Mitochondrial dysfunction in aging and Alzheimer's disease: strategies to protect neurons

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.

Mitochondrial DNA deletions and differential mitochondrial DNA content in Rhesus monkeys: implications for aging

The purpose of this study was to determine the relationship between mitochondrial DNA (mtDNA) deletions, mtDNA content and aging in rhesus monkeys. Using 2 sets of specific primers, we amplified an 8 kb mtDNA fragment covering a common 5.7 kb deletion and the entire 16.5 kb mitochondrial genome in the brain and buffy-coats of young and aged monkeys. We studied a total of 66 DNA samples: 39 were prepared from a buffy-coat and 27 were prepared from occipital cortex tissues. The mtDNA data were assessed using a permutation test to identify differences in mtDNA, in the different monkey groups. Using real-time RT-PCR strategy, we also assessed both mtDNA and nuclear DNA levels for young, aged and male and female monkeys. We found a 5.7 kb mtDNA deletion in 81.8% (54 of 66) of the total tested samples. In the young group of buffy-coat DNA, we found 5.7 kb deletions in 7 of 17 (41%), and in the aged group, we found 5.7 kb deletions in 12 of 22 (54%), suggesting that the prevalence of mtDNA deletions is related to age. We found decreased mRNA levels of mtDNA in aged monkeys relative to young monkeys. The increases in mtDNA deletions and mtDNA levels in aged rhesus monkeys suggest that damaged DNA accumulates as rhesus monkeys age and these altered mtDNA changes may have physiological relevance to compensate decreased mitochondrial function.

Tocopherols and tocotrienols plasma levels are associated with cognitive impairment

Vitamin E includes 8 natural compounds (4 tocopherols, 4 tocotrienols) with potential neuroprotective activity. α-Tocopherol has mainly been investigated in relation to cognitive impairment. We examined the relation of all plasma vitamin E forms and markers of vitamin E damage (α-tocopherylquinone, 5-nitro-γ-tocopherol) to mild cognitive impairment (MCI) and Alzheimer's disease (AD). Within the AddNeuroMed-Project, plasma tocopherols, tocotrienols, α-tocopherylquinone, and 5-nitro-γ-tocopherol were assessed in 168 AD cases, 166 MCI, and 187 cognitively normal (CN) people. Compared with cognitively normal subjects, AD and MCI had lower levels of total tocopherols, total tocotrienols, and total vitamin E. In multivariable-polytomous-logistic regression analysis, both MCI and AD cases had 85% lower odds to be in the highest tertile of total tocopherols and total vitamin E, and they were, respectively, 92% and 94% less likely to be in the highest tertile of total tocotrienols than the lowest tertile. Further, both disorders were associated with increased vitamin E damage. Low plasma tocopherols and tocotrienols levels are associated with increased odds of MCI and AD.

The abolishment of anesthesia-induced cognitive impairment by timely protection of mitochondria in the developing rat brain: the importance of free oxygen radicals and mitochondrial integrity

Early exposure to general anesthesia (GA) causes developmental neuroapoptosis in the mammalian brain and long-term cognitive impairment. Recent evidence suggests that GA also causes functional and morphological impairment of the immature neuronal mitochondria. Injured mitochondria could be a significant source of reactive oxygen species (ROS), which, if not scavenged in timely fashion, may cause excessive lipid peroxidation and damage of cellular membranes. We examined whether early exposure to GA results in ROS upregulation and whether mitochondrial protection and ROS scavenging prevent GA-induced pathomorphological and behavioral impairments. We exposed 7-day-old rats to GA with or without either EUK-134, a synthetic ROS scavenger, or R(+) pramipexole (PPX), a synthetic aminobenzothiazol derivative that restores mitochondrial integrity. We found that GA causes extensive ROS upregulation and lipid peroxidation, as well as mitochondrial injury and neuronal loss in the subiculum. As compared to rats given only GA, those also given PPX or EUK-134 had significantly downregulated lipid peroxidation, preserved mitochondrial integrity, and significantly less neuronal loss. The subiculum is highly intertwined with the hippocampal CA1 region, anterior thalamic nuclei, and both entorhinal and cingulate cortices; hence, it is important in cognitive development. We found that PPX or EUK-134 co-treatment completely prevented GA-induced cognitive impairment. Because mitochondria are vulnerable to GA-induced developmental neurotoxicity, they could be an important therapeutic target for adjuvant therapy aimed at improving the safety of commonly used GAs.

