Increased cardiac myocyte PDE5 levels in human and murine pressure overload hypertrophy contribute to adverse LV remodeling

Phosphodiesterases and Compartmentation of cAMP and cGMP Signaling in Regulation of Cardiac Contractility in Normal and Failing Hearts

Cardiac contractility is regulated by several neural, hormonal, paracrine, and autocrine factors. Amongst these, signaling through β-adrenergic and serotonin receptors generates the second messenger cyclic AMP (cAMP), whereas activation of natriuretic peptide receptors and soluble guanylyl cyclases generates cyclic GMP (cGMP). Both cyclic nucleotides regulate cardiac contractility through several mechanisms. Phosphodiesterases (PDEs) are enzymes that degrade cAMP and cGMP and therefore determine the dynamics of their downstream effects. In addition, the intracellular localization of the different PDEs may contribute to regulation of compartmented signaling of cAMP and cGMP. In this review, we will focus on the role of PDEs in regulating contractility and evaluate changes in heart failure.

Tadalafil treatment improves cardiac, renal and lower urinary tract dysfunctions in rats with heart failure

Tadalafil, a phosphodiesterase-5 (PDE5) inhibitor, shown to exert a protection to heart failure (HF) associated damage or lower urinary tract symptoms (LUTS). Thus, we investigated the contribution of tadalafil chronic treatment in the alterations of LUTS in HF rats. Male rats were subjected to aortocaval fistula model for HF induction. Echocardiography, cystometric, renal function and redox cell balance, as well as concentration-response curves to carbachol, KCl, ATP and frequency-response curves to electrical field stimulation (EFS) were evaluated in Sham, HF, Tadalafil and HF-Tadalafil (12 weeks endpoint) groups. HF group to present increased in left-ventricle (LV) mass and in LV end-diastolic- and LV end-systolic volume, with a decreased ejection fraction. Tadalafil treatment was able to decrease in hypertrophy and improve the LV function restoring cardiac function. For micturition function (in vivo), HF animals shown an increase in basal pressure, threshold pressure, no-voiding contractions and decreased bladder capacity, being that the tadalafil treatment restored the cystometric parameters. Contractile mechanism response (in vitro) to carbachol, KCl, ATP and EFS in the detrusor muscles (DM) were increased in the HF group, when compared to Sham group. However, tadalafil treatment restored the DM hypercontractility in the HF animals. Moreover, renal function as well as the oxidative mechanism was impaired in the HF animals, and the tadalafil treatment improved all renal and oxidative parameters in HF group. Our data shown that tadalafil has potential as multi-therapeutic drug and may be used as a pharmacological strategy for the treatment of cardiovascular, renal and urinary dysfunctions associated with HF.

Safety of Phosphodiesterase-5 Inhibitors in Valvular Heart Disease

ABSTRACT

Erectile dysfunction is a common entity in clinical practice. Primary erectile dysfunction, not related to vasculopathy or psychiatric disorder, can be readily treated with phosphodiesterase inhibitors. These drugs have many physiologic effects that can alter a patient's hemodynamic profile considerably, especially in the presence of concomitant structural heart disease, specifically valvular heart disease. Although some contraindications to the use of PDE5 inhibitors in patients with cardiovascular disease are defined, the effect of these drugs in the presence of valvular heart disease is not well documented. The purpose of this review is to analyze the data regarding the safety of PDE5 inhibitors in patients with valvular heart disease.

