Mitochondrial diseases of the brain

APC binds the Miro/Milton motor complex to stimulate transport of mitochondria to the plasma membrane

The role of adenomatous polyposis coli (APC) tumor suppressor at mitochondria is unclear. We show that APC associates with the Miro/Milton/kinesin complex to stimulate anterograde transport of mitochondria. This identifies the first regulatory role of APC in organelle transport. APC cancer mutations block this activity.

Mutations in adenomatous polyposis coli (APC) disrupt regulation of Wnt signaling, mitosis, and the cytoskeleton. We describe a new role for APC in the transport of mitochondria. Silencing of wild-type APC by small interfering RNA caused mitochondria to redistribute from the cell periphery to the perinuclear region. We identified novel APC interactions with the mitochondrial kinesin-motor complex Miro/Milton that were mediated by the APC C-terminus. Truncating mutations in APC abolished its ability to bind Miro/Milton and reduced formation of the Miro/Milton complex, correlating with disrupted mitochondrial distribution in colorectal cancer cells that could be recovered by reconstitution of wild-type APC. Using proximity ligation assays, we identified endogenous APC-Miro/Milton complexes at mitochondria, and live-cell imaging showed that loss of APC slowed the frequency of anterograde mitochondrial transport to the membrane. We propose that APC helps drive mitochondria to the membrane to supply energy for cellular processes such as directed cell migration, a process disrupted by cancer mutations.

Does PGC1α/FNDC5/BDNF Elicit the Beneficial Effects of Exercise on Neurodegenerative Disorders?

Neurodegenerative disorders such as Alzheimer's, Parkinson's and Huntington's diseases have high prevalence among the elderly. Many strategies have been established to alleviate the symptoms experienced by affected individuals. Recent studies have shown that exercise helps patients with neurological disorders to regain lost physical abilities. PGC1α/FNDC5/BDNF has emerged recently as a critical pathway for neuroprotection. PGC1α is a highly conserved co-activator of transcription factors that preserves and protects neurons against destruction. PGC1α regulates FNDC5 and its processed and secreted peptide Irisin, which has been proposed to play a critical role in energy expenditure and to promote neural differentiation of mouse embryonic stem cells. FNDC5 may also increase the expression of the neurotrophic factor BDNF, a neuroprotective agent, in the hippocampus. BDNF is secreted from hippocampus, amygdala, cerebral cortex and hypothalamus neurons and initiates intracellular signaling pathways through TrkB receptors. These pathways have positive feedback on CREB activities and lead to enhancement in PGC1α expression in neurons. Therefore, FNDC5 could behave as a key regulator in neuronal survival and development. This review presents recent findings on the PGC1α/FNDC5/BDNF pathway and its role in neuroprotection, and discusses the controversial promise of irisin as a mediator of the positive benefits of exercise.

An Effective Method to Identify Shared Pathways and Common Factors among Neurodegenerative Diseases

Groups of distinct but related diseases often share common symptoms, which suggest likely overlaps in underlying pathogenic mechanisms. Identifying the shared pathways and common factors among those disorders can be expected to deepen our understanding for them and help designing new treatment strategies effected on those diseases. Neurodegeneration diseases, including Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD), were taken as a case study in this research. Reported susceptibility genes for AD, PD and HD were collected and human protein-protein interaction network (hPPIN) was used to identify biological pathways related to neurodegeneration. 81 KEGG pathways were found to be correlated with neurodegenerative disorders. 36 out of the 81 are human disease pathways, and the remaining ones are involved in miscellaneous human functional pathways. Cancers and infectious diseases are two major subclasses within the disease group. Apoptosis is one of the most significant functional pathways. Most of those pathways found here are actually consistent with prior knowledge of neurodegenerative diseases except two cell communication pathways: adherens and tight junctions. Gene expression analysis showed a high probability that the two pathways were related to neurodegenerative diseases. A combination of common susceptibility genes and hPPIN is an effective method to study shared pathways involved in a group of closely related disorders. Common modules, which might play a bridging role in linking neurodegenerative disorders and the enriched pathways, were identified by clustering analysis. The identified shared pathways and common modules can be expected to yield clues for effective target discovery efforts on neurodegeneration.

Cell-free mitochondrial DNA in CSF is associated with early viral rebound, inflammation, and severity of neurocognitive deficits in HIV infection

Cell-free mitochondiral DNA (mtDNA) is an immunogenic molecule associated with many inflammatory conditions. We evaluated the relationship between cell-free mtDNA in cerebrospinal fluid (CSF) and neurocognitive performance and inflammation during HIV infection. In a cross-sectional analysis, we evaluated the association of mtDNA levels with clinical assessments, inflammatory markers, and neurocognitive performance in 28 HIV-infected individuals. In CSF, we measured mtDNA levels by droplet digital PCR, and soluble CD14 and CD163, neurofilament light, and neopterin by ELISA. In blood and CSF, we measured soluble IP-10, MCP-1, TNF-α, and IL-6 by ELISA, and intracellular expression of IL-2, IFN-γ, and TNF-α in CD4(+) and CD8(+) T cells by flow cytometry. We also evaluated the relationship between CSF pleocytosis and mtDNA longitudinally in another set of five individuals participating in an antiretroviral treatment (ART) interruption study. Cell-free CSF mtDNA levels strongly correlated with neurocognitive performance among individuals with neurocognitive impairment (NCI) (r = 0.77, p = 0.001). CSF mtDNA also correlated with levels of IP-10 in CSF (r = 0.70, p = 0.007) and MCP-1 in blood plasma (r = 0.66, p = 0.01) in individuals with NCI. There were no significant associations between inflammatory markers and mtDNA in subjects without NCI, and levels of mtDNA did not differ between subjects with and without NCI. MtDNA levels preceded pleocytosis and HIV RNA following ART interruption. Cell-free mtDNA in CSF was strongly associated with the severity of neurocognitive dysfunction and inflammation only in individuals with NCI. Our findings suggest that within a subset of subjects cell-free CSF mtDNA is associated with inflammation and degree of NCI.

