Decreased brain protein levels of cytochrome oxidase subunits in Alzheimer's disease and in hereditary spinocerebellar ataxia disorders: a nonspecific change?

Over-Representation of Torque Teno Mini Virus 9 in a Subgroup of Patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: A Pilot Study

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a chronic disorder classified by the WHO as postviral fatigue syndrome (ICD-11 8E49 code). Diagnosing ME/CFS, often overlapping with fibromyalgia (FM), is challenging due to nonspecific symptoms and lack of biomarkers. The etiology of ME/CFS and FM is poorly understood, but evidence suggests viral infections play a critical role. This study employs microarray technology to quantitate viral RNA levels in immune cells from ME/CFS, FM, or co-diagnosed cases, and healthy controls. The results show significant overexpression of the Torque Teno Mini Virus 9 (TTMV9) in a subgroup of ME/CFS patients which correlate with abnormal HERV and immunological profiles. Increased levels of TTMV9 transcripts accurately discriminate this subgroup of ME/CFS patients from the other study groups, showcasing its potential as biomarker for patient stratification and the need for further research into its role in the disease. Validation of the findings seems granted in extended cohorts by continuation studies.

COX6C expression driven by copy amplification of 8q22.2 regulates cell proliferation via mediation of mitosis by ROS-AMPK signaling in lung adenocarcinoma

Copy number variations (CNVs) play a vital role in regulating genes expression and tumorigenesis. We explored the copy number alterations in early-stage lung adenocarcinoma using high-throughput sequencing and nucleic acid flight mass spectrometry technology, and found that 8q22.1-22.2 is frequently amplified in lung adenocarcinoma tissues. COX6C localizes on the region and its expression is notably enhanced that driven by amplification in lung adenocarcinoma. Knockdown of COX6C significantly inhibits the cell proliferation, and induces S-G2/M cell cycle arrest, mitosis deficiency and apoptosis. Moreover, COX6C depletion causes a deficiency in mitochondrial fusion, and impairment of oxidative phosphorylation. Mechanistically, COX6C-induced mitochondrial deficiency stimulates ROS accumulation and activates AMPK pathway, then leading to abnormality in spindle formation and chromosome segregation, activating spindle assemble checkpoint, causing mitotic arrest, and ultimately inducing cell apoptosis. Collectively, we suggested that copy amplification-mediated COX6C upregulation might serves as a prospective biomarker for prognosis and targeting therapy in patients with lung adenocarcinoma.

Mitochondrial dysfunction in neurodegenerative disorders

Recent advances in understanding the role of mitochondrial dysfunction in neurodegenerative diseases have expanded the opportunities for neurotherapeutics targeting mitochondria to alleviate symptoms and slow disease progression. In this review, we offer a historical account of advances in mitochondrial biology and neurodegenerative disease. Additionally, we summarize current knowledge of the normal physiology of mitochondria and the pathogenesis of mitochondrial dysfunction, the role of mitochondrial dysfunction in neurodegenerative disease, current therapeutics and recent therapeutic advances, as well as future directions for neurotherapeutics targeting mitochondrial function. A focus is placed on reactive oxygen species and their role in the disruption of telomeres and their effects on the epigenome. The effects of mitochondrial dysfunction in the etiology and progression of Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson's disease, and Huntington's disease are discussed in depth. Current clinical trials for mitochondria-targeting neurotherapeutics are discussed.

Mitochondria-sequestered Aβ renders synaptic mitochondria vulnerable in the elderly with a risk of Alzheimer disease

Mitochondria are critical for neurophysiology, and mitochondrial dysfunction constitutes a characteristic pathology in both brain aging and Alzheimer disease (AD). Whether mitochondrial deficiency in brain aging and AD is mechanistically linked, however, remains controversial. We report a correlation between intrasynaptosomal amyloid β 42 (Aβ42) and synaptic mitochondrial bioenergetics inefficiency in both aging and amnestic mild cognitive impairment, a transitional stage between normal aging and AD. Experiments using a mouse model expressing nonmutant humanized Aβ (humanized Aβ-knockin [hAβ-KI] mice) confirmed the association of increased intramitochondrial sequestration of Aβ42 with exacerbated synaptic mitochondrial dysfunction in an aging factor- and AD risk-bearing context. Also, in comparison with global cerebral Aβ, intramitochondrial Aβ was relatively preserved from activated microglial phagocytosis in aged hAβ-KI mice. The most parsimonious interpretation of our results is that aging-related mitochondrial Aβ sequestration renders synaptic mitochondrial dysfunction in the transitional stage between normal aging and AD. Mitochondrial dysfunction in both brain aging and the prodromal stage of AD may follow a continuous transition in response to escalated intraneuronal, especially intramitochondrial Aβ, accumulation. Moreover, our findings further implicate a pivotal role of mitochondria in harboring early amyloidosis during the conversion from normal to pathological aging.

The Novel Role of Mitochondrial Citrate Synthase and Citrate in the Pathophysiology of Alzheimer's Disease

Citrate synthase is a key mitochondrial enzyme that utilizes acetyl-CoA and oxaloacetate to form citrate in the mitochondrial membrane, which participates in energy production in the TCA cycle and linked to the electron transport chain. Citrate transports through a citrate malate pump and synthesizes acetyl-CoA and acetylcholine (ACh) in neuronal cytoplasm. In a mature brain, acetyl-CoA is mainly utilized for ACh synthesis and is responsible for memory and cognition. Studies have shown low citrate synthase in different regions of brain in Alzheimer's disease (AD) patients, which reduces mitochondrial citrate, cellular bioenergetics, neurocytoplasmic citrate, acetyl-CoA, and ACh synthesis. Reduced citrate mediated low energy favors amyloid-β (Aβ) aggregation. Citrate inhibits Aβ25-35 and Aβ1-40 aggregation in vitro. Hence, citrate can be a better therapeutic option for AD by improving cellular energy and ACh synthesis, and inhibiting Aβ aggregation, which prevents tau hyperphosphorylation and glycogen synthase kinase-3 beta. Therefore, we need clinical studies if citrate reverses Aβ deposition by balancing mitochondrial energy pathway and neurocytoplasmic ACh production. Furthermore, in AD's silent phase pathophysiology, when neuronal cells are highly active, they shift ATP utilization from oxidative phosphorylation to glycolysis and prevent excessive generation of hydrogen peroxide and reactive oxygen species (oxidative stress) as neuroprotective action, which upregulates glucose transporter-3 (GLUT3) and pyruvate dehydrogenase kinase-3 (PDK3). PDK3 inhibits pyruvate dehydrogenase, which decreases mitochondrial-acetyl-CoA, citrate, and cellular bioenergetics, and decreases neurocytoplasmic citrate, acetyl-CoA, and ACh formation, thus initiating AD pathophysiology. Therefore, GLUT3 and PDK3 can be biomarkers for silent phase of AD.

