A Comprehensive Approach to Advance Hazard Assessments for Retinoid Signaling Disruption

Audrey Xuan Anh Phan, Ph.D.

Disertační práce

Abstract:

The growing production and use of chemicals pose an increasing challenge for environmental risk assessment, as current European frameworks struggle to keep pace with the scale and diversity of substances requiring evaluation. Among emerging pollutants, endocrine disrupting chemicals (EDCs) are of particular concern. While regulatory test guidelines focus namely on major endocrine pathways such as estrogen, androgen, thyroid, and steroidogenesis, assessment of retinoid signaling disruption remain limited, despite its essential role in embryonic development and its potential to cause teratogenic and neurodevelopmental effects. This thesis addresses this gap by developing an Adverse Outcome Pathway (AOP) for retinoid signaling disruption during early development with the zebrafish as a model organism. The research has three main objectives: (1) to establish empirical evidence linking retinoid-induced morphological defects to life-history traits relevant for population-level impacts; (2) to characterize receptor-specific contributions to developmental toxicity, including crosstalk with other endocrine pathways; and (3) to identify cellular and molecular key events underlying neural crest cell disruption as a driver of diverse teratogenic outcomes. To achieve these objectives, I conducted experimental studies across multiple biological levels in zebrafish, i.e., from molecular and cellular processes to organismal traits, to strengthen key event relationships, identify critical key events, and provide mechanistic anchors for hazard assessment. Across three studies, this work advances the mechanistic understanding of retinoid disruption. Study I developed an AOP network linking retinoic acid receptor (RAR) overactivation to organismal and population-level outcomes, supported by quantitative dose–response and sensitivity data. Study II experimentally validated RAR/RXR overactivation as the initiating event of multiple malformations, revealed a permissive role of RXR in retinoid-mediated toxicity, and identified the pesticide diclazuril as a novel RAR antagonist. Study III identified impaired neural crest cell migration as a central key event connecting molecular disruption to teratogenic outcomes and mapped associated biological processes and gene networks. Collectively, these findings contribute three major advances: (1) moving from descriptive teratogenicity toward mechanistically anchored AOPs; (2) refining receptor-specific roles in retinoid-mediated developmental toxicity; and (3) establishing impaired neural crest cell development as a unifying key event for multiple defects. By bridging molecular, cellular, organismal, and ecological scales, this thesis strengthens the biological basis for hazard assessment and underscores the urgent need to systematically integrate retinoid pathways into environmental risk assessment frameworks.

Keywords

AOP, teratogenicity, population-level outcomes, retinoic acid, ATRA, RAR, RXR, response-response relationship, craniofacial malformation, tail malformation, posterior swim bladder, eye malformation, neurodevelopmental toxicity, feeding, locomotion, survival

Jazyk práce: angličtina

Datum vytvoření / odevzdání či podání práce: 20. 2. 2026

Obhajoba závěrečné práce

• Obhajoba proběhla 24. 4. 2026
• Vedoucí: doc. Mgr. Klára Hilscherová, Ph.D.
• Oponent: Henrik Holbech, PhD, Prof. Dries Knapen, PhD

Masarykova univerzita

Přírodovědecká fakulta

Doktorský studijní program / obor:
Environmental Health Sciences / Environmental chemistry and toxicology