Transplantation of Astrocytic Mitochondria Modulates Neuronal Antioxidant Defense and Neuroplasticity and Promotes Functional Recovery after Intracerebral Hemorrhage

The neuroprotective role of Humanin in Alzheimer's disease: The molecular effects

Humanin (HN) is an endogenous micropeptide also known as a mitochondria-derived peptide. It has a neuroprotective effect against Alzheimer's disease (AD) and other neurodegenerative diseases by improving hippocampal acetylcholine and attenuating the development of oxidative stress and associated neurotoxicity. HN protects the neuron from the toxic effects of amyloid beta (Aβ). HN is regarded as a biomarker of mitochondrial stress. Interestingly, aging reduces brain expression of HN, leading to cognitive impairment and elevating the risk of neurodegeneration, including AD. However, in old subjects and AD patients, circulating HN levels increase as a compensatory mechanism to reduce neurodegeneration and mitochondrial dysfunction in AD. Conversely, other studies demonstrated a reduction in circulating HN levels in AD. These findings indicated controversial points regarding the precise mechanistic role of HN in AD. Therefore, the aim of this review was to discuss the exact role of HN in AD neuropathology and also to discuss the molecular mechanisms of HN in AD.

TRANSPLANTATION OF VIABLE ALLOGENEIC MITOCHONDRIA PROTECTS KIDNEY FUNCTION IN A MOUSE MODEL OF HEMORRHAGIC SHOCK AND RHABDOMYOLYSIS-INDUCED ACUTE RENAL INJURY

ABSTRACT

Background and Aims: Acute kidney injury (AKI) is independently associated with high mortality after major trauma. Because mitochondrial dysfunction in renal tubular cells is a critical early subcellular change in AKI, this study proposed that administration of freshly harvested viable mitochondria could ameliorate renal tubular injury in a mouse model of two-hit rhabdomyolysis-related AKI. Methods: Mice were subjected to acute hemorrhagic shock and rhabdomyolysis through blood withdrawal and intramuscular glycerol injection. Mitochondria (100 μg) were freshly isolated from the soleus muscles of naïve mice. Mitochondria or placebo solution was randomly delivered into arterial catheter 1 h after the induction of AKI. The mice were euthanized 36 h later, and blood samples and kidneys were collected for analysis. Results: IVIS imaging confirmed increased expression of fluorescence-labeled allogeneic mitochondrial accumulation in AKI kidneys. Mitochondrial transplantation significantly decreased the elevated serum levels of urea nitrogen, creatinine and potassium. The protein expression of endogenous antioxidant molecules (Nrf-2, heme oxygenase-1 and superoxide dismutases) was significantly increased. The BAX-to-Bcl-2 ratio and expression of cleaved caspace-3 were also reduced in the mitochondrial-transplanted animals, indicating the attenuation of mitochondrial-mediated apoptosis in the kidney tissues of AKI mice. Histopathological examination confirmed that degrees of renal tubular injury were improved following mitochondrial transplantation. Conclusions: Transplantation of freshly isolated mitochondria augments endogenous antioxidant capacity and ameliorates mitochondrial apoptosis in the injured kidney tissues after hemorrhagic shock and rhabdomyolysis-induced AKI. Allogeneic mitochondrial transplantation could be a potential and feasible therapeutic option for prevention and management of AKI secondary to major trauma.

Astrocytic mitochondria modulate poststroke splenic immune responses, promote interleukin 10 production, and mediate neuroprotection after intracerebral hemorrhage

We recently demonstrated that systemically transplanted astrocytic mitochondria enter the intracerebral hemorrhage (ICH)-affected brain, where they protect the neurons by mitigating oxidative damage via upregulation of the manganese superoxide dismutase (Mn-SOD), ultimately contributing to functional recovery after ICH in mice. Although our previous study clearly demonstrated the beneficial effects of mitochondria within the brain, the effect of transferred mitochondria on the peripheral system was not yet studied. Thus, here, we studied the impact of astrocytic mitochondria transfer on post-ICH recovery and modulation of systemic immune responses. We used the autologous blood injection model for the mouse ICH surgery. Mice subjected to ICH received astrocytic mitochondria intravenously at 1 h, 7, and 14 days post-ICH onset, and the splenic immune responses of these mice were analyzed at 21 days. An ICH-like injury was induced in vitro using primary cultured neurons treated with recombinant interleukin-10, and cell viability, reactive oxygen species levels, and gene expressions were analyzed. We demonstrate that systemic transplantation of astrocytic mitochondria increases the population of splenic B cells, production of interleukin-10 by B cells, and plasma interleukin-10 levels in mice after ICH. Furthermore, in the ICH-like injury in vitro, exogenous interleukin-10 (to model spleen-mediated interleukin-10 increase) upregulated Mn-SOD expression in the cultured neurons and promoted neuronal survival and neuroplasticity-related gene expressions, suggesting interleukin-10 role in cytoprotection and repair/recovery under ICH-like condition. Thus, systemic transfer of astrocytic mitochondria modulates post-ICH peripheral immune responses, which may participate in functional recovery.

Decoding ischemic stroke: Perspectives on the endoplasmic reticulum, mitochondria, and their crosstalk

Stroke is known for its high disability and mortality rates. Ischemic stroke (IS), the most prevalent form, imposes a considerable burden on affected individuals. Nevertheless, existing treatment modalities are hindered by limitations, including narrow therapeutic windows, substantial adverse effects, and suboptimal neurological recovery. Clarifying the pathological mechanism of IS is a prerequisite for developing new therapeutic strategies. In this context, the functional disruption of mitochondria, the endoplasmic reticulum (ER), and the crosstalk mechanisms between them have garnered increasing attention for their contributory roles in the progression of IS. Therefore, this review provides a comprehensive summary of the current pathomechanisms associated with the involvement of the ER and mitochondria in IS, emphasising Ca2+ destabilization homeostasis, ER stress, oxidative stress, disordered mitochondrial quality control, and mitochondrial transfer. Additionally, this article highlights the functional interaction between the ER and mitochondria, as well as the mitochondrial-ER contacts (MERCs) that structurally connect mitochondria and the ER, aiming to provide ideas and references for the research and treatment of IS.

Neuroprotective mechanisms of microglia in ischemic stroke: a review focused on mitochondria

Stroke encompasses a range of cerebrovascular disorders characterized by high morbidity, disability, and mortality, with ischemic stroke being the predominant type. This condition imposes significant socio-economic and healthcare burdens, and therapeutic options are currently limited. Microglia, the brain's resident immune cells, are rapidly activated following stroke-induced injury and play a pivotal role in the pathogenesis of neuroinflammation and ischemic tissues. Mitochondria participates in and influences the pathological processes of ischemic stroke, including oxidative stress, modulation of microglia phenotype, and axonal regenerative function, and is an essential and often overlooked target in the clinical management of stroke. This paper reviews recent advancements in research on microglia in ischemic stroke, specifically focusing on the contribution of the mitochondria, providing a reference for selecting therapeutic targets and guiding future research directions.

Astrocyte involvement in metabolic regulation and disease

Astrocytes, the predominant glial cell type in the mammalian brain, influence a wide variety of brain parameters including neuronal energy metabolism. Exciting recent studies have shown that obesity and diabetes can impact on astrocyte function. We review evidence that dysregulation of astrocytic lipid metabolism and glucose sensing contributes to dysregulation of whole-body energy balance, thermoregulation, and insulin sensitivity. In addition, we consider the overlooked topic of the sex-specific roles of astrocytes and their response to hormonal fluctuations that provide insights into sex differences in metabolic regulation. Finally, we provide an update on potential ways to manipulate astrocyte function, including genetic targeting, optogenetic and chemogenetic techniques, transplantation, and tailored exosome-based therapies, which may lead to improved treatments for metabolic disease.