A review on mitochondrial restorative mechanism of antioxidants in Alzheimer's disease and other neurological conditions

Neurodegenerative diseases are intricate in nature because of the involvement of the multiple pathophysiological events including mitochondrial dysfunction, neuroinflammation and oxidative stress. Alzheimer’s disease (AD) is a neurodegenerative disease explained by extracellular amyloid β deposits, intracellular neurofibrillary tangles and mitochondrial dysfunction. Increasing evidence has indicated that mitochondrial dysfunction displays significant role in the pathophysiological processes of AD. Mitochondrial dysfunction involves alterations in mitochondrial respiratory enzyme complex activities, oxidative stress, opening of permeability transition pore, and enhanced apoptosis. Various bioenergetics and antioxidants have been tried or under different investigational phase against AD and other neurodegenerative disorders (Parkinson’s disease, Huntington’s disease, and Amyotrophic lateral sclerosis) because of their complex and multiple site of action. These mitochondrial-targeting bioenergetics and antioxidant compounds such as coenzyme Q10, idebenone, creatine, mitoQ, mitovitE, MitoTEMPOL, latrepirdine, methylene blue, triterpenoids, SS peptides, curcumin, Ginkgo biloba, and omega-3 polyunsaturated fatty acids with potential efficacy in AD have been identified. Present review is intent to discuss mitochondrial restorative mechanisms of these bioenergetics and antioxidants as a potential alternative drug strategy for effective management of AD.

Melatonin attenuates impairments of structural hippocampal neuroplasticity in OXYS rats during active progression of Alzheimer's disease-like pathology

Translational research on Alzheimer's disease (AD) has often focused on reducing the high cerebral levels of amyloid-β (Aβ) as a key characteristic of AD pathogenesis. There is, however, a growing body of evidence that synaptic dysfunction may be crucial for the development of the most common (sporadic) form of AD. The applicability of melatonin (mainly produced by the pineal gland) to the treatment of AD is actively evaluated, but usually, such studies are based on animal models of early-onset AD, which is responsible for only ~5% of AD cases. We have shown previously that in OXYS rats (an established model of sporadic AD), accumulation of toxic forms of Aβ in the brain occurs later than does the development of signs of neurodegenerative changes and synaptic failure. In this regard, recently, we uncovered beneficial neuroprotective effects of melatonin (prophylactic dietary supplementation) in OXYS rats. Our aim here was to evaluate, starting at the age of active progression of AD-like pathology in OXYS rats, the effects of long-term oral administration of melatonin on the structure of synapses and on neuronal and glial cells of the hippocampus. Melatonin significantly increased hippocampal synaptic density and the number of excitatory synapses, decreased the number of inhibitory synapses, and upregulated pre- and postsynaptic proteins (synapsin I and PSD-95, respectively). Furthermore, melatonin improved the ultrastructure of neuronal and glial cells and reduced glial density. Based on our past and present results, the repair of neuroplasticity by melatonin is a promising strategy against AD.

Live-cell imaging study of mitochondrial morphology in mammalian cells exposed to X-rays

Morphological changes in mitochondria induced by X-irradiation in normal murine mammary gland cells were studied with a live-cell microscopic imaging technique. Mitochondria were visualised by staining with a specific fluorescent probe in the cells, which express fluorescent ubiquitination-based cell-cycle indicator 2 (Fucci2) probes to visualise cell cycle. In unirradiated cells, the number of cells with fragmented mitochondria was about 20 % of the total cells through observation period (96 h). In irradiated cells, the population with fragmented mitochondria significantly increased depending on the absorbed dose. Particularly, for 8 Gy irradiation, the accumulation of fragmentation persists even in the cells whose cell cycle came to a stand (80 % in G1 (G0-like) phase). The fraction reached to a maximum at 96 h after irradiation. The kinetics of the fraction with fragmented mitochondria was similar to that for cells in S/G2/M phase (20 %) through the observation period (120 h). The evidences show that, in irradiated cells, some signals are continually released from a nucleus or cytoplasm even in the G0-like cells to operate some sort of protein machineries involved in mitochondrial fission. It is inferred that this delayed mitochondrial fragmentation is strongly related to their dysfunction, and hence might modulate radiobiological effects such as mutation or cell death.

Prion-induced neurotoxicity: Possible role for cell cycle activity and DNA damage response

Protein misfolding neurodegenerative diseases arise through neurotoxicity induced by aggregation of host proteins. These conditions include Alzheimer’s disease, Huntington’s disease, Parkinson’s disease, motor neuron disease, tauopathies and prion diseases. Collectively, these conditions are a challenge to society because of the increasing aged population and through the real threat to human food security by animal prion diseases. It is therefore important to understand the cellular and molecular mechanisms that underlie protein misfolding-induced neurotoxicity as this will form the basis for designing strategies to alleviate their burden. Prion diseases are an important paradigm for neurodegenerative conditions in general since several of these maladies have now been shown to display prion-like phenomena. Increasingly, cell cycle activity and the DNA damage response are recognised as cellular events that participate in the neurotoxic process of various neurodegenerative diseases, and their associated animal models, which suggests they are truly involved in the pathogenic process and are not merely epiphenomena. Here we review the role of cell cycle activity and the DNA damage response in neurodegeneration associated with protein misfolding diseases, and suggest that these events contribute towards prion-induced neurotoxicity. In doing so, we highlight PrP transgenic Drosophila as a tractable model for the genetic analysis of transmissible mammalian prion disease.

Mitochondrial dysfunction and tissue injury by alcohol, high fat, nonalcoholic substances and pathological conditions through post-translational protein modifications

Mitochondria are critically important in providing cellular energy ATP as well as their involvement in anti-oxidant defense, fat oxidation, intermediary metabolism and cell death processes. It is well-established that mitochondrial functions are suppressed when living cells or organisms are exposed to potentially toxic agents including alcohol, high fat diets, smoking and certain drugs or in many pathophysiological states through increased levels of oxidative/nitrative stress. Under elevated nitroxidative stress, cellular macromolecules proteins, DNA, and lipids can undergo different oxidative modifications, leading to disruption of their normal, sometimes critical, physiological functions. Recent reports also indicated that many mitochondrial proteins are modified via various post-translation modifications (PTMs) and primarily inactivated. Because of the recently-emerging information, in this review, we specifically focus on the mechanisms and roles of five major PTMs (namely oxidation, nitration, phosphorylation, acetylation, and adduct formation with lipid-peroxides, reactive metabolites, or advanced glycation end products) in experimental models of alcoholic and nonalcoholic fatty liver disease as well as acute hepatic injury caused by toxic compounds. We also highlight the role of the ethanol-inducible cytochrome P450-2E1 (CYP2E1) in some of these PTM changes. Finally, we discuss translational research opportunities with natural and/or synthetic anti-oxidants, which can prevent or delay the onset of mitochondrial dysfunction, fat accumulation and tissue injury.

