Increased Interleukin-10 Expression by the Inhibition of Ca2+-Activated K+ Channel KCa3.1 in CD4+CD25+ Regulatory T Cells in the Recovery Phase in an Inflammatory Bowel Disease Mouse Model

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 (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 IBD 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-administered mice. Quantitative real-time polymerase chain reaction 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 IBD model mice compared with vehicle-administered mice. Among several positive and negative transcriptional regulators (TRs) for IL-10, three positive TRs-E4BP4, KLF4, and Blimp1-were upregulated by the inhibition of K_Ca3.1 in the mLN T_reg cells of IBD model mice. In mouse peripheral CD4⁺CD25⁺ T_reg cells induced by lectin stimulation, IL-10 expression and secretion were enhanced by the treatment with TRAM-34, together with the upregulation of E4BP4, KLF4, and Blimp1. Collectively, the present results demonstrated that the pharmacological inhibition of K_Ca3.1 decreased IBD symptoms in the IBD 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 upregulation of the transcriptional regulators of IL-10: Krüppel-like factor 4, E4 promoter-binding protein 4, and/or B lymphocyte-induced maturation protein 1. 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 such as inflammatory bowel disease.