RBM20 Is a Candidate Gene for Hypertrophic Cardiomyopathy.

BACKGROUND: The genetic basis of a considerable fraction of hypertrophic cardiomyopathy (HCM) cases remains unknown. Whether the gene encoding RNA binding motif protein 20 (RBM20) is implicated in HCM and the correlation of clinical characteristics of RBM20 heterozygotes with HCM remain unresolved. We aimed to investigate the association between RBM20 variants and HCM. METHODS: We compared rare variants in the RBM20 gene by exome sequencing in 793 patients with HCM and 414 healthy controls. Based on a case-control approach, we used optimal sequence kernel association test (SKAT-O) to explore whether RBM20 is associated with HCM. The genetic distribution of RBM20 rare variants was then compared between HCM heterozygotes and dilated cardiomyopathy (DCM) heterozygotes. Clinical features and prognosis of RBM20 heterozygotes were compared with nonheterozygotes. RESULTS: Gene-based association analysis implicated RBM20 as a susceptibility gene for developing HCM. Patients with RBM20 variants displayed a higher prevalence of sudden cardiac arrest (SCA) (6.7% vs 0.9%, P = 0.001), increased sudden cardiac death (SCD) risk factor counts and impaired left ventricle systolic function. Further survival analysis revealed that RBM20 heterozygotes had higher incidences of resuscitated cardiac arrest, recurrent nonsustained ventricular tachycardia, and malignant arrhythmias. Mendelian randomization suggested that RBM20 expression in the left ventricle was causally associated with HCM and DCM with opposite effects. CONCLUSIONS: This study identified RBM20 as a potential causal gene of HCM. RBM20 variants are associated with increased risk for SCA in HCM.

Ranolazine prevents pressure overload-induced cardiac hypertrophy and heart failure by restoring aberrant Na+ and Ca2+ handling.

BACKGROUND: Cardiac hypertrophy and heart failure are characterized by increased late sodium current and abnormal Ca2+ handling. Ranolazine, a selective inhibitor of the late sodium current, can reduce sodium accumulation and Ca 2+ overload. In this study, we investigated the effects of ranolazine on pressure overload-induced cardiac hypertrophy and heart failure in mice. METHODS AND RESULTS: Inhibition of late sodium current with the selective inhibitor ranolazine suppressed cardiac hypertrophy and fibrosis and improved heart function assessed by echocardiography, hemodynamics, and histological analysis in mice exposed to chronic pressure overload induced by transverse aortic constriction (TAC). Ca2+ imaging of ventricular myocytes from TAC mice revealed both abnormal SR Ca 2+ release and increased SR Ca 2+ leak. Ranolazine restored aberrant SR Ca 2+ handling induced by pressure overload. Ranolazine also suppressed Na + overload induced in the failing heart, and restored Na + -induced Ca 2+ overload in an sodium-calcium exchanger (NCX)-dependent manner. Ranolazine suppressed the Ca 2+ -dependent calmodulin (CaM)/CaMKII/myocyte enhancer factor-2 (MEF2) and CaM/CaMKII/calcineurin/nuclear factor of activated T-cells (NFAT) hypertrophy signaling pathways triggered by pressure overload. Pressure overload also prolonged endoplasmic reticulum (ER) stress leading to ER-initiated apoptosis, while inhibition of late sodium current or NCX relieved ER stress and ER-initiated cardiomyocyte apoptosis. CONCLUSIONS: Our study demonstrates that inhibition of late sodium current with ranolazine improves pressure overload-induced cardiac hypertrophy and systolic and diastolic function by restoring Na+ and Ca 2+ handling, inhibiting the downstream hypertrophic pathways and ER stress. Inhibition of late sodium current may provide a new treatment strategy for cardiac hypertrophy and heart failure.

Activation of AMP-activated protein kinase by metformin ablates angiotensin II-induced endoplasmic reticulum stress and hypertension in mice in vivo.

