The Role of PGRN Growth Factor in Osteoarthritis

描述(申请人提供)：骨关节炎(OA)是一种退行性关节疾病，仅在美国就有4600多万人受到影响。由于骨性关节炎继发的机制在很大程度上尚不清楚，因此没有有效预防和治疗该病的治疗靶点。然而，生长因子、细胞因子和基质降解酶与启动和加重骨性关节炎病变密切相关。因此，对这些分子之间相互作用的分子理解将为寻找新的OA治疗靶点提供宝贵的信息。我们对骨关节炎新的差异表达基因的全基因组筛选导致了原颗粒蛋白(PGRN)作为一种新的骨关节炎相关生长因子的分离。在随后的对PGRN结合蛋白的全局筛选中，我们惊讶地发现PGRN与肿瘤坏死因子受体(TNFR)结合。PGRN直接与TNFR2结合的亲和力约为肿瘤坏死因子？的600倍，而PGRN激活的靶基因在软骨细胞中的表达依赖于TNFR2。此外，PGRN还可阻断肿瘤坏死因子？抑制肿瘤坏死因子β诱导的软骨寡聚基质蛋白(COMP)对ADAMTS的裂解。PGRN基因的缺失会加剧，而重组的PGRN可以防止肿瘤坏死因子转基因小鼠的多发性关节炎的自发发展。这一建议特别侧重于这样一种假设，即PGRN通过与TNFR相互作用在OA的发病机制中发挥软骨保护作用。其具体目的是：(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和肿瘤坏死因子的作用。关于软骨细胞代谢、信号通路、靶基因表达及其在软骨细胞中的相互作用。我们将确定软骨细胞中PGRN功能对TNFR的依赖性，并对PGRN/TNFR受体复合体进行表征。将使用正常和关节炎人软骨细胞，以及野生型和PGRN-/-小鼠关节软骨细胞。(2)PGRN是否在骨性关节炎的发生和发展中起重要作用，其作用机制是什么？我们将利用系统性和诱导性的PGRN基因敲除小鼠来建立手术诱导的骨性关节炎模型。我们还将确定重组的PGRN是否能保护小鼠免受OA的攻击，以及PGRN是否能改善现有的OA。我们将确定哪种TNFR在介导PGRN在骨关节炎中的保护作用中起重要作用。通过将来自体外研究的见解(在目标1中提出)应用于分析小鼠模型中的早期和晚期事件，我们将获得对OA发生和进展的潜在分子事件的理解。这项研究的成功完成不仅将有助于我们理解生长因子和细胞因子在软骨细胞和骨关节炎中协同作用的分子机制，而且还可能导致对包括骨关节炎在内的退行性疾病的治疗干预策略的发展。 公共卫生相关性：拟议的研究将提出一种新的软骨保护性生长因子，并使人们更好地了解软骨细胞中的生长因子和细胞因子以及在OA发病机制中的作用。识别与软骨细胞相关的新分子及其衍生物是开发和优化新的治疗靶点在包括骨关节炎在内的软骨疾病中应用的基础。

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.