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Mitochondrial dysfunction in neurons has been implicated in hypoxia-ischemia-induced brain injury. Although mesenchymal stem cell therapy has emerged as a novel treatment for this pathology, the mechanisms are not fully understood. To address this issue, we first co-cultured 1.5 × 10 5 PC12 cells with mesenchymal stem cells that were derived from induced pluripotent stem cells at a ratio of 1:1, and then intervened with cobalt chloride (CoCl 2 ) for 24 hours. Reactive oxygen species in PC12 cells was measured by Mito-sox. Mitochondrial membrane potential (?Ψm) in PC12 cells was determined by JC-1 staining. Apoptosis of PC12 cells was detected by terminal deoxynucleotidal transferase-mediated dUTP nick end-labeling staining. Mitochondrial morphology in PC12 cells was examined by transmission electron microscopy. Transfer of mitochondria from the mesenchymal stem cells derived from induced pluripotent stem cells to damaged PC12 cells was measured by flow cytometry. Mesenchymal stem cells were induced from pluripotent stem cells by lentivirus infection containing green fluorescent protein in mitochondria. Then they were co-cultured with PC12 cells in Transwell chambers and treated with CoCl 2 for 24 hours to detect adenosine triphosphate level in PC12 cells. CoCl 2 -induced PC12 cell damage was dose-dependent. Co-culture with mesenchymal stem cells significantly reduced apoptosis and restored ?Ψm in the injured PC12 cells under CoCl 2 challenge. Co-culture with mesenchymal stem cells ameliorated mitochondrial swelling, the disappearance of cristae, and chromatin margination in the injured PC12 cells. After direct co-culture, mitochondrial transfer from the mesenchymal stem cells stem cells to PC12 cells was detected via formed tunneling nanotubes between these two types of cells. The transfer efficiency was greatly enhanced in the presence of CoCl 2 . More importantly, inhibition of tunneling nanotubes partially abrogated the beneficial effects of mesenchymal stem cells on CoCl 2 -induced PC12 cell injury. Mesenchymal stem cells reduced CoCl 2 -induced PC12 cell injury and these effects were in part due to efficacious mitochondrial transfer., Competing Interests: None

Obesity, insulin resistance and type 2 diabetes are accompanied by a variety of systemic and tissue-specific metabolic defects, including inflammation, oxidative and endoplasmic reticulum stress, lipotoxicity, and mitochondrial dysfunction. Over the past 30 years, association studies and genetic manipulations, as well as lifestyle and pharmacological invention studies, have reported contrasting findings on the presence or physiological importance of mitochondrial dysfunction in the context of obesity and insulin resistance. It is still unclear if targeting mitochondrial function is a feasible therapeutic approach for the treatment of insulin resistance and glucose homeostasis. Interestingly, recent studies suggest that intact mitochondria, mitochondrial DNA, or other mitochondrial factors (proteins, lipids, miRNA) are found in the circulation, and that metabolic tissues secrete exosomes containing mitochondrial cargo. While this phenomenon has been investigated primarily in the context of cancer and a variety of inflammatory states, little is known about the importance of exosomal mitochondrial transfer in obesity and diabetes. We will discuss recent evidence suggesting that (1) tissues with mitochondrial dysfunction shed their mitochondria within exosomes, and that these exosomes impair the recipient's cell metabolic status, and that on the other hand, (2) physiologically healthy tissues can shed mitochondria to improve the metabolic status of recipient cells. In this context the determination of whether mitochondrial transfer in obesity and diabetes is a friend or foe requires further studies. [ABSTRACT FROM AUTHOR]

Mitochondrial dysfunction has been linked to many diseases including organ degeneration and cancer. Mesenchymal stem cells/stromal cells (MSCs) provide a valuable source for stem cell-based therapy and represent an emerging therapeutic approach for tissue regeneration. Increasing evidence suggests that MSCs can directly donate mitochondria to recover from cell injury and rescue mitochondrial damage-provoked tissue degeneration. Meanwhile, cancer cells and cancer stromal cells also cross-talk through mitochondrial exchange to regulate cancer metastasis. This review summarizes the research on MSCs and their mitochondrial transfer. It provides an overview of the biology, function, niches and signaling that play a role in tissue repair. It also highlights the pathologies of cancer growth and metastasis linked to mitochondrial exchange between cancer cells and surrounding stromal cells. It becomes evident that the function of MSC mitochondrial transfer is a double-edged sword. MSC mitochondrial transfer may be a pharmaceutical target for tissue repair and cancer therapy., (© 2019 The Author(s).)

