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Communication within the nervous system relies on the calcium‐triggered release of neurotransmitter molecules by exocytosis of synaptic vesicles (SVs) at defined active zone release sites. While decades of research have provided detailed insight into the molecular machinery for SV fusion, much less is known about the mechanisms that form functional SVs during the development of synapses and that control local SV reformation following exocytosis in the mature nervous system. Here we review the current state of knowledge in the field, focusing on the pathways implicated in the formation and axonal transport of SV precursor organelles and the mechanisms involved in the local reformation of SVs within nerve terminals in mature neurons. We discuss open questions and outline perspectives for future research. [ABSTRACT FROM AUTHOR]

Mitochondria are dynamic bioenergetic hubs that become compromised with age. In neurons, declining mitochondrial axonal transport has been associated with reduced cellular health. However, it is still unclear to what extent the decline of mitochondrial transport and function observed during ageing are coupled, and if somal and axonal mitochondria display compartment‐specific features that make them more susceptible to the ageing process. It is also not known whether the biophysical state of the cytoplasm, thought to affect many cellular functions, changes with age to impact mitochondrial trafficking and homeostasis. Focusing on the mouse peripheral nervous system, we show that age‐dependent decline in mitochondrial trafficking is accompanied by reduction of mitochondrial membrane potential and intramitochondrial viscosity, but not calcium buffering, in both somal and axonal mitochondria. Intriguingly, we observe a specific increase in cytoplasmic viscosity in the neuronal cell body, where mitochondria are most polarised, which correlates with decreased cytoplasmic diffusiveness. Increasing cytoplasmic crowding in the somatic compartment of DRG neurons grown in microfluidic chambers reduces mitochondrial axonal trafficking, suggesting a mechanistic link between the regulation of cytoplasmic viscosity and mitochondrial dynamics. Our work provides a reference for studying the relationship between neuronal mitochondrial homeostasis and the viscoelasticity of the cytoplasm in a compartment‐dependent manner during ageing. [ABSTRACT FROM AUTHOR]

We report the first autopsy case of MM1‐type sporadic Creutzfeldt–Jakob disease (sCJD) who survived 80 months after long‐term artificial ventilatory support. The cerebral cortex and white matter exhibited severe atrophy, sparing the hippocampus. The prion protein aggregates of 10–20 μm in diameter were prominent. The structure consisted of granulofilamentous profiles. This case provides clues on how MM1‐type sCJD extends pathologically after a long clinical course. [ABSTRACT FROM AUTHOR]

Currently, there are more than 10 million patients with diabetes mellitus in Japan. Therefore, the need to explore the pathogenesis of diabetes and the complications leading to its cure is becoming increasingly urgent. Pathological examination of pancreatic tissues from patients with type 2 diabetes reveals a decrease in the volume of beta cells because of a combination of various stresses. In human type 2 diabetes, islet amyloid deposition is a unique pathological change characterized by proinflammatory macrophage (M1) infiltration into the islets. The pathological changes in the pancreas with islet amyloid were different according to clinical factors, which suggests that type 2 diabetes can be further subclassified based on islet pathology. On the other hand, diabetic peripheral neuropathy is the most frequent diabetic complication. In early diabetic peripheral neuropathy, M1 infiltration in the sciatic nerve evokes oxidative stress or attenuates retrograde axonal transport, as clearly demonstrated by in vitro live imaging. Furthermore, islet parasympathetic nerve density and beta cell volume were inversely correlated in type 2 diabetic Goto‐Kakizaki rats, suggesting that diabetic peripheral neuropathy itself may contribute to the decrease in beta cell volume. These findings suggest that the pathogenesis of diabetes mellitus and diabetic peripheral neuropathy may be interrelated. [ABSTRACT FROM AUTHOR]

Neurons are post‐mitotic cells, with microtubules playing crucial roles in axonal transport and growth. Kinesin family member 2c (KIF2C), a member of the Kinesin‐13 family, possesses the ability to depolymerize microtubules and is involved in remodelling the microtubule lattice. Myocyte enhancer factor 2c (MEF2C) was initially identified as a regulator of muscle differentiation but has recently been associated with neurological abnormalities such as severe cognitive impairment, stereotyping, epilepsy and brain malformations when mutated or deleted. However, further investigation is required to determine which target genes MEF2C acts upon to influence neuronal function as a transcription regulator. Our data demonstrate that knockdown of both Mef2c and Kif2c significantly impacts spinal motor neuron development and behaviour in zebrafish. Luciferase reporter assays and chromosome immunoprecipitation assays, along with down/upregulated expression analysis, revealed that MFE2C functions as a novel transcription regulator for the Kif2c gene. Additionally, the knockdown of either Mef2c or Kif2c expression in E18 cortical neurons substantially reduces the number of primary neurites and axonal branches during neuronal development in vitro without affecting neurite length. Finally, depletion of Kif2c eliminated the effects of overexpression of Mef2c on the neurite branching. Based on these findings, we provided novel evidence demonstrating that MEF2C regulates the transcription of the Kif2c gene thereby influencing the axonal branching. [ABSTRACT FROM AUTHOR]

The excitatory neurotransmitter glutamate has a role in neuronal migration and process elongation in the central nervous system (CNS). The effects of chronic glutamate hyperactivity on vesicular and protein transport within CNS neurons, that is, processes necessary for neurite growth, have not been examined previously. In this study, we measured the effects of lifelong hyperactivity of glutamate neurotransmission on axoplasmic transport in CNS neurons. We compared wild-type (wt) to transgenic (Tg) mice over-expressing the glutamate dehydrogenase gene Glud1 in CNS neurons and exhibiting increases in glutamate transmitter formation, release, and synaptic activation in brain throughout the lifespan. We found that Glud1 Tg as compared with wt mice exhibited increases in the rate of anterograde axoplasmic transport in neurons of the hippocampus measured in brain slices ex vivo, and in olfactory neurons measured in vivo. We also showed that the in vitro pharmacologic activation of glutamate synapses in wt mice led to moderate increases in axoplasmic transport, while exposure to selective inhibitors of ion channel forming glutamate receptors very significantly suppressed anterograde transport, suggesting a link between synaptic glutamate receptor activation and axoplasmic transport. Finally, axoplasmic transport in olfactory neurons of Tg mice in vivo was partially inhibited following 14-day intake of ethanol, a known suppressor of axoplasmic transport and of glutamate neurotransmission. The same was true for transport in hippocampal neurons in slices from Glud1 Tg mice exposed to ethanol for 2 h ex vivo. In conclusion, endogenous activity at glutamate synapses regulates and glutamate synaptic hyperactivity increases intraneuronal transport rates in CNS neurons. [ABSTRACT FROM AUTHOR]

Charcot–Marie‐Tooth type 2A (CMT2A) is an inherited sensorimotor neuropathy associated with mutations within the Mitofusin 2 (MFN2) gene. These mutations impair normal mitochondrial functioning via different mechanisms, disturbing the equilibrium between mitochondrial fusion and fission, of mitophagy and mitochondrial axonal transport. Although CMT2A disease causes a significant disability, no resolutive treatment for CMT2A patients to date. In this context, reliable experimental models are essential to precisely dissect the molecular mechanisms of disease and to devise effective therapeutic strategies. The most commonly used models are either in vitro or in vivo, and among the latter murine models are by far the most versatile and popular. Here, we critically revised the most relevant literature focused on the experimental models, providing an update on the mammalian models of CMT2A developed to date. We highlighted the different phenotypic, histopathological and molecular characteristics, and their use in translational studies for bringing potential therapies from the bench to the bedside. In addition, we discussed limitations of these models and perspectives for future improvement. [ABSTRACT FROM AUTHOR]

