The role of mitochondria in axon development and regeneration

Cytarabine prevents neuronal damage by enhancing AMPK to stimulate PINK1 / Parkin-involved mitophagy in Parkinson's disease model

Parkinson's disease (PD) is a common age-related neurodegenerative disorder, which may be largely due to the mitochondrial dysfunction and impaired mitophagy. Thus, it is of great importance to seek novel therapeutic strategies for PD targeting mitochondrial function and mitophagy. Cytarabine is a marine-derived antimetabolite used in the treatment of acute leukemia, which is also used in the study of the nervous system. In this study, we found that cytarabine pretreatment significantly inhibited the apoptosis and necrosis in the ROT-induced SH-SY5Y cell PD model and reduced the oxidative stress, as evidenced by the reduced MDA levels and the increased levels of SOD, GSH, and total antioxidant capacity. Cytarabine can also enhance mitochondrial vitality, improve mitochondrial respiratory function, and preserve mitochondrial morphology. Cytarabine also enhanced the expression of the mitophagy-related proteins PINK1, Parkin, VDAC1, and DJ-1, and its actions can be reversed by treatment with AMPK inhibitor - Compound C (CC), suggesting that AMPK activation may be involved in cytarabine-enhanced mitophagy. Furthermore, cytarabine can also ameliorate the motor symptoms in the MPTP-induced PD-like mice model, and attenuate the neuropathy in the substantia nigra (SN) of PD mice, while Compound C antagonized cytarabine's beneficial effects. In summary, marine-derived compound cytarabine could resist neurological damage both in vitro and in vivo by activating AMPK to increase PINK1/Parkin-induced mitophagy, serving as a promising disease modulator for treating neurodegenerative disease.

Bioenergetics of Axon Integrity and Its Regulation by Oligodendrocytes and Schwann Cells

Axons are long slender portions of neurons that transmit electrical impulses to maintain proper physiological functioning. Axons in the central nervous system (CNS) and peripheral nervous system (PNS) do not exist in isolation but are found to form a complex association with their surrounding glial cells, oligodendrocytes and Schwann cells. These cells not only myelinate them for faster nerve impulse conduction but are also known to provide metabolic support. Due to their incredible length, continuous growth, and distance from the cell body (where major energy synthesis takes place), axons are in high energetic demand. The stability and integrity of axons have long been associated with axonal energy levels. The current mini-review is thus focused on how axons accomplish their high energetic requirement in a cell-autonomous manner and how the surrounding glial cells help them in maintaining their integrity by fulfilling their energy demands (non-cell autonomous trophic support). The concept that adjacent glial cells (oligodendrocytes and Schwann cells) provide trophic support to axons and assist them in maintaining their integrity comes from the conditional knockout research and the studies in which the metabolic pathways controlling metabolism in these glial cells are modulated and its effect on axonal integrity is evaluated. In the later part of the mini-review, the current knowledge of axon-glial metabolic coupling during various neurodegenerative conditions was discussed, along with the potential lacunae in our current understanding of axon-glial metabolic coupling.

Genetic pathways in cerebral palsy: a review of the implications for precision diagnosis and understanding disease mechanisms

ABSTRACT

Cerebral palsy is a diagnostic term utilized to describe a group of permanent disorders affecting movement and posture. Patients with cerebral palsy are often only capable of limited activity, resulting from non-progressive disturbances in the fetal or neonatal brain. These disturbances severely impact the child's daily life and impose a substantial economic burden on the family. Although cerebral palsy encompasses various brain injuries leading to similar clinical outcomes, the understanding of its etiological pathways remains incomplete owing to its complexity and heterogeneity. This review aims to summarize the current knowledge on the genetic factors influencing cerebral palsy development. It is now widely acknowledged that genetic mutations and alterations play a pivotal role in cerebral palsy development, which can be further influenced by environmental factors. Despite continuous research endeavors, the underlying factors contributing to cerebral palsy remain are still elusive. However, significant progress has been made in genetic research that has markedly enhanced our comprehension of the genetic factors underlying cerebral palsy development. Moreover, these genetic factors have been categorized based on the identified gene mutations in patients through clinical genotyping, including thrombosis, angiogenesis, mitochondrial and oxidative phosphorylation function, neuronal migration, and cellular autophagy. Furthermore, exploring targeted genotypes holds potential for precision treatment. In conclusion, advancements in genetic research have substantially improved our understanding of the genetic causes underlying cerebral palsy. These breakthroughs have the potential to pave the way for new treatments and therapies, consequently shaping the future of cerebral palsy research and its clinical management. The investigation of cerebral palsy genetics holds the potential to significantly advance treatments and management strategies. By elucidating the underlying cellular mechanisms, we can develop targeted interventions to optimize outcomes. A continued collaboration between researchers and clinicians is imperative to comprehensively unravel the intricate genetic etiology of cerebral palsy.

DLK-dependent axonal mitochondrial fission drives degeneration following axotomy

Currently there are no effective treatments for an array of neurodegenerative disorders to a large part because cell-based models fail to recapitulate disease. Here we developed a reproducible human iPSC-based model where laser axotomy causes retrograde axon degeneration leading to neuronal cell death. Time-lapse confocal imaging revealed that damage triggers an apoptotic wave of mitochondrial fission proceeding from the site of injury to the soma. We demonstrated that this apoptotic wave is locally initiated in the axon by dual leucine zipper kinase (DLK). We found that mitochondrial fission and resultant cell death are entirely dependent on phosphorylation of dynamin related protein 1 (DRP1) downstream of DLK, revealing a new mechanism by which DLK can drive apoptosis. Importantly, we show that CRISPR mediated Drp1 depletion protected mouse retinal ganglion neurons from degeneration after optic nerve crush. Our results provide a powerful platform for studying degeneration of human neurons, pinpoint key early events in damage related neural death and new focus for therapeutic intervention.

Molecular cartography within axons

Recent advances in imaging methods begin to further illuminate the inner workings of neurons. Views of the axonal landscape through the lens of in situ cryo-electron tomography (cryo-ET) provide a high-resolution atlas of the macromolecular organization in near-native conditions, leading to our growing understanding of the vital roles of compositional and structural organization in maintaining neuronal homeostasis. In this review, we discuss the latest observations concerning the fundamental components found within neuronal compartments, with special emphasis on the axon, branch points, and growth cone. We describe the similarity and difference in organization of organelles and molecules in varying compartments. Finally, we highlight outstanding questions on the dynamics and localization of various components along the axon that may be answered using orthogonal approaches.

Neuronal glycolysis: focus on developmental morphogenesis and localized subcellular functions

Glycolysis is a metabolic pathway that directly generates adenosine triphosphate (ATP), provides metabolic intermediates for anabolism, and supports mitochondrial oxidative phosphorylation. This review addresses recent advances in our understanding of the functions of neuronal glycolysis during the development of neuronal morphogenesis, focusing on the emergent concept that neuronal glycolysis serves local subcellular bioenergetic roles in maintaining neuronal function. The current evidence indicates that glycolysis is subcellularly targeted to specific organelles and molecular machinery to locally supply bioenergetic support for defined subcellular mechanisms underlying neuronal morphogenesis (i.e. axon extension, axon retraction and axonal transport). Thus, the concept of glycolysis as a "housekeeping" mechanism in neurons would benefit revision and future work aim to further define its subcellular functions at varied developmental stages.

