The Role Of BRCA1 Regulatory System In MtDNA Damage Of Hippocampal Nerve Cells And Cognitive Impairment In Rats Induced By Aluminum Exposure

Objective:Aluminum can enter the body by a variety of ways and is considered as a major risk factor for neurodegenerative diseases.The brain is the accumulation site and the main target organ of aluminum.Chronic aluminum exposure can lead to neuron death and eventually a progressive memory loss symptom similar to AD.The incidence of neurodegenerative diseases is increasing year by year.Therefore,it is important to clarify the neurotoxicity effect of aluminum and the specific mechanism for early intervention and treatment of neurodegenerative diseases such as AD.The brain is the main oxygen-consuming organ of the human body.The neuron mitochondria have the highest oxygen consumption and generate much ROS,while the level of antioxidant enzymes in the brain is low,which determines that the earliest oxidative damage to the mitochondria would occur in the brain.In order to cope with the oxidative damage,NF-E2-related factor 2（Nrf2）will dissociate from the keap1 protein and enter the cell nucleus to combine with the antioxidant response elements,and induce the antioxidant enzymes expressions such as HO-1 and GCLC.At the same time,there are multiple repair mechanisms in the body,but DNA repair pathways in the mitochondria of brain neurons are limited,and mainly rely on base excision repair（BER）to repair DNA damage caused by oxidative stress.Breast cancer susceptibility gene 1（BRCA1）is an important tumor suppressor gene.In addition,it has important extra-tumor effects such as regulating gene transcription,oxidative stress,DNA repair,and cell proliferation.Studies have found that BRCA1levels in AD brains are significantly reduced.In the cerebral ischemia-reperfusion model,overexpression of BRCA1 activates Nrf2/ARE pathway and induces the antioxidant enzymes expression of HO-1 and NQO1,which can reduce the levels of ROS and lipid peroxidation.After long-term aluminum treatment of human breast cancer MCF-10A cells,BRCA1 mRNA and protein expression were significantly reduced,and oxidative stress was significantly increased.We use sub-chronic and chronic in vivo animal experiments to explore the possible role and mechanism of BRCA1 regulatory system in aluminum-induced neurotoxicity.Methods:In this study,sub-chronic（12 w）and chronic（36 w）aluminum exposure rat models were established by drinking water.Learning and memory ability of rats were detected by Morris water maze and shuttle box dark test;MDA and GSH contents in hippocampus were detect by kit;mitochondrial respiratory chain complex I（Complex I）and IV（Complex IV）,ATP,8-OHdG content were detected by Elisa kit;neuronal nDNA damage was detected by comet test;Real-time PCR and Western Blot were used to measure BRCA1,Nrf2,GCLC,HO-1,OGG1,APE1 mRNA and protein levels of rat hippocampal;immunofluorescence method was used to detect the content of Nrf2 in rat hippocampal;transmission electron microscope was used to observe the ultrastructure of neurons.Results:1.Hippocampus coefficient.Rat hippocampal coefficient was decreased in both sub-chronic and chronic AlCl₃-treated rats.2.Learning and memory ability.With the doses of sub-chronic and chronic AlCl₃ exposure increased,the swimming distance and escape latency of aluminum-exposed rats were increased and the swimming trajectories of aluminum-exposed rats looking for platforms were disordered;the residence time spent in target quadrant and numbers of target quadrant entering times in the AlCl₃-treated groups were significantly reduced.The purpose of the aluminum-exposed rat search platform gradually lost,and the high-dose group rarely entered the platform.In the dark avoidance test,the number of errors in sub-chronic and chronic AlCl₃ exposed rats was significantly increased and the latency to passive escape significantly was shortened at 6 h,24 h and 48 h.3.Oxidative damage.The content of MDA was significantly increased and the content of GSH was significantly decreased in hippocampus of sub-chronic and chronic AlCl₃-treated rats.4.Mitochondrial function.Complex I,Complex IV,ATP content were significantly decreased and 8-OHdG levels was increased in hippocampus of sub-chronic and chronic AlCl₃-treated rats.5.nDNA damage.The nDNA damage was significantly increased in hippocampus of sub-chronic and chronic AlCl₃-treated rats.6.BRCA1 level.The level of BRCA1 was significantly decreased in hippocampus of sub-chronic and chronic AlCl₃-treated rats.7.Changes in the Nrf2 pathway.Nrf2,HO-1 and GCLC were significantly reduced hippocampus of sub-chronic and chronic AlCl₃-treated rats.8.BER key enzyme levels.The levels of OGG1 and APE1 were increased in hippocampus of sub-chronic AlCl₃-treated rats;while the levels of OGG1 and APE1 were significantly decreased in hippocampus of sub-chronic AlCl₃-treated rats.9.Sub-chronic and chronic AlCl₃-treated rats had ultrastructural changes in hippocampal neurons,mitochondrial swelling,crista rupture,and increased mitochondrial vacuolation.Conclusions:1.Aluminum exposure could interfere with hippocampal tissue development.2.Aluminum exposure reduces the learning and memory abilities of rats.3.Aluminum exposure causes oxidative damage to rat hippocampus tissue.4.Aluminum exposure causes dysfunction of mitochondrial energy synthesis in rat hippocampal nerve cells and nDNA damage in nerve cells.5.Aluminum exposure reduces BRCA1expression in rat hippocampal nerve cells.6.Aluminum exposure could cause the expression of Nrf2,HO-1 and GCLC to decrease in rat hippocampal nerve cells,which may be related to the down-regulation of BRCA1.7.Sub-chronic aluminum exposure could compensatoryly activate the expression of OGG1 and APE1 in rat hippocampal nerve cells.Chronic aluminum exposure could inhibit the expression of OGG1 and APE1in rat hippocampal nerve cells.The dynamic changes of BER key enzymes may be regulated by the degree of oxidative stress and BRCA1.8.Aluminum exposure could damage the mitochondrial ultrastructure.9.After quercetin or resveratrol treatment,the above-mentioned injuries have been alleviated.