Succinate dehydrogenase/complex II is critical for metabolic and epigenetic regulation of T cell proliferation and inflammation

Robust and effective T cell-mediated immune responses require the proper allocation of metabolic resources to sustain energetically costly processes like growth, proliferation, and cytokine production. Epigenetic control of the genome also governs T cell transcriptome and T cell lineage commitment and maintenance. Cellular metabolic programs interact with epigenetic regulation by providing substrates for covalent modifications of chromatin. By employing complementary genetic, epigenetic, and metabolic approaches, we revealed that tricarboxylic acid (TCA) cycle flux fuels biosynthetic processes while controlling the ratio of α-ketoglutarate/succinate to modulate the activities of dioxygenases that are critical for driving T cell inflammation. In contrast to cancer cells, where succinate dehydrogenase (SDH)/complex II inactivation drives cell transformation and growth, SDH/complex II deficiency in T cells causes proliferation and survival defects when the TCA cycle is truncated, blocking carbon flux to support nucleosides biosynthesis. Accordingly, replenishing the intracellular nucleoside pool partially relieved the dependence of T cells on SDH/complex II for proliferation and survival. Conversely, SDH deficiency induces a pro-inflammatory gene signature in T cells and promotes T helper 1 (TH1) and T helper 17 (TH17) lineage differentiation. Mechanistically, the hypoxia-inducible factor 1 (HIF-1) is not required for succinate-induced inflammation in T cells. A reduced α-ketoglutarate/succinate ratio in SDH deficient T cells promotes inflammation through changing the pattern of the transcriptional and chromatin-accessibility signatures and consequentially increasing the expression of the transcription factor, B lymphocyte-induced maturation protein-1 (Blimp-1). Collectively, our studies revealed a critical role of SDH/complex II in allocating carbon resources for anabolic processes and epigenetic regulation in T cell proliferation and inflammation.