Minor effect of GLUT1 polymorphisms on susceptibility to diabetic nephropathy in type 1 diabetes

The pivotal role of glucose transporter 1 in diabetic kidney disease

Diabetes mellitus (DM) is a significant public health problem. Diabetic kidney disease (DKD) is the most common complication of DM, and its incidence has been increasing with the increasing prevalence of DM. Given the association between DKD and mortality in patients with DM, DKD is a significant burden on public health resources. Despite its significance in DM progression, the pathogenesis of DKD remains unclear. Aberrant glucose uptake by cells is an important pathophysiological mechanism underlying DKD renal injury. Glucose is transported across the bilayer cell membrane by a glucose transporter (GLUT) located on the cell membrane. Multiple GLUT proteins have been identified in the kidney, and GLUT1 is one of the most abundantly expressed isoforms. GLUT1 is a crucial regulator of intracellular glucose metabolism and plays a key pathological role in the phenotypic changes in DKD mesangial cells. In an attempt to understand the pathogenesis of DKD better, we here present a review of studies on the role of GLUT1 in the development and progression of DKD.

Genetic Modulation of the GLUT1 Transporter Expression-Potential Relevance in Complex Diseases

The human GLUT1 (SLC2A1) membrane protein is the key glucose transporter in numerous cell types, including red cells, kidney, and blood-brain barrier cells. The expression level of this protein has a role in several diseases, including cancer and Alzheimer's disease. In this work, to investigate a potential genetic modulation of the GLUT1 expression level, the protein level was measured in red cell membranes by flow cytometry, and the genetic background was analyzed by qPCR and luciferase assays. We found significant associations between red cell GLUT1 levels and four single nucleotide polymorphisms (SNP) in the coding SLC2A1 gene, that in individuals with the minor alleles of rs841848, rs1385129, and rs11537641 had increased, while those having the variant rs841847 had decreased erythrocyte GLUT1 levels. In the luciferase reporter studies performed in HEK-293T and HepG2 cells, a similar SNP-dependent modulation was observed, and lower glucose, serum, and hypoxic condition had variable, cell- and SNP-specific effects on luciferase expression. These results should contribute to a more detailed understanding of the genetic background of membrane GLUT1 expression and its potential role in associated diseases.

Glucose Metabolism and Dynamics of Facilitative Glucose Transporters (GLUTs) under the Influence of Heat Stress in Dairy Cattle

Heat stress is one of the main threats to dairy cow production; in order to resist heat stress, the animal exhibits a variety of physiological and hormonal responses driven by complex molecular mechanisms. Heat-stressed cows have high insulin activity, decreased non-esterified fatty acids, and increased glucose disposal. Glucose, as one of the important biochemical components of the energetic metabolism, is affected at multiple levels by the reciprocal changes in hormonal secretion and adipose metabolism under the influence of heat stress in dairy cattle. Therefore, alterations in glucose metabolism have negative consequences for the animal’s health, production, and reproduction under heat stress. Lactose is a major sugar of milk which is affected by the reshuffle of the whole-body energetic metabolism during heat stress, contributing towards milk production losses. Glucose homeostasis is maintained in the body by one of the glucose transporters’ family called facilitative glucose transporters (GLUTs encoded by SLC2A genes). Besides the glucose level, the GLUTs expression level is also significantly changed under the influence of heat stress. This review aims to describe the effect of heat stress on systemic glucose metabolism, facilitative glucose transporters, and its consequences on health and milk production.

Associations between the HaeIII Single Nucleotide Polymorphism in the SLC2A1 Gene and Diabetic Nephropathy in Korean Patients with Type 2 Diabetes Mellitus

BACKGROUND

Diabetic nephropathy (DN) is the most serious microvascular complication of diabetes mellitus and is one of the leading causes of end stage renal failure. In previous studies, the contribution of genetic susceptibility to DN showed inconsistent results. In this study, we investigated the association between the solute carrier family 2 facilitated glucose transporter member 1 (SLC2A1) HaeIII polymorphism and DN in Korean patients with type 2 diabetes mellitus (T2DM) according to disease duration.

METHODS

A total of 846 patients with T2DM (mean age, 61.3 ± 12.3 years; mean duration of T2DM, 10.3 ± 7.9 years; 55.3% men) who visited the Chungbuk National University Hospital were investigated. The HaeIII polymorphism of the SLC2A1 gene was determined by the real time polymerase chain reaction method. Genotyping results were presented as GG, AG, or AA. A subgroup analysis was performed according to duration of T2DM (≤ 10 years, > 10 years).

RESULTS

The AG + AA genotype showed a significantly higher risk of DN compared with the GG genotype in patients with a type 2 DM duration less than 10 years (12.4% vs. 4.2%; P < 0.001). No significant differences were observed in terms of other diabetic complications, including retinopathy, peripheral neuropathy, cardiovascular disease, cerebrovascular disease or peripheral artery disease, according to the genotypes of the SLC2A1 HaeIII polymorphism.

CONCLUSION

The SLC2A1 HaeIII polymorphism was associated with DN in Korean patients with T2DM, particularly in the group with a relatively short disease duration.

Risk variants disrupting enhancers of TH1 and TREG cells in type 1 diabetes

Functional interpretation of noncoding genetic variants identified by genome-wide association studies is a major challenge in human genetics and gene regulation. We generated epigenomics data using primary cells from type 1 diabetes patients. Using these data, we identified and validated multiple novel risk variants for this disease. In addition, our ranked list of candidate risk SNPs represents the most comprehensive annotation based on T1D-specific T-cell data. Because many autoimmune diseases share some genetic underpinnings, our dataset may be used to understand causal noncoding mutations in related autoimmune diseases.

