Mesenchymal stem cells rescue injured endothelial cells in an in vitro ischemia-reperfusion model via tunneling nanotube like structure-mediated mitochondrial transfer

Mesenchymal Stem Cells: The Past Present and Future

The biomedical applications of mesenchymal stem cells (MSCs) have gained expanding attention over the past three decades. MSCs are easily obtained from various tissue types (e.g. bone marrow, fat, cord blood, etc.), are capable of self-renewal, and could be induced to differentiate into several cell lineages for countless biomedical applications. In addition, when transplanted, MSCs are not detected by immune surveillance, thus do not lead to graft rejection. Moreover, they can home towards affected tissues and induce their therapeutic effect in a cell-base and/or a cell-free manner. These properties, and many others, have made MSCs appealing therapeutic cell candidates (for cell and/or gene therapy) in myriad clinical conditions. However, similar to any other therapeutic tool, MSCs still have their own limitations and grey areas that entail more research for better understanding and optimization. Herein, we present a brief overview of various pre-clinical/clinical applications of MSCs in regenerative medicine and discuss limitations and future challenges.

Mitochondria as a therapeutic target for ischemic stroke

Stroke is the leading cause of death and physical disability worldwide. Mitochondrial dysfunction has been considered as one of the hallmarks of ischemic stroke and contributes to the pathology of ischemia and reperfusion. Mitochondria is essential in promoting neural survival and neurological improvement following ischemic stroke. Therefore, mitochondria represent an important drug target for stroke treatment. This review discusses the mitochondrial molecular mechanisms underlying cerebral ischemia and involved in reactive oxygen species generation, mitochondrial electron transport dysfunction, mitochondria-mediated regulation of inflammasome activation, mitochondrial dynamics and biogenesis, and apoptotic cell death. We highlight the potential of mitochondrial transfer by stem cells as a therapeutic target for stroke treatment and provide valuable insights for clinical strategies. A better understanding of the roles of mitochondria in ischemia-induced cell death and protection may provide a rationale design of novel therapeutic interventions in the ischemic stroke.

Acute Myocardial Infarction Reduces Respiration in Rat Cardiac Fibers, despite Adipose Tissue Mesenchymal Stromal Cell Transplant

Adipose-derived mesenchymal stromal cell (AD-MSC) administration improves cardiac function after acute myocardial infarction (AMI). Although the mechanisms underlying this effect remain to be elucidated, the reversal of the mitochondrial dysfunction may be associated with AMI recovery. Here, we analyzed the alterations in the respiratory capacity of cardiomyocytes in the infarcted zone (IZ) and the border zone (BZ) and evaluated if mitochondrial function improved in cardiomyocytes after AD-MSC transplantation. Female rats were subjected to AMI by permanent left anterior descending coronary (LAD) ligation and were then treated with AD-MSCs or PBS in the border zone (BZ). Cardiac fibers were analyzed 24 hours (necrotic phase) and 8 days (fibrotic phase) after AMI for mitochondrial respiration, citrate synthase (CS) activity, F₀F₁-ATPase activity, and transmission electron microscopy (TEM). High-resolution respirometry of permeabilized cardiac fibers showed that AMI reduced numerous mitochondrial respiration parameters in cardiac tissue, including phosphorylating and nonphosphorylating conditions, respiration coupled to ATP synthesis, and maximal respiratory capacity. CS decreased in IZ and BZ at the necrotic phase, whereas it recovered in BZ and continued to drop in IZ over time when compared to Sham. Exogenous cytochrome c doubled respiration at the necrotic phase in IZ. F₀F₁-ATPase activity decreased in the BZ and, to more extent, in IZ in both phases. Transmission electron microscopy showed disorganized mitochondrial cristae structure, which was more accentuated in IZ but also important in BZ. All these alterations in mitochondrial respiration were still present in the group treated with AD-MSC. In conclusion, AMI led to mitochondrial dysfunction with oxidative phosphorylation disorders, and AD-MSC improved CS temporarily but was not able to avoid alterations in mitochondria function over time.

Stem Cell Ophthalmology Treatment Study (SCOTS): bone marrow derived stem cells in the treatment of Dominant Optic Atrophy

Background

We report the results of 6 patients with Dominant Optic Atrophy (DOA) who met inclusion criteria and were treated in the Stem Cell Ophthalmology Treatment Study (SCOTS). SCOTS/SCOTS 2 is an Institutional Review Board approved and NIH registered (NCT03011541) clinical study that uses autologous bone marrow derived stem cells (BMSC) in the treatment of optic nerve and retinal disease.

Methods

This is an open label, non-randomized clinical study using natural history of the disease as the comparator. BMSC were separated from aspirated autologous bone marrow with minimal manipulation using an FDA cleared Class II medical device. Patients were treated with combinations of retrobulbar, subtenons, intravitreal or subretinal placement of BMSC followed by intravenous injection of BMSC depending on the arm of the study chosen. There were no surgical complications.

Results

Of the patients treated, 83.3% (5 of 6 patients) experienced visual improvements and in all of these cases both eyes improved. Ten eyes or 83.3% experienced gains in visual acuity with a median improvement of 2.125 Snellen lines, or approximately 10.63 letters. Two eyes were considered unchanged compared to longstanding measurements. Using LogMAR, the average improvement in vision for all eyes was 29.5%. The averagevisual acuity increasein eyes that improved was 33.3%. Findings were statistically significant with P<0.001.

Conclusions

Using autologous BMSC per protocols developed in the SCOTS/SCOTS 2 clinical studies resulted in statistically significant visual acuity improvements in patients with DOA or Kjers Optic Neuropathy. Improvements occurred in 83.3% of eyes and averaged 29.5%. Mitochondrial transfer and neuroprotective exosome secretions from the BMSC may have been key to the improvements observed in this mitochondrial disease.

Mitochondria transfer via tunneling nanotubes is an important mechanism by which CD133+ scattered tubular cells eliminate hypoxic tubular cell injury

Renal CD133 + scattered tubular cells (STCs) have been regarded as progenitor-like cells in the kidney and participated in ischemic renal injury repair. However, the mechanism of this effect is not fully elucidated yet. The primary objective of this study was to investigate the hypothesis that the protective effect of CD133 + STCs depends on the transfer of mitochondria to injured tubular cells in vitro. In this study, renal ischemic reperfusion injury (IRI) rat model was established with one side kidney ischemic for 45 min and animals were sacrificed at 48 h after operation. Tubular cells were isolated and cultured in vitro, and then CD133 + STCs were selected from the cultured cells. Then, CD133 + STCs were co-cultured with CD133-tubular cells (TECs) to detect the tunneling nanotubes like structures, and the transfer of mitochondria from CD133 + STCs to injured tubular cells were detected by fluorescent imaging and flow cytometry. Further, cellular protective effects of CD133 + STCs were tested when cultured with TECs under hypoxic conditions. In results, renal CD133 + STCs were scattered throughout the normal kidney and increased upon ischemic injury. Nanotube formations were commonly found between CD133 + STCs and TECs, and the transfer of mitochondria was detected from CD133 + STCs to TECs. Further, CD133 + STCs exist significant anti-apoptosis and pro-proliferation effects for TECs under hypoxic culture conditions. Thus, this study was first described that renal CD133 + STCs could transfer mitochondria to injured TECs in vitro for its protective effects, which revealed an important novel mechanism for renal repair after ischemic injury.

