The association between methylation levels of targeted genes and albuminuria in patients with early diabetic kidney disease

Objective: The incidence of diabetes and its complications are greatly increasing world-wide. Diabeticnephropathy (DN) is the main cause of end-stage renal disease and is associated with high morbidity and mortality. It is important to predict patients with high risk for DN in the early stage. We selected the genes which have an important role on diabetic kidney disease. We aimed to investigate the association between DNA methylation levels of targeted genes and albuminuria in patients with early DN.

Methods: We collected the clinical data of patients with type 2 diabetes mellitus. We measured spot urine albumin creatinine ratio to calculate albuminuria level. We divided patients into two groups based on albumin excretion as patients with (n = 69) and without DN (n = 27). We performed methylation profiling after bisulfite conversion by pyrosequencing method. The mean value of percent methylation level of each gene was calculated.

Results: We compared targeted genes (TIMP-2, AKR1B1, MMP-2, MMP-9, MYL9, SCL2A4, SCL2A1, SCL4A3) methylation levels and albuminuria. We found significant negative correlation between TIMP-2 and AKR1B1 gene methylation levels and albuminuria levels.

Conclusions: The present study provided evidence that hypomethylation of TIMP-2 and AKR1B1 genes can be associated with albuminuria in patients with early DN. We may speculate that the hypomethylation of TIMP-2 and AKR1B1 genes may be an early surrogate marker of DN.

Modern methods of diagnosing chronic kidney disease in patients with diabetes mellitus

Chronic kidney disease (CKD) is a general concept that involves renal tissue regardless of the aetiology of the leading disease. CKD occurs in one out of every two patients with diabetes mellitus (DM) and appreciably limits the duration and quality of life. CKD can be diagnosed by glomerular filtration rate (GFR), which is recognised as the most representative indicator of the quantity and total workload of nephrons. However, the decrease in GFR occurs at an advanced stage of nephropathy and causes irreversible renal damage, which ultimately requires substitutive renal therapy and, thereby, increases the expense. In this regard, clinical trials have been conducted to identify the biomarkers of CKD reflecting renal damage at earlier stages of the disease. This article presents an overview of modern methods for the diagnosis of CKD and preclinical markers of kidney injury in patients with DM.

Role of Epigenetic Histone Modifications in Diabetic Kidney Disease Involving Renal Fibrosis

One of the commonest causes of end-stage renal disease is diabetic kidney disease (DKD). Renal fibrosis, characterized by the accumulation of extracellular matrix (ECM) proteins in glomerular basement membranes and the tubulointerstitium, is the final manifestation of DKD. The TGF-β pathway triggers epithelial-to-mesenchymal transition (EMT), which plays a key role in the accumulation of ECM proteins in DKD. DCCT/EDIC studies have shown that DKD often persists and progresses despite glycemic control in diabetes once DKD sets in due to prior exposure to hyperglycemia called "metabolic memory." These imply that epigenetic factors modulate kidney gene expression. There is evidence to suggest that in diabetes and hyperglycemia, epigenetic histone modifications have a significant effect in modulating renal fibrotic and ECM gene expression induced by TGF-β1, as well as its downstream profibrotic genes. Histone modifications are also implicated in renal fibrosis through its ability to regulate the EMT process triggered by TGF-β signaling. In view of this, efforts are being made to develop HAT, HDAC, and HMT inhibitors to delay, stop, or even reverse DKD. In this review, we outline the latest advances that are being made to regulate histone modifications involved in DKD.

Functional polymorphism rs710218 in the gene coding GLUT1 protein is associated with in-stent restenosis

Aim: To analyze the association between in-stent restenosis (ISR) and polymorphisms in genes coding IGF-1, IGFBP3, ITGB3 and GLUT1, which play an important role in the smooth muscle cell proliferation and extracellular matrix synthesis – the main components of neointima. Materials & methods: We analyzed 265 patients who underwent bare metal stent implantation. Results: The differences in the occurrence of ISR between genotypes of the analyzed polymorphisms in the IGF-1, IGFBP3 and ITGB3 were not statistically significant. The T/T genotype of the rs710218 polymorphism in the GLUT1 (SLC2A1) gene was more common in the ISR group compared with non-ISR patients (81.1 vs 64.8%; p = 0.02). In a multivariable model the A/A and A/T genotype remained correlated with lower occurrence of ISR (odds ratio: 0.45; 95% CI: 0.21–0.97; p = 0.03). Conclusion: The rs710218 polymorphism in the gene coding GLUT1 protein is a novel risk factor for ISR.

