Roles of cGMP-dependent protein kinase I (cGKI) and PDE5 in the regulation of Ang II-induced cardiac hypertrophy and fibrosis

Soluble guanylate cyclase stimulator riociguat and phosphodiesterase 5 inhibitor sildenafil ameliorate pulmonary hypertension due to left heart disease in mice

BACKGROUND

Presence of pulmonary hypertension (PH) and right ventricular dysfunction worsens prognosis in patients with chronic heart failure (CHF). Preclinical and clinical studies suggest a role for the impaired nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate (cGMP) signaling pathway in both PH and CHF. Hence, we examined the effects of the NO-sGC-cGMP pathway modulation by the PDE5 inhibitor sildenafil or sGC stimulator riociguat on pulmonary hemodynamics and heart function in a murine model of secondary PH induced by transverse aortic constriction.

METHODS

C57Bl/6N mice were subjected to transverse aortic constriction (TAC) for 6weeks to induce left heart failure and secondary PH and were subsequently treated with either sildenafil (100mg/kg/day) or riociguat (10mg/kg/day) or placebo for 2weeks.

RESULTS

Six weeks after surgery, TAC induced significant left ventricular hypertrophy and dysfunction associated with development of PH. Treatment with riociguat and sildenafil neither reduced left ventricular hypertrophy nor improved its function. However, both sildenafil and riociguat ameliorated PH, reduced pulmonary vascular remodeling and improved right ventricular function.

CONCLUSIONS

Thus, modulation of the NO-sGC-cGMP pathway by the PDE5 inhibitor sildenafil or sGC stimulator riociguat exerts direct beneficial effects on pulmonary hemodynamics and right ventricular function in the experimental model of secondary PH due to left heart disease and these drugs may offer a new therapeutic option for therapy of this condition.

The Effect of Sorafenib, Tadalafil and Macitentan Treatments on Thyroxin-Induced Hemodynamic Changes and Cardiac Abnormalities

Multikinase inhibitors (e.g. Sorafenib), phosphodiesterase-5 inhibitors (e.g. Tadalafil), and endothelin-1 receptor blockers (e.g. Macitentan) exert influential protection in a variety of animal models of cardiomyopathy; however, their effects on thyroxin-induced cardiomyopathy have never been investigated. The goal of the present study was to assess the functional impact of these drugs on thyroxin-induced hemodynamic changes, cardiac hypertrophy and associated altered responses of the contractile myocardium both in-vivo at the whole heart level and ex-vivo at the cardiac tissue level. Control and thyroxin (500 μg/kg/day)-treated mice with or without 2-week treatments of sorafenib (10 mg/kg/day; I.P), tadalafil (1 mg/kg/day; I.P or 4 mg/kg/day; oral), macitentan (30 and 100 mg/kg/day; oral), and their vehicles were studied. Blood pressure, echocardiography and electrocardiogram were non-invasively evaluated, followed by ex-vivo assessments of isolated multicellular cardiac preparations. Thyroxin increased blood pressure, resulted in cardiac hypertrophy and left ventricular dysfunction in-vivo. Also, it caused contractile abnormalities in right ventricular papillary muscles ex-vivo. None of the drug treatments were able to significantly attenuate theses hemodynamic changes or cardiac abnormalities in thyroxin-treated mice. We show here for the first time that multikinase (raf1/b, VEGFR, PDGFR), phosphodiesterase-5, and endothelin-1 pathways have no major role in thyroxin-induced hemodynamic changes and cardiac abnormalities. In particular, our data show that the involvement of endothelin-1 pathway in thyroxine-induced cardiac hypertrophy/dysfunction seems to be model-dependent and should be carefully interpreted.

A circular RNA protects the heart from pathological hypertrophy and heart failure by targeting miR-223

AIMS

Sustained cardiac hypertrophy accompanied by maladaptive cardiac remodelling represents an early event in the clinical course leading to heart failure. Maladaptive hypertrophy is considered to be a therapeutic target for heart failure. However, the molecular mechanisms that regulate cardiac hypertrophy are largely unknown.

METHODS AND RESULTS

Here we show that a circular RNA (circRNA), which we term heart-related circRNA (HRCR), acts as an endogenous miR-223 sponge to inhibit cardiac hypertrophy and heart failure. miR-223 transgenic mice developed cardiac hypertrophy and heart failure, whereas miR-223-deficient mice were protected from hypertrophic stimuli, indicating that miR-223 acts as a positive regulator of cardiac hypertrophy. We identified ARC as a miR-223 downstream target to mediate the function of miR-223 in cardiac hypertrophy. Apoptosis repressor with CARD domain transgenic mice showed reduced hypertrophic responses. Further, we found that a circRNA HRCR functions as an endogenous miR-223 sponge to sequester and inhibit miR-223 activity, which resulted in the increase of ARC expression. Heart-related circRNA directly bound to miR-223 in cytoplasm and enforced expression of HRCR in cardiomyocytes and in mice both exhibited attenuated hypertrophic responses.

