Protective Effects of Endothelial Progenitor Cell-Derived Extracellular Mitochondria in Brain Endothelium

Utilizing engineered extracellular vesicles as delivery vectors in the management of ischemic stroke: a special outlook on mitochondrial delivery

Ischemic stroke is a secondary cause of mortality worldwide, imposing considerable medical and economic burdens on society. Extracellular vesicles, serving as natural nano-carriers for drug delivery, exhibit excellent biocompatibility in vivo and have significant advantages in the management of ischemic stroke. However, the uncertain distribution and rapid clearance of extracellular vesicles impede their delivery efficiency. By utilizing membrane decoration or by encapsulating therapeutic cargo within extracellular vesicles, their delivery efficacy may be greatly improved. Furthermore, previous studies have indicated that microvesicles, a subset of large-sized extracellular vesicles, can transport mitochondria to neighboring cells, thereby aiding in the restoration of mitochondrial function post-ischemic stroke. Small extracellular vesicles have also demonstrated the capability to transfer mitochondrial components, such as proteins or deoxyribonucleic acid, or their sub-components, for extracellular vesicle-based ischemic stroke therapy. In this review, we undertake a comparative analysis of the isolation techniques employed for extracellular vesicles and present an overview of the current dominant extracellular vesicle modification methodologies. Given the complex facets of treating ischemic stroke, we also delineate various extracellular vesicle modification approaches which are suited to different facets of the treatment process. Moreover, given the burgeoning interest in mitochondrial delivery, we delved into the feasibility and existing research findings on the transportation of mitochondrial fractions or intact mitochondria through small extracellular vesicles and microvesicles to offer a fresh perspective on ischemic stroke therapy.

Mitochondrion-based organellar therapies for central nervous system diseases

As most traditional drugs used to treat central nervous system (CNS) diseases have a single therapeutic target, many of them cannot treat complex diseases or diseases whose mechanism is unknown and cannot effectively reverse the root changes underlying CNS diseases. This raises the question of whether multiple functional components are involved in the complex pathological processes of CNS diseases. Organelles are the core functional units of cells, and the replacement of damaged organelles with healthy organelles allows the multitargeted and integrated modulation of cellular functions. The development of therapies that target independent functional units in the cell, specifically, organelle-based therapies, is rapidly progressing. This article comprehensively discusses the pathogenesis of mitochondrial homeostasis disorders, which involve mitochondria, one of the most important organelles in CNS diseases, and the machanisms of mitochondrion-based therapies, as well as current preclinical and clinical studies on the efficacy of therapies targeting mitochondrial to treat CNS diseases, to provide evidence for use of organelle-based treatment strategies in the future.

Mitochondria transfer-based therapies reduce the morbidity and mortality of Leigh syndrome

Mitochondria transfer is a recently described phenomenon in which donor cells deliver mitochondria to acceptor cells1-3. One possible consequence of mitochondria transfer is energetic support of neighbouring cells; for example, exogenous healthy mitochondria can rescue cell-intrinsic defects in mitochondrial metabolism in cultured ρ0 cells or Ndufs4-/- peritoneal macrophages4-7. Exposing haematopoietic stem cells to purified mitochondria before autologous haematopoietic stem cell transplantation allowed for treatment of anaemia in patients with large-scale mitochondrial DNA mutations8,9, and mitochondria transplantation was shown to minimize ischaemic damage to the heart10-12, brain13-15 and limbs16. However, the therapeutic potential of using mitochondria transfer-based therapies to treat inherited mitochondrial diseases is unclear. Here we demonstrate improved morbidity and mortality of the Ndufs4-/- mouse model of Leigh syndrome (LS) in multiple treatment paradigms associated with mitochondria transfer. Transplantation of bone marrow from wild-type mice, which is associated with release of haematopoietic cell-derived extracellular mitochondria into circulation and transfer of mitochondria to host cells in multiple organs, ameliorates LS in mice. Furthermore, administering isolated mitochondria from wild-type mice extends lifespan, improves neurological function and increases energy expenditure of Ndufs4-/- mice, whereas mitochondria from Ndufs4-/- mice did not improve neurological function. Finally, we demonstrate that cross-species administration of human mitochondria to Ndufs4-/- mice also improves LS. These data suggest that mitochondria transfer-related approaches can be harnessed to treat mitochondrial diseases, such as LS.

Mitochondria-containing extracellular vesicles from mouse vs. human brain endothelial cells for ischemic stroke therapy

Ischemic stroke-induced mitochondrial dysfunction in the blood-brain barrier-forming brain endothelial cells (BECs) results in long-term neurological dysfunction post-stroke. We previously reported data from a pilot study where intravenous administration of human BEC (hBEC)-derived mitochondria-containing extracellular vesicles (EVs) showed a potential efficacy signal in a mouse middle cerebral artery occlusion (MCAo) model of stroke. We hypothesized that EVs harvested from donor species homologous to the recipient species (e.g., mouse) may improve therapeutic efficacy, and therefore, use of mouse BEC (mBEC)-derived EVs may improve post-stroke outcomes in MCAo mice. We investigated potential differences in the mitochondria transfer of EVs derived from the same species as the recipient cell (mBEC-EVs and recipient mBECs or hBECs-EVs and recipient hBECs) vs. cross-species EVs and recipient cells (mBEC-EVs and recipient hBECs or vice versa). Our results showed that while both hBEC- and mBEC-EVs transferred EV mitochondria, mBEC-EVs outperformed hBEC-EVs in increasing ATP levels and improved recipient mBEC mitochondrial function via increasing oxygen consumption rates. mBEC-EVs significantly reduced brain infarct volume and neurological deficit scores compared to vehicle-injected MCAo mice. The superior therapeutic efficacy of mBEC-EVs in MCAo mice support the continued use of mBEC-EVs to optimize the therapeutic potential of mitochondria-containing EVs in preclinical mouse models.

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.

Secretome of brain microvascular endothelial cells promotes endothelial barrier tightness and protects against hypoxia-induced vascular leakage

Cell-based therapeutic strategies have been proposed as an alternative for brain and blood vessels repair after stroke, but their clinical application is hampered by potential adverse effects. We therefore tested the hypothesis that secretome of these cells might be used instead to still focus on cell-based therapeutic strategies. We therefore characterized the composition and the effect of the secretome of brain microvascular endothelial cells (BMECs) on primary in vitro human models of angiogenesis and vascular barrier. Two different secretome batches produced in high scale (scHSP) were analysed by mass spectrometry. Human primary CD34+-derived endothelial cells (CD34+-ECs) were used as well as in vitro models of EC monolayer (CMECs) and blood-brain barrier (BBB). Cells were also exposed to oxygen-glucose deprivation (OGD) conditions and treated with scHSP during reoxygenation. Protein yield and composition of scHSP batches showed good reproducibility. scHSP increased CD34+-EC proliferation, tubulogenesis, and migration. Proteomic analysis of scHSP revealed the presence of growth factors and proteins modulating cell metabolism and inflammatory pathways. scHSP improved the integrity of CMECs, and upregulated the expression of junctional proteins. Such effects were mediated through the activation of the interferon pathway and downregulation of Wnt signalling. Furthermore, OGD altered the permeability of both CMECs and BBB, while scHSP prevented the OGD-induced vascular leakage in both models. These effects were mediated through upregulation of junctional proteins and regulation of MAPK/VEGFR2. Finally, our results highlight the possibility of using secretome from BMECs as a therapeutic alternative to promote brain angiogenesis and to protect from ischemia-induced vascular leakage.

Mitochondria Transplantation to Bone Marrow Stromal Cells Promotes Angiogenesis During Bone Repair

Angiogenesis is crucial for successful bone defect repair. Co-transplanting Bone Marrow Stromal Cells (BMSCs) and Endothelial Cells (ECs) has shown promise for vascular augmentation, but it face challenges in hostile tissue microenvironments, including poor cell survival and limited efficacy. In this study, the mitochondria of human BMSCs are isolated and transplanted to BMSCs from the same batch and passage number (BMSCsmito). The transplanted mitochondria significantly boosted the ability of BMSCsmito-ECs to promote angiogenesis, as assessed by in vitro tube formation and spheroid sprouting assays, as well as in vivo transplantation experiments in balb/c mouse and SD rat models. The Dll4-Notch1 signaling pathway is found to play a key role in BMSCsmito-induced endothelial tube formation. Co-transplanting BMSCsmito with ECs in a rat cranial bone defect significantly improves functional vascular network formation, and improve bone repair outcomes. These findings thus highlight that mitochondrial transplantation, by acting through the DLL4-Notch1 signaling pathway, represents a promising therapeutic strategy for enhancing angiogenesis and improving bone repair. Hence, mitochondrial transplantation to BMSCS as a therapeutic approach for promoting angiogenesis offers valuable insights and holds much promise for innovative regenerative medicine therapies.