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Hepatotoxic agents including alcohol and high fat elevate nitroxidative stress.

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Increased nitroxidative stress promotes post-translational protein modifications.

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Post-translational protein modifications of many proteins lead to their inactivation.

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Inactivation of mitochondrial proteins contributes to mitochondrial dysfunction.

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Mitochondrial dysfunction contributes to necrotic or apoptotic tissue injury.

Gene expression profiling for human iPS-derived motor neurons from sporadic ALS patients reveals a strong association between mitochondrial functions and neurodegeneration

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease that leads to widespread motor neuron death, general palsy and respiratory failure. The most prevalent sporadic ALS form is not genetically inherited. Attempts to translate therapeutic strategies have failed because the described mechanisms of disease are based on animal models carrying specific gene mutations and thus do not address sporadic ALS. In order to achieve a better approach to study the human disease, human induced pluripotent stem cell (hiPSC)-differentiated motor neurons were obtained from motor nerve fibroblasts of sporadic ALS and non-ALS subjects using the STEMCCA Cre-Excisable Constitutive Polycistronic Lentivirus system and submitted to microarray analyses using a whole human genome platform. DAVID analyses of differentially expressed genes identified molecular function and biological process-related genes through Gene Ontology. REVIGO highlighted the related functions mRNA and DNA binding, GTP binding, transcription (co)-repressor activity, lipoprotein receptor binding, synapse organization, intracellular transport, mitotic cell cycle and cell death. KEGG showed pathways associated with Parkinson's disease and oxidative phosphorylation, highlighting iron homeostasis, neurotrophic functions, endosomal trafficking and ERK signaling. The analysis of most dysregulated genes and those representative of the majority of categorized genes indicates a strong association between mitochondrial function and cellular processes possibly related to motor neuron degeneration. In conclusion, iPSC-derived motor neurons from motor nerve fibroblasts of sporadic ALS patients may recapitulate key mechanisms of neurodegeneration and may offer an opportunity for translational investigation of sporadic ALS. Large gene profiling of differentiated motor neurons from sporadic ALS patients highlights mitochondrial participation in the establishment of autonomous mechanisms associated with sporadic ALS.

High serum phosphate concentration as the result of smoking might underlie the lower risk of Parkinson's disease

Epidemiological studies have found a negative association between cigarette smoking and Parkinson's disease (PD): PD patients are approximately 50% less likely to have smoked cigarettes than age- and sex-matched controls. In both women and men, the PD protection effect of smoking may be explained by higher levels of phosphate in serum (S-P) and triglycerides (S-TG) in smokers compared to non-smokers. That is, the protecting effect from smoking could be mediated by either a high S-P or high S-TG levels. I suggest that higher S-P as the result of smoking may be associated with intracellular depletion of Pi in skeletal muscle and that this depletion of Pi is associated with increased availability of phosphate for the brain. This increased phosphate availability would protect against PD, as oxidative phosphorylation in the mitochondria is a central and persistent phenomenon in the pathogenesis cascade of PD. Phosphate is necessary for energy production in the form of creatine phosphate (CP) and adenosine-tri-phosphate (ATP) in the brain and skeletal muscle. As such, hypophosphatemia increases risk of cell death. In some clinical instances, this energy depletion may pre-dispose to dopamine neuron death. Mitochondrial dysfunction is associated with the generation of oxidative stress and mediates the induction of apoptosis. Studies with NMR spectroscopy reveal that an energy deficit in brain cells is a strong mark for PD although this differed for men and women. Compared to women, men had lower serum phosphate and ATP levels in the brain (about 15% lower). In addition to sex differences, age, stress, and malnutrition may cause low serum phosphate levels, a situation that could contribute to the lack of energy available to the brain and the risk of PD. As hypophosphatemia is present in overnutrition and has an inverse relation with a high BMI, both obesity and malnutrition are considered to be presumptive risk factor for PD.

Effect of coenzyme Q10 plus nicotinamide adenine dinucleotide supplementation on maximum heart rate after exercise testing in chronic fatigue syndrome - A randomized, controlled, double-blind trial

BACKGROUND & AIMS

Chronic Fatigue Syndrome (CFS) is a complex condition, characterized by severe disabling fatigue with no known cause, no established diagnostic tests, and no universally effective treatment. Several studies have proposed symptomatic treatment with coenzyme Q10 (CoQ10) and nicotinamide adenine dinucleotide (NADH) supplementation. The primary endpoint was to assess the effect of CoQ10 plus NADH supplementation on age-predicted maximum heart rate (max HR) during a cycle ergometer test. Secondary measures included fatigue, pain and sleep.

METHODS

A proof-of-concept, 8-week, randomized, controlled, double-blind trial was conducted in 80 CFS patients assigned to receive either CoQ10 plus NADH supplementation or matching placebo twice daily. Maximum HR was evaluated at baseline and at end of the run-in period using an exercise test. Fatigue, pain and sleep were evaluated at baseline, and then reassessed at 4- and 8-weeks through self-reported questionnaires.

RESULTS

The CoQ10 plus NADH group showed a significant reduction in max HR during a cycle ergometer test at week 8 versus baseline (P = 0.022). Perception of fatigue also showed a decrease through all follow-up visits in active group versus placebo (P = 0.03). However, pain and sleep did not improve in the active group. Coenzyme Q10 plus NADH was generally safe and well tolerated.

CONCLUSIONS

Our results suggest that CoQ10 plus NADH supplementation for 8 weeks is safe and potentially effective in reducing max HR during a cycle ergometer test and also on fatigue in CFS. Further additional larger controlled trials are needed to confirm these findings. Clinical trial registrationThis trial was registered at clinicaltrials.gov as NCT02063126.

