Phospholamban Expression Research Articles

Perimenopause Decreases SERCA2a Activity in the Hearts of a Mouse Model of Ovarian Failure.

Risk of cardiovascular disease mortality rises in women after menopause. While increased cardiovascular risk is largely attributed to postmenopausal declines in estrogens, the molecular changes in the heart that contribute to risk are poorly understood. Disruptions in intracellular calcium handling develop in ovariectomized mice and have been implicated in cardiac dysfunction. Using a mouse model of menopause in which ovarian failure occurs over 120 days, we sought to determine if perimenopause impacted calcium removal mechanisms in the heart and identify the molecular mechanisms. Mice were injected with 4-vinylcyclohexene diepoxide (VCD) to induce ovarian failure over 120 days, mimicking perimenopause. Hearts were removed at 60 and 120 days after VCD injections, representing the middle and end of perimenopause. SERCA2a function was significantly diminished at the end of perimenopause. Neither SERCA2a nor phospholamban expression changed at either time point, but phospholamban phosphorylation at S16 and T17 was dynamically altered. Intrinsic SERCA inhibitors sarcolipin and myoregulin increased >4-fold at day 60, as did the native activator DWORF. At the end of perimenopause, sarcolipin and myoregulin returned to baseline levels while DWORF was significantly reduced below controls. Sodium-calcium exchanger expression was significantly increased at the end of perimenopause. These results show that the foundation for increased cardiovascular disease mortality develops in the heart during perimenopause and that regulators of calcium handling exhibit significant fluctuations over time. Understanding the temporal development of cardiovascular risk associated with menopause and the underlying mechanisms is critical to developing interventions that mitigate the rise in cardiovascular mortality that arises after menopause.

Phosphorylation of phospholamban promotes SERCA2a activation by dwarf open reading frame (DWORF)

In cardiac myocytes, the type 2a sarco/endoplasmic reticulum Ca-ATPase (SERCA2a) plays a key role in intracellular Ca regulation. Due to its critical role in heart function, SERCA2a activity is tightly regulated by different mechanisms, including micropeptides. While phospholamban (PLB) is a well-known SERCA2a inhibitor, dwarf open reading frame (DWORF) is a recently identified SERCA2a activator. Since PLB phosphorylation is the most recognized mechanism of SERCA2a activation during adrenergic stress, we studied whether PLB phosphorylation also affects SERCA2a regulation by DWORF. By using confocal Ca imaging in a HEK293 expressing cell system, we analyzed the effect of the co-expression of PLB and DWORF using a bicistronic construct on SERCA2a-mediated Ca uptake. Under these conditions of matched expression of PLB and DWORF, we found that SERCA2a inhibition by non-phosphorylated PLB prevails over DWORF activating effect. However, when PLB is phosphorylated at PKA and CaMKII sites, not only PLB's inhibitory effect was relieved, but SERCA2a was effectively activated by DWORF. Förster resonance energy transfer (FRET) analysis between SERCA2a and DWORF showed that DWORF has a higher relative affinity for SERCA2a when PLB is phosphorylated. Thus, SERCA2a regulation by DWORF responds to the PLB phosphorylation status, suggesting that DWORF might contribute to SERCA2a activation during conditions of adrenergic stress.

ZBTB20 Regulates SERCA2a Activity and Myocardial Contractility Through Phospholamban.

Intracellular Ca2+ cycling determines myocardial contraction and relaxation in response to physiological demands. SERCA2a (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase 2a) is responsible for the sequestration of cytosolic Ca2+ into intracellular stores during cardiac relaxation, and its activity is reversibly inhibited by PLN (phospholamban). However, the regulatory hierarchy of SERCA2a activity remains unclear. Cardiomyocyte-specific ZBTB20 knockout mice were generated by crossing ZBTB20flox mice with Myh6-Cre mice. Echocardiography, blood pressure measurements, Langendorff perfusion, histological analysis and immunohistochemistry, quantitative reverse transcription-PCR, Western blot analysis, electrophysiological measurements, and chromatin immunoprecipitation assay were performed to clarify the phenotype and elucidate the molecular mechanisms. Specific ablation of ZBTB20 in cardiomyocyte led to a significant increase in basal myocardial contractile parameters both in vivo and in vitro, accompanied by an impairment in cardiac reserve and exercise capacity. Moreover, the cardiomyocytes lacking ZBTB20 showed an increase in sarcoplasmic reticular Ca2+ content and exhibited a remarkable enhancement in both SERCA2a activity and electrically stimulated contraction. Mechanistically, PLN expression was dramatically reduced in cardiomyocytes at the mRNA and protein levels by ZBTB20 deletion or silencing, and PLN overexpression could largely restore the basal contractility in ZBTB20-deficient cardiomyocytes. These data point to ZBTB20 as a fine-tuning modulator of PLN expression and SERCA2a activity, thereby offering new perspective on the regulation of basal contractility in the mammalian heart.

