Metabolic dysfunction in familial, but not sporadic, amyotrophic lateral sclerosis

Mitochondrial Dysfunction in Sporadic Amyotrophic Lateral Sclerosis Patients: Insights from High-Resolution Respirometry

Amyotrophic lateral sclerosis is a severe neurodegenerative disease whose exact cause is still unclear. Currently, research attention is turning to the mitochondrion as a critical organelle of energy metabolism. Current knowledge is sufficient to confirm the involvement of the mitochondria in the pathophysiology of the disease, since the mitochondria are involved in many processes in the cell; however, the exact mechanism of involvement is still unclear. We used peripheral blood mononuclear cells isolated from whole fresh blood from patients with amyotrophic lateral sclerosis for measurement and matched an age- and sex-matched set of healthy subjects. The group of patients consisted of patients examined and diagnosed at the neurological clinic of the University Hospital Martin. The set of controls consisted of healthy individuals who were actively searched, and controls were selected on the basis of age and sex. The group consisted of 26 patients with sporadic forms of ALS (13 women, 13 men), diagnosed based on the definitive criteria of El Escorial. The average age of patients was 54 years, and the average age of healthy controls was 56 years. We used a high-resolution O2K respirometry method, Oxygraph-2k, to measure mitochondrial respiration. Basal respiration was lower in patients by 29.48%, pyruvate-stimulated respiration (respiratory chain complex I) was lower by 29.26%, and maximal respiratory capacity was lower by 28.15%. The decrease in succinate-stimulated respiration (respiratory chain complex II) was 26.91%. Our data confirm changes in mitochondrial respiration in ALS patients, manifested by the reduced function of complex I and complex II of the respiratory chain. These defects are severe enough to confirm this disease's hypothesized mitochondrial damage. Therefore, research interest in the future should be directed towards a deeper understanding of the involvement of mitochondria and respiratory complexes in the pathophysiology of the disease. This understanding could develop new biomarkers in diagnostics and subsequent therapeutic interventions.

AAV-mediated upregulation of VDAC1 rescues the mitochondrial respiration and sirtuins expression in a SOD1 mouse model of inherited ALS

Mitochondrial dysfunction represents one of the most common molecular hallmarks of both sporadic and familial forms of amyotrophic lateral sclerosis (ALS), a neurodegenerative disorder caused by the selective degeneration and death of motor neurons. The accumulation of misfolded proteins on and within mitochondria, as observed for SOD1 G93A mutant, correlates with a drastic reduction of mitochondrial respiration and the inhibition of metabolites exchanges, including ADP/ATP and NAD+/NADH, across the Voltage-Dependent Anion-selective Channel 1 (VDAC1), the most abundant channel protein of the outer mitochondrial membrane. Here, we show that the AAV-mediated upregulation of VDAC1 in the spinal cord of transgenic mice expressing SOD1 G93A completely rescues the mitochondrial respiratory profile. This correlates with the increased activity and levels of key regulators of mitochondrial functions and maintenance, namely the respiratory chain Complex I and the sirtuins (Sirt), especially Sirt3. Furthermore, the selective increase of these mitochondrial proteins is associated with an increase in Tom20 levels, the receptor subunit of the TOM complex. Overall, our results indicate that the overexpression of VDAC1 has beneficial effects on ALS-affected tissue by stabilizing the Complex I-Sirt3 axis.

Mitochondria: A Promising Convergent Target for the Treatment of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterized by the progressive loss of motor neurons, for which current treatment options are limited. Recent studies have shed light on the role of mitochondria in ALS pathogenesis, making them an attractive therapeutic intervention target. This review contains a very comprehensive critical description of the involvement of mitochondria and mitochondria-mediated mechanisms in ALS. The review covers several key areas related to mitochondria in ALS, including impaired mitochondrial function, mitochondrial bioenergetics, reactive oxygen species, metabolic processes and energy metabolism, mitochondrial dynamics, turnover, autophagy and mitophagy, impaired mitochondrial transport, and apoptosis. This review also highlights preclinical and clinical studies that have investigated various mitochondria-targeted therapies for ALS treatment. These include strategies to improve mitochondrial function, such as the use of dichloroacetate, ketogenic and high-fat diets, acetyl-carnitine, and mitochondria-targeted antioxidants. Additionally, antiapoptotic agents, like the mPTP-targeting agents minocycline and rasagiline, are discussed. The paper aims to contribute to the identification of effective mitochondria-targeted therapies for ALS treatment by synthesizing the current understanding of the role of mitochondria in ALS pathogenesis and reviewing potential convergent therapeutic interventions. The complex interplay between mitochondria and the pathogenic mechanisms of ALS holds promise for the development of novel treatment strategies to combat this devastating disease.

Pathophysiology of ion channels in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) stands as the most prevalent and severe form of motor neuron disease, affecting an estimated 2 in 100,000 individuals worldwide. It is characterized by the progressive loss of cortical, brainstem, and spinal motor neurons, ultimately resulting in muscle weakness and death. Although the etiology of ALS remains poorly understood in most cases, the remodelling of ion channels and alteration in neuronal excitability represent a hallmark of the disease, manifesting not only during the symptomatic period but also in the early pre-symptomatic stages. In this review, we delve into these alterations observed in ALS patients and preclinical disease models, and explore their consequences on neuronal activities. Furthermore, we discuss the potential of ion channels as therapeutic targets in the context of ALS.

ERK1/2-dependent TSPO overactivation associates with the loss of mitophagy and mitochondrial respiration in ALS

Mitochondrial dysfunction and the loss of mitophagy, aimed at recycling irreversibly damaged organelles, contribute to the onset of amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease affecting spinal cord motor neurons. In this work, we showed that the reduction of mitochondrial respiration, exactly oxygen flows linked to ATP production and maximal capacity, correlates with the appearance of the most common ALS motor symptoms in a transgenic mouse model expressing SOD1 G93A mutant. This is the result of the equal inhibition in the respiration linked to complex I and II of the electron transport chain, but not their protein levels. Since the overall mitochondrial mass was unvaried, we investigated the expression of the Translocator Protein (TSPO), a small mitochondrial protein whose overexpression was recently linked to the loss of mitophagy in a model of Parkinson's disease. Here we clearly showed that levels of TSPO are significantly increased in ALS mice. Mechanistically, this increase is linked to the overactivation of ERK1/2 pathway and correlates with a decrease in the expression of the mitophagy-related marker Atg12, indicating the occurrence of impairments in the activation of mitophagy. Overall, our work sets out TSPO as a key regulator of mitochondrial homeostasis in ALS.

Integrative Profiling of Amyotrophic Lateral Sclerosis Lymphoblasts Identifies Unique Metabolic and Mitochondrial Disease Fingerprints

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease with a rapid progression and no effective treatment. Metabolic and mitochondrial alterations in peripheral tissues of ALS patients may present diagnostic and therapeutic interest. We aimed to identify mitochondrial fingerprints in lymphoblast from ALS patients harboring SOD1 mutations (mutSOD1) or with unidentified mutations (undSOD1), compared with age-/sex-matched controls. Three groups of lymphoblasts, from mutSOD1 or undSOD1 ALS patients and age-/sex-matched controls, were obtained from Coriell Biobank and divided into 3 age-/sex-matched cohorts. Mitochondria-associated metabolic pathways were analyzed using Seahorse MitoStress and ATP Rate assays, complemented with metabolic phenotype microarrays, metabolite levels, gene expression, and protein expression and activity. Pooled (all cohorts) and paired (intra-cohort) analyses were performed by using bioinformatic tools, and the features with higher information gain values were selected and used for principal component analysis and Naïve Bayes classification. Considering the group as a target, the features that contributed to better segregation of control, undSOD1, and mutSOD1 were found to be the protein levels of Tfam and glycolytic ATP production rate. Metabolic phenotypic profiles in lymphoblasts from ALS patients with mutSOD1 and undSOD1 revealed unique age-dependent different substrate oxidation profiles. For most parameters, different patterns of variation in experimental endpoints in lymphoblasts were found between cohorts, which may be due to the age or sex of the donor. In the present work, we investigated several metabolic and mitochondrial hallmarks in lymphoblasts from each donor, and although a high heterogeneity of results was found, we identified specific metabolic and mitochondrial fingerprints, especially protein levels of Tfam and glycolytic ATP production rate, that may have a diagnostic and therapeutic interest.

