Human Bone Marrow Mesenchymal Stem Cells Rescue Endothelial Cells Experiencing Chemotherapy Stress by Mitochondrial Transfer Via Tunneling Nanotubes

Transforming the concept of connectivity: unveiling tunneling nanotube biology and their roles in brain development and neurodegeneration

Tunneling nanotubes (TNTs) are thin tubular membrane protrusions that connect distant cells, generating a complex cellular network. Over the past few decades, research on TNTs has provided important insights into their biology, including structural composition, formation mechanisms, modulators, and functionality. It has been discovered that TNTs allow cytoplasmic continuity between connected cells, facilitating fast intercellular communication via both passive and active exchange of materials. These features are pivotal in the nervous system, where rapid processing of inputs is physiologically required. TNTs have been implicated in the progression of neurodegenerative diseases and cancer in various in vitro models, and TNT-like structures have also been observed in the developing brain and in vivo. This highlights their significant role in pathophysiological processes. In this comprehensive review we aim to provide an extensive overview of TNTs, starting from key structural features and mechanisms of formation and describing the main experimental techniques used to detect these structures both in vitro and in vivo. We focus primarily on the nervous system, where the discovery of TNTs could prompt a reconsideration of the brain functioning as individual units (the neuronal theory of Cajal) versus neurons being physically connected, as Golgi believed. We illustrate the involvement of TNTs in brain development and neurodegenerative states and highlight the limitations and future research needs in this field.

Therapeutic implications of mitochondrial transfer on stem cell fate in regenerative medicine

With the discovery of intercellular mitochondrial transfer, the intricate mitochondrial regulatory networks on stem cell fate have aroused intense academic interest. Apart from capturing freely released mitochondria from donor cells, stem cells are able to receive mitochondria through tunneling nanotubes (TNTs), gap junctional channels (GJCs) and extracellular vesicles (EVs), especially when undergoing stressful conditions such as inflammation, hypoxia, chemotherapy drug exposure, and irradiation. Stem cells that are potentiated by exogenous mitochondria show enhanced potential for proliferation, differentiation, and immunomodulation. The well-tolerated nature of either autogenous or allogenous mitochondria when locally injected in the human ischemic heart has validated the safety and therapeutic potential of mitochondrial transplantation. In children diagnosed with mitochondrial DNA deletion syndrome, functional improvements have been observed when empowering their hematopoietic stem cells with maternally derived mitochondria. Apart from the widely investigated applications of mitochondrial transfer in ischemia-reperfusion injury, neurodegenerative diseases and mitochondrial diseases etc., therapeutic potentials of mitochondrial transfer in tissue repair and regeneration are equally noteworthy, though there has been no systematic summary in this regard.This review analyzed the research and development trends of mitochondrial transfer in stem cells and regenerative medicine over the past decade from a bibliometric perspective, introduced the concept and associated mechanisms of mitochondrial transfer, summarized the regulations of intercellular mitochondrial transfer on stem cell fate. Finally, the therapeutic application of mitochondrial transplantation in diseases and tissue regeneration has been reviewed, including recent clinical studies related to mitochondrial transplantation.Mitochondrial transfer shows promise in modifying and reshaping the cellular properties of stem cells, making them more conducive to regeneration. Mesenchymal stem cells (MSCs)-derived mitochondria have shown multifaceted potential in promoting the revitalization and regeneration of cardiac, cutaneous, muscular, neuronal tissue. This review integrates novel research findings on mitochondrial transfer in stem cell biology and regenerative medicine, emphasizing the crucial translational value of mitochondrial transfer in regeneration. It serves to underscore the significant impact of mitochondrial transfer and provides a valuable reference for further exploration in this field.

In Vivo and In Vitro Evaluation of the Feasibility and Safety Profiles of Intraarticular Transplantation of Mitochondria for Future Use as a Therapy for Osteoarthritis

Osteoarthritis (OA) is the most common rheumatologic disease and a major cause of pain and disability in older adults. No efficient treatment is currently available. Mitochondrial dysfunction in chondrocytes drives molecular dysregulation in OA pathogenesis. Recently, mitochondrial transfer to chondrocytes had been described, enabling transplant of mitochondria as a new avenue to modify the OA process, although evidence on its feasibility and safety remains limited.The primary objective of this study was to demonstrate the feasibility and safety of intra-articular mitochondrial transplantation. Mitochondria were isolated from liver using the procedure described by Preble and coworkers combined with magnetic beads coupled to anti-TOM22 antibodies. The organelles obtained were analyzed to determine their purity and viability. The safety and viability of the administration of the isolated mitochondria into articular tissues as well as the integration and distribution of the transplanted mitochondria within joint tissues were analyzed using both in vitro and in vivo models. We established an efficient, reproducible, effective, and rapid protocol for isolating mitochondria from liver. We obtained mitochondria with high viability, yield, and purity. The isolated mitochondria were injected into joint tissue using both in vitro and in vivo models. Functional mitochondria were detected in the extracellular matrix of the cartilage, menisci and synovium. Our results establish a safe and viable protocol for mitochondrial isolation and intra-articular injection. The methodology and findings presented here pave the way for future studies in osteoarthritis models to validate mitochondrial transplantation as a potentially effective treatment for OA.

Protective effect of mesenchymal stromal cells in diabetic nephropathy: the In vitro and In vivo role of the M-Sec-tunneling nanotubes

Mitochondrial dysfunction plays an important role in the development of podocyte injury in diabetic nephropathy (DN). Tunnelling nanotubes (TNTs) are long channels that connect cells and allow organelle exchange. Mesenchymal stromal cells (MSCs) can transfer mitochondria to other cells through the M-Sec-TNTs system. However, it remains unexplored whether MSCs can form heterotypic TNTs with podocytes, thereby enabling the replacement of diabetes-damaged mitochondria. In this study, we analysed TNT formation, mitochondrial transfer, and markers of cell injury in podocytes that were pre-exposed to diabetes-related insults and then co-cultured with diabetic or non-diabetic MSCs. Furthermore, to assess the in vivo relevance, we treated DN mice with exogenous MSCs, either expressing or lacking M-Sec, carrying fluorescent-tagged mitochondria. MSCs formed heterotypic TNTs with podocytes, allowing mitochondrial transfer, via a M-Sec-dependent mechanism. This ameliorated mitochondrial function, nephrin expression, and reduced apoptosis in recipient podocytes. However, MSCs isolated from diabetic mice failed to confer cytoprotection due to Miro-1 down-regulation. In experimental DN, treatment with exogenous MSCs significantly improved DN, but no benefit was observed in mice treated with MSCs lacking M-Sec. Mitochondrial transfer from exogenous MSCs to podocytes occurred in vivo in a M-Sec-dependent manner. These findings demonstrate that the M-Sec-TNT-mediated transfer of mitochondria from healthy MSCs to diabetes-injured podocytes can ameliorate podocyte damage. Moreover, M-Sec expression in exogenous MSCs is essential for providing renoprotection in vivo in experimental DN.

