Temporal expression and spatial distribution of the proteoglycan versican during cardiac fibrosis development.

Cardiac fibrosis is a central pathological feature in several cardiac diseases, but the underlying molecular players are insufficiently understood. The extracellular matrix proteoglycan versican is elevated in heart failure and suggested to be a target for treatment. However, the temporal expression and spatial distribution of versican and the versican cleavage fragment containing the neoepitope DPEAAE in cardiac fibrosis remains to be elucidated. In this study, we have examined versican during cardiac fibrosis development in a murine pressure overload model and in patients with cardiomyopathies. We found that versican, mainly the V1 isoform, was expressed immediately after induction of pressure overload, preceding collagen accumulation, and versican protein levels extended from the perivascular region into the cardiac interstitium. In addition, we found increased production of versican by collagen expressing fibroblasts, and that it was deposited extensively in the fibrotic extracellular matrix during pressure overload. In cardiac cell cultures, the expression of versican was induced by the pro-fibrotic transforming growth factor beta and mechanical stretch. Furthermore, we observed that the proteolytic cleavage of versican (DPEAAE fragment) increased in the late phase of fibrosis development during pressure overload. In patients with hypertrophic and dilated cardiomyopathies, we found elevated levels of versican and a positive correlation between versican and collagen mRNA in the heart, as well as increased cleavage of full-length protein. Taken together, the temporal expression profile and the spatial distribution of both the full-length versican and the DPEAAE fragment observed in this study indicates a role for versican in development of cardiac fibrosis.

Cardiac Troponin T and NT-proBNP for Prediction of 30-Day Readmission or Death in Patients with Acute Dyspnea: Data from the Akershus Cardiac Examination 2 Study.

INTRODUCTION: N-terminal pro-B-type natriuretic peptide (NT-proBNP) and cardiac troponin T (cTnT) measurements are recommended in patients with acute dyspnea. We aimed to assess the prognostic merit of cTnT compared to NT-proBNP for 30-day readmission or death in patients hospitalized with acute dyspnea. METHODS: We measured cTnT and NT-proBNP within 24 h in 314 patients hospitalized with acute dyspnea and adjudicated the cause of the index admission. Time to first event of readmission or death ≤30 days after hospital discharge was recorded, and cTnT and NT-proBNP measurements were compared head-to-head. RESULTS: Patients who died (12/314) or were readmitted (71/314) within 30 days had higher cTnT concentrations (median: 32.6, Q1-Q3: 18.4-74.2 ng/L vs. median: 19.4, Q1-Q3: 8.4-36.1 ng/L; p for comparison <0.001) and NT-proBNP concentrations (median: 1,753.6, Q1-Q3: 464.2-6,862.0 ng/L vs. median 984, Q1-Q3 201-3,600 ng/L; for comparison p = 0.027) compared to patients who survived and were not readmitted. cTnT concentrations were associated with readmission or death within 30 days after discharge both in the total cohort (adjusted hazard ratio [aHR]: 1.64, 95% confidence interval [CI]: 1.30-2.05) and in patients with heart failure (HF) (aHR: 1.58, 95% CI: 1.14-2.18). In contrast, NT-proBNP concentrations were not associated with short-term events, neither in the total cohort (aHR: 1.10, 95% CI: 0.94-1.30) nor in patients with adjudicated HF (aHR: 1.06, 95% CI: 0.80-1.40). CONCLUSION: cTnT concentrations are associated with 30-day readmission or death in patients hospitalized with acute dyspnea, as well as in patients adjudicated HF.

BIN1, Myotubularin, and Dynamin-2 Coordinate T-Tubule Growth in Cardiomyocytes.

BACKGROUND: Transverse tubules (t-tubules) form gradually in the developing heart, critically enabling maturation of cardiomyocyte Ca2+ homeostasis. The membrane bending and scaffolding protein BIN1 (bridging integrator 1) has been implicated in this process. However, it is unclear which of the various reported BIN1 isoforms are involved, and whether BIN1 function is regulated by its putative binding partners MTM1 (myotubularin), a phosphoinositide 3'-phosphatase, and DNM2 (dynamin-2), a GTPase believed to mediate membrane fission. METHODS: We investigated the roles of BIN1, MTM1, and DNM2 in t-tubule formation in developing mouse cardiomyocytes, and in gene-modified HL-1 and human-induced pluripotent stem cell-derived cardiomyocytes. T-tubules and proteins of interest were imaged by confocal and Airyscan microscopy, and expression patterns were examined by RT-qPCR and Western blotting. Ca2+ release was recorded using Fluo-4. RESULTS: We observed that in the postnatal mouse heart, BIN1 localizes along Z-lines from early developmental stages, consistent with roles in initial budding and scaffolding of t-tubules. T-tubule proliferation and organization were linked to a progressive and parallel increase in 4 detected BIN1 isoforms. All isoforms were observed to induce tubulation in cardiomyocytes but produced t-tubules with differing geometries. BIN1-induced tubulations contained the L-type Ca2+ channel, were colocalized with caveolin-3 and the ryanodine receptor, and effectively triggered Ca2+ release. BIN1 upregulation during development was paralleled by increasing expression of MTM1. Despite no direct binding between MTM1 and murine cardiac BIN1 isoforms, which lack exon 11, high MTM1 levels were necessary for BIN1-induced tubulation, indicating a central role of phosphoinositide homeostasis. In contrast, the developing heart exhibited declining levels of DNM2. Indeed, we observed that high levels of DNM2 are inhibitory for t-tubule formation, although this protein colocalizes with BIN1 along Z-lines, and binds all 4 isoforms. CONCLUSIONS: These findings indicate that BIN1, MTM1, and DNM2 have balanced and collaborative roles in controlling t-tubule growth in cardiomyocytes.