Altered Bioenergetics and Metabolic Homeostasis in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that primarily affects motor neurons and causes muscle atrophy, paralysis, and death. While a great deal of progress has been made in deciphering the underlying pathogenic mechanisms, no effective treatments for the disease are currently available. This is mainly due to the high degree of complexity and heterogeneity that characterizes the disease. Over the last few decades of research, alterations to bioenergetic and metabolic homeostasis have emerged as a common denominator across many different forms of ALS. These alterations are found at the cellular level (e.g., mitochondrial dysfunction and impaired expression of monocarboxylate transporters) and at the systemic level (e.g., low BMI and hypermetabolism) and tend to be associated with survival or disease outcomes in patients. Furthermore, an increasing amount of preclinical evidence and some promising clinical evidence suggests that targeting energy metabolism could be an effective therapeutic strategy. This review examines the evidence both for and against these ALS-associated metabolic alterations and highlights potential avenues for therapeutic intervention.

The pathogenesis of amyotrophic lateral sclerosis: Mitochondrial dysfunction, protein misfolding and epigenetics

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with multiple complex mechanisms involved. Among them, mitochondrial dysfunction plays an important role in ALS. Multiple studies have shown that mitochondria are closely associated with reactive oxygen species production and oxidative stress and exhibit different functional states in different genetic backgrounds. In this review we explored the roles of Ca²⁺, autophagy, mitochondrial quality control in the regulation of mitochondrial homeostasis and their relationship with ALS. In addition, we also summarized and analyzed the roles of protein misfolding and abnormal aggregation in the pathogenesis of ALS. Moreover, we also discussed how epigenetic mechanisms such as DNA methylation and protein post-translational modification affect initiation and progression of ALS. Nevertheless, existing events still cannot fully explain the pathogenesis of ALS at present, more studies are required to explore pathological mechanisms of ALS.

Metabolic Remodeling in Skeletal Muscle Atrophy as a Therapeutic Target

Skeletal muscle is a highly responsive tissue, able to remodel its size and metabolism in response to external demand. Muscle fibers can vary from fast glycolytic to slow oxidative, and their frequency in a specific muscle is tightly regulated by fiber maturation, innervation, or external causes. Atrophic conditions, including aging, amyotrophic lateral sclerosis, and cancer-induced cachexia, differ in the causative factors and molecular signaling leading to muscle wasting; nevertheless, all of these conditions are characterized by metabolic remodeling, which contributes to the pathological progression of muscle atrophy. Here, we discuss how changes in muscle metabolism can be used as a therapeutic target and review the evidence in support of nutritional interventions and/or physical exercise as tools for counteracting muscle wasting in atrophic conditions.

Magnetic resonance spectroscopy reveals mitochondrial dysfunction in amyotrophic lateral sclerosis

Mitochondrial dysfunction is postulated to be central to amyotrophic lateral sclerosis (ALS) pathophysiology. Evidence comes primarily from disease models and conclusive data to support bioenergetic dysfunction in vivo in patients is currently lacking. This study is the first to assess mitochondrial dysfunction in brain and muscle in individuals living with ALS using 31P-magnetic resonance spectroscopy (MRS), the modality of choice to assess energy metabolism in vivo. We recruited 20 patients and 10 healthy age and gender-matched control subjects in this cross-sectional clinico-radiological study. 31P-MRS was acquired from cerebral motor regions and from tibialis anterior during rest and exercise. Bioenergetic parameter estimates were derived including: ATP, phosphocreatine, inorganic phosphate, adenosine diphosphate, Gibbs free energy of ATP hydrolysis (ΔGATP), phosphomonoesters, phosphodiesters, pH, free magnesium concentration, and muscle dynamic recovery constants. Linear regression was used to test for associations between brain data and clinical parameters (revised amyotrophic functional rating scale, slow vital capacity, and upper motor neuron score) and between muscle data and clinico-neurophysiological measures (motor unit number and size indices, force of contraction, and speed of walking). Evidence for primary dysfunction of mitochondrial oxidative phosphorylation was detected in the brainstem where ΔGATP and phosphocreatine were reduced. Alterations were also detected in skeletal muscle in patients where resting inorganic phosphate, pH, and phosphomonoesters were increased, whereas resting ΔGATP, magnesium, and dynamic phosphocreatine to inorganic phosphate recovery were decreased. Phosphocreatine in brainstem correlated with respiratory dysfunction and disability; in muscle, energy metabolites correlated with motor unit number index, muscle power, and speed of walking. This study provides in vivo evidence for bioenergetic dysfunction in ALS in brain and skeletal muscle, which appears clinically and electrophysiologically relevant. 31P-MRS represents a promising technique to assess the pathophysiology of mitochondrial function in vivo in ALS and a potential tool for future clinical trials targeting bioenergetic dysfunction.

Molecular and Cellular Mechanisms Affected in ALS

Amyotrophic lateral sclerosis (ALS) is a terminal late-onset condition characterized by the loss of upper and lower motor neurons. Mutations in more than 30 genes are associated to the disease, but these explain only ~20% of cases. The molecular functions of these genes implicate a wide range of cellular processes in ALS pathology, a cohesive understanding of which may provide clues to common molecular mechanisms across both familial (inherited) and sporadic cases and could be key to the development of effective therapeutic approaches. Here, the different pathways that have been investigated in ALS are summarized, discussing in detail: mitochondrial dysfunction, oxidative stress, axonal transport dysregulation, glutamate excitotoxicity, endosomal and vesicular transport impairment, impaired protein homeostasis, and aberrant RNA metabolism. This review considers the mechanistic roles of ALS-associated genes in pathology, viewed through the prism of shared molecular pathways.

Peroxisome Proliferator Activator Receptor Gamma Coactivator-1α Overexpression in Amyotrophic Lateral Sclerosis: A Tale of Two Transgenics

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder manifesting with upper and lower neuron loss, leading to impairments in voluntary muscle function and atrophy. Mitochondrial dysfunction in metabolism and morphology have been implicated in the pathogenesis of ALS, including atypical oxidative metabolism, reduced mitochondrial respiration in muscle, and protein aggregates in the mitochondrial outer membrane. Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) plays an essential role in the regulation of mitochondrial biogenesis, the process by which existing mitochondria grow and divide. PGC-1α has been previously reported to be downregulated in the spinal cord of individuals with ALS. Towards targeting PGC-1α as a therapeutic mechanism, we have previously reported improved motor function and survival in the SOD1^G93A mouse model of ALS by neuron-specific over-expression of PGC-1α under a neuron-specific enolase (NSE) promoter. As pharmacological intervention targeting PGC-1α would result in whole-body upregulation of this transcriptional co-activator, in the current study we investigated whether global expression of PGC-1α is beneficial in a SOD1^G93A mouse model, by generating transgenic mice with PGC-1α transgene expression driven by an actin promoter. Actin-PGC-1α expression levels were assayed and confirmed in spinal cord, brain, muscle, liver, kidney, and spleen. To determine the therapeutic effects of global expression of PGC-1α, wild-type, actin-PGC-1α, SOD1^G93A, and actin-PGC-1α/SOD1^G93A animals were monitored for weight loss, motor performance by accelerating rotarod test, and survival. Overexpression of actin-PGC-1α did not confer significant improvement in these assessed outcomes. A potential explanation for this difference is that the actin promoter may not induce levels of PGC-1α relevant to disease pathophysiology in the cells that are specifically relevant to the pathogenesis of ALS. This evidence strongly supports future therapeutic approaches that target PGC-1α primarily in neurons.

