Epigenetics of diabetic complications

DNA Methylation Profiles of PSMA6, PSMB5, KEAP1, and HIF1A Genes in Patients with Type 1 Diabetes and Diabetic Retinopathy

We explored differences in the DNA methylation statuses of PSMA6, PSMB5, HIF1A, and KEAP1 gene promoter regions in patients with type 1 diabetes and different diabetic retinopathy (DR) stages. Study subjects included individuals with no DR (NDR, n = 41), those with non-proliferative DR (NPDR, n = 27), and individuals with proliferative DR or those who underwent laser photocoagulation (PDR/LPC, n = 46). DNA methylation was determined by Zymo OneStep qMethyl technique. The methylation of PSMA6 (NDR 5.9 (3.9-8.7) %, NPDR 4.5 (3.8-5.7) %, PDR/LPC 6.6 (4.7-10.7) %, p = 0.003) and PSMB5 (NDR 2.2 (1.9-3.7) %, NPDR 2.2 (1.9-3.0) %, PDR/LPC 3.2 (2.5-7.1) %, p < 0.01) differed across the groups. Consistent correlations were observed between the methylation levels of HIF1A and PSMA6 in all study groups. DNA methylation levels of PSMA6, PSMB5, and HIF1A genes were positively correlated with the duration of diabetes, HbA1c, and albuminuria in certain study groups. Univariate regression models revealed a significant association between the methylation level z-scores of PSMA6, PSMB5, and HIF1A and severe DR (PSMA6: OR = 1.96 (1.15; 3.33), p = 0.013; PSMB5: OR = 1.90 (1.14; 3.16), p = 0.013; HIF1A: OR = 3.19 (1.26; 8.06), p = 0.014). PSMB5 remained significantly associated with DR in multivariate analysis. Our findings suggest significant associations between the severity of DR and the DNA methylation levels of the genes PSMA6, PSMB5, and HIF1A, but not KEAP1 gene.

Postprandial plasma glucose excursion is associated with an atherogenic lipid profile in individuals with type 2 diabetes mellitus: A cross-sectional study

Coronary heart disease (CHD) is a prevalent complication of type 2 diabetes mellitus (T2DM). The atherogenic low-density lipoprotein (LDL) cholesterol is an established risk factor of cardiovascular disease, and evidence also suggests that postprandial plasma glucose (PPG) levels closely delineate CHD mortality in diabetes. The investigators hypothesized that postprandial plasma glucose excursion (PPGE), defined as the difference between 2-hour PPG and fasting plasma glucose (FPG), may be associated with plasma LDL cholesterol levels in patients with T2DM. This study enrolled diabetic participants for whom FPG and lipid profile were sampled after a 12-hour fast, followed by PPG sampling two hours after consuming a standard meal with 75 grams of carbohydrates. The study enrolled 379 participants who were divided into PPGE tertiles according to the difference between their 2-hour PPG and FPG. Participants in the highest PPGE tertile had considerably greater plasma LDL cholesterol levels than patients in the lowest tertile (126.7 mg/dL vs. 99.5 mg/dL, P <0.001). Linear regression analysis also demonstrated that the PPGE was positively correlated with plasma LDL cholesterol levels (β coefficient: 0.165, P < 0.001). Postprandial glucose excursion positively correlated with plasma LDL cholesterol levels in individuals with T2DM. Participants with raised PPGE harbored greater LDL cholesterol levels than those with lower postprandial glucose fluctuations. Therefore, postprandial glucose excursion is associated with an atherogenic lipid profile and may be a modifiable risk factor of diabetic CHD.

Diabetic neuropathy and neuropathic pain: a (con)fusion of pathogenic mechanisms?

Neuropathy is a common complication of long-term diabetes that impairs quality of life by producing pain, sensory loss and limb amputation. The presence of neuropathy in both insulin-deficient (type 1) and insulin resistant (type 2) diabetes along with the slowing of progression of neuropathy by improved glycemic control in type 1 diabetes has caused the majority of preclinical and clinical investigations to focus on hyperglycemia as the initiating pathogenic lesion. Studies in animal models of diabetes have identified multiple plausible mechanisms of glucotoxicity to the nervous system including post-translational modification of proteins by glucose and increased glucose metabolism by aldose reductase, glycolysis and other catabolic pathways. However, it is becoming increasingly apparent that factors not necessarily downstream of hyperglycemia can also contribute to the incidence, progression and severity of neuropathy and neuropathic pain. For example, peripheral nerve contains insulin receptors that transduce the neurotrophic and neurosupportive properties of insulin, independent of systemic glucose regulation, while the detection of neuropathy and neuropathic pain in patients with metabolic syndrome and failure of improved glycemic control to protect against neuropathy in cohorts of type 2 diabetic patients has placed a focus on the pathogenic role of dyslipidemia. This review provides an overview of current understanding of potential initiating lesions for diabetic neuropathy and the multiple downstream mechanisms identified in cell and animal models of diabetes that may contribute to the pathogenesis of diabetic neuropathy and neuropathic pain.

