Ultrastructural changes of mitochondria in the skeletal muscle of patients with amyotrophic lateral sclerosis

Aberrant evoked calcium signaling and nAChR cluster morphology in a SOD1 D90A hiPSC-derived neuromuscular model

Familial amyotrophic lateral sclerosis (ALS) is a progressive neuromuscular disorder that is due to mutations in one of several target genes, including SOD1. So far, clinical records, rodent studies, and in vitro models have yielded arguments for either a primary motor neuron disease, or a pleiotropic pathogenesis of ALS. While mouse models lack the human origin, in vitro models using human induced pluripotent stem cells (hiPSC) have been recently developed for addressing ALS pathogenesis. In spite of improvements regarding the generation of muscle cells from hiPSC, the degree of maturation of muscle cells resulting from these protocols has remained limited. To fill these shortcomings, we here present a new protocol for an enhanced myotube differentiation from hiPSC with the option of further maturation upon coculture with hiPSC-derived motor neurons. The described model is the first to yield a combination of key myogenic maturation features that are consistent sarcomeric organization in association with complex nAChR clusters in myotubes derived from control hiPSC. In this model, myotubes derived from hiPSC carrying the SOD1 D90A mutation had reduced expression of myogenic markers, lack of sarcomeres, morphologically different nAChR clusters, and an altered nAChR-dependent Ca2+ response compared to control myotubes. Notably, trophic support provided by control hiPSC-derived motor neurons reduced nAChR cluster differences between control and SOD1 D90A myotubes. In summary, a novel hiPSC-derived neuromuscular model yields evidence for both muscle-intrinsic and nerve-dependent aspects of neuromuscular dysfunction in SOD1-based ALS.

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.

Targeting mitochondrial Ca2+ uptake for the treatment of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rare adult-onset neurodegenerative disease characterized by progressive motor neuron (MN) loss, muscle denervation and paralysis. Over the past several decades, researchers have made tremendous efforts to understand the pathogenic mechanisms underpinning ALS, with much yet to be resolved. ALS is described as a non-cell autonomous condition with pathology detected in both MNs and non-neuronal cells, such as glial cells and skeletal muscle. Studies in ALS patient and animal models reveal ubiquitous abnormalities in mitochondrial structure and function, and disturbance of intracellular calcium homeostasis in various tissue types, suggesting a pivotal role of aberrant mitochondrial calcium uptake and dysfunctional calcium signalling cascades in ALS pathogenesis. Calcium signalling and mitochondrial dysfunction are intricately related to the manifestation of cell death contributing to MN loss and skeletal muscle dysfunction. In this review, we discuss the potential contribution of intracellular calcium signalling, particularly mitochondrial calcium uptake, in ALS pathogenesis. Functional consequences of excessive mitochondrial calcium uptake and possible therapeutic strategies targeting mitochondrial calcium uptake or the mitochondrial calcium uniporter, the main channel mediating mitochondrial calcium influx, are also discussed.

Quantitative imaging and semiotic phenotyping of mitochondrial network morphology in live human cells

The importance of mitochondria in tissue homeostasis, stress responses and human diseases, combined to their ability to transition between various structural and functional states, makes them excellent organelles for monitoring cell health. There is therefore a need for technologies to accurately analyze and quantify changes in mitochondrial organization in a variety of cells and cellular contexts. Here we present an innovative computerized method that enables accurate, multiscale, fast and cost-effective analysis of mitochondrial shape and network architecture from confocal fluorescence images by providing more than thirty features. In order to facilitate interpretation of the quantitative results, we introduced two innovations: the use of Kiviat-graphs (herein named MitoSpider plots) to present highly multidimensional data and visualization of the various mito-cellular configurations in the form of morphospace diagrams (called MitoSigils). We tested our fully automated image analysis tool on rich datasets gathered from live normal human skin cells cultured under basal conditions or exposed to specific stress including UVB irradiation and pesticide exposure. We demonstrated the ability of our proprietary software (named MitoTouch) to sensitively discriminate between control and stressed dermal fibroblasts, and between normal fibroblasts and other cell types (including cancer tissue-derived fibroblasts and primary keratinocytes), showing that our automated analysis captures subtle differences in morphology. Based on this novel algorithm, we report the identification of a protective natural ingredient that mitigates the deleterious impact of hydrogen peroxide (H2O2) on mitochondrial organization. Hence we conceived a novel wet-plus-dry pipeline combining cell cultures, quantitative imaging and semiotic analysis for exhaustive analysis of mitochondrial morphology in living adherent cells. Our tool has potential for broader applications in other research areas such as cell biology and medicine, high-throughput drug screening as well as predictive and environmental toxicology.

Mitochondrial Dyshomeostasis as an Early Hallmark and a Therapeutic Target in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal multisystem disease characterized by progressive death of motor neurons, loss of muscle mass, and impaired energy metabolism. More than 40 genes are now known to be associated with ALS, which together account for the majority of familial forms of ALS and only 10% of sporadic ALS cases. To date, there is no consensus on the pathogenesis of ALS, which makes it difficult to develop effective therapy. Accumulating evidence indicates that mitochondria, which play an important role in cellular homeostasis, are the earliest targets in ALS, and abnormalities in their structure and functions contribute to the development of bioenergetic stress and disease progression. Mitochondria are known to be highly dynamic organelles, and their stability is maintained through a number of key regulatory pathways. Mitochondrial homeostasis is dynamically regulated via mitochondrial biogenesis, clearance, fission/fusion, and trafficking; however, the processes providing "quality control" and distribution of the organelles are prone to dysregulation in ALS. Here, we systematically summarized changes in mitochondrial turnover, dynamics, calcium homeostasis, and alterations in mitochondrial transport and functions to provide in-depth insights into disease progression pathways, which may have a significant impact on current symptomatic therapies and personalized treatment programs for patients with ALS.

Reversing Dysdynamism to Interrupt Mitochondrial Degeneration in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis is one of several chronic neurodegenerative conditions in which mitochondrial abnormalities are posited to contribute to disease progression. Therapeutic options targeting mitochondria include enhancing metabolism, suppressing reactive oxygen production and disrupting mitochondria-mediated programmed cell death pathways. Herein is reviewed mechanistic evidence supporting a meaningful pathophysiological role for the constellation of abnormal mitochondrial fusion, fission and transport, collectively designated mitochondrial dysdynamism, in ALS. Following this is a discussion on preclinical studies in ALS mice that seemingly validate the idea that normalizing mitochondrial dynamism can delay ALS by interrupting a vicious cycle of mitochondrial degeneration, leading to neuronal die-back and death. Finally, the relative benefits of suppressing mitochondrial fusion vs. enhancing mitochondrial fusion in ALS are speculated upon, and the paper concludes with the prediction that the two approaches could be additive or synergistic, although a side-by-side comparative trial may be challenging to perform.

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.

