The Role of PGRN Growth Factor in Osteoarthritis

描述（由申请人提供）：骨关节炎（OA）是一种退行性关节疾病，仅在美国就影响超过4600万人。由于骨性关节炎发生的机制在很大程度上是未知的，因此没有有效预防和治疗该疾病的治疗靶点。然而，生长因子、细胞因子和基质降解酶与OA病变的发生和加重密切相关。因此，对这些分子之间相互作用的分子理解将为寻找OA的新治疗靶点提供宝贵的信息。我们对OA中新颖的差异表达基因进行全基因组筛选，分离出了原颗粒蛋白（PGRN）作为OA相关的新型生长因子。在随后的PGRN结合蛋白的全局筛选中，我们惊讶地发现PGRN与TNF受体（TNFR）结合。PGRN直接与TNFR2结合，其亲和力比TNF？软骨细胞中pgrn激活的靶基因表达依赖于TNFR2。此外，PGRN阻断TNF？抑制TNF？诱导的ADAMTS裂解软骨寡聚基质蛋白（COMP）。在TNF转基因小鼠中，PGRN基因的缺失会加剧多发性关节炎，而重组PGRN则会阻止多发性关节炎的自发发展。本提案特别关注PGRN通过与TNFR相互作用在OA发病机制中发挥其软骨保护作用的假设。具体目的是：(1)PGRN调控软骨细胞代谢的分子机制和信号通路是什么？我们将定义PGRN和TNF的作用。软骨细胞代谢、信号通路、靶基因表达及相互作用。我们将确定软骨细胞中PGRN功能对TNFR的依赖性，并表征PGRN/TNFR受体复合物。将使用正常和关节炎的人软骨细胞，以及野生型和PGRN-/-小鼠关节软骨细胞。(2) PGRN在OA的发生和发展中是否起重要作用，其在OA中的作用机制是什么？我们将利用系统和诱导PGRN敲除小鼠来产生手术诱导的OA模型。我们还将确定重组PGRN是否能保护小鼠免受OA攻击，以及PGRN是否能改善现有的OA。我们将确定哪个TNFR对介导PGRN在OA中的保护作用是重要的。通过应用体外研究的见解（在Aim 1中提出）来分析小鼠模型的早期和晚期事件，我们将了解OA发生和进展的分子事件。该研究的成功完成不仅有助于我们理解生长因子和细胞因子在软骨细胞和骨性关节炎中协同作用的分子机制，而且还可能导致包括骨性关节炎在内的退行性疾病的新型治疗干预策略的发展。

DESCRIPTION (provided by applicant): Osteoarthritis (OA) is a degenerative joint disease that affects more than 46 million people in the United States alone. Since mechanisms by which OA ensues are largely unknown, there are no therapeutic targets that effectively prevent and treat the disease. However, growth factors, cytokines and matrix-degrading enzymes are strongly implicated in initiating and aggravating OA lesions. Thus, a molecular understanding of interplays among these molecules will provide invaluable information toward the search for novel therapeutic targets for OA. Our genome-wide screen for novel, differentially expressed genes in OA led to the isolation of progranulin (PGRN) as a novel OA-associated growth factor. In subsequent global screen for the binding proteins of PGRN, we were surprised to find that PGRN bound to TNF Receptors (TNFR). PGRN directly binds to TNFR2 with an approximately 600-fold higher affinity than TNF?, and PGRN-activated target gene expressions in chondrocytes depend on TNFR2. In addition, PGRN blocks the binding of TNF? to TNFR and inhibits TNF?-induced ADAMTS cleavage of cartilage oligomeric matrix protein (COMP). Deletion of the PGRN gene exacerbates, whereas recombinant PGRN prevents the spontaneous development of polyarthritis in TNF transgenic mice. This proposal specifically focuses on the hypothesis that PGRN exerts its chondroprotective role in the pathogenesis of OA by interacting with TNFR. The Specific Aims are: (1) what are the molecular mechanisms and signaling pathways by which PGRN regulates chondrocyte metabolism? We will define the effects of PGRN and TNF? on chondrocyte metabolism, their signaling pathways, target gene expressions and inter-plays in chondrocytes. We will determine the dependence of the PGRN function on TNFR in chondrocytes and characterize the PGRN/TNFR receptor complexes. Normal and arthritic human chondrocytes, as well as wild- type and PGRN-/- murine articular chondrocytes, will be used. (2) Does PGRN play an important role in the initiation and progression of OA, and what are the mechanisms of its action in OA? We will take advantage of both systematic and inducible PGRN knockout mice to generate surgically-induced OA models. We will also determine whether recombinant PGRN protects mice against OA challenge and whether PGRN ameliorates existing OA. We will determine which TNFR is important for mediating PGRN's protective role in OA. By applying insights from in vitro studies (proposed in Aim 1) to the analysis of early and late events in the mouse models, we will gain understanding of the molecular events underlying the initiation and progression of OA. Successful completion of the proposed research will not only benefit our understanding of the molecular mechanisms by which growth factor and cytokine act in concert in chondrocytes and in OA, but may also lead to the development of novel therapeutic intervention strategies for degenerative diseases, including OA. PUBLIC HEALTH RELEVANCE: The proposed studies will present a novel chondroprotective growth factor and provide a better understanding of growth factor and cytokine in chondrocytes and in the pathogenesis of OA. Identification of novel molecules and their derivatives relevant to chondrocytes is the basis for developing and optimizing the application of the novel therapeutic targets in cartilage disorders, including OA.