Retinoid signaling in skeletal development: Scoping the system for predictive toxicology

doi:10.1016/j.reprotox.2020.10.014

Reproductive Toxicology

Volume 99, January 2021, Pages 109-130

https://doi.org/10.1016/j.reprotox.2020.10.014 Get rights and content

Highlights

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Altered retinoic acid signaling thresholds can disrupt skeletal development.
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Midfacial, vertebral, and appendicular defects follow from FGF-WNT antagonism.
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Peak vulnerability coincides with regional patterning of skeletal rudiments.
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Many Adverse Outcome Pathways (AOPs) elucidated for predictive toxicology.
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This review supports an OECD Detailed Review Paper on assay development.

Abstract

All-trans retinoic acid (ATRA), the biologically active form of vitamin A, is instrumental in regulating the patterning and specification of the vertebrate embryo. Various animal models demonstrate adverse developmental phenotypes following experimental retinoid depletion or excess during pregnancy. Windows of vulnerability for altered skeletal patterning coincide with early specification of the body plan (gastrulation) and regional specification of precursor cell populations forming the facial skeleton (cranial neural crest), vertebral column (somites), and limbs (lateral plate mesoderm) during organogenesis. A common theme in physiological roles of ATRA signaling is mutual antagonism with FGF signaling. Consequences of genetic errors or environmental disruption of retinoid signaling include stage- and region-specific homeotic transformations to severe deficiencies for various skeletal elements. This review derives from an annex in Detailed Review Paper (DRP) of the OECD Test Guidelines Programme (Project 4.97) to support recommendations regarding assay development for the retinoid system and the use of resulting data in a regulatory context for developmental and reproductive toxicity (DART) testing.

Section snippets

Preface

All-trans retinoic acid (ATRA) is a conserved signal molecule during morphogenesis, growth and differentiation across diverse organ systems. This review of the literature derives from an annex in Detailed Review Paper (DRP) of the OECD Test Guidelines Programme (Project 4.97) that is intended to support recommendations regarding assay development to determine retinoid system toxicants for developmental and reproductive toxicity. Because mutations of the ATRA system tend to be disruptive of

Assessing prenatal developmental toxicity

Current developmental toxicity testing for regulatory purposes adheres largely to protocols suggested in 1966 involving the administration of test compound to pregnant laboratory animals. The skeleton is routinely examined in standard developmental toxicity bioassays (e.g., OECD 414) and has proven to be sensitive to a wide variety of chemical agents [3,4]. The fetal skeleton develops with >200 individual bones anatomically comprising an axial skeleton (vertebral column, ribs, skull) and paired

Overview of the retinoid signaling pathway

Retinoid signaling has a conserved ancestry from gastropods to humans [11]. Recent publications suggest that signaling by ATRA may be an ancestral feature of bilaterians rather than a chordate innovation; however, there is still no conclusive evidence showing that a retinoid is required for development of non-chordates [2].

ATRA is a metabolic derivative from dietary vitamin A, existing in isomers (9-cis, 13-cis, all trans). Apart from retinal, which is involved solely in the visual cycle, in

Altered ATRA signaling

Several lines of study have established functional evidence for retinoid signaling during pregnancy and development. One line of experimentation addresses the developmental consequences of retinoid deficiency, caused either by (i) dietary deficiency in vitamin A, (ii) inhibition of ATRA synthesis by functional inactivation of genes encoding retinaldehyde or alcohol dehydrogenases, (iii) administration of RALDH inhibitors, (iv) deletion of genes encoding RARs, or (v) administration of RAR

ATRA signaling in craniofacial development

Endogenous ATRA is essential for development of the facial bones and branchial arches. Craniofacial malformations induced by retinoid excess, including those of Cyp26(-/-) null mutant mice, have been linked to disruption of craniofacial mesenchyme primarily affecting the formation of bones in the midface. It may also be the case for the malformation of bones derived from the caudal branchial arches under conditions of ‘functional ATRA deficiency’ in RAR null mutant mice. Two migratory cell

