The role of mitochondria in amyotrophic lateral sclerosis

The role of mitochondrial dynamics in disease

Mitochondria are multifaceted and dynamic organelles regulating various important cellular processes from signal transduction to determining cell fate. As dynamic properties of mitochondria, fusion and fission accompanied with mitophagy, undergo constant changes in number and morphology to sustain mitochondrial homeostasis in response to cell context changes. Thus, the dysregulation of mitochondrial dynamics and mitophagy is unsurprisingly related with various diseases, but the unclear underlying mechanism hinders their clinical application. In this review, we summarize the recent developments in the molecular mechanism of mitochondrial dynamics and mitophagy, particularly the different roles of key components in mitochondrial dynamics in different context. We also summarize the roles of mitochondrial dynamics and target treatment in diseases related to the cardiovascular system, nervous system, respiratory system, and tumor cell metabolism demanding high-energy. In these diseases, it is common that excessive mitochondrial fission is dominant and accompanied by impaired fusion and mitophagy. But there have been many conflicting findings about them recently, which are specifically highlighted in this view. We look forward that these findings will help broaden our understanding of the roles of the mitochondrial dynamics in diseases and will be beneficial to the discovery of novel selective therapeutic targets.

scAAV9-VEGF alleviates symptoms of amyotrophic lateral sclerosis (ALS) mice through regulating aromatase

Amyotrophic lateral sclerosis (ALS) is an adult-onset, chronic, progressive, and fatal neurodegenerative disease that leads to progressive atrophy and weakness of the muscles throughout the body. Herein, we found that the intrathecal injection of adeno-associated virus (AAV)-delivered VEGF in SOD1-G93A transgenic mice, as well as ALS mice, could significantly delay disease onset and preserve motor functions and neurological functions, thus prolonging the survival of mice models. Moreover, we found that VEGF treatment could induce the elevated expression of aromatase, which is a key enzyme in estrogen synthesis, in neurons but not in astrocytes. On the other hand, the changes in the expression of oxidative stress-related factors HO-1 and GCLM and autophagy-related proteins p62 and LC3II upon the administration of VEGF revealed the involvement of oxidative stress and autophagy underlying the downstream of the VEGF-induced mitigation of ALS. In conclusion, this study proved the protective effects of VEGF in the onset and development of ALS and revealed the involvement of estrogen, oxidative stress and autophagy in the VEGF-induced alleviation of ALS. Our results highlighted the potential of VEGF as a promising therapeutic agent in the treatment of ALS.

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.

Combined RNA interference and gene replacement therapy targeting MFN2 as proof of principle for the treatment of Charcot-Marie-Tooth type 2A

Mitofusin-2 (MFN2) is an outer mitochondrial membrane protein essential for mitochondrial networking in most cells. Autosomal dominant mutations in the MFN2 gene cause Charcot-Marie-Tooth type 2A disease (CMT2A), a severe and disabling sensory-motor neuropathy that impacts the entire nervous system. Here, we propose a novel therapeutic strategy tailored to correcting the root genetic defect of CMT2A. Though mutant and wild-type MFN2 mRNA are inhibited by RNA interference (RNAi), the wild-type protein is restored by overexpressing cDNA encoding functional MFN2 modified to be resistant to RNAi. We tested this strategy in CMT2A patient-specific human induced pluripotent stem cell (iPSC)-differentiated motor neurons (MNs), demonstrating the correct silencing of endogenous MFN2 and replacement with an exogenous copy of the functional wild-type gene. This approach significantly rescues the CMT2A MN phenotype in vitro, stabilizing the altered axonal mitochondrial distribution and correcting abnormal mitophagic processes. The MFN2 molecular correction was also properly confirmed in vivo in the MitoCharc1 CMT2A transgenic mouse model after cerebrospinal fluid (CSF) delivery of the constructs into newborn mice using adeno-associated virus 9 (AAV9). Altogether, our data support the feasibility of a combined RNAi and gene therapy strategy for treating the broad spectrum of human diseases associated with MFN2 mutations.

ALS-Associated KIF5A Mutation Causes Locomotor Deficits Associated with Cytoplasmic Inclusions, Alterations of Neuromuscular Junctions, and Motor Neuron Loss

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting motor neurons. Recently, genome-wide association studies identified KIF5A as a new ALS-causing gene. KIF5A encodes a protein of the kinesin-1 family, allowing the anterograde transport of cargos along the microtubule rails in neurons. In ALS patients, mutations in the KIF5A gene induce exon 27 skipping, resulting in a mutated protein with a new C-terminal region (KIF5A Δ27). To understand how KIF5A Δ27 underpins the disease, we developed an ALS-associated KIF5A Drosophila model. When selectively expressed in motor neurons, KIF5A Δ27 alters larval locomotion as well as morphology and synaptic transmission at neuromuscular junctions in both males and females. We show that the distribution of mitochondria and synaptic vesicles is profoundly disturbed by KIF5A Δ27 expression. That is consistent with the numerous KIF5A Δ27-containing inclusions observed in motor neuron soma and axons. Moreover, KIF5A Δ27 expression leads to motor neuron death and reduces life expectancy. Our in vivo model reveals that a toxic gain of function underlies the pathogenicity of ALS-linked KIF5A mutant.SIGNIFICANCE STATEMENT Understanding how a mutation identified in patients with amyotrophic lateral sclerosis (ALS) causes the disease and the loss of motor neurons is crucial to fight against this disease. To this end, we have created a Drosophila model based on the motor neuron expression of the KIF5A mutant gene, recently identified in ALS patients. KIF5A encodes a kinesin that allows the anterograde transport of cargos. This model recapitulates the main features of ALS, including alterations of locomotion, synaptic neurotransmission, and morphology at neuromuscular junctions, as well as motor neuron death. KIF5A mutant is found in cytoplasmic inclusions, and its pathogenicity is because of a toxic gain of function.

Computational study of the motor neuron protein KIF5A to identify nsSNPs, bioactive compounds, and its key regulators

Introduction: Kinesin family member 5A (KIF5A) is a motor neuron protein expressed in neurons and involved in anterograde transportation of organelles, proteins, and RNA. Variations in the KIF5A gene that interfere with axonal transport have emerged as a distinguishing feature in several neurodegenerative disorders, including hereditary spastic paraplegia (HSP10), Charcot-Marie-Tooth disease type 2 (CMT2), and Amyotrophic Lateral Sclerosis (ALS). Methods: In this study, we implemented a computational structural and systems biology approach to uncover the role of KIF5A in ALS. Using the computational structural biology method, we explored the role of non-synonymous Single Nucleotide Polymorphism (nsSNPs) in KIF5A. Further, to identify the potential inhibitory molecule against the highly destabilizing structure variant, we docked 24 plant-derived phytochemicals involved in ALS. Results: We found KIF5AS291F variant showed the most structure destabilizing behavior and the phytocompound "epigallocatechin gallate" showed the highest binding affinity (-9.0 Kcal/mol) as compared to wild KIF5A (-8.4 Kcal/mol). Further, with the systems biology approach, we constructed the KIF5A protein-protein interaction (PPI) network to identify the associated Kinesin Families (KIFs) proteins, modules, and their function. We also constructed a transcriptional and post-transcriptional regulatory network of KIF5A. With the network topological parameters of PPIN (Degree, Bottleneck, Closeness, and MNC) using CytoHubba and computational knock-out experiment using Network Analyzer, we found KIF1A, 5B, and 5C were the significant proteins. The functional modules were highly enriched with microtubule motor activity, chemical synaptic transmission in neurons, GTP binding, and GABA receptor activity. In regulatory network analysis, we found KIF5A post-transcriptionally down-regulated by miR-107 which is further transcriptionally up-regulated by four TFs (HIF1A, PPARA, SREBF1, and TP53) and down-regulated by three TFs (ZEB1, ZEB2, and LIN28A). Discussion: We concluded our study by finding a crucial variant of KIF5A and its potential therapeutic target (epigallocatechin gallate) and KIF5A associated significant genes with important regulators which could decrypt the novel therapeutics in ALS and other neurodegenerative diseases.