Therapeutic Properties of Mesenchymal Stem Cell on Organ Ischemia-Reperfusion Injury

The shortage of donor organs is a major global concern. Organ failure requires the transplantation of functional organs. Donor’s organs are preserved for variable periods of warm and cold ischemia time, which requires placing them into a preservation device. Ischemia and reperfusion damage the organs, due to the lack of oxygen during the ischemia step, as well as the oxidative stress during the reperfusion step. Different methodologies are developed to prevent or to diminish the level of injuries. Preservation solutions were first developed to maximize cold static preservation, which includes the addition of several chemical compounds. The next chapter of organ preservation comes with the perfusion machine, where mechanical devices provide continuous flow and oxygenation ex vivo to the organs being preserved. In the addition of inhibitors of mitogen-activated protein kinase and inhibitors of the proteasome, mesenchymal stem cells began being used 13 years ago to prevent or diminish the organ’s injuries. Mesenchymal stem cells (e.g., bone marrow stem cells, adipose derived stem cells and umbilical cord stem cells) have proven to be powerful tools in repairing damaged organs. This review will focus upon the use of some bone marrow stem cells, adipose-derived stem cells and umbilical cord stem cells on preventing or decreasing the injuries due to ischemia-reperfusion.

Tunneling nanotube-mediated intercellular vesicle and protein transfer in the stroma-provided imatinib resistance in chronic myeloid leukemia cells

Intercellular communication within the bone marrow niche significantly promotes leukemogenesis and provides protection of leukemic cells from therapy. Secreted factors, intercellular transfer of mitochondria and the receptor-ligand interactions have been shown as mediators of this protection. Here we report that tunneling nanotubes (TNTs)-long, thin membranous structures, which have been identified as a novel mode of intercellular cross-talk-are formed in the presence of stroma and mediate transfer of cellular vesicles from stroma to leukemic cells. Importantly, transmission of vesicles via TNTs from stromal cells increases resistance of leukemic cells to the tyrosine kinase inhibitor, imatinib. Using correlative light-electron microscopy and electron tomography we show that stromal TNTs contain vesicles, provide membrane continuity with the cell bodies and can be open-ended. Moreover, trans-SILAC studies to reveal the non-autonomous proteome showed that specific sets of proteins are transferred together with cellular vesicles from stromal to leukemic cells, with a potential role in survival and adaptation. Altogether, our findings provide evidence for the biological role of the TNT-mediated vesicle exchange between stromal and leukemic cells, implicating the direct vesicle and protein transfer in the stroma-provided protection of leukemic cells.

Intercellular mitochondria trafficking highlighting the dual role of mesenchymal stem cells as both sensors and rescuers of tissue injury

Mitochondria are crucial organelles that not only regulate the energy metabolism, but also the survival and fate of eukaryotic cells. Mitochondria were recently discovered to be able to translocate from one cell to the other. This phenomenon was observed in vitro and in vivo, both in physiological and pathophysiological conditions including tissue injury and cancer. Mitochondria trafficking was found to exert prominent biological functions. In particular, several studies pointed out that this process governs some of the therapeutic effects of mesenchymal stem cells (MSCs). In this review, we give an overview of the current knowledge on MSC-dependent intercellular mitochondria trafficking and further discuss the recent findings on the intercellular mitochondria transfer between differentiated and mesenchymal stem cells, their biological significance and the mechanisms underlying this process.

Tunneling nanotubes mediate intercellular communication between endothelial progenitor cells and osteoclast precursors

Tunneling nanotube (TNT)-mediated cell communication play pivotal roles in a series of physiological and pathological processes in multicellular organism. This study was designed to investigate the existence of TNTs between EPCs and osteoclast precursors and evaluate their effects on the differentiation of osteoclast precursors. For these purposes, EPCs and osteoclast precursors (RAW264.7 cells) were stained with different fluorescent dyes before direct co-culture; then, the co-cultured cells were sorted by fluorescence activated cell sorter (FACS), and the differentiation of co-cultured RAW264.7 cells was evaluated. The results showed that the differentiation potential of RAW264.7 cells was significantly inhibited after their co-culture with EPCs. Additionally, the expression of macrophage migration inhibitory factor (MIF) was up-regulated in RAW264.7 cells after co-culture. Moreover, the MIF inhibitor ISO-1 could rescue the formation of TRAP-positive multinuclear osteoclasts and the expression of osteoclastogenesis-associated genes in the co-cultured RAW264.7 cells. The present study demonstrates that EPCs can affect the differentiation of osteoclast precursors through the TNT-like structures formed across these two types of cells and might inform new therapeutic strategies for osteolytic diseases.

Modulating the distribution and fate of exogenously delivered MSCs to enhance therapeutic potential: knowns and unknowns

Mesenchymal stem/stromal cells (MSCs) are undergoing intensive translational research for several debilitating conditions, including critical illnesses such as ARDS and sepsis. MSCs exert diverse biologic effects via their interaction with host tissues, via mechanisms that require the MSC to be in close proximity to the area of injury. Fully harnessing the therapeutic potential of advanced medicinal therapeutic products such as MSCs and their successful translation to clinical use requires a detailed understanding of MSC distribution and persistence in the injured tissues.

Key aspects include understanding MSC distribution within the body, the response of the host to MSC administration, and the ultimate fate of exogenously administered MSCs within the host. Factors affecting this interaction include the MSC tissue source, the in vitro MSC culture conditions, the route of MSC administration and the specific issues relating to the target disease state, each of which remains to be fully characterised. Understanding these factors may generate strategies to modify MSC distribution and fate that may enhance their therapeutic effect.

This review will examine our understanding of the mechanisms of action of MSCs, the early and late phase distribution kinetics of MSCs following in vivo administration, the ultimate fate of MSCs following administration and the potential importance of these MSC properties to their therapeutic effects. We will critique current cellular imaging and tracking methodologies used to track exogenous MSCs and their suitability for use in patients, discuss the insights they provide into the distribution and fate of MSCs after administration, and suggest strategies by which MSC biodistribution and fate may be modulated for therapeutic effect and clinical use.

In conclusion, a better understanding of patterns of biodistribution and of the fate of MSCs will add important additional safety data regarding MSCs, address regulatory requirements, and may uncover strategies to increase the distribution and/or persistence of MSC at the sites of injury, potentially increasing their therapeutic potential for multiple disorders.

