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Kuroda Y, Yoda M, Kawaai K, Tatenuma M, Mizoguchi T, Ito S, Kasahara M, Wu Y, Takano H, Momose A, Matsuo K. Developing long bones respond to surrounding tissues by trans-pairing of periosteal osteoclasts and endocortical osteoblasts. Development 2024; 151:dev202194. [PMID: 39119717 PMCID: PMC11423808 DOI: 10.1242/dev.202194] [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: 07/18/2023] [Accepted: 08/01/2024] [Indexed: 08/10/2024]
Abstract
Developing long bones alter their shape while maintaining uniform cortical thickness via coordinated activity of bone-forming osteoblasts and bone-resorbing osteoclasts at periosteal and endosteal surfaces, a process we designate trans-pairing. Two types of trans-pairing shift cortical bone in opposite orientations: peri-forming trans-pairing (peri-t-p) increases bone marrow space and endo-forming trans-pairing (endo-t-p) decreases it, via paired activity of bone resorption and formation across the cortex. Here, we focused on endo-t-p in growing bones. Analysis of endo-t-p activity in the cortex of mouse fibulae revealed osteoclasts under the periosteum compressed by muscles, and expression of RANKL in periosteal cells of the cambium layer. Furthermore, mature osteoblasts were localized on the endosteum, while preosteoblasts were at the periosteum and within cortical canals. X-ray tomographic microscopy revealed the presence of cortical canals more closely associated with endo- than with peri-t-p. Sciatic nerve transection followed by muscle atrophy and unloading induced circumferential endo-t-p with concomitant spread of cortical canals. Such canals likely supply the endosteum with preosteoblasts from the periosteum under endo-t-p, allowing bone shape to change in response to mechanical stress or nerve injury.
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Affiliation(s)
- Yukiko Kuroda
- Laboratory of Cell and Tissue Biology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan
| | - Masaki Yoda
- Laboratory of Cell and Tissue Biology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan
| | - Katsuhiro Kawaai
- Laboratory of Cell and Tissue Biology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan
| | - Motoharu Tatenuma
- Laboratory of Cell and Tissue Biology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan
| | | | - Shinichirou Ito
- Department of Pharmacology, Tokyo Dental College, Tokyo 101-0061, Japan
| | - Masataka Kasahara
- Department of Pharmacology, Tokyo Dental College, Tokyo 101-0061, Japan
| | - Yanlin Wu
- Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Katahira 2-1-1, Aoba, Sendai Miyagi 980-8577, Japan
| | - Hidekazu Takano
- Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Katahira 2-1-1, Aoba, Sendai Miyagi 980-8577, Japan
| | - Atsushi Momose
- Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Katahira 2-1-1, Aoba, Sendai Miyagi 980-8577, Japan
- JASRI/SPring-8, 1-1-1 Kouto, Sayo-cho, Hyogo 679-5198, Japan
| | - Koichi Matsuo
- Laboratory of Cell and Tissue Biology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan
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2
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Mitchell C, Emami K, Emami A, Hosseinzadeh S, Shore B, Novais EN, Kiapour AM. Effects of joint loading on the development of capital femoral epiphysis morphology. Arch Orthop Trauma Surg 2023; 143:5457-5466. [PMID: 36856839 DOI: 10.1007/s00402-023-04795-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Accepted: 01/22/2023] [Indexed: 03/02/2023]
Abstract
INTRODUCTION The deleterious influence of increased mechanical forces on capital femoral epiphysis development is well established; however, the growth of the physis in the absence of such forces remains unclear. The hips of non-ambulatory cerebral palsy (CP) patients provide a weight-restricted (partial weightbearing) model which can elucidate the influence of decreased mechanical forces on the development of physis morphology, including features related to development of slipped capital femoral epiphysis (SCFE). Here we used 3D image analysis to compare the physis morphology of children with non-ambulatory CP, as a model for abnormal hip loading, with age-matched native hips. MATERIALS AND METHODS CT images of 98 non-ambulatory CP hips (8-15 years) and 80 age-matched native control hips were used to measure height, width, and length of the tubercle, depth, width, and length of the metaphyseal fossa, and cupping height across different epiphyseal regions. The impact of age on morphology was assessed using Pearson correlations. Mixed linear model was used to compare the quantified morphological features between partial weightbearing hips and full weightbearing controls. RESULTS In partial weightbearing hips, tubercle height and length along with fossa depth and length significantly decreased with age, while peripheral cupping height increased with age (r > 0.2, P < 0.04). Compared to normally loaded (full weightbearing) hips and across all age groups, partially weightbearing hips' epiphyseal tubercle height and length were smaller (P < .05), metaphyseal fossa depth was larger (P < .01), and posterior, inferior, and anterior peripheral cupping heights were smaller (P < .01). CONCLUSIONS Smaller epiphyseal tubercle and peripheral cupping with greater metaphyseal fossa size in partial weightbearing hips suggests that the growing capital femoral epiphysis requires mechanical stimulus to adequately develop epiphyseal stabilizers. Deposit low prevalence and relevance of SCFE in CP, these findings highlight both the role of normal joint loading in proper physis development and how chronic abnormal loading may contribute to various pathomorphological changes of the proximal femur (i.e., capital femoral epiphysis).
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Affiliation(s)
- Charles Mitchell
- Department of Orthopaedic Surgery, Boston Children's Hospital, Harvard Medical School, 300 Longwood Ave, Boston, MA, 02115, USA
| | - Koroush Emami
- Department of Orthopaedic Surgery, Boston Children's Hospital, Harvard Medical School, 300 Longwood Ave, Boston, MA, 02115, USA
| | - Alex Emami
- Department of Orthopaedic Surgery, Boston Children's Hospital, Harvard Medical School, 300 Longwood Ave, Boston, MA, 02115, USA
| | - Shayan Hosseinzadeh
- Department of Orthopaedic Surgery, Boston Children's Hospital, Harvard Medical School, 300 Longwood Ave, Boston, MA, 02115, USA
| | - Benjamin Shore
- Department of Orthopaedic Surgery, Boston Children's Hospital, Harvard Medical School, 300 Longwood Ave, Boston, MA, 02115, USA
| | - Eduardo N Novais
- Department of Orthopaedic Surgery, Boston Children's Hospital, Harvard Medical School, 300 Longwood Ave, Boston, MA, 02115, USA
| | - Ata M Kiapour
- Department of Orthopaedic Surgery, Boston Children's Hospital, Harvard Medical School, 300 Longwood Ave, Boston, MA, 02115, USA.
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3
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Kablar B. Skeletal Muscle's Role in Prenatal Inter-organ Communication: A Phenogenomic Study with Qualitative Citation Analysis. ADVANCES IN ANATOMY, EMBRYOLOGY, AND CELL BIOLOGY 2023; 236:1-19. [PMID: 37955769 DOI: 10.1007/978-3-031-38215-4_1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/14/2023]
Abstract
Gene targeting in mice allows for a complete elimination of skeletal (striated or voluntary) musculature in the body, from the beginning of its development, resulting in our ability to study the consequences of this ablation on other organs. Here I focus on the relationship between the muscle and lung, motor neurons, skeleton, and special senses. Since the inception of my independent laboratory, in 2000, with my team, we published more than 30 papers (and a book chapter), nearly 400 pages of data, on these specific relationships. Here I trace, using Web of Science, nearly 600 citations of this work, to understand its impact. The current report contains a summary of our work and its impact, NCBI's Gene Expression Omnibus accession numbers of all our microarray data, and three clear future directions doable by anyone using our publicly available data. Together, this effort furthers our understanding of inter-organ communication during prenatal development.
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Affiliation(s)
- Boris Kablar
- Department of Medical Neuroscience, Anatomy and Pathology, Faculty of Medicine, Dalhousie University, Halifax, NS, Canada.
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4
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Murphy P, Rolfe RA. Building a Co-ordinated Musculoskeletal System: The Plasticity of the Developing Skeleton in Response to Muscle Contractions. ADVANCES IN ANATOMY, EMBRYOLOGY, AND CELL BIOLOGY 2023; 236:81-110. [PMID: 37955772 DOI: 10.1007/978-3-031-38215-4_4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/14/2023]
Abstract
The skeletal musculature and the cartilage, bone and other connective tissues of the skeleton are intimately co-ordinated. The shape, size and structure of each bone in the body is sculpted through dynamic physical stimuli generated by muscle contraction, from early development, with onset of the first embryo movements, and through repair and remodelling in later life. The importance of muscle movement during development is shown by congenital abnormalities where infants that experience reduced movement in the uterus present a sequence of skeletal issues including temporary brittle bones and joint dysplasia. A variety of animal models, utilising different immobilisation scenarios, have demonstrated the precise timing and events that are dependent on mechanical stimulation from movement. This chapter lays out the evidence for skeletal system dependence on muscle movement, gleaned largely from mouse and chick immobilised embryos, showing the many aspects of skeletal development affected. Effects are seen in joint development, ossification, the size and shape of skeletal rudiments and tendons, including compromised mechanical function. The enormous plasticity of the skeletal system in response to muscle contraction is a key factor in building a responsive, functional system. Insights from this work have implications for our understanding of morphological evolution, particularly the challenging concept of emergence of new structures. It is also providing insight for the potential of physical therapy for infants suffering the effects of reduced uterine movement and is enhancing our understanding of the cellular and molecular mechanisms involved in skeletal tissue differentiation, with potential for informing regenerative therapies.
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Affiliation(s)
- Paula Murphy
- School of Natural Sciences, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland.
| | - Rebecca A Rolfe
- School of Natural Sciences, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
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5
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Liu C, Zhou N, Li N, Xu T, Chen X, Zhou H, Xie A, Liu H, Zhu L, Wang S, Xiao J. Disrupted tenogenesis in masseter as a potential cause of micrognathia. Int J Oral Sci 2022; 14:50. [PMID: 36257937 PMCID: PMC9579150 DOI: 10.1038/s41368-022-00196-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Revised: 08/01/2022] [Accepted: 08/04/2022] [Indexed: 11/09/2022] Open
Abstract
Micrognathia is a severe craniofacial deformity affecting appearance and survival. Previous studies revealed that multiple factors involved in the osteogenesis of mandibular bone have contributed to micrognathia, but concerned little on factors other than osteogenesis. In the current study, we found that ectopic activation of Fgf8 by Osr2-cre in the presumptive mesenchyme for masseter tendon in mice led to micrognathia, masseter regression, and the disrupted patterning and differentiation of masseter tendon. Since Myf5-cre;Rosa26R-Fgf8 mice exhibited the normal masseter and mandibular bone, the possibility that the micrognathia and masseter regression resulted directly from the over-expressed Fgf8 was excluded. Further investigation disclosed that a series of chondrogenic markers were ectopically activated in the developing Osr2-cre;Rosa26R-Fgf8 masseter tendon, while the mechanical sensing in the masseter and mandibular bone was obviously reduced. Thus, it suggested that the micrognathia in Osr2-cre;Rosa26R-Fgf8 mice resulted secondarily from the reduced mechanical force transmitted to mandibular bone. Consistently, when tenogenic or myogenic components were deleted from the developing mandibles, both the micrognathia and masseter degeneration took place with the decreased mechanical sensing in mandibular bone, which verified that the loss of mechanical force transmitted by masseter tendon could result in micrognathia. Furthermore, it appeared that the micrognathia resulting from the disrupted tenogenesis was attributed to the impaired osteogenic specification, instead of the differentiation in the periosteal progenitors. Our findings disclose a novel mechanism for mandibular morphogenesis, and shed light on the prevention and treatment for micrognathia.
