Comparison of the dipeptidyl peptidase-4 gene methylation levels between severely obese subjects with and without the metabolic syndrome

Dipeptidyl Peptidase 4 (DPP4) as A Novel Adipokine: Role in Metabolism and Fat Homeostasis

Dipeptidyl peptidase 4 (DPP4) is a molecule implicated in the regulation of metabolic homeostasis and inflammatory processes, and it exerts its main action through its enzymatic activity. DPP4 represents the enzyme most involved in the catabolism of incretin hormones; thus, its activity impacts appetite, energy balance, and the fine regulation of glucose homeostasis. Indeed, DPP4 inhibitors represent a class of antidiabetic agents widely used for the treatment of Type 2 diabetes mellitus (T2DM). DPP4 also acts as an adipokine and is mainly secreted by the adipose tissue, mostly from mature adipocytes of the visceral compartment, where it exerts autocrine and paracrine activities. DPP4 can disrupt insulin signaling within the adipocyte and in other target cells and tissues, where it also favors the development of a proinflammatory environment. This is likely at the basis of the presence of elevated circulating DPP4 levels in several metabolic diseases. In this review, we summarize the most recent evidence of the role of the DPP4 as an adipokine-regulating glucose/insulin metabolism and fat homeostasis, with a particular focus on clinical outcomes associated with its increased secretion in the presence of adipose tissue accumulation and dysfunction.

Childhood trauma, the stress response and metabolic syndrome: A focus on DNA methylation

Childhood trauma (CT) is well established as a potent risk factor for the development of mental disorders. However, the potential of adverse early experiences to exert chronic and profound effects on physical health, including aberrant metabolic phenotypes, has only been more recently explored. Among these consequences is metabolic syndrome (MetS), which is characterised by at least three of five related cardiometabolic traits: hypertension, insulin resistance/hyperglycaemia, raised triglycerides, low high-density lipoprotein and central obesity. The deleterious effects of CT on health outcomes may be partially attributable to dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, which coordinates the response to stress, and the consequent fostering of a pro-inflammatory environment. Epigenetic tags, such as DNA methylation, which are sensitive to environmental influences provide a means whereby the effects of CT can be biologically embedded and persist into adulthood to affect health and well-being. The methylome regulates the transcription of genes involved in the stress response, metabolism and inflammation. This narrative review examines the evidence for DNA methylation in CT and MetS in order to identify shared neuroendocrine and immune correlates that may mediate the increased risk of MetS following CT exposure. Our review specifically highlights differential methylation of FKBP5, the gene that encodes FK506-binding protein 51 and has pleiotropic effects on stress responding, inflammation and energy metabolism, as a central candidate to understand the molecular aetiology underlying CT-associated MetS risk.

Obesity, metabolic health and omics: Current status and future directions

The growing obesity epidemic is becoming a major public health concern, and the associated costs represent a considerable burden on societies. Among the most common complications of severe obesity are the development of hypertension, dyslipidemia, type 2 diabetes, cardiovascular disease, and various types of cancer. Interestingly, some obese individuals have a favorable metabolic profile and appear to be somehow protected from the detrimental effects of excessive adipose tissue accumulation. These individuals remain normoglycemic, insulin sensitive, and hypotensive with proper blood lipid levels, despite their high body mass index and/or waist circumference. Multiple independent observations have led to the concept of the metabolically healthy obese (MHO) phenotype, yet no consensus has been reached to date regarding a universal definition or the main mechanism behind this phenomenon. Recent technological advances and the use of high-throughput analysis techniques have revolutionized different areas of biomedical research. A multi-omics approach, which is used to investigate changes at different molecular levels in an organism or tissue, may provide valuable insights into the interplay between the molecules or pathways and the roles of different factors involved in the mechanisms underlying metabolic health deterioration. The aim of this review is to present the current status regarding the use of omics technologies to investigate the MHO phenotype, as well as the results of targeted analyses conducted in MHO individuals.

