An E2F5-TFDP1-BRG1 Complex Mediates Transcriptional Activation of MYCN in Hepatocytes

Epigenetic regulation in liver regeneration

The liver is considered unique in its enormous capacity for regeneration and self-repair. In contrast to other regenerative organs (i.e., skin, skeletal muscle, and intestine), whether the adult liver contains a defined department of stem cells is still controversial. In order to compensate for the massive loss of hepatocytes following liver injury, the liver processes a precisely controlled transcriptional reprogram that can trigger cell proliferation and cell-fate switch. Epigenetic events are thought to regulate the organization of chromatin architecture and gene transcription during the liver regenerative process. In this review, we will summarize how changes to the chromatin by epigenetic modifiers are translated into cell fate transitions to restore liver homeostasis during liver regeneration.

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.

Myocardin-related transcription factor A, regulated by serum response factor, contributes to diabetic cardiomyopathy in mice

AIMS

Diabetic cardiomyopathy is a significant contributor to the global pandemic of heart failure. In the present study we investigated the involvement of myocardin-related transcription factor A (MRTF-A), a transcriptional regulator, in this process.

MATERIALS AND METHODS

Diabetic cardiomyopathy was induced in mice by feeding with a high-fat diet (HFD) or streptozotocin (STZ) injection.

KEY FINDINGS

We report that MRTF-A was up-regulated in the hearts of mice with diabetic cardiomyopathy. MRTF-A expression was also up-regulated by treatment with palmitate in cultured cardiomyocytes in vitro. Mechanistically, serum response factor (SRF) bound to the MRTF-A gene promoter and activated MRTF-A transcription in response to pro-diabetic stimuli. Knockdown of SRF abrogated MRTF-A induction in cardiomyocytes treated with palmitate. When cardiomyocytes conditional MRTF-A knockout mice (MRTF-A CKO) and wild type (WT) mice were placed on an HFD to induce diabetic cardiomyopathy, it was found that the CKO mice and the WT mice displayed comparable metabolic parameters including body weight, blood insulin concentration, blood cholesterol concentration, and glucose tolerance. However, both systolic and diastolic cardiac function were exacerbated by MRTF-A deletion in the heart.

SIGNIFICANCE

These data suggest that MRTF-A up-regulation might serve as an important compensatory mechanism to safeguard the deterioration of cardiac function during diabetic cardiomyopathy.

Slug enables redox-sensitive trans-activation of LRP1 by COUP-TFII: Implication in antifibrotic intervention in the kidneys

AIMS

Excessive fibrogenesis in the kidney causes structural and functional damages and is considered a hallmark event in end-stage renal diseases (ESRD). During renal fibrosis, resident fibroblasts undergo profound changes to become myofibroblasts. In the present study we investigated the involvement of Slug (encoded by Snai2) in this process.

MATERIALS AND METHODS

Renal fibrosis was induced by unilateral ureteral obstruction (UUO) in mice. Cellular transcriptome was evaluated by RNA-seq.

KEY FINDINGS

We report that Slug expression was up-regulated during fibroblast-myofibroblast transition (FMyT) in vivo and in vitro. Slug knockdown attenuated TGF-β induced FMyT in primary renal fibroblasts and ameliorated renal fibrosis in mice. RNA-seq analysis revealed that Slug promoted FMyT by enabling key pro-fibrogenic transcription factors including the orphan nuclear receptor COUP-TFII. Mechanistically, Slug enhanced intracellular ROS levels by modulating the expression of redox-related genes. Elevated ROS levels in turn stimulated transcription of LDL receptor related protein 1 (Lrp1) by COUP-TFII. Importantly, both a COUP-TFII antagonist and an Lrp1 neutralization antibody mitigated renal fibrosis in mice.

SIGNIFICANCE

Our data support a role for Slug in regulating FMyT and renal fibrosis.

Exploration of the core gene signatures and mechanisms between NAFLD and sarcopenia through transcriptomic level

INTRODUCTION

The increased prevalence of non-alcoholic fatty liver disease (NAFLD) and sarcopenia among the elderly are facing a significant challenge to the world's health systems. Our study aims to identify the coexpressed genes in NAFLD and sarcopenia patients.

METHODS

We downloaded the transcriptome data of NAFLD tissue from patients, as well as muscle tissues from sarcopenia patients, from the GEO database in order to investigate the shared transcriptional regulation mechanisms between these two diseases. Then, focusing on the genes that were frequently expressed in these diseases, together with GSVA and WGCNA, we utilized a range of analysis methods to identify the main co-expressed genes in both diseases by taking intersections. We investigated these changes after learning that they mostly affected lipid metabolism and oxidative stress injury pathways.

RESULTS

By analyzing these genes and their interactions with transcription factors and proteins, we were able to identify 8 genes that share common patterns. From these 8 genes, we were possible to forecast potential future medicines. Our research raises the possibility of NAFLD and sarcopenia transcriptome regulatory pathways in aging populations.

DISCUSSION

In conclusion, a complete transcription pattern mapping was carried out in order to identify the core genes, underlying biological mechanisms, and possible therapeutic targets that regulate aging in NAFLD and sarcopenia patients. It provides novel insights and proof in favor of decreasing the increased prevalence of sarcopenia in the elderly caused by NAFLD.

SIRT6 mediates MRTF-A deacetylation in vascular endothelial cells to antagonize oxLDL-induced ICAM-1 transcription

Oxidized low-density lipoprotein (oxLDL), a known risk factor for atherosclerosis, activates the transcription of adhesion molecules (ICAM-1) in endothelial cells. We previously showed that myocardin-related transcription factor A (MRTF-A) mediates oxLDL-induced ICAM-1 transcription. Here we confirm that ICAM-1 transactivation paralleled dynamic alterations in MRTF-A acetylation. Since treatment with the antioxidant NAC dampened MRTF-A acetylation, MRTF-A acetylation appeared to be sensitive to cellular redox status. Of interest, silencing of SIRT6, a lysine deacetylase, restored MRTF-A acetylation despite the addition of NAC. SIRT6 directly interacted with MRTF-A to modulate MRTF-A acetylation. Deacetylation of MRTF-A by SIRT6 led to its nuclear expulsion thus dampening MRTF-A occupancy on the ICAM-1 promoter. Moreover, SIRT6 expression was downregulated with oxLDL stimulation likely owing to promoter hypermethylation in endothelial cells. DNA methyltransferase 1 (DNMT1) was recruited to the SIRT6 promoter and mediated SIRT6 repression. The ability of DNMT1 to repress SIRT6 promoter partly was dependent on ROS-sensitive serine 154 phosphorylation. In conclusion, our data unveil a novel DNMT1-SIRT6 axis that contributes to the regulation of MRTF-A acetylation and ICAM-1 transactivation in endothelial cells.