A complicated case of hyperparathyroidism

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along alternative routes. We herein present a novel mechanism whereby such unequivocal commitment is achieved, based on microRNA (miRNA)dependent repression of an alternative cell fate. We show that the commitment of monocyte progenitors to active macrophage differentiation involves stimulation of miR-155 expression, which leads to the suppression of the alternative pathway; namely, RANK ligand-induced osteoclastogenesis. Rapid miR-155 upregulation represses the expression of MITF and PU.1, two transcription factors essential for osteoclast differentiation. A temporal asymmetry, whereby miR-155 expression precedes and overrides the activation of the osteoclast transcriptional program, provides the means for coherent macrophage differentiation, even in the presence of osteoclastogenic signals. Based on these findings, we propose that miRNA may provide a general mechanism for unequivocal commitment underlying stem cell differentiation. Disclosure of Interest: None declared Keywords: microrna, osteoclast doi:10.1016/j.bone.2010.04.035

IS35 Significance of MicroRNA control of bone formation and homeostasis J.B. Lian⁎1, G.S. Stein1, C. Croce2, J.L. Stein1, A.J. van Wijnen1, Z. Li1, M.Q. Hassan1, T. Gaur1, R. Aqeilan2, M. Jafferji1, Y. Zhang1 1 Cell Biology, University of Massachusetts Medical School, Worcester, United States 2 Department of Molecular Virology, Immunology and Medical Genetics and Comprehensive Cancer Center, Ohio State University, Columbus, United States Bone tissue arises from mesenchymal stem cells (MS) induced into osteoblast lineage by developmental signaling factors and indispensable transcription factors. MicroRNAs (miR) attenuation of protein translation has emerged as an important regulator of tissue morphogenesis, cell growth and differentiation by base pairing with 3’-UTR sequences of their target mRNAs to attenuate protein synthesis. Recent studies show that a program of microRNAs respond to the BMP osteogenic signal for commitment of MSCs to osteoblasts (Li, Proc Natl Acad Sci, 2008). During osteoblast differentiation approximately 40 miRs are continuously upregulated from the proliferation stage of preosteoblasts reaching peak levels during the mineralization stage of the ECM (Li, J Bio Chem, 2009). A single microRNA can target multiple mRNAs. Analyses of these target reveals that they include bone requiring factors that function as inhibitors and activators of osteogenesis in the TGFb, BMP and Wnt pathways. For example, miR29b promotes osteogenesis by binding to the 3’-UTR repressing known inhibitors of osteogenic signaling including HDAC4, TGFβ3, ACVR2A, CTNNBIP1 and DUSP2 and several inhibitors of the Wnt pathway at early differentiation stages, but also targets ECM proteins (e.g. COL1A1, COL5A3 and COL4A2) at later stages to regulate collagen synthesis. In this manner miRs can coordinately regulate multiple events necessary for the ordered formation of bone tissue. These concepts are further supported by in vivo studies in which the Dicer enzyme, which processes pre-miRs to the functional mature miRs, was deleted in osteoblast lineage cells by crossing Col-Cre and osteocalcin-Cre mice with DicerF1/F1 mice (Gaur, Dev Biol, 2010). We show that Dicer generated miRs are essential to promote bone formation before birth and control bone mass accrual in the adult. These discoveries provide novel opportunities for treating skeletal disorders. Disclosure of Interest: J. Lian Grant / Research support from 5R37 DE012528, G. Stein Grant / Research support from 5R01 AR039588, C. Croce: None declared, J. Stein: None declared, A. van Wijnen: None declared, Z. Li: None declared, M. Hassan: None declared, T. Gaur:

None declared, R. Aqeilan: None declared, M. Jafferji: None declared, Y. Zhang: None declared Keywords: dicer, high bone mass, microRNA doi:10.1016/j.bone.2010.04.036

