT/AβPP and AβPP mice. Using quantitative reverse transcriptase polymerase chain reaction and immunostaining analyses, we studied the expression of catalase, BACE1, the Alzheimer's disease (AD) markers, synaptophysin, APP, neprilysin, insulin-degrading enzyme and transthyretin in MCAT, AβPP, MCAT/AβPP and wild-type (WT) mice. Using the high pressure liquid chromatography analysis of 8-hydroxy-2-deoxyguanosine, we measured oxidative DNA damage in the cerebral cortical tissues from MCAT, AβPP, MCAT/AβPP and WT mice. We found that the AβPP transgenic mice that carried the human MCAT gene lived 5 months longer than did the AβPP mice. We also found that the overexpression of MCAT in the brain sections from the MCAT/AβPP transgenic mice significantly correlated with a reduction in the levels of full-length APP, CTF99, BACE1, Aβ levels (40 and 42), Aβ deposits and oxidative DNA damage relative to the brain sections from the AβPP mice. Interestingly, we found significantly increased levels of soluble APPα and CTF83 in the MCAT/AβPP mice, relative to the AβPP mice. These data provide direct evidence that oxidative stress plays a primary role in AD etiopathology and that in MCAT mice express Aβ, MCAT prevents abnormal APP processing, reduces Aβ levels and enhances Aβ-degrading enzymes in mice at different ages, corresponding to different stages of disease progression. These findings indicate that mitochondria-targeted molecules may be an effective therapeutic approach to treat patients with AD.

Brain rust: recent discoveries on the role of oxidative stress in neurodegenerative diseases

Oxidative stress (OS) and damages due to excessive reactive oxygen species (ROS) are common causes of injuries to cells and organisms. The prevalence of neurodegenerative diseases (ND) increases with aging and much of the research involving ROS and OS has emerged from works in this field. This text reviews some recent published articles about the role of OS in ND. Since there are many reviews in this field, the focus was centered in articles published recently. The Scientific Journals Directory supported by the Brazilian Ministry of Education Office for the Coordination of Higher Educational Personnel Improvement (CAPES) was used to search, download, and review articles. The search engine looked for the terms 'oxidative stress AND neurodegenerative diseases AND nutrition' in 10 different scientific collections. Biochemical markers for ND lack sensitivity or specificity for diagnosis or for tracking response to therapy today. OS has an intimate connection with ND, albeit low levels of ROS seem to protect the brain. Deleterious changes in mitochondria, OS, calcium, glucocorticoids, inflammation, trace metals, insulin, cell cycle, protein aggregation, and hundreds to thousands of genes occur in ND. The interaction of genes with their environment, may explain ND. Although OS has received much attention over the years, which increased the number of scientific works on antioxidant interventions, no one knows how to stop or delay ND at present. Interventions in vitro, in vivo, and in humans will continue to contribute for a better understanding of these pathologies.

Natural polyphenols against neurodegenerative disorders: potentials and pitfalls

Within the last years, a rapidly growing number of polyphenolic compounds with neuroprotective effects have been described. Many efforts have been made to explore the mechanisms behind the neuroprotective action of polyphenols. However, many pathways and mechanisms considered for mediating these effects are rather general than specific. Moreover, despite the beneficial effects of polyphenols in experimental treatment of neurodegeneration, little has been achieved in bringing them into routine clinical applications. In this review, we have summarized the protective effects of polyphenols against neurodegeneration, and we have also discussed some of the barricades in translating these biochemical compounds, into relevant therapeutics for neurodegenerative diseases.

Somatic mutations in aging, cancer and neurodegeneration

The somatic mutation theory of aging posits that the accumulation of mutations in the genetic material of somatic cells as a function of time results in a decrease in cellular function. In particular, the accumulation of random mutations may inactivate genes that are important for the functioning of the somatic cells of various organ systems of the adult, result in a decrease in organ function. When the organ function decreases below a critical level, death occurs. A significant amount of research has shown that somatic mutations play an important role in aging and a number of age related pathologies. In this review, we explore evidence for increases in somatic nuclear mutation burden with age and the consequences for aging, cancer, and neurodegeneration. We then review evidence for increases in mitochondrial mutation burden and the consequences for dysfunction in the disease processes.

Smilagenin attenuates beta amyloid (25-35)-induced degeneration of neuronal cells via stimulating the gene expression of brain-derived neurotrophic factor

The development of drugs that attenuate neurodegeneration is important for the treatment of Alzheimer's disease (AD). We previously found that smilagenin (SMI), a steroidal sapogenin from traditional Chinese medicinal herbs improves memory in animal models, is neither a cholinesterase inhibitor nor a glutamate receptor antagonist, but can significantly elevate the declined muscarinic receptor (M receptor) density. In this article, to clarify whether SMI represents a new approach for treating neurodegeneration disease, we first demonstrate that SMI pretreatment significantly attenuates the neurodegenerative changes induced by beta amyloid 25-35 (Aβ(25-35)) in cultured rat cortical neurons, including decreased cholinergic neuron number, shortened neurite outgrowth length, and declined M receptor density. Brain-derived neurotrophic factor (BDNF) protein levels in the culture medium were also decreased by Aβ(25-35) and significantly elevated by SMI. Parallel experiments revealed that when the trk receptors were inhibited by K252a or the action of BDNF was inhibited by a neutralizing anti-BDNF antibody, the effects of SMI on the Aβ(25-35)-induced neurodegeneration in rat cortical neurons were almost completely abolished. In the all-trans retinoic acid (RA)-differentiated SH-SY5Y neuroblastoma cells, the BDNF transcription rate measured by a nuclear run-on assay was significantly suppressed by Aβ(25-35) and elevated by SMI, but the BDNF degradation rate measured by half-life determination was unchanged by Aβ(25-35) and SMI. Transcript analysis of the SH-SY5Y cells using quantitative RT-PCR (qRT-PCR) showed that the IV and VI transcripts of BDNF mRNA were significantly decreased by Aβ(25-35) and elevated by SMI. Taken together, we conclude that SMI attenuates Aβ(25-35)-induced neurodegeneration in cultured rat cortical neurons and SH-SY5Y cells mainly through stimulating BDNF mRNA transcription implicating that SMI may represent a novel therapeutic strategy for AD.

