title: Macrophage colony stimulating factor-induced macrophage differentiation influences myotube elongation.
abstract: BACKGROUND
  Unaccustomed exercise, high-intensity dynamic sports activities, or the resumption of normal weight-bearing after a period of disuse can induce skeletal muscle injury, which activates an inflammatory response followed by muscle regeneration. Specific subsets of macrophages are involved in muscle regeneration. But the exact role of macrophage differentiation during muscle regeneration remains to be elucidated.
  
  
  OBJECTIVE
  The objective of the study was to examine the effect of macrophage colony stimulating factor (M-CSF)-differentiated, lipopolysaccharides (LPS)-stimulated-macrophage-conditioned medium on muscle-cell proliferation, fusion, and elongation, which are key events during muscle regeneration and myogenesis.
  
  
  METHODS
  Murine C2C12 myoblasts were cultured in conditioned medium obtained from PU5-1R macrophages that were (a) undifferentiated, unstimulated; (b) M-CSF-differentiated, unstimulated; (c) undifferentiated, LPS-stimulated; or (d) M-CSF-differentiated, LPS-stimulated. Myoblast proliferation ratio, nuclei number, and length were measured.
  
  
  RESULTS
  C2C12 cells cultured in conditioned medium from M-CSF-differentiated, LPS-stimulated macrophages had significantly more nuclei and greater length than cells cultured in conditioned medium from undifferentiated, LPS-stimulated macrophages. Dilution and denaturization of the M-CSF-differentiated, LPS-stimulated-macrophage medium prevented a marked increase in C2C12 nuclei number and length. However, the C2C12 myoblast proliferation ratio was significantly greater in conditioned medium from undifferentiated, LPS-stimulated macrophages than in conditioned medium from M-CSF-differentiated, LPS-stimulated macrophages.
  
  
  CONCLUSIONS
  M-CSF-differentiated, LPS-stimulated macrophages may influence myogenesis and the early and terminal stages of muscle regeneration. This knowledge may aid in developing therapies that will directly expedite muscle repair and lead to faster rehabilitation and reduced rehabilitation costs.
authors.affiliation: School of Nursing, University of Nevada, Las Vegas, USA.
authors.forename: Sara
authors.initials: S
authors.lastname: Keeling
authors.forename: Nadia
authors.initials: N
authors.lastname: Deashinta
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Howard
authors.forename: Sara
authors.initials: S
authors.lastname: Vigil
authors.forename: Sheniz
authors.initials: S
authors.lastname: Moonie
authors.forename: Barbara St Pierre
authors.initials: BS
authors.lastname: Schneider
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D017077:Culture Media, Conditioned; D016173:Macrophage Colony-Stimulating Factor / Q000502:physiology*; D008264:Macrophages / Q000166:cytology*; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000166:cytology*
chemical_list: D017077:Culture Media, Conditioned; D016173:Macrophage Colony-Stimulating Factor