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Extended reports
Up regulated expression of tumour necrosis factor α converting enzyme in peripheral monocytes of patients with early systemic sclerosis
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  1. T Bohgaki1,
  2. Y Amasaki1,
  3. N Nishimura2,
  4. M Bohgaki1,
  5. Y Yamashita1,
  6. M Nishio1,
  7. K-i Sawada3,
  8. S Jodo1,
  9. T Atsumi1,
  10. T Koike1
  1. 1Department of Medicine II, Hokkaido University Graduate School of Medicine, N-15 W-7, Kita-ku, Sapporo 060-8638, Japan
  2. 2GeneticLab Co, Ltd, N-27 W-6, Kita-ku, Sapporo 001-0027, Japan
  3. 3Department of Internal Medicine III, Akita University School of Medicine, 1-1-1 Hondo, Akita 010-8543, Japan
  1. Correspondence to:
    Dr Y Amasaki
    Department of Medicine II, Hokkaido University Graduate School of Medicine, Address: N-15 W-7, Kita-ku, Sapporo 060-8638, Japan; yamasakimed.hokudai.ac.jp

Abstract

Background: Systemic sclerosis (SSc) is accompanied by abnormalities in humoral and cellular immune systems.

Objective: To determine the genes specifically expressed in the immune system in SSc by analysis of the gene expression profile of peripheral blood mononuclear cells (PBMC) from patients with SSc, including those treated with haematopoietic stem cell transplantation (HSCT). Additionally, to investigate the clinical significance of the up regulation of tumour necrosis factor α (TNFα) converting enzyme (TACE).

Methods: PBMC from patients with SSc (n = 23) and other autoimmune diseases (systemic lupus erythematosus (SLE, n = 16), rheumatoid arthritis (RA, n = 29)), and from disease-free controls (n = 36) were examined. Complementary DNA arrays were used to evaluate gene expression of PBMC, in combination with real time quantitative polymerase chain reactions. TACE protein expression in PBMC was examined by fluorescence activated cell sorter (FACS).

Results: In patients with SSc 118 genes were down regulated after HSCT. Subsequent comparative analysis of SSc without HSCT and healthy controls indicated SSc-specific up regulation for three genes: monocyte chemoattractant protein-3 (p = 0.0015), macrophage inflammatory protein 3α (p = 0.0339), and TACE (p = 0.0251). In the FACS analysis, TACE protein was mainly expressed on CD14+ monocytes both in patients with SSc and controls. TACE expression on CD14+ cells was significantly increased in patients with early SSc (p = 0.0096), but not in those with chronic SSc, SLE, or RA. TACE protein levels in SSc monocytes correlated with the intracellular CD68 levels (p = 0.0016).

Conclusions: Up regulation of TACE expression was a unique profile in early SSc, and may affect the function of TNFα and other immunoregulatory molecules.

  • Ab, antibody
  • aCENP-B Ab, anticentromere protein-B Ab
  • ACR, American College of Rheumatology
  • ANA, antinuclear Ab
  • aRNP Ab, anti-ribonucleoprotein Ab
  • aTopo-I Ab, antitopoisomerase I Ab
  • CaMKIIβ, calcium/calmodulin dependent protein kinase II β
  • cDNA, complementary DNA
  • CRP, C reactive protein
  • CTGF, connective tissue growth factor
  • FACS, fluorescence activated cell sorter
  • FITC, fluorescein isothiocyanate
  • FSC, forward light scatter
  • GAPDH, glyceraldehyde-3-phosphate dehydrogenase
  • HSCT, haematopoietic stem cell transplantation
  • IL, interleukin
  • MCP, monocyte chemoattractant protein
  • MFI, mean fluorescence intensity
  • mIgG1, isotype matched control mouse IgG1
  • MIP, macrophage inflammatory protein
  • mRNA, messenger RNA
  • NF-κB, nuclear factor-κB
  • NIK, NF-κB inducing kinase
  • PBMC, peripheral blood mononuclear cells
  • PE, phycoerythrin
  • RA, rheumatoid arthritis
  • real time PCR, quantitative TaqMan real time polymerase chain reaction
  • RGS, regulators of G-protein signalling
  • SLE, systemic lupus erythematosus
  • SSc, systemic sclerosis
  • SSC, side light scatter
  • TACE, tumour necrosis factor α converting enzyme
  • TGFβ, transforming growth factor β
  • TNFα, tumour necrosis factor α
  • TNF-R, TNF receptor
  • systemic sclerosis
  • tumour necrosis factor α converting enzyme (TACE)
  • cDNA array
  • monocytes