Abstract 18550: Impaired Microtubule Mediated Protein Trafficking as a Mechanism of PLN R14del Dilated Cardiomyopathy

Introduction: Phospholamban (PLN) regulates calcium handling and contractility in the heart by altering its phosphorylation status, thereby activating or inhibiting the calcium ATPase SERCA2a. A pathogenic mutation in PLN at the Arginine 14 codon (R14del) results in dilated cardiomyopathy characterized by ventricular arrythmias and sudden cardiac death. Cytoplasmic aggregation of PLN is a hallmark of the disease. However, exactly how the R14del mutation causes DCM remains largely unknown. As PLN is trafficked to the cell membrane before it localizes to the t-tubules, we hypothesize that PLN protein trafficking may be impaired, contributing to the PLN aggregation and DCM. Methods: Induced pluripotent stem cell derived cardiomyocytes (iPSC- iPSC-CMs) from patients carrying the PLN R14del mutation and isogenic controls generated by CRISPR-Cas9 genome editing were tagged with biotin to quantify membrane-bound protein expression. Western blotting and mass spectrometry was used to identify differences membrane protein expression, and immunocytochemistry was used to image microtubule layout, PLN and junctional protein expression at the cell borderintercalated disc (do you mean the intercalated disk?) in micropatterned iPSC-CMs. Results: Quantification of membrane-bound proteins showed a significant decrease of PLN at the cell membrane and connexin 43 expression in the intercalated disk of R14del iPSC-CMs compared to isogenic controls. Additionally, we observed significantly reduced levels of EB1, the microtubule tip protein, at the cell border of PLN R14del iPSC-CMs by immunofluorescence imaging and western blot analysis. Finally, disruption of microtube polymerization by Nocodazole treatment, induced PLN aggregate formation in iPSC-CMs. Conclusion: Our data suggest that the transportation of PLN and Cx43 proteins by microtubules is impaired in PLN R14del iPSC-CMs, which results in PLN accumulation in the cytoplasm and a decrease of Cx43 expression in the intercalated disc. These findings provide a novel mechanism for the pathogenesis of PLN R14del cardiomyopathy and a possible therapeutic target.

Excitation and contraction of cardiac muscle and coronary arteries of brain-dead pigs.

Excitability and contraction of cardiac muscle from brain-dead donors critically influence the success of heart transplantation. Membrane physiology, Ca2+-handling, and force production of cardiac muscle and the contractile properties of coronary arteries were studied in hearts of brain-dead pigs. Cardiac muscle and vascular function after 12 h brain death (decapitation between C2 and C3) were compared with properties of fresh tissue. In both isolated cardiomyocytes (whole-cell patch clamp) and trabecular muscle (conventional microelectrodes), action potential duration was shorter in brain dead, compared to controls. Cellular shortening and Ca2+ transients were attenuated in the brain dead, and linked to lower mRNA expression of L-type calcium channels and a slightly lower ICa,L, current, as well as to a lower expression of phospholamban. The current-voltage relationship and the current above the equilibrium potential of the inward K+ (IK1) channel were altered in the brain-dead group, associated with lower mRNA expression of the Kir2.2 channel. Delayed K+ currents were detected (IKr, IKs) and were not different between groups. The transient outward K+ current (Ito) was not observed in the pig heart. Coronary arteries exhibited increased contractility and sensitivity to the thromboxane analogue (U46619), and unaltered endothelial relaxation. In conclusion, brain death involves changes in cardiac cellular excitation which might lower contractility after transplantation. Changes in the inward rectifier K+ channel can be associated with an increased risk for arrhythmia. Increased reactivity of coronary arteries may lead to increased risk of vascular spasm, although endothelial relaxant function was well preserved.

Alterations of sarcoplasmic reticulum-mediated Ca2+ uptake in a model of premature ventricular contraction (PVC)-induced cardiomyopathy.

Premature ventricular contractions (PVCs) are the most frequent ventricular arrhythmias in the overall population. PVCs are known to acutely enhance contractility by the post-extrasystolic potentiation phenomenon, but over time persistent PVCs promote PVC-induced cardiomyopathy (PVC-CM), characterized by a reduction of the left ventricular (LV) ejection fraction. Ca2+ cycling in myocytes commands muscle contraction and in this process, SERCA2 leads the Ca2+ reuptake into the sarcoplasmic reticulum (SR) shaping cytosolic Ca2+ signal decay and muscle relaxation. Altered Ca2+ reuptake can contribute to the contractile dysfunction observed in PVC-CM. To better understand Ca2+ handling using our PVC-CM model (canines with 50% PVC burden for 12weeks), SR-Ca2+ reuptake was investigated by measuring Ca2+ dynamics and analyzing protein expression. Kinetic analysis of Ca2+ reuptake in electrically paced myocytes showed a ~ 21ms delay in PVC-CM compared to Sham in intact isolated myocytes, along with a ~ 13% reduction in SERCA2 activity assessed in permeabilized myocytes. Although these trends were not statistically significant between groups using hierarchical statistics, relaxation of myocytes following contraction was significantly slower in PVC-CM vs Sham myocytes. Western blot analyses indicate a 22% reduction in SERCA2 expression, a 23% increase in phospholamban (PLN) expression, and a 50% reduction in PLN phosphorylation in PVC-CM samples vs Sham. Computational analysis simulating a 20% decrease in SR-Ca2+ reuptake resulted in a ~ 22ms delay in Ca2+ signal decay, consistent with the experimental result described above. In conclusion, SERCA2 and PLB alterations described above have a modest contribution to functional adaptations observed in PVC-CM.

