Conditional Disruption of miR17∼92 in Osteoclasts Led to Activation of Osteoclasts and Loss of Trabecular Bone in Part Through Suppression of the miR17-Mediated Downregulation of Protein-Tyrosine Phosphatase-oc in Mice

This study sought to understand the regulation of an osteoclastic protein-tyrosine phosphatase (PTP-oc), a positive regulator of osteoclast activity. Our past studies suggested that PTP-oc is regulated posttranscriptionally. The 3′-untranslated region (UTR) of PTP-oc mRNA contains a target site for miR17. During osteoclastic differentiation, there was an inverse relationship between the cellular levels of miR17 (expressed as one of the six cluster genes of miR17∼92) and PTP-oc mRNA. Overexpression of pre-miR17∼92 in mouse osteoclast precursors reduced PTP-oc mRNA level and the size of the derived osteoclasts, whereas deletion of miR17∼92 or inhibition of miR17 resulted in the formation of larger osteoclasts containing more nuclei that expressed higher PTP-oc mRNA levels and created larger resorption pits. Thus, PTP-oc–mediated osteoclast activation is modulated in part by miR17∼92, particularly miR17. The miR17∼92 osteoclast conditional knockout (cKO) mutants, generated by breeding miR17∼92^loxp/loxp mice with Ctsk-Cre mice, had lower trabecular bone volume/total volume (Tb.BV/TV), trabecular bone mineral density (Tb.BMD), trabecular connectivity density (Tb.Conn-Dens), trabecular number (Tb.N), and trabecular thickness (Tb.Th), but larger trabecular separation (Tb.Sp), and greater bone resorption without a change in bone formation compared to littermate controls. The cKO marrow-derived osteoclasts were twice as large, contained twice as many nuclei, and produced twice as large resorption pits as osteoclasts of littermate controls. The expression of genes associated with osteoclast activation was increased in cKO osteoclasts, suggesting that deletion of miR17∼92 in osteoclasts promotes osteoclast activation. The cKO osteoblasts did not show differences in cellular miR17 level, alkaline phosphatase activity, and bone nodule formation ability. In conclusion, miR17-92 negatively regulates the osteoclast activity, in part via the miR17-mediated suppression of PTP-oc in osteoclasts.