Mitochondria-containing extracellular vesicles from mouse vs . human brain endothelial cells for ischemic stroke therapy

Ischemic stroke-induced mitochondrial dysfunction in the blood-brain barrier-forming brain endothelial cells ( BECs ) results in long-term neurological dysfunction post-stroke. We previously data from a pilot study where intravenous administration of human BEC ( hBEC )-derived mitochondria-containing extracellular vesicles ( EVs ) showed a potential efficacy signal in a mouse middle cerebral artery occlusion ( MCAo ) model of stroke. We hypothesized that EVs harvested from donor species homologous to the recipient species ( e.g., mouse) may improve therapeutic efficacy, and therefore, use of mouse BEC ( mBEC )-derived EVs may improve post-stroke outcomes in MCAo mice. We investigated potential differences in the mitochondria transfer of EVs derived from the same species as the recipient cell (mBEC-EVs and recipient mBECs or hBECs-EVs and recipient hBECs) vs . cross-species EVs and recipient cells (mBEC-EVs and recipient hBECs or vice versa ). Our results showed that while both hBEC- and mBEC-EVs transferred EV mitochondria, mBEC-EVs outperformed hBEC-EVs in increasing ATP levels and improved recipient mBEC mitochondrial function via increasing oxygen consumption rates. mBEC-EVs significantly reduced brain infarct volume and neurological deficit scores compared to vehicle-injected MCAo mice. The superior therapeutic efficacy of mBEC-EVs in a mouse MCAo stroke support the continued use of mBEC-EVs to optimize the therapeutic potential of mitochondria-containing EVs in preclinical mouse models.

Oxidative stress induces release of mitochondrial DNA into the extracellular space in human placental villous trophoblast BeWo cells

Circulating cell-free mitochondrial DNA (ccf-mtDNA) is an indicator of cell death, inflammation, and oxidative stress. ccf-mtDNA in pregnancies with placental dysfunction differs from that in healthy pregnancies, and the direction of this difference depends on gestational age and method of mtDNA quantification. Reactive oxygen species (ROS) trigger release of mtDNA, yet it is unknown whether trophoblast cells release mtDNA in response to oxidative stress, a common feature of pregnancies with placental pathology. We hypothesized that oxidative stress would induce cell death and release of mtDNA from trophoblast cells. BeWo cells were treated with antimycin A (10-320 µM) or rotenone (0.2-50 µM) to induce oxidative stress. A multiplex real-time quantitative PCR (qPCR) assay was used to quantify mtDNA and nuclear DNA in membrane-bound, non-membrane-bound, and vesicle-bound forms in cell culture supernatants and cell lysates. Treatment with antimycin A increased ROS (P < 0.0001), induced cell necrosis (P = 0.0004) but not apoptosis (P = 0.6471), and was positively associated with release of membrane-bound and non-membrane-bound mtDNA (P < 0.0001). Antimycin A increased mtDNA content in exosome-like extracellular vesicles (vesicle-bound form; P = 0.0019) and reduced autophagy marker expression (LC3A/B, P = 0.0002; p62, P < 0.001). Rotenone treatment did not influence mtDNA release or cell death (P > 0.05). Oxidative stress induces release of mtDNA into the extracellular space and causes nonapoptotic cell death and a reduction in autophagy markers in BeWo cells, an established in vitro model of human trophoblast cells. Intersection between autophagy and necrosis may mediate the release of mtDNA from the placenta in pregnancies exposed to oxidative stress.NEW & NOTEWORTHY This is the first study to test whether trophoblast cells release mitochondrial (mt)DNA in response to oxidative stress and to identify mechanisms of release and biological forms of mtDNA from this cellular type. This research identifies potential cellular mechanisms that can be used in future investigations to establish the source and biomarker potential of circulating mtDNA in preclinical experimental models and humans.

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

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

Hypothermia promotes tunneling nanotube formation and the transfer of astrocytic mitochondria into oxygen-glucose deprivation/reoxygenation-injured neurons

Mitochondrial transfer occurs between cells, and it is important for damaged cells to receive healthy mitochondria to maintain their normal function and protect against cell death. Accumulating evidence suggests that the functional mitochondria of astrocytes are released and transferred to oxygen-glucose deprivation/reoxygenation (OGD/R)-injured neurons. Mild hypothermia (33 °C) is capable of promoting this process, which partially restores the function of damaged neurons. However, the pathways and mechanisms by which mild hypothermia facilitates mitochondrial transfer remain unclear. We are committed to studying the role of mild hypothermia in neuroprotection to provide reliable evidences and insights for the clinical application of mild hypothermia in brain protection. Tunneling nanotubes (TNTs) are considered to be one of the routes through which mitochondria are transferred between cells. In this study, an OGD/R-injured neuronal model was successfully established, and TNTs, mitochondria, neurons and astrocytes were double labeled using immunofluorescent probes. Our results showed that TNTs were present and involved in the transfer of mitochondria between cells in the mixed-culture system of neurons and astrocytes. When neurons were subjected to OGD/R exposure, TNT formation and mitochondrial transportation from astrocytes to injured neurons were facilitated. Further analysis revealed that mild hypothermia increased the quantity of astrocytic mitochondria transferred into damaged neurons through TNTs, raised the mitochondrial membrane potential (MMP), and decreased the neuronal damage and death during OGD/R. Altogether, our data indicate that TNTs play an important role in the endogenous neuroprotection of astrocytic mitochondrial transfer. Furthermore, mild hypothermia enhances astrocytic mitochondrial transfer into OGD/R-injured neurons via TNTs, thereby promoting neuroprotection and neuronal recovery.

Mitochondrial dysfunction and quality control lie at the heart of subarachnoid hemorrhage

The dramatic increase in intracranial pressure after subarachnoid hemorrhage leads to a decrease in cerebral perfusion pressure and a reduction in cerebral blood flow. Mitochondria are directly affected by direct factors such as ischemia, hypoxia, excitotoxicity, and toxicity of free hemoglobin and its degradation products, which trigger mitochondrial dysfunction. Dysfunctional mitochondria release large amounts of reactive oxygen species, inflammatory mediators, and apoptotic proteins that activate apoptotic pathways, further damaging cells. In response to this array of damage, cells have adopted multiple mitochondrial quality control mechanisms through evolution, including mitochondrial protein quality control, mitochondrial dynamics, mitophagy, mitochondrial biogenesis, and intercellular mitochondrial transfer, to maintain mitochondrial homeostasis under pathological conditions. Specific interventions targeting mitochondrial quality control mechanisms have emerged as promising therapeutic strategies for subarachnoid hemorrhage. This review provides an overview of recent research advances in mitochondrial pathophysiological processes after subarachnoid hemorrhage, particularly mitochondrial quality control mechanisms. It also presents potential therapeutic strategies to target mitochondrial quality control in subarachnoid hemorrhage.

The role of mitochondrial transfer via tunneling nanotubes in the central nervous system: A review

Tumour necrosis factor alpha-induced protein 2 (TNFAIP2) is a gene induced by tumor necrosis factor in endothelial cells. TNFAIP2 has important functions in physiological and pathological processes, including cell proliferation, adhesion, migration, angiogenesis, inflammation, tunneling nanotube (TNT) formation and tumorigenesis. Moreover, TNFAIP2 is the key factor in the formation of TNTs. TNTs are related to signal transduction between different cell types and are considered a novel means of cell-to-cell communication. Mesenchymal stem cells (MSCs) are pluripotent cells that exhibit self-renewal, multidirectional differentiation, paracrine function and immune-regulating ability. MSCs can transfer mitochondria through TNTs to improve the functions of target cells. This review revealed that TNFAIP2 promotes the formation of TNTs and that MSCs rely on TNTs for mitochondrial transfer to ameliorate cell dysfunction.