More than just an enzyme: Dipeptidyl peptidase-4 (DPP-4) and its association with diabetic kidney remodelling

PURPOSE OF THE REVIEW

This review article discusses recent advances in the mechanism of dipeptidyl peptidase-4 (DPP-4) actions in renal diseases, especially diabetic kidney fibrosis, and summarizes anti-fibrotic functions of various DPP-4 inhibitors in diabetic nephropathy (DN).

RECENT FINDINGS

DN is a common complication of diabetes and is a leading cause of the end-stage renal disease (ESRD). DPP-4 is a member of serine proteases, and more than 30 substrates have been identified that act via several biochemical messengers in a variety of tissues including kidney. Intriguingly, DPP-4 actions on the diabetic kidney is a complex mechanism, and a variety of pathways are involved including increasing GLP-1/SDF-1, disrupting AGE-RAGE pathways, and integrin-β- and TGF-β-Smad-mediated signalling pathways that finally lead to endothelial to mesenchymal transition. Interestingly, an array of DPP-4 inhibitors is well recognized as oral drugs to treat type 2 diabetic (T2D) patients, which promote better glycemic control. Furthermore, recent experimental and preclinical data reveal that DPP-4 inhibitors may also exhibit protective effects in renal disease progression including anti-fibrotic effects in the diabetic kidney by attenuating above signalling cascade(s), either singly or as a combinatorial effect. In this review, we discussed the anti-fibrotic effects of DPP-4 inhibitors based on recent reports along with the possible mechanism of actions and future perspectives to underscore the beneficial effects of DPP-4 inhibitors in DN.

SUMMARY

With recent experimental, preclinical, and clinical evidence, we summarized DPP-4 activities and its mechanism of actions in diabetic kidney diseases. A knowledge gap of DPP-4 inhibition in controlling renal fibrosis in DN has also been postulated in this review for future research perspectives.

Efficacy and short-term side effects of sitagliptin, vildagliptin and saxagliptin in Chinese diabetes: a randomized clinical trial

AIMS

To investigate the difference in the efficacy among dipeptidyl peptidase-4 (DPP-4) inhibitors in Chinese adults with newly diagnosed diabetes.

MATERIALS AND METHODS

In a multicenter, randomized study, we enrolled adults who were either treatment naive or off prior anti-hyperglycemic therapy for at least 3 months. Eligible patients had hemoglobin A1c (HbA1c) concentrations of 6.5-9.5%. Three hundred patients had been randomly allocated to sitagliptin 100 mg, once daily; vildagliptin 50 mg, twice daily and saxagliptin 5 mg, once daily for 12 weeks. Patients and investigators were masked to treatment assignment. The primary endpoint was change from baseline in HbA1c at week 12. This study was completed and registered with ClinicalTrials.gov, number NCT01703637.

RESULTS

Totally 277 patients were enrolled in the final analysis, and 93 patients received sitagliptin, 94 received vildagliptin and 90 received saxagliptin. Compared with baseline, adjusted mean differences in change from baseline HbA1c at week 12 were -0.50% (95% CI: -0.20 to -0.90), -0.65% (95% CI: -0.40 to -1.40), -0.70 (95% CI: -0.50 to -1.00) for sitagliptin, vildagliptin and saxagliptin group, respectively. The overall HbA1c-lowering effect was similar for all three selected DPP-4 inhibitors after adjustment for age and baseline HbA1c. Notably, in secondary outcome analysis, patients in vildagliptin group showed a significant decrease in total cholesterol levels, compared with participants in sitagliptin and saxagliptin groups. No significant between-group difference was shown in adverse events (AE).

CONCLUSIONS

The overall HbA1c-lowering effect and incidence of AE were similar for sitagliptin, vildagliptin and saxagliptin in Chinese adults with newly diagnosed diabetes.

