Aquaporin-4 protein expression in normal canine brains

Aquaporin-4 as a New Potential Molecular Biomarker for Prognosis of Low-Grade Glioma: Comprehensive Analysis Based on Online Platforms

OBJECTIVE

Aquaporin-4 (AQP4) is a significant factor in transcellular and transepithelial water movement, and abnormal expression of AQP4 has been detected in many types of tumors. The purpose of this study was to explore its role in low-grade gliomas (LGG) using freely available online bioinformatics tools.

METHODS

OncoLnc database was used to analyze Cox coefficients and compare AQP4 expression between various types of tumors; Tumor Immune Estimation Resource database and Gene Expression Profiling Interactive Analysis were used to compare gene expression between LGG and normal tissues; University of California Santa Cruz Xena browser generated Kaplan-Meier survival curves in the LGG cohort in The Cancer Genome Atlas and subgroups; LinkedOmics database screened the most relevant genes based on Pearson correlation coefficient; Gene Ontology Biological Process and Kyoto Encyclopedia of Genes and Genomes enrichment analysis were performed through gene set enrichment analysis to explore possible molecular mechanisms.

RESULTS

LGG had higher AQP4 expression compared with normal tissues and ranked first among 21 different types of cancer (P < 0.05). The oligodendroglioma group had the lowest AQP4 expression and the longest overall survival (OS) (P < 0.05). LGG with astrocytoma, isocitrate dehydrogenase mutation, or 1p/19q codeletion had lower AQP4 expression and longer OS (P < 0.001). LGG with lower AQP4 expression, without 1p/19q codeletion, without chemotherapy, and with or without radiation therapy had longer OS (P < 0.05). AQP4 and coexpressed genes were involved in complex biological processes in LGG, including regulation of neurotransmitter level, peroxisome proliferator-activated receptor signaling pathway, cell adhesion molecules, and others.

CONCLUSIONS

AQP4 is a prognostic marker in LGG and its subgroups. Patients with lower AQP4 expression may have longer OS.

A Novel Gating Mechanism of Aquaporin-4 Water Channel Mediated by Blast Shockwaves for Brain Edema

As the principal water channel in the brain, aquaporin-4 (AQP4) plays a vital role in brain edema, but its role in blast brain edema is unclear. On the basis of molecular simulations, we reveal the atomically detailed picture of AQP4 in response to blast shockwaves. The results show that the shockwave alone closes the AQP4 channel; however, shock-induced bubble collapse opens it. The jet from bubble collapse forcefully increases the distance between helices and the tilt angles of six helices relative to the membrane vertical direction in a very short time. The average channel size increases about 2.6 times, and the water flux rate is nearly 20 times higher than for normal states. It is responsible for abnormal water transport and a potential cause of acute blast brain edema. Additionally, the open AQP4 channel quickly returns to its normal state, which is in turn helpful for edema absorption. Thus, a novel gating mechanism for AQP4 related to the secondary structure change has been provided, which is different from the previous residue-mediated gating mechanism.