CKIP-1 mediates CK2 translocation to regulate Nav1.5 and Kir2.1 channel complexes in cardiomyocytes.

Sodium and potassium channels, especially Nav1.5 and Kir2.1, play key roles in the formation of action potentials in cardiomyocytes. These channels interact with, and are regulated by, synapse-associated protein 97 (SAP97). However, the regulatory role of SAP97 in myocyte remains incompletely understood. Here, we investigate the function of SAP97 phosphorylation in the regulation of Nav1.5 and Kir2.1 channel complexes and the upstream regulation of SAP97. We found that SAP97 is phosphorylated by casein kinase II (CK2) in vitro. In addition, transfection of casein kinase 2 interacting protein-1 (CKIP-1) into cardiomyocytes to drive CK2 from the nucleus to the cytoplasm, increased SAP97 phosphorylation and Nav1.5 and Kir2.1 current activity. These findings demonstrated that CKIP-1 modulates the subcellular translocation of CK2, which regulates Nav1.5 and Kir2.1 channel complex formation and activity in cardiomyocytes.

Borderline personality disorder and risk of atrial fibrillation: insights from a bidirectional Mendelian randomization study.

Background: Atrial fibrillation (AF) is one of the most common form of arrhythmia. Previous studies have shown a link between AF and mental illness. However, the causal relationship between mental illness and AF remains unclear. The purpose of this study was to investigate the bidirectional causal relationship between borderline personality disorder (BPD) and AF. Method: We used the bidirectional Two-sample Mendelian randomization (TSMR) method to evaluate the causal relationship between BPD and AF. Instrumental variables associated with BPD were derived from a genome-wide association study involving 214,816 Europeans (2,637 cases and 212,179 controls). We then obtained atrial fibrillation data from the GWAS meta-analysis (60,620 cases and 970,216 controls). The TSMR analyses were performed in five methods, namely fixed-effect inverse-variance weighted (IVW) method、random-effect IVW method, MR Egger regression method, Weighted median method and Simple mode method. Several sensitivity analyses are used to test the robustness of positive results. Results: The fixed-effect inverse-variance weighted model [Odds ratio (OR), 1.033, 95% confidence interval (CI), 1.011-1.056, P = 0.0031], random-effect inverse-variance weighted model (OR, 1.033; 95%CI, 1.005-1.062; P = 0.0191) and Weighted median (OR, 1.034; 95%CI, 1.002-1.068; P = 0.0394) all showed that genetically predicted BPD was associated with an increased risk of AF. Sensitivity analysis using other MR Methods, including the MR-Egger intercept, MR-Presso method, and leave-one-out analyses, showed that the results were robust. In reverse MR analysis, there was no causal relationship of AF on BPD. Conclusion: Our study provides a causal relationship between BPD and AF. This means that patients with BPD should be monitored for the occurrence of AF. Early screening and proper management of BPD may show anti-arrhythmic benefits.

miR-let-7a inhibits sympathetic nerve remodeling after myocardial infarction by downregulating the expression of nerve growth factor.

Objective: Sympathetic hyperinnervation following myocardial infarction (MI) is one of the primary causes of ventricular arrhythmias (VAs) after MI. Nerve growth factor (NGF) is a key molecule that induces sympathetic nerve remodeling. Previous studies have confirmed that microRNA (miR)-let-7a interacts with NGF. However, whether miR-let-7a is involved in sympathetic remodeling after MI remains unknown. We aimed to investigate whether miR-let-7a was associated with the occurrence of VA after MI. Methods and results: A rat model of myocardial infarction was established using left coronary artery ligation. miR-let-7a expression levels were analyzed by reverse transcription-quantitative PCR. Western blotting was also used to examine NGF expression levels in vivo and in M1 macrophages in vitro. The relationship between miR-let-7a and NGF levels was investigated using a luciferase reporter assay. The results revealed that the expression of miR-let-7a decreased significantly after MI, while NGF expression was significantly upregulated. In addition, overexpression of miR-let-7a effectively inhibited NGF expression in rats, which was also verified in M1 macrophages. Tyrosine hydroxylase and growth-associated protein 43 immunofluorescence results revealed that the administration of a miR-let-7a overexpression lentivirus to rats inhibited sympathetic remodeling after MI. Programmed electrical stimulation, renal sympathetic nerve activity recording, and heart rate variability measurements showed that miR-let-7a overexpression decreased sympathetic activity. Conclusions: These findings provide novel insights into the molecular mechanisms by which miR-let-7a and NGF contribute to the progression of sympathetic nerve remodeling after MI. Therefore, miR-let-7a may be a promising therapeutic target to reduce the incidence of arrhythmia following MI.

