Semaphorin 4A (Sema4A) plays critical roles in many physiological and pathological processes including neuronal development, angiogenesis, immune response regulation, autoimmunity, and infectious diseases. The present study aimed to investigate its expression and biological activity in rheumatoid arthritis (RA).
RNA and protein were isolated from synovial tissues in RA and osteoarthritis (OA) patients. Treatment with recombinant human Sema4A (rhSema4A) or small interfering RNA (siRNA) was applied to examine its effect on the biological activity of synovial fibroblasts of RA (RASFs). Expression of Sema4A and NF-κB were measured by quantitative RT-PCR (qRT-PCR) and Western blot after lipopolysaccharide (LPS) stimulation. Chromatin immunoprecipitation (ChIP) and siRNA targeting p50 and p60 were applied to detect the regulation of Nuclear factor kappa (NF-κB) on Sema4A. Sema4A, interleukin 1β (IL-1β), interleukin 6 (IL-6), and tumor necrosis factor-α (TNF-α) secretion were measured by ELISA-based assays.
Increased levels of Sema4A were detected in the synovial tissue and fluid of patients with RA compared with those with OA. Furthermore, synovial fluid level of Sema4A correlated with Disease Activity Score (DAS) in RA. Treatment with rhSema4A promoted invasion of RASFs by upregulating the expression of Matrix metallopeptidase3 (MMP3), MMP9, alpha-smooth muscle actin(α-SMA), and Vimentin, and exacerbated inflammation by promoting the production of IL-6 in RASFs, as well as IL-1β and TNF-α in THP-1 cells. The induction of IL-6 and TNF-α by Sema4A was confirmed at the protein level in fluid samples from patients with RA. Knock-down experiments showed the participation of Plexin B1 towards rhSema4A in the induction of cytokines. In addition, LPS stimulation induced Sema4A expression in RASFs in an NF-κB-dependent manner, and rhSema4A treatment could also activate NF-κB signaling.
These findings suggest an NF-κB-dependent modulation of Sema4A in the immune response. Further, increased expression of Sema4A is required to promote inflammation of RA.