Exposure to different surface-modified polystyrene nanoparticles caused anxiety, depression, and social deficit in mice via damaging mitochondria in neurons

Nanoplastics (NPs) are unavoidable hazardous materials that result from the human production and use of plastics. While there is evidence that NPs can bioaccumulate in the brain, no enough research regarding the pathways by which NPs reach the brain was conducted, and it is also urgently needed to evaluate the health threat to the nervous system. Here, we observed accumulation of polystyrene nanoplastics (PS-NPs) with different surface modifications (PS, PS-COOH, and PS-NH2) in mouse brains. Further studies showed that PS-NPs disrupted the tight junctions between endothelial cells and transport into endothelial cells via the endocytosis and macropinocytosis pathways. Additionally, NPs exposure induced a series of alternations in behavioral tests, including anxiety- and depression-like changes and impaired social interaction performance. Further results identified that NPs could be internalized into neurons and localized in the mitochondria, bringing about mitochondrial dysfunction and a concurrent decline of ATP production, which might be associated with abnormal animal behaviors. The findings provide novel insights into the neurotoxicity of NPs and provide a basis for the formulation of policy on plastic production and usage by relevant government agencies.

Stat3 Has a Different Role in Axon Growth During Development Than It Does in Axon Regeneration After Injury

Signal transducer and activator of transcription 3 (STAT3) is essential for neural development and regeneration as a key transcription factor and mitochondrial activator. However, the mechanism of Stat3 in axon development and regeneration has not been fully understood. In this study, using zebrafish posterior lateral line (PLL) axons, we demonstrate that Stat3 plays distinct roles in PLL axon embryonic growth and regeneration. Our experiments indicate that stat3 is required for PLL axon extension. In stat3 mutant zebrafish, the PLL axon ends were stalled at the level of the cloaca, and expression of stat3 rescues the PLL axon growth in a cell-autonomous manner. Jak/Stat signaling inhibition did not affect PLL axon growth indicating Jak/Stat was dispensable for PLL axon growth. In addition, we found that Stat3 was co-localized with mitochondria in PLL axons and important for the mitochondrial membrane potential and ATPase activity. The PLL axon growth defect of stat3 mutants was mimicked and rescued by rotenone and DCHC treatment, respectively, which suggests that Stat3 regulates PLL axon growth through mitochondrial Stat3. By contrast, mutation of stat3 or Jak/Stat signaling inhibition retarded PLL axon regeneration. Meanwhile, we also found Schwann cell migration was also inhibited in stat3 mutants. Taken together, Stat3 is required for embryonic PLL axon growth by regulating the ATP synthesis efficiency of mitochondria, whereas Stat3 stimulates PLL axon regeneration by regulating Schwann cell migration via Jak/Stat signaling. Our findings show a new mechanism of Stat3 in axon growth and regeneration.

Mitochondrial Transportation, Transplantation, and Subsequent Immune Response in Alzheimer's Disease: An Update

Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by memory impairment and a progressive decline in cognitive function. Mitochondrial dysfunction has been identified as an important contributor to the development of AD, leading to oxidative stress and energy deficits within the brain. While current treatments for AD aim to alleviate symptoms, there is an urgent need to target the underlying mechanisms. The emerging field of mitotherapy, which involves the transplantation of healthy mitochondria into damaged cells, has gained substantial attention and has shown promising results. However, research in the context of AD remains limited, necessitating further investigations. In this review, we summarize the mitochondrial pathways that contribute to the progression of AD. Additionally, we discuss mitochondrial transfer among brain cells and mitotherapy, with a focus on different administration routes, various sources of mitochondria, and potential modifications to enhance transplantation efficacy. Finally, we review the limited available evidence regarding the immune system's response to mitochondrial transplantation in damaged brain regions.

Cyfip2 controls the acoustic startle threshold through FMRP, actin polymerization, and GABAB receptor function

Animals process a constant stream of sensory input, and to survive they must detect and respond to dangerous stimuli while ignoring innocuous or irrelevant ones. Behavioral responses are elicited when certain properties of a stimulus such as its intensity or size reach a critical value, and such behavioral thresholds can be a simple and effective mechanism to filter sensory information. For example, the acoustic startle response is a conserved and stereotyped defensive behavior induced by sudden loud sounds, but dysregulation of the threshold to initiate this behavior can result in startle hypersensitivity that is associated with sensory processing disorders including schizophrenia and autism. Through a previous forward genetic screen for regulators of the startle threshold a nonsense mutation in Cytoplasmic Fragile X Messenger Ribonucleoprotein (FMRP)-interacting protein 2 (cyfip2) was found that causes startle hypersensitivity in zebrafish larvae, but the molecular mechanisms by which Cyfip2 establishes the acoustic startle threshold are unknown. Here we used conditional transgenic rescue and CRISPR/Cas9 to determine that Cyfip2 acts though both Rac1 and FMRP pathways, but not the closely related FXR1 or FXR2, to establish the acoustic startle threshold during early neurodevelopment. To identify proteins and pathways that may be downstream effectors of Rac1 and FMRP, we performed a candidate-based drug screen that indicated that Cyfip2 can also act acutely to maintain the startle threshold branched actin polymerization and N-methyl D-aspartate receptors (NMDARs). To complement this approach, we used unbiased discovery proteomics to determine that loss of Cyfip2 alters cytoskeletal and extracellular matrix components while also disrupting oxidative phosphorylation and GABA receptor signaling. Finally, we functionally validated our proteomics findings by showing that activating GABAB receptors, which like NMDARs are also FMRP targets, restores normal startle sensitivity in cyfip2 mutants. Together, these data reveal multiple mechanisms by which Cyfip2 regulates excitatory/inhibitory balance in the startle circuit to control the processing of acoustic information.

Chondroitin Sulfate Proteoglycans Revisited: Its Mechanism of Generation and Action for Spinal Cord Injury

Reactive astrocytes (RAs) produce chondroitin sulfate proteoglycans (CSPGs) in large quantities after spinal cord injury (SCI) and inhibit axon regeneration through the Rho-associated protein kinase (ROCK) pathway. However, the mechanism of producing CSPGs by RAs and their roles in other aspects are often overlooked. In recent years, novel generation mechanisms and functions of CSPGs have gradually emerged. Extracellular traps (ETs), a new recently discovered phenomenon in SCI, can promote secondary injury. ETs are released by neutrophils and microglia, which activate astrocytes to produce CSPGs after SCI. CSPGs inhibit axon regeneration and play an important role in regulating inflammation as well as cell migration and differentiation; some of these regulations are beneficial. The current review summarized the process of ET-activated RAs to generate CSPGs at the cellular signaling pathway level. Moreover, the roles of CSPGs in inhibiting axon regeneration, regulating inflammation, and regulating cell migration and differentiation were discussed. Finally, based on the above process, novel potential therapeutic targets were proposed to eliminate the adverse effects of CSPGs.

Development of Liposomes That Target Axon Terminals Encapsulating Berberine in Cultured Primary Neurons

Most of the energy in neurons is produced in mitochondria. Mitochondria generate the ATP that is essential for neuronal growth, function, and regeneration. Mitochondrial axonal transport plays a crucial role in maintaining neuronal homeostasis and biological activity. Decreased mitochondrial axonal transport at axon terminals, where the metabolism of substances is likely to be delayed, may contribute to neurological dysfunction. Therefore, regulation of mitochondrial dynamics at axon terminals has attracted considerable interest as a strategy to modulate neuronal function. Nanoparticles may be useful in controlling local mitochondrial dynamics. Nevertheless, there are few reports on the influence of drug delivery that nanoparticles impart on the mitochondrial dynamics in neurons. This paper reports the results of a study using liposomes (LPs) to examine local drug delivery and pharmacological actions on neurons. We tested berberine (BBR), which is an activator of AMP-activated protein kinase (AMPK), to examine the utility of this drug as a cellular energy sensor. Axon terminals targeting LPs were prepared. The amount of axon terminals targeting LPs was increased compared with treatment using cationic LPs. Moreover, axon terminal-targeting LPs increased anterograde transport by about 40% compared with that of either naked BBR or cationic LPs and suppressed axonal retraction. Our findings suggest that local drug delivery to neurons is important for enhancing pharmacological activity in axon terminals.

