Downregulation of the ornithine decarboxylase/polyamine system inhibits angiotensin-induced hypertrophy of cardiomyocytes through the NO/cGMP-dependent Protein kinase type-i pathway

Abstract

Background: Polyamines and nitric oxide (NO) have been involved in the pathogenesis of cardiac hypertrophy. NO can regulate cardiac ion channels by direct actions on G-proteins and adenyl cyclase. The present study was undertaken to elucidate the molecular mechanism of interactions with polyamines and NO in cardiac hypertrophy. Methods: Cardiaomyocyte hypertrophy was induced by angiotensinII (AngII). Hypertrophy was estimated by cell-surface area, atrial natriuretic peptide (ANP) mRNA expression, and the immunofluorescence of phalloidin. Pretreatment with alpha-difluoromethylornithine (DFMO) was done to deplete putrescine; KT5823 pretreatment was carried out to block the nitric oxide/cGMP-dependent protein kinase type-I (NO/PKG-I) pathway. Expressions of endothelial nitric oxide synthase (eNOS), PKG-I, c-fos and c-myc were analyzed by western blotting and immunofluorescence. The intracellular concentration of free calcium ([Ca 2+ ] i ) was determined by confocal laser scanning microscopy. Results: Hypertrophy of cardiomyocytes was induced by AngII, this caused an increase in putrescine, spermidine and total polyamine pool in association with a decreased level of NO. Expressions of eNOS and PKG-I were down-regulated, [Ca 2+ ] i was increased, and expressions of c-Fos and c-Myc upregulated. DFMO reversed these changes induced by AngII. Conclusions: Downregulation of polyamines inhibits cardiomyocyte hypertrophy, which is closely related to [Ca 2+ ] i and the NO/PKG-I pathway. Copyright © 2010 S. Karger AG, Basel.