Cellular Transdifferentiation: A Crucial Mechanism of Fibrosis in Systemic Sclerosis

Systemic Sclerosis (SSc) is a systemic autoimmune disease of unknown etiology with a highly complex pathogenesis that despite extensive investigation is not completely understood. The clinical and pathologic manifestations of the disease result from three distinct processes: 1) Severe and frequently progressive tissue fibrosis causing exaggerated and deleterious accumulation of interstitial collagens and other extracellular matrix molecules in the skin and various internal organs; 2) extensive fibroproliferative vascular lesions affecting small arteries and arterioles causing tissue ischemic alterations; and 3) cellular and humoral immunity abnormalities with the production of numerous autoantibodies, some with very high specificity for SSc. The fibrotic process in SSc is one of the main causes of disability and high mortality of the disease. Owing to its essentially universal presence and the severity of its clinical effects, the mechanisms involved in the development and progression of tissue fibrosis have been extensively investigated, however, despite intensive investigation, the precise molecular mechanisms have not been fully elucidated. Several recent studies have suggested that cellular transdifferentiation resulting in the phenotypic conversion of various cell types into activated myofibroblasts may be one important mechanism. Here, we review the potential role that cellular transdifferentiation may play in the development of severe and often progressive tissue fibrosis in SSc.

DNA methylation patterns in juvenile systemic sclerosis and localized scleroderma

Scleroderma refers to a group of chronic fibrotic immune-mediated diseases of unknown etiology. Characterizing epigenetic changes in childhood-onset scleroderma, systemic sclerosis or localized scleroderma, has not been previously performed. The aim of this study was to assess DNA methylation differences and similarities between juvenile systemic sclerosis (jSSc) and juvenile localized scleroderma (jLS) compared to matched healthy controls. Genome-wide DNA methylation changes in peripheral blood mononuclear cell samples were assessed using the MethylationEPIC array followed by bioinformatic analysis and limited functional assessment. We identified a total of 105 and 144 differentially methylated sites compared to healthy controls in jSSc and jLS, respectively. The majority of differentially methylated sites and genes represented were unique to either jSSc or jLS suggesting a different underlying epigenetic pattern in both diseases. Among shared differentially methylated genes, methylation levels in a CpG site in FGFR2 can distinguish between LS and healthy PBMCs with a high accuracy. Canonical pathway analysis revealed that inflammatory pathways were enriched in genes differentially methylated in jSSc, including STAT3, NF-κB, and IL-15 pathways. In contrast, the HIPPO signaling pathway was enriched in jLS. Our data also suggest a potential role for NOTCH3 in both jSSc and jLS, and revealed a number of transcription factors unique to each of the two diseases. In summary, our data revealed important insights into jSSc and jLS and suggest a potentially novel epigenetic diagnostic biomarker for LS.

CXCL13 produced by macrophages due to Fli1 deficiency may contribute to the development of tissue fibrosis, vasculopathy and immune activation in systemic sclerosis

CXCL13, a chemokine for B cells, follicular T cells, T helper 17 cells, and regulatory T cells, is reported to contribute to the development of systemic sclerosis (SSc), reflecting aberrant activation of immune system. To better understand the role of CXCL13 in SSc, we investigated the influence of Fli1 deficiency, a potential predisposing factor of this disease, on CXCL13 expression and assessed the clinical correlation of serum CXCL13 levels by multivariate regression analysis. Haploinsufficient loss of Fli1 remarkably induced CXCL13 expression in murine peritoneal macrophages, while gene silencing of FLI1 did not affect the expression of CXCL13 in human dermal fibroblasts and human dermal microvascular endothelial cells. Serum CXCL13 levels were elevated in SSc patients compared with healthy controls and correlated positively with skin score and negatively with pulmonary function test results. SSc patients with elevated serum CXCL13 levels had longer disease duration, diffuse cutaneous involvement, interstitial lung disease (ILD), heart involvement, pulmonary arterial hypertension, Raynaud's phenomenon, pitting scars, digital ulcers, telangiectasia, and high serum IgG levels more frequently than the other patients. In particular, serum CXCL13 levels were associated with ILD and digital ulcers by multivariate regression analysis. Taken together, these results indicate that CXCL13 expression is upregulated by Fli1 deficiency in macrophages, potentially contributing to the development of tissue fibrosis, vasculopathy and immune activation in SSc, especially ILD and digital ulcers.

Arecoline increases basic fibroblast growth factor but reduces expression of IL-1, IL-6, G-CSF and GM-CSF in human umbilical vein endothelium

BACKGROUND

Areca nut chewing is associated with oral submucous fibrosis (OSF). Raised vascular basic fibroblast growth factor may induce fibrosis. Arecoline is a muscarinic alkaloid in areca nut, which we earlier reported causes injury and necrosis of human endothelium.

