Cellular pyrimidine imbalance triggers mitochondrial DNA-dependent innate immunity [A33_OE_RNA-seq]

Cytosolic mitochondrial DNA (mtDNA) elicits a type I interferon response, but signals triggering the release of mtDNA from mitochondria remain enigmatic. Here, we show that mtDNA-dependent immune signalling via the cyclic GMP–AMP syn- thase‒stimulator of interferon genes‒TANK-binding kinase 1 (cGAS–STING–TBK1) pathway is under metabolic control and is induced by cellular pyrimidine deficiency. The mitochondrial protease YME1L preserves pyrimidine pools by supporting de novo nucleotide synthesis and by proteolysis of the pyrimidine nucleotide carrier SLC25A33. Deficiency of YME1L causes inflamma- tion in mouse retinas and in cultured cells. It drives the release of mtDNA and a cGAS–STING–TBK1-dependent inflammatory response, which requires SLC25A33 and is suppressed upon replenishment of cellular pyrimidine pools. Overexpression of SLC25A33 is sufficient to induce immune signalling by mtDNA. Similarly, depletion of cytosolic nucleotides upon inhibition of de novo pyrimidine synthesis triggers mtDNA-dependent immune responses in wild-type cells. Our results thus identify mtDNA release and innate immune signalling as a metabolic response to cellular pyrimidine deficiencies. Transcript profiles of wildtype (WT) or Slc25a33-MycFlag overexpressing HeLa cells treated with 40 µM 2',3' dideoxycytidine (ddC) for 72 h.

胞质线粒体DNA（mtDNA）可触发I型干扰素应答，但诱导线粒体mtDNA释放的信号机制仍尚未阐明。本研究发现，经由环鸟苷酸-腺苷酸合成酶-干扰素基因刺激因子-TANK结合激酶1（cyclic GMP–AMP synthase–stimulator of interferon genes–TANK-binding kinase 1, cGAS–STING–TBK1）通路介导的mtDNA依赖性免疫信号通路受代谢调控，且可因细胞嘧啶缺乏而被诱导。
线粒体蛋白酶YME1L通过支持核苷酸从头合成，以及降解嘧啶核苷酸转运体SLC25A33，维持细胞嘧啶池的稳态。YME1L缺失会导致小鼠视网膜及培养细胞发生炎症反应；其可驱动mtDNA释放，并引发依赖cGAS–STING–TBK1通路的炎症应答，该过程依赖SLC25A33，且可通过补充细胞嘧啶池得到抑制。过表达SLC25A33即可通过mtDNA诱导免疫信号通路激活。
类似地，抑制嘧啶从头合成途径导致胞质核苷酸耗竭时，也可在野生型细胞中触发mtDNA依赖性免疫应答。综上，本研究证实mtDNA释放与固有免疫信号通路是细胞对嘧啶缺乏产生的代谢应答。
本数据集包含经40 μM 2',3'-二脱氧胞苷（ddC）处理72小时的野生型（WT）或Slc25a33-MycFlag过表达HeLa细胞的转录组图谱。