BACKGROUND AND PURPOSE: Metformin, one of the most frequently prescribed medications for type 2 diabetes, reportedly exerts BP-lowering effects in patients with diabetes. However, the effects and underlying mechanisms of metformin on BP in non-diabetic conditions remain to be determined. The aim of the present study was to determine the effects of metformin on angiotensin II (Ang II) infusion-induced hypertension in vivo. EXPERIMENTAL APPROACH: The effects of metformin on BP were investigated in wild-type (WT) C57BL/6J mice and in mice lacking AMP-activated protein kinase α2 (AMPKα2) mice with or without Ang II infusion. Also, the effect of metformin on Ang II-induced endoplasmic reticulum (ER) stress was explored in cultured human vascular smooth muscle cells (hVSMCs). KEY RESULTS: Metformin markedly reduced BP in Ang II-infused WT mice but not in AMPKα2-deficient mice. In cultured hVSMCs, Ang II treatment resulted in inactivation of AMPK, as well as the subsequent induction of spliced X-box binding protein-1, phosphorylation of eukaryotic translation initiation factor 2α and expression of glucose-regulated protein 78 kDa, representing three well-characterized ER stress biomarkers. Moreover, AMPK activation by metformin ablated Ang II-induced ER stress in hVSMCs. Mechanistically, metformin-activated AMPKα2 suppressed ER stress by increasing phospholamban phosphorylation. CONCLUSION AND IMPLICATIONS: Metformin alleviates Ang II-triggered hypertension in mice by activating AMPKα2, which mediates phospholamban phosphorylation and inhibits Ang II-induced ER stress in vascular smooth muscle cells.

Deregulation of XBP1 expression contributes to myocardial vascular endothelial growth factor-A expression and angiogenesis during cardiac hypertrophy in vivo.

Endoplasmic reticulum (ER) stress has been reported to be involved in many cardiovascular diseases such as atherosclerosis, diabetes, myocardial ischemia, and hypertension that ultimately result in heart failure. XBP1 is a key ER stress signal transducer and an important pro-survival factor of the unfolded protein response (UPR) in mammalian cells. The aim of this study was to establish a role for XBP1 in the deregulation of pro-angiogenic factor VEGF expression and potential regulatory mechanisms in hypertrophic and failing heart. Western blots showed that myocardial XBP1s protein was significantly increased in both isoproterenol (ISO)-induced and pressure-overload-induced hypertrophic and failing heart compared to normal control. Furthermore, XBP1 silencing exacerbates ISO-induced cardiac dysfunction along with a reduction of myocardial capillary density and cardiac expression of pro-angiogenic factor VEGF-A in vivo. Consistently, experiments in cultured cardiomyocytes H9c2 (2-1) cells showed that UPR-induced VEGF-A upregulation was determined by XBP1 expression level. Importantly, VEGF-A expression was increased in failing human heart tissue and blood samples and was correlated with the levels of XBP1. These results suggest that XBP1 regulates VEGF-mediated cardiac angiogenesis, which contributes to the progression of adaptive hypertrophy, and might provide novel targets for prevention and treatment of heart failure.

MicroRNA regulation of unfolded protein response transcription factor XBP1 in the progression of cardiac hypertrophy and heart failure in vivo.

BACKGROUND: XBP1 is a key transcription factor of the unfolded protein response in mammalian cells, which is involved in several cardiovascular pathological progression including cardiac hypertrophy and myocardial infarction, but its expression trend, function and upstream regulate mechanism in the development of heart failure are unclear. In the present study, therefore, the potential role of miRNAs in the regulation of XBP1 expression in heart failure was examined. METHODS AND RESULTS: First, western blots showed that cardiac expression of ER stress marker XBP1 were induced in the early adaptive phase, but decreased in the maladaptive phase in hypertrophic and failing heart, while there was no obvious change of upstream ATF6 and IRE1 activity in this progression. Interestingly, we further found that XBP1 and its downstream target VEGF were attenuated by miR-30* and miR-214 in cardiomyocyte. Moreover, we found that miR-30* was significantly reduced in the early phase of cardiac hypertrophic animal model and in human failing hearts, while both miR-214 and miR-30* were increased in the maladaptive diseased heart, thereby contribute to impairment of cardiac XBP1 and VEGF expression. CONCLUSIONS: These results provide the first clear link between miRNAs and direct regulation of XBP1 in heart failure and reveal that miR-214 and miR-30* synergistically regulates cardiac VEGF expression and angiogenesis by targeting XBP1 in the progression from adaptive hypertrophy to heart failure.

