Cell-to-cell cross-talk between mesenchymal stem cells and cardiomyocytes in co-culture

Mitochondria in mesenchymal stem cell biology and cell therapy: From cellular differentiation to mitochondrial transfer

Mesenchymal stem cells (MSCs) are characterized to have the capacity of self-renewal and the potential to differentiate into mesoderm, ectoderm-like and endoderm-like cells. MSCs hold great promise for cell therapies due to their multipotency in vitro and therapeutic advantage of hypo-immunogenicity and lower tumorigenicity. Moreover, it has been shown that MSCs can serve as a vehicle to transfer mitochondria into cells after cell transplantation. Mitochondria produce most of the energy through oxidative phosphorylation in differentiated cells. It has been increasingly clear that the switch of energy supply from glycolysis to aerobic metabolism is essential for successful differentiation of MSCs. Post-translational modifications of proteins have been established to regulate mitochondrial function and metabolic shift during MSCs differentiation. In this article, we review and provide an integrated view on the roles of different protein kinases and sirtuins in the maintenance and differentiation of MSCs. Importantly, we provide evidence to suggest that alteration in the expression of Sirt3 and Sirt5 and relative changes in the acylation levels of mitochondrial proteins might be involved in the activation of mitochondrial function and adipogenic differentiation of adipose-derived MSCs. We summarize their roles in the regulation of mitochondrial biogenesis and metabolism, oxidative responses and differentiation of MSCs. On the other hand, we discuss recent advances in the study of mitochondrial dynamics and mitochondrial transfer as well as their roles in the differentiation and therapeutic application of MSCs to improve cell function in vitro and in animal models. Accumulating evidence has substantiated that the therapeutic potential of MSCs is conferred not only by cell replacement and paracrine effects but also by transferring mitochondria into injured tissues or cells to modulate the cellular metabolism in situ. Therefore, elucidation of the underlying mechanisms in the regulation of mitochondrial metabolism of MSCs may ultimately improve therapeutic outcomes of stem cell therapy in the future.

Biochip-based study of unidirectional mitochondrial transfer from stem cells to myocytes via tunneling nanotubes

Tunneling nanotubes (TNTs) are small membranous tubes of 50-1000 nm diameter observed to connect cells in culture. Transfer of subcellular organelles through TNTs was observed in vitro and in vivo, but the formation and significance of these structures is not well understood. A polydimethylsiloxane biochip-based coculture model was devised to constrain TNT orientation and explore both TNT-formation and TNT-mediated mitochondrial transfer. Two parallel microfluidic channels connected by an array of smaller microchannels enabled localization of stem cell and cardiomyocyte populations while allowing connections to form between them. Stem cells and cardiomyocytes were deposited in their respective microfluidic channels, and stem cell-cardiomyocyte pairs were formed via the microchannels. Formation of TNTs and transfer of stained mitochondria through TNTs was observed by 24 h real-time video recording. The data show that stem cells are 7.7 times more likely to initiate contact by initial extension of filopodia. By 24 h, 67% of nanotube connections through the microchannels are composed of cardiomyocyte membrane. Filopodial extension and retraction by stem cells draws an extension of TNTs from cardiomyocytes. MitoTracker staining shows that unidirectional transfer of mitochondria between stem cell-cardiomyocyte pairs invariably originates from stem cells. Control experiments with cardiac fibroblasts and cardiomyocytes show little nanotube formation between homotypic or mixed cell pairs and no mitochondrial transfer. These data identify a novel biological process, unidirectional mitochondrial transfer, mediated by heterotypic TNT connections. This suggests that the enhancement of cardiomyocyte function seen after stem-cell injection may be due to a bioenergetic stimulus provided by mitochondrial transfer.

Bone marrow-derived mesenchymal stem cells rescue injured H9c2 cells via transferring intact mitochondria through tunneling nanotubes in an in vitro simulated ischemia/reperfusion model

The transplantation of mesenchymal stem cells (MSCs) is considered to be a promising treatment for ischemic heart disease; however, the therapeutic effects and underlying mechanisms of action require further evaluation. Mitochondrial dysfunction is a key event in simulated ischemia/reperfusion (SI/R) injury. The purpose of the present study was to investigate the mechanism of mitochondrial transfer, which may be involved the antiapoptotic action of co-culture with MSCs. An in vitro model of simulated ischemia/reperfusion (SI/R) was used in the present study. The apoptotic indexes were significantly increased when H9c2 cardiomyocytes were induced in the SI/R group. Following co-culture with bone marrow-derived (BM)-MSCs, H9c2 cells exhibited marked resistance against the SI/R-induced apoptotic process. Besides, mitochondrial transfer via a tunneling nanotube (TNT) like structure was detected by confocal fluorescent microscopy. In addition, following pretreated with latrunculin-A (LatA), an inhibitor of TNT formation, the BM-MSCs were not able to rescue injured H9c2 cells from apoptosis, as previously observed. In conclusion, the anti-apoptotic ability of BM-MSCs may be partially attributed to the recovery of mitochondrial dysfunction in SI/R, and the formation of TNTs appears to be involved in this action of mitochondrial transfer between adjacent cells.

How to Improve the Survival of Transplanted Mesenchymal Stem Cell in Ischemic Heart?

Mesenchymal stem cell (MSC) is an intensely studied stem cell type applied for cardiac repair. For decades, the preclinical researches on animal model and clinical trials have suggested that MSC transplantation exerts therapeutic effect on ischemic heart disease. However, there remain major limitations to be overcome, one of which is the very low survival rate after transplantation in heart tissue. Various strategies have been tried to improve the MSC survival, and many of them showed promising results. In this review, we analyzed the studies in recent years to summarize the methods, effects, and mechanisms of the new strategies to address this question.

Rejuvenating cellular respiration for optimizing respiratory function: targeting mitochondria

Altered bioenergetics with increased mitochondrial reactive oxygen species production and degradation of epithelial function are key aspects of pathogenesis in asthma and chronic obstructive pulmonary disease (COPD). This motif is not unique to obstructive airway disease, reported in related airway diseases such as bronchopulmonary dysplasia and parenchymal diseases such as pulmonary fibrosis. Similarly, mitochondrial dysfunction in vascular endothelium or skeletal muscles contributes to the development of pulmonary hypertension and systemic manifestations of lung disease. In experimental models of COPD or asthma, the use of mitochondria-targeted antioxidants, such as MitoQ, has substantially improved mitochondrial health and restored respiratory function. Modulation of noncoding RNA or protein regulators of mitochondrial biogenesis, dynamics, or degradation has been found to be effective in models of fibrosis, emphysema, asthma, and pulmonary hypertension. Transfer of healthy mitochondria to epithelial cells has been associated with remarkable therapeutic efficacy in models of acute lung injury and asthma. Together, these form a 3R model--repair, reprogramming, and replacement--for mitochondria-targeted therapies in lung disease. This review highlights the key role of mitochondrial function in lung health and disease, with a focus on asthma and COPD, and provides an overview of mitochondria-targeted strategies for rejuvenating cellular respiration and optimizing respiratory function in lung diseases.