Adipose tissue dysfunction as a central mechanism leading to dysmetabolic obesity triggered by chronic exposure to p,p'-DDE

Endocrine-disrupting chemicals such as p,p’-dichlorodiphenyldichloroethylene (p,p’-DDE), are bioaccumulated in the adipose tissue (AT) and have been implicated in the obesity and diabetes epidemic. Thus, it is hypothesized that p,p’-DDE exposure could aggravate the harm of an obesogenic context. We explored the effects of 12 weeks exposure in male Wistar rats’ metabolism and AT biology, assessing a range of metabolic, biochemical and histological parameters. p,p’-DDE -treatment exacerbated several of the metabolic syndrome-accompanying features induced by high-fat diet (HF), such as dyslipidaemia, glucose intolerance and hypertension. A transcriptome analysis comparing mesenteric visceral AT (vAT) of HF and HF/DDE groups revealed a decrease in expression of nervous system and tissue development-related genes, with special relevance for the neuropeptide galanin that also revealed DNA methylation changes at its promoter region. Additionally, we observed an increase in transcription of dipeptidylpeptidase 4, as well as a plasmatic increase of the pro-inflammatory cytokine IL-1β. Our results suggest that p,p’-DDE impairs vAT normal function and effectively decreases the dynamic response to energy surplus. We conclude that p,p’-DDE does not merely accumulate in fat, but may contribute significantly to the development of metabolic dysfunction and inflammation. Our findings reinforce their recognition as metabolism disrupting chemicals, even in non-obesogenic contexts.

Hepatic DPP4 DNA Methylation Associates With Fatty Liver

Hepatic DPP4 expression is elevated in subjects with ectopic fat accumulation in the liver. However, whether increased dipeptidyl peptidase 4 (DPP4) is involved in the pathogenesis or is rather a consequence of metabolic disease is not known. We therefore studied the transcriptional regulation of hepatic Dpp4 in young mice prone to diet-induced obesity. Already at 6 weeks of age, expression of hepatic Dpp4 was increased in mice with high weight gain, independent of liver fat content. In the same animals, methylation of four intronic CpG sites was decreased, amplifying glucose-induced transcription of hepatic Dpp4 In older mice, hepatic triglyceride content was increased only in animals with elevated Dpp4 expression. Expression and release of DPP4 were markedly higher in the liver compared with adipose depots. Analysis of human liver biopsy specimens revealed a correlation of DPP4 expression and DNA methylation to stages of hepatosteatosis and nonalcoholic steatohepatitis. In summary, our results indicate a crucial role of the liver in participation to systemic DPP4 levels. Furthermore, the data show that glucose-induced expression of Dpp4 in the liver is facilitated by demethylation of the Dpp4 gene early in life. This might contribute to early deteriorations in hepatic function, which in turn result in metabolic disease such as hepatosteatosis later in life.

Association between DPP4 gene polymorphism and serum lipid levels in Chinese type 2 diabetes individuals

OBJECTIVE

The goal of the genetic investigation was to identify the associations of serum lipid levels and DPP-4 variants in Chinese type 2 diabetes patients.

METHODS

We detected four variants of the DPP4 gene in 190 Chinese individuals with type 2 diabetes and tested for an association with dyslipidemia in 82 selected samples. Data including basic information, HbA1c, FPG, serum lipid parameters were collected. Statistical analysis was performed by SPSS 13.0 through ANOVA and χ² test.

RESULTS

The genetic polymorphism of rs4664443, rs3788979, rs7608798 and rs1558957 in Chinese type 2 diabetes were consistent with Hardy-Weinberg equilibrium. The CT genotype of rs4664443 suffered from higher serum TG (P=0.013), LDL (P=0.044) and ApoB (P=0.006) levels, whereas the TT genotype of rs7608798 exhibited a lower serum TG level (P=0.037). For rs3788979, the serum TG level (P=0.034) and BMI (P=0.04) were significantly different among genotypes. Moreover, serum TG and TC levels and BMI showed a positive correlation with the number unfavorable alleles, and individuals with more than two unfavorable alleles had higher TG (P=0.004), TC (P=0.011), and BMI (P=0.044) values.

CONCLUSIONS

This is the first study to investigate DPP4 allelic distributions and their association with dyslipidemia in Chinese type 2 diabetes patients, which may have clinical significance.

