Myocyte Remodeling Research Articles

Rapid onset fibrotic remodeling and ventricular dysfunction induced by phenylephrine involve targeted reprogramming of myocyte and fibroblast transcriptomes.

Catecholamine dysregulation is a common feature of multiple acute and chronic cardiac conditions, including heart failure. To investigate the role of altered α-adrenergic stimulation on cardiac function, we developed a short-term exposure model, administering phenylephrine subcutaneously to mice for one week. Compared to vehicle-injected controls, phenylephrine-treated animals exhibited increased ejection fraction, decreased chamber size, diastolic dysfunction and ventricular hypertrophy in the absence of hypertension. Remarkably, these animals developed extensive fibrotic remodeling of the tissue that plateaued at 24 hours and myocyte hypertrophy localized to regions of fibrotic deposition after 3 days of treatment. Transcriptome analyses of purified myocyte and fibroblast populations from these hearts revealed an unexpected role for myocytes in the production of extracellular matrix. Comparison with other models of cardiac stress, including pressure overload hypertrophy and cytokine activation of fibroblasts, identified stimulus-specific transcriptional circuits associated with cardiac pathology. Given the rapid, robust fibrotic response that preceded myocyte hypertrophy, intercellular communication analyses were conducted to investigate fibroblast to myocyte signaling, identifying potential crosstalk between these cells. These studies thoroughly describe and phenotypically characterize a new model of short-term catecholamine stress and provide an atlas of transcriptional remodeling in myocytes and fibroblasts.

PDCD4 promotes inflammation/fibrosis by activating the PPAR‑γ/NF‑κB pathway in mouse atrial myocytes.

Fibrosis is the basis of structural remodeling in atrial fibrillation (AF), during which inflammation is crucial. Programmed cell death factor 4 (PDCD4) is a newly identified inflammatory gene, with unknown mechanisms of action in AF. The present study aimed to elucidate the effects of PDCD4 on the inflammation and structural remodeling of atrial myocytes. For this purpose, a PDCD4 overexpression plasmid (oePDCD4) and PDCD4 small interfering (si)RNA (siPDCD4) were used to modulate PDCD4 expression in mouse atrial myocytes (HL‑1 cells). The expression of PDCD4 was detected using reverse transcription‑quantitative PCR and western blot analysis. The optimal drug concentrations of peroxisome proliferator‑activated receptor γ (PPARγ) agonist (pioglitazone hydrochloride), NF‑κB inhibitor (CBL0137), PPARγ inhibitor (GW9962) and NF‑κB agonist (betulinic acid) were screened using a Cell Counting Kit‑8 assay. The levels of inflammatory factors were detected using enzyme‑linked immunosorbent assays, the expression levels of fibrosis‑related proteins and NF‑κB subunits were detected using western blot analysis, and the expression of phosphorylated (p‑)p65/p65 was detected using immunofluorescence staining. The results revealed that PDCD4 overexpression increased the levels of fibrotic factors (collagen I, collagen III, fibronectin, α‑smooth muscle actin and matrix metalloproteinase 2), pro‑inflammatory cytokines (IFN‑γ, IL‑6, IL‑17A and TNF‑α) and p‑p65, whereas it reduced the levels of anti‑inflammatory cytokines (IL‑4) in HL‑1 cells. Additionally, treatment with the PPARγ agonist and NF‑κB inhibitor reversed the levels of fibrotic‑, pro‑inflammatory and anti‑inflammatory factors in oePDCD4‑HL‑1 cells. By contrast, PDCD4 silencing exerted the opposite effects on fibrotic factors, pro‑inflammatory cytokines, anti‑inflammatory cytokines and p‑p65. In addition, treatment with the PPARγ inhibitor and NF‑κB agonist reversed the levels of fibrotic‑, pro‑inflammatory and anti‑inflammatory factors in siPDCD4‑HL‑1 cells. In conclusion, the present study demonstrated that PDCD4 may induce inflammation and fibrosis by activating the PPARγ/NF‑κB signaling pathway, thereby promoting the structural remodeling of atrial myocytes in AF.