Intravenous administration of muse cells improves cerebral ischemia outcome via immunomodulation in the spleen

Ischemic stroke is a leading cause of disability and death globally. Stem cell therapies are emerging as a frontier for enhancing post-stroke recovery, with Muse cells-a subclass of pluripotent stem cells-demonstrating considerable promise. Muse cells are notable not only for their potential in cell replacement but also for their role in modulating immune responses following cerebral infarction. In the present study, we administered Muse cells intravenously to mice after inducing a stroke via distal middle cerebral artery occlusion. We evaluated motor outcomes, splenocyte populations, cytokine profiles, and gene expression 2 weeks after inducing stroke. Additionally, comparisons were drawn between outcomes in splenectomized mice and those receiving adoptive splenocyte transfer to discern the specific influence of the spleen on treatment efficacy. Our findings revealed that Muse cell therapy facilitates motor recovery, an effect that is compromised in the absence of the spleen. Spleens in treated mice exhibited a shift in neutrophil counts, increased cytokine activity, and a notable uptick in the expression of genes related to protein folding. These insights affirm the potential therapeutic effect of Muse cells in post-stroke treatment strategies, with their efficacy attributed, at least in part, to immunomodulatory pathways involving the spleen.

Development of Functional Recovery Therapy for Post-Stroke Sequelae: Towards a Future without Stroke Aftereffects

Stroke remains a leading cause of mortality and morbidity globally, posing significant challenges to healthcare systems due to its impact on Activities of Daily Living, Quality of Life, and healthcare costs. Current treatments primarily focus on acute management through thrombolytic therapy and thrombectomy, but only a limited number of patients benefit, underscoring the need for effective therapies to aid chronic stroke recovery. Despite ongoing clinical trials, cell therapy faces substantial logistical and cost-related hurdles, limiting its widespread adoption. Strategies to minimalize post-stroke sequelae emphasize preventing cerebral infarction deterioration, utilizing predictive scoring systems for focused treatment, and exploring drug repositioning. The complex interplay within the Neurovascular Unit and Oligovascular Niche highlights the role of various cell types and neurotrophic factors in stroke pathophysiology and recovery phases. Notably, microglia and astrocytes exhibit dual phenotypes ─ either inflammatory or protective ─ depending on the environment, influencing neural damage or repair processes post-stroke. Mitochondrial therapy emerges as a promising avenue, leveraging the organelles' ability to migrate between cells and mitigate inflammatory responses. Studies suggest that mitochondria transferred from astrocytes or other sources could transform inflammatory astrocytes into protective ones, thereby promoting white matter integrity and potentially reducing dementia progression associated with stroke sequelae. In conclusion, addressing stroke's multifaceted challenges requires innovative therapeutic approaches targeting inflammatory mechanisms and enhancing neuroprotection. Early detection and intervention, coupled with advancements in mitochondrial therapy and understanding intercellular interactions, hold promise for improving stroke outcomes and reducing long-term neurological complications.

Progress of Astrocyte-Neuron Crosstalk in Central Nervous System Diseases

Neurons are the primary cells responsible for information processing in the central nervous system (CNS). However, they are vulnerable to damage and insult in a variety of neurological disorders. As the most abundant glial cells in the brain, astrocytes provide crucial support to neurons and participate in synapse formation, synaptic transmission, neurotransmitter recycling, regulation of metabolic processes, and the maintenance of the blood-brain barrier integrity. Though astrocytes play a significant role in the manifestation of injury and disease, they do not work in isolation. Cellular interactions between astrocytes and neurons are essential for maintaining the homeostasis of the CNS under both physiological and pathological conditions. In this review, we explore the diverse interactions between astrocytes and neurons under physiological conditions, including the exchange of neurotrophic factors, gliotransmitters, and energy substrates, and different CNS diseases such as Alzheimer's disease, Parkinson's disease, stroke, traumatic brain injury, and multiple sclerosis. This review sheds light on the contribution of astrocyte-neuron crosstalk to the progression of neurological diseases to provide potential therapeutic targets for the treatment of neurological diseases.

