Among IL-17 families, IL-17A and IL-17F share amino acid sequence similarity and bind to IL-17R type A. IL-17 signaling is implicated in the pathogenesis of various autoimmune diseases, but its role in the regulatory mechanism of extracellular matrix expression and its contribution to the phenotype of systemic sclerosis (SSc) both remain to be elucidated. This study revealed that IL-17A expression was significantly increased in the involved skin and sera of SSc patients, whereas the IL-17F levels did not increase. In contrast, the expression of IL-17R type A in SSc fibroblasts significantly decreased in comparison with that in normal fibroblasts, due to the intrinsic TGF-β1 activation in these cell types. Moreover, IL-17A, not IL-17F, reduced the protein expression of α1(I) collagen and connective tissue growth factor. miR-129-5p, one of the downregulated microRNAs in SSc fibroblasts, increased due to IL-17A and mediated the α1(I) collagen reduction. These results suggest that IL-17A signaling, not IL-17F, has an antifibrogenic effect via the upregulation of miR-129-5p and the downregulation of connective tissue growth factor and α1(I) collagen. IL-17A signaling is suppressed due to the downregulation of the receptor by the intrinsic activation of TGF-β1 in SSc fibroblasts, which may amplify the increased collagen accumulation and fibrosis characteristic of SSc. Increased IL-17A levels in the sera and involved skin of SSc may be due to negative feedback. Clarifying the novel regulatory mechanisms of fibrosis by the cytokine network consisting of TGF-β and IL-17A may lead to a new therapeutic approach for this disease.

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Systemic and localized scleroderma (SSc and LSc) is characterized by excessive deposition of collagen and tissue fibrosis in the skin. Although they have fundamental common characteristics including autoimmunity, little is known about the exact mechanism that mediates the excessive collagen expression in these disorders. In the current study, we tried to evaluate the possibility that microRNAs (miRNAs) play some roles in the pathogenesis of fibrosis seen in these diseases. miRNA expression patterns were evaluated by miRNA array analysis, real-time PCR, and in situ hybridization. The function of miRNAs in dermal fibroblasts was assessed using miRNA inhibitors, precursors, or protectors. In the mouse model of bleomycin-induced dermal sclerosis, the overexpression of miRNAs was performed by i.p. miRNA injection. We demonstrated let-7a expression was downregulated in SSc and LSc skin both in vivo and in vitro, compared with normal or keloid skin. The inhibition or overexpression of let-7a in human or mouse skin fibroblasts affected the protein expression of type I collagen or luciferase activity of collagen 3′-untranslated region. Also, we found let-7a was detectable and quantitative in the serum and investigated serum let-7a levels in patients with SSc or LSc. let-7a concentration was significantly decreased in these patients, especially in LSc patients. Moreover, we revealed that the intermittent overexpression of let-7a in the skin by i.p. miRNA injection improved the skin fibrosis induced by bleomycin in mice. Investigation of more detailed mechanisms of miRNA-mediated regulation of collagen expression may lead to new therapeutic approaches against SSc and LSc.

Decreased miR-424 expression and subsequently increased MEK1 or cyclin E1 may play a key role in the pathogenesis of psoriasis. Investigation of the regulatory mechanisms of keratinocyte proliferation by miRNA may lead to new treatments and a disease activity marker.

Previous reports indicated the significance of the TGF-β signaling in the pathogenesis of systemic sclerosis. We tried to evaluate the possibility that microRNAs (miRNAs) play a part in the type I collagen upregulation seen in normal fibroblasts stimulated with exogenous TGF-β and systemic sclerosis (SSc) fibroblasts. miRNA expression profile was evaluated by miRNA PCR array and real-time PCR. The protein expression of type I collagen was determined by immunoblotting. In vivo detection of miRNA in paraffin section was performed by in situ hybridization. Several miRNAs were found to be downregulated in both TGF-β–stimulated normal fibroblasts and SSc fibroblasts compared with normal fibroblasts by PCR array. Among them, miR-196a expression was decreased in SSc both in vivo and in vitro by real-time PCR or in situ hybridization. In SSc fibroblasts, miR-196a expression was normalized by TGF-β small interfering RNA. miR-196a inhibitor leads to the overexpression of type I collagen in normal fibroblasts, whereas overexpression of the miRNA resulted in the downregulation of type I collagen in SSc fibroblasts. In addition, miR-196a was detectable and quantitative in the serum of SSc patients. Patients with lower serum miR-196a levels had significantly higher ratio of diffuse cutaneous SSc:limited cutaneous SSc, higher modified Rodnan total skin thickness score, and higher prevalence of pitting scars than those without. miR-196a may play some roles in the pathogenesis of SSc. Investigation of the regulatory mechanisms of type I collagen expression by miR-196a may lead to new treatments using miRNA.