Abnormal mitochondrial morphology in sporadic Parkinson's and Alzheimer's disease cybrid cell lines

The cybrid model of sporadic Parkinson's disease

Parkinson's disease (PD) is the eponym attached to the most prevalent neurodegenerative movement disorder of adults, derived from observations of an early nineteenth century physician and paleontologist, James Parkinson, and is now recognized to encompass much more than a movement disorder clinically or dopamine neuron death pathologically. Most PD ( approximately 90%) is sporadic (sPD), is associated with mitochondrial deficiencies and has been studied in cell and animal models arising from the use of mitochondrial toxins that unfortunately have not predicted clinical efficacy to slow disease progression in humans. We have extensively studied the cytoplasmic hybrid ("cybrid") model of sPD in which donor mtDNAs are introduced into and expressed in neural tumor cells with identical nuclear genetic and environmental backgrounds. sPD cybrids demonstrate many abnormalities in which increased oxidative stress drives downstream antioxidant response and cell death activating signaling pathways. sPD cybrids regulate mitochondrial ETC genes and gene ontology families like sPD brain. sPD cybrids spontaneously form Lewy bodies and Lewy neurites, linking mtDNA expression to neuropathology, and demonstrate impaired organelle transport in processes and reduced mitochondrial respiration. Our recent studies show that near-infrared laser light therapy normalizes mitochondrial movement and can stimulate respiration in sPD cybrid neurons, and mitochondrial gene therapy can restore respiration and stimulate mitochondrial ETC gene and protein expression. sPD cybrids have provided multiple lines of circumstantial evidence linking mtDNA to sPD pathogenesis and can serve as platforms for therapy development. sPD cybrid models can be improved by the use of non-tumor human stem cell-derived neural precursor cells and by an introduction of postmortem brain mtDNA to test its causality directly.

Reduced axonal transport in Parkinson's disease cybrid neurites is restored by light therapy

BACKGROUND

It has been hypothesized that reduced axonal transport contributes to the degeneration of neuronal processes in Parkinson's disease (PD). Mitochondria supply the adenosine triphosphate (ATP) needed to support axonal transport and contribute to many other cellular functions essential for the survival of neuronal cells. Furthermore, mitochondria in PD tissues are metabolically and functionally compromised. To address this hypothesis, we measured the velocity of mitochondrial movement in human transmitochondrial cybrid "cytoplasmic hybrid" neuronal cells bearing mitochondrial DNA from patients with sporadic PD and disease-free age-matched volunteer controls (CNT). The absorption of low level, near-infrared laser light by components of the mitochondrial electron transport chain (mtETC) enhances mitochondrial metabolism, stimulates oxidative phosphorylation and improves redox capacity. PD and CNT cybrid neuronal cells were exposed to near-infrared laser light to determine if the velocity of mitochondrial movement can be restored by low level light therapy (LLLT). Axonal transport of labeled mitochondria was documented by time lapse microscopy in dopaminergic PD and CNT cybrid neuronal cells before and after illumination with an 810 nm diode laser (50 mW/cm2) for 40 seconds. Oxygen utilization and assembly of mtETC complexes were also determined.

RESULTS

The velocity of mitochondrial movement in PD cybrid neuronal cells (0.175 +/- 0.005 SEM) was significantly reduced (p < 0.02) compared to mitochondrial movement in disease free CNT cybrid neuronal cells (0.232 +/- 0.017 SEM). For two hours after LLLT, the average velocity of mitochondrial movement in PD cybrid neurites was significantly (p < 0.003) increased (to 0.224 +/- 0.02 SEM) and restored to levels comparable to CNT. Mitochondrial movement in CNT cybrid neurites was unaltered by LLLT (0.232 +/- 0.017 SEM). Assembly of complexes in the mtETC was reduced and oxygen utilization was altered in PD cybrid neuronal cells. PD cybrid neuronal cell lines with the most dysfunctional mtETC assembly and oxygen utilization profiles were least responsive to LLLT.

CONCLUSION

The results from this study support our proposal that axonal transport is reduced in sporadic PD and that a single, brief treatment with near-infrared light can restore axonal transport to control levels. These results are the first demonstration that LLLT can increase axonal transport in model human dopaminergic neuronal cells and they suggest that LLLT could be developed as a novel treatment to improve neuronal function in patients with PD.

Loss of PINK1 function promotes mitophagy through effects on oxidative stress and mitochondrial fission

Mitochondrial dysregulation is strongly implicated in Parkinson disease. Mutations in PTEN-induced kinase 1 (PINK1) are associated with familial parkinsonism and neuropsychiatric disorders. Although overexpressed PINK1 is neuroprotective, less is known about neuronal responses to loss of PINK1 function. We found that stable knockdown of PINK1 induced mitochondrial fragmentation and autophagy in SH-SY5Y cells, which was reversed by the reintroduction of an RNA interference (RNAi)-resistant plasmid for PINK1. Moreover, stable or transient overexpression of wild-type PINK1 increased mitochondrial interconnectivity and suppressed toxin-induced autophagy/mitophagy. Mitochondrial oxidant production played an essential role in triggering mitochondrial fragmentation and autophagy in PINK1 shRNA lines. Autophagy/mitophagy served a protective role in limiting cell death, and overexpressing Parkin further enhanced this protective mitophagic response. The dominant negative Drp1 mutant inhibited both fission and mitophagy in PINK1-deficient cells. Interestingly, RNAi knockdown of autophagy proteins Atg7 and LC3/Atg8 also decreased mitochondrial fragmentation without affecting oxidative stress, suggesting active involvement of autophagy in morphologic remodeling of mitochondria for clearance. To summarize, loss of PINK1 function elicits oxidative stress and mitochondrial turnover coordinated by the autophagic and fission/fusion machineries. Furthermore, PINK1 and Parkin may cooperate through different mechanisms to maintain mitochondrial homeostasis.

The cell-type specificity of mitochondrial dynamics

Recent advances in mitochondrial imaging have revealed that in many cells mitochondria can be highly dynamic. They can undergo fission/fusion processes modulated by various mitochondria-associated proteins and also by conformational transitions in the inner mitochondrial membrane. Moreover, precise mitochondrial distribution can be achieved by their movement along the cytoskeleton, recruiting various connector and motor proteins. Such movement is evident in various cell types ranging from yeast to mammalian cells and serves to direct mitochondria to cellular regions of high ATP demand or to transport mitochondria destined for elimination. Existing data also demonstrate that many aspects of mitochondrial dynamics, morphology, regulation and intracellular organization can be cell type-/tissue-specific. In many cells like neurons, pancreatic cells, HL-1 cells, etc., complex dynamics of mitochondria include fission, fusion, small oscillatory movements of mitochondria, larger movements like filament extension, retraction, fast branching in the mitochondrial network and rapid long-distance intracellular translocation of single mitochondria. Alternatively, mitochondria can be rather fixed in other cells and tissues like adult cardiomyocytes or skeletal muscles with a very regular organelle organization between myofibrils, providing the bioenergetic basis for contraction. Adult cardiac cells show no displacement of mitochondria with only very small-amplitude rapid vibrations, demonstrating remarkable, cell type-dependent differences in the dynamics and spatial arrangement of mitochondria. These variations and the cell-type specificity of mitochondrial dynamics could be related to specific cellular functions and demands, also indicating a significant role of integrations of mitochondria with other intracellular systems like the cytoskeleton, nucleus and endoplasmic reticulum (ER).