Synergistic and Attenuating Effect of Electroacupuncture on Aconitine in Improving Heart Failure and Its Calcium Regulation Mechanism.

Objective The objective is to observe the synergistic and attenuating effect of electroacupuncture (EA) on aconitine (ACO) in improving heart failure (HF) and to explore its underlying mechanism for calcium regulation. Methods Twenty-four male Sprague-Dawley rats were randomly divided into four groups: normal control (NC) (n = 6), HF(n = 6), ACO (n = 6), and ACO + EA (n = 6). The maximum rates of left ventricular pressure rising and declining (±dp/dtmax), arrhythmia, the left ventricular systolic pressure (LVSP), ejection fraction (LVEF), and fractional shortening (LVFS) were measured by physiological recorder and ultrasound, respectively. Protein expressions of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA2a), phospholamban (PLB), and Na+-Ca2+ exchange (NCX1) in the left ventricle tissue were detected by fluorescence immunoblotting. Results Compared with the NC group, LVSP, ±dp/dtmax, LVEF, and LVFS were decreased in the HF group; compared with the HF group, LVSP, ±dp/dtmax, LVEF, and LVFS were significantly increased in the ACO + EA group. Compared with the ACO group, the incidence and the degree of arrhythmia were significantly reduced in the ACO + EA group. Compared with the NC group, the activity of SERCA2a was decreased, and the expression of PLB and NCX1 was enhanced in the HF group; compared with the HF group and ACO group, the activity of SERCA2a was increased, and the expression of PLB and NCX1 was significantly attenuated in the ACO + EA group. Conclusions EA plays a synergistic and attenuated role in ACO improving HF, and the mechanism may be related to the enhancement of the SERCA2a activity and the decrease of the expression of PLB and NCX1 in cardiomyocytes.

Abstract 13287: Sex Differences in the Impact of Parental Obesity on Offspring Cardiac SIRT3 Expression, Mitochondrial Efficiency and Diastolic Function Early in Life

Introduction: Previous studies suggest that the perinatal environment can profoundly impact long-term metabolic health of the offspring. Hypothesis: We tested the hypothesis that parental (paternal + maternal) obesity impairs cardiac function in the offspring early in life. Methods: Within 1-3 days after weaning, offspring from obese rats fed a high fat diet (HFD-Offs) and age-matched offspring from lean rats (ND-Offs) were submitted to echocardiography and cardiac catheterization for assessment of pressure-volume relationships. Then, hearts were digested and isolated cardiomyocytes were used to determine contractile function, calcium transients, proteins related to calcium signaling, and mitochondrial bioenergetics. Results: Female and male HFD-Offs were heavier (72±2 and 61±4 vs 57±2 and 49 ±1 g), hyperglycemic (112±8 and 115±12 vs 92±10 and 96±8 mg/dL), with higher plasma insulin and leptin concentrations compared to female and male ND-Offs respectively. Compared to male ND-Offs controls, male HFD-Offs exhibited similar systolic function but impaired diastolic function as indicated by increased isovolumetric relaxation time (IVRT, 22±1 vs. 17±1 ms), the ratio of mitral peak velocity of early filling (E) to early diastolic mitral annular velocity (E’) (E/E’ ratio, 29±2 vs. 23±1) and Tau (5.7±0.2 vs. 4.8±0.2 ms). The impaired diastolic function was associated with reduced resting free Ca 2+ levels and phospholamban protein expression, increased activated matrix metalloproteinase 2 and reduced sirtuin 3 (SIRT3) protein expression, mitochondrial ATP reserve and ATP-linked respiration. We found no differences in diastolic function or SIRT3 expression levels in female HFD-Offs and ND-Offs. Conclusions: These results indicate that male and female offspring from obese parents have metabolic abnormalities early in life (1-3 days after weaning) and that male, but not female, Offs from obese parents have impaired diastolic dysfunction and reductions in cardiac SIRT3, resting free Ca +2 levels and mitochondrial bioenergetics. (R01 DK121411, NHLBI-PO1HL51971, NIGMS P20GM104357 and U54GM115428)

Preliminary study on mechanism of electroacupuncture with the involvement of SERCA2a/PLB on the synergistic and attenuated effect of aconitine in treatment of heart failure