Loss of mitochondrial Chchd10 or Chchd2 in zebrafish leads to an ALS-like phenotype and Complex I deficiency independent of the mitochondrial integrated stress response

Mutations in CHCHD10 and CHCHD2, encoding two paralogous mitochondrial proteins, have been identified in cases of amyotrophic lateral sclerosis, frontotemporal lobar degeneration, and Parkinson's disease. Their role in disease is unclear, though both have been linked to mitochondrial respiration and mitochondrial stress responses. Here, we investigated the biological roles of these proteins during vertebrate development using knockout (KO) models in zebrafish. We demonstrate that loss of either or both proteins leads to motor impairment, reduced survival and compromised neuromuscular junction integrity in larval zebrafish. Compensation by Chchd10 was observed in the chchd2^-/- model, but not by Chchd2 in the chchd10^-/- model. The assembly of mitochondrial respiratory chain Complex I was impaired in chchd10^-/- and chchd2^-/- zebrafish larvae, but unexpectedly not in a double chchd10^-/- and chchd2^-/- model, suggesting that reduced mitochondrial Complex I cannot be solely responsible for the observed phenotypes, which are generally more severe in the double KO. We observed transcriptional activation markers of the mitochondrial integrated stress response (mt-ISR) in the double chchd10^-/- and chchd2^-/- KO model, suggesting that this pathway is involved in the restoration of Complex I assembly in our double KO model. The data presented here demonstrates that the Complex I assembly defect in our single KO models arises independently of the mt-ISR. Furthermore, this study provides evidence that both proteins are required for normal vertebrate development.

TDP-43 dysregulation and neuromuscular junction disruption in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a disease characterized by upper and lower motor neuron (MN) loss with a signature feature of cytoplasmic aggregates containing TDP-43, which are detected in nearly all patients. Mutations in the gene that encodes TDP-43 (TARBDP) are known to result in both familial and sporadic ALS. In ALS, disruption of neuromuscular junctions (NMJs) constitutes a critical event in disease pathogenesis, leading to denervation atrophy, motor impairments and disability. Morphological defects and impaired synaptic transmission at NMJs have been reported in several TDP-43 animal models and in vitro, linking TDP-43 dysregulation to the loss of NMJ integrity in ALS. Through the lens of the dying-back and dying-forward hypotheses of ALS, this review discusses the roles of TDP-43 related to synaptic function, with a focus on the potential molecular mechanisms occurring within MNs, skeletal muscles and glial cells that may contribute to NMJ disruption in ALS.

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.

Metabolic Profile and Pathological Alterations in the Muscle of Patients with Early-Stage Amyotrophic Lateral Sclerosis

Diverse biomarkers and pathological alterations have been found in muscle of patients with Amyotrophic lateral sclerosis (ALS), but the relation between such alterations and dysfunction in energetic metabolism remains to be investigated. We established the metabolome of muscle and serum of ALS patients and correlated these findings with the clinical status and pathological alterations observed in the muscle. We obtained data from 20 controls and 17 ALS patients (disease duration: 9.4 ± 6.8 months). Multivariate metabolomics analysis identified a distinct serum metabolome for ALS compared to controls (p-CV-ANOVA < 0.035) and revealed an excellent discriminant profile for muscle metabolome (p-CV-ANOVA < 0.0012). Citramalate was discriminant for both muscle and serum. High lauroylcarnitine levels in muscle were associated with low Forced Vital Capacity. Transcriptomics analysis of key antioxidant enzymes showed an upregulation of SOD3 (p = 0.0017) and GLRX2(1) (p = 0.0022) in ALS muscle. Analysis of mitochondrial enzymatic activity in muscle revealed higher complex II/CS (p = 0.04) and lower LDH (p = 0.03) activity in ALS than in controls. Our study showed, for the first time, a global dysfunction in the muscle of early-stage ALS patients. Furthermore, we identified novel metabolites to be employed as biomarkers for diagnosis and prognosis of ALS patients.

Lysosomes Dysfunction Causes Mitophagy Impairment in PBMCs of Sporadic ALS Patients

Mitochondria alterations are present in tissues derived from patients and animal models, but no data are available for peripheral blood mononuclear cells (PBMCs) of ALS patients. This work aims to investigate mitophagy in PBMCs of sporadic (sALS) patients and how this pathway can be tuned by using small molecules. We found the presence of morphologically atypical mitochondria by TEM and morphological abnormalities by MitoTracker™. We found a decreased number of healthy mitochondria in sALS PBMCs and an impairment of mitophagy with western blot and immunofluorescence. After rapamycin treatment, we found a higher increase in the LC3 marker in sALS PBMCs, while after NH4Cl treatment, we found a lower increase in the LC3 marker. Finally, mTOR-independent autophagy induction with trehalose resulted in a significant decrease in the lysosomes level sALS PBMCs. Our data suggest that the presence of morphologically altered mitochondria and an inefficient turnover of damaged mitochondria in PBMCs of sALS patients rely on the impairment of the mitophagy pathway. We also found that the induction of the mTOR-independent autophagy pathway leads to a decrease in lysosomes level, suggesting a more sensitivity of sALS PBMCs to trehalose. Such evidence suggests that trehalose could represent an effective treatment for ALS patients.

Therapeutic Targets in Amyotrophic Lateral Sclerosis: Focus on Ion Channels and Skeletal Muscle

Amyotrophic Lateral Sclerosis is a neurodegenerative disease caused by progressive loss of motor neurons, which severely compromises skeletal muscle function. Evidence shows that muscle may act as a molecular powerhouse, whose final signals generate in patients a progressive loss of voluntary muscle function and weakness leading to paralysis. This pathology is the result of a complex cascade of events that involves a crosstalk among motor neurons, glia, and muscles, and evolves through the action of converging toxic mechanisms. In fact, mitochondrial dysfunction, which leads to oxidative stress, is one of the mechanisms causing cell death. It is a common denominator for the two existing forms of the disease: sporadic and familial. Other factors include excitotoxicity, inflammation, and protein aggregation. Currently, there are limited cures. The only approved drug for therapy is riluzole, that modestly prolongs survival, with edaravone now waiting for new clinical trial aimed to clarify its efficacy. Thus, there is a need of effective treatments to reverse the damage in this devastating pathology. Many drugs have been already tested in clinical trials and are currently under investigation. This review summarizes the already tested drugs aimed at restoring muscle-nerve cross-talk and on new treatment options targeting this tissue.

