Hypertrophy signaling pathways in experimental chronic aortic regurgitation

Puerarin attenuates isoproterenol‑induced myocardial hypertrophy via inhibition of the Wnt/β‑catenin signaling pathway

Myocardial hypertrophy (MH) is an independent risk factor for cardiovascular disease, which in turn lead to arrhythmia or heart failure. Therefore, attention must be paid to formulation of therapeutic strategies for MH. Puerarin is a key bioactive ingredient isolated from Pueraria genera of plants that is beneficial for the treatment of MH. However, its molecular mechanism of action has not been fully determined. In the present study, 40 µM puerarin was demonstrated to be a safe dose for human AC16 cells using Cell Counting Kit‑8 assay. The protective effects of puerarin against MH were demonstrated in AC16 cells stimulated with isoproterenol (ISO). These effects were characterized by a significant decrease in surface area of cells (assessed using fluorescence staining) and mRNA and protein expression levels of MH‑associated biomarkers, including atrial and brain natriuretic peptide, assessed using reverse transcription‑quantitative PCR and western blotting, as well as β‑myosin heavy chain mRNA expression levels. Mechanistically, western blotting demonstrated that puerarin inhibited activation of the Wnt signaling pathway. Puerarin also significantly decreased phosphorylation of p65; this was mediated via crosstalk between the Wnt and NF‑κB signaling pathways. An inhibitor (Dickkopf‑1) and activator (IM‑12) of the Wnt signaling pathway were used to demonstrate that puerarin‑mediated effects alleviated ISO‑induced MH via the Wnt signaling pathway. The results of the present study demonstrated that puerarin pre‑treatment may be a potential therapeutic strategy for preventing ISO‑induced MH and managing MH in the future.

Regional Replacement and Diffuse Interstitial Fibrosis in Aortic Regurgitation: Prognostic Implications From Cardiac Magnetic Resonance

OBJECTIVES

This study used cardiac magnetic resonance (CMR) to assess left ventricular (LV) remodeling in chronic aortic regurgitation (AR) to identify both forms of myocardial fibrosis and examine its association with clinical outcomes.

BACKGROUND

Chronic AR leads to LV remodeling, which is associated with 2 forms of myocardial fibrosis: regional replacement fibrosis that is directly imaged by late gadolinium enhancement (LGE) CMR; and diffuse interstitial fibrosis, which can be inferred by T1 mapping techniques.

METHODS

Patients with chronic AR who were undergoing contrast CMR with T1 mapping for valve assessment from 2011 to 2018 were enrolled. Patients with a confounding etiology of myocardial fibrosis were excluded. In addition to quantification of AR severity and LV volumetrics, LGE and T1 mapping pre- and post-contrast were performed to measure extracellular volume (ECV) and indexed ECV (iECV). Patients were followed up longitudinally to assess for the composite event of death and the need for aortic valve replacement.

RESULTS

A total of 177 patients with isolated chronic AR were included (66% males, median age 58 years [47.0 years-68.0 years]) with a median follow up of 2.5 years (1.07 years-3.56 years). The iECV significantly increased with AR severity (P < 0.001), whereas ECV and replacement fibrosis did not (P = NS). On multivariate analysis, iECV remained associated with the composite event (P = 0.01). On Kaplan-Meier analysis stratified by AR regurgitant fraction (RF) and iECV, patients with AR RF severity ≥30% and iECV ≥24 mL/m² demonstrated the highest event rate.

CONCLUSIONS

Among CMR biomarkers of fibrosis, iECV was more closely associated than replacement fibrosis or ECV with survival free of aortic valve replacement.

Left ventricular response in the transition from hypertrophy to failure recapitulates distinct roles of Akt, β-arrestin-2, and CaMKII in mice with aortic regurgitation

Background

Although aortic regurgitation (AR) is a clinically important condition that is becoming increasingly common, few relevant murine models and mechanistic studies exist for this condition. In this study, we attempted to delineate the pathological and molecular changes and address the roles of some potentially relevant molecules in an animal model of surgically induced AR.

Methods

AR was induced by puncturing the aortic valve leaflets in C57BL/6J mice under echocardiographic guidance.

Results

As early as 1 week following AR, the left ventricles (LV) displayed marked impairments in diastolic function and coronary flow reserve (CFR), as well as cardiac hypertrophy and chamber dilatation at both end-systole and end-diastole. LV free wall thickening and cardiomyocyte hypertrophy in LV were observed 2 weeks following of AR while a decline in ejection fraction was not seen until after 4 weeks. Nppa (natriuretic peptide A) and Nppb (natriuretic peptide B) increased over time, in conjunction with prominent Akt activation as well as slight CaMKII (Ca²⁺/calmodulin-dependent protein kinase II) activation and biphasic changes in β-arrestin-2 expression. Treatment of AR mice with Akt inhibition exacerbated the eccentric hypertrophy, while neither inhibition of CaMKII nor β-arrestin-2 overexpression influenced the response to AR.

