Serum chemokine and cytokine levels as indicators of disease activity in patients with systemic sclerosis

Proinflammatory effects of diesel exhaust nanoparticles on scleroderma skin cells

Autoimmune diseases are complex disorders of unknown etiology thought to result from interactions between genetic and environmental factors. We aimed to verify whether environmental pollution from diesel engine exhaust nanoparticulate (DEP) of actually operating vehicles could play a role in the development of a rare immune-mediated disease, systemic sclerosis (SSc), in which the pathogenetic role of environment has been highlighted. The effects of carbon-based nanoparticulate collected at the exhaust of newer (Euro 5) and older (Euro 4) diesel engines on SSc skin keratinocytes and fibroblasts were evaluated in vitro by assessing the mRNA expression of inflammatory cytokines (IL-1α, IL-6, IL-8, and TNF-α) and fibroblast chemical mediators (metalloproteases 2, 3, 7, 9, and 12; collagen types I and III; VEGF). DEP was shown to stimulate cytokine gene expression at a higher extent in SSc keratinocytes versus normal cells. Moreover, the mRNA gene expression of all MMPs, collagen types, and VEGF genes was significantly higher in untreated SSc fibroblasts versus controls. Euro 5 particle exposure increased the mRNA expression of MMP-2, -7, and -9 in SSc fibroblasts in a dose dependent manner and only at the highest concentration in normal cells. We suggest that environmental DEP could trigger the development of SSc acting on genetically hyperreactive cell systems.

What does global gene expression profiling tell us about the pathogenesis of systemic sclerosis?

PURPOSE OF REVIEW

The purpose of this study is to review recent hypothesis-driven studies that utilize global gene expression data for elucidating the molecular basis of systemic sclerosis (SSc) and its various clinical manifestations.

RECENT FINDINGS

The longitudinal skin gene expression studies indicate that the previously identified molecular subsets are stable over time and might identify inherent subgroups of SSc patients. Skin transcript follow-up studies indicate that the Wnt/β-catenin pathway plays an important role in promotion of fibrogenesis in fibroblasts and preadipocytes. Furthermore, the transcript profile of sclerodermatous graft-versus-host disease (sclGVHD) mice resembles the skin transcriptomes of a subgroup of SSc patientswith IL13/IL4-inducible skin signature wherein the profibrotic chemokine CCL2 plays a key role. The comparison of skin biopsies from SSc patients to skin lesions of patients with cutaneous lupus and dermatomyositis has provided valuable information about the interferon (IFN) signature in these autoimmune diseases. Furthermore, plasma IFN-inducible chemokines correlate with the IFN gene expression score in SSc patients, enabling researchers to examine this molecular signature in large SSc cohorts with serum or plasma collection.

SUMMARY

Global gene expression profiling in skin and peripheral blood can contribute to a better understanding of SSc pathogenesis and identify novel biomarkers and therapeutic targets.

Proteome-wide analysis and CXCL4 as a biomarker in systemic sclerosis

BACKGROUND

Plasmacytoid dendritic cells have been implicated in the pathogenesis of systemic sclerosis through mechanisms beyond the previously suggested production of type I interferon.

METHODS

We isolated plasmacytoid dendritic cells from healthy persons and from patients with systemic sclerosis who had distinct clinical phenotypes. We then performed proteome-wide analysis and validated these observations in five large cohorts of patients with systemic sclerosis. Next, we compared the results with those in patients with systemic lupus erythematosus, ankylosing spondylitis, and hepatic fibrosis. We correlated plasma levels of CXCL4 protein with features of systemic sclerosis and studied the direct effects of CXCL4 in vitro and in vivo.

