ATPase Of Sarcoplasmic Reticulum Research Articles

Ketogenic Diet Regulates Cardiac Remodeling and Calcium Homeostasis in Diabetic Rat Cardiomyopathy.

A ketogenic diet (KD) might alleviate patients with diabetic cardiomyopathy. However, the underlying mechanism remains unclear. Myocardial function and arrhythmogenesis are closely linked to calcium (Ca2+) homeostasis. We investigated the effects of a KD on Ca2+ homeostasis and electrophysiology in diabetic cardiomyopathy. Male Wistar rats were created to have diabetes mellitus (DM) using streptozotocin (65 mg/kg, intraperitoneally), and subsequently treated for 6 weeks with either a normal diet (ND) or a KD. Our electrophysiological and Western blot analyses assessed myocardial Ca2+ homeostasis in ventricular preparations in vivo. Unlike those on the KD, DM rats treated with an ND exhibited a prolonged QTc interval and action potential duration. Compared to the control and DM rats on the KD, DM rats treated with an ND also showed lower intracellular Ca2+ transients, sarcoplasmic reticular Ca2+ content, sodium (Na+)-Ca2+ exchanger currents (reverse mode), L-type Ca2+ contents, sarcoplasmic reticulum ATPase contents, Cav1.2 contents. Furthermore, these rats exhibited elevated ratios of phosphorylated to total proteins across multiple Ca2+ handling proteins, including ryanodine receptor 2 (RyR2) at serine 2808, phospholamban (PLB)-Ser16, and calmodulin-dependent protein kinase II (CaMKII). Additionally, DM rats treated with an ND demonstrated a higher frequency and incidence of Ca2+ leak, cytosolic reactive oxygen species, Na+/hydrogen-exchanger currents, and late Na+ currents than the control and DM rats on the KD. KD treatment may attenuate the effects of DM-dysregulated Na+ and Ca2+ homeostasis, contributing to its cardioprotection in DM.

Abstract 14399: Novel Mechanisms of Diastolic Dysfunction in Cardiac Aging

Aging is associated with a progressive decline in cardiac diastolic function. Membranous α-klotho, predominantly produced by the kidney, can be cleaved and form circulating α-klotho, which acts as an anti-aging hormone. Echocardiography showed klotho deficiency in 20-24-month-old heterozygous klotho (KL +/- ) mice aggravates left ventricular hypertrophy (LVH) and diastolic dysfunction (DD) compared with old wild type (OWT) littermates. Supplementation with α-Klotho (0.1mg/kg/day. i.p) for 10 weeks significantly reduced LV mass and ameliorated DD in both OWT and OKL. The improvement in DD was confirmed by Millar catheter measurement of -dP/dt. To gain mechanistic insights, we performed unbiased acetylomics using Acetyl-lysine antibody enrichment, followed by Tandem mass tag proteomics analysis. We identified 1215 lysine acetylation sites (K-Ac) on >1000 cardiac proteins, of which 220 K-Ac sites were significantly hyperacetylated in OWT hearts. There were 63 Ac-K sites >2-fold hyperacetylated in aged hearts (OWT vs. YWT). The comparison of OKL to YWT augmented the number of Ac-K sites to 82. These sites include redox proteins, several metabolic and mitochondrial proteins involved in fatty acid and amino acid metabolism, and the TCA cycle. Several isoforms of myosin heavy chains (MHC) were also hyperacetylated at multiple sites. Some hyperacetylated MHC (e.g. K941) are predicted to alter the molecular structure and relaxation kinetics by Molecular Dynamic Simulation. In addition to delayed Ca 2+ reuptake by myocardial sarcoplasmic reticulum ATPase (SERCA2a), decreased SERCA2a expression and increased acetylated SERCA2 in aged hearts, which was all corrected upon klotho supplementation, we found potential novel mechanisms of DD with hyperacetylation of MHC, concomitant with a decrease in Sirt1 deacetylase, in OWT mice that was aggravated in OKL, which was replenished upon klotho supplementation. Collectively, we demonstrated klotho deficiency aggravates cardiac aging phenotypes, associated with hyperacetylation of several cardiac proteins due to diminished Sirt1. Klotho supplementation rejuvenates several cardiac aging phenotypes, including regression of LVH and improvement of DD, in parallel with reversal of protein acetylation.

