Deficiency of PDK1 in liver results in glucose intolerance, impairment of insulin-regulated gene expression and liver failure.
The liver plays an important role in insulin-regulated glucose homoeostasis. To study the function of the PDK1 (3-phosphoinositide-dependent protein kinase-1) signalling pathway in mediating insulin's actions in the liver, we employed CRE recombinase/loxP technology to generate L(liver)-PDK1-/- mice, which lack expression of PDK1 in hepatocytes and in which insulin failed to induce activation of PKB in liver. The L-PDK1-/- mice were not insulin-intolerant, possessed normal levels of blood glucose and insulin under normal feeding conditions, but were markedly glucose-intolerant when injected with glucose. The L-PDK1-/- mice also possessed 10-fold lower levels of hepatic glycogen compared with control littermates, and were unable to normalize their blood glucose levels within 2 h after injection of insulin. The glucose intolerance of the L-PDK1-/- mice may be due to an inability of glucose to suppress hepatic glucose output through the gluconeogenic pathway, since the mRNA encoding hepatic PEPCK (phosphoenolpyruvate carboxykinase), G6Pase (glucose-6-phosphatase) and SREBP1 (sterol-regulatory-element-binding protein 1), which regulate gluconeogenesis, are no longer controlled by feeding. Furthermore, three other insulin-controlled genes, namely IGFBP1 (insulin-like-growth-factor-binding protein-1), IRS2 (insulin receptor substrate 2) and glucokinase, were regulated abnormally by feeding in the liver of PDK1-deficient mice. Finally, the L-PDK1-/- mice died between 4-16 weeks of age due to liver failure. These results establish that the PDK1 signalling pathway plays an important role in regulating glucose homoeostasis and controlling expression of insulin-regulated genes. They suggest that a deficiency of the PDK1 pathway in the liver could contribute to development of diabetes, as well as to liver failure.
Mora
Alfonso
A
MRC Protein Phosphorylation Unit, School of Life Sciences, MSI/WTB Complex, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland, UK. a.m.corral@dundee.ac.uk
Lipina
Christopher
C
Tronche
François
F
Sutherland
Calum
C
Alessi
Dario R
DR
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D004789:Enzyme Activation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects* / Q000235:genetics; D005943:Gluconeogenesis / Q000235:genetics; D005947:Glucose / Q000378:metabolism; D018149:Glucose Intolerance; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D006706:Homeostasis; D007328:Insulin / Q000494:pharmacology*; D008099:Liver / Q000201:enzymology* / Q000378:metabolism; D017093:Liver Failure / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology*; D051379:Mice; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D015996:Survival Rate
D007328:Insulin; D011518:Proto-Oncogene Proteins; D064413:3-Phosphoinositide-Dependent Protein Kinases; C578564:Pdpk1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D005947:Glucose