The malate shuttle detoxifies ammonia in exhausted T cells by producing 2-ketoglutarate.

The malate shuttle is traditionally understood to maintain NAD+/NADH balance between the cytosol and mitochondria. Whether the malate shuttle has additional functions is unclear. Here we show that chronic viral infections induce CD8+ T cell expression of GOT1, a central enzyme in the malate shuttle. Got1 deficiency decreased the NAD+/NADH ratio and limited antiviral CD8+ T cell responses to chronic infection; however, increasing the NAD+/NADH ratio did not restore T cell responses. Got1 deficiency reduced the production of the ammonia scavenger 2-ketoglutarate (2-KG) from glutaminolysis and led to a toxic accumulation of ammonia in CD8+ T cells. Supplementation with 2-KG assimilated and detoxified ammonia in Got1-deficient T cells and restored antiviral responses. These data indicate that the major function of the malate shuttle in CD8+ T cells is not to maintain the NAD+/NADH balance but rather to detoxify ammonia and enable sustainable ammonia-neutral glutamine catabolism in CD8+ T cells during chronic infection.

[Expression of caspase-3, Bcl-2, and Bax in pentavalent vanadium-induced neuronal apoptosis].

OBJECTIVE: To investigate the expression of caspase-3, Bcl-2, and Bax in pentavalent vanadium-induced neuronal apoptosis and the neurotoxicity of pentavalent vanadium to in vitro cultured rat neurons. METHODS: Neurons from rats were cultured in vitro and treated with different concentrations of V2O5. Neuronal apoptosis was evaluated by TdT-mediated dUTP-biotin nick end labeling (TUNEL). The expression of caspase-3, Bcl-2, and Bax in neurons was measured by Western blot. The images collected by gel imaging system and scanner were analyzed. RESULTS: The TUNEL showed that compared with the control group, the middle- and high-dose exposure groups had significantly increased apoptosis index (AI) of neurons (P < 0.05 or P < 0.01). The Western blot showed that compared with the control group, the middle- and high-dose exposure groups had significantly increased expression of caspase-3 and Bax and significantly decreased expression of Bcl-2 (P <0.05 or P < 0.01). The AI of neurons was positively correlated with the expression of caspase-3 and Bax (r = 0.943, P < 0.01; r = 0.937, P < 0.01) and negatively correlated with the expression of Bcl-2 (r = -0.908, P < 0.01). CONCLUSION: Pentavalent vanadium may induce neuronal apoptosis, and the expression of caspase-3, Bcl-2, and Bax, which regulate apoptosis, plays an important role in the neuronal apoptosis induced by pentavalent vanadium.