Role of Glutathione in Parkinson's Disease Pathophysiology and Therapeutic Potential of Polyphenols

Oxidative stress is recognized to have a central role in the initiation and progression of Parkinson's disease (PD). Within the brain, neurons are particularly sensitive to oxidation due in part to their weak intrinsic antioxidant defense. Theoretically, neurons mostly depend on neighboring astrocytes to provide antioxidant protection by supplying cysteine-containing products for glutathione (GSH) synthesis. Astrocytes and neurons possess several amino acid transport systems for GSH and its precursors. Indeed, GSH is the most abundant intrinsic antioxidant in the central nervous system. The GSH depletion and/or alterations in its metabolism in the brain contribute to the pathogenesis of PD. Noteworthy, polyphenols possess potent antioxidant activity and can augment the GSH redox system. Numerous in vitro and in vivo studies have indicated that polyphenols exhibit potent neuroprotective effects in PD. Epidemiological studies have found an association between the consumption of dietary polyphenols and a lower PD risk. In this review, we summarize current knowledge on the biosynthesis and metabolism of GSH in the brain, with an emphasis on their contribution and therapeutic potential in PD. In particular, we focus on polyphenols that can increase brain GSH levels against PD. Furthermore, some current challenges and future perspectives for polyphenol-based therapies are also discussed.

Molecular and cellular mechanisms of mitochondria transfer in models of central nervous system disease

In the central nervous system (CNS), neuronal function and dysfunction are critically dependent on mitochondrial integrity and activity. In damaged or diseased brains, mitochondrial dysfunction reduces adenosine triphosphate (ATP) levels and impairs ATP-dependent neural firing and neurotransmitter dynamics. Restoring mitochondrial capacity to generate ATP may be fundamental in restoring neuronal function. Recent studies in animals and humans have demonstrated that endogenous mitochondria may be released into the extracellular environment and transported or exchanged between cells in the CNS. Under pathological conditions in the CNS, intercellular mitochondria transfer contributes to new classes of signaling and multifunctional cellular activities, thereby triggering deleterious effects or promoting beneficial responses. Therefore, to take full advantage of the beneficial effects of mitochondria, it may be useful to transplant healthy and viable mitochondria into damaged tissues. In this review, we describe recent findings on the mechanisms of mitochondria transfer and provide an overview of experimental methodologies, including tissue sourcing, mitochondrial isolation, storage, and modification, aimed at optimizing mitochondria transplantation therapy for CNS disorders. Additionally, we examine the clinical relevance and potential strategies for the therapeutic application of mitochondria transplantation.

Ameliorating Mitochondrial Dysfunction for the Therapy of Parkinson's Disease

Parkinson's disease (PD) is currently the second most incurable central neurodegenerative disease resulting from various pathogenesis. As the "energy factory" of cells, mitochondria play an extremely important role in supporting neuronal signal transmission and other physiological activities. Mitochondrial dysfunction can cause and accelerate the occurrence and progression of PD. How to effectively prevent and suppress mitochondrial disorders is a key strategy for the treatment of PD from the root. Therefore, the emerging mitochondria-targeted therapy has attracted considerable interest. Herein, the relationship between mitochondrial dysfunction and PD, the causes and results of mitochondrial dysfunction, and major strategies for ameliorating mitochondrial dysfunction to treat PD are systematically reviewed. The study also prospects the main challenges for the treatment of PD.

Mitochondria Transplantation Promotes Corneal Epithelial Wound Healing

Purpose

The integrity of the corneal epithelium is essential in maintaining normal corneal function. Conditions disrupting the corneal epithelial layer range from chemical burns to dry eye disease and may result in impairment of both corneal transparency and sensation. Identifying factors that regulate corneal wound healing is key for the development of new treatment strategies. Here, we investigated a direct role of mitochondria in corneal wound healing via mitochondria transplantation.

Methods

Human corneal epithelial cells (hCECs) were isolated from human corneas and incubated with mitochondria which were isolated from human ARPE-19 cells. We determined the effect of mitochondria transplantation on wound healing and proliferation of hCECs. In vivo, we used a mouse model of corneal chemical injury. Mitochondria were isolated from mouse livers and topically applied to the ocular surface following injury. We evaluated the time of wound repair, corneal re-epithelization, and stromal abnormalities.

Results

Mitochondria transplantation induced the proliferation and wound healing of primary hCECs. Further, mitochondria transplantation promoted wound healing in vivo. Specifically, mice receiving mitochondria recovered twice as fast as control mice following corneal injury, presenting both enhanced and improved repair. Corneas treated with mitochondria demonstrated the re-epithelization of the wound area to a multi-layer appearance, compared to thinning and complete loss of the epithelium in control mice. Mitochondria transplantation also prevented the thickening and disorganization of the corneal stromal lamella, restoring normal corneal dehydration.