Diabetes Induces a Transcriptional Signature in Bone Marrow-Derived CD34+ Hematopoietic Stem Cells Predictive of Their Progeny Dysfunction

Hematopoietic stem/progenitor cells (HSPCs) participate in cardiovascular (CV) homeostasis and generate different types of blood cells including lymphoid and myeloid cells. Diabetes mellitus (DM) is characterized by chronic increase of pro-inflammatory mediators, which play an important role in the development of CV disease, and increased susceptibility to infections. Here, we aimed to evaluate the impact of DM on the transcriptional profile of HSPCs derived from bone marrow (BM). Total RNA of BM-derived CD34⁺ stem cells purified from sternal biopsies of patients undergoing coronary bypass surgery with or without DM (CAD and CAD-DM patients) was sequenced. The results evidenced 10566 expressed genes whose 79% were protein-coding genes, and 21% non-coding RNA. We identified 139 differentially expressed genes (p-value < 0.05 and |log2 FC| > 0.5) between the two comparing groups of CAD and CAD-DM patients. Gene Set Enrichment Analysis (GSEA), based on Gene Ontology biological processes (GO-BP) terms, led to the identification of fourteen overrepresented biological categories in CAD-DM samples. Most of the biological processes were related to lymphocyte activation, chemotaxis, peptidase activity, and innate immune response. Specifically, HSPCs from CAD-DM patients displayed reduced expression of genes coding for proteins regulating antibacterial and antivirus host defense as well as macrophage differentiation and lymphocyte emigration, proliferation, and differentiation. However, within the same biological processes, a consistent number of inflammatory genes coding for chemokines and cytokines were up-regulated. Our findings suggest that DM induces transcriptional alterations in HSPCs, which are potentially responsible of progeny dysfunction.

Diabetic keratopathy: Insights and challenges

Ocular complications from diabetes mellitus are common. Diabetic keratopathy, the most frequent clinical condition affecting the human cornea, is a potentially sight-threatening condition caused mostly by epithelial disturbances that are of clinical and research attention because of their severity. Diabetic keratopathy exhibits several clinical manifestations, including persistent corneal epithelial erosion, superficial punctate keratopathy, delayed epithelial regeneration, and decreased corneal sensitivity, that may lead to compromised visual acuity or permanent vision loss. The limited amount of clinical studies makes it difficult to fully understand the pathobiology of diabetic keratopathy. Effective therapeutic approaches are elusive. We summarize the clinical manifestations of diabetic keratopathy and discuss available treatments and up-to-date research studies in an attempt to provide a thorough overview of the disorder.

The emerging role of the epigenetic enzyme Sirtuin-1 and high mobility group Box 1 in patients with diabetic foot ulceration

BACKGROUND

Diabetic foot ulceration (DFU) is a serious diabetic complication that can progress to amputation and since SIRT1 regulates glucose metabolism, inflammation, and oxidative stress which are the major contributors in diabetic complications, So we aimed to discuss its role as an epigenetic biomarker in DFU and highlight its link to oxidative stress and inflammatory cytokines.

METHOD

60 DM patients were enrolled in the study, 30 without DFU and 30 with DFU in addition to 15 healthy subjects (control group). SIRT1 mRNA relative gene expression was assessed. Catalase activity, advanced glycation end products (AGEs), tumor necrosis factor alpha (TNFα), interleukin 6 (IL-6) and High mobility group box1 (HMGB1) levels were measured. DNA fragmentation was also performed.

RESULT

SIRT1 expression and catalase activity were significantly decreased in diabetic patients compared to control group with the lowest levels in DFU patients, TNFα, IL-6, HMGB 1 and AGEs levels were significantly higher in the diabetic patients compared to control group with the highest levels in DFU patients. DNA fragmentation was more profound in DFU patients.

CONCLUSION

The study revealed that SIRT1 mRNA expression can be considered as a novel biomarker in DFU being a major player involved in its pathogenesis.