Nanothin Coculture Membranes with Tunable Pore Architecture and Thermoresponsive Functionality for Transfer-Printable Stem Cell-Derived Cardiac Sheets

Coculturing stem cells with the desired cell type is an effective method to promote the differentiation of stem cells. The features of the membrane used for coculturing are crucial to achieving the best outcome. Not only should the membrane act as a physical barrier that prevents the mixing of the cocultured cell populations, but it should also allow effective interactions between the cells. Unfortunately, conventional membranes used for coculture do not sufficiently meet these requirements. In addition, cell harvesting using proteolytic enzymes following coculture impairs cell viability and the extracellular matrix (ECM) produced by the cultured cells. To overcome these limitations, we developed nanothin and highly porous (NTHP) membranes, which are ∼20-fold thinner and ∼25-fold more porous than the conventional coculture membranes. The tunable pore size of NTHP membranes at the nanoscale level was found crucial for the formation of direct gap junctions-mediated contacts between the cocultured cells. Differentiation of the cocultured stem cells was dramatically enhanced with the pore size-customized NTHP membrane system compared to conventional coculture methods. This was likely due to effective physical contacts between the cocultured cells and the fast diffusion of bioactive molecules across the membrane. Also, the thermoresponsive functionality of the NTHP membranes enabled the efficient generation of homogeneous, ECM-preserved, highly viable, and transfer-printable sheets of cardiomyogenically differentiated cells. The coculture platform developed in this study would be effective for producing various types of therapeutic multilayered cell sheets that can be differentiated from stem cells.

Mesenchymal stem cells use extracellular vesicles to outsource mitophagy and shuttle microRNAs

Mesenchymal stem cells (MSCs) and macrophages are fundamental components of the stem cell niche and function coordinately to regulate haematopoietic stem cell self-renewal and mobilization. Recent studies indicate that mitophagy and healthy mitochondrial function are critical to the survival of stem cells, but how these processes are regulated in MSCs is unknown. Here we show that MSCs manage intracellular oxidative stress by targeting depolarized mitochondria to the plasma membrane via arrestin domain-containing protein 1-mediated microvesicles. The vesicles are then engulfed and re-utilized via a process involving fusion by macrophages, resulting in enhanced bioenergetics. Furthermore, we show that MSCs simultaneously shed micro RNA-containing exosomes that inhibit macrophage activation by suppressing Toll-like receptor signalling, thereby de-sensitizing macrophages to the ingested mitochondria. Collectively, these studies mechanistically link mitophagy and MSC survival with macrophage function, thereby providing a physiologically relevant context for the innate immunomodulatory activity of MSCs.

Direct intercellular communications dominate the interaction between adipose-derived MSCs and myofibroblasts against cardiac fibrosis

The onset of cardiac fibrosis post myocardial infarction greatly impairs the function of heart. Recent advances of cell transplantation showed great benefits to restore myocardial function, among which the mesenchymal stem cells (MSCs) has gained much attention. However, the underlying cellular mechanisms of MSC therapy are still not fully understood. Although paracrine effects of MSCs on residual cardiomyocytes have been discussed, the amelioration of fibrosis was rarely studied as the hostile environment cannot support the survival of most cell populations and impairs the diffusion of soluble factors. Here in order to decipher the potential mechanism of MSC therapy for cardiac fibrosis, we investigated the interplay between MSCs and cardiac myofibroblasts (mFBs) using interactive co-culture method, with comparison to paracrine approaches, namely treatment by MSC conditioned medium and gap co-culture method. Various fibrotic features of mFBs were analyzed and the most prominent anti-fibrosis effects were always obtained using direct co-culture that allowed cell-to-cell contacts. Hepatocyte growth factor (HGF), a well-known anti-fibrosis factor, was demonstrated to be a major contributor for MSCs' anti-fibrosis function. Moreover, physical contacts and tube-like structures between MSCs and mFBs were observed by live cell imaging and TEM which demonstrate the direct cellular interactions.

Mesenchymal Stem Cells for Cardiac Regenerative Therapy: Optimization of Cell Differentiation Strategy

With the high mortality rate, coronary heart disease (CHD) has currently become a major life-threatening disease. The main pathological change of myocardial infarction (MI) is the induction of myocardial necrosis in infarction area which finally causes heart failure. Conventional treatments cannot regenerate the functional cell efficiently. Recent researches suggest that mesenchymal stem cells (MSCs) are able to differentiate into multiple lineages, including cardiomyocyte-like cells in vitro and in vivo, and they have been used for the treatment of MI to repair the injured myocardium and improve cardiac function. In this review, we will focus on the recent progress on MSCs derived cardiomyocytes for cardiac regeneration after MI.

Rapid fusion between mesenchymal stem cells and cardiomyocytes yields electrically active, non-contractile hybrid cells

Cardiac cell therapies involving bone marrow-derived human mesenchymal stem cells (hMSCs) have shown promising results, although their mechanisms of action are still poorly understood. Here, we investigated direct interactions between hMSCs and cardiomyocytes in vitro. Using a genetic Ca²⁺ indicator gCaMP3 to efficiently label hMSCs in co-cultures with neonatal rat ventricular myocytes (NRVMs), we determined that 25–40% of hMSCs (from 4 independent donors) acquired periodic Ca²⁺ transients and cardiac markers through spontaneous fusion with NRVMs. Sharp electrode and voltage-clamp recordings in fused cells showed action potential properties and Ca²⁺ current amplitudes in between those of non-fused hMSCs and NRVMs. Time-lapse video-microscopy revealed the first direct evidence of active fusion between hMSCs and NRVMs within several hours of co-culture. Application of blebbistatin, nifedipine or verapamil caused complete and reversible inhibition of fusion, suggesting potential roles for actomyosin bridging and Ca²⁺ channels in the fusion process. Immunostaining for Cx43, Ki67, and sarcomeric α-actinin showed that fused cells remain strongly coupled to surrounding NRVMs, but downregulate sarcomeric structures over time, acquiring a non-proliferative and non-contractile phenotype. Overall, these results describe the phenotype and mechanisms of hybrid cell formation via fusion of hMSCs and cardiomyocytes with potential implications for cardiac cell therapy.

Improving the Post-Stroke Therapeutic Potency of Mesenchymal Multipotent Stromal Cells by Cocultivation With Cortical Neurons: The Role of Crosstalk Between Cells

The goal of the present study was to maximally alleviate the negative impact of stroke by increasing the therapeutic potency of injected mesenchymal multipotent stromal cells (MMSCs). To pursue this goal, the intercellular communications of MMSCs and neuronal cells were studied in vitro. As a result of cocultivation of MMSCs and rat cortical neurons, we proved the existence of intercellular contacts providing transfer of cellular contents from one cell to another. We present evidence of intercellular exchange with fluorescent probes specifically occupied by cytosol with preferential transfer from neurons toward MMSCs. In contrast, we observed a reversed transfer of mitochondria (from MMSCs to neural cells). Intravenous injection of MMSCs in a postischemic period alleviated the pathological indexes of a stroke, expressed as a lower infarct volume in the brain and partial restoration of neurological status. Also, MMSCs after cocultivation with neurons demonstrated more profound neuroprotective effects than did unprimed MMSCs. The production of the brain-derived neurotrophic factor was slightly increased in MMSCs, and the factor itself was redistributed in these cells after cocultivation. The level of Miro1 responsible for intercellular traffic of mitochondria was increased in MMSCs after cocultivation. We conclude that the exchange by cellular compartments between neural and stem cells improves MMSCs' protective abilities for better rehabilitation after stroke. This could be used as an approach to enhance the therapeutic benefits of stem cell therapy to the damaged brain.

SIGNIFICANCE

The idea of priming stem cells before practical use for clinical purposes was applied. Thus, cells were preconditioned by coculturing them with the targeted cells (i.e., neurons for the treatment of brain pathological features) before the transfusion of stem cells to the organism. Such priming improved the capacity of stem cells to treat stroke. Some additional minimal study will be required to develop a detailed protocol for coculturing followed by cell separation.

