Change in the expression of aquaporin-4 in brain tissue after chronic cerebral ischemia

Abstract:

Objective：To investigate the change in the expression of aquaporin-4（AQP4） after chronic cerebral ischemia and the possible role of AQP4. Methods：A total of 40 Sprague-Dawley rats were randomly divided into control group（N group with 10 rats） and experimental group with 30 rats；according to the duration of cerebral ischemia，the experiment group was further divided into 2-week chronic cerebral ischemia group（2W group with 10 rats），1-month-old group（1M group with 10 rats），and 2-month-old group（2M group with 10 rats）. Ligation of both common carotid arteries was performed to establish a rat model of chronic cerebral ischemia. The wet-dry weight method was used to measure brain water content，hematoxylin and eosin staining was used to observe the histological changes of brain tissue，and Nissl staining was used to observe cell apoptosis. Immunofluorescence assay was used to measure the expression and distribution of AQP4，and Western blot was used to measure the relative expression level of AQP4 protein. Immunofluorescence assay was used to measure the expression of AQP4 and IBA1，a marker for microglial cells. Results：There was no significant difference in brain water content between the 2W/1M/2M groups and the N（77.778±0.042/77.813±0.142/77.805±0.027 vs. 77.786±0.029，F=0.136，P=0.936），and there was no significant difference between the 2W，1M，and 2M groups. Hematoxylin and eosin staining and Nissl staining showed that compared with the N group，the experimental group had disordered arrangement of brain cells，karyopyknosis or dis－appearance of nuclei in some cells，and a reduction in Nissl bodies. Immunofluorescence assay showed that compared with the N group，the 2W，1M，and 2M groups had significantly higher expression of AQP4 in the prefrontal lobe（166.722±3.660/200.347±0.284/229.333±5.033 vs. 90.000±1.000，F=1 089.311，P=0.000） and the parietal lobe（215.107±1.817/223.014±2.080/232.654±1.319 vs. 171.512±1.340，F=784.332，P=0.000），as well as activation and proliferation of microglial cells，and AQP4 was partially co-labeled with IBA1（prefrontal lobe：0.822±0.000/0.907±0.016/0.970±0.020 vs. 0.718±0.012，F=182.218，P=0.000；parietal lobe：0.912±0.005/0.966±0.003/0.751±0.003 vs. 0.861±0.009，F=785.416，P=0.000）. Western blotting showed that compared with the N group，the 2W，1M，and 2M groups had a significant increase in the expression of AQP4 in brain tissue over the time of ischemia（prefrontal lobe：0.938±0.028/1.185±0.011/1.515±0.060 vs. 0.589±0.026，F=587.102，P=0.000；parietal lobe：0.865±0.044/1.228±0.082/1.282±0.047 vs. 0.663±0.073，F=86.881，P=0.000）. Conclusion：After chronic cerebral ischemia，hypoxia and ischemia may cause neuronal apoptosis，activation and proliferation of microglial cells，and upregulation of AQP4 expression，suggesting that AQP4 may be involved in the inflammatory process after chronic cerebral ischemia.