Genetic Studies on Diabetic Microvascular Complications: Focusing on Genome-Wide Association Studies

Plasma thrombin-activatable fibrinolysis inhibitor and the 1040C/T polymorphism are risk factors for diabetic kidney disease in Chinese patients with type 2 diabetes

Background

Inflammatory and hemostatic disorders in diabetic microangiopathy (DMA) can be linked to thrombin-activatable fibrinolysis inhibitor (TAFI) and its own gene polymorphisms. Thus, the study aimed to investigate the associations of plasma TAFI and gene polymorphisms with DMA in Chinese patients with type 2 diabetes (T2D).

Methods

Plasma TAFI of 223 patients with T2D was measured, and the genotypes and alleles of the 1040C/T, 438G/A, and 505G/A polymorphisms of the TAFI gene were analyzed. A ROC curve was constructed to evaluate the identifying power of TAFI between patients with T2D and DMA, and logistic regression analysis was used to observe the correlation of plasma TAFI and gene polymorphisms with the risk for DMA.

Results

Plasma TAFI was higher in patients with DMA than in patients with only T2D (p < 0.05). TAFI exhibited the largest area under ROC in identifying diabetic kidney disease (DKD) from only T2D (0.763, 95% CI [0.674-0.853], p < 0.01), and adjusted multivariate analysis showed a high odds ratio (OR: 15.72, 95% CI [4.573-53.987], p < 0.001) for DKD. Higher frequencies of the CT genotype and T allele of the 1040C/T polymorphism were found in DKD compared with only T2D (respectively p < 0.05), and the CT genotype exhibited a high OR (1.623, 95% CI [1.173-2.710], p < 0.05) for DKD. DKD patients with the CT genotype had higher plasma TAFI levels, while T2D and DKD patients with CC/TT genotypes had lower plasma TAFI levels.

Conclusion

Plasma TAFI and the CT genotype and T allele of the 1040C/T polymorphism are independent risk factors for DKD in Chinese T2D patients.

Genetics of diabetes

Diabetes mellitus is a complicated disease characterized by a complex interplay of genetic, epigenetic, and environmental variables. It is one of the world's fastest-growing diseases, with 783 million adults expected to be affected by 2045. Devastating macrovascular consequences (cerebrovascular disease, cardiovascular disease, and peripheral vascular disease) and microvascular complications (like retinopathy, nephropathy, and neuropathy) increase mortality, blindness, kidney failure, and overall quality of life in individuals with diabetes. Clinical risk factors and glycemic management alone cannot predict the development of vascular problems; multiple genetic investigations have revealed a clear hereditary component to both diabetes and its related complications. In the twenty-first century, technological advancements (genome-wide association studies, next-generation sequencing, and exome-sequencing) have led to the identification of genetic variants associated with diabetes, however, these variants can only explain a small proportion of the total heritability of the condition. In this review, we address some of the likely explanations for this "missing heritability", for diabetes such as the significance of uncommon variants, gene-environment interactions, and epigenetics. Current discoveries clinical value, management of diabetes, and future research directions are also discussed.

The G Allele of the rs12050217 Polymorphism in the BDKRB1 Gene Is Associated with Protection for Diabetic Retinopathy

Purpose: The plasma kallikrein-kinin system is activated during vascular injury caused by diabetic retinopathy (DR), being involved in hyperpermeability and inflammation. Bradykinin B1 receptor (B1R) is expressed in human retina, and its levels are increased in murine models of diabetes. Experimental studies reveal that B1R antagonists ameliorate retinal injury caused by diabetes in rodents. Thus, the aim of this study was to investigate the association between the rs12050217A/G polymorphism in the BDKRB1 gene, the gene that codifies B1R, and DR in type 2 diabetes mellitus (T2DM) patients. Methods: We analyzed 636 T2DM patients and 443 non-diabetic subjects. T2DM patients were categorized by the presence of non-proliferative DR (NPDR, n = 267), proliferative DR (PDR, n = 197), and absence of DR (n = 172). The BDKRB1 rs12050217A/G polymorphism was genotyped by real-time PCR using TaqMan MGB probes. Results: The genotype frequencies of the BDKRB1 rs12050217A/G polymorphism are in Hardy-Weinberg equilibrium and did not differ between T2DM patients and non-diabetic subjects (P > 0.05). The presence of the genotypes containing the rs12050217 G allele was less frequent in patients with PDR when compared to patients with NPDR and without DR (32.0%, 41.9%, and 43.0%, P = 0.045, respectively). Interestingly, the presence of G allele was associated with ~40% protection for PDR, which was confirmed after correction for the presence of hypertension, ethnicity, age, HDL, and gender (odds ratio = 0.616, 95% confidence interval 0.385-0.986, P = 0.043). Conclusion: For the first time, we showed that BDKRB1 rs12050217 G allele is associated with protection for the advanced stage of DR in T2DM patients; however, further studies are needed to confirm this finding.

