Striatin Gene Variants Are Associated With Salt Sensitivity of Blood Pressure by Mechanisms That Differ in Women and Men

BACKGROUND

Salt sensitivity of blood pressure (SSBP) is a substantial risk factor for cardiovascular morbidity and mortality. Striatin (STRN) is critical for estrogen and aldosterone nongenomic signaling. However, the role of biological sex on the SSBP phenotype associated with STRN gene variants remains unexplored.

METHOD

Data from 1306 subjects participating in the Hypertensive Pathotype (HyperPATH) Consortium were used to identify STRN gene single-nucleotide variants associated with SSBP. Haploblock analysis revealed a novel diplotype in the upstream regulatory region of STRN (rs888083 and rs6744560), with 31% of subjects being homozygous for the risk diplotype.

RESULTS

Individuals homozygous for the risk diplotype had significantly greater SSBP than nonrisk diplotypes (P<0.009). While a significant genotype/SSBP association was present in both sexes, their potential mechanisms differed. Women, but not men homozygous risk diplotypes, had significantly greater aldosterone levels than nonrisk diplotypes (5.8±0.4 versus 3.2±0.7 ng/dl; P=0.01; liberal Na+ diet, adjusted). Men, but not women, homozygous risk diplotypes, had significantly reduced renal plasma flow response to Angiotensin II than nonrisk diplotypes (delta 95.2±5.2 versus 122.9±10.2 mL/min per 1.73 m2; P=0.01; liberal Na+ diet, adjusted). The single-nucleotide variants composing the risk diplotype were associated with lower STRN mRNA expression in human tissues (in silico).

CONCLUSION

In women, the primary driver of SSBP is increased aldosterone, while in men, it is reduced renal plasma flow responses. Thus, despite a common hypertensive phenotype (SSBP) in both sexes, the specific treatment approaches might differ to increase therapeutic gain and mitigate adverse effects. These genetic- and sex-based observational results require confirmation in a prospective clinical study.

Effects of Mineralocorticoid Receptor Blockade and Statins on Kidney Injury Marker 1 (KIM-1) in Female Rats Receiving L-NAME and Angiotensin II

Kidney injury molecule-1 (KIM-1) is a biomarker of renal injury and a predictor of cardiovascular disease. Aldosterone, via activation of the mineralocorticoid receptor, is linked to cardiac and renal injury. However, the impact of mineralocorticoid receptor activation and blockade on KIM-1 is uncertain. We investigated whether renal KIM-1 is increased in a cardiorenal injury model induced by L-NAME/ANG II, and whether mineralocorticoid receptor blockade prevents the increase in KIM-1. Since statin use is associated with lower aldosterone, we also investigated whether administering eiSther a lipophilic statin (simvastatin) or a hydrophilic statin (pravastatin) prevents the increase in renal KIM-1. Female Wistar rats (8-10 week old), consuming a high salt diet (1.6% Na+), were randomized to the following conditions for 14 days: control; L-NAME (0.2 mg/mL in drinking water)/ANG II (225 ug/kg/day on days 12-14); L-NAME/ANG II + eplerenone (100 mg/kg/day p.o.); L-NAME/ANG II + pravastatin (20 mg/kg/day p.o.); L-NAME/ANG II + simvastatin (20 mg/kg/day p.o.). Groups treated with L-NAME/ANG II had significantly higher blood pressure, plasma and urine aldosterone, cardiac injury/stroke composite score, and renal KIM-1 than the control group. Both eplerenone and simvastatin reduced 24-h urinary KIM-1 (p = 0.0046, p = 0.031, respectively) and renal KIM-1 immunostaining (p = 0.004, p = 0.037, respectively). Eplerenone also reduced renal KIM-1 mRNA expression (p = 0.012) and cardiac injury/stroke composite score (p = 0.04). Pravastatin did not affect these damage markers. The 24-h urinary KIM-1, renal KIM-1 immunostaining, and renal KIM-1 mRNA expression correlated with cardiac injury/stroke composite score (p < 0.0001, Spearman ranked correlation = 0.69, 0.66, 0.59, respectively). In conclusion, L-NAME/ANG II increases renal KIM-1 and both eplerenone and simvastatin blunt this increase in renal KIM-1.