Genome-wide association studies (GWASs) have revealed 59 genomic loci associated with type 1 diabetes (T1D). Functional interpretation of the SNPs located in the noncoding region of these loci remains challenging. We perform epigenomic profiling of two enhancer marks, H3K4me1 and H3K27ac, using primary T_H1 and T_REG cells isolated from healthy and T1D subjects. We uncover a large number of deregulated enhancers and altered transcriptional circuitries in both cell types of T1D patients. We identify four SNPs (rs10772119, rs10772120, rs3176792, rs883868) in linkage disequilibrium (LD) with T1D-associated GWAS lead SNPs that alter enhancer activity and expression of immune genes. Among them, rs10772119 and rs883868 disrupt the binding of retinoic acid receptor α (RARA) and Yin and Yang 1 (YY1), respectively. Loss of binding by YY1 also results in the loss of long-range enhancer–promoter interaction. These findings provide insights into how noncoding variants affect the transcriptomes of two T-cell subtypes that play critical roles in T1D pathogenesis.

Ion channels and transporters in diabetic kidney disease

Type 1 and 2 diabetes mellitus are major medical epidemics affecting millions of patients worldwide. Diabetes mellitus is the leading cause of diabetic kidney disease (DKD), which is the most common cause of end-stage renal disease (ESRD). DKD is associated with significant changes in renal hemodynamics and electrolyte transport. Alterations in renal ion transport triggered by pathophysiological conditions in diabetes can exacerbate hypertension, accelerate renal injury, and are integral to the development of DKD. Renal ion transporters and electrolyte homeostasis play a fundamental role in functional changes and injury to the kidney during DKD. With the large number of ion transporters involved in DKD, understanding the roles of individual transporters as well as the complex cascades through which they interact is essential in the development of effective treatments for patients suffering from this disease. This chapter aims to gather current knowledge of the major renal ion transporters with altered expression and activity under diabetic conditions, and provide a comprehensive overview of their interactions and collective functions in DKD.

The contribution of genetic variants of SLC2A1 gene in T2DM and T2DM-nephropathy: association study and meta-analysis

An association study was conducted to investigate the relation between 14 variants of glucose transporter 1 gene (SLC2A1) and the risk of type 2 diabetes (T2DM) leading to nephropathy. We also performed a meta-analysis of 11 studies investigating association between diabetic nephropathy (DN) and SLC2A1 variants. The cohort included 197 cases (T2DM with nephropathy), 155 diseased controls (T2DM without nephropathy) and 246 healthy controls. The association of variants with disease progression was tested using generalized odds ratio (ORG). The risk of type 2 diabetes leading to nephropathy was estimated by the OR of additive and co-dominant models. The mode of inheritance was assessed using the degree of dominance index (h-index). We synthesized results of 11 studies examining association between 5 SLC2A1 variants and DN. ORG was used to assess the association between variants and DN using random effects models. Significant results were derived for co-dominant model of rs12407920 [OR = 2.01 (1.17-3.45)], rs841847 [OR = 1.73 (1.17-2.56)] and rs841853 [OR = 1.74 (1.18-2.55)] and for additive model of rs3729548 [OR = 0.52 (0.29-0.90)]. The mode of inheritance for rs12407920, rs841847 and rs841853 was 'dominance of each minor allele' and for rs3729548 'non-dominance'. Frequency of one haplotype (C-G-G-A-T-C-C-T-G-T-C-C-A-G) differed significantly between cases and healthy controls [p = .014]. Regarding meta-analysis, rs841853 contributed to an increased risk of DN [(ORG = 1.43 (1.09-1.88); ORG = 1.58 (1.01-2.48)] between diseased controls versus cases and healthy controls versus cases, respectively. Further studies confirm the association of rs12407920, rs841847, rs841853, as well as rs3729548 and the risk of T2DM leading to nephropathy.

Polymorphism rs1385129 Within Glut1 Gene SLC2A1 Is Linked to Poor CD4+ T Cell Recovery in Antiretroviral-Treated HIV+ Individuals

Untreated HIV infection is associated with progressive CD4+ T cell depletion, which is generally recovered with combination antiretroviral therapy (cART). However, a significant proportion of cART-treated individuals have poor CD4+ T cell reconstitution. We investigated associations between HIV disease progression and CD4+ T cell glucose transporter-1 (Glut1) expression. We also investigated the association between these variables and specific single nucleotide polymorphisms (SNPs) within the Glut1 regulatory gene AKT (rs1130214, rs2494732, rs1130233, and rs3730358) and in the Glut1-expressing gene SLC2A1 (rs1385129 and rs841853) and antisense RNA 1 region SLC2A1-AS1 (rs710218). High CD4+Glut1+ T cell percentage is associated with rapid CD4+ T cell decline in HIV-positive treatment-naïve individuals and poor T cell recovery in HIV-positive individuals on cART. Evidence suggests that poor CD4+ T cell recovery in treated HIV-positive individuals is linked to the homozygous genotype (GG) associated with SLC2A1 SNP rs1385129 when compared to those with a recessive allele (GA/AA) (odds ratio = 4.67; P = 0.04). Furthermore, poor response to therapy is less likely among Australian participants when compared against American participants (odds ratio: 0.12; P = 0.01) despite there being no difference in prevalence of a specific genotype for any of the SNPs analyzed between nationalities. Finally, CD4+Glut1+ T cell percentage is elevated among those with a homozygous dominant genotype for SNPs rs1385129 (GG) and rs710218 (AA) when compared to those with a recessive allele (GA/AA and AT/TT respectively) (P < 0.04). The heterozygous genotype associated with AKT SNP 1130214 (GT) had a higher CD4+Glut1+ T cell percentage when compared to the dominant homozygous genotype (GG) (P = 0.0068). The frequency of circulating CD4+Glut1+ T cells and the rs1385129 SLC2A1 SNP may predict the rate of HIV disease progression and CD4+ T cell recovery in untreated and treated infection, respectively.

