α-Tocotrienol inhibits osteoclastic bone resorption by suppressing RANKL expression and signaling and bone resorbing activity

Vitamin E, an essential nutrient with powerful antioxidant activity, is the mixture of two classes of compounds, tocopherols (TPs) and tocotrienols (TTs). Although TTs exhibit better bone protective activity than α-TP, the underlying mechanism is poorly understood. In this study, we investigated whether α-TT and α-TP can modulate osteoclastic bone resorption. We found that α-TT but not α-TP inhibits osteoclastogenesis in coculture of osteoblasts and bone marrow cells induced by either IL-1 or combined treatment with 1α,25(OH)₂ vitamin D₃ and prostaglandin E₂. In accordance with this, only α-TT inhibited receptor activator of NF-κB ligand (RANKL) expression in osteoblasts. In addition, α-TT but not α-TP inhibited RANKL-induced osteoclast differentiation from precursors by suppression of c-Fos expression, possibly through inhibiting ERK and NF-κB activation. This anti-osteoclastogenic effect was reversed when c-Fos or an active form of NFATc1, a critical downstream of c-Fos during osteoclastogenesis, was overexpressed. Furthermore, only α-TT reduced bone resorbing activity of mature osteoclasts without affecting their survival. Overall, our results demonstrate that α-TT but not α-TP has anti-bone resorptive properties by inhibiting osteoclast differentiation and activation, suggesting that α-TT may have therapeutic value for treating and preventing bone diseases characterized by excessive bone destruction.     

Do mineral crystals stiffen bone by straitjacketing its collagen?

Theories that assume that the collagen and the mineral of bone have the same properties in bone as they do when they are by themselves have difficulty in accounting for bone's tensile stiffness. The collagen fibers are long but stretchy: the apatite crystals are stiff enough, but too short to be effective tension carriers. In bone the mineral is so finely divided that each collagen molecule may have a mineral crystal next to it. It is proposed that collagen is the prime tension carrier in bone, and that via short molecular struts the mineral crystals prevent the naturally kinky collagen molecules from straightening under tensile stress, which greatly increases the collagen's tensile stiffness.     

Regulation of breast cancer-induced bone lesions by β-catenin protein signaling

Breast cancer patients have an extremely high rate of bone metastases. Morphological analyses of the bones in most of the patients have revealed the mixed bone lesions, comprising both osteolytic and osteoblastic elements. β-Catenin plays a key role in both embryonic skeletogenesis and postnatal bone regeneration. Although this pathway is also involved in many bone malignancy, such as osteosarcoma and prostate cancer-induced bone metastases, its regulation of breast cancer bone metastases remains unknown. Here, we provide evidence that the β-catenin signaling pathway has a significant impact on the bone lesion phenotype. In this study, we established a novel mouse model of mixed bone lesions using intratibial injection of TM40D-MB cells, a breast cancer cell line that is highly metastatic to bone. We found that both upstream and downstream molecules of the β-catenin pathway are up-regulated in TM40D-MB cells compared with non-bone metastatic TM40D cells. TM40D-MB cells also have a higher T cell factor (TCF) reporter activity than TM40D cells. Inactivation of β-catenin in TM40D-MB cells through expression of a dominant negative TCF4 not only increases osteoclast differentiation in a tumor-bone co-culture system and enhances osteolytic bone destruction in mice, but also inhibits osteoblast differentiation. Surprisingly, although tumor cells overexpressing β-catenin did induce a slight increase of osteoblast differentiation in vitro, these cells display a minimal effect on osteoblastic bone formation in mice. These data collectively demonstrate that β-catenin acts as an important determinant in mixed bone lesions, especially in controlling osteoblastic effect within tumor-harboring bone environment.     

Could reduced bone mineral densities in HIV be caused by nanobacteria?

From the observations of different research groups reporting on reduced bone mineral density (BMD) and on a pronounced tendency for kidney stone formation, both in HIV-infected patients, and from results achieved in the treatment of severest peripheral neuropathy with lasers, it is concluded that nanobacteria (NB) could actively contribute to the reduction of BMD. A reduced BMD could primarily stem from NB, extracting calcium and phosphate from blood, affecting the calcium and phosphate homeostasis in humans.     