Artificial neural network applied to fragile X-associated tremor/ataxia syndrome stage diagnosis based on peripheral mitochondrial bioenergetics and brain imaging outcomes

No proven prognosis is available for the neurodegenerative disorder fragile X-associated tremor/ataxia syndrome (FXTAS). Artificial neural network analyses (ANN) were used to predict FXTAS progression using data from 127 adults (noncarriers and FMR1 premutation carriers with and without FXTAS) with five outcomes from brain MRI imaging and 22 peripheral bioenergetic outcomes from two cell types. Diagnosis accuracy by ANN predictions ranged from 41.7 to 86.3% (depending on the algorithm used), and those misclassified usually presented a higher FXTAS stage. ANN prediction of FXTAS stages was based on a combination of two imaging findings (white matter hyperintensity and whole-brain volumes adjusted for intracranial volume) and four bioenergetic outcomes. Those at Stage 3 vs. 0-2 showed lower mitochondrial mass, higher oxidative stress, and an altered electron transfer consistent with mitochondrial unfolded protein response activation. Those at Stages 4-5 vs. 3 had higher oxidative stress and glycerol-3-phosphate-linked ATP production, suggesting that targeting mGPDH activity may prevent a worse prognosis. This was confirmed by the bioenergetic improvement of inhibiting mGPDH with metformin in affected fibroblasts. ANN supports the prospect of an unbiased molecular definition in diagnosing FXTAS stages while identifying potential targets for personalized medicine.

Early Changes in Transcriptomic Profiles in Synaptodendrosomes Reveal Aberrant Synaptic Functions in Alzheimer’s Disease

Alzheimer’s disease (AD) is one of the most prevalent neurodegenerative disorders characterized by the progressive decline of cognitive functions, and is closely associated with the dysfunction of synapses, which comprise the basic structure that mediates the communication between neurons. Although the protein architecture and machinery for protein translation at synapses are extensively studied, the impact that local changes in the mRNA reservoir have on AD progression is largely unknown. Here, we investigated the changes in transcriptomic profiles in the synaptodendrosomes purified from the cortices of AD mice at ages 3 and 6 months, a stage when early signatures of synaptic dysfunction are revealed. The transcriptomic profiles of synaptodendrosomes showed a greater number of localized differentially expressed genes (DEGs) in 6-month-old AD mice compared with mice 3 months of age. Gene Ontology (GO) analysis showed that these DEGs are majorly enriched in mitochondrial biogenesis and metabolic activity. More specifically, we further identified three representative DEGs in mitochondrial and metabolic pathways—Prnp, Cst3, and Cox6c—that regulate the dendritic spine density and morphology in neurons. Taken together, this study provides insights into the transcriptomic changes in synaptodendrosomes during AD progression, which may facilitate the development of intervention strategies targeting local translation to ameliorate the pathological progression of AD.

Novel role of COX6c in the regulation of oxidative phosphorylation and diseases

Cytochrome c oxidase subunit VIc (COX6c) is one of the most important subunits of the terminal enzyme of the respiratory chain in mitochondria. Numerous studies have demonstrated that COX6c plays a critical role in the regulation of oxidative phosphorylation (OXPHOS) and energy production. The release of COX6c from the mitochondria may be a hallmark of the intrinsic apoptosis pathway. Moreover, The changes in COX6c expression are widespread in a variety of diseases and can be chosen as a potential biomarker for diagnosis and treatment. In light of its exclusive effects, we present the elaborate roles that COX6c plays in various diseases. In this review, we first introduced basic knowledge regarding COX6c and its functions in the OXPHOS and apoptosis pathways. Subsequently, we described the regulation of COX6c expression and activity in both positive and negative ways. Furthermore, we summarized the elaborate roles that COX6c plays in various diseases, including cardiovascular disease, kidney disease, brain injury, skeletal muscle injury, and tumors. This review highlights recent advances and provides a comprehensive summary of COX6c in the regulation of OXPHOS in multiple diseases and may be helpful for drug design and the prediction, diagnosis, treatment, and prognosis of diseases.

Activation of the Mitochondrial Unfolded Protein Response: A New Therapeutic Target?

Mitochondrial dysfunction is a key hub that is common to many diseases. Mitochondria's role in energy production, calcium homeostasis, and ROS balance makes them essential for cell survival and fitness. However, there are no effective treatments for most mitochondrial and related diseases to this day. Therefore, new therapeutic approaches, such as activation of the mitochondrial unfolded protein response (UPRmt), are being examined. UPRmt englobes several compensation processes related to proteostasis and antioxidant mechanisms. UPRmt activation, through an hormetic response, promotes cell homeostasis and improves lifespan and disease conditions in biological models of neurodegenerative diseases, cardiopathies, and mitochondrial diseases. Although UPRmt activation is a promising therapeutic option for many conditions, its overactivation could lead to non-desired side effects, such as increased heteroplasmy of mitochondrial DNA mutations or cancer progression in oncologic patients. In this review, we present the most recent UPRmt activation therapeutic strategies, UPRmt's role in diseases, and its possible negative consequences in particular pathological conditions.

Effects of Mild Excitotoxic Stimulus on Mitochondria Ca2+ Handling in Hippocampal Cultures of a Mouse Model of Alzheimer's Disease

In Alzheimer’s disease (AD), the molecular mechanisms involved in the neurodegeneration are still incompletely defined, though this aspect is crucial for a better understanding of the malady and for devising effective therapies. Mitochondrial dysfunctions and altered Ca²⁺ signaling have long been implicated in AD, though it is debated whether these events occur early in the course of the pathology, or whether they develop at late stages of the disease and represent consequences of different alterations. Mitochondria are central to many aspects of cellular metabolism providing energy, lipids, reactive oxygen species, signaling molecules for cellular quality control, and actively shaping intracellular Ca²⁺ signaling, modulating the intensity and duration of the signal itself. Abnormalities in the ability of mitochondria to take up and subsequently release Ca²⁺ could lead to changes in the metabolism of the organelle, and of the cell as a whole, that eventually result in cell death. We sought to investigate the role of mitochondria and Ca²⁺ signaling in a model of Familial Alzheimer’s disease and found early alterations in mitochondria physiology under stressful condition, namely, reduced maximal respiration, decreased ability to sustain membrane potential, and a slower return to basal matrix Ca²⁺ levels after a mild excitotoxic stimulus. Treatment with an inhibitor of the permeability transition pore attenuated some of these mitochondrial disfunctions and may represent a promising tool to ameliorate mitochondria and cellular functioning in AD and prevent or slow down cell loss in the disease.