Myocardial Impact of NHE1 Regulation by Sildenafil

The cardiac Na⁺/H⁺ exchanger (NHE1) is a membrane glycoprotein fundamental for proper cell functioning due its multiple housekeeping tasks, including regulation of intracellular pH, Na⁺ concentration, and cell volume. In the heart, hyperactivation of NHE1 has been linked to the development of different pathologies. Several studies in animal models that reproduce the deleterious effects of ischemia/reperfusion injury or cardiac hypertrophy have conclusively demonstrated that NHE1 inhibition provides cardioprotection. Unfortunately, NHE1 inhibitors failed to reproduce these effects in the clinical arena. The reasons for those discrepancies are not apparent yet. However, a reasonable clue to consider would be that drugs that completely abolish the exchanger activity, including that its essential housekeeping function may not be the best therapeutic approach. Therefore, interventions tending to specifically reduce its hyperactive state without affecting its basal activity emerge as a novel potential gold standard. In this regard, a promising goal seems to be the modulation of the phosphorylation state of the cytosolic tail of the exchanger. Recent own experiments demonstrated that Sildenafil, a phosphodiesterase 5A inhibitor drug that has been widely used for the treatment of erectile dysfunction is able to decrease NHE1 phosphorylation, and hence reduce its hyperactivity. In connection, growing evidence demonstrates cardioprotective properties of Sildenafil against different cardiac pathologies, with the distinctive characteristic of directly affecting cardiac tissue without altering blood pressure. This mini-review was aimed to focus on the regulation of NHE1 activity by Sildenafil. For this purpose, experimental data reporting Sildenafil effects in different animal models of heart disease will be discussed.

Cardiac Microvascular Endothelial Cells in Pressure Overload-Induced Heart Disease

BACKGROUND

Chronic pressure overload predisposes to heart failure, but the pathogenic role of microvascular endothelial cells (MiVEC) remains unknown. We characterized transcriptional, metabolic, and functional adaptation of cardiac MiVEC to pressure overload in mice and patients with aortic stenosis (AS).

METHODS

In Tie2-Gfp mice subjected to transverse aortic constriction or sham surgery, we performed RNA sequencing of isolated cardiac Gfp⁺-MiVEC and validated the signature in freshly isolated MiVEC from left ventricle outflow tract and right atrium of patients with AS. We next compared their angiogenic and metabolic profiles and finally correlated molecular and pathological signatures with clinical phenotypes of 42 patients with AS (50% women).

RESULTS

In mice, transverse aortic constriction induced progressive systolic dysfunction, fibrosis, and reduced microvascular density. After 10 weeks, 25 genes predominantly involved in matrix-regulation were >2-fold upregulated in isolated MiVEC. Increased transcript levels of Cartilage Intermediate Layer Protein (Cilp), Thrombospondin-4, Adamtsl-2, and Collagen1a1 were confirmed by quantitative reverse transcription polymerase chain reaction and recapitulated in left ventricle outflow tract-derived MiVEC of AS (P<0.05 versus right atrium-MiVEC). Fatty acid oxidation increased >2-fold in left ventricle outflow tract-MiVEC, proline content by 130% (median, IQR, 58%-474%; P=0.008) and procollagen secretion by 85% (mean [95% CI, 16%-154%]; P<0.05 versus right atrium-MiVEC for all). The altered transcriptome in left ventricle outflow tract-MiVEC was associated with impaired 2-dimensional-vascular network formation and 3-dimensional-spheroid sprouting (P<0.05 versus right atrium-MiVEC), profibrotic ultrastructural changes, and impaired diastolic left ventricle function, capillary density and functional status, especially in female AS.

CONCLUSIONS

Pressure overload induces major transcriptional and metabolic adaptations in cardiac MiVEC resulting in excess interstitial fibrosis and impaired angiogenesis. Molecular rewiring of MiVEC is worse in women, compromises functional status, and identifies novel targets for intervention.

Current Evidence and Future Perspectives on Pharmacological Treatment of Calcific Aortic Valve Stenosis

Calcific aortic valve stenosis (CAVS), the most common heart valve disease, is characterized by the slow progressive fibro-calcific remodeling of the valve leaflets, leading to progressive obstruction to the blood flow. CAVS is an increasing health care burden and the development of an effective medical treatment is a major medical need. To date, no effective pharmacological therapies have proven to halt or delay its progression to the severe symptomatic stage and aortic valve replacement represents the only available option to improve clinical outcomes and to increase survival. In the present report, the current knowledge and latest advances in the medical management of patients with CAVS are summarized, placing emphasis on lipid-lowering agents, vasoactive drugs, and anti-calcific treatments. In addition, novel potential therapeutic targets recently identified and currently under investigation are reported.