Conclusions

Mitochondria promote corneal re-epithelization and wound healing. Augmentation of mitochondria levels via mitochondria transplantation may serve as an effective treatment for inducing the rapid repair of corneal epithelial defects.

Zinc remodels mitochondrial network through SIRT3/Mfn2-dependent mitochondrial transfer in ameliorating spinal cord injury

Spinal cord injury (SCI) is a traumatic neuropathic condition that results in motor, sensory and autonomic dysfunction. Mitochondrial dysfunction caused by primary trauma is one of the critical pathogenic mechanisms. Moderate levels of zinc have antioxidant effects, promote neurogenesis and immune responses. Zinc normalises mitochondrial morphology in neurons after SCI. However, how zinc protects mitochondria within neurons is unknown. In the study, we used transwell culture, Western blot, Quantitative Real-time Polymerase Chain Reaction (QRT-PCR), ATP content detection, reactive oxygen species (ROS) activity assay, flow cytometry and immunostaining to investigate the relationship between zinc-treated microglia and injured neurons through animal and cell experiments. We found that zinc promotes mitochondrial transfer from microglia to neurons after SCI through Sirtuin 3 (SIRT3) regulation of Mitofusin 2 protein (Mfn2). It can rescue mitochondria in damaged neurons and inhibit oxidative stress, increase ATP levels and promote neuronal survival. Therefore, it can improve the recovery of motor function in SCI mice. In conclusion, our work reveals a potential mechanism to describe the communication between microglia and neurons after SCI, which may provide a new idea for future therapeutic approaches to SCI.

Astrocytes in intracerebral hemorrhage: impact and therapeutic objectives

Intracerebral hemorrhage (ICH) manifests precipitously and profoundly impairs the neurological function in patients who are affected. The etiology of subsequent injury post-ICH is multifaceted, characterized by the intricate interplay of various factors, rendering therapeutic interventions challenging. Astrocytes, a distinct class of glial cells, interact with neurons and microglia, and are implicated in a series of pathophysiological alterations following ICH. A comprehensive examination of the functions and mechanisms associated with astrocytic proteins may shed light on the role of astrocytes in ICH pathology and proffer innovative therapeutic avenues for ICH management.

The Crosstalk Between Immune Cells After Intracerebral Hemorrhage

The inflammatory mechanism of intracerebral hemorrhage (ICH) has been widely studied, and it is believed that the regulation of this mechanism is of great significance to the prognosis. In the early stage of the acute phase of ICH, the release of a large number of inflammatory factors around the hematoma can recruit more inflammatory cells to infiltrate the area, further release inflammatory factors, cause an inflammatory cascade reaction, aggravate the volume of cerebral hematoma and edema and further destroy the blood-brain barrier (BBB), according to this, the crosstalk between cells may be of great significance in secondary brain injury (SBI). Because most of the cells recruited are inflammatory immune cells, this paper mainly discusses the cells based on the inflammatory mechanism to discuss their functions after ICH, we found that among the main cells inherent in the brain, glial cells account for the majority, of which microglia are the most widely studied and it can interact with a variety of cells, which is reflected in the literature researches on its pathogenesis and treatment. We believe that exploring multi-mechanism and multi-cell regulated drugs may be the future development trend, and the existing research, the comparison and unification of modeling methods, and the observation of long-term efficacy may be the first problem that researchers need to solve.

Ameliorative Role of Mitochondrial Therapy in Cognitive Function of Vascular Dementia Mice

BACKGROUND

Mitochondrial dysfunction plays a vital role in the progression of vascular dementia (VaD). We hypothesized that transfer of exogenous mitochondria might be a beneficial strategy for VaD treatment.

OBJECTIVE

The study was aimed to investigate the role of mitochondrial therapy in cognitive function of VaD.