The Role and Implications of Epicardial Fat in Coronary Atherosclerotic Disease

The current minireview aims to assess the implications of epicardial fat secretory function in the development of coronary artery disease. The epicardial adipose tissue (EAT) is a visceral fat depot that has been described as a cardiovascular risk factor. In addition to its mechanical protection role and physiological secretory function, it seems that various secretion products of the epicardial fat are responsible for metabolic disturbances at the level of the cardiac muscle when in association with pre-existing pathological conditions, such as metabolic syndrome. There is a pathological reduction in sarcomere shortening, abnormal cytosolic Ca2+ fluxes, reduced expression of sarcoplasmic endoplasmic reticulum ATPase 2a and decreased insulin-mediated Akt-Ser473-phosphorylation in association with abnormal levels of epicardial fat tissue. Activin A, angiopoietin-2, and CD14-positive monocytes selectively accumulate in the diseased myocardium, resulting in reduced cardiomyocyte contractile function. At the same time, it is believed that these alterations in secretory products directly decrease the myocyte function via molecular changes, thus contributing to the development of coronary disease when certain comorbidities are associated.

Comparison of the antiremodeling effects of losartan and mirabegron in a rat model of uremic cardiomyopathy

Uremic cardiomyopathy is characterized by diastolic dysfunction (DD), left ventricular hypertrophy (LVH), and fibrosis. Angiotensin-II plays a major role in the development of uremic cardiomyopathy via nitro-oxidative and inflammatory mechanisms. In heart failure, the beta-3 adrenergic receptor (β3-AR) is up-regulated and coupled to endothelial nitric oxide synthase (eNOS)-mediated pathways, exerting antiremodeling effects. We aimed to compare the antiremodeling effects of the angiotensin-II receptor blocker losartan and the β3-AR agonist mirabegron in uremic cardiomyopathy. Chronic kidney disease (CKD) was induced by 5/6th nephrectomy in male Wistar rats. Five weeks later, rats were randomized into four groups: (1) sham-operated, (2) CKD, (3) losartan-treated (10 mg/kg/day) CKD, and (4) mirabegron-treated (10 mg/kg/day) CKD groups. At week 13, echocardiographic, histologic, laboratory, qRT-PCR, and Western blot measurements proved the development of uremic cardiomyopathy with DD, LVH, fibrosis, inflammation, and reduced eNOS levels, which were significantly ameliorated by losartan. However, mirabegron showed a tendency to decrease DD and fibrosis; but eNOS expression remained reduced. In uremic cardiomyopathy, β3-AR, sarcoplasmic reticulum ATPase (SERCA), and phospholamban levels did not change irrespective of treatments. Mirabegron reduced the angiotensin-II receptor 1 expression in uremic cardiomyopathy that might explain its mild antiremodeling effects despite the unchanged expression of the β3-AR.

Ca2+-ATPase Molecules as a Calcium-Sensitive Membrane-Endoskeleton of Sarcoplasmic Reticulum.

The Ca2+-transport ATPase of sarcoplasmic reticulum (SR) is an integral, transmembrane protein. It sequesters cytoplasmic calcium ions released from SR during muscle contraction, and causes muscle relaxation. Based on negative staining and transmission electron microscopy of SR vesicles isolated from rabbit skeletal muscle, we propose that the ATPase molecules might also be a calcium-sensitive membrane-endoskeleton. Under conditions when the ATPase molecules scarcely transport Ca2+, i.e., in the presence of ATP and ≤ 0.9 nM Ca2+, some of the ATPase particles on the SR vesicle surface gathered to form tetramers. The tetramers crystallized into a cylindrical helical array in some vesicles and probably resulted in the elongated protrusion that extended from some round SRs. As the Ca2+ concentration increased to 0.2 µM, i.e., under conditions when the transporter molecules fully carry out their activities, the ATPase crystal arrays disappeared, but the SR protrusions remained. In the absence of ATP, almost all of the SR vesicles were round and no crystal arrays were evident, independent of the calcium concentration. This suggests that ATP induced crystallization at low Ca2+ concentrations. From the observed morphological changes, the role of the proposed ATPase membrane-endoskeleton is discussed in the context of calcium regulation during muscle contraction.

Regional Differences in the Ghrelin-Growth Hormone Secretagogue Receptor Signalling System in Human Heart Disease

