The role of mammalian superaquaporins inside the cell

The mammalian two superaquaporins, AQP11 and AQP12, are present inside the cell and their null phenotypes in mice suggest their unusual functions.

The surveyed literature on these superaquaporins and our unpublished data has been incorporated to speculate their roles.

AQP11 and AQP12 have unique NPA boxes with a signature cysteine residue. Although some water permeability of AQP11 was demonstrated in liposomes and cultured cells, its permeability to glycerol is unknown. The function of AQP12 still remains to be clarified. AQP11 null mice develop polycystic kidneys following large intracellular vacuoles in the proximal tubule, which may be caused by ER stress or vesicle fusion failure. The role of AQP11 in the kidney and liver seems to alleviate the tissue damage and facilitate the recovery. Its expression in the sperm, thymus and brain suggests its potential roles in these organs in spite of the apparently normal null phenotype. Although AQP12 null mice appear normal, they suffer from severe pancreatitis, suggesting its role in the fusion of zymogen granules.

As many issues are unsolved, the clarification of the function and roles of the superaquaporin may lead to the identification of new roles of AQPs. This article is part of a Special Issue entitled Aquaporins.