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Proteostasis and bone
Abstracts
IS38 The effects of organic nitrates on osteoporosis S.A. Jamal⁎ Multidisciplinary Osteoporosis Program, Women's College Hospital, Toronto, Canada Learning Outcome 1: To briefly review the pathophysiology of osteoporosis with a specific focus on bone turnover and the role of nitric oxide in the regulations of bone turnover. Learning Outcome 2: To focus on the clinical data concerning nitric oxide donors and effects on bone turnover, bone mineral density, and fractures. Learning Outcome 3: To discuss future research directions. Abstract: Altered bone remodeling — excessive bone resorption and/or impaired bone formation — is a key risk factor for osteoporotic fracture and to date, the majority of pharmacologic agents developed for the prevention and treatment of osteoporosis act by inhibiting bone resorption (hormone replacement therapy, bisphosphonates and selective estrogen receptor modulators) or by stimulating bone formation (parathyroid hormone). Currently available agents have some limitations; they only target one part of the bone remodeling cycle; there are limited long term safety data (b 10 years); and generally speaking these agents are costly and not available worldwide. An optimal agent would be one that decreased bone resorption while increasing bone formation to have maximum effects on BMD, was inexpensive and available worldwide. One potential agent is nitric oxide (NO). NO is a short-lived free radical involved in the regulation of many physiological processes, including bone remodeling. The organic nitrates (e.g. nitroglycerin (NTG), isosorbide mononitrate (ISMO) and isosorbide dinitrate) which can act as NO donors are one source of NO. In vitro studies report that NO decreases bone resorption by decreasing osteoclast formation, motility and function. Administration of organic nitrates has been shown to prevent bone loss in oophorectomized rats and can alleviate bone loss induced by corticosteroid administration in rats. Nitrates may also have clinical utility in postmenopausal osteoporosis. We reported on the effects of NTG on bone turnover, bone density, bone geometry and strength in 144 postmenopausal women followed for 2 years. We found that compared with placebo NTG increased spine, femoral neck and total hip BMD, as well as cortical thickness, cortical area and periosteal circumference. NTG also increased indices of bending and twisting strength: polar section modulus and polar moment of inertia at the radius and tibia respectively. We also found that NTG ointment uncoupled bone formation from bone resorption: it increased a marker of bone formation and decreased a marker of bone resorption. The only significant adverse event associated with NTG use was the occurrence of headaches. Nitric oxide donors appear to have a unique mechanism of action: increasing bone formation and decreasing bone resorption — this may translate into greater antifracture efficacy. Further, nitrates are inexpensive and widely available with no known long term side effects. The efficacy of nitrates for reducing risk of fracture remains to be tested in a randomized controlled trial. This article is part of a Special Issue entitled ECTS 2012. Disclosure of interest: Consultant for Genzyme, Warner-Chillcott, Novartis, Shire, Speaker Bureau with Novartis, Amgen, Warner-Chillcott, Genzyme, Shire.
doi:10.1016/j.bone.2012.02.060
IS39 Chondrocyte ER stress as a pathogenic factor R. Boot-Handford⁎, L. Kung, M.D. Briggs WTCCMR, Faculty of Life Sciences, University of Manchester, Manchester, UK Learning Outcome 1: The process of endochondral ossification. Learning Outcome 2: The nature of ER stress and the resultant unfolded protein response. Learning Outcome 3: The mechanisms by which mutations in extracellular matrix macromolecules can cause disease. Abstract: A number of chondrodysplasias are caused by mutations in cartilage extracellular matrix (ECM) proteins. The mechanisms by which these mutations cause the associated pathology were until recently thought to involve either a deficiency of in the extracellular matrix if the mutant protein was retained in the chondrocyte, or alternatively, the assembly of a defect cartilage if secreted. Work from several laboratories has now demonstrated that the synthesis of mutant cartilage proteins is, in many instances, associated with increased endoplasmic reticulum (ER) stress and an unfolded protein response (UPR). We have recently demonstrated in vivo using mouse models that the targeted induction of ER stress in hypertrophic chondrocytes is sufficient to phenocopy metaphyseal chondrodysplasia type Schmid (MCDS) in the absence of mutations in type X collagen demonstrating directly the central role played by increased ER stress in the disease mechanism for this chondrodysplasia (Rajpar et al., 2009).
