Tartrate-resistant acid phosphatase knockout mice

Iron metabolism in rheumatic diseases

Iron is a crucial element for living organism in terms of oxygen transport, hematopoiesis, enzymatic activity, mitochondrial respiratory chain function and also immune system function. The human being has evolved a mechanism to regulate body iron. In some rheumatic diseases such as rheumatoid arthritis (RA), systemic lupus erythematous (SLE), systemic sclerosis (SSc), ankylosing spondylitis (AS), and gout, this balanced iron regulation is impaired. Altered iron homeostasis can contribute to disease progression through ROS production, fibrosis, inflammation, abnormal bone homeostasis, NETosis and cell senescence. In this review, we have focused on the iron metabolism in rheumatic disease and its role in disease progression.

Citrate: a key signalling molecule and therapeutic target for bone remodeling disorder

Bone remodeling is a continuous cyclic process that maintains and regulates bone structure and strength. The disturbance of bone remodeling leads to a series of bone metabolic diseases. Recent studies have shown that citrate, an intermediate metabolite of the tricarboxylic acid (TCA) cycle, plays an important role in bone remodeling. But the exact mechanism is still unclear. In this study, we focused on the systemic regulatory mechanism of citrate on bone remodeling, and found that citrate is involved in bone remodeling in multiple ways. The participation of citrate in oxidative phosphorylation (OXPHOS) facilitates the generation of ATP, thereby providing substantial energy for bone formation and resorption. Osteoclast-mediated bone resorption releases citrate from bone mineral salts, which is subsequently released as an energy source to activate the osteogenic differentiation of stem cells. Finally, the differentiated osteoblasts secrete into the bone matrix and participate in bone mineral salts formation. As a substrate of histone acetylation, citrate regulates the expression of genes related to bone formation and bone reabsorption. Citrate is also a key intermediate in the metabolism and synthesis of glucose, fatty acids and amino acids, which are three major nutrients in the organism. Citrate can also be used as a biomarker to monitor bone mass transformation and plays an important role in the diagnosis and therapeutic evaluation of bone remodeling disorders. Citrate imbalance due to citrate transporter could result in the supression of osteoblast/OC function through histone acetylation, thereby contributing to disorders in bone remodeling. Therefore, designing drugs targeting citrate-related proteins to regulate bone citrate content provides a new direction for the drug treatment of diseases related to bone remodeling disorders.

Emerging biomarkers in Gaucher disease

Gaucher disease (GD) is a rare lysosomal disorder characterized by the accumulation of glycosphingolipids in macrophages resulting from glucocerebrosidase (GCase) deficiency. The accumulation of toxic substrates, which causes the hallmark symptoms of GD, is dependent on the extent of enzyme dysfunction. Accordingly, three distinct subtypes have been recognized, with type 1 GD (GD1) as the common and milder form, while types 2 (GD2) and 3 (GD3) are categorized as neuronopathic and severe. Manifestations variably include hepatosplenomegaly, anemia, thrombocytopenia, easy bruising, inflammation, bone pain and other skeletal pathologies, abnormal eye movements and neuropathy. Although the molecular basis of GD is relatively well understood, currently used biomarkers are nonspecific and inadequate for making finer distinctions between subtypes and in evaluating changes in disease status and guiding therapy. Thus, there is continued effort to investigate and identify potential biomarkers to improve GD diagnosis, monitoring and potential identification of novel therapeutic targets. Here, we provide a comprehensive review of emerging biomarkers in GD that can enhance current understanding and improve quality of life through better testing, disease management and treatment.

Tartrate-resistant acid phosphatase (TRAP/ACP5) promotes bone length, regulates cortical and trabecular bone mass, and maintains growth plate architecture and width in a sex- and site-specific manner in mice

Tartrate-resistant acid phosphatase (TRAP) serum levels reflect osteoclast number, bone remodeling activity, and fracture risk. Deletion or loss of function of TRAP results in short stature in mice and man. Yet, the impact and mechanisms of TRAP for the site- and sex-specific development of bone and cartilage is not well understood. Here, we use a global TRAP knockout (TRAPKO) and wildtype littermate control (WT) mice of both sexes to investigate TRAP as a possible sex- and site-specific regulator of bone and growth plate development. TRAPKO mice of both sexes weighed less and had shorter tibial length than their WT, features that were more accentuated in male than female TRAPKO mice. These changes were not associated with a general reduction in growth as not all organs displayed a proportionally lower mass, and serum IGF-1 was unchanged. Using μCT and site-specificity analysis of the cortical bone revealed wider proximal tibia, a higher trabecular thickness, and lower trabecular separation in male TRAPKO compared to WT mice, an effect not seen in female mice. Histomorphometric analysis revealed that the growth plate height as well as height of terminal hypertrophic chondrocytes were markedly increased, and the number of columns was decreased in TRAPKO mice of both sexes. These effects were more accentuated in female mice. Proliferation and differentiation of bone marrow derived macrophages into osteoclasts, as well as C-terminal cross links were normal in TRAPKO mice of both sexes. Collectively, our results show that TRAP regulates bone and cartilage development in a sex-and site-specific manner in mice.

Research on the osteogenic properties of 3D-printed porous titanium alloy scaffolds loaded with Gelma/PAAM-ZOL composite hydrogels

Although titanium alloy is the most widely used endoplant material in orthopedics, the material is bioinert and good bone integration is difficult to achieve. Zoledronic acid (ZOL) has been shown to locally inhibit osteoclast formation and prevent osteoporosis, but excessive concentrations of ZOL exert an inhibitory effect on osteoblasts; therefore, stable and controlled local release of ZOL may reshape bone balance and promote bone regeneration. To promote the adhesion of osteoblasts to many polar groups, researchers have applied gelatine methacryloyl (Gelma) combined with polyacrylamide hydrogel (PAAM), which significantly increased the hydrogen bonding force between the samples and improved the stability of the coating and drug release. A series of experiments demonstrated that the Gelma/PAAM-ZOL bioactive coating on the surface of the titanium alloy was successfully prepared. The coating can induce osteoclast apoptosis, promote osteoblast proliferation and differentiation, achieve dual regulation of bone regeneration, successfully disrupt the balance of bone remodelling and promote bone tissue regeneration. Additionally, the coating improves the metal biological inertness on the surface of titanium alloys and improves the bone integration of the scaffold, offering a new strategy for bone tissue engineering to promote bone technology.

Elucidating the mechano-molecular dynamics of TRAP activity using CRISPR/Cas9 mediated fluorescent reporter mice

Osteoclasts are essential for bone remodeling by adapting their resorptive activity in response to their mechanical in vivo environment. However, the molecular mechanisms underlying this process remain unclear. Here, we demonstrated the role of tartrate-resistant acid phosphatase (TRAP, Acp5), a key enzyme secreted by osteoclasts, in bone remodeling and mechanosensitivity. Using CRISPR/Cas9 reporter mice, we demonstrated bone cell reporter (BCRIbsp/Acp5) mice feature fluorescent TRAP-deficient osteoclasts and examined their activity during mechanically driven trabecular bone remodeling. Although BCRIbsp/Acp5 mice exhibited trabecular bone impairments and reduced resorption capacity in vitro, RNA sequencing revealed unchanged levels of key osteoclast-associated genes such as Ctsk, Mmp9, and Calcr. These findings, in conjunction with serum carboxy-terminal collagen crosslinks (CTX) and in vivo mechanical loading outcomes collectively indicated an unaltered bone resorption capacity of osteoclasts in vivo. Furthermore, we demonstrated similar mechanoregulation during trabecular bone remodeling in BCRIbsp/Acp5 and wild-type (WT) mice. Hence, this study provides valuable insights into the dynamics of TRAP activity in the context of bone remodeling and mechanosensation.

