A role for mitochondrial phosphoenolpyruvate carboxykinase (PEPCK-M) in the regulation of hepatic gluconeogenesis.
Synthesis of phosphoenolpyruvate (PEP) from oxaloacetate is an absolute requirement for gluconeogenesis from mitochondrial substrates. Generally, this reaction has solely been attributed to the cytosolic isoform of PEPCK (PEPCK-C), although loss of the mitochondrial isoform (PEPCK-M) has never been assessed. Despite catalyzing the same reaction, to date the only significant role reported in mammals for the mitochondrial isoform is as a glucose sensor necessary for insulin secretion. We hypothesized that this nutrient-sensing mitochondrial GTP-dependent pathway contributes importantly to gluconeogenesis. PEPCK-M was acutely silenced in gluconeogenic tissues of rats using antisense oligonucleotides both in vivo and in isolated hepatocytes. Silencing PEPCK-M lowers plasma glucose, insulin, and triglycerides, reduces white adipose, and depletes hepatic glycogen, but raises lactate. There is a switch of gluconeogenic substrate preference to glycerol that quantitatively accounts for a third of glucose production. In contrast to the severe mitochondrial deficiency characteristic of PEPCK-C knock-out livers, hepatocytes from PEPCK-M-deficient livers maintained normal oxidative function. Consistent with its predicted role, gluconeogenesis rates from hepatocytes lacking PEPCK-M are severely reduced for lactate, alanine, and glutamine, but not for pyruvate and glycerol. Thus, PEPCK-M has a direct role in fasted and fed glucose homeostasis, and this mitochondrial GTP-dependent pathway should be reconsidered for its involvement in both normal and diabetic metabolism.
From the Departments of Internal Medicine and.
Romana
R
Stark
Fitsum
F
Guebre-Egziabher
Xiaojian
X
Zhao
Colleen
C
Feriod
Jianying
J
Dong
Tiago C
TC
Alves
Simona
S
Ioja
Rebecca L
RL
Pongratz
Sanjay
S
Bhanot
Michael
M
Roden
Gary W
GW
Cline
Gerald I
GI
Shulman
Richard G
RG
Kibbey
D000821:Animal Feed; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D005508:Food Deprivation; D015971:Gene Expression Regulation, Enzymologic; D020868:Gene Silencing; D005943:Gluconeogenesis; D005990:Glycerol / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D022781:Hepatocytes / Q000166:cytology; D006706:Homeostasis; D007328:Insulin / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D007527:Isoenzymes / Q000502:physiology; D019344:Lactic Acid / Q000378:metabolism; D008099:Liver / Q000201:enzymology* / Q000378:metabolism*; D008297:Male; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism; D016376:Oligonucleotides, Antisense / Q000737:chemistry; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D001786:Blood Glucose; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D016376:Oligonucleotides, Antisense; D019344:Lactic Acid; D006160:Guanosine Triphosphate; D006003:Glycogen; C582554:Pck1 protein, rat; D010729:Phosphoenolpyruvate Carboxykinase (GTP); D005990:Glycerol; D010100:Oxygen
Diabetes; GTPase; Gluconeogenesis; Glyceroneogenesis; Intermediary Metabolism; Metabolic Regulation; Metabolic Tracers; Metabolism; Mitochondrial Metabolism; Phosphoenolpyruvate Carboxykinase