Conclusions

Our structural, functional, molecular and therapeutic analyses reveal that Akt, but not CaMKII or β-arrestin-2, plays a regulatory role in the development of LV remodeling after AR in Mice. These results may shed important light on therapeutic targets for volume overloaded cardiomyopathy.

Assessing the role of extracellular signal-regulated kinases 1 and 2 in volume overload-induced cardiac remodelling

AIMS

Volume overload (VO) and pressure overload (PO) induce differential cardiac remodelling responses including distinct signalling pathways. Extracellular signal-regulated kinases 1 and 2 (ERK1/2), key signalling components in the mitogen-activated protein kinase (MAPK) pathways, modulate cardiac remodelling during pressure overload (PO). This study aimed to assess their role in VO-induced cardiac remodelling as this was unknown.

METHODS AND RESULTS

Aortocaval fistula (Shunt) surgery was performed in mice to induce cardiac VO. Two weeks of Shunt caused a significant reduction of cardiac ERK1/2 activation in wild type (WT) mice as indicated by decreased phosphorylation of the TEY (Thr-Glu-Tyr) motif (-28% as compared with Sham controls, P < 0.05). Phosphorylation of other MAPKs was unaffected. For further assessment, transgenic mice with cardiomyocyte-specific ERK2 overexpression (ERK2tg) were studied. At baseline, cardiac ERK1/2 phosphorylation in ERK2tg mice remained unchanged compared with WT littermates, and no overt cardiac phenotype was observed; however, cardiac expression of the atrial natriuretic peptide was increased on messenger RNA (3.6-fold, P < 0.05) and protein level (3.1-fold, P < 0.05). Following Shunt, left ventricular dilation and hypertrophy were similar in ERK2tg mice and WT littermates. Left ventricular function was maintained, and changes in gene expression indicated reactivation of the foetal gene program in both genotypes. No differences in cardiac fibrosis and kinase activation was found amongst all experimental groups, whereas apoptosis was similarly increased through Shunt in ERK2tg and WT mice.

CONCLUSIONS

VO-induced eccentric hypertrophy is associated with reduced cardiac ERK1/2 activation in vivo. Cardiomyocyte-specific overexpression of ERK2, however, does not alter cardiac remodelling during VO. Future studies need to define the pathophysiological relevance of decreased ERK1/2 signalling during VO.

Cardiac Disorders and Pathophysiology of Sarcomeric Proteins

The sarcomeric proteins represent the structural building blocks of heart muscle, which are essential for contraction and relaxation. During recent years, it has become evident that posttranslational modifications of sarcomeric proteins, in particular phosphorylation, tune cardiac pump function at rest and during exercise. This delicate, orchestrated interaction is also influenced by mutations, predominantly in sarcomeric proteins, which cause hypertrophic or dilated cardiomyopathy. In this review, we follow a bottom-up approach starting from a description of the basic components of cardiac muscle at the molecular level up to the various forms of cardiac disorders at the organ level. An overview is given of sarcomere changes in acquired and inherited forms of cardiac disease and the underlying disease mechanisms with particular reference to human tissue. A distinction will be made between the primary defect and maladaptive/adaptive secondary changes. Techniques used to unravel functional consequences of disease-induced protein changes are described, and an overview of current and future treatments targeted at sarcomeric proteins is given. The current evidence presented suggests that sarcomeres not only form the basis of cardiac muscle function but also represent a therapeutic target to combat cardiac disease.

New classification of geometric patterns considering left ventricular volume in patients with chronic aortic valve regurgitation: Prevalence and association with adverse cardiovascular outcomes

BACKGROUND

Left ventricular (LV) remodeling due to aortic regurgitation (AR) often leads to maladaptive responses. We assessed the prevalence and clinical implications of LV remodeling considering LV volume, mass, and relative wall thickness at the time of AR diagnosis.

METHODS AND RESULTS

Between 2008 and 2017, 370 consecutive patients (mean age 67.3 ± 16.1 years, 56.5% males), with moderate or severe AR, were retrospectively analyzed. LV geometric patterns and clinical outcomes (cardiovascular death, hospitalization for heart failure, or aortic valve replacement) were evaluated. LV dilatation (LV end-diastolic volume >75 mL/m² ) was present in 228 patients (61.6%). Applying the new LV remodeling classification system, 40 (10.8%) patients had normal geometry, 14 (3.8%) concentric remodeling, 43 (11.6%) concentric hypertrophy (LVH), 45 (12.2%) indeterminate LVH, 38 (10.3%) mixed LVH, 93 (25.1%) dilated LVH, 54 (14.6%) eccentric LVH, and 43 (11.6%) eccentric remodeling. During a median follow-up of 3.48 years (25th-75th percentile 0.91-5.57), 97 (26.2%) had the combined endpoint. LV dilation (P < 0.001), LVH (P < 0.001), and LV remodeling patterns were significantly associated with the combined endpoint. After multivariable adjustment for age, EF, aortic stenosis, CAD history, and moderate mitral regurgitation, dilated LVH (HR 7.61, IC 95% 1.82-31.80; P = 0.005) and eccentric LVH (HR 7.91, IC 95% 1.82-34.38; P = 0.006) were associated with adverse outcome compared to eccentric remodeling, that showed the best event-free survival rate.

