New microscopies, biomaterials: Two new axes for Morphologie

International audienc

Multiple myeloma and bone

Multiple myeloma (also called Kahler\u27s disease [MM]) is a hematological malignancy of B lymphocytes characterized by the expansion of a malignant plasma cell clone in the bone marrow. Five thousand cases of myeloma are diagnosed each year in France, 54% in men. In almost all cases, the malignant plasma cells secrete a monoclonal immunoglobulin or an immunoglobulin fragment (free light chain) which can be detected in the blood and/or urine. This is currently the most common way of diagnosis after having prescribed an electrophoresis or an immunofixation of serum proteins. Indeed, MM is often preceded by a monoclonal gammopathy of undetermined significance (MGUS), which requires a long term biological monitoring. MGUS are 100 times more common than MM (and are observed in 3–4% of the population after 50 years) and their evolution towards an overt myeloma is approximately 1% per year. MM is a hematological malignancy whose incidence is correlated to the aging of the population (the mean age at diagnosis is about 70 years)

Rachitismes et ostéomalacies à l’âge adulte

La principale cause de l’ostéomalacie chez l’adulte est la déficience sévère et prolongée en vitamine D, facilement reconnue aujourd’hui par le dosage de la 25-hydroxyvitamine D [25(OH)D]. Le contexte clinique, des anomalies biologiques phosphocalciques, des anomalies sur les examens d’imagerie (radiographies standard, scintigraphie osseuse), une densité parfois très basse mesurée en densitométrie osseuse, permettent d’évoquer la possibilité d’un trouble de la minéralisation de type ostéomalacique, diagnostic éventuellement confirmé par les données histomorphométriques de la biopsie osseuse trans-iliaque après double marquage aux cyclines. Une cause à la carence en vitamine D doit être recherchée et traitée. La supplémentation simple en vitamine D permet de guérir les patients. Des formes rares d’ostéomalacie, dénommées rachitismes vitamino-D-résistants (dépendants, type 1 et 2), sont dues à une anomalie génétique enzymatique (rachitisme pseudo-carentiel de Prader ou rachitisme vitamino-D-résistant de type 1, lié à un déficit en 1-alpha hydroxylase) ou à une anomalie du récepteur à la vitamine D (VDR ; rachitisme vitamino-D-dépendant de type 2) créant une résistance des organes cibles à l’action de la vitamine D. Dans cette dernière forme, le traitement est difficile, nécessitant le recours à des doses pharmacologiques fortes de vitamine D, en complément de la forte supplémentation calcique

Le canal dentaire et le nerf alvéolodentaire

International audienc

La microarchitecture du tissu osseux

Le capital osseux se constitue au cours de la vie par les mécanismes de modelage et de remodelage. Le tissu trabéculaire est constitué par un ensemble de travées (plaques et piliers) dont la répartition est hautement anisotrope : les travées se disposent parallèlement à la résultante des lignes de contraintes (Loi de Wolff). La microarchitecture trabéculaire apparaît conditionnée par les contraintes mécaniques qui s’exercent sur les pièces squelettiques. Cependant, peu de méthodes sont actuellement validées cliniquement pour apprécier et suivre l’évolution de la microarchitecture dans les ostéopathies. Les études les plus développées portent sur l’appréciation microarchitecturale par histomorphométrie osseuse grâce à l’utilisation de nouveaux algorithmes permettant d’apprécier en 2D différentes caractéristiques trabéculaires dont la connectivité. Plusieurs travaux ont montré que l’appréciation de la microarchitecture devait utiliser plusieurs techniques indépendantes. La microtomographie X (microCT), la micro IRM, le synchrotron permettent aussi de mesurer en 3D l’architecture trabéculaire de façon non destructive sur des prélèvements osseux. Cette revue décrit l’évolution des connaissances sur la microarchitecture osseuse, son rôle dans les maladies osseuses comme l’ostéoporose et les différentes méthodes d’évaluation histologique en 2D et en 3D

Hypophosphatasie : diagnostic et conduite à tenir

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Role of the A20-TRAF6 Axis in Lipopolysaccharide-mediated Osteoclastogenesis

Bacterial lipopolysaccharide (LPS) has long been suggested as a potent inducer of bone loss in vivo despite controversial effects on osteoclast precursors. Recently, the role of the deubiquitinating protease A20 in regulating the LPS response in various organs was reported. In the present study, we investigated whether A20 is expressed in osteoclast cultures in response to RANKL or LPS and whether this protein plays a role in osteoclast formation and activation. Human peripheral blood mononuclear cells were cultured in the presence of M-CSF ± RANKL ± LPS. Although LPS induced the formation of multinucleated TRAP-positive cells expressing OSCAR, cathepsin K, and the calcitonin receptor, these cells were not capable of lacunar resorption. Release of TNF-α was noted in LPS-treated cultures, and the addition of a neutralizing anti-TNF-α antibody abrogated osteoclast formation in these cultures. A20 appeared to be a late-expressed gene in LPS-treated cultures and was associated with TRAF6 degradation and NF-κB inhibition. Silencing of A20 restored TRAF6 expression and NF-κB activation and resulted in increased bone resorption in LPS-treated cultures. A20 appeared important in the control of bone resorption and could represent a therapeutic target to treat patients with bone resorption associated with inflammatory diseases

Disuse induced by botulinum toxin affects the bone marrow expression profile of bone genes leading to a rapid bone loss.