Oxidative stress induces release of mitochondrial DNA into the extracellular space in human placental villous trophoblast BeWo cells

Circulating cell-free mitochondrial DNA (ccf-mtDNA) is an indicator of cell death, inflammation, and oxidative stress. ccf-mtDNA differs in pregnancies with placental dysfunction from healthy pregnancies and the direction of this difference depends on gestational age and method of mtDNA quantification. Reactive oxygen species (ROS) trigger release of mtDNA from non-placental cells; yet it is unknown whether trophoblast cells release mtDNA in response to oxidative stress, a common feature of pregnancies with placental pathology. We hypothesized that oxidative stress would induce cell death and release of mtDNA from trophoblast cells. BeWo cells were treated with antimycin A (10-320 μM) or rotenone (0.2-50 μM) to induce oxidative stress. A multiplex real-time quantitative PCR (qPCR) assay was used to quantify mtDNA and nuclear DNA in membrane bound, non-membrane bound, and vesicular-bound forms in cell culture supernatants and cell lysates. Treatment with antimycin A increased ROS (p<0.0001), induced cell necrosis (p=0.0004) but not apoptosis (p=0.6471) and was positively associated with release of membrane-bound and non-membrane bound mtDNA (p<0.0001). Antimycin A increased mtDNA content in exosome-like extracellular vesicles (vesicular-bound form; p=0.0019) and reduced autophagy marker expression (LC3A/B, p=0.0002; p62, p<0.001). Rotenone treatment did not influence mtDNA release or cell death (p>0.05). Oxidative stress induces release of mtDNA into the extracellular space and causes non-apoptotic cell death and a reduction in autophagy markers in BeWo cells, an established in vitro model of human trophoblast cells. Intersection between autophagy and necrosis may mediate the release of mtDNA from the placenta in pregnancies exposed to oxidative stress.

NEW & NOTEWORTHY

This is the first study to test whether trophoblast cells release mitochondrial DNA in response to oxidative stress and to identify mechanisms of release and biological forms of mtDNA from this cellular type. This research identifies potential cellular mechanisms that can be used in future investigations to establish the source and biomarker potential of circulating mitochondrial DNA in preclinical experimental models and humans.

Angiogenic activity of mitochondria; beyond the sole bioenergetic organelle

Angiogenesis is a complex process that involves the expansion of the pre-existing vascular plexus to enhance oxygen and nutrient delivery and is stimulated by various factors, including hypoxia. Since the process of angiogenesis requires a lot of energy, mitochondria play an important role in regulating and promoting this phenomenon. Besides their roles as an oxidative metabolism base, mitochondria are potential bioenergetics organelles to maintain cellular homeostasis via sensing alteration in oxygen levels. Under hypoxic conditions, mitochondria can regulate angiogenesis through different factors. It has been indicated that unidirectional and bidirectional exchange of mitochondria or their related byproducts between the cells is orchestrated via different intercellular mechanisms such as tunneling nanotubes, extracellular vesicles, and gap junctions to maintain the cell homeostasis. Even though, the transfer of mitochondria is one possible mechanism by which cells can promote and regulate the process of angiogenesis under reperfusion/ischemia injury. Despite the existence of a close relationship between mitochondrial donation and angiogenic response in different cell types, the precise molecular mechanisms associated with this phenomenon remain unclear. Here, we aimed to highlight the possible role of mitochondria concerning angiogenesis, especially the role of mitochondrial transport and the possible relation of this transfer with autophagy, the housekeeping phenomenon of cells, and angiogenesis.

Extracellular vesicles set the stage for brain plasticity and recovery by multimodal signalling

Extracellular vesicles (EVs) are extremely versatile naturally occurring membrane particles that convey complex signals between cells. EVs of different cellular sources are capable of inducing striking therapeutic responses in neurological disease models. Differently from pharmacological compounds that act by modulating defined signalling pathways, EV-based therapeutics possess multiple abilities via a variety of effectors, thus allowing the modulation of complex disease processes that may have very potent effects on brain tissue recovery. When applied in vivo in experimental models of neurological diseases, EV-based therapeutics have revealed remarkable effects on immune responses, cell metabolism and neuronal plasticity. This multimodal modulation of neuroimmune networks by EVs profoundly influences disease processes in a highly synergistic and context-dependent way. Ultimately, the EV-mediated restoration of cellular functions helps to set the stage for neurological recovery. With this review we first outline the current understanding of the mechanisms of action of EVs, describing how EVs released from various cellular sources identify their cellular targets and convey signals to recipient cells. Then, mechanisms of action applicable to key neurological conditions such as stroke, multiple sclerosis and neurodegenerative diseases are presented. Pathways that deserve attention in specific disease contexts are discussed. We subsequently showcase considerations about EV biodistribution and delineate genetic engineering strategies aiming at enhancing brain uptake and signalling. By sketching a broad view of EV-orchestrated brain plasticity and recovery, we finally define possible future clinical EV applications and propose necessary information to be provided ahead of clinical trials. Our goal is to provide a steppingstone that can be used to critically discuss EVs as next generation therapeutics for brain diseases.

Mitochondria as secretory organelles and therapeutic cargos

Mitochondria have been primarily considered intracellular organelles that are responsible for generating energy for cell survival. However, accumulating evidence suggests that mitochondria are secreted into the extracellular space under physiological and pathological conditions, and these secreted mitochondria play diverse roles by regulating metabolism, the immune response, or the differentiation/maturation in target cells. Furthermore, increasing amount of research shows the therapeutic effects of local or systemic administration of mitochondria in various disease models. These findings have led to growing interest in exploring mitochondria as potential therapeutic agents. Here, we discuss the emerging roles of mitochondria as extracellularly secreted organelles to shed light on their functions beyond energy production. Additionally, we provide information on therapeutic outcomes of mitochondrial transplantation in animal models of diseases and an update on ongoing clinical trials, underscoring the potential of using mitochondria as a novel therapeutic intervention.

Blood-brain barrier dysfunction in multiple sclerosis: causes, consequences, and potential effects of therapies

Established by brain endothelial cells, the blood-brain barrier (BBB) regulates the trafficking of molecules, restricts immune cell entry into the CNS, and has an active role in neurovascular coupling (the regulation of cerebral blood flow to support neuronal activity). In the early stages of multiple sclerosis, around the time of symptom onset, inflammatory BBB damage is accompanied by pathogenic immune cell infiltration into the CNS. In the later stages of multiple sclerosis, dysregulation of neurovascular coupling is associated with grey matter atrophy. Genetic and environmental factors associated with multiple sclerosis, including dietary habits, the gut microbiome, and vitamin D concentrations, might contribute directly and indirectly to brain endothelial cell dysfunction. Damage to brain endothelial cells leads to an influx of deleterious molecules into the CNS, accelerating leakage across the BBB. Potential future therapeutic approaches might help to prevent BBB damage (eg, monoclonal antibodies targeting cell adhesion molecules and fibrinogen) and help to repair BBB dysfunction (eg, mesenchymal stromal cells) in people with multiple sclerosis.

Mitochondrial Transfer Between Mesenchymal Stem Cells and Cancer Cells

Mitochondrial transfer (MT) is a biological process that allows a donor cell to horizontally share its own mitochondria with a recipient cell. Mitochondria are highly dynamic membrane-bound sub-cellular organelles prominently involved in the regulation of the cell energy balance, calcium homeostasis, and apoptotic machinery activation. They physiologically undergo fusion and fission processes in response to the cell requirement, with a continuous morphological re-arrangement. This structural and functional plasticity is at the basis of the MT, described in tissue regeneration, cardiac and neurological diseases, as well as in cancer. Here, the MT has been observed in the tumor micro-environment (TME) from the adipose-derived stem cells (ASCs) to the cancer cells, eventually reverting the lack of the mitochondria respiration function, or enhancing their motility and drug resistance. In this chapter, we outline some key protocols for evaluating this exciting phenomenon of MT. These methodological and technical approaches are very important, considering all the limitations that scientists constantly face, especially in this field of the research.

