NIH AREA (R15) Program Heart failure (HF) is a major public health problem and defined as a chronic and complex clinical syndrome which results from any structural or functional cardiac disorder that impairs the ability of the heart to efficiently pump blood. ?-adrenergic receptor (?-AR) signaling is the primary mechanism to increase cardiac contractility. However, chronic ?-AR stimulation, which occurs in HF, results in reduced contractility due to desensitization of these receptors. Understanding how these perturbations in cardiac cell signaling lead to the development of HF is lacking, although many insightful studies have identified key signaling components involved in protein/gene expression, Ca2+ cycling, and post-translational modification. The diversity of this complex network of cellular responses is mediated by second messengers and achieved in part, by scaffolding proteins. Scaffolding proteins assemble intracellular signaling components of a network cascade into a specific complex within the cell, thereby enhancing signaling specificity as well as enhancing signaling efficiency. A-Kinase Anchoring Proteins (AKAPs) is an example of scaffolding proteins that fine-tune cellular responses ? cellular proximity and protein effective concentrations ? by forming multi-component protein complexes (signalosome). Through coordinating spatial-temporal signaling of proteins and enzymes that fine- tunes second messengers, gravin functions to regulate cAMP and thus substrate phosphorylation. This leads to changes in cellular Ca2+ availability, Ca2+ sensitivity and thus cardiac contractility. This project will focus on one particular AKAP, gravin (AKAP12). Gravin targets protein kinase A (PKA), among other proteins, to ?2-ARs and is involved in the desensitization/resensitization cycling of the receptor by facilitating PKA-dependent phosphorylation of the ?2-ARs. We will test the central hypothesis that gravin mediates ?2-AR desensitization during myocardial infarction induced HF. Specifically, inhibition of gravin scaffolding to ?2-AR will increase cardiac contractility during HF; whereas, overexpression of gravin will decrease cardiac contractility during HF. This will be achieved by two Specific Aims: (1) to determine that the absence of gravin signalosome mediated cardiac signaling improves cardiac function in failing hearts by blocking ?2-AR desensitization (Aim-1) and (2) to demonstrate that overexpression of gravin promotes ?2- AR desensitization thereby worsening cardiac function in failing hearts (Aim-2). Characterization of gravin scaffolding will improve our understanding for this central regulator of the kinase, phosphodiesterase, and phosphatase cardiac intracellular signaling. Overall, this study will (a) define the role of gravin scaffolding in mediating ?-AR desensitization and thereby cardiac contractility, (b) establish gravin as a potential target to ameliorate HF and (c) prepares the next generation of scientists to effectively confront current and future scientific challenges, theories and paradigms.
NIH AREA (R15) Program The diversity of complex cellular responses is mediated, in part, by scaffolding proteins. Scaffolding proteins assemble intracellular signaling components of a network cascade into a specific assembly within the cell, thereby enhancing signaling specificity as well as enhancing signaling efficiency. In particular, A-kinase anchoring proteins (AKAPs) are scaffolding protein ?signalosomes? that fine-tunes cellular responses by forming multi-component protein complexes. Through coordinating spatial-temporal signaling of proteins and enzymes, AKAP functions to coordinate substrate phosphorylation; ultimately leading to changes in calcium availability and calcium sensitivity.