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Affiliation(s)
- Chao Liu
- Department of Oral Pathology, Dalian Medical University School of Stomatology, Dalian, China.,Academician Laboratory of Immunology and Oral Development & Regeneration, Dalian Medical University, Dalian, China
| | - Nan Zhou
- Department of Oral Pathology, Dalian Medical University School of Stomatology, Dalian, China
| | - Nan Li
- Department of Oral Pathology, Dalian Medical University School of Stomatology, Dalian, China.,Academician Laboratory of Immunology and Oral Development & Regeneration, Dalian Medical University, Dalian, China
| | - Tian Xu
- Department of Oral Pathology, Dalian Medical University School of Stomatology, Dalian, China
| | - Xiaoyan Chen
- Department of Oral Pathology, Dalian Medical University School of Stomatology, Dalian, China
| | - Hailing Zhou
- Department of Oral Pathology, Dalian Medical University School of Stomatology, Dalian, China
| | - Ailun Xie
- Department of Oral Pathology, Dalian Medical University School of Stomatology, Dalian, China
| | - Han Liu
- Department of Oral Pathology, Dalian Medical University School of Stomatology, Dalian, China.,Academician Laboratory of Immunology and Oral Development & Regeneration, Dalian Medical University, Dalian, China
| | - Lei Zhu
- Department of Oral Pathology, Dalian Medical University School of Stomatology, Dalian, China.,Academician Laboratory of Immunology and Oral Development & Regeneration, Dalian Medical University, Dalian, China
| | - Songlin Wang
- Academician Laboratory of Immunology and Oral Development & Regeneration, Dalian Medical University, Dalian, China. .,Beijing Laboratory of Oral Health, Capital Medical University, Beijing, China.
| | - Jing Xiao
- Department of Oral Pathology, Dalian Medical University School of Stomatology, Dalian, China. .,Academician Laboratory of Immunology and Oral Development & Regeneration, Dalian Medical University, Dalian, China.
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6
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Hypothesis: Hypermobile Ehlers Danlos Syndrome Is a A Determinant of Fetal and Young Infant Bone Strength. Med Hypotheses 2022. [DOI: 10.1016/j.mehy.2022.110859] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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7
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Pierantoni M, Le Cann S, Sotiriou V, Ahmed S, Bodey AJ, Jerjen I, Nowlan NC, Isaksson H. Muscular loading affects the 3D structure of both the mineralized rudiment and growth plate at early stages of bone formation. Bone 2021; 145:115849. [PMID: 33454374 DOI: 10.1016/j.bone.2021.115849] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Revised: 01/13/2021] [Accepted: 01/13/2021] [Indexed: 11/25/2022]
Abstract
Fetal immobilization affects skeletal development and can lead to severe malformations. Still, how mechanical load affects embryonic bone formation is not fully elucidated. This study combines mechanobiology, image analysis and developmental biology, to investigate the structural effects of muscular loading on embryonic long bones. We present a novel approach involving a semi-automatic workflow, to study the spatial and temporal evolutions of both hard and soft tissues in 3D without any contrast agent at micrometrical resolution. Using high-resolution phase-contrast-enhanced X-ray synchrotron microtomography, we compare the humeri of Splotch-delayed embryonic mice lacking skeletal muscles with healthy littermates. The effects of skeletal muscles on bone formation was studied from the first stages of mineral deposition (Theiler Stages 23 and 24) to just before birth (Theiler Stage 27). The results show that muscle activity affects both growth plate and mineralized regions, especially during early embryonic development. When skeletal muscles were absent, there was reduced mineralization, altered tuberosity size and location, and, at early embryonic stages, decreased chondrocyte density, size and elongation compared to littermate controls. The proposed workflow enhances our understanding of mechanobiology of early bone formation and could be implemented for the study of other complex biological tissues.
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Affiliation(s)
- Maria Pierantoni
- Department of Biomedical Engineering, Lund University, Box 118, 221 00 Lund, Sweden.
| | - Sophie Le Cann
- Department of Biomedical Engineering, Lund University, Box 118, 221 00 Lund, Sweden
| | - Vivien Sotiriou
- Department of Bioengineering, Imperial College London, London SW7 2AZ, UK
| | - Saima Ahmed
- Department of Bioengineering, Imperial College London, London SW7 2AZ, UK
| | | | - Iwan Jerjen
- Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland
| | - Niamh C Nowlan
- Department of Bioengineering, Imperial College London, London SW7 2AZ, UK
| | - Hanna Isaksson
- Department of Biomedical Engineering, Lund University, Box 118, 221 00 Lund, Sweden
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8
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Pacharne S, Livesey M, Kadmiel M, Wang N, Caron KM, Richards GO, Skerry TM. Accelerated Development With Increased Bone Mass and Skeletal Response to Loading Suggest Receptor Activity Modifying Protein-3 as a Bone Anabolic Target. Front Endocrinol (Lausanne) 2021; 12:807882. [PMID: 35095771 PMCID: PMC8790142 DOI: 10.3389/fendo.2021.807882] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Accepted: 12/01/2021] [Indexed: 11/13/2022] Open
Abstract
Knockout technologies provide insights into physiological roles of genes. Studies initiated into endocrinology of heteromeric G protein-coupled receptors included deletion of receptor activity modifying protein-3, an accessory protein that alters ligand selectivity of calcitonin and calcitonin-like receptors. Initially, deletion of Ramp3-/- appeared phenotypically silent, but it has emerged that mice have a high bone mass phenotype, and more subtle alterations to angiogenesis, amylin homeostasis, and a small proportion of the effects of adrenomedullin on cardiovascular and lymphatic systems. Here we explore in detail, effects of Ramp3-/- deletion on skeletal growth/development, bone mass and response of bone to mechanical loading mimicking exercise. Mouse pups lacking RAMP3 are healthy and viable, having accelerated development of the skeleton as assessed by degree of mineralisation of specific bones, and by microCT measurements. Specifically, we observed that neonates and young mice have increased bone volume and mineralisation in hindlimbs and vertebrae and increased thickness of bone trabeculae. These changes are associated with increased osteoblast numbers and bone apposition rate in Ramp3-/- mice, and increased cell proliferation in epiphyseal growth plates. Effects persist for some weeks after birth, but differences in gross bone mass between RAMP3 and WT mice lose significance in older animals although architectural differences persist. Responses of bones of 17-week old mice to mechanical loading that mimics effects of vigorous exercise is increased significantly in Ramp3-/- mice by 30% compared with WT control mice. Studies on cultured osteoblasts from Ramp3-/- mice indicate interactions between mRNA expression of RAMPs1 and 3, but not RAMP2 and 3. Our preliminary data shows that Ramp3-/- osteoblasts had increased expression β-catenin, a component of the canonical Wnt signalling pathway known to regulate skeletal homeostasis and mechanosensitivity. Given interactions of RAMPs with both calcitonin and calcitonin-like receptors to alter ligand selectivity, and with other GPCRs to change trafficking or ligand bias, it is not clear whether the bone phenotype of Ramp3-/- mice is due to alterations in signalling mediated by one or more GPCRS. However, as antagonists of RAMP-interacting receptors are growing in availability, there appears the likelihood that manipulation of the RAMP3 signalling system could provide anabolic effects therapeutically.
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Affiliation(s)
- Suruchi Pacharne
- Department of Oncology and Metabolism, School of Medicine, University of Sheffield, Sheffield, United Kingdom
| | - Matthew Livesey
- Department of Oncology and Metabolism, School of Medicine, University of Sheffield, Sheffield, United Kingdom
| | - Mahita Kadmiel
- Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
| | - Ning Wang
- Department of Oncology and Metabolism, School of Medicine, University of Sheffield, Sheffield, United Kingdom
| | - Kathleen M. Caron
- Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
| | - Gareth O. Richards
- Department of Oncology and Metabolism, School of Medicine, University of Sheffield, Sheffield, United Kingdom
| | - Tim M. Skerry
- Department of Oncology and Metabolism, School of Medicine, University of Sheffield, Sheffield, United Kingdom
- *Correspondence: Tim M. Skerry,
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9
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Yamamoto M, Takada H, Ishizuka S, Kitamura K, Jeong J, Sato M, Hinata N, Abe S. Morphological association between the muscles and bones in the craniofacial region. PLoS One 2020; 15:e0227301. [PMID: 31923241 PMCID: PMC6953862 DOI: 10.1371/journal.pone.0227301] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2019] [Accepted: 12/16/2019] [Indexed: 01/02/2023] Open
Abstract
The strains of inbred laboratory mice are isogenic and homogeneous for over 98.6% of their genomes. However, geometric morphometric studies have demonstrated clear differences among the skull shapes of various mice strains. The question now arises: why are skull shapes different among the mice strains? Epigenetic processes, such as morphological interaction between the muscles and bones, may cause differences in the skull shapes among various mice strains. To test these predictions, the objective of this study is to examine the morphological association between a specific part of the skull and its adjacent muscle. We examined C57BL6J, BALB/cA, and ICR mice on embryonic days (E) 12.5 and 16.5 as well as on postnatal days (P) 0, 10, and 90. As a result, we found morphological differences between C57BL6J and BALB/cA mice with respect to the inferior spine of the hypophyseal cartilage or basisphenoid (SP) and the tensor veli palatini muscle (TVP) during the prenatal and postnatal periods. There was a morphological correlation between the SP and the TVP in the C57BL6J, BALB/cA, and ICR mice during E15 and P0. However, there were not correlation between the TVP and the SP during P10. After discectomy, bone deformation was associated with a change in the shape of the adjacent muscle. Therefore, epigenetic modifications linked to the interaction between the muscles and bones might occur easily during the prenatal period, and inflammation seems to allow epigenetic modifications between the two to occur.