Advanced Cardiac Conduction Abnormalities in Patients on Ibrutinib Therapy

Background: Bruton tyrosine kinase inhibitors, such as ibrutinib, are medications that are actively used for Chronic Lymphocytic Leukemia (CLL) and several lymphomas. They work by inhibiting Bruton’s tyrosine kinase therefore affecting B cell proliferation. Ibrutinib itself is associated with multiple cardiotoxicities including atrial fibrillation, ventricular arrhythmias, heart failure, and bleeding. There are well-established studies that show the incidence of atrial fibrillation with ibrutinib therapy. However, only a few reports show an association between ibrutinib therapy and advanced heart block. Case presentation: We present two unique cases of patients who presented to the emergency room with syncope while being on ibrutinib therapy for CLL. At presentation, the patients were found to have conduction abnormalities seen on their EKG that included complete heart block in one patient and sick sinus syndrome in the other. Ultimately, each patient was treated with a pacemaker, ibrutinib therapy was discontinued, and they were started on alternative therapy for their CLL. Discussion: No clear mechanism has been established for how ibrutinib therapy causes these conduction abnormalities. This case series proposes a possible mechanism of advanced conduction abnormalities that is caused by ibrutinib therapy that is associated with the NOTCH gene. We propose that the downregulation of the NOTCH gene may prevent cardiac myocyte remodeling and therefore can cause conduction abnormalities as seen in our patients along with others that presented with advanced heart block with ibrutinib therapy.

The autonomic nervous system in atrial fibrillation-pathophysiology and non-invasive assessment.

The autonomic nervous system plays a crucial role in atrial fibrillation pathophysiology. Parasympathetic hyperactivity result in a shortening of the action potential duration, a reduction of the conduction wavelength, and as such facilitates reentry in the presence of triggers. Further, autonomic remodeling of atrial myocytes in AF includes progressive sympathetic hyperinnervation by increased atrial sympathetic nerve density and sympathetic atrial nerve sprouting. Knowledge on the pathophysiological process in AF, including the contribution of the autonomic nervous system, may in the near future guide personalized AF management. This review focuses on the role of the autonomic nervous system in atrial fibrillation pathophysiology and non-invasive assessment of the autonomic nervous system.

Chronic Testosterone Deficiency Increases Late Inward Sodium Current and Promotes Triggered Activity in Ventricular Myocytes from Aging Male Mice.

Clinical studies suggest low testosterone levels are associated with cardiac arrhythmias, especially in later life. We investigated whether chronic exposure to low circulating testosterone promoted maladaptive electrical remodeling in ventricular myocytes from aging male mice and determined the role of late inward sodium current (INa-L) in this remodeling. C57BL/6 mice had a gonadectomy (GDX) or sham surgery (1-month) and were aged to 22-28-months. Ventricular myocytes were isolated; transmembrane voltage and currents were recorded (37°C). Action potential duration at 70 and 90% repolarization (APD70 and APD90) was prolonged in GDX compared to sham myocytes (APD90: 96.9±3.2 vs 55.4±2.0 ms; p<0.001). INa-L was also larger in GDX than sham (-2.4±0.4 vs -1.2±0.2 pA/pF; p=0.002). When cells were exposed to the INa-L antagonist ranolazine (10 µM), INa-L declined in GDX cells (-1.9±0.5 vs -0.4±0.2 pA/pF; p<0.001) and APD90 was reduced (96.3±14.8 vs 49.2±9.4 ms; p=0.001). GDX cells had more triggered activity (early/delayed afterdepolarizations, EADs/DADs) and spontaneous activity than sham. EADs were inhibited by ranolazine in GDX cells. The selective NaV1.8 blocker A-803467 (30 nM) also reduced INa-L, decreased APD and abolished triggered activity in GDX cells. Scn5a (NaV1.5) and Scn10a (NaV1.8) mRNA was increased in GDX ventricles, but only NaV1.8 protein abundance was increased in GDX compared to sham. In vivo studies showed QT prolongation and more arrhythmias in GDX mice. Thus, triggered activity in ventricular myocytes from aging male mice with long-term testosterone deficiency arises from APD prolongation mediated by larger NaV1.8- and NaV1.5-associated currents, which may explain the increase in arrhythmias.

Sarcomere remodeling of left atrial myocytes in non-failing atrial fibrillation patients.