Mutant huntingtin, abnormal mitochondrial dynamics, defective axonal transport of mitochondria, and selective synaptic degeneration in Huntington's disease

Huntington's disease (HD) is a progressive, fatal neurodegenerative disease caused by expanded polyglutamine repeats in the HD gene. HD is characterized by chorea, seizures, involuntary movements, dystonia, cognitive decline, intellectual impairment and emotional disturbances. Research into mutant huntingtin (Htt) and mitochondria has found that mutant Htt interacts with the mitochondrial protein dynamin-related protein 1 (Drp1), enhances GTPase Drp1 enzymatic activity, and causes excessive mitochondrial fragmentation and abnormal distribution, leading to defective axonal transport of mitochondria and selective synaptic degeneration. This article summarizes latest developments in HD research and focuses on the role of abnormal mitochondrial dynamics and defective axonal transport in HD neurons. This article also discusses the therapeutic strategies that decrease mitochondrial fragmentation and neuronal damage in HD.

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.

Evaluation of respiratory chain activity in lymphocytes of patients with Alzheimer disease

Alzheimer disease (AD) is a progressive neurodegenerative disease associated with cognitive impairment in multiple domains, such as memory and executive functions. Studies reveal damage in the electron transport chain of patients with AD, suggesting that this mitochondrial dysfunction plays an important role in the pathophysiology of the disease. Blood samples were taken from patients with AD (n = 20) and older subjects without dementia (n = 40) to evaluate the activity of complexes I, II, II-III, and IV of the mitochondrial respiratory chain in isolated lymphocytes. Results from the patient and control groups were compared. The activity of complexes II and IV was increased among patients compared to the control group. No significant difference was observed between controls who were not using psychotropic medication and patients. Our findings point out a mechanism of cellular compensation in which the mitochondrial respiratory chain requires an increase in electron transport to supply the energy needed for cellular functioning. Additional studies are needed to better clarify the mechanisms involved in the mitochondrial dynamics of AD.

Blue native/SDS-PAGE combined with iTRAQ analysis reveals advanced glycation end-product-induced changes of synaptosome proteins in C57 BL/6 mice

Evidence shows that administration of high-level D-galactose induces the production of advanced glycation end-products (AGEs) that have been implicated in the development of diabetic complications such as neuropathy. The deterioration of learning and memory during neuropathy might be associated with the altered expression of proteins in synapse. To evaluate AGE-induced protein network alterations in synapse, blue native/SDS-PAGE and iTRAQ proteomic methods were used to screen for differentially expressed synaptic proteins of cerebral cortex in D-galactose-induced C57 BL/6 mice. In total, the expression level of 84 proteins is changed during AGE accumulation. The significantly differentially expressed proteins mainly participate in neurotransmission, energy metabolism and signal transduction pathway, suggesting that energy metabolism is damaged and neurotransmission is attenuated in synapse. The results of in vivo activities of malondialdehyde and superoxide dismutase suggested that AGE accumulation in the brain leads to the generation of reactive oxygen species. Therefore, elucidating the differentially expressed proteins underlying the AGE accumulation will open a new window to the mechanism of learning and memory impairments in neuropathy.

Neuron specific toxicity of oligomeric amyloid-β: role for JUN-kinase and oxidative stress

Recent studies have demonstrated a potential role for oligomeric forms of amyloid-β (Aβ) in the pathogenesis of Alzheimer's disease (AD), although it remains unclear which aspects of AD may be mediated by oligomeric Aβ. In the present study, we found that primary cultures of rat cortical neurons exhibit a dose-dependent increase in cell death following Aβ oligomer administration, while primary cultures of astrocytes exhibited no overt toxicity with even the highest concentrations of oligomer treatment. Neither cell type exhibited toxicity when treated by equal concentrations of monomeric Aβ. The neuron death induced by oligomer treatment was associated with an increase in reactive oxygen species (ROS), altered expression of mitochondrial fission and fusion proteins, and JUN kinase activation. Pharmacological inhibition of JUN kinase ameliorated oligomeric Aβ toxicity in neurons. These data indicate that oligomeric Aβ is sufficient to selectively induce toxicity in neurons, but not astrocytes, with neuron death occurring in a JUN kinase-dependent manner. Additionally, these observations implicate a role for oligomeric Aβ as a contributor to neuronal oxidative stress and mitochondrial disturbances in AD.

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.

Mitochondrial dysfunction - the beginning of the end in Alzheimer's disease? Separate and synergistic modes of tau and amyloid-β toxicity

The pathology of Alzheimer's disease (AD) is characterized by amyloid plaques (aggregates of amyloid-β (Aβ)) and neurofibrillary tangles (aggregates of tau) and is accompanied by mitochondrial dysfunction, but the mechanisms underlying this dysfunction are poorly understood. In this review, we discuss the critical role of mitochondria and the close inter-relationship of this organelle with the two main pathological features in the pathogenic process underlying AD. Moreover, we summarize evidence from AD post-mortem brain as well as cellular and animal AD models showing that Aβ and tau protein trigger 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. A vicious cycle as well as several vicious circles within the cycle, each accelerating the other, can be drawn, emphasizing the synergistic deterioration of mitochondria by tau and Aβ.

