Date of Award
Doctor of Philosophy (PhD)
Synovial tissue fibrosis is an immune mediated disease characterized by fibroblast cell migration, proliferation and transition to a myofibroblast phenotype characterized by alpha smooth muscle actin (a-SMA) upregulation and stress fiber formation. Transforming growth factor-β (TGF-b) plays an important role in mediating the pathogenesis of synovial fibrosis. Synoviocytes produce proteoglycan-4 (PRG4; lubricin), a heavily glycosylated mucinous glycoprotein, and hyaluronic acid (HA). Both PRG4 and HA compete for binding to the CD44 receptor. Furthermore, rhPRG4 binds to TLR2 and TLR4 and acts as an antagonist to prevent TLR2 and TLR4 activation by bacterial ligands. In this work, we aimed to investigate the role of CD44 receptor and its ligands HA in regulating the activation of macrophages in response to TLR2 receptor stimulation in the context of an acute inflammatory response and study the impact of increasing intracellular cyclic adenosine monophosphate (cAMP) in OA fibroblast-like synoviocytes (OA-FLS) on regulating TGF-β linked expression of fibrotic genes and the contribution of PRG4 and HA to this effect. Also, we studied the significance of PRG4-CD44 interaction in mediating fibroblast to myofibroblast transition in vitro and regulation of synovial fibrosis in vivo. In the first manuscript, we found that anti-CD44 antibody and HA treatments reduced TLR2 induced-NF-κB nuclear translocation, IL-1β and TNF-α expression, and production by human macrophages. In the second manuscript, we have shown that forskolin (10μM) increased intracellular cAMP levels and reduced TGF-β 1-stimulated COL1A1, a-SMA, and TIMP-1 expression in OA synoviocytes. Forskolin treatment increased HA secretion and PRG4 expression and production. Moreover, HA and PRG4 reduced a-SMA expression and content, and PRG4 reduced COL1A1 expression and procollagen I content in OA synoviocytes. In the third manuscript, we found that rhPRG4 was internalized by OA synoviocytes via CD44 and rhPRG4 reduced the number of stress fiberpositive myofibroblasts and cell migration in TGF-b treated NIH3T3 fibroblasts. Synovial tissues of 9-months old Prg4GT/GT animals had higher a-SMA, collagen type-I and PLOD2 content and Prg4 re-expression reduced these markers. In conclusion, innate immune signals trigger macrophage activation which results in synovial inflammation. Ligand-CD44 interactions reduced the extent of innate immune-mediated macrophage activation and downstream fibroblasts’ response to TGF-b signals from immune cells. rhPRG4 may have potential therapeutic applications in mitigating synovitis and synovial fibrosis in advanced OA.
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Qadri, M. Synovial Fibrosis in Osteoarthritis of the Knee: Mechanism of Development and Potential Therapeutic Targets. [dissertation]. Irvine, CA: Chapman University; https://doi.org/10.36837/chapman.000208