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Werbenko E, de Gorter DJJ, Kleimann S, Beckmann D, Waltereit-Kracke V, Reinhardt J, Geers F, Paruzel P, Hansen U, Pap T, Stradal TEB, Dankbar B. Hem1 is essential for ruffled border formation in osteoclasts and efficient bone resorption. Sci Rep 2024; 14:8109. [PMID: 38582757 PMCID: PMC10998871 DOI: 10.1038/s41598-024-58110-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2023] [Accepted: 03/25/2024] [Indexed: 04/08/2024] Open
Abstract
Bone resorption is highly dependent on the dynamic rearrangement of the osteoclast actin cytoskeleton to allow formation of actin rings and a functional ruffled border. Hem1 is a hematopoietic-specific subunit of the WAVE-complex which regulates actin polymerization and is crucial for lamellipodia formation in hematopoietic cell types. However, its role in osteoclast differentiation and function is still unknown. Here, we show that although the absence of Hem1 promotes osteoclastogenesis, the ability of Hem1-/- osteoclasts to degrade bone was severely impaired. Global as well as osteoclast-specific deletion of Hem1 in vivo revealed increased femoral trabecular bone mass despite elevated numbers of osteoclasts in vivo. We found that the resorption defect derived from the morphological distortion of the actin-rich sealing zone and ruffled border deformation in Hem1-deficient osteoclasts leading to impaired vesicle transport and increased intracellular acidification. Collectively, our data identify Hem1 as a yet unknown key player in bone remodeling by regulating ruffled border formation and consequently the resorptive capacity of osteoclasts.
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Affiliation(s)
- Eugenie Werbenko
- Institute of Musculoskeletal Medicine, University Hospital Muenster, Albert-Schweitzer-Campus 1, Building D3, 48149, Muenster, Germany
| | - David J J de Gorter
- Institute of Musculoskeletal Medicine, University Hospital Muenster, Albert-Schweitzer-Campus 1, Building D3, 48149, Muenster, Germany
| | - Simon Kleimann
- Institute of Musculoskeletal Medicine, University Hospital Muenster, Albert-Schweitzer-Campus 1, Building D3, 48149, Muenster, Germany
| | - Denise Beckmann
- Institute of Musculoskeletal Medicine, University Hospital Muenster, Albert-Schweitzer-Campus 1, Building D3, 48149, Muenster, Germany
| | - Vanessa Waltereit-Kracke
- Institute of Musculoskeletal Medicine, University Hospital Muenster, Albert-Schweitzer-Campus 1, Building D3, 48149, Muenster, Germany
| | - Julia Reinhardt
- Institute of Musculoskeletal Medicine, University Hospital Muenster, Albert-Schweitzer-Campus 1, Building D3, 48149, Muenster, Germany
| | - Fabienne Geers
- Institute of Musculoskeletal Medicine, University Hospital Muenster, Albert-Schweitzer-Campus 1, Building D3, 48149, Muenster, Germany
| | - Peter Paruzel
- Institute of Musculoskeletal Medicine, University Hospital Muenster, Albert-Schweitzer-Campus 1, Building D3, 48149, Muenster, Germany
| | - Uwe Hansen
- Institute of Musculoskeletal Medicine, University Hospital Muenster, Albert-Schweitzer-Campus 1, Building D3, 48149, Muenster, Germany
| | - Thomas Pap
- Institute of Musculoskeletal Medicine, University Hospital Muenster, Albert-Schweitzer-Campus 1, Building D3, 48149, Muenster, Germany
| | - Theresia E B Stradal
- Department of Cell Biology, Helmholtz Centre for Infection Research (HZI), Braunschweig, Germany
| | - Berno Dankbar
- Institute of Musculoskeletal Medicine, University Hospital Muenster, Albert-Schweitzer-Campus 1, Building D3, 48149, Muenster, Germany.
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2
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Takito J, Nonaka N. Osteoclasts at Bone Remodeling: Order from Order. Results Probl Cell Differ 2024; 71:227-256. [PMID: 37996681 DOI: 10.1007/978-3-031-37936-9_12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2023]
Abstract
Osteoclasts are multinucleated bone-resorbing cells derived from the monocyte/macrophage lineage. The macrophage colony-stimulating factor/receptor activator of nuclear factor κB ligand (M-CSF/RANKL) signaling network governs the differentiation of precursor cells into fusion-competent mononucleated cells. Repetitive fusion of fusion-competent cells produces multinucleated osteoclasts. Osteoclasts are believed to die via apoptosis after bone resorption. However, recent studies have found that osteoclastogenesis in vivo proceeds by replacing the old nucleus of existing osteoclasts with a single newly differentiated mononucleated cell. Thus, the formation of new osteoclasts is minimal. Furthermore, the sizes of osteoclasts can change via cell fusion and fission in response to external conditions. On the other hand, osteoclastogenesis in vitro involves various levels of heterogeneity, including osteoclast precursors, mode of fusion, and properties of the differentiated osteoclasts. To better understand the origin of these heterogeneities and the plasticity of osteoclasts, we examine several processes of osteoclastogenesis in this review. Candidate mechanisms that create heterogeneity involve asymmetric cell division, osteoclast niche, self-organization, and mode of fusion and fission. Elucidation of the plasticity or fluctuation of the M-CSF/RANKL network should be an important topic for future researches.
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Affiliation(s)
- Jiro Takito
- Department of Oral Anatomy and Developmental Biology, School of Dentistry, Showa University, Tokyo, Japan.
| | - Naoko Nonaka
- Department of Oral Anatomy and Developmental Biology, School of Dentistry, Showa University, Tokyo, Japan
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3
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Zhu Q, Wang Y, Liu Y, Yang X, Shuai Z. Prostate transmembrane androgen inducible protein 1 (PMEPA1): regulation and clinical implications. Front Oncol 2023; 13:1298660. [PMID: 38173834 PMCID: PMC10761476 DOI: 10.3389/fonc.2023.1298660] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2023] [Accepted: 12/06/2023] [Indexed: 01/05/2024] Open
Abstract
Prostate transmembrane androgen inducible protein 1 (PMEPA1) can promote or inhibit prostate cancer cell growth based on the cancer cell response to the androgen receptor (AR). Further, it can be upregulated by transforming growth factor (TGF), which downregulates transforming growth factor-β (TGF-β) signaling by interfering with R-Smad phosphorylation to facilitate TGF-β receptor degradation. Studies have indicated the increased expression of PMEPA1 in some solid tumors and its functioning as a regulator of multiple signaling pathways. This review highlights the multiple potential signaling pathways associated with PMEPA1 and the role of the PMEPA1 gene in regulating prognosis, including transcriptional regulation and epithelial mesenchymal transition (EMT). Moreover, the relevant implications in and outside tumors, for example, as a biomarker and its potential functions in lysosomes have also been discussed.
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Affiliation(s)
- Qicui Zhu
- Department of Rheumatology and Immunology, The First Affiliated Hospital of Anhui Medical University, Hefei, China
| | - Yue Wang
- Department of Rheumatology and Immunology, The First Affiliated Hospital of Anhui Medical University, Hefei, China
| | - Yaqian Liu
- Department of Rheumatology and Immunology, The First Affiliated Hospital of Anhui Medical University, Hefei, China
| | - Xiaoke Yang
- Department of Rheumatology and Immunology, The First Affiliated Hospital of Anhui Medical University, Hefei, China
| | - Zongwen Shuai
- Department of Rheumatology and Immunology, The First Affiliated Hospital of Anhui Medical University, Hefei, China
- Inflammation and Immune Mediated Diseases Laboratory of Anhui, Hefei, China
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4
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Li X, Jiang Y, Liu X, Fu J, Du J, Luo Z, Xu J, Bhawal UK, Liu Y, Guo L. Mesenchymal stem cell-derived apoptotic bodies alleviate alveolar bone destruction by regulating osteoclast differentiation and function. Int J Oral Sci 2023; 15:51. [PMID: 38040672 PMCID: PMC10692139 DOI: 10.1038/s41368-023-00255-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 10/21/2023] [Accepted: 10/22/2023] [Indexed: 12/03/2023] Open
Abstract
Periodontitis is caused by overactive osteoclast activity that results in the loss of periodontal supporting tissue and mesenchymal stem cells (MSCs) are essential for periodontal regeneration. However, the hypoxic periodontal microenvironment during periodontitis induces the apoptosis of MSCs. Apoptotic bodies (ABs) are the major product of apoptotic cells and have been attracting increased attention as potential mediators for periodontitis treatment, thus we investigated the effects of ABs derived from MSCs on periodontitis. MSCs were derived from bone marrows of mice and were cultured under hypoxic conditions for 72 h, after which ABs were isolated from the culture supernatant using a multi-filtration system. The results demonstrate that ABs derived from MSCs inhibited osteoclast differentiation and alveolar bone resorption. miRNA array analysis showed that miR-223-3p is highly enriched in those ABs and is critical for their therapeutic effects. Targetscan and luciferase activity results confirmed that Itgb1 is targeted by miR-223-3p, which interferes with the function of osteoclasts. Additionally, DC-STAMP is a key regulator that mediates membrane infusion. ABs and pre-osteoclasts expressed high levels of DC-STAMP on their membranes, which mediates the engulfment of ABs by pre-osteoclasts. ABs with knock-down of DC-STAMP failed to be engulfed by pre-osteoclasts. Collectively, MSC-derived ABs are targeted to be engulfed by pre-osteoclasts via DC-STAMP, which rescued alveolar bone loss by transferring miR-223-3p to osteoclasts, which in turn led to the attenuation of their differentiation and bone resorption. These results suggest that MSC-derived ABs are promising therapeutic agents for the treatment of periodontitis.
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Grants
- National Key R&D Program of China (Grant NO. 2022YFC2504200), the National Nature Science Foundation of China (81991504 and 81974149), the Beijing Municipal Administration of Hospitals Clinical Medicine Development of Special Funding Support (ZYLX202121), Innovation Research Team Project of Beijing Stomatological Hospital, Capital Medical University (CXTD202202), the Beijing Municipal Administration of Hospitals’ Ascent Plan (DFL20181501)
- National Nature Science Foundation of China (82201052), Beijing Municipal Administration of Hospitals’ Youth Programme (QML20231505), the Beijing Stomatological Hospital, Capital Medical University Young Scientist Program (NO. YSP202103)
- Beijing Municipal Administration of Hospitals’ Youth Programme (QML20181501), Innovation Foundation of Beijing Stomatological Hospital, Capital Medical University (21-09-18)
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Affiliation(s)
- Xiaoyan Li
- Laboratory of Tissue Regeneration and Immunology and Department of Periodontics, Beijing Key Laboratory of Tooth Regeneration and Function Reconstruction, School of Stomatology, Capital Medical University, Beijing, China
| | - Yiyang Jiang
- Laboratory of Tissue Regeneration and Immunology and Department of Periodontics, Beijing Key Laboratory of Tooth Regeneration and Function Reconstruction, School of Stomatology, Capital Medical University, Beijing, China
| | - Xu Liu
- Laboratory of Tissue Regeneration and Immunology and Department of Periodontics, Beijing Key Laboratory of Tooth Regeneration and Function Reconstruction, School of Stomatology, Capital Medical University, Beijing, China
| | - Jingfei Fu
- Laboratory of Tissue Regeneration and Immunology and Department of Periodontics, Beijing Key Laboratory of Tooth Regeneration and Function Reconstruction, School of Stomatology, Capital Medical University, Beijing, China
| | - Juan Du
- Laboratory of Tissue Regeneration and Immunology and Department of Periodontics, Beijing Key Laboratory of Tooth Regeneration and Function Reconstruction, School of Stomatology, Capital Medical University, Beijing, China
| | - Zhenhua Luo
- Laboratory of Tissue Regeneration and Immunology and Department of Periodontics, Beijing Key Laboratory of Tooth Regeneration and Function Reconstruction, School of Stomatology, Capital Medical University, Beijing, China
| | - Junji Xu
- Laboratory of Tissue Regeneration and Immunology and Department of Periodontics, Beijing Key Laboratory of Tooth Regeneration and Function Reconstruction, School of Stomatology, Capital Medical University, Beijing, China
| | - Ujjal Kumar Bhawal
- Research Institute of Oral Science, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
- Center for Global Health Research, Saveetha Medical College and Hospitals, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai, Tamil Nadu, India.
| | - Yi Liu
- Laboratory of Tissue Regeneration and Immunology and Department of Periodontics, Beijing Key Laboratory of Tooth Regeneration and Function Reconstruction, School of Stomatology, Capital Medical University, Beijing, China.
| | - Lijia Guo
- Department of Orthodontics School of Stomatology, Capital Medical University, Beijing, China.
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5
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Lee JW, Lee IH, Watanabe H, Liu Y, Sawada K, Maekawa M, Uehara S, Kobayashi Y, Imai Y, Kong SW, Iimura T. Centrosome clustering control in osteoclasts through CCR5-mediated signaling. Sci Rep 2023; 13:20813. [PMID: 38012303 PMCID: PMC10681980 DOI: 10.1038/s41598-023-48140-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2023] [Accepted: 11/22/2023] [Indexed: 11/29/2023] Open
Abstract
Osteoclasts uniquely resorb calcified bone matrices. To exert their function, mature osteoclasts maintain the cellular polarity and directional vesicle trafficking to and from the resorbing bone surface. However, the regulatory mechanisms and pathophysiological relevance of these processes remain largely unexplored. Bone histomorphometric analyses in Ccr5-deficient mice showed abnormalities in the morphology and functional phenotype of their osteoclasts, compared to wild type mice. We observed disorganized clustering of nuclei, as well as centrosomes that organize the microtubule network, which was concomitant with impaired cathepsin K secretion in cultured Ccr5-deficient osteoclasts. Intriguingly, forced expression of constitutively active Rho or Rac restored these cytoskeletal phenotypes with recovery of cathepsin K secretion. Furthermore, a gene-disease enrichment analysis identified that PLEKHM1, a responsible gene for osteopetrosis, which regulates lysosomal trafficking in osteoclasts, was regulated by CCR5. These experimental results highlighted that CCR5-mediated signaling served as an intracellular organizer for centrosome clustering in osteoclasts, which was involved in the pathophysiology of bone metabolism.
