Transcriptional regulation of S100A1 and expression during mouse heart development

scParser: sparse representation learning for scalable single-cell RNA sequencing data analysis

The rapid rise in the availability and scale of scRNA-seq data needs scalable methods for integrative analysis. Though many methods for data integration have been developed, few focus on understanding the heterogeneous effects of biological conditions across different cell populations in integrative analysis. Our proposed scalable approach, scParser, models the heterogeneous effects from biological conditions, which unveils the key mechanisms by which gene expression contributes to phenotypes. Notably, the extended scParser pinpoints biological processes in cell subpopulations that contribute to disease pathogenesis. scParser achieves favorable performance in cell clustering compared to state-of-the-art methods and has a broad and diverse applicability.

S100A1 expression characterizes terminally differentiated superficial cells in the urothelium of the murine bladder and ureter

The urothelium is a stratified epithelium that lines the inner surface of the components of the urinary drainage system. It is composed of a layer of basal cells, one or several layers of intermediate cells, and a layer of large luminal superficial or umbrella cells. In the mouse, only a small set of markers is available that allows easy molecular distinction of these urothelial cell types. Here, we analyzed expression of S100A1, a member of the S100 family of calcium-binding proteins, in the urothelium of the two major organs of the murine urinary tract, the ureter and the bladder. Using RNA in situ hybridization analysis, we found exclusive expression of S100a1 mRNA in luminal cells of the ureter from embryonic day (E)17.5 onwards and of the bladder from E15.5 to adulthood. Immunofluorescence analysis showed that expression of S100A1 protein is confined to terminally differentiated superficial cells of both the ureter and bladder where it localized to the nucleus and cytoplasm. We conclude that S100A1 is a suitable marker for mature superficial cells in the urothelial lining of the drainage system of the developing and mature mouse.

S100A1 as a potential biomarker for the diagnosis of patients with acute aortic dissection

Objective

Acute aortic dissection (AAD) is a common life-threatening cardiovascular disease. This retrospective study was conducted to analyze the plasma concentration of S100A1 and its diagnostic value for AAD through receiver operating characteristic (ROC) curve and logistic regression analyses.

Methods

Seventy-eight patients with AAD and 77 healthy controls were included, and the relevant clinical data for each group were collected. According to the Stanford classification, the AAD patients were divided into types A and B. The plasma levels of S100A1, D-dimer, hypersensitive C-reactive protein, and cardiac troponin T were detected by enzyme-linked immunosorbent assays.

Results

The S100A1 concentrations in the healthy control, Stanford A, and Stanford B groups were 0.7 ± 0.6, 4.9 ± 2.6, and 3.5 ± 2.2 ng/mL, respectively. The concentration of S100A1 was increased in patients with AAD complicated with aortic regurgitation, pericardial effusion, or in-hospital death. ROC curve analysis showed that the area under the curve was 0.89. Logistic regression analysis revealed that the S100A1 level was an important risk factor for the development of AAD.

Conclusion

Plasma S100A1 is significantly elevated in patients with AAD, and its concentration has potential clinical value for diagnosing AAD.

Targeting S100B Protein as a Surrogate Biomarker and its Role in Various Neurological Disorders

Neurological disorders (ND) are the central nervous system (CNS) related complications originated by enhanced oxidative stress, mitochondrial failure and overexpression of proteins like S100B. S100B is a helix-loop-helix protein with the calcium-binding domain associated with various neurological disorders through activation of the MAPK pathway, increased NF-kB expression resulting in cell survival, proliferation and gene up-regulation. S100B protein plays a crucial role in Alzheimer's disease, Parkinson's disease, multiple sclerosis, Schizophrenia and epilepsy because the high expression of this protein directly targets astrocytes and promotes neuroinflammation. Under stressful conditions, S100B produces toxic effects mediated through receptor for advanced glycation end products (AGE) binding. S100B also mediates neuroprotection, minimizes microgliosis and reduces the expression of tumor necrosis factor (TNF-alpha) but that are concentration- dependent mechanisms. Increased level of S100B is useful for assessing the release of inflammatory markers, nitric oxide and excitotoxicity dependent neuronal loss. The present review summarizes the role of S100B in various neurological disorders and potential therapeutic measures to reduce the prevalence of neurological disorders.

