Weighing in on heart failure: the role of SERCA2a SUMOylation

SUMOylation as a Therapeutic Target for Myocardial Infarction

Myocardial infarction is a prevalent and life-threatening cardiovascular disease. The main goal of existing interventional therapies is to restore coronary reperfusion while few are designed to ameliorate the pathology of heart diseases via targeting the post-translational modifications of those critical proteins. Small ubiquitin-like modifier (SUMO) proteins are recently discovered to form a new type of protein post-translational modifications (PTM), known as SUMOylation. SUMOylation and deSUMOylation are dynamically balanced in the maintenance of various biological processes including cell division, DNA repair, epigenetic transcriptional regulation, and cellular metabolism. Importantly, SUMOylation plays a critical role in the regulation of cardiac functions and the pathology of cardiovascular diseases, especially in heart failure and myocardial infarction. This review summarizes the current understanding on the effects of SUMOylation and SUMOylated proteins in the pathophysiology of myocardial infarction and identifies the potential treatments against myocardial injury via targeting SUMO. Ultimately, this review recommends SUMOylation as a key therapeutic target for treating cardiovascular diseases.

Estrogen and calcium handling proteins: new discoveries and mechanisms in cardiovascular diseases

Estrogen deficiency is considered to be an important factor leading to cardiovascular diseases (CVDs). Indeed, the prevalence of CVDs in postmenopausal women exceeds that of premenopausal women and men of the same age. Recent research findings provide evidence that estrogen plays a pivotal role in the regulation of calcium homeostasis and therefore fine-tunes normal cardiomyocyte contraction and relaxation processes. Disruption of calcium homeostasis is closely associated with the pathological mechanism of CVDs. Thus, this paper maps out and summarizes the effects and mechanisms of estrogen on calcium handling proteins in cardiac myocytes, including L-type Ca²⁺ channel, the sarcoplasmic reticulum Ca²⁺ release channel named ryanodine receptor, sarco(endo)plasmic reticulum Ca²⁺-ATPase, and sodium-calcium exchanger. In so doing, we provide theoretical and experimental evidence for the successful design of estrogen-based prevention and treatment therapies for CVDs.

Probing the effects of nonannular lipid binding on the stability of the calcium pump SERCA

The calcium pump SERCA is a transmembrane protein that is critical for calcium transport in cells. SERCA resides in an environment made up largely by the lipid bilayer, so lipids play a central role on its stability and function. Studies have provided insights into the effects of annular and bulk lipids on SERCA activation, but the role of a nonannular lipid site in the E2 intermediate state remains elusive. Here, we have performed microsecond molecular dynamics simulations to probe the effects of nonannular lipid binding on the stability and structural dynamics of the E2 state of SERCA. We found that the structural integrity and stability of the E2 state is independent of nonannular lipid binding, and that occupancy of a lipid molecule at this site does not modulate destabilization of the E2 state, a step required to initiate the transition toward the competent E1 state. We also found that binding of the nonannular lipid does not induce direct allosteric control of the intrinsic functional dynamics the E2 state. We conclude that nonannular lipid binding is not necessary for the stability of the E2 state, but we speculate that it becomes functionally significant during the E2-to-E1 transition of the pump.

Luteolin improves cardiac dysfunction in heart failure rats by regulating sarcoplasmic reticulum Ca2+-ATPase 2a

We previously found that luteolin (Lut) appeared to improve the contractility of cardiomyocytes during ischemia/reperfusion in rats. The enhancement was associated with the alteration in sarcoplasmic reticulum Ca²⁺-ATPase 2a (SERCA2a). This finding prompted us to consider if the mechanism worked in heart failure (HF). We studied the regulation of SERCA2a by Lut in failing cardiomyocytes and intact heart of rats. Improvement of contractility and the mechanisms centered on SERCA2a were studied in isolated cardiomyocytes and intact heart. We found that Lut significantly improved contractility and Ca²⁺ transients, ameliorated expression, activity and stability of SERCA2a and upregulated expression of small ubiquitin-related modifier (SUMO) 1, which is a newfound SERCA2a regulator. Lut also increased phosphorylation of protein kinase B (Akt), phospholaban (PLB) and sumoylation of SERCA2a, specificity protein 1 (Sp1). Transcriptions of SUMO1 and SERCA2a were concurrently increased. Inhibition of posphatidylinositol 3 kinase/Akt (PI3K/Akt) pathway and SERCA2a activity both markedly abolished Lut-induced benefits in vitro and in vivo. Lut upregulated the expression ratio of Bcl-2/Bax, caspase-3/cleaved-Caspase3. Meanwhile, Lut ameliorated the myocardium fibrosis of HF. These discoveries provide an important potential therapeutic strategy that Lut targeted SERCA2a SUMOylation related to PI3K/Akt-mediated regulations on rescuing the dysfunction of HF.

Cardiomyocyte-specific overexpression of oestrogen receptor β improves survival and cardiac function after myocardial infarction in female and male mice

The study provides new insights into cardiomyocyte-specific effects of ERβ in the setting of chronic MI using a transgenic mouse model. ERβ-overexpressing mice of both sexes showed improved survival, less maladaptive LV remodelling, better cardiac function and less heart failure development.

