iPSC-MSCs with High Intrinsic MIRO1 and Sensitivity to TNF-α Yield Efficacious Mitochondrial Transfer to Rescue Anthracycline-Induced Cardiomyopathy

Mesenchymal stem cells and exosomes: A novel therapeutic approach for aging

Mesenchymal stem cells (MSCs), a vital component of the adult stem cell repertoire, are distinguished by their dual capacity for self-renewal and multilineage differentiation. The therapeutic effects of MSCs are primarily mediated through mechanisms such as homing, paracrine signaling, and cellular differentiation. Exosomes (Exos), a type of extracellular vesicles (EVs) secreted by MSCs via the paracrine pathway, play a pivotal role in conveying the biological functions of MSCs. Accumulating evidence from extensive research underscores the remarkable anti-aging potential of both MSCs and their Exos. This review comprehensively explores the impact of MSCs and their Exos on key hallmarks of aging, including genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, impaired macroautophagy, deregulated nutrient-sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, chronic inflammation, and dysbiosis. Furthermore, this paper highlights emerging strategies and novel approaches for modulating the aging process, offering insights into potential therapeutic interventions.

Mitochondria-Rich Extracellular Vesicles From Bone Marrow Stem Cells Mitigate Muscle Degeneration in Rotator Cuff Tears in a Rat Model Through Macrophage M2 Phenotype Conversion

PURPOSE

To investigate the protective effects of extracellular vesicles derived from bone marrow stem cells (BMSC-EVs) on muscle degeneration in a rat model of rotator cuff tendon and suprascapular nerve (SSN) transection (termed the RCT-SSN model), focusing on mitochondrial transfer.

METHODS

The EVs were identified and characterized. The RCT-SSN model was established by transecting the supraspinatus, infraspinatus tendons, and suprascapular nerve. Ninety-six rats were divided into 4 groups (n = 24 each): sham surgery, RCT-SSN treated with BMSC-EVs, RCT-SSN treated with EVs from rhodamine 6G-pretreated BMSCs (Rho-EVs), or phosphate-buffered saline. Intramuscular injections were administered every 2 weeks. After 12 weeks, supraspinatus muscles were analyzed for atrophy, fibrosis, oxidative stress, macrophage phenotypes, serum cytokines, and mitochondrial characteristics. In vitro experiments included EVs tracking in macrophages, macrophage phenotype characterization, and inflammatory cytokine profiling.

RESULTS

BMSC-EVs and Rho-EVs displayed similar morphology, but only BMSC-EVs contained functional mitochondria. BMSC-EVs significantly reduced muscle weight loss (0.047 ± 0.010% vs 0.145 ± 0.013%, P < .001), increased muscle fiber cross-sectional area (2037 ± 231.9 μm2 vs 527.9 ± 92.01 μm2, P < .001), and decreased fibrosis (12.09 ± 3.31% vs 25.69 ± 4.84%, P < .001) compared with phosphate-buffered saline. BMSC-EVs enhanced superoxide dismutase activity (93.3 ± 11.8 U/mg protein vs 53.4 ± 8.0 U/mg protein, P < .001), improved mitochondrial function, density and structure, and induced an anti-inflammatory macrophage shift, suppressing proinflammatory cytokines in vitro and in vivo. Rho-EVs showed no such effects.

CONCLUSIONS

This study showed that transecting the supraspinatus, infraspinatus tendons, and suprascapular nerve in a rat model induced muscle degeneration and fibrosis. BMSC-EVs, but not Rho-EVs, mitigated these effects by promoting an anti-inflammatory macrophage phenotype and protecting mitochondrial function through mitochondrial transfer.

CLINICAL RELEVANCE

Mitochondrial transfer via BMSC-EVs may offer a therapeutic strategy to prevent muscle degeneration in patients with rotator cuff tear.

Mitochondrial targeted therapies in MAFLD

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a clinical-pathological syndrome primarily characterized by excessive accumulation of fat in hepatocytes, independent of alcohol consumption and other well-established hepatotoxic agents. Mitochondrial dysfunction is widely acknowledged as a pivotal factor in the pathogenesis of various diseases, including cardiovascular diseases, cancer, neurodegenerative disorders, and metabolic diseases such as obesity and obesity-associated MAFLD. Mitochondria are dynamic cellular organelles capable of modifying their functions and structures to accommodate the metabolic demands of cells. In the context of MAFLD, the excess production of reactive oxygen species induces oxidative stress, leading to mitochondrial dysfunction, which subsequently promotes metabolic disorders, fat accumulation, and the infiltration of inflammatory cells in liver and adipose tissue. This review aims to systematically analyze the role of mitochondria-targeted therapies in MAFLD, evaluate current therapeutic strategies, and explore future directions in this rapidly evolving field. We specifically focus on the molecular mechanisms underlying mitochondrial dysfunction, emerging therapeutic approaches, and their clinical implications. This is of significant importance for the development of new therapeutic approaches for these metabolic disorders.

Therapeutic Potential of Adipose-Derived Regenerative Cells for Ischemic Diseases

Adipose-derived regenerative cells (ADRCs) are one of the most promising cell sources that possess significant therapeutic effects. They have now become a main source of cell therapy for the treatment of ischemic diseases due to their easy accessibility, expansion, and differentiation. Additionally, ADRCs can release multiple paracrine factors and extracellular vesicles that contribute to tissue regeneration by promoting angiogenesis, regulating inflammation, alleviating apoptosis, and inhibiting fibrosis. However, ADRCs still have some limitations to realize their full therapeutic potential. To address these issues, protective mechanistic studies and bioengineering studies have been carried out. This review focused on the recently studied mechanisms, such as paracrine factors, cell fusion, and mitochondrial transfer, involving the therapeutic potential of ADRCs in ischemic diseases and discussed some modification techniques of ADRCs.

Mitochondrial transplantation for cardioprotection and induction of angiogenesis in ischemic heart disease

To date, the regenerative potential of mitochondrial transplantation (MT) has been extensively investigated under several pathologies. Among various cardiovascular diseases, ischemic heart disease (IHD), the most prevalent pathological condition in human medicine, is induced by coronary artery narrowing, or occlusion, leading to bulk necrotic changes and fibrosis within the myocardium. Data associated with the pro-angiogenic activity of mitochondria have not been completely elucidated in terms of cardiac tissue regeneration. Here, we aimed to highlight the recent studies and advantages related to the application of mitochondrial mass in the ischemic myocardium. How and by which mechanisms, mitochondria can reduce aberrant myocardial tissue remodeling via different pathways such as angiogenesis and de novo blood formation was discussed in detail. We hope that data from the current review article help us understand the molecular and cellular mechanisms by which transplanted mitochondria exert their regenerative properties in the ischemic myocardium.

Mitochondria-rich extracellular vesicles derived from the culture supernatant of human synovial Fluid-derived mesenchymal stem cells Inhibited senescence of Stressed/inflammatory Licensed chondrocytes and Delayed Osteoarthritis progression

BACKGROUND

Mitochondrial dysfunction induces chondrocyte senescence, thereby precipitating articular cartilage (AC) degeneration in the pathogenesis of osteoarthritis (OA). Although the transfer of mitochondria from mesenchymal stem cells (MSCs) to host cells and their potential protective role have been demonstrated, whether MSCs can alleviate chondrocyte mitochondrial dysfunction or reverse OA progression remains unclear.