From dysfunction to healing: advances in mitochondrial therapy for Osteoarthritis

Osteoarthritis (OA) is a chronic degenerative joint condition characterised by cartilage deterioration and changes in bone morphology, resulting in pain and impaired joint mobility. Investigation into the pathophysiological mechanisms underlying OA has highlighted the significance of mitochondrial dysfunction in its progression. Mitochondria, which are cellular organelles, play a crucial role in regulating energy metabolism, generating reactive oxygen species, and facilitating essential biological processes including apoptosis. In recent years, the utilisation of exogenous drugs and MT to improve mitochondrial function in chondrocytes has shown great promise in OA treatment. Numerous studies have investigated the potential of stem cells and extracellular vesicles in mitochondrial transfer. This review aims to explore the underlying mechanisms of mitochondrial dysfunction in OA and assess the progress in utilising mitochondrial transfer as a therapeutic approach for this disease.

Mitochondrial transfer from mesenchymal stem cells: Mechanisms and functions

Mesenchymal stem cells based therapy has been used in clinic for almost 20 years and has shown encouraging effects in treating a wide range of diseases. However, the underlying mechanism is far more complicated than it was previously assumed. Mitochondria transfer is one way that recently found to be employed by mesenchymal stem cells to exert its biological effects. As one way of exchanging mitochondrial components, mitochondria transfer determines both mesenchymal stem cells and recipient cell fates. In this review, we describe the factors that contribute to MSCs-MT. Then, the routes and mechanisms of MSCs-MT are summarized to provide a theoretical basis for MSCs therapy. Besides, the advantages and disadvantages of MSCs-MT in clinical application are analyzed.

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.

The movement of mitochondria in breast cancer: internal motility and intercellular transfer of mitochondria

As a major energy source for cells, mitochondria are involved in cell growth and proliferation, as well as migration, cell fate decisions, and many other aspects of cellular function. Once thought to be irreparably defective, mitochondrial function in cancer cells has found renewed interest, from suggested potential clinical biomarkers to mitochondria-targeting therapies. Here, we will focus on the effect of mitochondria movement on breast cancer progression. Mitochondria move both within the cell, such as to localize to areas of high energetic need, and between cells, where cells within the stroma have been shown to donate their mitochondria to breast cancer cells via multiple methods including tunneling nanotubes. The donation of mitochondria has been seen to increase the aggressiveness and chemoresistance of breast cancer cells, which has increased recent efforts to uncover the mechanisms of mitochondrial transfer. As metabolism and energetics are gaining attention as clinical targets, a better understanding of mitochondrial function and implications in cancer are required for developing effective, targeted therapeutics for cancer patients.

Hydrogel Microneedle Patches Loaded with Stem Cell Mitochondria-Enriched Microvesicles Boost the Chronic Wound Healing

Rescuing or compensating mitochondrial function represents a promising therapeutic avenue for radiation-induced chronic wounds. Adult stem cell efficacies are primarily dependent on the paracrine secretion of mitochondria-containing extracellular vesicles (EVs). However, effective therapeutic strategies addressing the quantity of mitochondria and mitochondria-delivery system are lacking. Thus, in this study, we aimed to design an effective hydrogel microneedle patch (MNP) loaded with stem cell-derived mitochondria-rich EVs to gradually release and deliver mitochondria into the wound tissues and boost wound healing. We, first, used metformin to enhance mitochondrial biogenesis and thereby increasing the secretion of mitochondria-containing EVs (termed "Met-EVs") in adipose-derived stem cells. To verify the therapeutic effects of Met-EVs, we established an in vitro and an in vivo model of X-ray-induced mitochondrial dysfunction. The Met-EVs ameliorated the mitochondrial dysfunction by rescuing mitochondrial membrane potential, increasing adenosine 5'-triphosphate levels, and decreasing reactive oxygen species production by transferring active mitochondria. To sustain the release of EVs into damaged tissues, we constructed a Met-EVs@Decellularized Adipose Matrix (DAM)/Hyaluronic Acid Methacrylic Acid (HAMA)-MNP. Met-EVs@DAM/HAMA-MNP can load and gradually release Met-EVs and their contained mitochondria into wound tissues to alleviate mitochondrial dysfunction. Moreover, we found Met-EVs@DAM/HAMA-MNP can markedly promote macrophage polarization toward the M2 subtype with anti-inflammatory and regenerative functions, which can, in turn, enhance the healing process in mice with skin wounds combined radiation injuries. Collectively, we successfully fabricated a delivery system for EVs, Met-EVs@DAM/HAMA-MNP, to effectively deliver stem cell-derived mitochondria-rich EVs. The effectiveness of this system has been demonstrated, holding great potential for chronic wound treatments in clinic.

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.

Interplay Between Skeletal and Hematopoietic Cells in the Bone Marrow Microenvironment in Homeostasis and Aging

PURPOSE OF THE REVIEW

In this review, we discuss the most recent scientific advances on the reciprocal regulatory interactions between the skeletal and hematopoietic stem cell niche, focusing on immunomodulation and its interplay with the cell's mitochondrial function, and how this impacts osteoimmune health during aging and disease.

RECENT FINDINGS

Osteoimmunology investigates interactions between cells that make up the skeletal stem cell niche and immune system. Much work has investigated the complexity of the bone marrow microenvironment with respect to the skeletal and hematopoietic stem cells that regulate skeletal formation and immune health respectively. It has now become clear that these cellular components cooperate to maintain homeostasis and that dysfunction in their interaction can lead to aging and disease. Having a deeper, mechanistic appreciation for osteoimmune regulation will lead to better research perspective and therapeutics with the potential to improve the aging process, skeletal and hematologic regeneration, and disease targeting.

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.

Treatment of cytokine release syndrome-induced vascular endothelial injury using mesenchymal stem cells

Cytokine release syndrome (CRS) is an acute systemic inflammatory reaction in which hyperactivated immune cells suddenly release a large amount of cytokines, leading to exaggerated inflammatory responses, multiple organ dysfunction, and even death. Although palliative treatment strategies have significantly reduced the overall mortality, novel targeted treatment regimens with superior therapy efficacy are urgently needed. Vascular endothelial cells (ECs) are important target cells of systemic inflammation, and their destruction is considered to be the initiating event underlying many serious complications of CRS. Mesenchymal stem/stromal cells (MSCs) are multipotent cells with self-renewing differentiation capacity and immunomodulatory properties. MSC transplantation can effectively suppress the activation of immune cells, reduce the bulk release of cytokines, and repair damaged tissues and organs. Here, we review the molecular mechanisms underlying CRS-induced vascular endothelial injury and discuss potential treatments using MSCs. Preclinical studies demonstrate that MSC therapy can effectively repair endothelium damage and thus reduce the incidence and severity of ensuing CRS-induced complications. This review highlights the therapeutic role of MSCs in fighting against CRS-induced EC damage, and summarizes the possible therapeutic formulations of MSCs for improved efficacy in future clinical trials.

