Naturally occurring AQP5 mutations in rats and humans and their affected phenotypes

Thirteen members of aquaporin (AQP), a water channel, are expressed in mammals. In this review, we briefly overview these mammalian AQPs, then focus on AQP5, an exocrine gland-type AQP. Namely, we discuss: (1) the mechanism for coupling of AQP5 dynamics with the secretion and restoration cycle of amylase after isoproterenol (IPR) in the parotid gland (PG); (2) roles of parasympathetic nerve for maintaining AQP5 level in the submandibular gland (SMG), and; (3) AQP5 down-regulation in an experimental pathological model by LPS administration in the PG. We then move to the effects of single nucleotide mutation (SNP) found in rats and humans and its affected phenotypes. That is, G308A point mutation found in rat AQP5 cDNA resulted in amino acid substitutions of Gly103 for Asp103, and causes diminished expression of its protein product. In humans, several SNPs in AQP5 are found in European and Chinese families and cause autosomal-dominant diffuse nonepidermolytic palmoplantar keratoderma.