Unraveling the needs of a killer: Glucose required for CD8+ T-cell destruction of β-cells

Background: T-cell mitochondrial dysfunction has been linked with autoimmune disease. We have recently discovered that T-cells from T1D patients exhibit mitochondrial inner-membrane hyperpolarization and elevated proinflammatory function. We hypothesize that T-cells from patients with T1D display aberrant metabolism resulting in pathogenic functional activity, heightened effector function and resistance to mechanisms of peripheral deletion and regulation.

Methods: Here we used naive and Glucose-6-Phosphatase Catalytic Subunit 2 (IGRP) reactive CD8⁺ T-cells (CTLs) in cytotoxicity assays against human β-cells and naïve CD8⁺ T-cells in expansion and proliferative assays in substrate limitation/excess and metabolic inhibition. Additionally, we performed ¹H-NMR and ¹³C-NMR to establish metabolic pathways in effector CTLs.

Results: Metabolic inhibition during activation of naïve CD8+ T-cells demonstrated, when glucose utilization is blocked via 2-deoxyglucose (2DG: p<0.0001) or mitochondria inhibited with Antimycin A, T-cells cannot proliferate (p<0.0001).  Utilization of less energy efficient substrates, galactose or methylsuccinate, resulted in reduced T-cell proliferation (p>0.05).  Therefore, in human T-cells mitochondrial activity is essential for early activation and expansion.  CTL cytotoxic activity was unaltered in media containing 11, 5.5, 2.7 or 1mM glucose but was reduced in 0mM glucose (p>0.05 vs 5.5mM glucose). Addition of 2DG at equal molar levels to glucose abolished CTL activity (p<0.0001).  Inhibition of Oxidative Phosphorylation (OXPHOS) complex I, III, or IV or ATP transport out of the mitochondria with cATR had no effect on CTL lytic function.  Utilization of U-13C-glucose for 13C-NMR analyses after T-cell/?-cell co-cultures revealed that T-cells converted 75% of the glucose utilized to U-13C-lactate.

Conclusion:These data demonstrate that in human T-cells, mitochondrial ATP production is essential for efficient T-cell activation and proliferation.  Alternatively, activated CTLs don?t require OXPHOS, instead utilize glycolysis for ?-cell lysis.  Our data suggest that lymphocyte mitochondria and metabolic pathways are a promising and novel target for slowing down and reversing autoimmunity in the prevention of T1D.