Regenerative therapy for hippocampal degenerative diseases: lessons from preclinical studies

Increase in life expectancy has put neurodegenerative diseases on the rise. Amongst these, degenerative diseases involving hippocampus like Alzheimer's disease (AD) and temporal lobe epilepsy (TLE) are ranked higher as it is vulnerable to excitotoxicity induced neuronal dysfunction and death resulting in cognitive impairment. Modern medicines have not succeeded in halting the progression of these diseases rendering them incurable and often fatal. Under such scenario, regenerative studies employing stem cells or their by-products in animal models of AD and TLE have yielded encourageing results. This review focuses on the distinct cell types, such as hippocampal cell lines, neural precursor cells, embryonic stem cells derived neural precursor cells, induced pluripotent stem cells, induced neurons and mesenchymal stem cells, which can be employed to rescue hippocampal functions in neurodegenerative diseases like AD and TLE. Besides, the divergent mechanisms through which cell based therapy confer neuroprotection, current impediments and possible improvements in stem cell transplantation strategies are discussed. Authors are aware of the voluminous literature available on this issue and have made a sincere attempt to put forth the current status of research in the field of cell based therapy concurrently discussing the promise it holds for combating neurodegenerative diseases like AD and TLE in the near future. Copyright © 2015 John Wiley & Sons, Ltd.

Paracrine mechanisms of mesenchymal stem cell-based therapy: current status and perspectives

Mesenchymal stem cells (MSCs) are one of a few stem cell types to be applied in clinical practice as therapeutic agents for immunomodulation and ischemic tissue repair. In addition to their multipotent differentiation potential, a strong paracrine capacity has been proposed as the principal mechanism that contributes to tissue repair. Apart from cytokine/chemokine secretion, MSCs also display a strong capacity for mitochondrial transfer and microvesicle (exosomes) secretion in response to injury with subsequent promotion of tissue regeneration. These unique properties of MSCs make them an invaluable cell type to repair damaged tissues/organs. Although MSCs offer great promise in the treatment of degenerative diseases and inflammatory disorders, there are still many challenges to overcome prior to their widespread clinical application. Particularly, their in-depth paracrine mechanisms remain a matter for debate and exploration. This review will highlight the discovery of the paracrine mechanism of MSCs, regulation of the paracrine biology of MSCs, important paracrine factors of MSCs in modulation of tissue repair, exosome and mitochondrial transfer for tissue repair, and the future perspective for MSC-based therapy.

Nanotubes connect CD4+ T cells to airway smooth muscle cells: novel mechanism of T cell survival

Contact between airway smooth muscle (ASM) cells and activated CD4(+) T cells, a key interaction in diseases such as asthma, triggers ASM cell proliferation and enhances T cell survival. We hypothesized that direct contact between ASM and CD4(+) T cells facilitated the transfer of anti-apoptotic proteins via nanotubes, resulting in increased survival of activated CD4(+) T cells. CD4(+) T cells, isolated from PBMCs of healthy subjects, when activated and cocultured with ASM cells for 24 h, formed nanotubes that were visualized by immunofluorescence and atomic force microscopy. Cell-to-cell transfer of the fluorescent dye calcein-AM confirmed cytoplasmic communication via nanotubes. Immunoreactive B cell lymphoma 2 (Bcl-2) and induced myeloid leukemia cell differentiation protein (Mcl-1), two major anti-apoptotic proteins, were present within the nanotubes. Downregulation of Mcl-1 by small interfering RNA in ASM cells significantly increased T cell apoptosis, whereas downregulation of Bcl-2 had no effect. Transfer of GFP-tagged Mcl-1 from ASM cells to CD4(+) T cells via the nanotubes confirmed directionality of transfer. In conclusion, activated T cells communicate with ASM cells via nanotube formation. Direct transfer of Mcl-1 from ASM to CD(+) T cells via nanotubes is involved in T cell survival. This study provides a novel mechanism of survival of CD4(+) T cells that is dependent on interaction with a structural cell.

Iron oxide nanoparticle-mediated development of cellular gap junction crosstalk to improve mesenchymal stem cells' therapeutic efficacy for myocardial infarction

Electrophysiological phenotype development and paracrine action of mesenchymal stem cells (MSCs) are the critical factors that determine the therapeutic efficacy of MSCs for myocardial infarction (MI). In such respect, coculture of MSCs with cardiac cells has windowed a platform for cardiac priming of MSCs. Particularly, active gap junctional crosstalk of MSCs with cardiac cells in coculture has been known to play a major role in the MSC modification through coculture. Here, we report that iron oxide nanoparticles (IONPs) significantly augment the expression of connexin 43 (Cx43), a gap junction protein, of cardiomyoblasts (H9C2), which would be critical for gap junctional communication with MSCs in coculture for the generation of therapeutic potential-improved MSCs. MSCs cocultured with IONP-harboring H9C2 (cocultured MSCs: cMSCs) showed active cellular crosstalk with H9C2 and displayed significantly higher levels of electrophysiological cardiac biomarkers and a cardiac repair-favorable paracrine profile, both of which are responsible for MI repair. Accordingly, significantly improved animal survival and heart function were observed upon cMSC injection into rat MI models compared with the injection of unmodified MSCs. The present study highlights an application of IONPs in developing gap junctional crosstalk among the cells and generating cMSCs that exceeds the reparative potentials of conventional MSCs. On the basis of our finding, the potential application of IONPs can be extended in cell biology and stem cell-based therapies.

MitoCeption as a new tool to assess the effects of mesenchymal stem/stromal cell mitochondria on cancer cell metabolism and function

Mitochondrial activity is central to tissue homeostasis. Mitochondria dysfunction constitutes a hallmark of many genetic diseases and plays a key role in tumor progression. The essential role of mitochondria, added to their recently documented capacity to transfer from cell to cell, obviously contributes to their current interest. However, determining the proper role of mitochondria in defined biological contexts was hampered by the lack of suitable experimental tools. We designed a protocol (MitoCeption) to directly and quantitatively transfer mitochondria, isolated from cell type A, to recipient cell type B. We validated and quantified the effective mitochondria transfer by imaging, fluorescence-activated cell sorting (FACS) and mitochondrial DNA analysis. We show that the transfer of minute amounts of mesenchymal stem/stromal cell (MSC) mitochondria to cancer cells, a process otherwise occurring naturally in coculture, results in cancer cell enhanced oxidative phosphorylation (OXPHOS) activity and favors cancer cell proliferation and invasion. The MitoCeption technique, which can be applied to different cell systems, will therefore be a method of choice to analyze the metabolic modifications induced by exogenous mitochondria in host cells.

Transplantation in end-stage pulmonary hypertension (Third International Right Heart Failure Summit, part 3)

The Third International Right Heart Summit was organized for the purpose of bringing an interdisciplinary group of expert physician-scientists together to promote dialogue involving emerging concepts in the unique pathophysiology, clinical manifestation, and therapies of pulmonary vascular disease (PVD) and right heart failure (RHF). This review summarizes key ideas addressed in the section of the seminar entitled "Transplantation in End-Stage Pulmonary Hypertension." The first segment focused on paradigms of recovery for the failing right ventricle (RV) within the context of lung-alone versus dual-organ heart-lung transplantation. The subsequent 2-part section was devoted to emerging concepts in RV salvage therapy. A presentation of evolving cell-based therapy for the reparation of diseased tissue was followed by a contemporary perspective on the role of mechanical circulatory support in the setting of RV failure. The final talk highlighted cutting-edge research models utilizing stem cell biology to repair diseased tissue in end-stage lung disease-a conceptual framework within which new therapies for PVD have potential to evolve. Together, these provocative talks provided a novel outlook on how the treatment of PVD and RHF can be approached.

