Aquaporin in the proliferation and apoptosis of diabetic myocardial cells.

The aim of this study was to explore the effect of aquaporin on the molecular mechanism of human diabetic myocardial cell apoptosis. The methylthiazolyle tetrazolium assay was used to detect the inhibitory effect of different concentrations of aquaporin on cell growth. The rate of aquaporin-induced myocardial cell apoptosis was detected by flow cytometric analysis of Annexin V-fluorescein isothiocyanate/propidium iodide double-stained cells. We also attempted to quantify the expression of Bcl-2, Bax, caspase-3, and survivin in diabetic myocardial cells by western blot analysis. Aquaporin was found to inhibit the proliferation of diabetic myocardial cells in a concentration-dependent manner; the increase in aquaporin concentration led to an increase in Bax (apoptosis protein) expression, decrease in Bcl-2 expression (anti-apoptosis protein), increase in the Bax/Bcl-2 ratio, and a decrease in caspase-3 and survivin expression (P < 0.05). Therefore, aquaporin significantly inhibits the proliferation of diabetic myocardial cells and cell apoptosis in a dose-dependent manner by upregulating the ratio of Bax/Bcl-2 protein expression, activating the caspase-3 protein cascade, and regulating the expression of survivin.

The NPC motif of aquaporin-11, unlike the NPA motif of known aquaporins, is essential for full expression of molecular function.

The recently identified molecule aquaporin-11 (AQP11) has a unique amino acid sequence pattern that includes an Asn-Pro-Cys (NPC) motif, corresponding to the N-terminal Asn-Pro-Ala (NPA) signature motif of conventional AQPs. In this study, we examined the effect of the mutation of the NPC motif on the subcellular localization, oligomerization, and water permeability of AQP11 in transfected mammalian cells. Furthermore, the effect was also assessed using zebrafish. Site-directed mutation at the NPC motif did not affect the subcellular localization of AQP11 but reduced its oligomerization. A cell swelling assay revealed that cells expressing AQP11 with a mutated NPC motif had significantly lower osmotic water permeability than cells expressing wild-type AQP11. Zebrafish deficient in endogenous AQP11 showed a deformity in the tail region at an early stage of development. This phenotype was dramatically rescued by injection of human wild-type AQP11 mRNA, whereas the effect of mRNA for AQP11 with a mutated NPC motif was less marked. Although the NPA motif is known to be important for formation of water-permeable pores by conventional AQPs, our observations suggest that the corresponding NPC motif of AQP11 is essential for full expression of molecular function.

Urinary excretion of aquaporin-2 in pathological states of water metabolism.

Aquaporin-2 (AQP-2) is an arginine vasopressin (AVP)-regulated water channel in renal collecting duct cells. Approximately 3 % of AQP-2 in collecting duct cells is excreted into urine. Urinary excretion of AQP-2 varies widely in different physiological conditions, and it has a positive correlation with plasma AVP levels. Urinary excretion of AQP-2 was significantly increased by the single injection of AVP in patients with central diabetes insipidus. The urinary excretion of AQP-2 was one-eighth over in patients with central diabetes insipidus and three times greater in patients with impaired water excretion than that in normal subjects. In a hypertonic saline test, the urinary excretion of AQP-2 promptly increased 6-12-fold in normal subjects, but remained low in patients with central diabetes insipidus. In addition, exaggerated urinary excretion of AQP-2 persisted after an acute water load in patients with impaired water excretion. These results indicate that urinary excretion of AQP-2 is a potent marker for the diagnosis of water metabolism disorders dependent on AVP.