Glucose dependent miR-451a expression contributes to parathyroid hormone mediated osteoblast differentiation

Parathyroid hormone (PTH; amino acid 1-34, known as teriparatide) has reported promoting differentiation and glucose uptake in osteoblasts. However, how PTH regulates glucose metabolism to facilitate osteoblast differentiation is not understood. Here, we report that PTH promotes glucose dependent miR-451a expression which stimulates osteoblast differentiation. In addition to glucose uptake, PTH suppresses AMPK phosphorylation via PI3K-mTOR-AKT axis thereby preventing phosphorylation and inactivation of octamer-binding transcription factor 1 (OCT-1) which has been reported to act on the promoter region of miR-451a. Modulation of AMPK activity controls miR-451a levels in differentiating osteoblasts. Moreover, pharmacological inhibition of PI3K-mTOR-AKT axis suppressed miR-451a via increased AMPK activity. We report that this glucose regulated miRNA is an anabolic target and transfection of miR-451a mimic induces osteoblast differentiation and mineralization in vitro. These actions were mediated through the suppression of Odd-skipped related 1 (Osr1) and activation of Runx2 transcription. When injected in vivo, the miR-451a mimic significantly increased osteoblastogenesis, mineralization, reversed ovariectomy induced bone loss and improved bone strength. Together, these findings suggest that enhanced osteoblast differentiation associated with bone formation in case of PTH therapy is also a consequence of elevated miR-451a levels via glucose regulation. Consequently, this miRNA has the potential to be a therapeutic target for conditions of bone loss.