Type I diabetes leads to tissue-specific DNA hypomethylation in male rats

Maternal Distress during Pregnancy and the Postpartum Period: Underlying Mechanisms and Child's Developmental Outcomes-A Narrative Review

Maternal mental health may be considered a determining factor influencing fetal and child development. An essential factor with potentially negative consequences for a child's psychophysiological development is the presence of maternal distress during pregnancy and the postpartum period. The review is organized and presented to explore and describe the effects of anxiety, stress, and depression in pregnancy and the postpartum period on adverse child developmental outcomes. The neurobiology of maternal distress and the transmission mechanisms at the molecular level to the fetus and child are noted. In addition, the paper discusses the findings of longitudinal studies in which early child development is monitored concerning the presence of maternal distress in pregnancy and the postpartum period. This topic gained importance in the COVID-19 pandemic context, during which a higher frequency of maternal psychological disorders was observed. The need for further interdisciplinary research on the relationship between maternal mental health and fetal/child development was highlighted, especially on the biological mechanisms underlying the transmission of maternal distress to the (unborn) child, to achieve positive developmental outcomes and improve maternal and child well-being.

The Role of Epigenetic Modifications in Late Complications in Type 1 Diabetes

Type 1 diabetes is a chronic autoimmune disease in which the destruction of pancreatic β cells leads to hyperglycemia. The prevention of hyperglycemia is very important to avoid or at least postpone the development of micro- and macrovascular complications, also known as late complications. These include diabetic retinopathy, chronic renal failure, diabetic neuropathy, and cardiovascular diseases. The impact of long-term hyperglycemia has been shown to persist long after the normalization of blood glucose levels, a phenomenon known as metabolic memory. It is believed that epigenetic mechanisms such as DNA methylation, histone modifications, and microRNAs, play an important role in metabolic memory. The aim of this review is to address the impact of long-term hyperglycemia on epigenetic marks in late complications of type 1 diabetes.

Homocysteine, Vitamins B6 and Folic Acid in Experimental Models of Myocardial Infarction and Heart Failure—How Strong Is That Link?

Cardiovascular diseases are the leading cause of death and the main cause of disability. In the last decade, homocysteine has been found to be a risk factor or a marker for cardiovascular diseases, including myocardial infarction (MI) and heart failure (HF). There are indications that vitamin B6 plays a significant role in the process of transsulfuration in homocysteine metabolism, specifically, in a part of the reaction in which homocysteine transfers a sulfhydryl group to serine to form α-ketobutyrate and cysteine. Therefore, an elevated homocysteine concentration (hyperhomocysteinemia) could be a consequence of vitamin B6 and/or folate deficiency. Hyperhomocysteinemia in turn could damage the endothelium and the blood vessel wall and induce worsening of atherosclerotic process, having a negative impact on the mechanisms underlying MI and HF, such as oxidative stress, inflammation, and altered function of gasotransmitters. Given the importance of the vitamin B6 in homocysteine metabolism, in this paper, we review its role in reducing oxidative stress and inflammation, influencing the functions of gasotransmitters, and improving vasodilatation and coronary flow in animal models of MI and HF.

Letrozole-Induced Polycystic Ovary Syndrome Attenuates Cystathionine-β Synthase mRNA and Protein Abundance in the Ovaries of Female Sprague Dawley Rats

BACKGROUND

Polycystic ovary syndrome (PCOS) is an endocrine disorder that affects 10% of reproductive-aged women and leads to hyperandrogenism, anovulation, and infertility. PCOS has been associated with elevated serum homocysteine as well as altered methylation status; however, characterization of one-carbon metabolism (OCM) in PCOS remains incomplete.

OBJECTIVES

The aim of our research was to assess OCM in a letrozole-induced Sprague Dawley rat model of PCOS.

METHODS

Five-week-old female rats (n = 36) were randomly assigned to letrozole [0.9 mg/kg body weight (BW)] treatment or vehicle (carboxymethylcellulose) control that was administered via subcutaneously implanted slow-release pellets every 30 d. For both treatment groups, 12 rats were randomly assigned to be euthanized during proestrus at one of the following time points: 8, 16, or 24 wk of age. Daily BW was measured and estrous cyclicity was monitored during the last 30 d of the experimental period. Ovaries were collected to assess mRNA and protein abundance of OCM enzymes.

RESULTS

Letrozole-induced rats exhibited 1.9-fold higher cumulative BW gain compared with control rats across all age groups (P < 0.0001). Letrozole reduced the time spent at proestrus (P = 0.0001) and increased time in metestrus (P < 0.0001) of the estrous cycle. Cystathionine β-synthase (Cbs) mRNA abundance was reduced in the letrozole-induced rats at 16 (59%; P < 0.05) and 24 (77%; P < 0.01) wk of age. In addition, CBS protein abundance was 32% lower in 8-wk-old letrozole-induced rats (P = 0.02). Interestingly, betaine-homocysteine S-methyltransferase mRNA abundance increased as a function of age in letrozole-induced rats (P = 0.03).

CONCLUSION

These data demonstrate that letrozole-induced PCOS Sprague Dawley rats temporally decrease the ovarian abundance of Cbs mRNA and protein in the early stages of PCOS.

Epigenetic regulation of cellular functions in wound healing

Stringent spatiotemporal regulation of the wound healing process involving multiple cell types is associated with epigenetic mechanisms of gene regulation, such as DNA methylation, histone modification and chromatin remodelling, as well as non-coding RNAs. Here, we discuss the epigenetic changes that occur during wound healing and the rapidly expanding understanding of how these mechanisms affect healing resolution in both acute and chronic wound milieu. We provide a focussed overview of current research into epigenetic regulators that contribute to wound healing by specific cell type. We highlight the role of epigenetic regulators in the molecular pathophysiology of chronic wound conditions. The understanding of how epigenetic regulators can affect cellular functions during normal and impaired wound healing could lead to novel therapeutic approaches, and we outline questions that can provide guidance for future research on epigenetic-based interventions to promote healing. Dissecting the dynamic interplay between cellular subtypes involved in wound healing and epigenetic parameters during barrier repair will deepen our understanding of how to improve healing outcomes in patients affected by chronic non-healing wounds.

Ginsenoside Rg1 protects mice against streptozotocin-induced type 1 diabetic by modulating the NLRP3 and Keap1/Nrf2/HO-1 pathways

Ginseng has been traditionally used to treat diabetes mellitus (DM) in China. Ginsenoside Rg1 is a major active ingredient in processed ginseng, which elicits proven biological and pharmacological effects. Although a correlation between nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) and predisposition to type 1 diabetes mellitus (T1DM) has been identified, the mechanism underlying the potential function and activation of NLRP3 inflammasome in DM have not been elucidated to date. The present study aimed to elucidate the effects and underlying mechanism of Rg1 on streptozotocin (STZ)-induced T1DM in mice through short or long-term observation. Concurrently, we intended to explore the relationships between inflammasome, pyroptosis and oxidative stress and the role of NLRP3 and Keap1/Nrf2/HO-1 pathways in the development and progression of DM. Using ELISA and Western blot analysis, we found that Rg1 attenuated abnormally elevated blood glucose, reduced inflammatory factors IL-1β and IL-18 in the blood, decreased ALT and AST levels, promoted insulin secretion, and weakened the function of NLRP3 in mouse liver and pancreas. In addition, Rg1 protected against STZ-induced reactive oxygen species-mediated inflammation by upregulating Nrf2/ARE pathway, which further activated antioxidant enzymes. Interestingly, Rg1 also regulated H3K9 methylation in liver and pancreas, as detected by immunohistochemistry. In summary, these data provide new understanding about the mechanism of Rg1 action, suggesting that it is a potential drug applied for preventing the occurrence and development of T1DM.

Higher glycolytic capacities in muscle of carnivorous rainbow trout juveniles after high dietary carbohydrate stimulus at first feeding

Background

Rainbow trout is a “glucose-intolerant” carnivorous species. Using the metabolic programming strategy, we used early nutritional stimuli in order to modify carbohydrate utilization in trout juveniles.

Method

Fish were fed two diets during the first feeding, namely HP (no carbohydrate / high protein) diet and LP (high carbohydrate / low protein) diet. HP diet was used as the control diet and LP diet as an early stimulus diet. We also used another early stimulus with fish fed HP diet every other day during the first feeding (HP restriction feeding - HPR). After the first-feeding stage (4 weeks), all fish were subsequently subjected to a growth trial with a commercial diet followed by a challenge test with the LP diet (11 weeks). At the end of the first feeding stimulus and of the challenge test, we investigated growth performance, glucose metabolism-related parameters and global DNA C^mCGG methylation in trout.