CONCLUSIONS

These findings disclose a novel regulatory pathway that is composed of HRCR, miR-223, and ARC. Modulation of their levels provides an attractive therapeutic target for the treatment of cardiac hypertrophy and heart failure.

Molecular Screen Identifies Cardiac Myosin-Binding Protein-C as a Protein Kinase G-Iα Substrate

BACKGROUND

Pharmacological activation of cGMP-dependent protein kinase G I (PKGI) has emerged as a therapeutic strategy for humans with heart failure. However, PKG-activating drugs have been limited by hypotension arising from PKG-induced vasodilation. PKGIα antiremodeling substrates specific to the myocardium might provide targets to circumvent this limitation, but currently remain poorly understood.

METHODS AND RESULTS

We performed a screen for myocardial proteins interacting with the PKGIα leucine zipper (LZ)-binding domain to identify myocardial-specific PKGI antiremodeling substrates. Our screen identified cardiac myosin-binding protein-C (cMyBP-C), a cardiac myocyte-specific protein, which has been demonstrated to inhibit cardiac remodeling in the phosphorylated state, and when mutated leads to hypertrophic cardiomyopathy in humans. GST pulldowns and precipitations with cGMP-conjugated beads confirmed the PKGIα-cMyBP-C interaction in myocardial lysates. In vitro studies demonstrated that purified PKGIα phosphorylates the cMyBP-C M-domain at Ser-273, Ser-282, and Ser-302. cGMP induced cMyBP-C phosphorylation at these residues in COS cells transfected with PKGIα, but not in cells transfected with LZ mutant PKGIα, containing mutations to disrupt LZ substrate binding. In mice subjected to left ventricular pressure overload, PKGI activation with sildenafil increased cMyBP-C phosphorylation at Ser-273 compared with untreated mice. cGMP also induced cMyBP-C phosphorylation in isolated cardiac myocytes.

CONCLUSIONS

Taken together, these data support that PKGIα and cMyBP-C interact in the heart and that cMyBP-C is an anti remodeling PKGIα kinase substrate. This study provides the first identification of a myocardial-specific PKGIα LZ-dependent antiremodeling substrate and supports further exploration of PKGIα myocardial LZ substrates as potential therapeutic targets for heart failure.

Effects of Atrial Natriuretic Peptide on Rat Ventricular Fibroblasts During Differentiation Into Myofibroblasts

Atrial natriuretic peptide antifibrotic properties are mainly described in cardiac myocytes or in induced cardiac myofibroblasts (Angiotensin II or TGF-β induced differentiation). In the present work, we investigate the effects of ANP/NPRA/cGMP system in modulating rat cardiac fibroblasts function. Cardiac fibroblasts were isolated from adult Wistar male rats and cultured in the presence of serum in order to induce fibroblasts differentiation. Cultures were then treated with ANP (1 µM), 8-Br-cGMP (100 µM) or IBMX (100 µM), a non-specific phosphodiesterases inhibitor. ANP significantly decreased proliferation rate and collagen secretion. Its effect was mimicked by the cGMP analog, while combining ANP with 8-Br-cGMP did not lead to additional effects. Moreover intracellular cGMP levels were elevated when cells were incubated with ANP confirming that ANP intracellular pathway is mediated by cGMP. Additionally, immunoblotting and immunofluorescence were used to confirm the presence of guanylyl cyclase specific natriuretic peptide receptors A and B. Finally we scanned specific cGMP dependent PDEs via RT-qPCR, and noticed that inhibiting all PDEs led to an important decrease in proliferation rate. Effect of ANP became more prominent after 10 culture days, confirming the importance of ANP in fibroblasts to myofibroblasts differentiation. Uncovering cellular aspects of ANP/NPRA/cGMP signaling system provided more elements to help understand cardiac fibrotic process.

