Elevated basal PI 3-kinase activity and reduced insulin signaling in sucrose-induced hepatic insulin resistance.
Sucrose feeding reduces the ability of insulin to suppress glucose production and hepatic gluconeogenesis. The present study examined the effect of a high-sucrose diet on early insulin-signaling steps in the liver. Rats were provided a high-starch (STD, control diet) or high-sucrose diet (HSD) for 3 wk. On the day of study, overnight-fasted rats were anesthetized and injected with either saline (n = 5/diet group) or insulin (2 mU/kg, n = 5/diet group) via the portal vein. Portal venous blood and liver tissue were harvested 2 min after injections. Portal vein plasma glucose levels were not significantly different among groups, pooled average 147 +/- 12 mg/dl. Western blot analysis revealed no significant differences in the amount of insulin receptor (IR), insulin receptor substrates-1 and -2 (IRS-1, IRS-2), and the p85 subunit of phosphatidylinositol (PI) 3-kinase. In contrast, the amount of the p110beta subunit of PI 3-kinase was increased approximately 2-fold in HSD vs. STD (P < 0.05). After saline injection, tyrosine phosphorylation (pY) of IR, IRS-1, and IRS-2 was not significantly different between groups. However, PI 3-kinase activity associated with phosphorylated proteins was increased approximately 40% in HSD vs. STD (P < 0.05). After insulin injection, pY of the IR was not different between groups, whereas pY of IRS-1 and IRS-2 was reduced (P < 0.05) in HSD vs. STD. In addition, association of IRS-1 and IRS-2 with p85 was significantly reduced in HSD vs. STD. These data demonstrate that an HSD impairs insulin-stimulated early postreceptor signaling (pY of IRS proteins, IRS interaction with p85). Furthermore, the increased amount of p110beta and increased basal PI 3-kinase activity suggest a diet-induced compensatory response.
Pagliassotti
Michael J
MJ
Division of Endocrinology, Metabolism and Diabetes, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA. Mike.Pagliassotti@uchsc.edu
Kang
Jione
J
Thresher
Jeffrey S
JS
Sung
Chin K
CK
Bizeau
Michael E
ME
D000818:Animals; D015309:Glucose Clamp Technique; D007328:Insulin / Q000502:physiology*; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000502:physiology*; D008297:Male; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D011972:Receptor, Insulin / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013395:Sucrose / Q000494:pharmacology*; D014443:Tyrosine / Q000378:metabolism
D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin; D013395:Sucrose; D014443:Tyrosine; C526296:Irs1 protein, rat; C526299:Irs2 protein, rat