Mitochondrial DNA Haplogroup A Decreases the Risk of Drug Addiction but Conversely Increases the Risk of HIV-1 Infection in Chinese Addicts

Drug addiction is one of the most serious social problems in the world today and addicts are always at a high risk of acquiring HIV infection. Mitochondrial impairment has been reported in both drug addicts and in HIV patients undergoing treatment. In this study, we aimed to investigate whether mitochondrial DNA (mtDNA) haplogroup could affect the risk of drug addiction and HIV-1 infection in Chinese. We analyzed mtDNA sequence variations of 577 Chinese intravenous drug addicts (289 with HIV-1 infection and 288 without) and compared with 2 control populations (n = 362 and n = 850). We quantified the viral load in HIV-1-infected patients with and without haplogroup A status and investigated the potential effect of haplogroup A defining variants m.4824A > G and m.8794C > T on the cellular reactive oxygen species (ROS) levels by using an allotopic expression assay. mtDNA haplogroup A had a protective effect against drug addiction but appeared to confer an increased risk of HIV infection in addicts. HIV-1-infected addicts with haplogroup A had a trend for a higher viral load, although the mean viral load was similar between carriers of haplogroup A and those with other haplogroup. Hela cells overexpressing allele m.8794 T showed significantly decreased ROS levels as compared to cells with the allele m.8794C (P = 0.03). Our results suggested that mtDNA haplogroup A might protect against drug addiction but increase the risk of HIV-1 infection. The contradictory role of haplogroup A might be caused by an alteration in mitochondrial function due to a particular mtDNA ancestral variant.

Design and synthesis of a mitochondria-targeting carrier for small molecule drugs

A novel mitochondria-targeting carrier QCy7HA was developed. QCy7HA transported the covalently attached doxorubicin (DOX) to mitochondria specifically. The conjugate limited the effects of P-glycoprotein (Pgp) efflux pumps of multidrug-resistant cells on DOX, indicating that diverting drugs to mitochondria is a potential promising method for treatment of drug-resistant cancers.

11β-HSD1 reduces metabolic efficacy and adiponectin synthesis in hypertrophic adipocytes

Mitochondrial dysfunction in hypertrophic adipocytes can reduce adiponectin synthesis. We investigated whether 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) expression is increased in hypertrophic adipocytes and whether this is responsible for mitochondrial dysfunction and reduced adiponectin synthesis. Differentiated 3T3L1 adipocytes were cultured for up to 21 days. The effect of AZD6925, a selective 11β-HSD1 inhibitor, on metabolism was examined. db/db mice were administered 600 mg/kg AZD6925 daily for 4 weeks via gastric lavage. Mitochondrial DNA (mtDNA) content, mRNA expression levels of 11 β -H sd1 and mitochondrial biogenesis factors, adiponectin synthesis, fatty acid oxidation (FAO), oxygen consumption rate and glycolysis were measured. Adipocyte hypertrophy in 3T3L1 cells exposed to a long duration of culture was associated with increased 11 β -Hsd1 mRNA expression and reduced mtDNA content, mitochondrial biogenesis factor expression and adiponectin synthesis. These cells displayed reduced mitochondrial respiration and increased glycolysis. Treatment of these cells with AZD6925 increased adiponectin synthesis and mitochondrial respiration. Inhibition of FAO by etomoxir blocked the AZD6925-induced increase in adiponectin synthesis, indicating that 11β-HSD1-mediated reductions in FAO are responsible for the reduction in adiponectin synthesis. The expression level of 11 β -Hsd1 was higher in adipose tissues of db/db mice. Administration of AZD6925 to db/db mice increased the plasma adiponectin level and adipose tissue FAO. In conclusion, increased 11β-HSD1 expression contributes to reduced mitochondrial respiration and adiponectin synthesis in hypertrophic adipocytes.

Neurovascular and neurometabolic derailment in aging and Alzheimer's disease

The functional and structural integrity of the brain requires local adjustment of blood flow and regulated delivery of metabolic substrates to meet the metabolic demands imposed by neuronal activation. This process—neurovascular coupling—and ensued alterations of glucose and oxygen metabolism—neurometabolic coupling—are accomplished by concerted communication between neural and vascular cells. Evidence suggests that neuronal-derived nitric oxide (^•NO) is a key player in both phenomena. Alterations in the mechanisms underlying the intimate communication between neural cells and vessels ultimately lead to neuronal dysfunction. Both neurovascular and neurometabolic coupling are perturbed during brain aging and in age-related neuropathologies in close association with cognitive decline. However, despite decades of intense investigation, many aspects remain poorly understood, such as the impact of these alterations. In this review, we address neurovascular and neurometabolic derailment in aging and Alzheimer's disease (AD), discussing its significance in connection with ^•NO-related pathways.

Impaired mitochondrial energy metabolism in Alzheimer's disease: Impact on pathogenesis via disturbed epigenetic regulation of chromatin landscape

The amyloid cascade hypothesis for the pathogenesis of Alzheimer's disease (AD) was proposed over twenty years ago. However, the mechanisms of neurodegeneration and synaptic loss have remained elusive delaying the effective drug discovery. Recent studies have revealed that amyloid-β peptides as well as phosphorylated and fragmented tau proteins accumulate within mitochondria. This process triggers mitochondrial fission (fragmentation) and disturbs Krebs cycle function e.g. by inhibiting the activity of 2-oxoglutarate dehydrogenase. Oxidative stress, hypoxia and calcium imbalance also disrupt the function of Krebs cycle in AD brains. Recent studies on epigenetic regulation have revealed that Krebs cycle intermediates control DNA and histone methylation as well as histone acetylation and thus they have fundamental roles in gene expression. DNA demethylases (TET1-3) and histone lysine demethylases (KDM2-7) are included in the family of 2-oxoglutarate-dependent oxygenases (2-OGDO). Interestingly, 2-oxoglutarate is the obligatory substrate of 2-OGDO enzymes, whereas succinate and fumarate are the inhibitors of these enzymes. Moreover, citrate can stimulate histone acetylation via acetyl-CoA production. Epigenetic studies have revealed that AD is associated with changes in DNA methylation and histone acetylation patterns. However, the epigenetic results of different studies are inconsistent but one possibility is that they represent both coordinated adaptive responses and uncontrolled stochastic changes, which provoke pathogenesis in affected neurons. Here, we will review the changes observed in mitochondrial dynamics and Krebs cycle function associated with AD, and then clarify the mechanisms through which mitochondrial metabolites can control the epigenetic landscape of chromatin and induce pathological changes in AD.