Local glycolysis fuels actomyosin contraction during axonal retraction

In response to repulsive cues, axonal growth cones can quickly retract. This requires the prompt activity of contractile actomyosin, which is formed by the non-muscle myosin II (NMII) bound to actin filaments. NMII is a molecular motor that provides the necessary mechanical force at the expense of ATP. Here, we report that this process is energetically coupled to glycolysis and is independent of cellular ATP levels. Induction of axonal retraction requires simultaneous generation of ATP by glycolysis, as shown by chemical inhibition and genetic knock-down of GAPDH. Co-immunoprecipitation and proximal-ligation assay showed that actomyosin associates with ATP-generating glycolytic enzymes and that this association is strongly enhanced during retraction. Using microfluidics, we confirmed that the energetic coupling between glycolysis and actomyosin necessary for axonal retraction is localized to the growth cone and near axonal shaft. These results indicate a tight coupling between on-demand energy production by glycolysis and energy consumption by actomyosin contraction suggesting a function of glycolysis in axonal guidance.

Mitochondrial, cell cycle control and neuritogenesis alterations in an iPSC-based neurodevelopmental model for schizophrenia

Schizophrenia is a severe psychiatric disorder of neurodevelopmental origin that affects around 1% of the world's population. Proteomic studies and other approaches have provided evidence of compromised cellular processes in the disorder, including mitochondrial function. Most of the studies so far have been conducted on postmortem brain tissue from patients, and therefore, do not allow the evaluation of the neurodevelopmental aspect of the disorder. To circumvent that, we studied the mitochondrial and nuclear proteomes of neural stem cells (NSCs) and neurons derived from induced pluripotent stem cells (iPSCs) from schizophrenia patients versus healthy controls to assess possible alterations related to energy metabolism and mitochondrial function during neurodevelopment in the disorder. Our results revealed differentially expressed proteins in pathways related to mitochondrial function, cell cycle control, DNA repair and neuritogenesis and their possible implication in key process of neurodevelopment, such as neuronal differentiation and axonal guidance signaling. Moreover, functional analysis of NSCs revealed alterations in mitochondrial oxygen consumption in schizophrenia-derived cells and a tendency of higher levels of intracellular reactive oxygen species (ROS). Hence, this study shows evidence that alterations in important cellular processes are present during neurodevelopment and could be involved with the establishment of schizophrenia, as well as the phenotypic traits observed in adult patients. Neural stem cells (NSCs) and neurons were derived from induced pluripotent stem cells (iPSCs) from schizophrenia patients and controls. Proteomic analyses were performed on the enriched mitochondrial and nuclear fractions of NSCs and neurons. Whole-cell proteomic analysis was also performed in neurons. Our results revealed alteration in proteins related to mitochondrial function, cell cycle control, among others. We also performed energy pathway analysis and reactive oxygen species (ROS) analysis of NSCs, which revealed alterations in mitochondrial oxygen consumption and a tendency of higher levels of intracellular ROS in schizophrenia-derived cells.

Mitochondrial trafficking as a protective mechanism against chemotherapy drug-induced peripheral neuropathy: Identifying the key site of action

AIMS

Chemotherapy induced peripheral neuropathy (CIPN) is a common side effect seen in patients who have undergone most chemotherapy treatments to which there are currently no treatment methods. CIPN has been shown to cause axonal degeneration leading to Peripheral Neuropathy (PN), which can lead to major dosage reduction and may prevent further chemotherapy treatment due to oftentimes debilitating pain. Previously, we have determined the site-specific action of Paclitaxel (PTX), a microtubule targeting agent, as well as the neuroprotective effect of Fluocinolone Acetonide (FA) against Paclitaxel Induced Peripheral Neuropathy (PIPN).

MAIN METHODS

Mitochondrial trafficking analysis was determined for all sample sets, wherein FA showed enhanced anterograde (axonal) mitochondrial trafficking leading to neuroprotective effects for all samples.

KEY FINDINGS

Using this system, we demonstrate that PTX, Monomethyl auristatin E (MMAE), and Vincristine (VCR), are toxic at clinically prescribed levels when treated focally to axons. However, Cisplatin (CDDP) was determined to have a higher toxicity when treated to cell bodies. Although having different targeting mechanisms, the administration of FA was determined to have a significant neuroprotective effect for against all chemotherapy drugs tested.

SIGNIFICANCE

This study identifies key insights regarding site of action and neuroprotective strategies to further development as potential therapeutics against CIPN. FA was treated alongside each chemotherapy drug to identify the neuroprotective effect against CIPN, where FA was found to be neuroprotective for all drugs tested. This study found that treatment with FA led to an enhancement in the anterograde movement of mitochondria based on fluorescent imaging.

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.

Syntaphilin Inactivation Can Enhance Axonal Mitochondrial Transport to Improve Spinal Cord Injury

Mitochondria are important organelle of eukaryotic cells. They consists of a large number of different proteins that provide most of the ATP and supply power for the growth, function, and regeneration of neurons. Therefore, smitochondrial transport ensures that adequate ATP is supplied for metabolic activities. Spinal cord injury (SCI), a detrimental condition, has high morbidity and mortality rates. Currently, the available treatments only provide symptomatic relief for long-term disabilities. Studies have implicated mitochondrial transport as a critical factor in axonal regeneration. Hence, enhancing mitochondrial transports could be beneficial for ameliorating SCI. Syntaphilin (Snph) is a mitochondrial docking protein that acts as a "static anchor," and its inhibition enhances mitochondrial transports. Therefore, Snph as a key mediator of mitochondrial transports, may contribute to improving axonal regeneration following SCI. Herein, we examine Snph's biological effects and its relation to mitochondrial pathway. Then, we elaborate on mitochondrial transports after SCI, the possible role of Snph in SCI, and some possible therapeutic approaches by Snph.

Decoding muscle-resident Schwann cell dynamics during neuromuscular junction remodeling

Understanding neuromuscular junction (NMJ) repair mechanisms is essential for addressing degenerative neuromuscular conditions. Here, we focus on the role of muscle-resident Schwann cells in NMJ reinnervation. In young Sod1-/- mice, a model of progressive NMJ degeneration, we identified a clear NMJ 'regenerative window' that allowed us to define regulators of reinnervation and crossing Sod1-/- mice with S100GFP-tg mice permitted visualization and analysis of Schwann cells. High-resolution imaging and single-cell RNA sequencing provide a detailed analysis of Schwann cell number, morphology, and transcriptome revealing multiple subtypes, including a previously unrecognized terminal Schwann cell (tSC) population expressing a synapse promoting signature. We also discovered a novel SPP1-driven cellular interaction between myelin Schwann cells and tSCs and show that it promotes tSC proliferation and reinnervation following nerve injury in wild type mice. Our findings offer important insights into molecular regulators critical in NMJ reinnervation that are mediated through tSCs to maintain NMJ function.

Iron in multiple sclerosis - Neuropathology, immunology, and real-world considerations

Iron is an essential element involved in a multitude of bodily processes. It is tightly regulated, as elevated deposition in tissues is associated with diseases such as multiple sclerosis (MS). Iron accumulation in the central nervous system (CNS) of MS patients is linked to neurotoxicity through mechanisms including oxidative stress, glutamate excitotoxicity, misfolding of proteins, and ferroptosis. In the past decade, the combination of MRI and histopathology has enhanced our understanding of iron deposition in MS pathophysiology, including in the pro-inflammatory and neurotoxicity of iron-laden rims of chronic active lesions. In this regard, iron accumulation may not only have an impact on different CNS-resident cells but may also promote the innate and adaptive immune dysfunctions in MS. Although there are discordant results, most studies indicate lower levels of iron but higher amounts of the iron storage molecule ferritin in the circulation of people with MS. Considering the importance of iron, there is a need for evidence-guided recommendation for dietary intake in people living with MS. Potential novel therapeutic approaches include the regulation of iron levels using next generation iron chelators, as well as therapies to interfere with toxic consequences of iron overload including antioxidants in MS.

