Wenfeng Chu

The muscle-specific microRNAs miR-1 and miR-133 produce opposing effects on apoptosis by targeting HSP60, HSP70 and caspase-9 in cardiomyocytes.

The microRNAs miR-1 and miR-133 are preferentially expressed in cardiac and skeletal muscles and have been shown to regulate differentiation and proliferation of these cells. We report here a novel aspect of cellular function of miR-1 and miR-133 regulation of cardiomyocyte apoptosis. miR-1 and miR-133 produced opposing effects on apoptosis, induced by oxidative stress in H9c2 rat ventricular cells, with miR-1 being pro-apoptotic and miR-133 being anti-apoptotic. miR-1 level was significantly increased in response to oxidative stress. We identified single target sites for miR-1 only, in the 3′-untranslated regions of the HSP60 and HSP70 genes, and multiple putative target sites for miR-133 throughout the sequence of the caspase-9 gene. miR-1 reduced the levels of HSP60 and HSP70 proteins without changing their transcript levels, whereas miR-133 did not affect HSP60 and HSP70 expression at all. By contrast, miR-133 repressed caspase-9 expression at both the protein and mRNA levels. The post-transcriptional repression of HSP60 and HSP70 and caspase-9 was further confirmed by luciferase reporter experiments. Our results indicate that miR-1 and miR-133 are involved in regulating cell fate with increased miR-1 and/or decreased miR-133 levels favoring apoptosis and decreased miR-1 and/or miR-133 levels favoring survival. Post-transcriptional repression of HSP60 and HSP70 by miR-1 and of caspase-9 by miR-133 contributes significantly to their opposing actions.

A novel reciprocal loop between microRNA-21 and TGFβRIII is involved in cardiac fibrosis

Cardiac fibrosis is characterized by aberrant proliferation of cardiac fibroblasts and exaggerated deposition of extracellular matrix (ECM) in the myocardial interstitial, and ultimately impairs cardiac function. It is still controversial whether microRNA-21 (miR-21) participates in the process of cardiac fibrosis. Our previous study confirmed that transforming growth factor beta receptor III (TGFβRIII) is a negative regulator of TGF-β pathway. Here, we aimed to decipher the relationship between miR-21 and TGFβRIII in the pathogenic process of myocardial fibrosis. We found that TGF-β1 and miR-21 were up-regulated, whereas TGFβRIII was down-regulated in the border zone of mouse hearts in response to myocardial infarction. After transfection of miR-21 into cardiac fibroblasts, TGFβRIII expression was markedly reduced and collagen content was increased. And, luciferase results confirmed that TGFβRIII was a target of miR-21. It suggests that up-regulation of miR-21 could increase the collagen content and at least in part through inhibiting TGFβRIII. Conversely, we also confirmed that overexpression of TGFβRIII could inhibit the expression of miR-21 and reduce collagen production in fibroblasts. Further studies showed that overexpression of TGFβRIII could also deactivate TGF-β1 pathway by decreasing the expression of TGF-β1 and phosphorylated-Smad3 (p-Smad3). TGF-β1 has been proven as a positive regulator of miR-21. Taken together, we found a novel reciprocal loop between miR-21 and TGFβRIII in cardiac fibrosis caused by myocardial infarction in mice, and targeting this pathway could be a new strategy for the prevention and treatment of myocardial remodeling.

Tanshinone IIA protects against sudden cardiac death induced by lethal arrhythmias via repression of microRNA-1

Background and purpose:  Tanshinone IIA is an active component of a traditional Chinese medicine based on Salvia miltiorrhiza, which reduces sudden cardiac death by suppressing ischaemic arrhythmias. However, the mechanisms underlying the anti‐arrhythmic effects remain unclear.

Scutellarin-induced endothelium-independent relaxation in rat aorta

Scutellarin is a flavonoid extracted from the traditional Chinese herb, Erigeron breviscapus Hand Mazz. In the present study, the vasorelaxant effects of scutellarin and the underlying mechanism were investigated in isolated rat aorta. Scutellarin (3, 10, 30, 100 µm) caused a dose‐dependent relaxation in both endothelium‐intact and endothelium‐denuded rat aortic rings precontracted with noradrenaline bitartrate (IC50 = 7.7 ± 0.6 µm), but not with potassium chloride. Tetraethylammonium, glibenclamide, atropine, propranolol, indomethacin and N(G)‐nitro‐l‐arginine methyl ester had no influence on the vasorelaxant effect of scutellarin, which further excluded the involvement of potassium channels, muscarinic receptor, nitric oxide pathway and prostaglandin in this effect. Pretreatment with scutellarin decreased the tonic phase, but not the phasic phase of the noradrenaline bitartrate induced tension increment. Scutellarin also alleviated Ca2+‐induced vasoconstriction in Ca2+‐depleted/noradrenaline bitartrate pretreated rings in the presence of voltage‐dependent calcium channel blocker verapamil. The noradrenaline bitartrate evoked intracellular calcium increase was inhibited by scutellarin. Scutellarin had no effect on phorbol‐12,13‐diacetate induced contraction in a calcium‐free bath solution. These results showed that scutellarin could relax thoracic artery rings in an endothelium‐independent manner. The mechanism seems to be the inhibition of extracellular calcium influx independent of the voltage‐dependent calcium channel. Copyright