Transfer of mitochondria via tunneling nanotubes rescues apoptotic PC12 cells

Tunneling nanotubes (TNTs) are F-actin-based membrane tubes that form between cells in culture and in tissues. They mediate intercellular communication ranging from electrical signalling to the transfer of organelles. Here, we studied the role of TNTs in the interaction between apoptotic and healthy cells. We found that pheochromocytoma (PC) 12 cells treated with ultraviolet light (UV) were rescued when cocultured with untreated PC12 cells. UV-treated cells formed a different type of TNT with untreated PC12 cells, which was characterized by continuous microtubule localized inside these TNTs. The dynamic behaviour of mCherry-tagged end-binding protein 3 and the accumulation of detyrosinated tubulin in these TNTs indicate that they are regulated structures. In addition, these TNTs show different biophysical properties, for example, increased diameter allowing dye entry, prolonged lifetime and decreased membrane fluidity. Further studies demonstrated that microtubule-containing TNTs were formed by stressed cells, which had lost cytochrome c but did not enter into the execution phase of apoptosis characterized by caspase-3 activation. Moreover, mitochondria colocalized with microtubules in TNTs and transited along these structures from healthy to stressed cells. Importantly, impaired formation of TNTs and untreated cells carrying defective mitochondria were unable to rescue UV-treated cells in the coculture. We conclude that TNT-mediated transfer of functional mitochondria reverse stressed cells in the early stages of apoptosis. This provides new insights into the survival mechanisms of damaged cells in a multicellular context.

Transcriptional profiling reveals crosstalk between mesenchymal stem cells and endothelial cells promoting prevascularization by reciprocal mechanisms

Mesenchymal stem cells (MSCs) show great promise in blood vessel restoration and vascularization enhancement in many therapeutic situations. Typically, the co-implantation of MSCs with vascular endothelial cells (ECs) is effective for the induction of functional vascularization in vivo, indicating its potential applications in regenerative medicine. The effects of MSCs-ECs-induced vascularization can be modeled in vitro, providing simplified models for understanding their underlying communication. In this article, a contact coculture model in vitro and an RNA-seq approach were employed to reveal the active crosstalk between MSCs and ECs within a short time period at both morphological and transcriptional levels. The RNA-seq results suggested that angiogenic genes were significantly induced upon coculture, and this prevascularization commitment might require the NF-κB signaling. NF-κB blocking and interleukin (IL) neutralization experiments demonstrated that MSCs potentially secreted IL factors including IL1β and IL6 to modulate NF-κB signaling and downstream chemokines during coculture. Conversely, RNA-seq results indicated that the MSCs were regulated by the coculture environment to a smooth muscle commitment within this short period, which largely induced myocardin, the myogenic co-transcriptional factor. These findings demonstrate the mutual molecular mechanism of MSCs-ECs-induced prevascularization commitment in a quick response.

Nanotubular crosstalk with distressed cardiomyocytes stimulates the paracrine repair function of mesenchymal stem cells

Mesenchymal stem cells (MSC) are known to repair broken heart tissues primarily through a paracrine fashion while emerging evidence indicate that MSC can communicate with cardiomyocytes (CM) through tunneling nanotubes (TNT). Nevertheless, no link has been so far established between these two processes. Here, we addressed whether cell-to-cell communication processes between MSC and suffering cardiomyocytes and more particularly those involving TNT control the MSC paracrine regenerative function. In the attempt to mimic in vitro an injured heart microenvironment, we developed a species mismatch coculture system consisting of terminally differentiated CM from mouse in a distressed state and human multipotent adipose derived stem cells (hMADS). In this setting, we found that crosstalk between hMADS and CM through TNT altered the secretion by hMADS of cardioprotective soluble factors such as VEGF, HGF, SDF-1α, and MCP-3 and thereby maximized the capacity of stem cells to promote angiogenesis and chemotaxis of bone marrow multipotent cells. Additionally, engraftment experiments into mouse infarcted hearts revealed that in vitro preconditioning of hMADS with cardiomyocytes increased the cell therapy efficacy of naïve stem cells. In particular, in comparison with hearts treated with stem cells alone, those treated with cocultured ones exhibited greater cardiac function recovery associated with higher angiogenesis and homing of bone marrow progenitor cells at the infarction site. In conclusion, our findings established the first relationship between the paracrine regenerative action of MSC and the nanotubular crosstalk with CM and emphasize that ex vivo manipulation of these communication processes might be of interest for optimizing current cardiac cell therapies.

Evidence for Transfer of Membranes from Mesenchymal Stem Cells to HL-1 Cardiac Cells

This study examined the interaction of mouse bone marrow mesenchymal stem cells (MSC) with cardiac HL-1 cells during coculture by fluorescent dye labeling and then flow cytometry. MSC were layered onto confluent HL-1 cell cultures in a 1 : 4 ratio. MSC gained gap junction permeant calcein from HL-1 cells after 4 hours which was partially reduced by oleamide. After 20 hours, 99% MSC gained calcein, unaffected by oleamide. Double-labeling HL-1 cells with calcein and the membrane dye DiO resulted in transfer of both calcein and DiO to MSC. When HL-1 cells were labeled with calcein and MSC with DiO, MSC gained calcein while HL-1 cells gained DiO. Very little fusion was observed since more than 90% Sca-1 positive MSC gained DiO from HL-1 cells while less than 9% gained gap junction impermeant CMFDA after 20 hours with no Sca-1 transfer to HL-1 cells. Time dependent transfer of membrane DiD was observed from HL-1 cells to MSC (100%) and vice versa (50%) after 20 hours with more limited transfer of CMFDA. These results demonstrate that MSC and HL-1 cells exchange membrane components which may account for some of the beneficial effect of MSC in the heart after myocardial infarction.

Mitochondrial transfer of induced pluripotent stem cell-derived mesenchymal stem cells to airway epithelial cells attenuates cigarette smoke-induced damage

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.

Mesenchymal stem cell delivery strategies to promote cardiac regeneration following ischemic injury

Myocardial infarction (MI) is one of the leading causes of mortality worldwide and is associated with irreversible cardiomyocyte death and pathological remodeling of cardiac tissue. In the past 15 years, several animal models have been developed for pre-clinical testing to assess the potential of stem cells for functional tissue regeneration and the attenuation of left ventricular remodeling. The promising results obtained in terms of improved cardiac function, neo-angiogenesis and reduction in infarct size have motivated the initiation of clinical trials in humans. Despite the potential, the results of these studies have highlighted that the effective delivery and retention of viable cells within the heart remain significant challenges that have limited the therapeutic efficacy of cell-based therapies for treating the ischemic myocardium. In this review, we discuss key elements for designing clinically translatable cell-delivery approaches to promote myocardial regeneration. Key topics addressed include cell selection, with a focus on mesenchymal stem cells derived from the bone marrow (bMSCs) and adipose tissue (ASCs), including a discussion of their potential mechanisms of action. Natural and synthetic biomaterials that have been investigated as injectable cell delivery vehicles for cardiac applications are critically reviewed, including an analysis of the role of the biomaterials themselves in the therapeutic scheme.