Paeonol can improve hypoxic-induced H9c2 cells injury and ion channel activity by up-regulating the expression of CKIP-1.

BACKGROUND: Paeonol is a representative active ingredient of the traditional Chinese medicinal herbs Cortex Moutan, which has a well-established cardioprotective effect on ischemic heart disease. However, there is little evidence of the protective effect of paeonol, and its pharmacological mechanism is also unclear. This study aims to explore the protective effect and mechanism of Paeonol on myocardial infarction rat and hypoxic H9c2 cells. METHODS: Myocardial ischemia/reperfusion (I/R) was induced by occlusion of the left anterior descending coronary artery for 1 h followed by 3 h of reperfusion, and then gavage with Paeonol for 7 days. H9c2 cells were applied for the in vitro experiments and hypoxia/reoxygenation (H/R) model was established. CKIP-1 expression was evaluated by qPCR and western blot. The expression of genes involved in apoptosis, inflammation and ion channel was measured by western blot. The currents levels of Nav1.5 and Kir2.1 were measured by whole-cell patch-clamp recording. RESULTS: CKIP-1 expression was decreased in H/R-induced H9c2 cells, which was inversely increased after Paeonol treatment. Paeonol treatment could increase the viability of H/R-induced H9c2 cells and diminish the apoptosis and inflammation of H/R-induced H9c2 cells, while si-CKIP-1 treatment inhibited the phenomena. Moreover, the currents levels of Nav1.5 and Kir2.1 were reduced in H/R-induced H9c2 cells, which were inhibited after Paeonol treatment. Intragastric Paeonol can reduce the ventricular arrhythmias in rats with myocardial infarction. CONCLUSIONS: The protective effects of Paeonol on myocardial infarction rats and hypoxic H9c2 cells were achieved by up-regulating CKIP-1.

Protective effect of human epicardial adipose-derived stem cells on myocardial injury driven by poly-lactic acid nanopillar array.

We investigated if poly-lactic acid (PLA) nanopillar array can trigger the differentiation of human epicardial (ADSCs) (heADSCs) into cardiomyocyte-like cells and explored the effects of these cardiomyocyte-like cells on myocardial infarction (MI) in vivo. PLA nanopillar array (200 nm diameter) and plain PLA film (PLA planar) induced heADSCs were marked with carboxyfluorescein. After 7 days, the expressions of myocardiocyte-specific genes were significantly enhanced in cells seeded on PLA nanopillar array compared with that on PLA planar, especially CACNA1C, KCNH2, and MYL2 genes (p < 0.05). However, the expressions of cardiac troponin T (cTNT), KCNQ1, and KCNA5 were lower than those in PLA planar-induced heADSCs (p < 0.05), whereas GATA4 tended to increase with time. The cells with positively stained α-actinin and cTNT were elevated in heADSCs induced by PLA nanopillar array compared with those induced by PLA planar only (p < 0.05). In vivo experiments showed that cardiac function was improved after injecting PLA-nanopillar array-induced heADSCs into the ischemic heart (p < 0.05, compared with PLA planar + MI group). Furthermore, tyrosine hydroxylase density was significantly lower (p < 0.05). PLA nanopillar array directly drives the differentiation of heADSCs into cardiomyocyte-like cells, and the induced heADSCs exhibit a protective effect on ischemic myocardium by improving cardiac function in MI rats.

m6A methyltransferase METTL3 contributes to sympathetic hyperactivity post-MI via promoting TRAF6-dependent mitochondrial ROS production.