Targeting mitophagy for neurological disorders treatment: advances in drugs and non-drug approaches

Mitochondria serve as a vital energy source for nerve cells. The mitochondrial network also acts as a defense mechanism against external stressors that can threaten the stability of the nervous system. However, excessive accumulation of damaged mitochondria can lead to neuronal death. Mitophagy is an essential pathway in the mitochondrial quality control system and can protect neurons by selectively removing damaged mitochondria. In most neurological disorders, dysfunctional mitochondria are a common feature, and drugs that target mitophagy can improve symptoms. Here, we reviewed the role of mitophagy in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, stroke, and traumatic brain injuries. We also summarized drug and non-drug approaches to promote mitophagy and described their therapeutic role in neurological disorders in order to provide valuable insight into the potential therapeutic agents available for neurological disease treatment. However, most studies on mitophagy regulation are based on preclinical research using cell and animal models, which may not accurately reflect the effects in humans. This poses a challenge to the clinical application of drugs targeting mitophagy. Additionally, these drugs may carry the risk of intolerable side effects and toxicity. Future research should focus on the development of safer and more targeted drugs for mitophagy.

The power and potential of mitochondria transfer

Mitochondria are believed to have originated through an ancient endosymbiotic process in which proteobacteria were captured and co-opted for energy production and cellular metabolism. Mitochondria segregate during cell division and differentiation, with vertical inheritance of mitochondria and the mitochondrial DNA genome from parent to daughter cells. However, an emerging body of literature indicates that some cell types export their mitochondria for delivery to developmentally unrelated cell types, a process called intercellular mitochondria transfer. In this Review, we describe the mechanisms by which mitochondria are transferred between cells and discuss how intercellular mitochondria transfer regulates the physiology and function of various organ systems in health and disease. In particular, we discuss the role of mitochondria transfer in regulating cellular metabolism, cancer, the immune system, maintenance of tissue homeostasis, mitochondrial quality control, wound healing and adipose tissue function. We also highlight the potential of targeting intercellular mitochondria transfer as a therapeutic strategy to treat human diseases and augment cellular therapies.

Epithelial Transport in Disease: An Overview of Pathophysiology and Treatment

Epithelial transport is a multifaceted process crucial for maintaining normal physiological functions in the human body. This comprehensive review delves into the pathophysiological mechanisms underlying epithelial transport and its significance in disease pathogenesis. Beginning with an introduction to epithelial transport, it covers various forms, including ion, water, and nutrient transfer, followed by an exploration of the processes governing ion transport and hormonal regulation. The review then addresses genetic disorders, like cystic fibrosis and Bartter syndrome, that affect epithelial transport. Furthermore, it investigates the involvement of epithelial transport in the pathophysiology of conditions such as diarrhea, hypertension, and edema. Finally, the review analyzes the impact of renal disease on epithelial transport and highlights the potential for future research to uncover novel therapeutic interventions for conditions like cystic fibrosis, hypertension, and renal failure.

Muscle mitochondrial transplantation can rescue and maintain cellular homeostasis

Mitochondria control cellular functions through their metabolic role. Recent research that has gained considerable attention is their ability to transfer between cells. This has the potential of improving cellular functions in pathological or energy-deficit conditions, but little is known about the role of mitochondrial transfer in sustaining cellular homeostasis. Few studies have investigated the potential of skeletal muscle as a source of healthy mitochondria that can be transferred to other cell types. Thus, we isolated intermyofibrillar mitochondria from murine skeletal muscle and incubated them with host cells. We observed dose- and time-dependent increases in mitochondrial incorporation into myoblasts. This resulted in elongated mitochondrial networks and an enhancement of bioenergetic profile of the host cells. Mitochondrial donation also rejuvenated the functional capacities of the myoblasts when respiration efficiency and lysosomal function were inhibited by complex I inhibitor rotenone and bafilomycin A, respectively. Mitochondrial transfer was accomplished via tunneling nanotubes, extracellular vesicles, gap junctions, and by macropinocytosis internalization. Murine muscle mitochondria were also effectively transferred to human fibroblast cells having mitochondrial DNA mutations, resulting in augmented mitochondrial dynamics and metabolic functions. This improved cell function by diminishing reactive oxygen species (ROS) emission in the diseased cells. Our findings suggest that mitochondria from donor skeletal muscle can be integrated in both healthy and functionally compromised host cells leading to mitochondrial structural refinement and respiratory boost. This mitochondrial trafficking and bioenergetic reprogramming to maintain and revitalize tissue homeostasis could be a useful therapeutic strategy in treating diseases.NEW & NOTEWORTHY In our study, we have shown the potential of mouse skeletal muscle intermyofibrillar mitochondria to be transplanted in myoblasts and human fibroblast cells having mitochondrial DNA mutations. This resulted in an augmentation of mitochondrial dynamics and enhancement of bioenergetic profile in the host cells. Our findings suggest that mitochondria from donor skeletal muscle can be integrated into both healthy and functionally compromised host cells leading to mitochondrial structural refinement and respiratory boost.

Bone Marrow-Derived Mononuclear Cells in the Treatment of Neurological Diseases: Knowns and Unknowns

Bone marrow-derived mononuclear cells (BMMNCs) have been used for decades in preclinical and clinical studies to treat various neurological diseases. However, there is still a knowledge gap in the understanding of the underlying mechanisms of BMMNCs in the treatment of neurological diseases. In addition, prerequisite factors for the efficacy of BMMNC administration, such as the optimal route, dose, and number of administrations, remain unclear. In this review, we discuss known and unknown aspects of BMMNCs, including the cell harvesting, administration route and dose; mechanisms of action; and their applications in neurological diseases, including stroke, cerebral palsy, spinal cord injury, traumatic brain injury, amyotrophic lateral sclerosis, autism spectrum disorder, and epilepsy. Furthermore, recommendations on indications for BMMNC administration and the advantages and limitations of BMMNC applications for neurological diseases are discussed. BMMNCs in the treatment of neurological diseases. BMMNCs have been applied in several neurological diseases. Proposed mechanisms for the action of BMMNCs include homing, differentiation and paracrine effects (angiogenesis, neuroprotection, and anti-inflammation). Further studies should be performed to determine the optimal cell dose and administration route, the roles of BMMNC subtypes, and the indications for the use of BMMNCs in neurological conditions with and without genetic abnormalities.

Mitochondrial dysfunction in neurodegenerative disorders: Potential therapeutic application of mitochondrial transfer to central nervous system-residing cells

Mitochondrial dysfunction is reiteratively involved in the pathogenesis of diverse neurodegenerative diseases. Current in vitro and in vivo approaches support that mitochondrial dysfunction is branded by several molecular and cellular defects, whose impact at different levels including the calcium and iron homeostasis, energetic balance and/or oxidative stress, makes it difficult to resolve them collectively given their multifactorial nature. Mitochondrial transfer offers an overall solution since it contains the replacement of damage mitochondria by healthy units. Therefore, this review provides an introducing view on the structure and energy-related functions of mitochondria as well as their dynamics. In turn, we summarize current knowledge on how these features are deregulated in different neurodegenerative diseases, including frontotemporal dementia, multiple sclerosis, amyotrophic lateral sclerosis, Friedreich ataxia, Alzheimer´s disease, Parkinson´s disease, and Huntington's disease. Finally, we analyzed current advances in mitochondrial transfer between diverse cell types that actively participate in neurodegenerative processes, and how they might be projected toward developing novel therapeutic strategies.

Exploring the therapeutic potential of the mitochondrial transfer-associated enzymatic machinery in brain degeneration

Mitochondrial dysfunction is a central event in the pathogenesis of several degenerative brain disorders. It entails fission and fusion dynamics disruption, progressive decline in mitochondrial clearance, and uncontrolled oxidative stress. Many therapeutic strategies have been formulated to reverse these alterations, including replacing damaged mitochondria with healthy ones. Spontaneous mitochondrial transfer is a naturally occurring process with different biological functions. It comprises mitochondrial donation from one cell to another, carried out through different pathways, such as the formation and stabilization of tunneling nanotubules and Gap junctions and the release of extracellular vesicles with mitochondrial cargoes. Even though many aspects of regulating these mechanisms still need to be discovered, some key enzymatic regulators have been identified. This review summarizes the current knowledge on mitochondrial dysfunction in different neurodegenerative disorders. Besides, we analyzed the usage of mitochondrial transfer as an endogenous revitalization tool, emphasizing the enzyme regulators that govern this mechanism. Going deeper into this matter would be helpful to take advantage of the therapeutic potential of mitochondrial transfer.