Janus kinase inhibitors are potential therapeutics for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a poorly treated multifactorial neurodegenerative disease associated with multiple cell types and subcellular organelles. As with other multifactorial diseases, it is likely that drugs will need to target multiple disease processes and cell types to be effective. We review here the role of Janus kinase (JAK)/Signal transducer and activator of transcription (STAT) signalling in ALS, confirm the association of this signalling with fundamental ALS disease processes using the BenevolentAI Knowledge Graph, and demonstrate that inhibitors of this pathway could reduce the ALS pathophysiology in neurons, glia, muscle fibres, and blood cells. Specifically, we suggest that inhibition of the JAK enzymes by approved inhibitors known as Jakinibs could reduce STAT3 activation and modify the progress of this disease. Analysis of the Jakinibs highlights baricitinib as a suitable candidate due to its ability to penetrate the central nervous system and exert beneficial effects on the immune system. Therefore, we recommend that this drug be tested in appropriately designed clinical trials for ALS.

Mitochondria in health, disease, and aging

Mitochondria are well known as organelles responsible for the maintenance of cellular bioenergetics through the production of ATP. Although oxidative phosphorylation may be their most important function, mitochondria are also integral for the synthesis of metabolic precursors, calcium regulation, the production of reactive oxygen species, immune signaling, and apoptosis. Considering the breadth of their responsibilities, mitochondria are fundamental for cellular metabolism and homeostasis. Appreciating this significance, translational medicine has begun to investigate how mitochondrial dysfunction can represent a harbinger of disease. In this review, we provide a detailed overview of mitochondrial metabolism, cellular bioenergetics, mitochondrial dynamics, autophagy, mitochondrial damage-associated molecular patterns, mitochondria-mediated cell death pathways, and how mitochondrial dysfunction at any of these levels is associated with disease pathogenesis. Mitochondria-dependent pathways may thereby represent an attractive therapeutic target for ameliorating human disease.

Divergent single cell transcriptome and epigenome alterations in ALS and FTD patients with C9orf72 mutation

A repeat expansion in the C9orf72 (C9) gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Here we investigate single nucleus transcriptomics (snRNA-seq) and epigenomics (snATAC-seq) in postmortem motor and frontal cortices from C9-ALS, C9-FTD, and control donors. C9-ALS donors present pervasive alterations of gene expression with concordant changes in chromatin accessibility and histone modifications. The greatest alterations occur in upper and deep layer excitatory neurons, as well as in astrocytes. In neurons, the changes imply an increase in proteostasis, metabolism, and protein expression pathways, alongside a decrease in neuronal function. In astrocytes, the alterations suggest activation and structural remodeling. Conversely, C9-FTD donors have fewer high-quality neuronal nuclei in the frontal cortex and numerous gene expression changes in glial cells. These findings highlight a context-dependent molecular disruption in C9-ALS and C9-FTD, indicating unique effects across cell types, brain regions, and diseases.

Mitochondrial dysfunction in neurodegenerative disorders: Potential therapeutic application of mitochondrial transfer to central nervous system-residing cells

Mitochondrial dysfunction is reiteratively involved in the pathogenesis of diverse neurodegenerative diseases. Current in vitro and in vivo approaches support that mitochondrial dysfunction is branded by several molecular and cellular defects, whose impact at different levels including the calcium and iron homeostasis, energetic balance and/or oxidative stress, makes it difficult to resolve them collectively given their multifactorial nature. Mitochondrial transfer offers an overall solution since it contains the replacement of damage mitochondria by healthy units. Therefore, this review provides an introducing view on the structure and energy-related functions of mitochondria as well as their dynamics. In turn, we summarize current knowledge on how these features are deregulated in different neurodegenerative diseases, including frontotemporal dementia, multiple sclerosis, amyotrophic lateral sclerosis, Friedreich ataxia, Alzheimer´s disease, Parkinson´s disease, and Huntington's disease. Finally, we analyzed current advances in mitochondrial transfer between diverse cell types that actively participate in neurodegenerative processes, and how they might be projected toward developing novel therapeutic strategies.

Nutritional and metabolic factors in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a complex neurodegenerative disease that is classically thought to impact the motor system. Over the past 20 years, research has started to consider the contribution of non-motor symptoms and features of the disease, and how they might affect ALS prognosis. Of the non-motor features of the disease, nutritional status (for example, malnutrition) and metabolic balance (for example, weight loss and hypermetabolism) have been consistently shown to contribute to more rapid disease progression and/or earlier death. Several complex cellular changes observed in ALS, including mitochondrial dysfunction, are also starting to be shown to contribute to bioenergetic failure. The resulting energy depletion in high energy demanding neurons makes them sensitive to apoptosis. Given that nutritional and metabolic stressors at the whole-body and cellular level can impact the capacity to maintain optimal function, these factors present avenues through which we can identify novel targets for treatment in ALS. Several clinical trials are now underway evaluating the effectiveness of modifying energy balance in ALS, making this article timely in reviewing the evidence base for metabolic and nutritional interventions.

Current insights in the molecular genetic pathogenesis of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurodegenerative disease that leads to the massive loss of motor neurons in cerebrum, brain stem and spinal cord. It affects not only motor neurons but also other neurons and glial cells, resulting in the progressive muscle atrophy, the severe disability and the eventual death due to the respiratory failure. The pathogenesis of ALS is not fully understood. Currently, several factors are considered to be involved in the pathogenesis of ALS, such as genetic factors, imbalances in protein homeostasis, RNA metabolism disorders, mitochondrial dysfunctions, glutamate-mediated excitatory toxicities and intra-neuronal material transport disorders in neurons. The study of genetic mutations related to ALS pathogenesis will link the molecular and cellular mechanisms of the disease, thus enhancing the understanding of its occurrence and progression, thereby providing new insights for the pathogenesis of ALS. This review summarizes the current insights in the molecular genetic pathogenesis of ALS.