Mitochondrial Disorders in Alzheimer's Disease

Alzheimer's disease is the most common age-related neurodegenerative disease. Understanding of its etiology and pathogenesis is constantly expanding. Thus, the increasing attention of researchers is directed to the study of the role of mitochondrial disorders. In addition, in recent years, the concept of Alzheimer's disease as a stress-induced disease has begun to form more and more actively. The stress-induced damage to the neuronal system can trigger a vicious circle of pathological processes, among which mitochondrial dysfunctions have a significant place, since mitochondria represent a substantial component in the anti-stress activity of the cell. The study of mitochondrial disorders in Alzheimer's disease is relevant for at least two reasons: first, as important pathogenetic component in this disease; second, due to vital role of mitochondria in formation of the body resistance to various conditions, including stressful ones, throughout the life. This literature review analyzes the results of a number of recent studies assessing potential significance of the mitochondrial disorders in Alzheimer's disease. The probable mechanisms of mitochondrial disorders associated with the development of this disease are considered: bioenergetic dysfunctions, changes in mitochondrial DNA (including assessment of the significance of its haplogroup features), disorders in the dynamics of these organelles, oxidative damage to calcium channels, damage to MAM complexes (membranes associated with mitochondria; mitochondria-associated membranes), disruptions of the mitochondrial quality control system, mitochondrial permeability, etc. The issues of the "primary" or "secondary" mitochondrial damage in Alzheimer's disease are discussed. Potentials for the development of new methods for diagnosis and therapy of mitochondrial disorders in Alzheimer's disease are considered.

Mitochondria in Alzheimer's disease and their potential role in Alzheimer's proteostasis

Alzheimer's disease (AD) is a progressive brain disorder characterized by memory loss and the accumulation of two insoluble protein aggregates, tau neurofibrillary tangles and beta-amyloid plaques. Widespread mitochondrial dysfunction also occurs and mitochondria from AD patients display changes in number, ultrastructure, and enzyme activities. Mitochondrial dysfunction in AD presumably links in some way to its other disease characteristics, either as a cause or consequence. This review characterizes AD-associated mitochondrial perturbations and considers their position in its pathologic hierarchy. It focuses on the crosstalk that occurs between mitochondria, nuclear gene expression, and cytosolic signaling pathways that serves to maintain cell homeostasis. To this point, recent evidence indicates mitochondria trigger retrograde responses that influence cell proteostasis in general and AD proteostasis specifically. Potentially pertinent retrograde responses include the mitochondrial unfolded protein response (mtUPR), integrated stress response (ISR), autophagy/mitophagy, and proteasome function. A fuller perspective of mitochondrial dysfunction in AD, and its relation to protein aggregation, could enhance our overall understanding of this disease.

Transitions in metabolic and immune systems from pre-menopause to post-menopause: implications for age-associated neurodegenerative diseases

The brain undergoes two aging programs: chronological and endocrinological. This is particularly evident in the female brain, which undergoes programs of aging associated with reproductive competency. Comprehensive understanding of the dynamic metabolic and neuroinflammatory aging process in the female brain can illuminate windows of opportunities to promote healthy brain aging. Bioenergetic crisis and chronic low-grade inflammation are hallmarks of brain aging and menopause and have been implicated as a unifying factor causally connecting genetic risk factors for Alzheimer's disease and other neurodegenerative diseases. In this review, we discuss metabolic phenotypes of pre-menopausal, peri-menopausal, and post-menopausal aging and their consequent impact on the neuroinflammatory profile during each transition state. A critical aspect of the aging process is the dynamic metabolic neuro-inflammatory profiles that emerge during chronological and endocrinological aging. These dynamic systems of biology are relevant to multiple age-associated neurodegenerative diseases and provide a therapeutic framework for prevention and delay of neurodegenerative diseases of aging. While these findings are based on investigations of the female brain, they have a broader fundamental systems of biology strategy for investigating the aging male brain. Molecular characterization of alterations in fuel utilization and neuroinflammatory mechanisms during these neuro-endocrine transition states can inform therapeutic strategies to mitigate the risk of Alzheimer's disease in women. We further discuss a precision hormone replacement therapy approach to target symptom profiles during endocrine and chronological aging to reduce risk for age-related neurodegenerative diseases.

Evidence in support of chromosomal sex influencing plasma based metabolome vs APOE genotype influencing brain metabolome profile in humanized APOE male and female mice

Late onset Alzheimer’s disease (LOAD) is a progressive neurodegenerative disease with four well-established risk factors: age, APOE4 genotype, female chromosomal sex, and maternal history of AD. Each risk factor impacts multiple systems, making LOAD a complex systems biology challenge. To investigate interactions between LOAD risk factors, we performed multiple scale analyses, including metabolomics, transcriptomics, brain magnetic resonance imaging (MRI), and beta-amyloid assessment, in 16 months old male and female mice with humanized human APOE3 (hAPOE3) or APOE4 (hAPOE4) genes. Metabolomic analyses indicated a sex difference in plasma profile whereas APOE genotype determined brain metabolic profile. Consistent with the brain metabolome, gene and pathway-based RNA-Seq analyses of the hippocampus indicated increased expression of fatty acid/lipid metabolism related genes and pathways in both hAPOE4 males and females. Further, female transcription of fatty acid and amino acids pathways were significantly different from males. MRI based imaging analyses indicated that in multiple white matter tracts, hAPOE4 males and females exhibited lower fractional anisotropy than their hAPOE3 counterparts, suggesting a lower level of white matter integrity in hAPOE4 mice. Consistent with the brain metabolomic and transcriptomic profile of hAPOE4 carriers, beta-amyloid generation was detectable in 16-month-old male and female brains. These data provide therapeutic targets based on chromosomal sex and APOE genotype. Collectively, these data provide a framework for developing precision medicine interventions during the prodromal phase of LOAD, when the potential to reverse, prevent and delay LOAD progression is greatest.

Brain pyrimidine nucleotide synthesis and Alzheimer disease

Many patients suffering late-onset Alzheimer disease show a deficit in respiratory complex IV activity. The de novo pyrimidine biosynthesis pathway connects with the mitochondrial respiratory chain upstream from respiratory complex IV. We hypothesized that these patients would have decreased pyrimidine nucleotide levels. Then, different cell processes for which these compounds are essential, such as neuronal membrane generation and maintenance and synapses production, would be compromised. Using a cell model, we show that inhibiting oxidative phosphorylation function reduces neuronal differentiation. Linking these processes to pyrimidine nucleotides, uridine treatment recovers neuronal differentiation. To unmask the importance of these pathways in Alzheimer disease, we firstly confirm the existence of the de novo pyrimidine biosynthesis pathway in adult human brain. Then, we report altered mRNA levels for genes from both de novo pyrimidine biosynthesis and pyrimidine salvage pathways in brain from patients with Alzheimer disease. Thus, uridine supplementation might be used as a therapy for those Alzheimer disease patients with low respiratory complex IV activity.

