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Synaptic activity imposes large energy demands that are met by local adenosine triphosphate (ATP) synthesis through glycolysis and mitochondrial oxidative phosphorylation. ATP drives action potentials, supports synapse assembly and remodelling, and fuels synaptic vesicle filling and recycling, thus sustaining synaptic transmission. Given their polarized morphological features - including long axons and extensive branching in their terminal regions - neurons face exceptional challenges in maintaining presynaptic energy homeostasis, particularly during intensive synaptic activity. Recent studies have started to uncover the mechanisms and signalling pathways involved in activity-dependent and energy-sensitive regulation of presynaptic energetics, or 'synaptoenergetics'. These conceptual advances have established the energetic regulation of synaptic efficacy and plasticity as an exciting research field that is relevant to a range of neurological disorders associated with bioenergetic failure and synaptic dysfunction.
Assuntos
Metabolismo Energético/fisiologia , Receptores Pré-Sinápticos/metabolismo , Transmissão Sináptica/fisiologia , Trifosfato de Adenosina/metabolismo , Animais , Glicólise , Humanos , Vesículas SinápticasRESUMO
Spinal bulbar muscular atrophy (SBMA), the first identified CAG-repeat expansion disorder, is an X-linked neuromuscular disorder involving CAG-repeat-expansion mutations in the androgen receptor (AR) gene. We utilized CRISPR-Cas9 gene editing to engineer novel isogenic human induced pluripotent stem cell (hiPSC) models, consisting of isogenic AR knockout, control and disease lines expressing mutant AR with distinct repeat lengths, as well as control and disease lines expressing FLAG-tagged wild-type and mutant AR, respectively. Adapting a small-molecule cocktail-directed approach, we differentiate the isogenic hiPSC models into motor neuron-like cells with a highly enriched population to uncover cell-type-specific mechanisms underlying SBMA and to distinguish gain- from loss-of-function properties of mutant AR in disease motor neurons. We demonstrate that ligand-free mutant AR causes drastic mitochondrial dysfunction in neurites of differentiated disease motor neurons due to gain-of-function mechanisms and such cytotoxicity can be amplified upon ligand (androgens) treatment. We further show that aberrant interaction between ligand-free, mitochondria-localized mutant AR and F-ATP synthase is associated with compromised mitochondrial respiration and multiple other mitochondrial impairments. These findings counter the established notion that androgens are requisite for mutant AR-induced cytotoxicity in SBMA, reveal a compelling mechanistic link between ligand-free mutant AR, F-ATP synthase and mitochondrial dysfunction, and provide innovative insights into motor neuron-specific therapeutic interventions for SBMA.
Assuntos
Células-Tronco Pluripotentes Induzidas , Atrofia Muscular Espinal , Humanos , Receptores Androgênicos/genética , Receptores Androgênicos/metabolismo , Células-Tronco Pluripotentes Induzidas/metabolismo , Atrofia Muscular Espinal/genética , Atrofia Muscular Espinal/metabolismo , Atrofia Muscular , Mitocôndrias/metabolismo , Trifosfato de Adenosina/metabolismoRESUMO
The mitochondrial anchor syntaphilin (SNPH) is a key mitochondrial protein normally expressed in axons to maintain neuronal health by positioning mitochondria along axons for metabolic needs. However, in 2019 we discovered a novel form of excitotoxicity that results when SNPH is misplaced into neuronal dendrites in disease models. A key unanswered question about this SNPH excitotoxicity is the pathologic molecules that trigger misplacement or intrusion of SNPH into dendrites. Here, we identified two different classes of pathologic molecules that interact to trigger dendritic SNPH intrusion. Using primary hippocampal neuronal cultures from mice of either sex, we demonstrated that the pro-inflammatory cytokine IL-1ß interacts with NMDA to trigger SNPH intrusion into dendrites. First, IL-1ß and NMDA each individually triggers dendritic SNPH intrusion. Second, IL-1ß and NMDA do not act independently but interact. Thus, blocking NMDAR by the antagonist MK-801 blocks IL-1ß from triggering dendritic SNPH intrusion. Further, de-coupling the known interaction between IL-1ß and NMDAR by tyrosine inhibitors prevents either IL-1ß or NMDA from triggering dendritic SNPH intrusion. Third, neuronal toxicity caused by IL-1ß or NMDA are strongly ameliorated in SNPH-/- neurons. Taken together, we hypothesize that the