OBJECTIVES: Molecular events occurring in the bone marrow microenvironment of an immobilized mouse limb after Botulinum toxin (BTX) injection haven\u27t been characterized. BTX injection induces a localized disuse in which the tissue events have well been characterized. METHODS: BTX injection was performed in the right quadriceps; saline injection in the left side was used as control. Mice were sacrificed at 0, 7, 14, 21 and 28 days; tibias were used for microCT analysis; bone marrow from femurs for RT-PCR analysis. RESULTS: MicroCT revealed bone loss and microarchitectural damages on the immobilized side as from 7d; cortical area tended to be lower on the immobilized limb at 28d. Gene expression of formation factors was altered as from 7 days post-BTX: alkaline phosphatase, Tgfβ1, Lrp5, Sfrp2. Only Sfrp2 and Lrp5 were maintained altered until 28d. Expression of Dkk1 increased from 21d and represented a late inhibitor of formation. Gene expression of resorption markers increased as from 7d (Rankl, Tracp, Il1α, Il1β and Il6) and was maintained until 28d for Tracp and Il6. CONCLUSION: A localized disuse induces rapid modifications in the bone marrow gene expression leading to bone loss due to an early decrease of formation associated with an increase in resorption

Hypodynamia Alters Bone Quality and Trabecular Microarchitecture

Disuse induces a rapid bone loss in humans and animals; hypodynamia/sedentarity is now recognized as a risk factor for osteoporosis. Hypodynamia also decreases bone mass but its effects are largely unknown and only few animal models have been described. Hypodynamic chicken is recognized as a suitable model of bone loss but the effects on the quality have not been fully explored. We have used ten chickens bred in a large enclosure (FREE group); ten others were confined in small cages with little space to move around (HYPO group). They were sacrificed at 53 days and femurs were evaluated by microcomputed tomography (microCT) and nanoindentation. Sections (4 µm thick) were analyzed by Fourier Transform InfraRed Microspectroscopy (FTIR) to see the effects on mineralization and collagen and quantitative backscattered electron imaging (qBEI) to image the mineral of the bone matrix. Trabecular bone volume and microarchitecture were significantly altered in the HYPO group. FTIR showed a significant reduction of the mineral-to-matrix ratio in the HYPO group associated with an increase in the carbonate content and an increase in crystallinity (calculated as the area ratio of subbands located at 1020 and 1030 cm(-1)) indicating a poor quality of the mineral. Collagen maturity (calculated as the area ratio of subbands located at 1660 and 1690 cm(-1)) was significantly reduced in the HYPO group. Reduced biomechanical properties were observed at the tissue level. Confined chicken represents a new model for the study of hypodynamia because bone changes are not created by a surgical lesion or a traumatic method. Animals have a reduced bone mass and present with an altered bone matrix quality which is less mineralized and whose collagen contains less crosslinks than in control chicken

Glucose-dependent insulinotropic polypeptide (GIP) directly affects collagen fibril diameter and collagen cross-linking in osteoblast cultures.

Glucose-dependent insulinotropic polypeptide (GIP) is absolutely crucial in order to obtain optimal bone strength and collagen quality. However, as the GIPR is expressed in several tissues other than bone, it is difficult to ascertain whether the observed modifications of collagen maturity, reported in animal studies, were due to direct effects on osteoblasts or indirect through regulation of signals originating from other tissues. The aims of the present study were to investigate whether GIP can directly affect collagen biosynthesis and processing in osteoblast cultures and to decipher which molecular pathways were necessary for such effects. MC3T3-E1 cells were cultured in the presence of GIP ranged between 10 and 100pM. Collagen fibril diameter was investigated by electron microscopy whilst collagen maturity was determined by Fourier transform infra-red microspectroscopy (FTIRM). GIP treatment resulted in dose-dependent increases in lysyl oxidase activity and collagen maturity. Furthermore, GIP treatment shifted the collagen fiber diameter towards lower value but did not significantly affect collagen heterogeneity. GIP acted directly on osteoblasts by activating the adenylyl cyclase-cAMP pathway. This study provides evidences that GIP acts directly on osteoblasts and is capable of improving collagen maturity and fibril diameter