Intracardiac detection of angiotensinogen and renin: a localized renin-angiotensin system in neonatal rat heart

Abstract

There is increasing evidence that the renin-angiotensin system (RAS) modulates cardiovascular function through both blood-borne and tissue-derived components. The existence of a local RAS has been proposed in the heart based on biochemical and molecular biological studies that identify angiotensinogen and renin. We conducted the present study to determine the chamber localization of angiotensinogen and renin mRNA in neonatal rat heart and whether these components could be identified in cultured cardiomyocytes and fibroblasts obtained from neonatal rat heart. Experiments using polymerase chain reaction (PCR) indicated that whole hearts obtained from neonatal rats contained both angiotensinogen and renin mRNA. With the use of radiolabeled cDNA probes and in situ hybridization, angiotensinogen and renin transcripts were localized both in the atria and ventricles of neonatal rat hearts. Relative signal strengths for angiotensinogen were highest in the left and right ventricles. In contrast, renin signal strength was overall much lower and preferentially localized in the left ventricle. To investigate the cellular source of angiotensinogen and renin, cultured neonatal heart cardiomyocytes and ventricular fibroblasts were screened for angiotensinogen and renin messenger RNA and protein using PCR and indirect immunofluorescent staining, respectively. These experiments demonstrated that both cell types produce transcripts and the respective translation products for angiotensinogen and renin. These data suggest that the site of angiotensin II synthesis can occur at the level of the individual cardiomyocyte and fibroblast, where it may serve to directly and/or indirectly regulate cardiac rate, force, growth, and development in the neonate.

Pressure Overload Induces Cardiac Hypertrophy in Angiotensin II Type 1A Receptor Knockout Mice

“…[3][4][5][6][7][8][9][10] In addition, all components of the RAS are upregulated by pressure overload in the heart. 5,[11][12][13][14][15][16] All these results suggest that the RAS plays a critical role in the development of mechanical stressinduced cardiac hypertrophy. In the present study, however, we have demonstrated that hemodynamic overload fully induces cardiac hypertrophy in genetically engineered mice that lack the AT 1A gene, suggesting that AT 1 -mediated Ang II signaling is not indispensable for the development of pressure overload-induced cardiac hypertrophy.…”

“…8 -10 Many studies have demonstrated that hemodynamic overload activates the tissue RAS in the heart. [11][12][13][14][15][16] mRNA and/or protein levels of renin, 11 ACE, 12,13 angiotensinogen, 5,11,14 and Ang II receptors 15,16 have been reported to be increased in hypertrophied hearts. In addition to these in vivo studies, mechanisms by which mechanical stress induces cardiomyocyte hypertrophy have also been investigated in vitro with cultured cardiac myocytes.…”

Transcriptional Regulation of the Rat Renin Gene by Regulatory Elements in Intron I

“…However, a related rat skeletal muscle myoblast cell line, L6, has already been shown to express renin. 29 Transcription analysis of the different constructs revealed a complex pattern of 7 potential cis-regulating elements within the first 850 bp of intron I, 5 negative regulatory elements Figure 5. Sequence-specific DNA-binding in rat renin intron I. Protein-DNA complexes were formed with the first 65 nucleotides of intron I partially methylated and endlabelled with 32 P and 293 nuclear extracts.…”

Inhibition of p53 Function Prevents Renin-Angiotensin System Activation and Stretch-Mediated Myocyte Apoptosis

“…Myocytes possess the various components of RAS 29,33,34 and generate Ang II. 2,9 -11,29 Conditions of overload in vivo up-regulate this local system 34 and Ang II blockade improves the outcome of ventricular dysfunction and failure of ischemic and nonischemic origin.…”