The search for biomarkers in Parkinson's disease: a critical review

Parkinson's disease (PD) is a progressive neurodegenerative disorder that primarily presents with features of bradykinesia, rigidity and tremor, and has, as part of its core pathology, the degeneration of dopaminergic neurons in the substantia nigra pars compacta. There is a great need for the development of a reliable diagnostic tool to improve promptness of diagnosis, definition of disease subtypes, and to monitor disease progression and demonstrate treatment efficacy in the case of disease modifying therapies. Current biomarkers range from objective clinical tools, to neuroimaging, to 'wet' markers involving blood and cerebrospinal fluid. To date, all candidate biomarkers for PD have failed to be developed into a clinically useful tool. Ideally, a combination of sensitive markers will be needed, not only to predict the onset of PD, but also to help in subtype classification and to follow progression. Here, we critically review various PD biomarker studies.

Unregulated mitochondrial GSK3beta activity results in NADH: ubiquinone oxidoreductase deficiency

GSK3beta is prominent for its role in apoptosis signaling and has been shown to be involved in Parkinson's disease (PD) pathogenesis. The overall effects of GSK3beta activity on cell fate are well-established, but the effects of mitochondrial GSK3beta activity on mitochondrial function and cell fate are unknown. Here we selectively expressed constitutively active GSK3beta within the mitochondria and found that this enhanced the apoptosis signaling activated by the PD-mimetic NADH:ubiquinone oxidoreductase (complex I) inhibitors 1-methyl-4-phenylpyridinium ion (MPP+) and rotenone. Additionally, expression of GSK3beta in the mitochondria itself caused a significant decrease in complex I activity and ATP production. Increased mitochondrial a GSK3beta activity also increased reactive oxygen species production and perturbed the mitochondrial morphology. Conversely, chemical inhibitors of GSK3beta inhibited MPP+- and rotenone-induced apoptosis, and attenuated the mitochondrial GSK3beta-mediated impairment in complex I. These results indicate that unregulated mitochondrial GSK3beta activity can mimic some of the mitochondrial insufficiencies found in PD pathology.

Oxidative stress signaling in Alzheimer's disease

Multiple lines of evidence demonstrate that oxidative stress is an early event in Alzheimer's disease (AD), occurring prior to cytopathology, and therefore may play a key pathogenic role in AD. Oxidative stress not only temporally precedes the pathological lesions of the disease but also activates cell signaling pathways, which, in turn, contribute to lesion formation and, at the same time, provoke cellular responses such as compensatory upregulation of antioxidant enzymes found in vulnerable neurons in AD. In this review, we provide an overview of the evidence of oxidative stress and compensatory responses that occur in AD, particularly focused on potential sources of oxidative stress and the roles and mechanism of activation of stress-activated protein kinase pathways.

Declining brain glucose metabolism in normal individuals with a maternal history of Alzheimer disease

BACKGROUND

At cross-section, cognitively normal individuals (NL) with a maternal history of late-onset Alzheimer disease (AD) have reduced glucose metabolism (CMRglc) on FDG-PET in the same brain regions as patients with clinical AD as compared to those with a paternal and a negative family history (FH) of AD. This longitudinal FDG-PET study examines whether CMRglc reductions in NL subjects with a maternal history of AD are progressive.

METHODS

Seventy-five 50- to 82-year-old NL received 2-year follow-up clinical, neuropsychological, and FDG-PET examinations. These included 37 subjects with negative family history of AD (FH-), 9 with paternal (FHp), and 20 with maternal AD (FHm). Two subjects had parents with postmortem confirmed AD. Statistical parametric mapping was used to compare CMRglc across FH groups at baseline, follow-up, and longitudinally.

RESULTS

At both time points, the FH groups were comparable for demographic and neuropsychological characteristics. At baseline and at follow-up, FHm subjects showed CMRglc reductions in the parieto-temporal, posterior cingulate, and medial temporal cortices as compared to FH- and FHp (p < 0.001). Longitudinally, FHm had significant CMRglc declines in these regions, which were significantly greater than those in FH- and FHp (p < 0.05).

CONCLUSIONS

A maternal history of Alzheimer disease (AD) predisposes normal individuals to progressive CMRglc reductions in AD-vulnerable brain regions, which may be related to a higher risk for developing AD.

Estrogen actions on mitochondria--physiological and pathological implications

Estrogens are potent neuroprotective hormones and mitochondria are the site of cellular life-death decisions. As such, it is not surprising that we and others have shown that estrogens have remarkable effects on mitochondrial function. Herein we provide evidence for a primary effect of estrogens on mitochondrial function, achieved in part by the import of estrogen receptor beta (ERbeta) into the mitochondria where it mediates a number of estrogen actions on this vital organelle. ERbeta is imported into the mitochondria, through tethering to cytosolic chaperone protein and/or through direct interaction with mitochondrial import proteins. In the mitochondria, ERbeta can affect transcription of critical mitochondrial genes through the interaction with estrogen response elements (ERE) or through protein-protein interactions with mitochondrially imported transcription factors. The potent effects of estrogens on mitochondrial function, particularly during mitochondrial stress, argues for a role of estrogens in the treatment of mitochondrial defects in chronic neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD) and more acute conditions of mitochondrial compromise, like cerebral ischemia and traumatic brain injury.

Development of a stable, early stage unilateral model of Parkinson's disease in middle-aged rhesus monkeys

An important issue raised in testing new neuroprotective/restorative treatments for Parkinson's disease (PD) is the optimal stage in the disease process to initiate therapy. Current palliative treatments are effective in the early disease stages raising ethical concerns about substituting an experimental treatment for a proven therapy. Thus, we have endeavored to create a stable 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) nonhuman primate model of early PD. The new model was created by controlling for dose and route administration of MPTP (unilateral intracarotid infusion), and age of the animals (middleaged, 16-19 years old) in 27 female rhesus monkeys. All animals showed stable parkinsonian features lasting for up to 12-month as per behavioral evaluation. Compared with late-stage PD animals, postmortem analysis demonstrated that more dopaminergic neurons remained in the substantia nigra pars compacta, and more fibers were found in the striatum. In addition, tissue levels of striatal dopamine and its metabolites were also higher. Our results support that a milder but stable PD model can be produced in middle-aged rhesus monkeys.

