B-arrestins are multifunctional proteins that are recruited to G protein-coupled receptors (GCPRs) following agonist stimulation. While the classical role of (3-arrestin is to mediate receptor desensitization, work by investigators of this PPG have recently shown that P-arrestin can stimulate signaling in the absence of classical G protein activation. The existence of B-arrestin-mediated signaling independent of G proteins requires that receptors adopt multiple "active" conformations or "ligand selective states". The ability of unique ligand-receptor conformations to promote preferential B-arrestin signaling is an emerging concept known as "biased signaling". The molecular mechanisms that underlie p-an-estin-biased signaling for the p-adrenergic receptor of (PAR), and its physiological consequences in the heart, are not known. In this proposal, we will test the hypothesis that mutant p i - and P2 can be engineered that will selectively stimulate p-arrestinbiased signaling independent of G protein activation, and that p-arrestin-biased signaling will promote cardiomyocyte cell survival to limit the development of heart failure in response to pathological stimuli. Accordingly, the specific aims of the study are:
Aim 1 : To engineerBp1 AR mutants that show selective bias for p-arrestin recruitment.
Aim 2 : To identify the mechanism of activation and signaling pathways activated by P1AR and B2AR mutants in the absence of G protein activation.
Aim 3 : To test in adult cardiomyocytes whether p-arrestin-biasedBP2AR TYY and B1 AR mutants activate cardioprotective signaling in response to agonist stimulation and ischemia.
Aim 4 : To test in vivo whether the B-arrestin-biased Bp2AR TYY and pi AR mutant activities cardioprotective pathways under conditions of pathological stress. By exploring these aims, we will define the pathways by which G protein-Independent activation of BARs may lead to stimulation of cardioprotective signaling. If our hypothesis is correct, we will show that ligandstimulated PARS, which selectively activate B-arrestin signaling pathways, are cardioprotecitve. Since, by definition, the administration of a ligand that does not stimulate G protein signaling is B-blackade, we will have demonstrated proof-of concept for the development of an entirely novel class of receptor blockers. We believe these data will provide considerable impetus for the development of novel p-arrestin-biased therapeutic agents to treat human heart failure.
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