S25
COMP and matrilin-3 mutations causing pseudoachondroplasia (PSACH)/multiple epiphyseal dysplasia (MED) are often associated with increased ER stress and a UPR in proliferative zone chondrocytes (Nundall et al., 2010 and papers herein) rather than hypertrophic chondrocytes affected in MCDS. In order to determine the effects of increased ER stress in proliferative zone chondrocytes, we targeted the expression of an ER stress-inducing protein (Tgcog) to these cells using the collagen II promoter. Proliferative zone chondrocytes of mice carrying the Col2 Tgcog transgenic construct expressed and retained the Tgcog protein and exhibited increased ER stress and a UPR based on elevated levels of the ER chaperone BiP (Grp78). Mice expressing the ER stress-inducing transgene exhibited significant decreases in bone growth rates compared to their non-stressed controls. The decreases in bone growth rate related to decreased rates of chondrocyte proliferation as assessed by BrdU incorporation. The Col2 Tgcog mouse did not exhibit any abnormalities in apoptosis within the growth plate or in growth plate organisation. Microarray analyses are being performed to determine the effects of increased ER stress upon chondrocyte gene expression. These investigations illustrate that increased levels of ER stress in proliferative zone chondrocytes are sufficient to reduce bone growth rates but do not induce all of the phenotypic changes seen in the growth plate of MED mice expressing a matrilin-3 mutation such as dysregulated apoptosis and changes in cell shape accompanying defects in column formation. Rajpar et al. (2009), PLoS Genet 5(10): e1000691. Nundall et al. (2010), Cell Stress Chaperones.15(6):835–49 This article is part of a Special Issue entitled ECTS 2012. Disclosure of interest: None declared. doi:10.1016/j.bone.2012.02.061
IS40 Proteostasis and bone S. Cenci⁎ Division of Genetics and Cell Biology, San Raffaele Scientific Institute, Milano, Italy Learning Outcome 1: How the regulation of protein homeostasis is crucial to all cells. Learning Outcome 2: The relevance of protein degradation to bone cell biology. Learning Outcome 3: The mechanisms underlying the exquisite sensitivity of myeloma cells to proteasome inhibitors. Abstract: The ability of eukaryotic cells to adapt to changing environmental conditions, respond to stimuli, and differentiate relies on their ability to shape their proteome, thereby controlling the concentration, conformation, localization, and interaction of proteins. This capacity, referred to as protein homeostasis (proteostasis), consists of different integrated pathways and adaptive responses.1 Protein degradation, in particular, is critical to ensure proteostasis, and hence is carefully regulated. The focus on protein degradation in bone biology is growing in view of recent evidence implicating the main cellular proteocatabolic pathways, the ubiquitin–proteasome system and autophagy, in the differentiation and function of bone cells, as well as in skeletal homeostasis and diseases. Exemplar are recent insights on the biology and role of p62/ SQSTM1, mutated in the Paget's disease of bone, in conformational disorders,2,3 and the employment of alternative degradation strategies to dispose of different misfolded mutants accumulating in the endoplasmic reticulum, including mutated type I collagen variants in cellular models of osteogenesis imperfecta.4,5 Proteostasis regulators hold promise as therapeutic agents not only to harness cellular adaptive responses against aging and degenerative diseases (positive regulators), but also to turn cytotoxic stress against cancer (negative regulators).1 Proteasome inhibitors (PI), the prototypical proteostasis downregulators, proved powerful against a variety of tumors. Multiple myeloma, a frequent bone marrow plasma cell malignancy rooted in the bone environment, is the paradigmatic PIresponsive cancer, providing an established framework to dissect the integrated regulation of protein homeostasis. Mounting evidence links proteasome workload and capacity with proteasome vulnerability in malignant plasma cells.6,7 Multiple myeloma thus emerges as a valuable model to achieve a more comprehensive understanding of how cancer cells resist or succumb to proteasome stress, of potential use to design novel therapies and obviate PI resistance.8 1. Balch et al. Science. 2008;319:916–919. 2. Luciani et al. Nature Cell Biology. 2010;12:863–875. 3. Levine et al. Nature. 2011;469:323–335. 4. Fujita et al. Human Molecular Genetics. 2007;16:618–629. 5. Ishida et al. Molecular Biology of the Cell. 2009;20:2744–2754. 6. Meister et al. Cancer Res. 2007;67:1783–1792. 7. Bianchi et al. Blood. 2009;113:3040–3049. 8. Cenci et al. Current Opinion in Cell Biology. 2011;23:216–222. This article is part of a Special Issue entitled ECTS 2012. Disclosure of interest: None declared. doi:10.1016/j.bone.2012.02.062