Sildenafil Does Not Prevent Heart Hypertrophy and Fibrosis Induced by Cardiomyocyte Angiotensin II Type 1 Receptor Signaling

Analyses of several mouse models imply that the phosphodiesterase 5 (PDE5) inhibitor sildenafil (SIL), via increasing cGMP, affords protection against angiotensin II (Ang II)-stimulated cardiac remodeling. However, it is unclear which cell types are involved in these beneficial effects, because Ang II may exert its adverse effects by modulating multiple renovascular and cardiac functions via Ang II type 1 receptors (AT1Rs). To test the hypothesis that SIL/cGMP inhibit cardiac stress provoked by amplified Ang II/AT1R directly in cardiomyocytes (CMs), we studied transgenic mice with CM-specific overexpression of the AT1R under the control of the α-myosin heavy chain promoter (αMHC-AT1R(tg/+)). The extent of cardiac growth was assessed in the absence or presence of SIL and defined by referring changes in heart weight to body weight or tibia length. Hypertrophic marker genes, extracellular matrix-regulating factors, and expression patterns of fibrosis markers were examined in αMHC-AT1R(tg/+) ventricles (with or without SIL) and corroborated by investigating different components of the natriuretic peptide/PDE5/cGMP pathway as well as cardiac functions. cGMP levels in heart lysates and intact CMs were measured by competitive immunoassays and Förster resonance energy transfer. We found higher cardiac and CM cGMP levels and upregulation of the cGMP-dependent protein kinase type I with AT1R overexpression. However, even a prolonged SIL treatment regimen did not limit the progressive CM growth, fibrosis, or decline in cardiac functions in the αMHC-AT1R(tg/+) model, suggesting that SIL does not interfere with the pathogenic actions of amplified AT1R signaling in CMs. Hence, the cardiac/noncardiac cells involved in the cross-talk between SIL-sensitive PDE activity and Ang II/AT1R still need to be identified.

The emperor's new clothes: PDE5 and the heart

Phosphodiesterase-5 (PDE5) is highly expressed in the pulmonary vasculature, but its expression in the myocardium is controversial. Cyclic guanosine monophosphate (cGMP) activates protein kinase G (PKG), which has been hypothesized to blunt cardiac hypertrophy and negative remodeling in heart failure. Although PDE5 has been suggested to play a significant role in the breakdown of cGMP in cardiomyocytes and hence PKG regulation in the myocardium, the RELAX trial, which tested effect of PDE5 inhibition on exercise capacity in patients with heart failure with preserved ejection fraction (HFpEF) failed to show a beneficial effect. These results highlight the controversy regarding the role and expression of PDE5 in the healthy and failing heart. This study used one- and two-dimensional electrophoresis and Western blotting to examine PDE5 expression in mouse (before and after trans-aortic constriction), dog (control and HFpEF) as well as human (healthy and failing) heart. We were unable to detect PDE5 in any cardiac tissue lysate, whereas PDE5 was present in the murine and bovine lung samples used as positive controls. These results indicate that if PDE5 is expressed in cardiac tissue, it is present in very low quantities, as PDE5 was not detected in either humans or any model of heart failure examined. Therefore in cardiac muscle, it is unlikely that PDE5 is involved the regulation of cGMP-PKG signaling, and hence PDE5 does not represent a suitable drug target for the treatment of cardiac hypertrophy. These results highlight the importance of rigorous investigation prior to clinical trial design.

AVP-induced increase in AQP2 and p-AQP2 is blunted in heart failure during cardiac remodeling and is associated with decreased AT1R abundance in rat kidney

AIM

The objective was to examine the renal effects of long-term increased angiotensin II and vasopressin plasma levels in early-stage heart failure (HF). We investigated the regulations of the V2 vasopressin receptor, the type 1A angiotensin II receptor, the (pro)renin receptor, and the water channels AQP2, AQP1, AQP3, and AQP4 in the inner medulla of rat kidney.

METHODS

HF was induced by coronary artery ligation. Sixty-eight rats were allocated to six groups: Sham (N = 11), HF (N = 11), sodium restricted sham (N = 11), sodium restricted HF (N = 11), sodium restricted sham + DDAVP (N = 12), and sodium restricted HF + DDAVP (N = 12). 1-desamino-8-D-arginine vasopressin (0.5 ng h-1 for 7 days) or vehicle was administered. Pre- and post-treatment echocardiographic evaluation was performed. The rats were sacrificed at day 17 after surgery, before cardiac remodeling in rat is known to be completed.

RESULTS

HF rats on standard sodium diet and sodium restriction displayed biochemical markers of HF. These rats developed hyponatremia, hypo-osmolality, and decreased fractional excretion of sodium. Increase of AQP2 and p(Ser256)-AQP2 abundance in all HF groups was blunted compared with control groups even when infused with DDAVP and despite increased vasopressin V2 receptor and Gsα abundance. This was associated with decreased protein abundance of the AT1A receptor in HF groups vs. controls.

CONCLUSION

Early-stage HF is associated with blunted increase in AQP2 and p(Ser256)-AQP2 despite of hyponatremia, hypo-osmolality, and increased inner medullary vasopressin V2 receptor expression. Decreased type 1A angiotensin II receptor abundance likely plays a role in the transduction of these effects.