TRAK/Milton Motor-Adaptor Proteins Steer Mitochondrial Trafficking to Axons and Dendrites

Synaptic-mitochondrial transport: mechanisms in neural adaptation and degeneration

Synaptic plasticity is the basis for the proper functioning of the central nervous system. Synapses are the contact points between neurons and are crucial for information transmission, the structure and function of synapses change adaptively based on the different activities of neurons, thus affecting processes such as learning, memory, and neural development and repair. Synaptic activity requires a large amount of energy provided by mitochondria. Mitochondrial transport proteins regulate the positioning and movement of mitochondria to maintain normal energy metabolism. Recent studies have shown a close relationship between mitochondrial transport proteins and synaptic plasticity, providing a new direction for the study of adaptive changes in the central nervous system and new targets for the treatment of neurodegenerative diseases.

Mitochondrial transfer in endothelial cells and vascular health

Mitochondria play a vital role in cellular energy metabolism and vascular health, with their function directly influencing endothelial cell (EC) bioenergetics and integrity. Mitochondrial transfer has emerged as a key mechanism of intercellular communication, impacting angiogenesis, tissue repair, and cellular homeostasis. This review highlights recent findings on mitochondrial transfer, including natural mechanisms - such as tunneling nanotubes (TNTs) and extracellular vesicles (EVs) - and artificial approaches like mitochondrial transplantation. These processes enhance EC function and support vascularization under pathological conditions, including ischemia. While early clinical trials demonstrate therapeutic potential, challenges such as mitochondrial instability and scaling host-derived mitochondria persist. Continued research is essential to optimize mitochondrial transfer and advance its application as a therapeutic strategy for restoring vascular health.

Mitochondria-targeting materials and therapies for regenerative engineering

The hemostatic, inflammatory, proliferative, and remodeling phases of healing require precise spatiotemporal coordination and orchestration of numerous biological processes. As the primary energy generators in the cell, mitochondria play multifunctional roles in regulating metabolism, stress reactions, immunity, and cell density during the process of tissue regeneration. Mitochondrial dynamics involves numerous crucial processes, fusion, fission, autophagy, and translocation, which are all necessary for preserving mitochondrial function, distributing energy throughout cells, and facilitating cellular signaling. Tissue regeneration is specifically associated with mitochondrial dynamics due to perturbations of Ca2+, H2O2 and ROS levels, which can result in mitochondrial malfunction. Increasing evidence from multiple models suggests that clinical interventions or medicinal drugs targeting mitochondrial dynamics could be a promising approach. This review highlights significant advances in the understanding of mitochondrial dynamics in tissue regeneration, with specific attention on mitochondria-targeting biomaterials that accelerate multiple tissues' regeneration by regulating mitochondrial metabolism. The innovations in nanomaterials and nanosystems enhance mitochondrial-targeting therapies are critically examined with the prospects of modulating mitochondrial dynamics for new therapies in regenerative engineering.

Mitochondria in aging and age-associated diseases

Mitochondria, essential for cellular energy, are crucial in neurodegenerative disorders (NDDs) and their age-related progression. This review highlights mitochondrial dynamics, mitovesicles, homeostasis, and organelle communication. We examine mitochondrial impacts from aging and NDDs, focusing on protein aggregation and dysfunction. Prospective therapeutic approaches include enhancing mitophagy, improving respiratory chain function, maintaining calcium and lipid balance, using microRNAs, and mitochondrial transfer to protect function. These strategies underscore the crucial role of mitochondrial health in neuronal survival and cognitive functions, offering new therapeutic opportunities.

ARMC1 partitions between distinct complexes and assembles MIRO with MTFR to control mitochondrial distribution

Maintaining an optimal mitochondrial distribution is critical to ensure an adequate supply of energy and metabolites to support important cellular functions. How cells balance dynamic mitochondrial processes to achieve homeostasis is incompletely understood. Here, we show that ARMC1 partitioning between distinct mitochondrial protein complexes is a key determinant of mitochondrial distribution. In one complex, the mitochondrial trafficking adaptor MIRO recruits ARMC1, which mediates the assembly of a mitochondrial fission regulator (MTFR). MTFR stability depends on ARMC1, and MIRO-MTFR complexes specifically antagonize retrograde mitochondrial movement. In another complex, DNAJC11 facilitates ARMC1 release from mitochondria. Disrupting MIRO-MTFR assembly fails to rescue aberrant mitochondrial distributions clustered in the perinuclear area observed with ARMC1 deletion, while disrupting ARMC1 interaction with DNAJC11 leads to excessive mitochondrially localized ARMC1 and distinct mitochondrial defects. Thus, the abundance and trafficking impact of MIRO-MTFR complexes require ARMC1, whose mito-cytoplasmic shuttling balanced by DNAJC11 tunes steady-state mitochondrial distributions.

KIF1C activates and extends dynein movement through the FHF cargo adapter

Cellular cargos move bidirectionally on microtubules by recruiting opposite polarity motors dynein and kinesin. These motors show codependence, where one requires the activity of the other, although the mechanism is unknown. Here we show that kinesin-3 KIF1C acts as both an activator and a processivity factor for dynein, using in vitro reconstitutions of human proteins. Activation requires only a fragment of the KIF1C nonmotor stalk binding the cargo adapter HOOK3. The interaction site is separate from the constitutive factors FTS and FHIP, which link HOOK3 to small G-proteins on cargos. We provide a structural model for the autoinhibited FTS-HOOK3-FHIP1B (an FHF complex) and explain how KIF1C relieves it. Collectively, we explain codependency by revealing how mutual activation of dynein and kinesin occurs through their shared adapter. Many adapters bind both dynein and kinesins, suggesting this mechanism could be generalized to other bidirectional complexes.

Mitochondrial dysfunction in Alzheimer's disease: Guiding the path to targeted therapies

Alzheimer's disease (AD) is characterized by progressive neurodegeneration, marked by the accumulation of amyloid-β (Aβ) plaques and tau tangles. Emerging evidence suggests that mitochondrial dysfunction plays a pivotal role in AD pathogenesis, driven by impairments in mitochondrial quality control (MQC) mechanisms. MQC is crucial for maintaining mitochondrial integrity through processes such as proteostasis, mitochondrial dynamics, mitophagy, and precise communication with other subcellular organelles. In AD, disruptions in these processes lead to bioenergetic failure, gene dysregulation, the accumulation of damaged mitochondria, neuroinflammation, and lipid homeostasis impairment, further exacerbating neurodegeneration. This review elucidates the molecular pathways involved in MQC and their pathological relevance in AD, highlighting recent discoveries related to mitochondrial mechanisms underlying neurodegeneration. Furthermore, we explore potential therapeutic strategies targeting mitochondrial dysfunction, including gene therapy and pharmacological interventions, offering new avenues for slowing AD progression. The complex interplay between mitochondrial health and neurodegeneration underscores the need for innovative approaches to restore mitochondrial function and mitigate the onset and progression of AD.

