miR-148a is upregulated by Twist1 and T-bet and promotes Th1-cell survival by regulating the proapoptotic gene Bim.

Repeatedly activated T helper 1 (Th1) cells present during chronic inflammation can efficiently adapt to the inflammatory milieu, for example, by expressing the transcription factor Twist1, which limits the immunopathology caused by Th1 cells. Here, we show that in repeatedly activated murine Th1 cells, Twist1 and T-bet induce expression of microRNA-148a (miR-148a). miR-148a regulates expression of the proapoptotic gene Bim, resulting in a decreased Bim/Bcl2 ratio. Inhibition of miR-148a by antagomirs in repeatedly activated Th1 cells increases the expression of Bim, leading to enhanced apoptosis. Knockdown of Bim expression by siRNA in miR-148a antagomir-treated cells restores viability of the Th1 cells, demonstrating that miR-148a controls survival by regulating Bim expression. Thus, Twist1 and T-bet not only control the differentiation and function of Th1 cells, but also their persistence in chronic inflammation.

Persistence of effector memory Th1 cells is regulated by Hopx.

Th1 cells are prominent in inflamed tissue, survive conventional immunosuppression, and are believed to play a pivotal role in driving chronic inflammation. Here, we identify homeobox only protein (Hopx) as a critical and selective regulator of the survival of Th1 effector/memory cells, both in vitro and in vivo. Expression of Hopx is induced by T-bet and increases upon repeated antigenic restimulation of Th1 cells. Accordingly, the expression of Hopx is low in peripheral, naïve Th cells, but highly up-regulated in terminally differentiated effector/memory Th1 cells of healthy human donors. In murine Th1 cells, Hopx regulates the expression of genes involved in regulation of apoptosis and survival and makes them refractory to Fas-induced apoptosis. In vivo, adoptively transferred Hopx-deficient murine Th1 cells do not persist. Consequently, they cannot induce chronic inflammation in murine models of transfer-induced colitis and arthritis, demonstrating a key role of Hopx for Th1-mediated immunopathology.

Regulation of Fatty Acid Oxidation by Twist 1 in the Metabolic Adaptation of T Helper Lymphocytes to Chronic Inflammation.

OBJECTIVE: Inflamed tissue is characterized by low availability of oxygen and nutrients. Yet CD4+ T helper lymphocytes persist over time in such tissue and probably contribute to the chronicity of inflammation. This study was undertaken to analyze the metabolic adaptation of these cells to the inflamed environment. METHODS: Synovial and blood CD4+ T cells isolated ex vivo from patients with juvenile idiopathic arthritis (JIA) and murine CD4+ T cells were either stimulated once or stimulated repeatedly. Their dependency on particular metabolic pathways for survival was then analyzed using pharmacologic inhibitors. The role of the transcription factor Twist 1 was investigated by determining lactate production and oxygen consumption in Twist1-sufficient and Twist1-deficient murine T cells. The dependency of these murine cells on particular metabolic pathways was analyzed using pharmacologic inhibitors. RESULTS: Programmed death 1 (PD-1)+ T helper cells in synovial fluid samples from patients with JIA survived via fatty acid oxidation (mean ± SEM survival of 3.4 ± 2.85% in the presence of etomoxir versus 60 ± 7.08% in the absence of etomoxir on day 4 of culture) (P < 0.0002; n = 6) and expressed the E-box-binding transcription factor TWIST1 (2-14-fold increased expression) (P = 0.0156 versus PD-1- T helper cells; n = 6). Repeatedly restimulated murine T helper cells, which expressed Twist1 as well, needed Twist1 to survive via fatty acid oxidation. In addition, Twist1 protected the cells against reactive oxygen species. CONCLUSION: Our findings indicate that TWIST1 is a master regulator of metabolic adaptation of T helper cells to chronic inflammation and a target for their selective therapeutic elimination.