Mitochondrial Involvement in Cisplatin Resistance

Cisplatin is one of the worldwide anticancer drugs and, despite its toxicity and frequent recurrence of resistance phenomena, it still remains the only therapeutic option for several tumors. Circumventing cisplatin resistance remains, therefore, a major goal for clinical therapy and represents a challenge for scientific research. Recent studies have brought to light the fundamental role of mitochondria in onset, progression, and metastasis of cancer, as well as its importance in the resistance to chemotherapy. The aim of this review is to give an overview of the current knowledge about the implication of mitochondria in cisplatin resistance and on the recent development in this research field. Recent studies have highlighted the role of mitochondrial DNA alterations in onset of resistance phenomena, being related both to redox balance alterations and to signal crosstalk with the nucleus, allowing a rewiring of cell metabolism. Moreover, an important role of the mitochondrial dynamics in the adaptation mechanism of cancer cells to challenging environment has been revealed. Giving bioenergetic plasticity to tumor cells, mitochondria allow cells to evade death pathways in stressful conditions, including chemotherapy. So far, even if the central role of mitochondria is recognized, little is known about the specific mechanisms implicated in the resistance. Nevertheless, mitochondria appear to be promising pharmacological targets for overcoming cisplatin resistance, but further studies are necessary.

Silencing of SNHG12 Enhanced the Effectiveness of MSCs in Alleviating Ischemia/Reperfusion Injuries via the PI3K/AKT/mTOR Signaling Pathway

Previous studies have reported that the long non-coding RNA SNHG12 (lncRNA SNHG12) plays a critical role in regulating the function of mesenchymal stem cells (MSCs); however, the effect of lncRNA SNHG12 on MSCs in injured brain tissue has rarely been reported. We studied the effect and mechanism of lncRNA SNHG12-modified mesenchymal stem cells (MSCs) in treating brain injuries caused by ischemia/reperfusion (I/R). I/R treated rat brain microvascular endothelial cells (BMECs) were co-cultured with MSCs or I/R pretreated MSCs. Next, BMEC proliferation was detected by using CCK-8 and EdU assays, and cell apoptosis was determined by using flow cytometry and the Hoechst staining method. Autophagy of BMECs was determined using immunofluorescence and expression of associated pathway proteins were measured by western blotting. Moreover, BMEC proliferation, apoptosis, and autophagy were also determined after the BMECs had been co-cultured with shSNHG12-MSCs. In addition, a rat model of middle cerebral artery occlusion (MCAO) was used to further confirm the findings obtained with cells. I/R treatment significantly decreased the proliferation of BMECs, but increased their levels of SNHG12 expression, apoptosis, and autophagy. However, co-culturing of BMECs with MSCs markedly alleviated the reduction in BMEC proliferation and the increases in BMEC apoptosis and autophagy, as well as the phosphorylation of PI3K, AKT, and mTOR proteins in BMECs that had been induced by I/R. Furthermore, shSNHG12 remarkably enhanced the effects of MSCs. In addition, an injection MSCs reduced the infarct areas and rates of cell apoptosis in MACO rats, and reduced the phosphorylation of PI3K, AKT, and mTOR proteins. Moreover, shSNHG12 enhanced the ameliorative effect of MSCs in treating brain injuries in the MACO rats. In conclusion, silencing of SNHG12 enhanced the effects of MSCs in reducing apoptosis and autophagy of BMECs by activating the PI3K/AKT/mTOR signaling pathway.

Endocytosis-mediated mitochondrial transplantation: Transferring normal human astrocytic mitochondria into glioma cells rescues aerobic respiration and enhances radiosensitivity

Emerging evidence indicates that reprogramming of energy metabolism involving disturbances in energy production from a defect in cellular respiration with a shift to glycolysis is a core hallmark of cancer. Alterations in cancer cell energy metabolism are linked to abnormalities in mitochondrial function. Mitochondrial dysfunction of cancer cells includes increased glycolysis, decreased apoptosis, and resistance to radiotherapy. The study was designed for two main points: firstly, to investigate whether exogenous functional mitochondria can transfer into glioma cells and explore the underlying molecular mechanisms from the perspective of endocytosis; secondly, to further verify whether the mitochondrial transplantation is able to rescue aerobic respiration, attenuate the Warburg effect and enhance the radiosensitivity of gliomas.

Methods: Mitochondria were isolated from normal human astrocytes (HA) and immediately co-incubated with starved human glioma cells (U87). Confocal microscopy and gene sequencing were performed to evaluate the ability of isolated mitochondria internalization into U87 cells. The interaction between endocytosis and isolated mitochondria transfer were captured by 3D tomographic microscopy and transmission electron microscopy. NAD⁺, CD38, cADPR and Ca²⁺ release were determined by commercial kits, western blot, HLPC-MS and Fluo-3 AM respectively. PCR array expression profiling and Seahorse XF analysis were used to evaluate the effect of mitochondrial transplantation on energy phenotypes of U87 cells. U87 cells and U87 xenografts were both treated with mitochondrial transplantation, radiation, or a combination of mitochondrial transplantation and radiation. Apoptosis in vitro and in vivo were detected by cytochrome C, cleaved caspase 9 and TUNEL staining.

Results: We found that mitochondria from HA could be transferred into starved U87 cells by simple co-incubation. Starvation treatment slowed the rate of glycolysis and decreased the transformation of NAD⁺ to NADH in U87 cells. A large amount of accumulated NAD⁺ was released into the extracellular space. CD38 is a member of the NAD⁺ glycohydrolase family that catalyzes the cyclization of extracellular NAD⁺ to intracellular cADPR. cADPR triggered release of Ca²⁺ to promote cytoskeleton remodeling and plasma membrane invagination. Thus, endocytosis involving isolated mitochondria internalization was mediated by NAD⁺-CD38-cADPR-Ca²⁺ signaling. Mitochondrial transfer enhanced gene and protein expression related to the tricarboxylic acid (TCA) cycle, increased aerobic respiration, attenuated glycolysis, reactivated the mitochondrial apoptotic pathway, inhibited malignant proliferation of U87 cells. Isolated mitochondria injected into U87 xenograft tumors also entered cells, and inhibited glioma growth in nude mice. Mitochondrial transplantation could enhance the radiosensitivity of gliomas in vitro and in vivo.

Conclusion: These findings suggested that starvation-induced endocytosis via NAD⁺-CD38-cADPR-Ca²⁺ signaling could be a new mechanism of mitochondrial transplantation to rescue aerobic respiration and attenuate the Warburg effect. This mechanism could be a promising approach for radiosensitization.

Mesenchymal Stem Cells-Potential Applications in Kidney Diseases

Mesenchymal stem cells constitute a pool of cells present throughout the lifetime in numerous niches, characteristic of unlimited replication potential and the ability to differentiate into mature cells of mesodermal tissues in vitro. The therapeutic potential of these cells is, however, primarily associated with their capabilities of inhibiting inflammation and initiating tissue regeneration. Owing to these properties, mesenchymal stem cells (derived from the bone marrow, subcutaneous adipose tissue, and increasingly urine) are the subject of research in the settings of kidney diseases in which inflammation plays the key role. The most advanced studies, with the first clinical trials, apply to ischemic acute kidney injury, renal transplantation, lupus and diabetic nephropathies, in which beneficial clinical effects of cells themselves, as well as their culture medium, were observed. The study findings imply that mesenchymal stem cells act predominantly through secreted factors, including, above all, microRNAs contained within extracellular vesicles. Research over the coming years will focus on this secretome as a possible therapeutic agent void of the potential carcinogenicity of the cells.

Mesenchymal stem cells and their mitochondrial transfer: a double-edged sword

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.

