Lacrimal gland homeostasis is maintained by the AQP5 pathway by attenuating endoplasmic reticulum stress inflammation in the lacrimal gland of AQP5 knockout mice

PURPOSE: AQP5(−/−) mice spontaneously exhibit dry eye symptoms. The purpose of this study was to assess the endoplasmic reticulum (ER) stress-mediated inflammation generated by a deficiency of aquaporin 5 (AQP5) in the lacrimal gland. METHODS: Hematoxylin and eosin (H&E) staining, Oil Red O staining, and transmission electron microscopy (TEM) analysis were performed to identify structural changes in lacrimal gland epithelial cells because of AQP5 deficiency. Corneal epithelial defects were assessed with sodium fluorescein staining. The expression profiles of mRNA and proteins were determined by quantitative real-time reverse transcription PCR (qRT-PCR) and western blot. Mice in the quercetin group were injected intraperitoneally with 40 mg/kg of quercetin, and the control group was injected with an equal volume of dimethyl sulfoxide (DMSO) for 4 weeks. RESULTS: Aqueous tear secretion fell at about 50% in 1- and 6-month-old AQP5(−/−) mice compared with that of AQP5(+/+) mice. TEM showed that the ER structure was damaged. ER stress was significantly increased in the lacrimal gland of AQP5(−/−) mice. Lipid droplets accumulated in the matrix and acinar cells, and changes occurred in the lipid metabolism and gene expression levels for PPARα, CPT1α, and CPT2 in the AQP5(−/−) mice. Immune cell infiltration and increases in the gene expression levels of the chemokines CXCL1, CXCL2, and CCL5 were found in the lacrimal gland of AQP5(−/−) mice. Quercetin partially reversed ER stress levels, inflammation, and lipid accumulation, and it inhibited tear secretion. CONCLUSIONS: The study data indicated that a deficiency of AQP5 induced pathophysiological changes and functional decompensation of the lacrimal gland. Quercetin may improve the inflammation in the lacrimal glands of AQP5(−/−) mice by regulating the ER stress levels.