Abstract 324: RNAi Inhibition of Phosphodiesterase 1A Prevents Cold-Induced Hypertension and Cardiac Hypertrophy

Abstract

The calcium/calmodulin-dependent phosphodiesterase 1A (PDE1A) hydrolyzes the intracellular second messengers cAMP and cGMP, which are known to play an important role in regulating vascular tone and smooth muscle cell (VSMC) proliferation. Intermittent exposure to cold (6 hr/day) results in hypertension and cardiac hypertrophy. Interestingly, PDE1A expression was up-regulated in resistance arteries, kidneys and heart of rats exposed to cold. We hypothesize that RNAi inhibition of PDE1A would attenuate cold-induced hypertension (CIH) and cardiac hypertrophy (CICH). We constructed PDE1A shRNA (PDE1A-shRNA) plasmid, Control-shRNA plasmid, and LacZ plasmid driven by a CMV promoter. AAV-2 was used for in vivo gene delivery. Five groups of rats were used to test the effect of in vivo inhibition of PDE1A expression on the development of CIH and CICH. Four groups received an intravenous injection of AAV.PDE1A-shRNA, AAV.Control-shRNA, AAV.LacZ, and PBS, respectively, before intermittent exposure to moderate cold temperature (5°C), while the last group received PBS and was kept at room temperature (25°C) as a control. Blood pressure (BP), monitored using a telemetry system, was increased significantly in all cold-exposed groups except the group treated with PDE1A-shRNA, indicating that PDE1A-shRNA prevented the development of CIH. PDE1A-shRNA enhanced hypothesive responses to acetylcholine in cold-exposed rats, indicating improved endothelial dysfunction. The MRI analysis indicated that the in vivo left ventricle wall thickness was also decreased significantly in the cold-exposed rats treated with PDE1A-shRNA. All animals were sacrificed at 10 weeks after gene delivery. PDE1A-shRNA significantly attenuated the cold-induced increases in heart weight, cardiomyocyte sizes, and vascular wall thickness. PDE1A-shRNA increased intracellular cGMP and cAMP levels and decreased VSMC cell proliferation and migration. PDE1A protein expression was significantly decreased, indicating effective silence of PDE1A gene. RNAi inhibition prevented CIH, CICH and cold-induced vascular dysfunction and hypertrophy. Thus, PDE1A plays a critical role in the pathogenesis of CIH and CICH.