Lysosomes axonal transport impairments mediated by the ubiquitin-proteasome system

MG OTERO; TMM SAEZ; LE CROMBERG; M ALLOATTI; VM POZO DEVOTO; TL FALZONE

Puerto Varas

Workshop; EMBO Workshop: Emerging concepts on neuronal cytoeskeleton; 2015

EMBO

Alzheimer disease (AD) is the most frequent form of dementia. AD has as a common feature local accumulation of aberrant and misfolded protein that couldn´t be degraded, suggesting that a degradation pathway might be involved in the onset of this disease. The Ubiquitin-proteasome system (UPS) is the major route for cytosolic proteins degradation; in contrast, lysosomes are dynamic organelles that degrade macromolecules from the endocytic and autophagic pathways. Despite having different targets both system had been involved in AD. Though, it was suggested that UPS impairments occurs in early steps of the disease and lysosomes at later stages, the relationship between both systems remains obscure. To test whether proteasome impairments regulates the lysosomal pathway, we tracked the dynamics of acidic vesicles (lysotracker) under proteasome inhibition by live imaging in mouse hippocampal neurons. Here we showed a decreased number of vesicles being transported in the axon. To further test this system we measured under similar conditions the axonal transport of late endosomes using the Lamp1-eGFP marker. Sucrose density gradients showed early endosomes enlargements when proteasomes are inhibited, Moreover, a decrease in the endocytosis rate was revealed by Dextran-TR uptake. To test whether ubiquitin depletion is involved in lysosomal impairment we measured acidic vesicle transport under proteasome inhibition in neurons overexpressing ubiquitin, showing a restore in the lysosomal pathway even when proteasome were blocked. Our results suggest that UPS mediated ubiquitin depletion indirectly impairs the endo-lysosomal pathway dynamic demonstrating a relevant crosstalk between both degradation pathways with important implications for AD.