Epigenetic Repression of Chloride Channel Accessory 2 Transcription in Cardiac Fibroblast: Implication in Cardiac Fibrosis

The zinc-finger transcription factor KLF6 regulates cardiac fibrosis

AIMS

Heart failure (HF) is one of the most devastating consequences of cardiovascular diseases. Regardless of etiology, cardiac fibrosis is present and promotes the loss of heart function in HF patients. Cardiac resident fibroblasts, in response to a host of pro-fibrogenic stimuli, trans-differentiate into myofibroblasts to mediate cardiac fibrosis, the underlying mechanism of which remains incompletely understood.

METHODS

Fibroblast-myofibroblast transition was induced in vitro by exposure to transforming growth factor (TGF-β). Cardiac fibrosis was induced in mice by either transverse aortic constriction (TAC) or by chronic infusion with angiotensin II (Ang II).

RESULTS

Through bioinformatic screening, we identified Kruppel-like factor 6 (KLF6) as a transcription factor preferentially up-regulated in cardiac fibroblasts from individuals with non-ischemic cardiomyopathy (NICM) compared to the healthy donors. Further analysis showed that nuclear factor kappa B (NF-κB) bound to the KLF6 promoter and mediated KLF6 trans-activation by pro-fibrogenic stimuli. KLF6 knockdown attenuated whereas KLF6 over-expression enhanced TGF-β induced fibroblast-myofibroblast transition in vitro. More importantly, myofibroblast-specific KLF6 depletion ameliorated cardiac fibrosis and rescued heart function in mice subjected to the TAC procedure or chronic Ang II infusion.

SIGNIFICANCE

In conclusion, our data support a role for KLF6 in cardiac fibrosis.

SMARCA4 (BRG1) activates ABCC3 transcription to promote hepatocellular carcinogenesis

AIMS

Hepatocellular carcinoma (HCC) is a lead cause of cancer-related deaths. In the present study we investigated the role of Brahma-related gene 1 (BRG1), a chromatin remodeling protein, in HCC the pathogenesis focusing on identifying novel transcription targets.

METHODS AND MATERIALS

Hepatocellular carcinogenesis was modeled in mice by diethylnitrosamine (DEN). Cellular transcriptome was evaluated by RNA-seq.

RESULTS

Hepatocellular carcinoma was appreciably retarded in BRG1 knockout mice compared to wild type littermates. Transcriptomic analysis identified ATP Binding Cassette Subfamily C Member 3 (ABCC3) as a novel target of BRG1. BRG1 over-expression in BRG1low HCC cells (HEP1) up-regulated whereas BRG1 depletion in BRG1high HCC cells (SNU387) down-regulated ABCC3 expression. Importantly, BRG1 was detected to directly bind to the ABCC3 promoter to activate ABCC3 transcription. BRG1 over-expression in HEP1 cells promoted proliferation and migration, both of which were abrogated by ABCC3 silencing. On the contrary, BRG1 depletion in SNU387 cells decelerated proliferation and migration, both of which were rescued by ABCC3 over-expression. Importantly, high BRG1/ABCC3 expression predicted poor prognosis in HCC patients. Mechanistically, ABCC3 regulated hepatocellular carcinogenesis possibly by influencing lysosomal homeostasis.

SIGNIFICANCE

In conclusion, our data suggest that targeting BRG1 and its downstream target ABCC3 can be considered as a reasonable approach for the intervention of hepatocellular carcinoma.

The chromatin remodeling protein BRG1 regulates HSC-myofibroblast differentiation and liver fibrosis

Excessive fibrogenic response in the liver disrupts normal hepatic anatomy and function heralding such end-stage liver diseases as hepatocellular carcinoma and cirrhosis. Myofibroblasts, derived primarily from hepatic stellate cells (HSCs), are the effector of liver fibrosis. In the present study we investigated the mechanism by which Brahma-related gene 1 (BRG1, encoded by Smarca4) regulates HSC-myofibroblast transition and the implication in intervention against liver fibrosis. We report that BRG1 expression was elevated during HSC maturation in cell culture, in animal models, and in human cirrhotic liver biopsy specimens. HSC-specific deletion of BRG1 attenuated liver fibrosis in several different animal models. In addition, BRG1 ablation in myofibroblasts ameliorated liver fibrosis. RNA-seq identified IGFBP5 as a novel target for BRG1. Over-expression of IGFBP5 partially rescued the deficiency in myofibroblast activation when BRG1 was depleted. On the contrary, IGFBP5 knockdown suppressed HSC-myofibroblast transition in vitro and mollified liver fibrosis in mice. Mechanistically, IGFBP5 interacted with Bat3 to stabilize the Bat3-TβR complex and sustain TGF-β signaling. In conclusion, our data provide compelling evidence that BRG1 is a pivotal regulator of liver fibrosis by programming HSC-myofibroblast transition.

Epigenetic Regulation of Fibroblasts and Crosstalk between Cardiomyocytes and Non-Myocyte Cells in Cardiac Fibrosis

Epigenetic mechanisms and cell crosstalk have been shown to play important roles in the initiation and progression of cardiac fibrosis. This review article aims to provide a thorough overview of the epigenetic mechanisms involved in fibroblast regulation. During fibrosis, fibroblast epigenetic regulation encompasses a multitude of mechanisms, including DNA methylation, histone acetylation and methylation, and chromatin remodeling. These mechanisms regulate the phenotype of fibroblasts and the extracellular matrix composition by modulating gene expression, thereby orchestrating the progression of cardiac fibrosis. Moreover, cardiac fibrosis disrupts normal cardiac function by imposing myocardial mechanical stress and compromising cardiac electrical conduction. This review article also delves into the intricate crosstalk between cardiomyocytes and non-cardiomyocytes in the heart. A comprehensive understanding of the mechanisms governing epigenetic regulation and cell crosstalk in cardiac fibrosis is critical for the development of effective therapeutic strategies. Further research is warranted to unravel the precise molecular mechanisms underpinning these processes and to identify potential therapeutic targets.

