Background: Calcium-permeable channels are known to have roles in many mammalian cell types but the expression and contribution of such ion channels in synovial cells is mostly unknown. The objective of this study was to investigate the potential relevance of Transient Receptor Potential Melastatin 3 (TRPM3) channel to fibroblast-like synoviocytes (FLSs) of patients with rheumatoid arthritis.
Methods: The study used RT-PCR and immunofluorescence to detect mRNA and protein. Intracellular calcium measurement detected channel activity in a FLS cell-line and primary cultures of FLSs from patients with rheumatoid arthritis. Enzyme-linked immunosorbent assays measured hyaluronan.
Results: Endogenous expression of TRPM3 was detected. Previously reported stimulators of TRPM3 sphingosine and pregnenolone sulphate evoked sustained elevation of intracellular calcium in FLSs. The FLS cell-line showed an initial transient response to sphingosine which may be explained by TRPV4 channels but was not observed in FLSs from patients. Blocking antibody targeted to TRPM3 inhibited sustained sphingosine and pregnenolone sulphate responses. Secretion of hyaluronan, which contributes adversely in rheumatoid arthritis, was suppressed by pregnenolone sulphate in FLSs from patients and the effect was blocked by anti-TRPM3 antibody.
Conclusions: The data suggest that FLSs of patients with rheumatoid arthritis express TRPM3-containing ion channels that couple negatively to hyaluronan secretion and can be stimulated by pharmacological concentrations of pregnenolone sulphate.