S100A1: a multifaceted therapeutic target in cardiovascular disease

Pharmacological SERCA activation limits diet-induced steatohepatitis and restores liver metabolic function in mice

Metabolic dysfunction-associated steatotic liver disease is the most common form of liver disease and poses significant health risks to patients who progress to metabolic dysfunction-associated steatohepatitis. Fatty acid overload alters endoplasmic reticulum (ER) calcium stores and induces mitochondrial oxidative stress in hepatocytes, leading to hepatocellular inflammation and apoptosis. Obese mice have impaired liver sarco/ER Ca2+-ATPase (SERCA) function, which normally maintains intracellular calcium homeostasis by transporting Ca2+ ions from the cytoplasm to the ER. We hypothesized that restoration of SERCA activity would improve diet-induced steatohepatitis in mice by limiting ER stress and mitochondrial dysfunction. WT and melanocortin-4 receptor KO (Mc4r-/-) mice were placed on either chow or Western diet (WD) for 8 weeks. Half of the WD-fed mice were administered CDN1163 to activate SERCA, which reduced liver fibrosis and inflammation. SERCA activation also restored glucose tolerance and insulin sensitivity, improved histological markers of metabolic dysfunction-associated steatohepatitis, increased expression of antioxidant enzymes, and decreased expression of oxidative stress and ER stress genes. CDN1163 decreased hepatic citric acid cycle flux and liver pyruvate cycling, enhanced expression of mitochondrial respiratory genes, and shifted hepatocellular [NADH]/[NAD+] and [NADPH]/[NADP+] ratios to a less oxidized state, which was associated with elevated PUFA content of liver lipids. In sum, the data demonstrate that pharmacological SERCA activation limits metabolic dysfunction-associated steatotic liver disease progression and prevents metabolic dysfunction induced by WD feeding in mice.

From bench to bedside: Calprotectin (S100A8/S100A9) as a biomarker in rheumatoid arthritis

S100A9/S100A8 (calprotectin), a member of the S100 protein family, has been shown to play a pivotal role in innate immunity activation. Calprotectin plays a critical role in the pathogenesis of rheumatoid arthritis (RA), as it triggers chemotaxis, phagocyte migration and modulation of neutrophils and macrophages. Higher calprotectin levels have been found in synovial fluid, plasma, and serum from RA patients. Recent studies have demonstrated better correlations between serum or plasma calprotectin and composite inflammatory disease activity indexes than c-reactive protein (CRP) or the erythrocyte sedimentation rate (ESR). Calprotectin serum levels decreased after treatment, independently of the DMARD type or strategy. Calprotectin has shown the strongest correlations with other sensitive techniques to detect inflammation, such as ultrasound. Calprotectin independently predicts radiographic progression. However, its value as a biomarker of treatment response and flare after tapering is unclear. This update reviews the current understanding of calprotectin in RA and discusses possible applications as a biomarker in clinical practice.

S100 Proteins in Fatty Liver Disease and Hepatocellular Carcinoma

Non-alcoholic fatty liver disease (NAFLD) is a highly prevalent and slow progressing hepatic pathology characterized by different stages of increasing severity which can ultimately give rise to the development of hepatocellular carcinoma (HCC). Besides drastic lifestyle changes, few drugs are effective to some extent alleviate NAFLD and HCC remains a poorly curable cancer. Among the deregulated molecular mechanisms promoting NAFLD and HCC, several members of the S100 proteins family appear to play an important role in the development of hepatic steatosis, non-alcoholic steatohepatitis (NASH) and HCC. Specific members of this Ca²⁺-binding protein family are indeed significantly overexpressed in either parenchymal or non-parenchymal liver cells, where they exert pleiotropic pathological functions driving NAFLD/NASH to severe stages and/or cancer development. The aberrant activity of S100 specific isoforms has also been reported to drive malignancy in liver cancers. Herein, we discuss the implication of several key members of this family, e.g., S100A4, S100A6, S100A8, S100A9 and S100A11, in NAFLD and HCC, with a particular focus on their intracellular versus extracellular functions in different hepatic cell types. Their clinical relevance as non-invasive diagnostic/prognostic biomarkers for the different stages of NAFLD and HCC, or their pharmacological targeting for therapeutic purpose, is further debated.

Cues from human atrial extracellular matrix enrich the atrial differentiation of human induced pluripotent stem cell-derived cardiomyocytes

New robust and reproducible differentiation approaches are needed to generate induced pluripotent stem cell (iPSC)-derived cardiomyocytes of specific subtypes in predictable quantities for tissue-specific disease modeling, tissue engineering, and eventual clinical translation. Here, we assessed whether powdered decellularized extracellular matrix (dECM) particles contained chamber-specific cues that could direct the cardiac differentiation of human iPSCs toward an atrial phenotype. Human hearts were dissected and the left ventricle (LV) and left atria (LA) were isolated, minced, and decellularized using an adapted submersion decellularization technique to generate chamber-specific powdered dECM. Comparative proteomic analyses showed chamber-specific dECM segregation, with atrial- and ventricle-specific proteins uniquely present in powdered dECM-hA and dECM-hV, respectively. Cell populations differentiated in the presence of dECM-hA showed upregulated atrial molecular markers and a two-fold increase in the number of atrial-like cells as compared with cells differentiated with dECM-hV or no dECM (control). Finally, electrophysiological data showed an increase in action potentials characteristic of atrial-like cells in the dECM-hA group. These findings support the hypothesis that dECM powder derived from human atria retained endogenous cues to drive cardiac differentiation toward an atrial fate.

Simulation of the Positive Inotropic Peptide S100A1ct in Aqueous Environment by Gaussian Accelerated Molecular Dynamics

The S100A1ct peptide, consisting of the C-terminal 20 residues of the S100A1 protein fused to an N-terminal 6-residue hydrophilic tag, has been found to exert a positive inotropic effect, resulting in improved contractile performance of failing cardiac and skeletal muscle without arrhythmic side-effects. The S100A1ct peptide thus has high potential for the treatment of acute heart failure. As a step toward understanding its molecular mechanism of action, and to provide a basis for peptidomimetic design to optimize its properties, we here describe de novo structure predictions and molecular dynamics simulations to characterize the conformational landscape of S100A1ct in aqueous environment. In S100A1, the C-terminal 20 residues form an α-helix, but de novo peptide structure predictions indicate that other conformations are also possible. Conventional molecular dynamics simulations in implicit and explicit solvent corroborated this finding. To ensure adequate sampling, we performed simulations of a tagged 10-residue segment of S100A1ct, and we carried out Gaussian accelerated molecular dynamics simulations of the peptides. These simulations showed that although the helical conformation of S100A1ct was the most energetically stable, the peptide can adopt a range of kinked conformations, suggesting that its activity may be related to its ability to act as a conformational switch.

