Osteoblast-derived PTHrP is a physiological regulator of bone formation

Parathyroid hormone-related protein (PTHrP) acts as a paracrine regulator in several tissues, and its physiological roles also extend to bone. In this issue of the JCI, Miao et al. demonstrate that osteoblast-specific ablation of Pthrp in mice results in osteoporosis and impaired bone formation both in vivo and ex vivo (see the related article beginning on page 2402). These mice recapitulate the phenotype of mice with haploinsufficiency of Pthrp. The findings demonstrate that PTHrP plays a central role in the physiological regulation of bone formation, by promoting recruitment and survival of osteoblasts, and probably plays a role in the physiological regulation of bone resorption, by enhancing osteoclast formation. This has implications for both our understanding of the pathogenesis of osteoporosis and its treatment.