To investigate the mechanism of electroacupuncture (EA) with the involvement of sarcoplasmic reticulum Ca2+-ATPase2a (SERCA2a)/phospholamban (PLB) on the synergistic and attenuated effect of aconitine for heart failure. Thirty SPF-ranked SD rats were randomly divided into a control group, a model group, an EA group, an aconitine group and an EA plus aconitine group, with 6 rats in each group. The rat model of acute heart failure was established by infusion of high-dose propranolol hydrochloride solution into the right femoral vein. After stabilized for 10 min in the modeled rats, EA was exerted at "Neiguan" (PC 6), with disperse-dense wave, 2 Hz/15 Hz in frequency, 3 mA in intensity, for 30 min in the EA group and the EA plus aconitine group; aconitine solution (10 μg/kg) was injected from the left femoral veins in the rats in the aconitine group and the EA plus aconitine group. Hemodynamic indexes such as the left ventricular systolic pressure (LVSP) and the maximum rate of increase/decrease of left ventricular pressure (±dp/dtmax) were detected and arrhythmia types were observed and scored. SERCA2a protein and PLB protein expressions in left ventricular myocardial tissue of rats were detected by multiplex fluorescence Western blot. Compared with the control group, LVSP and ±dp/dtmax all were decreased after modeling and at each time point after intervention in the model group (P<0.01). Compared with the model group, ±dp/dtmax was increased in the aconitine group and the EA group at 1 min after intervention (P<0.01, P<0.05), +dp/dtmax was increased at 10 to 60 min after intervention in the aconitine group and at 20 to 60 min after intervention in the EA group (P<0.01, P<0.05), LVSP was increased at 1 min after intervention in the EA group (P<0.01), while LVSP and ±dp/dtmax were all increased at 1 to 60 min after intervention in the EA plus aconitine group (P<0.01, P<0.05). Compared with the aconitine group, LVSP and +dp/dtmax were increased at 1 min after intervention in the EA group (P<0.01, P<0.05), LVSP and ±dp/dtmax at 1 min after intervention while +dp/dtmax at 20 to 60 min after intervention were all increased in the EA plus aconitine group (P<0.01, P<0.05). Compared with the EA group, +dp/dtmax was higher at 10 to 60 min after intervention in the EA plus aconitine group (P<0.01). Compared with the model group, arrhythmia score was higher in the aconitine group (P<0.01). Compared with the aconitine group, arrhythmia score was lower in the EA group and the EA plus aconitine group (P<0.01). As compared with the control group, the expression of SERCA2a protein in the left ventricular cardiomyocytes was decreased (P<0.01), while the expression of PLB protein was increased in the model group (P<0.01). Compared with the model group, the expression of SERCA2a protein was increased in both the EA group and the EA plus aconitine group (P<0.05, P<0.01), and PLB protein expression was decreased in each intervention group respectively (P<0.01, P<0.05). As compared with the EA group and the aconitine group, the expression of SERCA2a protein was increased and the expression of PLB protein was decreased in the EA plus aconitine group separately (P<0.05, P<0.01). The intervention with electroacupuncture achieves the synergism/ attenuation effect of aconitine for the improvements in heart failure probably by up-regulating the expression of SERCA2a and down-regulating the expression of PLB in myocardial tissue.

Abstract P482: Elucidating And Characterizing The Molecular Mechanistic Role Of Phospholamban L39 Stop In The Pathophysiology Of Cardiomyopathy Using Patient-derived Human Induced Pluripotent Stem Cells And Humanized Knock-in Mouse Model Systems

Background: Heart failure (HF) is a complex clinical condition associated with substantial morbidity and mortality worldwide. The contractile dysfunction and arrhythmogenesis related to HF has been linked to the remodelling of calcium (Ca ++ ) handling. Phospholamban (PLN) has emerged as a key regulator of intracellular Ca ++ concentration. Of the PLN mutations, L39X is intriguing as it has not been fully characterized. This mutation is believed to be functionally equivalent to PLN null (KO) but contrary to PLN KO mice, L39X carriers develop a lethal cardiomyopathy (CMP). Our study aims at using induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CMs) from homozygous L39X carriers to elucidate the role of L39X in human pathophysiology. Our plan also involves the characterization of humanized L39X knock-in mice (KM), which we hypothesize will develop a CMP from mis-localization of PLN and disruption of Ca ++ signalling. Methodology and Results: Mononuclear cells from Hom L39X carriers were obtained to generate 11 integration-free patient-specific iPSC clones. The iPSC-CMs were derived using established protocols. Compared to the WT iPSC-CMs, the Hom L39X derived-CMs PLN had an abnormal cytoplasmic distribution and formed intracellular aggregates, with the loss of perinuclear localization. There was also a 70% and 50% reduction of mRNA and protein expression of PLN respectively in L39X compared to WT iPSC-CMs. These findings indicated that L39X PLN is both under-expressed and mis-localized within the cell. To validate this observation in-vivo, we genetically modified FVB mice to harbour the human L39X. Following electroporation, positively transfected mouse embryonic stem cells were injected into host blastocysts to make humanized KM that were subsequently used to generate either a protamine-Cre (endogenous PLN driven expression) or a cardiac TNT mouse (i.e., CMP specific). Conclusion: Our data confirm an abnormal intracellular distribution of PLN, with the loss of perinuclear accumulation and mis-localization, suggestive of ineffective targeting to or retention of L39X. The mouse model will be critically important to validate the in-vitro observations and provides an ideal platform for future studies centred on the development of novel therapeutic strategies including virally delivered CRISPR/Cas9 for in-vivo gene editing and testing of biochemical signalling pathways.