Mitochondria in endothelial cells angiogenesis and function: current understanding and future perspectives

Endothelial cells (ECs) angiogenesis is the process of sprouting new vessels from the existing ones, playing critical roles in physiological and pathological processes such as wound healing, placentation, ischemia/reperfusion, cardiovascular diseases and cancer metastasis. Although mitochondria are not the major sites of energy source in ECs, they function as important biosynthetic and signaling hubs to regulate ECs metabolism and adaptations to local environment, thus affecting ECs migration, proliferation and angiogenic process. The understanding of the importance and potential mechanisms of mitochondria in regulating ECs metabolism, function and the process of angiogenesis has developed in the past decades. Thus, in this review, we discuss the current understanding of mitochondrial proteins and signaling molecules in ECs metabolism, function and angiogeneic signaling, to provide new and therapeutic targets for treatment of diverse cardiovascular and angiogenesis-dependent diseases.

ROS-responsive exogenous functional mitochondria can rescue neural cells post-ischemic stroke

Background: The transfer of mitochondria from healthy mesenchymal stem cells (MSCs) to injured MSCs has been shown to have potential therapeutic benefits for neural cell post-ischemic stroke. Specifically, functional mitochondria can perform their normal functions after being internalized by stressed cells, leading to host cell survival. However, while this approach shows promise, there is still a lack of understanding regarding which neural cells can internalize functional mitochondria and the regulatory mechanisms involved. To address this gap, we investigated the ability of different neural cells to internalize exogenous functional mitochondria extracted from MSCs. Methods: Functional mitochondria (F-Mito) isolated from umbilical cord derived-MSCs (UCMSCs) were labeled with lentivirus of HBLV-mito-dsred-Null-PURO vector. The ability of stressed cells to internalize F-Mito was analyzed using a mouse (C57BL/6 J) middle cerebral artery occlusion (MCAO) model and an oxygen-glucose deprivation/reoxygenation (OGD/R) cell model. The cell viability was measured by CCK-8 kit. Time-course of intracellular ROS levels in stressed cells were analyzed by DCFH-DA staining after OGD/R and F-Mito treatment. MitoSOX, Mitotracker and WGA labeling were used to assess the relationship between ROS levels and the uptake of F-Mito at the single-cell level. Pharmacological modulation of ROS was performed using acetylcysteine (ROS inhibitor). Results: Our findings demonstrate that neurons and endothelial cells are more effective at internalizing mitochondria than astrocytes, both in vitro and in vivo, using an ischemia-reperfusion model. Additionally, internalized F-Mito decreases host cell reactive oxygen species (ROS) levels and rescues survival. Importantly, we found that the ROS response in stressed cells after ischemia is a crucial determinant in positively mediating the internalization of F-Mito by host cells, and inhibiting the generation of ROS chemicals in host cells may decrease the internalization of F-Mito. These results offer insight into how exogenous mitochondria rescue neural cells via ROS response in an ischemic stroke model. Overall, our study provides solid evidence for the translational application of MSC-derived mitochondria as a promising treatment for ischemic stroke.

Lineage-Mismatched Mitochondrial Replacement in an Inducible Mitochondrial Depletion Model Effectively Restores the Original Proteomic Landscape of Recipient Cells

In addition to critical roles in bioenergetics, mitochondria are key contributors to the regulation of many other functions in cells, ranging from steroidogenesis to apoptosis. Numerous studies further demonstrate that cell type-specific differences exist in mitochondria, with cells of a given lineage tailoring their endogenous mitochondrial population to suit specific functional needs. These findings, coupled with studies of the therapeutic potential of mitochondrial transplantation, provide a strong impetus to better understand how mitochondria can influence cell function or fate. Here an inducible mitochondrial depletion modelis used to study how cells lacking endogenous mitochondria respond, on a global protein expression level, to transplantation with lineage-mismatched (LM) mitochondria. It is shown that LM mitochondrial transplantation does not alter the proteomic profile in nonmitochondria-depleted recipient cells; however, enforced depletion of endogenous mitochondria results in dramatic changes in the proteomic landscape, which returns to the predepletion state following internalization of LM mitochondria. These data, derived from a cell system that can be rendered free of influence by endogenous mitochondria, indicate that transplantation of mitochondria-even from a source that differs significantly from the recipient cell population, effectively restores a normal proteomic landscape to cells lacking their own mitochondria.

Mitochondrial Transfer as a Novel Therapeutic Approach in Disease Diagnosis and Treatment

Mitochondrial dysfunction is a hallmark of numerous diseases, including neurodegenerative disorders, metabolic disorders, and cancer. Mitochondrial transfer, the transfer of mitochondria from one cell to another, has recently emerged as a potential therapeutic approach for restoring mitochondrial function in diseased cells. In this review, we summarize the current understanding of mitochondrial transfer, including its mechanisms, potential therapeutic applications, and impact on cell death pathways. We also discuss the future directions and challenges in the field of mitochondrial transfer as a novel therapeutic approach in disease diagnosis and treatment.

Exogenous mitochondrial transplantation improves survival and neurological outcomes after resuscitation from cardiac arrest

BACKGROUND

Mitochondrial transplantation (MTx) is an emerging but poorly understood technology with the potential to mitigate severe ischemia-reperfusion injuries after cardiac arrest (CA). To address critical gaps in the current knowledge, we test the hypothesis that MTx can improve outcomes after CA resuscitation.

METHODS

This study consists of both in vitro and in vivo studies. We initially examined the migration of exogenous mitochondria into primary neural cell culture in vitro. Exogenous mitochondria extracted from the brain and muscle tissues of donor rats and endogenous mitochondria in the neural cells were separately labeled before co-culture. After a period of 24 h following co-culture, mitochondrial transfer was observed using microscopy. In vitro adenosine triphosphate (ATP) contents were assessed between freshly isolated and frozen-thawed mitochondria to compare their effects on survival. Our main study was an in vivo rat model of CA in which rats were subjected to 10 min of asphyxial CA followed by resuscitation. At the time of achieving successful resuscitation, rats were randomly assigned into one of three groups of intravenous injections: vehicle, frozen-thawed, or fresh viable mitochondria. During 72 h post-CA, the therapeutic efficacy of MTx was assessed by comparison of survival rates. The persistence of labeled donor mitochondria within critical organs of recipient animals 24 h post-CA was visualized via microscopy.

RESULTS

The donated mitochondria were successfully taken up into cultured neural cells. Transferred exogenous mitochondria co-localized with endogenous mitochondria inside neural cells. ATP content in fresh mitochondria was approximately four times higher than in frozen-thawed mitochondria. In the in vivo survival study, freshly isolated functional mitochondria, but not frozen-thawed mitochondria, significantly increased 72-h survival from 55 to 91% (P = 0.048 vs. vehicle). The beneficial effects on survival were associated with improvements in rapid recovery of arterial lactate and glucose levels, cerebral microcirculation, lung edema, and neurological function. Labeled mitochondria were observed inside the vital organs of the surviving rats 24 h post-CA.

CONCLUSIONS

MTx performed immediately after resuscitation improved survival and neurological recovery in post-CA rats. These results provide a foundation for future studies to promote the development of MTx as a novel therapeutic strategy to save lives currently lost after CA.

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.

Rescuers from the Other Shore: Intercellular Mitochondrial Transfer and Its Implications in Central Nervous System Injury and Diseases

As the powerhouse and core of cellular metabolism and survival, mitochondria are the essential organelle in mammalian cells and maintain cellular homeostasis by changing their content and morphology to meet demands through mitochondrial quality control. It has been observed that mitochondria can move between cells under physiological and pathophysiological conditions, which provides a novel strategy for preserving mitochondrial homeostasis and also a therapeutic target for applications in clinical settings. Therefore, in this review, we will summarize currently known mechanisms of intercellular mitochondrial transfer, including modes, triggers, and functions. Due to the highly demanded energy and indispensable intercellular linkages of the central nervous system (CNS), we highlight the mitochondrial transfer in CNS. We also discuss future application possibilities and difficulties that need to be addressed in the treatment of CNS injury and diseases. This clarification should shed light on its potential clinical applications as a promising therapeutic target in neurological diseases. Intercellular mitochondrial transfer maintains the homeostasis of central nervous system (CNS), and its alteration is related to several neurological diseases. Supplementing exogenous mitochondrial donor cells and mitochondria, or utilizing some medications to regulate the process of transfer might mitigate the disease and injury.