Atrial fibrillation (AF) significantly contributes to adverse cardiac events like stroke. To identify novel pathways to target therapeutically, we performed mass spectrometry on left atrial (LA) tissue from patients in Sinus Rhythm (SR, n = 3) or with AF (n = 3), with no other cardiovascular disease that could confound interpretation. Pathway analysis identified inflammatory, metabolic, and extracellular matrix pathways as highly altered in AF, all of which are currently active areas of AF research. However, contractile proteins were also significantly altered, and the role of the sarcomere in AF remains mostly unstudied. To understand the functional impact of AF on the sarcomere, we measured force-calcium relationships in single cardiomyocytes from LA and left ventricular (LV) tissue from SR (n = 6) and AF (n = 3) patients. Surprisingly, maximal calcium-activated force (Fmax) was almost doubled in AF compared to SR patients. This result contradicts previous work which observed depressed contractile function in AF patients; however, these patients had heart failure and valve disease. Ventricular cells from these patients showed no change in Fmax (expected in non-failing patients), but a slight calcium sensitization in AF due to decreased troponin I (TnI) phosphorylation, possibly in compensation for elevated heart rate. Mass spec analysis showed that AF atria had decreased myosin-binding protein H-like, slow skeletal TnI, and increased alpha tropomyosin and beta-MHC (confirmed by gel electrophoresis). These changes suggest that AF drives a more “ventricular-like” or mature sarcomere in atrial myocytes, resulting in increased force production that is also similar to ventricular myocytes. Together, these data provide insight into the development and outcomes of atrial fibrillation in absence of other cardiovascular conditions in humans and suggests that the sarcomere may be a feasible therapeutic target in atrial fibrillation.

ODP065 Impact of Comorbid Adrenal Insufficiency on Outcomes During Hospitalization For Cardiogenic Shock

Abstract Background The catabolic stress associated with cardiogenic shock requires a robust metabolic, neuroendocrine, and immunologic response to mitigate, and adrenocortical hormones play a huge role in this process. On the other hand, excessive aldosterone production is known to play a key part in the long-term progression of myocardial insufficiency through myocyte remodeling. It is thus intriguing to understand how adrenocortical insufficiency impacts the outcomes of patients admitted for cardiogenic shock. Method: A retrospective cohort study was designed using data obtained from the 2016 to 2018 combined National Inpatient Sample (NIS) database. Adult patients (age &amp;gt;18) with principal admission diagnosis of cardiogenic shock were identified using the international diseases classification code, tenth revision (ICD 10), and separated into two cohorts based on the presence of a secondary diagnosis of adrenal insufficiency. Primary outcomes assessed were, mortality, length of stay (LOS) and total hospital charge. Secondary outcomes evaluated included rate of mechanical ventilation, mechanical circulatory support device use and cardiac arrest. Multivariate linear and logistic regressions were used to adjust for confounders. Results There was a total of 477,695 adult hospitalizations for cardiogenic shock, out of which 1.28% had associated secondary diagnosis of adrenal insufficiency. There was a statistically insignificant increased odds of mortality among patients with adrenal insufficiency (33.42% vs 33.35%, AOR: 1. 05, 95% CI: 0.93 to 1.19, p: 0.462). There was also an increased length of stay (18.91 days vs 11.35 days, adjusted mean difference: 6.5 days, 95%CI: 5.22 days to 7.78 days, p &amp;lt; 0. 001) and an increased total charge (364,864.5 vs 238,591.9 USD, adjusted mean difference: 105,491.9 USD, 95%CI: 78,252.2USD to 132,731.3 USD, p &amp;lt; 0. 001) among patients with adrenal insufficiency compared with the counterpart cohort group and these were statistically significant. Patients with adrenal insufficiency also had 42% increased odds of being mechanically ventilated during cardiogenic shock admission compared to patients without (55.67% vs 46.61%, AOR: 1.42, 95%CI: 1.26 to 1.60, p &amp;lt; 0. 001). Other secondary clinical outcomes assessed, including mechanical circulatory support devices use and cardiac arrest were not statistically different between the two groups. Conclusion Adrenal insufficiency as a comorbid diagnosis among patients admitted with cardiogenic shock was associated with increased odds of requiring mechanical ventilation, prolonged length of stay and higher total hospital charges. There was a trend towards increased mortality, but this was not statistically significant. There was no difference in other clinical outcomes including mechanical circulatory support devices and cardiac arrest rate. Presentation: No date and time listed

Inhibition of late sodium current via PI3K/Akt signaling prevents cellular remodeling in tachypacing-induced HL-1 atrial myocytes

An aberrant late sodium current (INa,Late) caused by a mutation in the cardiac sodium channel (Nav1.5) has emerged as a contributor to electrical remodeling that causes susceptibility to atrial fibrillation (AF). Although downregulation of phosphoinositide 3-kinase (PI3K)/Akt signaling is associated with AF, the molecular mechanisms underlying the negative regulation of INa,Late in AF remain unclear, and potential therapeutic approaches are needed. In this work, we constructed a tachypacing-induced cellular model of AF by exposing HL-1 myocytes to rapid electrical stimulation (1.5 V/cm, 4 ms, 10 Hz) for 6 h. Then, we gathered data using confocal Ca2+ imaging, immunofluorescence, patch-clamp recordings, and immunoblots. The tachypacing cells displayed irregular Ca2+ release, delayed afterdepolarization, prolonged action potential duration, and reduced PI3K/Akt signaling compared with controls. Those detrimental effects were related to increased INa,Late and were significantly mediated by treatment with the INa,Late blocker ranolazine. Furthermore, decreased PI3K/Akt signaling via PI3K inhibition increased INa,Late and subsequent aberrant myocyte excitability, which were abolished by INa,Late inhibition, suggesting that PI3K/Akt signaling is responsible for regulating pathogenic INa,Late. These results indicate that PI3K/Akt signaling is critical for regulating INa,Late and electrical remodeling, supporting the use of PI3K/Akt-mediated INa,Late as a therapeutic target for AF.

