Salivary Gland Dysplasia in Fgf10 Heterozygous Mice: A New Mouse Model of Xerostomia

Abstract

Xerostomia, or chronic dry mouth, is a common syndrome caused by a lack of saliva that can lead to severe eating difficulties, dental caries and oral candida infections. The prevalence of xerostomia increases with age and affects approximately 30% of people aged 65 or older. Given the large numbers of sufferers, and the potential increase in incidence given our aging population, it is important to understand the complex mechanisms that drive hyposalivation and the consequences for the dentition and oral mucosa. From this study we propose the Fgf10 +/- mouse as a model to investigate xerostomia. By following embryonic salivary gland development, in vivo and in vitro, we show that a reduction in Fgf10 causes a delay in branching of salivary glands. This leads to hypoplasia of the glands, a phenotype that is not rescued postnatally or by adulthood in both male and female Fgf10 +/- mice. Histological analysis of the glands showed no obvious defect in cellular differentiation or acini/ductal arrangements, however there was a significant reduction in their size and weight. Analysis of saliva secretion showed that hypoplasia of the glands led to a significant reduction in saliva production in Fgf10 +/- adults, giving rise to a reduced saliva pellicle in the oral cavity of these mice. Mature mice were shown to drink more and in many cases had severe tooth wear. The Fgf10 +/- mouse is therefore a useful model to explore the causes and effects of xerostomia.

Fig. (1)

Comparison of WT and Fgf10 +/- salivary glands at P14. General duct and acini arrangements of WT and Fgf10 +/- SMG and SLGs appeared normal at P14 (A-D). A reduction in size was seen in glandular lobes in Fgf10 +/- animal compared to WT littermates (black dotted line) (A, B). At E18.5 no apparent histological differences were observed in WT and Fgf10 +/- littermates (E, F). At P14 combined Fgf10 +/- SMGs and SLGs weighed significantly less compared to WT littermates (G). P14; scale bar = 200I1/4M. A-D shows glands from female specimens. E, F shows E18.5 glands; SMG (black line), SLG (red line), scale bar = 200I1/4M. (Color images available online).

Fig. (2)

Embryonic Fgf10 +/- salivary gland development. (A, B) At E14.5, in vivo salivary gland capsule size was the same in WT and Fgf10 +/- littermates (dotted line) however epithelial branching was reduced and epithelial endbuds appeared larger in Fgf10 +/- animals (arrows). Scale bar = 200I1/4M. (C-N) In vitro culture of E12.5 salivary glands. At E12.5, WT glands have reached the bud stage (C) while Fgf10 +/- glands show a smaller epithelial bud (G) or an absent bud (K). Delayed bud extension and downgrowth was observed in all Fgf10 +/- glands (H, I; L, M) compared to WT littermates (D, E), which resulted in severely reduced branching of heterozygous glands by 5 days of culture (J, N) compared to WT littermates (F). Fgf10 +/- glands showed failure to fill the mesenchymal capsule compared to WT tissue (F, J, N). Epithelial bud = dotted line (columns 1-3), mesenchymal capsule = dotted line (column 4), scale bar = 500I1/4M.

Fig. (3)

Comparison of adult salivary glands. (A, B) Smaller gland lobes are seen in Fgf10 +/- adult submandibular glands (arrows) (scale bar=3mm). (C) Male and female Fgf10 +/- adult salivary glands show a significant decrease in salivary gland weight compared to WT littermates. (D-G) Male glands; no histological differences are noted between WT and Fgf10 +/- SMGs (D, E) SLGs (F, G), and GCTs (inset images D, E). D-G scale bar=200I1/4m, inset scale bar=50I1/4M.

Fig. (4)

Saliva secretion from the (A) SMG/SLG and (B) parotid glands. Flow rate was significantly reduced in heterozygous adults compared to WT littermates. Saliva secretion was collected from the gland duct openings and was measured as microlitre of saliva produced in 10 minutes after pilocarpine stimulation (A l/min). Graph shows secretion rates of Fgf10 +/- animals normalized against WT secretion rate where WT secretion = 1. Data is expressed as mean A SEM.

Fig. (5)

Scanning electron microscopy of 10 week old adult female tongues. WT animals retained what appeared to be sheets of mucus covering the posterior CVP (A) and filliform papillae (C) while no mucus remained on Fgf10 +/- tongues following HCl treatment (B, D). Scale bar in B = 500um (same scale in A). Scale bar in D = 100um (same scale n C).

Fig. (6)

Analysis of signs of xerostomia in aging Fgf10 +/- mice. (A) Water intake/body weight in WT and Fgf10 +/- aged matched mice. Fgf10 +/- mice drank significantly more water over a 5 day period. (B) Enamel mineral content in WT and Fgf10 +/- aged matched mice. Fgf10 +/- have significantly less enamel on their crowns. (C, D) 3D reconstructions from microCT. Fgf10 +/- teeth are flattened compared to controls of the same age fed on the same diet, indicating tooth wear. Double arrowheads indicate tooth height from the level of root bifurcation to top of crown.