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Background Aluminum (Al) can cause irreversible damage to neurons and synapses function, and the mechanism may be connected to mitochondrial damage caused by glycogen synthase kinase-3β (GSK-3β) regulating dynamin-related protein 1 (DRP1), resulting in inhibition of the growth of neuronal protrusions. Objective To investigate the role of GSK-3β regulating DRP1 in the inhibition of primary hippocampal neurite growth induced by Al. Methods Neurons were extracted from the hippocampus of newborn mice (≤24 h old) for primary culture. On day 6, the purity of neurons was detected by immunofluorescence. On day 10, neurons with good growth state were selected for Al exposure and GSK-3β inhibitor SB216763 (SB) intervention. The experiment design included a blank control group, a dimethyl sulfoxide (DMSO) group, an Al (20 μmol·L−1) group, a SB (1 μmol·L−1) group, and a SB (1 μmol·L−1) + Al (20 μmol·L−1) group. After primary hippocampal neurons were treated with Al or SB for 48 h, cell viability was detected by CCK-8 assay, the mitochondrial morphology of primary hippocampal neurons was observed by transmission electron microscopy, the total protrusion length of primary hippocampal neurons was scanned and analyzed by laser confocal imaging, and their complexity was analyzed by Sholl analysis. The expression levels of phospho-GSK-3β, GSK-3β, and DRP1 were detected by Western blotting. Results The immunofluorescent results showed that the purity of primary neurons was higher than 90%. After the Al exposure and the SB intervention for 48 h, compared with the blank control group, there was no obvious difference in cell viability in the DMSO group and the SB group (P>0.05), and the Al group showed reduced cell viability (P=0.006); there was no obvious difference in cell viability between the SB+Al group and the Al group (P>0.05). Compared with the blank control group, there was no obvious difference in the average total length of protrusion in the DMSO group and the SB group (P>0.05), and the Al group showed reduced average total length of neurite (P<0.001); the average total neurite length in the SB+Al group was significantly increased compared with that in the Al group (P=0.001). The results of Sholl analysis revealed that, within 130 μm from the cytosol, the number of intersections of neurons in each group increased with the increase of distance. Above 130 μm from the cytosol, the number of intersections of neurons in each group decreased gradually with increase of distance. At 130 μm and 310 μm from the cytosol, compared with the blank control group, the number of neuronal intersections in the DMSO group and the SB group had no obvious difference (P>0.05), and that in the Al group was significantly reduced (P<0.05); there was no obvious difference in the number of neuronal intersections between the SB+Al group and the Al group (P>0.05). The mitochondrial structure of the blank control group was complete and the crest was clearly visible; there was no apparent variation in the mitochondrial structure in the DMSO group and the SB group; the mitochondria in the Al group were vacuolated and the crista disappeared; the SB+Al group showed clearer crista than the Al group. The difference in GSK-3β phosphorylation level among groups was statistically significant (F=45.841, P<0.001). Compared with the blank control group, the GSK-3β phosphorylation level showed not significantly different in the DMSO group (P>0.05), increased in the SB group (P=0.022), and significantly reduced in the Al group (P<0.001); the GSK-3β phosphorylation level was significantly higher in the SB+Al group than in the Al group (P<0.001). The difference in DRP1 protein level among groups was statistically significant (F=8.389, P=0.003). Compared with the blank control group, the DRP1 protein levels in the DMSO group and the SB group were not significantly different (P>0.05), and significantly increased in the Al group (P=0.001); the DRP1 protein level in the SB+Al group was significantly lower than that in the Al group (P=0.029). Conclusion Al may increase the level of DRP1 protein by activating GSK-3β, causing mitochondrial damage and inhibiting neuronal protrusions growth.