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

Tunneling nanotubes (TNTs) are newly discovered tubular structures between two distant cells that facilitate the intercellular exchange of signals and components. Recent reports show that mesenchymal stem cells (MSCs) can rescue injured target cells and promote recovery from a variety of stresses via TNT-mediated mitochondrial transfer. In this study, we explored how TNTs form between bone marrow MSCs and endothelial cells (ECs) by using a human umbilical cord vein endothelial cell (HUVEC) model. TNT formation between MSCs and HUVECs could be induced by treating HUVECs with cytarabine (Ara-C), and human bone marrow mesenchymal stem cells (hBMMSCs) could transfer mitochondria to injured HUVECs through TNTs. Mitochondrial transfer from hBMMSCs to HUVECs via TNTs rescued the injured HUVECs by reducing apoptosis, promoting proliferation and restoring the transmembrane migration ability as well as the capillary angiogenic capacity of HUVECs. This study provides novel insights into the cell-cell communication between MSCs and ECs and supports the results of prior studies indicating that ECs promote hematopoietic regeneration. An improved understanding of MSC-EC cross-talk will promote the development of MSC-directed strategies for improving EC function and hematopoietic system regeneration following myelosuppressive and myeloablative injuries.

Life and death of circulating cell-free DNA

Tumor-specific, circulating cell-free DNA in liquid biopsies is a promising source of biomarkers for minimally invasive serial monitoring of treatment responses in cancer management. We will review the current understanding of the origin of circulating cell-free DNA and different forms of DNA release (including various types of cell death and active secretion processes) and clearance routes. The dynamics of extracellular DNA in blood during therapy and the role of circulating DNA in pathophysiological processes (tumor-associated inflammation, NETosis, and pre-metastatic niche development) provide insights into the mechanisms that contribute to tumor development and metastases formation. Better knowledge of circulating tumor-specific cell-free DNA could facilitate the development of new therapeutic and diagnostic options for cancer management.

Differential roles of microtubules in the two formation stages of membrane nanotubes between human mesenchymal stem cells and neonatal mouse cardiomyocytes

Membrane nanotubes (MNTs) are a kind of novel way for communication between two distant cells. It was recently shown that MNTs can be formed between distressed cardiomyocytes (CMs) and mesenchymal stem cells (MSCs). As a cytoskeleton-containing structure, the role of microtubules in MNTs is not fully understood. Here, we investigated this question. By membrane dye staining, we found that the numbers of MNTs between human MSCs (hMSCs) and distressed neonatal mouse CMs (NMCMs) increased gradually from 3 to 16 h and remained constant from 16 to 30 h, which were identified as active formation stage (the 1st stage, ≤16 h in coculture), and mature and stable stage (the 2nd stage, >16 h in coculture), respectively. In the 1st stage, more MNTs originated from hMSCs, whereas more MNTs originated from NMCMs in the 2nd stage. The formation of MNTs was affected when microtubules were disrupted by nocodazole in the 1st stage, but not in the 2nd stage. MNTs became shorter and thinner when microtubules were disrupted in the 2nd stage. Immunofluorescence staining and flow cytometry showed that mitochondria in hMSCs were transported into distressed NMCMs, which was suppressed by nocodazole in the 2nd stage. Tunnel staining showed that hypoxia/reoxygenation-induced apoptosis of NMCMs only in the 2nd stage could be rescued by direct, but not indirect, coculture with hMSCs. This rescue function was weakened when the mitochondrial functions of cocultured hMSCs were disrupted by EtBr or microtubules in cocultures were disrupted by nocodazole. All these results suggested that there are two stages for MNT formation, and microtubules played differential roles in the two stages: During the 1st stage, microtubules were required for MNT formation, whereas during the 2nd stage, microtubules were related to the morphological features of MNTs and played a key role in anti-apoptosis of MNTs by mitochondrial transfer.

Mesenchymal stem/stromal cell function in modulating cell death

Mesenchymal stem/stromal cells (MSCs) delivered as cell therapy to individuals with degenerative and/or inflammatory disorders can help improve organ features and resolve inflammation, as demonstrated in preclinical studies and to some extent in clinical studies. MSCs have trophic, homing/migration, and immunosuppression functions, with many benefits in therapeutics. MSC functions are thought to depend on the paracrine action of soluble factors and/or the expression of membrane-bound molecules, mostly belonging to the molecular class of adhesion molecules, chemokines, enzymes, growth factors, and interleukins. Cutting-edge studies underline bioactive exchanges, including that of ions, nucleic acids, proteins, and organelles transferred from MSCs to stressed cells, thereby improving the cells' survival and function. From this aspect, MSC death modulation function appears as a decisive biological function that could carry a significant part of the therapeutic effects of MSCs. Identifying the function and modes of actions of MSCs in modulating cell death may be exploited to enhance consistency and efficiency of cell therapy that is based on MSCs as medical treatment for degenerative and/or inflammatory diseases. Here, we review the essentials of MSC functions in modulating cell death in unfit cells, and its modes of actions based on current advances and outline the clinical implications.

Mitochondrial transfer from mesenchymal stem cells to neural stem cells protects against the neurotoxic effects of cisplatin

Mesenchymal stem cells (MSCs) transfer healthy mitochondria to damaged acceptor cells via actin-based intercellular structures. In this study, we tested the hypothesis that MSCs transfer mitochondria to neural stem cells (NSCs) to protect NSCs against the neurotoxic effects of cisplatin treatment. Our results show that MSCs donate mitochondria to NSCs damaged in vitro by cisplatin. Transfer of healthy MSC-derived mitochondria decreases cisplatin-induced NSC death. Moreover, mitochondrial transfer from MSCs to NSCs reverses the cisplatin-induced decrease in mitochondrial membrane potential. Blocking the formation of actin-based intercellular structures inhibited the transfer of mitochondria to NSCs and abrogated the positive effects of MSCs on NSC survival. Conversely, overexpression of the mitochondrial motor protein Rho-GTPase 1 (Miro1) in MSCs increased mitochondrial transfer and further improved survival of cisplatin-treated NSCs.

In vivo, MSC administration prevented the loss of DCX+ neural progenitor cells in the subventricular zone and hippocampal dentate gyrus which occurs as a result of cisplatin treatment. We propose mitochondrial transfer as one of the mechanisms via which MSCs exert their therapeutic regenerative effects after cisplatin treatment.

Concise Review: Intercellular Communication Via Organelle Transfer in the Biology and Therapeutic Applications of Stem Cells

The therapeutic potential of stem cell-based therapies may be largely dependent on the ability of stem cells to modulate host cells rather than on their differentiation into host tissues. Within the last decade, there has been considerable interest in the intercellular communication mediated by the transfer of cytoplasmic material and organelles between cells. Numerous studies have shown that mitochondria and lysosomes are transported between cells by various mechanisms, such as tunneling nanotubes, microvesicles, and cellular fusion. This review will focus on the known instances of organelle transfer between stem cells and differentiated cells, what effects it has on recipient cells and how organelle transfer is regulated. Stem Cells 2019;37:14-25.