Inflammation and Syndecan-4 Shedding from Cardiac Cells in Ischemic and Non-Ischemic Heart Disease.

Circulating biomarkers reflecting cardiac inflammation are needed to improve the diagnostics and guide the treatment of heart failure patients. The cardiac production and shedding of the transmembrane proteoglycan syndecan-4 is upregulated by innate immunity signaling pathways. Here, we investigated the potential of syndecan-4 as a blood biomarker of cardiac inflammation. Serum syndecan-4 was measured in patients with (i) non-ischemic, non-valvular dilated cardiomyopathy (DCM), with (n = 71) or without (n = 318) chronic inflammation; (ii) acute myocarditis (n = 15), acute pericarditis (n = 3) or acute perimyocarditis (23) and (iii) acute myocardial infarction (MI) at day 0, 3 and 30 (n = 119). Syndecan-4 was investigated in cultured cardiac myocytes and fibroblasts (n = 6-12) treated with the pro-inflammatory cytokines interleukin (IL)-1ß and its inhibitor IL-1 receptor antagonist (IL-1Ra), or tumor necrosis factor (TNF)α and its specific inhibitor infliximab, an antibody used in treatment of autoimmune diseases. The levels of serum syndecan-4 were comparable in all subgroups of patients with chronic or acute cardiomyopathy, independent of inflammation. Post-MI, syndecan-4 levels were increased at day 3 and 30 vs. day 0. IL-1Ra attenuated IL-1ß-induced syndecan-4 production and shedding in vitro, while infliximab had no effect. In conclusion, syndecan-4 shedding from cardiac myocytes and fibroblasts was attenuated by immunomodulatory therapy. Although its circulating levels were increased post-MI, syndecan-4 did not reflect cardiac inflammatory status in patients with heart disease.

Inhibition of the extracellular enzyme A disintegrin and metalloprotease with thrombospondin motif 4 prevents cardiac fibrosis and dysfunction.

AIMS: Heart failure is a condition with high mortality rates, and there is a lack of therapies that directly target maladaptive changes in the extracellular matrix (ECM), such as fibrosis. We investigated whether the ECM enzyme known as A disintegrin and metalloprotease with thrombospondin motif (ADAMTS) 4 might serve as a therapeutic target in treatment of heart failure and cardiac fibrosis. METHODS AND RESULTS: The effects of pharmacological ADAMTS4 inhibition on cardiac function and fibrosis were examined in rats exposed to cardiac pressure overload. Disease mechanisms affected by the treatment were identified based on changes in the myocardial transcriptome. Following aortic banding, rats receiving an ADAMTS inhibitor, with high inhibitory capacity for ADAMTS4, showed substantially better cardiac function than vehicle-treated rats, including ∼30% reduction in E/e' and left atrial diameter, indicating an improvement in diastolic function. ADAMTS inhibition also resulted in a marked reduction in myocardial collagen content and a down-regulation of transforming growth factor (TGF)-ß target genes. The mechanism for the beneficial effects of ADAMTS inhibition was further studied in cultured human cardiac fibroblasts producing mature ECM. ADAMTS4 caused a 50% increase in the TGF-ß levels in the medium. Simultaneously, ADAMTS4 elicited a not previously known cleavage of TGF-ß-binding proteins, i.e. latent-binding protein of TGF-ß and extra domain A-fibronectin. These effects were abolished by the ADAMTS inhibitor. In failing human hearts, we observed a marked increase in ADAMTS4 expression and cleavage activity. CONCLUSION: Inhibition of ADAMTS4 improves cardiac function and reduces collagen accumulation in rats with cardiac pressure overload, possibly through a not previously known cleavage of molecules that control TGF-ß availability. Targeting ADAMTS4 may serve as a novel strategy in heart failure treatment, in particular, in heart failure with fibrosis and diastolic dysfunction.

Beneficial effects of exercise initiated before development of hypertrophic cardiomyopathy in genotype-positive mice.