Results

LP and HPR dietary stimuli have been a success as shown by the direct modifications of growth performance and mRNA levels for glucose metabolism-related genes at the end of first feeding compared to alevins fed the HP diet. At the end of the challenge trial, no variation in growth performance and hepatic metabolism of LP-history and HPR-history in trout juveniles were observed. However, in muscle of trout juvenile subjected to LP diet at the first feeding, we found an up-regulation of mRNA levels of some glucose metabolism (glucose transport and glycolysis)-related genes and an increase of activities of important glycolysis-related enzymes (hexokinase, phosphofructokinase and pyruvate kinase). These observations are associated with a decrease in the content of glycogen compared to fish fed the HP diet. Moreover, global C^mCGG DNA methylation in the muscle of fish with LP history was significantly lower than those fed the HP diet.

Conclusion

Dietary LP stimulus at first feeding could permanently modify glucose metabolism and global C^mCGG DNA methylation level in muscle of trout juveniles, showing that the first feeding stage is efficient for programming the glucose metabolism in fish.

Insights into the Role of DNA Methylation and Protein Misfolding in Diabetes Mellitus

Background:

Diabetes mellitus is a metabolic disorder that is characterized by impaired glucose tolerance resulting from defects in insulin secretion, insulin action, or both. Epigenetic modifications, which are defined as inherited changes in gene expression that occur without changes in gene sequence, are involved in the etiology of diabetes.

Methods:

In this review, we focused on the role of DNA methylation and protein misfolding and their contribution to the development of both type 1 and type 2 diabetes mellitus.

Results:

Changes in DNA methylation in particular are highly associated with the development of diabetes. Protein function is dependent on their proper folding in the endoplasmic reticulum. Defective protein folding and consequently their functions have also been reported to play a role. Early treatment of diabetes has proven to be of great benefit, as even transient hyperglycemia may lead to pathological effects and complications later on. This has been explained by the theory of the development of a metabolic memory in diabetes. The basis for this metabolic memory was attributed to oxidative stress, chronic inflammation, non-enzymatic glycation of proteins and importantly, epigenetic changes. This highlights the importance of linking new therapeutics targeting epigenetic mechanisms with traditional antidiabetic drugs.

Conclusion:

Although new data is evolving on the relation between DNA methylation, protein misfolding, and the etiology of diabetes, more studies are required for developing new relevant diagnostics and therapeutics.

Kruppel-Like Transcription Factor-4 Gene Expression and DNA Methylation Status in Type 2 Diabetes and Diabetic Nephropathy Patients

BACKGROUND/AIM

Diabetic nephropathy (DN) is one of the most serious microvascular complications in diabetic patients. The kruppel-like transcription factor-4 (KLF-4) affects the expression of genes involved in the pathogenesis of DN. The present study aims to identify the KLF-4 expression and DNA methylation (DNAMe) status in patients with type-2 diabetes (T2D) and DN and to reveal the contribution of the KLF-4 to the development of DN.

MATERIAL AND METHODS

The cohort study was performed with blood samples from 120 individuals; T2D group (n = 40), DN group (n = 40) and control group (n = 40). The expression level of the KLF-4 gene was analyzed using the real-time polymerase chain reaction (qRT-PCR) and the methylation profile detected using the methylation-specific PCR (MS-PCR) technique.

RESULTS

According to our findings, KLF-4 mRNA expression in the T2D group was 1.60 fold lower than in the control group (p = 0.001). In the DN group, the expression of KLF-4 mRNA was 2.92-fold less than that of the T2D group (p = 0.001). There was no significant alteration in the DNAMe status among the groups.

CONCLUSION

Our findings showed that regardless of the DNAMe status, KLF-4 gene expression may play a role in the development of T2D and DN. This suggests that the KLF-4 gene may be the target gene in understanding the mechanism of nephropathy, which is the most important complication of diabetes, and planning nephropathy-related treatments, but the data should be supported with more studies.

Gestational Diabetes Epigenetically Reprograms the Cart Promoter in Fetal Ovary, Causing Subfertility in Adult Life

Intrauterine exposure to various adverse conditions during fetal development can lead to epigenetic changes in fetal tissues, predisposing those tissues to disease conditions later in life. An example is gestational diabetes (GD), where the offspring has a higher risk of developing obesity, metabolic disorders, or cardiovascular disease in adult life. In this study, using two well-established GD (streptozotocin- and high-fat and high-sugar-induced) mouse models, we report that female offspring from GD dams are predisposed toward fertility problems later in life. This predisposition to fertility problems is due to altered ovarian expression of a peptide called cocaine- and amphetamine-regulated transcript (CART), which is known to negatively affect folliculogenesis and is induced by elevated leptin levels. Results show that the underlying cause of this altered expression is due to fetal epigenetic modifications involving glucose- and insulin-induced miRNA, miR-101, and the phosphatidylinositol 3-kinase/Akt pathway. These signaling events regulate Ezh2, a histone methyltransferase that promotes H3K27me3, a gene-repressive mark, and CBP/p300, a histone acetyltransferase that promotes H3K27ac, a transcription activation mark, in the fetal ovary. Moreover, the CART promoter has depleted 5-methylcytosine (5mC) and enriched 5-hydroxymethylcytosine (5hmC) levels. The depletion of H3K27me3 and 5mC repressive marks and subsequent increase in H3K27ac and 5hmC gene-activating marks convert the Cartpt promoter to a "superpromoter." This makes the Cartpt promoter more sensitive to leptin levels that predispose the GD offspring to fertility problems. Therefore, this study provides a mechanistic insight about fetal epigenome reprogramming that manifests to ovarian dysfunction and subfertility later in adult life.

Comparative DNA methylomic analyses reveal potential origins of novel epigenetic biomarkers of insulin resistance in monocytes from virally suppressed HIV-infected adults

BACKGROUND

Compared to healthy individuals, those with stably repressed HIV experience a higher risk of developing insulin resistance, a hallmark of pre-diabetes and a major determinant for cardiometabolic diseases. Although epigenetic processes, including in particular DNA methylation, appear to be dysregulated in individuals with insulin resistance, little is known about where these occur in the genomes of immune cells and the origins of these alterations in HIV-infected individuals. Here, we examined the genome-wide DNA methylation states of monocytes in HIV-infected individuals (n = 37) with varying levels of insulin sensitivity measured by the homeostatic model assessment of insulin resistance (HOMA-IR).

RESULTS

By profiling DNA methylation at single-nucleotide resolution using the Illumina Infinium HumanMethylation450 BeadChip in monocytes from insulin-resistant (IR; HOMA-IR ≥ 2.0; n = 14) and insulin-sensitive (IS; HOMA-IR < 2.0; n = 23) individuals, we identified 123 CpGs with significantly different DNA methylation levels. These CpGs were enriched at genes involved in pathways relating to glucose metabolism, immune activation, and insulin-relevant signaling, with the majority (86.2%) being hypomethylated in IR relative to IS individuals. Using a stepwise multiple logistic regression analysis, we observed 4 CpGs (cg27655935, cg02000426, cg10184328, and cg23085143) whose methylation levels independently predicted the insulin-resistant state at a higher confidence than that of clinical risk factors typically associated with insulin resistance (i.e., fasting glucose, 120-min oral glucose tolerance test, Framingham Risk Score, and Total to HDL cholesterol ratio). Interestingly, 79 of the 123 CpGs (64%) exhibited remarkably similar levels of methylation as that of hematopoietic stem cells (HSC) in monocytes from IR individuals, implicating epigenetic defects in myeloid differentiation as a possible origin for the methylation landscape underlying the insulin resistance phenotype. In support of this, gene ontology analysis of these 79 CpGs revealed overrepresentation of these CpGs at genes relevant to HSC function, including involvement in stem cell pluripotency, differentiation, and Wnt signaling pathways.

CONCLUSION

Altogether, our data suggests a possible role for DNA methylation in regulating monocyte activity that may associate with the insulin-resistant phenotype. The methylomic landscape of insulin resistance in monocytes could originate from epigenetic dysregulation during HSC differentiation through the myeloid lineage. Understanding the factors involved with changes in the myeloid trajectory may provide further insight into the development of insulin resistance. Furthermore, regulation of specific genes that were implicated in our analysis reveal possible targets for modulating immune activity to ameliorate insulin resistance.

