Evidence for the participation of nerve growth factor and its low-affinity receptor (p75NTR) in the regulation of the myogenic program.
We have studied expression and function of neurotrophins and their receptors during myogenic differentiation of C2C12 cells, a clonal cell line derived from mouse muscle that is capable of in vitro differentiation. The genes coding for nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and their common low-affinity receptor p75(neurotrophin receptor) (p75NTR) were shown to be expressed in C2C12 myoblasts and downregulated during myogenic differentiation and fusion into myotubes. Cocultures with dorsal root ganglia from day 8 chick embryos revealed neurite-promoting activities of C2C12 cells that ceased with myogenic differentiation. These data suggest a temporal and developmental window for the effect of myogenic cell-derived neurotrophins on neuronal as well as on myogenic cell populations. NGF was shown to increase DNA synthesis and cell growth of C2C12 myoblasts and to enhance myogenic differentiation in this cell line. We present evidence that NGF-mediated processes take place at stages preceding myogenic differentiation. Enhanced muscle differentiation was also seen in p75NTR-overexpressing C2C12 myoblasts which maintained high levels of receptors but ceased to produce NGF during differentiation. In contrast, when exogenous NGF was present at the onset of myogenic differentiation of receptor-overexpressing cells, muscle cell development was strongly repressed. This indicates that downregulation of p75NTR is necessary for guiding myogenic cells towards terminal differentiation. Since none of the trk high-affinity neurotrophin receptors could be demonstrated in C2C12 cells, we conclude that NGF mediates its nonneurotrophic effect via its low-affinity receptor in an autocrine fashion.
Seidl
K
K
Institute for Biochemistry and Biotechnology, Department of Cell and Molecular Biology, University of Braunschweig, Germany. k.seidl@tu-bs.de
Erck
C
C
Buchberger
A
A
D000818:Animals; D019208:Brain-Derived Neurotrophic Factor / Q000235:genetics; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D002642:Chick Embryo; D018920:Coculture Techniques; D004261:DNA Replication / Q000187:drug effects; D015536:Down-Regulation / Q000502:physiology; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D006651:Histocytochemistry; D007150:Immunohistochemistry; D051379:Mice; D024510:Muscle Development; D018995:Myosin Heavy Chains / Q000378:metabolism; D009414:Nerve Growth Factors / Q000235:genetics / Q000502:physiology*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism; D017475:Receptors, Nerve Growth Factor / Q000378:metabolism*; D014158:Transcription, Genetic / Q000235:genetics
D019208:Brain-Derived Neurotrophic Factor; D009414:Nerve Growth Factors; D012333:RNA, Messenger; D017475:Receptors, Nerve Growth Factor; D018995:Myosin Heavy Chains