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This mini-review presents a summary of research results of biotechnological production of alpha-ketoglutaric acid (KGA) by bacteria and yeasts. KGA is of particular industrial interest due to its broad application scope, e.g., as building block chemical for the chemical synthesis of heterocycles, dietary supplement, component of infusion solutions and wound healing compounds, or as main component of new elastomers with a wide range of interesting mechanical and chemical properties. Currently KGA is produced via different chemical pathways, which have a lot of disadvantages. As an alternative several bacteria and yeasts have already been studied for their ability to produce KGA as well as for conditions of overproduction and secretion of this intermediate of the tricarboxylic acid cycle. The aim of this mini-review was to summarize the known data and to discuss the potentials of biotechnological processes of KGA production.[PUBLICATION ABSTRACT]

The tumour suppressor TP53 is mutated in the majority of human cancers, and in over 70% of pancreatic ductal adenocarcinoma (PDAC) 1 , 2 . Wild-type p53 accumulates in response to cellular stress, and regulates gene expression to alter cell fate and prevent tumour development 2 . Wild-type p53 is also known to modulate cellular metabolic pathways 3 , although p53-dependent metabolic alterations that constrain cancer progression remain poorly understood. Here we find that p53 remodels cancer-cell metabolism to enforce changes in chromatin and gene expression that favour a premalignant cell fate. Restoring p53 function in cancer cells derived from KRAS-mutant mouse models of PDAC leads to the accumulation of α-ketoglutarate (αKG, also known as 2-oxoglutarate), a metabolite that also serves as an obligate substrate for a subset of chromatin-modifying enzymes. p53 induces transcriptional programs that are characteristic of premalignant differentiation, and this effect can be partially recapitulated by the addition of cell-permeable αKG. Increased levels of the αKG-dependent chromatin modification 5-hydroxymethylcytosine (5hmC) accompany the tumour-cell differentiation that is triggered by p53, whereas decreased 5hmC characterizes the transition from premalignant to de-differentiated malignant lesions that is associated with mutations in Trp53 . Enforcing the accumulation of αKG in p53-deficient PDAC cells through the inhibition of oxoglutarate dehydrogenase—an enzyme of the tricarboxylic acid cycle—specifically results in increased 5hmC, tumour-cell differentiation and decreased tumour-cell fitness. Conversely, increasing the intracellular levels of succinate (a competitive inhibitor of αKG-dependent dioxygenases) blunts p53-driven tumour suppression. These data suggest that αKG is an effector of p53-mediated tumour suppression, and that the accumulation of αKG in p53-deficient tumours can drive tumour-cell differentiation and antagonize malignant progression. Restoring the function of p53 in a mouse model of pancreatic ductal adenocarcinoma leads to the accumulation of α-ketoglutarate, which increases levels of the 5-hydroxymethylcytosine chromatin modification and results in reduced tumour-cell fitness.

Heart failure (HF) is a leading cause of death and repeated hospitalizations and often involves cardiac mitochondrial dysfunction. However, the underlying mechanisms largely remain elusive. Here, using a mouse model in which myocardial infarction (MI) was induced by coronary artery ligation, we show the metabolic basis of mitochondrial dysfunction in chronic HF. Four weeks after ligation, MI mice showed a significant decrease in myocardial succinyl-CoA levels, and this decrease impaired the mitochondrial oxidative phosphorylation (OXPHOS) capacity. Heme synthesis and ketolysis, and protein levels of several enzymes consuming succinyl-CoA in these events, were increased in MI mice, while enzymes synthesizing succinyl-CoA from α-ketoglutarate and glutamate were also increased. Furthermore, the ADP-specific subunit of succinyl-CoA synthase was reduced, while its GDP-specific subunit was almost unchanged. Administration of 5-aminolevulinic acid, an intermediate in the pathway from succinyl-CoA to heme synthesis, appreciably restored succinyl-CoA levels and OXPHOS capacity and prevented HF progression in MI mice. Previous reports also suggested the presence of succinyl-CoA metabolism abnormalities in cardiac muscles of HF patients. Our results identified that changes in succinyl-CoA usage in different metabolisms of the mitochondrial energy production system is characteristic to chronic HF, and although similar alterations are known to occur in healthy conditions, such as during strenuous exercise, they may often occur irreversibly in chronic HF leading to a decrease in succinyl-CoA. Consequently, nutritional interventions compensating the succinyl-CoA consumption are expected to be promising strategies to treat HF.

