PEPCK-M expression in mouse liver potentiates, not replaces, PEPCK-C mediated gluconeogenesis

Departament de Ciències Fisiològiques II, Universitat de Barcelona, L'Hospitalet de Llobregat, Barcelona, Spain.
Journal of Hepatology (Impact Factor: 11.34). 03/2013; 59(1). DOI: 10.1016/j.jhep.2013.02.020
Source: PubMed


Background & aims:
Hepatic gluconeogenesis helps maintain systemic energy homeostasis by compensating for discontinuities in nutrient supply. Liver-specific deletion of cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C) abolishes gluconeogenesis from mitochondrial substrates, deregulates lipid metabolism and affects TCA cycle. While the mouse liver almost exclusively expresses PEPCK-C, humans equally present a mitochondrial isozyme (PEPCK-M). Despite clear relevance to human physiology, the role of PEPCK-M and its gluconeogenic potential remain unknown. Here, we test the significance of PEPCK-M in gluconeogenesis and TCA cycle function in liver-specific PEPCK-C knockout and WT mice.

The effects of the overexpression of PEPCK-M were examined by a combination of tracer studies and molecular biology techniques. Partial PEPCK-C re-expression was used as a positive control. Metabolic fluxes were evaluated in isolated livers by NMR using (2)H and (13)C tracers. Gluconeogenic potential, together with metabolic profiling, was investigated in vivo and in primary hepatocytes.

PEPCK-M expression partially rescued defects in lipid metabolism, gluconeogenesis and TCA cycle function impaired by PEPCK-C deletion, while ∼10% re-expression of PEPCK-C normalized most parameters. When PEPCK-M was expressed in the presence of PEPCK-C, the mitochondrial isozyme amplified total gluconeogenic capacity, suggesting autonomous regulation of oxaloacetate to phosphoenolpyruvate fluxes by the individual isoforms.

We conclude that PEPCK-M has gluconeogenic potential per se, and cooperates with PEPCK-C to adjust gluconeogenic/TCA flux to changes in substrate or energy availability, hinting at a role in the regulation of glucose and lipid metabolism in the human liver.

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Available from: Andrés Méndez-Lucas, Jun 27, 2014
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    • "Although the metabolic characteristics of mPECK remain largely unknown, recent reports suggest that mPEPCK plays various roles in gluconeogenesis and anaplerotic reactions. For example, mPEPCK plays a role in mitochondrial GTP synthesis with insulin release through anaplerotic PEP cycling [19] and cooperates with cytosolic PEPCK to adjust gluconeogenic/TCA flux in response to changes in substrate or energy availability [8]. At present, we cannot explain the molecular mechanism linking mPEPCK expression and susceptibility of CRC cells to 5-FU or radiation. "
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