Molecular mechanic sum of the regulation and dies regulation of bone homeostasis and Development of therapeutic approaches

为了阐明维持骨骼系统结构和功能稳态的调节机制，以及阐明骨骼稳态系统破坏导致疾病发展的分子机制，本研究从以下三个方面进行：（1）阐明骨形成机制和骨形成受损导致疾病的发病机制：我们已经确定ΔFosB是骨机械负荷的早期反应基因（JBMR'04）。快速诱导的ΔFosB与JunD形成异源二聚体，并刺激其靶基因。IL-11是靶基因之一，ΔFosB /JunD异源二聚体与IL-11基因启动子上的AP-1位点结合。我们还发现，在无BMP-2刺激的情况下，机械刺激通过激活PECd而增强Smad 1的磷酸化，并且磷酸化的Smad 1与IL-11基因上的ΔFosB/JunD形成复合物促进了I-11基因的完全转录激活。（二） ...更多信息 多发性骨髓瘤破坏性骨损害的致病机制的阐明：我们以前发现多发性骨髓瘤通过产生MIP-1（一种C-C趋化因子）来增强骨细胞的骨吸收。（Blood '02，'04）在本研究中，我们发现骨髓瘤细胞组成性分泌sFRP-2，一种Wnt信号传导抑制剂，其强烈抑制成骨细胞分化。此外，TGF-β还抑制成骨细胞的终末分化。由于TGF-β通过增强骨吸收从骨基质中释放，这些结果暗示骨髓瘤-骨微环境中存在强烈的骨形成抑制。如果加入TGF-β拮抗剂，骨髓瘤细胞抑制的骨形成得到改善，终末成骨细胞分化的恢复显著抑制骨髓瘤细胞生长。这些结果与骨髓瘤-骨微环境中存在恶性循环的观点一致，其中骨髓瘤细胞增强骨吸收并抑制骨形成以延长骨破坏，并且骨髓瘤细胞衍生的sFRP-2以及通过增强的骨吸收从骨基质释放的TGF-β协同抑制骨形成。此外，成骨细胞成熟的抑制为骨髓瘤细胞生长提供了合适的环境，这可以称为“骨髓瘤小生境”。Wnt抑制剂和TGF-β拮抗剂可以成为开发新治疗方式的靶点。(3)阐明骨骼循环紊乱引起的疾病的致病机制：我们以前曾报道，糖皮质激素过量通过内皮中超氧化物的产生增加而减少NO，从而抑制内皮依赖性血管舒张反应（Circ Res '03）。我们进一步发现，糖皮质激素过量显著抑制尿NOx排泄和主动脉eNOS表达。此外，匹伐他汀拮抗糖皮质激素的作用。这些观察结果支持了我们的假设，即糖皮质激素过量导致股骨颈微血管循环障碍，这在特发性股骨颈骨坏死的发展中起着重要作用。具有高全身血液水平的他汀类药物可以成为预防超氧化物引起的循环障碍的新候选药物。少

In order to clarify the regulatory mechanisms for maintaining structural and functional homeostasis of skeletal system, as well as to elucidate the molecular mechanisms for the development of disorders caused by disruption of the skeletal homeostatic system, the present study was conducted in the following three areas :(1) Elucidation of the mechanism of bone formation and the pathogenesis of disorders due to impaired bone formation: We have identified ΔFosB as an early response gene to mechanical load to the bone (JBMR'04). Rapidly induced ΔFosB forms heterodimers with JunD), and stimulated its target genes. IL-11 is one of the target genes, and ΔFosB /JunD heterodimer binds to a putative AP-1 site on the IL-11 gene promoter We also found that echanical stimuli enhances phosphorylation of Smadl via an activation of PECd without stimulation by BMP-2, and that phosphorylated Smadl forms complex with ΔFosB/JunD on the IL-11 gene promote fir full transcriptional activation of I-11 gene.(2 … More ) Elucidation of the pathogenic mechanisms 'for the destructive bone lesions by multiple myeloma: We have previously found that multiple myeloma enhances osteoclastic bone resorption via the production of MIP-1, a C-C chemokine. (Blood '02, '04) In the present study, we found that myeloma cells constitutively secrete sFRP-2, an inhibitor of Wnt signaling, which strongly inhibits osteoblast differentiation. In addition, TGF-β also suppressed terminal differentiation of osteoblasts. Because TGF-β is released from bone matrix by enhanced bone resorption, these results imply that there is a strong suppression ofbone formation in myeloma-bone microenvironment. If a TGF-β antagonist was added, the suppressed bone formation by myeloma cells was ameliorated, and the restoration of terminal osteoblastic differentiation markedly suppressed myeloma cell growth. These results are consistent with the notion that there is a vicious cycle in myeloma-bone microenvironment, in which myeloma cells enhance bone resorption and suppress bone formation to extend bone destruction, and myeloma cell-derived sFRP-2 as well as TGF-β released from the bone matrix by the enhanced bone resorption co-operatively suppress bone formation. Furthermore, the suppression of osteoblast maturation provides a suitable environment for myeloma cell growth which can be called "myeloma niche". Wnt inhibitors and TGF-β antagonists can be targets for the development of new therapeutic modalities.(3) Elucidation of the pathogenic mechanisms for disorders caused by disturbances in skeletal circulation: We have previously reported that glucocorticoid excess suppresses endothelium-dependent vasodilatory responses via a reduction in NO by an enhanced production of superoxides in the endothelium (Circ Res '03). We further found that glucocorticoid excess markedly suppresses urinary NOx excretion and aortic eNOS expression. In addition, pitavastatin antagonizes the effects of glucocorticoids. These observations support our hypothesis that glucocorticoid excess causes circulatory disturbances in microvessels of the femoral neck, which plays an important role in the development of idiopathic osteonecrosis of the femoral neck. Statins with high systemic blood levels can be a new candidate for the prevention of superoxide-induced circulatory disturbances. Less