AQP2 and kidney disorder: Urinary extracellular vesicles (including exosomes) are considered to be “reservoirs” of altered proteins during PKD pathogenesis, in which many urinary proteins have been identified to be associated with kidney diseases or renal lesions, such as aquaporin 2 (AQP2), uromodulin, and beta-galactosidase (BGAL) (4).