known bipartite IL-1ß/NMDAR crosstalk converges to trigger misplacement of SNPH in dendrites as a final common pathway to cause neurodegeneration. Targeting dendritic SNPH in this novel tripartite IL-1ß/NMDAR/SNPH interaction could be a strategic downstream locus for ameliorating neurotoxicity in inflammatory diseases.SIGNIFICANCE STATEMENTThe mitochondrial anchor Syntaphilin (SNPH) is a key mitochondrial protein normally expressed specifically in healthy axons to help position mitochondria along axons to match metabolic needs. In 2019, we discovered that misplacement of SNPH into neuronal dendrites causes a novel form of excitotoxicity in rodent models of multiple sclerosis. A key unanswered question about this new form of dendritic SNPH toxicity concerns pathologic molecules that trigger toxic misplacement of SNPH into dendrites. Here we identified two major categories of pathologic molecules, the pro-inflammatory cytokines and NMDA, that interact and converge to trigger toxic misplacement of SNPH into dendrites. We propose that dendritic mitochondrial anchor provides a novel, single common target for ameliorating diverse inflammatory and excitatory injuries in neurodegenerative diseases.
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The formation and maintenance of synapses require long-distance delivery of newly synthesized synaptic proteins from the soma to distal synapses, raising the fundamental question of whether impaired transport is associated with neurodevelopmental disorders such as autism. We previously revealed that syntabulin acts as a motor adapter linking kinesin-1 motor and presynaptic cargos. Here, we report that defects in syntabulin-mediated transport and thus reduced formation and maturation of synapses are one of core synaptic mechanisms underlying autism-like synaptic dysfunction and social behavioral abnormalities. Syntabulin expression in the mouse brain peaks during the first 2 weeks of postnatal development and progressively declines during brain maturation. Neurons from conditional syntabulin-/- mice (stb cKO) display impaired transport of presynaptic cargos, reduced synapse density and active zones, and altered synaptic transmission and long-term plasticity. Intriguingly, stb cKO mice exhibit core autism-like traits, including defective social recognition and communication, increased stereotypic behavior, and impaired spatial learning and memory. These phenotypes establish a new mechanistic link between reduced transport of synaptic cargos and impaired maintenance of synaptic transmission and plasticity, contributing to autism-associated behavioral abnormalities. This notion is further confirmed by the human missense variant STB-R178Q, which is found in an autism patient and loses its adapter capacity for binding kinesin-1 motors. Expressing STB-R178Q fails to rescue reduced synapse formation and impaired synaptic transmission and plasticity in stb cKO neurons. Altogether, our study suggests that defects in syntabulin-mediated transport mechanisms underlie the synaptic dysfunction and behavioral abnormalities that bear similarities to autism.
Assuntos
Transtorno Autístico , Animais , Transtorno Autístico/genética , Células Cultivadas , Humanos , Camundongos , Neurônios , Sinapses , Transmissão SinápticaRESUMO
Recycling synaptic vesicles (SVs) transit through early endosomal sorting stations, which raises a fundamental question: are SVs sorted toward endolysosomal pathways? Here, we used snapin mutants as tools to assess how endolysosomal sorting and trafficking impact presynaptic activity in wild-type and snapin(-/-) neurons. Snapin acts as a dynein adaptor that mediates the retrograde transport of late endosomes (LEs) and interacts with dysbindin, a subunit of the endosomal sorting complex BLOC-1. Expressing dynein-binding defective snapin mutants induced SV accumulation at presynaptic terminals, mimicking the snapin(-/-) phenotype. Conversely, over-expressing snapin reduced SV pool size by enhancing SV trafficking to the endolysosomal pathway. Using a SV-targeted Ca(2+) sensor, we demonstrate that snapin-dysbindin interaction regulates SV positional priming through BLOC-1/AP-3-dependent sorting. Our study reveals a bipartite regulation of presynaptic activity by endolysosomal trafficking and sorting: LE transport regulates SV pool size, and BLOC-1/AP-3-dependent sorting fine-tunes the Ca(2+) sensitivity of SV release. Therefore, our study provides new mechanistic insights into the maintenance and regulation of SV pool size and synchronized SV fusion through snapin-mediated LE trafficking and endosomal sorting.