Optimization of an α-aminonaphthylmethylphosphonic acid inhibitor of purple acid phosphatase using rational structure-based design approaches

Purple acid phosphatases (PAPs) are ubiquitous binuclear metallohydrolases that have been isolated from various animals, plants and some types of fungi. In humans and mice, elevated PAP activity in osteoclasts is associated with osteoporosis, making human PAP an attractive target for the development of anti-osteoporotic drugs. Based on previous studies focusing on phosphonate scaffolds, as well as a new crystal structure of a PAP in complex with a derivative of a previously synthesized α-aminonaphthylmethylphosphonic acid, phosphonates 24-40 were designed as new PAP inhibitor candidates. Subsequent docking studies predicted that all of these compounds are likely to interact strongly with the active site of human PAP and most are likely to interact strongly with the active site of pig PAP. The seventeen candidates were synthesized with good yields and nine of them (26-28, 30, 33-36 and 38) inhibit in the sub-micromolar to nanomolar range against pig PAP, with 28 and 35 being the most potent mammalian PAP inhibitors reported with Ki values of 168 nM and 186 nM, respectively. This study thus paves the way for the next stage of drug development for phosphonate inhibitors of PAPs as anti-osteoporotic agents.

Iron, Zinc, Copper, Cadmium, Mercury, and Bone Tissue

The paper presents the current understanding on the effects of five metals on bone tissue, namely iron, zinc, copper, cadmium, and mercury. Iron, zinc, and copper contribute significantly to human and animal metabolism when present in sufficient amounts, but their excess or shortage increases the risk of developing bone disorders. In contrast, cadmium and mercury serve no physiological purpose and their long-term accumulation damages the osteoarticular system. We discuss the methods of action and interactions between the discussed elements as well as the concentrations of each element in distinct bone structures.

Tartrate resistant acid phosphatase 5 (TRAP5) mediates immune cell recruitment in a murine model of pulmonary bacterial infection

Introduction

During airway infection, upregulation of proinflammatory cytokines and subsequent immune cell recruitment is essential to mitigate bacterial infection. Conversely, during prolonged and non-resolving airway inflammation, neutrophils contribute to tissue damage and remodeling. This occurs during diseases including cystic fibrosis (CF) and COPD where bacterial pathogens, not least Pseudomonas aeruginosa, contribute to disease progression through long-lasting infections. Tartrate-resistant acid phosphatase (TRAP) 5 is a metalloenzyme expressed by alveolar macrophages and one of its target substrates is the phosphoglycoprotein osteopontin (OPN).

Methods

We used a knockout mouse strain (Trap5-/-) and BALB/c-Tg (Rela-luc)31Xen mice paired with siRNA administration or functional protein add-back to elucidate the role of Trap5 during bacterial infection. In a series of experiments, Trap5-/- and wild-type control mice received intratracheal administration of P.aerugniosa (Xen41) or LPS, with mice monitored using intravital imaging (IVIS). In addition, multiplex cytokine immunoassays, flow cytometry, multispectral analyses, histological staining were performed.

Results

In this study, we found that Trap5-/- mice had impaired clearance of P. aeruginosa airway infection and reduced recruitment of immune cells (i.e. neutrophils and inflammatory macrophages). Trap5 knockdown using siRNA resulted in a decreased activation of the proinflammatory transcription factor NF-κB in reporter mice and a subsequent decrease of proinflammatory gene expression. Add-back experiments of enzymatically active TRAP5 to Trap5-/- mice restored immune cell recruitment and bacterial killing. In human CF lung tissue, TRAP5 of alveolar macrophages was detected in proximity to OPN to a higher degree than in normal lung tissue, indicating possible interactions.

Discussion

Taken together, the findings of this study suggest a key role for TRAP5 in modulating airway inflammation. This could have bearing in diseases such as CF and COPD where excessive neutrophilic inflammation could be targeted by pharmacological inhibitors of TRAP5.

Inhibition of miR-29 Activity in the Myeloid Lineage Increases Response to Calcitonin and Trabecular Bone Volume in Mice

The miR-29-3p family (miR-29a, miR-29b, miR-29c) of microRNAs is increased during receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclastogenesis. In vivo, activation of a miR-29-3p tough decoy inhibitor in Cre recombinase under the control of the lysozyme 2 promoter-expressing cells (myeloid lineage) resulted in mice displaying enhanced trabecular and cortical bone volume because of decreased bone resorption. Calcitonin receptor (Calcr) is a miR-29 target that negatively regulates bone resorption. CALCR was significantly increased in RANKL-treated miR-29-decoy osteoclasts, and these cells were more responsive to the inhibitory effect of calcitonin on osteoclast formation. Further, cathepsin K (Ctsk), which is critical for resorption, was decreased in miR-29-decoy cells. CALCR is a Gs-coupled receptor and its activation raises cAMP levels. In turn, cAMP suppresses cathepsin K, and cAMP levels were increased in miR-29-decoy cells. siRNA-mediated knock-down of Calcr in miR-29 decoy osteoclasts allowed recovery of cathepsin K levels in these cells. Overall, using a novel knockin tough decoy mouse model, we identified a new role for miR-29-3p in bone homeostasis. In RANKL-driven osteoclastogenesis, as seen in normal bone remodeling, miR-29-3p promotes resorption. Consequently, inhibition of miR-29-3p activity in the myeloid lineage leads to increased trabecular and cortical bone. Further, this study documents an interrelationship between CALCR and CTSK in osteoclastic bone resorption, which is modulated by miR-29-3p.

Rational Design of Potent Inhibitors of a Metallohydrolase Using a Fragment-Based Approach

Metallohydrolases form a large group of enzymes that have fundamental importance in a broad range of biological functions. Among them, the purple acid phosphatases (PAPs) have gained attention due to their crucial role in the acquisition and use of phosphate by plants and also as a promising target for novel treatments of bone-related disorders and cancer. To date, no crystal structure of a mammalian PAP with drug-like molecules bound near the active site is available. Herein, we used a fragment-based design approach using structures of a mammalian PAP in complex with the Maybridge^TM fragment CC063346, the amino acid L-glutamine and the buffer molecule HEPES, as well as various solvent molecules to guide the design of highly potent and efficient mammalian PAP inhibitors. These inhibitors have improved aqueous solubility when compared to the clinically most promising PAP inhibitors available to date. Furthermore, drug-like fragments bound in newly discovered binding sites mapped out additional scaffolds for further inhibitor discovery, as well as scaffolds for the design of inhibitors with novel modes of action.

