Proinflammatory T cell polarization is already present in patients with early knee osteoarthritis

Deep immunophenotyping reveals that autoimmune and autoinflammatory disorders are spread along two immunological axes capturing disease inflammation levels and types

OBJECTIVES

Based on genetic associations, McGonagle and McDermott suggested a classification of autoimmune and autoinflammatory diseases as a continuum ranging from purely autoimmune to purely autoinflammatory diseases and comprising diseases with both components. We used deep immunophenotyping to identify immune cell populations and molecular targets characterising this continuum.

METHODS

We collected blood from 443 patients with one of 15 autoimmune or autoinflammatory diseases and 71 healthy volunteers. Deep phenotyping was performed using 13 flow cytometry panels characterising over 600 innate and adaptive cell populations. Unsupervised and supervised analyses were conducted to identify disease clusters with their common and specific cell parameters.

RESULTS

Unsupervised clustering categorised these diseases into five clusters. Principal component analysis deconvoluted this clustering into two immunological axes. The first axis was driven by the ratio of LAG3+ to ICOS+ in regulatory T lymphocytes (Tregs), and segregated diseases based on their inflammation levels. The second axis was driven by activated Tregs and type 3 innate lymphoid cells (ILC3s), and segregated diseases based on their types of affected tissues. We identified a signature of 23 cell populations that accurately characterised the five disease clusters.

CONCLUSIONS

We have refined the monodimensional continuum of autoimmune and autoinflammatory diseases as a continuum characterised by both disease inflammation levels and targeted tissues. Such classification should be helpful for defining therapies. Our results call for further investigations into the role of the LAG3+/ICOS+ balance in Tregs and the contribution of ILC3s in autoimmune and autoinflammatory diseases.

TRIAL REGISTRATION NUMBER

NCT02466217.

Inflammation in osteoarthritis: Our view on its presence and involvement in disease development over the years

Inflammation, both locally in the joint and systemic, is nowadays considered among the mechanisms involved in osteoarthritis (OA). However, this concept has not always been generally accepted. In fact, for long OA has been described as a relatively simple degeneration of articular cartilage as the result of wear and tear only. In this narrative review, we present what our understanding of OA was at the time of the inaugural release of Osteoarthritis and Cartilage about 30 years ago and discuss a set of pivotal papers that changed our view on the role of inflammation in OA development. Furthermore, we briefly discuss the current view on the involvement of inflammation in OA. Next, we use the example of transforming growth factor-β signaling to show how inflammation might influence processes in the joint in a manner that is beyond the simple interaction of ligand and receptor leading to the release of inflammatory and catabolic mediators. Finally, we discuss our view on what should be done in the future to bring the field forward.

Immunoengineering Biomaterials for Musculoskeletal Tissue Repair across Lifespan

Musculoskeletal diseases and injuries are among the leading causes of pain and morbidity worldwide. Broad efforts have focused on developing pro-regenerative biomaterials to treat musculoskeletal conditions; however, these approaches have yet to make a significant clinical impact. Recent studies have demonstrated that the immune system is central in orchestrating tissue repair and that targeting pro-regenerative immune responses can improve biomaterial therapeutic outcomes. However, aging is a critical factor negatively affecting musculoskeletal tissue repair and immune function. Hence, understanding how age affects the response to biomaterials is essential for improving musculoskeletal biomaterial therapies. This review focuses on the intersection of the immune system and aging in response to biomaterials for musculoskeletal tissue repair. The article introduces the general impacts of aging on tissue physiology, the immune system, and the response to biomaterials. Then, it explains how the adaptive immune system guides the response to injury and biomaterial implants in cartilage, muscle, and bone and discusses how aging impacts these processes in each tissue type. The review concludes by highlighting future directions for the development and translation of personalized immunomodulatory biomaterials for musculoskeletal tissue repair.

Bioinformatics and Integrative Experimental Method to Identifying and Validating Co-Expressed Ferroptosis-Related Genes in OA Articular Cartilage and Synovium

Purpose

Osteoarthritis (OA) is the most common joint disease worldwide and is the primary cause of disability and chronic pain in older adults.Ferroptosis is a type of programmed cell death characterized by aberrant iron metabolism and reactive oxygen species accumulation; however, its role in OA is not known.

Methods

To identify ferroptosis markers co-expressed in articular cartilage and synovium samples from patients with OA, in silico analysis was performed.Signature genes were analyzed and the results were evaluated using a ROC curve prediction model.The biological function, correlation between Signature genes, immune cell infiltration, and ceRNA network analyses were performed. Signature genes and ferroptosis phenotypes were verified through in vivo animal experiments and clinical samples. The expression levels of non-coding RNAs in samples from patients with OA were determined using qRT-PCR. ceRNA network analysis results were confirmed using dual-luciferase assays.

