Mechanical Stretch and Angiotensin II Differentially Upregulate the Renin-Angiotensin System in Cardiac Myocytes In Vitro

• Published in: Circulation research 1999-07, Vol.85 (2), p.137-146
• Main Authors: Malhotra, Ricky, Sadoshima, Junichi, Brosius, Frank C, Izumo, Seigo
• Format: Article
• Language: English
• Subjects: Angiotensin II - pharmacology; Angiotensinogen - genetics; Animals; Anti-Arrhythmia Agents - pharmacology; Antisense Elements (Genetics); Biological and medical sciences; Blotting, Southern; Cells, Cultured; Fibroblasts - cytology; Fibroblasts - drug effects; Fibroblasts - metabolism; Fundamental and applied biological sciences. Psychology; Gene Expression - drug effects; Gene Expression - physiology; Heart; Heart Ventricles - cytology; Heart Ventricles - enzymology; Imidazoles - pharmacology; In Vitro Techniques; Iodine Radioisotopes; Losartan - pharmacology; Muscle Fibers, Skeletal - cytology; Muscle Fibers, Skeletal - drug effects; Muscle Fibers, Skeletal - enzymology; Myocardial Contraction; Myocardium - chemistry; Myocardium - cytology; Myocardium - enzymology; Peptidyl-Dipeptidase A - genetics; Pyridines - pharmacology; Radioligand Assay; Rats; Rats, Wistar; Receptor, Angiotensin, Type 1; Receptors, Angiotensin - genetics; Renin - genetics; Renin-Angiotensin System - physiology; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - analysis; Space life sciences; Stress, Mechanical; Vertebrates: cardiovascular system
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.res.85.2.137

Pressure overload in vivo results in left ventricular hypertrophy and activation of the renin-angiotensin system in the heart. Mechanical stretch of neonatal rat cardiac myocytes in vitro causes secretion of angiotensin II (Ang II), which in turn plays a pivotal role in mechanical stretch-induced hypertrophy. Although in vivo data suggest that the stimulus of hemodynamic overload serves as an important modulator of cardiac renin-angiotensin system (RAS) activity, it is not clear whether observed upregulation of RAS genes is a direct effect of hemodynamic stress or is secondary to neurohumoral effects in response to hemodynamic overload. Moreover, it is unclear whether activation of the local RAS in response to hemodynamic overload predominantly occurs in cardiac myocytes or fibroblasts or both. In the present study, we examined the effect of mechanical stretch on expression of angiotensinogen, renin, angiotensin-converting enzyme (ACE), and Ang II receptor (AT1A, AT1B, and AT2) genes in neonatal rat cardiac myocytes and cardiac fibroblasts in vitro. The level of expression of angiotensinogen, renin, ACE, and AT1A genes was low in unstretched cardiac myocytes, but stretch upregulated expression of these genes at 8 to 24 hours. Stimulation of cardiac myocytes with Ang II also upregulated expression of angiotensinogen, renin, and ACE genes, whereas it downregulated AT1A and did not affect AT1B gene expression. Although losartan, a specific AT1 antagonist, completely inhibited Ang II-induced upregulation of angiotensinogen, renin, and ACE genes, as well as stretch-induced upregulation of AT1A expression, it did not block upregulation of angiotensinogen, renin, and ACE genes by stretch. Western blot analyses showed increased expression of angiotensinogen and renin protein at 16 to 24 hours of stretch. The ACE-like activity was also significantly elevated at 24 hours after stretch. Radioligand binding assays revealed that stretch significantly upregulated the AT1 density on cardiac myocytes. Interestingly, stretch of cardiac fibroblasts did not result in any discernible increases in the expression of RAS genes. Our results indicate that mechanical stretch in vitro upregulates both mRNA and protein expression of RAS components specifically in cardiac myocytes. Furthermore, components of the cardiac RAS are independently and differentially regulated by mechanical stretch and Ang II in neonatal rat cardiac myocytes.