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Affiliation(s)
- Masahito Yamamoto
- Department of Anatomy, Tokyo Dental College, Tokyo, Japan
- Tokyo Dental College Research Branding Project, Tokyo Dental College, Tokyo, Japan
| | | | - Satoshi Ishizuka
- Department of Anatomy, Tokyo Dental College, Tokyo, Japan
- Tokyo Dental College Research Branding Project, Tokyo Dental College, Tokyo, Japan
| | - Kei Kitamura
- Tokyo Dental College Research Branding Project, Tokyo Dental College, Tokyo, Japan
- Department of Histology and Developmental Biology, Tokyo Dental College, Tokyo, Japan
| | - Juhee Jeong
- Department of Basic Science and Craniofacial Biology, New York University College of Dentistry, New York, NY, United States of America
| | - Masaki Sato
- Tokyo Dental College Research Branding Project, Tokyo Dental College, Tokyo, Japan
- Laboratory of Biology, Tokyo Dental College, Tokyo, Japan
| | - Nobuyuki Hinata
- Department of Urology, Kobe University Graduate School of Medicine, Hyogo, Japan
| | - Shinichi Abe
- Department of Anatomy, Tokyo Dental College, Tokyo, Japan
- Tokyo Dental College Research Branding Project, Tokyo Dental College, Tokyo, Japan
- * E-mail:
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10
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Wang N, Niger C, Li N, Richards GO, Skerry TM. Cross-Species RNA-Seq Study Comparing Transcriptomes of Enriched Osteocyte Populations in the Tibia and Skull. Front Endocrinol (Lausanne) 2020; 11:581002. [PMID: 33071985 PMCID: PMC7543096 DOI: 10.3389/fendo.2020.581002] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Accepted: 08/21/2020] [Indexed: 12/17/2022] Open
Abstract
Local site-specific differences between bones in different regions of the skeleton account for their different properties and functions. To identify mechanisms behind these differences, we have performed a cross-species study comparing RNA transcriptomes of cranial and tibial osteocytes, from bones with very different primary functions and physiological responses, collected from the same individual mouse, rat, and rhesus macaque. Bioinformatic analysis was performed to identify 32 genes changed in the same direction between sites and shared across all three species. Several well-established key genes in bone growth and remodeling were upregulated in the tibias of all three species (BMP7, DKK1, FGF1, FRZB, SOST). Many of them associate or crosstalk with the Wnt signaling pathway. These results suggest Wnt signaling-related candidates for different control of regulatory mechanisms in bone homeostasis in the skull and tibia and indicate a different balance between genetically determined structure and feedback mechanisms to strains induced by mechanical loading at the different sites.
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Affiliation(s)
- Ning Wang
- Department of Oncology and Metabolism, Mellanby Centre for Bone Research, University of Sheffield, Sheffield, United Kingdom
| | - Corinne Niger
- Department of Oncology and Metabolism, Mellanby Centre for Bone Research, University of Sheffield, Sheffield, United Kingdom
| | - Nan Li
- Department of Neuroscience, Sheffield Institute for Translational Neuroscience (SITraN), University of Sheffield, Sheffield, United Kingdom
| | - Gareth O. Richards
- Department of Oncology and Metabolism, Mellanby Centre for Bone Research, University of Sheffield, Sheffield, United Kingdom
| | - Tim M. Skerry
- Department of Oncology and Metabolism, Mellanby Centre for Bone Research, University of Sheffield, Sheffield, United Kingdom
- *Correspondence: Tim M. Skerry
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11
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Abstract
Bone and skeletal muscle are integrated organs and their coupling has been considered mainly a mechanical one in which bone serves as attachment site to muscle while muscle applies load to bone and regulates bone metabolism. However, skeletal muscle can affect bone homeostasis also in a non-mechanical fashion, i.e., through its endocrine activity. Being recognized as an endocrine organ itself, skeletal muscle secretes a panel of cytokines and proteins named myokines, synthesized and secreted by myocytes in response to muscle contraction. Myokines exert an autocrine function in regulating muscle metabolism as well as a paracrine/endocrine regulatory function on distant organs and tissues, such as bone, adipose tissue, brain and liver. Physical activity is the primary physiological stimulus for bone anabolism (and/or catabolism) through the production and secretion of myokines, such as IL-6, irisin, IGF-1, FGF2, beside the direct effect of loading. Importantly, exercise-induced myokine can exert an anti-inflammatory action that is able to counteract not only acute inflammation due to an infection, but also a condition of chronic low-grade inflammation raised as consequence of physical inactivity, aging or metabolic disorders (i.e., obesity, type 2 diabetes mellitus). In this review article, we will discuss the effects that some of the most studied exercise-induced myokines exert on bone formation and bone resorption, as well as a brief overview of the anti-inflammatory effects of myokines during the onset pathological conditions characterized by the development a systemic low-grade inflammation, such as sarcopenia, obesity and aging.
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Affiliation(s)
- Marta Gomarasca
- IRCCS Istituto Ortopedico Galeazzi, Laboratory of Experimental Biochemistry & Molecular Biology, Milan, Italy
| | - Giuseppe Banfi
- IRCCS Istituto Ortopedico Galeazzi, Laboratory of Experimental Biochemistry & Molecular Biology, Milan, Italy; Vita-Salute San Raffaele University, Milan, Italy
| | - Giovanni Lombardi
- IRCCS Istituto Ortopedico Galeazzi, Laboratory of Experimental Biochemistry & Molecular Biology, Milan, Italy; Gdańsk University of Physical Education & Sport, Gdańsk, Pomorskie, Poland.
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12
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Tsutsumi R, Tran MP, Cooper KL. Changing While Staying the Same: Preservation of Structural Continuity During Limb Evolution by Developmental Integration. Integr Comp Biol 2018; 57:1269-1280. [PMID: 28992070 DOI: 10.1093/icb/icx092] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
More than 150 years since Charles Darwin published "On the Origin of Species", gradual evolution by natural selection is still not fully reconciled with the apparent sudden appearance of complex structures, such as the bat wing, with highly derived functions. This is in part because developmental genetics has not yet identified the number and types of mutations that accumulated to drive complex morphological evolution. Here, we consider the experimental manipulations in laboratory model systems that suggest tissue interdependence and mechanical responsiveness during limb development conceptually reduce the genetic complexity required to reshape the structure as a whole. It is an exciting time in the field of evolutionary developmental biology as emerging technical approaches in a variety of non-traditional laboratory species are on the verge of filling the gaps between theory and evidence to resolve this sesquicentennial debate.
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Affiliation(s)
- Rio Tsutsumi
- Division of Biological Sciences, University of California San Diego, La Jolla, CA 92093-0380, USA
| | - Mai P Tran
- Division of Biological Sciences, University of California San Diego, La Jolla, CA 92093-0380, USA
| | - Kimberly L Cooper
- Division of Biological Sciences, University of California San Diego, La Jolla, CA 92093-0380, USA
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13
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Kullmann FA, Chang HH, Gauthier C, McDonnell BM, Yeh JC, Clayton DR, Kanai AJ, de Groat WC, Apodaca GL, Birder LA. Serotonergic paraneurones in the female mouse urethral epithelium and their potential role in peripheral sensory information processing. Acta Physiol (Oxf) 2018; 222:10.1111/apha.12919. [PMID: 28719042 PMCID: PMC5963688 DOI: 10.1111/apha.12919] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Revised: 06/19/2017] [Accepted: 07/13/2017] [Indexed: 01/01/2023]
Abstract
AIM The mechanisms underlying detection and transmission of sensory signals arising from visceral organs, such as the urethra, are poorly understood. Recently, specialized ACh-expressing cells embedded in the urethral epithelium have been proposed as chemosensory sentinels for detection of bacterial infection. Here, we examined the morphology and potential role in sensory signalling of a different class of specialized cells that express serotonin (5-HT), termed paraneurones. METHODS Urethrae, dorsal root ganglia neurones and spinal cords were isolated from adult female mice and used for immunohistochemistry and calcium imaging. Visceromotor reflexes (VMRs) were recorded in vivo. RESULTS We identified two morphologically distinct groups of 5-HT+ cells with distinct regional locations: bipolar-like cells predominant in the mid-urethra and multipolar-like cells predominant in the proximal and distal urethra. Sensory nerve fibres positive for calcitonin gene-related peptide, substance P, and TRPV1 were found in close proximity to 5-HT+ paraneurones. In vitro 5-HT (1 μm) stimulation of urethral primary afferent neurones, mimicking 5-HT release from paraneurones, elicited changes in the intracellular calcium concentration ([Ca2+ ]i ) mediated by 5-HT2 and 5-HT3 receptors. Approximately 50% of 5-HT responding cells also responded to capsaicin with changes in the [Ca2+ ]i . In vivo intra-urethral 5-HT application increased VMRs induced by urethral distention and activated pERK in lumbosacral spinal cord neurones. CONCLUSION These morphological and functional findings provide insights into a putative paraneurone-neural network within the urethra that utilizes 5-HT signalling, presumably from paraneurones, to modulate primary sensory pathways carrying nociceptive and non-nociceptive (mechano-sensitive) information to the central nervous system.
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Affiliation(s)
- F. A. Kullmann
- Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - H. H. Chang
- Department of Urology, University of Southern California, Los Angeles, CA, USA
| | - C. Gauthier
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, USA
| | - B. M. McDonnell
- Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - J.-C. Yeh
- Department of Urology, University of Southern California, Los Angeles, CA, USA
| | - D. R. Clayton
- Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - A. J. Kanai
- Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - W. C. de Groat
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - G. L. Apodaca
- Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - L. A. Birder
- Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
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14
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Abstract
During embryogenesis, the musculoskeletal system develops while containing within itself a force generator in the form of the musculature. This generator becomes functional relatively early in development, exerting an increasing mechanical load on neighboring tissues as development proceeds. A growing body of evidence indicates that such mechanical forces can be translated into signals that combine with the genetic program of organogenesis. This unique situation presents both a major challenge and an opportunity to the other tissues of the musculoskeletal system, namely bones, joints, tendons, ligaments and the tissues connecting them. Here, we summarize the involvement of muscle-induced mechanical forces in the development of various vertebrate musculoskeletal components and their integration into one functional unit.
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Affiliation(s)
- Neta Felsenthal
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Elazar Zelzer
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel
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15
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Abstract
Premature infants have an increased risk of osteopenia due to limited bone mass accretion in utero and a greater need for bone nutrients. Until recently, most efforts to prevent osteopenia of prematurity focused on nutritional changes. Recent studies indicate that passive range-of-motion exercise of the extremities may lead to beneficial effects on body weight, increased bone mineralization, increased bone formation markers and leptin levels, and attenuation of the natural postnatal decline in bone speed of sound. These results suggest that exercise may play an important role in the prevention and treatment of osteopenia of prematurity. This review summarizes our current knowledge on the role of exercise in the prevention and treatment of osteopenia of prematurity.
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16
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Brunt LH, Begg K, Kague E, Cross S, Hammond CL. Wnt signalling controls the response to mechanical loading during zebrafish joint development. Development 2017; 144:2798-2809. [PMID: 28684625 PMCID: PMC5560048 DOI: 10.1242/dev.153528] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Accepted: 06/14/2017] [Indexed: 12/24/2022]
Abstract
Joint morphogenesis requires mechanical activity during development. Loss of mechanical strain causes abnormal joint development, which can impact long-term joint health. Although cell orientation and proliferation are known to shape the joint, dynamic imaging of developing joints in vivo has not been possible in other species. Using genetic labelling techniques in zebrafish we were able, for the first time, to dynamically track cell behaviours in intact moving joints. We identify that proliferation and migration, which contribute to joint morphogenesis, are mechanically controlled and are significantly reduced in immobilised larvae. By comparison with strain maps of the developing skeleton, we identify canonical Wnt signalling as a candidate for transducing mechanical forces into joint cell behaviours. We show that, in the jaw, Wnt signalling is reduced specifically in regions of high strain in response to loss of muscle activity. By pharmacological manipulation of canonical Wnt signalling, we demonstrate that Wnt acts downstream of mechanical activity and is required for joint patterning and chondrocyte maturation. Wnt16, which is also downstream of muscle activity, controls proliferation and migration, but plays no role in chondrocyte intercalation.
