The Roles And Underlying Mechanisms Of TSC1/mTOR Signaling In DC In Regulating Cd⁸⁺ T-cell Homeostasis

Dendritic cells?DCs?are innate immune cells which form a critical interface between innate and adaptive immunity and regulate T cell homeostasis and activation.There are evidences showing that many signaling pathways including metabolic programing are linked to DC development and function.However,the metabolism corresponding to distinct DC functions remain largely unresolved.mTOR forms two large complexes,namely mTORC1 and mTORC2,which integrate numerous extracellular and intracellular signals to regulate plenty of metabolic pathways,including proteins,lipids and nucleotides synthesis and also autophagy in demand of growth and proliferation.To investigate the role of mTOR signaling pathway regulated metabolism in DC homeostasis and function,we generated mice harboring specific ablation of Tsc1 in DC compartment(CD11c-cre-Tsc1-floxed,Tsc1^DC-/-),which results in constitutive activation of mTORC1.Specific ablation of Tsc1 in DC compartment largely preserved DC development,but led to pronounced reduction in CD8⁺T cells.The proliferation rate of CD8⁺T cells from Tsc1^DC-/-mice was comparable to WT mice but the apoptosis was significantly increased.Concomitant ablation of mTor(Tsc1/mTor^DC-/-)or Rptor(Tsc1/Rptor^DC-/-)in DCs fully rescued the defect of CD8⁺T cells in Tsc1^DC-/-mice,underscoring mTORC1 as the chief target for TSC1 in this process.Moreover,Tsc1^DC-/-mice were unable to launch efficient antigen-specific CD8⁺T effector responses required for containing Listeria monocytogenes and B16 melanomas,and this defect can also be rescued by Tsc1/mTor^DC-/-mice.Mechanistically,the expression of MHC-I and IL-7 were severely decreased in Tsc1 ablated DCs.In vitro co-culture experiments demonstrated that MHC-I was indispensable for DC mediated proliferation of na?ve OT-I CD8⁺T cells,and the ability of Tsc1^-/-DCs to induce na?ve OT-I CD8⁺T cell proliferation was drastically increased after MHC-I overexpression.In vivo,administration of IL-7 exerted notable effect on CD8⁺T cells in Tsc1^DC-/-mice.Moreover,our data suggest that the steady-state DCs tend to tune down de novo fatty acid synthesis and divert acetyl-CoA for histone acetylation,a process critically controlled by TSC1-mTOR.The expression of ACC1and fatty acids synthesis were significantly increased in Tsc1^-/-DCs,while the level of acetyl-CoA and H3K27ac and H3K9ac in the promoter region of MHC-I and IL-7 were markedly decreased.Remarkably,tempering ACC1 activity either by inhibitor or by shRNA mediated knockdown was able to divert cytosolic acetyl-CoA for histone acetylation and restore the gene expression program compromised by Tsc1-deficiency.In conclusion,our data uncover a crucial role for TSC1-mTOR signaling pathway in metabolic programing the homeostatic DCs for CD8⁺T cell homeostasis,and implicate metabolic-coupled epigenetic imprinting as a paradigm for DC specification.