Assuntos
Lisossomos/metabolismo , Modelos Neurológicos , Neurônios/fisiologia , Transmissão Sináptica/fisiologia , Vesículas Sinápticas/metabolismo , Proteínas de Transporte Vesicular/metabolismo , Animais , Transporte Biológico/fisiologia , Western Blotting , Cálcio/metabolismo , Fracionamento Celular , Células Cultivadas , Dicroísmo Circular , Disbindina , Proteínas Associadas à Distrofina , Imuno-Histoquímica , Camundongos , Microscopia Eletrônica , Imagem com Lapso de Tempo , Proteínas de Transporte Vesicular/genéticaRESUMO
The unique polarization and high-energy demand of neurons necessitates specialized mechanisms to maintain energy homeostasis throughout the cell, particularly in the distal axon. Mitochondria play a key role in meeting axonal energy demand by generating adenosine triphosphate through oxidative phosphorylation. Recent evidence demonstrates how axonal mitochondrial trafficking and anchoring are coordinated to sense and respond to altered energy requirements. If and when these mechanisms are impacted in pathological conditions, such as injury and neurodegenerative disease, is an emerging research frontier. Recent evidence also suggests that axonal energy demand may be supplemented by local glial cells, including astrocytes and oligodendrocytes. In this review, we provide an updated discussion of how oxidative phosphorylation, aerobic glycolysis, and oligodendrocyte-derived metabolic support contribute to the maintenance of axonal energy homeostasis.
Assuntos
Axônios/metabolismo , Encéfalo/metabolismo , Metabolismo Energético/fisiologia , Doenças Neurodegenerativas/metabolismo , Animais , Astrócitos/metabolismo , Astrócitos/patologia , Axônios/patologia , Encéfalo/patologia , Homeostase/fisiologia , Humanos , Mitocôndrias/metabolismo , Mitocôndrias/patologia , Doenças Neurodegenerativas/patologia , Oligodendroglia/metabolismo , Oligodendroglia/patologia , Transporte Proteico/fisiologiaRESUMO
Aging is associated with cognitive decline and increasing risk of neurodegeneration. Perturbation of mitochondrial function, dynamics, and trafficking are implicated in the pathogenesis of several age-associated neurodegenerative diseases. Despite this fundamental importance, the critical understanding of how organismal aging affects lifetime neuronal mitochondrial maintenance remains unknown, particularly in a physiologically relevant context. To address this issue, we performed a comprehensive in vivo analysis of age-associated changes in mitochondrial morphology, density, trafficking, and stress resistance in individual Caenorhabditis elegans neurons throughout adult life. Adult neurons display three distinct stages of increase, maintenance, and decrease in mitochondrial size and density during adulthood. Mitochondrial trafficking in the distal neuronal processes declines progressively with age starting from early adulthood. In contrast, long-lived daf-2 mutants exhibit delayed age-associated changes in mitochondrial morphology, constant mitochondrial density, and maintained trafficking rates during adulthood. Reduced mitochondrial load at late adulthood correlates with decreased mitochondrial resistance to oxidative stress. Revealing aging-associated changes in neuronal mitochondria in vivo is an essential precedent that will allow future elucidation of the mechanistic causes of mitochondrial aging. Thus, our study establishes the critical foundation for the future analysis of cellular pathways and genetic and pharmacological factors regulating mitochondrial maintenance in aging- and disease-relevant conditions. SIGNIFICANCE STATEMENT: Using Caenorhabditis elegans as a model, we address long-standing questions: How does aging affect neuronal mitochondrial morphology, density, trafficking, and oxidative stress resistance? Are these age-related changes amenable to genetic manipulations that slow down the aging process? Our study illustrates that mitochondrial trafficking declines progressively from the first day of adulthood, whereas mitochondrial size, density, and resistance to oxidative stress undergo three distinct stages: increase in early adulthood, maintenance at high levels during mid-adulthood, and decline during late adulthood. Thus, our study characterizes mitochondrial aging profile at the level of a single neuron in its native environment and establishes the critical foundation for the future genetic and pharmacological dissection of factors that influence long-term mitochondrial maintenance in neurons.