The effect of exercise on disease development in hypertrophic cardiomyopathy (HCM) genotype-positive individuals is unresolved. Our objective was to test the effect of exercise training initiated before phenotype development on cardiac fibrosis, morphology, and function in a mouse model of HCM. Genotype-positive Myh6 R403Q mice exposed to cyclosporine A (CsA) for induction of HCM (HCM mice) were allocated to high-intensity interval treadmill running or sedentary behavior for 6 wk. CsA was initiated from week 4 of the protocol. Cardiac imaging and exercise testing were performed at weeks 0, 3, and 6. After protocol completion, arrhythmia provocation was performed in isolated hearts, and left ventricles (LVs) were harvested for molecular biology and histology. Exercised HCM mice ran farther and faster and exhibited attenuated left atrial (LA) dilatation compared with sedentary mice. Exercised HCM mice had no difference in fibrosis compared with sedentary HCM mice despite lower expression of key extracellular matrix (ECM) genes collagen 1 and 3, fibronectin, and lysyl oxidase, accompanied by increased activation of Akt, GSK3b, and p38. Exercise did not have negative effects on LV function in HCM mice. Our findings indicate mild beneficial effects of exercise initiated before HCM phenotype development, specifically lower ECM gene expression and LA dilatation, and importantly, no detrimental effects.NEW & NOTEWORTHY Genotype-positive hypertrophic cardiomyopathy (HCM) mice had beneficial effects of exercise initiated before phenotype development. Exercised HCM mice had increased exercise capacity, smaller left atria, no increase in hypertrophy, or reduction of function, and a similar degree of fibrosis despite reduction of central extracellular matrix (ECM) genes, including collagens, compared with sedentary HCM mice.

Lumican accumulates with fibrillar collagen in fibrosis in hypertrophic cardiomyopathy.

AIMS: Familial hypertrophic cardiomyopathy (HCM) is the most common form of inherited cardiac disease. It is characterized by myocardial hypertrophy and diastolic dysfunction, and can lead to severe heart failure, arrhythmias, and sudden cardiac death. Cardiac fibrosis, defined by excessive accumulation of extracellular matrix (ECM) components, is central to the pathophysiology of HCM. The ECM proteoglycan lumican is increased during heart failure and cardiac fibrosis, including HCM, yet its role in HCM remains unknown. We provide an in-depth assessment of lumican in clinical and experimental HCM. METHODS: Left ventricular (LV) myectomy specimens were collected from patients with hypertrophic obstructive cardiomyopathy (n = 15), and controls from hearts deemed unsuitable for transplantation (n = 8). Hearts were harvested from a mouse model of HCM; Myh6 R403Q mice administered cyclosporine A and wild-type littermates (n = 8-10). LV tissues were analysed for mRNA and protein expression. Patient myectomy or mouse mid-ventricular sections were imaged using confocal microscopy, direct stochastic optical reconstruction microscopy (dSTORM), or electron microscopy. Human foetal cardiac fibroblasts (hfCFBs) were treated with recombinant human lumican (n = 3) and examined using confocal microscopy. RESULTS: Lumican mRNA was increased threefold in HCM patients (P < 0.05) and correlated strongly with expression of collagen I (R2  = 0.60, P < 0.01) and III (R2  = 0.58, P < 0.01). Lumican protein was increased by 40% in patients with HCM (P < 0.01) and correlated with total (R2  = 0.28, P = 0.05) and interstitial (R2  = 0.30, P < 0.05) fibrosis. In mice with HCM, lumican mRNA increased fourfold (P < 0.001), and lumican protein increased 20-fold (P < 0.001) in insoluble ECM lysates. Lumican and fibrillar collagen were located together throughout fibrotic areas in HCM patient tissue, with increased co-localization measured in patients and mice with HCM (patients: +19%, P < 0.01; mice: +13%, P < 0.01). dSTORM super-resolution microscopy was utilized to image interstitial ECM which had yet to undergo overt fibrotic remodelling. In these interstitial areas, collagen I deposits located closer to (-15 nm, P < 0.05), overlapped more frequently with (+7.3%, P < 0.05) and to a larger degree with (+5.6%, P < 0.05) lumican in HCM. Collagen fibrils in such deposits were visualized using electron microscopy. The effect of lumican on collagen fibre formation was demonstrated by adding lumican to hfCFB cultures, resulting in thicker (+53.8 nm, P < 0.001), longer (+345.9 nm, P < 0.001), and fewer (-8.9%, P < 0.001) collagen fibres. CONCLUSIONS: The ECM proteoglycan lumican is increased in HCM and co-localizes with fibrillar collagen throughout areas of fibrosis in HCM. Our data suggest that lumican may promote formation of thicker collagen fibres in HCM.

ADAMTSL3 knock-out mice develop cardiac dysfunction and dilatation with increased TGFß signalling after pressure overload.