Background: Olfactory dysfunction is known to be an early manifestation of Alzheimer's disease (AD). However, the underlying mechanism, particularly the specific molecular events that occur during the early stages of olfactory disorders, remains unclear. Methods: In this study, we utilized transcriptomic sequencing, bioinformatics analysis, and biochemical detection to investigate the specific pathological and molecular characteristics of the olfactory bulb (OB) in 4‐month‐old male triple transgenic 3xTg‐AD mice (PS1M146V/APPSwe/TauP301L). Results: Initially, during the early stages of olfactory impairment, no significant learning and memory deficits were observed. Correspondingly, we observed significant accumulation of amyloid‐beta (Aβ) and Tau pathology specifically in the OB, but not in the hippocampus. In addition, significant axonal morphological defects were detected in the olfactory bulb, cortex, and hippocampal brain regions of 3xTg‐AD mice. Transcriptomic analysis revealed a significant increase in the expression of neuroinflammation‐related genes, accompanied by a significant decrease in neuronal activity‐related genes in the OB. Moreover, immunofluorescence and immunoblotting demonstrated an activation of glial cell biomarkers Iba1 and GFAP, along with a reduction in the expression levels of neuronal activity‐related molecules Nr4a2 and FosB, as well as olfaction‐related marker OMP. Conclusion: In sum, the early accumulation of Aβ and Tau pathology induces neuroinflammation, which subsequently leads to a decrease in neuronal activity within the OB, causing axonal transport deficits that contribute to olfactory disorders. Nr4a2 and FosB appear to be promising targets for intervention aimed at improving early olfactory impairment in AD. [ABSTRACT FROM AUTHOR]

In neurons, fast axonal transport (FAT) of vesicles occurs over long distances and requires constant and local energy supply for molecular motors in the form of adenosine triphosphate (ATP). FAT is independent of mitochondrial metabolism. Indeed, the glycolytic machinery is present on vesicles and locally produces ATP, as well as nicotinamide adenine dinucleotide bonded with hydrogen (NADH) and pyruvate, using glucose as a substrate. It remains unclear whether pyruvate is transferred to mitochondria from the vesicles as well as how NADH is recycled into NAD+ on vesicles for continuous glycolysis activity. The optimization of a glycolytic activity test for subcellular compartments allowed the evaluation of the kinetics of vesicular glycolysis in the brain. This revealed that glycolysis is more efficient on vesicles than in the cytosol. We also found that lactate dehydrogenase (LDH) enzymatic activity is required for effective vesicular ATP production. Indeed, inhibition of LDH or the forced degradation of pyruvate inhibited ATP production from axonal vesicles. We found LDHA rather than the B isoform to be enriched on axonal vesicles suggesting a preferential transformation of pyruvate to lactate and a concomitant recycling of NADH into NAD+ on vesicles. Finally, we found that LDHA inhibition dramatically reduces the FAT of both dense‐core vesicles and synaptic vesicle precursors in a reconstituted cortico‐striatal circuit on‐a‐chip. Together, this shows that aerobic glycolysis is required to supply energy for vesicular transport in neurons, similar to the Warburg effect. [ABSTRACT FROM AUTHOR]

Recent publications report that although the mitochondria population in an axon can be quickly replaced by a combination of retrograde and anterograde axonal transport (often within less than 24 hours), the axon contains much older mitochondria. This suggests that not all mitochondria that reach the soma are degraded and that some are recirculating back into the axon. To explain this, we developed a model that simulates mitochondria distribution when a portion of mitochondria that return to the soma are redirected back to the axon rather than being destroyed in somatic lysosomes. Utilizing the developed model, we studied how the percentage of returning mitochondria affects the mean age and age density distributions of mitochondria at different distances from the soma. We also investigated whether turning off the mitochondrial anchoring switch can reduce the mean age of mitochondria. For this purpose, we studied the effect of reducing the value of a parameter that characterizes the probability of mitochondria transition to the stationary (anchored) state. The reduction in mitochondria mean age observed when the anchoring probability is reduced suggests that some injured neurons may be saved if the percentage of stationary mitochondria is decreased. The replacement of possibly damaged stationary mitochondria with newly synthesized ones may restore the energy supply in an injured axon. We also performed a sensitivity study of the mean age of stationary mitochondria to the parameter that determines what portion of mitochondria re‐enter the axon and the parameter that determines the probability of mitochondria transition to the stationary state. The sensitivity of the mean age of stationary mitochondria to the mitochondria stopping probability increases linearly with the number of compartments in the axon. High stopping probability in long axons can significantly increase mitochondrial age. [ABSTRACT FROM AUTHOR]

Parkinson's disease (PD) is an age‐related chronic neurological disorder, mainly characterized by the pathological feature of α‐synuclein (α‐syn) aggregation, with the exact disease pathogenesis unclear. During the onset and progression of PD, synaptic dysfunction, including dysregulation of axonal transport, impaired exocytosis, and endocytosis are identified as crucial events of PD pathogenesis. It has been reported that over‐expression of α‐syn impairs clathrin‐mediated endocytosis (CME) in the synapses. However, the underlying mechanisms still needs to be explored. In this study, we investigated the molecular events underlying the synaptic dysfunction caused by over‐expression of wild‐type human α‐syn and its mutant form, involving series of proteins participating in CME. We found that excessive human α‐syn causes impaired fission and uncoating of clathrin‐coated vesicles during synaptic vesicle recycling, leading to reduced clustering of synaptic vesicles near the active zone and increased size of plasma membrane and number of endocytic intermediates. Furthermore, over‐expressed human α‐syn induced changes of CME‐associated proteins, among which synaptojanin1 (SYNJ1) showed significant reduction in various brain regions. Over‐expression of SYNJ1 in primary hippocampal neurons from α‐syn transgenic mice recovered the synaptic vesicle density, clustering and endocytosis. Using fluorescence‐conjugated transferrin, we demonstrated that SYNJ1 re‐boosted the CME activity by restoring the phosphatidylinositol‐4,5‐bisphosphate homeostasis. Our data suggested that over‐expression of α‐syn disrupts synaptic function through interfering with vesicle recycling, which could be alleviated by re‐availing of SYNJ1. Our study unrevealed a molecular mechanism of the synaptic dysfunction in PD pathogenesis and provided a potential therapeutic target for treating PD. [ABSTRACT FROM AUTHOR]

The etiology of Tauopathies, a diverse class of neurodegenerative diseases associated with the Microtubule Associated Protein (MAP) Tau, is usually described by a common mechanism in which Tau dysfunction results in the loss of axonal microtubule stability. Here, we reexamine and build upon the canonical disease model to encompass other Tau functions. In addition to regulating microtubule dynamics, Tau acts as a modulator of motor proteins, a signaling hub, and a scaffolding protein. This diverse array of functions is related to the dynamic nature of Tau isoform expression, post‐translational modification (PTM), and conformational flexibility. Thus, there is no single mechanism that can describe Tau dysfunction. The effects of specific pathogenic mutations or aberrant PTMs need to be examined on all of the various functions of Tau in order to understand the unique etiology of each disease state. [ABSTRACT FROM AUTHOR]

Dynein is a microtubule‐dependent motor protein required for cell division, retrograde intracellular transport, and intraflagellar transport (IFT). Dynein 1 and dynein 2 serve as molecular motors in the cytoplasm and cilia, respectively. Each dynein consists of multiple subunits. Although the components of dynein 1 and dynein 2 are different and specific in most species, a previous study has suggested that dynein intermediate chain subunit DYCI‐1 is shared by both dynein 1 and 2 in Caenorhabditis elegans (C. elegans). Here, we show that C. elegans has two dynein intermediate chains—DYCI‐1 and WDR‐60—and their functions are different. Mutational analysis showed that dyci‐1 is essential for the retrograde axonal transport of synaptic vesicles. In the same mutant allele, IFT is not affected at all. Instead, wdr‐60 is essential for IFT. Thus, we suggest that dynein 1 and dynein 2 have specific intermediate chains in C. elegans as in other organisms. [ABSTRACT FROM AUTHOR]

We report a computational study of mitochondria transport in a branched axon with two branches of different sizes. For comparison, we also investigate mitochondria transport in an axon with symmetric branches and in a straight (unbranched) axon. The interest in understanding mitochondria transport in branched axons is motivated by the large size of arbors of dopaminergic neurons, which die in Parkinson's disease. Since the failure of energy supply of multiple demand sites located in various axonal branches may be a possible reason for the death of these neurons, we were interested in investigating how branching affects mitochondria transport. Besides investigating mitochondria fluxes between the demand sites and mitochondria concentrations, we also studied how the mean age of mitochondria and mitochondria age densities depend on the distance from the soma. We established that if the axon splits into two branches of unequal length, the mean ages of mitochondria and age density distributions in the demand sites are affected by how the mitochondria flux splits at the branching junction (what portion of mitochondria enter the shorter branch and what portion enter the longer branch). However, if the axon splits into two branches of equal length, the mean ages and age densities of mitochondria are independent of how the mitochondria flux splits at the branching junction. This even holds for the case when all mitochondria enter one branch, which is equivalent to a straight axon. Because the mitochondrial membrane potential (which many researchers view as a proxy for mitochondrial health) decreases with mitochondria age, the independence of mitochondria age on whether the axon is symmetrically branched or straight (providing the two axons are of the same length), and on how the mitochondria flux splits at the branching junction, may explain how dopaminergic neurons can sustain very large arbors and still maintain mitochondrial health across branch extremities. [ABSTRACT FROM AUTHOR]