Assuntos
Envelhecimento/fisiologia , Proteínas de Caenorhabditis elegans/metabolismo , Mitocôndrias/metabolismo , Neurônios/metabolismo , Neurônios/ultraestrutura , Aceleração , Fatores Etários , Análise de Variância , Animais , Animais Geneticamente Modificados , Caenorhabditis elegans , Proteínas de Caenorhabditis elegans/genética , Proteínas de Fluorescência Verde , Peróxido de Hidrogênio/farmacologia , Microscopia Eletrônica , Proteínas Mitocondriais/genética , Proteínas Mitocondriais/metabolismo , Estresse Oxidativo/fisiologia , Interferência de RNA/fisiologiaRESUMO
Mitochondria have a number of essential roles in neuronal function. Their complex mobility patterns within neurons are characterized by frequent changes in direction. Mobile mitochondria can become stationary or pause in regions that have a high metabolic demand and can move again rapidly in response to physiological changes. Defects in mitochondrial transport are implicated in the pathogenesis of several major neurological disorders. Research into the mechanisms that regulate mitochondrial transport is thus an important emerging frontier.
Assuntos
Homeostase/fisiologia , Mitocôndrias/fisiologia , Doenças Neurodegenerativas/patologia , Neurônios/patologia , Neurônios/ultraestrutura , Sinapses/fisiologia , Animais , Transporte Biológico/fisiologia , Cálcio/metabolismo , Humanos , Modelos Neurológicos , Doenças Neurodegenerativas/etiologia , Sinapses/patologiaRESUMO
Axonal degeneration is a primary cause of permanent neurological disability in individuals with the CNS demyelinating disease multiple sclerosis. Dysfunction of axonal mitochondria and imbalanced energy demand and supply are implicated in degeneration of chronically demyelinated axons. The purpose of this study was to define the roles of mitochondrial volume and distribution in axonal degeneration following acute CNS demyelination. We show that the axonal mitochondrial volume increase following acute demyelination of WT CNS axons does not occur in demyelinated axons deficient in syntaphilin, an axonal molecule that immobilizes stationary mitochondria to microtubules. These findings were supported by time-lapse imaging of WT and syntaphilin-deficient axons in vitro. When demyelinated, axons deficient in syntaphilin degenerate at a significantly greater rate than WT axons, and this degeneration can be rescued by reducing axonal electrical activity with the Na(+) channel blocker flecainide. These results support the concept that syntaphilin-mediated immobilization of mitochondria to microtubules is required for the volume increase of axonal mitochondria following acute demyelination and protects against axonal degeneration in the CNS.