Human tissue-specific MSCs demonstrate differential mitochondria transfer abilities that may determine their regenerative abilities

BACKGROUND

Recent studies have demonstrated mesenchymal stem cells (MSCs) as effective mitochondrial donors with therapeutic success in multiple experimental models of human disease. MSCs obtained from different tissue sources such as bone marrow (BM), adipose (AD), dental pulp (DP), and Wharton's jelly (WJ) are routinely used in clinical trials with no known study of their mitochondrial donor capacity. Here, we show for the first time that MSCs derived from different tissue sources have different mitochondrial donor properties and that this is correlated with their intrinsic respiratory states.

METHODS

MitoTracker^®-labeled MSCs were co-cultured with Cell Trace-labeled U87-MG cells or rat cardiomyocytes. Mitochondrial transfer abilities of MSCs were assessed by using flow cytometry analysis and fluorescence imaging. Mitochondrial reactive oxygen species (mtROS) levels were analyzed by using MitoSOX red-based staining, and mitochondrial respiration parameters were analyzed by using a Seahorse XF Analyzer.

RESULTS

AD-MSCs and BM-MSCs displayed higher mitochondrial transfer than DP-MSCs and WJ-MSCs. Counterintuitively, DP-MSCs and WJ-MSCs were more effective in suppressing mtROS levels in stressed recipient cells than AD-MSCs or BM-MSCs. Interestingly, the oxygen consumption rates and intrinsic mitochondrial respiration parameters like ATP levels, basal and maximal respiration, and mitochondrial DNA copy number in donor MSCs showed a highly significant inverse correlation with their mitochondrial donation.

CONCLUSIONS

We find that there are intrinsic differences in the mitochondrial respiration, donation capacity, and therapeutic efficacy among MSCs of different tissue origin. MSCs with high mitochondrial respiration capacities are associated with lower mitochondrial transfer but more effective suppression of mtROS in stressed recipient cells. This is most compatible with a model where recipient cells optimally regulate mitochondrial transfer such that they take more mitochondria from MSCs with lower mitochondrial function. Furthermore, it appears to be advantageous to use MSCs such as DP-MSCs or WJ-MSCs with higher mitochondrial respiratory abilities that achieved better therapeutic effect with lower mitochondrial transfer in our study. This opens up a new direction in stem cell therapeutics.

Mitochondrial targeting as a novel therapy for stroke

Stroke is a main cause of mortality and morbidity worldwide. Despite the increasing development of innovative treatments for stroke, most are unsuccessful in clinical trials. In recent years, an encouraging strategy for stroke therapy has been identified in stem cells transplantation. In particular, grafting cells and their secretion products are leading with functional recovery in stroke patients by promoting the growth and function of the neurovascular unit – a communication framework between neurons, their supply microvessels along with glial cells – underlying stroke pathology and recovery. Mitochondrial dysfunction has been recently recognized as a hallmark in ischemia/reperfusion neural damage. Emerging evidence of mitochondria transfer from stem cells to ischemic-injured cells points to transfer of healthy mitochondria as a viable novel therapeutic strategy for ischemic diseases. Hence, a more in-depth understanding of the cellular and molecular mechanisms involved in mitochondrial impairment may lead to new tools for stroke treatment. In this review, we focus on the current evidence of mitochondrial dysfunction in stroke, investigating favorable approaches of healthy mitochondria transfer in ischemic neurons, and exploring the potential of mitochondria-based cellular therapy for clinical applications. This paper is a review article. Referred literature in this paper has been listed in the references section. The data sets supporting the conclusions of this article are available online by searching various databases, including PubMed.

Mitochondria in Ischemic Stroke: New Insight and Implications

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.

Transplanting Mesenchymal Stem Cells for Treatment of Ischemic Stroke

Stroke is a major disease that leads to high mortality and morbidity. Given the ageing population and the potential risk factors, the prevalence of stroke and socioeconomic burden associated with stroke are expected to increase. During the past decade, both prophylactic and therapeutic strategies for stroke have made significant progress. However, current therapies still cannot adequately improve the outcomes of stroke and may not apply to all patients. One of the significant advances in modern medicine is cell-derived neurovascular regeneration and neuronal repair. Progress in stem cell biology has greatly contributed to ameliorating stroke-related brain injuries in preclinical studies and demonstrated clinical potential in stroke treatment. Mesenchymal stem cells (MSCs) have the differentiating potential of chondrocytes, adipocytes, and osteoblasts, and they have the ability to transdifferentiate into endothelial cells, glial cells, and neurons. Due to their great plasticity, MSCs have drawn much attention from the scientific community. This review will focus on MSCs, stem cells widely utilized in current medical research, and evaluate their effect and potential of improving outcomes in ischemic stroke.

Cell communication by tunneling nanotubes: Implications in disease and therapeutic applications

Intercellular communication is essential for the development and maintenance of multicellular organisms. Tunneling nanotubes (TNTs) are a recently recognized means of long and short distance communication between a wide variety of cell types. TNTs are transient filamentous membrane protrusions that connect cytoplasm of neighboring or distant cells. Cytoskeleton fiber-mediated transport of various cargoes occurs through these tubules. These cargoes range from small ions to whole organelles. TNTs have been shown to contribute not only to embryonic development and maintenance of homeostasis, but also to the spread of infectious particles and resistance to therapies. These functions in the development and progression of cancer and infectious disease have sparked increasing scrutiny of TNTs, as their contribution to disease progression lends them a promising therapeutic target. Herein, we summarize the current knowledge of TNT structure and formation as well as the role of TNTs in pathology, focusing on viral, prion, and malignant disease. We then discuss the therapeutic possibilities of TNTs in light of their varied functions. Despite recent progress in the growing field of TNT research, more studies are needed to precisely understand the role of TNTs in pathological conditions and to develop novel therapeutic strategies.

Mesenchymal Stem Cells for Frailty?

Frailty is a medical syndrome associated with advancing age characterized by reduced functional reserve, strength, endurance, and susceptibility to infection associated with high morbidity, hospitalization, and death. Nonspecific interventions to improve the healthspan of affected patients include physical therapy, exercise, improved nutrition, etc. Among the hallmarks of aging, depletion of stem cells with resultant compromise of regeneration and repair of tissues informs a rational stem cell-based replacement strategy. This hypothesis has been evaluated in a randomized, double-blind, placebo-controlled clinical trial utilizing human allogeneic mesenchymal stem cells (allo-hMSCs), a facile, scalable stem cell replacement therapy. Intravenous infusion of 100 or 200 million allo-hMSCs was deemed safe in aged frail individuals. However, modest improvement outcomes were limited to the lower dose, a finding that remains difficult to explain. Future studies are definitely warranted given the magnitude of this increasingly important medical syndrome.

Specialized Intercellular Communications via Cytonemes and Nanotubes

In recent years, thin membrane protrusions such as cytonemes and tunneling nanotubes have emerged as a novel mechanism of intercellular communication. Protrusion-based cellular interactions allow for specific communication between participating cells and have a distinct spectrum of advantages compared to secretion- and diffusion-based intercellular communication. Identification of protrusion-based signaling in diverse systems suggests that this mechanism is a ubiquitous and prevailing means of communication employed by many cell types. Moreover, accumulating evidence indicates that protrusion-based intercellular communication is often involved in pathogenesis, including cancers and infections. Here we review our current understanding of protrusion-based intercellular communication.

