Ke-Qiong Deng

The long noncoding RNA Chaer defines an epigenetic checkpoint in cardiac hypertrophy.

Epigenetic reprogramming is a critical process of pathological gene induction during cardiac hypertrophy and remodeling, but the underlying regulatory mechanisms remain to be elucidated. Here we identified a heart-enriched long noncoding (lnc)RNA, named cardiac-hypertrophy-associated epigenetic regulator (Chaer), which is necessary for the development of cardiac hypertrophy. Mechanistically, Chaer directly interacts with the catalytic subunit of polycomb repressor complex 2 (PRC2). This interaction, which is mediated by a 66-mer motif in Chaer, interferes with PRC2 targeting to genomic loci, thereby inhibiting histone H3 lysine 27 methylation at the promoter regions of genes involved in cardiac hypertrophy. The interaction between Chaer and PRC2 is transiently induced after hormone or stress stimulation in a process involving mammalian target of rapamycin complex 1, and this interaction is a prerequisite for epigenetic reprogramming and induction of genes involved in hypertrophy. Inhibition of Chaer expression in the heart before, but not after, the onset of pressure overload substantially attenuates cardiac hypertrophy and dysfunction. Our study reveals that stress-induced pathological gene activation in the heart requires a previously uncharacterized lncRNA-dependent epigenetic checkpoint.

The ubiquitin E3 ligase TRAF6 exacerbates pathological cardiac hypertrophy via TAK1-dependent signalling

Tumour necrosis factor receptor-associated factor 6 (TRAF6) is a ubiquitin E3 ligase that regulates important biological processes. However, the role of TRAF6 in cardiac hypertrophy remains unknown. Here, we show that TRAF6 levels are increased in human and murine hypertrophied hearts, which is regulated by reactive oxygen species (ROS) production. Cardiac-specific Traf6 overexpression exacerbates cardiac hypertrophy in response to pressure overload or angiotensin II (Ang II) challenge, whereas Traf6 deficiency causes an alleviated hypertrophic phenotype in mice. Mechanistically, we show that ROS, generated during hypertrophic progression, triggers TRAF6 auto-ubiquitination that facilitates recruitment of TAB2 and its binding to transforming growth factor beta-activated kinase 1 (TAK1), which, in turn, enables the direct TRAF6–TAK1 interaction and promotes TAK1 ubiquitination. The binding of TRAF6 to TAK1 and the induction of TAK1 ubiquitination and activation are indispensable for TRAF6-regulated cardiac remodelling. Taken together, we define TRAF6 as an essential molecular switch leading to cardiac hypertrophy in a TAK1-dependent manner.

Tumor Necrosis Factor Receptor–Associated Factor 3 Is a Positive Regulator of Pathological Cardiac Hypertrophy

Cardiac hypertrophy, a common early symptom of heart failure, is regulated by numerous signaling pathways. Here, we identified tumor necrosis factor receptor–associated factor 3 (TRAF3), an adaptor protein in tumor necrosis factor–related signaling cascades, as a key regulator of cardiac hypertrophy in response to pressure overload. TRAF3 expression was upregulated in hypertrophied mice hearts and failing human hearts. Four weeks after aortic banding, cardiac-specific conditional TRAF3-knockout mice exhibited significantly reduced cardiac hypertrophy, fibrosis, and dysfunction. Conversely, transgenic mice overexpressing TRAF3 in the heart developed exaggerated cardiac hypertrophy in response to pressure overload. TRAF3 also promoted an angiotensin II– or phenylephrine-induced hypertrophic response in isolated cardiomyocytes. Mechanistically, TRAF3 directly bound to TANK-binding kinase 1 (TBK1), causing increased TBK1 phosphorylation in response to hypertrophic stimuli. This interaction between TRAF3 and TBK1 further activated AKT signaling, which ultimately promoted the development of cardiac hypertrophy. Our findings not only reveal a key role of TRAF3 in regulating the hypertrophic response but also uncover TRAF3–TBK1–AKT as a novel signaling pathway in the development of cardiac hypertrophy and heart failure. This pathway may represent a potential therapeutic target for this pathological process.

