Coordinate regulation of residual bone marrow function by paracrine trafficking of AML exosomes

Abstract

We recently demonstrated that acute myeloid leukemia (AML) cell lines and patient-derived blasts release exosomes that carry RNA and protein; following an in vitro transfer, AML exosomes produce proangiogenic changes in bystander cells. We reasoned that paracrine exosome trafficking may have a broader role in shaping the leukemic niche. In a series of in vitro studies and murine xenografts, we demonstrate that AML exosomes downregulate critical retention factors (Scf, Cxcl12) in stromal cells, leading to hematopoietic stem and progenitor cell (HSPC) mobilization from the bone marrow. Exosome trafficking also regulates HSPC directly, and we demonstrate declining clonogenicity, loss of CXCR4 and c-Kit expression, and the consistent repression of several hematopoietic transcription factors, including c-Myb, Cebp-β and Hoxa-9. Additional experiments using a model of extramedullary AML or direct intrafemoral injection of purified exosomes reveal that the erosion of HSPC function can occur independent of direct cell–cell contact with leukemia cells. Finally, using a novel multiplex proteomics technique, we identified candidate pathways involved in the direct exosome-mediated modulation of HSPC function. In aggregate, this work suggests that AML exosomes participate in the suppression of residual hematopoietic function that precedes widespread leukemic invasion of the bone marrow directly and indirectly via stromal components.

Mesenchymal Stromal Cell-derived Extracellular Vesicles Promote Myeloid-biased Multipotent Hematopoietic Progenitor Expansion via Toll-Like Receptor Engagement

“…1B). Next, we generated EV preparations from all three sources according to protocols established in the lab (25,26). We characterized these EVs by transmission electron microscopy for morphology and size, nanoparticle tracking analysis for size and concentration, and Western analysis for characteristic vesicle-associated proteins.…”

“…We recently described the role of exosomes (a subtype of EVs, 30 -110 nm in diameter) released from leukemia cells and their ability to actively suppress HSPC function (25,26). Mesenchymal stromal cells similarly release EVs that confer regenerative capacity in several (non-hematopoietic) tissues (reviewed in Ref.…”

Extracellular vesicles impose quiescence on residual hematopoietic stem cells in the leukemic niche

“…Intriguingly, HSC in the leukemic niche enter quiescence through an unidentified process, yet appear to retain their repopulation capacity upon subsequent re-transplantation [22]. We recently showed that AML-EV, including exosomes, are highly abundant in microRNA (miR)-150 and miR-155, which both target the transcription factor c-Myb to suppress HSPC clonogenicity [17,[27][28][29]. We recently showed that AML-EV, including exosomes, are highly abundant in microRNA (miR)-150 and miR-155, which both target the transcription factor c-Myb to suppress HSPC clonogenicity [17,[27][28][29].…”

Proteomic analysis of the glutathione-deficient LEGSKO mouse lens reveals activation of EMT signaling, loss of lens specific markers, and changes in stress response proteins

“…Differential protein abundances between groups were determined by comparing the total reporter ion intensities using the Bioconductor package edgeR [10]. EdgeR was developed for serial analysis of gene expression data but its modeling is flexible enough to handle a variety of other data types such as TMT reporter ion intensities [11–13]. …”