Liposomal Resveratrol and/or Carvedilol Attenuate Doxorubicin-Induced Cardiotoxicity by Modulating Inflammation, Oxidative Stress and S100A1 in Rats

Doxorubicin (DOX) is a cytotoxic anthracycline antibiotic and one of the important chemotherapeutic agents for different types of cancers. DOX treatment is associated with adverse effects, particularly cardiac dysfunction. This study examined the cardioprotective effects of carvedilol (CAR) and/or resveratrol (RES) and liposomal RES (LIPO-RES) against DOX-induced cardiomyopathy, pointing to their modulatory effect on oxidative stress, inflammation, S100A1 and sarco/endoplasmic reticulum calcium ATPase2a (SERCA2a). Rats received CAR (30 mg/kg) and/or RES (20 mg/kg) or LIPO-RES (20 mg/kg) for 6 weeks and were challenged with DOX (2 mg/kg) twice per week from week 2 to week 6. DOX-administered rats exhibited a significant increase in serum creatine kinase-MB (CK-MB), troponin-I and lactate dehydrogenase (LDH) along with histological alterations, reflecting cardiac cell injury. Cardiac toll-like receptor 4 (TLR-4), inducible nitric oxide synthase (iNOS), tumor necrosis factor (TNF)-α and interleukin (IL)-6 protein expression were up-regulated, and lipid peroxidation was increased in DOX-administered rats. Treatment with CAR, RES or LIPO-RES as well as their alternative combinations ameliorated all observed biochemical and histological alterations with the most potent effect exerted by CAR/LIPO-RES. All treatments increased cardiac antioxidants, and the expression of S100A1 and SERCA2a. In conclusion, the present study conferred new evidence on the protective effects of CAR and its combination with either RES or LIPO-RES on DOX-induced inflammation, oxidative stress and calcium dysregulation.

Understanding Calcium-Dependent Conformational Changes in S100A1 Protein: A Combination of Molecular Dynamics and Gene Expression Study in Skeletal Muscle

The S100A1 protein, involved in various physiological activities through the binding of calcium ions (Ca²⁺), participates in several protein-protein interaction (PPI) events after Ca²⁺-dependent activation. The present work investigates Ca²⁺-dependent conformational changes in the helix-EF hand-helix using the molecular dynamics (MD) simulation approach that facilitates the understanding of Ca²⁺-dependent structural and dynamic distinctions between the apo and holo forms of the protein. Furthermore, the process of ion binding by inserting Ca²⁺ into the bulk of the apo structure was simulated by molecular dynamics. Expectations of the simulation were demonstrated using cluster analysis and a variety of structural metrics, such as interhelical angle estimation, solvent accessible surface area, hydrogen bond analysis, and contact analysis. Ca²⁺ triggered a rise in the interhelical angles of S100A1 on the binding site and solvent accessible surface area. Significant configurational regulations were observed in the holo protein. The findings would contribute to understanding the molecular basis of the association of Ca²⁺ with the S100A1 protein, which may be an appropriate study to understand the Ca²⁺-mediated conformational changes in the protein target. In addition, we investigated the expression profile of S100A1 in myoblast differentiation and muscle regeneration. These data showed that S100A1 is expressed in skeletal muscles. However, the expression decreases with time during the process of myoblast differentiation.

B-type natriuretic peptide and its role in altering Ca2+-regulatory proteins in heart failure-mechanistic insights

Heart failure (HF) is a worldwide disease with high levels of morbidity and mortality. The pathogenesis of HF is complicated and involves imbalances in hormone and electrolyte. B-type natriuretic peptide (BNP) has served as a biomarker of HF severity, and in recent years, it has been used to treat the disease, thanks to its cardio-protective effects, such as diuresis, natriuresis, and vasodilatation. In stage C/D HF, symptoms are severe despite elevated BNP. Disturbances in Ca²⁺ homeostasis are often a dominating feature of the disease, causing Ca²⁺-regulatory protein dysfunction, including reduced expression and activity of sarcoplasmic reticulum Ca²⁺-ATPase2a (SERCA2a), impaired ryanodine receptors (RYRs) function, intensive Na⁺-Ca²⁺ exchanger (NCX), and downregulation of S100A1. The relationship between natriuretic peptides (NPs) and Ca²⁺-regulatory proteins has been widely studied and represents important mechanisms in the etiology of HF. In this review, we present evidence that BNP may regulate Ca²⁺-regulatory proteins, in particular, suppressing SERCA2a and S100A1 expression. However, relationships between BNP and other Ca²⁺-regulatory proteins remain vague.

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.

Altered myocardial calcium cycling and energetics in heart failure--a rational approach for disease treatment

Cardiomyocyte function depends on coordinated movements of calcium into and out of the cell and the proper delivery of ATP to energy-utilizing enzymes. Defects in calcium-handling proteins and abnormal energy metabolism are features of heart failure. Recent discoveries have led to gene-based therapies targeting calcium-transporting or -binding proteins, such as the cardiac sarco(endo)plasmic reticulum calcium ATPase (SERCA2a), leading to improvements in calcium homeostasis and excitation-contraction coupling. Here we review impaired calcium cycling and energetics in heart failure, assessing their roles from both a mutually exclusive and interdependent viewpoint, and discuss therapies that may improve the failing myocardium.

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.

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.

Associations between two genetic variants in NKX2-5 and risk of congenital heart disease in Chinese population: a meta-analysis

Background

NKX2-5 is a transcriptional factor, which plays an important role in heart formation and development. Two genetic variants in the coding region of NKX2-5, 63A>G (rs2277923) and 606G>C (rs3729753), have been investigated in the risk of congenital heart disease (CHD), although with inconsistent results. Thus, a meta-analysis was performed to clarify the associations between the two variants and CHD risk in the Chinese population.

Methods and Results

Relevant studies were identified by searching PubMed, ISI Web of Science and CNKI databases and by reviewing the reference lists of retrieved articles. Then, the data from eligible studies were combined in an allelic model. A total of 7 and 4 studies were ultimately included for 63A>G and 606G>C, respectively. The results of overall meta-analyses showed that significant association was detected for 63A>G (OR = 1.26, 95% CI = 1.02–1.56, P_{heterogeneity} = 0.009, I² = 65.1%), but not for 606G>C (OR = 1.22, 95% CI = 0.75–1.96, P_{heterogeneity} = 0.412, I² = 0.0%). Regarding 63A>G variant, positive results were also obtained in the subgroups of atrial septal defect and large-sample-size study. Besides, the sensitivity analysis indicated that significant association was still detected after deletion of the individual studies with positive result and striking heterogeneity.

Conclusion

Our results revealed that the 63A>G variant in NKX2-5, but not the 606G>C, may contribute to CHD risk for Chinese.

Molecular evolution of a novel marsupial S100 protein (S100A19) which is expressed at specific stages of mammary gland and gut development

S100 proteins are calcium-binding proteins involved in controlling diverse intracellular and extracellular processes such as cell growth, differentiation, and antimicrobial function. We recently identified a S100-like cDNA from the tammar wallaby (Macropus eugenii) stomach. Phylogentic analysis shows wallaby S100A19 forms a new clade with other marsupial and monotreme S100A19, while this group shows similarity to eutherian S100A7 and S100A15 genes. This is also supported by amino acid and domain comparisons. We show S100A19 is developmentally-regulated in the tammar wallaby gut by demonstrating the gene is expressed in the forestomach of young animals at a time when the diet consists of only milk, but is absent in older animals when the diet is supplemented with herbage. During this transition the forestomach phenotype changes from a gastric stomach into a fermentation sac and intestinal flora changes with diet. We also show that S100A19 is expressed in the mammary gland of the tammar wallaby only during specific stages of lactation; the gene is up-regulated during pregnancy and involution and not expressed during the milk production phase of lactation. Comparison of the tammar wallaby S100A19 protein sequence with S100 protein sequences from eutherian, monotreme and other marsupial species suggest the marsupial S100A19 has two functional EF hand domains, and an extended His tail. An evolutionary analysis of S100 family proteins was carried out to gain a better understanding of the relationship between the S100 family member functions. We propose that S100A19 gene/protein is the ancestor of the eutherian S100A7 gene/protein, which has subsequently modified its original function in eutherians. This modified function may have arisen due to differentiation of evolutionary pressures placed on gut and mammary gland developmental during mammal evolution. The highly regulated differential expression patterns of S100A19 in the tammar wallaby suggests that S100A19 may play a role in gut development, which differs between metatherians and eutherians, and/or include a potential antibacterial role in order to establish the correct flora and protect against spiral bacteria in the immature forestomach. In the mammary gland it may protect the tissue from infection at times of vulnerability during the lactation cycle.

Immunohistochemical detection of S100A1 in the postmortem diagnosis of acute myocardial infarction

Background

Sudden cardiac death resulting from acute myocardial infarction (AMI) constitutes a significant percentage of the caseload for forensic and clinical pathologists. When sudden death occurs at an early stage (<6 h), pathologists experience difficulty in the postmortem diagnosis of AMI. Because of the specific tissue distribution of S100A1 and its relationship with acute ischemic heart disease, this study aimed to evaluate the performance of S100A1 in the postmortem diagnosis of AMI.