Urinary angiotensinogen as a novel early biomarker of intrarenal renin-angiotensin system activation in experimental type 1 diabetes

Urinary excretion of albumin (UAlb) is used clinically as a marker of diabetic nephropathy (DN). Although DN was thought to be a unidirectional process, recent studies demonstrated that a large proportion of patients diagnosed with DN reverted to normoalbuminuria. Moreover, despite the normoalbuminuria, one-third of them exhibited reduced renal function even during the microalbuminuric stage. This study was performed to investigate whether urinary angiotensinogen (UAGT) level may serve as a useful marker of the early stage of experimental type 1 diabetes (T1DM). T1DM was induced by a single intraperitoneal injection of streptozotocin. Control mice were injected with citrate buffer. Two days after streptozotocin injection, half of the mice received continuous insulin treatment. Our data showed that UAlb excretion was increased 6 days after streptozotocin injection compared to controls, whereas UAGT excretion was increased at an earlier time point. These increases were reversed by insulin treatment. The UAGT to UAlb ratio was increased in diabetic mice compared to control mice. Furthermore, the increased AGT expression in the kidneys was observed in diabetic mice. These data suggest that UAGT might be useful as a novel early biomarker of activation of the renin-angiotensin system in experimental type 1 diabetes.

Pre-clinical markers for diagnosis of diabetic nephropathy in patients with type 1 diabetes mellitus

Due to progressive nature of diabetic nephropathy (DN) and limited effectiveness of therapeutic efforts at clinically overt stages, diagnosisof pre-clinical (and, therefore, potentially reversible) DN is especially important. To date, however, test for microalbuminuriaremains the only technique applicable for early diagnostics of DN. Current review addresses search for potential markers of pre-clinical stage of DN in patients with type 1 diabetes mellitus and embracesdata from latest experimental and clinical studies in this area.

Common variants in the type 2 diabetes KCNQ1 gene are associated with impairments in insulin secretion during hyperglycaemic glucose clamp

BACKGROUND

Genome-wide association studies in Japanese populations recently identified common variants in the KCNQ1 gene to be associated with type 2 diabetes. We examined the association of these variants within KCNQ1 with type 2 diabetes in a Dutch population, investigated their effects on insulin secretion and metabolic traits and on the risk of developing complications in type 2 diabetes patients.

METHODOLOGY

The KCNQ1 variants rs151290, rs2237892, and rs2237895 were genotyped in a total of 4620 type 2 diabetes patients and 5285 healthy controls from the Netherlands. Data on macrovascular complications, nephropathy and retinopathy were available in a subset of diabetic patients. Association between genotype and insulin secretion/action was assessed in the additional sample of 335 individuals who underwent a hyperglycaemic clamp.

PRINCIPAL FINDINGS

We found that all the genotyped KCNQ1 variants were significantly associated with type 2 diabetes in our Dutch population, and the association of rs151290 was the strongest (OR 1.20, 95% CI 1.07-1.35, p = 0.002). The risk C-allele of rs151290 was nominally associated with reduced first-phase glucose-stimulated insulin secretion, while the non-risk T-allele of rs2237892 was significantly correlated with increased second-phase glucose-stimulated insulin secretion (p = 0.025 and 0.0016, respectively). In addition, the risk C-allele of rs2237892 was associated with higher LDL and total cholesterol levels (p = 0.015 and 0.003, respectively). We found no evidence for an association of KCNQ1 with diabetic complications.

CONCLUSIONS

Common variants in the KCNQ1 gene are associated with type 2 diabetes in a Dutch population, which can be explained at least in part by an effect on insulin secretion. Furthermore, our data suggest that KCNQ1 is also associated with lipid metabolism.

Urinary type IV collagen excretion predicts subsequent declining renal function in type 2 diabetic patients with proteinuria

Baseline urinary type IV collagen excretion was negatively correlated with the subsequent GFR change (r(s)=-0.39, p=0.04) in our cohort of 30 type 2 diabetic patients with proteinuria. Therefore, it could be used to predict subsequent declining renal function in type 2 diabetic patients with proteinuria.