Mitochondria are positioned at dendritic branch induction sites, a process requiring rhotekin2 and syndapin I

Proper neuronal development, function and survival critically rely on mitochondrial functions. Yet, how developing neurons ensure spatiotemporal distribution of mitochondria during expansion of their dendritic arbor remained unclear. We demonstrate the existence of effective mitochondrial positioning and tethering mechanisms during dendritic arborization. We identify rhotekin2 as outer mitochondrial membrane-associated protein that tethers mitochondria to dendritic branch induction sites. Rhotekin2-deficient neurons failed to correctly position mitochondria at these sites and also lacked the reduction in mitochondrial dynamics observed at wild-type nascent dendritic branch sites. Rhotekin2 hereby serves as important anchor for the plasma membrane-binding and membrane curvature-inducing F-BAR protein syndapin I (PACSIN1). Consistently, syndapin I loss-of-function phenocopied the rhotekin2 loss-of-function phenotype in mitochondrial positioning at dendritic branch induction sites. The finding that rhotekin2 deficiency impaired dendritic branch induction and that a syndapin binding-deficient rhotekin2 mutant failed to rescue this phenotype highlighted the physiological importance of rhotekin2 functions for neuronal network formation.

Optineurin-facilitated axonal mitochondria delivery promotes neuroprotection and axon regeneration

Optineurin (OPTN) mutations are linked to amyotrophic lateral sclerosis (ALS) and normal tension glaucoma (NTG), but a relevant animal model is lacking, and the molecular mechanisms underlying neurodegeneration are unknown. We find that OPTN C-terminus truncation (OPTN∆C) causes late-onset neurodegeneration of retinal ganglion cells (RGCs), optic nerve (ON), and spinal cord motor neurons, preceded by a decrease of axonal mitochondria in mice. We discover that OPTN directly interacts with both microtubules and the mitochondrial transport complex TRAK1/KIF5B, stabilizing them for proper anterograde axonal mitochondrial transport, in a C-terminus dependent manner. Furthermore, overexpressing OPTN/TRAK1/KIF5B prevents not only OPTN truncation-induced, but also ocular hypertension-induced neurodegeneration, and promotes robust ON regeneration. Therefore, in addition to generating animal models for NTG and ALS, our results establish OPTN as a facilitator of the microtubule-dependent mitochondrial transport necessary for adequate axonal mitochondria delivery, and its loss as the likely molecular mechanism of neurodegeneration.

The Huntingtin Transport Complex

A dynamic network of scaffolding molecules, adaptor proteins, and motor proteins work together to orchestrate the movement of proteins, mRNA, and vesicular cargoes. Defects in intracellular transport can often lead to neurodegeneration. Huntingtin (HTT) is a ubiquitously expressed scaffolding protein with a multitude of cellular roles, including regulating the transport of various organelles. HTT is remarkable in its ability to regulate the transport of a wide range of cargoes, including BDNF vesicles, APP vesicles, early endosomes, autophagosomes, lysosomes, and mitochondria. This interaction network allows huntingtin to control microtubule-based transport by kinesin and dynein, as well as actin-based transport by myosin VI. By forming complexes with multiple motor adaptors, huntingtin regulates a variety of cargoes and guides cargoes through the different stages of biosynthesis, signaling, and degradation. Accordingly, pathogenic polyglutamine expansions seen in Huntington's Disease (HD) dysregulate huntingtin transport complexes, resulting in defects in transport and neurodegeneration.

Metaxin-2 tunes mitochondrial transportation and neuronal function in Drosophila

Metaxins are a family of evolutionarily conserved proteins that reside on the mitochondria outer membrane (MOM) and participate in the protein import into the mitochondria. Metaxin-2 (Mtx2), a member of this family, has been identified as a key component in the machinery for mitochondrial transport in both C. elegans and human neurons. To deepen our understanding of Mtx2's role in neurons, we examined the homologous genes CG5662 and CG8004 in Drosophila. The CG5662 is a non-essential gene while CG8004 null mutants die at late pupal stages. The CG8004 protein is widely expressed throughout the Drosophila nervous system and is targeted to mitochondria. However, neuronal CG8004 is dispensable for animal survival and is partially required for mitochondrial distribution in certain neuropil regions. Conditional knockout of CG8004 in adult gustatory receptor neurons (GRNs) impairs mitochondrial trafficking along GRN axons and diminishes the mitochondrial quantities in axon terminals. The absence of CG8004 also leads to mitochondrial fragmentation within GRN axons, a phenomenon that may be linked to mitochondrial transport through its genetic interaction with the fusion proteins Marf and Opa1. While the removal of neuronal CG8004 is not lethal during the developmental stage, it does have consequences for the lifespan and healthspan of adult Drosophila. At last, double knockout (KO) of CG5662 and CG8004 shows similar phenotypes as the CG8004 single KO, suggesting that CG5662 does not compensate for the loss of CG8004. In summary, our findings suggest that CG8004 plays a conserved and context-dependent role in axonal mitochondrial transport, as well it is important for sustaining neuronal function. Therefore, we refer to CG8004 as the Drosophila Metaxin-2 (dMtx2).

Transcript and Lipid Profile Alterations in Astrocyte-Neuron Mitochondrial Transfer Under Lipopolysaccharide Exposure: An In Vitro Study

Sepsis-associated encephalopathy (SAE) is a brain dysfunction for which no effective therapy currently exists. Recent studies suggest that transferring mitochondria from astrocytes to neurons may benefit SAE patients, though the underlying mechanism remains unclear. We cultured astrocytes and neurons from mice in vitro. Astrocytes were stimulated with lipopolysaccharide (LPS) for 24 h, and the astrocyte-conditioned medium (ACM) was collected. Neuronal cultures were then treated with ACM or mitochondria-depleted ACM (mdACM) for further analysis. Mitochondrial transfer was examined under a fluorescence microscope. Western blotting analyzed the protein expression of genes related to apoptosis and mitochondrial metabolism. RNA sequencing and mass spectrometry were employed to investigate the mechanisms underlying mitochondrial transfer. Astrocyte-derived mitochondria migrated toward and connected with LPS-exposed neurons. The addition of ACM significantly attenuated LPS-induced alterations in the proteins linked to apoptosis and mitochondrial dynamics. RNA sequencing revealed notable alterations in the transcript profile of neurons upon ACM treatment, highlighting the involvement of mitochondria metabolism, inflammation, and apoptosis-related factors. Additionally, mitochondrial transfer modified the lipid composition of neurons, increasing phosphatidylserine levels, which correlated with neuroinflammation and enriched pathways related to cytokine and MAPK signaling. Our findings suggest that astrocyte-neuron mitochondrial transfer holds therapeutic potential for alleviating SAE, possibly through the anti-inflammatory effects of lipids, particularly phosphatidylserine.

From Cell Architecture to Mitochondrial Signaling: Role of Intermediate Filaments in Health, Aging, and Disease

The coordination of cytoskeletal proteins shapes cell architectures and functions. Age-related changes in cellular mechanical properties have been linked to decreased cellular and tissue dysfunction. Studies have also found a relationship between mitochondrial function and the cytoskeleton. Cytoskeleton inhibitors impact mitochondrial quality and function, including motility and morphology, membrane potential, and respiration. The regulatory properties of the cytoskeleton on mitochondrial functions are involved in the pathogenesis of several diseases. Disassembly of the axon's cytoskeleton and the release of neurofilament fragments have been documented during neurodegeneration. However, these changes can also be related to mitochondrial impairments, spanning from reduced mitochondrial quality to altered bioenergetics. Herein, we discuss recent research highlighting some of the pathophysiological roles of cytoskeleton disassembly in aging, neurodegeneration, and neuromuscular diseases, with a focus on studies that explored the relationship between intermediate filaments and mitochondrial signaling as relevant contributors to cellular health and disease.