Specific inhibition of mitochondrial oxidative stress suppresses inflammation and improves cardiac function in a rat pneumonia-related sepsis model

Using a mitochondria-targeted vitamin E (Mito-Vit-E) in a rat pneumonia-related sepsis model, we examined the role of mitochondrial reactive oxygen species in sepsis-mediated myocardial inflammation and subsequent cardiac contractile dysfunction. Sepsis was produced in adult male Sprague-Dawley rats via intratracheal injection of S. pneumonia (4 × 10(6) colony formation units per rat). A single dose of Mito-Vit-E, vitamin E, or control vehicle, at 21.5 μmol/kg, was administered 30 min postinoculation. Blood was collected, and heart tissue was harvested at various time points. Mito-Vit-E in vivo distribution was confirmed by mass spectrometry. In cardiac mitochondria, Mito-Vit-E improved total antioxidant capacity and suppressed H(2)O(2) generation, whereas vitamin E offered little effect. In cytosol, both antioxidants decreased H(2)O(2) levels, but only vitamin E strengthened antioxidant capacity. Mito-Vit-E protected mitochondrial structure and function in the heart during sepsis, demonstrated by reduction in lipid and protein oxidation, preservation of mitochondrial membrane integrity, and recovery of respiratory function. While both Mito-Vit-E and vitamin E suppressed sepsis-induced peripheral and myocardial production of proinflammatory cytokines (tumor necrosis factor-α, interleukin-1β, and interleukin-6), Mito-Vit-E exhibited significantly higher efficacy (P < 0.05). Stronger anti-inflammatory action of Mito-Vit-E was further shown by its near-complete inhibition of sepsis-induced myeloperoxidase accumulation in myocardium, suggesting its effect on neutrophil infiltration. Echocardiography analysis indicated that Mito-Vit-E ameliorated cardiac contractility of sepsis animals, shown by improved fractional shortening and ejection fraction. Together, our data suggest that targeted scavenging of mitochondrial reactive oxygen species protects mitochondrial function, attenuates tissue-level inflammation, and improves whole organ activities in the heart during sepsis.

Neuroprotective effects of anthocyanins on apoptosis induced by mitochondrial oxidative stress

OBJECTIVES

Mitochondrial oxidative stress (MOS) is a major factor in the underlying pathology of many neurodegenerative diseases. Here, we investigated the neuroprotective effects of a unique class of nutraceutical antioxidants, anthocyanins, against MOS-induced death of cultured cerebellar granule neurons (CGNs). Callistephin and kuromanin are anthocyanins derived from strawberries and black rice, respectively, whose neuroprotective properties have yet to be examined in detail.

METHODS

Glutathione (GSH)-sensitive MOS and intrinsic apoptosis were induced in CGNs by incubation with the Bcl-2 inhibitor, HA14-1. The effects of anthocyanin co-incubation on CGN survival were assessed.

RESULTS

The anthocyanins demonstrated significant protection from MOS-induced apoptosis which was equivalent to that provided by the green tea polyphenol, epigallocatechin 3-gallate; however, neither anthocyanin was as effective as GSH at rescuing CGNs. Inhibition of Bcl-2 caused a significant reduction of mitochondrial GSH which was prevented by the anthocyanins. Furthermore, the anthocyanins inhibited iron-induced lipid peroxidation in rat brain homogenates and prevented cardiolipin oxidation induced by MOS in CGNs. MOS-induced mitochondrial fragmentation and proteolytic cleavage of the optic atrophy 1 (OPA1) fusion GTPase were also attenuated by the anthocyanins. Finally, the anthocyanins significantly enhanced GSH peroxidase activity in a cell-free assay.

DISCUSSION

These data show that anthocyanins suppress MOS-induced apoptosis by preserving mitochondrial GSH and inhibiting cardiolipin oxidation and mitochondrial fragmentation. These nutraceutical antioxidants warrant further study as potential therapeutic agents for neurodegenerative diseases caused by MOS.

Abnormal interaction between the mitochondrial fission protein Drp1 and hyperphosphorylated tau in Alzheimer's disease neurons: implications for mitochondrial dysfunction and neuronal damage

We recently reported increased mitochondrial fission and decreased fusion, increased amyloid beta (Aβ) interaction with the mitochondrial fission protein Drp1, increased mitochondrial fragmentation, impaired axonal transport of mitochondria and synaptic degeneration in neurons affected by AD. In the present study, we extended our previous investigations to determine whether phosphorylated tau interacts with Drp1 and to elucidate mitochondrial damage in the progression of AD. We also investigated GTPase activity, which is critical for mitochondrial fragmentation, in postmortem brain tissues from patients with AD and brain tissues from APP, APP/PS1 and 3XTg.AD mice. Using co-immunoprecipitation and immunofluorescence analyses, for the first time, we demonstrated the physical interaction between phosphorylated tau and Drp1. Mitochondrial fission-linked GTPase activity was significantly elevated in the postmortem frontal cortex tissues from AD patients and cortical tissues from APP, APP/PS1 and 3XTg.AD mice. On the basis of these findings, we conclude that Drp1 interacts with Aβ and phosphorylated tau, likely leading to excessive mitochondrial fragmentation, and mitochondrial and synaptic deficiencies, ultimately possibly leading to neuronal damage and cognitive decline. Treatment designed to reduce the expression of Drp1, Aβ and/or phosphorylated tau may decrease the interaction between Drp1 and phosphorylated tau and the interaction between Drp1 and Aβ, conferring protection to neurons from toxic insults of excessive Drp1, Aβ and/or phosphorylated tau.

Dynamin-related protein 1 heterozygote knockout mice do not have synaptic and mitochondrial deficiencies

The objective of this study was to elucidate the effect of partial reduction of the mitochondrial fission protein, dynamin-related protein 1 (Drp1) on mitochondrial activity and synaptic viability. Recent knockout studies of Drp1 revealed that homozygote Drp1 knockout mice are embryonic lethal due to reduced mitochondrial fission, and that this reduced fission leads to developmental defects in the brain. In contrast, heterozygote Drp1 knockout mice appear to be normal in terms of lifespan, fertility, and viability, and phenotypically these animals are not different from wild-type mice. However, the effects of partial Drp1 reduction on mitochondrial function and synaptic activity are not well understood. In the present study, we sought to characterize synaptic, dendritic and mitochondrial proteins, and mitochondrial function and GTPase enzymatic activity, in Drp1 heterozygote knockout mice. Interestingly, we found no significant changes in synaptic, dendritic, and mitochondrial proteins in the Drp1 heterozygote knockout mice compared to the wild-type mice. Further, mitochondrial function and GTPase enzymatic activity appeared to be normal. However, H(2)O(2) and lipid peroxidation levels were significantly reduced in the Drp1 heterozygote knockout mice compared to the wild-type mice. These findings suggest that partial Drp1 reduction does not affect mitochondrial and synaptic viability and may have therapeutic use in treating patients with Alzheimer's disease and Huntington's disease.

