PPAR-γ/PCK1 metabolic pathway modulate synovitis and fibrosis in KOA rats

Background: Knee osteoarthritis (KOA) is a prevalent degenerative joint disease in which synovial inflammation and fibrosis are closely linked to pain, stiffness, and functional limitation. Growing evidence suggests that metabolic dysregulation, particularly in lipid metabolism, is involved in KOA pathogenesis, but the underlying mechanisms remain incompletely defined. Methods: Sprague Dawley rats underwent bilateral anterior cruciate ligament transection to establish a KOA model; sham-operated rats served as controls. RNA sequencing of synovial tissues was performed to identify differentially expressed genes (DEGs) and enriched pathways, followed by GO/KEGG and GSEA analyses. In vivo, adeno-associated virus vectors were used to overexpress or knock down PPAR-{gamma} and phosphoenolpyruvate carboxykinase 1 (PCK1) via intra-articular injection. Ex vivo, primary rat fibroblast-like synoviocytes (FLSs) were stimulated with IL-1{beta} and transfected with PPAR-{gamma} or PCK1 siRNA/overexpression plasmids. synovitis and fibrosis were evaluated by HE, Masson, and Sirius Red staining, immunofluorescence, ELISA, RT-qPCR, and Western blotting. Results: RNA-seq revealed 621 up-regulated and 228 down-regulated genes in KOA synovium versus sham, with DEGs significantly enriched in PPAR signaling, adipocytokine, and AMPK pathways. Metabolism-related genes including Fabp5, Plin1, Adipoq, Lep, and Pck1 were up-regulated. GSEA indicated downregulation of PPAR-{gamma} signaling in KOA synovium. In vivo and ex vivo, PPAR-{gamma} expression was reduced in KOA, whereas PCK1, FABP5, and ADIPOQ were increased. PPAR-{gamma} overexpression alleviated synovial inflammation, collagen I deposition, and fibrosis, and suppressed FABP5, ADIPOQ, and PCK1 expression; PPAR-{gamma} knockdown produced the opposite effects. Functional studies showed that PCK1 overexpression aggravated synovial inflammatory cell infiltration and fibrosis, elevated IL-1-{beta}, IL-18, and TGF-{beta}, and decreased TIMP1 levels in serum, synovial tissue, and FLSs supernatants, whereas PCK1 silencing reversed these changes. Conclusions: The PPAR-{gamma}/PCK1 metabolic axis modulates synovitis and fibrosis in KOA. Downregulation of PPAR-{gamma} and consequent upregulation of PCK1 promote synovitis and fibrotic remodeling. These findings identify the PPAR-{gamma}/PCK1 pathway as a potential therapeutic target for KOA.