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Affiliation(s)
- Lucy H Brunt
- Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol BS8 1TD, UK
| | - Katie Begg
- Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol BS8 1TD, UK
| | - Erika Kague
- Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol BS8 1TD, UK
| | - Stephen Cross
- Wolfson Bioimaging Facility, University of Bristol, Bristol BS8 1TD, UK
| | - Chrissy L Hammond
- Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol BS8 1TD, UK
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17
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Killion CH, Mitchell EH, Duke CG, Serra R. Mechanical loading regulates organization of the actin cytoskeleton and column formation in postnatal growth plate. Mol Biol Cell 2017; 28:1862-1870. [PMID: 28539407 PMCID: PMC5541837 DOI: 10.1091/mbc.e17-02-0084] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2017] [Revised: 04/21/2017] [Accepted: 05/17/2017] [Indexed: 12/14/2022] Open
Abstract
Longitudinal growth of bones occurs at the growth plates where chondrocytes align into columns that allow directional growth. Little is known about the mechanisms controlling the ability of chondrocytes to form columns. We hypothesize that mechanical load and the resulting force on chondrocytes are necessary during active growth for proper growth plate development and limb length. To test this hypothesis, we created a mouse model in which a portion of the sciatic nerve from one hind limb was transected at postnatal day 8 to cause paralysis to that limb. At 6 and 12 wk postsurgery, the hind limb had significantly less bone mineral density than contralateral controls, confirming reduced load. At 8 and 14 wk postsurgery, tibiae were significantly shorter than controls. The paralyzed growth plate showed disruptions to column organization, with fewer and shorter columns. Polarized light microscopy indicated alterations in collagen fiber organization in the growth plate. Furthermore, organization of the actin cytoskeleton in growth plate chondrocytes was disrupted. We conclude that mechanical load and force on chondrocytes within the growth plate regulate postnatal development of the long bones.
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Affiliation(s)
- Christy H Killion
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Elizabeth H Mitchell
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Corey G Duke
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Rosa Serra
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35294
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18
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Lombardi G, Sanchis-Gomar F, Perego S, Sansoni V, Banfi G. Implications of exercise-induced adipo-myokines in bone metabolism. Endocrine 2016; 54:284-305. [PMID: 26718191 DOI: 10.1007/s12020-015-0834-0] [Citation(s) in RCA: 80] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Accepted: 12/14/2015] [Indexed: 12/12/2022]
Abstract
Physical inactivity has been recognized, by the World Health Organization as the fourth cause of death (5.5 % worldwide). On the contrary, physical activity (PA) has been associated with improved quality of life and decreased risk of several diseases (i.e., stroke, hypertension, myocardial infarction, obesity, malignancies). Bone turnover is profoundly affected from PA both directly (load degree is the key determinant for BMD) and indirectly through the activation of several endocrine axes. Several molecules, secreted by muscle (myokines) and adipose tissues (adipokines) in response to exercise, are involved in the fine regulation of bone metabolism in response to the energy availability. Furthermore, bone regulates energy metabolism by communicating its energetic needs thanks to osteocalcin which acts on pancreatic β-cells and adipocytes. The beneficial effects of exercise on bone metabolism depends on the intermittent exposure to myokines (i.e., irisin, IL-6, LIF, IGF-I) which, instead, act as inflammatory/pro-resorptive mediators when chronically elevated; on the other hand, the reduction in the circulating levels of adipokines (i.e., leptin, visfatin, adiponectin, resistin) sustains these effects as well as improves the whole-body metabolic status. The aim of this review is to highlight the newest findings about the exercise-dependent regulation of these molecules and their role in the fine regulation of bone metabolism.
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Affiliation(s)
- Giovanni Lombardi
- Laboratory of Experimental Biochemistry & Molecular Biology, I.R.C.C.S. Istituto Ortopedico Galeazzi, Via Riccardo Galeazzi 4, 20161, Milan, Italy.
| | | | - Silvia Perego
- Laboratory of Experimental Biochemistry & Molecular Biology, I.R.C.C.S. Istituto Ortopedico Galeazzi, Via Riccardo Galeazzi 4, 20161, Milan, Italy
| | - Veronica Sansoni
- Laboratory of Experimental Biochemistry & Molecular Biology, I.R.C.C.S. Istituto Ortopedico Galeazzi, Via Riccardo Galeazzi 4, 20161, Milan, Italy
| | - Giuseppe Banfi
- Laboratory of Experimental Biochemistry & Molecular Biology, I.R.C.C.S. Istituto Ortopedico Galeazzi, Via Riccardo Galeazzi 4, 20161, Milan, Italy
- Vita-Salute San Raffaele University, Milan, Italy
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19
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Hillam RA, Goodship AE, Skerry TM. Peak strain magnitudes and rates in the tibia exceed greatly those in the skull: An in vivo study in a human subject. J Biomech 2015; 48:3292-8. [PMID: 26232812 PMCID: PMC4601046 DOI: 10.1016/j.jbiomech.2015.06.021] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2014] [Revised: 06/15/2015] [Accepted: 06/17/2015] [Indexed: 11/25/2022]
Abstract
Bone mass and architecture are the result of a genetically determined baseline structure, modified by the effect of internal hormonal/biochemical regulators and the effect of mechanical loading. Bone strain is thought to drive a feedback mechanism to regulate bone formation and resorption to maintain an optimal, but not excessive mass and organisation of material at each skeletal location. Because every site in the skeleton has different functions, we have measured bone strains induced by physiological and more unusual activities, at two different sites, the tibia and cranium of a young human male in vivo. During the most vigorous activities, tibial strains were shown to exceed 0.2%, when ground reaction exceeded 5 times body weight. However in the skull the highest strains recorded were during heading a heavy medicine/exercise ball where parietal strains were up to 0.0192%. Interestingly parietal strains during more physiological activities were much lower, often below 0.01%. Strains during biting were not dependent upon bite force, but could be induced by facial contortions of similar appearance without contact between the teeth. Rates of strain change in the two sites were also very different, where peak tibial strain rate exceeded rate in the parietal bone by more than 5 fold. These findings suggest that the skull and tibia are subject to quite different regulatory influences, as strains that would be normal in the human skull would be likely to lead to profound bone loss by disuse in the long bones.
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20
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Shea CA, Rolfe RA, Murphy P. The importance of foetal movement for co-ordinated cartilage and bone development in utero : clinical consequences and potential for therapy. Bone Joint Res 2015; 4:105-16. [PMID: 26142413 PMCID: PMC4602203 DOI: 10.1302/2046-3758.47.2000387] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Construction of a functional skeleton is accomplished
through co-ordination of the developmental processes of chondrogenesis,
osteogenesis, and synovial joint formation. Infants whose movement in
utero is reduced or restricted and who subsequently suffer
from joint dysplasia (including joint contractures) and thin hypo-mineralised
bones, demonstrate that embryonic movement is crucial for appropriate
skeletogenesis. This has been confirmed in mouse, chick, and zebrafish
animal models, where reduced or eliminated movement consistently yields
similar malformations and which provide the possibility of experimentation
to uncover the precise disturbances and the mechanisms by which
movement impacts molecular regulation. Molecular genetic studies have
shown the important roles played by cell communication signalling
pathways, namely Wnt, Hedgehog, and transforming growth factor-beta/bone
morphogenetic protein. These pathways regulate cell behaviours such
as proliferation and differentiation to control maturation of the
skeletal elements, and are affected when movement is altered. Cell
contacts to the extra-cellular matrix as well as the cytoskeleton
offer a means of mechanotransduction which could integrate mechanical
cues with genetic regulation. Indeed, expression of cytoskeletal
genes has been shown to be affected by immobilisation. In addition
to furthering our understanding of a fundamental aspect of cell control
and differentiation during development, research in this area is
applicable to the engineering of stable skeletal tissues from stem
cells, which relies on an understanding of developmental mechanisms
including genetic and physical criteria. A deeper understanding
of how movement affects skeletogenesis therefore has broader implications
for regenerative therapeutics for injury or disease, as well as
for optimisation of physical therapy regimes for individuals affected
by skeletal abnormalities. Cite this article: Bone Joint Res 2015;4:105–116
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Affiliation(s)
- C A Shea
- Trinity College Dublin, College Green, Dublin, D2, Ireland
| | | | - P Murphy
- Trinity College Dublin, College Green, Dublin, D2, Ireland
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21
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Zelzer E, Blitz E, Killian ML, Thomopoulos S. Tendon-to-bone attachment: from development to maturity. ACTA ACUST UNITED AC 2015; 102:101-12. [PMID: 24677726 DOI: 10.1002/bdrc.21056] [Citation(s) in RCA: 114] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2013] [Accepted: 01/14/2014] [Indexed: 12/13/2022]
Abstract
The attachment between tendon and bone occurs across a complex transitional tissue that minimizes stress concentrations and allows for load transfer between muscles and skeleton. This unique tissue cannot be reconstructed following injury, leading to high incidence of recurrent failure and stressing the need for new clinical approaches. This review describes the current understanding of the development and function of the attachment site between tendon and bone. The embryonic attachment unit, namely, the tip of the tendon and the bone eminence into which it is inserted, was recently shown to develop modularly from a unique population of Sox9- and Scx-positive cells, which are distinct from tendon fibroblasts and chondrocytes. The fate and differentiation of these cells is regulated by transforming growth factor beta and bone morphogenetic protein signaling, respectively. Muscle loads are then necessary for the tissue to mature and mineralize. Mineralization of the attachment unit, which occurs postnatally at most sites, is largely controlled by an Indian hedgehog/parathyroid hormone-related protein feedback loop. A number of fundamental questions regarding the development of this remarkable attachment system require further study. These relate to the signaling mechanism that facilitates the formation of an interface with a gradient of cellular and extracellular phenotypes, as well as to the interactions between tendon and bone at the point of attachment.
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Affiliation(s)
- Elazar Zelzer
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
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22
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Tagliaferri C, Wittrant Y, Davicco MJ, Walrand S, Coxam V. Muscle and bone, two interconnected tissues. Ageing Res Rev 2015; 21:55-70. [PMID: 25804855 DOI: 10.1016/j.arr.2015.03.002] [Citation(s) in RCA: 229] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Revised: 03/15/2015] [Accepted: 03/18/2015] [Indexed: 12/31/2022]
Abstract
As bones are levers for skeletal muscle to exert forces, both are complementary and essential for locomotion and individual autonomy. In the past decades, the idea of a bone-muscle unit has emerged. Numerous studies have confirmed this hypothesis from in utero to aging works. Space flight, bed rest as well as osteoporosis and sarcopenia experimentations have allowed to accumulate considerable evidence. Mechanical loading is a key mechanism linking both tissues with a central promoting role of physical activity. Moreover, the skeletal muscle secretome accounts various molecules that affect bone including insulin-like growth factor-1 (IGF-1), basic fibroblast growth factor (FGF-2), interleukin-6 (IL-6), IL-15, myostatin, osteoglycin (OGN), FAM5C, Tmem119 and osteoactivin. Even though studies on the potential effects of bone on muscle metabolism are sparse, few osteokines have been identified. Prostaglandin E2 (PGE2) and Wnt3a, which are secreted by osteocytes, osteocalcin (OCN) and IGF-1, which are produced by osteoblasts and sclerostin which is secreted by both cell types, might impact skeletal muscle cells. Cartilage and adipose tissue are also likely to participate to this control loop and should not be set aside. Indeed, chondrocytes are known to secrete Dickkopf-1 (DKK-1) and Indian hedgehog (Ihh) and adipocytes produce leptin, adiponectin and IL-6, which potentially modulate bone and muscle metabolisms. The understanding of this system will enable to define new levers to prevent/treat sarcopenia and osteoporosis at the same time. These strategies might include nutritional interventions and physical exercise.
