DNMT1-mediated PTEN hypermethylation confers hepatic stellate cell activation and liver fibrogenesis in rats

TRPM7 channel regulates PDGF-BB-induced proliferation of hepatic stellate cells via PI3K and ERK pathways

TRPM7, a non-selective cation channel of the TRP channel superfamily, is implicated in diverse physiological and pathological processes including cell proliferation. Recently, TRPM7 has been reported in hepatic stellate cells (HSCs). Here, we investigated the contribution role of TRPM7 in activated HSC-T6 cell (a rat hepatic stellate cell line) proliferation. TRPM7 mRNA and protein were measured by RT-PCR and Western blot in rat model of liver fibrosis in vivo and PDGF-BB-activated HSC-T6 cells in vitro. Both mRNA and protein of TRPM7 were dramatically increased in CCl4-treated rat livers. Stimulation of HSC-T6 cells with PDGF-BB resulted in a time-dependent increase of TRPM7 mRNA and protein. However, PDGF-BB-induced HSC-T6 cell proliferation was inhibited by non-specific TRPM7 blocker 2-aminoethoxydiphenyl borate (2-APB) or synthetic siRNA targeting TRPM7, and this was accompanied by downregulation of cell cycle proteins, cyclin D1, PCNA and CDK4. Blockade of TRPM7 channels also attenuated PDGF-BB induced expression of myofibroblast markers as measured by the induction of α-SMA and Col1α1. Furthermore, the phosphorylation of ERK and AKT, associated with cell proliferation, decreased in TRPM7 deficient HSC-T6 cells. These observations suggested that TRPM7 channels contribute to perpetuated fibroblast activation and proliferation of PDGF-BB induced HSC-T6 cells via the activation of ERK and PI3K pathways. Therefore, TRPM7 may constitute a useful target for the treatment of liver fibrosis.

Role of DNA methyltransferase 1 on the altered eNOS expression in human umbilical endothelium from intrauterine growth restricted fetuses

Reduced fetal growth associates with endothelial dysfunction and cardiovascular risk in both young and adult offspring and the nitric oxide (NO) system has been implicated in these effects. Epigenetic processes are likely to underlie such effects, but there is to date no evidence that endothelial dysfunction in early life results from epigenetic processes on key genes in the NO system, such as NOS3 (eNOS) and ARG2 (arginase-2). We determined basal DNA methylation status in NOS3 and ARG2 promoters, and DNA methyltransferase 1 (DNMT1) effect on eNOS and arginase-2 expression using human endothelial cells isolated from umbilical arteries (HUAEC) and veins (HUVEC) from control and intrauterine growth restricted (IUGR) fetuses. Compared with cells from control pregnancies, eNOS protein and mRNA levels were increased in HUAEC, but decreased in HUVEC, from IUGR, while arginase-2 levels were increased in IUGR-HUVEC. The NOS3 promoter showed a decrease in DNA methylation at CpG -352 in IUGR-HUAEC, and an increase in IUGR-HUVEC, when compared with control cells. Methylation in the hypoxia response element of the NOS3 promoter was increased in IUGR-HUAEC and decreased in HUVEC. Methylation in the AGR2 promoter in IUGR-HUVEC was decreased in a putative HRE, and without changes in IUGR-HUAEC. Silencing of DNMT1 expression normalized eNOS expression in IUGR endothelial cells, and restored the normal response to hypoxia in HUVEC, without effects on arginase-2. This data suggest that eNOS expression in IUGR-derived endothelial cells is programmed by altered DNA methylation, and can be reversed by transient silencing of the DNA methylation machinery.