Mindin regulates vascular smooth muscle cell phenotype and prevents neointima formation.

Mindin/spondin 2, an extracellular matrix (ECM) component that belongs to the thrombospondin type 1 (TSR) class of molecules, plays prominent roles in the regulation of inflammatory responses, angiogenesis and metabolic disorders. Our most recent studies indicated that mindin is largely involved in the initiation and development of cardiac and cerebrovascular diseases [Zhu et al. (2014) J. Hepatol. 60, 1046-1054; Bian et al. (2012) J. Mol. Med. 90, 895-910; Wang et al. (2013) Exp. Neurol. 247, 506-516; Yan et al. (2011) Cardiovasc. Res. 92, 85-94]. However, the regulatory functions of mindin in neointima formation remain unclear. In the present study, mindin expression was significantly down-regulated in platelet-derived growth factor-BB (PDGF-BB)-stimulated vascular smooth muscle cells (VSMCs) and wire injury-stimulated vascular tissue. Using a gain-of-function approach, overexpression of mindin in VSMCs exhibited strong anti-proliferative and anti-migratory effects on VSMCs, whereas significant suppression of intimal hyperplasia was observed in transgenic (TG) mice expressing mindin specifically in smooth muscle cells (SMCs). These mice exhibited blunted VSMC proliferation, migration and phenotypic switching. Conversely, deletion of mindin dramatically exacerbated neointima formation in a wire-injury mouse model, which was further confirmed in a balloon injury-induced vascular lesion model using a novel mindin-KO (knockout) rat strain. From a mechanistic standpoint, the AKT (Protein Kinase B)-GSK3β (glycogen synthase kinase 3β)/mTOR (mammalian target of rapamycin)-FOXO3A (forkhead box O)-FOXO1 signalling axis is responsible for the regulation of mindin during intimal thickening. Interestingly, an AKT inhibitor largely reversed mindin-KO-induced aggravated hyperplasia, suggesting that mindin-mediated neointima formation is AKT-dependent. Taken together, our findings demonstrate that mindin protects against vascular hyperplasia by suppression of abnormal VSMC proliferation, migration and phenotypic switching in an AKT-dependent manner. Up-regulation of mindin might represent an effective therapy for vascular-remodelling-related diseases.

Suppressor of IKKɛ is an essential negative regulator of pathological cardiac hypertrophy

Although pathological cardiac hypertrophy represents a leading cause of morbidity and mortality worldwide, our understanding of the molecular mechanisms underlying this disease is still poor. Here, we demonstrate that suppressor of IKKɛ (SIKE), a negative regulator of the interferon pathway, attenuates pathological cardiac hypertrophy in rodents and non-human primates in a TANK-binding kinase 1 (TBK1)/AKT-dependent manner. Sike-deficient mice develop cardiac hypertrophy and heart failure, whereas Sike-overexpressing transgenic (Sike-TG) mice are protected from hypertrophic stimuli. Mechanistically, SIKE directly interacts with TBK1 to inhibit the TBK1-AKT signalling pathway, thereby achieving its anti-hypertrophic action. The suppression of cardiac remodelling by SIKE is further validated in rats and monkeys. Collectively, these findings identify SIKE as a negative regulator of cardiac remodelling in multiple animal species due to its inhibitory regulation of the TBK1/AKT axis, suggesting that SIKE may represent a therapeutic target for the treatment of cardiac hypertrophy and heart failure.

Tripartite Motif 32 Prevents Pathological Cardiac Hypertrophy

This study presents the first evidence that TRIM32 protects against pathological cardiac hypertrophy by suppressing Akt-dependent signalling pathways. Therefore TRIM32 might be a potential therapeutic strategy for the prevention and treatment of cardiac hypertrophy and heart failure.