The role of metabolism and tunneling nanotube-mediated intercellular mitochondria exchange in cancer drug resistance

Intercellular communications play a major role in tissue homeostasis. In pathologies such as cancer, cellular interactions within the tumor microenvironment (TME) contribute to tumor progression and resistance to therapy. Tunneling nanotubes (TNTs) are newly discovered long-range intercellular connections that allow the exchange between cells of various cargos, ranging from ions to whole organelles such as mitochondria. TNT-transferred mitochondria were shown to change the metabolism and functional properties of recipient cells as reported for both normal and cancer cells. Metabolic plasticity is now considered a hallmark of cancer as it notably plays a pivotal role in drug resistance. The acquisition of cancer drug resistance was also associated to TNT-mediated mitochondria transfer, a finding that relates to the role of mitochondria as a hub for many metabolic pathways. In this review, we first give a brief overview of the various mechanisms of drug resistance and of the cellular communication means at play in the TME, with a special focus on the recently discovered TNTs. We further describe recent studies highlighting the role of the TNT-transferred mitochondria in acquired cancer cell drug resistance. We also present how changes in metabolic pathways, including glycolysis, pentose phosphate and lipid metabolism, are linked to cancer cell resistance to therapy. Finally, we provide examples of novel therapeutic strategies targeting mitochondria and cell metabolism as a way to circumvent cancer cell drug resistance.

Understanding the Role of Dysfunctional and Healthy Mitochondria in Stroke Pathology and Its Treatment

Stroke remains a major cause of death and disability in the United States and around the world. Solid safety and efficacy profiles of novel stroke therapeutics have been generated in the laboratory, but most failed in clinical trials. Investigations into the pathology and treatment of the disease remain a key research endeavor in advancing scientific understanding and clinical applications. In particular, cell-based regenerative medicine, specifically stem cell transplantation, may hold promise as a stroke therapy, because grafted cells and their components may recapitulate the growth and function of the neurovascular unit, which arguably represents the alpha and omega of stroke brain pathology and recovery. Recent evidence has implicated mitochondria, organelles with a central role in energy metabolism and stress response, in stroke progression. Recognizing that stem cells offer a source of healthy mitochondria—one that is potentially transferrable into ischemic cells—may provide a new therapeutic tool. To this end, deciphering cellular and molecular processes underlying dysfunctional mitochondria may reveal innovative strategies for stroke therapy. Here, we review recent studies capturing the intimate participation of mitochondrial impairment in stroke pathology, and showcase promising methods of healthy mitochondria transfer into ischemic cells to critically evaluate the potential of mitochondria-based stem cell therapy for stroke patients.

Reactive Oxygen Species and Mitochondrial Homeostasis as Regulators of Stem Cell Fate and Function

SIGNIFICANCE

The precise role and impact of reactive oxygen species (ROS) in stem cells, which are essential for lifelong tissue homeostasis and regeneration, remain of significant interest to the field. The long-term regenerative potential of a stem cell compartment is determined by the delicate balance between quiescence, self-renewal, and differentiation, all of which can be influenced by ROS levels. Recent Advances: The past decade has seen a growing appreciation for the importance of ROS and redox homeostasis in various stem cell compartments, particularly those of hematopoietic, neural, and muscle tissues. In recent years, the importance of proteostasis and mitochondria in relation to stem cell biology and redox homeostasis has garnered considerable interest.

CRITICAL ISSUES

Here, we explore the reciprocal relationship between ROS and stem cells, with significant emphasis on mitochondria as a core component of redox homeostasis. We discuss how redox signaling, involving cell-fate determining protein kinases and transcription factors, can control stem cell function and fate. We also address the impact of oxidative stress on stem cells, especially oxidative damage of lipids, proteins, and nucleic acids. We further discuss ROS management in stem cells, and present recent evidence supporting the importance of mitochondrial activity and its modulation (via mitochondrial clearance, biogenesis, dynamics, and distribution [i.e., segregation and transfer]) in stem cell redox homeostasis.

FUTURE DIRECTIONS

Therefore, elucidating the intricate links between mitochondria, cellular metabolism, and redox homeostasis is envisioned to be critical for our understanding of ROS in stem cell biology and its therapeutic relevance in regenerative medicine. Antioxid. Redox Signal. 00, 000-000.

Mitochondrial Dysfunction in Stroke: Implications of Stem Cell Therapy

Stroke is a debilitating condition which is also the second leading cause of death and disability worldwide. Despite the benefits and promises shown by numerous neuroprotective agents in animal stroke models, their clinical translation has not been a complete success. Hence, search for treatment options have directed researchers towards utilising stem cells. Mitochondria has a major involvement in the pathophysiology of stroke and a number of other conditions. Stem cells have shown the ability to transfer mitochondria to the damaged cells and to help revive cell energetics in the recipient cell. The present review discusses how stem cells could be employed to protect neurons and mitochondria in stroke and also the various mechanisms involved in neuroprotection.

Association of Inflammatory Responses and ECM Disorganization with HMGB1 Upregulation and NLRP3 Inflammasome Activation in the Injured Rotator Cuff Tendon

Inflammation and extracellular matrix (ECM) disorganization following the rotator cuff tendon injuries (RCTI) delay the repair and healing process and the molecular mechanisms underlying RCTI pathology are largely unknown. Here, we examined the role of HMGB1 and NLRP3 inflammasome pathway in the inflammation and ECM disorganization in RCTI. This hypothesis was tested in a tenotomy-RCTI rat model by transecting the RC tendon from the humerus. H&E and pentachrome staining revealed significant changes in the morphology, architecture and ECM organization in RC tendon tissues following RCTI when compared with contralateral control. Severity of the injury was high in the first two weeks with improvement in 3–4 weeks following RCTI, and this correlated with the healing response. The expression of proteins associated with increased HMGB-1 and upregulation of NLRP3 inflammasome pathway, TLR4, TLR2, TREM-1, RAGE, ASC, Caspase-1, and IL-1β, in the first two weeks following RCTI followed by decline in 3–4 weeks. These results suggest the association of inflammatory responses and ECM disorganization with HMGB1 upregulation and NLRP3 inflammasome activation in the RC tendons and could provide novel target(s) for development of better therapeutic strategies in the management of RCTI.

Stem Cell Ophthalmology Treatment Study: bone marrow derived stem cells in the treatment of Retinitis Pigmentosa

BACKGROUND

Seventeen patients with bilateral visual loss due to Retinitis Pigmentosa (RP) underwent autologous bone marrow derived stem cell (BMSC) treatment within the Stem Cell Ophthalmology Treatment Study (SCOTS and SCOTS 2). Both are National Institutes of Health (NIH) and Office of Human Research Protection (OHRP) compliant Institutional Review Board (IRB) approved clinical studies utilizing using autologous BMSC in the treatment of retinal and optic nerve diseases that meet inclusion criteria.