Multivariate meta-analyses of mitochondrial complex I and IV in major depressive disorder, bipolar disorder, schizophrenia, Alzheimer disease, and Parkinson disease

Complex I (NADH dehydrogenase, NDU) and complex IV (cytochrome-c-oxidase, COX) of the mitochondrial electron transport chain have been implicated in the pathophysiology of major psychiatric disorders, such as major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SZ), as well as in neurodegenerative disorders, such as Alzheimer disease (AD) and Parkinson disease (PD). We conducted meta-analyses comparing complex I and IV in each disorder MDD, BD, SZ, AD, and PD, as well as in normal aging. The electronic databases Pubmed, EMBASE, CENTRAL, and Google Scholar, were searched for studies published between 1980 and 2018. Of 2049 screened studies, 125 articles were eligible for the meta-analyses. Complex I and IV were assessed in peripheral blood, muscle biopsy, or postmortem brain at the level of enzyme activity or subunits. Separate meta-analyses of mood disorder studies, MDD and BD, revealed moderate effect sizes for similar abnormality patterns in the expression of complex I with SZ in frontal cortex, cerebellum and striatum, whereas evidence for complex IV alterations was low. By contrast, the neurodegenerative disorders, AD and PD, showed strong effect sizes for shared deficits in complex I and IV, such as in peripheral blood, frontal cortex, cerebellum, and substantia nigra. Beyond the diseased state, there was an age-related robust decline in both complexes I and IV. In summary, the strongest support for a role for complex I and/or IV deficits, is in the pathophysiology of PD and AD, and evidence is less robust for MDD, BD, or SZ.

Mitochondrial Translocase of the Outer Membrane Alterations May Underlie Dysfunctional Oxidative Phosphorylation in Alzheimer's Disease

BACKGROUND

The translocase of the outer membrane (TOM) is a vital mitochondrial transport system facilitating the importation of nuclear encoded proteins into the organelle. While mitochondrial dysfunction, including perturbation of oxidative phosphorylation (OXPHOS) complex, is evident in Alzheimer's disease (AD), it remains unclear whether the observed OXPHOS deficits may be associated with TOM alterations.

OBJECTIVES

To correlate TOM subunits with OXPHOS complex proteins in AD.

METHODS

Postmortem neocortex (BA40) from AD and age-matched controls were processed to obtain mitochondrial enriched homogenates for the measurement of Tom20, Tom22, Tom40, and Tom70 as well as components of OXPHOS complex I-V by immunoblotting.

RESULTS

Tom20 and Tom70 immunoreactivities were significantly reduced in AD, as were components of OXPHOS complex I and III. Both Tom20 and Tom70 positively correlated with complex III and V, while Tom20 also correlated withcomplex IV.

CONCLUSION

Reductions in certain TOM subunits and their correlations with specific OXPHOS complex proteins suggest that an impaired mitochondrial transportation system may contribute to previously observed oxidative phosphorylation deficits in AD. Follow-up studies are needed to corroborate the present correlative study.

Mitochondria, OxPhos, and neurodegeneration: cells are not just running out of gas

Mitochondrial respiratory deficiencies have been observed in numerous neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. For decades, these reductions in oxidative phosphorylation (OxPhos) have been presumed to trigger an overall bioenergetic crisis in the neuron, resulting in cell death. While the connection between respiratory defects and neuronal death has never been proven, this hypothesis has been supported by the detection of nonspecific mitochondrial DNA mutations in these disorders. These findings led to the notion that mitochondrial respiratory defects could be initiators of these common neurodegenerative disorders, instead of being consequences of a prior insult, a theory we believe to be misconstrued. Herein, we review the roots of this mitochondrial hypothesis and offer a new perspective wherein mitochondria are analyzed not only from the OxPhos point of view, but also as a complex organelle residing at the epicenter of many metabolic pathways.

Amyloid precursor protein-mediated mitochondrial regulation and Alzheimer's disease

Despite clear evidence of a neuroprotective physiological role of amyloid precursor protein (APP) and its non-amyloidogenic processing products, APP has been investigated mainly in animal and cellular models of amyloid pathology in the context of Alzheimer's disease. The rare familial mutations in APP and presenilin-1/2, which sometimes drive increased amyloid β (Aβ) production, may have unduly influenced Alzheimer's disease research. APP and its cleavage products play important roles in cellular and mitochondrial metabolism, but many studies focus solely on Aβ. Mitochondrial bioenergetic metabolism is essential for neuronal function, maintenance and survival, and multiple reports indicate mitochondrial abnormalities in patients with Alzheimer's disease. In this review, we focus on mitochondrial abnormalities reported in sporadic Alzheimer's disease patients and the role of full-length APP and its non-amyloidogenic fragments, particularly soluble APPα, on mitochondrial bioenergetic metabolism. We do not review the plethora of animal and in vitro studies using mutant APP/presenilin constructs or experiments using exogenous Aβ. In doing so, we aim to invigorate research and discussion around non-amyloidogenic APP processing products and the mechanisms linking mitochondria and complex neurodegenerative disorders such as sporadic Alzheimer's disease. LINKED ARTICLES: This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc.

Towards an Integrative Understanding of tRNA Aminoacylation-Diet-Host-Gut Microbiome Interactions in Neurodegeneration

Transgenic mice used for Alzheimer’s disease (AD) preclinical experiments do not recapitulate the human disease. In our models, the dietary tryptophan metabolite tryptamine produced by human gut microbiome induces tryptophanyl-tRNA synthetase (TrpRS) deficiency with consequent neurodegeneration in cells and mice. Dietary supplements, antibiotics and certain drugs increase tryptamine content in vivo. TrpRS catalyzes tryptophan attachment to tRNA^trp at initial step of protein biosynthesis. Tryptamine that easily crosses the blood–brain barrier induces vasculopathies, neurodegeneration and cell death via TrpRS competitive inhibition. TrpRS inhibitor tryptophanol produced by gut microbiome also induces neurodegeneration. TrpRS inhibition by tryptamine and its metabolites preventing tryptophan incorporation into proteins lead to protein biosynthesis impairment. Tryptophan, a least amino acid in food and proteins that cannot be synthesized by humans competes with frequent amino acids for the transport from blood to brain. Tryptophan is a vulnerable amino acid, which can be easily lost to protein biosynthesis. Some proteins marking neurodegenerative pathology, such as tau lack tryptophan. TrpRS exists in cytoplasmic (WARS) and mitochondrial (WARS2) forms. Pathogenic gene variants of both forms cause TrpRS deficiency with consequent intellectual and motor disabilities in humans. The diminished tryptophan-dependent protein biosynthesis in AD patients is a proof of our model-based disease concept.