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.

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.

Redox regulation of mitochondrial fission, protein misfolding, synaptic damage, and neuronal cell death: potential implications for Alzheimer's and Parkinson's diseases

Normal mitochondrial dynamics consist of fission and fusion events giving rise to new mitochondria, a process termed mitochondrial biogenesis. However, several neurodegenerative disorders manifest aberrant mitochondrial dynamics, resulting in morphological abnormalities often associated with deficits in mitochondrial mobility and cell bioenergetics. Rarely, dysfunctional mitochondrial occur in a familial pattern due to genetic mutations, but much more commonly patients manifest sporadic forms of mitochondrial disability presumably related to a complex set of interactions of multiple genes (or their products) with environmental factors (G × E). Recent studies have shown that generation of excessive nitric oxide (NO), in part due to generation of oligomers of amyloid-β (Aβ) protein or overactivity of the NMDA-subtype of glutamate receptor, can augment mitochondrial fission, leading to frank fragmentation of the mitochondria. S-Nitrosylation, a covalent redox reaction of NO with specific protein thiol groups, represents one mechanism contributing to NO-induced mitochondrial fragmentation, bioenergetic failure, synaptic damage, and eventually neuronal apoptosis. Here, we summarize our evidence in Alzheimer’s disease (AD) patients and animal models showing that NO contributes to mitochondrial fragmentation via S-nitrosylation of dynamin-related protein 1 (Drp1), a protein involved in mitochondrial fission. These findings may provide a new target for drug development in AD. Additionally, we review emerging evidence that redox reactions triggered by excessive levels of NO can contribute to protein misfolding, the hallmark of a number of neurodegenerative disorders, including AD and Parkinson’s disease. For example, S-nitrosylation of parkin disrupts its E3 ubiquitin ligase activity, and thereby affects Lewy body formation and neuronal cell death.

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.

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.

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.

Alzheimer's proteins, oxidative stress, and mitochondrial dysfunction interplay in a neuronal model of Alzheimer's disease

In this paper, we discuss the interplay between beta-amyloid (Aβ) peptide, Tau fragments, oxidative stress, and mitochondria in the neuronal model of cerebellar granule neurons (CGNs) in which the molecular events reminiscent of AD are activated. The identification of the death route and the cause/effect relationships between the events leading to death could be helpful to manage the progression of apoptosis in neurodegeneration and to define antiapoptotic treatments acting on precocious steps of the death process. Mitochondrial dysfunction is among the earliest events linked to AD and might play a causative role in disease onset and progression. Recent studies on CGNs have shown that adenine nucleotide translocator (ANT) impairment, due to interaction with toxic N-ter Tau fragment, contributes in a significant manner to bioenergetic failure and mitochondrial dysfunction. These findings open a window for new therapeutic strategies aimed at preserving and/or improving mitochondrial function.

Brain mitochondrial dysfunction in aging, neurodegeneration, and Parkinson's disease

Brain senescence and neurodegeneration occur with a mitochondrial dysfunction characterized by impaired electron transfer and by oxidative damage. Brain mitochondria of old animals show decreased rates of electron transfer in complexes I and IV, decreased membrane potential, increased content of the oxidation products of phospholipids and proteins and increased size and fragility. This impairment, with complex I inactivation and oxidative damage, is named “complex I syndrome” and is recognized as characteristic of mammalian brain aging and of neurodegenerative diseases. Mitochondrial dysfunction is more marked in brain areas as rat hippocampus and frontal cortex, in human cortex in Parkinson's disease and dementia with Lewy bodies, and in substantia nigra in Parkinson's disease. The molecular mechanisms involved in complex I inactivation include the synergistic inactivations produced by ONOO− mediated reactions, by reactions with free radical intermediates of lipid peroxidation and by amine–aldehyde adduction reactions. The accumulation of oxidation products prompts the idea of antioxidant therapies. High doses of vitamin E produce a significant protection of complex I activity and mitochondrial function in rats and mice, and with improvement of neurological functions and increased median life span in mice. Mitochondria-targeted antioxidants, as the Skulachev cations covalently attached to vitamin E, ubiquinone and PBN and the SS tetrapeptides, are negatively charged and accumulate in mitochondria where they exert their antioxidant effects. Activation of the cellular mechanisms that regulate mitochondrial biogenesis is another potential therapeutic strategy, since the process generates organelles devoid of oxidation products and with full enzymatic activity and capacity for ATP production.

