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Cytoplasmic DNA sensing by KU complex in aged CD4+ Tcell potentiates Tcell activation and aging-related autoimmune inflammation

Wang, Y;Fu, Z;Li, X;Liang, Y;Pei, S;Hao, S;Zhu, Q;Yu, T;Pei, Y;Yuan, J;Ye, J;Fu, J;Xu, J;Hong, J;Yang, R;Hou, H;Huang, X;Peng, C;Zheng, M;Xiao, Y;

Aging is associated with DNA accumulation and increased homeostatic proliferation of circulating T cells. Although these attributes are associated with aging-related autoimmunity, their direct contributions remain unclear. Conventionally, KU complex, the regulatory subunit of DNA-dependent protein kinase (DNA-PK), together with the catalytic subunit of DNA-PK (DNA-PKcs), mediates DNA damage repair in the nucleus. Here, we found KU complex abundantly expressed in the cytoplasm, where it recognized accumulated cytoplasmic DNA in aged human and mouse CD4+ T cells. This process enhanced T cell activation and pathology of experimental autoimmune encephalomyelitis (EAE) in aged mice. Mechanistically, KU-mediated DNA sensing facilitated DNA-PKcs recruitment and phosphorylation of the kinase ZAK. This activated AKT and mTOR pathways, promoting CD4+ T cell proliferation and activation. We developed a specific ZAK inhibitor, which dampened EAE pathology in aged mice. Overall, these findings demonstrate a KU-mediated cytoplasmic DNA-sensing pathway in CD4+ T cells that potentiates aging-related autoimmunity.