Bone tissue and histological and molecular events during development of the long bones

The bones are of mesenchymal or ectomesenchymal origin, form the skeleton of most vertebrates, and are essential for locomotion and organ protection. As a living tissue they are highly vascularized and remodelled throughout life to maintain intact. Bones consist of osteocytes entrapped in a mineralized extracellular matrix, and via their elaborated network of cytoplasmic processes they do not only communicate with each other but also with the cells on the bone surface (bone lining cells). Bone tissue develops through a series of fine-tuned processes, and there are two modes of bone formation, referred to either as intramembranous or endochondral ossification. In intramembranous ossification, bones develop directly from condensations of mesenchymal cells, and the flat bones of the skull, the clavicles and the perichondral bone cuff develop via this process. The bones of the axial (ribs and vertebrae) and the appendicular skeleton (e.g. upper and lower limbs) form through endochondral ossification where mesenchyme turns into a cartilaginous intermediate with the shape of the future skeletal element that is gradually replaced by bone. Endochondral ossification occurs in all vertebrate taxa and its onset involves differentiation of the chondrocytes, mineralization of the extracellular cartilage matrix and vascularization of the intermediate, followed by disintegration and resorption of the cartilage, bone formation, and finally - after complete ossification of the cartilage model - the establishment of an avascular articular cartilage. The epiphyseal growth plate regulates the longitudinal growth of the bones, achieved by a balanced proliferation and elimination of chondrocytes, and the question whether the late hypertrophic chondrocytes die or transform into osteogenic cells is still being hotly debated. The complex processes leading to endochondral ossification have been studied for over a century, and this review aims to give an overview of the histological and molecular events, arising from the long bones' (e.g. femur, tibia) development. The fate of the hypertrophic chondrocytes will be discussed in the light of new findings obtained from cell tracking studies.

The Role of Autophagy in Osteoclast Differentiation and Bone Resorption Function

Autophagy is an evolutionary conserved and highly regulated recycling process of cellular wastes. Having a housekeeping role, autophagy through the digestion of domestic cytosolic organelles, proteins, macromolecules, and pathogens, eliminates unnecessary materials and provides nutrients and energy for cell survival and maintenance. The critical role of autophagy and autophagy-related proteins in osteoclast differentiation, bone resorption, and maintenance of bone homeostasis has previously been reported. Increasing evidence reveals that autophagy dysregulation leads to alteration of osteoclast function and enhanced bone loss, which is associated with the onset and progression of osteoporosis. In this review, we briefly consolidate the current state-of-the-art technology regarding the role of autophagy in osteoclast function in both physiologic and pathologic conditions to have a more general view on this issue.

p53 positively regulates osteoprotegerin-mediated inhibition of osteoclastogenesis by downregulating TSC2-induced autophagy in vitro

Osteoclasts are terminally multinucleated cells that are regulated by nuclear factor-activated T cells c1 (NFATc1), and are responsible for bone resorption while the tartrate resistant acid phosphatase (TRAP) enzymes releases into bone resorption lacunae. Furthermore, tumor suppressor p53 is a negative regulator during osteoclastogenesis. Osteoprotegerin (OPG) inhibits osteoclastogenesis and bone resorption by activating autophagy, however, whether p53 is involved in OPG-mediated inhibition of osteoclastogenesis remains unclear. In the current study, OPG could enhance the expression of p53 and tuberin sclerosis complex 2 (TSC2). Moreover, the expression of p53 is regulated by autophagy during OPG-mediated inhibition of osteoclastogenesis. Inhibition of p53 by treated with pifithrin-α (PFTα) causing augments of osteoclastogenesis and bone resorption, also reversed OPG-mediated inhibition of osteoclastogenesis by reducing the expression of TSC2. In addition, knockdown of TSC2 using siRNA could rescue OPG-mediated inhibition of osteoclastogenesis by reducing autophagy, which is manifested by the decrease of the expression of Beclin1 and the phosphorylation of mammalian target of rapamycin (mTOR) and ribosomal protein S6 kinase beta 1 (S6K1, also known as p70S6K). Collectively, p53 plays a critical role during OPG-mediated inhibition of osteoclastogenesis via regulating the TSC2-induced autophagy in vitro.

Friend or Foe? Essential Roles of Osteoclast in Maintaining Skeletal Health

Heightened activity of osteoclast is considered to be the culprit in breaking the balance during bone remodeling in pathological conditions, such as osteoporosis. As a “foe” of skeletal health, many antiosteoporosis therapies aim to inhibit osteoclastogenesis. However, bone remodeling is a dynamic process that requires the subtle coordination of osteoclasts and osteoblasts. Severe suppression of osteoclast differentiation will impair bone formation because of the coupling effect. Thus, understanding the complex roles of osteoclast in maintaining proper bone remodeling is highly warranted to develop better management of osteoporosis. This review aimed to determine the varied roles of osteoclasts in maintaining skeletal health and to highlight the positive roles of osteoclasts in maintaining normal bone remodeling. Generally, osteoclasts interact with osteocytes to initiate targeted bone remodeling and have crosstalk with mesenchymal stem cells and osteoblasts via secreted factors or cell-cell contact to promote bone formation. We believe that a better outcome of bone remodeling disorders will be achieved when proper strategies are made to coordinate osteoclasts and osteoblasts in managing such disorders.

Gaucher Disease in Bone: From Pathophysiology to Practice

Gaucher disease (GD) is a rare, genetic lysosomal disorder leading to lipid accumulation and dysfunction in multiple organs. Involvement of the skeleton is one of the most prevalent aspects of GD and a major cause of pain, disability, and reduced quality of life. Uniform recommendations for contemporary evaluation and management are needed. To develop practical clinical recommendations, an international group of experienced physicians conducted a comprehensive review of 20 years' of the literature, defining terms according to pathophysiological understanding and pointing out best practice and unmet needs related to the skeletal features of this disorder. Abnormalities of bone modeling, reduced bone density, bone infarction, and plasma cell dyscrasias accompany the displacement of healthy adipocytes in adult marrow. Exposure to excess bioactive glycosphingolipids appears to affect hematopoiesis and the balance of osteoblast and osteoclast numbers and activity. Imbalance between bone formation and breakdown induces disordered trabecular and cortical bone modeling, cortical bone thinning, fragility fractures, and osteolytic lesions. Regular assessment of bone mineral density, marrow infiltration, the axial skeleton and searching for potential malignancy are recommended. MRI is valuable for monitoring skeletal involvement: It provides semiquantitative assessment of marrow infiltration and the degree of bone infarction. When MRI is not available, monitoring of painful acute bone crises and osteonecrosis by plain X-ray has limited value. In adult patients, we recommend DXA of the lumbar spine and left and right hips, with careful protocols designed to exclude focal disease; serial follow-up should be done using the same standardized instrument. Skeletal health may be improved by common measures, including adequate calcium and vitamin D and management of pain and orthopedic complications. Prompt initiation of specific therapy for GD is crucial to optimizing outcomes and preventing irreversible skeletal complications. Investing in safe, clinically useful, and better predictive methods for determining bone integrity and fracture risk remains a need. © 2019 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

Influence of Iron on Bone Homeostasis

Bone homeostasis is a complex process, wherein osteoclasts resorb bone and osteoblasts produce new bone tissue. For the maintenance of skeletal integrity, this sequence has to be tightly regulated and orchestrated. Iron overload as well as iron deficiency disrupt the delicate balance between bone destruction and production, via influencing osteoclast and osteoblast differentiation as well as activity. Iron overload as well as iron deficiency are accompanied by weakened bones, suggesting that balanced bone homeostasis requires optimal-not too low, not too high-iron levels. The goal of this review is to summarize our current knowledge about how imbalanced iron influence skeletal health. Better understanding of this complex process may help the development of novel therapeutic approaches to deal with the pathologic effects of altered iron levels on bone.