Skeletal muscle cell protein dysregulation highlights the pathogenesis mechanism of myopathy-associated p97/VCP R155H mutations

p97/VCP, a hexametric member of the AAA-ATPase superfamily, has been associated with a wide range of cellular protein pathways, such as proteasomal degradation, the unfolding of polyubiquitinated proteins, and autophagosome maturation. Autosomal dominant p97/VCP mutations cause a rare hereditary multisystem disorder called IBMPFD/ALS (Inclusion Body Myopathy with Paget's Disease and Frontotemporal Dementia/Amyotrophic Lateral Sclerosis), characterized by progressive weakness and subsequent atrophy of skeletal muscles, and impacting bones and brains, such as Parkinson's disease, Lewy body disease, Huntington's disease, and amyotrophic lateral ALS. Among all disease-causing mutations, Arginine 155 to Histidine (R155H/+) was reported to be the most common one, affecting over 50% of IBMPFD patients, resulting in disabling muscle weakness, which might eventually be life-threatening due to cardiac and respiratory muscle involvement. Induced pluripotent stem cells (iPSCs) offer an unlimited resource of cells to study pathology's underlying molecular mechanism, perform drug screening, and investigate regeneration. Using R155H/+ patients' fibroblasts, we generated IPS cells and corrected the mutation (Histidine to Arginine, H155R) to generate isogenic control cells before differentiating them into myotubes. The further proteomic analysis allowed us to identify differentially expressed proteins associated with the R155H mutation. Our results showed that R155H/+ cells were associated with dysregulated expression of several proteins involved in skeletal muscle function, cytoskeleton organization, cell signaling, intracellular organelles organization and function, cell junction, and cell adhesion. Our findings provide molecular evidence of dysfunctional protein expression in R155H/+ myotubes and offer new therapeutic targets for treating IBMPFD/ALS.

Mitochondrial genome study in blood of maternally inherited ALS cases

BACKGROUND

ALS is a heterogeneous disease in which different factors such as mitochondrial phenotypes act in combination with a genetic predisposition. This study addresses the question of whether homoplasmic (total mitochondrial genome of a sample is affected) and/or heteroplasmic mutations (wildtype and mutant mitochondrial DNA molecules coexist) might play a role in familial ALS. Blood was drawn from familial ALS patients with a possible maternal pattern of inheritance according to their pedigrees, which was compared to blood of ALS patients without maternal association as well as age-matched controls. In two cohorts, we analyzed the mitochondrial genome from whole blood or isolated white blood cells and platelets using a resequencing microarray (Affymetrix MitoChip v2.0) that is able to detect homoplasmic and heteroplasmic mitochondrial DNA mutations and allows the assessment of low-level heteroplasmy.

RESULTS

We identified an increase in homoplasmic ND5 mutations, a subunit of respiratory chain complex I, in whole blood of ALS patients that allowed maternal inheritance. This effect was more pronounced in patients with bulbar onset. Heteroplasmic mutations were significantly increased in different mitochondrial genes in platelets of patients with possible maternal inheritance. No increase of low-level heteroplasmy was found in maternal ALS patients.

CONCLUSION

Our results indicate a contribution of homoplasmic ND5 mutations to maternally associated ALS with bulbar onset. Therefore, it might be conceivable that specific maternally transmitted rather than randomly acquired mitochondrial DNA mutations might contribute to the disease process. This stands in contrast with observations from Alzheimer's and Parkinson's diseases showing an age-dependent accumulation of unspecific mutations in mitochondrial DNA.

Exploring the therapeutic potential of the mitochondrial transfer-associated enzymatic machinery in brain degeneration

Mitochondrial dysfunction is a central event in the pathogenesis of several degenerative brain disorders. It entails fission and fusion dynamics disruption, progressive decline in mitochondrial clearance, and uncontrolled oxidative stress. Many therapeutic strategies have been formulated to reverse these alterations, including replacing damaged mitochondria with healthy ones. Spontaneous mitochondrial transfer is a naturally occurring process with different biological functions. It comprises mitochondrial donation from one cell to another, carried out through different pathways, such as the formation and stabilization of tunneling nanotubules and Gap junctions and the release of extracellular vesicles with mitochondrial cargoes. Even though many aspects of regulating these mechanisms still need to be discovered, some key enzymatic regulators have been identified. This review summarizes the current knowledge on mitochondrial dysfunction in different neurodegenerative disorders. Besides, we analyzed the usage of mitochondrial transfer as an endogenous revitalization tool, emphasizing the enzyme regulators that govern this mechanism. Going deeper into this matter would be helpful to take advantage of the therapeutic potential of mitochondrial transfer.

Mitochondrial dysfunction: roles in skeletal muscle atrophy

Mitochondria play important roles in maintaining cellular homeostasis and skeletal muscle health, and damage to mitochondria can lead to a series of pathophysiological changes. Mitochondrial dysfunction can lead to skeletal muscle atrophy, and its molecular mechanism leading to skeletal muscle atrophy is complex. Understanding the pathogenesis of mitochondrial dysfunction is useful for the prevention and treatment of skeletal muscle atrophy, and finding drugs and methods to target and modulate mitochondrial function are urgent tasks in the prevention and treatment of skeletal muscle atrophy. In this review, we first discussed the roles of normal mitochondria in skeletal muscle. Importantly, we described the effect of mitochondrial dysfunction on skeletal muscle atrophy and the molecular mechanisms involved. Furthermore, the regulatory roles of different signaling pathways (AMPK-SIRT1-PGC-1α, IGF-1-PI3K-Akt-mTOR, FoxOs, JAK-STAT3, TGF-β-Smad2/3 and NF-κB pathways, etc.) and the roles of mitochondrial factors were investigated in mitochondrial dysfunction. Next, we analyzed the manifestations of mitochondrial dysfunction in muscle atrophy caused by different diseases. Finally, we summarized the preventive and therapeutic effects of targeted regulation of mitochondrial function on skeletal muscle atrophy, including drug therapy, exercise and diet, gene therapy, stem cell therapy and physical therapy. This review is of great significance for the holistic understanding of the important role of mitochondria in skeletal muscle, which is helpful for researchers to further understanding the molecular regulatory mechanism of skeletal muscle atrophy, and has an important inspiring role for the development of therapeutic strategies for muscle atrophy targeting mitochondria in the future.

Mitochondria as intracellular signalling organelles. An update

Traditionally, mitochondria are known as "the powerhouse of the cell," responsible for energy (ATP) generation (by the electron transport chain, oxidative phosphorylation, the tricarboxylic acid cycle, and fatty acid ß-oxidation), and for the regulation of several metabolic processes, including redox homeostasis, calcium signalling, and cellular apoptosis. The extensive studies conducted in the last decades portray mitochondria as multifaceted signalling organelles that ultimately command cells' survival or death. Based on current knowledge, we'll outline the mitochondrial signalling to other intracellular compartments in homeostasis and pathology-related mitochondrial stress conditions here. The following topics are discussed: (i) oxidative stress and mtROS signalling in mitohormesis, (ii) mitochondrial Ca²⁺ signalling; (iii) the anterograde (nucleus-to-mitochondria) and retrograde (mitochondria-to-nucleus) signal transduction, (iv) the mtDNA role in immunity and inflammation, (v) the induction of mitophagy- and apoptosis - signalling cascades, (vi) the mitochondrial dysfunctions (mitochondriopathies) in cardiovascular, neurodegenerative, and malignant diseases. The novel insights into molecular mechanisms of mitochondria-mediated signalling can explain mitochondria adaptation to metabolic and environmental stresses to achieve cell survival.