MicroRNA-214 Is Upregulated in Heart Failure Patients and Suppresses XBP1-Mediated Endothelial Cells Angiogenesis.

More and more miRNAs have been shown to regulate gene expression in the heart and dysregulation of their expression has been linked to cardiovascular diseases including the miR-199a/214 cluster. However, the signature of circulating miR-214 expression and its possible roles during the development of heart failure has been less well studied. In this study, we elucidated the biological and clinical significance of miR-214 dysregulation in heart failure. Firstly, circulating miR-214 was measured by quantitative PCR, and we found that miR-214 was upregulated in the serum of chronic heart failure patients, as well as in hypertrophic and failing hearts of humans and mice. Adeno-associated virus serotype 9 (AAV9)-mediated miR-214 silencing attenuates isoproterenol (ISO) infusion-induced cardiac dysfunction and impairment of cardiac angiogenesis in mice. Mechanistically, miR-214 overexpression reduces angiogenesis of HUVECs by targeting XBP1, an important transcription factor of unfolded protein response, and XBP1 silencing decreases HUVECs proliferation and angiogenesis similar to miR-214 overexpression. Furthermore, ectopic expression of XBP1 enhances endothelial cells proliferation and tube formation, and reverses anti-angiogenic effect of miR-214 over expression. All these findings suggest that miR-214 is an important regulator of angiogenesis in heart in vitro and in vivo, likely via regulating the expression of XBP1, and demonstrate that miR-214 plays an essential role in the control/inhibition of cardiac angiogenesis.

CYP epoxygenase 2J2 prevents cardiac fibrosis by suppression of transmission of pro-inflammation from cardiomyocytes to macrophages.

Cytochrome P450 epoxygenase (CYP450)-derived epoxyeicosatrienoic acids (EETs) are important regulators of cardiac remodeling; but the underlying mechanism remains unclear. The present study aimed to elucidate how EETs regulated cardiac fibrosis in response to isoprenaline (Iso) or angiotensin (Ang) II. Cardiac-specific human CYP2J2 transgenic mice (Tr) and wild-type (WT) C57BL/6 littermates were infused with Iso- or Ang II. Two weeks after infusion, Tr mice showed more alleviative cardiac fibrosis and inflammation compared with WT mice. In vitro, we found Iso or Ang II induced nuclear transfer of NF-κB p65 and inflammatory cytokines expression in cardiomyocytes. Furthermore, inflammation response emerged in macrophages cultured in cardiomyocytes-conditioned medium. When pretreatment with 14,15-EET in cardiomyocytes, the inflammatory response was markedly suppressed and the transmission of inflammation from cardiomyocytes to macrophages was reduced. In conclusion, CYP2J2 and EETs prevent cardiac fibrosis and cardiac dysfunction by suppressing transmission of pro-inflammation from cardiomyocytes to macrophages in heart, suggesting that elevation of EETs level could be a potential strategy to prevent cardiac fibrosis.

CYP2J2-derived epoxyeicosatrienoic acids suppress endoplasmic reticulum stress in heart failure.

Prolonged endoplasmic reticulum (ER) stress causes apoptosis and is associated with heart failure. Whether CYP2J2 and its arachidonic acid metabolites [epoxyeicosatrienoic acids (EETs)] have a protective influence on ER stress and heart failure has not been studied. Assays of myocardial samples from patients with end-stage heart failure showed evidence of ER stress. Chronic infusion of isoproterenol (ISO) or angiotensin II (AngII) by osmotic mini-pump induced cardiac hypertrophy and heart failure in mice as evaluated by hemodynamic measurements and echocardiography. Interestingly, transgenic (Tr) mice with cardiomyocyte-specific CYP2J2 expression were protected against heart failure compared with wild-type mice. ISO or AngII administration induced ER stress and apoptosis, and increased levels of intracellular Ca(2+). These phenotypes were abolished by CYP2J2 overexpression in vivo or exogenous EETs treatment of cardiomyocytes in vitro. ISO or AngII reduced sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA2a) expression in hearts or isolated cardiomyocytes; however, loss of SERCA2a expression was prevented in CYP2J2 Tr hearts in vivo or in cardiomyocytes treated with EETs in vitro. The reduction of SERCA2a activity was concomitant with increased oxidation of SERCA2a. EETs reversed SERCA2a oxidation through increased expression of antioxidant enzymes and reduced reactive oxygen species levels. Tempol, a membrane-permeable radical scavenger, similarly decreased oxidized SERCA2a levels, restored SERCA2a activity, and markedly reduced ER stress response in the mice treated with ISO. In conclusion, CYP2J2-derived EETs suppress ER stress response in the heart and protect against cardiac failure by maintaining intracellular Ca(2+) homeostasis and SERCA2a expression and activity.

