Endothelin-1 downregulates Mas receptor expression in human cardiomyocytes

Transcription factor ETV1 is essential for rapid conduction in the heart

Rapid impulse propagation in the heart is a defining property of pectinated atrial myocardium (PAM) and the ventricular conduction system (VCS) and is essential for maintaining normal cardiac rhythm and optimal cardiac output. Conduction defects in these tissues produce a disproportionate burden of arrhythmic disease and are major predictors of mortality in heart failure patients. Despite the clinical importance, little is known about the gene regulatory network that dictates the fast conduction phenotype. Here, we have used signal transduction and transcriptional profiling screens to identify a genetic pathway that converges on the NRG1-responsive transcription factor ETV1 as a critical regulator of fast conduction physiology for PAM and VCS cardiomyocytes. Etv1 was highly expressed in murine PAM and VCS cardiomyocytes, where it regulates expression of Nkx2-5, Gja5, and Scn5a, key cardiac genes required for rapid conduction. Mice deficient in Etv1 exhibited marked cardiac conduction defects coupled with developmental abnormalities of the VCS. Loss of Etv1 resulted in a complete disruption of the normal sodium current heterogeneity that exists between atrial, VCS, and ventricular myocytes. Lastly, a phenome-wide association study identified a link between ETV1 and bundle branch block and heart block in humans. Together, these results identify ETV1 as a critical factor in determining fast conduction physiology in the heart.

Angiotensin-(1-7) attenuated long-term hypoxia-stimulated cardiomyocyte apoptosis by inhibiting HIF-1α nuclear translocation via Mas receptor regulation

Extreme hypoxia often leads to myocardial apoptosis and causes heart failure. Angiotensin-(1-7)Ang-(1-7) is well known for its cardio-protective effects. However, the effects of Ang-(1-7) on long-term hypoxia (LTH)-induced apoptosis remain unknown. In this study, we found that Ang-(1-7) reduced myocardial apoptosis caused by hypoxia through the Mas receptor. Activation of the Ang-(1-7)/Mas axis down-regulated the hypoxia pro-apoptotic signaling cascade by decreasing the protein levels of hypoxia-inducible factor 1α (HIF-1α) and insulin-like growth factor binding protein-3 (IGFBP3). Moreover, the Ang-(1-7)/Mas axis further inhibited HIF-1α nuclear translocation. On the other hand, Ang-(1-7) activated the IGF1R/PI3K/Akt signaling pathways, which mediate cell survival. However, the above effects were abolished by A779 treatment or silencing of Mas expression. Taken together, our findings indicate that the Ang-(1-7)/Mas axis protects cardiomyocytes from LTH-stimulated apoptosis. The protective effect of Ang-(1-7) is associated with the inhibition of HIF-1α nuclear translocation and the induction of IGF1R and Akt phosphorylation.

Angiotensin-(1-7)/Mas Signaling Inhibits Lipopolysaccharide-Induced ADAM17 Shedding Activity and Apoptosis in Alveolar Epithelial Cells

A disintegrin and metalloproteinase (ADAM) 17, constitutively expressed in alveolar epithelium, is the pivotal shedding enzyme mediating acute lung inflammation. On the other hand, angiotensin (Ang)-(1-7)/Mas signaling has been shown to improve acute respiratory distress syndrome and protect alveolar epithelial cells from apoptosis. In this study, we explored the effect of Ang-(1-7)/Mas signaling on the expression and activity of ADAM17 and assessed its impact on apoptosis in lipopolysaccharide (LPS)-treated human alveolar epithelial cells. LPS markedly induced the shedding activity of ADAM17 in alveolar epithelial cells, which was blocked by selective c-Jun N-terminal kinase (JNK) inhibitor SP600125. Ang-(1-7) concentration-dependently inhibited LPS-induced ADAM17 shedding activity, which was abolished by selective Mas blocker A779 and Mas shRNA. LPS and Ang-(1-7) showed no significant effect on the expression of ADAM17. Overexpression of ADAM17 synergized with LPS on increasing the shedding activity of ADAM17 and apoptosis in alveolar epithelial cells, counteracting the inhibitory effects of Ang-(1-7). In addition, LPS significantly increased the JNK activity in alveolar epithelial cells; Ang-(1-7) concentration-dependently inhibited LPS-induced JNK activity, which was abolished by A779 and Mas shRNA. In conclusion, this study suggests that Ang-(1-7)/Mas signaling inhibits LPS-induced alveolar epithelial cell apoptosis by inhibiting LPS-induced shedding activity of ADAM17, likely by a JNK-dependent mechanism.