DNA Methylation Modulates Nociceptive Sensitization after Incision

DNA methylation is a key epigenetic mechanism controlling DNA accessibility and gene expression. Blockade of DNA methylation can significantly affect pain behaviors implicated in neuropathic and inflammatory pain. However, the role of DNA methylation with regard to postoperative pain has not yet been explored. In this study we sought to investigate the role of DNA methylation in modulating incisional pain and identify possible targets under DNA methylation and contributing to incisional pain. DNA methyltranferase (DNMT) inhibitor 5-Aza-2′-deoxycytidine significantly reduced incision-induced mechanical allodynia and thermal sensitivity. Aza-2′-deoxycytidine also reduced hindpaw swelling after incision, suggesting an anti-inflammatory effect. Global DNA methylation and DNMT3b expression were increased in skin after incision, but none of DNMT1, DNMT3a or DNMT3b was altered in spinal cord or DRG. The expression of proopiomelanocortin Pomc encoding β-endorphin and Oprm1 encoding the mu-opioid receptor were upregulated peripherally after incision; moreover, Oprm1 expression was further increased under DNMT inhibitor treatment. Finally, local peripheral injection of the opioid receptor antagonist naloxone significantly exacerbated incision-induced mechanical hypersensitivity. These results suggest that DNA methylation is functionally relevant to incisional nociceptive sensitization, and that mu-opioid receptor signaling might be one methylation regulated pathway controlling sensitization after incision.

DPP4 in Diabetes

Dipeptidyl-peptidase 4 (DPP4) is a glycoprotein of 110 kDa, which is ubiquitously expressed on the surface of a variety of cells. This exopeptidase selectively cleaves N-terminal dipeptides from a variety of substrates, including cytokines, growth factors, neuropeptides, and the incretin hormones. Expression of DPP4 is substantially dysregulated in a variety of disease states including inflammation, cancer, obesity, and diabetes. Since the incretin hormones, glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide (GIP), are major regulators of post-prandial insulin secretion, inhibition of DPP4 by the gliptin family of drugs has gained considerable interest for the therapy of type 2 diabetic patients. In this review, we summarize the current knowledge on the DPP4–incretin axis and evaluate most recent findings on DPP4 inhibitors. Furthermore, DPP4 as a type II transmembrane protein is also known to be cleaved from the cell membrane involving different metalloproteases in a cell-type-specific manner. Circulating, soluble DPP4 has been identified as a new adipokine, which exerts both para- and endocrine effects. Recently, a novel receptor for soluble DPP4 has been identified, and data are accumulating that the adipokine-related effects of DPP4 may play an important role in the pathogenesis of cardiovascular disease. Importantly, circulating DPP4 is augmented in obese and type 2 diabetic subjects, and it may represent a molecular link between obesity and vascular dysfunction. A critical evaluation of the impact of circulating DPP4 is presented, and the potential role of DPP4 inhibition at this level is also discussed.

Characterization of dedifferentiating human mature adipocytes from the visceral and subcutaneous fat compartments: fibroblast-activation protein alpha and dipeptidyl peptidase 4 as major components of matrix remodeling

Mature adipocytes can reverse their phenotype to become fibroblast-like cells. This is achieved by ceiling culture and the resulting cells, called dedifferentiated fat (DFAT) cells, are multipotent. Beyond the potential value of these cells for regenerative medicine, the dedifferentiation process itself raises many questions about cellular plasticity and the pathways implicated in cell behavior. This work has been performed with the objective of obtaining new information on adipocyte dedifferentiation, especially pertaining to new targets that may be involved in cellular fate changes. To do so, omental and subcutaneous mature adipocytes sampled from severely obese subjects have been dedifferentiated by ceiling culture. An experimental design with various time points along the dedifferentiation process has been utilized to better understand this process. Cell size, gene and protein expression as well as cytokine secretion were investigated. Il-6, IL-8, SerpinE1 and VEGF secretion were increased during dedifferentiation, whereas MIF-1 secretion was transiently increased. A marked decrease in expression of mature adipocyte transcripts (PPARγ2, C/EBPα, LPL and Adiponectin) was detected early in the process. In addition, some matrix remodeling transcripts (FAP, DPP4, MMP1 and TGFβ1) were rapidly and strongly up-regulated. FAP and DPP4 proteins were simultaneously induced in dedifferentiating mature adipocytes supporting a potential role for these enzymes in adipose tissue remodeling and cell plasticity.