Effects and pharmacological mechanism of Zhigancao Decoction on electrical and structural remodeling of the atrium of rabbits induced by rapid atrial pacing.

Zhigancao decoction (ZD) has a long history in China as a traditional Chinese medicine compound for the treatment of tachyarrhythmias. This study mainly explored the pharmacological mechanism of Zhigancao Decoction in preventing atrial fibrillation by altering the electrical and structural remodeling of the atrial in rabbits. In total, 30 male New Zealand white rabbits were randomly divided into 3 groups (ten rabbits for each). The first group was sham-operated (control group). The second group was intervened by the rapid right atrium pacing (RAP) to induce atrial fibrillation (AF group), while the third group was given ZD gavage and RAP (AF + ZD group). All rabbits were anesthetized before two monophasic action potential (MAP) catheters were sequentially inserted into the right atrium. After 8h of rapid right atrial pacing, the electrophysiological indexes and the induction rate of atrial fibrillation were observed in the three groups of rabbits, and the left atrial myocardium samples were taken to observe the ultrastructure. Single atrial myocytes were separated by enzymolysis, and the L-type calcium current (ICa-L) of atrial myocytes in different experimental groups was observed by whole-cell patch clamp technique. The fluorescence intensity of Ca2+ in atrial myocytes was observed after Fluo-3/AM fluorescent staining. The main components of ZD were identified by liquid chromatography-mass spectrometry-mass spectrometry (LC-MS/MS) method. Compared with the AF group, the maximum ascent rate (Max dV/dt) and plateau potential were significantly reduced in the ZD group, the action potential duration at 10% and 20% (APD10, APD20) were significantly shortened (P < 0.01), action potential duration at 50%, 70%, and 90% (APD50, APD70, APD90) were significantly prolonged, and atrial effective refractory period (AERP) was significantly prolonged (P < 0.01) in the ZD group. In the ZD group, the ICa-L amplitudes of rabbit atrial myocytes under each clamping voltage were significantly smaller than those in the AF group (P < 0.01) and the control group (P < 0.05). The Ca2+ fluorescence intensity in the rabbit atrial myocytes in the ZD group was significantly weaker than that in the AF group (P < 0.01) and the control group (P < 0.05). Electron microscopy displayed that the control group had neatly arranged atrial tissue myofilaments and intact mitochondria. However, the ultrastructural damage of the AF group was severe compared with that of the ZD group. LC-MS/MS analysis confirmed that ZD contained several antiarrhythmic compounds including ginsenoside, isoliensinine, catalpol, glycyrrhizinate and hesperetin. Rapid atrial pacing (RAP) could cause the electrical and structural remodeling of rabbit atrial myocytes. ZD might reverse the atrial electrical remodeling but could have little effect on structural remodeling, which might be the mechanism of ZD treatment on atrial fibrillation.

Effects of Sarcolemmal Background Ca2+ Entry and Sarcoplasmic Ca2+ Leak Currents on Electrophysiology and Ca2+ Transients in Human Ventricular Cardiomyocytes: A Computational Comparison.

The intricate regulation of the compartmental Ca2+ concentrations in cardiomyocytes is critical for electrophysiology, excitation-contraction coupling, and other signaling pathways. Research into the complex signaling pathways is motivated by cardiac pathologies including arrhythmia and maladaptive myocyte remodeling, which result from Ca2+ dysregulation. Of interest to this investigation are two types of Ca2+ currents in cardiomyocytes: 1) background Ca2+ entry, i.e., Ca2+ transport across the sarcolemma from the extracellular space into the cytosol, and 2) Ca2+ leak from the sarcoplasmic reticulum (SR) across the SR membrane into the cytosol. Candidates for the ion channels underlying background Ca2+ entry and SR Ca2+ leak channels include members of the mechano-modulated transient receptor potential (TRP) family. We used a mathematical model of a human ventricular myocyte to analyze the individual contributions of background Ca2+ entry and SR Ca2+ leak to the modulation of Ca2+ transients and SR Ca2+ load at rest and during action potentials. Background Ca2+ entry exhibited a positive relationship with both [Ca2+]i and [Ca2+]SR. Modulating SR Ca2+ leak had opposite effects of background Ca2+ entry. Effects of SR Ca2+ leak on Ca2+ were particularly pronounced at lower pacing frequency. In contrast to the pronounced effects of background and leak Ca2+ currents on Ca2+ concentrations, the effects on cellular electrophysiology were marginal. Our studies provide quantitative insights into the differential modulation of compartmental Ca2+ concentrations by the background and leak Ca2+ currents. Furthermore, our studies support the hypothesis that TRP channels play a role in strain-modulation of cardiac contractility. In summary, our investigations shed light on the physiological effects of the background and leak Ca2+ currents and their contribution to the development of disease caused by Ca2+ dysregulation.