Mitochondrial localization of alpha-synuclein protein in alpha-synuclein overexpressing cells

Alpha-synuclein (alpha-syn) is implicated in the pathogenesis of Parkinson's disease (PD). Mutations in alpha-syn gene or alpha-syn locus (SNCA) triplication are associated with mitochondrial abnormalities and early onset of familial PD. The goals of the present study were to examine whether alpha-syn is localized in the mitochondria of alpha-syn overexpressing cells (HEK-syn cells); and whether alpha-syn overexpression causes cells to be more vulnerable to mitochondrial toxin, rotenone. Western blotting and confocal microscopy techniques were employed to assess localization of alpha-syn in the mitochondria of HEK-293 cells that were stably transfected with human wild-type alpha-syn. The results demonstrated that the mitochondrial fractions that were isolated from HEK-syn cells showed the presence of alpha-syn, whereas, no alpha-syn was detected in the mitochondrial fractions of control HEK cells. The mitochondria of HEK-syn cells were found to be more susceptible to rotenone-induced toxicity when compared to control HEK cells. The intracellular ATP levels were significantly decreased in HEK-syn cells in response to sub toxic concentrations of rotenone. These results suggest that under overexpression conditions, alpha-syn may translocate to mitochondria and cause enhanced toxicity in response to sub toxic concentrations of mitochondrial toxins. This study has implications to the pathogenesis of familial PD where alpha-syn overexpression is mainly involved.

Dynamin-like protein 1 reduction underlies mitochondrial morphology and distribution abnormalities in fibroblasts from sporadic Alzheimer's disease patients

Mitochondrial function relies heavily on its morphology and distribution, alterations of which have been increasingly implicated in neurodegenerative diseases, such as Alzheimer's disease (AD). In this study, we found abnormal mitochondrial distribution characterized by elongated mitochondria that accumulated in perinuclear areas in 19.3% of sporadic AD (sAD) fibroblasts, which was in marked contrast to their normally even cytoplasmic distribution in the majority of human fibroblasts from normal subjects (>95%). Interestingly, levels of dynamin-like protein 1 (DLP1), a regulator of mitochondrial fission and distribution, were decreased significantly in sAD fibroblasts. To explore the potential role of DLP1 in mediating mitochondrial abnormalities in sAD fibroblasts, both the overexpression of a dominant negative DLP1 mutant and the reduced expression of DLP1 by miR RNAi in human fibroblasts from normal subjects significantly increased mitochondrial abnormalities. Moreover, overexpression of wild-type DLP1 in sAD fibroblasts rescued these mitochondrial abnormalities. Based on these data, we conclude that DLP1 reduction causes mitochondrial abnormalities in sAD fibroblasts. We further demonstrate that elevated oxidative stress and increased amyloid beta production are likely the potential pathogenic factors that cause DLP1 reduction and abnormal mitochondrial distribution in AD cells.

Chronic intraventricular administration of 1-methyl-4-phenylpyridinium as a progressive model of Parkinson's disease

Animal models of Parkinson's disease (PD) that more closely exhibit the chronic neuropathology seen in the human condition are needed in order to reveal processes involved with progressive neurodegeneration and for testing potential interventions for retarding dopamine (DA) neuronal loss. Here we describe the recently developed chronic rat model of PD in which 1-methyl-4-phenylpyridinium ion (MPP(+)) is infused chronically into the lateral cerebral ventricle. We review features of this model that include loss of nigral DA neurons, swollen and abnormal mitochondria, striatal inclusion-like bodies and microgliosis. Advantages as well as limitations of the model are addressed.

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.

Animal models of Parkinson's disease progression

Parkinson's disease (PD) is a progressive neurodegenerative disorder whose etiology is not understood. This disease occurs both sporadically and through inheritance of single genes, although the familial types are rare. Over the past decade or so, experimental and clinical data suggest that PD could be a multifactorial, neurodegenerative disease that involves strong interactions between the environment and genetic predisposition. Our understanding of the pathophysiology and motor deficits of the disease relies heavily on fundamental research on animal models and the last few years have seen an explosion of toxin-, inflammation-induced and genetically manipulated models. The insight gained from the use of such models has strongly advanced our understanding of the progression and stages of the disease. The models have also aided the development of novel therapies to improve symptomatic management, and they are critical for the development of neuroprotective strategies. This review critically evaluates these in vivo models and the roles they play in mimicking the progression of PD.

Mitochondria in cybrids containing mtDNA from persons with mitochondriopathies

The cytoplasmic hybrid (cybrid) technique allows investigators to express selected mitochondrial DNA (mtDNA) sequences against fixed nuclear DNA (nDNA) backgrounds. Cybrids have been used to study the effects of known mtDNA mutations on mitochondrial biochemistry, mtDNA-nDNA inter-species compatibility, and mtDNA integrity in persons without mtDNA mutations defined previously. This review discusses events leading up to creation of the cybrid technique, as well as data obtained via application of the cybrid strategies listed above. Although interpreting cybrid data requires awareness of technique limitations, valuable insights into mtDNA genotype-functional phenotype relationships are suggested.

Effects of beta-amyloid peptide and estrogen on platelet mitochondrial function of Sprague-Dawley rats

Beta-amyloid peptide (Abeta) peptides play a central role in the development of Alzheimer's disease. They are known to induce mitochondrial dysfunction and caspase activation, resulting in apoptosis of neuronal cells. In the present experiment, an Abeta-induced damage model of platelets was established to observe the effects of Abeta, estradiol benzoate (EB) and genistein on platelets and platelet mitochondria. It was found that after the addition of Abeta, platelet number, platelet mitochondrial membrane potential (DeltaPsim) and adenosine triphosphate (ATP) content were lowered while no protective effects of EB and genistein had been observed. The platelets could serve as a biomarker for detection of mitochondrial function and age related disease.

Maternal family history of Alzheimer's disease predisposes to reduced brain glucose metabolism

Having a parent affected with late-onset Alzheimer's disease (AD) is a risk factor for developing AD among cognitively normal subjects. We examined whether cognitively normal subjects with a parental family history of AD show cerebral metabolic rate of glucose (CMRglc) reductions consistent with AD as compared with those without a family history and whether there are parent gender effects. Forty-nine 50- to 80-year-old normal subjects were examined who received clinical, neuropsychological, and 2-[(18)F]fluoro-2-deoxy-d-glucose-positron emission tomography examinations, including 16 subjects with a maternal (FHm) and eight with a paternal (FHp) family history of AD and 25 with no family history (FH(-)). FH groups were comparable for demographic and neuropsychological measures. As compared with both FH(-) and FHp groups, FHm subjects showed CMRglc reductions in the same regions as clinically affected AD patients, involving the posterior cingulate cortex/precuneus, parietotemporal and frontal cortices, and medial temporal lobes (P < 0.05, corrected for multiple comparisons). These effects remained significant after accounting for possible risk factors for AD, including age, gender, education, apolipoprotein E genotype, and subjective memory complaints. No CMRglc differences were found between FHp and FH(-) subjects. This study shows a relationship between reduced CMRglc in AD-vulnerable brain regions and a maternal family history of AD in cognitively normal individuals.

