Johannes H. Riffel

Wnt Signaling Is Critical for Maladaptive Cardiac Hypertrophy and Accelerates Myocardial Remodeling

The evolutionary conserved Wnt signaling pathway regulates cardiogenesis. However, members of the Wnt pathway are also expressed in the adult heart. Although Wnt-signaling is quiescent under normal conditions, we noticed activation on pathological stress of the heart, such as chronic afterload increase. To examine the role of Wnt signaling on the postnatal heart, we modified the expression and function of the Wnt regulator dishevelled 1 (Dvl-1) both in transgenic mice with cardiac-specific overexpression of Dvl-1 (Dvl-1-Tg) and in cultured cardiac myocytes. Dvl-1-Tg mice (3 months) had severe cardiac hypertrophy (heart weight:body weight ratio: 5.2±0.3 mg/g wild-type [WT] versus 6.4±0.7 mg/g Dvl-1-Tg; P<0.01), an increase in cardiomyocyte size (86% increase in Dvl-1-Tg compared with WT; P<0.01) and marked raise of atrial natriuretic factor expression (12-fold increase versus WT; P<0.01). Hypertrophy was associated with left ventricular dilatation in Dvl-1-Tg and a reduction of ejection fraction (4.4±0.1 mm versus 5.5±0.2 mm, 80±2% and 43±4% in WT versus Dvl-1-Tg, respectively; P<0.01). Transgenic animals died prematurely before 6 months of age. Both canonical as well as noncanonical Wnt signaling branches were activated in the Dvl-1-Tg animals. Small interfering RNA–mediated depletion of Dvl-1 was used to further characterize the role of Dvl-1 in cardiac myocytes. Whereas baseline parameters were unaltered, &bgr;-adrenergic hypertrophic response was abrogated in Dvl-1 knockdown cardiac myocytes, indicating a mandatory role in &bgr;-adrenergic stimulation. Therefore, activation of Wnt signaling is sufficient and critical for the induction of myocardial hypertrophy and cardiomyopathy.

Calcium/Calmodulin-Dependent Protein Kinase II Couples Wnt Signaling With Histone Deacetylase 4 and Mediates Dishevelled-Induced Cardiomyopathy

Activation of Wnt signaling results in maladaptive cardiac remodeling and cardiomyopathy. Recently, calcium/calmodulin-dependent protein kinase II (CaMKII) was reported to be a pivotal participant in myocardial remodeling. Because CaMKII was suggested as a downstream target of noncanonical Wnt signaling, we aimed to elucidate the role of CaMKII in dishevelled-1–induced cardiomyopathy and the mechanisms underlying its function. Dishevelled-1–induced cardiomyopathy was reversed by deletion of neither CaMKII&dgr; nor CaMKII&ggr;. Therefore, dishevelled-1–transgenic mice were crossed with CaMKII&dgr;&ggr; double-knockout mice. These mice displayed a normal cardiac phenotype without cardiac hypertrophy, fibrosis, apoptosis, or left ventricular dysfunction. Further mechanistic analyses unveiled that CaMKII&dgr;&ggr; couples noncanonical Wnt signaling to histone deacetylase 4 and myosin enhancer factor 2. Therefore, our findings indicate that the axis, consisting of dishevelled-1, CaMKII, histone deacetylase 4, and myosin enhancer factor 2, is an attractive therapeutic target for prevention of cardiac remodeling and its progression to left ventricular dysfunction.

Augmentation of autophagy by mTOR-inhibition in myocardial infarction: When size matters.

