4.2 Progressive Systemic Scleroderma

4.2 Progressive Systemic Scleroderma Nicolas Hunzelmann and Thomas Krieg Introduction Systemic sclerosis (SSc) belongs to the group of “diffuse inflammatory connective tissue diseases” or “collagen vascular diseases” comprising a variety of severe, sometimes life-threatening systemic diseases which often have a chronic, debilitating course. SSc is characterized by the involvement of the skin and various internal organs (e.g. kidney, lung, heart). The inflammatory and fibrotic process destroys the normal architecture of the affected organs leading to dysfunction and failure. The disease activity is highly variable and often unpredictable. The severity of the disease process in SSc leads to a re- duced lifespan, impaired mobility and loss of autonomy. SSc mainly evolves along pathological changes of the vascular system, the immune system and of the extracellular matrix including its major cell type, the fibroblast. The resulting fibrosis leading to atrophy and failure of the affected organs largely determines the outcome of the disease process. How- ever, despite intense research efforts the relationship and interaction between the pathophysiological processes affecting the vascular system, the immune system and the extracellular matrix are only incompletely understood. Immune Dysregulation One of the hallmarks of SSc is a perturbed immunoregulation (resulting in the presence of autoantibodies), which appears to be influenced by additional factors such as genetic and exogenous factors. Autoimmunity in SSc is characterized by HLA gene restricted autoantibody responses against nuclear and nucleolar antigens. The mechanisms inducing the antibody production are unknown but clinical associations with autoantibody specificities suggest that these antigen-restricted responses are involved in disease specific pathology. These autoimmune phenomena are in a not well understood way related to the inflammatory process with lymphocytic perivascular infiltrates in the skin 166 Nicolas Hunzelmann and Thomas Krieg and lung evident early on in the disease process and preceding the develop- ment of fibrosis. The similarity of the condition with some aspects of graft versus host disease has frequently been noted. Recently it was suggested that microchimerism, i.e. the persistence of foetal cells in the maternal bone marrow and other organs like the skin might be a risk factor, also explaining the female excess (Artlett et al. 1998; Evans et al. 1999). However, subsequent studies found similar frequencies of microchimerisms compared to normal controls but nevertheless an increased number of microchimeric fetal cells in patients (Burastero et al 2003). Vascular Pathology The relationship between autoimmune responses and the vascular pathology is unclear, as Raynaud’s syndrome and vascular abnormalities may be evident many years prior to the onset of disease (Blockmans et al. 1996). The morphological changes that can be observed on a ultrastructural level, i.e. basement membrane thickening, intimal hyperplasia and inflammatory cell infiltration have been interpreted as a sign indicating microvascular injury as a primary event in this disease (Prescott et al. 1992). Depending on the study population and statistical methodology, between 5 and 20% of all individuals presenting with Raynaud’s phenomenon are reported to subsequently develop SSc. A constellation of additional signs and symptoms indicative of microvascular damage separates SSc patients from others presenting with Raynaud’s phenomenon. These include nailfold capil- laroscopic changes (Maricq et al. 1980), hand/foot edema, digital ulcers, cal- cifications and teleangiectasia. The combination of a fibrotic microvascular and hyperreactive vasoconstrictor status is thought to represent the primary lesion responsible for the vasospastic episodes. Tissue hypoxia normally in- duces new blood vessel growth by induction of a variety of angiogenic factors. In SSc, loss of capillaries is a typical and early disease manifestation which has been related to an increase in angiostatic factors and programmed endothelial cell death (apoptosis) where a number of possible mechanisms have been proposed (Sgonc et al. 1996; Kahaleh and Fan 1997; Hebbar et al, 2000). A recent study suggests that latent cytomegalovirus infection contributes to the known phenomenon of endothelial cell cytotoxicity of scleroderma se- rum by identifying IgG autoantibodies that bind a cytomegalovirus protein and induce apoptosis in human endothelial cells (Lunardi et al. 2000). Dysregulation of Extracellular Matrix Synthesis The dysregulation of extracellular matrix synthesis is the third major patho- physiologic change, with the extent and progression of the fibrotic process Progressive Systemic Scleroderma 167 being