title: THE ROLE OF KNEE SYNOVIUM IN THE PATHOPHYSIOLOGY OF OSTEOARTHRITIS
Creators: name: Jamal, Juliana
Publisher: name: University of Liverpool Repository
Year: 2023

description: Osteoarthritis (OA), a chronic degenerative arthritis affects all joint tissues. Previous studies of OA pathogenesis focused on cartilage. This study evaluated the synovium in OA by comparing the complex stress responses of synovium derived from end-stage knee OA to those of patients with different knee injuries but without OA, i.e. traumatic joint injury (trauma) and soft tissue injury (scope). Changes in synovial structure and function were investigated by histological and expression array analyses. The responsiveness of primary synovial fibroblasts (SFb) isolated from synovium of OA-pre-obese (OA-Pob), OA-obese (OA-ob), scope and scope with cartilage damage (scope-CD) patients, towards OA-inflammatory stressor conditioned media (OA-CM) and mechanical tensile load was evaluated by changes in expression of selected genes. OA synovium demonstrated a significantly higher synovitis score with inflammatory B-cells, T-cells and macrophages infiltrate than scope or trauma synovium and correlated positively with poorest functional scores. The OA synovium intima layer demonstrated reactivity to embedded cartilage fragments and enhanced angiogenesis. Adipocyte hypertrophy and hyperplasia in OA synovium correlated with an overweight body mass index (BMI) and with dyslipidaemia. OA synovial lining hyperplasia with cartilage inclusion was more prominent in the OA BMI &lt; 30 kg/m2. Knee trauma induced changes in the synovial subintima characteristic of an acute inflammatory reaction. Scope synovium presented a mild inflammatory morphology. Gene expression profiling identified 2,084 genes differentially expressed across all comparator datasets with a predominant contribution being from endocytosis mechanisms. End-stage OA synovium displayed an enhanced upregulation of 95% of differential gene expression (DGE) coding for large, glycosylated proteins compared with scope or trauma synovium. Gene Ontology biological process analysis in OA synovium indicated an upregulation of endoplasmic reticulum stress that drives a signaling network of the Unfolded Protein Response pathway through synoviolin (SYVN1), being the top upstream regulator gene activated. Upregulation of SYVN1 and heat-shock 70kDa protein 4 (HSPA4) in OA synovium was confirmed by immunohistochemistry. Differential gene expression changes within canonical pathways were influenced by OA-risk factors BMI and gender. Primary SFb showed distinctive DGE profiles compared to their parental tissues. Multiplex ELISA assays identified enhanced secretion of inflammatory mediator proteins, CXCL8, COL4A1, CCL4, SPARC and FGF2 into the OA-Pob:CM paralleling the histological detection of inflammatory cells infiltrated within the OA-Pob synovium. In-vitro mechanical tensile load stimulated lubricin (PRG4) production in scope:SFb, and increased TGFβ1 expression in scope-CD:SFb and OA-Pob:SFb. The effects of OA-Pob:CM in driving all SFb towards inflammatory response was higher than the OA-ob:CM, stimulating higher expression of pro-inflammatory cytokines, IL1β, IL6, COX2 and aggrecanases, ADAMTS4 and ADAMTS5, and reduced extracellular matrix, COL1A1 expression in all SFb. OA-ob:SFb were unresponsive but expressed higher pro-inflammatory cytokines under OA-Pob:CM treatment. Thus, both mechanical and inflammatory stressors regulated SFb gene expression with responses being pathology-dependent. These findings demonstrated that synovium responds differentially through changes in cellular composition and gene expression specific to each different insult encountered, influenced by OA-risk factors BMI and dyslipidaemia. Differential synovial activity will impact its cartilage maintenance functions. In-depth understanding of these responses may offer new therapeutic strategies to slow the OA progression.