An analysis of the polymorphisms of the GLUT1 gene in urothelial cell carcinomas of the bladder and its correlation with p53, Ki67 and GLUT1 expressions

Frequencies of two glucose transporter 1 (GLUT1) single-nucleotide polymorphisms (SNPs) (XbaI G>T and HaeIII T>C) were studied with urothelial cell carcinomas of the bladder (UCC) and 204 normal persons. And the expression of the p53, Ki67 and GLUT1 was assayed by immunohistochemistry. The frequency of the TT genotype and T allele of the XbaI G>T SNP was decreased in the patients with UCC. The frequency of the CC genotype and C allele of the HaeIII T>C SNP was decreased in the patients with UCC. The GLUT1 XbaI genotype GG was more frequent in higher tumor stage and higher tumor grade patients. In the XbaI G>T SNP, the GG genotype was significantly related to higher Remmele immunoreactive score (IRS) of Ki67 and higher IRS of GLUT1. In conclusion, the TT genotype in XbaI G>T SNP and CC genotype of HaeIII T>C SNP may have protective effect in the carcinogenesis process of UCC. In the XbaI G>T SNP, the GG genotype of was positively related to tumor proliferation, glucose metabolism, tumor grade and stage. Therefore, the variant might become a possible proliferation-related prognostic factor for UCC.

Association of HaeIII single nucleotide polymorphisms in the SLC2A1 gene with risk of diabetic nephropathy; evidence from Kurdish patients with type 2 diabetes mellitus

AIMS

Given the growing rate of patients with type 2 diabetes mellitus, uncovering the effects of gene polymorphism on diabetes pathogenesis has attracted a lot of attention. Because glucose transporter 1 is involved in glucose uptake, the polymorphism of this gene may be an important risk factor in type 2 diabetes mellitus or in the progression of diabetes complications such as diabetic nephropathy. As far as the authors are concerned, this study is the first one aiming at evaluating the probable effects of solute carrier family 2 facilitated glucose transporter member 1 (SLC2A1) HaeIII polymorphism on clinical and laboratory outcomes of Kurdish patients with type 2 diabetes mellitus.

METHODS

This study was conducted involving 126 diabetic nephropathy patients and 150 diabetic patients without renal involvement. Serum levels of Cystatin C, fasting blood glucose, creatinine and urinary albumin; levels of glycated hemoglobin and estimated glomerular filtration rate were measured. Moreover, the Hae III polymorphism of SLC2A1 gene was determined by PCR-restriction fragment length polymorphism (RFLP).

RESULTS

The rate of CC genotype was higher (37%) in patients with diabetic nephropathy compared with controls. There were a significant correlation between the CC genotype and risk of diabetic nephropathy. There were significant correlations between genotypes, serum Cystatin C and estimated glomerular filtration rate in patients with diabetic nephropathy.

CONCLUSIONS

The results demonstrated the high frequency of C allele of SLC2A1 HaeIII in Kurdish patients with diabetic nephropathy. It was also found that this polymorphism is a significant risk factor for diabetic nephropathy. The effect of this polymorphism on clinical and laboratory characteristics of diabetic nephropathy patients was significant.

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.

Genetic studies of myelomeningocele

INTRODUCTION

Myelomeningocele is one of the major congenital malformations involving the central nervous system. It is caused by a disruption of the neural tube closure, which is completed at 3-4 weeks of gestation.

DISCUSSION

Multidisciplinary approach is necessary to treat and support this malformation which is a huge burden to the patient, family, and the society. This is a characteristic anomaly that it is known that taking folic acid during the periconceptional period, it is possible to reduce the risk of having a neural tube defect (NTD). Although folate fortification had dramatically reduced the incidence, it was not possible to diminish the risk. To date, many studies have been conducted focusing on candidate genes related to folate and glucose metabolism. We will describe a brief review of genetic etiology of candidate genes of metabolic pathways of folate and glucose, animal models of NTDs, and finally recent studies of microRNA.

Relationship between five GLUT1 gene single nucleotide polymorphisms and diabetic nephropathy: a systematic review and meta-analysis

So far, case-control studies on the association between glucose transporter 1 (GLUT1) gene single nucleotide polymorphisms (SNPs) and diabetic nephropathy (DN) have generated considerable controversy. To clarify the linkage of GLUT1 SNPs on the risk of DN, a systematic review and meta-analysis was performed. A comprehensive literature search of electronic databases was conducted to obtain relative studies. Nine case-control studies were included. Significant differences were found between XbaI SNP (rs841853) and increased risk of DN in all genetic models. Subgroup analyses for Caucasians population and DN from both type 1 and type 2 diabetes also revealed positive results. For Enh2-1 SNP (rs841847), Enh2-2 SNP (rs841848) and HaeIII SNP (rs1385129), obvious linkages were demonstrated in recessive model. However, analysis for the association between HpyCH4V SNP (rs710218) and the susceptibility of DN showed no significance. Likewise, negative outcome was also found in the assessment for the influence of XbaI or Enh2-2 SNP on the pathogenesis progress of DN. The evidence currently available shows that XbaI, Enh2 and HaeIII SNPs, but not HpyCH4V SNP, in GLUT1 gene may be genetic susceptibility to DN. However, data does not support the association between either XbaI or Enh2-2 SNP and the severity of DN.

