Objective: To identify pathogenic and/or disease-specific short peptides in sera from patients with systemic sclerosis (SSc).
Methods: Serum samples from 40 patients with SSc, 30 patients with systemic lupus erythematosus, 21 patients with rheumatoid arthritis, 30 patients with osteoarthritis, and 26 healthy donors were tested. Short peptides with molecular weights of smaller than approximately 3 kd, purified from the sera by magnetic bead-based hydrophobic interaction chromatography 18, were detected and their amino acid sequences determined using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. Effects of the identified peptides on fibroblasts and microvascular endothelial cells were tested using synthesized peptides and sera containing the peptides.
Results: A group of peptides with mass/charge (m/z) values of 1,865, 1,778, 1,691, 1,563, and 1,450 were detected predominantly in the SSc sera. These peptides were identified as family members of complement C3f-des-arginine (DRC3f) derived from C3b. The level of DRC3f (m/z 1,865) was related to vascular involvement in SSc and to SSc disease activity. The synthesized peptides of DRC3f and C3f, as well as the filtrated sera containing DRC3f, enhanced proliferation of microvascular endothelial cells, but not fibroblasts. Both DRC3f and C3f increased production of transforming growth factor beta1 by dermal microvascular endothelial cells.
Conclusion: This comprehensive peptidomics analysis revealed the predominance of DRC3f in the sera of patients with SSc. Investigation of DRC3f may be a useful tool for the diagnosis and evaluation of disease activity in SSc. Moreover, its demonstrated effects on endothelial cells suggest a potential role for DRC3f in the pathophysiologic mechanisms of SSc.