title: Endosome-mediated endocytic mechanism replenishes the majority of synaptic vesicles at mature CNS synapses in an activity-dependent manner.
abstract: Whether synaptic vesicles (SVs) are recovered via endosome-mediated pathways is a matter of debate; however, recent evidence suggests that clathrin-independent bulk endocytosis (CIE) via endosomes is functional and preferentially replenishes SV pools during strong stimulation. Here, using brefeldin-A (BFA) to block CIE, we found that CIE retrieved a minority of SVs at developing CNS synapses during strong stimulation, but its contribution increased up to 61% at mature CNS synapses. Contrary to previous views, BFA not only blocked SV formation from the endosome but also blocked the endosome formation at the plasma membrane. Adaptor protein 1 and 3 (AP-1/3) have key roles in SV reformation from endosomes during CIE, and AP-1 also affects bulk endosome formation from the plasma membrane. Finally, temporary blocking of chronic or acute neuronal activity with tetrodotoxin in mature neurons redirected most SV retrieval to endosome-independent pathways. These results show that during high neuronal activity, CIE becomes the major endocytic pathway at mature CNS synapses. Moreover, mature neurons use clathrin-mediated endocytosis and the CIE pathway to different extents depending on their previous activity; this may result in activity-dependent alterations of the SV composition which ultimately influence transmitter release and contribute to synaptic plasticity.
authors.affiliation: Department of Physiology and Biomedical Sciences, Seoul National University College of Medicine, Seoul 110-799, South Korea.|Biomembrane Plasticity Research Center, Seoul National University College of Medicine, Seoul 110-799, South Korea.
authors.forename: Joohyun
authors.initials: J
authors.lastname: Park
authors.affiliation: Biomembrane Plasticity Research Center, Seoul National University College of Medicine, Seoul 110-799, South Korea.|Interdisciplinary Program in Neuroscience, Seoul National University College of Medicine, Seoul 110-799, South Korea.
authors.forename: Oh Yeon
authors.initials: OY
authors.lastname: Cho
authors.affiliation: Biomembrane Plasticity Research Center, Seoul National University College of Medicine, Seoul 110-799, South Korea.|Interdisciplinary Program in Neuroscience, Seoul National University College of Medicine, Seoul 110-799, South Korea.
authors.forename: Jung Ah
authors.initials: JA
authors.lastname: Kim
authors.affiliation: Department of Physiology and Biomedical Sciences, Seoul National University College of Medicine, Seoul 110-799, South Korea.|Biomembrane Plasticity Research Center, Seoul National University College of Medicine, Seoul 110-799, South Korea.|Interdisciplinary Program in Neuroscience, Seoul National University College of Medicine, Seoul 110-799, South Korea.|Neuroscience Research Institute, Medical Research Center, Seoul National University College of Medicine, Seoul 110-799, South Korea.
authors.forename: Sunghoe
authors.initials: S
authors.lastname: Chang
mesh_terms: D033963:Adaptor Protein Complex 3 / Q000378:metabolism; D000818:Animals; D020126:Brefeldin A / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism*; D002490:Central Nervous System / Q000378:metabolism*; D004705:Endocytosis / Q000235:genetics / Q000502:physiology*; D011992:Endosomes / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013572:Synaptic Vesicles / Q000378:metabolism*
chemical_list: D033963:Adaptor Protein Complex 3; D020126:Brefeldin A