Pro-fibrotic effect of IL-6 via aortic adventitial fibroblasts indicates IL-6 as a treatment target in Takayasu arteritis

Objective This study aimed to clarify potential mechanism of IL-6 involved in adventitial fibrosis via adventitial fibroblast in Takayasu arteritis (TAK). Methods Immunohistochemistry and double-labelled immunofluorescence were performed on vascular tissue from patients with TAK and controls. Human aorta adventitial fibroblast (AAF) was cultured and stimulated with interleukine 6 (IL-6)/IL-6 receptor (IL-6R). Real-time PCR, western blot, enzyme-linked immunosorbent assays, chromatin immunoprecipitation (ChIP) and reporter assay were conducted in vitro experiments to determine effect of IL-6/IL-6R on AAF. Results The expression of IL-6, IL-6R, collagen I, collagen III, fibronectin, alpha-smooth muscle actin (alpha-SMA), and transforming growth factor (TGF-beta) in TAK arteries was significantly higher than that in the normal arteries. Co-localisation of alpha-SMA and IL-6 and a positive correlation between their expression were observed in local lesions. In vitro experiments, collagen I, collagen III, fibronectin, alpha-SMA, and TGF-beta expression increased significantly after stimulation and this fibrogenesis of AAFs was induced in TGF-beta-dependent and-independent manners. Additionally, phosphorylation of JAK2, STAT3 and Akt was significantly enhanced both in IL-6/IL-6R-treated AAFs in vitro and in TAK adventitial alpha-SMA positive cells. When AAFs were pretreated with inhibitors against JAK2, STAT3, and Akt, fibrosis was significantly reduced. Furthermore, IL-6/IL-6R promoted mRNA expression of IL-6 and MCP-1 in AAFs. Finally, according to ChIP and reporter assay results, STAT3 was the main transcriptional factor in the fibrosis of AAFs induced by IL-6/IL-6R. Conclusion IL-6/IL-6R induces fibrogenesis of AAFs via the JAK2/STAT3 and JAK2/Akt pathways, which provides theoretical evidence for IL-6 as a treatment target in TAK.