Anti-fibrotic effects of valproic acid: role of HDAC inhibition and associated mechanisms

Tissue injuries and pathological insults produce oxidative stress, genetic and epigenetic alterations, which lead to an imbalance between pro- and anti-fibrotic molecules, and subsequent accumulation of extracellular matrix, thereby fibrosis. Various molecular pathways play a critical role in fibroblasts activation, which promotes the extracellular matrix production and accumulation. Recent reports highlighted that histone deacetylases (HDACs) are upregulated in various fibrotic disorders and play a central role in fibrosis, while HDAC inhibitors exert antifibrotic effects. Valproic acid is a first-line anti-epileptic drug and a proven HDAC inhibitor. This review provides the current research and novel insights on antifibrotic effects of valproic acid in various fibrotic conditions with an emphasis on the possible strategies for treatment of fibrosis.

The lost correlation between heat shock protein 70 (HSPA1A) and plasminogen activator inhibitor-1 in patients with type 2 diabetes and albuminuria

We aimed to study the relation between plasma levels of stress-induced heat shock protein 70 (HSPA1A) with plasminogen activator inhibitor-1 (PAI-1) and high-density lipoprotein cholesterol (HDL-C), apolipoprotein A1 (Apo-A1), and HDL-C/Apo-A1 ratio. In a matched case-control study on patients with diabetes (40 patients with albuminuria and 40 without albuminuria matched for age, sex, and body mass index), we observed that plasma levels of HSPA1A and PAI-1 are increased in patients with albuminuria (0.55 ± 0.02 vs. 0.77 ± 0.04 ng/ml, p value <0.001 for HSPA1A; 25.9 ± 2 vs. 31.8 ± 2.4 ng/ml, p value <0.05 for PAI-1). There was a significant correlation between HSPA1A and PAI-1 in diabetic patients without albuminuria (r = 0.28; p value = 0.04), but not in those with albuminuria (r = 0.07; p value = 0.63). No association was found between HSPA1A and HDL-C, between HSPA1A and Apo-A1, or between HSPA1A and HDL-C/Apo-A1 ratio. We concluded that there is a direct correlation between plasma HSPA1A and PAI-1 levels in patients with diabetes, which is lost when they develop albuminuria.

Gallic Acid Decreases Inflammatory Cytokine Secretion Through Histone Acetyltransferase/Histone Deacetylase Regulation in High Glucose-Induced Human Monocytes

Hyperglycemia contributes to diabetes and several diabetes-related complications. Gallic acid is a polyhydroxy phenolic compound found in various natural products. In this study, we investigated the effects and mechanism of gallic acid on proinflammatory cytokine secretion in high glucose-induced human monocytes (THP-1 cells). THP-1 cells were cultured under normoglycemic or hyperglycemic conditions, in the absence or presence of gallic acid. Hyperglycemic conditions significantly induced histone acetylation, nuclear factor-κB (NF-κB) activation, and proinflammatory cytokine release from THP-1 cells, whereas gallic acid suppressed NF-κB activity and cytokine release. It also significantly reduced CREB-binding protein/p300 (CBP/p300, a NF-κB coactivator) gene expression, acetylation levels, and CBP/p300 histone acetyltransferase (HAT) activity. In addition, histone deacetylase 2 (HDAC2) expression was significantly induced. These results suggest that gallic acid inhibits hyperglycemic-induced cytokine production in monocytes through epigenetic changes involving NF-κB. Therefore, gallic acid may have potential for the treatment and prevention of diabetes and its complications.

Epigenetic mechanisms in the pathogenesis of diabetic retinopathy

Diabetic retinopathy (DR), which arises as a result of an increasing incidence of diabetes mellitus, has gradually become a common disease. Due to its complex pathogenesis, the treatment means of DR are very limited. The findings of several studies have shown that instituting tight glycemic control in diabetic patients does not immediately benefit the progression of retinopathy, and the benefits of good control persist beyond the period of good glycemic control. This has led to the concept of persistent epigenetic changes. Epigenetics has now become an increasingly important area of biomedical research. Recently, important roles of various epigenetic mechanisms have been identified in the pathogenesis of diabetes and its complications. The aim of this review is to provide an overview of the epigenetics and epigenetic mechanisms in diabetes and diabetes complications, and the focus is on the emerging evidence for aberrant epigenetic mechanisms in DR.

Luteolin inhibits hyperglycemia-induced proinflammatory cytokine production and its epigenetic mechanism in human monocytes

