Inhibition of Mas G-protein signaling improves coronary blood flow, reduces myocardial infarct size, and provides long-term cardioprotection

Abstract

The Mas receptor is a class I G-protein-coupled receptor that is expressed in brain, testis, heart, and kidney. The intracellular signaling pathways activated downstream of Mas are still largely unknown. In the present study, we examined the expression pattern and signaling of Mas in the heart and assessed the participation of Mas in cardiac ischemia-reperfusion injury. Mas mRNA and protein were present in all chambers of human hearts, with cardiomyocytes and coronary arteries being sites of enriched expression. Expression of Mas in either HEK293 cells or cardiac myocytes resulted in constitutive coupling to the G(q) protein, which in turn activated phospholipase C and caused inositol phosphate accumulation. To generate chemical tools for use in probing the function of Mas, we performed a library screen and chemistry optimization program to identify potent and selective nonpeptide agonists and inverse agonists. Mas agonists activated G(q) signaling in a dose-dependent manner and reduced coronary blood flow in isolated mouse and rat hearts. Conversely, treatment of isolated rat hearts with Mas inverse agonists improved coronary flow, reduced arrhythmias, and provided cardioprotection from ischemia-reperfusion injury, an effect that was due, at least in part, to decreased cardiomyocyte apoptosis. Participation of Mas in ischemia-reperfusion injury was confirmed in Mas knockout mice, which had reduced infarct size relative to mice with normal Mas expression. These results suggest that activation of Mas during myocardial infarction contributes to ischemia-reperfusion injury and further suggest that inhibition of Mas-G(q) signaling may provide a new therapeutic strategy directed at cardioprotection.

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli

“…Adenovirus-mediated overexpression of MAS in rat neonatal cardiomyocytes caused IP3 accumulation and myocyte hypertrophy through Ga q -mediated signaling (Zhang et al, 2012). Constitutive activity of the MAS in overexpressing cells activates G-protein signaling pathways (Dias-Peixoto et al, 2008;Shemesh et al, 2008;Gomes et al, 2012;Zhang et al, 2012;Tirupula et al, 2014). Similar to Ang(1-7) the analogs A-779 and AVE 0991 fail to activate G-protein signaling through MAS Wiemer et al, 2002;Kluskens et al, 2009).…”

“…Consequently, these other physiologic peptides reported as endogenous ligands for MAS remain incompletely characterized. Few reports indicate that G-proteins are activated by MAS in response to few physiologic peptides and "surrogate" nonpeptide ligands in transfected cells but not in response to Ang(1-7) (Bikkavilli et al, 2006;Canals et al, 2006;Shemesh et al, 2008;Tirupula et al, 2014;Zhang et al, 2012). MAS shares significant similarity with Mas-related G-protein-coupled receptors or paralogs, which are predominantly expressed in State of the Angiotensin Receptors neurons and immune cells (Young et al, 1986;Dong et al, 2001;Bender et al, 2002).…”

“…Therefore, the role of MAS as the receptor for only Ang(1-7) qualifying it as an integral constituent of the RAS is unclear. MAS appears to be a GPCR with high constitutive activity and may not have a unique cognate endogenous ligand (Canals et al, 2006;Zhang et al, 2012;Tirupula et al, 2014). Many physiologic modulators of MAS activity may exist; important among them may include peptides such as Ang(1-7) and neuropeptide FF.…”

“…Although MAS is a GPCR, there is no evidence for Ang(1-7)-mediated conventional G-protein signaling as measured by the levels of second messenger molecules like calcium, IP3, and cAMP in MAS-transfected cells (Bikkavilli et al, 2006;Shemesh et al, 2008;Zhang et al, 2012;Tirupula et al, 2014). This observation is, however, disputed by reports in kidney, where Ang (1)(2)(3)(4)(5)(6)(7) treatment is reported to increased cAMP levels and protein kinase A activation, suggesting Ga s activation by MAS.…”

“…MAS was shown to constitutively couple to Ga i , Ga q , and Ga 12/13 proteins (Zohn et al, 1998;Whitehead et al, 2001;Booden et al, 2002;Chen and Ikeda, 2004;Singh et al, 2010a;Tirupula et al, 2014). Adenovirus-mediated overexpression of MAS in rat neonatal cardiomyocytes caused IP3 accumulation and myocyte hypertrophy through Ga q -mediated signaling (Zhang et al, 2012). Constitutive activity of the MAS in overexpressing cells activates G-protein signaling pathways (Dias-Peixoto et al, 2008;Shemesh et al, 2008;Gomes et al, 2012;Zhang et al, 2012;Tirupula et al, 2014).…”