PARP-1 involvement in neurodegeneration: A focus on Alzheimer's and Parkinson's diseases

DNA damage is the prime activator of the enzyme poly(ADP-ribose)polymerase1 (PARP-1) whose overactivation has been proven to be associated with the pathogenesis of numerous central nervous system disorders, such as ischemia, neuroinflammation, and neurodegenerative diseases. Under oxidative stress conditions PARP-1 activity increases, leading to an accumulation of ADP-ribose polymers and NAD(+) depletion, that induces energy crisis and finally cell death. This review aims to explain the contribution of PARP-1 in neurodegenerative diseases, focusing on Alzheimer's and Parkinson's disease, to stimulate further studies on this issue and thereby engage a new perspective regarding the design of possible therapeutic agents or the identification of biomarkers.

Modulation of mitochondrial complex I activity averts cognitive decline in multiple animal models of familial Alzheimer's Disease

Development of therapeutic strategies to prevent Alzheimer's Disease (AD) is of great importance. We show that mild inhibition of mitochondrial complex I with small molecule CP2 reduces levels of amyloid beta and phospho-Tau and averts cognitive decline in three animal models of familial AD. Low-mass molecular dynamics simulations and biochemical studies confirmed that CP2 competes with flavin mononucleotide for binding to the redox center of complex I leading to elevated AMP/ATP ratio and activation of AMP-activated protein kinase in neurons and mouse brain without inducing oxidative damage or inflammation. Furthermore, modulation of complex I activity augmented mitochondrial bioenergetics increasing coupling efficiency of respiratory chain and neuronal resistance to stress. Concomitant reduction of glycogen synthase kinase 3β activity and restoration of axonal trafficking resulted in elevated levels of neurotrophic factors and synaptic proteins in adult AD mice. Our results suggest metabolic reprogramming induced by modulation of mitochondrial complex I activity represents promising therapeutic strategy for AD.

Effect of nicotinamide mononucleotide on brain mitochondrial respiratory deficits in an Alzheimer's disease-relevant murine model

Background

Mitochondrial dysfunction is a hallmark of neurodegenerative diseases including Alzheimer’s disease (AD), with morphological and functional abnormalities limiting the electron transport chain and ATP production. A contributing factor of mitochondrial abnormalities is loss of nicotinamide adenine dinucleotide (NAD), an important cofactor in multiple metabolic reactions. Depletion of mitochondrial and consequently cellular NAD(H) levels by activated NAD glycohydrolases then culminates in bioenergetic failure and cell death. De Novo NAD⁺ synthesis from tryptophan requires a multi-step enzymatic reaction. Thus, an alternative strategy to maintain cellular NAD⁺ levels is to administer NAD⁺ precursors facilitating generation via a salvage pathway. We administered nicotinamide mononucleotide (NMN), an NAD⁺ precursor to APP_(swe)/PS1_(ΔE9) double transgenic (AD-Tg) mice to assess amelioration of mitochondrial respiratory deficits. In addition to mitochondrial respiratory function, we examined levels of full-length mutant APP, NAD⁺-dependent substrates (SIRT1 and CD38) in homogenates and fission/fusion proteins (DRP1, OPA1 and MFN2) in mitochondria isolated from brain. To examine changes in mitochondrial morphology, bigenic mice possessing a fluorescent protein targeted to neuronal mitochondria (CaMK2a-mito/eYFP), were administered NMN.

Methods

Mitochondrial oxygen consumption rates were examined in N2A neuroblastoma cells and non-synaptic brain mitochondria isolated from mice (3 months). Western blotting was utilized to assess APP, SIRT1, CD38, DRP1, OPA1 and MFN2 in brain of transgenic and non-transgenic mice (3–12 months). Mitochondrial morphology was assessed with confocal microscopy. One-way or two-way analysis of variance (ANOVA) and post-hoc Holm-Sidak method were used for statistical analyses of data. Student t-test was used for direct comparison of two groups.

Results

We now demonstrate that mitochondrial respiratory function was restored in NMN-treated AD-Tg mice. Levels of SIRT1 and CD38 change with age and NMN treatment. Furthermore, we found a shift in dynamics from fission to fusion proteins in the NMN-treated mice.

Conclusions

This is the first study to directly examine amelioration of NAD⁺ catabolism and changes in mitochondrial morphological dynamics in brain utilizing the immediate precursor NMN as a potential therapeutic compound. This might lead to well-defined physiologic abnormalities that can serve an important role in the validation of promising agents such as NMN that target NAD⁺ catabolism preserving mitochondrial function.

Oxidative modulation of K+ channels in the central nervous system in neurodegenerative diseases and aging

SIGNIFICANCE

Oxidative stress and damage are well-established components of neurodegenerative diseases, contributing to neuronal death during disease progression. Here, we consider key K(+) channels as target proteins that can undergo oxidative modulation, describe what is understood about how this influences disease progression, and consider regulation of these channels by gasotransmitters as a means of cellular protection.

RECENT ADVANCES

Oxidative regulation of the delayed rectifier Kv2.1 and the Ca(2+)- and voltage-sensitive BK channel are established, but recent studies contest how their redox sensitivity contributes to altered excitability, progression of neurodegenerative diseases, and healthy aging.

CRITICAL ISSUES

Both Kv2.1 and BK channels have recently been established as target proteins for regulation by the gasotransmitters carbon monoxide and hydrogen sulfide. Establishing the molecular basis of such regulation, and exactly how this influences excitability and vulnerability to apoptotic cell death will determine whether such regulation can be exploited for therapeutic benefit.