METHODS

A mitochondrial tracer was used to investigate the transfer of mitochondria-rich extracellular vesicles (MEV) derived from the culture supernatant of human synovial fluid-derived mesenchymal stem cells (hSF-MSCs). Human articular chondrocytes (hACs) impaired by oxidative stress co-incubated with MEV were used for experimental research in vitro. Healthy hACs and stressed hACs were cultured separately acting as the control groups. The MEV was injected into the OA rats' knee joint serving as experimental group. Healthy and OA rats were served as the control groups. Quantitative reverse transcription polymerase chain reaction (qRT-PCR), western blot (WB), enzyme- linked immunosorbent assay (ELISA), flow cytometry (FC), immunofluorescence (IF), fluorescence spectrophotometer (FS), immunohistochemistry (IHC) and other methods are used to analyze the effect of MEV on hACs and OA progression.

RESULTS

MEV derived from hSF-MSCs could transfer into hACs. Compared to the negative control group, co-incubation with MEV resulted in a significant down-regulation of oxidative stress markers and senescence-associated proteins in hACs, while improved mitochondrial function of hACs. Moreover, the MEV could traverse the dense interstitial layer and migrate towards the deeper cartilage, while intra-articular injection of MEV could effectively attenuate AC degeneration.

CONCLUSION

The transfer of MEV derived from hSF-MSCs represents a promising strategy for safeguarding AC, thereby offering a potential avenue and mechanism for the treatment of OA.

Oxidative High Mobility Group Box-1 Accelerates Mitochondrial Transfer from Mesenchymal Stem Cells to Colorectal Cancer Cells Providing Cancer Cell Stemness

Mitochondria are important organelles for cell metabolism and tissue survival. Their cell-to-cell transfer is important for the fate of recipient cells. Recently, bone marrow mesenchymal stem cells (BM-MSCs) have been reported to provide mitochondria to cancer cells and rescue mitochondrial dysfunction in cancer cells. However, the details of the mechanism have not yet been fully elucidated. In this study, we investigated the humoral factors inducing mitochondrial transfer (MT) and the mechanisms. BM-MSCs produced MT in colorectal cancer (CRC) cells damaged by 5-fluorouracil (5-FU), but were suppressed by the anti-high mobility group box-1 (HMGB1) antibody. BM-MSCs treated with oxidized HMGB1 had increased expression of MT-associated genes, whereas reduced HMGB1 did not. Inhibition of nuclear factor-κB, a downstream factor of HMGB1 signaling, significantly decreased MT-associated gene expression. CRC cells showed increased stemness and decreased 5-FU sensitivity in correlation with MT levels. In a mouse subcutaneous tumor model of CRC, 5-FU sensitivity decreased and stemness increased by the MT from host mouse BM-MSCs. These results suggest that oxidized HMGB1 induces MTs from MSCs to CRC cells and promotes cancer cell stemness. Targeting of oxidized HMGB1 may attenuate stemness of CRCs.

The adaptor protein Miro1 modulates horizontal transfer of mitochondria in mouse melanoma models

Recent research has shown that mtDNA-deficient cancer cells (ρ0 cells) acquire mitochondria from tumor stromal cells to restore respiration, facilitating tumor formation. We investigated the role of Miro1, an adaptor protein involved in movement of mitochondria along microtubules, in this phenomenon. Inducible Miro1 knockout (Miro1KO) mice markedly delayed tumor formation after grafting ρ0 cancer cells. Miro1KO mice with fluorescently labeled mitochondria revealed that this delay was due to hindered mitochondrial transfer from the tumor stromal cells to grafted B16 ρ0 cells, which impeded recovery of mitochondrial respiration and tumor growth. Miro1KO led to the perinuclear accumulation of mitochondria and impaired mobility of the mitochondrial network. In vitro experiments revealed decreased association of mitochondria with microtubules, compromising mitochondrial transfer via tunneling nanotubes (TNTs) in mesenchymal stromal cells. Here we show the role of Miro1 in horizontal mitochondrial transfer in mouse melanoma models in vivo and its involvement with TNTs.

Exosomes Derived from Apelin-Pretreated Mesenchymal Stem Cells Ameliorate Sepsis-Induced Myocardial Dysfunction by Alleviating Cardiomyocyte Pyroptosis via Delivery of miR-34a-5p

Background

Exosomes sourced from mesenchymal stem cells (MSC-EXOs) have become a promising therapeutic tool for sepsis-induced myocardial dysfunction (SMD). Our previous study demonstrated that Apelin pretreatment enhanced the therapeutic benefit of MSCs in myocardial infarction by improving their paracrine effects. This study aimed to determine whether EXOs sourced from Apelin-pretreated MSCs (Apelin-MSC-EXOs) would have potent cardioprotective effects against SMD and elucidate the underlying mechanisms.

Methods

MSC-EXOs and Apelin-MSC-EXOs were isolated and identified. Mice neonatal cardiomyocytes (NCMs) were treated with MSC-EXOs or Apelin-MSC-EXOs under lipopolysaccharide (LPS) condition in vitro. Cardiomyocyte pyroptosis was determined by TUNEL staining. RNA sequencing was used to identify differentially expressed functional miRNAs between MSC-EXOs and Apelin-MSC-EXOs. MSC-EXOs and Apelin-MSC-EXOs were transplanted into a mouse model of SMD induced by cecal ligation puncture (CLP) via the tail vein. Heart function was evaluated by echocardiography.

Results

Compared with MSC-EXOs, Apelin-MSC-EXO transplantation greatly enhanced cardiac function in SMD mice. Both MSC-EXOs and Apelin-MSC-EXOs suppressed cardiomyocyte pyroptosis in vivo and in vitro, with the latter exhibiting superior protective effects. miR-34a-5p effectively mediated Apelin-MSC-EXOs to exert their cardioprotective effects in SMD with high mobility group box-1 (HMGB1) as the potential target. Mechanistically, Apelin-MSC-EXOs delivered miR-34a-5p into injured cardiomyocytes, thereby ameliorating cardiomyocyte pyroptosis via regulation of the HMGB1/AMPK axis. These cardioprotective effects were partially abrogated by downregulation of miR-34a-5p in Apelin-MSC-EXOs.

Conclusion

Our study revealed miR-34a-5p as a key component of Apelin-MSC-EXOs that protected against SMD via mediation of the HMGB1/AMPK signaling pathway.

Recommendations for mitochondria transfer and transplantation nomenclature and characterization

Intercellular mitochondria transfer is an evolutionarily conserved process in which one cell delivers some of their mitochondria to another cell in the absence of cell division. This process has diverse functions depending on the cell types involved and physiological or disease context. Although mitochondria transfer was first shown to provide metabolic support to acceptor cells, recent studies have revealed diverse functions of mitochondria transfer, including, but not limited to, the maintenance of mitochondria quality of the donor cell and the regulation of tissue homeostasis and remodelling. Many mitochondria-transfer mechanisms have been described using a variety of names, generating confusion about mitochondria transfer biology. Furthermore, several therapeutic approaches involving mitochondria-transfer biology have emerged, including mitochondria transplantation and cellular engineering using isolated mitochondria. In this Consensus Statement, we define relevant terminology and propose a nomenclature framework to describe mitochondria transfer and transplantation as a foundation for further development by the community as this dynamic field of research continues to evolve.