Characterization of Mitochondria Degeneration in Spinal Motor Neurons Triggered by Chronic Over-activation of α-Amino-3-Hydroxy-5-Methylisoxazole-4-Propionic Acid Receptors in the Rat Spinal Cord in Vivo

Mitochondrial damage is a central mechanism involved in neurological disorders as Alzheimer's, and Parkinson's diseases and amyotrophic lateral sclerosis. Energy production is the most studied mitochondrial function; however, mitochondria are also involved in processes like calcium buffering homeostasis, and cell death control during apoptosis and necrosis. Using transmission electron microscopy, in this in vivo study in male rats, we describe ultrastructural mitochondrial alterations of spinal motor neurons along chronic AMPA-induced excitotoxicity, which has been described as one of the most relevant mechanisms in ALS disease. Mitochondrial alterations begin with a crest swelling, which progresses to a full mitochondrial swelling and crest disruption. Changes on the mitochondrial morphology from elongated to a circular shape also occur along the AMPA-excitotoxicity process. In addition, by combining the TUNEL assay and immunohistochemistry for mitochondrial enzymes, we show evidence of mitochondrial DNA damage. Evidence of mitochondrial alterations during an AMPA-excitotoxic event is relevant because resembles the mitochondrial alterations previously reported in ALS patients and in transgenic familial ALS models, suggesting that a chronic excitotoxic model can be related to sporadic ALS (as has been shown in recent papers), which represent more than the 90% of the ALS cases. Understanding the mechanisms involved in motor neuron degenerative process, such as the ultrastructural mitochondrial changes permits to design strategies for MN-degeneration treatments in ALS.

Glucose Hypometabolism Prompts RAN Translation and Exacerbates C9orf72-related ALS/FTD Phenotypes

The most prevalent genetic cause of both amyotrophic lateral sclerosis and frontotemporal dementia is a (GGGGCC)n nucleotide repeat expansion (NRE) occurring in the first intron of the C9orf72 gene (C9). Brain glucose hypometabolism is consistently observed in C9-NRE carriers, even at pre-symptomatic stages, although its potential role in disease pathogenesis is unknown. Here, we identified alterations in glucose metabolic pathways and ATP levels in the brain of asymptomatic C9-BAC mice. We found that, through activation of the GCN2 kinase, glucose hypometabolism drives the production of dipeptide repeat proteins (DPRs), impairs the survival of C9 patient-derived neurons, and triggers motor dysfunction in C9-BAC mice. We also found that one of the arginine-rich DPRs (PR) can directly contribute to glucose metabolism and metabolic stress. These findings provide a mechanistic link between energy imbalances and C9-ALS/FTD pathogenesis and support a feedforward loop model that opens several opportunities for therapeutic intervention.

Altered Metabolism in Motor Neuron Diseases: Mechanism and Potential Therapeutic Target

Motor Neuron Diseases (MND) are neurological disorders characterized by a loss of varying motor neurons resulting in decreased physical capabilities. Current research is focused on hindering disease progression by determining causes of motor neuron death. Metabolic malfunction has been proposed as a promising topic when targeting motor neuron loss. Alterations in metabolism have also been noted at the neuromuscular junction (NMJ) and skeletal muscle tissue, emphasizing the importance of a cohesive system. Finding metabolism changes consistent throughout both neurons and skeletal muscle tissue could pose as a target for therapeutic intervention. This review will focus on metabolic deficits reported in MNDs and propose potential therapeutic targets for future intervention.

Molecular Chaperones' Potential against Defective Proteostasis of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neuronal degenerative condition identified via a build-up of mutant aberrantly folded proteins. The native folding of polypeptides is mediated by molecular chaperones, preventing their pathogenic aggregation. The mutant protein expression in ALS is linked with the entrapment and depletion of chaperone capacity. The lack of a thorough understanding of chaperones' involvement in ALS pathogenesis presents a significant challenge in its treatment. Here, we review how the accumulation of the ALS-linked mutant FUS, TDP-43, SOD1, and C9orf72 proteins damage cellular homeostasis mechanisms leading to neuronal loss. Further, we discuss how the HSP70 and DNAJ family co-chaperones can act as potential targets for reducing misfolded protein accumulation in ALS. Moreover, small HSPB1 and HSPB8 chaperones can facilitate neuroprotection and prevent stress-associated misfolded protein apoptosis. Designing therapeutic strategies by pharmacologically enhancing cellular chaperone capacity to reduce mutant protein proteotoxic effects on ALS pathomechanisms can be a considerable advancement. Chaperones, apart from directly interacting with misfolded proteins for protein quality control, can also filter their toxicity by initiating strong stress-response pathways, modulating transcriptional expression profiles, and promoting anti-apoptotic functions. Overall, these properties of chaperones make them an attractive target for gaining fundamental insights into misfolded protein disorders and designing more effective therapies against ALS.

Integrated Omic Analysis Delineates Pathways Modulating Toxic TDP-43 Protein Aggregates in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a multi-systemic, incurable, amyloid disease affecting the motor neurons, resulting in the death of patients. The disease is either sporadic or familial with SOD1, C9orf72, FUS, and TDP-43 constituting the majority of familial ALS. Multi-omics studies on patients and model systems like mice and yeast have helped in understanding the association of various signaling and metabolic pathways with the disease. The yeast model system has played a pivotal role in elucidating the gene amyloid interactions. We carried out an integrated transcriptomic and metabolomic analysis of the TDP-43 expressing yeast model to elucidate deregulated pathways associated with the disease. The analysis shows the deregulation of the TCA cycle, single carbon metabolism, glutathione metabolism, and fatty acid metabolism. Transcriptomic analysis of GEO datasets of TDP-43 expressing motor neurons from mice models of ALS and ALS patients shows considerable overlap with experimental results. Furthermore, a yeast model was used to validate the obtained results using metabolite addition and gene knock-out experiments. Taken together, our result shows a potential role for the TCA cycle, cellular redox pathway, NAD metabolism, and fatty acid metabolism in disease. Supplementation of reduced glutathione, nicotinate, and the keto diet might help to manage the disease.

Role of Sirtuin 3 in Degenerative Diseases of the Central Nervous System

An NAD⁺-dependent deacetylase called Sirtuin 3 (Sirt3) is involved in the metabolic processes of the mitochondria, including energy generation, the tricarboxylic acid cycle, and oxidative stress. Sirt3 activation can slow down or prevent mitochondrial dysfunction in response to neurodegenerative disorders, demonstrating a strong neuroprotective impact. The mechanism of Sirt3 in neurodegenerative illnesses has been elucidated over time; it is essential for neuron, astrocyte, and microglial function, and its primary regulatory factors include antiapoptosis, oxidative stress, and the maintenance of metabolic homeostasis. Neurodegenerative disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS), may benefit from a thorough and in-depth investigation of Sirt3. In this review, we primarily cover Sirt3's role and its regulation in the nerve cells and the connection between Sirt3 and neurodegenerative disorders.

