Interferon regulatory factor 7 functions as a novel negative regulator of pathological cardiac hypertrophy

Canonical and Non-Canonical Aspects of JAK-STAT Signaling: Lessons from Interferons for Cytokine Responses

Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signal transduction mediates cytokine responses. Canonical signaling is based on STAT tyrosine phosphorylation by activated JAKs. Downstream of interferon (IFN) receptors, activated JAKs cause the formation of the transcription factors IFN-stimulated gene factor 3 (ISGF3), a heterotrimer of STAT1, STAT2 and interferon regulatory factor 9 (IRF9) subunits, and gamma interferon-activated factor (GAF), a STAT1 homodimer. In recent years, several deviations from this paradigm were reported. These include kinase-independent JAK functions as well as extra- and intranuclear activities of U-STATs without phosphotyrosines. Additionally, transcriptional control by STAT complexes resembling neither GAF nor ISGF3 contributes to transcriptome changes in IFN-treated cells. Our review summarizes the contribution of non-canonical JAK-STAT signaling to the innate antimicrobial immunity imparted by IFN. Moreover, we touch upon functions of IFN pathway proteins beyond the IFN response. These include metabolic functions of IRF9 as well as the regulation of natural killer cell activity by kinase-dead TYK2 and different phosphorylation isoforms of STAT1.

Smad Nuclear Interacting Protein 1 Acts as a Protective Regulator of Pressure Overload-Induced Pathological Cardiac Hypertrophy

Background

Smad nuclear interacting protein 1 (SNIP1) plays a critical role in cell proliferation, transformation of embryonic fibroblasts, and immune regulation. However, the role of SNIP1 in cardiac hypertrophy remains unclear.

Methods and Results

Here we examined the role of SNIP1 in pressure overload–induced cardiac hypertrophy and its mechanisms. Our results demonstrated that SNIP1 expression was downregulated in human dilated cardiomyopathic hearts, aortic banding‐induced mice hearts, and angiotensin II–treated cardiomyocytes. Accordingly, SNIP1 deficiency significantly exacerbated aortic banding–induced cardiac hypertrophy, fibrosis, and contractile dysfunction, whereas cardiac‐specific overexpression of SNIP1 markedly recovered pressure overload–induced cardiac hypertrophy and fibrosis. Besides that, SNIP1 protected neonatal rat cardiomyocytes against angiotensin II–induced hypertrophy in vitro. Moreover, we identified that SNIP1 suppressed nuclear factor‐κB signaling during pathological cardiac hypertrophy, and inhibition of nuclear factor‐κB signaling by a cardiac‐specific conditional inhibitor of κB^S32A/S36A transgene blocked these adverse effects of SNIP1 deficiency on hearts.

Conclusions

Together, our findings demonstrated that SNIP1 had protective effects in pressure overload–induced pathological cardiac hypertrophy via inhibition of nuclear factor‐κB signaling. Thus, SNIP1 may be a novel approach for the treatment of heart failure.

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.

Regulator of G protein signalling 14 attenuates cardiac remodelling through the MEK-ERK1/2 signalling pathway

In the past 10 years, several publications have highlighted the role of the regulator of G protein signalling (RGS) family in multiple diseases, including cardiovascular diseases. As one of the multifunctional family members, RGS14 is involved in various biological processes, such as synaptic plasticity, cell division, and phagocytosis. However, the role of RGS14 in cardiovascular diseases remains unclear. In the present study, we used a genetic approach to examine the role of RGS14 in pathological cardiac remodelling in vivo and in vitro. We observed that RGS14 was down-regulated in human failing hearts, murine hypertrophic hearts, and isolated hypertrophic cardiomyocytes. Moreover, the extent of aortic banding-induced cardiac hypertrophy and fibrosis was exacerbated in RGS14 knockout mice, whereas RGS14 transgenic mice exhibited a significantly alleviated response to pressure overload. Furthermore, research of the underlying mechanism revealed that the RGS14-dependent rescue of cardiac remodelling was attributed to the abrogation of mitogen-activated protein kinase (MEK)–extracellular signal-regulated protein kinase (ERK) 1/2 signalling. The results showed that constitutive activation of MEK1 nullified the cardiac protection in RGS14 transgenic mice, and inhibition of MEK–ERK1/2 by U0126 reversed RGS14 deletion-related hypertrophic aggravation. These results demonstrated that RGS14 attenuated the development of cardiac remodelling through MEK–ERK1/2 signalling. RGS14 exhibited great potential as a target for the treatment of pathological cardiac remodelling.

