Prevention of Axonal Degeneration by Perineurium Injection of Mitochondria in a Sciatic Nerve Crush Injury Model

Mitochondrial dysfunction: mechanisms and advances in therapy

Mitochondria, with their intricate networks of functions and information processing, are pivotal in both health regulation and disease progression. Particularly, mitochondrial dysfunctions are identified in many common pathologies, including cardiovascular diseases, neurodegeneration, metabolic syndrome, and cancer. However, the multifaceted nature and elusive phenotypic threshold of mitochondrial dysfunction complicate our understanding of their contributions to diseases. Nonetheless, these complexities do not prevent mitochondria from being among the most important therapeutic targets. In recent years, strategies targeting mitochondrial dysfunction have continuously emerged and transitioned to clinical trials. Advanced intervention such as using healthy mitochondria to replenish or replace damaged mitochondria, has shown promise in preclinical trials of various diseases. Mitochondrial components, including mtDNA, mitochondria-located microRNA, and associated proteins can be potential therapeutic agents to augment mitochondrial function in immunometabolic diseases and tissue injuries. Here, we review current knowledge of mitochondrial pathophysiology in concrete examples of common diseases. We also summarize current strategies to treat mitochondrial dysfunction from the perspective of dietary supplements and targeted therapies, as well as the clinical translational situation of related pharmacology agents. Finally, this review discusses the innovations and potential applications of mitochondrial transplantation as an advanced and promising treatment.

Elevating the significance of legume intake: A novel strategy to counter aging-related mitochondrial dysfunction and physical decline

Mitochondrial dysfunction increasingly becomes a target for promoting healthy aging and longevity. The dysfunction of mitochondria with age ultimately leads to a decline in physical functions. Among them, biogenesis dysfunction and the imbalances in the metabolism of reactive oxygen species and mitochondria as signaling organelles in the aging process have aroused our attention. Dietary intervention in mitochondrial dysfunction and physical decline during aging processes is essential, and greater attention should be directed toward healthful legume intake. Legumes are constantly under investigation for their nutritional and bioactive properties, and their consumption may yield antiaging and mitochondria-protecting benefits. This review summarizes mitochondrial dysfunction with age, discusses the benefits of legumes on mitochondrial function, and introduces the potential role of legumes in managing aging-related physical decline. Additionally, it reveals the benefits of legume intake for the elderly and offers a viable approach to developing legume-based functional food.

MSC-derived mitochondria promote axonal regeneration via Atf3 gene up-regulation by ROS induced DNA double strand breaks at transcription initiation region

BACKGROUND

The repair of peripheral nerve injury poses a clinical challenge, necessitating further investigation into novel therapeutic approaches. In recent years, bone marrow mesenchymal stromal cell (MSC)-derived mitochondrial transfer has emerged as a promising therapy for cellular injury, with reported applications in central nerve injury. However, its potential therapeutic effect on peripheral nerve injury remains unclear.

METHODS

We established a mouse sciatic nerve crush injury model. Mitochondria extracted from MSCs were intraneurally injected into the injured sciatic nerves. Axonal regeneration was observed through whole-mount nerve imaging. The dorsal root ganglions (DRGs) corresponding to the injured nerve were harvested to test the gene expression, reactive oxygen species (ROS) levels, as well as the degree and location of DNA double strand breaks (DSBs).

RESULTS

The in vivo experiments showed that the mitochondrial injection therapy effectively promoted axon regeneration in injured sciatic nerves. Four days after injection of fluorescently labeled mitochondria into the injured nerves, fluorescently labeled mitochondria were detected in the corresponding DRGs. RNA-seq and qPCR results showed that the mitochondrial injection therapy enhanced the expression of Atf3 and other regeneration-associated genes in DRG neurons. Knocking down of Atf3 in DRGs by siRNA could diminish the therapeutic effect of mitochondrial injection. Subsequent experiments showed that mitochondrial injection therapy could increase the levels of ROS and DSBs in injury-associated DRG neurons, with this increase being correlated with Atf3 expression. ChIP and Co-IP experiments revealed an elevation of DSB levels within the transcription initiation region of the Atf3 gene following mitochondrial injection therapy, while also demonstrating a spatial proximity between mitochondria-induced DSBs and CTCF binding sites.

