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: Steven D Rhodes, Xiaohua Wu, Yongzheng He, Shi Chen, Hao Yang, Karl W Staser, Jiapeng Wang, Ping Zhang, Chang Jiang, Hiroki Yokota, Ruizhi Dong, Xianghong Peng, Xianlin Yang, Sreemala Murthy, Mohamad Azhar, Khalid S Mohammad, Mingjiang Xu, Theresa A Guise, Feng-Chun Yang
• Journal: Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research (J Bone Miner Res) Vol. 28 Issue 12 Pg. 2476-89 (Dec 2013) ISSN: 1523-4681 [Electronic] United States
• PMID: 23703870 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)
• Copyright: © 2013 American Society for Bone and Mineral Research.

Chemical References

• Cyclin-Dependent Kinase Inhibitor p21
• Neurofibromin 1
• Receptors, Transforming Growth Factor beta
• Smad Proteins
• Transforming Growth Factor beta1
• Protein Serine-Threonine Kinases
• Receptor, Transforming Growth Factor-beta Type I
• Cre recombinase
• Integrases
• Matrix Metalloproteinase 2
• Matrix Metalloproteinase 9
• ras Proteins

Topics

• Animals
• Bone and Bones (abnormalities, metabolism, pathology)
• Cell Differentiation
• Cyclin-Dependent Kinase Inhibitor p21 (metabolism)
• Disease Models, Animal
• Gene Dosage
• Haploinsufficiency
• Humans
• Integrases (metabolism)
• Matrix Metalloproteinase 2 (metabolism)
• Matrix Metalloproteinase 9 (metabolism)
• Mesenchymal Stem Cells (metabolism)
• Mice
• Mice, Transgenic
• Models, Biological
• Neurofibromatosis 1 (metabolism, pathology)
• Neurofibromin 1 (deficiency, genetics)
• Osteoblasts (metabolism, pathology)
• Protein Serine-Threonine Kinases (metabolism)
• Receptor, Transforming Growth Factor-beta Type I
• Receptors, Transforming Growth Factor beta (metabolism)
• Signal Transduction
• Smad Proteins (metabolism)
• Transforming Growth Factor beta1 (metabolism)
• ras Proteins (metabolism)