FUTURE DIRECTIONS

Developing a more comprehensive picture of the oxidative modulation of K(+) channels (and, indeed, other ion channels) within the central nervous system in health and disease will enable us to better understand processes associated with healthy aging as well as distinct processes underlying progression of neurodegenerative diseases. Advances in the growing understanding of how gasotransmitters can regulate ion channels, including redox-sensitive K(+) channels, are a research priority for this field, and will establish their usefulness in design of future approaches for the treatment of such diseases.

Pathologic and therapeutic implications for the cell biology of parkin

Mutations in the E3 ligase parkin are the most common cause of autosomal recessive Parkinson's disease (PD), but it is believed that parkin dysfunction may also contribute to idiopathic PD. Since its discovery, parkin has been implicated in supporting multiple neuroprotective pathways, many revolving around the maintenance of mitochondrial health quality control and governance of cell survival. Recent advances across the structure, biochemistry, and cell biology of parkin have provided great insights into the etiology of parkin-linked and idiopathic PD and may ultimately generate novel therapeutic strategies to slow or halt disease progression. This review describes the various pathways in which parkin acts and the mechanisms by which parkin may be targeted for therapeutic intervention. This article is part of a Special Issue entitled 'Neuronal Protein'.

Mitochondrial iron homeostasis and its dysfunctions in neurodegenerative disorders

Synthesis of the iron-containing prosthetic groups-heme and iron-sulfur clusters-occurs in mitochondria. The mitochondrion is also an important producer of reactive oxygen species (ROS), which are derived from electrons leaking from the electron transport chain. The coexistence of both ROS and iron in the secluded space of the mitochondrion makes this organelle particularly prone to oxidative damage. Here, we review the elements that configure mitochondrial iron homeostasis and discuss the principles of iron-mediated ROS generation in mitochondria. We also review the evidence for mitochondrial dysfunction and iron accumulation in Alzheimer's disease, Huntington Disease, Friedreich's ataxia, and in particular Parkinson's disease. We postulate that a positive feedback loop of mitochondrial dysfunction, iron accumulation, and ROS production accounts for the process of cell death in various neurodegenerative diseases in which these features are present.

Energy metabolism disorders in rare and common diseases. Toward bioenergetic modulation therapy and the training of a new generation of European scientists

Energy metabolism alterations are found in a large number of rare and common diseases of genetic or environmental origin. The number of patients that could benefit from bioenergetic modulation therapy (BIOMET) is therefore very important and includes individuals with pathologies as diverse as mitochondrial diseases, acute coronary syndrome, chronic kidney disease, asthma or even cancer. Although, the alteration of energy metabolism is disease specific and sometimes patient specific, the strategies for BIOMET could be common and target a series of bioenergetic regulatory mechanisms discussed in this article. An excellent training of scientists in the field of energy metabolism, related human diseases and drug discovery is also crucial to form a young generation of MDs, PHDs and Pharma or CRO-group leaders who will discover novel personalized bioenergetic medicines, through pharmacology, genetics, nutrition or adapted exercise training. The Mitochondrial European Educational Training (MEET) consortium was created to pursue this goal, and we dedicated here a special issue of Organelle in Focus (OiF) to highlight their objectives. A total of 10 OiFs articles constitute this Directed Issue on Mitochondrial Medicine. As part of this editorial article, we asked timely questions to the PR. Jan W. Smeitink, professor of Mitochondrial Medicine and CEO of Khondrion, a mitochondrial medicine company. He shared with us his objectives and strategies for the study of mitochondrial diseases and the identification of future treatments. This article is part of a Directed Issue entitled: Energy Metabolism Disorders and Therapies.

ABCD1 deletion-induced mitochondrial dysfunction is corrected by SAHA: implication for adrenoleukodystrophy

X-linked Adrenoleukodystrophy (X-ALD), an inherited peroxisomal metabolic neurodegenerative disorder, is caused by mutations/deletions in the ATP-binding cassette transporter (ABCD1) gene encoding peroxisomal ABC transporter adrenoleukodystrophy protein (ALDP). Metabolic dysfunction in X-ALD is characterized by the accumulation of very long chain fatty acids ≥ C22:0) in the tissues and plasma of patients. Here, we investigated the mitochondrial status following deletion of ABCD1 in B12 oligodendrocytes and U87 astrocytes. This study provides evidence that silencing of peroxisomal protein ABCD1 produces structural and functional perturbations in mitochondria. Activities of electron transport chain-related enzymes and of citric acid cycle (TCA cycle) were reduced; mitochondrial redox status was dysregulated and the mitochondrial membrane potential was disrupted following ABCD1 silencing. A greater reduction in ATP levels and citrate synthase activities was observed in oligodendrocytes as compared to astrocytes. Furthermore, most of the mitochondrial perturbations induced by ABCD1 silencing were corrected by treating cells with suberoylanilide hydroxamic acid, an Histone deacetylase inhibitor. These observations indicate a novel relationship between peroxisomes and mitochondria in cellular homeostasis and the importance of intact peroxisomes in relation to mitochondrial integrity and function in the cell types that participate in the pathobiology of X-ALD. These observations suggest suberoylanilide hydroxamic acid as a potential therapy for X-ALD. Schematic description of the effects of loss of peroxisomal ATP-binding cassette transporter D1 (ABCD1) gene on cellular Redox and mitochondrial activities and their correction by suberoylanilide hydroxamic acid (SAHA) treatment. Pathogenomic accumulation of very long chain fatty acids (VLCFA) as a result of loss of ABCD1 leads to dysfunctions of mitochondrial biogenesis and its activities. Treatment with SAHA corrects mitochondrial dysfunctions. These studies describe unique cooperation between mitochondria and peroxisome for cellular activities.

Formulation and optimization of mitochondria-targeted polymeric nanoparticles

Targeted delivery of therapeutics to the mitochondria of cells without alteration of drug properties can be a vital technique in the treatment of a variety of mitochondrial-dysfunction-related diseases. Herein, we describe a detailed protocol for synthesis and characterization of a functionalized polymer to build mitochondria-targeted nanoparticles (NPs). The block polymer was decorated with a lipophilic triphenylphosphonium (TPP) cation for mitochondrial trafficking of payload-loaded polymeric NPs. TPP-based lipophilic cations have the ability to cross the mitochondrial membrane. A mitochondria-targeted block copolymer poly(DL-lactide-co-glycolide)-b-polyethylene glycol-TPP and a nontargeted poly(DL-lactide-co-glycolide)-b-polyethylene glycol polymer were synthesized and their NPs were prepared. A nanoprecipitation method combined with polymer blending technology was adopted in order to get suitable size and charged NPs for efficient mitochondrial trafficking.

