A tool for evaluating novel osteoarthritis therapies using multivariate analyses of human cartilage-synovium explant co-culture

Baicalin Maintains Articular Cartilage Homeostasis and Alleviates Osteoarthritis by Activating FOXO1

Baicalin has been acknowledged for its anti-inflammatory properties. However, its potential impact on osteoarthritis (OA) has not yet been explored. Therefore, our study aimed to examine the effects of Baicalin on OA, both in laboratory and animal models. To evaluate its efficacy, human chondrocytes affected by OA were treated with interleukin-1β and/or Baicalin. The effects were then assessed through viability tests using the cell counting kit-8 (CCK-8) method and flow cytometry. In addition, we analyzed the expressions of various factors such as FOXO1, autophagy, apoptosis, and cartilage synthesis and breakdown to corroborate the effects of Baicalin. We also assessed the severity of OA through analysis of tissue samples. Our findings demonstrate that Baicalin effectively suppresses inflammatory cytokines and MMP-13 levels caused by collagenase-induced osteoarthritis, while simultaneously preserving the levels of Aggrecan and Col2. Furthermore, Baicalin has been shown to enhance autophagy. Through the use of FOXO1 inhibitors, lentivirus-mediated knockdown, and chromatin immunoprecipitation, we verified that Baicalin exerts its protective effects by activating FOXO1, which binds to the Beclin-1 promoter, thereby promoting autophagy. In conclusion, our results show that Baicalin has potential as a therapeutic agent for treating OA (Clinical Trial Registration number: 2023-61).

The circUbqln1, regulated by XBP1s, interplays with 14-3-3ζ to inhibit collagen synthesis and promote osteoarthritis by controlling PRODH activity and proline metabolism

INTRODUCTION

Osteoarthritis (OA) is a degenerative bone disease associated with ageing, characterized by joint pain, stiffness, swelling and deformation. Currently, pharmaceutical options for the clinical treatment of OA are very limited. Circular RNAs(cirRNAs) have garnered significant attention in OA and related drug development due to their unique RNA sequence characteristics.Therefore,exploring the role of cirRNAs in the occurrence and development of OA is of paramount importance for the development of effective medications for OA.

OBJECTIVES

To identify a novel circRNA, circUbqln1, for treating osteoarthritis and elucidate its pathophysiological role and mechanisms in the treatment of OA.

METHODS

The circUbqln1 expression and distribution were determined by qRT-PCR and FISH. XBP1 gene knockout(XBP1 cKO) spontaneous OA and DMM model and WT mouse CIOA model were used to explore the role of XBP1 and circUbqln1 in OA.Overexpression or knockdown of circUbqln1 lentivirus was used to observe the impacts of circUbqln1 on primary chondrocytes,C28/I2 and mice in vitro and in vivo.Chromatin immunoprecipitation,luciferase reporter assay,RNA pulldown,mass spectrometry,RNA immunoprecipitation,fluorescence in situ hybridization,and flow cytometry to explore the molecular mechanisms of circUbqln1.

RESULTS

It was found that cartilage-specific XBP1 cKO mice exhibited a faster OA progression compared to normal's.Importantly,transcript factor XBP1s has the capacity to impede the biogenesis of circUbqln1,derived from Ubqln1. The circUbqln1 promotes cartilage catabolism and inhibits anabolism, therefore accelerates the occurrence of OA.Mechanismly,circUbqln1 can translocate to the chondrocyte nucleus with the assistance of phosphorylated 14-3-3ζ, upregulate the transcriptional activity of the proline dehydrogenase(Prodh) promoter and PRODH enzyme activity. Consequently, this leads to the promotion of proline degradation and the inhibition of collagen synthesis,ultimately culminating in the impairment of cartilage and its structural integrity.

CONCLUSION

CircUbqln1 plays a crucial role in the occurrence and development of OA, indicating that the inhibition of circUbqln1 holds promise as a significant approach for treating OA in the future.

Comprehensive analysis of arachidonic acid metabolism-related genes in diagnosis and synovial immune in osteoarthritis: based on bulk and single-cell RNA sequencing data

BACKGROUND

Osteoarthritis (OA) is one of degenerative-related arthritis, which can be aggravated by low-grade synovitis. It is known that arachidonic acid (AA) dysmetabolism brings OA synovitis. However, the impact of synovial AA metabolism pathway (AMP) related genes on OA remains uncovered.

METHODS

Here, we conducted a comprehensive analysis to explore the impact of AA metabolism genes in OA synovium. We obtained transcriptome expression profiles from three raw datasets related to OA synovium (GSE12021, GSE29746, GSE55235) and identified the hub genes of AA metabolism pathways (AMP) in OA synovium. An OA occurrence diagnostic model was constructed and validated based on the identified hub genes. Then, we explored the correlation between hub gene expression and the immune-related module using CIBERSORT and MCP-counter analysis. The unsupervised consensus clustering analysis and weighted correlation network analysis (WGCNA) were utilized to identify robust clusters of identified genes in each cohort. Moreover, the interaction between the hub genes of AMP and immune cells was elucidated through single-cell RNA (scRNA) analysis by scRNA sequencing data from GSE152815.