Cardiac Phosphodiesterases and Their Modulation for Treating Heart Disease

An important hallmark of cardiac failure is abnormal second messenger signaling due to impaired synthesis and catabolism of cyclic adenosine 3',5'- monophosphate (cAMP) and cyclic guanosine 3',5'- monophosphate (cGMP). Their dysregulation, altered intracellular targeting, and blunted responsiveness to stimulating pathways all contribute to pathological remodeling, muscle dysfunction, reduced cell survival and metabolism, and other abnormalities. Therapeutic enhancement of either cyclic nucleotides can be achieved by stimulating their synthesis and/or by suppressing members of the family of cyclic nucleotide phosphodiesterases (PDEs). The heart expresses seven of the eleven major PDE subtypes - PDE1, 2, 3, 4, 5, 8, and 9. Their differential control over cAMP and cGMP signaling in various cell types, including cardiomyocytes, provides intriguing therapeutic opportunities to counter heart disease. This review examines the roles of these PDEs in the failing and hypertrophied heart and summarizes experimental and clinical data that have explored the utility of targeted PDE inhibition.

Medical Treatment of Aortic Stenosis

Untreated, severe, symptomatic aortic stenosis is associated with a dismal prognosis. The only treatment shown to improve survival is aortic valve replacement; however, before symptoms occur, aortic stenosis is preceded by a silent, latent phase characterized by a slow progression at the molecular, cellular, and tissue levels. In theory, specific medical therapy should halt aortic stenosis progression, reduce its hemodynamic repercussions on left ventricular function and remodeling, and improve clinical outcomes. In the present report, we performed a systematic review of studies focusing on the medical treatment of patients with aortic stenosis. Lipid-lowering therapy, antihypertensive drugs, and anticalcific therapy have been the main drug classes studied in this setting and are reviewed in depth. A critical appraisal of the preclinical and clinical evidence is provided, and future research avenues are presented.

Long-term effect of sildenafil on echocardiographic parameters in dogs with asymptomatic myxomatous mitral valve degeneration

Sildenafil is a selective phosphodiesterase-5 inhibitor that has been demonstrated to delay ventricular remodeling in humans and experimental animals. The aim of this prospective study was to assess the chronic effects of sildenafil administration on echocardiographic indices and N-terminal pro-B-type natriuretic peptide (NT-proBNP) in dogs with naturally occurring, asymptomatic myxomatous mitral valve degeneration. Thirty client-owned dogs with ACVIM class B1 or B2 were enrolled. Dogs were randomly assigned to treatment (sildenafil 1–3 mg/kg, PO, BID for 180 days) or control groups. A total of 12 dogs completed the 180 days trial in the sildenafil group, whereas 10 dogs remained in control group. When comparing the difference from baseline values obtained over time between groups, the stroke volume (SV) at day 30 was significantly higher in the sildenafil group (P=0.038). The LA/Ao and the MR jet area were significantly lower beginning at day 30 (only MR jet area; P=0.006), day 90 (P=0.006 and P=0.027, respectively) and day 180 (P=0.029 and P=0.032, respectively). The 2D-LA was significantly lower at day 90 when compared with control group (P=0.028). The differences of NTproBNP from baseline were significantly lower when compared with control group at the same timepoint (D90, P=0.017 and D180, P=0.013). In conclusion, this study suggested that long-term treatment with sildenafil prevented aggravation of disease progression as suggested by several echocardiographic indices (i.e. SV, LA/Ao, MR jet area, 2D-LA) and reduced NTproBNP level at the indicated timepoints in dogs with asymptomatic mitral valve degeneration.