MATERIALS AND METHODS

Human umbilical vein endothelial cells were exposed to arecoline with or without tumor necrosis factor-α, and separately to acetylcholine, muscarine, or nicotine. Protein levels of basic fibroblast growth factor, as well as the inflammatory cytokines: granulocyte colony stimulating factor (G-CSF), granulocyte-macrophage colony stimulating factor, and Interleukins-6, 1-α and 1-β, were determined by enzyme-linked immunosorbent assay. mRNA levels were established by real-time reverse transcription polymerase chain reaction.

RESULTS

Basic fibroblast growth factor was released into the culture medium at arecoline levels causing necrosis (P < 0.05). This contrasted with an opposite effect of arecoline on levels of the inflammatory cytokines (P < 0.05). Tumor necrosis factor-α increased IL-6 and granulocyte-macrophage colony stimulated factor, but arecoline reduced this stimulated expression (P < 0.05). Arecoline had no effect on mRNA for basic fibroblast growth factor, although there was reduced mRNA for the separate inflammatory cytokines studied. The effect of acetylcholine, muscarine, and nicotine was minimal and dissimilar to that of arecoline.

CONCLUSIONS

Data raise the possibility that arecoline-induced, vascular basic fibroblast growth factor contributes to OSF, by combining increased growth factor expression with endothelial necrosis, and thus driving fibroblast proliferation.

Epidermolysis bullosa - a group of skin diseases with different causes but commonalities in gene expression

Epidermolysis bullosa (EB) is a group of hereditary skin disorders. Although each subtype is caused by mutations in genes encoding differentially located components of the skin, the resulting phenotype is similar. In this study, we investigated similarities in the gene expression profiles of each subtype on mRNA level. Type XVI collagen (COL16A1), G0/G1 switch 2 (G0S2), fibronectin (FN1), ribosomal protein S27A (RPS27A) and low density lipoprotein receptor (LDLR) were shown to exhibit corresponding changes in gene expression in all three EB subtypes. While COL16A1, G0S2 and FN1 are up-regulated, LDLR and RPS27A mRNA levels are decreased. These data indicate that EB cells seem to take measures increasing their mechanical stability. Apoptosis is likely to be exacerbated, and migratory potential appears to be elevated. Protein degradation is hampered, and the release of fatty acids and glycerol is restricted, probably to save energy. These commonalities might benefit existing EB treatment strategies or could help to reveal new starting points for the treatment of EB in the future.

Role of connective tissue growth factor and its interaction with basic fibroblast growth factor and macrophage chemoattractant protein-1 in skin fibrosis

Activation of the immune system and abnormal growth of skin fibroblasts cause systemic sclerosis. Growth factors have various biological activities, including mediation of immune reactions. The growth factor family includes basic fibroblast growth factor (bFGF), transforming growth factor-beta (TGF-beta), and connective tissue growth factor (CTGF). CTGF, an important downstream mediator of TGF-beta in fibrosis, has been suggested to play a specific role in fibrotic disorders. We have directed our attention to the role of CTGF in sustaining skin fibrosis. To better understand its effects in vivo, we established an animal model of skin fibrosis induced by exogenous application of growth factors. In this model, bFGF transiently induced subcutaneous fibrosis. Simultaneous injection of bFGF and CTGF increased skin fibrosis compared with a single injection of bFGF. Serial injections of bFGF for 3 days followed by CTGF for 4 days, or of CTGF followed by bFGF, did not cause skin fibrosis but simultaneous injections increased macrophage chemoattractant protein-1 (MCP-1) mRNA expression levels. To further define the mechanisms of skin fibrosis in vivo, bFGF and CTGF were injected simultaneously into MCP-1 knockout mice, resulting in decreased collagen levels in granulation tissues on day 8. The number of inflammatory cells, such as mast cells, macrophages and lymphocytes, was significantly decreased in MCP-1 knockout mice compared with wild-type mice. These results suggest that bFGF induces collagen production by stimulating skin fibroblasts and CTGF cooperates with bFGF. Our results indicate that the induction of MCP-1 is necessary for infiltration of inflammatory cells.

Current concepts in normal and defective angiogenesis: implications for systemic sclerosis

Vascular abnormalities are a major component of systemic sclerosis, but little is known about the events or mechanisms that initiate vascular injury and prevent its repair. Early stages of systemic sclerosis are characterized by an exaggerated angiogenic response later replaced by defective wound healing and fibrosis. In this review, we summarize the current knowledge of the angiogenic imbalance in systemic sclerosis.