Neurological disorders are prevalent in horses, but their study is challenging due to anatomic constraints and the large body size; very few host‐specific in vitro models have been established to study these types of diseases, particularly from adult donor tissue. Here we report the generation of primary neuronal dorsal root ganglia (DRG) cultures from adult horses: the mixed, dissociated cultures, containing neurons and glial cells, remained viable for at least 90 days. Similar to DRG neurons in vivo, cultured neurons varied in size, and they developed long neurites. The mitochondrial movement was detected in cultured cells and was significantly slower in glial cells compared to DRG‐derived neurons. In addition, mitochondria were more elongated in glial cells than those in neurons. Our culture model will be a useful tool to study the contribution of axonal transport defects to specific neurodegenerative diseases in horses as well as comparative studies aimed at evaluating species‐specific differences in axonal transport and survival. [ABSTRACT FROM AUTHOR]

Analysis of rodent muscles affords an opportunity to glean key insights into neuromuscular development and the detrimental impact of disease‐causing genetic mutations. Muscles of the distal leg, for instance the gastrocnemius and tibialis anterior, are commonly used in such studies with mice and rats. However, thin and flat muscles, which can be dissected, processed and imaged without major disruption to muscle fibres and nerve‐muscle contacts, are more suitable for accurate and detailed analyses of the peripheral motor nervous system. One such wholemount muscle is the predominantly fast twitch epitrochleoanconeus (ETA), which is located in the upper forelimb, innervated by the radial nerve, and contains relatively large and uniformly flat neuromuscular junctions (NMJs). To facilitate incorporation of the ETA into the experimental toolkit of the neuromuscular disease field, here, we describe a simple method for its rapid isolation (<5 min), supported by high‐resolution videos and step‐by‐step images. Furthermore, we outline how the ETA can be imaged in live, anaesthetised mice, to enable examination of dynamic cellular processes occurring at the NMJ and within intramuscular axons, including transport of organelles, such as mitochondria and signalling endosomes. Finally, we present reference data on wild‐type ETA fibre‐type composition in young adult, male C57BL6/J mice. Comparative neuroanatomical studies of different muscles in rodent models of disease can generate critical insights into pathogenesis and pathology; dissection of the wholemount ETA provides the possibility to diversify the repertoire of muscles analysed for this endeavour. [ABSTRACT FROM AUTHOR]

The article "The role of micrometastasis in high‐risk skin cancers" discusses the possibility of skin cancer metastasis through the nervous system. While previous research has focused on metastasis through blood vessels and lymph vessels, this article suggests that axonal transport, a bidirectional process in nerve cells, may also play a role in the spread of skin cancer. The article explores the mechanisms of axonal transport and its potential implications for the metastasis of neuroectodermal tumors. It also discusses the involvement of the nervous system in the spread of tumor-promoting factors and the potential impact on treatment outcomes. The findings suggest that metastasis via the nervous system may be a significant factor in skin cancer metastasis, regardless of the presence of micrometastasis. The article concludes by noting that this form of metastasis may not be limited to skin cancer and could potentially explain metastasis to the skin in other types of cancer. [Extracted from the article]

The proteasome is essential for cellular responses to various physiological stressors. However, how proteasome function impacts the stress resilience of regenerative damaged motor neurons remains unclear. Here, we develop a unique mouse model using a regulatory element of the activating transcription factor (Atf3) gene to label mitochondria in a damage‐induced manner while simultaneously genetically disrupting the proteasome. Using this model, we observed that in injury‐induced proteasome‐deficient mouse motor neurons, the increase of mitochondrial influx from soma into axons is inhibited because neurons fail to disassemble ankyrin G, an organizer of the axon initial segment (AIS), in a proteasome‐dependent manner. Further, these motor neurons exhibit amyotrophic lateral sclerosis (ALS)‐like degeneration despite having regenerative potential. Selectively vulnerable motor neurons in SOD1G93A ALS mice, which induce ATF3 in response to pathological damage, also fail to disrupt the AIS, limiting the number of axonal mitochondria at a pre‐symptomatic stage. Thus, damage‐induced proteasome‐sensitive AIS disassembly could be a critical post‐translational response for damaged motor neurons to temporarily transit to an immature state and meet energy demands for axon regeneration or preservation. Synopsis: How the proteasome impacts stress resilience of damaged motor neurons remains unclear. Using unique genetically engineered mice, the proteasome is observed to temporarily dismantle the barrier against mitochondrial axonal entry upon injury to meet energy demands for axon regeneration. Mouse models are developed wherein genetic disruption of the proteosome and mitochondrial labeling co‐occur in response to damage.Motor neurons temporarily dismantle the axon initial segment (AIS) in a proteasome‐dependent manner following injury, permitting increased mitochondrial influx into axons to satisfy the energy demand to drive axon regeneration.Injury‐induced proteasome‐deficient motor neurons in mice fail to dismantle the AIS, which restricts the increase of mitochondria and results in ALS‐like degeneration. [ABSTRACT FROM AUTHOR]

Localization of mRNA facilitates spatiotemporally controlled protein expression in neurons. In axons, mRNA transport followed by local protein synthesis plays a critical role in axonal growth and guidance. However, it is not yet clearly understood how mRNA is transported to axonal subcellular sites and what regulates axonal mRNA localization. Using a transgenic mouse model in which endogenous β‐actin mRNA is fluorescently labeled, we investigated β‐actin mRNA movement in axons of hippocampal neurons. We cultured neurons in microfluidic devices to separate axons from dendrites and performed single‐particle tracking of axonal β‐actin mRNA. Compared with dendritic β‐actin mRNA, axonal β‐actin mRNA showed less directed motion and exhibited mostly subdiffusive motion, especially near filopodia and boutons in mature dissociated hippocampal neurons. We found that axonal β‐actin mRNA was likely to colocalize with actin patches (APs), regions that have a high density of filamentous actin (F‐actin) and are known to have a role in branch initiation. Moreover, simultaneous imaging of F‐actin and axonal β‐actin mRNA in live neurons revealed that moving β‐actin mRNA tended to be docked in the APs. Our findings reveal that axonal β‐actin mRNA localization is facilitated by actin networks and suggest that localized β‐actin mRNA plays a potential role in axon branch formation. [ABSTRACT FROM AUTHOR]

A GGGGCC (G4C2) repeat expansion in the C9orf72 gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Although disruptions in axonal transport are implicated in the pathogenesis of multiple neurodegenerative diseases, the underlying mechanisms causing these defects remain unclear. Here, we performed live imaging of Drosophila motor neurons expressing expanded G4C2 repeats in third‐instar larvae and investigated the axonal transport of multiple organelles in vivo. Expression of expanded G4C2 repeats causes an increase in static axonal lysosomes, while it impairs trafficking of late endosomes (LEs) and dense core vesicles (DCVs). Surprisingly, however, axonal transport of mitochondria is unaffected in motor axons expressing expanded G4C2 repeats. Thus, our data indicate that expanded G4C2 repeat expression differentially impacts axonal transport of vesicular organelles and mitochondria in Drosophila models of C9orf72‐associated ALS/FTD. Synopsis: Axonal transport is an indispensable cellular process responsible for movement of cargos along the axon in order to maintain the long‐distance communication between soma and synapses. For decades, it has been reported that axonal transport defects are observed in motor neuron diseases, including ALS. In this study, we report that Drosophila motor neurons expressing expanded GGGGCC repeats to model C9orf72‐associated ALS show specific disruptions in organelle transport for endo‐lysosomes and dense core vesicles, but not for mitochondria. [ABSTRACT FROM AUTHOR]

Microtubules are dynamic cytoskeletal filaments composed of alpha‐ (α) and beta (β)‐tubulin proteins. α‐tubulin proteins are posttranslationally acetylated, and loss of acetylation is associated with axonal transport defects, a common alteration contributing to the pathomechanisms of several neurodegenerative diseases. Restoring α‐tubulin acetylation by pharmacological inhibition of HDAC6, a primary α‐tubulin deacetylase, can rescue impaired transport. Therefore, HDAC6 is considered a promising therapeutic target for neurodegenerative diseases, but currently, there is no clinically approved inhibitor for this purpose. In this study, using drug repurposing strategy, we aimed to identify compounds possessing HDAC6 inhibition activity and inducing α‐tubulin acetylation. We systematically analyzed the FDA‐approved library by utilizing virtual screening and consensus scoring approaches. Inhibition activities of promising compounds were tested using in vitro assays. Motor neuron‐like NSC34 cells were treated with the candidate compounds, and α‐tubulin acetylation levels were determined by Western blot. Our results demonstrated that rutin, a natural flavonoid, inhibits cellular HDAC6 activity without inducing any toxicity, and it significantly increases α‐tubulin acetylation level in motor neuron‐like cells. [ABSTRACT FROM AUTHOR]

Objective: The objective of this study is to develop a novel method for monitoring the integrity of motor neurons in vivo by quantifying net retrograde axonal transport. Methods: The method uses single photon emission computed tomography to quantify retrograde transport to spinal cord of tetanus toxin fragment C (125I‐TTC) following intramuscular injection. We characterized the transport profiles in 3 transgenic mouse models carrying amyotrophic lateral sclerosis (ALS)‐associated genes, aging mice, and SOD1G93A transgenic mice following CRISPR/Cas9 gene editing. Lastly, we studied the effect of prior immunization of tetanus toxoid on the transport profile of TTC. Results: This technique defines a quantitative profile of net retrograde axonal transport of TTC in living mice. The profile is distinctly abnormal in transgenic SOD1G93A mice as young as 65 days (presymptomatic) and worsens with disease progression. Moreover, this method detects a distinct therapeutic benefit of gene editing in transgenic SOD1G93A mice well before other clinical parameters (eg, grip strength) show improvement. Symptomatic transgenic PFN1C71G/C71G ALS mice display gross reductions in net retrograde axonal transport, which is also disturbed in asymptomatic mice harboring a human C9ORF72 transgene with an expanded GGGGCC repeat motif. In wild‐type mice, net retrograde axonal transport declines with aging. Lastly, prior immunization with tetanus toxoid does not preclude use of this assay. Interpretation: This assay of net retrograde axonal transport has broad potential clinical applications and should be particularly valuable as a physiological biomarker that permits early detection of benefit from potential therapies for motor neuron diseases. ANN NEUROL 2022;91:716–729 [ABSTRACT FROM AUTHOR]

Dystonia, neurodegeneration, axonal transport, dynactin, optic neuropathy Keywords: dystonia; dynactin; neurodegeneration; axonal transport; optic neuropathy EN dystonia dynactin neurodegeneration axonal transport optic neuropathy 535 539 5 05/13/22 20220501 NES 220501 Axonal transport is essential to provide nutrients to axons and nerve terminals and to clear up misfolded proteins to avoid the accumulation of toxic aggregates. [Extracted from the article]

Mitochondria and intermediate filament (IF) accumulations often occur during imbalanced axonal transport leading to various types of neurological diseases. It is still poorly understood whether a link between neuronal IFs and mitochondrial mobility exist. In Caenorhabditis elegans, among the 11 cytoplasmic IF family proteins, IFB‐1 is of particular interest as it is expressed in a subset of sensory neurons. Depletion of IFB‐1 leads to mild dye‐filling and significant chemotaxis defects as well as reduced life span. Sensory neuron development is affected and mitochondrial transport is slowed down leading to reduced densities of these organelles. Mitochondria tend to cluster in neurons of IFB‐1 mutants likely independent of the fission and fusion machinery. Oxygen consumption and mitochondrial membrane potential is measurably reduced in worms carrying mutations in the ifb‐1 gene. Membrane potential also seems to play a role in transport such as carbonyl cyanide p‐(trifluoromethoxy)phenylhydrazone treatment led to increased directional switching of mitochondria. Mitochondria co‐localize with IFB‐1 in worm neurons and appear in a complex with IFB‐1 in pull‐down assays. In summary, we propose a model in which neuronal IFs may serve as critical (transient) anchor points for mitochondria during their long‐range transport in neurons for steady and balanced transport. [ABSTRACT FROM AUTHOR]

The Kinesin superfamily proteins (KIFs) are major molecular motors that transport diverse set of cargoes along microtubules to both the axon and dendrite of a neuron. Much of our knowledge about kinesin function is obtained from studies on axonal transport. Emerging evidence reveals how specific kinesin motor proteins carry cargoes to dendrites, including proteins, mRNAs and organelles that are crucial for synapse development and plasticity. In this review, we will summarize the major kinesin motors and their associated cargoes that have been characterized to regulate postsynaptic function in neuron. We will also discuss how specific kinesins are selectively involved in the development of excitatory and inhibitory postsynaptic compartments, their regulation by post‐translational modifications (PTM), as well as their roles beyond conventional transport carrier. [ABSTRACT FROM AUTHOR]

Background: Mesenchymal stem cells' (MSC) therapeutic potential has been investigated for the treatment of several neurodegenerative diseases. The fact these cells can mediate a beneficial effect in different neurodegenerative contexts strengthens their competence to target diverse mechanisms. On the other hand, distinct disorders may share similar mechanisms despite having singular neuropathological characteristics. Methods: We have previously shown that MSC can be beneficial for two disorders, one belonging to the groups of Lysosomal Storage Disorders (LSDs) – the Krabbe Disease or Globoid Cell Leukodystrophy, and the other to the family of Polyglutamine diseases (PolyQs) – the Machado‐Joseph Disease or Spinocerebellar ataxia type 3. We gave also input into disease characterization since neuropathology and MSC's effects are intrinsically associated. This review aims at describing MSC's multimode of action in these disorders while emphasizing to possible mechanistic alterations they must share due to the accumulation of cellular toxic products. Results: Lysosomal storage disorders and PolyQs have different aetiology and associated symptoms, but both result from the accumulation of undegradable products inside neuronal cells due to inefficient clearance by the endosomal/lysosomal pathway. Moreover, numerous cellular mechanisms that become compromised latter are also shared by these two disease groups. Conclusions: Here, we emphasize MSC's effect in improving proteostasis and autophagy cycling turnover, neuronal survival, synaptic activity and axonal transport. LSDs and PolyQs, though rare in their predominance, collectively affect many people and require our utmost dedication and efforts to get successful therapies due to their tremendous impact on patient s' lives and society. [ABSTRACT FROM AUTHOR]

The mechanochemical coupling of ATPase hydrolysis and conformational dynamics in kinesin motors facilitates intramolecular interaction cycles between the kinesin motor and neck domains, which are essential for microtubule‐based motility. Here, we characterized a charge‐inverting KIF1A‐E239K mutant that we identified in a family with axonal‐type Charcot‐Marie‐Tooth disease and also in 24 cases in human neuropathies including spastic paraplegia and hereditary sensory and autonomic neuropathy. We show that Glu239 in the β7 strand is a key residue of the motor domain that regulates the motor‐neck interaction. Expression of the KIF1A‐E239K mutation has decreased ability to complement Kif1a+/– neurons, and significantly decreases ATPase activity and microtubule gliding velocity. X‐ray crystallography shows that this mutation causes an excess positive charge on β7, which may electrostatically interact with a negative charge on the neck. Quantitative mass spectrometric analysis supports that the mutation hyper‐stabilizes the motor‐neck interaction at the late ATP hydrolysis stage. Thus, the negative charge of Glu239 dynamically regulates the kinesin motor‐neck interaction, promoting release of the neck from the motor domain upon ATP hydrolysis. Synopsis: KIF1A‐mediated axonal transport is driven by interaction cycles between the kinesin's motor and neck domains. Characterization of a KIF1A mutant identified in a family with Charcot‐Marie‐Tooth disease reveals that dynamic dissociation of the motor‐neck interaction via the β7 domain is essential for neuronal function. A familial charge‐inverting KIF1A‐E239K variant is associated with axonal‐type Charcot‐Marie‐Tooth disease and other cases of human neuropathies.KIF1A‐E239K exhibits impaired ability to complement Kif1a+/– neurons.Mutant KIF1A shows significantly reduced velocity and ATPase activity.Excess positive charge on the β7 strand caused by E239K mutation electrostatically interacts with a negative charge on the neck.E239K mutation hyper‐stabilizes motor‐neck interaction in a late ATP hydrolysis state, leading to a delay in the ATPase cycle. [ABSTRACT FROM AUTHOR]

Charcot‐Marie‐Tooth disease type 2D (CMT2D), is a hereditary peripheral neuropathy caused by mutations in the gene encoding glycyl‐tRNA synthetase (GARS1). Here, human induced pluripotent stem cell (hiPSC)‐based models of CMT2D bearing mutations in GARS1 and their use for the identification of predictive biomarkers amenable to therapeutic efficacy screening is described. Cultures containing spinal cord motor neurons generated from this line exhibit network activity marked by significant deficiencies in spontaneous action potential firing and burst fire behavior. This result matches clinical data collected from a patient bearing a GARS1P724H mutation and is coupled with significant decreases in acetylated α‐tubulin levels and mitochondrial movement within axons. Treatment with histone deacetylase 6 inhibitors, tubastatin A and CKD504, improves mitochondrial movement and α‐tubulin acetylation in these cells. Furthermore, CKD504 treatment enhances population‐level electrophysiological activity, highlighting its potential as an effective treatment for CMT2D. [ABSTRACT FROM AUTHOR]

Injury to long axonal projections is a central pathological feature at the early phase of intracerebral hemorrhage (ICH). It has been reported to contribute to persistent functional disability following ICH. However, the molecular mechanisms that drive axonal degeneration remain unclear. Autologous blood was injected into the striatum to mimic the pathology of ICH. Observed significant swollen axons with characteristic retraction bulbs were found around the striatal hematoma at 24 h after ICH. Electronic microscopic examination revealed highly disorganized microtubule and swollen mitochondria in the retraction bulbs. MEC17 is a specific α‐tubulin acetyltransferase, ablation of acetylated α‐tubulin in MEC17−/− mice aggravated axonal injury, axonal transport mitochondria dysfunction, and motor dysfunction. In contrast, treatment with tubastatin A (TubA), which promotes microtubule acetylation, significantly alleviated axonal injury and protected the integrity of the corticospinal tract and fine motor function after ICH. Moreover, results showed that 41% mitochondria were preferentially bundled to the acetylated α‐tubulin in identifiable axons and dendrites in primary neurons. This impaired axonal transport of mitochondria in primary neurons of MEC17−/− mice. Given that opening of mitochondrial permeability transition pore (mPTP) induces mitochondrial dysfunction and impairs ATP supply thereby promoting axonal injury, we enhanced the availability of acetylated α‐tubulin using TubA and inhibited mPTP opening with cyclosporin A. The results indicated that this combined treatment synergistically protected corticospinal tract integrity and promoted fine motor control recovery. These findings reveal key intracellular mechanisms that drive axonal degeneration after ICH and highlight the need to target multiple factors and respective regulatory mechanisms as an effective approach to prevent axonal degeneration and motor dysfunction after ICH. [ABSTRACT FROM AUTHOR]

Recent experimental observations have shown evidence of an unexpected sudden drop‐off in the dense core vesicles (DCVs) content at the ends of certain types of axon endings. This article seeks to determine whether these observations may be explained without modifying the parameters characterizing the ability of distal en passant boutons to capture and accumulate DCVs. We developed a mathematical model that is based on the conservation of captured and transiting DCVs in boutons. The model consists of 77 ordinary differential equations and is solved using a standard Matlab solver. We hypothesize that the drop in DCV content in distal boutons is due to an insufficient supply of anterogradely moving DCVs coming from the soma. As anterogradely moving DCVs are captured (and eventually destroyed) in more proximal boutons on their way to the end of the terminal, the fluxes of anterogradely moving DCVs between the boutons become increasingly smaller, and the most distal boutons are left without DCVs. We tested this hypothesis by modifying the flux of DCVs entering the terminal and found that the number of most distal boutons left unfilled increases if the DCV flux entering the terminal is decreased. The number of anterogradely moving DCVs in the axon can be increased either by the release of a portion of captured DCVs into the anterograde component or by an increase of the anterograde DCV flux into the terminal. This increase could lead to having enough anterogradely moving DCVs such that they could reach the most distal bouton and then turn around by changing molecular motors that propel them. The model suggests that this could result in an increased concentration of resident DCVs in distal boutons beginning with bouton 2 (the most distal is bouton 1). This is because in distal boutons, DCVs have a larger chance to be captured from the transiting state as they pass the boutons moving anterogradely and then again as they pass the same boutons moving retrogradely. [ABSTRACT FROM AUTHOR]

Nucleolin is a multifunctional RNA Binding Protein (RBP) with diverse subcellular localizations, including the nucleolus in all eukaryotic cells, the plasma membrane in tumor cells, and the axon in neurons. Here we show that the glycine arginine rich (GAR) domain of nucleolin drives subcellular localization via protein‐protein interactions with a kinesin light chain. In addition, GAR sequences mediate plasma membrane interactions of nucleolin. Both these modalities are in addition to the already reported involvement of the GAR domain in liquid‐liquid phase separation in the nucleolus. Nucleolin transport to axons requires the GAR domain, and heterozygous GAR deletion mice reveal reduced axonal localization of nucleolin cargo mRNAs and enhanced sensory neuron growth. Thus, the GAR domain governs axonal transport of a growth controlling RNA‐RBP complex in neurons, and is a versatile localization determinant for different subcellular compartments. Localization determination by GAR domains may explain why GAR mutants in diverse RBPs are associated with neurodegenerative disease. SYNOPSIS: Nucleolin is a multifunctional RNA Binding Protein with diverse subcellular localizations. Here we show that the glycine arginine rich (GAR) domain drives localization of nucleolin via direct interaction with a kinesin light chain and plasma membrane association of arginine rich sequences. Nucleolin GAR domain binds a kinesin light chain, directly linking nucleolin‐mRNA complexes to kinesin motors for axonal transport.Heterozygous nucleolin GAR deletion neurons reveal deficits in axonal localization of nucleolin cargo mRNAs.Heterozygous nucleolin GAR deletion neurons reveal increased axonal outgrowth.The GAR domain is also required for membrane targeting of nucleolin. [ABSTRACT FROM AUTHOR]

Tubulin polyglutamylation is a post‐translational modification of the microtubule cytoskeleton, which is generated by a variety of enzymes with different specificities. The "tubulin code" hypothesis predicts that modifications generated by specific enzymes selectively control microtubule functions. Our recent finding that excessive accumulation of polyglutamylation in neurons causes their degeneration and perturbs axonal transport provides an opportunity for testing this hypothesis. By developing novel mouse models and a new glutamylation‐specific antibody, we demonstrate here that the glutamylases TTLL1 and TTLL7 generate unique and distinct glutamylation patterns on neuronal microtubules. We find that under physiological conditions, TTLL1 polyglutamylates α‐tubulin, while TTLL7 modifies β‐tubulin. TTLL1, but not TTLL7, catalyses the excessive hyperglutamylation found in mice lacking the deglutamylase CCP1. Consequently, deletion of TTLL1, but not of TTLL7, prevents degeneration of Purkinje cells and of myelinated axons in peripheral nerves in these mice. Moreover, loss of TTLL1 leads to increased mitochondria motility in neurons, while loss of TTLL7 has no such effect. By revealing how specific patterns of tubulin glutamylation, generated by distinct enzymes, translate into specific physiological and pathological readouts, we demonstrate the relevance of the tubulin code for homeostasis. SYNOPSIS: Polyglutamylation is a posttranslational modification of tubulin that is highly enriched in neurons. Here we demonstrate that two neuronal polyglutamylases, TTLL1 and TTLL7, have distinct enzymatic activities, which generate unique patterns of polyglutamylation in vivo. We find that TTLL1, but not TTLL7 affects mitochondria transport and neuronal survival, in both central and peripheral nervous system. TTLL1 polyglutamylates α‐tubulin, while TTLL7 modifies β‐tubulin in vivo.In the absence of the deglutamylase CCP1, excessive polyglutamylation leading to neurodegeneration is generated by TTLL1, but not by TTLL7.Degeneration of neurons in both, central and peripheral nervous system, can be avoided by inactivating TTLL1, but not TTLL7.Polyglutamylation generated by TTLL1, but not by TTLL7 affects mitochondria mobility in axons of hippocampal neurons. [ABSTRACT FROM AUTHOR]

