Encalada, S. E. | bioRxiv Science

bioRxiv2020

Endosomal Sorting Drives the Formation of Mutant Prion Endoggresomes

Intra-axonal misfolded protein aggregates are a pathological feature of neurodegenerative diseases. How aggregates are formed and cleared is key to maintaining proteostasis. By systematically analyzing the trafficking itinerary of a misfolded GPI-anchored prion protein (PrP) mutant, we unveil endocytic pathways that drive its immediate degradation in the soma, versus its aggregation in axons inside endosomal structures we termed endoggresomes. Axonal sorting occurs post-Golgi, by association of mutant PrP vesicles with Arl8b/kinesin-1/HOPS, a complex that earmarks them for axonal entry, fusion, and aggregation via a mechanism of axonal rapid endosomal sorting and transport-dependent aggregation (ARESTA). Endoggresomes persist in axons due to transport and lysosomal deficits, impairing calcium dynamics and accelerating neuronal death. Reducing ARESTA inhibits endoggresome formation and circumvents these defects. These data identify the endo-lysosomal system as critical for the sorting of misfolded PrP, and ARESTA as an actionable anti-aggregation target that can ameliorate axonal dysfunction in the prionopathies.

neuroscience↗

bioRxiv2020

LC3B phosphorylation regulates FYCO1 binding anddirectional transport of autophagosomes

Macroautophagy (hereafter referred to as autophagy) is a conserved process that promotes cellular homeostasis through the degradation of cytosolic components, also known as cargo. During autophagy, cargo is sequestered into double-membrane vesicles called autophagosomes, which are predominantly transported in the retrograde direction to the perinuclear region to fuse with lysosomes, thus ensuring cargo degradation [1]. The mechanisms regulating directional autophagosomal transport remain unclear. The ATG8 family of proteins associate with autophagosome membranes [2] and play key roles in autophagy, such as the movement of autophagosomes. This is achieved via the interaction of ATG8 with adaptor proteins, including FYCO1, a protein involved in the anterograde transport of autophagosomes toward the cell periphery [1,3-5]. We previously reported that phosphorylation of LC3B/ATG8 on threonine 50 (LC3B-T50) by the Hippo kinase STK4 is required for autophagy through unknown mechanisms [6]. Here, we show that LC3B-T50 phosphorylation decreases the interaction between LC3B and FYCO1, which in turn regulates the starvation-induced perinuclear positioning of autophagosomes. Moreover, non-phosphorylatable LC3B-T50A aberrantly switches the predominant retrograde movement of autophagosomes to anterograde movement towards the cell periphery in multiple cell types, including in mouse primary hippocampal neurons. Our data support a role of a nutrient-sensitive STK4-LC3B-FYCO1 axis in the regulation of the directional transport of autophagosomes via the post-translational regulation of LC3B. Given that autophagy is impaired in many human conditions, including neurodegenerative diseases, our findings may highlight new principles of vesicle transport regulation critical for disease etiology. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=133 SRC="FIGDIR/small/081638v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@158d7fforg.highwire.dtl.DTLVardef@1ccde6eorg.highwire.dtl.DTLVardef@11f3af2org.highwire.dtl.DTLVardef@156f5d4_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