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Event: 2089

Key Event Title

A descriptive phrase which defines a discrete biological change that can be measured. More help

Altered Bone Cell Homeostasis

Short name

The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. More help

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Biological Context

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Level of Biological Organization
Cellular

Cell term

The location/biological environment in which the event takes place.The biological context describes the location/biological environment in which the event takes place. For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable. For individual/population events, the organ context is not applicable. Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Cell term
eukaryotic cell

Organ term

Key Event Components

The KE, as defined by a set structured ontology terms consisting of a biological process, object, and action with each term originating from one of 14 biological ontologies (Ives, et al., 2017; https://aopwiki.org/info_pages/2/info_linked_pages/7#List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling).Biological process describes dynamics of the underlying biological system (e.g., receptor signaling). The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signaling by that receptor). Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description. To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons. If a desired term does not exist, a new term request may be made via Term Requests. Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add. Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Process	Object	Action
osteoblast differentiation		decreased
osteoclast differentiation		increased

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE.Clicking on the name of the AOP will bring you to the individual page for that AOP. More help

AOP Name	Role of event in AOP	Point of Contact	Author Status	OECD Status
Deposition of energy leading to bone loss	KeyEvent	Vinita Chauhan (send email)	Open for citation & comment	Under Review

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KE.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help

Term	Scientific Term	Evidence	Link
human	Homo sapiens	Low	NCBI
rat	Rattus norvegicus	Moderate	NCBI
mouse	Mus musculus	Moderate	NCBI

Life Stages

An indication of the the relevant life stage(s) for this KE. More help

Life stage	Evidence
All life stages	Low

Sex Applicability

An indication of the the relevant sex for this KE. More help

Term	Evidence
Unspecific	Moderate

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. More help

Osteogenesis is the process by which new bone is formed through the balanced action of bone depositing osteoblasts and bone resorbing osteoclasts. Osteogenesis is regulated by the differentiation and activity of osteoblasts/clasts. Dysregulation of bone cell differentiation and functional activity leads to imbalanced osteogenesis and altered bone matrix (Smith, 2020).

Osteoclast precursors are of hematopoietic origin and differentiated into mature, multi-nucleated osteoclasts based on external signals in the microenvironment, of which the cytokine macrophage colony stimulating factor (M-CSF, also known as CSF-1) and receptor activator of NF-κB ligand (RANKL, aka TNFSF11) are key components (Donaubauer et al., 2020; Smith, 2020). Osteoclasts bone resorbing activity is a result of enzymes expressed in cellular lysosomes that are involved in the degradation extracellular components, including tartrate-resistant acid phosphatase (TRAP), cathepsin K (CTSK), and matrix metalloproteinases (MMPs), among others. Cellular lysosomes are shuttled to the resorption lacunae, located under the ruffled osteoclast membrane, from which they begin degrading the bone matrix (Lacombe, Karsenty, and Ferron, 2013; Smith, 2020).

Osteoblasts differentiate from precursors of mesenchymal origin through various differentiation pathways activated by growth factors and signaling proteins such as bone morphogenic protein 2 (BMP-2) and transforming growth factor B (TGF-ß), among others. Pre-osteoblasts migrate to the site of bone resorption, where they become fully functioning osteoblasts capable of depositing new bone matrix (Donaubauer et al., 2020). Osteoblasts will synthesize and secrete bone matrix, most importantly collagen, and participate in the mineralization of bone to regulate the balance of calcium and phosphate ions in bone. Key molecular components involved in bone formation are alkaline phosphatase (ALP), osteocalcin (OCN), and procollagen type I C- and N-terminal propeptides (PICP and PINP), among others (Chen, Deng, and Ling, 2012; Rowe et al., 2021).

How It Is Measured or Detected

A description of the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements.These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA). Do not provide detailed protocols. More help

Listed below are common methods for detecting the KE; however, there may be other comparable methods that are not listed.

