title: The angiotensin-calcineurin-NFAT pathway mediates stretch-induced up-regulation of matrix metalloproteinases-2/-9 in atrial myocytes.
abstract: OBJECTIVE
  During atrial fibrillation, arterial hypertension and systolic or diastolic heart failure, atrial myocytes are exposed to increased baseline stretch. Atrial stretch has been shown to induce cellular hypertrophy and extracellular matrix remodeling (ECM) via angiotensin-II dependent pathways and the matrix metalloproteinases system (MMPs). We hypothesized that atrial myocytes exposed to static stretch may increase their ECM remodeling activity via up-regulation of MMP-2/-9. We then tested the hypothesis that the membrane bound angiotensin-II type 1 (AT1) receptor and the intracellular calcineurin (Cn)-NFAT signaling pathway are potential mediators of stretch-induced MMP alterations, since Cn-NFAT is one important contributor to myocyte hypertrophy.
  
  
  RESULTS
  Neonatal rat atrial myocytes (NRAM) were cultured under conditions of static stretch by 21%. The differential effects of selective AT1 receptor blockade by losartan, Cn blockade by Cyclosporine-A (CsA) or NFAT inhibition by 11R-VIVIT (VIV), were analyzed. Stretch resulted in a significant up-regulation of active-MMP-2/-9 protein amount (active-MMP-2 ng/microg: control 8.95 +/- 0.64 vs. stretch 13.11 +/- 0.74 / active-MMP-9 ng/microg: control 1.45 +/- 0.18 vs. stretch 1.94 +/- 0.21, all n = 5) and enzyme activity (MMP-2 in %: control 1 +/- 0.0 vs. stretch 1.87 +/- 0.25, n = 7) associated with a significant increase of the membrane-type-1-MMP (MT1-MMP) protein expression (MT1-MMP in %: control 1 +/- 0.0 vs. stretch 2.17 +/- 0.21, n = 8). These observations were accompanied by an activation of the Cn-NFAT pathway (Cn-activity in nmol PO(4) release/20 microg protein/30 min: control 0.37 +/- 0.08 vs. stretch 0.65 +/- 0.09, n = 3 / NFATc1-DNA binding activity in %: control 1 +/- 0.0 vs. stretch 1.53 +/- 0.17, n = 3). Losartan, CsA or VIV abolished stretch-induced alterations in MMP-2/-9 and MT1-MMP expression and enzyme activity by normalizing the Cn-activity and the DNA binding activity of NFATc1.
  
  
  CONCLUSIONS
  Our results present new insights in molecular mechanisms of ECM remodeling activity of atrial myocytes exposed to static stretch. The AT1-Cn-NFAT pathway is a potential mediator of MMP activation.
authors.affiliation: Dept. of Cardiology, Medical Clinic I, University Hospital Rheinisch Westfälische Technische Hochschule Aachen, Pauwelsstrasse 30, 52074, Aachen, Germany. esaygili@ukaachen.de
authors.forename: Erol
authors.initials: E
authors.lastname: Saygili
authors.forename: Obaida R
authors.initials: OR
authors.lastname: Rana
authors.forename: Christian
authors.initials: C
authors.lastname: Meyer
authors.forename: Christopher
authors.initials: C
authors.lastname: Gemein
authors.forename: Michael G
authors.initials: MG
authors.lastname: Andrzejewski
authors.forename: Andreas
authors.initials: A
authors.lastname: Ludwig
authors.forename: Christian
authors.initials: C
authors.lastname: Weber
authors.forename: Ulrich
authors.initials: U
authors.lastname: Schotten
authors.forename: Alexander
authors.initials: A
authors.lastname: Krüttgen
authors.forename: Joachim
authors.initials: J
authors.lastname: Weis
authors.forename: Robert H G
authors.initials: RH
authors.lastname: Schwinger
authors.forename: Karl
authors.initials: K
authors.lastname: Mischke
authors.forename: Tienush
authors.initials: T
authors.lastname: Rassaf
authors.forename: Malte
authors.initials: M
authors.lastname: Kelm
authors.forename: Patrick
authors.initials: P
authors.lastname: Schauerte
mesh_terms: D000809:Angiotensins / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western; D019703:Calcineurin / Q000378:metabolism*; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000502:physiology; D004797:Enzyme-Linked Immunosorbent Assay; D005109:Extracellular Matrix / Q000378:metabolism; D006325:Heart Atria / Q000378:metabolism*; D020778:Matrix Metalloproteinase 2 / Q000096:biosynthesis; D020780:Matrix Metalloproteinase 9 / Q000096:biosynthesis; D020782:Matrix Metalloproteinases / Q000096:biosynthesis*; D032342:Muscle Cells / Q000378:metabolism*; D050778:NFATC Transcription Factors / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D015854:Up-Regulation
chemical_list: D000809:Angiotensins; D050778:NFATC Transcription Factors; D044140:Receptor, Angiotensin, Type 1; D019703:Calcineurin; D020782:Matrix Metalloproteinases; D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9