Mitochondrial base excision repair in mouse synaptosomes during normal aging and in a model of Alzheimer's disease

Brain aging is associated with synaptic decline and synaptic function is highly dependent on mitochondria. Increased levels of oxidative DNA base damage and accumulation of mitochondrial DNA (mtDNA) mutations or deletions lead to mitochondrial dysfunction, playing an important role in the aging process and the pathogenesis of several neurodegenerative diseases. Here we have investigated the repair of oxidative base damage, in synaptosomes of mouse brain during normal aging and in an AD model. During normal aging, a reduction in the base excision repair (BER) capacity was observed in the synaptosomal fraction, which was associated with a decrease in the level of BER proteins. However, we did not observe changes between the synaptosomal BER activities of presymptomatic and symptomatic AD mice harboring mutated amyolid precursor protein (APP), Tau, and presinilin-1 (PS1) (3xTgAD). Our findings suggest that the age-related reduction in BER capacity in the synaptosomal fraction might contribute to mitochondrial and synaptic dysfunction during aging. The development of AD-like pathology in the 3xTgAD mouse model was, however, not associated with deficiencies of the BER mechanisms in the synaptosomal fraction when the whole brain was analyzed.

Increasing measurement accuracy of age-related BOLD signal change: minimizing vascular contributions by resting-state-fluctuation-of-amplitude scaling

In this report we demonstrate a hemodynamic scaling method with resting-state fluctuation of amplitude (RSFA) in healthy adult younger and older subject groups. We show that RSFA correlated with breath hold (BH) responses throughout the brain in groups of younger and older subjects which RSFA and BH performed comparably in accounting for age-related hemodynamic coupling changes, and yielded more veridical estimates of age-related differences in task-related neural activity. BOLD data from younger and older adults performing motor and cognitive tasks were scaled using RSFA and BH related signal changes. Scaling with RSFA and BH reduced the skew of the BOLD response amplitude distribution in each subject and reduced mean BOLD amplitude and variability in both age groups. Statistically significant differences in intrasubject amplitude variation across regions of activated cortex, and intersubject amplitude variation in regions of activated cortex were observed between younger and older subject groups. Intra- and intersubject variability differences were mitigated after scaling. RSFA, though similar to BH in minimizing skew in the unscaled BOLD amplitude distribution, attenuated the neural activity-related BOLD amplitude significantly less than BH. The amplitude and spatial extent of group activation were lower in the older than in the younger group before and after scaling. After accounting for vascular variability differences through scaling, age-related decreases in activation volume were observed during the motor and cognitive tasks. The results suggest that RSFA-scaled data yield age-related neural activity differences during task performance with negligible effects from non-neural (i.e., vascular) sources.

Mitochondrial dysfunction: common final pathway in brain aging and Alzheimer's disease--therapeutic aspects

As a fully differentiated organ, our brain is very sensitive to cumulative oxidative damage of proteins, lipids, and DNA occurring during normal aging because of its high energy metabolism and the relative low activity of antioxidative defense mechanisms. As a major consequence, perturbations of energy metabolism including mitochondrial dysfunction, alterations of signaling mechanisms and of gene expression culminate in functional deficits. With the increasing average life span of humans, age-related cognitive disorders such as Alzheimer's disease (AD) are a major health concern in our society. Age-related mitochondrial dysfunction underlies most neurodegenerative diseases, where it is potentiated by disease-specific factors. AD is characterized by two major histopathological hallmarks, initially intracellular and with the progression of the disease extracellular accumulation of oligomeric and fibrillar beta-amyloid peptides and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein. In this review, we focus on findings in AD animal and cell models indicating that these histopathological alterations induce functional deficits of the respiratory chain complexes and therefore consecutively result in mitochondrial dysfunction and oxidative stress. These parameters lead synergistically with the alterations of the brain aging process to typical signs of neurodegeneration in the later state of the disease, including synaptic dysfunction, loss of synapses and neurites, and finally neuronal loss. We suggest that mitochondrial protection and subsequent reduction of oxidative stress are important targets for prevention and long-term treatment of early stages of AD.

S-nitrosylation of Drp1 links excessive mitochondrial fission to neuronal injury in neurodegeneration

Neurons are known to use large amounts of energy for their normal function and activity. In order to meet this demand, mitochondrial fission, fusion, and movement events (mitochondrial dynamics) control mitochondrial morphology, facilitating biogenesis and proper distribution of mitochondria within neurons. In contrast, dysfunction in mitochondrial dynamics results in reduced cell bioenergetics and thus contributes to neuronal injury and death in many neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease, and Huntington's disease. We recently reported that amyloid-beta peptide, thought to be a key mediator of AD pathogenesis, engenders S-nitrosylation and thus hyperactivation of the mitochondrial fission protein Drp1. This activation leads to excessive mitochondrial fragmentation, bioenergetic compromise, and synaptic damage in models of AD. Here, we provide an extended commentary on our findings of nitric oxide-mediated abnormal mitochondrial dynamics.

