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

Unraveling the role of macrophages in diabetes: Impaired phagocytic function and therapeutic prospects

The rising aging population and changing lifestyles have led to a global increase in diabetes and its complications, making it one of the most prevalent diseases worldwide. Chronic inflammation is a key pathogenic feature of diabetes and its complications, yet the precise mechanisms remain unclear, impeding the development of targeted therapies. Recent studies have highlighted the β cell-macrophage crosstalk pathway as a crucial factor in chronic low-grade inflammation and glucose homeostasis imbalance in both type 1 and type 2 diabetes. Furthermore, impaired macrophage phagocytic functions, including pathogen phagocytosis, efferocytosis, and autophagy, play a significant role in diabetes complications. Given their high plasticity, macrophages represent a promising research target. This review summarizes recent findings on macrophage phagocytic dysfunction in diabetes and its complications, and explores emerging therapies targeting macrophage phagocytic function. We also discuss the current challenges in translating basic research to clinical practice, aiming to guide researchers in developing targeted treatments to regulate macrophage status and phagocytic function, thus preventing and treating metabolic inflammatory diseases.

The Impact of Modifiable Risk Factors on the Endothelial Cell Methylome and Cardiovascular Disease Development

Cardiovascular disease (CVD) is the most prevalent cause of mortality and morbidity in the Western world. A common underlying hallmark of CVD is the plaque-associated arterial thickening, termed atherosclerosis. Although the molecular mechanisms underlying the aetiology of atherosclerosis remain unknown, it is clear that both its development and progression are associated with significant changes in the pattern of DNA methylation within the vascular cell wall. The endothelium is the major regulator of vascular homeostasis, and endothelial cell dysfunction (ED) is considered an early marker for atherosclerosis. Thus, it is speculated that changes in DNA methylation within endothelial cells may, in part, be causal in ED, leading to atherosclerosis and CVD generally. This review will evaluate the extensive evidence that environmental risk factors, known to be associated with atherosclerosis, such as diabetes, metabolic disorder, smoking, hypertension and hypercholesterolaemia etc. can affect the methylome of the endothelium and consequently act to alter gene transcription and function. Further, the potential mechanisms whereby such risk factors might impact upon the activities and/or specificities of the epigenetic writers and erasers which determine the methylome [the DNA methyl transferases (DNMTs) and Ten Eleven translocases (TETs)] are considered here. Notably, the TET proteins are members of the 2-oxoglutarate-dependent dioxygenase superfamily which require molecular oxygen (O2) and α-ketoglutarate (α-KG) as substrates and iron-2+ (Fe II) as a cofactor. This renders their activities subject to modulation by hypoxia, metabolic flux and cellular redox. The potential significance of this, with respect to the impact of modifiable risk factors upon the activities of the TETs and the methylome of the endothelium is discussed.

[Gly14]-Humanin ameliorates high glucose-induced endothelial senescence via SIRT6

High glucose (HG) induced endothelial senescence is related to endothelial dysfunction and cardiovascular complications in diabetic patients. Humanin, a member of mitochondrial derived peptides (MDPs), is thought to contribute to aging-related cardiovascular protection. The goal of the study is to explore the pathogenesis of HG-induced endothelial senescence and potential anti-senescent effects of Humanin. Human umbilical vein endothelial cells (HUVECs) were exposed to glucose to induce senescence, determined by β-galactosidase staining and the expressions of p21, p53, and p16. A clinically relevant dose of HG (15 mM, HG) induced endothelial senescence after 72 h incubation without elevated apoptosis. HG-induced senescence was attributed to the induction of reactive oxygen species (ROS) caused by SIRT6 downregulation, as ROS inhibitor N-acetyl cysteine blocked HG-induced senescence, while inactivation of SIRT6 increased ROS levels and promoted senescence. Strikingly. pretreatment with [Gly14]-Humanin (HNG) antagonized the downregulation of SIRT6 in response to HG and alleviated ROS production and cell senescence. HG-induced reduction of SIRT6 results in ROS overproduction and endothelial senescence. Humanin protects against HG-induced endothelial senescence via SIRT6. This study provides new directions for biological products related to Humanin to be a potential candidate for the prevention of vascular aging in diabetes.