RESULTS

Proteome-wide analysis and validation showed that CXCL4 is the predominant protein secreted by plasmacytoid dendritic cells in systemic sclerosis, both in circulation and in skin. The mean (±SD) level of CXCL4 in patients with systemic sclerosis was 25,624±2652 pg per milliliter, which was significantly higher than the level in controls (92.5±77.9 pg per milliliter) and than the level in patients with systemic lupus erythematosus (1346±1011 pg per milliliter), ankylosing spondylitis (1368±1162 pg per milliliter), or liver fibrosis (1668±1263 pg per milliliter). CXCL4 levels correlated with skin and lung fibrosis and with pulmonary arterial hypertension. Among chemokines, only CXCL4 predicted the risk and progression of systemic sclerosis. In vitro, CXCL4 down-regulated expression of transcription factor FLI1, induced markers of endothelial-cell activation, and potentiated responses of toll-like receptors. In vivo, CXCL4 induced the influx of inflammatory cells and skin transcriptome changes, as in systemic sclerosis.

CONCLUSIONS

Levels of CXCL4 were elevated in patients with systemic sclerosis and correlated with the presence and progression of complications, such as lung fibrosis and pulmonary arterial hypertension. (Funded by the Dutch Arthritis Association and others.).

Skin gene expression correlates of severity of interstitial lung disease in systemic sclerosis

OBJECTIVE

We undertook this hypothesis-generating study to identify skin transcripts correlating with severity of interstitial lung disease (ILD) in systemic sclerosis (SSc).

METHODS

Skin biopsy samples from 59 patients enrolled in the Genetics versus Environment in Scleroderma Outcome Study (GENISOS) cohort or an open-label imatinib study (baseline visit) were examined by global gene expression analysis using Illumina HT-12 arrays. Skin transcripts correlating with concomitantly obtained forced vital capacity (FVC) values and the modified Rodnan skin thickness score (MRSS) were identified by quantitative trait analysis. Also, immunofluorescence staining for selected transcripts was performed in affected skin and lung tissue. Plasma levels of CCL2, soluble SELP, and soluble P-selectin glycoprotein ligand 1 (sPSGL-1) were examined in all patients enrolled in the GENISOS cohort (n = 266).

RESULTS

Eighty-two skin transcripts correlated significantly with FVC. This gene list distinguished patients with more severe ILD (FVC <70% predicted) in unsupervised hierarchical clustering analysis (P < 0.001). These genes included SELP, CCL2, and matrix metalloproteinase 3, which are involved in extravasation and adhesion of inflammatory cells. Among the FVC correlates, 8 genes (CCL2, HAPLN3, GPR4, ADCYAP1, WARS, CDC25B, PLP1, and STXBP6) also correlated with the MRSS. Immunofluorescence staining revealed that SELP and CCL2 were also overexpressed in affected skin and lung tissue from SSc patients compared to those from controls. Plasma levels of CCL2 and sPSGL-1 correlated with concomitantly obtained FVC values (r = -0.22, P = 0.001 and r = 0.17, P = 0.015, respectively). This relationship was independent of potential confounders (age, sex, ethnicity, smoking status, anti-topoisomerase I positivity, treatment with immunosuppressive agents, MRSS, disease type, and disease duration).

CONCLUSION

A limited number of skin transcripts including genes involved in extravasation and adhesion of inflammatory cells correlate with severity of ILD.

Chemokine (C-X-C motif) ligand (CXCL)10 in autoimmune diseases

(C-X-C motif) ligand (CXCL)10 (CXCL10) belongs to the ELR(-) CXC subfamily chemokine. CXCL10 exerts its function through binding to chemokine (C-X-C motif) receptor 3 (CXCR3), a seven trans-membrane receptor coupled to G proteins. CXCL10 and its receptor, CXCR3, appear to contribute to the pathogenesis of many autoimmune diseases, organ specific (such as type 1 diabetes, autoimmune thyroiditis, Graves' disease and ophthalmopathy), or systemic (such as rheumatoid arthritis, psoriatic arthritis, systemic lupus erythematosus, mixed cryoglobulinemia, Sjögren syndrome, or systemic sclerosis). The secretion of CXCL10 by cluster of differentiation (CD)4+, CD8+, natural killer (NK) and NK-T cells is dependent on interferon (IFN)-γ, which is itself mediated by the interleukin-12 cytokine family. Under the influence of IFN-γ, CXCL10 is secreted by several cell types including endothelial cells, fibroblasts, keratinocytes, thyrocytes, preadipocytes, etc. Determination of high level of CXCL10 in peripheral fluids is therefore a marker of host immune response, especially T helper (Th)1 orientated T-cells. In tissues, recruited Th1 lymphocytes may be responsible for enhanced IFN-γ and tumor necrosis factor-α production, which in turn stimulates CXCL10 secretion from a variety of cells, therefore creating an amplification feedback loop, and perpetuating the autoimmune process. Further studies are needed to investigate interactions between chemokines and cytokines in the pathogenesis of autoimmune diseases and to evaluate whether CXCL10 is a novel therapeutic target in various autoimmune diseases.