Assuntos
Axônios , Mitocôndrias/metabolismo , Esclerose Múltipla/metabolismo , Bainha de Mielina/metabolismo , Proteínas do Tecido Nervoso/fisiologia , Proteínas de Transporte Vesicular/fisiologia , Feminino , Humanos , Proteínas de Membrana , Esclerose Múltipla/genética , Imagem com Lapso de TempoRESUMO
The demyelinating disease multiple sclerosis (MS) has an early inflammatory phase followed by an incurable progressive phase with subdued inflammation and poorly understood neurodegenerative mechanism. In this study, we identified various parallelisms between progressive MS and the dysmyelinating mouse model Shiverer and then genetically deleted a major neuron-specific mitochondrial anchoring protein Syntaphilin (SNPH) from the mouse. Prevailing evidence suggests that deletion of SNPH is harmful in demyelination. Surprisingly, SNPH deletion produces striking benefits in the Shiverer by prolonging survival, reducing cerebellar damage, suppressing oxidative stress, and improving mitochondrial health. In contrast, SNPH deletion does not benefit clinical symptoms in experimental autoimmune encephalomyelitis (EAE), a model for early-phase MS. We propose that deleting mitochondrial anchoring is a novel, specific treatment for progressive MS.
Assuntos
Modelos Animais de Doenças , Proteínas Associadas aos Microtúbulos/deficiência , Proteínas Associadas aos Microtúbulos/genética , Mitocôndrias/metabolismo , Esclerose Múltipla Crônica Progressiva/genética , Animais , Cerebelo/patologia , Cerebelo/ultraestrutura , Encefalomielite Autoimune Experimental/genética , Substância Cinzenta/patologia , Proteínas de Membrana , Camundongos , Camundongos Endogâmicos , Camundongos Knockout , Proteínas Associadas aos Microtúbulos/metabolismo , Mitocôndrias/genética , Esclerose Múltipla Crônica Progressiva/terapia , Proteínas do Tecido Nervoso , Estresse Oxidativo/genética , Análise de Sobrevida , Substância Branca/patologiaRESUMO
Mitochondria are cellular power plants that supply ATP to power various biological activities essential for neuronal growth, survival, and function. Due to unique morphological features, neurons face exceptional challenges to maintain ATP and Ca(2+) homeostasis. Neurons require specialized mechanisms distributing mitochondria to distal areas where energy and Ca(2+) buffering are in high demand, such as synapses and axonal branches. These distal compartments also undergo development- and activity-dependent remodeling, thereby altering mitochondrial trafficking and distribution. Mitochondria move bi-directionally, pause briefly, and move again, frequently changing direction. In mature neurons, only one-third of axonal mitochondria are motile. Stationary mitochondria serve as local energy sources and buffer intracellular Ca(2+). The balance between motile and stationary mitochondria responds quickly to changes in axonal and synaptic physiology. Furthermore, neurons are postmitotic cells surviving for the lifetime of the organism; thus, mitochondria need to be removed when they become aged or dysfunction. Mitochondria also alter their motility under stress conditions or when their integrity is impaired. Therefore, regulation of mitochondrial transport is essential to meet altered metabolic requirements and to remove aged and damaged mitochondria or replenish healthy ones to distal terminals. Defects in mitochondrial transport and altered distribution are implicated in the pathogenesis of several major neurological disorders. Thus, research into the mechanisms regulating mitochondrial motility is an important emerging frontier in neurobiology. This short review provides an updated overview on motor-adaptor machineries that drive and regulate mitochondrial transport and docking receptors that anchor axonal mitochondria in response to the changes in synaptic activity, metabolic requirement, and altered mitochondrial integrity. The review focuses on microtubule (MT)-based mitochondrial trafficking and anchoring. Additional insight from different perspectives can be found in other in-depth reviews.