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.

Mesenchymal Stem Cells Target Gastric Cancer and Deliver Epirubicin via Tunneling Nanotubes for Enhanced Chemotherapy

BACKGROUND

A reduced effective local concentration significantly contributes to the unsatisfactory therapeutic results of epirubicin in gastric cancer. Mesenchymal stem cells exhibit targeted chemotaxis towards solid tumors and form tunneling nanotubes with tumor cells, facilitating the delivery of various substances. This study demonstrates the novelty of mesenchymal stem cells in releasing epirubicin into gastric cancer cells through tunneling nanotubes.

OBJECTIVE

Epirubicin delivery to gastric cancer cells using mesenchymal stem cells.

METHODS

In vitro transwell migration assays, live cell tracking, and in vivo targeting assays were used to demonstrate the chemotaxis of mesenchymal stem cells towards gastric cancer. We verified the targeted chemotaxis of mesenchymal stem cells towards gastric cancer cells and the epirubicin loading ability using a high-content imaging system (Equipment type:Operetta CLS). Additionally, tunneling nanotube formation and the targeted release of epirubicin-loaded mesenchymal stem cells co-cultured with gastric cancer cells through mesenchymal stem cell-tunneling nanotubes into gastric cancer cells was observed using Operetta CLS.

RESULTS

Mesenchymal stem cells demonstrated targeted chemotaxis towards gastric cancer, with effective epirubicin loading and tolerance. Co-culturing induced tunneling nanotube formation between these cells. Epirubicin-loaded mesenchymal stem cells were released into gastric cancer cells through tunneling nanotubes, significantly increasing their non-viability compared to the negative control group (p < 0.05).

CONCLUSIONS

We identified a novel approach for precisely targeting epirubicin release in gastric cancer cells. Therefore, mesenchymal stem cell-tunneling nanotubes could serve as a potential tool for targeted delivery of drugs, enhancing their chemotherapeutic effects in cancer cells.

Mitochondrial transfer in hematological malignancies

Mitochondria are energy-generated organelles and take an important part in biological metabolism. Mitochondria could be transferred between cells, which serves as a new intercellular communication. Mitochondrial transfer improves mitochondrial defects, restores the biological functions of recipient cells, and maintains the high metabolic requirements of tumor cells as well as drug resistance. In recent years, it has been reported mitochondrial transfer between cells of bone marrow microenvironment and hematological malignant cells play a critical role in the disease progression and resistance during chemotherapy. In this review, we discuss the patterns and mechanisms on mitochondrial transfer and their engagement in different pathophysiological contexts and outline the latest knowledge on intercellular transport of mitochondria in hematological malignancies. Besides, we briefly outline the drug resistance mechanisms caused by mitochondrial transfer in cells during chemotherapy. Our review demonstrates a theoretical basis for mitochondrial transfer as a prospective therapeutic target to increase the treatment efficiency in hematological malignancies and improve the prognosis of patients.

Tunneling Nanotube: An Enticing Cell-Cell Communication in the Nervous System

The field of neuroscience is rapidly progressing, continuously uncovering new insights and discoveries. Among the areas that have shown immense potential in research, tunneling nanotubes (TNTs) have emerged as a promising subject of study. These minute structures act as conduits for the transfer of cellular materials between cells, representing a mechanism of communication that holds great significance. In particular, the interplay facilitated by TNTs among various cell types within the brain, including neurons, astrocytes, oligodendrocytes, glial cells, and microglia, can be essential for the normal development and optimal functioning of this complex organ. The involvement of TNTs in neurodegenerative disorders, such as Alzheimer's disease, Huntington's disease, and Parkinson's disease, has attracted significant attention. These disorders are characterized by the progressive degeneration of neurons and the subsequent decline in brain function. Studies have predicted that TNTs likely play critical roles in the propagation and spread of pathological factors, contributing to the advancement of these diseases. Thus, there is a growing interest in understanding the precise functions and mechanisms of TNTs within the nervous system. This review article, based on our recent work on Rhes-mediated TNTs, aims to explore the functions of TNTs within the brain and investigate their implications for neurodegenerative diseases. Using the knowledge gained from studying TNTs could offer novel opportunities for designing targeted treatments that can stop the progression of neurodegenerative disorders.

Tunneling nanotubes-based intercellular mitochondrial trafficking as a novel therapeutic target in dry eye

Cell-to-cell mitochondria transfer via tunneling nanotubes (TNTs) has recently been revealed as a spontaneous way to protect damaged cells. Previously, we have reported mesenchymal stem cells (MSCs) can rescue retinal ganglion cell and corneal epithelium through intercellular mitochondrial trafficking. Mitochondrial damage and oxidative stress in corneal epithelial cells are vital in dry eye disease (DED). However, whether intercellular mitochondrial transfer is involved in the pathological and repair process of DED is currently unknown. Therefore, in this study, we designed a coculture system to evaluate the role of intercellular mitochondrial transfer between human corneal epithelial cells (CEC) in DED. In addition, we successfully discovered the ROCK inhibitor, Y-27632 as an intensifier to improve the efficiency of intercellular mitochondrial transport. As expected, the enhanced mitochondrial transfer promotes the regeneration of CECs. Moreover, through further exploration of mechanisms, it was demonstrated that F-actin-mediated cell morphological changes and cytoskeletal remodeling may be potential mechanisms for Y-27632 to induce mitochondrial metastasis. In conclusion, we established a new method for cell repair in DED that healthy CEC offered mitochondria to damaged CEC, providing a new insight into the cellular mechanism of corneal epithelium homeostatic regenerative therapeutics in DED.

Mitochondrial transfer from bone mesenchymal stem cells protects against tendinopathy both in vitro and in vivo

BACKGROUND

Although mesenchymal stem cells (MSCs) have been effective in tendinopathy, the mechanisms by which MSCs promote tendon healing have not been fully elucidated. In this study, we tested the hypothesis that MSCs transfer mitochondria to injured tenocytes in vitro and in vivo to protect against Achilles tendinopathy (AT).