Heterogeneous myocyte remodelling and spatial heterogeneity of repolarization within the myocardial infarction border zone

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Fund for Scientific Research-Flanders (FWO) Background Sudden cardiac death due to ventricular arrhythmias is a major cause of mortality after myocardial infarction (MI). The border zone (BZ) surrounding the infarct is the dominant source of arrhythmias. Here a substrate of heterogeneous repolarization is implicated, which could be due to heterogeneous myocyte remodelling. Objective To examine myocyte remodelling within the BZ, in comparison to the remote myocardium, and evaluate the local profile of repolarization of these regions in vivo. Methods MI was induced by 120-minute occlusion of the left anterior descending coronary artery followed by reperfusion in 6 domestic pigs. After 4 weeks, magnetic resonance imaging was performed to assess infarct remodelling and local wall thickness. Within 3 days, electro-anatomical mapping was performed. A non-contact recording of a 64-electrode array was translated to 2048 electrograms distributed over the LV and local activation-recovery-interval (ARI) determined by custom software. After recovery (2-4 days), the pigs were sacrificed, and samples collected from the BZ and remote region for RNA analysis and single cardiomyocyte isolation. Cell dimensions were measured and cellular AP duration (APD) was optically recorded using a fluorescent voltage dye, Di-8-Annepps (stimulation at 1Hz, 37°C). Expression and variability of cardiomyocyte hypertrophy biomarkers were extracted from single nuclear RNA sequencing data (10x Genomics). Results Cardiomyocyte APD in large population samples (&amp;gt; 100 cells per region in each pig) revealed higher heterogeneity in the BZ than the remote region, quantified as the standard deviation (SD) (BZ: 105.9 ± 17.0ms vs remote: 73.9 ± 8.6ms, P = 0.001). Cellular APD heterogeneity correlated strongly with in vivo local ARI heterogeneity, which demonstrated increased heterogeneity in the BZ (R2 = 0.67, P = 0.002). BZ myocytes were hypertrophied with greater increase in cell width than length, and cellular hypertrophy was more heterogeneous by SD in the BZ (BZ: 12.9 ± 2.4μm vs remote: 8.3 ± 1.1μm, P &amp;lt; 0.001). NPPB transcripts reporting on hypertrophic remodelling were higher in BZ than remote (mean lognorm gene expression, BZ: 0.431 ± 0.014 vs remote: 0.107 ± 0.004, P &amp;lt; 0.001), and showed greater heterogeneity in expression between cells by proportion of hypertrophic (NPPB +ve) cells (BZ: 30.86% vs remote: 8.37%, P &amp;lt; 0.001). Wall thickness variance was higher in the BZ compared to the remote region (anterior BZ: 0.15 ± 0.02mm, septal BZ: 0.16 ± 0.04mm vs remote: 0.04 ± 0.02mm, P &amp;lt; 0.001), contributing to increased heterogeneity of local wall stress in BZ. Conclusion Cardiomyocyte remodelling in the BZ is heterogeneous, possibly related to differences in local wall stress, which may contribute to heterogeneous repolarization in vivo and underlie arrhythmia vulnerability within the BZ.

MBNL1 drives dynamic transitions between fibroblasts and myofibroblasts in cardiac wound healing.

Dynamic fibroblast to myofibroblast state transitions underlie the heart's fibrotic response. Because transcriptome maturation by muscleblind-like 1 (MBNL1) promotes differentiated cell states, this study investigated whether tactical control of MBNL1 activity could alter myofibroblast activity and fibrotic outcomes. In healthy mice, cardiac fibroblast-specific overexpression of MBNL1 transitioned the fibroblast transcriptome to that of a myofibroblast and after injury promoted myocyte remodeling and scar maturation. Both fibroblast- and myofibroblast-specific loss of MBNL1 limited scar production and stabilization, which was ascribed to negligible myofibroblast activity. The combination of MBNL1 deletion and injury caused quiescent fibroblasts to expand and adopt features of cardiac mesenchymal stem cells, whereas transgenic MBNL1 expression blocked fibroblast proliferation and drove the population into a mature myofibroblast state. These data suggest MBNL1 is a post-transcriptional switch, controlling fibroblast state plasticity during cardiac wound healing.

