Biodistribution of Mesenchymal Stem Cell-Derived Extracellular Vesicles in a Radiation Injury Bone Marrow Murine Model

We have previously shown that injury induced by irradiation to murine marrow can be partially or completely reversed by exposure to human or murine mesenchymal stem cell (MSC)-derived extracellular vesicles (EVs). Investigation of the biodistribution of EVs in vivo is essential for understanding EV biology. In this study, we evaluated the DiD lipid dye labeled MSC-EV biodistribution in mice under different conditions, including different MSC-EV doses and injection schedules, time post MSC-EV injection, and doses of radiation. DiD-labeled MSC-EVs appeared highest in the liver and spleen; lower in bone marrow of the tibia, femur, and spine; and were undetectable in the heart, kidney and lung, while a predominant EV accumulation was detected in the lung of mice infused with human lung fibroblast cell derived EVs. There was significantly increased MSC-EV accumulation in the spleen and bone marrow (tibia and femur) post radiation appearing with an increase of MSC-EV uptake by CD11b+ and F4/80+ cells, but not by B220 cells, compared to those organs from non-irradiated mice. We further demonstrated that increasing levels of irradiation caused a selective increase in vesicle homing to marrow. This accumulation of MSC-EVs at the site of injured bone marrow could be detected as early as 1 h after MSC- EV injection and was not significantly different between 2 and 24 h post MSC-EV injection. Our study indicates that irradiation damage to hematopoietic tissue in the spleen and marrow targets MSC-EVs to these tissues

Daily rhythms influence the ability of lung-derived extracellular vesicles to modulate bone marrow cell phenotype.

Extracellular vesicles (EVs) are important mediators of intercellular communication and have been implicated in myriad physiologic and pathologic processes within the hematopoietic system. Numerous factors influence the ability of EVs to communicate with target marrow cells, but little is known about how circadian oscillations alter EV function. In order to explore the effects of daily rhythms on EV-mediated intercellular communication, we used a well-established model of lung-derived EV modulation of the marrow cell transcriptome. In this model, co-culture of whole bone marrow cells (WBM) with lung-derived EVs induces expression of pulmonary specific mRNAs in the target WBM. To determine if daily rhythms play a role in this phenotype modulation, C57BL/6 mice were entrained in 12-hour light/12-hour dark boxes. Lungs harvested at discrete time-points throughout the 24-hour cycle were co-cultured across a cell-impermeable membrane with murine WBM. Alternatively, WBM harvested at discrete time-points was co-cultured with lung-derived EVs. Target WBM was collected 24hrs after co-culture and analyzed for the presence of pulmonary specific mRNA levels by RT-PCR. In both cases, there were clear time-dependent variations in the patterns of pulmonary specific mRNA levels when either the daily time-point of the lung donor or the daily time-point of the recipient marrow cells was altered. In general, WBM had peak pulmonary-specific mRNA levels when exposed to lung harvested at Zeitgeber time (ZT) 4 and ZT 16 (ZT 0 defined as the time of lights on, ZT 12 defined as the time of lights off), and was most susceptible to lung-derived EV modulation when target marrow itself was harvested at ZT 8- ZT 12. We found increased uptake of EVs when the time-point of the receptor WBM was between ZT 20 -ZT 24, suggesting that the time of day-dependent changes in transcriptome modulation by the EVs were not due simply to differential EV uptake. Based on these data, we conclude that circadian rhythms can modulate EV-mediated intercellular communication

Expression of Cell Cycle–Related Genes With Cytokine-Induced Cell Cycle Progression of Primitive Hematopoietic Stem Cells

Primitive marrow lineage-negative rhodamine low and Hoechst low (LRH) stem cells isolated on the basis of quiescence respond to the cytokines thrombopoietin, FLT3L, and steel factor by synchronously progressing through cell cycle. We have now profiled the mRNA expression, as determined by real-time RT-PCR, of 47 hematopoietic or cell cycle-related genes, focusing on the variations in the cell cycle regulators with cycle transit. LRH stem cells, at isolation, showed expression of all interrogated genes, but at relatively low levels. In our studies, there was a good deal of consistency with regard to cell cycle regulatory genes involved in the G1/S progression point of LRH murine stem cells. The observed pattern of expression of cyclin A2 is consistent with actions at these phases of cell cycle. Minimal elevations were seen at 16 h with higher elevations at 24, 32, 40, and 48 h times encompassing S, G2, and M phases. CDK2 expression pattern was also consistent with a role in G1/S transition with a modest elevation at 24 h and more substantial elevation at 32 h. The observed pattern of expression of cyclin F mRNA with marked elevations at 16–40 h was also consistent with actions in S and G2 phases. Cyclin D1 expression pattern was less consistent with its known role in G1 progression. The alterations in multiple other cell cycle regulators were consistent with previous information obtained in other cell systems. The cycle regulatory mechanics appears to be preserved across broad ranges of cell types