AQP4, or Aquaporin-4, is a protein that functions as a water channel in the cell membranes of various tissues, particularly in the brain and spinal cord. It plays a crucial role in regulating water balance and maintaining the proper function of cells by facilitating the movement of water in and out of cells. This is essential for processes such as maintaining osmotic balance and supporting neuronal function. AQP4 is primarily found in astrocytes, a type of glial cell in the central nervous system. Its presence is vital for the brain's response to changes in water levels, which can occur during conditions like edema or stroke. Abnormalities in AQP4 function have been linked to several neurological disorders, highlighting its importance in brain health.