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Regulation of pyruvate dehydrogenase complex related to lactate switch in CHO cells.

ABSTRACT: The metabolism of Chinese hamster ovary (CHO) cell lines is typically characterized by high rates of aerobic glycolysis with increased lactate formation, known as the "Warburg" effect. Although this metabolic state can switch to lactate consumption, the involved regulations of the central metabolism have only been partially studied so far. An important reaction transferring the lactate precursor, pyruvate, into the tricarboxylic acid cycle is the decarboxylation reaction catalyzed by the pyruvate dehydrogenase enzyme complex (PDC). Among other mechanisms, PDC is mainly regulated by phosphorylation-dephosphorylation at the three sites Ser232, Ser293, and Ser300. In this work, the PDC phosphorylation in antibody-producing CHO DP-12 cell culture is investigated during the lactate switch. Batch cultivations were carried out with frequent sampling (every 6 h) during the transition from lactate formation to lactate uptake, and the PDC phosphorylation levels were quantified using a novel indirect flow cytometry protocol. Contrary to the expected activation of PDC (i.e., reduced PDC phosphorylation) during lactate consumption, Ser293 and Ser300 phosphorylation levels were 33% higher compared to the phase of glucose excess. At the same time, the relative phosphorylation level of Ser232 increased steadily throughout the cultivation (66% increase overall). The intracellular pyruvate was found to accumulate only during the period of high lactate production, while acetyl-CoA showed nearly no accumulation. These results indicate a deactivation of PDC and reduced oxidative metabolism during lactate switch even though the cells undergo a metabolic transition to lactate-based cell growth and metabolism. Overall, this study provides a unique view on the regulation of PDC during the lactate switch, which contributes to an improved understanding of PDC and its interaction with the bioprocess.

SUBMITTER: Moller J

PROVIDER: S-EPMC7923601 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND & AIMS:Acute liver failure is a rapidly progressive deterioration of hepatic function resulting in high mortality and morbidity. Metabolic enzymes can translocate to the nucleus to regulate histone acetylation and gene expression. METHODS:Levels and activities of pyruvate dehydrogenase complex (PDHC) and lactate dehydrogenase (LDH) were evaluated in nuclear fractions of livers of mice exposed to various hepatotoxins including CD95-antibody, ?-amanitin, and acetaminophen. Whole-genome gene expression profiling by RNA-seq was performed in livers of mice with acute liver failure and analyzed by gene ontology enrichment analysis. Cell viability was evaluated in cell lines knocked-down for PDHA1 or LDH-A and in cells incubated with the LDH inhibitor galloflavin after treatment with CD95-antibody. We evaluated whether the histone acetyltransferase inhibitor garcinol or galloflavin could reduce liver damage in mice with acute liver failure. RESULTS:Levels and activities of PDHC and LDH were increased in nuclear fractions of livers of mice with acute liver failure. The increase of nuclear PDHC and LDH was associated with increased concentrations of acetyl-CoA and lactate in nuclear fractions, and histone H3 hyper-acetylation. Gene expression in livers of mice with acute liver failure suggested that increased histone H3 acetylation induces the expression of genes related to damage response. Reduced histone acetylation by the histone acetyltransferase inhibitor garcinol decreased liver damage and improved survival in mice with acute liver failure. Knock-down of PDHC or LDH improved viability in cells exposed to a pro-apoptotic stimulus. Treatment with the LDH inhibitor galloflavin that was also found to inhibit PDHC, reduced hepatic necrosis, apoptosis, and expression of pro-inflammatory cytokines in mice with acute liver failure. Mice treated with galloflavin also showed a dose-response increase in survival. CONCLUSION:PDHC and LDH translocate to the nucleus, leading to increased nuclear concentrations of acetyl-CoA and lactate. This results in histone H3 hyper-acetylation and expression of damage response genes. Inhibition of PDHC and LDH reduces liver damage and improves survival in mice with acute liver failure. Thus, PDHC and LDH are targets for therapy of acute liver failure. LAY SUMMARY:Acute liver failure is a rapidly progressive deterioration of liver function resulting in high mortality. In experimental mouse models of acute liver failure, we found that two metabolic enzymes, namely pyruvate dehydrogenase complex and lactic dehydrogenase, translocate to the nucleus resulting in detrimental gene expression. Treatment with an inhibitor of these two enzymes was found to reduce liver damage and to improve survival.

Project description:The stopped-flow kinetic studies described in this and the following paper (Südi, 1974) demonstrate that a Haldane-type description of the reversible lactate dehydrogenase reaction presents an experimentally feasible task. Combined results of these two papers yield numerical values for the six rate constants defined by the following equilibrium scheme, where E represents lactate dehydrogenase: [Formula: see text] The experiments were carried out at pH8.4 at a relatively low temperature (6.3 degrees C) with the pig heart enzyme. Identification of the above two intermediates and determination of the corresponding rate constants actually involve four series of independent observations in these studies, since (a) the reaction can be followed in both directions, and (b) both the u.v. absorption and the fluorescence of the coenzymes are altered in the reaction, and it is shown that these two spectral changes do not occur simultaneously. Kinetic observations made in the reverse direction are reported in this paper. It is demonstrated that the fluorescence of NADH can no longer be observed in the ternary complex E(NADH) (Pyr). Even though the oxidation-reduction reaction rapidly follows the formation of this complex, the numerical values of k(-4) (8.33x10(5)m(-1).s(-1)) and k(+4) (222s(-1)) are easily obtained from a directly observed second-order reaction step in which fluorescent but not u.v.-absorbing material is disappearing. U.v.-absorption measurements do not clearly resolve the subsequent oxidation-reduction step from the dissociation of lactate. It is shown that this must be due partly to the instrumental dead time, and partly to a low transient concentration of E(NAD+) (Lac) in the two-step sequential reaction in which the detectable disappearance of u.v.-absorbing material takes place. It is estimated that about one-tenth of the total change in u.v. absorption is due to a ;burst reaction' in which E(NAD+) (Lac) is produced, and this estimation yields, from k(obs.)=120s(-1), k(-2)=1200s(-1).

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Regulation of pyruvate dehydrogenase complex related to lactate switch in CHO cells.

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