Exposure to Aroclor 1254 persistently suppresses the functions of pancreatic β-cells and deteriorates glucose homeostasis in male mice

Polychlorinated biphenyls (PCBs) are a class of persistent organic pollutants that have been shown to be related to the occurrence of type 2 diabetes mellitus (T2DM). Nevertheless, it is necessary to further explore the development of T2DM caused by PCBs and its underlying mechanisms. In the present study, 21-day-old C57BL/6 male mice were orally treated with Aroclor 1254 (0.5, 5, 50 or 500 μg kg^-1) once every three days. After exposure for 66 d, the mice showed impaired glucose tolerance, 13% and 14% increased fasting serum insulin levels (FSIL), and 63% and 69% increases of the pancreatic β-cell mass in the 50 and 500 μg kg^-1 groups, respectively. After stopping exposure for 90 d, treated mice returned to normoglycemia and normal FSIL. After re-exposure of these recovered mice to Aroclor 1254 for 30 d, fasting plasma glucose showed 15%, 28% and 16% increase in the 5, 50 and 500 μg kg^-1 treatments, FSIL exhibited 35%, 27%, 30% and 32% decrease in the 0.5, 5, 50 or 500 μg kg^-1 groups respectively, and there was no change in pancreatic β-cell mass. Transcription of the pancreatic insulin gene (Ins2) was significantly down-regulated in the 50 and 500 μg kg^-1 groups, while DNA-methylation levels were simultaneously increased in the Ins2 promoter during the course of exposure, recovery and re-exposure. Reduced insulin levels were initially rescued by a compensative increase in β-cell mass. However, β-cell mass eventually failed to make sufficient levels of insulin, resulting in significant increases in fasting blood glucose, and indicating the development of T2DM.

Altered metabolic and hormonal responses in male rats exposed to acute bright light-at-night associated with global DNA hypo-methylation

The association between light pollution and disruption of daily rhythms, metabolic and hormonal disorders, as well as cancer progression is well-recognized. These adverse effects could be due to nocturnal melatonin suppression. The signaling pathway by which light pollution affects metabolism and endocrine responses is unclear. We studied the effects of artificial light at night (ALAN¹) on body mass, food and water intake, daily rhythms of body temperature, serum glucose and insulin in male rats. Daily rhythms of urine production and urinary 6-sulfatoxymelatonin (6-SMT²), as well as global DNA methylation in pancreas and liver tissues were also assessed. Mass gain was higher in ALAN rats compared with controls. Food intake, water consumption, glucose, insulin, and 6-SMT levels markedly lessened in response to ALAN. Conversely, urine production and body temperature were elevated in ALAN rats compared with controls. Significant 24-h rhythms were detected for all variables that were altered in mesor, amplitude, and acrophase occurrences under ALAN conditions. DNA hypo-methylation was detected in ALAN pancreatic tissue compared with controls, but not in hepatic tissue. Overall, ALAN affects metabolic and hormonal physiology in different levels in which flexible crosstalk between melatonin and both epigenetics and metabolic levels expressed as body temperature rhythm, is suggested to mediate the environmental exposure at the molecular level and subsequently physiology is altered. The flexibility of epigenetic modifications provides a potential therapeutic target for rectifying ALAN adverse effects by epigenetic markers such as melatonin and behavioral lifestyle interventions for confining ALAN exposures as much as possible.

Effect of TET2 on the pathogenesis of diabetic nephropathy through activation of transforming growth factor β1 expression via DNA demethylation

AIMS

Transforming growth factor β1 (TGFβ1) plays a pivotal role in the pathogenesis of diabetic nephropathy (DN). However, the mechanism of its expression and activation induced by high glucose (HG) is still unclear. We mainly explored the role of ten-eleven translocation enzyme-2 (TET2) in regulating TGFβ1 expression in the process of DN.

MAIN METHODS

Human mesangial cells (HMCs) and db/db mice were used to analyze the biological effects of hyperglycemia both in vivo and in vitro. Gene expression levels, cell proliferation, protein recruitment levels to TGFβ1 regulatory region, DNA methylation statues and pathological changes in kidney were tested in different groups. Short hairpin RNA(shRNA) and oral inhibitor were used to knock down or inhibit TET2 expression.

KEY FINDINGS

Our study demonstrated that TET2 expression was increased in the renal cortex of db/db mice and in HMCs inducing by HG. We also found that TET2 binding was increased while DNA methylation of CpG islands was reduced in the TGFβ1 regulation region in HG, resulting in the increased expression level of TGFβ1 and cell phenotype transformation. More importantly, clinical research revealed that gradually decreased DNA methylation in the TGFβ1 regulatory region was also present in patients with diabetes and DN.

SIGNIFICANCE

Our work suggests that TET2 plays an important role in the pathogenesis of DN by activating TGFβ1 expression through demethylation of CpG islands in the TGFβ1 regulatory region. This may provide a potential new therapeutic target for DN.

GADD45a Promotes Active DNA Demethylation of the MMP-9 Promoter via Base Excision Repair Pathway in AGEs-Treated Keratinocytes and in Diabetic Male Rat Skin

Diabetes elevates matrix metalloproteinase (MMP)-9 levels in the skin and its keratinocytes, and activated MMP-9 impairs skin wound healing. Epigenetic regulation of the DNA methylation status within the MMP-9 promoter plays an important role in the alteration of MMP-9 expression. Our aim was to investigate the role and mechanism of growth arrest and DNA damage-inducible 45a (GADD45a), a well-known DNA demethylation regulatory protein that mediates DNA methylation, in the regulation of MMP-9 expression. In this study, we showed that GADD45a was markedly upregulated in skin tissues from patients with diabetic foot ulcers, in diabetic rats, and in human keratinocyte (HaCaT) cells exposed to advanced glycation end products. We observed a substantial positive correlation between the levels of GADD45a and MMP-9 expression. Knockdown of GADD45a ameliorated the increase in MMP-9 transcription induced by a diabetic condition by inhibiting demethylation in the MMP-9 promoter and promoted diabetic HaCaT cell migration, but GADD45a knockdown did not affect HaCaT cell proliferation or apoptosis. Additionally, we demonstrated that overexpression of GADD45a activated MMP-9 expression by inducing promoter demethylation. Moreover, we found that GADD45a binds to the promoter of MMP-9 and recruits thymine-DNA glycosylase for base excision repair-mediated demethylation in diabetic HaCaT cells and diabetic rat skin. Our results reveal a mechanism in which GADD45a is required for demethylation of the MMP-9 promoter and the induction of diabetic wound healing. The inhibition of GADD45a might be a therapeutic strategy for diabetic foot ulcers.

Effect of diabetes status and hyperglycemia on global DNA methylation and hydroxymethylation

Type 2 diabetes mellitus (T2DM) is characterized by oxidative stress that could lead to chronic micro- and macrovascular complications. We hypothesized that some of the target organ damage is mediated by oxidative alterations in epigenetic mechanisms involving DNA methylation (5mC) and DNA hydroxymethylation (5hmC). We analyzed global DNA methylation and hydroxymethylation in peripheral blood cells in well-controlled and poorly controlled patients with T2DM and compared them with healthy controls. We also analyzed microarrays of DNA methylation and gene expression of other important tissues in the context of diabetes from the GEO database repository and then compared these results with our experimental gene expression data. DNA methylation and, more importantly, DNA hydroxymethylation levels were increased in poorly controlled patients compared to well-controlled and healthy individuals. Both 5mC and 5hmC measurements were correlated with the percentage of glycated hemoglobin, indicating a direct impact of hyperglycemia on changes over the epigenome. The analysis of methylation microarrays was concordant, and 5mC levels were increased in the peripheral blood of T2DM patients. However, the DNA methylation levels were the opposite of those in other tissues, such as the pancreas, adipose tissue and skeletal muscle. We hypothesize that a process of DNA oxidation associated with hyperglycemia may explain the DNA demethylation in which the activity of ten-eleven translocation (TET) proteins is not sufficient to complete the process. High levels of glucose lead to cellular oxidation, which triggers the process of DNA demethylation aided by TET enzymes, resulting in epigenetic dysregulation of the damaged tissues.

