Insulin and wnt1 pathways cooperate to induce reserve cell activation in differentiation and myotube hypertrophy.
During ex vivo myoblast differentiation, a pool of quiescent mononucleated myoblasts, reserve cells, arise alongside myotubes. Insulin/insulin-like growth factor (IGF) and PKB/Akt-dependent phosphorylation activates skeletal muscle differentiation and hypertrophy. We have investigated the role of glycogen synthase kinase 3 (GSK-3) inhibition by protein kinase B (PKB)/Akt and Wnt/beta-catenin pathways in reserve cell activation during myoblast differentiation and myotube hypertrophy. Inhibition of GSK-3 by LiCl or SB216763, restored insulin-dependent differentiation of C2ind myoblasts in low serum, and cooperated with insulin in serum-free medium to induce MyoD and myogenin expression in C2ind myoblasts, quiescent C2 or primary human reserve cells. We show that LiCl treatment induced nuclear accumulation of beta-catenin in C2 myoblasts, thus mimicking activation of canonical Wnt signaling. Similarly to the effect of GSK-3 inhibitors with insulin, coculturing C2 reserve cells with Wnt1-expressing fibroblasts enhanced insulin-stimulated induction of MyoD and myogenin in reserve cells. A similar cooperative effect of LiCl or Wnt1 with insulin was observed during late ex vivo differentiation and promoted increased size and fusion of myotubes. We show that this synergistic effect on myotube hypertrophy involved an increased fusion of reserve cells into preexisting myotubes. These data reveal insulin and Wnt/beta-catenin pathways cooperate in muscle cell differentiation through activation and recruitment of satellite cell-like reserve myoblasts.
Institut de Génétique Humaine, Centre National de la Recherche Scientifique, UPR-1142, 34396 Montpellier Cedex 5, France.
Anne
A
Rochat
Anne
A
Fernandez
Marie
M
Vandromme
Jeàn-Pierre
JP
Molès
Triston
T
Bouschet
Gilles
G
Carnac
Ned J C
NJ
Lamb
D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D002459:Cell Fusion; D002460:Cell Line; D048429:Cell Size; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D006984:Hypertrophy; D007211:Indoles / Q000378:metabolism; D007328:Insulin / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D018021:Lithium Chloride / Q000378:metabolism; D008301:Maleimides / Q000378:metabolism; D051379:Mice; D032342:Muscle Cells / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000166:cytology* / Q000502:physiology; D010766:Phosphorylation; D015398:Signal Transduction / Q000502:physiology*; D051153:Wnt Proteins; D051155:Wnt1 Protein
D007211:Indoles; D007328:Insulin; D036341:Intercellular Signaling Peptides and Proteins; D008301:Maleimides; C417521:SB 216763; C495247:WNT1 protein, human; D051153:Wnt Proteins; D051155:Wnt1 Protein; C495246:Wnt1 protein, mouse; D038362:Glycogen Synthase Kinase 3; D018021:Lithium Chloride