Evidence for altered osteoclastogenesis in splenocyte cultures from VDR knockout mice

The indirect action of 1α,25(OH)₂-vitamin-D₃ (1,25D) on the osteoclast through stromal signalling is well established. The role of vitamin D in osteoclasts through direct 1,25D-VDR signalling is less well known. We showed previously that local 1,25D synthesis in osteoclasts modified osteoclastogenesis and osteoclastic resorptive activity. In this study, we hypothesised that osteoclasts lacking VDR expression would display an enhanced resorptive capacity due to the loss of 1,25D signalling. Splenocytes were cultured under osteoclast-differentiating conditions from mice with global deletion of the Vdr gene (VDRKO) and this was compared with age-matched wild-type littermate controls (WT). In VDRKO cultures, osteoclastogenesis was reduced, as indicated by fewer TRAP-positive multinucleated cells at all time points measured (p<0.05) compared to WT levels. However, VDRKO osteoclasts demonstrated greater resorption on a per cell basis than their WT counterparts. VDRKO cultures expressed greatly increased c-Fos mRNA compared to WT. In addition, the ratio of expression of the pro-apoptotic gene Bax to the pro-survival gene Bcl-2 was decreased in VDRKO cultures, implying that these osteoclasts may survive longer than WT osteoclasts. Our data indicate abnormal osteoclastogenesis due to the absence of Vdr expression, consistent with direct effects of vitamin D signalling being important for regulating the maturation and resorptive activities of osteoclasts.

Impact of isolation method on doubling time and the quality of chondrocyte and osteoblast differentiated from murine dental pulp stem cells

Background

Stem cells are normally isolated from dental pulps using the enzymatic digestion or the outgrowth method. However, the effects of the isolation method on the quality of the isolated stem cells are not studied in detail in murine models. The aim of this study was to compare the matrices secreted by osteoblast and chondrocytes differentiated from dental pulp stem cells isolated through different means.

Method

DPSC from murine incisors were isolated through either the outgrowth (DPSC-OG) or the enzymatic digestion (DPSC-ED) method. Cells at passage 4 were used in this study. The cells were characterized through morphology and expression of cell surface markers. The cells’ doubling time when cultured using different seeding densities was calculated and analyzed using one-way ANOVA and Tukey’s multiple comparison post-test. The ability of cells to differentiate to chondrocyte and osteoblast was evaluated through staining and analysis on the matrices secreted.

Results

Gene expression analysis showed that DPSC-OG and DPSC-ED expressed dental pulp mesenchymal stem cell markers, but not hematopoietic stem cell markers. The least number of cells that could have been used to culture DPSC-OG and DPSC-ED with the shortest doubling time was 5 × 10² cells/cm² (11.49 ± 2.16 h) and 1 × 10² cells/cm² (10.55 h ± 0.50), respectively. Chondrocytes differentiated from DPSC-ED produced  2 times more proteoglycan and at a faster rate than DPSC-OG. FTIR revealed that DPSC-ED differentiated into osteoblast also secreted matrix, which more resembled a calvaria.

Discussion

Isolation approaches might have influenced the cell populations obtained. This, in turn, resulted in cells with different proliferation and differentiation capability. While both DPSC-OG and DPSC-ED expressed mesenchymal stem cell markers, the percentage of cells carrying each marker might have differed between the two methods. Regardless, enzymatic digestion clearly yielded cells with better characteristics than outgrowth.

Ablation of Y1 receptor impairs osteoclast bone-resorbing activity

Y₁ receptor (Y₁R)-signalling pathway plays a pivotal role in the regulation of bone metabolism. The lack of Y₁R-signalling stimulates bone mass accretion that has been mainly attributed to Y₁R disruption from bone-forming cells. Still, the involvement of Y₁R-signalling in the control of bone-resorbing cells remained to be explored. Therefore, in this study we assessed the role of Y₁R deficiency in osteoclast formation and resorption activity. Here we demonstrate that Y₁R germline deletion (Y₁R^−/−) led to increased formation of highly multinucleated (n > 8) osteoclasts and enhanced surface area, possibly due to monocyte chemoattractant protein-1 (MCP-1) overexpression regulated by RANKL-signalling. Interestingly, functional studies revealed that these giant Y₁R^−/− multinucleated cells produce poorly demineralized eroded pits, which were associated to reduce expression of osteoclast matrix degradation markers, such as tartrate-resistant acid phosphatase-5b (TRAcP5b), matrix metalloproteinase-9 (MMP-9) and cathepsin-K (CTSK). Tridimensional (3D) morphologic analyses of resorption pits, using an in-house developed quantitative computational tool (BonePit), showed that Y₁R^−/− resorption pits displayed a marked reduction in surface area, volume and depth. Together, these data demonstrates that the lack of Y₁Rs stimulates the formation of larger multinucleated osteoclasts in vitro with reduced bone-resorbing activity, unveiling a novel therapeutic option for osteoclastic bone diseases based on Y₁R-signalling ablation.

Functional Dissociation of the Basolateral Transcytotic Compartment from the Apical Phago-lysosomal Compartment in Human Osteoclasts

Tartrate-resistant acid phosphatase (TRAP) is essential for elimination of Staphylococcus aureus, the main infectious agent responsible for osteomyelitis. This in vitro study investigated uptake and processing of fluorescence-labeled S. aureus by human osteoclasts and dendritic cells. The cells were stained for TRAP and the acidic compartment using a fluorescence-based protocol. In dendritic cells, TRAP and bacteria were colocalized. In osteoclasts, there was no colocalization of bacteria, TRAP, or the acidic compartment, indicating that there are three distinct vesicular compartments: the apical phago-lysosomal compartment, the basal secretory compartment, and the basolateral transcytotic compartment. Dissociation of the TRAP-containing transcytotic vesicles from the apical phago-lysosomal compartment may restrain osteoclasts from eliminating S. aureus.

The extended human PTPome: a growing tyrosine phosphatase family

Tyr phosphatases are, by definition, enzymes that dephosphorylate phospho-Tyr (pTyr) from proteins. This activity is found in several structurally diverse protein families, including the protein Tyr phosphatase (PTP), arsenate reductase, rhodanese, haloacid dehalogenase (HAD) and His phosphatase (HP) families. Most of these families include members with substrate specificity for non-pTyr substrates, such as phospho-Ser/phospho-Thr, phosphoinositides, phosphorylated carbohydrates, mRNAs, or inorganic moieties. A Cys is essential for catalysis in PTPs, rhodanese and arsenate reductase enzymes, whereas this work is performed by an Asp in HAD phosphatases and by a His in HPs, via a catalytic mechanism shared by all of the different families. The category that contains most Tyr phosphatases is the PTP family, which, although it received its name from this activity, includes Ser, Thr, inositide, carbohydrate and RNA phosphatases, as well as some inactive pseudophosphatase proteins. Here, we propose an extended collection of human Tyr phosphatases, which we call the extended human PTPome. The addition of new members (SACs, paladin, INPP4s, TMEM55s, SSU72, and acid phosphatases) to the currently categorized PTP group of enzymes means that the extended human PTPome contains up to 125 proteins, of which ~ 40 are selective for pTyr. We set criteria to ascribe proteins to the extended PTPome, and summarize the more important features of the new PTPome members in the context of their phosphatase activity and their relationship with human disease.

