Control of fibrosis in systemic scleroderma

Serum levels of soluble CD21 in patients with systemic sclerosis

Systemic sclerosis (SSc) is a systemic disorder that typically results in fibrosis of the skin and multiple internal organ systems. Although the precise mechanism is unknown, overproduction of extracellular matrix proteins, including collagens and fibronectins, and aberrant immune activation might be involved in the pathogenesis. The soluble cluster of differentiation 21 (sCD21) represents the extracellular portion of the CD21 glycoprotein that is released by shedding from the cell surfaces into plasma. sCD21 binds complement fragments and activates monocytes through binding to membrane CD23. The present study was undertaken to investigate the serum levels of sCD21 in patients with SSc. Serum sCD21 levels were reduced with age both in patients with SSc and normal controls. Serum sCD21 levels in patients with SSc were significantly decreased compared to those in control subjects. When we divided patients with SSc into limited cutaneous SSc (lcSSc) and diffuse cutaneous SSc (dcSSc), patients with lcSSc had lower levels of serum sCD21 than those with dcSSc. Moreover, the prevalence of pulmonary fibrosis in the patients with dcSSc inversely correlated with serum sCD21 levels. Our finding may support the notion that B-cell activation is involved in the mechanism for pulmonary fibrosis and skin sclerosis.

Serum levels of tissue inhibitors of metalloproteinase 2 in patients with systemic sclerosis with duration more than 2 years: correlation with cardiac and pulmonary abnormalities

In this study, we measured the serum concentration of TIMP-2 in patients with systemic sclerosis (SSc) and explored its possible correlation with cardiac and pulmonary lesions. We studied 42 patients with SSc, with duration equal to or more than 2 years. CT chest, ECG, echocardiography, and serum TIMP-2 concentration measurement using ELISA technique were performed in all patients and in 25 normal controls. The mean serum levels of TIMP-2 in patients was higher than in controls (P = .005). The mean CT score of dSSc patients with elevated TIMP-2 levels was significantly higher than dSSc patients with normal levels (P = .013). Four patients out of five with elevated TIMP-2 levels showed diastolic dysfunction (80%), compared to 2 out of 15 lSSc patients with normal levels (13.3%), with P = .014. Our research, though involving a small group of patients, points to the probable role of TIMP-2 in the development of pulmonary lesions in dSSc patients and cardiac lesions in lSSc patients with duration equal to or more than 2 years.

Chemokines and Chemokine Receptors in Scleroderma

Scleroderma is a connective tissue disease with unknown etiology characterized by excessive deposition of extracellular matrix in the skin. Cellular infiltrates of certain immune cells and proinflammatory mediators are suggested to play a crucial role in cutaneous fibrosis, forming complicated networks between fibroblasts and immune cells via cell-cell communications. Tissue-selective trafficking of leukocytes is mediated by combinations of adhesion molecules and chemokines. Recent studies have shown that an increase in proinflammatory chemokines has been associated with the initiation and/or development of skin fibrosis/sclerosis, suggesting that chemokines and their receptors may be important mediators of inflammation and fibrosis in scleroderma. This review will focus on the roles of chemokines and their receptors during the process of cutaneous sclerosis and will also provide a current insight into the potential mechanisms of scleroderma.

Epidermal development and wound healing in matrix metalloproteinase 13-deficient mice

Degradation of the extracellular matrix, which is an indispensable step in tissue remodelling processes such as embryonic development and wound healing of the skin, has been attributed to collagenolytic activity of members of the matrix metalloproteinase family (MMPs). Here, we employed mmp13 knockout mice to elucidate the function of MMP13 in embryonic skin development, skin homeostasis, and cutaneous wound healing. Overall epidermal architecture and dermal composition of non-injured skin were indistinguishable from wild-type mice. Despite robust expression of MMP13 in the early phase of wound healing, wild-type and mmp13 knockout animals did not differ in their efficiency of re-epithelialization, inflammatory response, granulation tissue formation, angiogenesis, and restoration of basement membrane. Yet, among other MMPs also expressed during wound healing, MMP8 was found to be enhanced in wounds of MMP13-deficient mice. In summary, skin homeostasis and also tissue remodelling processes like embryonic skin development and cutaneous wound healing are independent of MMP13 either owing to MMP13 dispensability or owing to functional substitution by other collagenolytic proteinases such as MMP8.

