RANKL/OPG-Mediated Control of Vascular Calcification

描述（由申请人提供）：血管钙化对心血管发病率和死亡率有显著影响。它在动脉粥样硬化病变中以非常类似于骨生成的过程发展。特别是，它与骨质疏松症相关，与年龄无关。其机制尚不清楚。我们以前的研究表明，血管细胞钙化实际上是成骨分化，最终导致骨组织形成。该建议的指导假设是，骨骼骨代谢的一些关键调节因子也以相互的方式调节动脉壁中的骨形成。两个主要的调节因子是RANKL（TNF-α超家族成员）和OPG（其可溶性诱饵受体）。在骨中，RANKL通过破骨细胞促进骨吸收，破骨细胞在该组织中丰富。然而，在破骨细胞罕见的血管系统中，RANKL治疗不会促进再吸收，但更重要的是，它似乎积极促进钙化。RANKL激活性钙化的一种可能机制可能在于其已知的NF-κ B激活。在软骨细胞中，已经显示NF-kB诱导有效的成骨因子BMP-2。我们认为，这一途径可能是负责，部分，血管钙化及其矛盾的关联与骨质疏松症。最近的重要证据支持这一假设：1）在钙化动脉中，RANKL上调，OPG下调，2）OPG缺乏的小鼠发生血管钙化，3）RANKL诱导瓣膜肌纤维母细胞中的骨生成和矿化。在初步研究中，我们发现RANKL可诱导体外血管细胞钙化，OPG可抑制其钙化。我们还发现致动脉粥样硬化脂质和高脂血症抑制OPG表达，这将使RANKL活性不受抑制。这一机制为致动脉粥样硬化因素对骨和动脉壁中生物矿化的矛盾作用提供了统一的解释。我们假设RANKL刺激血管钙化，OPG抑制血管钙化，致动脉粥样硬化脂质增加RANKL活性。在目标1中，我们将测试OPG缺乏症中的血管钙化是否由无对抗的RANKL活性和BMP-2的上调引起。我们还将测试另一种OPG配体TRAIL是否通过隔离OPG而促进钙化。在目的2中，我们将检测致动脉粥样硬化脂质抑制OPG表达是否导致无对抗的RANKL活性。作为推论，我们还将测试OPG治疗是否可以预防动脉粥样硬化钙化。在目的3中，我们将通过产生血管系统中RANKL过表达的转基因小鼠（SM 22-rankl（tg）小鼠）来检验RANKL直接诱导体内血管钙化的假设。我们将使用血管特异性启动子来避免骨表型的混淆效应。这些拟议的研究将阐明RANKL和OPG在血管钙化中的作用，并可能为钙化性血管疾病定义一种新的治疗模式。动脉壁钙化有助于心血管疾病，它矛盾地与骨质疏松症一起发生。基于新的支持性证据，这项研究将测试促进骨矿物质损失的特定调节因子是否也促进动脉壁中矿物质的获得。

DESCRIPTION (provided by applicant): Vascular calcification contributes significantly to cardiovascular morbidity and mortality. It develops in atherosclerotic lesions in a process closely resembling osteogenesis. Paradoxically, it is associated, age independently, with osteoporosis. The mechanism is unknown. We previously showed that vascular cell calcification is, in fact, osteogenic differentiation, ultimately leading to bone tissue formation. The guiding hypothesis of this proposal is that some critical regulator(s) of skeletal bone metabolism also regulate, in a reciprocal manner, bone formation in the artery wall. Two of the major regulators are RANKL, a TNF-alpha superfamily member, and OPG, its soluble decoy receptor. In bone, RANKL promotes bone resorption by osteoclasts, which are abundant in this tissue. In the vasculature, however, where osteoclasts are rare, RANKL treatment does not promote resorption, but, more importantly, it appears to actively promote calcification. One possible mechanism for active calcification by RANKL may lie in its known activation of NF-kB. In chondrocytes, it has been shown that NF-kB induces the potent osteogenic factor, BMP-2. We propose that this pathway may be responsible, in part, for vascular calcification and its paradoxical association with osteoporosis. Significant recent evidence supports this hypothesis: 1) RANKL is upregulated, and OPG is downregulated, in calcified arteries, 2) mice deficient in OPG develop vascular calcification, and 3) RANKL induces osteogenesis and mineralization in valvular myofibroblastic cells. In preliminary studies, we have found that in vitro vascular cell calcification is induced by RANKL and inhibited by OPG. We also found that atherogenic lipids and hyperlipidemia inhibit OPG expression, which would leave RANKL activity unopposed. This mechanism offers a unified explanation for the paradoxical effects of atherogenic factors on biomineralization in bone and in the artery wall. We hypothesize that RANKL stimulates, and OPG inhibits, vascular calcification and that atherogenic lipids increase RANKL activity. In Aim 1, we will test whether vascular calcification in OPG deficiency results from unopposed RANKL activity and upregulation of BMP-2. We will also test whether another OPG ligand, TRAIL, contributes to calcification by sequestering OPG. In Aim 2, we will test whether atherogenic lipid inhibition of OPG expression results in unopposed RANKL activity. As a corollary, we will also test whether OPG treatment prevents atherosclerotic calcification. In Aim 3, we will test the hypothesis that RANKL directly induces vascular calcification in vivo by generating transgenic mice with RANKL overexpression in the vasculature (SM22-rankl(tg) mice). We will use a vascular-specific promoter to avoid the confounding effects of a bone phenotype. These proposed studies will elucidate the roles of RANKL and OPG in vascular calcification and may define a new therapeutic paradigm for calcific vascular disease. Artery wall calcification contributes to cardiovascular disease, and it paradoxically occurs in conjunction with osteoporosis. Based on new supportive evidence, this research will test whether specific regulatory factors that promote loss of mineral from bone also promote gain of mineral in the artery wall.