Functional consequences of a tissue-engineered myocardial patch for cardiac repair in a rat infarct model

Cell therapies have emerged as a promising treatment for the prevention of heart failure after myocardial infarction (MI). This study evaluated the capacity of an aligned, fibrin-based, stretch-conditioned cardiac patch consisting of either the native population or a cardiomyocyte (CM)-depleted population (i.e., CM+ or CM- patches) of neonatal rat heart cells to ameliorate left ventricular (LV) remodeling in the acute-phase postinfarction in syngeneic, immunocompetent rats. Patches were exposed to 7 days of static culture and 7 days of cyclic stretching prior to implantation. Within 1 week of implantation, both patches became vascularized, and non-CMs began migrating from CM+ patches. By week 4, patches had been remodeled into collagenous tissue, and live, elongated, donor CMs were found within grafted CM+ patches. Significant improvement in cardiac contractile function was seen with the administration of the CM+ patch (ejection fraction increased from 35.1% ± 4.0% for MI only to 58.8% ± 7.3% with a CM+ patch, p<0.05) associated with a 77% reduction in infarct size (61.3% ± 7.9% for MI only, 13.9% ± 10.8% for CM+ patch, p<0.05), and the elimination of LV free-wall thinning. Decreased infarct size and reduced wall thinning also occurred with the administration of the CM- patch (infarct size 36.9% ± 10.2%, LV wall thickness: 1058.2 ± 135.4 μm for CM- patch, 661.3 ± 37.4 μm for MI only, p<0.05), but without improvements in cardiac function. Approximately 36.5% of the transplanted CMs survived at 4 weeks; however, they remained separated and electrically uncoupled from the host myocardium by a layer of CM-free tissue, which suggests that the benefits of CM+ patch transplantation resulted from paracrine mechanisms originating from CMs. Collectively, these observations suggest that the transplantation of CM-containing engineered heart tissue patches can lead to dramatic improvements in cardiac function and remodeling after acute MI.

Characterization of contracting cardiomyocyte colonies in the primary culture of neonatal rat myocardial cells: a model of in vitro cardiomyogenesis

The unmet clinical need for myocardial repair after irreversible ischemic injury requires a better understanding of the biological properties of cardiac stem cells (CSCs). Using a primary culture of neonatal rat myocardial cells, we describe the formation and maturation of contracting cardiomyocyte colonies stemming from c-kit(+), Sca(+), or Isl1(+) CSCs, which occurs in parallel to the hypertrophy of the major cardiac myocyte population. The contracting cardiomyocyte colonies (~1-2 colonies per 1 × 10(5) of myocardial cells) were identified starting from eighth day of culturing. At first, spontaneous weak, asynchronous, and arrhythmic contractions of the colonies at a rate of 2-3 beats/min were registered. Over time, the contractions of the colonies became more synchronous and frequent, with a contraction rate of 58-60 beats/min by the 30th day of culturing. The colonies were characterized by the CSCs subtype-specific pattern of growth and structure. The cells of the colonies were capable of spontaneous cardiomyogenic differentiation, demonstrating expression of both sarcomeric α-actinin and α-sarcomeric actin as well as the maturation of contractile machinery and typical Ca(2+) responses to caffeine (5 mМ) and K(+) (120 mМ). Electromechanical coupling, characterized by cardiac muscle-specific Ca(2+)-induced Ca(2+) release, was evident at 3 weeks of culturing. Thus, the co-cultivation of CSCs with mature cardiac cells resulted in the formation of contracting cardiomyocyte colonies, resembling the characteristics of in vivo cardiomyogenesis. The proposed model can be used for the investigation of fundamental mechanisms underlying cardiomyogenic differentiation of CSCs as well as for drug testing and/or other applications.

When Cells Become Organelle Donors

More than 40 variations of intercellular organelle transfer, such as a mitochondria or lysosome originating in one cell being transported to another cell, have been described. We review the mechanisms and subcellular structures by which, and conditions under which, transfer occurs, with particular attention paid to the role of external cell stress in activating transfer. We propose a research agenda for answering key questions in this burgeoning field.

Mesenchymal stem or stromal cells: a review of clinical applications and manufacturing practices

Mesenchymal stem cells (MSCs) have recently generated great interest in the fields of regenerative medicine and immunotherapy due to their unique biologic properties. In this review we attempt to provide an overview of the current clinical status of MSC therapy, primarily focusing on immunomodulatory and regenerative or tissue repair applications of MSCs. In addition, current manufacturing is reviewed with attention to variation in practices (e.g., starting material, approach to culture and product testing). There is considerable variation among the 218 clinical trials assessed here; variations include proposed mechanisms of action, optimal dosing strategy, and route of administration. To ensure the greatest likelihood of success in clinical trials as the field progresses, attention must be given to the optimization of MSC culture.

Membrane nanotubes: novel communication between distant cells

The many kinds of cell structures involved in cell-cell communication include tight junction, adherens junction and gap junction, but almost all are between adjacent cells. Recently, a general and dynamic membrane tether, termed tunneling nanotubes or membrane nanotubes (MNTs), was discovered to be involved in communication between distant cells. By facilitating intercellular communication, MNTs contribute to many biological functions and pathologic changes in cells. Many works have revealed the structure, formation and functional properties of MNTs. However, as novel structures, further research is needed.

Bone regeneration by transplantation of human mesenchymal stromal cells in a rabbit mandibular distraction osteogenesis model

Ex vivo expanded mesenchymal stromal cells (MSCs) represent a potential cell population for tissue regeneration strategy. Xenogeneic transplantation using human MSCs (hMSCs) can be an approach to reveal what hMSCs guide in bone regeneration with distinguishable gene expression from a host animal. In this study, we investigated the regenerating effect of hMSCs varying injection time point in a rabbit distraction osteogenesis model. Undifferentiated hMSCs (2×10(6) cells) were injected transcutaneously into the osteotomy site of one side of the mandible 1 day before the onset of distraction (Group 1) or after distraction (Group 2). The contralateral side of the mandible, which was subjected to distraction, but no hMSC injection, was used as the control in each group. hMSCs showed lack of major histocompatibility complex class II expression and suppression of xenogeneic lymphocyte proliferation stimulated by a proinflammatory cytokine. A microcomputed tomography-based evaluation showed a significant increase in new bone volume in the distracted callus in Group 1 compared to the contralateral side. Injection of hMSCs increased the bone mineral density (BMD) of the regenerated bone in both Group 1 and 2, although the former had a higher BMD than the latter. hMSCs of Group 1 subjected to distraction after injection expressed insulin-like growth factor-1 (IGF-1) and fibronectin (FN), while the expression of most osteoblast differentiation-related markers and growth factors was negligible. These results demonstrated that hMSCs exerted immune suppressive behavior in rabbit T cells in vitro, and hMSC transplantation into the distracted callus of a rabbit model provided osteogenic benefits that were more pronounced when the hMSCs were injected just before distraction than at the end of distraction. The beneficial effect of hMSCs might be mediated, partly by the expression of matrix proteins or IGF-1, which are known to favor bone formation.

Comparison of the direct effects of human adipose- and bone-marrow-derived stem cells on postischemic cardiomyoblasts in an in vitro simulated ischemia-reperfusion model

Regenerative therapies hold a promising and exciting future for the cure of yet untreatable diseases, and mesenchymal stem cells are in the forefront of this approach. However, the relative efficacy and the mechanism of action of different types of mesenchymal stem cells are still incompletely understood. We aimed to evaluate the effects of human adipose- (hASC) and bone-marrow-derived stem cells (hBMSCs) and adipose-derived stem cell conditioned media (ACM) on the viability of cardiomyoblasts in an in vitro ischemia-reperfusion (I-R) model. Flow cytometric viability analysis revealed that both cell treatments led to similarly increased percentages of living cells, while treatment with ACM did not (I-R model: 12.13 ± 0.75%; hASC: 24.66 ± 2.49%; hBMSC: 25.41 ± 1.99%; ACM: 13.94 ± 1.44%). Metabolic activity measurement (I-R model: 0.065 ± 0.033; hASC: 0.652 ± 0.089; hBMSC: 0.607 ± 0.059; ACM: 0.225 ± 0.013; arbitrary units) and lactate dehydrogenase assay (I-R model: 0.225 ± 0.006; hASC: 0.148 ± 0.005; hBMSC: 0.146 ± 0.004; ACM: 0.208 ± 0.009; arbitrary units) confirmed the flow cytometric results while also indicated a slight beneficial effect of ACM. Our results highlight that mesenchymal stem cells have the same efficacy when used directly on postischemic cells, and differences found between them in preclinical and clinical investigations are rather related to other possible causes such as their immunomodulatory or angiogenic properties.

