Role of genetic background in determining phenotypic severity throughout postnatal development and at peak bone mass in Col1a2 deficient mice (oim)

Abstract

Osteogenesis imperfecta (OI) is a genetically and clinically heterogeneous disease characterized by extreme bone fragility. Although fracture numbers tend to decrease post-puberty, OI patients can exhibit significant variation in clinical outcome, even among related individuals harboring the same mutation. OI most frequently results from mutations in type I collagen genes, yet how genetic background impacts phenotypic outcome remains unclear. Therefore, we analyzed the phenotypic severity of a known proα2(I) collagen gene defect (oim) on two genetic backgrounds (congenic C57BL/6J and outbred B6C3Fe) throughout postnatal development to discern the phenotypic contributions of the Col1a2 locus relative to the contribution of the genetic background.To this end, femora and tibiae were isolated from wildtype (Wt) and homozygous (oim/oim) mice of each strain at 1, 2 and 4 months of age. Femoral geometry was determined via µCT prior to torsional loading to failure to assess bone structural and material biomechanical properties. Changes in mineral composition, collagen content and bone turnover were determined using neutron activation analyses, hydroxyproline content and serum pyridinoline crosslinks.Corresponding Author: Charlotte L. Phillips, Ph.D., Associate Professor, Departments of Biochemistry and Child Health, University of Missouri-Columbia, 1 Hospital Dr., M743 Medical Sciences Bldg., Columbia, MO 65212, Phone: (573) 882-5122, Fax: (573) 884-4597, Email: PhillipsCL@missouri.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. µCT analysis demonstrated genotype-, strain-and age-associated changes in femoral geometry as well as a marked decrease in the amount of bone in oim/oim mice of both strains. Oim/oim mice of both strains, as well as C57BL/6J (B6) mice of all genotypes, had reduced femoral biomechanical strength properties compared to Wt at all ages, although they improved with age. Mineral levels of fluoride, magnesium and sodium were associated with biomechanical strength properties in both strains and all genotypes at all ages. Oim/oim animals also had reduced collagen content as compared to Wt at all ages. Serum pyridinoline crosslinks were highest at two months of age, regardless of strain or genotype. NIH Public AccessStrain differences in bone parameters exist throughout development, implicating a role for genetic background in determining biomechanical strength. Age-associated improvements indicate that oim/ oim animals partially compensate for their weaker bone material, but never attain Wt levels. These studies indicate the importance of genetic back...

Myostatin deficiency partially rescues the bone phenotype of osteogenesis imperfecta model mice

“…To evaluate bone biomechanical integrity, femora from Wt, +/ mstn, +/mstn +/oim, and +/oim mice were analyzed by torsional loading to failure [21]. The torsional ultimate strength (T max ), a whole bone property measuring the maximum force required to break the bone, of +/mstn +/oim femora displayed a 25 % improvement relative to +/oim femora although the improvement did not reach significance (Fig.…”

“…Torsional ultimate strength (T max , Nmm), strain energy to failure (U, Nmm), and stiffness (torsional stiffness, Nmm/rad) are whole bone parameters reflecting the contributions of both the bone geometry and the bone material properties. The bone material properties, tensile strength (Su, N/mm 2 ), and shear modulus of elasticity (N/mm 2 ) are independent of bone size and shape [21].…”

“…Each femora was then subjected to torsional loading to failure analyses to determine the mechanical properties of the whole bone and the bone material using the TA-HDi testing machine (Stable Micro Systems, Surrey, UK) as previously described [21]. Applied torque T (Nmm) was determined and evaluated as a function of relative angular displacement θ (degrees) (Fig.…”

“…The geometric parameters of the right femora were determined by μCT analyses (MicroCAT II, Siemens Medical), and the image slices reconstructed using the Amira 5.3.3 software package (Mercury Computer Systems/TGS, Chelmsford, MA) to give a cubic voxel dimension of 0.083 mm 3 as previously described [21]. Each femora was then subjected to torsional loading to failure analyses to determine the mechanical properties of the whole bone and the bone material using the TA-HDi testing machine (Stable Micro Systems, Surrey, UK) as previously described [21].…”

Decreasing maternal myostatin programs adult offspring bone strength in a mouse model of osteogenesis imperfecta

“…Collagen content was determined by an indirect assay quantifying hydroxyproline, as described in SI Methods and previously (36). Tibial cortical bone cross-sections were evaluated by Raman spectroscopy, as described in SI Methods.…”