Genome-wide association study identifies new susceptibility loci for diabetic nephropathy in Korean patients with type 2 diabetes mellitus

Genetic factors are considered to be important in the pathogenesis of diabetic nephropathy (DN). Despite several genome-wide association studies (GWASs) demonstrating that specific polymorphisms of candidate genes were associated with DN, there were some limitations in previous studies. We conducted a GWAS using customized DNA chips to identify novel susceptibility loci for DN in Korean. We analyzed a total of 414 DN cases and 474 normoalbuminuric diabetic hyper-controls across two stages using customized DNA chips containing 98 667 single nucleotide polymorphisms (SNPs). We explored the associations between SNPs and DN in samples from 87 DN cases, mostly confirmed by renal biopsy, and 104 diabetic hyper-controls, and replicated these associations in independent cohort samples with 327 DN cases and 370 diabetic hyper-controls. The top significant SNPs from the discovery samples were selected for replication in the independent cohort. rs3765156 in PIK3C2B was significantly associated with DN in the replication cohort after multiple test. The SNPs identified in our study provide new insights into the pathogenesis of DN in the Korean population. Additional studies are needed to determine biological effects and clinical utility of our findings.

Precision medicine in diabetes prevention, classification and management

Diabetes has become a major burden of healthcare expenditure. Diabetes management following a uniform treatment algorithm is often associated with progressive treatment failure and development of diabetic complications. Recent advances in our understanding of the genomic architecture of diabetes and its complications have provided the framework for development of precision medicine to personalize diabetes prevention and management. In the present review, we summarized recent advances in the understanding of the genetic basis of diabetes and its complications. From a clinician's perspective, we attempted to provide a balanced perspective on the utility of genomic medicine in the field of diabetes. Using genetic information to guide management of monogenic forms of diabetes represents the best-known examples of genomic medicine for diabetes. Although major strides have been made in genetic research for diabetes, its complications and pharmacogenetics, ongoing efforts are required to translate these findings into practice by incorporating genetic information into a risk prediction model for prioritization of treatment strategies, as well as using multi-omic analyses to discover novel drug targets with companion diagnostics. Further research is also required to ensure the appropriate use of this information to empower individuals and healthcare professionals to make personalized decisions for achieving the optimal outcome.

Altered expression of WFS1 and NOTCH2 genes associated with diabetic nephropathy in T2DM patients

AIM

The increased incidence of type 2 diabetes mellitus (T2DM) and the importance of early identification and management of its complications, especially diabetic nephropathy (DN), have spotted the light on genetic factors that increase risk of T2DM and its related nephropathy. The present study aimed at investigating expression of (KCNJ11, ABCC8, JAZF1, WFS1, PPARG, NOTCH2 and EXOSC4) genes in peripheral blood of T2DM patients.

METHOD

The study included 30 non-complicated T2DM patients, 30 patients with DN and 40 healthy controls. Quantitative Real Time PCR Array was used to study gene expression.

RESULTS

NOTCH2 showed higher expression while KCNJ11, JAZF1, WFS1 and PPARG genes showed lower expression in DN patients compared to non-complicated patients. KCNJ11, JAZF1, WFS1, PPARG, and EXOSC4 expression showed significant negative correlation with microalbumin, while NOTCH2 expression was significantly positively correlated with microalbumin. AS regard HbA1c and studied genes expression, there was significant negative correlation between WFS1 expression and HbA1c, while NOTCH2, KCNJ11, JAZF1, PPARG, EXOSC4 expression didn't show significant correlation with HbA1c. Risk ratio of studied genes expression showed that WFS1 and NOTCH2 had highest risk ratio (30) and highest sensitivity and specificity, in relation to DN and they were the best predictors in the group of studied genes at cut off value of ≤0.861 for WFS1 and ≥0.678 for NOTCH2.