CONCLUSION

These findings suggest that MSC-derived mitochondria injected into the injured nerves can be retrogradely transferred to DRG neuron somas via axoplasmic transport, and increase the DSBs at the transcription initiation regions of the Atf3 gene through ROS accumulation, which rapidly release the CTCF-mediated topological constraints on chromatin interactions. This process may enhance spatial interactions between the Atf3 promoter and enhancer, ultimately promoting Atf3 expression. The up-regulation of Atf3 induced by mitochondria further promotes the expression of downstream regeneration-associated genes and facilitates axon regeneration.

Identification of critical mitochondrial hub gene for facial nerve regeneration

Mitochondria play a critical role in nerve regeneration, yet the impact of gene expression changes related to mitochondria in facial nerve regeneration remains unknown. To address this knowledge gap, we analyzed the expression profile of the facial motor nucleus (FMN) using data obtained from the Gene Expression Omnibus (GEO) database (GSE162977). By comparing different time points in the data, we identified differentially expressed genes (DEGs). Additionally, we collected mitochondria-related genes from the Gene Ontology (GO) database and intersected them with the DEGs, resulting in the identification of mitochondria-related DEGs (MIT-DEGs). To gain further insights, we performed functional enrichment and pathway analysis of the MIT-DEGs. To explore the interactions among these MIT-DEGs, we constructed a protein-protein interaction (PPI) network using the STRING database and identified hub genes using the Degree algorithm of Cytoscape software. To validate the relevance of these genes to nerve regeneration, we established a rat facial nerve injury (FNI) model and conducted a series of experiments. Through these experiments, we confirmed three MIT-DEGs (Myc, Lyn, and Cdk1) associated with facial nerve regeneration. Our findings provide valuable insights into the transcriptional changes of mitochondria-related genes in the FMN following FNI, which can contribute to the development of new treatment strategies for FNI.

Melatonin Enhanced Microglia M2 Polarization in Rat Model of Neuro-inflammation Via Regulating ER Stress/PPARδ/SIRT1 Signaling Axis

Neuro-inflammation involves distinct alterations of microglial phenotypes, containing nocuous pro-inflammatory M1-phenotype and neuroprotective anti-inflammatory M-phenotype. Currently, there is no effective treatment for modulating such alterations. M1/M2 marker of primary microglia influenced by Melatonin were detected via qPCR. Functional activities were explored by western blotting, luciferase activity, EMSA, and ChIP assay. Structure interaction was assessed by molecular docking and LIGPLOT analysis. ER-stress detection was examined by ultrastructure TEM, calapin activity, and ERSE assay. The functional neurobehavioral evaluations were used for investigation of Melatonin on the neuroinflammation in vivo. Melatonin had targeted on Peroxisome Proliferator Activated Receptor Delta (PPARδ) activity, boosted LPS-stimulated alterations in polarization from the M1 to the M2 phenotype, and thereby inhibited NFκB-IKKβ activation in primary microglia. The PPARδ agonist L-165,041 or over-expression of PPARδ plasmid (ov-PPARδ) showed similar results. Molecular docking screening, dynamic simulation approaches, and biological studies of Melatonin showed that the activated site was located at PPARδ (phospho-Thr256-PPARδ). Activated microglia had lowered PPARδ activity as well as the downstream SIRT1 formation via enhancing ER-stress. Melatonin, PPARδ agonist and ov-PPARδ all effectively reversed the above-mentioned effects. Melatonin blocked ER-stress by regulating calapin activity and expression in LPS-activated microglia. Additionally, Melatonin or L-165,041 ameliorated the neurobehavioral deficits in LPS-aggravated neuroinflammatory mice through blocking microglia activities, and also promoted phenotype changes to M2-predominant microglia. Melatonin suppressed neuro-inflammation in vitro and in vivo by tuning microglial activation through the ER-stress-dependent PPARδ/SIRT1 signaling cascade. This treatment strategy is an encouraging pharmacological approach for the remedy of neuro-inflammation associated disorders.