Digoxin Combined with Aerobic Interval Training Improved Cardiomyocyte Contractility.

Digoxin is a cardiotonic that increases the cardiac output without causing deleterious effects on heart, as well as improves the left ventricular performance during physical exercise. We tested whether the association between chronic digoxin administration and aerobic interval training (AIT) promotes beneficial cardiovascular adaptations by improving the myocardial contractility and calcium (Ca2+) handling. Male Wistar rats were randomly assigned to sedentary control (C), interval training (T), sedentary digoxin (DIGO) and T associated to digoxin (TDIGO). AIT was performed on a treadmill (1h/day, 5 days/week) for 60 days, consisting of successive 8-min periods at 80% and 20% of VO2máx for 2 min. Digoxin was administered by orogastric gavage for 60 days. Left ventricle samples were collected to analysis of Ca2+ handling proteins; contractility and Ca2+ handling were performed on isolated cardiomyocytes. TDIGO group had a greater elevation in fractional shortening (44%) than DIGO, suggesting a cardiomyocyte contractile improvement. In addition, T or TDIGO groups showed no change in cardiomyocytes properties after Fura2-acetoxymethyl ester, as well as in sarcoplasmic reticulum Ca2+-ATPase (SERCA2a), phospholamban and calcineurin expressions. The main findings indicate that association of digoxin and aerobic interval training improved the cardiomyocyte contractile function, but these effects seem to be unrelated to Ca2+ handling.

Abstract 15218: Structural and Functional Alterations in a Premature Ventricular Contractions-induced Cardiomyopathy Model

Introduction: Previous studies of premature ventricular contractions (PVC)-induced cardiomyopathy (PVC-CM) in canines have showed reduction in L-type Ca 2+ current and Ca 2+ transient amplitude in isolated ventricular myocytes, concomitant with eccentric hypertrophy and a decline in left ventricular (LV) ejection fraction. Objectives: Assess potential alterations of PVC-CM related to: 1) the efficiency of the Ca 2+ recycling machinery in the sarcoplasmic reticulum (SR), and 2) the overall ultrastructural integrity of myocytes. Methods: Modified pacemakers were implanted in healthy canines to reproduce PVC-CM after 3 months of bigeminal PVC (50% burden at 200-220 ms coupling interval). Animals were randomized to either 50% PVC or no PVC (sham). Ventricular cardiomyocytes were isolated and paced to measure Ca 2+ transients using Fura2. Permeabilized cardiomyocytes loaded with Fluo-5N were used to assess SERCA2 activity in vitro . Additionally, expression of SERCA2, and phosphorylated versus total phospholamban (PLN) were measured with Western blot (WB). LV wall muscle was fixed, en-block stained with uranyl acetate, and thin-sectioned for electron microscopy (EM). Results: There was a non-statistically significant trend towards a reduction of SR-Ca 2+ reuptake efficiency in PVC-CM vs sham, evidenced by a 21% slower decay of the electrically-evoked cytosolic Ca 2+ transient and a 23% slower maximal rate of SR Ca 2+ uptake (PVC-CM n=42 cells, 4 animals vs sham n=50 cells, 3 animals). WB analysis showed a 23% reduction in SERCA2 expression (0.76 ± 0.18 vs 1 ± 0.25, P =0.002, n=6 animals each), a 40% increase in PLN expression (1.4 ± 0.18 vs 1 ± 0.1, P &lt;0.0001, n= 3 animals each), and a 64% reduction in phospho-PLN (0.35 ± 0.15 vs 1 ± 0.18, P &lt;0.0001, n=3 animals each) in PVC-CM vs sham. In addition, EM showed intact dyads, regularly shaped SR, but noticeable myofibril disorder in the PVC-CM derived samples. Conclusions: In PVC-CM, there is impaired electrically-evoked Ca 2+ cycling due to a combination of reduced L-type Ca 2+ channels and reduced SERCA-mediated SR Ca 2+ uptake. This combined with the apparent ultrastructural remodeling, underscore long-term cellular adaptations leading to LV systolic dysfunction associated to the chronic exposure to PVC.

Effects of Standardized Green Tea Extract and Its Main Component, EGCG, on Mitochondrial Function and Contractile Performance of Healthy Rat Cardiomyocytes.

We recently showed that the long-term in vivo administration of green tea catechin extract (GTE) resulted in hyperdynamic cardiomyocyte contractility. The present study investigates the mechanisms underlying GTE action in comparison to its major component, epigallocatechin-3-gallate (EGCG), given at the equivalent amount that would be in the entirety of GTE. Twenty-six male Wistar rats were given 40 mL/day of a tap water solution with either standardized GTE or pure EGCG for 4 weeks. Cardiomyocytes were then isolated for the study. Cellular bioenergetics was found to be significantly improved in both GTE- and EGCG-fed rats compared to that in controls as shown by measuring the maximal mitochondrial respiration rate and the cellular ATP level. Notably, the improvement of mitochondrial function was associated with increased levels of oxidative phosphorylation complexes, whereas the cellular mitochondrial mass was unchanged. However, only the GTE supplement improved cardiomyocyte mechanics and intracellular calcium dynamics, by lowering the expression of total phospholamban (PLB), which led to an increase of both the phosphorylated-PLB/PLB and the sarco-endoplasmic reticulum calcium ATPase/PLB ratios. Our findings suggest that GTE might be a valuable adjuvant tool for counteracting the occurrence and/or the progression of cardiomyopathies in which mitochondrial dysfunction and alteration of intracellular calcium dynamics constitute early pathogenic factors.