Assuntos
Mitocôndrias/metabolismo , Neurônios/metabolismo , Animais , Transporte Biológico , Humanos , Proteínas Motores Moleculares/metabolismo , Transdução de SinaisRESUMO
Autophagy is a highly regulated membrane remodeling process that allows the lysosome-mediated degradation of cytoplasmic entities by sequestrating them in double-membrane autophagosomes. Autophagy is hence highly intertwined with the endocytic trafficking pathway, sharing similar molecular machinery. Atg14L, also known as Beclin 1-associated autophagy-related key regulator (Barkor), directly interacts with Beclin 1 through its coiled-coil domain and enhances phosphatidylinositol 3-phosphate kinase class III (PI3KC3) activity to induce autophagosome membrane nucleation, highlighting its essential role in the early stage of mammalian autophagy. Here, we report a novel function of Atg14L in the endocytic trafficking pathway wherein Atg14L binds to and colocalizes with the fusogenic SNARE effector protein Snapin to facilitate endosome maturation. Atg14L specifically binds to Snapin and this interaction effectively facilitates endosomal maturation without affecting autophagic cargo degradation. Consequently, atg14l knockdown significantly delayed the late stage of endocytic trafficking, as evidenced by the retarded kinetics of internalized surface receptor degradation. This phenotype was effectively complemented by wild-type Atg14L or Beclin 1-binding mutant, but not by its Snapin-binding mutant. Taken together, our study demonstrates that Atg14L functions as a multivalent trafficking effector that regulates endosome maturation as well as autophagosome formation, reflecting the complexity of the crosstalk between autophagic and endocytic vesicle trafficking in higher eukaryotes.
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Proteínas Adaptadoras de Transporte Vesicular , Proteínas Reguladoras de Apoptose , Endocitose/genética , Proteínas de Membrana , Proteínas de Transporte Vesicular , Proteínas Adaptadoras de Transporte Vesicular/genética , Proteínas Adaptadoras de Transporte Vesicular/metabolismo , Animais , Proteínas Reguladoras de Apoptose/genética , Proteínas Reguladoras de Apoptose/metabolismo , Autofagia/genética , Proteínas Relacionadas à Autofagia , Proteína Beclina-1 , Classe III de Fosfatidilinositol 3-Quinases/metabolismo , Endossomos/genética , Endossomos/metabolismo , Fibroblastos/citologia , Fibroblastos/metabolismo , Células HEK293 , Células HeLa , Humanos , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Camundongos , Fagossomos/metabolismo , Ligação Proteica , Transporte Proteico , Proteínas SNARE/genética , Proteínas SNARE/metabolismo , Proteínas de Transporte Vesicular/genética , Proteínas de Transporte Vesicular/metabolismoRESUMO
Disruption of synapse assembly and maturation leads to a broad spectrum of neurodevelopmental disorders. Presynaptic proteins are largely synthesized in the soma, where they are packaged into precursor vesicles and transported into distal axons to ensure precise assembly and maintenance of presynapses. Due to their morphological features, neurons face challenges in the delivery of presynaptic cargos to nascent boutons. Thus, targeted axonal transport is vital to build functional synapses. A growing number of mutations in genes encoding the transport machinery have been linked to neurodevelopmental disorders. Emerging lines of evidence have started to uncover presynaptic mechanisms underlying axonal transport defects, thus broadening the view of neurodevelopmental disorders beyond postsynaptic mechanisms. In this review, we discuss presynaptic perspectives of neurodevelopmental disorders by focusing on impaired axonal transport and disturbed assembly and maintenance of presynapses. We also discuss potential strategies for restoring axonal transport as an early therapeutic intervention.
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Transporte Axonal , Transtornos do Neurodesenvolvimento , Terminações Pré-Sinápticas , Humanos , Axônios , Corpo Celular , Mutação , Transtornos do Neurodesenvolvimento/genéticaRESUMO
The unique morphology and functionality of central nervous system (CNS) neurons necessitate specialized mechanisms to maintain energy metabolism throughout long axons and extensive terminals. Oligodendrocytes (OLs) enwrap CNS axons with myelin sheaths in a multilamellar fashion. Apart from their well-established function in action potential propagation, OLs also provide intercellular metabolic support to axons by transferring energy metabolites and delivering exosomes consisting of proteins, lipids, and RNAs. OL-derived metabolic support is crucial for the maintenance of axonal integrity; its dysfunction has emerged as an important player in neurological disorders that are associated with axonal energy deficits and degeneration. In this review, we discuss recent advances in how these transcellular signaling pathways maintain axonal energy metabolism in health and neurological disorders.