Dying transplanted neural stem cells mediate survival bystander effects in the injured brain

Neural stem and progenitor cell (NSPC) transplants provide neuroprotection in models of acute brain injury, but the underlying mechanisms are not fully understood. Here, we provide evidence that caspase-dependent apoptotic cell death of NSPCs is required for sending survival signals to the injured brain. The secretome of dying NSPCs contains heat-stable proteins, which protect neurons against glutamate-induced toxicity and trophic factor withdrawal in vitro, and from ischemic brain damage in vivo. Our findings support a new concept suggesting a bystander effect of apoptotic NSPCs, which actively promote neuronal survival through the release of a protective "farewell" secretome. Similar protective effects by the secretome of apoptotic NSPC were also confirmed in human neural progenitor cells and neural stem cells but not in mouse embryonic fibroblasts (MEF) or human dopaminergic neurons, suggesting that the observed effects are cell type specific and exist for neural progenitor/stem cells across species.

Mitochondria on the move: Horizontal mitochondrial transfer in disease and health

Mammalian genes were long thought to be constrained within somatic cells in most cell types. This concept was challenged recently when cellular organelles including mitochondria were shown to move between mammalian cells in culture via cytoplasmic bridges. Recent research in animals indicates transfer of mitochondria in cancer and during lung injury in vivo, with considerable functional consequences. Since these pioneering discoveries, many studies have confirmed horizontal mitochondrial transfer (HMT) in vivo, and its functional characteristics and consequences have been described. Additional support for this phenomenon has come from phylogenetic studies. Apparently, mitochondrial trafficking between cells occurs more frequently than previously thought and contributes to diverse processes including bioenergetic crosstalk and homeostasis, disease treatment and recovery, and development of resistance to cancer therapy. Here we highlight current knowledge of HMT between cells, focusing primarily on in vivo systems, and contend that this process is not only (patho)physiologically relevant, but also can be exploited for the design of novel therapeutic approaches.

Mitochondria-containing extracellular vesicles (EV) reduce mouse brain infarct sizes and EV/HSP27 protect ischemic brain endothelial cultures

Ischemic stroke causes brain endothelial cell (BEC) death and damages tight junction integrity of the blood-brain barrier (BBB). We harnessed the innate mitochondrial load of BEC-derived extracellular vesicles (EVs) and utilized mixtures of EV/exogenous 27 kDa heat shock protein (HSP27) as a one-two punch strategy to increase BEC survival (via EV mitochondria) and preserve their tight junction integrity (via HSP27 effects). We demonstrated that the medium-to-large (m/lEV) but not small EVs (sEV) transferred their mitochondrial load, that subsequently colocalized with the mitochondrial network of the recipient primary human BECs. Recipient BECs treated with m/lEVs showed increased relative ATP levels and mitochondrial function. To determine if the m/lEV-meditated increase in recipient BEC ATP levels was associated with m/lEV mitochondria, we isolated m/lEVs from donor BECs pre-treated with oligomycin A (OGM, mitochondria electron transport complex V inhibitor), referred to as OGM-m/lEVs. BECs treated with naïve m/lEVs showed a significant increase in ATP levels compared to untreated OGD cells, OGM-m/lEVs treated BECs showed a loss of ATP levels suggesting that the m/lEV-mediated increase in ATP levels is likely a function of their innate mitochondrial load. In contrast, sEV-mediated ATP increases were not affected by inhibition of mitochondrial function in the donor BECs. Intravenously administered m/lEVs showed a reduction in brain infarct sizes compared to vehicle-injected mice in a mouse middle cerebral artery occlusion model of ischemic stroke. We formulated binary mixtures of human recombinant HSP27 protein with EVs: EV/HSP27 and ternary mixtures of HSP27 and EVs with a cationic polymer, poly (ethylene glycol)-b-poly (diethyltriamine): (PEG-DET/HSP27)/EV. (PEG-DET/HSP27)/EV and EV/HSP27 mixtures decreased the paracellular permeability of small and large molecular mass fluorescent tracers in oxygen glucose-deprived primary human BECs. This one-two punch approach to increase BEC metabolic function and tight junction integrity may be a promising strategy for BBB protection and prevention of long-term neurological dysfunction post-ischemic stroke.

A novel circ_0018553 protects against angiotensin-induced cardiac hypertrophy in cardiomyocytes by modulating the miR-4731/SIRT2 signaling pathway

Due to the complicated pathophysiology of cardiac hypertrophy, there are no effective therapies for the treatment of pathological cardiac hypertrophy. Accumulating evidence has demonstrated that circRNAs participate in the pathophysiology of cardiac hypertrophy. In this study, we investigated the regulatory mechanisms of the novel circ_0018553 in angiotensin II (Ang II)-induced cardiac hypertrophy. Circ_0018553 was enriched in endothelial progenitor cell (EPC)-derived exosomes, and circ_0018553 expression was downregulated in a cellular model of Ang II-induced cardiac hypertrophy. Silencing circ_0018553 promoted cardiac hypertrophy in the Ang II-induced cardiac hypertrophy cellular model, while overexpression of circ_0018553 significantly attenuated Ang II-induced cardiac hypertrophy in cardiomyocytes. Moreover, mechanistic studies revealed that circ_0018553 acted as a sponge for miR-4731 and that miR-4731 repressed sirtuin 2 (SIRT2) expression by targeting the 3'UTR of SIRT2. MiR-4731 overexpression promoted cardiac hypertrophy in the Ang II-induced cardiac hypertrophy cellular model, while inhibition of miR-4731 significantly attenuated Ang II-induced cardiac hypertrophy in cardiomyocytes. The rescue experiments showed that miR-4731 overexpression attenuated the protective effects of circ_0018553 overexpression on the cardiac hypertrophy induced by Ang II; SIRT2 silencing also attenuated the protective effects of miR-4731 inhibition on the Ang II-induced cardiac hypertrophy. In conclusion, our results indicated that EPC-derived exosomal circ_0018553 protected against Ang II-induced cardiac hypertrophy by modulating the miR-4731/SIRT2 signaling pathway.

Mitochondrial Transplantation in Mitochondrial Medicine: Current Challenges and Future Perspectives

Mitochondrial diseases (MDs) are inherited genetic conditions characterized by pathogenic mutations in nuclear DNA (nDNA) or mitochondrial DNA (mtDNA). Current therapies are still far from being fully effective and from covering the broad spectrum of mutations in mtDNA. For example, unlike heteroplasmic conditions, MDs caused by homoplasmic mtDNA mutations do not yet benefit from advances in molecular approaches. An attractive method of providing dysfunctional cells and/or tissues with healthy mitochondria is mitochondrial transplantation. In this review, we discuss what is known about intercellular transfer of mitochondria and the methods used to transfer mitochondria both in vitro and in vivo, and we provide an outlook on future therapeutic applications. Overall, the transfer of healthy mitochondria containing wild-type mtDNA copies could induce a heteroplasmic shift even when homoplasmic mtDNA variants are present, with the aim of attenuating or preventing the progression of pathological clinical phenotypes. In summary, mitochondrial transplantation is a challenging but potentially ground-breaking option for the treatment of various mitochondrial pathologies, although several questions remain to be addressed before its application in mitochondrial medicine.

Mitochondria in Cell-Based Therapy for Stroke

Despite a relatively developed understanding of the pathophysiology underlying primary and secondary mechanisms of cell death after ischemic injury, there are few established treatments to improve stroke prognoses. A major contributor to secondary cell death is mitochondrial dysfunction. Recent advancements in cell-based therapies suggest that stem cells may be revolutionary for treating stroke, and the reestablishment of mitochondrial integrity may underlie these therapeutic benefits. In fact, functioning mitochondria are imperative for reducing oxidative damage and neuroinflammation following stroke and reperfusion injury. In this review, we will discuss the role of mitochondria in establishing the anti-oxidative effects of stem cell therapies for stroke.