CONCLUSION

Altered expression of WFS1 and NOTCH2 genes may play a role in pathogenesis and development of DN in patients with T2DM. These results may contribute in early identification and management of DN.

Diabetic polyneuropathy, deep white matter lesions, and carotid atherosclerosis: is there any association?

The morphologic and functional damages of diabetes mellitus (DM) on microcirculation can play a role in the pathogenesis of both polyneuropathy and cerebral white matter lesions. The aim of this study is to investigate the relation between polyneuropathy and cerebral deep white matter lesions (DWMLs) and carotid atherosclerosis in patients with type 2 DM. Sixty-six patients with type 2 DM without any disorder that may cause polyneuropathy, and vascular risk factors except for DM and hyperlipidemia were included in the study. DWMLs and carotid atherosclerosis were investigated in patients with and without polyneuropathy. Forty patients (60.6%) had diabetic sensorimotor polyneuropathy. DWMLs were more frequent in patients with polyneuropathy compared to patients without polyneuropathy (p = 0.003). Logistic regression analysis confirmed association between polyneuropathy and DWMLs after adjusted for age (p = 0.013), duration of DM (p = 0.007), and both age and duration of DM (p = 0.016). No statistically significant difference was found between patients with and without polyneuropathy for carotid atherosclerosis. Among patients with polyneuropathy, those having DWMLs had higher mean age (p = 0.003) and longer symptom duration (p = 0.020) compared to patients without DWMLs. No association was found between DWMLs and carotid atherosclerosis. Polyneuropathy and cerebral DWMLs in type 2 DM patients may share common pathogenesis; presence and duration of polyneuropathy symptoms may predict ischemic white matter damage independent of carotid atherosclerosis.

Normoalbuminuric diabetic kidney disease

Diabetic kidney disease (DKD) is one of the primary causes of end-stage renal disease (ESRD). Early diagnosis is very important in preventing the development of DKD. Urinary albumin excretion rate (UAER) and glomerular filtration rate (GFR) are widely accepted as criteria for the diagnosis and clinical grading of DKD, and microalbuminuria has been recommended as the first clinical sign of DKD. The natural history of DKD has been divided into three stages: normoalbuminuria, microalbuminuria, and macroalbuminuria. However, this clinical paradigm has been questioned recently, as studies have shown that a portion of diabetes mellitus (DM) patients with normoalbuminuria have progressive renal insufficiency, referred to as normoalbuminuric diabetic kidney disease (NADKD) or nonalbuminuric diabetic nephropathy. Epidemiologic research has demonstrated that normoalbuminuric diabetic kidney disease is common, and the large number of NADKD patients suggests that the traditional paradigm needs to be shifted. Currently, the pathogenesis of NADKD remains unclear, but many clinical studies have identified some clinical and pathological features of NADKD. In addition, the long-term outcomes of NADKD patients remain controversial. In this article, we reviewed the latest studies addressing the pathogenesis, pathology, treatment and prevention of NADKD.

Diabetic macular oedema: clinical risk factors and emerging genetic influences

Diabetic macular oedema is the major cause of visual impairment in type 1 and type 2 diabetes. As type 2 diabetes becomes more prevalent worldwide, the prevalence of diabetic macular oedema is also expected to rise. Current management of diabetic macular oedema is challenging, expensive and not optimal in a subset of patients. Therefore, it is important to increase our understanding of the risk factors involved and develop preventative strategies. While clinical risk factors for diabetic macular oedema have been identified, few studies have addressed potential genetic risk factors. Epidemiology and family studies suggest genetic influences are of importance. In this review, we summarise known clinical risk factors, as well as discuss the small number of genetic studies that have been performed for diabetic macular oedema.

