SCAMP5 coordinates AP-4-dependent sorting of ATG9A for presynaptic autophagy by recruiting PI4KIIIβ and generating PtdInsP4 at the trans-Golgi network

Abstract

Presynaptic autophagosome formation requires the trafficking of ATG9A, an autophagy transmembrane protein that serves as a specific cargo of the AP-4 complex at the trans-Golgi network (TGN). However, the molecular mechanisms governing ATG9A sorting at the TGN for presynaptic delivery remain poorly understood. Here, we identify SCAMP5, a synaptic vesicle protein critical for presynaptic plasticity, as highly enriched at the TGN and essential for presynaptic autophagosome formation. SCAMP5 knockdown significantly impaired autophagosome assembly at presynaptic boutons. Mechanistically, we demonstrate that SCAMP5 interacts with phosphatidylinositol 4-kinase IIIβ (PI4KIIIβ) to regulate its TGN recruitment, thereby controlling local phosphatidylinositol 4-phosphate (PtdIns4P) production. Since PtdIns4P is required for AP-4 recruitment to the TGN, SCAMP5 depletion disrupts this process, leading to abnormal ATG9A accumulation at the TGN and impaired axonal trafficking. Consequently, presynaptic autophagy is compromised, disrupting synaptic protein turnover and homeostasis. These findings establish SCAMP5 as a critical regulator of ATG9A-dependent presynaptic autophagy through its control of PI4KIIIβ recruitment and PtdIns4P synthesis at the TGN, revealing a novel mechanism linking synaptic vesicle machinery to presynaptic protein quality control.