http://dx.doi.org/10.1136/ard.2004.030338

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    Systemic sclerosis (SSc) is a multisystem disorder of connective tissue. Increased biosynthesis of multiple matrix proteins by interstitial fibroblasts is the hallmark of SSc, with development of skin sclerosis and involvement of visceral organs.1 The pathogenesis of SSc includes vasculopathy associated with endothelial cell dysfunction, and extensive fibrosis secondary to fibroblast activation.2,3 Functional abnormality in T and B lymphocytes has been considered in the pathogenesis, based on the presence of disease-specific autoantibodies and hypergammaglobulinaemia in SSc.4,5 Growth factors and cytokines are also thought to play a part in the progression of connective tissue fibrosis in SSc. Among them, transforming growth factor β (TGFβ) and the Smad system have a central role in the SSc dermis.6 However, the molecular basis of the pathogenesis of SSc has remained unclear.

    The use of gene expression profiling, such as the complementary DNA (cDNA) array system, is increasingly being used for various diseases, and is used in the aetiological study of SSc.7,8 Increased expression of several genes has been suggested, but a disease-specific gene profile of SSc has not yet been determined, possibly owing to the difficulty of achieving disease remission in SSc, which is necessary for a comparative analysis of the active and disease-free status. Recently, the efficacy of high dose chemotherapy after autologous haematopoietic stem cell transplantation (HSCT) for refractory autoimmune diseases has been reported.9,10 HSCT has been performed in a number of cases of SSc, with good results.11–,13 When we performed autologous CD34 selected HSCT for our patients with SSc, we observed a prompt and persistent improvement of skin sclerosis and stabilisation of organ disease. Under this condition, it was possible to carry out a comparative analysis of gene expression profile between an active (pre-HSCT) and a remission status (post-HSCT) in the same patient with SSc.

    We studied the gene expression profile in peripheral blood mononuclear cells (PBMC) from patients with SSc treated with HSCT, and found that expression of tumour necrosis factor α (TNFα) converting enzyme (TACE) was increased in circulating monocytes from patients with SSc. The correlation of TACE expression with the clinical findings in patients with SSc was analysed and is discussed below.

    PATIENTS AND METHODS

    Patients and controls

    Twenty three Japanese patients with SSc who fulfilled the 1980 criteria of the American College of Rheumatology (ACR) were assessed in this study.14 These patients were categorised as those with diffuse cutaneous type disease characterised by generalised or widespread skin thickening.15 Table 1⇓ summarises their clinical features. Patients were classified as having early SSc (n = 12) if the disease duration after the appearance of the first non-Raynaud’s phenomenon was within 3 years.11 Other patients with SSc with a longer disease duration were classified as having chronic SSc (n = 11). Of the 12 patients with early SSc, three were treated with HSCT using autologous CD34+ selected peripheral blood stem cells; blood samples were obtained throughout the clinical course. Other patients with autoimmune diseases had rheumatoid arthritis (RA) or systemic lupus erythematosus (SLE). These patients fulfilled the criteria of the ACR, respectively.16,17 As healthy controls, 36 disease-free Japanese volunteers, mean (SD) age 40.0 (11.5) years, were enrolled in the study.

