MTORC1 promotes T-bet phosphorylation to regulate Th1 differentiation

CD4+ T cells lacking the mTORC1 activator Rheb fail to secrete IFN-g under Th1 polarizing conditions. We hypothesized that this phenotype is due to defects in regulation of the canonical Th1 transcription factor T-bet at the level of protein phosphorylation downstream of mTORC1. To test this hypothesis, we employed targeted mass-spectrometry proteomic analysis-multiple reaction monitoring mass spectrometry. We used this method to detect and quantify predicted phosphopeptides derived from T-bet. By analyzing activated murine wild-type and Rheb-deficient CD4+ T cells, as well as murine CD4+ T cells activated in the presence of rapamycin, a pharmacologic inhibitor of mTORC1, we were able to identify six T-bet phosphorylation sites. Five of these are novel, and four sites are consistently dephosphorylated in both Rheb-deficient CD4+ T cells and T cells treated with rapamycin, suggesting mTORC1 signaling controls their phosphorylation. Alanine mutagenesis of each of the six phosphorylation sites was tested for the ability to impair IFN-g expression. Single phosphorylation site mutants still support induction of IFN-g expression; however, simultaneous mutation of three of the mTORC1-dependent sites results in significantly reduced IFN-g expression. The reduced activity of the triple mutant T-bet is associated with its failure to recruit chromatin remodeling complexes to the Ifng gene promoter. These results establish a novel mechanism by which mTORC1 regulates Th1 differentiation, through control of T-bet phosphorylation

Myeloid-Derived Suppressor Cells (MDSCs) in Aged Mice: Focus on Inflammation

As people get older, the homeostatic functions of many systems in the body like the immune system decline, which contributes to increase susceptibility to disease. The bone marrow of healthy individuals continually generates myeloid cells, which differentiate into mature cells like granulocytes, macrophages, or dendritic cells. However, under inflammatory conditions, there is an increased frequency of immature myeloid cells that can suppress T cell responses in peripheral secondary lymph organs in both human and murine hosts. The heterogeneous population of cells known as myeloid-derived suppressor cells (MDSCs), consisting of myeloid progenitors and immature myeloid cells, share a biological function: immunosuppression. This chapter reviews novel findings in mice about the nature of MDSCs and, in this context, discusses current knowledge about these cells during the aging process. MDSCs may have an important role in the regulation of the immune response during aging. MDSC dysfunction in aged mice may compromise the innate and adaptive immune systems, and thus understanding their role during aging may be useful for potential future therapeutics.Fil: Pistoresi, Maria Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; ArgentinaFil: Harman, María Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; ArgentinaFil: Castell, Sofía Daiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; Argentin