Methods

We constructed a rat model of AMI through permanent ligation of the left anterior descending coronary artery (LAD) to investigate the depletion of S100A1 from ischemic cardiomyocytes by immunohistochemistry and measuring S100A1 plasma concentrations by enzyme-linked immunosorbent assay at varying post-infarction intervals. In addition, immunohistochemical staining of S100A1 for definite infarction, suspected early infarction, and in normal human hearts, was also performed to test its practical feasibility for postmortem diagnosis of AMI at an early stage.

Results

As early as 15 min after ligation of the LAD, depletion of S100A1 was observed in ischemic cardiomyocytes, and S100A1 plasma concentration was also significantly higher than that of the sham-operated group (P < 0.001). With continuation of the occlusion time, the depleted areas of S100A1 further expanded and S100A1 plasma concentrations further increased. For autopsy material, all human cases of definite myocardial infarction and suspected early infarction showed well-defined areas without S100A1 staining. None of the normal human cases showed diffuse depletion of S100A1.

Conclusion

Our results suggest that immunohistochemical detection of S100A1 is useful for the postmortem diagnosis of AMI at an early stage.

Virtual slides

The virtual slide(s) for this article can be found here:

http://www.diagnosticpathology.diagnomx.eu/vs/4366650979519818

Altered sarcoplasmic reticulum calcium cycling--targets for heart failure therapy

Cardiac myocyte function is dependent on the synchronized movements of Ca(2+) into and out of the cell, as well as between the cytosol and sarcoplasmic reticulum. These movements determine cardiac rhythm and regulate excitation-contraction coupling. Ca(2+) cycling is mediated by a number of critical Ca(2+)-handling proteins and transporters, such as L-type Ca(2+) channels (LTCCs) and sodium/calcium exchangers in the sarcolemma, and sarcoplasmic/endoplasmic reticulum calcium ATPase 2a (SERCA2a), ryanodine receptors, and cardiac phospholamban in the sarcoplasmic reticulum. The entry of Ca(2+) into the cytosol through LTCCs activates the release of Ca(2+) from the sarcoplasmic reticulum through ryanodine receptor channels and initiates myocyte contraction, whereas SERCA2a and cardiac phospholamban have a key role in sarcoplasmic reticulum Ca(2+) sequesteration and myocyte relaxation. Excitation-contraction coupling is regulated by phosphorylation of Ca(2+)-handling proteins. Abnormalities in sarcoplasmic reticulum Ca(2+) cycling are hallmarks of heart failure and contribute to the pathophysiology and progression of this disease. Correcting impaired intracellular Ca(2+) cycling is a promising new approach for the treatment of heart failure. Novel therapeutic strategies that enhance myocyte Ca(2+) homeostasis could prevent and reverse adverse cardiac remodeling and improve clinical outcomes in patients with heart failure.

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".

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 Ca(2+) 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 Ca(2+) 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: a pluripotent regulator of cardiac and vascular function

S100A1, a small EF-hand Ca(2+)-binding protein with intracellular and extracellular functions, is predominantly expressed in cardiac muscle where it plays a crucial role as a modulator of Ca(2+) homeostasis, energy metabolism and contractile performance. Essentially, its beneficial effects on heart function have been attributed to its direct interaction with, and effects on, sarcoplasmic reticulum calcium handling proteins sarco(endo) plasmic reticulum Ca(2+) ATPase and the ryanodine receptor. Downregulated levels of S100A1 in cardiomyocytes postmyocardial infarction have been linked to diminished cardiac reserve and contribute to the development of heart failure. Interestingly, S100A1 expression has recently been described in endothelial cells where it is downregulated in heart failure and has been shown to modulate intracellular Ca(2+) levels and nitric oxide production. Absence of the Ca(2+) sensor protein in endothelial cells is associated with endothelial dysfunction and hypertension. Thus, S100A1 is emerging as a potential therapeutic target for diverse cardiovascular conditions.

S100A1: a regulator of striated muscle sarcoplasmic reticulum Ca2+ handling, sarcomeric, and mitochondrial function