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.

Identifying pathways that cause pathological cardiac hypertrophy holds great therapeutic potential. Here the authors discover one such pathway and show that SIKE, an inhibitor of interferon signalling, prevents pathological but not physiological cardiac hypertrophy by interacting with TBK1 and modulating the TBK1/AKT signalling in rodents and monkeys.

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.

Age-related changes in murine myometrial transcript profile are mediated by exposure to the female sex hormones

In humans, the risk of operative first delivery increases linearly with maternal age. We previously hypothesized that prolonged, cyclical, prepregnancy exposure to estrogen and progesterone contributes to uterine aging. Here, we test this hypothesis. Myometrium was obtained from four groups of virgin mice: (i) 10- to 12-week- and 28- to 30-week-old mice; (ii) 10- to 12-week- and 38- to 40-week-old mice; (iii) 38-week-old mice that had an ovariectomy or sham operation early in life; (iv) 38-week-old mice that had been treated with progesterone or vehicle containing implants from 8 to 36 weeks. Transcript profiling was carried out using Affymetrix Gene ST 1.1 arrays, and data were normalized. We identified 60 differentially regulated transcripts associated with advancing age (group 1). We validated these changes in group 2 (P for overlap = 5.8 × 10(-46) ). Early ovariectomy prevented the age-related changes in myometrial transcript profile. Similarly, progesterone-mediated long-term ovarian suppression prevented the age-related changes in myometrial transcript profile. Interferon regulatory factor 7 (Irf7) mRNA was regulated by age and hormonal exposure, and was identified as a predicted regulator of the other differentially expressed transcripts by both promoter sequence and canonical pathway activation analysis (P = 8.47 × 10(-5) and P < 10(-10) , respectively). Immunohistochemistry demonstrated IRF7 in both mouse and human myometrium. We conclude the following: (i) Myometrial aging in mice is associated with reproducible changes in transcript profile; (ii) these changes can be prevented by interventions which inhibit cyclical changes in the female sex hormones; and (iii) IRF7 may be an important regulator of myometrial function and aging.

The potential role of lysosome-associated membrane protein 3 (LAMP3) on cardiac remodelling

Lysosome-associated membrane protein 3 (LAMP3) was first identified as a cell surface marker of mature dendritic cells and specifically expressed in lung tissues. Recently studies demonstrated that LAMP3 plays a critical role in several cancers, and regulated by hypoxia. However, whether LAMP3 expressed in the heart and cardiomyocytes and changed its expression level in the hearts with cardiac remodelling was largely unknown. In this study, we first cultured H9C2 (a clonal muscle cell line from rat heart) and stimulated with 1 μM angiotensin II (Ang II), or 100 μM isoproterenol (ISO), or 100 μM phenylephrine (PE) for indicated times. We found that LAMP3 expression level was significantly increased after these stimulation. Next, the pressure overload-induced cardiac remodelling mouse model was performed in the wild type C57BL/6J mice. After 4 and 8 weeks of transverse aortic constriction (TAC), obvious cardiac remodelling was observed in the wild type mice compared with sham group. Importantly, LAMP3 expression level was gradually elevated from 2 weeks to 8 weeks after TAC surgery. Furthermore, in human dilated cardiomyopathy (DCM) hearts, severe cardiac remodelling was observed, as evidenced by remarkably increased cardiomyocytes cross sectional area and collagen deposition. Notably, the mRNA and protein level of LAMP3 were significantly increased in the DCM hearts compared with donor hearts. Immunohistochemistry assay showed that LAMP3 was expression in the cardiomyocytes and responsible for its increased expression in the hearts. Our data indicated that LAMP3 might have a potential role in the process of cardiac remodelling.