The promotion of bone regeneration by nanofibrous hydroxyapatite/chitosan scaffolds by effects on integrin-BMP/Smad signaling pathway in BMSCs

In bone tissue engineering, a combination of biomimetic nanofibrous scaffolds with renewable stem cells has recently emerged as a new strategy for promoting bone regeneration. We have previously developed a biomimetic nanocomposite nanofibrous scaffold of hydroxyapatite/chitosan (nHAp/CTS) [1]. However, the mechanism behind the supportive function of the scaffolds has not yet been adequately explored. Here, we evaluated the effect of nHAp/CTS seeded with bone marrow mesenchymal stem cells (BMSCs) on bone regeneration and examined the underlying mechanism in vitro and in vivo. The scaffolds of nHAp/CTS induced higher proliferation of BMSCs than membranous hydroxyapatite/chitosan (mHAp/CTS) and electrospun nanofibrous chitosan (nCTS) did. Interestingly, regardless the nanfibrous effect, nHAp/CTS and mHAp/CTS supported the spindle-shaped morphology, in contrast to the spherical shape of BMSCs on nCTS, indicating that HAp supports cell adhesion. Furthermore, the levels of the mRNA for Smad1, BMP-2/4, Runx2, ALP, collagen I, integrin subunits together with myosins were significantly up-regulated on nHAp/CTS whereas these genes were expressed at markedly low levels on mHAp/CTS and nCTS even in osteogenic medium. In addition, the critical proteins pSmad1/5/8 in BMP pathway showed clear nuclear localization and osteocalcin were significantly elevated on nHAp/CTS than mHAp/CTS (P < 0.01) and nCTS (P < 0.01). Similarly, the cells exhibited higher ALP activity on nHAp/CTS than mHAp/CTS (P < 0.01) and nCTS (P < 0.05). Therefore, the findings indicated the activating of intergrin-BMP/Smad signaling pathway of BMSCs on nHAp/CTS. Finally, in vivo, nHAp/CTS/BMSCs had a superior ability of bone reconstruction than other groups for cranial bone defects. In conclusion, our results demonstrated that nHAp/CTS scaffold promotes bone regeneration by supporting the adhesion, proliferation and activating integrin-BMP/Smad signaling pathway of BMSCs both in vitro and in vivo.

Mesenchymal stem cell-cardiomyocyte interactions under defined contact modes on laser-patterned biochips

Understanding how stem cells interact with cardiomyocytes is crucial for cell-based therapies to restore the cardiomyocyte loss that occurs during myocardial infarction and other cardiac diseases. It has been thought that functional myocardial repair and regeneration could be regulated by stem cell-cardiomyocyte contact. However, because various contact modes (junction formation, cell fusion, partial cell fusion, and tunneling nanotube formation) occur randomly in a conventional coculture system, the particular regulation corresponding to a specific contact mode could not be analyzed. In this study, we used laser-patterned biochips to define cell-cell contact modes for systematic study of contact-mediated cellular interactions at the single-cell level. The results showed that the biochip design allows defined stem cell-cardiomyocyte contact-mode formation, which can be used to determine specific cellular interactions, including electrical coupling, mechanical coupling, and mitochondria transfer. The biochips will help us gain knowledge of contact-mediated interactions between stem cells and cardiomyocytes, which are fundamental for formulating a strategy to achieve stem cell-based cardiac tissue regeneration.

Multifunction co-culture model for evaluating cell-cell interactions

Interactions within the same cell population (homotypic) and between different cell types (heterotypic) are essential for tissue development, repair, and homeostasis. To elucidate the underlying mechanisms of these cellular interactions, co-culture models have been used extensively to investigate the role of cell-cell physical contact, autocrine and/or paracrine interactions on cell function, as well as stem cell differentiation. Specifically, the mixed co-culture model is often optimal for interpreting the effects of cell-cell contact on cellular behavior in vitro, while indirect co-culture can be used to study the effects of paracrine signaling on cell reactions. Additionally, cell-cell contact can be controlled by establishing physical barriers, which are used to regulate spatial and temporal cell distribution patterns in co-culture. In this chapter, we describe a method for forming a removable permeable divider for temporally and spatially controlling cellular interactions. This model can be used to study the impact of both cell-cell contact and paracrine signaling on the behavior of the mixed population as a whole and on the response of each subpopulation of cells in co-culture.

Pretreatment of therapeutic cells with poly(ADP-ribose) polymerase inhibitor enhances their efficacy in an in vitro model of cell-based therapy in myocardial infarct

The potential of cell-based therapies in diseases involving ischemia-reperfusion is greatly hampered by the excessive loss of administered cells in the harsh and oxidative environment where these cells are supposed to act. Therefore, we investigated if inhibition of poly(ADP-ribose) polymerase (PARP) in the therapeutically added cells would lead to their increased viability and, subsequently, to an enhanced effect in an in vitro simulated ischemia-reperfusion (I-R) setting. Ischemic conditions were simulated by oxygen and glucose deprivation for 160 min using H9c2 rat cardiomyoblast cells. After 30 min of reperfusion, these cells received 4 types of treatments: no added cells (I-R model), fluorescently labeled (Vybrant DiD) therapeutic H9c2 cells with vehicle (H9c2) or PARP inhibitor (10 μM or 100 μM PJ34) pretreatment. We assessed viability (live, apoptotic and necrotic) of both ‘postischemic’ and therapeutic cells with flow cytometric analysis using calcein-AM/ethidium homodimer-2 fluorescent staining after 24 h of co-culture. Further measurements on necrosis and metabolic activity were performed using lactate dehydrogenase (LDH) release and resazurin based assays. The percentage of surviving therapeutic cells increased significantly with PARP inhibition (untreated, 52.02±5.01%; 10 μM PJ34, 63.38±4.50%; 100 μM PJ34, 64.99±3.47%). The percentage of necrotic cells decreased in a similar manner (untreated, 37.23±4.40%; 10 μM PJ34, 26.83±3.49%; 100 μM PJ34, 24.96±2.43%). Notably, the survival of the cells that suffered I-R injury was also significantly higher when treated with PARP-inhibited therapeutic cells (I-R model, 36.44±5.05%; H9c2, 42.81±5.11%; 10 μM PJ34, 52.07±5.80%; 100 μM PJ34, 54.95±5.55%), while necrosis was inhibited (I-R model, 43.64±4.00%; H9c2, 37.29±4.55%; 10 μM PJ34, 30.18±4.60%; 100 μM PJ34, 25.52±3.47%). In subsequent experiments, PARP inhibition decreased LDH-release of the observed combined cell population and enhanced the metabolic activity. Thus, our results suggest that pretreating the therapeutically added cells with a PARP inhibitor could be beneficial in the setting of cell-based therapies.

