title: Intracellular Angiotensin-II Interacts With Nuclear Angiotensin Receptors in Cardiac Fibroblasts and Regulates RNA Synthesis, Cell Proliferation, and Collagen Secretion.
abstract: BACKGROUND
  Cardiac fibroblasts play important functional and pathophysiological roles. Intracellular ("intracrine") angiotensin-II (Ang-II) signaling regulates intercellular communication, excitability, and gene expression in cardiomyocytes; however, the existence and role of intracrine Ang-II signaling in cardiac fibroblasts is unstudied. Here, we evaluated the localization of Ang-II receptors on atrial fibroblast nuclei and associated intracrine effects of potential functional significance.
  
  
  RESULTS
  Immunoblots of subcellular protein-fractions from isolated canine atrial fibroblasts indicated the presence of nuclear Ang-II type 1 receptors (AT1Rs) and Ang-II type 2 receptors (AT2Rs). Fluorescein isothiocyanate-Ang-II binding displaceable by AT1R- and AT2R-blockers was present on isolated fibroblast nuclei. G-protein subunits, including Gαq/11, Gαi/3, and Gβ, were observed in purified fibroblast nuclear fractions by immunoblotting and intact-fibroblast nuclei by confocal immunocytofluorescence microscopy. Nuclear AT1Rs and AT2Rs regulated de novo RNA synthesis ([α32P]UTP incorporation) via IP3R- and NO-dependent pathways, respectively. In intact cultured fibroblasts, intracellular Ang-II release by photolysis of a membrane-permeable caged Ang-II analog led to IP3R-dependent nucleoplasmic Ca2+-liberation, with IP3R3 being the predominant nuclear isoform. Intracellular Ang-II regulated fibroblast proliferation ([3H]thymidine incorporation), collagen-1A1 mRNA-expression, and collagen secretion. Intracellular Ang-II and nuclear AT1R protein levels were significantly increased in a heart failure model in which atrial fibrosis underlies atrial fibrillation.
  
  
  CONCLUSIONS
  Fibroblast nuclei possess AT1R and AT2R binding sites that are coupled to intranuclear Ca2+-mobilization and NO liberation, respectively. Intracellular Ang-II signaling regulates fibroblast proliferation, collagen gene expression, and collagen secretion. Heart failure upregulates Ang-II intracrine signaling-components in atrial fibroblasts. These results show for the first time that nuclear angiotensin-II receptor activation and intracrine Ang-II signaling control fibroblast function and may have pathophysiological significance.
authors.affiliation: Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal, Quebec, Canada.
authors.forename: Artavazd
authors.initials: A
authors.lastname: Tadevosyan
authors.affiliation: Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal, Quebec, Canada.
authors.forename: Jiening
authors.initials: J
authors.lastname: Xiao
authors.affiliation: Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal, Quebec, Canada.
authors.forename: Sirirat
authors.initials: S
authors.lastname: Surinkaew
authors.affiliation: Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal, Quebec, Canada.
authors.forename: Patrice
authors.initials: P
authors.lastname: Naud
authors.affiliation: Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal, Quebec, Canada.
authors.forename: Clémence
authors.initials: C
authors.lastname: Merlen
authors.affiliation: Department of Cardiology, Fujita Health University School of Medicine, Toyoake, Japan.
authors.forename: Masahide
authors.initials: M
authors.lastname: Harada
authors.affiliation: Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal, Quebec, Canada.
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Qi
authors.affiliation: Institut National de la Recherche Scientifique-Institut Armand Frappier, Laval, Québec, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Chatenet
authors.affiliation: Institut National de la Recherche Scientifique-Institut Armand Frappier, Laval, Québec, Canada.
authors.forename: Alain
authors.initials: A
authors.lastname: Fournier
authors.affiliation: Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal, Quebec, Canada stanley.nattel@icm-mhi.org bruce.g.allen@umontreal.ca.|Department of Biochemistry and Molecular Medicine, Université de Montréal, Quebec, Canada.|Department of Pharmacology and Therapeutics, McGill University, Montréal, Quebec, Canada.
authors.forename: Bruce G
authors.initials: BG
authors.lastname: Allen
authors.affiliation: Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal, Quebec, Canada stanley.nattel@icm-mhi.org bruce.g.allen@umontreal.ca.|Department of Pharmacology and Therapeutics, McGill University, Montréal, Quebec, Canada.|Institute of Pharmacology, West German Heart and Vascular Center, University Duisburg-Essen, Duisburg, Germany.
authors.forename: Stanley
authors.initials: S
authors.lastname: Nattel
mesh_terms: D000804:Angiotensin II / Q000502:physiology*; D047228:Angiotensin II Type 1 Receptor Blockers / Q000494:pharmacology; D057912:Angiotensin II Type 2 Receptor Blockers / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation; D003094:Collagen / Q000378:metabolism*; D024042:Collagen Type I / Q000235:genetics; D004195:Disease Models, Animal; D004285:Dogs; D005347:Fibroblasts / Q000378:metabolism*; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism; D044387:GTP-Binding Protein beta Subunits / Q000378:metabolism; D006325:Heart Atria / Q000166:cytology*; D006333:Heart Failure / Q000378:metabolism*; D015151:Immunoblotting; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism; D008856:Microscopy, Fluorescence; D009569:Nitric Oxide / Q000378:metabolism; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism; D044139:Receptor, Angiotensin, Type 2 / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D047228:Angiotensin II Type 1 Receptor Blockers; D057912:Angiotensin II Type 2 Receptor Blockers; D024042:Collagen Type I; D044387:GTP-Binding Protein beta Subunits; D053496:Inositol 1,4,5-Trisphosphate Receptors; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D000804:Angiotensin II; D009569:Nitric Oxide; D003094:Collagen; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D002118:Calcium
keywords: atrial fibrillation; fibroblasts; intracrine angiotensin system; nuclear receptors; remodeling