Apoptosis-Inducing Factor Regulates Skeletal Muscle Progenitor Cell Number and Muscle Phenotype

Anne-Sophie Armand,Leon J De Windt,Anne T Bertrand,Iman Laziz,Olivier Biondi,Sylvie Lécolle,Christophe Chanoine,Dounia Djeghloul,Marc Tjwa

doi:10.1371/journal.pone.0027283

Abstract

Apoptosis Inducing Factor (AIF) is a highly conserved, ubiquitous flavoprotein localized in the mitochondrial intermembrane space. In vivo, AIF provides protection against neuronal and cardiomyocyte apoptosis induced by oxidative stress. Conversely in vitro, AIF has been demonstrated to have a pro-apoptotic role upon induction of the mitochondrial death pathway, once AIF translocates to the nucleus where it facilitates chromatin condensation and large scale DNA fragmentation. Given that the aif hypomorphic harlequin (Hq) mutant mouse model displays severe sarcopenia, we examined skeletal muscle from the aif hypomorphic mice in more detail. Adult AIF-deficient skeletal myofibers display oxidative stress and a severe form of atrophy, associated with a loss of myonuclei and a fast to slow fiber type switch, both in “slow” muscles such as soleus, as well as in “fast” muscles such as extensor digitorum longus, most likely resulting from an increase of MEF2 activity. This fiber type switch was conserved in regenerated soleus and EDL muscles of Hq mice subjected to cardiotoxin injection. In addition, muscle regeneration in soleus and EDL muscles of Hq mice was severely delayed. Freshly cultured myofibers, soleus and EDL muscle sections from Hq mice displayed a decreased satellite cell pool, which could be rescued by pretreating aif hypomorphic mice with the manganese-salen free radical scavenger EUK-8. Satellite cell activation seems to be abnormally long in Hq primary culture compared to controls. However, AIF deficiency did not affect myoblast cell proliferation and differentiation. Thus, AIF protects skeletal muscles against oxidative stress-induced damage probably by protecting satellite cells against oxidative stress and maintaining skeletal muscle stem cell number and activation.

Highlights

Mitochondria are the main source of cellular energy production and defects in mitochondrial function is linked to a variety of inherited human disorders, including cardiomyopathies and myopathies
In response to increased reactive oxygen species (ROS) production, cells induce the expression of a series of antioxidant enzymes, including the enzymes involved in the synthesis of glutathione: the glutamate cysteine ligase (GCL), and the glutathione synthetase (GS)
The adult skeletal muscle stem cell pool was not impaired in vivo in the p66ShcA mouse model while p66ShcA knockout mice regenerated faster [16], showing that p66ShcA and oxidative stress play an important role in skeletal muscle regeneration

Summary

Introduction

Mitochondria are the main source of cellular energy production and defects in mitochondrial function is linked to a variety of inherited human disorders, including cardiomyopathies and myopathies. The adult skeletal muscle stem cell pool was not impaired in vivo in the p66ShcA mouse model while p66ShcA knockout mice regenerated faster [16], showing that p66ShcA and oxidative stress play an important role in skeletal muscle regeneration. Given the well-characterized contribution of muscle progenitor cells to myofiber genesis, fiber specification and renewal, skeletal muscle represents a valuable model to study whether oxidative stress can affect stem cell number and function, and what factors play germane roles in such process. Adult AIF-deficient skeletal myofibers develop atrophy with a loss of myonuclei and associated with a fast to slow fiber type switch, both in ‘‘slow’’ muscles such as soleus, as well as in ‘‘fast’’ muscles such as extensor digitorum longus (EDL). AIF protects skeletal muscles against oxidative stress-induced damage probably by protecting satellite cells against oxidative stress and maintaining skeletal muscle stem cell number and activation

Materials and Methods

Results

Discussion