Core 3. Genetics, Genomics and Congenital CV Disorders
Session Title: The Curse of Aging and Strategies to Address It
Abstract 11645: Upregulation of Cardiac Beta3-Adrenergic Receptor-Activated Inducible Nitric Oxide Synthase Promotes Cardiac Aging: Role of Oxidant Stress
Background. Cardiac aging (CA) is accompanied by oxidative stress and cardiac dysfunction; the link between the two is unclear. Although β3-adrenergic receptor (AR)-mediated nitric oxide synthase (NOS) uncoupling is increasingly emerging as a major mediator of cardiovascular pathologies including heart failure, the NOS isoforms involved are controversial. Moreover, its functional role in CA is unknown. We tested the hypothesis that increased cardiac peroxynitrite (NT) formation deriving from inducible nitric oxide synthase (iNOS) uncoupling via the activated β3-AR is responsible for age-related cardiac dysfunction.
Methods. We determined alterations on cardiomyocyte expressions of NOS, GTP cyclodrolase I (GTPCHI), and NT; β1- and β3-AR and SERCA 2α and compared myocyte contractile and [Ca2+]i transient ([Ca2+]iT) responses to isoproterenol (ISO, 10-8 M) in myocytes obtained from 2 young (Y) (∼6 mo) and 2 aged (A) (∼28 mo) groups (5/group) of wild-type (WT) and β3-AR knockout (β3KO) mice.
Results. Compared with YWT, AWT myocytes had significantly increased iNOS (0.46 vs 0.23) and activity, but unchanged eNOS and nNOS accompanied with significantly decreased GTPCHI (- 41%), elevated NT (+101%) and β3-AR (+81%). There were significantly decreased protein levels of β1-AR (-39%) and SERCA 2α (-65%). These changes were associated with reduced basal cell contraction (dL/dtmax) (81.4 vs 122.8 μm/s), relaxation (dR/dtmax) (60.9 vs 94.3 μm/s) and [Ca2+]iT (0.16 vs 0.24) accompanied by a diminished ISO-stimulated inotropic response. Compared with YWT, Yβ3KO had significantly reduced iNOS (0.18 vs 0.23) with no significant differences in GTPCHI, NT, basal myocyte contraction and ISO responses. Importantly, in contrast to age-caused changes in AWT, compared with Yβ3KO, in Aβ3KO myocytes, there were no significant alterations in iNOS (0.19), GTPCHI, NT, β1-AR and SERCA 2α. Aβ3KO myocytes had normal cell contraction and relaxation with preserved ISO-stimulated positive inotropic response.
Conclusions. Oxidant stress from upregulation of cardiac β3-AR-activated iNOS uncoupling promotes CA. Chronic β3-AR deficiency reverses CA-caused changes and plays a protective effect. Thus, antagonizing β3-AR could be a new therapeutic strategy for CA.