Calcium (Ca²⁺) signaling plays a key role in a wide range of physiological functions including control of cardiac and skeletal muscle performance. To assure a precise coordination of both temporally and spatially transduction of intracellular Ca²⁺ oscillations to downstream signaling networks and target operations, Ca²⁺ cycling regulation in muscle tissue is conducted by a plethora of diverse molecules. Ca²⁺ S100A1 is a member of the Ca²⁺-binding S100 protein family and represents the most abundant S100 isoform in cardiac and skeletal muscle. Early studies revealed distinct expression patterns of S100A1 in healthy and diseased cardiac tissue from animal models and humans. Further elaborate investigations uncovered S100A1 protein as a basic requirement for striated muscle Ca²⁺ handling integrity. S100A1 is a critical regulator of cardiomyocyte Ca²⁺ cycling and contractile performance. S100A1-mediated inotropy unfolds independent and on top of βAR-stimulated contractility with unchanged βAR downstream signaling. S100A1 has further been detected at different sites within the cardiac sarcomere indicating potential roles in myofilament function. More recently, a study reported a mitochondrial location of S100A1 in cardiomyocytes. Additionally, normalizing the level of S100A1 protein by means of viral cardiac gene transfer in animal heart failure models resulted in a disrupted progression towards cardiac failure and enhanced survival. This brief review is confined to the physiological and pathophysiological relevance of S100A1 in cardiac and skeletal muscle Ca²⁺ handling with a particular focus on its potential as a molecular target for future therapeutic interventions.

S100A1 in cardiovascular health and disease: closing the gap between basic science and clinical therapy

Calcium (Ca(2+)) signaling plays a major role in a wide range of physiological functions including control and regulation of cardiac and skeletal muscle performance and vascular tone. As all Ca(2+) signals require proteins to relay intracellular Ca(2+) oscillations downstream to different signaling networks, a specific toolkit of Ca(2+)-sensor proteins involving members of the EF-hand S100 Ca(2+) binding protein superfamily maintains the integrity of the Ca(2+) signaling in a variety of cardiac and vascular cells, transmitting the message with great precision and in a temporally and spatially coordinated manner. Indeed, the possibility that S100 proteins might contribute to heart and vascular diseases was first suggested by the discovery of distinctive patterns of S100 expression in healthy and diseased hearts and vasculature from humans and animal heart failure (HF) models. Based on more elaborate genetic studies in mice and strategies to manipulate S100 protein expression in human cardiac, skeletal muscle and vascular cells, it is now apparent that the integrity of distinct S100 protein isoforms in striated muscle and vascular cells such as S100A1, S100A4, S100A6, S100A8/A9 or S100B is a basic requirement for normal cardiovascular and muscular development and function; loss of integrity would naturally lead to profound deregulation of the implicated Ca(2+) signaling systems with detrimental consequences to cardiac, skeletal muscle, and vascular function. The brief debate and discussion here are confined by design to the biological actions and pathophysiological relevance of the EF-hand Ca(2+)-sensor protein S100A1 in the heart, vasculature and skeletal muscle with a particular focus on current translational therapeutic strategies. By virtue of its ability to modulate the activity of numerous key effector proteins that are essentially involved in the control of Ca(2+) and NO homeostasis in cardiac, skeletal muscle and vascular cells, S100A1 has been proven to play a critical role both in cardiac performance, blood pressure regulation and skeletal muscle function. Given that deregulated S100A1 expression in cardiomyocytes and endothelial cells has recently been linked to heart failure and hypertension, it is arguably a molecular target of considerable clinical interest as S100A1 targeted therapies have already been successfully investigated in preclinical translational studies.

S100A1: Structure, Function, and Therapeutic Potential

S100A1 is a member of the S100 family of calcium-binding proteins. As with most S100 proteins, S100A1 undergoes a large conformational change upon binding calcium as necessary to interact with numerous protein targets. Targets of S100A1 include proteins involved in calcium signaling (ryanidine receptors 1 & 2, Serca2a, phopholamban), neurotransmitter release (synapsins I & II), cytoskeletal and filament associated proteins (CapZ, microtubules, intermediate filaments, tau, mocrofilaments, desmin, tubulin, F-actin, titin, and the glial fibrillary acidic protein GFAP), transcription factors and their regulators (e.g. myoD, p53), enzymes (e.g. aldolase, phosphoglucomutase, malate dehydrogenase, glycogen phosphorylase, photoreceptor guanyl cyclases, adenylate cyclases, glyceraldehydes-3-phosphate dehydrogenase, twitchin kinase, Ndr kinase, and F1 ATP synthase), and other Ca2+-activated proteins (annexins V & VI, S100B, S100A4, S100P, and other S100 proteins). There is also a growing interest in developing inhibitors of S100A1 since they may be beneficial for treating a variety of human diseases including neurological diseases, diabetes mellitus, heart failure, and several types of cancer. The absence of significant phenotypes in S100A1 knockout mice provides some early indication that an S100A1 antagonist could have minimal side effects in normal tissues. However, development of S100A1-mediated therapies is complicated by S100A1's unusual ability to function as both an intracellular signaling molecule and as a secreted protein. Additionally, many S100A1 protein targets have only recently been identified, and so fully characterizing both these S100A1-target complexes and their resulting functions is a necessary prerequisite.

