Salivary Acinar Cell Apoptosis: Regulation of p53 by Akt

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DESCRIPTION (provided by applicant): The salivary gland hypofunction that occurs following irradiation for treatment of head and neck cancer decreases the effectiveness of anti-cancer therapies and diminishes the quality of life for these patients. This application is directed towards understanding whether gamma-irradiation induced apoptosis in the salivary gland can be modulated to prevent salivary gland dysfunction. Data from our lab indicate that 25-30% of salivary acinar cells are apoptotic 24 hours post irradiation with a single dose of 5 Gy. Head and neck irradiation of transgenic mice that express activated Akt in the salivary gland results in diminished apoptosis and salivary gland dysfunction following irradiation. These data suggest apoptosis may cause irradiation-induced salivary gland dysfunction. Based upon this lead we determined whether molecules that activate Akt can suppress irradiation-induced salivary gland dysfunction. New data demonstrates that injection of mice with insulin-like growth factor-1 (IGF-1) prior to irradiation activates Akt, and suppresses salivary dysfunction in irradiated mice. This is the first demonstration that irradiation-induced salivary gland dysfunction can be prevented by a simple pretreatment. In this application we will determine the parameters of treatment with IGF-1 that prevent irradiation-induced salivary gland dysfunction. Dose, timing, and the effect of repeated treatment with IGF-1 in preventing dysfunction resulting from serial irradiation will be determined. We have demonstrated that activated Akt suppresses apoptosis of salivary acinar cells by an Akt-> mdm2-> p53 pathway. We posit that IGF-1 suppresses salivary acinar cell apoptosis by this same pathway. We propose to demonstrate in vitro and in vivo. Tissue-specific recombination will be used to eliminate mdm2 from the salivary glands of mice prior to treatment with IGF-1 and irradiation to confirm the pathway by which IGF-1 functions to suppress salivary gland dysfunction. We also posit that IGF-1 and myr-Aktl may suppress apoptosis by altering the expression of genes that regulate apoptosis. DNA microarrays will be used to identify genes whose expression is altered in the salivary glands of IGF-1-treated and myr-Akt1 transgenic mice following irradiation. We can examine the role of these candidate genes in suppressing apoptosis in vitro using vectors to overexpress these genes, or siRNA vectors to eliminate expression of these genes. These studies will establish the parameters for the use of IGF-1 to prevent salivary gland dysfunction, identify the mechanism by which IGF-1 suppresses salivary gland dysfunction, and identify new therapeutic targets that could be used to enhance protection of the salivary gland from -irradiation-induced damage. The development of a pre-clinical animal model that allows development of therapies that prevent irradiation-induced salivary gland dysfunction is great clinical significance to oral health.