Chronic exposure to titanium dioxide nanoparticles induces deficits of locomotor behavior by disrupting the development of NMJ in Drosophila

Titanium dioxide nanoparticles (TiO2 NPs) are widely used in several consumer products. However, because of their neurotoxic nature, exposure to TiO2 NPs could impair locomotor behavior. Whether the impairment in locomotor behavior caused by TiO2 NPs exposure is sustained and the effects is gender-specific has remained elusive, warranting further studies to elucidate the underlying mechanisms. Thus, we established a Drosophila model to study the effects of chronic TiO2 NPs exposure on the locomotor behavior of Drosophila in different generations and explore the underlying mechanisms. Chronic TiO2 NPs exposure caused accumulation of Ti in the body and affected the life history traits of Drosophila. Furthermore, chronic exposure to TiO2 NPs decreased the total crawling distance of larvae and the total movement distance of adult males in the F3 generation, indicating the damage caused to the locomotor behavior of Drosophila. Impaired neuromuscular junction (NMJ) morphology was observed, manifested by the reduced number of boutons, size of boutons, and branch length of NMJ. In addition, several differentially expressed genes (DEGs) related to NMJ development were selected by RNA sequencing and their expression was confirmed by quantitative real-time-polymerase chain reaction (qRT-PCR). Compared with the control group, the gene expression of Cyp6a17, frac, and kek2 in the TiO2 NPs exposure group decreased, whereas that of Gba1a, Hll and List was elevated. These findings indicated that chronic TiO2 NPs exposure damage the morphology of NMJ by altering the expression of genes related to NMJ development, consequently causing locomotor behavior deficits in Drosophila.