IS36 Lessons from rare bone diseases R. Smith⁎1 1 Nuffield Orthopaedic Centre, Oxford, United Kingdom Investigation of so-called experiments of nature illuminates normal physiology and provides clues to the cause of more common disorders. Lessons from rare bone diseases depend on the cornerstone of clinical diagnosis, upon which biochemical and genomic methods can be built. Of particular relevance are those genetic conditions where there is either too little or too much bone in the skeleton, or where bone is formed outside the skeleton. Study of the various forms of osteogenesis imperfecta (OI) has emphasised the importance of collagen to the skeleton. In addition, the discovery that the osteoporosis-pseudoglioma syndrome, initially thought to be a form of OI, is due to mutations in the LRP5 gene, strikingly demonstrated the effect of Wnt signalling on skeletal mass. Too much bone in the skeleton can result from excessive bone formation or reduced bone resorption. Sclerosteosis is a dramatic example of the former. Other examples of increased bone formation include Camurati-Engelmann disease, with mutations in the TGFβ1 gene, and familial high bone density with LRP5 mutations. Reduced bone resorption in osteopetrosis is caused by many different mutations blocking osteoclast function, including acidification and enzyme production. The formation of bone outside the skeleton - to produce a second skeleton - can lead to catastrophic disability. This occurs in the rare condition of fibrodysplasia (previously myositis) ossificans progressiva (FOP). This is due to a specific mutation in the gene for a bone morphogenetic receptor ACVR1, a finding which has opened a new chapter in bone physiology. Disclosure of Interest: None declared Keywords: bone, rare doi:10.1016/j.bone.2010.04.037

IS37 A complicated case of hyperparathyroidism D.J. Hosking⁎1 1 Dept Diabetes and Endocrinology, City Hospital, Nottingham, United Kingdom The clinical presentation of primary hyperparathyroidism has changed over the last thirty years from the classical symptoms of “stones, bones and abdominal groans” to a condition which is characterised by mild asymptomatic hypercalcaemia. Occasional cases present with severe hypercalcaemia complicated by end organ failure where the differentiation from malignancy may present problems. Moreover management is complicated by renal impairment, severe post parathyroidectomy hypocalcaemia and the risk of tonic clonic seizures, which in the presence of weakened bones can cause pathological fractures. Since both hyperparathyroidism and malignancy are common they may present simultaneously and control of hypercalcaemia is a priority to allow rational management of the clinically most severe condition. The availability of potent intravenous bisphosphonates allows suppression of bone resorption

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but in hyperparathyroidism the renal effects of PTH may prevent the restoration of adequate control of hypercalcaemia. The recent availability of drugs which modify the calcium sensing receptor on the parathyroid cell (calcimimetics) adds another dimension to the treatment of complicated situations where both bone and kidney contribute to the production of severe hypercalcaemia. These concepts will be illustrated by clinical examples of how current therapy can be used to manage severe hypercalcaemia due to a complicated pathogenesis. Disclosure of Interest: D. Hosking Grant / Research support from MSD, Nycomed, Novartis, Amgen, Consultant for MSD Nycomed Amgen, Novartis, Speaker Bureau with MSD, Amgen Nycomed Novartis Keywords: bisphosphonates, calcimimetic, hyperparathyroidism doi:10.1016/j.bone.2010.04.038

