Two weeks of metformin treatment enhances mitochondrial respiration in skeletal muscle of AMPK kinase dead but not wild type mice

PLoS One. 2013;8(1):e53533. doi: 10.1371/journal.pone.0053533. Epub 2013 Jan 14.

Abstract

Metformin is used as an anti-diabetic drug. Metformin ameliorates insulin resistance by improving insulin sensitivity in liver and skeletal muscle. Reduced mitochondrial content has been reported in type 2 diabetic muscles and it may contribute to decreased insulin sensitivity characteristic for diabetic muscles. The molecular mechanism behind the effect of metformin is not fully clarified but inhibition of complex I in the mitochondria and also activation of the 5'AMP activated protein kinase (AMPK) has been reported in muscle. Furthermore, both AMPK activation and metformin treatment have been associated with stimulation of mitochondrial function and biogenesis. However, a causal relationship in skeletal muscle has not been investigated. We hypothesized that potential effects of in vivo metformin treatment on mitochondrial function and protein expressions in skeletal muscle are dependent upon AMPK signaling. We investigated this by two weeks of oral metformin treatment of muscle specific kinase dead α(2) (KD) AMPK mice and wild type (WT) littermates. We measured mitochondrial respiration and protein activity and expressions of key enzymes involved in mitochondrial carbohydrate and fat metabolism and oxidative phosphorylation. Mitochondrial respiration, HAD and CS activity, PDH and complex I-V and cytochrome c protein expression were all reduced in AMPK KD compared to WT tibialis anterior muscles. Surprisingly, metformin treatment only enhanced respiration in AMPK KD mice and thereby rescued the respiration defect compared to the WT mice. Metformin did not influence protein activities or expressions in either WT or AMPK KD mice.We conclude that two weeks of in vivo metformin treatment enhances mitochondrial respiration in the mitochondrial deficient AMPK KD but not WT mice. The improvement seems to be unrelated to AMPK, and does not involve changes in key mitochondrial proteins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3-Hydroxyacyl CoA Dehydrogenases / metabolism
  • AMP-Activated Protein Kinases / metabolism*
  • Animals
  • Blotting, Western
  • Cell Respiration / drug effects
  • Citrate (si)-Synthase / metabolism
  • Cytochromes c / metabolism
  • Electron Transport / drug effects
  • Female
  • Metformin / administration & dosage
  • Metformin / pharmacology*
  • Mice
  • Mice, Inbred C57BL
  • Mitochondria / drug effects
  • Mitochondria / enzymology
  • Mitochondria / metabolism*
  • Mitochondrial Proteins / metabolism
  • Muscle, Skeletal / drug effects
  • Muscle, Skeletal / enzymology*
  • Muscle, Skeletal / pathology
  • Phosphorylation / drug effects
  • Phosphoserine / metabolism
  • Pyruvate Dehydrogenase Complex / metabolism
  • Substrate Specificity / drug effects

Substances

  • Mitochondrial Proteins
  • Pyruvate Dehydrogenase Complex
  • Phosphoserine
  • Cytochromes c
  • Metformin
  • 3-Hydroxyacyl CoA Dehydrogenases
  • Citrate (si)-Synthase
  • AMP-Activated Protein Kinases

Grant support

The study was supported by: Danish Medical Research Council; The Novo Nordisk Foundation; The Danish Diabetes Association; The Lundbeck Foundation; The Nordea Foundation. Danish Ministry of Science, Technology and Innovation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.