Two Weeks of Metformin Treatment Enhances Mitochondrial Respiration in Skeletal Muscle of AMPK Kinase Dead but Not Wild Type Mice

Jonas M. Kristensen,Steen Larsen,Jørgen F. P. Wojtaszewski,Flemming Dela,Jørn W. Helge,Makoto Kanzaki

doi:10.1371/journal.pone.0053533

Jonas M. Kristensen, Steen Larsen

Open Access

https://doi.org/10.1371/journal.pone.0053533

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Journal: PLoS ONE	Publication Date: Jan 14, 2013
Citations: 98	License type: CC BY 4.0

Affiliation: University of Copenhagen, University of Southern Denmark

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 α2 (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.

Highlights

Metformin is worldwide the most prevalently used drug to treat type 2 diabetes and have been utilized in the clinic for more than five decades to improve insulin sensitivity [1,2]
Decreased state 3 mitochondrial respiration in AMPK kinase dead a2 (KD) compared to wild type (WT) muscle is normalized after metformin treatment
Mitochondrial respiration was significantly decreased in TA muscles of saline treated AMPK KD compared to WT mice when measured per milligram of muscle (Fig. 1A)

Summary

Introduction

Metformin is worldwide the most prevalently used drug to treat type 2 diabetes and have been utilized in the clinic for more than five decades to improve insulin sensitivity [1,2]. It has been reported that diabetic muscles have reduced mitochondrial content as well as protein expressions and activities and this may contribute to skeletal muscle insulin resistance [3,4,5]. Metformin-induced activation of the 59-AMP activated protein kinase (AMPK) has been shown in rodent muscles [18,19,20], and in human skeletal muscles from patients with type 2 diabetes [21,22]. Instead activation has been suggested to be linked to the inhibition of mitochondrial complex I, that may lead to a disturbance in cell energy balance and AMPK activation [13,27,28], other studies suggest that the metformin-induced activation is not dependent of such changes in the energy status of the cell [26,29]

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