Mesenchymal stromal cells (MSC) have been shown to reverse radiation damage to marrow stem cells. We have evaluated the capacity of MSC-derived extracellular vesicles (MSC-EVs) to mitigate radiation injury to marrow stem cells at 4 hours to 7 days after irradiation. Significant restoration of marrow stem cell engraftment at 4, 24 and 168 hours post-irradiation by exposure to MSC-EVs was observed at 3 weeks to 9 months after transplant and further confirmed by secondary engraftment. Intravenous injection of MSC-EVs to 500cGy exposed mice led to partial recovery of peripheral blood counts and restoration of the engraftment of marrow. The murine hematopoietic cell line, FDC-P1 exposed to 500 cGy, showed reversal of growth inhibition, DNA damage and apoptosis on exposure to murine or human MSC-EVs. Both murine and human MSC-EVs reverse radiation damage to murine marrow cells and stimulate normal murine marrow stem cell/progenitors to proliferate. A preparation with both exosomes and microvesicles was found to be superior to either microvesicles or exosomes alone. Biologic activity was seen in freshly isolated vesicles and in vesicles stored for up to 6 months in 10% DMSO at −80°C. These studies indicate that MSC-EVs can reverse radiation damage to bone marrow stem cells.

Objective-Microvesicles have been shown to mediate intercellular communication. Previously, we have correlated entry of murine lung-derived microvesicles into murine bone marrow cells with expression of pulmonary epithelial cell-specific mRNA in these marrow cells. The present studies establish that entry of lung-derived microvesicles into marrow cells is a prerequisite for marrow expression of pulmonary epithelial cell-derived mRNA.Methods/Results-Murine bone marrow cells co-cultured with rat lung, but separated from them using a cell-impermeable membrane (0.4 micron pore size), were analyzed using species-specific primers (for rat or mouse). These studies revealed that surfactant B and C mRNA produced by murine marrow cells were of both rat and mouse origin. Similar results were obtained using murine lung cocultured with rat bone marrow cells or when bone marrow cells were analyzed for the presence of species-specific albumin mRNA after co-culture with rat or murine liver. These studies show that microvesicles both deliver mRNA to marrow cells and also mediate marrow cell transcription of tissue-specific mRNA. The latter likely underlies the longer term stable change in genetic phenotype which has been observed. We have also observed microRNA in lung-derived microvesicles and Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Conflict of interest disclosureNo financial interest/relationships with financial interest relating to the topic of this article have been declared. studies with RNase-treated microvesicles indicate that microRNA negatively modulates pulmonary epithelial cell-specific mRNA levels in co-cultured marrow cells. In addition, we have also observed tissue-specific expression of brain, heart and liver mRNA in co-cultured marrow cells suggesting that microvesicle-mediated cellular phenotype change is a universal phenomena. NIH Public AccessConclusion-These studies suggest that cellular systems are more phenotypically labile then previously considered.

These findings suggest that circulating or MSC-EXOs may modulate pulmonary hypertensive effects based on their miR cargo. The ability of MSC-EXOs to reverse MCT-PH offers a promising potential target for new PAH therapies.

Growing evidence suggests that transcriptional regulators and secreted RNA molecules encapsulated within membrane vesicles modify the phenotype of target cells. Membrane vesicles, actively released by cells, represent a mechanism of intercellular communication that is conserved evolutionarily and involves the transfer of molecules able to induce epigenetic changes in recipient cells. Extracellular vesicles, which include exosomes and microvesicles, carry proteins, bioactive lipids, and nucleic acids, which are protected from enzyme degradation. These vesicles can transfer signals capable of altering cell function and/or reprogramming targeted cells. In the present review we focus on the extracellular vesicle-induced epigenetic changes in recipient cells that may lead to phenotypic and functional modifications. The relevance of these phenomena in stem cell biology and tissue repair is discussed.

Numerous animal studies have demonstrated that adult marrow-derived cells can contribute to the cellular component of the lung. Lung injury is a major variable in this process; however, the mechanism remains unknown. We hypothesize that injured lung is capable of inducing epigenetic modifications of marrow cells, influencing them to assume phenotypic characteristics of lung cells. We report that under certain conditions, radiation-injured lung induced expression of pulmonary epithelial cell-specific genes and prosurfactant B protein in cocultured whole bone marrow cells separated by a cell-impermeable membrane. Lung-conditioned media had a similar effect on cocultured whole bone marrow cells and was found to contain pulmonary epithelial cell-specific RNA-filled microvesicles that entered whole bone marrow cells in culture. Also, whole bone marrow cells cocultured with lung had a greater propensity to produce type II pneumocytes after transplantation into irradiated mice. These findings demonstrate alterations of marrow cell phenotype by lung-derived microvesicles and suggest a novel mechanism for marrow cell-directed repair of injured tissue.