Reciprocal Antagonism between MicroRNA-138 and SIRT1 and Its Implications for the Angiogenesis of Endothelial Cells

MicroRNAs and sirtuins are important epigenetic regulators of gene expression and both contribute significantly to postnatal vascular development. However, the crosstalk between miRNAs and sirtuins in the modulation of angiogenesis has rarely been discussed. Here, we investigated the interactions between miR-138 and sirtuins in the process of angiogenesis. We found that overexpression of miR-138 markedly suppressed the proliferation, migration, and tube-forming capacities of the endothelial cells. And, miR-138 inhibitor-treated endothelial cells showed a reversed phenotype. Furthermore, miR-138 plays a negative role in vascular development in vivo. Western blot and qPCR assays demonstrated that SIRT1 was silenced by miR-138, and a luciferase reporter assay showed that miR-138 bound to the 3'-UTR of SIRT1. The re-expression of SIRT1 alleviated miR-138-mediated suppression of angiogenesis. Furthermore, silencing SIRT1 could boost the level of miR-138. And, upon miR-138 inhibitor treatment, SIRT1 silencing no longer reduced the angiogenic ability of endothelial cells significantly. These results demonstrated that the circuitry involving miR-138 and SIRT1 may participate in vascular homeostasis and also offered the possibility of identifying a new approach in the treatment of angiogenic diseases.

S100A1 is a sensitive and specific cardiac biomarker for early diagnosis and prognostic assessment of acute myocardial infarction measured by chemiluminescent immunoassay

BACKGROUND

A member of the S100 family of Ca²⁺-binding proteins, S100A1 is highly expressed in cardiac muscle tissue. Although this protein is considered an indicator of acute myocardial infarction (AMI), high-throughput and sensitive detection methods are still urgently needed. We constructed a rapid and sensitive method for detecting S100A1 and to investigate the clinical utility of S100A1 as a biomarker for the early diagnosis of AMI and subsequent prognostic assessments. We developed an automated chemiluminescent immunoassay to detect S100A1. We then analyzed the performance of the newly developed assay including evaluation of the analytical sensitivity, analytical selectivity, linear range, accuracy and repeatability.

METHODS

We recruited 87 patients with AMI or angina pectoris to explore the value of this marker for the early diagnosis and prognostic assessment.

RESULTS

The chemiluminescent-immune-based S100A1 assay had functional analytical sensitivity with a detection limit of 0.13 ng/ml, and a wide linear range of 0.13-31.66 ng/ml. It also exhibited good repeatability with intra-assay and inter-assay findings of <5% and <15%, respectively. Plasma S100A1 was found to have a higher diagnostic sensitivity than conventional cardiac biomarkers (creatine kinase-MB and cardiac troponin T). The survival analysis showed that a higher concentration of plasma S100A1 (>1.02 ng/ml) was notably associated with the poor prognosis of AMI patients after first PCI.

CONCLUSIONS

Measurement of circulating S100A1 concentrations with our newly developed chemiluminescent-immune-based assay shows potential for use in the clinic. This assay could enable early identification and prognostic assessment of AMI.

Reynoutrin Improves Ischemic Heart Failure in Rats Via Targeting S100A1

This study investigated the effects of reynoutrin on the improvement of ischemic heart failure (IHF) and its possible mechanism in rats. The rat heart failure model was established by permanently ligating the left anterior descending coronary artery (LAD) and administering different doses of reynoutrin. Cardiac function, inflammatory factors releasing, oxidative stress, cardiomyocytes apoptosis, and myocardial fibrosis were evaluated. Western blotting was used to determine protein expression levels of S100 calcium-binding protein A1 (S100A1), matrix metallopeptidase 2(MMP2), MMP9, phosphorylated (p-) p65, and transforming growth factor -β1 (TGF-β1) in myocardial tissue of the left ventricle. Results showed that reynoutrin significantly improved cardiac function, suppressed the release of inflammatory factors, reduced oxidative stress, inhibited cardiomyocytes apoptosis, and attenuated myocardial fibrosis in rats with IHF. In rat myocardial tissue, permanent LAD-ligation resulted in a significant down-regulation in S100A1 expression, whereas reynoutrin significantly up-regulated S100A1 protein expression while down-regulating MMP2, MMP9, p-p65, and TGF-β1 expressions. However, when S100A1 was knocked down in myocardial tissue, the above-mentioned positive effects of reynoutrin were significantly reversed. Reynoutrin is a potential natural drug for the treatment of IHF, and its mechanism of action involves the up-regulation of S100A1 expression, thereby inhibiting expressions of MMPs and the transcriptional activity of nuclear factor kappa-B.

Calcium and s100a1 protein balance in the brain-heart axis in diabetic male Wistar rats

Objectives Calcium deregulation in diabetes mellitus (DM) is central to the brain-heart axis pathology. This has led to the use of medical plants in complementary medicine such as Amaranthus hypochondriacus (GA). The objective of the study was to establish the effects of grain amaranth feed supplementation on calcium, s100al protein and antioxidant levels on the brain-heart axis in diabetic male Wistar rats. Methods The study involved six groups (n=5) with DM being induced in 20 rats. To the diabetic rats, Group I received mixtard®, Group II was positive control, Groups III and IV received GA feed supplementation at 25 and 50%. In the nondiabetic rats (n=10), Group V received 50% grain amaranth while Group VI was the negative control. The brain and heart tissues were harvested after five weeks and processed using standard methods. Results Grain amaranth feed supplementation led to improved calcium levels in DM as compared to the positive control. This also led to increased s100a1, antioxidant levels in the brain-heart axis during DM. This then protected the tissues against oxidative damage, thus preserving tissue function and structure. Conclusions Grain amaranth's actions on calcium signaling subsequently affected s100a1 protein levels, leading to improved tissue function in diabetes.

Friend or Foe: S100 Proteins in Cancer

S100 proteins are widely expressed small molecular EF-hand calcium-binding proteins of vertebrates, which are involved in numerous cellular processes, such as Ca²⁺ homeostasis, proliferation, apoptosis, differentiation, and inflammation. Although the complex network of S100 signalling is by far not fully deciphered, several S100 family members could be linked to a variety of diseases, such as inflammatory disorders, neurological diseases, and also cancer. The research of the past decades revealed that S100 proteins play a crucial role in the development and progression of many cancer types, such as breast cancer, lung cancer, and melanoma. Hence, S100 family members have also been shown to be promising diagnostic markers and possible novel targets for therapy. However, the current knowledge of S100 proteins is limited and more attention to this unique group of proteins is needed. Therefore, this review article summarises S100 proteins and their relation in different cancer types, while also providing an overview of novel therapeutic strategies for targeting S100 proteins for cancer treatment.

