Targeting AQP4 localization as a novel therapeutic target in CNS edema

Homeostatic status of thyroid hormones and brain water movement as determinant factors in biology of cerebral gliomas: a pilot study using a bioinformatics approach

Introduction

The expression and localization of the water channel transporters, aquaporins (AQPs), in the brain are substantially modified in gliomas during tumorigenesis, cell migration, edema formation, and resolution. We hypothesized that the molecular changes associated with AQP1 and AQP4 in the brain may potentially be anticancer therapeutic targets. To test this hypothesis, a bioinformatics analysis of publicly available data from international consortia was performed.

Methods

We used RNA-seq as an experimental strategy and identified the number of differential AQP1 and AQP4 transcript expressions in glioma tissue compared to normal brain tissue.

Results

AQPs genes are overexpressed in patients with glioma. Among the glioma subtypes, AQP1 and AQP4 were overexpressed in astrocytoma (low-grade glioma) and classical (high-grade glioma). Overall survival analysis demonstrated that both AQP genes can be used as prognostic factors for patients with low-grade glioma. Additionally, we observed a correlation between the expression of genes involved in the tyrosine and thyroid hormone pathways and AQPs, namely: PNMT, ALDH1A3, AOC2, HGDATP1B1, ADCY5, PLCB4, ITPR1, ATP1A3, LRP2, HDAC1, MED24, MTOR, and ACTB1 (Spearman's coefficient = geq 0.20 and p-value = ≤ 0.05).

Conclusion

Our findings indicate that the thyroid hormone pathways and AQPs 1 and 4 are potential targets for new anti-tumor drugs and therapeutic biomarkers for malignant gliomas.

Astaxanthin ameliorates spinal cord edema and astrocyte activation via suppression of HMGB1/TLR4/NF-κB signaling pathway in a rat model of spinal cord injury

Spinal cord edema is a quick-onset phenomenon with long-term effects. This complication is associated with inflammatory responses, as well as poor motor function. No effective treatment has been developed against spinal edema, which urges the need to provide novel therapies. Astaxanthin (AST) is a fat-soluble carotenoid with anti-inflammatory effects and a promising candidate for treating neurological disorders. This study aimed to investigate the underlying mechanism of AST on the inhibition of spinal cord edema, astrocyte activation, and reduction of inflammatory responsesin a rat compression spinal cord injury (SCI) model. Male rats underwent laminectomy at thoracic 8-9, and the SCI model was induced using an aneurysm clip. After SCI, rats received dimethyl sulfoxide or AST via intrathecal injection. The effects of AST were examined on the motor function, spinal cord edema, integrity of blood-spinal cord barrier (BSCB), and expression of high mobility group box 1 (HMGB1), toll-like receptor 4 (TLR4), nuclear factor-kappa B (NF-κB), glial fibrillary acidic protein (GFAP), and aquaporin-4 (AQP4), and matrix metallopeptidase- 9 (MMP-9) post-SCI. We showed that AST potentially improved the recovery of motor function and inhibited the spinal cord edema via maintaining the integrity of BSCB, reducing the expression of HMGB1, TLR4, and NF-κB, MMP-9 as well as downregulation of astrocyte activation (GFAP) and AQP4 expression. AST improves motor function and reduces edema and inflammatory responses in the spinal tissue. These effects are mediated by suppression of the HMGB1/TLR4/NF-κB signaling pathway, suppressing post-SCI astrocyte activation, and decreasing AQP4 and MMP-9 expression.

The role of aquaporin 4 (AQP4) in spinal cord injury

Aquaporin-4 (AQP-4) is an aquaporin composed of six helical transmembrane domains and two highly conserved ASN-pro-ALA (NPA) motifs. It is strongly expressed in rodent and human spinal cord tissues and plays a key role in the pathological process after SCI. After SCI, edema, glial scarring, and inflammation can accelerate the progression of injury and lead to deterioration of function. Many studies have reported that AQP-4 plays an important role in SCI. In particular, it plays an important role in secondary pathological processes (spinal cord edema, glial scar formation, and inflammatory response) after SCI. Loss of AQP-4 has been associated with reduced spinal edema and improved prognosis after SCI in mice. In addition, downregulation of AQP-4 reduces glial scar formation and the inflammatory response after SCI. There is a consensus from numerous studies that AQP-4 may be a potential target for SCI therapy, which guides the ongoing investigation for molecular therapy of SCI. Here, we review the structure of AQP-4, its expression in normal and damaged spinal cord, and its role in SCI, as well as discuss the theoretical basis for the treatment of SCI.