S100A1's single cysteine is an indispensable redox switch for the protection against diastolic calcium waves in cardiomyocytes.

The EF-hand calcium (Ca2+) sensor protein S100A1 combines inotropic with antiarrhythmic potency in cardiomyocytes (CMs). Oxidative posttranslational modification (ox-PTM) of S100A1's conserved, single-cysteine residue (C85) via reactive nitrogen species (i.e., S-nitrosylation or S-glutathionylation) has been proposed to modulate conformational flexibility of intrinsically disordered sequence fragments and to increase the molecule's affinity toward Ca2+. Considering the unknown biological functional consequence, we aimed to determine the impact of the C85 moiety of S100A1 as a potential redox switch. We first uncovered that S100A1 is endogenously glutathionylated in the adult heart in vivo. To prevent glutathionylation of S100A1, we generated S100A1 variants that were unresponsive to ox-PTMs. Overexpression of wild-type (WT) and C85-deficient S100A1 protein variants in isolated CM demonstrated equal inotropic potency, as shown by equally augmented Ca2+ transient amplitudes under basal conditions and ß-adrenergic receptor (ßAR) stimulation. However, in contrast, ox-PTM defective S100A1 variants failed to protect against arrhythmogenic diastolic sarcoplasmic reticulum (SR) Ca2+ waves and ryanodine receptor 2 (RyR2) hypernitrosylation during ßAR stimulation. Despite diastolic performance failure, C85-deficient S100A1 protein variants exerted similar Ca2+-dependent interaction with the RyR2 than WT-S100A1. Dissecting S100A1's molecular structure-function relationship, our data indicate for the first time that the conserved C85 residue potentially acts as a redox switch that is indispensable for S100A1's antiarrhythmic but not its inotropic potency in CMs. We, therefore, propose a model where C85's ox-PTM determines S100A1's ability to beneficially control diastolic but not systolic RyR2 activity.NEW & NOTEWORTHY S100A1 is an emerging candidate for future gene-therapy treatment of human chronic heart failure. We aimed to study the significance of the conserved single-cysteine 85 (C85) residue in cardiomyocytes. We show that S100A1 is endogenously glutathionylated in the heart and demonstrate that this is dispensable to increase systolic Ca2+ transients, but indispensable for mediating S100A1's protection against sarcoplasmic reticulum (SR) Ca2+ waves, which was dependent on the ryanodine receptor 2 (RyR2) nitrosylation status.

Raising NAD+ Level Stimulates Short-Chain Dehydrogenase/Reductase Proteins to Alleviate Heart Failure Independent of Mitochondrial Protein Deacetylation.

BACKGROUND: Strategies to increase cellular NAD+ (oxidized nicotinamide adenine dinucleotide) level have prevented cardiac dysfunction in multiple models of heart failure, but molecular mechanisms remain unclear. Little is known about the benefits of NAD+-based therapies in failing hearts after the symptoms of heart failure have appeared. Most pretreatment regimens suggested mechanisms involving activation of sirtuin, especially Sirt3 (sirtuin 3), and mitochondrial protein acetylation. METHODS: We induced cardiac dysfunction by pressure overload in SIRT3-deficient (knockout) mice and compared their response with nicotinamide riboside chloride treatment with wild-type mice. To model a therapeutic approach, we initiated the treatment in mice with established cardiac dysfunction. RESULTS: We found nicotinamide riboside chloride improved mitochondrial function and blunted heart failure progression. Similar benefits were observed in wild-type and knockout mice. Boosting NAD+ level improved the function of NAD(H) redox-sensitive SDR (short-chain dehydrogenase/reductase) family proteins. Upregulation of Mrpp2 (mitochondrial ribonuclease P protein 2), a multifunctional SDR protein and a subunit of mitochondrial ribonuclease P, improves mitochondrial DNA transcripts processing and electron transport chain function. Activation of SDRs in the retinol metabolism pathway stimulates RXRα (retinoid X receptor α)/PPARα (proliferator-activated receptor α) signaling and restores mitochondrial oxidative metabolism. Downregulation of Mrpp2 and impaired mitochondrial ribonuclease P were found in human failing hearts, suggesting a shared mechanism of defective mitochondrial biogenesis in mouse and human heart failure. CONCLUSIONS: These findings identify SDR proteins as important regulators of mitochondrial function and molecular targets of NAD+-based therapy. Furthermore, the benefit is observed regardless of Sirt3-mediated mitochondrial protein deacetylation, a widely held mechanism for NAD+-based therapy for heart failure. The data also show that NAD+-based therapy can be useful in pre-existing heart failure.