Repolarization heterogeneity within the myocardial infarction border zone correlates with variability of myocyte remodeling

Abstract Background Myocardial infarction (MI) results in a regional scar, with a border zone (BZ) of surviving myocytes interspersed with fibrosis providing an anatomical substrate for re-entry. Heterogeneous repolarization within the BZ may add a functional component aggravating re-entrant arrhythmias. Purpose We studied BZ heterogeneity and developed novel methodology for high resolution mapping of local in vivo activation-repolarization intervals (ARI) within the BZ and for studying the relation to cellular action potential (AP) profiles of cells isolated from the BZ. Methods Anterior-septal myocardial infarction was induced in 5 domestic pigs by 120-minute occlusion of the left anterior descending artery followed by reperfusion (18.9±4.7% of the left ventricle). After 1-month, electro-anatomical mapping was performed. Contact mapping was used to define the BZ (bipolar voltage 0.5–1.5mV). A non-contact recording of a 64-electrode array was translated to 2048 non-contact electrograms distributed over the LV. The non-contact electrograms were processed to determine the ARIs using a custom-made algorithm, validated against monophasic action potential recordings. After 2–4 days recovery, single cardiomyocytes were enzymatically isolated from the anterior-septal BZs and remote regions. Cardiomyocytes were field stimulated at 1Hz at 37°C and cellular AP duration (APD) was optically recorded (fluorescent voltage-sensitive dye Di-8-Annepps). Results In vivo, regional ARIs tended to be longer in the BZs than remote. ARI heterogeneity, quantified as the standard deviation of ARIs in a neighborhood of 1cm radius, was increased in the BZ (anterior BZ: 3.4±1.0 ms, P=0.052, septal BZ: 3.6±1.7 ms, P=0.027 vs remote: 2.0±0.5 ms). Cellular APD was measured in large population samples (&amp;gt;100 cells per region in each pig) and was longer in BZ myocytes compared to the remote region. Cellular APD heterogeneity, measured as the standard deviation within cell population samples pooled by region per animal, was increased in the BZ (anterior BZ: 105.9±17.0 ms, P=0.0010; septal BZ: 98.1±20.8 ms, P=0.0127 vs remote: 73.9±8.6 ms). Cell APD correlated to in vivo ARI (R2=0.34, P=0.021) and cellular heterogeneity correlated strongly with in vivo heterogeneity (R2=0.67, P=0.002). Conclusion In the BZ of MI, in vivo regional heterogeneity adds a functional substrate for re-entry that may result from heterogeneous cellular remodeling and increased cell-cell APD variability. Funding Acknowledgement Type of funding sources: Public Institution(s). Main funding source(s): KU Leuven BOF-C1 “Blood pressure induced premature ventricular beats as triggers for ventricular arrhythmia in ischemic cardiomyopathy”

Calcineurin Aβ gene knockdown inhibits transient outward potassium current ion channel remodeling in hypertrophic ventricular myocyte.

It has been shown that the activation of calcineurin is involved in regulating ion channel remodeling in hypertrophic cardiomyocytes. But the precise role of calcineurin in the regulation of transient outward potassium current (I to), an ion channel associated with fatal arrhythmia, remains controversial. This study aimed to examine the effects of calcineurin Aβ (CnAβ) gene knockdown on I to channel remodeling and action potential duration (APD) in the hypertrophic ventricular myocytes of neonatal rats. Results showed that phenylephrine stimulation caused hypertrophy of ventricular myocytes, upregulation of CnAβ protein expression, downregulation of Kv4.2 mRNA and protein expression, a decrease in I to current density, and prolongation of APD. CnAβ gene knockdown significantly inhibited the effects of phenylephrine stimulation. Our data indicate that CnAβ gene knockdown can inhibit I to channel remodeling and APD prolongation in hypertrophic neonatal rat ventricular myocytes. This finding suggests that calcineurin may be a potential target for the prevention of malignant ventricular arrhythmia in a hypertrophic heart.

