BMP2 signaling of the development of osetoarthritis

描述(申请人提供)：骨关节炎(OA)影响着全球超过2亿人，其中包括2700万美国人，据估计，美国每年在与OA相关的医疗保健上花费1280亿美元(1，2)。目前治疗骨性关节炎的方法侧重于减轻疼痛，同时改善关节活动(3)。由于所有这些治疗方法都不能恢复因骨性关节炎进展而受损的关节结构，因此通常需要关节置换，在美国每年进行的关节置换手术超过60万例(4)。因此，旨在改善OA的战略代表着一个非常重要的机会，可以在控制医疗成本的同时提高许多美国人的生活质量。骨形态发生蛋白(BMPs)在骨性关节炎发病机制中的作用尽管有多年的研究，但仍存在争议。BMP活性是在骨骼发育过程中启动软骨形成所必需的，也是形成滑膜关节所必需的(5-11)。BMP信号也参与了出生后滑膜关节功能的维持(12)。矛盾的是，太多了 骨形态发生蛋白活性也与骨性关节炎(18-20岁)有关。在这项建议中，我们重点研究BMP2，并研究其在维持出生后滑膜关节功能中的作用。我们以BMP2为靶点的决定是基于早期肢体间充质细胞缺乏BMP2表达的小鼠的表型(Prx1cre；21，22)。随着年龄的增长，这些小鼠失去了正常的骨骼功能，表现为四肢骨骼的自发性骨折和启动骨折修复的能力(22-24)，以及28周龄时膝、肘、腕和脚踝的骨性关节炎的逐渐发展(图1)。BMP2Prx1Cre小鼠的骨性关节炎的发展类似于人类骨性关节炎的疾病进展，在引发疾病的事件和关节炎关节的发展之间有很长的延迟。如果骨形态发生蛋白2的丢失确实先于骨关节炎的病理关节改变，那么将骨形态发生蛋白2维持在正常生理水平可能是减缓或阻止骨关节炎关节改变的一种手段。然而，Bmp2Prx1cre小鼠存在多种发育肢体缺陷，这些缺陷可能导致滑膜关节发生骨关节炎(25，26)，必须对这些混杂因素进行分类，以确定关节软骨中BMP2信号水平变化在骨关节炎发病机制中的重要性。我们建议通过追踪BMP2在成人滑膜关节中的表达和BMP信号转导来直接评估BMP2在OA中的作用(目标1)，并确定BMP2在关节软骨中的特异性丢失是否导致 向进行性骨性关节炎表型转变(目标2)。为了进行这些实验，我们将BMP2报告小鼠与BMP信号报告小鼠和驱动关节软骨中BMP2缺失的小鼠结合使用。我们还采用了两项最先进的技术来评估OA进展：超高分辨率微型CT，它允许对矿化和软组织进行亚微米三维检查(27，28)，以及基于原子力显微镜的纳米压痕(AFM-N)，这是一种允许量化不规则形状的小体积肌肉骨骼组织的局部机械特性的方法(29)。这些技术使我们能够获得我们计划研究的转基因小鼠关节组织的精确图像和相应的功能评估。

DESCRIPTION (provided by applicant): Osteoarthritis (OA) affects over 200 million people worldwide including 27 million Americans, and it is estimated that the US spends $128 billion dollars each year on OA related health care (1, 2). Current therapies for OA focus on decreasing pain while improving joint movement (3). As none of these treatments can restore joint structures damaged by the progression of OA, joint replacement is often required, with more than 600,000 joint replacement surgeries performed yearly in the US (4). As such, strategies aimed at ameliorating OA represent a highly significant opportunity to contain health care costs while enhancing the quality of life for many Americans. The role of bone morphogenetic proteins (BMPs), in the pathogenesis of OA remains controversial despite many years of study. BMP activity is necessary for initiating chondrogenesis during skeletal development and is required for formation of synovial joints (5-11). BMP signaling is also involved in the maintenance of functional synovial joints after birth (12). Paradoxically, too much BMP activity is also associated with OA (18-20). In this proposal, we focus on BMP2 and examine its role in maintaining postnatal synovial joint function. Our decision to target BMP2 is based on the phenotype of mice lacking BMP2 expression in mesenchymal cells of the early limb (Prx1cre; 21, 22). These mice lose normal skeletal function as they age, as evidenced by spontaneous fractures throughout the limb skeleton and an ability to initiate fracture repair (22-24) and the progressive development of OA of the knee, elbow, wrist and ankle by 28 weeks of age (Fig 1). The development of OA in BMP2Prx1Cre mice is analogous to disease progression in human OA where there is a long delay between the event that initiates the disease and the development of an arthritic joint. If loss of BMP2 does indeed precede the pathological joint changes seen in OA, maintaining BMP2 at normal physiological levels may be a means to slow or halt joint changes that characterize OA. However, Bmp2Prx1cre mice have a variety of developmental limb defects that may predispose synovial joints to develop OA (25, 26) and these confounding factors must be sorted out in order to determine the importance of changing levels of BMP2 signaling in articular cartilage in the pathogenesis of OA. We propose to directly assess the role of BMP2 in OA by tracking BMP2 expression and BMP signaling in adult synovial joints (Aim 1) and determining if loss of BMP2 specifically from articular cartilage leads to a progressive OA phenotype (Aim 2). To perform these experiments we combine the use of BMP2 reporter mice with BMP signaling reporter mice and mice that drive deletion of BMP2 in articular cartilage. We also employ two state-of-the-art technologies to assess OA progression: ultra high resolution micro CT that allows for submicron 3-dimensional examination of both mineralized and soft tissues (27, 28) and atomic force microscopy -based nanoindentation (AFM-N), a method that allows for the quantification of the local mechanical properties of irregularly shaped, small volume musculoskeletal tissues (29). These technologies allow us to obtain precise images and corresponding functional assessments of joint tissues in the transgenic mice we plan to study.