Abstract 14375: Reversal of Aging-Induced Upregulation of Cardiac Inducible Nitric Oxide Synthase and Beta-Adrenergic Desensitization in Mice Deficient in Beta3-Adrenoreceptor
Background: We showed previously that aging-induced cardiac dysfunction and β- adrenergic receptors (AR) desensitization was prevented in β3-AR knockout (β3KO) aged mice. However, the molecular mechanisms are unclear. We hypothesize that reversal of aging-induced upregulation of cardiac inducible nitric oxide synthase (iNOS) by β3KO may play a key role in the protective effects.
Methods: We compared iNOS and iNOS phosphorylation protein levels, β1- and β3-AR expressions, and cell contractility, relaxation, [Ca2+]i transient ([Ca2+]iT) and L-type Ca2+ current (ICa,L) responses to isoproterenol (ISO, 10-8 M) in LV myocytes obtained from 2 young (Y) (6 mo) and 2 aged (A) (28 mo) groups (6/group) of wild-type (WT) and β3KO mice, respectively.
Results: Compared with YWT, AWT myocytes had significantly elevated iNOS (0.51 vs 0.25) expression with augmented iNOS activity. The iNOS phosphorylation at tyrosine position 151 increased. The ratio of phospho-protein to actin elevated 129% (0.32 vs 0.14). β3-AR (0.30 vs 0.15) increased, but β1-AR (0.40 vs 0.59) decreased. These changes were associated with reduced basal myocyte contraction (dL/dtmax, 82.9 vs 123.9 μm/s), relaxation (dR/dtmax, 62.49 vs 96.2 μm/s), [Ca2+]iT(0.15 vs 0.23) and ICa,L (4.3 vs 7.6 pA/pF) accompanied by diminished ISO-stimulated inotropic responses. In AWT, ISO (10-8 M) caused less increases in dL/dtmax (35% vs 82%), dR/dtmax(24% vs 61%), [Ca2+]iT (16% vs 37%) and ICa,L (15% vs 34%). Compared with YWT, Yβ3KO had significantly reduced iNOS (0.17 vs 0.24), but similar β1-AR (0.63 vs 0.61) expression. Importantly, in contrast to AWT, Aβ3KO myocytes had significantly reduced iNOS (0.18), but increased β1-AR expression (0.64). These changes correlated with normal basal cell contraction and relaxation with preserved ISO-stimulated inotropic response. ISO caused similar increases in dL/dtmax (87% vs 84%), [Ca2+]iT (33% vs 38%) and ICa,L (32% vs 35%) compared to Yβ3KO mice.
Conclusions: Chronic β3-AR deficiency reverses upregulation of cardiac iNOS and prevents aging-induced downregulation of β1-ARs, leading to the preservation of myocyte function, [Ca2+]iT, ICa,L and β-adrenergic reserve in aged hearts, suggesting that blocking β3-AR may provide a new strategy to retard cardiac aging.
Author Disclosures: H. Cheng: None. P. Zhou: None. T. Li: None. Z. Zhang: None. D.W. Kitzman: None. L. Groban: None. C. Cheng: None.
- © 2016 by American Heart Association, Inc.