Actin cytoskeletal dynamics do not impose an energy drain on growth cone bioenergetics

The regulation of the intracellular level of ATP is a fundamental aspect of bioenergetics. Actin cytoskeletal dynamics have been reported to be an energetic drain in developing neurons and platelets. We addressed the role of actin dynamics in primary embryonic chicken neurons using luciferase assays, and by measurement of the ATP/ADP ratio using the ratiometric reporter PercevalHR and the ATP level using the ratiometric reporter mRuby-iATPSnFR. None of the methods revealed an effect of suppressing actin dynamics on the decline in the neuronal ATP level or the ATP/ADP ratio following shutdown of ATP production. Similarly, we find that treatments that elevate or suppress actin dynamics do not alter the ATP/ADP ratio in growth cones, the subcellular domain with the highest actin dynamics in developing neurons. Collectively, the data indicate that actin cytoskeletal dynamics are not a significant energy drain in developing neurons and that the ATP/ADP ratio is maintained when energy utilization varies. Discrepancies between prior work and the current data are discussed with emphasis on methodology and interpretation of the data.

How neurons maintain their axons long-term: an integrated view of axon biology and pathology

Axons are processes of neurons, up to a metre long, that form the essential biological cables wiring nervous systems. They must survive, often far away from their cell bodies and up to a century in humans. This requires self-sufficient cell biology including structural proteins, organelles, and membrane trafficking, metabolic, signalling, translational, chaperone, and degradation machinery-all maintaining the homeostasis of energy, lipids, proteins, and signalling networks including reactive oxygen species and calcium. Axon maintenance also involves specialised cytoskeleton including the cortical actin-spectrin corset, and bundles of microtubules that provide the highways for motor-driven transport of components and organelles for virtually all the above-mentioned processes. Here, we aim to provide a conceptual overview of key aspects of axon biology and physiology, and the homeostatic networks they form. This homeostasis can be derailed, causing axonopathies through processes of ageing, trauma, poisoning, inflammation or genetic mutations. To illustrate which malfunctions of organelles or cell biological processes can lead to axonopathies, we focus on axonopathy-linked subcellular defects caused by genetic mutations. Based on these descriptions and backed up by our comprehensive data mining of genes linked to neural disorders, we describe the 'dependency cycle of local axon homeostasis' as an integrative model to explain why very different causes can trigger very similar axonopathies, providing new ideas that can drive the quest for strategies able to battle these devastating diseases.

The Translocase of the Outer Mitochondrial Membrane (TOM40) is required for mitochondrial dynamics and neuronal integrity in Dorsal Root Ganglion Neurons

Polymorphisms and altered expression of the Translocase of the Outer Mitochondrial Membrane - 40 kD (Tom40) are observed in neurodegenerative disease subjects. We utilized in vitro cultured dorsal root ganglion (DRG) neurons to investigate the association of TOM40 depletion to neurodegeneration, and to unravel the mechanism of neurodegeneration induced by decreased levels of TOM40 protein. We provide evidence that severity of neurodegeneration induced in the TOM40 depleted neurons increases with the increase in the depletion of TOM40 and is exacerbated by an increase in the duration of TOM40 depletion. We also demonstrate that TOM40 depletion causes a surge in neuronal calcium levels, decreases mitochondrial motility, increases mitochondrial fission, and decreases neuronal ATP levels. We observed that alterations in the neuronal calcium homeostasis and mitochondrial dynamics precede BCL-xl and NMNAT1 dependent neurodegenerative pathways in the TOM40 depleted neurons. This data also suggests that manipulation of BCL-xl and NMNAT1 may be of therapeutic value in TOM40 associated neurodegenerative disorders.

Pyruvate dehydrogenase beta subunit (Pdhb) promotes peripheral axon regeneration by regulating energy supply and gene expression

Key metabolic enzymes not only regulate Glucose, lipid, amino acid metabolism to serve the cellular energy needs, but also modulate noncanonical or nonmetabolic signaling pathway such as gene expression, cell-cycle progression, DNA repair, apoptosis and cell proliferation in regulating the pathologic progression of disease. However, the role of glycometabolism in peripheral nerve axon regeneration is little known. In this study, we investigated the expression of Pyruvate dehydrogenase E1(PDH), a key enzyme linking glycolysis and the tricarboxylic acid (TCA) cycle, with qRT-PCR and found that pyruvate dehydrogenase beta subunit (Pdhb) is up-regulated at the early stage during peripheral nerve injury. The knockdown of Pdhb inhibits neurite outgrowth of primary DRG neurons in vitro and restrains axon regeneration of sciatic nerve after crush injury. Pdhb overexpression promoting axonal regeneration is reversed by knockdown of Monocarboxylate transporter 2(Mct2), a transporter involved in the transport and metabolism of lactate, indicating Pdhb promoting axon regeneration depends on lactate for energy supply. Given the nucleus-localization of Pdhb, further analysis revealed that Pdhb enhances the acetylation of H3K9 and affecting the expression of genes involved in arachidonic acid metabolism and Ras signaling pathway, such as Rsa-14-44 and Pla2g4a, thereby promoting axon regeneration. Collectively, our data indicates that Pdhb is a positive dual modulator of energy generation and gene expression in regulating peripheral axon regeneration.

Maternal pre-eclampsia serum increases neurite growth and mitochondrial function through a potential IL-6-dependent mechanism in differentiated SH-SY5Y cells

Introduction: Pre-eclampsia (PE) is a common and serious hypertensive disorder of pregnancy, which affects 3%-5% of first-time pregnancies and is a leading cause of maternal and neonatal morbidity and mortality. Prenatal exposure to PE is associated with an increased risk of neurodevelopmental disorders in affected offspring, although the cellular and molecular basis of this increased risk is largely unknown. Methods: Here, we examined the effects of exposure to maternal serum from women with PE or a healthy uncomplicated pregnancy on the survival, neurite growth and mitochondrial function of neuronally differentiated human SH-SY5Y neuroblastoma cells, which are commonly used to study neurite growth. Neurite growth and mitochondrial function are two strongly linked neurodevelopmental parameters in which alterations have been implicated in neurodevelopmental disorders. Following this, we investigated the pleiotropic cytokine interleukin-6 (IL-6) levels as a potential mechanism. Results: Cells exposed to 3% (v/v) PE serum for 72 h exhibited increased neurite growth (p < 0.05), which was validated in the human neural progenitor cell line, ReNcell^® VM (p < 0.01), and mitochondrial respiration (elevated oxygen consumption rate (p < 0.05), basal mitochondrial respiration, proton leak, ATP synthesis, and non-mitochondrial respiration) compared to control serum-treated cells. ELISA analysis showed elevations in maternal IL-6 in PE sera (p < 0.05) and placental explants (p < 0.05). In support of this, SH-SY5Y cells exposed to 3% (v/v) PE serum for 24 h had increased phospho-STAT3 levels, which is a key intracellular mediator of IL-6 signalling (p < 0.05). Furthermore, treatment with anti-IL-6 neutralizing antibody blocked the effects of PE serum on neurite growth (p < 0.05), and exposure to IL-6 promoted neurite growth in SH-SY5Y cells (p < 0.01). Discussion: Collectively these data show elevated serum levels of maternal IL-6 in PE, which increases neurite growth and mitochondrial function in SH-SY5Y cells. This rationalizes the further study of IL-6 as a potential mediator between PE exposure and neurodevelopmental outcome in the offspring.

