On the axonal transport of lipid nanoparticles in primary hippocampal neurons

Axonal transport is a crucial process in healthy neurons as it supports the intra-cellular movement of nutrients, endogenous substances, and vesicles regulating a broad set of biological functions. Notably, this physiological mechanism is efficiently exploited by a variety of viruses to infect multiple cells within the central nervous system and, thus, it has been proposed as a strategy to enhance the brain penetrance of macromolecules and nanoparticles. In this work, the retrograde and anterograde transport of lipid nanoparticles (LNP) is systematically analyzed in primary hippocampal neurons cultured in compartmentalized microfluidic chips, where neurites are left to grow within 150 μm-long channels connecting the somal and synaptic compartments. After characterizing the physico-chemical properties, toxicological profile, and cell internalization efficiency, the axonal trafficking of fluorescently labeled LNP was monitored over time via live-cell microscopy. Both naïve LNP and apolipoprotein E-coated LNP (ApoE-LNP) were considered under two different experimental configurations, with the LNP being either added to the somal or the synaptic compartment for anterograde or retrograde transport analyses, respectively. ApoE-LNP only were very efficiently uptaken by neurons and rapidly relocated in a perinuclear position. Also, ApoE-LNP incubated in the somal compartment did not translocate along the neurites (null anterograde transport), whereas ApoE-LNP added to the synaptic compartment were detected near the soma already at 30 min post incubation demonstrating retrograde transport velocities up to ∼ 160 nm/s. This preliminary study suggests that ApoE-LNP could be efficiently used to rapidly transport a variety of therapeutic and imaging cargos from the synaptic cleft to the somal compartment.