OBJECTIVES: N6-methyladenosine (m6A) is the most prevalent post-translational modification in eukaryotic mRNA. Recently, m6A editing modified by methyltransferase-like enzyme 3 (METTL3), the core m6A methyltransferase, has been demonstrated to be involved in cardiac sympathetic hyperactivity. This study aimed to clarify the effects and underlying mechanisms of METTL3 in the paraventricular nucleus (PVN) in mediating sympathetic activity following myocardial infarction (MI). METHODS: We established rat MI models by left anterior descending coronary artery ligation. m6A quantification was performed.The expression of METTL3 and its downstream gene, tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6), were determined. The functional role of METTL3 in sympathetic hyperactivity and electrical conduction stability were verified by assessing renal sympathetic nerve activity (RSNA), norepinephrine (NE) levels, and programmed electrical stimulation. Rescue experiments were also conducted. The mechanism by which m6A is involved in mitochondrial reactive oxygen species (mROS) production, mediated by TRAF6/ECSIT pathway, was explored in lipopolysaccharide (LPS) treated primary microglial cells. RESULTS: METTL3 was predominantly localized in the microglia and significantly increased within the PVN at 3 days post-MI. Inhibition of METTL3 decreased m6A levels, TRAF6 expression, and mROS production; downregulated sympathoexcitation, indicated by attenuated NE concentration and RSNA; decreased the incidence of ventricular tachycardia or fibrillation; and improved cardiac function. Mechanistically, downregulation of METTL3 prevented TRAF6 translocation to the mitochondria in the microglia and subsequent TRAF6/ECSIT pathway activation, resulting in decreased mROS production. CONCLUSIONS: This study demonstrates that METTL3-mediated m6A modification promotes sympathetic hyperactivity through TRAF6/ECSIT pathway and mitochondrial oxidative stress in the PVN, thereby leading to ventricular arrhythmias post-MI.

The protective effect of gamma aminobutyric acid B receptor activation on sympathetic nerve remodeling via the regulation of M2 macrophage polarization after myocardial infarction.

INTRODUCTION & OBJECTIVES: Acute myocardial infarction (AMI) in coronary heart disease is a leading cause of sudden death primarily due to malignant ventricular arrhythmias (VAs). Inflammatory cell infiltration and inflammation-induced overactivation of sympathetic nerves are the major cause of VAs in AMI pathophysiological processes. Type 2 macrophages play an anti-inflammatory role in AMI. Targeting macrophages may be a therapeutic strategy to prevent VAs post AMI. We found that gamma aminobutyric acid (GABA) promotes macrophages polarized to M2 and hypothesized that GABA might exert anti-inflammatory effects by promoting type 2 macrophage polarization in AMI. We aim to characterized GABAB receptor distribution, function, and mechanisms in M2 macrophage polarization and explored the functional aspect of GABAB receptor activation in sympathetic remodeling. RESULTS: Gamma aminobutyric acid B receptors were expressed on macrophage surface both in vitro and in vivo. GABAB receptor agonist baclofen, GABA promoted macrophage switch to M2. While GABAB receptor antagonist CGP52432 blocked a baclofen induced switch to M2 polarization. GABA and baclofen increased M2 macrophage percentage and CGP52432 blocked this process in vivo. Also, IL-10 and TGF-ß1 released by M2 were increased in both AMI and baclofen/AMI group; Serum NE levels were decreased by baclofen. All the above effects were reversed by CGP52432 treatment. Baclofen decreased TH and GAP-43 staining while CGP52432 enhanced their expression post AMI indicating GABAB receptor activation inhibited sympathetic nerve sprouting and activity by reducing NE release. CONCLUSIONS: Gamma aminobutyric acid B receptor activation promoted M2 polarization and protested AMI heart by regulating sympathetic nerve remodeling.

Impact of ATP synthase/coupling factor 6 in hypoxic pulmonary arterial hypertension: An experimental rat model.

