Species-Specific Differential AhR Expression Protects Human Neural Progenitor Cells against Developmental Neurotoxicity of PAHs

BACKGROUND: Because of their lipophilicity, persistent organic pollutants (POPs) cross the human placenta, possibly affecting central nervous system development. Most POPs are known aryl hydrocarbon receptor (AhR) ligands and activators of AhR signaling. Therefore, AhR activation has been suggested to cause develop-mental neurotoxicity (DNT). OBJECTIVE: We studied the effects of AhR ligands on basic processes of brain development in two comparative in vitro systems to determine whether AhR-activation is the underlying mechanism for reported DNT of POPs in humans. METHODS: We employed neurosphere cultures based on human neural progenitor cells (hNPCs) and wild-type and AhR-deficient mouse NPCs (mNPCs) and studied the effects of different AhR agonists [3-methylcholanthrene (3-MC), benzo(a) pyrene [B(a) P], and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)] and an antagonist [3'-methoxy-4'-nitroflavone (MNF)] on neurosphere development. Moreover, we analyzed expression of AhR and genes involved in AhR signaling. RESULTS: In contrast to wild-type mNPCs, hNPCs and AhR-deficient mNPCs were insensitive to AhR agonism or antagonism. Although AhR modulation attenuated wild-type mNPC proliferation and migration, hNPCs and AhR-deficient mNPCs remained unaffected. Results also suggest that species-specific differences resulted from non-functional AhR signaling in hNPCs. CONCLUSION: Our findings suggest that in contrast to wild-type mNPCs, hNPCs were protected against polycyclic aromatic hydrocarbon-induced DNT because of an absence of AhR. This difference may contribute to species-specific differences in sensitivity to POPs.