Transgenerational inheritance of susceptibility to diabetes-induced male subfertility

Male infertility is a worldwide problem associated with genetic background, environmental factors, and diseases. One of the suspected contributing factors to male infertility is diabetes mellitus. We investigated the molecular and morphological changes in sperms and testicular tissue of diabetic males. The study was performed in streptozotocin-induced type 1 diabetes mouse model. Diabetes decreased sperm concentration and viability and increased sperm apoptosis. Changes in protamine 1/protamine 2 ratio indicated reduced sperm quality. The testicular tissue of diabetic males showed significant tissue damage, disruption of meiotic progression, and changes in the expression of genes encoding proteins important for spermiogenesis. Paternal diabetes altered sperm quality and expression pattern in the testes in offspring of two subsequent generations. Our study revealed that paternal diabetes increased susceptibility to infertility in offspring through gametic alternations. Our data also provide a mechanistic basis for transgenerational inheritance of diabetes-associated pathologies since protamines may be involved in epigenetic regulations.

The role of «metabolic memory» mechanisms in the development and progression of vascular complications of diabetes mellitus

The study of diabetes mellitus (DM), its complications and related pathologies has been continuously performed for many years; however, despite the substantial work and outstanding achievements in studying the mechanisms of DM development and the success of new medicinal products for controlling glycaemia, the problems associated with the late complications of DM continue to increase. The importance of glycaemic control in the early stages of DM for the development of complications is seen only after a sufficiently long period of observation. Such a delayed effect of primary good or unsatisfactory metabolic control, which shapes the patients clinical fate to a greater extent, is termed metabolic memory. The disorders developed under the influence of hyperglycaemia persist for long periods after the normalisation of carbohydrate metabolism; moreover, the effect of previous hyperglycaemia extends over the next 20 and even 30 years. Current research is focused on the possible mechanisms of metabolic memory development, including oxidative stress, advanced glycation end products and epigenetic mechanisms. This research will provide insight into potential markers for the early development and progression of vascular complications and new therapeutic possibilities for the future. However, determining the probable point of no return is more important, which implies that a point exists; after this point is crossed, the progression of vascular complications associated with DM cannot be prevented or reversed. The results of numerous experimental studies demonstrate that the prerequisite components of metabolic memory can be used as potential markers of the progression of DM complications, and may be potential therapeutic targets.

Folic Acid Reduces Tau Phosphorylation by Regulating PP2A Methylation in Streptozotocin-Induced Diabetic Mice

High incidence rate of Alzheimer’s disease (AD) is observed in patients with type 2 diabetes. Aggregated β-amyloid (Aβ) and hyperphosphorylated tau are the hallmarks of AD. Hyperphosphorylated tau has been detected in diabetic animals as well as in diabetic patients. Folates mediate the transfer of one carbon unit, required in various biochemical reactions. The effect of folate on tau phosphorylation in diabetic models still remains unknown. In this study, we investigated the effect and mechanism of folic acid on hyperphosphorylation of tau in streptozotocin (STZ)-induced diabetic mice. Diabetic mice induced by STZ, at the age of 10 weeks, were administered with three levels of folic acid: folic acid-deficient diet, diet with normal folic acid content, and 120 μg/kg folic acid diet for 8 weeks. Levels of serum folate and blood glucose were monitored. Tau phosphorylation, protein phosphatase 2A (PP2A) methylation, and Glycogen synthase kinase 3β (GSK-3β) phosphorylation were detected using Western blot. The S-adenosyl methionine:S-adenosyl homocysteine ratio (SAM:SAH) in brain tissues was also determined. DNA methyltransferase (DNMT) mRNA expression levels were detected using real-time PCR. Folic acid reduced tau hyperphosphorylation at Ser396 in the brain of diabetes mellitus (DM) mice. In addition, PP2A methylation and DNMT1 mRNA expression were significantly increased in DM mice post folic acid treatment. GSK-3β phosphorylation was not regulated by folic acid administration. Folic acid can reduce tau phosphorylation by regulating PP2A methylation in diabetic mice. These results support that folic acid can serve as a multitarget neuronal therapeutic agent for treating diabetes-associated cognitive dysfunction.

Epigenetics of kidney disease

DNA methylation and histone modifications determine renal programming and the development and progression of renal disease. The identification of the way in which the renal cell epigenome is altered by environmental modifiers driving the onset and progression of renal diseases has extended our understanding of the pathophysiology of kidney disease progression. In this review, we focus on current knowledge concerning the implications of epigenetic modifications during renal disease from early development to chronic kidney disease progression including renal fibrosis, diabetic nephropathy and the translational potential of identifying new biomarkers and treatments for the prevention and therapy of chronic kidney disease and end-stage kidney disease.

The Folate Cycle As a Cause of Natural Killer Cell Dysfunction and Viral Etiology in Type 1 Diabetes

The folate pathway is critical to proper cellular function and metabolism. It is responsible for multiple functions, including energy (ATP) production, methylation reactions for DNA and protein synthesis and the production of immunomodulatory molecules, inosine and adenosine. These play an important role in immune signaling and cytotoxicity. Herein, we hypothesize that defects in the folate pathway in genetically susceptible individuals could lead to immune dysfunction, permissive environments for chronic cyclical latent/lytic viral infection, and, ultimately, the development of unchecked autoimmune responses to infected tissue, in this case islet beta cells. In the context of type 1 diabetes (T1D), there has been a recent increase in newly diagnosed cases of T1D in the past 20 years that has exceeded previous epidemiological predictions with yet unidentified factor(s). This speaks to a potential environmental trigger that adversely affects immune responses. Most research into the immune dysfunction of T1D has focused on downstream adaptive responses of T and B cells neglecting the role of the upstream innate players such as natural killer (NK) cells. Constantly, surveilling the blood and tissues for pathogens, NK cells remove threats through direct cytotoxic responses and recruitment of adaptive responses using cytokines, such as IL-1β and IFN-γ. One long-standing hypothesis suggests viral infection as a potential trigger for the autoimmune response in T1D. Recent data suggest multiple viruses as potential causal agents. Intertwined with this is an observed reduced NK cell enumeration, cytotoxicity, and cytokine signaling in T1D patients. Many of the viruses implicated in T1D are chronic latent/lysogenic infections with demonstrated capacity to reduce NK cell response and number through mechanisms that resemble those of pregnancy tolerance. Defects in the folate pathway in T1D patients could result in decreased immune response to viral infection or viral reactivation. Dampened NK responses to infections result in improper signaling, improper antigen presentation, and amplified CD8⁺ lymphocyte proliferation and cytotoxicity, a hallmark of beta cell infiltrates in patients with T1D onset. This would suggest a critical role for NK cells in T1D development linked to viral infection and the importance of the folate pathway in maintaining proper NK response.

Epigenetics in type 1 diabetes: TNFa gene promoter methylation status in Chilean patients with type 1 diabetes mellitus

TNF-α is a pro-inflammatory cytokine that is involved in type 1 diabetes (T1D) pathogenesis. The TNFa gene is subject of epigenetic regulation in which folate and homocysteine are important molecules because they participate in the methionine cycle where the most important methyl group donor (S-adenosylmethionine) is formed. We investigated whether TNFa gene promoter methylation status in T1D patients was related to blood folate, homocysteine and TNF-α in a transversal case-control study. We studied T1D patients (n 25, mean=13·7 years) and healthy control subjects (n 25, mean=31·1 years), without T1D and/or other autoimmune diseases or direct family history of these diseases. A blood sample was obtained for determination of serum folate, plasma homocysteine and TNF-α concentrations. Whole blood was used for the extraction of DNA to determine the percentage of methylation by real-time PCR and melting-curve analysis. Results are expressed as means and standard deviations for parametric variables and as median (interquartile range) for non-parametric variables. T1D patients showed a higher TNFa gene promoter methylation (39·2 (sd 19·5) %) when compared with control subjects (25·4 (sd 13·7) %) (P=0·008). TNFa gene promoter methylation was positively associated only with homocysteine levels in T1D patients (r 0·55, P=0·007), but not in control subjects (r -0·122, P=0·872). To our knowledge, this is the first work that reports the methylation status of the TNFa gene promoter and its relationship with homocysteine metabolism in Chilean T1D patients without disease complications.