Sarcoplasmic reticulum calcium mishandling: central tenet in heart failure?

Excitation-contraction coupling links excitation of the sarcolemmal surface membrane to mechanical contraction. In the heart this link is established via a Ca²⁺-induced Ca²⁺ release process, which, following sarcolemmal depolarisation, prompts Ca²⁺ release from the sarcoplasmic reticulum (SR) though the ryanodine receptor (RyR2). This substantially raises the cytoplasmic Ca²⁺ concentration to trigger systole. In diastole, Ca²⁺ is removed from the cytoplasm, primarily via the sarcoplasmic-endoplasmic reticulum Ca²⁺-dependent ATPase (SERCA) pump on the SR membrane, returning Ca²⁺ to the SR store. Ca²⁺ movement across the SR is thus fundamental to the systole/diastole cycle and plays an essential role in maintaining cardiac contractile function. Altered SR Ca²⁺ homeostasis (due to disrupted Ca²⁺ release, storage, and reuptake pathways) is a central tenet of heart failure and contributes to depressed contractility, impaired relaxation, and propensity to arrhythmia. This review will focus on the molecular mechanisms that underlie asynchronous Ca²⁺ cycling around the SR in the failing heart. Further, this review will illustrate that the combined effects of expression changes and disruptions to RyR2 and SERCA2a regulatory pathways are critical to the pathogenesis of heart failure.

Molecular Basis of S100A1 Activation and Target Regulation Within Physiological Cytosolic Ca2+ Levels

The S100A1 protein regulates cardiomyocyte function through its binding of calcium (Ca²⁺) and target proteins, including titin, SERCA, and RyR. S100A1 presents two Ca²⁺ binding domains, a high-affinity canonical EF-hand (cEF) and a low-affinity pseudo EF-hand (pEF), that control S100A1 activation. For wild-type S100A1, both EF hands must be bound by Ca²⁺ to form the open state necessary for target peptide binding, which requires unphysiological high sub-millimolar Ca²⁺ levels. However, there is evidence that post-translational modifications at Cys85 may facilitate the formation of the open state at sub-saturating Ca²⁺ concentrations. Hence, post-translational modifications of S100A1 could potentially increase the Ca²⁺-sensitivity of binding protein targets, and thereby modulate corresponding signaling pathways. In this study, we examine the mechanism of S100A1 open-closed gating via molecular dynamics simulations to determine the extent to which Cys85 functionalization, namely via redox reactions, controls the relative population of open states at sub-saturating Ca²⁺ and capacity to bind peptides. We further characterize the protein's ability to bind a representative peptide target, TRKT12 and relate this propensity to published competition assay data. Our simulation results indicate that functionalization of Cys85 may stabilize the S100A1 open state at physiological, micromolar Ca²⁺ levels. Our conclusions support growing evidence that S100A1 serves as a signaling hub linking Ca²⁺ and redox signaling pathways.

Pathophysiology of Calcium Mediated Ventricular Arrhythmias and Novel Therapeutic Options with Focus on Gene Therapy

Cardiac arrhythmias constitute a major health problem with a huge impact on mortality rates and health care costs. Despite ongoing research efforts, the understanding of the molecular mechanisms and processes responsible for arrhythmogenesis remains incomplete. Given the crucial role of Ca²⁺-handling in action potential generation and cardiac contraction, Ca²⁺ channels and Ca²⁺ handling proteins represent promising targets for suppression of ventricular arrhythmias. Accordingly, we report the different roles of Ca²⁺-handling in the development of congenital as well as acquired ventricular arrhythmia syndromes. We highlight the therapeutic potential of gene therapy as a novel and innovative approach for future arrhythmia therapy. Furthermore, we discuss various promising cellular and mitochondrial targets for therapeutic gene transfer currently under investigation.

Intracavernosal Adeno-Associated Virus-Mediated S100A1 Gene Transfer Enhances Erectile Function in Diabetic Rats by Promoting Cavernous Angiogenesis via VEGF-A/VEGFR2 Signaling

INTRODUCTION

Novel therapeutic targets for diabetes-induced erectile dysfunction (DED) are urgently needed. Previous studies have proved that S100A1, a small Ca²⁺-binding protein, is a pluripotent regulator of cardiovascular pathophysiology. Its absence is associated with endothelial dysfunction, the central event linking cardiovascular changes in diabetes. However, the role of S100A1 in DED remains unknown.

AIM

To explore the effect and underlying mechanisms of S100A1 in restoring erectile function in type I diabetic rat model.

METHODS

Diabetes was induced by intraperitoneal injection of streptozotocin and then screened by apomorphine (APO) to confirm erectile dysfunction. Rats that met the criteria of penile erection were marked as APO-positive; otherwise, the result was APO-negative. In experiment 1, S100A1 gene expression alterations in the corpus cavernosum in moderate and established stages of DED were analyzed. In experiment 2, S100A1 and control GFP gene were delivered into the corpus cavernosum in APO-negative rats by adeno-associated virus (AAV) serotype 9. Erectile function was assessed at 4 weeks after gene therapy.

MAIN OUTCOME MEASURES

Erectile response, histologic and molecular alterations.

RESULTS

S100A1 protein was localized to the area surrounding the cavernosal sinusoids in the penis, and it was gradually downregulated synchronized with the progression of DED. Compared with an injection of AAV-GFP, a single injection of AAV-S100A1 significantly restored erectile function in diabetic rats. S100A1 overexpression significantly upregulated the expression of endogenous VEGF-A, promoted VEGFR2 internalization, and subsequently triggered the protein kinase B-endothelial nitric oxide synthase pathway in diabetic erectile tissues. Marked increases in nitric oxide and endothelial content were noted in AAV-S100A1-treated diabetic rats.

CLINICAL IMPLICATIONS

Local S100A1 overexpression may be an alternative therapy for DED and should be further investigated by future clinical studies.

STRENGTH & LIMITATIONS

This is the first study demonstrating the angiogenic role of S100A1 in DED, but does not preclude the contribution of the effects of S100A1 in other tissues such as the neuronal tissue on the functional effects observed in erectile responses.

CONCLUSION

The decreased expression of S100A1 during hyperglycemia might be important in the development of erectile dysfunction. S100A1 may play a potential role in restoring erectile function in rats with DED through modulating cavernous angiogenesis. Yu Z, Zhang Y, Tang Z, et al. Intracavernosal Adeno-Associated Virus-Mediated S100A1 Gene Transfer Enhances Erectile Function in Diabetic Rats by Promoting Cavernous Angiogenesis via VEGF-A/VEGFR2 Signaling. J Sex Med 2019;16:1344-1354.

