Inhibitory cross-talk between the AMPK and ERK pathways mediates endoplasmic reticulum stress-induced insulin resistance in skeletal muscle.
OBJECTIVE
Endoplasmic reticulum (ER) stress has been implicated in the pathogeneses of insulin resistance and type 2 diabetes, and extracellular signal-regulated kinase (ERK) antagonist is an insulin sensitizer that can restore muscle insulin responsiveness in both tunicamycin-treated muscle cells and type 2 diabetic mice. The present study was undertaken to determine whether the chemical or genetic inhibition ER stress pathway targeting by ERK results in metabolic benefits in muscle cells.


METHODS
ER stress was induced in L6 myotubes using tunicamycin (5 μg·mL(-1) ) or thapsigargin (300 nM) and cells were transfected with siRNA ERK or AMPKα2. Changes in ER stress and in the ERK and AMPK signalling pathways were explored by Western blotting. The phosphorylation levels of insulin receptor substrate 1 were analysed by immunoprecipitation and using glucose uptake assay.


RESULTS
ER stress dampened insulin-stimulated signals and glucose uptake, whereas treatment with the specific ERK inhibitor U0126 (25 μM) rescued impaired insulin signalling via AMPK activation. In db/db mice, U0126 administration decreased markers of insulin resistance and increased the phosphorylations of Akt and AMPK in muscle tissues.


CONCLUSIONS
Inhibition of ERK signalling pathways by a chemical inhibitor and knockdown of ERK improved AMPK and Akt signallings and reversed ER stress-induced insulin resistance in L6 myotubes. These findings suggest that ERK signalling plays an important role in the regulation of insulin signals in muscle cells under ER stress.
College of Pharmacy, Yeungnam University, Gyeongsan, Republic of Korea.
Seung-Lark
SL
Hwang
Yong-Tae
YT
Jeong
Xian
X
Li
Yong Deuk
YD
Kim
Yue
Y
Lu
Young-Chae
YC
Chang
In-Kyu
IK
Lee
Hyeun Wook
HW
Chang
D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress / Q000235:genetics / Q000502:physiology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D007328:Insulin / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D007333:Insulin Resistance; D020935:MAP Kinase Signaling System / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034741:RNA, Small Interfering / Q000008:administration & dosage; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection
D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D034741:RNA, Small Interfering; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D055372:AMP-Activated Protein Kinases