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Affiliation(s)
- Ji-Won Lee
- Department of Pharmacology, Faculty and Graduate School of Dental Medicine, Hokkaido University, Sapporo, 060-8586, Japan.
- Department of Oral Molecular Microbiology, Faculty and Graduate School of Dental Medicine, Hokkaido University, Sapporo, Japan.
| | - In-Hee Lee
- Computational Health and Informatics Program, Boston Children's Hospital, Boston, MA, USA
| | - Haruhisa Watanabe
- Department of Pharmacology, Faculty and Graduate School of Dental Medicine, Hokkaido University, Sapporo, 060-8586, Japan
| | - Yunqing Liu
- Department of Pharmacology, Faculty and Graduate School of Dental Medicine, Hokkaido University, Sapporo, 060-8586, Japan
| | - Kazuaki Sawada
- NIKON SOLUTIONS CO., LTD., Oi Plant 6-3, Nishioi 1-Chome, Shinagawa-ku, Tokyo, Japan
| | - Masashi Maekawa
- Division of Physiological Chemistry and Metabolism, Graduate School of Pharmaceutical Sciences, Keio University, Tokyo, Japan
| | - Shunsuke Uehara
- Department of Biochemistry, Matsumoto Dental University, Nagano, Japan
| | - Yasuhiro Kobayashi
- Division of Hard Tissue Research, Institute for Oral Science, Matsumoto Dental University, Nagano, Japan
| | - Yuuki Imai
- Division of Integrative Pathophysiology, Proteo-Science Center, Ehime University, Ehime, Japan
- Department of Pathophysiology, Ehime University Graduate School of Medicine, Ehime, Japan
| | - Sek Won Kong
- Computational Health and Informatics Program, Boston Children's Hospital, Boston, MA, USA
- Department of Pediatrics, Harvard Medical School, Boston, MA, USA
| | - Tadahiro Iimura
- Department of Pharmacology, Faculty and Graduate School of Dental Medicine, Hokkaido University, Sapporo, 060-8586, Japan.
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6
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Hou J, Liu J, Huang Z, Wang Y, Yao H, Hu Z, Shi C, Xu J, Wang Q. Structure and function of the membrane microdomains in osteoclasts. Bone Res 2023; 11:61. [PMID: 37989999 PMCID: PMC10663511 DOI: 10.1038/s41413-023-00294-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Revised: 09/07/2023] [Accepted: 09/18/2023] [Indexed: 11/23/2023] Open
Abstract
The cell membrane structure is closely related to the occurrence and progression of many metabolic bone diseases observed in the clinic and is an important target to the development of therapeutic strategies for these diseases. Strong experimental evidence supports the existence of membrane microdomains in osteoclasts (OCs). However, the potential membrane microdomains and the crucial mechanisms underlying their roles in OCs have not been fully characterized. Membrane microdomain components, such as scaffolding proteins and the actin cytoskeleton, as well as the roles of individual membrane proteins, need to be elucidated. In this review, we discuss the compositions and critical functions of membrane microdomains that determine the biological behavior of OCs through the three main stages of the OC life cycle.
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Affiliation(s)
- Jialong Hou
- Department of Orthopaedic Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, China
- Department of Orthopaedics, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, China
| | - Jian Liu
- Department of Orthopaedic Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, China
- Department of Orthopaedics, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, China
| | - Zhixian Huang
- Department of Orthopaedic Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, China
- Department of Orthopaedics, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, China
| | - Yining Wang
- Department of Orthopaedic Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, China
- Department of Orthopaedics, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, China
| | - Hanbing Yao
- Department of Orthopaedics, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, China
| | - Zhenxin Hu
- Department of Spine Surgery, Peking University Fourth School of Clinical Medicine, Beijing, China
| | - Chengge Shi
- Department of Orthopaedics, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, China
| | - Jiake Xu
- School of Biomedical Sciences, The University of Western Australia, Perth, WA, Australia.
- Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China.
| | - Qingqing Wang
- Department of Orthopaedic Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, China.
- Department of Orthopaedics, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, China.
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7
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Elson A, Anuj A, Barnea-Zohar M, Reuven N. The origins and formation of bone-resorbing osteoclasts. Bone 2022; 164:116538. [PMID: 36028118 DOI: 10.1016/j.bone.2022.116538] [Citation(s) in RCA: 30] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/09/2022] [Revised: 08/17/2022] [Accepted: 08/18/2022] [Indexed: 02/07/2023]
Abstract
Osteoclasts (OCLs) are hematopoietic cells whose physiological function is to degrade bone. OCLs are key players in the processes that determine and maintain the mass, shape, and physical properties of bone. OCLs adhere to bone tightly and degrade its matrix by secreting protons and proteases onto the underlying surface. The combination of low pH and proteases degrades the mineral and protein components of the matrix and forms a resorption pit; the degraded material is internalized by the cell and then secreted into the circulation. Insufficient or excessive activity of OCLs can lead to significant changes in bone and either cause or exacerbate symptoms of diseases, as in osteoporosis, osteopetrosis, and cancer-induced bone lysis. OCLs are derived from monocyte-macrophage precursor cells whose origins are in two distinct embryonic cell lineages - erythromyeloid progenitor cells of the yolk sac, and hematopoietic stem cells. OCLs are formed in a multi-stage process that is induced by the cytokines M-CSF and RANKL, during which the cells differentiate, fuse to form multi-nucleated cells, and then differentiate further to become mature, bone-resorbing OCLs. Recent studies indicate that OCLs can undergo fission in vivo to generate smaller cells, called "osteomorphs", that can be "re-cycled" by fusing with other cells to form new OCLs. In this review we describe OCLs and discuss their cellular origins and the cellular and molecular events that drive osteoclastogenesis.
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Affiliation(s)
- Ari Elson
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel.
| | - Anuj Anuj
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Maayan Barnea-Zohar
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Nina Reuven
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel
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8
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Ahmadzadeh K, Vanoppen M, Rose CD, Matthys P, Wouters CH. Multinucleated Giant Cells: Current Insights in Phenotype, Biological Activities, and Mechanism of Formation. Front Cell Dev Biol 2022; 10:873226. [PMID: 35478968 PMCID: PMC9035892 DOI: 10.3389/fcell.2022.873226] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Accepted: 03/17/2022] [Indexed: 12/21/2022] Open
Abstract
Monocytes and macrophages are innate immune cells with diverse functions ranging from phagocytosis of microorganisms to forming a bridge with the adaptive immune system. A lesser-known attribute of macrophages is their ability to fuse with each other to form multinucleated giant cells. Based on their morphology and functional characteristics, there are in general three types of multinucleated giant cells including osteoclasts, foreign body giant cells and Langhans giant cells. Osteoclasts are bone resorbing cells and under physiological conditions they participate in bone remodeling. However, under pathological conditions such as rheumatoid arthritis and osteoporosis, osteoclasts are responsible for bone destruction and bone loss. Foreign body giant cells and Langhans giant cells appear only under pathological conditions. While foreign body giant cells are found in immune reactions against foreign material, including implants, Langhans giant cells are associated with granulomas in infectious and non-infectious diseases. The functionality and fusion mechanism of osteoclasts are being elucidated, however, our knowledge on the functions of foreign body giant cells and Langhans giant cells is limited. In this review, we describe and compare the phenotypic aspects, biological and functional activities of the three types of multinucleated giant cells. Furthermore, we provide an overview of the multinucleation process and highlight key molecules in the different phases of macrophage fusion.
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Affiliation(s)
- Kourosh Ahmadzadeh
- Laboratory of Immunobiology, Department Microbiology and Immunology, Rega Institute, KU Leuven – University of Leuven, Leuven, Belgium
- *Correspondence: Kourosh Ahmadzadeh, ; Carine Helena Wouters,
| | - Margot Vanoppen
- Laboratory of Immunobiology, Department Microbiology and Immunology, Rega Institute, KU Leuven – University of Leuven, Leuven, Belgium
| | - Carlos D. Rose
- Division of Pediatric Rheumatology Nemours Children’s Hospital, Thomas Jefferson University, Philadelphia, PA, United States
| | - Patrick Matthys
- Laboratory of Immunobiology, Department Microbiology and Immunology, Rega Institute, KU Leuven – University of Leuven, Leuven, Belgium
| | - Carine Helena Wouters
- Laboratory of Immunobiology, Department Microbiology and Immunology, Rega Institute, KU Leuven – University of Leuven, Leuven, Belgium
- Division Pediatric Rheumatology, UZ Leuven, Leuven, Belgium
- European Reference Network for Rare Immunodeficiency, Autoinflammatory and Autoimmune Diseases (RITA) at University Hospital Leuven, Leuven, Belgium
- *Correspondence: Kourosh Ahmadzadeh, ; Carine Helena Wouters,
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9
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Karanth DS, Martin ML, Holliday LS. Plasma Membrane Receptors Involved in the Binding and Response of Osteoclasts to Noncellular Components of the Bone. Int J Mol Sci 2021; 22:ijms221810097. [PMID: 34576260 PMCID: PMC8466431 DOI: 10.3390/ijms221810097] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 09/13/2021] [Accepted: 09/16/2021] [Indexed: 12/21/2022] Open
Abstract
Osteoclasts differentiate from hematopoietic cells and resorb the bone in response to various signals, some of which are received directly from noncellular elements of the bone. In vitro, adherence to the bone triggers the reduction of cell–cell fusion events between osteoclasts and the activation of osteoclasts to form unusual dynamic cytoskeletal and membrane structures that are required for degrading the bone. Integrins on the surface of osteoclasts are known to receive regulatory signals from the bone matrix. Regulation of the availability of these signals is accomplished by enzymatic alterations of the bone matrix by protease activity and phosphorylation/dephosphorylation events. Other membrane receptors are present in osteoclasts and may interact with as yet unidentified signals in the bone. Bone mineral has been shown to have regulatory effects on osteoclasts, and osteoclast activity is also directly modulated by mechanical stress. As understanding of how osteoclasts and other bone cells interact with the bone has emerged, increasingly sophisticated efforts have been made to create bone biomimetics that reproduce both the structural properties of the bone and the bone’s ability to regulate osteoclasts and other bone cells. A more complete understanding of the interactions between osteoclasts and the bone may lead to new strategies for the treatment of bone diseases and the production of bone biomimetics to repair defects.
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Affiliation(s)
- Divakar S. Karanth
- Department of Orthodontics, College of Dentistry, University of Florida, Gainesville, FL 32610, USA; (D.S.K.); (M.L.M.)
| | - Macey L. Martin
- Department of Orthodontics, College of Dentistry, University of Florida, Gainesville, FL 32610, USA; (D.S.K.); (M.L.M.)
| | - Lexie S. Holliday
- Department of Orthodontics, College of Dentistry, University of Florida, Gainesville, FL 32610, USA; (D.S.K.); (M.L.M.)
- Department of Anatomy & Cell Biology, College of Medicine, University of Florida, Gainesville, FL 32610, USA
- Correspondence:
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10
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Chu A, Zirngibl RA, Manolson MF. The V-ATPase a3 Subunit: Structure, Function and Therapeutic Potential of an Essential Biomolecule in Osteoclastic Bone Resorption. Int J Mol Sci 2021; 22:ijms22136934. [PMID: 34203247 PMCID: PMC8269383 DOI: 10.3390/ijms22136934] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Revised: 06/18/2021] [Accepted: 06/21/2021] [Indexed: 12/29/2022] Open
Abstract
This review focuses on one of the 16 proteins composing the V-ATPase complex responsible for resorbing bone: the a3 subunit. The rationale for focusing on this biomolecule is that mutations in this one protein account for over 50% of osteopetrosis cases, highlighting its critical role in bone physiology. Despite its essential role in bone remodeling and its involvement in bone diseases, little is known about the way in which this subunit is targeted and regulated within osteoclasts. To this end, this review is broadened to include the three other mammalian paralogues (a1, a2 and a4) and the two yeast orthologs (Vph1p and Stv1p). By examining the literature on all of the paralogues/orthologs of the V-ATPase a subunit, we hope to provide insight into the molecular mechanisms and future research directions specific to a3. This review starts with an overview on bone, highlighting the role of V-ATPases in osteoclastic bone resorption. We then cover V-ATPases in other location/functions, highlighting the roles which the four mammalian a subunit paralogues might play in differential targeting and/or regulation. We review the ways in which the energy of ATP hydrolysis is converted into proton translocation, and go in depth into the diverse role of the a subunit, not only in proton translocation but also in lipid binding, cell signaling and human diseases. Finally, the therapeutic implication of targeting a3 specifically for bone diseases and cancer is discussed, with concluding remarks on future directions.
