Neuronal activity promotes secretory autophagy for the extracellular release of α-synuclein
Yoshitsugu Nakamura, Taiki Sawai, Kensuke Kakiuchi, Shigeki Arawaka
Abstract
Extracellular secretion is an essential mechanism for α-synuclein (α-syn) proteostasis. Although it has been reported that neuronal activity affects α-syn secretion, the underlying mechanisms remain unclear. Here, we investigated the autophagic processes that regulate the physiological release of α-syn in mouse primary cortical neurons and SH-SY5Y cells. Stimulating neuronal activity with glutamate or depolarization with high KCl enhanced α-syn secretion. This glutamate-induced α-syn secretion was blocked by a mixture of NMDA receptor antagonist AP5 and AMPA receptor antagonist NBQX, as well as by cytosolic Ca 2+ chelator BAPTA-AM. Additionally, mTOR inhibitor rapamycin increased α-syn and p62/SQSTM1 (p62) secretion, and this effect of rapamycin was reduced in primary cortical neurons deficient in the autophagy regulator beclin 1 (derived from BECN1 +/− mice). Glutamate-induced α-syn and p62 secretion was suppressed by the knockdown of ATG5 , which is required for autophagosome formation. Glutamate increased LC3-II generation and decreased intracellular p62 levels, and the increase in LC3-II levels was blocked by BAPTA-AM. Moreover, glutamate promoted co-localization of α-syn with LC3-positive puncta, but not with LAMP1-positive structures in the neuronal somas. Glutamate-induced α-syn and p62 secretion were also reduced by the knockdown of RAB8A , which is required for autophagosome fusion with the plasma membrane. Collectively, these findings suggest that stimulating neuronal activity mediates autophagic α-syn secretion in a cytosolic Ca 2+ -dependent manner, and autophagosomes may participate in autophagic secretion by functioning as α-syn carriers.