In vivo heat production dynamics during a contraction-relaxation cycle in rat single skeletal muscle fibers.

Skeletal muscle generates heat via contraction-dependent (shivering) and independent (nonshivering) mechanisms. While this thermogenic capacity of skeletal muscle undoubtedly contributes to the body temperature homeostasis of animals and impacts various cellular functions, the intracellular temperature and its dynamics in skeletal muscle in vivo remain elusive. We aimed to determine the intracellular temperature and its changes within skeletal muscle in vivo during contraction and following relaxation. In addition, we tested the hypothesis that sarcoplasmic reticulum Ca2+ ATPase (SERCA) generates heat and increases the myocyte temperature during a transitory Ca2+-induced contraction-relaxation cycle. The intact spinotrapezius muscle of anesthetized adult male Wistar rats (n = 18) was exteriorized and loaded with the fluorescent probe Cellular Thermoprobe for Fluorescence Ratio (49.3 µM) by microinjection over 1 s. The fluorescence ratio (i.e., 580 nm/515 nm) was measured in vivo during 1) temperature increases induced by means of an external heater, and 2) Ca2+ injection (3.9 nL, 2.0 mM). The fluorescence ratio increased as a linear function of muscle surface temperature from 25 °C to 40 °C (r2 = 0.97, P < 0.01). Ca2+ injection (3.9 nL, 2.0 mM) significantly increased myocyte intracellular temperature: An effect that was suppressed by SERCA inhibition with cyclopiazonic acid (CPA, Ca2+: 38.3 ± 1.4 °C vs Ca2++CPA: 28.3 ± 2.8 °C, P < 0.01 at 1 min following injection). While muscle shortening occurred immediately after the Ca2+ injection, the increased muscle temperature was maintained during the relaxation phase. In this investigation, we demonstrated a novel model for measuring the intracellular temperature of skeletal muscle in vivo and further that heat generation occurs concomitant principally with SERCA functioning and muscle relaxation.

Cardiac-specific overexpression of insulin-like growth factor II receptor-α interferes with the regulation of calcium homeostasis in the heart under hyperglycemic conditions.

BACKGROUND: Diabetic cardiomyopathy is a progressive disease caused by inexplicit mechanisms, and a novel factor, insulin-like growth factor II receptor-α (IGF-IIRα), may contribute to aggravating its pathogenesis. We hypothesized that IGF-IIRα could intensify diabetic heart injury. METHODS AND RESULTS: To demonstrate the potential role of IGF-IIRα in the diabetic heart, we used (SD-TG [IGF-IIRα]) transgenic rat model with cardiac-specific overexpression of IGF-IIRα, along with H9c2 cells, to study the effects of IGF-IIRα in the heart under hyperglycemic conditions. IGF-IIRα was found to remodel calcium homeostasis and intracellular Ca2+ overload-induced autophagy disturbance in the heart during diabetes. IGF-IIRα overexpression induced intracellular Ca2+ alteration by downregulating phosphorylated phospholamban/sarcoplasmic/endoplasmic reticulum calcium-ATPase 2a (PLB/SERCA2a), resulting in the suppression of Ca2+ uptake into the endoplasmic reticulum. Additionally, IGF-IIRα itself contributed to Ca2+ withdrawal from the endoplasmic reticulum by increasing the expression of CaMKIIδ in the active form. Furthermore, alterations in Ca2+ homeostasis significantly dysregulated autophagy in the heart during diabetes. CONCLUSIONS: Our study reveals the novel role of IGF-IIRα in regulating cardiac intracellular Ca2+ homeostasis and its related autophagy interference, which contribute to the development of diabetic cardiomyopathy. In future, the present study findings have implications in the development of appropriate therapy to reduce diabetic cardiomyopathy.

A hydroalcoholic extract of Senecio nutans SCh. Bip (Asteraceae); its effects on cardiac function and chemical characterization.