Female fertility declines dramatically over the age of 35 due to age-related decreases in oocyte quality and quantity. Although mitochondrial transfer promises to be a technology that can improve the quality of such age-impaired oocytes, the ideal mitochondrial donor remains elusive. In the present study, we aimed to identify whether aged adipose-derived stem cells constitute an excellent mitochondrial donor that would improve the quality of aged mouse oocytes. We showed that aging significantly impaired the mitochondrial function in mouse oocytes, but did not significantly affect the mitochondrial function of adipose-derived stem cells. However, the mitochondrial transfer from aged adipose-derived stem cells did not mitigate the poor fertilization and embryonic development rates of aged oocytes., (© 2019 Wiley Periodicals, Inc.)

Rationale : Retinal ganglion cell (RGC) degeneration is extremely hard to repair or regenerate and is often coupled with mitochondrial dysfunction. Mesenchymal stem cells (MSCs)-based treatment has been demonstrated beneficial for RGC against degeneration. However, underlying mechanisms of MSC-provided RGC protection are largely unknown other than neuroprotective paracrine actions. In this study, we sought to investigate whether mitochondrial donation from induced pluripotent stem cell-derived MSC (iPSC-MSCs) could preserve RGC survival and restore retinal function. Methods : iPSC-MSCs were injected into the vitreous cavity of one eye in NADH dehydrogenase (ubiquinone) Fe-S protein 4 ( Ndufs4 ) knockout (KO) and wild type mice. Phosphate buffer saline (PBS) or rotenone treated iPSC-MSCs were injected as control groups. Retinal function was detected by flash electroretinogram (ERG). Whole-mount immunofluorescence (IF), morphometric analysis, confocal microscopy imaging, polymerase chain reaction (PCR) of the retinas were conducted to investigate mitochondrial transfer from human iPSC-MSCs to mouse retina. Quantitative mouse cytokine arrays were carried out to measure retinal inflammatory response under difference treatments. Results : RGC survival in the iPSC-MSC injected retina of Ndufs4 KO mice was significantly increased with improved retinal function. GFP labelled human mitochondria from iPSC-MSC were detected in the RGCs in the retina of Ndufs4 KO mice starting from 96 hours post injection. PCR result showed only human mitochondrial DNA without human nuclear DNA could be detected in the mouse retinas after iPSC-MSC treatment in Ndufs4 KO mice eye. Quantitative cytokine array analysis showed pro-inflammatory cytokines was also downregulated by this iPSC-MSC treatment. Conclusion : Intravitreal transplanted iPSC-MSCs can effectively donate functional mitochondria to RGCs and protect against mitochondrial damage-induced RGC loss., Competing Interests: Competing Interests: The authors have declared that no competing interest exists.

We previously identified an immunomodulatory role of human induced pluripotent stem cell (iPSC)-derived mesenchymal stem cells (MSCs) in asthmatic inflammation. Mitochondrial transfer from bone marrow MSCs to epithelial cells can result in the attenuation of acute lung injury in mice. However, the effects of mitochondrial transfer from iPSC-MSCs to epithelial cells in asthma and the mechanisms underlying these effects are unclear. We found that iPSC-MSC transplantation significantly reduced T helper 2 cytokines, attenuated the mitochondrial dysfunction of epithelial cells, and alleviated asthma inflammation in mice. Tunneling nanotubes (TNTs) were formed between iPSC-MSCs and epithelial cells, and mitochondrial transfer from iPSC-MSCs to epithelial cells via TNTs was observed both in vitro and in mice. Overexpression or silencing of connexin 43 (CX43) in iPSC-MSCs demonstrated that CX43 plays a critical role in the regulation of TNT formation by mediating mitochondrial transfer between iPSC-MSCs and epithelial cells. This study provides a therapeutic strategy for targeting asthma inflammation., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

Stroke is the leading cause of death and adult disability worldwide. Mitochondrial dysfunction has been regarded as one of the hallmarks of ischemia/reperfusion (I/R) induced neuronal death. Maintaining the function of mitochondria is crucial in promoting neuron survival and neurological improvement. In this article, we review current progress regarding the roles of mitochondria in the pathological process of cerebral I/R injury. In particular, we emphasize on the most critical mechanisms responsible for mitochondrial quality control, as well as the recent findings on mitochondrial transfer in acute stroke. We highlight the potential of mitochondria as therapeutic targets for stroke treatment and provide valuable insights for clinical strategies.

