Synaptotagmin-1 overexpression under inflammatory conditions affects secretion in salivary glands from Sjögren's syndrome patients

Publication date: Available online 31 October 2018

Source: Journal of Autoimmunity

Author(s): Juan Cortés, Jorge Hidalgo, Sergio Aguilera, Isabel Castro, Mónica Brito, Hery Urra, Paola Pérez, María-José Barrera, Patricia Carvajal, Ulises Urzúa, Sergio González, Claudio Molina, Verónica Bahamondes, Marcela Hermoso, María-Julieta González

Abstract

Sjögren's syndrome (SS) is an autoimmune exocrinopathy associated with severe secretory alterations by disruption of the glandular architecture integrity, which is fundamental for a correct function and localization of the secretory machinery. Syt-1, PI(4,5)P₂ and Ca²⁺ are significant factors controlling exocytosis in different secretory cells, the Ca²⁺ role being the most studied. Salivary acinar cells from SS-patients show a defective agonist-regulated intracellular Ca²⁺ release together with a decreased IP3R expression level, and this condition may explain a reduced water release. However, there are not reports where Syt-1, PI(4,5)P₂ and Ca²⁺ in acinar cells of SS patients had been studied. In the present study, we analyzed the expression and/or localization of Syt-1 and PI(4,5)P₂ in acinar cells of labial salivary gland biopsies from SS-patients and control individuals. Also, we evaluated whether the overexpression of Syt-1 and the loss of cell polarity induced by TNF-α or loss of interaction between acinar cell and basal lamina, alters directionality of the exocytosis process, Ca²⁺ signaling and α-amylase secretion in a 3D-acini model stimulated with cholinergic or β-adrenergic agonists. In addition, the correlation between Syt-1 protein levels and clinical parameters was evaluated. The results showed an increase of Syt-1 mRNA and protein levels, and a high number of co-localization points of Syt-1/STX4 and PI(4,5)P₂/Ezrin in the acinar basolateral region of LSG from SS-patients. With regard to 3D-acini, Syt-1 overexpression increased exocytosis in the apical pole compared to control acini. TNF-α stimulation increased exocytic events in the basal pole, which was further enhanced by Syt-1 overexpression. Additionally, altered acinar cell polarity affected Ca²⁺ signaling and amylase secretion. Overexpression of Syt-1 was associated with salivary gland alterations revealing that the secretory dysfunction in SS-patients is linked to altered expression and/or localization of secretory machinery components together with impaired epithelial cell polarity. These findings provide a novel insight on the pathological mechanism implicated in ectopic secretory products to the extracellular matrix of LSG from SS-patients, which might initiate inflammation.

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