METHODS

The activity and integrity of isolated mitochondria were detected using MitoTracker and Janus Green B staining assays. After VaD mice were intravenously injected with exogenous mitochondria, Morris water maze and passive avoidance tests were used to detect cognitive function of VaD mice. Haematoxylin and eosin, Nissl, TUNEL, and Golgi staining assays were utilized to measure neuronal and synaptic injury in the hippocampus of VaD mice. Detection kits were performed to detect mitochondrial membrane potential (ΔΨ), SOD activity and the levels of ATP, ROS, and MDA in the brains of VaD mice.

RESULTS

The results showed that isolated mitochondria were intact and active. Mitochondrial therapy could ameliorate cognitive performance of VaD mice. Additionally, mitochondrial administration could attenuate hippocampal neuronal and synaptic injury, improve mitochondrial ΔΨ, ATP level and SOD activity, and reduce ROS and MDA levels in the brains of VaD mice.

CONCLUSIONS

The study reports profitable effect of mitochondrial therapy against cognitive impairment of VaD, making mitochondrial treatment become a promising therapeutic strategy for VaD.

Neuroprotective Action of Humanin and Humanin Analogues: Research Findings and Perspectives

Humanin is a 24-mer peptide first reported in the early 2000s as a new neuroprotective/cytoprotective factor rescuing neuronal cells from death induced by various Alzheimer's disease-associated insults. Nowadays it is known that humanin belongs to the novel class of the so-called mitochondrial-derived peptides (which are encoded by mitochondrial DNA) and has been shown to exert beneficial cytoprotective effects in a series of in vitro and/or in vivo experimental models of human diseases, including not only neurodegenerative disorders but other human diseases as well (e.g., age-related macular degeneration, cardiovascular diseases, or diabetes mellitus). This review article is focused on the presentation of recent in vitro and in vivo research results associated with the neuroprotective action of humanin as well as of various, mainly synthetic, analogues of the peptide; moreover, the main mode(s)/mechanism(s) through which humanin and humanin analogues may exert in vitro and in vivo regarding neuroprotection have been reported. The prospects of humanin and humanin analogues to be further investigated in the frame of future research endeavors against neurodegenerative/neural diseases have also been briefly discussed.

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.

Exploring Molecular Targets for Mitochondrial Therapies in Neurodegenerative Diseases

The progressive deterioration of function and structure of brain cells in neurodegenerative diseases is accompanied by mitochondrial dysfunction, affecting cellular metabolism, intracellular signaling, cell differentiation, morphogenesis, and the activation of programmed cell death. However, most of the efforts to develop therapies for Alzheimer's and Parkinson's disease have focused on restoring or maintaining the neurotransmitters in affected neurons, removing abnormal protein aggregates through immunotherapies, or simply treating symptomatology. However, none of these approaches to treating neurodegeneration can stop or reverse the disease other than by helping to maintain mental function and manage behavioral symptoms. Here, we discuss alternative molecular targets for neurodegeneration treatments that focus on mitochondrial functions, including regulation of calcium ion (Ca2+) transport, protein modification, regulation of glucose metabolism, antioxidants, metal chelators, vitamin supplementation, and mitochondrial transference to compromised neurons. After pre-clinical evaluation and studies in animal models, some of these therapeutic compounds have advanced to clinical trials and are expected to have positive outcomes in subjects with neurodegeneration. These mitochondria-targeted therapeutic agents are an alternative to established or conventional molecular targets that have shown limited effectiveness in treating neurodegenerative diseases.

Young Astrocytic Mitochondria Attenuate the Elevated Level of CCL11 in the Aged Mice, Contributing to Cognitive Function Improvement

