Differential signalling mechanisms predisposing primary human skeletal muscle cells to altered proliferation and differentiation: roles of IGF-I and TNFalpha.
To gain a clearer insight into the mechanisms of skeletal muscle cell growth, differentiation and maintenance, we have developed a primary adult human skeletal muscle cell model. Cells were cultured from biopsies of rectus muscle from the anterior abdominal wall of patients undergoing elective surgery. Under differentiating conditions, all cultures formed myotubes, irrespective of initial myoblast number. Stimulation with both IGF-I and tumour necrosis factor alpha (TNFalpha) increased cellular proliferation but while IGF-I subsequently increased myoblast differentiation, via both hyperplasia and hypertrophy, TNFalpha inhibited the initiation of differentiation, but did not induce apoptosis. Addition of IGF-I stimulated both the MAP kinase and the phosphatidylinositide 3-kinase (PI 3-kinase) signalling pathways while treatment with TNFalpha preferentially led to MAP kinase activation although with a very different profile of activation compared to IGF-I. Data using the MEK inhibitor UO126 showed MAP kinase activity is not only needed for cellular proliferation but is also necessary for both the initiation and the progression of primary human myoblast differentiation. The PI 3-kinase pathway is also involved in differentiation, but activation of this pathway could not relieve inhibition of differentiation by TNFalpha or UO126. Our results show that the controlled temporal and amplitude of activation of multiple signalling pathways is needed for successful myoblast differentiation.
Division of Surgery, University of Bristol, Bristol Royal Infirmary, Bristol, BS2 8HW, UK. foulstone@bristol.ac.uk
Emily J
EJ
Foulstone
Camille
C
Huser
Anna L
AL
Crown
Jeff M P
JM
Holly
Claire E H
CE
Stewart
D000328:Adult; D000368:Aged; D017209:Apoptosis; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D003402:Creatine Kinase / Q000378:metabolism; D005260:Female; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology* / Q000502:physiology; D020935:MAP Kinase Signaling System; D008297:Male; D008875:Middle Aged; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D018485:Muscle Fibers, Skeletal / Q000166:cytology; D018482:Muscle, Skeletal / Q000166:cytology* / Q000187:drug effects; D032448:Myoblasts, Skeletal / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D009369:Neoplasms / Q000473:pathology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology* / Q000502:physiology
D000081082:Phosphoinositide-3 Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D014409:Tumor Necrosis Factor-alpha; D007334:Insulin-Like Growth Factor I; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D038362:Glycogen Synthase Kinase 3; D003402:Creatine Kinase