METHODS

Bone marrow MSCs and H₂O₂-injured tenocytes were co-cultured, and mitochondrial transfer was visualized by MitoTracker dye staining. Mitochondrial function, including mitochondrial membrane potential, oxygen consumption rate, and adenosine triphosphate content, was quantified in sorted tenocytes. Tenocyte proliferation, apoptosis, oxidative stress, and inflammation were analyzed. Furthermore, a collagenase type I-induced rat AT model was used to detect mitochondrial transfer in tissues and evaluate Achilles tendon healing.

RESULTS

MSCs successfully donated healthy mitochondria to in vitro and in vivo damaged tenocytes. Interestingly, mitochondrial transfer was almost completely blocked by co-treatment with cytochalasin B. Transfer of MSC-derived mitochondria decreased apoptosis, promoted proliferation, and restored mitochondrial function in H₂O₂-induced tenocytes. A decrease in reactive oxygen species and pro-inflammatory cytokine levels (interleukin-6 and -1β) was observed. In vivo, mitochondrial transfer from MSCs improved the expression of tendon-specific markers (scleraxis, tenascin C, and tenomodulin) and decreased the infiltration of inflammatory cells into the tendon. In addition, the fibers of the tendon tissue were neatly arranged and the structure of the tendon was remodeled. Inhibition of mitochondrial transfer by cytochalasin B abrogated the therapeutic efficacy of MSCs in tenocytes and tendon tissues.

CONCLUSIONS

MSCs rescued distressed tenocytes from apoptosis by transferring mitochondria. This provides evidence that mitochondrial transfer is one mechanism by which MSCs exert their therapeutic effects on damaged tenocytes.

Progress of bone marrow mesenchymal stem cell mitochondrial transfer in organ injury repair

There has been an upsurge of interest in the bone marrow mesenchymal stem cell (BMSC) mitochondrial transfer as a potential therapeutic innovation in organ injury repair. Previous research mainly focused on its transfer routes and therapeutic effects. However, its intrinsic mechanism has not been well deciphered. The current research status needs to be summarized for the clarification of future research direction. Therefore, we review the recent significant progress in the application of BMSC mitochondrial transfer in organ injury repair. The transfer routes and effects are summarized, and some suggestions on the future research direction are provided.

Non-Classical Intercellular Communications: Basic Mechanisms and Roles in Biology and Medicine

In multicellular organisms, interactions between cells and intercellular communications form the very basis of the organism’s survival, the functioning of its systems, the maintenance of homeostasis and adequate response to the environment. The accumulated experimental data point to the particular importance of intercellular communications in determining the fate of cells, as well as their differentiation and plasticity. For a long time, it was believed that the properties and behavior of cells were primarily governed by the interactions of secreted or membrane-bound ligands with corresponding receptors, as well as direct intercellular adhesion contacts. In this review, we describe various types of other, non-classical intercellular interactions and communications that have recently come into the limelight—in particular, the broad repertoire of extracellular vesicles and membrane protrusions. These communications are mediated by large macromolecular structural and functional ensembles, and we explore here the mechanisms underlying their formation and present current data that reveal their roles in multiple biological processes. The effects mediated by these new types of intercellular communications in normal and pathological states, as well as therapeutic applications, are also discussed. The in-depth study of novel intercellular interaction mechanisms is required for the establishment of effective approaches for the control and modification of cell properties both for basic research and the development of radically new therapeutic strategies.

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.

Mechanisms behind therapeutic potentials of mesenchymal stem cell mitochondria transfer/delivery

Mesenchymal stromal/stem cells (MSCs) perform their therapeutic effects through various mechanisms, including their ability to differentiate, producing different growth factors, immunomodulatory factors, and extracellular vesicles (EVs). In addition to the mentioned mechanisms, a new aspect of the therapeutic potential of MSCs has recently been noticed, which occurs through mitochondrial transfer. Various methods of MSCs mitochondria transfer have been used in studies to benefit from their therapeutic potential. Among these methods, mitochondrial transfer after MSCs transplantation in cell-to-cell contact, EVs-mediated transfer of mitochondria, and the use of MSCs isolated mitochondria (MSCs-mt) are well studied. Pathological conditions can affect the cells in the damaged microenvironment and lead to cells mitochondrial damage. Since the defect in the mitochondrial function of the cell leads to a decrease in ATP production and the subsequent cell death, restoring the mitochondrial content, functions, and hemostasis can affect the functions of the damaged cell. Various studies show that the transfer of MSCs mitochondria to other cells can affect vital processes such as proliferation, differentiation, cell metabolism, inflammatory responses, cell senescence, cell stress, and cell migration. These changes in cell attributes and behavior are very important for therapeutic purposes. For this reason, their investigation can play a significant role in the direction of the researchers'.

Mitochondrial-Derived Vesicles-Link to Extracellular Vesicles and Implications in Cardiovascular Disease

Mitochondria are dynamic organelles regulating metabolism, cell death, and energy production. Therefore, maintaining mitochondrial health is critical for cellular homeostasis. Mitophagy and mitochondrial reorganization via fission and fusion are established mechanisms for ensuring mitochondrial quality. In recent years, mitochondrial-derived vesicles (MDVs) have emerged as a novel cellular response. MDVs are shed from the mitochondrial surface and can be directed to lysosomes or peroxisomes for intracellular degradation. MDVs may contribute to cardiovascular disease (CVD) which is characterized by mitochondrial dysfunction. In addition, evidence suggests that mitochondrial content is present in extracellular vesicles (EVs). Herein, we provide an overview of the current knowledge on MDV formation and trafficking. Moreover, we review recent findings linking MDV and EV biogenesis and discuss their role in CVD. Finally, we discuss the role of vesicle-mediated mitochondrial transfer and its potential cardioprotective effects.

Bone marrow mesenchymal stem cells in premature ovarian failure: Mechanisms and prospects

Premature ovarian failure (POF) is a common female reproductive disorder and characterized by menopause, increased gonadotropin levels and estrogen deficiency before the age of 40 years old. The etiologies and pathogenesis of POF are not fully clear. At present, hormone replacement therapy (HRT) is the main treatment options for POF. It helps to ameliorate perimenopausal symptoms and related health risks, but can't restore ovarian function and fertility fundamentally. With the development of regenerative medicine, bone marrow mesenchymal stem cells (BMSCs) have shown great potential for the recovery of ovarian function and fertility based on the advantages of abundant sources, high capacity for self-renewal and differentiation, low immunogenicity and less ethical considerations. This systematic review aims to summarize the possible therapeutic mechanisms of BMSCs for POF. A detailed search strategy of preclinical studies and clinical trials on BMSCs and POF was performed on PubMed, MEDLINE, Web of Science and Embase database. A total of 21 studies were included in this review. Although the standardization of BMSCs need more explorations, there is no doubt that BMSCs transplantation may represent a prospective therapy for POF. It is hope to provide a theoretical basis for further research and treatment for POF.

