Study on mechanism of the coupling between bone resorption and bone formation

本研究的目的：RANKL的发现阐明了破骨细胞分化和功能受成骨细胞调控的机制。骨保护素（OPG）是RANKL的可溶性诱饵受体，可抑制破骨细胞的分化和功能。OPG缺陷（OPG-/-）小鼠表现出严重的骨质疏松症引起的骨细胞骨吸收增强。OPG缺乏可导致幼年型佩吉特病。先前的形态学研究表明，成骨细胞骨形成在OPG-/-小鼠中被激活。这些结果表明，成骨细胞骨吸收巧合地诱导成骨细胞骨形成的未知因素（称为耦合因子）。在本研究中，我们研究了一种可能性，即成熟的破骨细胞产生细胞因子，影响骨代谢，使用成熟的破骨细胞与LPS处理。以OPG -/-小鼠为研究对象，探讨了OPG -/-小鼠骨组织中是否存在这种偶联因子。 关于我们 Lly参与骨髓巨噬细胞（破骨细胞前体）向破骨细胞的分化。p38 MAP激酶信号通路在成熟破骨细胞中全部死亡。（2）成熟的破骨细胞在LPS刺激下产生成骨细胞活化因子，但不产生骨吸收因子IL-1和IL-6。（3）OPG-/-小鼠血中骨钙素和碱性磷酸酶水平明显升高。骨组织形态计量学研究表明，OPG-/-小鼠的骨吸收和骨形成均被激活。（4）OPG-/-小鼠血清可溶性RANKL水平也升高。（5）1，25（OH）_2D_3可使OPG-/-小鼠和野生型小鼠血清RANKL浓度显著升高，而野生型小鼠血清RANKL浓度无明显变化。（6）OPO -/-成骨细胞在培养液中释放大量的RANKL，OPG完全抑制RANKL的释放。（7）当向OPG -/-小鼠注射双膦酸盐（利塞膦酸盐）时，治疗组小鼠的骨形成相关参数以及骨吸收相关参数急剧下降。（8）利塞膦酸钠治疗OPG -/-小鼠可降低血清骨钙素和ALP水平，但不降低血清RANKL水平。（9）BMP诱导的OPG -/-小鼠异位成骨不明显。结论：（1）成熟破骨细胞产生偶联因子，而不产生骨吸收因子;（2）在骨吸收发生部位，骨吸收与骨形成紧密偶联。少

Aim of the study :The discovery of RANKL elucidates the mechanism of osteoclast differentiation and function regulated by osteoblasts. Osteoprotegerin (OPG), a soluble decoy receptor of RANKL, inhibits both differentiation and function of osteoclasts. OPG-deficient (OPG-/-) mice exhibited severe osteoporosis caused by enhanced osteoclastic bone resorption. Deficiency of OPG in human has been shown to result in juvenile Paget's disease. The previous morphological study showed that osteoblastic bone formation was activated in OPG-/-mice. These results suggest that osteoclastic bone resorption coincidentally induces osteoblastic bone formation by an unknown factor (called coupling factor). In the present study, we examined a possibility that mature osteoclasts produce cytokines which influence bone metabolism using mature osteoclasts treated with LPS. Using OPG -/-mice, we also explored whether such a coupling factor is present in bone in OPG -/-mice.Results :(1)p38MAP kinase was essentia … More lly involved in the differentiation of bone marrow macrophages (osteoclast precursors) into osteoclasts. The p38MAP kinase-signaling pathway was all dead in mature osteoclasts. (2)Mature osteoclasts were shown to produce an osteoblast-activating factor but not bone-resorbing cytokines such as IL-1 and IL-6 in response to LPS. (3)Blood levels of osteocalcin and ALP of OPG-/-mice were markedly increased in OPG-/-mice. Bone histomorphometric studies showed that both bone resorption and bone formation were activated in OPG-/-mice. (4)Serum levels of soluble RANKL were also elevated in OPG-/-mice. (5)When 1,25(OH)_2D_3 was administered into OPG -/-and wild-type mice, serum RANKL concentrations were markedly increased in OPG-/-mice but not in wild-type mice. (6)OPO -/-osteoblasts released a large amount of RANKL in the culture medium, which was completely inhibited by adding OPG (7)When bisphosphonate (risedronate) was injected into OPG -/-mice, bone formation -related parameters as well as bone resorption-related parameters were sharply decreased in the treated mice. (8)Treatment of OPG -/-mice with risedronate decreased serum osteocalcin and ALP levels but not the serum RANKL level. (9)Ectopic bone formation induced by BMP is not accelerated in OPG -/-mice.Conclusion :These results suggest (1)that mature osteoclast produce a coupling factor but not bone resorbing factors, and (2)that bone resorption is tightly coupled with bone formation at the sites where borne resorption takes place. Less