Effects of hyperglycemia and aging on nuclear sirtuins and DNA damage of mouse hepatocytes

Unraveling the multifaceted role of SIRT7 and its therapeutic potential in human diseases

Sirtuins, as NAD+-dependent deacetylases, are widely found in eubacteria, archaea, and eukaryotes, and they play key roles in regulating cellular functions. Among these, SIRT7 stands out as a member discovered relatively late and studied less extensively. It is localized within the nucleus and displays enzymatic activity as an NAD+-dependent deacetylase, targeting a diverse array of acyl groups. The role of SIRT7 in important cellular processes like gene transcription, cellular metabolism, cellular stress responses, and DNA damage repair has been documented in a number of studies conducted recently. These studies have also highlighted SIRT7's strong correlation with human diseases like aging, cancer, neurological disorders, and cardiovascular diseases. In addition, a variety of inhibitors against SIRT7 have been reported, indicating that targeting SIRT7 may be a promising strategy for inhibiting tumor growth. The purpose of this review is to thoroughly look into the structure and function of SIRT7 and to explore its potential value in clinical applications, offering an essential reference for research in related domains.

SIRT7: the seventh key to unlocking the mystery of aging

Aging is a chronic yet natural physiological decline of the body. Throughout life, humans are continuously exposed to a variety of exogenous and endogenous stresses, which engender various counteractive responses at the cellular, tissue, organ, as well as organismal levels. The compromised cellular and tissue functions that occur because of genetic factors or prolonged stress (or even the stress response) may accelerate aging. Over the last two decades, the sirtuin (SIRT) family of lysine deacylases has emerged as a key regulator of longevity in a variety of organisms. SIRT7, the most recently identified member of the SIRTs, maintains physiological homeostasis and provides protection against aging by functioning as a watchdog of genomic integrity, a dynamic sensor and modulator of stresses. SIRT7 decline disrupts metabolic homeostasis, accelerates aging, and increases the risk of age-related pathologies including cardiovascular and neurodegenerative diseases, pulmonary and renal disorders, inflammatory diseases, and cancer, etc. Here, we present SIRT7 as the seventh key to unlock the mystery of aging, and its specific manipulation holds great potential to ensure healthiness and longevity.

Epigenetic aging of mammalian gametes

The process of aging refers to physiological changes that occur to an organism as time progresses and involves changes to DNA, proteins, metabolism, cells, and organs. Like the rest of the cells in the body, gametes age, and it is well established that there is a decline in reproductive capabilities in females and males with aging. One of the major pathways known to be involved in aging is epigenetic changes. The epigenome is the multitude of chemical modifications performed on DNA and chromatin that affect the ability of chromatin to be transcribed. In this review, we explore the effects of aging on female and male gametes with a focus on the epigenetic changes that occur in gametes throughout aging. Quality decline in oocytes occurs at a relatively early age. Epigenetic changes constitute an important part of oocyte aging. DNA methylation is reduced with age, along with reduced expression of DNA methyltransferases (DNMTs). Histone deacetylases (HDAC) expression is also reduced, and a loss of heterochromatin marks occurs with age. As a consequence of heterochromatin loss, retrotransposon expression is elevated, and aged oocytes suffer from DNA damage. In sperm, aging affects sperm number, motility and fecundity, and epigenetic changes may constitute a part of this process. 5 methyl-cytosine (5mC) methylation is elevated in sperm from aged men, but methylation on Long interspersed nuclear elements (LINE) elements is reduced. Di and trimethylation of histone 3 lysine 9 (H3K9me2/3) is reduced in sperm from aged men and trimethylation of histone 3 lysine 27 (H3K27me3) is elevated. The protamine makeup of sperm from aged men is also changed, with reduced protamine expression and a misbalanced ratio between protamine proteins protamine P1 and protamine P2. The study of epigenetic reproductive aging is recently gaining interest. The current status of the field suggests that many aspects of gamete epigenetic aging are still open for investigation. The clinical applications of these investigations have far-reaching consequences for fertility and sociological human behavior.