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11
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Hirata H, Xu X, Nishioka K, Matsuhisa F, Kitajima S, Kukita T, Murayama M, Urano Y, Miyamoto H, Mawatari M, Kukita A. PMEPA1 and NEDD4 control the proton production of osteoclasts by regulating vesicular trafficking. FASEB J 2021; 35:e21281. [PMID: 33484199 DOI: 10.1096/fj.202001795r] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Revised: 11/13/2020] [Accepted: 12/01/2020] [Indexed: 11/11/2022]
Abstract
Osteoclast bone resorption activity is critically regulated to maintain bone homeostasis. Osteoclasts resorb bone by producing protons and acid hydrolase via lysosomal secretion, however, a detailed mechanism remains elusive. PMEPA1 is a vesicular membrane protein, which binds to the NEDD4 family member of ubiquitin ligases. We have previously reported that Pmepa1 is highly expressed in bone resorbing osteoclasts, and regulates bone resorption. Here, we investigated the mechanism of bone resorption regulated by PMEPA1. Mutant mice lacking NEDD4-binding domains of PMEPA1 displayed enhanced bone volume, and reduced bone resorption activity in comparison with those of WT mice. Analysis with pH-sensitive fluorescence probe revealed that proton secretion from osteoclasts significantly decreased in Pmepa1 mutant osteoclasts. Immunofluorescence analysis revealed that PMEPA1 was colocalized with NEDD4, V0A3, and V0D2 subunits of vacuolar ATPase, which regulate the proton production of osteoclasts. In addition, Nedd4 knockdown reduced bone resorption and proton secretion of osteoclasts. Furthermore, Pmepa1 mutation and Nedd4 knockdown altered the cytoplasmic distribution of components of V-ATPase and expression of autophagy-related proteins, suggesting that lysosomal secretion is affected. Collectively, these findings indicate that PMEPA1 controls proton secretion from osteoclasts via NEDD4 by regulating vesicular trafficking, and NEDD4 is an important regulator of bone resorption.
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Affiliation(s)
- Hirohito Hirata
- Department of Pathology and Microbiology, Faculty of Medicine, Saga University, Saga, Japan.,Department of Orthopedic Surgery, Faculty of Medicine, Saga University, Saga, Japan
| | - Xianghe Xu
- Department of Pathology and Microbiology, Faculty of Medicine, Saga University, Saga, Japan.,Department of Molecular Cell Biology & Oral Anatomy, Kyushu University, Fukuoka, Japan
| | - Kenichi Nishioka
- Department of Internal Medicine, Musashimurayama Hospital, Tokyo, Japan
| | - Fumikazu Matsuhisa
- Division of Biological Resources and Development, Analytical Research Center for Experimental Sciences, Saga University, Saga, Japan
| | - Shuji Kitajima
- Division of Biological Resources and Development, Analytical Research Center for Experimental Sciences, Saga University, Saga, Japan
| | - Toshio Kukita
- Department of Molecular Cell Biology & Oral Anatomy, Kyushu University, Fukuoka, Japan
| | - Masatoshi Murayama
- Department of Pathology and Microbiology, Faculty of Medicine, Saga University, Saga, Japan.,Department of Orthopedic Surgery, Faculty of Medicine, Saga University, Saga, Japan
| | - Yasuteru Urano
- Department of Chemical Biology & Molecular Imaging, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.,Department of Chemistry & Biology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
| | - Hiroshi Miyamoto
- Department of Pathology and Microbiology, Faculty of Medicine, Saga University, Saga, Japan
| | - Masaaki Mawatari
- Department of Orthopedic Surgery, Faculty of Medicine, Saga University, Saga, Japan
| | - Akiko Kukita
- Department of Pathology and Microbiology, Faculty of Medicine, Saga University, Saga, Japan
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12
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Elson A, Stein M, Rabie G, Barnea-Zohar M, Winograd-Katz S, Reuven N, Shalev M, Sekeres J, Kanaan M, Tuckermann J, Geiger B. Sorting Nexin 10 as a Key Regulator of Membrane Trafficking in Bone-Resorbing Osteoclasts: Lessons Learned From Osteopetrosis. Front Cell Dev Biol 2021; 9:671210. [PMID: 34095139 PMCID: PMC8173195 DOI: 10.3389/fcell.2021.671210] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Accepted: 04/23/2021] [Indexed: 12/30/2022] Open
Abstract
Bone homeostasis is a complex, multi-step process, which is based primarily on a tightly orchestrated interplay between bone formation and bone resorption that is executed by osteoblasts and osteoclasts (OCLs), respectively. The essential physiological balance between these cells is maintained and controlled at multiple levels, ranging from regulated gene expression to endocrine signals, yet the underlying cellular and molecular mechanisms are still poorly understood. One approach for deciphering the mechanisms that regulate bone homeostasis is the characterization of relevant pathological states in which this balance is disturbed. In this article we describe one such “error of nature,” namely the development of acute recessive osteopetrosis (ARO) in humans that is caused by mutations in sorting nexin 10 (SNX10) that affect OCL functioning. We hypothesize here that, by virtue of its specific roles in vesicular trafficking, SNX10 serves as a key selective regulator of the composition of diverse membrane compartments in OCLs, thereby affecting critical processes in the sequence of events that link the plasma membrane with formation of the ruffled border and with extracellular acidification. As a result, SNX10 determines multiple features of these cells either directly or, as in regulation of cell-cell fusion, indirectly. This hypothesis is further supported by the similarities between the cellular defects observed in OCLs form various models of ARO, induced by mutations in SNX10 and in other genes, which suggest that mutations in the known ARO-associated genes act by disrupting the same plasma membrane-to-ruffled border axis, albeit to different degrees. In this article, we describe the population genetics and spread of the original arginine-to-glutamine mutation at position 51 (R51Q) in SNX10 in the Palestinian community. We further review recent studies, conducted in animal and cellular model systems, that highlight the essential roles of SNX10 in critical membrane functions in OCLs, and discuss possible future research directions that are needed for challenging or substantiating our hypothesis.
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Affiliation(s)
- Ari Elson
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot, Israel
| | - Merle Stein
- Institute of Comparative Molecular Endocrinology, University of Ulm, Ulm, Germany
| | - Grace Rabie
- Hereditary Research Laboratory and Department of Life Sciences, Bethlehem University, Bethlehem, Palestine
| | - Maayan Barnea-Zohar
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot, Israel
| | | | - Nina Reuven
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot, Israel
| | - Moran Shalev
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot, Israel
| | - Juraj Sekeres
- Department of Immunology, The Weizmann Institute of Science, Rehovot, Israel
| | - Moien Kanaan
- Hereditary Research Laboratory and Department of Life Sciences, Bethlehem University, Bethlehem, Palestine
| | - Jan Tuckermann
- Institute of Comparative Molecular Endocrinology, University of Ulm, Ulm, Germany
| | - Benjamin Geiger
- Department of Immunology, The Weizmann Institute of Science, Rehovot, Israel
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13
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Delaisse JM, Søe K, Andersen TL, Rojek AM, Marcussen N. The Mechanism Switching the Osteoclast From Short to Long Duration Bone Resorption. Front Cell Dev Biol 2021; 9:644503. [PMID: 33859985 PMCID: PMC8042231 DOI: 10.3389/fcell.2021.644503] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Accepted: 02/22/2021] [Indexed: 12/28/2022] Open
Abstract
The current models of osteoclastic bone resorption focus on immobile osteoclasts sitting on the bone surface and drilling a pit into the bone matrix. It recently appeared that many osteoclasts also enlarge their pit by moving across the bone surface while resorbing. Drilling a pit thus represents only the start of a resorption event of much larger amplitude. This prolonged resorption activity significantly contributes to pathological bone destruction, but the mechanism whereby the osteoclast engages in this process does not have an answer within the standard bone resorption models. Herein, we review observations that lead to envision how prolonged resorption is possible through simultaneous resorption and migration. According to the standard pit model, the “sealing zone” which surrounds the ruffled border (i.e., the actual resorption apparatus), “anchors” the ruffled border against the bone surface to be resorbed. Herein, we highlight that continuation of resorption demands that the sealing zone “glides” inside the cavity. Thereby, the sealing zone emerges as the structure responsible for orienting and displacing the ruffled border, e.g., directing resorption against the cavity wall. Importantly, sealing zone displacement stringently requires thorough collagen removal from the cavity wall - which renders strong cathepsin K collagenolysis indispensable for engagement of osteoclasts in cavity-enlargement. Furthermore, the sealing zone is associated with generation of new ruffled border at the leading edge, thereby allowing the ruffled border to move ahead. The sealing zone and ruffled border displacements are coordinated with the migration of the cell body, shown to be under control of lamellipodia at the leading edge and of the release of resorption products at the rear. We propose that bone resorption demands more attention to osteoclastic models integrating resorption and migration activities into just one cell phenotype.
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Affiliation(s)
- Jean-Marie Delaisse
- Clinical Cell Biology, Department of Pathology, Odense University Hospital, Odense, Denmark.,Clinical Cell Biology, Pathology Research Unit, Department of Clinical Research, University of Southern Denmark, Odense, Denmark.,Department of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - Kent Søe
- Clinical Cell Biology, Department of Pathology, Odense University Hospital, Odense, Denmark.,Clinical Cell Biology, Pathology Research Unit, Department of Clinical Research, University of Southern Denmark, Odense, Denmark.,Department of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - Thomas Levin Andersen
- Clinical Cell Biology, Department of Pathology, Odense University Hospital, Odense, Denmark.,Clinical Cell Biology, Pathology Research Unit, Department of Clinical Research, University of Southern Denmark, Odense, Denmark.,Department of Molecular Medicine, University of Southern Denmark, Odense, Denmark.,Department of Forensic Medicine, Aarhus University, Aarhus, Denmark
| | | | - Niels Marcussen
- Department of Molecular Medicine, University of Southern Denmark, Odense, Denmark
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14
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Akisaka T, Yoshida A. Surface distribution of heterogenous clathrin assemblies in resorbing osteoclasts. Exp Cell Res 2020; 399:112433. [PMID: 33359468 DOI: 10.1016/j.yexcr.2020.112433] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Revised: 12/06/2020] [Accepted: 12/12/2020] [Indexed: 01/04/2023]
Abstract
Osteoclasts seeded on either glass coverslips or apatite pellets have at least two morphologically distinct substrate adhesion sites: actin-based adhesion structures including podosome belts and sealing zones, and adjacent clathrin sheets. Clathrin-coated structures are exclusively localized at the podosome belts and sealing zone, in both of which the plasma membrane forms a tight attachment to the substrate surface. When cultured on apatite osteoclasts can degrade the apatite leading to the formation of resorption lacunae. The sealing zone divides the ventral membrane into different domains, outside and inside of the sealing zones. The former facing the smooth-surfaced intact apatite contains relatively solitary or networks of larger flat clathrin structures; and the latter, facing the rough-surfaced degraded apatite in the resorption lacunae contain clathrin in various shapes and sizes. Clathrin assemblies on the membrane domain facing not only a resorption lacuna, or trails but also intact apatite indeed were observed to be heterogeneous in size and intensity, suggesting that they appeared to follow variations in the surface topography of the apatite surface. These results provide a detailed insight into the flat clathrin sheets that have been suggested to be the sites of adhesion and mechanosensing in co-operation with podosomes.
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Affiliation(s)
- Toshitaka Akisaka
- Department of Oral Anatomy and Neurobiology, Graduate School of Dentistry, Osaka University, Japan.
| | - Atsushi Yoshida
- Department of Oral Anatomy and Neurobiology, Graduate School of Dentistry, Osaka University, Japan.
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15
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Roy M, Stephens E, Bouhour S, Roux S. RabGAP TBC1D25 is involved in human osteoclast activity. Eur J Cell Biol 2020; 100:151145. [PMID: 33353759 DOI: 10.1016/j.ejcb.2020.151145] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2020] [Revised: 12/06/2020] [Accepted: 12/08/2020] [Indexed: 01/01/2023] Open
Abstract
The osteoclast cell polarization and the ruffled border formation during bone resorption are major vesicle trafficking events. Rab GTPases have been shown to be involved in these processes, however very little is known about their regulators, such as Rab GTPase activating proteins (RabGAPs). In osteoclasts, we previously identified two spliced isoforms of TBC1D25, encoding a RabGAP which had never been studied in these cells. Using in vitro cultures, we evaluated the expression of TBC1D25 in human osteoclasts. TBC1D25 was expressed at the sealing zone co-localizing with F-actin, with an annular distribution, and also at the ruffled membrane with a less intense colocalization with LAMP2 and cathepsin K, but none with Rab7 or V-ATPase. Inhibiting TBC1D25 expression significantly decreased bone resorption, as well as the formation of multinucleated cells and the number of nuclei per cell. These results suggest that TBC1D25 has a role in bone resorption via the regulation of osteoclast polarization and resorption, and multinucleation as well.
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Affiliation(s)
- Michèle Roy
- Division of Rheumatology, Department of Medicine, Faculty of Medicine and Health Sciences, University of Sherbrooke, 3001, 12th Avenue North, Sherbrooke, PQ, Canada
| | - Elizabeth Stephens
- Division of Rheumatology, Department of Medicine, Faculty of Medicine and Health Sciences, University of Sherbrooke, 3001, 12th Avenue North, Sherbrooke, PQ, Canada
| | - Sophie Bouhour
- Division of Rheumatology, Department of Medicine, Faculty of Medicine and Health Sciences, University of Sherbrooke, 3001, 12th Avenue North, Sherbrooke, PQ, Canada
| | - Sophie Roux
- Division of Rheumatology, Department of Medicine, Faculty of Medicine and Health Sciences, University of Sherbrooke, 3001, 12th Avenue North, Sherbrooke, PQ, Canada.