S100A4 inhibits cell proliferation by interfering with the S100A1-RAGE V domain

The Ca2+-dependent human S100A4 (Mts1) protein is part of the S100 family. Here, we studied the interactions of S100A4 with S100A1 using nuclear magnetic resonance (NMR) spectroscopy. We used the chemical shift perturbed residues from HSQC to model S100A4 and S100A1 complex with HADDOCK software. We observed that S100A1 and the RAGE V domain have an analogous binding area in S100A4. We discovered that S100A4 acts as an antagonist among the RAGE V domain and S100A1, which inhibits tumorigenesis and cell proliferation. We used a WST-1 assay to examine the bioactivity of S100A1 and S100A4. This study could possibly be beneficial for evaluating new proteins for the treatment of diseases.

Association between serum S100A1 level and Global Registry of Acute Coronary Events score in patients with non-ST-segment elevation acute coronary syndrome

Objective Acute coronary syndrome (ACS) is associated with several clinical syndromes, one of which is acute non-ST-segment ACS (NSTE-ACS). S100A1 is a calcium-dependent regulator of heart contraction and relaxation. We investigated the association between the serum S100A1 level and the Global Registry of Acute Coronary Events (GRACE) risk score in patients with NSTE-ACS and the potential of using the serum S100A1 level to predict the 30-day prognosis of NSTE-ACS. Methods The clinical characteristics of 162 patients with NSTE-ACS were analyzed to determine the GRACE score. The serum S100A1 concentration was determined using fasting antecubital venous blood. The patients were divided into different groups according to the serum S100A1 level, and the 30-day NSTE-ACS prognosis was evaluated using Kaplan-Meier analysis. Results The serum S100A1 levels differed significantly among the groups. Correlation analysis showed that the serum S100A1 level was positively correlated with the GRACE score. Kaplan-Meier analysis revealed that the number of 30-day cardiac events was significantly higher in patients with an S100A1 level of >3.41 ng/mL. Conclusions S100A1 is a potential biomarker that can predict the progression of NSTE-ACS and aid in its early risk stratification and prognosis.

S100B as an antagonist to block the interaction between S100A1 and the RAGE V domain

Ca2+-binding human S100A1 protein is a type of S100 protein. S100A1 is a significant mediator during inflammation when Ca2+ binds to its EF-hand motifs. Receptors for advanced glycation end products (RAGE) correspond to 5 domains: the cytoplasmic, transmembrane, C2, C1, and V domains. The V domain of RAGE is one of the most important target proteins for S100A1. It binds to the hydrophobic surface and triggers signaling transduction cascades that induce cell growth, cell proliferation, and tumorigenesis. We used nuclear magnetic resonance (NMR) spectroscopy to characterize the interaction between S100A1 and the RAGE V domain. We found that S100B could interact with S100A1 via NMR 1H-15N HSQC titrations. We used the HADDOCK program to generate the following two binary complexes based on the NMR titration results: S100A1-RAGE V domain and S100A1-S100B. After overlapping these two complex structures, we found that S100B plays a crucial role in blocking the interaction site between RAGE V domain and S100A1. A cell proliferation assay WST-1 also supported our results. This report could potentially be useful for new protein development for cancer treatment.

Thirty Years of Saying NO: Sources, Fate, Actions, and Misfortunes of the Endothelium-Derived Vasodilator Mediator

Endothelial cells control vascular tone by releasing nitric oxide (NO) produced by endothelial NO synthase. The activity of endothelial NO synthase is modulated by the calcium concentration and by post-translational modifications (eg, phosphorylation). When NO reaches vascular smooth muscle, soluble guanylyl cyclase is its primary target producing cGMP. NO production is stimulated by circulating substances (eg, catecholamines), platelet products (eg, serotonin), autacoids formed in (eg, bradykinin) or near (eg, adiponectin) the vascular wall and physical factors (eg, shear stress). NO dysfunction can be caused, alone or in combination, by abnormal coupling of endothelial cell membrane receptors, insufficient supply of substrate (l-arginine) or cofactors (tetrahydrobiopterin), endogenous inhibitors (asymmetrical dimethyl arginine), reduced expression/presence/dimerization of endothelial NO synthase, inhibition of its enzymatic activity, accelerated disposition of NO by reactive oxygen species and abnormal responses (eg, biased soluble guanylyl cyclase activity producing cyclic inosine monophosphate) of the vascular smooth muscle. Major culprits causing endothelial dysfunction, irrespective of the underlying pathological process (aging, obesity, diabetes mellitus, and hypertension), include stimulation of mineralocorticoid receptors, activation of endothelial Rho-kinase, augmented presence of asymmetrical dimethyl arginine, and exaggerated oxidative stress. Genetic and pharmacological interventions improve dysfunctional NO-mediated vasodilatations if protecting the supply of substrate and cofactors for endothelial NO synthase, preserving the presence and activity of the enzyme and reducing reactive oxygen species generation. Common achievers of such improvement include maintained levels of estrogens and increased production of adiponectin and induction of silent mating-type information regulation 2 homologue 1. Obviously, endothelium-dependent relaxations are not the only beneficial action of NO in the vascular wall. Thus, reduced NO-mediated responses precede and initiate the atherosclerotic process.

Molecular Basis of S100A1 Activation at Saturating and Subsaturating Calcium Concentrations

The S100A1 protein mediates a wide variety of physiological processes through its binding of calcium (Ca(2+)) and endogenous target proteins. S100A1 presents two Ca(2+)-binding domains: a high-affinity "canonical" EF (cEF) hand and a low-affinity "pseudo" EF (pEF) hand. Accumulating evidence suggests that both Ca(2+)-binding sites must be saturated to stabilize an open state conducive to peptide recognition, yet the pEF hand's low affinity limits Ca(2+) binding at normal physiological concentrations. To understand the molecular basis of Ca(2+) binding and open-state stabilization, we performed 100 ns molecular dynamics simulations of S100A1 in the apo/holo (Ca(2+)-free/bound) states and a half-saturated state, for which only the cEF sites are Ca(2+)-bound. Our simulations indicate that the pattern of oxygen coordination about Ca(2+) in the cEF relative to the pEF site contributes to the former's higher affinity, whereas Ca(2+) binding strongly reshapes the protein's conformational dynamics by disrupting β-sheet coupling between EF hands. Moreover, modeling of the half-saturated configuration suggests that the open state is unstable and reverts toward a closed state in the absence of the pEF Ca(2+) ion. These findings indicate that Ca(2+) binding at the cEF site alone is insufficient to stabilize opening; thus, posttranslational modification of the protein may be required for target peptide binding at subsaturating intracellular Ca(2+) levels.