CCAAT/enhancer binding protein β-deficiency enhances type 1 diabetic bone phenotype by increasing marrow adiposity and bone resorption

Bone loss in type 1 diabetes is accompanied by increased marrow fat, which could directly reduce osteoblast activity or result from altered bone marrow mesenchymal cell lineage selection (adipocyte vs. osteoblast). CCAAT/enhancer binding protein beta (C/EBPβ) is an important regulator of both adipocyte and osteoblast differentiation. C/EBPβ-null mice have delayed bone formation and defective lipid accumulation in brown adipose tissue. To examine the balance of C/EBPβ functions in the diabetic context, we induced type 1 diabetes in C/EBPβ-null (knockout, KO) mice. We found that C/EBPβ deficiency actually enhanced the diabetic bone phenotype. While KO mice had reduced peripheral fat mass compared with wild-type mice, they had 5-fold more marrow adipocytes than diabetic wild-type mice. The enhanced marrow adiposity may be attributed to compensation by C/EBPδ, peroxisome proliferator-activated receptor-γ2, and C/EBPα. Concurrently, we observed reduced bone density. Relative to genotype controls, trabecular bone volume fraction loss was escalated in diabetic KO mice (-48%) compared with changes in diabetic wild-type mice (-22%). Despite greater bone loss, osteoblast markers were not further suppressed in diabetic KO mice. Instead, osteoclast markers were increased in the KO diabetic mice. Thus, C/EBPβ deficiency increases diabetes-induced bone marrow (not peripheral) adipose depot mass, and promotes additional bone loss through stimulating bone resorption. C/EBPβ-deficiency also reduced bone stiffness and diabetes exacerbated this (two-way ANOVA P < 0.02). We conclude that C/EBPβ alone is not responsible for the bone vs. fat phenotype switch observed in T1 diabetes and that suppression of CEBPβ levels may further bone loss and decrease bone stiffness by increasing bone resorption.     

Synergistic enhancement of bone regeneration by LMP-1 and HIF-1α delivered by adipose derived stem cells

Objectives

To investigate the effect of the combination of LMP-1 and HIF-1α delivered by adipose-derived stem cells (ADSCs) on osteogenesis in vitro and in vivo.

Results

Cells expressing both LMP-1 and HIF-1α genes had elevated mRNA expression of BMP-2, RunX2, alkaline phosphatase, osteocalcin, collagen I and alkaline phosphatase activity compared to cells from other groups. Furthermore, mineralization at day 14 in the cells expressing both LMP-1 and HIF-1α was significantly higher than in all the other groups. In vivo, H&E staining and immunohistochemical analysis of the cell-scaffolds also showed more ectopic bone formation at 4 weeks compared to other groups. More new vessel formation was apparent in the pLVX-rHIF-1α and pLVX-rLMP-1-rHIF-1α groups.

Conclusion

LMP-1 and HIF-1α gene delivery synergistically enhanced the osteo-differentiation of ADSCs in vitro and promoted osteogenesis in vivo compared with LMP-1 alone or HIF-1α alone.

     

Measuring metacarpal cortical bone by digital x-ray radiogrammetry: a step forward?

Changes in metacarpal cortical bone mineral density (BMD) using digital x-ray radiogrammetry were studied in patients with early rheumatoid arthritis. After 1, 2, and 5 years, large BMD losses were found: -1.7%, -2.8%, and -5.6%, respectively. Elevated erythrocyte sedimentation rate and anti-cyclic citrullinated peptide levels were independent predictors of bone loss, indicating that the largest amount of bone loss was found in patients with severe inflammation and high production of auto-antibodies, who are known to be at the highest risk of developing radiological bone damage. Studies are needed about the spatial and time relationship between erosions and juxta-articular and metacarpal bone loss.     

TREM2 and β-catenin regulate bone homeostasis by controlling the rate of osteoclastogenesis

TREM2 is an immunoreceptor expressed on osteoclasts (OC) and microglia that transmits intracellular signals through the adaptor DAP12. Individuals with genetic mutations inactivating TREM2 or DAP12 develop the Nasu-Hakola disease (NHD) with cystic-like lesions of the bone and brain demyelination that lead to fractures and presenile dementia. The mechanisms of this disease are poorly understood. In this study, we report that TREM2-deficient mice have an osteopenic phenotype reminiscent of NHD. In vitro, lack of TREM2 impairs proliferation and β-catenin activation in osteoclast precursors (OcP) in response to M-CSF. This defect results in accelerated differentiation of OcP into mature OC. Corroborating the importance of a balanced proliferation and differentiation of OcP for bone homeostasis, we show that conditional deletion of β-catenin in OcP also results in reduced OcP proliferation and accelerated osteoclastogenesis in vitro as well as osteopenia in vivo. These results reveal that TREM2 regulates the rate of osteoclastogenesis and provide a mechanism for the bone pathology in NHD.     

