Background Sjögren’s syndrome patients (SS) have oral and ocular dryness attributed to alterations in the quantity and quality of saliva and tears (1). We have demonstrated that disruption of cell-cell and cell-extracellular matrix (ECM) interactions that could modify the secretory pathway (2). Salivary acinar cells of SS-patients display alterations in their cell-polarity, affecting the correct localization and function of proteins composing the secretory machinery. SNARE-complexes are responsible for the secretion of proteins which are essential components of saliva. VAMP-2 and STX2 are SNARE-proteins that participate in the constitutive and regulated secretion. VAMP-2 is located in secretory granules next to the basolateral plasma membrane and it is involved in vesicular traffic towards the apical and basolateral poles, while STX2 is exclusively located in the apical plasma membrane (3).
Objectives To determine the expression and localization of VAMP-2 and STX2, as well as their ability to form SNARE complexes under basal conditions in salivary acinar cells of SS-patients.
Methods In labial salivary glands from SS-patients (n=27) and control subjects (n=17) mRNA and proteins levels of SNARE complex components were determined by real-time PCR and Western blotting, respectively. Protein localization was evaluated by immunofluorescence and confocal microscopy.
Results In controls and SS-patients, STX2 and VAMP-2 mRNA levels remained unchanged. STX2 protein levels were found significantly augmented in SS-patients, while VAMP-2 protein levels did not change. In SS-patients, VAMP-2 showed a significant increase in apical staining, while STX2 showed decreased apical staining and apico-basal redistribution. Interestingly, increased formation of SNARE complexes containing VAMP-2 or STX2 in a manner independent of external secretory stimuli was detected in SS-patients.
Conclusions In SS-patients, VAMP-2 was relocated to the apical cytoplasm; a change that might compensate the significant decrease of VAMP-8 observed in the apical region, as reported previously (4). Apical relocalization of VAMP-2 has been reported in VAMP-8 knockout mice, associated to a significant increase of VAMP-2 protein levels. Regardless of VAMP-2 relocalization, these mice show a decreased the secretory response to secretagogues (5). Conversely, STX2 protein levels increased significantly and showed a strong relocation from apical to basal plasma membrane. These findings suggest a probable loss of exocytic ability by the apical pole of acinar cells that may affect the destination of secretion proteins, thus impairing physiological production of saliva. Furthermore, a higher quantity of fusion complexes containing the studied proteins has been detected in SS-patients. The ectopic formation of SNARE-complexes in the basal domain of acinar cells is probably enhanced.
FONDECYT #1120062, 1080006 and CONICYT PhD fellowship (BMJ).
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Disclosure of Interest None Declared