Chronic inhibition of cGMP-specific phosphodiesterase 5 suppresses endoplasmic reticulum stress in heart failure.

BACKGROUND AND PURPOSE: Inhibition of the cGMP-specific phosphodiesterase 5 (PDE5) exerts profound beneficial effects on failing hearts. However, the mechanisms underlying the therapeutic effects of PDE5 inhibition on heart failure are unclear. The purpose of this study was to investigate whether PDE5 inhibition decreases endoplasmic reticulum (ER) stress, a key event in heart failure. EXPERIMENTAL APPROACH: Heart failure was induced by isoprenaline s.c. injection in Sprague-Dawley rats and transverse aortic constriction (TAC) in mice. PDE5 was inhibited with sildenafil. Heart function was detected by invasive pressure-volume analysis and echocardiography. ER stress markers were analysed by Western blotting. Apoptosis was measured by flow cytometric analysis. KEY RESULTS: PDE5 inhibition markedly attenuated isoprenaline-induced and TAC-induced cardiac hypertrophy and dysfunction, and reduced ER stress and apoptosis. Further, PDE5 inhibition with sildenafil largely prevented ER stress and reduced apoptosis in isoprenaline- or thapsigargin-treated cardiomyocytes. PKG inhibition markedly prevented the protective effects of sildenafil in vivo and in vitro. To further understand the mechanism of the effect of PDE5 inhibition on ER stress, we demonstrated that PDE5 inhibitor increased sarco-(endo)-plasmic reticulum Ca(2+) -ATPase activity via phosphorylation of phospholamban at Ser(16) . This may contribute to the attenuation of ER stress induced by PDE5 inhibition. CONCLUSION AND IMPLICATIONS: These results suggest that PDE5 inhibition can attenuate ER stress and improve cardiac function in vivo and in vitro. Suppression of ER stress by inhibiting PDE5 may contribute to the therapeutic effects on heart failure.

Endoplasmic reticulum stress participates in aortic valve calcification in hypercholesterolemic animals.

OBJECTIVES: Aortic valve (AV) calcification occurs via a pathophysiological process that includes lipoprotein deposition, inflammation, and osteoblastic differentiation of valvular interstitial cells. Here, we investigated the association between endoplasmic reticulum (ER) stress and AV calcification. APPROACH AND RESULTS: We identified ER stress activation in AV of patients with calcified AV stenosis. We generated an AV calcification model in hypercholesterolemic rabbits and mice, respectively, and found marked AV ER stress induction. Classical ER stress inhibitor, tauroursodeoxycholic acid, administration markedly prevented AV calcification, and attenuated AV osteoblastic differentiation and inflammation in both rabbit and mouse models of AV calcification via inhibition of ER stress. In cultured valvular interstitial cells (VICs), we found that oxidized low density lipoprotein (oxLDL) caused ER stress in a cytosolic [Ca](2+)i-dependent manner. OxLDL promoted osteoblastic differentiation via ER stress-mediated protein kinase-like ER kinase/activating transcription factor 4/osteocalcin and inositol-requiring transmembrane kinase and endonuclease-1α (IRE1α)/spliced X-box-binding protein 1/Runx2 pathway, and induced inflammatory responses through IRE1α/c-Jun N-terminal kinase and IRE1α/nuclear factor kappa-light-chain-enhancer of activated B cells signaling in VICs. Inhibition of ER stress by either tauroursodeoxycholic acid or 4-phenyl butyric acid could both suppress oxLDL-induced osteoblastic differentiation and inflammatory responses in VICs. CONCLUSIONS: These data provide novel evidence that ER stress participates in AV calcification development, and suggest that ER stress may be a novel target for AV calcification prevention and treatment.