Swim Training Modulates Mouse Skeletal Muscle Energy Metabolism and Ameliorates Reduction in Grip Strength in a Mouse Model of Amyotrophic Lateral Sclerosis

Metabolic reprogramming in skeletal muscles in the human and animal models of amyotrophic lateral sclerosis (ALS) may be an important factor in the diseases progression. We hypothesized that swim training, a modulator of cellular metabolism via changes in muscle bioenergetics and oxidative stress, ameliorates the reduction in muscle strength in ALS mice. In this study, we used transgenic male mice with the G93A human SOD1 mutation B6SJL-Tg (SOD1^G93A) 1Gur/J and wild type B6SJL (WT) mice. Mice were subjected to a grip strength test and isolated skeletal muscle mitochondria were used to perform high-resolution respirometry. Moreover, the activities of enzymes involved in the oxidative energy metabolism and total sulfhydryl groups (as an oxidative stress marker) were evaluated in skeletal muscle. ALS reduces muscle strength (-70% between 11 and 15 weeks, p < 0.05), modulates muscle metabolism through lowering citrate synthase (CS) (-30% vs. WT, p = 0.0007) and increasing cytochrome c oxidase and malate dehydrogenase activities, and elevates oxidative stress markers in skeletal muscle. Swim training slows the reduction in muscle strength (-5% between 11 and 15 weeks) and increases CS activity (+26% vs. ALS I, p = 0.0048). Our findings indicate that swim training is a modulator of skeletal muscle energy metabolism with concomitant improvement of skeletal muscle function in ALS mice.

Discrete mitochondrial aberrations in the spinal cord of sporadic ALS patients

Amyotrophic lateral sclerosis (ALS) is an adult onset neurodegenerative disease characterized by progressive motor neuron degeneration in the brain and spinal cord leading to muscle atrophy, paralysis, and death. Mitochondrial dysfunction is a major contributor to motor neuron degeneration associated with ALS progression. Mitochondrial abnormalities have been determined in spinal cords of animal disease models and ALS patients. However, molecular mechanisms leading to mitochondrial dysfunction in sporadic ALS (sALS) patients remain unclear. Also, segmental or regional variation in mitochondrial activity in the spinal cord has not been extensively examined in ALS. In our study, the activity of mitochondrial electron transport chain complex IV was examined in post-mortem gray and white matter of the cervical and lumbar spinal cords from male and female sALS patients and controls. Mitochondrial distribution and density in spinal cord motor neurons, lateral funiculus, and capillaries in gray and white matter were analyzed by immunohistochemistry. Results showed that complex IV activity was significantly decreased only in gray matter in both cervical and lumbar spinal cords from ALS patients. In ALS cervical and lumbar spinal cords, significantly increased mitochondrial density and altered distribution were observed in motor neurons, lateral funiculus, and cervical white matter capillaries. Discrete decreased complex IV activity in addition to changes in mitochondria distribution and density determined in the spinal cord in sALS patients are novel findings. These explicit mitochondrial defects in the spinal cord may contribute to ALS pathogenesis and should be considered in development of therapeutic approaches for this disease.

The role of mitochondria in amyotrophic lateral sclerosis

Mitochondria are unique organelles that are essential for a variety of cellular processes including energy metabolism, calcium homeostasis, lipid biosynthesis, and apoptosis. Mitochondrial dysfunction is a prevalent feature of many neurodegenerative diseases including motor neuron disorders such as amyotrophic lateral sclerosis (ALS). Disruption of mitochondrial structure, dynamics, bioenergetics and calcium buffering has been extensively reported in ALS patients and model systems and has been suggested to be directly involved in disease pathogenesis. Here we review the alterations in mitochondrial parameters in ALS and examine the common pathways to dysfunction.

Creatine Supplementation Improves Dopaminergic Cell Survival and Protects against MPP+ Toxicity in an Organotypic Tissue Culture System

Cell replacement therapy using mesencephalic precursor cells is an experimental approach for the treatment of Parkinson's disease (PD). A significant problem associated with this procedure is the poor survival of grafted neurons. Impaired energy metabolism is considered to contribute to neuronal cell death after transplantation. Creatine is a substrate for mitochondrial and cytosolic creatine kinases (CK) and buffers cellular ATP resources. Furthermore, elevated cellular creatine levels facilitate metabolic channeling and show anti-apoptotic properties. Exogenous creatine supplementation therefore might offer a tool for improvement of dopaminergic neuron survival. The present study aimed at investigating the effects of creatine on cell survival of rat embryonic day 14 (E14) ventral mesencephalic neurons grown as organotypic free-floating roller tube (FFRT) cultures. We found that the brain-specific isoform of CK (BB-CK) and the ubiquitous mitochondrial isoform (uMt-CK) are expressed at high levels in FFRT cultures and colocalize with tyrosine hydroxylase immunoreactive (TH-ir) cells. Exposure of these cultures to creatine induced an increase in the content of the BB-CK isotype. Creatine (5 mM) administration starting at day in vitro (DIV) 7 resulted in a significant increase (+35%) in TH-ir cell density at DIV21. In addition, we observed that creatine treatment provided neuroprotection against 1-methyl-4-phenyl pyridinium ion (MPP+)-induced TH-ir cell loss in the FFRT culture system, resulting in a significantly higher density (+19%) of TH-ir neurons in creatine-treated cultures compared to corresponding controls. The decrease of TH-ir neurons in the MPP+-treated group corresponded with an increase in immunoreactivity for active caspase-3, an effect that was not seen in the group receiving creatine supplementation. In conclusion, our data imply that creatine administration is beneficial for the survival of TH-ir neurons encountering harmful conditions.

Triheptanoin Protects Motor Neurons and Delays the Onset of Motor Symptoms in a Mouse Model of Amyotrophic Lateral Sclerosis

There is increasing evidence that energy metabolism is disturbed in Amyotrophic Lateral Sclerosis (ALS) patients and animal models. Treatment with triheptanoin, the triglyceride of heptanoate, is a promising approach to provide alternative fuel to improve oxidative phosphorylation and aid ATP generation. Heptanoate can be metabolized to propionyl-CoA, which after carboxylation can produce succinyl-CoA and thereby re-fill the tricarboxylic acid (TCA) cycle (anaplerosis). Here we tested the hypothesis that treatment with triheptanoin prevents motor neuron loss and delays the onset of disease symptoms in female mice overexpressing the mutant human SOD1^G93A (hSOD1^G93A) gene. When oral triheptanoin (35% of caloric content) was initiated at P35, motor neuron loss at 70 days of age was attenuated by 33%. In untreated hSOD1^G93A mice, the loss of hind limb grip strength began at 16.7 weeks. Triheptanoin maintained hind limb grip strength for 2.8 weeks longer (p<0.01). Loss of balance on the rotarod and reduction of body weight were delayed by 13 and 11 days respectively (both p<0.01). Improved motor function occurred in parallel with alterations in the expression of genes associated with muscle metabolism. In gastrocnemius muscles, the mRNA levels of pyruvate, 2-oxoglutarate and succinate dehydrogenases and methyl-malonyl mutase were reduced by 24–33% in 10 week old hSOD1^G93A mice when compared to wild-type mice, suggesting that TCA cycling in skeletal muscle may be slowed in this ALS mouse model at a stage when muscle strength is still normal. At 25 weeks of age, mRNA levels of succinate dehydrogenases, glutamic pyruvic transaminase 2 and the propionyl carboxylase β subunit were reduced by 69–84% in control, but not in triheptanoin treated hSOD1^G93A animals. Taken together, our results suggest that triheptanoin slows motor neuron loss and the onset of motor symptoms in ALS mice by improving TCA cycling.