Response of knee fibrocartilage to joint destabilization

OBJECTIVE

A major challenge to understanding osteoarthritis (OA) pathology is identifying the cellular events that precede the onset of cartilage damage. The objective of this study is to determine the effect of joint destabilization on early changes to fibrocartilage in the joint.

DESIGN/METHODS

The anterior cruciate ligament was transected in collagen reporter mice (Col1CFP and ColXRFP). Mineralization labels were given every 2 weeks to measure new mineralized cartilage apposition. Novel fluorescent histology of mineralized tissue was used to characterize the changes in fibrocartilage at 2 and 4 weeks post-injury.

RESULTS

Changes in fibrocartilaginous structures of the joint occur as early as 2 weeks after injury and are well developed by 4 weeks. The alterations are seen in multiple entheses and in the medial surface of the femoral and tibial condyles. In the responding entheses, mineral apposition towards the ligament midsubstance results in thickening of the mineralize fibrocartilage. These changes are associated with increases in ColX-RFP, Col1-CFP reporter activity and alkaline phosphatase enzyme activity. Mineral apposition also occurs in the fibrocartilage of the non-articular regions of the medial condyles by 2 weeks and develops into osteophytes by 4 weeks post-injury. An unexpected observation is punctate expression of tartrate resistant acid phosphatase activity in unmineralized fibrochondrocytes adjacent to active appositional mineralization.

DISCUSSION

These observations suggest that fibrocartilage activates prior to degradation of the articular cartilage. Thus clinical and histological imaging of fibrocartilage may be an earlier indicator of disease initiation and may indicate a more appropriate time to start preventative treatment.

The many faces of interferon tau

Interferon tau (IFNT) was discovered as the pregnancy recognition signal in ruminants, but is now known to have a plethora of physiological functions in the mammalian uterus. The mammalian uterus includes, from the outer surface to the lumen, the serosa, myometrium and endometrium. The endometrium consists of the luminal, superficial glandular, and glandular epithelia, each with a unique phenotype, stromal cells, vascular elements, nerves and immune cells. The uterine epithelia secrete or selectively transport molecules into the uterine lumen that are collectively known as histotroph. Histotroph is required for growth and development of the conceptus (embryo and its associated extra-embryonic membranes) and includes nutrients such as amino acids and glucose, enzymes, growth factors, cytokines, lymphokines, transport proteins for vitamins and minerals and extracellular matrix molecules. Interferon tau and progesterone stimulate transport of amino acids in histotroph, particularly arginine. Arginine stimulates the mechanistic target of rapamycin pathway to induce proliferation, migration and protein synthesis by cells of the conceptus, and arginine is the substrate for synthesis of nitric oxide and polyamines required for growth and development of the conceptus. In ruminants, IFNT also acts in concert with progesterone from the corpus luteum to increase expression of genes for transport of nutrients into the uterine lumen, as well as proteases, protease inhibitors, growth factors for hematopoiesis and angiogenesis and other molecules critical for implantation and placentation. Collectively, the pleiotropic effects of IFNT contribute to survival, growth and development of the ruminant conceptus.

Pregnancy-secreted Acid phosphatase, uteroferrin, enhances fetal erythropoiesis

Uteroferrin (UF) is a progesterone-induced acid phosphatase produced by uterine glandular epithelia in mammals during pregnancy and targeted to sites of hematopoiesis throughout pregnancy. The expression pattern of UF is coordinated with early fetal hematopoietic development in the yolk sac and then liver, spleen, and bone to prevent anemia in fetuses. Our previous studies suggested that UF exerts stimulatory impacts on hematopoietic progenitor cells. However, the precise role and thereby the mechanism of action of UF on hematopoiesis have not been investigated previously. Here, we report that UF is a potent regulator that can greatly enhance fetal erythropoiesis. Using primary fetal liver hematopoietic cells, we observed a synergistic stimulatory effect of UF with erythropoietin and other growth factors on both burst-forming unit-erythroid and colony-forming unit-erythroid formation. Further, we demonstrated that UF enhanced erythropoiesis at terminal stages using an in vitro culture system. Surveying genes that are crucial for erythrocyte formation at various stages revealed that UF, along with erythropoietin, up-regulated transcription factors required for terminal erythrocyte differentiation and genes required for synthesis of hemoglobin. Collectively, our results demonstrate that UF is a cytokine secreted by uterine glands in response to progesterone that promotes fetal erythropoiesis at various stages of pregnancy, including burst-forming unit-erythroid and colony-forming unit-erythroid progenitor cells and terminal stages of differentiation of hematopoietic cells in the erythroid lineage.

Osteoclasts: more than 'bone eaters'

As the only cells definitively shown to degrade bone, osteoclasts are key mediators of skeletal diseases including osteoporosis. Bone-forming osteoblasts, and hematopoietic and immune system cells, each influence osteoclast formation and function, but the reciprocal impact of osteoclasts on these cells is less well appreciated. We highlight here the functions that osteoclasts perform beyond bone resorption. First, we consider how osteoclast signals may contribute to bone formation by osteoblasts and to the pathology of bone lesions such as fibrous dysplasia and giant cell tumors. Second, we review the interaction of osteoclasts with the hematopoietic system, including the stem cell niche and adaptive immune cells. Connections between osteoclasts and other cells in the bone microenvironment are discussed within a clinically relevant framework.

Mechanisms of osteoclast-dependent bone formation

Should we believe that osteoclasts are only involved in bone resorption? What about their contribution to bone formation? In this article I will review evidence that bone formation can be regulated by osteoclasts. Why is this? Likely because in the physiologic condition of bone remodeling, bone resorption and formation are balanced, and there is no better way to control this equilibrium than through a concerted action between the two cell types. Although the influence of osteoblasts on osteoclastic bone resorption is well documented and consolidated over time, what osteoclasts do to regulate osteoblast activity is still matter of intense investigation. The original hypothesis that all is in the osteoblast-seeking factors stored in the bone matrix, released and activated during bone resorption, is now being challenged by several studies, suggesting that osteoclasts are also capable of producing 'clastokines' that regulate osteoblast performance. Indeed, several of them have been demonstrated to orchestrate osteoclast-osteoblast activities. However, we are probably still at the dawn of a new era, and future work will tell us whether any of these clastokines can be exploited to stimulate bone formation and rebalance bone remodeling in skeletal diseases.

Impairment of rat tooth eruption in pups born to mothers exposed to chronic stress during pregnancy

OBJECTIVE

Tooth eruption is a multifactorial process in which bone tissue plays a prevailing role. In this study we evaluated the bone overlying the developing tooth germ and the degree of tooth eruption of the first mandibular molar in pups born to mothers subjected to constant light during pregnancy.

