AN ACTIVE PRONGF/P75NTR AXIS IN ARTHRITIS PATIENTS INFLUENCES CYTOKINE PRODUCTION IN SYNOVIAL FIBROBLASTS

Introduction: In addition to its well-known neurotrophic activity, the nerve growth factor (NGF) is involved in the immune regulation. Our previous studies showed that the immature NGF, proNGF, is the prevalent form in synovial fluids of patients with juvenile idiopathic arthritis (JIA) and rheumatoid arthritis (RA). The distinct roles of NGF, pro-NGF and their different receptors (TrkA and p75NTR) in the regulation of the inflammatory response are still unclear. Objectives: To investigate if p75NTR and its specific ligand proNGF modulate the activity of synovial fibroblasts and mononuclear cells playing a role in the inflammatory response in the synovia of arthritis patients. Methods: Mononuclear cells (MNC) were purified from blood and synovial fluids of JIA patients. Fibroblasts-like synoviocytes (FLS), obtained from synovial tissue of RA patients (RA FLS), were used to evaluate pro-inflammatory activity of proNGF. Skin fibroblasts (SF) from healthy donors (HD) were used as controls. TrkA, p75NTR, Sortilin, NGF, and cytokines expression were evaluated by quantitative PCR (qPCR). Specific ELISA were used to analyze NGF, proNGF and cytokine concentrations. p75NTR was inhibited using a synthetic inhibitors (LM11A-31) or by small interference RNA in order to evaluate how its inhibition can modify proinflammatory pathways. Results: Our data showed that p75NTR expression was significantly up-regulated in MNC purified from blood and synovial fluid of JIA patients and in FLS of RA patients. TrkA expression was highest in HD cells and down-regulated in patient cells. Patient FLS but not MNC expressed high levels of NGF mRNA and high amounts of proNGF. On the contrary, low levels of mature NGF were detected in their conditioned media. Inflammatory stimuli, such as IL-1?, IL-6, LPS, TNF?, further up-regulated both p75NTR expression and proNGF production in synovial FLS. The inhibition of the binding of proNGF to its specific receptor p75NTR using synthetic inhibitor LM11A-31 in synovial FLS resulted in a marked reduction of IL-6 release induced by either IL- 1? or other inflammatory stimuli. Conclusion: The abnormal p75NTR expression levels and the modified p75NTR/TrkA ratio observed in JIA and RA patients might have a crucial role in the chronicity of the inflammatory response. In addition to inducing p75NTR up-regulation, inflammatory stimuli increased the release of proNGF in synovial FLS. ProNGF further enhances pro-inflammatory cytokine production, creating a vicious circle that amplify the inflammatory response. Blocking the binding of endogenous proNGF to its receptor p75NTR, using a specific p75NTR inhibitor, strongly reduces the production of inflammatory mediators and suggests the use of p75NTR inhibitors as a new therapeutic approach to chronic arthritis. Disclosure of Interest G. Minnone: None Declared, L. Farina: None Declared, M. Soligo: None Declared, L. Manni: None Declared, A. Manzo: None Declared, P. Miossec: None Declared, F. De Benedetti Grant/Research Support from: BMS, Pfizer, Abbvie, Novartis, Novimmune, Roche, SOBI, Sanofi, UBC, Consultant for: Roche, Novartis, Novimmune, SOBI, L. Bracci-Laudiero: None Declared