A study on mechanisms of activating the RhoA/cofilin pathway to disrupt hippocampal synaptic plasticity to participate in aluminum toxicity-induced learning and memory impairments

GUO Jianxiong; LIU Wenjing; WANG Xiaoyi; CHENG Houzhi; ZHANG Lifeng; LIAO Suchan; LI Yanli; HUANG Junjie

doi:10.3969/j.issn.1674-3806.2024.07.17

Abstract：Objective To explore the effect of Ras homolog gene family member A(RhoA)/cofilin pathway activation on hippocampal synaptic plasticity and the mechanistic role of RhoA/cofilin pathway activation in aluminum toxicity-induced learning and memory impairments.Methods Twenty rats were randomly selected from 30 specific pathogen-free Sprague-Dawley rats and were injected intraperitoneally with maltol-aluminum solution for 2 months to establish a rat model of chronic aluminum intoxication.The aluminum-intoxicated model rats were divided into aluminum intoxication model group(10 rats)and RhoA inhibitor group(10 rats),and the latter group was injected intraperitoneally with Rhosin hydrochloride for 30 days.The remaining 10 normal rats from the 30 specific pathogen-free SD rats were used as blank control group.The learning and memory abilities of the rats were tested by Morris water maze experiment.Transmission electron microscopy was used to observe changes in the ultrastructure of synapses in the CA1 region of the hippocampus of the rats.Real-time fluorescent quantitative polymerase chain reaction(RT-qPCR)and immunohistochemical staining were used to detect the localized expressions of RhoA,cofilin,post-synaptic density protein-95(PSD-95)and synap-tophysin(SYN)in the CA1 region of the hippocampal tissues of the rats.Results The results of Morris water maze experi-ment showed that the latency period of the rats in the aluminum intoxication model group was significantly longer than that in the blank control group(P＜0.05),and the latency period of the rats in the RhoA inhibitor group was signifi-cantly shorter than that in the aluminum intoxication model group(P＜0.05).The results of RT-qPCR showed that compared with those in the blank control group,the level of RhoA mRNA expression in CA1 region of the hippocampal tissues in the aluminum intoxication model group increased,while the levels of cofilin mRNA,PSD-95 mRNA and SYN mRNA expressions decreased,and the differences were statistically significant(P＜0.05).Compared with those in the aluminum intoxication model group,the level of RhoA mRNA expression in the CA1 region of the hippocampal tissues of the rats in the RhoA inhibitor group decreased,and the levels of cofilin mRNA,PSD-95 mRNA and SYN mRNA expres-sions increased,and the differences were statistically significant(P＜0.05).The results of immunohistochemical staining showed that compared with the blank control group,the aluminum intoxication model group had an increase in the per-centage of RhoA-positive cells in the CA1 region of the hippocampus,while the aluminum intoxication model group had decreases in the percentages of cofilin-,PSD-95-,and SYN-positive cells,and the differences were statistically sig-nificant(P＜0.05).Compared with the aluminum intoxication model group,the RhoA inhibitor group had a decrease in the percentage of RhoA-positive cells in the CA1 region of the hippocampus,while the RhoA inhibitor group had increases in the percentages of cofilin-,PSD-95-,and SYN-positive cells,and the differences were statistically significant(P＜0.05).The results of the observations by using transmission electron microscopy revealed that compared with those in the blank control group,the number of synapses was less,and the thickness of the postsynaptic dense substance became thinner,and the width of the synaptic cleft became narrower in the aluminum intoxication model group,and the differ-ences were statistically significant(P＜0.05).The results of the observations by using transmission electron microscopy revealed that compared with those in the aluminum intoxication model group,the number of synapses was more,and the thickness of the postsynaptic dense substance became thicker,and the width of the synaptic cleft became wider in the RhoA inhibitor group,and the differences were statistically significant(P＜0.05).Compared with those in the blank control group,the mitochondrial morphology in the aluminum intoxication model group changed significantly,and the mitochondria in the RhoA inhibitor group slightly dilated and the membrane structure remained intact,and the mito-chondrial morphology and synaptic ultrastructure in the RhoA inhibitor group were better than those in the aluminum intoxi-cation model group.Conclusion Aluminum intoxication can disrupt hippocampal synaptic plasticity through the acti-vation of the RhoA/cofilin signaling pathway,subsequently affecting learning and memory abilities.