Endogenous parathyroid hormone (PTH) signals through osteoblasts via RANKL during fracture healing to affect osteoclasts.

AIM:To investigate the effect of endogenous PTH deficiency on osteoclasts during fracture healing and its mechanism. METHODS:A femoral fracture model was used to determine the role of endogenous PTH in fracture healing. Immunohistochemistry, qPCR, and Western blot were used to determine the potential functions and mechanisms of endogenous PTH. RESULT:In this study, we found that expression of RANKL and CK was lower in PTH knockout (KO) mice than in wild type (WT) mice. In vitro culture of osteoclasts showed that under the same stimulation, there was no statistical difference in the number of osteoclasts and the area of bone resorption areas in PTH WT mice and PTH KO mice. We found that a high concentration of RANKL could promote the number and activity of osteoclasts. Upon induction of osteoblasts in vitro, those from the PTH WT group expressed higher RANKL protein and mRNA than those from the PTH KO group. Lastly, we confirmed that the pathway promotes RANKL increase from osteoblasts. CONCLUSION:During fracture healing, endogenous PTH deficiency can affect osteoclast activity by reducing RANKL expression in osteoblasts.

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