IS38 The effects of organic nitrates on osteoporosis S.A. Jamal⁎ Multidisciplinary Osteoporosis Program, Women's College Hospital, Toronto, Canada Learning Outcome 1: To briefly review the pathophysiology of osteoporosis with a specific focus on bone turnover and the role of nitric oxide in the regulations of bone turnover. Learning Outcome 2: To focus on the clinical data concerning nitric oxide donors and effects on bone turnover, bone mineral density, and fractures. Learning Outcome 3: To discuss future research directions. Abstract: Altered bone remodeling — excessive bone resorption and/or impaired bone formation — is a key risk factor for osteoporotic fracture and to date, the majority of pharmacologic agents developed for the prevention and treatment of osteoporosis act by inhibiting bone resorption (hormone replacement therapy, bisphosphonates and selective estrogen receptor modulators) or by stimulating bone formation (parathyroid hormone). Currently available agents have some limitations; they only target one part of the bone remodeling cycle; there are limited long term safety data (b 10 years); and generally speaking these agents are costly and not available worldwide. An optimal agent would be one that decreased bone resorption while increasing bone formation to have maximum effects on BMD, was inexpensive and available worldwide. One potential agent is nitric oxide (NO). NO is a short-lived free radical involved in the regulation of many physiological processes, including bone remodeling. The organic nitrates (e.g. nitroglycerin (NTG), isosorbide mononitrate (ISMO) and isosorbide dinitrate) which can act as NO donors are one source of NO. In vitro studies report that NO decreases bone resorption by decreasing osteoclast formation, motility and function. Administration of organic nitrates has been shown to prevent bone loss in oophorectomized rats and can alleviate bone loss induced by corticosteroid administration in rats. Nitrates may also have clinical utility in postmenopausal osteoporosis. We reported on the effects of NTG on bone turnover, bone density, bone geometry and strength in 144 postmenopausal women followed for 2 years. We found that compared with placebo NTG increased spine, femoral neck and total hip BMD, as well as cortical thickness, cortical area and periosteal circumference. NTG also increased indices of bending and twisting strength: polar section modulus and polar moment of inertia at the radius and tibia respectively. We also found that NTG ointment uncoupled bone formation from bone resorption: it increased a marker of bone formation and decreased a marker of bone resorption. The only significant adverse event associated with NTG use was the occurrence of headaches. Nitric oxide donors appear to have a unique mechanism of action: increasing bone formation and decreasing bone resorption — this may translate into greater antifracture efficacy. Further, nitrates are inexpensive and widely available with no known long term side effects. The efficacy of nitrates for reducing risk of fracture remains to be tested in a randomized controlled trial. This article is part of a Special Issue entitled ECTS 2012. Disclosure of interest: Consultant for Genzyme, Warner-Chillcott, Novartis, Shire, Speaker Bureau with Novartis, Amgen, Warner-Chillcott, Genzyme, Shire.
doi:10.1016/j.bone.2012.02.060
IS39 Chondrocyte ER stress as a pathogenic factor R. Boot-Handford⁎, L. Kung, M.D. Briggs WTCCMR, Faculty of Life Sciences, University of Manchester, Manchester, UK Learning Outcome 1: The process of endochondral ossification. Learning Outcome 2: The nature of ER stress and the resultant unfolded protein response. Learning Outcome 3: The mechanisms by which mutations in extracellular matrix macromolecules can cause disease. Abstract: A number of chondrodysplasias are caused by mutations in cartilage extracellular matrix (ECM) proteins. The mechanisms by which these mutations cause the associated pathology were until recently thought to involve either a deficiency of in the extracellular matrix if the mutant protein was retained in the chondrocyte, or alternatively, the assembly of a defect cartilage if secreted. Work from several laboratories has now demonstrated that the synthesis of mutant cartilage proteins is, in many instances, associated with increased endoplasmic reticulum (ER) stress and an unfolded protein response (UPR). We have recently demonstrated in vivo using mouse models that the targeted induction of ER stress in hypertrophic chondrocytes is sufficient to phenocopy metaphyseal chondrodysplasia type Schmid (MCDS) in the absence of mutations in type X collagen demonstrating directly the central role played by increased ER stress in the disease mechanism for this chondrodysplasia (Rajpar et al., 2009).