Versican is upregulated in circulating monocytes in patients with systemic sclerosis and amplifies a CCL2-mediated pathogenic loop

Introduction

Altered phenotypes of circulating monocytes of patients with systemic sclerosis (SSc) have been reported, but the role of these alterations in the pathogenesis of SSc remains unclear. This study was undertaken to identify molecules that are preferentially expressed by SSc monocytes, and to investigate the roles of these molecules in the pathogenic process of SSc.

Methods

We analyzed circulating CD14⁺ monocytes isolated from 36 patients with SSc and 32 healthy control subjects. The monocytes' gene expression profiles were assessed by Oligo GEArray^® (SABiosciences, Frederic, MA, USA) and semiquantitative or quantitative PCR; their protein expression was evaluated in culture supernatants of unstimulated monocytes by immunoblotting or ELISA, and by immunocytostaining. Monocyte chemoattractant activity of CCL2 was assessed in a TransWell^® system (Corning Incorporated, Corning, NY, USA) in the presence or absence of chondroitin sulfate (CS).

Results

A step-wise approach to profiling gene expression identified that versican and CCL2 were upregulated in SSc monocytes. Subsequent analysis of proteins expressed in monocyte culture supernatants confirmed enhanced production of versican and CCL2 in SSc monocytes compared with control monocytes. CCL2 bound to CS chains of versican and colocalized with versican in the monocytes' Golgi apparatus. Finally, CCL2 had a greater ability to mediate monocyte migration when bound to CS chains, because this binding provided efficient formation of CCL2 gradients and protection from protease attack.

Conclusion

Circulating monocytes with elevated versican and CCL2 levels may contribute to the fibrotic process in a subset of SSc patients by amplifying a positive feedback loop consisting of versican, CCL2, and the influx of monocytes.

Serum chemokine levels as prognostic markers in patients with early systemic sclerosis: a multicenter, prospective, observational study

OBJECTIVE

To assess the utility of serum chemokine levels as a prognostic indicator of disease progression in systemic sclerosis (SSc) patients with early onset disease.

METHODS

Seventy Japanese patients with early onset SSc presenting with diffuse skin sclerosis and/or interstitial lung disease were registered in a multicenter, observational study. Concentrations of CCL2, CCL5, CXCL8, CXCL9, and CXCL10 in serum samples from all patients were measured using cytometric beads array. In 33 patients, chemokine levels were measured each year for 4 years. The ability of baseline chemokine levels to predict changes in clinical features were evaluated statistically by multiple regression analysis.

RESULTS

At their first visit, serum levels of CCL2, CCL5, CXCL8, CXCL9, and CXCL10 were significantly elevated in patients with SSc compared with healthy controls. There were significant associations between CCL2 and CXCL8 levels and between CXCL9 and CXCL10 levels in patients. The initial serum CXCL8 levels were significantly associated with the HAQ-DI at the fourth year while the %VC of baseline tended to be negatively associated with HAQ-DI at the fourth year. Initial chemokine levels were not associated with other clinical features including skin thickness score and the respiratory function.

CONCLUSION

Serum CXCL8 level may serve as a prognostic indicator of the physical dysfunction in SSc. Further longitudinal studies of larger populations are needed to confirm these findings.