CaMKIIδC Drives Early Adaptive Ca2+ Change and Late Eccentric Cardiac Hypertrophy.

CaMKII (Ca2+-Calmodulin dependent protein kinase) δC activation is implicated in pathological progression of heart failure (HF) and CaMKIIδC transgenic mice rapidly develop HF and arrhythmias. However, little is known about early spatio-temporal Ca2+ handling and CaMKII activation in hypertrophy and HF. To measure time- and location-dependent activation of CaMKIIδC signaling in adult ventricular cardiomyocytes, during transaortic constriction (TAC) and in CaMKIIδC transgenic mice. We used human tissue from nonfailing and HF hearts, 4 mouse lines: wild-type, KO (CaMKIIδ-knockout), CaMKIIδC transgenic in wild-type (TG), or KO background, and wild-type mice exposed to TAC. Confocal imaging and biochemistry revealed disproportional CaMKIIδC activation and accumulation in nuclear and perinuclear versus cytosolic regions at 5 days post-TAC. This CaMKIIδ activation caused a compensatory increase in sarcoplasmic reticulum Ca2+ content, Ca2+ transient amplitude, and [Ca2+] decline rates, with reduced phospholamban expression, all of which were most prominent near and in the nucleus. These early adaptive effects in TAC were entirely mimicked in young CaMKIIδ TG mice (6-8 weeks) where no overt cardiac dysfunction was present. The (peri)nuclear CaMKII accumulation also correlated with enhanced HDAC4 (histone deacetylase) nuclear export, creating a microdomain for transcriptional regulation. At longer times both TAC and TG mice progressed to overt HF (at 45 days and 11-13 weeks, respectively), during which time the compensatory Ca2+ transient effects reversed, but further increases in nuclear and time-averaged [Ca2+] and CaMKII activation occurred. CaMKIIδ TG mice lacking δB exhibited more severe HF, eccentric myocyte growth, and nuclear changes. Patient HF samples also showed greatly increased CaMKIIδ expression, especially for CaMKIIδC in nuclear fractions. We conclude that in early TAC perinuclear CaMKIIδC activation promotes adaptive increases in myocyte Ca2+ transients and nuclear transcriptional responses but that chronic progression of this nuclear Ca2+-CaMKIIδC axis contributes to eccentric hypertrophy and HF.

The role of phospholamban and GSK3 in regulating rodent cardiac SERCA function.

Cardiac contractile function is largely mediated by the regulation of Ca2+ cycling throughout the lifespan. The sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA) pump is paramount to cardiac Ca2+ regulation, and it is well established that SERCA dysfunction pathologically contributes to cardiomyopathy and heart failure. Phospholamban (PLN) is a well-known inhibitor of the SERCA pump and its regulation of SERCA2a-the predominant cardiac SERCA isoform-contributes significantly to proper cardiac function. Glycogen synthase kinase 3 (GSK3) is a serine/threonine kinase involved in several metabolic pathways, and we and others have shown that it regulates SERCA function. In this mini-review, we highlight the underlying mechanisms behind GSK3's regulation of SERCA function specifically discussing changes in SERCA2a and PLN expression and its potential protection against oxidative stress. Ultimately, these recent findings that we discuss could have clinical implications in the treatment and prevention of cardiomyopathies and heart failure.

Abstract 530: Mechanisms Underlying Phospholamban L39 Stop (PLN L39X) Cardiomyopathy

Background: Defective calcium (Ca++) handling is a hallmark of HF across species. Together with the Sarco/Endoplasmic Reticulum Ca-ATPase (SERCA2a), Phospholamban (PLN) has emerged as a critical regulator of Ca++homeostasis. Worldwide, PLN mutations are identified with increasing frequency in patients with dilated, hypertrophic and arrhythmogenic cardiomyopathy (CMPs) but the causative defects leading to the CMP remain incompletely understood. While preclinical studies have unequivocally shown that absence of PLN (PLNKO) is therapeutic in rodent HF models, the discovery of a human pathogenic mutation (L39X) presumed to be the human equivalent of the PLNKO lead to the conclusion that PLN ablation was lethal in human, mitigating any enthusiasm in targeting PLN inhibition in PLN-associated disease or HF treatment. The objective of this proposal is to levarge the use of “induced-pluripotent” stem cells (iPSCs) derived cardiomyocytes (CM) from homozygote L39X carriers to elucidate the role of PLN (L39) in human pathophysiology. Methodology and Results: We obtained mononuclear cells from Homozygotes (Hom) L39 carriers and generated 11 iPSC clones. To derive CMs, we used the direct differentiation method temporally modulating the Wnt/β-catenin signaling. Immunocytostaining revealed positive expression of cardiac troponin T as well as PLN. In Hom L39 derived CMs, PLN showed an abnormal cytoplasmic distribution, formed intracellular aggregates and there was loss of perinuclear localization when compared to matched WT iPSC-CMs. Using fura-2AM, we observed decreased calcium transient amplitude in iPSC-CMs from L39 compared to WT with prolongation of the time constant of relaxation and early after depolarization (EAD). Lastly, we saw a 70% and 50% reduction in the protein and mRNA expression of PLN and SERCA2a respectively. Conclusions: Our data suggest that the L39 PLN mutant is expressed but mis-located within the cardiomyocytes. The mis-location of PLN was associated to decreased SERCA2a expression impaired Ca++ handling and increased arrhythmogenicity. Further studies will be required to fully elucidate the impact of the mutation in HF pathophysiology