Bcl6 Sets a Threshold for Antiviral Signaling by Restraining IRF7 Transcriptional Program

The coordination of restraining and priming of antiviral signaling constitute a fundamental aspect of immunological functions. However, we currently know little about the molecular events that can translate the pathogenic cues into the appropriate code for antiviral defense. Our present study reports a specific role of B cell lymphoma (Bcl)6 as a checkpoint in the initiation of the host response to cytosolic RNA viruses. Remarkably, Bcl6 specifically binds to the interferon-regulatory factor (IRF)7 loci and restrains its transcription, thereby functioning as a negative regulator for interferon (IFN)-β production and antiviral responses. The signal-controlled turnover of the Bcl6, most likely mediated by microRNA-127, coordinates the antiviral response and inflammatory sequelae. Accordingly, de-repression of Bcl6 resulted in a phenotypic conversion of macrophages into highly potent IFN-producing cells and rendered mice more resistant to pathogenic RNA virus infection. The failure to remove the Bcl6 regulator, however, impedes the antiviral signaling and exaggerates viral pneumonia in mice. We thus reveal a novel key molecular checkpoint to orchestrate antiviral innate immunity.

Regulator of G-Protein Signaling 10 Negatively Regulates Cardiac Remodeling by Blocking Mitogen-Activated Protein Kinase–Extracellular Signal-Regulated Protein Kinase 1/2 Signaling

Regulator of G-protein signaling 10 (RGS10) is an important member of the RGS family and produces biological effects in multiple organs. We used a genetic approach to study the role of RGS10 in the regulation of pathological cardiac hypertrophy and found that RGS10 can negatively influence pressure overload–induced cardiac remodeling. RGS10 expression was markedly decreased in failing human hearts and hypertrophic murine hearts. The extent of aortic banding–induced cardiac hypertrophy, dysfunction, and fibrosis in RGS10-knockout mice was exacerbated, whereas the heart of transgenic mice with cardiac-specific RGS10 overexpression exhibited an alleviated response to pressure overload. Consistently, RGS10 also inhibited an angiotensin II–induced hypertrophic response in isolated cardiomyocytes. Mechanistically, cardiac remodeling improvement elicited by RGS10 was associated with the abrogation of mitogen-activated protein kinase kinase 1/2–extracellular signal-regulated protein kinase 1/2 signaling. Furthermore, the inhibition of mitogen-activated protein kinase kinase–extracellular signal-regulated protein kinase 1/2 transduction abolished RGS10 deletion-induced hypertrophic aggravation. These findings place RGS10 and its downstream signaling mitogen-activated protein kinase kinase–extracellular signal-regulated protein kinase 1/2 as crucial regulators of pathological cardiac hypertrophy after pressure overload and identify this pathway as a potential therapeutic target to attenuate the pressure overload–driven cardiac remodeling.

5-Azacytidine modulates interferon regulatory factor 1 in macrophages to exert a cardioprotective effect