Cellular component transfer between photoreceptor cells of the retina

Photoreceptor transplantation is a potential therapeutic strategy for degenerative retinal diseases. Studies on mechanisms contributing to retinal regeneration and vision repair identified cellular components transfer (CCT) as playing a role, in addition to somatic augmentation (referred to as "cell replacement" in this paper). In CCT, donor photoreceptors shuttle proteins, RNA, and mitochondria to host photoreceptors through intercellular connections. The discovery of CCT in the transplantation context triggered a re-interpretation of prior transplantation studies that generally did not include specific CCT assays and thereby broadly emphasized the cell replacement model, reflecting the prevailing understanding of retinal transplantation biology at that time. In addition to clarifying our understanding of photoreceptor biology, CCT has raised the possibility of developing treatments to replenish molecular deficiencies in diseased photoreceptor cells. As the CCT field evolves, investigators have used diverse terminology, and implemented different CCT assays following transplantation in animal models. The non-standardized terminology of CCT and absent minimal assay standards for detection can hinder communication between investigators and comparison between studies. In this review, we discuss the current understanding of CCT, provide an overview of transplantation and regeneration studies in small and large animals, and propose terminology and a minimal assay standard for CCT. Further research on CCT may eventually provide new avenues to treat a range of hereditary and acquired retinopathies while illuminating mechanisms of cell-cell interaction in the retina.

Intercellular Mitochondrial transfer: Therapeutic implications for energy metabolism in heart failure

Heart failure (HF) remains one of the leading causes of high morbidity and mortality globally. Impaired cardiac energy metabolism plays a critical role in the pathological progression of HF. Various forms of HF exhibit marked differences in energy metabolism, particularly in mitochondrial function and substrate utilization. Recent studies have increasingly highlighted that improving energy metabolism in HF patients as a crucial treatment strategy. Mitochondrial transfer is emerging as a promising and precisely regulated therapeutic strategy for treating metabolic disorders. This paper specifically reviews the characteristics of mitochondrial energy metabolism across different types of HF and explores the modes and mechanisms of mitochondrial transfer between different cell types in the heart, such as cardiomyocytes, fibroblasts, and immune cells. We focused on the therapeutic potential of intercellular mitochondrial transfer in improving energy metabolism disorders in HF. We also discuss the role of signal transduction in mitochondrial transfer, highlighting that mitochondria not only function as energy factories but also play crucial roles in intercellular communication, metabolic regulation, and tissue repair. This study provides new insights into improving energy metabolism in heart failure patients and proposes promising new therapeutic strategies.

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.

Mitochondrial transfer in the progression and treatment of cardiac disease

Mitochondria are the primary site for energy production and play a crucial role in supporting normal physiological functions of the human body. In cardiomyocytes (CMs), mitochondria can occupy up to 30 % of the cell volume, providing sufficient energy for CMs contraction and relaxation. However, some pathological conditions such as ischemia, hypoxia, infection, and the side effect of drugs, can cause mitochondrial dysfunction in CMs, leading to various myocardial injury-related diseases including myocardial infarction (MI), myocardial hypertrophy, and heart failure. Self-control of mitochondria quality and conversion of metabolism pathway in energy production can serve as the self-rescue measure to avoid autologous mitochondrial damage. Particularly, mitochondrial transfer from the neighboring or extraneous cells enables to mitigate mitochondrial dysfunction and restore their biological functions in CMs. Here, we described the homeostatic control strategies and related mechanisms of mitochondria in injured CMs, including autologous mitochondrial quality control, mitochondrial energy conversion, and especially the exogenetic mitochondrial donation. Additionally, this review emphasizes on the therapeutic effects and potential application of utilizing mitochondrial transfer in reducing myocardial injury. We hope that this review can provide theoretical clues for the developing of advanced therapeutics to treat cardiac diseases.

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.

Unveiling the immunogenicity of allogeneic mesenchymal stromal cells: Challenges and strategies for enhanced therapeutic efficacy

Mesenchymal stromal cells (MSCs) exhibit significant potential in the context of cell therapy because of their capacity to perform a range of interconnected functions in damaged tissues, including immune modulation, hematopoietic support, and tissue regeneration. MSCs are hypoimmunogenic because of their diminished expression of major histocompatibility molecules, absence of costimulatory molecules, and presence of coinhibitory molecules. While autologous MSCs reduce the risk of rejection and infection, variability in cell numbers and proliferation limits their potential applications. Conversely, allogeneic MSCs (allo-MSCs) possess broad clinical applications unconstrained by donor physiology. Nonetheless, preclinical and clinical investigations highlight that transplanted allo-MSCs are subject to immune attack from recipients. These cells exhibit anti-inflammatory and proinflammatory phenotypes contingent on the microenvironment. Notably, the proinflammatory phenotype features enhanced immunogenicity and diminished immunosuppression, potentially triggering allogeneic immune reactions that impede long-term clinical efficacy. Consequently, preserving the low immunogenicity of allo-MSCs in vivo and mitigating immune rejection in diverse microenvironments represent crucial challenges for the widespread clinical application of MSCs. In this review, we elucidate the immune regulation of allo-MSCs, specifically focusing on two distinct subgroups, MSC1 and MSC2, that exhibit varying polarization states and immunogenicity. We discuss the factors and underlying mechanisms that induce MSC immunogenicity and polarization, highlighting the crucial role of major histocompatibility complex class I/II molecules in rejection post-transplantation. Additionally, we summarize the immunogenic regulatory targets and applications of allo-MSCs and outline strategies to address challenges in this promising field, aiming to enhance allo-MSC therapeutic efficacy for patients.

MSC-mediated mitochondrial transfer restores mitochondrial DNA and function in neural progenitor cells of Leber's hereditary optic neuropathy

Leber's hereditary optic neuropathy (LHON) is a debilitating mitochondrial disease associated with mutations in mitochondrial DNA (mtDNA). Unfortunately, the available treatment options for LHON patients are limited due to challenges in mitochondrial replacement. In our study, we reprogramming LHON urine cells into induced pluripotent stem cells (iPSCs) and differentiating them into neural progenitor cells (NPCs) and neurons for disease modeling. Our research revealed that LHON neurons exhibited significantly higher levels of mtDNA mutations and reduced mitochondrial function, confirming the disease phenotype. However, through co-culturing LHON iPSC-derived NPCs with mesenchymal stem cells (MSCs), we observed a remarkable rescue of mutant mtDNA and a significant improvement in mitochondrial metabolic function in LHON neurons. These findings suggest that co-culturing with MSCs can enhance mitochondrial function in LHON NPCs, even after their differentiation into neurons. This discovery holds promise as a potential therapeutic strategy for LHON patients.

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.

Connexin 43 regulates intercellular mitochondrial transfer from human mesenchymal stromal cells to chondrocytes

BACKGROUND

The phenomenon of intercellular mitochondrial transfer from mesenchymal stromal cells (MSCs) has shown promise for improving tissue healing after injury and has potential for treating degenerative diseases like osteoarthritis (OA). Recently MSC to chondrocyte mitochondrial transfer has been documented, but the mechanism of transfer is unknown. Full-length connexin 43 (Cx43, encoded by GJA1) and the truncated, internally translated isoform GJA1-20k have been implicated in mitochondrial transfer between highly oxidative cells, but have not been explored in orthopaedic tissues. Here, our goal was to investigate the role of Cx43 in MSC to chondrocyte mitochondrial transfer. In this study, we tested the hypotheses that (a) mitochondrial transfer from MSCs to chondrocytes is increased when chondrocytes are under oxidative stress and (b) MSC Cx43 expression mediates mitochondrial transfer to chondrocytes.

