title: Notch inhibits osteoblast differentiation and causes osteopenia.
abstract: Notch receptors are determinants of cell fate decisions. To define the role of Notch in the adult skeleton, we created transgenic mice overexpressing the Notch intracellular domain (NICD) under the control of the type I collagen promoter. First-generation transgenics were small and osteopenic. Bone histomorphometry revealed that NICD caused a decrease in bone volume, secondary to a reduction in trabecular number; osteoblast and osteoclast number were decreased. Low fertility of founder mice and lethality of young pups did not allow the complete establishment of transgenic lines. To characterize the effect of Notch overexpression in vitro, NICD was induced in osteoblasts and stromal cells from Rosa(notch) mice, in which a STOP cassette flanked by lox(P) sites is upstream of NICD, by transduction with an adenoviral vector expressing Cre recombinase (Cre) under the control of the cytomegalovirus (CMV) promoter (Ad-CMV-Cre). NICD impaired osteoblastogenesis and inhibited Wnt/beta-catenin signaling. To determine the effects of notch1 deletion in vivo, mice in which notch1 was flanked by lox(P) sequences (notch1(loxP/loxP)) were mated with mice expressing Cre recombinase under the control of the osteocalcin promoter. Conditional null notch1 mice had no obvious skeletal phenotype, possibly because of rescue by notch2; however, 1-month-old females exhibited a modest increase in osteoclast surface and eroded surface. Osteoblasts from notch1(loxP/loxP) mice, transduced with Ad-CMV-Cre and transfected with Notch2 small interfering RNA, displayed increased alkaline phosphatase activity. In conclusion, Notch signaling in osteoblasts causes osteopenia and impairs osteo-blastogenesis by inhibiting the Wnt/beta-catenin pathway.
authors.affiliation: Department of Research, Saint Francis Hospital and Medical Center, 114 Woodland Street, Hartford, Connecticut 06105-1299, USA.
authors.forename: Stefano
authors.initials: S
authors.lastname: Zanotti
authors.forename: Anna
authors.initials: A
authors.lastname: Smerdel-Ramoya
authors.forename: Lisa
authors.initials: L
authors.lastname: Stadmeyer
authors.forename: Deena
authors.initials: D
authors.lastname: Durant
authors.forename: Freddy
authors.initials: F
authors.lastname: Radtke
authors.forename: Ernesto
authors.initials: E
authors.lastname: Canalis
mesh_terms: D000818:Animals; D001851:Bone Diseases, Metabolic / Q000235:genetics*; D002454:Cell Differentiation / Q000235:genetics*; D002478:Cells, Cultured; D024042:Collagen Type I / Q000235:genetics; D005260:Female; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010006:Osteoblasts / Q000378:metabolism / Q000502:physiology*; D010012:Osteogenesis / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D051881:Receptor, Notch1 / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics; D014162:Transfection; D051153:Wnt Proteins / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism
chemical_list: D024042:Collagen Type I; C497762:Notch1 protein, mouse; D051881:Receptor, Notch1; D051153:Wnt Proteins; D051176:beta Catenin