Results

JUN, ATF3, and CDKN1A were identified as OA- and ferroptosis-associated signature genes. GSEA analysis demonstrated an enrichment of these genes in immune and inflammatory responses, and amino acid metabolism. The CIBERSORT algorithm showed a negative correlation between T cells and these signature genes in the cartilage, and a positive correlation in the synovium. Moreover, RP5-894D12.5 and FAM95B1 regulated the expression of JUN, ATF3, and CDKN1A by competitively binding to miR-1972, miR-665, and miR-181a-2-3p. In vivo, GPX4 was downregulated in both OA cartilage and synovium; however, GPX4 and GSH were downregulated, while ferrous ions were upregulated in patient OA cartilage and synovium samples, indicating that ferroptosis was involved in the pathogenesis of OA. Furthermore, JUN, ATF3, and CDKN1A expression was downregulated in both mouse and human OA synovial and cartilage tissues. qRT-PCR demonstrated that miR-1972, RP5-894D12.5, and FAM95B1 were differentially expressed in OA tissues. Targeted interactions between miR-1972 and JUN, and a ceRNA regulatory mechanism between RP5-894D12.5, miR-1972, and JUN were confirmed by dual-luciferase assays.

Conclusion

This study identified JUN, ATF3, and CDKN1A as possible diagnostic biomarkers and therapeutic targets for joint synovitis and OA. Furthermore, our finding indicated that RP5-894D12.5/miR-1972/JUN was a potential ceRNA regulatory axis in OA, providing an insight into the connection between ferroptosis and OA.

The Impact of 45S5-Bioactive Glass on Synovial Cells in Knee Osteoarthritis-An In Vitro Study

Synovial inflammation in osteoarthritis (OA) is characterized by the release of cartilage-degrading enzymes and inflammatory cytokines. 45S5-bioactive glass (45S5-BG) can modulate inflammation processes; however, its influence on OA-associated inflammation has hardly been investigated. In this study, the effects of 45S5-BG on the release of cartilage-degrading metalloproteinases and cytokines from synovial membrane cells (SM) isolated from patients with knee OA was assessed in vitro. SM were cultivated as SM monocultures in the presence or absence of 45S5-BG. On day 1 (d1) and d7 (d7), the concentrations of Matrix Metalloproteinases (MMPs) and cytokines were assessed. In 45S5-BG-treated SM cultures, MMP9 concentration was significantly reduced at d1 and d7, whilst MMP13 was significantly increased at d7. Concentrations of interleukin (IL)-1B and C-C motif chemokine ligand 2 (CCL2) in 45S5-BG-treated SM cultures were significantly increased at both time points, as were interferon gamma (IFNG) and IL-6 at d7. Our data show an effect of 45S5-BG on SM activity, which was not clearly protective, anti-inflammatory, or pro-inflammatory. The influence of 45S5-BG on MMP release was more suggestive of a cartilage protective effect, but 45S5-BG also increased the release of pro-inflammatory cytokines. Further studies are needed to analyze the effect of BGs on OA inflammation, including the anti-inflammatory modification of BG compositions.

Exploration of effective biomarkers and infiltrating Immune cells in Osteoarthritis based on bioinformatics analysis

Osteoarthritis (OA) is a multi-factorial chronic joint disease mainly identified by synovial inflammation, cartilage damage, and degeneration. Our study applied bioinformatics analysis to uncover the immunity in OA and tried to explore the underlying immune-related molecular mechanism. First, OA-related gene-expression profiling data were retrieved from GEO database. Then, we analysed a series of datadata with using the xCell algorithm, GEO2R, enrichment analysis of SangerBox website, CytoHubba, ROC logistic regression and correlation analysis. Finally, Nine infiltrating immune cells with differential abundance between OA and normal samples were obtained. There were 42 IODEGs in OA, and their functions were associated with immune cells and corresponding biological processes. Moreover, 5 hub genes, including GREM1, NRP1, VEGFA, FYN and IL6R, were identified. Correlation analysis demonstrated that NRP1 was negatively associated with NKT cells, NRP1 and GREM1 were positively associated with aDC, VEGFA was positively associated with CD8+ naïve T cells, while VEGFA, FYN and IL6R were negatively associated with Macrophages M1. The 5 hub genes could be employed as effective diagnostic biomarkers for OA. In addition, they may participate in OA pathogenesis via interactions with infiltrating immune cells.

Identification of key genes and their correlation with immune infiltration in osteoarthritis using integrative bioinformatics approaches and machine-learning strategies

