title: Skeletal muscle alterations and exercise performance decrease in erythropoietin-deficient mice: a comparative study.
abstract: BACKGROUND
  Erythropoietin (EPO) is known to improve exercise performance by increasing oxygen blood transport and thus inducing a higher maximum oxygen uptake (VO2max). Furthermore, treatment with (or overexpression of) EPO induces protective effects in several tissues, including the myocardium. However, it is not known whether EPO exerts this protective effect when present at physiological levels. Given that EPO receptors have been identified in skeletal muscle, we hypothesized that EPO may have a direct, protective effect on this tissue. Thus, the objectives of the present study were to confirm a decrease in exercise performance and highlight muscle transcriptome alterations in a murine EPO functional knock-out model (the EPO-d mouse).
  
  
  METHODS
  We determined VO2max peak velocity and critical speed in exhaustive runs in 17 mice (9 EPO-d animals and 8 inbred controls), using treadmill enclosed in a metabolic chamber. Mice were sacrificed 24h after a last exhaustive treadmill exercise at critical speed. The tibialis anterior and soleus muscles were removed and total RNA was extracted for microarray gene expression analysis.
  
  
  RESULTS
  The EPO-d mice's hematocrit was about 50% lower than that of controls (p<0.05) and their performance level was about 25% lower (p<0.001). A total of 1583 genes exhibited significant changes in their expression levels. However, 68 genes were strongly up-regulated (normalized ratio>1.4) and 115 were strongly down-regulated (normalized ratio<0.80). The transcriptome data mining analysis showed that the exercise in the EPO-d mice induced muscle hypoxia, oxidative stress and proteolysis associated with energy pathway disruptions in glycolysis and mitochondrial oxidative phosphorylation.
  
  
  CONCLUSIONS
  Our results showed that the lack of functional EPO induced a decrease in the aerobic exercise capacity. This decrease was correlated with the hematocrit and reflecting poor oxygen supply to the muscles. The observed alterations in the muscle transcriptome suggest that physiological concentrations of EPO exert both direct and indirect muscle-protecting effects during exercise. However, the signaling pathway involved in these protective effects remains to be described in detail.
authors: Unité de Biologie Intégrative des Adaptations à l'Exercice - INSERM 902, Genopole, F-91058, Evry, France. laurence.hamard@inserm.fr
authors: Laurence
authors: L
authors: Mille-Hamard
authors: Veronique L
authors: VL
authors: Billat
authors: Elodie
authors: E
authors: Henry
authors: Blandine
authors: B
authors: Bonnamy
authors: Florence
authors: F
authors: Joly
authors: Philippe
authors: P
authors: Benech
authors: Eric
authors: E
authors: Barrey
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000818:Animals; D001692:Biological Transport / Q000235:genetics; D003599:Cytoskeleton / Q000235:genetics; D015536:Down-Regulation / Q000235:genetics; D004921:Erythropoietin / Q000172:deficiency* / Q000378:metabolism; D005260:Female; D006400:Hematocrit; D000860:Hypoxia / Q000150:complications / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology* / Q000503:physiopathology; D009133:Muscular Atrophy / Q000150:complications / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D020411:Oligonucleotide Array Sequence Analysis; D010101:Oxygen Consumption; D010805:Physical Conditioning, Animal; D059748:Proteolysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics; D015854:Up-Regulation / Q000235:genetics
chemical_list: D004921:Erythropoietin; D000255:Adenosine Triphosphate