Neoinnervation and neovascularization of acellular pericardial-derived scaffolds in myocardial infarcts

Engineered bioimplants for cardiac repair require functional vascularization and innervation for proper integration with the surrounding myocardium. The aim of this work was to study nerve sprouting and neovascularization in an acellular pericardial-derived scaffold used as a myocardial bioimplant. To this end, 17 swine were submitted to a myocardial infarction followed by implantation of a decellularized human pericardial-derived scaffold. After 30 days, animals were sacrificed and hearts were analyzed with hematoxylin/eosin and Masson's and Gallego's modified trichrome staining. Immunohistochemistry was carried out to detect nerve fibers within the cardiac bioimplant by using βIII tubulin and S100 labeling. Isolectin B4, smooth muscle actin, CD31, von Willebrand factor, cardiac troponin I, and elastin antibodies were used to study scaffold vascularization. Transmission electron microscopy was performed to confirm the presence of vascular and nervous ultrastructures. Left ventricular ejection fraction (LVEF), cardiac output (CO), stroke volume, end-diastolic volume, end-systolic volume, end-diastolic wall mass, and infarct size were assessed by using magnetic resonance imaging (MRI). Newly formed nerve fibers composed of several amyelinated axons as the afferent nerve endings of the heart were identified by immunohistochemistry. Additionally, neovessel formation occurred spontaneously as small and large isolectin B4-positive blood vessels within the scaffold. In summary, this study demonstrates for the first time the neoformation of vessels and nerves in cell-free cardiac scaffolds applied over infarcted tissue. Moreover, MRI analysis showed a significant improvement in LVEF (P = 0.03) and CO (P = 0.01) and a 43 % decrease in infarct size (P = 0.007).

S100A1 DNA-based Inotropic Therapy Protects Against Proarrhythmogenic Ryanodine Receptor 2 Dysfunction

Restoring expression levels of the EF-hand calcium (Ca(2+)) sensor protein S100A1 has emerged as a key factor in reconstituting normal Ca(2+) handling in failing myocardium. Improved sarcoplasmic reticulum (SR) function with enhanced Ca(2+) resequestration appears critical for S100A1's cyclic adenosine monophosphate-independent inotropic effects but raises concerns about potential diastolic SR Ca(2+) leakage that might trigger fatal arrhythmias. This study shows for the first time a diminished interaction between S100A1 and ryanodine receptors (RyR2s) in experimental HF. Restoring this link in failing cardiomyocytes, engineered heart tissue and mouse hearts, respectively, by means of adenoviral and adeno-associated viral S100A1 cDNA delivery normalizes diastolic RyR2 function and protects against Ca(2+)- and β-adrenergic receptor-triggered proarrhythmogenic SR Ca(2+) leakage in vitro and in vivo. S100A1 inhibits diastolic SR Ca(2+) leakage despite aberrant RyR2 phosphorylation via protein kinase A and calmodulin-dependent kinase II and stoichiometry with accessory modulators such as calmodulin, FKBP12.6 or sorcin. Our findings demonstrate that S100A1 is a regulator of diastolic RyR2 activity and beneficially modulates diastolic RyR2 dysfunction. S100A1 interaction with the RyR2 is sufficient to protect against basal and catecholamine-triggered arrhythmic SR Ca(2+) leak in HF, combining antiarrhythmic potency with chronic inotropic actions.

Cardiomyocytes, endothelial cells and cardiac fibroblasts: S100A1's triple action in cardiovascular pathophysiology

Over the past decade, basic and translational research delivered comprehensive evidence for the relevance of the Ca(2+)-binding protein S100A1 in cardiovascular diseases. Aberrant expression levels of S100A1 surfaced as molecular key defects, driving the pathogenesis of chronic heart failure, arterial and pulmonary hypertension, peripheral artery disease and disturbed myocardial infarction healing. Loss of intracellular S100A1 renders entire Ca(2+)-controlled networks dysfunctional, thereby leading to cardiomyocyte failure and endothelial dysfunction. Lack of S100A1 release in ischemic myocardium compromises cardiac fibroblast function, entailing impaired damage healing. This review focuses on molecular pathways and signaling cascades regulated by S100A1 in cardiomyocytes, endothelial cells and cardiac fibroblasts in order to provide an overview of our current mechanistic understanding of S100A1's action in cardiovascular pathophysiology.

Role of S100A1 in hypoxia-induced inflammatory response in cardiomyocytes via TLR4/ROS/NF-κB pathway

Objectives

S100A1 plays a crucial role in hypoxia-induced inflammatory response in cardiomyocytes. However, the role of S100A1 in hypoxia-induced inflammatory response in cardiomyocytes is still unknown.

Methods

enzyme-linked immunosorbent assay (ELISA) was performed for the determination of inflammatory cytokines. Immunocytochemistry and immunofluorescence, Western blot analysis and Real-time polymerase chain reaction (RT-PCR) were conducted to assess protein or mRNA expressions. Fluorogenic probe dihydroethidium (DHE) was used to evaluate the generation of reactive oxygen species (ROS) while Hoechst 33342 staining for apoptosis. Small interfering RNA (siRNA) for S100A1 was used to evaluate the role of S100A1.

Key findings

The levels of ROS and inflammatory cytokine including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and IL-8 in H9c2 cells were increased remarkably by hypoxia. However, IL-37 protein or mRNA levels were decreased significantly. Both Toll-like receptor 4 (TLR4) inhibitor Ethyl (6R)-6-[N-(2-Chloro-4fluorophenyl)sulfamoyl]cyclohex-1-ene-1-carboxylate (TAK-242) treatment or siRNA S100A1 downregulated TLR4 expression and inflammatory cytokine level and mRNA in H9c2 cells, as well as weakening ROS and phospho-p65 Nuclear factor (NF)-κB levels. Further, S100A1 treatment significantly reduced TNF-α protein or mRNA level whereas enhanced IL-37 protein or mRNA level, and could attenuate ROS and phospho-p65 NF-κB levels.

Conclusions

Our results demonstrate that S100A1 can regulate the inflammatory response and oxidative stress in H9C2 cells via TLR4/ROS/NF-κB pathway. These findings provide an interesting strategy for protecting cardiomyocytes from hypoxia-induced inflammatory response.

S100 proteins in cancer

In humans, the S100 protein family is composed of 21 members that exhibit a high degree of structural similarity, but are not functionally interchangeable. This family of proteins modulates cellular responses by functioning both as intracellular Ca(2+) sensors and as extracellular factors. Dysregulated expression of multiple members of the S100 family is a common feature of human cancers, with each type of cancer showing a unique S100 protein profile or signature. Emerging in vivo evidence indicates that the biology of most S100 proteins is complex and multifactorial, and that these proteins actively contribute to tumorigenic processes such as cell proliferation, metastasis, angiogenesis and immune evasion. Drug discovery efforts have identified leads for inhibiting several S100 family members, and two of the identified inhibitors have progressed to clinical trials in patients with cancer. This Review highlights new findings regarding the role of S100 family members in cancer diagnosis and treatment, the contribution of S100 signalling to tumour biology, and the discovery and development of S100 inhibitors for treating cancer.