The choroid plexus: a missing link in our understanding of brain development and function

Studies of the choroid plexus lag behind those of the more widely known blood-brain barrier, despite a much longer history. This review has two overall aims. The first is to outline long-standing areas of research where there are unanswered questions, such as control of cerebrospinal fluid (CSF) secretion and blood flow. The second aim is to review research over the past 10 years where the focus has shifted to the idea that there are choroid plexuses located in each of the brain's ventricles that make specific contributions to brain development and function through molecules they generate for delivery via the CSF. These factors appear to be particularly important for aspects of normal brain growth. Most research carried out during the twentieth century dealt with the choroid plexus, a brain barrier interface making critical contributions to the composition and stability of the brain's internal environment throughout life. More recent research in the twenty-first century has shown the importance of choroid plexus-generated CSF in neurogenesis, influence of sex and other hormones on choroid plexus function, and choroid plexus involvement in circadian rhythms and sleep. The advancement of technologies to facilitate delivery of brain-specific therapies via the CSF to treat neurological disorders is a rapidly growing area of research. Conversely, understanding the basic mechanisms and implications of how maternal drug exposure during pregnancy impacts the developing brain represents another key area of research.

Mitochondrial regulatory mechanisms in spinal cord injury: A narrative review

Spinal cord injury is a severe central nervous system injury that results in the permanent loss of motor, sensory, and autonomic functions below the level of injury with limited recovery. The pathological process of spinal cord injury includes primary and secondary injuries, characterized by a progressive cascade. Secondary injury impairs the ability of the mitochondria to maintain homeostasis and leads to calcium overload, excitotoxicity, and oxidative stress, further exacerbating the injury. The defective mitochondrial function observed in these pathologies accelerates neuronal cell death and inhibits regeneration. Treatment of spinal cord injury by preserving mitochondrial biological function is a promising, although still underexplored, therapeutic strategy. This review aimed to explore mitochondrial-based therapeutic advances after spinal cord injury. Specifically, it briefly describes the characteristics of spinal cord injury. It then broadly discusses the drugs used to protect the mitochondria (e.g., cyclosporine A, acetyl-L-carnitine, and alpha-tocopherol), phenomena associated with mitochondrial damage processes (e.g., mitophagy, ferroptosis, and cuproptosis), mitochondrial transplantation for nerve cell regeneration, and innovative mitochondrial combined protection therapy.

The ANC-1 (Nesprin-1/2) organelle-anchoring protein functions through mitochondria to polarize axon growth in response to SLT-1

A family of giant KASH proteins, including C. elegans ANC-1 and mammalian Nesprin-1 and -2, are involved in organelle anchoring and are associated with multiple neurodevelopmental disorders including autism, bipolar disorder, and schizophrenia. However, little is known about how these proteins function in neurons. Moreover, the role of organelle anchoring in axon development is poorly understood. Here, we report that ANC-1 functions with the SLT-1 extracellular guidance cue to polarize ALM axon growth. This role for ANC-1 is specific to its longer ANC-1A and ANC-1C isoforms, suggesting that it is mechanistically distinct from previously described roles for ANC-1. We find that ANC-1 is required for the localization of a cluster of mitochondria to the base of the proximal axon. Furthermore, genetic and pharmacological studies indicate that ANC-1 functions with mitochondria to promote polarization of ALM axon growth. These observations reveal a mechanism whereby ANC-1 functions through mitochondria to polarize axon growth in response to SLT-1.

Traumatic brain injury recapitulates developmental changes of axons

During development, half of brain white matter axons are maintained for growth, while the remainder undergo developmental axon degeneration. After traumatic brain injury (TBI), injured axons also appear to follow pathways leading to either degeneration or repair. These observations raise the intriguing, but unexamined possibility that TBI recapitulates developmental axonal programs. Here, we examined axonal changes in the developing brain in young rats and after TBI in adult rat. Multiple shared changes in axonal microtubule (MT) through tubulin post-translational modifications and MT associated proteins (MAPs), tau and MAP6, were found in both development and TBI. Specifically, degenerating axons in both development and TBI underwent phosphorylation of tau and excessive tubulin tyrosination, suggesting MT instability and depolyermization. Conversely, nearby axons without degenerating morphologies, had increased MAP6 expression and maintenance of tubulin acetylation, suggesting enhanced MT stabilization, thereby supporting survival or repair. Quantitative proteomics revealed similar signaling pathways of axon degeneration and growth/repair, including protein clusters and networks. This comparison approach demonstrates how focused evaluation of developmental processes may provide insight into pathways initiated by TBI. In particular, the data suggest that TBI may reawaken dormant axonal programs that direct axons towards either degeneration or growth/repair, supporting further study in this area.

Mitochondrial Dysfunction in Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a devastating neuromuscular disorder caused by recessive mutations in the SMN1 gene, globally affecting ~8-14 newborns per 100,000. The severity of the disease depends on the residual levels of functional survival of motor neuron protein, SMN. SMN is a ubiquitously expressed RNA binding protein involved in a plethora of cellular processes. In this review, we discuss the effects of SMN loss on mitochondrial functions in the neuronal and muscular systems that are the most affected in patients with spinal muscular atrophy. Our aim is to highlight how mitochondrial defects may contribute to disease progression and how restoring mitochondrial functionality may be a promising approach to develop new therapies. We also collected from previous studies a list of transcripts encoding mitochondrial proteins affected in various SMA models. Moreover, we speculate that in adulthood, when motor neurons require only very low SMN levels, the natural deterioration of mitochondria associated with aging may be a crucial triggering factor for adult spinal muscular atrophy, and this requires particular attention for therapeutic strategies.

Lower Availability of Mitochondrial Complex I in Anterior Cingulate Cortex in Autism: A Positron Emission Tomography Study

OBJECTIVE

Mitochondrial dysfunction has been implicated in the pathophysiology of autism spectrum disorder (ASD) in previous studies of postmortem brain or peripheral samples. The authors investigated whether and where mitochondrial dysfunction occurs in the living brains of individuals with ASD and to identify the clinical correlates of detected mitochondrial dysfunction.

METHODS

This case-control study used positron emission tomography (PET) with 2-tert-butyl-4-chloro-5-{6-[2-(2-[¹⁸F]fluoroethoxy)-ethoxy]-pyridin-3-ylmethoxy}-2H-pyridazin-3-one ([¹⁸F]BCPP-EF), a radioligand that binds to the mitochondrial electron transport chain complex I, to examine the topographical distribution of mitochondrial dysfunction in living brains of individuals with ASD. Twenty-three adult males with high-functioning ASD, with no psychiatric comorbidities and free of psychotropic medication, and 24 typically developed males with no psychiatric diagnoses, matched with the ASD group on age, parental socioeconomic background, and IQ, underwent [¹⁸F]BCPP-EF PET measurements. Individuals with mitochondrial disease were excluded by clinical evaluation and blood tests for abnormalities in lactate and pyruvate levels.

RESULTS

Among the brain regions in which mitochondrial dysfunction has been reported in postmortem studies of autistic brains, participants with ASD had significantly decreased [¹⁸F]BCPP-EF availability specifically in the anterior cingulate cortex compared with typically developed participants. The regional specificity was revealed by a significant interaction between diagnosis and brain regions. Moreover, the lower [¹⁸F]BCPP-EF availability in the anterior cingulate cortex was significantly correlated with the more severe ASD core symptom of social communication deficits.

CONCLUSIONS

This study provides direct evidence to link in vivo brain mitochondrial dysfunction with ASD pathophysiology and its communicational deficits. The findings support the possibility that mitochondrial electron transport chain complex I is a novel therapeutic target for ASD core symptoms.