Branched-chain keto acids inhibit mitochondrial pyruvate carrier and suppress gluconeogenesis in hepatocytes.

Branched-chain amino acid (BCAA) metabolism is linked to glucose homeostasis, but the underlying signaling mechanisms are unclear. We find that gluconeogenesis is reduced in mice deficient of Ppm1k, a positive regulator of BCAA catabolism, which protects against obesity-induced glucose intolerance. Accumulation of branched-chain keto acids (BCKAs) inhibits glucose production in hepatocytes. BCKAs suppress liver mitochondrial pyruvate carrier (MPC) activity and pyruvate-supported respiration. Pyruvate-supported gluconeogenesis is selectively suppressed in Ppm1k-deficient mice and can be restored with pharmacological activation of BCKA catabolism by BT2. Finally, hepatocytes lack branched-chain aminotransferase that alleviates BCKA accumulation via reversible conversion between BCAAs and BCKAs. This renders liver MPC most susceptible to circulating BCKA levels hence a sensor of BCAA catabolism.

Metabolic mechanisms in physiological and pathological cardiac hypertrophy: new paradigms and challenges.

Cardiac metabolism is vital for heart function. Given that cardiac contraction requires a continuous supply of ATP in large quantities, the role of fuel metabolism in the heart has been mostly considered from the perspective of energy production. However, the consequence of metabolic remodelling in the failing heart is not limited to a compromised energy supply. The rewired metabolic network generates metabolites that can directly regulate signalling cascades, protein function, gene transcription and epigenetic modifications, thereby affecting the overall stress response of the heart. In addition, metabolic changes in both cardiomyocytes and non-cardiomyocytes contribute to the development of cardiac pathologies. In this Review, we first summarize how energy metabolism is altered in cardiac hypertrophy and heart failure of different aetiologies, followed by a discussion of emerging concepts in cardiac metabolic remodelling, that is, the non-energy-generating function of metabolism. We highlight challenges and open questions in these areas and finish with a brief perspective on how mechanistic research can be translated into therapies for heart failure.

Upregulation of mitochondrial ATPase inhibitory factor 1 (ATPIF1) mediates increased glycolysis in mouse hearts.

In hypertrophied and failing hearts, fuel metabolism is reprogrammed to increase glucose metabolism, especially glycolysis. This metabolic shift favors biosynthetic function at the expense of ATP production. Mechanisms responsible for the switch are poorly understood. We found that inhibitory factor 1 of the mitochondrial FoF1-ATP synthase (ATPIF1), a protein known to inhibit ATP hydrolysis by the reverse function of ATP synthase during ischemia, was significantly upregulated in pathological cardiac hypertrophy induced by pressure overload, myocardial infarction, or α-adrenergic stimulation. Chemical cross-linking mass spectrometry analysis of hearts hypertrophied by pressure overload suggested that increased expression of ATPIF1 promoted the formation of FoF1-ATP synthase nonproductive tetramer. Using ATPIF1 gain- and loss-of-function cell models, we demonstrated that stalled electron flow due to impaired ATP synthase activity triggered mitochondrial ROS generation, which stabilized HIF1α, leading to transcriptional activation of glycolysis. Cardiac-specific deletion of ATPIF1 in mice prevented the metabolic switch and protected against the pathological remodeling during chronic stress. These results uncover a function of ATPIF1 in nonischemic hearts, which gives FoF1-ATP synthase a critical role in metabolic rewiring during the pathological remodeling of the heart.

Increasing fatty acid oxidation elicits a sex-dependent response in failing mouse hearts.