ETHNOPHARMACOLOGY RELEVANCE: The plant Senecio nutans SCh. Bip. is used by Andean communities to treat altitude sickness. Recent evidence suggests it may produce vasodilation and negative cardiac inotropy, though the cellular mechanisms have not been elucidated. PURPOSE: To determinate the mechanisms action of S. nutans on cardiovascular function in normotensive animals. METHODS: The effect of the extract on rat blood pressure was measured with a transducer in the carotid artery and intraventricular pressure by a Langendorff system. The effects on sheep ventricular intracellular calcium handling and contractility were evaluated using photometry. Ultra-high-performance liquid-chromatography with diode array detection coupled with heated electrospray-ionization quadrupole-orbitrap mass spectrometric detection (UHPLC-DAD-ESI-Q-OT-MSn) was used for extract chemical characterization. RESULTS: In normotensive rats, S. nutans (10 mg/kg) reduced mean arterial pressure (MAP) by 40% (p < 0.05), causing a dose-dependent coronary artery dilation and decreased left ventricular pressure. In isolated cells, S. nutans extract (1 µg/ml) rapidly reduced the [Ca2+]i transient amplitude and sarcomere shorting by 40 and 49% (p < 0.001), respectively. The amplitude of the caffeine evoked [Ca2+]i transient was reduced by 24% (p < 0.001), indicating reduced sarcoplasmic reticulum (SR) Ca2+ content. Sodium-calcium exchanger (NCX) activity increased by 17% (p < 0.05), while sarcoendoplasmic reticulum Ca2+-ATPase (SERCA) activity was decreased by 21% (p < 0.05). LC-MS results showed the presence of vitamin C, malic acid, and several antioxidant phenolic acids reported for the first time. Dihydroeuparin and 4-hydroxy-3-(3-methylbut-2-enyl) acetophenone were abundant in the extract. CONCLUSION: In normotensive animals, S. nutans partially reduces MAP by decreasing heart rate and cardiac contractility. This negative inotropy is accounted for by decreased SERCA activity and increased NCX activity which reduces SR Ca2+ content. These results highlight the plant's potential as a source of novel cardio-active phytopharmaceuticals or nutraceuticals.

Sarco/endoplasmic reticulum Ca2+ ATPase (SERCA)-mediated ER stress crosstalk with autophagy is involved in tris(2-chloroethyl) phosphate stress-induced cardiac fibrosis.

Excessive organophosphate flame retardant (OPFR) use in consumer products has been reported to increase human disease susceptibility. However, the adverse effects of tris(2-chloroethyl) phosphate (TCEP) (a chlorinated alkyl OPFR) on the heart remain unknown. In this study, we tested whether cardiac fibrosis occurred in animal models of TCEP (10 mg/kg b.w./day) administered continuously by gavage for 30 days and evaluated the specific role of sarco/endoplasmic reticulum Ca2+ ATPase (SERCA). First, we confirmed that TCEP could trigger cardiac fibrosis by histopathological observation and cardiac fibrosis markers. We further verified that cardiac fibrosis occurred in animal models of TCEP exposure accompanied by SERCA2a, SERCA2b and SERCA2c downregulation. Notably, inductively coupled plasma-mass spectrometry (ICP-MS) analysis revealed that the cardiac concentrations of Ca2+ increased by 45.3% after TCEP exposure. Using 4-Isopropoxy-N-(2-methylquinolin-8-yl)benzamide (CDN1163, a small molecule SERCA activator), we observed that Ca2+ overload and subsequent cardiac fibrosis caused by TCEP were both alleviated. Simultaneously, the protein levels of endoplasmic reticulum (ER) markers (protein kinase R-like endoplasmic reticulum kinase (PERK), inositol requiring protein 1α (IRE1α), eukaryotic initiation factor 2 α (eIF2α)) were upregulated by TCEP, which could be abrogated by CDN1163 pretreatment. Furthermore, we observed that CDN1163 supplementation prevented overactive autophagy induced by TCEP in the heart. Mechanistically, TCEP could lead to Ca2+ overload by inhibiting the expression of SERCA, thereby triggering ER stress and overactive autophagy, eventually resulting in cardiac fibrosis. Together, our results suggest that the Ca2+ overload/ER stress/autophagy axis can act as a driver of cardiotoxicity induced by TCEP.

IgE-dependent human basophil responses are inversely associated with the sarcoplasmic reticulum Ca2+-ATPase (SERCA).

Basophils crucially contribute to allergies and other Th2-driven diseases by rapidly releasing inflammatory and immunomodulatory mediators following high-affinity IgE-receptor crosslinking. Although these basophil-mediated responses depend on sensitization with antigen-specific IgE, this does not necessarily predict clinical symptom severity. It is thought that the balance of early stimulatory (e.g. SYK) and inhibitory (e.g. SHIP-1) intracellular signals are associated with basophil responsiveness, which is also critically dependent on calcium mobilization. Previous studies suggest that the sarcoplasmic reticulum Ca2+-ATPase (SERCA2), which regulates cytosolic calcium levels, may be inversely associated with airway smooth muscle reactivity in asthma. Since basophils are implicated in asthma severity, our aims were to address whether SERCA2 is implicated in human basophil responses, especially following IgE-mediated activation. Human basophils were obtained from buffy coats, following research ethics approval, and further purified by immunomagnetic cell sorting. Expressions of SERCA2, and other isoforms, were determined by Western blotting in parallel to measuring IgE-dependent histamine releases from the same donors. The effects of a SERCA-activator and inhibitor were also assessed on their abilities to modulate basophil histamine release. We observed an inverse correlation between basophil responsiveness to IgE-dependent stimulation and SERCA2 expression. Thapsigargin, a highly-specific SERCA inhibitor, stimulated basophil histamine release and potentiated IgE-dependent secretion of the amine. Conversely, disulfiram, a SERCA activator, inhibited IgE-dependent basophil activation. The results obtained from this exploratory study indicate that SERCA2 may be an additional regulator of basophil reactivity alongside early excitatory or inhibitory signal transduction pathways.

