Complement system deregulation in SAPHO syndrome revealed by proteomic profiling

SAPHO syndrome is an inflammatory disease invading the skin and bones, whose diagnosis has been difficult due to its low incidence and diversified manifestation. We investigated the serum proteomic profile of SAPHO patients to identify key proteins associated with SAPHO syndrome, trying to find clinical biomarkers or functional molecules for this rare disease. Blood samples from 8 SAPHO patients and 8 healthy controls were detected and analyzed using data independent acquisition (DIA) method to identify differentially expressed proteins (DEPs) specific to SAPHO. A total of 57 differentially expressed proteins were identified (p < 0.05, fold change >1.2), in which 27 proteins were upregulated and 30 downregulated. DEPs may participate in GO terms such as "lipid particle" and "Notch signaling pathway", as well as KEGG pathways including "complement and coagulation cascades" and "mTOR signaling pathway". The overexpression of inhibitors of the complement system (CFH and C4BP), were verified in a larger cohort (16 SAPHO patients, 8 AS patients and 24 healthy controls) with ELISA, and the combined diagnostic ability of CFH and C4BP was predicted by ROC curve with an AUC of 0.91, which may be molecular candidates for further study on diagnosis and pathology of this rare disease. SIGNIFICANCE: Our research provided the first insight into plasma proteomic profile for SAPHO patients，offering potential biomarkers for disease diagnosis. We found that inhibitors of complement system such as CFH and C4BP were up-regulated in SAPHO syndrome, which may play important roles in the pathogenesis of SAPHO syndrome.