Roles of BLOC-1 and Adaptor Protein-3 Complexes in Cargo Sorting to Synaptic Vesicles

• Type of Material: Article
• Authors: Karen Newell, Emory University; Gloria Salazar, Emory University; Yoland Smith, Emory University; Victor Faundez, Emory University
• Language: English
• Date: 2009-03-01
• Publisher: American Society for Cell Biology
• Publication Version: Final Published Version
• Copyright Statement: © 2009 by The American Society for Cell Biology
• Final Published Version (URL): http://www.molbiolcell.org/content/20/5/1441
• Title of Journal or Parent Work: Molecular Biology of the Cell
• ISSN: 1059-1524
• Volume: 20
• Issue: 5
• Start Page: 1441
• End Page: 1453
• Grant/Funding Information: K.N.-L. was supported by a grant-in-aid of research from the National Academy of Sciences, administered by Sigma Xi, The Scientific Research Society.; This work was supported by National Institutes of Health grants NS-42599 and GM-077569 (to V. F.) and F31NS058163 (to K.N.-L.).
• Research Categories: Biology, Neuroscience; Biology, Cell; Biology, Molecular

Abstract

Neuronal lysosomes and their biogenesis mechanisms are primarily thought to clear metabolites and proteins whose abnormal accumulation leads to neurodegenerative disease pathology. However, it remains unknown whether lysosomal sorting mechanisms regulate the levels of membrane proteins within synaptic vesicles. Using high-resolution deconvolution microscopy, we identified early endosomal compartments where both selected synaptic vesicle and lysosomal membrane proteins coexist with the adaptor protein complex 3 (AP-3) in neuronal cells. From these early endosomes, both synaptic vesicle membrane proteins and characteristic AP-3 lysosomal cargoes can be similarly sorted to brain synaptic vesicles and PC12 synaptic-like microvesicles. Mouse knockouts for two Hermansky–Pudlak complexes involved in lysosomal biogenesis from early endosomes, the ubiquitous isoform of AP-3 (Ap3b1−/−) and muted, defective in the biogenesis of lysosome-related organelles complex 1 (BLOC-1), increased the content of characteristic synaptic vesicle proteins and known AP-3 lysosomal proteins in isolated synaptic vesicle fractions. These phenotypes contrast with those of the mouse knockout for the neuronal AP-3 isoform involved in synaptic vesicle biogenesis (Ap3b2−/−), in which the content of select proteins was reduced in synaptic vesicles. Our results demonstrate that lysosomal and lysosome-related organelle biogenesis mechanisms regulate steady-state synaptic vesicle protein composition from shared early endosomes.