Osteoarthritis (OA) is a common degenerative joint disease and is closely associated with chronic, low-grade inflammation. Regulating ferroptosis by targeting ferroptosis-related genes may be a fast and effective way to delay the degeneration of OA. However, the molecular mechanisms and gene targets related to ferroptosis in OA are still unclear. Data of OA samples from 3 gene expression omnibus (GEO) datasets were combined to identify differentially expressed genes (DEGs). Ferroptosis-related genes (FRGs) retrieved by the Ferroptosis database were intersected with DEGs, and the intersected hub genes were used for functional enrichment analysis. The feature genes were obtained from the least absolute shrinkage and selection operator (LASSO) algorithm, support vector machine recursive feature elimination (SVM-RFE) algorithm, and random forest (RF) algorithm. Single sample gene set enrichment analysis (ssGSEA) was used to compare immune infiltration between OA patients and normal controls, and the correlation between feature genes and immune cells was analyzed. The expression levels of feature genes were confirmed by RT-PCR. In addition, to explore the applicability of these genes, we extended the bioinformatics analysis of these feature genes to cancer. Finally, 4 feature genes, GABARAPL1, TNFAIP3, ARNTL, and JUN, were confirmed in OA. Theirs expression level were validated by RT-PCR. ROC curves of the 4 genes exhibit excellent diagnostic efficiency for OA, suggesting that the 4 genes were associated with the pathogenesis of OA. Another GEO dataset validated this result. Further analysis revealed that the 4 feature genes were all closely related to the immune infiltration cells in OA. Additionally, results of prognosis analysis indicated that JUN might be a promising therapeutic target for cancer. GABARAPL1, TNFAIP3, ARNTL, and JUN may be predicted biomarkers for OA. The feature genes and association between feature genes and immune infiltration may provide potential biomarkers for OA prediction along with the better assessment of the disease.

Neuroimmune Mechanisms Underlying Post-acute Sequelae of SARS-CoV-2 (PASC) Pain, Predictions from a Ligand-Receptor Interactome

PURPOSE OF REVIEW

Individuals with post-acute sequelae of SARS-CoV-2 (PASC) complain of persistent musculoskeletal pain. Determining how COVID-19 infection produces persistent pain would be valuable for the development of therapeutics aimed at alleviating these symptoms.

RECENT FINDINGS

To generate hypotheses regarding neuroimmune interactions in PASC, we used a ligand-receptor interactome to make predictions about how ligands from PBMCs in individuals with COVID-19 communicate with dorsal root ganglia (DRG) neurons to induce persistent pain. In a structured literature review of -omics COVID-19 studies, we identified ligands capable of binding to receptors on DRG neurons, which stimulate signaling pathways including immune cell activation and chemotaxis, the complement system, and type I interferon signaling. The most consistent finding across immune cell types was an upregulation of genes encoding the alarmins S100A8/9 and MHC-I. This ligand-receptor interactome, from our hypothesis-generating literature review, can be used to guide future research surrounding mechanisms of PASC-induced pain.

Cellular characterisation of advanced osteoarthritis knee synovium

OBJECTIVES

Osteoarthritis (OA) is increasingly recognised as a whole joint disease, with an important role for synovium. However, the repertoire of immune cells and fibroblasts that constitute OA synovium remains understudied. This study aims to characterise the cellular composition of advanced OA synovium and to explore potential correlations between different cell types and patient demographics or clinical scores.

METHODS

Synovium, collected from 10 patients with advanced OA during total knee replacement surgery, was collagenase-digested, and cells were stained for flow cytometry analysis. Formalin-fixed paraffin-embedded synovium was sectioned, stained with immunofluorescence, and imaged using the multiplex Cell DIVE platform. Patient demographics and clinical scores were also collected.

RESULTS

The proportion of immune cells in OA synovium varied between patients (8-38% of all cells). Macrophages and T cells were the dominant immune cell populations, together representing 76% of immune cells. Age positively correlated with the proportion of macrophages, and negatively correlated with T cells. CCR6+ T cells were found in 6/10 patients; these patients had a higher mean Kellgren-Lawrence grade across the three knee compartments. Immunofluorescence staining showed that macrophages were present in the lining as well as distributed throughout the sublining, while T and B cells were mainly localised near vessels in the sublining. Fibroblast subsets (CD45-PDPN+) based on the expression of CD34/CD90 or FAP/CD90 were identified in all patient samples, and some populations correlate with the percentage of immune cells or clinical scores. Immunofluorescence staining showed that FAP expression was particularly strong in the lining layer, but also present throughout the sublining layer. CD90 expression was exclusively found around vessels in the sublining, while CD34 was mostly found in the sublining but also occasionally in the lining layer.

CONCLUSIONS

There are significant differences in the relative proportions and subsets of immune cells in OA synovium; exploratory correlative analyses suggest that these differences might be correlated with age, clinical scores, or fibroblast subsets. Additional studies are required to understand how different cell types affect OA pathobiology, and if the presence or proportion of cell subsets relates to disease phenotypes.

Cartilage regeneration and inflammation modulation in knee osteoarthritis following injection of allogeneic adipose-derived mesenchymal stromal cells: a phase II, triple-blinded, placebo controlled, randomized trial

BACKGROUND

Intra-articular injection of mesenchymal stromal cells (MSCs) with immunomodulatory features and their paracrine secretion of regenerative factors proposed a noninvasive therapeutic modality for cartilage regeneration in knee osteoarthritis (KOA).

METHODS

Total number of 40 patients with KOA enrolled in two groups. Twenty patients received intra-articular injection of 100 × 10⁶ allogeneic adipose-derived mesenchymal stromal cells (AD-MSCs), and 20 patients as control group received placebo (normal saline). Questionnaire-based measurements, certain serum biomarkers, and some cell surface markers were evaluated for 1 year. Magnetic resonance imaging (MRI) before and 1 year after injection was performed to measure possible changes in the articular cartilage.