Markers of Osteoblast differentiation and activity:

Method(s) of Measurement	References	Description / Marker	OECD-Approved Assay
L-type Wako ALP J2 assay  Iso-ALP assay   Tandem-R Ostase assay  Alkphase-B assay	Abe et al., 2019    Calvo, Eyre, and Gundberg, 1996	These assays measure a mineralization protein produced by osteoblasts, Alkaline phosphatase (ALP).	No
Tandem-MP Ostase immunoassay	Broyles et al., 1998	This assay measures a mineralization protein produced by osteoblasts, bone-specific alkaline phosphatase (BAP)	No
Bovine assays: Ostk-PR assay  NovoCalcin assay  Human assays: OSCAtest osteocalcin assay  Intact osteocalcin assay  ELISA-OST-NAT assay  ELIS-OSTEO assay  Mid-Tact osteocalcin assay	Calvo, Eyre, and Gundberg, 1996	These assays measure a mineralization protein produced by osteoblasts, osteocalcin (OCN).	No
Procollagen PICP assay  Prolagen-C assay	Calvo, Eyre, and Gundberg, 1996	Type I collagen (COL1A1 gene) is the most common form of collagen found in bone. During osteoblastic collagen production and processing, procollagen type I N-terminal peptide (PINP) and procollagen I C-terminal (PICP) are generated and released into the bloodstream.	No
Proliferation assay:  Bromodeoxyuridine (BrdU) labelling	Bodine and Komm, 2006	Measures cell proliferation.	No
Osteoblast numbers and surface	Willey et al., 2011	Osteoblast formation can be determined by comparing the number of osteoblasts before and after a stressor in cell culture and histological bone samples.	No
Alizarin red stain for calcium deposition	Huang et al., 2019	Alizarin red staining can be used to visualize calcified elements of the bone, the final step of osteoblastic bone formation and mineralization activity.	No

Markers of Osteoclast differentiation and activity: 

Method(s) of Measurement	References	Description / Marker	OECD-Approved Assay
BoneTRAP assay	Calvo, Eyre, and Gundberg, 1996   Wu et al., 2009	Measures tartrate-resistant acid phosphatase (TRAP), an osteoclast specific bone-resorbing molecule.	No
Pirijinorin ICTP via RIA2 antibody assay   ICTP assay  Crosslap assay  CTX assays	Abe et al., 2019 Calvo, Eyre, and Gundberg, 1996 Seibel, 2005	Measures C-terminal type I collagen telopeptide (ICTP or CTX), a product of bone collagen degradation.	No
Osteomark Ntx urine or serum ELISA assay NTX assays	Calvo, Eyre, and Gundberg, 1996 Seibel, 2005	Measures N-terminal type I collagen telopeptide (NTX), a product of bone collagen degradation.	No
Colorimetric assays  HPLC-UV  Hypronosticon assay	Calvo, Eyre, and Gundberg, 1996	Measures hydroxyproline, a product of bone collagen degradation.	No
HPLC  ELISA	Seibel, 2005	Measures hydroxylysine glycosides, products of bone collagen degradation.   Hydroxylysine glycosides include:  Galactosyl hydroxylysine (GHYL or GHL)  Glycosyl-galactosyl-hydroxylysine (GGHL)	No
Pyrilinks assay  Pyrilinks D assay  Total Dpy assay  Free Dpy assay	Seibel, 2005	Measures deoxypyridinoline (dpy), a product of bone collagen degradation.	No
Immunocytochemical assays for cathepsin K	Seibel, 2005	Measures cathepsin K, a collagen cleaving molecule.	No
Immunoassays for non-collagenous matrix proteins	Seibel, 2005	Non-collagenous matrix proteins, such as bone sialoprotein (BSP), osteonectin, osteopontin, and matrix gla protein (MGP) can be measured via immunoassays. Changes in the amount of non-collagenous matrix proteins before and after a stressor indicate alterations in bone formation.	No
Osteoclast numbers and surface	Willey et al., 2011	Osteoclast formation can be determined by comparing the number of osteoclasts before and after a stressor.	No

Domain of Applicability

A description of the scientific basis for the indicated domains of applicability and the WoE calls (if provided). More help

Taxonomic applicability: Altered bone cell homeostasis is applicable to all vertebrates such as humans, mice, and rats (Donaubauer et al., 2020; Smith, 2020).

Life stage applicability: There is insufficient data on life stage applicability of this KE.

Sex applicability: Osteoblast/osteoclastogenesis is sexually dimorphic and influenced by genetic factors (Lorenzo J. 2020; Zanotti et al., 2014; Steppe et al., 2022; Mun et al., 2021).

Evidence for perturbation by a stressor: Multiple studies show that bone cell homeostasis can be disrupted by many types of stressors including ionizing radiation and altered gravity (Donaubauer et al., 2020; Smith, 2020).

