Extensive cytokine analysis in synovial fluid of osteoarthritis patients

Fibrocyte Phenotype of ENTPD1+CD55+ Cells and Its Association with Pain in Osteoarthritic Synovium

Osteoarthritis (OA) is a prevalent degenerative joint disorder characterized by cartilage erosion, structural changes, and inflammation. Synovial fibroblasts play a crucial role in OA pathophysiology, with abnormal fibroblastic cells contributing significantly to joint pathology. Fibrocytes, expressing markers of both hematopoietic and stromal cells, are implicated in inflammation and fibrosis, yet their marker and role in OA remain unclear. ENTPD1, an ectonucleotidase involved in purinergic signaling and expressed in specific fibroblasts in fibrotic conditions, led us to speculate that ENTPD1 plays a role in OA pathology by being expressed in fibrocytes. This study aimed to investigate the phenotype of ENTPD1+CD55+ and ENTPD1-CD55+ synovial fibroblasts in OA patients. Proteomic analysis revealed a distinct molecular profile in ENTPD1+CD55+ cells, including the upregulation of fibrocyte markers and extracellular matrix-related proteins. Pathway analysis suggested shared mechanisms between OA and rheumatoid arthritis. Correlation analysis revealed an association between ENTPD1+CD55+ fibrocytes and resting pain in OA. These findings highlight the potential involvement of ENTPD1 in OA pain and suggest avenues for targeted therapeutic strategies. Further research is needed to elucidate the underlying molecular mechanisms and validate potential therapeutic targets.

ASIC1a-CMPK2-mediated M1 macrophage polarization exacerbates chondrocyte senescence in osteoarthritis through IL-18

PURPOSE

Identification of a role for, and the mechanism of action of, the acid-sensing ion channel 1a (ASIC1a) in M1 macrophage polarization, which results in osteoarthritis (OA)-associated chondrocyte senescence.

METHOD

ASIC1a expression in synovial M1 macrophages of OA patients was assessed by immunofluorescence. A role for ASIC1a in M1 macrophage and chondrocyte senescence was assessed in a mouse OA model.

RESULTS

ASIC1a expression was found to be upregulated in synovial M1 macrophages of OA patients. Extracellular acidification (pH 6.0) promoted M1 polarization of bone marrow derived macrophages (BMDMs), which was reversed by PcTx-1 or ASIC1a-siRNA. RNA-seq transcriptome results demonstrated a downregulation of M1 macrophage-associated genes in BMDMs after PcTx-1 treatment. Mechanistically, a role for the ASIC1a-cytidine/uridine monophosphate kinase 2 (CMPK2) axis in M1 macrophage polarization was demonstrated. The concentration of IL-18 was elevated in synovial fluid and supernatants of acid-activated BMDMs. In vitro, IL-18 stimulation or co-culture with acid-activated macrophages promoted chondrocyte senescence. In vivo, intra-articular administration of PcTx-1 reduced articular cartilage destruction and chondrocytes senescence in OA mice, which related to reduced numbers of M1 macrophages and IL-18 in affected joints.

CONCLUSION

These results demonstrate a novel pathogenic process that results in OA cartilage damage, in which M1 macrophage derived IL-18 induces articular chondrocytes senescence. Further, the ASIC1a-CMPK2 axis was shown to positively regulate M1 macrophage polarization. Hence, ASIC1a is a promising treatment target for M1 macrophage-mediated diseases, such as OA.

Effect of immunology biomarkers associated with hip fracture and fracture risk in older adults

Osteoporosis is a skeletal disease that can increase the risk of fractures, leading to adverse health and socioeconomic consequences. However, current clinical methods have limitations in accurately estimating fracture risk, particularly in older adults. Thus, new technologies are necessary to improve the accuracy of fracture risk estimation. In this observational study, we aimed to explore the association between serum cytokines and hip fracture status in older adults, and their associations with fracture risk using the FRAX reference tool. We investigated the use of a proximity extension assay (PEA) with Olink. We compared the characteristics of the population, functional status and detailed body composition (determined using densitometry) between groups. We enrolled 40 participants, including 20 with hip fracture and 20 without fracture, and studied 46 cytokines in their serum. After conducting a score plot and two unpaired t-tests using the Benjamini-Hochberg method, we found that Interleukin 6 (IL-6), Lymphotoxin-alpha (LT-α), Fms-related tyrosine kinase 3 ligand (FLT3LG), Colony stimulating factor 1 (CSF1), and Chemokine (C-C motif) ligand 7 (CCL7) were significantly different between fracture and non-fracture patients (p < 0.05). IL-6 had a moderate correlation with FRAX (R2 = 0.409, p < 0.001), while CSF1 and CCL7 had weak correlations with FRAX. LT-α and FLT3LG exhibited a negative correlation with the risk of fracture. Our results suggest that targeted proteomic tools have the capability to identify differentially regulated proteins and may serve as potential markers for estimating fracture risk. However, longitudinal studies will be necessary to validate these results and determine the temporal patterns of changes in cytokine profiles.