Cellular and molecular mechanisms of bleomycin-induced murine scleroderma: current update and future perspective

Scleroderma is a fibrotic condition characterized by immunologic abnormalities, vascular injury and increased accumulation of matrix proteins in the skin. Although the aetiology of scleroderma is not fully elucidated, a growing body of evidence suggests that extracellular matrix overproduction by activated fibroblasts results from complex interactions among endothelial cells, lymphocytes, macrophages and fibroblasts, via a number of mediators. Cytokines, chemokines and growth factors secreted by inflammatory cells and mesenchymal cells (fibroblasts and myofibroblasts) play an important role in the fibrotic process of scleroderma. Recently, we established a murine model of scleroderma by repeated local injections of bleomycin. Dermal sclerosis was induced in various mouse strains, although the intensity of dermal sclerosis varied among various strains. Histopathological and biochemical analysis demonstrated that this experimental murine scleroderma reflected a number of aspects of human scleroderma. Further investigation of the cellular and molecular mechanisms of inflammatory reaction, fibroblast activation and extracellular matrix deposition following dermal injury by bleomycin treatment will lead to the better understanding of the pathophysiology and the exploration of effective treatment against scleroderma. This review summarizes recent progress of the cellular and molecular events in the pathogenesis of bleomycin-induced scleroderma; moreover, further perspective by using this mouse model has been discussed.

Mast cells enhance contraction of three-dimensional collagen lattices by fibroblasts by cell-cell interaction: role of stem cell factor/c-kit

Reorganization of the extracellular matrix is important in many biological and pathophysiological processes, including tissue remodelling, wound healing, or cancer metastasis. The ability of cultured fibroblasts to reorganize and contract three-dimensional type I collagen gels is regarded as an in vitro model for this process. In tissue fibrosis, complex interactions among fibroblasts, inflammatory cells and the extracellular matrix are taking place. Mast cells have often been discussed to play a role in several fibrotic conditions including scleroderma, scar formation, or wound healing. In this study, we examined the effects of mast cells on contraction of collagen lattices. The results demonstrate that co-culture of dermal fibroblasts with a human mast cell line (HMC-1) significantly enhanced contraction of the three-dimensional collagen lattices, whereas mast cells alone failed to contract the gel. Addition of culture supernatants of mast cells did not enhance the speed of gel contraction, indicating the importance of cell-cell contact. Morphological analysis showed that mast cells were incorporated into the lattices. Histological examination also demonstrated that within the lattices, mast cells were localized in close contact to, or attached to, fibroblasts. As fibroblasts and mast cells are known to attach via stem cell factor (SCF)/c-kit interaction when co-cultured in monolayers, we also examined the effect of antibodies against SCF and c-kit in this system. Addition of both antibodies inhibited gel contraction up to 70%. In contrast, antibodies against interleukin-4 (IL-4) and IL-4 receptor did not affect gel contraction. These results indicate that mast cells enhance fibroblast-mediated contraction of collagen lattices via direct cell-cell contact, mediated in part by SCF/c-kit interactions.

Expression of a dominant-negative type II transforming growth factor beta (TGF-beta) receptor in the epidermis of transgenic mice blocks TGF-beta-mediated growth inhibition

To determine whether a functional type II receptor of transforming growth factor beta (TGF-beta) is required to mediate the growth inhibitory effect of TGF-beta on the skin in vivo, we have generated transgenic mice that overexpress a dominant negative-type II TGF-beta receptor (delta beta RII) in the epidermis. The delta beta RII mice exhibited a thickened and wrinkled skin, and histologically the epidermis was markedly hyperplastic and hyperkeratotic. In vivo labeling with BrdUrd showed a 2.5-fold increase in the labeling index over controls, with labeled nuclei occurring in both basal and suprabasal cells of transgenic epidermis. In heterozygotes, this skin phenotype gradually diminished, and by 10-14 days after birth the transgenic mice were indistinguishable from their normal siblings. However, when F1 mice were mated to homozygosity, perinatal lethality occurred due to the severe hyperkeratotic phenotype, which restricted movement. Cultured primary keratinocytes from delta beta RII mice also exhibited an increased rate of growth in comparison with nontransgenic controls, and were resistant to TGF-beta-induced growth inhibition. These data document the role of the type II TGF-beta receptor in mediating TGF-beta-induced growth inhibition of the epidermis in vivo and in maintenance of epidermal homeostasis.

