Angiotensin II and the ERK pathway mediate the induction of myocardin by hypoxia in cultured rat neonatal cardiomyocytes

Abstract

Hypoxic injury to cardiomyocytes is a stress that causes cardiac pathology through cardiac-restricted gene expression. SRF (serum-response factor) and myocardin are important for cardiomyocyte growth and differentiation in response to myocardial injuries. Previous studies have indicated that AngII (angiotensin II) stimulates both myocardin expression and cardiomyocyte hypertrophy. In the present study, we evaluated the expression of myocardin and AngII after hypoxia in regulating gene transcription in neonatal cardiomyocytes. Cultured rat neonatal cardiomyocytes were subjected to hypoxia, and the expression of myocardin and AngII were evaluated. Different signal transduction pathway inhibitors were used to identify the pathway(s) responsible for myocardin expression. An EMSA (electrophoretic mobility-shift assay) was used to identify myocardin/SRF binding, and a luciferase assay was used to identify transcriptional activity of myocardin/SRF in neonatal cardiomyocytes. Both myocardin and AngII expression increased after hypoxia, with AngII appearing at an earlier time point than myocardin. Myocardin expression was stimulated by AngII and ERK (extracellular-signal-regulated kinase) phosphorylation, but was suppressed by an ARB (AngII type 1 receptor blocker), an ERK pathway inhibitor and myocardin siRNA (small interfering RNA). AngII increased both myocardin expression and transcription in neonatal cardiomyocytes. Binding of myocardin/SRF was identified using an EMSA, and a luciferase assay indicated the transcription of myocardin/SRF in neonatal cardiomyocytes. Increased BNP (B-type natriuretic peptide), MHC (myosin heavy chain) and [3H]proline incorporation into cardiomyocytes was identified after hypoxia with the presence of myocardin in hypertrophic cardiomyocytes. In conclusion, hypoxia in cardiomyocytes increased myocardin expression, which is mediated by the induction of AngII and the ERK pathway, to cause cardiomyocyte hypertrophy. Myocardial hypertrophy was identified as an increase in transcriptional activities, elevated hypertrophic and cardiomyocyte phenotype markers, and morphological hypertrophic changes in cardiomyocytes.

Angiotensin II and the JNK pathway mediate urotensin II expression in response to hypoxia in rat cardiomyocytes

“…This study yielded results similar to our previous reports (Chiu et al 2010 regarding the putative mechanism involved in the UII increase observed in cardiomyocytes subjected to 2.5% hypoxia. Mild hypoxia (10 or 5%) did not induce significant oxidative stress to lead to an increase in UII expression.…”

Thirty years of the heart as an endocrine organ: physiological role and clinical utility of cardiac natriuretic hormones

“…Furthermore, myocardial ischemia and perhaps hypoxia per se can induce the synthesis/ secretion of BNP and its related peptides by ventricular cells, even when isolated and cultured (8,12,33,89,94) (Fig. 1).…”

STAT3 Protein Regulates Vascular Smooth Muscle Cell Phenotypic Switch by Interaction with Myocardin

“…Although myocardin is considered as a critical component of the contractile "switch" in SMC, the signals that regulate myocardin are only partially understood. Extracellular signals can mediate this molecular switch through alterations in effector pathways, and indeed myocardin-mediated gene activation is regulated by ligands such as TGF␤1 and angiotensin II (16), as well as intracellular signal transduction mediators such as YAP1, glycogen synthase kinase 3 (GSK3), and extracellular signal-regulated kinase (ERK) and the C terminus of Hsc70-interacting protein (ChIP) (17)(18)(19)(20). Although the regulation of myocardin gene expression has been widely explored, there are few studies that address the cellular signal pathways underlying the regulation of myocardin-mediated SMC phenotypic changes.…”