Neuromuscular Junction Dysfunction in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder characterized by progressive degeneration of motor neurons leading to skeletal muscle denervation. Earlier studies have shown that motor neuron degeneration begins in motor cortex and descends to the neuromuscular junction (NMJ) in a dying forward fashion. However, accumulating evidences support that ALS is a distal axonopathy where early pathological changes occur at the NMJ, prior to onset of clinical symptoms and propagates towards the motor neuron cell body supporting "dying back" hypothesis. Despite several evidences, series of events triggering NMJ disassembly in ALS are still obscure. Neuromuscular junction is a specialized tripartite chemical synapse which involves a well-coordinated communication among the presynaptic motor neuron, postsynaptic skeletal muscle, and terminal Schwann cells. This review provides comprehensive insight into the role of NMJ in ALS pathogenesis. We have emphasized the molecular alterations in cellular components of NMJ leading to loss of effective neuromuscular transmission in ALS. Further, we provide a preview into research involved in exploring NMJ as potential target for designing effective therapies for ALS.

KLF15 overexpression in myocytes fails to ameliorate ALS-related pathology or extend the lifespan of SOD1G93A mice

Amyotrophic Lateral Sclerosis (ALS) is a currently incurable disease that causes progressive motor neuron loss, paralysis and death. Skeletal muscle pathology occurs early during the course of ALS. It is characterized by impaired mitochondrial biogenesis, metabolic dysfunction and deterioration of the neuromuscular junction (NMJ), the synapse through which motor neurons communicate with muscles. Therefore, a better understanding of the molecules that underlie this pathology may lead to therapies that slow motor neuron loss and delay ALS progression. Kruppel Like Factor 15 (KLF15) has been identified as a transcription factor that activates alternative metabolic pathways and NMJ maintenance factors, including Fibroblast Growth Factor Binding Protein 1 (FGFBP1), in skeletal myocytes. In this capacity, KLF15 has been shown to play a protective role in Duchenne muscular dystrophy (DMD) and spinal muscular atrophy (SMA), however its role in ALS has not been evaluated. Here, we examined whether muscle-specific KLF15 overexpression promotes the health of skeletal muscles and NMJs in the SOD1^G93A ALS mouse model. We show that muscle-specific KLF15 overexpression did not elicit a significant beneficial effect on skeletal muscle atrophy, NMJ health, motor function, or survival in SOD1^G93A ALS mice. Our findings suggest that, unlike in mouse models of DMD and SMA, KLF15 overexpression has a minimal impact on ALS disease progression in SOD1^G93A mice.

MitoCellPhe reveals mitochondrial morphologies in single fibroblasts and clustered stem cells

Mitochondria are dynamic organelles that differ significantly in their morphologies across cell types, reflecting specific cellular needs and stages in development. Despite the wide biological significance in disease and in health, delineating mitochondrial morphologies in complex systems remains challenging. Here, we present the Mitochondrial Cellular Phenotype (MitoCellPhe) tool developed for quantifying mitochondrial morphologies and demonstrate its utility in delineating differences in mitochondrial morphologies in a human fibroblast and human induced pluripotent stem cell (hiPSC) line. MitoCellPhe generates 24 parameters, allowing for a comprehensive analysis of mitochondrial structures and importantly allows for quantification to be performed on mitochondria in images containing single cells or clusters of cells. With this tool, we were able to validate previous findings that show networks of mitochondria in healthy fibroblast cell lines and a more fragmented morphology in hiPSCs. Using images generated from control and diseased fibroblasts and hiPSCs, we also demonstrate the efficacy of the toolset in delineating differences in morphologies between healthy and the diseased state in both stem cell (hiPSC) and differentiated fibroblast cells. Our results demonstrate that MitoCellPhe enables high-throughput, sensitive, detailed, and quantitative mitochondrial morphological assessment and thus enables better biological insights into mitochondrial dynamics in health and disease.

Skeletal Muscle Metabolism: Origin or Prognostic Factor for Amyotrophic Lateral Sclerosis (ALS) Development?

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive and selective loss of motor neurons, amyotrophy and skeletal muscle paralysis usually leading to death due to respiratory failure. While generally considered an intrinsic motor neuron disease, data obtained in recent years, including our own, suggest that motor neuron protection is not sufficient to counter the disease. The dismantling of the neuromuscular junction is closely linked to chronic energy deficit found throughout the body. Metabolic (hypermetabolism and dyslipidemia) and mitochondrial alterations described in patients and murine models of ALS are associated with the development and progression of disease pathology and they appear long before motor neurons die. It is clear that these metabolic changes participate in the pathology of the disease. In this review, we summarize these changes seen throughout the course of the disease, and the subsequent impact of glucose–fatty acid oxidation imbalance on disease progression. We also highlight studies that show that correcting this loss of metabolic flexibility should now be considered a major goal for the treatment of ALS.

Autophagy and ALS: mechanistic insights and therapeutic implications

Mechanisms of protein homeostasis are crucial for overseeing the clearance of misfolded and toxic proteins over the lifetime of an organism, thereby ensuring the health of neurons and other cells of the central nervous system. The highly conserved pathway of autophagy is particularly necessary for preventing and counteracting pathogenic insults that may lead to neurodegeneration. In line with this, mutations in genes that encode essential autophagy factors result in impaired autophagy and lead to neurodegenerative conditions such as amyotrophic lateral sclerosis (ALS). However, the mechanistic details underlying the neuroprotective role of autophagy, neuronal resistance to autophagy induction, and the neuron-specific effects of autophagy-impairing mutations remain incompletely defined. Further, the manner and extent to which non-cell autonomous effects of autophagy dysfunction contribute to ALS pathogenesis are not fully understood. Here, we review the current understanding of the interplay between autophagy and ALS pathogenesis by providing an overview of critical steps in the autophagy pathway, with special focus on pivotal factors impaired by ALS-causing mutations, their physiologic effects on autophagy in disease models, and the cell type-specific mechanisms regulating autophagy in non-neuronal cells which, when impaired, can contribute to neurodegeneration. This review thereby provides a framework not only to guide further investigations of neuronal autophagy but also to refine therapeutic strategies for ALS and related neurodegenerative diseases.Abbreviations: ALS: amyotrophic lateral sclerosis; Atg: autophagy-related; CHMP2B: charged multivesicular body protein 2B; DPR: dipeptide repeat; FTD: frontotemporal dementia; iPSC: induced pluripotent stem cell; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; PINK1: PTEN induced kinase 1; RNP: ribonuclear protein; sALS: sporadic ALS; SPHK1: sphingosine kinase 1; TARDBP/TDP-43: TAR DNA binding protein; TBK1: TANK-binding kinase 1; TFEB: transcription factor EB; ULK: unc-51 like autophagy activating kinase; UPR: unfolded protein response; UPS: ubiquitin-proteasome system; VCP: valosin containing protein.

New Neuroprotective Effect of Lemon IntegroPectin on Neuronal Cellular Model

Lemon IntegroPectin obtained via hydrodynamic cavitation of organic lemon processing waste in water shows significant neuroprotective activity in vitro, as first reported in this study investigating the effects of both lemon IntegroPectin and commercial citrus pectin on cell viability, cell morphology, reactive oxygen species (ROS) production, and mitochondria perturbation induced by treatment of neuronal SH-SY5Y human cells with H2O2. Mediated by ROS, including H2O2 and its derivatives, oxidative stress alters numerous cellular processes, such as mitochondrial regulation and cell signaling, propagating cellular injury that leads to incurable neurodegenerative diseases. These results, and the absence of toxicity of this new pectic substance rich in adsorbed flavonoids and terpenes, suggest further studies to investigate its activity in preventing, retarding, or even curing neurological diseases.

