Vitamin D supplementation during pregnancy and pregnancy outcomes

not submitted. doi:10.1016/j.bone.2012.02.057 IS36 What is the function of tartrate resistant acid phosphatase 5B? G. Andersson, B. Ek-Rylander Laboratory Medicine, Karolinska Institutet, Huddinge, Sweden Learning Outcome 1: Knowledge of the protein structure of TRAP and to understand the events at different subcellular levels for generation of TRAP 5B. Learning Outcome 2: What substrates are acted on by TRAP 5B and the biological implications. Learning Outcome 3: Clinical indications for TRAP 5B as a biomarker and characteristics of currently available assays for TRAP 5B. Abstract: Tartrate resistant acid phosphatase (TRAP, TRAcP, AcP 5) was originally discovered as a histochemical marker for identifying osteoclasts in bone sections and now becoming increasingly used as a bone resorption biomarker in various clinical situations such as for monitoring therapy response in osteoporosis and skeletal metastasis. Tartrate-resistant acid phosphatase is now recognized to be a molecule of wide-spread occurrence in both the skeleton and the immune system. Besides osteoclasts, TRAP is also expressed by certain macrophages and dendritic cells with a postulated role in innate immunity. Studies on TRAP-depleted and over-expressing mice suggest that the protein exerts a critical role in many biological processes including skeletal development, bone remodeling and repair, cell adhesion and migration, collagen synthesis and degradation, sorting of lysosomal enzymes, cytokine production, macrophage recruitment, dendritic cell maturation and a role in the development of Th1 cell responses. Expression of TRAP displays a complex regulation both at the transcriptional and post-translational levels. As a consequence, there are two TRAP isoforms present in tissues and blood. The TRAP 5A isoform represents a less enzymatically active precursor to the more active TRAP 5B. Conversion of TRAP 5A to 5B requires several proteolytic processing steps in different intraand extra-cellular compartments. The major difference between the TRAP isoforms resides in the presence (5A) or absence (5B) of a repressive loop domain in the protein. Osteopontin (OPN) is a bone matrix phosphoprotein important for osteoclast adhesion to bone and osteoclast polarization. TRAP 5B acts as a very effective osteopontin phosphatase, and TRAP 5B secreted from osteoclasts induces a migratory response in osteoclasts on OPN. There is now compelling evidence that OPN not only plays an important role in bone resorption, but also acts as an inducible inhibitor of mineralization and a stimulator of innate immune responses. For instance, OPN induces IL-12 and inhibits IL-10 expression, and is required for the production of type I interferon in plasmacytoid dendritic cells. Importantly, several of the biological activities of OPN seem to depend on phosphorylation of the protein. Conspicuously, TRAP and OPN seems to be involved in similar biological processes. Humans with recessive inactivating mutations in the TRAP gene display a mild skeletal dysplasia and a variety of autoimmune diseases including SLE. The mutations were associated with hyperphosphorylation of osteopontin, suggesting that TRAP regulation of osteopontin phosphorylation is important for skeletal properties as well as for modulation of the activation of the innate immune system. Elucidation of substrates for TRAP 5B with functional roles e.g. osteopontin, opens up new avenues for understanding the pathogenesis of various metabolic and inflammatory skeletal diseases as well as disorders of the immune system. This article is part of a Special Issue entitled ECTS 2012. Disclosure of interest: None declared. doi:10.1016/j.bone.2012.02.058 IS37 NO signaling in mechanical adaptation of bone J. Klein-Nulend⁎, R.G. Bacabac, A. Vatsa, C.M. Semeins, A.D. Bakker Oral Cell Biology, ACTA-University of Amsterdam and VU University Amsterdam, Research Institute MOVE, Amsterdam, Netherlands Physics, University of San Carlos, Cebu City, Philippines Regenerative Medicine, School of Science and Technology and Health, University Campus Suffolk, Ipswich, UK Learning Outcome 1: The critical role of intercellular communication via chemical signals like nitric oxide (NO) in the dynamic process of bone remodeling. Learning Outcome 2: The NO response of bone cells to dynamic stress: rate rather than magnitude of loading is important for the effect of mechanical loading on bone. Learning Outcome 3: Force traction, morphology change, and the release of NO are all related in similar pathways in response to environmental stress conditions. Abstract: Intercellular signaling is an important physiological phenomenon involved in maintaining homeostasis in all tissues. In bone, intercellular communication via chemical signals like nitric oxide (NO) plays a critical role in the dynamic process of bone remodeling. It is believed that osteocytes are the mechanosensors in bone. If bones are mechanically loaded, the resulting shear stress caused by strainderived interstitial fluid flow can activate them. Activated osteocytes produce signaling molecules like NO, which modulate the activity of the bone forming osteoblasts, and the bone resorbing osteoclasts, thereby orchestrating bone adaptation to mechanical loading. This single-cell level mechanosensing and intercellular signaling is essential for bone adaptation to mechanical loading. Since NO production is essential for loadinginduced bone formation in vivo, the NO production in response to mechanical stimulation is a meaningful parameter for measuring bone cell activation. Several studies have shown that NO production is rapidly increased in response to mechanical stress in bone cells, including isolated osteocytes. How a mechanically-stimulated single osteocyte functions in a social context via intercellular communication, was studied by monitoring changes in intracellular NO production, using DAR-4M AM chromophore, in the surrounding osteocytes. A single mechanically-stimulated osteocyte activates its surrounding osteocytes via direct and/ or indirect intercellular signaling. In single osteocytes, mechanical stimulation of both cell body and cell process results in upregulation of intracellular NO production, indicating that both cell body and cell process might play a role in mechanosensing and mechanotransduction in bone. Osteocytes with round-suspended morphology require lower force stimulation to show an increase in NO production, even though they are an order of magnitude more elastic compared to flat-adherent cells. Apparently, elastic osteocytes seem to require less mechanical forces in order to respond with increased NO production than stiffer cells. Bone cells release increased amounts of NO in relation to the rate of fluid shear stress as demonstrated by bone cells in a broad range of frequencies induced by vibration stress. This supports the notion that bone formation in vivo is stimulated by dynamic rather than static loads. This rate-dependent response occurs provided that the cells initially experience a stress-kick. The bone cell response to stress is enhanced by the addition of noise, i.e. the NO released by bone cells reaches a maximum at the application of an optimum noise-level by fluid shear stress. Since mechanical stimuli and NO production enhance the fracture resistance of bone, these data may facilitate the development of novel osteoporosis treatments. This article is part of a Special Issue entitled ECTS 2012. Disclosure of interest: J. Klein-Nulend Grant/research support from SRON Netherlands Institute for Space Research, project # MG-055; ALW/FOM/NWO project # 01FB28/2, R. Bacabac: none declared, A. Vatsa: none declared, C. Semeins: none declared, A. Bakker: none declared. doi:10.1016/j.bone.2012.02.059 Abstracts S24