    View this table:
    Table 1

     Clinical features of the study subjects*

    Study design

    To search for specific genes which changed between the active and remission status, before and after HSCT, we first analysed gene expression profiles of PBMC from patients treated with HSCT using cDNA array (n = 3). Next, specific up regulated genes in patients with SSc were explored using cDNA array by comparing mRNA levels in PBMC of patients with SSc who had not received HSCT (n = 6) and healthy controls (n = 5). Specific gene candidates were confirmed by real time polymerase chain reaction (PCR) in patients with SSc without HSCT (n = 9) and controls (n = 6). Finally, protein expression levels were analysed by a fluorescence activated cell sorter (FACS) analysis.

    PBMC isolation

    Blood sampling was carried out after obtaining written informed consent according to the guidelines of the ethical committee of Hokkaido University. PBMC were obtained from heparinised venous blood, using gradient centrifugation over Ficoll-Paque Plus (Amersham Biosciences Corp, NJ).

    RNA extraction and cDNA array analysis

    Total RNAs from PBMC were isolated using TRIzol reagent (Invitrogen, Carlsbad, CA). Poly(A) RNA was isolated from total RNA using a MagExtractor (TOYOBO, Osaka, Japan), and poly(A) RNA (2 μg) was reverse transcribed by ReverTraAce (TOYOBO), in the presence of cDNA synthesis primers and biotin-16-deoxyuridine triphosphate (TOYOBO), according to the manufacturer’s instructions. cDNA array analysis was performed using human cDNA expression filters (Human Immunology Filters (TOYOBO)), on which 621 species of human cDNA fragments and housekeeping genes are spotted in duplicate: (http://www.toyobo.co.jp/seihin/xr/product/genenavi/genenavigator.html, accessed 5 May 2005)). Hybridisation and subsequent cDNA array analyses were carried out as described previously,23 with some modification. Briefly, after standard prehybridisation, cDNA array filters were hybridised with a biotin labelled cDNA probe in PerfectHyb solution (TOYOBO) overnight at 68°C. After washing under conditions of high stringency, specific signals on the filters were visualised using Phototope-Star Detection Kits (New England Biolabs, Beverly, MA). Fluorescence signals for mRNA expression levels were obtained using a Fluor-S Multiimager system (Nippon Bio-Rad Laboratories, Tokyo, Japan). The signal intensity among filters was compared in an E-Gene Navigator Analysis (GeneticLab, Sapporo, Japan), and was expressed as an mRNA expression index to the intensity of the internal glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene expression.

    Quantitative TaqMan real time polymerase chain reaction (real time PCR)

    A two step PCR was carried out on serial dilutions of cDNA samples from PBMC from the patients with SSc and the controls. Real time PCR amplification and determination of cDNA transcripts were carried out with the ABI PRISM 7000 sequence detection system (Applied Biosystems, Foster City, CA) and gene-specific sets of TaqMan Universal PCR master mix and assays-on-demand gene expression probes (Applied Biosystems).

    FACS analysis

    The following mouse monoclonal antibodies were purchased from BD Biosciences Pharmingen (San Diego, CA): antihuman CD3-Cy-chrome, CD4-fluorescein isothiocyanate (FITC), CD8-phycoerythrin (PE) and FITC, CD56-FITC, CD19-FITC, CD68-PE, and CD69-PE. Monoclonal mouse antihuman-CD14-FITC, CD71-PE (Beckman Coulter Inc, Fullerton, CA) and antihuman TACE-PE (R&D systems, Abingdon, UK) were also used for surface immunostaining of the cells. The specificity of antihuman TACE has been characterised.24 In the case of CD68, intracellular staining was done using Cytofix/Cytoperm Plus (BD Biosciences Pharmingen, San Diego, CA), according to the manufacturer’s instructions. After washing twice with phosphate buffered saline (PBS), cells were subjected to FACS analysis of immunostained cells using a FACSCalibur flow cytometer (Becton Dickinson Immunocytometry Systems, San Jose, CA).