RESULTS

Forty patients allocated including 4 men (10%) and 36 women (90%) with average age of 56.1 ± 7.2 years in control group and 52.8 ± 7.5 years in AD-MSCs group. Four patients (two patients from AD-MSCs group and two patients from the control group) excluded during the study. Clinical outcome measures showed improvement in AD-MSCs group. Hyaluronic acid and cartilage oligomeric matrix protein levels in blood serum decreased significantly in patients who received AD-MSCs (P < 0.05). Although IL-10 level significantly increased after 1 week (P < 0.05), the serum level of inflammatory markers dramatically decreased after 3 months (P < 0.001). Expressions of CD3, CD4, and CD8 have a decreasing trend during 6-month follow-up (P < 0.05), (P < 0.001), and (P < 0.001), respectively. However, the number of CD25⁺ cells increased remarkably in the treatment group 3 months after intervention (P < 0.005). MRI findings showed a slight increase in the thickness of tibial and femoral articular cartilages in AD-MSCs group. The changes were significant in the medial posterior and medial anterior areas of ​​the tibia with P < 0.01 and P < 0.05, respectively.

CONCLUSION

Inter-articular injection of AD-MSCs in patients with KOA is safe. Laboratory data, MRI findings, and clinical examination of patients at different time points showed notable articular cartilage regeneration and significant improvement in the treatment group.

TRIAL REGISTRATION

Iranian registry of clinical trials (IRCT, https://en.irct.ir/trial/46 ), IRCT20080728001031N23. Registered 24 April 2018.

T Helper 17-Like Regulatory T Cells in Equine Synovial Fluid Are Associated With Disease Severity of Naturally Occurring Posttraumatic Osteoarthritis

BACKGROUND

Infiltration of cluster of differentiation (CD) 3⁺ (CD3⁺) T cells into the synovium and synovial fluid occurs in most patients with posttraumatic osteoarthritis. During disease progression, proinflammatory T helper 17 cells and anti-inflammatory regulatory T cells infiltrate the joint in response to inflammation. This study aimed to characterize the dynamics of regulatory T and T helper 17 cell populations in synovial fluid from equine clinical patients with posttraumatic osteoarthritis to determine whether phenotype and function are associated with potential immunotherapeutic targets.

HYPOTHESIS

An imbalance of the ratio of regulatory T cells and T helper 17 cells would be associated with disease progression in posttraumatic osteoarthritis, suggesting opportunities for immunomodulatory therapy.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Synovial fluid was aspirated from the joints of equine clinical patients undergoing arthroscopic surgery for posttraumatic osteoarthritis resulting from intra-articular fragmentation. Joints were classified as having mild or moderate posttraumatic osteoarthritis. Synovial fluid was also obtained from nonoperated horses with normal cartilage. Peripheral blood was obtained from horses with normal cartilage and those with mild and moderate posttraumatic osteoarthritis. Synovial fluid and peripheral blood cells were analyzed by flow cytometry, and native synovial fluid was analyzed by enzyme-linked immunosorbent assay.

RESULTS

CD3⁺ T cells represented 81% of lymphocytes in synovial fluid, which increased in animals with moderate posttraumatic osteoarthritis to 88.3% (P = .02). CD14⁺ macrophages were doubled in those with moderate posttraumatic osteoarthritis compared with mild posttraumatic osteoarthritis and controls (P < .001). Less than 5% of CD3⁺ T cells found within the joint were forkhead box P3 protein⁺ (Foxp3⁺) regulatory T cells, but a 4- to 8-times higher percentage of nonoperated and mild posttraumatic osteoarthritis joint regulatory T cells secreted interleukin (IL)-10 than peripheral blood Tregs (P < .005). T regulatory-1 cells that secreted IL-10 but did not express Foxp3 accounted for approximately 5% of CD3⁺ T cells in all joints. T helper 17 cells and Th17-like regulatory T cells were increased in those with moderate posttraumatic osteoarthritis (P < .0001) compared with mild and nonoperated patients. IL-10, IL-17A, IL-6, chemokine (C-C motif) ligand (CCL) 2 (CCL2), and CCL5 concentrations detected by enzyme-linked immunosorbent assay in synovial fluid were not different between groups.

CONCLUSIONS

An imbalance of the ratio of regulatory T cells and T helper 17 cells and an increase in T helper 17 cell-like regulatory T cells in synovial fluid from joints with more severe disease provide novel insights into immunological mechanisms that are associated with posttraumatic osteoarthritis progression and pathogenesis.

CLINICAL RELEVANCE

Early and targeted use of immunotherapeutics in the mitigation of posttraumatic osteoarthritis may improve patient clinical outcomes.

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.

