IADR Abstract Archives
Control of Hypoxia-inducible Factor-2α Is Critical to Maitain Bone Homeostasis
Objectives: Bone homeostasis is maintained by balance between osteoclastic and osteoblastic activities. Deregulation of bone homeostasis causes pathophysiological bone diseases such as osteoporosis, which is the most common metabolic bone disease. The bone microenvironments are hypoxic, and hypoxia-inducible factor (HIF) is known to play notable roles in bone remodeling. However, the relevant functions of HIF-2α are not well understood. First of all, we confirm that HIF-2α deficiency in calvarial defect mouse models increases bone regeneration by affecting the differentiation of osteoblasts. We hypothesized that Hif-2α is inhibited bone formation by controlling osteoblast differentiation.
Methods: Osteoporosis animal model were used for in vivo studies. The surgical osteoporosis model was induced by ovariectomy in wild type, EPAS1 knock out and EPAS1 conditional knock out mice. EPAS1-induced regulation of bone homeostasis were examined by micro-CT and bone histomorphometry analysis. Primary cultured pre-osteoblast were used for in vitro experiment. Expression levels of EPAS1 and osteoblast differentiation related genes were examined by immunostaining, RT-PCR and qRT-PCR during osteoblast differentiation. Regulation of osteoblast differentiation by EPAS1 was determined by infected with EPAS1 adenovirus or transfected with EPAS1 siRNA in primary cultured pre-osteoblasts.
Results: Our in vitro results indicated that Hif-2α inhibits osteoblast differentiation by suppression of osteoblast-related markers, including Bglap and Cbfa1 and Tnsfsf11. Furthermore, we confirmed the upregulation of Twist2 in HIF-2a-overexpressing cells. Our results indicated that HIF-2α inhibits osteoblast differentiation by targeting Twist2. Additionally, we found that HIF-2α overexpression enhanced the transcript level of Tnfsf11 and the ratio of Tnfsf11 to Opg (a decoy receptor for RANKL) during the differentiation of calvarial pre-osteoblasts. Our in vivo results indicated that HIF-2α deficiency alleviated ovariectomy- and aging-induced bone loss, osteoblast-specific EPAS1 knockout mice increased bone mass.
Conclusions: Collectively, our results suggest that upregulation of HIF-2α was induced inhibition of osteoblast differentiation and is critical for the maintenance of bone homeostasis.
Methods: Osteoporosis animal model were used for in vivo studies. The surgical osteoporosis model was induced by ovariectomy in wild type, EPAS1 knock out and EPAS1 conditional knock out mice. EPAS1-induced regulation of bone homeostasis were examined by micro-CT and bone histomorphometry analysis. Primary cultured pre-osteoblast were used for in vitro experiment. Expression levels of EPAS1 and osteoblast differentiation related genes were examined by immunostaining, RT-PCR and qRT-PCR during osteoblast differentiation. Regulation of osteoblast differentiation by EPAS1 was determined by infected with EPAS1 adenovirus or transfected with EPAS1 siRNA in primary cultured pre-osteoblasts.
Results: Our in vitro results indicated that Hif-2α inhibits osteoblast differentiation by suppression of osteoblast-related markers, including Bglap and Cbfa1 and Tnsfsf11. Furthermore, we confirmed the upregulation of Twist2 in HIF-2a-overexpressing cells. Our results indicated that HIF-2α inhibits osteoblast differentiation by targeting Twist2. Additionally, we found that HIF-2α overexpression enhanced the transcript level of Tnfsf11 and the ratio of Tnfsf11 to Opg (a decoy receptor for RANKL) during the differentiation of calvarial pre-osteoblasts. Our in vivo results indicated that HIF-2α deficiency alleviated ovariectomy- and aging-induced bone loss, osteoblast-specific EPAS1 knockout mice increased bone mass.
Conclusions: Collectively, our results suggest that upregulation of HIF-2α was induced inhibition of osteoblast differentiation and is critical for the maintenance of bone homeostasis.