Heart failure is a major cause of morbidity and mortality worldwide, and can result from pressure overload, where cardiac remodelling is characterized by cardiomyocyte hypertrophy and death, fibrosis, and inflammation. In failing hearts, transforming growth factor (TGF)ß drives cardiac fibroblast (CFB) to myofibroblast differentiation causing excessive extracellular matrix production and cardiac remodelling. New strategies to target pathological TGFß signalling in heart failure are needed. Here we show that the secreted glycoprotein ADAMTSL3 regulates TGFß in the heart. We found that Adamtsl3 knock-out mice develop exacerbated cardiac dysfunction and dilatation with increased mortality, and hearts show increased TGFß activity and CFB activation after pressure overload by aortic banding. Further, ADAMTSL3 overexpression in cultured CFBs inhibits TGFß signalling, myofibroblast differentiation and collagen synthesis, suggesting a cardioprotective role for ADAMTSL3 by regulating TGFß activity and CFB phenotype. These results warrant future investigation of the potential beneficial effects of ADAMTSL3 in heart failure.

Cardiomyocyte-specific overexpression of syndecan-4 in mice results in activation of calcineurin-NFAT signalling and exacerbated cardiac hypertrophy.

BACKGROUND: Cardiomyocyte hypertrophy is a hallmark of cardiac dysfunction in patients with aortic stenosis (AS), and can be triggered by left ventricular (LV) pressure overload in mice by aortic banding (AB). Syndecan-4 is a transmembrane heparan sulphate proteoglycan which is found increased in the myocardium of AS patients and AB mice. The role of syndecan-4 in cardiomyocyte hypertrophy is not well understood. PURPOSE OF THE STUDY: We developed mice with cardiomyocyte-specific overexpression of syndecan-4 (Sdc4-Tg) and subjected these to AB to examine the role of syndecan-4 in hypertrophy and activation of the pro-hypertrophic calcineurin-NFAT signalling pathway. METHODS AND RESULTS: Sdc4-Tg mice showed exacerbated cardiac remodelling upon AB compared to wild type (WT). At 2-6 weeks post-AB, Sdc4-Tg and WT mice showed similar hypertrophic growth, while at 20 weeks post-AB, exacerbated hypertrophy and dysfunction were evident in Sdc4-Tg mice. After cross-breeding of Sdc4-Tg mice with NFAT-luciferase reporter mice, we found increased NFAT activation in Sdc4-Tg hearts after AB. Immunoprecipitation showed that calcineurin bound to syndecan-4 in Sdc4-Tg hearts. Isolated cardiomyocytes from Sdc4-Tg mice showed alterations in Ca2+ fluxes, suggesting that syndecan-4 regulated Ca2+ levels, and thereby, activating the syndecan-4-calcineurin complex resulting in NFAT activation and hypertrophic growth. Similarly, primary cardiomyocyte cultures from neonatal rats showed increased calcineurin-NFAT-dependent hypertrophic growth upon viral Sdc4 overexpression. CONCLUSION: Our study of mice with cardiomyocyte-specific overexpression of Sdc4 have revealed that syndecan-4 is important for activation of the Ca2+-dependent calcineurin-NFAT signalling pathway, hypertrophic remodelling and dysfunction in cardiomyocytes in response to pressure overload.

The female syndecan-4-/- heart has smaller cardiomyocytes, augmented insulin/pSer473-Akt/pSer9-GSK-3ß signaling, and lowered SCOP, pThr308-Akt/Akt and GLUT4 levels.

Background: In cardiac muscle, the ubiquitously expressed proteoglycan syndecan-4 is involved in the hypertrophic response to pressure overload. Protein kinase Akt signaling, which is known to regulate hypertrophy, has been found to be reduced in the cardiac muscle of exercised male syndecan-4-/- mice. In contrast, we have recently found that pSer473-Akt signaling is elevated in the skeletal muscle (tibialis anterior, TA) of female syndecan-4-/- mice. To determine if the differences seen in Akt signaling are sex specific, we have presently investigated Akt signaling in the cardiac muscle of sedentary and exercised female syndecan-4-/- mice. To get deeper insight into the female syndecan-4-/- heart, alterations in cardiomyocyte size, a wide variety of different extracellular matrix components, well-known syndecan-4 binding partners and associated signaling pathways have also been investigated. Methods: Left ventricles (LVs) from sedentary and exercise trained female syndecan-4-/- and WT mice were analyzed by immunoblotting and real-time PCR. Cardiomyocyte size and phosphorylated Ser473-Akt were analyzed in isolated adult cardiomyocytes from female syndecan-4-/- and WT mice by confocal imaging. LV and skeletal muscle (TA) from sedentary male syndecan-4-/- and WT mice were immunoblotted with Akt antibodies for comparison. Glucose levels were measured by a glucometer, and fasting blood serum insulin and C-peptide levels were measured by ELISA. Results: Compared to female WT hearts, sedentary female syndecan-4-/- LV cardiomyocytes were smaller and hearts had higher levels of pSer473-Akt and its downstream target pSer9-GSK-3ß. The pSer473-Akt inhibitory phosphatase PHLPP1/SCOP was lowered, which may be in response to the elevated serum insulin levels found in the female syndecan-4-/- mice. We also observed lowered levels of pThr308-Akt/Akt and GLUT4 in the female syndecan-4-/- heart and an increased LRP6 level after exercise. Otherwise, few alterations were found. The pThr308-Akt and pSer473-Akt levels were unaltered in the cardiac and skeletal muscles of sedentary male syndecan-4-/- mice. Conclusion: Our data indicate smaller cardiomyocytes, an elevated insulin/pSer473-Akt/pSer9-GSK-3ß signaling pathway, and lowered SCOP, pThr308-Akt/Akt and GLUT4 levels in the female syndecan-4-/- heart. In contrast, cardiomyocyte size, and Akt signaling were unaltered in both cardiac and skeletal muscles from male syndecan-4-/- mice, suggesting important sex differences.