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16
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Johnson IRD, Nguyen CT, Wise P, Grimm D. Implications of Altered Endosome and Lysosome Biology in Space Environments. Int J Mol Sci 2020; 21:ijms21218205. [PMID: 33147843 PMCID: PMC7663135 DOI: 10.3390/ijms21218205] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 10/30/2020] [Accepted: 10/31/2020] [Indexed: 12/17/2022] Open
Abstract
Space exploration poses multiple challenges for mankind, not only on a technical level but also to the entire physiology of the space traveller. The human system must adapt to several environmental stressors, microgravity being one of them. Lysosomes are ubiquitous to every cell and essential for their homeostasis, playing significant roles in the regulation of autophagy, immunity, and adaptation of the organism to changes in their environment, to name a few. Dysfunction of the lysosomal system leads to age-related diseases, for example bone loss, reduced immune response or cancer. As these conditions have been shown to be accelerated following exposure to microgravity, this review elucidates the lysosomal response to real and simulated microgravity. Microgravity activates the endo-lysosomal system, with resulting impacts on bone loss, muscle atrophy and stem cell differentiation. The investigation of lysosomal adaptation to microgravity can be beneficial in the search for new biomarkers or therapeutic approaches to several disease pathologies on earth as well as the potential to mitigate pathophysiology during spaceflight.
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Affiliation(s)
- Ian R. D. Johnson
- Research in Space Environments Group, UniSA Clinical and Health Sciences, University of South Australia, Adelaide, SA 5000, Australia;
- Correspondence:
| | - Catherine T. Nguyen
- Research in Space Environments Group, UniSA Clinical and Health Sciences, University of South Australia, Adelaide, SA 5000, Australia;
| | - Petra Wise
- Department of Hematology and Oncology, Children’s Hospital of Los Angeles, Los Angeles, CA 90027, USA;
| | - Daniela Grimm
- Department of Microgravity and Translational Regenerative Medicine, Clinic for Plastic, Aesthetic and Hand Surgery, Otto-von-Guericke-University Magdeburg, 39106 Magdeburg, Germany;
- Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark
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17
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Roy M, Roux S. Rab GTPases in Osteoclastic Bone Resorption and Autophagy. Int J Mol Sci 2020; 21:ijms21207655. [PMID: 33081155 PMCID: PMC7589333 DOI: 10.3390/ijms21207655] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2020] [Revised: 10/11/2020] [Accepted: 10/13/2020] [Indexed: 12/17/2022] Open
Abstract
Small guanosine triphosphate hydrolases (GTPases) of the Rab family are involved in plasma membrane delivery, fusion events, and lysosomal and autophagic degradation pathways, thereby regulating signaling pathways and cell differentiation and function. Osteoclasts are bone-resorbing cells that maintain bone homeostasis. Polarized vesicular trafficking pathways result in the formation of the ruffled border, the osteoclast’s resorptive organelle, which also assists in transcytosis. Here, we reviewed the different roles of Rab GTPases in the endomembrane machinery of osteoclasts and in bone diseases caused by the dysfunction of these proteins, with a particular focus on autophagy and bone resorption. Understanding the molecular mechanisms underlying osteoclast-related bone disease development is critical for developing and improving therapies.
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18
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Borggaard XG, Pirapaharan DC, Delaissé JM, Søe K. Osteoclasts' Ability to Generate Trenches Rather Than Pits Depends on High Levels of Active Cathepsin K and Efficient Clearance of Resorption Products. Int J Mol Sci 2020; 21:ijms21165924. [PMID: 32824687 PMCID: PMC7460581 DOI: 10.3390/ijms21165924] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2020] [Revised: 08/12/2020] [Accepted: 08/14/2020] [Indexed: 12/19/2022] Open
Abstract
Until recently, it was well-accepted that osteoclasts resorb bone according to the resorption cycle model. This model is based on the assumption that osteoclasts are immobile during bone erosion, allowing the actin ring to be firmly attached and thereby provide an effective seal encircling the resorptive compartment. However, through time-lapse, it was recently documented that osteoclasts making elongated resorption cavities and trenches move across the bone surface while efficiently resorbing bone. However, it was also shown that osteoclasts making rounded cavities and pits indeed resorb bone while they are immobile. Only little is known about what distinguishes these two different resorption modes. This is of both basic and clinical interest because these resorption modes are differently sensitive to drugs and are affected by the gender as well as age of the donor. In the present manuscript we show that: 1. levels of active cathepsin K determine the switch from pit to trench mode; 2. pit and trench mode depend on clathrin-mediated endocytosis; and 3. a mechanism integrating release of resorption products and membrane/integrin recycling is required for prolongation of trench mode. Our study therefore contributes to an improved understanding of the molecular and cellular determinants for the two osteoclastic bone resorption modes.
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Affiliation(s)
- Xenia G. Borggaard
- Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, 7100 Vejle, Denmark; (D.C.P.); (J.-M.D.)
- Department of Regional Health Research, University of Southern Denmark, 7100 Vejle, Denmark
- Clinical Cell Biology, Department of Pathology, Odense University Hospital, 5000 Odense C, Denmark
- Clinical Cell Biology, Pathology Research Unit, Department of Clinical Research, University of Southern Denmark, 5000 Odense C, Denmark
- Clinical Cell Biology, Department of Molecular Medicine, University of Southern Denmark, 5000 Odense C, Denmark
- Correspondence: (X.G.B.); (K.S.); Tel.: +45-65413190 (K.S.)
| | - Dinisha C. Pirapaharan
- Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, 7100 Vejle, Denmark; (D.C.P.); (J.-M.D.)
- Department of Regional Health Research, University of Southern Denmark, 7100 Vejle, Denmark
| | - Jean-Marie Delaissé
- Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, 7100 Vejle, Denmark; (D.C.P.); (J.-M.D.)
- Department of Regional Health Research, University of Southern Denmark, 7100 Vejle, Denmark
- Clinical Cell Biology, Department of Pathology, Odense University Hospital, 5000 Odense C, Denmark
- Clinical Cell Biology, Pathology Research Unit, Department of Clinical Research, University of Southern Denmark, 5000 Odense C, Denmark
- Clinical Cell Biology, Department of Molecular Medicine, University of Southern Denmark, 5000 Odense C, Denmark
| | - Kent Søe
- Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, 7100 Vejle, Denmark; (D.C.P.); (J.-M.D.)
- Department of Regional Health Research, University of Southern Denmark, 7100 Vejle, Denmark
- Clinical Cell Biology, Department of Pathology, Odense University Hospital, 5000 Odense C, Denmark
- Clinical Cell Biology, Pathology Research Unit, Department of Clinical Research, University of Southern Denmark, 5000 Odense C, Denmark
- Clinical Cell Biology, Department of Molecular Medicine, University of Southern Denmark, 5000 Odense C, Denmark
- Correspondence: (X.G.B.); (K.S.); Tel.: +45-65413190 (K.S.)
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19
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Vacher J, Bruccoleri M, Pata M. Ostm1 from Mouse to Human: Insights into Osteoclast Maturation. Int J Mol Sci 2020; 21:ijms21165600. [PMID: 32764302 PMCID: PMC7460669 DOI: 10.3390/ijms21165600] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Revised: 07/29/2020] [Accepted: 08/04/2020] [Indexed: 12/14/2022] Open
Abstract
The maintenance of bone mass is a dynamic process that requires a strict balance between bone formation and resorption. Bone formation is controlled by osteoblasts, while osteoclasts are responsible for resorption of the bone matrix. The opposite functions of these cell types have to be tightly regulated not only during normal bone development, but also during adult life, to maintain serum calcium homeostasis and sustain bone integrity to prevent bone fractures. Disruption of the control of bone synthesis or resorption can lead to an over accumulation of bone tissue in osteopetrosis or conversely to a net depletion of the bone mass in osteoporosis. Moreover, high levels of bone resorption with focal bone formation can cause Paget’s disease. Here, we summarize the steps toward isolation and characterization of the osteopetrosis associated trans-membrane protein 1 (Ostm1) gene and protein, essential for proper osteoclast maturation, and responsible when mutated for the most severe form of osteopetrosis in mice and humans.
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Affiliation(s)
- Jean Vacher
- Institut de Recherches Cliniques de Montreal (IRCM), Montreal, QC H2W 1R7, Canada; (M.B.); (M.P.)
- Departement de Medecine, Universite de Montreal, Montreal, QC H2W 1R7, Canada
- Department of Medicine, Division of Experimental Medicine, McGill University, Montreal, QC H3A 1A3, Canada
- Correspondence:
| | - Michael Bruccoleri
- Institut de Recherches Cliniques de Montreal (IRCM), Montreal, QC H2W 1R7, Canada; (M.B.); (M.P.)
- Departement de Medecine, Universite de Montreal, Montreal, QC H2W 1R7, Canada
| | - Monica Pata
- Institut de Recherches Cliniques de Montreal (IRCM), Montreal, QC H2W 1R7, Canada; (M.B.); (M.P.)
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20
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Abstract
Minodronate is a heterocyclic nitrogen-containing bisphosphonate with high potency in inhibiting bone resorption, and is developed for clinical use in Japan. Minodronate has very high potency in inhibiting farnesyl pyrophosphate synthase, and shows lower affinity for bone matrix hydroxyapatite at both neutral and acidic pH. As a result, small amount of minodronate is deposited in bone but can exert strong anti-resorptive activity in vivo. In this review on minodronate, we summarize the mechanism of action, physico-chemical properties, effects on bone quality in animals, and effects on bone turnover, bone mineral density and fracture prevention, as well as safety in the treatment of patients with osteoporosis.
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Affiliation(s)
- Toshio Matsumoto
- Fujii Memorial Institute of Medical Sciences, Tokushima University, Japan.
| | - Itsuro Endo
- Department of Bioregulatory Sciences, Tokushima University Graduate School of Medical Sciences, Tokushima, Japan
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21
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Søe K, Delaisse JM, Borggaard XG. Osteoclast formation at the bone marrow/bone surface interface: Importance of structural elements, matrix, and intercellular communication. Semin Cell Dev Biol 2020; 112:8-15. [PMID: 32563679 DOI: 10.1016/j.semcdb.2020.05.016] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Revised: 05/17/2020] [Accepted: 05/19/2020] [Indexed: 12/28/2022]
Abstract
Osteoclasts, the multinucleated cells responsible for bone resorption, have an enormous destructive power which demands to be kept under tight control. Accordingly, the identification of molecular signals directing osteoclastogenesis and switching on their resorptive activity have received much attention. Mandatory factors were identified, but a very essential aspect of the control mechanism of osteoclastic resorption, i.e. its spatial control, remains poorly understood. Under physiological conditions, multinucleated osteoclasts are only detected on the bone surface, while their mono-nucleated precursors are only in the bone marrow. How are pre-osteoclasts targeted to the bone surface? How is their progressive differentiation coordinated with their approach to the bone surface sites to be resorbed, which is where they finally fuse? Here we review the information on the bone marrow distribution of differentiating pre-osteoclasts relative to the position of the mandatory factors for their differentiation as well as relative to physical entities that may affect their access to the remodelling sites. This info allows recognizing an "osteoclastogenesis route" through the bone marrow and leading to the coincident fusion/resorption site - but also points to what still remains to be clarified regarding this route and regarding the restriction of fusion at the resorption site. Finally, we discuss the mechanism responsible for the start of resorption and its spatial extension. This review underscores that fully understanding the control of bone resorption requires to consider it in both space and time - which demands taking into account the context of bone tissue.
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Affiliation(s)
- Kent Søe
- Clinical Cell Biology, Department of Pathology, Odense University Hospital, 5000 Odense C, Denmark; Department of Clinical Research, University of Southern Denmark, 5230 Odense M, Denmark; Department of Molecular Medicine, University of Southern Denmark, 5230 Odense M, Denmark.
| | - Jean-Marie Delaisse
- Clinical Cell Biology, Department of Pathology, Odense University Hospital, 5000 Odense C, Denmark; Department of Clinical Research, University of Southern Denmark, 5230 Odense M, Denmark; Department of Molecular Medicine, University of Southern Denmark, 5230 Odense M, Denmark.
| | - Xenia Goldberg Borggaard
- Clinical Cell Biology, Department of Pathology, Odense University Hospital, 5000 Odense C, Denmark; Department of Clinical Research, University of Southern Denmark, 5230 Odense M, Denmark; Department of Molecular Medicine, University of Southern Denmark, 5230 Odense M, Denmark.
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22
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Abstract
Skeletal involvement is a frequent and troublesome complication in advanced cancers. In the process of tumor cells homing to the skeleton to form bone metastases (BM), different mechanisms allow tumor cells to interact with cells of the bone microenvironment and seed in the bone tissue. Among these, tumor acidosis has been directly associated with tumor invasion and aggressiveness in several types of cancer although it has been less explored in the context of BM. In bone, the association of local acidosis and cancer invasiveness is even more important for tumor expansion since the extracellular matrix is formed by both organic and hard inorganic matrices and bone cells are used to sense protons and adapt or react to a low pH to maintain tissue homeostasis. In the BM microenvironment, increased concentration of protons may derive not only from glycolytic tumor cells but also from tumor-induced osteoclasts, the bone-resorbing cells, and may influence the progression or symptoms of BM in many different ways, by directly enhancing cancer cell motility and aggressiveness, or by modulating the functions of bone cells versus a pro-tumorigenic phenotype, or by inducing bone pain. In this review, we will describe and discuss the cause of acidosis in BM, its role in BM microenvironment, and which are the final effectors that may be targeted to treat metastatic patients.
