The Role of PGRN Growth Factor in Osteoarthritis

骨关节炎（OA）是一种退行性关节疾病，在美国影响超过4600万人 一个人由于OA增强的机制在很大程度上是未知的，因此没有有效治疗的靶点。 预防和治疗疾病。然而，生长因子、细胞因子和基质降解酶是 与引发和加重OA病变密切相关。因此，对相互作用的分子理解 在这些分子中，将为寻找新的治疗靶点提供宝贵的信息， OA。我们对OA中新的差异表达基因的全基因组筛选导致了颗粒蛋白前体的分离 （PGRN）作为一种新的OA相关生长因子。在随后的PGRN结合蛋白的总体筛选中， 我们惊奇地发现PGRN与TNF受体（TNFR）结合。PGRN直接与TNFR2结合， 比TNF α高约600倍的亲和力，以及软骨细胞中PGRN激活的靶基因表达 依赖TNFR2。此外，PGRN阻断TNF α与TNFR的结合，并抑制TNF α诱导的TNFR的表达。 软骨寡聚基质蛋白（COMP）的ADAMTS切割。PGRN基因的缺失会加剧， 而重组PGRN预防TNF转基因小鼠中多关节炎的自发发展。 该建议特别关注PGRN在发病机制中发挥其软骨保护作用的假设 与TNFR相互作用。具体目的是：（1）分子机制是什么 PGRN调节软骨细胞代谢的信号通路？我们将定义 PGRN和TNF α对软骨细胞代谢、信号通路、靶基因表达及相互作用的影响 在软骨细胞中。我们将确定PGRN功能对软骨细胞中TNFR的依赖性， 表征PGRN/TNFR受体复合物。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是否在启动中起重要作用 和进展的OA，它的作用机制是什么？我们将利用 系统性和诱导性PGRN敲除小鼠以产生手术诱导的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是否改善了小鼠的OA攻击。 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。通过应用 从体外研究（Aim 1中提出）到小鼠模型中早期和晚期事件分析的见解， 我们将了解OA发生和发展的分子基础。成功 完成这项研究不仅有助于我们了解分子机制， 生长因子和细胞因子在软骨细胞和OA中协同作用，但也可能导致 为退行性疾病（包括OA）开发新的治疗干预策略。

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 TNFα, and PGRN-activated target gene expressions in chondrocytes depend on TNFR2. In addition, PGRN blocks the binding of TNFα to TNFR and inhibits TNFα-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 TNFα on chondrocyte metabolism, their signaling pathways, target gene expressions and interplays 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 wildtype 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 Aim1) 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.