Decreased expression of alpha 2 beta 1 integrin in scleroderma fibroblasts

Systemic scleroderma (SSc) is a complex connective tissue disorder of unknown etiology. In early stages of the disease, fibroblasts are activated to produce large amounts of collagen with subsequent fibrosis. Collagen metabolism of fibroblasts is modulated by their contact with the extracellular matrix (ECM), which involves distinct receptors on the cell surface, mainly belonging to the integrins. We investigated the expression of collagen receptor alpha 2 beta 1 in SSc and normal fibroblasts, since this receptor has been shown to be utilized by fibroblasts for adhesion to and reorganization of collagen I. 9 strains of scleroderma fibroblasts grown as monolayer cultures were first analyzed with respect to their collagen I expression. 6 of these strains were similar to controls "low" producers) and 3 strains showed up to 2-3 x higher levels of collage I mRNA expression ("high" producers). Northern hybridization using a cDNA probe specific for the alpha 2 integrin subunit revealed a decrease of the corresponding mRNA in SSc fibroblasts as compared to controls (75% versus 100%). "High" collagen producing cell strains displayed the lowest values for alpha 2 integrin mRNA. The decrease of alpha 2 integrin subunit expression at the mRNA level in selected fibroblasts was further substantiated by radioimmunoprecipitation using specific mAbs directed against alpha 2 integrin subunit. No significant changes in beta 1 integrin expression could be observed - neither at mRNA nor at the protein level. Our data indicate a correlation between excessive synthesis of collagen and low levels of alpha 2 integrin subunit expression in SSc fibroblasts. Further experiments should clarify whether this observation is a phenomenon specific for scleroderma or whether it reflects an "activated" state of fibroblasts.

A targeted mutation at the known collagenase cleavage site in mouse type I collagen impairs tissue remodeling

Degradation of type I collagen, the most abundant collagen, is initiated by collagenase cleavage at a highly conserved site between Gly775 and Ile776 of the alpha 1 (I) chain. Mutations at or around this site render type I collagen resistant to collagenase digestion in vitro. We show here that mice carrying a collagenase-resistant mutant Col1a-1 transgene die late in embryo-genesis, ascribable to overexpression of the transgene, since the same mutation introduced into the endogenous Col1a-1 gene by gene targeting permitted normal development of mutant mice to young adulthood. With increasing age, animals carrying the targeted mutation developed marked fibrosis of the dermis similar to that in human scleroderma. Postpartum involution of the uterus in the mutant mice was also impaired, with persistence of collagenous nodules in the uterine wall. Although type I collagen from the homozygous mutant mice was resistant to cleavage by human or rat fibroblast collagenases at the helical site, only the rat collagenase cleaved collagen trimers at an additional, novel site in the nonhelical N-telopeptide domain. Our results suggest that cleavage by murine collagenase at the N-telopeptide site could account for resorption of type I collagen during embryonic and early adult life. During intense collagen resorption, however, such as in the immediate postpartum uterus and in the dermis later in life, cleavage at the helical site is essential for normal collagen turnover. Thus, type I collagen is degraded by at least two differentially controlled mechanisms involving collagenases with distinct, but overlapping, substrate specificities.

Adhesion molecules in scleroderma: collagen binding integrins

In summary, adhesion molecules are likely to play a prominent role in scleroderma pathogenesis and evolution. Endothelial adhesion molecules required for leukocyte extravasation are upregulated in affected tissue, though the mechanism is unclear. Certainly, endothelial adhesion molecule expression is seen in the context of other diseases not characterized by fibrosis. Adhesion molecules on the fibroblast, particularly those that play a role in fibroblast collagen interactions, may be very important. The ability of fibroblasts to organize collagen fibrils, and to exert forces across collagenous tissue, is likely to involve a prominent role of alpha 2 beta 1 integrin. Enhanced organization and contraction of newly formed collagen, as well as unregulated procollagen production, may be intimately linked in this disease process. At least two factors that strongly enhance fibroblast force generation could potentially influence other aspects of scleroderma. TGF beta is a potent stimulus for collagen production and has been found to be elevated in lesional scleroderma. Endothelin 1 is also a potent vasoconstrictor and is elevated in scleroderma patient serum as well [60,62-65]. Its apparent role in other fibrocontractive diseases suggests that its potential role in the pathogenesis of scleroderma deserves additional attention.