H. Follet

Dual function of ERRα in breast cancer and bone metastasis formation: implication of VEGF and osteoprotegerin.

Bone metastasis is a complication occurring in up to 70% of advanced breast cancer patients. The estrogen receptor-related receptor alpha (ERRα) has been implicated in breast cancer and bone development, prompting us to examine whether ERRα may function in promoting the osteolytic growth of breast cancer cells in bone. In a mouse xenograft model of metastatic human breast cancer, overexpression of wild-type ERRα reduced metastasis, whereas overexpression of a dominant negative mutant promoted metastasis. Osteoclasts were directly affected and ERRα upregulated the osteoclastogenesis inhibitor, osteoprotegerin (OPG), providing a direct mechanistic basis for understanding how ERRα reduced breast cancer cell growth in bone. In contrast, ERRα overexpression increased breast cancer cell growth in the mammary gland. ERRα-overexpressing primary tumors were highly vascularized, consistent with an observed upregulation of angiogenic growth factor, the VEGF. In support of these findings, we documented that elevated expression of ERRα mRNA in breast carcinomas was associated with high expression of OPG and VEGF and with disease progression. In conclusion, our results show that ERRα plays a dual role in breast cancer progression in promoting the local growth of tumor cells, but decreasing metastatic growth of osteolytic lesions in bone.

Effects of preexisting microdamage, collagen cross-links, degree of mineralization, age, and architecture on compressive mechanical properties of elderly human vertebral trabecular bone.

Previous studies have shown that the mechanical properties of trabecular bone are determined by bone volume fraction (BV/TV) and microarchitecture. The purpose of this study was to explore other possible determinants of the mechanical properties of vertebral trabecular bone, namely collagen cross‐link content, microdamage, and mineralization. Trabecular bone cores were collected from human L2 vertebrae (n = 49) from recently deceased donors 54–95 years of age (21 men and 27 women). Two trabecular cores were obtained from each vertebra, one for preexisting microdamage and mineralization measurements, and one for BV/TV and quasi‐static compression tests. Collagen cross‐link content (PYD, DPD, and PEN) was measured on surrounding trabecular bone. Advancing age was associated with impaired mechanical properties, and with increased microdamage, even after adjustment by BV/TV. BV/TV was the strongest determinant of elastic modulus and ultimate strength (r2 = 0.44 and 0.55, respectively). Microdamage, mineralization parameters, and collagen cross‐link content were not associated with mechanical properties. These data indicate that the compressive strength of human vertebral trabecular bone is primarily determined by the amount of trabecular bone, and notably unaffected by normal variation in other factors, such as cross‐link profile, microdamage and mineralization.

Association between collagen cross-links and trabecular microarchitecture properties of human vertebral bone

UNLABELLED It has been suggested that age-related deterioration in trabecular microarchitecture and changes in collagen cross-link concentrations may contribute to skeletal fragility. To further explore this hypothesis, we determined the relationships among trabecular bone volume fraction (BV/TV), microarchitecture, collagen cross-link content, and bone turnover in human vertebral trabecular bone. Trabecular bone specimens from L2 vertebrae were collected from 51 recently deceased donors (54-95 years of age; 20 men and 30 women). Trabecular bone volume and microarchitecture was assessed by microCT and bone formation, reflected by osteoid surface (OS/BS, %), was measured by 2D histomorphometry. Pyridinoline (PYD), deoxypyridinoline (DPD), pentosidine (PEN) and collagen content in the cancellous bone were analysed by high-performance liquid chromatography. Associations between variables were investigated by Pearson correlations and multiple regression models, which were constructed with BV/TV and collagen cross-links as explanatory variables and microarchitecture parameters as the dependent variables. RESULTS Microarchitecture parameters were modestly to strongly correlated with BV/TV (r(2)=0.10-0.71). The amount of mature enzymatic PYD and DPD cross-links were not associated with the microarchitecture, either before or after adjustment for BV/TV. However, there was a positive correlation between PEN content and trabecular number (r=0.45, p=0.001) and connectivity density (r=0.40, p=0.004), and a negative correlation between PEN content and trabecular separation (r=-0.29, p=0.04). In the multiple regression models including BV/TV, age and PEN content was still significantly associated with several of the microarchitecture variables. In summary, this study suggests a link between trabecular microarchitecture and the collagen cross-link profile. As PEN reflects non-enzymatic glycation of collagen and generally increases with bone age, the association between PEN and trabecular architecture suggests that the preserved trabeculae may contain mainly old bone and have undergone little remodeling. Thus, vertebral fragility may not only be due to alterations in bone architecture but also to modification of collagen cross-link patterns thereby influencing bones mechanical behavior.