RESULTS

We found that the expression of AMP-related genes was up-regulated in OA synovium, and seven hub genes (LTC4S, PTGS2, PTGS1, MAPKAPK2, CBR1, PTGDS, and CYP2U1) were identified. The diagnostic model that combined the identified hub genes showed great clinical validity in diagnosing OA (AUC = 0.979). Moreover, significant associations were noticed between the hub genes' expression, immune cell infiltration, and inflammatory cytokine levels. The 30 OA patients were randomized and clustered into three groups using WGCNA analysis based on the hub genes, and diverse immune status was found in different clusters. Of interest, older patients were more likely to be classified into a cluster with higher levels of inflammatory cytokines IL-6 and less infiltration of immune cells. Based on the scRNA-sequencing data, we found that the hub genes had relatively higher expression in macrophages and B cells than other immune cells. Moreover, inflammation-related pathways were significantly enriched in macrophages.

CONCLUSION

These results suggest that AMP-related genes are closely involved in alterations of OA synovial inflammation. The transcriptional level of hub genes could serve as a potential diagnostic marker for OA.

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.

Inflammatory cytokines and mechanical injury induce post-traumatic osteoarthritis-like changes in a human cartilage-bone-synovium microphysiological system

Background

Traumatic knee injuries in humans trigger an immediate increase in synovial fluid levels of inflammatory cytokines that accompany impact damage to joint tissues. We developed a human in vitro cartilage-bone-synovium (CBS) coculture model to study the role of mechanical injury and inflammation in the initiation of post-traumatic osteoarthritis (PTOA)-like disease.

Methods

Osteochondral plugs (cartilage-bone, CB) along with joint capsule synovium explants (S) were harvested from 25 cadaveric distal femurs from 16 human donors (Collin’s grade 0–2, 23–83years). Two-week monocultures (cartilage (C), bone (B), synovium (S)) and cocultures (CB, CBS) were established. A PTOA-like disease group was initiated via coculture of synovium explants with mechanically impacted osteochondral plugs (CBS+INJ, peak stress 5MPa) with non-impacted CB as controls. Disease-like progression was assessed through analyses of changes in cell viability, inflammatory cytokines released to media (10-plex ELISA), tissue matrix degradation, and metabolomics profile.

Results

Immediate increases in concentrations of a panel of inflammatory cytokines occurred in CBS+INJ and CBS cocultures and cultures with S alone (IL-1, IL-6, IL-8, and TNF-α among others). CBS+INJ and CBS also showed increased chondrocyte death compared to uninjured CB. The release of sulfated glycosaminoglycans (sGAG) and associated ARGS-aggrecan neoepitope fragments to the medium was significantly increased in CBS and CBS+INJ groups. Distinct metabolomics profiles were observed for C, B, and S monocultures, and metabolites related to inflammatory response in CBS versus CB (e.g., kynurenine, 1-methylnicotinamide, and hypoxanthine) were identified.

Conclusion

CBS and CBS+INJ models showed distinct cellular, inflammatory, and matrix-related alterations relevant to PTOA-like initiation/progression. The use of human knee tissues from donors that had no prior history of OA disease suggests the relevance of this model in highlighting the role of injury and inflammation in earliest stages of PTOA progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02881-z.

Tissue catabolism and donor-specific dexamethasone response in a human osteochondral model of post-traumatic osteoarthritis

Background

Post-traumatic osteoarthritis (PTOA) does not currently have clinical prognostic biomarkers or disease-modifying drugs, though promising candidates such as dexamethasone (Dex) exist. Many challenges in studying and treating this disease stem from tissue interactions that complicate understanding of drug effects. We present an ex vivo human osteochondral model of PTOA to investigate disease effects on cartilage and bone homeostasis and discover biomarkers for disease progression and drug efficacy.

Methods

Human osteochondral explants were harvested from normal (Collins grade 0–1) ankle talocrural joints of human donors (2 female, 5 male, ages 23–70). After pre-equilibration, osteochondral explants were treated with a single-impact mechanical injury and TNF-α, IL-6, and sIL-6R ± 100 nM Dex for 21 days and media collected every 2–3 days. Chondrocyte viability, tissue DNA content, and glycosaminoglycan (sGAG) percent loss to the media were assayed and compared to untreated controls using a linear mixed effects model. Mass spectrometry analysis was performed for both cartilage tissue and pooled culture medium, and the statistical significance of protein abundance changes was determined with the R package limma and empirical Bayes statistics. Partial least squares regression analyses of sGAG loss and Dex attenuation of sGAG loss against proteomic data were performed.

Results

Injury and cytokine treatment caused an increase in the release of matrix components, proteases, pro-inflammatory factors, and intracellular proteins, while tissue lost intracellular metabolic proteins, which was mitigated with the addition of Dex. Dex maintained chondrocyte viability and reduced sGAG loss caused by injury and cytokine treatment by 2/3 overall, with donor-specific differences in the sGAG attenuation effect. Biomarkers of bone metabolism had mixed effects, and collagen II synthesis was suppressed with both disease and Dex treatment by 2- to 5-fold. Semitryptic peptides associated with increased sGAG loss were identified. Pro-inflammatory humoral proteins and apolipoproteins were associated with lower Dex responses.

Conclusions

Catabolic effects on cartilage tissue caused by injury and cytokine treatment were reduced with the addition of Dex in this osteochondral PTOA model. This study presents potential peptide biomarkers of early PTOA progression and Dex efficacy that can help identify and treat patients at risk of PTOA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02828-4.