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23
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Galea GL, Meakin LB, Savery D, Taipaleenmaki H, Delisser P, Stein GS, Copp AJ, van Wijnen AJ, Lanyon LE, Price JS. Planar cell polarity aligns osteoblast division in response to substrate strain. J Bone Miner Res 2015; 30:423-35. [PMID: 25264362 PMCID: PMC4333081 DOI: 10.1002/jbmr.2377] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/12/2014] [Revised: 08/21/2014] [Accepted: 09/10/2014] [Indexed: 02/06/2023]
Abstract
Exposure of bone to dynamic strain increases the rate of division of osteoblasts and also influences the directional organization of the cellular and molecular structure of the bone tissue that they produce. Here, we report that brief exposure to dynamic substrate strain (sufficient to rapidly stimulate cell division) influences the orientation of osteoblastic cell division. The initial proliferative response to strain involves canonical Wnt signaling and can be blocked by sclerostin. However, the strain-related orientation of cell division is independently influenced through the noncanonical Wnt/planar cell polarity (PCP) pathway. Blockade of Rho-associated coiled kinase (ROCK), a component of the PCP pathway, prevents strain-related orientation of division in osteoblast-like Saos-2 cells. Heterozygous loop-tail mutation of the core PCP component van Gogh-like 2 (Vangl2) in mouse osteoblasts impairs the orientation of division in response to strain. Examination of bones from Vangl2 loop-tail heterozygous mice by µCT and scanning electron microscopy reveals altered bone architecture and disorganized bone-forming surfaces. Hence, in addition to the well-accepted role of PCP involvement in response to developmental cues during skeletal morphogenesis, our data reveal that this pathway also acts postnatally, in parallel with canonical Wnt signaling, to transduce biomechanical cues into skeletal adaptive responses. The simultaneous and independent actions of these two pathways appear to influence both the rate and orientation of osteoblast division, thus fine-tuning bone architecture to meet the structural demands of functional loading.
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Affiliation(s)
- Gabriel L Galea
- School of Veterinary Sciences, University of Bristol, Bristol, UK
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24
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Abstract
There is growing interest in the interaction between skeletal muscle and bone, particularly at the genetic and molecular levels. However, the genetic and molecular linkages between muscle and bone are achieved only within the context of the essential mechanical coupling of the tissues. This biomechanical and physiological linkage is readily evident as muscles attach to bone and induce exposure to varied mechanical stimuli via functional activity. The responsiveness of bone cells to mechanical stimuli, or their absence, is well established. However, questions remain regarding how muscle forces applied to bone serve to modulate bone homeostasis and adaptation. Similarly, the contributions of varied, but unique, stimuli generated by muscle to bone (such as low-magnitude, high-frequency stimuli) remains to be established. The current article focuses upon the mechanical relationship between muscle and bone. In doing so, we explore the stimuli that muscle imparts upon bone, models that enable investigation of this relationship, and recent data generated by these models.
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Affiliation(s)
- Keith G. Avin
- Center for Translational Musculoskeletal Research and Department of Physical Therapy, School of the Health and Rehabilitation Sciences, Indiana University, 1140 W. Michigan St., CF-120, Indianapolis, IN, USA,
| | - Susan A. Bloomfield
- Department of Health and Kinesiology, Texas A&M University, College Station, TX, USA,
| | - Ted S. Gross
- Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, WA, USA,
| | - Stuart J. Warden
- Center for Translational Musculoskeletal Research and Department of Physical Therapy, School of the Health and Rehabilitation Sciences, Indiana University, 1140 W. Michigan St., CF-120, Indianapolis, IN, USA
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25
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Galea GL, Hannuna S, Meakin LB, Delisser PJ, Lanyon LE, Price JS. Quantification of Alterations in Cortical Bone Geometry Using Site Specificity Software in Mouse models of Aging and the Responses to Ovariectomy and Altered Loading. Front Endocrinol (Lausanne) 2015; 6:52. [PMID: 25954246 PMCID: PMC4407614 DOI: 10.3389/fendo.2015.00052] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/26/2015] [Accepted: 04/03/2015] [Indexed: 11/13/2022] Open
Abstract
Investigations into the effect of (re)modeling stimuli on cortical bone in rodents normally rely on analysis of changes in bone mass and architecture at a narrow cross-sectional site. However, it is well established that the effects of axial loading produce site-specific changes throughout bones' structure. Non-mechanical influences (e.g., hormones) can be additional to or oppose locally controlled adaptive responses and may have more generalized effects. Tools currently available to study site-specific cortical bone adaptation are limited. Here, we applied novel site specificity software to measure bone mass and architecture at each 1% site along the length of the mouse tibia from standard micro-computed tomography (μCT) images. Resulting measures are directly comparable to those obtained through μCT analysis (R (2) > 0.96). Site Specificity analysis was used to compare a number of parameters in tibiae from young adult (19-week-old) versus aged (19-month-old) mice; ovariectomized and entire mice; limbs subjected to short periods of axial loading or disuse induced by sciatic neurectomy. Age was associated with uniformly reduced cortical thickness and site-specific decreases in cortical area most apparent in the proximal tibia. Mechanical loading site-specifically increased cortical area and thickness in the proximal tibia. Disuse uniformly decreased cortical thickness and decreased cortical area in the proximal tibia. Ovariectomy uniformly reduced cortical area without altering cortical thickness. Differences in polar moment of inertia between experimental groups were only observed in the proximal tibia. Aging and ovariectomy also altered eccentricity in the distal tibia. In summary, site specificity analysis provides a valuable tool for measuring changes in cortical bone mass and architecture along the entire length of a bone. Changes in the (re)modeling response determined at a single site may not reflect the response at different locations within the same bone.
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Affiliation(s)
- Gabriel L. Galea
- School of Veterinary Sciences, University of Bristol, Bristol, UK
- *Correspondence: Gabriel L. Galea, School of Veterinary Sciences, University of Bristol, Southwell Street, Bristol BS2 8EJ, UK
| | - Sion Hannuna
- Faculty of Engineering, University of Bristol, Bristol, UK
| | - Lee B. Meakin
- School of Veterinary Sciences, University of Bristol, Bristol, UK
| | | | - Lance E. Lanyon
- School of Veterinary Sciences, University of Bristol, Bristol, UK
| | - Joanna S. Price
- School of Veterinary Sciences, University of Bristol, Bristol, UK
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26
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Shwartz Y, Blitz E, Zelzer E. One load to rule them all: Mechanical control of the musculoskeletal system in development and aging. Differentiation 2013; 86:104-11. [DOI: 10.1016/j.diff.2013.07.003] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2013] [Revised: 07/01/2013] [Accepted: 07/12/2013] [Indexed: 12/24/2022]
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27
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Abstract
Development of the various components of a normal skeleton requires highly regulated signalling systems that co-ordinate spatial and temporal patterns of cell division, cell differentiation, and morphogenesis. Much work in recent decades has revealed cascades of molecular signalling, acting through key transcription factors to regulate, for example, organized chondrogenic and osteogenic differentiation. It is now clear that mechanical stimuli are also required for aspects of skeletogenesis but very little is known about how the mechanical signals are integrated with classic biochemical signalling. Spatially organized differentiation is vital to the production of functionally appropriate tissues contributing to precise, region specific morphologies, for example transient chondrogenesis of long bone skeletal rudiments, which prefigures osteogenic replacement of the cartilage template, compared with the production of permanent cartilage at the sites of articulation. Currently a lack of understanding of how these tissues are differentially regulated hampers efforts to specifically regenerate stable bone and cartilage. Here, we review current research revealing the influence of mechanical stimuli on specific aspects of skeletal development and refer to other developing systems to set the scene for current and future work to uncover the molecular mechanisms involved. We integrate this with a brief overview of the effects of mechanical stimulation on stem cells in culture bringing together developmental and tissue engineering aspects of mechanoregulation of cell behavior. A better understanding of the molecular mechanisms that link mechanical stimuli to transcriptional control guiding cell differentiation will lead to new ideas about how to effectively prime stem cells for tissue engineering and regenerative therapies.
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Affiliation(s)
- Rebecca Rolfe
- Department of Zoology, School of Natural Sciences, Trinity College, Dublin, Ireland
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28
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Fiaz AW, Léon-Kloosterziel KM, Gort G, Schulte-Merker S, van Leeuwen JL, Kranenbarg S. Swim-training changes the spatio-temporal dynamics of skeletogenesis in zebrafish larvae (Danio rerio). PLoS One 2012; 7:e34072. [PMID: 22529905 PMCID: PMC3329525 DOI: 10.1371/journal.pone.0034072] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2011] [Accepted: 02/20/2012] [Indexed: 11/19/2022] Open
Abstract
Fish larvae experience many environmental challenges during development such as variation in water velocity, food availability and predation. The rapid development of structures involved in feeding, respiration and swimming increases the chance of survival. It has been hypothesized that mechanical loading induced by muscle forces plays a role in prioritizing the development of these structures. Mechanical loading by muscle forces has been shown to affect larval and embryonic bone development in vertebrates, but these investigations were limited to the appendicular skeleton. To explore the role of mechanical load during chondrogenesis and osteogenesis of the cranial, axial and appendicular skeleton, we subjected zebrafish larvae to swim-training, which increases physical exercise levels and presumably also mechanical loads, from 5 until 14 days post fertilization. Here we show that an increased swimming activity accelerated growth, chondrogenesis and osteogenesis during larval development in zebrafish. Interestingly, swim-training accelerated both perichondral and intramembranous ossification. Furthermore, swim-training prioritized the formation of cartilage and bone structures in the head and tail region as well as the formation of elements in the anal and dorsal fins. This suggests that an increased swimming activity prioritized the development of structures which play an important role in swimming and thereby increasing the chance of survival in an environment where water velocity increases. Our study is the first to show that already during early zebrafish larval development, skeletal tissue in the cranial, axial and appendicular skeleton is competent to respond to swim-training due to increased water velocities. It demonstrates that changes in water flow conditions can result into significant spatio-temporal changes in skeletogenesis.
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Affiliation(s)
- Ansa W Fiaz
- Experimental Zoology Group, Department of Animal Sciences, Wageningen University and Research Centre, Wageningen, The Netherlands.
