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In this study, we developed methods to detect endogenous retrovirus activation focusing on the detection of dsRNA.To develop our dsRNA assays, we used the J2 anti-dsRNA IgG2a monoclonal antibody. These antibodies have become the gold standard in dsRNA detection. J2 can be used to detect dsRNA intermediates of viruses as diverse as Hepatitis C virus, Dengue virus, rhinovirus, Chikungunya virus, Rabies virus, Poliovirus, and many more in cultured cells and in fixed paraffin-embedded histological samples. Flow cytometry experiments using J2 antibody were performed in A549 cells exposed to gamma, galactic cosmic radiation (GCR), and gamma+ microgravity. Notably, increases in average median fluorescence intensity (aMFI) were seen in cells exposed to 8 Gy gamma compared to unirradiated control cells (1.30-fold increase/p=0.0175) at 2 days post radiation. Combining two stressors (10 Gy Gamma and microgravity) showed a 1.73-fold increase (p=0.0002) in aMFI compared to normal gravity controls and a 1.94-fold increase (p<0.0001) in aMFI compared to 10 Gy Gamma only treated samples. Five-day post-radiation results, however, showed statistical significance across all experimental treatment groups; 8 Gy Gamma, 10 Gy Gamma, and microgravity-treated samples showed a 1.33-fold increase (p=0.0155), 2.13-fold increase (p=0.0004), and 2.41-fold increase (p=0.0004) in aMFI, respectively. Combined effects of 10 Gy Gamma and microgravity at the 5-day post-radiation time point showed a 4.72-fold (p<0.0001) increase in aMFI compared to normal gravity controls and a 1.96-fold (p=0.0215) increase in aMFI compared to microgravity only treated samples. One-day post-radiation samples irradiated with GCR5-ion displayed a 1.21-fold increase in aMFI although it was not statistically significant (p=0.47).
We also utilized the J2 antibody to evaluate dsRNA in tissues from mice (lung, liver, heart, brain) from mice exposed to gamma, oxygen ion, iron ion, or GCR radiation compared to age-matched unirradiated mice. Statistically, the tissues most affected were: 1) livers in iron-irradiated mice; 2) brains in oxygen-irradiated mice; and 3) livers and brains of gamma-irradiated mice. The number of animals per radiation group examined was relatively low (n=3), so we pooled the average intensities from iron, oxygen, and gamma-irradiated mice. The intensities measured from the livers, brains, lungs, and hearts were all greater than the corresponding tissues from the unirradiated control animals. The intensities measured in the livers and hearts met statistical significance, but the intensities measured in the brains and lungs failed to meet statistical significance.
Overall, an increase in the presence of double-stranded RNA as evidenced by the increase in immunofluorescence intensity of J2 staining in radiation conditions versus control was seen in both acute (cell-based studies) as well as in chronic (mouse-tissue based) radiation studies. Notably, the tissues evaluated in this study were obtained from mice that had been exposed to various types of radiation 17-18 months prior to euthanasia and tissue banking. A single dose of radiation has a long-lasting effect on the presence of double-stranded DNA indicating a continuing pro-inflammatory environment following the initial exposure. Future work would consist of evaluating tissues obtained from animals euthanized at earlier time points post-radiation to better understand the kinetics of dsRNA expression post-radiation.
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