Genetic variation of glucose transporter-1 (GLUT1) and albuminuria in 10,278 European Americans and African Americans: a case-control study in the Atherosclerosis Risk in Communities (ARIC) study

Background

Evidence suggests glucose transporter-1(GLUT1) genetic variation affects diabetic nephropathy and albuminuria. Our aim was to evaluate associations with albuminuria of six GLUT1 single nucleotide polymorphisms(SNPs), particularly XbaI and the previously associated Enhancer-2(Enh2) SNP.

Methods

A two-stage case-control study was nested in a prospective cohort study of 2156 African Americans and 8122 European Americans with urinary albumin-to-creatinine ratio(ACR). Cases comprised albuminuria(N = 825; ≥ 30 μg/mg) and macroalbuminuria(N = 173; ≥ 300 μg/mg). ACR < 30 μg/mg classified controls(n = 9453). Logistic regression and odds ratios(OR) assessed associations. The evaluation phase(stage 1, n = 2938) tested associations of albuminuria(n = 305) with six GLUT1 SNPs: rs841839, rs3768043, rs2297977, Enh2(rs841847) XbaI(rs841853), and rs841858. Enh2 was examined separately in the replication phase(stage 2, n = 7340) and the total combined sample (n = 10,278), with all analyses stratified by race and type 2 diabetes.

Results

In European Americans, after adjusting for diabetes and other GLUT1 SNPs in stage 1, Enh2 risk genotype(TT) was more common in albuminuric cases(OR = 3.37, P = 0.090) whereas XbaI (OR = 0.94, p = 0.931) and remaining SNPs were not. In stage 1, the Enh2 association with albuminuria was significant among diabetic European Americans(OR = 2.36, P = 0.025). In African Americans, Enh2 homozygosity was rare(0.3%); XbaI was common(18.0% AA) and not associated with albuminuria. In stage 2(n = 7,340), Enh2 risk genotype had increased but non-significant OR among diabetic European Americans(OR = 1.66, P = 0.192) and not non-diabetics(OR = 0.99, p = 0.953), not replicating stage 1. Combining stages 1 and 2, Enh2 was associated with albuminuria(OR 2.14 [1.20-3.80], P = 0.009) and macroalbuminuria(OR 2.69, [1.02-7.09], P = 0.045) in diabetic European Americans. The Enh2 association with macroalbuminuria among non-diabetic European Americans with fasting insulin(OR = 1.84, P = 0.210) was stronger at the highest insulin quartile(OR = 4.08, P = 0.040).

Conclusions

As demonstrated with type 1 diabetic nephropathy, the GLUT1 Enh2 risk genotype, instead of XbaI, may be associated with type 2 diabetic albuminuria among European Americans, though an association is not conclusive. The association among diabetic European Americans found in stage 1 was not replicated in stage 2; however, this risk association was evident after combining all diabetic European Americans from both stages. Additionally, our results suggest this association may extend to non-diabetics with high insulin concentrations. Rarity of the Enh2 risk genotype among African Americans precludes any definitive conclusions, although data suggest a risk-enhancing role.

A 10 bp deletion polymorphism and 2 new variations in the GLUT1 gene associated with meningomyelocele

We sought to examine the diversity and extent of sequence variations in GLUT1 in patients with myelomeningocele (MM) and to identify variations conferring risk of MM. Sequences of the 10 exons and exon-intron boundaries of GLUT1 for 96 patients with MM (48 Caucasians and 48 Mexican Americans) were determined by direct sequencing of DNA. Two new variants were identified. One is located within intron 7 (c.972+17t>a), 17 bases from exon 7. The other is within exon 8 (c.1016T>C) and results in an amino acid change at isoleucine 339 (p.Ile339Thr). A 10 base pair (bp) deletion within intron 9 was genotyped for 457 patients with MM and showed it to be more common in Caucasian MM patients than in Caucasian controls (P = .02). The physiologic role of the 2 newly identified variants in the GLUT1 gene and the 10 bp deletion associated with risk of MM in Caucasian patients is under investigation.

Genetics of diabetic nephropathy

The increasing prevalence of diabetes mellitus has led to a growing number of chronic complications including diabetic nephropathy (DN). In addition to its high prevalence, DN is associated with high morbidity and mortality especially due to cardiovascular diseases. It is well established that genetic factors play a role in the pathogenesis of DN and genetically susceptible individuals can develop it after being exposed to environmental factors. DN is probably a complex, polygenic disease. Two main strategies have been used to identify genes associated to DN: analysis of candidate genes, and more recently genome-wide scan. Great efforts have been made to identify these main genes, but results are still inconsistent with different genes associated to a small effect in specific populations. The identification of the main genes would allow the detection of those individuals at high risk for DN and better understanding of its pathophysiology as well.

The XbaI G>T polymorphism of the glucose transporter 1 gene modulates 18F-FDG uptake and tumor aggressiveness in breast cancer

We investigated the relevance of single-nucleotide polymorphisms (SNPs) in the glucose transporter 1 (GLUT1) gene to the uptake of (18)F-FDG and tumor aggressiveness in breast cancer.

