Loss of sympathetic nerve fibers (SNF) is a general principle in inflammatory lesions as we demonstrated in experimental arthritis, rheumatoid arthritis, Charcot arthropathy, Crohn’s disease, experimental colitis, atopic dermatitis, and others. In parallel, we found nerve repellent factors such as semaphorin 3C and 3F in inflamed tissue, which are most probably responsible for loss of SNF. In the previous project, we intended to block effects of semaphorins to allow outgrowth of SNF using an Fc-fusion construct of the semaphorin receptor neuropilin-2 (NPN-2fc). Unexpectedly, NPN-2fc had a strong agonistic effect on SNF repulsion as determined in the neurite outgrowth assay. In addition, NPN-2fc increased severity in experimental arthritis, and soluble NPN-2 was higher in synovial fluid of rheumatoid arthritis compared to osteoarthritis patients. In this present project, we want to continue this line of research by focusing on the co-receptor of NPN-2 called plexin A2 or A3. Plexin A2/A3 is the signal transducing receptor needed to build a heterotrimeric complex of neuropilin-2 and semaphorins 3F or 3C. It is the main goal in this project to neutralize both, NPN-2 together with plexin A2 (or A3), and to study effects of inhibition of this important receptor in vitro and in vivo. We will generate a super-construct of neuropilin-2 linked to plexin A2 (or A3) to be used in the outgrowth assay and in the animal model of collagen type II arthritis. On the basis of these findings, we will test further modifications of the blocking peptide in the outgrowth assay.