Glutamatergic and N-Acetylaspartate Metabolites in Bipolar Disorder: A Systematic Review and Meta-Analysis of Proton Magnetic Resonance Spectroscopy Studies

The exact neurobiological mechanisms of bipolar disorder (BD) remain unknown. However, some neurometabolites could be implicated, including Glutamate (Glu), Glutamine (Gln), Glx, and N-acetylaspartate (NAA). Proton Magnetic Resonance Spectroscopy (¹H-MRS) allows one to quantify these metabolites in the human brain. Thus, we conducted a systematic review and meta-analysis of the literature to compare their levels between BD patients and healthy controls (HC). The main inclusion criteria for inclusion were ¹H-MRS studies comparing levels of Glu, Gln, Glx, and NAA in the prefrontal cortex (PFC), anterior cingulate cortex (ACC), and hippocampi between patients with BD in clinical remission or a major depressive episode and HC. Thirty-three studies were included. NAA levels were significantly lower in the left white matter PFC (wmPFC) of depressive and remitted BD patients compared to controls and were also significantly higher in the left dorsolateral PFC (dlPFC) of depressive BD patients compared to HC. Gln levels were significantly higher in the ACC of remitted BD patients compared to in HC. The decreased levels of NAA of BD patients may be related to the alterations in neuroplasticity and synaptic plasticity found in BD patients and may explain the deep white matter hyperintensities frequently observed via magnetic resonance imagery.

Deltamethrin induces apoptosis in cerebrum neurons of quail via promoting endoplasmic reticulum stress and mitochondrial dysfunction

Deltamethrin (DLM) is a widely used and highly effective insecticide. DLM exposure is harmful to animal and human. Quail, as a bird model, has been widely used in the field of toxicology. However, there is little information available in the literature about quail cerebrum damage caused by DLM. Here, we investigated the effect of DLM on quail cerebrum neurons. Four groups of healthy quails were assigned (10 quails in each group), respectively given 0, 15, 30, and 45 mg/kg DLM by gavage for 12 weeks. Through the measurements of quail cerebrum, it was found that DLM exposure induced obvious histological changes, oxidative stress, and neurons apoptosis. To further explore the possible molecular mechanisms, we performed real-time quantitative PCR to detect the expression of endoplasmic reticulum (ER) stress-related mRNA such as glucose regulated protein 78 kD, activating transcription factor 6, inositol requiring enzyme, and protein kinase RNA (PKR)-like ER kinase. In addition, we detected ATP content in quail cerebrum to evaluate the functional status of mitochondria. The study showed that DLM exposure significantly increased the expression of ER stress-related mRNA and decreased ATP content in quail cerebrum tissues. These results suggest that chronic exposure to DLM induces apoptosis of quail cerebrum neurons via promoting ER stress and mitochondrial dysfunction. Furthermore, our results provide a novel explanation for DLM-induced apoptosis of avian cerebrum neurons.

Programming axonal mitochondrial maintenance and bioenergetics in neurodegeneration and regeneration

Mitochondria generate ATP essential for neuronal growth, function, and regeneration. Due to their polarized structures, neurons face exceptional challenges to deliver mitochondria to and maintain energy homeostasis throughout long axons and terminal branches where energy is in high demand. Chronic mitochondrial dysfunction accompanied by bioenergetic failure is a pathological hallmark of major neurodegenerative diseases. Brain injury triggers acute mitochondrial damage and a local energy crisis that accelerates neuron death. Thus, mitochondrial maintenance defects and axonal energy deficits emerge as central problems in neurodegenerative disorders and brain injury. Recent studies have started to uncover the intrinsic mechanisms that neurons adopt to maintain (or reprogram) axonal mitochondrial density and integrity, and their bioenergetic capacity, upon sensing energy stress. In this review, we discuss recent advances in how neurons maintain a healthy pool of axonal mitochondria, as well as potential therapeutic strategies that target bioenergetic restoration to power neuronal survival, function, and regeneration.

Djhsp60 Is Required for Planarian Regeneration and Homeostasis

HSP60, a well-known mitochondrial chaperone, is essential for mitochondrial homeostasis. HSP60 deficiency causes dysfunction of the mitochondria and is lethal to animal survival. Here, we used freshwater planarian as a model system to investigate and uncover the roles of HSP60 in tissue regeneration and homeostasis. HSP60 protein is present in all types of cells in planarians, but it is relatively rich in stem cells and head neural cells. Knockdown of HSP60 by RNAi causes head regression and the loss of regenerating abilities, which is related to decrease in mitotic cells and inhibition of stem cell-related genes. RNAi-HSP60 disrupts the structure of the mitochondria and inhibits the mitochondrial-related genes, which mainly occur in intestinal tissues. RNAi-HSP60 also damages the integrity of intestinal tissues and downregulates intestine-expressed genes. More interestingly, RNAi-HSP60 upregulates the expression of the cathepsin L-like gene, which may be the reason for head regression and necrotic-like cell death. Taking these points together, we propose a model illustrating the relationship between neoblasts and intestinal cells, and also highlight the essential role of the intestinal system in planarian regeneration and tissue homeostasis.

Elp1 is required for development of visceral sensory peripheral and central circuitry

Cardiovascular instability and a blunted respiratory drive in hypoxic conditions are hallmark features of the genetic sensory and autonomic neuropathy, familial dysautonomia (FD). FD results from a mutation in the gene ELP1, the encoded protein of which is a scaffolding subunit of the six-subunit Elongator complex. In mice, we and others have shown that Elp1 is essential for the normal development of neural crest-derived dorsal root ganglia sensory neurons. Whether Elp1 is also required for development of ectodermal placode-derived visceral sensory receptors, which are required for normal baroreception and chemosensory responses, has not been investigated. Using mouse models for FD, we here show that the entire circuitry underlying baroreception and chemoreception is impaired due to a requirement for Elp1 in the visceral sensory neuron ganglia, as well as for normal peripheral target innervation, and in their central nervous system synaptic partners in the medulla. Thus, Elp1 is required in both placode- and neural crest-derived sensory neurons, and its reduction aborts the normal development of neuronal circuitry essential for autonomic homeostasis and interoception.

This article has an associated First Person interview with the first author of the paper.

Summary: Our data indicate that Elp1 is required in both placode- and neural crest-derived sensory neurons, and that it exerts comparable effects, including survival, axonal morphology and target innervation in both lineages.

Maternal Inflammation During Pregnancy and Offspring Brain Development: The Role of Mitochondria

The association between maternal immune activation (MIA) during pregnancy and risk for offspring neuropsychiatric disorders has been increasingly recognized over the past several years. Among the mechanistic pathways that have been described through which maternal inflammation during pregnancy may affect fetal brain development, the role of mitochondria has received little attention. In this review, the role of mitochondria as a potential mediator of the association between MIA during pregnancy and offspring brain development and risk for psychiatric disorders will be proposed. As a basis for this postulation, convergent evidence is presented supporting the obligatory role of mitochondria in brain development, the role of mitochondria as mediators and initiators of inflammatory processes, and evidence of mitochondrial dysfunction in preclinical MIA exposure models and human neurodevelopmental disorders. Elucidating the role of mitochondria as a potential mediator of MIA-induced alterations in brain development and neurodevelopmental disease risk may not only provide new insight into the pathophysiology of mental health disorders that have their origins in exposure to infection/immune activation during pregnancy but also offer new therapeutic targets.

Selective axonal transport through branch junctions is directed by growth cone signaling and mediated by KIF1/kinesin-3 motors

Development and function of nerve cells rely on the orchestration of microtubule-based transport from the cell body into distal axonal terminals. Neurons often have highly elaborate branches innervating multiple targets, but how protein or membrane cargos navigate through branch junctions to specific branch targets is unknown. Here, we demonstrate that anterograde transport of membrane vesicles through axonal branch junctions is highly selective, which is influenced by branch length and more strongly by growth cone motility. Using an optogenetic tool, we demonstrate that signaling from the growth cone can rapidly direct transport through branch junctions. We further demonstrate that such transport selectivity is differentially regulated for different vesicles and mediated by the KIF1/kinesin-3 family motors. We propose that this transport regulation through branch junctions could broadly impact neuronal development, function, and regeneration.