DESIGN

Pregnant rats were divided into two groups: mothers chronically exposed to a 12:12 light/light cycle (LL) from day 10 to 20 of pregnancy and controls (C) maintained on a 12:12 h light/dark cycle. Pups from each group were euthanized at the age 3 or 15 days. Buccolingually oriented sections of mandibles were stained with haematoxylin-eosin or for histochemical detection of tartrate resistant acid phosphatase (TRAP). The histomorphometric parameters evaluated were bone volume, number of osteoclasts, TRAP+ bone surface, number of TRAP+ and TRAP- osteoclasts per mm(2) and degree of tooth eruption (mm).

RESULTS

It was found an increase in bone volume (LL: 58.14±4.24 vs. C: 32.31±2.16; p<0.01) and a decrease in the number of osteoclasts (LL: 3.5±0.65 vs. C: 8.03±1.31; p<0.01) and TRAP+ cells (LL: 0.84±0.53 vs. C: 8.59±1.26; p<0.01) in 3-day-old pups born to LL-exposed mothers. These observations are consistent with the decrease in the degree of tooth eruption observed in 15-day-old experimental pups (LL: -0.605±0.05 vs. C: -0.342±0.02; p<0.0001).

CONCLUSION

Our results suggest that chronic constant light applied as a pre-natal stressor impairs the resorptive capacity of osteoclasts involved in the formation of the eruption pathway and consequently the degree of tooth eruption.

Role of tartrate-resistant acid phosphatase (TRAP) in long bone development

Tartrate resistant acid phosphatase (TRAP) was shown to be critical for skeleton development, and TRAP deficiency leads to a reduced resorptive activity during endochondral ossification resulting in an osteopetrotic phenotype and shortened long bones in adult mice. A proper longitudinal growth depends on a timely, well-coordinated vascularization and formation of the secondary ossification center (SOC) of the long bones epiphysis. Our results demonstrate that TRAP is not essential for the formation of the epiphyseal vascular network. Therefore, in wild type (Wt) controls as well as TRAP deficient (TRAP^−/−) mutants vascularised cartilage canals are present from postnatal day (P) five. However, in the epiphysis of the TRAP^−/− mice cartilage mineralization, formation of the marrow cavity and the SOC occur prematurely compared with the controls. In the mutant mice the entire growth plate is widened due to an expansion of the hypertrophic zone. This is not seen in younger animals but first detected at week (W) three and during further development. Moreover, an enhanced number of thickened trabeculae, indicative of the osteopetrotic phenotype, are observed in the metaphysis beginning with W three. Epiphyseal excavation was proposed as an important function of TRAP, and we examined whether TRAP deficiency affects this process. We therefore evaluated the marrow cavity volume (MCV) and the epiphyseal volume (EV) and computed the MCV to EV ratio (MCV/EV). We investigated developmental stages until W 12. Our results indicate that both epiphyseal excavation and establishment of the SOC are hardly impaired in the knockouts. Furthermore, no differences in the morphology of the epiphyseal bone trabeculae and remodeling of the articular cartilage layers are noted between Wt and TRAP^−/− mice. We conclude that in long bones, TRAP is critical for the development of the growth plate and the metaphysis but apparently not for the epiphyseal vascularization, excavation, and establishment of the SOC.

Assay of in vitro osteoclast activity on dentine, and synthetic calcium phosphate bone substitutes

Resorption of synthetic bone substitute materials is essential for the integration of these materials into the natural bone remodeling process. Osteoclast behavior in the presence of calcium phosphate bioceramics (CaPB) is partially understood, and a better understanding of the underlying mechanisms is expected to facilitate the development of new synthetic bone substitutes to improve bone regeneration. In the present study, our aim was to investigate osteoclastic resorption of various synthetic CaPB. We used neonatal total rabbit bone cells to generate osteoclasts. Osteoclast-generated resorption on dentine and multiple CaPB was investigated by quantifying the surface resorbed and measuring tartrate resistant acid phosphatase (TRAP) enzyme activity. In this study, we observed that osteoclastic cells responded in a different way to each substrate. Both dentine and CaPB were resorbed but the quantitative results for the surface resorbed and TRAP activity showed a specific response to each substrate and that increased mineral density seemed to inhibit osteoclast activity.

Osteoclasts in bone modeling, as revealed by in vivo imaging, are essential for organogenesis in fish

Bone modeling is the central system controlling the formation of bone including bone growth and shape in early development, in which bone is continuously resorbed by osteoclasts and formed by osteoblasts. However, this system has not been well documented, because it is difficult to trace osteoclasts and osteoblasts in vivo during development. Here we showed the important role of osteoclasts in organogenesis by establishing osteoclast-specific transgenic medaka lines and by using a zebrafish osteoclast-deficient line. Using in vivo imaging of osteoclasts in the transgenic medaka carrying an enhanced GFP (EGFP) or DsRed reporter gene driven by the medaka TRAP (Tartrate-Resistant Acid Phosphatase) or Cathepsin K promoter, respectively, we examined the maturation and migration of osteoclasts. Our results showed that mononuclear or multinucleated osteoclasts in the vertebral body were specifically localized at the inside of the neural and hemal arches, but not at the vertebral centrum. Furthermore, transmission electron microscopic (TEM) analyses revealed that osteoclasts were flat-shaped multinucleated cells, suggesting that osteoclasts initially differentiate from TRAP-positive mononuclear cells residing around bone. The zebrafish panther mutant lacks a functional c-fms (receptor for macrophage colony-stimulating factor) gene crucial for osteoclast proliferation and differentiation and thus has a low number of osteoclasts. Analysis of this mutant revealed deformities in both its neural and hemal arches, which resulted in abnormal development of the neural tube and blood vessels located inside these arches. Our results provide the first demonstration that bone resorption during bone modeling is essential for proper development of neural and vascular systems associated with fish vertebrae.

Delayed bone age due to a dual effect of FGFR3 mutation in Achondroplasia

Achondroplasia (ACH), the most common form of human dwarfism is caused by a mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene, resulting in constitutive activation of the receptor. Typical radiological features include shortening of the tubular bones and macrocephaly, due to disruption of endochondral ossification. Consequently, FGFR3 has been described as a negative regulator of bone growth. Studying a large cohort of ACH patients, a delay in bone age was observed shortly after birth (for boys p=2.6×10(-9) and for girls p=1.2×10(-8)). This delay was no longer apparent during adolescence. In order to gain further insight into bone formation, bone development was studied in a murine model of chondrodysplasia (Fgfr3(Y367C/+)) from birth to 6weeks of age. Delayed bone age was also observed in Fgfr3(Y367C/+) mice at 1week of age followed by an accelerated secondary ossification center formation. A low level of chondrocyte proliferation was observed in the normal growth plate at birth, which increased with bone growth. In the pathological condition, a significantly high level of proliferative cells was present at birth, but exhibited a transient decrease only to rise again subsequently. Histological and in situ analyses suggested the altered endochondral ossification process may result from delayed chondrocyte differentiation, disruption of vascularization and osteoblast invasion of the femur. All these data provide evidence that FGFR3 regulates normal chondrocyte proliferation and differentiation during bone growth and suggest that constitutive activation of the receptor disrupts both processes. Therefore, the consequences of FGFR3 activation on the physiological process of bone development appear to be dependent on spatial and temporal occurrence. In conclusion, these observations support the notion that FGFR3 has a dual effect, as both a negative and a positive regulator of the endochondral ossification process during post-natal bone development.