References

List of the literature that was cited for this KE description. More help

Abe, Y., et al. (2019), “Increase in Bone Metabolic Markers and Circulating Osteoblast-Lineage Cells after Orthognathic Surgery”, Scientific Reports, Vol. 9, Nature, https://doi.org/10.1038/s41598-019-56484-x.

Bodine, P. V. N., and B. S. Komm (2006), “Wnt Signaling and Osteoblastogenesis”, Reviews in Endocrine and Metabolic Disorders, Vol. 7, Nature, https://doi.org/10.1007/s11154-006-9002-4. 

Broyles, D. L., et al. (1998), “Analytical and Clinical Performance Characteristics of Tandem-MP Ostase, a New Immunoassay for Serum Bone Alkaline Phosphatase”, Clinical Chemistry, Vol. 44/10, Oxford University Press, Oxford, https://doi.org/10.1093/clinchem/44.10.2139. 

Calvo, M. S., D. R. Eyre, and C. M. Gundberg (1996), “Molecular Basis and Clinical Application of Biological Markers of Bone Turnover”, Endocrine Reviews, Vol. 17, Oxford University Press, Oxford, https://doi.org/10.1210/edrv-17-4-333

Chen, G., C. Deng, and Y.-P. Ling (2012), “TGF-ß and BMP signaling in osteoblast differentiation and bone formation”, International Journal of Biological Sciences. Vol. 8/2, Ivyspring International Publisher, https://doi.org/10.7150/ijbs.2929

Donaubauer, A., et al. (2020), “The Influence of Radiation on Bone and Bone cells – Differential Effects on Osteoclasts and Osteoblasts”, International Journal of Molecular Sciences, Vol. 21/17, MDPI, Basel, https://doi.org/10.3390/ijms21176377

Huang, B. et al. (2019), “Amifostine Suppresses the Side Effects of Radiation on BMSCs by Promoting Cell Proliferation and Reducing ROS Production”, Stem cells international, Vol. 2019, Hindawi, https://doi.org/10.1155/2019/8749090

Lacombe, J., G. Karsenty, and M. Ferron (2013), “Regulation of Lysosome Biogenesis and Functions in Osteoclasts”, Cell Cycle, Vol. 12/17, Informa, London, https://doi.org/10.4161/cc.25825

Lorenzo J. (2020), “Sexual Dimorphism in Osteoclasts” Cells, 9(9), 2086. https://doi.org/10.3390/cells9092086

Mun, S. H. et al., (2021) “Sexual Dimorphism in Differentiating Osteoclast Precursors Demonstrates Enhanced Inflammatory Pathway Activation in Female Cells” Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research, 36(6), 1104–1116. https://doi.org/10.1002/jbmr.4270

Rowe, P., A. Koller, and S. Sharma (Updated January 2022), “Physiology, Bone Remodeling”, StatPearls Publishing, www.ncbi.nlm.nih.gov/books/NBK499863/

Seibel, M. J. (2005), “Biochemical Markers of Bone Turnover: Part I: Biochemistry and Variability”, The Clinical Biochemist Reviews, Vol. 26/4, pp. 97–122. 

Smith, J.K. (2020), “Osteoclasts and Microgravity”, Life, Vol. 10/9, MDPI, Basel, https://doi.org/10.3390/life10090207

Steppe, L. et al., (2022) "Bone Mass and Osteoblast Activity Are Sex-Dependent in Mice Lacking the Estrogen Receptor α in Chondrocytes and Osteoblast Progenitor Cells" International Journal of Molecular Sciences 23, no. 5: 2902. https://doi.org/10.3390/ijms23052902

Willey, J. S. et al. (2011), "Space Radiation and Bone Loss", Gravitational and space biology bulletin, Vol. 25/1, pp. 14-21.

Wu, Y., et al. (2009), “Tartrate-Resistant Acid Phosphatase (TRACP 5b): A Biomarker of Bone Resorption Rate in Support of Drug Development: Modification, Validation and Application of the BoneTRAP® Kit Assay”, Journal of Pharmaceutical and Biomedical Analysis, Vol. 49/5, Elsevier, Amsterdam, https://doi.org/10.1016/j.jpba.2009.03.002.

Zanotti, S. et al., (2014) “Sex and genetic factors determine osteoblastic differentiation potential of murine bone marrow stromal cells” PloS one, 9(1), e86757. https://doi.org/10.1371/journal.pone.0086757