KIF5A regulates axonal repair and time-dependent axonal transport of SFPQ granules and mitochondria in human motor neurons

Mutations in the microtubule-binding motor protein kinesin 5 A (KIF5A) are implicated in several adult-onset motor neuron diseases, including Amyotrophic Lateral Sclerosis, Spastic Paraplegia Type 10 and Charcot-Marie-Tooth Disease Type 2. While KIF5 family members transport a variety of cargos along axons, the specific cargos affected by KIF5A mutations remain poorly understood. Here, we generated KIF5Anull mutant human motor neurons and analyzed the impact on axonal transport and motor neuron outgrowth and regeneration in vitro. KIF5A deficiency caused reduced neurite complexity in young neurons (DIV14) and defects in axonal regeneration. KIF5A deficiency did not affect neurofilament transport but impaired mitochondrial motility and anterograde speed at DIV42. Notably, KIF5A deficiency strongly reduced anterograde transport of splicing factor proline/glutamine-rich (SFPQ)-associated RNA granules in DIV42 axons. Hence, KIF5A plays a critical role in promoting axonal regrowth after injury and in driving the anterograde transport of mitochondria and especially SFPQ-associated RNA granules in mature neurons.

Spatiotemporal proteomics reveals the biosynthetic lysosomal membrane protein interactome in neurons

Lysosomes are membrane-bound organelles critical for maintaining cellular homeostasis. Delivery of biosynthetic lysosomal proteins to lysosomes is crucial to orchestrate proper lysosomal function. However, it remains unknown how the delivery of biosynthetic lysosomal proteins to lysosomes is ensured in neurons, which are highly polarized cells. Here, we developed Protein Origin, Trafficking And Targeting to Organelle Mapping (POTATOMap), by combining trafficking synchronization and proximity-labelling based proteomics, to unravel the trafficking routes and interactome of the biosynthetic lysosomal membrane protein LAMP1 at specified time points. This approach, combined with advanced microscopy, enables us to identify the neuronal domain-specific trafficking machineries of biosynthetic LAMP1. We reveal a role in replenishing axonal lysosomes, in delivery of newly synthesized axonal synaptic proteins, and interactions with RNA granules to facilitate hitchhiking in the axon. POTATOMap offers a robust approach to map out dynamic biosynthetic protein trafficking and interactome from their origin to destination.

SEC-SAXS/MC Ensemble Structural Studies of the Microtubule Binding Protein Cdt1 Show Monomeric, Folded-Over Conformations

Cdt1 is a mixed folded protein critical for DNA replication licensing and it also has a "moonlighting" role at the kinetochore via direct binding to microtubules and the Ndc80 complex. However, it is unknown how the structure and conformations of Cdt1 could allow it to participate in these multiple, unique sets of protein complexes. While robust methods exist to study entirely folded or unfolded proteins, structure-function studies of combined, mixed folded/disordered proteins remain challenging. In this work, we employ orthogonal biophysical and computational techniques to provide structural characterization of mitosis-competent human Cdt1. Thermal stability analyses shows that both folded winged helix domains1 are unstable. CD and NMR show that the N-terminal and linker regions are intrinsically disordered. DLS shows that Cdt1 is monomeric and polydisperse, while SEC-MALS confirms that it is monomeric at high concentrations, but without any apparent inter-molecular self-association. SEC-SAXS enabled computational modeling of the protein structures. Using the program SASSIE, we performed rigid body Monte Carlo simulations to generate a conformational ensemble of structures. We observe that neither fully extended nor extremely compact Cdt1 conformations are consistent with SAXS. The best-fit models have the N-terminal and linker disordered regions extended into the solution and the two folded domains close to each other in apparent "folded over" conformations. We hypothesize the best-fit Cdt1 conformations could be consistent with a function as a scaffold protein that may be sterically blocked without binding partners. Our study also provides a template for combining experimental and computational techniques to study mixed-folded proteins.

Nesprin-2 coordinates opposing microtubule motors during nuclear migration in neurons

Nuclear migration is critical for the proper positioning of neurons in the developing brain. It is known that bidirectional microtubule motors are required for nuclear transport, yet the mechanism of the coordination of opposing motors is still under debate. Using mouse cerebellar granule cells, we demonstrate that Nesprin-2 serves as a nucleus-motor adaptor, coordinating the interplay of kinesin-1 and dynein. Nesprin-2 recruits dynein-dynactin-BicD2 independently of the nearby kinesin-binding LEWD motif. Both motor binding sites are required to rescue nuclear migration defects caused by the loss of function of Nesprin-2. In an intracellular cargo transport assay, the Nesprin-2 fragment encompassing the motor binding sites generates persistent movements toward both microtubule minus and plus ends. Nesprin-2 drives bidirectional cargo movements over a prolonged period along perinuclear microtubules, which advance during the migration of neurons. We propose that Nesprin-2 keeps the nucleus mobile by coordinating opposing motors, enabling continuous nuclear transport along advancing microtubules in migrating cells.

Synaptic mitochondria: A crucial factor in the aged hippocampus

Aging is a multifaceted biological process characterized by progressive molecular and cellular damage accumulation. The brain hippocampus undergoes functional deterioration with age, caused by cellular deficits, decreased synaptic communication, and neuronal death, ultimately leading to memory impairment. One of the factors contributing to this dysfunction is the loss of mitochondrial function. In neurons, mitochondria are categorized into synaptic and non-synaptic pools based on their location. Synaptic mitochondria, situated at the synapses, play a crucial role in maintaining neuronal function and synaptic plasticity, whereas non-synaptic mitochondria are distributed throughout other neuronal compartments, supporting overall cellular metabolism and energy supply. The proper function of synaptic mitochondria is essential for synaptic transmission as they provide the energy required and regulate calcium homeostasis at the communication sites between neurons. Maintaining the structure and functionality of synaptic mitochondria involves intricate processes, including mitochondrial dynamics such as fission, fusion, transport, and quality control mechanisms. These processes ensure that mitochondria remain functional, replace damaged organelles, and sustain cellular homeostasis at synapses. Notably, deficiencies in these mechanisms have been increasingly associated with aging and the onset of age-related neurodegenerative diseases. Synaptic mitochondria from the hippocampus are particularly vulnerable to age-related changes, including alterations in morphology and a decline in functionality, which significantly contribute to decreased synaptic activity during aging. This review comprehensively explores the critical roles that mitochondrial dynamics and quality control mechanisms play in preserving synaptic activity and neuronal function. It emphasizes the emerging evidence linking the deterioration of synaptic mitochondria to the aging process and the development of neurodegenerative diseases, highlighting the importance of these organelles from hippocampal neurons as potential therapeutic targets for mitigating cognitive decline and synaptic degeneration associated with aging. The novelty of this review lies in its focus on the unique vulnerability of hippocampal synaptic mitochondria to aging, underscoring their importance in maintaining brain function across the lifespan.

Age-specific and compartment-dependent changes in mitochondrial homeostasis and cytoplasmic viscosity in mouse peripheral neurons

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.