Craniofacial teratogenesis

Many teratogenic effects described for exogenous retinoids in laboratory animal models and humans reflect alterations to tissues derived from cranial neural crest cells (CNCs) [61]. Clinical observations following isotretinoin (13-cisRA, Accutane) exposure during pregnancy in humans [62,63] and nonhuman primates [64] have shown a spectrum of malformations including craniofacial defects linked to hypoplasia of the 1st (mandibular) and 2nd (hyoid) branchial arches. Isotretinoin has a low affinity

ATRA signaling in vertebral development

Trunk organization in Vertebrata involves the establishment of a metameric primary body axis leading to formation of the neural tube and paraxial mesoderm (somites). ATRA signaling participates in the organization of both systems (neural tube, vertebral column) although only the vertebral system is considered here. The onset of ATRA signaling in the mouse embryo, based on expression of RDH10, RALDH2, is GD 7.5; however, ectopic or excessive retinoid signaling can disrupt three morphogenetic

Retinoids in Appendicular Development

The appendicular skeleton (upper and lower extremities in bipeds, forelimb and hindlimb in quadrupeds) is defined in three segments along the proximodistal axis: stylopod (humerus, femur), zeugopod (radius-ulna, tibia-fibula), and autopod (hand, foot). A secondary axis defines anterior-posterior asymmetry (e.g., digits I through V in mouse and humans) and a tertiary axis dorsal-ventral asymmetry. The rudimentary ‘limb-bud’ forms as outcroppings of the flank (forelimb bud, hindlimb bud) composed

Limb teratogenesis

Kochhar in 1973 was among the first to identify teratogenic effects of exogenous ATRA on the mouse limb, invoking dose-dependent phocomelia following a single dose in the range of 1- to 100 mg/kg the pregnant dam [127]. The window of vulnerability in mouse (GD 10–12) coincided with the formation of precartilaginous mesenchymal condensations. ATRA caused dose-dependent phocomelia and digital defects when administered to pregnant mice at 20- to 80 mg/kg on GD 11, where the deficiencies to

Adverse Outcome Pathway (AOP) framework

Performance-based models that address the regulation, homeostasis, and biological activity of the retinoid signaling pathway will be useful for predictive toxicology based on alternative (non-mammalian) tests. An AOP framework is necessary to organize the relevant data, information and knowledge on molecular initiating events (MIEs) reflecting a disruption in retinoid signaling at critical stages of gestation, and the ensuing cascade of key events (KEs) and their relationships (KERs) leading to

New Approach Methodologies (NAMs)

Opportunities exist for refining and supplanting current developmental toxicity testing protocols using in vitro data and in silico models in the design and review of revolutionary alternatives to animal testing by experts in the field, alongside their independent validation [241]. New Approach Methodologies (NAMs) is the term adopted as a broadly descriptive reference to any technology, methodology, approach, or combination thereof that can be used to provide information on chemical hazard and

Conclusions

This review underscores the importance of ATRA homeostasis to patterning and differentiation of the fetal skeleton. These pathways are complex and connected directly or indirectly to morphogenetic signaling. A critical role of ATRA signaling during gastrulation and early organogenesis influences regional specification and fate of precursor cell populations in the cranial neural crest, paraxial mesoderm, and lateral plate mesoderm. To date, no OECD test guidelines specifically capture the

Funding

This work was supported by the Chemical Safety for Sustainability (CSS) National Research Program, Virtual Tissue Models (CSS 5.3) project of the U.S. Environmental Protection Agency.

Disclaimer

The views expressed in this article are those of the authors and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

Disclosure

The authors contributed this work as an annex of OECD’s Detailed Review Paper on the retinoid system.

Conflict of interest

The authors declare no conflict of interest.

Declaration of Competing Interest

The authors report no declarations of interest.

