Phd in IINNOVATION IN IMMUNO-MEDIATED AND HEMATOLOGICAL DISORDERS

Thesis title: Pro Nerve Growth Factor and its receptor p75NTR activate inflammatory responses in synovial fibroblasts: a novel targetable mechanism in arthritis

We have recently provided new evidence for a role of p75NTR receptor and its preferential ligand proNGF in amplifying inflammatory responses in synovial mononuclear cells of chronic arthritis patients. In the present study, to better investigate how activation of the p75NTR/proNGF axis impacts synovial inflammation, we have studied the effects of p75NTR on fibroblast-like synoviocytes (FLS), which play a central role in modulating local immune responses and in activating pro-inflammatory pathways. Using single cell RNA sequencing in synovial tissues from active and treatment-naïve rheumatoid arthritis (RA) patients, we demonstrated that p75NTR and sortilin, which form a high affinity receptor complex for proNGF, are highly expressed in PRG4pos lining and THY1posCOL1A1pos sublining fibroblast clusters in RA synovia but decreased in RA patients in sustained clinical remission. Ex vivo experiments confirming these data demonstrating a markedly higher expression of p75NTR and sortilin in RA-FLS, which are indeed the majour sources of proNGF, the specific ligand of p75NTR, so thus creating a vicious circle that amplify proinflammatory response. The inhibition of p75NTR receptor, using a small molecules LM11A -31, that specifically blocks the binding with proNGF, reduce the release of proinflammatory cytokines and the activation on both p38 and JNK pathway in RA-FLS, indicating the involment of proNGF/p75NTR axis in sustained inflammatory condition. Finally, we tested the effect of p75NTR blockade with LM11A-31 during the acute phase of murine antigen-induced arthritis (AIA): we found that LM11A-31 significantly reduced knee swelling, cartilage damage, bone erosion, inflammatory infiltrate and expression of inflammatory cytokines. This decrease in the inflammatory milieu, not only protects the joint of AIA-treated mice but also affects the spleen decreasing influx of monocytes and reducing spleen volume and red pulp surface extension. Moreover, we found an higher concentration of p75NTR-ECD in blood and sinovial fluids collected from Juvenile Idiopatic Arthritis (JIA) patients at onset more than remission state. In addition, p75NTR-ECD founded in blood of JIA sample, strongly correlates with IL-6 and TNF which are cytokines driver in inflammation, so thus indicating that there is a correlation of the shedding of ectodomain of p75NTR and inflammatory state in arthitis patients. Overall, our data demonstrate that an active proNGF/p75NTR axis promotes pro-inflammatory responses in synovial fibroblasts, thereby contributing to chronic synovial inflammation, and point to the possible use of p75NTR inhibitors as a novel therapeutic approach in chronic arthritis.