Hyperactivation of p21ras and PI3K cooperate to alter murine and human neurofibromatosis type 1–haploinsufficient osteoclast functions
Feng-Chun Yang, … , David A. Ingram, D. Wade Clapp
Feng-Chun Yang, … , David A. Ingram, D. Wade Clapp
Published November 1, 2006
Citation Information: J Clin Invest. 2006;116(11):2880-2891. https://doi.org/10.1172/JCI29092.
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Research Article Bone Biology

Hyperactivation of p21ras and PI3K cooperate to alter murine and human neurofibromatosis type 1–haploinsufficient osteoclast functions

Abstract

Individuals with neurofibromatosis type 1 (NF1) have a high incidence of osteoporosis and osteopenia. However, understanding of the cellular and molecular basis of these sequelae is incomplete. Osteoclasts are specialized myeloid cells that are the principal bone-resorbing cells of the skeleton. We found that Nf1+/– mice contain elevated numbers of multinucleated osteoclasts. Both osteoclasts and osteoclast progenitors from Nf1+/– mice were hyperresponsive to limiting concentrations of M-CSF and receptor activator of NF-κB ligand (RANKL) levels. M-CSF–stimulated p21ras-GTP and Akt phosphorylation was elevated in Nf1+/– osteoclasts associated with gains of function in survival, proliferation, migration, adhesion, and lytic activity. These gains of function are associated with more severe bone loss following ovariectomy as compared with that in syngeneic WT mice. Intercrossing Nf1+/– mice and mice deficient in class 1A PI3K (p85α) restored elevated PI3K activity and Nf1+/– osteoclast functions to WT levels. Furthermore, in vitro–differentiated osteoclasts from NF1 patients also displayed elevated Ras/PI3K activity and increased lytic activity analogous to those in murine Nf1+/– osteoclasts. Collectively, our results identify a what we believe to be a novel cellular and biochemical NF1-haploinsufficient phenotype in osteoclasts that has potential implications for the pathogenesis of NF1 bone disease.

Authors

Feng-Chun Yang, Shi Chen, Alexander G. Robling, Xijie Yu, Todd D. Nebesio, Jincheng Yan, Trent Morgan, Xiaohong Li, Jin Yuan, Janet Hock, David A. Ingram, D. Wade Clapp

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Figure 1

Nf1+/– mice have increased numbers of osteoclast progenitors and osteoclasts in vivo.

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Nf1+/– mice have increased numbers of osteoclast progenitors and osteoc...
Data in B, C, and E represent the mean ± SEM of 5 independent experiments. (A) Clonogenic assays were established to determine the number of CFU-Ms per femur. Representative TRAP– CFU-M (left panel) and TRAP+ CFU-M (right panel). (B) Total CFU-Ms per femur from Nf1+/– or WT mice. *P < 0.01, Nf1+/– CFU-Ms versus WT CFU-Ms by Student’s t test. (C) TRAP+ CFU-Ms per femur from mice of the indicated genotypes. *P < 0.01, Nf1+/– versus WT. (D) Representative photomicrographs (magnification, ×10) of WT and Nf1+/– distal femoral metaphyses following TRAP staining. Arrows indicate selected osteoclasts. (E) Average size of osteoclasts from Nf1+/– and WT mice. Ten high-power fields per experimental mouse were scored. **P < 0.05, Nf1+/– versus WT osteoclasts.