S-nitrosylation in brain of mice exposed to low or high doses of gamma rays
Creators: name: Nicolas, Fadia
Publisher: name: No Publisher Supplied
Year: 2018

description: Extensive experimental studies and several human epidemiological surveys have revealed  that exposure to high doses of ionizing radiation (&gt;100 mSv) causes significant adverse  health outcomes. The mechanisms underlying these effects have been well characterized.  In contrast, the biological effects and health risks of exposure to low doses of radiation  (&lt;100 mSv) continue to be unclear and are a current subject of conflicting considerations.  Due to insufficient statistical power in the limited number of available epidemiological  studies evaluating health risks of human exposures to effective doses less than 100 mSv,  mechanistic studies in cultured cells and animal models have been considered to be vital  for understanding biological effects, and reducing the uncertainty in predicting health risks.  This project builds on the body of studies characterizing the biochemical and  biological effects of low dose ionizing radiation, but the emphasis is on characterizing post  translational modification of proteins, namely S-nitrosylation, an area that is under-studied,  even though it could greatly impact radiation sensitivity. Here, changes in S-nitrosylation  were studied following in vivo exposure to either a low (0.1 Gy) or high doses (4 Gy) of  137Cs g rays, which mimics doses received in diagnostic and therapeutic radiation,  respectively. The goal was to investigate whether similar or distinct S-nitrosylation events  are induced in brain tissue following low and high dose g ray irradiation to test the  following hypothesis: “Depending on radiation dose, S-nitrosylation triggers groups of  proteins into participating in specific pathways that are protective (e.g. DNA repair,  antioxidation reactions) or detrimental (loss of healthy cells, oxidative stress)”.  Young adult C57BL/6J male mice were exposed to either 0, 0.1 or 4 Gy of Cesium-  137 g rays delivered uniformly to the whole body. Thirteen days after irradiation, the  animals were euthanized, and the brains were harvested. The proteins were immediately  extracted and processed for mass spectrometry analyses of global changes in Snitrosylation.  Using Bioinformatic tools, the mass spectrometry results were analyzed by  the R/Bioconductor statistical package. Several clustering approaches were used in order  to create groups of proteins showing similar levels of S-nitrosylation for dose independent  responses to radiation exposure, and dissimilar levels of S-nitrosylation for dose dependent  responses. Clustering methods used a range of methods from purely mathematical to more  intuitive manual approaches with somewhat arbitrary cutoff to analyze the proteomic data  from irradiated and control samples. Additional clustering techniques like k-means and  hierarchical clustering with several different numbers of clusters were applied to eliminate  the cutoff bias. In addition, Ingenuity Pathway Analysis (IPA) software package was used  to elucidate biological significance of the different groups of proteins. Depending on the  clustering approaches used, several significant pathways were identified. For example,  relative to control, the neuronal nitric oxide synthase (nNOS) pathway showed inactivation  under low dose irradiation and activation under high dose irradiation. This pathway is  under control of the N-methyl-D-aspartate receptor (NMDAR) activity, which becomes  hyper-activated under high dose irradiation resulting in neurotoxicity.    In conclusion, our results suggest that mouse exposure to low doses of Cesium-137  g rays may result in modulation of signaling pathways that promote protective effects  through S-nitrosylation of certain key proteins and de-S-nitrosylation of others. This is an  area that needs further investigation to elucidate the exact mechanism by which Snitrosylation  occurs, and to confirm the role of the modulated pathways suggested by IPA  in regulating cellular/tissue responses that impact sensitivity to radiation.