水通道蛋白4在阿尔兹海默病脑组织间液引流改变中的作用

目的：通过磁共振成像（magnetic resonance imaging, MRI）示踪剂钆喷酸葡胺（gadolinium-diethylene triamine pentacetic acid, Gd-DTPA）在脑组织间隙（extracellular space，ECS）内扩散的特征,反映大鼠阿尔兹海默病（Alzheimer’s disease，AD）脑组织间液（interstitial fluid，ISF）引流的改变及水通道蛋白4（aquaporin-4，Aqp4）在AD中发挥的作用。方法：将野生型SD大鼠（300～350 g）和Aqp4基因敲除（Aqp4-/-）SD大鼠(300～350 g)分别分为Sham组（10只）、AD组（10只）、Aqp4-/--Sham组（10只）、Aqp4-/--AD组（10只）。Sham组和Aqp4-/- Sham组连续6周每天腹腔注射生理盐水，AD组和Aqp4-/- AD组连续6周每天腹腔注射D-半乳糖。将示踪剂Gd DTPA（10 mmol/L，2 μL）注射到大鼠海马区，分别于0.5 h、1 h、1.5 h、2 h、3 h 进行MRI扫描，观察示踪剂在海马区的动态分布，并测量示踪剂的扩散速率D*值、清除速率k′ 值和半衰期t1/2值。结果：Sham组示踪剂在ECS 内的扩散率D*值为（2.66±0.36）×10-6 mm2/s，AD组D*值（2.72±0.62）×10-6 mm2/s ，Aqp4-/--Sham组D*值（2.75±0.47）×10-6 mm2/s，Aqp4-/--AD组D*值（2.802±0.55）×10-6 mm2/s，4组之间差异无统计学意义（One-Way ANOVA，P>0.05）。Sham组海马区的示踪剂清除速率k′ 为（4.57±0.14）×10-4/s，AD组k′ 为（3.68±0.22）×10-4/s，Aqp4-/- Sham组k′ 为（3.17±0.16）×10-4/s，Aqp4-/--AD组k′ 为（2.59±0.19）×10-4/s，4组之间两两比较差异均具有统计学意义（one-way ANOVA，P<0.05），4组之间的示踪剂清除半衰期t1/2值依次延长,Sham组海马区的t1/2为（0.67±0.12） h，AD组t1/2为(0.88±0.08) h，Aqp4-/- Sham组t1/2 为（1.12±0.15） h，Aqp4-/- AD组t1/2 为（1.58±0.11） h，两两比较差异均具有统计学意义（One-Way ANOVA，P<0.05）。结论：AD的退行性病变使脑内ISF引流减慢，Aqp4的缺失使AD大鼠脑内ISF引流明显减慢，Aqp4对清除脑组织间隙的代谢废物具有重要作用。

Role of aquaporin-4 in the change of interstitial fluid drainage in Alzheimer's disease

Objective:To observe the characteristics of the interstitial fluid (ISF) drainage in the Alzheimer's disease (AD) rats through magnetic resonance imaging (MRI) tracer gadolinium-diethylene triamine pentacetic acid (Gd-DTPA)spread in the brain extracellular space (ECS) and to discuss the role of aquaporin-4 (Aqp4) in the AD.Methods:Wild type SD rats (300-350 g) and Aqp4 gene knock out (Aqp4-/-) SD rats (300-350g) were divided into Sham group,AD group,Aqp4-/--Sham group and Aqp4-/--AD group.Sham group and Aqp4-/--Sham group were injected with saline by intraperitoneal each day for 6 weeks,and the AD group and Aqp4-/--AD group were injected with D-galactose by intraperitoneal each day for 6 weeks.MRI tracer Gd-DTPA (10 mmol/L,2 μL) was injected into the hippocampus of the rats.MRI scan was performed at the end of 0.5 h,1.5 h,1 h,2 h,and 3 h to observe the dynamic distribution of the Gd-DTPA in the hippocampus and the diffusion rate D *,clearance rate k'and half-life t1/2 measured.Results:The diffusion rate D* in Sham group was (2.66 ±0.36) × 10-6 mm2/s,the diffusion rate D* in AD group was (2.72 ±0.62) × 10-6 mm2/s,the diffusion rate D* in Aqp4-/--Sham group was (2.75 ± 0.47) × 10-6 mm2/s,the diffusion rate D* in Aqp4-/--AD group was (2.802 ±0.55) × 10-6 mm2/s,and there was no statistically significant difference in the four groups (One-Way ANOVA,P ＞ 0.05).The clearance rate k'in Sham group was (4.57 ±0.14) ×10-4/s,the clearance rate k'in AD group was (3.68 ±0.22) × 10-4/s,the clearance rate k'in Aqp4-/--Sham group was (3.17 ±0.16) × 10-4/s,the clearance rate k'in Aqp4-/--AD group was (2.59 0.19) × 10-4/s,and there was significant difference in the four groups (OneWay ANOVA,P ＜ 0.05).The half-life t1/2 in Sham group was (0.67 ± 0.12) h,the half-life t1/2 in AD group was (0.88 ±0.08) h,the half-life t1/2 in Aqp4-/--Sham group was (1.12 ±0.15) h,the halflife t1/2 in Aqp4-/--AD group was (1.58 ± 0.11) h,and there was significance difference in the four groups(one-way ANOVA,P ＜ 0.05).Conclusion:The ISF drainage is slow after AD and the loss of Aqp4 in the AD makes the ISF drainage obviously slow down,Aqp4 plays an important role in AD to remove the metabolism of waste out of the brain.