METHODS

In 52 individuals with breast cancer, a diagnostic PET/CT scan was obtained, and the standardized uptake value was determined as a measure of (18)F-FDG uptake using a region-of-interest technique. Three GLUT1 SNPs (XbaI G>T, HpyCH4V A>T, and HaeIII T>C) were investigated in genomic DNA that was isolated from the paraffin-embedded specimens of all patients. Tumors were typed and graded according to the World Health Organization classifications.

RESULTS

The GG genotype of the XbaI G>T SNP was associated with increased tumor uptake of (18)F-FDG, with a mean standardized uptake value of 11.7 (TT/GT genotypes, 5.9; P = 0.03). Furthermore, the GG genotype was positively related to enhanced tumor proliferation (mitotic count, P = 0.01). In line with this finding, the GG genotype was absent in grade 1 carcinomas and increasingly prevalent in tumors with higher malignancy (grade 2, 28.0%; grade 3, 50%; P = 0.04).

CONCLUSION

This study found that the XbaI G>T SNP of the GLUT1 gene is associated with an increased (18)F-FDG uptake and a more advanced tumor grade or growth in breast cancer. Thus, this genetic variant might favor aggressive phenotypes by modulating the efficiency of cancer cells to recruit glucose and escalate growth rate, suggesting the XbaI G>T SNP as a proliferation-related prognostic factor.

Frequency distribution of XbaIG > T and HaeIIIT > C GLUT1 polymorphisms among different Brazilian ethnic groups

GLUT is the major glucose transporter in mammalian cells. Single nucleotide polymorphisms (SNP) at GLUT1 promoter and regulatory regions have been associated to the risk of developing nephropathy in different type 1 and type 2 diabetic populations. It has been demonstrated that differences in allelic and genotypic frequencies of GLUT1 gene (SLC2A1) polymorphisms occur among different populations. Therefore, ethnic differences in distribution of GLUT1 gene polymorphisms may be an important factor in determining gene-disease association. In this study, we investigated the XbaIG > T and HaeIIIT > C polymorphisms in six different Brazilian populations: 102 individuals from Salvador population (Northern Brazil), 56 European descendants from Joinville (South Brazil), 85 Indians from Tiryió tribe (North Brazil) and 127 samples from Southern Brazil: 44 from European descendants, 42 from African descendants and 41 from Japanese descendants. Genotype frequencies from both sites did not differ significantly from those expected under the Hardy-Weinberg equilibrium. We verified that the allele frequencies of both polymorphisms were heterogeneous in these six Brazilian ethnic groups.

Polymorphisms at GLUT1 gene are not associated with the development of TSP/HAM in Brazilian HTLV-1 infected individuals and the discovery of a new polymorphism at GLUT1 gene

The development of HTLV-1 associated clinical manifestations, such as TSP/HAM and ATLL, occur in 2-4% of the infected population and it is still unclear why this infection remains asymptomatic in most infected carriers. Recently, it has been demonstrated that HTLV uses the Glucose transporter type 1 (GLUT1) to infect T-CD4(+) lymphocytes and that single nucleotide polymorphisms (SNP) in the GLUT1 gene are associated with diabetic nephropathy in patients with diabetes mellitus in different populations. These polymorphisms could contribute to a higher GLUT1 protein expression on cellular membrane, facilitating the entry of HTLV and its transmission cell by cell. This could result in a higher provirus load and consequently in the development of TSP/HAM. To evaluate the role of GLUT1 gene polymorphisms in the development of TSP/HAM in HTLV-1 infected individuals, the g.22999G > T, g.15339T > C and c.-2841A > T sites were analyzed by PCR/RFLP or sequencing in 244 infected individuals and 102 normal controls. The proviral load of the HTLV-1 infected patients was also analyzed using Real Time Quantitative PCR. Genotypic and allelic frequencies of the three sites did not differ significantly between controls and HTLV-1 infected individuals. There was no difference in genotypic and allelic distributions among patients as to the presence or absence of HTLV-1 associated clinic manifestations. As regards the quantification of the provirus load, we observed a significant reduction in the asymptomatic individuals compared with the oligosymptomatic and TSP/HAM individuals. These results suggest that g.22999G > T, g.15339T > C, and c.-2841A > T SNP do not contribute to HTLV-1 infection nor to the genetic susceptibility of TSP/HAM in Brazilian HTLV-1 infected individuals.

Association of glucose transporter 1 polymorphisms with type 2 diabetes in the Tunisian population

BACKGROUND

T2DM is a complex metabolic disease. Genetic studies on T2DM have been of little help so far because several genetic association studies have shown conflicting results. In this study, we report the findings of a case-control study on three SNPs in the GLUT1 gene. For this, we investigated the association of GLUT1 genotypes and haplotypes with T2DM.

RESEARCH DESIGN AND METHODS

All 273 T2DM subjects (cases) and 343 healthy subjects (controls) were genotyped using the polymerase chain reaction restriction fragment length polymorphism.

RESULTS

Results showed that the GT genotype of XbaI SNP could increase the risk of susceptibility to T2DM to 2.4 and that TAT is a 'risk haplotype' conferring a risk of 3.4 to T2DM.

CONCLUSION

The TAT haplotype of the GLUT1 gene confers susceptibility to T2DM in the Tunisian population.

