Senescence of Pre-Osteoclasts in Non-Traumatic OA

总结/摘要 骨关节炎（OA）是最常见的与年龄相关的慢性关节疾病。虽然直接的关节损伤和 过度的机械超载被认为是OA发展的重要因素，只有 大约12%的症状性OA的总体患病率可归因于髋关节的创伤后OA， 膝盖或者脚踝衰老被认为是OA最重要的危险因素，代谢表型 成为临床研究中入组患者中第二常见的OA亚型。近日更 已经认识到细胞衰老是创伤后OA进展的关键驱动因素。然而，在这方面， 衰老细胞（SnCs）是否以及如何参与非创伤性OA的发展仍然不清楚， 明白在我们的初步研究中，我们发现在关节软骨下骨髓中积累的SnCs， 自发衰老OA小鼠和STR/Ort小鼠，一种与代谢失调相关的自发OA小鼠。 在创伤后OA小鼠的软骨下骨髓中未检测到增加的SnCs。因此，我们认为， 软骨下骨髓细胞衰老可能是非创伤性OA亚型的独特特征 与创伤后OA不同。此外，我们发现，近80%的SnCs是骨髓 前破骨细胞（Pre-OC）。相对于年轻小鼠，从老年小鼠分离的前OC表达增加， 常见的衰老相关分泌表型（SASP）因子和高得多的 血管生成因子PDGF-BB是一种有效的血管生成因子。众所周知，增加的软骨下骨 血管生成是OA发展的主要因素。因此，过度的PDGF-BB分泌， 软骨下骨髓SnCs可能有助于异常的软骨下骨血管生成。我们的中央 假设衰老前OC通过分泌过量的 PDGF-BB，导致OA相关的关节结构损伤。该假设将通过以下具体测试进行检验： 目标。在目标1中，我们将追踪滑膜组织，关节软骨和软骨下骨组织中的SnCs。 通过检测自发老化OA小鼠和STR/Ort小鼠关节的细胞衰老标志物，我们将 并追踪OC不同阶段的SnCs，验证骨髓中细胞的SASP表型 的老鼠。目的2将检查Pre-OCs来源的PDGF-BB在年龄相关性中的必要性和充分性。 软骨下骨血管生成和OA发展。在目标3中，我们将首先定义细胞的贡献， 通过选择性消除OA小鼠中的SnCs来促进软骨下骨血管生成和成骨。 然后，我们将使用遗传学和药理学方法来测试是否阻断前OC衰老 减弱OA进展。

SUMMARY/ABSTRACT Osteoarthritis (OA) is the most prevalent age-associated chronic joint disease. Although direct joint injury and excessive mechanical overloading are considered as important contributors to the development of OA, only approximately 12% of the overall prevalence of symptomatic OA is attributable to posttraumatic OA of the hip, knee, or ankle. Aging is recognized as the most important risk factor for OA, and the metabolic phenotype becomes the second most frequent subtype of OA among patients enrolled in clinical studies. Recently, it has been recognized that cellular senescence is a key driver for the progression of post-traumatic OA. However, whether and how senescent cells (SnCs) are involved in the development of non-traumatic OA remain poorly understood. In our preliminary study, we found accumulated SnCs at the joint subchondral bone marrow of both spontaneous aging OA mice and STR/Ort mice, a spontaneous OA mice associated with metabolic dysregulation. Increased SnCs were not detected in subchondral bone marrow of a post-traumatic OA mice. Therefore, subchondral bone marrow cell senescence may represent a unique feature of non-traumatic subtype of OA distinguishable from post-traumatic OA. Moreover, we identified that close to 80% of the SnCs are bone marrow Pre-osteoclast (Pre-OC). Pre-OCs isolated from old mice, relative to young mice, had increased expression of common senescence-associated secretory phenotype (SASP) factors and much higher expression of angiogenesis factor PDGF-BB, a potent angiogenesis factor. It is known that increased subchondral bone angiogenesis is a major contributor to the development of OA. Therefore, the excessive PDGF-BB secreted by subchondral bone marrow SnCs may contribute to aberrant subchondral bone angiogenesis. Our central hypothesis is that senescent Pre-OCs induce aberrant subchondral bone angiogenesis by secreting excessive PDGF-BB, leading to OA-related joint structural damage. The hypothesis will be tested by the following Specific Aims. In Aim 1, we will trace the SnCs in synovial tissue, articular cartilage, and subchondral bone tissue of the joints by detecting the cellular senescence markers in spontaneous aging OA mice and STR/Ort mice. We will also trace the SnCs at different stages of OC lineage and verify the SASP phenotype of the cells in bone marrow of the mice. Aim 2 will examine the necessity and sufficiency of Pre-OCs-derived PDGF-BB in age-associated subchondral bone angiogenesis and OA development. In Aim 3, we will first define the contribution of cellular senescence to subchondral bone angiogenesis and osteogenesis by selectively eliminating the SnCs in OA mice. We will then test if blockage of Pre-OC senescence using both genetic and pharmacologic approaches attenuates OA progression.