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动态平衡的调控机制，以及阐明骨骼动态平衡系统紊乱导致疾病发生的分子机制，本研究从以下三个方面进行了研究：(1)阐明骨形成的机制和骨形成障碍的发病机制：我们已将ΔFosB确定为对骨的机械负荷的早期反应基因(JBMR‘04)。快速诱导ΔFosB与JUND形成异源二聚体，并激活其靶基因。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，机械刺激通过激活PECD而增强Smad1的磷酸化，而不受BMP-2的刺激，并且磷酸化的Smad1与IL-11基因上的ΔFosB/Jund形成复合体，促进I-11基因的全面转录激活(2…)。更多)阐明多发性骨髓瘤破坏性骨损害的发病机制：我们先前发现多发性骨髓瘤通过产生C-C趋化因子MIP-1促进破骨细胞性骨吸收。(血液‘02，’04)在本研究中，我们发现骨髓瘤细胞结构性地分泌SFRP-2，这是一种Wnt信号的抑制剂，它强烈地抑制成骨细胞的分化。此外，转化生长因子-β还抑制成骨细胞的终末分化。由于转化生长因子-β通过促进骨吸收而从骨基质中释放出来，这些结果表明骨髓瘤-骨微环境对骨形成有很强的抑制作用。如果加入转化生长因子-β拮抗剂，骨髓瘤细胞抑制的骨形成得到改善，成骨细胞终末分化的恢复明显抑制骨髓瘤细胞的生长。这些结果与骨髓瘤-骨微环境中骨髓瘤细胞促进骨吸收和抑制骨形成以扩大骨破坏的恶性循环是一致的，骨髓瘤细胞来源的sFRP-2和骨基质通过促进骨吸收而释放的转化生长因子-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的生长提供了合适的环境，可以称之为骨髓瘤利基。WNT抑制剂和转化生长因子-β拮抗剂可作为开发新的治疗方法的靶点。(3)阐明骨骼循环障碍引起的疾病的发病机制：我们先前已报道，糖皮质激素过量通过促进内皮中超氧化物的产生而减少NO，从而抑制内皮依赖性的血管扩张反应(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，匹伐他汀还能拮抗糖皮质激素的作用。这些观察结果支持我们的假设，即糖皮质激素过量导致股骨颈微血管的循环障碍，这在特发性股骨颈骨坏死的发生发展中起着重要作用。他汀类药物具有较高的全身血液水平，可作为预防超氧物引起的循环障碍的新候选药物。较少

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