BACKGROUND: Reduced fatty acid oxidation (FAO) is a hallmark of metabolic remodeling in heart failure. Enhancing mitochondrial long-chain fatty acid uptake by Acetyl-CoA carboxylase 2 (ACC2) deletion increases FAO and prevents cardiac dysfunction during chronic stresses, but therapeutic efficacy of this approach has not been determined. METHODS: Male and female ACC2 f/f-MCM (ACC2KO) and their respective littermate controls were subjected to chronic pressure overload by TAC surgery. Tamoxifen injection 3 weeks after TAC induced ACC2 deletion and increased FAO in ACC2KO mice with pathological hypertrophy. RESULTS: ACC2 deletion in mice with pre-existing cardiac pathology promoted FAO in female and male hearts, but improved cardiac function only in female mice. In males, pressure overload caused a downregulation in the mitochondrial oxidative function. Stimulating FAO by ACC2 deletion caused unproductive acyl-carnitine accumulation, which failed to improve cardiac energetics. In contrast, mitochondrial oxidative capacity was sustained in female pressure overloaded hearts and ACC2 deletion improved myocardial energetics. Mechanistically, we revealed a sex-dependent regulation of PPARα signaling pathway in heart failure, which accounted for the differential response to ACC2 deletion. CONCLUSION: Metabolic remodeling in the failing heart is sex-dependent which could determine the response to metabolic intervention. The findings suggest that both mitochondrial oxidative capacity and substrate preference should be considered for metabolic therapy of heart failure.

Metabolic Remodeling Promotes Cardiac Hypertrophy by Directing Glucose to Aspartate Biosynthesis.

RATIONALE: Hypertrophied hearts switch from mainly using fatty acids (FAs) to an increased reliance on glucose for energy production. It has been shown that preserving FA oxidation (FAO) prevents the pathological shift of substrate preference, preserves cardiac function and energetics, and reduces cardiomyocyte hypertrophy during cardiac stresses. However, it remains elusive whether substrate metabolism regulates cardiomyocyte hypertrophy directly or via a secondary effect of improving cardiac energetics. OBJECTIVE: The goal of this study was to determine the mechanisms of how preservation of FAO prevents the hypertrophic growth of cardiomyocytes. METHODS AND RESULTS: We cultured adult rat cardiomyocytes in a medium containing glucose and mixed-chain FAs and induced pathological hypertrophy by phenylephrine. Phenylephrine-induced hypertrophy was associated with increased glucose consumption and higher intracellular aspartate levels, resulting in increased synthesis of nucleotides, RNA, and proteins. These changes could be prevented by increasing FAO via deletion of ACC2 (acetyl-CoA-carboxylase 2) in phenylephrine-stimulated cardiomyocytes and in pressure overload-induced cardiac hypertrophy in vivo. Furthermore, aspartate supplementation was sufficient to reverse the antihypertrophic effect of ACC2 deletion demonstrating a causal role of elevated aspartate level in cardiomyocyte hypertrophy. 15N and 13C stable isotope tracing revealed that glucose but not glutamine contributed to increased biosynthesis of aspartate, which supplied nitrogen for nucleotide synthesis during cardiomyocyte hypertrophy. CONCLUSIONS: Our data show that increased glucose consumption is required to support aspartate synthesis that drives the increase of biomass during cardiac hypertrophy. Preservation of FAO prevents the shift of metabolic flux into the anabolic pathway and maintains catabolic metabolism for energy production, thus preventing cardiac hypertrophy and improving myocardial energetics.

Fatty Acids Enhance the Maturation of Cardiomyocytes Derived from Human Pluripotent Stem Cells.

Although human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) have emerged as a novel platform for heart regeneration, disease modeling, and drug screening, their immaturity significantly hinders their application. A hallmark of postnatal cardiomyocyte maturation is the metabolic substrate switch from glucose to fatty acids. We hypothesized that fatty acid supplementation would enhance hPSC-CM maturation. Fatty acid treatment induces cardiomyocyte hypertrophy and significantly increases cardiomyocyte force production. The improvement in force generation is accompanied by enhanced calcium transient peak height and kinetics, and by increased action potential upstroke velocity and membrane capacitance. Fatty acids also enhance mitochondrial respiratory reserve capacity. RNA sequencing showed that fatty acid treatment upregulates genes involved in fatty acid ß-oxidation and downregulates genes in lipid synthesis. Signal pathway analyses reveal that fatty acid treatment results in phosphorylation and activation of multiple intracellular kinases. Thus, fatty acids increase human cardiomyocyte hypertrophy, force generation, calcium dynamics, action potential upstroke velocity, and oxidative capacity. This enhanced maturation should facilitate hPSC-CM usage for cell therapy, disease modeling, and drug/toxicity screens.

Glucose promotes cell growth by suppressing branched-chain amino acid degradation.