Characterization of phenolic compounds and antioxidant properties of Glycyrrhiza glabra L. rhizomes and roots

The present work aims to characterize and quantify the phenolic composition and to evaluate the antioxidant activity of Glycyrrhiza glabra L. (commonly known as licorice) rhizomes and roots.

Role of sigma-1 receptors in neurodegenerative diseases

Neurodegenerative diseases with distinct genetic etiologies and pathological phenotypes appear to share common mechanisms of neuronal cellular dysfunction, including excitotoxicity, calcium dysregulation, oxidative damage, ER stress and mitochondrial dysfunction. Glial cells, including microglia and astrocytes, play an increasingly recognized role in both the promotion and prevention of neurodegeneration. Sigma receptors, particularly the sigma-1 receptor subtype, which are expressed in both neurons and glia of multiple regions within the central nervous system, are a unique class of intracellular proteins that can modulate many biological mechanisms associated with neurodegeneration. These receptors therefore represent compelling putative targets for pharmacologically treating neurodegenerative disorders. In this review, we provide an overview of the biological mechanisms frequently associated with neurodegeneration, and discuss how sigma-1 receptors may alter these mechanisms to preserve or restore neuronal function. In addition, we speculate on their therapeutic potential in the treatment of various neurodegenerative disorders.

Bioenergetic medicine

Here we discuss a specific therapeutic strategy we call 'bioenergetic medicine'. Bioenergetic medicine refers to the manipulation of bioenergetic fluxes to positively affect health. Bioenergetic medicine approaches rely heavily on the law of mass action, and impact systems that monitor and respond to the manipulated flux. Since classically defined energy metabolism pathways intersect and intertwine, targeting one flux also tends to change other fluxes, which complicates treatment design. Such indirect effects, fortunately, are to some extent predictable, and from a therapeutic perspective may also be desirable. Bioenergetic medicine-based interventions already exist for some diseases, and because bioenergetic medicine interventions are presently feasible, new approaches to treat certain conditions, including some neurodegenerative conditions and cancers, are beginning to transition from the laboratory to the clinic.

Acute focal brain damage alters mitochondrial dynamics and autophagy in axotomized neurons

Mitochondria are key organelles for the maintenance of life and death of the cell, and their morphology is controlled by continual and balanced fission and fusion dynamics. A balance between these events is mandatory for normal mitochondrial and neuronal function, and emerging evidence indicates that mitochondria undergo extensive fission at an early stage during programmed cell death in several neurodegenerative diseases. A pathway for selective degradation of damaged mitochondria by autophagy, known as mitophagy, has been described, and is of particular importance to sustain neuronal viability. In the present work, we analyzed the effect of autophagy stimulation on mitochondrial function and dynamics in a model of remote degeneration after focal cerebellar lesion. We provided evidence that lesion of a cerebellar hemisphere causes mitochondria depolarization in axotomized precerebellar neurons associated with PTEN-induced putative kinase 1 accumulation and Parkin translocation to mitochondria, block of mitochondrial fusion by Mfn1 degradation, increase of calcineurin activity and dynamin-related protein 1 translocation to mitochondria, and consequent mitochondrial fission. Here we suggest that the observed neuroprotective effect of rapamycin is the result of a dual role: (1) stimulation of autophagy leading to damaged mitochondria removal and (2) enhancement of mitochondria fission to allow their elimination by mitophagy. The involvement of mitochondrial dynamics and mitophagy in brain injury, especially in the context of remote degeneration after acute focal brain damage, has not yet been investigated, and these findings may offer new target for therapeutic intervention to improve functional outcomes following acute brain damage.

Mitochondrial dynamic changes in health and genetic diseases

Mitochondria are highly specialized in function, but mitochondrial and, therefore, cellular integrity is maintained through their dynamic nature. Through the frequent processes of fusion and fission, mitochondria continuously change in shape and adjust function to meet cellular requirements. Abnormalities in fusion/fission dynamics generate cellular dysfunction that may lead to diseases. Mutations in the genes encoding mitochondrial fusion/fission proteins, such as MFN2 and OPA1, have been associated with an increasing number of genetic disorders, including Charcot-Marie-Tooth disease type 2A (CMT2A) and autosomal dominant optic atrophy. In this review, we address the mitochondrial dynamic changes in several important genetic diseases, which will bring the new insight of clinical relevance of mitochondrial genetics.

Amyotrophic lateral sclerosis: a long preclinical period?

The onset of amyotrophic lateral sclerosis (ALS) is conventionally considered as commencing with the recognition of clinical symptoms. We propose that, in common with other neurodegenerations, the pathogenic mechanisms culminating in ALS phenotypes begin much earlier in life. Animal models of genetically determined ALS exhibit pathological abnormalities long predating clinical deficits. The overt clinical ALS phenotype may develop when safety margins are exceeded subsequent to years of mitochondrial dysfunction, neuroinflammation or an imbalanced environment of excitation and inhibition in the neuropil. Somatic mutations, the epigenome and external environmental influences may interact to trigger a metabolic cascade that in the adult eventually exceeds functional threshold. A long preclinical and subsequent presymptomatic period pose a challenge for recognition, since it offers an opportunity for protective and perhaps even preventive therapeutic intervention to rescue dysfunctional neurons. We suggest, by analogy with other neurodegenerations and from SOD1 ALS mouse studies, that vulnerability might be induced in the perinatal period.