Integrin α11ß1 and syndecan-4 dual receptor ablation attenuate cardiac hypertrophy in the pressure overloaded heart.

Pathological myocardial hypertrophy in response to an increase in left ventricular (LV) afterload may ultimately lead to heart failure. Cell surface receptors bridge the interface between the cell and the extracellular matrix (ECM) in cardiac myocytes and cardiac fibroblasts and have been suggested to be important mediators of pathological myocardial hypertrophy. We identify for the first time that integrin α11 (α11) is preferentially upregulated among integrin ß1 heterodimer-forming α-subunits in response to increased afterload induced by aortic banding (AB) in wild-type (WT) mice. Mice were anesthetized in a chamber with 4% isoflurane and 95% oxygen before being intubated and ventilated with 2.5% isoflurane and 97% oxygen. For pre- and postoperative analgesia, animals were administered 0.02-mL buprenorphine (0.3 mg/mL) subcutaneously. Surprisingly, mice lacking α11 develop myocardial hypertrophy following AB comparable to WT. In the mice lacking α11, we further show a compensatory increase in the expression of another mechanoreceptor, syndecan-4, following AB compared with WT AB mice, indicating that syndecan-4 compensated for lack of α11. Intriguingly, mice lacking mechanoreceptors α11 and syndecan-4 show ablated myocardial hypertrophy following AB compared with WT mice. Expression of the main cardiac collagen isoforms col1a2 and col3a1 was significantly reduced in AB mice lacking mechanoreceptors α11 and syndecan-4 compared with WT AB.NEW & NOTEWORTHY Despite their putative importance in stress sensing, the specific integrin α-subunit(s) involved in cardiac hypertrophy has not been identified. Here, we show that α11 and syndecan-4 are critical and interdependent mediators of the hypertrophic response to increased LV afterload. We demonstrate in cells lacking both receptors an interdependent reduction in cell attachment to the major cardiac extracellular matrix components, suggesting that their interplay represents an important mechanism for stress sensing in cardiac cells.

Prognostic value of cardiac biomarkers and National Early Warning Score 2 in acute dyspnoea.

OBJECTIVE: Patients hospitalised with acute dyspnoea due to acute heart failure (AHF) have a grave prognosis, but the European Society of Cardiology guidelines recommend no system to risk stratify these patients. The prognostic value of combining National Early Warning Score (NEWS) 2 and established cardiac biomarkers is not known. METHODS: We measured high-sensitivity cardiac troponin T (hs-cTnT) and N-terminal pro-B-type natriuretic peptide (NT-proBNP) and calculated NEWS2 in 314 patients with acute dyspnoea within 24 hours of hospitalisation. Their prognostic merits were assessed in the total cohort and for the subgroup with AHF separately. RESULTS: The median age was 73 (quartile (Q) 1-3, 63-81) years, 48% were women and 143 patients (46%) were hospitalised with AHF. The 114 patients (36%) who died during follow-up (median 823 days, Q1-3, 471-998) had higher concentrations of hs-cTnT (62 vs 33 ng/L, p<0.001) and NT-proBNP (6995 vs 2605 ng/L, p<0.001), and higher NEWS2 (6.1 vs 4.5 points, p<0.001), compared with survivors. Patients with increased vs low NEWS2 clinical risk had higher mortality rates in adjusted analyses in the total cohort (HR 2.11, 95% CI 1.28 to 3.48) and in patients with AHF (HR 2.00, 95% CI 1.54 to 2.60). NEWS2 provided incremental prognostic information compared with biomarkers alone for the total cohort: area under the curve 0.72 vs 0.70, p=0.042, and for the subpopulation with AHF: 0.70 vs 0.67, p=0.014. CONCLUSION: NEWS2 predicts long-term mortality in patients hospitalised due to acute dyspnoea and the subgroup with AHF and provide incremental prognostic information to hs-cTnT and NT-proBNP.

Extreme altitude induces divergent mass reduction of right and left ventricle in mountain climbers.