Each cell in the human body, with the exception of red blood cells, contains multiple copies of mitochondria that house their own genetic material, the maternally inherited mitochondrial DNA. Mitochondria are the cell's powerplant due to their massive ATP generation. However, the mitochondrion is also a hub for metabolite production from the TCA cycle, fatty acid beta-oxidation, and ketogenesis. In addition to producing macromolecules for biosynthetic reactions and cell replication, several mitochondrial intermediate metabolites serve as cofactors or substrates for epigenome modifying enzymes that regulate chromatin structure and impact gene expression. Here, we discuss connections between mitochondrial metabolites and enzymatic writers and erasers of chromatin modifications. We do this from the unique perspective of cell-to-cell mitochondrial transfer and its potential impact on mitochondrial replacement therapies., Competing Interests: The authors do not have any conflicts of interest to declare

Mesenchymal stem/stromal cells (MSC) are adult stem cells which have been shown to improve survival, enhance bacterial clearance and alleviate inflammation in pre-clinical models of acute respiratory distress syndrome (ARDS) and sepsis. These diseases are characterised by uncontrolled inflammation often underpinned by bacterial infection. The mechanisms of MSC immunomodulatory effects are not fully understood yet. We sought to investigate MSC cell contact-dependent communication with alveolar macrophages (AM), professional phagocytes which play an important role in the lung inflammatory responses and anti-bacterial defence. With the use of a basic direct co-culture system, confocal microscopy and flow cytometry we visualised and effectively quantified MSC mitochondrial transfer to AM through tunnelling nanotubes (TNT). To model the human AM , primary monocytes were isolated from human donor blood and differentiated into macrophages (monocyte derived macrophages, MDM) in the presence of granulocyte macrophage colony-stimulating factor (GM-CSF), thus allowing adaptation of an AM-like phenotype (de Almeida et al ., 2000; Guilliams et al. , 2013). Human bone-marrow derived MSC, were labelled with mitochondria-specific fluorescent stain, washed extensively, seeded into the tissue culture plate with MDMs at the ratio of 1:20 (MSC/MDM) and co-cultured for 24 h. TNT formation and mitochondrial transfer were visualised by confocal microscopy and semi-quantified by flow cytometry. By using the method we described here we established that MSC use TNTs as the means to transfer mitochondria to macrophages. Further studies demonstrated that mitochondrial transfer enhances macrophage oxidative phosphorylation and phagocytosis. When TNT formation was blocked by cytochalasin B, MSC effect on macrophage phagocytosis was completely abrogated. This is the first study to demonstrate TNT-mediated mitochondrial transfer from MSC to innate immune cells.

Recently, we showed that generation of tumours in syngeneic mice by cells devoid of mitochondrial (mt) DNA (ρ 0 cells) is linked to the acquisition of the host mtDNA. However, the mechanism of mtDNA movement between cells remains unresolved. To determine whether the transfer of mtDNA involves whole mitochondria, we injected B16ρ 0 mouse melanoma cells into syngeneic C57BL/6N su9-DsRed2 mice that express red fluorescent protein in their mitochondria. We document that mtDNA is acquired by transfer of whole mitochondria from the host animal, leading to normalisation of mitochondrial respiration. Additionally, knockdown of key mitochondrial complex I (NDUFV1) and complex II (SDHC) subunits by shRNA in B16ρ 0 cells abolished or significantly retarded their ability to form tumours. Collectively, these results show that intact mitochondria with their mtDNA payload are transferred in the developing tumour, and provide functional evidence for an essential role of oxidative phosphorylation in cancer.