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Background Aluminum can cause synaptic plasticity damage in the hippocampus, probably due to blocked interneuronal signal transmission. MicroRNA-29a (miR-29a) can target phosphatase and tensin homolog deleted on chromosome ten (PTEN) expression and participate in the generation of neuronal networks, and may be involved in the effect of aluminum on the electrical activity of neuronal networks. Objective To study the role and mechanism of miR-29a-targeted PTEN in aluminum-induced neuronal network injury in primary hippocampal neurons of ICR mice treated with maltol aluminum [Al(mal)3] in vitro. Methods Primary hippocampal neurons of ICR mice born within 24 h were cultured in vitro. The purity of neurons was determined by labeling neuron-specific microtubule-associated protein 2 (MAP2) by immunofluorescence staining on day six of the culture; neurons were treated with different concentrations of Al(mal)3, and divided into a control group, and 10, 20, and 40 μmol·L−1 Al(mal)3 groups, and neuronal cell viability was detected by CCK-8 method. Al(mal)3 at 20 μmol·L−1 was selected for subsequent experiments to establish a neuronal network injury model for intervention. The lentivirus infection method was used to transfect miR-29a into neurons, which were divided into mNG, mNG+20 μmol·L−1 Al(mal)3, miR-29a, and miR-29a+20 μmol·L−1 Al(mal)3 groups, and micro-electrode array (MEA) was used to analyze the firing of neuronal network. The expressions of miR-29a and PTEN mRNA in each group were detected by real-time PCR (RT-PCR), and the expression of PTEN protein in each group was detected by Western blotting. Results The purity of primary mouse hippocampal neurons was greater than 90%, and the viability of the neurons was above 80% in all groups. At 48 h of the designed Al(mal)3 treatments, the changes in spike frequency, burst frequency, network burst frequency, and synchrony index of neurons cultivated on MEA plates in the control group were 207.56%±38.70%, 73.19%±46.43%, 75.42%±33.04%, and 117.13%±15.54%, respectively; the Al(mal)3 groups’ neuronal network electrical activity showed a decreasing trend. Compared with the control group, the spike frequency, burst frequency, network burst frequency, and synchrony index of the 20 and 40 μmol·L−1 Al(mal)3 groups significantly decreased (The changes were 171.70%±28.08%, 49.20%±23.23%, 50.20%±18.18%, and 85.45%±20.30%; 150.68%±26.15%, 43.43%±15.54%, 52.05%±26.31%, and 26.80%±8.29%, respectively, P < 0.05). Compared with the control group (1.00), the miR-29a relative expression levels were significantly decreased in the 20 μmol·L−1 Al(mal)3 group (0.74±0.09) and the 40 μmol·L−1 Al(mal)3 group (0.62±0.12) (P < 0.05); the relative expression levels of PTEN mRNA were significantly increased in the 20 μmol·L−1 Al(mal)3 group (1.32±0.12) and the 40 μmol·L−1 Al(mal)3 group (1.48±0.11) (P < 0.05); the PTEN protein relative expression levels (1.29±0.12 and 1.82±0.10, respectively) were also significantly increased (P < 0.05). By overexpressing miR-29a in mouse primary hippocampal neurons, the spike frequency, burst frequency, and network burst frequency were significantly higher in the miR-29a group compared with the mNG group (The changes were 252.80%±62.03%, 171.65%±56.30%, and 197.75%±27.12%, respectively, P<0.05). The mNG+20 μmol·L−1 Al(mal)3 group showed a significant decrease in all indicators of neuronal network electrical activity (The changes were 123.28%±47.31%, 66.62%±31.53%, 70.60%±12.48%, and 52.86%±20.26%, respectively, P < 0.05). Compared with the mNG+20 μmol·L−1 Al(mal)3 group, the electrical activity indicators of neuronal network were significantly higher in the miR-29a+20 μmol·L−1 Al(mal)3 group (The changes were 161.41%±42.13%, 101.16%±30.63%, 127.02%±29.58%, and 109.73%±15.61%, respectively, P < 0.05). Compared with the mNG group (1.00), the neuronal PTEN mRNA relative expression (0.67±0.11) and the PTEN protein expression (0.75±0.08) were decreased in the miR-29a group (P < 0.05); the PTEN mRNA relative expression (1.32±0.12) and the PTEN protein relative expression (1.46±0.15) in the mNG+20 μmol·L−1 Al(mal)3 group were increased (P < 0.05). Compared with the mNG+20 μmol·L−1 Al(mal)3 group, the PTEN mRNA relative expression (0.93±0.06) and the PTEN protein relative expression (0.92±0.09) were decreased in the miR-29a+20 μmol·L−1 Al(mal)3 group (P < 0.05). Conclusion Aluminum significantly inhibits the electrical activity of hippocampal neuronal networks, and miRNA-29a may be involved in the aluminum-induced impairment of hippocampal neuronal network electrical activity by regulating PTEN expression.