Clinical worthlessness of genetic prediction of common forms of diabetes mellitus and related chronic complications: A position statement of the Italian Society of Diabetology

AIM

We are currently facing several attempts aimed at marketing genetic data for predicting multifactorial diseases, among which diabetes mellitus is one of the more prevalent. The present document primarily aims at providing to practicing physicians a summary of available data regarding the role of genetic information in predicting diabetes and its chronic complications.

DATA SYNTHESIS

Firstly, general information about characteristics and performance of risk prediction tools will be presented in order to help clinicians to get acquainted with basic methodological information related to the subject at issue. Then, as far as type 1 diabetes is concerned, available data indicate that genetic information and counseling may be useful only in families with many affected individuals. However, since no disease prevention is possible, the utility of predicting this form of diabetes is at question. In the case of type 2 diabetes, available data really question the utility of adding genetic information on top of well performing, easy available and inexpensive non-genetic markers. Finally, the possibility of using the few available genetic data on diabetic complications for improving our ability to predict them will also be presented and discussed. For cardiovascular complication, the addition of genetic information to models based on clinical features does not translate in a substantial improvement in risk discrimination. For all other diabetic complications genetic information are currently very poor and cannot, therefore, be used for improving risk stratification.

CONCLUSIONS

In all, nowadays the use of genetic testing for predicting diabetes and its chronic complications is definitively of little value in clinical practice.

Biomarkers of Diabetic Retinopathy

Diabetic retinopathy (DR), a leading cause of acquired vision loss, is a microvascular complication of diabetes. While traditional risk factors for diabetic retinopathy including longer duration of diabetes, poor blood glucose control, and dyslipidemia are helpful in stratifying patient's risk for developing retinopathy, many patients without these traditional risk factors develop DR; furthermore, there are persons with long diabetes duration who do not develop DR. Thus, identifying biomarkers to predict DR or to determine therapeutic response is important. A biomarker can be defined as a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention. Incorporation of biomarkers into risk stratification of persons with diabetes would likely aid in early diagnosis and guide treatment methods for those with DR or with worsening DR. Systemic biomarkers of DR include serum measures including genomic, proteomic, and metabolomics biomarkers. Ocular biomarkers including tears and vitreous and retinal vascular structural changes have also been studied extensively to prognosticate the risk of DR development. The current studies on biomarkers are limited by the need for larger sample sizes, cross-validation in different populations and ethnic groups, and time-efficient and cost-effective analytical techniques. Future research is important to explore novel DR biomarkers that are non-invasive, rapid, economical, and accurate to help reduce the incidence and progression of DR in people with diabetes.

Screening of long non-coding RNA and TUG1 inhibits proliferation with TGF-β induction in patients with COPD

Objective

To evaluate differentially expressed long noncoding RNAs (lncRNAs) and the potential role of lncRNA TUG1 in patients with chronic obstructive pulmonary disease (COPD).

Methods

Total RNA was extracted from both COPD and non-COPD lung tissues, and microarray analysis was performed with 25,628 lncRNA probes and 20,106 mRNA probes. In addition, five up-regulated and five down-regulated lncRNAs were selected for identification using quantitative real-time polymerase chain reaction. COPD cell model was established by transforming growth factor β (TGF-β) treatment. Cell Counting Kit-8 assay was used to detect BEAS-2B and HFL1 cell proliferation after TUG-siRNA transfection with TGF-β treatment. In addition, the expression levels of α-SMA and fibronectin proteins were determined using Western blot in BEAS-2B and HFL1 cells after TUG-siRNA transfection with TGF-β treatment.

Results

There were 8,376 (32.7%) differentially expressed lncRNAs and 5,094 (25.3%) differentially expressed mRNAs in COPD lung tissues compared with non-COPD lung tissues. Five of the analyzed lncRNAs (BC038205, BC130595, TUG1, MEG3, and LOC646329) were markedly increased, while five lncRNAs (LOC729178, PLAC2, LOC339529, LINC00229, and SNHG5) were significantly decreased in COPD lung tissues compared with non-COPD lung tissues (n=20) (***P<0.001). Knockdown of lncRNA TUG1 promotes BEAS-2B and HFL1 cell proliferation after TGF-β treatment through inhibiting the expression levels of α-SMA and fibronectin.