S100 proteins in cancer

In humans, the S100 protein family is composed of 21 members that exhibit a high degree of structural similarity, but are not functionally interchangeable. This family of proteins modulates cellular responses by functioning both as intracellular Ca(2+) sensors and as extracellular factors. Dysregulated expression of multiple members of the S100 family is a common feature of human cancers, with each type of cancer showing a unique S100 protein profile or signature. Emerging in vivo evidence indicates that the biology of most S100 proteins is complex and multifactorial, and that these proteins actively contribute to tumorigenic processes such as cell proliferation, metastasis, angiogenesis and immune evasion. Drug discovery efforts have identified leads for inhibiting several S100 family members, and two of the identified inhibitors have progressed to clinical trials in patients with cancer. This Review highlights new findings regarding the role of S100 family members in cancer diagnosis and treatment, the contribution of S100 signalling to tumour biology, and the discovery and development of S100 inhibitors for treating cancer.

Progress in gene therapy for heart failure

Recent advances in our understanding of the pathophysiology of myocardial dysfunction in the setting of congestive heart failure have created a new opportunity in developing nonpharmacological approaches to treatment. Gene therapy has emerged as a powerful tool in targeting the molecular mechanisms of disease by preventing the ventricular remodeling and improving bioenergetics in heart failure. Refinements in vector technology, including the creation of recombinant adeno-associated viruses, have allowed for safe and efficient gene transfer. These advancements have been coupled with evolving delivery methods that include vascular, pericardial, and direct myocardial approaches. One of the most promising targets, SERCA2a, is currently being used in clinical trials. The recent success of the Calcium Upregulation by Percutaneous Administration of Gene Therapy in Cardiac Disease phase 2 trials using adeno-associated virus 1-SERCA2a in improving outcomes highlights the importance of gene therapy as a future tool in treating congestive heart failure.

Use of isosorbide dinitrate and hydralazine in African-Americans with heart failure 9 years after the African-American Heart Failure Trial

The 2013 American College of Cardiology Foundation/American Heart Association guidelines recommend combined isosorbide dinitrate (ISDN) and hydralazine to reduce mortality and morbidity for African-Americans with symptomatic heart failure (HF) and reduced ejection fraction, currently receiving optimal medical therapy (class I, level A). Nitrates can alleviate HF symptoms, but continuous use is limited by tolerance. Hydralazine may mitigate nitrate tolerance, and the ISDN-hydralazine combination in the Vasodilators in Heart Failure Trial (V-HeFT) I improved survival and exercise tolerance in men with dilated cardiomyopathy or HF with reduced ejection fraction, most notably in self-identified black participants. In the subsequent V-HeFT II, survival was greater with enalapril than with ISDN-hydralazine in the overall cohort, but mortality rate was similar in the enalapril and ISDN-hydralazine groups in the self-identified black patients. Consequently, in the African-American Heart Failure Trial (A-HeFT) in self-identified black patients with symptomatic HF, adding a fixed-dose combination ISDN-hydralazine to modern guideline-based care improved outcomes versus placebo, including all-cause mortality, and led to early trial termination. Hypertension underlies HF, especially in African-Americans; the A-HeFT and its substudies demonstrated not only improvements in echocardiographic parameters, morbidity, and mortality but also a decrease in hospitalizations, potentially affecting burgeoning HF health-care costs. Genetic characteristics may, therefore, determine response to ISDN-hydralazine, and the Genetic Risk Assessment in Heart Failure substudy demonstrated important hypothesis-generating pharmacogenetic data.

S100A1 is released from ischemic cardiomyocytes and signals myocardial damage via Toll-like receptor 4

Members of the S100 protein family have been reported to function as endogenous danger signals (alarmins) playing an active role in tissue inflammation and repair when released from necrotic cells. Here, we investigated the role of S100A1, the S100 isoform with highest abundance in cardiomyocytes, when released from damaged cardiomyocytes during myocardial infarction (MI). Patients with acute MI showed significantly increased S100A1 serum levels. Experimental MI in mice induced comparable S100A1 release. S100A1 internalization was observed in cardiac fibroblasts (CFs) adjacent to damaged cardiomyocytes. In vitro analyses revealed exclusive S100A1 endocytosis by CFs, followed by Toll-like receptor 4 (TLR4)-dependent activation of MAP kinases and NF-κB. CFs exposed to S100A1 assumed an immunomodulatory and anti-fibrotic phenotype characterized i.e. by enhanced intercellular adhesion molecule-1 (ICAM1) and decreased collagen levels. In mice, intracardiac S100A1 injection recapitulated these transcriptional changes. Moreover, antibody-mediated neutralization of S100A1 enlarged infarct size and worsened left ventricular functional performance post-MI. Our study demonstrates alarmin properties for S100A1 from necrotic cardiomyocytes. However, the potentially beneficial role of extracellular S100A1 in MI-related inflammation and repair warrants further investigation.

Induction of microRNA-138 by pro-inflammatory cytokines causes endothelial cell dysfunction

Exposure to pro-inflammatory cytokines, such as Angiotensin II, endothelin-1 or TNF leads to endothelial dysfunction, characterized by the reduced production of nitric oxide via endothelial nitric oxide synthase (eNOS). We recently identified the Ca(2+) binding protein S100A1 as an essential factor required for eNOS activity. Here we report that pro-inflammatory cytokines down-regulate expression of S100A1 in primary human microvascular endothelial cells (HMVECs) via induction of microRNA-138 (miR-138), in a manner that depends on the stabilization of HIF1-α. We show that loss of S100A1 in ECs reduces stimulus-induced NO production, which can be prevented by inhibition of miR-138. Our study suggests that targeting miR-138 might be beneficial for the treatment of cardiovascular disease.

Genetic modulation of the SERCA activity does not affect the Ca(2+) leak from the cardiac sarcoplasmic reticulum

The Ca(2+) content in the sarcoplasmic reticulum (SR) determines the amount of Ca(2+) released, thereby regulating the magnitude of Ca(2+) transient and contraction in cardiac muscle. The Ca(2+) content in the SR is known to be regulated by two factors: the activity of the Ca(2+) pump (SERCA) and Ca(2+) leak through the ryanodine receptor (RyR). However, the direct relationship between the SERCA activity and Ca(2+) leak has not been fully investigated in the heart. In the present study, we evaluated the role of the SERCA activity in Ca(2+) leak from the SR using a novel saponin-skinned method combined with transgenic mouse models in which the SERCA activity was genetically modulated. In the SERCA overexpression mice, the Ca(2+) uptake in the SR was significantly increased and the Ca(2+) transient was markedly increased. However, Ca(2+) leak from the SR did not change significantly. In mice with overexpression of a negative regulator of SERCA, sarcolipin, the Ca(2+) uptake by the SR was significantly decreased and the Ca(2+) transient was markedly decreased. Again, Ca(2+) leak from the SR did not change significantly. In conclusion, the selective modulation of the SERCA activity modulates Ca(2+) uptake, although it does not change Ca(2+) leak from the SR.

