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Influence of aldosterone on collagen synthesis and proliferation of rat cardiac fibroblasts.

ABSTRACT: 1. Previous in vivo studies in men and experimental animal models have shown that hyperaldosteronemia is correlated with cardiac fibrosis due to increased total collagen synthesis. As yet, it is unclear whether aldosterone has direct pro-fibrogenic effect on cardiac fibroblasts, the fibrogenic effector cell in the myocardium, and if so which procollagens specifically are synthesized at higher rates. 2. The present study aims at establishing whether de novo collagen synthesis by cardiac fibroblasts is enhanced following exposure for 2x24 h to pharmacological (10(-7) - 10(-8) M), near-physiological (10(-9) M) or physiological (10(-10) - 10(-11) M) aldosterone concentrations. During the last 24 h, cells were metabolically labelled with [35S]-methionine/[35S]-cysteine. Labelled procollagens were immunoprecipitated quantitatively using antibodies against specific procollagens. Contrary to expectations, 10(-7) M aldosterone inhibited significantly de novo synthesis of procollagens type I and IV (-35% and -42%, respectively). For procollagen type III, only a tendency towards inhibition was observed. At lower concentrations of aldosterone (10(-8) - 10(-10) M), synthesis of procollagens type I, III or IV was unaffected. 3. Cellular DNA synthesis under influence of aldosterone was evaluated by measuring BrdU incorporation. Cells were treated with aldosterone, while BrdU was added during the last 16 h of treatment. Aldosterone had no demonstrable effect on cellular proliferation. 4. Reverse transcription-polymerase chain reaction (RT - PCR) clearly demonstrated the presence of mineralocorticoid receptor mRNA in cardiac fibroblasts. 5. In spite of the expression of the mineralocorticoid receptor by cultured cardiac fibroblasts, the pro-fibrogenic effect of aldosterone as observed in vivo, is not likely to be due to a direct effect of this hormone in cardiac fibroblasts.

SUBMITTER: Rombouts K

PROVIDER: S-EPMC1572936 | biostudies-literature | 2001 Sep

REPOSITORIES: biostudies-literature

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Influence of aldosterone on collagen synthesis and proliferation of rat cardiac fibroblasts.

Rombouts K K Wielant A A Hellemans K K Schuppan D D Geerts A A

British journal of pharmacology 20010901 1

1. Previous in vivo studies in men and experimental animal models have shown that hyperaldosteronemia is correlated with cardiac fibrosis due to increased total collagen synthesis. As yet, it is unclear whether aldosterone has direct pro-fibrogenic effect on cardiac fibroblasts, the fibrogenic effector cell in the myocardium, and if so which procollagens specifically are synthesized at higher rates. 2. The present study aims at establishing whether de novo collagen synthesis by cardiac fibroblas ...[more]

PMID: 11522615

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Project description: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 ([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. 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.

Dataset Information

Influence of aldosterone on collagen synthesis and proliferation of rat cardiac fibroblasts.

Publications

Influence of aldosterone on collagen synthesis and proliferation of rat cardiac fibroblasts.

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