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.
View: Text | PDF
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

×

Figure 4

Effect of heterozygosity of Nf1 on osteoclast haptotaxis and F-actin content in response to recombinant murine M-CSF.

Options: View larger image (or click on image) Download as PowerPoint
Effect of heterozygosity of Nf1 on osteoclast haptotaxis and F-actin con...
(A) Haptotaxis of WT and Nf1+/– osteoclasts in response to M-CSF. A representative photomicrograph (magnification, ×20) from 1 of 5 experiments. (B) Quantitative evaluation of migration in response to M-CSF. Results represent the mean ± SEM of 5 experiments. *P < 0.01, Nf1+/– versus WT by Student’s t test. (C) Photomicrographs (magnification, ×10) of M-CSF–stimulated osteoclast adhesion to αVβ3. Genotypes and length of adhesion are indicated. (D) Quantitative evaluation (mean ± SEM; n = 5) of osteoclast adhesion 10–60 minutes following incubation with M-CSF. Genotypes and length of adhesion are indicated. *P < 0.01, Nf1+/– versus WT osteoclasts by Student’s t test. (E) M-CSF–mediated F-actin polymerization. Osteoclasts were stimulated with 10 ng/ml M-CSF and fixed at the time points indicated. WT and Nf1+/– cells were examined in triplicate. Results are expressed as mean channel fluorescence (MCF). **P < 0.001, Nf1+/– osteoclasts versus WT osteoclasts by Student’s t test.