title: Hyperactive Ras/MAPK signaling is critical for tibial nonunion fracture in neurofibromin-deficient mice.
abstract: Neurofibromatosis type 1 (NF1) is a common genetic disorder affecting 1 in 3500 individuals. Patients with NF1 are predisposed to debilitating skeletal manifestations, including osteopenia/osteoporosis and long bone pseudarthrosis (nonunion fracture). Hyperactivation of the Ras/mitogen-activated protein kinase (MAPK) pathway in NF1 is known to underlie aberrant proliferation and differentiation in cell lineages, including osteoclast progenitors and mesenchymal stem cells (MSCs) also known as osteoblast progenitors (pro-OBLs). Our current study demonstrates the hyper Ras/MAPK as a critical pathway underlying the pathogenesis of NF1-associated fracture repair deficits. Nf1-deficient pro-OBLs exhibit Ras/MAPK hyperactivation. Introduction of the NF1 GTPase activating-related domain (NF1 GAP-related domain) in vitro is sufficient to rescue hyper Ras activity and enhance osteoblast (OBL) differentiation in Nf1(-/-) pro-OBLs and NF1 human (h) MSCs cultured from NF1 patients with skeletal abnormalities, including pseudarthrosis or scoliosis. Pharmacologic inhibition of mitogen-activated protein kinase kinase (MEK) signaling with PD98059 partially rescues aberrant Erk activation while enhancing OBL differentiation and expression of OBL markers, osterix and osteocalcin, in Nf1-deficient murine pro-OBLs. Similarly, MEK inhibition enhances OBL differentiation of hMSCs. In addition, PD98059 rescues aberrant osteoclast maturation in Nf1 haploinsufficient bone marrow mononuclear cells (BMMNCs). Importantly, MEK inhibitor significantly improves fracture healing in an NF1 murine model, Col2.3Cre;Nf1(flox/-). Collectively, these data indicate the Ras/MAPK cascade as a critical pathway in the pathogenesis of bone loss and pseudarthrosis related to NF1 mutations. These studies provide evidence for targeting the MAPK pathway to improve bone mass and treat pseudarthrosis in NF1.
authors.affiliation: Departments of Pediatrics.
authors.forename: Richa
authors.initials: R
authors.lastname: Sharma
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Wu
authors.forename: Steven D
authors.initials: SD
authors.lastname: Rhodes
authors.forename: Shi
authors.initials: S
authors.lastname: Chen
authors.forename: Yongzheng
authors.initials: Y
authors.lastname: He
authors.forename: Jin
authors.initials: J
authors.lastname: Yuan
authors.forename: Jiliang
authors.initials: J
authors.lastname: Li
authors.forename: Xianlin
authors.initials: X
authors.lastname: Yang
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Li
authors.forename: Li
authors.initials: L
authors.lastname: Jiang
authors.forename: Edward T
authors.initials: ET
authors.lastname: Kim
authors.forename: David A
authors.initials: DA
authors.lastname: Stevenson
authors.forename: David
authors.initials: D
authors.lastname: Viskochil
authors.forename: Mingjiang
authors.initials: M
authors.lastname: Xu
authors.forename: Feng-Chun
authors.initials: FC
authors.lastname: Yang
mesh_terms: D000818:Animals; D019070:Cell Lineage; D002478:Cells, Cultured; D004195:Disease Models, Animal; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009456:Neurofibromatosis 1 / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D025542:Neurofibromin 1 / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D010006:Osteoblasts / Q000502:physiology; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011542:Pseudarthrosis / Q000188:drug therapy / Q000235:genetics / Q000473:pathology / Q000503:physiopathology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013234:Stem Cells / Q000187:drug effects / Q000378:metabolism; D013978:Tibial Fractures / Q000503:physiopathology; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D005419:Flavonoids; D025542:Neurofibromin 1; D047428:Protein Kinase Inhibitors; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one