BackgroundThe hormone ghrelin and its receptor, the growth hormone secretagogue receptor (GHSR) are expressed in myocardium. GHSR binding activates signalling pathways coupled to cardiomyocyte survival and contractility. These properties have made the ghrelin-GHSR axis a candidate for a biomarker of cardiac function. The dynamics of ghrelin-GHSR are altered significantly in late stages of heart failure (HF) and cardiomyopathy, when left ventricular (LV) function is failing. We examined the relationship of GHSR with ghrelin in cardiac tissue from patients with valvular disease with no detectable changes in LV function. MethodsBiopsy samples from the left ventricle and left atrium were obtained from 25 patients with valvular disease (of whom 13 also had coronary artery disease) and preserved LV ejection fraction, and compared to control samples obtained via autopsy. Using quantitative confocal fluorescence microscopy, levels of GHSR were determined using [Dpr3(n-octanoyl),Lys19(sulfo-Cy5)]ghrelin(1-19), and immunofluorescence determined ghrelin, the heart failure marker natriuretic peptide type-B (BNP), and contractility marker sarcoplasmic reticulum ATPase pump (SERCA2a). ResultsA positive correlation between GHSR and ghrelin was apparent in only diseased tissue. Ghrelin and BNP significantly correlated in the left ventricle and strongly colocalized to the same intracellular compartment in diseased and control tissue. GHSR, ghrelin, and BNP all strongly and significantly correlated with SERCA2a in the left ventricle of diseased tissue only. ConclusionsOur results suggest that the dynamics of the myocardial ghrelin-GHSR axis is altered in cardiovascular disease in the absence of measurable changes in heart function, and might accompany a regional shift in endocrine programming.

Preserved Ca2+ handling and excitation-contraction coupling in muscle fibres from diet-induced obese mice.

Disrupted intracellular Ca2+ handling is known to play a role in diabetic cardiomyopathy but it has also been postulated to contribute to obesity- and type 2 diabetes-associated skeletal muscle dysfunction. Still, there is so far very limited functional insight into whether, and if so to what extent, muscular Ca2+ homeostasis is affected in this situation, so as to potentially determine or contribute to muscle weakness. In differentiated muscle, force production is under the control of the excitation-contraction coupling process: upon plasma membrane electrical activity, the CaV1.1 voltage sensor/Ca2+ channel in the plasma membrane triggers opening of the ryanodine receptor Ca2+ release channel in the sarcoplasmic reticulum (SR) membrane. Opening of the ryanodine receptor triggers the rise in cytosolic Ca2+, which activates contraction while Ca2+ uptake by the SR ATPase Ca2+-pump promotes relaxation. These are the core mechanisms underlying the tight control of muscle force by neuronal electrical activity. This study aimed at characterising their inherent physiological function in a diet-induced mouse model of obesity and type 2 diabetes. Intact muscle fibres were isolated from mice fed either with a standard chow diet or with a high-fat, high-sucrose diet generating obesity, insulin resistance and glucose intolerance. Properties of muscle fibres were investigated with a combination of whole-cell voltage-clamp electrophysiology and confocal fluorescence imaging. The integrity and density of the plasma membrane network (transverse tubules) that carries the membrane excitation throughout the muscle fibres was assessed with the dye Di-8-ANEPPS. CaV1.1 Ca2+ channel activity was studied by measuring the changes in current across the plasma membrane elicited by voltage-clamp depolarising pulses of increasing amplitude. SR Ca2+ release through ryanodine receptors was simultaneously detected with the Ca2+-sensitive dye Rhod-2 in the cytosol. CaV1.1 voltage-sensing activity was separately characterised from the properties of intra-plasma-membrane charge movement produced by short voltage-clamp depolarising pulses. Spontaneous Ca2+ release at rest was assessed with the Ca2+-sensitive dye Fluo-4. The rate of SR Ca2+ uptake was assessed from the time course of cytosolic Ca2+ recovery after the end of voltage excitation using the Ca2+-sensitive dye Fluo-4FF. The response to a fatigue-stimulation protocol was determined from the time course of decline of the peak Fluo-4FF Ca2+ transients elicited by 30 trains of 5-ms-long depolarising pulses delivered at 100Hz. The transverse tubule network architecture and density were well preserved in the fibres from the obese mice. The CaV1.1 Ca2+ current and voltage-sensing properties were also largely unaffected with mean values for maximum conductance and maximum amount of charge of 234 ± 12 S/F and 30.7 ± 1.6 nC/μF compared with 196 ± 13 S/F and 32.9 ± 2.0 nC/μF in fibres from mice fed with the standard diet, respectively. Voltage-activated SR Ca2+ release through ryanodine receptors also exhibited very similar properties in the two groups with mean values for maximum rate of Ca2+ release of 76.0 ± 6.5 and 78.1 ± 4.4μmoll-1ms-1, in fibres from control and obese mice, respectively. The response to a fatigue protocol was also largely unaffected in fibres from the obese mice, and so were the rate of cytosolic Ca2+ removal and the spontaneous Ca2+ release activity at rest. The functional properties of the main mechanisms involved in the control of muscle Ca2+ homeostasis are well preserved in muscle fibres from obese mice, at the level of both the plasma membrane and of the SR. We conclude that intracellular Ca2+ handling and excitation-contraction coupling in skeletal muscle fibres are not primary targets of obesity and type 2 diabetes. Graphical abstract.

