Excitation-contraction coupling and contractile protein function in failing and nonfailing human myocardium

The gut microbiota metabolite trimethylamine N-oxide promotes cardiac hypertrophy by activating the autophagic degradation of SERCA2a

Trimethylamine oxide (TMAO) is a newly found intestinal microbiota metabolite. Here, we aimed to explore the effects of TMAO on calcium homeostasis and its implication in cardiac hypertrophy, especially focusing on the regulatory mechanism of TMAO on the key calcium transporter SERCA2a. Echocardiography and histological assessment showed that mice fed with TMAO or Choline for 8 weeks exhibited significant pathological changes of cardiac hypertrophy, which is accompanied by increased plasma levels of TMAO. The results indicated that TMAO could increase the intracellular Ca2+ level, up-regulate the expression of ANP and MYH7, and down-regulate SERCA2a expression, which could be reversed by overexpressing of SERCA2a and BAPTA-AM. Meanwhile, TMAO treatment promotes autophagy in vitro and in vivo. By employing immunofluorescence staining and immunoprecipitation assay, it was found that SERCA2a bound to ATG5 and transported to autophagosomes via the ATG5 complex for degradation under TMAO conditions. Furthermore, either 3MA or siATG5 could ameliorate TMAO-induced cardiomyocyte hypertrophy and SERCA2a degradation. Finally, in vivo intervention showed that 3MA could relieve cardiac hypertrophy and rescue the down-regulation of SERCA2a in TMAO-fed mice. The current study identifies a mechanism in which TMAO promotes cardiac hypertrophy via elevated intracellular Ca2+ levels and enhanced autophagy degradation of SERCA2a.

Water-soluble alkaloids extracted from Aconiti Radix lateralis praeparata protect against chronic heart failure in rats via a calcium signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Many studies have shown the beneficial effects of aconite water-soluble alkaloid extract (AWA) in experimental models of heart disease, which have been ascribed to the presence of aconine, hypaconine, talatisamine, fuziline, neoline, and songorine. This study evaluated the effects of a chemically characterized AWA by chemical content, evaluated its effects in suprarenal abdominal aortic coarctation surgery (AAC)-induced chronic heart failure (CHF) in rats, and revealed the underlying mechanisms of action by proteomics.

METHODS

Rats were distributed into different groups: sham, model, and AWA-treated groups (10, 20, and 40 mg/kg/day). Sham rats received surgery without AAC, whereas model rats an AWA-treated groups underwent AAC surgery. after 8 weeks, the treatment group was fed AWA for 4 weeks, and body weight was assessed weekly. At the end of the treatment, heart function was tested by echocardiography. AAC-induced chronic heart failure, including myocardial fibrosis, cardiomyocyte hypertrophy, and apoptosis, was evaluated in heart tissue and plasma by RT-qPCR, ELISA, hematoxylin and eosin (H&E) staining, Masson's trichrome staining, TUNEL staining, and immunofluorescence staining of α-SMA, Col Ⅰ, and Col Ⅲ. Then, a proteomics approach was used to explore the underlying mechanisms of action of AWA in chronic heart failure.

RESULTS

AWA administration reduced body weight gain, myocardial fibrosis, cardiomyocyte hypertrophy, and apoptosis, and rats showed improvement in cardiac function compared to model group. The extract significantly ameliorated the AAC-induced altered expression of heart failure markers such as ANP, NT-proBNP, and β-MHC, as well as fibrosis, hypertrophy markers MMP-2 and MMP-9, and other heart failure-related factors including plasma levels of TNF-α and IL-6. Furthermore, the extract reduced the protein expression of α-SMA, Col Ⅰ, and Col Ⅲ in the left ventricular (LV), thus inhibiting the LV remodeling associated with CHF. In addition, proteomics characterization of differentially expressed proteins showed that AWA administration inhibited left ventricular remodeling in CHF rats via a calcium signaling pathway, and reversed the expression of RyR2 and SERCA2a.

CONCLUSIONS

AWA extract exerts beneficial effects in an AAC-induced CHF model in rats, which was associated with an improvement in LV function, hypertrophy, fibrosis, and apoptotic status. These effects may be related to the regulation of calcium signaling by the altered expression of RyR2 and SERCA2a.