BACKGROUND: Hypoxia-induced pulmonary arterial hypertension (PAH) is characterized by prostacyclin (PGI2 ) disorder, which manifests in the same manner as in monocrotaline (MCT)-induced PAH. Endogenous PGI2 inhibitor coupling factor 6 (CF6) is involved in MCT-induced PAH. This study aimed to explore the presence or absence of a correlation between hypoxia-induced PAH and CF6. METHODS: This study was conducted between January 2019 and June 2020. A total of 135 male Wistar rats (aged 8 weeks and weighing 200-250 g) were randomly divided into five groups: (A) control, (B) 1 week of hypoxia, (C) 2 weeks of hypoxia, (D) 3 weeks of hypoxia, and (E) 4 weeks of hypoxia. CF6 expression in both lung tissue and blood samples from the lung vasculature and tail vein was measured by western blotting, immunohistochemistry, reverse transcription polymerase chain reaction, and enzyme-linked immunosorbent assay. RESULTS: Hemodynamic and morphological changes in hypoxia-induced rats indicated PAH development. The results showed the presence of a correlation between the mRNA and protein levels of CF6 in lung tissue, activity of mitochondrial ATP synthase, and hypoxia time, and there was a significant increment in the group exposed to hypoxia for 4 weeks compared to the control group. The decrement expression of ATPase inhibitory factor 1 (IF 1) mRNA was consistent with the outcomes of ATP synthase activity in lung tissue in the 4 weeks of hypoxia group compared with the control group. However, the levels of CF6 and ATP synthase activity did not differ between blood samples from the lung vasculature and tail vein. DISCUSSION: : In hypoxia-induced PAH, CF6 showed downregulated expression in lung tissue, but not in pulmonary vasculature and circulation. Therefore, we speculated that CF6 and ATP synthase may play important roles in hypoxia-induced PAH.

m6A methyltransferase METTL3 participated in sympathetic neural remodeling post-MI via the TRAF6/NF-κB pathway and ROS production.

OBJECTIVE: Sudden cardiac death caused by ventricular arrhythmias (VAs) is the main cause of high mortality in patients with myocardial infarction (MI). Sympathetic neural remodeling caused by inflammation after MI is closely associated with the occurrence of VAs. METTL3, the earliest identified m6A methyltransferase, is critical in mediating inflammatory responses. Our aim was to investigate whether the m6A methyltransferase METTL3 was involved in sympathetic remodeling post-MI and its specific mechanism. METHODS AND RESULTS: A rat MI model was established via left coronary artery ligation. The expression of METTL3, TRAF6, NOX2, and NF-κB increased at 3 days and remained elevated at 7 days after MI, as determined via Western blotting. METTL3 was primarily present in macrophages, as determined via immunofluorescence. Intramyocardial injection of lentivirus carrying METTL3-shRNA inhibited METTL3 expression in vivo. Methylated immunoprecipitation-qPCR determined the METTL3 knockdown inhibited the m6A level of TRAF6 mRNA 3'-UTR. The co-immunoprecipitation experiment proved that METTL3 combines with TRAF6. Western blotting showed that silencing METTL3 inhibited TRAF6 level, NF-κB activation, and ROS production; decreased cytokine release (TNF-α and IL-1ß); and downregulated nerve growth factor expression. Finally, METTL3 knockdown reduced sympathetic remodeling after MI, as determined via immunofluorescence assays of tyrosine hydroxylase and growth-associated protein 43. Programmed electrical stimulation, renal sympathetic nerve activity recording, and haemodynamic measurements showed that METTL3 inhibition decreased sympathetic activity and improved cardiac function. CONCLUSIONS: Downregulation of METTL3 expression attenuated the excessive sympathetic neural remodeling induced by MI, further reducing the incidence of VAs and improving cardiac function. This was partly associated with the inhibition of the TRAF6/NF-κB pathway and ROS production.

Successful radiofrequency ablation of swallowing-induced atrial tachycardia arising from left superior ganglionated plexus.

A man in his early 40s developed palpitations brought on by swallowing and was found to have short runs of atrial tachycardia induced by swallowing solid food. Atrial tachycardia during swallowing was documented on electrocardiography and 24-hour Holter monitoring. No structural heart disease or esophageal disorders were found by echocardiography. The patient then underwent an electrophysiological study and catheter ablation. We mapped the left atrium with a multipolar mapping catheter while the patient swallowed bread and found that the earliest endocardial breakthrough was on the left anterior superior atrium, where the left superior ganglionated plexus was located. We successfully eliminated the paroxysmal atrial tachycardia at this site. Interestingly, in the process of ablation, atrioventricular node reentrant tachycardia was triggered. After the slow-pathway ablation procedure, no further tachycardia was induced.