Abstract 122: Effect Of Tie2-cre Endothelial Caveolin-1 Deficiency Mice On Murine Cardiovascular And Metabolic Phenotypes

In humans, caveolin-1 (cav-1) gene polymorphisms confer a metabolic syndrome (MetS) phenotype and higher aldosterone (Aldo) levels. Further, global cav-1 knock out (KO) mice recapitulate the MetS phenotype, with both cardiovascular (CV) and metabolic dysfunction. We have shown that vascular dysfunction in the cav-1 KO is dissociated from the metabolic phenotype and is mediated by an endothelial crosstalk between cav-1 and the Aldo-mineralocorticoid receptor (MR) signaling pathway. Hence, we hypothesized endothelial cav-1 deficiency in mice is a major contributor to CV (but not metabolic) dysfunction.To assess this hypothesis, we generated Tie-2 mediated endothelium-specific cav-1 KO (ECKO) and appropriate genetic wild type (WT) control mice and studied their metabolic and CV traits in response to 1) changes in dietary salt intake (0.03% (LS) vs. 1.6% Na + (HS)) and 2) 3-weeks of Aldo infusion (200μg/kg/day) during sodium loading. Our results showed no difference in glucose, lipids and HOMA-IR in ECKO vs. WT mice, irrespective of the dietary intervention. However, on a HS (but not a LS) diet, ECKO vs. WT mice displayed similar CV dysfunction as previously shown in the full cav-1 KO: increased Aldo levels (73.7±11.1 vs 47.8±4.7ng/dl, p<0.05) and systolic BP (116.4±1.5 vs111±1.4 mmHg, p<0.015). Further, ECKO vs. WT mice had increased cardiac MR, eNOS, PAI-1 and CD68 expression (p<0.05 for each) as well as left ventricular hypertrophy (echocardiogram, p<0.05). In addition, 3-week HS diet led to higher albuminuria (p<0.05) and kidney/body weight ratios in ECKO vs. WT (7.2±0.2 vs 6.3±0.1). Surprisingly, as compared to placebo, Aldo infusion induced significant CV and renal damage only in the WT, but not in the ECKO. However, as compared to WT, Aldo infused ECKO had increased cardiac hypertrophy (5.9±0.2 vs 5.2±0.1) and molecular markers noted above (p<0.05 for each).In conclusion, lack of endothelial cav-1 in the mouse segregated the metabolic and CV phenotypes, and the associated CV phenotype resembles that described for the global cav-1 KO. Further, the CV and renal damage in the ECKO at baseline cannot be further enhanced by Aldo infusion. These data confirm our hypothesis that endothelial cav-1 is a major player in CV but not metabolic homeostasis.

Salt Sensitivity of Blood Pressure and Aldosterone: Interaction Between the Lysine-specific Demethylase 1 Gene, Sex, and Age

CONTEXT

Salt sensitivity of blood pressure (SSBP) is associated with increased cardiovascular risk, especially in individuals of African descent, although the underlying mechanisms remain obscure. Lysine-specific demethylase 1 (LSD1) is a salt-sensitive epigenetic regulator associated with SSBP and aldosterone dysfunction. An LSD1 risk allele in humans is associated with SSBP and lower aldosterone levels in hypertensive individuals of African but not European descent. Heterozygous knockout LSD1 mice display SSBP and aldosterone dysregulation, but this effect is modified by age and biological sex. This might explain differences in cardiovascular risk with aging and biological sex in humans.

OBJECTIVE

This work aims to determine if LSD1 risk allele (rs587618) carriers of African descent display a sex-by-age interaction with SSBP and aldosterone regulation.

METHODS

We analyzed 297 individuals of African and European descent from the HyperPATH cohort. We performed multiple regression analyses for outcome variables related to SSBP and aldosterone.