4-chloro-orto-cresol activates ryanodine receptor more selectively and potently than 4-chloro-meta-cresol

In this study we performed the comprehensive pharmacological analysis of two stereoisomers of 4-chloro-meta-cresol (4CMC), a popular ryanodine receptor (RyR) agonist used in muscle research. Experiments investigating the Ca2+-releasing action of the isomers demonstrated that the most potent isomer was 4-chloro-orto-cresol (4COC) (EC50 = 55 ± 14 μM), although 3-chloro-para-cresol (3CPC) was more effective, as it was able to induce higher magnitude of Ca2+ flux from isolated terminal cisterna vesicles. Nevertheless, 3CPC stimulated the hydrolytic activity of the sarcoplasmic reticulum ATP-ase (SERCA) with an EC50 of 91 ± 17 μM, while 4COC affected SERCA only in the millimolar range (IC50 = 1370 ± 88 μM). IC50 of 4CMC for SERCA pump was 167 ± 8 μM, indicating that 4CMC is not a specific RyR agonist either, as it activated RyR in a similar concentration (EC50 = 121 ± 20 μM).Our data suggest that the use of 4COC might be more beneficial than 4CMC in experiments, when Ca2+ release should be triggered through RyRs without influencing SERCA activity.

A Coupled Electromechanical Myocyte Model to Assess the Effects of 2‐deoxy‐ATP on Contractile Function in the Heart

IntroductionHeart failure (HF) remains a significant cause of morbidity, mortality, and medical costs. HF is characterized by reduced contractile function and inability of the heart to pump sufficient blood to meet the body’s demands. Existing treatments for HF do not permanently restore cardiac function and can lead to side effects such as impaired ventricular relaxation. 2‐deoxy‐ATP (dATP), a novel heart failure therapeutic, has been shown to increase contractile function while enhancing relaxation [1]. Previous studies have shown that dATP increases the rate of crossbridge cycling [2]. It has also been shown that dATP acts on the sarcoplasmic reticulum ATPase (SERCA), the pump responsible for removing calcium (Ca2+) from the cytosol, which could explain the enhanced relaxation kinetics seen experimentally [3]. However, the mechanism of dATP is still not fully understood. Further, it is not clear whether the increased rate of crossbridge cycling with dATP treatment could aggravate energy starvation in HF.MethodsTo assess the full mechanism of dATP at the cellular level, we utilized a myocyte model containing several ion channels, including SERCA [4]. We coupled this model to a mitochondria model to investigate whether dATP treatment aggravates energy starvation by tracking ATP, ADP, Pi, and oxygen concentrations over time [5]. We also coupled the myocyte model to a previously developed 5 state Markov model of crossbridge cycling, which captures regulation of contraction via Ca2+ binding to troponin [2]. The crossbridge cycling model was modified to capture the effects of sarcomere length on Ca2+ sensitivity. dATP treatment was simulated by adjusting the ATP and Ca2+ binding rates in the SERCA model and the rate of crossbridge cycling in the sarcomere model based on previous studies [2, 3].Results and ConclusionsWe found that the combined effects of dATP on both SERCA and the sarcomere within the coupled myocyte model could explain the increase in fractional shortening and time to 50% and 90% relaxation of the Ca2+ transient seen experimentally more accurately than either model alone. Additionally, we found no evidence that dATP aggravates energy starvation, affirming dATP as a promising therapeutic for HF.Support or Funding InformationNIH HLT32 TG

Empagliflozin Attenuates Myocardial Sodium and Calcium Dysregulation and Reverses Cardiac Remodeling in Streptozotocin-Induced Diabetic Rats.

