Acetylcytidine modification of Amotl1 by N-acetyltransferase 10 contributes to cardiac fibrotic expansion in mice after myocardial infarction.

Cardiac fibrosis is a pathological scarring process that impairs cardiac function. N-acetyltransferase 10 (Nat10) is recently identified as the key enzyme for the N4-acetylcytidine (ac4C) modification of mRNAs. In this study, we investigated the role of Nat10 in cardiac fibrosis following myocardial infarction (MI) and the related mechanisms. MI was induced in mice by ligation of the left anterior descending coronary artery; cardiac function was assessed with echocardiography. We showed that both the mRNA and protein expression levels of Nat10 were significantly increased in the infarct zone and border zone 4 weeks post-MI, and the expression of Nat10 in cardiac fibroblasts was significantly higher compared with that in cardiomyocytes after MI. Fibroblast-specific overexpression of Nat10 promoted collagen deposition and induced cardiac systolic dysfunction post-MI in mice. Conversely, fibroblast-specific knockout of Nat10 markedly relieved cardiac function impairment and extracellular matrix remodeling following MI. We then conducted ac4C-RNA binding protein immunoprecipitation-sequencing (RIP-seq) in cardiac fibroblasts transfected with Nat10 siRNA, and revealed that angiomotin-like 1 (Amotl1), an upstream regulator of the Hippo signaling pathway, was the target gene of Nat10. We demonstrated that Nat10-mediated ac4C modification of Amotl1 increased its mRNA stability and translation in neonatal cardiac fibroblasts, thereby increasing the interaction of Amotl1 with yes-associated protein 1 (Yap) and facilitating Yap translocation into the nucleus. Intriguingly, silencing of Amotl1 or Yap, as well as treatment with verteporfin, a selective and potent Yap inhibitor, attenuated the Nat10 overexpression-induced proliferation of cardiac fibroblasts and prevented their differentiation into myofibroblasts in vitro. In conclusion, this study highlights Nat10 as a crucial regulator of myocardial fibrosis following MI injury through ac4C modification of upstream activators within the Hippo/Yap signaling pathway.

Crosstalk between PML and p53 in response to TGF-ß1: A new mechanism of cardiac fibroblast activation.

Cardiac fibrosis is a common pathological cardiac remodeling in a variety of heart diseases, characterized by the activation of cardiac fibroblasts. Our previous study uncovered that promyelocytic leukemia protein (PML)-associated SUMO processes is a new regulator of cardiac hypertrophy and heart failure. The present study aimed to explore the role of PML in cardiac fibroblasts activation. Here we found that PML is significantly upregulated in cardiac fibrotic tissue and activated cardiac fibroblasts treated with transforming growth factor-ß1 (TGF-ß1). Gain- and loss-of-function experiments showed that PML impacted cardiac fibroblasts activation after TGF-ß1 treatment. Further study demonstrated that p53 acts as the transcriptional regulator of PML, and participated in TGF-ß1 induced the increase of PML expression and PML nuclear bodies (PML-NBs) formation. Knockdown or pharmacological inhibition of p53 produced inhibitory effects on the activation of cardiac fibroblasts. We further found that PML also may stabilize p53 through inhibiting its ubiquitin-mediated proteasomal degradation in cardiac fibroblasts. Collectively, this study suggests that PML crosstalk with p53 regulates cardiac fibroblasts activation, which provides a novel therapeutic strategy for cardiac fibrosis.

Melatonin promotes cardiomyocyte proliferation and heart repair in mice with myocardial infarction via miR-143-3p/Yap/Ctnnd1 signaling pathway.

The neonatal heart possesses the ability to proliferate and the capacity to regenerate after injury; however, the mechanisms underlying these processes are not fully understood. Melatonin has been shown to protect the heart against myocardial injury through mitigating oxidative stress, reducing apoptosis, inhibiting mitochondrial fission, etc. In this study, we investigated whether melatonin regulated cardiomyocyte proliferation and promoted cardiac repair in mice with myocardial infarction (MI), which was induced by ligation of the left anterior descending coronary artery. We showed that melatonin administration significantly improved the cardiac functions accompanied by markedly enhanced cardiomyocyte proliferation in MI mice. In neonatal mouse cardiomyocytes, treatment with melatonin (1 µM) greatly suppressed miR-143-3p levels. Silencing of miR-143-3p stimulated cardiomyocytes to re-enter the cell cycle. On the contrary, overexpression of miR-143-3p inhibited the mitosis of cardiomyocytes and abrogated cardiomyocyte mitosis induced by exposure to melatonin. Moreover, Yap and Ctnnd1 were identified as the target genes of miR-143-3p. In cardiomyocytes, inhibition of miR-143-3p increased the protein expression of Yap and Ctnnd1. Melatonin treatment also enhanced Yap and Ctnnd1 protein levels. Furthermore, Yap siRNA and Ctnnd1 siRNA attenuated melatonin-induced cell cycle re-entry of cardiomyocytes. We showed that the effect of melatonin on cardiomyocyte proliferation and cardiac regeneration was impeded by the melatonin receptor inhibitor luzindole. Silencing miR-143-3p abrogated the inhibition of luzindole on cardiomyocyte proliferation. In addition, both MT1 and MT2 siRNA could cancel the beneficial effects of melatonin on cardiomyocyte proliferation. Collectively, the results suggest that melatonin induces cardiomyocyte proliferation and heart regeneration after MI by regulating the miR-143-3p/Yap/Ctnnd1 signaling pathway, providing a new therapeutic strategy for cardiac regeneration.

