Effects Of AMPA Receptor And PSD-95 Palmitoylation Imbalance On LTP Damage Induced By Aluminum In Rats

Objecetive:To study the role and mechanism of palmitoylation imbalance of amino-3-hydroxy-5-methyl-4-isoxazolyl propionic acid（AMPA）receptor and postsynaptic density protein 95（PSD-95）in aluminum-induced the damage of LTP of hippocampus in rats.Methods:To establish animal model of aluminum exposure:60 healthy and aged 2 months male SD rats were randomly and equally divided into four groups:normal saline（blank control group）、10?mol/kg、20?mol/kg and 40?mol/kg Al（mal）₃.The rats were exposed to Al（mal）₃ for 12 weeks by intraperitoneal injection,every other day,respectively.1.LTP of hippocampus was detected by electrophysiology after exposure.2.The expression level of AMPA receptor was detected by Immunohistochemistry.3.Palmitoylation levels of AMPA receptor and PSD-95 were determined by acyl biotin exchange method.4.The expression of zDHHC3 and PPT1 was detected by Western-Blot and RT-PCR.Results:1.The results of LTP showed that the amplitude of 60min in the 10?mol/kg Al（mal）₃group was lower than that in the blank control group（P<0.05）.The amplitude of the20?mol/kg Al（mal）₃ group was decreased in 1min compared with blank control and10?mol/kg Al（mal）₃ group,the amplitude caused a decrease in 60min compared with blank control group（P<0.05）.The amplitude of the 40?mol/kg Al（mal）₃ group was decreased in 1min compared with blank control and 10?mol/kg Al（mal）₃ group,the amplitude caused a decrease in 60min in the blank control、10?mol/kg Al（mal）₃ and40?mol/kg Al（mal）₃ group（P<0.05）.2.Immunohistochemical results showed that the expression level of GluR1 protein in the 10?mol/kg Al（mal）₃,20?mol/kg Al（mal）₃ and 40?mol/kg Al（mal）₃ groups was significantly different from that in the blank control group（P<0.05）.The difference between the 20?mol/kg Al（mal）₃ group and the 10?mol/kg Al（mal）₃ group was statistically significant（P<0.05）.The difference between the 40?mol/kg Al（mal）₃ group and the10?mol/kg Al（mal）₃ and 20?mol/kg Al（mal）₃ group was statistically significant（P<0.05）.The expression level of GluR2 protein in 10?mol/kg Al（mal）₃,20?mol/kg Al（mal）₃ and40?mol/kg Al（mal）₃ groups was significantly different from that in blank control group（P<0.05）,and the 40?mol/kg Al（mal）₃ group was lower than 10?mol/kg Al（mal）₃and 20?mol/kg Al（mal）₃ group（P<0.05）.3.The results of acyl biotin exchange showed that the 20?mol/kg Al（mal）₃ and40?mol/kg Al（mal）₃ group was lower than blank control group in level of GluR1palmitoylation（P<0.05）.The 20?mol/kg Al（mal）₃ group was decreased in level of GluR2palmitoylation compared with blank control group（P<0.05）.The level of GluR2palmitoylation in the 40?mol/kg Al（mal）₃ group was lower than that in the blank control group,the 40?mol/kg Al（mal）₃ group was lower than blank control,10?mol/kg Al（mal）₃and20?mol/kg Al（mal）₃ group（P<0.05）.The level of PSD-95 palmitoylation in the 20?mol/kg Al（mal）₃ and 40?mol/kg Al（mal）₃ groups was decreased with the blank control group（P<0.05）.4.Western-Blot results showed that the levels of zDHHC3 in blank control,10?mol/kg Al（mal）₃,20?mol/kg Al（mal）₃ and 40?mol/kg Al（mal）₃ group were 1±0.00,0.76±0.15,0.60±0.06,0.53±0.08,respectively.The difference between the 40?mol/kg Al（mal）₃ group and the blank control group was statistically significant（P<0.05）,and the40?mol/kg Al（mal）₃ group was lower than 10?mol/kg Al（mal）₃ group（P<0.05）.The levels of PPT1 in blank control,10?mol/kg Al（mal）₃,20?mol/kg Al（mal）₃ and 40?mol/kg Al（mal）₃ group were 1±0.00,1.28±0.32,1.56±0.36,1.61±0.28,respectively.There was significant difference between 40?mol/kg Al（mal）₃ group and blank control group（P<0.05）.5.RT-PCR results showed that the expression of zDHHC3 was decrease with the increase of aluminum exposure.The expression of zDHHC3 gene in 10?mol/kg Al（mal）₃,20?mol/kg Al（mal）₃ and 40?mol/kg Al（mal）₃ groups decreased by 16%,15%and 32%compared with blank control group.The expression of zDHHC3 gene in 10?mol/kg Al（mal）₃ and 20?mol/kg Al（mal）₃ groups had significant difference compared with blank control group（P<0.05）.The 40?mol/kg Al（mal）₃ group had significant difference with other groups（P<0.05）.The expression of PPT1 gene increased with the increase of aluminum exposure.Compared with the blank control group,the expression of PPT1 gene in 10?mol/kg Al（mal）₃,20?mol/kg Al（mal）₃ and 40?mol/kg Al（mal）₃ groups increased by58%,72%and 81%,respectively.The expression of PPT1 gene in 10?mol/kg Al（mal）₃,20?mol/kg Al（mal）₃ and 40?mol/kg Al（mal）₃ groups was higher than blank control group（P<0.05）,and 20?mol/kg Al（mal）₃ and 40?mol/kg Al（mal）₃ groups was higher than10?mol/kg Al（mal）₃ groups（P<0.05）.Conclusions:1.Subchronic intraperitoneal injection of aluminum reduced the excitatory postsynaptic potential,LTP and AMPAR expression in the hippocampus CA1 region of rats.2.The degree of palmitoylation in hippocampus of rats that exposed to aluminum was decreased,suggesting that aluminum may decrease the expression of AMPAR and PSD-95by affecting its palmitoylation,which may lead to the damage of LTP.3.The expression of zDHHC3 is decreased at gene and protein levels and the expression of PPT1 is increased at gene and protein levels in the hippocampus of rats that exposed to aluminum.These results suggest that aluminum may lead to abnormal expression of palmitoylated and depalmitoylated enzymes,which may lead to the imbalance of palmitoylation.