ERK mediated survival signaling is dependent on the Gq-G-protein coupled receptor type and subcellular localization in adult cardiac myocytes

Abstract

G protein-coupled receptors that signal through Gαq (GqPCRs), like α1-adrenergic and angiotensin receptors (α1-AR, AT-R), are traditionally thought to mediate pathologic remodeling in heart failure, including cardiac myocyte death. However, we previously demonstrated that α1- ARs are cardioprotective and identified an α1A-subtype-ERK survival-signaling pathway in adult cardiac myocytes. Recently, we demonstrated that α1-ARs localize to and signal from the nucleus, whereas AT-R localize to and signal from the sarcolemma in adult cardiac myocytes. Thus, we proposed a novel paradigm, predicated on compartmentalization of GqPCR signaling, to explain the phenotypic diversity of GqPCRs. Here, we tested the hypothesis that differential subcellular compartmentalization of α1-AR and AT-R mediated activation of ERK might explain the differential effects of these receptors on cardiac myocyte survival. Using a fluorescent ERK activity FRET-based biosensor, EKAR, to measure subcellular localization and extent of receptor-mediated ERK activation in single adult cardiac myocytes, we found that α1-ARs induced ERK activity at the nucleus and in the cytosol in 60% of cardiac myocytes, whereas AT-Rs showed no consistent ERK activation. The cell-specific α1-mediated activation of ERK in 60% of adult cardiac myocytes showed concordance with previous studies indicating that the α1A-subtype is expressed in only 60% of cardiac myocytes. Consistent with the ability to activate ERK, we found that only α1-ARs induced phosphorylation of Bcl-2 family member Bad, improved mitochondrial membrane stability, and promoted cardiac myocyte survival. In summary, our results suggest that compartmentalization of GqPCRs dictate activation of ERK and cardiac myocyte survival in adult cardiac myocytes.

Keywords: Angiotensin receptors; Cardiac myocytes; Cell signaling; ERK; Fluorescent lifetime imaging microscopy; α1-adrenergic receptors.