Calcium-Activated Potassium Channels: Potential Target for Cardiovascular Diseases.

Ca(2+)-activated K(+) channels (KCa) are classified into three subtypes: big conductance (BKCa), intermediate conductance (IKCa), and small conductance (SKCa) KCa channels. The three types of KCa channels have distinct physiological or pathological functions in cardiovascular system. BKCa channels are mainly expressed in vascular smooth muscle cells (VSMCs) and inner mitochondrial membrane of cardiomyocytes, activation of BKCa channels in these locations results in vasodilation and cardioprotection against cardiac ischemia. IKCa channels are expressed in VSMCs, endothelial cells, and cardiac fibroblasts and involved in vascular smooth muscle proliferation, migration, vessel dilation, and cardiac fibrosis. SKCa channels are widely expressed in nervous and cardiovascular system, and activation of SKCa channels mainly contributes membrane hyperpolarization. In this chapter, we summarize the physiological and pathological roles of the three types of KCa channels in cardiovascular system and put forward the possibility of KCa channels as potential target for cardiovascular diseases.

Blockage of peripheral NPY Y1 and Y2 receptors modulates barorefex sensitivity of diabetic rats.

BACKGROUND/AIMS: Abnormal baroreceptor reflex sensitivity (BRS) and elevated plasma neuropeptide Y (NPY) are prevalent in diabetic patients. The present study was conducted to determine whether NPY Y1 receptor (Y1R) and NPY Y2 receptor (Y2R) contribute to the regulatin of BRS in diabetic rats. METHODS: Diabetes mellitus (DM) rats with hyperlipidemia were developed by an emulsion diet enriched with fat, sucrose and fructose followed by streptozocin (STZ). Y1R and Y2R specific antagonists (BIBP 3226 and BIIE 0246) were administered by a mini-osmotic pump. Systolic blood pressure (SBP), heart rate (HR), BRS and heart functions, as well as the plasma NPY and lipid level were measured after treatment for 4 weeks. RESULTS: Both BIBP 3226 and BIIE 0246 treatment reversed the elevated total cholesterol (TC) and low density lipoprotein (LDL-C) level, and reduced high density lipoprotein (HDL-C) level in DM rats. BIIE 0246 may attenuate the increased triglyceride (TG) level in DM rats. In addition, neither BIBP 3226 nor BIIE 0246 treatment produced significant effects on BRS, SBP or HR (P>0.05) in DM rats, even after PE and SNP challenge. However, BIBP 3226 and BIIE 0246 further impaired LVSP, LVEDP, +dp/dtmax and -dp/dtmax. CONCLUSION: This study provided us with the evidence that the inhibition of peripheral Y1R and Y2R did not affect impaired BRS but amplified the deterioration of the compromised cardiac function in STZ-induced DM rats with hyperlipidemia.

Arsenic trioxide induces the apoptosis in bone marrow mesenchymal stem cells by intracellular calcium signal and caspase-3 pathways.

