Phosphodiesterase 1 (PDE1) Regulation of Myocardial Calcium and Function - PROJECT SUMMARY The cyclic nucleotide cAMP serves as a second messenger critical in multiple cellular processes. Two proteins help to regulate the level of cAMP. G-protein coupled receptors (GPCRs) are transmembrane proteins involved in cAMP production. G proteins are heterotrimeric, and a subset of GPCRs consists of a stimulatory, catalytic G⍺ subunit (G⍺s) that upon receptor ligand binding, increase adenylyl cyclase (AC) production of cAMP. Phosphodiesterases (PDEs), on the other hand, hydrolyze cAMP into AMP. In heart failure animal models and human patients, PDE1 inhibition helps to improve cardiac function by increasing myocardial contractility, improving relaxation, and vasodilating to lower hemodynamic stress on the heart. These effects are similar to those upon PDE3 inhibition, but whereas the latter is associated with fatal arrhythmias, no arrhythmic events have been associated with PDE1 inhibitor use. Compartmentalized cAMP signaling that is unique to PDE1 vs PDE3 may help to explain this important difference. It is known that specific PDE-GPCR pairings work together to regulate distinct pools of cAMP. The heart expresses more than 200 GPCRs and 3 cAMP-hydrolyzing PDEs (1, 3, and 4). Unique pairings help to establish compartmentalized gradients of cAMP signaling that enable the modulation of specific cellular processes in response to different stimuli. While multiple GPCR pairings with PDE3 or PDE4 have been known, which GPCR(s) pair with PDE1 remains unknown. In this Diversity Supplemental project, we will identify the GPCR(s) that functionally enhance(s) the positive inotropic effects of PDE1 inhibition. We will do so by employing cardiomyocyte contractility and calcium, and forster resonance energy transfer (FRET) imaging experiments, and cardiac slice physiologic studies. Guinea pig hearts, which are much more like the human heart in PDE biology versus the commonly used rat and mouse models will be used. Our hypothesis is that PDE1 will establish a G⍺s- associated cAMP gradient that is distinct from that regulated by PDE3. This is an important question because of clinical potentials of PDE1 inhibition in patients with Parkinson’s Disease or heart failure. The completion of our aim will thus contribute original findings with direct clinical relevance that can potentially help improve the health and life quality of patients.
