Smooth muscle cell mineralocorticoid receptors are mandatory for aldosterone-salt to induce vascular stiffness

Abstract

Arterial stiffness is recognized as a risk factor for many cardiovascular diseases. Aldosterone via its binding to and activation of the mineralocorticoid receptors (MRs) is a main regulator of blood pressure by controlling renal sodium reabsorption. Although both clinical and experimental data indicate that MR activation by aldosterone is involved in arterial stiffening, the molecular mechanism is not known. In addition to the kidney, MR is expressed in both endothelial and vascular smooth muscle cells (VSMCs), but the specific contribution of the VSMC MR to aldosterone-induced vascular stiffness remains to be explored. To address this question, we generated a mouse model with conditional inactivation of the MR in VSMC (MR(SMKO)). MR(SMKO) mice show no alteration in renal sodium handling or vascular structure, but they have decreased blood pressure when compared with control littermate mice. In vivo at baseline, large vessels of mutant mice presented with normal elastic properties, whereas carotids displayed a smaller diameter when compared with those of the control group. As expected after aldosterone/salt challenge, the arterial stiffness increased in control mice; however, it remained unchanged in MR(SMKO) mice, without significant modification in vascular collagen/elastin ratio. Instead, we found that the fibronectin/α5-subunit integrin ratio is profoundly altered in MR(SMKO) mice because the induction of α5 expression by aldosterone/salt challenge is prevented in mice lacking VSMC MR. Altogether, our data reveal in the aldosterone/salt hypertension model that MR activation specifically in VSMC leads to the arterial stiffening by modulation of cell-matrix attachment proteins independent of major vascular structural changes.

Keywords: aldosterone; carotid arteries; integrins; mice, transgenic; receptors, mineralocorticoid; vascular stiffness.

Figures

Figure 1

Decreased mineralocorticoid receptor (MR) expression in vascular smooth muscle cell (VSMC) of MRSMKO mice. Quantitative real-time polymerase chain reaction (A) and Western blot (B) analysis of MR expression in the aorta from control (CTL) mice and MRSMKO mice. C, Immunolocalization of MR in aorta sections. Scale bars, 20 μm. Data are expressed as a percentage of mean control value±SEM. ###P<0.001 vs CTL. n=4 to 6 mice per group.

Figure 2

Renal function in control (CTL) mice and MRSMKO mice. No differences in estimated creatinine clearance (A) and urinary protein excretion (B) were observed between CTL (white bar) and MRSMKO (black bar) mice housed in metabolic cages. Urinary sodium (UNa+) excretion was not modified after an acute sodium load (C) and with a low-salt diet (D). n=5 to 8 mice per group. Data are mean±SEM. MR indicates mineralocorticoid receptor.

Figure 3

Systolic arterial pressure (SAP) in conscious control (CTL) and MRSMKO mice (n=6–9; A). Distensibility–AP curves (B), Einc–wall stress curves (C), and the mean distensibility within the 80- to 116-mm Hg range of pressure (D) in carotid artery of untreated CTL (n=11), nephrectomy–aldosterone–salt (NAS) control (n=9), untreated MRSMKO (n=10), and NAS MRSMKO (n=9) mice. Under basal condition, SAP in conscious MRSMKO mice is significantly lower than in conscious CTL mice. NAS treatment significantly increased SAP to a similar level in conscious CTL and MRSMKO mice. MDist80–116 and MWS300–750 were calculated from the Dist and Einc–WS curves, respectively. At the baseline, MDist80–116 and MWS300–750 were not different between MRSMKO and CTL mice (Table). NAS treatment significantly reduced the MDist80–116 and MWS300–750 in CTL mice. However, this was not observed in MRSMKO mice (Table). Data are mean±SEM. *P<0.05, **P<0.01, ***P<0.001 vs baseline; and #P<0.05 vs CTL mice. Einc indicates incremental elastic modulus; mean distensibility within the 80- to 116-mm Hg range of pressure; MR, mineralocorticoid receptor; and MWS300–750, mean wall stress within the 300- to 750-kPa range of Einc.

Figure 4

Effects of NAS treatment on fibronectin, collagen I, and integrins expression in arteries from control (CTL) and MRSMKO mice. A, mRNA levels of fibronectin, Col1α, α5, α1, and αV subunits of integrins in the carotid arteries. B, Protein levels of Col1, α5, and αV subunits of integrins in aorta (Western blots are shown in Figure S2). Data are expressed as a fold change of mean value in untreated CTL mice±SEM. *P<0.05, **P<0.01, ***P<0.001 vs untreated mice; ###P<0.001 vs CTL mice. n=5 mice per group. C, Schematic model for the role of vascular smooth muscle (VSM) MR to regulate the vascular stiffness in large arteries. ROS indicates reactive oxygen species.