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Nowlan NC, Dumas G, Tajbakhsh S, Prendergast PJ, Murphy P. Biophysical stimuli induced by passive movements compensate for lack of skeletal muscle during embryonic skeletogenesis. Biomech Model Mechanobiol 2012; 11:207-19. [PMID: 21505895 PMCID: PMC4794622 DOI: 10.1007/s10237-011-0304-4] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2010] [Accepted: 03/19/2011] [Indexed: 01/29/2023]
Abstract
In genetically modified mice with abnormal skeletal muscle development, bones and joints are differentially affected by the lack of skeletal muscle. We hypothesise that unequal levels of biophysical stimuli in the developing humerus and femur can explain the differential effects on these rudiments when muscle is absent. We find that the expression patterns of four mechanosensitive genes important for endochondral ossification are differentially affected in muscleless limb mutants, with more extreme changes in the expression in the humerus than in the femur. Using finite element analysis, we show that the biophysical stimuli induced by muscle forces are similar in the humerus and femur, implying that the removal of muscle contractile forces should, in theory, affect the rudiments equally. However, simulations in which a displacement was applied to the end of the limb, such as could be caused in muscleless mice by movements of the mother or normal littermates, predicted higher biophysical stimuli in the femur than in the humerus. Stimuli induced by limb movement were much higher than those induced by the direct application of muscle forces, and we propose that movements of limbs caused by muscle contractions, rather than the direct application of muscle forces, provide the main mechanical stimuli for normal skeletal development. In muscleless mice, passive movement induces unequal biophysical stimuli in the humerus and femur, providing an explanation for the differential effects seen in these mice. The significance of these results is that forces originating external to the embryo may contribute to the initiation and progression of skeletal development when muscle development is abnormal.
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Affiliation(s)
- Niamh C Nowlan
- Trinity Centre for Bioengineering, School of Engineering, Trinity College Dublin, Dublin, Ireland.
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Harms CA, Cooper D, Tanaka H. Exercise Physiology of Normal Development, Sex Differences, and Aging. Compr Physiol 2011; 1:1649-78. [DOI: 10.1002/cphy.c100065] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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Kadmiel M, Fritz-Six K, Pacharne S, Richards GO, Li M, Skerry TM, Caron KM. Research resource: Haploinsufficiency of receptor activity-modifying protein-2 (RAMP2) causes reduced fertility, hyperprolactinemia, skeletal abnormalities, and endocrine dysfunction in mice. Mol Endocrinol 2011; 25:1244-53. [PMID: 21566080 DOI: 10.1210/me.2010-0400] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Receptor activity-modifying protein-2 (RAMP2) is a single-pass transmembrane protein that can regulate the trafficking, ligand binding, and signaling of several G protein-coupled receptors (GPCR). The most well-characterized role of RAMP2 is in the regulation of adrenomedullin (AM) binding to calcitonin receptor-like receptor (CLR), and our previous studies using knockout mouse models support this canonical signaling paradigm. For example, Ramp2(-/-) mice die at midgestation with a precise phenocopy of the AM(-/-) and Calcrl(-/-) mice. In contrast, Ramp2(+/-) mice are viable and exhibit an expanded variety of phenotypes that are distinct from those of Calcrl(+/-) mice. Using Ramp2(+/-) female mice, we demonstrate that a modest decrease in Ramp2 expression causes severe reproductive defects characterized by fetal growth restriction, fetal demise, and postnatal lethality that is independent of the genotype and gender of the offspring. Ramp2(+/-) female mice also exhibit hyperprolactinemia during pregnancy and in basal conditions. Consistent with hyperprolactinemia, Ramp2(+/-) female mice have enlarged pituitary glands, accelerated mammary gland development, and skeletal abnormalities including delayed bone development and decreased bone mineral density. Because RAMP2 has been shown to associate with numerous GPCR, it is likely that signaling of one or more of these GPCR is compromised in Ramp2(+/-) mice, yet the precise identification of these receptors remains to be elucidated. Taken together, this work reveals an essential role for RAMP2 in endocrine physiology and provides the first in vivo evidence for a physiological role of RAMP2 beyond that of AM/CLR signaling.
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Affiliation(s)
- Mahita Kadmiel
- Department of Cell and Molecular Physiology, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA
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Bonneau N, Simonis C, Seringe R, Tardieu C. Study of femoral torsion during prenatal growth: interpretations associated with the effects of intrauterine pressure. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 2011; 145:438-45. [PMID: 21541926 DOI: 10.1002/ajpa.21521] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2010] [Accepted: 01/31/2011] [Indexed: 01/25/2023]
Abstract
The developing fetus is protected from external environmental influences by maternal tissues. However, these structures have a limited elasticity, such that the fetus must grow in a confined space, constraining its size at the end of pregnancy. Can these constraints modify the morphology of the fetal skeleton? The intensity of these constraints increases between 5 months and birth, making it the most appropriate period to address this question. A sample of 89 fetal femora was analyzed, and results provide evidence that during this period, the torsion of the femoral shaft (quantified by means of a new three-dimensional method) increases gradually. Two explanations were considered: this increase could signal effects of constraints induced by the intrauterine cavity, developmental patterning, or some combination of these two. Different arguments tend to support the biomechanical explanation, rather than a programming pattern formation. Indeed, the identification of the femur as a first degree lever, created by the hyperflexion of the fetal lower limbs on the pelvis, could explain the increase in femoral shaft torsion during prenatal life. A comparison with femora of infants is in accordance with this mechanical interpretation, which is possible through bone modeling/remodeling. Although genetic and epigenetic mechanisms may regulate timing of fetal development, our data suggest that at birth, the fetal skeleton also has an intrauterine mechanical history through adaptive bone plasticity.
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Affiliation(s)
- Noémie Bonneau
- UMR CNRS-Muséum National d'Histoire Naturelle, Paris, France.
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Mechanical influences on morphogenesis of the knee joint revealed through morphological, molecular and computational analysis of immobilised embryos. PLoS One 2011; 6:e17526. [PMID: 21386908 PMCID: PMC3046254 DOI: 10.1371/journal.pone.0017526] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Accepted: 02/03/2011] [Indexed: 11/19/2022] Open
Abstract
Very little is known about the regulation of morphogenesis in synovial joints. Mechanical forces generated from muscle contractions are required for normal development of several aspects of normal skeletogenesis. Here we show that biophysical stimuli generated by muscle contractions impact multiple events during chick knee joint morphogenesis influencing differential growth of the skeletal rudiment epiphyses and patterning of the emerging tissues in the joint interzone. Immobilisation of chick embryos was achieved through treatment with the neuromuscular blocking agent Decamethonium Bromide. The effects on development of the knee joint were examined using a combination of computational modelling to predict alterations in biophysical stimuli, detailed morphometric analysis of 3D digital representations, cell proliferation assays and in situ hybridisation to examine the expression of a selected panel of genes known to regulate joint development. This work revealed the precise changes to shape, particularly in the distal femur, that occur in an altered mechanical environment, corresponding to predicted changes in the spatial and dynamic patterns of mechanical stimuli and region specific changes in cell proliferation rates. In addition, we show altered patterning of the emerging tissues of the joint interzone with the loss of clearly defined and organised cell territories revealed by loss of characteristic interzone gene expression and abnormal expression of cartilage markers. This work shows that local dynamic patterns of biophysical stimuli generated from muscle contractions in the embryo act as a source of positional information guiding patterning and morphogenesis of the developing knee joint.
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Nowlan NC, Sharpe J, Roddy KA, Prendergast PJ, Murphy P. Mechanobiology of embryonic skeletal development: Insights from animal models. BIRTH DEFECTS RESEARCH. PART C, EMBRYO TODAY : REVIEWS 2010; 90:203-13. [PMID: 20860060 PMCID: PMC4794623 DOI: 10.1002/bdrc.20184] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
A range of clinical conditions in which fetal movement is reduced or prevented can have a severe effect on skeletal development. Animal models have been instrumental to our understanding of the interplay between mechanical forces and skeletal development, particularly the mouse and the chick model systems. In the chick, the most commonly used means of altering the mechanical environment is by pharmaceutical agents which induce paralysis, whereas genetically modified mice with nonfunctional or absent skeletal muscle offer a valuable tool for examining the interplay between muscle forces and skeletogenesis in mammals. This article reviews the body of research on animal models of bone or joint formation in vivo in the presence of an altered or abnormal mechanical environment. In both immobilized chicks and "muscleless limb" mice, a range of effects are seen, such as shorter rudiments with less bone formation, changes in rudiment and joint shape, and abnormal joint cavitation. However, although all bones and synovial joints are affected in immobilized chicks, some rudiments and joints are unaffected in muscleless mice. We propose that extrinsic mechanical forces from movements of the mother or littermates impact on skeletogenesis in mammals, whereas the chick embryo is reliant on intrinsic movement for mechanical stimulation. The insights gained from animal models into the mechanobiology of embryonic skeletal development could provide valuable cues to prospective tissue engineers of cartilage and bone and contribute to new or improved treatments to minimize the impact on skeletal development of reduced movement in utero.
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Buck LT, Stock JT, Foley RA. Levels of Intraspecific Variation Within the Catarrhine Skeleton. INT J PRIMATOL 2010. [DOI: 10.1007/s10764-010-9428-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Abstract
UNLABELLED Intrauterine fracture is an extremely rare finding, but can occur as the result of maternal trauma, osteogenesis imperfecta (OI), or theoretically other metabolic/structural abnormalities. Increased clinical awareness of the diagnosis and optimal management of these cases can lead to more positive outcomes for the patient and her child. Blunt abdominal trauma late in gestation increases the risk of fetal skull fracture, while a known diagnosis of OI or other abnormalities leading to decreased fetal bone density creates concern for long bone fracture. Biochemical and genetic tests can aid in the prenatal diagnosis of OI, while ultrasound is the best overall imaging modality for identifying fetal fracture of any etiology. When fetal fracture is diagnosed radiologically, specific management is recommended to promote optimal outcomes for mother and fetus, with special consideration given to the mother with OI. With the exception of fetal fractures due to lethal conditions, cesarean delivery is recommended in most cases, especially when fetal or maternal well-being cannot be assured. When a patient presents with risk factors for intrauterine fracture, careful evaluation via thorough history-taking, ultrasonography of the entire fetal skeleton, and laboratory tests should be performed. Heightened awareness of intrauterine fracture allows better postpartum management, whether for simple fracture care or for long-term care of patients with OI or genetic/metabolic abnormalities. TARGET AUDIENCE Obstetricians & Gynecologist, Family Physicians. LEARNING OBJECTIVES After completion of this educational activity, the reader will be able to compare x-ray, ultrasound modalities and MRI and their utility in diagnosing fetal fracture. Formulate a differential diagnosis for fetal fracture. Propose a delivery plan for a patient whose fetus has a prenatally diagnosed fetal fracture.