Fluorescence microscopic platforms imaging mitochondrial abnormalities in neurodegenerative diseases

Neurodegenerative diseases (NDs) are progressive disorders that cause the degeneration of neurons. Mitochondrial dysfunction is a common symptom in NDs and plays a crucial role in neuronal loss. Mitochondrial abnormalities can be observed in the early stages of NDs and evolve throughout disease progression. Visualizing mitochondrial abnormalities can help understand ND progression and develop new therapeutic strategies. Fluorescence microscopy is a powerful tool for dynamically imaging mitochondria due to its high sensitivity and spatiotemporal resolution. This review discusses the relationship between mitochondrial dysfunction and ND progression, potential biomarkers for imaging dysfunctional mitochondria, advances in fluorescence microscopy for detecting organelles, the performance of fluorescence probes in visualizing ND-associated mitochondria, and the challenges and opportunities for developing new generations of fluorescence imaging platforms for monitoring mitochondria in NDs.

Mitophagy regulation in aging and neurodegenerative disease

Mitochondria are the primary cellular energy generators, supplying the majority of adenosine triphosphate through oxidative phosphorylation, which is necessary for neuron function and survival. Mitophagy is the metabolic process of eliminating dysfunctional or redundant mitochondria. It is a type of autophagy and it is crucial for maintaining mitochondrial and neuronal health. Impaired mitophagy leads to an accumulation of damaged mitochondria and proteins leading to the dysregulation of mitochondrial quality control processes. Recent research shows the vital role of mitophagy in neurons and the pathogenesis of major neurodegenerative diseases. Mitophagy also plays a major role in the process of aging. This review describes the alterations that are being caused in the mitophagy process at the molecular level in aging and in neurodegenerative diseases, particularly Alzheimer's, Parkinson's, and Huntington's diseases and amyotrophic lateral sclerosis, also looks at how mitophagy can be exploited as a therapeutic target for these diseases.

Masitinib: The promising actor in the next season of the Amyotrophic Lateral Sclerosis treatment series

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease with high mortality and morbidity rate affecting both upper and lower motor neurons (MN). Muscle force reduction, behavioral change, pseudobulbar affect, and cognitive impairments are the most common clinical manifestations of ALS. The main physiopathology of ALS is still unclear, though several studies have identified that oxidative stress, proteinopathies, glutamate-related excitotoxicity, microglial activation, and neuroinflammation may be involved in the pathogenesis of ALS. From 1995 until October 2022, only Riluzole, Dextromethorphan Hydrobromide (DH) with Quinidine sulfate (Q), Edaravone, and Sodium phenylbutyrate with Taurursodiol (PB/TUDCO) have achieved FDA approval for ALS treatment. Despite the use of these four approved agents, the survival rate and quality of life of ALS patients are still low. Thus, finding novel treatments for ALS patients is an urgent requirement. Masitinib, a tyrosine kinase inhibitor, emphasizes the neuro-inflammatory activity of ALS by targeting macrophages, mast cells, and microglia cells. Masitinib downregulates the proinflammatory cytokines, indirectly reduces inflammation, and induces neuroprotection. Also, it was effective in phase 2/3 and 3 clinical trials (CTs) by increasing overall survival and delaying motor, bulbar, and respiratory function deterioration. This review describes the pathophysiology of ALS, focusing on Masitinib's mechanism of action and explaining why Masitinib could be a promising actor in the treatment of ALS patients. In addition, Masitinib CTs and other competitor drugs in phase 3 CTs have been discussed.

Sigma-1 receptor maintains ATAD3A as a monomer to inhibit mitochondrial fragmentation at the mitochondria-associated membrane in amyotrophic lateral sclerosis

Organelle contact sites are multifunctional platforms for maintaining cellular homeostasis. Alternations of the mitochondria-associated membranes (MAM), one of the organelle contact sites where the endoplasmic reticulum (ER) is tethered to the mitochondria, have been involved in the pathogenesis of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). However, the detailed mechanisms through which MAM integrity is disrupted in ALS have not been fully elucidated. Here, we examined whether AAA ATPase domain-containing protein 3A (ATAD3A), a mitochondrial membrane AAA ATPase accumulating at the MAM, is involved in ALS. We found that sigma-1 receptor (σ1R), an ER-resident MAM protein causative for inherited juvenile ALS, required ATAD3A to maintain the MAM. In addition, σ1R retained ATAD3A as a monomer, which is associated with an inhibition of mitochondrial fragmentation. ATAD3A dimerization and mitochondrial fragmentation were significantly induced in σ1R-deficient or SOD1-linked ALS mouse spinal cords. Overall, these observations indicate that MAM induction by σ1R depends on ATAD3A and that σ1R maintains ATAD3A as a monomer to inhibit mitochondrial fragmentation. Our findings suggest that targeting σ1R-ATAD3A axis would be promising for a novel therapeutic strategy to treat mitochondrial dysfunction in neurological disorders, including ALS.

Compartment specific mitochondrial dysfunction in Drosophila knock-in model of ALS reversed by altered gene expression of OXPHOS subunits and pro-fission factor Drp1

Amyotrophic Lateral Sclerosis (ALS) is a fatal multisystem neurodegenerative disease, characterized by a loss in motor function. ALS is genetically diverse, with mutations in genes ranging from those regulating RNA metabolism, like TAR DNA-binding protein (TDP-43) and Fused in sarcoma (FUS), to those that act to maintain cellular redox homeostasis, like superoxide dismutase 1 (SOD1). Although varied in genetic origin, pathogenic and clinical commonalities are clearly evident between cases of ALS. Defects in mitochondria is one such common pathology, thought to occur prior to, rather than as a consequence of symptom onset, making these organelles a promising therapeutic target for ALS, as well as other neurodegenerative diseases. Depending on the homeostatic needs of neurons throughout life, mitochondria are normally shuttled to different subcellular compartments to regulate metabolite and energy production, lipid metabolism, and buffer calcium. While originally considered a motor neuron disease due to the dramatic loss in motor function accompanied by motor neuron cell death in ALS patients, many studies have now implicated non-motor neurons and glial cells alike. Defects in non-motor neuron cell types often preceed motor neuron death suggesting their dysfunction may initiate and/or facilitate the decline in motor neuron health. Here, we investigate mitochondria in a Drosophila Sod1 knock-in model of ALS. In depth, in vivo, examination reveals mitochondrial dysfunction evident prior to onset of motor neuron degeneration. Genetically encoded redox biosensors identify a general disruption in the electron transport chain (ETC). Compartment specific abnormalities in mitochondrial morphology is observed in diseased sensory neurons, accompanied by no apparent defects in the axonal transport machinery, but instead an increase in mitophagy in synaptic regions. The decrease in networked mitochondria at the synapse is reversed upon downregulation of the pro-fission factor Drp1. Furthermore, altered expression of specific OXPHOS subunits reverses ALS-associated defects in mitochondrial morphology and function.

