Tau acts as a selective barrier along microtubules to regulate multi-motor cargo transport.

Abstract

Organelles and vesicular cargoes are transported by teams of kinesin and dynein motors along microtubules. Tau is a neuronal MAP that stabilizes microtubules within the axon. While single-molecule studies show that tau differentially regulates the motility of kinesins and dynein in vitro, less is known about its role in modulating the trafficking of endogenous cargoes transported by their native teams of motors. To dissect tau's role in regulating transport, we isolate endocytic organelles from cells and reconstitute their motility along tau-decorated microtubules in vitro. We asked how the sets of motors transporting a cargo determine its motility characteristics and response to tau. Here, we found that early phagosomes (EPs) undergo unidirectional retrograde transport while late phagosomes (LPs) move bidirectionally. Correspondingly, different numbers and combinations of kinesins-1, -2, -3, and dynein are bound to EPs and LPs. Previous studies showed that tau preferentially inhibits kinesin motors, which biases the transport of LPs towards the microtubule minus-end. Recently, we showed that tau strongly inhibits long-range, dynein-mediated EP motility. Dynein is the dominant motor in EP transport, and tau strongly impedes forces generated by teams of multiple dynein motors and accelerates dynein unbinding under load. These results are surprising, as previous single-molecule studies showed that dynein is less sensitive to tau compared to kinesin. Our results show that specific cargoes differentially respond to tau, where dynein-complexes on EPs are more sensitive to tau inhibition than those on LPs, suggesting that pathological changes in tau associated with Alzheimer's disease and other tauopathies will also have disparate impact on cargoes. We will next compare the effects of pathogenic tau mutations on the transport of different cargoes in iPSC-derived neurons with the aim of identifying the pathways most disrupted in neurodegenerative disease.