High glucose induces DNA methyltransferase 1 dependent epigenetic reprogramming of the endothelial exosome proteome in type 2 diabetes

In response to hyperglycemia, endothelial cells (ECs) release exosomes with altered protein content and contribute to paracrine signalling, subsequently leading to vascular dysfunction in type 2 diabetes (T2D). High glucose reprograms DNA methylation patterns in various cell/tissue types, including ECs, resulting in pathologically relevant changes in cellular and extracellular proteome. However, DNA methylation-based proteome reprogramming in endothelial exosomes and associated pathological implications in T2D are not known. Hence, in the present study, we used Human umbilical vein endothelial cells (HUVECs), High Fat Diet (HFD) induced diabetic mice (C57BL/6) and clinical models to understand epigenetic basis of exosome proteome regulation in T2D pathogenesis . Exosomes were isolated by size exclusion chromatography and subjected to tandem mass tag (TMT) labelled quantitative proteomics and bioinformatics analysis. Immunoblotting was performed to validate exosome protein signature in clinically characterized individuals with T2D. We observed ECs cultured in high glucose and aortic ECs from HFD mouse expressed elevated DNA methyltransferase1 (DNMT1) levels. Quantitative proteomics of exosomes isolated from ECs treated with high glucose and overexpressing DNMT1 showed significant alterations in both protein levels and post translational modifications which were aligned to T2D associated vascular functions. Based on ontology and gene-function-disease interaction analysis, differentially expressed exosome proteins such as Thrombospondin1, Pentraxin3 and Cystatin C related to vascular complications were significantly increased in HUVECs treated with high glucose and HFD animals and T2D individuals with higher levels of glycated hemoglobin. These proteins were reduced upon treatment with 5-Aza-2'-deoxycytidine. Our study shows epigenetic regulation of exosome proteome in T2D associated vascular complications.

Understanding the role of ten-eleven translocation family proteins in kidney diseases

Epigenetic mechanisms play a critical role in the pathogenesis of human diseases including kidney disorders. As the erasers of DNA methylation, Ten-eleven translocation (TET) family proteins can oxidize 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC), thus leading to passive or active DNA demethylation. Similarly, TET family proteins can also catalyze the same reaction on RNA. In addition, TET family proteins can also regulate chromatin structure and gene expression in a catalytic activity-independent manner through recruiting the SIN3A/HDAC co-repressor complex. In 2012, we reported for the first time that the genomic 5-hydroxymethylcytosine level and the mRNA levels of Tet1 and Tet2 were significantly downregulated in murine kidneys upon ischemia and reperfusion injury. Since then, accumulating evidences have eventually established an indispensable role of TET family proteins in not only acute kidney injury but also chronic kidney disease. In this review, we summarize the upstream regulatory mechanisms and the pathophysiological role of TET family proteins in major types of kidney diseases and discuss their potential values in clinical diagnosis and treatment.

The influence of epigenetics and inflammation on cardiometabolic risks

Cardiometabolic diseases include metabolic syndrome, obesity, type 2 diabetes mellitus, and hypertension. Epigenetic modifications participate in cardiometabolic diseases through several pathways, including inflammation, vascular dysfunction, and insulin resistance. Epigenetic modifications, which encompass alterations to gene expression without mutating the DNA sequence, have gained much attention in recent years, since they have been correlated with cardiometabolic diseases and may be targeted for therapeutic interventions. Epigenetic modifications are greatly influenced by environmental factors, such as diet, physical activity, cigarette smoking, and pollution. Some modifications are heritable, indicating that the biological expression of epigenetic alterations may be observed across generations. Moreover, many patients with cardiometabolic diseases present with chronic inflammation, which can be influenced by environmental and genetic factors. The inflammatory environment worsens the prognosis of cardiometabolic diseases and further induces epigenetic modifications, predisposing patients to the development of other metabolism-associated diseases and complications. A deeper understanding of inflammatory processes and epigenetic modifications in cardiometabolic diseases is necessary to improve our diagnostic capabilities, personalized medicine approaches, and the development of targeted therapeutic interventions. Further understanding may also assist in predicting disease outcomes, especially in children and young adults. This review describes epigenetic modifications and inflammatory processes underlying cardiometabolic diseases, and further discusses advances in the research field with a focus on specific points for interventional therapy.

The role of sirtuins in the regulatin of oxidative stress during the progress and therapy of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder characterized by insulin resistance and impaired glucose homeostasis. Oxidative stress, arising from an imbalance between reactive oxygen species (ROS) production and antioxidant defense systems, plays a significant role in the development and progression of T2DM. The sirtuin family, particularly Sirt1, Sirt3, and Sirt6, have emerged as key regulators of oxidative stress in various cellular processes. This review aims to explore the role of the sirtuin family in oxidative stress during the progression of T2DM and their potential as therapeutic targets. We discussed the mechanisms through which sirtuins modulate oxidative stress, their impact on insulin sensitivity, and beta-cell function involved in T2DM. Furthermore, we highlight drugs targeting sirtuin activation and related complications in T2DM. This review summarizes the role as well as mechanism of sirtuins in the regulation of oxidative stress in T2DM and available drugs targeting sirtuins in clinic, which may provide novel insights into the mechanism and therapy of T2DM.

