Abstract 17270: Nitric Oxide Synthase&-Activated Protein Kinase Dependent Signaling Pathways are Involved in the Anti-Hypertrophic Effect of The Human Beta 3 Adrenoreceptor
Background: The human heart contains β3ARs which are coupled to nitric oxide (NO) synthesis; however, their role in cardiac remodeling is unclear.
Methods: Mice with cardiomyocyte-specific overexpression of human β3AR (TG) & wild-type littermates (WT) were treated with isoproterenol (Iso 30mg/kg/d, 10d), angiotensin II (AngII 2mg/kg/d), or saline by osmotic minipump, with/without L-NAME (2mg/mL). In vitro hypertrophic responses, signaling & NO production (EPR) were analyzed in neonatal rat ventricular myocytes infected with an adenovirus expressing the human β3AR (hβ3-NRVMs). Subcellular localization of β3AR was studied in adult ventricular myocytes using the proximity ligation assay (PLA).
Results: LV function was similar between WT & TG at baseline, & following acute Iso infusion. In adult myocytes, PLA showed colocalization of the β3AR & eNOS with caveolin-3, which coimmunoprecipitated with AMP-activated protein kinase (AMPK) & eNOS. Following 10 day Iso or AngII, cardiac myocyte hypertrophy & an upregulation of βMHC mRNA expression were observed in WT (µm²: 682±18 Sal vs 914±54 Iso; p<0.001; n=9), but not TG mice (697±16 Sal vs 783±39 Iso; p=ns; n=9). L-NAME treatment abrogated the protection from Iso-induced hypertrophy in TG mice (728±30 L-NAME vs 963±60 L-NAME+Iso; p<0.001; n = 9). In vitro, when compared to GFP-NRVMs, hβ3-NRVMs showed higher NO production (GFP 2108±245; hβ3 3631±341; n =4) & failed to show a cardiac hypertrophic response (assessed by measurement of cell size, protein synthesis & NFAT activation) following PE stimulation. Treatment of hβ3-NRVMs with L-NAME abolished the protection from PE-induced hypertrophy. In GFP-NRVMs, PE inhibited AMPK (measured as phospho-Thr172 AMPK), an inhibitor of protein synthesis & cardiac hypertrophy, yet in hβ3-NRVMs AMPK phosphorylation was preserved after PE.
Conclusion: Cardiac-specific overexpression of β3ARs does not alter LV function but inhibits hypertrophy following neurohormone stimulation in vivo & in vitro, partly through NO-dependent & AMPK-dependent mechanisms, consistent with colocalization of hβ3AR with NOS in caveolae. Cardiac β3ARs may be a therapeutic target in the treatment of cardiac remodeling associated with elevated sympathetic tone.
- © 2012 by American Heart Association, Inc.