IS38 Use of Teriparatide (TP) in fracture healing A.K. Bhalla⁎1 1 NHS Foundation Trust, Royal National Hospital for Rheumatic Diseases, Bath, United Kingdom Of the 7.9 million fractures occurring annually in the United States, 5-20% result in delayed or impaired healing. A number of therapies have been used to accelerate fracture healing including low intensity ultrasound and bone morphogenetic protein. To date no pharmacological intervention for fracture repair is available. In young and older rats the intermittent administration of TP enhances callus formation and mechanical strength of fractures. In Cynomolgus monkeys, who have the Haversian remodelling system, the administration of TP following femoral osteotomy resulted in complete bone union in both placebo and treated groups. However, the stress and elastic modulus in fractured femurs were significantly higher in the TP group than in controls. TP decreased callus size and accelerated callus maturation and increased the degree of mineralisation of the fractured callus. In experiments on mice, TP was shown to promote, in the callus following fracture, the differentiation of bone marrow derived mesenchymal stem cells to the osteoblast lineage. A number of case reports and an observation cohort study indicate that TP may enhance fracture healing in cases of non-union or delayed union suggesting that fracture repair in humans may be stimulated by TP treatment. So far, the only placebo-controlled trial has failed to substantiate these findings. In this study post-menopausal women with distal radial fractures were treated with either placebo, TP 20 μg or 40 μg within 10 days of fracture. The median time from fracture to first radiographic evidence of complete cortical bridging in 3 of the 4 cortices was not different between the three groups. However, post-hoc analysis showed that the time to healing was shorter in TP 20 μg group than placebo. This was not seen in the TP 40 μg group. Whilst the results suggest that fracture repair can be accelerated by 20 μg TP in humans, these results need to be confirmed with further placebo-controlled trials. However, the results of this one particular study does not preclude the beneficial effect of TP in states of fracture, non-union or delayed union and also at sites where weightbearing may enhance the effects of TP. The identification of a systemically administered drug that may enhance healing of fractures will be important particularly for the elderly who may be unfit for surgical intervention. Disclosure of Interest: None declared Keywords: None doi:10.1016/j.bone.2010.04.039

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IS39 Bisphosphonate use and subtrochanteric fractures J. Compston⁎1 1 Medicine, University of Cambridge, Cambridge, United Kingdom The first report of atypical fractures in patients treated with alendronate was published in 2005 and subsequently a number of other reports have appeared. The femoral shaft or sub-trochanteric region is most commonly affected, although fractures at other sites have been described. The fractures typically occur after minimal trauma and there is often prodromal pain. Femoral fractures are usually simple or oblique, often bilateral and are slow to heal. Radiologically, there is cortical thickening on the lateral side of the affected region of the femoral shaft and a medial cortical spike or beaking. Possible factors predisposing to atypical femoral fractures include although glucocorticoid therapy, co-treatment with other anti-resorptives, vitamin D deficiency and longer duration of use of alendronate. Co-morbidities such as rheumatoid arthritis and diabetes mellitus and co-medications, for example proton pump inhibitors, have also been suggested as contributing factors. The question of whether these fractures are causally linked to bisphosphonate therapy is widely debated but as yet unresolved. Consequences of long-term suppression of bone turnover include increased mineralization of bone, alterations in the composition of its mineral/matrix composite and increased microdamage, all of which may reduce bone strength. Even if there is a causal link between these fractures and bisphosphonate therapy the benefit/risk ratio of bisphosphonate therapy in patients at high risk of fracture remains overwhelmingly positive. Nevertheless, limitation of treatment duration to five years with evaluation of the need to continue therapy thereafter may be appropriate in clinical practice. In patients who continue to be at high fracture risk, treatment should be continued. In those at lower risk of fracture after five years treatment a “drug holiday” can be considered, with the option of resuming treatment after a few years. Disclosure of Interest: None declared Keywords: atypical femoral fractures, bisphosphonate, suppressed bone turnover doi:10.1016/j.bone.2010.04.040

IS40 Regulation of bone formation by gut-derived serotonin G. Karsenty⁎1, P.A. Marks1 1 Genetics & Development, Columbia University, New York, United States The study of the regulation of bone mass by lrp5 has been a focus of study in our laboratory for several years. Against all our expectations when we invalidated β catenin in osteoblasts we saw a defect in bone resorption but none in bone formation as it is the case in absence of Lrp5. This unexpected result forced us to have a more open minded approach to the biology of this gene. We first verified that Lrp5 does not affect the production of collagen, the major protein of the bone extracellular matrix but simply osteoblast proliferation. We also preformed a microarray analysis comparing WT, β catenin -/and lrp5 -/- bones. This analysis revealed that the gene expressed in absence of β catenin and in the absence of lrp5 were totally different. This unambiguous molecular result further disproves the Wnt hypothesis as the basis of lrp5 function in bone. Instead what we observed is that expression of Tph1 was greatly increased in lrp5 -/mice. Tph1 is primarily expressed in enterochromaffin cells of the duodenum where its expression was also increased in lrp5 -/- mice. Tph1 encodes the initial and rate limiting enzyme in the synthesis of