Cross talk between cardiac myocytes and fibroblasts: from multiscale investigative approaches to mechanisms and functional consequences

The heart is comprised of a syncytium of cardiac myocytes (CM) and surrounding nonmyocytes, the majority of which are cardiac fibroblasts (CF). CM and CF are highly interspersed in the myocardium with one CM being surrounded by one or more CF. Bidirectional cross talk between CM and CF plays important roles in determining cardiac mechanical and electrical function in both normal and diseased hearts. Genetically engineered animal models and in vitro studies have provided evidence that CM and CF can regulate each other's function. Their cross talk contributes to structural and electrical remodeling in both atria and ventricles and appears to be involved in the pathogenesis of various heart diseases that lead to heart failure and arrhythmia disorders. Mechanisms of CM-CF cross talk, which are not yet fully understood, include release of paracrine factors, direct cell-cell interactions via gap junctions and potentially adherens junctions and nanotubes, and cell interactions with the extracellular matrix. In this article, we provide an overview of the existing multiscale experimental and computational approaches for the investigation of cross talk between CM and CF and review recent progress in our understanding of the functional consequences and underlying mechanisms. Targeting cross talk between CM and CF could potentially be used therapeutically for the modulation of the cardiac remodeling response in the diseased heart and may lead to new strategies for the treatment of heart failure or rhythm disturbances.

Regenerative pulmonary medicine: potential and promise, pitfalls and challenges

BACKGROUND

Chronic lung diseases contribute significantly to the morbidity and mortality of the population. There are few effective treatments for many chronic lung diseases, and even fewer therapies that can arrest or reverse the progress of the disease.

DESIGN

In this review, we present the current state of regenerative therapies for the treatment of chronic lung diseases. We focus on endothelial progenitor cells, mesenchymal stem cells, and endogenous lung stem/progenitor cells; summarize the work to date in models of lung diseases for each of these therapies; and consider their potential benefits and risks as viable therapies for patients with lung diseases.

CONCLUSIONS

Cell-based regenerative therapies for lung diseases offer great promise, with preclinical studies suggesting that the next decade should provide the evidence necessary for their ultimate application to our therapeutic armamentarium.

Vascular smooth muscle cells initiate proliferation of mesenchymal stem cells by mitochondrial transfer via tunneling nanotubes

Multipotent mesenchymal stem cells (MSCs) are promising candidates for regenerative cell-based therapy. The mechanisms underlying MSC differentiation and other functions relevant to therapeutic avenues remain however a matter of debate. Recent reports imply a critical role for intercellular contacts in MSC differentiation. We studied MSC differentiation to vascular smooth muscle cells (VSMCs) in a coculture model using human primary MSCs and VSMCs. We observed that under these conditions, MSCs did not undergo the expected differentiation process. Instead, they revealed an increased proliferation rate. The upregulated MSC proliferation was initiated by direct contacts of MSCs with VSMCs; indirect coculture of both cell types in transwells was ineffective. Intercellular contacts affected cell growth in a unidirectional fashion, since VSMC proliferation was not changed. We observed formation of so-called tunneling nanotubes (TNTs) between MSCs and VSMCs that revealed an intercellular exchange of a fluorescent cell tracker dye. Disruption of TNTs using cytochalasin D or latrunculin B abolished increased proliferation of MSCs initiated by contacts with VSMCs. Using specific fluorescent markers, we identified exchange of mitochondria via TNTs. By generation of VSMCs with mitochondrial dysfunction, we show that mitochondrial transfer from VSMCs to MSCs was required to regulate MSC proliferation in coculture. Our data suggest that MSC interaction with other cell types does not necessarily result in the differentiation process, but rather may initiate a proliferative response. They further point to complex machinery of intercellular communications at the place of vascular injury and to an unrecognized role of mitochondria in these processes.

Intercellular cytosolic transfer correlates with mesenchymal stromal cell rescue of umbilical cord blood cell viability during ex vivo expansion

Background aims. Mesenchymal stromal cells (MSC) have been observed to participate in tissue repair and to have growth-promoting effects on ex vivo co-culture with other stem cells. Methods. In order to evaluate the mechanism of MSC support on ex vivo cultures, we performed co-culture of MSC with umbilical cord blood (UCB) mononuclear cells (MNC) (UCB-MNC). Results. Significant enhancement in cell growth correlating with cell viability was noted with MSC co-culture (defined by double-negative staining for Annexin-V and 7-AAD; P<0.01). This was associated with significant enhancement of mitochondrial membrane potential (P<0.01). We postulated that intercellular transfer of cytosolic substances between MSC and UCB-MNC could be one mechanism mediating the support. Using MSC endogenously expressing green fluorescent protein (GFP) or labeled with quantum dots (QD), we performed co-culture of UCB-MNC with these MSC. Transfer of these GFP and QD was observed from MSC to UCB-MNC as early as 24 h post co-culture. Transwell experiments revealed that direct contact between MSC and UCB-MNC was necessary for both transfer and viability support. UCB-MNC tightly adherent to the MSC layer exhibited the most optimal transfer and rescue of cell viability. DNA analysis of the viable, GFP transfer-positive UCB-MNC ruled out MSC transdifferentiation or MSC-UCB fusion. In addition, there was statistical correlation between higher levels of cytosolic transfer and enhanced UCB-MNC viability (P< 0.0001). Conclusions. Collectively, the data suggest that intercellular transfer of cytosolic materials could be one novel mechanism for preventing UCB cell death in MSC co-culture.

Mitochondria to the rescue

A new study using a mouse model of lung diseases is the first demonstration in vivo that bone marrow–derived stromal cells can repair tissue injury through the transfer of mitochondria (pages 759-765). This suggests that rescue of injured cells through mitochondrial transfer may be an important process in many diseases.

Mitochondrial transfer from bone-marrow-derived stromal cells to pulmonary alveoli protects against acute lung injury

Bone marrow-derived stromal cells (BMSCs) protect against acute lung injury (ALI). To determine the role of BMSC mitochondria in this protection, we airway-instilled mice first with lipopolysaccharide (LPS) and then with either mouse BMSCs (mBMSCs) or human BMSCs (hBMSCs). Live optical studies revealed that the mBMSCs formed connexin 43 (Cx43)-containing gap junctional channels (GJCs) with the alveolar epithelia in these mice, releasing mitochondria-containing microvesicles that the epithelia engulfed. The presence of BMSC-derived mitochondria in the epithelia was evident optically, as well as by the presence of human mitochondrial DNA in mouse lungs instilled with hBMSCs. The mitochondrial transfer resulted in increased alveolar ATP concentrations. LPS-induced ALI, as indicated by alveolar leukocytosis and protein leak, inhibition of surfactant secretion and high mortality, was markedly abrogated by the instillation of wild-type mBMSCs but not of mutant, GJC-incompetent mBMSCs or mBMSCs with dysfunctional mitochondria. This is the first evidence, to our knowledge, that BMSCs protect against ALI by restituting alveolar bioenergetics through Cx43-dependent alveolar attachment and mitochondrial transfer.

Multi-level communication of human retinal pigment epithelial cells via tunneling nanotubes

Background

Tunneling nanotubes (TNTs) may offer a very specific and effective way of intercellular communication. Here we investigated TNTs in the human retinal pigment epithelial (RPE) cell line ARPE-19. Morphology of TNTs was examined by immunostaining and scanning electron microscopy. To determine the function of TNTs between cells, we studied the TNT-dependent intercellular communication at different levels including electrical and calcium signalling, small molecular diffusion as well as mitochondrial re-localization. Further, intercellular organelles transfer was assayed by FACS analysis.