MINFLUX reveals dynein stepping in live neurons

Dynein is the primary molecular motor responsible for retrograde intracellular transport of a variety of cargoes, performing successive nanometer-sized steps within milliseconds. Due to the limited spatiotemporal precision of established methods for molecular tracking, current knowledge of dynein stepping is essentially limited to slowed-down measurements in vitro. Here, we use MINFLUX fluorophore localization to directly track CRISPR/Cas9-tagged endogenous dynein with nanometer/millisecond precision in living primary neurons. We show that endogenous dynein primarily takes 8 nm steps, including frequent sideways steps but few backward steps. Strikingly, the majority of direction reversals between retrograde and anterograde movement occurred on the time scale of single steps (16 ms), suggesting a rapid regulatory reversal mechanism. Tug-of-war-like behavior during pauses or reversals was unexpectedly rare. By analyzing the dwell time between steps, we concluded that a single rate-limiting process underlies the dynein stepping mechanism, likely arising from just one adenosine 5'-triphosphate hydrolysis event being required during each step. Our study underscores the power of MINFLUX localization to elucidate the spatiotemporal changes underlying protein function in living cells.

LFHP-1c improves cognitive function after TBI in mice by reducing oxidative stress through the PGAM5-NRF2-KEAP1 ternary complex

Traumatic brain injury (TBI) is a leading cause of disability and death. Thus, timely and effective secondary brain injury intervention is crucial, with potential to improve the prognosis of TBI. Oxidative stress contributes to post-traumatic secondary cognitive impairment, and the reduction of post-traumatic oxidative stress effectively enhances cognitive function. Phosphoglycerate-mutating enzyme 5 (PGAM5), a member of the phosphoglycerate transporter enzyme family, is upregulated in TBI and induces mitochondrial autophagy. This further exacerbates damage following TBI. The present study focused on the small molecule drug, LFHP-1c, which is a novel inhibitor of PGAM5. The present study used an in vivo mouse model incorporating a controlled cortical impact-induced TBI, to examine the impact of LFHP-1c on oxidative stress and cognitive function. The present study aimed to determine the impact of LFHP-1c on the PGAM5-Kelch-like ECH-associated protein 1 (KEAP1)- nuclear factor erythroid 2-related factor 2 (NRF2) ternary complex within the TBI context. Results of the present study indicated that LFHP-1c suppresses PGAM5 expression and inhibits the development of the PGAM5-KEAP1-NRF2 ternary complex, thereby promoting the release of NRF2 and KEAP1. This in turn promotes the entry of NRF2 into the nucleus following TBI, leading to increased expression of anti-oxidative stress downstream factors, such as heme oxygenase-1, glutathione peroxidase 1 and superoxide dismutase 1. In addition, LFHP-1c also released KEAP1, leading to mitochondrial Rho GTPase 2 degradation and reducing perinuclear aggregation of mitochondria in the cell, which reduced oxidative stress and ultimately improved cognitive function after TBI.

KIF5A regulates axonal repair and time-dependent axonal transport of SFPQ granules and mitochondria in human motor neurons

Mutations in the microtubule binding motor protein, kinesin family member 5A (KIF5A), cause the fatal motor neuron disease, Amyotrophic Lateral Sclerosis. While KIF5 family members transport a variety of cargos along axons, it is still unclear which cargos are affected by KIF5A mutations. We generated KIF5A null mutant human motor neurons to investigate the impact of KIF5A loss on the transport of various cargoes and its effect on motor neuron function at two different timepoints in vitro. The absence of KIF5A resulted in reduced neurite complexity in young motor neurons (DIV14) and significant defects in axonal regeneration capacity at all developmental stages. KIF5A loss did not affect neurofilament transport but resulted in decreased mitochondria motility and anterograde speed at DIV42. More prominently, KIF5A depletion strongly reduced anterograde transport of SFPQ-associated RNA granules in DIV42 motor neuron axons. We conclude that KIF5A most prominently functions in human motor neurons to promote axonal regrowth after injury as well as to anterogradely transport mitochondria and, to a larger extent, SFPQ-associated RNA granules in a time-dependent manner.

Generation of an Armcx1 Conditional Knockout Mouse

Armadillo repeat-containing X-linked protein-1 (Armcx1) is a poorly characterized transmembrane protein that regulates mitochondrial transport in neurons. Its overexpression has been shown to induce neurite outgrowth in embryonic neurons and to promote retinal ganglion cell (RGC) survival and axonal regrowth in a mouse optic nerve crush model. In order to evaluate the functions of endogenous Armcx1 in vivo, we have created a conditional Armcx1 knockout mouse line in which the entire coding region of the Armcx1 gene is flanked by loxP sites. This Armcx1fl line was crossed with mouse strains in which Cre recombinase expression is driven by the promoters for β-actin and Six3, in order to achieve deletion of Armcx1 globally and in retinal neurons, respectively. Having confirmed deletion of the gene, we proceeded to characterize the abundance and morphology of RGCs in Armcx1 knockout mice aged to 15 months. Under normal physiological conditions, no evidence of aberrant retinal or optic nerve development or RGC degeneration was observed in these mice. The Armcx1fl mouse should be valuable for future studies investigating mitochondrial morphology and transport in the absence of Armcx1 and in determining the susceptibility of Armcx1-deficient neurons to degeneration in the setting of additional heritable or environmental stressors.

Functional magnetic resonance imaging alternations in suicide attempts individuals and their association with gene expression

BACKGROUND

Functional Magnetic Resonance Imaging (fMRI) has shown brain activity alterations in individuals with a history of attempted suicide (SA) who are diagnosed with depression disorder (DD) or bipolar disorder (BD). However, patterns of spontaneous brain activity and their genetic correlations need further investigation.

METHODS

A voxel-based meta-analysis of 19 studies including 26 datasets, involving 742 patients with a history of SA and 978 controls (both nonsuicidal patients and healthy controls) was conducted. We examined fMRI changes in SA patients and analyzed the association between these changes and gene expression profiles using data from the Allen Human Brain Atlas by partial least squares regression analysis.

RESULTS

SA patients demonstrated increased spontaneous brain activity in several brain regions including the bilateral inferior temporal gyrus, hippocampus, fusiform gyrus, and right insula, and decreased activity in areas like the bilateral paracentral lobule and inferior frontal gyrus. Additionally, 5,077 genes were identified, exhibiting expression patterns associated with SA-related fMRI alterations. Functional enrichment analyses demonstrated that these SA-related genes were enriched for biological functions including glutamatergic synapse and mitochondrial structure. Concurrently, specific expression analyses showed that these genes were specifically expressed in the brain tissue, in neurons cells, and during early developmental periods.

CONCLUSION

Our findings suggest a neurobiological basis for fMRI abnormalities in SA patients with DD or BD, potentially guiding future genetic and therapeutic research.

An aggregated mitochondrial distribution in preimplantation embryos disrupts nuclear morphology, function, and developmental potential

A dispersed cytoplasmic distribution of mitochondria is a hallmark of normal cellular organization. Here, we have utilized the expression of exogenous Trak2 in mouse oocytes and embryos to disrupt the dispersed distribution of mitochondria by driving them into a large cytoplasmic aggregate. Our findings reveal that aggregated mitochondria have minimal impact on asymmetric meiotic cell divisions of the oocyte. In contrast, aggregated mitochondria during the first mitotic division result in daughter cells with unequal sizes and increased micronuclei. Further, in two-cell embryos, microtubule-mediated centering properties of the mitochondrial aggregate prevent nuclear centration, distort nuclear shape, and inhibit DNA synthesis and the onset of embryonic transcription. These findings demonstrate the motor protein-mediated distribution of mitochondria throughout the cytoplasm is highly regulated and is an essential feature of cytoplasmic organization to ensure optimal cell function.

