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Normal Function
The AQP2 gene provides instructions for making a protein called aquaporin 2. This protein forms a channel that carries water molecules across cell membranes. It is found in the kidneys in structures called collecting ducts, which are a series of small tubes that reabsorb water from the kidneys into the bloodstream.
The aquaporin 2 water channel plays an essential role in maintaining the body's water balance. The placement of these channels is controlled by a hormone called arginine vasopressin (AVP), which is sometimes also called antidiuretic hormone (ADH). When a person's fluid intake is low or when a lot of fluid is lost (for example, through sweating), AVP is released from the brain, where it is produced and stored. This hormone triggers chemical reactions that ultimately insert aquaporin 2 water channels into the membrane of collecting duct cells. These channels allow water to be reabsorbed into the bloodstream, which makes the urine more concentrated. When fluid intake is adequate, less AVP is released, and aquaporin 2 water channels are removed from the membrane of collecting duct cells. At these times, less water is reabsorbed into the bloodstream and the urine is more dilute.
Health Conditions Related to Genetic Changes
Arginine vasopressin resistance
Multiple variants (also called mutations) in the AQP2 gene have been identified in people with arginine vasopressin resistance. People with this condition produce an excessive amount of urine (polyuria), which depletes the amount of water in the body. This water loss also leads to excessive thirst (polydipsia).
Most of the AQP2 gene variants that cause this condition produce an aquaporin 2 protein that is folded incorrectly. The misfolded protein remains trapped within the cell, where it is unable to reach the cell membrane to transport water molecules. Some variants result in the production of functional aquaporin 2 water channels, but these channels are misrouted within the cell and do not reach the cell membrane.
If aquaporin 2 water channels are not inserted into the membrane of collecting duct cells, the kidneys are unable to respond to signals from AVP. As a result, collecting ducts do not reabsorb water as they should, leading to polyuria in people with arginine vasopressin resistance.
More About This Health ConditionOther Names for This Gene
- AQP-2
- AQP-CD
- AQP2_HUMAN
- aquaporin-2
- aquaporin-CD
- water-channel aquaporin 2
- WCH-CD
Additional Information & Resources
Tests Listed in the Genetic Testing Registry
Scientific Articles on PubMed
Catalog of Genes and Diseases from OMIM
References
- Chen L, Higgins PJ, Zhang W. Development and Diseases of the Collecting Duct System. Results Probl Cell Differ. 2017;60:165-203. doi: 10.1007/978-3-319-51436-9_7. Citation on PubMed
- Deen PM, Verdijk MA, Knoers NV, Wieringa B, Monnens LA, van Os CH, van Oost BA. Requirement of human renal water channel aquaporin-2 for vasopressin-dependent concentration of urine. Science. 1994 Apr 1;264(5155):92-5. doi: 10.1126/science.8140421. Citation on PubMed
- Knoers NV, Deen PM. Molecular and cellular defects in nephrogenic diabetes insipidus. Pediatr Nephrol. 2001 Dec;16(12):1146-52. doi: 10.1007/s004670100051. Citation on PubMed
- Loonen AJ, Knoers NV, van Os CH, Deen PM. Aquaporin 2 mutations in nephrogenic diabetes insipidus. Semin Nephrol. 2008 May;28(3):252-65. doi: 10.1016/j.semnephrol.2008.03.006. Citation on PubMed
- Noda Y, Sasaki S. Updates and Perspectives on Aquaporin-2 and Water Balance Disorders. Int J Mol Sci. 2021 Nov 30;22(23):12950. doi: 10.3390/ijms222312950. Citation on PubMed
- Noda Y, Sohara E, Ohta E, Sasaki S. Aquaporins in kidney pathophysiology. Nat Rev Nephrol. 2010 Mar;6(3):168-78. doi: 10.1038/nrneph.2009.231. Epub 2010 Jan 26. Citation on PubMed
- Robben JH, Knoers NV, Deen PM. Cell biological aspects of the vasopressin type-2 receptor and aquaporin 2 water channel in nephrogenic diabetes insipidus. Am J Physiol Renal Physiol. 2006 Aug;291(2):F257-70. doi: 10.1152/ajprenal.00491.2005. Citation on PubMed
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