2-Oxoglutarate (2OG) oxygenases are validated agrochemical and human drug targets. The potential for modulating their activity with 2OG derivatives has not been explored, possibly due to concerns regarding selectivity. We report proof-of-principle studies demonstrating selective enhancement or inhibition of 2OG oxygenase activity by 2-oxo acids. The human 2OG oxygenases studied, factor inhibiting hypoxia-inducible transcription factor HIF-α (FIH) and aspartate/asparagine-β-hydroxylase (AspH), catalyze C3 hydroxylations of Asp/Asn-residues. Of 35 tested 2OG derivatives, 10 enhance and 17 inhibit FIH activity. Comparison with results for AspH reveals that 2OG derivatives selectively enhance or inhibit FIH or AspH. Comparison of FIH structures complexed with 2OG derivatives to those for AspH provides insight into the basis of the observed selectivity. 2-Oxo acid derivatives have potential as drugs, for use in biomimetic catalysis, and in functional studies. The results suggest that the in vivo activity of 2OG oxygenases may be regulated by natural 2-oxo acids other than 2OG. The human 2-oxoglutarate (2OG) oxygenases FIH and AspH are relevant drug targets. Here, the authors show that synthetic and naturally occurring 2OG derivatives can selectively modulate FIH and AspH activities, suggesting that these compounds may serve as a basis to develop 2OG oxygenase-targeting probes and drugs.

Enzymatic transformation is now an attractive alternative for α-ketoglutaric acid (α-KG) production, but the oxidative deamination from l-glutamic acid to α-KG is along with H2O2 accumulation. To remove the effect of H2O2 on α-KG production, in vitro cascade biocatalysis was designed using the purified l-glutamate oxidase (LGOX) from Streptomyces ghanaensis and catalase (KatG) from Escherichia coli W3110, and the optimal ratio of LGOX:KatG (2.0:1250) was detected in this system. To achieve this ratio, in vivo cascade biocatalysis was constructed by varying promoters and ribosome binding sites (RBSs), and optimized by promoter engineering, such as adjusting the junctions between the SD sequence and start codon ATG and tuning the strengths of RBSs. When the final ratio of LGOX:KatG (2.1:1185) in strain E. coli-(T7)LGOX-(rbs2)KatG was used, α-KG concentration and its conversion rate were increased to 106 g L−1 and 96%, respectively. This strategy described here paves the way to the development of cascade biocatalysis for enzymatic production of other chemicals.

How glutamine metabolism orchestrates macrophage activation is unclear. Ho and colleagues show glutamine metabolism tailors the immune responses of macrophages through metabolic and epigenetic reprogramming. Glutamine metabolism provides synergistic support for macrophage activation and elicitation of desirable immune responses; however, the underlying mechanisms regulated by glutamine metabolism to orchestrate macrophage activation remain unclear. Here we show that the production of α-ketoglutarate (αKG) via glutaminolysis is important for alternative (M2) activation of macrophages, including engagement of fatty acid oxidation (FAO) and Jmjd3-dependent epigenetic reprogramming of M2 genes. This M2-promoting mechanism is further modulated by a high αKG/succinate ratio, whereas a low ratio strengthens the proinflammatory phenotype in classically activated (M1) macrophages. As such, αKG contributes to endotoxin tolerance after M1 activation. This study reveals new mechanistic regulations by which glutamine metabolism tailors the immune responses of macrophages through metabolic and epigenetic reprogramming.

The genus Solanum comprises three food crops (potato, tomato, and eggplant), which are consumed on daily basis worldwide and also producers of notorious anti-nutritional steroidal glycoalkaloids (SGAs). Hydroxylated SGAs (i.e. leptinines) serve as precursors for leptines that act as defenses against Colorado Potato Beetle ( Leptinotarsa decemlineata Say), an important pest of potato worldwide. However, SGA hydroxylating enzymes remain unknown. Here, we discover that 2-OXOGLUTARATE-DEPENDENT-DIOXYGENASE (2-ODD) enzymes catalyze SGA-hydroxylation across various Solanum species. In contrast to cultivated potato, Solanum chacoense , a widespread wild potato species, has evolved a 2-ODD enzyme leading to the formation of leptinines. Furthermore, we find a related 2-ODD in tomato that catalyzes the hydroxylation of the bitter α -tomatine to hydroxytomatine, the first committed step in the chemical shift towards downstream ripening-associated non-bitter SGAs (e.g. esculeoside A). This 2-ODD enzyme prevents bitterness in ripe tomato fruit consumed today which otherwise would remain unpleasant in taste and more toxic. Steroidal glycoalkaloids (SGAs) accumulate in Solanum , but their hydroxylating enzymes are unknown. Here, the authors report 2-OXOGLUTARATE DEPENDENT DIOXYGENASE enzymes that catalyze the committed hydroxylation steps in the biosynthesis of leptinine insecticidal compounds in wild potato or non-bitter SGAs in cultivated tomato.