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.

Mitochondria-targeted antioxidant attenuates high glucose-induced P38 MAPK pathway activation in human neuroblastoma cells

Excessive mitochondrial free radical production and the related mitogen-activated protein kinase P38 (P38 MAPK) activation are key regulators in the pathogenesis of high glucose-induced cell stress. Increasing evidence has emphasized the impact of hyperglycemia on neurons and the consequent neuronal stresses eventually resulting in neurodegeneration and neuronal death. In this study, we employed a novel mitochondria-targeted antioxidant, SS31 peptide, on high glucose-insulted neuroblastoma cells (SH-SY5Y). Our results showed that high glucose promoted significantly increased P38 phosphorylation which was efficiently suppressed by the application of the SS31 peptide under the experimental conditions. The inhibition of high glucose-induced P38 activation by the SS31 peptide was associated with the impact of the SS31 peptide on attenuating high glucose-induced mitochondrial ROS (reactive oxygen species) elevation and mitochondrial membrane potential collapse. The addition of SS31 peptide significantly attenuated high-gluose-induced apoptosis. Therefore, our study suggests that elimination of high glucose-induced mitochondrial oxidative stress helps to rescue SH-SY5Y cells from high glucose-related P38 MAPK pathway disturbances, and the SS31 peptide has the potential to serve as a new treatment strategy against hyperglycemia-instigated neuronal perturbations.

CART peptide is a potential endogenous antioxidant and preferentially localized in mitochondria

The multifunctional neuropeptide Cocaine and Amphetamine Regulated Transcript (CART) is secreted from hypothalamus, pituitary, adrenal gland and pancreas. It also can be found in circulatory system. This feature suggests a general role for CART in different cells. In the present study, we demonstrate that CART protects mitochondrial DNA (mtDNA), cellular proteins and lipids against the oxidative action of hydrogen peroxide, a widely used oxidant. Using cis-parinaric acid as a sensitive reporting probe for peroxidation in membranes, and a lipid-soluble azo initiator of peroxyl radicals, 2,2'-azobis(2,4-dimethylvaleronitrile) we found that CART is an antioxidant. Furthermore, we found that CART localized to mitochondria in cultured cells and mouse brain neuronal cells. More importantly, pretreatment with CART by systemic injection protects against a mouse oxidative stress model, which mimics the main features of Parkinson's disease. Given the unique molecular structure and biological features of CART, we conclude that CART is an antioxidant peptide (or antioxidant hormone). We further propose that it may have strong therapeutic properties for human diseases in which oxidative stress is strongly involved such as Parkinson's disease.

Mitochondrial abnormalities in Alzheimer's disease: possible targets for therapeutic intervention

Mitochondria from persons with Alzheimer's disease (AD) differ from those of age-matched control subjects. Differences in mitochondrial morphology and function are well documented, and are not brain-limited. Some of these differences are present during all stages of AD, and are even seen in individuals who are without AD symptoms and signs but who have an increased risk of developing AD. This chapter considers the status of mitochondria in AD subjects, the potential basis for AD subject mitochondrial perturbations, and the implications of these perturbations. Data from multiple lines of investigation, including epidemiologic, biochemical, molecular, and cytoplasmic hybrid studies, are reviewed. The possibility that mitochondria could potentially constitute a reasonable AD therapeutic target is discussed, as are several potential mitochondrial medicine treatment strategies.

The mitochondria-targeted antioxidant MitoQ prevents loss of spatial memory retention and early neuropathology in a transgenic mouse model of Alzheimer's disease

Considerable evidence suggests that mitochondrial dysfunction and oxidative stress contribute to the progression of Alzheimer's disease (AD). We examined the ability of the novel mitochondria-targeted antioxidant MitoQ (mitoquinone mesylate: [10-(4,5-dimethoxy-2-methyl-3,6-dioxo-1,4-cycloheexadienl-yl) decyl triphenylphosphonium methanesulfonate]) to prevent AD-like pathology in mouse cortical neurons in cell culture and in a triple transgenic mouse model of AD (3xTg-AD). MitoQ attenuated β-amyloid (Aβ)-induced neurotoxicity in cortical neurons and also prevented increased production of reactive species and loss of mitochondrial membrane potential (Δψ(m)) in them. To determine whether the mitochondrial protection conferred by MitoQ was sufficient to prevent the emergence of AD-like neuropathology in vivo, we treated young female 3xTg-AD mice with MitoQ for 5 months and analyzed the effect on the progression of AD-like pathologies. Our results show that MitoQ prevented cognitive decline in these mice as well as oxidative stress, Aβ accumulation, astrogliosis, synaptic loss, and caspase activation in their brains. The work presented herein suggests a central role for mitochondria in neurodegeneration and provides evidence supporting the use of mitochondria-targeted therapeutics in diseases involving oxidative stress and metabolic failure, namely AD.

Upregulation of heme oxygenase-1 by acteoside through ERK and PI3 K/Akt pathway confer neuroprotection against beta-amyloid-induced neurotoxicity

Our previous study has shown that acteoside, an antioxidative phenylethanoid glycoside, protect against beta-amyloid (Aβ)-induced cytotoxicity in vitro. However, the precise protective mechanisms remains unclear. Heme oxygenase-1 (HO-1) is a crucial factor in the response to oxidative injury, protecting neurons against Aβ-induced injury. In the present study we examined to determine whether acteoside upregulates HO-1 expression, and thereby protects PC12 cells against Aβ-induced cell death. It was revealed that acteoside is an activator of Nrf2 and inducer of HO-1 expression. We showed that acteoside increased HO-1 expression in vitro and in vivo. Acteoside treatment resulted in nuclear translocation of the transcription factor NF-E2-related factor 2 (Nrf2). Acteoside activated both ERK and PI3 K/Akt, and treatments with the specific ERK inhibitor PD98059, the PI3 K inhibitor LY294002, and the specific Nrf2 siRNA suppressed the acteoside-induced HO-1 expression. The HO-1 inhibitor ZnPP, PD98059, and LY294002 markedly abolished the neuroprotective effect of acteoside against Aβ-induced neurotoxicity. Taken together, these results demonstrate that acteoside is an activator of Nrf2 and inducer of HO-1 expression. We also showed that acteoside increased HO-1 expression through activation of ERK and PI3 K/Akt signal pathways in vitro. Upregulation of HO-1 by acteoside may involve in the neuroprotection against Aβ-induced neurotoxicity.

