Aquaporin 4

Aquaporin 4 also known as AQP4 is a is_associated_with::protein which in humans is encoded by the AQP4 is_associated_with::gene. AQP4 belongs to the is_associated_with::aquaporin family of is_associated_with::integral membrane proteins that conduct water through the is_associated_with::cell membrane.

Function
AQP4 is constitutively expressed in the basolateral cell membrane of principal collecting duct cells in the kidney and provide a pathway for water to exit these cells.

AQP4 is also expressed in is_associated_with::astrocytes and is upregulated by direct insult to the is_associated_with::central nervous system.

Pathology
Aquaporin-4 is the primary autoimmune target in is_associated_with::neuromyelitis optica, in which AQP4-specific IgG antibodies target astrocytic AQP4, resulting in complement activation and inflammation.