Challenges in osteoarthritis treatment

Osteoarthritis (OA) is the most common form of arthritis and a degenerative joint cartilage disease that is the most common cause of disability in the world among the elderly. It leads to social, psychological, and economic costs with financial consequences. The principles of OA treatment are to reduce pain and stiffness as well as maintain function. In recent years, due to a better understanding of the underlying pathophysiology of OA, a number of potential therapeutic advances have been made, which include tissue engineering, immune system manipulation, surgical technique, pharmacological, and non-pharmacological treatments. Despite this, there is still no certain cure for OA, and different OA treatments are usually considered in relation to the stage of the disease. The purpose of the present review is to summarize and discuss the latest results of new treatments for OA and potential targets for future research.

Extensive Phenotypic Characterization of T Cells Infiltrating Liver Metastasis from Colorectal Cancer: A Potential Role in Precision Medicine

Colorectal cancer (CRC) is one of the most common cancers worldwide, with liver metastasis being its main cause of death. This study harvested fresh biological material from non-tumor and tumor tissue from 47 patients with CRC liver metastasis after surgery, followed by mechanical cellular extraction and stain-lyse-wash direct immunofluorescence technique. Here, 60 different T-cell populations were characterized by flow cytometry. Tumor samples were also subdivided according to their growth pattern into desmoplastic and non-desmoplastic. When we compared tumor versus non-tumor samples, we observed a significantly lower percentage of T-lymphocyte infiltration in the tumor in which the CD4⁺ T-cell density increased compared to the CD8⁺ T cells. T regulatory cells also increased within the tumor, even with an activated phenotype (HLA-DR⁺). A higher percentage of IL-17-producing cells was present in tumor samples and correlated with the metastasis size. In contrast, we also observed a significant increase in CD8⁺ follicular-like T cells (CD185⁺), suggesting a cytotoxic response to cancer cells. Additionally, most infiltrated T cells exhibit an intermediate activation phenotype (CD25⁺). In conclusion, our results revealed potential new targets and prognostic biomarkers that could take part in an algorithm for personalized medicine approaches improving CRC patients' outcomes.

Collagenase-Induced Mouse Model of Osteoarthritis-A Thorough Flow Cytometry Analysis

OBJECTIVES

Osteoarthritis (OA) is a chronic degenerative disorder of the joint characterized by cartilage breakdown and synovial inflammation. A number of different cells of innate and adaptive immunity contribute to joint pathology during OA inflammation. The interaction between the local synovial and systemic inflammatory cellular response and the structural changes in the joint is still unknown. The objective of this study was to investigate the role of the different types of immune cells in the development of OA.

METHODS

Collagenase-induced osteoarthritis was induced in Balb/c mice; flow cytometry analysis; and histopathological damages were assessed in histological sections stained with H&E, Toluidine blue, and Safranin O.

RESULTS

Flow cytometry analysis showed B lymphocyte infiltration in the active phase of inflammation and an increase in the effector T cell population into the synovium. An increased activation state of cytotoxic T cells and of NK cell populations in the spleen and synovium was also found. The differentiation of NK cells from a cytotoxic phenotype in early OA to cells with an effector phenotype in the chronic phase of the disease followed.

CONCLUSIONS

A number of different cells contribute to inflammatory processes in OA. The correlation between their phenotype and the inflammatory pathophysiology could result in the development of novel approaches to suppress destructive changes in the joint.

Secreted Factors and Extracellular Vesicles Account for the Immunomodulatory and Tissue Regenerative Properties of Bone-Marrow-Derived Mesenchymal Stromal Cells for Osteoarthritis

Bone-marrow-derived mesenchymal stromal cells (BMSCs) showed therapeutic potential in the treatment of musculoskeletal diseases, including osteoarthritis (OA). Their soluble mediators and extracellular vesicles (EVs), which make up the secretome, suppress immune response, attenuate inflammation and promote cartilage repair. EVs, as well as the whole secretome, have been investigated as cell free approaches for OA although, to date, a disease-tailored molecular fingerprint is missing. In this study, soluble mediators and miRNAs were sifted in the BMSCs' secretome and EVs, respectively, and analyzed in the frame of cell types and factors involved in OA. The majority of identified molecules repress the activation of immune cells and the production of OA-related inflammatory mediators, as well as promote cartilage protection by acting on both chondrocytes homeostasis and extracellular matrix-degrading enzymes. These data provide the molecular ground for the therapeutic potential of BMSCs for regenerative applications for OA and support the use of secretome or EVs as cell-free applications in joint diseases.