Complex I specific increase in superoxide formation and respiration rate by PrP-null mouse brain mitochondria

An imbalance in free radical production and removal is considered by many to be an important factor in the etiology of many degenerative diseases. Since mitochondria are a major source of free radicals, we have examined mitochondrial free radical production in relation to oxidative phosphorylation in PrP-null mice. Quantitative electron paramagnetic resonance spectroscopy revealed up to a 70% increase in superoxide production from Complex I of submitochondrial particles prepared from PrP-null mice. This was accompanied by elevated respiratory capacity through Complex I without any discernible alteration in respiratory efficiency. These differences are associated with changes in superoxide dismutase levels and defects in mitochondrial morphology, confirming previously reported results. Our results demonstrate a clear difference in free radical production and oxygen consumption by mitochondrial Complex I between PrP-null mice and wild-type controls, pointing to Complex I as a potential target for pathological change, suggesting similarities between prion-related and other neurodegenerative diseases.

Mitochondrial cascade hypothesis of Alzheimer's disease: myth or reality?

Mitochondria are recognized to play a pivotal role in neuronal cell survival or death because they are regulators of both energy metabolism and apoptotic pathways. Morphologic, biochemical, and molecular genetic studies suggest that mitochondria might be a convergence point for neurodegeneration, including Alzheimer's disease (AD). The functions and properties of mitochondria might render subsets of selectively vulnerable neurons intrinsically susceptible to cellular aging and stress. However, the question, "Is mitochondrial dysfunction a necessary step in neurodegeneration?" is still unanswered. This review presents the ways in which malfunctioning mitochondria and oxidative stress might contribute to neuronal death in AD.

Mitochondrial mechanisms of estrogen neuroprotection

Oxidative stress, bioenergetic failure and mitochondrial dysfunction are all implicated in the etiology of neurodegenerative diseases such as Alzheimer's disease (AD). The mitochondrial involvement in neurodegenerative diseases reflects the regulatory role mitochondrial failure plays in both necrotic cell death and apoptosis. The potent feminizing hormone, 17 beta-estradiol (E2), is neuroprotective in a host of cell and animal models of stroke and neurodegenerative diseases. The discovery that 17alpha-estradiol, an isomer of E2, is equally as neuroprotective as E2 yet is >200-fold less active as a hormone, has permitted development of novel, more potent analogs where neuroprotection is independent of hormonal potency. Studies of structure-activity relationships and mitochondrial function have led to a mechanistic model in which these steroidal phenols intercalate into cell membranes where they block lipid peroxidation reactions, and are in turn recycled. Indeed, the parental estrogens and novel analogs stabilize mitochondria under Ca(2+) loading otherwise sufficient to collapse membrane potential. The neuroprotective and mitoprotective potencies for a series of estrogen analogs are significantly correlated, suggesting that these compounds prevent cell death in large measure by maintaining functionally intact mitochondria. This therapeutic strategy is germane not only to sudden mitochondrial failure in acute circumstances, such as during a stroke or myocardial infarction, but also to gradual mitochondrial dysfunction associated with chronic degenerative disorders such as AD.

Depletion of mitochondrial DNA by ethidium bromide treatment inhibits the proliferation and tumorigenesis of T47D human breast cancer cells

In order to investigate the role of mitochondrial DNA (mtDNA) in human breast cancer cell proliferation and apoptosis, a mtDNA-deficient cell line, T47D rho(0), was generated following a long-term exposure to ethidium bromide (EtBr). T47D rho(0) cells showed a marked decrease in mitochondrial membrane potential (DeltaPsi(m)). However, the apoptosis rate of T47D rho(0) cells was the same as that of their parental cells, suggesting that the change in DeltaPsi(m) was insufficient to induce cell death. Electromicroscopy revealed a profound alteration of mitochondrial morphology, which was consistent with the loss of mtDNA and the decrease in DeltaPsi(m). Disruption of mtDNA resulted in a slower proliferation rate in tissue culture and a reduction in anchorage-independent growth. An in vivo assay revealed a severe impairment of tumorigenicity in T47D rho(0) cells, indicating the biological relevance of in vitro studies. Taken together, our results suggest that the integrity of mtDNA plays a critical role in human breast cancer cell proliferation and tumorigenesis.

Mitochondria mass is low in mouse substantia nigra dopamine neurons: Implications for Parkinson's disease

In Parkinson's disease (PD) there is a selective loss of certain midbrain dopaminergic (DA) neurons. The most vulnerable neurons reside in the substantia nigra zona compacta (SNC), whereas the DA neurons in the ventral tegmental area (VTA) and interfascicular (IF) nucleus are less vulnerable to degeneration. Many sporadic PD patients have a defect in mitochondria respiration, and some of the genes that cause PD are mitochondrial-related (e.g., PINK1, Parkin, DJ1). The present study sought to determine whether mitochondria mass is different in SNC neurons compared to other midbrain DA neurons and to non-DA neurons in the mouse. At the electron microscopic level, mitochondria in the SN DA neurons occupy 40% less of the soma and dendritic area than in the SN non-DA neurons. The area occupied by mitochondria in the SN DA neurons is also lower than in the VTA neurons, although not different from the IF neurons. The red nucleus somata have the largest percentage of the somata occupied by mitochondria (12%). Mitochondria size is related to somata size; the largest mitochondria are found in the red nucleus neurons and the smallest mitochondria are found in the IF neurons. At the light microscopic level, SNC, VTA and IF DA neurons have <50% of the cytoplasm immunostained with the mitochondrial antibody 1D6, whereas non-DA neurons in the same midbrain regions contain mitochondria areas up to >65% of the cytoplasm area. These data indicate that mitochondria size and mass are not the same for all neurons, and the SNC DA neurons have relatively low mitochondria mass. The low mitochondria mass in SNC DA neurons may contribute to the selective vulnerability of these neurons in certain rodent models of PD.

Basal ganglia lesions after MPTP administration in rhesus monkeys

In monkeys, intracarotid infusion of a single low dose of MPTP reliably induces a hemiparkinsonian syndrome that is stable over time. This model has been widely used to assess novel anti-parkinsonian therapies. Here, we report the exceptional finding of severe necrotic lesions that were observed in the basal ganglia (but not in the substantia nigra) of monkeys that received a single intracarotid injection of MPTP followed by gene therapy treatments. Although extensive unilateral dopaminergic nigrostriatal loss was found in all the animals, partial behavioral recovery was observed in the subjects that presented pallidal necrotic lesions. This report discusses possible causes and effects of the necrotic lesions and their locations and the value of the intracarotid MPTP model. Testing novel therapies in monkey models has become an essential step before clinical trials. These results indicate that evaluation of any treatment should consider possible confounding factors that may affect the results.

