New findings showing how DNA methylation influences diseases

In 1975, Holliday and Pugh as well as Riggs independently hypothesized that DNA methylation in eukaryotes could act as a hereditary regulation mechanism that influences gene expression and cell differentiation. Interest in the study of epigenetic processes has been inspired by their reversibility as well as their potentially preventable or treatable consequences. Recently, we have begun to understand that the features of DNA methylation are not the same for all cells.Major differences have been found between differentiated cells and stem cells.Methylation influences various pathologies, and it is very important to improve the understanding of the pathogenic mechanisms. Epigenetic modifications may take place throughout life and have been related to cancer, brain aging, memory disturbances, changes in synaptic plasticity, and neurodegenerative diseases,such as Parkinson's disease and Huntington's disease. DNA methylation also has a very important role in tumor biology. Many oncogenes are activated by mutations in carcinogenesis. However, many genes with tumor-suppressor functions are "silenced" by the methylation of CpG sites in some of their regions.Moreover, the role of epigenetic alterations has been demonstrated in neurological diseases. In neuronal precursors, many genes associated with development and differentiation are silenced by CpG methylation. In addition,recent studies show that DNA methylation can also influence diseases that do not appear to be related to the environment, such as IgA nephropathy, thus affecting,the expression of some genes involved in the T-cell receptor signaling. In conclusion, DNA methylation provides a whole series of fundamental information for the cell to regulate gene expression, including how and when the genes are read, and it does not depend on the DNA sequence.     

Retinal ganglion cells of high cytochrome oxidase activity in the rat

Retinal ganglion cells in the rat were studied using the heavy metal intensified cytochrome oxidase and horseradish peroxidase histochemical methods.The results show that a population of large retinal ganglion cells was consistently observed with the cytochrome oxidase staining method in retinas of normal rats or rats which received unilateral thalamotomy at birth.These cytochrome oxidase rich ganglion cells appeared to have large somata,3-6 primary dendrites and extensive dendritic arbors,and are comparable to ganglion cells labeled by the wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP).However,the morphological details of some of the cells revealed by the cytochrome oxidase staining method are frequently better than those shown by the HRP histochemical method.These results suggest that the mitochondrial enzyme cytochrome oxidase can be used as a simple but reliable marker for identifying and studying a population of retinal genglion cells with high metabolic rate in the rat.     

Immunosenescence and age-related viral diseases

Immunosenescence is described as a decline in the normal functioning of the immune system associated with physiologic ageing.Immunosenescence contributes to reduced efficacy to vaccination and increased susceptibility to infectious diseases in the elderly.Extensive studies of laboratory animal models of ageing or donor lymphocyte analysis have identified changes in immunity caused by the ageing process.Most of these studies have identified phenotypic and functional changes in innate and adaptive immunity.However,it is unclear which of these defects are critical for impaired immune defense against infection.This review describes the changes that occur in innate and adaptive immunity with ageing and some age-related viral diseases where defects in a key component of immunity contribute to the high mortality rate in mouse models of ageing.     

Evaluating alternative stem cell hypotheses for adult corneal epithelial maintenance

In this review we evaluate evidence for three different hypotheses that explain how the corneal epithelium is maintained. The limbal epithelial stem cell(LESC)hypothesis is most widely accepted. This proposes that stem cells in the basal layer of the limbal epithelium, at the periphery of the cornea, maintain themselves and also produce transient(or transit) amplifying cells(TACs). TACs then move centripetally to the centre of the cornea in the basal layer of the corneal epithelium and also replenish cells in the overlying suprabasal layers. The LESCs maintain the corneal epithelium during normal homeostasis and become more active to repair significant wounds. Second, the corneal epithelial stem cell(CESC) hypothesis postulates that, during normal homeostasis, stem cells distributed throughout the basal corneal epithelium, maintain the tissue. According to this hypothesis, LESCs are present in the limbus but are only active during wound healing. We also consider a third possibility, that the corneal epithelium is maintained during normal homeostasis by proliferation of basal corneal epithelial cells without any input from stem cells. After reviewing the published evidence, we conclude that the LESC and CESC hypotheses are consistent with more of the evidence than the third hypothesis, so we do not consider this further. The LESC and CESC hypotheses each have difficulty accounting for one main type of evidence so we evaluate the two key lines of evidence that discriminate between them. Finally, we discuss how lineage-tracing experiments have begun to resolve the debate in favour of the LESC hypothesis. Nevertheless, it also seems likely that some basal corneal epithelial cells can act as long-term progenitors if limbal stem cell function is compromised. Thus, this aspect of the CESC hypothesis may have a lasting impact on our understanding of corneal epithelial maintenance, even if it is eventually shown that stem cells are restricted to the limbus as proposed by the LESC hypothesis.     