S100A1: a novel inotropic regulator of cardiac performance. Transition from molecular physiology to pathophysiological relevance

Here we review the considerable body of evidence that has accumulated to support the notion of S100A1, a cardiac-specific Ca2+-sensor protein of the EF-hand type, as a physiological regulator of excitation-contraction coupling and inotropic reserve mechanisms in the mammalian heart. In particular, molecular mechanisms will be discussed conveying the Ca2+-dependent inotropic actions of S100A1 protein in cardiomyocytes occurring independently of β-adrenergic signaling. Moreover, we will shed light on the molecular structure-function relationship of S100A1 with its cardiac target proteins at the sarcoplasmic reticulum, the sarcomere, and the mitochondria. Furthermore, pathophysiological consequences of disturbed S100A1 protein expression on altered Ca2+handling and intertwined systems in failing myocardium will be highlighted. Subsequently, therapeutic options by means of genetic manipulation of cardiac S100A1 expression will be discussed, aiming to complete our current understanding of the role of S100A1 in diseased myocardium.

Regulation of Na+/Ca2+ exchange current in the normal and failing heart

Cardiac NCX is modulated by diverse regulatory elements. Although there is consensus about the regulatory function of Na+ and Ca2+ and other elements, for example, ATP, there is still a controversial debate about the functional role of cyclic nucleotides and protein kinases. Future studies should focus on that topic since disturbances of cAMP/cGMP concentration and kinase activity may lead to severe functional disorders in the diseased heart. S100A1 is presumably a novel regulator of NCX.

S100A1 decreases calcium spark frequency and alters their spatial characteristics in permeabilized adult ventricular cardiomyocytes

S100A1, a Ca2+-sensor protein of the EF-hand type, exerts positive inotropic effects in the heart via enhanced cardiac ryanodine receptor (RyR2) activity. Here we report that S100A1 protein (0.1microM) interacts with the RyR2 in resting permeabilized cardiomyocytes at free Ca2+-levels comparable to diastolic Ca2+-concentrations ( approximately 150nM). Alterations of RyR2 function due to S100A1 binding was assessed via analysis of Ca2+-spark characteristics. Ca2+-spark frequency, amplitude and duration were all reduced upon perfusion with 0.1microM S100A1 protein by 38%, 14% and 18%, respectively. Most likely, these effects were conveyed through the S100A1 C-terminus (S100A1-ct; amino acids 75-94) as the corresponding S100A1-ct peptide (0.1microM) inhibited S100A1 protein binding to the RyR2 and similarly attenuated frequency, amplitude and duration of Ca2+-sparks by 52%, 8% and 26%, respectively. Accordingly, the sarcoplasmic reticulum (SR) Ca2+-content was slightly increased but the stoichiometry of other accessory RyR2 modulators (sorcin/FKBP12.6) remained unaltered by S100A1. Hence, we propose S100A1 as a novel inhibitory modulator of RyR2 function at diastolic Ca2+-concentrations in rabbit ventricular cardiomyocytes.

Pathologies involving the S100 proteins and RAGE

The S100 proteins are exclusively expressed in vertebrates and are the largest subgroup within the superfamily of EF-hand Ca2(+)-binding proteins Generally, S100 proteins are organized as tight homodimers (some as heterodimers). Each subunit is composed of a C-terminal, 'canonical' EF-hand, common to all EF-hand proteins, and a N-terminal, 'pseudo' EF-hand, characteristic of S100 proteins. Upon Ca2(+)-binding, the C-terminal EF-hand undergoes a large conformational change resulting in the exposure of a hydrophobic surface responsible for target binding A unique feature of this protein family is that some members are secreted from cells upon stimulation, exerting cytokine- and chemokine-like extracellular activities via the Receptor for Advanced Glycation Endproducts, RAGE. Recently, larger assemblies of some S100 proteins (hexamers, tetramers, octamers) have been also observed and are suggested to be the active extracellular species required for receptor binding and activation through receptor multimerization Most S100 genes are located in a gene cluster on human chromosome 1q21, a region frequently rearranged in human cancer The functional diversification of S100 proteins is achieved by their specific cell- and tissue-expression patterns, structural variations, different metal ion binding properties (Ca2+, Zn2+ and Cu2+) as well as their ability to form homo-, hetero- and oligomeric assemblies Here, we review the most recent developments focussing on the biological functions of the S100 proteins and we discuss the presently available S100-specific mouse models and their possible use as human disease models In addition, the S100-RAGE interaction and the activation of various cellular pathways will be discussed. Finally, the close association of S100 proteins with cardiomyopathy, cancer, inflammation and brain diseases is summarized as well as their use in diagnosis and their potential as drug targets to improve therapies in the future.

