Comprehensive characterization of pathogenic synovial fluid extracellular vesicles from knee osteoarthritis

Plasma extracellular vesicles carry immune system-related peptides that predict human longevity

Extracellular vesicles (EVs) play crucial roles in aging. In this National Institutes on Aging-funded study, we sought to identify circulating extracellular vesicle (EV) biomarkers indicative of longevity. The plasma EV proteome of 48 older adults (mean age 77.2 ± 1.7 years [range 72-80]; 50% female, 50% Black, 50% < 2-year survival, 50% ≥ 10-year survival) was analyzed by high-resolution mass spectrometry and flow cytometry. The ability of EV peptides to predict longevity was evaluated in discovery (n = 32) and validation (n = 16) datasets with areas under receiver operating characteristic curves (AUCs). Longevity-associated large EV (LEV) plasma subpopulations were mainly related to immune cells (HLA-ABC+, CD9+, and CD31+) and muscle cells (MCAD+ and RyR2+). Of 7960 identified plasma EV peptides (519 proteins), 46.4% were related to the immune system and 10.1% to muscle. Compared with short-lived older adults, 756 EV peptides (131 proteins) had a higher abundance, and 130 EV peptides (78 proteins) had a lower abundance in long-lived adults. Among longevity-associated peptides, 437 (58 proteins) were immune system related, and 12 (2 proteins) were muscle related. Using just three to five plasma EV peptides (mainly complement components C2-C6), we achieved high predictive accuracy for longevity (AUC range 0.91-1 in a hold-out validation dataset). Our findings suggest that immune cells produce longevity-associated plasma EVs and elucidate fundamental mechanisms regulating aging and longevity. EV longevity predictors suggest there may be merit in targeting complement pathways to extend lifespan, for instance, with any one of the multiple complement inhibitors currently available or in clinical development.

Roles of innate immune system and receptor Dectin-1 in synovium and cartilage homeostasis of osteoarthritis

BACKGROUND

Innate immunity is crucial in the progression of osteoarthritis (OA); however, its mechanisms require further exploration. This study aims to investigate the mechanisms of innate immunity in OA synovitis.

METHODS

RNA sequencing data were analyzed to detect the expression characteristics of innate immunity-related genes in OA synovium. The Search Tool for the Retrieval of Interaction Gene/Proteins (STRING) database was used to identify hub genes, and an OA diagnostic model was constructed using 113 combinations of machine learning algorithms. Single-cell sequencing data were used to identify the expression patterns of hub genes and innate immunity-related pathways in cell clusters and to illustrate the interactions among cell populations. The functional mechanism of Dectin-1 in OA was validated experimentally.

RESULTS

Innate immunity-related genes and pathways were significantly expressed in the synovium of patients with OA. We constructed an OA diagnostic model, and HLA-DRA+ cells were identified as a critical cell population. The innate immune receptor Dectin-1 on macrophages regulated macrophage M1 polarization and cartilage homeostasis via the Dectin-1/Syk/NF-κB pathway, influencing the progression of OA.

CONCLUSION

This study reveals the expression patterns of innate immunity-related genes and pathways in the OA synovium and highlights the role of Dectin-1 in macrophages.

The communication role of extracellular vesicles in the osteoarthritis microenvironment

Osteoarthritis (OA) is the most common degenerative joint disease worldwide, characterized by synovial inflammation, cartilage loss, and reactive hyperplasia of subchondral bone, affecting the quality of life of hundreds of millions of people. However, the molecular mechanisms underlying the occurrence and progression of OA remain unclear, and there is no therapy can substantially interrupt or reverse the destructive process of OA. More insight into the pathogenesis of OA may result in innovative therapeutics. The OA microenvironment plays a pivotal role in the development and progression of OA, which encompasses chondrocytes, adipocytes, synovial fibroblasts, endothelial cells, and immune cells. Extracellular vesicles (EVs) have emerged as a novel form of intercellular communication, mediating the transfer of a range of bioactive molecules to create a specific microenvironment. Recent studies have reported that the cargos of EVs play a crucial role in the pathogenesis of OA, including noncoding RNAs (ncRNAs), proteins, and lipids. This review systematically analyzes and summarizes the biological characteristics and functionalities of EVs derived from diverse cellular sources, especially how EVs mediate communication between different cells in the OA microenvironment, with a view to providing new insights into the pathogenesis of OA.

