Enhanced antinatriuresis in response to angiotensin II in essential hypertension

Extracellular vesicle-mediated transfer of donor genomic DNA to recipient cells is a novel mechanism for genetic influence between cells

Extracellular vesicles (EVs) carry signals within or at their limiting membranes, providing a mechanism by which cells can exchange more complex information than what was previously thought. In addition to mRNAs and microRNAs, there are DNA fragments in EVs. Solexa sequencing indicated the presence of at least 16434 genomic DNA (gDNA) fragments in the EVs from human plasma. Immunofluorescence study showed direct evidence that acridine orange-stained EV DNAs could be transferred into the cells and localize to and inside the nuclear membrane. However, whether the transferred EV DNAs are functional or not is not clear. We found that EV gDNAs could be homologously or heterologously transferred from donor cells to recipient cells, and increase gDNA-coding mRNA, protein expression, and function (e.g. AT1 receptor). An endogenous promoter of the AT1 receptor, NF-κB, could be recruited to the transferred DNAs in the nucleus, and increase the transcription of AT1 receptor in the recipient cells. Moreover, the transferred EV gDNAs have pathophysiological significance. BCR/ABL hybrid gene, involved in the pathogenesis of chronic myeloid leukemia, could be transferred from K562 EVs to HEK293 cells or neutrophils. Our present study shows that the gDNAs transferred from EVs to cells have physiological significance, not only to increase the gDNA-coding mRNA and protein levels, but also to influence function in recipient cells.

A novel-1364A/C aquaporin 5 gene promoter polymorphism influences the responses to salt loading of the renin-angiotensin-aldosterone system and of blood pressure in young healthy men

BACKGROUND

The family of aquaporin water channels contributes to water and salt homeostasis. AQP5 is a ubiquitously expressed exocrine-type water channel. Functional single nucleotide polymorphisms in AQP5 which alter gene transcription have not yet been described. We, therefore, sequenced the human AQP5 promoter to detect novel sequence variants which could impact upon AQP5 expression and contribute to the phenotypic variability of the renin-angiotensin-aldosterone system (RAAS).

METHOD AND RESULTS

Sequencing of the whole AQP5 promoter revealed a novel-1364A/C polymorphism. Substitution of C for A was associated with increased transcription factor binding as tested by electrophoretic mobility shift assay, but significantly reduced transcriptional activation of the AQP5 gene by cAMP and serum. The C allele was associated with significantly decreased mRNA in human heart and with decreased protein expression in erythrocyte membranes. Finally, we associated AQP5 genotypes with the variability of the RAAS in two independent study cohorts. First, we studied the phenotypic variability of the RAAS in 103 young (26 +/- 3 years) healthy males under an increased dietary salt intake. Increasing salt intake decreased plasma angiotensin II by 25% in AC/CC genotypes but only by 2% in AA genotypes (P = 0.012), and it decreased serum aldosterone by 34% in subjects with AC/CC genotypes but only by 19% in the AA genotypes (P = 0.005). Both genotypes had increased blood pressure under salt diet (P < 0.01), which was significantly more pronounced in AA genotypes (P = 0.029). Second, we investigated associations with variables of the RAAS in 96 old patients (68 +/- 10 years) with coronary artery disease scheduled for coronary artery bypass grafting. Aldosterone serum concentrations were 2-fold (P < 0.001) and angiotensin II plasma concentrations were 4-fold higher in AA genotypes than in AC/CC genotypes while ADH plasma concentrations did not differ.

CONCLUSION

A novel single nucleotide polymorphism in the AQP5 gene promoter alters AQP5 expression in different in vitro systems and cells, and is associated with alterations of variables of the RAAS both in young healthy males and in patients with coronary artery disease.

Nonmodulation and essential hypertension

Nonmodulation is a process in which there is a disorder in angiotensin-dependent control of the renal circulation and adrenal aldosterone release. The abnormalities are associated with an inability to handle a sodium load and salt-sensitive hypertension. All of the features are corrected by angiotensin-converting enzyme inhibition. A striking family history of hypertension and concordance of responses to angiotensin II in sibling pairs have suggested a familial factor. Genes governing renin substrate (angiotensinogen) production showed gene polymorphisms in nonmodulators. As nonmodulation occurs in approximately 40% of patients with essential hypertension, clearly other genes must contribute.

Reduced activity of the kallikrein-kinin system predominates over renin-angiotensin system overactivity in all conditions of sodium balance in essential hypertensives and family-related hypertension

OBJECTIVE

To study the renin-angiotensin-aldosterone and kallikrein-kinin systems in essential hypertensives and offspring of hypertensive parents during different sodium loads, and to explore their possible influence on renal hemodynamics.