    Statistical analysis and clinical significance

    Calculations were made using the statistical software package StatView 5.0 (Abacus Concepts, Berkeley, CA). Comparisons of mRNA expression of PBMC were made using Mann-Whitney statistics. Group mean comparisons of the TACE protein expression levels, represented by mean fluorescence intensity (MFI), and TACE positive cells were based on Kruskal-Wallis H statistics. A paired t test was used to analyse the difference in blood cell counts of patients with SSc before and after HSCT. The data are presented as the means (SD). Differences were examined based on analysis of variance, and p values <0.05 were considered significant.

    RESULTS

    Comprehensive analysis of up regulated genes in PBMC from patients with SSc using cDNA array and real time PCR

    We first analysed mRNA expression in PBMC from three patients with SSc treated with HSCT, in order to search for genes with expression levels down regulated after this treatment. In these patients, skin involvement, as expressed by the modified Rodnan total thickness skin score improved significantly by 54% (from 30.3 (6.8) to 12.6 (13.2)) and the modified Health Assessment Questionnaire improved by 22.8% (from 1.67 (0.88) to 1.29 (1.04)) at 6 months after effective HSCT. This improvement persisted even 3 years after this treatment. PBMC specimens were obtained from these patients before (<1 month before mobilisation) and 6 months after HSCT, and were processed for mRNA extraction followed by cDNA array analyses.

    At 6 months after this treatment, down regulation of mRNA expression levels was seen in 118 genes using cDNA array (table 2⇓). In patients with SSc without HSCT, 17 genes were specifically up regulated compared with controls (table 3⇓). In addition, the profile of mRNA expression between baseline and after 6 months in patients with SSc without HSCT was very similar, thus a “natural state for 6 months” did not modify the mRNA levels examined in this study (data not shown). Real time PCR showed that only four gene expression levels had statistical significance as disease-specific genes in 17 patients with SSc who had not received HSCT (fig 1⇓). As a result, gene expression levels of monocyte chemoattractant protein (MCP)-3, macrophage inflammatory protein (MIP)-3α, and TACE were down regulated after HSCT in the cDNA array and up regulated specifically in patients with SSc without HSCT by real time PCR (fig 2⇓). In this study, we further investigated the expression of TACE, which has a crucial role in the immune system. A role for chemokines, including MCP and MIP families, in the pathogenesis of scleroderma has been suggested (reviewed by Atamas and White25).

    View this table:
    Table 2

     Down regulated genes expressed in PBMC from patients with SSc at 6 months after HSCT as indicated by a cDNA array

    View this table:
    Table 3

     Up regulated genes expressed in PBMC from patients with SSc without HSCT as indicated by a cDNA array

    Figure 1
    Figure 1

     Quantitative analysis of up regulated genes in PBMC from patients with SSc, assessed using real time PCR. cDNA specimen from patients with SSc (n = 9) and disease-free volunteers (n = 6) were analysed for six genes species (TACE, interleukin (IL) 1β, MIP-3α, MIP-1β, MCP-3, and a regulator of G-protein signalling (RGS)-1), indicated from the cDNA array study (table 3⇑). *p<0.05.

    Figure 2
    Figure 2

     Changes of mRNA expression levels of IL1β, MIP-1β, MCP-3, MIP3-α, RGS-1, and TACE in patients with SSc before and after HSCT using cDNA array. RNA specimens were obtained from individual patients before (<1 month before mobilisation) and 6 months after HSCT. Relative expression levels of mRNA were determined using cDNA arrays performed simultaneously. The expression levels of each cDNA transcript were displayed as a relative mRNA expression index compared with the levels of internal GAPDH gene expression, as described in “Patients and methods”.