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Axônios , Oligodendroglia , Axônios/fisiologia , Bainha de Mielina/metabolismo , Sistema Nervoso Central/fisiologia , Metabolismo Energético/fisiologiaRESUMO
Reduced axonal mitochondrial transport has been observed in major neurodegenerative diseases, including fALS patients and SOD1(G93A) mice. However, it is unclear whether this defect plays a critical role in axonal degeneration or simply reflects sequelae of general transport alteration. Using genetic mouse models combined with time-lapse imaging of live neurons, we previously discovered that axon-targeted syntaphilin (SNPH) acts as a docking receptor specific for axonal mitochondria. Deletion of the snph gene in mice results in a substantially higher proportion of axonal mitochondria in the mobile state without any effect on the transport of other axonal organelles. Here we address whether increased (rescued) axonal mitochondrial mobility changes the disease course by crossing fALS-linked transgenic SOD1(G93A) and snph(-/-) knock-out mice. We found that a 2-fold increase in axonal mitochondrial mobility in SOD1(G93A)/snph(-/-) mice did not affect the onset of ALS-like symptoms. Both SOD1(G93A) and SOD1(G93A)/snph(-/-) mice exhibit similar weight loss, deterioration in motor function and motor neuron loss, significant gliosis, and a lifespan of 152-154 days. Thus, for the first time, our study provides genetic and pathological evidence that the impairment of mitochondrial transport seen in SOD1(G93A) mice plays a minimal role in the rapid-onset of fALS-linked pathology.
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Esclerose Lateral Amiotrófica , Modelos Animais de Doenças , Superóxido Dismutase , Esclerose Lateral Amiotrófica/genética , Esclerose Lateral Amiotrófica/metabolismo , Esclerose Lateral Amiotrófica/patologia , Animais , Axônios , Cruzamentos Genéticos , Deleção de Genes , Proteínas de Membrana , Camundongos , Camundongos Knockout , Camundongos Mutantes , Proteínas Associadas aos Microtúbulos , Mitocôndrias , Mutação de Sentido Incorreto , Proteínas do Tecido Nervoso , Superóxido Dismutase-1RESUMO
Central nervous system (CNS) neurons typically fail to regenerate their axons after injury leading to neurological impairment. Axonal regeneration is a highly energy-demanding cellular program that requires local mitochondria to supply most energy within injured axons. Recent emerging lines of evidence have started to reveal that injury-triggered acute mitochondrial damage and local energy crisis contribute to the intrinsic energetic restriction that accounts for axon regeneration failure in the CNS. Characterizing and reprogramming bioenergetic signaling and mitochondrial maintenance after axon injury-ischemia is fundamental for developing therapeutic strategies that can restore local energy metabolism and thus facilitate axon regeneration. Therefore, establishing reliable and reproducible neuronal model platforms is critical for assessing axonal energetic metabolism and regeneration capacity after injury-ischemia. In this focused methodology article, we discuss recent advances in applying cutting-edge microfluidic chamber devices in combination with state-of-the-art live-neuron imaging tools to monitor axonal regeneration, mitochondrial transport, bioenergetic metabolism, and local protein synthesis in response to injury-ischemic stress in mature CNS neurons.
RESUMO
Mitochondria generate ATP essential for neuronal growth, function, and regeneration. Due to their polarized structures, neurons face exceptional challenges to deliver mitochondria to and maintain energy homeostasis throughout long axons and terminal branches where energy is in high demand. Chronic mitochondrial dysfunction accompanied by bioenergetic failure is a pathological hallmark of major neurodegenerative diseases. Brain injury triggers acute mitochondrial damage and a local energy crisis that accelerates neuron death. Thus, mitochondrial maintenance defects and axonal energy deficits emerge as central problems in neurodegenerative disorders and brain injury. Recent studies have started to uncover the intrinsic mechanisms that neurons adopt to maintain (or reprogram) axonal mitochondrial density and integrity, and their bioenergetic capacity, upon sensing energy stress. In this review, we discuss recent advances in how neurons maintain a healthy pool of axonal mitochondria, as well as potential therapeutic strategies that target bioenergetic restoration to power neuronal survival, function, and regeneration.