Macrophages are actively involved in inflammatory responses during the progression of cardiac injury, including myocardial infarction (MI). A previous study showed that 5-azacytidine (5AZ), a DNA methylation inhibitor, can ameliorate cardiac injury by shifting macrophages toward an anti-inflammatory phenotype via iNOS inhibition. Here, we show that the beneficial effect of 5AZ is associated with sumoylation of interferon regulatory factor-1 (IRF1) in macrophages. IRF1 is a critical transcription factor for iNOS induction and is antagonized by IRF2. In the stimulated macrophages, IRF1 accumulated in the nucleus without degradation by 5AZ treatment. In animal study, 5AZ administration resulted in significant improvements in cardiac function and fibrosis. IRF1-expressing macrophages were more abundant in the 5AZ-treated MI group than in the PBS-treated MI group. Because sumoylated IRF1 is known to mimic IRF2, we examined the IRF1 sumoylation. Sumoylated IRF1 was resistant to degradation and significantly increased in the 5AZ-treated MI group. Collectively, 5AZ had a protective effect after MI by potentiation of IRF1 sumoylation and is suggested as a novel therapeutic intervention for cardiac repair.

SH2B1 is critical for the regulation of cardiac remodelling in response to pressure overload

AIMS

Src homology 2 (SH2) B adaptor protein 1 (SH2B1) is expressed in various tissues, including the heart. Previous studies have demonstrated that SH2B1 is involved in a variety of biological process, such as maintaining neuronal differentiation, regulating energy and glucose homeostasis, and promoting cell proliferation and motility. However, the role of SH2B1 in cardiac hypertrophy remains unclear. This study aimed at identifying the effects and the underlying mechanisms of SH2B1 in cardiac hypertrophy.

METHODS AND RESULTS

We performed gain- and loss-of-function studies using genetic approaches, and cardiac hypertrophy was evaluated through pathological, echocardiographic, haemodynamic, and molecular analyses. We found that SH2B1 expression was significantly increased in both failing human hearts and hypertrophic murine hearts. Mice overexpressing SH2B1 specifically in the heart displayed increased aortic banding (AB)-induced cardiac hypertrophy, fibrosis, ventricular dilation, and dysfunction compared with controls, whereas loss of SH2B1 produced the opposite phenotype. Consistently, similar results were observed in a global SH2B1-knockout rat model. Mechanistically, the pro-hypertrophic effects elicited by SH2B1 were associated with activation of the Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signalling cascade. Furthermore, rescue experiments revealed that pharmacological inactivation of JAK2 rescued pressure overload-induced cardiac abnormalities in transgenic mice with cardiac-specific SH2B1 overexpression.

CONCLUSION

Taken together, our data demonstrate, for the first time, that SH2B1 is a key positive mediator of pathological cardiac hypertrophy, and that it primarily acts by regulating JAK2/STAT3 signalling.

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.

The interferon regulatory factors as novel potential targets in the treatment of cardiovascular diseases

The family of interferon regulatory factors (IRFs) consists of nine members (IRF1-IRF9) in mammals. They act as transcription factors for the interferons and thus exert essential regulatory functions in the immune system and in oncogenesis. Recent clinical and experimental studies have identified critically important roles of the IRFs in cardiovascular diseases, arising from their participation in divergent and overlapping molecular programmes beyond the immune response. Here we review the current knowledge of the regulatory effects and mechanisms of IRFs on the immune system. The role of IRFs and their potential molecular mechanisms as novel stress sensors and mediators of cardiovascular diseases are highlighted.

Interferon regulatory factor 7 protects against vascular smooth muscle cell proliferation and neointima formation

Background

Interferon regulatory factor 7 (IRF7), a member of the interferon regulatory factor family, plays important roles in innate immunity and immune cell differentiation. However, the role of IRF7 in neointima formation is currently unknown.