SIRT6's function in controlling the metabolism of lipids and glucose in diabetic nephropathy

Diabetic nephropathy (DN) is a complication of diabetes mellitus (DM) and the main cause of excess mortality in patients with type 2 DM. The pathogenesis and progression of DN are closely associated with disorders of glucose and lipid metabolism. As a member of the sirtuin family, SIRT6 has deacetylation, defatty-acylation, and adenosine diphosphate-ribosylation enzyme activities as well as anti-aging and anticancer activities. SIRT6 plays an important role in glucose and lipid metabolism and signaling, especially in DN. SIRT6 improves glucose and lipid metabolism by controlling glycolysis and gluconeogenesis, affecting insulin secretion and transmission and regulating lipid decomposition, transport, and synthesis. Targeting SIRT6 may provide a new therapeutic strategy for DN by improving glucose and lipid metabolism. This review elaborates on the important role of SIRT6 in glucose and lipid metabolism, discusses the potential of SIRT6 as a therapeutic target to improve glucose and lipid metabolism and alleviate DN occurrence and progression of DN, and describes the prospects for future research.

Targeting high glucose-induced epigenetic modifications at cardiac level: the role of SGLT2 and SGLT2 inhibitors

BACKGROUND

Sodium-glucose co-transporters (SGLT) inhibitors (SGLT2i) showed many beneficial effects at the cardiovascular level. Several mechanisms of action have been identified. However, no data on their capability to act via epigenetic mechanisms were reported. Therefore, this study aimed to investigate the ability of SGLT2 inhibitors (SGLT2i) to induce protective effects at the cardiovascular level by acting on DNA methylation.

METHODS

To better clarify this issue, the effects of empagliflozin (EMPA) on hyperglycemia-induced epigenetic modifications were evaluated in human ventricular cardiac myoblasts AC16 exposed to hyperglycemia for 7 days. Therefore, the effects of EMPA on DNA methylation of NF-κB, SOD2, and IL-6 genes in AC16 exposed to high glucose were analyzed by pyrosequencing-based methylation analysis. Modifications of gene expression and DNA methylation of NF-κB and SOD2 were confirmed in response to a transient SGLT2 gene silencing in the same cellular model. Moreover, chromatin immunoprecipitation followed by quantitative PCR was performed to evaluate the occupancy of TET2 across the investigated regions of NF-κB and SOD2 promoters.

RESULTS

Seven days of high glucose treatment induced significant demethylation in the promoter regions of NF-kB and SOD2 with a consequent high level in mRNA expression of both genes. The observed DNA demethylation was mediated by increased TET2 expression and binding to the CpGs island in the promoter regions of analyzed genes. Indeed, EMPA prevented the HG-induced demethylation changes by reducing TET2 binding to the investigated promoter region and counteracted the altered gene expression. The transient SGLT2 gene silencing prevented the DNA demethylation observed in promoter regions, thus suggesting a role of SGLT2 as a potential target of the anti-inflammatory and antioxidant effect of EMPA in cardiomyocytes.

CONCLUSIONS

In conclusion, our results demonstrated that EMPA, mainly acting on SGLT2, prevented DNA methylation changes induced by high glucose and provided evidence of a new mechanism by which SGLT2i can exert cardio-beneficial effects.

SIRT6 in Aging, Metabolism, Inflammation and Cardiovascular Diseases

As an important NAD⁺-dependent enzyme, SIRT6 has received significant attention since its discovery. In view of observations that SIRT6-deficient animals exhibit genomic instability and metabolic disorders and undergo early death, SIRT6 has long been considered a protein of longevity. Recently, growing evidence has demonstrated that SIRT6 functions as a deacetylase, mono-ADP-ribosyltransferase and long fatty deacylase and participates in a variety of cellular signaling pathways from DNA damage repair in the early stage to disease progression. In this review, we elaborate on the specific substrates and molecular mechanisms of SIRT6 in various physiological and pathological processes in detail, emphasizing its links to aging (genomic damage, telomere integrity, DNA repair), metabolism (glycolysis, gluconeogenesis, insulin secretion and lipid synthesis, lipolysis, thermogenesis), inflammation and cardiovascular diseases (atherosclerosis, cardiac hypertrophy, heart failure, ischemia-reperfusion injury). In addition, the most recent advances regarding SIRT6 modulators (agonists and inhibitors) as potential therapeutic agents for SIRT6-mediated diseases are reviewed.