Functions of S100 proteins

The S100 protein family consists of 24 members functionally distributed into three main subgroups: those that only exert intracellular regulatory effects, those with intracellular and extracellular functions and those which mainly exert extracellular regulatory effects. S100 proteins are only expressed in vertebrates and show cell-specific expression patterns. In some instances, a particular S100 protein can be induced in pathological circumstances in a cell type that does not express it in normal physiological conditions. Within cells, S100 proteins are involved in aspects of regulation of proliferation, differentiation, apoptosis, Ca2+ homeostasis, energy metabolism, inflammation and migration/invasion through interactions with a variety of target proteins including enzymes, cytoskeletal subunits, receptors, transcription factors and nucleic acids. Some S100 proteins are secreted or released and regulate cell functions in an autocrine and paracrine manner via activation of surface receptors (e.g. the receptor for advanced glycation end-products and toll-like receptor 4), G-protein-coupled receptors, scavenger receptors, or heparan sulfate proteoglycans and N-glycans. Extracellular S100A4 and S100B also interact with epidermal growth factor and basic fibroblast growth factor, respectively, thereby enhancing the activity of the corresponding receptors. Thus, extracellular S100 proteins exert regulatory activities on monocytes/macrophages/microglia, neutrophils, lymphocytes, mast cells, articular chondrocytes, endothelial and vascular smooth muscle cells, neurons, astrocytes, Schwann cells, epithelial cells, myoblasts and cardiomyocytes, thereby participating in innate and adaptive immune responses, cell migration and chemotaxis, tissue development and repair, and leukocyte and tumor cell invasion.

Novel interactions of the TRTK12 peptide with S100 protein family members: specificity and thermodynamic characterization

The S100 protein family consists of small, dimeric proteins that exert their biological functions in response to changing calcium concentrations. S100B is the best-studied member and has been shown to interact with more than 20 binding partners in a calcium-dependent manner. The TRTK12 peptide, derived from the consensus binding sequence for S100B, has previously been found to interact with S100A1 and has been proposed to be a general binding partner of the S100 family. To test this hypothesis and gain a better understanding of the specificity of binding for the S100 proteins, 16 members of the human S100 family were screened against this peptide and its alanine variants. Novel interactions were found with only two family members, S100P and S100A2, indicating that TRTK12 selectively interacts with a small subset of the S100 proteins. Substantial promiscuity was observed in the binding site of S100B thereby accommodating variations in the peptide sequence, while S100A1, S100A2, and S100P exhibited larger differences in the binding constants for the TRTK12 alanine variants. This suggests that single-point substitutions can be used to selectively modulate the affinity of TRTK12 peptides for individual S100 proteins. This study has important implications for the rational drug design of inhibitors for the S100 proteins, which are involved in a variety of cancers and neurodegenerative diseases.

Gene transfer for congestive heart failure: update 2013

Congestive heart failure is a major cause of morbidity and mortality with increasing social and economic costs. There have been no new high impact therapeutic agents for this devastating disease for more than a decade. However, many pivotal regulators of cardiac function have been identified using cardiac-directed transgene expression and gene deletion in preclinical studies. Some of these increase function of the failing heart. Altering the expression of these pivotal regulators using gene transfer is now either being tested in clinical gene transfer trials, or soon will be. In this review, we summarize recent progress in cardiac gene transfer for clinical congestive heart failure.

Cardiac gene therapy: from concept to reality

Heart failure is increasing in incidence throughout the world, especially in industrialized countries. Although the current therapeutic modalities have been successful in stabilizing the course of heart failure, morbidity and mortality remain quite high and there remains a great need for innovative breakthroughs that will offer new treatment strategies for patients with advanced forms of the disease. The past few years have witnessed a greater understanding of the molecular underpinnings of the failing heart, paving the way for novel strategies in modulating the cellular environment. As such, gene therapy has recently emerged as a powerful tool offering the promise of a new paradigm for alleviating heart failure. Current gene therapy research for heart failure is focused on exploring potential cellular targets and preclinical and clinical studies are ongoing toward the realization of this goal. Efforts also include the development of sophisticated viral vectors and vector delivery methods for efficient transduction of cardiomyocytes.

S100A1 gene therapy in small and large animals

Myocardial in vivo gene delivery is a valuable technique to investigate the relevance of a protein of interest on cardiac contractile function, hypertrophy, and energy state in healthy animals as well as in a variety of models of cardiovascular disease. Rodent models are used to screen effects and to investigate molecular mechanisms, while large animal models, more closely reflecting human anatomy, physiology, and function, are inevitable for translational therapeutic approaches. The gene of interest, whose expression is driven by a non-cardioselective or cardioselective promotor is cloned into a viral vector. This vehicle is then delivered using an appropriate administration route to target the heart and to achieve efficient protein expression in myocardium. Here we describe myocardial gene therapy in small and large animal models of postischemic heart failure used to reveal the positive inotrope, antihypertrophic, and pro-energetic action of the small calcium sensor protein S100A1.

An efficient expression and purification strategy for the production of S100 proteins in Escherichia coli

S100 proteins belong to a family of small, acidic, EF-hand Ca ( 2+) -binding proteins and have been found to exert both intracellular and extracellular functions in regulation of Ca ( 2+) homeostasis, cytoskeletal dynamics, cell cycle, motility and differentiation. As a result, they have been widely investigated for their association with diseases, such as, neurological diseases, cardiomyopathy, neoplasias and inflammatory diseases. To facilitate further studies of S100 proteins, we reported a simple and efficient method for the expression and purification of human S100A4 and S100A11 proteins in Escherichia coli. Since S100 proteins share many common physical and chemical characteristics, we expect that this approach can be extended to the production of most S100 proteins.

Post-translational S-nitrosylation is an endogenous factor fine tuning the properties of human S100A1 protein

BACKGROUND

S100A1 protein is a proposed target of molecule-guided therapy for heart failure.

RESULTS

S-Nitrosylation of S100A1 is present in cells, increases Ca(2+) binding, and tunes the overall protein conformation.

CONCLUSION

Thiol-aromatic molecular switch is responsible for NO-related modification of S100A1 properties.

