Assessing the neurotoxicity of airborne nano-scale particulate matter in human iPSC-derived neurons using a transcriptomics benchmark dose model

Airborne nano-scale particulate matter (nPM) exposure is a risk factor for neurological diseases. However, to date, there has been no comprehensive evaluation of ambient nPM's neurotoxicity. We examined the toxic effects of nPM on human neurons derived from induced pluripotent stem cells (iPSCs) at doses ranging from 0 to 200 μg/mL, and employed whole-genome RNA-sequencing in different dose groups to gain further insight into the neurotoxicity of ambient nPM. Our findings showed that nPM was absorbed by neurons, and induced a variety of toxic effects. The apical benchmark dose lower confidence bound (aBMDL) values of each effect endpoint were ranked as follows, in ascending order: mitochondrial membrane potential, neurite length, early apoptosis, cell viability. BMD analysis based on transcriptomic data revealed that the point of departure (PoD) of the 20 pathways with the lowest p-values (0.75 μg/mL), the top 20 upstream regulators (0.79 μg/mL) and the neurological diseases (0.77 μg/mL) could be appropriate for nPM neurotoxicity evaluation. The transcriptomic PoDs (tPoDs) were similar to apical PoDs (aPoDs) since their absolute fold differences were within 10-fold. Further analysis of the transcriptomic data revealed that nPM exposure could disturb the pathways related to ferroptosis, neurotransmitters, xenobiotic metabolism, etc., which might be critical in regulating nPM neurotoxicity. We also found that low-dose nPM induced cytokine signaling pathways, while high doses of nPM activated cell-cycle regulation and DNA repair pathways. Our results indicate that BMD modeling based on transcriptomic data could be useful in illustrating the neurotoxic mechanism, and also could be a promising method for evaluating the potential health risks of nPM.