important prognostic factors in the disease process. It has been well established by in situ hybridization and by fibroblast cultures obtained from involved tissue (e.g. skin or lung) that scleroderma fibroblasts display an activated phenotype producing increased amounts of various collagens and expressing adhesion molecules such as ICAM-1 (LeRoy et al. 1974; Uitto et al. 1979; Scharffetter et al. 1988; Majewski et al. 1995). The newly synthe- sized extracellular matrix is deposited particularly around skin appendages and at the border of the dermis to the subcutaneous tissue, partially replac- ing the latter (Perlish et al. 1985). The collagen bundles running parallel with the skin surface show swelling and variation in thickness. Although the biosynthesis of collagens has been investigated in detail, its metabolism and turnover in vivo is not yet fully understood. In physiological situations in- volving increased collagen synthesis, as e.g. in wound healing, the amount of collagen in the tissue is obviously tightly controlled by its similarly increased degradation. Similarly, in a fibrotic disease, the net gain of collagens must thus involve a disturbed balance between the synthetic and degradative processes. The most commonly used approach to study collagen degradation is the study of collagen degrading enzymes (Herrmann et al. 1991; Mauch et al. 1998). However, the results are difficult to interprete in terms of the in vivo situation, as a combination of several enzymes including the corresponding inhibitors are likely to be involved in the degradation of a single collagen fi- ber. A different approach to this question is to study the degradation prod- ucts as they appear in vivo. Interestingly, we and others could demonstrate that increased levels of ICTP, a degradation product of cross-linked type I collagen, are common in patients with SSc (Heickendorff et al. 1995; Hunzel- mann et al. 1998b). They correlate well with the skin score, a commonly used indicator of the severity of the disease (Subcommittee of the ARA 1980; Kaha- leh et al. 1986). This indicates that the concentrations of circulating ICTP re- flect the type I collagen load in this disease. We found the highest values in patients with very active and extensive disease. Recently, a study on the uri- nary excretion of two mature cross-links of collagen, hydroxylysyl and lysyl pyridinoline, also suggested that in SSc more fibrillar collagens are degraded than in the normal state (Stone et al. 1995). Furthermore these crosslinks can usually only be detected in bone, suggesting that occurence of these crosslinks in the skin is related to the sclerotic process. Therefore these studies indicate that the increased deposition of type I collagen is accompanied by an increased turnover and altered crosslink formation of this molecule, indicating an even more complex derangement of synthetic and degradative processes in this disease than previously acknowledged. The factors which finally lead to the activated phenotype of scleroderma fibroblasts are not entirely clear. Several studies suggest the contribution of transforming growth factor-b (TGF-b) (Kulozik et al. 1990), a potent inducer of collagen synthesis, to the progression of skin sclerosis. This notion is fur- ther supported by the detection of connective tissue growth factor (CTGF) gene expression in skin biopsies of SSc patients (Igarashi et al. 1995) and SSc 168 Nicolas Hunzelmann and Thomas Krieg fibroblasts (Shi-Wen et al. 2000) as TGF-b is also known to induce CTGF. Recent studies indicate that a deficiency in SMAD-7 an inhibitory protein in the TGF-b signalling pathway is characteristic of scleroderma fibroblasts (Dong et al. 2002). The increased biosynthesis of collagen is accompanied by an el- evation of the steady-state mRNA levels in vitro and in vivo of about 1.5–2x which appears to be due to both increased transcriptional activation as well as increased mRNA stability (Eckes et al. 1996; Jimenez and Saitta, 2000). Clinical Appearence/Classification The incidence of SSc is reported to be 2–20/million population and the prev- alence 4–290/million population. Based on distinct clinical aspects and courses of the disease an internationally accepted classification was established with two forms: limited cutaneous SSc (lSSc) and diffuse cutaneous SSc (dSSc). The disease is much commoner in females than males for reasons that are not entirely clear with a female-to-male ratio of 3–9:1. There are some popu- lations at high risk as e.g. the Choctaw Indians from Oklahoma suggesting that genetic factors are critical. However, twin studies are inconclusive and familial aggregation is rare. Both forms, however, lead to life threatening involvement of internal organs and large areas

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