Ionizing Radiation-induced Changes Of MiRNA Expression Profile And The Preliminary Study On Anti-radiation Effect Of Epigallocatechin Gallate

Ionizing radiation(IR)is one of radiation,and it can cause organism injury by direct or indirect way.MicroRNA(miRNA)is a class of non-coding small RNA,which is closely related with the mechanism of IR-induced damage.Epigallocatechin gallate(EGCG)is the component with highest antioxidant activity in tea polyphenols,and it exerts anti-radiation function by scavenging free radicals.At present,many EGCG related researches focus on the function of anti-radiation,while the molecular mechanism of EGCG still needs to be further explored.In order to study the molecular anti-radiation mechanism of EGCG based on miRNA,the IR-mouse model was established,and dysregulated miRNAs were screened by high throughput sequencing.After a total dose of 4 Gy,IR induced 48 differentially expressed miRNAs in mouse liver,including 20 up-regulated miRNAs and 28 down-regulated miRNAs.Similarly,there were 112 differentially expressed miRNAs in mouse thymus,including 77 up-regulated miRNAs and down-regulated 35 miRNAs.The qRT-PCR results were consistent with the high throughput sequencing.Moreover,target prediction results showed that the target genes of dysregulated miRNAs were mainly involved in the replication,recombination and repair of gene,signal transduction mechanism and transcriptional regulation mechanism,also in the liver metabolic pathway and the the thymic signal pathway related with T-lymphocytic maturation.According to the results of high-throughput sequencing,miR-34 a was selected to further explore the molecular anti-radiation mechanism of EGCG in vitro and in vivo.The CCK8 results showed that the cell viability of AML-12 cells treated with EGCG(0?5?10?20?50?100 ?M)was dose-dependently increased at the time point of 24 h.After 2 or 4 Gy irradiation,the cell viability of AML-12 cells treated with EGCG was significantly increased at the time point of 0,12 h(p < 0.05 vs IR group).Besides,the cell viability of AML-12 cells showed a dose-dependently increase at 24 h(p < 0.05 vs IR group).The qRT-PCR results showed that the miR-34 a expression was significantly up-regulated by IR in the AML-12 cells(0.001 < p < 0.01 vs Control group).Through treated with EGCG,the expression of miR-34 a was down-regulated after IR(p < 0.05 vs IR group).Cell transfection experiment showed that overexpression of miR-34 a inhibited Sirt1(Sirtuin type 1)expression in vitro(p < 0.05 vs miR-control group).After 4 Gy irradiation in vivo,the expression of miR-34 a was significantly up-regulated(p < 0.01 vs Control group)and Sirt1 expression was down-regulated in mouse liver(p <0.001 vs Control group).Interstingly,miR-34 a was significantly decreased after feeding the EGCG of different concentrations at(30,60,120 mg / kg BW · d)(p < 0.05 vs IR group),and the expression of Sirt1 was up-regulated(p > 0.05 vs IR group).In this paper,high-throughput sequencing was used to screen the differentially expressed miRNAs induced by IR.Then,the miR-34 a as the research object was involved in further studying about the molecular mechanism of EGCG.The results indicated that IR could affect the expression of miRNAs in vivo,and more dysregulated miRNAs in mouse thymus was identified than those in liver.It is implicated that organism conducted self-repair and defense through miRNA regulating target involved in complicated biological network.Moreover,EGCG effectively inhibited the decrease of cells activity induced by IR,and might reduce the radiation-induced apoptosis by promoting Sirt1 expression and inhibiting miR-34 a expression,further protected the organism from IR.