Selective neuronal vulnerability to oxidative stress in the brain

Oxidative stress (OS), caused by the imbalance between the generation and detoxification of reactive oxygen and nitrogen species (ROS/RNS), plays an important role in brain aging, neurodegenerative diseases, and other related adverse conditions, such as ischemia. While ROS/RNS serve as signaling molecules at physiological levels, an excessive amount of these molecules leads to oxidative modification and, therefore, dysfunction of proteins, nucleic acids, and lipids. The response of neurons to this pervasive stress, however, is not uniform in the brain. While many brain neurons can cope with a rise in OS, there are select populations of neurons in the brain that are vulnerable. Because of their selective vulnerability, these neurons are usually the first to exhibit functional decline and cell death during normal aging, or in age-associated neurodegenerative diseases, such as Alzheimer's disease. Understanding the molecular and cellular mechanisms of selective neuronal vulnerability (SNV) to OS is important in the development of future intervention approaches to protect such vulnerable neurons from the stresses of the aging process and the pathological states that lead to neurodegeneration. In this review, the currently known molecular and cellular factors that contribute to SNV to OS are summarized. Included among the major underlying factors are high intrinsic OS, high demand for ROS/RNS-based signaling, low ATP production, mitochondrial dysfunction, and high inflammatory response in vulnerable neurons. The contribution to the selective vulnerability of neurons to OS by other intrinsic or extrinsic factors, such as deficient DNA damage repair, low calcium-buffering capacity, and glutamate excitotoxicity, are also discussed.

Neuronal calcium signaling, mitochondrial dysfunction, and Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder among the aged worldwide. AD is characterized by extensive synaptic and neuronal loss that leads to impaired memory and cognitive decline. The cause of AD is not completely understood and no effective therapy has been developed. The accumulation of toxic amyloid-beta42 (Abeta42) peptide oligomers and aggregates in AD brain has been proposed to be primarily responsible for the pathology of the disease, an idea dubbed the 'amyloid hypothesis' of AD etiology. In addition to the increase in Abeta42 levels, disturbances in neuronal calcium (Ca2+) signaling and alterations in expression levels of Ca2+ signaling proteins have been observed in animal models of familial AD and in studies of postmortem brain samples from sporadic AD patients. Based on these data, the 'Ca2+ hypothesis of AD' has been proposed. In particular, familial AD has been linked with enhanced Ca2+ release from the endoplasmic reticulum and elevated cytosolic Ca2+ levels. The augmented cytosolic Ca2+ levels can trigger signaling cascades that affect synaptic stability and function and can be detrimental to neuronal health, such as activation of calcineurin and calpains. Here we review the latest results supporting the 'Ca2+ hypothesis' of AD pathogenesis. We further argue that over time, supranormal cytosolic Ca2+ signaling can impair mitochondrial function in AD neurons. We conclude that inhibitors and stabilizers of neuronal Ca2+ signaling and mitochondrial function may have therapeutic potential for AD treatment. We also discuss latest and planned AD therapeutic trials of agents targeting Ca2+ channels and mitochondria.

Altered brain mitochondrial metabolism in healthy aging as assessed by in vivo magnetic resonance spectroscopy

A decline in brain function is a characteristic feature of healthy aging; however, little is known about the biologic basis of this phenomenon. To determine whether there are alterations in brain mitochondrial metabolism associated with healthy aging, we combined (13)C/(1)H magnetic resonance spectroscopy with infusions of [1-(13)C]glucose and [2-(13)C]acetate to quantitatively characterize rates of neuronal and astroglial tricarboxylic acid cycles, as well as neuroglial glutamate-glutamine cycling, in healthy elderly and young volunteers. Compared with young subjects, neuronal mitochondrial metabolism and glutamate-glutamine cycle flux was approximately 30% lower in elderly subjects. The reduction in individual subjects correlated strongly with reductions in N-acetylaspartate and glutamate concentrations consistent with chronic reductions in brain mitochondrial function. In elderly subjects infused with [2-(13)C]acetate labeling of glutamine, C4 and C3 differed from that of the young subjects, indicating age-related changes in glial mitochondrial metabolism. Taken together, these studies show that healthy aging is associated with reduced neuronal mitochondrial metabolism and altered glial mitochondrial metabolism, which may in part be responsible for declines in brain function.