Glucose and branched-chain amino acids (BCAAs) are essential nutrients and key determinants of cell growth and stress responses. High BCAA level inhibits glucose metabolism but reciprocal regulation of BCAA metabolism by glucose has not been demonstrated. Here we show that glucose suppresses BCAA catabolism in cardiomyocytes to promote hypertrophic response. High glucose inhibits CREB stimulated KLF15 transcription resulting in downregulation of enzymes in the BCAA catabolism pathway. Accumulation of BCAA through the glucose-KLF15-BCAA degradation axis is required for the activation of mTOR signaling during the hypertrophic growth of cardiomyocytes. Restoration of KLF15 prevents cardiac hypertrophy in response to pressure overload in wildtype mice but not in mutant mice deficient of BCAA degradation gene. Thus, regulation of KLF15 transcription by glucose is critical for the glucose-BCAA circuit which controls a cascade of obligatory metabolic responses previously unrecognized for cell growth.

A proteolytic fragment of histone deacetylase 4 protects the heart from failure by regulating the hexosamine biosynthetic pathway.

The stress-responsive epigenetic repressor histone deacetylase 4 (HDAC4) regulates cardiac gene expression. Here we show that the levels of an N-terminal proteolytically derived fragment of HDAC4, termed HDAC4-NT, are lower in failing mouse hearts than in healthy control hearts. Virus-mediated transfer of the portion of the Hdac4 gene encoding HDAC4-NT into the mouse myocardium protected the heart from remodeling and failure; this was associated with decreased expression of Nr4a1, which encodes a nuclear orphan receptor, and decreased NR4A1-dependent activation of the hexosamine biosynthetic pathway (HBP). Conversely, exercise enhanced HDAC4-NT levels, and mice with a cardiomyocyte-specific deletion of Hdac4 show reduced exercise capacity, which was characterized by cardiac fatigue and increased expression of Nr4a1. Mechanistically, we found that NR4A1 negatively regulated contractile function in a manner that depended on the HBP and the calcium sensor STIM1. Our work describes a new regulatory axis in which epigenetic regulation of a metabolic pathway affects calcium handling. Activation of this axis during intermittent physiological stress promotes cardiac function, whereas its impairment in sustained pathological cardiac stress leads to heart failure.

Metabolism in cardiomyopathy: every substrate matters.

Cardiac metabolism is highly adaptive to changes in fuel availability and the energy demand of the heart. This metabolic flexibility is key for the heart to maintain its output during the development and in response to stress. Alterations in substrate preference have been observed in multiple disease states; a clear understanding of their impact on cardiac function in the long term is critical for the development of metabolic therapies. In addition, the contribution of cellular metabolism to growth, survival, and other signalling pathways through the generation of metabolic intermediates has been increasingly noted, adding another layer of complexity to the impact of metabolism on cardiac function. In a quest to understand the complexity of the cardiac metabolic network, genetic tools have been engaged to manipulate cardiac metabolism in a variety of mouse models. The ability to engineer cardiac metabolism in vivo has provided tremendous insights and brought about conceptual innovations. In this review, we will provide an overview of the cardiac metabolic network and highlight alterations observed during cardiac development and pathological hypertrophy. We will focus on consequences of altered substrate preference on cardiac response to chronic stresses through energy providing and non-energy providing pathways.

Defective Branched-Chain Amino Acid Catabolism Disrupts Glucose Metabolism and Sensitizes the Heart to Ischemia-Reperfusion Injury.

Elevated levels of branched-chain amino acids (BCAAs) have recently been implicated in the development of cardiovascular and metabolic diseases, but the molecular mechanisms are unknown. In a mouse model of impaired BCAA catabolism (knockout [KO]), we found that chronic accumulation of BCAAs suppressed glucose metabolism and sensitized the heart to ischemic injury. High levels of BCAAs selectively disrupted mitochondrial pyruvate utilization through inhibition of pyruvate dehydrogenase complex (PDH) activity. Furthermore, downregulation of the hexosamine biosynthetic pathway in KO hearts decreased protein O-linked N-acetylglucosamine (O-GlcNAc) modification and inactivated PDH, resulting in significant decreases in glucose oxidation. Although the metabolic remodeling in KO did not affect baseline cardiac energetics or function, it rendered the heart vulnerable to ischemia-reperfusion injury. Promoting BCAA catabolism or normalizing glucose utilization by overexpressing GLUT1 in the KO heart rescued the metabolic and functional outcome. These observations revealed a novel role of BCAA catabolism in regulating cardiac metabolism and stress response.

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 ß-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.

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.

Heart failure gene therapy: the path to clinical practice.

