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A murine model of neurofibromatosis type 1 tibial pseudarthrosis featuring proliferative fibrous tissue and osteoclast‐like cells
Author(s) -
ElHoss Jad,
Sullivan Kate,
Cheng Tegan,
Yu Nicole YC,
Bobyn Justin D,
Peacock Lauren,
Mikulec Kathy,
Baldock Paul,
Alexander Ian E,
Schindeler Aaron,
Little David G
Publication year - 2012
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1002/jbmr.528
Subject(s) - neurofibromatosis , neurofibromin 1 , osteoclast , bromodeoxyuridine , bone healing , tartrate resistant acid phosphatase , bone marrow , null cell , biology , pathology , medicine , immunohistochemistry , cell culture , in vitro , anatomy , genetics
Neurofibromatosis type 1 (NF1) is a common genetic condition caused by mutations in the NF1 gene. Patients often suffer from tissue‐specific lesions associated with local double‐inactivation of NF1 . In this study, we generated a novel fracture model to investigate the mechanism underlying congenital pseudarthrosis of the tibia (CPT) associated with NF1. We used a Cre‐expressing adenovirus (AdCre) to inactivate Nf1 in vitro in cultured osteoprogenitors and osteoblasts, and in vivo in the fracture callus of Nf1 flox/flox and Nf1 flox/− mice. The effects of the presence of Nf1 null cells were extensively examined. Cultured Nf1 null ‐committed osteoprogenitors from neonatal calvaria failed to differentiate and express mature osteoblastic markers, even with recombinant bone morphogenetic protein‐2 (rhBMP‐2) treatment. Similarly, Nf1 null ‐inducible osteoprogenitors obtained from Nf1 MyoD nullmouse muscle were also unresponsive to rhBMP‐2. In both closed and open fracture models in Nf1 flox/flox and Nf1 flox/− mice, local AdCre injection significantly impaired bone healing, with fracture union being <50% that of wild type controls. No significant difference was seen between Nf1 flox/flox and Nf1 flox/− mice. Histological analyses showed invasion of the Nf1 null fractures by fibrous and highly proliferative tissue. Mean amounts of fibrous tissue were increased upward of 10‐fold in Nf1 null fractures and bromodeoxyuridine (BrdU) staining in closed fractures showed increased numbers of proliferating cells. In Nf1 null fractures, tartrate‐resistant acid phosphatase–positive (TRAP+) cells were frequently observed within the fibrous tissue, not lining a bone surface. In summary, we report that local Nf1 deletion in a fracture callus is sufficient to impair bony union and recapitulate histological features of clinical CPT. Cell culture findings support the concept that Nf1 double inactivation impairs early osteoblastic differentiation. This model provides valuable insight into the pathobiology of the disease, and will be helpful for trialing therapeutic compounds. © 2012 American Society for Bone and Mineral Research