Protein Kinase C θ Plays a Fundamental Role in Different Types of Chronic Colitis

Background & Aims: Dysregulated host/microbial interactions induce the development of colitis by activating deleterious acquired immune responses. Activation of CD4⁺ T cells is mainly induced through signaling machinery associated with immunologic synapse (IS). A key molecule associated with the IS is protein kinase C (PKC) θ. However, the role of PKCθ in the pathogenesis of colitis has not fully been defined. Methods: The role of PKCθ for the acquired-immune responses involved in the development of different types of colitis (CD45RB model, T-cell receptor [TCR] α knockout [KO] mice and interleukin [IL]-2KO mice) was examined by generating double KO mice and by utilizing cell transfer approaches. Results: Adoptive transfer of PKCθ-deficient naïve CD4⁺ T cells failed to induce T helper cell (Th) 1-mediated colitis in the immune-deficient host (CD45RB model). Development of Th2-mediated colitis in TCRαKO mice was also inhibited by the absence of PKCθ. In IL-2KO mice, which develop colitis because of dysregulated T-cell homeostasis, deficiency of PKCθ in CD4⁺ T cells failed to induce the development of severe colitis. Interestingly, absence of PKCθ led to a remarkable decrease in the proliferation, but not apoptosis, of colonic memory CD4⁺ T cells. This impaired proliferation resulted in a marked decrease in the colonic CD4⁺ T cells that are capable of producing IL-17. In addition, deficiency of PKCθ inhibited the production of Th2 cytokines by colonic CD4⁺ T cells. Conclusions: PKCθ serves as a common and fundamental signaling molecule in the development of different types of colitis and may represent an attractive target for treating inflammatory bowel disease.