α-Synuclein (α-syn) is a key molecule linked to Parkinson’s disease pathology. Physiologically, the monomeric α-syn in the presynaptic termini is involved in regulation of neurotransmission, but the pathophysiology of extracellular monomeric α-syn is still unknown. Utilizing both in vivo and in vitro approaches, we investigated how extracellular α-syn impact presynaptic structure and function. Our data revealed that treatment with exogenous α-syn leads to increased tonic and decreased depolarization-evoked synaptic vesicle (SV) recycling and glutamate release. This was associated with mobilization of molecularly distinct SV pools and reorganization of active zone components. Our study also showed that exogenous α-syn impaired neuronal cholesterol level and that the cholesterol binding domain of α-syn was sufficient to exert the same presynaptic phenotype as the full-length protein. The present study sheds new light on physiological functions of extracellular α-syn in overall maintenance of presynaptic activity that involves the reorganization of both presynaptic compartment and cholesterol-rich plasma membrane domains.

α-突触核蛋白 (α-syn) 是与帕金森病病理学相关的关键分子。生理学上，突触前末端的单体α-syn参与神经传递的调节，但细胞外单体α-syn的病理生理学仍不清楚。利用体内和体外方法，我们研究了细胞外 α-syn 如何影响突触前结构和功能。我们的数据显示，用外源 α-syn 治疗会导致强直增加，并减少去极化诱发的突触小泡 (SV) 回收和谷氨酸释放。这与分子上不同的 SV 库的动员和活性区成分的重组有关。我们的研究还表明，外源性 α-syn 会损害神经元胆固醇水平，并且 α-syn 的胆固醇结合域足以发挥与全长蛋白相同的突触前表型。本研究为细胞外 α-syn 在突触前活动整体维持中的生理功能提供了新的线索，其中涉及突触前区室和富含胆固醇的质膜域的重组。