Successes achieved and challenges ahead in translating biomarkers into clinical applications

Biomarkers are important tools for identifying and stratifying diseases, predicting their progression and determining the effectiveness, safety, and doses of therapeutic interventions. This is important for common chronic diseases such as diabetic nephropathy, osteoporosis, and rheumatoid arthritis which affect large numbers of patients worldwide. This article summarizes the current knowledge of established and novel biomarkers for each of these diseases as presented at the 2008 AAPS/ACCP joint symposium "Success Achieved and Challenges Ahead in Translating Biomarkers into Clinical Applications," in Atlanta, Georgia. The advantages and disadvantages of various proteomic, metabolomic, genomic, and imaging biomarkers are discussed in relation to disease diagnosis and stratification, prognosis, drug development, and potential clinical applications. The use of biomarkers as a means to determine therapeutic interventions is also considered. In addition, we show that biomarkers may be useful for adapting therapies for individual needs by allowing the selection of patients who are most likely to respond or react adversely to a particular treatment. They may also be used to determine whether the development of a novel therapy is worth pursuing by informing crucial go/no go decisions around safety and efficacy. Indeed, regulatory bodies now suggest that effective integration of biomarkers into clinical drug development programs is likely to promote the development of novel therapeutics and more personalized medicine.

Overproduction of phosphoprotein enriched in diabetes (PED) induces mesangial expansion and upregulates protein kinase C-beta activity and TGF-beta1 expression

AIMS/HYPOTHESIS

Overproduction of phosphoprotein enriched in diabetes (PED, also known as phosphoprotein enriched in astrocytes-15 [PEA-15]) is a common feature of type 2 diabetes and impairs insulin action in cultured cells and in mice. Nevertheless, the potential role of PED in diabetic complications is still unknown.

METHODS

We studied the effect of PED overproduction and depletion on kidney function in animal and cellular models.

RESULTS

Transgenic mice overexpressing PED (PEDTg) featured age-dependent increases of plasma creatinine levels and urinary volume, accompanied by expansion of the mesangial area, compared with wild-type littermates. Serum and kidney levels of TGF-beta1 were also higher in 6- and 9-month-old PEDTg. Overexpression of PED in human kidney 2 cells significantly increased TGF-beta1 levels, SMAD family members (SMAD)2/3 phosphorylation and fibronectin production. Opposite results were obtained following genetic silencing of PED in human kidney 2 cells by antisense oligonucleotides. Inhibition of phospholipase D and protein kinase C-beta by 2-butanol and LY373196 respectively reduced TGF-beta1, SMAD2/3 phosphorylation and fibronectin production. Moreover, inhibition of TGF-beta1 receptor activity and SMAD2/3 production by SB431542 and antisense oligonucleotides respectively reduced fibronectin secretion by about 50%. TGF-beta1 circulating levels were significantly reduced in Ped knockout mice and positively correlated with PED content in peripheral blood leucocytes of type 2 diabetic patients.

CONCLUSIONS/INTERPRETATION

These data indicate that PED regulates fibronectin production via phospholipase D/protein kinase C-beta and TGF-beta1/SMAD pathways in kidney cells. Raised PED levels may therefore contribute to the abnormal accumulation of extracellular matrix and renal dysfunction in diabetes.

Transcription factors in the pathogenesis of diabetic nephropathy

Approximately a third of patients with diabetes develop diabetic kidney disease, and diabetes is the leading cause of end-stage renal disease in most developed countries. Hyperglycaemia is known to activate genes that ultimately lead to extracellular matrix accumulation, the hallmark of diabetic nephropathy. Several transcription factors have been implicated in glucose-mediated expression of genes involved in diabetic nephropathy. This review focuses on the transcription factors upstream stimulatory factors 1 and 2 (USF1 and 2), activator protein 1 (AP-1), nuclear factor (NF)-kappaB, cAMP-response-element-binding protein (CREB), nuclear factor of activated T cells (NFAT), and stimulating protein 1 (Sp1). In response to high glucose, several of these transcription factors regulate the gene encoding the profibrotic cytokine transforming growth factor beta, as well as genes for a range of other proteins implicated in inflammation and extracellular matrix turnover, including thrombospondin 1, the chemokine CCL2, osteopontin, fibronectin, decorin, plasminogen activator inhibitor 1 and aldose reductase. Identifying the molecular mechanisms by which diabetic nephropathy occurs has important clinical implications as therapies can then be tailored to target those at risk. Strategies to specifically target transcription factor activation and function may be employed to halt the progression of diabetic nephropathy.