RANKL-RANK signaling regulates expression of xenotropic and polytropic virus receptor (XPR1) in osteoclasts

Formation of multinucleated bone-resorbing osteoclasts results from activation of the receptor activated NF-kappaB ligand (RANKL)-receptor activated NF-kappaB (RANK) signaling pathway in primary bone marrow macrophages and a macrophage cell line (RAW 264.7). Osteoclasts, through bone remodeling, are key participants in the homeostatic regulation of calcium and phosphate levels within the body. Microarray analysis using Gene Expression Dynamic Inspector (GEDI) clustering software indicated that osteoclast differentiation is correlated with an increase in xenotropic and polytropic virus receptor 1 (XPR1) mRNA transcripts. XPR1 is a receptor of the xenotropic and polytropic murine leukemia virus and homolog of yeast Syg1 and plant Pi transporter PHO1. Quantitative PCR was used to validate the up-regulation of XPR1 message following RANKL stimulation in both primary bone marrow cells and a macrophage cell line. Immunostaining for the XPR1 protein showed that there is translocation of XPR1 to the membranes of the sealing zone in mature osteoclasts. This study is the first to demonstrate that the expression of retro-viral receptor, XPR1, is regulated by RANKL-RANK signaling.

Complex regulation of tartrate-resistant acid phosphatase (TRAP) expression by interleukin 4 (IL-4): IL-4 indirectly suppresses receptor activator of NF-kappaB ligand (RANKL)-mediated TRAP expression but modestly induces its expression directly

Interleukin 4 (IL-4) inhibits receptor activator of NF-kappaB ligand (RANKL)-induced osteoclast formation and functional activity in a STAT6-dependent manner. IL-4 down-regulates expression of tartrate-resistant acid phosphatase (TRAP) in mature osteoclasts. To determine whether IL-4 regulates TRAP promoter activity, RAW264.7 cells were transfected with a TRAP promoter-luciferase reporter. Treatment with IL-4 alone modestly enhanced TRAP luciferase activity. However, IL-4 suppressed the ability of RANKL to up-regulate TRAP-luciferase activity, suggesting that IL-4 has multiple effects on TRAP transcription. IL-4 also reduced the RANKL-induced association of RNA polymerase II with the TRAP gene in osteoclasts. The TRAP promoter contains a STAT6-binding motif, and STAT6 bound to the endogenous TRAP promoter after IL-4 treatment. To determine the impact of STAT6 binding, we transfected cells with STAT6VT, a constitutively active STAT6 mutant. STAT6VT alone up-regulated TRAP-luciferase activity; this effect was abrogated by mutating the STAT6 binding site in the minimal TRAP promoter. STAT6VT did not inhibit the potent up-regulation of TRAP promoter activity caused by overexpression of NFATc1, PU.1, and microphthalmia transcription factor, downstream targets of macrophage colony-stimulating factor and RANKL. IL-4 down-regulated the expression of c-Fos and NFATc1 in mature osteoclasts. Knockdown of NFATc1 by short interfering RNA caused TRAP expression to be down-regulated, and ectopic expression of NFATc1 abrogated the IL-4-induced down-regulation of TRAP. These results suggest that STAT6 plays two distinct roles in TRAP expression. The IL-4-induced activation of STAT6 mediates suppression of the RANKL-induced TRAP promoter activity indirectly by inhibiting NFATc1 expression. However, in the absence of RANKL and osteoclast differentiation, STAT6 binds the TRAP promoter after IL-4 treatment and directly enhances TRAP expression.

Localization of tartrate-resistant acid phosphatase (TRAP), membrane type-1 matrix metalloproteinases (MT1-MMP) and macrophages during early endochondral bone formation

Endochondral bone formation, the process by which most parts of our skeleton evolve, leads to the establishment of the diaphyseal primary (POC) and epiphyseal secondary ossification centre (SOC) in long bones. An essential event for the development of the SOC is the early generation of vascularized cartilage canals that requires the proteolytic cleavage of the cartilaginous matrix. This in turn will allow the canals to grow into the epiphysis. In the present study we therefore initially investigated which enzymes and types of cells are involved in this process. We have chosen the mouse as an animal model and focused our studies on the distal part of the femur during early stages after birth. The formation of the cartilage canals was promoted by tartrate-resistant acid phosphatase (TRAP) and membrane type-1 matrix metalloproteinases (MT1-MMP). In addition, macrophages and cells containing numerous lysosomes contributed to the establishment of the canals and enabled their further advancement into the epiphysis. As development continued, the SOC was formed, and in mice aged 10 days a distinct layer of type I collagen (= osteoid) was laid down onto the cartilage scaffold. The events leading to the establishment of the SOC were compared with those of the POC. Basically these processes were quite similar, and in both ossification centers, TRAP-positive chondroclasts resorbed the cartilage matrix. However, occasionally co-expression of TRAP and MT1-MMP was noted in a small subpopulation of this cell type. Furthermore, numerous osteoblasts expressed MT1-MMP from the start of endochondral ossification, whereas others did not. In osteocytogenesis, MT1-MMP has been shown to be critical for the establishment of the cytoplasmic processes mediating the communication between osteocytes and bone-lining cells. Considering the well-known fact that not all osteoblasts transform into osteocytes, and in accordance with the present data, we suggest that MT1-MMP is needed at the very beginning of osteocytogenesis and may additionally determine whether an osteoblast further differentiates into an osteocyte.

Immunolocalisation of the uterine secretory proteins uterocalin, uteroferrin and uteroglobin in the mare's uterus and placenta throughout pregnancy

Previous studies have shown that the equine uterus produces many progesterone-dependent proteins throughout gestation. In particular, uterocalin and uteroferrin are detectable using electrophoresis or blot analyses but information regarding the immunohistochemical placental distribution of these two proteins is rare and information regarding uteroglobin is still lacking. The aim of the present study was to co-immunolocalise these three secretory proteins in the mare's uterus throughout gestation in an effort to understand their functional role in the maintenance of pregnancy. Therefore, endometrial biopsy samples were obtained from 20 pregnant mares between 16 and 309 days of gestation and labelled immunohistochemically for uteroglobin, uteroferrin and uterocalin. Uteroferrin remained detectable in almost every endometrial gland at all stages but with an increase in staining intensity as gestation advanced. The most progesterone-dependent protein, uterocalin, showed variable staining throughout gestation with the most intense labelling in early pregnancy and during the period of endometrial cup reaction. Uteroglobin secretion was only detectable in traces and only in individual glands throughout gestation. The results indicate that uterocalin and uteroferrin, but not uteroglobin, may play important roles in supplying nutrients for the conceptus, thereby contributing to the maintenance of pregnancy. However, further investigations are necessary to understand the role of uteroglobin during gestation.