Diabetes mellitus (DM) has significant effects on cardiac calcium (Ca2+) and sodium (Na+) regulation. Clinical studies have shown that empagliflozin (Jardiance™) has cardiovascular benefits, however the mechanisms have not been fully elucidated. This study aimed to investigate whether empagliflozin modulates cardiac electrical activity as well as Ca2+/Na+ homeostasis in DM cardiomyopathy. Electrocardiography, echocardiography, whole-cell patch-clamp, confocal microscopic examinations, and Western blot, were performed in the ventricular myocytes of control and streptozotocin-induced DM rats, with or without empagliflozin (10 mg/kg for 4 weeks). The results showed that the control and empagliflozin-treated DM rats had smaller left ventricular end-diastolic diameters and shorter QT intervals than the DM rats. In addition, the prolonged action potential duration in the DM rats was attenuated in the empagliflozin-treated DM rats. Moreover, the DM rats had smaller sarcoplasmic reticular Ca2+ contents, intracellular Ca2+ transients, L-type Ca2+, reverse mode Na+-Ca2+exchanger currents, lower protein expressions of sarcoplasmic reticulum ATPase, ryanodine receptor 2 (RyR2), but higher protein expressions of phosphorylated RyR2 at serine 2808 than the control and empagliflozin-treated DM rats. The incidence and frequency of Ca2+ sparks, cytosolic and mitochondrial reactive oxygen species, and late Na+ current and Na+/hydrogen-exchanger currents were greater in the DM rats than in the control and empagliflozin-treated DM rats. Empagliflozin significantly changed Ca2+ regulation, late Na+ and Na+/hydrogen-exchanger currents and electrophysiological characteristics in DM cardiomyopathy, which may contribute to its cardioprotective benefits in DM patients.

Mechanism of the E2 to E1 transition in Ca2+ pump revealed by crystal structures of gating residue mutants

Ca2+-ATPase of sarcoplasmic reticulum (SERCA1a) pumps two Ca2+ per ATP hydrolyzed from the cytoplasm and two or three protons in the opposite direction. In the E2 state, after transferring Ca2+ into the lumen of sarcoplasmic reticulum, all of the acidic residues that coordinate Ca2+ are thought to be protonated, including the gating residue Glu309. Therefore a Glu309Gln substitution is not expected to significantly perturb the structure. Here we report crystal structures of the Glu309Gln and Glu309Ala mutants of SERCA1a under E2 conditions. The Glu309Gln mutant exhibits, unexpectedly, large structural rearrangements in both the cytoplasmic and transmembrane domains, apparently uncoupling them. However, the structure definitely represents E2 and, together with the help of quantum chemical calculations, allows us to postulate a mechanism for the E2 → E1 transition triggered by deprotonation of Glu309.

A Stem Cell-Based Screening Platform Identifies Compounds that Desensitize Motor Neurons to Endoplasmic Reticulum Stress.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease selectively targeting motor neurons in the brain and spinal cord. The reasons for differential motor neuron susceptibility remain elusive. We developed a stem cell-based motor neuron assay to study cell-autonomous mechanisms causing motor neuron degeneration, with implications for ALS. A small-molecule screen identified cyclopiazonic acid (CPA) as a stressor to which stem cell-derived motor neurons were more sensitive than interneurons. CPA induced endoplasmic reticulum stress and the unfolded protein response. Furthermore, CPA resulted in an accelerated degeneration of motor neurons expressing human superoxide dismutase 1 (hSOD1) carrying the ALS-causing G93A mutation, compared to motor neurons expressing wild-type hSOD1. A secondary screen identified compounds that alleviated CPA-mediated motor neuron degeneration: three kinase inhibitors and tauroursodeoxycholic acid (TUDCA), a bile acid derivative. The neuroprotective effects of these compounds were validated in human stem cell-derived motor neurons carrying a mutated SOD1 allele (hSOD1A4V). Moreover, we found that the administration of TUDCA in an hSOD1G93A mouse model of ALS reduced muscle denervation. Jointly, these results provide insights into the mechanisms contributing to the preferential susceptibility of ALS motor neurons, and they demonstrate the utility of stem cell-derived motor neurons for the discovery of new neuroprotective compounds.

