Impact of Peripheral Ketolytic Deficiency on Hepatic Ketogenesis and Gluconeogenesis during the Transition to Birth

David G Cotter,Baris Ercal,D André D'Avignon,Dennis J Dietzen,Peter A Crawford

doi:10.1074/jbc.m113.454868

Abstract

Preservation of bioenergetic homeostasis during the transition from the carbohydrate-laden fetal diet to the high fat, low carbohydrate neonatal diet requires inductions of hepatic fatty acid oxidation, gluconeogenesis, and ketogenesis. Mice with loss-of-function mutation in the extrahepatic mitochondrial enzyme CoA transferase (succinyl-CoA:3-oxoacid CoA transferase, SCOT, encoded by nuclear Oxct1) cannot terminally oxidize ketone bodies and develop lethal hyperketonemic hypoglycemia within 48 h of birth. Here we use this model to demonstrate that loss of ketone body oxidation, an exclusively extrahepatic process, disrupts hepatic intermediary metabolic homeostasis after high fat mother's milk is ingested. Livers of SCOT-knock-out (SCOT-KO) neonates induce the expression of the genes encoding peroxisome proliferator-activated receptor γ co-activator-1a (PGC-1α), phosphoenolpyruvate carboxykinase (PEPCK), pyruvate carboxylase, and glucose-6-phosphatase, and the neonate's pools of gluconeogenic alanine and lactate are each diminished by 50%. NMR-based quantitative fate mapping of (13)C-labeled substrates revealed that livers of SCOT-KO newborn mice synthesize glucose from exogenously administered pyruvate. However, the contribution of exogenous pyruvate to the tricarboxylic acid cycle as acetyl-CoA is increased in SCOT-KO livers and is associated with diminished terminal oxidation of fatty acids. After mother's milk provokes hyperketonemia, livers of SCOT-KO mice diminish de novo hepatic β-hydroxybutyrate synthesis by 90%. Disruption of β-hydroxybutyrate production increases hepatic NAD(+)/NADH ratios 3-fold, oxidizing redox potential in liver but not skeletal muscle. Together, these results indicate that peripheral ketone body oxidation prevents hypoglycemia and supports hepatic metabolic homeostasis, which is critical for the maintenance of glycemia during the adaptation to birth.

Highlights

SCOT-KO mice cannot oxidize ketone bodies and die within 48 h of birth, due to hyperketonemic hypoglycemia
Increased abundances of the mRNAs encoding peroxisome proliferatoractivated receptor ␥ co-activator-1a (PGC-1␣, encoded by Ppargc1a), pyruvate carboxylase, phosphoenolpyruvate carboxykinase (PEPCK, encoded by Pck1), and glucose-6-phosphatase were observed in livers of postnatal day 1 (P1, the day immediately following delivery) SCOT-KO mice (Fig. 1A), and as expected, hepatic glycogen content was depleted in livers of P1 SCOT-KO mice (Fig. 1B)
Blood concentrations of the anaplerotic amino acid glutamate, which can replenish tricarboxylic acid (TCA) cycle intermediates following conversion to ␣-ketoglutarate, were diminished 40% in SCOT-KO neonates. This contrasted with many glucogenic/ ketogenic, glucogenic, ketogenic, and urea cycle amino acids, whose circulating concentrations were increased in P1 SCOT-KO mice (Fig. 1D; see supplemental Tables S4 and S5 for complete P0 and P1 blood amino acid profiles, respectively, of wild-type and SCOT-KO mice), suggesting enhanced skeletal muscle proteolysis in P1 SCOT-KO mice

Summary

Background

SCOT-KO mice cannot oxidize ketone bodies and die within 48 h of birth, due to hyperketonemic hypoglycemia. Mice with loss-of-function mutation in the extrahepatic mitochondrial enzyme CoA transferase (succinyl-CoA:3-oxoacid CoA transferase, SCOT, encoded by nuclear Oxct1) cannot terminally oxidize ketone bodies and develop lethal hyperketonemic hypoglycemia within 48 h of birth We use this model to demonstrate that loss of ketone body oxidation, an exclusively extrahepatic process, disrupts hepatic intermediary metabolic homeostasis after high fat mother’s milk is ingested. Glucose utilization is thought to support only ϳ70% of the neonatal brain’s energetic needs, and additional substrates, including ketone bodies, are required to supply the balance [2] To meet this demand, a coordinated hepatic metabolic program integrates ␤-oxidation and terminal oxidation of fatty acids, gluconeogenesis, and ketogenesis [1]. To determine whether the absence of extrahepatic ketone body oxidation influences hepatic glucose production and intermediary metabolic homeostasis, we used biochemical approaches to quantify dynamic metabolism in livers of germline neonatal SCOT-KO mice

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION