Role of Estrogen Receptor beta in Normal and Aged Bone Healing.

摘要

Orthopaedic surgeons are challenged by impaired or delayed bone healing in elderly women, which requires prolongation of rehabilitation process or even induces high mortality. Up to date, there are no satisfactory therapeutic modalities for promoting aged bone healing clinically, and alternative therapeutic stratagem is therefore desirable. Bone healing recapitulates postnatal bone development. Direct periosteam-dependent bone formation (intramembranous ossification) and the formation of bone through a cartilage intermediate (endochondral ossification) are the two important processes during bone healing. Evidences from Estrogen Receptor beta (ERbeta), gene knockout female mouse studies have demonstrated that ERbeta signaling participates in inhibiting both intramembranous and endochondral ossification during bone development. Clinical biopsy data demonstrated that the number of ERbeta positive proliferative chondrocytes within fracture callus was increased in postmenopausal women. However, the role of ERbeta in normal and aged bone healing is not examined yet.;This study examined role of ERbeta in normal and aged bone healing and the future pharmaceutical application though the following part: 1) Establish an intramembranous ossification-dominant bone healing model. 2) Examine the role of ERbeta in normal bone healing though two models. 3) Examine the role of ERbeta in aged bone healing and investigate the potential therapeutical efficacy of an ERbeta antagonist PHTPP in aged bone healing.;Study I was to establish an intramembranous ossification dominant bone healing mouse model. Previous available mouse femoral shaft fracture model was a endochondral ossification dominant bone healing model. This model was technically difficult to generate high reproducibility and the inside metal stabilization devices prevented the application of high-resolution in vivo micro-CT monitoring due to the metal artifact. In order to examine the role of ERbeta in intramembranous ossification and apply the micro-CT monitoring technique, a drill-hole defect mouse model was developed. The study also confirmed bone healing was impaired in mice with ovariectomy-induced osteoporosis in drill-hole defect model.;Study II was to test the hypothesis that blockade of ERbeta could promote normal bone healing. ERbeta knockout mice were employed in this study and the hypothesis was examined in two models, the first is the traditional mouse femoral shaft fracture model, and the second is the drill-hole defect model that was developed in study I. Both models demonstrated that the bone healing in ERbeta knockout mice was enhanced in the early stage of neovascularization and the middle stage of ossification but not by the end of healing compare to the wild type mice.;Study III was designed to further investigate the role of ERbeta in aged bone healing. Femoral shaft fracture model was created in aged mice. The healing process was compared between the ERbeta knockout mice and wild type mice. The results demonstrated that ERbeta knockout mice was enhanced in the early stage of neovascularization, the middle stage of ossification and end stage of mechanical strength. The findings implied blockade of ERbeta can be considered as another therapeutic strategy for aged fracture healing. PHTPP (4-[2-Phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl] phenol), an ERbeta antagonist, was employed in aged mice femoral shaft fracture model. The bone healing quality of treated mice was compared with that of the vehicle control mice. It showed PHTPP treated mice had enhanced neovascularization, callus ossification and finally better mechanical properties than vehicle mice.;The present study depicted the role of ERbeta in normal and aged bone healing. Key processes including neovascularization, intramembranous and endochondral ossification were all enhanced by blockade of ERbeta, which led to fast callus formation, mineralization in normal bone and better mechanical properties in aged bone. ERbeta antagonist PHTPP could promote aged bone healing in mouse osteotomy model. This study raised an alternative therapeutic stratagem for bone healing and provided solid basis for future clinical trials.