What skeletal muscle has to say in amyotrophic lateral sclerosis: Implications for therapy

Amyotrophic lateral sclerosis (ALS) is an adult onset disorder characterized by progressive neuromuscular junction (NMJ) dismantling and degeneration of motor neurons leading to atrophy and paralysis of voluntary muscles responsible for motion and breathing. Except for a minority of patients harbouring genetic mutations, the origin of most ALS cases remains elusive. Peripheral tissues, and particularly skeletal muscle, have lately demonstrated an active contribution to disease pathology attracting a growing interest for these tissues as therapeutic targets in ALS. In this sense, molecular mechanisms essential for cell and tissue homeostasis have been shown to be deregulated in the disease. These include muscle metabolism and mitochondrial activity, RNA processing, tissue-resident stem cell function responsible for muscle regeneration, and proteostasis that regulates muscle mass in adulthood. This review aims to compile scientific evidence that demonstrates the role of skeletal muscle in ALS pathology and serves as reference for development of novel therapeutic strategies targeting this tissue to delay disease onset and progression. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.6/issuetoc.

Amyotrophic Lateral Sclerosis and Autophagy: Dysfunction and Therapeutic Targeting

Over the past 20 years, there has been a drastically increased understanding of the genetic basis of Amyotrophic Lateral Sclerosis. Despite the identification of more than 40 different ALS-causing mutations, the accumulation of neurotoxic misfolded proteins, inclusions, and aggregates within motor neurons is the main pathological hallmark in all cases of ALS. These protein aggregates are proposed to disrupt cellular processes and ultimately result in neurodegeneration. One of the main reasons implicated in the accumulation of protein aggregates may be defective autophagy, a highly conserved intracellular "clearance" system delivering misfolded proteins, aggregates, and damaged organelles to lysosomes for degradation. Autophagy is one of the primary stress response mechanisms activated in highly sensitive and specialised neurons following insult to ensure their survival. The upregulation of autophagy through pharmacological autophagy-inducing agents has largely been shown to reduce intracellular protein aggregate levels and disease phenotypes in different in vitro and in vivo models of neurodegenerative diseases. In this review, we explore the intriguing interface between ALS and autophagy, provide a most comprehensive summary of autophagy-targeted drugs that have been examined or are being developed as potential treatments for ALS to date, and discuss potential therapeutic strategies for targeting autophagy in ALS.

Amyotrophic Lateral Sclerosis: A Neurodegenerative Motor Neuron Disease With Ocular Involvement

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that causes degeneration of the lower and upper motor neurons and is the most prevalent motor neuron disease. This disease is characterized by muscle weakness, stiffness, and hyperreflexia. Patients survive for a short period from the onset of the disease. Most cases are sporadic, with only 10% of the cases being genetic. Many genes are now known to be involved in familial ALS cases, including some of the sporadic cases. It has also been observed that, in addition to genetic factors, there are numerous molecular mechanisms involved in these pathologies, such as excitotoxicity, mitochondrial disorders, alterations in axonal transport, oxidative stress, accumulation of misfolded proteins, and neuroinflammation. This pathology affects the motor neurons, the spinal cord, the cerebellum, and the brain, but recently, it has been shown that it also affects the visual system. This impact occurs not only at the level of the oculomotor system but also at the retinal level, which is why the retina is being proposed as a possible biomarker of this pathology. The current review discusses the main aspects mentioned above related to ALS, such as the main genes involved, the most important molecular mechanisms that affect this pathology, its ocular involvement, and the possible usefulness of the retina as a biomarker.

Functional skeletal muscle model derived from SOD1-mutant ALS patient iPSCs recapitulates hallmarks of disease progression

Recent findings suggest a pathologic role of skeletal muscle in amyotrophic lateral sclerosis (ALS) onset and progression. However, the exact mechanism by which this occurs remains elusive due to limited human-based studies. To this end, phenotypic ALS skeletal muscle models were developed from induced pluripotent stem cells (iPSCs) derived from healthy individuals (WT) and ALS patients harboring mutations in the superoxide dismutase 1 (SOD1) gene. Although proliferative, SOD1 myoblasts demonstrated delayed and reduced fusion efficiency compared to WT. Additionally, SOD1 myotubes exhibited significantly reduced length and cross-section. Also, SOD1 myotubes had loosely arranged myosin heavy chain and reduced acetylcholine receptor expression per immunocytochemical analysis. Functional analysis indicated considerably reduced contractile force and synchrony in SOD1 myotubes. Mitochondrial assessment indicated reduced inner mitochondrial membrane potential (ΔΨm) and metabolic plasticity in the SOD1-iPSC derived myotubes. This work presents the first well-characterized in vitro iPSC-derived muscle model that demonstrates SOD1 toxicity effects on human muscle regeneration, contractility and metabolic function in ALS. Current findings align with previous ALS patient biopsy studies and suggest an active contribution of skeletal muscle in NMJ dysfunction. Further, the results validate this model as a human-relevant platform for ALS research and drug discovery studies.

Proteotoxicity and Neurodegenerative Diseases

Neurodegenerative diseases are a major burden for our society, affecting millions of people worldwide. A main goal of past and current research is to enhance our understanding of the mechanisms underlying proteotoxicity, a common theme among these incurable and debilitating conditions. Cell proteome alteration is considered to be one of the main driving forces that triggers neurodegeneration, and unraveling the biological complexity behind the affected molecular pathways constitutes a daunting challenge. This review summarizes the current state on key processes that lead to cellular proteotoxicity in Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis, providing a comprehensive landscape of recent literature. A foundational understanding of how proteotoxicity affects disease etiology and progression may provide essential insight towards potential targets amenable of therapeutic intervention.

Mechanisms underlying the predictive power of high skeletal muscle uptake of FDG in amyotrophic lateral sclerosis

Background

We recently reported that enhanced [18F]-fluorodeoxyglucose (FDG) uptake in skeletal muscles predicts disease aggressiveness in patients with amyotrophic lateral sclerosis (ALS). The present experimental study aimed to assess whether this predictive potential reflects the link between FDG uptake and redox stress that has been previously reported in different tissues and disease models.

Methods

The study included 15 SOD1^G93A mice (as experimental ALS model) and 15 wildtype mice (around 120 days old). Mice were submitted to micro-PET imaging. Enzymatic pathways and response to oxidative stress were evaluated in harvested quadriceps and hearts by biochemical, immunohistochemical, and immunofluorescence analysis. Colocalization between the endoplasmic reticulum (ER) and the fluorescent FDG analog 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG) was performed in fresh skeletal muscle sections. Finally, mitochondrial ultrastructure and bioenergetics were evaluated in harvested quadriceps and hearts.

