The Research On Circulating MicroRNA Responding To Ionizing Radiation

Rapid development of manned space flight,nuclear power and nuclear medicine presents new objectives and challenges for radiation safety and protection.Traditional physical dosimeters and biomarkers have considerable limitations.Noninvasive biomarkers that can rapidly assess the exposure risk in early stages are urgently needed for optimal medical treatments in case of a radiation accident.Circulating microRNA(miRNA)is one kind of small noncoding RNA which can stably exist in blood.It is easy for collection and detection,stable in extraction and preservation,and conservative in sequence and function.All these features make it become ideal biomarkers.Many circulating miRNAs have been reported as candidates of cancer biomarkers.However,there are few studies about circulating miRNAs in response to radiation up to date,especially for heavy ion radiation like carbon ions and iron ions et al.In addition,whether the circulating miRNA play any roles in the organism after exposure is still unclear.The circulating miRNA in response to different kinds of radiation with different dose and time points were investigated in this dissertation.Through screening of mi RNA by PCR array and validation of real-time quantitative PCR,we identified a set of candidate miRNAs which can be universal biomarkers for radiation.In order to solve the problem of how to use these miRNAs to assessment radiation damage,we distinguished different dose into different exposure degree.A mathematical model based on these miRNAs was built by multiple logistic regression and was verified by many ways.Additionally,miRNA of nematoid and mimics(agomiRNA)of the candidate miRNA were tail injected into mouse model to investigate the enrichment of the circulating miRNA in the body and its possible function after exposure.We obtained results through these experiments and summarized in three hands as follows:Firstly,in aspect of characteristics of circulating mi RNA in response to radiaton,we found that a number of circulating miRNAs are sensitive to irradiation.Further,Five circulating miRNAs were identified as potential radio-biomarkers which are miR-183,mi R-9,mi R-200 b,miR-342 and mi R-574.These miRNAs are highly sensitive to carbon ions,iron ions and X-rays radiation,from 0.1Gy-2Gy in dose and 6-72 h in time.They have the potential of serving as biomarkers for radiation.It is notable that the relative fold changes of these 5 miRNAs increase or decrease with increased doses and reach a plateau at a dose threshold like 0.5Gy-1Gy rather than a linear relationship simply.In addition,The background of expression levels of most circulating miRNAs,including 5 candidate biomarker miRNAs are similar in different individuals.Secondly,in order to investigate how to use circulating miRNA to assess radiation risk,this study analysed behaviors of 5 candidate miRNAs in response to radiation.A universal model combining different radiosensitive miRNAs was built by multiple linear regression equation,and this model was applicable for carbon ions,iron ions and X-rays irradiation.Receiver operating characteristic analysis showed remarkable specificity and sensitivity.The cross validation analysis showed highly accuracy of this model in predicting radiation exposure degree.Finally,in investigation of the function of radiosensitive circulating miRNA,we found that circulating miRNAs mainly aggregate in liver,spleen and lung,and a few miRNAs can enter into the cells of bone marrow,lymphocytes,kidneys,heart and intestine.Moreover,up-regulation of miR-342 which is sensitive to radiation in blood after exposure can significantly relieve the depletion of leukocyte caused by radiation.In summary of this study,we identified a set of miRNAs as ideal radio-biomarkers,and presented a method of multiple linear regression for the assessment of radiation exposure degree for the first time.This finding can provide new method for the radiation risk assessment in future.Moreover,this study confirms that radiosensitive circulating miRNAs can reduce immunological injury induced by radiation.It will put new sights into the strategies of radiation protection.