title: Hyperactive transforming growth factor-β1 signaling potentiates skeletal defects in a neurofibromatosis type 1 mouse model.
abstract: Dysregulated transforming growth factor beta (TGF-β) signaling is associated with a spectrum of osseous defects as seen in Loeys-Dietz syndrome, Marfan syndrome, and Camurati-Engelmann disease. Intriguingly, neurofibromatosis type 1 (NF1) patients exhibit many of these characteristic skeletal features, including kyphoscoliosis, osteoporosis, tibial dysplasia, and pseudarthrosis; however, the molecular mechanisms mediating these phenotypes remain unclear. Here, we provide genetic and pharmacologic evidence that hyperactive TGF-β1 signaling pivotally underpins osseous defects in Nf1(flox/-) ;Col2.3Cre mice, a model which closely recapitulates the skeletal abnormalities found in the human disease. Compared to controls, we show that serum TGF-β1 levels are fivefold to sixfold increased both in Nf1(flox/-) ;Col2.3Cre mice and in a cohort of NF1 patients. Nf1-deficient osteoblasts, the principal source of TGF-β1 in bone, overexpress TGF-β1 in a gene dosage-dependent fashion. Moreover, Nf1-deficient osteoblasts and osteoclasts are hyperresponsive to TGF-β1 stimulation, potentiating osteoclast bone resorptive activity while inhibiting osteoblast differentiation. These cellular phenotypes are further accompanied by p21-Ras-dependent hyperactivation of the canonical TGF-β1-Smad pathway. Reexpression of the human, full-length neurofibromin guanosine triphosphatase (GTPase)-activating protein (GAP)-related domain (NF1 GRD) in primary Nf1-deficient osteoblast progenitors, attenuated TGF-β1 expression levels and reduced Smad phosphorylation in response to TGF-β1 stimulation. As an in vivo proof of principle, we demonstrate that administration of the TGF-β receptor 1 (TβRI) kinase inhibitor, SD-208, can rescue bone mass deficits and prevent tibial fracture nonunion in Nf1(flox/-) ;Col2.3Cre mice. In sum, these data demonstrate a pivotal role for hyperactive TGF-β1 signaling in the pathogenesis of NF1-associated osteoporosis and pseudarthrosis, thus implicating the TGF-β signaling pathway as a potential therapeutic target in the treatment of NF1 osseous defects that are refractory to current therapies.
authors.affiliation: Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA; Herman B. Wells Center for Pediatric Research, Indiana University School of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Rhodes
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Wu
authors.forename: Yongzheng
authors.initials: Y
authors.lastname: He
authors.forename: Shi
authors.initials: S
authors.lastname: Chen
authors.forename: Hao
authors.initials: H
authors.lastname: Yang
authors.forename: Karl W
authors.initials: KW
authors.lastname: Staser
authors.forename: Jiapeng
authors.initials: J
authors.lastname: Wang
authors.forename: Ping
authors.initials: P
authors.lastname: Zhang
authors.forename: Chang
authors.initials: C
authors.lastname: Jiang
authors.forename: Hiroki
authors.initials: H
authors.lastname: Yokota
authors.forename: Ruizhi
authors.initials: R
authors.lastname: Dong
authors.forename: Xianghong
authors.initials: X
authors.lastname: Peng
authors.forename: Xianlin
authors.initials: X
authors.lastname: Yang
authors.forename: Sreemala
authors.initials: S
authors.lastname: Murthy
authors.forename: Mohamad
authors.initials: M
authors.lastname: Azhar
authors.forename: Khalid S
authors.initials: KS
authors.lastname: Mohammad
authors.forename: Mingjiang
authors.initials: M
authors.lastname: Xu
authors.forename: Theresa A
authors.initials: TA
authors.lastname: Guise
authors.forename: Feng-Chun
authors.initials: FC
authors.lastname: Yang
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000002:abnormalities* / Q000378:metabolism* / Q000473:pathology; D002454:Cell Differentiation; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004195:Disease Models, Animal; D018628:Gene Dosage; D057895:Haploinsufficiency; D006801:Humans; D019426:Integrases / Q000378:metabolism; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D059630:Mesenchymal Stem Cells / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D009456:Neurofibromatosis 1 / Q000378:metabolism* / Q000473:pathology*; D025542:Neurofibromin 1 / Q000172:deficiency / Q000235:genetics; D010006:Osteoblasts / Q000378:metabolism / Q000473:pathology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D015398:Signal Transduction; D051785:Smad Proteins / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism
chemical_list: D050759:Cyclin-Dependent Kinase Inhibitor p21; D025542:Neurofibromin 1; D018125:Receptors, Transforming Growth Factor beta; D051785:Smad Proteins; D053773:Transforming Growth Factor beta1; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; C045073:Cre recombinase; D019426:Integrases; D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9; D018631:ras Proteins
keywords: FRACTURE NONUNION; NEUROFIBROMATOSIS TYPE 1; OSTEOPOROSIS; SMAD; TGF-β; TRANSFORMING GROWTH FACTOR-BETA