Headway and the remaining hurdles of mesenchymal stem cells therapy for bronchopulmonary dysplasia

OBJECTIVE

Preterm infants are at a high risk of developing BPD. Although progression in neonatal care has improved, BPD still causes significant morbidity and mortality, which can be attributed to the limited therapeutic choices for BPD. This review discusses the potential of MSC in treating BPD as well as their hurdles and possible solutions.

DATA SOURCES

The search for data was not limited to any sites but was mostly performed on all clinical trials available in ClinicalTrials.gov as well as on PubMed by applying the following keywords: lung injury, preterm, inflammation, neonatal, bronchopulmonary dysplasia and mesenchymal stem cells.

STUDY SELECTIONS

The articles chosen for this review were collectively determined to be relevant and appropriate in discussing MSC not only as a potential treatment strategy for curbing the incidence of BPD but also including insights on problems regarding MSC treatment for BPD.

RESULTS

Clinical trials regarding the use of MSC for BPD had good results but also illustrated insights on problems to be addressed in the future regarding the treatment strategy. Despite that, the clinical trials had mostly favourable reviews.

CONCLUSION

With BPD existing as a constant threat and there being no permanent solutions, the idea of regenerative medicine such as MSC may prove to be a breakthrough strategy when it comes to treating BPD. The success in clinical trials led to the formulation of prospective MSC-derived products such as PNEUMOSTEM®, and there is the possibility of a stem cell medication and permanent treatment for BPD in the near future.

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.

Mesenchymal Stromal Cell Mitochondrial Transfer as a Cell Rescue Strategy in Regenerative Medicine: A Review of Evidence in Preclinical Models

Mesenchymal stromal cells (MSC) have excellent clinical potential and numerous properties that ease its clinical translation. Mitochondria play a crucial role in energy metabolism, essential for cellular activities, such as proliferation, differentiation, and migration. However, mitochondrial dysfunction can occur due to diseases and pathological conditions. Research on mitochondrial transfer from MSCs to recipient cells has gained prominence. Numerous studies have demonstrated that mitochondrial transfer led to increased adenosine triphosphate (ATP) production, recovered mitochondrial bioenergetics, and rescued injured cells from apoptosis. However, the complex mechanisms that lead to mitochondrial transfer from healthy MSCs to damaged cells remain under investigation, and the factors contributing to mitochondrial bioenergetics recovery in recipient cells remain largely ambiguous. Therefore, this review demonstrates an overview of recent findings in preclinical studies reporting MSC mitochondrial transfer, comprised of information on cell sources, recipient cells, dosage, route of administration, mechanism of transfer, pathological conditions, and therapeutic effects. Further to the above, this research discusses the potential challenges of this therapy in its clinical settings and suggestions to overcome its challenges.

Tunneling Nanotube-Mediated Mitochondrial Transfer Rescues Nucleus Pulposus Cells from Mitochondrial Dysfunction and Apoptosis

Stem cell-based therapy has been indicated to be beneficial for intervertebral disc regeneration. However, the underlying mechanisms have not been fully identified. The present study showed that bone marrow mesenchymal stem cells (BMSCs) donated mitochondria to adjacent nucleus pulposus cells (NPCs) in a coculture system. The mode of mitochondrial transfer between these cells was intercellular tunneling nanotube (TNT), which acted as a transportation expressway for mitochondria. NPCs acquired additional mitochondria from BMSCs in a concentration-dependent manner after rotenone-induced mitochondrial dysfunction in NPCs. Further research demonstrated that TNT-mediated mitochondrial transfer rescued NPCs from mitochondrial dysfunction and apoptosis, which was indicated by the recovery of the mitochondrial respiratory chain, the increase in mitochondrial membrane potential, and the decreases in reactive oxygen species (ROS) levels and apoptosis rates. Furthermore, Miro1, a critical protein that regulates mitochondrial movement, was knocked down in BMSCs and significantly reduced mitochondrial transfer from BMSCs to NPCs. These results suggested that Miro1 depletion inhibited the rescue of NPCs with mitochondrial dysfunction. Taken together, our data shed light on a novel mechanism by which BMSCs rescue impaired NPCs, providing a concrete foundation to study the critical role of intercellular interactions in disc regeneration.

Cellular therapies for the treatment and prevention of SARS-CoV-2 infection

Patients with blood disorders who are immune suppressed are at increased risk for infection with severe acute respiratory syndrome coronavirus 2. Sequelae of infection can include severe respiratory disease and/or prolonged duration of viral shedding. Cellular therapies may protect these vulnerable patients by providing antiviral cellular immunity and/or immune modulation. In this recent review of the field, phase 1/2 trials evaluating adoptive cellular therapies with virus-specific T cells or natural killer cells are described along with trials evaluating the safety, feasibility, and preliminary efficacy of immune modulating cellular therapies including regulatory T cells and mesenchymal stromal cells. In addition, the immunologic basis for these therapies is discussed.

Diversified Treatment Options of Adult Stem Cells for Optic Neuropathies

Optic neuropathies refer to a group of ocular disorders with abnormalities or dysfunction of the optic nerve, sharing a common pathophysiology of retinal ganglion cell (RGC) death and axonal loss. RGCs, as the retinal neurons in the central nervous system, show limited capacity in regeneration or recovery upon diseases or after injuries. Critically, there is still no effective clinical treatment to cure most types of optic neuropathies. Recently, stem cell therapy was proposed as a potential treatment strategy for optic neuropathies. Adult stem cells, including mesenchymal stem cells and hematopoietic stem cells, have been applied in clinical trials based on their neuroprotective properties. In this article, the applications of adult stem cells on different types of optic neuropathies and the related mechanisms will be reviewed. Research updates on the strategies to enhance the neuroprotective effects of human adult stem cells will be summarized. This review article aims to enlighten the research scientists on the diversified functions of adult stem cells and consideration of adult stem cells as a potential treatment for optic neuropathies in future clinical practices.

Mitochondrial Transfer in Cardiovascular Disease: From Mechanisms to Therapeutic Implications

Mitochondrial dysfunction has been proven to play a critical role in the pathogenesis of cardiovascular diseases. The phenomenon of intercellular mitochondrial transfer has been discovered in the cardiovascular system. Studies have shown that cell-to-cell mitochondrial transfer plays an essential role in regulating cardiovascular system development and maintaining normal tissue homeostasis under physiological conditions. In pathological conditions, damaged cells transfer dysfunctional mitochondria toward recipient cells to ask for help and take up exogenous functional mitochondria to alleviate injury. In this review, we summarized the mechanism of mitochondrial transfer in the cardiovascular system and outlined the fate and functional role of donor mitochondria. We also discussed the advantage and challenges of mitochondrial transfer strategies, including cell-based mitochondrial transplantation, extracellular vesicle-based mitochondrial transplantation, and naked mitochondrial transplantation, for the treatment of cardiovascular disorders. We hope this review will provide perspectives on mitochondrial-targeted therapeutics in cardiovascular diseases.