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Affiliation(s)
- Sofia Avnet
- Orthopaedic Pathophysiology and Regenerative Unit, IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy.
| | - Gemma Di Pompo
- Orthopaedic Pathophysiology and Regenerative Unit, IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy
| | - Silvia Lemma
- Orthopaedic Pathophysiology and Regenerative Unit, IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy
| | - Nicola Baldini
- Orthopaedic Pathophysiology and Regenerative Unit, IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy
- Department of Biomedical and Neuromotor Sciences, University of Bologna, 40123, Bologna, Italy
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23
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Al Mamun MA, Asim MMH, Sahin MAZ, Al-Bari MAA. Flavonoids compounds from Tridax procumbens inhibit osteoclast differentiation by down-regulating c-Fos activation. J Cell Mol Med 2020; 24:2542-2551. [PMID: 31919976 PMCID: PMC7028861 DOI: 10.1111/jcmm.14948] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Revised: 12/01/2019] [Accepted: 12/09/2019] [Indexed: 01/04/2023] Open
Abstract
The total flavonoids from Tridax procumbens (TPFs) have been reported significantly to suppress on RANKL‐induced osteoclast differentiation and bone resorption in mouse primary cultured osteoclasts. However, the effects of ethyl ether fraction of Tridax procumbens flavonoids (TPF) on osteoclastogenesis remain unknown. In this study, we investigated the effects of TPF on lipopolysaccharides (LPS)‐induced osteoclast differentiation, actin ring formation, and explored its molecular mechanism in vitro. Matured osteoclast was counted as the number of tartrate‐resistant acid phosphatase (TRAP)‐positive multinucleated cells, and activity of osteoclast was assessed by performing the pit formation assays. Real‐time polymerase chain reaction (RT‐PCR) was performed for evaluation of the expression of osteoclast differentiation‐related genes. TPF reduced the TRAP‐positive multinucleated osteoclasts, inhibited TRAP and acid phosphatase (ACP) activities and decreased the expression of osteoclast differentiating genes, including cathepsin K, metalloproteinase‐2 (MMP‐2), MMP‐9, MMP‐13 and osteoclast‐associated receptor (OSCAR). Furthermore, osteoclast‐dependent actin rings formation and resorption pits were dramatically inhibited by the treatment with TPF. TPF markedly decreased the expression levels of transcription factors such as c‐Fos, nuclear factor of activated T cells cytoplasmic 1 (NFATc1) and activator protein‐1 (AP‐1). Taken together, our findings indicated that TPF suppressed both osteoclast differentiation and activities. Therefore, TPF might be a promising and emerging drug candidate for the treatment of bone diseases such as osteoporosis.
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Affiliation(s)
- Md Abdullah Al Mamun
- Department of Genetic Engineering and Biotechnology, Shahjalal University of Science and Technology, Sylhet, Bangladesh
| | - Md Muzammal Haque Asim
- Department of Genetic Engineering and Biotechnology, Shahjalal University of Science and Technology, Sylhet, Bangladesh
| | - Md Ali Zaber Sahin
- Department of Genetic Engineering and Biotechnology, Shahjalal University of Science and Technology, Sylhet, Bangladesh
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24
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Madel MB, Ibáñez L, Wakkach A, de Vries TJ, Teti A, Apparailly F, Blin-Wakkach C. Immune Function and Diversity of Osteoclasts in Normal and Pathological Conditions. Front Immunol 2019; 10:1408. [PMID: 31275328 PMCID: PMC6594198 DOI: 10.3389/fimmu.2019.01408] [Citation(s) in RCA: 118] [Impact Index Per Article: 23.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Accepted: 06/04/2019] [Indexed: 12/31/2022] Open
Abstract
Osteoclasts (OCLs) are key players in controlling bone remodeling. Modifications in their differentiation or bone resorbing activity are associated with a number of pathologies ranging from osteopetrosis to osteoporosis, chronic inflammation and cancer, that are all characterized by immunological alterations. Therefore, the 2000s were marked by the emergence of osteoimmunology and by a growing number of studies focused on the control of OCL differentiation and function by the immune system. At the same time, it was discovered that OCLs are much more than bone resorbing cells. As monocytic lineage-derived cells, they belong to a family of cells that displays a wide heterogeneity and plasticity and that is involved in phagocytosis and innate immune responses. However, while OCLs have been extensively studied for their bone resorption capacity, their implication as immune cells was neglected for a long time. In recent years, new evidence pointed out that OCLs play important roles in the modulation of immune responses toward immune suppression or inflammation. They unlocked their capacity to modulate T cell activation, to efficiently process and present antigens as well as their ability to activate T cell responses in an antigen-dependent manner. Moreover, similar to other monocytic lineage cells such as macrophages, monocytes and dendritic cells, OCLs display a phenotypic and functional plasticity participating to their anti-inflammatory or pro-inflammatory effect depending on their cell origin and environment. This review will address this novel vision of the OCL, not only as a phagocyte specialized in bone resorption, but also as innate immune cell participating in the control of immune responses.
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Affiliation(s)
- Maria-Bernadette Madel
- CNRS, Laboratoire de PhysioMédecine Moléculaire, Faculté de Médecine, UMR7370, Nice, France.,Faculé de Médecine, Université Côte d'Azur, Nice, France
| | - Lidia Ibáñez
- Department of Pharmacy, Cardenal Herrera-CEU University, València, Spain
| | - Abdelilah Wakkach
- CNRS, Laboratoire de PhysioMédecine Moléculaire, Faculté de Médecine, UMR7370, Nice, France.,Faculé de Médecine, Université Côte d'Azur, Nice, France
| | - Teun J de Vries
- Department of Periodontology, Academic Centre of Dentistry Amsterdam, University of Amsterdam and Vrije Univeristeit, Amsterdam, Netherlands
| | - Anna Teti
- Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila, L'Aquila, Italy
| | | | - Claudine Blin-Wakkach
- CNRS, Laboratoire de PhysioMédecine Moléculaire, Faculté de Médecine, UMR7370, Nice, France.,Faculé de Médecine, Université Côte d'Azur, Nice, France
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25
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Membrane trafficking in osteoclasts and implications for osteoporosis. Biochem Soc Trans 2019; 47:639-650. [PMID: 30837319 PMCID: PMC6490703 DOI: 10.1042/bst20180445] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2018] [Revised: 02/03/2019] [Accepted: 02/05/2019] [Indexed: 12/20/2022]
Abstract
Osteoclasts are large multinucleated cells exquisitely adapted to resorb bone matrix. Like other eukaryotes, osteoclasts possess an elaborate ensemble of intracellular organelles through which solutes, proteins and other macromolecules are trafficked to their target destinations via membrane-bound intermediaries. During bone resorption, membrane trafficking must be tightly regulated to sustain the structural and functional polarity of the osteoclasts’ membrane domains. Of these, the ruffled border (RB) is most characteristic, functioning as the osteoclasts' secretory apparatus. This highly convoluted organelle is classically considered to be formed by the targeted fusion of acidic vesicles with the bone-facing plasma membrane. Emerging findings disclose new evidence that the RB is far more complex than previously envisaged, possessing discrete subdomains that are serviced by several intersecting endocytic, secretory, transcytotic and autophagic pathways. Bone-resorbing osteoclasts therefore serve as a unique model system for studying polarized membrane trafficking. Recent advances in high-resolution microscopy together with the convergence of genetic and cell biological studies in humans and in mice have helped illuminate the major membrane trafficking pathways in osteoclasts and unmask the core molecular machinery that governs these distinct vesicle transport routes. Among these, small Rab GTPases, their binding partners and members of the endocytic sorting nexin family have emerged as critical regulators. This mini review summarizes our current understanding of membrane trafficking in osteoclasts, the key molecular participants, and discusses how these transport machinery may be exploited for the development of new therapies for metabolic disorders of bone-like osteoporosis.
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26
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Plotkin LI, Bruzzaniti A. Molecular signaling in bone cells: Regulation of cell differentiation and survival. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2019; 116:237-281. [PMID: 31036293 PMCID: PMC7416488 DOI: 10.1016/bs.apcsb.2019.01.002] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The achievement of proper bone mass and architecture, and their maintenance throughout life requires the concerted actions of osteoblasts, the bone forming cells, and osteoclasts, the bone resorbing cells. The differentiation and activity of osteoblasts and osteoclasts are regulated by molecules produced by matrix-embedded osteocytes, as well as by cross talk between osteoblasts and osteoclasts through secreted factors. In addition, it is likely that direct contact between osteoblast and osteoclast precursors, and the contact of these cells with osteocytes and cells in the bone marrow, also modulates bone cell differentiation and function. With the advancement of molecular and genetic tools, our comprehension of the intracellular signals activated in bone cells has evolved significantly, from early suggestions that osteoblasts and osteoclasts have common precursors and that osteocytes are inert cells in the bone matrix, to the very sophisticated understanding of a network of receptors, ligands, intracellular kinases/phosphatases, transcription factors, and cell-specific genes that are known today. These advances have allowed the design and FDA-approval of new therapies to preserve and increase bone mass and strength in a wide variety of pathological conditions, improving bone health from early childhood to the elderly. We have summarized here the current knowledge on selected intracellular signal pathways activated in osteoblasts, osteocytes, and osteoclasts.
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Affiliation(s)
- Lilian I Plotkin
- Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN, United States; Indiana Center for Musculoskeletal Health, Indianapolis, IN, United States; Roudebush Veterans Administration Medical Center, Indianapolis, IN, United States.
| | - Angela Bruzzaniti
- Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN, United States; Indiana Center for Musculoskeletal Health, Indianapolis, IN, United States; Department of Biomedical and Applied Sciences, Indiana University School of Dentistry, Indianapolis, IN, United States
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27
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Gu W, Chen K, Zhao X, Geng H, Li J, Qin Y, Bai X, Chang YN, Xia S, Zhang J, Ma S, Wu Z, Xing G, Xing G. Highly Dispersed Fullerenols Hamper Osteoclast Ruffled Border Formation by Perturbing Ca 2+ Bundles. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2018; 14:e1802549. [PMID: 30334332 DOI: 10.1002/smll.201802549] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Revised: 09/29/2018] [Indexed: 06/08/2023]
Abstract
Osteoporosis, a common and serious bone disorder affecting aged people and postmenopausal women, is characterized by osteoclast overactivity. One therapeutic strategy is suppressing the bone resorption function of hyperactive osteoclasts, but there is no effective drug in clinical practice so far. Herein, it is demonstrated that fullerenols suppress the bone resorption of osteoclasts by inhibiting ruffled borders (RBs) formation. The RBs formation, which is supported by well-aligned actin bundles (B-actins), is a critical event for osteoclast bone resorption. To facilitate this function, osteoclast RBs dynamics is regulated by variable microenvironments to bundle F-actins, protrude cell membrane, and so on. B-actin perturbation by fullerenols is determined here, offering an opportunity to regulate osteoclast function by destroying RBs. In vivo, the therapeutic effect of fullerenols on overactive osteoclasts is confirmed in a mouse model of lipopolysaccharide-induced bone erosion. Collectively, the findings suggest that fullerenols adhere to F-actin surfaces and inhibit RBs formation in osteoclasts, mainly through hampering Ca2+ from bundling F-actins, and this is likely due to the stereo-hindrance effect caused by adherent fullerenols.
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Affiliation(s)
- Weihong Gu
- CAS Key Laboratory for Biomedical Effects of Nanomaterial and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Kui Chen
- CAS Key Laboratory for Biomedical Effects of Nanomaterial and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Xiaoyi Zhao
- University of Chinese Academy of Sciences, Beijing, 100049, China
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences (CAS), Beijing, 100049, China
| | - Huan Geng
- Department of Orthopedics, General Hospital of Chinese People's Armed Police Forces, Beijing, 100039, China
| | - Juan Li
- CAS Key Laboratory for Biomedical Effects of Nanomaterial and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
| | - Yanxia Qin
- CAS Key Laboratory for Biomedical Effects of Nanomaterial and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
| | - Xue Bai
- CAS Key Laboratory for Biomedical Effects of Nanomaterial and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Ya-Nan Chang
- CAS Key Laboratory for Biomedical Effects of Nanomaterial and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
| | - Shibo Xia
- CAS Key Laboratory for Biomedical Effects of Nanomaterial and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Jiaxin Zhang
- CAS Key Laboratory for Biomedical Effects of Nanomaterial and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Sihan Ma
- CAS Key Laboratory for Biomedical Effects of Nanomaterial and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
| | - Zhonghua Wu
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences (CAS), Beijing, 100049, China
| | - Gengyan Xing
- Department of Orthopedics, General Hospital of Chinese People's Armed Police Forces, Beijing, 100039, China
| | - Gengmei Xing
- CAS Key Laboratory for Biomedical Effects of Nanomaterial and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
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28
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Septins are critical regulators of osteoclastic bone resorption. Sci Rep 2018; 8:13016. [PMID: 30158637 PMCID: PMC6115361 DOI: 10.1038/s41598-018-31159-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 08/07/2018] [Indexed: 12/23/2022] Open
Abstract
Septins are known to play key roles in supporting cytoskeletal stability, vesicular transport, endo-/exocytosis, stabilizing cellular membranes and forming diffusion barriers. Their function in mammalian cells is poorly investigated. The osteoclast offers an interesting tool to investigate septins because all cellular activities septins were reported to be involved in are critical for osteoclasts. However, the existence of septins in osteoclasts has not even been reported. Here we show that the SEPT9 gene and Septin 9 (SEPT9) protein are expressed and synthesized during differentiation of human osteoclasts. Pharmacological stabilization of septin filaments dose dependently inhibits bone resorption of human osteoclasts in vitro suggesting a role for septins in bone resorption. Attesting to this, conditional deletion of Sept9 in mice leads to elevated levels of trabecular bone and diminished femoral growth in vivo. Finally, systematic interrogation of the spatial organization of SEPT9 by confocal microscopy reveals that SEPT9 is closely associated to the structures known to be critical for osteoclast activity. We propose that septins in general and SEPT9 in particular play a previously unappreciated role in osteoclastic bone resorption.
