Neuronal fusion pore assembly requires membrane cholesterol

Abstract

Cholesterol has been proposed to play a critical role in regulating neurotransmitter release and synaptic plasticity. The neuronal porosome/fusion pore, the secretory machinery at the nerve terminal, is a 12−17 nm cup-shaped lipoprotein structure composed of cholesterol and a number of proteins, among them calcium channels, and the t-SNARE proteins syntaxin-1 and SNAP-25. During neurotransmission, synaptic vesicles dock and fuse at the porosome via interaction of their v-SNARE protein with t-SNAREs at the porosome base. Membrane-associated neuronal t-SNAREs interact in a circular array with liposome-associated neuronal v-SNARE, to form the t-/v-SNARE ring complex. The SNARE complex along with calcium is required for the establishment of continuity between opposing bilayers. Here we show that although cholesterol is an integral component of the neuronal porosome and is required for maintaining its physical integrity and function, it has no influence on the conformation of the SNARE ring complex.

Functional Organization of the Porosome Complex and Associated Structures Facilitating Cellular Secretion

“…Interaction of VAMP with synaptophysin and myosin V had also been reported (88). In agreement with these earlier findings, our studies (20,21,51,60) demonstrate the association of SNAP-23, syntaxin 2, cytoskeletal proteins actin, ␣-fodrin, vimentin, and calcium channels ␤3 and ␣1c, together with the SNARE regulatory protein NSF, at the porosome complex (20,21,51,60). Additionally, chloride ion channels ClC2 and ClC3 were also identified as part of the porosome complex.…”

“…The neuronal porosome is an order of magnitude smaller (10-15 nm) compared with porosome in the exocrine pancreas (100-180 nm). Note the central plug and eight interconnected ridges within the porosome complex (20). H: electron density maps of negatively stained electron micrographs of isolated neuronal porosome protein complexe.…”

Niemann-Pick C disease and mobilization of lysosomal cholesterol by cyclodextrin

“…A more recent mouse model carries the D1005G mutation in NPC1 ( 73 ). This mutation is in the cysteinerich loop of NPC1, the site at which the most common mutations occur in human NPC patients, and these mice have a more slowly progressing disease than that of NPC1-null by guest, on May 10, 2018 www.jlr.org Downloaded from addition, the formation of presynaptic SNARE complexes, the interaction between synaptobrevin and synaptophysin, the fusion of synaptic vesicles with presynaptic membranes, and the sorting of synaptic vesicles during endocytosis all depend on cholesterol (120)(121)(122)(123)(124). Thus, extraction of cholesterol from neurons, by brief incubation with cyclodextrin, impaired exocytosis and endocytosis of synaptic vesicles ( 114,(125)(126)(127)(128).…”

Another decade of advances in research on primary cilia, porosomes and neosis: Some passing thoughts at 70

“…Now that it is generally accepted that primary cilia are complex signal-receiving organelles, their membranes studded with receptors of many different kinds sensing a wide variety of ligands 1 email wheatley@abdn.ac.uk Table 1 The porosome: tracing its discovery and elucidation of its function in Cell Biology International 1998Jeong et al, 19982000Jena, 20002002Cho et al, 2002aCho et al, 2002bCho et al, 2004Jeremic et al, 2004;Kelly et al, 2004Cho et al, 2007Potoff et al, 2008Cho et al, 2009Jena, 2010 that elicit responses in the cells through their second messenger pathways, could it be that they also act as transmitters (emitters), sending signals back out into their environments, perhaps even in response to signals that have come via the main cell body rather than the primary cilium itself? I am not aware of any evidence to support this idea, but I see no reason why they should not work both ways.…”