Adeno-associated virus-mediated gene therapy in cardiovascular disease

PURPOSE OF REVIEW

The use of adeno-associated virus (AAV) as an efficient, cardiotropic, and safe vector, coupled with the identification of key molecular targets, has placed gene-based therapies within reach of cardiovascular diseases. The purpose of this review is to provide a focused update on the current advances related to AAV-mediated gene therapy in cardiovascular diseases, and particularly in heart failure (HF), wherein gene therapy has recently made important progress.

RECENT FINDINGS

Multiple successful preclinical studies suggest a potential utility of AAV gene therapy for arrhythmias and biological heart pacing, as well as RNA overexpression. Moreover, AAV-mediated overexpression of several molecular targets involved in HF has demonstrated promising results in clinically relevant large animal models. In humans, a safe and successful completion of a phase 2 clinical trial targeting the sarcoplasmic reticulum calcium ATPase pump with AAV has been reported. Serial studies are ongoing to further prove the efficacy of AAV-mediated sarcoplasmic reticulum calcium ATPase pump gene transfer in human HF.

SUMMARY

Significant progress in clinical translation of AAV-mediated cardiac gene therapy has been achieved in recent years. This will prompt further clinical trials, and positive results could open a new era for cardiac gene therapy.

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.

Alterations in ryanodine receptors and related proteins in heart failure

Sarcoplasmic reticulum (SR) Ca(2+) release plays an essential role in mediating cardiac myocyte contraction. Depolarization of the plasma membrane results in influx of Ca(2+) through l-type Ca(2+) channels (LTCCs) that in turn triggers efflux of Ca(2+) from the SR through ryanodine receptor type-2 channels (RyR2). This process known as Ca(2+)-induced Ca(2+)release (CICR) occurs within the dyadic region, where the adjacent transverse (T)-tubules and SR membranes allow RyR2 clusters to release SR Ca(2+) following Ca(2+) influx through adjacent LTCCs. SR Ca(2+) released during systole binds to troponin-C and initiates actin-myosin cross-bridging, leading to muscle contraction. During diastole, the cytosolic Ca(2+) concentration is restored by the resequestration of Ca(2+) into the SR by SR/ER Ca(2+)-ATPase (SERCA2a) and by the extrusion of Ca(2+) via the Na(+)/Ca(2+)-exchanger (NCX1). This whole process, entitled excitation-contraction (EC) coupling, is highly coordinated and determines the force of contraction, providing a link between the electrical and mechanical activities of cardiac muscle. In response to heart failure (HF), the heart undergoes maladaptive changes that result in depressed intracellular Ca(2+) cycling and decreased SR Ca(2+) concentrations. As a result, the amplitude of CICR is reduced resulting in less force production during EC coupling. In this review, we discuss the specific proteins that alter the regulation of Ca(2+) during HF. In particular, we will focus on defects in RyR2-mediated SR Ca(2+) release. This article is part of a Special Issue entitled: Heart failure pathogenesis and emerging diagnostic and therapeutic interventions.

Functional decorations: post-translational modifications and heart disease delineated by targeted proteomics

The more than 300 currently identified post-translational modifications (PTMs) provides great scope for subtle or dramatic alteration of protein structure and function. Furthermore, the rapid and transient nature of many PTMs allows efficient signal transmission in response to internal and environmental stimuli. PTMs are predominantly added by enzymes, and the enzymes responsible (such as kinases) are thus attractive targets for therapeutic interventions. Modifications can be grouped according to their stability or transience (reversible versus irreversible): irreversible types (such as irreversible redox modifications or protein deamidation) are often associated with aging or tissue injury, whereas transient modifications are associated with signal propagation and regulation. This is particularly important in the setting of heart disease, which comprises a diverse range of acute (such as ischemia/reperfusion), chronic (such as heart failure, dilated cardiomyopathy) and genetic (such as hypertrophic cardiomyopathy) disease states, all of which have been associated with protein PTM. Recently the interplay between diverse PTMs has been suggested to also influence cellular function, with cooperation or competition for sites of modification possible. Here we discuss the utility of proteomics for examining PTMs in the context of the molecular mechanisms of heart disease.

Modulation of cardiac contractility by the phospholamban/SERCA2a regulatome

Heart disease remains the leading cause of death and disability in the Western world. Current therapies aim at treating the symptoms rather than the subcellular mechanisms, underlying the etiology and pathological remodeling in heart failure. A universal characteristic, contributing to the decreased contractile performance in human and experimental failing hearts, is impaired calcium sequestration into the sarcoplasmic reticulum (SR). SR calcium uptake is mediated by a Ca(2+)-ATPase (SERCA2), whose activity is reversibly regulated by phospholamban (PLN). Dephosphorylated PLN is an inhibitor of SERCA and phosphorylation of PLN relieves this inhibition. However, the initial simple view of a PLN/SERCA regulatory complex has been modified by our recent identification of SUMO, S100 and the histidine-rich Ca-binding protein as regulators of SERCA activity. In addition, PLN activity is regulated by 2 phosphoproteins, the inhibitor-1 of protein phosphatase 1 and the small heat shock protein 20, which affect the overall SERCA-mediated Ca-transport. This review will highlight the regulatory mechanisms of cardiac contractility by the multimeric SERCA/PLN-ensemble and the potential for new therapeutic avenues targeting this complex by using small molecules and gene transfer methods.