BMP2 signaling of the development of osetoarthritis

描述（由申请人提供）：骨关节炎（OA）影响全球超过2亿人，包括2700万美国人，据估计，美国每年在OA相关医疗保健上花费1280亿美元（1，2）。目前OA的治疗重点是减少疼痛，同时改善关节运动（3）。由于这些治疗方法都不能恢复因OA进展而受损的关节结构，因此通常需要进行关节置换术，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的策略代表了一个非常重要的机会，以控制医疗保健成本，同时提高许多美国人的生活质量。骨形态发生蛋白（BMPs）在OA发病机制中的作用尽管经过多年的研究仍存在争议。BMP活性对于在骨骼发育期间启动软骨形成是必需的，并且对于滑膜关节的形成是必需的（5-11）。BMP信号传导也参与出生后功能性滑膜关节的维持（12）。巧合的是，太多了 BMP活性也与OA相关（18-20）。在这项建议中，我们专注于BMP 2和检查其在维持出生后滑膜关节功能的作用。我们决定靶向BMP 2是基于小鼠早期肢体间充质细胞中缺乏BMP 2表达的表型（Prx 1cre; 21，22）。这些小鼠随着年龄的增长而失去正常的骨骼功能，如整个肢体骨骼的自发性骨折和启动骨折修复的能力（22-24）以及到28周龄时膝关节、肘关节、腕关节和踝关节OA的进行性发展所证明的（图1）。BMP 2 Prx 1Cre小鼠中OA的发展类似于人类OA中的疾病进展，其中在引发疾病的事件和关节炎关节的发展之间存在长时间的延迟。如果BMP 2的丢失确实先于OA中观察到的病理性关节变化，则将BMP 2维持在正常生理水平可能是减缓或停止表征OA的关节变化的手段。然而，Bmp 2 Prx 1cre小鼠具有多种发育性肢体缺陷，这些缺陷可能使滑膜关节易于发展为OA（25，26），必须将这些混杂因素整理出来，以确定关节软骨中BMP 2信号传导水平变化在OA发病机制中的重要性。我们建议通过追踪BMP 2在成人滑膜关节中的表达和BMP信号传导，直接评估BMP 2在OA中的作用（目的1），并确定关节软骨中BMP 2的特异性缺失是否导致OA的发生。 进展性OA表型（Aim 2）。为了进行这些实验，我们将BMP 2报告小鼠与BMP信号转导报告小鼠和驱动关节软骨中BMP 2缺失的小鼠组合使用联合收割机。我们还采用了两种最先进的技术来评估OA进展：超高分辨率显微CT，允许对矿化组织和软组织进行亚微米三维检查（27，28）和基于原子力显微镜的纳米压痕（AFM-N），这是一种允许对不规则形状、小体积肌肉骨骼组织的局部机械特性进行量化的方法（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.