Abstract 191: Phosphodiesterase 9a Modulates Cardiomyocyte Natriuretic Peptide-Stimulated cGMP Pool and Cardiac Hypertrophy

Abstract

Cardiac hypertrophy in response to pathologic stress is a major contributor to heart disease. Many studies have revealed that compartmentalized cyclic guanosine monophosphate (cGMP) regulation by phosphodiesterases (PDEs) can potently modify acute and chronic cardiac stress responses. PDE5a normally regulates cGMP generated from nitric oxide (NO)-stimulated soluble guanylate cyclase (sGC) but not natriuretic peptide (NP)-stimulated cGMP. Its inhibition blunts maladaptive hypertrophy and remodeling. Regulators of NP-cGMP remain uncertain. Here we reveal that PDE9a, a highly cGMP-specific PDE (×100 affinity vs PDE5a) that is expressed predominantly in the brain modulates myocyte cGMP as well, targeting NP-stimulated pools. PDE9a gene expression is observed in rat neonatal cardiac myocytes (RNCM) and adult mouse myocytes. Protein expression was identified in myocytes by immunohistochemistry, using gene silencing models as a negative control. PDE9a expression is upregulated by various hypertrophic stimuli (phenylephrine (PE) or endothelin-1 (ET-1), and observed in myocytes from pressure-overloaded whole myocardium. PDE9a inhibition with a selective antagonist (PF-9613) or gene silencing significantly abrogated PE- or ET-1-dependent upregulation of pathological-hypertrophy fetal genes and NFAT activity in RNCM, and PDE9a inhibition attenuated ET-1-induced hypertrophy in adult mouse myocytes. PF-9613 had no impact in cells lacking PDE9a (from knockout mice) or after gene silencing. Biochemical and cGMP-sensitive fluorescent probe studies shows PDE9a inhibition augments ANP- but not NO-dependent cGMP stimuli in RNCM and adult myocytes. PDE9a knockout (KO) mice were protected against hypertrophy/remodeling after pressure-overload, accompanied by a rise in myocardial cGMP. In PDE9a KO mice also exhibited less fibrosis and reduced expression of fibrotsis-related genes over wild-type mice. Together, these data identify PDE9a as a novel regulator of myocyte cGMP and hypertrophy that impacts a different compartmentalized cGMP pool to that by PDE5a. Our observations may provide a novel therapeutic approach in the treatment of heart failure.