Mitochondria as a therapeutic: a potential new frontier in driving the shift from tissue repair to regeneration

Fibrosis, or scar tissue development, is associated with numerous pathologies and is often considered a worst-case scenario in terms of wound healing or the implantation of a biomaterial. All that remains is a disorganized, densely packed and poorly vascularized bundle of connective tissue, which was once functional tissue. This creates a significant obstacle to the restoration of tissue function or integration with any biomaterial. Therefore, it is of paramount importance in tissue engineering and regenerative medicine to emphasize regeneration, the successful recovery of native tissue function, as opposed to repair, the replacement of the native tissue (often with scar tissue). A technique dubbed 'mitochondrial transplantation' is a burgeoning field of research that shows promise in in vitro, in vivo and various clinical applications in preventing cell death, reducing inflammation, restoring cell metabolism and proper oxidative balance, among other reported benefits. However, there is currently a lack of research regarding the potential for mitochondrial therapies within tissue engineering and regenerative biomaterials. Thus, this review explores these promising findings and outlines the potential for mitochondrial transplantation-based therapies as a new frontier of scientific research with respect to driving regeneration in wound healing and host-biomaterial interactions, the current successes of mitochondrial transplantation that warrant this potential and the critical questions and remaining obstacles that remain in the field.

Highly Specialized Mechanisms for Mitochondrial Transport in Neurons: From Intracellular Mobility to Intercellular Transfer of Mitochondria

The highly specialized structure and function of neurons depend on a sophisticated organization of the cytoskeleton, which supports a similarly sophisticated system to traffic organelles and cargo vesicles. Mitochondria sustain crucial functions by providing energy and buffering calcium where it is needed. Accordingly, the distribution of mitochondria is not even in neurons and is regulated by a dynamic balance between active transport and stable docking events. This system is finely tuned to respond to changes in environmental conditions and neuronal activity. In this review, we summarize the mechanisms by which mitochondria are selectively transported in different compartments, taking into account the structure of the cytoskeleton, the molecular motors and the metabolism of neurons. Remarkably, the motor proteins driving the mitochondrial transport in axons have been shown to also mediate their transfer between cells. This so-named intercellular transport of mitochondria is opening new exciting perspectives in the treatment of multiple diseases.

Human umbilical cord-derived mesenchymal stem cells-harvested mitochondrial transplantation improved motor function in TBI models through rescuing neuronal cells from apoptosis and alleviating astrogliosis and microglia activation

Each year, traumatic brain injury (TBI) causes a high rate of mortality throughout the world and those who survive have lasting disabilities. Given that the brain is a particularly dynamic organ with a high energy consumption rate, the inefficiency of current TBI treatment options highlights the necessity of repairing damaged brain tissue at the cellular and molecular levels, which according to research is aggravated due to ATP deficiency and reactive oxygen species surplus. Taking into account that mitochondria contribute to generating energy and controlling cellular stress, mitochondrial transplantation as a new treatment approach has lately reduced complications in a number of diseases by supplying healthy and functional mitochondria to the damaged tissue. For this reason, in this study, we used this technique to transplant human umbilical cord-derived mesenchymal stem cells (hUC-MSCs)-derived mitochondria as a suitable source for mitochondrial isolation into rat models of TBI to examine its therapeutic benefit and the results showed that the successful mitochondrial internalisation in the neuronal cells significantly reduced the number of brain cells undergoing apoptosis, alleviated astrogliosis and microglia activation, retained normal brain morphology and cytoarchitecture, and improved sensorimotor functions in a rat model of TBI. These data indicate that human umbilical cord-derived mesenchymal stem cells-isolated mitochondrial transplantation improves motor function in a rat model of TBI via rescuing neuronal cells from apoptosis and alleviating astrogliosis and microglia activation, maybe as a result of restoring the lost mitochondrial content.

Evaluation of the Aging Effect on Peripheral Nerve Regeneration: A Systematic Review

INTRODUCTION

Peripheral nerve injuries have been associated with increased healthcare costs and decreased patients' quality of life. Aging represents one factor that slows the speed of peripheral nervous system (PNS) regeneration. Since cellular homeostasis imbalance associated with aging lead to an increased failure in nerve regeneration in mammals of advanced age, this systematic review aims to determine the main molecular and cellular mechanisms involved in peripheral nerve regeneration in aged murine models after a peripheral nerve injuries.

METHODS

Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a literature search of 4 databases was conducted in July 2022 for studies comparing the peripheral nerve regeneration capability between young and aged murine models.

RESULTS

After the initial search yielded 744 publications, ten articles fulfilled the inclusion criteria. These studies show that age-related changes such as chronic inflammatory state, delayed macrophages' response to injury, dysfunctional Schwann Cells (SCs), and microenvironment alterations cause a reduction in the regenerative capability of the PNS in murine models. Furthermore, identifying altered gene expression patterns of SC after nerve damage can contribute to the understanding of physiological modifications produced by aging.