Targeting Ca2 + Handling Proteins for the Treatment of Heart Failure and Arrhythmias

Diseases of the heart, such as heart failure and cardiac arrhythmias, are a growing socio-economic burden. Calcium (Ca²⁺) dysregulation is key hallmark of the failing myocardium and has long been touted as a potential therapeutic target in the treatment of a variety of cardiovascular diseases (CVD). In the heart, Ca²⁺ is essential for maintaining normal cardiac function through the generation of the cardiac action potential and its involvement in excitation contraction coupling. As such, the proteins which regulate Ca²⁺ cycling and signaling play a vital role in maintaining Ca²⁺ homeostasis. Changes to the expression levels and function of Ca²⁺-channels, pumps and associated intracellular handling proteins contribute to altered Ca²⁺ homeostasis in CVD. The remodeling of Ca²⁺-handling proteins therefore results in impaired Ca²⁺ cycling, Ca²⁺ leak from the sarcoplasmic reticulum and reduced Ca²⁺ clearance, all of which contributes to increased intracellular Ca²⁺. Currently, approved treatments for targeting Ca²⁺ handling dysfunction in CVD are focused on Ca²⁺ channel blockers. However, whilst Ca²⁺ channel blockers have been successful in the treatment of some arrhythmic disorders, they are not universally prescribed to heart failure patients owing to their ability to depress cardiac function. Despite the progress in CVD treatments, there remains a clear need for novel therapeutic approaches which are able to reverse pathophysiology associated with heart failure and arrhythmias. Given that heart failure and cardiac arrhythmias are closely associated with altered Ca²⁺ homeostasis, this review will address the molecular changes to proteins associated with both Ca²⁺-handling and -signaling; their potential as novel therapeutic targets will be discussed in the context of pre-clinical and, where available, clinical data.

CRISPLD1: a novel conserved target in the transition to human heart failure

Heart failure is a major health problem worldwide with a significant morbidity and mortality rate. Although studied extensively in animal models, data from patients at the compensated disease stage are lacking. We sampled myocardium biopsies from aortic stenosis patients with compensated hypertrophy and moderate heart failure and used transcriptomics to study the transition to failure. Sequencing and comparative analysis of analogous samples of mice with transverse aortic constriction identified 25 candidate genes with similar regulation in response to pressure overload, reflecting highly conserved molecular processes. The gene cysteine-rich secretory protein LCCL domain containing 1 (CRISPLD1) is upregulated in the transition to failure in human and mouse and its function is unknown. Homology to ion channel regulatory toxins suggests a role in Ca²⁺ cycling. CRISPR/Cas9-mediated loss-of-function leads to dysregulated Ca²⁺ handling in human-induced pluripotent stem cell-derived cardiomyocytes. The downregulation of prohypertrophic, proapoptotic and Ca²⁺-signaling pathways upon CRISPLD1-KO and its upregulation in the transition to failure implicates a contribution to adverse remodeling. These findings provide new pathophysiological data on Ca²⁺ regulation in the transition to failure and novel candidate genes with promising potential for therapeutic interventions.

Correcting Calcium Dysregulation in Chronic Heart Failure Using SERCA2a Gene Therapy

Chronic heart failure (CHF) is a major contributor to cardiovascular disease and is the leading cause of hospitalization for those over the age of 65, which is estimated to account for close to seventy billion dollars in healthcare costs by 2030 in the US alone. The successful therapies for preventing and reversing CHF progression are urgently required. One strategy under active investigation is to restore dysregulated myocardial calcium (Ca²⁺), a hallmark of CHF. It is well established that intracellular Ca²⁺ concentrations are tightly regulated to control efficient myocardial systolic contraction and diastolic relaxation. Among the many cell surface proteins and intracellular organelles that act as the warp and woof of the regulatory network controlling intracellular Ca²⁺ signals in cardiomyocytes, sarco/endoplasmic reticulum Ca²⁺ ATPase type 2a (SERCA2a) undoubtedly plays a central role. SERCA2a is responsible for sequestrating cytosolic Ca²⁺ back into the sarcoplasmic reticulum during diastole, allowing for efficient uncoupling of actin-myosin and subsequent ventricular relaxation. Accumulating evidence has demonstrated that the expression of SERCA2a is downregulated in CHF, which subsequently contributes to severe systolic and diastolic dysfunction. Therefore, restoring SERCA2a expression and improving cardiomyocyte Ca²⁺ handling provides an excellent alternative to currently used transplantation and mechanical assist devices in the treatment of CHF. Indeed, advancements in safe and effective gene delivery techniques have led to the emergence of SERCA2a gene therapy as a potential therapeutic choice for CHF patients. This mini-review will succinctly detail the progression of SERCA2a gene therapy from its inception in plasmid and animal models, to its clinical trials in CHF patients, highlighting potential avenues for future work along the way.