METHODS

Oxidative stress was induced in immortalized human chondrocytes using tert-Butyl hydroperoxide (t-BHP) and cells were evaluated for mitochondrial membrane depolarization and reactive oxygen species (ROS) production. Human bone-marrow derived MSCs were transduced for mitochondrial fluorescence using lentiviral vectors. MSC Cx43 expression was knocked down using siRNA or overexpressed (GJA1 + and GJA1-20k+) using lentiviral transduction. Chondrocytes and MSCs were co-cultured for 24 h in direct contact or separated using transwells. Mitochondrial transfer was quantified using flow cytometry. Co-cultures were fixed and stained for actin and Cx43 to visualize cell-cell interactions during transfer.

RESULTS

Mitochondrial transfer was significantly higher in t-BHP-stressed chondrocytes. Contact co-cultures had significantly higher mitochondrial transfer compared to transwell co-cultures. Confocal images showed direct cell contacts between MSCs and chondrocytes where Cx43 staining was enriched at the terminal ends of actin cellular extensions containing mitochondria in MSCs. MSC Cx43 expression was associated with the magnitude of mitochondrial transfer to chondrocytes; knocking down Cx43 significantly decreased transfer while Cx43 overexpression significantly increased transfer. Interestingly, GJA1-20k expression was highly correlated with incidence of mitochondrial transfer from MSCs to chondrocytes.

CONCLUSIONS

Overexpression of GJA1-20k in MSCs increases mitochondrial transfer to chondrocytes, highlighting GJA1-20k as a potential target for promoting mitochondrial transfer from MSCs as a regenerative therapy for cartilage tissue repair in OA.

ALDH2 regulates mesenchymal stem cell senescence via modulation of mitochondrial homeostasis

Although mitochondrial aldehyde dehydrogenase 2 (ALDH2) is involved in aging and aging-related diseases, its role in the regulation of human mesenchymal stem cell (MSC) senescence has not been investigated. This study aimed to determine the role of ALDH2 in regulating MSC senescence and illustrate the potential mechanisms. MSCs were isolated from young (YMSCs) and aged donors (AMSCs). Senescence-associated β-galactosidase (SA-β-gal) staining and Western blotting were used to assess MSC senescence. Reactive oxygen species (ROS) generation and mitochondrial membrane potential were determined to evaluate mitochondrial function. We showed that the expression of ALDH2 increased alongside cellular senescence of MSCs. Overexpression of ALDH2 accelerated YMSC senescence whereas down-regulation alleviated premature senescent phenotypes of AMSCs. Transcriptome and biochemical analyses revealed that an elevated ROS level and mitochondrial dysfunction contributed to ALDH2 function in MSC senescence. Using molecular docking, we identified interferon regulatory factor 7 (IRF7) as the potential target of ALDH2. Mechanistically, ectopic expression of ALDH2 led to mitochondrial dysfunction and accelerated senescence of MSCs by increasing the stability of IRF7 through a direct physical interaction. These effects were partially reversed by knockdown of IRF7. These findings highlight a crucial role of ALDH2 in driving MSC senescence by regulating mitochondrial homeostasis, providing a novel potential strategy against human aging-related diseases.

Artificial mitochondrial transplantation (AMT) reverses aging of mesenchymal stromal cells and improves their immunomodulatory properties in LPS-induced synoviocytes inflammation

Nowadays, regenerative medicine techniques are usually based on the application of mesenchymal stromal cells (MSCs) for the repair or restoration of injured damaged tissues. However, the effectiveness of autologous therapy is limited as therapeutic potential of MSCs declines due to patient's age, health condition and prolonged in vitro cultivation as a result of decreased growth rate. For that reason, there is an urgent need to develop strategies enabling the in vitro rejuvenation of MSCs prior transplantation in order to enhance their in vivo therapeutic efficiency. In presented study, we attempted to mimic the naturally occurring mitochondrial transfer (MT) between neighbouring cells and verify whether artificial MT (AMT) could reverse MSCs aging and improve their biological properties. For that reason, mitochondria were isolated from healthy donor equine adipose-derived stromal cells (ASCs) and transferred into metabolically impaired recipient ASCs derived from equine metabolic syndrome (EMS) affected horses, which were subsequently subjected to various analytical methods in order to verify the cellular and molecular outcomes of the applied AMT. Mitochondria recipient cells were characterized by decreased apoptosis, senescence and endoplasmic reticulum stress while insulin sensitivity was enhanced. Furthermore, we observed increased mitochondrial fragmentation and associated PARKIN protein accumulation, which indicates on the elimination of dysfunctional organelles via mitophagy. AMT further promoted physioxia and regulated autophagy fluxes. Additionally, rejuvenated ASCs displayed an improved anti-inflammatory activity toward LPS-stimulated synoviocytes. The presented findings highlight AMT as a promising alternative and effective method for MSCs rejuvenation, for potential application in autologous therapies in which MSCs properties are being strongly deteriorated due to patients' condition.

Advancements and Innovative Strategies in Induced Pluripotent Stem Cell-Derived Mesenchymal Stem Cell Therapy: A Comprehensive Review

The effectiveness and safety of mesenchymal stem cell (MSC) therapy have been substantiated across various diseases. Nevertheless, challenges such as the restricted in vitro expansion capacity of tissue-derived MSCs and the clinical instability due to the high heterogeneity of isolated cells require urgent resolution. The induced pluripotent stem cell-derived MSCs (iPSC-MSCs), which is differentiated from iPSCs via specific experimental pathways, holds considerable potential as a substitute for tissue derived MSCs. Multiple studies have demonstrated that iPSCs can be differentiated into iPSC-MSCs through diverse differentiation strategies. Research suggests that iPSC-MSCs, when compared to tissue derived MSCs, exhibit superior characteristics in terms of proliferation ability, immune modulation capacity, and biological efficiency. In this review, we meticulously described and summarized the experimental methods of iPSC differentiation into iPSC-MSCs, the application of iPSC-MSCs in various disease models, the latest advancements in clinically relevant iPSC-derived cell products, and the development strategies for the next generation of iPSC-derived therapy products (not only cell products but also their derivatives).

Beyond mitochondrial transfer, cell fusion rescues metabolic dysfunction and boosts malignancy in adenoid cystic carcinoma

Cancer cells with mitochondrial dysfunction can be rescued by cells in the tumor microenvironment. Using human adenoid cystic carcinoma cell lines and fibroblasts, we find that mitochondrial transfer occurs not only between human cells but also between human and mouse cells both in vitro and in vivo. Intriguingly, spontaneous cell fusion between cancer cells and fibroblasts could also emerge; specific chromosome loss might be essential for nucleus reorganization and the post-hybrid selection process. Both mitochondrial transfer through tunneling nanotubes (TNTs) and cell fusion "selectively" revive cancer cells, with mitochondrial dysfunction as a key motivator. Beyond mitochondrial transfer, cell fusion significantly enhances cancer malignancy and promotes epithelial-mesenchymal transition. Mechanistically, mitochondrial dysfunction in cancer cells causes L-lactate secretion to attract fibroblasts to extend TNTs and TMEM16F-mediated phosphatidylserine externalization, facilitating TNT formation and cell-membrane fusion. Our findings offer insights into mitochondrial transfer and cell fusion, highlighting potential cancer therapy targets.