CONCLUSIONS

The interaction between macrophages and SC plays a crucial role in the nerve regeneration of aged models. Therefore, studies aimed at developing new and promising therapies for nerve regeneration should focus on these cellular groups to enhance the regenerative capabilities of the PNS in elderly populations.

Optic Nerve Injury Enhanced Mitochondrial Fission and Increased Mitochondrial Density without Altering the Uniform Mitochondrial Distribution in the Unmyelinated Axons of Retinal Ganglion Cells in a Mouse Model

Glaucomatous optic neuropathy (GON), a major cause of blindness, is characterized by the loss of retinal ganglion cells (RGCs) and the degeneration of their axons. Mitochondria are deeply involved in maintaining the health of RGCs and their axons. Therefore, lots of attempts have been made to develop diagnostic tools and therapies targeting mitochondria. Recently, we reported that mitochondria are uniformly distributed in the unmyelinated axons of RGCs, possibly owing to the ATP gradient. Thus, using transgenic mice expressing yellow fluorescent protein targeting mitochondria exclusively in RGCs within the retina, we assessed the alteration of mitochondrial distributions induced by optic nerve crush (ONC) via in vitro flat-mount retinal sections and in vivo fundus images captured with a confocal scanning ophthalmoscope. We observed that the mitochondrial distribution in the unmyelinated axons of survived RGCs after ONC remained uniform, although their density increased. Furthermore, via in vitro analysis, we discovered that the mitochondrial size is attenuated following ONC. These results suggest that ONC induces mitochondrial fission without disrupting the uniform mitochondrial distribution, possibly preventing axonal degeneration and apoptosis. The in vivo visualization system of axonal mitochondria in RGCs may be applicable in the detection of the progression of GON in animal studies and potentially in humans.

Targeted Mitochondrial Delivery to Hepatocytes: A Review

Defects in mitochondria are responsible for various genetic and acquired diseases. Mitochondrial transplantation, a method that involves introduction of healthy donor mitochondria into cells with dysfunctional mitochondria, could offer a novel approach to treat such diseases. Some studies have demonstrated the therapeutic benefit of mitochondrial transplantation and targeted delivery in vivo and in vitro within hepatocytes and the liver. This review discusses the issues regarding isolation and delivery of mitochondria to hepatocytes and the liver, and examines the existing literature in order to elucidate the utility and practicality of mitochondrial transplantation in the treatment of liver disease. Studies reviewed demonstrate that mitochondrial uptake could specifically target hepatocytes, address the challenge of non-specific localization of donor mitochondria, and provide evidence of changes in liver function following injection of mitochondria into mouse and rat disease models. While potential benefits and advantages of mitochondrial transplantation are evident, more research is needed to determine the practicality of mitochondrial transplantation for the treatment of genetic and acquired liver diseases.

Oxidative stress facilitates exogenous mitochondria internalization and survival in retinal ganglion precursor-like cells

Ocular cells are highly dependent on mitochondrial function due to their high demand of energy supply and their constant exposure to oxidative stress. Indeed, mitochondrial dysfunction is highly implicated in various acute, chronic, and genetic disorders of the visual system. It has recently been shown that mitochondrial transplantation (MitoPlant) temporarily protects retinal ganglion cells (RGCs) from cell death during ocular ischemia. Here, we characterized MitoPlant dynamics in retinal ganglion precursor-like cells, in steady state and under oxidative stress. We developed a new method for detection of transplanted mitochondria using qPCR, based on a difference in the mtDNA sequence of C57BL/6 and BALB/c mouse strains. Using this approach, we show internalization of exogenous mitochondria already three hours after transplantation, and a decline in mitochondrial content after twenty four hours. Interestingly, exposure of target cells to moderate oxidative stress prior to MitoPlant dramatically enhanced mitochondrial uptake and extended the survival of mitochondria in recipient cells by more than three fold. Understanding the factors that regulate the exogenous mitochondrial uptake and their survival may promote the application of MitoPlant for treatment of chronic and genetic mitochondrial diseases.

