Expression of aquaporin 4 in contused brain tissue and its relationship with brain edema

Objective To observe the expression of aquaporin 4 (AQP-4) in contused brain tissue and its relationship with brain edema following brain trauma. Methods A retrospective case control analysis was made on 42 patients with severe brain trauma admitted from January 2015 to March 2016. There were 23 males and 19 females, aged from 23 to 62 years [(35.5±5.6)years]. Glasgow coma score (GCS) was 3-5 points in 7 patients, 6-8 points in 23 and 9-10 points in 12. Brain tissue removed from the area 1 cm near the contusion during the cranial surgery were allocated to study group (n=42), while brain tissue removed far from the contusion after internal decompression were used as control (n=8). Ultrastructure of brain tissues was observed under electron microscope. Water content of brain tissue was measured by dry-wet weight method and expression of AQP-4 was measured by immunohistochemical method at postinjury hours 96. Results Morphology and structure of brain tissue in control group were normal. Whereas in study group, the intracellular and interstitial edema were obvious and morphological structure were damaged. Water content and AQP-4 expression in control group showed no obvious increase after operation(73.55±0.10, 0.193±0.016). Water content in study group increased significantly compared to control group and reached the peak value (81.28±0.56) at postinjury 24-72 hours (P<0.01). AQP-4 expression in study group increased at postinjury 6 hours (0.242±0.023) and reached a peak at postinjury 24-72 hours (0.338±0.013), with significant difference compared to control group (P<0.05). Correlation analysis showed change of brain water content was positively correlated with expression level of AQP-4 (r=0.931, P<0.01). Conclusion Expression of AQP-4 in the injured area of brain trauma is significantly increased along with the increase of water content, suggests that the upregulation of AQP-4 plays an important role in traumatic brain edema. Key words: Craniocerebral trauma; Brain edema; Aquaporin 4; Ultrastructure