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van Turnhout MC, Schipper H, Engel B, Buist W, Kranenbarg S, van Leeuwen JL. Postnatal development of collagen structure in ovine articular cartilage. BMC DEVELOPMENTAL BIOLOGY 2010; 10:62. [PMID: 20529268 PMCID: PMC2906441 DOI: 10.1186/1471-213x-10-62] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/29/2010] [Accepted: 06/07/2010] [Indexed: 12/01/2022]
Abstract
Background Articular cartilage (AC) is the layer of tissue that covers the articulating ends of the bones in diarthrodial joints. Across species, adult AC shows an arcade-like structure with collagen predominantly perpendicular to the subchondral bone near the bone, and collagen predominantly parallel to the articular surface near the articular surface. Recent studies into collagen fibre orientation in stillborn and juvenile animals showed that this structure is absent at birth. Since the collagen structure is an important factor for AC mechanics, the absence of the adult Benninghoff structure has implications for perinatal AC mechanobiology. The current objective is to quantify the dynamics of collagen network development in a model animal from birth to maturity. We further aim to show the presence or absence of zonal differentiation at birth, and to assess differences in collagen network development between different anatomical sites of a single joint surface. We use quantitative polarised light microscopy to investigate properties of the collagen network and we use the sheep (Ovis aries) as our model animal. Results Predominant collagen orientation is parallel to the articular surface throughout the tissue depth for perinatal cartilage. This remodels to the Benninghoff structure before the sheep reach sexual maturity. Remodelling of predominant collagen orientation starts at a depth just below the future transitional zone. Tissue retardance shows a minimum near the articular surface at all ages, which indicates the presence of zonal differentiation at all ages. The absolute position of this minimum does change between birth and maturity. Between different anatomical sites, we find differences in the dynamics of collagen remodelling, but no differences in adult collagen structure. Conclusions The collagen network in articular cartilage remodels between birth and sexual maturity from a network with predominant orientation parallel to the articular surface to a Benninghoff network. The retardance minimum near, but not at, the articular surface at all ages shows that a zonal differentiation is already present in the perinatal animals. In these animals, the zonal differentiation can not be correlated to the collagen network orientation. We find no difference in adult collagen structure in the nearly congruent metacarpophalangeal joint, but we do find differences in the dynamics of collagen network remodelling.
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Affiliation(s)
- Mark C van Turnhout
- Wageningen University, Department of Animal Sciences, Experimental Zoology Group, 6700 AH Wageningen, the Netherlands.
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Leppänen OV, Sievänen H, Jokihaara J, Pajamäki I, Kannus P, Cooper DM, Järvinen TLN. The effects of loading and estrogen on rat bone growth. J Appl Physiol (1985) 2010; 108:1737-44. [DOI: 10.1152/japplphysiol.00989.2009] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study evaluated the contributions of locomotive loading and estrogen to the development of diaphysis of rat femur. A randomized 2 × 2 study design was used. Altogether, 70 female Sprague-Dawley rats were used, of which 10 were euthanized at entry. Of the remaining rats, 16 served as controls, and the rest, 44, underwent a unilateral sciatic neurectomy. The effect of estrogen was removed by ovariectomizing one-half of the neurectomized rats. After 27 wk, the animals were euthanized, and the femora were excised. Irrespective of loading or estrogen, the femur length and mineral mass increased by 142 and 687%, respectively. Axial growth was not modulated either by locomotive loading or estrogen, but the loading resulted in direction-specific changes in the cross-sectional geometry. The estrogen-related gains were evident on the endocortical surface, while the loading-related gains occurred on the periosteal surface. The loading and estrogen were significantly associated with increased bone strength (21 and 15%, respectively) in the mediolateral direction, but not in the anteroposterior direction. Axial growth and accrual of bone mineral mass of the rat femur are largely independent of locomotive loading or estrogen, whereas these factors specifically account for the femur function, as either a mechanical lever or a mineral reservoir for reproduction, respectively.
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Affiliation(s)
- Olli V. Leppänen
- Medical School and the Institute of Medical Technology, University of Tampere,
- Division of Orthopaedics and Traumatology, Department of Trauma, Musculoskeletal Surgery and Rehabilitation, Tampere University Hospital, and
| | - Harri Sievänen
- The Bone Research Group, UKK Institute, Tampere, Finland
| | - Jarkko Jokihaara
- Medical School and the Institute of Medical Technology, University of Tampere,
- Division of Orthopaedics and Traumatology, Department of Trauma, Musculoskeletal Surgery and Rehabilitation, Tampere University Hospital, and
- Department of Orthopaedics, University of British Columbia, Vancouver, British Columbia; and
| | - Ilari Pajamäki
- Medical School and the Institute of Medical Technology, University of Tampere,
- Division of Orthopaedics and Traumatology, Department of Trauma, Musculoskeletal Surgery and Rehabilitation, Tampere University Hospital, and
| | - Pekka Kannus
- Medical School and the Institute of Medical Technology, University of Tampere,
- Division of Orthopaedics and Traumatology, Department of Trauma, Musculoskeletal Surgery and Rehabilitation, Tampere University Hospital, and
- The Bone Research Group, UKK Institute, Tampere, Finland
| | - David M. Cooper
- Department of Anatomy and Cell Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Teppo L. N. Järvinen
- Medical School and the Institute of Medical Technology, University of Tampere,
- Division of Orthopaedics and Traumatology, Department of Trauma, Musculoskeletal Surgery and Rehabilitation, Tampere University Hospital, and
- Department of Orthopaedics, University of British Columbia, Vancouver, British Columbia; and
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Nowlan NC, Bourdon C, Dumas G, Tajbakhsh S, Prendergast PJ, Murphy P. Developing bones are differentially affected by compromised skeletal muscle formation. Bone 2010; 46:1275-85. [PMID: 19948261 PMCID: PMC2860222 DOI: 10.1016/j.bone.2009.11.026] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/09/2009] [Revised: 10/19/2009] [Accepted: 11/20/2009] [Indexed: 12/03/2022]
Abstract
Mechanical forces are essential for normal adult bone function and repair, but the impact of prenatal muscle contractions on bone development remains to be explored in depth in mammalian model systems. In this study, we analyze skeletogenesis in two 'muscleless' mouse mutant models in which the formation of skeletal muscle development is disrupted; Myf5(nlacZ/nlacZ):MyoD(-/-) and Pax3(Sp/Sp) (Splotch). Ossification centers were found to be differentially affected in the muscleless limbs, with significant decreases in bone formation in the scapula, humerus, ulna and femur, but not in the tibia. In the scapula and humerus, the morphologies of ossification centers were abnormal in muscleless limbs. Histology of the humerus revealed a decreased extent of the hypertrophic zone in mutant limbs but no change in the shape of this region. The elbow joint was also found to be clearly affected with a dramatic reduction in the joint line, while no abnormalities were evident in the knee. The humeral deltoid tuberosity was significantly reduced in size in the Myf5(nlacZ/nlacZ):MyoD(-/-) mutants while a change in shape but not in size was found in the humeral tuberosities of the Pax3(Sp/Sp) mutants. We also examined skeletal development in a 'reduced muscle' model, the Myf5(nlacZ/+):MyoD(-/-) mutant, in which skeletal muscle forms but with reduced muscle mass. The reduced muscle phenotype appeared to have an intermediate effect on skeletal development, with reduced bone formation in the scapula and humerus compared to controls, but not in other rudiments. In summary, we have demonstrated that skeletal development is differentially affected by the lack of skeletal muscle, with certain rudiments and joints being more severely affected than others. These findings indicate that the response of skeletal progenitor cells to biophysical stimuli may depend upon their location in the embryonic limb, implying a complex interaction between mechanical forces and location-specific regulatory factors affecting bone and joint development.
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Affiliation(s)
- Niamh C. Nowlan
- Department of Zoology, School of Natural Sciences, Trinity College Dublin, Ireland
- Trinity Centre for Bioengineering, School of Engineering, Trinity College Dublin, Ireland
| | - Céline Bourdon
- Department of Zoology, School of Natural Sciences, Trinity College Dublin, Ireland
- Trinity Centre for Bioengineering, School of Engineering, Trinity College Dublin, Ireland
| | - Gérard Dumas
- Stem Cells & Development, Department of Developmental Biology, Institut Pasteur, Paris, France
| | - Shahragim Tajbakhsh
- Stem Cells & Development, Department of Developmental Biology, Institut Pasteur, Paris, France
| | - Patrick J. Prendergast
- Trinity Centre for Bioengineering, School of Engineering, Trinity College Dublin, Ireland
| | - Paula Murphy
- Department of Zoology, School of Natural Sciences, Trinity College Dublin, Ireland
- Trinity Centre for Bioengineering, School of Engineering, Trinity College Dublin, Ireland
- Corresponding author. Fax: +353 677 8094.
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Hamrick MW, McNeil PL, Patterson SL. Role of muscle-derived growth factors in bone formation. JOURNAL OF MUSCULOSKELETAL & NEURONAL INTERACTIONS 2010; 10:64-70. [PMID: 20190381 PMCID: PMC3753580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Muscle and bone anabolism and catabolism are tightly coupled during growth, development, and aging, yet the cellular and molecular mechanisms linking these two tissues are not well understood. Here we show that FGF-2 and IGF-1, two growth factors known to play a major role in regulating bone formation, are localized to muscle fibers along the muscle-bone interface of the mouse forelimb. Likewise, receptors for these growth factors are also abundant in periosteum adjacent to fleshy muscle attachments along the diaphysis of long bones. Growth factor levels were quantified from homogenized mouse forelimb muscles and IGF-1 was found to be the most abundant factor with FGF-2 also detected. Growth factor levels were also analyzed in conditioned medium from cultured myotubes, and IGF-1 and FGF-2 were again detected at significant levels. Mechanically wounding C2C12 myotubes increased the release of FGF-2 into conditioned medium, whereas IGF-1 was secreted at lower concentrations than FGF-2 following injury. Together these findings suggest that muscle is an important, local source of growth factors for bone tissue. Hence, the integrated growth and development of bone and muscle is likely to be regulated in part by paracrine mechanisms at the muscle-bone interface involving growth factor signaling.
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Affiliation(s)
- M W Hamrick
- Department of Cellular Biology and Anatomy, Institute of Molecular Medicine and Genetics, GA, USA.
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Ahmad I, Nemet D, Eliakim A, Koeppel R, Grochow D, Coussens M, Gallitto S, Rich J, Pontello A, Leu SY, Cooper DM, Waffarn F. Body composition and its components in preterm and term newborns: A cross-sectional, multimodal investigation. Am J Hum Biol 2010; 22:69-75. [PMID: 19533616 DOI: 10.1002/ajhb.20955] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
A prospective, cross-sectional, observational study in preterm and term infants was performed to compare multimodal measurements of body composition, namely, limb ultrasound, bone quantitative ultrasound, and dual X-ray absorptiometry (DXA). One hundred and two preterm and term infants appropriate for gestational age were enrolled from the newborn nursery and neonatal intensive care unit. Infants were included when they were medically stable, in an open crib, on full enteral feeds and within 1 week of anticipated discharge. Correlations among the various measurements of body composition were performed using standard techniques. A comparison between preterm infant (born at 28-32 weeks) reaching term to term-born infants was performed. Limb ultrasound estimates of cross-sectional areas of lean and fat tissue in a region of tissue (i.e., the leg) were remarkably correlated with regional and whole-body estimates of fat-free mass and fat obtained from DXA suggesting the potential usefulness of muscle ultrasound as an investigative tool for studying aspects of body composition in this fragile population. There was a weak but significant correlation between quantitative ultrasound measurements of bone strength and DXA-derived bone mineral density (BMD). Preterm infants reaching term had significantly lower body weight, length, head circumference, muscle and fat cross-sectional area, bone speed of sound, whole-body and regional lean body mass, fat mass, and BMD compared to term-born infants. Current postnatal care and nutritional support in preterm infants is still unable to match the in-utero environment for optimal growth and bone development. The use of relatively simple bedside, noninvasive body composition measurements may assist in understanding how changes in different components of body composition early in life affect later growth and development.
