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Background— Chromogranin A (CgA) levels have previously been found to predict mortality in heart failure (HF), but currently no information is available regarding CgA processing in HF and whether the CgA fragment catestatin (CST) may directly influence cardiomyocyte function. Methods and Results— CgA processing was characterized in postinfarction HF mice and in patients with acute HF, and the functional role of CST was explored in experimental models. Myocardial biopsies from HF, but not sham-operated mice, demonstrated high molecular weight CgA bands. Deglycosylation treatment attenuated high molecular weight bands, induced a mobility shift, and increased shorter CgA fragments. Adjusting for established risk indices and biomarkers, circulating CgA levels were found to be associated with mortality in patients with acute HF, but not in patients with acute exacerbation of chronic obstructive pulmonary disease. Low CgA-to-CST conversion was also associated with increased mortality in acute HF, thus, supporting functional relevance of impaired CgA processing in cardiovascular disease. CST was identified as a direct inhibitor of CaMKIIδ (Ca 2+ /calmodulin-dependent protein kinase IIδ) activity, and CST reduced CaMKIIδ-dependent phosphorylation of phospholamban and the ryanodine receptor 2. In line with CaMKIIδ inhibition, CST reduced Ca 2+ spark and wave frequency, reduced Ca 2+ spark dimensions, increased sarcoplasmic reticulum Ca 2+ content, and augmented the magnitude and kinetics of cardiomyocyte Ca 2+ transients and contractions. Conclusions— CgA-to-CST conversion in HF is impaired because of hyperglycosylation, which is associated with clinical outcomes in acute HF. The mechanism for increased mortality may be dysregulated cardiomyocyte Ca 2+ handling because of reduced CaMKIIδ inhibition.

Background: Circulating chromogranin A (CgA) levels have been found associated with clinical outcomes in cardiovascular disease, but whether the CgA fragment catestatin (CST) may directly modulate cardiomyocyte Ca 2+ handling is not known. Methods: The prognostic utility of circulating CgA levels were compared between patients with acute HF (n=143) and chronic acute obstructive pulmonary disease (COPD, n=84). Functional effects of CST were assessed in isolated cardiomyocyte and explanted hearts. Results: CgA levels were associated with mortality in acute HF patients, but not in acute COPD. (Figure; patients stratified according to CgA quartiles on hospital admission). Admission CgA levels were also associated with mortality after adjusting for other risk factors in multivariate analysis. We found CST to interact with Ca 2+ /calmodulin (CaM)-dependent protein kinase II δ (CaMKIIδ) and to inhibit CaMKIIδ activity. CST also reduced CaMKIIδ-dependent phosphorylation of the ryanodine receptor 2 and phospholamban. In line with CaMKIIδ inhibition, CST reduced Ca 2+ spark and wave frequency, attenuated Ca 2+ sparkdimensions, increased sarcoplasmic reticulum Ca 2+ content, andaugmented magnitude and kinetics of cardiomyocyte Ca 2+ transients and contractions. Frequency dependent acceleration of relaxation was most pronounced in the Control group, an indication of CaMKIIδ activation, and this was attenuated by CST. Conclusions: CgA regulates cardiomyocyte Ca 2+ handling via CaMKIIδ inhibition, which makes CgA an interesting CV biomarker and potential compensatory mechanism in situations of enhanced CaMKIIδ activity.

BackgroundSecretoneurin (SN) levels are increased in patients with heart failure (HF), but whether SN provides prognostic information and influences cardiomyocyte function is unknown.ObjectivesThis study sought to evaluate the merit of SN as a cardiovascular biomarker and assess effects of SN on cardiomyocyte Ca2+ handling.MethodsWe assessed the association between circulating SN levels and mortality in 2 patient cohorts and the functional properties of SN in experimental models.ResultsIn 143 patients hospitalized for acute HF, SN levels were closely associated with mortality (n = 66) during follow-up (median 776 days; hazard ratio [lnSN]: 4.63; 95% confidence interval: 1.93 to 11.11; p = 0.001 in multivariate analysis). SN reclassified patients to their correct risk strata on top of other predictors of mortality. In 155 patients with ventricular arrhythmia–induced cardiac arrest, SN levels were also associated with short-term mortality (n = 51; hazard ratio [lnSN]: 3.33; 95% confidence interval: 1.83 to 6.05; p < 0.001 in multivariate analysis). Perfusing hearts with SN yielded markedly increased myocardial levels and SN internalized into cardiomyocytes by endocytosis. Intracellularly, SN reduced Ca2+/calmodulin (CaM)-dependent protein kinase II δ (CaMKIIδ) activity via direct SN-CaM and SN-CaMKII binding and attenuated CaMKIIδ-dependent phosphorylation of the ryanodine receptor. SN also reduced sarcoplasmic reticulum Ca2+ leak, augmented sarcoplasmic reticulum Ca2+ content, increased the magnitude and kinetics of cardiomyocyte Ca2+ transients and contractions, and attenuated Ca2+ sparks and waves in HF cardiomyocytes.ConclusionsSN provided incremental prognostic information to established risk indices in acute HF and ventricular arrhythmia–induced cardiac arrest.

Sustained pressure overload leads to compensatory myocardial hypertrophy and subsequent heart failure, a leading cause of morbidity and mortality. Further unraveling of the cellular processes involved is essential for development of new treatment strategies. We have investigated the hypothesis that the transmembrane Z-disc proteoglycan syndecan-4, a coreceptor for integrins, connecting extracellular matrix proteins to the cytoskeleton, is an important signal transducer in cardiomyocytes during development of concentric myocardial hypertrophy following pressure overload. Echocardiographic, histochemical and cardiomyocyte size measurements showed that syndecan-4 -/- mice did not develop concentric myocardial hypertrophy as found in wild-type mice, but rather left ventricular dilatation and dysfunction following pressure overload. Protein and gene expression analyses revealed diminished activation of the central, pro-hypertrophic calcineurinnuclear factor of activated T-cell (NFAT) signaling pathway. Cardiomyocytes from syndecan-4-/- -NFAT-luciferase reporter mice subjected to cyclic mechanical stretch, a hypertrophic stimulus, showed minimal activation of NFAT (1.6-fold) compared to 5.8-fold increase in NFAT-luciferase control cardiomyocytes. Accordingly, overexpression of syndecan-4 or introducing a cell-permeable membrane-targeted syndecan-4 polypeptide (gain of function) activated NFATc4 in vitro. Pulldown experiments demonstrated a direct intracellular syndecan-4-calcineurin interaction. This interaction and activation of NFAT were increased by dephosphorylation of serine 179 (pS179) in syndecan-4. During pressure overload, phosphorylation of syndecan-4 was decreased, and association between syndecan-4, calcineurin and its co-activator calmodulin increased. Moreover, calcineurin dephosphorylated pS179, indicating that calcineurin regulates its own binding and activation. Finally, patients with hypertrophic myocardium due to aortic stenosis had increased syndecan-4 levels with decreased pS179 which was associated with increased NFAT activation. In conclusion, our data show that syndecan-4 is essential for compensatory hypertrophy in the pressure overloaded heart. Specifically, syndecan-4 regulates stretch-induced activation of the calcineurin-NFAT pathway in cardiomyocytes. Thus, our data suggest that manipulation of syndecan-4 may provide an option for therapeutic modulation of calcineurin-NFAT signaling. © 2011 Finsen et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.