Mitochondrial dysfunction in blood cells from amyotrophic lateral sclerosis patients

Mitochondrial dysfunction is implicated in amyotrophic lateral sclerosis, where the progressive degeneration of motor neurons results in muscle atrophy, paralysis and death. Abnormalities in both central nervous system and muscle mitochondria have previously been demonstrated in patient samples, indicating systemic disease. In this case-control study, venous blood samples were acquired from 24 amyotrophic lateral sclerosis patients and 21 age-matched controls. Platelets and peripheral blood mononuclear cells were isolated and mitochondrial oxygen consumption measured in intact and permeabilized cells with additions of mitochondrial substrates, inhibitors and titration of an uncoupler. Respiratory values were normalized to cell count and for two markers of cellular mitochondrial content, citrate synthase activity and mitochondrial DNA, respectively. Mitochondrial function was correlated with clinical staging of disease severity. Complex IV (cytochrome c-oxidase)-activity normalized to mitochondrial content was decreased in platelets from amyotrophic lateral sclerosis patients both when normalized to citrate synthase activity and mitochondrial DNA copy number. In mononuclear cells, complex IV-activity was decreased when normalized to citrate synthase activity. Mitochondrial content was increased in amyotrophic lateral sclerosis patient platelets. In mononuclear cells, complex I activity declined and mitochondrial content increased progressively with advancing disease stage. The findings are, however, based on small subsets of patients and need to be confirmed. We conclude that when normalized to mitochondria-specific content, complex IV-activity is reduced in blood cells from amyotrophic lateral sclerosis patients and that there is an apparent compensatory increase in cellular mitochondrial content. This supports systemic involvement in amyotrophic lateral sclerosis and suggests further study of mitochondrial function in blood cells as a future biomarker for the disease.

Selective vulnerability of motoneuron and perturbed mitochondrial calcium homeostasis in amyotrophic lateral sclerosis: implications for motoneurons specific calcium dysregulation

Amyotrophic lateral sclerosis (ALS) is a lethal neurodegenerative disorder characterized by the selective degeneration of defined subgroups of motoneuron in the brainstem, spinal cord and motor cortex with signature hallmarks of mitochondrial Ca²⁺ overload, free radical damage, excitotoxicity and impaired axonal transport. Although intracellular disruptions of cytosolic and mitochondrial calcium, and in particular low cytosolic calcium ([Ca²⁺]_c) buffering and a strong interaction between metabolic mechanisms and [Ca²⁺]_i have been identified predominantly in motoneuron impairment, the causes of these disruptions are unknown. The existing evidence suggests that the mutant superoxide dismutase1 (mtSOD1)-mediated toxicity in ALS acts through mitochondria, and that alteration in cytosolic and mitochondria-ER microdomain calcium accumulation are critical to the neurodegenerative process. Furthermore, chronic excitotoxcity mediated by Ca²⁺-permeable AMPA and NMDA receptors seems to initiate vicious cycle of intracellular calcium dysregulation which leads to toxic Ca²⁺ overload and thereby selective neurodegeneration. Recent advancement in the experimental analysis of calcium signals with high spatiotemporal precision has allowed investigations of calcium regulation in-vivo and in-vitro in different cell types, in particular selectively vulnerable/resistant cell types in different animal models of this motoneuron disease. This review provides an overview of latest advances in this field, and focuses on details of what has been learned about disrupted Ca²⁺ homeostasis and mitochondrial degeneration. It further emphasizes the critical role of mitochondria in preventing apoptosis by acting as a Ca²⁺ buffers, especially in motoneurons, in pathophysiological conditions such as ALS.

Mitochondrial dysfunction in amyotrophic lateral sclerosis - a valid pharmacological target?

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease characterized by the selective death of upper and lower motor neurons which ultimately leads to paralysis and ultimately death. Pathological changes in ALS are closely associated with pronounced and progressive changes in mitochondrial morphology, bioenergetics and calcium homeostasis. Converging evidence suggests that impaired mitochondrial function could be pivotal in the rapid neurodegeneration of this condition. In this review, we provide an update of recent advances in understanding mitochondrial biology in the pathogenesis of ALS and highlight the therapeutic value of pharmacologically targeting mitochondrial biology to slow disease progression.

Mitochondrial diseases of the brain

Neurodegenerative disorders are debilitating diseases of the brain, characterized by behavioral, motor and cognitive impairments. Ample evidence underpins mitochondrial dysfunction as a central causal factor in the pathogenesis of neurodegenerative disorders including Parkinson's disease, Huntington's disease, Alzheimer's disease, Amyotrophic lateral sclerosis, Friedreich's ataxia and Charcot-Marie-Tooth disease. In this review, we discuss the role of mitochondrial dysfunction such as bioenergetics defects, mitochondrial DNA mutations, gene mutations, altered mitochondrial dynamics (mitochondrial fusion/fission, morphology, size, transport/trafficking, and movement), impaired transcription and the association of mutated proteins with mitochondria in these diseases. We highlight the therapeutic role of mitochondrial bioenergetic agents in toxin and in cellular and genetic animal models of neurodegenerative disorders. We also discuss clinical trials of bioenergetics agents in neurodegenerative disorders. Lastly, we shed light on PGC-1α, TORC-1, AMP kinase, Nrf2-ARE, and Sirtuins as novel therapeutic targets for neurodegenerative disorders.

Mitochondrial damage revealed by immunoselection for ALS-linked misfolded SOD1

Mutant superoxide dismutase 1 (SOD1) selectively associates with spinal cord mitochondria in rodent models of SOD1-mediated amyotrophic lateral sclerosis. A portion of mutant SOD1 exists in a non-native/misfolded conformation that is selectively recognized by conformational antibodies. Misfolded SOD1 is common to all mutant SOD1 models, is uniquely found in areas affected by the disease and is considered to mediate toxicity. We report that misfolded SOD1 recognized by the antibody B8H10 is present in greater abundance in mitochondrial fractions of SOD1(G93A) rat spinal cords compared with oxidized SOD1, as recognized by the C4F6 antibody. Using a novel flow cytometric assay, we detect an age-dependent deposition of B8H10-reactive SOD1 on spinal cord mitochondria from both SOD1(G93A) rats and SOD1(G37R) mice. Mitochondrial damage, including increased mitochondrial volume, excess superoxide production and increased exposure of the toxic BH3 domain of Bcl-2, tracks positively with the presence of misfolded SOD1. Lastly, B8H10 reactive misfolded SOD1 is present in the lysates and mitochondrial fractions of lymphoblasts derived from ALS patients carrying SOD1 mutations, but not in controls. Together, these results highlight misfolded SOD1 as common to two ALS rodent animal models and familial ALS patient lymphoblasts with four different SOD1 mutations. Studies in the animal models point to a role for misfolded SOD1 in mitochondrial dysfunction in ALS pathogenesis.

Is SOD1 loss of function involved in amyotrophic lateral sclerosis?