Effect of TLR4/MyD88/NF-kB axis in paraventricular nucleus on ventricular arrhythmias induced by sympathetic hyperexcitation in post-myocardial infarction rats.

Sympathetic activation after myocardial infarction (MI) leads to ventricular arrhythmias (VAs), which can result in sudden cardiac death (SCD). The toll-like receptor 4 (TLR4)/myeloid differentiation primary response 88 (MyD88)/nuclear factor-kappa B (NF-kB) axis within the hypothalamic paraventricular nucleus (PVN), a cardiac-neural sympathetic nerve centre, plays an important role in causing VAs. An MI rat model and a PVN-TLR4 knockdown model were constructed. The levels of protein were detected by Western blotting and immunofluorescence, and localizations were visualized by multiple immunofluorescence staining. Central and peripheral sympathetic activation was visualized by immunohistochemistry for c-fos protein, renal sympathetic nerve activity (RSNA) measurement, heart rate variability (HRV) analysis and norepinephrine (NE) level detection in serum and myocardial tissue measured by ELISA. The arrhythmia scores were measured by programmed electrical stimulation (PES), and cardiac function was detected by the pressure-volume loop (P-V loop). The levels of TLR4 and MyD88 and the nuclear translocation of NF-kB within the PVN were increased after MI, while sympathetic activation and arrhythmia scores were increased and cardiac function was decreased. However, inhibition of TLR4 significantly reversed these conditions. PVN-mediated sympathetic activation via the TLR4/MyD88/NF-kB axis ultimately leads to the development of VAs after MI.

New insights into the central sympathetic hyperactivity post-myocardial infarction: Roles of METTL3-mediated m6 A methylation.

Ventricular arrhythmias (VAs) triggers by sympathetic nerve hyperactivity contribute to sudden cardiac death in myocardial infarction (MI) patients. Microglia-mediated inflammation in the paraventricular nucleus (PVN) is involved in sympathetic hyperactivity after MI. N6-methyladenosine (m6 A), the most prevalent mRNA and epigenetic modification, is critical for mediating cell inflammation. We aimed to explore whether METTL3-mediated m6 A modification is involved in microglia-mediated sympathetic hyperactivity after MI in the PVN. MI model was established by left coronary artery ligation. METTL3-mediated m6 A modification was markedly increased in the PVN at 3 days after MI, and METTL3 was primarily located in microglia by immunofluorescence. RNA-seq, MeRIP-seq, MeRIP-qPCR, immunohistochemistry, ELISA, heart rate variability measurements, renal sympathetic nerve activity recording and programmed electrical stimulation confirmed that the elevated toll-like receptor 4 (TLR4) expression by m6 A modification on TLR4 mRNA 3'-UTR region combined with activated NF-κB signalling led to the overwhelming production of pro-inflammatory cytokines IL-1ß and TNF-α in the PVN, thus inducing the sympathetic hyperactivity and increasing the incidence of VAs post-MI. Targeting METTL3 attenuated the inflammatory response and sympathetic hyperactivity and reduced the incidence of VAs post-MI.

EphrinB2-RhoA upregulation attenuates sympathetic hyperinnervation and decreases the incidence of ventricular arrhythmia after myocardial infarction.

BACKGROUND: Cardiac sympathetic hyperinnervation after myocardial infarction (MI) is associated with a high incidence of lethal arrhythmia. Erythropoietin-producing hepatoma interactor B2 (EphrinB2), a diffusible axonal chemorepellent that can induce growth cone collapse and axon repulsion of several neuronal populations, is crucial in neurodevelopment during disease development and progression. However, whether EphrinB2 could inhibit cardiac sympathetic hyperinnervation after MI remains unclear. METHODS AND RESULTS: A rat model of MI was developed by left anterior descending coronary artery ligation. EphrinB2 expression was markedly increased in the infarcted border at 3 days after MI. Downregulation of EphrinB2 by intramyocardial injection of lentivirus carrying EphrinB2-shRNA significantly increased sympathetic hyperinnervation along with downregulated RhoA expression. In contrast, injection of EphrinB2-overexpressing lentivirus markedly upregulated EphrinB2, concomitant with inhibition of sympathetic sprouting and upregulated RhoA expression, accompanied by decreased incidence of ventricular arrhythmias (VAs). However, co-administering EphrinB2-overexpressing lentivirus and Fasudil (Rho kinase inhibitor) nearly abolished the inhibition of nerve sprouting effect. Additionally, EphrinB2 expression did not affect nerve growth factor level in the infarcted heart. CONCLUSIONS: Overexpression of EphrinB2 may ameliorate MI-induced sympathetic hyperinnervation and further reduce the incidence of VAs, at least in part by activating RhoA-mediated axonal retraction.