Mountain climbing at high altitude implies exposure to low levels of oxygen, low temperature, wind, physical and psychological stress, and nutritional insufficiencies. We examined whether right ventricular (RV) and left ventricular (LV) myocardial masses were reversibly altered by exposure to extreme altitude. Magnetic resonance imaging and echocardiography of the heart, dual x-ray absorptiometry scan of body composition, and blood samples were obtained from ten mountain climbers before departure to Mount Everest or Dhaulagiri (baseline), 13.5 ± 1.5 days after peaking the mountain (post-hypoxia), and six weeks and six months after expeditions exceeding 8000 meters above sea level. RV mass was unaltered after extreme altitude, in contrast to a reduction in LV mass by 11.8 ± 3.4 g post-hypoxia (p = 0.001). The reduction in LV mass correlated with a reduction in skeletal muscle mass. After six weeks, LV myocardial mass was restored to baseline values. Extreme altitude induced a reduction in LV end-diastolic volume (20.8 ± 7.7 ml, p = 0.011) and reduced E', indicating diastolic dysfunction, which were restored after six weeks follow-up. Elevated circulating interleukin-18 after extreme altitude compared to follow-up levels, might have contributed to reduced muscle mass and diastolic dysfunction. In conclusion, the mass of the RV, possibly exposed to elevated afterload, was not changed after extreme altitude, whereas LV mass was reduced. The reduction in LV mass correlated with reduced skeletal muscle mass, indicating a common denominator, and elevated circulating interleukin-18 might be a mechanism for reduced muscle mass after extreme altitude.

AKAP18δ Anchors and Regulates CaMKII Activity at Phospholamban-SERCA2 and RYR.

BACKGROUND: The sarcoplasmic reticulum (SR) Ca2+-ATPase 2 (SERCA2) mediates Ca2+ reuptake into SR and thereby promotes cardiomyocyte relaxation, whereas the ryanodine receptor (RYR) mediates Ca2+ release from SR and triggers contraction. Ca2+/CaMKII (CaM [calmodulin]-dependent protein kinase II) regulates activities of SERCA2 through phosphorylation of PLN (phospholamban) and RYR through direct phosphorylation. However, the mechanisms for CaMKIIδ anchoring to SERCA2-PLN and RYR and its regulation by local Ca2+ signals remain elusive. The objective of this study was to investigate CaMKIIδ anchoring and regulation at SERCA2-PLN and RYR. METHODS: A role for AKAP18δ (A-kinase anchoring protein 18δ) in CaMKIIδ anchoring and regulation was analyzed by bioinformatics, peptide arrays, cell-permeant peptide technology, immunoprecipitations, pull downs, transfections, immunoblotting, proximity ligation, FRET-based CaMKII activity and ELISA-based assays, whole cell and SR vesicle fluorescence imaging, high-resolution microscopy, adenovirus transduction, adenoassociated virus injection, structural modeling, surface plasmon resonance, and alpha screen technology. RESULTS: Our results show that AKAP18δ anchors and directly regulates CaMKIIδ activity at SERCA2-PLN and RYR, via 2 distinct AKAP18δ regions. An N-terminal region (AKAP18δ-N) inhibited CaMKIIδ through binding of a region homologous to the natural CaMKII inhibitor peptide and the Thr17-PLN region. AKAP18δ-N also bound CaM, introducing a second level of control. Conversely, AKAP18δ-C, which shares homology to neuronal CaMKIIα activator peptide (N2B-s), activated CaMKIIδ by lowering the apparent Ca2+ threshold for kinase activation and inducing CaM trapping. While AKAP18δ-C facilitated faster Ca2+ reuptake by SERCA2 and Ca2+ release through RYR, AKAP18δ-N had opposite effects. We propose a model where the 2 unique AKAP18δ regions fine-tune Ca2+-frequency-dependent activation of CaMKIIδ at SERCA2-PLN and RYR. CONCLUSIONS: AKAP18δ anchors and functionally regulates CaMKII activity at PLN-SERCA2 and RYR, indicating a crucial role of AKAP18δ in regulation of the heartbeat. To our knowledge, this is the first protein shown to enhance CaMKII activity in heart and also the first AKAP (A-kinase anchoring protein) reported to anchor a CaMKII isoform, defining AKAP18δ also as a CaM-KAP.

Biological variation of secretoneurin; a novel cardiovascular biomarker implicated in arrhythmogenesis.

BACKGROUND: Secretoneurin is a novel prognostic biomarker that may predict mortality in heart failure and the occurrence of ventricular arrhythmias. This study reports the within subject variation (CVI), between subject variation (CVG), reference change values (RCV) and index of individuality (II) of secretoneurin. METHODS: Thirty healthy volunteers were included. Non-fasting samples were obtained between 8 and 10 am once a week for ten weeks. Secretoneurin was analyzed in duplicate using ELISA. No outliers were present according to Burnett and Reeds' criteria. Simple linear regression did not identify significant trends. Variance homogeneity in the analytical variance and CVI were tested using Cochrane's and Bartlett's tests and four participants were excluded. Calculation of CVI, CVG and RCV were done on ln transformed data as described by Fokkema, the II was calculated using retransformed data. RESULTS: The median age of the participants was 36 years and 53% were female. Non-fasting glucose, eGFR(CKD-EPI), cTnT and NT-proBNP concentrations were within the normal range. Median secretoneurin concentrations were 38 pmol/L (women) and 33 pmol/L (men), p-value < 0.001. CVI and CVG were 9.8% (CI 8.7% to 11.0%) and 20.0 (CI 15.4% to 28.0%), respectively. RCV were 38.7% (CI 35.5% to 42.7%) and -27.9 (CI -29.9 to -26.2) and the II were 0.60 (CI 0.42-0.78). No gender differences were present. CONCLUSION: Secretoneurin has a fairly low CVI, CVG, RCV and II, indicating that it could be suitable as a diagnostic or prognostic biomarker and that delta values in serial samplings may be preferable for identifying clinical changes.