Mitochondrial Dysfunction in Diseases, Longevity, and Treatment Resistance: Tuning Mitochondria Function as a Therapeutic Strategy

Mitochondria are very important intracellular organelles because they have various functions. They produce ATP, are involved in cell signaling and cell death, and are a major source of reactive oxygen species (ROS). Mitochondria have their own DNA (mtDNA) and mutation of mtDNA or change the mtDNA copy numbers leads to disease, cancer chemo/radioresistance and aging including longevity. In this review, we discuss the mtDNA mutation, mitochondrial disease, longevity, and importance of mitochondrial dysfunction in cancer first. In the later part, we particularly focus on the role in cancer resistance and the mitochondrial condition such as mtDNA copy number, mitochondrial membrane potential, ROS levels, and ATP production. We suggest a therapeutic strategy employing mitochondrial transplantation (mtTP) for treatment-resistant cancer.

Mitotherapy: Unraveling a Promising Treatment for Disorders of the Central Nervous System and Other Systemic Conditions

Mitochondria are key players of aerobic respiration and the production of adenosine triphosphate and constitute the energetic core of eukaryotic cells. Furthermore, cells rely upon mitochondria homeostasis, the disruption of which is reported in pathological processes such as liver hepatotoxicity, cancer, muscular dystrophy, chronic inflammation, as well as in neurological conditions including Alzheimer’s disease, schizophrenia, depression, ischemia and glaucoma. In addition to the well-known spontaneous cell-to-cell transfer of mitochondria, a therapeutic potential of the transplant of isolated, metabolically active mitochondria has been demonstrated in several in vitro and in vivo experimental models of disease. This review explores the striking outcomes achieved by mitotherapy thus far, and the most relevant underlying data regarding isolated mitochondria transplantation, including mechanisms of mitochondria intake, the balance between administration and therapy effectiveness, the relevance of mitochondrial source and purity and the mechanisms by which mitotherapy is gaining ground as a promising therapeutic approach.

Mitochondrial function in development and disease

Mitochondria are organelles with vital functions in almost all eukaryotic cells. Often described as the cellular 'powerhouses' due to their essential role in aerobic oxidative phosphorylation, mitochondria perform many other essential functions beyond energy production. As signaling organelles, mitochondria communicate with the nucleus and other organelles to help maintain cellular homeostasis, allow cellular adaptation to diverse stresses, and help steer cell fate decisions during development. Mitochondria have taken center stage in the research of normal and pathological processes, including normal tissue homeostasis and metabolism, neurodegeneration, immunity and infectious diseases. The central role that mitochondria assume within cells is evidenced by the broad impact of mitochondrial diseases, caused by defects in either mitochondrial or nuclear genes encoding for mitochondrial proteins, on different organ systems. In this Review, we will provide the reader with a foundation of the mitochondrial 'hardware', the mitochondrion itself, with its specific dynamics, quality control mechanisms and cross-organelle communication, including its roles as a driver of an innate immune response, all with a focus on development, disease and aging. We will further discuss how mitochondrial DNA is inherited, how its mutation affects cell and organismal fitness, and current therapeutic approaches for mitochondrial diseases in both model organisms and humans.

Dual Regeneration of Muscle and Nerve by Intramuscular Infusion of Mitochondria in a Nerve Crush Injury Model

BACKGROUND

Peripheral nerve injuries result in muscle denervation and apoptosis of the involved muscle, which subsequently reduces mitochondrial content and causes muscle atrophy. The local injection of mitochondria has been suggested as a useful tool for restoring the function of injured nerves or the brain.

OBJECTIVE

To determine outcomes following the administration of isolated mitochondria into denervated muscle after nerve injury that have not been investigated.

METHODS

Muscle denervation was conducted in a sciatic nerve crushed by a vessel clamp and the denervated gastrocnemius muscle was subjected to 195 μg hamster green fluorescent protein (GFP)-mitochondria intramuscular infusion for 10 min.

RESULTS

The mitochondria were homogeneously distributed throughout the denervated muscle after intramuscular infusion. The increases in caspase 3, 8-oxo-dG, Bad, Bax, and ratio of Bax/Bcl-2 levels in the denervated muscle were attenuated by mitochondrial infusion, and the downregulation of Bcl-2 expression was prevented by mitochondrial infusion. In addition, the decrease in the expression of desmin and the acetylcholine receptor was counteracted by mitochondrial infusion; this effect paralleled the amount of distributed mitochondria. The restoration of the morphology of injured muscles and nerves was augmented by the local infusion of mitochondria. Mitochondrial infusion also led to improvements in sciatic functional indexes, compound muscle action potential amplitudes, and conduction latencies as well as the parameters of CatWalk (Noldus) gait analysis.

CONCLUSION

The local infusion of mitochondria can successfully prevent denervated muscle atrophy and augment nerve regeneration by reducing oxidative stress in denervated muscle.

