Study Of The Effect Of Nrf2 Knockout On The Acute Intestinal Injuries Induced By Ionzing Radiation

Objective To explore the effect of Nuclear factor-erythroid 2-related factor 2(Nrf2)knockout on radiation-induced intestinal injuries(RIII),and to clarify the molecular mechanisms of Nrf2 and NF-κB in the radiation-induced intestinal injuries.Method The model of RIII in Nrf2 knockout(Nrf2-/-)mice and wild-type(Nrf2+/+)C57BL/6J mice was constructed by 13 Gy abdominal irradiation(ABI).The survival curve and body weight of mice post-ABI were recorded within 30 days.The spleen coefficient and thymus coefficient of mice post-ABI were calculated.The numbers of various blood cell types,white blood cells(WBC),platelets(PLT),and lymphocytes were counted.The DNA damage to peripheral blood lymphocytes of mice post-ABI was evaluated by the comet assay.The crypt-villus structure in the small intestine of mice was examined at 3.5 and 5 days post-ABI by haematoxylin and eosin staining.The rate of apoptosis of the small intestine was detected at 6 hours after ABI by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling(TUNEL)assay.The number of Lgr5-intestinal stem cells(ISCs)and their daughter cells including Ki67+transient amplifying cells,Villin+ enterocytes,and lysozyme+ Paneth cells were analyzed by the immunohistochemical analysis.The activation of NF-κB in the small intestine after ABI was detected by the immunohistochemical analysis and western blot,and the mRNA expression of NF-κB target genes Bcl-2,uPA,and XIAP was assessed by real-time quantitative polymerase chain reaction(RT qPCR).Results(1)The survival rate:Compared with that of Nrf2-/+ mice,the survival rate of Nrf2-/-mice after ABI was elevated,and the survival rate of Nrf2-/-mice after total body irradiation was decreased.(2)The immune function:The peripheral blood lymphocyte count and thymus coefficient of Nrf2-/-mice post-ABI were higher than that of Nrf2+/+ mice,and the DNA damage of peripheral blood lymphocytes in Nrf2-/-mice was signficantly decreased compared with that of Nrf2+/+ mice.(3)The intestinal epithelial integrity:The intestinal villi in Nrf2+/+ mice after ABI were obviously stunted and blunt,and the number of intestinal crypts was decreased.In contrast,the damage to crypt-villus structure in the small intestines of Nrf2-/-mice after ABI was less than that of Nrf2+/+ mice.The apoptosis of intestinal epithelial cells(IECs)of Nrf2-/-mice were lower than Nrf2+/+ mice.(4)The repair response of small intestine:Compared with that of Nrf2+/+ mice,the number of Lgr5+ ISCs and their daughter cells,including Ki67+transient amplifying cells,Villin+ enterocytes,and lysozyme+ Paneth cells,in the small intestine of Nrf2-/-mice were increased.(5)The activation of NF-κB:The expression of nuclear factor-κB(NF-κB)in the crypt base nuclei of the small intestine of Nrf2-/-mice post-ABI was higher than that of Nrf2+/+ mice.The mRNA expression of NF-κB target genes Bcl-2,uPA,and XIAP from Nr2-/-mice were significantly enhanced compared with that of Nrf2+/+ mice.Conclusions Nrf2 knockout decreased the survival of the mice exposed to ABI,and reduced the damage to the immune function and the intestinal epithelial integrity.The molecular mechanisms of the protective effect of Nrf2 knockout on small intestine damage is that Nrf2 knockout elevated the proliferation and differentiation of small intestinal stem cells and activated NF-κB signal pathway to promote the repair of the damaged small intestine.