Gene therapy, aimed at the correction of key pathologies being out of reach for conventional drugs, bears the potential to alter the treatment of cardiovascular diseases radically and thereby of heart failure. Heart failure gene therapy refers to a therapeutic system of targeted drug delivery to the heart that uses formulations of DNA and RNA, whose products determine the therapeutic classification through their biological actions. Among resident cardiac cells, cardiomyocytes have been the therapeutic target of numerous attempts to regenerate systolic and diastolic performance, to reverse remodeling and restore electric stability and metabolism. Although the concept to intervene directly within the genetic and molecular foundation of cardiac cells is simple and elegant, the path to clinical reality has been arduous because of the challenge on delivery technologies and vectors, expression regulation, and complex mechanisms of action of therapeutic gene products. Nonetheless, since the first demonstration of in vivo gene transfer into myocardium, there have been a series of advancements that have driven the evolution of heart failure gene therapy from an experimental tool to the threshold of becoming a viable clinical option. The objective of this review is to discuss the current state of the art in the field and point out inevitable innovations on which the future evolution of heart failure gene therapy into an effective and safe clinical treatment relies.

S100A1 deficiency impairs postischemic angiogenesis via compromised proangiogenic endothelial cell function and nitric oxide synthase regulation.

RATIONALE: Mice lacking the EF-hand Ca2+ sensor S100A1 display endothelial dysfunction because of distorted Ca2+ -activated nitric oxide (NO) generation. OBJECTIVE: To determine the pathophysiological role of S100A1 in endothelial cell (EC) function in experimental ischemic revascularization. METHODS AND RESULTS: Patients with chronic critical limb ischemia showed almost complete loss of S100A1 expression in hypoxic tissue. Ensuing studies in S100A1 knockout (SKO) mice subjected to femoral artery resection unveiled insufficient perfusion recovery and high rates of autoamputation. Defective in vivo angiogenesis prompted cellular studies in SKO ECs and human ECs, with small interfering RNA-mediated S100A1 knockdown demonstrating impaired in vitro and in vivo proangiogenic properties (proliferation, migration, tube formation) and attenuated vascular endothelial growth factor (VEGF)-stimulated and hypoxia-stimulated endothelial NO synthase (eNOS) activity. Mechanistically, S100A1 deficiency compromised eNOS activity in ECs by interrupted stimulatory S100A1/eNOS interaction and protein kinase C hyperactivation that resulted in inhibitory eNOS phosphorylation and enhanced VEGF receptor-2 degradation with attenuated VEGF signaling. Ischemic SKO tissue recapitulated the same molecular abnormalities with insufficient in vivo NO generation. Unresolved ischemia entailed excessive VEGF accumulation in SKO mice with aggravated VEGF receptor-2 degradation and blunted in vivo signaling through the proangiogenic phosphoinositide-3-kinase/Akt/eNOS cascade. The NO supplementation strategies rescued defective angiogenesis and salvaged limbs in SKO mice after femoral artery resection. CONCLUSIONS: Our study shows for the first time downregulation of S100A1 expression in patients with critical limb ischemia and identifies S100A1 as critical for EC function in postnatal ischemic angiogenesis. These findings link its pathological plasticity in critical limb ischemia to impaired neovascularization, prompting further studies to probe the microvascular therapeutic potential of S100A1.

S100A1 gene therapy for heart failure: a novel strategy on the verge of clinical trials.

Representing the common endpoint of various cardiovascular disorders, heart failure (HF) shows a dramatically growing prevalence. As currently available therapeutic strategies are not capable of terminating the progress of the disease, HF is still associated with a poor clinical prognosis. Among the underlying molecular mechanisms, the loss of cardiomyocyte Ca(2+) cycling integrity plays a key role in the pathophysiological development and progression of the disease. The cardiomyocyte EF-hand Ca(2+) sensor protein S100A1 emerged as a regulator both of sarcoplasmic reticulum (SR), sarcomere and mitochondrial function implicating a significant role in cardiac physiology and dysfunction. In this review, we aim to recapitulate the translation of S100A1-based investigation from first clinical observations over basic research experiments back to a near-clinical setting on the verge of clinical trials today. We also address needs for further developments towards "second-generation" gene therapy and discuss the therapeutic potential of S100A1 gene therapy for HF as a promising novel strategy for future cardiologists. This article is part of a Special Section entitled "Special Section: Cardiovascular Gene Therapy".