Intratracheal Gene Delivery of SERCA2a Ameliorates Chronic Post-Capillary Pulmonary Hypertension: A Large Animal Model.

BACKGROUND: Pulmonary hypertension (PH) is characterized by pulmonary arterial remodeling that results in increased pulmonary vascular resistance, right ventricular (RV) failure, and premature death. Down-regulation of sarcoplasmic reticulum Ca(2+)-ATPase 2a (SERCA2a) in the pulmonary vasculature leads to perturbations in calcium ion (Ca(2+)) homeostasis and transition of pulmonary artery smooth muscle cells to a proliferative phenotype. OBJECTIVES: We assessed the feasibility of sustained pulmonary vascular SERCA2a gene expression using aerosolized delivery of adeno-associated virus type 1 (AAV1) in a large animal model of chronic PH and evaluated the efficacy of gene transfer regarding progression of pulmonary vascular and RV remodeling. METHODS: A model of chronic post-capillary PH was created in Yorkshire swine by partial pulmonary vein banding. Development of chronic PH was confirmed hemodynamically, and animals were randomized to intratracheal administration of aerosolized AAV1 carrying the human SERCA2a gene (n = 10, AAV1.SERCA2a group) or saline (n = 10). Therapeutic efficacy was evaluated 2 months after gene delivery. RESULTS: Transduction efficacy after intratracheal delivery of AAV1 was confirmed by ß-galactosidase detection in the distal pulmonary vasculature. Treatment with aerosolized AAV1.SERCA2a prevented disease progression as evaluated by mean pulmonary artery pressure, vascular resistance, and limited vascular remodeling quantified by histology. Therapeutic efficacy was supported further by the preservation of RV ejection fraction (p = 0.014) and improvement of the RV end-diastolic pressure-volume relationship in PH pigs treated with aerosolized AAV1.SERCA2a. CONCLUSIONS: Airway-based delivery of AAV vectors to the pulmonary arteries was feasible, efficient, and safe in a clinically relevant chronic PH model. Vascular SERCA2a overexpression resulted in beneficial effects on pulmonary arterial remodeling, with attendant improvements in pulmonary hemodynamics and RV performance, and might offer therapeutic benefit by modifying fundamental pathophysiology in pulmonary vascular diseases.

Targeting myocardial remodelling to develop novel therapies for heart failure: a position paper from the Working Group on Myocardial Function of the European Society of Cardiology.

The failing heart is characterized by complex tissue remodelling involving increased cardiomyocyte death, and impairment of sarcomere function, metabolic activity, endothelial and vascular function, together with increased inflammation and interstitial fibrosis. For years, therapeutic approaches for heart failure (HF) relied on vasodilators and diuretics which relieve cardiac workload and HF symptoms. The introduction in the clinic of drugs interfering with beta-adrenergic and angiotensin signalling have ameliorated survival by interfering with the intimate mechanism of cardiac compensation. Current therapy, though, still has a limited capacity to restore muscle function fully, and the development of novel therapeutic targets is still an important medical need. Recent progress in understanding the molecular basis of myocardial dysfunction in HF is paving the way for development of new treatments capable of restoring muscle function and targeting specific pathological subsets of LV dysfunction. These include potentiating cardiomyocyte contractility, increasing cardiomyocyte survival and adaptive hypertrophy, increasing oxygen and nutrition supply by sustaining vessel formation, and reducing ventricular stiffness by favourable extracellular matrix remodelling. Here, we consider drugs such as omecamtiv mecarbil, nitroxyl donors, cyclosporin A, SERCA2a (sarcoplasmic/endoplasmic Ca(2 +) ATPase 2a), neuregulin, and bromocriptine, all of which are currently in clinical trials as potential HF therapies, and discuss novel molecular targets with potential therapeutic impact that are in the pre-clinical phases of investigation. Finally, we consider conceptual changes in basic science approaches to improve their translation into successful clinical applications.

Parasitoid wasp venom SERCA regulates Drosophila calcium levels and inhibits cellular immunity.