In Vitro Anti-Inflammatory and Regenerative Effects of Autologous Conditioned Serum from Dogs with Osteoarthritis

Osteoarthritis (OA) is mostly incurable and non-regenerative with long-term complications. Autologous conditioned serum (ACS), which is enriched in Interleukin 1 receptor antagonists (IL-1RA) and growth factors, could be an alternative treatment to accelerate the positive therapeutic effects. ACS is proposed to alleviate inflammation by blocking IL-1 receptors. However, to date, there is no report focusing on the cell-mediated anti-inflammation and regenerative effect caused by ACS, especially the ACS from patients. Therefore, this study aims to investigate the therapeutic potential of ACS generated from dogs with spontaneous OA, focusing on its promising anti-inflammatory and regenerative properties in vitro compared to the matched plasma. We found that ACS prepared from ten OA dogs contained significant concentrations of IL-1RA, vascular endothelial growth factor, and transforming growth factor beta, which are key cytokines in anti-inflammation and angiogenesis. Furthermore, we found that ACS suppressed T cell activity by reducing proliferation of effector T cells and simultaneously expanding numbers of immune suppressive FOXP3+ T cells. Lastly, we showed that ACS enhanced the proliferation of osteocytes and fibroblasts and promoted extracellular matrix gene expression in primary chondrocyte culture. Therefore, these studies indicate that ACS prepared from dogs with OA is active as an immunomodulatory and regenerative strategy for use in OA management.

Biological Targets of Multimolecular Therapies in Middle-Age Osteoarthritis

Knee osteoarthritis (OA) is a common condition, prevalent in middle-agedness, associated with chronic pain and impaired quality of life. Two interrelated biological processes fuel early OA progression: inflammation and structural tissues catabolism. Procatabolic and proinflammatory mediators are interconnected and form part of a self-perpetuating loop. They leverage OA research complexity because of the impossibility to discern certain spatiotemporal tissues' changes from others. Both are shared targets of versatile regenerative multimolecular therapies. In particular, platelet-rich plasma can interfere with inflammation and inflammatory pain. The therapeutic approach is to alter the vicious inflammatory loop by modifying the molecular composition of the synovial fluid, thereby paracrine cellular cross talk. Intra-articular injections of platelet-rich plasma can provide key factors balancing proinflammatory and anti-inflammatory factors, targeting macrophage dysfunction and modulating immune mechanisms within the knee.

Infiltration Profile of Regulatory T Cells in Osteoarthritis-Related Pain and Disability

Emerging evidence indicates that regulatory T cells (Treg) intervene in the inflammatory processes that drive osteoarthritis (OA). However, whether polarized Tregs affect clinical features of the disease in the short- or long-term, and if so, what their role in OA-related pain and functional disability really is, remains elusive. Thus, the aim of the current study was to characterize the infiltration profile of Tregs in systemic (peripheral blood) and joint-derived (synovial fluid and synovial membrane) samples from patients with knee OA in relation to OA-induced symptoms. To this end, Treg infiltration (CD4⁺CD25^+/high CD127^low/−) was analyzed in matched samples of peripheral blood (PB), synovial fluid (SF) and synovial membrane (SM) from a total of 47 patients undergoing elective knee arthroplasty using flow cytometry. At the same time, knee pain and function were assessed and correlated with Treg proportions in different compartments (PB, SF, SM). Interestingly, matched-pair analysis revealed significantly higher Treg proportions in joint-derived samples than in PB, which was mainly attributed to the high Treg frequency in SF. Moreover, we found significant associations between infiltrating Tregs and OA-related symptoms which indicate that lower Treg proportions—especially in the SM—are related to increased pain and functional disability in knee OA. In conclusion, this study highlights the importance of local cellular inflammatory processes in OA pathology. Intra-articular Treg infiltration might play an important role not only in OA pathogenesis but also in the development of OA-related symptoms.

Involvement of complement peptides C3a and C5a in osteoarthritis pathology

Osteoarthritis (OA) affects more than 500 million people worldwide and is among the five diseases in Germany causing the highest suffering of the patients and cost for the society. The quality of life of OA patients is severely compromised, and adequate therapy is lacking owing to a knowledge gap that acts as a major barrier to finding safe and effective solutions. Chronic, low-grade inflammation plays a central role in OA pathogenesis and is associated with both OA pain and disease progression. Innate immune pathways, such as the complement- and pattern-recognition receptor pathways, are pivotal to the inflammation in OA and key components of the innate immune system implicated in OA include DAMP-TLR signaling, the complement system, carboxypeptidase B (CPB), and mononuclear cells. Anaphylatoxins C3a and C5a are small polypeptides (77 and 74 amino acids, respectively) which are released by proteolytic cleavage of the complement components C3 and C5. The alternative complement pathway seems to play a crucial role in OA pathogenesis as these complement components, mostly C3 and its activation peptide C3a, were detected at high levels in osteoarthritic cartilage, synovial membrane, and cultured chondrocytes. Targeting the complement system by using anti-complement drugs as a therapeutic option bears the risk of major side effects such as increasing the risk of infection, interfering with cell regeneration and metabolism, and suppressing the clearance of immune complexes. Despite those adverse effects, several synthetic complement peptide antagonists show promising effects in ameliorating inflammatory cell responses also in joint tissues.