Review: Acetylation Mechanisms andTargeted Therapies in Cardiac Fibrosis

Cardiac fibrosis is a common pathophysiological remodeling process that occurs in a variety of cardiovascular diseases and greatly influences heart structure and function, progressively leading to the development of heart failure. However, to date, few effective therapies for cardiac fibrosis exist. Abnormal proliferation, differentiation, and migration of cardiac fibroblasts are responsible for the excessive deposition of extracellular matrix in the myocardium. Acetylation, a widespread and reversible protein post-translational modification, plays an important role in the development of cardiac fibrosis by adding acetyl groups to lysine residues. Many acetyltransferases and deacetylases regulate the dynamic alterations of acetylation in cardiac fibrosis, regulating a range of pathogenic conditions including oxidative stress, mitochondrial dysfunction, and energy metabolism disturbance. In this review, we demonstrate the critical roles that acetylation modifications caused by different types of pathological injury play in cardiac fibrosis. Furthermore, we propose therapeutic acetylation-targeting strategies for the prevention and treatment of patients with cardiac fibrosis.

An MRTF-A-ZEB1-IRF9 axis contributes to fibroblast-myofibroblast transition and renal fibrosis

Myofibroblasts, characterized by the expression of the matricellular protein periostin (Postn), mediate the profibrogenic response during tissue repair and remodeling. Previous studies have demonstrated that systemic deficiency in myocardin-related transcription factor A (MRTF-A) attenuates renal fibrosis in mice. In the present study, we investigated the myofibroblast-specific role of MRTF-A in renal fibrosis and the underlying mechanism. We report that myofibroblast-specific deletion of MRTF-A, achieved through crossbreeding Mrtfa-flox mice with Postn-Cre^ERT2 mice, led to amelioration of renal fibrosis. RNA-seq identified zinc finger E-Box binding homeobox 1 (Zeb1) as a downstream target of MRTF-A in renal fibroblasts. MRTF-A interacts with TEA domain transcription factor 1 (TEAD1) to bind to the Zeb1 promoter and activate Zeb1 transcription. Zeb1 knockdown retarded the fibroblast-myofibroblast transition (FMyT) in vitro and dampened renal fibrosis in mice. Transcriptomic assays showed that Zeb1 might contribute to FMyT by repressing the transcription of interferon regulatory factor 9 (IRF9). IRF9 knockdown overcame the effect of Zeb1 depletion and promoted FMyT, whereas IRF9 overexpression antagonized TGF-β-induced FMyT. In conclusion, our data unveil a novel MRTF-A-Zeb1-IRF9 axis that can potentially contribute to fibroblast-myofibroblast transition and renal fibrosis. Screening for small-molecule compounds that target this axis may yield therapeutic options for the mollification of renal fibrosis.

The circular RNA circHelz enhances cardiac fibrosis by facilitating the nuclear translocation of YAP1

Cardiac fibrosis is a common pathological change in the development of heart disease. Circular RNA (circRNA) has been shown to be related to the occurrence and development of various cardiovascular diseases. This study aimed to evaluate the effects and potential mechanisms of circHelz in cardiac fibrosis. Knockdown of circHelz alleviated cardiac fibrosis and myocardial fibroblast activation induced by myocardial infarction (MI) or angiotensin II (AngII) in vivo and transforming growth factor-β (TGF-β) in vitro. Overexpression of circHelz exacerbated cell proliferation and differentiation. Mechanistically, nuclear factor of activated T cells, cytoplasmic 2 (NFATc2) was found to act as a transcriptional activator to upregulate the expression of circHelz. The increased circHelz was demonstrated to bind to Yes-associated protein (YAP) and facilitate its localization in the nucleus to promote cell proliferation and growth. Moreover, silencing YAP1 reversed the detrimental effects caused by circHelz in vitro, as indicated by the observed decreases in cell viability, fibrotic marker expression levels, proliferation and migration. Collectively, the protective effect of circHelz knockdown against cardiac fibrosis injury is accomplished by inhibiting the nuclear translocation of YAP1. Thus, circHelz may be a novel target for the prevention and treatment of cardiovascular disease.

Roles of Epigenetics in Cardiac Fibroblast Activation and Fibrosis

Cardiac fibrosis is a common pathophysiologic process associated with numerous cardiovascular diseases, resulting in cardiac dysfunction. Cardiac fibroblasts (CFs) play an important role in the production of the extracellular matrix and are the essential cell type in a quiescent state in a healthy heart. In response to diverse pathologic stress and environmental stress, resident CFs convert to activated fibroblasts, referred to as myofibroblasts, which produce more extracellular matrix, contributing to cardiac fibrosis. Although multiple molecular mechanisms are implicated in CFs activation and cardiac fibrosis, there is increasing evidence that epigenetic regulation plays a key role in this process. Epigenetics is a rapidly growing field in biology, and provides a modulated link between pathological stimuli and gene expression profiles, ultimately leading to corresponding pathological changes. Epigenetic modifications are mainly composed of three main categories: DNA methylation, histone modifications, and non-coding RNAs. This review focuses on recent advances regarding epigenetic regulation in cardiac fibrosis and highlights the effects of epigenetic modifications on CFs activation. Finally, we provide some perspectives and prospects for the study of epigenetic modifications and cardiac fibrosis.