Mechanism of Tgfbr2 in chondroprotection

描述（由申请人提供）：骨关节炎是工业化国家残疾的主要原因，但对骨关节炎相关的软骨破坏机制知之甚少。最近在小鼠遗传操作方面的进展导致了与理解人类骨关节炎相关的新动物模型和新概念。我实验室的长期目标是了解介导关节软骨发育、持续和修复的因素，并确定骨关节炎预防和治疗策略的具体目标。TGF-β是一种多功能肽，已被证明可调节细胞分化和组织特异性基因表达。先前，我们产生了在关节软骨中表达TGF-β II型受体（Tgfbr 2）显性负突变的转基因小鼠。对TGF-β的反应性改变导致了一种类似于人类骨关节炎的进行性骨骼疾病。我们最近确定了几个TGF-β的下游靶点，这些靶点调节关节软骨中主要细胞外基质蛋白的翻译后加工。特别是3-Prime-Phoshoadenosine 5-Prime-Phosphosulfate Synthase 2（Papss 2），与人类脊柱干骺端发育不良相关，并且是软骨中蛋白聚糖适当硫酸化所必需的。除了TGF-β，转录因子Sox 9也与成熟关节软骨的维持有关。我们的初步研究表明，TGF-β增强软骨细胞中Sox 9蛋白的水平，与mRNA的变化无关。初步数据表明，用TGF-β处理导致Sox 9的sumoylation。类小泛素化已被证明可以调节蛋白质的稳定性、活性和细胞定位。我们假设TGF-β维持着 永久性软骨（如关节软骨）中的分化软骨细胞表型，通过蛋白类小泛素化调节Sox 9水平和活性。我们提出用以下具体目标来测试该模型：1a）确定Sox 9上的哪些位点响应于TGF-β而被SUMO化，并确定SUMO化在TGF-β介导的Sox 9水平、定位和活性中的作用; 1b）确定TGF-β介导的Sox 9 SUMO化的机制; 2）确定TGF-β介导的Sox 9 SUMO化的机制。3）确定当TGF-β信号传导被破坏时，Papss 2活性是否可以减轻软骨退化，并确定TGF-β的软骨保护信号的激活是否可以恢复OA软骨的生物化学和生物力学特性。这些研究将确定可用作骨关节炎治疗靶点的软骨保护机制。

DESCRIPTION (provided by applicant): Osteoarthritis is a leading cause of disability in the industrialized world but little is known about mechanisms of cartilage destruction associated with osteoarthritis. Recent advances in the genetic manipulation of mice have lead to new animal models and new concepts that are relevant to understanding osteoarthritis in humans. The long-term objective of my laboratory is to understand the factors that mediate the development, persistence, and repair of articular cartilage and to identify specific targets for prevention and treatment strategies for osteoarthritis. TGF-¿ is a multifunctional peptide that has been shown to regulate cellular differentiation and tissue-specific gene expression. Previously, we generated transgenic mice that express a dominant-negative mutation of the TGF-¿ type II receptor (Tgfbr2) in articular cartilage. Altered responsiveness to TGF-¿ resulted in a progressive skeletal disease that resembled osteoarthritis in humans. We recently identified several down-stream targets of TGF-¿ that regulate post-translational processing of the major extracellular matrix proteins in articular cartilage. One in particular, 3-Prime-Phoshoadenosine 5-Prime-Phosphosulfate Synthase 2 (Papss2), has been associated with Spondyloepimetaphyseal Dysplasias in humans and is required for proper sulfation of proteoglycans in cartilage. In addition to TGF-¿, the transcription factor Sox9 is also associated with the maintenance of mature articular cartilage. Our preliminary studies indicate that TGF-¿ enhances the level of Sox9 protein in chondrocytes independently of changes in mRNA. The preliminary data suggest that treatment with TGF-¿ results in sumoylation of Sox9. Sumoylation has been shown to regulate protein stability, activity and cellular localization. We hypothesize that TGF-¿ maintains the differentiated chondrocyte phenotype in permanent cartilages, like articular cartilage, by regulating Sox9 levels and activity via protein sumoylation. We propose to test this model with the following specific aims: 1a) to determine which sites on Sox9 are sumoylated in response to TGF-¿ and determine the role of sumoylation in TGF-¿-mediated Sox9 levels, localization, and activity; 1b) to determine the mechanism of TGF-¿-mediated sumoylation of Sox9; 2) to determine the mechanism of TGF-¿ mediated expression of Papss2 and 3) to determine if Papss2 activity can alleviate cartilage degeneration when TGF-¿ signaling is disrupted and determine if activation of TGF-¿'s chondroprotective signals can restore biochemical and biomechanical properties to OA cartilage. These studies will identify mechanisms of chondroprotection that can be used as targets for therapies in osteoarthritis.