Modeling the Effect of Vesicle Traps on Mass Transfer and Traffic Jam Formation in Fast Axonal Transport

This paper simulates effects of structural changes in the microtubule (MT) system on mass transfer in an axon. Understanding this process is important for understanding the underlying reasons for many neurodegenerative diseases, such as Alzheimer’s disease. In particular, it is investigated how the degree of polar mismatching in an MT swirl affects organelle trap regions in the axon and inhibiting transport of organelles down the axon. The model is based on modified Smith-Simmons equations governing molecular-motor-assisted transport in neurons. It is established that the structure that develops as a result of a region with disoriented MTs (the MT swirl) consists of two organelle traps, the trap to the left of the swirl region accumulates plus-end oriented organelles and the trap to the right of this region accumulates minus-end oriented organelles. The presence of such a structure is shown to decrease the transport of organelles toward the synapse of the axon. Four cases with a different degree of polar mismatching in the swirl region are investigated; the results are compared with simulations for a healthy axon, in which case organelle traps are absent.