Because parasite virulence factors target host immune responses, identification and functional characterization of these factors can provide insight into poorly understood host immune mechanisms. The fruit fly Drosophila melanogaster is a model system for understanding humoral innate immunity, but Drosophila cellular innate immune responses remain incompletely characterized. Fruit flies are regularly infected by parasitoid wasps in nature and, following infection, flies mount a cellular immune response culminating in the cellular encapsulation of the wasp egg. The mechanistic basis of this response is largely unknown, but wasps use a mixture of virulence proteins derived from the venom gland to suppress cellular encapsulation. To gain insight into the mechanisms underlying wasp virulence and fly cellular immunity, we used a joint transcriptomic/proteomic approach to identify venom genes from Ganaspis sp.1 (G1), a previously uncharacterized Drosophila parasitoid species, and found that G1 venom contains a highly abundant sarco/endoplasmic reticulum calcium ATPase (SERCA) pump. Accordingly, we found that fly immune cells termed plasmatocytes normally undergo a cytoplasmic calcium burst following infection, and that this calcium burst is required for activation of the cellular immune response. We further found that the plasmatocyte calcium burst is suppressed by G1 venom in a SERCA-dependent manner, leading to the failure of plasmatocytes to become activated and migrate toward G1 eggs. Finally, by genetically manipulating plasmatocyte calcium levels, we were able to alter fly immune success against G1 and other parasitoid species. Our characterization of parasitoid wasp venom proteins led us to identify plasmatocyte cytoplasmic calcium bursts as an important aspect of fly cellular immunity.

Augmentation of left ventricular mechanics by recirculation-mediated AAV2/1-SERCA2a gene delivery in experimental heart failure.

AIMS: Down-regulation of sarcoplasmic reticulum calcium ATPase (SERCA2a) is a key molecular abnormality in heart failure (HF), which is not currently addressed by specific pharmacotherapy. We sought to evaluate, in detail, the impact of augmented SERCA2a expression on left ventricular (LV) mechanics in a large animal model of HF. METHODS AND RESULTS: Heart failure was induced in adult sheep by rapid pacing (180 b.p.m.) for 1 month, followed by delivery of adeno-associated virus (AAV) 2/1-SERCA, using a percutaneous, recirculating system for gene delivery over a 10 min period. Left ventricular mechanics was investigated by echocardiography and conductance catheter measurements in sheep receiving AAV2/1-SERCA2a after a further 4 weeks of pacing in comparison with untreated HF controls. Left ventricular function was significantly improved in the AAV2/1-SERCA2a-treated group, despite continued pacing, as measured by fractional shortening (delta absolute FS, control -4.2 ± 1.5% vs. treatment 4.4 ± 1.5%; P < 0.01) and conductance catheterization (delta Ees, control -1.22 ± 0.60 vs. treatment 0.65 ± 0.51; P < 0.05). Western blots showed an increase in SERCA protein in AAV2/1-SERCA2a-treated animals, and an analysis of gene delivery showed no evidence of regional myocardial heterogeneity in the distribution of AAV2/1-SERCA. CONCLUSION: In a large animal model, AAV2/1-mediated SERCA2a gene delivery using percutaneous, recirculating cardiac delivery leads to improved LV function.

SERCA1 expression enhances the metabolic efficiency of improved contractility in post-ischemic heart.

Myocardial stunning is characterized by a metabolic uncoupling from function as mitochondrial tricarboxylic acid (TCA) cycle and oxygen consumption remain normal despite reduced contractility. Overexpression of the sarco-endoplasmic reticulum Ca2+-ATPase (SERCA1) in hearts has recently been reported to reduce dysfunction at reperfusion. In this study we determine whether the metabolic coupling to function improves with SERCA treatment. PBS (control) or adenovirus carrying the cDNA for SERCA1 was delivered via coronary perfusion in vivo to Sprague-Dawley rat hearts. Three days following gene transfer, isolated hearts were perfused with 0.4 mM [2,4,6,8,10,12,14,16-13C8] palmitate and 5 mM glucose, and subjected to 15-min ischemia followed by 40-min reperfusion. Consistent with myocardial stunning, rate pressure product (RPP) and left ventricular developed pressure (LVDP) were depressed 30-40% (p<0.05) in the PBS group. With SERCA1 overexpression, dP/dt was 20% greater than controls (p<0.05), and LVDP and RPP recovered to pre-ischemic values. From dynamic 13C NMR, TCA cycle flux at reperfusion was similar to pre-ischemic values for both groups. Therefore, the efficiency of coupling between cardiac work and TCA cycle flux was restored with SERCA1 treatment. Oxidative efficiency was also enhanced with SERCA1 as cytosolic NADH transport into the mitochondria was significantly greater compared to the PBS group. In addition, the phosphocreatine to ATP ratio (PCr/ATP) was not compromised with SERCA1 expression, despite enhanced function, and depressed fatty acid oxidation at 40-min reperfusion in the PBS group was not reversed with SERCA1. These data demonstrate that metabolic coupling and NADH transport are significantly improved with SERCA1 treatment.