Results

FDG retention was significantly higher in hindlimb skeletal muscles of symptomatic SOD1^G93A mice with respect to control ones. This difference was not explained by any acceleration in glucose degradation through glycolysis or cytosolic pentose phosphate pathway (PPP). Similarly, it was independent of inflammatory infiltration. Rather, the high FDG retention in SOD1^G93A skeletal muscle was associated with an accelerated generation of reactive oxygen species. This redox stress selectively involved the ER and the local PPP triggered by hexose-6P-dehydrogenase. ER involvement was confirmed by the colocalization of the 2-NBDG with a vital ER tracker. The oxidative damage in transgenic skeletal muscle was associated with a severe impairment in the crosstalk between ER and mitochondria combined with alterations in mitochondrial ultrastructure and fusion/fission balance. The expected respiratory damage was confirmed by a deceleration in ATP synthesis and oxygen consumption rate. These same abnormalities were represented to a markedly lower degree in the myocardium, as a sample of non-voluntary striated muscle.

Conclusion

Skeletal muscle of SOD1^G93A mice reproduces the increased FDG uptake observed in ALS patients. This finding reflects the selective activation of the ER-PPP in response to significant redox stress associated with alterations of mitochondrial ultrastructure, networking, and connection with the ER itself. This scenario is less severe in cardiomyocytes suggesting a relevant role for either communication with synaptic plaque or contraction dynamics.

The effects of diet and sex in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease with no known cure. Approximately 90% of ALS cases are sporadic, suggesting there are multiple contributing factors that influence the disease risk, onset, and progression. Diet and sex are two factors that have been reported to alter ALS risk, onset and progression in humans and in animal models, providing potential modifiers of disease. Several epidemiological studies have identified diets that positively affect ALS patients, including various high-calorie fat or sugar-based diets, while animal models have been developed to test how these diets are working on a molecular level. These diets may offset the metabolic alterations that occur in ALS, such as hypermetabolism, lowered body mass index(BMI), and hyperlipidemia. Sex-dependent differences have also come forth from large-scale epidemiological studies as well as mouse-model studies. In addition, sex hormones have been shown to affect disease risk or progression. Herein, studies on the effects of diet and sex on ALS risk, onset, and progression will be reviewed. Understanding these diet- and sex-dependent outcomes may lead to optimized patient-specific therapies for ALS.

P2X7 activation enhances skeletal muscle metabolism and regeneration in SOD1G93A mouse model of amyotrophic lateral sclerosis

Muscle weakness plays an important role in neuromuscular disorders comprising amyotrophic lateral sclerosis (ALS). However, it is not established whether muscle denervation originates from the motor neurons, the muscles or more likely both. Previous studies have shown that the expression of the SOD1G93A mutation in skeletal muscles causes denervation of the neuromuscular junctions, inability to regenerate and consequent atrophy, all clear symptoms of ALS. In this work, we used SOD1G93A mice, a model that best mimics some pathological features of both familial and sporadic ALS, and we investigated some biological effects induced by the activation of the P2X7 receptor in the skeletal muscles. The P2X7, belonging to the ionotropic family of purinergic receptors for extracellular ATP, is abundantly expressed in the healthy skeletal muscles, where it controls cell duplication, differentiation, regeneration or death. In particular, we evaluated whether an in vivo treatment in SOD1G93A mice with the P2X7 specific agonist 2'(3')-O-(4-Benzoylbenzoyl) adenosine5'-triphosphate (BzATP) just before the onset of a pathological neuromuscular phenotype could exert beneficial effects in the skeletal muscles. Our findings indicate that stimulation of P2X7 improves the innervation and metabolism of myofibers, moreover elicits the proliferation/differentiation of satellite cells, thus preventing the denervation atrophy of skeletal muscles in SOD1G93A mice. Overall, this study suggests that a P2X7-targeted and site-specific modulation might be a strategy to interfere with the complex multifactorial and multisystem nature of ALS.

Dysregulated mitochondrial Ca2+ and ROS signaling in skeletal muscle of ALS mouse model

Amyotrophic lateral sclerosis (ALS) is a devastating neuromuscular disease characterized by motor neuron loss and prominent skeletal muscle wasting. Despite more than one hundred years of research efforts, the pathogenic mechanisms underlying neuromuscular degeneration in ALS remain elusive. While the death of motor neuron is a defining hallmark of ALS, accumulated evidences suggested that in addition to being a victim of motor neuron axonal withdrawal, the intrinsic skeletal muscle degeneration may also actively contribute to ALS disease pathogenesis and progression. Examination of spinal cord and muscle autopsy/biopsy samples of ALS patients revealed similar mitochondrial abnormalities in morphology, quantity and disposition, which are accompanied by defective mitochondrial respiratory chain complex and elevated oxidative stress. Detailing the molecular/cellular mechanisms and the role of mitochondrial dysfunction in ALS relies on ALS animal model studies. This review article discusses the dysregulated mitochondrial Ca2+ and reactive oxygen species (ROS) signaling revealed in live skeletal muscle derived from ALS mouse models, and a potential role of the vicious cycle formed between the dysregulated mitochondrial Ca2+ signaling and excessive ROS production in promoting muscle wasting during ALS progression.

Perspective: Mitochondria-ER Contacts in Metabolic Cellular Stress Assessed by Microscopy

The interplay of mitochondria with the endoplasmic reticulum and their connections, called mitochondria-ER contacts (MERCs) or mitochondria-associated ER membranes (MAMs), are crucial hubs in cellular stress. These sites are essential for the passage of calcium ions, reactive oxygen species delivery, the sorting of lipids in whole-body metabolism. In this perspective article, we focus on microscopic evidences of the pivotal role of MERCs/MAMs and their changes in metabolic diseases, like obesity, diabetes, and neurodegeneration.

Mortal engines: Mitochondrial bioenergetics and dysfunction in neurodegenerative diseases

Mitochondria are best known for their role in ATP generation. However, studies over the past two decades have shown that mitochondria do much more than that. Mitochondria regulate both necrotic and apoptotic cell death pathways, they store and therefore coordinate cellular Ca²⁺ signaling, they generate and metabolize important building blocks, by-products and signaling molecules, and they also generate and are targets of free radical species that modulate many aspects of cell physiology and pathology. Most estimates suggest that although the brain makes up only 2 percent of body weight, utilizes about 20 percent of the body's total ATP. Thus, mitochondrial dysfunction greatly impacts brain functions and is indeed associated with numerous neurodegenerative diseases. Furthermore, a number of abnormal disease-associated proteins have been shown to interact directly with mitochondria, leading to mitochondrial dysfunction and subsequent neuronal cell death. Here, we discuss the role of mitochondrial dynamics impairment in the pathological processes associated with neurodegeneration and suggest that a therapy targeting mitochondrialdysfunction holds a great promise.

