Decreased Excretion of Urinary Exosomal Aquaporin-2 in a Puromycin Aminonucleoside-Induced Nephrotic Syndrome Model.

Urinary exosomes, small extracellular vesicles present in urine, are secreted from all types of renal epithelial cells. Aquaporin-2 (AQP2), a vasopressin-regulated water channel protein, is known to be selectively excreted into the urine through exosomes (UE-AQP2), and its renal expression is decreased in nephrotic syndrome. However, it is still unclear whether excretion of UE-AQP2 is altered in nephrotic syndrome. In this study, we examined the excretion of UE-AQP2 in an experimental rat model of nephrotic syndrome induced by the administration of puromycin aminonucleoside (PAN). Rats were assigned to two groups: a control group administered saline and a PAN group given a single intraperitoneal injection of PAN (125 mg/kg) at day 0. The experiment was continued for 8 days, and samples of urine, blood, and tissue were collected on days 2, 5, and 8. The blood and urine parameters revealed that PAN induced nephrotic syndrome on days 5 and 8, and decreases in the excretion of UE-AQP2 were detected on days 2 through 8 in the PAN group. Immunohistochemistry showed that the renal expression of AQP2 was decreased on days 5 and 8. The release of exosomal marker proteins into the urine through UEs was decreased on day 5 and increased on day 8. These data suggest that UE-AQP2 is decreased in PAN-induced nephrotic syndrome and that this reflects its renal expression in the marked proteinuria phase after PAN treatment.

Trimethylamine-N-oxide (TMAO) increased aquaporin-2 expression in spontaneously hypertensive rats.

Recent evidence suggests that elevated plasma levels of Trimethylamine-N-oxide (TMAO) can prolong the duration of elevated blood pressure in rats. The purpose of this study was to investigate the plasma TMAO level in Spontaneously Hypertensive Rats (SHR) and to explore the possible relationship between TMAO and aquaporin-2 (AQP-2) in the formation of hypertension. Twelve-week-old, male Spontaneously Hypertensive rats (SHR, n = 40) and Wistar-Kyoto rats (WKY, n = 40) were accordingly grouped into SHR group and WKY group. Each group was divided randomly into four subgroups: Untreated group, TMAO group, TMAO+Tolvaptan (TMAO+TVP) group, and TVP group, respectively. Systolic blood pressure (SBP), plasma TMAO, plasma osmolality (POsm), plasma vasopressin (PAVP), and plasma AQP-2 (PAQP-2) concentration were measured, and the expression of AQP-2 in kidney medulla was detected by RT-PCR and Western blot. At 14 weeks, rats in SHR TMAO group were shown the increased plasma TMAO, POsm, PAVP, and PAQP-2 levels, while those rats in SHR TMAO+TVP group were shown the decreased plasma TMAO, POsm, and PAQP-2 levels, but an even higher PAVP (due to the blockage of TVP to V2 receptor). These findings indicate that an increase of plasma TMAO levels in SHR leads to a higher plasma osmotic pressure, triggers the regulation of the TMAO-AVP-AQP-2 axis in SHR, elicits the greater water reabsorption, and eventually leads to hypertension.

Expression and significance of aquaporin-2 and serum hormones in placenta of patients with preeclampsia.

To evaluate the relationship between serum hormone or aquaporin-2 (AQP-2) and preeclampsia, patients with severe preeclampsia (A group), mild preeclampsia (B group), chronic hypertension (C group) and normal pregnant women (D group) were recruited and analysed. The AQP-2 level in placenta tissues was detected and the correlations of AQP-2 with serum hormone levels were analysed using linear correlation regression analysis. The differences of alpha foetal protein (AFP) and human chorionic gonadotropin (HCG) levels during mid-pregnancy, as well as the levels of AFP, HCG, unconjugated oestriol and progesterone during late pregnancy were significant among A, B, C and D groups (p < .05). The AQP-2 level in placenta tissues was higher in A group than that in other groups (p < .05). The AQP-2 was correlated with HCG (p < .05). In conclusion, AQP-2 may be involved in the development of severe preeclampsia, which may be related to serum HCG.