Membrane-mediated modulation of mitochondrial physiology by terahertz waves

Extensive studies have demonstrated the diverse impacts of electromagnetic waves at gigahertz and terahertz (THz) frequencies on cytoplasmic membrane properties. However, there is little evidence of these impacts on intracellular membranes, particularly mitochondrial membranes crucial for mitochondrial physiology. In this study, human neuroblast-like cells were exposed to continuous 0.1 THz radiation at an average power density of 33 mW/cm2. The analysis revealed that THz exposure significantly altered the mitochondrial ultrastructure. THz waves enhanced the enzymatic activity of the mitochondrial respiratory chain but disrupted supercomplex assembly, compromising mitochondrial respiration. Molecular dynamics simulations revealed altered rates of change in the quantity of hydrogen bonds and infiltration of water molecules in lipid bilayers containing cardiolipin, indicating the specific behavior of cardiolipin, a signature phospholipid in mitochondria, under THz exposure. These findings suggest that THz radiation can significantly alter mitochondrial membrane properties, impacting mitochondrial physiology through a mechanism related to mitochondrial membrane, and provide deeper insight into the bioeffects of THz radiation.

Kinesin Regulation in the Proximal Axon is Essential for Dendrite-selective Transport

Neurons are polarized and typically extend multiple dendrites and one axon. To maintain polarity, vesicles carrying dendritic proteins are arrested upon entering the axon. To determine whether kinesin regulation is required for terminating anterograde axonal transport, we overexpressed the dendrite-selective kinesin KIF13A. This caused mistargeting of dendrite-selective vesicles to the axon and a loss of dendritic polarity. Polarity was not disrupted if the kinase MARK2/Par1b was coexpressed. MARK2/Par1b is concentrated in the proximal axon, where it maintains dendritic polarity-likely by phosphorylating S1371 of KIF13A, which lies in a canonical 14-3-3 binding motif. We probed for interactions of KIF13A with 14-3-3 isoforms and found that 14-3-3β and 14-3-3ζ bound KIF13A. Disruption of MARK2 or 14-3-3 activity by small molecule inhibitors caused a loss of dendritic polarity. These data show that kinesin regulation is integral for dendrite-selective transport. We propose a new model in which KIF13A that moves dendrite-selective vesicles in the proximal axon is phosphorylated by MARK2. Phosphorylated KIF13A is then recognized by 14-3-3, which causes dissociation of KIF13A from the vesicle and termination of transport. These findings define a new paradigm for the regulation of vesicle transport by localized kinesin tail phosphorylation, to restrict dendrite-selective vesicles from entering the axon.

Role of microRNAs in tumor progression by regulation of kinesin motor proteins

Aberrant cell proliferation is one of the main characteristics of tumor cells that can be affected by many cellular processes and signaling pathways. Kinesin superfamily proteins (KIFs) are motor proteins that are involved in cytoplasmic transportations and chromosomal segregation during cell proliferation. Therefore, regulation of the KIF functions as vital factors in chromosomal stability is necessary to maintain normal cellular homeostasis and proliferation. KIF deregulations have been reported in various cancers. MicroRNAs (miRNAs) and signaling pathways are important regulators of KIF proteins. MiRNAs have key roles in regulation of the cell proliferation, migration, and apoptosis. In the present review, we discussed the role of miRNAs in tumor biology through the regulation of KIF proteins. It has been shown that miRNAs have mainly a tumor suppressor function via the KIF targeting. This review can be an effective step to introduce the miRNAs/KIFs axis as a probable therapeutic target in tumor cells.

Horizontal mitochondrial transfer as a novel bioenergetic tool for mesenchymal stromal/stem cells: molecular mechanisms and therapeutic potential in a variety of diseases

Intercellular mitochondrial transfer (MT) is a newly discovered form of cell-to-cell signalling involving the active incorporation of healthy mitochondria into stressed/injured recipient cells, contributing to the restoration of bioenergetic profile and cell viability, reduction of inflammatory processes and normalisation of calcium dynamics. Recent evidence has shown that MT can occur through multiple cellular structures and mechanisms: tunneling nanotubes (TNTs), via gap junctions (GJs), mediated by extracellular vesicles (EVs) and other mechanisms (cell fusion, mitochondrial extrusion and migrasome-mediated mitocytosis) and in different contexts, such as under physiological (tissue homeostasis and stemness maintenance) and pathological conditions (hypoxia, inflammation and cancer). As Mesenchimal Stromal/ Stem Cells (MSC)-mediated MT has emerged as a critical regulatory and restorative mechanism for cell and tissue regeneration and damage repair in recent years, its potential in stem cell therapy has received increasing attention. In particular, the potential therapeutic role of MSCs has been reported in several articles, suggesting that MSCs can enhance tissue repair after injury via MT and membrane vesicle release. For these reasons, in this review, we will discuss the different mechanisms of MSCs-mediated MT and therapeutic effects on different diseases such as neuronal, ischaemic, vascular and pulmonary diseases. Therefore, understanding the molecular and cellular mechanisms of MT and demonstrating its efficacy could be an important milestone that lays the foundation for future clinical trials.

Polarized localization of kinesin-1 and RIC-7 drives axonal mitochondria anterograde transport

Mitochondria transport is crucial for axonal mitochondria distribution and is mediated by kinesin-1-based anterograde and dynein-based retrograde motor complexes. While Miro and Milton/TRAK were identified as key adaptors between mitochondria and kinesin-1, recent studies suggest the presence of additional mechanisms. In C. elegans, ric-7 is the only single gene described so far, other than kinesin-1, that is absolutely required for axonal mitochondria localization. Using CRISPR engineering in C. elegans, we find that Miro is important but is not essential for anterograde traffic, whereas it is required for retrograde traffic. Both the endogenous RIC-7 and kinesin-1 act at the leading end to transport mitochondria anterogradely. RIC-7 binding to mitochondria requires its N-terminal domain and partially relies on MIRO-1, whereas RIC-7 accumulation at the leading end depends on its disordered region, kinesin-1, and metaxin2. We conclude that transport complexes containing kinesin-1 and RIC-7 polarize at the leading edge of mitochondria and are required for anterograde axonal transport in C. elegans.

