E2f1-deficient NOD/SCID mice have dry mouth due to a change of acinar/duct structure and the down-regulation of AQP5 in the salivary gland.

Non-obese diabetic (NOD) mice have been used as a model for dry mouth. NOD mice lacking the gene encoding E2f1, a transcription factor, develop hyposalivation more rapidly progressively than control NOD mice. However, the model mice are associated with an underlying disease such as diabetes. We have now established E2f1-deficient NOD/severe combined immunodeficiency disease (NOD/SCID.E2f1(-/-)) mice to avoid the development of diabetes (Matsui-Inohara et al., Exp Biol Med (Maywood) 234(12):1525-1536, 2009). In this study, we investigated the pathophysiological features of dry mouth using NOD/SCID.E2f1(-/-) mice. In NOD/SCID.E2f1(-/-) mice, the volume of secreted saliva stimulated with pilocarpine is about one third that of control NOD/SCID mice. In behavioral analysis, NOD/SCID.E2f1(-/-) mice drank plenty of water when they ate dry food, and the frequency and time of water intake were almost double compared with control NOD/SCID mice. Histological analysis of submandibular glands with hematoxylin-eosin stain revealed that NOD/SCID.E2f1(-/-) mice have more ducts than NOD/SCID mice. In western blot analysis, the expression of aquaporin 5 (AQP5), a marker of acinar cells, in parotid and in submandibular glands of NOD/SCID.E2f1(-/-) mice was lower than in NOD/SCID mice. Immunohistochemical analysis of parotid and submandibular acini revealed that the localization of AQP5 in NOD/SCID.E2f1(-/-) mice differs from that in NOD/SCID mice; AQP5 was leaky and diffusively localized from the apical membrane to the cytosol in NOD/SCID.E2f1(-/-) mice. The ubiquitination of AQP5 was detected in submandibular glands of NOD/SCID.E2f1(-/-) mice. These findings suggest that the change of acinar/duct structure and the down-regulation of AQP5 in the salivary gland cause the pathogenesis of hyposalivation in NOD/SCID.E2f1(-/-) mice.