Impaired mitochondrial biogenesis, defective axonal transport of mitochondria, abnormal mitochondrial dynamics and synaptic degeneration in a mouse model of Alzheimer's disease

Increasing evidence suggests that the accumulation of amyloid beta (Aβ) in synapses and synaptic mitochondria causes synaptic mitochondrial failure and synaptic degeneration in Alzheimer's disease (AD). The purpose of this study was to better understand the effects of Aβ in mitochondrial activity and synaptic alterations in neurons from a mouse model of AD. Using primary neurons from a well-characterized Aβ precursor protein transgenic (AβPP) mouse model (Tg2576 mouse line), for the first time, we studied mitochondrial activity, including axonal transport of mitochondria, mitochondrial dynamics, morphology and function. Further, we also studied the nature of Aβ-induced synaptic alterations, and cell death in primary neurons from Tg2576 mice, and we sought to determine whether the mitochondria-targeted antioxidant SS31 could mitigate the effects of oligomeric Aβ. We found significantly decreased anterograde mitochondrial movement, increased mitochondrial fission and decreased fusion, abnormal mitochondrial and synaptic proteins and defective mitochondrial function in primary neurons from AβPP mice compared with wild-type (WT) neurons. Transmission electron microscopy revealed a large number of small mitochondria and structurally damaged mitochondria, with broken cristae in AβPP primary neurons. We also found an increased accumulation of oligomeric Aβ and increased apoptotic neuronal death in the primary neurons from the AβPP mice relative to the WT neurons. Our results revealed an accumulation of intraneuronal oligomeric Aβ, leading to mitochondrial and synaptic deficiencies, and ultimately causing neurodegeneration in AβPP cultures. However, we found that the mitochondria-targeted antioxidant SS31 restored mitochondrial transport and synaptic viability, and decreased the percentage of defective mitochondria, indicating that SS31 protects mitochondria and synapses from Aβ toxicity.

Abnormal mitochondrial dynamics and synaptic degeneration as early events in Alzheimer's disease: implications to mitochondria-targeted antioxidant therapeutics

Synaptic pathology and mitochondrial oxidative damage are early events in Alzheimer's disease (AD) progression. Loss of synapses and synaptic damage are the best correlates of cognitive deficits found in AD patients. Recent research on amyloid beta (Aβ) and mitochondria in AD revealed that Aβ accumulates in synapses and synaptic mitochondria, leading to abnormal mitochondrial dynamics and synaptic degeneration in AD neurons. Further, recent studies using live-cell imaging and primary neurons from amyloid beta precursor protein (AβPP) transgenic mice revealed reduced mitochondrial mass, defective axonal transport of mitochondria and synaptic degeneration, indicating that Aβ is responsible for mitochondrial and synaptic deficiencies. Tremendous progress has been made in studying antioxidant approaches in mouse models of AD and clinical trials of AD patients. This article highlights the recent developments made in Aβ-induced abnormal mitochondrial dynamics, defective mitochondrial biogenesis, impaired axonal transport and synaptic deficiencies in AD. This article also focuses on mitochondrial approaches in treating AD, and also discusses latest research on mitochondria-targeted antioxidants in AD. This article is part of a Special Issue entitled: Antioxidants and Antioxidant Treatment in Disease.

Mutant huntingtin's interaction with mitochondrial protein Drp1 impairs mitochondrial biogenesis and causes defective axonal transport and synaptic degeneration in Huntington's disease

The purpose of this study was to investigate the link between mutant huntingtin (Htt) and neuronal damage in relation to mitochondria in Huntington's disease (HD). In an earlier study, we determined the relationship between mutant Htt and mitochondrial dynamics/synaptic viability in HD patients. We found mitochondrial loss, abnormal mitochondrial dynamics and mutant Htt association with mitochondria in HD patients. In the current study, we sought to expand on our previous findings and further elucidate the relationship between mutant Htt and mitochondrial and synaptic deficiencies. We hypothesized that mutant Htt, in association with mitochondria, alters mitochondrial dynamics, leading to mitochondrial fragmentation and defective axonal transport of mitochondria in HD neurons. In this study, using postmortem HD brains and primary neurons from transgenic BACHD mice, we identified mutant Htt interaction with the mitochondrial protein Drp1 and factors that cause abnormal mitochondrial dynamics, including GTPase Drp1 enzymatic activity. Further, using primary neurons from BACHD mice, for the first time, we studied axonal transport of mitochondria and synaptic degeneration. We also investigated the effect of mutant Htt aggregates and oligomers in synaptic and mitochondrial deficiencies in postmortem HD brains and primary neurons from BACHD mice. We found that mutant Htt interacts with Drp1, elevates GTPase Drp1 enzymatic activity, increases abnormal mitochondrial dynamics and results in defective anterograde mitochondrial movement and synaptic deficiencies. These observations support our hypothesis and provide data that can be utilized to develop therapeutic targets that are capable of inhibiting mutant Htt interaction with Drp1, decreasing mitochondrial fragmentation, enhancing axonal transport of mitochondria and protecting synapses from toxic insults caused by mutant Htt.

Neuroprotective strategies involving ROS in Alzheimer disease

Alzheimer disease (AD) is a neurodegenerative disorder in which oxidative stress is a key hallmark. It occurs early in disease pathogenesis and can exacerbate its progression. Several causes of oxidative stress have been determined over the years. First, mitochondria play an important role in the generation and accumulation of free radicals. In addition to mitochondria, inflammation can also induce oxidative damage, especially via microglia, and microglia are also important for Aβ clearance. In AD, both mitochondrial function and inflammatory response are affected, leading to increased ROS formation and oxidative damage to lipid, proteins, and nucleic acids. Some other sources have also been identified. From these findings, various neuroprotective strategies against ROS-mediated damages have been elaborated in AD research. This review recapitulates some of the major strategies used to prevent oxidative stress and disease progression. Outcomes from in vitro and in vivo studies using models of AD are encouraging. However, only a few clinical trials have provided positive results in terms of slowing down cognitive decline. Nonetheless, there is still hope for improved compounds that would better target pathways implicated in ROS production. In fact, facilitating the endogenous antioxidant system by modulating transcription has great promise for AD therapy.