Mitochondrial Dysfunction and Synaptic Transmission Failure in Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder, in which multiple risk factors converge. Despite the complexity of the etiology of the disease, synaptic failure is the pathological basis of cognitive impairment, the cardinal sign of AD. Decreased synaptic density, compromised synaptic transmission, and defected synaptic plasticity are hallmark synaptic pathologies accompanying AD. However, the mechanisms by which synapses are injured in AD-related conditions have not been fully elucidated. Mitochondria are a critical organelle in neurons. The pivotal role of mitochondria in supporting synaptic function and the concomitant occurrence of mitochondrial dysfunction with synaptic stress in postmortem AD brains as well as AD animal models seem to lend the credibility to the hypothesis that mitochondrial defects underlie synaptic failure in AD. This concept is further strengthened by the protective effect of mitochondrial medicine on synaptic function against the toxicity of amyloid-β, a key player in the pathogenesis of AD. In this review, we focus on the association between mitochondrial dysfunction and synaptic transmission deficits in AD. Impaired mitochondrial energy production, deregulated mitochondrial calcium handling, excess mitochondrial reactive oxygen species generation and release play a crucial role in mediating synaptic transmission deregulation in AD. The understanding of the role of mitochondrial dysfunction in synaptic stress may lead to novel therapeutic strategies for the treatment of AD through the protection of synaptic transmission by targeting to mitochondrial deficits.

Molecular Mechanisms and Cellular Pathways Implicated in Machado-Joseph Disease Pathogenesis

Machado-Joseph disease (MJD) is a dominantly inherited disorder originally described in people of Portuguese descent, and associated with the expansion of a CAG tract in the coding region of the causative gene MJD1/ATX3. The CAG repeats range from 10 to 51 in the normal population and from 55 to 87 in SCA3/MJD patients. MJD1 encodes ataxin-3, a protein whose physiological function has been linked to ubiquitin-mediated proteolysis. Despite the identification of the causative mutation, the pathogenic process leading to the neurodegeneration observed in the disease is not yet completely understood. In the past years, several studies identified different molecular mechanisms and cellular pathways as being impaired or deregulated in MJD. Autophagy, proteolysis or post-translational modifications, among other processes, were implicated in MJD pathogenesis. From these studies it was possible to identify new targets for therapeutic intervention, which in some cases proved successful in models of disease.

Amyloid precursor protein drives down-regulation of mitochondrial oxidative phosphorylation independent of amyloid beta

Amyloid precursor protein (APP) and its extracellular domain, soluble APP alpha (sAPPα) play important physiological and neuroprotective roles. However, rare forms of familial Alzheimer’s disease are associated with mutations in APP that increase toxic amyloidogenic cleavage of APP and produce amyloid beta (Aβ) at the expense of sAPPα and other non-amyloidogenic fragments. Although mitochondrial dysfunction has become an established hallmark of neurotoxicity, the link between Aβ and mitochondrial function is unclear. In this study we investigated the effects of increased levels of neuronal APP or Aβ on mitochondrial metabolism and gene expression, in human SH-SY5Y neuroblastoma cells. Increased non-amyloidogenic processing of APP, but not Aβ, profoundly decreased respiration and enhanced glycolysis, while mitochondrial DNA (mtDNA) transcripts were decreased, without detrimental effects to cell growth. These effects cannot be ascribed to Aβ toxicity, since higher levels of endogenous Aβ in our models do not cause oxidative phosphorylation (OXPHOS) perturbations. Similarly, chemical inhibition of β-secretase decreased mitochondrial respiration, suggesting that non-amyloidogenic processing of APP may be responsible for mitochondrial changes. Our results have two important implications, the need for caution in the interpretation of mitochondrial perturbations in models where APP is overexpressed, and a potential role of sAPPα or other non-amyloid APP fragments as acute modulators of mitochondrial metabolism.

Triad of Risk for Late Onset Alzheimer's: Mitochondrial Haplotype, APOE Genotype and Chromosomal Sex

Brain is the most energetically demanding organ of the body, and is thus vulnerable to even modest decline in ATP generation. Multiple neurodegenerative diseases are associated with decline in mitochondrial function, e.g., Alzheimer’s, Parkinson’s, multiple sclerosis and multiple neuropathies. Genetic variances in the mitochondrial genome can modify bioenergetic and respiratory phenotypes, at both the cellular and system biology levels. Mitochondrial haplotype can be a key driver of mitochondrial efficiency. Herein, we focus on the association between mitochondrial haplotype and risk of late onset Alzheimer’s disease (LOAD). Evidence for the association of mitochondrial genetic variances/haplotypes and the risk of developing LOAD are explored and discussed. Further, we provide a conceptual framework that suggests an interaction between mitochondrial haplotypes and two demonstrated risk factors for Alzheimer’s disease (AD), apolipoprotein E (APOE) genotype and chromosomal sex. We posit herein that mitochondrial haplotype, and hence respiratory capacity, plays a key role in determining risk of LOAD and other age-associated neurodegenerative diseases. Further, therapeutic design and targeting that involve mitochondrial haplotype would advance precision medicine for AD and other age related neurodegenerative diseases.

Facilitation of brain mitochondrial activity by 5-aminolevulinic acid in a mouse model of Alzheimer's disease

The activities of mitochondrial enzymes, which are essential for neural function, decline with age and in age-related disease. In particular, the activity of cytochrome c oxidase (COX/complex IV) decreases in patients with Alzheimer's disease (AD). COX, a mitochondrial inner membrane protein complex that contains heme, plays an essential role in the electron transport chain that generates ATP. Heme synthesis begins with 5-aminolevulinic acid (5-ALA) in mitochondria. 5-ALA synthetase is the rate-limiting enzyme in heme synthesis, suggesting that supplementation with 5-ALA might help preserve mitochondrial activity in the aged brain. We administered a diet containing 5-ALA to triple-transgenic AD (3xTg-AD) model mice for 6 months, starting at 3 months of age. COX activity and protein expression, as well as mitochondrial membrane potential, were significantly higher in brains of 5-ALA-fed mice than in controls. Synaptotagmin protein levels were also significantly higher in 5-ALA-fed mice, suggesting improved preservation of synapses. Although brain Aβ levels tended to decrease in 5-ALA-fed mice, we observed no other significant changes in other biochemical and pathological hallmarks of AD. Nevertheless, our study suggests that daily oral administration of 5-ALA could preserve mitochondrial enzyme activities in the brains of aged individuals, thereby contributing to the preservation of neural activity.

