Contribution of dysfunctional telomeres to primary osteoarthritis

原发性骨关节炎（OA）具有非常强的遗传成分;然而，仅确定了少量OA风险等位基因。在这个建议中，我们专注于端粒缩短作为一个表观遗传因素有助于原发性OA。端粒对位于附近的基因的沉默效应被称为端粒位置效应，并且被端粒缩短所破坏，这是先前在OA患者中检测到的。本申请的目的是证明或反驳端粒缩短与OA的发病机制具有机械关系的概念，并显示SIRT 6激活剂的治疗效果。我们的中心假设是端粒缩短通过上调端粒近端基因的表达促进OA的发展，而SIRT 6可拮抗端粒近端基因的表达。我们还提出，软骨和滑膜中的端粒缩短触发了关节中的端粒相关分泌表型（TASP）和含端粒重复序列的RNA（TERRA）的表达。这一假设是基于当前文献和初步数据提出的，这些数据揭示了端粒较短的OA软骨中SIRT 6表达增加，显示在关节置换手术期间从50名膝关节OA患者中获得的受影响软骨与未受影响软骨中端粒显着缩短，这表明在具有非常短的端粒的软骨中靠近端粒的差异表达基因的富集，并显示NMN的抑制作用对软骨细胞衰老的影响在初步数据的指导下，将通过追求三个具体目标来测试该假设：1）确定SIRT 6激活剂如烟酰胺单核苷酸（NMN）对受影响的软骨细胞中OA进展的影响; 2）确定端粒延伸是否可以沉默上调的端粒近端基因;和3）确定TERRA转录物是否存在于OA患者的滑液外来体中，以及它们的水平是否对软骨细胞的炎症反应具有直接影响。该研究表明，端粒缩短影响的端粒位置效应是软骨老化和OA病理学的重要新机制，具有重要意义。该项目的新奇在于，它探索了一种新的表观遗传机制，有助于OA的病因学。

Primary osteoarthritis (OA) has a very strong genetic component; however, only a small number of OA risk alleles have been identified. In this proposal we focus on telomere shortening as an epigenetic factor contributing to primary OA. The silencing effect of telomeres on the genes located nearby is known as telomere position effect and is disrupted by telomere shortening, which was detected previously in patients with OA. The objective of this application is to prove or refute the concept that telomere shortening has a mechanistic relationship to the pathogenesis of OA and to show a therapeutic effect of SIRT6 activators. Our central hypothesis is that telomere shortening contributes to the development of OA through upregulated expression of telomere-proximal genes, which is antagonized by SIRT6. We also propose that telomere shortening in cartilage and synovium triggers telomere-associated secretory phenotype (TASP) in the joint and expression of telomeric repeat-containing RNA (TERRA). This hypothesis has been formulated on the basis of the current literature and preliminary data revealing increased SIRT6 expression in OA cartilage with short telomeres, showing significant shortening of telomeres in affected versus unaffected cartilage obtained from 50 patients with knee OA during joint replacement surgery, indicating enrichment in differentially expressed genes located close to telomeres in cartilage with very short telomeres and showing a suppressive effect of NMN on chondrocyte senescence. Guided by preliminary data, this hypothesis will be tested by pursuing three specific aims: 1) Determine the effect of SIRT6 activators such as nicotinamide mononucleotide (NMN) on progression of OA in affected chondrocytes; 2) Determine if telomere extension can silence upregulated telomere-proximal genes; and 3) Determine if TERRA transcripts are present in synovial fluid exosomes of OA patients and if their level has a direct effect on the inflammatory response of chondrocytes. The proposed research is significant because it indicates telomere position effect affected by telomere shortening as the new important mechanism contributing to cartilage aging and OA pathology. The novelty of this project is that it explores a new epigenetic mechanism contributing to etiology of OA.