Background Rheumatoid arthritis (RA) is a chronic autoimmune disease characterised by inflammation of diarthrodial joints. Sensory neurons expressing transient receptor potential (TRP) channels, a wide family of non-selective cation channels, have been shown to play a role in the pathogenesis of RA1. Transient receptor potential 5 (TRPC5) is a member of the canonical family of TRPC channels and is abundantly expressed in the central nervous system and periphery2, including CD55+ fibroblast-like synoviocytes3, but the role of TRPC5 in arthritis is unknown.
Objectives To evaluate the for the first time, the contribution of TRPC5 in an in vivo model of arthritis and investigate the role of TRPC5 in the modulation of hyperalgesia and joint inflammation.
Methods All experiments were conducted under the guidelines of the United Kingdom Home Office Animals (Scientific Procedures) Act 1986. Age-matched, male 129S1/SvImJ wildtype (WT) and TRPC5 knockout (KO) mice littermates bred from heterozygotic mice provided by Prof. D.E. Clapham, USA2. Induction of arthritis using CFA was performed as previously described1; inflammation was allowed to progress to 14 days. Nociceptive tests were carried out weekly. Synovial blood flow was assessed in anaesthetised WT and TRPC5 KO mice using a full-field laser perfusion imager (FLPI)4 on day 14. Ex vivo analysis included assessment of cellular infiltration in the knee joint, and determination of cytokine concentrations. In separate studies, WT and TRPC5 KO mice received the TRPC4/5 antagonist, ML2045(2mg/kg, i.p., n=6) or vehicle (2% DMSO in saline, n=4) daily following i.art. injection of CFA. Results are presented as mean ± s.e.m. and analysed by 2-way ANOVA and Bonferonni post hoc test.
Results WT mice developed primary hyperalgesia with a significant reduction in withdrawal threshold compared to baseline responses (334.7±25.7 vs 452.2±8.2 gram force (gf); p<0.01]). Primary hyperalgesia was exacerbated in TRPC5 KO mice compared to WT mice on day 14 (267.4±34.2 vs 334.7±25.4gf; p<0.05]). This was associated with similar deficits in weight-bearing on the ipsilateral hind-limb which was significantly reduced compared to WT mice. Ipsilateral synovial blood flow was significantly increased in TRPC5 KO mice compared to the contralateral synovium (291.3±50.2 vs 198.2±21.4 flux units (AU); p<0.01), and WT ipsilateral synovium (p<0.001). Pharmacological antagonism of TRPC5 in WT mice corroborated the results observed in TRPC5 KO mice, where hyperalgesia and joint inflammation was significantly exacerbated compared to vehicle treated WT mice.
Conclusions Our results reveal a protective ability of TRPC5 in inflammatory joint conditions in vivo. Genetic deletion or pharmacological antagonism of TRPC5 resulted in an exacerbated inflammatory response highlighted by heightened nociceptive responses, increased cellular infiltration and cytokine concentrations in the knee joint.
Fernandes, E.S., et al. 2011. Arthritis Rheum 63, 819–829.
Riccio, A., et al. 2009. Cell 137, 761–772.
Xu, S.Z., et al. 2008. Nature 451, 69–72
Fernandes, E.S., et al. 2016. Arthritis Res Ther 18(1), 7
Miller, M., et al. 2011. J Biol Chem 286, 33436–46.
Acknowledgement Supported by Arthritis Research UK.
Disclosure of Interest None declared