lncRNA LOC100911717-targeting GAP43-mediated sympathetic remodeling after myocardial infarction in rats.

Objective: Sympathetic remodeling after myocardial infarction (MI) is the primary cause of ventricular arrhythmias (VAs), leading to sudden cardiac death (SCD). M1-type macrophages are closely associated with inflammation and sympathetic remodeling after MI. Long noncoding RNAs (lncRNAs) are critical for the regulation of cardiovascular disease development. Therefore, this study aimed to identify the lncRNAs involved in MI and reveal a possible regulatory mechanism. Methods and results: M0- and M1-type macrophages were selected for sequencing and screened for differentially expressed lncRNAs. The data revealed that lncRNA LOC100911717 was upregulated in M1-type macrophages but not in M0-type macrophages. In addition, the lncRNA LOC100911717 was upregulated in heart tissues after MI. Furthermore, an RNA pull-down assay revealed that lncRNA LOC100911717 could interact with growth-associated protein 43 (GAP43). Essentially, immunofluorescence assays and programmed electrical stimulation demonstrated that GAP43 expression was suppressed and VA incidence was reduced after lncRNA LOC100911717 knockdown in rat hearts using an adeno-associated virus. Conclusions: We observed a novel relationship between lncRNA LOC100911717 and GAP43. After MI, lncRNA LOC100911717 was upregulated and GAP43 expression was enhanced, thus increasing the extent of sympathetic remodeling and the frequency of VA events. Consequently, silencing lncRNA LOC100911717 could reduce sympathetic remodeling and VAs.

Overexpressing microRNA-203 alleviates myocardial infarction via interacting with long non-coding RNA MIAT and mitochondrial coupling factor 6.

Myocardial infarction (MI) is one of the leading causes of high mortality worldwide. Long non-coding RNA myocardial infarction associated transcript (MIAT) and mitochondrial coupling factor 6 (CF6) aggravate MI. This study aimed to elucidate whether miR-203 interacted with MIAT and CF6 in MI. Results revealed that MIAT and CF6 expressions were upregulated and that miR-203 was downregulated in mouse myocardial tissues after MI, as well as in hypoxic mouse cardiomyocytes. The overexpression of MIAT in mouse cardiomyocytes raised CF6 expression, whereas the knockdown of MIAT had the opposite effect. Mechanistically, the luciferase reporter and RNA pull-down assays corroborated the binding between miR-203 and CF6 3'UTR and between miR-203 and MIAT. The simultaneous overexpression of miR-203 and MIAT restored the reduction of CF6 caused by miR-203 overexpression alone, and the overexpression of miR-203 diminished the percentage of infarct area and the apoptosis of cardiomyocytes in vivo. Our findings corroborate that overexpressing miR-203 alleviates MI via interacting with MIAT and CF6.

Targeting blockade of nuclear factor-κB in the hypothalamus paraventricular nucleus to prevent cardiac sympathetic hyperinnervation post myocardial infarction.