METHODS

The average age of the patients treated was 48.8 years. The average duration of disease prior to treatment was 27.6 years and ranged from 4 to approximately 60 years. Affected eyes were treated with either retrobulbar, subtenons and intravenous BMSC or retrobulbar, subtenons, intravitreal and intravenous. Follow up was provided a minimum of 6 months. The primary outcome was visual acuity as measured by Snellen or converted to LogMAR.

RESULTS

Following therapy in SCOTS or SCOTS 2, 11 patients (64.7%) showed improved binocular vision averaging 10.23 lines of Snellen acuity per eye over pre-treatment acuity; 8 patients (35.3%) remaining stable over the follow up period; no patients experiencing loss of overall acuity. In 33 treated eyes, 15 eyes (45.5%) improved an average of 7.9 lines of Snellen acuity, 15 eyes (45.5%) remained stable, and 3 eyes (9%) worsened by an average of 1.7 lines of Snellen acuity. Improvements ranged from 1 to 27 lines of vision. Using the LogMAR Scale and calculating delta as a ratio to pre-treatment vision in improved eyes, acuity improvement ranged from 23% to 90% with an average of 40.9% visual acuity improvement over baseline vision. Evaluation of all patients and eyes capable of LogMAR vision showed an average of 31% improvement in vision over baseline. Findings were of statistical significance (P=0.016). There were no surgical complications.

CONCLUSIONS

The BMSC protocols of the SCOTS achieved meaningful visual acuity improvements or stability in RP that were of statistical significance. Duration of disease did not appear to affect the ability of eyes to respond. Safety was confirmed. Possible mechanisms by which improvement occurred may include transdifferentiation of BMSC into Neuronal Nuclei (NeuN) positive cells, BMSC paracrine secretions or neurotrophic factors and hormones, transfer of mitochondria, release of messenger RNA or other compounds via exosomes or microvesicles. Given the successful outcome in this otherwise progressive condition, consideration should be given to providing this treatment option.

Homotypic endothelial nanotubes induced by wheat germ agglutinin and thrombin

Endothelial barrier formation is maintained by intercellular communication through junctional proteins. The mechanisms involved in maintaining endothelial communication subsequent to barrier disruption remain unclear. It is known that low numbers of endothelial cells can be interconnected by homotypic actin-driven tunneling nanotubes (TNTs) which could be important for intercellular transfer of information in vascular physiology. Here we sought insight into the triggers for TNT formation. Wheat germ agglutinin, a C-type lectin and known label for TNTs, unexpectedly caused striking induction of TNTs. A succinylated derivative was by contrast inactive, suggesting mediation by a sialylated protein. Through siRNA-mediated knockdown we identified that this protein was likely to be CD31, an important sialylated membrane protein normally at endothelial cell junctions. We subsequently considered thrombin as a physiological inducer of endothelial TNTs because it reduces junctional contact. Thrombin reduced junctional contact, redistributed CD31 and induced TNTs, but its effect on TNTs was CD31-independent. Thrombin-induced TNTs nevertheless required PKCα, a known mediator of thrombin-dependent junctional remodelling, suggesting a necessity for junctional proteins in TNT formation. Indeed, TNT-inducing effects of wheat germ agglutinin and thrombin were both correlated with cortical actin rearrangement and similarly Ca²⁺-dependent, suggesting common underlying mechanisms. Once formed, Ca²⁺ signalling along TNTs was observed.

Stem cell-derived mitochondria transplantation: a novel strategy and the challenges for the treatment of tissue injury

Damage of mitochondria in the initial period of tissue injury aggravates the severity of injury. Restoration of mitochondria dysfunction and mitochondrial-based therapeutics represent a potentially effective therapeutic strategy. Recently, mitochondrial transfer from stem cells has been demonstrated to play a significant role in rescuing injured tissues. The possible mechanisms of mitochondria released from stem cells, the pathways of mitochondria transfer between the donor stem cells and recipient cells, and the internalization of mitochondria into recipient cells are discussed. Moreover, a novel strategy for tissue injury based on the concept of stem cell-derived mitochondrial transplantation is pointed out, and the advantages and challenges are summarized.

Regenerative abilities of mesenchymal stem cells through mitochondrial transfer

The past decade has witnessed an upsurge in studies demonstrating mitochondrial transfer as one of the emerging mechanisms through which mesenchymal stem cells (MSCs) can regenerate and repair damaged cells or tissues. It has been found to play a critical role in healing several diseases related to brain injury, cardiac myopathies, muscle sepsis, lung disorders and acute respiratory disorders. Several studies have shown that various mechanisms are involved in mitochondrial transfer that includes tunnel tube formation, micro vesicle formation, gap junctions, cell fusion and others modes of transfer. Few studies have investigated the mechanisms that contribute to mitochondrial transfer, primarily comprising of signaling pathways involved in tunnel tube formation that facilitates tunnel tube formation for movement of mitochondria from one cell to another. Various stress signals such as release of damaged mitochondria, mtDNA and mitochondrial products along with elevated reactive oxygen species levels trigger the transfer of mitochondria from MSCs to recipient cells. However, extensive cell signaling pathways that lead to mitochondrial transfer from healthy cells are still under investigation and the changes that contribute to restoration of mitochondrial bioenergetics in recipient cells remain largely elusive. In this review, we have discussed the phenomenon of mitochondrial transfer from MSCs to neighboring stressed cells, and how this aids in cellular repair and regeneration of different organs such as lung, heart, eye, brain and kidney. The potential scope of mitochondrial transfer in providing novel therapeutic strategies for treatment of various pathophysiological conditions has also been discussed.

Hydrogels-Assisted Cell Engraftment for Repairing the Stroke-Damaged Brain: Chimera or Reality

The use of advanced biomaterials as a structural and functional support for stem cells-based therapeutic implants has boosted the development of tissue engineering applications in multiple clinical fields. In relation to neurological disorders, we are still far from the clinical reality of restoring normal brain function in neurodegenerative diseases and cerebrovascular disorders. Hydrogel polymers show unique mechanical stiffness properties in the range of living soft tissues such as nervous tissue. Furthermore, the use of these polymers drastically enhances the engraftment of stem cells as well as their capacity to produce and deliver neuroprotective and neuroregenerative factors in the host tissue. Along this article, we review past and current trends in experimental and translational research to understand the opportunities, benefits, and types of tentative hydrogel-based applications for the treatment of cerebral disorders. Although the use of hydrogels for brain disorders has been restricted to the experimental area, the current level of knowledge anticipates an intense development of this field to reach clinics in forthcoming years.

Neuroprotective Effects of Bioactive Compounds and MAPK Pathway Modulation in "Ischemia"-Stressed PC12 Pheochromocytoma Cells

This review surveys the efforts taken to investigate in vitro neuroprotective features of synthetic compounds and cell-released growth factors on PC12 clonal cell line temporarily deprived of oxygen and glucose followed by reoxygenation (OGD/R). These cells have been used previously to mimic some of the properties of in vivo brain ischemia-reperfusion-injury (IRI) and have been instrumental in identifying common mechanisms such as calcium overload, redox potential, lipid peroxidation and MAPKs modulation. In addition, they were useful for establishing the role of certain membrane penetrable cocktails of antioxidants as well as potential growth factors which may act in neuroprotection. Pharmacological mechanisms of neuroprotection addressing modulation of the MAPK cascade and increased redox potential by natural products, drugs and growth factors secreted by stem cells, in either undifferentiated or nerve growth factor-differentiated PC12 cells exposed to ischemic conditions are discussed for future prospects in neuroprotection studies.

