Publication Date
8-1-2022
Journal
Journal of Bone and Mineral Research
DOI
10.1002/jbmr.4633
PMID
35690920
PMCID
PMC9378557
PubMedCentral® Posted Date
8-1-2023
PubMedCentral® Full Text Version
Author MSS
Published Open-Access
yes
Keywords
Animals, Bone Density, Bone Matrix, Bone and Bones, Disease Models, Animal, Female, Fractures, Bone, Male, Mice, Neurofibromatosis 1, Tibia, bone quality, bound water, Raman spectroscopy, genetic disease, micro-computed tomography, nuclear magnetic resonance, mechanical testing
Abstract
Three-to-four percent of children with neurofibromatosis type 1 (NF1) present with unilateral tibia bowing, fracture, and recalcitrant healing. Alkaline phosphatase enzyme therapy prevented poor bone mineralization and poor mechanical properties in mouse models of NF1 skeletal dysplasia; but transition to clinical trials is hampered by the lack of a technique that i) identifies NF1 patients at risk of tibia bowing and fracture making them eligible for trial enrollment and ii) monitors treatment effects on matrix characteristics related to bone strength. Therefore, we assessed the ability of matrix-sensitive techniques to provide characteristics that differentiate between cortical bone from mice characterized by postnatal loss of Nf1 in Osx-creTet-Off;Nf1flox/flox osteoprogenitors (cKO) and from wild-type (WT) mice. Following euthanasia at two timepoints of bone disease progression, femur and tibia were harvested from both genotypes (n≥8/age/sex/genotype). A reduction in the mid-diaphysis ultimate force during three-point bending at 20-wks confirmed deleterious changes in bone induced by Nf1 deficiency, regardless of sex. Pooling females and males, low bound water (BW) and low cortical volumetric bone mineral density (Ct.vBMD) were the most accurate outcomes in distinguishing cKO from WT femurs with accuracy improving with age. Ct.vBMD and the average unloading slope (Avg-US) from cyclic reference point indentation tests were the most sensitive in differentiating WT from cKO tibiae. Mineral-to-matrix ratio and carbonate substitution from Raman spectroscopy were not good classifiers. However, when combined with Ct.vBMD and BW (femur), they helped predict bending strength. Nf1 deficiency in osteoprogenitors negatively affected bone micro-structure and matrix quality with deficits in properties becoming more pronounced with duration of Nf1 deficiency. Clinically measurable without ionizing radiation, BW and Avg-US are sensitive to deleterious changes in bone matrix in a preclinical model of NF1 bone dysplasia and require further clinical investigation as potential indicators of an onset of bone weakness in children with NF1.