Systemic sclerosis (SSc) is characterized by chronic inflammation and fibrosis. N-Formyl peptide receptors (FPRs) are chemotactic receptors involved in inflammation. Three FPRs have been identified: FPR1, FPR2, and FPR3.
We have examined, by RT-PCR, Western blot and immunohistochemistry, FPRs expression in skin fibroblasts from normal subjects and SSc patients, showing an increased expression in SSc fibroblasts.
Several functions of FPRs occur through the interaction with the chemotactic domain (residues 88SRSRY92) of the urokinase-type plasminogen activator receptor (uPAR). Western blot and immunohistochemistry analysis also showed an increased expression in SSc fibroblasts of a cleaved uPAR form exposing the SRSRY sequence at its N-terminus (DIIDIII-uPAR88–92).
We demonstrated that FPRs stimulation promoted radical oxygen species (ROS) generation in normal and SSc fibroblasts. Upon stimulation, ROS production was due to FPRs interaction with uPAR and to beta 1 integrin engagement. FPRs cross-talk with uPAR and integrins led to Rac1 and ERKs activation. Rac1 is a cytosolic component of the NADPH oxidase system. Active GTP-Rac1 binds to p67phox that translocates to the membrane and associates with the catalytic gp91phox. FPRs stimulation promoted gp91phox and p67phox expression as well the direct interaction between GTP-Rac1 and p67phox in fibroblast cells.
Finally, we were able to show that C37, a new small molecule inhibiting the structural and functional interaction between FPRs and uPAR, and Selumetinib, a clinically approved MAPKK/ERK inhibitor, blocked FPRs-mediated ROS production in fibroblasts, thus suggesting new therapeutic strategies for the treatment of fibrosis in SSc