Armcx1 Reduces Neurological Damage Via a Mitochondrial Transport Pathway Involving Miro1 After Traumatic Brain Injury

Armcx1 is a member of the ARMadillo repeat-Containing protein on the X chromosome (ARMCX) family, which is recognized to have evolutionary conserved roles in regulating mitochondrial transport and dynamics. Previous research has shown that Armcx1 is expressed at higher levels in mice after axotomy and in adult retinal ganglion cells after crush injury, and this protein increases neuronal survival and axonal regeneration. However, its role in traumatic brain injury (TBI) is unclear. Therefore, the aim of this study was to assess the expression of Armcx1 after TBI and to explore possible related mechanisms by which Armcx1 is involved in TBI. We used C57BL/6 male mice to model TBI and evaluated the role of Armcx1 in TBI by transfecting mice with Armcx1 small interfering RNA (siRNA) to inhibit Armcx1 expression 24 h before TBI modeling. Western blotting, immunofluorescence, terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining, Nissl staining, transmission electron microscopy, adenosine triphosphate (ATP) level measurement, neuronal apoptosis analysis, neurological function scoring and the Morris water maze were performed. The results demonstrated that Armcx1 protein expression was elevated after TBI and that the Armcx1 protein was localized in neurons and astroglial cells in cortical tissue surrounding the injury site. In addition, inhibition of Armcx1 expression further led to impaired mitochondrial transport, abnormal morphology, reduced ATP levels, aggravation of neuronal apoptosis and neurological dysfunction, and decrease Miro1 expression. In conclusion, our findings indicate that Armcx1 may exert neuroprotective effects by ameliorating neurological injury after TBI through a mitochondrial transport pathway involving Miro1.

Mitochondrial dynamics, quality control, and mtDNA in alcohol-associated liver disease and liver cancer

Mitochondria are intracellular organelles responsible for energy production, glucose and lipid metabolism, cell death, cell proliferation, and innate immune response. Mitochondria are highly dynamic organelles that constantly undergo fission, fusion, and intracellular trafficking, as well as degradation and biogenesis. Mitochondrial dysfunction has been implicated in a variety of chronic liver diseases including alcohol-associated liver disease, metabolic dysfunction-associated steatohepatitis, and HCC. In this review, we provide a detailed overview of mitochondrial dynamics, mitophagy, and mitochondrial DNA-mediated innate immune response, and how dysregulation of these mitochondrial processes affects the pathogenesis of alcohol-associated liver disease and HCC. Mitochondrial dynamics and mitochondrial DNA-mediated innate immune response may thereby represent an attractive therapeutic target for ameliorating alcohol-associated liver disease and alcohol-associated HCC.

Miro-mediated mitochondrial transport: A new dimension for disease-related abnormal cell metabolism?

Mitochondria are versatile and highly dynamic organelles found in eukaryotic cells that play important roles in a variety of cellular processes. The importance of mitochondrial transport in cell metabolism, including variations in mitochondrial distribution within cells and intercellular transfer, has grown in recent years. Several studies have demonstrated that abnormal mitochondrial transport represents an early pathogenic alteration in a variety of illnesses, emphasizing its significance in disease development and progression. Mitochondrial Rho GTPase (Miro) is a protein found on the outer mitochondrial membrane that is required for cytoskeleton-dependent mitochondrial transport, mitochondrial dynamics (fusion and fission), and mitochondrial Ca2+ homeostasis. Miro, as a critical regulator of mitochondrial transport, has yet to be thoroughly investigated in illness. This review focuses on recent developments in recognizing Miro as a crucial molecule in controlling mitochondrial transport and investigates its roles in diverse illnesses. It also intends to shed light on the possibilities of targeting Miro as a therapeutic method for a variety of diseases.

Cargo specificity, regulation, and therapeutic potential of cytoplasmic dynein

Intracellular retrograde transport in eukaryotic cells relies exclusively on the molecular motor cytoplasmic dynein 1. Unlike its counterpart, kinesin, dynein has a single isoform, which raises questions about its cargo specificity and regulatory mechanisms. The precision of dynein-mediated cargo transport is governed by a multitude of factors, including temperature, phosphorylation, the microtubule track, and interactions with a family of activating adaptor proteins. Activating adaptors are of particular importance because they not only activate the unidirectional motility of the motor but also connect a diverse array of cargoes with the dynein motor. Therefore, it is unsurprising that dysregulation of the dynein-activating adaptor transport machinery can lead to diseases such as spinal muscular atrophy, lower extremity, and dominant. Here, we discuss dynein motor motility within cells and in in vitro, and we present several methodologies employed to track the motion of the motor. We highlight several newly identified activating adaptors and their roles in regulating dynein. Finally, we explore the potential therapeutic applications of manipulating dynein transport to address diseases linked to dynein malfunction.

A mammalian-specific Alex3/Gαq protein complex regulates mitochondrial trafficking, dendritic complexity, and neuronal survival

Mitochondrial dynamics and trafficking are essential to provide the energy required for neurotransmission and neural activity. We investigated how G protein-coupled receptors (GPCRs) and G proteins control mitochondrial dynamics and trafficking. The activation of Gαq inhibited mitochondrial trafficking in neurons through a mechanism that was independent of the canonical downstream PLCβ pathway. Mitoproteome analysis revealed that Gαq interacted with the Eutherian-specific mitochondrial protein armadillo repeat-containing X-linked protein 3 (Alex3) and the Miro1/Trak2 complex, which acts as an adaptor for motor proteins involved in mitochondrial trafficking along dendrites and axons. By generating a CNS-specific Alex3 knockout mouse line, we demonstrated that Alex3 was required for the effects of Gαq on mitochondrial trafficking and dendritic growth in neurons. Alex3-deficient mice had altered amounts of ER stress response proteins, increased neuronal death, motor neuron loss, and severe motor deficits. These data revealed a mammalian-specific Alex3/Gαq mitochondrial complex, which enables control of mitochondrial trafficking and neuronal death by GPCRs.

Autoinhibition and activation of kinesin-1 and their involvement in amyotrophic lateral sclerosis

Kinesin-1, composed of kinesin heavy chain and kinesin light chain, is a founding member of kinesin superfamily and transports various neuronal cargos. Kinesin-1 is one of the most abundant ATPases in the cell and thus need to be tightly regulated to avoid wastage of energy. It has been well established that kinesin-1 is regulated by the autoinhibition mechanism. This review focuses on the recent researches that have contributed to the understanding of mechanisms for the autoinhibition of kinesin-1 and its unlocking. Recent electron microscopic studies have shown an unanticipated structure of autoinhibited kinesin-1. Biochemical reconstitution have revealed detailed molecular mechanisms how the autoinhibition is unlocked. Importantly, misregulation of kinesin-1 is emerging as one of the major causes of amyotrophic lateral sclerosis.

Making the connection: How membrane contact sites have changed our view of organelle biology

The view of organelles and how they operate together has changed dramatically over the last two decades. The textbook view of organelles was that they operated largely independently and were connected by vesicular trafficking and the diffusion of signals through the cytoplasm. We now know that all organelles make functional close contacts with one another, often called membrane contact sites. The study of these sites has moved to center stage in cell biology as it has become clear that they play critical roles in healthy and developing cells and during cell stress and disease states. Contact sites have important roles in intracellular signaling, lipid metabolism, motor-protein-mediated membrane dynamics, organelle division, and organelle biogenesis. Here, we summarize the major conceptual changes that have occurred in cell biology as we have come to appreciate how contact sites integrate the activities of organelles.

