The Role of Chaperone-mediated Endolysosomal Degradation (CMED) in Presynaptic Proteostasis
KATARZYNA GROCHOWSKA (Hamburg)
CHRISTIAN REOSENMUND (Berlin)
NOAM ZIV (Haifa)
The function and extent to which endolysosomal degradation shapes presynaptic and axonal proteostasis remain largely unexplored. This project investigates chaperone-mediated endolysosomal degradation (CMED) – an umbrella term encompassing both chaperone-mediated autophagy (CMA) and endosomal microautophagy (eMI) – in presynaptic protein homeostasis. Both pathways are orchestrated by the chaperone HSC70 and target soluble cytoplasmic proteins containing KFERQ-like recognition motifs for lysosomal degradation.
Preliminary data demonstrate that distal axons of mature neurons contain numerous mobile, catabolically active organelles positive for CMED markers, a fraction of which localizes at presynaptic terminals. Importantly, these CMED-related organelles are segregated from the presynaptic macroautophagy pathway.
Many cytoskeletal matrix proteins of the active zone, including Bassoon and Piccolo, are large, short-lived, and poorly soluble; they belong to the supersaturated proteome – a group of proteins balancing at the aggregation tipping point. These proteins undergo liquid-liquid phase separation to form presynaptic condensates while maintaining continuous exchange between condensed and cytosolic phases, making them accessible to chaperones for CMED targeting. Of note, numerous presynaptic proteins contain multiple KFERQ motifs. We aim to develop an advanced toolbox for CMED manipulation and characterization. We will employ nanoscopy techniques, advanced live-imaging assays, correlative light-electron microscopy, and mass spectrometry to provide a systematic description of CMED machinery in axons and investigate CMED’s contributions to presynaptic proteome regulation and synaptic function.
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