PROJECT 3: ABSTRACT The overall objective of Project 3 is to link radionuclide exposure and the elemental signature left behind with biomarkers of that exposure, be they histological, cellular or molecular in nature. Our motivation to do this stems from the fact that radiation from internal emitters is very unevenly distributed in organs, tissues, and cells and the fact that this remains little understood. Heterogeneity of radionuclide distribution is dependent upon a complex set of parameters that relate to the radionuclide itself and the organism’s response to it, such as radionuclide half-life, decay schema, activity, concentration, particle size, morphology, chemical form, and solubility, whereas the biological response patterns are dictated by the genotype and phenotype of the cells, tissues and organs, intake route and the organism as a whole. Because the in vivo footprint of radionuclide exposure is multi-scale, e.g., DNA damage and cell death at the (sub)cellular level, or chemokine/cytokine production at the cell/tissue level, it essentially means that biomarkers of that exposure are best registered along the same multi-dimensional NANO-, MICRO- and MESO scale, which is our goal. For example, micro-RNA expression will be registered in the context of immune cell infiltration in a tissue, particularly macrophages. Arguably, the most compelling aspect to our project can be seen in the use of X-ray fluorescent microscopy (XFM) as a powerful tool for radionuclide mapping, which forms the backbone to our approach. Applying XFM technology to explore the incredibly rich resource that the Northwestern University Radiation Animal (NURA) Archive, combined with contemporary animal models gives us the unique opportunity to trace back the biological consequences of radionuclide exposures, and opens up the path towards biomarker, and ultimately, to mitigator discovery. Canine and murine tissues from an enormous number of animals exposed to a variety of radionuclides and over different times add critical mass and rigor to our study. Collectively, our team can draw from a diverse set of expertise in nuclear medicine, cellular and molecular biology, radiobiology, XFM, radiation protection and mitigation, normal tissue radiobiology and immunology. We are ideally placed to carry out the proposed studies addressing the complexity of radionuclide exposure in a comprehensive and integrated way. Our hope is to gain important insights into the biological consequences of internal radiation emitters that are relevant to real life accidental and incidental exposure scenarios and that cannot be modeled using conventional external beam radiation or nuclear medicine approaches. Yet, the concepts underlying the interaction between radiation-damaged cells and tissues, danger signaling, the engagement of immune system and the road to recovery are likely applicable in a much broader context.