Aging and amyloid beta-induced oxidative DNA damage and mitochondrial dysfunction in Alzheimer's disease: implications for early intervention and therapeutics

Alzheimer's disease (AD) is an age-related progressive neurodegenerative disease affecting thousands of people in the world and effective treatment is still not available. Over two decades of intense research using AD postmortem brains, transgenic mouse and cell models of amyloid precursor protein and tau revealed that amyloid beta (Aβ) and hyperphosphorylated tau are synergistically involved in triggering disease progression. Accumulating evidence also revealed that aging and amyloid beta-induced oxidative DNA damage and mitochondrial dysfunction initiate and contributes to the development and progression of the disease. The purpose of this article is to summarize the latest progress in aging and AD, with a special emphasis on the mitochondria, oxidative DNA damage including methods of its measurement. It also discusses the therapeutic approaches against oxidative DNA damage and treatment strategies in AD.

Protective efficacy of mitochondrial targeted antioxidant MitoQ against dichlorvos induced oxidative stress and cell death in rat brain

Dichlorvos is a synthetic insecticide that belongs to the family of chemically related organophosphate (OP) pesticides. It can be released into the environment as a major degradation product of other OPs, such as trichlorfon, naled, and metrifonate. Dichlorvos exerts its toxic effects in humans and animals by inhibiting neural acetylcholinesterase. Chronic low-level exposure to dichlorvos has been shown to result in inhibition of the mitochondrial complex I and cytochrome oxidase in rat brain, resulting in generation of reactive oxygen species (ROS). Enhanced ROS production leads to disruption of cellular antioxidant defense systems and release of cytochrome c (cyt c) from mitochondria to cytosol resulting in apoptotic cell death. MitoQ is an antioxidant, selectively targeted to mitochondria and protects it from oxidative damage and has been shown to decrease mitochondrial damage in various animal models of oxidative stress. We hypothesized that if oxidative damage to mitochondria does play a significant role in dichlorvos induced neurodegeneration, then MitoQ should ameliorate neuronal apoptosis. Administration of MitoQ (100 μmol/kg body wt/day) reduced dichlorvos (6 mg/kg body wt/day) induced oxidative stress (decreased ROS production, increased MnSOD activity and glutathione levels) with decreased lipid peroxidation, protein and DNA oxidation. In addition, MitoQ also suppressed DNA fragmentation, cyt c release and caspase-3 activity in dichlorvos treated rats compared to the control group. Further electron microscopic studies revealed that MitoQ attenuates dichlorvos induced mitochondrial swelling, loss of cristae and chromatin condensation. These results indicate that MitoQ may be beneficial against OP (dichlorvos) induced neurodegeneration.

Impaired mitochondrial dynamics and abnormal interaction of amyloid beta with mitochondrial protein Drp1 in neurons from patients with Alzheimer's disease: implications for neuronal damage

The purpose of our study was to better understand the relationship between mitochondrial structural proteins, particularly dynamin-related protein 1 (Drp1) and amyloid beta (Aβ) in the progression of Alzheimer's disease (AD). Using qRT-PCR and immunoblotting analyses, we measured mRNA and protein levels of mitochondrial structural genes in the frontal cortex of patients with early, definite and severe AD and in control subjects. We also characterized monomeric and oligomeric forms of Aβ in these patients. Using immunoprecipitation/immunoblotting analysis, we investigated the interaction between Aβ and Drp1. Using immunofluorescence analysis, we determined the localization of Drp1 and intraneuronal and oligomeric Aβ in the AD brains and primary hippocampal neurons from Aβ precursor protein (AβPP) transgenic mice. We found increased expression of the mitochondrial fission genes Drp1 and Fis1 (fission 1) and decreased expression of the mitochondrial fusion genes Mfn1 (mitofusin 1), Mfn2 (mitofusin 2), Opa1 (optic atrophy 1) and Tomm40. The matrix gene CypD was up-regulated in AD patients. Results from our qRT-PCR and immunoblotting analyses suggest that abnormal mitochondrial dynamics increase as AD progresses. Immunofluorescence analysis of the Drp1 antibody and the Aβ antibodies 6E10 and A11 revealed the colocalization of Drp1 and Aβ. Drp1 immunoprecipitation/immunoblotting analysis of Aβ antibodies 6E10 and A11 revealed that Drp1 interacts with Aβ monomers and oligomers in AD patients, and these abnormal interactions are increased with disease progression. Primary neurons that were found with accumulated oligomeric Aβ had lost branches and were degenerated, indicating that oligomeric Aβ may cause neuronal degeneration. These findings suggest that in patients with AD, increased production of Aβ and the interaction of Aβ with Drp1 are crucial factors in mitochondrial fragmentation, abnormal mitochondrial dynamics and synaptic damage. Inhibiting, these abnormal interactions may be a therapeutic strategy to reduce mitochondrial fragmentation, neuronal and synaptic damage and cognitive decline in patients with AD.

Resveratrol acts not through anti-aggregative pathways but mainly via its scavenging properties against Aβ and Aβ-metal complexes toxicity

It has been recently suggested that resveratrol can be effective in slowing down Alzheimer's disease (AD) development. As reported in many biochemical studies, resveratrol seems to exert its neuro-protective role through inhibition of β-amyloid aggregation (Aβ), by scavenging oxidants and exerting anti-inflammatory activities. In this paper, we demonstrate that resveratrol is cytoprotective in human neuroblastoma cells exposed to Aβ and or to Aβ-metal complex. Our findings suggest that resveratrol acts not through anti-aggregative pathways but mainly via its scavenging properties.

Mitochondria as a therapeutic target for aging and neurodegenerative diseases

Mitochondria are cytoplasmic organelles responsible for life and death. Extensive evidence from animal models, postmortem brain studies of and clinical studies of aging and neurodegenerative diseases suggests that mitochondrial function is defective in aging and neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Several lines of research suggest that mitochondrial abnormalities, including defects in oxidative phosphorylation, increased accumulation of mitochondrial DNA defects, impaired calcium influx, accumulation of mutant proteins in mitochondria, and mitochondrial membrane potential dissipation are important cellular changes in both early and late-onset neurodegenerative diseases. Further, emerging evidence suggests that structural changes in mitochondria, including increased mitochondrial fragmentation and decreased mitochondrial fusion, are critical factors associated with mitochondrial dysfunction and cell death in aging and neurodegenerative diseases. This paper discusses research that elucidates features of mitochondria that are associated with cellular dysfunction in aging and neurodegenerative diseases and discusses mitochondrial structural and functional changes, and abnormal mitochondrial dynamics in neurodegenerative diseases. It also outlines mitochondria-targeted therapeutics in neurodegenerative diseases.