Thyroid hormone treatment counteracts cellular phenotypical remodeling in diabetic organs

Diabetes mellitus and alterations in thyroid hormone (TH) signaling are closely linked. Though the role of TH signaling in cell differentiation and growth is well known, it remains unclear whether its alterations contribute to the pathobiology of diabetic cells. Here, we aim to investigate whether the administration of exogenous T3 can counteract the cellular remodeling that occurs in diabetic cardiomyocytes, podocytes, and pancreatic beta cells. Treating diabetic rats with T3 prevents dedifferentiation, pathological growth, and ultrastructural alterations in podocytes and cardiomyocytes. In vitro, T3 reverses glucose-induced growth in human podocytes and cardiomyocytes, restores cardiomyocyte cytoarchitecture, and reverses pathological alterations in kidney and cardiac organoids. Finally, T3 treatment counteracts glucose-induced transdifferentiation, cell growth, and loss in pancreatic beta cells through TH receptor alpha1 activation. Our studies indicate that TH signaling activation substantially counteracts diabetes-induced pathological remodeling, and provide a potential therapeutic approach for the treatment of diabetes and its complications.

Magnesium and Liver Metabolism Through the Lifespan

Within the organism, the liver is the main organ responsible for metabolic homeostasis and xenobiotic transformation. To maintain an adequate liver weight-to-bodyweight ratio, this organ has an extraordinary regenerative capacity and is able to respond to an acute insult or partial hepatectomy. Maintenance of hepatic homeostasis is crucial for the proper functioning of the liver, and in this context, adequate nutrition with macro- and micronutrient intake is mandatory. Among all known macro-minerals, magnesium has a key role in energy metabolism and in metabolic and signaling pathways that maintain liver function and physiology throughout its life span. In the present review, the cation is reported as a potential key molecule during embryogenesis, liver regeneration, and aging. The exact role of the cation during liver formation and regeneration is not fully understood due to its unclear role in the activation and inhibition of those processes, and further research in a developmental context is needed. As individuals age, they may develop hypomagnesemia, a condition that aggravates the characteristic alterations. Additionally, risk of developing liver pathologies increases with age, and hypomagnesemia may be a contributing factor. Therefore, magnesium loss must be prevented by adequate intake of magnesium-rich foods such as seeds, nuts, spinach, or rice to prevent age-related hepatic alterations and contribute to the maintenance of hepatic homeostasis. Since magnesium-rich sources include a variety of foods, a varied and balanced diet can meet both macronutrient and micronutrient needs.

Sirtuin 7 serves as a promising therapeutic target for cardiorenal diseases

Cardiovascular disorders and associated renal diseases account for the main cause of morbidity and mortality worldwide, necessitating the development of novel effective approaches for the prevention and treatment of cardiorenal diseases. Mammalian sirtuins (SIRTs) function as nicotinamide adenine dinucleotide (NAD+)-dependent protein/histone deacetylases. Seven members of SIRTs share a highly invariant catalytic core domain responsible for the specific enzymatic activity. Intriguingly, the broad distribution of SIRTs and alternative isoforms implicate its distinct functions in diverse cardiac and renal cells and tissue types. Notably, SIRT7 has been shown to exert beneficial effects in cardiorenal physiology and pathophysiology via modulation of senescence, DNA damage repair, ribosomal RNA synthesis, protein biosynthesis, angiogenesis, apoptosis, superoxide generation, cardiorenal metabolism, and dysfunction. Furthermore, SIRT7 has emerged as a critical modulator of a broad range of cellular activities including oxidative stress, inflammation response, endoplasmic reticulum stress, and mitochondrial homeostasis, which are all of great significance in postponing the progression of cardiorenal diseases. More importantly, SIRT7 has been implicated in cardiorenal hypertrophy, fibrosis, remodeling, heart failure, atherosclerosis as well as renal acid-base and electrolyte homeostasis as an essential regulator. In this review, we focus on the involvement in cardiorenal physiology and pathophysiology, diverse actions and underlying mechanisms of the SIRT7 signaling, highlighting its updated research progress in heart failure, atherosclerosis, diabetic nephropathy and other cardiorenal diseases. Targeting SIRT7 signaling could be potentially exploited as a therapeutic strategy aiming to prevent and treat cardiorenal diseases.

