Impaired mitochondrial oxidative phosphorylation limits the self-renewal of T cells exposed to persistent antigen.

The majority of tumor-infiltrating T cells exhibit a terminally exhausted phenotype, marked by a loss of self-renewal capacity. How repetitive antigenic stimulation impairs T cell self-renewal remains poorly defined. Here, we show that persistent antigenic stimulation impaired ADP-coupled oxidative phosphorylation. The resultant bioenergetic compromise blocked proliferation by limiting nucleotide triphosphate synthesis. Inhibition of mitochondrial oxidative phosphorylation in activated T cells was sufficient to suppress proliferation and upregulate genes linked to T cell exhaustion. Conversely, prevention of mitochondrial oxidative stress during chronic T cell stimulation allowed sustained T cell proliferation and induced genes associated with stem-like progenitor T cells. As a result, antioxidant treatment enhanced the anti-tumor efficacy of chronically stimulated T cells. These data reveal that loss of ATP production through oxidative phosphorylation limits T cell proliferation and effector function during chronic antigenic stimulation. Furthermore, treatments that maintain redox balance promote T cell self-renewal and enhance anti-tumor immunity.

Proline biosynthesis is a vent for TGFß-induced mitochondrial redox stress.

The production and secretion of matrix proteins upon stimulation of fibroblasts by transforming growth factor-beta (TGFß) play a critical role in wound healing. How TGFß supports the bioenergetic cost of matrix protein synthesis is not fully understood. Here, we show that TGFß promotes protein translation at least in part by increasing the mitochondrial oxidation of glucose and glutamine carbons to support the bioenergetic demand of translation. Surprisingly, we found that in addition to stimulating the entry of glucose and glutamine carbon into the TCA cycle, TGFß induced the biosynthesis of proline from glutamine in a Smad4-dependent fashion. Metabolic manipulations that increased mitochondrial redox generation promoted proline biosynthesis, while reducing mitochondrial redox potential and/or ATP synthesis impaired proline biosynthesis. Thus, proline biosynthesis acts as a redox vent, preventing the TGFß-induced increase in mitochondrial glucose and glutamine catabolism from generating damaging reactive oxygen species (ROS) when TCA cycle activity exceeds the ability of oxidative phosphorylation to convert mitochondrial redox potential into ATP. In turn, the enhanced synthesis of proline supports TGFß-induced production of matrix proteins.

Mitochondrial NADP(H) generation is essential for proline biosynthesis.

The coenzyme nicotinamide adenine dinucleotide phosphate (NADP+) and its reduced form (NADPH) regulate reductive metabolism in a subcellularly compartmentalized manner. Mitochondrial NADP(H) production depends on the phosphorylation of NAD(H) by NAD kinase 2 (NADK2). Deletion of NADK2 in human cell lines did not alter mitochondrial folate pathway activity, tricarboxylic acid cycle activity, or mitochondrial oxidative stress, but rather led to impaired cell proliferation in minimal medium. This growth defect was rescued by proline supplementation. NADK2-mediated mitochondrial NADP(H) generation was required for the reduction of glutamate and hence proline biosynthesis. Furthermore, mitochondrial NADP(H) availability determined the production of collagen proteins by cells of mesenchymal lineage. Thus, a primary function of the mitochondrial NADP(H) pool is to support proline biosynthesis for use in cytosolic protein synthesis.

Copper depletion modulates mitochondrial oxidative phosphorylation to impair triple negative breast cancer metastasis.

