Characterising the iron dependence of T-cells

Thesis

Iron is an essential micronutrient which interacts with ~400 different protein types in human cells. Meanwhile, iron deficiency remains globally prevalent affecting >1.2 billion people. Pre-clinical studies demonstrate that iron restriction impairs T-cell proliferation, activation and effector function in models of vaccination, autoimmunity and infection. However, the biochemical mechanisms underlying these effects remain undefined. In this thesis, in silico, in vitro and in vivo methods were used to examine Tcell iron usage and dependence. Initial mathematical modelling predicted T-cells dramatically increase iron demands post-activation. Further transcriptomic and proteomic profiling of in vitro activated iron deficient CD8+ T-cells revealed induction of the P53 cell cycle arrest pathway and suppression of mTORC1 and MYC signalling, together indicative of aberrant metabolic rewiring. Iron deprived CD8+ T-cells show increased mROS generation suggestive of electron transport chain dysfunction, and impaired tricarboxylic acid (TCA) cycle progression through the iron dependent enzymes aconitase 2 and succinate dehydrogenase, such that downstream metabolites α- ketoglutarate, fumarate and malate are depleted. The repressive histone mark H3K27me3 is normally removed by the iron and α-ketoglutarate dependent enzymes, KDM6A/B, but accumulates in iron deprived T-cells. Despite TCA cycle dysfunction, aspartate, which is produced downstream of the TCA cycle, was unexpectedly increased in iron restriction. Higher aspartate is proposed to be partly driven by suppressed aspartate usage by downstream iron-dependent pathways including translation and nucleotide synthesis. Interestingly, exogenous aspartate substantially rescues the proliferation of iron deprived CD8+ T-cells suggesting that endogenous aspartate sources are unusable, possibly due to trapping of aspartate within the mitochondria. Overall, this thesis demonstrates that iron deprivation impairs T-cell biochemistry at multiple nodes providing insight as to how metabolic and iron modulatory interventions could be coupled to augment or suppress immunity.

Authors: Teh, MR

• DOI: 10.5287/ora-2nqr5ogke
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Iron; TCA cycle; Immunology; Demethylation; Metabolism; Immunity; Mitochondria; T-cell; Aspartate
• Subjects: Metabolism; Iron; Immunology