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

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

Mitochondrial Transfer as a Strategy for Enhancing Cancer Cell Fitness:Current Insights and Future Directions

It is now recognized that tumors are not merely masses of transformed cells but are intricately interconnected with healthy cells in the tumor microenvironment (TME), forming complex and heterogeneous structures. Recent studies discovered that cancer cells can steal mitochondria from healthy cells to empower themselves, while reducing the functions of their target organ. Mitochondrial transfer, i.e. the intercellular movement of mitochondria, is recently emerging as a novel process in cancer biology, contributing to tumor growth, metastasis, and resistance to therapy by shaping the metabolic landscape of the tumor microenvironment. This review highlights the influence of transferred mitochondria on cancer bioenergetics, redox balance and apoptotic resistance, which collectively foster aggressive cancer phenotype. Furthermore, the therapeutic implications of mitochondrial transfer are discussed, emphasizing the potential of targeting these pathways to overcome drug resistance and improve treatment efficacy.

Targeting mitochondrial quality control: new therapeutic strategies for major diseases

Mitochondria play a crucial role in maintaining the normal physiological state of cells. Hence, ensuring mitochondrial quality control is imperative for the prevention and treatment of numerous diseases. Previous reviews on this topic have however been inconsistencies and lack of systematic organization. Therefore, this review aims to provide a comprehensive and systematic overview of mitochondrial quality control and explore the possibility of targeting the same for the treatment of major diseases. This review systematically summarizes three fundamental characteristics of mitochondrial quality control, including mitochondrial morphology and dynamics, function and metabolism, and protein expression and regulation. It also extensively examines how imbalances in mitochondrial quality are linked to major diseases, such as ischemia-hypoxia, inflammatory disorders, viral infections, metabolic dysregulations, degenerative conditions, and tumors. Additionally, the review explores innovative approaches to target mitochondrial quality control, including using small molecule drugs that regulate critical steps in maintaining mitochondrial quality, nanomolecular materials designed for precise targeting of mitochondria, and novel cellular therapies, such as vesicle therapy and mitochondrial transplantation. This review offers a novel perspective on comprehending the shared mechanisms underlying the occurrence and progression of major diseases and provides theoretical support and practical guidance for the clinical implementation of innovative therapeutic strategies that target mitochondrial quality control for treating major diseases.

Mitochondrial transfer between BMSCs and Müller promotes mitochondrial fusion and suppresses gliosis in degenerative retina

Mitochondrial dysfunction and Müller cells gliosis are significant pathological characteristics of retinal degeneration (RD) and causing blinding. Stem cell therapy is a promising treatment for RD, the recently accepted therapeutic mechanism is cell fusion induced materials transfer. However, whether materials including mitochondrial transfer between grafted stem cells and recipient's cells contribute to suppressing gliosis and mechanism are unclear. In present study, we demonstrated that bone marrow mesenchymal stem cells (BMSCs) transferred mitochondria to Müller cells by cell fusion and tunneling nanotubes. BMSCs-derived mitochondria (BMSCs-mito) were integrated into mitochondrial network of Müller cells, improving mitochondrial function, reducing oxidative stress and gliosis, which protected visual function partially in the degenerative rat retina. RNA sequencing analysis revealed that BMSCs-mito increased mitochondrial DNA (mtDNA) content and facilitated mitochondrial fusion in damaged Müller cells. It suggests that mitochondrial transfer from BMSCs remodels Müller cells metabolism and suppresses gliosis; thus, delaying the degenerative progression of RD.

An update of the molecular mechanisms underlying anthracycline induced cardiotoxicity

Anthracycline drugs mainly include doxorubicin, epirubicin, pirarubicin, and aclamycin, which are widely used to treat a variety of malignant tumors, such as breast cancer, gastrointestinal tumors, lymphoma, etc. With the accumulation of anthracycline drugs in the body, they can induce serious heart damage, limiting their clinical application. The mechanism by which anthracycline drugs cause cardiotoxicity is not yet clear. This review provides an overview of the different types of cardiac damage induced by anthracycline-class drugs and delves into the molecular mechanisms behind these injuries. Cardiac damage primarily involves alterations in myocardial cell function and pathological cell death, encompassing mitochondrial dysfunction, topoisomerase inhibition, disruptions in iron ion metabolism, myofibril degradation, and oxidative stress. Mechanisms of uptake and transport in anthracycline-induced cardiotoxicity are emphasized, as well as the role and breakthroughs of iPSC in cardiotoxicity studies. Selected novel cardioprotective therapies and mechanisms are updated. Mechanisms and protective strategies associated with anthracycline cardiotoxicity in animal experiments are examined, and the definition of drug damage in humans and animal models is discussed. Understanding these molecular mechanisms is of paramount importance in mitigating anthracycline-induced cardiac toxicity and guiding the development of safer approaches in cancer treatment.

Molecular Prospective on Malignant Transformation of Mesenchymal Stem Cells: An Issue in Cell Therapy

Mesenchymal stem cell (MSCs) therapy, as a rapidly developing area of medicine, holds great promise for the treatment of a variety of medical conditions. MSCs are multipotent stem cells that can be isolated from various tissues and could self-renew and differentiate. They secrete cytokines and trophic factors that create a regenerative microenvironment and have immunomodulatory properties. Although clinical trials have been conducted with MSCs in various diseases, concerns regarding the possibility of malignant transformation of these cells have been raised. The studies showed a higher rate of hematological malignancy and carcinogenesis in experimental models after MSC transplantation. The mechanisms underlying malignant transformation of MSCs are complex and not fully understood, but they are believed to involve the presence of special signaling molecules and alterations in cell behavior regulation pathways. Possible pathways that lead to MSCs' oncogenic transformation occur through two mechanisms: spontaneous and stimulated malignant transformation, including cell fusion, fusion proteins, and the tumor microenvironment. MSC-based therapies have the potential to revolutionize medicine, and addressing the issue of malignancy is crucial to ensure their safety and efficacy. Therefore, the purpose of the present review is to summarize the potential mechanisms of the malignant transformation of MSCs. [Figure: see text].

Mitochondria transplantation alleviates cardiomyocytes apoptosis through inhibiting AMPKα-mTOR mediated excessive autophagy

The disruption of mitochondria homeostasis can impair the contractile function of cardiomyocytes, leading to cardiac dysfunction and an increased risk of heart failure. This study introduces a pioneering therapeutic strategy employing mitochondria derived from human umbilical cord mesenchymal stem cells (hu-MSC) (MSC-Mito) for heart failure treatment. Initially, we isolated MSC-Mito, confirming their functionality. Subsequently, we monitored the process of single mitochondria transplantation into recipient cells and observed a time-dependent uptake of mitochondria in vivo. Evidence of human-specific mitochondrial DNA (mtDNA) in murine cardiomyocytes was observed after MSC-Mito transplantation. Employing a doxorubicin (DOX)-induced heart failure model, we demonstrated that MSC-Mito transplantation could safeguard cardiac function and avert cardiomyocyte apoptosis, indicating metabolic compatibility between hu-MSC-derived mitochondria and recipient mitochondria. Finally, through RNA sequencing and validation experiments, we discovered that MSC-Mito transplantation potentially exerted cardioprotection by reinstating ATP production and curtailing AMPKα-mTOR-mediated excessive autophagy.

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.