Astrocyte-to-neuron transportation of enhanced green fluorescent protein in cerebral cortex requires F-actin dependent tunneling nanotubes

Tunneling nanotube (TNT), a dynamic cell–cell contact, is dependent on actin polymerization. TNTs are efficient in transporting ions, proteins and organelles intercellularly, which are important mechanisms in physiological and pathological processes. Reported studies on the existence and function of TNTs among neural cells focus on cultured cell for the convenience in detecting TNTs’ ultrastructure. In this study, the adeno-associated virus (AAV-GFAP-EGFP-p2A-cre) was injected into the cerebral cortex of knock-in mice ROSA26 GNZ. GFAP promoter initiated the expression of enhanced green fluorescent protein (EGFP) in infected astrocytes. At 10 days post injection (10 DPI), EGFP transferred from astrocytes in layer I–III to neurons in layer V. The dissemination of EGFP was not through endocytosis or exosome. Applying microscopes, we found that the intercellular transportation of EGFP through contact connection was F-actin dependent. Therefore, we concluded that EGFP transported from astrocytes to neurons in cortex via F-actin dependent TNTs. This study first proved that proteins transported intercellularly via TNTs in brain.

A Review on Mesenchymal Stem Cells for Treatment of Retinal Diseases

Mesenchymal Stem Cells (MSCs) have been studied extensively for the treatment of several retinal diseases. The therapeutic potential of MSCs lies in its ability to differentiate into multiple lineages and secretome enriched with immunomodulatory, anti-angiogenic and neurotrophic factors. Several studies have reported the role of MSCs in repair and regeneration of the damaged retina where the secreted factors from MSCs prevent retinal degeneration, improve retinal morphology and function. MSCs also donate mitochondria to rescue the function of retinal cells and exosomes secreted by MSCs were found to have anti-apoptotic and anti-inflammatory effects. Based on several promising results obtained from the preclinical studies, several clinical trials were initiated to explore the potential advantages of MSCs for the treatment of retinal diseases. This review summarizes the various properties of MSCs that help to repair and restore the damaged retinal cells and its potential for the treatment of retinal degenerative diseases.

Secretome and Tunneling Nanotubes: A Multilevel Network for Long Range Intercellular Communication between Endothelial Cells and Distant Cells

As a cellular interface between the blood and tissues, the endothelial cell (EC) monolayer is involved in the control of key functions including vascular tone, permeability and homeostasis, leucocyte trafficking and hemostasis. EC regulatory functions require long-distance communications between ECs, circulating hematopoietic cells and other vascular cells for efficient adjusting thrombosis, angiogenesis, inflammation, infection and immunity. This intercellular crosstalk operates through the extracellular space and is orchestrated in part by the secretory pathway and the exocytosis of Weibel Palade Bodies (WPBs), secretory granules and extracellular vesicles (EVs). WPBs and secretory granules allow both immediate release and regulated exocytosis of messengers such as cytokines, chemokines, extracellular membrane proteins, coagulation or growth factors. The ectodomain shedding of transmembrane protein further provide the release of both receptor and ligands with key regulatory activities on target cells. Thin tubular membranous channels termed tunneling nanotubes (TNTs) may also connect EC with distant cells. EVs, in particular exosomes, and TNTs may contain and transfer different biomolecules (e.g., signaling mediators, proteins, lipids, and microRNAs) or pathogens and have emerged as a major triggers of horizontal intercellular transfer of information.

Mitochondrial transplantation in cardiomyocytes: foundation, methods, and outcomes

Mitochondrial transplantation is emerging as a novel cellular biotherapy to alleviate mitochondrial damage and dysfunction. Mitochondria play a crucial role in establishing cellular homeostasis and providing cell with the energy necessary to accomplish its function. Owing to its endosymbiotic origin, mitochondria share many features with their bacterial ancestors. Unlike the nuclear DNA, which is packaged into nucleosomes and protected from adverse environmental effects, mitochondrial DNA are more prone to harsh environmental effects, in particular that of the reactive oxygen species. Mitochondrial damage and dysfunction are implicated in many diseases ranging from metabolic diseases to cardiovascular and neurodegenerative diseases, among others. While it was once thought that transplantation of mitochondria would not be possible due to their semiautonomous nature and reliance on the nucleus, recent advances have shown that it is possible to transplant viable functional intact mitochondria from autologous, allogenic, and xenogeneic sources into different cell types. Moreover, current research suggests that the transplantation could positively modulate bioenergetics and improve disease outcome. Mitochondrial transplantation techniques and consequences of transplantation in cardiomyocytes are the theme of this review. We outline the different mitochondrial isolation and transfer techniques. Finally, we detail the consequences of mitochondrial transplantation in the cardiovascular system, more specifically in the context of cardiomyopathies and ischemia.

MSCs and Inflammatory Cells Crosstalk in Regenerative Medicine: Concerted Actions for Optimized Resolution Driven by Energy Metabolism

Mesenchymal stromal cells (MSCs) are currently widely used in cell based therapy regarding to their remarkable efficacy in controlling the inflammatory status in patients. Despite recent progress and encouraging results, inconstant therapeutic benefits are reported suggesting that significant breakthroughs in the understanding of MSCs immunomodulatory mechanisms of action remains to be investigated and certainly apprehended from original point of view. This review will focus on the recent findings regarding MSCs close relationship with the innate immune compartment, i.e. granulocytes and myeloid cells. The review will also consider the intercellular mechanism of communication involved, such as factor secretion, cell-cell contact, extracellular vesicles, mitochondria transfer and efferocytosis. Immune-like-properties of MSCs supporting part of their therapeutic effect in the clinical setting will be discussed, as well as their potentials (immunomodulatory, anti-bacterial, anti-inflammatory, anti-oxidant defenses and metabolic adaptation…) and effects mediated, such as cell polarization, differentiation, death and survival on various immune and tissue cell targets determinant in triggering tissue regeneration. Their metabolic properties in term of sensing, reacting and producing metabolites influencing tissue inflammation will be highlighted. The review will finally open to discussion how ongoing scientific advances on MSCs could be efficiently translated to clinic in chronic and age-related inflammatory diseases and the current limits and gaps that remain to be overcome to achieving tissue regeneration and rejuvenation.

