Molecular mechanism of the carboxyl terminus of Hsc70-interacting protein in TAU hyperphosphorylation induced by AlCl3 in N2a cells.

Aluminum (Al) is recognized as a neurotoxin. Studies have confirmed that the neurotoxicity induced by Al may be related to tau hyperphosphorylation. Phosphorylated tau is degraded through the ubiquitin-proteasome pathway (UPP), in which the carboxyl terminus of Hsc70-interacting protein (CHIP) plays an important role. However, whether the CHIP plays a role in regulating tau hyperphosphorylation induced by Al is yet to be determined. The purpose of this study was to explore the molecular mechanism of the CHIP in tau hyperphosphorylation induced by AlCl3 in N2a cells. Mouse neuroblastoma cells (N2a) were exposed to different concentrations of AlCl3 (0, 0.5, 1, and 2 mM) and treated with CHIP/CHIP shRNA/CHIP (ΔU-box)/CHIP (ΔTPR) plasmid transfection. The cell viability was determined by the CCK-8 kit. Protein expression was detected by Western blot. The interaction between CHIP and AlCl3 exposure on the proteins was analyzed by factorial design ANOVA. The results showed that Al can cause tau hyperphosphorylation, mainly affecting the pThr231, pSer262, and pSer396 sites of tau in N2a cells. UPP is involved in the degradation of tau hyperphosphorylation induced by Al in N2a cells, of which CHIP may be the main regulatory target. Both the U-box and TPR domains of CHIP are indispensable and play an important role in the regulation of tau hyperphosphorylation induced by AlCl3 in N2a cells.

Mechanism by Which Aluminum Regulates the Abnormal Phosphorylation of the Tau Protein in Different Cell Lines.

Aluminum (Al) is an environmental neurotoxin to which humans are extensively exposed; however, the molecular mechanism of aluminum toxicity is unclear. Several studies have indicated that exposure to aluminum can cause abnormal phosphorylation of the tau protein. The purpose of this study was to investigate respectively the special molecular mechanism of abnormal regulation on synthesis and degradation of the tau protein induced by AlCl3 in cells of different species. The results of tau protein showed that the sites of abnormal tau phosphorylation induced by AlCl3 are Thr231, Ser262, and Ser396 in N2a cells. Meanwhile, the expressions of Thr181, Thr231, and Ser262 increased abnormally in SH-SY5Y cells. The result of the study showed that PP2A expression was high in N2a cells, while GSK-3ß and PP2A in SH-SY5Y cells were involved in the synthesis process of abnormal tau phosphorylation induced by AlCl3. In N2a cells, the ubiquitin-proteasome pathway (UPP) mainly regulated tau phosphorylation at Ser262 and Ser396. Meanwhile, in SH-SY5Y cells, the UPP mainly regulated tau phosphorylation at Thr231 and Ser396. In summary, the UPP is involved in the degradation of Tau that is abnormally phosphorylated induced by AlCl3, but this process is site-specific and differs in cells of different species.

Cross-sectional study based on occupational aluminium exposure population.

To evaluate the different characteristics of cognitive impairment caused by occupational aluminium exposure at different ages, we surveyed 1660 workers in Shanxi Aluminium Plant, China, and assessed their cognitive function and plasma aluminium concentration. In multiple linear regression, the scores of the digit-span test (DST) and digit-span backward test (DSBT) were negatively correlated with plasma aluminium concentration when concentration reached 34.52 µg/L in younger group (＜40 years), while in the middle-aged group (≥40 years) only found when concentration reached 42.25 µg/L (ß<0, P < 0.05). In logistic regression, when plasma aluminum concentration reached 42.25µg/L, odds ratios (95 % confidence interval) were 1.695 (1.062-2.705) and 3.270 (1.615-6.620) for DST, 7.644 (3.846-15.192) and 15.308 (4.180-56.059) for DSBT in middle-aged group and younger group, respectively. These results showed that aluminium exposures were associated with cognitive impairment among aluminium-exposed workers, particularly for young workers who were more susceptible.

[Regulatory role of Ca MK-â ¡ and PP2A on hyperphosphorylated tau induced by Al Cl_3 in SH-SY5Y cells].

OBJECTIVE: To explore the role of calcium/calmodulin-dependent protein kinase Ⅱ(CaMK-Ⅱ) and protein phosphatase-2 A(PP2 A) on hyperphosphorylation of tau induced by AlCl_3 in SH-SY5 Y cell. METHODS: SH-SY5 Y cells were assigned to the control group, AlCl_3 low, middle, high exposed groups(200, 400800 µmol/L Al~(3+)), KN93 intervention group(800 µmol/L Al~(3+)+0. 5 µmol/L KN93) and sphingosine intervention group(800 µmol/L Al~(3+)+5 nmol/L sphingosine). After 48 h of exposure and intervention, the viabilities of cells were measured by CCK-8 assay, the contents of CaMK-Ⅱ and PP2 A were determined by ELISA, and the expression of tau5 and phosphorylation of Thr-181, Thr-231, Ser-262 and Ser-396 were detected by Western-Blot. RESULTS: The viabilities of cells in AlCl_3 middle and high exposed groups were significantly lower than that of the control group(P<0. 05). Compared with the AlCl_3 high exposed group, the viabilities of cells in KN93 intervention group and sphingosine intervention group were significantly increased(P<0. 05), as well as the difference of the cell viability between sphingosine intervention group and the control group was not statistically significant. Compared with the control group, the contents of CaMK-Ⅱin AlCl_3 low, middle, high exposed groups were significantly increased(P<0. 05), while the contents of PP2 A in those groups were significantly decreased(P<0. 05). Compared with AlCl_3 high exposed group, the contents of CaMK-Ⅱ in KN93 intervention group and sphingosine intervention group were significantly decreased(P<0. 05), and PP2 A in those groups were significantly increased(P<0. 05). The expression of tau5 and phosphorylation of Thr-181, Thr-231, Ser-396 in AlCl_3 low, middle, high exposed group showed significantly higher than those of the control group(P<0. 05), while the phosphorylation of Ser-262 in AlCl_3 high exposed group showed significantly higher than that of the control group(P<0. 05). After intervention with KN93 and sphingosine, the expression of tau5, and phosphorylation of Thr-181, Thr-231, Ser-262, Ser-396 in KN93 intervention group and sphingosine intervention group were significantly lower than those of AlCl_3 high exposed group( P<0. 05), as well as compared with the control group, the phosphorylation of Ser-262 in KN93 intervention group and Thr-181, Thr-231 and Ser-396 in sphingosine intervention group were not statistical difference. CONCLUSION: AlCl_3 could increase the phosphorylation of Thr-181, Thr-231, Ser-262 and Ser396 in SH-SY5 Y cells, which mechanism may relate to the changes of CaMK-Ⅱand PP2 A. CaMK-Ⅱ mainly regulates the phosphorylation of Ser-262 induced by AlCl_3, while PP2 A mainly regulates the phosphorylation of Thr-181, Thr-231 and Ser-396 induced by AlCl_3. It is suggested that hyperphosphorylated tau protein induced by AlCl_3 is closely related to PP2 A.