S100A1 enhances the L-type Ca2+ current in embryonic mouse and neonatal rat ventricular cardiomyocytes

S100A1 is an EF-hand type Ca2+-binding protein with a muscle-specific expression pattern. The highest S100A1 protein levels are found in cardiomyocytes, and it is expressed already at day 8 in the heart during embryonic development. Since S100A1 is known to be involved in the regulation of Ca2+ homeostasis, we tested whether extracellular S100A1 plays a role in regulating the L-type Ca2+ current (I(Ca)) in ventricular cardiomyocytes. Murine embryonic (day 16.5 postcoitum) ventricular cardiomyocytes were incubated with S100A1 (0.001-10 microM) for different time periods (20 min to 48 h). I(Ca) density was found to be significantly increased as early as 20 min (from -10.8 +/- 1 pA/pF, n = 18, to -22.9 +/- 1.4 pA/pF; +112.5 +/- 13%, n = 9, p < 0.001) after the addition of S100A1 (1 microM). S100A1 also enhanced I(Ca) current density in neonatal rat cardiomyocytes. Fluorescence and capacitance measurements evidenced a fast translocation of rhodamine-coupled S100A1 from the extracellular space into cardiomyocytes. S100A1 treatment did not affect cAMP levels. However, protein kinase inhibitor, a blocker of cAMP-dependent protein kinase A (PKA), abolished the S100A1-induced enhancement of I(Ca). Accordingly, measurements of PKA activity yielded a significant increase in S100A1-treated cardiomyocytes. In vitro reconstitution assays further demonstrated that S100A1 enhanced PKA activity. We conclude that the Ca2+-binding protein S100A1 augments transsarcolemmal Ca2+ influx via an increase of PKA activity in ventricular cardiomyocytes and hence represents an important regulator of cardiac function.

Ca2+ -dependent interaction of S100A1 with the sarcoplasmic reticulum Ca2+ -ATPase2a and phospholamban in the human heart

The Ca(2+)-binding S100A1 protein displays a specific and high expression level in the human myocardium and is considered to be an important regulator of heart contractility. Diminished protein levels detected in dilated cardiomyopathy possibly contribute to impaired Ca(2+) handling and contractility in heart failure. To elucidate the S100A1 signaling pathway in the human heart, we searched for S100A1 target proteins by applying S100A1-specific affinity chromatography and immunoprecipitation techniques. We detected the formation of a Ca(2+)-dependent complex of S100A1 with SERCA2a and PLB in the human myocardium. Using confocal laser scanning microscopy, we showed that all three proteins co-localize at the level of the SR in primary mouse cardiomyocytes and confirmed these results by immunoelectron microscopy in human biopsies. Our results support a regulatory role of S100A1 in the contraction-relaxation cycle in the human heart.

Differential expression of S100 proteins in the developing human hippocampus and temporal cortex

S100 calcium binding proteins have long been known to express in the adult nervous system, but their distribution in the developing brain, especially the human fetal brain, is largely unknown. We used an immunohistochemical method to determine the expression of three S100 proteins, namely S100A4, S100A5, and S100A13, in the human fetal hippocampus and temporal cortex from 12 to 33 weeks of gestation. At 12 weeks, S100A5 was strongly expressed in the cells and fibers of the polymorphic, pyramidal, and molecular layers of the hippocampus. Thereafter, its expression decreased with age. In the temporal cortex, S100A5 expression was detected from 12 weeks onwards, peaked at 20 to 24 weeks, and then decreased with age. The horizontal fibers of the marginal zone were immunoreactive at all stages examined. S100A13 immunoreactivity was also detected in both cells and fibers of the hippocampus at 12 weeks, became slightly stronger at 20 weeks, and then decreased with age. In the temporal cortex, S100A13 immunoreactivity was also strong in all cellular layers at 12 to 24 weeks before it declined with age from 28 weeks onwards. Among the three proteins examined, S100A4 showed the weakest expression, which was detected in the cells and fibers of the hippocampus and the temporal cortex at all stages examined. Our results have demonstrated for the first time, in the human fetal hippocampus and temporal cortex, specific spatio-temporal patterns of expression of these proteins, all of which are likely to have different roles to play during development despite their pronounced sequence homology.

