AQP4 is an Emerging Regulator of Pathological Pain: A Narrative Review.

Pathological pain presents significant challenges in clinical practice and research. Aquaporin-4 (AQP4), which is primarily found in astrocytes, is being considered as a prospective modulator of pathological pain. This review examines the association between AQP4 and pain-related diseases, including cancer pain, neuropathic pain, and inflammatory pain. In cancer pain, upregulated AQP4 expression in tumor cells is linked to increased pain severity, potentially through tumor-induced inflammation and edema. Targeting AQP4 may offer therapeutic strategies for managing cancer pain. AQP4 has also been found to play a role in nerve damage. Changes in AQP4 expression have been detected in pain-related regions of the brain and spinal cord; thus, modulating AQP4 expression or function may provide new avenues for treating neuropathic pain. Of note, AQP4-deficient mice exhibit reduced chronic pain responses, suggesting potential involvement of AQP4 in chronic pain modulation, and AQP4 is involved in pain modulation during inflammation, so understanding AQP4-mediated pain modulation may lead to novel anti-inflammatory and analgesic therapies. Recent advancements in magnetic resonance imaging (MRI) techniques enable assessment of AQP4 expression and localization, contributing to our understanding of its involvement in brain edema and clearance pathways related to pathological pain. Furthermore, targeting AQP4 through gene therapies and small-molecule modulators shows promise as a potential therapeutic intervention. Future research should focus on utilizing advanced MRI techniques to observe glymphatic system changes and the exchange of cerebrospinal fluid and interstitial fluid. Additionally, investigating the regulation of AQP4 by non-coding RNAs and exploring novel small-molecule medicines are important directions for future research. This review shed light on AQP4-based innovative therapeutic strategies for the treatment of pathological pain. Dark blue cells represent astrocytes, green cells represent microglia, and red ones represent brain microvasculature.