title: Altered signal transduction pathways and induction of autophagy in human myotonic dystrophy type 1 myoblasts.
abstract: Congenital myotonic dystrophy type 1 (CDM1) affects patients from birth and is associated with mental retardation and impaired muscle development. CDM1 patients carry 1000-3000 CTG repeats in the DMPK gene and display defective skeletal muscles differentiation, resulting in reduced size of myotubes and decreased number of satellite cells. In this study, human myoblasts in culture deriving from control and DM1 embryos (3200 CTG repeats) were analyzed using both a biochemical and electron microscopic approach, in order to provide new insights into the molecular mechanisms underlying such alteration. Interestingly, electron microscopy analysis showed not only ultrastructural features of abnormal differentiation but also revealed the presence of autophagic vacuoles in DM1 myoblasts not undergoing differentiation. In accordance with the electron microscopic findings, the autophagic markers LC3 and ATG5, but not apoptotic markers, were significantly up regulated in DM1 myoblasts after differentiating medium addition. The induction of autophagic processes in DM1 myoblasts was concomitant to p53 over-expression and inhibition of the mTOR-S6K1 pathway, causatively involved in autophagy. Moreover biochemical alterations of the two main signal transduction pathways involved in differentiation were observed in DM1 myoblasts, in particular decreased activation of p38MAPK and persistent activation of the MEK-ERK pathway. This work, while demonstrating that major signaling pathways regulating myoblasts differentiation are profoundly deranged in DM1 myoblasts, for the first time provides evidence of autophagy induction, possibly mediated by p53 activation in response to metabolic stress which might contribute to the dystrophic alterations observed in the muscles of congenital DM1 patients.
authors.affiliation: Istituto di Fisiologia Clinica, CNR, Pisa, Italy.
authors.forename: Pascale
authors.initials: P
authors.lastname: Beffy
authors.forename: Renata
authors.initials: R
authors.lastname: Del Carratore
authors.forename: Matilde
authors.initials: M
authors.lastname: Masini
authors.forename: Denis
authors.initials: D
authors.lastname: Furling
authors.forename: Jack
authors.initials: J
authors.lastname: Puymirat
authors.forename: Pellegrino
authors.initials: P
authors.lastname: Masiello
authors.forename: Marcella
authors.initials: M
authors.lastname: Simili
mesh_terms: D001343:Autophagy / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000096:biosynthesis; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis; D006801:Humans; D015151:Immunoblotting; D020935:MAP Kinase Signaling System; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D017570:MyoD Protein / Q000378:metabolism; D032446:Myoblasts / Q000378:metabolism / Q000473:pathology*; D018008:Myogenin / Q000378:metabolism; D009223:Myotonic Dystrophy / Q000378:metabolism / Q000473:pathology; D015398:Signal Transduction
chemical_list: C493956:CDKN1A protein, human; C109198:CIB1 protein, human; D002135:Calcium-Binding Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D017570:MyoD Protein; C057363:MyoD1 myogenic differentiation protein; D018008:Myogenin; D020928:Mitogen-Activated Protein Kinases