AQP4 (aquaporin-4) is a water-specific channel protein that forms the structural and functional foundation of the brain's glymphatic system 1. As the most abundantly expressed aquaporin in the central nervous system, AQP4 is localized to astrocyte end-feet and is essential for maintaining brain water homeostasis by facilitating water exchange across the blood-brain interface 1. The channel mediates cerebrospinal fluid influx into brain parenchyma along paravascular spaces surrounding penetrating arteries and enables interstitial fluid drainage along paravenous pathways, thereby supporting solute clearance including beta-amyloid peptides crucial for neurological health 1. AQP4 also modulates extracellular space volume and potassium buffering, factors regulating neuronal excitability 2. AQP4 dysfunction is pathologically relevant across multiple CNS disorders. In neuromyelitis optica spectrum disorder (NMOSD), serum autoantibodies against AQP4 (AQP4-IgG) serve as a biomarker present in approximately 80% of cases 3. Higher AQP4 antibody titers correlate with increased disease severity and visual disability 4. AQP4 alterations also associate with epilepsy pathogenesis and multiple neurodegenerative conditions 1, positioning AQP4 as a promising therapeutic target for CNS disorders affecting glymphatic clearance function.