Amyotrophic lateral sclerosis (ALS) is a fatal non‐cell‐autonomous neurodegenerative disease characterized by the loss of motor neurons (MNs). Mutations in CRMP4 are associated with ALS in patients, and elevated levels of CRMP4 are suggested to affect MN health in the SOD1G93A‐ALS mouse model. However, the mechanism by which CRMP4 mediates toxicity in ALS MNs is poorly understood. Here, by using tissue from human patients with sporadic ALS, MNs derived from C9orf72‐mutant patients, and the SOD1G93A‐ALS mouse model, we demonstrate that subcellular changes in CRMP4 levels promote MN loss in ALS. First, we show that while expression of CRMP4 protein is increased in cell bodies of ALS‐affected MN, CRMP4 levels are decreased in the distal axons. Cellular mislocalization of CRMP4 is caused by increased interaction with the retrograde motor protein, dynein, which mediates CRMP4 transport from distal axons to the soma and thereby promotes MN loss. Blocking the CRMP4‐dynein interaction reduces MN loss in human‐derived MNs (C9orf72) and in ALS model mice. Thus, we demonstrate a novel CRMP4‐dependent retrograde death signal that underlies MN loss in ALS. Synopsis: Identification of an intracellular mechanism that mediates motor neuron (MN) death in Amyotrophic Lateral Sclerosis (ALS). CRMP4 binds the motor protein dynein and transports from distal axons to the soma where it promotes MN death. Blocking the CRMP4‐dynein interaction reduces MN death in human‐derived MNs (C9orf72) and in ALS mice. CRMP4 protein level is altered along ALS diseased motor unit.Dynein mediates CRMP4 mislocalization in motor neurons via specific CRMP4 motif.CRMP4‐dynein complexes are enhanced in ALS diseased MNs.CRMP4‐dynein complex formation facilitates selective neuronal loss in ALS. [ABSTRACT FROM AUTHOR]

The noncoding RNA 7SK is a critical regulator of transcription by adjusting the activity of the kinase complex P‐TEFb. Release of P‐TEFb from 7SK stimulates transcription at many genes by promoting productive elongation. Conversely, P‐TEFb sequestration by 7SK inhibits transcription. Recent studies have shown that 7SK functions are particularly important for neuron development and maintenance and it can thus be hypothesized that 7SK is at the center of many signaling pathways contributing to neuron function. 7SK activates neuronal gene expression programs that are key for terminal differentiation of neurons. Proteomics studies revealed a complex protein interactome of 7SK that includes several RNA‐binding proteins. Some of these novel 7SK subcomplexes exert non‐canonical cytosolic functions in neurons by regulating axonal mRNA transport and fine‐tuning spliceosome production in response to transcription alterations. Thus, a picture emerges according to which 7SK acts as a multi‐functional RNA scaffold that is integral for neuron homeostasis. [ABSTRACT FROM AUTHOR]

TDP‐43 is the major component of pathological inclusions in most ALS patients and in up to 50% of patients with frontotemporal dementia (FTD). Heterozygous missense mutations in TARDBP, the gene encoding TDP‐43, are one of the common causes of familial ALS. In this study, we investigate TDP‐43 protein behavior in induced pluripotent stem cell (iPSC)‐derived motor neurons from three ALS patients with different TARDBP mutations, three healthy controls and an isogenic control. TARDPB mutations induce several TDP‐43 changes in spinal motor neurons, including cytoplasmic mislocalization and accumulation of insoluble TDP‐43, C‐terminal fragments, and phospho‐TDP‐43. By generating iPSC lines with allele‐specific tagging of TDP‐43, we find that mutant TDP‐43 initiates the observed disease phenotypes and has an altered interactome as indicated by mass spectrometry. Our findings also indicate that TDP‐43 proteinopathy results in a defect in mitochondrial transport. Lastly, we show that pharmacological inhibition of histone deacetylase 6 (HDAC6) restores the observed TDP‐43 pathologies and the axonal mitochondrial motility, suggesting that HDAC6 inhibition may be an interesting therapeutic target for neurodegenerative disorders linked to TDP‐43 pathology. SYNOPSIS: Mutant TDP‐43 iPSC‐derived motor neurons recapitulate ALS‐related phenotypes. The use of allele‐specific tagged cell lines allowed us to directly link TDP‐43 pathology with axonal transport defects in patient iPSC‐derived motor neurons. We found that both the pathological hallmarks and axonal transport defects can be rescued by genetic correction of the mutation using CRISPR/Cas9 or by treatment with a selective HDAC6 inhibitor. Mutant TARDPB iPSC‐derived spinal motor neurons recapitulate TDP‐43‐related ALS phenotypes.Allele‐specific endogenous tagging of TDP‐43 shows that mutant TDP‐43 initiates the observed disease phenotypes and has an altered interactome.Observed TDP‐43 proteinopathy results in a defect in mitochondrial transport.Pharmacological inhibition of HDAC6 restores the observed TDP‐43 pathologies and the axonal mitochondrial motility. [ABSTRACT FROM AUTHOR]

Amyotrophic lateral sclerosis (ALS) is an adult disease causing a progressive loss of upper and lower motoneurons, muscle paralysis and early death. ALS has a poor prognosis of 3–5 years after diagnosis with no effective cure. The aetiopathogenic mechanisms involved include glutamate excitotoxicity, oxidative stress, protein misfolding, mitochondrial alterations, disrupted axonal transport and inflammation. Sigma non‐opioid intracellular receptor 1 (sigma 1 receptor) is a protein expressed in motoneurons, mainly found in the endoplasmic reticulum (ER) on the mitochondria‐associated ER membrane (MAM) or in close contact with cholinergic postsynaptic sites. MAMs are sites that allow the assembly of several complexes implicated in essential survival cell functions. The sigma 1 receptor modulates essential mechanisms for motoneuron survival including excitotoxicity, calcium homeostasis, ER stress and mitochondrial dysfunction. This review updates sigma 1 receptor mechanisms and its alterations in ALS, focusing on MAM modulation, which may constitute a novel target for therapeutic strategies. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.6/issuetoc [ABSTRACT FROM AUTHOR]

Aims: Plectin, a universally expressed multi‐functional cytolinker protein, is crucial for intermediate filament networking, including crosstalk with actomyosin and microtubules. In addition to its involvement in a number of diseases affecting skin, skeletal muscle, heart, and other stress‐exposed tissues, indications for a neuropathological role of plectin have emerged. Having identified P1c as the major isoform expressed in neural tissues in previous studies, our aim for the present work was to investigate whether, and by which mechanism(s), the targeted deletion of this isoform affects neuritogenesis and proper nerve cell functioning. Methods: For ex vivo phenotyping, we used dorsal root ganglion and hippocampal neurons derived from isoform P1c‐deficient and plectin‐null mice, complemented by in vitro experiments using purified proteins and cell fractions. To assess the physiological significance of the phenotypic alterations observed in P1c‐deficient neurons, P1c‐deficient and wild‐type littermate mice were subjected to standard behavioural tests. Results: We demonstrate that P1c affects axonal microtubule dynamics by isoform‐specific interaction with tubulin. P1c deficiency in neurons leads to altered dynamics of microtubules and excessive association with tau protein, affecting neuritogenesis, neurite branching, growth cone morphology, and translocation and directionality of movement of vesicles and mitochondria. On the organismal level, we found P1c deficiency manifesting as impaired pain sensitivity, diminished learning capabilities and reduced long‐term memory of mice. Conclusions: Revealing a regulatory role of plectin scaffolds in microtubule‐dependent nerve cell functions, our results have potential implications for cytoskeleton‐related neuropathies. [ABSTRACT FROM AUTHOR]

SLC2A3 encodes the predominantly neuronal glucose transporter 3 (GLUT3), which facilitates diffusion of glucose across plasma membranes. The human brain depends on a steady glucose supply for ATP generation, which consequently fuels critical biochemical processes, such as axonal transport and neurotransmitter release. Besides its role in the central nervous system, GLUT3 is also expressed in nonneural organs, such as the heart and white blood cells, where it is equally involved in energy metabolism. In cancer cells, GLUT3 overexpression contributes to the Warburg effect by answering the cell's increased glycolytic demands. The SLC2A3 gene locus at chromosome 12p13.31 is unstable and prone to non‐allelic homologous recombination events, generating multiple copy number variants (CNVs) of SLC2A3 which account for alterations in SLC2A3 expression. Recent associations of SLC2A3 CNVs with different clinical phenotypes warrant investigation of the potential influence of these structural variants on pathomechanisms of neuropsychiatric, cardiovascular, and immune diseases. In this review, we accumulate and discuss the evidence how SLC2A3 gene dosage may exert diverse protective or detrimental effects depending on the pathological condition. Cellular states which lead to increased energetic demand, such as organ development, proliferation, and cellular degeneration, appear particularly susceptible to alterations in SLC2A3 copy number. We conclude that better understanding of the impact of SLC2A3 variation on disease etiology may potentially provide novel therapeutic approaches specifically targeting this GLUT. [ABSTRACT FROM AUTHOR]

