Pathogenesis of scleroderma

Research project P 14466 Pathogenesis of scleroderma Georg WICK 08.05.2000 Systemic sclerosis (SSc - scleroderma) belongs to the group of connective tissue diseases. It is a chronic, inflammatory-fibrotic disease that generally starts in the skin but later also spreads to internal organs. Clinical symptoms in the first acute stage consist in edema and microscopical perivascular mononuclear cell infiltration. In the following subacute stage first signs of fibrosis emerge, based on proliferation of fibroblasts and an increase of extracellular matrix (ECM) proteins, mainly collagen, in the neighbourhood of the infiltrates. In addition to the skin, internal organs, notably the esophagus, the lung and the kidney also become afflicted by inflammatory and early fibrotic alterations. In the chronic final stage, the mononuclear cell infiltrate subsides and alterations in the skin and in internal organs are now characterized by fibrosis due to an excessive increase of collagen and severely impaired function. Vascular occlusion, especially in hand and feet, are a characteristic early symptom of scleroderma, leading to the so called Raynaud`s syndrome, associated with cold hypersensitivity, pain and the development and necrotic lesions. So far, the etiology and exact pathogenetic mechanisms of SSc are still not known, but there are indications that it is most likely an autoimmune disease. Among the serologic hallmarks of SSc is the occurrence of antinuclear autoantibodies (ANA) with defined specificity. Nevertheless, the specific antigen(s) that is (are) primarily involved in the pathogenesis of SSc has (have) still not been identified. It is also not yet clear, whether the cellular and humoral autoimmune reactions found in patients with SSc are primary or secondary in nature. SSc is a chronic disease where clinicians are only rarely confronted with the early stage. The initial disease stage without any clinical symptoms is not accessible to immunopathological investigations. This latter problem can only be overcome by studying an appropriate animal model where all stages, including even the period before the occurrence of symptoms, are accessible for investigations. The University of California at Davis 200 (UCD 200) strain of chickens has been proven to represent an excellent spontaneously occurring animal model for SSc where even the embryo can be analyzed. In parallel comparative studies on this model and in human patients, we have in the past made several important observations which may shed light on some still enigmatic issues concerning this disease. The two most important points that emerged recently are the following: (a) In contrast to current dogma, endothelial cell (EC) apoptosis rather than perivascular mononuclear cell infiltration is the first pathogenetic event in the pathogenesis of scleroderma. In the avian model and in subsequent studies also in human patients, we have shown that EC apoptosis is induced by anti-EC autoantibodies (A-ECA) via a process called antibody-dependent cellular cytotoxicity (ADCC). (b) In addition to the characteristic alter HS 01 tile proportional abundance of collagen types 1, 111 and we have identified a so far unknown 115 bp a2G) transcript, the expression of which is significantly upregulated in skin and internal organs of UCD 200, but not normal chickens. The present project will, therefore, focus on two problems, viz.: (1) EC apoptosis, especially the identification of EC antigens recognized by AECA as well as possibilities to interfere with the apaptosis-inducing effect of these antibodies with the goal to develop novel diagnostic and therapeutic strategies. (2 To extend the investigations on the alterations of ECM protein deposition into the human situation, especially with respect to the first newly discovered hallmark of fibrosis, i.e. the expression of the 115 bp procollagen type I alpha2-chain transcript and its potential role for a generalized fibrotic process.

Systemic sclerosis or scleroderma is a chronic autoimmune disease affecting the skin and internal organs. The term scleroderma means "hard skin", which describes thickening of the skin caused, by increased collagen deposition. Most people with scleroderma have painful cold-induced spasms of small blood vessels in their hands or feet, known as Raynaud`s phenomenon, causing the fingers or toes to turn white or blue. Many patients have decreased hand function because of joint disfigurement or finger ulcers. Lung, heart and kidney damage are the most frequent causes of severe disability and death. Scleroderma affects women more frequently than men. The cause of scleroderma is unknown, and so far there is no known cure for it. What is known, is that (a) systemic sclerosis is associated with over-activation of the immune system, which attacks the bodies own cells (autoimmunity), (b) small blood vessels are damaged, and (c) over-production of collagen leads to fibrosis. The study of the initial disease stage requires animal models, since patients usually see the doctor only when they already have severe complaints. The only animal model known to show all hallmarks of the human disease is the UCD-200 line of chickens, which develops spontaneously 1-2 weeks after hatching a scleroderma-like disease. In an earlier study comparing skin from these chickens and human scleroderma skin from various :disease stages with healthy controls we have shown that the primary targets of the autoimmune attack are endothelial cells that line small blood vessels. Now we could show that autoantibodies, which are produced by the over-active immune system of both, scleroderma patients and UCD-200 chickens, bind to the endothelial cell (anti-endothelial cell antibodies). Natural killer cells - these are cells, which usually kill infected cells and tumour cells - recognize endothelial cells with bound antibodies, and kill them by inducing a special form of cell death, so called apoptosis. Anti-endothelial cell antibodies can also activate endothelial cells, which then open the way for inflammatory cells to infiltrate the surrounding tissue. Both, activated endothelial cells` and inflammatory cells produce cytokines. These are proteins, which act as mediators between cells, and can stimulate or inhibit the production of proteins. We have studied the` effect of such cytokines that are known to have an effect on fibroblast proliferation and collagen synthesis, and found that transforming growth factor beta-2 (TGFß2) reduces the production of a profibrotic collagen variant by chicken fibroblasts. We further showed that fibroblasts of scleroderma chickens produce 4 times less TGF-ß2 than healthy controls; suggesting that TGF-ß2 might be antifibrotic, in contrast to current believe. Our findings not only provide insight into the pathogenesis of this enigmatic and severe disease, but also might open new ways to rational therapy of scleroderma.