The extent of adverse myocardial remodeling contributes essentially to the prognosis after myocardial infarction (MI). Currently, therapeutic strategies that inhibit remodeling are limited to inhibition of neurohumoral activation. mTOR-dependent signaling mechanisms are centrally involved in the myocardial remodeling process. There exists a controversy as to whether autophagy is beneficial in the setting of myocardial infarction. We now provide evidence that induction of autophagy by inhibition of mTOR with everolimus (RAD) prevents adverse left ventricular remodeling and limits infarct size following myocardial infarction. mTOR inhibition increases autophagy and concomitantly decreases proteasome activity especially in the border zone of the infarcted myocardium. The induction of autophagy via mTOR inhibition is a novel potential therapeutic approach to limit infarct size and to attenuate adverse left ventricular remodeling following MI.

Dapper-1 Induces Myocardial Remodeling Through Activation of Canonical Wnt Signaling in Cardiomyocytes

Heart failure has an increasing contribution to cardiovascular disease burden and is governed by the myocardial remodeling process. The contribution of Wnt signaling to cardiac remodeling has recently drawn significant attention. Here, we report that upregulation of Dapper-1 in a transgenic mouse model activates the canonical/&bgr;-catenin–dependent Wnt pathway through dishevelled-2. These mice exhibited increased heart weight/tibia length ratio, myocyte cross-sectional area, and upregulation of hypertrophic marker genes compared with wild-type mice. Furthermore, impairment of left ventricular systolic and diastolic function was observed in all indicating features of myocardial remodeling. Depletion of Dapper-1 and dishevelled-2 in cardiomyocytes demonstrated that Dapper-1 functions upstream of dishevelled-2 and that activity of both Dapper-1 and dishevelled-2 is essential for activating canonical Wnt signaling. Moreover, Dapper-1 depletion alleviated Wnt3a- and phenylephrine-induced cardiomyocyte hypertrophy. These observations provide evidence that Dapper-1–mediated activation of canonical Wnt signaling is necessary and sufficient to induce cardiomyocyte hypertrophy. Inhibition of this pathway may thus serve as a novel therapeutic strategy for alleviating cardiac hypertrophy.

Dapper‐1 is essential for Wnt5a induced cardiomyocyte hypertrophy by regulating the Wnt/PCP pathway

The Wnt signaling pathway was identified as crucial mediator of cardiomyocyte hypertrophy. In this study we found that activation of non‐canonical Wnt signaling by Wnt5a stimulates protein synthesis and enlargement of cardiomyocyte surface area. These hypertrophic features were inhibited in Dapper‐1 (Dpr1) depleted cells. On the molecular level, we observed inhibition of the non‐canonical Wnt/planar‐cell‐polarity (PCP) pathway denoted by reduction of c‐jun‐n‐terminal‐kinase (JNK) phosphorylation. Upstream of JNK, increased protein levels of the Wnt/PCP trans‐membrane receptor van‐Gogh‐like‐2 (Vangl2) were observed along with an enrichment of Vangl2 in perinuclear located vesicles. The findings suggest that Dpr1 is essential for execution of the Wnt/PCP pathway and regulation of the Vangl2/JNK axis. Depletion of Dpr1 inhibits non‐canonical Wnt signaling induced cardiomyocyte hypertrophy by blocking Wnt/PCP signaling.

Chronic Akt blockade aggravates pathological hypertrophy and inhibits physiological hypertrophy