BACKGROUND AND OBJECTIVES: Nuclear factor-κB (NF-κB) is considered to be a master inflammation regulator and involved in sympathetic neural hyperinnervation after myocardial infarction (MI). Paraventricular nucleus (PVN), acts as the sympathetic outflow tract, has been proven to play an important role during MI, but whether NF-κB pathway in the PVN participates in the pathogenesis of sympathetic sprouting and reinnervation after MI are unclear. METHODS AND RESULTS: MI was induced by coronary artery ligation, NF-κB was activated and interleukin-1ß (IL-1ß) and nerve growth factor (NGF) levels were increased in the PVN after MI. Lipopolysaccharide (LPS) stimulation also can activate NF-κB pathway, followed by increasing the expressions of IL-1ß and NGF in the PVN, once combining with gevokizumab (an IL-1ß inhibitor) significantly reduced the expressions of IL-1ß and NGF, but could not affect the NF-κB expression in the PVN. Furthermore, micro-injection of the NF-κB inhibitor pyrrolidine dithiocarbamate into PVN in MI rats, significantly inhibited the activation of NF-κB and further reduced the expression of IL-1ß and NGF in the PVN, finally blunting sympathetic hyperinnervation in the heart, moreover, the blockade of NF-κB in the PVN reduced the incidence of ventricular arrhythmias (VAs). CONCLUSIONS: Cardiac nerve sprouting after MI is associated in part with NF-κB activation in the PVN, and IL-1ß is involved in the process. Targeting blockade of NF-κB in the PVN may be a potential approach to ameliorate sympathetic hyperinnervation and reduce the incidence of VAs after MI.

A novel sympathetic neuronal GABAergic signalling system regulates NE release to prevent ventricular arrhythmias after acute myocardial infarction.

AIM: Overactivation of the sympathetic nerve may lead to severe ventricular arrhythmias (VAs) after myocardial infarction (MI). Thus, targeting sympathetic nerve activity is an effective strategy to prevent VAs clinically. The superior cervical ganglion (SCG), the extracardiac sympathetic ganglion innervating cardiac muscles, has been found to have a GABAergic signalling system, the physiological significance of which is obscure. We aimed to explore the functional significance of SCG post MI and whether the GABAergic signal system is involved in the process. METHODS: Adult male Sprague-Dawley rats were divided into seven different groups. Rats in the MI groups underwent ligation of the left anterior descending coronary artery. All animals were used for electrophysiological testing, renal sympathetic nerve activity (RSNA) testing, and ELISA. Primary SCG sympathetic neurons were used for the in vitro study. RESULTS: The GABAA receptor agonist muscimol significantly decreased the ATP-induced increase in intracellular Ca2+ (P < 0.05). GABA treatment in MI rats significantly attenuated the level of serum and cardiac norepinephrine (NE; P < 0.05). Sympathetic activity and inducible VAs were also lower in MI + GABA rats than in MI rats (P < 0.05). Knockdown of the GABAA Rs ß2 subunit (GABAA Rß2 ) in the SCG of MI rats increased the NE levels in serum and cardiac tissue, RSNA and inducible VAs compared with vehicle shRNA (P < 0.05). CONCLUSION: The GABAergic signalling system is functionally expressed in SCG sympathetic neurons, and activation of this system suppresses sympathetic activity, thereby facilitating cardiac protection and making it a potential target to alleviate VAs.

TLR4 participates in sympathetic hyperactivity Post-MI in the PVN by regulating NF-κB pathway and ROS production.

Sympathetic nerve hyperactivity is a primary reason for fatal ventricular arrhythmias (VAs) following myocardial infarction (MI). Pro-inflammatory cytokines produced in the paraventricular nucleus (PVN) post-MI are associated with sympathetic overexcitation; however, the precise mechanism needs further investigation. Our aim was to explore the mechanism of toll-like receptor 4 (TLR4) and its downstream molecular pathway in mediating sympathetic activity post-MI within the PVN. A rat MI model was developed via left anterior descending coronary artery ligation. TLR4 was primarily localized in microglia and increased markedly within the PVN at 3 days in MI rats. Sympathoexcitation also increased, as indicated by high levels of renal sympathetic nerve activity (RSNA) and norepinephrine (NE) concentration. TLR4 knockdown via shRNA microinjection to the PVN resulted in decreased activation of Fos protein (+) neurons in the PVN and peripheral sympathetic nerve activity. TLR4 knockdown also exhibited a lower arrhythmia score following programmed electrical stimulation than those treated with MI surgery only, indicating that the knockdown of TLR4 decreased the incidence of malignant ventricular arrhythmias following MI. LPS-induced inflammatory response was analyzed to explore the underlying mechanism of TLR4 in sympathetic hyperactivity. High levels of NF-κB protein, the pro-inflammatory cytokines IL-1ß and TNF-α, and ROS production were observed in the LPS group. PVN-targeted injection of the NF-κB inhibitor PDTC attenuated NF-κB expression and sympathetic activity. Taken together, the results suggested that knockdown of microglial TLR4 within the PVN decreased sympathetic hyperactivity and subsequent VAs post-MI. The downstream NF-κB pathway and ROS production participated in the process. Interventions targeting TLR4 signaling in the PVN may be a novel approach to ameliorate the incidence of VAs post-MI.