Impaired cardiac contractility response to hemodynamic stress in S100A1-deficient mice

Ca(2+) signaling plays a central role in cardiac contractility and adaptation to increased hemodynamic demand. We have generated mice with a targeted deletion of the S100A1 gene coding for the major cardiac isoform of the large multigenic S100 family of EF hand Ca(2+)-binding proteins. S100A1(-/-) mice have normal cardiac function under baseline conditions but have significantly reduced contraction rate and relaxation rate responses to beta-adrenergic stimulation that are associated with a reduced Ca(2+) sensitivity. In S100A1(-/-) mice, basal left-ventricular contractility deteriorated following 3-week pressure overload by thoracic aorta constriction despite a normal adaptive hypertrophy. Surprisingly, heterozygotes also had an impaired response to acute beta-adrenergic stimulation but maintained normal contractility in response to chronic pressure overload that coincided with S100A1 upregulation to wild-type levels. In contrast to other genetic models with impaired cardiac contractility, loss of S100A1 did not lead to cardiac hypertrophy or dilation in aged mice. The data demonstrate that high S100A1 protein levels are essential for the cardiac reserve and adaptation to acute and chronic hemodynamic stress in vivo.

Translocation of S100A1(1) calcium binding protein during heart surgery

Myocardial ischemia during cardiopulmonary bypass terminated by reperfusion generally leads to different degrees of damage of the cardiomyocytes induced by transient cytosolic Ca(2+) overload. Recently, much attention has been paid to the role of heart-specific Ca(2+)-binding proteins in the pathogenesis of myocardial ischemia-reperfusion injury. S100A1 is a heart-specific EF-hand Ca(2+)-binding protein that is directly involved in a variety of Ca(2+)-mediated functions in myocytes. The aim of our study was to investigate the localization and translocation of S100A1 in the human heart under normal (baseline) conditions and after prolonged ischemia and reperfusion of the myocardium. Our data suggest that S100A1 is directly involved in the transient perioperative myocardial damage caused by ischemia during open heart surgery in humans. Given its role in the contractile function of muscle cells, this S100 protein could be an important "intracellular link" in ischemia-reperfusion injury of the heart.

S100A1 modulates skeletal muscle contraction by desensitizing calcium activation of isometric tension, stiffness and ATPase

S100, a subfamily of the EF-hand type calcium sensing proteins, is implicated in many cellular functions including muscle contractility. Two isoforms, S100A1 and S100B, at 2-10 microM significantly inhibit active tension, stiffness and ATPase of skinned single rabbit psoas muscle fibers at sub-maximal (pCa approximately 6.1-5.6), but not at maximal levels of activation (pCa 4.0). S100A1 is a more potent inhibitor than S100B. Hill analysis of the ATPase-pCa and tension-pCa curves indicates that these proteins reduce calcium sensitivity and enhance the cooperativity toward calcium. We propose S100A1, and perhaps S100B, are viable candidates as physiological modulators of muscle contraction.

Immunolocalization of the calcium binding S100A1, S100A5 and S100A6 proteins in the dog cochlea during postnatal development

The immunolocalization of three members of the S100 calcium-binding protein family was investigated in the dog cochlea during normal postnatal development. Sections of decalcified and paraffin-embedded cochleae from 16 beagle puppies aged from birth to 3 months were treated with polyclonal antisera raised against the human recombinant S100A1, S100A5, and S100A6 proteins. At birth, in the dog cochlea, S100A1 was expressed in the immature Deiter's cells, and slightly in the pillar cells. From the second week, S100A1 was detected in the supporting structures of the organ of Corti, i.e. the Deiter's, the pillar, the border, and the Hensen's cells, and in the reticular membrane. From birth onwards, S100A5 remained a neuronal-specific protein, only located in a subpopulation of neurons in the spiral ganglion. S100A6 was not expressed at birth. From the second week of life, the Schwann cells and nerve sheaths in the modiolus, in the spiral ganglion, and running in the direction of the organ of Corti exhibited S100A6-labeling. From the 12th postnatal day, some scattered intermediate cells started to express S100A6 protein in the stria vascularis. The number of labeled intermediate cells increased during the third week. At adult stage, the intermediate cells were S100A6-stained with cytoplasmic labeling throughout the stria vascularis from the base to the apex of the cochlea. None of the other cochlear structures expressed the S100 proteins under study during the postnatal development of the dog cochlea. The S100A1, S100A5, S100A6 immunostaining was limited to specific cell types in dog cochlea. These S100 proteins were useful markers in the study of supporting cells, neurons, nerve fibers sheaths and stria vascularis (S100A6) during the normal postnatal development of the dog cochlea.