Advancing physiological maturation in human induced pluripotent stem cell-derived cardiac muscle by gene editing an inducible adult troponin isoform switch.

Advancing maturation of stem cell-derived cardiac muscle represents a major barrier to progress in cardiac regenerative medicine. Cardiac muscle maturation involves a myriad of gene, protein, and cell-based transitions, spanning across all aspects of cardiac muscle form and function. We focused here on a key developmentally controlled transition in the cardiac sarcomere, the functional unit of the heart. Using a gene-editing platform, human induced pluripotent stem cell (hiPSCs) were engineered with a drug-inducible expression cassette driving the adult cardiac troponin I (cTnI) regulatory isoform, a transition shown to be a rate-limiting step in advancing sarcomeric maturation of hiPSC cardiac muscle (hiPSC-CM) toward the adult state. Findings show that induction of the adult cTnI isoform resulted in the physiological acquisition of adult-like cardiac contractile function in hiPSC-CMs in vitro. Specifically, cTnI induction accelerated relaxation kinetics at baseline conditions, a result independent of alterations in the kinetics of the intracellular Ca2+ transient. In comparison, isogenic unedited hiPSC-CMs had no cTnI induction and no change in relaxation function. Temporal control of adult cTnI isoform induction did not alter other developmentally regulated sarcomere transitions, including myosin heavy chain isoform expression, nor did it affect expression of SERCA2a or phospholamban. Taken together, precision genetic targeting of sarcomere maturation via inducible TnI isoform switching enables physiologically relevant adult myocardium-like contractile adaptations that are essential for beat-to-beat modulation of adult human heart performance. These findings have relevance to hiPSC-CM structure-function and drug-discovery studies in vitro, as well as for potential future clinical applications of physiologically optimized hiPSC-CM in cardiac regeneration/repair.

Metoprolol alleviates arginine vasopressin-induced cardiomyocyte hypertrophy by upregulating the AKT1\u2013SERCA2 cascade in H9C2 cells

BackgroundArginine vasopressin (AVP) is elevated in patients with heart failure, and the increase in the AVP concentration in plasma is positively correlated with disease severity and mortality. Metoprolol (Met) is a beta blocker that is widely used in the clinic to treat pathological cardiac hypertrophy and to improve heart function. However, the specific mechanism by which Met alleviates AVP-induced pathological cardiac hypertrophy is still unknown. Our current study aimed to evaluate the inhibitory effects of Met on AVP-induced cardiomyocyte hypertrophy and the underlying mechanisms.MethodsAVP alone or AVP plus Met was added to the wild type or AKT1-overexpressing rat cardiac H9C2 cell line. The cell surface areas and ANP/BNP/β-MHC expressions were used to evaluate the levels of hypertrophy. Western bolting was used to analyze AKT1/P-AKT1, AKT2/P-AKT2, total AKT, SERCA2, and Phospholamban (PLN) expression. Fluo3-AM was used to measure the intracellular Ca2+ stores.ResultsIn the current study, we found that AKT1 but not AKT2 mediated the pathogenesis of AVP-induced cardiomyocyte hypertrophy. Sustained stimulation (48 h) with AVP led to hypertrophy in the H9C2 rat cardiomyocytes, resulting in the downregulation of AKT1 (0.48 fold compared to control) and SERCA2 (0.62 fold), the upregulation of PLN (1.32 fold), and the increase in the cytoplasmic calcium concentration (1.52 fold). In addition, AKT1 overexpression increased the expression of SERCA2 (1.34 fold) and decreased the expression of PLN (0.48 fold) in the H9C2 cells. Moreover, we found that Met could attenuate the AVP-induced changes in AKT1, SERCA2 and PLN expression and decreased the cytoplasmic calcium concentration in the H9C2 cells.ConclusionsOur results demonstrated that the AKT1–SERCA2 cascade served as an important regulatory pathway in AVP-induced pathological cardiac hypertrophy.

