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.