Enhanced insulin action on glucose transport and insulin signaling in 7-day unweighted rat soleus muscle.
Hindlimb suspension (HS), a model of simulated weightlessness, enhances insulin action on glucose transport in unweighted rat soleus muscle. In the present study, we tested the hypothesis that these changes in glucose transport in 3- and 7-day HS soleus of juvenile, female Sprague-Dawley rats were due to increased functionality of insulin signaling factors, including insulin receptor (IR), IR substrate-1 (IRS-1), phosphatidylinositol 3-kinase (PI3-kinase), and Akt. Insulin-stimulated (2 mU/ml) glucose transport was significantly (P < 0.05) enhanced in 3- and 7-day HS soleus by 59 and 113%, respectively, compared with weight-bearing controls. Insulin-stimulated tyrosine phosphorylation of IR and Ser(473) phosphorylation of Akt was not altered by unweighting. Despite decreased (34 and 64%) IRS-1 protein in 3- and 7-day HS soleus, absolute insulin-stimulated tyrosine phosphorylation of IRS-1 was not diminished, indicating relative increases in IRS-1 phosphorylation of 62 and 184%, respectively. In the 7-day HS soleus, this was accompanied by increased (47%) insulin-stimulated IRS-1 associated with the p85 subunit of PI3-kinase. Interestingly, the enhanced insulin-stimulated glucose transport in the unweighted soleus was not completely inhibited (89-92%) by wortmannin, a PI3-kinase inhibitor. Finally, protein expression and activation of p38 MAPK, a stress-activated serine/threonine kinase associated with insulin resistance, was decreased by 32 and 18% in 7-day HS soleus. These results indicate that the increased insulin action on glucose transport in the 7-day unweighted soleus is associated with increased insulin signaling through IRS-1 and PI3-kinase and decreased p38 MAPK protein expression. However, PI3-kinase-independent mechanisms must also play a small role in this adaptive response to HS.
Department of Physiology, University of Arizona, Tucson, AZ 85721-0093, USA.
Matthew P
MP
O'Keefe
Felipe R
FR
Perez
Julie A
JA
Sloniger
Marc E
ME
Tischler
Erik J
EJ
Henriksen
D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D001835:Body Weight / Q000502:physiology; D002950:Citrate (si)-Synthase / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D006593:Hexokinase / Q000378:metabolism; D007328:Insulin / Q000502:physiology*; D007333:Insulin Resistance / Q000502:physiology; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D009929:Organ Size / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D011972:Receptor, Insulin / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D014280:Triglycerides / Q000378:metabolism; D018474:Weightlessness Simulation / Q000009:adverse effects*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D002950:Citrate (si)-Synthase; D005947:Glucose; D051275:Glucose Transporter Type 4; D006593:Hexokinase; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin; D014280:Triglycerides; D048051:p38 Mitogen-Activated Protein Kinases; C495694:Slc2a4 protein, rat; C494920:Akt1 protein, rat