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并形成许多炎症和免疫疾病。IL-1诱导软骨细胞中的TLR2和TLR4，两种tlr在OA软骨中原位升高。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，在软骨外植体和培养的软骨细胞中，共享的TLR和IL-1受体接头蛋白MyD88（但不是可溶性IL-1受体拮抗剂）减弱了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双敲除（TLR2/4 dKO）小鼠软骨外植体和软骨细胞保留了IL-1的响应性，但对OA关节中存在的两种内源性TLR2和TLR4配体低分子量透明质酸寡糖（lw - ha）和HMGB1失去了响应性。此外，TLR2/4 dKO小鼠软骨细胞失去了在软骨细胞中进行分解代谢反应的能力，不仅透明质酸酶-2（催化lw - ha形成）的表达增加，HMGB1的表达也增加。该建议的中心和翻译假设是，TLR2和TLR4信号的抑制在体外和体内都具有软骨保护作用，并为开发改善疾病的OA治疗提供了新的手段。我们将在体外研究软骨外植体和软骨细胞对lw - ha和HMGB1的反应，以确定TLR2和TLR4信号传导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TLR2和TLR4信号传导选择性所需的TIRAP/Mal。我们还将使用手术不稳定诱导的膝关节OA模型进行体内研究，以评估是否通过双重敲除TLR2和TLR4或通过单一敲除TIRAP/Mal来抑制OA进展，以及敲除MyD88是否比敲除IL-1受体具有更好的OA抑制保护作用。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OA进展提供新的见解，并为有效的OA疾病改变提供至少一个潜在的可药物靶点。相关性：骨关节炎（OA）是最常见的与衰老相关的关节疾病。软骨低度炎症可促进骨性关节炎的进展。白细胞介素-1 （IL-1）是一种炎症介质，可促进OA的进展，但通过IL-1抑制OA的结果尚不完整。目前迫切需要确定除IL-1外驱动OA进展的介质，以便开发出真正有效的疾病改善治疗方法。公共卫生相关性：骨关节炎（OA）是最常见的与衰老相关的关节疾病。软骨低度炎症可促进骨性关节炎的进展。迫切需要开发有效的疾病调节治疗OA。关节中的TLR2/4先天免疫信号是OA的新靶点。

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.