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29
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Rab GTPases in Osteoclastic Endomembrane Systems. BIOMED RESEARCH INTERNATIONAL 2018; 2018:4541538. [PMID: 30186859 PMCID: PMC6114073 DOI: 10.1155/2018/4541538] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/25/2018] [Accepted: 07/18/2018] [Indexed: 12/13/2022]
Abstract
Osteoclasts (OCs) are bone-resorbing cells that maintain bone homeostasis. OC differentiation, survival, and activity are regulated by numerous small GTPases, including those of the Rab family, which are involved in plasma membrane delivery and lysosomal and autophagic degradation pathways. In resorbing OCs, polarized vesicular trafficking pathways also result in formation of the ruffled membrane, the resorbing organelle, and in transcytosis.
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30
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The Sealing Zone in Osteoclasts: A Self-Organized Structure on the Bone. Int J Mol Sci 2018; 19:ijms19040984. [PMID: 29587415 PMCID: PMC5979552 DOI: 10.3390/ijms19040984] [Citation(s) in RCA: 67] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Revised: 03/22/2018] [Accepted: 03/23/2018] [Indexed: 01/08/2023] Open
Abstract
Osteoclasts form a specialized cell-matrix adhesion structure, known as the "sealing zone", during bone resorption. The sealing zone is a dynamic actin-rich structure that defines the resorption area of the bone. The detailed dynamics and fine structure of the sealing zone have been elusive. Osteoclasts plated on glass do not form a sealing zone, but generate a separate supra-molecular structure called the "podosome belt". Podosomes are integrin-based adhesion complexes involved in matrix adhesion, cell migration, matrix degradation, and mechanosensing. Invadopodia, podosome-like protrusions in cancer cells, are involved in cell invasion into other tissues by promoting matrix degradation. Both podosomes and invadopodia exhibit actin pattern transitions during maturation. We previously found that Arp2/3-dependent actin flow occurs in all observed assembly patterns of podosomes in osteoclasts on glass. It is known that the actin wave in Dictyostelium cells exhibits a similar pattern transition in its evolution. Because of significant advances in our understanding regarding the mechanism of podosomes/invadopodia formation over the last decade, we revisited the structure and function of the sealing zone in this review, highlighting the possible involvement of self-organized actin waves in the organogenesis of the sealing zone.
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31
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Søe K, Delaissé JM. Time-lapse reveals that osteoclasts can move across the bone surface while resorbing. J Cell Sci 2017; 130:2026-2035. [PMID: 28473470 PMCID: PMC5482982 DOI: 10.1242/jcs.202036] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2017] [Accepted: 04/28/2017] [Indexed: 12/29/2022] Open
Abstract
Bone erosion both demands that the osteoclast resorbs bone matrix and moves over the bone surface. It is widely accepted that these two activities alternate, because they are considered mutually exclusive since resorption is believed to involve an immobilizing seal to the bone surface. However, clear real-time observations are still lacking. Herein, we used specific markers and time-lapse to monitor live the spatiotemporal generation of resorption events by osteoclasts cultured on bone slices. In accordance with the current view, we found alternating episodes of resorption and migration resulting in the formation of clusters of round pits. However, very importantly, we also demonstrate that more than half of the osteoclasts moved laterally, displacing their extracellular bone-resorbing compartment over the bone surface without disassembling and reconstructing it, thereby generating long trenches. Compared to pit events, trench events show properties enabling higher aggressiveness: long duration (days), high erosion speed (two times faster) and long-distance erosion (several 100 µm). Simultaneous resorption and migration reflect a unique situation where epithelial/secretory and mesenchymal/migratory characteristics are integrated into just one cell phenotype, and deserves attention in future research. Summary: Bone erosion requires that osteoclasts both resorb and migrate. According to common belief, these activities are mutually exclusive and alternate. Paradoxically, we show here simultaneous resorption and migration.
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Affiliation(s)
- Kent Søe
- Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark, 7100 Vejle, Denmark
| | - Jean-Marie Delaissé
- Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark, 7100 Vejle, Denmark
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32
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Knowles HJ. Hypoxia-Induced Fibroblast Growth Factor 11 Stimulates Osteoclast-Mediated Resorption of Bone. Calcif Tissue Int 2017; 100:382-391. [PMID: 28097375 PMCID: PMC5336535 DOI: 10.1007/s00223-016-0228-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Accepted: 12/20/2016] [Indexed: 12/17/2022]
Abstract
Over-activation of osteoclasts is directly responsible for pathological bone loss in conditions such as rheumatoid arthritis and cancer metastasis to bone. Hypoxia is a common feature of these conditions, associated with poor prognosis, which also stimulates osteoclast-mediated bone resorption via induction of the hypoxia-inducible transcription factor HIF-1α. Here, we investigate the effects of fibroblast growth factor 11 (FGF11) on osteoclast function. FGF11 is an intracellular FGF that was induced both by hypoxia (2% O2, p < 0.01) and by inhibition of the HIF-regulating prolyl hydroxylase enzymes (CoCl2, p < 0.001) in osteoclasts. Isoform-specific siRNA demonstrated that the induction of Fgf11 mRNA expression by hypoxia is HIF-1α-dependent (p < 0.01). Hypoxic stimulation of bone resorption was inhibited in osteoclasts treated with siRNA targeting FGF11 (p < 0.05). This was at least partially due to reduced secretion of an unidentified pro-resorptive factor downstream of FGF11. FGF11 expression within hypoxic, resorbing osteoclasts co-localised with microtubule-associated alpha-tubulin. FGF11 was also abundantly expressed in osteoclasts within the rheumatoid synovium and in giant cell tumour of bone. This study suggests FGF11 as a novel factor driving pathological bone resorption in osteolytic disease and as a potential target for the development of new anti-resorptive therapeutic agents.
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Affiliation(s)
- Helen J Knowles
- Botnar Research Centre, Nuffield Department of Orthopaedics Rheumatology & Musculoskeletal Sciences, University of Oxford, Headington, Oxford, OX3 7LD, UK.
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33
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Castillo LM, Guerrero CA, Acosta O. Expression of typical osteoclast markers by PBMCs after PEG-induced fusion as a model for studying osteoclast differentiation. J Mol Histol 2017; 48:169-185. [PMID: 28343338 DOI: 10.1007/s10735-017-9717-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Accepted: 03/20/2017] [Indexed: 01/27/2023]
Abstract
Bone is a metabolically active organ subjected to continuous remodeling process that involves resorption by osteoclast and subsequent formation by osteoblasts. Osteoclast involvement in this physiological event is regulated by macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor κB ligand (RANKL). Fusion of mono-nuclear pre-osteoclasts is a critical event for osteoclast differentiation and for bone resorption. Here we show that PBMCs can be successfully fused with polyethylenglicol (PEG) in order to generated viable osteoclast-like cells that exhibit tartrate-resistant acid phosphatase (TRAP) and bone resorptive activities. PEG-fused PBMCs expressed additional markers compatible with osteoclastogenic differentiation such as carbonic anhydrase II (CAII), calcitonin receptor (CR), cathepsin K (Cat K), vacuolar ATPase (V-ATPase) subunit C1 (V-ATPase), integrin β3, RANK and cell surface aminopeptidase N/CD13. Actin redistribution in PEG-fused cells was found to be affected by cell cycle synchronization at G0/G1 or G2/M phases. PEG-induced fusion also led to expression of tyrosine kinases c-Src and Syk in their phosphorylated state. Scanning electron microscopy images showed morphological features typical of osteoclast-like cells. The results here shown allow concluding that PEG-induced fusion of PBMCs provides a suitable model system for understanding the mechanisms involved in osteoclastogenesis and for assaying new therapeutic strategies.
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Affiliation(s)
- Luz M Castillo
- Departamento de Ciencias Fisiológicas, Facultad de Medicina, Universidad Nacional de Colombia, Bogotá, Colombia
| | - Carlos A Guerrero
- Departamento de Ciencias Fisiológicas, Facultad de Medicina, Universidad Nacional de Colombia, Bogotá, Colombia.
| | - Orlando Acosta
- Departamento de Ciencias Fisiológicas, Facultad de Medicina, Universidad Nacional de Colombia, Bogotá, Colombia
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34
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Erkhembaatar M, Gu DR, Lee SH, Yang YM, Park S, Muallem S, Shin DM, Kim MS. Lysosomal Ca 2+ Signaling is Essential for Osteoclastogenesis and Bone Remodeling. J Bone Miner Res 2017; 32:385-396. [PMID: 27589205 PMCID: PMC9850942 DOI: 10.1002/jbmr.2986] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Revised: 08/29/2016] [Accepted: 08/31/2016] [Indexed: 01/21/2023]
Abstract
Lysosomal Ca2+ emerges as a critical component of receptor-evoked Ca2+ signaling and plays a crucial role in many lysosomal and physiological functions. Lysosomal Ca2+ release is mediated by the transient receptor potential (TRP) family member TRPML1, mutations that cause the lysosomal storage disease mucolipidosis type 4. Lysosomes play a key role in osteoclast function. However, nothing is known about the role of lysosomal Ca2+ signaling in osteoclastogenesis and bone metabolism. In this study, we addressed this knowledge gap by studying the role of lysosomal Ca2+ signaling in osteoclastogenesis, osteoclast and osteoblast functions, and bone homeostasis in vivo. We manipulated lysosomal Ca2+ signaling by acute knockdown of TRPML1, deletion of TRPML1 in mice, pharmacological inhibition of lysosomal Ca2+ influx, and depletion of lysosomal Ca2+ storage using the TRPML agonist ML-SA1. We found that knockdown and deletion of TRPML1, although it did not have an apparent effect on osteoblast differentiation and bone formation, markedly attenuated osteoclast function, RANKL-induced cytosolic Ca2+ oscillations, inhibited activation of NFATc1 and osteoclastogenesis-controlling genes, suppressed the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells (MNCs), and markedly reduced the differentiation of bone marrow-derived macrophages into osteoclasts. Moreover, deletion of TRPML1 resulted in enlarged lysosomes, inhibition of lysosomal secretion, and attenuated the resorptive activity of mature osteoclasts. Notably, depletion of lysosomal Ca2+ with ML-SA1 similarly abrogated RANKL-induced Ca2+ oscillations and MNC formation. Deletion of TRPML1 in mice reduced the TRAP-positive bone surfaces and impaired bone remodeling, resulting in prominent osteopetrosis. These findings demonstrate the essential role of lysosomal Ca2+ signaling in osteoclast differentiation and mature osteoclast function, which play key roles in bone homeostasis. © 2016 American Society for Bone and Mineral Research.
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Affiliation(s)
- Munkhsoyol Erkhembaatar
- Department of Oral Physiology, and Institute of Biomaterial-Implant, College of Dentistry, Wonkwang University, Iksan, Republic of Korea.,Department of Physiology, School of Pharmacy and Bio-Medicine, Mongolian National University of Medical Science, Ulaanbaatar, Mongolia
| | - Dong Ryun Gu
- Center for Metabolic Function Regulation (CMFR), School of Medicine, Wonkwang University, Iksan, Republic of Korea.,Department of Oral Microbiology and Immunology, College of Dentistry, Wonkwang University, Iksan, Republic of Korea
| | - Seoung Hoon Lee
- Center for Metabolic Function Regulation (CMFR), School of Medicine, Wonkwang University, Iksan, Republic of Korea.,Department of Oral Microbiology and Immunology, College of Dentistry, Wonkwang University, Iksan, Republic of Korea
| | - Yu-Mi Yang
- Department of Oral Biology, BK21 PLUS Project, Yonsei University College of Dentistry, Seoul, Republic of Korea
| | - Soonhong Park
- Department of Oral Biology, BK21 PLUS Project, Yonsei University College of Dentistry, Seoul, Republic of Korea
| | - Shmuel Muallem
- Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA
| | - Dong Min Shin
- Department of Oral Biology, BK21 PLUS Project, Yonsei University College of Dentistry, Seoul, Republic of Korea
| | - Min Seuk Kim
- Department of Oral Physiology, and Institute of Biomaterial-Implant, College of Dentistry, Wonkwang University, Iksan, Republic of Korea
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35
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Ultrastructural analysis of apatite-degrading capability of extended invasive podosomes in resorbing osteoclasts. Micron 2016; 88:37-47. [DOI: 10.1016/j.micron.2016.05.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2016] [Revised: 05/13/2016] [Accepted: 05/13/2016] [Indexed: 01/11/2023]
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36
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Lemma S, Sboarina M, Porporato PE, Zini N, Sonveaux P, Di Pompo G, Baldini N, Avnet S. Energy metabolism in osteoclast formation and activity. Int J Biochem Cell Biol 2016; 79:168-180. [PMID: 27590854 DOI: 10.1016/j.biocel.2016.08.034] [Citation(s) in RCA: 138] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2016] [Revised: 08/09/2016] [Accepted: 08/29/2016] [Indexed: 01/07/2023]
Abstract
Osteoclastogenesis and osteolysis are energy-consuming processes supported by high metabolic activities. In human osteoclasts derived from the fusion of monocytic precursors, we found a substantial increase in the number of mitochondria with differentiation. In mature osteoclasts, mitochondria were also increased in size, rich of cristae and arranged in a complex tubular network. When compared with immature cells, fully differentiated osteoclasts showed higher levels of enzymes of the electron transport chain, a higher mitochondrial oxygen consumption rate and a lower glycolytic efficiency, as evaluated by extracellular flux analysis and by the quantification of metabolites in the culture supernatant. Thus, oxidative phosphorylation appeared the main bioenergetic source for osteoclast formation. Conversely, we found that bone resorption mainly relied on glycolysis. In fact, osteoclast fuelling with galactose, forcing cells to depend on Oxidative Phosphorylation by reducing the rate of glycolysis, significantly impaired Type I collagen degradation, whereas non-cytotoxic doses of rotenone, an inhibitor of the mitochondrial complex I, enhanced osteoclast activity. Furthermore, we found that the enzymes associated to the glycolytic pathway are localised close to the actin ring of polarised osteoclasts, where energy-demanding activities associated with bone degradation take place. In conclusion, we demonstrate that the energy required for osteoclast differentiation mainly derives from mitochondrial oxidative metabolism, whereas the peripheral cellular activities associated with bone matrix degradation are supported by glycolysis. A better understanding of human osteoclast energy metabolism holds the potential for future therapeutic interventions aimed to target osteoclast activity in different pathological conditions of bone.