The extracellular matrix glycoprotein ADAMTSL2 is increased in heart failure and inhibits TGFß signalling in cardiac fibroblasts.

Fibrosis accompanies most heart diseases and is associated with adverse patient outcomes. Transforming growth factor (TGF)ß drives extracellular matrix remodelling and fibrosis in the failing heart. Some members of the ADAMTSL (a disintegrin-like and metalloproteinase domain with thrombospondin type 1 motifs-like) family of secreted glycoproteins bind to matrix microfibrils, and although their function in the heart remains largely unknown, they are suggested to regulate TGFß activity. The aims of this study were to determine ADAMTSL2 levels in failing hearts, and to elucidate the role of ADAMTSL2 in fibrosis using cultured human cardiac fibroblasts (CFBs). Cardiac ADAMTSL2 mRNA was robustly increased in human and experimental heart failure, and mainly expressed by fibroblasts. Over-expression and treatment with extracellular ADAMTSL2 in human CFBs led to reduced TGFß production and signalling. Increased ADAMTSL2 attenuated myofibroblast differentiation, with reduced expression of the signature molecules α-smooth muscle actin and osteopontin. Finally, ADAMTSL2 mitigated the pro-fibrotic CFB phenotypes, proliferation, migration and contractility. In conclusion, the extracellular matrix-localized glycoprotein ADAMTSL2 was upregulated in fibrotic and failing hearts of patients and mice. We identified ADAMTSL2 as a negative regulator of TGFß in human cardiac fibroblasts, inhibiting myofibroblast differentiation and pro-fibrotic properties.

Performance of a Novel Research-Use-Only Secretoneurin ELISA in Patients with Suspected Acute Coronary Syndrome: Comparison with an Established Secretoneurin Radioimmunoassay.

BACKGROUND: Circulating secretoneurin (SN) concentrations, as measured by established radioimmunoassay (RIA), risk stratify patients with cardiovascular disease. We now report data for a recently developed research-use-only SN enzyme-linked immunosorbent assay (ELISA) in patients with suspected acute coronary syndrome (ACS). METHODS: SN ELISA was developed according to industry standards and tested in 401 unselected chest pain patients. Blood samples were drawn <24 h from admission, and we adjudicated all hospitalizations as ACS or non-ACS. The mean follow-up was 6.2 years. RESULTS: SN ELISA with 2 monoclonal sheep anti-SN antibodies has a measuring range of 10-250 pmol/L and demonstrates excellent analytical precision and accuracy across the range of SN concentrations. SN measured by ELISA and RIA correlated in the chest pain patients: rho = 0.39, p < 0.001. SN concentrations were higher in ACS patients (n = 161 [40%]) than in non-ACS patients (n = 240) for both assays, with an area under the curve (AUC) of 0.66 (95% CI: 0.61-0.71) for ELISA and 0.59 (0.54-0.65) for RIA. SN concentrations were also higher in nonsurvivors (n = 65 [16%]) than survivors, with an AUC of 0.72 (0.65-0.79) for ELISA versus 0.64 (0.56-0.72) for RIA, p = 0.007, for difference between assays. Adjusting for age, sex, blood pressure, previous myocardial infarction, atrial fibrillation, and heart failure in multivariable analysis, SN concentrations as measured by ELISA, but not RIA, remained associated with mortality, with a hazard ratio of 1.71 (1.03-2.84), p = 0.038. CONCLUSIONS: The novel SN ELISA has excellent performance, higher AUC for diagnosis, and superior prognostic accuracy compared to the established RIA in chest pain patients.

Circulating MicroRNA-210 Concentrations in Patients with Acute Heart Failure: Data from the Akershus Cardiac Examination 2 Study.

