Cell . . . How to cure the central nervous system edema - targeting the membrane positioning of the water channel protein AQP4.

Brain edema and spinal cord edema are usually referred to as central nervous system edema (CNS edema). They are mainly caused by trauma, infection, tumor growth and blood supply disorders, affecting millions of people every year.cytotoxic edema and vasogenic edema are two important reasons for the formation of CNS edema.cytotoxic edema refers to excessive accumulation of water in cells.for example, hypoxia can cause energy dependent solute homeostasis to be disrupted, so that water will flow along the osmotic gradient into the astrocytes around the blood vessels, causing them to swell. Br / >, which may lead to the accumulation of water in the blood barrier (BBB), which may lead to the accumulation of water in the brain.aquaporins (AQPs) play an important role in the development of cytotoxic edema.among them, AQP4 is the most important subtype of CNS, and is expressed in astrocytes in large quantities [1].the researchers found that brain edema induced by ischemia in aqp4-ko mice was reduced by 35% compared with that in the control group [2], indicating that AQP4 is a potential target for the treatment of CNS edema.unfortunately, despite years of efforts, up to now, all aquaporin inhibitors have stopped in clinical trials, which means that the only treatment option at present is to relieve the symptoms caused by edema, which can only "cure the symptoms", not "cure the symptoms".on May 14, 2020, Professor Roslyn M. bill from the school of life and Health Sciences, University of Aston, UK, and Professor Alex C. conner and Professor Zubair Ahmed from the school of medicine and dentistry, University of Birmingham, jointly published a study entitled targeting aquaporin-4 subcellular localization to treatment central nervous system edema on May 14, 2020.in this study, they developed an alternative approach to improve CNS edema by targeting AQP4 membrane localization rather than directly inhibiting AQP4 activity, and achieved success in rats with spinal cord injury.in 2015, Professor Alex C. Conner's team demonstrated that inhibition of calmodulin cam and kinase PKA activity can reduce the localization of AQP4 on cell membrane caused by hypotonic [3].previous studies have shown that controlling the size of astrocytes is the key to avoid CNS edema induced injury.therefore, the authors first tested whether the membrane localization of AQP4 was changed in the hypotonic and hypoxic models in astrocytes. The results showed that both the ATPase inhibitor (trp-704) and ATPase (trp-704) could inhibit the formation of astrocytes.in order to explore the role of cam in PKA activation, the authors detected the accumulation of camp in cells.the authors found that cAMP levels increased 10 fold under hypotonic treatment, but cam inhibitors could completely reverse this phenomenon.these experiments indicate that the activation of cam mediated by Ca2 + is necessary for PKA activation, and their activation is very important for the localization of AQP4 on astrocyte membrane.in order to explore whether reducing AQP4 membrane localization is effective in alleviating CNS edmema in vivo, the authors conducted a study in a rat model of spinal cord injury (SCI). the authors found that cam inhibitor (TFP) and PKA inhibitor (H89) can effectively inhibit the increase of spinal water content caused by spinal injury. at the same time, AQP4 membrane localization was increased in rats with spinal injury, while TFP and H89 treatment decreased AQP4 membrane localization, which was consistent with the previous results of spinal water content. in addition, the authors noted that TFP and H89 not only reduced the membrane localization of AQP4 on bscb, but also reduced the expression of AQP4 protein. Further experiments showed that these two inhibitors regulated AQP4 expression through pka-akt-foxo3a axis. the above experiments show that cam inhibitor (TFP) and PKA inhibitor (H89) can effectively reduce the membrane localization and expression of AQP4 and alleviate CNS edmema. in previous studies, we found that phosphorylation of AQP4 S276 site catalyzed by PKA is necessary but not sufficient for AQP4 membrane localization. This suggests that cam has other functions besides regulating AQP4 membrane through pKa, such as directly binding with AQP4. in fact, cam does report binding to other AQPs proteins [4]. by comparing with calmodulin target database, we found a cam binding sequence on the C-terminal of AQP4. through the structure prediction, the hydrophobic plane composed of three phenylalanine in this sequence may be the key region for cam binding. However, in vitro experiments showed that the full-length AQP4 could bind to cam, while the C-terminal deleted AQP4 (AQP4 - Δ 256) and phenylalanine substituted (aqp4-f258 / 262 / 266a) mutants lost the ability to bind to cam. This conclusion was further verified in the intracellular interaction experiments. at the same time, the authors demonstrated in vitro that the binding of AQP4 to cam could be antagonized by TFP in a concentration gradient manner. in addition, intracellular results showed that the time required for membrane localization of aqp4-f258 / 262 / 266a mutant was longer than that of aqp4-wt. these results indicate that the combination of cam and AQP4 is very important for the membrane localization of AQP4. finally, the electrophysiology and behavior of SCI model rats were verified. the results showed that TFP and H89 could significantly improve the perception and motor ability of spinal injury rats. in addition, the damage degree of bscb and the size of lesion cavity in the treatment group were also significantly improved compared with the control group. in conclusion: the team first elucidated how cam and PKA mediate the membrane localization of AQP4 on astrocytes (see figure below). secondly, on the basis of their previous work, they found a drug approved for clinical use - TFP, which can effectively relieve the edema of the central nervous system in rat models, and is expected to be applied in clinical practice in the future. although TFP, as an antagonist of dopamine and epinephrine receptors, is widely used as an antidepressant [5], the author ruled out that TFP plays a role through them. finally, this work provides a new idea for the intervention of central nervous system edema in the future. (2007). Aquaporin-4 and brain edema. Pediatr. Nephrol. 22, 778 – 784.2. Manley, g.t., Fujimura, M., Ma, T., noshita, N., N., Filiz, F., Bollen, A.W., Chan, P., and verkman, A.S. (2000). Aquaporin-4 and brain edema. Pediatr. Nephrol. 22, 778 – 784.2. Manley, g.t., Fujimura, M., Ma, T., nosita, N., N., Filiz, F., Bollen, A.W., Chan, P., and verkman, A.S., A.S. (2000), aquaporin-4 deletion in in in in-4 diabetes mellitus, in China's, A.S., and verkman, A.S. (2000), aquaporin brain edema after acute water intoxication and ischemic stroke. Nat. Med. 6, 159–163.3. Kitchen, P., Day, R.E., Taylor, L.H., Salman, M.M., Bill, R.M., Conner, M.T., and Conner, A.C. (2015). Identification and molecular mechanisms of the rapid tonicity-induced relocalization of the aquaporin 4 channel. J. Biol. Chem. 290, 16873–16881.4. Rabaud, N.E., Song, L., Wang, Y., Agre, P., Yasui, M., and Carbrey, J.M. (2009). Aquaporin 6 binds calmodulin in a calcium-dependent manner. Biochem. Biophys. Res. Commun. 383, 54–57.5. Creese, I., Burt, D.R., and Snyder, S.H. (1996). Dopamine receptor binding predicts clinical and pharmacological potencies of antischizophrenic drugs. J. Neuropsychiatry Clin. Neurosci. 8, 223–226.