SNAP23 is selectively expressed in airway secretory cells and mediates baseline and stimulated mucin secretion

Abstract

SNAP23 (23-kDa paralogue of synaptosome-associated protein of 25 kDa) is expressed in secretory but not ciliated cells of airway epithelium, suggesting that it mediates regulated but not constitutive secretion in polarized epithelia. Baseline but not stimulated mucin secretion in heterozygous mutant mice is fully compensated by increased intracellular stores.

Inducible epithelial resistance against acute Sendai virus infection prevents chronic asthma‐like lung disease in mice

“…These were analysed using a flexiVent (Scireq, Montreal, Canada) forced oscillation ventilator system as described (Ren et al, ). Briefly, mice were anaesthetized with urethane (2 mg·g −1 i.p.)…”

“…Slides were rinsed in water, blocked in horse serum (Vector Laboratories, Cat# S‐2012, ) or goat serum (Jackson ImmunoResearch Labs, Cat# 005‐000‐001, ) for 1 hr and then rinsed again and incubated with primary antibodies diluted in blocking solution at 4°C overnight. Primary antibodies used were goat anti‐mouse IL‐33 (R and D Systems, Cat# AF3626, ; 1:1000), rabbit anti‐Muc5ac (gift from Dr. Camille Ehre, 1:500; Ehre et al, ) and mouse monoclonal antibody MDA‐3E1 (Millipore, Cat# MABT899;1:500) to detect Muc5b (Ren et al, ). After incubation, secondary antibodies—biotinylated horse anti‐goat IgG (Vector Laboratories, Cat# AP‐9500, ), HRP‐labelled goat anti‐rabbit (Millipore, Cat# AP132P, ) or HRP‐labelled goat anti‐mouse antibody (Thermo Fisher Scientific, Cat# 31430, )—were added for 2 hr at room temperature.…”

Different Munc18 Proteins Mediate Baseline and Stimulated Airway Mucin Secretion

“…We hypothesize that Munc18c function is Since Munc18 proteins partner with specific Syntaxins t-SNAREs (23), our findings here suggest that the exocytic SM-SNARE machinery is mostly different between baseline and stimulated mucin secretion. This inference is supported by the role of the v-SNARE VAMP8 predominantly in stimulated secretion (21), even though SNAP23 functions in both processes (20). What might be the adaptive value of utilizing different exocytic machines for baseline and stimulated secretion rather than utilizing a single machine capable of running at different rates?…”

“…At high levels of intracellular calcium, the fast, low-affinity exocytic calcium sensor Synaptotagmin-2 promotes mucin secretion (19). Baseline secretion is thought to be primarily responsible for clearance of inhaled particles and pathogens, while stimulated secretion can induce airway obstruction protectively to trap helminths or pathologically in asthma (11,12).Defects in mucin secretion in SNAP23 and VAMP8 mutant mice implicate the highly conserved SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) machinery in mucin exocytosis (20,21). The SNARE complex is a four-helix bundle comprised of three helices attached to the target membrane (t-SNAREs) and M.J. Tuvim and B.F. Dickey conceived the study.…”

“…Defects in mucin secretion in SNAP23 and VAMP8 mutant mice implicate the highly conserved SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) machinery in mucin exocytosis (20,21). The SNARE complex is a four-helix bundle comprised of three helices attached to the target membrane (t-SNAREs) and M.J. Tuvim and B.F. Dickey conceived the study.…”