RESULTS

LSD1 risk allele carriers of African (but not European) descent had greater SSBP than nonrisk homozygotes. Female LSD1 risk allele carriers of African descent had greater SSBP, mainly relationship-driven by women with low estrogen (postmenopausal). There was a statistically significant LSD1 genotype-sex interaction in aldosterone response to angiotensin II stimulation in individuals aged 50 years or younger, with female carriers displaying decreased aldosterone responsiveness.

CONCLUSION

SSBP associated with LSD1 risk allele status is driven by women with a depleted estrogen state. Mechanisms related to a resistance to develop SSBP in females are uncertain but may relate to an estrogen-modulating effect on mineralocorticoid receptor (MR) activation and/or LSD1 epigenetic regulation of the MR.

Biological sex modifies aldosterone's secretion at a cellular level

Inconsistencies have been reported on the effect of sex on aldosterone (ALDO) levels leading to clinical confusion. The reasons for these inconsistencies are uncertain but include estrogen and/or its receptor modulating target gene responses to mineralocorticoid receptor activation and ALDO secretagogues' levels. This study's goal was to determine whether ALDO's biosynthesis also differed by sex. Two approaches were used. First, plasma renin activity and aldosterone were measured in rats. Both were significantly higher in males. Secondly, using rat zona glomerulosa (ZG) cells, we assessed three ex vivo areas: (1) activity/levels of early steps in ALDO's biosynthesis (StAR and CYP11A1); (2) activity/levels of a late step (CYP11B2); and (3) the status of the mineralocorticoid receptor (MR)-mediated, ultrashort feedback loop. Females had higher expression of CYP11A1 and StAR and increased CYP11A1 activity (increased pregnenolone/corticosterone levels) but did not differ in CYP11B2 expression or activity (ALDO levels). Activating the ZG's MR (thereby activating the ultrashort feedback loop) reduced CYP11B2's activity similarly in both sexes. Exvivo, these molecular effects were accompanied, in females, by lower ALDO basally but higher ALDO with angiotensin II stimulation. In conclusion, we documented that not only was there a sex-mediated difference in the activity of ALDO's biosynthesis but also these differences at the molecular level help explain the variable reports on ALDO's circulating levels. Basally, both in vivo and ex vivo, males had higher ALDO levels, likely secondary to higher ALDO secretagogue levels. However, in response to acute stimulation, ALDO levels are higher in females because of the greater levels and/or activity of their StAR/CYP11A1.

Enhanced Thrombotic Responses Are Associated With Striatin Deficiency and Aldosterone

Background In addition to its role on blood pressure, aldosterone (ALDO) also affects the hemostatic system leading to increased experimental thrombosis. Striatin is an intermediate in the rapid, nongenomic actions of ALDO. Striatin heterozygote knockout (Strn+/-) mice have salt sensitivity of blood pressure and mildly chronically increased ALDO levels. In addition, in humans, striatin polymorphic gene variants are associated with increased salt sensitivity of blood pressure. Thus, we hypothesized that striatin deficiency would be associated with an increased prothrombotic response. Methods and Results Strn+/ - mice and wild-type littermates were maintained on a liberal sodium diet (1.6%). We measured in vivo thrombus formation following laser-induced injury in cremaster arterioles using intravital microscopy. Mice were randomized to intravenous administration of ALDO or its vehicle. Acutely, ALDO increased thrombotic responses in wild-type mice (P<0.01) versus controls within minutes as determined by increased platelet accumulation and fibrin deposition at the site of laser injury. We then compared thrombus formation without ALDO administration in Strn+/- and wild-type mice. Strn+/- mice showed highly significant increases in laser-induced thrombosis (P<0.001), as shown by increased platelet accumulation and fibrin deposition. Interestingly, the response in the Strn+/- mice basally was far greater than the wild-type mice with ALDO administration, and ALDO administration produced no additional effect on thrombus responses in Strn+/- mice. Conclusions These results demonstrate a novel protective role of striatin in experimental thrombosis. Such a protective effect may be reduced in human striatin risk allele carriers, given the similar salt sensitivity of blood pressure in these individuals and Strn+/- mice.