Control of Pathological Cardiac Hypertrophy by Transcriptional Corepressor IRF2BP2 (Interferon Regulatory Factor-2 Binding Protein 2)

The transcription factor NFAT1 (nuclear factor of activated T-cells 1), with the aid of transcriptional coactivators, has been recognized for its necessity and sufficiency to drive pathological cardiac hypertrophy. However, how the transcriptional activity of NFAT1 in terms of cardiac hypertrophy is controlled at the transcriptional level has not been well defined. Herein, we showed that a cardiac-enriched protein IRF2BP2 (interferon regulatory factor-2 binding protein 2) was further upregulated in both human and mouse hypertrophied myocardium and negatively regulated cardiomyocyte hypertrophic response in vitro. By generating cardiomyocyte-specific Irf2bp2 knockout and Irf2bp2-transgenic mouse strains, our in vivo experiments showed that, whereas IRF2BP2 loss-of-function exacerbated both aortic banding- and angiotensin II infusion-induced cardiac hypertrophic response, IRF2BP2 overexpression exerted a strong protective effect against these maladaptive processes. Particularly, IRF2BP2 directly interacted with the C-terminal transactivation domain of NFAT1 by competing with myocyte enhancer factor-2C and disturbing their transcriptional synergism, thereby impeding NFAT1-transactivated hypertrophic transcriptome. As a result, the devastating effect of Irf2bp2 deficiency on cardiac hypertrophy was largely rescued by NFAT1 blockage. Our study, thus, defined IRF2BP2 as a novel negative regulator in controlling pathological cardiac hypertrophy at the transcriptional level.

Tripartite Motif 8 Contributes to Pathological Cardiac Hypertrophy Through Enhancing Transforming Growth Factor β–Activated Kinase 1–Dependent Signaling PathwaysNovelty and Significance

Tripartite motif (TRIM) 8 functions as an E3 ubiquitin ligase, interacting with and ubiquitinating diverse substrates, and is implicated in various pathological processes. However, the function of TRIM8 in the heart remains largely uncharacterized. This study aims to explore the role of TRIM8 in the development of pathological cardiac hypertrophy. Mice and isolated neonatal rat cardiomyocytes overexpressing or lacking TRIM8 were examined in several experiments. The effect of aortic banding–induced cardiac hypertrophy was analyzed by echocardiographic, pathological and molecular analyses. Our results indicated that the TRIM8 overexpression in hearts exacerbated the cardiac hypertrophy triggered by aortic banding. In contrast, the development of pathological cardiac hypertrophy was profoundly blocked in TRIM8-deficient hearts. Mechanistically, our study suggests that TRIM8 may elicit cardiodetrimental effects by promoting the activation of transforming growth factor &bgr;–activated kinase 1 (TAK1)-p38/JNK signaling pathways. Similar results were observed in cultured neonatal rat cardiomyocytes treated with angiotensin II. The rescue experiments using the TAK1-specific inhibitor 5z-7-ox confirmed the requirement of TAK1 activation in TRIM8-mediated pathological cardiac hypertrophy. Furthermore, TRIM8 contributed to TAK1 activation by binding to and promoting TAK1 ubiquitination. In conclusion, our study demonstrates that TRIM8 plays a deleterious role in pressure overload–induced cardiac hypertrophy by accelerating the activation of TAK1-dependent signaling pathways.

Restoration of Circulating MFGE8 (Milk Fat Globule-EGF Factor 8) Attenuates Cardiac Hypertrophy Through Inhibition of Akt Pathway

