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Objective To investigate the effect and mechanism of proteasome inhibitor MG132 on memory impairment induced by chronic hypoxia in mice. Methods (1) A hypoxic model of the mouse midbrain dopaminergic neuron cell line MN9D was established using a hypoxia workstation. To observe the effects of hypoxia on the expression of TH, Ub-K48 and Ub-K63, MN9D cells were divided into normoxia group and hypoxia (12 h, 24 h and 48 h) groups. To observe the effects of MG132 on the expression of the above-mentioned proteins, MN9D cells were divided into normoxia group, hypoxia group and hypoxia + MG132 (25, 50, 100, 200 μmol/L) group. (2) A mouse model of memory impairment was established using a hypobaric chamber. To observe the effects of hypobaric hypoxia on the expression of TH, Ub-K48 and Ub-K63 in the substantia nigra compacta (SNc) of mice, thirty C57BL/6 mice were randomly and equally divided into normoxia group and hypobaric hypoxia (3 d and 21 d) groups, 10 in each group. To observe the effects of MG132 on spatial memory impairment induced by hypobaric hypoxia, twenty-four C57BL/6 mice were randomly and equally divided into normoxia group, hypobaric hypoxia 21 d group and hypobaric hypoxia 21 d+MG132 group, 8 in each group. (3) The protein expression levels of TH, Ub-K48, and Ub-K63 in MN9D cells which were either subjected to different durations of hypoxia treatment or pre-treated with MG132 prior to hypoxia treatment were detected using Western blotting (WB). The novel object recognition test was used to detect the memory function of mice. Immunofluorescence was used to detect the proportion of positive immunoreactive area of TH response in the SNc region. The expression levels of TH, Ub-K48, and Ub-K63 in the SNc region were detected by WB. Results (1) Compared with normoxia group, MN9D cells in hypoxia 24 h group showed increasing expression of Ub-K48 and Ub-K63 (P<0.05), and decreasing expression of TH (P<0.05), and MN9D cells in all hypoxia groups showed increasing expression of Ub-K48/TH and Ub-K63/TH (P<0.05). Compared with hypoxia group, MN9D cells showed decreasing expression of Ub-K48/TH and Ub-K63/TH in hypoxia + MG132 100 umol/L group and hypoxia + MG132 200 umol/L group (P<0.05). (2) Compared with the mice in normoxia group, mice in 3 d and 21 d hypobaric hypoxia groups showed decreasing expression of TH (P<0.001), and increasing expression of Ub-K48/TH and Ub-K63/TH (P<0.05) in the SNc region. Compared with normoxia group, the mice in 21 d hypobaric hypoxia group showed a lower new object recognition index (P<0.01), and the proportion of positive immunoreactive area of TH response in the SNc region (P<0.05). Compared with 21 d hypobaric hypoxia group, the mice in hypobaric hypoxia 21 d+MG132 group showed a higher new object recognition index (P<0.01). Conclusion The proteasome inhibitor MG132 could alleviate the memory impairment induced by chronic hypoxia in mice, and its mechanism may be related to the inhibition of Ub-K63 and Ub-K48, which in turn upregulates expression of TH in dopaminergic neurons.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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