Mitochondrial transfer mediates endothelial cell engraftment through mitophagy

Ischaemic diseases such as critical limb ischaemia and myocardial infarction affect millions of people worldwide1. Transplanting endothelial cells (ECs) is a promising therapy in vascular medicine, but engrafting ECs typically necessitates co-transplanting perivascular supporting cells such as mesenchymal stromal cells (MSCs), which makes clinical implementation complicated2,3. The mechanisms that enable MSCs to facilitate EC engraftment remain elusive. Here we show that, under cellular stress, MSCs transfer mitochondria to ECs through tunnelling nanotubes, and that blocking this transfer impairs EC engraftment. We devised a strategy to artificially transplant mitochondria, transiently enhancing EC bioenergetics and enabling them to form functional vessels in ischaemic tissues without the support of MSCs. Notably, exogenous mitochondria did not integrate into the endogenous EC mitochondrial pool, but triggered mitophagy after internalization. Transplanted mitochondria co-localized with autophagosomes, and ablation of the PINK1-Parkin pathway negated the enhanced engraftment ability of ECs. Our findings reveal a mechanism that underlies the effects of mitochondrial transfer between mesenchymal and endothelial cells, and offer potential for a new approach for vascular cell therapy.

Translating mesenchymal stem cell and their exosome research into GMP compliant advanced therapy products: Promises, problems and prospects

Mesenchymal stem cells (MSCs) are one of the few stem cell types used in clinical practice as therapeutic agents for immunomodulation and ischemic tissue repair, due to their unique paracrine capacity, multiple differentiation potential, active components in exosomes, and effective mitochondria donation. At present, MSCs derived from tissues such as bone marrow and umbilical cord are widely applied in preclinical and clinical studies. Nevertheless, there remain challenges to the maintenance of consistently good quality MSCs derived from different donors or tissues, directly impacting their application as advanced therapy products. In this review, we discuss the promises, problems, and prospects associated with translation of MSC research into a pharmaceutical product. We review the hurdles encountered in translation of MSCs and MSC-exosomes from the research bench to an advanced therapy product compliant with good manufacturing practice (GMP). These difficulties include how to set up GMP-compliant protocols, what factors affect raw material selection, cell expansion to product formulation, establishment of quality control (QC) parameters, and quality assurance to comply with GMP standards. To avoid human error and reduce the risk of contamination, an automatic, closed system that allows real-time monitoring of QC should be considered. We also highlight potential advantages of pluripotent stem cells as an alternative source for MSC and exosomes generation and manufacture.

Miro1 improves the exogenous engraftment efficiency and therapeutic potential of mitochondria transfer using Wharton's jelly mesenchymal stem cells

Mitochondria are important for maintaining cellular energy metabolism and regulating cellular senescence. Mitochondrial DNA (mtDNA) encodes subunits of the OXPHOS complexes which are essential for cellular respiration and energy production. Meanwhile, mtDNA variants have been associated with the pathogenesis of neurodegenerative diseases, including MELAS, for which no effective treatment has been developed. To alleviate the pathological conditions involved in mitochondrial disorders, mitochondria transfer therapy has shown promise. Wharton's jelly mesenchymal stem cells (WJMSCs) have been identified as suitable mitochondria donors for mitochondria-defective cells, wherein mitochondrial functions can be rescued. Miro1 participates in mitochondria trafficking by anchoring mitochondria to microtubules. In this study, we identified Miro1 over-expression as a factor that could help to enhance the efficiency of mitochondrial delivery. More specifically, we reveal that Miro1 over-expressed WJMSCs significantly improved intercellular communications, cell proliferation rates, and mitochondrial membrane potential, while restoring mitochondrial bioenergetics in mitochondria-defective fibroblasts. Furthermore, Miro1 over-expressed WJMSCs decreased rates of induced apoptosis and ROS production in MELAS fibroblasts; although, Miro1 over-expression did not rescue mtDNA mutation ratios nor mitochondrial biogenesis. This study presents a potentially novel therapeutic strategy for treating mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS), and other diseases associated with dysfunctional mitochondria, while the pathophysiological relevance of our results should be further verified by animal models and clinical studies.

Miro-mediated mitochondrial transport: A new dimension for disease-related abnormal cell metabolism?

Mitochondria are versatile and highly dynamic organelles found in eukaryotic cells that play important roles in a variety of cellular processes. The importance of mitochondrial transport in cell metabolism, including variations in mitochondrial distribution within cells and intercellular transfer, has grown in recent years. Several studies have demonstrated that abnormal mitochondrial transport represents an early pathogenic alteration in a variety of illnesses, emphasizing its significance in disease development and progression. Mitochondrial Rho GTPase (Miro) is a protein found on the outer mitochondrial membrane that is required for cytoskeleton-dependent mitochondrial transport, mitochondrial dynamics (fusion and fission), and mitochondrial Ca2+ homeostasis. Miro, as a critical regulator of mitochondrial transport, has yet to be thoroughly investigated in illness. This review focuses on recent developments in recognizing Miro as a crucial molecule in controlling mitochondrial transport and investigates its roles in diverse illnesses. It also intends to shed light on the possibilities of targeting Miro as a therapeutic method for a variety of diseases.

Exosomal miR-9-5p derived from iPSC-MSCs ameliorates doxorubicin-induced cardiomyopathy by inhibiting cardiomyocyte senescence

Doxorubicin (DOX) is a chemotherapeutic agent widely used for tumor treatment. Nonetheless its clinical application is heavily limited by its cardiotoxicity. There is accumulated evidence that transplantation of mesenchymal stem cell-derived exosomes (MSC-EXOs) can protect against Dox-induced cardiomyopathy (DIC). This study aimed to examine the cardioprotective effects of EXOs isolated from human induced pluripotent stem cell-derived MSCs (iPSC-MSCs) against DIC and explore the potential mechanisms. EXOs were isolated from the cultural supernatant of human BM-MSCs (BM-MSC-EXOs) and iPSC-MSCs (iPSC-MSC-EXOs) by ultracentrifugation. A mouse model of DIC was induced by intraperitoneal injection of Dox followed by tail vein injection of PBS, BM-MSC-EXOs, or iPSC-MSC-EXOs. Cardiac function, cardiomyocyte senescence and mitochondrial dynamics in each group were assessed. In vitro, neonatal mouse cardiomyocytes (NMCMs) were subjected to Dox and treated with BM-MSC-EXOs or iPSC-MSC-EXOs. The mitochondrial morphology and cellular senescence of NMCMs were examined by Mitotracker staining and senescence-associated-β-galactosidase assay, respectively. Compared with BM-MSC-EXOs, mice treated with iPSC-MSC-EXOs displayed improved cardiac function and decreased cardiomyocyte mitochondrial fragmentation and senescence. In vitro, iPSC-MSC-EXOs were superior to BM-MSC-EXOs in attenuation of cardiomyocyte mitochondrial fragmentation and senescence caused by DOX. MicroRNA sequencing revealed a higher level of miR-9-5p in iPSC-MSC-EXOs than BM-MSC-EXOs. Mechanistically, iPSC-MSC-EXOs transported miR-9-5p into DOX-treated cardiomyocytes, thereby suppressing cardiomyocyte mitochondrial fragmentation and senescence via regulation of the VPO1/ERK signal pathway. These protective effects and cardioprotection against DIC were largely reversed by knockdown of miR-9-5p in iPSC-MSC-EXOs. Our results showed that miR-9-5p transferred by iPSC-MSC-EXOs protected against DIC by alleviating cardiomyocyte senescence via inhibition of the VPO1/ERK pathway. This study offers new insight into the application of iPSC-MSC-EXOs as a novel therapeutic strategy for DIC treatment.