Methods and Results

Significant decreases in IRF7 expression were observed in vascular smooth muscle cells (VSMCs) following carotid artery injury in vivo and platelet‐derived growth factor‐BB (PDGF‐BB) stimulation in vitro. Compared with non‐transgenic (NTG) controls, SMC‐specific IRF7 transgenic (IRF7‐TG) mice displayed reduced neointima formation and VSMC proliferation in response to carotid injury, whereas a global knockout of IRF7 (IRF7‐KO) resulted in the opposite effect. Notably, a novel IRF7‐KO rat strain was successfully generated and used to further confirm the effects of IRF7 deletion on the acceleration of intimal hyperplasia based on a balloon injury‐induced vascular lesion model. Mechanistically, IRF7's inhibition of carotid thickening and the expression of VSMC proliferation markers was dependent on the interaction of IRF7 with activating transcription factor 3 (ATF3) and its downstream target, proliferating cell nuclear antigen (PCNA). The evidence that IRF7/ATF3‐double‐TG (DTG) and IRF7/ATF3‐double‐KO (DKO) mice abolished the regulatory effects exhibited by the IRF7‐TG and IRF7‐KO mice, respectively, validated the underlying molecular events of IRF7‐ATF3 interaction.

Conclusions

These findings demonstrated that IRF7 modulated VSMC proliferation and neointima formation by interacting with ATF3, thereby inhibiting the ATF3‐mediated induction of PCNA transcription. The results of this study indicate that IRF7 is a novel modulator of neointima formation and VSMC proliferation and may represent a promising target for vascular disease therapy.

Interferon regulatory factor 9 is an essential mediator of heart dysfunction and cell death following myocardial ischemia/reperfusion injury

This study aimed to investigate whether interferon regulatory factor 9 (IRF9) is involved in the pathogenesis of myocardial ischemia-reperfusion (I/R) injury and to explore the underlying molecular mechanisms of this process. Cell death plays a major role in myocardial I/R injury. We recently determined the importance of IRF9 in coordinating molecular events in response to hypertrophic stress in cardiomyocytes. However, the roles of IRF9 in lethal myocardial injury remain to be elucidated. The involvement of IRF9 was assessed via functional assays in a mouse myocardial I/R injury model by genetic knockout and cardiomyocyte-specific transgenic overexpression of IRF9, and its effects on cardiomyocyte apoptosis and inflammation were further studied in vivo and in vitro. IRF9 was upregulated in human ischemic heart tissue and mouse hearts after I/R injury. Ablation of IRF9 protected the heart against I/R-induced cardiomyocyte death, development of inflammation, and loss of heart function. In contrast, cardiomyocyte-specific transgenic overexpression of IRF9 aggravated myocardial reperfusion injury and inflammation. IRF9 negatively regulated the Sirt1-p53 axis under I/R conditions in vivo and in vitro. Downregulation of Sirt1 expression and its downstream apoptosis-related signaling cascade, which results from I/R, was ameliorated by loss of IRF9 and exacerbated by overexpression of IRF9. Cardiomyocyte-specific deletion of Sirt1 abolished the protective effect of IRF9 knockout against I/R injury, which further indicated that IRF9 mediated myocardial reperfusion injury by modulating the Sirt1-p53 axis. Thus, IRF9 may be a novel therapeutic target for the prevention of I/R injury resulting from revascularization therapy after acute myocardial infarction (MI).

Interferon Regulatory Factor 1 Is Required for Cardiac Remodeling in Response to Pressure Overload

Interferon regulatory factor 1 (IRF1), a critical member of the IRF family, was previously shown to be associated with the immune system and to be involved in apoptosis and tumor suppression. However, the role of IRF1 in pressure overload–induced cardiac remodeling has remained unclear. Using genetic approaches, we established a central role for the IRF1 transcription factor in the regulation of cardiac remodeling both in vivo and in vitro, and we determined the mechanism underlying this process. The expression level of IRF1 was remarkably altered in both failing human hearts and hypertrophic murine hearts. Transgenic mice with cardiac-specific IRF1 overexpression exacerbated aortic banding–induced cardiac hypertrophy, ventricular dilation, fibrosis, and dysfunction, whereas IRF1-deficient (knockout) mice exhibited a significant reduction in the hypertrophic response. Similar results were observed in a global IRF1-knockout rat model. Mechanistically, the prohypertrophic effects elicited by IRF1 in response to pathological stimuli were associated with the direct activation of inducible nitric oxide synthase (iNOS). Furthermore, we identified 1 IRF1-binding site in the promoter region of the iNOS gene, which was essential for its transcription. To examine the IRF1-iNOS axis in vivo, we generated IRF1-transgenic/iNOS-knockout mice. IRF1 exerted profoundly detrimental effects in these mice; however, these effects were nullified by iNOS ablation. These data suggest the IRF1–iNOS axis as a crucial regulator of cardiac remodeling and that IRF1 could be a potent therapeutic target for cardiac remodeling.