Modulations of Cardiac Functions and Pathogenesis by Reactive Oxygen Species and Natural Antioxidants

Homeostasis in the level of reactive oxygen species (ROS) in cardiac myocytes plays a critical role in regulating their physiological functions. Disturbance of balance between generation and removal of ROS is a major cause of cardiac myocyte remodeling, dysfunction, and failure. Cardiac myocytes possess several ROS-producing pathways, such as mitochondrial electron transport chain, NADPH oxidases, and nitric oxide synthases, and have endogenous antioxidation mechanisms. Cardiac Ca2+-signaling toolkit proteins, as well as mitochondrial functions, are largely modulated by ROS under physiological and pathological conditions, thereby producing alterations in contraction, membrane conductivity, cell metabolism and cell growth and death. Mechanical stresses under hypertension, post-myocardial infarction, heart failure, and valve diseases are the main causes for stress-induced cardiac remodeling and functional failure, which are associated with ROS-induced pathogenesis. Experimental evidence demonstrates that many cardioprotective natural antioxidants, enriched in foods or herbs, exert beneficial effects on cardiac functions (Ca2+ signal, contractility and rhythm), myocytes remodeling, inflammation and death in pathological hearts. The review may provide knowledge and insight into the modulation of cardiac pathogenesis by ROS and natural antioxidants.

Adherens junction engagement regulates functional patterning of the cardiac pacemaker cell lineage.

Cardiac pacemaker cells (CPCs) rhythmically initiate the electrical impulses that drive heart contraction. CPCs display the highest rate of spontaneous depolarization in the heart despite being subjected to inhibitory electrochemical conditions that should theoretically suppress their activity. While several models have been proposed to explain this apparent paradox, the actual molecular mechanisms that allow CPCs to overcome electrogenic barriers to their function remain poorly understood. Here, we have traced CPC development at single-cell resolution and uncovered a series of cytoarchitectural patterning events that are critical for proper pacemaking. Specifically, our data reveal that CPCs dynamically modulate adherens junction (AJ) engagement to control characteristics including surface area, volume, and gap junctional coupling. This allows CPCs to adopt a structural configuration that supports their overall excitability. Thus, our data have identified a direct role for local cellular mechanics in patterning critical morphological features that are necessary for CPC electrical activity.

The role of TRPV2 on physiological and pathological remodeling of myocytes

Hemodynamic stress and extracellular matrix stiffness provide essential information for homeostatic regulation and functional adaptation on the physiological and pathological remodeling of myocytes. Previously, we have reported that transient receptor potential cation channel vanilloid-family type 2 (TRPV2) is a candidate of myocyte mechanosensor, and crucial for the maintenance of cardiac structure and function. Here, we show the role of TRPV2 in the physiological and pathological remodeling of myocytes. TRPV2-deficient neonatal cardiomyocytes exhibited no sarcomere formation, reduced Ca2+ contents of sarcoplasmic reticulum, or spontaneous beating, suggesting that TRPV2-dificiency affects myocyte maturation. The elimination of TRPV2 from juveniles showed the reduction of myofilaments and mildly chamber dilation in adult stage. Isolated myocytes from these mice showed the impaired Ca2+ handling with excitation-contraction coupling and contractile dysfunction. In hypertrophic response, increased actin-myosin cross-bridge formation enhance passive cardiomyocytes stiffness in the transverse direction. However, TRPV2-deficent hearts showed no change of myofilament protein expression and severe cardiac dysfunction to pressure-overload. Thus, TRPV2 is critical for compensate hypertrophic response to mechanical stress.

Abstract 17259: Identification of Biological Pathways of Candidate Atrial Fibrillation Risk Genes Through the Use of Weighted Gene Coexpression Network Analysis

Introduction: Over 135 genetic loci have been linked to atrial fibrillation (AF), yet the biological pathways of AF pathophysiology remain elusive. Weighted gene coexpression network analysis (WGCNA) constructs gene modules within a network based on correlations in gene expression, and identifies mechanisms related to AF risk. Objective: To identify biological pathways of candidate AF risk genes that will advance our understanding of AF mechanisms. Methods: RNA-sequencing was performed on left atrial appendage tissue from 265 patients. RNA-seq data were adjusted for differences in AF rhythm state and other known AF risk factors. Correlations from adjusted data were further adjusted for latent factors then spatial quantile normalized to correct for mean-variance bias. WGCNA was applied to the resulting adjusted and normalized gene-gene correlations to identify gene modules. Ingenuity Pathway Analysis and gene set over representation analysis (GSOR) were applied to each module. Results: WGCNA identified 63 modules from 17,434 genes; 47 of these contained at least one candidate AF risk gene. AF risk genes were overrepresented in 7 modules (Table 1). Notable top pathways of AF overrepresented modules include apelin signaling, heme metabolism, intracellular ion homeostasis, and the unfolded protein response. These are known to be involved in calcium signaling, iron homeostasis, glucose regulation, heat shock response, and protein ubiquitination during states of high energy demand and stress. These pathways coincide with larger cellular processes of myocyte remodeling, apoptosis, and cell survival, which were also prominent. Conclusions: Biological pathways identified through WGCNA and GSOR suggest that sustained increases in energy demand during AF promotes stress-induced cellular remodeling. Changes in calcium signaling, iron homeostasis, the unfolded protein response and glucose regulation are likely primary mechanisms of AF pathophysiology.