SAXS/MC studies of the mixed-folded protein Cdt1 reveal monomeric, folded over conformations

Cdt1 is a protein critical for DNA replication licensing and is well-established to be a binding partner of the minichromosome maintenance (MCM) complex. Cdt1 has also been demonstrated to have an emerging, "moonlighting" role at the kinetochore via direct binding to microtubules and to the Ndc80 complex. However, it is not known how the structure and conformations of Cdt1 could allow for these multiple, completely unique sets of protein complexes. And while there exist multiple robust methods to study entirely folded or entirely unfolded proteins, structure-function studies of combined, mixed folded/disordered proteins remain challenging. It this work, we employ multiple orthogonal biophysical and computational techniques to provide a detailed structural characterization of human Cdt1 92-546. DSF and DSCD show both folded winged helix (WH) domains of Cdt1 are relatively unstable. CD and NMR show the N-terminal and the linker regions are intrinsically disordered. Using DLS and SEC-MALS, we show that Cdt1 is polydisperse, monomeric at high concentrations, and without any apparent inter-molecular self-association. SEC-SAXS of the monomer in solution enabled computational modeling of the protein in silico. Using the program SASSIE, we performed rigid body Monte Carlo simulations to generate a conformational ensemble. Using experimental SAXS data, we filtered for conformations which did and did not fit our data. We observe that neither fully extended nor extremely compact Cdt1 conformations are consistent with our SAXS data. The best fit models have the N-terminal and linker regions extended into solution and the two folded domains close to each other in apparent "folded over" conformations. The best fit Cdt1 conformations are consistent with a function as a scaffold protein which may be sterically blocked without the presence of binding partners. Our studies also provide a template for combining experimental and computational biophysical techniques to study mixed-folded proteins.

Interaction between the mitochondrial adaptor MIRO and the motor adaptor TRAK

MIRO (mitochondrial Rho GTPase) consists of two GTPase domains flanking two Ca2+-binding EF-hand domains. A C-terminal transmembrane helix anchors MIRO to the outer mitochondrial membrane, where it functions as a general adaptor for the recruitment of cytoskeletal proteins that control mitochondrial dynamics. One protein recruited by MIRO is TRAK (trafficking kinesin-binding protein), which in turn recruits the microtubule-based motors kinesin-1 and dynein-dynactin. The mechanism by which MIRO interacts with TRAK is not well understood. Here, we map and quantitatively characterize the interaction of human MIRO1 and TRAK1 and test its potential regulation by Ca2+ and/or GTP binding. TRAK1 binds MIRO1 with low micromolar affinity. The interaction was mapped to a fragment comprising MIRO1's EF-hands and C-terminal GTPase domain and to a conserved sequence motif within TRAK1 residues 394 to 431, immediately C-terminal to the Spindly motif. This sequence is sufficient for MIRO1 binding in vitro and is necessary for MIRO1-dependent localization of TRAK1 to mitochondria in cells. MIRO1's EF-hands bind Ca2+ with dissociation constants (KD) of 3.9 μM and 300 nM. This suggests that under cellular conditions one EF-hand may be constitutively bound to Ca2+ whereas the other EF-hand binds Ca2+ in a regulated manner, depending on its local concentration. Yet, the MIRO1-TRAK1 interaction is independent of Ca2+ binding to the EF-hands and of the nucleotide state (GDP or GTP) of the C-terminal GTPase. The interaction is also independent of TRAK1 dimerization, such that a TRAK1 dimer can be expected to bind two MIRO1 molecules on the mitochondrial surface.

The interaction between alpha-synuclein and mitochondrial dysfunction in Parkinson's disease

Parkinson's disease (PD) is an aging-associated neurodegenerative disorder with the hallmark of abnormal aggregates of alpha-synuclein (α-syn) in Lewy bodies (LBs) and Lewy neurites (LNs). Currently, pathogenic α-syn and mitochondrial dysfunction have been considered as prominent roles that give impetus to the PD onset. This review describes the α-syn pathology and mitochondrial alterations in PD, and focuses on how α-syn interacts with multiple aspects of mitochondrial homeostasis in the pathogenesis of PD.

Mitochondrial Proteomes in Neural Cells: A Systematic Review

Mitochondria are ancient endosymbiotic double membrane organelles that support a wide range of eukaryotic cell functions through energy, metabolism, and cellular control. There are over 1000 known proteins that either reside within the mitochondria or are transiently associated with it. These mitochondrial proteins represent a functional subcellular protein network (mtProteome) that is encoded by mitochondrial and nuclear genomes and significantly varies between cell types and conditions. In neurons, the high metabolic demand and differential energy requirements at the synapses are met by specific modifications to the mtProteome, resulting in alterations in the expression and functional properties of the proteins involved in energy production and quality control, including fission and fusion. The composition of mtProteomes also impacts the localization of mitochondria in axons and dendrites with a growing number of neurodegenerative diseases associated with changes in mitochondrial proteins. This review summarizes the findings on the composition and properties of mtProteomes important for mitochondrial energy production, calcium and lipid signaling, and quality control in neural cells. We highlight strategies in mass spectrometry (MS) proteomic analysis of mtProteomes from cultured cells and tissue. The research into mtProteome composition and function provides opportunities in biomarker discovery and drug development for the treatment of metabolic and neurodegenerative disease.

Autoinhibited kinesin-1 adopts a hierarchical folding pattern

Conventional kinesin-1 is the primary anterograde motor in cells for transporting cellular cargo. While there is a consensus that the C-terminal tail of kinesin-1 inhibits motility, the molecular architecture of a full-length autoinhibited kinesin-1 remains unknown. Here, we combine crosslinking mass spectrometry (XL-MS), electron microscopy (EM), and AlphaFold structure prediction to determine the architecture of the full-length autoinhibited kinesin-1 homodimer (kinesin-1 heavy chain [KHC]) and kinesin-1 heterotetramer (KHC bound to kinesin light chain 1 [KLC1]). Our integrative analysis shows that kinesin-1 forms a compact, bent conformation through a break in coiled-coil 3. Moreover, our XL-MS analysis demonstrates that kinesin light chains stabilize the folded inhibited state rather than inducing a new structural state. Using our structural model, we show that disruption of multiple interactions between the motor, stalk, and tail domains is required to activate the full-length kinesin-1. Our work offers a conceptual framework for understanding how cargo adaptors and microtubule-associated proteins relieve autoinhibition to promote activation.

Calcium signals tune AMPK activity and mitochondrial homeostasis in dendrites of developing neurons

Dendritic outgrowth in immature neurons is enhanced by neuronal activity and is considered one of the mechanisms of neural circuit optimization. It is known that calcium signals affect transcriptional regulation and cytoskeletal remodeling necessary for dendritic outgrowth. Here, we demonstrate that activity-dependent calcium signaling also controls mitochondrial homeostasis via AMP-activated protein kinase (AMPK) in growing dendrites of differentiating mouse hippocampal neurons. We found that the inhibition of neuronal activity induced dendritic hypotrophy with abnormally elongated mitochondria. In growing dendrites, AMPK is activated by neuronal activity and dynamically oscillates in synchrony with calcium spikes, and this AMPK oscillation was inhibited by CaMKK2 knockdown. AMPK activation led to phosphorylation of MFF and ULK1, which initiate mitochondrial fission and mitophagy, respectively. Dendritic mitochondria in AMPK-depleted neurons exhibited impaired fission and mitophagy and displayed multiple signs of dysfunction. Genetic inhibition of fission led to dendritic hypoplasia that was reminiscent of AMPK-deficient neurons. Thus, AMPK activity is finely tuned by the calcium-CaMKK2 pathway and regulates mitochondrial homeostasis by facilitating removal of damaged components of mitochondria in growing neurons during normal brain development.