Remodelling of the hepatic epigenetic landscape of glucose-intolerant rainbow trout (Oncorhynchus mykiss) by nutritional status and dietary carbohydrates

The rainbow trout, a carnivorous fish, displays a 'glucose-intolerant' phenotype revealed by persistent hyperglycaemia when fed a high carbohydrate diet (HighCHO). Epigenetics refers to heritable changes in gene activity and is closely related to environmental changes and thus to metabolism adjustments governed by nutrition. In this study we first assessed in the trout liver whether and how nutritional status affects global epigenome modifications by targeting DNA methylation and histone marks previously reported to be affected in metabolic diseases. We then examined whether dietary carbohydrates could affect the epigenetic landscape of duplicated gluconeogenic genes previously reported to display changes in mRNA levels in trout fed a high carbohydrate diet. We specifically highlighted global hypomethylation of DNA and hypoacetylation of H3K9 in trout fed a HighCHO diet, a well-described phenotype in diabetes. g6pcb2 ohnologs were also hypomethylated at specific CpG sites in these animals according to their up-regulation. Our findings demonstrated that the hepatic epigenetic landscape can be affected by both nutritional status and dietary carbohydrates in trout. The mechanism underlying the setting up of these epigenetic modifications has now to be explored in order to improve understanding of its impact on the glucose intolerant phenotype in carnivorous teleosts.

Contribution of epigenetics in diabetic retinopathy

Diabetes has become the epidemic of the 21st century, and with over 90% patients with diabetes becoming at a risk of developing retinopathy, diabetic retinopathy has emerged as a major public health concern. In spite of cutting edge research in the field, how retina and its vasculature are damaged by the diabetic milieu remains ambiguous. The environmental factors, life style or disease process can also bring in modifications in the DNA, and these epigenetic modifications either silence or activate a gene without altering the DNA sequence. Diabetic environment up- or downregulates a number of genes in the retina, and emerging research has shown that it also facilitates epigenetic modifications. In the pathogenesis of diabetic retinopathy, the genes associated with important enzymes (e.g., mitochondrial superoxide dismutase, matrix metalloproteinase-9 and thioredoxin interacting protein) and transcriptional factors are epigenetically modified, the enzymes responsible for these epigenetic modifications are either activated or inhibited, and the levels of microRNAs are altered. With epigenetic modifications taking an important place in diabetic retinopathy, it is now becoming critical to evaluate these modifications, and understand their impact on this slow progressing blinding disease.

Skewed Epigenetics: An Alternative Therapeutic Option for Diabetes Complications

Vascular complications are major causes of morbidity and mortality in type 2 diabetes patients. Mitochondrial reactive oxygen species (ROS) generation and a lack of efficient antioxidant machinery, a result of hyperglycaemia, mainly contribute to this problem. Although advances in therapy have significantly reduced both morbidity and mortality in diabetic individuals, diabetes-associated vascular complications are still one of the most challenging health problems worldwide. New healing options are urgently needed as current therapeutics are failing to improve long-term outcomes. Particular effort has recently been devoted to understanding the functional relationship between chromatin structure regulation and the persistent change in gene expression which is driven by hyperglycaemia and which accounts for long-lasting diabetic complications. A detailed investigation into epigenetic chromatin modifications in type 2 diabetes is underway. This will be particularly useful in the design of mechanism-based therapeutics which interfere with long-lasting activating epigenetics and improve patient outcomes. We herein provide an overview of the most relevant mechanisms that account for hyperglycaemia-induced changes in chromatin structure; the most relevant mechanism is called "metabolic memory."

Parp inhibition prevents ten-eleven translocase enzyme activation and hyperglycemia-induced DNA demethylation

Studies from human cells, rats, and zebrafish have documented that hyperglycemia (HG) induces the demethylation of specific cytosines throughout the genome. We previously documented that a subset of these changes become permanent and may provide, in part, a mechanism for the persistence of complications referred to as the metabolic memory phenomenon. In this report, we present studies aimed at elucidating the molecular machinery that is responsible for the HG-induced DNA demethylation observed. To this end, RNA expression and enzymatic activity assays indicate that the ten-eleven translocation (Tet) family of enzymes are activated by HG. Furthermore, through the detection of intermediates generated via conversion of 5-methyl-cytosine back to the unmethylated form, the data were consistent with the use of the Tet-dependent iterative oxidation pathway. In addition, evidence is provided that the activity of the poly(ADP-ribose) polymerase (Parp) enzyme is required for activation of Tet activity because the use of a Parp inhibitor prevented demethylation of specific loci and the accumulation of Tet-induced intermediates. Remarkably, this inhibition was accompanied by a complete restoration of the tissue regeneration deficit that is also induced by HG. The ultimate goal of this work is to provide potential new avenues for therapeutic discovery.

Role of epigenetic mechanisms in the development of chronic complications of diabetes

There is growing evidence that epigenetic regulation of gene expression including post-translational histone modifications (PTHMs), DNA methylation and microRNA (miRNA)-regulation of mRNA translation could play a crucial role in the development of chronic, diabetic complications. Hyperglycemia can induce an abnormal action of PTHMs and DNA methyltransferases as well as alter the levels of numerous miRNAs in endothelial cells, vascular smooth muscle cells, cardiomyocytes, retina, and renal cells. These epigenetic abnormalities result in changes in the expression of numerous genes contributing to effects such as development of chronic inflammation, impaired clearance of reactive oxygen species (ROS), endothelial cell dysfunction and/or the accumulation of extracellular matrix in the kidney, which causing the development of retinopathy, nephropathy or cardiomyopathy. Some epigenetic modifications, for example PTHMs and DNA methylation, become irreversible over time. Therefore, these processes have gained much attention in explaining the long-lasting detrimental consequences of hyperglycaemia causing the development of chronic complications even after improved glycaemic control is achieved. Our review suggests that the treatment of chronic complications should focus on erasing metabolic memory by targeting chromatin modification enzymes and by restoring miRNA levels.

Epigenetics in adipose tissue, obesity, weight loss, and diabetes

Given the role that diet and other environmental factors play in the development of obesity and type 2 diabetes, the implication of different epigenetic processes is being investigated. Although it is well known that external factors can cause cell type-dependent epigenetic changes, including DNA methylation, histone tail modifications, and chromatin remodeling, the regulation of these processes, the magnitude of the changes and the cell types in which they occur, the individuals more predisposed, and the more crucial stages of life remain to be elucidated. There is evidence that obese and diabetic people have a pattern of epigenetic marks different from nonobese and nondiabetic individuals. The main long-term goals in this field are the identification and understanding of the role of epigenetic marks that could be used as early predictors of metabolic risk and the development of drugs or diet-related treatments able to delay these epigenetic changes and even reverse them. But weight gain and insulin resistance/diabetes are influenced not only by epigenetic factors; different epigenetic biomarkers have also been identified as early predictors of weight loss and the maintenance of body weight after weight loss. The characterization of all the factors that are able to modify the epigenetic signatures and the determination of their real importance are hindered by the following factors: the magnitude of change produced by dietary and environmental factors is small and cumulative; there are great differences among cell types; and there are many factors involved, including age, with multiple interactions between them.

Genetic and epigenetic factors in etiology of diabetes mellitus type 1

Diabetes mellitus type 1 (T1D) is a complex disease resulting from the interplay of genetic, epigenetic, and environmental factors. Recent progress in understanding the genetic basis of T1D has resulted in an increased recognition of childhood diabetes heterogeneity. After the initial success of family-based linkage analyses, which uncovered the strong linkage and association between HLA gene variants and T1D, genome-wide association studies performed with high-density single-nucleotide polymorphism genotyping platforms provided evidence for a number of novel loci, although fine mapping and characterization of these new regions remains to be performed. T1D is one of the most heritable common diseases, and among autoimmune diseases it has the largest range of concordance rates in monozygotic twins. This fact, coupled with evidence of various epigenetic modifications of gene expression, provides convincing proof of the complex interplay between genetic and environmental factors. In T1D, epigenetic phenomena, such as DNA methylation, histone modifications, and microRNA dysregulation, have been associated with altered gene expression. Increasing epidemiologic and experimental evidence supports the role of genetic and epigenetic alterations in the etiopathology of diabetes. We discuss recent results related to the role of genetic and epigenetic factors involved in development of T1D.

Epigenetic modifications and diabetic retinopathy

Diabetic retinopathy remains one of the most debilitating chronic complications, but despite extensive research in the field, the exact mechanism(s) responsible for how retina is damaged in diabetes remains ambiguous. Many metabolic pathways have been implicated in its development, and genes associated with these pathways are altered. Diabetic environment also facilitates epigenetics modifications, which can alter the gene expression without permanent changes in DNA sequence. The role of epigenetics in diabetic retinopathy is now an emerging area, and recent work has shown that genes encoding mitochondrial superoxide dismutase (Sod2) and matrix metalloproteinase-9 (MMP-9) are epigenetically modified, activates of epigenetic modification enzymes, histone lysine demethylase 1 (LSD1), and DNA methyltransferase are increased, and the micro RNAs responsible for regulating nuclear transcriptional factor and VEGF are upregulated. With the growing evidence of epigenetic modifications in diabetic retinopathy, better understanding of these modifications has potential to identify novel targets to inhibit this devastating disease. Fortunately, the inhibitors and mimics targeted towards histone modification, DNA methylation, and miRNAs are now being tried for cancer and other chronic diseases, and better understanding of the role of epigenetics in diabetic retinopathy will open the door for their possible use in combating this blinding disease.