Tanshinone IIA Inhibits miR-1 Expression through p38 MAPK Signal Pathway in Post-infarction Rat Cardiomyocytes

Tanshinone IIA is a fat-soluble pharmacologically active ingredient of Danshen, a well-known traditional Chinese medicine used for cardiovascular diseases such as coronary heart disease. Tanshinone IIA has been confirmed to suppress miR-1 and reduce the arrhythmogenesis after myocardial infarction (MI). However, the modulation mechanism is not clear. Tanshinone IIA was administrated daily for 7 days before ligation of the left anterior descending artery (LAD) and lasted for 3 months after LAD. Neonatal cardiomyocytes were exposed to 2% O2+95% N2 condition for 24 h to simulate ischemia in vivo. Protein expression was examined with Western blot and miR-1 level was quantified by Real-time PCR. Our results showed that tanshinone IIA relieved ischemia-induced injury by improving the cardiac function. This beneficial effect may due to the depression of the elevated miR-1 level in ischemic and hypoxic cardiomyocytes, which subsequently restored its target Cx43 protein. Furthermore, tanshinone IIA could inhibit activated p38 MAPK and heart special transcription factors SRF and MEF2, in ischemic and hypoxic cardiomyocytes. Pretreatment with p38 MAPK inhibitor, SB203580 (10 uM), significantly relieved hypoxia-induced miR-1 increment and restored its downstream target Cx43 protein expression. These data suggest that tanshinone IIA play a role in protection cardiomyocytes from ischemic and hypoxic injury. The effect is based on inhibiting miR-1 expression through p38 MAPK signal pathway. This might provide us a new target to explore the novel strategy for ischemic cardioprotection.

TGFBR3, a potential negative regulator of TGF-β signaling, protects cardiac fibroblasts from hypoxia-induced apoptosis.

A lot of evidence indicates that cardiac fibroblasts are essential for maintaining the structure and function of heart. The present study examined whether TGFBR3 (transforming growth factor type III receptor, also known as betaglycan) could prevent hypoxia‐induced injury in neonatal mice cardiac fibroblasts, if so, its possible molecular targets. MTT, electron microscopy and TUNEL assay were used to identify cell viability and apoptosis in neonatal mice cardiac fibroblasts. Results showed that hypoxia for 24 h markedly reduce cell viability by 49.8 ± 8.9%, largely via apoptosis. However, hypoxia‐induced apoptosis in cardiac fibroblasts were almost completely prevented by overexpression of TGFBR3. In the present study, hypoxia also induced TGF‐β1, p‐Smad2/3 expression, TGFBR1–TGFBR2 complex formation and collagen production in cardiac fibroblasts, which were attenuated substantially by TGFBR3 overexpression. TGFBR3 also reversed Bax up‐regulation, Bcl‐2 down‐regulation and Caspase‐3 activation induced by hypoxia in cardiac fibroblasts. Hypoxia or TGF‐β1 itself triggered an increase of [Ca2+]i in cardiac fibroblasts, which were both inhibited by TGFBR3 overexpression. Taken together, our results indicate that TGFBR3 may act as a protective factor in apoptotic process of cardiac fibroblasts by negative regulation of TGF‐β signaling and represent a potential therapeutic target for heart remodeling after hypoxia injury. J. Cell. Physiol. 226: 2586–2594, 2011.

Arsenic-induced interstitial myocardial fibrosis reveals a new insight into drug-induced long QT syndrome.

AIMS Arsenic trioxide (ATO), an effective therapeutic agent for acute promyelocytic leukaemia, can cause sudden cardiac death due to long QT syndrome (LQTS). The present study was designed to determine whether ATO could induce cardiac fibrosis and explore whether cardiac fibroblasts (CFs) are involved in the development of LQTS by ATO. METHODS AND RESULTS ATO treatment of guinea pigs caused substantial interstitial myocardial fibrosis and LQTS, which was accompanied by an increase in transforming growth factor β1(TGF-β1) secretion and a decrease in ether-à-go-go-related gene (HERG) and inward rectifying potassium channel (I(K1)) subunit Kir2.1 protein levels. ATO promoted collagen production and TGF-β1 expression and secretion in cultured CFs. Whole-cell patch clamp and western blotting showed that treatment with TGF-β1 markedly reduced HERG and I(K1) current densities and downregulated HERG and Kir2.1 protein expression in HEK293 cells stably transfected with the human recombinant HERG channel and in cardiomyocytes (CMs). These changes were completely reversed by treatment with the protein kinase A (PKA) antagonist, H89. CM and CF co-cultures showed that ATO significantly increased TGF-β1 levels in the culture medium, whereas markedly reduced HERG and Kir2.1 protein levels were observed in CMs compared with ATO-treated CMs not co-cultured with CFs. Finally, in vivo administration of LY364947, a pharmacological antagonist of TGF-β signalling, dramatically prevented interstitial fibrosis and LQTS and abolished aberrant expression of TGF-β1, HERG, and Kir2.1 in ATO-treated guinea pigs. CONCLUSION ATO-induced TGF-β1 secretion from CFs aggravates QT prolongation, suggesting that modulation of TGF-β signalling may provide a novel strategy for the treatment of drug-induced LQTS.