Impaired platelet mitochondrial activity in Alzheimer's disease and mild cognitive impairment

Mitochondrial abnormalities are found in Alzheimer's disease (AD), but previous reports have not examined at-risk groups. In subjects with AD, mild cognitive impairment (MCI), and non-demented aged controls, platelet and lymphocyte mitochondria were isolated and analyzed for Complexes I, III, and IV of the electron transport chain. Western blots were used to control for differential enrichment of samples. Results demonstrated significant declines in Complexes III and IV in AD, and a significant decline in Complex IV in MCI. This report confirms mitochondrial deficiencies in AD, extends them to MCI, and suggests they are present at the earliest symptomatic stages of disease.

Genetic basis of Alzheimer's dementia: role of mtDNA mutations

Alzheimer's disease (AD) is the most common neurodegenerative disorder associated to dementia in late adulthood. Amyloid precursor protein, presenilin 1 and presenilin 2 genes have been identified as causative genes for familial AD, whereas apolipoprotein E epsilon4 allele has been associated to the risk for late onset AD. However, mutations on these genes do not explain the majority of cases. Mitochondrial respiratory chain (MRC) impairment has been detected in brain, muscle, fibroblasts and platelets of Alzheimer's patients, indicating a possible involvement of mitochondrial DNA (mtDNA) in the aetiology of the disease. Several reports have identified mtDNA mutations in Alzheimer's patients, suggesting the existence of related causal factors probably of mtDNA origin, thus pointing to the involvement of mtDNA in the risk contributing to dementia, but there is no consensual opinion in finding the cause for impairment. However, mtDNA mutations might modify age of onset, contributing to the neurodegenerative process, probably due to an impairment of MRC and/or translation mechanisms.

Cell and animal models of mtDNA biology: progress and prospects

The past two decades have witnessed an evolving understanding of the mitochondrial genome's (mtDNA) role in basic biology and disease. From the recognition that mutations in mtDNA can be responsible for human disease to recent efforts showing that mtDNA mutations accumulate over time and may be responsible for some phenotypes of aging, the field of mitochondrial genetics has greatly benefited from the creation of cell and animal models of mtDNA mutation. In this review, we critically discuss the past two decades of efforts and insights gained from cell and animal models of mtDNA mutation. We attempt to reconcile the varied and at times contradictory findings by highlighting the various methodologies employed and using human mtDNA disease as a guide to better understanding of cell and animal mtDNA models. We end with a discussion of scientific and therapeutic challenges and prospects for the future of mtDNA transfection and gene therapy.

Rat model of Parkinson's disease: Chronic central delivery of 1-methyl-4-phenylpyridinium (MPP+)

Mitochondrial dysfunction is observed in sporadic Parkinson's disease (PD) and may contribute to progressive neurodegeneration. While acute models of mitochondrial dysfunction have been used for many years to investigate PD, chronic models may better replicate the cellular disturbances caused by long-standing mitochondrial derangements and may represent a better model for neurotherapeutic testing. This study sought to develop a chronic model of PD that has the advantages of continuous low level toxin delivery, low mortality, unilateral damage to minimize aphagia and adipsia as well as minimal animal handling to reduce stress-related confounds. Infusion by osmotic minipump of the complex I toxin, 1-methyl-4-phenylpyridinium (MPP+), for 28 days into the left cerebral ventricle in rats caused a selective ipsilateral loss of nigral tyrosine hydroxylase immunoreactive somata (35% loss). In animals that were sacrificed 14 days after the chronic MPP+ administration, there was an even greater loss of nigral tyrosine hydroxylase cells (65% loss). Lewy-body-like structures that stained positive for ubiquitin and alpha-synuclein were found in striatal neurons near the infusion site but were not observed in nigral neurons. At the electron microscope level, however, swollen and abnormal mitochondria were observed in the nigral dopamine neurons, which may represent the early formation of an inclusion body. There were no animal deaths with the chronic treatment regimen that was utilized, and the magnitude of nigrostriatal neuronal loss was relatively consistent among the animals. This model of progressive neurodegeneration of nigrostriatal dopamine neurons may be useful for studying neuroprotective therapeutic agents for PD.

Novel mechanisms for estrogen-induced neuroprotection

Estrogens are gonadal steroid hormones that are present in the circulation of both males and females and that can no longer be considered within the strict confines of reproductive function. In fact, the bone, the cardiovascular system, and extrahypothalamic regions of the brain are now well-established targets of estrogens. Among the numerous aspects of brain function regulated by estrogens are their effects on mood, cognitive function, and neuronal viability. Here, we review the supporting evidence for estrogens as neuroprotective agents and summarize the various mechanisms that may be involved in this effect, focusing particularly on the mitochondria as an important target. On the basis of this evidence, we discuss the clinical applicability of estrogens in treating various age-related disorders, including Alzheimer disease and stroke, and identify the caveats that must be considered.

Melatonin in Alzheimer's disease and other neurodegenerative disorders

Increased oxidative stress and mitochondrial dysfunction have been identified as common pathophysiological phenomena associated with neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). As the age-related decline in the production of melatonin may contribute to increased levels of oxidative stress in the elderly, the role of this neuroprotective agent is attracting increasing attention. Melatonin has multiple actions as a regulator of antioxidant and prooxidant enzymes, radical scavenger and antagonist of mitochondrial radical formation. The ability of melatonin and its kynuramine metabolites to interact directly with the electron transport chain by increasing the electron flow and reducing electron leakage are unique features by which melatonin is able to increase the survival of neurons under enhanced oxidative stress. Moreover, antifibrillogenic actions have been demonstrated in vitro, also in the presence of profibrillogenic apoE4 or apoE3, and in vivo, in a transgenic mouse model. Amyloid-β toxicity is antagonized by melatonin and one of its kynuramine metabolites. Cytoskeletal disorganization and protein hyperphosphorylation, as induced in several cell-line models, have been attenuated by melatonin, effects comprising stress kinase downregulation and extending to neurotrophin expression. Various experimental models of AD, PD and HD indicate the usefulness of melatonin in antagonizing disease progression and/or mitigating some of the symptoms. Melatonin secretion has been found to be altered in AD and PD. Attempts to compensate for age- and disease-dependent melatonin deficiency have shown that administration of this compound can improve sleep efficiency in AD and PD and, to some extent, cognitive function in AD patients. Exogenous melatonin has also been reported to alleviate behavioral symptoms such as sundowning. Taken together, these findings suggest that melatonin, its analogues and kynuric metabolites may have potential value in prevention and treatment of AD and other neurodegenerative disorders.

Mitochondrial dysfunction in sporadic and genetic Alzheimer's disease

Increasing evidence suggests an important role of mitochondrial dysfunction in the pathogenesis of many common age-related neurodegenerative diseases, including Alzheimer's disease (AD). AD is the most common neurodegenerative disorder characterized by dementia, memory loss, neuronal apoptosis and eventually death of the affected individuals. AD is characterized by two pathologic hallmark lesions that consist of extracellular plaques of amyloid-beta peptides and intracellular neurofibrillary tangles composed of hyperphosphorylated microtubular protein tau. Even though the idea that amyloid beta peptide accumulation is the primary event in the pathogenesis of Alzheimer's disease has become the leading hypothesis, the causal link between aberrant amyloid precursor protein and tau alterations in this type of dementia remains controversial.

