Bone sialoprotein plays a functional role in bone formation and osteoclastogenesis.

International audienceBone sialoprotein (BSP) and osteopontin (OPN) are both highly expressed in bone, but their functional specificities are unknown. OPN knockout ((-/-)) mice do not lose bone in a model of hindlimb disuse (tail suspension), showing the importance of OPN in bone remodeling. We report that BSP(-/-) mice are viable and breed normally, but their weight and size are lower than wild-type (WT) mice. Bone is undermineralized in fetuses and young adults, but not in older (>/=12 mo) BSP(-/-) mice. At 4 mo, BSP(-/-) mice display thinner cortical bones than WT, but greater trabecular bone volume with very low bone formation rate, which indicates reduced resorption, as confirmed by lower osteoclast surfaces. Although the frequency of total colonies and committed osteoblast colonies is the same, fewer mineralized colonies expressing decreased levels of osteoblast markers form in BSP(-/-) versus WT bone marrow stromal cultures. BSP(-/-) hematopoietic progenitors form fewer osteoclasts, but their resorptive activity on dentin is normal. Tail-suspended BSP(-/-) mice lose bone in hindlimbs, as expected. In conclusion, BSP deficiency impairs bone growth and mineralization, concomitant with dramatically reduced bone formation. It does not, however, prevent the bone loss resulting from loss of mechanical stimulation, a phenotype that is clearly different from OPN(-/-) mice

« Bronzes grecs et romains, recherches récentes » — Hommage à Claude Rolley

Philologue, archéologue, historien, spécialiste des bronzes, Claude Rolley, disparu en 2007, occupa une place originale parmi les spécialistes du monde méditerranéen antique. Marqué par la découverte du cratère de Vix (en 1953) qu’il ne cessa d’étudier tout au long de sa carrière, il sut croiser recherches et approches sur les périodes à la fois classique et proto-historique, de la Laconie à la Bourgogne jusqu’à la Grande Grèce. Les bronzes, de toutes dimensions ou origines, dont il tint la chronique pendant près de 25 ans dans la Revue archéologique, étaient pour lui une source de réflexion multiple : stylistique, technique – il prenait en compte aussi bien les questions d’assemblage ou de fonte que la composition chimique des objets –, ou culturelle – ses travaux ont apporté des éclairages décisifs sur la formation des ateliers et la circulation des objets d’un centre de production à l’autre. À l’initiative de plusieurs de ses disciples, un colloque lui a rendu hommage (INHA, 16-17 juin 2009) : les textes qui suivent en sont le fruit

In vitro histomechanical effects of enzymatic degradation in carotid arteries during inflation tests with pulsatile loading

International audienceIn this paper, the objective is to assess the histomechanical effects of collagen proteolysis in arteries under loading conditions reproducing in vivo environment. Thirteen segments of common porcine carotid arteries (8 proximal and 5 distal) were immersed in a bath of bacterial collagenase and tested with a pulsatile tension/inflation machine. Diameter, pressure and axial load were monitored throughout the tests and used to derive the stress-stretch curves and to determine the secant circumferential stiffness. Results were analyzed separately for proximal and distal segments, before and after 1, 2 and 3 hours of enzymatic degradation. A histological analysis was performed to relate the arterial microstructure to its mechanical behavior under collagen proteolysis. Control (before enzymatic degradation) and treated populations (after 1, 2 or 3 hours of enzymatic degradation) were found statistically incomparable, and histology confirmed the alteration of the fibrous structure of collagen bundles induced by the collagenase treatment. A decrease of the secant circumferential stiffness of the arterial wall was noticed mostly at the beginning of the treatment, and was less pronounced after 1 hour. These results constitute an important set of enzymatically damaged arteries that can be used to validate biomechanical computational models correlating structure and properties of blood vessels

Osteoblast and Osteoclast Differentiation in an In Vitro Three-Dimensional Model of Bone.

International audienceThere is increasing interest in developing new in vitro tissue models using typical tissue engineering approaches. This study was designed to (1) develop a novel three-dimensional (3D) in vitro model of bone by seeding murine primary osteoblasts and osteoclast precursors on a resorbable porous ceramic scaffold based on silicon-stabilized tricalcium phosphate (Skelite((R))), and (2) investigate bone cell interactions in a 3D environment mimicking an in vivo condition and compare it to traditional two-dimensional (2D) cultures. Murine primary osteoblasts from C57Bl6/J mice and osteoclast precursors from C57Bl/6-Tg(ACTB-EGFP)1Osb/J mice were co-cultured on 3D Skelite scaffolds and on standard plastic culture dishes. The differentiation of these cells in both culture conditions was compared by histology (hematoxylin-eosin staining and polarized light analysis), immunohistochemistry (collagen type I), and gene expression analysis by real-time PCR for Runt-related transcription factor 2, osterix, osteocalcin, cathepsin K, and tartrate resistant acid phosphatase. To analyze and compare bone turnover in 3D and 2D co-cultures, we evaluated the modulation of RANKL and OPG mRNA expression. We observed an enhancement of osteoblast differentiation in the 3D mineralized environment that in turn promoted earlier osteoclast differentiation. In this paper, we also report that the increased osteoblast differentiation in the 3D model led to a deposition of extracellular matrix that faithfully reflected the morphology of bone tissue

The effect of dual frequency cyclic compression on matrix deposition by osteoblast-like cells grown in 3D scaffolds and on modulation of VEGF variant expression.

