Ammons Dylan T, Chow Lyndah, Goodrich Laurie, Bass Luke, Larson Blaine, Williams Zoë J, Stoneback Jason W, Dow Steven, Pezzanite Lynn M
Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, USA.
Department of Orthopedics, University of Colorado Anschutz Medical Campus, Aurora, CO, USA.
Ann Transl Med. 2024 Oct 20;12(5):88. doi: 10.21037/atm-24-40. Epub 2024 Oct 15.
Osteoarthritis (OA) is a major source of pain and disability worldwide. Understanding of disease progression is evolving, but OA is increasingly thought to be a multifactorial disease in which the innate immune system plays a role in regulating and perpetuating low-grade inflammation. The aim of this study was to enhance our understanding of OA immunopathogenesis through characterization of the transcriptomic responses in OA joints, with the goal to facilitate the development of targeted therapies.
Single-cell RNA sequencing (scRNA-seq) was completed on cells isolated from the synovial fluid of three normal and three OA equine joints. In addition to synovial fluid, scRNA-seq was also performed on synovium from one normal joint and one OA joint.
Characterization of 28,639 cells isolated from normal and OA-affected equine synovial fluid revealed the composition to be entirely immune cells (CD45) with 8 major populations and 26 subpopulations identified. In synovial fluid, we found myeloid cells (macrophage and dendritic cells) to be overrepresented and T cells (CD4 and CD8) to be underrepresented in OA relative to normal joints. Through subcluster and differential abundance analysis of T cells we further identified a relative overrepresentation of IL23R gamma-delta (γδ) T cells in OA-affected joints (a cell type we report to be enriched in gene signatures associated with T helper 17 mediated immunity). Analysis of an additional 17,690 cells (11 distinct cell type clusters) obtained from synovium of one horse led to the identification of an OA-associated reduction in the relative abundance of synovial macrophages, which contrasts with the increased relative abundance of macrophages in synovial fluid. Completion of cell-cell interaction analysis implicated myeloid cells in disease progression, suggesting that the myeloid-myeloid interactions were increased in OA-affected joints.
Overall, this work provides key insights into the composition of equine synovial fluid and synovium in health and OA. The data generated in this study provides equine-specific cell type gene signatures which can be applied to future investigations. Furthermore, our analysis highlights the potential role of macrophages and IL23R γδ T cells in OA immunopathogenesis.
骨关节炎（OA）是全球疼痛和残疾的主要原因。对疾病进展的认识正在不断发展，但OA越来越被认为是一种多因素疾病，其中固有免疫系统在调节和维持低度炎症中发挥作用。本研究的目的是通过对OA关节转录组反应的表征来加深我们对OA免疫发病机制的理解，以促进靶向治疗的开发。
对从三个正常和三个OA马关节滑液中分离出的细胞进行了单细胞RNA测序（scRNA-seq）。除了滑液，还对一个正常关节和一个OA关节的滑膜进行了scRNA-seq。
对从正常和OA影响的马滑液中分离出的28639个细胞的表征显示，其组成完全是免疫细胞（CD45），共鉴定出8个主要群体和26个亚群体。在滑液中，我们发现与正常关节相比，OA中髓样细胞（巨噬细胞和树突状细胞）的比例过高，而T细胞（CD4和CD8）的比例过低。通过对T细胞的亚群分析和差异丰度分析，我们进一步发现OA影响的关节中IL23R γδ T细胞相对比例过高（我们报告这种细胞类型在与辅助性T细胞17介导的免疫相关的基因特征中富集）。对从一匹马的滑膜中获得的另外17690个细胞（11个不同的细胞类型簇）的分析导致发现OA相关的滑膜巨噬细胞相对丰度降低，这与滑液中巨噬细胞相对丰度增加形成对比。细胞间相互作用分析的结果表明髓样细胞参与了疾病进展，这表明OA影响的关节中髓样细胞-髓样细胞相互作用增加。
总体而言，这项工作为健康和OA状态下马滑液和滑膜的组成提供了关键见解。本研究产生的数据提供了马特异性细胞类型基因特征，可应用于未来的研究。此外，我们的分析突出了巨噬细胞和IL23R γδ T细胞在OA免疫发病机制中的潜在作用。