Abstract P228: Mineralocorticoid Receptor Antagonist And Lipophilic Statin Reduce Urinary Kidney Injury Marker 1 (Kim-1) In Female Rats Receiving L-NAME And Angiotensin II

Statins have beneficial cardiovascular effects some of which appear to be cholesterol-independent and the mechanisms for these latter effects are still unclear. Urinary kidney injury molecule-1 (Kim-1) is a sensitive biomarker of acute renal injury and in clinical studies predicts cardiovascular disease. Aldosterone causes both cardiac and renal injury and a few studies suggest that aldosterone is associated with increased Kim-1. Therefore, in this study we used the N omega-nitro-L-arginine methyl ester (L-NAME)/Angiotensin II (AngII) model of cardiorenal injury to determine whether urinary Kim-1 correlates with the degree of cardiac injury/stroke and whether blockade of the mineralocorticoid receptor prevents increases in urinary Kim-1. Further, since our group reported previously that lipophilic statins, but not hydrophilic statins reduce aldosterone levels, we also asked whether administration of either a lipophilic or a hydrophilic statin affects Kim-1 levels.

To test the hypothesis, 8-10 week-old, female Wistar rats consuming liberal salt diet (1.6% Na + ) were randomized to the following conditions for 14 days: control; L-NAME (0.2 mg/ml in drinking water)/AngII (225ug/kg/day for days 12-14 only); L-NAME/AngII + eplerenone (100 mg/kg/day p.o.); L-NAME/Ang II + pravastatin (hydrophilic statin-20 mg/kg/day p.o.); L-NAME/Ang II + simvastatin (lipophilic statin-20 mg/kg/day p.o.) groups.

Groups treated with L-NAME/AngII had significantly higher blood pressure, urine aldosterone and plasma aldosterone levels compared to control. L-NAME/AngII treatment increased cardiac injury/stroke composite score, including cardiac histopathology evaluation and stroke status, and

24 hour-urinary Kim-1 compared to control. Eplerenone reduced cardiac injury/stroke composite score (p=0.04) and both eplerenone and simvastatin reduced urinary Kim-1 (p=0.0046, p=0.031, respectively). Pravastatin had no effect on these damage markers. Urinary Kim-1 correlated with cardiac injury/stroke composite score (p<0.0001, spearman ranked correlation=0.67).

In conclusion, in a rat model of L-NAME/AngII induced cardiovascular injury, urinary Kim-1 predicts cardiac/stroke injury; eplerenone and simvastatin reduced urinary Kim-1.

mTORC1 Deficiency Modifies Volume Homeostatic Responses to Dietary Sodium in a Sex-Specific Manner

The mechanistic target of the rapamycin (mTOR) pathway plays a role in features common to both excess salt/aldosterone and cardiovascular/renal diseases. Dietary sodium can upregulate mTORC1 signaling in cardiac and renal tissue, and the inhibition of mTOR can prevent aldosterone-associated, salt-induced hypertension. The impact of sex and age on mTOR's role in volume homeostasis and the regulation of aldosterone secretion is largely unknown. We hypothesize that both age and sex modify mTOR's interaction with volume homeostatic mechanisms. The activity of 3 volume homeostatic mechanisms-cardiovascular, renal, and hormonal (aldosterone [sodium retaining] and brain natriuretic peptide [BNP; sodium losing])-were assessed in mTORC1 deficient (Raptor+/-) and wild-type male and female littermates at 2 different ages. The mice were volume stressed by being given a liberal salt (LibS) diet. Raptor+/-mice of both sexes when they aged: (1) reduced their blood pressure, (2) increased left ventricular internal diameter during diastole, (3) decreased renal blood flow, and (4) increased mineralocorticoid receptor expression. Aldosterone levels did not differ by sex in young Raptor+/- mice. However, as they aged, compared to their littermates, aldosterone decreased in males but increased in females. Finally, given the level of Na+ intake, BNP was inappropriately suppressed, but only in Raptor+/- males. These data indicate that Raptor+/- mice, when stressed with a LibS diet, display inappropriate volume homeostatic responses, particularly with aging, and the mechanisms altered, differing by sex.