    Cell surface TACE expression

    We first examined PBMC from healthy controls for the expression of TACE protein. In PBMC from healthy subjects, a small population was brightly stained by an antihuman TACE monoclonal antibody (fig 3A⇓). Multicolour FACS analyses showed that surface TACE expression was barely detectable on CD4+CD3+, CD8+CD3+, CD19+, and CD56+ populations. In contrast, surface TACE expression was detected on the CD14+ population (fig 3B⇓). It was confirmed that these CD14+ populations were monocytes, by profiles of forward and side light scatter (SSC), as well as by intracellular CD68 protein expression. Surface TACE expression levels on monocytes were not affected by the age and sex of the controls (data not shown).

    Figure 3
    Figure 3

     Expression of TACE protein in PBMC of healthy controls and patients. (A, left panel) A small population was detected in a high fluorescence intensity. (A, right panel) Solid line, cells stained with anti-TACE monoclonal Ab; dotted line, cells stained with isotype matched control mouse IgG1 Ab. (B) Expression of TACE protein in PBMC subsets from a healthy control. (C) Representative cell surface expression of TACE protein on monocytes from patients with autoimmune diseases and controls. Solid line, cells stained with anti-TACE monoclonal Ab; dotted line, cells stained with mIgG1 Ab. Results are representative of three independent experiments.

    We next investigated expression levels of TACE protein in subsets of PBMC from patients with SSc. In these patients, surface TACE expression was also detected on monocytes but not on CD4+CD3+, CD8+CD3+, CD19+, and CD56+ populations, respectively (data not shown). Figure 3C⇑ shows representative FACS profiles of TACE protein expression for CD14+ monocytes. In the patients with SSc, TACE expression in monocytes was significantly increased in comparison with findings in healthy controls, and in patients with RA and SLE (fig 3C⇑). When analysed statistically, cell surface TACE protein levels of monocytes and TACE positive cells in peripheral blood were significantly increased in patients with SSc, especially in patients with early SSc with disease duration of <3 years, in comparison with controls and patients with non-SSc autoimmune diseases, as well as those with chronic SSc (fig 4⇓). In addition, TACE protein levels correlated with mRNA expression levels by real time PCR (r = 0.640, p = 0.0462). Thus, we concluded that up regulated expression of TACE protein by monocytes was a unique profile of early SSc.

    Figure 4
    Figure 4

     (A) Comparison of cell surface TACE expression by monocytes of patients with early SSc, chronic SSc, RA, SLE, and healthy controls. Cell surface expression levels of TACE were evaluated using FACS, gating on monocytes by forward and side light scatter and on CD14+ cells. The levels of TACE protein expression were represented by the MFI. mIgG1 Ab-PE staining was performed in all measurements, and showed identical levels of background staining. *p<0.05, (p = 0.0065 (Kruskal-Wallis H statistics)). (B) Comparison of TACE positive cells in PBMC of patients with early SSc, chronic SSc, RA, SLE, and healthy controls evaluated using FACS. TACE positive cells were defined on gate R1 in fig 3B⇑. *p<0.05.

    Relationship between cell surface TACE expression and maturation/activation markers of monocytes

    To better understand the mechanism of TACE up regulation in monocytes in SSc, we next investigated correlations between TACE and activation/differentiation markers of monocytes from patients with SSc. Coexpression of surface CD69, CD71, and intracellular CD68 with TACE was evaluated using FACS analysis (fig 5⇓). These proteins were variously expressed on SSc monocytes, but only intracellular CD68 protein levels showed a significant correlation with cell surface TACE protein expression levels (r = 0.671, p = 0.0016), while cell surface CD69 and CD71 proteins did not correlate.

    Figure 5
    Figure 5

     Correlation of TACE protein expression levels and maturation/activation markers on monocytes, and serum CRP levels in patients with SSc. Correlation of TACE protein levels with intracellular CD68 expression, cell surface CD69 expression, cell surface CD71 expression, and serum C reactive protein (CRP) levels are displayed. Cells were stained with anti-TACE-PE monoclonal antibody, or with FITC-anti-CD68, CD69, and CD71, in the presence of anti-CD14-FITC. Intracellular or cell surface levels of each marker were measured by FACS, gating on the monocytes as described above. The expression levels of individual proteins, represented by the MFI, were plotted on the horizontal axis (CD68, CD69, and CD71) and on the vertical axis (TACE), respectively. Serum CRP levels were measured by a latex agglutination test. *p<0.05.