Redox modulation by S-nitrosylation contributes to protein misfolding, mitochondrial dynamics, and neuronal synaptic damage in neurodegenerative diseases

The pathological processes of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases engender synaptic and neuronal cell damage. While mild oxidative and nitrosative (nitric oxide (NO)-related) stress mediates normal neuronal signaling, excessive accumulation of these free radicals is linked to neuronal cell injury or death. In neurons, N-methyl-D-aspartate (NMDA) receptor (NMDAR) activation and subsequent Ca(2+) influx can induce the generation of NO via neuronal NO synthase. Emerging evidence has demonstrated that S-nitrosylation, representing covalent reaction of an NO group with a critical protein thiol, mediates the vast majority of NO signaling. Analogous to phosphorylation and other posttranslational modifications, S-nitrosylation can regulate the biological activity of many proteins. Here, we discuss recent studies that implicate neuropathogenic roles of S-nitrosylation in protein misfolding, mitochondrial dysfunction, synaptic injury, and eventual neuronal loss. Among a growing number of S-nitrosylated proteins that contribute to disease pathogenesis, in this review we focus on S-nitrosylated protein-disulfide isomerase (forming SNO-PDI) and dynamin-related protein 1 (forming SNO-Drp1). Furthermore, we describe drugs, such as memantine and newer derivatives of this compound that can prevent both hyperactivation of extrasynaptic NMDARs as well as downstream pathways that lead to nitrosative stress, synaptic damage, and neuronal loss.

Mitochondrial division: molecular machinery and physiological functions

Mitochondrial division has emerged as a key mechanism for this essential organelle to maintain its structural integrity, intracellular distribution, and functional competence. An evolutionarily conserved dynamin-related GTPase, Dnm1p/Drp1, interacts with other proteins to form the core machinery involved in mitochondrial division. We summarize recent progress in understanding how the division machinery assembles onto mitochondria and how mitochondrial division contributes to cellular physiology and human diseases.

Melatonin in mitochondrial dysfunction and related disorders

Mitochondrial dysfunction is considered one of the major causative factors in the aging process, ischemia/reperfusion (I/R), septic shock, and neurodegenerative disorders like Parkinson's disease (PD), Alzheimer's disease (AD), and Huntington's disease (HD). Increased free radical generation, enhanced mitochondrial inducible nitric oxide (NO) synthase activity, enhanced NO production, decreased respiratory complex activity, impaired electron transport system, and opening of mitochondrial permeability transition pore all have been suggested as factors responsible for impaired mitochondrial function. Melatonin, the major hormone of the pineal gland, also acts as an antioxidant and as a regulator of mitochondrial bioenergetic function. Both in vitro and in vivo, melatonin was effective for preventing oxidative stress/nitrosative stress-induced mitochondrial dysfunction seen in experimental models of PD, AD, and HD. In addition, melatonin is known to retard aging and to inhibit the lethal effects of septic shock or I/R lesions by maintaining respiratory complex activities, electron transport chain, and ATP production in mitochondria. Melatonin is selectively taken up by mitochondrial membranes, a function not shared by other antioxidants. Melatonin has thus emerged as a major potential therapeutic tool for treating neurodegenerative disorders such as PD or AD, and for preventing the lethal effects of septic shock or I/R.

Assessment of newly synthesized mitochondrial DNA using BrdU labeling in primary neurons from Alzheimer's disease mice: Implications for impaired mitochondrial biogenesis and synaptic damage

The purpose of our study was to assess mitochondrial biogenesis and distribution in murine primary neurons. Using 5-bromo-2-deoxyuridine (BrdU) incorporation and primary neurons, we studied the mitochondrial biogenesis and mitochondrial distribution in hippocampal neurons from amyloid beta precursor protein (AβPP) transgenic mice and wild-type (WT) neurons treated with oxidative stressors, rotenone and H(2)O(2). We found that after 20h of labeling, BrdU incorporation was specific to porin-positive mitochondria. The proportion of mitochondrial area labeled with BrdU was 40.3±6.3% at 20h. The number of mitochondria with newly synthesized DNA was higher in AβPP neuronal cell bodies than in the cell bodies of WT neurons (AβPP, 45.23±2.67 BrdU-positive/cell body; WT, 32.92±2.49 BrdU-positive/cell body; p=0.005). In neurites, the number of BrdU-positive mitochondria decreased in AβPP cultures compared to WT neurons (AβPP, 0.105±0.008 BrdU-positive/μm neurite; WT, 0.220±0.036 BrdU-positive/μm neurite; p=0.010). Further, BrdU in the cell body increased when neurons were treated with low doses of H(2)O(2) (49.6±2.7 BrdU-positive/cell body, p=0.0002 compared to untreated cells), while the neurites showed decreased BrdU staining (0.122±0.010 BrdU-positive/μm neurite, p=0.005 compared to the untreated). BrdU labeling was increased in the cell body under rotenone treatment. Additionally, under rotenone treatment, the content of BrdU labeling decreased in neurites. These findings suggest that Aβ and mitochondrial toxins enhance mitochondrial fragmentation in the cell body, and may cause impaired axonal transport of mitochondria leading to synaptic degeneration.

Mitochondria, Amyloid β, and Alzheimer's Disease

Hypometabolism is a hallmark of Alzheimer's disease (AD) and implicates a mitochondrial role in the neuropathology associated with AD. Mitochondrial amyloid-beta (Aβ) accumulation precedes extracellular Aβ deposition. In addition to increasing oxidative stress, Aβ has been shown to directly inhibit mitochondrial enzymes. Inhibition of mitochondrial enzymes as a result of oxidative damage or Aβ interaction perpetuates oxidative stress and leads to a hypometabolic state. Additionally, Aβ has also been shown to interact with cyclophilin D, a component of the mitochondrial permeability transition pore, which may promote cell death. Therefore, ample evidence exists indicating that the mitochondrion plays a vital role in the pathophysiology observed in AD.

