An Evaluation of Otopathology in the MOV-13 Transgenic Mutant Mouse a

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72482/1/j.1749-6632.1991.tb19595.x.pd

Generalized Connective Tissue Disease in Crtap-/- Mouse

Mutations in CRTAP (coding for cartilage-associated protein), LEPRE1 (coding for prolyl 3-hydroxylase 1 [P3H1]) or PPIB (coding for Cyclophilin B [CYPB]) cause recessive forms of osteogenesis imperfecta and loss or decrease of type I collagen prolyl 3-hydroxylation. A comprehensive analysis of the phenotype of the Crtap-/- mice revealed multiple abnormalities of connective tissue, including in the lungs, kidneys, and skin, consistent with systemic dysregulation of collagen homeostasis within the extracellular matrix. Both Crtap-/- lung and kidney glomeruli showed increased cellular proliferation. Histologically, the lungs showed increased alveolar spacing, while the kidneys showed evidence of segmental glomerulosclerosis, with abnormal collagen deposition. The Crtap-/- skin had decreased mechanical integrity. In addition to the expected loss of proline 986 3-hydroxylation in α1(I) and α1(II) chains, there was also loss of 3Hyp at proline 986 in α2(V) chains. In contrast, at two of the known 3Hyp sites in α1(IV) chains from Crtap-/- kidneys there were normal levels of 3-hydroxylation. On a cellular level, loss of CRTAP in human OI fibroblasts led to a secondary loss of P3H1, and vice versa. These data suggest that both CRTAP and P3H1 are required to maintain a stable complex that 3-hydroxylates canonical proline sites within clade A (types I, II, and V) collagen chains. Loss of this activity leads to a multi-systemic connective tissue disease that affects bone, cartilage, lung, kidney, and skin

Radiographic analysis of zebrafish skeletal defects

AbstractSystematic identification of skeletal dysplasias in model vertebrates provides insight into the pathogenesis of human skeletal disorders and can aid in the identification of orthologous human genes. We are undertaking a mutagenesis screen for skeletal dysplasias in adult zebrafish, using radiography to detect abnormalities in skeletal anatomy and bone morphology. We have isolated chihuahua, a dominant mutation causing a general defect in bone growth. Heterozygous chihuahua fish have phenotypic similarities to human osteogenesis imperfecta, a skeletal dysplasia caused by mutations in the type I collagen genes. Mapping and molecular characterization of the chihuahua mutation indicates that the defect resides in the gene encoding the collagen I(α1) chain. Thus, chihuahua accurately models osteogenesis imperfecta at the biologic and molecular levels, and will prove an important resource for studies on the disease pathophysiology. Radiography is a practical screening tool to detect subtle skeletal abnormalities in the adult zebrafish. The identification of chihuahua demonstrates that mutant phenotypes analogous to human skeletal dysplasias will be discovered

Genetic randomization reveals functional relationships among morphologic and tissue-quality traits that contribute to bone strength and fragility

We examined femora from adult AXB/BXA recombinant inbred (RI) mouse strains to identify skeletal traits that are functionally related and to determine how functional interactions among these traits contribute to genetic variability in whole-bone stiffness, strength, and toughness. Randomization of A/J and C57BL/6J genomic regions resulted in each adult male and female RI strain building mechanically functional femora by assembling unique sets of morphologic and tissue-quality traits. A correlation analysis was conducted using the mean trait values for each RI strain. A third of the 66 correlations examined were significant, indicating that many bone traits covaried or were functionally related. Path analysis revealed important functional interactions among bone slenderness, cortical thickness, and tissue mineral density. The path coefficients describing these functional relations were similar for both sexes. The causal relationship among these three traits suggested that cellular processes during growth simultaneously regulate bone slenderness, cortical thickness, and tissue mineral density so that the combination of traits is sufficiently stiff and strong to satisfy daily loading demands. A disadvantage of these functional interactions was that increases in tissue mineral density also deleteriously affected tissue ductility. Consequently, slender bones with high mineral density may be stiff and strong but they are also brittle. Thus, genetically randomized mouse strains revealed a basic biological paradigm that allows for flexibility in building bones that are functional for daily activities but that creates preferred sets of traits under extreme loading conditions. Genetic or environmental perturbations that alter these functional interactions during growth would be expected to lead to loss of function and suboptimal adult bone quality

Mechanical and material property changes in bone with experimental diabetes: a murine model

