Analysis of extracellular superoxide dismutase in fibroblasts from patients with systemic sclerosis

Systemic sclerosis (SSc) is a chronic disease of connective tissue characterized by vascular damage, autoantibody production and extensive fibrosis of skin, skeletal muscles, vessels and visceral organs. Fibrosis is a biological process involving inflammatory response and reactive oxygen species (ROS) accumulation leading to fibroblast activation. Extracellular superoxide dismutase (SOD3), a copper and zinc superoxide dismutase, which is expressed in selected tissues, is secreted into the extracellular space and catalyzes the dismutation of superoxide radical to hydrogen peroxide and molecular oxygen. Moreover, SOD3 is associated to inflammatory responses in some experimental models. In this paper we analysed, by RT-PCR and immunofluorescence, SOD3 expression and intracellular localization in dermal fibroblasts from both healthy donors and patients affected by diffuse form of SSc. Moreover, we determined SOD3 enzymatic activity in fibroblast culture medium with the xanthine/xanthine oxidase method. Increased expression of SOD3 mRNA was detected in systemic sclerosis fibroblasts (SScF), as compared to control healthy fibroblasts (HF), and SOD3 immunofluorescence staining displayed a characteristic pattern of secretory proteins in both HF and SScF. Superoxide dismutase assay demonstrated that SOD3 enzymatic activity in SScF culture medium is four times more than in HF culture medium. These data suggest that an alteration in SOD3 expression and activity could be associated to SSc fibrosis.