New Therapeutics to Modulate Mitochondrial Function in Neurodegenerative Disorders

BACKGROUND

Mitochondrial function and energy metabolism are impaired in neurodegenerative diseases. There is evidence for these functional declines both within the brain and systemically in Alzheimer's disease, Parkinson's disease, and Amyotrophic Lateral Sclerosis. Due to these observations, therapeutics targeted to alter mitochondrial function and energy pathways are increasingly studied in pre-clinical and clinical settings.

METHODS

The goal of this article was to review therapies with specific implications on mitochondrial energy metabolism published through May 2016 that have been tested for treatment of neurodegenerative diseases.

RESULTS

We discuss implications for mitochondrial dysfunction in neurodegenerative diseases and how this drives new therapeutic initiatives.

CONCLUSION

Thus far, treatments have achieved varying degrees of success. Further investigation into the mechanisms driving mitochondrial dysfunction and bioenergetic failure in neurodegenerative diseases is warranted.

Sporadic amyotrophic lateral sclerosis (SALS) - skeletal muscle response to cerebrospinal fluid from SALS patients in a rat model

Skeletal muscle atrophy is the most prominent feature of amyotrophic lateral sclerosis (ALS), an adult-onset neurodegenerative disease of motor neurons. However, the contribution of skeletal muscle to disease progression remains elusive. Our previous studies have shown that intrathecal injection of cerebrospinal fluid from sporadic ALS patients (ALS-CSF) induces several degenerative changes in motor neurons and glia of neonatal rats. Here, we describe various pathologic events in the rat extensor digitorum longus muscle following intrathecal injection of ALS-CSF. Adenosine triphosphatase staining and electron microscopic (EM) analysis revealed significant atrophy and grouping of type 2 fibres in ALS-CSF-injected rats. Profound neuromuscular junction (NMJ) damage, such as fragmentation accompanied by denervation, were revealed by α-bungarotoxin immunostaining. Altered expression of key NMJ proteins, rapsyn and calpain, was also observed by immunoblotting. In addition, EM analysis showed sarcolemmal folding, Z-line streaming, structural alterations of mitochondria and dilated sarcoplasmic reticulum. The expression of trophic factors was affected, with significant downregulation of vascular endothelial growth factor (VEGF), marginal reduction in insulin-like growth factor-1 (IGF-1), and upregulation of brain-derived neurotrophic factor (BDNF) and glial-derived neurotrophic factor (GDNF). However, motor neurons might be unable to harness the enhanced levels of BDNF and GDNF, owing to impaired NMJs. We propose that ALS-CSF triggers motor neuronal degeneration, resulting in pathological changes in the skeletal muscle. Muscle damage further aggravates the motor neuronal pathology, because of the interdependency between them. This sets in a vicious cycle, leading to rapid and progressive loss of motor neurons, which could explain the relentless course of ALS.This article has an associated First Person interview with the first author of the paper.

Deterministic Ratchet for Sub-micrometer (Bio)particle Separation

Resolving the heterogeneity of particle populations by size is important when the particle size is a signature of abnormal biological properties leading to disease. Accessing size heterogeneity in the sub-micrometer regime is particularly important to resolve populations of subcellular species or diagnostically relevant bioparticles. Here, we demonstrate a ratchet migration mechanism capable of separating sub-micrometer sized species by size and apply it to biological particles. The phenomenon is based on a deterministic ratchet effect, is realized in a microfluidic device, and exhibits fast migration allowing separation in tens of seconds. We characterize this phenomenon extensively with the aid of a numerical model allowing one to predict the speed and resolution of this method. We further demonstrate the deterministic ratchet migration with two sub-micrometer sized beads as model system experimentally as well as size-heterogeneous mouse liver mitochondria and liposomes as model system for other organelles. We demonstrate excellent agreement between experimentally observed migration and the numerical model.

Methods for imaging mammalian mitochondrial morphology: A prospective on MitoGraph

Mitochondria are found in a variety of shapes, from small round punctate structures to a highly interconnected web. This morphological diversity is important for function, but complicates quantification. Consequently, early quantification efforts relied on various qualitative descriptors that understandably reduce the complexity of the network leading to challenges in consistency across the field. Recent application of state-of-the-art computational tools have resulted in more quantitative approaches. This prospective highlights the implementation of MitoGraph, an open-source image analysis platform for measuring mitochondrial morphology initially optimized for use with Saccharomyces cerevisiae. Here Mitograph was assessed on five different mammalian cells types, all of which were accurately segmented by MitoGraph analysis. MitoGraph also successfully differentiated between distinct mitochondrial morphologies that ranged from entirely fragmented to hyper-elongated. General recommendations are also provided for confocal imaging of labeled mitochondria (using mito-YFP, MitoTracker dyes and immunostaining parameters). Widespread adoption of MitoGraph will help achieve a long-sought goal of consistent and reproducible quantification of mitochondrial morphology.

What is "Hyper" in the ALS Hypermetabolism?

The progressive and fatal loss of upper (brain) and lower (spinal cord) motor neurons and muscle denervation concisely condenses the clinical picture of amyotrophic lateral sclerosis (ALS). Despite the multiple mechanisms believed to underlie the selective loss of motor neurons, ALS aetiology remains elusive and obscure. Likewise, there is also a cluster of alterations in ALS patients in which muscle wasting, body weight loss, eating dysfunction, and abnormal energy dissipation coexist. Defective energy metabolism characterizes the ALS progression, and such paradox of energy balance stands as a challenge for the understanding of ALS pathogenesis. The hypermetabolism in ALS will be examined from tissue-specific energy imbalance (e.g., skeletal muscle) to major energetic pathways (e.g., AMP-activated protein kinase) and whole-body energy alterations including glucose and lipid metabolism, nutrition, and potential involvement of interorgan communication. From the point of view here expressed, the hypermetabolism in ALS should be evaluated as a magnifying glass through which looking at the ALS pathogenesis is from a different perspective in which defective metabolism can disclose novel mechanistic interpretations and lines of intervention.

The Role of Skeletal Muscle in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal adult-onset disease primarily characterized by upper and lower motor neuron degeneration, muscle wasting and paralysis. It is increasingly accepted that the pathological process leading to ALS is the result of multiple disease mechanisms that operate within motor neurons and other cell types both inside and outside the central nervous system. The implication of skeletal muscle has been the subject of a number of studies conducted on patients and related animal models. In this review, we describe the features of ALS muscle pathology and discuss on the contribution of muscle to the pathological process. We also give an overview of the therapeutic strategies proposed to alleviate muscle pathology or to deliver curative agents to motor neurons. ALS muscle mainly suffers from oxidative stress, mitochondrial dysfunction and bioenergetic disturbances. However, the way by which the disease affects different types of myofibers depends on their contractile and metabolic features. Although the implication of muscle in nourishing the degenerative process is still debated, there is compelling evidence suggesting that it may play a critical role. Detailed understanding of the muscle pathology in ALS could, therefore, lead to the identification of new therapeutic targets.