Over 23 million people in the United States are plagued by diabetes mellitus. Studies have shown that those with diabetes have a higher occurrence of bone fractures than those without the disease, but risk factors associated with diabetes account for only a portion of these fractures (Schwartz 2003; Vestergaard 2006). This implies that there are properties of diabetic bones that account for this increase in fractures. Research has been performed on the bone mineral density (BMD) of those with and without diabetes. However, studying this singular property of bones does not fully explain the increase in bone fractures in the diabetic population. Additionally, this research has yielded inconclusive results: some studies show that diabetes leads to an increase in BMD while others show a decrease in this property (Krakauer et al. 1995; Retzepi \u26 Donos 2010). The objective of this study is to analyze the effect of experimental diabetes on bone properties in mice. This relationship is explored through analyzing different mouse strains to determine a potential genetic link, kidney removal to mimic the effects of nephropathy, and an LXR agonist to explore a potential diabetes treatment. We hypothesize that diabetes will negatively impact bone properties across multiple strains of mice, kidney removal will further degrade bone properties and the LXR agonist will improve some of the negative bone effects that diabetes causes. In general, STZ-induced diabetes was accompanied by decreases in physical and compositional bone properties in both strains of mice. Kidney removal and treatment with an LXR-agonist had little to no effects on these bone properties. Kidney removal was performed in skeletally mature mice; this old age may have contributed to the lack of effects. Similarly, the LXR agonist was administered over a short time period, and the detrimental effects from the diabetes were not able to be overcome. The data presented here provides evidence that experimentally-induced diabetes corresponds with a decrease in bone properties and nephropathy. While LXR agonists hold promise for mitigating bone property changes in diabetes, further analysis is required to determine their potential effects

Nell-1, a key Functional Mediator of Runx2, Partially Rescues Calvarial Defects in Runx2+/− Mice

Mesenchymal stem cell commitment to an osteoprogenitor lineage requires the activity of Runx2, a molecule implicated in the etiopathology of multiple congenital craniofacial anomalies. Through promoter analyses, we have recently identified a new direct transcriptional target of Runx2, Nell-1, a craniosynostosis (CS)–associated molecule with potent osteogenic properties. This study investigated the mechanistic and functional relationship between Nell-1 and Runx2 in regulating osteoblast differentiation. The results showed that spatiotemporal distribution and expression levels of Nell-1 correlated closely with those of endogenous Runx2 during craniofacial development. Phenotypically, cross-mating Nell-1 overexpression transgenic (CMV-Nell-1) mice with Runx2 haploinsufficient (Runx2+/−) mice partially rescued the calvarial defects in the cleidocranial dysplasia (CCD)–like phenotype of Runx2+/− mice, whereas Nell-1 protein induced mineralization and bone formation in Runx2+/− but not Runx2−/− calvarial explants. Runx2-mediated osteoblastic gene expression and/or mineralization was severely reduced by Nell-1 siRNA oligos transfection into Runx2+/+ newborn mouse calvarial cells (NMCCs) or in N-ethyl-N-nitrosourea (ENU)–induced Nell-1−/− NMCCs. Meanwhile, Nell-1 overexpression partially rescued osteoblastic gene expression but not mineralization in Runx2 null (Runx2−/−) NMCCs. Mechanistically, irrespective of Runx2 genotype, Nell-1 signaling activates ERK1/2 and JNK1 mitogen-activated protein kinase (MAPK) pathways in NMCCs and enhances Runx2 phosphorylation and activity when Runx2 is present. Collectively, these data demonstrate that Nell-1 is a critical downstream Runx2 functional mediator insofar as Runx2-regulated Nell-1 promotes osteoblastic differentiation through, in part, activation of MAPK and enhanced phosphorylation of Runx2, and Runx2 activity is significantly reduced when Nell-1 is blocked or absent. © 2011 American Society for Bone and Mineral Research

Variable bone fragility associated with an Amish COL1A2 variant and a knock-in mouse model

Osteogenesis imperfecta (OI) is a heritable form of bone fragility typically associated with a dominant COL1A1 or COL1A2 mutation. Variable phenotype for OI patients with identical collagen mutations is well established, but phenotype variability is described using the qualitative Sillence classification. Patterning a new OI mouse model on a specific collagen mutation therefore has been hindered by the absence of an appropriate kindred with extensive quantitative phenotype data. We benefited from the large sibships of the Old Order Amish (OOA) to define a wide range of OI phenotypes in 64 individuals with the identical COL1A2 mutation. Stratification of carrier spine (L1–4) areal bone mineral density (aBMD) Z -scores demonstrated that 73% had moderate to severe disease (less than −2), 23% had mild disease (−1 to −2), and 4% were in the unaffected range (greater than −1). A line of knock-in mice was patterned on the OOA mutation. Bone phenotype was evaluated in four F 1 lines of knock-in mice that each shared approximately 50% of their genetic background. Consistent with the human pedigree, these mice had reduced body mass, aBMD, and bone strength. Whole-bone fracture susceptibility was influenced by individual genomic factors that were reflected in size, shape, and possibly bone metabolic regulation. The results indicate that the G610C OI (Amish) knock-in mouse is a novel translational model to identify modifying genes that influence phenotype and for testing potential therapies for OI. © 2010 American Society for Bone and Mineral ResearchPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65040/1/90720_ftp.pd