Defective Akt activation is associated with glucose- but not glucosamine-induced insulin resistance

Am J Physiol Endocrinol Metab. 2002 Mar;282(3):E497-506. doi: 10.1152/ajpendo.00438.2001.

Abstract

3T3-L1 adipocytes develop insulin-resistant glucose transport upon preincubation with high glucose or glucosamine, provided insulin (0.6 nM) is present during preincubation. Insulin receptor substrate-1 (IRS-1)-associated phosphatidylinositol (PI) 3-kinase activity is unaffected (30). Total cellular IRS-1, PI 3-kinase, or Akt concentrations were unchanged. Akt activation in subcellular fractions was assessed by immunoblotting with two phospho-Akt-specific antibodies. Upon acute 100 nM insulin stimulation, plasma membrane (PM)-associated phospho-Akt was highest in cells preincubated in low glucose with no insulin, less in high glucose with no insulin, even less in low glucose+insulin, and lowest in high glucose+insulin. Only high glucose+insulin caused insulin-resistant glucose transport. Acute insulin stimulation increased total PM-Akt about twofold after preincubation without insulin in low or high glucose. Preincubation with 0.6 nM insulin decreased Akt PM translocation by approximately 25% in low and approximately 50% in high glucose. Preincubation with glucosamine did not affect Akt phosphorylation or translocation.

Conclusions: chronic exposure to high glucose or insulin downregulates acute insulin-stimulated Akt activation, acting synergistically distal to PI 3-kinase. Maximal insulin activates more Akt than required for maximal glucose transport stimulation. Insulin resistance may ensue when PM-associated phospho-Akt decreases below a threshold. High glucose and glucosamine cause insulin resistance by different mechanisms in 3T3-L1 adipocytes.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3T3 Cells
  • Adipocytes / drug effects*
  • Adipocytes / metabolism
  • Animals
  • Biological Transport
  • Electrophoresis, Polyacrylamide Gel
  • Enzyme Activation / drug effects
  • Glucosamine / pharmacology*
  • Glucose / administration & dosage
  • Glucose / metabolism
  • Glucose / pharmacology*
  • Glucose Transporter Type 4
  • Immunoblotting
  • Insulin / administration & dosage
  • Insulin / pharmacology
  • Insulin Receptor Substrate Proteins
  • Insulin Resistance*
  • Mice
  • Monosaccharide Transport Proteins / metabolism
  • Muscle Proteins*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphoproteins / metabolism
  • Phosphorylation
  • Phosphoserine / metabolism
  • Phosphothreonine / metabolism
  • Protein-Serine-Threonine Kinases*
  • Protein-Tyrosine Kinases / metabolism*
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-akt

Substances

  • Glucose Transporter Type 4
  • Insulin
  • Insulin Receptor Substrate Proteins
  • Irs1 protein, mouse
  • Monosaccharide Transport Proteins
  • Muscle Proteins
  • Phosphoproteins
  • Proto-Oncogene Proteins
  • Slc2a4 protein, mouse
  • Phosphothreonine
  • Phosphoserine
  • Phosphatidylinositol 3-Kinases
  • Protein-Tyrosine Kinases
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Glucose
  • Glucosamine