Objective-Previous studies have demonstrated the production of various types of lung cells from marrow cells under diverse experimental conditions. Our aim was to identify some of the variables that influence conversion in the lung. Methods-In separate experiments, mice received various doses of total-body irradiation followed by transplantation with whole bone marrow or various subpopulations of marrow cells (Lin −/+ , ckit −/+ , Sca-1 −/+ ) from GFP + (C57BL/6-TgN[ACTbEGFP]1Osb) mice. Some were given intramuscular cardiotoxin and/or mobilized with granulocyte colony-stimulating factor (G-CSF).Results-The production of pulmonary epithelial cells from engrafted bone marrow was established utilizing green fluorescent protein (GFP) antibody labeling to rule out autofluorescence and deconvolution microscopy to establish the colocaliztion of GFP and cytokeratin and the absence of CD45 in lung samples after transplantation. More donor-derived lung cells (GFP + /CD45 − ) were seen with increasing doses of radiation (5.43% of all lung cells, 1200 cGy). In the 900-cGy group, 61.43% of GFP + /CD45 − cells were also cytokeratin + . Mobilization further increased GFP + / CD45 − cells to 7.88% in radiation-injured mice. Up to 1.67% of lung cells were GFP + /CD45 − in radiation-injured mice transplanted with Lin − , c-kit + , or Sca-1 + marrow cells. Lin + , c-kit − , and Sca-1 − subpopulations did not significantly engraft the lung. Conclusions-We have established that marrow cells are capable of producing pulmonary epithelial cells and identified radiation dose and G-CSF mobilization as variables influencing the production of lung cells from marrow cells. Furthermore, the putative lung cell-producing marrow cell has the phenotype of a hematopoietic stem cell.

Marrow stem cell regulation represents a complex and flexible system. It has been assumed that the system was intrinsically hierarchical in nature, but recent data has indicated that at the progenitor/stem cell level the system may represent a continuum with reversible alterations in phenotype occurring as the stem cells transit cell cycle. Short and long-term engraftment, in vivo and in vitro differentiation, gene expression, and progenitor numbers have all been found to vary reversibly with cell cycle. In essence, the stem cells appear to show variable potential, probably based on transcription factor access, as they proceed through cell cycle. Another critical component of the stem cell regulation is the microenvironment, so-called niches. We propose that there are not just several unique niche cells, but a wide variety of niche cells which continually change phenotype to appropriately interact with the continuum of stem cell phenotypes. A third component of the regulatory system is microvesicle transfer of genetic information between cells. We have shown that marrow cells can express the genetic phenotype of pulmonary epithelial cells after microvesicle transfer from lung to marrow cells. Similar transfers of tissue specific mRNA occur between liver, brain, and heart to marrow cells. Thus, there would appear to be a continuous genetic modulation of cells through microvesicle transfer between cells. We propose that there is an interactive triangulated Venn diagram with continuously changing stem cells interacting with continuously changing areas of influence, both being modulated by transfer of genetic information by microvesicles.

Cell phenotype alteration by cell-derived vesicles presents a new aspect for consideration of cell fate. Accumulating data indicates that vesicles from many cells interact with or enter different target cells from other tissues, altering their phenotype toward that of the cell releasing the vesicles. Cells may be changed by direct interactions, transfer of cell surface receptors or epigenetic reprogramming via transcriptional regulators. Induced epigenetic changes appear to be stable and result in significant functional effects. These data force a reconsideration of the cellular context in which transcription regulates the proliferative and differentiative fate of tissues and suggests a highly plastic cellular system, which might underlay a relatively stable tissue system. The capacity of marrow to convert to non-hematopoietic cells related to vesicle crosscommunication may underlie the phenomena of stem cell plasticity. Additionally, vesicles have promise in the clinical arenas of disease biomarkers, tissue restoration and control of neoplastic cell growth. KeywordsCell-derived vesicles; stem cell plasticity; epigenetic alteration; cellular injury; disease biomarker; tissue restoration IntroductionMolecular control of cellular differentiation and phenotype is well established, as is the central role of transcription factors. However, the cellular context in which this regulation takes place is less well established and concepts of the stability of cellular phenotypes may have, in fact, confused the field. The capacity of microvesicle transfer to alter genetic cell phenotype alters our perceptions of phenotype regulation and will be explored in depth here. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Mechanisms of Cellular ConversionThe capacity of cells to change phenotype has been clearly demonstrated by studies of cell fusion and nuclear transfer. Formation of heterokaryons by cell fusion showed that dormant gene expression programs can be activated [1]. Cell fusion has also been invoked to explain the phenotype shifts seen in experiments where bone marrow stem cells were transplanted into lethally irradiated mice, so-called "stem cell plasticity" [2]. Nuclear transfer was also established as another mode of dramatic alteration of cell phenotype, which in the extreme, could lead to the formation of a whole animal [3][4][5]. Organ regeneration in newts and salamanders has also been cited as examples of cellular fate change, although in these instances, production of differentiated cells from rare stem cell populations was never ruled out [6...