VAMP8 is the v-SNARE that mediates basolateral exocytosis in a mouse model of alcoholic pancreatitis

Abstract

In rodents and humans, alcohol exposure has been shown to predispose the pancreas to cholinergic or viral induction of pancreatitis. We previously developed a rodent model in which exposure to an ethanol (EtOH) diet, followed by carbachol (Cch) stimulation, redirects exocytosis from the apical to the basolateral plasma membrane of acinar cells, resulting in ectopic zymogen enzyme activation and pancreatitis. This redirection of exocytosis involves a soluble NSF attachment receptor (SNARE) complex consisting of syntaxin-4 and synapseassociated protein of 23 kDa (SNAP-23). Here, we investigated the role of the zymogen granule (ZG) SNARE vesicle-associated membrane protein 8 (VAMP8) in mediating basolateral exocytosis. In WT mice, in vitro EtOH exposure or EtOH diet reduced Cch-stimulated amylase release by redirecting apical exocytosis to the basolateral membrane, leading to alcoholic pancreatitis. Further reduction of zymogen secretion, caused by blockade of both apical and basolateral exocytosis and resulting in a more mild induction of alcoholic pancreatitis, was observed in Vamp8 -/-mice in response to these treatments. In addition, although ZGs accumulated in Vamp8 -/-acinar cells, ZG-ZG fusions were reduced compared with those in WT acinar cells, as visualized by electron microscopy. This reduction in ZG fusion may account for reduced efficiency of apical exocytosis in Vamp8 -/-acini. These findings indicate that VAMP8 is the ZG-SNARE that mediates basolateral exocytosis in alcoholic pancreatitis and that VAMP8 is critical for ZG-ZG homotypic fusion.

Syntaxin-4 mediates exocytosis of pre-docked and newcomer insulin granules underlying biphasic glucose-stimulated insulin secretion in human pancreatic beta cells

“…We previously reported that pancreatic acini employed Munc18c-Syn-4-VAMP8-SNAP23 as the putative SM-SNARE complex mediating basolateral exocytosis that causes pancreatitis [25][26][27]. We showed that all beta cell Syns displayed promiscuous binding to VAMP2 and VAMP8 and to SNAP25 and SNAP23, although each Syn has a preference for a particular VAMP [16,17].…”

Syntaxin-3 regulates newcomer insulin granule exocytosis and compound fusion in pancreatic beta cells

“…insulin secretion in diabetes, mast cell secretion in allergic reactions) [28]. One mode is fusion of secretory granules, either by orderly sequential fusion as in pancreatic acinar cells [13,20] or by prior homotypic fusion leading to compound exocytosis, as in mast cells [35]. Islet beta cells employ fusion of secretory granules [31,36], but to a much lesser extent than other secretory cells.…”

“…This is of importance, as first-phase GSIS is much reduced in patients with type 2 diabetes, and this has been attributed in part to greatly reduced islet SYN-1A levels [23], along with reduction of cognate SNAREs (SNAP25 and VAMP2) and the Sec1/Munc18-like protein (SM) Munc18a. SYN-3 was shown in pancreatic acinar cells to preferentially form complexes with VAMP8 [20] and Munc18b [38,39], which are also present in beta cells [40][41][42]. We recently reported, employing the Vamp8-knockout mice [43], that VAMP8 also mediated the recruitment and fusion of newcomer SGs, and was the putative cognate v-SNARE that binds SYN-3.…”

“…In retinal cells, SYN-3 is produced in ribbon synapses but its role in neurotransmitter release remains unknown [16,17]. In pancreatic acinar cells [18], SYN-3 was localised to zymogen granule membrane [19] and complexed with VAMP8 to mediate SG-SG fusion [20].…”

Calmodulin protects against alcohol-induced pancreatic trypsinogen activation elicited via Ca 2+ release through IP 3 receptors

“…The evidence implicating FAEEs as important mediators of the crucial intracellular trypsinogen activation initiating alcoholrelated pancreatitis does not exclude other effects of alcohol (16,17). In view of the variable acute effects of ethanol itself on isolated pancreatic acinar cells (8) we have carried out a detailed study of the action of alcohol, using two-photon permeabilized cells, which have turned out to be useful preparations for studies of Ca 2+ homeostasis (12,18,19).…”