Does the mitochondrial genome play a role in the etiology of Alzheimer's disease?

We report here the analyses of complete mtDNA coding region sequences from more than 270 Alzheimer's disease (AD) patients and normal controls to determine if inherited mtDNA mutations contribute to the etiology of AD. The AD patients and normal individuals were carefully screened and drawn from two populations of European descent in an effort to avoid spurious effects due to local population anomalies. Overall, there were no significant haplogroup associations in the combined AD and normal control sequence sets. Reduced median network analysis revealed that the AD mtDNA sequences contained a higher number of substitutions in tRNA genes, and that there was an elevated frequency of replacement substitutions in the complex I genes of the control sequences. Analysis of the replacement substitutions indicated that those arising in the AD mtDNAs were no more deleterious, on average, than those in the control mtDNAs. The only evidence for the synergistic action of mutations was the presence of both a rare non-conservative replacement substitution and a tRNA mutation in 2 AD mtDNAs, from a total of 145, whereas such a combination of mutations was not observed in the control sequences. Overall, the results reported here indicate that pathogenic inherited mtDNA mutations do not constitute a major etiological factor in sporadic AD. At most, a small proportion of AD patients carry a pathogenic mtDNA mutation and a small proportion of cognitively normal aged individuals carry a mtDNA mutation that reduces the risk of AD.

Mitochondrial morphology and dynamics in yeast and multicellular eukaryotes

Mitochondria form dynamic tubular networks that continually change their shape and move throughout the cell. In eukaryotes, these organellar gymnastics are controlled by numerous pathways that preserve proper mitochondrial morphology and function. The best understood of these are the fusion and fission pathways, which rely on conserved GTPases and their binding partners to regulate organelle connectivity and copy number in healthy cells and during apoptosis. In budding yeast, mitochondrial shape is also maintained by proteins acting in the tubulation pathway. Novel proteins and pathways that control mitochondrial dynamics continue to be discovered, indicating that the mechanisms governing this organelle's behavior are more sophisticated than previously appreciated. Here we review recent advances in the field of mitochondrial dynamics and highlight the importance of these pathways to human health.

Upregulation of Matrix Metalloproteinase 1 and Disruption of Mitochondrial Network in Skin Fibroblasts of Patients with MERRF Syndrome

By using cDNA microarray and RT-PCR techniques, we investigated the genome-wide alteration of gene expression in skin fibroblasts from patients with myoclonic epilepsy and ragged-red fibers (MERRF) syndrome. By screening for the genes with altered levels of expression, we first discovered that matrix metalloproteinase 1 (MMP1) was highly induced in the primary culture of skin fibroblasts of a female patient in a four-generation family with MERRF syndrome. This phenomenon was confirmed in skin fibroblasts from three other MERRF patients harboring about 85% of mtDNA with A8344G mutation. A further study revealed that the expression of MMP1 could be further induced by treatment of the skin fibroblasts with 200 microM hydrogen peroxide (H2O2) and inhibited by 1 mM N-acetylcysteine. Moreover, the intracellular level of H2O2 in skin fibroblasts of the female MERRF patient was higher than those of the asymptomatic family members and age-matched healthy controls. These findings imply that the increase in the expression of MMP1 may represent one of the responses to the increased oxidative stress in the skin fibroblasts of MERRF patients. We suggest that in affected tissues the oxidative stress-elicited overexpression of MMP1, and probably other matrix metalloproteinases involved in cytoskeleton remodeling, may play an important role in the pathogenesis and progression of mitochondrial encephalomyopathies such as MERRF syndrome.

Lipid- and receptor-binding regions of apolipoprotein E4 fragments act in concert to cause mitochondrial dysfunction and neurotoxicity

Apolipoprotein (apo) E4, a 299-aa protein and a major risk factor for Alzheimer's disease, can be cleaved to generate C-terminal-truncated fragments that cause neurotoxicity in vitro and neurodegeneration and behavioral deficits in transgenic mice. To investigate this neurotoxicity, we expressed apoE4 with C- or N-terminal truncations or mutations in transfected Neuro-2a cells. ApoE4 (1-272) was neurotoxic, but full-length apoE4(1-299) and apoE4(1-240) were not, suggesting that the lipid-binding region (amino acids 241-272) mediates the neurotoxicity and that amino acids 273-299 are protective. A quadruple mutation in the lipid-binding region (I250A, F257A, W264R, and V269A) abolished the neurotoxicity of apoE4(1-272), and single mutations in the region of amino acids 273-299 (L279Q, K282A, or Q284A) made full-length apoE4 neurotoxic. Immunofluorescence staining showed that apoE4(1-272) formed filamentous inclusions containing phosphorylated tau in some cells and interacted with mitochondria in others, leading to mitochondrial dysfunction as determined by MitoTracker staining and flow cytometry. ApoE4(241-272) did not cause mitochondrial dysfunction or neurotoxicity, suggesting that the lipid-binding region alone is insufficient for neurotoxicity. Truncation of N-terminal sequences (amino acids 1-170) containing the receptor-binding region (amino acids 135-150) and triple mutations within that region (R142A, K146A, and R147A) abolished the mitochondrial interaction and neurotoxicity of apoE4(1-272). Further analysis showed that the receptor-binding region is required for escape from the secretory pathway and that the lipid-binding region mediates mitochondrial interaction. Thus, the lipid- and receptor-binding regions in apoE4 fragments act together to cause mitochondrial dysfunction and neurotoxicity, which may be important in Alzheimer's disease pathogenesis.

Gradual alteration of mitochondrial structure and function by beta-amyloids: importance of membrane viscosity changes, energy deprivation, reactive oxygen species production, and cytochrome c release

Intracellular amyloid beta-peptide (A beta) accumulation is considered to be a key pathogenic factor in sporadic Alzheimer's disease (AD), but the mechanisms by which it triggers neuronal dysfunction remain unclear. We hypothesized that gradual mitochondrial dysfunction could play a central role in both initiation and progression of sporadic AD. Thus, we analyzed changes in mitochondrial structure and function following direct exposure to increasing concentrations of A beta(1--42) and A beta(25--35) in order to look more closely at the relationships between mitochondrial membrane viscosity, ATP synthesis, ROS production, and cytochrome c release. Our results show the accumulation of monomeric A beta within rat brain and muscle mitochondria. Subsequently, we observed four different and additive modes of action of A beta, which were concentration dependent: (i) an increase in mitochondrial membrane viscosity with a concomitant decrease in ATP/O, (ii) respiratory chain complexes inhibition, (iii) a potentialization of ROS production, and (iv) cytochrome c release.