New insight in molecular mechanisms regulating SIRT6 expression in diabetes: Hyperglycaemia effects on SIRT6 DNA methylation

Conflicting data are reported on the relationship between hyperglycaemia, diabetes and SIRT6 expression. To elucidate hyperglycaemia-induced molecular mechanisms regulating SIRT6 expression, the effect of hyperglycaemia on DNA methylation and SIRT6 expression has been evaluated in human aortic endothelial cells exposed to high glucose. DNA methylation of SIRT6 and any potential clinical implication was also evaluated in type 2 diabetic patients and compared with healthy controls. Endothelial cells exposed to high glucose showed lower methylation levels in SIRT6 promoter and increased SIRT6 and TET2 expression. The high glucose-induced epigenetic changes persisted after 48 h of glucose normalization. Diabetic patients showed lower levels of SIRT6 DNA methylation compared with nondiabetic patients. SIRT6 DNA methylation levels inversely correlated with plasma glucose. Our results firstly demonstrate the involvement of epigenetic mechanisms in regulating SIRT6 expression. Further experiments are necessary to clarify metabolic memory mechanisms driving to diabetic complications and how SIRT6 is potentially involved.

Association between SIRT6 Methylation and Human Longevity in a Chinese Population

BACKGROUND

Sirtuin 6 gene (SIRT6) is a longevity gene that is involved in a variety of metabolic pathways, but the relationship between SIRT6 methylation and longevity has not been clarified.

METHODS

We conducted a case-control study on 129 residents with a family history of longevity (1 of parents, themselves, or siblings aged ≥90 years) and 86 individuals without a family history of exceptional longevity to identify the association. DNA pyrosequencing was performed to analyze the methylation status of SIRT6 promoter CpG sites. qRT-PCR and ELISA were used to estimate the SIRT6 messenger RNA (mRNA) levels and protein content. Six CpG sites (P1-P6) were identified as methylation variable positions in the SIRT6 promoter region.

RESULTS

At the P2 and P5 CpG sites, the methylation rates of the longevity group were lower than those of the control group (p < 0.001 and p = 0.009), which might be independent determinants of longevity. The mRNA and protein levels of SIRT6 decreased in the control group (p < 0.0001 and p = 0.038). The mRNA level negatively correlated with the methylation rates at the P2 (rs = -0.173, p = 0.011) and P5 sites (rs = -0.207, p = 0.002). Furthermore, the protein content positively correlated with the methylation rate at the P5 site (rs = 0.136, p = 0.046) but showed no significant correlation with the methylation rate at the P2 site.

CONCLUSION

The low level of SIRT6 methylation may be a potential protective factor of Chinese longevity.

HDAC8 cooperates with SMAD3/4 complex to suppress SIRT7 and promote cell survival and migration

NAD⁺-dependent SIRT7 deacylase plays essential roles in ribosome biogenesis, stress response, genome integrity, metabolism and aging, while how it is transcriptionally regulated is still largely unclear. TGF-β signaling is highly conserved in multicellular organisms, regulating cell growth, cancer stemness, migration and invasion. Here, we demonstrate that histone deacetylase HDAC8 forms complex with SMAD3/4 heterotrimer and occupies SIRT7 promoter, wherein it deacetylates H4 and thus suppresses SIRT7 transcription. Treatment with HDAC8 inhibitor compromises TGF-β signaling via SIRT7-SMAD4 axis and consequently, inhibits lung metastasis and improves chemotherapy efficacy in breast cancer. Our data establish a regulatory feedback loop of TGF-β signaling, wherein HDAC8 as a novel cofactor of SMAD3/4 complex, transcriptionally suppresses SIRT7 via local chromatin remodeling and thus further activates TGF-β signaling. Targeting HDAC8 exhibits therapeutic potential for TGF-β signaling related diseases.