Mesenchymal stromal cells for improvement of cardiac function following acute myocardial infarction: a matter of timing

Acute myocardial infarction (AMI) is the leading cause of cardiovascular death and remains the most common cause of heart failure. Reopening of the occluded artery, i.e., reperfusion, is the only way to save the myocardium. However, the expected benefits of reducing infarct size are disappointing due to the reperfusion paradox, which also induces specific cell death. These ischemia-reperfusion (I/R) lesions can account for up to 50% of final infarct size, a major determinant for both mortality and the risk of heart failure (morbidity). In this review, we provide a detailed description of the cell death and inflammation mechanisms as features of I/R injury and cardioprotective strategies such as ischemic postconditioning as well as their underlying mechanisms. Due to their biological properties, the use of mesenchymal stromal/stem cells (MSCs) has been considered a potential therapeutic approach in AMI. Despite promising results and evidence of safety in preclinical studies using MSCs, the effects reported in clinical trials are not conclusive and even inconsistent. These discrepancies were attributed to many parameters such as donor age, in vitro culture, and storage time as well as injection time window after AMI, which alter MSC therapeutic properties. In the context of AMI, future directions will be to generate MSCs with enhanced properties to limit cell death in myocardial tissue and thereby reduce infarct size and improve the healing phase to increase postinfarct myocardial performance.

Connexin 43 Regulates Intercellular Mitochondrial Transfer from Human Mesenchymal Stromal Cells to Chondrocytes

Background

The phenomenon of intercellular mitochondrial transfer from mesenchymal stromal cells (MSCs) has shown promise for improving tissue healing after injury and has potential for treating degenerative diseases like osteoarthritis (OA). Recently MSC to chondrocyte mitochondrial transfer has been documented, but the mechanism of transfer is unknown. Full-length connexin43 (Cx43, encoded by GJA1 ) and the truncated internally translated isoform GJA1-20k have been implicated in mitochondrial transfer between highly oxidative cells, but have not been explored in orthopaedic tissues. Here, our goal was to investigate the role of Cx43 in MSC to chondrocyte mitochondrial transfer. In this study, we tested the hypotheses that (a) mitochondrial transfer from MSCs to chondrocytes is increased when chondrocytes are under oxidative stress and (b) MSC Cx43 expression mediates mitochondrial transfer to chondrocytes.

Methods

Oxidative stress was induced in immortalized human chondrocytes using tert-Butyl hydroperoxide (t-BHP) and cells were evaluated for mitochondrial membrane depolarization and reactive oxygen species (ROS) production. Human bone-marrow derived MSCs were transduced for mitochondrial fluorescence using lentiviral vectors. MSC Cx43 expression was knocked down using siRNA or overexpressed (GJA1+ and GJA1-20k+) using lentiviral transduction. Chondrocytes and MSCs were co-cultured for 24 hrs in direct contact or separated using transwells. Mitochondrial transfer was quantified using flow cytometry. Co-cultures were fixed and stained for actin and Cx43 to visualize cell-cell interactions during transfer.

Results

Mitochondrial transfer was significantly higher in t-BHP-stressed chondrocytes. Contact co-cultures had significantly higher mitochondrial transfer compared to transwell co-cultures. Confocal images showed direct cell contacts between MSCs and chondrocytes where Cx43 staining was enriched at the terminal ends of actin cellular extensions containing mitochondria in MSCs. MSC Cx43 expression was associated with the magnitude of mitochondrial transfer to chondrocytes; knocking down Cx43 significantly decreased transfer while Cx43 overexpression significantly increased transfer. Interestingly, GJA1-20k expression was highly correlated with incidence of mitochondrial transfer from MSCs to chondrocytes.

Conclusions

Overexpression of GJA1-20k in MSCs increases mitochondrial transfer to chondrocytes, highlighting GJA1-20k as a potential target for promoting mitochondrial transfer from MSCs as a regenerative therapy for cartilage tissue repair in OA.

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.

Mitochondria in the Central Nervous System in Health and Disease: The Puzzle of the Therapeutic Potential of Mitochondrial Transplantation

Mitochondria, the energy suppliers of the cells, play a central role in a variety of cellular processes essential for survival or leading to cell death. Consequently, mitochondrial dysfunction is implicated in numerous general and CNS disorders. The clinical manifestations of mitochondrial dysfunction include metabolic disorders, dysfunction of the immune system, tumorigenesis, and neuronal and behavioral abnormalities. In this review, we focus on the mitochondrial role in the CNS, which has unique characteristics and is therefore highly dependent on the mitochondria. First, we review the role of mitochondria in neuronal development, synaptogenesis, plasticity, and behavior as well as their adaptation to the intricate connections between the different cell types in the brain. Then, we review the sparse knowledge of the mechanisms of exogenous mitochondrial uptake and describe attempts to determine their half-life and transplantation long-term effects on neuronal sprouting, cellular proteome, and behavior. We further discuss the potential of mitochondrial transplantation to serve as a tool to study the causal link between mitochondria and neuronal activity and behavior. Next, we describe mitochondrial transplantation's therapeutic potential in various CNS disorders. Finally, we discuss the basic and reverse-translation challenges of this approach that currently hinder the clinical use of mitochondrial transplantation.

Extracellular Delivery of Functional Mitochondria Rescues the Dysfunction of CD4+ T Cells in Aging

Mitochondrial dysfunction alters cellular metabolism, increases tissue oxidative stress, and may be principal to the dysregulated signaling and function of CD4+ T lymphocytes in the elderly. In this proof of principle study, it is investigated whether the transfer of functional mitochondria into CD4+ T cells that are isolated from old mice (aged CD4+ T cells), can abrogate aging-associated mitochondrial dysfunction, and improve the aged CD4+ T cell functionality. The results show that the delivery of exogenous mitochondria to aged non-activated CD4+ T cells led to significant mitochondrial proteome alterations highlighted by improved aerobic metabolism and decreased cellular mitoROS. Additionally, mito-transferred aged CD4+ T cells showed improvements in activation-induced TCR-signaling kinetics displaying markers of activation (CD25), increased IL-2 production, enhanced proliferation ex vivo. Importantly, immune deficient mouse models (RAG-KO) showed that adoptive transfer of mito-transferred naive aged CD4+ T cells, protected recipient mice from influenza A and Mycobacterium tuberculosis infections. These findings support mitochondria as targets of therapeutic intervention in aging.

The Research Progress of Mitochondrial Transplantation in the Treatment of Mitochondrial Defective Diseases

Mitochondria are double-membrane organelles that are involved in energy production, apoptosis, and signaling in eukaryotic cells. Several studies conducted over the past decades have correlated mitochondrial dysfunction with various diseases, including cerebral ischemia, myocardial ischemia-reperfusion, and cancer. Mitochondrial transplantation entails importing intact mitochondria from healthy tissues into diseased tissues with damaged mitochondria to rescue the injured cells. In this review, the different mitochondrial transplantation techniques and their clinical applications have been discussed. In addition, the challenges and future directions pertaining to mitochondrial transplantation and its potential in the treatment of diseases with defective mitochondria have been summarized.

