G protein-coupled receptors (GPCRs) are essential mediators of neurohormonal signaling in both the normal and failing heart. ?-adrenergic receptors (?ARs) in particular control many facets of cardiomyocyte function, including contractility and survival signaling, through the activation of both G protein-dependent and ?-arrestin-dependent signaling pathways. ?-blockers are commonly used in the treatment of heart failure and act to block cardiomyocyte cell death. While G protein-dependent ?AR signaling enhances cardiomyocyte death during heart failure, ?-arrestin-biased ?AR signaling has been suggested to promote cardiomyocyte survival in the heart following acute cardiac injury or during heart failure. Although the clinically used ?-blocker carvedilol has been shown to induce ?-arrestin-biased ?AR signaling in model cells, we have found that carvedilol actually ablates cardiomyocyte contraction. Thus, we believe ?-arrestin-biased ?AR modulators that promote survival, but not at the expense of cardiomyocyte contractility, would serve as more effective therapeutic agents for heart failure. Our recent work has detailed the development of pepducins, palmitoylated peptides from the intracellular loops of a GPCR that selectively confer biased signaling via either G protein- or arrestin-dependent pathways. In particular, several pepducins designed from the first intracellular loop of the ?2AR were discovered to be completely ?-arrestin-biased. Further, we have shown for the first time that the most potent of these compounds, ICL1-9, enhances cardiomyocyte contraction in a ?2AR- and ?-arrestin-dependent manner. This is the first demonstration of a ?-arrestin-biased ?2AR modulator enhancing cardiomyocyte contractility in the absence of G protein activation, an exciting finding that has the potential to greatly improve heart failure therapeutics. We hypothesize that compounds that promote ?-arrestin-biased ?2AR signaling will be useful in the treatment of heart failure and propose to identify and further characterize the ability of such compounds to improve cardiac function. To test this hypothesis we will: 1) Dissect the mechanism of ?-arrestin-biased ?2AR signaling using ICL1-9 as a model; 2) Perform high throughput screening and characterization of compounds that promote ?-arrestin-biased ?2AR signaling and define their target and mechanism of action; 3) Determine the mechanism of ?-arrestin-biased ?2AR-mediated cardiomyocyte contractility and its impact on cardiac function in vivo; and 4) Evaluate the effects of ?-arrestin-biased ?2AR signaling on cardiomyocyte survival in vitro and in response to acute cardiac injury in vivo. Overall, the goal of this project is to understand the mechanism of ?-arrestin-biased ?2AR signaling and its impact on cardiomyocyte survival and function with a long-term goal of developing novel therapeutics for the treatment of heart failure.
Heart failure is a progressive disease affecting over 5 million people in the U.S. with an annual cost exceeding $60 billion; therefore, understanding the molecular details regulating normal and abnormal cardiac function is critical to the development of new therapies. To better understand this process, we have focused on the ?2-adrenergic receptor (?2AR) and now provide the first demonstration of a ?-arrestin-biased ?2AR modulator that enhances cardiomyocyte contractility in the absence of G protein activation. We propose to better understand the mechanism of ?-arrestin-biased ?2AR signaling and its impact on cardiomyocyte survival and function with a long-term goal of developing novel therapeutics for the treatment of heart failure.
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