Circulating miR-30a, miR-195 and let-7b associated with acute myocardial infarction.

BACKGROUND: MicroRNAs (miRNAs) play key roles in diverse biological and pathological processes, including the regulation of proliferation, apoptosis, angiogenesis and cellular differentiation. Recently, circulating miRNAs have been reported as potential biomarkers for various pathologic conditions. This study investigated miR-30a, miR-195 and let-7b as potential of biomarker for acute myocardial infarction (AMI). METHODS AND RESULTS: Plasma samples from 18 patients with AMI and 30 healthy adults were collected. Total RNA was extracted from plasma with TRIzol LS Reagent. MiRNA levels and plasma cardiac troponin I (cTnI) concentrations were measured by quantitative real-time PCR and ELISA assay, respectively. Results showed that circulating miR-30a in AMI patients was highly expressed at 4 h, 8 h and 12 h after onset of AMI, and miR-195 was highly expressed at 8 h and 12 h. However, let-7b was lower in AMI patients than in controls throughout the whole time points. Interestingly, in these patients, circulating miR-30a, miR-195 and let-7b all reached their expression peak at 8 h. By the receiver operating characteristic (ROC) curve analyses, these plasma miRNAs were of significant diagnostic value for AMI. The combined ROC analysis revealed the an AUC value of 0.93 with 94% sensitivity and 90% specificity at 8 h after onset, and an AUC value of 0.92 with 90% sensitivity and 90% specificity at 12 h after onset, in discriminating the AMI patients from healthy controls. CONCLUSIONS: Our results imply that the plasma concentration of miR-30a, miR-195 and let-7b can be potential indicators for AMI.

Protective effects of Acyl-coA thioesterase 1 on diabetic heart via PPARα/PGC1α signaling.

BACKGROUND: Using fatty acids (FAs) exclusively for ATP generation was reported to contribute to the development of diabetic cardiomyopathy. We studied the role of substrate metabolism related genes in the heart of the diabetes to find out a novel therapeutic target for diabetic cardiomyopathy. METHODS AND RESULTS: By microarray analysis of metabolic gene expression, acyl-CoA thioesterase 1 (acot1) was clearly upregulated in the myocardia of db/db mice, compared with normal control C57BL/Ks. Therefore, gain-of-function and loss-of-function approaches were employed in db/db mice to investigate the functions of ACOT1 in oxidative stress, mitochondrial dysfunction and heart function. We found that in the hearts of db/db mice which overexpressed ACOT1, H(2)O(2) and malondialdehyde (MDA) were reduced, the activities of ATPases in mitochondria associated with mitochondrial function were promoted, the expression of uncoupling protein 3 (UCP3) contributing to oxygen wastage for noncontractile purposes was decreased, and cardiac dysfunction was attenuated, as determined by both hemodynamic and echocardiographic detections. Consistently, ACOT1 deficiency had opposite effects, which accelerated the cardiac damage induced by diabetes. Notably, by real-time PCR, we found that overexpression of ACOT1 in diabetic heart repressed the peroxisome proliferator-activated receptor alpha/PPARγ coactivator 1α (PPARα/PGC1α) signaling, as shown by decreased expression of PGC1α and the downstream genes involved in FAs use. CONCLUSION: Our results demonstrated that ACOT1 played a crucial protective role in diabetic heart via PPARα/PGC1α signaling.

Human circulating microRNA-1 and microRNA-126 as potential novel indicators for acute myocardial infarction.

Circulating miRNAs have been shown as promising biomarkers for various pathologic conditions. The aim of this study was to clarify that circulating miR-1 and miR-126 in human plasma might be useful as biomarkers in acute myocardial infarction (AMI). In our study, after pre-test, two candidate miRNAs were detected by using real-time RT-PCR. Cardiac troponin I (cTnI) concentrations were measured by ELISA assay in plasma from patients with AMI (n=17) and healthy subjects (n=25), simultaneously. Increased miR-1 and decreased miR-126 in plasma from patients with AMI after the onset of symptoms compared with healthy subjects were found. A remarkable finding in this study is that miR-1, miR-126 and cTnI expression levels exhibited the same trend. Our results suggest that the plasma concentrations of miR-1 and miR-126 may be useful indicators for AMI.