Conclusion

Abundant, differentially expressed lncRNAs and mRNAs were identified by microarray analysis and these might play a partial or key role in the diagnosis of patients with COPD. LncRNA TUG1 may become a very important class of biomarker and may act as a potential diagnostic and therapeutic target for patients with COPD.

Association Between Heme Oxygenase-1 Promoter Polymorphisms and the Development of Albuminuria in Type 2 Diabetes: A Case-Control Study

Heme oxygenase (HO)-1 is a key enzyme in cytoprotective mechanisms against oxidative stress in the cardiovascular-renal system. The T(-413)A single nucleotide polymorphism (SNP) and (GT)n microsatellite polymorphism in the HO-1 gene promoter modulate the HO-1 gene transcriptional activity and these polymorphisms are associated with various human diseases.We investigated the association between HO-1 promoter polymorphisms and nephropathy in type 2 diabetes. We sequenced the T(-413)A SNP and (GT)n repeat segments of the HO-1 gene promoter in 536 patients with type 2 diabetes. (GT)n alleles were divided into 2 groups: short (S, ≤25 GT repeats) and long (L, >25 GT repeats) alleles. The presence of albuminuria was used as a marker of diabetic nephropathy.Patients with the TT genotype in the T(-413)A SNP were significantly more susceptible to albuminuria development than those carrying the A allele, with an odds ratio of 1.577 (95% confidence interval, 1.088 - 2.285; P = 0.016). Subgroup analysis showed that patients carrying the TT genotype with long duration of diabetes (≥20 years), poor glycemic control, male gender and without hypertension had higher odds ratios for the development of albuminuria. In vitro, promoter activity of the T(-413)A SNP was higher with A allele than T allele. Regarding to the (GT)n repeats, the LL genotype showed a higher odds ratio for the development of albuminuria only in patients with hypertension when compared to the S allele.In conclusion, the T(-413)A SNP in the HO-1 promoter is significantly associated with albuminuria development in type 2 diabetes patients, especially with longer duration and poor glycemic control.

Biomarkers in Diabetic Retinopathy

There is a global diabetes epidemic correlating with an increase in obesity. This coincidence may lead to a rise in the prevalence of type 2 diabetes. There is also an as yet unexplained increase in the incidence of type 1 diabetes, which is not related to adiposity. Whilst improved diabetes care has substantially improved diabetes outcomes, the disease remains a common cause of working age adult-onset blindness. Diabetic retinopathy is the most frequently occurring complication of diabetes; it is greatly feared by many diabetes patients. There are multiple risk factors and markers for the onset and progression of diabetic retinopathy, yet residual risk remains. Screening for diabetic retinopathy is recommended to facilitate early detection and treatment. Common biomarkers of diabetic retinopathy and its risk in clinical practice today relate to the visualization of the retinal vasculature and measures of glycemia, lipids, blood pressure, body weight, smoking, and pregnancy status. Greater knowledge of novel biomarkers and mediators of diabetic retinopathy, such as those related to inflammation and angiogenesis, has contributed to the development of additional therapeutics, in particular for late-stage retinopathy, including intra-ocular corticosteroids and intravitreal vascular endothelial growth factor inhibitors ('anti-VEGFs') agents. Unfortunately, in spite of a range of treatments (including laser photocoagulation, intraocular steroids, and anti-VEGF agents, and more recently oral fenofibrate, a PPAR-alpha agonist lipid-lowering drug), many patients with diabetic retinopathy do not respond well to current therapeutics. Therefore, more effective treatments for diabetic retinopathy are necessary. New analytical techniques, in particular those related to molecular markers, are accelerating progress in diabetic retinopathy research. Given the increasing incidence and prevalence of diabetes, and the limited capacity of healthcare systems to screen and treat diabetic retinopathy, there is need to reliably identify and triage people with diabetes. Biomarkers may facilitate a better understanding of diabetic retinopathy, and contribute to the development of novel treatments and new clinical strategies to prevent vision loss in people with diabetes. This article reviews key aspects related to biomarker research, and focuses on some specific biomarkers relevant to diabetic retinopathy.