Decreased Soluble Guanylate Cyclase Contributes to Cardiac Dysfunction Induced by Chronic Doxorubicin Treatment in Mice

AIMS

The use of doxorubicin, a potent chemotherapeutic agent, is limited by cardiotoxicity. We tested the hypothesis that decreased soluble guanylate cyclase (sGC) enzyme activity contributes to the development of doxorubicin-induced cardiotoxicity.

RESULTS

Doxorubicin administration (20 mg/kg, intraperitoneally [IP]) reduced cardiac sGC activity in wild-type (WT) mice. To investigate whether decreased sGC activity contributes to doxorubicin-induced cardiotoxicity, we studied mice with cardiomyocyte-specific deficiency of the sGC α1-subunit (mice with cardiomyocyte-specific deletion of exon 6 of the sGCα1 allele [sGCα1^-/-CM]). After 12 weeks of doxorubicin administration (2 mg/kg/week IP), left ventricular (LV) systolic dysfunction was greater in sGCα1^-/-CM than WT mice. To further assess whether reduced sGC activity plays a pathogenic role in doxorubicin-induced cardiotoxicity, we studied a mouse model in which decreased cardiac sGC activity was induced by cardiomyocyte-specific expression of a dominant negative sGCα1 mutant (DNsGCα1) upon doxycycline removal (Tet-off). After 8 weeks of doxorubicin administration, DNsGCα1^tg/+, but not WT, mice displayed LV systolic dysfunction and dilatation. The difference in cardiac function and remodeling between DNsGCα1^tg/+ and WT mice was even more pronounced after 12 weeks of treatment. Further impairment of cardiac function was attenuated when DNsGCα1 gene expression was inhibited (beginning at 8 weeks of doxorubicin treatment) by administering doxycycline. Furthermore, doxorubicin-associated reactive oxygen species generation was higher in sGCα1-deficient than WT hearts. Innovation and Conclusion: These data demonstrate that a reduction in cardiac sGC activity worsens doxorubicin-induced cardiotoxicity in mice and identify sGC as a potential therapeutic target. Various pharmacological sGC agonists are in clinical development or use and may represent a promising approach to limit doxorubicin-associated cardiotoxicity. Antioxid. Redox Signal. 26, 153-164.

Carbon-11 and Fluorine-18 Radiolabeled Pyridopyrazinone Derivatives for Positron Emission Tomography (PET) Imaging of Phosphodiesterase-5 (PDE5)

The cyclic guanosine monophosphate (cGMP) specific phosphodiesterase type 5 (PDE5) plays an important role in various pathologies including pulmonary arterial hypertension and cardiomyopathy. PDE5 represents an important therapeutic and/or prognostic target, but noninvasive assessment of PDE5 expression is lacking. The purpose of this study was to develop and evaluate pyridopyrazinone derivatives labeled with carbon-11 or fluorine-18 as PDE5-specific PET tracers. In biodistribution studies, highest PDE5-specific retention was observed for [¹¹C]-12 and [¹⁸F]-17 in the lungs of wild-type mice and in the myocardium of transgenic mice with cardiomyocyte-specific PDE5 overexpression at 30 min postinjection. In vivo dynamic microPET images in rats revealed that both tracers crossed the blood-brain barrier but brain retention was not PDE5-specific. Both [¹¹C]-12 and [¹⁸F]-17 showed specific binding to PDE5 in myocardium of transgenic mice; however [¹⁸F]-17 showed significantly higher PDE5-specific inhibitable binding than [¹¹C]-12.

