title: Decreased saliva secretion and down-regulation of AQP5 in submandibular gland in irradiated rats.
abstract: The molecular mechanisms of radiation-induced xerostomia remain unclear. The purpose of this study was to investigate the alterations of aquaporins (AQPs) and Na(+)/K(+)-ATPase in irradiated rat submandibular glands and to test the hypothesis that down-regulation of AQP5 expression in irradiated salivary glands is one of the mechanisms of radiation-induced xerostomia. Saliva from control and irradiated rat submandibular glands was analyzed. The mRNA level of AQP5 in the submandibular glands was assessed by semi-quantitative RT-PCR and in situ hybridization. The protein expression of AQP5, AQP1 and Na(+)/K(+)-ATPase was determined by Western blotting and immunohistochemistry. The body weight, submandibular gland weight, and saliva secretion of irradiated rats significantly decreased by 12, 24 and 32% on day 3 and 24, 16 and 38% on day 30 postirradiation, respectively. There was a significant increase in the protein concentration and osmolality of saliva in irradiated rats on days 3 and 30 postirradiation. However, there was no significant difference between irradiated and control rats in total saliva protein secretion. RT-PCR analysis showed that mRNA expression of AQP5 was significantly down-regulated by 37 and 51% in irradiated rats on days 3 and 30 postirradiation, respectively. Immunoblotting showed that the AQP5 protein level was decreased by 40 and 60% in irradiated glands, in contrast to the slight reductions of AQP1 and Na(+)/K(+)-ATPase proteins. Immunohistochemical analysis demonstrated that loss of AQP5 protein occurred throughout the irradiated glands, while no significant reduction was detected in AQP1 and Na(+)/ K(+)-ATPase labeling density. These results suggest that the preferential down-regulation of AQP5 with minor effects on AQP1 and Na(+)/K(+)-ATPase may contribute to radiation-induced salivary dysfunction.
authors.affiliation: Department of Oral Radiology, College of Stomatology, Jilin University, Changchun, China.
authors.forename: Zhimin
authors.initials: Z
authors.lastname: Li
authors.forename: Dan
authors.initials: D
authors.lastname: Zhao
authors.forename: Baijuan
authors.initials: B
authors.lastname: Gong
authors.forename: Yongzhong
authors.initials: Y
authors.lastname: Xu
authors.forename: Hongchen
authors.initials: H
authors.lastname: Sun
authors.forename: Baoxue
authors.initials: B
authors.lastname: Yang
authors.forename: Xuejian
authors.initials: X
authors.lastname: Zhao
mesh_terms: D000818:Animals; D051402:Aquaporin 5 / Q000378:metabolism*; D015536:Down-Regulation / Q000502:physiology / Q000528:radiation effects; D008297:Male; D011832:Radiation Injuries / Q000209:etiology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012463:Saliva / Q000378:metabolism*; D012472:Salivation / Q000528:radiation effects; D013363:Submandibular Gland / Q000378:metabolism* / Q000528:radiation effects*; D014916:Whole-Body Irradiation / Q000009:adverse effects*; D014987:Xerostomia / Q000209:etiology / Q000378:metabolism*
chemical_list: C496040:Aqp5 protein, rat; D051402:Aquaporin 5