Analyzing the anisotropic Hooke's law for children's cortical bone.

Child cortical bone tissue is rarely studied because of the difficulty of obtaining samples. Yet the preparation and ultrasonic characterization of the small samples available, while challenging, is one of the most promising ways of obtaining information on the mechanical behavior of non-pathological children׳s bone. We investigated children׳s cortical bone obtained from chirurgical waste. 22 fibula or femur samples from 21 children (1-18 years old, mean age: 9.7±5.8 years old) were compared to 16 fibula samples from 16 elderly patients (50-95 years old, mean age: 76.2±13.5 years old). Stiffness coefficients were evaluated via an ultrasonic method and anisotropy ratios were calculated as the ratio of C33/C11, C33/C22 and C11/C22. Stiffness coefficients were highly correlated with age in children (R>0.56, p<0.01). No significant difference was found between C11 and C22 for either adult or child bone (p>0.5), nor between C44 and C55 (p>0.5). We observe a transverse isotropy with C33>C22=C11>C44C55>C66. For both groups, we found no correlation between age and anisotropy ratios. This study offers the first complete analysis of stiffness coefficients in the three orthogonal bone axes in children, giving some indication of how bone anisotropy is related to age. Future perspectives include studying the effect of the structure and composition of bone on its mechanical behavior.

The role of bone intrinsic properties measured by infrared spectroscopy in whole lumbar vertebra mechanics: organic rather than inorganic bone matrix?

Whole bone strength is determined by bone mass, microarchitecture and intrinsic properties of the bone matrix. However, few studies have directly investigated the contribution of bone tissue material properties to whole bone strength in humans. This study assessed the role of bone matrix composition on whole lumbar vertebra mechanics. We obtained 17 fresh frozen human lumbar spines (8 W, 9 M, aged 76±11years). L3 bone mass was measured by DXA and microarchitecture by μ-CT with a 35 μm-isotropic resolution. Microarchitectural parameters were directly measured: Tb.BV/TV, SMI, Tb.Th, DA, Ct.Th, Ct.Po and radius of anterior cortical curvature. Failure load (N), stiffness (N/mm) and work to failure (N.mm) were extracted from quasi-static uniaxial compressive testing performed on L3 vertebral bodies. FTIRM analysis was performed on 2 μm-thick sections from L2 trabecular cores, with a Perkin-Elmer GXII Auto-image Microscope equipped with a wide band detector. Twenty measurements per sample were performed at 30∗100 μm of spatial resolution. Each spectrum was collected at 4 cm(-1) resolution and 50 scans in transmission mode. Mineral and collagen maturity, and mineralization and crystallinity index were measured. There was no association between the bone matrix characteristics and bone mass or microarchitecture. Mineral maturity, mineralization and crystallinity index were not related to whole vertebra mechanics. However, collagen maturity was positively correlated with whole vertebra failure load and stiffness (r=0.64, p=0.005 and r=0.54, p=0.025, respectively). The collagen maturity (3rd step) in combination with bone mass (i.e., BMC, 1st step) and microarchitecture (i.e., Tb.Th, 2nd step) improved the prediction of whole vertebra mechanical properties in forward stepwise multiple regression models, together explaining 71% of the variability in whole vertebra stiffness (p=0.001). In conclusion, we demonstrated a substantial contribution of collagen maturity, but not mineralization parameters, to whole bone strength of human lumbar vertebrae that was independent of bone mass and microarchitecture.

Characterisation of the difference in fracture mechanics between children and adult cortical bone

Clinical literature describes a specific type of children bone fracture, known as “greenstick facture” which is never encountered for adult bone. Concerning children bone, there is a tremendous lack of mechanical references. Indeed, the few studies which explored the mechanical characteristics of growing process in bone dealt with samples close to cancerous cells [1], or with samples from cadavers [2]. These studies gave dispersive results and did not provide insights to the two different kinds of fracture (i.e. brittle for mature bone and plastic for growing bone). Part of the answer could lie in the evolution of the biochemical composition of cortical bone; indeed, Bala et al. [3] have shown that the elasticity depends on the mineral part of the bone matrix and the plasticity on the organic part (collagen 1). This organic part of cortical bone seems to differ between adult and children. Saito et al. [4] have shown that the main non enzymatic crosslinks in mature bone (PYD+DPD) are different from those of growing bone (DHLNL+HLNL). It seems to us that the difference between plastic growing bone fractures and brittle adult bone fractures could be explained by this difference in the non enzymatic collagen crosslinking. We performed three point microbending tests on children and adult bone to evaluate the mechanical Young’s modulus (Em) and the plastic strain energy (ωp). The results are in agreement with the clinical observations. The goal of this study is to explain these differences in mechanical behaviour between children and adult bone by using a biochemical analysis of the organic part quantifying the composition of the collagen.