Identification of Biomarkers Associated with Diagnosis of Osteoarthritis Patients Based on Bioinformatics and Machine Learning

Osteoarthritis (OA) is thought to be the most prevalent chronic joint disease. The incidence of OA is rising because of the ageing population and the epidemic of obesity. This research was designed for the identification of novel diagnostic biomarkers for OA and analyzing the possible association between critical genes and infiltrated immune cells. 10 OA samples from patients with spinal OA and 10 normal samples were collected. GSE55235 and GSE55457 datasets including human OA and normal samples were downloaded from the GEO datasets. Differentially expressed genes (DEGs) were identified between 20 OA and 20 controls. SVM-RFE analysis and LASSO regression model were carried out to screen possible markers. The compositional patterns of the 22 types of immune cell fraction in OA were determined by the use of CIBERSORT. The expression level of the biomarkers in OA was examined by the use of RT-PCR. In this study, an overall 44 DEGs were identified: 18 genes were remarkably upregulated and 26 genes were distinctly downregulated. KEGG pathway analyses revealed that pathways were significantly enriched including IL-17 signal path, rheumatoid arthritis, TNF signal path, and lipid and atherosclerosis. Based on the results of machine learning, we identified APOLD1 and EPYC as critical diagnostic genes in OA, which were further confirmed using ROC assays. Immune cell infiltration analysis revealed that APOLD1 was correlated with mastocytes stimulated, NK cells resting, T cells CD4 memory resting, DCs stimulated, T cells gamma delta, macrophages M0, NK cells stimulated, and mastocytes resting. Moreover, we found that EPYC was correlated with mastocytes stimulated, NK cells resting, T cells CD4 memory resting, DCs stimulated, T cells gamma delta, macrophages M0, NK cells stimulated, and mastocytes resting. Overall, our findings might provide some novel clue for the exploration of novel markers for OA diagnosis. The critical genes and their associations with immune infiltration may offer new insight into understanding OA developments.

CD8+ T Cells in OA Knee Joints Are Differentiated into Subsets Depending on OA Stage and Compartment

Osteoarthritis (OA) is no longer considered a purely degenerative disease. OA is defined as a disease of the entire joint, in which inflammation occurs in various joint tissues. The overall aim of this study was to analyze the presence and polarization of CD8⁺ T cell subsets in OA knee joints, in relation to the OA stage and compartment (synovial fluid (SF), synovial membrane (SM,) peripheral blood (PB)). A quantitative flow analysis of CD8⁺ T cell subsets to compare the SF, SM, PB, was performed in patients with different stages of OA (early, unicondylar and bicondylar OA). Samples of the SF, SM and PB were harvested from a total of 55 patients at the time of surgery. Early OA was confirmed by independent surgeons intraoperatively. Uni- and bicondylar OA was confirmed and graded by two plane radiographs. Samples were analyzed by flow cytometry for surface markers, and cytokines by intracellular staining (ICS). CD8⁺ T cells were shown to be differentiated into pro-inflammatory IFN-γ producing Tc1 and IL-17A producing Tc17, as well as anti-inflammatory IL-4 producing Tc2. All CD8⁺ T cell subsets (Tc1, Tc17, and Tc2) were detected in both the SM and SF. The percentage of CD8⁺ T cell subsets of the total CD8⁺ T cell population was dependent on the OA stage and compartment. Compared with the peripheral blood (PB), the proportion of CD8⁺IFN-γ⁺ Tc1 and CD8⁺IL-17A⁺ Tc17 was significantly increased in OA SF. This was confirmed in our data for both early OA and end-stage OA. In the SM samples of end-stage OA patients, the proportion of CD8⁺IL-17A⁺ Tc17 was significantly increased compared to the PB. Comparing SF and SM samples of end-stage OA patients, the proportion of CD8⁺IFN-γ⁺ Tc1 was significantly increased in SF, whereas there were no differences concerning CD8⁺IL-4⁺ Tc2 and CD8⁺IL-17A⁺ Tc17. End-stage OA samples showed a significant increase of CD8⁺IL-4⁺ Tc2 in the SM for both unicondylar and bicondylar OA compared to early OA. CD8⁺ T cells infiltrating the SM and SF in OA knees are differentiated into IFN-γ-, IL-17A-, and IL-4-producing CD8⁺ T cell subsets (Tc1, Tc17, Tc2). This differentiation depends on the OA stage and OA compartment. Further investigation of CD8⁺ T cell subsets and their interaction with other inflammatory cells such as CD4⁺ T cells and macrophages may help to identify novel therapeutic anti-inflammatory strategies for containing OA progression.

The Genesis of Pain in Osteoarthritis: Inflammation as a Mediator of Osteoarthritis Pain

Chronic pain is a substantial personal and societal burden worldwide. Osteoarthritis (OA) is one of the leading causes of chronic pain and is increasing in prevalence in accordance with a global aging population. In addition to affecting patients' physical lives, chronic pain also adversely affects patients' mental wellbeing. However, there remain no pharmacologic interventions to slow down the progression of OA and pain-alleviating therapies are largely unsuccessful. The presence of low-level inflammation in OA has been recognized for many years as a major pathogenic driver of joint damage. Inflammatory mechanisms can occur locally in joint tissues, such as the synovium, within the sensory nervous system, as well as systemically, caused by modifiable and unmodifiable factors. Understanding how inflammation may contribute to, and modify pain in OA will be instrumental in identifying new druggable targets for analgesic therapies. In this narrative review, we discuss recent insights into inflammatory mechanisms in OA pain. We discuss how local inflammation in the joint can contribute to mechanical sensitization and to the structural neuroplasticity of joint nociceptors, through pro-inflammatory factors such as nerve growth factor, cytokines, and chemokines. We consider the role of synovitis, and the amplifying mechanisms of neuroimmune interactions. We then explore emerging evidence around the role of neuroinflammation in the dorsal root ganglia and dorsal horn. Finally, we discuss how systemic inflammation associated with obesity may modify OA pain and suggest future research directions.