A comprehensive review of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a late-onset fatal neurodegenerative disease affecting motor neurons with an incidence of about 1/100,000. Most ALS cases are sporadic, but 5–10% of the cases are familial ALS. Both sporadic and familial ALS (FALS) are associated with degeneration of cortical and spinal motor neurons. The etiology of ALS remains unknown. However, mutations of superoxide dismutase 1 have been known as the most common cause of FALS. In this study, we provide a comprehensive review of ALS. We cover all aspects of the disease including epidemiology, comorbidities, environmental risk factor, molecular mechanism, genetic factors, symptoms, diagnostic, treatment, and even the available supplement and management of ALS. This will provide the reader with an advantage of receiving a broad range of information about the disease.

ALS-related misfolded protein management in motor neurons and muscle cells

Amyotrophic Lateral Sclerosis (ALS) is the most common form of adult-onset motor neuron disease. It is now considered a multi-factorial and multi-systemic disorder in which alterations of the crosstalk between neuronal and non-neuronal cell types might influence the course of the disease. In this review, we will provide evidence that dysfunctions of affected muscle cells are not only a marginal consequence of denervation associated to motor neurons loss, but a direct consequence of cell muscle toxicity of mutant SOD1. In muscle, the misfolded state of mutant SOD1 protein, unlike in motor neurons, does not appear to have direct effects on protein aggregation and mitochondrial functionality. Muscle cells are, in fact, more capable than motor neurons to handle misfolded proteins, suggesting that mutant SOD1 toxicity in muscle is not mediated by classical mechanisms of intracellular misfolded proteins accumulation. Several recent works indicate that a higher activation of molecular chaperones and degradative systems is present in muscle cells, which for this reason are possibly able to better manage misfolded mutant SOD1. However, several alterations in gene expression and regenerative potential of skeletal muscles have also been reported as a consequence of the expression of mutant SOD1 in muscle. Whether these changes in muscle cells are causative of ALS or a consequence of motor neuron alterations is not yet clear, but their elucidation is very important, since the understanding of the mechanisms involved in mutant SOD1 toxicity in muscle may facilitate the design of treatments directed toward this specific tissue to treat ALS or at least to delay disease progression.

A splicing mutation in the novel mitochondrial protein DNAJC11 causes motor neuron pathology associated with cristae disorganization, and lymphoid abnormalities in mice

Mitochondrial structure and function is emerging as a major contributor to neuromuscular disease, highlighting the need for the complete elucidation of the underlying molecular and pathophysiological mechanisms. Following a forward genetics approach with N-ethyl-N-nitrosourea (ENU)-mediated random mutagenesis, we identified a novel mouse model of autosomal recessive neuromuscular disease caused by a splice-site hypomorphic mutation in a novel gene of unknown function, DnaJC11. Recent findings have demonstrated that DNAJC11 protein co-immunoprecipitates with proteins of the mitochondrial contact site (MICOS) complex involved in the formation of mitochondrial cristae and cristae junctions. Homozygous mutant mice developed locomotion defects, muscle weakness, spasticity, limb tremor, leucopenia, thymic and splenic hypoplasia, general wasting and early lethality. Neuropathological analysis showed severe vacuolation of the motor neurons in the spinal cord, originating from dilatations of the endoplasmic reticulum and notably from mitochondria that had lost their proper inner membrane organization. The causal role of the identified mutation in DnaJC11 was verified in rescue experiments by overexpressing the human ortholog. The full length 63 kDa isoform of human DNAJC11 was shown to localize in the periphery of the mitochondrial outer membrane whereas putative additional isoforms displayed differential submitochondrial localization. Moreover, we showed that DNAJC11 is assembled in a high molecular weight complex, similarly to mitofilin and that downregulation of mitofilin or SAM50 affected the levels of DNAJC11 in HeLa cells. Our findings provide the first mouse mutant for a putative MICOS protein and establish a link between DNAJC11 and neuromuscular diseases.

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.

Multiple mitochondrial alterations in a case of myopathy

Mitochondrial alterations are the most common feature of human myopathies. A biopsy of quadriceps muscle from a 50-year-old woman exhibiting myopathic symptoms was examined by transmission electron microscopy. Biopsied fibers from quadriceps muscle displayed numerous subsarcolemmal mitochondria that contained crystalloids. Numbering 1-6 per organelle, these consisted of rows of punctuate densities measuring ∼0.34 nm; the parallel rows of these dots had a periodicity of ∼0.8 nm. The crystalloids were ensconced within cristae or in the outer compartment. Some mitochondria without crystalloids had circumferential cristae, leaving a membrane-free center that was filled with a farinaceous material. Other scattered fibrocyte defects included disruption of the contractile apparatus or its sporadic replacement by a finely punctuate material in some myofibers. Intramitochondrial crystalloids, although morphologically striking, do not impair organelle physiology to a significant degree, so the muscle weakness of the patient must originate elsewhere.

Transcranial magnetic stimulation and amyotrophic lateral sclerosis: pathophysiological insights

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disorder of the motor neurons in the motor cortex, brainstem and spinal cord. A combination of upper and lower motor neuron dysfunction comprises the clinical ALS phenotype. Although the ALS phenotype was first observed by Charcot over 100 years ago, the site of ALS onset and the pathophysiological mechanisms underlying the development of motor neuron degeneration remain to be elucidated. Transcranial magnetic stimulation (TMS) enables non-invasive assessment of the functional integrity of the motor cortex and its corticomotoneuronal projections. To date, TMS studies have established motor cortical and corticospinal dysfunction in ALS, with cortical hyperexcitability being an early feature in sporadic forms of ALS and preceding the clinical onset of familial ALS. Taken together, a central origin of ALS is supported by TMS studies, with an anterograde transsynaptic mechanism implicated in ALS pathogenesis. Of further relevance, TMS techniques reliably distinguish ALS from mimic disorders, despite a compatible peripheral disease burden, thereby suggesting a potential diagnostic utility of TMS in ALS. This review will focus on the mechanisms underlying the generation of TMS measures used in assessment of cortical excitability, the contribution of TMS in enhancing the understanding of ALS pathophysiology and the potential diagnostic utility of TMS techniques in ALS.