Mitochondrial Dysfunction and Oxidative Stress in Asthma: Implications for Mitochondria-Targeted Antioxidant Therapeutics

Asthma is a complex, inflammatory disorder characterized by airflow obstruction of variable degrees, bronchial hyper-responsiveness, and airway inflammation. Asthma is caused by environmental factors and a combination of genetic and environmental stimuli. Genetic studies have revealed that multiple loci are involved in the etiology of asthma. Recent cellular, molecular, and animal-model studies have revealed several cellular events that are involved in the progression of asthma, including: increased Th2 cytokines leading to the recruitment of inflammatory cells to the airway, and an increase in the production of reactive oxygen species and mitochondrial dysfunction in the activated inflammatory cells, leading to tissue injury in the bronchial epithelium. Further, aging and animal model studies have revealed that mitochondrial dysfunction and oxidative stress are involved and play a large role in asthma. Recent studies using experimental allergic asthmatic mouse models and peripheral cells and tissues from asthmatic humans have revealed antioxidants as promising treatments for people with asthma. This article summarizes the latest research findings on the involvement of inflammatory changes, and mitochondrial dysfunction/oxidative stress in the development and progression of asthma. This article also addresses the relationship between aging and age-related immunity in triggering asthma, the antioxidant therapeutic strategies in treating people with asthma.

Amelioration of amyloid β-induced cognitive deficits by Zataria multiflora Boiss. essential oil in a rat model of Alzheimer's disease

INTRODUCTION

The limitations of current Alzheimer's disease (AD) therapeutics have prompted investigation into innovative therapeutics focused on antiinflammatory, antioxidant, and neuroprotective agents including those from medicinal plants. Numerous plants have been tested for their potential for alleviating symptoms of AD.

AIMS

Zataria multiflora Boiss. (ZM) a member of Lamiaceae family has been used in Iranian traditional medicine for its beneficial effects on mental abilities. Therefore, the effect of its essential oil was evaluated in a rat model of AD.

METHODS

Amyloid β-protein (Aβ) fragment 25-35 was injected bilaterally in the CA1 region of rats hippocampus and the effect of different doses of ZM essential oil (50, 100, or 200 μL/kg) on cognitive function was investigated in the Morris water maze. Acute toxicity of the essential oil was also studied.

RESULTS

The results showed increases in escape latency, traveled distance, heading angle, and decreases in target quadrant entries in Aβ-received groups as compared to the control group. This impairment was reversed by ZM essential oil. The results of acute toxicity testing revealed that the calculated LD50 (1264.9 μL/kg) is much higher than the therapeutic dose (100 μL/kg).

CONCLUSIONS

It seems that antioxidant, antiinflammatory, and anticholinesterase activities of ZM or its main constituents might contribute to its beneficial effects in this model. Our findings suggest that ZM may be a potentially valuable source of natural therapeutic agents for the treatment of AD. However, further investigations are necessary to establish its clinical efficacy and potential toxicity, before any recommendations concerning its use as a medication in the treatment of AD.

Abnormal mitochondrial dynamics, mitochondrial loss and mutant huntingtin oligomers in Huntington's disease: implications for selective neuronal damage

The purpose of our study was to determine the relationship between mutant huntingtin (Htt) and mitochondrial dynamics in the progression of Huntington's disease (HD). We measured the mRNA levels of electron transport chain genes, and mitochondrial structural genes, Drp1 (dynamin-related protein 1), Fis1 (fission 1), Mfn1 (mitofusin 1), Mfn2 (mitofusin 2), Opa1 (optric atrophy 1), Tomm40 (translocase of outermembrane 40) and CypD (cyclophilin D) in grade III and grade IV HD patients and controls. The mutant Htt oligomers and the mitochondrial structural proteins were quantified in the striatum and frontal cortex of HD patients. Changes in expressions of the electron transport chain genes were found in HD patients and may represent a compensatory response to mitochondrial damage caused by mutant Htt. Increased expression of Drp1 and Fis1 and decreased expression of Mfn1, Mfn2, Opa1 and Tomm40 were found in HD patients relative to the controls. CypD was upregulated in HD patients, and this upregulation increased as HD progressed. Significantly increased immunoreactivity of 8-hydroxy-guanosine was found in the cortical specimens from stage III and IV HD patients relative to controls, suggesting increased oxidative DNA damage in HD patients. In contrast, significantly decreased immunoreactivities of cytochrome oxidase 1 and cytochrome b were found in HD patients relative to controls, indicating a loss of mitochondrial function in HD patients. Immunoblotting analysis revealed 15, 25 and 50 kDa mutant Htt oligomers in the brain specimens of HD patients. All oligomeric forms of mutant Htt were significantly increased in the cortical tissues of HD patients, and mutant Htt oligomers were found in the nucleus and in mitochondria. The increase in Drp1, Fis1 and CypD and the decrease in Mfn1 and Mfn2 may be responsible for abnormal mitochondrial dynamics that we found in the cortex of HD patients, and may contribute to neuronal damage in HD patients. The presence of mutant Htt oligomers in the nucleus of HD neurons and in mitochondria may disrupt neuronal functions. Based on these findings, we propose that mutant Htt in association with mitochondria imbalance and mitochondrial dynamics impairs axonal transport of mitochondria, decreases mitochondrial function and damages neurons in affected brain regions of HD patients.

Toxicity of neurons treated with herbicides and neuroprotection by mitochondria-targeted antioxidant SS31

The purpose of this study was to determine the neurotoxicity of two commonly used herbicides: picloram and triclopyr and the neuroprotective effects of the mitochondria-targeted antioxidant, SS31. Using mouse neuroblastoma (N2a) cells and primary neurons from C57BL/6 mice, we investigated the toxicity of these herbicides, and protective effects of SS1 peptide against picloram and triclopyr toxicity. We measured total RNA content, cell viability and mRNA expression of peroxiredoxins, neuroprotective genes, mitochondrial-encoded electron transport chain (ETC) genes in N2a cells treated with herbicides and SS31. Using primary neurons from C57BL/6 mice, neuronal survival was studied in neurons treated with herbicides, in neurons pretreated with SS31 plus treated with herbicides, neurons treated with SS31 alone, and untreated neurons. Significantly decreased total RNA content, and cell viability in N2a cells treated with picloram and triclopyr were found compared to untreated N2a cells. Decreased mRNA expression of neuroprotective genes, and ETC genes in cells treated with herbicides was found compared to untreated cells. Decreased mRNA expression of peroxiredoxins 1-6 in N2a cells treated with picloram was found, suggesting that picloram affects the antioxidant enzymes in N2a cells. Immunofluorescence analysis of primary neurons revealed that decreased neuronal branching and degenerating neurons in neurons treated with picloram and triclopyr. However, neurons pretreated with SS31 prevented degenerative process caused by herbicides. Based on these results, we propose that herbicides--picloram and triclopyr appear to damage neurons, and the SS31 peptide appears to protect neurons from herbicide toxicity.