Mitochondrial Behavior in Axon Degeneration and Regeneration

Mitochondria are organelles responsible for bioenergetic metabolism, calcium homeostasis, and signal transmission essential for neurons due to their high energy consumption. Accumulating evidence has demonstrated that mitochondria play a key role in axon degeneration and regeneration under physiological and pathological conditions. Mitochondrial dysfunction occurs at an early stage of axon degeneration and involves oxidative stress, energy deficiency, imbalance of mitochondrial dynamics, defects in mitochondrial transport, and mitophagy dysregulation. The restoration of these defective mitochondria by enhancing mitochondrial transport, clearance of reactive oxidative species (ROS), and improving bioenergetic can greatly contribute to axon regeneration. In this paper, we focus on the biological behavior of axonal mitochondria in aging, injury (e.g., traumatic brain and spinal cord injury), and neurodegenerative diseases (Alzheimer's disease, AD; Parkinson's disease, PD; Amyotrophic lateral sclerosis, ALS) and consider the role of mitochondria in axon regeneration. We also compare the behavior of mitochondria in different diseases and outline novel therapeutic strategies for addressing abnormal mitochondrial biological behavior to promote axonal regeneration in neurological diseases and injuries.

Extracellular Mitochondria Signals in CNS Disorders

Mitochondria actively participate in the regulation of cell respiratory mechanisms, metabolic processes, and energy homeostasis in the central nervous system (CNS). Because of the requirement of high energy, neuronal functionality and viability are largely dependent on mitochondrial functionality. In the context of CNS disorders, disruptions of metabolic homeostasis caused by mitochondrial dysfunction lead to neuronal cell death and neuroinflammation. Therefore, restoring mitochondrial function becomes a primary therapeutic target. Recently, accumulating evidence suggests that active mitochondria are secreted into the extracellular fluid and potentially act as non-cell-autonomous signals in CNS pathophysiology. In this mini-review, we overview findings that implicate the presence of cell-free extracellular mitochondria and the critical role of intercellular mitochondrial transfer in various rodent models of CNS disorders. We also discuss isolated mitochondrial allograft as a novel therapeutic intervention for CNS disorders.

One step forward: extracellular mitochondria transplantation

Mitochondria play a key role in cellular energy production and contribute to cell metabolism, homeostasis, intracellular signalling and organelle's quality control, among other roles. Viable, respiratory-competent mitochondria exist also outside the cells. Such extracellular/exogenous mitochondria occur in the bloodstream, being released by platelets, activated monocytes and endothelial progenitor cells. In the nervous system, the cerebrospinal fluid contains mitochondria discharged by astrocytes. Various pathologies, including the cardiovascular and neurodegenerative diseases, are associated with mitochondrial dysfunction. A strategy to reverse dysfunction and restore cell normality is the transplantation of mitochondria (freshly isolated from a healthy tissue) into the zone at risk, such as the ischemic heart and/or damaged nervous tissue. The functional exogenous mitochondria will replace the harmed ones, ensuing cardioprotective and neuroprotective effects. The diversity of transplantation settings (in vitro, in animal models and patients) offered variable answers (including lack of consensus) on efficacy of this strategy. Therefore, a critical overview of the current and future trends in mitochondrial transplantation seems to be required. Here, we outline the recent developments on (i) extracellular mitochondria types and roles, (ii) transplantation protocols, (iii) mechanisms of mitochondrial incorporation, (iv) the benefit of extracellular mitochondria transplantation in human health and diseases and (v) open questions that deserve urgent answers.

The therapeutic potential of mitochondrial transplantation for the treatment of neurodegenerative disorders

Mitochondrial activity is essential to support neural functions, and changes in the integrity and activity of the mitochondria can contribute to synaptic damage and neuronal death, especially in degenerative diseases associated with age, such as Alzheimer's and Parkinson's disease. Currently, different approaches are used to treat these conditions, and one strategy under research is mitochondrial transplantation. For years, mitochondria have been shown to be transferred between cells of different tissues. This process has allowed several attempts to develop transplantation schemes by isolating functional mitochondria and introducing them into damaged tissue in particular to counteract the harmful effects of myocardial ischemia. Recently, mitochondrial transfer between brain cells has also been reported, and thus, mitochondrial transplantation for disorders of the nervous system has begun to be investigated. In this review, we focus on the relevance of mitochondria in the nervous system, as well as some mitochondrial alterations that occur in neurodegenerative diseases associated with age. In addition, we describe studies that have performed mitochondrial transplantation in various tissues, and we emphasize the advances in mitochondrial transplantation aimed at treating diseases of the nervous system.