Effect of purple sweet potato anthocyanins on beta-amyloid-mediated PC-12 cells death by inhibition of oxidative stress

Amyloid-beta peptide (Abeta) is known to induce the redox imbalance, mitochondrial dysfunction and caspase activation, resulting in neuronal cell death. Treatment with antioxidants provided a new therapeutic strategy for Alzheimer's disease (AD) patients. Here we investigate the effects of purple sweet potato anthocyanins (PSPA), the known strong free radical scavengers, on Abeta toxicity in PC12 cells. The results showed that pretreatment of PC12 cells with PSPA reduced Abeta-induced toxicity, intracellular reactive oxygen species (ROS) generation and lipid peroxidation dose-dependently. In parallel, cell apoptosis triggered by Abeta characterized with the DNA fragmentation and caspase-3 activity were also inhibited by PSPA. The concentration of intracellular Ca(2+) and membrane potential loss associated with cell apoptosis were attenuated by PSPA. These results suggested that PSPA could protect the PC-12 cell from Abeta-induced injury through the inhibition of oxidative damage, intracellular calcium influx, mitochondria dysfunction and ultimately inhibition of cell apoptosis. The present study indicates that PSPA may be a promising approach for the treatment of AD and other oxidative-stress-related neurodegenerative diseases.

Role of mitochondria in neurodegenerative diseases: mitochondria as a therapeutic target in Alzheimer's disease

A growing body of evidence suggests that mitochondrial abnormalities are involved in aging and in age-related neurodegenerative diseases as well as cancer, diabetes, and several other diseases known to be affected by mitochondria. Causal factors for most age-related neurodegenerative diseases-including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis (ALS), and Friedrich ataxia (FRDA)-are largely unknown. Genetic defects are reported to cause a small number of neurodegenerative diseases, but cellular, molecular, and pathological mechanisms of disease progression and selective neuronal cell death are not understood fully in these diseases. However, based on several cellular, molecular, and animal model studies of Alzheimer's disease, Parkinson's disease, ALS, FRDA, cancer, and diabetes, aging may play a large role in cell death in these diseases. Age-dependent, mitochondrially-generated reactive oxygen species (ROS) have been identified as important factors responsible for disease progression and cell death, particularly in late-onset diseases, in which genetic mutations are not causal factors.

Amyloid beta, mitochondrial structural and functional dynamics in Alzheimer's disease

Mitochondria are the major source of energy for the normal functioning of brain cells. Increasing evidence suggests that the amyloid precursor protein (APP) and amyloid beta (Abeta) accumulate in mitochondrial membranes, cause mitochondrial structural and functional damage, and prevent neurons from functioning normally. Oligomeric Abeta is reported to induce intracellular Ca(2+) levels and to promote the excess accumulation of intracellular Ca(2+) into mitochondria, to induce the mitochondrial permeability transition pore to open, and to damage mitochondrial structure. Based on recent gene expression studies of APP transgenic mice and AD postmortem brains, and APP/Abeta and mitochondrial structural studies, we propose that the overexpression of APP and the increased production of Abeta may cause structural changes of mitochondria, including an increase in the production of defective mitochondria, a decrease in mitochondrial trafficking, and the alteration of mitochondrial dynamics in neurons affected by AD. This article discusses some critical issues of APP/Abeta associated with mitochondria, mitochondrial structural and functional damage, and abnormal intracellular calcium regulation in neurons from AD patients. This article also discusses the link between Abeta and impaired mitochondrial dynamics in AD.

Is multiple sclerosis a mitochondrial disease?

Multiple sclerosis (MS) is a relatively common and etiologically unknown disease with no cure. It is the leading cause of neurological disability in young adults, affecting over two million people worldwide. Traditionally, MS has been considered a chronic, inflammatory disorder of the central white matter in which ensuing demyelination results in physical disability. Recently, MS has become increasingly viewed as a neurodegenerative disorder in which axonal injury, neuronal loss, and atrophy of the central nervous system leads to permanent neurological and clinical disability. In this article, we discuss the latest developments on MS research, including etiology, pathology, genetic association, EAE animal models, mechanisms of neuronal injury and axonal transport, and therapeutics. In this article, we also focus on the mechanisms of mitochondrial dysfunction that are involved in MS, including mitochondrial DNA defects, and mitochondrial structural/functional changes.