Elastic properties of collagen in bone determined by measuring the Debye–Waller factor

Force constant values for thermal vibrational motion of a collagen molecule along the helix axis in tendon, completely demineralized bone (CDB), and partially demineralized bone (PDB) were estimated by determining the Debye–Waller factor (DW factor) for the diffracted X-ray intensity from these specimens. The DW factor for nominal value of 0.286 nm meridional diffraction representing a period along the helical axis of a collagen molecule was measured. As the atomic scattering factor of mineral constituents is much larger than that of collagen, it is difficult to detect the diffraction from collagen in bone specimen. Therefore, PDB was used in this study. In order to compare obtained force constant value for CDB with mechanical properties of collagen in the literature, the value was translated into Young's modulus value using the cross-sectional area of a collagen molecule. In the case of collagen in PDB, i.e., collagen with the close presence of HAp mineral particles, as the DW factor of the diffracted intensity by hydroxyapatite (HAp) was considered to be negligible compared with that of collagen, the DW factor determined was interpreted as that of collagen molecule in PDB specimen. The force constant value obtained for collagen in PDB was significantly larger than that of collagen in CDB. This result was thought to be a manifestation of the hardening of collagen matrix in bone by HAp mineral particles and the first straightforward evidence for a difference in collagen properties depending on the presence of HAp mineral particles. The method employed in this study can be utilized for detecting mechanical properties of the individual constituents of composite materials.     

Osthole inhibits osteoclasts formation and bone resorption by regulating NF-κB signaling and NFATc1 activations stimulated by RANKL

Chinese herbal medicine Fructus Cnidii has an outstanding effect on chronic lumbar pain and impotence, also has been used against osteoporosis with high frequency. Yet, the mechanisms of osthole, a derivative of Fructus Cnidii, on osteoclasts remains barely known. In this study, it was found out that osthole (10⁻⁶mol/L, 10⁻⁵mol/L) had the influence of inhibiting osteoclast formation and bone resorptive activities induced by receptor activator of nuclear factor κB ligand (RANKL), rather than affecting the viability of osteoclast-like cells. Furthermore, osthole could also inhibit the messenger RNA expressions of c-Src, tartrate-resistant acid phosphatase, β3-Integrin, matrix metallopeptidase 9, and cathepsin K. The results of the mechanistic study indicated that osthole regulated the nuclear factor of activated T-cells cytoplasmic 1 (NFATc1) and nuclear factor-κB (NF-κB) activations following the RANKL stimulation. These findings suggested that the inhibitory effects of osthole were associated with restraining the activations of NFATc1 and NF-κB induced by RANKL. Thus osthole can be used as a potential treatment for abnormal bone-resorption related diseases.     

Analysis of avian bone response to mechanical loading—Part One: Distribution of bone fluid shear stress induced by bending and axial loading

Mechanical loading-induced signals are hypothesized to be transmitted and integrated by a bone-connected cellular network (CCN) before reaching the bone surfaces where adaptation occurs. Our objective is to establish a computational model to explore how bone cells transmit the signals through intercellular communication. In this first part of the study the bone fluid shear stress acting on every bone cell in a CCN is acquired as the excitation signal for the computational model. Bending and axial loading-induced fluid shear stress is computed in transverse sections of avian long bones for two adaptation experiments (Gross et al. in J Bone Miner Res 12:982-988, 1997 and Judex et al. in J Bone Miner Res 12:1737-1745, 1997). The computed fluid shear stress is found to be correlated with the radial strain gradient but not with bone formation. These results suggest that the radial strain gradient is the driving force for bone fluid flow in the radially distributed lacunar-canalicular system and that bone formation is not linearly related to the loading-induced local stimulus.     