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Background Aluminum can induce irreversible structural and synaptic functional damage, and the associated mechanism may be related to the neurite damage regulated by glycogen synthase kinase-3β (GSK-3β)/collapsin response mediator protein 2 (CRMP2). Objective This experiment is conducted to investigate the effect of aluminum-maltolate [Al(mal)3] on primary hippocampal neuron neurites in mice, and reveal the role of GSK-3β-CRMP2 in this process. Methods The hippocampus of newborn ICR mice (≤ 24 h old) was used for primary neuronal cultures. On the 5th day in vitro (DIV5), neuron purity detection were performed by confocal laser scanning microscopy. On DIV7, the neurons were transfected with lentiviral vector-mediated mNeonGreen. On DIV10, the neurons with mNeonGreen fluorescence in good growth state were treated with Al(mal)3. The stage I experimental groups were blank control group, maltol group, 10 µmol·L−1 Al group, 20 µmol·L−1 Al group, and 40 µmol·L−1 Al group. Then 20 µmol·L−1 Al was used to establish a model of neurite injury and for the intervention. The stage II experimental groups were blank control group, dimethyl sulfoxide (DMSO) group, Al (20 µmol·L−1) group, SB (GSK-3β inhibitor, 1 µmol·L−1), and SB (1 µmol·L−1)+Al (20 µmol·L−1) group. CCK-8 method was used to detect the viability of neurons. The primary hippocampal neurons of mice were scanned with high content analysis system at 0 h and 48 h after Al or SB treatment, and the density and length of neurites were analyzed. Western blotting was used to detect the expression and phosphorylation levels of CRMP2 and GSK-3β in primary hippocampal neurons of mice. Results The immunofluorescence results showed that the purity of primary neurons was more than 90%. Compared with the blank control group in stage I, the cell viability rates of the 10, 20, and 40 µmol·L−1 Al groups were decreased after 48h of Al(mal)3 treatment (P<0.05), while the cell viability rate of the maltol group had no significant change. There was no significant difference in cell viability rate among the DMSO group, the SB group, and the control group after 48h of SB treatment, and the viability rate of neurons in the SB+Al group was higher than that in the Al group (P<0.05) in stage II. The 48 h/0 h ratios of average number and length of neurites in the control group were 90.13%±11.70% and 113.24%±8.34%, respectively. The 48 h/0 h ratios in the Al group were 56.47%±16.36% and 62.06%±6.75%, respectively, which were lower than those in the control group (P<0.05). The 48 h/0 h ratios of average number of neurites in the SB group (99.03%±21.83%) was not significantly different from that in the control group, but the 48 h/0 h ratio of average length of neurites in the SB group (128.72%±15.39%) was higher than that in the control group (P<0.05). The 48 h/0 h ratios of average number (72.59%±10.89%) and length of neurites (93.84%±14.65%) in the SB+Al group were significantly increased compared with those in the Al group (P<0.05). Western blotting results showed that: There was no significant difference in GSK-3β protein level among all groups; compared with the control group (1.00±0.18), the protein level of p-GSK-3β in the Al group (0.45±0.05) was significantly decreased, and that in the SB group (1.32±0.23) was significantly increased; the protein level of p-GSK-3β in the SB+Al group (0.80±0.05) was significantly higher than that in the Al group (P<0.05). Compared with the control group (1.00±0.07), the CRMP2 protein level in the Al group (0.66±0.11) was significantly decreased (P<0.05), while that in the SB group (1.01±0.02) was not significantly changed. Compared with the control group (1.00±0.13), the p-CRMP2 protein level in the Al group (1.50±2.18) was significantly increased, and that in the SB group (0.62±0.09) was significantly decreased (P<0.05); the protein level of p-CRMP2 in the SB+Al group (1.28±0.24) was lower than that in the Al group (P<0.05). Conclusion Aluminum may activate GSK-3β, increase CRMP2 phosphorylation level, and damage neurite growth.