Doxorubicin-induced chronic dilated cardiomyopathy-the apoptosis hypothesis revisited

The chemotherapeutic agent doxorubicin (DOX) has significantly increased survival rates of pediatric and adult cancer patients. However, 10% of pediatric cancer survivors will 10-20 years later develop severe dilated cardiomyopathy (DCM), whereby the exact molecular mechanisms of disease progression after this long latency time remain puzzling. We here revisit the hypothesis that elevated apoptosis signaling or its increased likelihood after DOX exposure can lead to an impairment of cardiac function and cause a cardiac dilation. Based on recent literature evidence, we first argue why a dilated phenotype can occur when little apoptosis is detected. We then review findings suggesting that mature cardiomyocytes are protected against DOX-induced apoptosis downstream, but not upstream of mitochondrial outer membrane permeabilisation (MOMP). This lack of MOMP induction is proposed to alter the metabolic phenotype, induce hypertrophic remodeling, and lead to functional cardiac impairment even in the absence of cardiomyocyte apoptosis. We discuss findings that DOX exposure can lead to increased sensitivity to further cardiomyocyte apoptosis, which may cause a gradual loss in cardiomyocytes over time and a compensatory hypertrophic remodeling after treatment, potentially explaining the long lag time in disease onset. We finally note similarities between DOX-exposed cardiomyocytes and apoptosis-primed cancer cells and propose computational system biology as a tool to predict patient individual DOX doses. In conclusion, combining recent findings in rodent hearts and cardiomyocytes exposed to DOX with insights from apoptosis signal transduction allowed us to obtain a molecularly deeper insight in this delayed and still enigmatic pathology of DCM.

S-nitrosylation of PDE5 increases its ubiquitin-proteasomal degradation

Phosphodiesterase type 5 (PDE5) expression is upregulated in human failing heart, and overexpression of PDE5 in transgenic mice exacerbates stress-induced left-ventricular dysfunction, suggesting that increased PDE5 expression might contribute to the development of congestive heart failure. However, the underlying mechanisms for increased PDE5 expression are not totally understood. In the present study, we found that PDE5 activity and expression were regulated by S-nitrosylation, a covalent modification of cysteine residues by nitric oxide (NO). S-nitrosylation of PDE5 occurs at Cys220, which is located in the GAFA domain. Upon S-nitrosylation, PDE5 exhibits reduced activity and degradation via the ubiquitin-proteasome system. The decrease in PDE5 expression induced by NO could be blunted by mutation of Cys220 or the phosphorylation site of PDE5 (S102), as well as by pretreatment with H2O2. Conversely, decreased NO bioavailability by nitric oxide synthase (NOS) inhibitors or knockout of NOS3 increased PDE5 expression in cardiomyocytes. Collectively, to the best of our knowledge, our data demonstrate for the first time that S-nitrosylation is one of the mechanisms for PDE5 degradation. This novel regulatory mechanism probably accounts for the increase in PDE5 in the failing heart and other diseases in which NO bioavailability is decreased by oxidative stress.

Right ventricular cyclic nucleotide signaling is decreased in hyperoxia-induced pulmonary hypertension in neonatal mice

Pulmonary hypertension (PH) and right ventricular hypertrophy (RVH) affect 25-35% of premature infants with significant bronchopulmonary dysplasia (BPD), increasing morbidity and mortality. We sought to determine the role of phosphodiesterase 5 (PDE5) in the right ventricle (RV) and left ventricle (LV) in a hyperoxia-induced neonatal mouse model of PH and RVH. After birth, C57BL/6 mice were placed in room air (RA) or 75% O2 (CH) for 14 days to induce PH and RVH. Mice were euthanized at 14 days or recovered in RA for 14 days or 42 days prior to euthanasia at 28 or 56 days of age. Some pups received sildenafil or vehicle (3 mg·kg(-1)·dose(-1) sc) every other day from P0. RVH was assessed by Fulton's index [RV wt/(LV + septum) wt]. PDE5 protein expression was analyzed via Western blot, PDE5 activity was measured by commercially available assay, and cGMP was measured by enzyme-linked immunoassay. Hyperoxia induced RVH in mice after 14 days, and RVH did not resolve until 56 days of age. Hyperoxia increased PDE5 expression and activity in RV, but not LV + S, after 14 days. PDE5 expression normalized by 28 days of age, but PDE5 activity did not normalize until 56 days of age. Sildenafil given during hyperoxia prevented RVH, decreased RV PDE5 activity, and increased RV cGMP levels. Mice with cardiac-specific overexpression of PDE5 had increased RVH in RA. These findings suggest normal RV PDE5 function is disrupted by hyperoxia, and elevated PDE5 contributes to RVH and remodeling. Therefore, in addition to impacting the pulmonary vasculature, sildenafil also targets PDE5 in the neonatal mouse RV and decreases RVH.