Crosstalk between Oxidative Stress and Aging in Neurodegeneration Disorders

The world population is aging rapidly, and increasing lifespan exacerbates the burden of age-related health issues. On the other hand, premature aging has begun to be a problem, with increasing numbers of younger people suffering aging-related symptoms. Advanced aging is caused by a combination of factors: lifestyle, diet, external and internal factors, as well as oxidative stress (OS). Although OS is the most researched aging factor, it is also the least understood. OS is important not only in relation to aging but also due to its strong impact on neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), Alzheimer's disease (AD), and Parkinson's disease (PD). In this review, we will discuss the aging process in relation to OS, the function of OS in neurodegenerative disorders, and prospective therapeutics capable of relieving neurodegenerative symptoms associated with the pro-oxidative condition.

Oxidative Stress and Antioxidants in Neurodegenerative Disorders

Neurodegenerative disorders constitute a substantial proportion of neurological diseases with significant public health importance. The pathophysiology of neurodegenerative diseases is characterized by a complex interplay of various general and disease-specific factors that lead to the end point of neuronal degeneration and loss, and the eventual clinical manifestations. Oxidative stress is the result of an imbalance between pro-oxidant species and antioxidant systems, characterized by an elevation in the levels of reactive oxygen and reactive nitrogen species, and a reduction in the levels of endogenous antioxidants. Recent studies have increasingly highlighted oxidative stress and associated mitochondrial dysfunction to be important players in the pathophysiologic processes involved in neurodegenerative conditions. In this article, we review the current knowledge of the general effects of oxidative stress on the central nervous system, the different specific routes by which oxidative stress influences the pathophysiologic processes involved in Alzheimer's disease, Parkinson's disease, Amyotrophic Lateral Sclerosis and Huntington's disease, and how oxidative stress may be therapeutically reversed/mitigated in order to stall the pathological progression of these neurodegenerative disorders to bring about clinical benefits.

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.

Mitochondria-Targeted Antioxidants, an Innovative Class of Antioxidant Compounds for Neurodegenerative Diseases: Perspectives and Limitations

Neurodegenerative diseases comprise a wide spectrum of pathologies characterized by progressive loss of neuronal functions and structures. Despite having different genetic backgrounds and etiology, in recent years, many studies have highlighted a point of convergence in the mechanisms leading to neurodegeneration: mitochondrial dysfunction and oxidative stress have been observed in different pathologies, and their detrimental effects on neurons contribute to the exacerbation of the pathological phenotype at various degrees. In this context, increasing relevance has been acquired by antioxidant therapies, with the purpose of restoring mitochondrial functions in order to revert the neuronal damage. However, conventional antioxidants were not able to specifically accumulate in diseased mitochondria, often eliciting harmful effects on the whole body. In the last decades, novel, precise, mitochondria-targeted antioxidant (MTA) compounds have been developed and studied, both in vitro and in vivo, to address the need to counter the oxidative stress in mitochondria and restore the energy supply and membrane potentials in neurons. In this review, we focus on the activity and therapeutic perspectives of MitoQ, SkQ1, MitoVitE and MitoTEMPO, the most studied compounds belonging to the class of MTA conjugated to lipophilic cations, in order to reach the mitochondrial compartment.

PINK1/Parkin-mediated mitophagy in neurodegenerative diseases

Mitochondria play key roles in bioenergetics, metabolism, and signaling; therefore, stable mitochondrial function is essential for cell survival, particularly in energy-intensive neuronal cells. In neurodegenerative diseases, damaged mitochondria accumulate in neurons causing associated bioenergetics deficiency, impaired cell signaling, defective cytoplasmic calcium buffering, and other pathological changes. Mitochondrial quality control is an important mechanism to ensure the maintenance of mitochondrial health, homeostasis, and mitophagy, the latter of which is a pathway that delivers defective mitochondria to the lysosome for degradation. Defective mitophagy is thought to be responsible for the accumulation of damaged mitochondria, which leads to cellular dysfunction and/or death in neurodegenerative diseases. PINK1/Parkin mainly regulates ubiquitin-dependent mitophagy, which is crucial for many aspects of mitochondrial physiology, particularly the initiation of autophagic mechanisms. Therefore, in the present review, we summarize the current knowledge of the conventional mitophagy pathway, focusing on the molecular mechanisms underlying mitophagy dysregulation in prion disease and other age-related neurodegenerative diseases, especially in relation to the PINK1/Parkin pathway. Moreover, we list the inducers of mitophagy that possess neuroprotective effects, in addition to their mechanisms related to the PINK1/Parkin pathway. These mechanisms may provide potential interventions centered on the regulation of mitophagy and offer therapeutic strategies for the treatment of neurodegenerative diseases.

Analysis of Mitochondrial Dynamics in Adult Drosophila Axons

Neuronal survival depends on the generation of ATP from an ever-changing mitochondrial network. This requires a fine balance between the constant degradation of damaged mitochondria, biogenesis of new mitochondria, movement along microtubules, dynamic processes, and adequate functional capacity to meet firing demands. The distribution of mitochondria needs to be tightly controlled throughout the entire neuron, including its projections. Axons in particular can be enormous structures compared to the size of the cell soma, and how mitochondria are maintained in these compartments is poorly defined. Mitochondrial dysfunction in neurons is associated with aging and neurodegenerative diseases, with the axon being preferentially vulnerable to destruction. Drosophila offer a unique way to study these organelles in fully differentiated adult neurons in vivo. Here, we briefly review the regulation of neuronal mitochondria in health, aging, and disease and introduce two methodological approaches to study mitochondrial dynamics and transport in axons using the Drosophila wing system.

Honokiol alleviated neurodegeneration by reducing oxidative stress and improving mitochondrial function in mutant SOD1 cellular and mouse models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease affecting both upper and lower motor neurons (MNs) with large unmet medical needs. Multiple pathological mechanisms are considered to contribute to the progression of ALS, including neuronal oxidative stress and mitochondrial dysfunction. Honokiol (HNK) has been reported to exert therapeutic effects in several neurologic disease models including ischemia stroke, Alzheimer's disease and Parkinson's disease. Here we found that honokiol also exhibited protective effects in ALS disease models both in vitro and in vivo. Honokiol improved the viability of NSC-34 motor neuron-like cells that expressed the mutant G93A SOD1 proteins (SOD1-G93A cells for short). Mechanistical studies revealed that honokiol alleviated cellular oxidative stress by enhancing glutathione (GSH) synthesis and activating the nuclear factor erythroid 2-related factor 2 (NRF2)-antioxidant response element (ARE) pathway. Also, honokiol improved both mitochondrial function and morphology via fine-tuning mitochondrial dynamics in SOD1-G93A cells. Importantly, honokiol extended the lifespan of the SOD1-G93A transgenic mice and improved the motor function. The improvement of antioxidant capacity and mitochondrial function was further confirmed in the spinal cord and gastrocnemius muscle in mice. Overall, honokiol showed promising preclinical potential as a multiple target drug for ALS treatment.

