S100A1 acts positive inotropic and prevents Ca2+ triggered after-contractions in a model of Engineered Heart Tissue

The small calcium (Ca2+) binding protein S100A1 is as a critical regulator of cardiomyocyte Ca2+ handling thereby enhancing cardiac performance in vivo and in vitro. Our previous studies demonstrated that the positive inotropic effects of S100A1 are due to enhanced Ca2+ transients and sarcoplasmic reticulum (SR) Ca2+ load in isolated adult cardiomyocytes. These effects are independent of and in addition to cAMP-dependent positive inotropic mechanisms. However, inotropic interventions come at the risk of arrhythmogenic diastolic Ca2+ leakage when the SR Ca2+ content exceeds the threshold for spontaneous diastolic Ca2+ release. In a more recent study we could demonstrate that enhanced Ca2+ transients after S100A1 overexpression are associated with a reduced incidence of diastolic Ca2+ sparks and Ca2+ waves. These results favor the assumption that S100A1 might reduce the diastolic RyR2 leak, thereby impeding the development of pro-arrhythmogenic events. Thus, the aim of this work was to investigate the effect of S100A1 on diastolic Ca2+ handling and on the impact of Ca2+-triggered arrhythmias in a multicellular system. For this reason, the 3-dimensional tissue culture model of Engineered Heart Tissue (EHT) was chosen. Due to its syncytial architecture, EHT closely mimics functional alterations, intercellular communication and reverse remodeling of whole hearts in vivo despite eased handling and pharmacological as well as therapeutic manipulations. Pharmacological stimulation of EHT with endothelin-1 resulted in a heart failure-like phenotype with strong impairment of contractile performance. Adenoviral-mediated S100A1 overexpression was able to rescue failing EHT and resulted in superior contractility in normal EHT. Triggered contraction abnormalities, referred to as after-contractions, were induced by Ca2+ and β-AR stimulation and served as a surrogate of SOICR (store-overload-induced-Ca2+-release). S100A1 overexpression significantly protected against Ca2+ and β-adrenergic receptor (β-AR) triggered after-contractions in normal and failing EHT. Despite persistent abnormal phosphorylation-dependent changes at the RyR2 and altered complex formation with accessory proteins, S100A1 overexpression enhanced S100A1/RyR2 stoichiometry, which seems to be key for S100A1’s effects, combining inotropic and anti-arrhythmic potency

S100A1: A Multifaceted Therapeutic Target in Cardiovascular Disease

Cardiovascular disease is the leading cause of death worldwide, showing a dramatically growing prevalence. It is still associated with a poor clinical prognosis, indicating insufficient long-term treatment success of currently available therapeutic strategies. Investigations of the pathomechanisms underlying cardiovascular disorders uncovered the Ca2+ binding protein S100A1 as a critical regulator of both cardiac performance and vascular biology. In cardiomyocytes, S100A1 was found to interact with both the sarcoplasmic reticulum ATPase (SERCA2a) and the ryanodine receptor 2 (RyR2), resulting in substantially improved Ca2+ handling and contractile performance. Additionally, S100A1 has been described to target the cardiac sarcomere and mitochondria, leading to reduced pre-contractile passive tension as well as enhanced oxidative energy generation. In endothelial cells, molecular analyses revealed a stimulatory effect of S100A1 on endothelial NO production by increasing endothelial nitric oxide synthase activity. Emphasizing the pathophysiological relevance of S100A1, myocardial infarction in S100A1 knockout mice resulted in accelerated transition towards heart failure and excessive mortality in comparison with wild-type controls. Mice lacking S100A1 furthermore displayed significantly elevated blood pressure values with abrogated responsiveness to bradykinin. On the other hand, numerous studies in small and large animal heart failure models showed that S100A1 overexpression results in reversed maladaptive myocardial remodeling, long-term rescue of contractile performance, and superior survival in response to myocardial infarction, indicating the potential of S100A1-based therapeutic interventions. In summary, elaborate basic and translational research established S100A1 as a multifaceted therapeutic target in cardiovascular disease, providing a promising novel therapeutic strategy to future cardiologists

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"

Gene therapy targets in heart failure: the path to translation

Heart failure (HF) is the common end point of cardiac diseases. Despite the optimization of therapeutic strategies and the consequent overall reduction in HF-related mortality, the key underlying intracellular signal transduction abnormalities have not been addressed directly. In this regard, the gaps in modern HF therapy include derangement of β-adrenergic receptor (β-AR) signaling, Ca(2+) disbalances, cardiac myocyte death, diastolic dysfunction, and monogenetic cardiomyopathies. In this review we discuss the potential of gene therapy to fill these gaps and rectify abnormalities in intracellular signaling. We also examine current vector technology and currently available vector-delivery strategies, and related to the transfer of successful preclinical gene therapy approaches to HF treatment in the clinic, as well as impending strategies aimed at overcoming these limitations

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

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

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

The WD40-repeat protein Han11 functions as a scaffold protein to control HIPK2 and MEKK1 kinase functions

Han11 (also called WDR68/DCAF7) is described as novel scaffolding protein that regulates osmotic stress in both human cells and C.elegans by virtue of its interaction with MEKK1, Dyrk1 and HIPK2