This Key Event Relationship is licensed under the Creative Commons BY-SA license. This license allows reusers to distribute, remix, adapt, and build upon the material in any medium or format, so long as attribution is given to the creator. The license allows for commercial use. If you remix, adapt, or build upon the material, you must license the modified material under identical terms.

Relationship: 3113

Title

A descriptive phrase which clearly defines the two KEs being considered and the sequential relationship between them (i.e., which is upstream, and which is downstream). More help

RAR agonism leads to Decreased proliferation of cortical NPCs

Upstream event

The causing Key Event (KE) in a Key Event Relationship (KER). More help

RAR agonism

Downstream event

The responding Key Event (KE) in a Key Event Relationship (KER). More help

Decreased proliferation of cortical NPCs

Key Event Relationship Overview

The utility of AOPs for regulatory application is defined, to a large extent, by the confidence and precision with which they facilitate extrapolation of data measured at low levels of biological organisation to predicted outcomes at higher levels of organisation and the extent to which they can link biological effect measurements to their specific causes.Within the AOP framework, the predictive relationships that facilitate extrapolation are represented by the KERs. Consequently, the overall WoE for an AOP is a reflection in part, of the level of confidence in the underlying series of KERs it encompasses. Therefore, describing the KERs in an AOP involves assembling and organising the types of information and evidence that defines the scientific basis for inferring the probable change in, or state of, a downstream KE from the known or measured state of an upstream KE. More help

AOPs Referencing Relationship

AOP Name	Adjacency	Weight of Evidence	Quantitative Understanding	Point of Contact	Author Status	OECD Status
Retinoic acid receptor agonism during neurodevelopment leading to impaired learning and memory	non-adjacent	Moderate	Not Specified	Diana Lupu (send email)	Under development: Not open for comment. Do not cite
Retinoic acid receptor agonism during neurodevelopment leading to microcephaly	non-adjacent	Moderate	Not Specified	Diana Lupu (send email)	Under development: Not open for comment. Do not cite

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 KER.In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER. More help

Term	Scientific Term	Evidence	Link
Homo sapiens	Homo sapiens	Moderate	NCBI

Sex Applicability

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

Life Stage Applicability

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

Term	Evidence
During brain development	High

Key Event Relationship Description

Provides a concise overview of the information given below as well as addressing details that aren’t inherent in the description of the KEs themselves. More help

Evidence Collection Strategy

Include a description of the approach for identification and assembly of the evidence base for the KER. For evidence identification, include, for example, a description of the sources and dates of information consulted including expert knowledge, databases searched and associated search terms/strings. Include also a description of study screening criteria and methodology, study quality assessment considerations, the data extraction strategy and links to any repositories/databases of relevant references.Tabular summaries and links to relevant supporting documentation are encouraged, wherever possible. More help

A systematic search was performed in PubMed database. Search and acquisition dates: July 2023

Search terms: neuronal progenitor AND proliferation AND retinoic acid;

Search returned 121 results, Screened abstracts: 63

Exclusion criteria: proliferation at any postnatal stage, proliferation in carcinoma-derived cells (dysregulated cell cycle), proliferation of neuroblastoma cells (are carcinomas and often extracranial in origin), proliferation of non-neuronal progenitors

Evidence Supporting this KER

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help

Biological Plausibility

Addresses the biological rationale for a connection between KEupstream and KEdownstream. This field can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured. More help

Rara and Rarb are co-expressed in the developing mouse telencephalon, particularly in the corpus striatum, hippocampus and cortex (Ruberte et al., 1993; Yamagata et al., 1994), and exposure to retinoids during prenatal development can lead to microcephaly in humans (Lammer et al., 1985), rodents (Colakoğlu and Kükner, 2004; Shenefelt, 1972; Irving et al., 1986), zebrafish (Herrmann, 1995) and Xenopus (Durston et al., 1989). Furthermore, active transcriptional repression mediated by unligated RARs is necessary for correct specification of anterior structures, including the forebrain (Niederreither and Dollé, 2008). As evidenced by studies in Xenopus laevis, RAR activation during early neurodevelopment leads to anterior truncations. Expressing a dominant-negative co-repressor, which inhibits RAR-mediated transcriptional repression, or reducing RARα protein with morpholino antisense oligonucleotides, results in neurodevelopmental defects that parallel those caused by excess RA (Koide et al., 2001). Later on, active RAR signalling instructs corticogenesis, through an atRA gradient secreted from the meninges (Siegenthaler et al., 2009).