The Role of Genetics and Epigenetic Regulation in the Pathogenesis of Osteoarthritis

Osteoarthritis (OA) is progressive disease characterised by cartilage degradation, subchondral bone remodelling and inflammation of the synovium. The disease is associated with obesity, mechanical load and age. However, multiple pro-inflammatory immune mediators regulate the expression of metalloproteinases, which take part in cartilage degradation. Furthermore, genetic factors also contribute to OA susceptibility. Recent studies have highlighted that epigenetic mechanisms may regulate the expression of OA-associated genes. This review aims to present the mechanisms of OA pathogenesis and summarise current evidence regarding the role of genetics and epigenetics in this process.

Effects of synovial macrophages in osteoarthritis

Osteoarthritis (OA) is a common degenerative disease in mammals. However, its pathogenesis remains unclear. Studies indicate that OA is not only an aging process that but also an inflammation-related disease. Synovitis is closely related to the progression of OA, and synovial macrophages are crucial participants in synovitis. Instead of being a homogeneous population, macrophages are polarized into M1 or M2 subtypes in OA synovial tissues. Polarization is highly associated with OA severity. However, the M1/M2 ratio cannot be the only factor in OA prognosis because intermediate stages of macrophages also exist. To better understand the mechanism of this heterogeneous disease, OA subtypes of synovial macrophages classified by gene expression were examined. Synovial macrophages do not act alone; they interact with surrounding cells such as synovial fibroblasts, osteoclasts, chondrocytes, lymphocytes and even adipose cells through a paracrine approach to exacerbate OA. Treatments targeting synovial macrophages and their polarization are effective in relieving pain and protecting cartilage during OA development. In this review, we describe how synovial macrophages and their different polarization states influence the progression of OA. We summarize the current knowledge of the interactions between macrophages and other joint cells and examine the current research on new medications targeting synovial macrophages.

Expression and diagnostic significance of integrin beta-2 in synovial fluid of patients with osteoarthritis

OBJECTIVE

Osteoarthritis (OA) is characterized by synovial cartilage degeneration and is the leading cause of disability and pain worldwide. This study sought to investigate the expression of integrin beta-2 (ITGB2) in synovial fluid of OA patients and its clinical significance.

METHODS

A total of 110 OA patients were enrolled, who were classified into grade I (N = 35), II (N = 42), and III (N = 33) according to the Kellgren-Lawrence classification, with 110 healthy subjects as controls, and their clinical data were compared. ITGB2 level was detected by RT-qPCR. The receiver operating characteristic curve was used to analyze the predictive value of ITGB2 on OA occurrence. The correlation between ITGB2 and bone metabolism indexes procollagen type I N-terminal peptide (PINP), bone glaprotein (BGP), bone alkaline phosphatase (BALP), and β-collagen I telopeptide (β-CTX) was analyzed by the Pearson method. Logistic regression model was performed to analyze the influencing factors of OA.

RESULTS

The content of red blood cells, white blood cells, PINP, BGP, and BALP was lowered in OA patients, while β-CTX was elevated. ITGB2 was highly-expressed in OA patients, negatively-correlated with PINP, BGP, and BALP, but positively-correlated with β-CTX. ITGB2 level increased with the elevation of OA grade. The ITGB2 level >1.375 had certain diagnostic values for OA. ITGB2 level is related to OA severity and may be a biomarker for OA classification. ITGB2 was an independent risk factor for OA.

CONCLUSION

High expression of ITGB2 in synovial fluid can assist OA diagnosis and may be a biomarker for OA grade.

Healthy and Osteoarthritis-Affected Joints Facing the Cellular Crosstalk

Osteoarthritis (OA) is a chronic, progressive, severely debilitating, and multifactorial joint disease that is recognized as the most common type of arthritis. During the last decade, it shows an incremental global rise in prevalence and incidence. The interaction between etiologic factors that mediate joint degradation has been explored in numerous studies. However, the underlying processes that induce OA remain obscure, largely due to the variety and complexity of these mechanisms. During synovial joint dysfunction, the osteochondral unit undergoes cellular phenotypic and functional alterations. At the cellular level, the synovial membrane is influenced by cartilage and subchondral bone cleavage fragments and extracellular matrix (ECM) degradation products from apoptotic and necrotic cells. These "foreign bodies" serve as danger-associated molecular patterns (DAMPs) that trigger innate immunity, eliciting and sustaining low-grade inflammation in the synovium. In this review, we explore the cellular and molecular communication networks established between the major joint compartments-the synovial membrane, cartilage, and subchondral bone of normal and OA-affected joints.