Mitochondrial transplantation ameliorates ischemia/reperfusion-induced kidney injury in rat

No real therapeutic modality is currently available for Acute kidney injury (AKI) and if any, they are mainly supportive in nature. Therefore, developing a new therapeutic strategy is crucial. Mitochondrial dysfunction proved to be a key contributor to renal tubular cell death during AKI. Thus, replacement or augmentation of damaged mitochondria could be a proper target in AKI treatment. Here, in an animal model of AKI, we auto-transplanted normal mitochondria isolated from healthy muscle cells to injured kidney cells through injection to renal artery. The mitochondria transplantation prevented renal tubular cell death, restored renal function, ameliorated kidney damage, improved regenerative potential of renal tubules, and decreased ischemia/reperfusion-induced apoptosis. Although further studies including clinical trials are required in this regard, our findings suggest a novel therapeutic strategy for treatment of AKI. Improved quality of life of patients suffering from renal failure and decreased morbidity and mortality rates would be the potential advantages of this therapeutic strategy.

Down-Regulated Expression of Magnesium Transporter Genes Following a High Magnesium Diet Attenuates Sciatic Nerve Crush Injury

BACKGROUND

Magnesium supplementation has potential for use in nerve regeneration. The expression of some magnesium transporter genes is reflective of the intracellular magnesium levels.

OBJECTIVE

To assess the expression of various magnesium transporter genes as they relate to neurological alterations in a sciatic nerve injury model.

METHODS

Sciatic nerve injury was induced in rats, which were then fed either basal or high magnesium diets. Magnesium concentrations and 5 magnesium transporter genes (SLC41A1, MAGT1, CNNM2, TRPM6, and TRPM7) were measured in the tissue samples.

RESULTS

The high magnesium diet attenuated cytoskeletal loss in a dose-dependent manner in isolated nerve explants. The high magnesium diet augmented nerve regeneration and led to the restoration of nerve structure, increased S-100, and neurofilaments. This increased regeneration was consistent with the improvement of neurobehavioral and electrophysiological assessment. The denervated muscle morphology was restored with the high magnesium diet, and that was also highly correlated with the increased expression of desmin and acetylcholine receptors in denervated muscle. The plasma magnesium levels were significantly elevated after the animals consumed a high magnesium diet and were reciprocally related to the down-regulation of CNNM2, MagT1, and SCL41A1 in the blood monocytes, nerves, and muscle tissues of the nerve crush injury model.

CONCLUSION

The increased plasma magnesium levels after consuming a high magnesium diet were highly correlated with the down-regulation of magnesium transporter genes in monocytes, nerves, and muscle tissues after sciatic nerve crush injury. The study findings suggest that there are beneficial effects of administering magnesium after a nerve injury.

Increased angiogenesis by the rotational muscle flap is crucial for nerve regeneration

Background

The gold standard surgical treatment of nerve injury includes direct repair, nerve graft, and neurolysis. The underlying effects (either beneficial or detrimental) of angiogenesis during nerve regeneration by rotational muscle flap have not yet determined. We assess the neurological outcome and angiogenesis of nerve injury following a rotational muscle flap.

Methods

We retrospectively analyzed the outcome of the patients with severe radial nerve injury by neurolysis and rotational muscle flap; we also mimicked the clinical situation by nerve crush followed by rotational muscle flap in animals to assess associated angiogenesis factor expression.

Results

Twenty-three out of 25 (92%) cases of severe radial nerve injury underwent neurolysis assisted by muscle flap rotation and eventually reached their preinjury neurological outcome. In the animal study, both FITC–dextran and Dil infusion showed a remarkably increased vascular structure in the crushed nerve integrated by the muscle flap and abolished by Avastin injection. The rotational muscle flap significantly increased angiogenesis factor expression, and this was attenuated by Avastin injection. The increased angiogenesis factor expression paralleled the improvement seen in neurobehavioral and electrophysiological studies as well as the significant expression of nerve regeneration markers and the restoration of denervated muscle morphology.

Conclusion

Based on the clinical and animal data analysis, we conclude that muscle flap rotation provides a platform for angiogenesis in the acceleration of nerve regeneration. It appears that the muscle flap rotation augmented the nerve regeneration process which may be beneficial for nerve repair in clinical application.

