Spatial diversity of GPCR-mediated ERK signaling and its role in cardiovascular disease - Project Summary G-protein-coupled receptors (GPCRs), the largest family of membrane receptors, play a key role in maintaining heart function1,2. In particular, β1-adrenergic receptor (β1AR) contributes to normal cardiac function including regulation of heart rate and contractility, but its overstimulation by circulating catecholamines such as adrenaline and noradrenaline can induce cardiac hypertrophy, leading to heart failure3-6. Recent findings reveal that β1ARs are not only active at the plasma membrane but are also localized on the Golgi membrane of cardiac myocytes, activating the cAMP/PKA pathway and regulating PLCε-mediated cardiac hypertrophy in NRVMs11. A major downstream signaling component of β1AR is Extracellular Signal-Regulated Kinase (ERK), a master regulator of cell survival, growth, and metabolism9. Although ERK activity has also been implicated in cardiac hypertrophy10, the mechanism underlying β1AR-mediated ERK activation and how it contributes to cardiac hypertrophy are still not well understood. In preliminary studies, I showed that distinct pools of adrenaline-activated β1ARs can activate ERK at the plasma membrane and the Golgi, respectively, suggesting that the β1AR-ERK signaling is also spatially regulated. The subcellular pools of β1AR were also found to regulate the downstream ERK activation via different mechanisms - through the Gβγ complex of heterotrimeric G proteins and β-arrestin for plasma membrane and Golgi ERK respectively. Additionally, only the plasma membrane pool of β1AR propagated ERK activity into the nucleus, establishing a novel spatial diversity in GPCR-effector protein coupling mechanisms that could have major implications for the role of ERK in cardiac physiology. Thus, the overarching hypothesis of the proposed project is that the coordination of ERK activation by distinct subcellular pools of β1ARs regulates cardiac hypertrophy. The project will have two aims consisting of (1) illuminating the spatial organization of β1AR-mediated ERK activation at subcellular compartments, and (2) studying the functional impact of compartmentalized β1AR-mediated ERK signaling on cardiac hypertrophy. These aims will be tested using fluorescent biosensor imaging, targeted biochemical perturbations, and cellular assays in cardiomyocytes. The proposed studies will elucidate the mechanisms of compartmentalized β1AR-mediated ERK signaling and provide a better understanding of their critical roles in regulating cardiac health, paving the way for novel therapeutic strategies.
