Gene Expression Profiling in the Atrophic Rat Submandibular Gland

Salivary gland atrophy is clinically important in dental research because salivary glands, which secrete saliva, are vital for the protection of the oral environment. Histological examination has shown that salivary gland atrophy includes degranulation, significant acinar cell loss and ductal cell proliferation. However, the molecular characteristics of glandular atrophy are largely unknown. Objectives: To examine gene expression patterns in the ligated atrophic submandibular gland model. Method: Under recovery anaesthesia, the excretory duct of the right submandibular gland in the rat model (n=5) was ligated twice with thread to induce atrophy. Atrophic right submandibular glands were removed after 14 days of ligation under terminal anaesthesia, and investigated using histological staining to confirm atrophy, cell phenotype and cell proliferation. Microarray analysis and quantitative real-time PCR (Q-RT-PCR) to confirm microarray results were performed. Results: Histology confirmed atrophy of experimental glands, including ductal cell degranulation and de-differentiation. A significant decrease in acinar cells, indicated by actin staining of surrounding myoepithelial cells was seen in the experimental glands when compared with the control glands, while an increase in ki67-positive proliferating cells was seen. Microarray analysis of control glands revealed TON (tonin), present in granular ducts, and SMR2 (submaxillary gland androgen regulated protein 2) and AQP5 (aquaporin 5) present in acinar cells to be highly expressed. Further analysis by Q-RT-PCR in the atrophic glands showed TON gene expression levels to be significantly downregulated to near background levels. However, although SMR2 and AQP5 gene expression showed a significant decrease in the atrophic glands, relative gene expression levels of SMR2 and AQP5, when compared with TON, remained high. Conclusion: Although gene expression levels of TON expectedly mirrors de-differentiation of granular ductal cells, SMR2 and AQP5 levels suggest that remaining acinar cells either maintain, or take more time to lose their differentiated state. Acknowledgements: Supported by the Wellcome Trust