Regulation of oligodendrocyte progenitor cell maturation by PPARδ: effects on bone morphogenetic proteins

In EAE (experimental autoimmune encephalomyelitis), agonists of PPARs (peroxisome proliferator-activated receptors) provide clinical benefit and reduce damage. In contrast with PPARγ, agonists of PPARδ are more effective when given at later stages of EAE and increase myelin gene expression, suggesting effects on OL (oligodendrocyte) maturation. In the present study we examined effects of the PPARδ agonist GW0742 on OPCs (OL progenitor cells), and tested whether the effects involve modulation of BMPs (bone morphogenetic proteins). We show that effects of GW0742 are mediated through PPARδ since no amelioration of EAE clinical scores was observed in PPARδ-null mice. In OPCs derived from E13 mice (where E is embryonic day), GW0742, but not the PPARγ agonist pioglitazone, increased the number of myelin-producing OLs. This was due to activation of PPARδ since process formation was reduced in PPARδ-null compared with wild-type OPCs. In both OPCs and enriched astrocyte cultures, GW0742 increased noggin protein expression; however, noggin mRNA was only increased in astrocytes. In contrast, GW0742 reduced BMP2 and BMP4 mRNA levels in OPCs, with lesser effects in astrocytes. These findings demonstrate that PPARδ plays a role in OPC maturation, mediated, in part, by regulation of BMP and BMP antagonists.     

Repairing cartilage defects with bone marrow mesenchymal stem cells induced by CDMP and TGF-β1

The aim of this study was to explore the ability for chondrogenic differentiation of bone marrow mesenchymal stems cells (BMSCs) induced by either cartilage-derived morphogenetic protein 1 (CDMP-1) alone or in the presence of transforming growth factor-β₁ (TGF-β₁) in vivo and in vitro. BMSCs and poly-lactic acid/glycolic acid copolymer (PLGA) scaffold were analyzed for chondrogenic capacity induced by CDMP-1 and TGF-β₁ in vivo and in vitro. Chondrogenic differentiation of BMSCs into chondrocytes using a high density pellet culture system was tested, whether they could be maintained in 3-D PLGA scaffold instead of pellet culture remains to be explored. Under the culture of high-density cell suspension and PLGA frame, BMSCs were observed the ability to repair cartilage defects by either CDMP-1 alone or in the presence of TGF-β₁ in vitro. Then the cell-scaffold complex was implanted into animals for 4 and 8 weeks for in vivo test. The content of collagen type II and proteoglycan appeared to increase over time in the constructs of the induced groups (CDMP in the presence of TGF-β₁), CDMP group and TGF group. However, the construct of the control group did not express them during the whole culture time. At 4 and 8 weeks, the collagen type II expression of the induced group was higher than the sum of TGF group and CDMP group by SSPS17.0 analysis. BMSCs and PLGA complex induced by CDMP-1 and TGF- β₁ can repair cartilage defects more effectively than that induced by CDMP-1 or TGF-β₁ only.     

In vitro purging of clonogenic leukaemic cells from human bone marrow by interferon-γ-activated monocytes

With a view to the immunologically mediated purging of autologous bone marrow transplants in acute myeloid leukaemia, the efficacy of cytotoxic monocytes to cradicate leukaemic cells has been studied using clonogenic assays. U937 cells were found to be sensitive to highly purified and interferon--activated human monocytes whereas HL60 cells were rather resistant as measured in an MTT-based cytotoxicity assay under liquid conditions. A spectrophotometric clonogenic assay measured almost complete inhibition of clonogenic activity for U937 cells at low effector-to-target cell (E/T) ratios of at least 0.1. Limiting dilution analysis detected a 2–3 log₁₀ unit reduction in clonogenic activity. In an experimental mixture of U937 cells with a 20-fold excess of normal bone marrow nuclear cells a maximum 2-log₁₀-unit killing could be measured at E/T=10. Only at high E/T ratios could a reduction in granulocyte/macrophage-colony-forming units (cfu) be observed with only marginal effects on erythroid cfu and erythroid burst-forming. In conclusion, cytotoxic monocytes are highly potent anti-leukaemic effector cells, as measured in clonogenic assays, that do not compromise normal human progenitors.     

Anisotropic post-yield response of cancellous bone simulated by stress–strain curves of bulk equivalent structures

During the last decade, finite element (FE) modelling has become ubiquitous in understanding complex mechanobiological phenomena, e.g. bone–implant interactions. The extensive computational effort required to achieve biorealistic results when modelling the post-yield behaviour of microstructures like cancellous bone is a major limitation of these techniques. This study describes the anisotropic biomechanical response of cancellous bone through stress–strain curves of equivalent bulk geometries. A cancellous bone segment, reverse engineered by micro computed tomography, was subjected to uniaxial compression. The material's constitutive law, obtained by nano-indentations, was considered during the simulation of the experimental process. A homodimensionally bulk geometry was employed to determine equivalent properties, resulting in a similar anisotropic response to the trabecular structure. The experimental verification of our model sustained that the obtained stress–strain curves can adequately reflect the post-yield behaviour of the sample. The introduced approach facilitates the consideration of nonlinearity and anisotropy of the tissue, while reducing the geometrical complexity of the model to a minimum.     

