Abstract

Inflammatory bowel diseases (IBD) are chronic inflammatory diseases of the gastrointestinal tract arising from abnormal responses of the innate and adaptative immune systems. Interleukin-10 (IL-10)-producing CD4⁺CD25⁺ regulatory T (T_reg) cells play a protective role in the recovery phase of IBD. In the present study, the effects of the administration of the selective Ca²⁺-activated K⁺ channel K_Ca3.1 inhibitor TRAM-34 on disease activities were examined in chemically-induced, semi-chronic IBD (scIBD) model mice. IBD disease severity, as assessed by diarrhea, visible fecal blood, inflammation, and crypt damage in the colon, was significantly lower in mice administered 1 mg/kg TRAM-34 than in vehicle-administrated mice. Quantitative real-time PCR examinations showed that IL-10 expression levels in the recovery phase were markedly increased by the inhibition of K_Ca3.1 in mesenteric lymph node (mLN) T_reg cells of scIBD model mice compared with in vehicle-administered mice. Among several positive and negative transcriptional regulators (TRs) for IL-10, three positive TRs, E4BP4, KLF4, and Blimp1 were up-regulated by the inhibition of K_Ca3.1 in the mLN T_reg cells of scIBD model mice. In mouse peripheral CD4⁺CD25⁺ T_reg cells induced by a lectin stimulation, IL-10 expression and secretion were enhanced by the treatment with TRAM-34, together with the up-regulation of E4BP4, KLF4, and Blimp1. Collectively, the present results demonstrated that the pharmacological inhibition of K_Ca3.1 decreased IBD symptoms in scIBD model by increasing IL-10 production in peripheral T_reg cells, and that IL-10^high T_reg cells produced by the treatment with K_Ca3.1 inhibitor may contribute to efficient T_reg therapy for chronic inflammatory disorders, including IBD.

Significance Statement Pharmacological inhibition of Ca²⁺-activated K⁺ channel K_Ca3.1 increased IL-10 expression in peripheral T_reg cells, together with the up-regulation of the transcriptional regulators of IL-10: KLF4, E4BP4, and/or Blimp1. The manipulation of IL-10^high-producing T_reg cells by the pharmacological inhibition of K_Ca3.1 may be beneficial in the treatment of chronic inflammatory diseases like IBD.