JAK/STAT and TGF-ß activation as potential adverse outcome pathway of TiO₂NPs phototoxicity in Caenorhabditis elegans

Titanium dioxide nanoparticles (TiO₂NPs) are widely used nanoparticles, whose catalytic activity is mainly due to photoactivation. In this study, the toxicity of TiO₂NPs was investigated on the nematode Caenorhabditis elegans, with and without UV activation. Comparative analyses across the four treatments revealed that UV-activated TiO₂NPs led to significant reproductive toxicity through oxidative stress. To understand the underlying molecular mechanism, transcriptomics and metabolomics analyses were conducted, followed by whole-genome network-based pathway analyses. Differential expression analysis from microarray data revealed only 4 DEGs by exposure to TiO₂NPs alone, compared to 3,625 and 3,286 DEGs by UV alone and UV-activated TiO₂NPs, respectively. Pathway analyses suggested the possible involvement of the JAK/STAT and TGF-ß pathways in the phototoxicity of TiO₂NPs, which correlated with the observation of increased gene expression of those pathways. Comparative analysis of C. elegans response across UV activation and TiO₂NPs exposure was performed using loss-of-function mutants of genes in these pathways. Results indicated that the JAK/STAT pathway was specific to TiO₂NPs, whereas the TGF-ß pathway was specific to UV. Interestingly, crosstalk between these pathways was confirmed by further mutant analysis. We consider that these findings will contribute to understand the molecular mechanisms of toxicity of TiO₂NPs in the natural environment.