ER stress negatively modulates the expression of the miR-199a/214 cluster to regulates tumor survival and progression in human hepatocellular cancer.

BACKGROUND: Recent studies have emphasized causative links between microRNAs (miRNAs) deregulation and tumor development. In hepatocellular carcinoma (HCC), more and more miRNAs were identified as diagnostic and prognostic cancer biomarkers, as well as additional therapeutic tools. This study aimed to investigate the functional significance and regulatory mechanism of the miR-199a2/214 cluster in HCC progression. METHODS AND FINDINGS: In this study, we showed that miR-214, as well as miR-199a-3p and miR-199a-5p levels were significantly reduced in the majority of examined 23 HCC tissues and HepG2 and SMMC-7721 cell lines, compared with their nontumor counterparts. To further explore the role of miR-214 in hepatocarcinogenesis, we disclosed that the ER stress-induced pro-survival factor XBP-1 is a target of miR-214 by using western blot assay and luciferase reporter assay. Re-expression of miR-214 in HCC cell lines (HepG2 and SMMC-7721) inhibited proliferation and induced apoptosis. Furthermore, ectopic expression of miR-214 dramatically suppressed the ability of HCC cells to form colonies in vitro and to develop tumors in a subcutaneous xenotransplantation model of the BALB/c athymic nude mice. Moreover, reintroduction of XBP-1s attenuated miR-214-mediated suppression of HCC cells proliferation, colony and tumor formation. To further understand the mechanism of the miR-199a/214 cluster down-expression in HCC, we found that thapsigargin (TG) and tunicamycin (TM) or hypoxia-induced unfolded protein response (UPR) suppresses the expression of the miR-199a/214 cluster in HCC cells. By promoter analysis of the miR-199a2/214 gene, we conjectured NFκB as a potential negative regulator. We further found that UPR and LPS-induced NFκB activation suppressed miR-199a2/214 transcription, and this suppression was reversed by NFκB inhibition in HCC cells. CONCLUSIONS: Our study suggest that modulation of miR-214 levels may provide a new therapeutic approach for cancer treatment and revealed that UPR may offer a new explanation for why the miR-199a/214 cluster were down-regulated in the progression in HCC.

ß-AR blockers suppresses ER stress in cardiac hypertrophy and heart failure.

BACKGROUND: Long-term ß-adrenergic receptor (ß-AR) blockade reduces mortality in patients with heart failure. Chronic sympathetic hyperactivity in heart failure causes sustained ß-AR activation, and this can deplete Ca(2+) in endoplasmic reticulum (ER) leading to ER stress and subsequent apoptosis. We tested the effect of ß-AR blockers on ER stress pathway in experimental model of heart failure. METHODS AND DISCUSSIONS: ER chaperones were markedly increased in failing hearts of patients with end-stage heart failure. In Sprague-Dawley rats, cardiac hypertrophy and heart failure was induced by abdominal aortic constriction or isoproterenol subcutaneous injection. Oral ß-AR blockers treatment was performed in therapy groups. Cardiac remodeling and left ventricular function were analyzed in rats failing hearts. After 4 or 8 weeks of banding, rats developed cardiac hypertrophy and failure. Cardiac expression of ER chaperones was significantly increased. Similar to the findings above, sustained isoproterenol infusion for 2 weeks induced cardiac hypertrophy and failure with increased ER chaperones and apoptosis in hearts. ß-AR blockers treatment markedly attenuated these pathological changes and reduced ER stress and apoptosis in failing hearts. On the other hand, ß-AR agonist isoproterenol induced ER stress and apoptosis in cultured cardiomyocytes. ß-AR blockers largely prevented ER stress and protected myocytes against apoptosis. And ß-AR blockade significantly suppressed the overactivation of CaMKII in isoproterenol-stimulated cardiomyocytes and failing hearts in rats. CONCLUSIONS: Our results demonstrated that ER stress occurred in failing hearts and this could be reversed by ß-AR blockade. Alleviation of ER stress may be an important mechanism underlying the therapeutic effect of ß-AR blockers on heart failure.