Abstract

Fibroblast-like synoviocytes (FLS) are a key cell-type involved in rheumatoid arthritis (RA) progression. We previously identified the KCa1.1 potassium channel (Maxi-K, BK, Slo 1, KCNMA1) as a regulator of FLS and that KCa1.1 inhibition reduces disease severity in RA animal models. However, systemic KCa1.1 block causes multiple side effects and in this study, we aimed to determine whether the KCa1.1 β1-3-specific venom peptide blocker iberiotoxin (IbTX) reduces disease severity in animal models of RA without inducing major side effects. We used immunohistochemistry to identify IbTX-sensitive KCa1.1 subunits in joints of rats with a model of RA. Patch clamp and functional assays were used to determine if IbTX can regulate FLS through targeting KCa1.1. We then tested the efficacy of IbTX in ameliorating disease in two rat models of RA. Finally, we determined if IbTX causes side-effects including incontinence or tremors in rats, compared to those treated with the small molecule KCa1.1 blocker paxilline. IbTX-sensitive subunits of KCa1.1 are expressed by FLS in joints of rats with experimental arthritis. IbTX inhibits KCa1.1 channels expressed by FLS from patients with RA and by FLS from rat models of RA and reduces FLS invasiveness. IbTX significantly reduces disease severity in two rat models of RA. Unlike paxilline, IbTX does not induce tremors or incontinence in rats. Overall, IbTX inhibits KCa1.1 channels on FLS and treats rat models of RA without inducing side effects associated with non-specific KCa1.1 blockade and could become the basis for the development of a new treatment for RA.