Osteopontin regulates type I collagen fibril formation in bone tissue

Osteopontin (OPN) is a non-collagenous protein involved in biomineralization of bone tissue. Beyond its role in biomineralization, we show that osteopontin is essential to the quality of collagen fibrils in bone. Transmission electron microscopy revealed that, in Opn−/− tissue, the organization of the collagen fibrils was highly heterogeneous, more disorganized than WT bone and comprised of regions of both organized and disorganized matrix with a reduced density. The Opn−/− bone tissue also exhibited regions in which the collagen had lost its characteristic fibrillar structure, and the crystals were disorganized. Using nanobeam electron diffraction, we show that damage to structural integrity of collagen fibrils in Opn−/- bone tissue and their organization causes mineral disorganization, which could ultimately affect its mechanical integrity

Finite element dependence of stress evaluationfor human trabecular bone

International audienceNumerical simulation using finite element models (FEM) has become more and moresuitable to estimate the mechanical properties of trabecular bone. The size and kind ofelements involved in the models, however, may influence the results. The purpose of thisstudy is to analyze the influence of hexahedral elements formulation on the evaluation ofmechanical stress applied to trabeculae bone during a compression test simulation.Trabecular bone cores were extracted from 18 L2 vertebrae (12 women and 6 men, meanage: 76711, BV/TV¼7.571.9%). Samples were micro-CT scanned at 20 mm isotropic voxelsize. Micro-CT images have been sub-sampled (20, 40 and 80 mm) to create 5.6mm cubicFEM. For each sample, a compression test FEM has been created, using either 8-nodeslinear hexahedral elements with full or reduced integration or 20-nodes quadratichexahedral elements fully integrated, resulting in nine models per samples. Bonemechanical properties have been assumed isotropic, homogenous and to follow a linearelastic behavior law (Young modulus: 8 GPa, Poisson ratio: 0.3).Despite micro-architecture modifications (loss of connectivity, trabeculae thickening)due to voxel size increase, apparent mechanical properties calculated with low resolutionmodels are significantly correlated with high resolution results, no matter the elementformulation. However, stress distributions are more sensitive to both resolution andelement formulation modifications. With linear elements, increasing voxel size leads toan alteration of stress concentration areas due to stiffening errors. On the opposite, the useof reduced integration induces severe smoothing and underestimation of stress fieldsresulting in stress raisers loss. Notwithstanding their high computational cost, quadraticelements are most appropriate for stress prediction in low resolution trabecular bone FEM.These observations are dependent on trabecular bone micro-architecture, and are moresignificant for low density sample displaying low trabecular thickness.In conclusion, we found that element formulation is almost important as element sizewhen evaluating trabecular bone mechanical behavior at trabeculae scale. Therefore,element type should be chosen carefully when evaluating trabecular bone behaviorusing FEM

Immature and Mature Collagen Crosslinks Quantification Using High-Performance Liquid Chromatography and High-Resolution Mass Spectrometry in Orbitrap

Different methodologies for collagen quantification have been described in the past. Introduction of mass spectrometry combined with high-performance liquid chromatography (HPLC) is a high-resolution tool, which has generated novel applications in biomedical research. In this study, HPLC coupled to electrospray ionization (ESI) tandem mass spectrometry (HPLC-ESI-MS/MS) was used to characterize tissue samples from AVFs done in rats. These findings helped create a protocol for identifying and quantifying components of immature and mature collagen crosslink moieties. Two different internal standards were used: epinephrine and pyridoxine. Quantification curves were drawn by means of these standards. The goal of the experiment was to achieve accurate quantification with the minimum amount of sample. Time and cost of experiment were considerably minimized. Up to date, this method has not been tested for crosslinking quantification