An IL-6 haplotype on human chromosome 7p21 confers risk for impaired renal function in type 2 diabetic patients

The human chromosome 7p21 locus harbors a major gene that influences variation of glomerular filtration rate and development of end-stage renal disease. The pro-inflammatory IL-6 cytokine is a candidate gene since chronic inflammation has been implicated in diabetic nephropathy and this gene is located under the peak of linkage. To test this, single nucleotide polymorphism (SNP) and haplotype analyses were performed using a case-control study of 295 patients consisting of 138 with proteinuria, 157 with chronic renal failure and these were compared to 174 control patients with normal albumin excretion. Five tagging SNPs were selected for analysis based on linkage disequilibrium patterns and proximity to the functionally important -634G>C SNP in the IL-6 promoter. Initial analysis suggested that a -174G>C polymorphism may be associated with risk of chronic renal failure but this was not significant after Bonferroni correction. While haplotype analyses showed no association with proteinuria; a significant association with chronic renal failure was found. There was significantly more of the GGGAGC haplotype among patients with chronic renal failure compared to controls and this association remained significant even after correction for multiple testing. Our study has found a specific IL-6 haplotype conferring risk for impaired renal function in patients with type 2 diabetes.

Gatifloxacin affects GLUT1 gene expression and disturbs glucose homeostasis in vitro

Gatifloxacin may induce life-threatening dysglycemia. The facilitated glucose transporter type 1 (GLUT1) protein is ubiquitously expressed in many tissues. Disturbed GLUT1 protein function weakens the systemic glycemic control and may cause dysglycemia. In this study we demonstrate that gatifloxacin modulates the transcription and reduces the expression and function of GLUT1 gene in HepG2 cells. When treated with gatifloxacin at concentrations of 3.4 mug/ml (8.4 muM) and 17 mug/ml (42 muM), GLUT1 promoter activity was stimulated by 2.8 and 3.8 folds, GLUT1 mRNA expression was decreased by 41% and 31%, and glucose uptake was decreased by 41% and 52%, respectively. Our findings imply that disturbed GLUT1 gene expression and protein function may underlie the dysglycemic effect of gatifloxacin.

Saliva as a viable alternative source of human genomic DNA in genetic epidemiology

BACKGROUND

Saliva is a potentially useful but untapped source of genomic DNA for genetic epidemiological studies. However, current commercial methods are mainly concerned with DNA extraction and do not address important issues concerning saliva preservation and storage. As such, we evaluated how various saliva storage conditions affected DNA yield and quality obtained using a new commercially available method that proposes to integrate these aspects in a single kit.

METHODS

The conditions involved the extraction of the DNA immediately after saliva collection (condition 1) or when stored at air-conditioned room temperature (20 degrees C) for 1 month (condition 2) and 6 months (condition 3) as well as at -80 degrees C for 6 months (condition 4). The effect of incorporating an additional incubation of saliva samples at 30 degrees C for 2 weeks was also examined.

RESULTS

Overall average DNA yield from 2 ml of saliva was 35.5 microg (8.5-85.2 microg). DNA yield was unaffected by incubation of saliva at 30 degrees C but DNA yield under condition 3 was significantly higher compared to conditions 1 and 2. OD260/280 values were acceptable and comparable across all conditions. Differences in storage conditions did not impact DNA quality in real time PCR experiments and genotyping fidelity remained undiminished.

CONCLUSION

Saliva is a viable alternative source of human genomic DNA for genetic epidemiological studies and that this new commercial method and possibly other related techniques can be effective means towards this end.

Glucose transporter polymorphisms are associated with clear-cell renal carcinoma

Clear-cell renal cell carcinoma (CCRCC) is identified by abundant glycogen-rich cytoplasm, due to the aberrant influx and storage of glucose. The objective was to investigate the frequency of polymorphisms of the facilitative glucose transporter (GLUT1). GLUT1 is a downstream target of Hypoxia-inducible factor (HIF-1alpha), a mediator of hypoxia-controlled angiogenesis. In this study, we examine the allelic frequency of polymorphisms in the promoter and the second intron of the GLUT1 gene. Genomic DNA was extracted from normal tissue of 92 patients undergoing nephrectomy for CCRCC, and 99 normal cord blood DNA samples were used to provide control frequencies. The regions of DNA encompassing the polymorphisms were amplified and digested with appropriate endonuclases. The products were separated and viewed by gel electrophoresis. There was a highly significant decrease in the A-2841 genotype (P=0.0004) in the promoter region of those patients with CCRCC compared to the control population. There was also a significant decrease in the T+22999 allele in the intron 2 of those patents with CCRCC (P=0.004) compared to the same control population. This study suggests that GLUT1 is one of a number of genes that may increase susceptibility to developing CCRCC.

Genetic basis of diabetic nephropathy

Diabetes mellitus is the leading cause of end-stage renal disease. Development and progression of diabetic nephropathy result from a combination of genetic susceptibility and metabolic and hemodynamic abnormalities. In America, some racial and ethnic minorities have a significant burden of diabetic nephropathy, and, although genetic studies suggest that inherited factors play a major role in the pathogenesis of diabetic nephropathy, little information has been gained on the genes and molecular mechanisms involved. The genetic background of diabetic nephropathy is believed to be polygenic, and the genes predisposing to the development and progression of diabetic nephropathy are actively being investigated. New knowledge in identifying and understanding the role of susceptibility gene(s) will provide valuable information that could help develop new preventive and therapeutic strategies.

