Intracellular Angiotensin-II Interacts With Nuclear Angiotensin Receptors in Cardiac Fibroblasts and Regulates RNA Synthesis, Cell Proliferation, and Collagen Secretion

• Published in: Journal of the American Heart Association 2017-04, Vol.6 (4)
• Main Authors: Tadevosyan, Artavazd, Xiao, Jiening, Surinkaew, Sirirat, Naud, Patrice, Merlen, Clémence, Harada, Masahide, Qi, Xiaoyan, Chatenet, David, Fournier, Alain, Allen, Bruce G, Nattel, Stanley
• Format: Article
• Language: English
• Subjects: Angiotensin II - physiology; Angiotensin II Type 1 Receptor Blockers - pharmacology; Angiotensin II Type 2 Receptor Blockers - pharmacology; Animals; atrial fibrillation; Biochemistry, Molecular Biology; Calcium - metabolism; Cell Nucleus - metabolism; Cell Proliferation; Cellular Biology; Collagen - metabolism; Collagen Type I - genetics; Disease Models, Animal; Dogs; fibroblasts; Fibroblasts - metabolism; Genomics; GTP-Binding Protein alpha Subunits, Gi-Go - metabolism; GTP-Binding Protein alpha Subunits, Gq-G11 - metabolism; GTP-Binding Protein beta Subunits - metabolism; Heart Atria - cytology; Heart Failure - metabolism; Immunoblotting; Inositol 1,4,5-Trisphosphate Receptors - metabolism; intracrine angiotensin system; Life Sciences; Microscopy, Fluorescence; Nitric Oxide - metabolism; nuclear receptors; Original Research; Receptor, Angiotensin, Type 1 - metabolism; Receptor, Angiotensin, Type 2 - metabolism; remodeling; Transcription, Genetic
• ISSN: 2047-9980; 2047-9980
• DOI: 10.1161/JAHA.116.004965

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. 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 ([α P]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 Ca -liberation, with IP3R3 being the predominant nuclear isoform. Intracellular Ang-II regulated fibroblast proliferation ([ H]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. Fibroblast nuclei possess AT1R and AT2R binding sites that are coupled to intranuclear Ca -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.