Long non-coding RNAs (lncRNAs) are thought to have various functions other than RNA silencing. We tried to evaluate the expression of lncRNAs in patients with systemic sclerosis (SSc) and determined whether lncRNAs controls collagen expression in dermal fibroblasts. lncRNA expression was determined by real-time PCR and in situ hybridization. Protein and mRNA levels of collagen were analysed using immunoblotting and real-time PCR. We found TSIX, one of the lncRNAs, was overexpressed in SSc dermal fibroblasts both in vivo and in vitro, which was inhibited by the transfection of transforming growth factor (TGF)-β1 siRNA. TSIX siRNA reduced the mRNA expression of type I collagen in normal and SSc dermal fibroblasts, but not the levels of major disease-related cytokines. In addition, TSIX siRNA significantly reduced type I collagen mRNA stability, but not protein half-lives. Furthermore, we first investigated serum lncRNA levels in patients with SSc, and serum TSIX levels were significantly increased in SSc patients. TSIX is a new regulator of collagen expression which stabilizes the collagen mRNA. The upregulation of TSIX seen in SSc fibroblasts may result from activated endogenous TGF-β signalling and may play a role in the constitutive upregulation of collagen in these cells. Further studies on the regulatory mechanism of tissue fibrosis by lncRNAs in SSc skin lead to a better understanding of the pathogenesis, new diagnostic methods by their serum levels and new therapeutic approaches using siRNAs.

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IL-12 family cytokines are implicated in the pathogenesis of various autoimmune diseases, but their role in the regulation of extracellular matrix expression and its contribution to the phenotype of systemic sclerosis (SSc) remain to be elucidated. Among the IL-12 family members, IL-35 decreases type I collagen expression in cultured dermal fibroblasts. IL-35 consists of p35 and EBI3 subunits, and EBI3 alone could downregulate the protein and mRNA expression of type I or type III collagen in the presence or absence of TGF-β costimulation. We found that collagen mRNA stability was reduced by EBI3 via the induction of miR-4500. The IL-35 levels in the sera or on the surface of T cells were not altered in SSc patients, while EBI3 expression was decreased in the keratinocytes of the epidermis and regulatory T cells of the dermis in SSc skin compared with normal skin, which may induce collagen synthesis in SSc dermal fibroblasts. We also found that gp130, the EBI3 receptor, was expressed in both normal and SSc fibroblasts. Moreover, we revealed that EBI3 supplementation by injection into the skin improves mice skin fibrosis. Decreased EBI3 in SSc skin may contribute to an increase in collagen accumulation and skin fibrosis. Clarifying the mechanism regulating the extracellular matrix expression by EBI3 in SSc skin may lead to better understanding of this disease and new therapeutic strategies using ointment or microinjection of the subunit.