Targeted regulation of sympathetic activity in paraventricular nucleus reduces inducible ventricular arrhythmias in rats after myocardial infarction.

BACKGROUND: The hypothalamic paraventricular nucleus (PVN) is the center of the regulation of autonomic nervous system functions and cardiovascular activity. Phosphoinositide-3 kinase (PI3K)-AKT pathway in PVN contributes to mediate sympathetic nerve activity and is activated in spontaneously hypertensive rats. Overactivation of the sympathetic output was considered as an important mechanism of the arrhythmias. In the present study, we aimed to explore whether targeted regulation of sympathetic activity in PVN could reduce the peripheral sympathoexcitatory and attenuate the ventricular arrhythmias (VAs) in myocardial infarction (MI) rats via PI3K-AKT pathway. METHODS: A stainless steel gauge guide cannula was stereotaxically implanted into the PVN, and 7 days later, rats were randomly divided into the following 4 groups: group A, control+dimethyl sulfoxide (DMSO); group B, control+LY294002; group C, MI surgery+DMSO; and group D, MI surgery+LY294002. Studies were conducted seven days post-MI. Myocardial function, infarct size, inducible VAs by programmed electrical stimulation, renal sympathetic nerve activity (RSNA), and protein level of PI3K and AKT were measured. RESULTS: MI increased the protein ratios of p-PI3K-to-total-PI3K and p-AKT-to-total-AKT in PVN but can be reduced by LY294002 treatment. Inhibition of sympathetic nerve activity in PVN led to a reversion in plasma norepinephrine, RSNA and inducible VAs in MI rats. CONCLUSIONS: PI3K-AKT pathway in the PVN was a main mechanism in regulating sympathetic activity and arrhythmias in MI rats. Targeted inhibition of sympathetic activity in PVN may be a potential treatment for the VAs via PI3K-AKT pathway.

Microglial Mincle receptor in the PVN contributes to sympathetic hyperactivity in acute myocardial infarction rat.

Malignant ventricular arrhythmias (VAs) following myocardial infarction (MI) is a lethal complication resulting from sympathetic nerve hyperactivity. Numerous evidence have shown that inflammation within the paraventricular nucleus (PVN) participates in sympathetic hyperactivity. Our aim was to explore the role of Macrophage-inducible C-type lectin (Mincle) within the PVN in augmenting sympathetic activity following MI,and whether NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome/IL-1ß axis is involved in this activity. MI was induced by coronary artery ligation. Mincle expression localized in microglia within the PVN was markedly increased at 24 hours post-MI together with sympathetic hyperactivity, as indicated by measurement of the renal sympathetic nerve activity (RSNA) and norepinephrine (NE) concentration. Mincle-specific siRNA was administrated locally to the PVN, which consequently decreased microglial activation and sympathetic nerve activity. The MI rats exhibited a higher arrhythmia score after programmed electric stimulation than that treated with Mincle siRNA, suggesting that the inhibition of Mincle attenuated foetal ventricular arrhythmias post-MI. The underlying mechanism of Mincle in sympathetic hyperactivity was investigated in lipopolysaccharide (LPS)-primed naïve rats. Recombinant Sin3A-associated protein 130kD (rSAP130), an endogenous ligand for Mincle, induced high levels of NLRP3 and mature IL-1ß protein. PVN-targeted injection of NLRP3 siRNA or IL-1ß antagonist gevokizumab attenuated sympathetic hyperactivity. Together, the data indicated that the knockdown of Mincle in microglia within the PVN prevents VAs by attenuating sympathetic hyperactivity and ventricular susceptibility, in part by inhibiting its downstream NLRP3/IL-1ß axis following MI. Therapeutic interventions targeting Mincle signalling pathway could constitute a novel approach for preventing infarction injury.