Amyloid beta impairs mitochondrial anterograde transport and degenerates synapses in Alzheimer's disease neurons

Loss of synapses and synaptic damage are the best correlates of cognitive decline identified in patients with Alzheimer's disease (AD), and mitochondrial oxidative damage and synaptic pathology have been identified as early events in the progression of AD. The progressive accumulation of amyloid beta (Aβ) in synapses and synaptic mitochondria are hypothesized to cause synaptic degeneration and cognitive decline in patients with AD. However, the precise mechanistic link between Aβ and mitochondria is not well understood. The purpose of this study was to better understand the effects of Aβ on mitochondrial axonal transport and synaptic alterations in AD. Using mouse hippocampal neurons and Aβ(25-35) peptide, we studied axonal transport of mitochondria, including mitochondrial motility, mitochondrial length and size, mitochondrial index per neurite, and synaptic alterations of the hippocampal neurons. In the PBS-treated neurons, 36.4±4.7% of the observed mitochondria were motile, with 21.0±1.3% moving anterograde and 15.4±3.4% moving retrograde and the average speed of movement was 12.1±1.8μm/min. In contrast, in the Aβ-treated neurons, the number of motile mitochondria were significantly less, at 20.4±2.6% (P<0.032), as were those moving anterograde (10.1±2.6%, P<0.016) relative to PBS-treated neurons, suggesting that the Aβ(25-35) peptide impairs axonal transport of mitochondria in AD neurons. In the Aβ-treated neurons, the average speed of motile mitochondria was also less, at 10.9±1.9μm/min, and mitochondrial length was significantly decreased. Further, synaptic immunoreactivity was also significantly less in the Aβ-treated neurons relative to the PBS-treated neurons, indicating that Aβ affects synaptic viability. These findings suggest that, in neurons affected by AD, Aβ is toxic, impairs mitochondrial movements, reduces mitochondrial length, and causes synaptic degeneration.

Dynamin-related protein 1 and mitochondrial fragmentation in neurodegenerative diseases

The purpose of this article is to review the recent developments of abnormal mitochondrial dynamics, mitochondrial fragmentation, and neuronal damage in neurodegenerative diseases, including Alzheimer's, Parkinson's, Huntington's, and amyotrophic lateral sclerosis. The GTPase family of proteins, including fission proteins, dynamin related protein 1 (Drp1), mitochondrial fission 1 (Fis1), and fusion proteins (Mfn1, Mfn2 and Opa1) are essential to maintain mitochondrial fission and fusion balance, and to provide necessary adenosine triphosphate to neurons. Among these, Drp1 is involved in several important aspects of mitochondria, including shape, size, distribution, remodeling, and maintenance of mitochondria in mammalian cells. In addition, recent advancements in molecular, cellular, electron microscopy, and confocal imaging studies revealed that Drp1 is associated with several cellular functions, including mitochondrial and peroxisomal fragmentation, phosphorylation, SUMOylation, ubiquitination, and cell death. In the last two decades, tremendous progress has been made in researching mitochondrial dynamics, in yeast, worms, and mammalian cells; and this research has provided evidence linking Drp1 to neurodegenerative diseases. Researchers in the neurodegenerative disease field are beginning to recognize the possible involvement of Drp1 in causing mitochondrial fragmentation and abnormal mitochondrial dynamics in neurodegenerative diseases. This article summarizes research findings relating Drp1 to mitochondrial fission and fusion, in yeast, worms, and mammals. Based on findings from the Reddy laboratory and others', we propose that mutant proteins of neurodegenerative diseases, including AD, PD, HD, and ALS, interact with Drp1, activate mitochondrial fission machinery, fragment mitochondria excessively, and impair mitochondrial transport and mitochondrial dynamics, ultimately causing mitochondrial dysfunction and neuronal damage.

Amyloid-beta and mitochondria in aging and Alzheimer's disease: implications for synaptic damage and cognitive decline

This article reviews the role of amyloid-beta (Abeta) and mitochondria in synaptic damage and cognitive decline found in patients with Alzheimer's disease (AD). Recent molecular, cellular, animal model, and postmortem brain studies have revealed that Abeta and mitochondrial abnormalities are key factors that cause synaptic damage and cognitive decline in AD. Abeta is reported to accumulate in subcellular compartments and to impair the normal function of neurons in AD patients. Further, recent studies using biochemical methods and electron microscopy have revealed that the accumulation of Abeta at nerve terminals affect synaptic activities, including the release of neurotransmitters and synaptic vesicles. Recent studies of the relationship between mitochondria and Abeta in AD patients suggest that in mitochondria, structural changes caused by Abeta result in increased mitochondrial fragmentation, decreased mitochondrial fusion, mitochondrial dysfunction, and synaptic damage. This paper discusses the latest research on Abeta, mitochondria, age-dependent factors of AD in the brain, and synaptic damage in AD. This paper also briefly discusses potential mitochondrial therapeutics in the treatment of patients with AD.

Amyloid-beta and mitochondria in aging and Alzheimer's disease: implications for synaptic damage and cognitive decline

This article reviews the role of amyloid-beta (Abeta) and mitochondria in synaptic damage and cognitive decline found in patients with Alzheimer's disease (AD). Recent molecular, cellular, animal model, and postmortem brain studies have revealed that Abeta and mitochondrial abnormalities are key factors that cause synaptic damage and cognitive decline in AD. Abeta is reported to accumulate in subcellular compartments and to impair the normal function of neurons in AD patients. Further, recent studies using biochemical methods and electron microscopy have revealed that the accumulation of Abeta at nerve terminals affect synaptic activities, including the release of neurotransmitters and synaptic vesicles. Recent studies of the relationship between mitochondria and Abeta in AD patients suggest that in mitochondria, structural changes caused by Abeta result in increased mitochondrial fragmentation, decreased mitochondrial fusion, mitochondrial dysfunction, and synaptic damage. This paper discusses the latest research on Abeta, mitochondria, age-dependent factors of AD in the brain, and synaptic damage in AD. This paper also briefly discusses potential mitochondrial therapeutics in the treatment of patients with AD.