Project Details
Projekt
The Role of Chaperone-mediated Endolysosomal Degradation (CMED) in Presynaptic Proteostasis
Applicants
Dr. Katarzyna Grochowska, Ph.D.; Professor Dr. Christian Rosenmund; Professor Noam Ziv, Ph.D.
Subject Area
Molecular and Cellular Neurology and Neuropathology
Term
since 2026
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 447288260
Despite decades of progress in understanding endolysosomal degradation, its functions in presynaptic and axonal proteostasis remain largely unexplored. This project investigates chaperone-mediated endolysosomal degradation (CMED) - 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. In CMA, cargo recognized by HSC70 binds to the transiently oligomerized CMA receptor LAMP2A, leading to membrane translocation and degradation. In eMI, chaperone-cargo complexes bind to late endosomal membranes, triggering cargo loading orchestrated by ESCRT complexes. 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. Notably, many cytoskeletal matrix proteins of the active zone (AZ), including Bassoon (3 KFERQ motifs) and Piccolo (12 KFERQ motifs), contain multiple KFERQ motifs and belong to the supersaturated proteome - proteins at risk of aggregation due to concentrations near solubility limits. 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. The remarkably short half-lives of CAZ proteins (Bassoon ~2.5 days in culture, ~8-11 days in adult mice) despite their enormous sizes and poor solubility suggest the involvement of active degradation mechanisms. To gain deeper understanding of CMED's roles in presynaptic proteostasis, we will develop an advanced toolbox for CMED manipulation and characterization. Using nanoscopy techniques, advanced live-imaging assays, correlative light-electron microscopy, and mass spectrometry, we aim to provide the first systematic description of CMED machinery prevalence, characteristics, and activity in axons. Building on this foundation, we will investigate CMED's contributions to dynamic regulation of the presynaptic proteome and its roles in maintaining presynaptic function and structure.
DFG Programme
Research Units
International Connection
Israel
