Exercise-enhanced satellite cell proliferation and new myonuclear accretion in rat skeletal muscle

Abstract

The effects of increased functional loading on early cellular regenerative events after exercise-induced injury in adult skeletal muscle were examined with the use of in vivo labeling of replicating myofiber nuclei and immunocyto- and histochemical techniques. Satellite cell proliferation in the soleus (Sol) of nonexercised rats (0.4 +/- 0.2% of fibers) was unchanged after an initial bout of declined treadmill exercise but was elevated after two (1.0 +/- 0.2%, P < or = 0.01), but not four or seven, daily bouts of the same task. Myonuclei produced over the 7-day period comprised 0.9-1.9% of myonuclei in isolated fibers of Sol, tibialis anterior, and vastus intermedius of nonexercised rats. The accretion of new myonuclei was enhanced (P < or = 0.05) in Sol and vastus intermedius by the initial exercise followed by normal activity (to 3.1-3.4% of myonuclei) and more so by continued daily exercise (4.2-5.3%). Observed coincident with a lower incidence of histological fiber injury and unchanged fiber diameter and myonuclei per millimeter, the greater new myonuclear accretion induced by continued muscle loading may contribute to an enhanced fiber repair and regeneration after exercise-induced injury.

In Vivo Fusion of Circulating Fluorescent Cells with Dystrophin-Deficient Myofibers Results in Extensive Sarcoplasmic Fluorescence Expression but Limited Dystrophin Sarcolemmal Expression

“…22 Hybrid myotubes formed in vitro by the fusion of normal rat and dystrophic mdx mouse myoblasts showed that dystrophin was present over the entire membrane of all hybrid myotubes even when nuclei ratio normal/dystrophic was low (as low as 1 of 12). 22 In vivo transplantation of normal myoblasts into mdx mouse muscle 23 in which myogenic cells fuse with pre-existing fibers, showed that the dystrophin nuclear domain is ϳ300 to 400 m. 24,25 These results are very similar to those we observed after BM transplantation (116 m). In a previous study using direct myoblast injection in mdx muscle, the dystrophin domain was shown to be twofold to threefold smaller than that of soluble cytoplasmic ␤-galactosidase used as a reporter gene.…”

Erythropoietin improves functional and histological recovery of traumatized skeletal muscle tissue

“…Sections were counterstained with hemalaun and examined by light microscopy (Axioskop 40, Zeiss, Göttingen, Germany). By labeling of laminin, which is present in the basement membrane, confirmation of proliferating satellite cells was able through their localization beneath the laminin-positive basal lamina in the survival zone, as described by Smith et al 19 in the soleus muscle of rats. The fact that the penumbra areas still revealed myocytes allowed us to identify proliferating satellite cells due to their localization beneath their basal lamina.…”

Id3 Is a Direct Transcriptional Target of Pax7 in Quiescent Satellite Cells

“…Satellite cells are a small population of myogenic progenitors that reside between the sarcolemma and basal lamina of the muscle fiber, and they play a crucial role in postnatal muscle growth and regeneration (reviewed in Zammit et al, 2006). Following skeletal muscle injury or exercise-induced activation, the normally quiescent Pax7-expressing satellite cells proliferate extensively and up-regulate expression of MyoD (Smith et al, 2001;Yan et al, 2003;Montarras et al, 2005) and Myf-5 (Conboy and Rando, 2002;Yan et al, 2003), before differentiation into skeletal muscle.…”

“…Satellite cells are a small population of myogenic progenitors that reside between the sarcolemma and basal lamina of the muscle fiber, and they play a crucial role in postnatal muscle growth and regeneration (reviewed in Zammit et al, 2006). Following skeletal muscle injury or exercise-induced activation, the normally quiescent Pax7-expressing satellite cells proliferate extensively and up-regulate expression of MyoD (Smith et al, 2001;Yan et al, 2003;Montarras et al, 2005) and Myf-5 (Conboy and Rando, 2002;Yan et al, 2003), before differentiation into skeletal muscle.Pax3 and Pax7 are members of the Pax transcription factor family and contain both paired (PD) and homeodomain (HD) DNA binding motifs. Pax3 and Pax7 can bind to DNA sequences containing either a consensus paired domain binding site (GTCAC A/G C/G A/T T/C) or a homeodomain binding site (ATTA) (Chalepakis et al, 1994;Chalepakis and Gruss, 1995).…”