Aquaporin 4 and brain-related disorders: Insights into its apoptosis roles

Evaluation of AQP4 functional variants and its association with fragile X-associated tremor/ataxia syndrome

Introduction

Fragile X-associated tremor/ataxia syndrome (FXTAS, OMIM# 300623) is a late-onset neurodegenerative disorder with reduced penetrance that appears in adult FMR1 premutation carriers (55-200 CGGs). Clinical symptoms in FXTAS patients usually begin with an action tremor. After that, different findings including ataxia, and more variably, loss of sensation in the distal lower extremities and autonomic dysfunction, may occur, and gradually progress. Cognitive deficits are also observed, and include memory problems and executive function deficits, with a gradual progression to dementia in some individuals. Aquaporin 4 (AQP4) is a commonly distributed water channel in astrocytes of the central nervous system. Changes in AQP4 activity and expression have been implicated in several central nervous system disorders. Previous studies have suggested the associations of AQP4 single nucleotide polymorphisms (SNPs) with brain-water homeostasis, and neurodegeneration disease. To date, this association has not been studied in FXTAS.

Methods

To investigate the association of AQP4 SNPs with the risk of presenting FXTAS, a total of seven common AQP4 SNPs were selected and genotyped in 95 FMR1 premutation carriers with FXTAS and in 65 FMR1 premutation carriers without FXTAS.

Results

The frequency of AQP4-haplotype was compared between groups, denoting 26 heterozygous individuals and 5 homozygotes as carriers of the minor allele in the FXTAS group and 25 heterozygous and 2 homozygotes in the no-FXTAS group. Statistical analyses showed no significant associations between AQP4 SNPs/haplotypes and development of FXTAS.

Discussion

Although AQP4 has been implicated in a wide range of brain disorders, its involvement in FXTAS remains unclear. The identification of novel genetic markers predisposing to FXTAS or modulating disease progression is critical for future research involving predictors and treatments.

The role of aquaporin 4 in brain tumors: implications for pathophysiology, diagnosis and therapy

Primary brain tumors are a heterogeneous group of tumors that arise from cells intrinsic to the central nervous system (CNS). Aquaporin-4 (AQP4) has been implicated in the pathogenesis of brain tumors. Previous reports have documented a relationship between AQP4 and several molecular pathways associated with the etiology of brain tumors, such as apoptosis, invasion and cell migration. AQP4 affects apoptosis via cytochrome C, Bad and Bcl-2, as well as invasion and migration via IDO1/TDO-Kyn-AhR axis, lncRNA LINC00461, miR-216a, miRNA-320a and MMPs. In addition, inhibition of AQP4 mitigates the progression of brain tumors. This review summarizes current knowledge and evidence regarding the relationship between AQP4 and brain tumors, and the mechanisms involved.

Aquaporin 4 in Traumatic Brain Injury: From Molecular Pathways to Therapeutic Target

Traumatic brain injury (TBI) is known as an acute degenerative pathology of the central nervous system, and has been shown to increase brain aquaporin 4 (AQP4) expression. Various molecular mechanisms affect AQP4 expression, including neuronal high mobility group box 1, forkhead box O3a, vascular endothelial growth factor, hypoxia-inducible factor-1 α (HIF-1 α) sirtuin 2, NF-κB, Malat1, nerve growth factor and Angiotensin II receptor type 1. In addition, inhibition of AQP4 with FK-506, MK-801 (indirectly by targeting N-methyl-D-aspartate receptor), inactivation of adenosine A2A receptor, levetiracetam, adjudin, progesterone, estrogen, V1aR inhibitor, hypertonic saline, erythropoietin, poloxamer 188, brilliant blue G, HIF-1alpha inhibitor, normobaric oxygen therapy, astaxanthin, epigallocatechin-3-gallate, sesamin, thaliporphine, magnesium, prebiotic fiber, resveratrol and omega-3, as well as AQP4 gene silencing lead to reduced edema upon TBI. This review summarizes current knowledge and evidence on the relationship between AQP4 and TBI, and the potential mechanisms involved.