title: Losartan inhibits endothelial-to-mesenchymal transformation in mitral valve endothelial cells by blocking transforming growth factor-β-induced phosphorylation of ERK.
abstract: 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 (CAEC) as a control. Expression of EndMT target genes α-smooth muscle actin (α-SMA), Snai1, Slug, and MMP-2 were used to monitor EndMT. We show that TGFβ-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-β-induced p-ERK directly with the MEK1/2 inhibitor RDEA119 was sufficient to prevent EndMT. In mitral VECs, TGFβ had only modest effects on phosphorylation of the canonical TGF-β signaling mediator mothers against decapentaplegic homolog 3 (SMAD3). These results indicate a predominance of the non-canonical p-ERK pathway in TGFβ-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.
authors.affiliation: Vascular Biology Program and Department of Surgery, Boston Children's Hospital and Harvard Medical School, Boston, MA 02115, United States.
authors.forename: Jill
authors.initials: J
authors.lastname: Wylie-Sears
authors.affiliation: Cardiac Ultrasound Laboratory, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02115, United States.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Levine
authors.affiliation: Vascular Biology Program and Department of Surgery, Boston Children's Hospital and Harvard Medical School, Boston, MA 02115, United States. Electronic address: joyce.bischoff@childrens.harvard.edu.
authors.forename: Joyce
authors.initials: J
authors.lastname: Bischoff
mesh_terms: D047228:Angiotensin II Type 1 Receptor Blockers / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D058750:Epithelial-Mesenchymal Transition / Q000187:drug effects*; D019808:Losartan / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008943:Mitral Valve / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011945:Receptors, Angiotensin / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D012756:Sheep; D015398:Signal Transduction / Q000187:drug effects; D051900:Smad3 Protein / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D047228:Angiotensin II Type 1 Receptor Blockers; D011945:Receptors, Angiotensin; D011994:Recombinant Proteins; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D019808:Losartan
keywords: ERK; Endothelial cells; Endothelial to mesenchymal transformation; Losartan; Mitral valve; TGFβ