A phenolic glycoside from Moringa oleifera Lam. improves the carbohydrate and lipid metabolisms through AMPK in db/db mice

The increasing incidence of metabolic syndrome requires more functional food products with low cost and excellent effects to assist treatment. The crude extract of Moringa oleifera Lam. showed excellent hypoglycemic activity. The current study was designed to investigate the effects and mechanism of niazirin, a bioactive component from Moringa oleifera Lam. seed, on diabetic metabolic syndrome. C57BL/6J mice were treated daily with 5 mL/kg/body weight (BW) of saline, while db/db mice were similarly treated with 5 mL/kg/BW of saline, 10 and 20 mg/kg/BW of niazirin, respectively. Results indicated that niazirin could significantly reduce body weight, water and food intake, improve hyperglycemia, insulin resistance, inflammation, carbohydrate and lipid metabolism, non-alcoholic fatty liver. Furthermore, niazirin improved the hepatic energy metabolism via AMPK signaling pathway. Our study provides an evidence of an edible plant product, niazirin, may help in the treatment of metabolic syndrome.

Epigenetic changes during aging and their reprogramming potential

The aging process results in significant epigenetic changes at all levels of chromatin and DNA organization. These include reduced global heterochromatin, nucleosome remodeling and loss, changes in histone marks, global DNA hypomethylation with CpG island hypermethylation, and the relocalization of chromatin modifying factors. Exactly how and why these changes occur is not fully understood, but evidence that these epigenetic changes affect longevity and may cause aging, is growing. Excitingly, new studies show that age-related epigenetic changes can be reversed with interventions such as cyclic expression of the Yamanaka reprogramming factors. This review presents a summary of epigenetic changes that occur in aging, highlights studies indicating that epigenetic changes may contribute to the aging process and outlines the current state of research into interventions to reprogram age-related epigenetic changes.

Reduction in Histone H3 Acetylation and Chromatin Remodeling in Corneas of Alloxan-Induced Diabetic Rats

PURPOSE

To evaluate acetylation of histone H3, chromatin remodeling, nuclear size and shape, DNA ploidy, and distribution of nucleolus organizing regions (NORs) in corneal epithelial and stromal cells of diabetic and nondiabetic rats.

METHODS

Diabetes was induced by a single intraperitoneal injection of alloxan. All diabetic rats (n = 20) included in the study had 4 weeks of moderate-to-severe hyperglycemia (plasma glucose levels >400 mg/dL). Acetylated histone H3 levels were quantified in corneal tissue using a colorimetric assay. Chromatin remodeling, nuclear sizes (area/perimeter) and shapes (circularity), and DNA ploidies were evaluated from Feulgen-stained tissue sections using video image analysis. Distributions of NORs were studied in tissue sections impregnated with silver ions. Ophthalmic clinical parameters, including corneal sensitivity, were investigated. Twenty nondiabetic rats were used as controls.

RESULTS

Acetylation of histone H3 was reduced in the corneas of the diabetic rats. Nuclei in corneal epithelial cells of diabetic rats compacted chromatin, increased in size, modified their shapes, and elevated DNA ploidy. The only nuclear change observed in the corneal stromal cells of diabetic rats was chromatin decompaction. The size of the silver-stained NOR did not differ between the study samples. The corneal sensitivity in diabetic rats was 51.8% lower than that in nondiabetic rats.

CONCLUSIONS

The results of this study show that alloxan-induced diabetes altered the histone H3 acetylation pattern and compromised the chromatin supraorganization in corneal tissue/cells. Continued research is needed to understand the clinical and morphofunctional significance of changes in corneal cell nuclei of diabetic individuals.