Cumulative effects of the ApoE genotype and gender on the synaptic proteome and oxidative stress in the mouse brain

Elderly females, particularly those carrying the apolipoprotein E (ApoE)-ε4 allele, have a higher risk of developing Alzheimer's disease (AD). However, the underlying mechanism for this increased susceptibility remains unclear. In this study, we investigated the effects of the ApoE genotype and gender on the proteome of synaptosomes. We isolated synaptosomes and used label-free quantitative proteomics, to report, for the first time, that the synaptosomal proteomic profiles in the cortex of female human-ApoE4 mice exhibited significantly reduced expression of proteins related to energy metabolism, which was accompanied by increased levels of oxidative stress. In addition, we also first demonstrated that the proteomic response in synaptic termini was more susceptible than that in the soma to the adverse effects induced by genders and genotypes. This suggests that synaptic mitochondria might be 'older' than mitochondria in the soma of neurons; therefore, they might contain increased cumulative damage from oxidative stress. Furthermore, female human-ApoE4 mice had much lower oestrogen levels in the cortex and treatment with oestrogen protected ApoE3 stable transfected C6 neurons from oxidative stress. Overall, this study reveals complex ApoE- and gender-dependent effects on synaptic function and also provides a basis for future studies of candidates based on specific pathways involved in the pathogenesis of AD. The lack of oestrogen-mediated protection regulated by the ApoE genotype led to synaptic mitochondrial dysfunction and increased oxidative stress, which might make older females more susceptible to AD.

Mitochondrial DNA sequence associations with dementia and amyloid-β in elderly African Americans

Mitochondrial dysfunction occurs early in the course of several neurodegenerative diseases, and is potentially related to increased oxidative damage and amyloid-β (Aβ) formation in Alzheimer's disease. The goals of this study were to assess mtDNA sequence associations with dementia risk, 10-year cognitive change, and markers of oxidative stress and Aβ among 1089 African-Americans in the population-based Health, Aging, and Body Composition Study. Participants were free of dementia at baseline, and incidence was determined in 187 (18%) cases over 10 to 12 follow-up years. Haplogroup L1 participants were at increased risk for developing dementia (odds ratio = 1.88, 95% confidence interval = 1.23-2.88, p = 0.004), lower plasma Aβ42 levels (p = 0.03), and greater 10-year decline on the Digit Symbol Substitution Test (p = 0.04) when compared with common haplogroup L3. The p.V193I, ND2 substitution was associated with significantly higher Aβ42 levels (p = 0.0012), and this association was present in haplogroup L3 (p = 0.018) but not L1 (p = 0.90) participants. All associations were independent of potential confounders, including APOEε4 status and nuclear genetic ancestry. Identification of mtDNA sequence variation associated with dementia risk and cognitive decline may contribute to the development of new treatment targets and diagnostic tests that identify responders to interventions targeting mitochondria.

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

SIGNIFICANCE

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

RECENT ADVANCES

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

CRITICAL ISSUES AND FUTURE DIRECTIONS

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

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

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

The effect of 5-aminolevulinic acid on cytochrome c oxidase activity in mouse liver

Background

5-Aminolevulinic acid (ALA) is a precursor of heme that is fundamentally important in aerobic energy metabolism. Among the enzymes involved in aerobic energy metabolism, cytochrome c oxidase (COX) is crucial. In this study, the effect of ALA on cytochrome c oxidase activity was measured.

Findings

c57BL/6N species of mice were administered ALA orally for 15 weeks. After ALA administration, mice were sacrificed and livers were obtained. COX activity in mitochondria from ALA-administered mouse livers was 1.5-fold higher than that in mitochondria from PBS-administered mouse livers (P < 0.05). Furthermore, ATP levels in ALA-administered mouse livers were much higher than those in PBS-administered mouse livers. These data suggest that oral administration of ALA promotes aerobic energy metabolism, especially COX activity.

Conclusions

This is the first report of a drug that functions in aerobic energy metabolism directly. Since COX activity is decreased in various diseases and aging, the pharmacological effects of ALA will be expanding.

Mitochondria and Alzheimer's disease: amyloid-beta peptide uptake and degradation by the presequence protease, hPreP

Several lines of evidence suggest mitochondrial dysfunction as a possible underlying mechanism of Alzheimer's disease (AD). Accumulation of the amyloid-beta peptide (Abeta), a neurotoxic peptide implicated in the pathogenesis of AD, has been detected in brain mitochondria of AD patients and AD transgenic mouse models. In vitro evidence suggests that the Abeta causes mitochondrial dysfunction e.g. oxidative stress, mitochondrial fragmentation and decreased activity of cytochrome c oxidase and TCA cycle enzymes. Here we review the link between mitochondrial dysfunctions and AD. In particular we focus on the mechanism for Abeta uptake by mitochondria and on the recently identified Abeta degrading protease in human brain mitochondria.

Regional brain metabolism with cytochrome c oxidase histochemistry in a PS1/A246E mouse model of autosomal dominant Alzheimer's disease: correlations with behavior and oxidative stress

Mitochondrial dysfunction and brain metabolic alteration are early neurofunctional aspects in Alzheimer's disease (AD). Regional brain metabolism was analyzed by cytochrome c oxidase (COX) histochemistry in PS1-A246E mouse mutants, a model of autosomal dominant AD overexpressing beta-amyloid (Abeta) peptide without amyloidosis or cell degeneration. Immunohistochemical samples were analyzed on adjacent sections for regional Abeta1-42 levels, as well as DNA oxidative damage with 8-hydroxy-2-deoxyguanosine (8-OHdG). COX activity increased in the basal forebrain nuclear complex, specific parts of the amygdala and hippocampus, as well as in striatum and connected regions. On the contrary, a hypometabolism was observed in midline thalamic, interpeduncular, and pedonculopontine nuclei. The integration of these regions in circuitries subserving emotions, arousal, and cognitive functions may explain why neurochemical alterations in specific brain regions were linearly correlated with psychomotor slowing and disinhibition previously reported in the mutant. As the PS1-A246E model appears to mimick prodromal AD, the results support the existence of mitochondrial abnormalities prior to AD-related cognitive deficits. However, since affected PS1-A246E brain regions were not primarily those altered in AD-associated histopathological features and did not systematically display either Abeta overexpression or higher 8-OHdG immunolabelling, the hypermetabolism observed seems to comprise a compensatory reaction to early mitochondrial abnormalities; furthermore, neuronal synaptic function should be considered as particularly relevant in COX activity changes.

