Background and objectives T helper type 1 (Th1) cells are involved in rheumatic diseases such as Crohn´s disease or rheumatoid arthritis and have a history of chronic autoantigenic stimulation. We have shown that Th1 cells adapt to chronic inflammation by upregulating the expression of the microRNA (miR)-148a. MiR-148a promotes the survival of chronically activated Th1 cells by regulating the expression of the proapoptotic protein Bim. Thus, we tested the suitability of miR-148a as a therapeutic target for the selective elimination of proinflammatory Th1 cells in a preclinical model of colitis.
Methods Chronically activated Th1 cells were transferred into Rag1-deficient mice to induce colitis. Then, mice were intravenously injected with antagomirs that specifically target the microRNA-148a (antagomir-148a) or with control antagomirs (antagomir-scr). For assessing the function of T cell-intrinsic expression of miR-148a in colitis, we transduced Th1 cells with inducible microRNA sponges prior to transfer into Rag1-deficient mice. Colitic inflammation was determined by the weight-to-length ratios of colons. Colonic Th cells were sorted by FACS to measure miR-148a expression by qRT-PCR. The expression of Bim and Bcl-2 as well as numbers of viable Th1 cells, were determined by flow cytometry.
Results Systemic inhibition of miR-148a by antagomirs alleviated colitis in mice as measured by reduced weight-to-length ratios of their colons. The numbers of viable Th1 cells were reduced up to 50% in mice that were treated with antagomir-148a when compared to mice that were injected with antagomir-scr. Antagomir-148a injections were efficient and resulted in a 30% reduction of miR-148a in colonic Th1 cells. The expression of the proapoptotic protein Bim was increased up to 30% in Th cells from antagomir-148a treated mice, while the anti-apoptotic protein Bcl-2 was unchanged. Th cell specific inhibition of miR-148a by miR-sponges during colitis led to a 30% reduction of Th cells in the colons of colitic mice and reduced the weight-to-length ratio.
Conclusions We suggest that miR-148a controls the survival of proinflammatory Th1 cells in chronic inflammation by inhibiting Bim expression in a Th cell intrinsic fashion. Thus, miR-148a might represent a suitable target for the selective depletion of proinflammatory Th1 cells in chronic inflammation.