Finite element vertebral model for fracture risk prediction: comparison of a full CT-based model versus two media simplified model, a preliminary study

Osteoporotic fracture risk assessment is currently based on bone mineral density (BMD) measured by a cheap and fast modality: dual X-ray absorptiometry at the hip and at the spine. CT-scan-based finite element models (FEMs) have been proposed to evaluate more precisely vertebral strength and fracture risk (Crawford et al. 2003). However, the main limitation of such approach in routine osteoporotic diagnosis is the cost and radiation exposure of the CT-scan. Because of these limitations, developing an accurate FEM which is deployable at a large scale is still a challenge. Travert et al. (2011) and Sapin-de Brosses et al. (2012) proposed a 3D vertebral FEM from dual energy stereo-radiography based on the EOS system. This model used a geometry reconstructed from EOS, and a BMD was measured with a dual X-ray EOS to personalise two media. This model was evaluated against in vitro compression tests (R 2 1⁄4 0.79). Compared to CT-based FEM, this kind of model (referred to as 2D-BMD-based model), is limited by two factors: the approximation of geometry resulting from a pair of 2D X-ray (Humbert et al. 2009) and BMD heterogeneities that are not taken into account. The objective of this study was to compare the modelling approaches used in CT-based FEM and in 2DBMD-based FEM. A complete CT-based FEM has been built on isolated vertebrae, and simplifications regarding geometry and BMD distribution have been performed to measure their impact on the computed strength.

Effect of intra-tibial injection on mechanical properties of mouse bone

The skeleton is a common organ affected by metastatic cancers (Coleman 1997), such as breast, prostate and lung cancer. Bone metastases are often lytic, i.e. destroying the local bone tissue. Metastatic bones are more likely to fail and therefore have to be monitored by physicians, who have to decide which treatment is the best suited to each case. However, the tools at their disposal do not allow to accurately predict whether a bone will fail or not (Van der Linden et al. 2004). Several studies showed that patient-specific finite element models were a promising tool to fulfill this prediction (Derikx et al. 2015). In these previous studies, it was assumed that metastases played no mechanical role, and were accordingly modeled as holes in the bone. Nevertheless, practical cases showed that metastases do play a mechanical role in bone strength, because if the previous theory was true, the bone would have failed. Thus, the aim of our core study is to investigate and quantify the real impact of metastases (according to the different types) on bone strength by a mechanical test, and to try to simulate the experimental test through numerical modelling. To reach this final aim, 1-month-old BALB/c nude mice were injected intra-tibialy with different tumor cells in their right limb and by phosphate-buffered saline (PBS) in their contra-lateral limb, as has been advised (Wright et al. 2016) to create a sham control. However, the impact of the intra tibial injection of PBS on mechanical properties of the tibia was never quantified. Thus, the current aim of this sub study is to determine the impact of this type of injection on mice tibia assuming that the intra-tibial injection degrades the mechanical properties of the bone.

Influence of the degree of mineralization of the cortical bone on toughness

Bone quality and fracture prediction are dependent topics that have long been blurry, quite unreachable links to establish. The International Osteoporosis Foundation expects an increase of nearly three times more hip fractures in the population by 2050. Regarding this expectation, the MULTIPS project aims to predict the bone fracture risk by quantifying the bone quality using different methods. One of them is the Degree of Mineralization of the Bone (DMB (g.cm?3)) analysis by X-ray scanning of a 100 ± 1 ?m thick section of embedded bone. The aim of the present study is to assess the effect of bone mineralization (DMB) on the toughness of the bone which is the propensity to resist to fracture.

A methodology to assess non-axial loading on the distal radius

Osteoporosis is a worldwide health problem related to bone fragility. Micro-finite element analysis (μFEA) based on high-resolution peripheral quantitative computed tomography (HR-pQCT, Scanco) ima...