BACKGROUND: MicroRNA (miR)-210 expression is induced by acute and chronic hypoxia and provides prognostic information in patients with aortic stenosis and acute coronary syndrome. We hypothesized that circulating miR-210 concentrations could provide diagnostic and prognostic information in patients with acute heart failure (HF). METHODS: We measured miR-210 concentrations in serum samples on admission from 314 patients hospitalized for acute dyspnea and 9 healthy control subjects. The diagnostic and prognostic properties of miR-210 were tested in patients after adjudication of all diagnoses and with median follow-up of 464 days. RESULTS: All patients and control subjects had miR-210 concentrations within the range of detection, and the analytical variation was low as the coefficient of variation of synthetic spike-in RNA was 4%. Circulating miR-210 concentrations were increased in patients with HF compared to healthy control subjects, but miR-210 concentrations did not separate patients with acute HF (n = 143) from patients with non-HF-related dyspnea (n = 171): the area under the curve was 0.50 (95% CI 0.43-0.57). Circulating miR-210 concentrations were associated with mortality (n = 114) after adjustment for clinical risk factors (hazard ratio 1.65 [95% CI 1.03-2.62] per unit miR-210 increase), but this association was attenuated and not significant after adjustment for established cardiac protein biomarkers. CONCLUSIONS: Circulating miR-210 concentrations are associated with mortality, but do not add to established protein biomarkers for diagnosis or prognosis in patients with acute dyspnea.

Sacubitril/valsartan ameliorates cardiac hypertrophy and preserves diastolic function in cardiac pressure overload.

AIMS: Sacubitril/valsartan (sac/val) has shown superior effect compared with blockade of the renin-angiotensin-aldosterone system in heart failure with reduced ejection fraction. We aimed to investigate effects of sac/val compared with valsartan in a pressure overload model of heart failure with preserved ejection fraction (HFpEF). METHODS AND RESULTS: Sprague-Dawley rats underwent aortic banding or sham (n = 16) surgery and were randomized to sac/val (n = 28), valsartan (n = 29), or vehicle (n = 26) treatment for 8 weeks. Sac/val reduced left ventricular weight by 11% compared with vehicle (P = 0.01) and 9% compared with valsartan alone (P = 0.04). Only valsartan reduced blood pressure compared with sham (P = 0.02). Longitudinal early diastolic strain rate was preserved in sac/val compared with sham, while it was reduced by 23% in vehicle (P = 0.03) and 24% in valsartan (P = 0.02). Diastolic dysfunction, measured by E/e'SR, increased by 68% in vehicle (P < 0.01) and 80% in valsartan alone (P < 0.001), while sac/val showed no increase. Neither sac/val nor valsartan prevented interstitial fibrosis. Although ejection fraction was preserved, we observed mild systolic dysfunction, with vehicle showing a 28% decrease in longitudinal strain (P < 0.01). Neither sac/val nor valsartan treatment improved this dysfunction. CONCLUSIONS: In a model of HFpEF induced by cardiac pressure overload, sac/val reduced hypertrophy compared with valsartan alone and ameliorated diastolic dysfunction. These effects were independent of blood pressure. Early systolic dysfunction was not affected, supporting the notion that sac/val has the largest potential in conditions characterized by reduced ejection fraction. Observed anti-hypertrophic effects in preserved ejection fraction implicate potential benefit of sac/val in the clinical setting of hypertrophic remodelling and impaired diastolic function.

High-sensitivity cardiac troponin T and N-terminal pro-B-type natriuretic peptide in acute heart failure: Data from the ACE 2 study.

BACKGROUND: To assess if cardiac troponins can improve diagnostics of acute heart failure (AHF) and provide prognostic information in patients with acute dyspnea. METHODS: We measured cardiac troponin T with a high-sensitivity assay (hs-cTnT) in 314 patients hospitalized with acute dyspnea. The index diagnosis was adjudicated and AHF patients were stratified into AHF with reduced or preserved ejection fraction (HFrEF/HFpEF). The prognostic and diagnostic merit of hs-cTnT was compared to the merit of N-terminal pro-B-type natriuretic peptide (NT-proBNP). RESULTS: In the total population, median age was 73 (quartile [Q] 1-3 63-81) years and 48% were women. One-hundred-forty-three patients were categorized as AHF (46%) and these patients had higher hs-cTnT concentrations than patients with non-AHF-related dyspnea: median 38 (Q1-3 22-75) vs. 13 (4-25) ng/L; p < 0.001. hs-cTnT concentrations were similar between patients with HFrEF and HFpEF (p = 0.80), in contrast to NT-proBNP, which was higher in HFrEF (p < 0.001). C-statistics for discriminating HFpEF from non-AHF-related dyspnea was 0.80 (95% CI 0.73-0.86) for hs-cTnT, 0.79 (0.73-0.86) for NT-proBNP, and 0.83 (0.76-0.89) for hs-cTnT and NT-proBNP in combination. Elevated hs-cTnT remained associated with HFpEF in logistic regression analysis after adjusting for demographics, comorbidities and renal function. During median 27 months of follow-up, 114 (36%) patients died in the total population. Higher hs-cTnT concentrations were associated with increased risk of all-cause mortality after adjustment for clinical variables and NT-proBNP: hazard ratio 1.30 (95% CI 1.07-1.58), p = 0.009. CONCLUSION: hs-cTnT measurements improve diagnostic accuracy for HFpEF and provide independent prognostic information in unselected patients with acute dyspnea.