Mechanical loading of joint modulates T cells in lymph nodes to regulate osteoarthritis

Injury and obesity differentially and synergistically induce dysregulation of synovial immune cells in osteoarthritis

OBJECTIVES

The heterogeneity and phenotype of immune cells orchestrate many physiologic and pathologic processes. Recent evidence suggests that immune cells play critical roles in the progression of osteoarthritis (OA). We hypothesised that injury and obesity, two major risk factors for OA, affect the immunophenotype of the synovium, the primary reservoir of immune cells in the joint.

METHODS

Using single-cell transcriptomics, immunoprofiling, transgenic mouse models, and genetic fate mapping methods, we characterised the presence and fate of multiple populations of immune cells found in the knee joint capsule.

RESULTS

We found that joint injury and obesity differentially and synergistically alter the architectural, cellular, and molecular profiles of the synovial capsule. We observed fewer patrolling monocytes in obese animals and found a significantly higher influx of proinflammatory monocyte-derived macrophages in the first 3 days after joint injury in obese compared with that in control animals. We also showed a significant loss of barrier-forming synovial lining macrophages 3 days after destabilisation of medial meniscus surgery, with a significant restoration of their numbers in normal weight but not in obese mice in advanced stages of OA. Finally, we characterised the presence and changes of other immune cell subtypes, including T, B, and mast cells and neutrophils, as well as local synovial fluid cytokines associated with injury and obesity.

CONCLUSIONS

Our data revealed that injury and obesity independently and synergistically contribute to the dysregulation of the synovial immune landscape, providing new insight into their role in the pathogenesis of OA.

The role of the immune system in osteoarthritis: mechanisms, challenges and future directions

Osteoarthritis (OA) is a chronic joint disease that has long been considered a simple wear-and-tear condition. Over the past decade, research has revealed that various inflammatory features of OA, such as low-grade peripheral inflammation and synovitis, contribute substantially to the pathophysiology of the disease. Technological advances in the past 5 years have revealed a large diversity of innate and adaptive immune cells in the joints, particularly in the synovium and infrapatellar fat pad. Notably, the presence of synovial lymphoid structures, circulating autoantibodies and alterations in memory T cell and B cell populations have been documented in OA. These data indicate a potential contribution of self-reactivity to the disease pathogenesis, blurring the often narrow and inaccurate line between chronic inflammatory and autoimmune diseases. The diverse immune changes associated with OA pathogenesis can vary across disease phenotypes, and a better characterization of their underlying molecular endotypes will be key to stratifying patients, designing novel therapeutic approaches and ultimately ameliorating treatment allocation. Furthermore, examining both articular and systemic alterations, including changes in the gut-joint axis and microbial dysbiosis, could open up novel avenues for OA management.

Osteoarthritis increases the risk of inflammatory arthritis due to immune checkpoint inhibitors associated with tissue-resident memory T cells

OBJECTIVE

Immune checkpoint inhibitors (ICIs) have significantly advanced cancer treatment, but they can also lead to immune-related adverse events (irAEs), including inflammatory arthritis. Understanding the risk factors and underlying mechanisms of irAE pathogenesis is crucial for optimal patient management. Increasing evidence suggests that ICI-mediated activation of tissue-resident memory T cells (TRM) significantly eliminates cancer cells and is associated with irAE-related colitis and dermatitis. However, it remains unknown why the development of these irAEs is restricted to a subset of patients. We hypothesized that osteoarthritis (OA) associated tissue damage and chronic inflammation lead to the recruitment and differentiation of joint TRM cells, predisposing individuals to ICI-induced arthritis.

METHODS

Using a comprehensive approach, we compared the prevalence of OA in patients with irAE-arthritis to those with irAE non-arthritis and those without irAEs. Additionally, we used advanced immunophenotyping techniques to characterize T-cell populations in the blood and synovial fluid of patients with OA and irAE-arthritis.

RESULTS

Our findings revealed a significantly higher prevalence of OA in patients who developed irAE-arthritis than controls. Furthermore, the multivariable analysis identified OA, body mass index, and smoking as independent risk factors for the development of irAE-arthritis. TRM cells expressing programmed cell death protein-1 (PD-1) were the predominant synovial T cells in OA joints. These cells were directly targeted by ICIs, resulting in an inflammatory immune response and the transition from OA to irAE-arthritis.

CONCLUSION

This study, the first of its kind, identifies OA as a significant risk factor for irAEarthritis. It reveals a potential mechanism by which ICIs activate PD-1-positive TRM cells in OA joints, resulting in tissue inflammation and irAE-arthritis. This research could significantly enhance the management and treatment of patients with cancer receiving ICIs.