S25
COMP and matrilin-3 mutations causing pseudoachondroplasia (PSACH)/multiple epiphyseal dysplasia (MED) are often associated with increased ER stress and a UPR in proliferative zone chondrocytes (Nundall et al., 2010 and papers herein) rather than hypertrophic chondrocytes affected in MCDS. In order to determine the effects of increased ER stress in proliferative zone chondrocytes, we targeted the expression of an ER stress-inducing protein (Tgcog) to these cells using the collagen II promoter. Proliferative zone chondrocytes of mice carrying the Col2 Tgcog transgenic construct expressed and retained the Tgcog protein and exhibited increased ER stress and a UPR based on elevated levels of the ER chaperone BiP (Grp78). Mice expressing the ER stress-inducing transgene exhibited significant decreases in bone growth rates compared to their non-stressed controls. The decreases in bone growth rate related to decreased rates of chondrocyte proliferation as assessed by BrdU incorporation. The Col2 Tgcog mouse did not exhibit any abnormalities in apoptosis within the growth plate or in growth plate organisation. Microarray analyses are being performed to determine the effects of increased ER stress upon chondrocyte gene expression. These investigations illustrate that increased levels of ER stress in proliferative zone chondrocytes are sufficient to reduce bone growth rates but do not induce all of the phenotypic changes seen in the growth plate of MED mice expressing a matrilin-3 mutation such as dysregulated apoptosis and changes in cell shape accompanying defects in column formation. Rajpar et al. (2009), PLoS Genet 5(10): e1000691. Nundall et al. (2010), Cell Stress Chaperones.15(6):835–49 This article is part of a Special Issue entitled ECTS 2012. Disclosure of interest: None declared. doi:10.1016/j.bone.2012.02.061
IS40 Proteostasis and bone S. Cenci⁎ Division of Genetics and Cell Biology, San Raffaele Scientific Institute, Milano, Italy Learning Outcome 1: How the regulation of protein homeostasis is crucial to all cells. Learning Outcome 2: The relevance of protein degradation to bone cell biology. Learning Outcome 3: The mechanisms underlying the exquisite sensitivity of myeloma cells to proteasome inhibitors. Abstract: The ability of eukaryotic cells to adapt to changing environmental conditions, respond to stimuli, and differentiate relies on their ability to shape their proteome, thereby controlling the concentration, conformation, localization, and interaction of proteins. This capacity, referred to as protein homeostasis (proteostasis), consists of different integrated pathways and adaptive responses.1 Protein degradation, in particular, is critical to ensure proteostasis, and hence is carefully regulated. The focus on protein degradation in bone biology is growing in view of recent evidence implicating the main cellular proteocatabolic pathways, the ubiquitin–proteasome system and autophagy, in the differentiation and function of bone cells, as well as in skeletal homeostasis and diseases. Exemplar are recent insights on the biology and role of p62/ SQSTM1, mutated in the Paget's disease of bone, in conformational disorders,2,3 and the employment of alternative degradation strategies to dispose of different misfolded mutants accumulating in the endoplasmic reticulum, including mutated type I collagen variants in cellular models of osteogenesis imperfecta.4,5 Proteostasis regulators hold promise as therapeutic agents not only to harness cellular adaptive responses against aging and degenerative diseases (positive regulators), but also to turn cytotoxic stress against cancer (negative regulators).1 Proteasome inhibitors (PI), the prototypical proteostasis downregulators, proved powerful against a variety of tumors. Multiple myeloma, a frequent bone marrow plasma cell malignancy rooted in the bone environment, is the paradigmatic PIresponsive cancer, providing an established framework to dissect the integrated regulation of protein homeostasis. Mounting evidence links proteasome workload and capacity with proteasome vulnerability in malignant plasma cells.6,7 Multiple myeloma thus emerges as a valuable model to achieve a more comprehensive understanding of how cancer cells resist or succumb to proteasome stress, of potential use to design novel therapies and obviate PI resistance.8 1. Balch et al. Science. 2008;319:916–919. 2. Luciani et al. Nature Cell Biology. 2010;12:863–875. 3. Levine et al. Nature. 2011;469:323–335. 4. Fujita et al. Human Molecular Genetics. 2007;16:618–629. 5. Ishida et al. Molecular Biology of the Cell. 2009;20:2744–2754. 6. Meister et al. Cancer Res. 2007;67:1783–1792. 7. Bianchi et al. Blood. 2009;113:3040–3049. 8. Cenci et al. Current Opinion in Cell Biology. 2011;23:216–222. This article is part of a Special Issue entitled ECTS 2012. Disclosure of interest: None declared. doi:10.1016/j.bone.2012.02.062