The insulin-like growth factor family: molecular mechanisms, redox regulation, and clinical implications

Insulin-like growth factor (IGF)-induced signaling networks are vital in modulating multiple fundamental cellular processes, such as cell growth, survival, proliferation, and differentiation. Aberrations in the generation or action of IGF have been suggested to play an important role in several pathological conditions, including metabolic disorders, neurodegenerative diseases, and multiple types of cancer. Yet the exact mechanism involved in the pathogenesis of these diseases by IGFs remains obscure. Redox pathways involving reactive oxygen species (ROS) and reactive nitrogen species (RNS) contribute to the pathogenetic mechanism of various diseases by modifying key signaling pathways involved in cell growth, proliferation, survival, and apoptosis. Furthermore, ROS and RNS have been demonstrated to alter IGF production and/or action, and vice versa, and thereby have the ability to modulate cellular functions, leading to clinical manifestations of diseases. In this review, we provide an overview on the IGF system and discuss the potential role of IGF-1/IGF-1 receptor and redox pathways in the pathophysiology of several diseases.

Mitochondrial structural and functional dynamics in Huntington's disease

Huntington's disease (HD) is an autosomal, dominantly inherited neurodegenerative disorder, characterized by chorea, involuntary movements, and cognitive impairments. Tremendous progress has been made since the discovery of HD gene in 1993, in terms of developing animal models to study the disease process, unraveling the expression and function of wild-type and mutant huntingtin (Htt) proteins in the central and peripheral nervous systems, and understanding expanded CAG repeat containing mutant Htt protein interactions with CNS proteins in the disease process. HD progression has been found to involve several pathomechanisms, including expanded CAG repeat protein interaction with other CNS proteins, transcriptional dysregulation, calcium dyshomeostasis, abnormal vesicle trafficking, and defective mitochondrial bioenergetics. Recent studies have found that mutant Htt is associated with mitochondria and causes mitochondrial structural changes, decreases mitochondrial trafficking, and impairs mitochondrial dynamics in the neurons affected by HD. This article discusses recent developments in HD research, with a particular focus on intracellular and intramitochondrial calcium influx, mitochondrial DNA defects, and mitochondrial structural and functional abnormalities in HD development and progression. Further, this article outlines the current status of mitochondrial therapeutics with a special reference to Dimebon.

Methylthioninium chloride reverses cognitive deficits induced by scopolamine: comparison with rivastigmine

RATIONALE

The cholinergic system is involved in cognition as well as in age-related cognitive decline and Alzheimer disease (AD). Cholinergic enhancers ameliorate AD symptoms and represent the main current therapy for AD. MTC (Methylthioninium chloride), an antioxidant with metabolism-enhancing properties may be a novel candidate with pro-cognitive capacities.

OBJECTIVES

This study was performed: (1) to assess the pro-cognitive efficacy of MTC and establish its dose-response; (2) to compare the efficacy of MTC with rivastigmine and (3) to determine the potential for combination therapy by co-administration of MTC and rivastigmine.

METHODS

Spatial cognition of female NMRI mice was tested in a reference memory water maze task. Subjects received intra-peritoneal injections of scopolamine (0.5 mg/kg) followed by vehicle, and/or MTC and/or rivastigmine (0.15-4 mg/kg MTC; 0.1-0.5 mg/kg rivastigmine) in mono or combination treatment.

RESULTS

Scopolamine treatment prevented spatial learning in NMRI female mice and the deficit was reversed by both rivastigmine and MTC in a dose-dependent manner. Mono-therapy with high doses of rivastigmine (>0.5 mg/kg) caused severe side effects but MTC was safe up to 4 mg/kg. Co-administration of sub-effective doses of both drugs acted synergistically in reversing learning deficits and scopolamine-induced memory impairments.

CONCLUSIONS

In our model, MTC reversed the spatial learning impairment. When combined with the ChEI rivastigmine, the effect of MTC appeared to be amplified indicating that combination therapy could potentially improve not only symptoms but also contribute beneficially to neuronal metabolism by minimising side effects at lower doses.

Molecular mechanisms and clinical implications of reversible protein S-glutathionylation

Sulfhydryl chemistry plays a vital role in normal biology and in defense of cells against oxidants, free radicals, and electrophiles. Modification of critical cysteine residues is an important mechanism of signal transduction, and perturbation of thiol-disulfide homeostasis is an important consequence of many diseases. A prevalent form of cysteine modification is reversible formation of protein mixed disulfides (protein-SSG) with glutathione (GSH). The abundance of GSH in cells and the ready conversion of sulfenic acids and S-nitroso derivatives to S-glutathione mixed disulfides suggests that reversible S-glutathionylation may be a common feature of redox signal transduction and regulation of the activities of redox sensitive thiol-proteins. The glutaredoxin enzyme has served as a focal point and important tool for evolution of this regulatory mechanism, because it is a specific and efficient catalyst of protein-SSG deglutathionylation. However, mechanisms of control of intracellular Grx activity in response to various stimuli are not well understood, and delineation of specific mechanisms and enzyme(s) involved in formation of protein-SSG intermediates requires further attention. A large number of proteins have been identified as potentially regulated by reversible S-glutathionylation, but only a few studies have documented glutathionylation-dependent changes in activity of specific proteins in a physiological context. Oxidative stress is a hallmark of many diseases which may interrupt or divert normal redox signaling and perturb protein-thiol homeostasis. Examples involving changes in S-glutathionylation of specific proteins are discussed in the context of diabetes, cardiovascular and lung diseases, cancer, and neurodegenerative diseases.

