Inhibitory effects of different concentrations of glutamate on neuronal activity
We used CCK8 assay to detect the effect of different concentrations of glutamate on HT22 cell line and primary cell activity. In HT22 cell line, the results showed that HT22 cell activity decreased significantly when treated with 2 mM and 8 mM glutamate for 24 h. Compared with the control group, there was statistical significance (P < 0.05). The inhibitory effect of 4 mM glutamate treatment for 24 h was weaker than that of 2 mM and 8 mM treatment groups, and there was no significant difference compared with the control group. When treated with high concentration glutamate (16, 32 mM), we did not observe the inhibitory effect of glutamate on the cells, and there was no significant difference compared with the control group. (Fig. 1a). Moreover, in primary cells, the results showed that cell activity decreased significantly after 24 h of glutamate treatment. Compared with the control group, the difference was statistically significant (P < 0.05). The inhibitory effect of 0.025 mM glutamate for 24 h was 50% compared with the control group. (Fig. 1b).
Glutamate treatment presented a time-dependent increase in mRNA levels of PINK1 in neurons
RT-PCR was used to detect mRNA level changes of PINK1 gene in HT22 cells treated with 8 mM glutamate for different periods of time. The results showed that the mRNA level of PINK1 presented a time-dependent increase, and the expression of PINK1 increased significantly at 6h of treatment. (Fig. 2a); Similarly, the mRNA level of PINK1 gene in primary cells treated with 0.025 mm glutamate for different time was detected by RT qPCR. The results showed that the mRNA level of PINK1 increased in a time-dependent manner, which was consistent with the results of HT22. The expression of PINK1 increased significantly after 6 h of treatment, which was statistically significant compared with the control group. After 12 h and 24 h treatment, PINK1 mRNA level increased, but the increase was slower than that of 6 h treatment. (Fig. 2b).
The effect of glutamate treatment on PINK1 translation in neurons at different times showed a trend of first increase and then decrease
The expression of PINK1 was detected by Western blot. In HT22 cells, the cells were treated with 8 mM glutamate for 3, 6, 12 and 24 h, The expression of PINK1 had a certain regularity at different time and reached the peak at 6 h. (Fig. 3a). After quantification, the expression of PINK1 reached the peak at 6 h, which was statistically significant compared with the control group (p < 0.05). In addition, after 3 h and 12 h treatment, the expression level of PINK1 also increased, which was statistically significant compared with the control group. However, the results showed that the expression of PINK1 had no statistical significance after glutamate treatment for 24 h. (Fig. 3c) Therefore, in the following experiment, the glutamate excitotoxicity model was established in HT22 cells under the condition of 8 mM / 6 h. In the primary neurons, the cells were treated with 0.025 mM glutamate for 3 h, 6 h, 12 h and 24 h. Western blot showed that the expression of PINK1 changed significantly at different time points. After 3 h, 6 h and 12 h, the expression of PINK1 increased significantly; (Fig. 3b). The quantitative results showed that the expression of PINK1 increased significantly after glutamate treatment for 3 h, 6 h, 12 h and 24 h, and reached the peak at 6 h, which was statistically significant compared with the control group. (Fig. 3d) Therefore, in the following experiment, the glutamate excitotoxicity model of primary neurons was established with 0.025 mM/6 h. Therefore, in the following experiment, we used 0.025 mM / 6 h to establish the glutamate excitotoxicity model of primary neurons.
The protein expression of PINK1 in neurons showed a trend of first increase and then decrease and localized in the cytosol
We further explored the expression and localization of PINK1 by immunofluorescence staining. The results showed that HT22 cells were treated with 8 mM glutamate for 3 h, 6 h, 12 h and 24 h, respectively. It was found that the fluorescence intensity was the highest at 6 h. The fluorescence intensity at 3 h was the second. After 12 h and 24 h treatment, the fluorescence intensity was the weakest. (Fig. 4a) The results of quantification confirmed our preliminary observation. The fluorescence intensity of cells after 6 h treatment was the strongest, which was statistically significant compared with the control group (P < 0.05). The fluorescence intensity after 3 h treatment was the second, and the results after 12 h and 24 h treatment were not statistically significant compared with the control group. (Fig. 4c) Similarly, the primary cells were treated with 0.025 mM glutamate for 3 h, 6 h, 12 h and 24 h, respectively. Preliminary observation showed that the fluorescence intensity was the highest at 6 h. The fluorescence intensity at 3 h and 12 h followed. After 24 h treatment, the fluorescence intensity was lower than that of the control group (Fig. 4b). The results of quantification confirmed our preliminary observation that the fluorescence intensity of cells treated for 6 h was the strongest, which was statistically significant compared with the control group (P < 0.05), followed by that of cells treated for 12 h, and that of cells treated for 3 h was weaker, and that of cells treated for 24 h was lower than that of the control group (Fig. 4d). On the other hand, immunofluorescence results showed that PINK1 was in the cytoplasm.
HT22 cells were transfected with LV-PINK1, CON-313, PINK1-RNAi (58770-2), PINK1-RNAi (58771-1), and PINK1-RNAi (58772-1) lentiviruses for 72 h)(Fig. S a). Proteins and RNA were extracted, and PINK1 transfection efficiency was detected by Western Blot, RT-PCR, and immunofluorescence staining. The results showed that PINK1 was significantly reduced at both transcriptional (Fig. S b) and translational (Fig. S c) levels after PINK1-RNAi (58771-1) transfection into HT22 cells, and empty virus vector CON-313 had no significant effect on PINK1 expression in HT22 cells. The results of fluorescence assay showed that LV-PINK1 and PINK1-RNAi (58771-1) lentiviruses were successfully transfected into HT22 cells (Fig. S d).
This part of the experiment was divided into five groups: control group (without any intervention), L-Glu group (to establish glutamate excitotoxicity model group), vehicle/L-Glu group (using control empty virus intervention and glutamate treatment), PINK1-RNAi/L-Glu group (using PINK1 interference lentivirus intervention and glutamate treatment), and LV-PINK1/L-Glu group (using PINK1 overexpression lentivirus intervention and glutamate treatment). The results showed that compared with the control group, the cell viability of the L-Glu group was significantly decreased; there was no significant difference in the cell viability of the vehicle/L-Glu group; compared with the vehicle/L-Glu group, the cell viability of the PINK1-RNAi/L-Glu group was significantly decreased while the cell viability of the LV-PINK1/L-Glu group was significantly increased (Fig. 5).