The effect of poly(lactic-co-glycolic acid) conduit loading insulin-like growth factor 1 modified by a collagen-binding domain on peripheral nerve injury in rats

Peripheral nerve injury (PNI) exists widely and seriously affects patients' daily lives. However, the effect of nerve repair is still limited, and only 50% of patients can recover useful functions. To overcome these obstacles, collagen-coated poly(lactic-co-glycolic acid) (PLGA) conduits loaded with CBD-IGF-1 were designed and tested in vitro and in vivo. The physical characterization of the conduit was tested by scanning electron microscopy, and the static water contact angle, release rate, and nerve regeneration ability of the conduit were verified in a rat sciatic nerve injury model. The results showed that the PLGA/col/CBD-IGF-1 conduit had a rough surface and good hydrophilicity. CBD-IGF-1 could be released slowly from the PLGA/col/CBD-IGF-1 conduit. In the in vivo experiment, gait analysis and electrophysiological evaluation showed that the sciatic functional index and electrophysiological parameters were best in the group treated with the PLGA/col/CBD-IGF-1 conduit. The pathological examination results for the sciatic nerve and gastrocnemius muscle in the group treated with the PLGA/col/CBD-IGF-1 conduit were better than those in the other three groups. In short, this study demonstrated the beneficial effects of CBD-IGF-1 in nerve regeneration. The PLGA/col/CBD-IGF-1 conduit has therapeutic potential for use in the treatment of PNI.

Mitochondria and Other Organelles in Neural Development and Their Potential as Therapeutic Targets in Neurodegenerative Diseases

The contribution of organelles to neural development has received increasing attention. Studies have shown that organelles such as mitochondria, endoplasmic reticulum (ER), lysosomes, and endosomes play important roles in neurogenesis. Specifically, metabolic switching, reactive oxygen species production, mitochondrial dynamics, mitophagy, mitochondria-mediated apoptosis, and the interaction between mitochondria and the ER all have roles in neurogenesis. Lysosomes and endosomes can regulate neurite growth and extension. Moreover, metabolic reprogramming represents a novel strategy for generating functional neurons. Accordingly, the exploration and application of mechanisms underlying metabolic reprogramming will be beneficial for neural conversion and regenerative medicine. There is adequate evidence implicating the dysfunction of cellular organelles—especially mitochondria—in neurodegenerative disorders, and that improvement of mitochondrial function may reverse the progression of these diseases through the reinforcement of adult neurogenesis. Therefore, these organelles have potential as therapeutic targets for the treatment of neurodegenerative diseases. In this review, we discuss the function of these organelles, especially mitochondria, in neural development, focusing on their potential as therapeutic targets in neurodegenerative disorders, including Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, and amyotrophic lateral sclerosis.

Targeting the multifaceted roles of mitochondria in intracerebral hemorrhage and therapeutic prospects

Intracerebral hemorrhage (ICH) is a severe, life-threatening subtype of stoke that constitutes a crucial health and socioeconomic problem worldwide. However, the current clinical treatment can only reduce the mortality of patients to a certain extent, but cannot ameliorate neurological dysfunction and has a high recurrence rate. Increasing evidence has demonstrated that mitochondrial dysfunction occurs in the early stages of brain injury and participates in all stages of secondary brain injury (SBI) after ICH. As the energy source of cells, various pathobiological processes that lead to SBI closely interact with the mitochondria, such as oxidative stress, calcium overload, and neuronal injury. In this review, we discussed the structure and function of mitochondria and the abnormal morphological changes after ICH. In addition, we discussed recent research on the involvement of mitochondrial dynamics in the pathological process of SBI after ICH and introduced the pathological variations and related molecular mechanisms of mitochondrial dysfunction in the occurrence of brain injury. Finally, we summarized the latest progress in mitochondrion-targeted agents for ICH, which provides a direction for the development of emerging therapeutic strategies targeting the mitochondria after ICH.

Localized glucose import, glycolytic processing, and mitochondria generate a focused ATP burst to power basement-membrane invasion

Invasive cells use transient, energy-consuming protrusions to breach basement membrane (BM) barriers. Using the ATP sensor PercevalHR during anchor cell (AC) invasion in Caenorhabditis elegans, we show that BM invasion is accompanied by an ATP burst from mitochondria at the invasive front. RNAi screening and visualization of a glucose biosensor identified two glucose transporters, FGT-1 and FGT-2, which bathe invasive front mitochondria with glucose and facilitate the ATP burst to form protrusions. FGT-1 localizes at high levels along the invasive membrane, while FGT-2 is adaptive, enriching most strongly during BM breaching and when FGT-1 is absent. Cytosolic glycolytic enzymes that process glucose for mitochondrial ATP production cluster with invasive front mitochondria and promote higher mitochondrial membrane potential and ATP levels. Finally, we show that UNC-6 (netrin), which polarizes invasive protrusions, also orients FGT-1. These studies reveal a robust and integrated energy acquisition, processing, and delivery network that powers BM breaching.

Neurofilament Light Regulates Axon Caliber, Synaptic Activity, and Organelle Trafficking in Cultured Human Motor Neurons

Neurofilament light (NFL) is one of the proteins forming multimeric neuron-specific intermediate filaments, neurofilaments, which fill the axonal cytoplasm, establish caliber growth, and provide structural support. Dominant missense mutations and recessive nonsense mutations in the neurofilament light gene (NEFL) are among the causes of Charcot–Marie–Tooth (CMT) neuropathy, which affects the peripheral nerves with the longest axons. We previously demonstrated that a neuropathy-causing homozygous nonsense mutation in NEFL led to the absence of NFL in patient-specific neurons. To understand the disease-causing mechanisms, we investigate here the functional effects of NFL loss in human motor neurons differentiated from induced pluripotent stem cells (iPSC). We used genome editing to generate NEFL knockouts and compared them to patient-specific nonsense mutants and isogenic controls. iPSC lacking NFL differentiated efficiently into motor neurons with normal axon growth and regrowth after mechanical axotomy and contained neurofilaments. Electrophysiological analysis revealed that motor neurons without NFL fired spontaneous and evoked action potentials with similar characteristics as controls. However, we found that, in the absence of NFL, human motor neurons 1) had reduced axonal caliber, 2) the amplitude of miniature excitatory postsynaptic currents (mEPSC) was decreased, 3) neurofilament heavy (NFH) levels were reduced and no compensatory increases in other filament subunits were observed, and 4) the movement of mitochondria and to a lesser extent lysosomes was increased. Our findings elaborate the functional roles of NFL in human motor neurons. NFL is not only a structural protein forming neurofilaments and filling the axonal cytoplasm, but our study supports the role of NFL in the regulation of synaptic transmission and organelle trafficking. To rescue the NFL deficiency in the patient-specific nonsense mutant motor neurons, we used three drugs, amlexanox, ataluren (PTC-124), and gentamicin to induce translational read-through or inhibit nonsense-mediated decay. However, the drugs failed to increase the amount of NFL protein to detectable levels and were toxic to iPSC-derived motor neurons.

Baicalin attenuates amyloid β oligomers induced memory deficits and mitochondria fragmentation through regulation of PDE-PKA-Drp1 signalling

RATIONALE

Mitochondrial fragmentation contributes to the initiation of Alzheimer's disease (AD) pathology. Baicalin plays a significant role in rescuing mitochondrial dysfunction. However, the effect of baicalin treatment on the modulation of mitochondrial fragmentation has not yet been assessed.

OBJECTIVES

The present study was designed to evaluate the effect of baicalin on memory and understand its mechanism of action.

RESULTS

Baicalin treatment significantly reversed the altered learning and memory behaviours in AD mouse model. We found that baicalin treatment significantly improved the levels of microtubule association protein-2 and enhanced the expression of synaptophysin and postsynaptic density protein 95 (PSD95). Moreover, treatment with baicalin reversed amyloid-β oligomer (AβO)-induced abnormalities in the succinate dehydrogenase complex iron sulphur subunit B (SDHB) and cytochrome c oxidase components I (COXI) and mitochondrial fragmentation in the hippocampus. Further, we found that baicalin decreased the PDE4 levels and upregulated the levels of phosphorylated Ser157 site of vasodilator-stimulated phosphoprotein (pVASP^s157) and phosphorylated Ser637 site of mitochondrial dynamin-related protein 1 (pDrp1^S637). Moreover, in AβO-treated HT-22 cells, H89 inhibited the effect of baicalin on PSD95, mitochondrial fragmentation, SDHB and COXI, PDE4, pVASP^s157, and pDrp1^S637.

