Abstract
Coupling glycolysis and mitochondrial tricarboxylic acid cycle, pyruvate dehydrogenase (PDH) complex (PDHC) is highly responsive to cellular demands through multiple mechanisms, including PDH phosphorylation. PDHC also produces acetyl-CoA for protein acetylation involved in circadian regulation of metabolism. Thiamine (vitamin B1) diphosphate (ThDP) is known to activate PDH as both coenzyme and inhibitor of the PDH inactivating kinases. Molecular mechanisms integrating the function of thiamine-dependent PDHC into general redox metabolism, underlie physiological fitness of a cell or an organism. Here, we characterize the daytime- and thiamine-dependent changes in the rat brain PDHC function, expression and phosphorylation, assessing their impact on protein acetylation and metabolic regulation. Morning administration of thiamine significantly downregulates both the PDH phosphorylation at Ser293 and SIRT3 protein level, the effects not observed upon the evening administration. This action of thiamine nullifies the daytime-dependent changes in the brain PDHC activity and mitochondrial acetylation, inducing diurnal difference in the cytosolic acetylation and acetylation of total brain proteins. Screening the daytime dependence of central metabolic enzymes and proteins of thiol/disulfide metabolism reveals that thiamine also cancels daily changes in the malate dehydrogenase activity, opposite to those of the PDHC activity. Correlation analysis indicates that thiamine abrogates the strong positive correlation between the total acetylation of the brain proteins and PDHC function. Simultaneously, thiamine heightens interplay between the expression of PDHC components and total acetylation or SIRT2 protein level. These thiamine effects on the brain acetylation system change metabolic impact of acetylation. The changes are exemplified by the thiamine enhancement of the SIRT2 correlations with metabolic enzymes and proteins of thiol-disulfide metabolism. Thus, we show the daytime- and thiamine-dependent changes in the function and phosphorylation of brain PDHC, contributing to regulation of the brain acetylation system and redox metabolism. The daytime-dependent action of thiamine on PDHC and SIRT3 may be of therapeutic significance in correcting perturbed diurnal regulation.
Highlights
The brain energy metabolism strongly depends on glucose oxidation, with the mitochondrial pyruvate dehydrogenase (PDH) multienzyme complex (PDHC) playing a key regulatory role in coupling the glycolytic and mitochondrial parts of the glucose oxidation pathway
We show the daily changes in the brain PDHC activity, their abolition by thiamine administration which reduces phosphorylation of the PDHA Ser293 and the levels of sirtuin 3 (SIRT3) in the morning
Thiamine administration in the morning significantly decreases the level of phosphorylated Ser293 of PDHA1, compared to the control rats (p = 0.02), with the effect not observed upon the evening administration of thiamine (Figure 1A)
Summary
The brain energy metabolism strongly depends on glucose oxidation, with the mitochondrial pyruvate dehydrogenase (PDH) multienzyme complex (PDHC) playing a key regulatory role in coupling the glycolytic and mitochondrial parts of the glucose oxidation pathway. Perturbations in this coupling occur in different pathologies linked to essential metabolic transformations, such as occurring in malignancies or diabetes. Isoenzymes of PDH kinases (PDK1–4) and phosphatases (PDP1–2) determine phosphorylation status of PDHA (alpha subunit of PDH component of the complex), controlling the PDHC activity. PDK2 preferentially phosphorylates Ser293 [1], while the PDH phosphatases are more active at the other sites [1,3]. PDK2 and PDP1 are the most important and abundant players in the phosphorylation-dependent regulation of PDH [4]
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