Study Question: Does in vivo aging of mouse oocytes affect mitochondrial function?, Summary Answer: Mitochondrial function was impaired in post-ovulatory in vivo-aged mouse oocytes and microinjection of somatic cell mitochondria did not rescue poor fertilization and embryonic development rates., What Is Known Already: The mechanisms underlying the decline in oocyte quality associated with oocyte aging remain unknown, although studies have suggested that the decline is regulated by mitochondrial dysfunction. However, only a limited number of studies have provided direct evidence implicating mitochondrial dysfunction in oocyte quality during the aging of oocytes., Study Design, Size, Duration: We used post-ovulatory, in vivo-aged mouse oocytes as a model for studying low-quality oocytes in oocyte aging., Participants/materials, Setting, Method: Superovulated oocytes released from the oviduct at 14 h and 20-24 h post-hCG injection were designated as 'fresh' and 'aged' oocytes, respectively. Membrane potentials and oxygen consumption in single oocytes were evaluated as measures of mitochondrial function in fresh and aged oocytes. Mitochondrial transcriptional factor A (TFAM) expression levels were examined by western blotting, and colocalization of mitochondria and TFAM was analyzed by measuring immunofluorescence in fresh and aged oocytes. IVF and blastocyst formation rates were calculated after oocyte microinjection with mitochondria derived from liver cells., Main Results and the Role of Chance: The average mitochondrial membrane potential in fresh oocytes was significantly higher than that in aged oocytes (P < 0.05). The average oxygen consumption rate in aged oocytes was significantly lower than that in fresh oocytes (P < 0.05). Although total TFAM expression was unchanged, its colocalization with mitochondria decreased in aged oocytes. IVF and blastocyst formation rates for mitochondrion-injected aged oocytes were not significantly different from those for buffer-injected aged oocytes., Large Scale Data: Not applicable., Limitations, Reasons for Caution: A limitation of this study is that we did not examine the effects of microinjecting mitochondria from other somatic cell types into aged oocytes on their fertilization and embryonic development rates., Wider Implications of the Findings: The results from the present study showed that poor embryonic development was associated with impairment of mitochondrial functions in in vivo-aged oocytes. However, the microinjection of mitochondria from liver cells did not improve the low fertilization and embryonic development rates of aged oocytes. It remains to be demonstrated whether oocyte quality can be rescued by the transfer of cytosolic factors or cellular organelles, such as the endoplasmic reticulum or mitochondria, from specific cell types., Study Funding/competing Interests: This study was supported by Grants-in-Aid for General Science Research to Toshifumi Takahashi (No. 25462550) and Hideki Igarashi (No. 26462474). The funding source played no role in study design in the collection, analysis, and interpretation of data; in the writing of the report; and in the decision to submit the article for publication. The authors have no conflict of interest to disclose., (© The Author 2016. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Transplantation of mesenchymal stem cells (MSCs) holds great promise in the repair of cigarette smoke (CS)-induced lung damage in chronic obstructive pulmonary disease (COPD). Because CS leads to mitochondrial dysfunction, we aimed to investigate the potential benefit of mitochondrial transfer from human-induced pluripotent stem cell-derived MSCs (iPSC-MSCs) to CS-exposed airway epithelial cells in vitro and in vivo. Rats were exposed to 4% CS for 1 hour daily for 56 days. At Days 29 and, human iPSC-MSCs or adult bone marrow-derived MSCs (BM-MSCs) were administered intravenously to CS-exposed rats. CS-exposed rats exhibited severe alveolar destruction with a higher mean linear intercept (Lm) than sham air-exposed rats (P < 0.001) that was attenuated in the presence of iPSC-MSCs or BM-MSCs (P < 0.01). The attenuation of Lm value and the severity of fibrosis was greater in the iPSC-MSC-treated group than in the BM-MSC-treated group (P < 0.05). This might have contributed to the novel observation of mitochondrial transfer from MSCs to rat airway epithelial cells in lung sections exposed to CS. In vitro studies further revealed that transfer of mitochondria from iPSC-MSCs to bronchial epithelial cells (BEAS-2B) was more effective than from BM-MSCs, with preservation of adenosine triphosphate contents. This distinct mitochondrial transfer occurred via the formation of tunneling nanotubes. Inhibition of tunneling nanotube formation blocked mitochondrial transfer. Our findings indicate a higher mitochondrial transfer capacity of iPSC-MSCs than BM-MSCs to rescue CS-induced mitochondrial damage. iPSC-MSCs may thus hold promise for the development of cell therapy in COPD.