Increased Akt protein expression is associated with decreased ceramide content in skeletal muscle of troglitazone-treated mice.
Although it is generally believed that thiazolidinediones ameliorate insulin resistance by lowering circulating free fatty acids, direct effects of these drugs in skeletal muscle may also contribute to their antidiabetic action. We report that troglitazone administration to mice for 1 day increased the protein expression of Akt (two-fold induction, P<0.001) in skeletal muscle without significant changes in the levels of free fatty acids in plasma. Increased Akt protein expression was associated with reduced phospho-AMP-activated protein kinase abundance and with a fall in the phosphorylation of acetyl-CoA carboxylase, which in turn resulted in an increase in the content of muscular malonyl-CoA (2.4-fold, P<0.05) and lactate (1.4-fold, P<0.05). Troglitazone treatment did not affect the mRNA levels of either Akt1 or Akt2, suggesting that a transcriptional mechanism was not involved, but caused a dramatic reduction in the content of muscular ceramides (76%, P<0.001), lipid-derived second messengers known to increase Akt degradation. Our data indicate that troglitazone treatment inhibited de novo ceramide synthesis, since the content of its precursor, palmitoyl-CoA, was reduced (55%, P=0.05). These results were confirmed in C2C12 myotubes, where troglitazone treatment increased Akt protein expression and prevented the reduction of this protein and the increase in ceramide levels caused by palmitate. These findings implicate ceramide as an important intermediate in the regulation of Akt after troglitazone treatment.
Planavila
Anna
A
Pharmacology Unit, Department of Pharmacology and Therapeutic Chemistry, Faculty of Pharmacy, University of Barcelona, Spain.
Alegret
Marta
M
Sánchez
Rosa M
RM
Rodríguez-Calvo
Ricardo
R
Laguna
Juan Carlos
JC
Vázquez-Carrera
Manuel
M
D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002518:Ceramides / Q000378:metabolism*; D002839:Chromans / Q000494:pharmacology*; D006861:Hydrogen Peroxide / Q000032:analysis; D015151:Immunoblotting; D019344:Lactic Acid / Q000032:analysis / Q000378:metabolism; D008297:Male; D008316:Malonyl Coenzyme A / Q000032:analysis / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D009097:Multienzyme Complexes / Q000187:drug effects / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000187:drug effects* / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000187:drug effects* / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D045162:Thiazolidinediones / Q000494:pharmacology*; D000077288:Troglitazone
D002518:Ceramides; D002839:Chromans; D009097:Multienzyme Complexes; D011518:Proto-Oncogene Proteins; D045162:Thiazolidinediones; D019344:Lactic Acid; D008316:Malonyl Coenzyme A; D006861:Hydrogen Peroxide; C494922:Akt2 protein, mouse; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase; D000077288:Troglitazone