Aldosterone promotes vascular remodeling by direct effects on smooth muscle cell mineralocorticoid receptors

OBJECTIVE

Vascular remodeling occurs after endothelial injury, resulting in smooth muscle cell (SMC) proliferation and vascular fibrosis. We previously demonstrated that the blood pressure-regulating hormone aldosterone enhances vascular remodeling in mice at sites of endothelial injury in a placental growth factor-dependent manner. We now test the hypothesis that SMC mineralocorticoid receptors (MRs) directly mediate the remodeling effects of aldosterone and further explore the mechanism.

APPROACH AND RESULTS

A wire-induced carotid injury model was performed in wild-type mice and mice with inducible SMC-specific deletion of the MR. Aldosterone did not affect re-endothelialization after injury in wild-type mice. Deletion of SMC-MR prevented the 79% increase in SMC proliferation induced by aldosterone after injury in MR-Intact littermates. Moreover, both injury-induced and aldosterone-enhanced vascular fibrosis were attenuated in SMC-specific MR knockout mice. Further exploration of the mechanism revealed that aldosterone-induced vascular remodeling is prevented by in vivo blockade of the placental growth factor-specific receptor, type 1 vascular endothelial growth factor receptor (VEGFR1), the receptor for placental growth factor. Immunohistochemistry of carotid vessels shows that the induction of VEGFR1 expression in SMC after vascular injury is attenuated by 72% in SMC-specific MR knockout mice. Moreover, aldosterone induction of vascular placental growth factor mRNA expression and protein release are also prevented in vessels lacking SMC-MR.

CONCLUSIONS

These studies reveal that SMC-MR is necessary for aldosterone-induced vascular remodeling independent of renal effects on blood pressure. SMC-MR contributes to induction of SMC VEGFR1 in the area of vascular injury and to aldosterone-enhanced vascular placental growth factor expression and hence the detrimental effects of aldosterone are prevented by VEGFR1 blockade. This study supports exploring MR antagonists and VEGFR1 blockade to prevent pathological vascular remodeling induced by aldosterone.

Aldosterone increases early atherosclerosis and promotes plaque inflammation through a placental growth factor-dependent mechanism

Background

Aldosterone levels correlate with the incidence of myocardial infarction and mortality in cardiovascular patients. Aldosterone promotes atherosclerosis in animal models, but the mechanisms are poorly understood.

Methods and Results

Aldosterone was infused to achieve pathologically relevant levels that did not increase blood pressure in the atherosclerosis‐prone apolipoprotein E–knockout mouse (ApoE−/−). Aldosterone increased atherosclerosis in the aortic root 1.8±0.1‐fold after 4 weeks and in the aortic arch 3.7±0.2‐fold after 8 weeks, without significantly affecting plaque size in the abdominal aorta or traditional cardiac risk factors. Aldosterone treatment increased lipid content of plaques (2.1±0.2‐fold) and inflammatory cell content (2.2±0.3‐fold), induced early T‐cell (2.9±0.3‐fold) and monocyte (2.3±0.3‐fold) infiltration into atherosclerosis‐prone vascular regions, and enhanced systemic inflammation with increased spleen weight (1.52±0.06‐fold) and the circulating cytokine RANTES (regulated and normal T cell secreted; 1.6±0.1‐fold). To explore the mechanism, 7 genes were examined for aldosterone regulation in the ApoE−/− aorta. Further studies focused on the proinflammatory placental growth factor (PlGF), which was released from aldosterone‐treated ApoE−/− vessels. Activation of the mineralocorticoid receptor by aldosterone in human coronary artery smooth muscle cells (SMCs) caused the release of factors that promote monocyte chemotaxis, which was inhibited by blocking monocyte PlGF receptors. Furthermore, PlGF‐deficient ApoE−/− mice were resistant to early aldosterone‐induced increases in plaque burden and inflammation.

Conclusions

Aldosterone increases early atherosclerosis in regions of turbulent blood flow and promotes an inflammatory plaque phenotype that is associated with rupture in humans. The mechanism may involve SMC release of soluble factors that recruit activated leukocytes to the vessel wall via PlGF signaling. These findings identify a novel mechanism and potential treatment target for aldosterone‐induced ischemia in humans.

Mineralocorticoid receptor antagonism inhibits vein graft remodeling in mice

OBJECTIVE

Vein graft failure rates resulting from adverse graft remodeling remain high with no effective therapy. The mineralocorticoid receptor (MR) plays a role in pathologic arterial remodeling. We demonstrated recently that the MR is upregulated in venous tissues after grafting and hypothesized that MR inhibition would reduce vein graft remodeling.

METHODS

Reverse transcription polymerase chain reaction and immunoblotting were used to examine the expression of the MR and other components of the renin-angiotensin-aldosterone system in human vein and primary human saphenous vein smooth muscle cells (HSVSMC). Adenoviral reporter gene assays were used to explore MR transcriptional activity in HSVSMC. The effect of MR inhibition on vein graft remodeling in vivo was characterized in a mouse vein graft model.

RESULTS

Messenger RNAs encoding the MR, 11-β-hydroxysteroid dehydrogenase 2, angiotensin type 1 receptor, and the angiotensin-converting enzyme are expressed in whole HSVSMC. MR and 11-β-hydroxysteroid dehydrogenase 2 protein expression is confirmed, and MR-dependent transcriptional regulation is demonstrated at physiologic aldosterone concentrations in HSVSMC. Treatment of mice with the MR antagonist spironolactone, at doses that do not lower blood pressure (20 mg/kg per day), reduces maximal vein graft intima-media thickness by 68%, with an associated reduction in graft inflammatory cell infiltration and fibrosis.

CONCLUSIONS

MR is expressed in human venous tissue and cells and modulates gene expression in HSVSMC in response to physiologic aldosterone concentrations. In vivo, MR inhibition reduces vein graft thickening and inflammation. These preclinical data support the potential to use MR antagonists as novel treatments to preserve vein graft patency.