Determinants of Diastolic Dysfunction in Swine with HFpEF Arising From Transient Repetitive Left Ventricular Pressure Overload

ObjectiveWe recently demonstrated that swine subjected to 2‐weeks of repetitive pressure overload (RPO) exhibit adaptive myocardial remodeling in the absence of left ventricular (LV) hypertrophy. This remodeling is similar to that arising in many patients with heart failure and a preserved ejection fraction (HFpEF). While LV compliance is markedly reduced, the relative contribution of altered myocardial relaxation vs. passive myocardial properties to this is unclear. Accordingly, the objective of the present study was to determine how RPO affects passive myocardial stiffness and active myocardial relaxation, two key components of LV diastolic function.MethodsSwine (n=14) were subjected to 2‐weeks of RPO via daily infusions of phenylephrine (300 ug/min, 2 hours/day). Invasive measurements of LV performance were collected before and after RPO at rest and during alterations in loading conditions elicited by transient manipulation of venous return. To assess reversibility, a subset of animals (n=6) underwent repeat studies 2‐weeks after cessation of RPO. After the final study, myocardial tissue was collected from the LV free wall for post‐mortem assessment of calcium handling protein expression (western blot; n=8), passive myocardial stiffness (uniaxial tensile testing; n=3), and quantification of interstitial fibrosis (picrosirius red staining).ResultsCompared with baseline measurements, 2‐weeks of RPO did not significantly affect the LV relaxation time constant (Tau) or the rate of LV pressure change during isovolumic relaxation (dP/dtmin; Table ). Consistent with this observation, myocardial expression of calcium handling proteins SERCA (from 0.58±0.24 to 0.52±0.25, p=0.62), ryanodine receptor (from 0.37±0.17 to 0.36±0.14, p=0.99), and phospholamban (from 0.46±0.21 to 0.33±0.15, p=0.17) was not different following RPO vs. normal controls (n=8). However, assessment of LV performance under altered loading conditions revealed a significant increase in the LV stiffness coefficient (β) during IVC occlusion as well as the ΔEDP/ΔEDV ratio during rapid saline loading. These functional changes persisted for 2‐weeks following cessation of RPO and were accompanied by a significant increase in passive myocardial stiffness and interstitial fibrosis.ConclusionsThese results demonstrate that the reduction in LV compliance arising after RPO is not related to delayed active myocardial relaxation at rest or altered expression of sarcoplasmic reticulum calcium handling proteins. However, RPO elicits a persistent increase in passive myocardial stiffness that is likely mediated by interstitial collagen deposition. These passive diastolic properties may explain exercise intolerance in HFpEF patients despite normal resting hemodynamics and the absence of anatomic LV hypertrophy.Support or Funding InformationFunding Sources: The National Heart Lung and Blood Institute (HL‐061610), the American Heart Association (17SDG33660200), the National Center for Advancing Translational Sciences (UL1TR001412), the Department of Veterans Affairs (1IO1BX002659), the Community Foundation for Greater Buffalo, and the Albert and Elizabeth Rekate Fund in Cardiovascular Medicine. Baseline/Control RPO Cessation of RPO Tau (ms) 36.5 ± 1.6 35.9 ± 1.6 34.3 ± 1.7 dP/dtmin (mmHg/s) −2116 ± 369 −2301 ± 133 −2464 ± 272 Diastolic Stiffness Coefficient (β) 0.025 ± 0.003 0.054 ± 0.007 * 0.043 ± 0.009 * ΔEDP/ΔEDV During Saline Loading (mmHg/mL) 0.09 ± 0.02 0.21 ± 0.04 * 0.23 ± 0.03 * Ex Vivo Passive Stiffness (kPa) 77.8 ± 11.0 ‐‐‐ 131.0 ± 6.1 * Interstitial Fibrosis (%) 6.6 ± 0.7 12.9 ± 1.8 * 16.3 ± 1.1 * Values are mean ± SEM. *p&lt;0.05 vs. Baseline/Control

Resistance training promotes reduction in Visceral Adiposity without improvements in Cardiomyocyte Contractility and Calcium handling in Obese Rats.

Resistance training (RT) improves the cardiomyocyte calcium (Ca2+) cycling during excitation-contraction coupling. However, the role of RT in cardiomyocyte contractile function associated with Ca2+ handling in obesity is unclear. Wistar rats were distributed into four groups: control, sedentary obese, control plus RT, and obesity plus RT. The 10-wk RT protocol was used (4-5 vertical ladder climbs, 60-second interval, 3× a week, 50-100% of maximum load). Metabolic, hormonal, cardiovascular and biochemical parameters were determined. Reduced leptin levels, epididymal, retroperitoneal and visceral fat pads, lower body fat, and adiposity index were observed in RT. Obesity promoted elevation of collagen, but RT did not promote modifications of LV collagen in ObRT. RT induced elevation in maximum rates of contraction and relaxation, and reduction of time to 50% relaxation. ObRT group did not present improvement in the cardiomyocyte contractile function in comparison to Ob group. Reduced cardiac PLB serine16 phosphorylation (pPLB Ser16) and pPLB Ser16/PLB ratio with no alterations in sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) and phospholamban (PLB) expression were observed in Ob groups. Resistance training improved body composition reduced fat pads and plasma leptin levels but did not promote positive alterations in cardiomyocyte contractile function, Ca2+ handling and phospholamban phosphorylation.