Osteoimmunology in Osteoarthritis: Unraveling the Interplay of Immunity, Inflammation, and Joint Degeneration

Osteoarthritis (OA) is a degenerative joint disease influenced by multiple factors, with its etiology arising from intricate interactions among mechanical stress, inflammatory processes, and disruptions in bone metabolism. Recent research in bone immunology indicates that immune-mediated mechanisms significantly contribute to the progression of OA, highlighting the interactions among immune cells, cytokine networks, and bone components. Immune cells interact with osteoclasts, osteoblasts, and chondrocytes in a variety of ways. These interactions foster a pro-inflammatory microenvironment, contributing to cartilage breakdown, synovial inflammation, and the sclerosis of subchondral bone. In this article, we present a comprehensive review of bone immunology in OA, focusing on the critical role of immune cells and their cytokine-mediated feedback loops in the pathophysiology of OA. In addition, we are exploring novel therapeutic strategies targeting bone immune pathways, including macrophage polarization, T-cell differentiation, and stem cell therapy to restore the metabolic balance between immunity and bone. By integrating cutting-edge research in bone immunology, this review integrates the latest advancements in bone immunology to construct a comprehensive framework for unraveling the pathogenesis of OA, laying a theoretical foundation for the development of innovative precision therapies.

Advancing Osteoarthritis Research: Insights from Rodent Models and Emerging Trends

Osteoarthritis (OA) is a degenerative joint disease that affects millions of individuals worldwide, causing pain, disability, and a significant burden on public health. Preclinical research using animal models is essential to our understanding of the underlying pathogenesis of OA and developing therapeutic strategies. Rodent models, in particular, have become indispensable in studying OA due to their ability to mimic various features of human disease. This review provides an overview of commonly used rodent models of OA, including surgical induction (e.g., destabilization of the medial meniscus and anterior cruciate ligament transection), chemical induction (e.g., monoiodoacetate-induced cartilage degeneration), and genetically modified models. Additionally, age-related OA models that naturally develop OA-like symptoms in aged rodents are also discussed. Despite their utility, rodent models face limitations in fully recapitulating the complexity of human OA. Emerging trends in OA research, including the use of 3D imaging for joint analysis, molecular profiling for deeper insights into disease mechanisms, and advancements in biomarkers for early detection and treatment, are highlighted. These innovations provide new opportunities to refine existing models and enhance the translation of findings to clinical therapies. This critical review provides comprehensive information for researchers working in OA and related fields, promoting a better understanding of the available rodent models and their applications in OA research.

The role of Th/Treg immune cells in osteoarthritis

Osteoarthritis (OA) is a prevalent clinical condition affecting the entire joint, characterized by its multifactorial etiology and complex pathophysiology. The onset of OA is linked to inflammatory mediators produced by the synovium, cartilage, and subchondral bone, all of which are closely tied to cartilage degradation. Consequently, OA may also be viewed as a systemic inflammatory disorder. Emerging studies have underscored the significance of T cells in the development of OA. Notably, imbalances in Th1/Th2 and Th17/Treg immune cells may play a crucial role in the pathogenesis of OA. This review aims to compile recent advancements in understanding the role of T cells and their Th/Treg subsets in OA, examines the immune alterations and contributions of Th/Treg cells to OA progression, and proposes novel directions for future research, including potential therapeutic strategies for OA.

PTH treatment before cyclic joint loading improves cartilage health and attenuates load-induced osteoarthritis development in mice

Osteoarthritis (OA) treatment is limited by the lack of effective nonsurgical interventions to slow disease progression. Here, we examined the contributions of the subchondral bone properties to OA development. We used parathyroid hormone (PTH) to modulate bone mass before OA initiation and alendronate (ALN) to inhibit bone remodeling during OA progression. We examined the spatiotemporal progression of joint damage by combining histopathological and transcriptomic analyses across joint tissues. The additive effect of PTH pretreatment before OA initiation and ALN treatment during OA progression most effectively attenuated load-induced OA pathology. Individually, PTH directly improved cartilage health and slowed the development of cartilage damage, whereas ALN primarily attenuated subchondral bone changes associated with OA progression. Joint damage reflected early transcriptomic changes. With both treatments, the structural changes were associated with early modulation of immunoregulation and immunoresponse pathways that may contribute to disease mechanisms. Overall, our results demonstrate the potential of subchondral bone-modifying therapies to slow the progression of OA.

Skeletal interoception in osteoarthritis

The interoception maintains proper physiological conditions and metabolic homeostasis by releasing regulatory signals after perceving changes in the internal state of the organism. Among its various forms, skeletal interoception specifically regulates the metabolic homeostasis of bones. Osteoarthritis (OA) is a complex joint disorder involving cartilage, subchondral bone, and synovium. The subchondral bone undergoes continuous remodeling to adapt to dynamic joint loads. Recent findings highlight that skeletal interoception mediated by aberrant mechanical loads contributes to pathological remodeling of the subchondral bone, resulting in subchondral bone sclerosis in OA. The skeletal interoception is also a potential mechanism for chronic synovial inflammation in OA. In this review, we offer a general overview of interoception, specifically skeletal interoception, subchondral bone microenviroment and the aberrant subchondral remedeling. We also discuss the role of skeletal interoception in abnormal subchondral bone remodeling and synovial inflammation in OA, as well as the potential prospects and challenges in exploring novel OA therapies that target skeletal interoception.