Disease-Associated Signatures Persist in Extracellular Vesicles from Reprogrammed Cells of Osteoarthritis Patients

Osteoarthritis (OA) is a prevalent joint disorder that lacks effective therapies to halt cartilage degeneration. Mesenchymal stromal cell (MSC)-derived small extracellular vesicles (sEVs) are being investigated as promising chondroprotective agents. Compared to primary MSCs, induced pluripotent stem cell (iPSC)-derived MSCs (MLCs) offer superior scalability and enhanced paracrine activity. The aim of this study was to explore the feasibility of using autologous MLC-derived sEVs as a potential therapeutic strategy for OA through the analysis of their protein cargo. iPSCs from an OA patient and a healthy donor were differentiated into MLCs. sEVs were isolated from these MLCs and characterized, with a particular focus on their protein cargo. Both iPSC lines were successfully differentiated into MLCs, which secreted sEVs with comparable size distributions and yields. The analysis of differentially expressed proteins revealed a high abundance of proteins associated with OA pathology and cartilage degradation in sEVs from OA MLCs compared to those from healthy MLCs. The persistence of OA-associated protein signatures in autologous MLC-derived sEVs may limit their therapeutic efficacy. These findings underscore the importance of carefully evaluating disease-specific protein profiles in sEVs for regenerative applications.

Osteoarthritis Year in Review 2024: Molecular biomarkers of osteoarthritis

OBJECTIVE

To provide a comprehensive and insightful summary of studies on molecular biomarkers at the gene, protein, and metabolite levels across different sample types and joints affected by osteoarthritis (OA).

METHODS

A literature search using the PubMed database for publications on OA biomarkers published between April 1, 2023 and April 30, 2024 was performed. Publications were then screened, examined at length, and summarized in a narrative review.

RESULTS

Out of the 364 papers initially identified, 44 publications met inclusion criteria, were relevant to OA, and were further examined for data extraction and discussion. These studies included 1 genomic analysis, 22 on protein markers, 6 on metabolite markers, 9 on inflammatory mediators, and 6 integrating multiple molecular levels.

CONCLUSIONS

Significant advancements have been made in identifying molecular biomarkers for OA, encompassing various joints, sample types, and molecular levels. Despite this progress, gaps remain, particularly in the need for validation, larger sample sizes, the integration of more clinical data, and consideration of covariates. For early detection and improved treatment of OA, continued efforts in biomarker identification are needed. This effort should seek to identify effective biomarkers that advance early detection, support prevention, evaluate interventions, and improve patient outcomes.

Immune System-Related Plasma Pathogenic Extracellular Vesicle Subpopulations Predict Osteoarthritis Progression

Certain molecules found on the surface or within the cargo of extracellular vesicles (EVs) are linked to osteoarthritis (OA) severity and progression. We aimed to identify plasma pathogenic EV subpopulations that can predict knee radiographic OA (rOA) progression. We analyzed the mass spectrometry-based proteomic data of plasma EVs and synovial fluid (SF) EVs from knee OA patients (n = 16, 50% female). The identified surface markers of interest were further evaluated in plasma EVs from an independent cohort of knee OA patients (n = 30, 47% female) using flow cytometry. A total of 199 peptides with significant correlation between plasma and SF EVs were identified. Of these, 41.7% were linked to immune system processes, 15.5% to inflammatory responses, and 16.7% to the complement system. Crucially, five previously identified knee rOA severity-indicating surface markers-FGA, FGB, FGG, TLN1, and AMBP-were confirmed on plasma EV subpopulations in an independent cohort. These markers' baseline frequencies on large plasma EVs predicted rOA progression with an AUC of 0.655-0.711. Notably, TLN1 was expressed in OA joint tissue, whereas FGA, FGB, FGG, and AMBP were predominantly liver derived. These surface markers define specific pathogenic EV subpopulations, offering potential OA prognostic biomarkers and novel therapeutic targets for disease modification.