CONCLUSIONS

In a contemporary cohort of patients with AR, applying the new LV remodeling classification system, only a minority had normal geometry. Dilated LVH and eccentric LVH showed distinct outcome penalty after adjustment for confounders.

Molecular Mechanisms and New Treatment Paradigm for Atrial Fibrillation

BACKGROUND

Atrial fibrillation represents the most common arrhythmia leading to increased morbidity and mortality, yet, current treatment strategies have proven inadequate. Conventional treatment with antiarrhythmic drugs carries a high risk for proarrhythmias. The soluble epoxide hydrolase enzyme catalyzes the hydrolysis of anti-inflammatory epoxy fatty acids, including epoxyeicosatrienoic acids from arachidonic acid to the corresponding proinflammatory diols. Therefore, the goal of the study is to directly test the hypotheses that inhibition of the soluble epoxide hydrolase enzyme can result in an increase in the levels of epoxyeicosatrienoic acids, leading to the attenuation of atrial structural and electric remodeling and the prevention of atrial fibrillation.

METHODS AND RESULTS

For the first time, we report findings that inhibition of soluble epoxide hydrolase reduces inflammation, oxidative stress, atrial structural, and electric remodeling. Treatment with soluble epoxide hydrolase inhibitor significantly reduces the activation of key inflammatory signaling molecules, including the transcription factor nuclear factor κ-light-chain-enhancer, mitogen-activated protein kinase, and transforming growth factor-β.

CONCLUSIONS

This study provides insights into the underlying molecular mechanisms leading to atrial fibrillation by inflammation and represents a paradigm shift from conventional antiarrhythmic drugs, which block downstream events to a novel upstream therapeutic target by counteracting the inflammatory processes in atrial fibrillation.

Sildenafil treatment attenuates ventricular remodeling in an experimental model of aortic regurgitation

BACKGROUND

Currently there is no reliable medical treatment for aortic regurgitation (AR).

METHODS

Thirty-nine Sprague-Dawley rats underwent creation of AR or sham operation. Treated rats were assigned to early or late institution of sildenafil therapy (100 mg/kg/day) for a total of 10 weeks. Treatment-effects were measured by serial echocardiography, invasive hemodynamic measurements, and tissue analysis.

RESULTS

Rats assigned to early treatment developed less remodeling than untreated rats. Thus, left ventricular (LV) dilation was blunted by sildenafil with end-systolic diameter being significantly smaller (6.6 ± 0.4 vs. 7.7 ± 0.4 mm, respectively, p < 0.05). Also, LV wall thickness was significantly decreased in treated rats compared to controls (2.23 ± 0.08 vs. 2.16 ± 0.05 mm, p < 0.01). Fractional shortening was improved by treatment (p < 0.05). Myocardial fibrosis was borderline decreased by treatment (p = 0.09). Akt was increased in treated compared to controls (p < 0.05).

CONCLUSION

Sildenafil slightly inhibits LV remodeling and improves fractional shortening in rats with AR when treatment is initiated early.

Left ventricular sphericity index predicts systolic dysfunction in rats with experimental aortic regurgitation

Although an increased left ventricular (LV) diastolic diameter (DD) and a decreased ejection fraction have been used as markers for the surgical replacement of an insufficient aortic valve, these signals may be observed when irreversible myocardium damage has already occurred. The aim of this study was to determine whether change in LV geometry predicts systolic dysfunction in experimental aortic regurgitation. Male Wistar rats underwent surgical acute aorta regurgitation (aorta regurgitation group; n = 23) or a sham operation (sham group; n = 12). After the procedure, serial transthoracic echocardiograms were performed at 1, 4, 8, and 16 wk. At the end of protocol, the LV, lungs, and liver were dissected and weighed. During the follow-up, no animal developed overt heart failure. There was a correlation between the LV sphericity index and reduced fractional shortening ( P < 0.001) over time. A multiple regression model showed that the LVDD-sphericity index association at 8 wk was a better predictor of decreased fractional shortening at week 16 ( R2 = 0.50; P < 0.001) than was the LVDD alone ( R2 = 0.39; P = 0.001). LV geometry associated with increased LVDD improved the prediction of systolic dysfunction in experimental aortic regurgitation.