Aquaporin-4 is a protein that functions as a water channel in cell membranes, primarily found in the brain and spinal cord. It plays a crucial role in regulating water balance in the central nervous system, facilitating the movement of water in and out of cells. This helps maintain proper hydration and supports various physiological processes. Mutations or dysfunctions in aquaporin-4 can lead to neurological disorders, such as neuromyelitis optica, which is characterized by inflammation and damage to the spinal cord and optic nerves. Understanding aquaporin-4 is essential for developing potential treatments for these conditions.