Immune system-related plasma extracellular vesicles in healthy aging

Objectives

To identify age-related plasma extracellular vehicle (EVs) phenotypes in healthy adults.

Methods

EV proteomics by high-resolution mass spectrometry to evaluate EV protein stability and discover age-associated EV proteins (n=4 with 4 serial freeze-thaws each); validation by high-resolution flow cytometry and EV cytokine quantification by multiplex ELISA (n=28 healthy donors, aged 18-83 years); quantification of WI-38 fibroblast cell proliferation response to co-culture with PKH67-labeled young and old plasma EVs. The EV samples from these plasma specimens were previously characterized for bilayer structure, intra-vesicle mitochondria and cytokines, and hematopoietic cell-related surface markers.

Results

Compared with matched exo-EVs (EV-depleted supernatants), endo-EVs (EV-associated) had higher mean TNF-α and IL-27, lower mean IL-6, IL-11, IFN-γ, and IL-17A/F, and similar mean IL-1β, IL-21, and IL-22 concentrations. Some endo-EV and exo-EV cytokine concentrations were correlated, including TNF-α, IL-27, IL-6, IL-1β, and IFN-γ, but not IL-11, IL-17A/F, IL-21 or IL-22. Endo-EV IFN-γ and exo-EV IL-17A/F and IL-21 declined with age. By proteomics and confirmed by flow cytometry, we identified age-associated decline of fibrinogen (FGA, FGB and FGG) in EVs. Age-related EV proteins indicated predominant origins in the liver and innate immune system. WI-38 cells (>95%) internalized similar amounts of young and old plasma EVs, but cells that internalized PKH67-EVs, particularly young EVs, underwent significantly greater cell proliferation.

Conclusion

Endo-EV and exo-EV cytokines function as different biomarkers. The observed healthy aging EV phenotype reflected a downregulation of EV fibrinogen subpopulations consistent with the absence of a pro-coagulant and pro-inflammatory condition common with age-related disease.

Pain sensitivity genes as therapeutic targets in knee osteoarthritis: A comprehensive analysis

Pain sensitivity is a significant factor in knee osteoarthritis (KOA), influencing patient outcomes and complicating treatment. Genetic differences, particularly in pain-sensing genes (PSRGs), are known to contribute to the variability in pain experiences among KOA patients. This study aims to systematically analyze PSRGs in KOA to better understand their role and potential as therapeutic targets. We utilized bulk RNA-seq data from the GSE114007 and GSE169077 datasets to identify differentially expressed genes, with 20 genes found to be significantly altered. Key PSRGs, including PENK, NGF, HOXD1, and TRPA1, were identified using LASSO, SVM, and random forest algorithms. Further, KEGG and GO enrichment analyses revealed pathways such as "Neuroactive ligand-receptor interaction" and "ECM-receptor interaction," which were validated through external datasets. Single-cell RNA-seq analysis from GSE152805, GSE133449, and GSE104782 datasets demonstrated the heterogeneity and dynamic expression of PSRGs across different cell subpopulations in synovium, meniscus, and cartilage samples. UMAP and pseudotime analyses were used to visualize spatial distribution and developmental trajectories of these genes. The findings emphasize the critical roles of PSRGs in KOA, highlighting their potential as therapeutic targets and suggesting that integrating genetic information into clinical practice could significantly improve pain management and treatment strategies for KOA.

The Role of Extracellular Vesicles in the Pathogenesis and Treatment of Rheumatoid Arthritis and Osteoarthritis

Cells can communicate with each other through extracellular vesicles (EVs), which are membrane-bound structures that transport proteins, lipids and nucleic acids. These structures have been found to mediate cellular differentiation and proliferation apoptosis, as well as inflammatory responses and senescence, among others. The cargo of these vesicles may include immunomodulatory molecules, which can then contribute to the pathogenesis of various diseases. By contrast, EVs secreted by mesenchymal stem cells (MSCs) have shown important immunosuppressive and regenerative properties. Moreover, EVs can be modified and used as drug carriers to precisely deliver therapeutic agents. In this review, we aim to summarize the current evidence on the roles of EVs in the progression and treatment of rheumatoid arthritis (RA) and osteoarthritis (OA), which are important and prevalent joint diseases with a significant global burden.