Mitochondria are transported along microtubules in membrane nanotubes to rescue distressed cardiomyocytes from apoptosis

Membrane nanotubes (MNTs) act as “highways” between cells to facilitate the transfer of multiple signals and play an important role in many diseases. Our previous work reported on the transfer of mitochondria via MNTs between cardiomyocytes (CMs) and cardiac myofibroblasts (MFs); however, the elucidation of the underlying mechanism and pathophysiological significance of this transfer requires additional study. In this study, we determined that the mean movement velocity of mitochondria in MNTs between CMs and MFs was approximately 17.5 ± 2.1 nm/s. Meanwhile, treatment with microtubule polymerisation inhibitors nocodazole or colcemid in cell culture decreased mitochondrial velocity, and knockdown of the microtubule motor protein kinesin family member 5B (KIF5B) led to a similar effect, indicating that mitochondrial movement was dependent on microtubules and the motor protein KIF5B. Furthermore, we showed that hypoxia/reoxygenation-induced CM apoptosis was attenuated by coculture with intact or hypoxia/reoxygenation-treated MFs, which transferred mitochondria to CMs. This rescue was prevented either by separating the cells using Transwell culture or by impairing mitochondrial transfer with nocodazole or colcemid treatment. In conclusion, as a novel means of intercellular communication, MNTs rescue distressed CMs from apoptosis by transporting mitochondria along microtubules via KIF5B.

Cell adhesion-mediated mitochondria transfer contributes to mesenchymal stem cell-induced chemoresistance on T cell acute lymphoblastic leukemia cells

BACKGROUND

Despite the high cure rate of T cell acute lymphoblastic leukemia (T-ALL), drug resistance to chemotherapy remains a significant clinical problem. Bone marrow mesenchymal stem cells (MSCs) protect leukemic cells from chemotherapy, but the underlying mechanisms are poorly understood. In this study, we aimed to uncover the mechanism of MSC-induced chemoresistance in T-ALL cells, thus providing a promising clinical therapy target.

METHODS

Cell viability was determined using the viability assay kit CCK-8. The mitochondrial ROS levels were detected using the fluorescent probe MitoSOX™ Red, and fluorescence intensity was measured by flow cytometry. In vitro, MSCs and Jurkat cells were cocultured. MSCs were labeled with green fluorescent protein (GFP), and Jurkat cells were labeled with the mitochondria-specific dye MitoTracker Red. Bidirectional mitochondrial transfer was detected by flow cytometry and confocal microscopy. The mechanism of mitochondria transfer was analyzed by inhibitor assays. Transcripts related to Jurkat cell/MSC adhesion in the coculture system were assessed by qRT-PCR. After treatment with a neutralizing antibody against a key adhesion molecule, mitochondria transfer from Jurkat cells to MSCs was again detected by flow cytometry and confocal microscopy. Finally, we verified our findings using human primary T-ALL cells cocultured with MSCs.

RESULTS

Chemotherapeutic drugs caused intracellular oxidative stress in Jurkat cells. Jurkat cells transfer mitochondria to MSCs but receive few mitochondria from MSCs, resulting in chemoresistance. This process of mitochondria transfer is mediated by tunneling nanotubes, which are protrusions that extend from the cell membrane . Moreover, we found that most Jurkat cells adhered to MSCs in the coculture system, which was mediated by the adhesion molecule ICAM-1. Treatment with a neutralizing antibody against ICAM-1 led to a decreased number of adhering Jurkat cells, decreased mitochondria transfer, and increased chemotherapy-induced cell death.

CONCLUSIONS

We show evidence that mitochondria transfer from Jurkat cells to MSCs, which is mediated by cell adhesion, may be a potential therapeutic target for T-ALL treatment.

Mesenchymal Stromal Cells Modulate Macrophages in Clinically Relevant Lung Injury Models by Extracellular Vesicle Mitochondrial Transfer

RATIONALE

Acute respiratory distress syndrome (ARDS) remains a major cause of respiratory failure in critically ill patients. Mesenchymal stromal cells (MSCs) are a promising candidate for a cell-based therapy. However, the mechanisms of MSCs' effects in ARDS are not well understood. In this study, we focused on the paracrine effect of MSCs on macrophage polarization and the role of extracellular vesicle (EV)-mediated mitochondrial transfer.

OBJECTIVES

To determine the effects of human MSCs on macrophage function in the ARDS environment and to elucidate the mechanisms of these effects.

METHODS

Human monocyte-derived macrophages (MDMs) were studied in noncontact coculture with human MSCs when stimulated with LPS or bronchoalveolar lavage fluid (BALF) from patients with ARDS. Murine alveolar macrophages (AMs) were cultured ex vivo with/without human MSC-derived EVs before adoptive transfer to LPS-injured mice.

MEASUREMENTS AND MAIN RESULTS

MSCs suppressed cytokine production, increased M2 macrophage marker expression, and augmented phagocytic capacity of human MDMs stimulated with LPS or ARDS BALF. These effects were partially mediated by CD44-expressing EVs. Adoptive transfer of AMs pretreated with MSC-derived EVs reduced inflammation and lung injury in LPS-injured mice. Inhibition of oxidative phosphorylation in MDMs prevented the modulatory effects of MSCs. Generating dysfunctional mitochondria in MSCs using rhodamine 6G pretreatment also abrogated these effects.

CONCLUSIONS

In the ARDS environment, MSCs promote an antiinflammatory and highly phagocytic macrophage phenotype through EV-mediated mitochondrial transfer. MSC-induced changes in macrophage phenotype critically depend on enhancement of macrophage oxidative phosphorylation. AMs treated with MSC-derived EVs ameliorate lung injury in vivo.

Defining the momiome: Promiscuous information transfer by mobile mitochondria and the mitochondrial genome

Mitochondria are complex intracellular organelles that have long been identified as the powerhouses of eukaryotic cells because of the central role they play in oxidative metabolism. A resurgence of interest in the study of mitochondria during the past decade has revealed that mitochondria also play key roles in cell signaling, proliferation, cell metabolism and cell death, and that genetic and/or metabolic alterations in mitochondria contribute to a number of diseases, including cancer. Mitochondria have been identified as signaling organelles, capable of mediating bidirectional intracellular information transfer: anterograde (from nucleus to mitochondria) and retrograde (from mitochondria to nucleus). More recently, evidence is now building that the role of mitochondria extends to intercellular communication as well, and that the mitochondrial genome (mtDNA) and even whole mitochondria are indeed mobile and can mediate information transfer between cells. We define this promiscuous information transfer function of mitochondria and mtDNA as "momiome" to include all mobile functions of mitochondria and the mitochondrial genome. Herein, we review the "momiome" and explore its role in cancer development, progression, and treatment.