High-glucose toxicity is mediated by AICAR-transformylase/IMP cyclohydrolase and mitigated by AMP-activated protein kinase in Caenorhabditis elegans

The enzyme AICAR-transformylase/IMP cyclohydrolase (ATIC) catalyzes the last two steps of purine de novo synthesis. It metabolizes 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), which is an AMP analogue, leading to activation of AMP-activated kinase (AMPK). We investigated whether the AICAR-ATIC pathway plays a role in the high glucose (HG)-mediated DNA damage response and AICAR-mediated AMPK activation, explaining the detrimental effects of glucose on neuronal damage and shortening of the lifespan. HG up-regulated the expression and activity of the Caenorhabditis elegans homologue of ATIC, C55F2.1 (atic-1), and increased the levels of reactive oxygen species and methylglyoxal-derived advanced glycation end products. Overexpression of atic-1 decreased the lifespan and head motility and increased neuronal damage under both standard and HG conditions. Inhibition of atic-1 expression, by RNAi, under HG was associated with increased lifespan and head motility and reduced neuronal damage, reactive oxygen species, and methylglyoxal-derived advanced glycation end product accumulation. This effect was independent of an effect on DNA damage or antioxidant defense pathways, such as superoxide dismutase (sod-3) or glyoxalase-1 (glod-4), but was dependent on AMPK and accumulation of AICAR. Through AMPK, AICAR treatment also reduced the negative effects of HG. The mitochondrial inhibitor rotenone abolished the AICAR/AMPK-induced amelioration of HG effects, pointing to mitochondria as a prime target of the glucotoxic effects in C. elegans We conclude that atic-1 is involved in glucotoxic effects under HG conditions, either by blocked atic-1 expression or via AICAR and AMPK induction.

Polyploidy and nuclear phenotype characteristics of cardiomyocytes from diabetic adult and normoglycemic aged mice

The frequency of polyploid nuclei in the aging human heart is in sharp contrast with that in the human liver. An inverse pattern exists between the mouse heart and liver cells. Ploidy degrees in mouse hepatocytes under hyperglycemic conditions are elevated to higher levels than those in aged hepatocytes. In this study, image analysis cytometry was used to investigate the effect of diabetes and aging on Feulgen-DNA quantities, ploidy degrees, nuclear shapes and chromatin texture in mouse cardiomyocytes compared to previously reported data for mouse hepatocytes. Adult, non-obese diabetic (NOD) hyperglycemic and normoglycemic females and 56-week-old normoglycemic BALB/c females were used. A small percentage (∼7%) of the cardiomyocyte nuclei in severely hyperglycemic NOD adult mice possessed higher ploidy values than those in the 8-week-old normoglycemic mice. Surprisingly, the Feulgen-DNA values and the frequency of nuclei belonging to the 4C and 8C ploidy classes were even higher (∼6%) in normoglycemic NOD specimens than in age-matched hyperglycemic NOD specimens. Additionally, a pronounced elongated nuclear shape was observed especially in adult normoglycemic NOD mice. In conclusion, NOD mice, irrespective of their glycemic level, exhibit a moderate increase in ploidy degrees within cardiomyocyte nuclei during the adult lifetime. As expected, aging did not affect the Feulgen-DNA values and the ploidy degrees of cardiomyocytes in BALB/c mice. The differences in ploidy degrees and chromatin textures such as absorbance variability and entropy, between adult NOD and aged BALB/c mice are consistent with other reports, indicating dissimilarities in chromatin functions between diabetes and aging.

Advances in Cellular Characterization of the Sirtuin Isoform, SIRT7

SIRT7 is one of seven mammalian sirtuins that functions as an NAD⁺-dependent histone/protein deacetylase. SIRT7 is the least well-known member of the sirtuin family, but recent efforts have identified its involvement in various cellular processes, such as ribosome biogenesis, gene expression, cellular metabolism and cancer. Here we provide an update on the functions and mechanisms of SIRT7 in cellular regulation and disease.