Utility of transcranial magnetic stimulation in delineating amyotrophic lateral sclerosis pathophysiology

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disorder of the motor neurons in the motor cortex, brainstem, and spinal cord. The clinical phenotype of ALS is underscored by a combination of upper and lower motor neuron dysfunction. Although this phenotype was observed over 100 years ago, the site of ALS onset and the pathophysiological mechanisms underlying the development of motor neuron degeneration remain to be elucidated. Transcranial magnetic stimulation (TMS) enables noninvasive assessment of the functional integrity of the motor cortex and its corticomotoneuronal projections. To date, TMS studies have established cortical dysfunction in ALS, with cortical hyperexcitability being an early feature in sporadic forms of ALS and preceding the clinical onset of familial ALS. Taken together, a central origin of ALS is supported by TMS studies, with an anterograde dying-forward mechanism implicated in ALS pathogenesis. Of further relevance, TMS techniques reliably distinguish ALS from mimic disorders, despite a compatible peripheral disease burden, thereby suggesting a potential diagnostic utility of TMS in ALS. This chapter reviews the mechanisms underlying the generation of TMS parameters utilized in assessment of cortical excitability, the contribution of TMS in enhancing the understanding of ALS pathophysiology, and the potential diagnostic utility of TMS techniques in ALS.

The Drosophila inner-membrane protein PMI controls crista biogenesis and mitochondrial diameter

Cristae are mitochondrial inner-membrane structures that concentrate respiratory chain complexes and hence regulate ATP production. Mechanisms controlling crista morphogenesis are poorly understood and few crista determinants have been identified. Among them are the Mitofilins that are required to establish crista junctions and ATP-synthase subunits that bend the membrane at the tips of the cristae. We report here the phenotypic consequences associated with the in vivo inactivation of the inner-membrane protein Pantagruelian Mitochondrion I (PMI) both at the scale of the whole organism, and at the level of mitochondrial ultrastructure and function. We show that flies in which PMI is genetically inactivated experience synaptic defects and have a reduced life span. Electron microscopy analysis of the inner-membrane morphology demonstrates that loss of PMI function increases the average length of mitochondrial cristae in embryonic cells. This phenotype is exacerbated in adult neurons in which cristae form a dense tangle of elongated membranes. Conversely, we show that PMI overexpression is sufficient to reduce crista length in vivo. Finally, these crista defects are associated with impaired respiratory chain activity and increases in the level of reactive oxygen species. Since PMI and its human orthologue TMEM11 are regulators of mitochondrial morphology, our data suggest that, by controlling crista length, PMI influences mitochondrial diameter and tubular shape.

Neuroprotection: the emerging concept of restorative neural stem cell biology for the treatment of neurodegenerative diseases

During the past decades Neural Stem Cells have been considered as an alternative source of cells to replace lost neurons and NSC transplantation has been indicated as a promising treatment for neurodegenerative disorders. Nevertheless, the current understanding of NSC biology suggests that, far from being mere spare parts for cell replacement therapies, NSCs could play a key role in the pharmacology of neuroprotection and become protagonists of innovative treatments for neurodegenerative diseases. Here, we review this new emerging concept of NSC biology.

Analysis of neuromuscular junctions and effects of anabolic steroid administration in the SOD1G93A mouse model of ALS

Several lines of evidence indicate that neuromuscular junction (NMJ) destruction and disassembly is an early phenomenon in amyotrophic lateral sclerosis (ALS). Here we analyzed by confocal and electron microscopy the NMJ structure in the diaphragm of SOD1G93A mice at symptom onset. In these mice, which provide a model for familial ALS, diaphragm denervation (~50%) as well as gastrocnemius denervation (~40%) was found. In addition, the size of the synaptic vesicle pool was reduced and alterations of mitochondria were observed in approximately 40% of the remaining presynaptic terminals. Chronic treatment of SOD1G93A mice with the anabolic steroid nandrolone during the presymptomatic stage preserved the diaphragm muscle mass and features indicative of synaptic activity. These features were represented by the number of vesicles docked within 200 nm from the presynaptic membrane and area of acetylcholine receptor clusters. Structural preservation of mitochondria was documented in presynaptic terminals. However, innervation of diaphragm muscle fibers was only slightly increased in nandrolone-treated SOD1-mutant mice. Altogether the results point out and define fine structural alterations of diaphragm NMJs in the murine model of familial ALS at symptom onset, and indicate that nandrolone may prevent or delay structural alterations in NMJ mitochondria and stimulate presynaptic activity but does not prevent muscle denervation during the disease.

Mitochondrial dysfunction in skeletal muscle of amyloid precursor protein-overexpressing mice

Inclusion body myositis, the most common muscle disorder in the elderly, is partly characterized by abnormal expression of amyloid precursor protein (APP) and intracellular accumulation of its proteolytic fragments collectively known as β-amyloid. The present study examined the effects of β-amyloid accumulation on mitochondrial structure and function of skeletal muscle from transgenic mice (MCK-βAPP) engineered to accumulate intramyofiber β-amyloid. Electron microscopic analysis revealed that a large fraction of myofibers from 2-3-month-old MCK-βAPP mice contained numerous, heterogeneous alterations in mitochondria, and other cellular organelles. [(1)H-decoupled](13)C NMR spectroscopy showed a substantial reduction in TCA cycle activity and indicated a switch from aerobic to anaerobic glucose metabolism in the MCK-βAPP muscle. Isolated muscle fibers from the MCK-βAPP mice also exhibited a reduction in cytoplasmic pH, an increased rate of ROS production, and a partially depolarized plasmalemma. Treatment of MCK-βAPP muscle cells with Ru360, a mitochondrial Ca(2+) uniporter antagonist, reversed alterations in the plasmalemmal membrane potential (V(m)) and pH. Consistent with altered redox state of the cells, treatment of MCK-βAPP muscle cells with glutathione reversed the effects of β-amyloid accumulation on Ca(2+) transient amplitudes. We conclude that structural and functional alterations in mitochondria precede the reported appearance of histopathological and clinical features in the MCK-βAPP mice and may represent key early events in the pathogenesis of inclusion body myositis.

Mitochondria as a therapeutic target for aging and neurodegenerative diseases

Mitochondria are cytoplasmic organelles responsible for life and death. Extensive evidence from animal models, postmortem brain studies of and clinical studies of aging and neurodegenerative diseases suggests that mitochondrial function is defective in aging and neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Several lines of research suggest that mitochondrial abnormalities, including defects in oxidative phosphorylation, increased accumulation of mitochondrial DNA defects, impaired calcium influx, accumulation of mutant proteins in mitochondria, and mitochondrial membrane potential dissipation are important cellular changes in both early and late-onset neurodegenerative diseases. Further, emerging evidence suggests that structural changes in mitochondria, including increased mitochondrial fragmentation and decreased mitochondrial fusion, are critical factors associated with mitochondrial dysfunction and cell death in aging and neurodegenerative diseases. This paper discusses research that elucidates features of mitochondria that are associated with cellular dysfunction in aging and neurodegenerative diseases and discusses mitochondrial structural and functional changes, and abnormal mitochondrial dynamics in neurodegenerative diseases. It also outlines mitochondria-targeted therapeutics in neurodegenerative diseases.