Mesenchymal Stem Cell-Derived Mitochondria Enhance Extracellular Matrix-Derived Grafts for the Repair of Nerve Defect

Peripheral nerve injuries (PNI) can lead to mitochondrial dysfunction and energy depletion within the affected microenvironment. The objective is to investigate the potential of transplanting mitochondria to reshape the neural regeneration microenvironment. High-purity functional mitochondria with an intact structure are extracted from human umbilical cord-derived mesenchymal stem cells (hUCMSCs) using the Dounce homogenization combined with ultracentrifugation. Results show that when hUCMSC-derived mitochondria (hUCMSC-Mitos) are cocultured with Schwann cells (SCs), they promote the proliferation, migration, and respiratory capacity of SCs. Acellular nerve allografts (ANAs) have shown promise in nerve regeneration, however, their therapeutic effect is not satisfactory enough. The incorporation of hUCMSC-Mitos within ANAs has the potential to remodel the regenerative microenvironment. This approach demonstrates satisfactory outcomes in terms of tissue regeneration and functional recovery. Particularly, the use of metabolomics and bioenergetic profiling is used for the first time to analyze the energy metabolism microenvironment after PNI. This remodeling occurs through the enhancement of the tricarboxylic acid cycle and the regulation of associated metabolites, resulting in increased energy synthesis. Overall, the hUCMSC-Mito-loaded ANAs exhibit high functionality to promote nerve regeneration, providing a novel regenerative strategy based on improving energy metabolism for neural repair.

MELAS-Derived Neurons Functionally Improve by Mitochondrial Transfer from Highly Purified Mesenchymal Stem Cells (REC)

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episode (MELAS) syndrome, caused by a single base substitution in mitochondrial DNA (m.3243A>G), is one of the most common maternally inherited mitochondrial diseases accompanied by neuronal damage due to defects in the oxidative phosphorylation system. There is no established treatment. Our previous study reported a superior restoration of mitochondrial function and bioenergetics in mitochondria-deficient cells using highly purified mesenchymal stem cells (RECs). However, whether such exogenous mitochondrial donation occurs in mitochondrial disease models and whether it plays a role in the recovery of pathological neuronal functions is unknown. Here, utilizing induced pluripotent stem cells (iPSC), we differentiated neurons with impaired mitochondrial function from patients with MELAS. MELAS neurons and RECs/mesenchymal stem cells (MSCs) were cultured under contact or non-contact conditions. Both RECs and MSCs can donate mitochondria to MELAS neurons, but RECs are more excellent than MSCs for mitochondrial transfer in both systems. In addition, REC-mediated mitochondrial transfer significantly restored mitochondrial function, including mitochondrial membrane potential, ATP/ROS production, intracellular calcium storage, and oxygen consumption rate. Moreover, mitochondrial function was maintained for at least three weeks. Thus, REC-donated exogenous mitochondria might offer a potential therapeutic strategy for treating neurological dysfunction in MELAS.

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.

Mitochondrial transfer between cell crosstalk - An emerging role in mitochondrial quality control

Intercellular signaling and component conduction are essential for multicellular organisms' homeostasis, and mitochondrial transcellular transport is a key example of such cellular component exchange. In physiological situations, mitochondrial transfer is linked with biological development, energy coordination, and clearance of harmful components, remarkably playing important roles in maintaining mitochondrial quality. Mitochondria are engaged in many critical biological activities, like oxidative metabolism and biomolecular synthesis, and are exclusively prone to malfunction in pathological processes. Importantly, severe mitochondrial damage will further amplify the defects in the mitochondrial quality control system, which will mobilize more active mitochondrial transfer, replenish exogenous healthy mitochondria, and remove endogenous damaged mitochondria to facilitate disease outcomes. This review explores intercellular mitochondrial transport in cells, its role in cellular mitochondrial quality control, and the linking mechanisms in cellular crosstalk. We also describe advances in therapeutic strategies for diseases that target mitochondrial transfer.

Therapeutic Effects of Mesenchymal Stromal Cells Require Mitochondrial Transfer and Quality Control

Due to their beneficial effects in an array of diseases, Mesenchymal Stromal Cells (MSCs) have been the focus of intense preclinical research and clinical implementation for decades. MSCs have multilineage differentiation capacity, support hematopoiesis, secrete pro-regenerative factors and exert immunoregulatory functions promoting homeostasis and the resolution of injury/inflammation. The main effects of MSCs include modulation of immune cells (macrophages, neutrophils, and lymphocytes), secretion of antimicrobial peptides, and transfer of mitochondria (Mt) to injured cells. These actions can be enhanced by priming (i.e., licensing) MSCs prior to exposure to deleterious microenvironments. Preclinical evidence suggests that MSCs can exert therapeutic effects in a variety of pathological states, including cardiac, respiratory, hepatic, renal, and neurological diseases. One of the key emerging beneficial actions of MSCs is the improvement of mitochondrial functions in the injured tissues by enhancing mitochondrial quality control (MQC). Recent advances in the understanding of cellular MQC, including mitochondrial biogenesis, mitophagy, fission, and fusion, helped uncover how MSCs enhance these processes. Specifically, MSCs have been suggested to regulate peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC1α)-dependent biogenesis, Parkin-dependent mitophagy, and Mitofusins (Mfn1/2) or Dynamin Related Protein-1 (Drp1)-mediated fission/fusion. In addition, previous studies also verified mitochondrial transfer from MSCs through tunneling nanotubes and via microvesicular transport. Combined, these effects improve mitochondrial functions, thereby contributing to the resolution of injury and inflammation. Thus, uncovering how MSCs affect MQC opens new therapeutic avenues for organ injury, and the transplantation of MSC-derived mitochondria to injured tissues might represent an attractive new therapeutic approach.

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.

Mitochondria Transplantation from Stem Cells for Mitigating Sarcopenia

Sarcopenia is defined as the age-related loss of muscle mass and function that can lead to prolonged hospital stays and decreased independence. It is a significant health and financial burden for individuals, families, and society as a whole. The accumulation of damaged mitochondria in skeletal muscle contributes to the degeneration of muscles with age. Currently, the treatment of sarcopenia is limited to improving nutrition and physical activity. Studying effective methods to alleviate and treat sarcopenia to improve the quality of life and lifespan of older people is a growing area of interest in geriatric medicine. Therapies targeting mitochondria and restoring mitochondrial function are promising treatment strategies. This article provides an overview of stem cell transplantation for sarcopenia, including the mitochondrial delivery pathway and the protective role of stem cells. It also highlights recent advances in preclinical and clinical research on sarcopenia and presents a new treatment method involving stem cell-derived mitochondrial transplantation, outlining its advantages and challenges.

Intercellular mitochondrial transfer alleviates pyroptosis in dental pulp damage

Mitochondrial transfer is emerging as a promising therapeutic strategy for tissue repair, but whether it protects against pulpitis remains unclear. Here, we show that hyperactivated nucleotide-binding domain and leucine-rich repeat protein3 (NLRP3) inflammasomes with pyroptotic cell death was present in pulpitis tissues, especially in the odontoblast layer, and mitochondrial oxidative stress (OS) was involved in driving this NLRP3 inflammasome-induced pathology. Using bone marrow mesenchymal stem cells (BMSCs) as mitochondrial donor cells, we demonstrated that BMSCs could donate their mitochondria to odontoblasts via tunnelling nanotubes (TNTs) and, thus, reduce mitochondrial OS and the consequent NLRP3 inflammasome-induced pyroptosis in odontoblasts. These protective effects of BMSCs were mostly blocked by inhibitors of the mitochondrial function or TNT formation. In terms of the mechanism of action, TNF-α secreted from pyroptotic odontoblasts activates NF-κB signalling in BMSCs via the paracrine pathway, thereby promoting the TNT formation in BMSCs and enhancing mitochondrial transfer efficiency. Inhibitions of NF-κB signalling and TNF-α secretion in BMSCs suppressed their mitochondrial donation capacity and TNT formation. Collectively, these findings demonstrated that TNT-mediated mitochondrial transfer is a potential protective mechanism of BMSCs under stress conditions, suggesting a new therapeutic strategy of mitochondrial transfer for dental pulp repair.