Sirtuins and Their Roles in Brain Aging and Neurodegenerative Disorders

Sirtuins (SIRT1-SIRT7) are unique histone deacetylases (HDACs) whose activity depends on NAD⁺ levels and thus on the cellular metabolic status. SIRTs regulate energy metabolism and mitochondrial function. They orchestrate the stress response and damage repair. Through these functions sirtuins modulate the course of aging and affect neurodegenerative diseases. SIRTSs interact with multiple signaling proteins, transcription factors (TFs) and poly(ADP-ribose) polymerases (PARPs) another class of NAD⁺-dependent post-translational protein modifiers. The cross-talk between SIRTs TFs and PARPs is a highly promising research target in a number of brain pathologies. This review describes updated results on sirtuins in brain aging/neurodegeneration. It focuses on SIRT1 but also on the roles of mitochondrial SIRTs (SIRT3, 4, 5) and on SIRT6 and SIRT2 localized in the nucleus and in cytosol, respectively. The involvement of SIRTs in regulation of insulin-like growth factor signaling in the brain during aging and in Alzheimer's disease was also focused. Moreover, we analyze the mechanism(s) and potential significance of interactions between SIRTs and several TFs in the regulation of cell survival and death. A critical view is given on the application of SIRT activators/modulators in therapy of neurodegenerative diseases.

PGC-1α, glucose metabolism and type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a chronic disease characterized by glucose metabolic disturbance. A number of transcription factors and coactivators are involved in this process. Peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) is an important transcription coactivator regulating cellular energy metabolism. Accumulating evidence has indicated that PGC-1α is involved in the regulation of T2DM. Therefore, a better understanding of the roles of PGC-1α may shed light on more efficient therapeutic strategies. Here, we review the most recent progress on PGC-1α and discuss its regulatory network in major glucose metabolic tissues such as the liver, skeletal muscle, pancreas and kidney. The significant associations between PGC-1α polymorphisms and T2DM are also discussed in this review.

Sirtuin 7 in cell proliferation, stress and disease: Rise of the Seventh Sirtuin!

Sirtuin 7 is a member of the sirtuin family of proteins. Sirtuins were originally discovered in yeast for its role in prolonging replicative lifespan. Until recently SIRT7 happened to be the least studied sirtuin of the seven mammalian sirtuins. However, a number of recent breakthrough reports have provided significant clarity to SIRT7 biology. SIRT7 is now seen as a vital regulator of rRNA and protein synthesis for maintenance of normal cellular homeostasis. Proteins like p53, H3K18, PAF53, NPM1 and GABP-β1 are the known substrates for the deacetylase activity of SIRT7, thereby making it a key mediator of many cellular activities. Studies using in vitro based assays and also knockout mice have revealed a role of SIRT7 in certain disease pathologies as well. High expression of SIRT7 has been reported in few cancer types and is steadily propelling SIRT7 towards an oncogene status. The role of SIRT7 as a pro-survival adaptor molecule in conditions of cellular stress has recently emerged in view of the fact that SIRT7 can regulate molecules like HIF and IRE1α. Additionally, SIRT7 plays a key role in maintenance of the epigenome as it caused the deacetylation of histone (H3K18) and global proteomics studies have shown its interaction with many chromatin remodelling complexes such as B-WICH and other proteins. Lately, the role of SIRT7 in hepatic lipid metabolism has been debated. This review attempts to summarize these recent findings and present the role of SIRT7 as an important cellular regulator.

Increased age is associated with epigenetic and structural changes in chromatin from neuronal nuclei

Chromatin organization has been considered to play a major role on aging, by regulating DNA accessibility to transcription and repair machinery. Such organization can be modulated by epigenetic events, such as DNA methylation and histone post-translational modifications. Since changes on gene expression profiles have been described in aged neurons, our aim was to study the age-dependent relationship between structural and epigenetic alterations on chromatin of cortical neurons from mice. For this purpose, isolated neuronal nuclei from mice of two ages were studied by image analysis after cytochemistry, or assessed for chromatin accessibility by enzymatic digestion. Additionally, two epigenetic marks, for open and for densely packed chromatin fibers were quantified. Results indicate epigenetically driven alterations on chromatin organization of cortical neurons with advancing age, whose fibers seem to undergo redistribution and unpackaging. Since increased transcriptional activity is not characteristic of aged neurons, these loosened chromatin fibers may be associated with impaired genome stability, as well as with increased accessibility of repair machinery to a life span damaged DNA.