Piper laetispicum C. DC is one of the Chinese herbal medicines used for alleviating depressive disorders. G11‐5 [3‐(3, 4‐methylenedioxy‐5‐trifluoromethyl phenyl)‐2E‐propenoic acid isobutyl amide] is synthesized based on the chemical structure of an active integrant of Piper laetispicum C. DC. The present study assessed the antidepressant effect of G11‐5 and investigated the underlying mechanism with learned helplessness (LH) and social defeat stress (SDS) mice model of depression. In the LH model, mice were exposed to 60 inescapable electric shocks once a day for three consecutive days followed by 2‐week drug administration and helpless behaviour assessment. In the SDS model, mice were subjected to repeated social defeat by an aggressive CD‐1 mouse once a day for consecutive 10 days. Following oral administration for 2 weeks, the mice were subjected to a series of behavioural tests including social interaction test. G11‐5 significantly decreased the number of escape failures induced by LH paradigm, meanwhile increased the social interaction ratio and shortened the immobility time in forced swimming test for the SDS‐exposed mice, suggesting remarkable antidepressant effect. Moreover, G11‐5 ameliorated the changes in mitophagy‐related proteins induced by two stress exposures and restored retrograde axonal transport and neurotransmitter release. Our findings suggested that G11‐5 exhibited an obvious antidepressant through TSPO‐mediated mitophagy pathway. [ABSTRACT FROM AUTHOR]

One of the characteristic features of different classes of neurons that is vital for their proper functioning within neuronal networks is the shape of their dendritic arbors. To properly develop dendritic trees, neurons need to accurately control the intracellular transport of various cellular cargo (e.g., mRNA, proteins, and organelles). Microtubules and motor proteins (e.g., dynein and kinesins) that move along microtubule tracks play an essential role in cargo sorting and transport to the most distal ends of neurons. Equally important are motor adaptors, which may affect motor activity and specify cargo that is transported by the motor. Such transport undergoes very dynamic fine‐tuning in response to changes in the extracellular environment and synaptic transmission. Such regulation is achieved by the phosphorylation of motors, motor adaptors, and cargo, among other mechanisms. This review focuses on the contribution of the dynein–dynactin complex, kinesins, their adaptors, and the phosphorylation of these proteins in the formation of dendritic trees by maturing neurons. We primarily review the effects of the motor activity of these proteins in dendrites on dendritogenesis. We also discuss less anticipated mechanisms that contribute to dendrite growth, such as dynein‐driven axonal transport and non‐motor functions of kinesins. [ABSTRACT FROM AUTHOR]

Objectives: Huntington's disease (HD) is a devastating neurodegenerative disease caused by polyglutamine (polyQ) expansion in the huntingtin (HTT) gene. Mutant huntingtin (mHTT) is the main cause of HD and is associated with impaired mitochondrial dynamics, ubiquitin‐proteasome system and autophagy, as well as tauopathy. In this study, we aimed to establish a new neural stem cell line for HD studies. Materials and methods: YAC128 mice are a yeast artificial chromosome (YAC)‐based transgenic mouse model of HD. These mice express a full‐length human mutant HTT gene with 128 CAG repeats and exhibit various pathophysiological features of HD. In this study, we isolated a new neural stem cell line from the forebrains of YAC128 mouse embryos (E12.5) and analysed its characteristics using cellular and biochemical methods. Results: Compared to wild‐type (WT) NSCs, the YAC128 NSC line exhibited greater proliferation and migration capacity. In addition to mHTT expression, increased intracellular Ca2+ levels and dysfunctional mitochondrial membrane potential were observed in the YAC128 NSCs. YAC128 NSCs had defects in mitochondrial dynamics, including a deficit in mitochondrial axonal transport and unbalanced fusion and fission processes. YAC128 NSCs also displayed decreased voltage response variability and Na+ current amplitude. Additionally, the ubiquitin‐proteasome and autophagy systems were impaired in the YAC128 NSCs. Conclusions: We have established a new neural stem line from YAC128 transgenic mice, which may serve as a useful resource for studying HD pathogenesis and drug screening. [ABSTRACT FROM AUTHOR]

The hallmark pathologies of the Alzheimer's disease (AD) brain are amyloid beta (Aβ)‐containing senile plaques and neurofibrillary tangles formed from the microtubule (MT)‐binding tau protein. Tau becomes hyperphosphorylated and disengages from MTs in AD, with evidence of resulting MT structure/function defects. Brain‐penetrant MT‐stabilizing compounds can normalize MTs and axonal transport in mouse models with tau pathology, thereby reducing neuron loss and decreasing tau pathology. MT dysfunction is also observed in dystrophic axons adjacent to Aβ plaques, resulting in accumulation of amyloid precursor protein (APP) and BACE1 with the potential for enhanced localized Aβ generation. We have examined whether the brain‐penetrant MT‐stabilizing compound CNDR‐51657 might decrease plaque‐associated axonal dystrophy and Aβ release in 5XFAD mice that develop an abundance of Aβ plaques. Administration of CNDR‐51657 to 1.5‐month‐old male and female 5XFAD mice for 4 or 7 weeks led to decreased soluble brain Aβ that coincided with reduced APP and BACE1 levels, resulting in decreased formation of insoluble Aβ deposits. These data suggest a vicious cycle whereby initial Aβ plaque formation causes MT disruption in nearby axons, resulting in the local accumulation of APP and BACE1 that facilitates additional Aβ generation and plaque deposition. The ability of a MT‐stabilizing compound to attenuate this cycle, and also reduce deficits resulting from reduced tau binding to MTs, suggests that molecules of this type hold promise as potential AD therapeutics. [ABSTRACT FROM AUTHOR]

Mutations in the nuclear matrix protein Matrin 3 (MATR3) have been identified in amyotrophic lateral sclerosis and myopathy. To investigate the mechanisms underlying MATR3 mutations in neuromuscular diseases and efficiently screen for modifiers of MATR3 toxicity, we generated transgenic MATR3 flies. Our findings indicate that expression of wild‐type or mutant MATR3 in motor neurons reduces climbing ability and lifespan of flies, while their expression in indirect flight muscles (IFM) results in abnormal wing positioning and muscle degeneration. In both motor neurons and IFM, mutant MATR3 expression results in more severe phenotypes than wild‐type MATR3, demonstrating that the disease‐linked mutations confer pathogenicity. We conducted a targeted candidate screen for modifiers of the MATR3 abnormal wing phenotype and identified multiple enhancers involved in axonal transport. Knockdown of these genes enhanced protein levels and insolubility of mutant MATR3. These results suggest that accumulation of mutant MATR3 contributes to toxicity and implicate axonal transport dysfunction in disease pathogenesis. [ABSTRACT FROM AUTHOR]

Background and Purpose: Early retinal neurodegeneration occurs as one of the complications of diabetes even before clinically detectable diabetic vascular retinopathy. The pathogenesis of retinal diabetic neuropathy is still not well understood. We investigated the serial changes or fluctuations in intraocular pressure (IOP) and examined their roles in the pathogenesis of neuronal degeneration in diabetic retina.Experimental Approach: Male Sprague Dawley rats with streptozotocin-induced diabetes were treated with ophthalmic preparations of brinzolamide, latanoprost, both drugs (combined treatment) or saline for 8 weeks. IOP was measured daily under general anaesthesia using a rebound tonometer. Antegrade axoplasmic flow in the optic nerve was assessed with a fluorescent substrate. Immunohistochemical staining, TUNEL assays and western blots were also used.Key Results: The fluctuation of IOP was higher in the diabetes group than in the normal control or the combined treatment group. Diabetes-induced apoptosis of retinal ganglion cells was decreased by combined treatment. Increased expression of glial fibrillary acidic protein or Iba-1 in the retina or optic nerve head, induced by diabetes, was attenuated only by the combined treatment. Intercellular adhesion molecule-1 was increased in diabetic rats but not in the combined treatment group. Diabetes-induced loss of antegrade axoplasmic transport was partially relieved with combined treatment.Conclusion and Implications: Elevated IOP fluctuations seemed to be associated with the gliosis, neuroinflammation, and neurodegeneration induced by diabetes. The loss of retinal ganglion cells might be relieved by IOP-lowering medication. The improvement of unstable perfusion pressure could play a role in neuroprotection in the diabetic retina. [ABSTRACT FROM AUTHOR]