Therapeutic effects of udenafil on pressure-overload cardiac hypertrophy

This study was performed to determine whether the newly developed phosphodiesterase type 5 (PDE5) inhibitor udenafil had beneficial effects on pressure-overload cardiac hypertrophy. Pressure overload cardiac hypertrophy was created by using suprarenal aortic constriction (SAC) in male Sprague-Dawley rats. Rats were divided into three groups: sham (n=19), SAC (n=18) and SAC+udenafil (n=14) groups. Three-week periods of SAC provoked significant left ventricular (LV) hypertrophy. Udenafil was administered (20 mg kg(-1) PO, daily) between the 3rd and 20th weeks after SAC in the SAC+udenafil group. Udenafil improved the survival rate (log-rank P=0.012) and exercise capacity (maximal exercise duration at the 20th week after surgery: 448±54 s for the SAC+udenafil group versus 317±73 s for the SAC group, P<0.05) of the rats with SAC. Serial echocardiographic examinations showed that udenafil attenuated LV remodeling processes following SAC (mean LV end-diastolic dimension at the 20th week after surgery: 9.84±0.59 mm for SAC and 9.05±0.58 mm for SAC+udenafil group, P<0.05). Invasive hemodynamic studies showed that udenafil improved the LV performance. Udenafil-attenuated myocardial fibrosis and apoptosis. Udenafil also decreased myocardial matrix metalloproteinase-9 expression and augmented serum interleukin-10 concentration. Long-term udenafil use prevented cardiac remodeling and improved exercise capacity and survival in rats exposed to pressure-overload cardiac hypertrophy.

PDE5 inhibitor efficacy is estrogen dependent in female heart disease

Inhibition of cGMP-specific phosphodiesterase 5 (PDE5) ameliorates pathological cardiac remodeling and has been gaining attention as a potential therapy for heart failure. Despite promising results in males, the efficacy of the PDE5 inhibitor sildenafil in female cardiac pathologies has not been determined and might be affected by estrogen levels, given the hormone's involvement in cGMP synthesis. Here, we determined that the heart-protective effect of sildenafil in female mice depends on the presence of estrogen via a mechanism that involves myocyte eNOS-dependent cGMP synthesis and the cGMP-dependent protein kinase Iα (PKGIα). Sildenafil treatment failed to exert antiremodeling properties in female pathological hearts from Gαq-overexpressing or pressure-overloaded mice after ovary removal; however, estrogen replacement restored the effectiveness of sildenafil in these animals. In females, sildenafil-elicited myocardial PKG activity required estrogen, which stimulated tonic cardiomyocyte cGMP synthesis via an eNOS/soluble guanylate cyclase pathway. In contrast, eNOS activation, cGMP synthesis, and sildenafil efficacy were not estrogen dependent in male hearts. Estrogen and sildenafil had no impact on pressure-overloaded hearts from animals expressing dysfunctional PKGIα, indicating that PKGIα mediates antiremodeling effects. These results support the importance of sex differences in the use of PDE5 inhibitors for treating heart disease and the critical role of estrogen status when these agents are used in females.

Sex, drugs, and trial design: sex influences the heart and drug responses

Preclinical studies indicate that the phosphodiesterase 5 (PDE5) inhibitor sildenafil is protective against hypertrophy-induced cardiac remodeling. Despite an initial clinical study demonstrating sildenafil-dependent amelioration of pathological remodeling, the cardioprotective effect of this drug was not significant in a large placebo-controlled clinical trail. In this issue, Sasaki and colleagues reveal that the efficacy of PDE5 inhibition in female mice requires estrogen. Induction of cardiac stress in male and intact female mice resulted in increased activation of protein kinase G (PKG) signaling, which was further enhanced by sildenafil. PKG activity was not enhanced in ovariectomized (OVX) female mice as a result of cardiac stress, but administration of estrogen restored PKG activation and enhancement by sildenafil. These data highlight the importance of considering sex-specific differences and drug responses in clinical trial design.

