title: A high-content, high-throughput siRNA screen identifies cyclin D2 as a potent regulator of muscle progenitor cell fusion and a target to enhance muscle regeneration.
abstract: Cell-mediated regenerative approaches using muscle progenitor cells hold promises for the treatment of many forms of muscle disorders. Their applicability in the clinic, however, is hindered by the low levels of regeneration obtained after transplantation and the large number of cells required to achieve an effect. To better understand the mechanisms that regulate the temporal switch of replicating muscle progenitor cells into terminally differentiated cells and to develop new strategies that could enhance muscle regeneration, we have developed and performed a high-throughput screening (HTS) capable of identifying genes that play active roles during myogenesis. Secondary and tertiary screens were used to confirm the effects of RNAi in vitro and in vivo and to select for candidate hits that significantly increase regeneration into skeletal muscles. Downregulation of cyclin D2 (CCND2) was shown to dramatically enhance myogenic differentiation of muscle progenitor cells and to induce a robust regeneration after cell transplantation into skeletal muscles of dystrophin-deficient mice. Protein interaction network and pathway analysis revealed that CCND2 directly interacts with the cyclin-dependent kinase Cdk4 to inhibit phosphorylation of the retinoblastoma protein (pRb), thus blocking the activation of the myogenic switch during fusion. These studies identify CCND2 as a new key regulator of terminal differentiation in muscle progenitor cells and open new possibilities for the treatment of many forms of muscle disorders characterized by impaired regeneration and loss of muscle mass.
authors.affiliation: Department of Neurology, David Geffen School of Medicine, University of California Los Angeles, 710 Westwood Plaza, Los Angeles, CA 90095, USA.
authors.forename: Michael V
authors.initials: MV
authors.lastname: Khanjyan
authors.forename: Jonathan
authors.initials: J
authors.lastname: Yang
authors.forename: Refik
authors.initials: R
authors.lastname: Kayali
authors.forename: Thomas
authors.initials: T
authors.lastname: Caldwell
authors.forename: Carmen
authors.initials: C
authors.lastname: Bertoni
mesh_terms: D000818:Animals; D002459:Cell Fusion; D002478:Cells, Cultured; D056742:Cyclin D2 / Q000235:genetics* / Q000378:metabolism*; D051358:Cyclin-Dependent Kinase 4 / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D024510:Muscle Development / Q000235:genetics*; D020388:Muscular Dystrophy, Duchenne / Q000235:genetics / Q000378:metabolism; D017570:MyoD Protein / Q000235:genetics / Q000378:metabolism; D032448:Myoblasts, Skeletal / Q000502:physiology* / Q000637:transplantation; D051787:Myogenic Regulatory Factor 5 / Q000235:genetics / Q000378:metabolism; D018008:Myogenin / Q000235:genetics / Q000378:metabolism; D025941:Protein Interaction Mapping; D034741:RNA, Small Interfering; D012038:Regeneration; D016160:Retinoblastoma Protein / Q000378:metabolism
chemical_list: C486196:Ccnd2 protein, mouse; D056742:Cyclin D2; C497418:Myf5 protein, mouse; D017570:MyoD Protein; C057363:MyoD1 myogenic differentiation protein; C503801:Myog protein, mouse; D051787:Myogenic Regulatory Factor 5; D018008:Myogenin; D034741:RNA, Small Interfering; D016160:Retinoblastoma Protein; C495902:Cdk4 protein, mouse; D051358:Cyclin-Dependent Kinase 4