Enhanced expression of β3-adrenoceptors in cardiac myocytes attenuates neurohormone-induced hypertrophic remodeling through nitric oxide synthase

BACKGROUND - : β1-2-adrenergic receptors (AR) are key regulators of cardiac contractility and remodeling in response to catecholamines. β3-AR expression is enhanced in diseased human myocardium, but its impact on remodeling is unknown. METHODS AND RESULTS - : Mice with cardiac myocyte-specific expression of human β3-AR (β3-TG) and wild-type (WT) littermates were used to compare myocardial remodeling in response to isoproterenol (Iso) or Angiotensin II (Ang II). β3-TG and WT had similar morphometric and hemodynamic parameters at baseline. β3-AR colocalized with caveolin-3, endothelial nitric oxide synthase (NOS) and neuronal NOS in adult transgenic myocytes, which constitutively produced more cyclic GMP, detected with a new transgenic FRET sensor. Iso and Ang II produced hypertrophy and fibrosis in WT mice, but not in β3-TG mice, which also had less re-expression of fetal genes and transforming growth factor β1. Protection from Iso-induced hypertrophy was reversed by nonspecific NOS inhibition at low dose Iso, and by preferential neuronal NOS inhibition at high-dose Iso. Adenoviral overexpression of β3-AR in isolated cardiac myocytes also increased NO production and attenuated hypertrophy to Iso and phenylephrine. Hypertrophy was restored on NOS or protein kinase G inhibition. Mechanistically, β3-AR overexpression inhibited phenylephrine-induced nuclear factor of activated T-cell activation. CONCLUSIONS - : Cardiac-specific overexpression of β3-AR does not affect cardiac morphology at baseline but inhibits the hypertrophic response to neurohormonal stimulation in vivo and in vitro, through a NOS-mediated mechanism. Activation of the cardiac β3-AR pathway may provide future therapeutic avenues for the modulation of hypertrophic remodeling. © 2013 American Heart Association, Inc

EPR studies on understanding the intricacy of HbNO complexes

Hemoglobin is a representative for proteins of quaternary structure and allosteric regulation. In reaction with natural metabolite, nitric oxide forms the paramagnetic complex, nitrosyl hemoglobin (HbNO). Electron paramagnetic resonance is the method of choice to investigate nitrosyl species in biological systems. The interpretation of HbNO EPR spectra belongs to the biggest challenges in biologically oriented EPR spectroscopy. The recorded EPR spectrum is sensitive to geometric and electronic structure of the essential moiety, heme-NO unit. The composite character of the HbNO spectrum is apparent. The contributions from the \alpha and \beta subunits of the tetramer, as well as the two possible heme coordination states, are recognized. The magnetic signatures of these structural variants are determined from EPR signals. The chapter presents the intuitive explanation of the basic EPR parameters, g- and A-tensors, as the structural fingerprints of HbNO. The overview of the temperature and pH-dependent effects on the spectral shape is given. The application of EPR as a tool for quantitation of different HbNO levels in biological samples is also discussed

Characterization of Iron Dinitrosyl Species Formed in the Reaction of Nitric Oxide with a Biological Rieske Center

Reactions of nitric oxide with cysteine-ligated iron−sulfur cluster proteins typically result in disassembly of the iron−sulfur core and formation of dinitrosyl iron complexes (DNICs). Here we report the first evidence that DNICs also form in the reaction of NO with Rieske-type [2Fe-2S] clusters. Upon treatment of a Rieske protein, component C of toluene/o-xylene monooxygenase from Pseudomonas sp. OX1, with an excess of NO(g) or NO-generators S-nitroso-N-acetyl-d,l-pencillamine and diethylamine NONOate, the absorbance bands of the [2Fe-2S] cluster are extinguished and replaced by a new feature that slowly grows in at 367 nm. Analysis of the reaction products by electron paramagnetic resonance, Mössbauer, and nuclear resonance vibrational spectroscopy reveals that the primary product of the reaction is a thiolate-bridged diiron tetranitrosyl species, [Fe[subscript 2](μ-SCys)[subscript 2](NO)[subscript 4]], having a Roussin’s red ester (RRE) formula, and that mononuclear DNICs account for only a minor fraction of nitrosylated iron. Reduction of this RRE reaction product with sodium dithionite produces the one-electron-reduced RRE, having absorptions at 640 and 960 nm. These results demonstrate that NO reacts readily with a Rieske center in a protein and suggest that dinuclear RRE species, not mononuclear DNICs, may be the primary iron dinitrosyl species responsible for the pathological and physiological effects of nitric oxide in such systems in biology.National Institute of General Medical Sciences (U.S.) (grant GM032134)United States. Dept. of Energy (DOE OBER)National Institute of General Medical Sciences (U.S.) (GM065440)National Institutes of Health (U.S.). Biotechnology Training Fellowship (Grant T32 GM08334)National Institute of General Medical Sciences (U.S.) (1 F32 GM082031-03