Blood-CNS barrier dysfunction in amyotrophic lateral sclerosis: Proposed mechanisms and clinical implications

There is strong evidence for blood-brain and blood-spinal cord barrier dysfunction at the early stages of many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Since impairment of the blood-central nervous system barrier (BCNSB) occurs during the pre-symptomatic stages of ALS, the mechanisms underlying this pathology are likely also involved in the ALS disease process. In this review, we explore how drivers of ALS disease, particularly mitochondrial dysfunction, astrocyte pathology and neuroinflammation, may contribute to BCNSB impairment. Mitochondria are highly abundant in BCNSB tissue and mitochondrial dysfunction in ALS contributes to motor neuron death. Likewise, astrocytes adopt key physical, transport and metabolic functions at the barrier, many of which are impaired in ALS. Astrocytes also show raised expression of inflammatory markers in ALS and ablating ALS-causing transgenes in astrocytes slows disease progression. In addition, key drivers of neuroinflammation, including TAR DNA-binding protein 43 (TDP-43) pathology, matrix metalloproteinase activation and systemic inflammation, affect BCNSB integrity in ALS. Finally, we discuss the translational implications of BCNSB dysfunction in ALS, including the development of biomarkers for disease onset and progression, approaches aimed at restoring BCNSB integrity and in vitro modelling of the neurogliovascular system.

Mitochondrial calcium cycling in neuronal function and neurodegeneration

Mitochondria are essential for proper cellular function through their critical roles in ATP synthesis, reactive oxygen species production, calcium (Ca2+) buffering, and apoptotic signaling. In neurons, Ca2+ buffering is particularly important as it helps to shape Ca2+ signals and to regulate numerous Ca2+-dependent functions including neuronal excitability, synaptic transmission, gene expression, and neuronal toxicity. Over the past decade, identification of the mitochondrial Ca2+ uniporter (MCU) and other molecular components of mitochondrial Ca2+ transport has provided insight into the roles that mitochondrial Ca2+ regulation plays in neuronal function in health and disease. In this review, we discuss the many roles of mitochondrial Ca2+ uptake and release mechanisms in normal neuronal function and highlight new insights into the Ca2+-dependent mechanisms that drive mitochondrial dysfunction in neurologic diseases including epilepsy, Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. We also consider how targeting Ca2+ uptake and release mechanisms could facilitate the development of novel therapeutic strategies for neurological diseases.

Multiple Copies of microRNA Binding Sites in Long 3'UTR Variants Regulate Axonal Translation

Rapid responses to changes within subcellular compartments of highly polarized cells, such as neuron axons, depend on local translation and post-transcriptional regulation. The mechanism by which microRNAs (miRNAs) regulate this process is not fully understood. Here, using live cell imaging and RNA sequencing analysis, we demonstrated how miRNAs can differentially control hundreds of transcripts at the subcellular level. We demonstrated that the seed match length of the miRNA target-sequence regulates both mRNA stability and protein translation rates. While longer seed matches have an increased inhibitory effect, transcriptome analysis did not reveal differences in seed match length between axonal and somata mRNAs of motor neurons. However, mRNA variants with longer 3'UTR are enriched in axons and contain multiple repeats of specific miRNA target sequences. Finally, we demonstrated that the long 3'UTR mRNA variant of the motor protein Kif5b is enriched explicitly in motor neuron axons and contains multiple sequence repeats for binding miR-129-5p. This subsequently results in the differential post-transcriptional regulation of kif5b and its synthesis in axons. Thus, we suggest that the number of miRNA binding sites at the 3'UTR of the mRNA, rather than the miRNA seed match length, regulates the axonal transcriptome.

Protective Effects of Hexarelin and JMV2894 in a Human Neuroblastoma Cell Line Expressing the SOD1-G93A Mutated Protein

Amyotrophic lateral sclerosis (ALS) is an incurable motor neuron disease whose etiology remains unresolved; nonetheless, mutations of superoxide dismutase 1 (SOD1) have been associated with several variants of ALS. Currently available pharmacologic interventions are only symptomatic and palliative in effect; therefore, there is a pressing demand for more effective drugs. This study examined potential therapeutic effects of growth hormone secretagogues (GHSs), a large family of synthetic compounds, as possible candidates for the treatment of ALS. Human neuroblastoma cells expressing the SOD1-G93A mutated protein (SH-SY5Y SOD1^G93A cells) were incubated for 24 h with H₂O₂ (150 µM) in the absence, or presence, of GHS (1 µM), in order to study the protective effect of GHS against increased oxidative stress. The two GHSs examined in this study, hexarelin and JMV2894, protected cells from H₂O₂-induced cytotoxicity by activating molecules that regulate apoptosis and promote cell survival processes. These findings suggest the possibility of developing new GHS-based anti-oxidant and neuroprotective drugs with improved therapeutic potential. Further investigations are required for the following: (i) to clarify GHS molecular mechanisms of action, and (ii) to envisage the development of new GHSs that may be useful in ALS therapy.

Prospects for gene replacement therapies in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating and incurable neurodegenerative disease characterized by the progressive loss of upper and lower motor neurons. ALS causes death, usually within 2-5 years of diagnosis. Riluzole, the only drug currently approved in Europe for the treatment of this condition, offers only a modest benefit, increasing survival by 3 months on average. Recent advances in our understanding of causative or disease-modifying genetic variants and in the development of genetic therapy strategies present exciting new therapeutic opportunities for ALS. In addition, the approval of adeno-associated virus-mediated delivery of functional copies of the SMN1 gene to treat spinal muscular atrophy represents an important therapeutic milestone and demonstrates the potential of gene replacement therapies for motor neuron disorders. In this Review, we describe the current landscape of genetic therapies in ALS, highlighting achievements and critical challenges. In particular, we discuss opportunities for gene replacement therapy in subgroups of people with ALS, and we describe loss-of-function mutations that are known to contribute to the pathophysiology of ALS and could represent novel targets for gene replacement therapies.

Neurodegenerative disease and antioxidant biomarkers: A bidirectional Mendelian randomization study

Objective

Previous observational studies have suggested that antioxidant imbalance is correlated with neurodegenerative diseases, while its cause-effect remains unclear. Thus, the goal of the present study is to explore the causal relationship between 11 antioxidant biomarkers and 3 most common neurodegenerative diseases [Alzheimer's disease (AD), Amyotrophic Lateral Sclerosis (ALS) and Parkinson's disease (PD)].

Methods

A bidirectional Mendelian randomization (MR) study was performed to investigate the causal effects by using 3 main methods (Variance Weighted (IVW), Weighted Median (WM), and MR-Egger regression) in the European population. The data of 11 antioxidant biomarkers were obtained from the open database by the most up-to-date Genome-Wide Association Studies (GWAS), the summary statistics of PD and ALS were obtained from the International Parkinson's Disease Genomics Consortium (IPDGC) (33,674 cases, and 449,056 controls), and the International Amyotrophic Lateral Sclerosis Genomics Consortium (IALSC) (20,806 cases and 59,804 controls), respectively. For AD, we specifically used two recently published GWAS data, one from the International Genomics of Alzheimer's Project (IGAP) (21,982 cases and 41,944 controls), and the other from a large meta-analysis (71,880 cases and 383,378 controls) as validation data.