Therapeutic potential of PDE modulation in treating heart disease

Altered cyclic nucleotide-mediated signaling plays a critical role in the development of cardiovascular pathology. By degrading cAMP/cGMP, the action of cyclic nucleotide PDEs is essential for controlling cyclic nucleotide-mediated signaling intensity, duration, and specificity. Altered expression, localization and action of PDEs have all been implicated in causing changes in cyclic nucleotide signaling in cardiovascular disease. Accordingly, pharmacological inhibition of PDEs has gained interest as a treatment strategy and as an area of drug development. While targeting of certain PDEs has the potential to ameliorate cardiovascular disease, inhibition of others might actually worsen it. This review will highlight recent research on the physiopathological role of cyclic nucleotide signaling, especially with regard to PDEs. While the physiological roles and biochemical properties of cardiovascular PDEs will be summarized, the primary emphasis will be pathological. Research into the potential benefits and hazards of PDE inhibition will also be discussed.

Myosin phosphatase isoforms and related transcripts in the pig coronary circulation and effects of exercise and chronic occlusion

Myosin phosphatase (MP) is a key target of signaling pathways that regulate smooth muscle tone and blood flow. Alternative splicing of MP targeting subunit (MYPT1) exon 24 (E24) generates isoforms with variable presence of a C-terminal leucine zipper (LZ) required for activation of MP by NO/cGMP. Here we examined the expression of MP and associated genes in a disease model in the coronary circulation. Female Yucatan miniature swine remained sedentary or were exercise-trained beginning eight weeks after placement of an ameroid constrictor around the left circumflex (LCX) artery. Fourteen weeks later epicardial arteries (~1mm) and resistance arterioles (~125 μm) were harvested and assayed for gene expression. MYPT1 isoforms were distinct in the epicardial arteries (E24-/LZ+) and resistance arterioles (E24+/LZ-) and unchanged by exercise training or coronary occlusion. MYPT1, CPI-17 and PDE5 mRNA levels were not different between arteries and arterioles while Kir2.1 and eNOS were 6.6-fold and 3.9-fold higher in the arterioles. There were no significant changes in transcript abundance in epicardial arteries of the collateralized (LCX) vs. non-occluded left anterior descending (LAD) territories, or in exercise-trained vs. sedentary pigs. There was a significant 1.2 fold increase in CPI-17 in collateral-dependent arterioles, independent of exercise, and a significant 1.7 fold increase in PDE5 in arterioles from exercise-trained pigs, independent of occlusion. We conclude that differences in MYPT1 E24 (LZ) isoforms, eNOS, and Kir2.1 distinguish epicardial arteries and resistance coronary arterioles. Up-regulation of coronary arteriolar PDE5 by exercise and CPI-17 by chronic occlusion could contribute to altered vasomotor responses and requires further study.

Targeting NOS as a therapeutic approach for heart failure

Nitric oxide is a key signaling molecule in the heart and is produced endogenously by three isoforms of nitric oxide synthase, neuronal NOS (NOS1), endothelial NOS (NOS3), and inducible NOS (NOS2). Nitric oxide signals via cGMP-dependent or independent pathways to modulate downstream proteins via specific post translational modifications (i.e. cGMP-dependent protein kinase phosphorylation, S-nitrosylation, etc.). Dysfunction of NOS (i.e. altered expression, location, coupling, activity, etc.) exists in various cardiac disease conditions, such as heart failure, contributing to the contractile dysfunction, adverse remodeling, and hypertrophy. This review will focus on the signaling pathways of each NOS isoform during health and disease, and discuss current and potential therapeutic approaches targeting nitric oxide signaling to treat heart disease.