Vesicle Cholesterol Controls Exocytotic Fusion Pore

Abstract

In lysosomal storage diseases (LSD) cholesterol accumulates in vesicles, which may affect vesicle fusion with the plasmalemma, where the fusion pore, a channel between the vesicle lumen and the extracellular space, is formed. Super-resolution microscopy revealed that after stimulation of exocytosis, pituitary lactotroph vesicles discharge cholesterol which transfers to the plasmalemma. Cholesterol depletion in lactotrophs and astrocytes evokes vesicle hormonal secretion. A new model of cholesterol-dependent fusion pore regulation is proposed. High-resolution membrane capacitance measurements, used to monitor fusion pore conductance, a parameter related to fusion pore diameter, confirm that reducing cholesterol increases, while enrichment with cholesterol decreases the conductance of the fusion pore. In fibroblasts lacking the Npc1 protein, a cellular model of LSD in which cholesterol accumulates in vesicles, the fusion pore conductance is smaller than in controls, showing that vesicle cholesterol controls fusion pore and is relevant for pathophysiology of LSD.