Molecular oxygen (O 2) sustains intracellular bioenergetics and is consumed by numerous biochemical reactions, making it essential for most species on Earth. Accordingly, decreased O 2 concentrations (hypoxia) is a major stressor that generally subverts life of aerobic species and is a prominent feature of pathological states encountered in bacterial infection, inflammation, wounds, cardiovascular defects, and cancer. Therefore, key adaptive mechanisms to cope with hypoxia have evolved in mammals. Systemically, these adaptations include increased ventilation, cardiac output, blood vessel growth, and circulating red blood cell numbers. On a cellular level, ATP consuming reactions are suppressed and metabolism is altered until oxygen homeostasis is restored. A critical question is how mammalian cells sense O 2 levels to coordinate diverse biological outputs during hypoxia. The best studied mechanism of response to hypoxia involves hypoxia inducible factors (HIFs), which are stabilized by low oxygen availability and control the expression of a multitude of genes, including those involved in cell survival, angiogenesis, glycolysis, and invasion/ metastasis. Importantly, changes in O 2 can also be sensed via other stress pathways as well as changes in metabolite levels and the generation of reactive oxygen species (ROS) by mitochondria. Collectively, this leads to cellular adaptations of protein synthesis, energy metabolism, mitochondrial respiration, lipid and carbon metabolism as well as nutrient acquisition. These mechanisms are integral inputs into fine tuning the responses to hypoxic stress.

Maddocks, O. D. K. et al. (2017) Modulating the therapeutic response of tumours to dietary serine and glycine starvation. Nature, 544(7650), pp. 372-376.There may be differences between this version and the published version. You are advised to consult the publisher's version if you wish to cite from it.http://eprints.gla.ac.uk/140432/ AbstractThe non-essential amino acids serine and glycine are used in multiple anabolic processes that support cancer cell growth and proliferation (reviewed in ref. 1). While some cancer cells upregulate de novo serine synthesis 2,3,4 , many others rely on exogenous serine for optimal growth 5,6,7 . Restriction of dietary serine and glycine can reduce tumour growth in xenograft and allograft models 7,8 . Here we show that this observation translates into more clinically relevant autochthonous tumours in genetically engineered mouse models of intestinal cancer (driven by Apc inactivation) or lymphoma (driven by Myc activation). The increased survival following dietary restriction of serine and glycine in these models was further improved by antagonizing the anti-oxidant response. Disruption of mitochondrial oxidative phosphorylation (using biguanides) led to a complex response that could improve or impede the anti-tumour effect of serine and glycine starvation. Notably, Krasdriven mouse models of pancreatic and intestinal cancers were less responsive to depletion of serine and glycine, reflecting an ability of activated Kras to increase the expression of enzymes that are part of the serine synthesis pathway and thus promote de novo serine synthesis.To assess the effect of dietary serine and glycine (SG) restriction in autochthonous tumour models, we used genetically engineered mouse models (GEMMs) of lymphoma (Eμ-Myc) and intestinal tumours (defective Apc). Eμ-Myc mice develop pre-neoplastic lesions within 28-42 days after birth 9 , and adenoma initiation is evident days after birth in Apc Min/+ mice 10 . Accordingly, Apc Min/+ mice carried high tumour numbers at 80 days, which subsequently increased in size but not number (Extended Data Fig. 1a). Transferring mice from normal chow diet to experimental diets 60-80 days after birth showed that an SG-free diet significantly extended survival in these models carrying pre-malignant lesions (Fig. 1a, b), with a slightly lower tumour burden in Apc Min/+ mice on the SG-free diet at clinical end point (Extended Data Fig. 1a). The diet reproducibly decreased serum SG from around 150 μM to 65 μM (Fig. 1c-e), while showing minimal or inconsistent impact on other amino acids, glucose and lactate (Fig. 1c, d and Extended Data Figs 1b, 2a, b), These results were further validated using an inducible intestinal tumour model (Lgr5-creER;Apc fl/fl ); transferring mice to the SG-free diet a week after induction. Again, the experimental diet caused a significant increase in survival compared to control diet (containing purified amino acids) or normal chow (containing whole protein as a source of amino acids) (Fig. 1f). (c, control, n = 14; control,...

SummaryRegulation of metabolic pathways plays an important role in controlling cell growth, proliferation, and survival. TIGAR acts as a fructose-2,6-bisphosphatase, potentially promoting the pentose phosphate pathway to produce NADPH for antioxidant function and ribose-5-phosphate for nucleotide synthesis. The functions of TIGAR were dispensable for normal growth and development in mice but played a key role in allowing intestinal regeneration in vivo and in ex vivo cultures, where growth defects due to lack of TIGAR were rescued by ROS scavengers and nucleosides. In a mouse intestinal adenoma model, TIGAR deficiency decreased tumor burden and increased survival, while elevated expression of TIGAR in human colon tumors suggested that deregulated TIGAR supports cancer progression. Our study demonstrates the importance of TIGAR in regulating metabolism for regeneration and cancer development and identifies TIGAR as a potential therapeutic target in diseases such as ulcerative colitis and intestinal cancer.