The Diagnostic and Prognostic Value of Synovial Fluid Analysis in Joint Diseases

Liquid biopsy is an emergent test method for the diagnosis and prognosis in the clinic. Joint fluid, also known as synovial fluid, contains a variety of bioactive constituents that can be selectively detected and further evaluated in a convenient fashion. Therefore, synovial fluid analysis functions as a specific form of liquid biopsy and plays a vital role in numerous joint diseases. In spite of the component analysis of aspirated synovial fluid beingconsidered as the gold standard for diagnosis of joint infections, biopsy of joint fluid benefits the initial diagnosis and long-term prognosis of degenerative, inflammatory, autoimmune, traumatic, congenital, and even neoplastic joint diseases. The convenience and accuracy for disease evaluation are significantly elevated as a result of the combination of synovial fluid analysis and other novel clinical technologies. In this review, we shed light on the latent role of synovial fluid in the diagnosis and prognosis of articular diseases and proposed future prospects for relevant research in this field.

Towards Precision Medicine for Osteoarthritis: Focus on the Synovial Fluid Proteome

Osteoarthritis (OA) is a joint degenerative disease that most affects old age. The study of proteomics in synovial fluid (SF) has the task of providing additional elements to diagnose and predict the progress of OA. This review aims to identify the most significant biomarkers in the study of OA and to stimulate their routine use. Some of the major components of the ECM, such as proteoglycan aggrecan and decorin, were found considerably reduced in OA. Some biomarkers have proved useful for staging the temporality of OA: Periostin was found to be increased in early OA, while CRTA1 and MMPs were found to be increased in late OA. In its natural attempt at tissue regeneration, Collagen III was found to be increased in early OA while decreased in late OA. Some molecules studied in other areas, such as ZHX3 (oncological marker), LYVE1, and VEGF (lymph and angiogenesis markers), also have been found to be altered in OA. It also has been recorded that alteration of the hormonal pathway, using a dosage of PPAR-γ and RETN, can influence the evolution of OA. IL-1, one of the most investigated biomarkers in OA-SF, is not as reliable as a target of OA in recent studies. The study of biomarkers in SF appears to be, in combination with the clinical and radiological aspects, an additional weapon to address the diagnosis and staging of OA. Therefore, it can guide us more appropriately towards the indication of arthroplasty in patients with OA.

Human Mesenchymal Stem Cell-Derived Miniature Joint System for Disease Modeling and Drug Testing

Diseases of the knee joint such as osteoarthritis (OA) affect all joint elements. An in vitro human cell-derived microphysiological system capable of simulating intraarticular tissue crosstalk is desirable for studying etiologies/pathogenesis of joint diseases and testing potential therapeutics. Herein, a human mesenchymal stem cell-derived miniature joint system (miniJoint) is generated, in which engineered osteochondral complex, synovial-like fibrous tissue, and adipose tissue are integrated into a microfluidics-enabled bioreactor. This novel design facilitates different tissues communicating while still maintaining their respective phenotypes. The miniJoint exhibits physiologically relevant changes when exposed to interleukin-1β mediated inflammation, which are similar to observations in joint diseases in humans. The potential of the miniJoint in predicting in vivo efficacy of drug treatment is confirmed by testing the "therapeutic effect" of the nonsteroidal anti-inflammatory drug, naproxen, as well as four other potential disease-modifying OA drugs. The data demonstrate that the miniJoint recapitulates complex tissue interactions, thus providing a robust organ chip model for the study of joint pathology and the development of novel therapeutic interventions.

Monocytes, Macrophages, and Their Potential Niches in Synovial Joints - Therapeutic Targets in Post-Traumatic Osteoarthritis?

Synovial joints are complex structures that enable normal locomotion. Following injury, they undergo a series of changes, including a prevalent inflammatory response. This increases the risk for development of osteoarthritis (OA), the most common joint disorder. In healthy joints, macrophages are the predominant immune cells. They regulate bone turnover, constantly scavenge debris from the joint cavity and, together with synovial fibroblasts, form a protective barrier. Macrophages thus work in concert with the non-hematopoietic stroma. In turn, the stroma provides a scaffold as well as molecular signals for macrophage survival and functional imprinting: “a macrophage niche”. These intricate cellular interactions are susceptible to perturbations like those induced by joint injury. With this review, we explore how the concepts of local tissue niches apply to synovial joints. We introduce the joint micro-anatomy and cellular players, and discuss their potential interactions in healthy joints, with an emphasis on molecular cues underlying their crosstalk and relevance to joint functionality. We then consider how these interactions are perturbed by joint injury and how they may contribute to OA pathogenesis. We conclude by discussing how understanding these changes might help identify novel therapeutic avenues with the potential of restoring joint function and reducing post-traumatic OA risk.