Myocardial injury following an ischemic insult continues to be a challenge in terms of effectively managing or repairing the damage as well as preventing development of chronic heart failure (HF). A real urgency exists to delineate molecular pathological mechanisms for potential new therapeutic targets. Accordingly, we have identified a key role for G protein- coupled receptor (GPCR) kinase-2 (GRK2) in the pathophysiology of injured or stressed myocardium. Inhibition of GRK2 activity in small animal models of HF can improve cardiac function and morphology. This has primarily been done using a peptide inhibitor of GRK2, the PARKct, however, recent studies using cardiomyocyte-specific GRK2 knockout (KO) mice have provided similar beneficial results in ischemic HF. Canonically, GRK2 phosphorylates agonist-activated GPCRs, such as p-adrenergic receptors (jJARs) in the heart, triggering the process of desensitization. GRK-mediated phosphorylation causes p-arrestin binding to the receptor, which blocks further G protein signaling. Interestingly, |3-arrestins (P-arrestin1 and p-arrestin2) can also initiate intracellular signaling pathways after interacting with desensitized receptors through kinase scaffolding, which is Independent of G protein signaling. A goal in this proposal is to discover novel GRK2 and p- arrestin dependent mechanisms involved in myocardial ischemic injury and repair processes. We now have data that suggests that beneficial GRK2-dependent mechanisms in the injured heart go beyond |3AR signaling and control of contractility and include myocyte survival. In this proposal we will test whether acute and/or chronic cardioprotection might be due to events beyond cellular contractile signaling including regeneration targeted through either myocytes or stem/progenitor cells. First and foremost, regardless of mechanism, data with the pARKct in failing rodent hearts shows real promise in reversing cardiac dysfunction and since an overall goal of this PPG group is to translate novel molecular findings to improve post-ischemic cardiac repair - we have a great opportunity to ultimately determine if inhibition of GRK2 can provide a novel therapeutic option in a large animal model of ischemic HF. This pre-clinical testing of pARKct is timely given that gene therapy for human HF is becoming a reality. This proposal will also begin the novel investigation into the role of p-arrestins, acting downstream of GRK activity, in myocardial ischemic injury and repair. Our Central Hypothesis is that GRK2 activity and subsequent p-arrestin function play novel roles downstream of GPCR desensitization that are critically involved in the heart's response to ischemic injury including potential repair and regeneration. Moreover, GRK2 inhibition with the pARKct is a viable therapeutic option for HF that can be translated after testing in a pre-clinical pig model.
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