BACKGROUND: Radon is a known human lung carcinogen, whose underlying 
carcinogenic mechanism remains unclear. Recently, circular RNA (circRNA), a 
class of endogenous non-protein coding RNAs that contain a circular loop, was 
found to exhibit multiple biological effects. In this study, circRNA profiles in 
mouse lung tissues between control and radon exposure were analyzed.
METHODS: Six mice were exposed to radon at concentration of 100,000 Bq/m3, 
12 h/d, for up to cumulative doses of 60 working level months (WLM). H&E 
staining and immunohistochemistry of caspase-3 were used to detect the damages 
in lung tissue. The lung tissue of control and exposed group were selected for 
circRNA microarray study. The circRNA/microRNA interaction was analyzed by 
starBase prediction software. 5 highest expressing circRNAs were selected by 
real-time PCR to validate the consistency in mouse lung tissue exposed to radon.
RESULTS: Inflammatory reaction was found in mouse lung tissue exposed to radon, 
and caspase-3 expression was significantly increased. Microarray screening 
revealed 107 up-regulated and 83 down-regulated circRNAs, among which top 30 
circRNAs with the highest fold changes were chosen for further analysis, with 5 
microRNAs binding sites listed for each circRNA. Consistency of the top 5 
circRNAs with the highest expressions were confirmed in mice exposed with 60WLM 
of radon.
CONCLUSION: Mouse lung tissue was severely injured when exposed to radon through 
pathological diagnosis and immunohistochemical analysis. A series of 
differentially expressed circRNAs demonstrated that they may play an important 
role in pulmonary toxicity induced by radon.