Mitochondria Donation by Mesenchymal Stem Cells: Current Understanding and Mitochondria Transplantation Strategies

The phenomenon of mitochondria donation is found in various tissues of humans and animals and is attracting increasing attention. To date, numerous studies have described the transfer of mitochondria from stem cells to injured cells, leading to increased ATP production, restoration of mitochondria function, and rescue of recipient cells from apoptosis. Mitochondria transplantation is considered as a novel therapeutic approach for the treatment of mitochondrial diseases and mitochondrial function deficiency. Mitochondrial dysfunction affects cells with high energy needs such as neural, skeletal muscle, heart, and liver cells and plays a crucial role in type 2 diabetes, as well as Parkinson's, Alzheimer's diseases, ischemia, stroke, cancer, and age-related disorders. In this review, we summarize recent findings in the field of mitochondria donation and mechanism of mitochondria transfer between cells. We review the existing clinical trials and discuss advantages and disadvantages of mitochondrial transplantation strategies based on the injection of stem cells, isolated functional mitochondria, or EVs containing mitochondria.

Opportunities and Challenges in Tunneling Nanotubes Research: How Far from Clinical Application?

Tunneling nanotubes (TNTs) are recognized long membrane nanotubes connecting distance cells. In the last decade, growing evidence has shown that these subcellular structures mediate the specific transfer of cellular materials, pathogens, and electrical signals between cells. As intercellular bridges, they play a unique role in embryonic development, collective cell migration, injured cell recovery, cancer treatment resistance, and pathogen propagation. Although TNTs have been considered as potential drug targets for treatment, there is still a long way to go to translate the research findings into clinical practice. Herein, we emphasize the heterogeneous nature of TNTs by systemically summarizing the current knowledge on their morphology, structure, and biogenesis in different types of cells. Furthermore, we address the communication efficiency and biological outcomes of TNT-dependent transport related to diseases. Finally, we discuss the opportunities and challenges of TNTs as an exciting therapeutic approach by focusing on the development of efficient and safe drugs targeting TNTs.

Mitochondrial transplant to replenish damaged mitochondria: A novel therapeutic strategy for neurodegenerative diseases?

Neurodegenerative diseases are currently some of the most debilitating and incurable illness, including highly prevalent disorders, such as Alzheimer's and Parkinson's disease. Despite impressive advances in understanding the molecular basis of neurodegenerative diseases, several clinical trials have failed in identifying drugs that successfully delay or stop disease progression. New targets are likely necessary to successfully combat these devastating diseases. In this chapter, we review the evidence indicating that impairment in the cellular energy machinery in the form of mitochondrial damage and dysfunction may be at the root of neurodegeneration. We also propose that transplant of functional isolated mitochondria may overcome the energetic damage and delay the progression of neurodegenerative diseases.

Mesenchymal Stem/Stromal Cell-Mediated Mitochondrial Transfer and the Therapeutic Potential in Treatment of Neurological Diseases

Mesenchymal stem/stromal cells (MSCs) are multipotent stem cells that can be derived from various tissues. Due to their regenerative and immunomodulatory properties, MSCs have been extensively researched and tested for treatment of different diseases/indications. One mechanism that MSCs exert functions is through the transfer of mitochondria, a key player involved in many biological processes in health and disease. Mitochondria transfer is bidirectional and has an impact on both donor and recipient cells. In this review, we discussed how MSC-mediated mitochondrial transfer may affect cellular metabolism, survival, proliferation, and differentiation; how this process influences inflammatory processes; and what is the molecular machinery that mediates mitochondrial transfer. In the end, we summarized recent advances in preclinical research and clinical trials for the treatment of stroke and spinal cord injury, through application of MSCs and/or MSC-derived mitochondria.

Mechanisms underlying the protective effects of mesenchymal stem cell-based therapy

Mesenchymal stem cells (MSCs) have been extensively investigated for the treatment of various diseases. The therapeutic potential of MSCs is attributed to complex cellular and molecular mechanisms of action including differentiation into multiple cell lineages and regulation of immune responses via immunomodulation. The plasticity of MSCs in immunomodulation allow these cells to exert different immune effects depending on different diseases. Understanding the biology of MSCs and their role in treatment is critical to determine their potential for various therapeutic applications and for the development of MSC-based regenerative medicine. This review summarizes the recent progress of particular mechanisms underlying the tissue regenerative properties and immunomodulatory effects of MSCs. We focused on discussing the functional roles of paracrine activities, direct cell-cell contact, mitochondrial transfer, and extracellular vesicles related to MSC-mediated effects on immune cell responses, cell survival, and regeneration. This will provide an overview of the current research on the rapid development of MSC-based therapies.

Bioenergetic Crosstalk between Mesenchymal Stem Cells and various Ocular Cells through the intercellular trafficking of Mitochondria

Rationale: Mitochondrial disorders preferentially affect tissues with high energy requirements, such as the retina and corneal endothelium, in human eyes. Mesenchymal stem cell (MSC)-based treatment has been demonstrated to be beneficial for ocular degeneration. However, aside from neuroprotective paracrine actions, the mechanisms underlying the beneficial effect of MSCs on retinal and corneal tissues are largely unknown. In this study, we investigated the fate and associated characteristics of mitochondria subjected to intercellular transfer from MSCs to ocular cells.

Methods: MSCs were cocultured with corneal endothelial cells (CECs), 661W cells (a photoreceptor cell line) and ARPE-19 cells (a retinal pigment epithelium cell line). Immunofluorescence, fluorescence activated cell sorting and confocal microscopy imaging were employed to investigate the traits of intercellular mitochondrial transfer and the fate of transferred mitochondria. The oxygen consumption rate of recipient cells was measured to investigate the effect of intercellular mitochondrial transfer. Transcriptome analysis was performed to investigate the expression of metabolic genes in recipient cells with donated mitochondria.

Results: Mitochondrial transport is a ubiquitous intercellular mechanism between MSCs and various ocular cells, including the corneal endothelium, retinal pigmented epithelium, and photoreceptors. Additionally, our results indicate that the donation process depends on F-actin-based tunneling nanotubes. Rotenone-pretreated cells that received mitochondria from MSCs displayed increased aerobic capacity and upregulation of mitochondrial genes. Furthermore, living imaging determined the ultimate fate of transferred mitochondria through either degradation by lysosomes or exocytosis as extracellular vesicles.

Conclusions: For the first time, we determined the characteristics and fate of mitochondria undergoing intercellular transfer from MSCs to various ocular cells through F-actin-based tunneling nanotubes, helping to characterize MSC-based treatment for ocular tissue regeneration.