Postnatal maturation of cardiomyocytes is characterized by a metabolic switch from glycolysis to fatty acid oxidation, chromatin reconfiguration and exit from the cell cycle, instating a barrier for adult heart regeneration 1 , 2 . Here, to explore whether metabolic reprogramming can overcome this barrier and enable heart regeneration, we abrogate fatty acid oxidation in cardiomyocytes by inactivation of Cpt1b . We find that disablement of fatty acid oxidation in cardiomyocytes improves resistance to hypoxia and stimulates cardiomyocyte proliferation, allowing heart regeneration after ischaemia–reperfusion injury. Metabolic studies reveal profound changes in energy metabolism and accumulation of α-ketoglutarate in Cpt1b -mutant cardiomyocytes, leading to activation of the α-ketoglutarate-dependent lysine demethylase KDM5 (ref.  3 ). Activated KDM5 demethylates broad H3K4me3 domains in genes that drive cardiomyocyte maturation, lowering their transcription levels and shifting cardiomyocytes into a less mature state, thereby promoting proliferation. We conclude that metabolic maturation shapes the epigenetic landscape of cardiomyocytes, creating a roadblock for further cell divisions. Reversal of this process allows repair of damaged hearts. Inhibition of the fatty acid oxidation metabolic pathway through inactivation of Cpt1b enhances cardiomyocyte survival and proliferation and allows heart regeneration in adult mice.

l -Glutamine is a nutritionally semi-essential amino acid for proper growth in most cells and tissues, and plays an important role in the determination and guarding of the normal metabolic processes of the cells. With the help of transport systems, extracellular l -glutamine crosses the plasma membrane and is converted into alpha-ketoglutarate (AKG) through two pathways, namely, the glutaminase (GLS) I and II pathway. Reversely, AKG can be converted into glutamine by glutamate dehydrogenase (GDH) and glutamine synthetase (GS), or be converted into CO 2 via the tricarboxylic acid (TCA) cycle and provide energy for the cells. Different steps of glutamine metabolism (the glutamine-AKG axis) are regulated by several factors, rendering the glutamine-AKG axis a potential target to counteract cancer. Moreover, intracellular glutamine plays an important role in cellular homeostasis not only as a precursor for protein synthesis, but also for its nutritional roles in cell growth, lipid metabolism, insulin secretion, and so on. The main objective of this review is to highlight the metabolic pathways of glutamine to AKG, with special emphasis on nutritional and therapeutic use of glutamine-AKG axis to improve the health and well-being of animals and humans.

Aging usually involves the progressive development of certain illnesses, including diabetes and obesity. Due to incapacity to form new white adipocytes, adipose expansion in aged mice primarily depends on adipocyte hypertrophy, which induces metabolic dysfunction. On the other hand, brown adipose tissue burns fatty acids, preventing ectopic lipid accumulation and metabolic diseases. However, the capacity of brown/beige adipogenesis declines inevitably during the aging process. Previously, we reported that DNA demethylation in the Prdm16 promoter is required for beige adipogenesis. DNA methylation is mediated by ten–eleven family proteins (TET) using alpha‐ketoglutarate (AKG) as a cofactor. Here, we demonstrated that the circulatory AKG concentration was reduced in middle‐aged mice (10‐month‐old) compared with young mice (2‐month‐old). Through AKG administration replenishing the AKG pool, aged mice were associated with the lower body weight gain and fat mass, and improved glucose tolerance after challenged with high‐fat diet (HFD). These metabolic changes are accompanied by increased expression of brown adipose genes and proteins in inguinal adipose tissue. Cold‐induced brown/beige adipogenesis was impeded in HFD mice, whereas AKG rescued the impairment of beige adipocyte functionality in middle‐aged mice. Besides, AKG administration up‐regulated Prdm16 expression, which was correlated with an increase of DNA demethylation in the Prdm16 promoter. In summary, AKG supplementation promotes beige adipogenesis and alleviates HFD‐induced obesity in middle‐aged mice, which is associated with enhanced DNA demethylation of the Prdm16 gene. The circulatory alpha‐ketoglutarate concentration was dramatically reduced in aged mice. Alpha‐ketoglutarate administration facilitates DNA demethylation in the Prdm16 promoter, which enhances its expression and brown/beige adipogenesis and improves metabolic health of aged mice challenged with high‐fat diet.