Can the Drosophila model help in paving the way for translational medicine in heart failure?

Chronic heart failure is a common consequence of various heart diseases. Mechanical force is known to play a key role in heart failure development through regulating cardiomyocyte hypertrophy. In order to understand the complex disease mechanism, this article discussed a multi-disciplinary approach that may aid the illustration of heart failure molecular process.

Remodeling of calcium handling in human heart failure

Heart failure (HF) is an increasing public health problem accelerated by a rapidly aging global population. Despite considerable progress in managing the disease, the development of new therapies for effective treatment of HF remains a challenge. To identify targets for early diagnosis and therapeutic intervention, it is essential to understand the molecular and cellular basis of calcium handling and the signaling pathways governing the functional remodeling associated with HF in humans. Calcium (Ca(2+)) cycling is an essential mediator of cardiac contractile function, and remodeling of calcium handling is thought to be one of the major factors contributing to the mechanical and electrical dysfunction observed in HF. Active research in this field aims to bridge the gap between basic research and effective clinical treatments of HF. This chapter reviews the most relevant studies of calcium remodeling in failing human hearts and discusses their connections to current and emerging clinical therapies for HF patients.

Transmural heterogeneity and remodeling of ventricular excitation-contraction coupling in human heart failure

BACKGROUND

Excitation-contraction (EC) coupling is altered in end-stage heart failure. However, spatial heterogeneity of this remodeling has not been established at the tissue level in failing human heart. The objective of this article was to study functional remodeling of excitation-contraction coupling and calcium handling in failing and nonfailing human hearts.

METHODS AND RESULTS

We simultaneously optically mapped action potentials and calcium transients in coronary perfused left ventricular wedge preparations from nonfailing (n=6) and failing (n=5) human hearts. Our major findings are the following. First, calcium transient duration minus action potential duration was longer at subendocardium in failing compared with nonfailing hearts during bradycardia (40 bpm). Second, the transmural gradient of calcium transient duration was significantly smaller in failing hearts compared with nonfailing hearts at fast pacing rates (100 bpm). Third, calcium transient in failing hearts had a flattened plateau at the midmyocardium and exhibited a 2-component slow rise at the subendocardium in 3 failing hearts. Fourth, calcium transient relaxation was slower at the subendocardium than at the subepicardium in both groups. Protein expression of sarcoplasmic reticulum Ca(2+)-ATPase 2a was lower at the subendocardium than the subepicardium in both nonfailing and failing hearts. Sarcoplasmic reticulum Ca(2+)-ATPase 2a protein expression at subendocardium was lower in hearts with ischemic cardiomyopathy compared with those with nonischemic cardiomyopathy.

CONCLUSIONS

For the first time, we present direct experimental evidence of transmural heterogeneity of excitation-contraction coupling and calcium handling in human hearts. End-stage heart failure is associated with the heterogeneous remodeling of excitation-contraction coupling and calcium handling.

Left Ventricular Mechanoenergetics in Small Animals

Studies on left ventricular mechanical work and energetics in rat and mouse hearts are reviewed. First, left ventricular linear end-systolic pressure-volume relation (ESPVR) and curved end-diastolic pressure-volume relation (EDPVR) in canine hearts and left ventricular curved ESPVR and curved EDPVR in rat hearts are reviewed. Second, as an index for total mechanical energy per beat in rat hearts as in canine hearts, a systolic pressure-volume area (PVA) is proposed. By the use of our original system for measuring continuous oxygen consumption for rat left ventricular mechanical work, the linear left ventricular myocardial oxygen consumption per beat (VO2)-PVA relation is obtained as in canine hearts. The slope of VO2-PVA relation (oxygen cost of PVA) indicates a ratio of chemomechanical energy transduction. VO2 intercept (PVA-independent VO2) indicates the summation of oxygen consumption for Ca2+ handling in excitation-contraction coupling and for basal metabolism. An equivalent maximal elastance (eEmax) is proposed as a new left ventricular contractility index based on PVA at the midrange left ventricular volume. The slope of the linear relation between PVA-independent VO2 and eEmax (oxygen cost of eEmax) indicates changes in oxygen consumption for Ca2+ handling in excitation-contraction coupling per unit changes in left ventricular contractility. The key framework of VO2-PVA-eEmax can give us a better understanding for the biology and mechanisms of physiological and various failing rat heart models in terms of mechanical work and energetics.

