Muscle Cell Growth

Nutritional and hormonal control of skeletal-muscle cell growth and differentiation

“…Glucocorticoids appear to have few direct effects on muscle cell proliferation and differentiation, although there has been one report of the synthetic glucocorticoid dexamethasone inhibiting differentiation of L8 myoblasts (Schonberg et al 1981). Dexamethasone, however, has been shown to consistently enhance the mitogenic effects of IGF-I (for review, see Harper & Buttery, 1995;Dodson et al 1996), via increases in the IGF-1R signalling pathway (Giorgino & Smith, 1995).…”

“…EGF also enhances differentiation, as measured by specific activity of the marker enzyme creatine kinase (Harper & Buttery, 1995 The fibroblast growth factors (FGF; acidic and basic) have been shown to stimulate proliferation (Dodson et al 1996), but to inhibit differentiation of muscle cells (Lathrop et al 1985). Transforming growth factor (TGF)-B, which has many isoforms, has been shown to have variable effects on proliferation, dependent on whether serum or other growth factors are present in the culture medium (Cook et al 1993), but it has been shown to consistently inhibit differentiation.…”

“…Thus, factors such as EGF, P-adrenergic agonists, insulin and the IGF have all been shown to increase protein synthesis and to decrease protein breakdown in cultured muscle cells, whereas growth hormone (GH) was found to have no effect, and dexamethasone had variable effects on protein synthesis, but increased protein breakdown (for review, see Harper & Buttery, 1992).…”

“…Epidermal growth factor (EGF) and related peptides all bind to a common receptor, and stimulate the growth of normal muscle cells (see Blachowski et al Harper & Buttery, 1995). EGF also enhances differentiation, as measured by specific activity of the marker enzyme creatine kinase (Harper & Buttery, 1995 The fibroblast growth factors (FGF; acidic and basic) have been shown to stimulate proliferation (Dodson et al 1996), but to inhibit differentiation of muscle cells (Lathrop et al 1985).…”

“…However, this does not imply that the muscle precursor cells cease to grow at this stage, as the DNA content continues to increase until the animal approaches its mature size. Extra nuclei are recruited into muscle fibres from mononucleate myogenic cells known as satellite cells, which are enclosed beneath the basement membrane of the muscle fibres (see Harper & Buttery, 1992). Muscle cell differentiation, the process whereby mononucleate myoblasts become postmitotic and fuse into multinucleate myotubes, therefore takes place during the late gestation and neonatal periods, with differentiation in the neonatal period involving the fusion of satellite cells with the existing muscle fibres.…”