Differentiated Alzheimer's disease transmitochondrial cybrid cell lines exhibit reduced organelle movement

The axonal transport and function of organelles like mitochondria and lysosomes may be impaired and play an important role in the pathogenesis of Alzheimer's disease (AD). Unique cybrid cell lines that model AD pathology were created by fusing platelets containing mitochondria from age-matched AD and control volunteers with mitochondrial DNA-free SH-SY5Y human neuroblastoma cells. These cybrid lines were differentiated to form process-bearing neuronal cells. Mitochondria and lysosomes in the neurites of each cybrid line were fluorescently labeled to determine the kinetics of organelle movement. The mitochondria in AD cybrid neurites were elongate, whereas the mitochondria in control cybrid neurites were short and more punctate. The mean velocity of mitochondrial movement, as well as the percentage of moving mitochondria, was significantly reduced in AD cybrids. The velocity of lysosomal movement was also reduced in the processes of AD cybrid cells, suggesting that the axonal transport machinery may be compromised in cybrid cell lines that contain mitochondrial DNA derived from AD patients. Reduced mitochondrial and lysosomal movement in susceptible neurons may compromise function in metabolically demanding structures like synaptic terminals and participate in the terminal degeneration that is characteristic of AD.

Activation of p38 and N-acetylcysteine-sensitive c-Jun NH2-terminal kinase signaling cascades is required for induction of apoptosis in Parkinson's disease cybrids

Cytoplasmic hybrid cells (cybrids) are created by selective amplification of mitochondrial genes against constant nuclear genetic and environmental backgrounds. Cybrids from patients with sporadic Parkinson's disease (PD) recapitulate disease features such as decreased complex I activity, increased oxidative stress, elevated activation of NF-kappaB, and production of Lewy body inclusions. We examined the activation of signaling pathways and NF-kappaB in PD cybrids after exposure to MAPK inhibitors and/or the antioxidant N-acetylcysteine (NAC). Under basal replicating conditions, PD cybrids have decreased viability that is associated with increased DNA condensation and poly-ADP ribose polymerase (PARP) cleavage as well as elevated p38 and JNK activity. Pharmacological inhibition of oxidative stress diminished the elevated p38, JNK activity and PARP cleavage, and enhanced PD cybrid viability. PD mitochondrial genes expressed in cybrids stimulate pro-apoptotic cell signaling and biochemistry through oxidative stress. These results support development of antioxidative therapeutics for PD.

Endogenous oxidative stress in sporadic Alzheimer's disease neuronal cybrids reduces viability by increasing apoptosis through pro-death signaling pathways and is mimicked by oxidant exposure of control cybrids

Although oxidative stress and mitochondrial dysfunction have been linked to neurodegenerative diseases such as Alzheimer's disease (AD), it is not fully understood how mitochondrial oxidative stress may induce neuronal death. We used mitochondrial transgenic neuronal cell cybrid models of sporadic AD (SAD) to investigate the effects of endogenously generated reactive oxygen species (ROS) on viability and cell death mechanisms. Compared to control (CTL) cybrids, SAD cybrids have increased accumulation of oxidative stress markers and increased apoptosis that is blocked by N-acetylcysteine (NAC) and zVAD.fmk. SAD cybrids also have increased basal activation of the MAPKs, Akt, and NF-kappa B. NF-kappa B activation and cybrid viability are enhanced by NAC. Inhibiting the activity of the PI3K pathway or NF-kappa B aggravates neuronal death. Exposure of CTL cybrids to H2O2 decreased viability and activated in a NAC-sensitive manner, the same intracellular signaling pathways active under basal conditions in SAD cybrids.

Mitochondria in health and disease: perspectives on a new mitochondrial biology

The integrity of mitochondrial function is fundamental to cell life. It follows that disturbances of mitochondrial function will lead to disruption of cell function, expressed as disease or even death. In this review, I consider recent developments in our knowledge of basic aspects of mitochondrial biology as an essential step in developing our understanding of the contributions of mitochondria to disease. The identification of novel mechanisms that govern mitochondrial biogenesis and replication, and the delicately poised signalling pathways that coordinate the mitochondrial and nuclear genomes are discussed. As fluorescence imaging has made the study of mitochondrial function within cells accessible, the application of that technology to the exploration of mitochondrial bioenergetics is reviewed. Mitochondrial calcium uptake plays a major role in influencing cell signalling and in the regulation of mitochondrial function, while excessive mitochondrial calcium accumulation has been extensively implicated in disease. Mitochondria are major producers of free radical species, possibly also of nitric oxide, and are also major targets of oxidative damage. Mechanisms of mitochondrial radical generation, targets of oxidative injury and the potential role of uncoupling proteins as regulators of radical generation are discussed. The role of mitochondria in apoptotic and necrotic cell death is seminal and is briefly reviewed. This background leads to a discussion of ways in which these processes combine to cause illness in the neurodegenerative diseases and in cardiac reperfusion injury. The demands of mitochondria and their complex integration into cell biology extends far beyond the provision of ATP, prompting a radical change in our perception of mitochondria and placing these organelles centre stage in many aspects of cell biology and medicine.

Influence of a mitochondrial genetic defect on capacitative calcium entry and mitochondrial organization in the osteosarcoma cells

Effects of T8993G mutation in mitochondrial DNA (mtDNA), associated with neurogenical muscle weakness, ataxia and retinitis pigmentosa (NARP), on the cytoskeleton, mitochondrial network and calcium homeostasis in human osteosarcoma cells were investigated. In 98% NARP and rho(0) (lacking mtDNA) cells, the organization of the mitochondrial network and actin cytoskeleton was disturbed. Capacitative calcium entry (CCE) was practically independent of mitochondrial energy status in osteosarcoma cell lines. The significantly slower Ca(2+) influx rates observed in 98% NARP and rho(0), in comparison to parental cells, indicates that proper actin cytoskeletal organization is important for CCE in these cells.

A "mitochondrial cascade hypothesis" for sporadic Alzheimer's disease

Alzheimer's disease (AD) includes etiologically heterogeneous disorders characterized by senile or presenile dementia, extracellular amyloid protein aggregations containing an insoluble amyloid precursor protein derivative, and intracytoplasmic tau protein aggregations. Recent studies also show excess neuronal aneuploidy, programmed cell death (PCD), and mitochondrial dysfunction. The leading AD molecular paradigm, the "amyloid cascade hypothesis", is based on studies of rare autosomal dominant variants and does not specify what initiates the common late-onset, sporadic form. We propose for late-onset, sporadic AD a "mitochondrial cascade hypothesis" that comprehensively reconciles seemingly disparate histopathologic and pathophysiologic features. In our model, the inherited, gene-determined make-up of an individual's electron transport chain sets basal rates of reactive oxygen species (ROS) production, which determines the pace at which acquired mitochondrial damage accumulates. Oxidative mitochondrial DNA, RNA, lipid, and protein damage amplifies ROS production and triggers three events: (1) a reset response in which cells respond to elevated ROS by generating the beta-sheet protein, beta amyloid, which further perturbs mitochondrial function, (2) a removal response in which compromised cells are purged via PCD mechanisms, and (3) a replace response in which neuronal progenitors unsuccessfully attempt to re-enter the cell cycle, with resultant aneuploidy, tau phosphorylation, and neurofibrillary tangle formation. In addition to defining a role for aging in AD pathogenesis, the mitochondrial cascade hypothesis also allows and accounts for histopathologic overlap between the sporadic, late-onset and autosomal dominant, early onset forms of the disease.