An evolutionary model for identifying genetic adaptation to high altitude

Coordinated maternal/fetal responses to pregnancy are required to ensure continuous O2 delivery to the developing organism. Mammals employ distinctive reproductive strategies that afford their young an improved chance of survival through the completion or the reproductive period. Thus, mortality prior to the end of the reproductive period is concentrated in the earliest phases of the lifecycle. At high altitude, fetal growth restriction reduces birth weight and likely compromises survival during the early postnatal period. Population variation in the frequency of the altitude-associated increase in intrauterine growth restriction (IUGR) demonstrates that multigenerational Tibetan and Andean high-altitude populations are protected compared with shorter duration, European or Han (Chinese) residents. This experiment of nature permits testing the hypothesis that genetic factors (a) influence susceptibility to altitude-associated IUGR, (b) act on maternal vascular adjustments to pregnancy determining uteroplacental blood flow, and (c) involve genes which regulate and/or are regulated by hypoxia-inducible factors (HIFs). Serial, studies during pregnancy as well as postpartum in Andean and European residents of high (3600 m) and low (300 m) altitude will permit evaluation of whether uteroplacental O2 delivery is lower in the European than Andean women and, if so, the physiological factors responsible. Comparisons of HIF-targeted vasoactive substances and SNPs in or near HIF-regulatory or targeted genes will permit determination of whether these regions are distinctive in the Andean population. Studies coupling genetic and genomic approaches with more traditional physiological measures may be productively employed for determining the genetic mechanisms influencing physiological adaptation to high altitude.

Assessment of 115 candidate genes for diabetic nephropathy by transmission/disequilibrium test

Several lines of evidence, including familial aggregation, suggest that allelic variation contributes to risk of diabetic nephropathy. To assess the evidence for specific susceptibility genes, we used the transmission/disequilibrium test (TDT) to analyze 115 candidate genes for linkage and association with diabetic nephropathy. A comprehensive survey of this sort has not been undertaken before. Single nucleotide polymorphisms and simple tandem repeat polymorphisms located within 10 kb of the candidate genes were genotyped in a total of 72 type 1 diabetic families of European descent. All families had at least one offspring with diabetes and end-stage renal disease or proteinuria. As a consequence of the large number of statistical tests and modest P values, findings for some genes may be false-positives. Furthermore, the small sample size resulted in limited power, so the effects of some tested genes may not be detectable, even if they contribute to susceptibility. Nevertheless, nominally significant TDT results (P < 0.05) were obtained with polymorphisms in 20 genes, including 12 that have not been studied previously: aquaporin 1; B-cell leukemia/lymphoma 2 (bcl-2) proto-oncogene; catalase; glutathione peroxidase 1; IGF1; laminin alpha 4; laminin, gamma 1; SMAD, mothers against DPP homolog 3; transforming growth factor, beta receptor II; transforming growth factor, beta receptor III; tissue inhibitor of metalloproteinase 3; and upstream transcription factor 1. In addition, our results provide modest support for a number of candidate genes previously studied by others.

Glucose transporters in diabetic nephropathy

Changes in glucose transporter expression in glomerular cells occur early in diabetes. These changes, especially the GLUT1 increase in mesangial cells, appear to play a pathogenic role in the development of ECM expansion and perhaps other features of diabetic nephropathy. In addition, it appears that at least some diabetic patients may be predisposed to nephropathy because of polymorphisms in their GLUT1 genes. GLUT1 overexpression leads to increased glucose metabolic flux which in turn triggers the polyol pathway and activation of PKC alpha and B1. Activation of these PKC isoforms can lead directly to AP-1 induced increases in fibronectin expression and ECM accumulation. Other, more novel effects of GLUT1 on cellular hypertrophy and injury could also promote changes of diabetic nephropathy. Strategies to prevent GLUT1 overexpression could ameliorate or prevent the progression of diabetic nephropathy.

A novel polymorphism in the 5' flanking region of the glucose transporter (GLUT1) gene is strongly associated with diabetic nephropathy in patients with Type 1 diabetes mellitus

Glucose transporter 1 (GLUT1) activity has been implicated in renal hypertrophy and extracellular matrix formation in mesangial cells. Recent studies have suggested that polymorphisms in the GLUT1 gene are associated with susceptibility to diabetic nephropathy (DN) in patients with diabetes mellitus. In this study, a novel polymorphism (A-2841T) in the 5' flanking region of GLUT1 was examined in 288 patients with Type 1 diabetes mellitus (T1DM) and 101 normal controls. The polymorphisms were amplified and the fragment digested with the enzyme HpyCH4V. There was a highly significant increase in the frequency of the TT-2841 genotype in patients with nephropathy (n=131) compared with those with either no microvascular complications after a 20-year duration of diabetes (uncomplicated; n=72; 54.5% vs. 2.7%, chi=79.4, P<.000001). There was no difference between the uncomplicated group and those who only had retinopathy (n=50; 2.7% vs. 4.0%, respectively). The frequency in recently diagnosed patients was 17.1% and only 2.0% in normal controls. In contrast, the AA genotype was found in 13.6% of the nephropaths, 76.3% of uncomplicated, 48.0% of retinopaths, and 65% of normal controls. These results confirm previous reports of an association between the GLUT1 gene and susceptibility to DN but not retinopathy. The localisation of this polymorphism suggests that it may be involved in the expression of the gene.