It was previously reported that excessive arsenic trioxide would produce cardiovascular toxicity. Bone marrow mesenchymal stem cells (BMSCs) have been shown to play a supporting role in cardiovascular functions. The increasing apoptosis of BMSCs commonly would promote the development of cardiovascular diseases. Thus we hypothesize that arsenic trioxide caused apoptosis in BMSCs, which provided a better understanding of arsenic toxicity in hearts. The present study was designed to investigate the proapoptotic effects of arsenic trioxide on BMSCs and explore the mechanism underlying arsenic trioxide-induced BMSCs apoptosis. We demonstrate that arsenic trioxide significantly inhibited survival ratios of BMSCs in a concentration-dependent and time-dependent manner. The Annexin V/PI staining and terminal deoxynucleotidyl transferasemediated dUTP nick-end labelling (TUNEL) assay also showed that arsenic trioxide markedly induced the apoptosis of BMSCs. The caspase-3 activity was obviously enhanced in the presence of arsenic trioxide in a concentration-dependent manner in BMSCs. Additionally, arsenic trioxide caused the increase of intracellular free calcium ([Ca(2+)](i)) in rat BMSCs. BAPTA pretreatment may attenuate the apoptosis of BMSCs induced by arsenic trioxide. Taken together, arsenic trioxide could inhibit the proliferation and induce the apoptosis of BMSCs by modulating intracellular [Ca(2+)](i), and activating the caspase-3 activity.

Arsenic trioxide induces the apoptosis in vascular smooth muscle cells via increasing intracellular calcium and ROS formation.

The present study was designed to investigate whether arsenic trioxide induced the apoptosis in rat mesenteric arterial smooth muscle cells (SMCs), which provides new insights into mechanisms of arsenic-related vascular diseases. Here, we found that arsenic trioxide significantly decreased the viability of SMCs in a dose-dependent manner. In addition, higher level of arsenic trioxide directly caused cellular necrosis. The Hoechst and AO/EB staining demonstrated that apoptotic morphological change was presented in SMCs exposed to arsenic trioxide. The TUNEL assay displayed that more positive apoptotic signal appeared in SMCs treated with arsenic trioxide. The following result showed that ROS formation was markedly increased in arsenic trioxide-treated SMCs. Pretreatment with N-acetylcysteine, an anti-oxidant reagent, obviously attenuated the enhancement of ROS production and the reduction of cell viability induced by arsenic trioxide in SMCs. Arsenic trioxide also enhanced free intracellular Ca(2+) level in SMCs. BAPTA also significantly prevented the increased intracellular Ca(2+) and decreased cell viability induced by arsenic trioxide in SMCs. These results suggested that arsenic trioxide obviously induced apoptosis in SMCs, and its mechanism was partially associated with intracellular ROS formation and free Ca(2+) increasing.

[A novel target for the regulation of cardiac arrhythmias--microRNAs].

microRNAs are one kind of endogenous no-encoding RNA with about 22 nucleotides in length, and inhibited the translation of mRNAs by partially complementary binding to the 3' UTR of target mRNAs in the post-transcriptional level. Recent research shows that miRNAs function in the physiological and pathological processes of heart, especially involved in the occurrence and progress of arrhythmias. Abnormal miRNAs alters the protein expression of ion channels, causes the cardiac dysfunction, and triggers heart arrhythmias. The article summarized recent advances about roles of miRNA in arrhythmias and related cardiomyopathy, and discussed the therapeutic potential of miRNAs for heart diseases.

Role of M3 receptor in aconitine/barium-chloride-induced preconditioning against arrhythmias in rats.

We demonstrated here that an initial treatment with aconitine- or barium-chloride-induced arrhythmias and resulted in reduced susceptibility of the heart to the induction of arrhythmias by a repeated drug treatment 24 h after the initial one, a delayed preconditioning cardioprotection. This delayed preconditioning was accompanied by enhanced expression of cardiac muscarinic M(3) receptor and abolished by M(3)-selective antagonist. We conclude that muscarinic M(3) receptors might play an important role in conferring the pharmacological preconditioning against arrhythmias. This study thus expands our understanding of the cellular function and pathophysiological roles of muscarinic M(3) receptor and reconsolidates our view of cardioprotective effects of muscarinic M(3) receptor on myocardium.

Homocysteine inhibits potassium channels in human atrial myocytes.

1. A large body of evidence indicates that elevated homocysteine (Hcy) levels portend an increased risk for atrial fibrillation. However, little is known about the electrophysiological effects of Hcy on atrial myocytes. The present study was conducted to investigate the direct effects of Hcy on ion channels in human atria. 2. Whole-cell patch-clamp techniques were used to record potassium currents in human atrial cells. 3. In human atrial myocytes, transient outward potassium currents were significantly decreased by 24.8 +/- 5.9 and 38.4 +/- 10.4% in the presence of 50 and 500 micromol/L Hcy, respectively. The ultrarapid delayed rectifier potassium currents were decreased by approximately 30% when exposed to 500 micromol/L Hcy. The inward rectifier potassium currents were increased by approximately 40% in the presence of 500 micromol/L Hcy. 4. The results of the present study indicate that Hcy, an important risk factor for atrial fibrillation, could cause electrophysiological disturbances of potassium currents in human atrial myocytes.