Targeting calcium cycling proteins in heart failure through gene transfer

Our understanding of cardiac excitation-contraction coupling has improved significantly over the last 10 years. Furthermore, defects in the various steps of excitation-contraction coupling that characterize cardiac dysfunction have been identified in human and experimental models of heart failure. The various abnormalities in ionic channels, transporters, kinases and various signalling pathways collectively contribute to the 'failing phenotype.' However, deciphering the causative changes continues to be a challenge. An important tool in dissecting the importance of the various changes in heart failure has been the use of cardiac gene transfer. To achieve effective cardiac gene transfer a number of obstacles remain, including appropriate vectors for gene delivery, appropriate delivery systems, and a better understanding of the biology of the disease. In this review, we will examine our current understanding of these various factors. Gene transfer provides not only a potential therapeutic modality but also an approach to identifying and validating molecular targets.

Origin of contractile dysfunction in heart failure: calcium cycling versus myofilaments

BACKGROUND

Chronic congestive heart failure is a common, often lethal disorder of cardiac contractility. The fundamental pathophysiology of the contractile failure remains unclear, the focus being on abnormal Ca2+ cycling despite emerging evidence for depressed myofilament function.

METHODS AND RESULTS

We measured intracellular Ca2+ concentration ([Ca2+]i) and contractile force in intact ventricular muscle from SHHF rats with spontaneous heart failure and from age-matched controls. At physiological concentrations of extracellular Ca2+ ([Ca2+]o), [Ca2+]i transients were equal in amplitude in the 2 groups, but [Ca2+]i peaked later in SHHF muscles. Twitch force peaked slowly and was equivalent or modestly decreased in amplitude relative to controls. Steady-state analysis revealed a much greater (53%) depression of maximal Ca2+-activated force in SHHF muscles, which, had other factors been equal, would have produced an equivalent suppression of twitch force. Phase-plane analysis reveals that the slowing of Ca2+ cycling prolongs the time available for Ca2+ to activate the myofilaments in failing muscle, partially compensating for the marked dysfunction of the contractile machinery.

CONCLUSIONS

Our results indicate that myofilament activation is severely blunted in heart failure, but concomitant changes in [Ca2+]i kinetics minimize the contractile depression. These results challenge prevailing concepts regarding the pathophysiology of heart failure: the myofilaments emerge as central players, whereas changes in Ca2+ cycling are reinterpreted as compensatory rather than causative.

Reduced contraction and altered frequency response of isolated ventricular myocytes from patients with heart failure

BACKGROUND

Previous work has failed to demonstrate reduced maximal contraction of isolated ventricular myocytes from failing human hearts compared with nonfailing control hearts. The effect of alterations in stimulation frequency and temperature on the contraction of isolated ventricular myocytes has been investigated. Left ventricular myocytes were isolated from the hearts of patients with severe heart failure undergoing heart transplantation and compared with myocytes isolated from myocardial biopsies from patients with coronary disease but preserved left ventricular systolic function or from myocytes from rejected donor hearts.

METHODS AND RESULTS

Myocytes were exposed to either a maximally activating level of extracellular calcium at 37 degrees C or to 2 mmol/L calcium at 32 degrees C. There was no significant difference in the contraction amplitude between myocytes from failing and nonfailing hearts at 0.2 Hz. With increasing stimulation frequency, there was a reduction in contraction amplitude in cells from failing hearts relative to control hearts in both maximal calcium from 0.33 Hz (4.5% versus 6.6%) to 1.4 Hz (3.9% versus 8.8%) (ANCOVA, P < .001) and at 2 mmol/L calcium from 0.50 Hz (2.3% versus 3.5%) to 1.4 Hz (1.8% versus 3.9%) (ANCOVA, P < .001). The time to peak contraction and the times to 50% and 90% relaxation were prolonged in myocytes from failing hearts at stimulation rate of 0.2 Hz (P < .01), but only the time to 50% relaxation was prolonged at 1.0 Hz (P < .05).

CONCLUSIONS

Reduced contraction, slowed relaxation, and impaired frequency response occurring at the level of the individual ventricular myocyte can be demonstrated in human heart failure. This demonstrates that disruption of myocyte function can contribute to both the systolic and the diastolic abnormalities that occur in the failing human heart.