Direct administration of mesenchymal stem cell-derived mitochondria improves cardiac function after infarction via ameliorating endothelial senescence

Mitochondrial dysfunction is considered to be a key contributor to the development of heart failure. Replacing injured mitochondria with healthy mitochondria to restore mitochondrial bioenergy in myocardium holds great promise for cardioprotection after infarction. This study aimed to investigate whether direct transplantation of exogenous mitochondria derived from mesenchymal stem cells (MSC-mt) is beneficial and superior in protecting cardiac function in a mouse model of myocardial infarction (MI) compared to mitochondria derived from skin fibroblast (FB-mt) and to explore the underlying mechanisms from their effects on the endothelial cells. The isolated MSC-mt presented intact mitochondrial morphology and activity, as determined by electron microscopy, JC-1 mitochondrial membrane potential assay, and seahorse assay. Direct injection of MSC-mt into the peri-infarct region in a mouse MI model enhanced blood vessel density, inhibited cardiac remodeling and apoptosis, thus improving heart function compared with FB-mt group. The injected MSC-mt can be tracked in the endothelial cells. In vitro, the fluorescence signal of MSC-mt can be detected in human umbilical vein endothelial cells (HUVECs) by confocal microscopy and flow cytometry after coculture. Compared to FB-mt, MSC-mt more effectively protected the HUVECs from oxidative stress-induced apoptosis and reduced mitochondrial production of reactive oxygen species. MSC-mt presented superior capacity in inducing tube formation, enhancing SCF secretion, ATP content and cell proliferation in HUVECs compared to FB-mt. Mechanistically, MSC-mt administration alleviated oxidative stress-induced endothelial senescence via activation of ERK pathway. These findings suggest that using MSCs as sources of mitochondria is feasible and that proangiogenesis could be the mechanism by which MSC-mt transplantation attenuates MI. MSC-mt transplantation might serve as a new therapeutic strategy for treating MI.

Mitochondrial transfer/transplantation: an emerging therapeutic approach for multiple diseases

Mitochondria play a pivotal role in energy generation and cellular physiological processes. These organelles are highly dynamic, constantly changing their morphology, cellular location, and distribution in response to cellular stress. In recent years, the phenomenon of mitochondrial transfer has attracted significant attention and interest from biologists and medical investigators. Intercellular mitochondrial transfer occurs in different ways, including tunnelling nanotubes (TNTs), extracellular vesicles (EVs), and gap junction channels (GJCs). According to research on intercellular mitochondrial transfer in physiological and pathological environments, mitochondrial transfer hold great potential for maintaining body homeostasis and regulating pathological processes. Multiple research groups have developed artificial mitochondrial transfer/transplantation (AMT/T) methods that transfer healthy mitochondria into damaged cells and recover cellular function. This paper reviews intercellular spontaneous mitochondrial transfer modes, mechanisms, and the latest methods of AMT/T. Furthermore, potential application value and mechanism of AMT/T in disease treatment are also discussed.

The Role of Extracellular Vesicles in Optic Nerve Injury: Neuroprotection and Mitochondrial Homeostasis

Stem cell therapies hold great promise as alternative treatments for incurable optic nerve disorders. Although mesenchymal stem cells exhibit various tissue regeneration and recovery capabilities that may serve as valuable therapies, the clinical applications remain limited. Thus, we investigated the utility of extracellular vesicles (EVs) from human placenta-derived mesenchymal stem cells (hPSCs) in this context. Hypoxically preconditioned hPSCs (HPPSCs) were prepared via short-term incubation under 2.2% O2 and 5.5% CO2. The EVs were then isolated. R28 cells (retinal precursor cells) were exposed to CoCl2 and treated with EVs for 24 h. Cell proliferation and regeneration were measured using a BrdU assay and immunoblotting; ATP quantification revealed the extent of the mitochondrial function. The proteome was determined via liquid chromatography-tandem mass spectroscopy. Differentially expressed proteins (DEPs) were detected and their interactions identified. HPPSC_EVs functions were explored using animal models of optic nerve compression. HPPSC_EVs restored cell proliferation and mitochondrial quality control in R28 cells damaged by CoCl2. We identified DEPs (p < 0.05) that aided recovery. The mitochondrial DEPs included LONP1; PARK7; VDAC1, 2, and 3; HSPD1; and HSPA9. EVs regulated the levels of mitophagic proteins in R28 cells injured by hypoxia; the protein levels did not increase in LONP1 knockdown cells. LONP1 is a key mediator of the mitophagy that restores mitochondrial function after hypoxia-induced optic nerve injury.

Engineering Extracellular Vesicles to Modulate Their Innate Mitochondrial Load

Introduction

Extracellular vesicles (EVs) are promising carriers for the delivery of biotherapeutic cargo such as RNA and proteins. We have previously demonstrated that the innate EV mitochondria in microvesicles (MVs), but not exosomes (EXOs) can be transferred to recipient BECs and mouse brain slice neurons. Here, we sought to determine if the innate EV mitochondrial load can be further increased via increasing mitochondrial biogenesis in the donor cells. We hypothesized that mitochondria-enriched EVs ("mito-EVs") may increase the recipient BEC ATP levels to a greater extent than naïve MVs.

Methods

We treated NIH/3T3, a fibroblast cell line and hCMEC/D3, a human brain endothelial cell (BEC) line using resveratrol to activate peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α), the central mediator of mitochondrial biogenesis. Naïve EVs and mito-EVs isolated from the non-activated and activated donor cells were characterized using transmission electron microscopy, dynamic light scattering and nanoparticle tracking analysis. The effect of mito-EVs on resulting ATP levels in the recipient BECs were determined using Cell Titer Glo ATP assay. The uptake of Mitotracker Red-stained EVs into recipient BECs and their colocalization with recipient BEC mitochondria were studied using flow cytometry and fluorescence microscopy.

Results

Resveratrol treatment increased PGC-1α expression in the donor cells. Mito-MVs but not mito-EXOs showed increased expression of mitochondrial markers ATP5A and TOMM20 compared to naïve MVs. TEM images showed that a greater number of mito-MVs contained mitochondria compared to naïve MVs. Mito-MVs but not mito-EXOs showed a larger particle diameter compared to their naïve EV counterparts from the non-activated cells suggesting increased mitochondria incorporation. Mito-EVs were generated at higher particle concentrations compared to naïve EVs from non-activated cells. Mito-EVs increased the cellular ATP levels and transferred their mitochondrial load into the recipient BECs. Mito-MV mitochondria also colocalized with recipient BEC mitochondria.

Conclusions

Our results suggest that the pharmacological modulation of mitochondrial biogenesis in the donor cells can change the mitochondrial load in the secreted MVs. Outcomes of physicochemical characterization studies and biological assays confirmed the superior effects of mito-MVs compared to naïve MVs-suggesting their potential to improve mitochondrial function in neurovascular and neurodegenerative diseases.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-022-00738-8.

Intercellular mitochondrial transfer as a means of revitalizing injured glomerular endothelial cells

BACKGROUND

Recent studies have demonstrated that mesenchymal stem cells (MSCs) can rescue injured target cells via mitochondrial transfer. However, it has not been fully understood how bone marrow-derived MSCs repair glomeruli in diabetic kidney disease (DKD).

AIM

To explore the mitochondrial transfer involved in the rescue of injured glomerular endothelial cells (GECs) by MSCs, both in vitro and in vivo.

METHODS

In vitro experiments were performed to investigate the effect of co-culture with MSCs on high glucose-induced GECs. The transfer of mitochondria was visualized using fluorescent microscopy. GECs were freshly sorted and ultimately tested for apoptosis, viability, mRNA expression by real-time reverse transcriptase-polymerase chain reaction, protein expression by western blot, and mitochondrial function. Moreover, streptozotocin-induced DKD rats were infused with MSCs, and renal function and oxidative stress were detected with an automatic biochemical analyzer and related-detection kits after 2 wk. Kidney histology was analyzed by hematoxylin and eosin, periodic acid-Schiff, and immunohistochemical staining.

RESULTS

Fluorescence imaging confirmed that MSCs transferred mitochondria to injured GECs when co-cultured in vitro. We found that the apoptosis, proliferation, and mitochondrial function of injured GECs were improved following co-culture. Additionally, MSCs decreased pro-inflammatory cytokines [interleukin (IL)-6, IL-1β, and tumor necrosis factor-α] and pro-apoptotic factors (caspase 3 and Bax). Mitochondrial transfer also enhanced the expression of superoxide dismutase 2, B cell lymphoma-2, glutathione peroxidase (GPx) 3, and mitofusin 2 and inhibited reactive oxygen species (ROS) and dynamin-related protein 1 expression. Furthermore, MSCs significantly ameliorated functional parameters (blood urea nitrogen and serum creatinine) and decreased the production of malondialdehyde, advanced glycation end products, and ROS, whereas they increased the levels of GPx and superoxide dismutase in vivo. In addition, significant reductions in the glomerular basement membrane and renal interstitial fibrosis were observed following MSC treatment.