Hepatic DNA methylation modifications in early development of rats resulting from perinatal BPA exposure contribute to insulin resistance in adulthood

AIMS/HYPOTHESIS

Perinatal exposure to bisphenol A (BPA), a widely distributed environmental endocrine disruptor, is associated with insulin resistance and diabetes in offspring. The underlying molecular mechanisms could involve epigenetics, as adverse effects induced by environmental exposure in early life are suggested through DNA methylation. In this study we sought to elucidate the relationship between perinatal BPA exposure and alteration of hepatic DNA methylation.

METHODS

Pregnant Wistar rats were administered BPA (50 μg/kg/day) or corn oil by oral gavage throughout gestation and lactation. Variables associated with insulin resistance and hepatic DNA methylation were examined at postnatal week 3 and week 21 in male offspring.

RESULTS

In BPA-treated offspring, serum insulin and HOMA-insulin resistance were increased, and the insulin sensitivity index and hepatic glycogen storage were decreased compared with controls at week 21. At week 3, none of these variables were significantly changed. However, hepatic global DNA methylation was decreased, accompanied by overexpression of DNA methyltransferase 3B mRNA at week 3. Meanwhile, perinatal exposure to BPA induced promoter hypermethylation and a reduction in gene expression of hepatic glucokinase. Moreover, increased promoter hypermethylation of Gck became more pronounced in BPA-treated offspring at week 21.

CONCLUSIONS/INTERPRETATION

Abnormal DNA methylation in hepatic tissue precedes development of insulin resistance induced by perinatal BPA exposure. These findings support the potential role of epigenetics in fetal reprogramming by BPA-induced metabolic disorders.

Exercise prevents hyperhomocysteinemia in a dietary folate-restricted mouse model

Hyperhomocysteinemia is a condition that results from altered methyl group metabolism and is associated with numerous pathological conditions. A number of nutritional and hormonal factors have been shown to influence circulating homocysteine concentrations; however, the impact of exercise on homocysteine and methyl group balance is not well understood. Our hypothesis was that exercise represents an effective means to prevent hyperhomocysteinemia in a folate-independent manner. The purpose of this study was to determine the influence of exercise on homocysteine metabolism in a dietary folate-restricted mouse model characterized by moderate hyperhomocysteinemia. Female outbred mice (12 weeks old) were assigned to either a sedentary or free-access wheel exercise group. Following a 4-week acclimation period, half of the mice in each group were provided a folate-restricted diet for 7-weeks prior to euthanasia and tissue collection. As expected, folate-restricted sedentary mice exhibited a 2-fold increase in plasma total homocysteine concentrations; however, exercise completely prevented the increase in circulating homocysteine concentrations. Moreover, exercise reduced plasma homocysteine concentrations 36% within the group fed only the control diet. The prevention of hyperhomocysteinemia by exercise appears, at least in part, to be the result of increased folate-independent homocysteine remethylation owing to a 2-fold increase in renal betaine homocysteine S-methyltransferase. To our knowledge, this is the first report demonstrating the prevention of hyperhomocysteinemia by exercise in a dietary folate-restriction model. Future research will be directed at determining if exercise can have a positive impact on other nutritional, hormonal, and genetic models of hyperhomocysteinemia relevant to humans.

Hepatic methionine homeostasis is conserved in C57BL/6N mice on high-fat diet despite major changes in hepatic one-carbon metabolism

Obesity is an underlying risk factor in the development of cardiovascular disease, dyslipidemia and non-alcoholic fatty liver disease (NAFLD). Increased hepatic lipid accumulation is a hallmark in the progression of NAFLD and impairments in liver phosphatidylcholine (PC) metabolism may be central to the pathogenesis. Hepatic PC biosynthesis, which is linked to the one-carbon (C1) metabolism by phosphatidylethanolamine N-methyltransferase, is known to be important for hepatic lipid export by VLDL particles. Here, we assessed the influence of a high-fat (HF) diet and NAFLD status in mice on hepatic methyl-group expenditure and C1-metabolism by analyzing changes in gene expression, protein levels, metabolite concentrations, and nuclear epigenetic processes. In livers from HF diet induced obese mice a significant downregulation of cystathionine β-synthase (CBS) and an increased betaine-homocysteine methyltransferase (BHMT) expression were observed. Experiments in vitro, using hepatoma cells stimulated with peroxisome proliferator activated receptor alpha (PPARα) agonist WY14,643, revealed a significantly reduced Cbs mRNA expression. Moreover, metabolite measurements identified decreased hepatic cystathionine and L-α-amino-n-butyrate concentrations as part of the transsulfuration pathway and reduced hepatic betaine concentrations, but no metabolite changes in the methionine cycle in HF diet fed mice compared to controls. Furthermore, we detected diminished hepatic gene expression of de novo DNA methyltransferase 3b but no effects on hepatic global genomic DNA methylation or hepatic DNA methylation in the Cbs promoter region upon HF diet. Our data suggest that HF diet induces a PPARα-mediated downregulation of key enzymes in the hepatic transsulfuration pathway and upregulates BHMT expression in mice to accommodate to enhanced dietary fat processing while preserving the essential amino acid methionine.

Germ cell abnormalities in streptozotocin induced diabetic mice do not correlate with blood glucose level

PURPOSE

To assess the effect of streptozotocin induced hyperglycemia on germ cell integrity, DNA ploidy and methylation status for a period of two spermatogenesis cycles in adult male Swiss albino mice.

METHODS

Streptozotocin injected mice were monitored for hyperglycemia at a regular interval for a period of 36 and 72 days. The DNA integrity in epididymal spermatozoa was determined by the comet assay. Flow cytometric analysis was done in germ cells to assess the DNA ploidy. The global methylation analysis in germ cells was done by 5-methyl cytosine immunostaining.

RESULTS

Streptozotocin administration successfully resulted in hyperglycemic response which significantly affected serum testosterone level, sperm DNA integrity and DNA ploidy at the end of 36 days. However, no changes were observed in either epididymal sperm concentration or germ cell methylation status. In contrast, at the end of 76 days, although serum testosterone level, sperm DNA integrity and DNA ploidy status were unperturbed significantly in hyperglycemic group, the epididymal sperm concentration and methylation status of preleptotene/zygotene cells were significantly altered. Importantly, an attempt to find out the association between the blood glucose levels and the abnormalities in hyperglycemic group failed to demonstrate any correlation.

CONCLUSIONS

The germ cell abnormalities observed in hyperglycemic group could be interpreted as a primary effect of streptozotocin and not due to hyperglycemia. Our results call for further evaluation of streptozotocin before its application to study the hyperglycemic responses on male germ cells.

Metabolic memory and chronic diabetes complications: potential role for epigenetic mechanisms

Recent estimates indicate that diabetes mellitus currently affects more than 10 % of the world's population. Evidence from both the laboratory and large scale clinical trials has revealed that prolonged hyperglycemia induces chronic complications which persist and progress unimpeded even when glycemic control is pharmaceutically achieved via the phenomenon of metabolic memory. The epigenome is comprised of all chromatin modifications including post translational histone modification, expression control via miRNAs and the methylation of cytosine within DNA. Modifications of these epigenetic marks not only allow cells and organisms to quickly respond to changing environmental stimuli but also confer the ability of the cell to "memorize" these encounters. As such, these processes have gained much attention as potential molecular mechanisms underlying metabolic memory and chronic diabetic complications. Here we present a review of the very recent literature published pertaining to this subject.