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Lesões Encefálicas , Doenças Neurodegenerativas , Axônios/metabolismo , Lesões Encefálicas/metabolismo , Metabolismo Energético , Humanos , Mitocôndrias/metabolismo , Doenças Neurodegenerativas/metabolismo , RegeneraçãoRESUMO
Lysosomes serve as degradation hubs for the turnover of endocytic and autophagic cargos, which is essential for neuron function and survival. Deficits in lysosome function result in progressive neurodegeneration in most lysosomal storage disorders and contribute to the pathogenesis of aging-related neurodegenerative diseases. Given their size and highly polarized morphology, neurons face exceptional challenges in maintaining cellular homeostasis in regions far removed from the cell body where mature lysosomes are enriched. Neurons therefore require coordinated bidirectional intracellular transport to sustain efficient clearance capacity in distal axonal regions. Emerging lines of evidence have started to uncover mechanisms and signaling pathways regulating endolysosome transport and maturation to maintain axonal homeostasis, or "axonostasis," that is relevant to a range of neurologic disorders. In this review, we discuss recent advances in how axonal endolysosomal trafficking, distribution, and lysosomal functionality support neuronal health and become disrupted in several neurodegenerative diseases.
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Axônios/metabolismo , Endossomos/metabolismo , Lisossomos/metabolismo , Animais , Autofagia , Transporte Biológico , Humanos , Doenças Neurodegenerativas/metabolismo , Doenças Neurodegenerativas/patologiaRESUMO
Different types of cargo vesicles containing presynaptic proteins are transported from the nerve cell body to the nerve terminal, and participate in the formation of active zones. However, the identity of the membranous cargoes and the nature of the motor-cargo interactions remain unsolved. Here, we report the identification of a syntaxin-1-binding protein named syntabulin. Syntabulin attaches syntaxin-containing vesicles to microtubules and migrates with syntaxin within the processes of hippocampal neurons. Knock-down of syntabulin expression with targeted small interfering RNAs (siRNAs) or interference with the syntabulin-syntaxin interaction inhibit attachment of syntaxin-cargo vesicles to microtubules and reduce syntaxin-1 distribution in neuronal processes. Furthermore, conventional kinesin I heavy chain binds to syntabulin and associates with syntabulin-linked syntaxin vesicles in vivo. These findings suggest that syntabulin functions as a linker molecule that attaches syntaxin-cargo vesicles to kinesin I, enabling the transport of syntaxin-1 to neuronal processes.
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Proteínas de Transporte/metabolismo , Proteínas de Membrana/metabolismo , Proteínas dos Microtúbulos/metabolismo , Proteínas Associadas aos Microtúbulos/metabolismo , Neurônios/metabolismo , Sequência de Aminoácidos , Animais , Transporte Biológico , Células COS , Células Cultivadas , Chlorocebus aethiops , Proteínas de Fluorescência Verde , Hipocampo/citologia , Humanos , Peptídeos e Proteínas de Sinalização Intracelular , Cinesinas/metabolismo , Proteínas Luminescentes/metabolismo , Proteínas de Membrana/química , Proteínas dos Microtúbulos/química , Proteínas Associadas aos Microtúbulos/química , Microtúbulos/química , Microtúbulos/metabolismo , Dados de Sequência Molecular , Neurônios/citologia , Ligação Proteica , Estrutura Terciária de Proteína , Proteínas Qa-SNARE , RNA Interferente Pequeno/metabolismo , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/metabolismo , Homologia de Sequência de Aminoácidos , Sintaxina 1RESUMO
Pathogenic mutations in the kinase LRRK2 have been implicated in Parkinson's disease. A new study shows that hyperactivation of this kinase reduces the processivity of autophagosomal retrograde transport in axons through an unproductive 'tug-of-war' between anterograde and retrograde motors, thus contributing to autophagy dysfunction and axonal degeneration.