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Affiliation(s)
- Silvia Lemma
- Orthopaedic Pathophysiology and Regenerative Medicine Unit, Istituto Ortopedico Rizzoli (IOR), via di Barbiano 1/10, 40136 Bologna, Italy; Department of Biomedical and Neuromotor Sciences, University of Bologna, 40136 Bologna, Italy
| | - Martina Sboarina
- Pole of Pharmacology, Institute of Experimental and Clinical Research (IREC), Université catholique de Louvain (UCL) Medical School, Brussels 1200, Belgium
| | - Paolo E Porporato
- Pole of Pharmacology, Institute of Experimental and Clinical Research (IREC), Université catholique de Louvain (UCL) Medical School, Brussels 1200, Belgium
| | - Nicoletta Zini
- CNR - National Research Council of Italy, Institute of Molecular Genetics, 40136 Bologna, Italy; Laboratory of Musculoskeletal Cell Biology, Istituto Ortopedico Rizzoli (IOR), 40136 Bologna, Italy
| | - Pierre Sonveaux
- Pole of Pharmacology, Institute of Experimental and Clinical Research (IREC), Université catholique de Louvain (UCL) Medical School, Brussels 1200, Belgium
| | - Gemma Di Pompo
- Orthopaedic Pathophysiology and Regenerative Medicine Unit, Istituto Ortopedico Rizzoli (IOR), via di Barbiano 1/10, 40136 Bologna, Italy
| | - Nicola Baldini
- Orthopaedic Pathophysiology and Regenerative Medicine Unit, Istituto Ortopedico Rizzoli (IOR), via di Barbiano 1/10, 40136 Bologna, Italy; Department of Biomedical and Neuromotor Sciences, University of Bologna, 40136 Bologna, Italy
| | - Sofia Avnet
- Orthopaedic Pathophysiology and Regenerative Medicine Unit, Istituto Ortopedico Rizzoli (IOR), via di Barbiano 1/10, 40136 Bologna, Italy.
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Bongio M, Lopa S, Gilardi M, Bersini S, Moretti M. A 3D vascularized bone remodeling model combining osteoblasts and osteoclasts in a CaP nanoparticle-enriched matrix. Nanomedicine (Lond) 2016; 11:1073-91. [PMID: 27078586 DOI: 10.2217/nnm-2015-0021] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
AIM We aimed to establish a 3D vascularized in vitro bone remodeling model. MATERIALS & METHODS Human umbilical endothelial cells (HUVECs), bone marrow mesenchymal stem cells (BMSCs), and osteoblast (OBs) and osteoclast (OCs) precursors were embedded in collagen/fibrin hydrogels enriched with calcium phosphate nanoparticles (CaPn). We assessed vasculogenesis in HUVEC-BMSC coculture, osteogenesis with OBs, osteoclastogenesis with OCs, and, ultimately, cell interplay in tetraculture. RESULTS HUVECs developed a robust microvascular network and BMSCs differentiated into mural cells. Noteworthy, OB and OC differentiation was increased by their reciprocal coculture and by CaPn, and even more by the combination of the tetraculture and CaPn. CONCLUSION We successfully developed a vascularized 3D bone remodeling model, whereby cells interacted and exerted their specific function.
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Affiliation(s)
- Matilde Bongio
- Cell and Tissue Engineering Laboratory, IRCCS Galeazzi Orthopaedic Institute, 20161 Milan, Italy
| | - Silvia Lopa
- Cell and Tissue Engineering Laboratory, IRCCS Galeazzi Orthopaedic Institute, 20161 Milan, Italy
| | - Mara Gilardi
- Cell and Tissue Engineering Laboratory, IRCCS Galeazzi Orthopaedic Institute, 20161 Milan, Italy.,PhD School in Life Sciences, Department of Biotechnology & Biosciences, University of Milano-Bicocca, 20126 Milan, Italy
| | - Simone Bersini
- Cell and Tissue Engineering Laboratory, IRCCS Galeazzi Orthopaedic Institute, 20161 Milan, Italy
| | - Matteo Moretti
- Cell and Tissue Engineering Laboratory, IRCCS Galeazzi Orthopaedic Institute, 20161 Milan, Italy.,Regenerative Medicine Technologies Lab, Ente Ospedaliero Cantonale (EOC), 6900 Lugano, Switzerland.,Swiss Institute of Regenerative Medicine (SIRM), 6900 Lugano, Switzerland.,Fondazione Cardiocentro Ticino, 6900 Lugano, Switzerland
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In vitro model of bone to facilitate measurement of adhesion forces and super-resolution imaging of osteoclasts. Sci Rep 2016; 6:22585. [PMID: 26935172 PMCID: PMC4776281 DOI: 10.1038/srep22585] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Accepted: 02/18/2016] [Indexed: 11/08/2022] Open
Abstract
To elucidate processes in the osteoclastic bone resorption, visualise resorption and related actin reorganisation, a combination of imaging technologies and an applicable in vitro model is needed. Nanosized bone powder from matching species is deposited on any biocompatible surface in order to form a thin, translucent, smooth and elastic representation of injured bone. Osteoclasts cultured on the layer expressed matching morphology to ones cultured on sawed cortical bone slices. Resorption pits were easily identified by reflectance microscopy. The coating allowed actin structures on the bone interface to be visualised with super-resolution microscopy along with a detailed interlinked actin networks and actin branching in conjunction with V-ATPase, dynamin and Arp2/3 at actin patches. Furthermore, we measured the timescale of an adaptive osteoclast adhesion to bone by force spectroscopy experiments on live osteoclasts with bone-coated AFM cantilevers. Utilising the in vitro model and the advanced imaging technologies we localised immunofluorescence signals in respect to bone with high precision and detected resorption at its early stages. Put together, our data supports a cyclic model for resorption in human osteoclasts.
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Merrild DM, Pirapaharan DC, Andreasen CM, Kjærsgaard-Andersen P, Møller AM, Ding M, Delaissé JM, Søe K. Pit- and trench-forming osteoclasts: a distinction that matters. Bone Res 2015; 3:15032. [PMID: 26664853 PMCID: PMC4665108 DOI: 10.1038/boneres.2015.32] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Revised: 10/06/2015] [Accepted: 10/13/2015] [Indexed: 11/09/2022] Open
Abstract
Osteoclasts (OCs) seeded on bone slices either drill round pits or dig long trenches. Whereas pits correspond to intermittent resorption, trenches correspond to continuous and faster resorption and require a distinct assembly of the resorption apparatus. It is unknown whether the distinction between pits and trenches has any biological relevance. Using OCs prepared from different blood donors, we found that female OCs achieved increased resorption mainly through pit formation, whereas male OCs did so through trench formation. Trench formation went along with high collagenolytic activity and high cathepsin K (CatK) expression, thereby allowing deeper demineralization. A specific CatK inhibitor abrogated the generation of trenches, while still allowing the generation of pits. OCs obtained from bone marrow were more prone to generate trenches than those obtained from blood. Scanning electron microscopy of bone surfaces eroded in vivo showed trenches and pits of similar size as those made by OCs in culture. We conclude that the distinction between trench- and pit-forming OCs is relevant to the differences among OCs from different skeletal sites, different individuals, including gender, and results from differences in collagenolytic power. This indicates a biological relevance and highlights the importance of discriminating between pits and trenches when assessing resorption.
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Affiliation(s)
- Ditte Mh Merrild
- Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark , Vejle, Denmark
| | - Dinisha C Pirapaharan
- Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark , Vejle, Denmark
| | - Christina M Andreasen
- Orthopaedic Research Laboratory, Department of Orthopedic Surgery and Traumatology, Odense University Hospital, University of Southern Denmark , Odense C, Denmark
| | | | - Anaïs Mj Møller
- Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark , Vejle, Denmark
| | - Ming Ding
- Orthopaedic Research Laboratory, Department of Orthopedic Surgery and Traumatology, Odense University Hospital, University of Southern Denmark , Odense C, Denmark
| | - Jean-Marie Delaissé
- Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark , Vejle, Denmark
| | - Kent Søe
- Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark , Vejle, Denmark
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Baek JM, Min JY, Kim JY, Yoon KH, Choi MK, Oh J, Lee MS. The inhibitory effects of Citrus unshiu Markovich extracts on the receptor activator of nuclear factor-kappa-B ligand-mediated osteoclast differentiation and function. Food Sci Biotechnol 2015. [DOI: 10.1007/s10068-015-0240-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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41
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Georgess D, Machuca-Gayet I, Blangy A, Jurdic P. Podosome organization drives osteoclast-mediated bone resorption. Cell Adh Migr 2015; 8:191-204. [PMID: 24714644 DOI: 10.4161/cam.27840] [Citation(s) in RCA: 129] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Osteoclasts are the cells responsible for physiological bone resorption. A specific organization of their most prominent cytoskeletal structures, podosomes, is crucial for the degradation of mineralized bone matrix. Each podosome is constituted of an F-actin-enriched central core surrounded by a loose F-actin network, called the podosome cloud. In addition to intrinsic actin dynamics, podosomes are defined by their adhesion to the extracellular matrix, mainly via core-linking CD44 and cloud-linking integrins. These properties allow podosomes to collectively evolve into different patterns implicated in migration and bone resorption. Indeed, to resorb bone, osteoclasts polarize, actively secrete protons, and proteases into the resorption pit where these molecules are confined by a podosome-containing sealing zone. Here, we review recent advancements on podosome structure and regulatory pathways in osteoclasts. We also discuss the distinct functions of different podosome patterns during the lifespan of a single osteoclast.
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Affiliation(s)
- Dan Georgess
- Institut de Génomique Fonctionnelle de Lyon; Université de Lyon; Ecole Normale Supérieure de Lyon; Lyon, France
| | - Irma Machuca-Gayet
- Institut de Génomique Fonctionnelle de Lyon; Université de Lyon; Ecole Normale Supérieure de Lyon; Lyon, France
| | - Anne Blangy
- Centre de Recherche de Biochimie Macromoléculaire; CNRS UMR 5237; Montpellier University; Montpellier, France
| | - Pierre Jurdic
- Institut de Génomique Fonctionnelle de Lyon; Université de Lyon; Ecole Normale Supérieure de Lyon; Lyon, France
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Akisaka T, Yoshida A. Visualization of structural organization of ventral membranes of sheared-open resorbing osteoclasts attached to apatite pellets. Cell Tissue Res 2015; 360:347-62. [PMID: 25582780 DOI: 10.1007/s00441-014-2085-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2014] [Accepted: 10/30/2014] [Indexed: 01/15/2023]
Abstract
Osteoclasts are highly polarized cells from both morphological and functional points of view. Using quick-freeze, rotary-replication methods combined with cell-shearing, we clarified the variability of cytoplasmic surface of the polarized membranes of osteoclasts seeded on apatite. As to the organization of actin filaments and clathrin sheets, we confirmed almost the same ventral membrane specializations of osteoclasts on apatite as seen on glass plates. The organized actin filaments and membrane-associated particles supported the ruffled border membranes. Inside the actin sealing zone, membrane specializations were not always occupied with the ruffled border but also with other types of membranes. Some osteoclasts formed an actin ring but lacked the ruffled border projections. We report a unique and distinctive membrane modification of apatite-attached osteoclasts, i.e., the presence of dense aggregates of membrane-associated particles and related structures not found in the osteoclasts seeded on glass plates. Actin filament polarity in the podosomes was determined by decoration with myosin S1. The actin filament polarity within podosome appears to be oriented predominantly with its barbed ends toward the core, whereas the interconnecting F-actin appears to be mixed oriented. Two different types of clathrin plaques displayed different distributions: clathrin-dependent endocytosis was observed in the ruffled border regions, whereas flat clathrin sheets were found in the leading edge of lamellipodia and near podosomes. The clathrin sheets adhered to the apatite surface tightly on the ventral membranes overlaying the resorption lacunae. All these membrane specializations as mentioned above may indicate the functional variability of osteoclasts seeded on apatite.