    Association of cell surface TACE expression levels with clinical features of SSc

    We then analysed the correlation of cell surface TACE protein levels of monocytes from patients with SSc (including patients with early and chronic disease) with clinical features of the disease. The expression levels of TACE protein on monocytes in patients with SSc, however, did not significantly correlate with titres of autoantibodies, including antinuclear Ab (ANA), antitopoisomerase I Ab (aTopo-I Ab), anticentromere protein-B Ab (aCENP-B Ab), anti-ribonucleoprotein Ab (aRNP Ab), as well as levels of serum immunoglobulins. The TACE protein levels did not correlate either with CRP in patients with SSc (fig 4⇑, r = −0.216, p = 0.3599). The expression levels of TACE protein did not differ significantly between patients with SSc with or without visceral organ disease, including interstitial pneumonia and gastrointestinal complications (data not shown).

    DISCUSSION

    HSCT can be an effective treatment for subjects with severe autoimmune diseases, including SSc.11–,13 In our three patients with SSc who received HSCT, significant improvement of skin sclerosis was promptly achieved and persisted without any immunosuppressant drug treatment. In such patients, the gene expression profile can be studied comparatively between the active and remission state of SSc, with a minimum background of therapeutic reagents. In this study we performed a cDNA analysis of PBMC from patients with SSc who had undergone HSCT. After extensive analyses, up regulation of MCP-3, MIP-3α, and TACE in PBMC from patients with SSc who had not had HSCT was evident.

    It was notable that these genes are commonly expressed by monocytes/macrophages. In SSc, although the earliest pathological events include dysfunction of microvascular systems and dermal fibroblasts,26,27 cells and factors that mediate such abnormalities have not been defined. Histological studies of early SSc showed that cells infiltrating the skin of patients with early stage SSc are mainly CD14+ monocytes/macrophages,28,29 indicating the crucial role of these cells.

    A role for chemokines has been suggested in the pathogenesis of SSc.25,30–,32 Our observation about MCP-3 and MIP-3α in PBMC from patients with SSc in this study is consistent with previous findings.33–,35

    In addition, overexpression of TACE in PBMC appeared to be a new hallmark of early stage SSc. In PBMC subpopulations, TACE protein expression was almost limited to monocytes (fig 3B⇑), whereas widespread distribution of TACE mRNA in tissue was suggested and its expression of protein levels in blood cells has not been yet described in detail.36,37 TACE protein levels on monocytes were significantly higher in SSc than in controls (figs 3C⇑ and 4⇑), suggesting a possible association between TACE and the function of TACE-expressing monocytes with the pathoaetiology of SSc. In autoimmune diseases, up regulation of TACE in inflammatory synovial tissue from patients with RA and increased TACE mRNA expression in PBMC of patients with multiple sclerosis have been suggested, but the disease specificity has been unclear.38–,40 Our report provides the first evidence of disease-specific up regulation of TACE in peripheral monocytes in SSc, both at mRNA and protein expression levels.

    TACE is a metalloproteinase of the ADAM (a disintegrin and metalloproteinase) family, and was initially described as a protease responsible for processing the membrane anchored TNFα precursor to the mature secreted form.36,37 It is now accepted that substrates of TACE also include various cell surface proteins other than pro-TNFα; TNF receptors type I (TNF-RI) and type II (TNF-RII), L-selectin, IL6 receptor α chain, TNF related activation induced cytokine, and fractalkine (reviewed by Mezyk et al41). TACE mRNA is expressed by various types of cells, and can be induced by various extracellular stimuli.41,42 We found that expression of TACE increased at mRNA levels in PBMC from patients with SSc (table 3⇑, fig 1⇑). Moreover, expression levels of TACE protein correlated with that of intracellular CD68, a lysosomal antigen expressed during differentiation of monocytes to macrophages, and did not correlate with CD69, CD71, activation markers in blood cell, and CRP levels (fig 5⇑).43 In patients with RA with positive CRP, surface TACE protein levels in peripheral monocytes also had no correlation (r = −0.277, p = 0.1459). Monocytes from patients with early stage SSc were likely to be activated in vivo, expressing TACE, independently of general acute reactants. Expression of TACE mRNA is regulated by transcription factors, including AP-2 and SP-1.44 Analysis of these factors may help in understanding the mechanism of TACE up regulation.

