title: Synergism between AT1 receptor and hyperhomocysteinemia during vascular remodeling.
abstract: BACKGROUND
  Hyperhomocysteinemia (HHcy) is an independent risk factor of cardiovascular diseases. Extracellular signal-regulated kinase-1/2 (ERK-1/2) and the JAK/STAT pathway kinase, signal transducer and activator of transcription 3 (STAT3), are involved in matrix metalloproteinase-9 (MMP-9) induction and matrix remodeling. However, their role in homocysteine (Hcy)-mediated MMP-9 induction and matrix remodeling is unclear. Clinical and experimental evidence indicates that HHcy and activation of the renin-angiotensin system, mediated by angiotensin II type 1 (AT1) receptor, are involved in a variety of vascular pathologies. Despite this fact, the relationship between HHcy and activation of the renin-angiotensin system has not been comprehensively characterized. Therefore, we hypothesized that Hcy activates AT1 receptor that potentiates STAT3 via ERK-1/2 phosphorylation. STAT3 modulates target MMP-9 and collagen, resulting in vascular remodeling.
  
  
  METHODS
  Mouse aortic endothelial cells (MAEC) were treated with various doses of Hcy for different time periods. The levels of AT1 receptor, ERK-1/2, STAT3, MMP-9 and collagen type-1 were measured by immunoblot analyses. The activation of ERK-1/2 and STAT3 were determined by measuring ERK-1/2 phosphorylation and phosphoserine (727) STAT3.
  
  
  RESULTS
  Although Hcy dose-dependently induced AT1 receptor expression in the endothelial cells, a significant induction was observed at 100 microM at 48 h. We investigated Hcy-induced ERK-1/2 and STAT3 phosphorylation through AT1 receptor induction, and our results suggest that Hcy activated AT1 receptor which led to ERK-1/2 and STAT3 phosphorylation. In addition, findings of this study suggest that Hcy-mediated STAT3 activation regulated MMP-9 and collagen type-1. However, AT1 receptor blocker, valsartan, and the specific STAT3 inhibitor peptide attenuated MMP-9 and collagen type-1 induction.
  
  
  CONCLUSIONS
  These findings demonstrate for the first time the contribution of AT1 receptor in HHcy-induced atherosclerotic diseases; Hcy-induced activation of AT1 receptor involves MMP-9 and collagen type-1 modulation using ERK-1/2 and STAT3 signaling cascades.
authors.affiliation: Department of Physiology and Biophysics, University of Louisville School of Medicine, Louisville, KY 40202, USA.
authors.forename: Utpal
authors.initials: U
authors.lastname: Sen
authors.forename: Markus
authors.initials: M
authors.lastname: Herrmann
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Herrmann
authors.forename: Suresh C
authors.initials: SC
authors.lastname: Tyagi
mesh_terms: D000818:Animals; D001808:Blood Vessels / Q000503:physiopathology*; D015153:Blotting, Western; D002478:Cells, Cultured; D024042:Collagen Type I / Q000378:metabolism; D004730:Endothelium, Vascular / Q000201:enzymology / Q000503:physiopathology*; D006710:Homocysteine / Q000502:physiology; D020138:Hyperhomocysteinemia / Q000503:physiopathology*; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D044140:Receptor, Angiotensin, Type 1 / Q000502:physiology*; D050796:STAT3 Transcription Factor / Q000378:metabolism
chemical_list: D024042:Collagen Type I; D044140:Receptor, Angiotensin, Type 1; D050796:STAT3 Transcription Factor; D006710:Homocysteine; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020780:Matrix Metalloproteinase 9