Mutations in the gene superoxide dismutase 1 (SOD1) are causative for familial forms of the neurodegenerative disease amyotrophic lateral sclerosis. When the first SOD1 mutations were identified they were postulated to give rise to amyotrophic lateral sclerosis through a loss of function mechanism, but experimental data soon showed that the disease arises from a—still unknown—toxic gain of function, and the possibility that loss of function plays a role in amyotrophic lateral sclerosis pathogenesis was abandoned. Although loss of function is not causative for amyotrophic lateral sclerosis, here we re-examine two decades of evidence regarding whether loss of function may play a modifying role in SOD1–amyotrophic lateral sclerosis. From analysing published data from patients with SOD1–amyotrophic lateral sclerosis, we find a marked loss of SOD1 enzyme activity arising from almost all mutations. We continue to examine functional data from all Sod1 knockout mice and we find obvious detrimental effects within the nervous system with, interestingly, some specificity for the motor system. Here, we bring together historical and recent experimental findings to conclude that there is a possibility that SOD1 loss of function may play a modifying role in amyotrophic lateral sclerosis. This likelihood has implications for some current therapies aimed at knocking down the level of mutant protein in patients with SOD1–amyotrophic lateral sclerosis. Finally, the wide-ranging phenotypes that result from loss of function indicate that SOD1 gene sequences should be screened in diseases other than amyotrophic lateral sclerosis.

Redox proteomics in selected neurodegenerative disorders: from its infancy to future applications

Several studies demonstrated that oxidative damage is a characteristic feature of many neurodegenerative diseases. The accumulation of oxidatively modified proteins may disrupt cellular functions by affecting protein expression, protein turnover, cell signaling, and induction of apoptosis and necrosis, suggesting that protein oxidation could have both physiological and pathological significance. For nearly two decades, our laboratory focused particular attention on studying oxidative damage of proteins and how their chemical modifications induced by reactive oxygen species/reactive nitrogen species correlate with pathology, biochemical alterations, and clinical presentations of Alzheimer's disease. This comprehensive article outlines basic knowledge of oxidative modification of proteins and lipids, followed by the principles of redox proteomics analysis, which also involve recent advances of mass spectrometry technology, and its application to selected age-related neurodegenerative diseases. Redox proteomics results obtained in different diseases and animal models thereof may provide new insights into the main mechanisms involved in the pathogenesis and progression of oxidative-stress-related neurodegenerative disorders. Redox proteomics can be considered a multifaceted approach that has the potential to provide insights into the molecular mechanisms of a disease, to find disease markers, as well as to identify potential targets for drug therapy. Considering the importance of a better understanding of the cause/effect of protein dysfunction in the pathogenesis and progression of neurodegenerative disorders, this article provides an overview of the intrinsic power of the redox proteomics approach together with the most significant results obtained by our laboratory and others during almost 10 years of research on neurodegenerative disorders since we initiated the field of redox proteomics.

Caprylic triglyceride as a novel therapeutic approach to effectively improve the performance and attenuate the symptoms due to the motor neuron loss in ALS disease

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder of motor neurons causing progressive muscle weakness, paralysis, and finally death. ALS patients suffer from asthenia and their progressive weakness negatively impacts quality of life, limiting their daily activities. They have impaired energy balance linked to lower activity of mitochondrial electron transport chain enzymes in ALS spinal cord, suggesting that improving mitochondrial function may present a therapeutic approach for ALS. When fed a ketogenic diet, the G93A ALS mouse shows a significant increase in serum ketones as well as a significantly slower progression of weakness and lower mortality rate. In this study, we treated SOD1-G93A mice with caprylic triglyceride, a medium chain triglyceride that is metabolized into ketone bodies and can serve as an alternate energy substrate for neuronal metabolism. Treatment with caprylic triglyceride attenuated progression of weakness and protected spinal cord motor neuron loss in SOD1-G93A transgenic animals, significantly improving their performance even though there was no significant benefit regarding the survival of the ALS transgenic animals. We found that caprylic triglyceride significantly promoted the mitochondrial oxygen consumption rate in vivo. Our results demonstrated that caprylic triglyceride alleviates ALS-type motor impairment through restoration of energy metabolism in SOD1-G93A ALS mice, especially during the overt stage of the disease. These data indicate the feasibility of using caprylic acid as an easily administered treatment with a high impact on the quality of life of ALS patients.

Mitochondrial dysfunction in familial amyotrophic lateral sclerosis

A growing body of evidence suggests that mitochondrial dysfunctions play a crucial role in the pathogenesis of various neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS), a neurodegenerative disease affecting both upper and lower motor neurons. Although ALS is predominantly a sporadic disease, approximately 10% of cases are familial. The most frequent familial form is caused by mutations in the gene encoding Cu/Zn superoxide dismutase 1 (SOD1). A dominant toxic gain of function of mutant SOD1 has been considered as the cause of the disease and mitochondria are thought to be key players in the pathogenesis. However, the exact nature of the link between mutant SOD1 and mitochondrial dysfunctions remains to be established. Here, we briefly review the evidence for mitochondrial dysfunctions in familial ALS and discuss a possible link between mutant SOD1 and mitochondrial dysfunction.

Mitochondrial pathobiology in ALS

Amyotrophic lateral sclerosis (ALS) is the third most common human adult-onset neurodegenerative disease. Some forms of ALS are inherited, and disease-causing genes have been identified. Nevertheless, the mechanisms of neurodegeneration in ALS are unresolved. Genetic, biochemical, and morphological analyses of human ALS as well as cell and animal models of ALS reveal that mitochondria could have roles in this neurodegeneration. The varied functions and properties of mitochondria might render subsets of selectively vulnerable neurons intrinsically susceptible to cellular aging and stress and overlying genetic variations. Changes occur in mitochondrial respiratory chain enzymes and mitochondrial programmed cell death proteins in ALS. Transgenic mouse models of ALS reveal possible principles governing the biology of neurodegeneration that implicate mitochondria and the mitochondrial permeability transition pore. This paper reviews how mitochondrial pathobiology might contribute to the mechanisms of neurodegeneration in ALS.

Biology of mitochondria in neurodegenerative diseases

Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS) are the most common human adult-onset neurodegenerative diseases. They are characterized by prominent age-related neurodegeneration in selectively vulnerable neural systems. Some forms of AD, PD, and ALS are inherited, and genes causing these diseases have been identified. Nevertheless, the mechanisms of the neuronal degeneration in these familial diseases, and in the more common idiopathic (sporadic) diseases, are unresolved. Genetic, biochemical, and morphological analyses of human AD, PD, and ALS, as well as their cell and animal models, reveal that mitochondria could have roles in this neurodegeneration. The varied functions and properties of mitochondria might render subsets of selectively vulnerable neurons intrinsically susceptible to cellular aging and stress and the overlying genetic variations. In AD, alterations in enzymes involved in oxidative phosphorylation, oxidative damage, and mitochondrial binding of Aβ and amyloid precursor protein have been reported. In PD, mutations in mitochondrial proteins have been identified and mitochondrial DNA mutations have been found in neurons in the substantia nigra. In ALS, changes occur in mitochondrial respiratory chain enzymes and mitochondrial programmed cell death proteins. Transgenic mouse models of human neurodegenerative disease are beginning to reveal possible principles governing the biology of selective neuronal vulnerability that implicate mitochondria and the mitochondrial permeability transition pore. This chapter reviews several aspects of mitochondrial biology and how mitochondrial pathobiology might contribute to the mechanisms of neurodegeneration in AD, PD, and ALS.