MIAT Is a Pro-fibrotic Long Non-coding RNA Governing Cardiac Fibrosis in Post-infarct Myocardium.

A long non-coding RNA (lncRNA), named myocardial infarction associated transcript (MIAT), has been documented to confer risk of myocardial infarction (MI). The aim of this study is to elucidate the pathophysiological role of MIAT in regulation of cardiac fibrosis. In a mouse model of MI, we found that MIAT was remarkably up-regulated, which was accompanied by cardiac interstitial fibrosis. MIAT up-regulation in MI was accompanied by deregulation of some fibrosis-related regulators: down-regulation of miR-24 and up-regulation of Furin and TGF-β1. Most notably, knockdown of endogenous MIAT by its siRNA reduced cardiac fibrosis and improved cardiac function and restored the deregulated expression of the fibrosis-related regulators. In cardiac fibroblasts treated with serum or angiotensin II, similar up-regulation of MIAT and down-regulation of miR-24 were consistently observed. These changes promoted fibroblasts proliferation and collagen accumulation, whereas knockdown of MIAT by siRNA or overexpression of miR-24 with its mimic abrogated the fibrogenesis. Our study therefore has identified MIAT as the first pro-fibrotic lncRNA in heart and unraveled the role of MIAT in the pathogenesis of MI. These findings also promise that normalization of MIAT level may prove to be a therapeutic option for the treatment of MI-induced cardiac fibrosis and the associated cardiac dysfunction.

Beta-adrenoceptor regulates miRNA expression in rat heart

Summary Background MicroRNAs (miRNAs) are noncoding RNAs of 18–25 nucleotides that post-transcriptionally regulate gene expression and are involved in a wide range of physiological and pathological conditions. The β-adrenergic signaling pathway plays a fundamental role in regulation of heart function. The present study was designed to investigate the expression profile of miRNAs and functional implications under conditions of β-adrenoceptor activation or inhibition in rat heart. Material/Methods Hemodynamic parameters were measured to assess heart function in Wistar rats treated with isoproterenol (ISO) or propranolol (PRO). miRNA expression was analyzed by miRNA Microarray and confirmed by real-time quantitative reverse transcription PCR (real-time qRT-PCR). Results Isoproterenol (ISO, a β-adrenoceptor activator) and propranolol (PRO, a β-adrenoceptor inhibitor) induced differential miRNA expression profiles. Out of 349 miRNAs measured, 43 were upregulated and nine downregulated in the ISO group, while five miRNAs were upregulated and 28 downregulated in PRO group. Among these altered miRNAs in both PRO and ISO groups, 11 were cardiac abundant and 11 showed opposite profiles between the PRO and ISO groups. The recognized anti-hypertrophic miRNAs miR-1, miR-21 and miR-27b, and the pro-hypertrophic miRNAs miR-22, miR-24, miR-199a, miR-212 and miR-214, were upregulated in the ISO group. In the PRO group, pro-hypertrophic miRNA miR-30c was upregulated, whereas miR-212 was downregulated. Conclusions β-adrenoceptor intervention alters miRNA expression profile, and miRNAs may be involved in the β-adrenoceptor signaling pathway. Cardiomyocyte hypertrophy is a balanced process between pro-hypertrophic and anti-hypertrophic regulation and involves, at the very least, miRNA participation.

Mild hypoxia-induced cardiomyocyte hypertrophy via up-regulation of HIF-1α-mediated TRPC signalling.

Hypoxia‐inducible factor‐1 alpha (HIF‐1α) is a central transcriptional regulator of hypoxic response. The present study was designed to investigate the role of HIF‐1α in mild hypoxia‐induced cardiomyocytes hypertrophy and its underlying mechanism. Mild hypoxia (MH, 10% O2) caused hypertrophy in cultured neonatal rat cardiac myocytes, which was accompanied with increase of HIF‐1α mRNA and accumulation of HIF‐1α protein in nuclei. Transient receptor potential canonical (TRPC) channels including TRPC3 and TRPC6, except for TRPC1, were increased, and Ca2+‐calcineurin signals were also enhanced in a time‐dependent manner under MH condition. MH‐induced cardiomyocytes hypertrophy, TRPC up‐regulation and enhanced Ca2+‐calcineurin signals were inhibited by an HIF‐1α specific blocker, SC205346 (30 μM), whereas promoted by HIF‐1α overexpression. Electrophysiological voltage‐clamp demonstrated that DAG analogue, OAG (30 μM), induced TRPC current by as much as 170% in neonatal rat cardiomyocytes overexpressing HIF‐1α compared to negative control. These results implicate that HIF‐1α plays a key role in development of cardiac hypertrophy in responses to hypoxic stress. Its mechanism is associated with up‐regulating TRPC3, TRPC6 expression, activating TRPC current and subsequently leading to enhanced Ca2+‐calcineurin signals.