Epigenetic modifications and diabetic nephropathy

Diabetic nephropathy (DN) is a major complication associated with both type 1 and type 2 diabetes, and a leading cause of end-stage renal disease. Conventional therapeutic strategies are not fully efficacious in the treatment of DN, suggesting an incomplete understanding of the gene regulation mechanisms involved in its pathogenesis. Furthermore, evidence from clinical trials has demonstrated a "metabolic memory" of prior exposure to hyperglycemia that continues to persist despite subsequent glycemic control. This remains a major challenge in the treatment of DN and other vascular complications. Epigenetic mechanisms such as DNA methylation, nucleosomal histone modifications, and noncoding RNAs control gene expression through regulation of chromatin structure and function and post-transcriptional mechanisms without altering the underlying DNA sequence. Emerging evidence indicates that multiple factors involved in the etiology of diabetes can alter epigenetic mechanisms and regulate the susceptibility to diabetes complications. Recent studies have demonstrated the involvement of histone lysine methylation in the regulation of key fibrotic and inflammatory genes related to diabetes complications including DN. Interestingly, histone lysine methylation persisted in vascular cells even after withdrawal from the diabetic milieu, demonstrating a potential role of epigenetic modifications in metabolic memory. Rapid advances in high-throughput technologies in the fields of genomics and epigenomics can lead to the identification of genome-wide alterations in key epigenetic modifications in vascular and renal cells in diabetes. Altogether, these findings can lead to the identification of potential predictive biomarkers and development of novel epigenetic therapies for diabetes and its associated complications.

Metabonomic analysis of the therapeutic effect of Zhibai Dihuang Pill in treatment of streptozotocin-induced diabetic nephropathy

ETHNOPHARMACOLOGICAL RELEVANCE

Zhibai Dihuang Pill (ZDP) is one of ancient traditional Chinese medicines (TCMs), which is usually used for the treatment of kidney deficiency for thousands of years in China.

AIM OF THE STUDY

Traditional Chinese medicines (TCMs) usually operate in vivo through multi-components, multi-ways and multi-targets. However, the molecular mechanisms of TCMs remain unclear. In the present work, nuclear magnetic resonance (NMR)-based metabonomic analysis was used to evaluate the therapeutic effect of Zhibai Dihuang Pill (ZDP) on diabetic nephropathy (DN) rats induced by streptozotocin and to address the underlying molecular mechanism.

MATERIALS AND METHODS

Male rats were divided into three groups: control, DN and ZDP-treated DN (ZDP-DN), respectively. Based on (1)H NMR spectra of sera, urine and kidney extracts from the rats, principle component analysis (PCA) was performed to identify different metabolic profiles. Kidney portions and serum and urine samples were also subjected to histopathological or biochemical examination.

RESULTS

PCA scores plots demonstrate that the cluster of DN rats is separated from that of control rats, while some of ZDP-DN rats are located close to control rats, indicating that metabolic profiles of these ZDP-DN rats are restored toward those of control rats. Our results illustrate that ZDP treatment could lower the levels of lipids and 3-hydrobutyrate, and raise the level of lactate in sera of DN rats. Moreover, ZDP treatment could also reduce the levels of glucose, 3-hydrobutyrate and lactate, enhance the level of betaine in kidney tissues.

CONCLUSION

Our study indicates that ZDP treatment can ameliorate DN symptoms by intervening in some dominating metabolic pathways, such as inhibiting glucose and lipid metabolism, enhancing methylamine metabolism. Our work may be of benefit to both evaluation of the therapeutic effect of TCM and elucidation of the underlying molecular mechanism.

Polyploidy and chromatin remodeling in hepatocytes from insulin-dependent diabetic and normoglycemic aged mice

Changes in polyploidization, chromatin supraorganization, and chromatin accessibility were investigated in hepatocytes collected from adult, nonobese diabetic (NOD) mice with increasing hyperglycemia and compared with adult normoglycemic controls and 56-week-old normoglycemic BALB/c mice. Our goal was to determine the changes in ploidy degrees and chromatin characteristics in mouse hepatocytes that are associated with insulin-dependent diabetes and to detect similarities in these aspects with those verified with aging, with greater accuracy than previous studies. Image analysis of Feulgen-stained nuclei revealed changes in ploidy degrees and chromatin supraorganization. Chromatin accessibility was assessed with micrococcal nuclease (MNase) digestion. Increased polyploidy was associated with increasing levels of glycemia, and this trend toward polyploidy was found even under normoglycemic conditions in NOD mice. Although high degrees of ploidy were also detected in aged BALB/c mice, the magnitude of polyploidy was not the same magnitude as that in the diabetic mice. While there was increased homogeneity of chromatin packaging with increasing polyploidy under conditions of severe hyperglycemia (and even under conditions of normoglycemia) in NOD mice, an inverse relationship was observed in aged BALB/c mice. Chromatin accessibility to MNase increased under severe hyperglycemia and advanced age, but it was much higher in the diabetic mice. In conclusion, although similarities in polyploidy were observed between the hepatocytes from increasingly hyperglycemic adult mice and those from normoglycemic aged mice, the relationship between chromatin remodeling and increases in ploidy degrees was not the same between the hepatocytes of these two groups. These findings demonstrate that strict similarities between diabetes and aging are not always true at the cellular level. This discordance is likely due to differences in the metabolic state of mouse hepatocytes during aging and diabetic conditions consequent to specificities in their gene regulatory programs.

Mitochondria DNA replication and DNA methylation in the metabolic memory associated with continued progression of diabetic retinopathy

PURPOSE

Diabetic retinopathy fails to halt after cessation of hyperglycemic insult, and a vicious cycle of mitochondria damage continues. The aim of our study was to investigate the effect of termination of hyperglycemia on retinal mtDNA replication, and elucidate the mechanism responsible for the continued mtDNA damage.

METHODS

Polymerase gamma 1 (POLG1), the catalytic subunit of the mitochondrial DNA replication enzyme, and the damage to the displacement loop region of mtDNA (D-loop) were analyzed in the retina from streptozotocin-diabetic rats maintained in poor glycemic control (PC, glycated hemoglobin ∼11%) or in good glycemic control (GC, glycated hemoglobin ∼6%) for 6 months, or in PC for three months followed by GC for three months (Rev). To understand the mechanism DNA methylation status of POLG1 promoter was investigated by methylation-specific PCR. The key parameters were confirmed in the isolated retinal endothelial cells exposed to high glucose, followed by normal glucose.

RESULTS

POLG1 continued to be down-regulated, the D-loop region damaged, and the CpG islands at the regulatory region of POLG hyper-methylated even after three months of GC that had followed three months of PC (Rev group). Similar results were observed in the retinal endothelial cells exposed to normal glucose after being exposed to high glucose.

CONCLUSIONS

Continued hypermethylation of the CpG sites at the regulatory region of POLG affects its binding to the mtDNA, compromising the transcriptional activity. Modulation of DNA methylation using pharmaceutic or molecular means could help maintain mitochondria homeostasis, and prevent further progression of diabetic retinopathy.

Methionine restriction affects the phenotypic and transcriptional response of rainbow trout (Oncorhynchus mykiss) to carbohydrate-enriched diets

Mammalian studies report that methionine restriction (MR) as a dietary regimen extends life span, delays the onset of age-related diseases and enhances fat oxidation in obese subjects with metabolic syndromes. However, the underlying cellular signalling pathways are poorly understood. Rainbow trout (Oncorhynchus mykiss) is a glucose-intolerant species, providing an excellent model for the study of carbohydrate metabolism. MR diets in combination with 12 % (+/-) and 22 % (+/-) carbohydrate-rich meals were fed to rainbow trout for a period of 8 weeks and phenotypic and transcript expression changes in the liver and white muscle were assessed. Fish fed MR diets, irrespective of carbohydrate load, were shown to abolish the glucose-intolerant phenotype 6 h post-feeding. There was a distinct switch in glucose and glycogen content in the liver of fish fed MR diets, with a significantly higher concentration of glycogen, suggesting reduced glycolytic capacity. Transcriptional responses to MR demonstrated decreased expression of hepatic fatty acid synthase, sterol regulatory binding protein 1, PPARγ coactivator 1-α and PPARα, indicative of a reduction in the de novo synthesis of fatty acids and cholesterol, and a potential decrease in hepatic fat oxidative capacity. Muscle adenylate charge was depressed under MR, and increased expression of AMP-activated protein kinase α1 was detected, indicative of reduced energy availability. Total DNA methylation showed that carbohydrate load, rather than MR, dictated hypomethylation of genomic DNA. This is the first study which demonstrates that MR can abolish a glucose-intolerant phenotype in trout, and identifies trout as a suitable model for studying metabolic syndromes.

