Progressive fibrosis of the skin and internal organs is the pathologic hallmark of scleroderma or systemic sclerosis (SSc). The etiology of SSc is unknown but both genetic and environmental factors have been proposed. Based on the genetic evidence that defects in the gene for fibrillin-1 may contribute to the etiology of SSc, we studied the cellular metabolism and matrix incorporation of fibrillin-1 using dermal fibroblasts explanted from both Choctaw and non-Choctaw patients with SSc. These studies demonstrated that the SSc cells assembled fibrillin-1 into microfibrils, but that these microfibrils were unstable to biochemical manipulation. These preliminary results are the basis of the hypotheses to be tested in this grant proposal. We hypothesize that patients with SSc have a genetic defect that leads to degradation of fibrillin-1-containing microfibrils in tissues. The degradation of microfibrils causes release of TGF-beta from sites of sequestration in microfibrils. In addition, the release of microfibril fragments leads to an autoimmune response and the generation of antifibrillin-1 antibodies. The long-term goal of the proposed research is to understand the contribution of microfibril defects to the etiology of SSc.
The specific aims are the following: (1) characterize microfibril abnormalities in fibroblast cell strains from ethnically diverse individuals with SSc and related disorders; (2) determine if fibroblast cell strains of first-degree relatives of SSc patients have microfibril abnormalities similar to those observed in the SSc patients' cells; (3) determine if the microfibrils assembled by SSc fibroblasts are turned over more rapidly, are more sensitive to proteolytic degradation, and release more microfibril fragments into the media of the cultures than microfibrils made by normal fibroblasts; (4) confirm that TGF-beta1 is associated with fibrillin-1-containing microfibrils in dermal fibroblast cultures, and determine if there is more TGF-beta1 released from the microfibrils in the cultures of SSc cells than in control cells; (5) determine if SSc patients have anti-fibrillin-1 autoantibodies in the serum and if the presence of these autoantibodies correlates with the clinical disease. The research proposed in this grant will determine the contribution of abnormalities in fibrillin-1-containing microfibrils to the activation of fibroblasts, which leads to the fibrosis that characterizes SSc.
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