Acknowledgements

The authors gratefully acknowledge helpful comments on the DRP draft annex from the following experts: John M. Rogers (US EPA, ORD/CPHEA), Paul C. Brown (US FDA, CDER), Amy C. Nostrandt (US FDA, CDER), Karen L. Hamernik (US EPA, OCSPP), Robert L. Sprando (US FDA, CFSAN), Bruce Blumberg (University of California Irvine, Dept. Developmental and Cell Biology), Shirlee W. Tan (Endocrine Society), Scott M. Belcher (North Carolina State University, Dept. Biological Sciences), Alice Baynes (Institute

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There are several potential non-EATS modalities and seven have been suggested to be of particular relevance to ED effects, including vitamin D, peroxisome proliferator-activated receptor (PPAR) signaling and retinoid signaling (OECD, 2012). The retinoid signaling pathway has received increased attention within chemical risk assessment and regulation in recent years, with emerging evidence suggesting the pathway to be vulnerable to endocrine disruptors and a likely contributor to human endocrine disorders (Grignard et al., 2020; Knudsen et al., 2020; Martyniuk et al., 2021; OECD, 2012). Retinoid signaling is essential for normal development and is involved in numerous processes from axial patterning to organogenesis and reproductive development.
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Published by Elsevier Inc.

Retinoid signaling in skeletal development: Scoping the system for predictive toxicology

Highlights

Abstract

Section snippets

Preface

Assessing prenatal developmental toxicity

Overview of the retinoid signaling pathway

Altered ATRA signaling

ATRA signaling in craniofacial development

Craniofacial teratogenesis

ATRA signaling in vertebral development

Retinoids in Appendicular Development

Limb teratogenesis

Adverse Outcome Pathway (AOP) framework

New Approach Methodologies (NAMs)

Conclusions

Funding

Disclaimer

Disclosure

Conflict of interest

Declaration of Competing Interest

Acknowledgements

Reprod. Toxicol.

Reprod. Toxicol.

Dev. Biol. (Basel)

Curr. Top. Dev. Biol.

Adv. Drug Deliv. Rev.

Mol. Cell. Endocrinol.

Am. J. Ophthalmol.

Curr. Top. Dev. Biol.

J. Biol. Chem.

Pharmacol. Ther.

Gene

J. Steroid Biochem. Mol. Biol.

J. Biol. Chem.

J. Lipid Res.

Cell

Cell

Dev. Biol. (Basel)

Ann. Anat.

J. Biol. Chem.

Mech. Dev.

Dev. Biol. (Basel)

Mech. Dev.

J. Steroid Biochem. Mol. Biol.

Dev. Biol. (Basel)

Dev. Biol. (Basel)

Dev. Biol. (Basel)

Dev. Biol. (Basel)

Dev. Biol. (Basel)

J. Biosci. Bioeng.

Dev. Biol. (Basel)

Curr. Top. Dev. Biol.

Mech. Dev.

Bone development

Annu. Rev. Cell Dev. Biol.

Retinoic acid signaling pathways

Development

Comparison of rat and rabbit embryo-fetal developmental toxicity data for 379 pharmaceuticals: on the nature and severity of developmental effects

Crit. Rev. Toxicol.

Retinoic acid synthesis and functions in early embryonic development

Cell Biosci.

Retinoic acid signalling during development

Development

The pleiotropic role of retinoic Acid/Retinoic acid receptors signaling: from vitamin a metabolism to gene rearrangements in acute promyelocytic leukemia

Int. J. Mol. Sci.

Cellular metabolism and actions of 13-cis-retinoic acid

J. Am. Acad. Dermatol.

An analysis of the syndrome of malformations induced by maternal vitamin A deficiency. Effects of restoration of vitamin A at various times during gestation

Am. J. Anat.

Vitamin A Absorption, Storage and Mobilization

Subcell. Biochem.

RAR/RXR-mediated signaling

Investigation of retinoic acid function during embryonic brain development using retinaldehyde-rescued Rdh10 knockout mice

Dev. Dyn.

Visualization of an endogenous retinoic acid gradient across embryonic development

Nature

Transcriptional factors mediating retinoic acid signals in the control of energy metabolism

Int. J. Mol. Sci.

Vitamin A receptors