Synovial inflammation in osteoarthritis progression

Osteoarthritis (OA) is a progressive degenerative disease resulting in joint deterioration. Synovial inflammation is present in the OA joint and has been associated with radiographic and pain progression. Several OA risk factors, including ageing, obesity, trauma and mechanical loading, play a role in OA pathogenesis, likely by modifying synovial biology. In addition, other factors, such as mitochondrial dysfunction, damage-associated molecular patterns, cytokines, metabolites and crystals in the synovium, activate synovial cells and mediate synovial inflammation. An understanding of the activated pathways that are involved in OA-related synovial inflammation could form the basis for the stratification of patients and the development of novel therapeutics. This Review focuses on the biology of the OA synovium, how the cells residing in or recruited to the synovium interact with each other, how they become activated, how they contribute to OA progression and their interplay with other joint structures.

Osteoarthritis Pathophysiology: Therapeutic Target Discovery may Require a Multifaceted Approach

Molecular understanding of osteoarthritis (OA) has greatly increased through careful analysis of tissue samples, preclinical models, and large-scale agnostic "-omic" studies. There is broad acceptance that systemic and biomechanical signals affect multiple tissues of the joint, each of which could potentially be targeted to improve patient outcomes. In this review six experts in different aspects of OA pathogenesis provide their independent view on what they believe to be good tractable approaches to OA target discovery. We conclude that molecular discovery has been high but future transformative studies require a multidisciplinary holistic approach to develop therapeutic strategies with high clinical efficacy.

Unraveling the Signaling Secretome of Platelet-Rich Plasma: Towards a Better Understanding of Its Therapeutic Potential in Knee Osteoarthritis

Platelets and their secretory products play an important role in determining the balance between tissue repair and tissue damage. To obtain novel insights into the molecular composition of platelet-rich plasma (PRP) and contextualize them in knee osteoarthritis (OA), two different plasma formulations, namely PRP and platelet-poor plasma (PPP), were prepared from six healthy donors following a biobank-automated protocol. Inter-donor differences were analyzed, and pools were created before performing multiplexing protein arrays. In addition, PRP and PPP were prepared from six patients following our in-house protocols. Supernatants from PRP and PPP were harvested one hour after calcium chloride activation. Multiplexing protein arrays were performed in parallel for all plasma formulations. Results were normalized to fold change in relation to PPP and examined using Ingenuity Pathway Analysis Software. Bioinformatic predictions showed that PRPs constitute a signaling system with interrelated networks of inflammatory and angiogenic proteins, including but not limited to interleukin-6 and -8 (IL-6, IL-8), insulin like growth factor 1 (IGF-1), transforming growth factor beta, (TGF-b), and vascular endothelial growth factor (VEGF) signaling, underlying biological actions. Predictions of canonical systems activated with PRP molecules include various inflammatory pathways, including high-mobility group box protein (HMGB1) and interleukin 17 (IL-17) signaling, neuroinflammation, and nuclear factor-kappa b (NF-κB) pathways. Eventually, according to these predictions and OA evolving knowledge, selected PRP formulations should be tailored to modulate different inflammatory phenotypes, i.e., meta-inflammation, inflame-aging or posttraumatic inflammatory osteoarthritis. However, further research to discriminate the peculiarities of autologous versus allogeneic formulations and their effects on the various OA inflammatory phenotypes is needed to foster PRPs.

Anti-Inflammatory Therapeutic Approaches to Prevent or Delay Post-Traumatic Osteoarthritis (PTOA) of the Knee Joint with a Focus on Sustained Delivery Approaches

Inflammation plays a central role in the pathogenesis of knee PTOA after knee trauma. While a comprehensive therapy capable of preventing or delaying post-traumatic osteoarthritis (PTOA) progression after knee joint injury does not yet clinically exist, current literature suggests that certain aspects of early post-traumatic pathology of the knee joint may be prevented or delayed by anti-inflammatory therapeutic interventions. We discuss multifaceted therapeutic approaches that may be capable of effectively reducing the continuous cycle of inflammation and concomitant processes that lead to cartilage degradation as well as those that can simultaneously promote intrinsic repair processes. Within this context, we focus on early disease prevention, the optimal timeframe of treatment and possible long-lasting sustained delivery local modes of treatments that could prevent knee joint-associated PTOA symptoms. Specifically, we identify anti-inflammatory candidates that are not only anti-inflammatory but also anti-degenerative, anti-apoptotic and pro-regenerative.