Cartilage Innate Immunity in Osteoarthritis

描述(由申请人提供)：原始Toll样受体(TLR)介导的先天免疫反应触发和塑造许多炎症和免疫疾病。IL-1可诱导软骨细胞表达TLR2和TLR4，在骨性关节炎软骨中这两种TLR2和TLR4原位表达增加。此外，微生物TLR2和TLR4配体刺激软骨细胞的分解代谢反应。我们的初步数据显示，共有的TLR和IL-1受体适配器蛋白MyD88(但不是可溶性IL-1受体拮抗剂)可以钝化在软骨外植体和培养的软骨细胞中测试的所有炎症诱导的分解代谢和分化反应。我们进一步观察到，TLR2、TLR4双基因敲除(TLR2/4 dKO)小鼠软骨外植体和软骨细胞保留了IL-1的反应性，但对低分子透明质酸寡糖(LMW-HA)和HMGB1(存在于OA关节中的两种内源性TLR2和TLR4配体)失去了反应性。此外，TLR2/4 dKO小鼠软骨细胞失去了在软骨细胞中建立分解代谢反应的能力，不仅增加了催化LMW-HA形成的透明质酸酶-2的表达，而且还增加了HMGB1的表达。这一建议的中心和翻译假设是，抑制TLR2和TLR4信号在体外和体内都具有软骨保护作用，并为开发治疗疾病的OA提供了新的手段。我们将进行软骨移植和软骨细胞对LMW-HA和HMGB1的体外反应研究，以确定TLR2和TLR4信号如何促进软骨细胞肥大和软骨分解代谢，不仅使用MyD88，还使用TIRAP/MAL，TIRAP/MAL是TLR2和TLR4信号选择性所需的。我们还将使用手术不稳定诱导的膝关节骨关节炎模型进行体内研究，以评估TLR2和TLR4的双重敲除以及TIRAP/MAL的单一敲除是否抑制了OA的进展，以及MyD88敲除是否比IL-1受体敲除对OA的抑制具有更好的保护作用。这些研究的完成将为软骨中的先天免疫炎症反应如何促进骨性关节炎的进展提供新的见解，并为有效地治疗骨性关节炎疾病提供至少一个潜在的可用药靶点。相关性：骨关节炎(OA)是最常见的与衰老有关的关节疾病。软骨中的低度炎症促进了骨性关节炎的进展。白介素1(IL-1)是一种炎症介质，可促进骨性关节炎的进展，但通过抑制IL-1来抑制骨性关节炎的研究结果尚不完全。迫切需要确定IL-1以外的促进骨性关节炎进展的介质，以便开发出真正有效的疾病修饰治疗方法。公共卫生相关性：骨关节炎(OA)是最常见的与衰老有关的关节疾病。软骨中的低度炎症促进了骨性关节炎的进展。目前迫切需要为骨性关节炎开发有效的疾病修正治疗方法。关节中的TLR2/4先天免疫信号代表了骨关节炎的一个新靶点。

DESCRIPTION (provided by applicant): Primitive Toll-like receptor (TLR)-mediated innate immune responses trigger and shape many inflammatory and immune disorders. IL-1 induces TLR2 and TLR4 in chondrocytes and both TLRs are increased in OA cartilage in situ. Moreover, microbial TLR2 and TLR4 ligands stimulate catabolic responses in chondrocytes. Our preliminary data reveal that the shared TLR and IL-1 receptor adaptor protein MyD88 (but not soluble IL-1 receptor antagonist) blunts all inflammation-induced catabolic and differentiation responses tested in cartilage explants and cultured chondrocytes. We further observe that TLR2, TLR4 double knockout (TLR2/4 dKO) mouse cartilage explants and chondrocytes retain IL-1 responsiveness, but lose responsiveness to low molecular weight hyaluronan oligosaccharides (LMW-HA) and HMGB1, two endogenous TLR2 and TLR4 ligands present in OA joints. In addition, TLR2/4 dKO mouse chondrocytes lose the capacity to mount a catabolic response in chondrocytes with increased expression of not only hyaluronidase-2 which catalyzes LMW-HA formation but also HMGB1. The central and translational hypothesis of this proposal is that inhibition of both TLR2 and TLR4 signaling is chondroprotective both in vitro and in vivo and offers novel means to develop disease-modifying OA therapy. We will perform in vitro studies on responses of cartilage explants and chondrocytes to LMW-HA and HMGB1 to determine how TLR2 and TLR4 signaling promotes chondrocyte hypertrophy and cartilage catabolism using not only MyD88, but also TIRAP/Mal which is selectively required for TLR2 and TLR4 signaling. We will also perform in vivo studies using a surgical instability-induced knee OA model to assess if OA progression is suppressed by dual knockout of TLR2 and TLR4, and alternatively by single knockout of TIRAP/Mal, and if knockout of MyD88 has superior protective effects than knockout of IL-1 receptor for OA suppression. Completion of these studies will provide new insights into how innate immune inflammatory responses in cartilage promote OA progression and provide at least one potentially druggable target for effective OA disease modification. Relevance: Osteoarthritis (OA) is the most common joint disease related to aging. Progression of OA is promoted by low- grade inflammation in cartilage. Interleukin-1 (IL-1), an inflammatory mediator, promotes the progression of OA, but results have been incomplete for suppression of OA via IL-1 inhibition. There is a pressing need to identify mediators beyond IL-1 that drive OA progression, in order to develop true and effective disease modifying treatment of this disease. PUBLIC HEALTH RELEVANCE: Osteoarthritis (OA) is the most common joint disease related to aging. Progression of OA is promoted by low-grade inflammation in cartilage. There is a pressing need to develop effective disease modifying treatment for OA. TLR2/4 innate immune signaling in the joint represents a novel target for OA.