The Alzheimer's disease mitochondrial cascade hypothesis: an update

In 2004 we proposed the mitochondrial cascade hypothesis of sporadic Alzheimer's disease (AD). Our hypothesis assumed sporadic and autosomal dominant AD are not etiologically homogeneous, considered evidence that AD pathology is not brain-limited, and incorporated aging theory. The mitochondrial cascade hypothesis asserted: (1) inheritance determines mitochondrial baseline function and durability; (2) mitochondrial durability influences how mitochondria change with age; and (3) when mitochondrial change reaches a threshold, AD histopathology and symptoms ensue. We now review the reasoning used to formulate the hypothesis, discuss pertinent interim data, and update its tenants. Readers are invited to consider the conceptual strengths and weaknesses of this hypothesis.

The neurodegenerative mitochondriopathies

Mitochondria are physically or functionally altered in many neurodegenerative diseases. This is the case for very rare neurodegenerative disorders as well as extremely common age-related ones such as Alzheimer's disease and Parkinson's disease. In some disorders very specific patterns of altered mitochondrial function or systemic mitochondrial dysfunction are demonstrable. Some disorders arise from mitochondrial DNA mutation, some from nuclear gene mutation, and for some the etiology is not definitively known. This review classifies neurodegenerative diseases using mitochondrial dysfunction as a unifying feature, and in doing so defines a group of disorders called the neurodegenerative mitochondriopathies. It discusses what mitochondrial abnormalities have been identified in various neurodegenerative diseases, what is currently known about the mitochondria-neurodegeneration nexus, and speculates on the significance of mitochondrial function in some disorders not classically thought of as mitochondriopathies.

Amyloid-beta-induced mitochondrial dysfunction

As an important molecule in the pathogenesis of Alzheimer's disease (AD), amyloid-beta (Abeta) interferes with multiple aspects of mitochondrial function, including energy metabolism failure, production of reactive oxygen species (ROS) and permeability transition pore formation. Recent studies have demonstrated that Abeta progressively accumulates within mitochondrial matrix, providing a direct link to mitochondrial toxicity. Abeta-binding alcohol dehydrogenase (ABAD) is localized to the mitochondrial matrix and binds to mitochondrial Abeta. Interaction of ABAD with Abeta exaggerates Abeta-mediated mitochondrial and neuronal perturbation, leading to impaired synaptic function, and dysfunctional spatial learning/memory. Thus, blockade of ABAD/Abeta interaction may be a potential therapeutic strategy for AD.

Screening of AMP-activated protein kinase alpha2 subunit interacting proteins by bacterial two-hybrid system

AMP-activated protein kinase (AMPK) is a ubiquitous eukaryotic protein kinase regulating cellular metabolism and energy demand. In brain AMPK plays a role as a multidimensional energy sensor and AMPK alpha2 subunit is expressed at higher levels than AMPK alpha1 subunit. In order to identify potential targets of AMPK in brain, we perform bacterial two-hybrid screening of a rat fetal brain cDNA library using AMPK alpha2 subunit as bait. Here, we present seven potential AMPK alpha2 subunit interacting proteins, including 6-phosphofructo-1-kinase (PFK-1), polyubiquitin, cytochrome c oxidase subunit I (COX I), heat shock protein 8 (HSP8), HLA-B-associated transcript 3 (BAT3) isoform 1, protein tyrosine phosphatase receptor type D (PTPRD) and islet-brain 1 (IB1). They are involved in glycolysis, protein degradation, mitochondrial electron transport and apoptosis pathways participating in energy regulation directly or indirectly. These data may provide new insight into further studying the pathways of AMPK energy regulation in brain and possible mechanisms of AMPK-mediated neuroprotective effect.

Mitochondrial dysfunction enhances susceptibility to oxidative stress by down-regulation of thioredoxin in human neuroblastoma cells

Increasing evidence suggests that Alzheimer's disease is associated with mitochondrial dysfunction and oxidative damage. To develop a cellular model of Alzheimer's disease, we investigated the effects of thioredoxin (Trx) expression in the response to mitochondrial dysfunction-enhanced oxidative stress in the SH-SY5Y human neuroblastoma cells. Treatment of SH-SY5Y cells with 15 mM of NaN3, an inhibitor of cytochrome c oxidase (complex IV), led to alteration of mitochondrial membrane potential but no significant changes in cell viability. Therefore, cells were first treated with 15 mM NaN3 to induce mitochondrial dysfunction, then, exposed to different concentrations of H2O2. Cell susceptibility was assessed by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay and morphological observation. Expressions of Trx mRNA and protein were determined by RT-PCR; and Western-blot analysis, respectively. It was found that the SH-SY5Y cells with mitochondrial impairment had lower levels of Trx mRNA and protein, and were significantly more vulnerable than the normal cells after exposure to H2O2 while no significant changes of Trx mRNA and protein in SH-SY5Y cells exposed to H2O2 but without mitochondrial complex IV inhibition. These results, together with our previous study in primary cultured neurons, demonstrated that the increased susceptibility to oxidative stress is induced at least in part by the down-regulation of Trx in SH-SY5Y human neuroblastoma cells with mitochondrial impairment and also suggest the mitochondrial dysfunction-enhanced oxidative stress could be used as a cellular model to study the mechanisms of Alzheimer's disease and agents for prevention and treatment.

Beta-amyloid mediated nitration of manganese superoxide dismutase: implication for oxidative stress in a APPNLH/NLH X PS-1P264L/P264L double knock-in mouse model of Alzheimer's disease

Alzheimer's disease is a multifactorial, progressive, age-related neurodegenerative disease. In familial Alzheimer's disease, Abeta is excessively produced and deposited because of mutations in the amyloid precursor protein, presenilin-1, and presenilin-2 genes. Here, we generated a double homozygous knock-in mouse model that incorporates the Swedish familial Alzheimer's disease mutations and converts mouse Abeta to the human sequence in amyloid precursor protein and had the P264L familial Alzheimer's disease mutation in presenilin-1. We observed Abeta deposition in double knock-in mice beginning at 6 months as well as an increase in the levels of insoluble Abeta1-40/1-42. Brain homogenates from 3-, 6-, 9-, 12-, and 14-month-old mice showed that protein levels of manganese superoxide dismutase (MnSOD) were unchanged in the double knock-in mice compared to controls. Genotype-associated increases in nitrotyrosine levels were observed. Protein immunoprecipitation revealed MnSOD as a target of this nitration. Although the levels of MnSOD protein did not change, MnSOD activity and mitochondrial respiration decreased in knock-in mice, suggesting compromised mitochondrial function. The compromised activity of MnSOD, a primary antioxidant enzyme protecting mitochondria, may explain mitochondrial dysfunction and provide the missing link between Abeta-induced oxidative stress and Alzheimer's disease.

