Fig. 5

The role of proteoglycan 4 (PRG4) resident in synovial fluids from patients with osteoarthritis (OA) and produced by OA fibroblast-like synoviocytes (OA FLS) in modulating interleukin-1 beta (IL-1β)-induced OA FLS proliferation. Data are presented as mean ± standard deviation of at least three independent experiments. OA FLS proliferation of the different experimental groups was normalized to untreated control cells; *p < 0.001, **p < 0.05. a Impact of synovial fluid PRG4 depletion on cellular proliferation in an in vitro model of IL-1β-induced OA FLS proliferation over 48 hours. IL-1β induced OA FLS proliferation and OA SF (10%) did not alter the effect of IL-1β on OA FLS. PRG4-depleted OA SF (OA SF – PRG4) enhanced the proliferative effect of IL-1β on OA FLS. b Impact of synovial fluid PRG4 depletion on cellular proliferation in an in vitro model of IL-1β-induced OA FLS proliferation over 48 hours. IL-1β induced OA FLS proliferation and OA SF (20%) significantly reduced IL-1β-induced OA FLS proliferation. PRG4 depletion reversed the effect of OA SF and enhanced the proliferative effect of IL-1β on OA FLS. c PRG4 gene knockdown in OA FLS using PRG4 small interfering RNA (siRNA). Treatment with a non-targeting negative control (NC) siRNA over a 48-hour period did not alter PRG4 gene expression. PRG4 siRNA treatment reduced endogenous PRG4 expression in OA FLS. Data are normalized to PRG4 expression in untreated control OA FLS. d Impact of PRG4 knockdown on OA FLS proliferation under unstimulated and IL-1β stimulated conditions. PRG4 knockdown enhanced OA FLS proliferation under basal conditions compared to NC treatment over 24 hours. PRG4 knockdown enhanced IL-1β-induced OA FLS proliferation compared to NC treatment over 24 hours