Empirical Evidence

Provides specific (citable) evidence that supports the idea of a change in the upstream KE (KEupstream) leading to, or being associated with, a subsequent change in the downstream KE (KEdownstream), assuming the perturbation of KEupstream is sufficient. More help

Current evidence suggests that activation of RAR reduces proliferation of human cortical NPCs (Koch et al., manuscript in preparation; Culbreth et al., 2012). Data regarding the effects of RAR agonism on cortical NPC proliferation in other species is lacking, although a few studies suggest that proliferation of various populations of neural progenitors may also be negatively affected by exposure to RAR agonists in rat (Goncalves et al, 2009), mouse (Kim et al., 2009; Wohl and Weiss, 1998), chicken (Salvarezza and Rovasio, 1997), zebrafish (Kinikoglu et al., 2014), and xenopus (Janesick et al., 2013).

RAR activation using atRA reduces human cortical NPC proliferation in cultured NPCs (Nestin and Sox2-positive) derived from cortices of 16- to 19-week old fetuses (Koch et al., manuscript in preparation). This Neurosphere Assay for the assessment of NPC proliferation through BrdU incorporation (called NPC1) was developed and scientifically validated at the Leibniz Research Institute for Environmental Medicine (Koch et al., 2022). The NPC1 assay is part of the developmental neurotoxicity in vitro test battery under consideration by the OECD and EFSA (Fritsche et al., 2017; Masjosthusmann et al., 2020; Sachana et al., 2021).

Another study showing decreased proliferation upon exposure to atRA of human NPC cells has used the ReNcell CX (ReN CX) model (Culbreth et al., 2012). Nestin- and Sox2-positive ReN CX cells, which are immortalised human neural progenitors obtained from 14-week fetal cortex (Donato et al., 2007), were exposed to 1-30 μM atRA for 24 hours and proliferation was assessed through a BrdU incorporation assay. The authors reported that 30 μM atRA was the threshold concentration observed to induce at least a 50% decrease in BrdU incorporation (Culbreth et al., 2012).

It is not yet established which RAR isotype is responsible for mediating the reduction in cortical NPC proliferation, but there is some indication that RARα mediates this effect in forebrain progenitors. Goncalves et al., showed that selective activation of RARα in cultured rat fetal forebrain NPCs decreases proliferation, whereas activation of RARβ increases NPC proliferation, as assessed using ki67 staining (Goncalves et al, 2009).

Uncertainties and Inconsistencies

Addresses inconsistencies or uncertainties in the relationship including the identification of experimental details that may explain apparent deviations from the expected patterns of concordance. More help

Known modulating factors

This table captures specific information on the MF, its properties, how it affects the KER and respective references.1.) What is the modulating factor? Name the factor for which solid evidence exists that it influences this KER. Examples: age, sex, genotype, diet 2.) Details of this modulating factor. Specify which features of this MF are relevant for this KER. Examples: a specific age range or a specific biological age (defined by...); a specific gene mutation or variant, a specific nutrient (deficit or surplus); a sex-specific homone; a certain threshold value (e.g. serum levels of a chemical above...) 3.) Description of how this modulating factor affects this KER. Describe the provable modification of the KER (also quantitatively, if known). Examples: increase or decrease of the magnitude of effect (by a factor of...); change of the time-course of the effect (onset delay by...); alteration of the probability of the effect; increase or decrease of the sensitivity of the downstream effect (by a factor of...) 4.) Provision of supporting scientific evidence for an effect of this MF on this KER. Give a list of references. More help

Quantitative Understanding of the Linkage

Captures information that helps to define how much change in the upstream KE, and/or for how long, is needed to elicit a detectable and defined change in the downstream KE. More help

Response-response Relationship

Provides sources of data that define the response-response relationships between the KEs. More help

Time-scale

Information regarding the approximate time-scale of the changes in KEdownstream relative to changes in KEupstream (i.e., do effects on KEdownstream lag those on KEupstream by seconds, minutes, hours, or days?). More help

Known Feedforward/Feedback loops influencing this KER

Define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits. More help

Domain of Applicability

A free-text section of the KER description that the developers can use to explain their rationale for the taxonomic, life stage, or sex applicability structured terms. More help

References

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

1. Ruberte E, Friederich V, Chambon P, Morriss-Kay G. Retinoic acid receptors and cellular retinoid binding proteins. III. Their differential transcript distribution during mouse nervous system development. Development. 1993;118(1):267-82.

2. Yamagata T, Momoi MY, Yanagisawa M, Kumagai H, Yamakado M, Momoi T. Changes of the expression and distribution of retinoic acid receptors during neurogenesis in mouse embryos. Brain Res Dev Brain Res. 1994;77(2):163-76.