Heritable transmission of diabetic metabolic memory in zebrafish correlates with DNA hypomethylation and aberrant gene expression

Metabolic memory (MM) is the phenomenon whereby diabetes complications persist and progress after glycemic recovery is achieved. Here, we present data showing that MM is heritable and that the transmission correlates with hyperglycemia-induced DNA hypomethylation and aberrant gene expression. Streptozocin was used to induce hyperglycemia in adult zebrafish, and then, following streptozocin withdrawal, a recovery phase was allowed to reestablish a euglycemic state. Blood glucose and serum insulin returned to physiological levels during the first 2 weeks of the recovery phase as a result of pancreatic β-cell regeneration. In contrast, caudal fin regeneration and skin wound healing remained impaired to the same extent as in diabetic fish, and this impairment was transmissible to daughter cell tissue. Daughter tissue that was never exposed to hyperglycemia, but was derived from tissue that was, did not accumulate AGEs or exhibit increased levels of oxidative stress. However, CpG island methylation and genome-wide microarray expression analyses revealed the persistence of hyperglycemia-induced global DNA hypomethylation that correlated with aberrant gene expression for a subset of loci in this daughter tissue. Collectively, the data presented here implicate the epigenetic mechanism of DNA methylation as a potential contributor to the MM phenomenon.

Tissue-specific alterations of methyl group metabolism with DNA hypermethylation in the Zucker (type 2) diabetic fatty rat

BACKGROUND

Altered methyl group and homocysteine metabolism were tissue-specific, persistent, and preceded hepatic DNA hypomethylation in type 1 diabetic rats. Similar metabolic perturbations have been shown in the Zucker (type 2) diabetic fatty (ZDF) rat in the pre-diabetic and early diabetic stages, but tissue specificity and potential impact on epigenetic marks are unknown, particularly during pathogenesis.

METHODS

ZDF (fa/fa) and lean (+/?) control rats were killed at 12 and 21 weeks of age, representing early and advanced diabetic conditions. Blood and tissues were analysed with respect to methyl group and homocysteine metabolism, including DNA methylation.

RESULTS

At 12 weeks, hepatic glycine N-methyltransferase (GNMT), methionine synthase, and cystathionine β-synthase (CBS) activity and/or abundance were increased in ZDF rats. At 21 weeks, GNMT activity was increased in liver and kidney; however, only hepatic CBS protein abundance (12 weeks) and betaine-homocysteine S-methyltransferase mRNA expression (21 weeks) were significantly elevated (78 and 100%, respectively). Hepatic phosphatidylethanolamine N-methyltransferase expression was also elevated in the ZDF rat. Homocysteine concentrations were decreased in plasma and kidney, but not in liver, at 12 and 21 weeks. In contrast to hepatic DNA hypomethylation in the type 1 diabetic rat, genomic DNA was hypermethylated at 12 and 21 weeks in the liver of ZDF rats, concomitant with an increase in DNA methyltransferase 1 expression at 21 weeks.

CONCLUSIONS

The pathogenesis of type 2 diabetes in the ZDF rat was associated with tissue and disease stage-specific aberrations of methyl group and homocysteine metabolism, with persistent hepatic global DNA hypermethylation.

Insulin administration abrogates perturbation of methyl group and homocysteine metabolism in streptozotocin-treated type 1 diabetic rats

Modifications in methyl group and homocysteine metabolism are associated with a number of pathologies, including vascular disease, cancer, and neural tube defects. A diabetic state is known to alter both methyl group and homocysteine metabolism, and glycine N-methyltransferase (GNMT) is a major regulatory protein that controls the supply and utilization of methyl groups. We have shown previously that diabetes induces GNMT expression and reduces plasma homocysteine pools by stimulating both its catabolism and folate-independent remethylation. This study was conducted to determine whether insulin plays a role in the control of homocysteine concentrations and GNMT as well as other key regulatory proteins. Male Sprague-Dawley rats were randomly assigned to one of three groups: control, streptozotocin (STZ)-induced diabetic (60 mg/kg body wt), and insulin-treated diabetic (1.0 U bid). After 5 days, rats were anesthetized (ketamine-xylazine) for procurement of blood and tissues. A 1.5-fold elevation in hepatic GNMT activity and hypohomocysteinemia in diabetic rats was completely prevented by insulin treatment. Additionally, diabetes-mediated alterations in methionine synthase, phosphatidylethanolamine N-methyltransferase, and DNA methylation were also prevented by insulin. We hypothesize that the concentration of blood glucose may represent a regulatory signal to modify GNMT and homocysteine. In support of this, blood glucose concentrations were negatively correlated with total plasma homocysteine (r = -0.75, P < 0.001) and positively correlated with GNMT activity (r = 0.77, P < 0.001). Future research will focus on further elucidating the role of glucose or insulin as a signal for regulating homocysteine and methyl group metabolism.

Epigenetics: deciphering its role in diabetes and its chronic complications

1. Increasing evidence suggests that epigenetic factors might regulate the complex interplay between genes and the environment, and affect human diseases, such as diabetes and its complications. 2. Clinical trials have underscored the long lasting beneficial effects of strict glycaemic control for reducing the progression of diabetic complications. They have also shown that diabetic complications, such as diabetic nephropathy, a chronic kidney disorder, can continue even after blood glucose normalization, suggesting a metabolic memory of the prior glycaemic state. 3. Dysregulation of epigenetic post-transcriptional modifications of histones in chromatin, including histone lysine methylation, has been implicated in aberrant gene regulation associated with the pathology of diabetes and its complications. Genome-wide studies have shown cell-type specific changes in histone methylation patterns under diabetic conditions. In addition, studies in vascular cells have shown long lasting changes in epigenetic modifications at key inflammatory gene promoters after prior exposure to diabetic conditions, suggesting a possible mechanism for metabolic memory. 4. Recent studies have shown roles for histone methylation, DNA methylation, as well as microRNA in diabetic nephropathy. Whether these epigenetic factors play a role in metabolic memory of diabetic kidney disease is less well understood. 5. The incidence of diabetes is growing rapidly, as also the cost of treating the resulting complications. A better understanding of metabolic memory and the potential involvement of epigenetic mechanisms in this phenomenon could enable the development of new therapeutic targets for the treatment and/or prevention of sustained diabetic complications.

Prenatal origin of obesity and their complications: Gestational diabetes, maternal overweight and the paradoxical effects of fetal growth restriction and macrosomia

Pregestational (PGDM) and gestational (GDM) diabetes may be associated with a variety of fetal effects including increased rate of spontaneous abortions, intrauterine fetal death, congenital anomalies, neurodevelopmental problems and increased risk of perinatal complications. Additional problems of concern are fetal growth disturbances causing increased or decreased birth weight. Optimal control of maternal blood glucose is known to reduce these changes. Among the long lasting effects of these phenomena are a high rate of overweight and obesity at childhood and a high tendency to develop the "metabolic syndrome" characterized by hypertension, cardio-vascular complications and type 2 diabetes. Similarly, maternal overweight and obesity during pregnancy or excessive weight gain are also associated with increased obesity and complications in the offspring. Although there are different causes for fetal growth restriction (FGR) or for fetal excessive growth (macrosomis), paradoxically both are associated with the "metabolic syndrome" and its long term consequences. The exact mechanism(s) underlying these long term effects on growth are not fully elucidated, but they involve insulin resistance, fetal hyperleptinemia, hypothalamic changes and most probably epigenetic changes. Preventive measures to avoid the metabolic syndrome and its complications seem to be a tight dietary control and physical activity in the children born to obese or diabetic mothers or who had antenatal growth disturbances for other known or unknown reasons.

Epigenetic mechanisms in diabetic vascular complications

There has been a rapid increase in the incidence of diabetes as well the associated vascular complications. Both genetic and environmental factors have been implicated in these pathologies. Increasing evidence suggests that epigenetic factors play a key role in the complex interplay between genes and the environment. Actions of major pathological mediators of diabetes and its complications such as hyperglycaemia, oxidant stress, and inflammatory factors can lead to dysregulated epigenetic mechanisms that affect chromatin structure and gene expression. Furthermore, persistence of this altered state of the epigenome may be the underlying mechanism contributing to a 'metabolic memory' that results in chronic inflammation and vascular dysfunction in diabetes even after achieving glycaemic control. Further examination of epigenetic mechanisms by also taking advantage of recently developed next-generation sequencing technologies can provide novel insights into the pathology of diabetes and its complications and lead to the discovery of much needed new drug targets for these diseases. In this review, we highlight the role of epigenetics in diabetes and its vascular complications, and recent technological advances that have significantly accelerated the field.