THE GROWTH HORMONE SECRETAGOGUE RECEPTOR, GHRELIN AND BIOCHEMICAL SIGNALING MOLECULES IN HUMAN HEART DISEASE

Diagnosis of heart disease (HD) is based on clinical features, imaging, and circulating biomarkers, such as B-type natriuretic peptide (BNP), the gold standard heart failure biomarker. However, a cardiac-specific biomarker with potential to detect and might have the potential to predict the development of contractile dysfunction is lacking. The growth hormone secretagogue receptor (GHSR) and its ligand ghrelin may be cardiac-specific biomarkers. We have characterized a fluorescent analog of ghrelin, [Ghrelin(1-19), Lys19(Sulf-cyanine5)] to detect changes in cardiac GHSR in situ in diabetic cardiomyopathy and heart failure. We are now using this tool to map changes in regional and cellular distribution of GHSR in HD. Tissue was obtained from the left ventricle (LV) and right atrium (RA) of 23 patients who had aortic valve reconstruction (AVR). Ten patients also had coronary artery bypass grafting (CABG). GHSR levels were measured by quantitative fluorescence microscopy using Cy5-ghrelin(1-19). Immunofluorescence was used to measure ghrelin, BNP, sarcoplasmic reticulum ATPase pump (SERCA, marker of contractility) and phosphorylated extracellular signal-related kinase (pERK, marker of cell metabolism). Fluorescence intensities from 4 slides per patient were quantified using ImageJ FIJI. Data were analysed by two-tailed t-test, one-way ANOVA and Tukey test, Pearson correlation and linear regression (p<0.05). A strong positive correlation (p<0.001) was noted between ghrelin and GHSR (r=0.857) or BNP (r=0.769). Ghrelin strongly correlated with SERCA2a (r=0.789, p<0.0001) and pERK (r=0.430, p<0.0319) relative to BNP (r=0.619, p=0.001 and r=0.508, p=0.0095 respectively). Regional localization analyses showed marked differences in the RA compared with the LV; there were highly significant correlations (p<0.0001) between ghrelin and BNP (r=0.802) or SERCA2a (r=0.847), and GHSR and SERCA2a (r=0.875), only in the RA. In both males and females, there was strong correlation between GHSR and ghrelin. In females BNP was more strongly correlated with ghrelin (r=0.827, p=0.0032) and GHSR (r=0.860, p=0.0014) while in males, SERCA2A was more strongly correlated with GHSR (r=0.714, p=0.0019) and ghrelin (r=0.8243, p<0.0001). Those who also underwent CABG showed significant correlations with ghrelin and BNP (r=0.792, p=0.0013) or SERCA2a (r=0.772, p=0.0033), and GHSR and SERCA2a (r=0.745, p=0.0054). GHSR expression in HD has shown differences in its sensitivity as a biomarker according to regional tissue distribution, gender and HD etiology. These results highlight the potential use of GHSR/ghrelin as a new cardiac-specific biomarker for HD detection from the RA and coronary artery disease, and also highlights the need for gender-specific biomarkers of HD.

Annonacin promotes selective cancer cell death via NKA-dependent and SERCA-dependent pathways

In the healthcare sector, phytocompounds are known to be beneficial by contributing or alleviating a variety of diseases. Studies have demonstrated the progressive effects of phytocompounds on immune-related diseases and to exhibit anticancer effects. Graviola tree is an evergreen tree with its extracts (leafs and seeds) been reported having anticancer properties, but the precise target of action is not clear. Using an in silico approach, we predicted that annonacin, an Acetogenin, the active agent found in Graviola leaf extract (GLE) to potentially act as a novel inhibitor of both sodium/potassium (NKA) and sarcoplasmic reticulum (SERCA) ATPase pumps. We were able to validate and confirm the in silico studies by showing that GLE inhibited NKA and SERCA activity in intact cells. In the present study, we also demonstrated the antiproliferative and anticancer effects of GLE in a variety of cancer cell lines with limited toxic effects on non-transformed cells. Moreover, our results revealed that known inhibitors of both NKA and SERCA pumps could also promote cell death in several cancer cell lines. In addition, a mouse xenograft cancer model showed GLE as able to reduce tumor size and progression. Finally, bioprofiling studies indicated a strong correlation between overexpression of both NKA and SERCA gene expression vs. survival rates. Overall, our results demonstrated that GLE can promote selective cancer cell death via inhibiting NKA and SERCA, and thus can be considered as a potential novel treatment for cancer. After molecular analysis of GLE by liquid chromatography–mass spectrometry and ESI–QTOF–MS analysis, it was found that the MS spectrum of the high abundant chromatographic peak purified sample highly consisted of annonacin.

Activation of CaMKIIδA promotes Ca2+ leak from the sarcoplasmic reticulum in cardiomyocytes of chronic heart failure rats.

Activation of the Ca2+/calmodulin-dependent protein kinase II isoform δA (CaMKIIδA) disturbs intracellular Ca2+ homeostasis in cardiomyocytes during chronic heart failure (CHF). We hypothesized that upregulation of CaMKIIδA in cardiomyocytes might enhance Ca2+ leak from the sarcoplasmic reticulum (SR) via activation of phosphorylated ryanodine receptor type 2 (P-RyR2) and decrease Ca2+ uptake by inhibition of SR calcium ATPase 2a (SERCA2a). In this study, CHF was induced in rats by ligation of the left anterior descending coronary artery. We found that CHF caused an increase in the expression of CaMKIIδA and P-RyR2 in the left ventricle (LV). The role of CaMKIIδA in regulation of P-RyR2 was elucidated in cardiomyocytes isolated from neonatal rats in vitro. Hypoxia induced upregulation of CaMKIIδA and activation of P-RyR2 in the cardiomyocytes, which both were attenuated by knockdown of CaMKIIδA. Furthermore, we showed that knockdown of CaMKIIδA significantly decreased the Ca2+ leak from the SR elicited by hypoxia in the cardiomyocytes. In addition, CHF also induced a downregulation of SERCA2a in the LV of CHF rats. Knockdown of CaMKIIδA normalized hypoxia-induced downregulation of SERCA2a in cardiomyocytes in vitro. The results demonstrate that the inhibition of CaMKIIδA may improve cardiac function by preventing SR Ca2+ leak through downregulation of P-RyR2 and upregulation of SERCA2a expression in cardiomyocytes in CHF.