Mitochondria in neurodegeneration

Many neurodegenerative diseases demonstrate abnormal mitochondrial morphology and biochemical dysfunction. Alterations are often systemic rather than brain-limited. Mitochondrial dysfunction may arise as a consequence of abnormal mitochondrial DNA, mutated nuclear proteins that interact directly or indirectly with mitochondria, or through unknown causes. In most cases it is unclear where mitochondria sit in relation to the overall disease cascades that ultimately causes neuronal dysfunction and death, and there is still controversy regarding the question of whether mitochondrial dysfunction is a necessary step in neurodegeneration. In this chapter we highlight and catalogue mitochondrial perturbations in some of the major neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD). We consider data that suggest mitochondria may be critically involved in neurodegenerative disease neurodegeneration cascades.

Autoimmunity in amyotrophic lateral sclerosis: past and present

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting particularly motor neurons for which no cure or effective treatment is available. Although the cause of ALS remains unknown, accumulative evidence suggests an autoimmune mechanism of pathogenesis. In this paper, we will summarize the current research related to autoimmunity in the sporadic form of ALS and discuss the potential underlying pathogenic mechanisms and perspectives. Presented data supports the view that humoral immune responses against motor nerve terminals can initiate a series of physiological changes leading to alteration of calcium homeostasis. In turn, loss of calcium homeostasis may induce neuronal death through apoptotic signaling pathways. Additional approaches identifying specific molecular features of this hypothesis are required, which will hopefully allow us to develop techniques of early diagnosis and effective therapies.

Peroxisome proliferator activator receptor gamma coactivator-1alpha (PGC-1α) improves motor performance and survival in a mouse model of amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that affects spinal cord and cortical motor neurons. An increasing amount of evidence suggests that mitochondrial dysfunction contributes to motor neuron death in ALS. Peroxisome proliferator-activated receptor gamma co-activator-1α (PGC-1α) is a principal regulator of mitochondrial biogenesis and oxidative metabolism.

RESULTS

In this study, we examined whether PGC-1α plays a protective role in ALS by using a double transgenic mouse model where PGC-1α is over-expressed in an SOD1 transgenic mouse (TgSOD1-G93A/PGC-1α). Our results indicate that PGC-1α significantly improves motor function and survival of SOD1-G93A mice. The behavioral improvements were accompanied by reduced blood glucose level and by protection of motor neuron loss, restoration of mitochondrial electron transport chain activities and inhibition of stress signaling in the spinal cord.

CONCLUSION

Our results demonstrate that PGC-1α plays a beneficial role in a mouse model of ALS, suggesting that PGC-1α may be a potential therapeutic target for ALS therapy.

Respiration and ROS production in brain and spinal cord mitochondria of transgenic rats with mutant G93a Cu/Zn-superoxide dismutase gene

Mitochondrial dysfunction is involved in the pathogenesis of motor neuron degeneration in the G93A mutant transgenic (tgmSOD1) animal model of ALS. However, it is unknown whether mitochondriopathy is a primary or secondary event. We isolated brain (BM) and spinal cord (SCM) mitochondria from 2 month old presymptomatic tgmSOD1 rats and studied respiration and generation of reactive oxygen species (ROS) using a new metabolic paradigm (Panov et al., Am. J. Physiol., Regul. Integr. Comp. Physiol., 2011). The yields of BM and SCM from tgmSOD1 rats were 27% and 58% lower than normal rats (WT). The rates of the State 3 and State 3U respiration of tgBM and tgSCM were normal with glutamate+pyruvate+malate as substrates but were inhibited with pyruvate+malate in tgBM and glutamate+malate in tgSCM. In tgSCM the State 4 respiration with all substrates was significantly (1.5-2 fold) increased as compared with WT-SCM. Western blot analysis showed that tgSCM had lower contents of complexes III (-60%) and IV (-35%), and the presence of mutated SOD1 protein in both tgBM and tgSCM. With glutamate+pyruvate+malate or succinate+glutamate+pyruvate+malate as substrates, tgBM and tgSCM generated 5-7 fold more ROS than normal mitochondria, and tgSCM generated two times more ROS than tgBM. We show that the major damaging ROS species in tgmSOD1 animals is H(2)O(2). It is known that mutated SOD1, damaged by H(2)O(2), associates with mitochondria, and we suggest that this further increases production of H(2)O(2). We also show that the total tissue calcium content remained normal in the brain but was diminished by 26% in the spinal cord of presymptomatic tgmSOD1 rats.

CONCLUSION

In tgSCM abnormally high rates of ROS generation, associated with reverse electron transport, result in accelerated mitochondriopathy, and the Ca(2+)-dependent excitotoxic death of motor neurons. Thus mitochondrial dysfunction is a key early element in pathogenesis of motor neuron degeneration in tgmSOD1 rats.

G37R SOD1 mutant alters mitochondrial complex I activity, Ca(2+) uptake and ATP production

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by selective death of motor neurons. Mutations in Cu/Zn superoxide dismutase-1 (SOD1) cause familial ALS but the molecular mechanisms whereby these mutations induce motor neuron death remain controversial. Here, we show that stable overexpression of mutant human SOD1 (G37R) - but not wild-type SOD1 (wt-SOD1) - in mouse neuroblastoma cells (N2a) results in morphological abnormalities of mitochondria accompanied by several dysfunctions. Activity of the oxidative phosphorylation complex I was significantly reduced in G37R cells and correlated with lower mitochondrial membrane potential and reduced levels of cytosolic ATP. Using targeted chimeric aequorin we further analyzed the consequences of mitochondrial dysfunction on cellular Ca(2+) handling. Mitochondrial Ca(2+) uptake, elicited by IP(3)-induced Ca(2+) release from endoplasmic reticulum (ER) was significantly reduced in G37R cells, while uptake induced by a brief Ca(2+) pulse was not affected in permeabilized cells. The decreased mitochondrial Ca(2+) uptake resulted in increased cytosolic Ca(2+) transients, whereas ER Ca(2+) load and resting cytosolic Ca(2+) levels were not affected. Together, these findings suggest that the mechanism linking mutant G37R SOD1 and ALS involves mitochondrial respiratory chain deficiency resulting in ATP loss and impairment of mitochondrial and cytosolic Ca(2+) homeostasis.

Proteomic analysis of mitochondrial dysfunction in neurodegenerative diseases

Alzheimer's, Parkinson's and Huntington's disease, and amyotrophic lateral sclerosis are the most relevant neurodegenerative syndromes worldwide. The identification of the etiology and additional factors contributing to the onset and progression of these diseases is of great importance in order to develop both preventive and therapeutic intervention. A common feature of these pathologies is the formation of aggregates, containing mutated and/or misfolded proteins, in specific subsets of neurons, which progressively undergo functional impairment and die. The relationship between protein aggregation and the molecular events leading to neurodegeneration has not yet been clarified. In the last decade, several lines of evidence pointed to a major role for mitochondrial dysfunction in the onset of these pathologies. Here, we review how proteomics has been applied to neurodegenerative diseases in order to characterize the relationship existing between protein aggregation and mitochondrial alterations. Moreover, we highlight recent advances in the use of proteomics to identify protein modifications caused by oxidative stress. Future developments in this field are expected to significantly contribute to the full comprehension of the molecular mechanisms at the heart of neurodegeneration.