Mitochondrial transport in neurons and evidence for its involvement in acute neurological disorders

Ensuring mitochondrial quality is essential for maintaining neuronal homeostasis, and mitochondrial transport plays a vital role in mitochondrial quality control. In this review, we first provide an overview of neuronal mitochondrial transport, followed by a detailed description of the various motors and adaptors associated with the anterograde and retrograde transport of mitochondria. Subsequently, we review the modest evidence involving mitochondrial transport mechanisms that has surfaced in acute neurological disorders, including traumatic brain injury, spinal cord injury, spontaneous intracerebral hemorrhage, and ischemic stroke. An in-depth study of this area will help deepen our understanding of the mechanisms underlying the development of various acute neurological disorders and ultimately improve therapeutic options.

Pathological Impact of Tau Proteolytical Process on Neuronal and Mitochondrial Function: a Crucial Role in Alzheimer's Disease

Tau protein plays a pivotal role in the central nervous system (CNS), participating in microtubule stability, axonal transport, and synaptic communication. Research interest has focused on studying the role of post-translational tau modifications in mitochondrial failure, oxidative damage, and synaptic impairment in Alzheimer's disease (AD). Soluble tau forms produced by its pathological cleaved induced by caspases could lead to neuronal injury contributing to oxidative damage and cognitive decline in AD. For example, the presence of tau cleaved by caspase-3 has been suggested as a relevant factor in AD and is considered a previous event before neurofibrillary tangles (NFTs) formation.Interestingly, we and others have shown that caspase-cleaved tau in N- or C- terminal sites induce mitochondrial bioenergetics defects, axonal transport impairment, neuronal injury, and cognitive decline in neuronal cells and murine models. All these abnormalities are considered relevant in the early neurodegenerative manifestations such as memory and cognitive failure reported in AD. Therefore, in this review, we will discuss for the first time the importance of truncated tau by caspases activation in the pathogenesis of AD and how its negative actions could impact neuronal function.

Autoinhibited kinesin-1 adopts a hierarchical folding pattern

Conventional kinesin-1 is the primary anterograde motor in cells for transporting cellular cargo. While there is a consensus that the C-terminal tail of kinesin-1 inhibits motility, the molecular architecture of a full-length autoinhibited kinesin-1 remains unknown. Here, we combine cross-linking mass spectrometry (XL-MS), electron microscopy (EM), and AlphaFold structure prediction to determine the architecture of the full-length autoinhibited kinesin-1 homodimer [kinesin-1 heavy chain (KHC)] and kinesin-1 heterotetramer [KHC bound to kinesin light chain 1 (KLC1)]. Our integrative analysis shows that kinesin-1 forms a compact, bent conformation through a break in coiled coil 3. Moreover, our XL-MS analysis demonstrates that kinesin light chains stabilize the folded inhibited state rather than inducing a new structural state. Using our structural model, we show that disruption of multiple interactions between the motor, stalk, and tail domains is required to activate the full-length kinesin-1. Our work offers a conceptual framework for understanding how cargo adaptors and microtubule-associated proteins relieve autoinhibition to promote activation.

Mitochondrial dynamics in health and disease: mechanisms and potential targets

Mitochondria are organelles that are able to adjust and respond to different stressors and metabolic needs within a cell, showcasing their plasticity and dynamic nature. These abilities allow them to effectively coordinate various cellular functions. Mitochondrial dynamics refers to the changing process of fission, fusion, mitophagy and transport, which is crucial for optimal function in signal transduction and metabolism. An imbalance in mitochondrial dynamics can disrupt mitochondrial function, leading to abnormal cellular fate, and a range of diseases, including neurodegenerative disorders, metabolic diseases, cardiovascular diseases and cancers. Herein, we review the mechanism of mitochondrial dynamics, and its impacts on cellular function. We also delve into the changes that occur in mitochondrial dynamics during health and disease, and offer novel perspectives on how to target the modulation of mitochondrial dynamics.

Optogenetic cleavage of the Miro GTPase reveals the direct consequences of real-time loss of function in Drosophila

Miro GTPases control mitochondrial morphology, calcium homeostasis, and regulate mitochondrial distribution by mediating their attachment to the kinesin and dynein motor complex. It is not clear, however, how Miro proteins spatially and temporally integrate their function as acute disruption of protein function has not been performed. To address this issue, we have developed an optogenetic loss of function "Split-Miro" allele for precise control of Miro-dependent mitochondrial functions in Drosophila. Rapid optogenetic cleavage of Split-Miro leads to a striking rearrangement of the mitochondrial network, which is mediated by mitochondrial interaction with the microtubules. Unexpectedly, this treatment did not impact the ability of mitochondria to buffer calcium or their association with the endoplasmic reticulum. While Split-Miro overexpression is sufficient to augment mitochondrial motility, sustained photocleavage shows that Split-Miro is surprisingly dispensable to maintain elevated mitochondrial processivity. In adult fly neurons in vivo, Split-Miro photocleavage affects both mitochondrial trafficking and neuronal activity. Furthermore, functional replacement of endogenous Miro with Split-Miro identifies its essential role in the regulation of locomotor activity in adult flies, demonstrating the feasibility of tuning animal behaviour by real-time loss of protein function.

Neuroprotection in glaucoma: Mechanisms beyond intraocular pressure lowering

Glaucoma is a common, complex, multifactorial neurodegenerative disease characterized by progressive dysfunction and then loss of retinal ganglion cells, the output neurons of the retina. Glaucoma is the most common cause of irreversible blindness and affects ∼80 million people worldwide with many more undiagnosed. The major risk factors for glaucoma are genetics, age, and elevated intraocular pressure. Current strategies only target intraocular pressure management and do not directly target the neurodegenerative processes occurring at the level of the retinal ganglion cell. Despite strategies to manage intraocular pressure, as many as 40% of glaucoma patients progress to blindness in at least one eye during their lifetime. As such, neuroprotective strategies that target the retinal ganglion cell and these neurodegenerative processes directly are of great therapeutic need. This review will cover the recent advances from basic biology to on-going clinical trials for neuroprotection in glaucoma covering degenerative mechanisms, metabolism, insulin signaling, mTOR, axon transport, apoptosis, autophagy, and neuroinflammation. With an increased understanding of both the basic and clinical mechanisms of the disease, we are closer than ever to a neuroprotective strategy for glaucoma.

Mitochondrial regulation of local supply of energy in neurons

Brain computation is metabolically expensive and requires the supply of significant amounts of energy. Mitochondria are highly specialized organelles whose main function is to generate cellular energy. Due to their complex morphologies, neurons are especially dependent on a set of tools necessary to regulate mitochondrial function locally in order to match energy provision with local demands. By regulating mitochondrial transport, neurons control the local availability of mitochondrial mass in response to changes in synaptic activity. Neurons also modulate mitochondrial dynamics locally to adjust metabolic efficiency with energetic demand. Additionally, neurons remove inefficient mitochondria through mitophagy. Neurons coordinate these processes through signalling pathways that couple energetic expenditure with energy availability. When these mechanisms fail, neurons can no longer support brain function giving rise to neuropathological states like metabolic syndromes or neurodegeneration.