Intestinal Flora Reduces Ionizing Radiation Induced DNA Damage Through TLRs And Its Mechanism Research

Generally, The gut commensal bacteria has a symbiotic relationship with the host,the gut bacteria plays a positive role in the host nutrient and energy balance, theevolution and the maintenance of the host immune system function and in turn, the hostprovides a survival environment for gut bacteria and gut bacteria obtain the nutrientsfrom this environment, and ensures the hidded and the spreaded of baceterias betweendifferent individuals. Studies have shown that intestinal endogenous flora can activateTLRs with its components, then protect mice form intestinal epithelial injury caused byDSS and maintain the intestinal epithelial homeostasis of the host. Other reports havealso shown that TLR5and TLR4activated by different components of bacterias canprotect mice form ionizing radiation. The DNA damage is one of the specificity of theionizing radiation damage and the DNA damage repair is a dynamic process in normallife. The intestinal flora is one part of the body, along with the process of life. This studywill focus on the DNA damage of mice hematopoietic cells induced by ionizingradiation, in order to find whether the commensal bacteria can reduce the DNA damageinduced by ionizing radiation and its related molecular mechanism.Broad-spectrum antibiotics were uesed to remove the intestinal endogenous floraof mice. With2Gy gamma irradiation, the rate of chromosome aberration and thelength of comet-tail increased significantly, shown that the ionizing radiation-inducedDNA damage increased significantly in these mice, this result suggest that intestinalendogenous flora may play an important role in protecting mice form the DNA damageinduced by ionizing radiation. In order to further research whether this effect has to dowith the activation of TLRs, we use the Elisa method to test the change of Flagellin,LPS and Lipopeptede in mice serum, and we find that these TLRs ligands have different degrees of reduced, so we speculate that the presence of endogenous gut microbes isnecessary for C57mice to reduce the DNA damage caused by ionizing radiation. Inorder to determine whether the TLR’s ligands from the component of bacterias have theeffect of reducing DNA damage by ionizing radiation, we return these ligands to normalmice and gut commensal bacteria depleted mice to activate TLR5, TLR4and TLR2/6respectively, and find that the activation of TLRs can significantly reduce the ionizingradiation-induced DNA damage, the similar phenomenon can be found in commensalbacterial depleted mice.In order to further explore the molecular mechanism of that the activation of TLRscan reduce the DNA damage induced by ionizing radiation, CBLB502is used toactivate TLR5and with micro-array method,87different expressed genes have beenselected, among the total85genes are upregulated and2genes are downregulated. Fivegenes associated with DNA damage repair process have been chosen, respectively areIrg1, Apex2, Gadd45β, Sod2and Rad21. Next we use Real Time-PCR method to testthe expression levels of these genes during the activation of TLR2, TLR4, TLR5andTLR6, and find that these genes have different degrees of up-regulation.These results suggest that TLRs can be activated by gut commensal bacteriacomponents, then up-regulate the expression of genes associated with TLRs, thesegenes can involve in the DNA damage repair process. In the same way, the activation ofToll-like receptors by Gut Commensal Bacteria can also participate in DNA damagerepair process under steady-state conditions. Our results reveal an unexpected protectiverole of TLRs and provide a new perspective on host-commensal symbiosis.