    It was notable that TACE up regulation in monocytes was not seen in patients with chronic SSc with diffuse skin sclerosis (fig 4⇑). Hence, up regulation of TACE in circulating monocytes was probably not a secondary outcome from a persistent fibrotic condition. In the pathogenesis of SSc, TGFβ and connective tissue growth factor (CTGF) dysfunction has been considered.8,45 In addition, the up regulated TNFα/TNF-R system has also been suggested in recent studies. It has been reported that the serum soluble TNF-R levels significantly correlated with the activity and disease progression of SSc.46,47 Furthermore, Ellman and MacDonald reported a significant improvement in the skin score of patients with SSc after administration of recombinant anti-TNFα antibody.48 These findings are consistent with involvement of an aberrant function of the TNFα/TNF-R system in SSc. The up regulation of TACE may be involved in such abnormality in TNF signalling in SSc through the cleaving function of TACE.

    The effect of TACE on the function of the TNFα/TNF-R system in vivo is not fully understood, but the soluble form of TNFα can interact with both TNF-RI and TNF-RII.49–,51 Ligation of TNF-RI leads to recruitment of intracellular signalling proteins, resulting in the bifurcation of TNF-RI signalling: one is the apoptotic signal delivered through caspase-8, and the other is activation of proinflammatory properties delivered through nuclear factor-κB (NF-κB) inducing kinase (NIK) and NF-κB.52 Unlike TNF-RI, signalling through TNF-RII largely leads to activation of NIK dependent and NF-κB dependent signalling.53 Thus, increased activity of TACE can shift the balance of signals mediated by distinct types of TNF receptors and downstream events, including activation or death of target cells. Interestingly, mice with a targeted mutation in TACE were perinatally lethal and had morphological defects in the skin, indicating the essential role of TACE in normal skin development.54

    Thus, it is intriguing to consider that TACE may participate in the progression of skin involvement in SSc, especially at the early stage. However, TNFα can also down regulate the expression of CTGF and indirectly modulate expression of type II TGFβ receptor in human fibroblasts.55,56 In addition, TACE can also cleave other functional molecules as well as TNFα and the receptors.41 Such pleiotrophic action of TACE makes it difficult to predict a bona fide role of TACE up regulation in SSc. Further investigation of the function of TACE, including analysis of laboratory animals that overexpress TACE, may provide information about the significance of TACE in SSc.

    In summary, this study described for the first time the aberrant expression of TACE on monocytes from patients with early SSc. Recently, several chemical compounds have been reported to inhibit the activities of metalloproteinases, including TACE.57 Such reagents may have a role in cases of TACE associated chronic inflammatory disease, including SSc. In addition, expression of TACE levels may also be a useful clinical measure of SSc, reflecting disease stages and the clinical prognosis of individual patients. Analysis of TACE function in SSc monocytes may not only provide insight into the pathogenesis but may also be a new diagnostic and therapeutic target for SSc.

    Acknowledgments

    We thank Ms Akiko Hirano for expert technical assistance, Drs Hiroshi Kataoka, Akira Furusaki, Katsuya Fujimoto, and Tomoyuki Endo for clinical procedures related to HSCT.

    This work was supported by a national grant aid (14570004) from the Ministry of Education, Science, Technology, Sports, and Culture of Japan and a research grant for the study of the action of short fatty chain acid on cytokine gene regulation.

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