Synaptic vesicle fusion promotes phosphatidylinositol 4-phosphate synthesis for efficient synaptic transmission.

Efficient synaptic vesicle (SV) recycling is essential for sustaining synaptic transmission. While the multiple roles of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂) in SV recycling are well documented, presynaptic regulation of phosphatidylinositol 4-phosphate (PI(4)P) synthesis and its potential role in SV recycling remain poorly understood. Here, we identify phosphatidylinositol 4-kinase IIIα (PI4KIIIα) as the key enzyme responsible for both the maintenance and activity-dependent production of presynaptic PI(4)P. Notably, we find that SVs are nearly devoid of PI(4)P and PI(4,5)P₂ but are rich in phosphatidylinositol (PI) and that PI(4)P synthesis is triggered upon SV fusion as vesicular PI is delivered to the plasma membrane. Furthermore, when PI(4)P levels are selectively reduced without affecting basal PI(4,5)P₂ levels, SV exo-endocytosis is significantly impaired, primarily due to reduced conductivity of voltage-gated Ca²⁺ channels. This reveals a PI(4,5)P₂-independent homeostatic mechanism in which continuous PI(4)P production, driven by SV fusion, sustains efficient synaptic transmission.