A mitochondrial paradigm of metabolic and degenerative diseases, aging, and cancer: a dawn for evolutionary medicine

Life is the interplay between structure and energy, yet the role of energy deficiency in human disease has been poorly explored by modern medicine. Since the mitochondria use oxidative phosphorylation (OXPHOS) to convert dietary calories into usable energy, generating reactive oxygen species (ROS) as a toxic by-product, I hypothesize that mitochondrial dysfunction plays a central role in a wide range of age-related disorders and various forms of cancer. Because mitochondrial DNA (mtDNA) is present in thousands of copies per cell and encodes essential genes for energy production, I propose that the delayed-onset and progressive course of the age-related diseases results from the accumulation of somatic mutations in the mtDNAs of post-mitotic tissues. The tissue-specific manifestations of these diseases may result from the varying energetic roles and needs of the different tissues. The variation in the individual and regional predisposition to degenerative diseases and cancer may result from the interaction of modern dietary caloric intake and ancient mitochondrial genetic polymorphisms. Therefore the mitochondria provide a direct link between our environment and our genes and the mtDNA variants that permitted our forbears to energetically adapt to their ancestral homes are influencing our health today.

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 abnormalities in Alzheimer brain: mechanistic implications

Reductions in cerebral metabolism sufficient to impair cognition in normal individuals also occur in Alzheimer's disease (AD). The degree of clinical disability in AD correlates closely to the magnitude of the reduction in brain metabolism. Therefore, we tested whether impairments in tricarboxylic acid (TCA) cycle enzymes of mitochondria correlate with disability. Brains were from patients with autopsy-confirmed AD and clinical dementia ratings (CDRs) before death. Significant (p < 0.01) decreases occurred in the activities of the pyruvate dehydrogenase complex (-41%), isocitrate dehydrogenase (-27%), and the alpha-ketoglutarate dehydrogenase complex (-57%). Activities of succinate dehydrogenase (complex II) (+44%) and malate dehydrogenase (+54%) were increased (p < 0.01). Activities of the other four TCA cycle enzymes were unchanged. All of the changes in TCA cycle activities correlated with the clinical state (p < 0.01), suggesting a coordinated mitochondrial alteration. The highest correlation was with pyruvate dehydrogenase complex (r = 0.77, r2= 0.59). Measures to improve TCA cycle metabolism might benefit AD patients.

Oxidative stress in the brain: novel cellular targets that govern survival during neurodegenerative disease

Despite our present knowledge of some of the cellular pathways that modulate central nervous system injury, complete therapeutic prevention or reversal of acute or chronic neuronal injury has not been achieved. The cellular mechanisms that precipitate these diseases are more involved than initially believed. As a result, identification of novel therapeutic targets for the treatment of cellular injury would be extremely beneficial to reduce or eliminate disability from nervous system disorders. Current studies have begun to focus on pathways of oxidative stress that involve a variety of cellular pathways. Here we discuss novel pathways that involve the generation of reactive oxygen species and oxidative stress, apoptotic injury that leads to nuclear degradation in both neuronal and vascular populations, and the early loss of cellular membrane asymmetry that mitigates inflammation and vascular occlusion. Current work has identified exciting pathways, such as the Wnt pathway and the serine-threonine kinase Akt, as central modulators that oversee cellular apoptosis and their downstream substrates that include Forkhead transcription factors, glycogen synthase kinase-3beta, mitochondrial dysfunction, Bad, and Bcl-x(L). Other closely integrated pathways control microglial activation, release of inflammatory cytokines, and caspase and calpain activation. New therapeutic avenues that are just open to exploration, such as with brain temperature regulation, nicotinamide adenine dinucleotide modulation, metabotropic glutamate system modulation, and erythropoietin targeted expression, may provide both attractive and viable alternatives to treat a variety of disorders that include stroke, Alzheimer's disease, and traumatic brain injury.

Transgenic mice expressing the human C99 terminal fragment of betaAPP: effects on cytochrome oxidase activity in skeletal muscle and brain

In order to furnish a combined model of relevance to human inclusion-body myopathy and Alzheimer's disease, transgenic mice expressing human betaAPP-C99 in skeletal muscle and brain under the control of the cytomegalovirus/beta-actin promoter were produced (Tg13592). These transgenic mice develop Abeta deposits in muscles but not in brain. Cell metabolic activity was analyzed in brain regions and muscle by cytochrome oxidase (CO) histochemistry, the terminal enzyme of the electron transport chain. By comparison to age-matched controls of the C57BL/6 strain, CO activity was selectively increased in dark skeletal muscle fibers of Tg13592 mice. In addition, only increases in CO activity were obtained in those brain regions where a significant difference appeared. The CO activity of Tg13592 mice was elevated in several thalamic nuclei, including laterodorsal, ventromedial, and midline as well as submedial, intralaminar, and reticular. In contrast, the groups did not differ in most cortical regions, except for prefrontal, secondary motor, and auditory cortices, and in most brainstem regions, except for cerebellar (fastigial and interpositus) nuclei and related areas (red and lateral vestibular nuclei). No variation in cell density and surface area appeared in conjunction with these enzymatic alterations. The overproduction of betaAPP-C99 fragments in brain without (amyloidosis did not appear to affect the metabolic activity of structures particularly vulnerable in Alzheimer's disease.

Alzheimer's brains harbor somatic mtDNA control-region mutations that suppress mitochondrial transcription and replication

Defects in mitochondrial oxidative phosphorylation have frequently been associated with Alzheimer's disease (AD), and both inherited and somatic mtDNA mutations have been reported in certain AD cases. To determine whether mtDNA mutations contribute more generally to the etiology of AD, we have investigated the sequence of the mtDNA control region (CR) from AD brains for possible disease-causing mutations. Sixty-five percent of the AD brains harbored the T414G mutation, whereas this mutation was absent from all controls. Moreover, cloning and sequencing of the mtDNA CR from patient and control brains revealed that all AD brains had an average 63% increase in heteroplasmic mtDNA CR mutations and that AD brains from patients 80 years and older had a 130% increase in heteroplasmic CR mutations. In addition, these mutations preferentially altered known mtDNA regulatory elements. Certain AD brains harbored the disease-specific CR mutations T414C and T477C, and several AD brains between 74 and 83 years of age harbored the CR mutations T477C, T146C, and T195C, at levels up to 70-80% heteroplasmy. AD patient brains also had an average 50% reduction in the mtDNA L-strand ND6 transcript and in the mtDNA/nuclear DNA ratio. Because reduced ND6 mRNA and mtDNA copy numbers would reduce brain oxidative phosphorylation, these CR mutations could account for some of the mitochondrial defects observed in AD.