Mitochondrial transplantation as a potential and novel master key for treatment of various incurable diseases

Mitochondria are attractive cellular organelles which are so interesting in both basic and clinical research, especially after it was found that they were arisen as a bacterial intruder in ancient cells. Interestingly, even now, they are the focus of many investigations and their function and relevance to health and disease have remained open questions. More recently, research on mitochondria have turned out their potential application in medicine as a novel therapeutic intervention. The importance of this issue is highlighted when we know that mitochondrial dysfunction can be observed in a variety of diseases such as cardiovascular diseases, neurodegenerative diseases, ischemia, diabetes, renal failure, skeletal muscles disorders, liver diseases, burns, aging, and cancer progression. In other words, transplantation of viable mitochondria into the injured tissues would replace or augment damaged mitochondria, allowing the rescue of cells and restoration of the normal function. Therefore, mitochondrial transplantation would be revolutionary for the treatment of a variety of diseases in which conventional therapies have proved unsuccessful. Here, we describe pieces of evidence of mitochondrial transplantation, discuss and highlight the current and future directions to show why mitochondrial transplantation could be a master key for treatment of a variety of diseases or injuries.

Axonal fusion: An alternative and efficient mechanism of nerve repair

Injuries to the nervous system can cause lifelong morbidity due to the disconnect that occurs between nerve cells and their cellular targets. Re-establishing these lost connections is the ultimate goal of endogenous regenerative mechanisms, as well as those induced by exogenous manipulations in a laboratory or clinical setting. Reconnection between severed neuronal fibers occurs spontaneously in some invertebrate species and can be induced in mammalian systems. This process, known as axonal fusion, represents a highly efficient means of repair after injury. Recent progress has greatly enhanced our understanding of the molecular control of axonal fusion, demonstrating that the machinery required for the engulfment of apoptotic cells is repurposed to mediate the reconnection between severed axon fragments, which are subsequently merged by fusogen proteins. Here, we review our current understanding of naturally occurring axonal fusion events, as well as those being ectopically produced with the aim of achieving better clinical outcomes.

The Molecular Interplay between Axon Degeneration and Regeneration

Neurons face a series of morphological and molecular changes following trauma and in the progression of neurodegenerative disease. In neurons capable of mounting a spontaneous regenerative response, including invertebrate neurons and mammalian neurons of the peripheral nervous system (PNS), axons regenerate from the proximal side of the injury and degenerate on the distal side. Studies of Wallerian degeneration slow (Wld^S /Ola) mice have revealed that a level of coordination between the processes of axon regeneration and degeneration occurs during successful repair. Here, we explore how shared cellular and molecular pathways that regulate both axon regeneration and degeneration coordinate the two distinct outcomes in the proximal and distal axon segments. © 2018 Wiley Periodicals, Inc. Develop Neurobiol 00: 000-000, 2018.

Oxidative Stress Induces Disruption of the Axon Initial Segment

The axon initial segment (AIS), the domain responsible for action potential initiation and maintenance of neuronal polarity, is targeted for disruption in a variety of central nervous system pathological insults. Previous work in our laboratory implicates oxidative stress as a potential mediator of structural AIS alterations in two separate mouse models of central nervous system inflammation, as these effects were attenuated following reactive oxygen species scavenging and NADPH oxidase-2 ablation. While these studies suggest a role for oxidative stress in modulation of the AIS, the direct effects of reactive oxygen and nitrogen species (ROS/RNS) on the stability of this domain remain unclear. Here, we demonstrate that oxidative stress, as induced through treatment with 3-morpholinosydnonimine (SIN-1), a spontaneous ROS/RNS generator, drives a reversible loss of AIS protein clustering in primary cortical neurons in vitro. Pharmacological inhibition of both voltage-dependent and intracellular calcium (Ca²⁺) channels suggests that this mechanism of AIS disruption involves Ca²⁺ entry specifically through L-type voltage-dependent Ca²⁺ channels and its release from IP₃-gated intracellular stores. Furthermore, ROS/RNS-induced AIS disruption is dependent upon activation of calpain, a Ca²⁺-activated protease previously shown to drive AIS modulation. Overall, we demonstrate for the first time that oxidative stress, as induced through exogenously applied ROS/RNS, is capable of driving structural alterations in the AIS complex.