Association between the GLUT1 gene polymorphism and the risk of diabetic nephropathy: a meta-analysis

The association between diabetic nephropathy (DN) and the XbalphaI polymorphism in the GLUT1 gene has been investigated in several case-control studies. These studies rendered contradictory results: the allele XbalphaI(-) was shown either to be a risk factor or neutral, or even protective for the development of the disease. To shed some light on these inconclusive findings, a meta-analysis of all available studies relating the XbalphaI polymorphism to the risk of developing DN was conducted. Five out of six identified studies included Caucasian populations, and only one involved samples from an Asian population. Overall, the meta-analysis suggested large heterogeneity between studies (P<0.01, I2=68%) and lack of association between allele XbalphaI(-) and the risk of developing DN relative to allele XbalphaI(+): random effects odds ratio (OR)=1.26 [95% CI (0.93, 1.69)]. Excluding one study with the controls not in Hardy-Weinberg equilibrium, the sensitivity analysis revealed that heterogeneity (P=0.28, I2=21%) could be explained, and then, there is an overall association: fixed effects OR=1.34 [95% CI (1.13, 1.60)]. Then, significant ORs were also found on analysis of subgroups: for the Caucasian population, fixed effects OR=1.29 [95% CI (1.08, 1.56)] and for the type 2 diabetic patients fixed effects OR=1.69 [95% CI (1.09, 2.63)]. In type 1 diabetes, there is a moderate heterogeneity (P=0.19, I2=41%) with fixed effects OR=1.29 [95% CI (1.06, 1.56)] and random effects OR=1.32 [95% CI (1.01, 1.71)]. There is a source of bias in the selected studies: large studies failed to show association while small studies claimed an association. Although there is evidence of association between GLUT1 and DN, the above findings reinforce the need for further and more rigorous association studies.

Cellular basis of diabetic nephropathy: III. In vitro GLUT1 mRNA expression and risk of diabetic nephropathy in type 1 diabetic patients

AIMS/HYPOTHESIS

Altered glucose transporter expression has been implicated in the pathogenesis of diabetic nephropathy. There is increasing evidence that genetic factors convey risk of, or protection from, diabetic nephropathy and that the behaviour of cultured skin fibroblasts from type 1 diabetic patients may reflect these genetic influences. This study aimed to compare GLUT1 mRNA expression levels in skin fibroblasts from type 1 diabetic patients with either rapid ("fast-track", n=25) or slow ("slow-track", n=25) development of diabetic nephropathy and from non-diabetic normal control subjects (controls, n=25).

METHODS

Skin fibroblasts were cultured in Dulbecco's Modified Eagle's Medium with 25 mmol/l glucose for 36 h. Total RNA was isolated, and GLUT1 mRNA levels were estimated by microarray analysis and RT-PCR.

RESULTS

Levels of GLUT1 mRNA expression in skin fibroblasts from "slow-track" patients were greater than those from "fast-track" patients (p=0.02), as initially detected by microarray. GLUT1 mRNA expression levels were confirmed by RT-PCR to be higher in skin fibroblasts from "slow-track" patients (4.59+/-2.04) than in those from "fast-track" patients (3.34+/-1.2, p=0.02), and were also higher than in skin fibroblasts from control subjects (3.52+/-1.66, p=0.03). There was no statistically significant difference between levels of expression in the "fast-track" patients and the control subjects.

CONCLUSIONS/INTERPRETATION

This finding is consistent with the presence of cellular protection factors against diabetic nephropathy in the "slow-track" patients. These factors could be associated with the regulation of the GLUT1 pathway and may be genetically determined.

Genomic strategies for diabetic nephropathy

Insight into the molecular mechanisms that underlie the origin and progression of diabetic nephropathy remains limited in part because conventional research tools have restricted investigators to focus on single genes or isolated pathways. Microarray technologies provide opportunities for evaluating genetic factors and environmental effects at a genomic scale during the pathogenesis of diabetic nephropathy. Despite the enormous power of the microarray technology, there are several pitfalls that need to be considered. This article discusses conceptual, practical, statistical, and logistical considerations for the use of microarrays in studies of experimental and human diabetic renal disease. New knowledge in this field will facilitate new approaches for molecular diagnosis and drug discovery.

Diabetes and nephropathy

PURPOSE OF REVIEW

Diabetic nephropathy is the single most common disorder leading to renal failure. Its annual incidence has more than doubled in the past decade to reach 44% of all end-stage renal disease, despite recent therapeutic advances. Thus, research into diabetic nephropathy pathophysiology that could lead to new treatment approaches is urgently needed and this review aims to summarize the work performed in this area in the past year.

RECENT FINDINGS

There have been advances in the understanding of diabetic nephropathy pathology. Clearly, structural changes may be advanced before any clinical findings are apparent. Not all functional consequences of the condition are explained by current structural analyses. Genetic studies have connected the disorder risk to multiple candidate genes and a few genetic loci, but the exact genetic predisposition or protectors are not fully described. Perturbations in multiple metabolic pathways are associated with diabetic nephropathy in animals and humans, but their relative importance requires further work. Glycemia and blood pressure control are crucial for diabetic nephropathy prevention and treatment, but new modalities are needed.

SUMMARY

Recent advances in molecular biology and genetics will bring new insights to the mechanisms involved in diabetic nephropathy development. This will allow early identification of patients at risk of, or safe from, diabetic nephropathy and will hopefully lead to preventive strategies, based on the understanding of the pathophysiology of the disorder. Meanwhile, aggressive implementation of proven therapies to prevent (glycemic control) and slow (antihypertensive therapy, especially with renin-angiotensin system blockers) the progression of diabetic nephropathy are strongly recommended.