Changes in liver cell DNA methylation status in diabetic mice affect its FT-IR characteristics

Background

Lower levels of cytosine methylation have been found in the liver cell DNA from non-obese diabetic (NOD) mice under hyperglycemic conditions. Because the Fourier transform-infrared (FT-IR) profiles of dry DNA samples are differently affected by DNA base composition, single-stranded form and histone binding, it is expected that the methylation status in the DNA could also affect its FT-IR profile.

Methodology/Principal Findings

The DNA FT-IR signatures obtained from the liver cell nuclei of hyperglycemic and normoglycemic NOD mice of the same age were compared. Dried DNA samples were examined in an IR microspectroscope equipped with an all-reflecting objective (ARO) and adequate software.

Conclusions/Significance

Changes in DNA cytosine methylation levels induced by hyperglycemia in mouse liver cells produced changes in the respective DNA FT-IR profiles, revealing modifications to the vibrational intensities and frequencies of several chemical markers, including ν_as –CH₃ stretching vibrations in the 5-methylcytosine methyl group. A smaller band area reflecting lower energy absorbed in the DNA was found in the hyperglycemic mice and assumed to be related to the lower levels of –CH₃ groups. Other spectral differences were found at 1700–1500 cm⁻¹ and in the fingerprint region, and a slight change in the DNA conformation at the lower DNA methylation levels was suggested for the hyperglycemic mice. The changes that affect cytosine methylation levels certainly affect the DNA-protein interactions and, consequently, gene expression in liver cells from the hyperglycemic NOD mice.

Changes in human sirtuin 6 gene promoter methylation during aging

Aging is a natural process during which changes at the cellular level increase death risk by developing susceptibility to a variety of diseases. Sirtuins have been shown to regulate lifespan in various organisms by deacetylating a number of important transcription factors. Of the 7 identified mammalian sirtuins (SIRT1-7), SIRT6 depletion is associated with severe symptoms of premature aging. In this study, we investigated the association between human longevity and SIRT6 promoter methylation. Genomic DNA from blood samples of 55 individuals (34 females and 21 males) was examined to detect methylation levels by quantitative polymerase chain reaction analysis following bisulfite treatment. While the results indicated 43.21% methylation in the 9-19 age group, this ratio was found to be increased up to 65.63% in the 20-79 age group and decreased to 52.15% in the 80-95 age group. Our results demonstrated that the SIRT6 gene is more active between 9-19 and 80-95 years compared to 20-79 years.

Genomic profiling of type-1 adult diabetic and aged normoglycemic mouse liver

BACKGROUND

Hyperglycemia induces chromatin remodeling with consequences on differential gene expression in mouse hepatocytes, similar to what occurs during aging. The liver is the central organ for the regulation of glucose homeostasis and xenobiotic and lipid metabolism and is affected by insulin signaling. The precise transcriptional profiling of the type-1 diabetic liver and its comparison to aging have not been elucidated yet.

METHODS

Here, we studied the differential genomic expression of mouse liver cells under adult hyperglycemic and aged normoglycemic conditions using expression arrays.

RESULTS

Differential gene expression involved in an increase in glucose and impaired lipid metabolism were detected in the type-1 diabetic liver. In this regard, Ppargc1a presents an increased expression and is a key gene that might be regulating both processes. The differential gene expression observed may also be associated with hepatic steatosis in diabetic mouse liver, as a secondary disease. Similarly, middle-aged mice presented differential expression of genes involved in glucose, lipid and xenobiotic metabolism. These genes could be associated with an increase in polyploidy, but the consequences of differential expression were not as drastic as those observed in diabetic animals.

CONCLUSIONS

Taken together, these findings provide new insights into gene expression profile changes in type-1 diabetic liver. Ppargc1a was found to be the key-gene that increases glucose metabolism and impairs lipid metabolism impairment. The novel results reported here open new areas of investigation in diabetic research and facilitate the development of new strategies for gene therapy.