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.
To investigate potential species-specific differences, we employed comparative in vitro test systems for brain development based on neurosphere cultures from human and mouse neural progenitor cells (hNPCs and mNPCs, respectively).
Both hNPCs and mNPCs were cultured in proliferation medium [DMEM and Hams F12 (3:1) supplemented with B27 (Invitrogen GmBH, Karlsruhe, Germany), 20 ng/mL epidermal growth factor (EGF; Biosource, Karlsruhe, Germany), 20 ng/mL recombinant human fibroblast growth factor (FGF; R&D Systems, Wiesbaden-Nordenstadt, Germany), 100 U/mL penicillin, and 100 [micro]g/ml.
AhR agonism or antagonism does not cause cytotoxicity in hNPCs and mNPCs. Cells were exposed to the AhR agonists 3-MC (10 [micro]M; a synthetic model compound for AhR-activating metabolized PAH), B(a)P (10 [micro]M; a metabolized, environmentally relevant PAH), TCDD (1 nM; a nonmetabolized, environmentally relevant PAH), or the AhR antagonist MNF (1 [micro]M; model compound).
Proliferation of mNPCs, but not hNPCs, is inhibited by AhR blockage.
We monitored proliferation of mNPCs over only 7 days because of a size-restricted halt in sphere growth beyond that time.
Neural cell migration is affected by AhR stimulation in mNPCs but not hNPCs.
In contrast to the results in hNPCs, AhR activation reduced migration distance in wild-type mNPCs by 16% [+ or -] 5% (1 [micro]M 3-MC), 21% [+ or -] 13% (10 [micro]M 3-MC), and 32% [+ or -] 10% [10 [micro]M B(a)P] compared with solvent controls, whereas migration was comparable with controls after exposure to the AhR antagonist MNF (Figure 2B,D).
AhR-dependent gene transcription is inducible only in mNPCs, and not in hNPCs because of low abundance of AhR and ARNT transcripts and absence of AhR protein in human cells.
Comparison of mRNA expression levels between hNPCs and mNPCs showed that genes belonging to the AhR machinery and AhR-dependent genes were generally expressed in higher copy numbers/1,000 copies [beta]-actin in mNPCs than in hNPCs (Table 1).
Specifically, in this study we discovered that proliferation of hNPCs was not affected by AhR agonists (3-MC, TCDD) or the AhR antagonist MNF (Figure 1A-C), whereas proliferation of wild-type mNPCs was completely blocked by AhR antagonism (Figure ID-F).
In contrast to hNPCs, proliferation of mNPCs was completely blocked by MNF (Figure 1D-F).