The attenuation of adverse myocardial remodeling and pathological left ventricular (LV) hypertrophy is one of the hallmarks for improving the prognosis after myocardial infarction (MI). The protein kinase Akt plays a central role in regulating cardiac hypertrophy, but the in vivo effects of chronic pharmacological inhibition of Akt are unknown. We investigated the effect of chronic Akt blockade with deguelin on the development of pathological [MI and aortic banding (AB)] and physiological (controlled treadmill running) hypertrophy. Primary cardiomyocyte cultures were incubated with 10 μmol deguelin for 48 h, and Wistar rats were treated orally with deguelin (4.0 mg·kg(-1)·day(-1)) for 4 wk starting 1 day after the induction of MI or AB. Exercise-trained animals received deguelin for 4 wk during the training period. In vitro, we observed reduced phosphorylation of Akt and glycogen synthase kinase (GSK)-3β after an incubation with deguelin, whereas MAPK signaling was not significantly affected. In vivo, treatment with deguelin led to attenuated phosphorylation of Akt and GSK-3β 4 wk after MI. These animals showed significantly increased heart weights and impaired LV function with increased end-diastolic diameters (12.0 ± 0.3 vs. 11.1 ± 0.3 mm, P < 0.05), end-diastolic volumes (439 ± 8 vs. 388 ± 18 μl, P < 0.05), and cardiomyocyte sizes (+20%, P < 0.05) compared with MI animals receiving vehicle treatment. Furthermore, activation of Ca(2+)/calmodulin-dependent kinase II in deguelin-treated MI animals was increased compared with the vehicle-treated group. Four wk after AB, we observed an augmentation of pathological hypertrophy in the deguelin-treated group with a significant increase in heart weights and cardiomyocyte sizes (>20%, P < 0.05). In contrast, the development of physiological hypertrophy was inhibited by deguelin treatment in exercise-trained animals. In conclusion, chronic Akt blockade with deguelin aggravates adverse myocardial remodeling and antagonizes physiological hypertrophy.

Standardized assessment of global longitudinal and circumferential strain - a modality independent software approach

Mean GLS values were -16.2±5.3% and -17.3±5.3% for echocardiography and CMR, respectively. GLS did not differ significantly between the two imaging modalities, which showed strong correlation (r=0.86), a small bias (-1.1%) and narrow 95% limits of agreement (LOA, ±5.4%). Mean GCS values were -17.9±6.3% and -24.4 ±7.8% for echocardiography and CMR, respectively. GCS was significantly underestimated by echocardiography (p<0.001). A weaker correlation (r=0.73), a higher bias (-6.5%) and wider LOA (±10.5%) were observed for GCS. GLS showed a strong correlation (r=0.92) when image quality was good, while correlation dropped to r=0.82 with poor acoustic windows in echocardiography. GCS assessment revealed only a strong correlation (r=0.87) when echocardiographic image quality was good. No significant differences for GLS between two different echocardiographic vendors could be detected. Conclusions Quantitative assessment of GLS using a standardized software algorithm allows the direct comparison of values acquired irrespective of the imaging modality. GLS may therefore serve as a reliable parameter for the assessment of global left ventricular function in clinical routine besides standard evaluation of the ejection fraction.

Diagnostic and Prognostic Value of Long-Axis Strain and Myocardial Contraction Fraction Using Standard Cardiovascular MR Imaging in Patients with Nonischemic Dilated Cardiomyopathies

Purpose To assess the utility of established functional markers versus two additional functional markers derived from standard cardiovascular magnetic resonance (MR) images for their incremental diagnostic and prognostic information in patients with nonischemic dilated cardiomyopathy (NIDCM). Materials and Methods Approval was obtained from the local ethics committee. MR images from 453 patients with NIDCM and 150 healthy control subjects were included between 2005 and 2013 and were analyzed retrospectively. Myocardial contraction fraction (MCF) was calculated by dividing left ventricular (LV) stroke volume by LV myocardial volume, and long-axis strain (LAS) was calculated from the distances between the epicardial border of the LV apex and the midpoint of a line connecting the origins of the mitral valve leaflets at end systole and end diastole. Receiver operating characteristic curve, Kaplan-Meier method, Cox regression, and classification and regression tree (CART) analyses were performed for diagnostic and prognostic performances. Results LAS (area under the receiver operating characteristic curve [AUC] = 0.93, P < .001) and MCF (AUC = 0.92, P < .001) can be used to discriminate patients with NIDCM from age- and sex-matched control subjects. A total of 97 patients reached the combined end point during a median follow-up of 4.8 years. In multivariate Cox regression analysis, only LV ejection fraction (EF) and LAS independently indicated the combined end point (hazard ratio = 2.8 and 1.9, respectively; P < .001 for both). In a risk stratification approach with classification and regression tree analysis, combined LV EF and LAS cutoff values were used to stratify patients into three risk groups (log-rank test, P < .001). Conclusion Cardiovascular MR-derived MCF and LAS serve as reliable diagnostic and prognostic markers in patients with NIDCM. LAS, as a marker for longitudinal contractile function, is an independent parameter for outcome and offers incremental information beyond LV EF and the presence of myocardial fibrosis.