Ellagic Acid exerts anti‐inflammatory actions via disruption of store‐operated Ca entry (SOCE) pathway activators and coupling mediators[Office1

Pharmacological agents that can modulate Ca2+ homeostasis are being extensively explored as potential anti‐inflammatory agents. Ellagic acid (EA), a polyphenolic compound found in many fruits and plant extracts, has been known to possess anti‐inflammatory properties. However, the mechanism of action behind its anti‐inflammatory action is unclear. We studied the effects of EA on Ca2+ handling, in particular, store‐operated Ca2+ entry (SOCE), a process critical to proper T cell function. EA is thought to modulate Ca2+ homeostasis by enhancing sarcoplasmic endoplasmic reticulum ATPase pump (SERCA) activity, however effects of EA on Ca2+ signaling is not clearly understood. We demonstrate that acute addition of EA induced Ca2+ release (EC50= 63 μM). A 12 h incubation of Jurkat T cells with EA decreased the ATP‐induced Ca2+ release and diminished the SOCE‐mediated Ca2+ influx in a dose dependent manner (IC50= 23 μM). The inhibition of SOCE was also confirmed by reduced Mn2+ entry rates in the EA‐treated cells. The two important components of SOCE are the endoplasmic reticulum (ER)‐Ca2+ sensor Stromal Interaction Molecule (STIM), and highly‐Ca2+ selective plasma membrane (PM) Orai channels. EA treatment attenuated the ATP‐induced Ca2+ influx in EA‐treated HEK293 cells transiently transfected with SOCE channel Orai1‐myc and ER‐sensor stromal interaction molecule (STIM1) (HEKSTIM/Orai). Furthermore, EA treatment interfered with the Orai1 and STIM1 coupling by disrupting STIM1 puncta formation in the HEKSTIM/Orai cells. Since expression of certain cytokines is directly dependent on Ca2+ influx, we measured the levels of IL‐2 and INFγ in EA‐treated Jurkat cells. Indeed, EA‐treated resulted in a significant decrease in IL‐2 and INFγ expression. The activity of nuclear factor of activated T‐cell (NFAT), a transcriptional factor has been shown to be dependent on SOCE mediated Ca2+ influx. Prolong exposure to EA decreased the translocation of nuclear factor of activated T‐cell in stimulated T cells. Hence, by inhibiting SOCE mediated Ca2+ influx, EA decreased downstream activation of pro‐inflammatory mediators. These observations suggest a novel target to EA‐mediated effects and provide insight into the mechanisms underlying EA mediated anti‐inflammatory effects.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Pharmacological Targeting of Serca May Have Potential for Cellular Protection

We previously reported that CGP-37157 and K201, two benzothiazepines (BZT) with cardioprotective action, inhibit the Ca2+ ATPase of sarcoplasmic reticulum (SR) intracellular Ca2+ stores (SERCA). We tested if SERCA block could be part of the mechanism by which drugs protect cells from ischemic damage. We also screened structural characteristics in BZT that could affect their drug potency as SERCA inhibitors. SR microsomes isolated from rabbit skeletal muscle (SkM) and pig heart ventricle were utilized to measure modulation of SR Ca2+ loading and SERCA-mediated ATPase activity by drugs. Seven out of twenty cell-protective drugs tested (including pimozide, EGCG, KN-93 and carvedilol) inhibited, at least partially, SR Ca2+ loading and Ca2+-stimulated ATPase activity in SkM and heart SR microsomes. We also screened ten novel BZT derivatives and seven FDA-approved benzodiazepines (BZD; including bromazepam and clonazepam), which have close homology to CGP37157. Ca2+-dependent block of SERCA was found in four BZT's, which displayed higher (PH000995, PH000902) and similar potency (PH000902, PH006796) compared to CGP. BZD were all ineffective, which suggest that the sulfur atom in the BZT ring (substituted by nitrogen in BZD) is crucial for their SERCA blocking ability. All compounds above, were tested on ryanodine receptor (RyR) activity (planar bilayers, SR leak, [3H] ryanodine binding). None of these agents directly inhibited RyR function in heart and muscle. In contrast, some agents (BZT and BZD) had mild agonistic action on channel function. We think that SERCA block by these drugs, which persists at pH ∼6.5, may benefit ischemic cells by preventing SR Ca2+ overload, known to trigger, upon reperfusion, abnormal RyR-mediated Ca2+ leak associated with cell death and tissue injury. BZT have potential as templates for therapeutic targeting of SERCA (Supported by AHA and Eskridge Foundation).

