To investigate whether aquaporins (AQPs) are involved in salivary gland dysfunction in patients with neuromyelitis optica (NMO) complicated with Sjögren's syndrome (SS).
Eight primary SS (pSS) patients, four NMO spectrum disorder (NMOsd) patients complicated with SS (NMOsd-SS), and three control subjects were enrolled. Immunohistochemistry of labial salivary glands (LSGs) was performed to determine the expressions of AQP4, AQP5, and tumor necrosis factor-alpha (TNF-α). In vitro expression of AQP5 was examined by Western blotting in cultured primary salivary gland epithelial cells (SGECs).
No expression of AQP4 was shown in all LSGs. AQP5 was clearly expressed in the all acini, but the predominant localization of AQP5 in the apical side was diminished in the patients with pSS or NMOsd-SS compared with the controls and tended to be even lower in NMOsd-SS than pSS. The abnormal localization of AQP5 was associated with poor saliva secretion. No difference was found in TNF-α expression in the LSGs between patients with pSS and NMOsd-SS. AQP5 expression of SGECs in vitro was not changed by TNF-α or interleukin-10.
Our results suggest that AQP5 but not AQP4 contributes to salivary secretion in patients with SS including those with NMO complicated with SS.