New advances of DNA methylation in liver fibrosis, with special emphasis on the crosstalk between microRNAs and DNA methylation machinery

Epigenetics refers to the study of heritable changes in the pattern of gene expression that is controlled by a mechanism specifically not due to changes the primary DNA sequence. Well-known epigenetic mechanisms include DNA methylation, post-translational histone modifications and RNA-based mechanisms including those controlled by small non-coding RNAs (miRNAs). Recent studies have shown that epigenetic modifications orchestrate the hepatic stellate cell (HSC) activation and liver fibrosis. In this review we focus on the aberrant methylation of CpG island promoters of select genes is the prominent epigenetic mechanism to effectively silence gene transcription facilitating HSC activation and liver fibrosis. Furthermore, we also discuss epigenetic dysregulation of tumor-suppressor miRNA genes by promoter DNA methylation and the interaction of DNA methylation with miRNAs involved in the regulation of HSC activation and liver fibrosis. Recent advances in epigenetics alterations in the pathogenesis of liver fibrosis and their possible use as new therapeutic targets and biomarkers.

The epigenetic feedback loop between DNA methylation and microRNAs in fibrotic disease with an emphasis on DNA methyltransferases

Epigenetic processes play a key regulatory role in many cancers. Recently, it also has been demonstrated to participate in fibrogenesis, especially in fibrotic disease. Fibrotic disease is a pathological response to tissue injury which can occur in any organ. Mechanisms that orchestrate fibrotic disorders in different organs are amazingly generic, involving generation of activated fibroblasts and myofibroblasts by differentiation processes that require extensive alterations in gene expression. Apart from genetic and environmental factors, epigenetic modifications including a combination of microRNAs and DNA methylation are supposed as regulatory mechanisms to control myofibroblast differentiation. It has become obvious that microRNAs, which act as regulators of gene expression at a post-transcriptional level, are differentially expressed in differentiating cells and play important roles in governing DNA methyltransferases (DNMTs) which are enzymes responsible for setting up and maintaining DNA methylation patterns at specific regions of the genome. Some microRNAs targeting DNMT transcripts lead to the demethylation and transcriptional activation of numerous protein coding gene sequences, thereby contributing to gene expression. Moreover, DNMTs also have a critical role in controlling some specific microRNA expression. This cooperative action among DNMTs, microRNAs and DNA methylation indicates that DNMTs may participate in the pathogenesis of myofibroblast differentiation through silencing of certain gene transcription. In this review, we summarize the current knowledge of a potential link between microRNA expression and DNA methylation on how DNMTs work in the process of fibrogenesis.

Choline's role in maintaining liver function: new evidence for epigenetic mechanisms

PURPOSE OF REVIEW

Humans eating diets low in choline develop fatty liver and liver damage. Rodents fed choline-methionine-deficient diets not only develop fatty liver, but also progress to develop fibrosis and hepatocarcinoma. This review focuses on the role of choline in liver function, with special emphasis on the epigenetic mechanisms of action.

RECENT FINDINGS

Dietary intake of methyl donors like choline influences the methylation of DNA and histones, thereby altering the epigenetic regulation of gene expression. The liver is the major organ within which methylation reactions occur, and many of the hepatic genes involved in pathways for the development of fatty liver, hepatic fibrosis, and hepatocarcinomas are epigenetically regulated.

SUMMARY

Dietary intake of choline varies over a three-fold range and many humans have genetic polymorphisms that increase their demand for choline. Choline is an important methyl donor needed for the generation of S-adenosylmethionine. Dietary choline intake is an important modifier of epigenetic marks on DNA and histones, and thereby modulates the gene expression in many of the pathways involved in liver function and dysfunction.

DNA methylation: new therapeutic implications for hepatic fibrosis

DNA methylation refers to a heritable alteration in the pattern of gene expression that is regulated by a mechanism specifically not owing to changes in the primary nucleotide sequence. The transcriptional silencing caused by DNA methylation affects genes involved in the main cellular pathways: cell cycle control, Ras signaling, apoptosis, and detoxification. Recent studies have shown that methylation modifications orchestrate the activation of hepatic stellate cells (HSCs) characterized by excessive accumulation of extracellular matrices (ECMs). The activation of HSCs is mediated by multiple signal transduction pathways and is generally regarded as the major ECM producer responsible for liver fibrosis. In addition, aberrant methylation of specific gene involved in the activation of multiple signal transduction pathways in liver fibrosis. The aim of this review is to compile recent information on aberrant DNA methylation in hepatic fibrosis and to highlight key genes and molecular pathways in hepatic fibrosis formation.