The Importance of Dendritic Mitochondria in the Morphogenesis and Plasticity of Spines and Synapses

The proper intracellular distribution of mitochondria is assumed to be critical for normal physiology of neuronal cells, but direct evidence for this idea is lacking. Extension or movement of mitochondria into dendritic protrusions correlates with the development and morphological plasticity of spines. Molecular manipulations of dynamin-like GTPases Drp1 and OPA1 that reduce dendritic mitochondria content lead to loss of synapses and dendritic spines, whereas increasing dendritic mitochondrial content or mitochondrial activity enhances the number and plasticity of spines and synapses. Thus, the dendritic distribution of mitochondria is essential and limiting for the support of synapses. Reciprocally, synaptic activity modulates the motility and fusion/fission balance of mitochondria and controls mitochondrial distribution in dendrites.

High frequency of mitochondrial complex I mutations in Parkinson’s disease and aging

Idiopathic Parkinson's disease (PD) involves a systemic loss of activity of complex I of the mitochondrial electron transport chain. This biochemical lesion plays a key pathogenic role. Transfer of PD mitochondrial DNA recapitulates this loss of activity and several other pathogenic features of PD suggesting that this lesion may arise, at least in part, from mitochondrial DNA. We investigated this possibility by an extensive clonal sequencing of the seven mitochondrial genes encoding complex I subunits in PD and age-matched control frontal cortex. Each gene was completely sequenced an average of 94.4 times for each subject. Aminoacid-changing mutations were found at the frequency of 59.3 per million bases in both PD and controls, corresponding to approximately 32% of the mitochondrial genomes in the average sample having at least one mutation in a complex I gene. Individual low frequency mutations had an abundance of 1-10%. Significant interindividual variation in mutation frequency was observed. Several aminoacid-changing mutations were identified and multiple PD brains but not in controls. Genetic algorithm analysis detected areas in ND genes with a higher mutation frequency in PD that allowed differentiation of PD from controls. Total mutational burden due to low-abundance heteroplasmy is high and may play a role in human disease.

Oxidative Stress Level in Circulating Neutrophils Is Linked to Neurodegenerative Diseases

Alzheimer's and Parkinson's diseases are the most common neurodegenerative conditions. Oxidative lesions are a hallmark of both diseases, but the respective roles of systemic and cerebral dysfunction are not elucidated. As circulating neutrophils are the most powerful sources of reactive oxygen species, we measured oxidative stress levels in resting neutrophils from 44 Alzheimer's and Parkinson's disease patients and compared them to 40 healthy counterparts. Significantly increased oxidative stress levels were observed in patients' groups, while control groups had very similar levels irrespective of age. One-third of the neurodegenerative patients presented with oxidative stress levels higher than those of any healthy donor. This increase was not due to an elevated production of reactive oxygen species during the neutrophil oxidative burst. Mitochondrial mass and activity were altered in neutrophils of the Parkinsonian group compared to controls, but not in those from Alzheimer's disease group. To our knowledge, this is the first report linking oxidative stress and mitochondrial parameters in circulating neutrophils from neurodegenerative and normal donors. Our results indicate that oxidative stress levels in circulating neutrophils are of interest for further mechanistic studies of neurodegenerative diseases and might open the perspective of a diagnostic tool.

Redox imbalance

Substantial evidence implies that redox imbalance attributable to an overproduction of reactive oxygen species or reactive nitrogen species that overwhelm the protective defense mechanism of cells contributes to all forms of Parkinson's disease. Factors such as dopamine, neuromelanin, and transition metals may, under certain circumstances, contribute to the formation of oxygen species such as H(2)O(2), superoxide radicals, and hydroxyl radicals and react with reactive nitrogen species such as nitric oxide or peroxinitrite. Mitochodrial dysfunction and excitotoxicity may be a cause and a result of oxidative stress. Consequences of this redox imbalance are lipid peroxidation, oxidation of proteins, DNA damage, and interference of reactive oxygen species with signal transduction pathways. These consequences become even more harmful when genetic variations impair the normal degradation of altered proteins. Therefore, therapeutic strategies must aim at reducing free-radical formation and scavenging free-radicals.

Mitochondria dysfunction of Alzheimer's disease cybrids enhances Abeta toxicity

Alzheimer's disease (AD) brain reveals high rates of oxygen consumption and oxidative stress, altered antioxidant defences, increased oxidized polyunsaturated fatty acids, and elevated transition metal ions. Mitochondrial dysfunction in AD is perhaps relevant to these observations, as such may contribute to neurodegenerative cell death through the formation of reactive oxygen species (ROS) and the release of molecules that initiate programmed cell death pathways. In this study, we analyzed the effects of beta-amyloid peptide (Abeta) on human teratocarcinoma (NT2) cells expressing endogenous mitochondrial DNA (mtDNA), mtDNA from AD subjects (AD cybrids), and mtDNA from age-matched control subjects (control cybrids). In addition to finding reduced cytochrome oxidase activity, elevated ROS, and reduced ATP levels in the AD cybrids, when these cell lines were exposed to Abeta 1-40 we observed excessive mitochondrial membrane potential depolarization, increased cytoplasmic cytochrome c, and elevated caspase-3 activity. When exposed to Abeta, events associated with programmed cell death are activated in AD NT2 cybrids to a greater extent than they are in control cybrids or the native NT2 cell line, suggesting a role for mtDNA-derived mitochondrial dysfunction in AD degeneration.

Toxicity of amyloid beta peptide: tales of calcium, mitochondria, and oxidative stress

Alzheimer's disease (AD) is characterized by the accumulation of amyloid-beta (Abeta) peptides. Although the disease undoubtedly reflects the interaction of complex multifactorial processes, Abeta itself is toxic to neurons in vitro and the load of Abeta in vivo correlates well with the degree of cognitive impairment. There has therefore been considerable interest in the mechanism(s) of Abeta neurotoxicity. We here review the basic biology of Abeta processing and consider some of the major areas of focus of this research. It is clear that both AD and Abeta toxicity are characterized by oxidative stress, alterations in the activity of enzymes of intermediary metabolism, and mitochondrial dysfunction, especially impaired activity of cytochrome c oxidase. Studies in vitro also show alterations in cellular calcium signaling. We consider the mechanisms proposed to mediate cell injury and explore evidence to indicate which of these many changes in function are primary and which secondary.