Methodology and Principal Findings

Microscopy showed that cultured ARPE-19 cells are frequently connected by TNTs, which are not attached to the substratum. The TNTs were straight connections between cells, had a typical diameter of 50 to 300 nm and a length of up to 120 µm. We observed de novo formation of TNTs by diverging from migrating cells after a short time of interaction. Scanning electron microscopy confirmed characteristic features of TNTs. Fluorescence microscopy revealed that TNTs between ARPE-19 cells contain F-actin but no microtubules. Depolymerisation of F-actin, induced by addition of latrunculin-B, led to disappearance of TNTs. Importantly, these TNTs could function as channels for the diffusion of small molecules such as Lucifer Yellow, but not for large molecules like Dextran Red. Further, organelle exchange between cells via TNTs was observed by microscopy. Using Ca²⁺ imaging we show the intercellular transmission of calcium signals through TNTs. Mechanical stimulation led to membrane depolarisation, which expand through TNT connections between ARPE-19 cells. We further demonstrate that TNTs can mediate electrical coupling between distant cells. Immunolabelling for Cx43 showed that this gap junction protein is interposed at one end of 44% of TNTs between ARPE-19 cells.

Conclusions and Significance

Our observations indicate that human RPE cell line ARPE-19 cells communicate by tunneling nanotubes and can support different types of intercellular traffic.

Mesenchymal stem cells transfer mitochondria to the cells with virtually no mitochondrial function but not with pathogenic mtDNA mutations

It has been reported that human mesenchymal stem cells (MSCs) can transfer mitochondria to the cells with severely compromised mitochondrial function. We tested whether the reported intercellular mitochondrial transfer could be replicated in different types of cells or under different experimental conditions, and tried to elucidate possible mechanism. Using biochemical selection methods, we found exponentially growing cells in restrictive media (uridine⁻ and bromodeoxyuridine [BrdU]⁺) during the coculture of MSCs (uridine-independent and BrdU-sensitive) and 143B-derived cells with severe mitochondrial dysfunction induced by either long-term ethidium bromide treatment or short-term rhodamine 6G (R6G) treatment (uridine-dependent but BrdU-resistant). The exponentially growing cells had nuclear DNA fingerprint patterns identical to 143B, and a sequence of mitochondrial DNA (mtDNA) identical to the MSCs. Since R6G causes rapid and irreversible damage to mitochondria without the removal of mtDNA, the mitochondrial function appears to be restored through a direct transfer of mitochondria rather than mtDNA alone. Conditioned media, which were prepared by treating mtDNA-less 143B ρ⁰ cells under uridine-free condition, induced increased chemotaxis in MSC, which was also supported by transcriptome analysis. Cytochalasin B, an inhibitor of chemotaxis and cytoskeletal assembly, blocked mitochondrial transfer phenomenon in the above condition. However, we could not find any evidence of mitochondrial transfer to the cells harboring human pathogenic mtDNA mutations (A3243G mutation or 4,977 bp deletion). Thus, the mitochondrial transfer is limited to the condition of a near total absence of mitochondrial function. Elucidation of the mechanism of mitochondrial transfer will help us create a potential cell therapy-based mitochondrial restoration or mitochondrial gene therapy for human diseases caused by mitochondrial dysfunction.

Mesenchymal stem cells and glioma cells form a structural as well as a functional syncytium in vitro

The interaction of human mesenchymal stem cells (hMSCs) and tumor cells has been investigated in various contexts. HMSCs are considered as cellular treatment vectors based on their capacity to migrate towards a malignant lesion. However, concerns about unpredictable behavior of transplanted hMSCs are accumulating. In malignant gliomas, the recruitment mechanism is driven by glioma-secreted factors which lead to accumulation of both, tissue specific stem cells as well as bone marrow derived hMSCs within the tumor. The aim of the present work was to study specific cellular interactions between hMSCs and glioma cells in vitro. We show, that glioma cells as well as hMSCs differentially express connexins, and that they interact via gap-junctional coupling. Besides this so-called functional syncytium formation, we also provide evidence of cell fusion events (structural syncytium). These complex cellular interactions led to an enhanced migration and altered proliferation of both, tumor and mesenchymal stem cell types in vitro. The presented work shows that glioma cells display signs of functional as well as structural syncytium formation with hMSCs in vitro. The described cellular phenomena provide new insight into the complexity of interaction patterns between tumor cells and host cells. Based on these findings, further studies are warranted to define the impact of a functional or structural syncytium formation on malignant tumors and cell based therapies in vivo.

Priming of mesenchymal stem cells with oxytocin enhances the cardiac repair in ischemia/reperfusion injury

Oxytocin stimulates the cardiomyogenesis of embryonic stem cells and adult cardiac stem cells. We previously reported that oxytocin has a promigratory effect on umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs). In this study, UCB-MSCs were cultured with oxytocin and examined for their therapeutic effect in an infarcted heart. UCB-MSCs were pretreated with 100 nM oxytocin and cardiac markers were assessed by immunofluorescence staining. Next, oxytocin-supplemented USC-MSCs (OT-USCs) were cocultured with hypoxia/reoxygenated neonatal rat cardiomyocytes and cardiac markers and dye transfer were then examined. For the in vivo study, ischemia/reperfusion was induced in rats, and phosphate-buffered saline (group 1), 1-day OT-USCs (group 2), or 7-day OT-USCs (group 3) were injected into the infarcted myocardium. Two weeks after injection, histological changes and cardiac function were examined. UCB-MSCs expressed connexin 43 (Cnx43), cardiac troponin I (cTnI), and α-sarcomeric actin (α-SA) after oxytocin supplementation and coculture with cardiomyocytes. Functional gap junction formation was greater in group 3 than in groups 1 and 2. Cardiac fibrosis and macrophage infiltration were lower in group 3 than in group 2. Restoration of Cnx43 expression was greater in group 3 than in group 2. Cnx43- and cTnI-positive OT-USCs in the peri-infarct zone were observed in group 2 and more frequently in group 3. The ejection fraction (EF) was increased in groups 2 and 3 in 2 weeks. The improved EF was sustained for 4 weeks only in group 3. Our findings suggest that the supplementation of UCB-MSCs with oxytocin can contribute to the cardiogenic potential for cardiac repair.

Long-distance intercellular connectivity between cardiomyocytes and cardiofibroblasts mediated by membrane nanotubes

AIMS

Intercellular interactions between cardiomyocytes (CMs) and cardiofibroblasts (FBs) are important in the physiological and pathophysiological heart. Understanding such interactions is important for developing effective heart disease therapies. However, until recently, little has been known about these interactions. We aimed to investigate structural and functional connections between CMs and FBs that are distinct from gap junctions.

METHODS AND RESULTS

By membrane dye staining, we observed long, thin membrane nanotubular structures containing actin and microtubules that connected neonatal rat ventricular CMs and FBs. By single-particle tracking, we observed vehicles moving between CMs and FBs within the membrane nanotubes. By dual colour staining, confocal imaging and flow cytometry, we observed mitochondria exchange between CMs and FBs in a coculture system. By combined atomic force microscopy (AFM) and confocal microscopy, we observed calcium signal propagation from AFM-stimulated CM (or FB) to unstimulated FB (or CM) via membrane nanotubes. By membrane and cytoskeleton staining, we observed similar nanotubular structures in adult mouse heart tissue, which suggests their physiological relevance.

CONCLUSIONS

As a novel type of CM to FB communication, membrane nanotubes observed in vitro and in vivo provide structural and functional connectivity between CMs and FBs over long distances.