Abstract

Microvesicles (MV) (also know as exosomes) are small membrane-bound vesicles released by numerous cell types that contain proteins, mRNA and microRNA. We found that MV from activated monocytes drove survival and differentiation in naïve cells. We therefore were interested in understanding the content of MV produced by activated mononuclear phagocytes. Purified peripheral blood monocytes were treated in vitro for 24 h with or without the monocyte survival factors, GM-CSF or M-CSF, respectively. Examination of monocytes and macrophages by electron microscopy or culture supernatants by flow cytometry demonstrated that monocytes produced MV, which quantitatively increased upon differentiation. Treatment with GM-CSF resulted in more MV production than M-CSF-treated monocytes. To examine whether MV from differentiated cells induced myeloid maturation, the MV were collected and added to fresh monocytes; only MV derived from GM-CSF treated cells induced differentiation of naïve monocytes into macrophages. We next hypothesized that expression of microRNA contained in the MV modulated differentiation of monocytes. Profiling of MV from GM-CSF and M-CSF derived macrophages revealed only two significantly expressed microRNAs. We found that mir-155 was significantly elevated by two-fold in MV from GM-CSF-treated cells, while mir-340 was significantly increased seven-fold in M-CSF-derived MV. Notably, mir- 223 was the highest expressed microRNA in MV from both GM-CSF and M-CSF-treated cells. Recent data suggest that expression of mir-223 regulates myeloid, granulocytic and osteoclasts differentiation, and has a role in hematopoietic stem cell proliferation. While mir-223 is present in MV from both GM-CSF and M-CSF treated cells, it is possible that the low abundance of MV produce from M-CSF-treated cells resulted in less effective concentration to induce differentiation. In this model, it is also possible that regulation of proteins targeted by the increase in mir-155 and decrease mir-340 in the GM-CSF-derived MV are responsible for myeloid differentiation. Since changes in microRNA expression including mir-223 has been reported in AML, our data suggest that myeloid-derived MV in the peripheral blood containing mir-223 may be altered contributing to leukemogenesis.

Disclosures: No relevant conflicts of interest to declare.

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