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Affiliation(s)
- Irfan Ahmad
- Department of Pediatrics, University of California, Irvine, USA
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Mochida H, Fortin G, Champagnat J, Glover JC. Differential Involvement of Projection Neurons During Emergence of Spontaneous Activity in the Developing Avian Hindbrain. J Neurophysiol 2009; 101:591-602. [DOI: 10.1152/jn.90835.2008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To better characterize the emergence of spontaneous neuronal activity in the developing hindbrain, spontaneous activity was recorded optically from defined projection neuron populations in isolated preparations of the brain stem of the chicken embryo. Ipsilaterally projecting reticulospinal (RS) neurons and several groups of vestibuloocular (VO) neurons were labeled retrogradely with Calcium Green-1 dextran amine and spontaneous calcium transients were recorded using a charge-coupled-device camera mounted on a fluorescence microscope. Simultaneous extracellular recordings were made from one of the trigeminal motor nerves (nV) to register the occurrence of spontaneous synchronous bursts of activity. Two types of spontaneous activity were observed: synchronous events (SEs), which occurred in register with spontaneous bursts in nV once every few minutes and were tetrodotoxin (TTX) dependent, and asynchronous events (AEs), which occurred in the intervals between SEs and were TTX resistant. AEs occurred developmentally before SEs and were in general smaller and more variable in amplitude than SEs. SEs appeared at the same stage as nV bursts early on embryonic day 4, first in RS neurons and then in VO neurons. All RS neurons participated equally in SEs from the outset, whereas different subpopulations of VO neurons participated differentially, both in terms of the proportion of neurons that exhibited SEs, the fidelity with which the SEs in individual neurons followed the nV bursts, and the developmental stage at which SEs appeared and matured. The results show that spontaneous activity is expressed heterogeneously among hindbrain projection neuron populations, suggesting its differential involvement in the formation of different functional neuronal circuits.
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Arnsdorf EJ, Tummala P, Kwon RY, Jacobs CR. Mechanically induced osteogenic differentiation--the role of RhoA, ROCKII and cytoskeletal dynamics. J Cell Sci 2009; 122:546-53. [PMID: 19174467 DOI: 10.1242/jcs.036293] [Citation(s) in RCA: 282] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Many biochemical factors regulating progenitor cell differentiation have been examined in detail; however, the role of the local mechanical environment on stem cell fate has only recently been investigated. In this study, we examined whether oscillatory fluid flow, an exogenous mechanical signal within bone, regulates osteogenic, adipogenic or chondrogenic differentiation of C3H10T1/2 murine mesenchymal stem cells by measuring Runx2, PPARgamma and SOX9 gene expression, respectively. Furthermore, we hypothesized that the small GTPase RhoA and isometric tension within the actin cytoskeleton are essential in flow-induced differentiation. We found that oscillatory fluid flow induces the upregulation of Runx2, Sox9 and PPARgamma, indicating that it has the potential to regulate transcription factors involved in multiple unique lineage pathways. Furthermore, we demonstrate that the small GTPase RhoA and its effector protein ROCKII regulate fluid-flow-induced osteogenic differentiation. Additionally, activated RhoA and fluid flow have an additive effect on Runx2 expression. Finally, we show RhoA activation and actin tension are negative regulators of both adipogenic and chondrogenic differentiation. However, an intact, dynamic actin cytoskeleton under tension is necessary for flow-induced gene expression.
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Affiliation(s)
- Emily J Arnsdorf
- Bone and Joint R&D Center, VA Palo Alto Health Care System, 3801 Miranda Avenue, Palo Alto, CA 94304, USA.
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Ward SR, Kim CW, Eng CM, Gottschalk LJ, Tomiya A, Garfin SR, Lieber RL. Architectural analysis and intraoperative measurements demonstrate the unique design of the multifidus muscle for lumbar spine stability. J Bone Joint Surg Am 2009; 91:176-85. [PMID: 19122093 PMCID: PMC2663324 DOI: 10.2106/jbjs.g.01311] [Citation(s) in RCA: 198] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
BACKGROUND Muscular instability is an important risk factor for lumbar spine injury and chronic low-back pain. Although the lumbar multifidus muscle is considered an important paraspinal muscle, its design features are not completely understood. The purpose of the present study was to determine the architectural properties, in vivo sarcomere length operating range, and passive mechanical properties of the human multifidus muscle. We hypothesized that its architecture would be characterized by short fibers and a large physiological cross-sectional area and that it would operate over a relatively wide range of sarcomere lengths but would have very stiff passive material properties. METHODS The lumbar spines of eight cadaver specimens were excised en bloc from T12 to the sacrum. Multifidus muscles were isolated from each vertebral level, permitting the architectural measurements of mass, sarcomere length, normalized fiber length, physiological cross-sectional area, and fiber length-to-muscle length ratio. To determine the sarcomere length operating range of the muscle, sarcomere lengths were measured from intraoperative biopsy specimens that were obtained with the spine in the flexed and extended positions. The material properties of single muscle fibers were obtained from passive stress-strain tests of excised biopsy specimens. RESULTS The average muscle mass (and standard error) was 146 +/- 8.7 g, and the average sarcomere length was 2.27 +/- 0.06 microm, yielding an average normalized fiber length of 5.66 +/- 0.65 cm, an average physiological cross-sectional area of 23.9 +/- 3.0 cm(2), and an average fiber length-to-muscle length ratio of 0.21 +/- 0.03. Intraoperative sarcomere length measurements revealed that the muscle operates from 1.98 +/- 0.15 microm in extension to 2.70 +/- 0.11 microm in flexion. Passive mechanical data suggested that the material properties of the muscle are comparable with those of muscles of the arm or leg. CONCLUSIONS The architectural design (a high cross-sectional area and a low fiber length-to-muscle length ratio) demonstrates that the multifidus muscle is uniquely designed as a stabilizer to produce large forces. Furthermore, multifidus sarcomeres are positioned on the ascending portion of the length-tension curve, allowing the muscle to become stronger as the spine assumes a forward-leaning posture.
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Affiliation(s)
- Samuel R. Ward
- Departments of Orthopaedic Surgery (S.R.W., C.W.K., C.M.E., L.J.G. IV, A.T., S.R.G., and R.L.L.), Radiology (S.R.W.), and Bioengineering (R.L.L.), V.A. Medical Center and University of California at San Diego, 3350 La Jolla Village Drive, San Diego, CA 92161. E-mail address for R.L. Lieber:
| | - Choll W. Kim
- Departments of Orthopaedic Surgery (S.R.W., C.W.K., C.M.E., L.J.G. IV, A.T., S.R.G., and R.L.L.), Radiology (S.R.W.), and Bioengineering (R.L.L.), V.A. Medical Center and University of California at San Diego, 3350 La Jolla Village Drive, San Diego, CA 92161. E-mail address for R.L. Lieber:
| | - Carolyn M. Eng
- Departments of Orthopaedic Surgery (S.R.W., C.W.K., C.M.E., L.J.G. IV, A.T., S.R.G., and R.L.L.), Radiology (S.R.W.), and Bioengineering (R.L.L.), V.A. Medical Center and University of California at San Diego, 3350 La Jolla Village Drive, San Diego, CA 92161. E-mail address for R.L. Lieber:
| | - Lionel J. Gottschalk
- Departments of Orthopaedic Surgery (S.R.W., C.W.K., C.M.E., L.J.G. IV, A.T., S.R.G., and R.L.L.), Radiology (S.R.W.), and Bioengineering (R.L.L.), V.A. Medical Center and University of California at San Diego, 3350 La Jolla Village Drive, San Diego, CA 92161. E-mail address for R.L. Lieber:
| | - Akihito Tomiya
- Departments of Orthopaedic Surgery (S.R.W., C.W.K., C.M.E., L.J.G. IV, A.T., S.R.G., and R.L.L.), Radiology (S.R.W.), and Bioengineering (R.L.L.), V.A. Medical Center and University of California at San Diego, 3350 La Jolla Village Drive, San Diego, CA 92161. E-mail address for R.L. Lieber:
| | - Steven R. Garfin
- Departments of Orthopaedic Surgery (S.R.W., C.W.K., C.M.E., L.J.G. IV, A.T., S.R.G., and R.L.L.), Radiology (S.R.W.), and Bioengineering (R.L.L.), V.A. Medical Center and University of California at San Diego, 3350 La Jolla Village Drive, San Diego, CA 92161. E-mail address for R.L. Lieber:
| | - Richard L. Lieber
- Departments of Orthopaedic Surgery (S.R.W., C.W.K., C.M.E., L.J.G. IV, A.T., S.R.G., and R.L.L.), Radiology (S.R.W.), and Bioengineering (R.L.L.), V.A. Medical Center and University of California at San Diego, 3350 La Jolla Village Drive, San Diego, CA 92161. E-mail address for R.L. Lieber:
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The response of bone to mechanical loading and disuse: fundamental principles and influences on osteoblast/osteocyte homeostasis. Arch Biochem Biophys 2008; 473:117-23. [PMID: 18334226 DOI: 10.1016/j.abb.2008.02.028] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2008] [Accepted: 02/18/2008] [Indexed: 02/04/2023]
Abstract
Bone's response to increased or reduced loading/disuse is a feature of many clinical circumstances, and our daily life, as habitual activities change. However, there are several misconceptions regarding what constitutes loading or disuse and why the skeleton gains or loses bone. The main purpose of this article is to discuss the fundamentals of the need for bone to experience the effects of loading and disuse, why bone loss due to disuse occurs, and how it is the target of skeletal physiology which drives pathological bone loss in conditions that may not be seen as being primarily due to disuse. Fundamentally, if we accept that hypertrophy of bone in response to increased loading is a desirable occurrence, then disuse is not a pathological process, but simply the corollary of adaptation to increased loads. If adaptive processes occur to increase bone mass in response to increased load, then the loss of bone in disuse is the only way that adaptation can fully tune the skeleton to prevailing functional demands when loading is reduced. The mechanisms by which loading and disuse cause bone formation or resorption are the same, although the direction of any changes is different. The osteocyte and osteoblast are the key cells involved in sensing and communicating the need for changes in mass or architecture as a result of changes in experienced loading. However, as those cells are affected by numerous other influences, the responses of bone to loading or disuse are not simple, and alter under different circumstances. Understanding the principles of disuse and loading and the mechanisms underlying them therefore represents an important feature of bone physiology and the search for targets for anabolic therapies for skeletal pathology.
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