Regulation of neurokinin-1 receptor messenger RNA expression in synovial fibroblasts of patients with rheumatoid arthritis

We examined whether soluble mediators regulate the expression of tachykinin receptor mRNAs in synovial fibroblasts of patients with rheumatoid arthritis (RA). mRNAs encoding long and short isomers of neurokinin 1 receptor (NK1R), and neurokinin 2 receptor (NK2R) were confirmed by reverse transcription-polymerase chain reaction (RT-PCR) analysis. Level of long, but not the short, of NK1R mRNA was increased by treatment with 10-100 ng/ml basic fibroblast growth factor (bFGF) or 20 ng/ml tumor necrosis factor-α (TNF-α), but not with 1 ng/ml interleukin 1β (IL-1β). TNF-α upregulated NK2R mRNA as well as long NK1R mRNA whereas bFGF had no effect on NK2R mRNA. Expression of neurokinin 3 receptor (NK3R) mRNA was not observed in RA fibroblasts, and its expression was not induced by bFGF and TNF-α. The basal and increased levels of long NK1R mRNA were inhibited by treatment with 20 μM SU5402, an inhibitor of the tyrosine kinase activity of FGF receptor 1 (FGFR1), or 10 ng/ml transforming growth factor-β1 (TGF-β1). SU5402 and TGF-β1 had no effect on the basal level of short NK1R mRNA. Immunocytochemistry revealed the enhancement by bFGF of immunoreactive NK1Rs in the cells at 24 h after treatment. These results suggest that bFGF, TGF-β1, and TNF-α in synovial tissue and fluid play a role in the regulation of long NK1R expression in synovial fibroblasts of RA patients. It appears that the pathway of downregulation by TGF-β1 is more dominant in the long NK1R mRNA expression than that of upregulation by bFGF or TNF-α. Furthermore, the regulation of short NK1R mRNA expression seems to be performed via a different pathway from that of long isomer mRNA.