Selenoprotein expression is regulated at multiple levels in prostate cells

Selenium supplementation in a population with low basal blood selenium levels has been reported to decrease the incidence of several cancers including prostate cancer. Based on the clinical findings, it is likely that the antioxidant function of one or more selenoproteins is responsible for the chemopreventive effect, although low molecular weight seleno-compounds have also been posited to selectively induce apoptosis in transformed cells. To address the effects of selenium supplementation on selenoprotein expression in prostate cells, we have undertaken an analysis of antioxidant selenoprotein expression as well as selenium toxicity in non-tumorigenic prostate epithelial cells （RWPE- 1 ） and prostate cancer cells （LNCaP and PC-3）. Our results show that two of the glutathione peroxidase family members （GPX1 and GPX4） are highly induced by supplemental selenium in prostate cancer cells but only slightly induced in RWPE-1 cells. In addition, GPX 1 levels are dramatically lower in PC-3 cells as compared to RWPE- 1 or LNCaP cells. GPX2 protein and mRNA, however, are only detectable in RWPE-1 cells. Of the three selenium compounds tested （sodium selenite, sodium selenate and selenomethionine）, only sodium selenite shows toxicity in a physiological range of selenium concentrations. Notably and in contrast to previous studies, RWPE-1 cells were significantly more sensitive to selenite than either of the prostate cancer cell lines. These results demonstrate that selenoproteins and selenium metabolism are regulated at multiple levels in prostate cells.     

Evaluating the antitumor activity of combined photochemotherapy mediated by a meso-substituted tetracationic porphyrin and adriamycin

The combined anticancer modality comprising porphyrins as photodynamic sensitizers and anticancer drugs has been an interesting subject for many researchers. In this study, the photochemotherapeutic effect mediated by simultaneous photoactivation of tetracationic meso-tetrakis（N-methyl-4-pyridyl） porphine tetratosylate （TMPyP） and adriamycin （ADM） were explored using human hepatocellular carcinoma cell line （HePG2）. The efficiency of TMPyP acting in concert with ADM in the dark and in the presence of photoirradiation was evaluated, by studying cell viability, caspase-3 activity and ultrastructural changes in the cells after incubation with each of the two agents, separately, or simultaneously as a co-mixture. Under dark conditions, the simultaneous incubation of cells with TMPyP and ADM significantly enhanced cell death by 1.8 folds and 1.3 folds, compared with TMPyP or ADM treatment, respectively. After photoirradiation, the antiproliferative effect of the co-treatment with TMPyP and ADM increased further by 2 folds. Transmission electron microscopy and the measurements of caspase-3 levels in treated cells revealed that the co-treatment of cells with ADM and TMPyP followed by light irradiation directed the cell death towards necrosis and abrogated the apoptotic cell death pathway, which was exhibited in cells treated with ADM in absence and in presence of photoirradiation.     

Mesenchymal stromal cell-dependent immunoregulation in chemically-induced acute liver failure

Drug-induced liver injury(DILI),which refers to liver damage caused by a drug or its metabolites,has emerged as an important cause of acute liver failure(ALF)in recent years.Chemically-induced ALF in animal models mimics the pathology of DILI in humans;thus,these models are used to study the mechanism of potentially effective treatment strategies.Mesenchymal stromal cells(MSCs)possess immunomodulatory properties,and they alleviate acute liver injury and decrease the mortality of animals with chemically-induced ALF.Here,we summarize some of the existing research on the interaction between MSCs and immune cells,and discuss the possible mechanisms underlying the immunomodulatory activity of MSCs in chemically-induced ALF.We conclude that MSCs can impact the phenotype and function of macrophages,as well as the differentiation and maturation of dendritic cells,and inhibit the proliferation and activation of T lymphocytes or B lymphocytes.MSCs also have immunomodulatory effects on the production of cytokines,such as prostaglandin E2 and tumor necrosis factor-alpha-stimulated gene 6,in animal models.Thus,MSCs have significant benefits in the treatment of chemically-induced ALF by interacting with immune cells and they may be applied to DILI in humans in the near future.