Atlantic salmon (Salmo salar L.) parr fed genetically modified soybeans and maize: Histological, digestive, metabolic, and immunological investigations

Physiological and health related responses to dietary inclusion of genetically modified (GM) full-fat soybean meal (Roundup Ready; GM-soy) and maize (MON810 Bt-maize; GM-maize), as well as non-parental, untransformed lines (nGM-soy and nGM-maize D2), were evaluated in farmed Atlantic salmon (Salmo salar L.) parr during the first 8 months of feeding. Significant effects of dietary GM presence were only found in intestinal Na+-dependent d-glucose uptake and SGLT1 protein level in the region pyloric caeca in which the highest values were found in the GM-soy, intermediate in the nGM-soy, and lowest in the standard FM fed groups. Data from this study confirm that GM soybeans (RRS) and maize (MON810) at inclusion levels of about 6% appear to be as safe as commercially available nGM soy and maize in diets for Atlantic salmon parr. Results from studies with higher inclusion levels and with non-modified, isogenic or near-isogenic parental lines as control groups are pending.

Structure, formation and role of cartilage canals in the developing bone

In the long bones, endochondral bone formation proceeds via the development of a diaphyseal primary ossification centre (POC) and an epiphyseal secondary ossification centre (SOC). The growth plate, the essential structure for longitudinal bone growth, is located between these two sites of ossification. Basically, endochondral bone development depends upon neovascularization, and the early generation of vascularized cartilage canals is an initial event, clearly preceding the formation of the SOC. These canals form a discrete network within the cartilaginous epiphysis giving rise to the formation of the marrow space followed by the establishment of the SOC. These processes require excavation of the provisional cartilaginous matrix which is eventually replaced by permanent bone matrix. In this review, we discuss the formation of the cartilage canals and the importance of their cells in the ossification process. Special attention is paid to the enzymes required in disintegration of the cartilaginous matrix which, in turn, will allow for the invasion of new vessels. Furthermore, we show that the mesenchymal cells of the cartilage canals express bone-relevant proteins and transform into osteocytes. We conclude that the canals are essential for normal epiphyseal bone development, the establishment of the growth plate and ultimately longitudinal growth of the bones.

Monomeric tartrate resistant acid phosphatase induces insulin sensitive obesity

BACKGROUND

Obesity is associated with macrophage infiltration of adipose tissue, which may link adipose inflammation to insulin resistance. However, the impact of inflammatory cells in the pathophysiology of obesity remains unclear. Tartrate resistant acid phosphatase (TRAP) is an enzyme expressed by subsets of macrophages and osteoclasts that exists either as an enzymatically inactive monomer or as an active, proteolytically processed dimer.

PRINCIPAL FINDINGS

Using mice over expressing TRAP, we show that over-expression of monomeric, but not the dimeric form in adipose tissue leads to early onset spontaneous hyperplastic obesity i.e. many small fat cells. In vitro, recombinant monomeric, but not proteolytically processed TRAP induced proliferation and differentiation of mouse and human adipocyte precursor cells. In humans, monomeric TRAP was highly expressed in the adipose tissue of obese individuals. In both the mouse model and in the obese humans the source of TRAP in adipose tissue was macrophages. In addition, the obese TRAP over expressing mice exhibited signs of a low-grade inflammatory reaction in adipose tissue without evidence of abnormal adipocyte lipolysis, lipogenesis or insulin sensitivity.

CONCLUSION

Monomeric TRAP, most likely secreted from adipose tissue macrophages, induces hyperplastic obesity with normal adipocyte lipid metabolism and insulin sensitivity.

A new heterozygous mutation (R714C) of the osteopetrosis gene, pleckstrin homolog domain containing family M (with run domain) member 1 (PLEKHM1), impairs vesicular acidification and increases TRACP secretion in osteoclasts

We studied phenotypic and cellular aspects in a patient with a heterozygous mutation of the PLEKHM1 gene and obtained some indications regarding the role of the protein in bone cell function. Plekhm1 is involved in osteoclast endosomal vesicle acidification and TRACP exocytosis, contributing to events involved in osteoclast-osteoblast cross-talk.

INTRODUCTION

The gene PLEKHM1 encodes a nonsecretory adaptor protein that localizes to endosomal vesicles. A highly truncated Plekhm1 protein was previously found in a patient with intermediate autosomal recessive osteopetrosis.

MATERIALS AND METHODS

We describe a new heterozygous mutation in the PLEKHM1 gene in a patient presenting with low vertebral and femoral T-scores and areas of focal sclerosis. Clinical evaluation, mutational analysis, assessment of in vitro osteoclast morphology and activity, transfection studies, and evaluation of osteoclast-osteoblast cross-talk were carried out.

RESULTS

Direct DNA sequencing showed a heterozygous C to T substitution on cDNA position 2140 of the PLEKHM1 gene, predicted to lead to an R714C mutant protein. The mutation was not found in 104 control chromosomes. In vitro, patient's osteoclasts showed normal formation rate, morphology, number of nuclei, and actin rings but lower TRACP activity and higher endosomal pH than control osteoclasts. The patient had high serum PTH and TRACP, despite low TRACP activity in osteoclasts in vitro. HEK293 cells overexpressing either wildtype or Plekhm1-R714C showed no difference in localization of the variants, and co-transfection with a TRACP vector confirmed low TRACP activity in cells carrying the R714C mutation. RAW 264.7 osteoclast-like cells expressing the Plekhm1-R714C variant also showed low TRACP activity and reduced ability to acidify endosomal compartments compared with cells expressing the wildtype protein. Reduced intracellular TRACP was caused by increased protein secretion rather than reduced expression. TRACP-containing conditioned medium was able to increase osteoblast alkaline phosphatase, suggesting the focal osteosclerosis is a result of increased osteoclast-osteoblast coupling.

CONCLUSIONS

We provide further evidence for a role of Plekhm-1 in osteoclasts by showing that a novel mutation in PLEKHM1 is associated with a complex bone phenotype of generalized osteopenia combined with "focal osteosclerosis." Our data suggest that the mutation affects endosomal acidification/maturation and TRACP exocytosis, with implications for osteoclast-osteoblast cross-talk.

Is cell culture stressful? Effects of degradable and nondegradable culture surfaces on U937 cell function

In vitro cell culture has become one of the most widely used techniques in biological and health sciences research, with the most common culture supports being either tissue culture grade polystyrene (TCPS) or polydimethylsiloxane (PDMS). It has previously been shown that monocyte-derived macrophages (MDMs) respond to material surface chemistry, synthesizing and releasing degradative activities that could produce products, which alter the cell's response. In this study, functional parameters of differentiated U937 macrophage-like cells were compared when cultured on nondegradable standard control surfaces versus models of biomaterials (polycarbonate-based polyurethanes) used in the manufacture of medical devices previously shown to degrade and/or elicit pathways of inflammation. Although the influence of PDMS and TCPS on cell function is often underappreciated by investigators, both surfaces elicited enzyme markers of inflammation. Cells on TCPS had the highest intracellular and released esterase activities and protein levels. Cells on PDMS had the most released acid phosphatase activity and protein (P<0.001), as well as de novo 57− and 59− kDa released proteins. The criteria for defining an activated cell phenotype become critically important when materials such as PDMS and TCPS are used as standard control surfaces whether in experiments for research in elucidating metabolic pathways or in screening drugs and materials for therapeutic uses.