Chronic Intermittent Hypobaric Hypoxia Attenuates Hippocampus Damage Induced By Radiation In Mice Via Increasing Autophagy And Reducing Endoplasmic Reticulum

Objective:To observe the manifestations of radiation induced hippoca-mpus damage and the potential injury mechanisms in mice.To examine the protective effects with chronic intermittent hypobaric hypoxia?CIHH?on radiation induced hippocampus damage.Methods:A total of 48 male adult C57/BL mice were randomly divided into four groups as control group?group A?,CIHH group?group B?,irradiation group?group C?and CIHH plus irradiation group?group D?.1 Groups:Whole brain irradiation was delivered to them with a single fraction of 10.0Gy?at a dose rate of 1.8Gy/min?from a precise type medical high-energy linear accelerator producing 6MV X-ray and were freely housed one month after irradiation.2 CIHH pretreament:Before irradiation,mice were treated with CIHH in a hypobaric chamber which mimicked 5000m altitude(P_B=404mmHg,P_O2=84mmHg,6hrs/day)for 28 consecutive days.3 Mirros water maze test:Thirty days later,the Mirros water maze test was used to evaluate the memory and cognitive function of the mice?To record and analyze the average escape latency in the positioning navigation test,the target quadrant residence time and the number of passing through the platform in the space exploration experiment?.4 Histopathological evluation:Morphological alterations of hippocampal CA1 area were examined by Nissl staining.5 Western blot and Immunofluorescence:The expression level of mTOR,Beclin-1,LC3?/?,GRP78 and CHOP were quantitatively analyzed by Western blot.The expression of doublecortin?DCX?in the subgranular zone?SGZ?of dentate gyrus?DG?in hippocampus was detected by immuno-fluorescence to evaluate the neurogenesis.Results:1.Behavioral cognitive function in mice:In the basic environment,escape latency was increased on day3,from 45.70S to 57.63 S?P<0.001?,day4from 43.75 to 57.94S?P<0.001?and day5 from 53.13 to 37.21S?P<0.001?following radiation but such an effect was inhibited?day4 from 57.94S to 50.90S,P<0.05,day5 from 53.13S to 45.4S,P<0.01?by CIHH prior to radiation.After remove the platform,we found that the space exploration function was reduced,exploring time in the quadrant within 1 minute was reduced from 21.7542S to 7.42333S?P<0.001?,the times of cross the platform was decreased from 3.42 times to 0.83 times?P<0.001?.However,pretreament with CIHH can improve this situation:exploring time in the first quadrant within 1 minute from 14.1192S to 7.42333S,?P<0.05?,the times of cross the platform from2.08 times to 0.83 times,?P<0.05?.2.Histomorphological evaluation:Nissl staining from paraffin section:Irradiation induced significantly neuronal cells swelling,nuclear deviation,unclear structure,obvious necrosis,and even neuronal degeneration,neuronal necrosis.Nissl body was significantly decreased.Pretreament with CIHH to some extent improved damages as mentioned above.3.Western blot and immunofluorescence:?1?Western blot:The levels of GRP78,CHOP,Beclin-1,LC3?/?were incresed by irradiation?P<0.05 for both?and Mtor was decreased by irradiation?P<0.05?,However,the levels of GRP78?CHOP?Mtor were decreased?P<0.05 for both?with the pretreatment of CIHH,and the levels of Beclin-1,LC3?/?were increased?P<0.05 for both?.?2?Immunofluorescence:The expression of DCX in CA1 area was decr-eased by irradiation but the latter was increased after pretreatment with CIHH.Conclusion:1.Irradiation could cause histopathological damage in hippocampus in mice.2.Radiation induced histopathological damages in mice hippocampus mainly including neuronal cell degeneration,necrosis and Nissl body redu-ction.3.The potential mechanisms of radiation induced hippocampus damage might be attributed to ER stress and neurogenesis reduction.Simultaneously,irradiation could activate autophagy in hippocampus,which might play a protective role by reducing the damage of ER stress.4 Pretreated with CIHH could attenuates irradiation induced hippoc-ampus injury by inducting of autophagy as well as increasing the neurogenesis in CA1 region in mice.