Aging drives cognitive decline, and mitochondrial dysfunction is a hallmark of age-induced neurodegeneration. Recently, we demonstrated that astrocytes secrete functional mitochondria (Mt), which help adjacent cells to resist damage and promote repair after neurological injuries. However, the relationship between age-dependent changes in astrocytic Mt function and cognitive decline remains poorly understood. Here, we established that aged astrocytes secret less functional Mt compared to young astrocytes. We found the aging factor C-C motif chemokine 11 (CCL11) is elevated in the hippocampus of aged mice, and that its level is reduced upon systemic administration of young Mt, in vivo. Aged mice receiving young Mt, but not aged Mt improved cognitive function and hippocampal integrity. Using a CCL11-induced aging-like model in vitro, we found that astrocytic Mt protect hippocampal neurons and enhance a regenerative environment through upregulating synaptogenesis-related gene expression and anti-oxidants that were suppressed by CCL11. Moreover, the inhibition of CCL11-specific receptor C-C chemokine receptor 3 (CCR3) boosted the expression of synaptogenesis-related genes in the cultured hippocampal neurons and restored the neurite outgrowth. This study suggests that young astrocytic Mt can preserve cognitive function in the CCL11-mediated aging brain by promoting neuronal survival and neuroplasticity in the hippocampus.

Neurotoxicity of ischemic astrocytes involves STAT3-mediated metabolic switching and depends on glycogen usage

Astrocytic responses are critical for the maintenance of neuronal networks in health and disease. In stroke, reactive astrocytes undergo functional changes potentially contributing to secondary neurodegeneration, but the mechanisms of astrocyte-mediated neurotoxicity remain elusive. Here, we investigated metabolic reprogramming in astrocytes following ischemia-reperfusion in vitro, explored their role in synaptic degeneration, and verified the key findings in a mouse model of stroke. Using indirect cocultures of primary mouse astrocytes and neurons, we demonstrate that transcription factor STAT3 controls metabolic switching in ischemic astrocytes promoting lactate-directed glycolysis and hindering mitochondrial function. Upregulation of astrocytic STAT3 signaling associated with nuclear translocation of pyruvate kinase isoform M2 and hypoxia response element activation. Reprogrammed thereby, the ischemic astrocytes induced mitochondrial respiration failure in neurons and triggered glutamatergic synapse loss, which was prevented by inhibiting astrocytic STAT3 signaling with Stattic. The rescuing effect of Stattic relied on the ability of astrocytes to utilize glycogen bodies as an alternative metabolic source supporting mitochondrial function. After focal cerebral ischemia in mice, astrocytic STAT3 activation was associated with secondary synaptic degeneration in the perilesional cortex. Inflammatory preconditioning with LPS increased astrocytic glycogen content, reduced synaptic degeneration, and promoted neuroprotection post stroke. Our data indicate the central role of STAT3 signaling and glycogen usage in reactive astrogliosis and suggest novel targets for restorative stroke therapy.

Commentary: Can astrocytic mitochondria therapy be used as antioxidant conditioning to protect neurons?

In the context of central nervous system (CNS) disease, oxidative stress may cause progression of cell death and neuroinflammation. Therefore, restoring mitochondrial antioxidant ability within cells is a major therapeutic strategy in many CNS disorders. A recent study uncovers a novel mechanism of astrocytic mitochondria being neuroprotective after intracerebral hemorrhage in mice. In their work, systemic administration of mitochondria obtained from astrocytes restores neuronal antioxidant defense, prevents neuronal death while promoting neurite outgrowth, indicating that extracellular mitochondria may play key roles in mediating beneficial non-cell autonomous effects. Given that mitochondria are also responsible for tolerance to stress and injury, is it possible that exogenous mitochondria signals may regulate cellular conditioning by boosting antioxidant ability? Further studies are warranted to build on these emerging findings in the pursuit of conditioning therapies mediated by mitochondrial transplantation in CNS injury and disease.

Mitochondria Transfer in Brain Injury and Disease

Intercellular mitochondria transfer is a novel form of cell signalling in which whole mitochondria are transferred between cells in order to enhance cellular functions or aid in the degradation of dysfunctional mitochondria. Recent studies have observed intercellular mitochondria transfer between glia and neurons in the brain, and mitochondrial transfer has emerged as a key neuroprotective mechanism in a range of neurological conditions. In particular, artificial mitochondria transfer has sparked widespread interest as a potential therapeutic strategy for brain disorders. In this review, we discuss the mechanisms and effects of intercellular mitochondria transfer in the brain. The role of mitochondrial transfer in neurological conditions, including neurodegenerative disease, brain injury, and neurodevelopmental disorders, is discussed as well as therapeutic strategies targeting mitochondria transfer in the brain.