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Modulation of in vivo cardiac function by myocyte-specific nitric oxide synthase-3
Hunter C Champion1, Dimitrios Georgakopoulos, Eiki Takimoto
1Division of Cardiology, Department of Medicine, Johns Hopkins Hospital, Baltimore, MD 21287, USA.
Abstract:
Nitric oxide (NO) functions principally as a diffusible paracrine effector. The exception is in cardiomyocytes where both NO synthases (NOS) and target proteins coexist, allowing NO to work in an autocrine/intracrine fashion. However, the most abundant myocyte isoform (NOS3) is far more expressed in vascular endothelium; thus, the in vivo contribution of myocyte-NOS3 remains less clear. The present study tested this role by transfecting whole hearts of NOS3-null (NOS3(-/-)) mice with adenovirus-expressing NOS3 coupled to a alpha-MHC promoter (AdV(NOS3)), comparing results to hearts transfected with marker-gene beta-galactosidase (AdVbeta(gal)). Total myocardial NOS3 protein and activity were restored to near wild-type (WT) levels in NOS3(-/-)+AdV(NOS3) hearts, and NOS3 relocalized normally with caveolin-3. Ejection function by pressure-volume analysis was enhanced in NOS3(-/-)+AdVbeta(gal) over WT or NOS3(-/-)+AdV(NOS3). More prominently, isoproterenol (ISO)-stimulated systolic and diastolic function in WT was amplified in NOS3(-/-)+AdVbeta(gal), whereas NOS3(-/-)+AdV(NOS3) returned the response to control. ISO-activated systolic function was inhibited 85% by concomitant muscarinic stimulation (carbachol) in NOS3(-/-)+AdV(NOS3) but not NOS3(-/-)+AdVbeta(gal) hearts. Lastly, NOS3(-/-)+AdVbeta(gal) mice displayed enhanced inotropy and lusitropy over WT at slower heart rates but a blunted rate augmentation versus controls. A more positive rate response was restored in NOS3(-/-)+AdV(NOS3) (P<0.001). Thus, myocyte autocrine/intracrine NOS3 regulation in vivo can underlie key roles in beta-adrenergic, muscarinic, and frequency-dependent cardiac regulation.
Insights
Myocyte nitric oxide synthase 3 (NOS3) plays a key role in heart function. Restoring NOS3 in cardiomyocytes revealed its autocrine/intracrine regulation of cardiac responses to beta-adrenergic, muscarinic, and heart rate changes.
Area of Science:
- Cardiovascular Physiology
- Molecular Cardiology
- Nitric Oxide Signaling
Background:
- Nitric oxide (NO) typically acts as a paracrine mediator.
- Cardiomyocytes possess NO synthases (NOS) and targets, enabling autocrine/intracrine NO signaling.
- The in vivo role of myocyte-specific NOS3, despite lower expression than in endothelium, remains unclear.
Purpose of the Study:
- To investigate the in vivo functional significance of autocrine/intracrine nitric oxide synthase 3 (NOS3) in cardiomyocytes.
- To elucidate the role of myocyte NOS3 in cardiac regulation, including responses to adrenergic and muscarinic stimulation, and heart rate dependency.
Main Methods:
- Utilized NOS3-null (NOS3(-/-)) mice, transfecting hearts with adenovirus expressing NOS3 under an alpha-MHC promoter (AdV(NOS3)) or a control marker gene (AdVbeta(gal)).
- Assessed cardiac function using pressure-volume analysis.
- Evaluated responses to isoproterenol (ISO) and carbachol stimulation, and analyzed heart rate-dependent contractility and relaxation.
Main Results:
- AdV(NOS3) transfection restored myocardial NOS3 protein and activity to near wild-type (WT) levels.
- NOS3(-/-)+AdVbeta(gal) hearts showed enhanced ejection function and amplified ISO-stimulated systolic/diastolic function compared to WT.
- Myocyte NOS3 (NOS3(-/-)+AdV(NOS3)) inhibited ISO-stimulated function, mediated carbachol inhibition, and normalized rate-dependent cardiac function.
Conclusions:
- Autocrine/intracrine NOS3 signaling in cardiomyocytes is crucial for regulating beta-adrenergic and muscarinic responses.
- Myocyte NOS3 plays a significant role in modulating heart rate-dependent cardiac function.
- These findings highlight the distinct in vivo roles of myocyte-derived NO in cardiac physiology.