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Losartan inhibits endothelial-to-mesenchymal transformation in mitral valve endothelial cells by blocking transforming growth factor-?-induced phosphorylation of ERK.

ABSTRACT: Adult cardiac valve endothelial cells (VEC) undergo endothelial to mesenchymal transformation (EndMT) in response to transforming growth factor-? (TGF?). EndMT has been proposed as a mechanism to replenish interstitial cells that reside within the leaflets and further, as an adaptive response that increases the size of mitral valve leaflets after myocardial infarction. To better understand valvular EndMT, we investigated TGF?-induced signaling in mitral VEC, and carotid artery endothelial cells (CAEC) as a control. Expression of EndMT target genes ?-smooth muscle actin (?-SMA), Snai1, Slug, and MMP-2 were used to monitor EndMT. We show that TGF?-induced EndMT increases phosphorylation of ERK (p-ERK), and this is blocked by Losartan, an FDA-approved antagonist of the angiotensin II type 1 receptor (AT1), that is known to indirectly inhibit phosphorylation of ERK (p-ERK). Blocking TGF-?-induced p-ERK directly with the MEK1/2 inhibitor RDEA119 was sufficient to prevent EndMT. In mitral VECs, TGF? had only modest effects on phosphorylation of the canonical TGF-? signaling mediator mothers against decapentaplegic homolog 3 (SMAD3). These results indicate a predominance of the non-canonical p-ERK pathway in TGF?-mediated EndMT in mitral VECs. AT1 and angiotensin II type 2 (AT2) were detected in mitral VEC, and high concentrations of angiotensin II (AngII) stimulated EndMT, which was blocked by Losartan. The ability of Losartan or MEK1/2 inhibitors to block EndMT suggests these drugs may be useful in manipulating EndMT to prevent excessive growth and fibrosis that occurs in the leaflets after myocardial infarction.

SUBMITTER: Wylie-Sears J

PROVIDER: S-EPMC4007266 | biostudies-literature | 2014 Apr

REPOSITORIES: biostudies-literature

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Losartan inhibits endothelial-to-mesenchymal transformation in mitral valve endothelial cells by blocking transforming growth factor-β-induced phosphorylation of ERK.

Wylie-Sears Jill J Levine Robert A RA Bischoff Joyce J

Biochemical and biophysical research communications 20140312 4

Adult cardiac valve endothelial cells (VEC) undergo endothelial to mesenchymal transformation (EndMT) in response to transforming growth factor-β (TGFβ). EndMT has been proposed as a mechanism to replenish interstitial cells that reside within the leaflets and further, as an adaptive response that increases the size of mitral valve leaflets after myocardial infarction. To better understand valvular EndMT, we investigated TGFβ-induced signaling in mitral VEC, and carotid artery endothelial cells ...[more]

PMID: 24632204

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Project description:BackgroundAfter myocardial infarction (MI), mitral valve (MV) tethering stimulates adaptive leaflet growth, but counterproductive leaflet thickening and fibrosis augment mitral regurgitation (MR), doubling heart failure and mortality. MV fibrosis post-MI is associated with excessive endothelial-to-mesenchymal transition (EMT), driven by transforming growth factor (TGF)-β overexpression. In vitro, losartan-mediated TGF-β inhibition reduces EMT of MV endothelial cells.ObjectivesThis study tested the hypothesis that profibrotic MV changes post-MI are therapeutically accessible, specifically by losartan-mediated TGF-β inhibition.MethodsThe study assessed 17 sheep, including 6 sham-operated control animals and 11 with apical MI and papillary muscle retraction short of producing MR; 6 of the 11 were treated with daily losartan, and 5 were untreated, with flexible epicardial mesh comparably limiting left ventricular (LV) remodeling. LV volumes, tethering, and MV area were quantified by using three-dimensional echocardiography at baseline and at 60 ± 6 days, and excised leaflets were analyzed by histopathology and flow cytometry.ResultsPost-MI LV dilation and tethering were comparable in the losartan-treated and untreated LV constraint sheep. Telemetered sensors (n = 6) showed no significant losartan-induced changes in arterial pressure. Losartan strongly reduced leaflet thickness (0.9 ± 0.2 mm vs. 1.6 ± 0.2 mm; p < 0.05; 0.4 ± 0.1 mm sham animals), TGF-β, and downstream phosphorylated extracellular-signal-regulated kinase and EMT (27.2 ± 12.0% vs. 51.6 ± 11.7% α-smooth muscle actin-positive endothelial cells, p < 0.05; 7.2 ± 3.5% sham animals), cellular proliferation, collagen deposition, endothelial cell activation (vascular cell adhesion molecule-1 expression), neovascularization, and cells positive for cluster of differentiation (CD) 45, a hematopoietic marker associated with post-MI valve fibrosis. Leaflet area increased comparably (17%) in constrained and losartan-treated sheep.ConclusionsProfibrotic changes of tethered MV leaflets post-MI can be modulated by losartan without eliminating adaptive growth. Understanding the cellular and molecular mechanisms could provide new opportunities to reduce ischemic MR.

Dataset Information

Losartan inhibits endothelial-to-mesenchymal transformation in mitral valve endothelial cells by blocking transforming growth factor-?-induced phosphorylation of ERK.

Publications

Losartan inhibits endothelial-to-mesenchymal transformation in mitral valve endothelial cells by blocking transforming growth factor-β-induced phosphorylation of ERK.

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