AI-facilitated assessment of exosome-mediated bystander effects of low-dose ionizing radiation

A. Ray, Keck Graduate Institute (Principal Investigator)

K. Ganguly, Los Alamos National Laboratory (Co-Principal Investigator)

M. Freeman, Los Alamos National Laboratory (Co-Investigator)

B. McMahon, Los Alamos National Laboratory (Co-Investigator)

P. Mach, Los Alamos National Laboratory (Co-Investigator)

  This study aims to understand how low-dose ionizing radiation (LDIR), such as low-dose X-ray or gamma ray, affects immune cell function

at a distance from the site of irradiation. LDIR comes from natural and artificial sources, including high-altitude airplane flights and space

travel, exposure to medical scans and armament dust, and is everywhere around us. Studies show it can lead to various health effects,

both harmful and protective.

  It is challenging to link specific health problems directly to LDIR exposure due to many factors, the chief among which is a lack of clear

explanation of how it affects human tissues. Ionizing radiation does not just affect the cells it directly hits but also nearby and distant

organs through what is known as the radiation-induced bystander effect (RIBE). This latter effect can mimic the biological effects of direct

radiation damage, including producing typical signs of harm due to radiation, including the appearance of chromosome breaks. There are,

however, distinct differences between the direct effects of radiation and bystander effects, especially related to dose-response

characteristics—at lower doses of radiation the bystander effects are not reduced proportionately. Recent research suggests that part of

RIBE involves tiny particles called exosomes or similar extra-cellular vesicles secreted by human cells. These carry RNA, proteins, and

signaling molecules. This study tests the idea that RNA in exosomes released after LDIR exposure affects immune cells, even when those

immune cells were not directly exposed to the radiation.

  The study will use human skin cell cultures exposed to low doses of radiation to analyze changes in RNA and protein carried by

exosomes. It will then expose unirradiated human immune cells to these exosomes and examine the formers’ responses using advanced

genetic and biochemical techniques, including cellular assays, single-cell transcriptomics and proteomics. The measured responses will be

integrated using high-dimensional machine-learning methods, helping to generate mechanistic explanations of how LDIR RIBE works.

Goals include: 1) Understanding how the contents of exosomes change in response to different radiation doses; 2) Using machine learning to find links between radiation dose, genes, and exosome contents; and 3) Examining how these exosomes affect immune cells by using

detailed single-cell genomics and biochemical analysis.

   By disrupting identified genes or RNA in immune cells which respond to the LDIR RIBE, we will aim to understand how LDIR

affects immune responses. This could reveal new biomarkers of radiation exposure for future testing through 'liquid biopsies'. Ultimately, the study seeks to explain how LDIR affects the immune system, potentially influencing health responses across the body.