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Mast cell degranulation requires N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs)6 and mammalian unc18 (Munc18) fusion accessory proteins for membrane fusion. However, it is still unknown how their interaction supports fusion. Here we found that siRNA-mediated silencing of the isoform Munc18-2 in mast cells inhibits cytoplasmic secretory granule (SG) release but not CCL2 chemokine secretion. Silencing of its SNARE binding partner Syntaxin 3 (STX3) also markedly inhibited degranulation, while combined knock-down produced an additive inhibitory effect. Strikingly, while Munc18-2 silencing impaired SG translocation, silencing of STX3 inhibited fusion demonstrating unique roles of each protein. Immunogold studies showed that both Munc18-2 and STX3 are located on the granule surface, but also within the granule matrix and in small nocodazole-sensitive clusters of the cytoskeletal meshwork surrounding SG. After stimulation clusters containing both effectors were detected at fusion sites. In resting cells, Munc18-2, but not STX3, interacted with tubulin. This interaction was sensitive to nocodazole treatment and decreased after stimulation. Our results indicate that Munc18-2 dynamically couples the membrane fusion machinery to the microtubule cytoskeleton and demonstrate that Munc18-2 and STX3 perform distinct, but complementary, functions to support, respectively, SG translocation and membrane fusion in mast cells.

Our findings provide the first evidence for a complex network of paracrine and membrane interactions between MCs and Eos. The prosurvival phenotype induced by this MC-Eos interplay may be critical for sustaining chronic allergic inflammation.

NGF peptide and tryptase activity were shown to be significantly and persistently higher in saliva of BMS subjects, with respect to control values. Conversely the salivary levels of SP were shown to be significantly lower, while neutrophil markers didn't show any change. We conclude that the neuropathic origin of the disease is confirmed at salivary level. Furthermore, the higher tryptase activity indicates a possible involvement of mast cells. The salivary neuropeptide concentration in BMS subjects, together with mast cell derived compounds, could be useful biomarkers for diagnosis and monitoring of this disease.

No abstract