Effects of Actin Filaments on NGF Retrograde Transport

Abstract

Actin filament is an essential component of the cell cytoskeletal system under the physiological conditions. In addition to their roles in supporting cell shape, actin filaments act as molecular tracks for myosin motors that are involved in the movement of organelles such as mitochondria in the axon. However, how actin filaments regulate axonal transport processes are yet to be fully elucidated. Nerve growth factor binds and activates its receptor located at axon terminus, which intriguers the complex to be endocytosed sorted into signaling endosomes. NGF-containing endosomes are retrogradely transported from the axon terminus to the cell body. In this study, we investigated the effects of actin filiments on axonal transport by tracking the transport of single NGF modified with the quantum dot using microfluidic device. Embryonic DRG neurons were cultured in the microfluidic nerve cell chambers made by PDMS. The microfluidic chamber allows us to apply latrunculin B, an actin de-polymerization inhibitor, exclusively to the middle segment of axon. This treatment would not affect signaling processes in the cell body or the endocytosis process that happens at the axon termini. We monitored the retrograde transport of Qdot-NGF in actin-depleted axons using TIRF microscopy. We found that NGF axonal transport continues in axons that are depleted of actin filiments, confirming previous reports that NGF transport is a microtubule-based process. However, we found that the average speed of axonal transport slowed down in Latrunculin B treated axons. Detailed analysis of why actin depolymerization affects axonal transport is still in progress.