MO002THE EXPRESSION OF AQUAPORINS IN A MOUSE CEREBRAL ISCHEMIC MODEL WITH MANNITOL EFFECTS
Authors: Tanaka Yasuko , Koike Shin , Kashima Kaho , Kaseda Asuka , Ishibashi Kenichi 
Published: May 2021

Abstract

Background and Aims
As the brain edema influences the outcomes of many edematous brain diseases due to the limited intracranial space, the role of aquaporins (AQPs) in brain edema needs to be clarified to advance its treatment especially in increasing ischemic brain diseases. Although the importance of AQP4 at the Blood Brain Barrier (BBB) has been well characterized, the roles of other AQPs is still unknown, especially a relatively new AQP11. As AQP11 is expressed in the brain capillary (Koike S et al. Int J Mol Sci. 17:861, 2016), AQP11 may also be important for the regulation of brain edema. The aim of the present study is to clarify the role of AQP11 in cerebral ischemic model to identify new treatment of cerebral edema.

Method
AQP expression in the brain was examined by RT-PCR. Common cervical artery was ligated for 15 min to produce ischemic-reperfusion model of brain infarction to induce brain edema. As the first step to study the involvement of AQPs in this process, the mRNA expression of AQP1, AQP4, AQP11 and GFAP were monitored after reperfusion which are expressed at BBB. As mannitol is often employed for the treatment of brain edema, the effects of single or twice doses of 1.1M mannitol 0.1 mL/g body weight i.p. on the expression of AQP1, AQP4 and AQP11 mRNA were examined after 6 h in control mice. Furthermore, hypertonic 2M NaCl was also challenged to simulate the osmotic effect: a single or twice doses of 2M NaCl 0.16 mL/g body weight were administered intraperitoneally, i.p.

Results
The expression of AQP1 mRNA increased by 20% one and two hours after 15-min ligation, while the expression of AQP4 mRNA decreased transiently just after the ligation but increased at 24 h by 10%. On the other hand, the expression of AQP11 mRNA started to decrease from 30 min after the ligation to continue decreasing up to 24h by 40% in wild mice, while the decrease of AQP11 mRNA only observed at 24h by 20% in AQP11 heterogenous KO mice. A single mannitol i.p. did not change serum osmolality from 320 to 317 mOsm, while twice i.p. in 6 h interval increased serum osmolality to 328 mOsm. Both procedures similarly decreased the expression of all AQPs: AQP1 by 80%, AQP4 by 40%, and AQP11 by 50%. Similar studies were conducted with 2M NaCl. A single dose of 2M NaCl increased serum Na/Osm from 151/319 to 154/322 mEq/mOsm, which decreased AQP1 by 50%, AQP11 by 35% and no change of AQP4. On the other hand, twice doses in 3 h interval increased serum Na/Osm to 208/435 mEq/Osm, which did not change all AQP expressions.

Conclusion
As AQP4 KO mice survive longer in brain edema models, decrease of AQP4 by mannitol will be beneficial as brain infarction increased AQP4 expression in our study. However, further decrease of AQP11 by mannitol will be detrimental as AQP11 was already decreased in brain infarction. As AQP11 KO mice die within a month due to polycystic kidneys, the studies on brain infarction in brain capillary specific AQP11 conditionaly KO mice are currently underway.