SYNOPSIS
Bone is one of the most important oral tissues. Osteoclasts play important roles in bone tissue engineering. Previously, we profiled microRNA (miRNA) expression during osteoclastogenesis using microarrays. miRNAs are small, noncoding RNAs that are involved in various biological processes, including cellular differentiation, proliferation, apoptosis, and organ development. Recently, the presence of miRNAs in extracellular microvesicles was reported. It is not known whether osteoclasts secrete extracellular microvesicles containing miRNAs. We investigated miRNA expression in extracellular microvesicles in conditioned medium of cultured osteoclasts using RT-PCR. Specifically, we investigated eight miRNAs deemed important for osteoclastogenesis in our previous study: let-7e, miR-21, miR-33, miR-155, miR-210, miR-223, miR-378, and miR-1224. Of these, the expression levels of miR-378, miR-210, and miR-21 were very high, while no significant miR-33 or miR-1224 expression was detected. These results suggest that osteoclasts secrete extracellular microvesicles containing specific miRNAs, but that they do not contain the entire set of intracellular miRNAs.

Key words: MicroRNA, Extracellular Microvesicle, Exosome, Osteoclast