The emerging antioxidant paradigm of mesenchymal stem cell therapy

Mesenchymal stem cells (multipotent stromal cells; MSCs) have been under investigation for the treatment of diverse diseases, with many promising outcomes achieved in animal models and clinical trials. The biological activity of MSC therapies has not been fully resolved which is critical to rationalizing their use and developing strategies to enhance treatment efficacy. Different paradigms have been constructed to explain their mechanism of action, including tissue regeneration, trophic/anti-inflammatory secretion, and immunomodulation. MSCs rarely engraft and differentiate into other cell types after in vivo administration. Furthermore, it is equivocal whether MSCs function via the secretion of many peptide/protein ligands as their therapeutic properties are observed across xenogeneic barriers, which is suggestive of mechanisms involving mediators conserved between species. Oxidative stress is concomitant with cellular injury, inflammation, and dysregulated metabolism which are involved in many pathologies. Growing evidence supports that MSCs exert antioxidant properties in a variety of animal models of disease, which may explain their cytoprotective and anti-inflammatory properties. In this review, evidence of the antioxidant effects of MSCs in in vivo and in vitro models is explored and potential mechanisms of these effects are discussed. These include direct scavenging of free radicals, promoting endogenous antioxidant defenses, immunomodulation via reactive oxygen species suppression, altering mitochondrial bioenergetics, and donating functional mitochondria to damaged cells. Modulation of the redox environment and oxidative stress by MSCs can mediate their anti-inflammatory and cytoprotective properties and may offer an explanation to the diversity in disease models treatable by MSCs and how these mechanisms may be conserved between species.

Tunneling Nanotubes-Mediated Protection of Mesenchymal Stem Cells: An Update from Preclinical Studies

Tunneling nanotubes (TNTs) are thin membrane elongations among the cells that mediate the trafficking of subcellular organelles, biomolecules, and cues. Mesenchymal stem cells (MSCs) receive substantial attention in tissue engineering and regenerative medicine. Many MSCs-based clinical trials are ongoing for dreadful diseases including cancer and neurodegenerative diseases. Mitochondrial trafficking through TNTs is one of the mechanisms used by MSCs to repair tissue damage and to promote tissue regeneration. Preclinical studies linked with ischemia, oxidative stress, mitochondrial damage, inflammation, and respiratory illness have demonstrated the therapeutic efficacy of MSCs via TNTs-mediated transfer of mitochondria and other molecules into the injured cells. On the other hand, MSCs-based cancer studies showed that TNTs may modulate chemoresistance in tumor cells as a result of mitochondrial trafficking. In the present review, we discuss the role of TNTs from preclinical studies associated with MSCs treatment. We discuss the impact of TNTs formation between MSCs and cancer cells and emphasize to study the importance of TNTs-mediated MSCs protection in disease models.

Future Trends in Nebulized Therapies for Pulmonary Disease

Aerosol therapy is a key modality for drug delivery to the lungs of respiratory disease patients. Aerosol therapy improves therapeutic effects by directly targeting diseased lung regions for rapid onset of action, requiring smaller doses than oral or intravenous delivery and minimizing systemic side effects. In order to optimize treatment of critically ill patients, the efficacy of aerosol therapy depends on lung morphology, breathing patterns, aerosol droplet characteristics, disease, mechanical ventilation, pharmacokinetics, and the pharmacodynamics of cell-drug interactions. While aerosol characteristics are influenced by drug formulations and device mechanisms, most other factors are reliant on individual patient variables. This has led to increased efforts towards more personalized therapeutic approaches to optimize pulmonary drug delivery and improve selection of effective drug types for individual patients. Vibrating mesh nebulizers (VMN) are the dominant device in clinical trials involving mechanical ventilation and emerging drugs. In this review, we consider the use of VMN during mechanical ventilation in intensive care units. We aim to link VMN fundamentals to applications in mechanically ventilated patients and look to the future use of VMN in emerging personalized therapeutic drugs.

Expression and functional regulation of gap junction protein connexin 43 in dermal mesenchymal stem cells from psoriasis patients

BACKGROUND

Psoriasis is a chronic recurrent inflammatory disease. Mesenchymal stem cells (MSCs) can regulate the inflammatory microenvironment, thereby controlling the proliferation, differentiation, and migration of immune cells. Connexin 43(Cx43), a key gap junction protein, has been shown to form gap junctions for communication between neighboring cells.

OBJECTIVE

We investigated the expression of Cx43 in dermal mesenchymal stem cells (DMSCs) derived from psoriasis patients and explored the relationship between the Cx43-mediated gap junction intercellular communication (GJIC) and DMSCs.

METHODS

Human DMSCs were isolated and propagated in adherent culture. Quantitative real-time reverse transcription PCR and western blot and immunofluorescence were used to detect the expression and localization of Cx43 in DMSCs. Fluorescence redistribution after photobleaching was performed to assess adjacent DMSCs GJIC. CCK8 was used to detect the proliferation of DMSCs before and after gap junction blocker (18α-glycyrrhetinic acid; AGA) treatment. Cell energy metabolism was analyzed with an energy metabolism analyzer.

RESULTS

Cx43 was located in the cytoplasm and cytomembrane, as well as partially in the nucleus of DMSCs. The expression of Cx43 in psoriasis DMSCs was higher than that in control samples and the gap junction function was enhanced. In addition, the glycolysis and mitochondrial respiration of psoriasis DMSCs were also enhanced. However, AGA inhibited the expression of Cx43, attenuated GJIC function, and inhibited the proliferation of DMSCs.

CONCLUSIONS

Our results indicated that the expression of Cx43 in DMSCs from psoriasis lesions is increased and that the inhibition of Cx43 leads to the inhibition of both GJIC and DMSCs proliferation.

Downregulated miR-150 in bone marrow mesenchymal stem cells attenuates the apoptosis of LPS-stimulated RAW264.7 via MTCH2-dependent mitochondria transfer

Mesenchymal stem cells (MSCs) are promising therapeutic cells for preventing apoptosis and abrogating cellular injury. Apoptosis of macrophages and the resulting dysfunction play a critical pathogenic role in acute respiratory distress syndrome (ARDS). Herein, the anti-apoptosis effects of bone marrow MSCs (BMSCs) on RAW264.7 were investigated by transwell assay. Compared to lipopolysaccharide (LPS) stimulation, the treatment of BMSCs decreased the level of cleaved caspase-3 protein, the ratio of terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells, the level of caspase3-positive cells, and the accumulation of reactive oxygen species (ROS). Moreover, the expression of Bcl-2 and the level of mitochondrial membrane potential (MMP) were increased. Also, it was found that miR-150 disruption of BMSCs remarkably improved the efficiency of the treatment with LPS-stimulated RAW264.7 cells. The study demonstrated that the suppression of miR-150 facilitated the translation of MTCH2 gene and MTCH2-regulated mitochondria transfer from BMSCs to RAW264.7 cells, suggested that miR-150-mediated BMSCs has therapeutic potential for ARDS.