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Affiliation(s)
- Toshitaka Akisaka
- Department of Oral Anatomy and Neurobiology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka, 565-0871, Japan,
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Itzstein C, Coxon FP, Rogers MJ. The regulation of osteoclast function and bone resorption by small GTPases. Small GTPases 2014; 2:117-130. [PMID: 21776413 DOI: 10.4161/sgtp.2.3.16453] [Citation(s) in RCA: 106] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2011] [Revised: 04/22/2011] [Accepted: 05/10/2011] [Indexed: 01/11/2023] Open
Abstract
Osteoclasts are multinucleated cells that are responsible for resorption of bone, and increased activity of these cells is associated with several common bone diseases, including postmenopausal osteoporosis. Upon adhesion to bone, osteoclasts become polarized and reorganise their cytoskeleton and membrane to form unique domains including the sealing zone (SZ), which is a dense ring of F-actin-rich podosomes delimiting the ruffled border (RB), where protons and proteases are secreted to demineralise and degrade the bone matrix, respectively. These processes are dependent on the activity of small GTPases. Rho GTPases are well known to control the organization of F-actin and adhesion structures of different cell types, affecting subsequently their migration. In osteoclasts, RhoA, Rac, Cdc42, RhoU and also Arf6 regulate podosome assembly and their organization into the SZ. By contrast, the formation of the RB involves vesicular trafficking pathways that are regulated by the Rab family of GTPases, in particular lysosomal Rab7. Finally, osteoclast survival is dependent on the activity of Ras GTPases. The correct function of almost all these GTPases is absolutely dependent on post-translational prenylation, which enables them to localize to specific target membranes. Bisphosphonate drugs, which are widely used in the treatment of bone diseases such as osteoporosis, act by preventing the prenylation of small GTPases, resulting in the loss of the SZ and RB and therefore inhibition of osteoclast activity, as well as inducing osteoclast apoptosis. In this review we summarize current understanding of the role of specific prenylated small GTPases in osteoclast polarization, function and survival.
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Affiliation(s)
- Cecile Itzstein
- Musculoskeletal Research Programme; Institute of Medical Sciences; University of Aberdeen; Aberdeen, Scotland UK
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44
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Aconitum pseudo-laeve var. erectum inhibits receptor activator of nuclear factor kappa-B ligand-induced osteoclastogenesis via the c-Fos/nuclear factor of activated T-cells, cytoplasmic 1 signaling pathway and prevents lipopolysaccharide-induced bone loss in mice. Molecules 2014; 19:11628-44. [PMID: 25100255 PMCID: PMC6270969 DOI: 10.3390/molecules190811628] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Revised: 07/29/2014] [Accepted: 07/30/2014] [Indexed: 11/16/2022] Open
Abstract
Aconitum pseudo-laeve var. erectum (APE) has been widely shown in herbal medicine to have a therapeutic effect on inflammatory conditions. However, there has been no evidence on whether the extract of APE is involved in the biological bone metabolism process, particularly osteoclast-mediated bone resorption. In this study, we confirmed that the administration of APE could restore normal skeletal conditions in a murine model of lipopolysaccharide (LPS)-induced bone loss via a decrease in the receptor activator of nuclear factor kappa-B ligand (RANKL)/osteoprotegerin (OPG) ratio and osteoclast number. We then investigated the effect of APE on the RANKL-induced formation and function of osteoclasts to elucidate its underlying molecular mechanisms. APE suppressed the formation of tartrate-resistant acid phosphatase (TRAP)-positive cells, as well as the bone-resorbing activity of mature osteoclasts. Furthermore, APE attenuated nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1) and c-Fos without affecting any early signal pathway of osteoclastogenesis. Subsequently, APE significantly downregulated the expression of various genes exclusively expressed in osteoclasts. These results demonstrate that APE restores LPS-induced bone loss through a decrease of the serum RANKL/OPG ratio, and inhibits osteoclast differentiation and function, suggesting the promise of APE as a potential cure for various osteoclast-associated bone diseases.
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Abstract
The adult skeleton undergoes bone remodeling that consists of bone formation by osteoblasts and bone resorption by osteoclasts. When the amount of bone resorbed is greater than the amount of new bone formed, low bone mass results, putting individuals at increased risk for osteoporosis and osteoporotic bone fracture. Nitrogenous bisphosphonates (NBPs) are the most common first line treatment for conditions of low bone mass. NBPs reduce osteoclast bone resorption by impairing the post-translational modification of small GTPases. Small GTPases play crucial roles in the differentiation, function, and survival of osteoclasts. Understanding the roles of individual small GTPases in osteoclast biology may lead to more targeted therapies for the treatment of low bone mass. In this review, we discuss recent investigations into the in vivo effects of individual GTPase deletion in osteoclasts and the molecular roles for small GTPases in osteoclast biology.
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46
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Ochotny N, Voronov I, Owen C, Aubin JE, Manolson MF. The R740S mutation in the V-ATPase a3 subunit results in osteoclast apoptosis and defective early-stage autophagy. J Cell Biochem 2013; 114:2823-33. [DOI: 10.1002/jcb.24630] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Accepted: 07/22/2013] [Indexed: 11/06/2022]
Affiliation(s)
- Noelle Ochotny
- Faculty of Dentistry; Dental Research Institute; University of Toronto; Toronto; Ontario; Canada
| | - Irina Voronov
- Faculty of Dentistry; Dental Research Institute; University of Toronto; Toronto; Ontario; Canada
| | - Celeste Owen
- Centre for Modeling Human Disease; Samuel Lunenfeld Research Institute; Mt. Sinai Hospital; Toronto; Ontario; Canada
| | | | - Morris F. Manolson
- Faculty of Dentistry; Dental Research Institute; University of Toronto; Toronto; Ontario; Canada
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Sakai H, Li G, Hino Y, Moriura Y, Kawawaki J, Sawada M, Kuno M. Increases in intracellular pH facilitate endocytosis and decrease availability of voltage-gated proton channels in osteoclasts and microglia. J Physiol 2013; 591:5851-66. [PMID: 24081153 DOI: 10.1113/jphysiol.2013.263558] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Voltage-gated proton channels (H(+) channels) are highly proton-selective transmembrane pathways. Although the primary determinants for activation are the pH and voltage gradients across the membrane, the current amplitudes fluctuate often when these gradients are constant. The aim of this study was to investigate the role of the intracellular pH (pHi) in regulating the availability of H(+) channels in osteoclasts and microglia. In whole-cell clamp recordings, the pHi was elevated after exposure to NH4Cl and returned to the control level after washout. However, the H(+) channel conductance did not recover fully when the exposure was prolonged (>5 min). Similar results were observed in osteoclasts and microglia, but not in COS7 cells expressing a murine H(+) channel gene (mVSOP). As other electrophysiological properties, like the gating kinetics and voltage dependence for activation, were unchanged, the decreases in the H(+) channel conductance were probably due to the decreases in H(+) channels available at the plasma membrane. The decreases in the H(+) channel conductances were accompanied by reductions in the cell capacitance. Exposure to NH4Cl increased the uptake of the endocytosis marker FM1-43, substantiating the idea that pHi increases facilitated endocytosis. In osteoclasts, whose plasma membrane expresses V-ATPases and H(+) channels, pHi increases by these H(+)-transferring molecules in part facilitated endocytosis. The endocytosis and decreases in the H(+) channel conductance were reduced by dynasore, a dynamin blocker. These results suggest that pHi increases in osteoclasts and microglia decrease the numbers of H(+) channels available at the plasma membrane through facilitation of dynamin-dependent endocytosis.
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Affiliation(s)
- Hiromu Sakai
- M. Kuno: Department of Physiology, Osaka City University Graduate School of Medicine, 1-4-3 Asahimachi, Abeno-ku, Osaka 545-8585, Japan.
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Søe K, Merrild DMH, Delaissé JM. Steering the osteoclast through the demineralization-collagenolysis balance. Bone 2013; 56:191-8. [PMID: 23777960 DOI: 10.1016/j.bone.2013.06.007] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/21/2013] [Revised: 06/05/2013] [Accepted: 06/08/2013] [Indexed: 11/17/2022]
Abstract
There is a lot of interest for how and how much osteoclasts resorb bone. However, little is known about the mechanism which controls the orientation and the duration of a resorptive event, thereby determining the specific geometry of a cavitation. Here we show that the relative rate of collagenolysis vs. demineralization plays a critical role in this process. First we observed that when culturing osteoclasts on bone slices, excavations appeared either as round pits containing demineralized collagen, or as elongated trenches without demineralized collagen. This suggests that round pits are generated when collagen degradation is slower than demineralization, and trenches when collagen degradation is as fast as demineralization. Next we treated the osteoclasts with a low dose of a carbonic anhydrase inhibitor to slightly decrease the rate of demineralization, thereby allowing collagen degradation to proceed as fast as demineralization. This resulted in about a two-fold increase of the proportion of trenches, thus supporting our hypothesis. The same result was obtained if facilitating collagen degradation by pre-treating the bone slices with NaOCl. In contrast, when decreasing the rate of collagenolysis vs. demineralization by the addition of a cathepsin K specific inhibitor, the proportion of trenches fell close to 0%, and furthermore the round pits became almost half as deep. These observations lead to a model where the osteoclast resorption route starts perpendicularly to the bone surface, forming a pit, and continues parallel to the bone surface, forming a trench. Importantly, we show that the progress of the osteoclast along this route depends on the balance between the rate of collagenolysis and demineralization. We propose that the osteocytes and bone lining cells surrounding the osteoclast may act on this balance to steer the osteoclast resorptive activity in order to give the excavations a specific shape.
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Affiliation(s)
- Kent Søe
- Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark, Kabbeltoft 25, 7100 Vejle, Denmark.
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Matsumoto T, Nagase Y, Hirose J, Tokuyama N, Yasui T, Kadono Y, Ueki K, Kadowaki T, Nakamura K, Tanaka S. Regulation of bone resorption and sealing zone formation in osteoclasts occurs through protein kinase B-mediated microtubule stabilization. J Bone Miner Res 2013; 28:1191-202. [PMID: 23239117 DOI: 10.1002/jbmr.1844] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Revised: 11/09/2012] [Accepted: 11/29/2012] [Indexed: 01/16/2023]
Abstract
We investigated the role of protein kinase B (Akt), a downstream effector of phosphatidylinositol 3-kinase, in bone-resorbing activity of mature osteoclasts. Treatment with a specific Akt inhibitor disrupted sealing zone formation and decreased the bone-resorbing activity of osteoclasts. The normal microtubule structures were lost and the Akt inhibitor reduced the amount of acetylated tubulin, which reflects stabilized microtubules, whereas forced Akt activation by adenovirus vectors resulted in the opposite effect. Forced Akt activation increased the binding of the microtubule-associated protein adenomatous polyposis coli (APC), the APC-binding protein end-binding protein 1 (EB1) and dynactin, a dynein activator complex, with microtubules. Depletion of Akt1 and Akt2 resulted in a disconnection of APC/EB1 and a decrease in bone-resorbing activity along with reduced sealing zone formation, both of which were recovered upon the addition of LiCl, a glycogen synthase kinase-3β (GSK-3β) inhibitor. The Akt1 and Akt2 double-knockout mice exhibited osteosclerosis due to reduced bone resorption. These findings indicate that Akt controls the bone-resorbing activity of osteoclasts by stabilizing microtubules via a regulation of the binding of microtubule associated proteins.
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Affiliation(s)
- Takumi Matsumoto
- Department of Orthopaedic Surgery, Faculty of Medicine, The University of Tokyo, Tokyo, Japan
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50
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Szewczyk KA, Fuller K, Chambers TJ. Distinctive subdomains in the resorbing surface of osteoclasts. PLoS One 2013; 8:e60285. [PMID: 23555944 PMCID: PMC3605329 DOI: 10.1371/journal.pone.0060285] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2012] [Accepted: 02/25/2013] [Indexed: 11/19/2022] Open
Abstract
We employed a novel technique to inspect the substrate-apposed surface of activated osteoclasts, the cells that resorb bone, in the scanning electron microscope. The surface revealed unexpected complexity. At the periphery of the cells were circles and crescents of individual or confluent nodules. These corresponded to the podosomes and actin rings that form a 'sealing zone', encircling the resorptive hemivacuole into which protons and enzymes are secreted. Inside these rings and crescents the osteoclast surface was covered with strips and patches of membrane folds, which were flattened against the substrate surface and surrounded by fold-free membrane in which many orifices could be seen. Corresponding regions of folded and fold-free membrane were found by transmission electron microscopy in osteoclasts incubated on bone. We correlated these patterns with the distribution of several proteins crucial to resorption. The strips and patches of membrane folds corresponded in distribution to vacuolar H+-ATPase, and frequently co-localized with F-actin. Cathepsin K localized to F-actin-free foci towards the center of cells with circular actin rings, and at the retreating pole of cells with actin crescents. The chloride/proton antiporter ClC-7 formed a sharply-defined band immediately inside the actin ring, peripheral to vacuolar H+-ATPase. The sealing zone of osteoclasts is permeable to molecules with molecular mass up to 10,000. Therefore, ClC-7 might be distributed at the periphery of the resorptive hemivacuole in order to prevent protons from escaping laterally from the hemivacuole into the sealing zone, where they would dissolve the bone mineral. Since the activation of resorption is attributable to recognition of the αVβ3 ligands bound to bone mineral, such leakage would, by dissolving bone mineral, release the ligands and so terminate resorption. Therefore, ClC-7 might serve not only to provide the counter-ions that enable proton pumping, but also to facilitate resorption by acting as a 'functional sealing zone'.
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Affiliation(s)
- Kinga A. Szewczyk
- Division of Basic Medical Sciences, St George's, University of London, Cranmer Terrace, Tooting, London, United Kingdom
| | - Karen Fuller
- Division of Basic Medical Sciences, St George's, University of London, Cranmer Terrace, Tooting, London, United Kingdom
| | - Tim J. Chambers
- Division of Basic Medical Sciences, St George's, University of London, Cranmer Terrace, Tooting, London, United Kingdom
- * E-mail:
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