Project 1: Targeting GRK5 in Cardiac Injury and Repair

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Project 1 - SUMMARY The clinical syndrome heart failure (HF) continues to be a major health problem world-wide. It is an end-point after cardiac injury/stress, which is usually preceded by cardiac hypertrophy and adverse ventricular remodeling. Over the last two decades, our laboratory has studied HF development with a focus on the role of G protein- coupled receptor (GPCR) signaling. In particular, we are interested in how GPCR kinases (GRKs) regulate normal and diseased myocardial signaling and function. These kinases canonically regulate GPCRs via phosphorylation causing desensitization and a loss of response. GRK2 and GRK5 are the major GRKs expressed in the heart and both have been found to be up-regulated in failing human myocardium and also in animal models. Recently, we have identified a non-GPCR role for GRK5 in the heart as a pathological facilitator of hypertrophy and the maladaptive transition to HF via its localization and activity in the nucleus of cardiomyocytes. In fact, hypertrophic stress induces nuclear translocation of GRK5 where it can act as a Class II histone deacetylase (HDAC) kinase causing de-repression of hypertrophic gene transcription through MEF2. In addition, GRK5, in an apparent non-catalytic manner, can facilitate nuclear NFAT activity on hypertrophic gene transcription. Of interest, GRK5 has been shown to bind to DNA directly and new preliminary data has identified several gene targets via chromatin precipitation and sequencing (ChIP-Seq). The pathological nature of GRK5, a least in pressure-overload, appears to be primarily through its nuclear localization, which appears dependent on calcium-calmodulin (Ca2+-CaM) binding to a region within the amino-terminus of GRK5 (GRK5nt). What isn’t known is whether GRK5 or its nuclear activity participates in cardiac pathology after ischemic injury and this will be determined in this proposal where we have preliminary data suggesting increased GRK5 in myocytes plays a novel role in post-ischemic HF via regulation and modulation of immune cell infiltration and inflammation. Interestingly, this pathology differs significantly from that of GRK2. We have existing and novel mouse models available to us to determine the role of nuclear GRK5 in HF and whether its pathological mechanisms involve pathways and gene targets that do not require the catalytic activity of GRK5. These models will be employed in this Project to investigate these novels aspects of GRK5 in HF development post-stress and to test our Central Hypothesis that GRK5 plays a critical (patho)-physiological role in the heart’s response to injury and targeting and manipulating its unique cellular localization and/or activity in myocytes is a novel therapeutic repair strategy for the injured heart. Our associated Specific Aims are: [1] to determine the DNA/gene targets of nuclear GRK5 in hypertrophy and determine whether kinase activity is involved in its gene regulation; [2] To determine if a translational approach can be employed therapeutically to limit pathological nuclear GRK5 activity; [3] To determine the mechanistic action of GRK5 in the pathophysiology of myocardial ischemic injury and how this specifically differs from GRK2-mediated injury.