Results

Based on the Bonferroni correction p < 0.0015, there was no significant causal evidence for the antioxidant biomarkers on neurodegenerative diseases, however, the reverse analysis found that AD was significantly related to the decrease in retinol (IVW: beta = -0.023, p = 0.0007; WM: beta = -0.025, p = 0.0121), while the same analysis was carried out between the AD validation database and retinol, the results were consistent (IVW: beta = -0.064, p = 0.025). Moreover, AD on Glutathione S-transferase (GST), PD on Glutathione Peroxidase (GPX) as well as PD on uric acid (UA) also indicated potential causal-and-effect associations (IVW: p = 0.025; p = 0.027; p = 0.021, respectively).

Conclusions

There was no sufficient evidence that antioxidant imbalance has a significant causal effect on neurodegenerative diseases. However, this study revealed that genetically predicted AD was significantly related to the decrease in retinol, which provides a new insight into previous research and indicates the possibility to regard retinol as potential biomarker for the diagnosis and progress of AD.

Dysregulated expression and distribution of Kif5α in neurites of wobbler motor neurons

Impaired axonal transport has been observed in patients with amyotrophic lateral sclerosis (ALS) and in animal models, suggesting that transport proteins likely play a critical role in the pathological mechanism of ALS. Dysregulation of Kinesin-family-member 5α (Kif5α), a neuron-specific isoform of heavy chain kinesin family, has been described in several neurological disorders, in humans and animal models, including ALS. In this study, we determined Kif5α expression by gene sequencing, quantitative reverse transcription-polymerase chain reaction, and western blot assay in the cervical spinal cord of wobbler mice and immunofluorescence staining in dissociated cultures of the ventral horn. Further, we observed the distribution of Kif5α and mitochondria along motor neuronal branches by confocal imaging. Our results showed that Kif5α expression was greatly dysregulated in wobbler mice, which resulted in altered distribution of Kif5α along motor neuronal branches with an abnormal mitochondrial distribution. Thus, our results indicate that dysregulation of Kif5 and therefore abnormal transport in motor neuronal branches in this ALS model could be causative for several pathological findings at the cellular level, like misallocation of cytoskeletal proteins or organelles like mitochondria.

Boosting Mitochondrial Potential: An Imperative Therapeutic Intervention in Amyotrophic Lateral Sclerosis

BACKGROUND

Amyotrophic Lateral Sclerosis (ALS) is a progressive and terminal neurodegenerative disorder. Mitochondrial dysfunction, imbalance of cellular bioenergetics, electron chain transportation and calcium homeostasis are deeply associated with the progression of this disease. Impaired mitochondrial functions are crucial in rapid neurodegeneration. The mitochondria of ALS patients are associated with deregulated Ca2+ homeostasis and elevated levels of reactive oxygen species (ROS), leading to oxidative stress. Overload of mitochondrial calcium and ROS production leads to glutamatereceptor mediated neurotoxicity. This implies mitochondria are an attractive therapeutic target.

OBJECTIVE

The aim of this review is to brief the latest developments in the understanding of mitochondrial pathogenesis in ALS and emphasize the restorative capacity of therapeutic candidates.

RESULTS

In ALS, mitochondrial dysfunction is a well-known phenomenon. Various therapies targeted towards mitochondrial dysfunction aim at decreasing ROS generation, increasing mitochondrial biogenesis, and inhibiting apoptotic pathways. Some of the therapies briefed in this review may be categorized as synthetic, natural compounds, genetic materials, and cellular therapies.

CONCLUSION

The overarching goals of mitochondrial therapies in ALS are to benefit ALS patients by slowing down the disease progression and prolonging overall survival. Despite various therapeutic approaches, there are many hurdles in the development of a successful therapy due to the multifaceted nature of mitochondrial dysfunction and ALS progression. Intensive research is required to precisely elucidate the molecular pathways involved in the progression of mitochondrial dysfunctions that ultimately lead to ALS. Because of the multifactorial nature of ALS, a combination therapy approach may hold the key to cure and treat ALS in the future.

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.

Exercise and mitochondrial remodeling to prevent age-related neurodegeneration

Healthy brain activity requires precise ion and energy management creating a strong reliance on mitochondrial function. Age-related neurodegeneration leads to a decline in mitochondrial function and increased oxidative stress, with associated declines in mitochondrial mass, respiration capacity, and respiration efficiency. The interdependent processes of mitochondrial protein turnover and mitochondrial dynamics, known together as mitochondrial remodeling, play essential roles in mitochondrial health and therefore brain function. This mini-review describes the role of mitochondria in neurodegeneration and brain health, current practices for assessing both aspects of mitochondrial remodeling, and how exercise mitigates the adverse effects of aging in the brain. Exercise training elicits functional adaptations to improve brain health, and current literature strongly suggests that mitochondrial remodeling plays a vital role in these positive adaptations. Despite substantial implications that the two aspects of mitochondrial remodeling are interdependent, very few investigations have simultaneously measured mitochondrial dynamics and protein synthesis. An improved understanding of the partnership between mitochondrial protein turnover and mitochondrial dynamics will provide a better understanding of their role in both brain health and disease, as well as how they induce protection following exercise.

Drug discovery and amyotrophic lateral sclerosis: Emerging challenges and therapeutic opportunities

Amyotrophic lateral sclerosis (ALS) is characterized by the degeneration of upper and lower motor neurons (MNs) leading to paralysis and, ultimately, death by respiratory failure 3-5 years after diagnosis. Edaravone and Riluzole, the only drugs currently approved for ALS treatment, only provide mild symptomatic relief to patients. Extraordinary progress in understanding the biology of ALS provided new grounds for drug discovery. Over the last two decades, mitochondria and oxidative stress (OS), iron metabolism and ferroptosis, and the major regulators of hypoxia and inflammation - HIF and NF-κB - emerged as promising targets for ALS therapeutic intervention. In this review, we focused our attention on these targets to outline and discuss current advances in ALS drug development. Based on the challenges and the roadblocks, we believe that the rational design of multi-target ligands able to modulate the complex network of events behind the disease can provide effective therapies in a foreseeable future.

Mechanisms Underlying Neurodegenerative Disorders and Potential Neuroprotective Activity of Agrifood By-Products

Neurodegenerative diseases, characterized by progressive loss in selected areas of the nervous system, are becoming increasingly prevalent worldwide due to an aging population. Despite their diverse clinical manifestations, neurodegenerative diseases are multifactorial disorders with standard features and mechanisms such as abnormal protein aggregation, mitochondrial dysfunction, oxidative stress and inflammation. As there are no effective treatments to counteract neurodegenerative diseases, increasing interest has been directed to the potential neuroprotective activities of plant-derived compounds found abundantly in food and in agrifood by-products. Food waste has an extremely negative impact on the environment, and recycling is needed to promote their disposal and overcome this problem. Many studies have been carried out to develop green and effective strategies to extract bioactive compounds from food by-products, such as peel, leaves, seeds, bran, kernel, pomace, and oil cake, and to investigate their biological activity. In this review, we focused on the potential neuroprotective activity of agrifood wastes obtained by common products widely produced and consumed in Italy, such as grapes, coffee, tomatoes, olives, chestnuts, onions, apples, and pomegranates.