Cartilage Innate Immunity in Osteoarthritis

描述（由申请人提供）：原始Toll样受体（TLR）介导的先天免疫应答触发并形成许多炎症和免疫疾病。IL-1诱导软骨细胞中的TLR 2和TLR 4，并且这两种TLR在OA软骨中原位增加。此外，微生物TLR 2和TLR 4配体刺激软骨细胞中的分解代谢反应。我们的初步数据表明，共享TLR和IL-1受体衔接蛋白MyD 88（但不可溶性IL-1受体拮抗剂）钝化所有炎症诱导的分解代谢和分化反应测试软骨外植体和培养的软骨细胞。我们进一步观察到TLR 2、TLR 4双敲除（TLR 2/4 dKO）小鼠软骨外植体和软骨细胞保留了IL-1反应性，但失去了对低分子量透明质酸低聚糖（LMW-HA）和HMGB 1（OA关节中存在的两种内源性TLR 2和TLR 4配体）的反应性。此外，TLR 2/4 dKO小鼠软骨细胞失去了在软骨细胞中产生分解代谢反应的能力，不仅催化LMW-HA形成的透明质酸酶-2的表达增加，而且催化HMGB 1的表达增加。该提议的核心和翻译假设是，抑制TLR 2和TLR 4信号传导在体外和体内都具有软骨保护作用，并提供了开发疾病修饰OA治疗的新方法。我们将对软骨外植体和软骨细胞对LMW-HA和HMGB 1的反应进行体外研究，以确定TLR 2和TLR 4信号传导如何促进软骨细胞肥大和软骨细胞增殖，不仅使用MyD 88，而且使用TLR 2和TLR 4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OA进展是否被TLR 2和TLR 4的双重敲除抑制，或者被TIRAP/Mal的单一敲除抑制，以及MyD 88的敲除是否比IL-1受体的敲除对OA抑制具有上级的保护作用。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OA进展提供新的见解，并为有效的OA疾病修饰提供至少一个潜在的药物靶点。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OA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，但通过抑制IL-1抑制OA的结果尚不完整。迫切需要鉴定驱动OA进展的IL-1以外的介质，以开发这种疾病的真正有效的疾病修饰治疗。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OA的进展。迫切需要开发有效的OA疾病缓解治疗。关节中的TLR 2/4先天免疫信号转导代表了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.