Effects of Nitrosyl Iron Complexes with Thiocarbamide and Its Aliphatic Derivatives on Activities of Ca2+-ATPase of Sarcoplasmic Reticulum and cGMP Phosphodiesterase.

We studied the effects of water-soluble cationic dinitrosyl iron complexes with thiocarbamide and its aliphatic derivatives, new synthetic analogs of natural NO donors, active centers of nitrosyl [1Fe-2S]proteins, on activities of Ca2+-ATPase of sarcoplasmic reticulum and cGMP phosphodiesterase. Nitrosyl iron complexes [Fe(C3N2H8S)Cl(NO)2]0[Fe(NO)2(C3N2H8S)2]+Cl- (I), [Fe(SC(N(CH3)2)2(NO)2]Cl (II), [Fe(SC(NH2)2)2(NO)2Cl×H2O (III), and [Fe(SC(NH2)2)2(NO)2]2SO4×H2O (IV) in a concentration of 10-4 M completely inhibited the transporting and hydrolytic functions of Ca2+-ATPase. In a concentration of 10-5 M, they inhibited active Ca2+ transport by 57±6, 75±8, 80±8, and 85±9% and ATP hydrolysis by 0, 40±4, 48±5, and 38±4%, respectively. Complex II reversibly and noncompetitively inhibited the hydrolytic function of Ca2+-ATPase (Ki=1.7×10-6 M). All the studied iron-sulphur complexes in a concentration of 10-4 M inhibited cGMP phosphodiesterase function. These data suggest that the studied complexes can exhibit antimetastatic, antiaggregation, vasodilatatory, and antihypertensive activities.

Effect of acute peritonitis on rocuronium-induced intraperitoneal pressure reduction and the uptake function of the sarcoplasmic reticulum.

Previous studies have reported the incomplete relaxation effect of neuromuscular blockers on skeletal muscles in acute peritonitis (AP) and other inflammatory processes; however, the underlying mechanisms responsible for this effect have not yet been satisfactorily identified. The impaired removal of cytosolic Ca2+ through sarcoendoplasmic Ca2+-ATPase (SERCA) and defects in sarcoplasmic reticulum (SR) Ca2+ uptake are the major contributing factors to diastolic dysfunction. Previous studies on the effects of neuromuscular blockers have primarily focused on neuromuscular transmission. Because of the reduced calcium uptake in the SR itself, even when neuromuscular transmission is fully blocked, the muscle is not able to relax effectively. In the present study, the impact of AP on rocuronium-induced intraperitoneal pressure reduction and rectus abdominal muscle relaxation, and SERCA uptake function was investigated. AP was induced via gastric perforation and changes in the intraperitoneal pressure before and after the administration of rocuronium were recorded. Muscle contractile properties, uptake and release functions and SERCA activity in the rectus abdominal muscles of AP model rats were measured. The half-relaxation time in the AP group was significantly prolonged compared with that in the control group (P<0.01). The peak rate of SR Ca2+ uptake for whole muscle homogenates was significantly reduced (P<0.05) in AP model rats without reduction of the rate of Ca2+ release evoked through AgNO3. In conclusion, gastric perforation-induced AP attenuates the intraperitoneal pressure-reducing effect of rocuronium, and AP induces diastolic dysfunction of the rectus abdominal muscle. The SR Ca2+-ATPase uptake rate was also reduced by AP.

Mn2+ transport by Ca2+ -ATPase of sarcoplasmic reticulum.

Ca(2+) -ATPase of sarcoplasmic reticulum is known to pump Mn(2+) in addition to Ca(2+) , but whether its transport mechanism is identical to that of Ca(2+) is ambiguous. To clarify, we examined, by atomic absorption spectroscopy, competition between Mn(2+) and Ca(2+) in active transport using vesicles of sarcoplasmic reticulum (SR). Here, we demonstrate that Ca(2+) -ATPase transports Ca(2+) and Mn(2+) concomitantly but has a much lower affinity for Mn(2+) (apparent Kd ~ 0.5 mm). Stoichiometries of transported ions per ATP hydrolysed, Vmax values and activation energies are very similar. Altogether, Ca(2+) -ATPase appears to use the same mechanism for transporting Mn(2+) as that for Ca(2+) .