Fibrosis in frozen shoulder: Activation of IL-6 through PI3K-Akt signaling pathway in synovial fibroblast

Fibrosis is the main cause of limited range of motion (ROM) of shoulder in patients with frozen shoulder (FS). Overexpression of Interleukin 6 (IL-6) has been correlated with pathogenesis of FS. However, the underlying mechanism remains largely unexplored. In the current study, we focused on isolating synovial fibroblasts of FS and determining the influence of IL-6 as well as PI3K-Akt signaling pathway on the fibrotic process of synovial fibroblasts in FS by using RNA Sequencing (RNA-seq) and other molecular biology techniques. Synovial fibroblasts of FS express more extra cellular matrix (ECM) than that of control. RNA-seq results and bioinformatic analysis indicate that PI3K-Akt signaling pathway play an important role in the fibrotic process of FS, and IL-6 is the most related gene among those related to this process. The expression levels of IL-6 / IL-6R in FS synovial fibroblasts and IL-6 in culture supernatant were both significantly increased. siRNA interference with the expression of IL-6 attenuates the fibrosis level of FS as well as phosphorylation level of Akt. The findings suggest that synovial fibroblasts are key effector cells of fibrosis of FS. Activation of PI3K-Akt pathway can promote fibrosis of synovial fibroblasts in FS. IL-6 is up-regulated in synovial fibroblasts of FS and promoted the FS fibrosis through PI3K-Akt signaling pathway. •Synovial fibroblasts are key effector cells in the fibrogenesis of frozen shoulder.•Inflammation of synovial fibroblasts induces the fibrotic process.•IL-6 promotes fibrosis through PI3K-Akt signaling pathway.