Hyperglycemia is a key feature in diabetes. Hyperglycemia has been implicated as a major contributor to several complications of diabetes. High glucose levels induce the release of proinflammatory cytokines. Luteolin is a flavone isolated from celery, green pepper, perilla leaf, and chamomile tea. Luteolin has been reported to possess antimutagenic, antitumorigenic, antioxidant, and anti-inflammatory properties. In this study, we investigated the effects of luteolin on proinflammatory cytokine secretion and its underlying epigenetic regulation in high-glucose-induced human monocytes. Human monocytic (THP-1) cells were cultured under controlled (14.5 mM mannitol), normoglycemic (NG, 5.5 mM glucose), or hyperglycemic (HG, 20 mM glucose) conditions, in the absence or presence of luteolin. Luteolin (3-10 μM) was added for 48 h. While hyperglycemic conditions significantly induced histone acetylation, NF-κB activation, and proinflammatory cytokine (IL-6 and TNF-α) release from THP-1 cells, luteolin suppressed NF-κB activity and cytokine release. Luteolin also significantly reduced CREB-binding protein/p300 (CBP/p300) gene expression, as well as the levels of acetylation and histone acetyltransferase (HAT) activity of the CBP/p300 protein, which is a known NF-κB coactivator. These results suggest that luteolin inhibits HG-induced cytokine production in monocytes, through epigenetic changes involving NF-κB. We therefore suggest that luteolin may be a potential candidate for the treatment and prevention of diabetes and its complications.

Systemic perturbations of key metabolites in diabetic rats during the evolution of diabetes studied by urine metabonomics

BACKGROUND

Elucidation of metabolic profiles during diabetes progression helps understand the pathogenesis of diabetes mellitus. In this study, urine metabonomics was used to identify time-related metabolic changes that occur during the development of diabetes mellitus and characterize the biochemical process of diabetes on a systemic, metabolic level.

METHODOLOGY/PRINCIPAL FINDINGS

Urine samples were collected from diabetic rats and age-matched controls at different time points: 1, 5, 10, and 15 weeks after diabetes modeling. (1)H nuclear magnetic resonance ((1)H NMR) spectra of the urine samples were obtained and analyzed by multivariate data analysis and quantitative statistical analysis. The metabolic patterns of diabetic groups are separated from the controls at each time point, suggesting that the metabolic profiles of diabetic rats were markedly different from the controls. Moreover, the samples from the diabetic 1-wk group are closely associated, whereas those of the diabetic 15-wk group are scattered, suggesting that the presence of various of complications contributes significantly to the pathogenesis of diabetes. Quantitative analysis indicated that urinary metabolites related to energy metabolism, tricarboxylic acid (TCA) cycle, and methylamine metabolism are involved in the evolution of diabetes.

CONCLUSIONS/SIGNIFICANCE

The results highlighted that the numbers of metabolic changes were related to diabetes progression, and the perturbed metabolites represent potential metabolic biomarkers and provide clues that can elucidate the mechanisms underlying the generation and development of diabetes as well as its complication.

Perspectives on systems biology applications in diabetic kidney disease

Diabetic kidney disease (DKD) is a microvascular complication of type 1 and 2 diabetes with a devastating impact on individuals with the disease, their families, and society as a whole. DKD is the single most frequent cause of incident chronic kidney disease cases and accounts for over 40% of the population with end-stage renal disease. Contributing factors for the high prevalence are the increase in obesity and subsequent diabetes combined with an improved long-term survival with diabetes. Environment and genetic variations contribute to DKD susceptibility and progressive loss of kidney function. How the molecular mechanisms of genetic and environmental exposures interact during DKD initiation and progression is the focus of ongoing research efforts. The development of standardized, unbiased high-throughput profiling technologies of human DKD samples opens new avenues in capturing the multiple layers of DKD pathobiology. These techniques routinely interrogate analytes on a genome-wide scale generating comprehensive DKD-associated fingerprints. Linking the molecular fingerprints to deep clinical phenotypes may ultimately elucidate the intricate molecular interplay in a disease stage and subtype-specific manner. This insight will form the basis for accurate prognosis and facilitate targeted therapeutic interventions. In this review, we present ongoing efforts from large-scale data integration translating "-omics" research efforts into improved and individualized health care in DKD.

The role of epigenetics in the pathology of diabetic complications

Diabetes is associated with significantly accelerated rates of several debilitating microvascular complications such as nephropathy, retinopathy, and neuropathy, and macrovascular complications such as atherosclerosis and stroke. While several studies have been devoted to the evaluation of genetic factors related to type 1 and type 2 diabetes and associated complications, much less is known about epigenetic changes that occur without alterations in the DNA sequence. Environmental factors and nutrition have been implicated in diabetes and can also affect epigenetic states. Exciting research has shown that epigenetic changes in chromatin can affect gene transcription in response to environmental stimuli, and changes in key chromatin histone methylation patterns have been noted under diabetic conditions. Reports also suggest that epigenetics may be involved in the phenomenon of metabolic memory observed in clinic trials and animal studies. Further exploration into epigenetic mechanisms can yield new insights into the pathogenesis of diabetes and its complications and uncover potential therapeutic targets and treatment options to prevent the continued development of diabetic complications even after glucose control has been achieved.