The supra-occipital bone in cetaceans and burrowing rodents. morphological convergence induced by the post-cephalic pole?

A comparative study of the cranial morphologies of cetaceans and of rodents that use their incisors for burrowing brings out morphological convergences concerning the supra-occipital bone. These phyletically very remote groups are both subject to the same mechanical constraint, viz. the need for the spinal column to be aligned with the anteroposterior axis of the skull. This constraint, which is related to swimming in cetaceans and burrowing in rodents, entails three major points of convergence: 1) a clearly backward facing foramen magnum; 2) a shortened or even greatly shortened neck, sometimes with cervical vertebrae fused together; and 3) an uprighted or even forward tilted supra-occipital bone.     

Gentiopicroside promotes the osteogenesis of bone mesenchymal stem cells by modulation of β-catenin-BMP2 signalling pathway

Osteoporosis is characterized by increased bone fragility, and the drugs used at present to treat osteoporosis can cause adverse reactions. Gentiopicroside (GEN), a class of natural compounds with numerous biological activities such as anti-resorptive properties and protective effects against bone loss. Therefore, the aim of this work was to explore the effect of GEN on bone mesenchymal stem cells (BMSCs) osteogenesis for a potential osteoporosis therapy. In vitro, BMSCs were exposed to GEN at different doses for 2 weeks, whereas in vivo, ovariectomized osteoporosis was established in mice and the therapeutic effect of GEN was evaluated for 3 months. Our results in vitro showed that GEN promoted the activity of alkaline phosphatase, increased the calcified nodules in BMSCs and up-regulated the osteogenic factors (Runx2, OSX, OCN, OPN and BMP2). In vivo, GEN promoted the expression of Runx2, OCN and BMP2, increased the level of osteogenic parameters, and accelerated the osteogenesis of BMSCs by activating the BMP pathway and Wnt/β-catenin pathway, effect that was inhibited using the BMP inhibitor Noggin and Wnt/β-catenin inhibitor DKK1. Silencing the β-catenin gene and BMP2 gene blocked the osteogenic differentiation induced by GEN in BMSCs. This block was also observed when only β-catenin was silenced, although the knockout of BMP2 did not affect β-catenin expression induced by GEN. Therefore, GEN promotes BMSC osteogenesis by regulating β-catenin-BMP signalling, providing a novel strategy in the treatment of osteoporosis.     

Perspective on liver regeneration by bone marrow–derived stem cells—A scientific realization or a paradox

Bone marrow (BM)-derived stem cells are reported to have cellular plasticity, which provoked many investigators to use of these cells in the regeneration of nonhematopoietic tissues. However, adult stem cell plasticity contradicts our classic understanding on progressive restriction of the developmental potential of a cell type. Many alternate mechanisms have been proposed to explain this phenomenon; the working hypotheses for elucidating the cellular plasticity of BM-derived stem cells are on the basis of direct differentiation and/or fusion between donor and recipient cells. This review dissects the different outcomes of the investigations on liver regeneration, which were performed with the use of BM-derived stem cells in experimental animals, and reveals some critical factors to explain cellular plasticity. It has been hypothesized that the competent BM-derived stem/progenitor cells, under the influence of liver-regenerating cues, can directly differentiate into hepatic cells. This differentiation takes place as a result of genetic reprogramming, which may be possible in the chemically induced acute liver injury model or at the stage of fetal liver development. Cellular plasticity emerges as an important phenomenon in cell-based therapies for the treatment of many liver diseases in which tissue regeneration is necessary.     

Nuclear medicine studies of aging—III. Radial bone mineral content by single and dual photon absorptiometry

Measurement of bone mineral content of the radius has been possible by single photon absorptiometry. Recently, dual photon devices have become widely used for measuring the quantity of lumbar vertebral bone mineral. Therefore, we studied the utility of a dual beam machine for quantifying the bone mineral content of the radius, and compared results with those obtained by single photon absorptiometry in the same patient on the same day. There was an excellent correlation between single and dual beam measurements of the radius. The present study indicates that a dual photon machine can be used for assessing not only vertebral, but radial bone mineral content as well. This may facilitate studies of the two sites by use of one machine.