Journal
RESPIRATORY PHYSIOLOGY & NEUROBIOLOGY
Volume 159, Issue 3, Pages 324-330Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.resp.2007.02.012
Keywords
water permeability; AQP; pulmonary edema; alveolus; epithelium; transgenic mouse
Categories
Funding
- NEI NIH HHS [EY13574, R01 EY013574-10, R01 EY013574] Funding Source: Medline
- NHLBI NIH HHS [R01 HL073856-08, HL59198, R01 HL059198-09, R01 HL073856, R01 HL059198, HL73856] Funding Source: Medline
- NIBIB NIH HHS [EB00415, R37 EB000415-18, R01 EB000415, R37 EB000415] Funding Source: Medline
- NIDDK NIH HHS [DK72517, P30 DK072517, DK35124, R37 DK035124-22, R01 DK035124, P30 DK072517-05, R37 DK035124] Funding Source: Medline
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Aquaporins (AQPs) are small, integral membrane proteins that facilitate water transport across cell membranes in response to osmotic gradients. Water transport across epithelia and endothelia in the peripheral lung and airways occurs during airway hydration, alveolar fluid transport and submucosal gland secretion. Several AQPs are expressed in the lung and airways: AQP1 in microvascular endothelia, AQP3 and AQP4 in airway epithelia, and AQP5 in type I alveolar epithelial cells, submucosal gland acini, and a subset of airway epithelial cells. Phenotype analysis of transgenic knockout mice lacking AQPs has defined their roles in the lung and airways. AQP1 and AQP5 provide the principal route for osmotically driven water transport between airspace and capillary compartments; however, alveolar fluid clearance in the neonatal and adult lung is not affected by their deletion, nor is lung fluid accumulation in experimental models of lung injury. In the airways, though AQP3 and AQP4 facilitate osmotic water transport, their deletion does not impair airway hydration, regulation of airway surface liquid, or fluid absorption. In contrast to these negative findings, AQP5 deletion in submucosal glands reduced fluid secretion by >50%. The substantially slower fluid transport in the lung compared to renal and secretory epithelia probably accounts for the lack of functional significance of AQPs in the lung and airways. Recent data outside of the lung implicating the involvement of AQPs in cell migration and proliferation suggests possible new roles for lung AQPs to be explored. (C) 2007 Elsevier B.V. All rights reserved.
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