Hemodynamic and transcriptomic studies suggest early left ventricular dysfunction in a preclinical model of severe mitral regurgitation

ObjectivePrimary mitral regurgitation is a valvular lesion in which the left ventricular ejection fraction remains preserved for long periods, delaying a clinical trigger for mitral valve intervention. In this study, we sought to investigate whether adverse left ventricular remodeling occurs before a significant fall in ejection fraction and characterize these changes. MethodsSixty-five rats were induced with severe mitral regurgitation by puncturing the mitral valve leaflet with a 23-G needle using ultrasound guidance. Rats underwent longitudinal cardiac echocardiography at biweekly intervals and hearts explanted at 2 weeks (n = 15), 10 weeks (n = 15), 20 weeks (n = 15), and 40 weeks (n = 15). Sixty age- and weight-matched healthy rats were used as controls. Unbiased RNA-sequencing was performed at each terminal point. ResultsRegurgitant fraction was 40.99 ± 9.40%, with pulmonary flow reversal in the experimental group, and none in the control group. Significant fall in ejection fraction occurred at 14 weeks after mitral regurgitation induction. However, before 14 weeks, end-diastolic volume increased by 93.69 ± 52.38% (P < .0001 compared with baseline), end-systolic volume increased by 118.33 ± 47.54% (P < .0001 compared with baseline), and several load-independent pump function indices were reduced. Transcriptomic data at 2 and 10 weeks before fall in ejection fraction indicated up-regulation of myocyte remodeling and oxidative stress pathways, whereas those at 20 and 40 weeks indicated extracellular matrix remodeling. ConclusionsIn this rodent model of mitral regurgitation, left ventricular ejection fraction was preserved for a long duration, yet rapid and severe left ventricular dilatation, and biological remodeling occurred before a clinically significant fall in ejection fraction.

Shensong Yangxin Protects Against Metabolic Syndrome-Induced Ventricular Arrhythmias by Inhibiting Electrical Remodeling.

Shensong Yangxin (SSYX) is a traditional Chinese medicine, which has been proven to improve the clinical symptoms of arrhythmia. However, the role of SSYX in metabolic syndrome (MetS)-induced electrical remodeling remains to be fully elucidated. Here, we sought to clarify whether SSYX can alter the electrophysiological remodeling of cardiac myocytes from MetS rats by regulating transient outward potassium current (I to) and calcium current (I Ca-L). Male Wistar rats were subjected to 16 weeks of high-carbohydrate, high-fat to produce a MetS model group. SSYX (0.4 g/kg) was administrated by daily gavage 8 weeks following high-carbohydrate, high-fat for 8 weeks. In vivo electrophysiological study was performed to evaluated ventricular arrhythmias (VA) vulnerability and electrophysiological properties. The potential electrical mechanisms were estimated by whole-cell patch-clamp and molecular analysis. The H9C2 cells were used to verify the protective role of SSYX in vitro. After 16-week high-carbohydrate, high-fat feeding, MetS model rats showed increased body weight (BW), blood pressure (BP), blood sugar (BS), heart rate (HR) and heart weights to tibia length (HW/TL) ratio. Furthermore, MetS rats depicted increased VA inducibility, shortened effective refractory period (ERP) and prolonged action potential duration (APD). Lower I Ca-L and I to current densities were observed in MetS rats than CTL rats. Additionally, MetS rats exhibited significantly increased cardiac fibrosis, decreased Cx43 expression and protein levels of Cav1.2, Kv4.2, Kv4.3 than CTL group. As expected, these MetS-induced effects above were reversed when SSYX was administrated. Mechanistically, SSYX administrated significantly down-regulated the TLR4/MyD88/CaMKII signaling pathway both in vivo and in vitro. Collectively, our data indicated that the electrical remodeling induced by MetS contributed to the increased VA susceptibility. SSYX protects against MetS-induced VA by inhibiting electrical remodeling through TLR4/MyD88/CaMKII signaling pathway.