Innate Inflammation in Osteoarthritis

描述(由申请人提供)： 项目摘要/摘要：骨性关节炎(OA)与既往软骨生物力学损伤和衰老有关。然而，生物力学损伤和衰老并不必然导致骨性关节炎。这项建议将集中在骨性关节炎中以软骨细胞为中心的先天炎症机制。我们已经确定了促进软骨细胞分解代谢的作用，以促进炎症介导的多功能蛋白转谷氨酰胺酶2(TG2)的释放。TG2在骨关节炎软骨细胞外基质中含量丰富，在老化的软骨中TG2转酰化催化活性增加。我们观察到TG2是膝骨性关节炎严重程度的生物标志物，我们验证了整体TG2基因敲除对不稳定诱导的小鼠膝关节骨性关节炎具有保护作用。为了准确定位生物力学损伤和应激诱导的软骨先天炎症反应，这些反应提供了触发或加速骨关节炎的基础，我们将研究TG2释放和XBP1(X盒结合蛋白1)激活在软骨细胞先天炎症中的联系，我们提出的这种机制是骨关节炎发生和发展的中心切换机制。XBP1的激活是内质网应激的特异性激活，成功地化解内质网应激可促进细胞从损伤中恢复和存活。然而，XBP1的激活在先天性炎症的多个器官模型中也发挥着核心作用，包括通过Toll样受体激活。我们观察到生物力学损伤诱导了软骨细胞内质网应激的激活。此外，我们检测到活性XBP1在人膝关节骨性关节炎软骨细胞中增加。我们还观察到，培养的TG2缺陷软骨细胞降低了XBP1的活性，但细胞外TG2诱导了XBP1的激活。此外，我们还建立了软骨特异的XBP1基因敲除小鼠，以探索XBP1在软骨细胞中的功能。在这里，我们将测试一个假想的模型，在该模型中，TG2和XBP1通过转导和/或放大对生物力学损伤和氧化应激的反应，开启软骨细胞固有的炎症应激，促进骨关节炎的发生和发展。我们的主要目的是：1.验证TG2通过HIF-2α激活和TG2鸟嘌呤核苷酸结合增强培养软骨细胞生物力学损伤和氧化应激相关的分解代谢和凋亡反应的假设。2.验证TG2通过激活XBP1和降低AMPK活性来增强损伤和氧化应激诱导的软骨细胞分解代谢和凋亡反应的假说。3.在小鼠的互补性研究中验证这一假设，即软骨特异性TG2和XBP1缺陷都对OA的发生和进展具有保护作用。这些研究的完成将为阐明与生物力学损伤和衰老相关的OA的发病机制提供新的线索，并确定潜在的新治疗靶点。

DESCRIPTION (provided by applicant): Project summary/abstract: Osteoarthritis (OA) is associated with past biomechanical injury to cartilage and with aging. However, biomechanical injury and aging do not inevitably lead to OA. This proposal will focus on chondrocyte-centered innate inflammatory mechanisms in OA. We have characterized cartilage catabolism- promoting effects on chondrocytes for inflammation-mediated release of the multifunctional protein transglutaminase 2 (TG2). TG2 is abundant in the OA cartilage extracellular matrix and TG2 transamidation catalytic activity increases in aging cartilage. We observed that TG2 is a biomarker of OA severity, and we validated that global TG2 knockout is protective for instability-induced knee OA in mice. To pinpoint biomechanical injury and stress induced cartilage innate inflammatory responses that provide a foundation upon which OA is then triggered or accelerated, we will examine the linkage of TG2 release and XBP1 (X-box binding protein 1) activation in chondrocyte innate inflammation, proposed by us as a central switching mechanism for OA development and progression. XBP1 activation is specific to activation of ER stress, and successful resolution of ER stress promotes cell recovery and survival from injury. However, XBP1 activation also plays a central role in multiple organ models of innate inflammation, including via Toll-like receptor activation. We observe that biomechanical injury induces activation of ER stress in chondrocytes. Moreover, we detect active XBP1 increased in human knee OA chondrocytes. We also observe that cultured TG2 deficient chondrocytes have decreased XBP1 activation, but that extracellular TG2 induces XBP1 activation. Furthermore, we have generated cartilage-specific XBP1 knockout mice to probe for XBP1 function in chondrocytes. Here, we will test a hypothetical model in which TG2 and XBP1, by transducing and/or amplifying responses to biomechanical injury and oxidative stress, switch on chondrocyte innate inflammatory stress to promote OA development and progression. We specifically aim to: 1. Test the hypothesis that TG2 increases biomechanical injury-induced and oxidative stress-related catabolic and apoptotic responses of cultured chondrocytes mediated by HIF-2alpha activation and TG2 guanine nucleotide binding. 2. Test the hypothesis that TG2 increases injury and oxidative stress-induced catabolic and apoptotic responses of cultured chondrocytes critically mediated by XBP1 activation and decreased AMPK activity. 3. Test the hypothesis, in complementary studies in mice, that both cartilage-specific TG2 and XBP1 deficiency are protective against development and progression of OA. Completion of these studies will shed new light on the pathogenesis of OA related to biomechanical injury and aging, and identify potential new therapeutic targets.