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OA增强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强烈牵连在启动和加重OA病变。因此，这些分子之间的相互作用的分子理解将提供宝贵的信息，对寻找新的治疗OA的目标。我们在全基因组范围内筛选OA中新的差异表达基因，从而分离出一种新的OA相关生长因子颗粒蛋白前体（PGRN）。在随后对PGRN结合蛋白的全面筛选中，我们惊奇地发现PGRN与肿瘤坏死因子受体（TNFR）结合。PGRN与TNFR 2的直接结合亲和力比TNF？高约600倍，软骨细胞中PGRN激活的靶基因表达依赖于TNFR 2。此外，PGRN阻断TNF？TNFR和抑制TNF？-诱导软骨寡聚基质蛋白（COMP）的ADAMTS切割。在TNF转基因小鼠中，PGRN基因的缺失加重了多发性关节炎，而重组PGRN可预防多发性关节炎的自发发展。该建议特别关注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调节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？对软骨细胞代谢、其信号传导途径、靶基因表达和软骨细胞中的相互作用的影响。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-/-鼠关节软骨细胞. (2)PGRN是否在OA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型PGRN敲除小鼠来产生骨诱导的OA模型。我们还将确定重组PGRN是否保护小鼠免受OA攻击以及PGRN是否改善现有OA。我们将确定哪种TNFR对调节PGRN在OA中的保护作用是重要的。通过将体外研究（目标1中提出）的见解应用于小鼠模型中早期和晚期事件的分析，我们将了解OA发生和进展的分子事件。成功完成拟议的研究将不仅有利于我们了解生长因子和细胞因子在软骨细胞和OA中协同作用的分子机制，而且还可能导致开发新的退行性疾病（包括OA）的治疗干预策略。

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.