Copper serves as a co-factor for a host of metalloenzymes that contribute to malignant progression. The orally bioavailable copper chelating agent tetrathiomolybdate (TM) has been associated with a significant survival benefit in high-risk triple negative breast cancer (TNBC) patients. Despite these promising data, the mechanisms by which copper depletion impacts metastasis are poorly understood and this remains a major barrier to advancing TM to a randomized phase II trial. Here, using two independent TNBC models, we report a discrete subpopulation of highly metastatic SOX2/OCT4+ cells within primary tumors that exhibit elevated intracellular copper levels and a marked sensitivity to TM. Global proteomic and metabolomic profiling identifies TM-mediated inactivation of Complex IV as the primary metabolic defect in the SOX2/OCT4+ cell population. We also identify AMPK/mTORC1 energy sensor as an important downstream pathway and show that AMPK inhibition rescues TM-mediated loss of invasion. Furthermore, loss of the mitochondria-specific copper chaperone, COX17, restricts copper deficiency to mitochondria and phenocopies TM-mediated alterations. These findings identify a copper-metabolism-metastasis axis with potential to enrich patient populations in next-generation therapeutic trials.

Stable Isotope Tracers for Metabolic Pathway Analysis.

Stable isotope tracing allows a metabolic substrate to be followed through downstream biochemical reactions, thereby providing unparalleled insights into the metabolic wiring of cells. This approach stops short of modeling absolute fluxes but is relatively straightforward and has become increasingly accessible due to the widespread adoption of high-resolution mass spectrometers. Analysis of both dynamic and steady-state labeling patterns in downstream metabolites provides valuable qualitative information as to their origin and relative rates of production. Stable isotope tracing is, therefore, a powerful way to understand the impact of genetic alterations and defined perturbations on metabolism. In this chapter, we describe a liquid chromatography-mass spectrometry (LC-MS) protocol for stable isotope tracing using 13C-L-arginine in a macrophage cell line. A similar approach can be used to follow other stable isotope tracers, and notes are provided with advice on how this protocol can be generalized for use in other settings.

Transsulfuration Activity Can Support Cell Growth upon Extracellular Cysteine Limitation.

Cysteine acts both as a building unit for protein translation and as the limiting substrate for glutathione synthesis to support the cellular antioxidant system. In addition to transporter-mediated uptake, cellular cysteine can also be synthesized from methionine through the transsulfuration pathway. Here, we investigate the regulation of transsulfuration and its role in sustaining cell proliferation upon extracellular cysteine limitation, a condition reported to occur in human tumors as they grow in size. We observed constitutive expression of transsulfuration enzymes in a subset of cancer cell lines, while in other cells, these enzymes are induced following cysteine deprivation. We show that both constitutive and inducible transsulfuration activities contribute to the cellular cysteine pool and redox homeostasis. The rate of transsulfuration is determined by the cellular capacity to conduct methylation reactions that convert S-adenosylmethionine to S-adenosylhomocysteine. Finally, our results demonstrate that transsulfuration-mediated cysteine synthesis is critical in promoting tumor growth in vivo.

PON1 gene polymorphisms in patients with chronic obstructive pulmonary disease.

AIMS: Chronic obstructive pulmonary disease (COPD) is characterised with oxidative stress. Paraoxonase 1 (PON1) is an enzyme, coded by PON1 gene, with distinctive antiatherogenic and antioxidative roles. We aimed to investigate the frequencies of Q192R, L55M and -108C>T polymorphisms and association of those polymorphisms with paraoxonase and arylesterase activities in patients with COPD. METHODS: PON1 genotype was determined by PCR-restriction fragment length polymorphism method. PON1 activity was measured by paraoxon and phenylacetate. RESULTS: Only -108C>T polymorphism resulted in significantly different distribution of genotypes and alleles, with higher frequency of TT genotype and T allele in patients compared with control subjects. Moreover, T allele (OR 2.29 (95% CI 1.54 to 3.41); p<0.001) as well as TT genotype (OR 5.00 (95% CI 2.19 to 11.43); p<0.001) showed an association with the disease. -108C>T polymorphism was suggested as a significant diagnostic predictor for the disease (OR (95% CI) 2.65 (1.53 to 4.59), p=0.001), with an area under the receiver operating characteristic curve of 0.90 (95% CI 0.84 to 0.93) and with 83.90% of correctly classified cases. CONCLUSIONS: Higher frequency of TT genotype and T allele could contribute to the observed reduction of PON1 activity in patients with COPD. T allele and TT genotype are associated with COPD, and the PON1-108C>T polymorphism could be a potential predictor of the disease.