METHODS

Forty-five essential hypertensives (35 +/- 4 years old, 25 males), 30 offspring of hypertensive parents (26 +/- 8 years old, 16 males) and 30 normotensive controls (28 +/- 5 years old, 20 males) were submitted to three different sodium loads (high, 250 mmol/l; normal, 140 mmol/l; and low, 20 mmol/l). Blood pressure, plasma renin activity, serum aldosterone, total kallikrein and urinary kallikrein-like activity were measured after each period. Effective renal plasma flow and glomerular filtration rate were also measured. In essential hypertensive subjects, renal hemodynamic and hormonal parameters were also measured after 3 days of 20 mg enalapril administration.

RESULTS

Plasma renin activity and serum aldosterone were higher in normotensives, essential hypertensives and offspring of hypertensive parents only during low sodium intake, whereas urinary kallikrein activity was lower in hypertensive offspring and essential hypertensives, compared with normotensives, during the three diet conditions. Effective renal plasma flow was found to be reduced in hypertensives and normotensive offspring, while the glomerular filtration rated was similar in the three groups. Angiotensin converting enzyme inhibitor (ACEI) administration to essential hypertensives for 3 days normalized effective renal plasma flow, increased plasma renin activity and decreased aldosterone and urinary kallikrein activity.

CONCLUSIONS

Our observations confirmed the presence of a hormonal imbalance between the renin-angiotensin-aldosterone system and the kallikrein-kinin system, not only in essential hypertensives but also in the offspring of hypertensive parents. This imbalance probably affects the renal circulation and sodium homeostasis, since there was reduced effective renal plasma flow in both populations compared with normotensive subjects. The positive effect of ACEI, resulting in normalization of the effective renal plasma flow in essential hypertensive patients, suggests the involvement of both systems in impaired renal circulation.

Altered aldosterone response to salt intake and angiotensin II infusion in young normotensive men with parental history of arterial hypertension

OBJECTIVE

An increased sensitivity to angiotensin II (Ang II) has been observed in patients with established hypertension. In the current study we tested whether young normotensive subjects with positive family history of arterial hypertension exhibit an increased sensitivity to Ang II, thereby potentially contributing to the pathogenesis of essential hypertension in these subjects.

METHODS AND DESIGN

Normotensive young men (25 +/- 2 years) with positive family history (PFH) (n = 28) and negative family history (NFH) (n = 60) of arterial hypertension were investigated to study aldosterone response, and systemic and renal haemodynamic changes (p-aminohippurate- and inulin-clearance) to Ang II infusion (0.5 and 3.0 ng/min per kg). In addition, aldosterone response to salt loading (5 g/day for 1 week) was analysed.

RESULTS

Ambulatory blood pressure (ABP) (mean: 84 +/- 4 versus 83 +/- 4 mmHg; NS), body mass index (23.5 +/- 2.5 versus 24.1 +/- 2.4 kg/m(2); NS), and urinary sodium excretion (191 +/- 55 versus 170 +/- 73 mmol/24 h; NS) did not differ between PFH and NFH at baseline. Changes in BP, urinary sodium and potassium excretion were similar between PFH and NFH in response to salt loading. However, salt loading did not result in an adequate suppression of aldosterone in PFH compared with NFH (8 +/- 62 versus -32 +/- 39 pg/ml; P < 0.001). Baseline values and changes in mean arterial BP (NFH: +13.4 +/- 7.6; PFH: +14.4 +/- 5.3 mmHg; NS), renal plasma flow (NFH: - 113 +/- 68; PFH: - 122 +/- 64 ml/min; NS) and glomerular filtration rate (NFH: +5.0 +/- 5.3; PFH: +4.2 +/- 8.3 ml/min; NS) in response to Ang II (3.0 ng/min per kg) were similar between the two groups. In contrast, the increases in serum aldosterone (PFH: 63.6 +/- 70.1 versus NFH: 37.7 +/- 46.8 pg/ml; P < 0.05) and urinary potassium excretion (PFH: 0.05 +/- 0.1 versus NFH: -0.01 +/- 0.07 mmol/min; P < 0.05) 30 min after stopping Ang II infusion were more pronounced and prolonged in PFH than in NFH.

CONCLUSIONS

Our findings suggest that young normotensive subjects with parental history of arterial hypertension are characterized by an inadequate suppression of aldosterone production in response to salt loading and an exaggerated and prolonged hyper-responsiveness of aldosterone secretion in response to Ang II. This might contribute to the increased risk for the development of essential hypertension in subjects with positive family history of arterial hypertension.