Interferon regulatory factor 3 protects against adverse neo-intima formation

AIMS

Vascular smooth muscle cell (VSMC) proliferation is central to the pathophysiology of neo-intima formation. Interferon regulatory factor 3 (IRF3) inhibits the growth of cancer cells and fibroblasts. However, the role of IRF3 in vascular neo-intima formation is unknown. We evaluated the protective role of IRF3 against neo-intima formation in mice and the underlying mechanisms.

METHODS AND RESULTS

IRF3 expression was down-regulated in VSMCs after carotid wire injury in vivo, and in SMCs after platelet-derived growth factor (PDGF)-BB challenge in vitro. Global knockout of IRF3 (IRF3-KO) led to accelerated neo-intima formation and proliferation of VSMCs, whereas the opposite was seen in SMC-specific IRF3 transgenic mice. Mechanistically, we identified IRF3 as a novel regulator of peroxisome proliferator-activated receptor γ (PPARγ), a negative regulator of SMC proliferation after vascular injury. Binding of IRF3 to the AB domain of PPARγ in the nucleus of SMCs facilitated PPARγ transactivation, resulting in decreased proliferation cell nuclear antigen expression and suppressed proliferation. Overexpression of wild-type, but not truncated, IRF3 with a mutated IRF association domain (IAD) retained the ability to exert anti-proliferative effect.

CONCLUSIONS

IRF3 inhibits VSMC proliferation and neo-intima formation after vascular injury through PPARγ activation.

Thyroid Hormone-Regulated Cardiac microRNAs are Predicted to Suppress Pathological Hypertrophic Signaling

Cardiomyocyte size in the healthy heart is in part determined by the level of circulating thyroid hormone (TH). Higher levels of TH induce ventricular hypertrophy, primarily in response to an increase in hemodynamic load. Normal cardiac function is maintained in this form of hypertrophy, whereas progressive contractile dysfunction is a hallmark of pathological hypertrophy. MicroRNAs (miRNAs) are important modulators of signal-transduction pathways driving adverse remodeling. Because little is known about the involvement of miRNAs in cardiac TH action and hypertrophy, we examined the miRNA expression profile of the hypertrophied left ventricle (LV) using a mouse model of TH-induced cardiac hypertrophy. C57Bl/6J mice were rendered hypothyroid by treatment with propylthiouracil and were subsequently treated for 3 days with TH (T3) or saline. T3 treatment increased LV weight by 38% (p < 0.05). RNA was isolated from the LV and expression of 641 mouse miRNAs was determined using Taqman Megaplex arrays. Data were analyzed using RQ-manager and DataAssist. A total of 52 T3-regulated miRNAs showing a >2-fold change (p < 0.05) were included in Ingenuity Pathway Analysis to predict target mRNAs involved in cardiac hypertrophy. The analysis was further restricted to proteins that have been validated as key factors in hypertrophic signal transduction in mouse models of ventricular remodeling. A total of 27 mRNAs were identified as bona fide targets. The predicted regulation of 19% of these targets indicates enhancement of physiological hypertrophy, while 56% indicates suppression of pathological remodeling. Our data suggest that cardiac TH action includes a novel level of regulation in which a unique set of TH-dependent miRNAs primarily suppresses pathological hypertrophic signaling. This may be relevant for our understanding of the progression of adverse remodeling, since cardiac TH levels are known to decrease substantially in various forms of pathological hypertrophy.