SIGNIFICANCE

Post-translational S-nitrosylation may provide functional diversity and specificity to S100A1 and other S100 protein family members. S100A1 is a member of the Ca(2+)-binding S100 protein family. It is expressed in brain and heart tissue, where it plays a crucial role as a modulator of Ca(2+) homeostasis, energy metabolism, neurotransmitter release, and contractile performance. Biological effects of S100A1 have been attributed to its direct interaction with a variety of target proteins. The (patho)physiological relevance of S100A1 makes it an important molecular target for future therapeutic intervention. S-Nitrosylation is a post-translational modification of proteins, which plays a role in cellular signal transduction under physiological and pathological conditions. In this study, we confirmed that S100A1 protein is endogenously modified by Cys(85) S-nitrosylation in PC12 cells, which are a well established model system for studying S100A1 function. We used isothermal calorimetry to show that S-nitrosylation facilitates the formation of Ca(2+)-loaded S100A1 at physiological ionic strength conditions. To establish the unique influence of the S-nitroso group, our study describes high resolution three-dimensional structures of human apo-S100A1 protein with the Cys(85) thiol group in reduced and S-nitrosylated states. Solution structures of the proteins are based on NMR data obtained at physiological ionic strength. Comparative analysis shows that S-nitrosylation fine tunes the overall architecture of S100A1 protein. Although the typical S100 protein intersubunit four-helix bundle is conserved upon S-nitrosylation, the conformation of S100A1 protein is reorganized at the sites most important for target recognition (i.e. the C-terminal helix and the linker connecting two EF-hand domains). In summary, this study discloses cysteine S-nitrosylation as a new factor responsible for increasing functional diversity of S100A1 and helps explain the role of S100A1 as a Ca(2+) signal transmitter sensitive to NO/redox equilibrium within cells.

Gene targeting in ischemic heart disease and failure: translational and clinical studies

Alternative and innovative targeted strategies hold relevance in improving the current treatments for ischemic heart disease (IHD). One potential treatment modality, gene targeting, may provide a unique alternative to current IHD therapies. The principal function of gene targeting in IHD is to augment the expression of an endogenous gene through amplification of an exogenous gene, delivered by a plasmid or a viral vector to enhance myocardial perfusion, and limit the long-term sequelae. The initial clinical studies of gene targeting in IHD were focused upon induction of angiogenic factors and the outcomes were equivocal. Nevertheless, significant advancements have been made in viral vectors, mode of delivery, and potentially relevant targets for IHD. Several of these advancements, particularly with a focus on translational large animal studies, are the focus of this review. The development of novel vectors with prolonged transduction efficiency and minimal inflammation, coupled with hybrid perfusion-mapping delivery devices, and improving the safety of vector use and efficacy of gene systems are but a few of the exciting progresses that are likely to proceed to clinical studies in the near future.

Myocardial infarction in a patient with left ventricular noncompaction: a case report

We describe a 73-year-old male patient with left ventricular noncompaction (LVNC) who was diagnosed with acute myocardial infarction (MI), three-vessel coronary artery disease, a fresh intraventricular thrombus, and mitral regurgitation. He was treated with full anticoagulant therapy, coronary artery bypass grafting, and mitral valve repair. This case adds to a small but growing literature showing association between LVNC and MI and/or coronary artery disease. We suggest that patients with LVNC could be considered at heightened risk for MI, and the two conditions might have a common genetic underpinning in some cases.

Nitric oxide modulation as a therapeutic strategy in heart failure

Nitric oxide (NO) is recognized as one of the most important cardiovascular signaling molecules, with multiple regulatory effects on myocardial and vascular tissue as well as on other tissues and organ systems. With the growth in understanding of the range and mechanisms of NO effects on the cardiovascular system, it is now possible to consider pharmaceutical interventions that directly target NO or key steps in NO effector pathways. This article reviews aspects of the cardiovascular effects of NO, abnormalities in NO regulation in heart failure, and clinical trials of drugs that target specific aspects of NO signaling pathways.

Functional evidence for an active role of B-type natriuretic peptide in cardiac remodelling and pro-arrhythmogenicity

AIMS

During heart failure (HF), the left ventricle (LV) releases B-type natriuretic peptide (BNP), possibly contributing to adverse cardiovascular events including ventricular arrhythmias (VAs) and LV remodelling. We investigated the cardiac effects of chronic BNP elevation in healthy mice and compared the results with a model of HF after myocardial infarction (PMI mice).

METHODS AND RESULTS

Healthy mice were exposed to circulating BNP levels (BNP-Sham) similar to those measured in PMI mice. Telemetric surface electrocardiograms showed that in contrast with fibrotic PMI mice, electrical conduction was not affected in BNP-Sham mice. VAs were observed in both BNP-Sham and PMI but not in Sham mice. Analysis of heart rate variability indicated that chronic BNP infusion increased cardiac sympathetic tone. At the cellular level, BNP reduced Ca(2+) transients and impaired Ca(2+) reuptake in the sarcoplasmic reticulum, in line with blunted SR Ca(2+) ATPase 2a and S100A1 expression. BNP increased Ca(2+) spark frequency, reflecting Ca(2+) leak through ryanodine receptors, elevated diastolic Ca(2+), and promoted spontaneous Ca(2+) waves. Similar effects were observed in PMI mice. Most of these effects were reduced in BNP-Sham and PMI mice by the selective β1-adrenergic blocker metoprolol.

CONCLUSION

Elevated BNP levels, by inducing sympathetic overdrive and altering Ca(2+) handling, promote adverse cardiac remodelling and VAs, which could account in part for the progression of HF after MI. The early use of β-blockers to prevent the deleterious effects of chronic BNP exposure may be beneficial in HF.

S100 calcium binding proteins and ion channels

S100 Ca(2+)-binding proteins have been associated with a multitude of intracellular Ca(2+)-dependent functions including regulation of the cell cycle, cell differentiation, cell motility and apoptosis, modulation of membrane-cytoskeletal interactions, transduction of intracellular Ca(2+) signals, and in mediating learning and memory. S100 proteins are fine tuned to read the intracellular free Ca(2+) concentration and affect protein phosphorylation, which makes them candidates to modulate certain ion channels and neuronal electrical behavior. Certain S100s are secreted from cells and are found in extracellular fluids where they exert unique extracellular functions. In addition to their neurotrophic activity, some S100 proteins modulate neuronal electrical discharge activity and appear to act directly on ion channels. The first reports regarding these effects suggested S100-mediated alterations in Ca(2+) fluxes, K(+) currents, and neuronal discharge activity. Recent reports revealed direct and indirect interactions with Ca(2+), K(+), Cl(-), and ligand activated channels. This review focuses on studies of the physical and functional interactions of S100 proteins and ion channels.