The legs at odd angles (Loa) mutation in cytoplasmic dynein ameliorates mitochondrial function in SOD1G93A mouse model for motor neuron disease

Amyotrophic lateral sclerosis (ALS) is a debilitating and fatal late-onset neurodegenerative disease. Familial cases of ALS (FALS) constitute ∼10% of all ALS cases, and mutant superoxide dismutase 1 (SOD1) is found in 15–20% of FALS. SOD1 mutations confer a toxic gain of unknown function to the protein that specifically targets the motor neurons in the cortex and the spinal cord. We have previously shown that the autosomal dominant Legs at odd angles (Loa) mutation in cytoplasmic dynein heavy chain (Dync1h1) delays disease onset and extends the life span of transgenic mice harboring human mutant SOD1^G93A. In this study we provide evidence that despite the lack of direct interactions between mutant SOD1 and either mutant or wild-type cytoplasmic dynein, the Loa mutation confers significant reductions in the amount of mutant SOD1 protein in the mitochondrial matrix. Moreover, we show that the Loa mutation ameliorates defects in mitochondrial respiration and membrane potential observed in SOD1^G93A motor neuron mitochondria. These data suggest that the Loa mutation reduces the vulnerability of mitochondria to the toxic effects of mutant SOD1, leading to improved mitochondrial function in SOD1^G93A motor neurons.

Mitochondrial and Cell Death Mechanisms in Neurodegenerative Diseases

Alzheimer’s disease (AD), Parkinson’s disease (PD) and amyotrophic lateral sclerosis (ALS) are the most common human adult-onset neurodegenerative diseases. They are characterized by prominent age-related neurodegeneration in selectively vulnerable neural systems. Some forms of AD, PD, and ALS are inherited, and genes causing these diseases have been identified. Nevertheless, the mechanisms of the neuronal cell death are unresolved. Morphological, biochemical, genetic, as well as cell and animal model studies reveal that mitochondria could have roles in this neurodegeneration. The functions and properties of mitochondria might render subsets of selectively vulnerable neurons intrinsically susceptible to cellular aging and stress and overlying genetic variations, triggering neurodegeneration according to a cell death matrix theory. In AD, alterations in enzymes involved in oxidative phosphorylation, oxidative damage, and mitochondrial binding of Aβ and amyloid precursor protein have been reported. In PD, mutations in putative mitochondrial proteins have been identified and mitochondrial DNA mutations have been found in neurons in the substantia nigra. In ALS, changes occur in mitochondrial respiratory chain enzymes and mitochondrial cell death proteins. Transgenic mouse models of human neurodegenerative disease are beginning to reveal possible principles governing the biology of selective neuronal vulnerability that implicate mitochondria and the mitochondrial permeability transition pore. This review summarizes how mitochondrial pathobiology might contribute to neuronal death in AD, PD, and ALS and could serve as a target for drug therapy.

Dynamic NAD(P)H post-synaptic autofluorescence signals for the assessment of mitochondrial function in a neurodegenerative disease: monitoring the primary motor cortex of G93A mice, an amyotrophic lateral sclerosis model

Abnormal mitochondrial function was reported in patients and models for amyotrophic lateral sclerosis (ALS). It is therefore important to set up sensitive tools for the monitoring of active agents that enhance energy metabolism delay onset, and extend lifespan of transgenic G93A-SOD1 ALS mice. In this report, primary motor cortex slices from G93A mice at different stages of disease were studied, using NAD(P)H autofluorescence post-synaptic signals following ultraviolet stimuli, as a probe to evaluate mitochondrial function. We observed consistent age-related alterations of responses in G93A primary motor cortex slices versus controls. We conclude that NAD(P)H autofluorescence post-synaptic signal is a highly sensitive real-time technique to detect mitochondrial function failure in primary cortex from living tissues.

Excitotoxic motoneuron degeneration induced by glutamate receptor agonists and mitochondrial toxins in organotypic cultures of chick embryo spinal cord

Glutamate receptor-mediated excitotoxicity and mitochondrial dysfunction appear to play an important role in motoneuron (MN) degeneration in amyotrophic lateral sclerosis (ALS). In the present study we used an organotypic slice culture of chick embryo spinal cord to explore the responsiveness of mature MNs to different excitotoxic stimuli and mitrochondrial inhibition. We found that, in this system, MNs are highly vulnerable to excitotoxins such as glutamate, N-methyl-D-aspartate (NMDA), and kainate (KA), and that the neuroprotective drug riluzole rescues MNs from KA-mediated excitotoxic death. MNs are also sensitive to chronic mitochondrial inhibition induced by malonate and 3-nitropropionic acid (3-NP) in a dose-dependent manner. MN degeneration induced by treatment with mitochondrial toxins displays structural changes similar to those seen following excitotoxicity and can be prevented by applying either the antiexcitotoxic drug 6-cyano-7-nitroquinoxaline-2,3-dione disodium (CNQX) or riluzole. Excitotoxicity results in an increased frequency of normal spontaneous Ca2+ oscillations in MNs, which is followed by a sustained deregulation of intracellular Ca2+. Tolerance to excitotoxic MN death resulting from chronic exposure to excitotoxins correlates with a reduced excitotoxin-induced increase in intracellular Ca2+ and increased thapsigargin-sensitive Ca2+ stores.

The mitochondrial permeability transition pore: a molecular target for amyotrophic lateral sclerosis therapy

Effective therapies are needed for the treatment of amyotrophic lateral sclerosis (ALS), a fatal type of motor neuron disease. Morphological, biochemical, molecular genetic, and cell/animal model studies suggest that mitochondria have potentially diverse roles in neurodegenerative disease mechanisms and neuronal cell death. In human ALS, abnormalities have been found in mitochondrial structure, mitochondrial respiratory chain enzymes, and mitochondrial cell death proteins indicative of some non-classical form of programmed cell death. Mouse models of ALS are beginning to reveal possible principles governing the biology of selective neuronal vulnerability that implicate mitochondria. This minireview summarizes work on the how malfunctioning mitochondria might contribute to neuronal death in ALS through the biophysical entity called the mitochondrial permeability pore (mPTP). The major protein components of the mPTP are enriched in mouse motor neurons. Early in the course of disease in ALS mice expressing human mutant superoxide dismutase-1, mitochondria in motor neurons undergo trafficking abnormalities and dramatic remodeling resulting in the formation of mega-mitochondria and coinciding with increased protein carbonyl formation and nitration of mPTP components. The genetic deletion of a major mPTP component, cyclophilin D, has robust effects in ALS mice by delaying disease onset and extending survival. Thus, attention should be directed to the mPTP as a rational target for the development of drugs designed to treat ALS.

Light therapy and supplementary Riboflavin in the SOD1 transgenic mouse model of familial amyotrophic lateral sclerosis (FALS)

BACKGROUND AND OBJECTIVE

Familial amyotrophic lateral sclerosis (FALS) is a neurodegenerative disease characterized by progressive loss of motor neurons and death. Mitochondrial dysfunction and oxidative stress play an important role in motor neuron loss in ALS. Light therapy (LT) has biomodulatory effects on mitochondria. Riboflavin improves energy efficiency in mitochondria and reduces oxidative injury. The purpose of this study was to examine the synergistic effect of LT and riboflavin on the survival of motor neurons in a mouse model of FALS.

STUDY DESIGN/MATERIALS AND METHODS

G93A SOD1 transgenic mice were divided into four groups: Control, Riboflavin, Light, and Riboflavin+Light (combination). Mice were treated from 51 days of age until death. A single set of LT parameters was used: 810 nm diode laser, 140-mW output power, 1.4 cm(2) spot area, 120 seconds treatment duration, and 12 J/cm(2) energy density. Behavioral tests and weight monitoring were done weekly. At end stage of the disease, mice were euthanized, survival data was collected and immunohistochemistry and motor neuron counts were performed.

RESULTS

There was no difference in survival between groups. Motor function was not significantly improved with the exception of the rotarod test which showed significant improvement in the Light group in the early stage of the disease. Immunohistochemical expression of the astrocyte marker, glial fibrilary acidic protein, was significantly reduced in the cervical and lumbar enlargements of the spinal cord as a result of LT. There was no difference in the number of motor neurons in the anterior horn of the lumbar enlargement between groups.