CONCLUSION

MSCs can rejuvenate damaged GECs via mitochondrial transfer. Additionally, the improvement of renal function and pathological changes in DKD by MSCs may be related to the mechanism of mitochondrial transfer.

Unraveling the potential of endothelial progenitor cells as a treatment following ischemic stroke

Ischemic stroke is becoming one of the most common causes of death and disability in developed countries. Since current therapeutic options are quite limited, focused on acute reperfusion therapies that are hampered by a very narrow therapeutic time window, it is essential to discover novel treatments that not only stop the progression of the ischemic cascade during the acute phase, but also improve the recovery of stroke patients during the sub-acute or chronic phase. In this regard, several studies have shown that endothelial progenitor cells (EPCs) can repair damaged vessels as well as generate new ones following cerebrovascular damage. EPCs are circulating cells with characteristics of both endothelial cells and adult stem cells presenting the ability to differentiate into mature endothelial cells and self-renew, respectively. Moreover, EPCs have the advantage of being already present in healthy conditions as circulating cells that participate in the maintenance of the endothelium in a direct and paracrine way. In this scenario, EPCs appear as a promising target to tackle stroke by self-promoting re-endothelization, angiogenesis and vasculogenesis. Based on clinical data showing a better neurological and functional outcome in ischemic stroke patients with higher levels of circulating EPCs, novel and promising therapeutic approaches would be pharmacological treatment promoting EPCs-generation as well as EPCs-based therapies. Here, we will review the latest advances in preclinical as well as clinical research on EPCs application following stroke, not only as a single treatment but also in combination with new therapeutic approaches.

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

Astrocytes release functional mitochondria (Mt) that play regulatory and prosurvival functions on entering adjacent cells. We recently demonstrated that these released Mts could enter microglia to promote their reparative/prophagocytic phenotype that assists in hematoma cleanup and neurological recovery after intracerebral hemorrhage (ICH). However, the relevance of astrocytic Mt transfer into neurons in protecting brain after ICH is unclear. Here, we found that ICH causes a robust increase in superoxide generation and elevated oxidative damage that coincides with loss of the mitochondrial enzyme manganese superoxide dismutase (Mn-SOD). The damaging effect of ICH was reversed by intravenous transplantation of astrocytic Mt, which on entering the brain (and neurons), restored Mn-SOD levels and reduced neurological deficits in male mice subjected to ICH. Using an in vitro ICH-like injury model in cultured neurons, we established that astrocytic Mt on entering neurons prevented reactive oxygen species-induced oxidative stress and neuronal death by restoring neuronal Mn-SOD levels while at the same time promoted neurite extension and upregulation of synaptogenesis-related gene expression. Furthermore, we found that Mt genome-encoded small peptide humanin, which is normally abundant in Mt, could simulate Mt-transfer effect on neuronal Mn-SOD expression, oxidative stress, and neuroplasticity under ICH-like injury. This study demonstrates that adoptive astrocytic Mt transfer enhances neuronal Mn-SOD-mediated antioxidative defense and neuroplasticity in the brain, which potentiate functional recovery following ICH.SIGNIFICANCE STATEMENT Mitochondrial dysfunction and antioxidant defense play essential roles in brain damage after ICH. Astrocytes release functional Mt that enters adjacent cells to help brain homeostatic function. Here, we show that systemic transplantation of astrocytic Mt restores ICH-impaired neuronal antioxidative defense, enhances neurite outgrowth, and improves stroke recovery after ICH. Our study suggests that systemic transplantation of astrocytic Mt could be considered as a novel and potentially promising strategy for ICH treatment.

Dynamic behavior of cell-free mitochondrial DNA in human saliva

Mitochondria contain their own genome that can be released in multiple biofluids such as blood and cerebrospinal fluid, as cell-free mitochondrial DNA (cf-mtDNA). In clinical studies, blood cf-mtDNA predicts mortality and higher cf-mtDNA levels are associated with mental and physical stress. However, the dynamics of cf-mtDNA has not been defined, and whether it can be measured non-invasively like other neuroendocrine markers in saliva has not been examined. Here we report cf-mtDNA in human saliva and establish its natural within-person dynamic behavior across multiple weeks. In a small proof-of-principle cohort of healthy adults, we first develop an approach to rapidly quantify salivary cf-mtDNA without DNA isolation, and demonstrate the existence of salivary cf-mtDNA. We then deploy this approach to perform an intensive repeated-measures analysis of two healthy men studied at 4 daily timepoints over 53-60 consecutive days (n = 212-220 observations each) with parallel measures of steroid hormones, self-reported daily mood, and health-related behaviors. Salivary cf-mtDNA exhibited a robust awakening response reaching up to two orders of magnitude 30-45 min after awakening, varied from day-to-day, and moderately correlated with the cortisol awakening response. In exploratory analyses, no consistent association with self-reported daily mood/health-related behaviors were found, although this requires further examination in future studies. Dynamic variation in cf-mtDNA was inversely related with salivary interleukin 6 (IL-6), inconsistent with a pro-inflammatory effect of salivary cf-mtDNA. The highly dynamic behavior of salivary cf-mtDNA opens the door to non-invasive studies examining the relevance of mtDNA signaling in relation to human health.

Ginsenoside Rb1 inhibits astrocyte activation and promotes transfer of astrocytic mitochondria to neurons against ischemic stroke

Astrocytes activation in response to stroke results in altered mitochondrial exchange with neurons. Ginsenoside Rb1is a major ginsenoside of Panax ginseng particularly known for its neuroprotective potential. This work aimed to investigate if Rb1 could rescue neurons from ischemic insult via astrocyte inactivation and mitochondrial transfer. We prepared conditioned astrocytes-derived medium for co-culture with neurons and examined the role of Rb1 in mitochondrial transfer from astrocytes to neurons. The neuroprotective potential of Rb1 was further confirmed in vivo using a mouse model of brain ischemia. In response to oxygen-glucose deprivation and reperfusion (OGD/R), astrocytes were reactivated and produced reactive oxygen species (ROS), an action that was blocked by Rb1. Mechanistically, Rb1 inhibited NADH dehydrogenase in mitochondrial complex I to block reverse electron transport-derived ROS production from complex I, and thus inactivated astrocytes to protect the mitochondria. Mitochondrial signal, mitochondrial membrane potential and ATP production detected in conditioned astrocyte-derived medium indicated that Rb1 protected functional mitochondria and facilitated their transfer. When neurons were injured by OGD/R insult, co-culturing with conditioned medium increased mitochondrial membrane potential and oxygen consumption rate within the neurons, indicating the protection conferred on them by Rb1 via mitochondrial transfer from astrocytes. Using the ischemic mouse brain model, CD38 knockdown in the cerebral ventricles diminished the neuroprotective effects of Rb1, providing evidence in support of the role of astrocyte mitochondrial transfer. Transient inhibition of mitochondrial complex I by Rb1 reduced mitochondrial ROS production and consequently avoided astrocyte activation. Astrocyte mitochondrial transfer therefore seemed a means by which Rb1 could promote neuronal survival and function. Different from the neurocentric view, these findings suggest the astrocytes may be a promising target for pharmacological interventions in ischemic brain injury.

Horizontal mtDNA transfer between cells is common during mouse development

Cells transmit their genomes vertically to daughter cells during cell divisions. Here, we demonstrate the occurrence and extent of horizontal mitochondrial (mt)DNA acquisition between cells that are not in a parent-offspring relationship. Extensive single-cell sequencing from various tissues and organs of adult chimeric mice composed of cells carrying distinct mtDNA haplotypes showed that a substantial fraction of individual cardiomyocytes, neurons, glia, intestinal, and spleen cells captured donor mtDNA at high levels. In addition, chimeras composed of cells with wild-type and mutant mtDNA exhibited increased trafficking of wild-type mtDNA to mutant cells, suggesting that horizontal mtDNA transfer may be a compensatory mechanism to restore compromised mitochondrial function. These findings establish the groundwork for further investigations to identify mtDNA donor cells and mechanisms of transfer that could be critical to the development of novel gene therapies.

•

Individual cells in adult mouse chimeras acquire donor mtDNA horizontally

•

Significant percentage of cardiomyocytes, neurons, and glia were heteroplasmic

•

Donor mtDNA heteroplasmy in these cells can reach up to 50%

•

Pathogenic mtDNA mutations may potentiate horizontal acquisition of wild-type mtDNA