3. Lammer EJ, Chen DT, Hoar RM, Agnish ND, Benke PJ, Braun JT, et al. Retinoic acid embryopathy. N Engl J Med. 1985;313(14):837-41.

4. Colakoğlu N, Kükner A. Teratogenicity of retinoic acid and its effects on TGF-beta2 expression in the developing cerebral cortex of the rat. J Mol Histol. 2004;35(8-9):823-7.

5. Shenefelt RE. Morphogenesis of malformations in hamsters caused by retinoic acid: relation to dose and stage at treatment. Teratology. 1972;5(1):103-18.

6. Irving DW, Willhite CC, Burk DT. Morphogenesis of isotretinoin-induced microcephaly and micrognathia studied by scanning electron microscopy. Teratology. 1986;34(2):141-53.

7. Herrmann K. Teratogenic effects of retinoic acid and related substances on the early development of the zebrafish (Brachydanio rerio) as assessed by a novel scoring system. Toxicol In Vitro. 1995;9(3):267-83.

8. Durston AJ, Timmermans JP, Hage WJ, Hendriks HF, de Vries NJ, Heideveld M, et al. Retinoic acid causes an anteroposterior transformation in the developing central nervous system. Nature. 1989;340(6229):140-4.

9. Niederreither K, Dollé P. Retinoic acid in development: towards an integrated view. Nat Rev Genet. 2008;9(7):541-53.

10. Koide T, Downes M, Chandraratna RA, Blumberg B, Umesono K. Active repression of RAR signaling is required for head formation. Genes Dev. 2001;15(16):2111-21.

11. Siegenthaler JA, Ashique AM, Zarbalis K, Patterson KP, Hecht JH, Kane MA, et al. Retinoic acid from the meninges regulates cortical neuron generation. Cell. 2009;139(3):597-609.

12. Culbreth ME, Harrill JA, Freudenrich TM, Mundy WR, Shafer TJ. Comparison of chemical-induced changes in proliferation and apoptosis in human and mouse neuroprogenitor cells. Neurotoxicology. 2012;33(6):1499-510.

13. Goncalves MB, Agudo M, Connor S, McMahon S, Minger SL, Maden M, et al. Sequential RARbeta and alpha signalling in vivo can induce adult forebrain neural progenitor cells to differentiate into neurons through Shh and FGF signalling pathways. Dev Biol. 2009;326(2):305-13.

14. Kim M, Habiba A, Doherty JM, Mills JC, Mercer RW, Huettner JE. Regulation of mouse embryonic stem cell neural differentiation by retinoic acid. Dev Biol. 2009;328(2):456-71.

15. Wohl CA, Weiss S. Retinoic acid enhances neuronal proliferation and astroglial differentiation in cultures of CNS stem cell-derived precursors. J Neurobiol. 1998;37(2):281-90.

16. Salvarezza SB, Rovasio RA. Exogenous retinoic acid decreases in vivo and in vitro proliferative activity during the early migratory stage of neural crest cells. Cell Prolif. 1997;30(2):71-80.

17. Kinikoglu B, Kong Y, Liao EC. Characterization of cultured multipotent zebrafish neural crest cells. Exp Biol Med (Maywood). 2014;239(2):159-68.

18. Janesick A, Abbey R, Chung C, Liu S, Taketani M, Blumberg B. ERF and ETV3L are retinoic acid-inducible repressors required for primary neurogenesis. Development. 2013;140(15):3095-106.

19. Koch K, Bartmann K, Hartmann J, Kapr J, Klose J, Kuchovská E, et al. Scientific Validation of Human Neurosphere Assays for Developmental Neurotoxicity Evaluation. Front Toxicol. 2022;4:816370.

20. Fritsche E, Crofton KM, Hernandez AF, Hougaard Bennekou S, Leist M, Bal-Price A, et al. OECD/EFSA workshop on developmental neurotoxicity (DNT): The use of non-animal test methods for regulatory purposes. ALTEX. 2017;34(2):311-5.

21. Masjosthusmann S, Blum J, Bartmann K, Dolde X, Holzer A-K, Stürzl L-C, et al. Establishment of an a priori protocol for the implementation and interpretation of an in-vitro testing battery for the assessment of developmental neurotoxicity. EFSA Supporting Publications. 2020;17(10):1938E.

22. Sachana M, Shafer TJ, Terron A. Toward a Better Testing Paradigm for Developmental Neurotoxicity: OECD Efforts and Regulatory Considerations. Biology (Basel). 2021;10(2).

23. Donato R, Miljan EA, Hines SJ, Aouabdi S, Pollock K, Patel S, et al. Differential development of neuronal physiological responsiveness in two human neural stem cell lines. BMC Neurosci. 2007;8:36.