Right ventricular long axis strain—validation of a novel parameter in non-ischemic dilated cardiomyopathy using standard cardiac magnetic resonance imaging

PURPOSE Right ventricular longitudinal axis strain (RV-LAS) is a simple measure of RV longitudinal function. The purpose of this study was the evaluation of its diagnostic performance in non-ischemic dilated cardiomyopathy (NIDCM) and the determination of reference values in controls. METHODS 217 NIDCM patients and 200 healthy controls were analysed retrospectively regarding the diagnostic performance of RV-LAS using receiver operating characteristic curves in comparison with RV ejection fraction (RVEF), tricuspid annular plane systolic excursion (TAPSE) and global longitudinal strain (RV-GLS). Hereby, four different approaches were evaluated to assess RV-LAS based on different reference points. RV-LAS LVapex/mid was defined as the change in distance between the LV apex and the middle of a line connecting the origins of the tricuspidal valve leaflets in systole and diastole. The ethical approval was obtained in all participants. RESULTS NIDCM and controls were 48 years in mean. Controls were equally gender distributed, while the proportion of men with NIDCM was higher with 77%. Among the four approaches RV-LAS LVapex/mid provided the highest diagnostic performance for discrimination between NIDCM and controls (AUC=0.94). Of all RV functional parameters RV-LAS LVapex/mid preformed significantly better than RVEF (delta AUC=0.05; p=0.003), TAPSE (delta AUC=0.23; p<0.0001) and RV-GLS (delta AUC=0.31; p<0.0001). A significant correlation was found between RV-LAS LVapex/mid and RVEF (r=-0.65; p<0.0001). The reference mean values for RV-LAS LVapex/mid were -17.4±3.5 for men and -18.5±3.7 for women. CONCLUSION RV-LAS showed better diagnostic accuracy for RV dysfunction than RVEF, TAPSE and RV-GLS. Furthermore, it has a rapid accessibility and low intra- and interobserver variability.

Prognostic significance of semiautomatic quantification of left ventricular long axis shortening in systemic light-chain amyloidosis

Abstract Aims: To assess left ventricular long axis shortening (LAS) in patients with AL amyloidosis as a potential predictor for outcome. Methods and results: We performed a de novo echocardiographic analysis of LAS in 120 patients with biopsy-proven AL amyloidosis evaluated at first presentation before specific treatment. Additionally, 47 control subjects were analyzed retrospectivly. LAS was measured using a semiautomatic tissue motion annular displacement software algorithm (TMAD). LAS was significantly better than ejection fraction (EF) (p < 0.0001) and M-mode-derived mitral annular plane systolic excursion (MAPSE) (p < 0.05) discriminating AL patients from control subjects, while being non-inferior compared to tissue Doppler-derived peak systolic mitral annular velocity. One year outcome analysis in patients with AL amyloidosis showed that LAS remained the only significant echocardiographic parameter (HR:0.76; p < 0.005) in a multivariable Cox regression model of echocardiographic values. In a comprehensive clinical model, LAS (HR:0.72, p < 0.0001), cardiac troponin-T (HR:2.86, p < 0.01) and free light chain difference (HR:1.00; p < 0.05) were independently associated with the outcome. Assessment of LAS led to a significant integrated discrimination improvement and offered incremental information compared to EF and biomarkers. The cut-off value for LAS discriminating the endpoint was 5.8%. Conclusion: LAS was an independent predictor of survival within the first year and offers incremental information in patients with AL amyloidosis evaluated prior to specific treatment.