Aquaporin-2 urinary excretion in preterm infants: relationship to diuresis and vasopressin.

AIMS: Few investigations have explored the urinary aquaporin-2 (u-AQP2) excretion pattern after birth in preterm infants with conflicting results regarding the correlation between u-AQP2, urinary osmolality and vasopressin. The aims of this study were to evaluate u-AQP2 excretion during the first week of life in preterm infants, to correlate u-AQP2 with other markers of renal function and to investigate the relationship between u-AQP2, urinary tonicity and arginine-vasopressin in the immature kidney. METHODS: In infants born less than 33 weeks daily diuresis, u-AQP2, urinary arginine-vasopressin, urine and plasma tonicity, creatinine and electrolytes were measured through the first 7 days of life. RESULTS: Fifty-five infants were evaluated. u-AQP2 excretion showed the following profile: the highest u-AQP2 levels were found on day 2 and values remained significantly higher until day 5 with respect to day 1. On day 6, u-AQP2 levels significantly decreased to values closer to those found on day 1. u-AQP2 excretion was not associated with arginine-vasopressin while significant, but weak association was found with urinary tonicity (r = -0.20; -0.32 < r < -0.11; P < 0.05). u-AQP2 excretion and creatinine clearance were significantly associated during the study period (r = 0.19; 0.08 < r < 0.29; P < 0.05). There was a strong association between totally u-AQP2 excretion and diuresis over the week (r = 0.72; 0.66 < r < 0.76; P < 0.0001). CONCLUSION: Significant variations occur in AQP2 expression levels during the first week of life in preterm infants. AQP2 does not seem to contribute to the urinary concentration ability after birth. Further investigations are required to elucidate the mechanisms underlying the strong association between diuresis and u-AQP2 excretion in early postnatal life.

Compound heterozygous mutation of aquaporin 2 gene in woman patient with congenital nephrogenic diabetes insipidus.

We performed mutational analyses of a woman patient with congenital nephrogenic diabetes insipidus referred to us during pregnancy. The diagnosis was made during the neonatal period, after which she was treated with spironolactone and hydrochlorothiazide. Our examination showed the patient to be apparently in good health without definite evidence of dehydration. Serum and urine osmolality were 220 mOsm/L and 50 mOsm/L, respectively, and the serum concentration of AVP was 2.7 pg/mL. Results of a water-deprivation test performed after delivery were compatible with nephrogenic diabetes insipidus. Mutational analyses showed that the patient was a compound heterozygote with point mutations at nucleotide position 298 (G to A; G100R) in exon 1 and nucleotide position 374 (C to T; T125M) in exon 2 of the aquaporin 2 gene, which have been previously described.

Novel mutations underlying nephrogenic diabetes insipidus in Arab families.

PURPOSE: Nephrogenic Diabetes Insipidus (NDI) is genetically heterogeneous and may be inherited in an X-linked or autosomal recessive manner. We aimed to investigate the molecular basis of NDI among Arab families. METHODS: Direct sequencing of coding regions for AQP2 and AVPR2 was used to identify underlying mutations. One large deletion required Southern blot analysis and a PCR-based strategy to identify deletion junctions. RESULTS: We identified two novel missense mutations (AQP2:p.Gly100Arg and p.Gly180Ser) in AQP2 and one novel missense mutation (AVPR2:p.Gly122Asp), one previously reported missense mutation (AVPR2:p.Arg137His) and one novel contiguous deletion (AVPR2:c.25 + 273_ARHGAP4o:2650-420del) affecting AVPR2. We also describe evidence of lyonization associated with the novel deletion. CONCLUSIONS: Two novel mutations were identified in each of AVPR2 and AQP2 underlying CNDI in Arab families. Identification of these mutations will facilitate early diagnosis of CNDI, counseling of families and provide opportunities for early intervention aimed at reducing morbidity. The presence of affected females and consanguinity, as is often observed in Arab communities should not be used to rule out AVPR2 as a candidate when considering diagnostic testing. Careful observation of phenotypic heterogeneity should be used in referring such families for both AQP2 and AVPR2 molecular genetic testing.