Rasti, M. | Search bioRxiv

bioRxiv2026

Joint tissue explant model using psoriatic arthritis synovial fluid as a tool to capture patient-specific responses to treatments

ObjectiveWe developed a patient- and joint-specific explant co-culture system to model active psoriatic arthritis (PsA) and capture donor-specific tissue responses to therapeutic interventions. MethodsBased on convergent joint pathology between end-stage osteoarthritis (OA) and PsA, OA cartilage-bone and synovium tissues from arthroplasty patients were exposed to synovial fluid (SF) obtained from PsA and OA patients. Histological outcomes (synovitis, proteoglycan distribution), curated gene expression, soluble mediators, and proteinase activity were assessed over 7-21-days. Model responses to dexamethasone (DEX) and the anti-tumor necrosis factor antibody adalimumab (ADA) were evaluated. ResultsPsA SF induced distinct inflammatory and tissue remodeling responses compared to OA SF and control conditions, including altered cartilage proteoglycan distribution, increased synovitis, and tissue-specific transcriptional changes. Multivariate analyses identified distinct osteochondral and synovial transcriptional responses to PsA SF, characterized by reduced osteochondral COL2A1 expression and increased synovial expression of inflammatory and matrix-remodeling genes, including MMP1 and CXCL8. DEX and ADA elicited donor-specific responses across histological, transcriptional, and protein readouts. Among multivariable model outputs, histologic synovitis scores emerged as the most clinically aligned parameter, demonstrating associations with baseline PsA donor disease activity, active joint counts, pain, high-sensitivity C-reactive protein (hsCRP), and radiographic scores. Synovitis score changes to DEX and ADA treatments also aligned with corresponding PsA SF donor clinical improvements to corticosteroid and TNF-modifying therapies. ConclusionThis osteochondral-synovial explant co-culture model captured donor-specific inflammatory and treatment-responsive features of PsA SF-induced pathology, thereby providing a clinically relevant ex vivo platform for studying patient-specific therapeutic responses in PsA.

immunology↗

bioRxiv2025

Mesenchymal Stromal Cells Immunosuppress Osteoarthritis Synovial Fluid Tolerized Monocytes via IL-6

BackgroundMesenchymal stromal cell (MSC) interactions with monocytes/macrophages are central to their therapeutic effects in knee osteoarthritis (KOA); however, mechanisms of these interactions are not fully understood. HypothesisWe hypothesize that MSC soluble factors, particularly interleukin-6 (IL-6) and C-C motif chemokine ligand (CCL2) modulate monocytes in KOA environment. MethodsUsing healthy donor CD14+ monocytes exposed to KOA synovial fluid (SF) in the presence or absence of marrow-derived MSC(M) directly or conditioned medium (CM), we evaluated cell surface markers and signaling via signal transducer and activator of transcription (STAT3), nuclear factor kappa-light-chain-enhancer of activated B (NF-{kappa}B) and c-Jun Terminal Kinase (JNK); functional responses were measured by secretion of tumor necrosis factor (TNF) and IL-1, and by phagocytosis of pHrodo Red E-coli. ResultsCD14+ monocytes demonstrated a mixed phenotype in KOA SF with increased CD163, CD206 and unchanged HLA-DR, CD86 marker expression. This was accompanied by activated STAT3, JNK and NF-{kappa}B signaling. TNF and IL-1 secreted levels were unchanged, but phagocytosis was impaired, indicative of a net dysfunctional repair phenotype and functionality. CD14+ monocytes in KOA SF were hyporesponsive to additional lipopolysaccharide re-challenge, based on TNF and IL-1 secretion. Addition of MSC(M) to KOA SF programmed CD14+ monocytes resolved the dysfunctional phenotype and functionality, with significant increases in CD163, CD206; significant reductions in HLA-DR and CD86 expression; this was accompanied by significantly increased activated STAT3, and decreased activated JNK and NF-{kappa}B. TNF and IL-1 secretion were also significantly reduced, and phagocytic capacity restored. Blocking IL-6, or to a lesser extent, CCL2, partially abrogated MSC(M) soluble factor effects. MSC(M) experienced apoptosis in KOA SF; however, apoptotic bodies did not fully recapitulate MSC(M) soluble factor effects. ConclusionIL-6, CCL2, other soluble factors and apoptotic bodies from MSC(M) secretome mitigate the dysfunctional effects of KOA SF on CD14+ monocytes resulting in immunosuppressed phenotype and functionality.

immunology↗