AQP5 and Sjogren syndrome: Research in AQP5 mutant rats (Murdiastuti et al., 2006), AQP5 knockout mice (Ma et al., 1999), and Sjögren’s syndrome patients (Steinfeld et al., 2001; Ichiyama et al., 2018; Hosoi et al., 2020) has demonstrated that abnormal expression of AQP5 leads to decreased salivary secretion and hypertonic and viscous saliva, which induces thirst or dryness in the oral cavity.