Effects of iron overload on cognitive function and autophagy of hippocampal neurons in rats / 中华行为医学与脑科学杂志

ABSTRACT

Objective:To explore the effect of iron overload on the cognitive function of rats and its possible internal mechanism.Methods:Thirty 8-week-old male Sprague Dawley rats of SPF degree were randomly divided into 2 groups, iron overload group(IO group) and control group(Sham group), with 15 in each group.The rats in IO group were injected intraperitoneally iron dextran(100 mg/(kg·d)) for 28 days.The cognitive function of rats was detected by Morris water maze method. Western blot method was used to detect the expression of TfR1 and autophagy-related protein p-AMPK, LC3 and Beclin1 in the hippocampus of rats. Immunofluorescence was used to observe the expression of LC3 and Beclin1 in the hippocampus of rats. HE staining was used to observe the morphological changes of neurons in the hippocampus. Transmission electron microscopy was used to observe the number of autophagosomes and the morphology of endoplasmic reticulum in hippocampus.The software of SPSS 20.0 was used for repeated measurement ANOVA and t-test. Results:Morris water maze test showed that there were significant interaction between the group factor and training time factor of escape latency( F=3.55, P<0.01). And the simple effect analysis showed that compared with the Sham group((28.09±18.41)s, (21.42±15.53)s, (16.96±8.35)s, (10.24±3.75)s), the average escape latency of rats(2nd-5th day) in IO group((56.68±30.65)s, (58.21±36.09)s, (36.58±13.54)s, (27.29±14.30)s )were significantly longer ( t=8.57, 6.81, 9.51, 7.12, P<0.01). The platform was removed on 6th day of the space exploration experiment, compared with the Sham group ((41.89±3.89)%), the percentage of time spent in the target quadrant of IO group ((25.46±3.56)%) was significantly decreased( t=24.06, P<0.01). Western blot showed that the relative expression levels of (TfR1 (2.10±0.48), p-AMPK (0.74±0.10), LC3 (1.11±0.40), Beclin1 (1.05±0.20)) in IO group in the hippocampus of the rats were significantly higher than those of the Sham group(TfR1(0.11±0.18), p-AMPK(0.19±0.02), LC3(0.22±0.11), Beclin1(0.17±0.02))( t=1.58, 14.58, 10.06, 20.65, P<0.01)). HE staining showed that compared with the Sham group, the neuron in the hippocampus of the IO group were sparsely arranged, morphologically irregular, and the number of the neurons was significantly reduced. Transmission electron microscopy showed that compared with the Sham group, the number of autophagosomes in the hippocampus of IO group was increased. Conclusion:Iron overload may exert its neurotoxic effect by increasing the level of autophagy in the hippocampus, causing cognitive dysfunction.