Benzo[a]pyrene-induced AHR activation in human ESCs primes premature neurogenesis in cerebral organoids

Benzo[a]pyrene (BaP), a representative polycyclic aromatic hydrocarbon (PAH), is a widespread environmental toxicant and potent ligand of the aryl hydrocarbon receptor (AHR). Yet, how early developmental exposure to BaP influences human neurodevelopment remains poorly understood. To identify an appropriate exposure window, we characterized AHR expression during human embryonic stem cell (ESC)-derived cerebral organoid development and observed the highest expression at the ESC stage, followed by a decline during subsequent differentiation, highlighting the ESC stage as a potentially vulnerable stage for AHR-mediated environmental perturbation. Based on this observation, ESCs were exposed to BaP (0.1, 1 μM) for 7 days prior to organoid generation. BaP exposure did not alter pluripotency, proliferation, cell death, or global transcription of ESCs but increased expression of a subset of AHR target genes. Remarkably, however, organoids derived from BaP-exposed ESCs exhibited profound morphological defects resulting from premature neurogenesis, characterized by disrupted neural rosette organization, reduced EOMES⁺ intermediate progenitors, and increased BCL11B⁺ neurons. Pharmacological inhibition of AHR with CH-223191 attenuated AHR activation and rescued the progenitor-neuron imbalance. These findings identify AHR signaling as a critical upstream mediator of BaP-induced developmental neurotoxicity and highlight the vulnerability of early pluripotent stages to environmental insults.