CONCLUSIONS

The lack of significant improvement in survival and motor performance indicates study interventions were ineffective in altering disease progression in the G93A SOD1 mice. Our findings have potential implications for the conceptual use of light to treat other neurodegenerative diseases that have been linked to mitochondrial dysfunction.

Mitochondrial approaches for neuroprotection

A large body of evidence from postmortem brain tissue and genetic analysis in humans and biochemical and pathological studies in animal models (transgenic and toxin) of neurodegeneration suggest that mitochondrial dysfunction is a common pathological mechanism. Mitochondrial dysfunction from oxidative stress, mitochondrial DNA deletions, pathological mutations, altered mitochondrial morphology, and interaction of pathogenic proteins with mitochondria leads to neuronal demise. Therefore, therapeutic approaches targeting mitochondrial dysfunction and oxidative damage hold great promise in neurodegenerative diseases. This review discusses the potential therapeutic efficacy of creatine, coenzyme Q10, idebenone, synthetic triterpenoids, and mitochondrial targeted antioxidants (MitoQ) and peptides (SS-31) in in vitro studies and in animal models of Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and Alzheimer's disease. We have also reviewed the current status of clinical trials of creatine, coenzyme Q10, idebenone, and MitoQ in neurodegenerative disorders. Further, we discuss newly identified therapeutic targets, including peroxisome proliferator-activated receptor-gamma-coactivator and sirtuins, which provide promise for future therapeutic developments in neurodegenerative disorders.

Isolated cytochrome c oxidase deficiency in G93A SOD1 mice overexpressing CCS protein

G93A SOD1 transgenic mice overexpressing CCS protein develop an accelerated disease course that is associated with enhanced mitochondrial pathology and increased mitochondrial localization of mutant SOD1. Because these results suggest an effect of mutant SOD1 on mitochondrial function, we assessed the enzymatic activities of mitochondrial respiratory chain complexes in the spinal cords of CCS/G93A SOD1 and control mice. CCS/G93A SOD1 mouse spinal cord demonstrates a 55% loss of complex IV (cytochrome c oxidase) activity compared with spinal cord from age-matched non-transgenic or G93A SOD1 mice. In contrast, CCS/G93A SOD1 spinal cord shows no reduction in the activities of complex I, II, or III. Blue native gel analysis further demonstrates a marked reduction in the levels of complex IV but not of complex I, II, III, or V in spinal cords of CCS/G93A SOD1 mice compared with non-transgenic, G93A SOD1, or CCS/WT SOD1 controls. With SDS-PAGE analysis, spinal cords from CCS/G93A SOD1 mice showed significant decreases in the levels of two structural subunits of cytochrome c oxidase, COX1 and COX5b, relative to controls. In contrast, CCS/G93A SOD1 mouse spinal cord showed no reduction in levels of selected subunits from complexes I, II, III, or V. Heme A analyses of spinal cord further support the existence of cytochrome c oxidase deficiency in CCS/G93A SOD1 mice. Collectively, these results establish that CCS/G93A SOD1 mice manifest an isolated complex IV deficiency which may underlie a substantial part of mutant SOD1-induced mitochondrial cytopathy.

Mitochondrial alterations in the spinal cord of patients with sporadic amyotrophic lateral sclerosis

Little information is available about morphologic changes of mitochondria in sporadic amyotrophic lateral sclerosis (ALS). We examined the anterior horns of the lumbar spinal cord in 14 patients with sporadic ALS and 15 age-matched controls by electron microscopy to illuminate the subject. In the controls, one patient showed occasional swollen mitochondria with markedly increased cristae and marked accumulation of mitochondria in the somata of anterior horn neurons. Another patient had periodic, stubby protrusions on the outer membrane. Among the patients with ALS, 7 showed filamentous structures in the inner compartment of the mitochondria mainly of the somata and only occasionally of the axons. The structures were composed of a stack of multilayered cristae consisting of linear structures on a longitudinal section. Other abnormal structures were periodic transverse processes like rungs of a ladder predominantly in somata and only occasionally in the axons, marked accumulation of mitochondria in the somata, dendrites or proximal axons (axon hillock and initial segment), stubby protrusions on the outer membrane, and swollen mitochondria with markedly increased cristae in the somata. The findings in this study may reflect the metabolic disturbance of mitochondria, probably associated with the pathomechanism of degenerative processes of anterior horn neurons in sporadic ALS.

Pathways and genes differentially expressed in the motor cortex of patients with sporadic amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal disorder caused by the progressive degeneration of motoneurons in brain and spinal cord. Despite identification of disease-linked mutations, the diversity of processes involved and the ambiguity of their relative importance in ALS pathogenesis still represent a major impediment to disease models as a basis for effective therapies. Moreover, the human motor cortex, although critical to ALS pathology and physiologically altered in most forms of the disease, has not been screened systematically for therapeutic targets.

RESULTS

By whole-genome expression profiling and stringent significance tests we identify genes and gene groups de-regulated in the motor cortex of patients with sporadic ALS, and interpret the role of individual candidate genes in a framework of differentially expressed pathways. Our findings emphasize the importance of defense responses and cytoskeletal, mitochondrial and proteasomal dysfunction, reflect reduced neuronal maintenance and vesicle trafficking, and implicate impaired ion homeostasis and glycolysis in ALS pathogenesis. Additionally, we compared our dataset with publicly available data for the SALS spinal cord, and show a high correlation of changes linked to the diseased state in the SALS motor cortex. In an analogous comparison with data for the Alzheimer's disease hippocampus we demonstrate a low correlation of global changes and a moderate correlation for changes specifically linked to the SALS diseased state.

CONCLUSION

Gene and sample numbers investigated allow pathway- and gene-based analyses by established error-correction methods, drawing a molecular portrait of the ALS motor cortex that faithfully represents many known disease features and uncovers several novel aspects of ALS pathology. Contrary to expectations for a tissue under oxidative stress, nuclear-encoded mitochondrial genes are uniformly down-regulated. Moreover, the down-regulation of mitochondrial and glycolytic genes implies a combined reduction of mitochondrial and cytoplasmic energy supply, with a possible role in the death of ALS motoneurons. Identifying candidate genes exclusively expressed in non-neuronal cells, we also highlight the importance of these cells in disease development in the motor cortex. Notably, some pathways and candidate genes identified by this study are direct or indirect targets of medication already applied to unrelated illnesses and point the way towards the rapid development of effective symptomatic ALS therapies.

Mitochondriopathy in Parkinson disease and amyotrophic lateral sclerosis

The causes of the selective neurodegeneration in Parkinson disease (PD) and amyotrophic lateral sclerosis (ALS) are unknown and commonalities among these and other age-related neurodegenerative diseases continue to be sought. Morphologic, biochemical, molecular genetic, and cell/animal model studies suggest that mitochondria might be a convergence point for neurodegeneration. The functions and properties of mitochondria might render subsets of selectively vulnerable neurons intrinsically susceptible to cellular aging and stress. In PD, mutations in putative mitochondrial proteins have been identified recently and mitochondrial DNA mutations have been found in nigral neurons. In ALS, changes occur in mitochondrial respiratory chain enzymes and in mitochondrial cell death proteins, indicative of an activation of programmed cell death pathways. Mouse models are beginning to reveal possible principles governing the biology of selective neuronal vulnerability that implicate mitochondria in neuronal death processes ranging from apoptosis to necrosis. This review presents how malfunctioning mitochondria might contribute to neuronal death in PD and ALS.