International audienceAs a strategy to optimise osteointegration of biomaterials by inducing proper extracellular matrix synthesis, and specifically angiogenic growth factor production and storage, we tested the effects of cyclic mechanical compression on 3D cultures of human osteoblast-like cells. MG-63 cells were seeded into 3D porous hydroxyapatite ceramics under vacuum to enable a homogenous cellular distribution. A four-day culture period allowed cell proliferation throughout the scaffolds. Low amplitude cyclic compressions were then applied to the scaffolds for 15 min with different regimens generated by the ZetOS system. A 3 Hz sinusoidal (sine) signal increased slightly collagen and fibronectin expression. When 50 Hz or 100 Hz vibrations were superimposed to the 3 Hz signal, matrix protein expression was down-regulated. In contrast, adding a 25 Hz vibration up-regulated significantly collagen and fibronectin. Moreover, expression of a matrix-bound variant of vascular endothelial growth factor-A (VEGF-A) was specifically stimulated compared to control or 3 Hz sine, and non-soluble VEGF protein was increased. Our study enabled us to identify low-amplitude, high-frequency strain regimen able to increase major matrix proteins of bone tissue and to regulate the expression of VEGF variants, showing that an appropriate combined loading has the potential to functionalise cellularized bone-like constructs

In Vivo Evaluation of Immediately Loaded Stainless Steel and Titanium Orthodontic Screws in a Growing Bone

International audienceThe present work intends to evaluate the use of immediate loaded orthodontic screws in a growing model, and to study the specific bone response. Thirty-two screws (half of stainless steel and half of titanium) were inserted in the alveolar bone of 8 growing pigs. The devices were immediately loaded with a 100 g orthodontic force. Two loading periods were assessed: 4 and 12 weeks. Both systems of screws were clinically assessed. Histological observations and histomorphometric analysis evaluated the percent of ‘‘bone-to-implant contact’’ and static and dynamic bone parameters in the vicinity of the devices (test zone) and in a bone area located 1.5 cm posterior to the devices (control zone). Both systems exhibit similar responses for the survival rate; 87.5% and 81.3% for stainless steel and titanium respectively (p = 0.64; 4-week period), and 62.5% and 50.0% for stainless steel and titanium respectively (p = 0.09; 12-week period). No significant differences between the devices were found regarding the percent of ‘‘bone-to-implant contact’’ (p = 0.1) or the static and dynamic bone parameters. However, the 5% threshold of ‘‘bone-to-implant contact’’ was obtained after 4 weeks with the stainless steel devices, leading to increased survival rate values. Bone in the vicinity of the miniscrew implants showed evidence of a significant increase in bone trabecular thickness when compared to bone in the control zone (p = 0.05). In our study, it is likely that increased trabecular thickness is a way for low density bone to respond to the stress induced by loading

Biaxial loading of arterial tissues with 3D in situ observations of adventitia fibrous microstructure: a method coupling multi-photon confocal microscopy and bulge inflation test

International audienceDisorders in the wall microstructure underlie all forms of vascular disease, such as the aortic aneurysm, the rupture of which is necessarily triggered at the microscopic level. In this context, we developed an original experimental approach, coupling a bulge inflation test to multiphoton confocal microscopy, for visualizing the 3D micro-structure of porcine, human non-aneurysmal and aneurysmal aortic adventitial collagen under increasing pressurization. The experiment complexity on such tissues led to deeply address the acquisition major hurdles. The important innovative features of the methodology are presented, especially regarding region-of-interest tracking, definition of a stabilization period prior to imaging and correction of z-motion, z being the objective's axis. Such corrections ensured consistent 3D qualitative and quantitative analyses without z-motion. Qualitative analyses of the stable 3D images showed dense undulated collagen fiber bundles in the unloaded state which tended to progressive straightening and separation into a network of thinner bundles at high pressures. Quantitative analyses were made using a combination of weighted 2D structure tensors and fitting of 4 independent Gaussian functions to measure parameters related to straightening and orientation of the fibers. They denoted 3 principal fibers directions, approximately 45°, 135° and 90° with respect to the circumferential axis in the circumferential-axial plane without any evident reorientation of the fibers under pressurization. Results also showed that fibers at zero-pressure state were straighter and less dispersed in orientation for human samples – especially aneurysms – than for pigs. Progressive straightening and decrease in dispersion were quantified during the inflation. These findings provide further insight into the micro-architectural changes within the arterial wall

Synchrotron Radiation Micro-CT at the Micrometer Scale for the Analysis of the Three-Dimensional Morphology of Microcracks in Human Trabecular Bone

International audienceBone quality is an important concept to explain bone fragility in addition to bone mass. Among bone quality factors, microdamage which appears in daily life is thought to have a marked impact on bone strength and plays a major role in the repair process. The starting point for all studies designed to further our understanding of how bone microdamage initiate or dissipate energy, or to investigate the impact of age, gender or disease, remains reliable observation and measurement of microdamage. In this study, 3D Synchrotron Radiation (SR) micro-CT at the micrometric scale was coupled to image analysis for the three-dimensional characterization of bone microdamage in human trabecular bone specimens taken from femoral heads. Specimens were imaged by 3D SR micro-CT with a voxel size of 1.4 mm. A new tailored 3D image analysis technique was developed to segment and quantify microcracks. Microcracks from human trabecular bone were observed in different tomographic sections as well as from 3D renderings. New 3D quantitative measurements on the microcrack density and morphology are reported on five specimens. The 3D microcrack density was found between 3.1 and 9.4/mm3 corresponding to a 2D density between 0.55 and 0.76 /mm2. The microcrack length and width measured in 3D on five selected microcrack ranged respectively from 164 mm to 209 mm and 100 mm to 120 mm. This is the first time that various microcracks in unloaded human trabecular bone-from the simplest linear crack to more complex cross-hatch cracks-have been examined and quantified by 3D imaging at this scale. The suspected complex morphology of microcracks is here considerably more evident than in the 2D observations. In conclusion, this technique opens new perspective for the 3D investigation of microcracks and the impact of age, disease or treatment