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The Malate Shuttle Detoxifies Ammonia in Exhausted T Cells by Producing 2-Ketoglutarate

ABSTRACT: The malate shuttle is traditionally known to maintain the NAD+/NADH balance between the cytosol and mitochondria. Whether the malate shuttle has additional functions was unknown. Here we show that chronic viral infections induced the expression of GOT1, the key enzyme in the malate shuttle, in CD8+ T cells. Got1 deficiency indeed decreased the NAD+/NADH ratio and dampened antiviral CD8+ T cell responses to chronic infection; however, increasing the NAD+/NADH ratio did not restore antiviral T cell responses. Got1 deficiency reduced the production of the ammonia scavenger 2-ketoglutarate and led to toxic ammonia accumulation in CD8+ T cells. Supplementation with 2-ketoglutarate assimilated and detoxified ammonia in Got1-deficient T cells and restored antiviral responses. This study suggests that the major function of the malate shuttle in CD8+ T cells is not to maintain the NAD+/NADH ratio, but rather to detoxify ammonia and enable sustainable ammonia-neutral glutamine catabolism in CD8+ T cells during chronic infections.

ORGANISM(S): Mus musculus

PROVIDER: GSE220876 | GEO | 2023/09/01

REPOSITORIES: GEO

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Project description:Previous findings have demonstrated that the NADH/NAD+ ratio has a strong impact on the glycolytic flux in C. glutamicum under anaerobic conditions in the absence of external electron acceptors. During an attempt to rewire anaerobic metabolism to achieve high yield formation of ethanol, we inactivated the malate dehydrogenase and lactate dehydrogenase in a C. glutamicum strain expressing pyruvate decarboxylase and alcohol dehydrogenase, to eliminate formation of the by-products succinate and lactate, respectively. This modification increased the yield of ethanol but had a negative effect on glycolysis, which we found to correlate with an elevated NADH/NAD+ ratio. The pyruvate dehydrogenase (PDH) of C. glutamicum is active under anaerobic conditions, and can potentially exacerbate the negative effect on glycolysis, due to NADH formation. To reduce PDH activity under anaerobic conditions, we decided to replace the gene encoding the E3 subunit of PDH with its Escherichia coli counterpart, as E. coli PDH has been reported to be functional under aerobic conditions only. The resultant strain JS133 produced far less acetate with a further increased ethanol production, however, the glycolytic flux was still low. After observing differences in glycolytic flux for JS133 on glucose and fructose, we speculated that the pentose phosphate pathway (PPP) might be involved in the reduced flux on glucose. To prove this, we deleted the zwf gene, encoding glucose-6-phosphate dehydrogenase, which is the entry point into PPP, and immediately observed a stimulating effect on glycolysis. Subsequent characterization revealed a direct correlation between the intracellular NADH/NAD+ and NADPH/NADP+ ratios under anoxic conditions. Based on these findings we managed to re-channel the metabolism of C. glutamicum successfully towards either to ethanol or D-lactate with 92% and 98% of the theoretical yield respectively, which is the highest yields for D-lactate production thus far reported in the literature.

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The Malate Shuttle Detoxifies Ammonia in Exhausted T Cells by Producing 2-Ketoglutarate

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