Efavirenz induces neuronal autophagy and mitochondrial alterations

Efavirenz (EFV) is a non-nucleoside reverse-transcriptase inhibitor in wide use for the treatment of human immunodeficiency virus infection. Although EFV is generally well tolerated, neuropsychiatric toxicity has been well documented. The toxic effects of EFV in hepatocytes and keratinocytes have been linked to mitochondrial perturbations and changes in autophagy. Here, we studied the effect of EFV on mitochondria and autophagy in neuronal cell lines and primary neurons. In SH-SY5Y cells, EFV induced a drop in ATP production, which coincided with increased autophagy, mitochondrial fragmentation, and mitochondrial depolarization. EFV-induced mitophagy was also detected by colocalization of mitochondria and autophagosomes and use of an outer mitochondrial membrane tandem fluorescent vector. Pharmacologic inhibition of autophagy with 3-methyladenine increased the cytotoxic effect of EFV, suggesting that autophagy promotes cell survival. EFV also reduces ATP production in primary neurons, induces autophagy, and changes mitochondrial morphology. Overall, EFV is able to acutely induce autophagy and mitochondrial changes in neurons. These changes may be involved in the mechanism leading to central nervous system toxicity observed in clinical EFV use.

PSEA-Quant: a protein set enrichment analysis on label-free and label-based protein quantification data

The majority of large-scale proteomics quantification methods yield long lists of quantified proteins that are often difficult to interpret and poorly reproduced. Computational approaches are required to analyze such intricate quantitative proteomics data sets. We propose a statistical approach to computationally identify protein sets (e.g., Gene Ontology (GO) terms) that are significantly enriched with abundant proteins with reproducible quantification measurements across a set of replicates. To this end, we developed PSEA-Quant, a protein set enrichment analysis algorithm for label-free and label-based protein quantification data sets. It offers an alternative approach to classic GO analyses, models protein annotation biases, and allows the analysis of samples originating from a single condition, unlike analogous approaches such as GSEA and PSEA. We demonstrate that PSEA-Quant produces results complementary to GO analyses. We also show that PSEA-Quant provides valuable information about the biological processes involved in cystic fibrosis using label-free protein quantification of a cell line expressing a CFTR mutant. Finally, PSEA-Quant highlights the differences in the mechanisms taking place in the human, rat, and mouse brain frontal cortices based on tandem mass tag quantification. Our approach, which is available online, will thus improve the analysis of proteomics quantification data sets by providing meaningful biological insights.

Brain temperature and its fundamental properties: a review for clinical neuroscientists

Brain temperature, as an independent therapeutic target variable, has received increasingly intense clinical attention. To date, brain hypothermia represents the most potent neuroprotectant in laboratory studies. Although the impact of brain temperature is prevalent in a number of common human diseases including: head trauma, stroke, multiple sclerosis, epilepsy, mood disorders, headaches, and neurodegenerative disorders, it is evident and well recognized that the therapeutic application of induced hypothermia is limited to a few highly selected clinical conditions such as cardiac arrest and hypoxic ischemic neonatal encephalopathy. Efforts to understand the fundamental aspects of brain temperature regulation are therefore critical for the development of safe, effective, and pragmatic clinical treatments for patients with brain injuries. Although centrally-mediated mechanisms to maintain a stable body temperature are relatively well established, very little is clinically known about brain temperature's spatial and temporal distribution, its physiological and pathological fluctuations, and the mechanism underlying brain thermal homeostasis. The human brain, a metabolically "expensive" organ with intense heat production, is sensitive to fluctuations in temperature with regards to its functional activity and energy efficiency. In this review, we discuss several critical aspects concerning the fundamental properties of brain temperature from a clinical perspective.

Joint genetic analysis of hippocampal size in mouse and human identifies a novel gene linked to neurodegenerative disease

BACKGROUND

Variation in hippocampal volume has been linked to significant differences in memory, behavior, and cognition among individuals. To identify genetic variants underlying such differences and associated disease phenotypes, multinational consortia such as ENIGMA have used large magnetic resonance imaging (MRI) data sets in human GWAS studies. In addition, mapping studies in mouse model systems have identified genetic variants for brain structure variation with great power. A key challenge is to understand how genetically based differences in brain structure lead to the propensity to develop specific neurological disorders.

RESULTS

We combine the largest human GWAS of brain structure with the largest mammalian model system, the BXD recombinant inbred mouse population, to identify novel genetic targets influencing brain structure variation that are linked to increased risk for neurological disorders. We first use a novel cross-species, comparative analysis using mouse and human genetic data to identify a candidate gene, MGST3, associated with adult hippocampus size in both systems. We then establish the coregulation and function of this gene in a comprehensive systems-analysis.

CONCLUSIONS

We find that MGST3 is associated with hippocampus size and is linked to a group of neurodegenerative disorders, such as Alzheimer's.

Mitochondrial dysfunction induced by a post-translationally modified amyloid linked to a familial mutation in an alternative model of neurodegeneration

Familial British dementia (FBD) is an early-onset non-amyloid-β (Aβ) cerebral amyloidosis that presents with severe cognitive decline and strikingly similar neuropathological features to those present in Alzheimer's disease (AD). FBD is associated with a T to A single nucleotide transition in the stop codon of a gene encoding BRI2, leading to the production of an elongated precursor protein. Furin-like proteolytic processing at its C-terminus releases a longer-than-normal 34 amino acid peptide, ABri, exhibiting amyloidogenic properties not seen in its 23 amino acid physiologic counterpart Bri1-23. Deposited ABri exhibits abundant post-translational pyroglutamate (pE) formation at the N-terminus, a feature seen in truncated forms of Aβ found in AD deposits, and co-exists with neurofibrillary tangles almost identical to those found in AD. We tested the impact of the FBD mutation alone and in conjunction with the pE post-translational modification on the structural properties and associated neurotoxicity of the ABri peptide. The presence of pE conferred to the ABri molecule enhanced hydrophobicity and accelerated aggregation/fibrillization properties. ABri pE was capable of triggering oxidative stress, loss of mitochondrial membrane potential and activation of caspase-mediated apoptotic mechanisms in neuronal cells, whereas homologous peptides lacking the elongated C-terminus and/or the N-terminal pE were unable to induce similar detrimental cellular pathways. The data indicate that the presence of N-terminal pE is not in itself sufficient to induce pathogenic changes in the physiologic Bri1-23 peptides but that its combination with the ABri mutation is critical for the molecular pathogenesis of FBD.