High-fat diet feeding impairs both the expression and activity of AMPKa in rats' skeletal muscle.
OBJECTIVE
To investigate the effects of high-fat feeding on the expression and activity of AMPK in rats' skeletal muscle.


METHODS
Total 40 male Wistar rats were randomly divided into three groups and received either a rat maintenance diet (Control group) or an isocaloric rich-fat diet (HF group and MET group) for five months. Metformin was administered orally with the daily dose of 300mg in MET group during the last month of high-fat feeding. Hyperinsulinemic-euglycemic clamp study was performed to estimate whole-body insulin sensitivity. The ability of insulin-stimulated glucose uptake in isolated skeletal muscle was detected just before execution. mRNA levels of AMPKa1, AMPKa2, and Glut4 of rats' skeletal muscle were determined using real-time PCR. Protein contents of AMPKa, P-AMPKa, P-ACC, and Glut4 in rats' skeletal muscle were measured using Western blot.


RESULTS
(1) Hyperinsulinemic-euglycemic clamp study revealed a significantly impaired insulin action at the whole-body level after high-fat feeding (p<0.01). Also, both basal and insulin-stimulated glucose uptake in isolated skeletal muscle decreased after high-fat feeding (p<0.05), indicating onset of high-fat induced insulin resistance. (2) Five months of high-fat treatment induced a significant decrease of AMPKa protein contents and AMPKa2 mRNA levels in rats' skeletal muscles (p<0.05), while it did not alter AMPKa1 mRNA levels. Protein levels of P-AMPKa also decreased after high-fat feeding (p<0.01). These data suggest that high-fat exposure might impair AMPKa expression and activities. (3) P-ACC protein contents, mRNA and protein levels of Glut4 in rats' skeletal muscles also decreased after high-fat treatment (p<0.05). (4) Compared with HF group, although no significant alternations of AMPKa expression in rats' skeletal muscles were detected, P-AMPKa levels revealed a 162% increase after metformin treatment (p<0.05), demonstrating the AMPK-activating effect of metformin. Accompanied with activation of AMPKa, rats in MET group exhibited significantly elevated P-ACC contents, Glut4 mRNA and protein levels, and an obviously enhanced insulin sensitivity at both whole-body and skeletal muscle levels (p<0.05).


CONCLUSIONS
High-fat feeding impaired both the expression and activities of AMPKa, while activating AMPKa by metformin obviously ameliorated high-fat induced insulin resistance, thus indicating a possible role of AMPKa in lipotoxicity.
Liu
Yi
Y
Shandong Provincial Hospital Shandong University, Jinan 250021, China.
Wan
Qiang
Q
Guan
Qingbo
Q
Gao
Ling
L
Zhao
Jiajun
J
D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase / Q000378:metabolism; D000821:Animal Feed; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D004032:Diet; D004041:Dietary Fats / Q000008:administration & dosage / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D051275:Glucose Transporter Type 4 / Q000235:genetics / Q000378:metabolism; D007328:Insulin / Q000097:blood; D008297:Male; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000201:enzymology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D001786:Blood Glucose; D004041:Dietary Fats; D051275:Glucose Transporter Type 4; D007328:Insulin; D009097:Multienzyme Complexes; C495694:Slc2a4 protein, rat; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase