Department of Orthopedic Surgery, School of Medicine, Kitasato University, 1-15-1 Minami-ku Kitasato, Sagamihara City 252-0374, Kanagawa, Japan.
Medical Sciences Research Institute, Shonan University, Nishikubo 500, Chigasaki City 253-0083, Kanagawa, Japan.
Int J Mol Sci. 2024 Oct 22;25(21):11369. doi: 10.3390/ijms252111369.
Knee osteoarthritis (KOA) is a degenerative joint disease characterized by inflammation and cartilage degradation. The infrapatellar fat pad (IFP), located beneath the patella within the knee joint, serves as a key anatomical structure involved in cushioning and supporting the knee. It is also an active endocrine organ that secretes various bioactive substances, potentially influencing the local inflammatory environment and contributing to KOA pathogenesis. Netrin-4 (NTN4), a protein primarily known for its role in neuronal guidance, has been implicated in various non-neuronal functions, including inflammatory processes and tissue remodeling. This study aims to explore the involvement of NTN4 in KOA, focusing on its expression in the IFP and its potential impact on disease progression. This study involved 82 patients with radiographically confirmed KOA undergoing total knee arthroplasty (TKA). The correlation between expression and OA pathology, including Kellgren-Lawrence (K/L) grades, was investigated. -expressing cells were identified in the stromal vascular fraction, including fibroblastic, hematopoietic, and endothelial cells of the IFP. To elucidate the molecular effects of NTN4, RNA sequencing (RNA-seq) was performed on fibroblastic cells treated with recombinant NTN4. Subsequent quantitative PCR (qPCR) was used to validate the RNA-seq findings. expression was significantly elevated in the IFP of patients with advanced KOA (K/L grades 3 and 4) compared to those with early-stage disease (K/L grade 2). Higher expression was found in fibroblastic cells, and RNA-seq analysis revealed upregulation of genes associated with pro-inflammatory pathways, including IL-17 and TNF-α signaling, and matrix degradation. Notably, genes including , , , and were significantly elevated, as confirmed by qPCR, indicating NTN4's role in promoting an inflammatory and catabolic environment. Our findings suggest that NTN4 plays a significant role in the pathogenesis of KOA by promoting inflammation and matrix degradation within the IFP. Although expression was not directly correlated with clinical symptoms, its elevated expression in fibroblastic cells and influence on inflammatory and degradative pathways suggest a potential mechanism for exacerbating joint damage. Targeting NTN4 could offer a novel therapeutic approach to mitigating inflammation and slowing disease progression in KOA, ultimately improving patient outcomes. Further research is needed to clarify NTN4's specific roles and therapeutic potential in OA management.
膝骨关节炎（KOA）是一种退行性关节疾病，其特征为炎症和软骨降解。髌下脂肪垫（IFP）位于膝关节内的髌骨下方，是缓冲和支撑膝关节的关键解剖结构。它还是一种活跃的内分泌器官，分泌各种生物活性物质，可能影响局部炎症环境并导致 KOA 发病机制。轴突导向因子 4（NTN4）主要因其在神经元导向中的作用而闻名，但也参与了各种非神经元功能，包括炎症过程和组织重塑。本研究旨在探讨 NTN4 在 KOA 中的作用，重点研究其在 IFP 中的表达及其对疾病进展的潜在影响。
这项研究纳入了 82 名经影像学证实的接受全膝关节置换术（TKA）的 KOA 患者。研究人员调查了表达与 OA 病理学之间的相关性，包括 Kellgren-Lawrence（K/L）分级。免疫荧光染色显示，NTN4 在 IFP 的基质血管部分表达，包括成纤维细胞、造血细胞和内皮细胞。为了阐明 NTN4 的分子作用，对用重组 NTN4 处理的成纤维细胞进行了 RNA 测序（RNA-seq）。随后，进行了定量 PCR（qPCR）验证 RNA-seq 结果。
研究结果显示，与早期疾病（K/L 分级 2）相比，晚期 KOA（K/L 分级 3 和 4）患者 IFP 中的表达显著升高。在成纤维细胞中发现更高的表达，RNA-seq 分析显示与促炎途径相关的基因上调，包括 IL-17 和 TNF-α 信号通路以及基质降解。值得注意的是，qPCR 证实包括、、、和在内的基因显著升高，表明 NTN4 在促进炎症和分解代谢环境中发挥作用。
我们的研究结果表明，NTN4 通过促进 IFP 中的炎症和基质降解，在 KOA 的发病机制中发挥重要作用。尽管表达与临床症状没有直接相关性，但在成纤维细胞中的高表达及其对炎症和降解途径的影响表明，它可能是加剧关节损伤的潜在机制。针对 NTN4 可能为 KOA 提供一种新的治疗方法，减轻炎症并减缓疾病进展，从而改善患者的预后。需要进一步研究来阐明 NTN4 在 OA 管理中的具体作用和治疗潜力。