Cardiac hypertrophy occurs in response to numerous stimuli like neurohumoral stress, pressure overload, infection, and injury, and leads to heart failure. Mfge8 (milk fat globule-EGF factor 8) is a secreted protein involved in various human diseases, but its regulation and function during cardiac hypertrophy remain unexplored. Here, we found that circulating MFGE8 levels declined significantly in failing hearts from patients with dilated cardiomyopathy. Correlation analyses revealed that circulating MFGE8 levels were negatively correlated with the severity of cardiac dysfunction and remodeling in affected patients. Deleting Mfge8 in mice maintained normal heart function at basal level but substantially exacerbated the hypertrophic enlargement of cardiomyocytes, reprogramming of pathological genes, contractile dysfunction, and myocardial fibrosis after aortic banding surgery. In contrast, cardiac-specific Mfge8 overexpression in transgenic mice significantly blunted aortic banding–induced cardiac hypertrophy. Whereas MAPK (mitogen-activated protein kinase) pathways were unaffected in either Mfge8-knockout or Mfge8-overexpressing mice, the activated Akt/PKB (protein kinase B)–Gsk-3&bgr; (glycogen synthase kinase-3&bgr;)/mTOR (mammalian target of rapamycin) pathway after aortic banding was significantly potentiated by Mfge8 deficiency but suppressed by Mfge8 overexpression. Inhibition of Akt with MK-2206 blocked the prohypertrophic effects of Mfge8 deficiency in angiotensin II–treated neonatal rat cardiomyocytes. Finally, administering a recombinant human MFGE8 in mice in vivo alleviated cardiac hypertrophy induced by aortic banding. Our findings indicate that Mfge8 is an endogenous negative regulator of pathological cardiac hypertrophy and may, thus, have potential both as a novel biomarker and as a therapeutic target for treatment of cardiac hypertrophy.

Targeting Transmembrane BAX Inhibitor Motif Containing 1 Alleviates Pathological Cardiac Hypertrophy

Background: Cardiac hypertrophy and its resultant heart failure are among the most common causes of mortality worldwide. Abnormal protein degradation, especially the impaired lysosomal degradation of large organelles and membrane proteins, is involved in the progression of cardiac hypertrophy. However, the underlying mechanisms have not been fully elucidated. Methods: We investigated cardiac transmembrane BAX inhibitor motif containing 1 (TMBIM1) mRNA and protein expression levels in samples from patients with heart failure and mice with aortic banding (AB)–induced cardiac hypertrophy. We generated cardiac-specific Tmbim1 knockout mice and cardiac-specific Tmbim1-overexpressing transgenic mice and then challenged them with AB surgery. We used microarray, confocal image, and coimmunoprecipitation analyses to identify the downstream targets of TMBIM1 in cardiac hypertrophy. Tmbim1/Tlr4 double-knockout mice were generated to investigate whether the effects of TMBIM1 on cardiac hypertrophy were Toll-like receptor 4 (TLR4) dependent. Finally, lentivirus-mediated TMBIM1 overexpression in a monkey AB model was performed to evaluate the therapeutic potential of TMBIM1. Results: TMBIM1 expression was significantly downregulated on hypertrophic stimuli in both human and mice heart samples. Silencing cardiac Tmbim1 aggravated AB-induced cardiac hypertrophy. This effect was blunted by Tmbim1 overexpression. Transcriptome profiling revealed that the TLR4 signaling pathway was disrupted dramatically by manipulation of Tmbim1. The effects of TMBIM1 on cardiac hypertrophy were shown to be dependent on TLR4 in double-knockout mice. Fluorescent staining indicated that TMBIM1 promoted the lysosome-mediated degradation of activated TLR4. Coimmunoprecipitation assays confirmed that TMBIM1 directly interacted with tumor susceptibility gene 101 via a PTAP motif and accelerated the formation of multivesicular bodies that delivered TLR4 to the lysosomes. Finally, lentivirus-mediated TMBIM1 overexpression reversed AB-induced cardiac hypertrophy in monkeys. Conclusions: TMBIM1 protects against pathological cardiac hypertrophy through promoting the lysosomal degradation of activated TLR4. Our findings reveal the central role of TMBIM1 as a multivesicular body regulator in the progression of pathological cardiac hypertrophy, as well as the role of vesicle trafficking in signaling regulation during cardiac hypertrophy. Moreover, targeting TMBIM1 could be a novel therapeutic strategy for treating cardiac hypertrophy and heart failure.