The Constituent-Dependent Translocation Mechanism for PM to Travel through the Olfactory Pathway.

The neurotoxic risk of PM is of worldwide concern, but the pathways through which PM gets to the central nervous system are still under debate. The olfactory pathway provides a promising shortcut to the brain, which bypasses the blood-brain barrier for PM. However, direct evidence is lacking, and the translocation mechanism is still unclear. This study used the primary murine olfactory sensory neurons (OSNs) as an model to explore the translocation mechanism of PM in the olfactory system. We found that PM can be internalized into the OSNs via vesicle transportation. This process responds only to the water-insoluble compositions of PM (WIS-PM) and cannot be affected by the water-soluble compositions of PM (WS-PM). PM can further disrupt the integrity of the barrier constituted by the OSNs, and WS-PM plays a heightened role in inducing the damages. Our results suggested that both cellular and paracellular pathways are possibly involved in the translocation of PM in the olfactory system. More advanced microscopy techniques need to be developed to explore the whole translocation process in the olfactory-brain pathway in both and models.