Circulating biomarkers of interstitial lung disease in systemic sclerosis

Interstitial lung disease (ILD) is a major cause of morbidity and mortality in patients with systemic sclerosis (SSc). Although a large proportion of SSc patients have only limited interstitial involvement with an indolent course, in a significant minority ILD is progressive, requiring prompt treatment and careful monitoring. One of the main challenges for the clinician treating this highly variable disease is the early identification of patients at risk of progressive ILD, while avoiding potentially toxic treatments in those whose disease is inherently stable. Easily available and repeatable biomarkers that allow estimation of the risk of ILD progression and early response to treatment are highly desirable. In this paper, we review the evidence for circulating biomarkers with potential roles in diagnosis, monitoring of disease activity, or determining prognosis. Peripheral blood biomarkers offer the advantages of being readily obtained, non-invasive, and serially monitored. Several possible candidates have emerged from studies performed so far, including SP-D, KL-6, and CCL18. Presently however, there are few prospective studies evaluating the predictive ability of prospective biomarkers after adjustment for disease severity. Future carefully designed, prospective studies of well characterised patients with ILD, with optimal definition of disease severity and outcome measures are needed.

Clinical and pathological significance of interleukin 6 overexpression in systemic sclerosis

OBJECTIVE

To determine the potential clinical and pathological significance of altered expression of interleukin 6 (IL-6) in systemic sclerosis (SSc).

METHODS

Serum IL-6 and soluble IL-6 receptor levels were measured in patients with SSc (n=68) and healthy controls (n=15). Associations between serum IL-6 level and C reactive protein, platelet count and key clinical outcomes in SSc were explored. Expression of IL-6 in skin biopsies was also examined and western blot and reverse transcription PCRanalysis were performed using cultured dermal fibroblasts. The effect of IL-6 trans-signalling on production of extracellular matrix proteins was assessed and downstream signalling pathways were examined using pharmacological inhibitors.

RESULTS

Serum IL-6 level was frequently elevated in patients with SSc, particularly in those with diffuse cutaneous SSc (dcSSc) with thrombocytosis and elevated acute phase markers. Prominent expression in the skin was observed in dermal fibroblasts, mononuclear cells and endothelial cells in patients with early dcSSc. In vitro experiments supported a potent profibrotic effect of IL-6 trans-signalling via the JAK2/STAT3 and ERK pathways. High IL-6 expression early in dcSSc appears to be associated with more severe skin involvement at 3 years and worse long-term survival than in those without elevated IL-6 levels.

CONCLUSION

Our results confirm the overexpression of IL-6 in dcSSc and support the potential of IL-6 as a surrogate marker for clinical outcome in this disease. The data also provide rationale for clinical studies targeting IL-6 trans-signalling as a potential antifibrotic therapy for SSc.

Interleukin 6 in Systemic Sclerosis and Potential Implications for Targeted Therapy

Objective.

The purpose of this study was to review the potential importance of interleukin 6 (IL-6) in systemic sclerosis (SSc).

Methods.

PubMed and Scopus databases and American College of Rheumatology (from 2009–10) and European League Against Rheumatism abstracts (2009–11) were searched using keywords “scleroderma; SSc; cytokines; interleukins; interleukin 6” and publications were excluded if not pertaining to IL-6 in SSc. Data were extracted from selected articles to construct a cell interaction model of the effects of IL-6 in SSc.

Results.

A total of 416 reports were found (PubMed, n = 82; Scopus, n = 331; 3 abstracts); 372 were excluded (irrelevant) leaving 41 publications and 3 abstracts (39 from PubMed, 18 from Scopus; but 16 were repeated from PubMed search), where 40 suggested IL-6 was important in SSc and 4 did not. Effects of IL-6 in SSc were summarized schematically.

Conclusion.

Of the 44 publications, 40 suggested that IL-6 may be important in SSc, allowing for a conceptual framework within SSc including effects on macrophages, fibroblasts, plasma cells, monocytes, and extracellular matrix.