Epigenetic Modifications and Non-Coding RNA in Diabetes-Mellitus-Induced Coronary Artery Disease: Pathophysiological Link and New Therapeutic Frontiers

Diabetes mellitus (DM) is a glucose metabolism disorder characterized by chronic hyperglycemia resulting from a deficit of insulin production and/or action. DM affects more than 1 in 10 adults, and it is associated with an increased risk of cardiovascular morbidity and mortality. Cardiovascular disease (CVD) accounts for two thirds of the overall deaths in diabetic patients, with coronary artery disease (CAD) and ischemic cardiomyopathy as the main contributors. Hyperglycemic damage on vascular endothelial cells leading to endothelial dysfunction represents the main initiating factor in the pathogenesis of diabetic vascular complications; however, the underlying pathophysiological mechanisms are still not entirely understood. This review addresses the current knowledge on the pathophysiological links between DM and CAD with a focus on the role of epigenetic modifications, including DNA methylation, histone modifications and noncoding RNA control. Increased knowledge of epigenetic mechanisms has contributed to the development of new pharmacological treatments ("epidrugs") with epigenetic targets, although these approaches present several challenges. Specific epigenetic biomarkers may also be used to predict or detect the development and progression of diabetes complications. Further studies on diabetes and CAD epigenetics are needed in order to identify possible new therapeutic targets and advance personalized medicine with the prediction of individual drug responses and minimization of adverse effects.

Mitochondrial Sirtuins in Chronic Degenerative Diseases: New Metabolic Targets in Colorectal Cancer

Sirtuins (SIRTs) are a family of class III histone deacetylases (HDACs) consisting of seven members, widely expressed in mammals. SIRTs mainly participate in metabolic homeostasis, DNA damage repair, cell survival, and differentiation, as well as other cancer-related biological processes. Growing evidence shows that SIRTs have pivotal roles in chronic degenerative diseases, including colorectal cancer (CRC), the third most frequent malignant disease worldwide. Metabolic alterations are gaining attention in the context of CRC development and progression, with mitochondrion representing a crucial point of complex and intricate molecular mechanisms. Mitochondrial SIRTs, SIRT2, SIRT3, SIRT4 and SIRT5, control mitochondrial homeostasis and dynamics. Here, we provide a comprehensive review on the latest advances on the role of mitochondrial SIRTs in the initiation, promotion and progression of CRC. A deeper understanding of the pathways by which mitochondrial SIRTs control CRC metabolism may provide new molecular targets for future innovative strategies for CRC prevention and therapy.

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

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

Hypermethylation Effects of Yiqihuoxue Decoction in Diabetic Atherosclerosis Using Genome-Wide DNA Methylation Analyses

Purpose

To investigate if a traditional Chinese medicine formulation, called “Yiqihuoxue” (YQHX), could improve diabetic atherosclerosis (DA) and explore potential mechanisms based on DNA methylation.

Methods

Apolipoprotein E-knockout mice were administered streptozotocin (50 mg/d, i.p.) for 5 days and fed a high-fat diet for 16 weeks. Mice were divided randomly into DA model, rosiglitazone, as well as low-, medium-, and high-dose YQHX groups. Ten healthy C57BL/6J mice were the control group. Serum levels of fasting insulin, blood glucose, homeostasis model-insulin resistance index (HOMA-IR), serum lipids, and inflammatory factors were analyzed after the final treatment. Aorta tissues were collected for staining (hematoxylin and eosin, and Oil red O). Genomic DNA was extracted for methyl-capture sequencing (MC-seq). Kyoto Encyclopedia of Genes and Genomes (KEGG) and Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) databases were used to analyze differentially methylated genes. Pyrosequencing was used to verify MC-seq data.

Results

Low-dose and high-dose YQHX could reduce the HOMA-IR (P < 0.05). Low-dose YQHX reduced expression of total cholesterol (TC), low-density lipoprotein-cholesterol (LDL-C), TNF-α, andI L-6 in serum compared with that in the model group (P < 0.05). Medium-dose YQHX decoction inhibited the expression level of TNF-α (P < 0.05). High-dose YQHX decreased the expression level of IL-6 (P < 0.05). Staining also showed the anti-atherosclerosis effects of YQHX (P < 0.05). MC-seq revealed many abnormally hypermethylated and hypomethylated genes in DA mice compared with those in the control group. KEGG database analysis showed that the hypermethylated genes induced by YQHX treatment were related to pathways in cancer, Hippo signaling, and mitogen activated protein kinase. The network analysis suggested that the hypermethylated genes epidermal growth factor receptor(Egfr) and phosphoinositide-3-kinase regulatory subunit 1(Pik3r1) induced by YQHX treatment had important roles in DA. Pyrosequencing revealed that YQHX treatment increased methylation of AKT1, Nr1h3 and Fabp4 significantly (P < 0.05).

Conclusion

YQHX decoction had positive treatment effects against DA, because it could regulate aberrant hypomethylation of DNA.