Cleavage of amyloid precursor protein (APP) by BACE‐1 (β‐site APP cleaving enzyme 1) is the rate‐limiting step in amyloid‐β (Aβ) production and a neuropathological hallmark of Alzheimer's disease (AD). Despite decades of research, mechanisms of amyloidogenic APP processing remain highly controversial. Here, we show that in neurons, APP processing and Aβ production are controlled by the protein complex‐2 (AP‐2), an endocytic adaptor known to be required for APP endocytosis. Now, we find that AP‐2 prevents amyloidogenesis by additionally functioning downstream of BACE1 endocytosis, regulating BACE1 endosomal trafficking and its delivery to lysosomes. AP‐2 is decreased in iPSC‐derived neurons from patients with late‐onset AD, while conditional AP‐2 knockout (KO) mice exhibit increased Aβ production, resulting from accumulation of BACE1 within late endosomes and autophagosomes. Deletion of BACE1 decreases amyloidogenesis and mitigates synapse loss in neurons lacking AP‐2. Taken together, these data suggest a mechanism for BACE1 intracellular trafficking and degradation via an endocytosis‐independent function of AP‐2 and reveal a novel role for endocytic proteins in AD. Synopsis: BACE1 promotes A• production and is a neuropathological hallmark of Alzheimer's disease. This study shows that the endocytic adaptor protein complex‐2 promotes trafficking and degradation of BACE1 in neurons and reduces amyloidogenesis. BACE1 proteins levels are increased in AP‐2 deficient brains.AP‐2 functions downstream of BACE1 endocytosis and promotes BACE1 trafficking en route to lysosomes.Neurodegeneration in AP‐2 KO mice can be rescued by BACE1 haploinsufficiency. [ABSTRACT FROM AUTHOR]

Vesicular transport serves as an important mechanism for cell shape regulation during development. Although the semaphorin signaling molecule, a well‐known regulator of axon guidance, induces endocytosis in the growth cone and the axonal transport of vertebrate neurons, the underlying molecular mechanisms remain largely unclear. Here, we show that the Caenorhabditis elegans SNT‐1/synaptotagmin‐UNC‐41/stonin2 system, whose role in synaptic vesicle recycling in neurons has been studied extensively, is involved in semaphorin‐regulated vesicular transport in larval epidermal cells. Mutations in the snt‐1/unc‐41 genes strongly suppressed the cell shape defects of semaphorin mutants. The null mutation in the semaphorin receptor gene, plx‐1, altered the expression and localization pattern of endocytic and exocytic markers in the epidermal cells while repressing the transport of SNT‐1‐containing vesicles toward late endosome/lysosome pathways. Our findings suggest that the nematode semaphorins regulate the vesicular transport in epidermal cells in a manner distinct from that of vertebrate semaphorins in neurons. [ABSTRACT FROM AUTHOR]

We established microRNA (miRNA) profiles in gray and white matter multiple sclerosis (MS) lesions and identified seven miRNAs which were significantly more upregulated in the gray matter lesions. Five of those seven miRNAs, miR‐330‐3p, miR‐4286, miR‐4488, let‐7e‐5p, miR‐432‐5p shared the common target synaptotagmin7 (Syt7). Immunohistochemistry and transcript analyses using nanostring technology revealed a maldistribution of Syt7, with Syt7 accumulation in neuronal soma and decreased expression in axonal structures. This maldistribution could be at least partially explained by an axonal Syt7 transport disturbance. Since Syt7 is a synapse‐associated molecule, this maldistribution could result in impairment of neuronal functions in MS patients. Thus, our results lead to the hypothesis that the overexpression of these five miRNAs in gray matter lesions is a cellular mechanism to reduce further endogenous neuronal Syt7 production. Therefore, miRNAs seem to play an important role as modulators of neuronal structures in MS. [ABSTRACT FROM AUTHOR]

Parkinson's disease (PD) is the second most common neurodegenerative disease. The molecular mechanisms of PD at the cellular level involve oxidative stress, mitochondrial dysfunction, autophagy, axonal transport, and neuroinflammation. Induced pluripotent stem cells (iPSCs) with patient-specific genetic background are capable of directed differentiation into dopaminergic neurons. Cell models based on iPSCs are powerful tools for studying the molecular mechanisms of PD. The iPSCs used for PD studies were mainly from patients carrying mutations in synuclein alpha (SNCA), leucine-rich repeat kinase 2 (LRRK2), PTEN-induced putative kinase 1 (PINK1), parkin RBR E3 ubiquitin protein ligase (PARK2), cytoplasmic protein sorting 35 (VPS35), and variants in glucosidase beta acid (GBA). In this review, we summarized the advances in molecular mechanisms of Parkinson's disease using iPSC models. [ABSTRACT FROM AUTHOR]

Signalling endosomes are essential for trafficking of activated ligand–receptor complexes and their distal signalling, ultimately leading to neuronal survival. Although deficits in signalling endosome transport have been linked to neurodegeneration, our understanding of the mechanisms controlling this process remains incomplete. Here, we describe a new modulator of signalling endosome trafficking, the insulin‐like growth factor 1 receptor (IGF1R). We show that IGF1R inhibition increases the velocity of signalling endosomes in motor neuron axons, both in vitro and in vivo. This effect is specific, since IGF1R inhibition does not alter the axonal transport of mitochondria or lysosomes. Our results suggest that this change in trafficking is linked to the dynein adaptor bicaudal D1 (BICD1), as IGF1R inhibition results in an increase in the de novo synthesis of BICD1 in the axon of motor neurons. Finally, we found that IGF1R inhibition can improve the deficits in signalling endosome transport observed in a mouse model of amyotrophic lateral sclerosis (ALS). Taken together, these findings suggest that IGF1R inhibition may be a new therapeutic target for ALS. Synopsis: IGF1R regulates axonal retrograde transport of signalling endosomes by altering the local translation of the motor adaptor BICD1. Inhibition or knockdown of IGF1R leads to an increase in retrograde velocity of signalling endosomes in the axon.This effect is mediated by decreased Akt activation.IGF1R inhibition leads to an increase in the expression of the dynein adaptor BICD1 in the axon. [ABSTRACT FROM AUTHOR]

Model organisms are increasingly used to study and understand how neurofilament (NF)‐based neurological diseases develop. However, whether a NF homolog exists in C. elegans remains unclear. We characterize TAG‐63 as a NF‐like protein with sequence homologies to human NEFH carrying various coiled coils as well as clustered phosphorylation sites. TAG‐63 also exhibits features of NFL such as a molecular weight of around 70 kD, the lack of KSP repeats and the ability to form 10 nm filamentous structures in transmission electron micrographs. An anti‐NEFH antibody detects a band at the predicted molecular weight of TAG‐63 in Western blots of whole worm lysates and this band cannot be detected in tag‐63 knockout worms. A transcriptional tag‐63 reporter expresses in a broad range of neurons, and various anti‐NFH antibodies stain worm neurons with an overlapping expression of axonal vesicle transporter UNC‐104(KIF1A). Cultured neurons grow shorter axons when incubating with drugs known to disintegrate the NF network and rhodamine‐labeled in vitro reconstituted TAG‐63 filaments disintegrate upon drug exposure. Speeds of UNC‐104 motors are diminished in tag‐63 mutant worms with visibly increased accumulations of motors along axons. UNC‐104/TAG‐63 and SNB‐1/TAG‐63 not only colocalize in neurons but also revealed positive BiFC (bimolecular fluorescence assay) signals. In summary, we identified and characterized TAG‐63 in C. elegans, and demonstrate that lack of this protein limits axonal transport efficiencies. Additionally, this study would aid in developing NF‐related disease models in the future. [ABSTRACT FROM AUTHOR]