Dissecting the role of Dkk-1 in the pathogenesis of postmenopausal osteoporosis

大约40%的绝经后妇女患有骨质疏松症，这是妇女最常见的疾病之一。这种疾病的特征是骨密度降低和骨质量受损，导致骨折风险增加。绝经引起的雌激素丢失导致破骨细胞的产生增加，这进一步促进绝经后骨质疏松症的诱导。此外，似乎Wnt信号传导的抑制，这是骨量的关键调节因子，可能是这种疾病发展的一个可能原因。到目前为止，对雌激素的调节及其在骨质疏松症发病机制中的作用知之甚少。最近的研究报道了在患有绝经后骨质疏松症的患者中增加的Dickkopf-1（Dkk-1）（Wnt信号传导抑制剂）水平，这表明Dkk-1在绝经后骨质疏松症的发病机制中的作用。因此，我们假设Dkk-1是由成骨细胞、骨细胞和T细胞产生的，它有助于雌激素缺乏诱导的骨丢失。为了验证这一假设，我们将通过使用相应的动物模型来研究由成骨细胞或骨细胞产生的Dkk-1对绝经后骨质疏松症中骨形成抑制的影响。因此，Dkk-1-floxed小鼠将分别与Osx-和Dmp 1-Cre小鼠杂交，以产生在成骨细胞和骨细胞中特异性缺乏Dkk-1的小鼠。通过进行卵巢切除术，雌激素缺乏和由此导致的骨质流失应该被模仿和研究。此外，我们将分析17 b-雌二醇在体外成骨细胞和骨细胞中对Dkk-1的调节。在这里，我们计划使用原代成骨细胞以及永生化细胞系（MC 3 T3-E1，IDG-SW 3），应与不同浓度的17 b-雌二醇处理不同的细胞培养实验。此外，还应分析雌激素受体的影响，通过siRNA降低其表达或DNA诱导其表达。当前骨质疏松症治疗的效果也应该通过用PTH或二膦酸盐治疗成骨细胞和骨细胞来解决。由于T细胞也可能参与绝经后骨质疏松症的发病机制，我们将分析T细胞产生的Dkk-1的影响。因此，Dkk-1-floxed小鼠将与Lck-Cre小鼠杂交，以产生缺乏Dkk-1的小鼠，特别是在T细胞中。随后，雌激素缺乏将通过执行卵巢切除术来重新调整。为了在体外验证这一点，应建立成骨细胞和T细胞的共培养实验。详细了解绝经后妇女骨形成抑制的分子机制可能有助于更好地预防或治疗这些患者的骨丢失。

Approximately 40% of the postmenopausal women suffer from osteoporosis, one of the most frequent diseases in women. This disease is characterized by a decrease in bone density and a compromised bone quality leading to an increased fracture risk. Loss of estrogens induced by the menopause leads to an increased production of osteoclasts which further promotes the induction of postmenopausal osteoporosis. Furthermore, it seems that the inhibition of Wnt signaling, which is a critical regulator of bone mass, could be one possible reason for the development of this disease. So far, little is known about its regulation by estrogens and its role in the pathogenesis of osteoporosis. Recent studies reported increased levels of Dickkopf-1 (Dkk-1), an inhibitor of Wnt signaling, in patients suffering from postmenopausal osteoporosis suggesting a role for Dkk-1 in the pathogenesis of postmenopausal osteoporosis. Thus, we hypothesize that Dkk-1 which is produced by osteoblasts, osteocytes, and T cells contributes to bone loss induced by estrogen deficiency. To test this hypothesis we will investigate the influence of Dkk-1, produced by osteoblasts or osteocytes, on the inhibited bone formation in postmenopausal osteoporosis by utilizing corresponding animal models. Therefore, Dkk-1-floxed mice will be crossed with Osx- and Dmp1-Cre mice, respectively, to generate mice lacking Dkk-1 specifically in osteoblasts and osteocytes. By performing an ovariectomy, estrogen deficiency and the resulting loss of bone mass should be imitated and investigated. Furthermore, we will analyze the regulation of Dkk-1 by 17b-estradiol in osteoblasts and osteocytes in vitro. Here, we planned different cell culture experiments using primary osteoblasts as well as immortalized cell lines (MC3T3-E1, IDG-SW3) which should be treated with different concentrations of 17b-estradiol. In addition, the influence of the estrogen receptor should be analyzed too, by using siRNA to reduce its expression or DNA to induce its expression. The effect of current osteoporosis therapeutics should also be addressed by treating osteoblasts and osteocytes with PTH or bisphosphonates. Because also T cells could contribute to the pathogenesis of postmenopausal osteoporosis, we will analyze the influence of Dkk-1 produced by T cells. Therefore, Dkk-1-floxed mice will be crossed with Lck-Cre mice to generate mice lacking Dkk-1 especially in T cells. Subsequently, estrogen deficiency will be readjusted by performing ovariectomy. To test this in vitro, co-culture experiments of osteoblasts and T cells should be established. A detailed knowledge of the molecular mechanisms underlying inhibited bone formation in postmenopausal women may help to better prevent or treat bone loss in these patients.