CONCLUSION

The effect of baicalin on memory improvement may be due to improved synaptic plasticity, mitochondrial fragmentation, and rescue of dysfunction via the inhibition of PDE4, which leads to activation of pDrp1^S637 in the AβO-induced model.

SARM1 Suppresses Axon Branching Through Attenuation of Axonal Cytoskeletal Dynamics

Axon branching is a fundamental aspect of neuronal morphogenesis, neuronal circuit formation, and response of the nervous system to injury. Sterile alpha and TIR motif containing 1 (SARM1) was initially identified as promoting Wallerian degeneration of axons. We now report a novel function of SARM1 in postnatal sensory neurons; the suppression of axon branching. Axon collateral branches develop from axonal filopodia precursors through the coordination of the actin and microtubule cytoskeleton. In vitro analysis revealed that cultured P0-2 dorsal root ganglion sensory neurons from a SARM1 knockout (KO) mouse exhibit increased numbers of collateral branches and axonal filopodia relative to wild-type neurons. In SARM1 KO mice, cutaneous sensory endings exhibit increased branching in the skin in vivo with normal density of innervation. Transient axonal actin patches serve as cytoskeletal platforms from which axonal filopodia emerge. Live imaging analysis of axonal actin dynamics showed that SARM1 KO neurons exhibit increased rates of axonal actin patch formation and increased probability that individual patches will give rise to a filopodium before dissipating. SARM1 KO axons contain elevated levels of drebrin and cortactin, two actin regulatory proteins that are positive regulators of actin patches, filopodia formation, and branching. Live imaging of microtubule plus tip dynamics revealed an increase in the rate of formation and velocity of polymerizing tips along the axons of SARM1 KO neurons. Stationary mitochondria define sites along the axon where branches may arise, and the axons of SARM1 KO sensory neurons exhibit an increase in stationary mitochondria. These data reveal SARM1 to be a negative regulator of axonal cytoskeletal dynamics and collateral branching.

Aerobic Glycolysis: A DeOxymoron of (Neuro)Biology

The term ‘aerobic glycolysis’ has been in use ever since Warburg conducted his research on cancer cells’ proliferation and discovered that cells use glycolysis to produce adenosine triphosphate (ATP) rather than the more efficient oxidative phosphorylation (oxphos) pathway, despite an abundance of oxygen. When measurements of glucose and oxygen utilization by activated neural tissue indicated that glucose was consumed without an accompanied oxygen consumption, the investigators who performed those measurements also termed their discovery ‘aerobic glycolysis’. Red blood cells do not contain mitochondria and, therefore, produce their energy needs via glycolysis alone. Other processes within the central nervous system (CNS) and additional organs and tissues (heart, muscle, and so on), such as ion pumps, are also known to utilize glycolysis only for the production of ATP necessary to support their function. Unfortunately, the phenomenon of ‘aerobic glycolysis’ is an enigma wherever it is encountered, thus several hypotheses have been produced in attempts to explain it; that is, whether it occurs in cancer cells, in activated neural tissue, or during postprandial or exercise metabolism. Here, it is argued that, where the phenomenon in neural tissue is concerned, the prefix ‘aerobic’ in the term ‘aerobic glycolysis’ should be removed. Data collected over the past three decades indicate that L-lactate, the end product of the glycolytic pathway, plays an essential role in brain energy metabolism, justifying the elimination of the prefix ‘aerobic’. Similar justification is probably appropriate for other tissues as well.

Imaging Axonal Transport in Ex Vivo Central and Peripheral Nerves

Neurones are highly polarized cells with extensive axonal projections that rely on transport of proteins, RNAs, and organelles in a bidirectional manner to remain healthy. This process, known as axonal transport, can be imaged in real time through epifluorescent imaging of fluorescently labeled proteins, organelles, and other cargoes. While this is most conveniently done in primary neuronal cultures, it is more physiologically relevant when carried out in the context of a developed nerve containing both axons and glia. Here we outline how to image axonal transport ex vivo in sciatic and optic nerves, and the fimbria of the fornix. These methods could be altered to image other fluorescently labeled molecules, as well as different mechanisms of intracellular transport.

Tau phosphorylation and PAD exposure in regulation of axonal growth

Introduction: Tau is a microtubule associated phosphoprotein found principally in neurons. Prevailing dogma continues to define microtubule stabilization as the major function of tau in vivo, despite several lines of evidence suggesting this is not the case. Most importantly, tau null mice have deficits in axonal outgrowth and neuronal migration while still possessing an extensive microtubule network. Instead, mounting evidence suggests that tau may have a major function in the regulation of fast axonal transport (FAT) through activation of neuronal signaling pathways. Previous studies identified a phosphatase activating domain (PAD) at the tau N-terminal that is normally sequestered, but is constitutively exposed in tauopathies. When exposed, the PAD activates a signaling cascade involving PP1 and GSK3β which affects cellular functions including release of cargo from kinesin. Furthermore, we discovered that PAD exposure can be regulated by a single phosphorylation at T205. Exposure of the PAD is an early event in multiple tauopathies and a major contributing factor to neurodegeneration associated with tau hyperphosphorylation. However, effects of tau PAD exposure on anterograde FAT raised the interesting possibility that this pathway may be a mechanism for physiological regulation of cargo delivery through site-specific phosphorylation of tau and transient activation of PP1 and GSK3β. Significantly, there is already evidence of local control of PP1 and GSK3β at sites which require cargo delivery. Methods: To investigate this hypothesis, first we evaluated cellular localization of tau PAD exposure, pT205 tau phosphorylation, and active GSK3β in primary hippocampal neurons during development. Second, we analyzed the axonal outgrowth of tau knockout neurons following transfection with full length hTau40-WT, hTau40-ΔPAD, or hTau40-T205A. Results and Discussion: The results presented here suggest that transient activation of a PP1-GSK3β signaling pathway through locally regulated PAD exposure is a mechanism for cargo delivery, and thereby important for neurite outgrowth of developing neurons.

Identification of key genes involved in recovery from spinal cord injury in adult zebrafish

Zebrafish are an effective vertebrate model to study the mechanisms underlying recovery after spinal cord injury. The subacute phase after spinal cord injury is critical to the recovery of neurological function, which involves tissue bridging and axon regeneration. In this study, we found that zebrafish spontaneously recovered 44% of their swimming ability within the subacute phase (2 weeks) after spinal cord injury. During this period, we identified 7762 differentially expressed genes in spinal cord tissue: 2950 were up-regulated and 4812 were down-regulated. These differentially expressed genes were primarily concentrated in the biological processes of the respiratory chain, axon regeneration, and cell-component morphogenesis. The genes were also mostly involved in the regulation of metabolic pathways, the cell cycle, and gene-regulation pathways. We verified the gene expression of two differentially expressed genes, clasp2 up-regulation and h1m down-regulation, in zebrafish spinal cord tissue in vitro. Pathway enrichment analysis revealed that up-regulated clasp2 functions similarly to microtubule-associated protein, which is responsible for axon extension regulated by microtubules. Down-regulated h1m controls endogenous stem cell differentiation after spinal cord injury. This study provides new candidate genes, clasp2 and h1m, as potential therapeutic intervention targets for spinal cord injury repair by neuroregeneration. All experimental procedures and protocols were approved by the Animal Ethics Committee of Tianjin Institute of Medical & Pharmaceutical Sciences (approval No. IMPS-EAEP-Q-2019-02) on September 24, 2019.