Regulating Osteogenic Differentiation by Suppression of Exosomal MicroRNAs

Exosomes are membranous nanovesicles that naturally transport biomolecules, including miRNAs, and play critical roles in intercellular communication. We found that the growth condition milieu of preosteoblast exosomes contains a high level of the let-7 miRNAs. After blocking exosome secretion, we found that osteogenic differentiation of preosteoblasts (MC3T3-E1 cells) decreased significantly whereas addition of exosomes from growth condition recovered osteogenic ability. The expression levels of osteogenic markers in MC3T3-E1 cells were changed through the ectopic expression of the let-7 mimics or inhibitors. These findings suggest that this occurred due to the let-7 in the exosomes. Furthermore, exosomes whose let-7 was inactivated by inhibitors via electroporation efficiently lost their osteogenic differentiation capacity. Genetically modified exosomes may thus serve as highly effective biomaterials for developmental control, including osteogenesis regulation. Impact Statement We investigated the role of exosomes in osteogenesis and the use of miRNA inhibitor-transfected exosomes to control osteogenic differentiation. RNA-sequencing (RNA-seq) of exosomal miRNAs revealed that growth condition of milieu of preosteoblast exosomes harbors high levels of let-7, which plays a critical role in osteogenesis regulation. We modified exosomes by transfecting let-7 inhibitor into exosomes under growth condition in MC3T3-E1 cells and revealed that exosomes whose let-7 was inactivated by engineering lost the ability to recover osteogenic differentiation. Genetically modified exosomes may serve as powerful biomaterials for developmental control, including of osteogenesis regulation.