Identification of STC1 as an beta-amyloid activated gene in human brain microvascular endothelial cells using cDNA microarray

To explore the molecular basis underlying beta-amyloid peptide (Abeta)-induced toxicity in the cerebrovasculature, we performed a cDNA microarray analysis to investigate the transcriptional profile induced by Abeta in human brain microvascular endothelial cells (HBMECs). This study identified 24 differentially expressed genes in HBMECs upon Abeta treatment. Among these genes, we found that the gene for a well-characterized calcium-regulating hormone, stanniocalcin-1 (STC1) was specifically up-regulated by Abeta treatment in a time and dose-dependent manner. Moreover, using overexpression and knock-down strategies, we found that overexpression of STC1 decreased transmigration of monocytes induced by Abeta and prevented Abeta-induced apoptosis of HBMECs. In addition, we explored the possible mechanisms underlying the effects of STC1, showing that overexpression of STC1 attenuated the effect of Abeta on up-regulating early growth response-1 (Egr-1), macrophage inflammatory protein-1beta (MIP-1beta), or cleaved caspase-8. Our data thus indicate a key role of STC1 in the response of HBMECs to Abeta exposure.

Dopaminergic midbrain neurons are the prime target for mitochondrial DNA deletions

Mitochondrial dysfunction is a consistent finding in neurodegenerative disorders like Alzheimer's (AD) or Parkinson's disease (PD) but also in normal human brain aging. In addition to respiratory chain defects, damage to mitochondrial DNA (mtDNA) has been repeatedly reported in brains from AD and PD patients. Most studies though failed to detect biologically significant point mutation or deletion levels in brain homogenate. By employing quantitative single cell techniques, we were recently able to show significantly high levels of mtDNA deletions in dopaminergic substantia nigra (SN) neurons from PD patients and age-matched controls. In the present study we used the same approach to quantify the levels of mtDNA deletions in single cells from three different brain regions (putamen, frontal cortex, SN) of patients with AD (n = 9) as compared to age-matched controls (n = 8). There were no significant differences between patients and controls in either region but in both groups the deletion load was markedly higher in dopaminergic SN neurons than in putamen or frontal cortex (p < 0.01; ANOVA). This data shows that there is a specific susceptibility of dopaminergic SN neurons to accumulate substantial amounts of mtDNA deletions, regardless of the underlying clinical phenotype.

Mitochondrial medicine for aging and neurodegenerative diseases

Mitochondria are key cytoplasmic organelles, responsible for generating cellular energy, regulating intracellular calcium levels, altering the reduction-oxidation potential of cells, and regulating cell death. Increasing evidence suggests that mitochondria play a central role in aging and in neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and Freidriech ataxia. Further, several lines of evidence suggest that mitochondrial dysfunction is an early event in most late-onset neurodegenerative diseases. Biochemical and animal model studies of inherited neurodegenerative diseases have revealed that mutant proteins of these diseases are associated with mitochondria. Mutant proteins are reported to block the transport of nuclear-encoded mitochondrial proteins to mitochondria, interact with mitochondrial proteins and disrupt the electron transport chain, induce free radicals, cause mitochondrial dysfunction, and, ultimately, damage neurons. This article discusses critical issues of mitochondria causing dysfunction in aging and neurodegenerative diseases, and discusses the potential of developing mitochondrial medicine, particularly mitochondrially targeted antioxidants, to treat aging and neurodegenerative diseases.

Amyloid beta, mitochondrial dysfunction and synaptic damage: implications for cognitive decline in aging and Alzheimer's disease

Recent studies of postmortem brains from Alzheimer's disease (AD) patients and transgenic mouse models of AD suggest that oxidative damage, induced by amyloid beta (Abeta), is associated with mitochondria early in AD progression. Abeta and amyloid-precursor protein 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. Furthermore, accumulation of Abeta at synaptic terminals might contribute to synaptic damage and cognitive decline in patients with AD. Here, we describe recent studies regarding the roles of Abeta and mitochondrial function in AD progression and particularly in synaptic damage and cognitive decline.