Homozygous carriers of the TCF7L2 rs7903146 T-allele show altered postprandial response in triglycerides and triglyceride-rich lipoproteins

Association of TCF7L2 Variants in Type 2 Diabetes Mellitus with Hypertriglyceridemia - A Case-Control Study

Background

Type 2 Diabetes Mellitus (T2DM) is a chronic metabolic condition involving various genetic and environmental factors leading to impaired insulin secretion, resulting in hyperglycemia. The transcription factor 7-like 2 (TCF7L2) gene is an element of the Wnt signaling pathway that plays an important role in glucose and lipid metabolism. The aim of this study is to evaluate the association of TCF7L2 rs7903146 and rs12255372 polymorphisms in T2DM with hypertriglyceridemia.

Methods

We investigated the effect of rs7903146 and rs12255372 on T2DM with high triglyceride (TG) levels in 60 patients and 20 controls. The anthropometric measurements and biochemical tests were assessed. Peripheral blood samples were collected, and genomic DNA was extracted. The genotyping of TCF7L2 polymorphisms was carried out using polymerase chain reaction (PCR)-based direct sequencing and allele-specific PCR methods. The T2DM patients and controls were compared by means of the t-test, Chi-square test, odds ratio (OR), and 95% confidence interval (CI) using Epi Info v7.

Results

The HbA1c was found to be 9.7 ± 2.1 and 5.4 ± 0.5% in patients and controls, respectively. The average TG levels (P < 0.005) in patients were 205.2 ± 145.7 and 106.4 ± 27.4mg/dl in controls. Significant evidence of association was found in T2DM patients having high TG levels with rs7903146 CT/TT (OR: 4.89; P = 0.0105) and rs12255372 GT/TT (OR: 5.23; P = 0.0101) genotypes when compared to controls.

Conclusion

The results of this study show that TCF7L2 rs7903146 CT/TT and rs12255372 GT/TT genotypes are significantly associated with the risk of hypertriglyceridemia in individuals with T2DM among the studied population.

TCF7L2 gene associated postprandial triglyceride dysmetabolism- a novel mechanism for diabetes risk among Asian Indians

AIM

TCF7L2 gene is believed to increase the risk of T2DM by its effects on insulin secretion. However, the exact mechanism of this enhanced risk is not clearly known. While TCF7L2 gene has been shown to affect lipid metabolism, these effects have remained largely unexplored in the context of diabetes risk.

METHODS

Postprandial lipid responses to a standardized fat challenge test were performed in 620 Asian Indian subjects (310 with NGT and 310 with T2DM/prediabetes) and compared between the risk and wild genotypes of the rs7903146 TCF7L2 gene. In 30 subjects scheduled to undergo abdominal surgery (10 each with NGT, Prediabetes and T2DM), adipocyte TCF7L2 gene expression was also performed by real time qPCR and confirmed by protein expression in western blot.

RESULTS

T allele of rs7903146 TCF7L2 gene was confirmed as the risk allele for T2DM (OR=1.8(1.2-2.74), p=0.005). TT+CT genotypes of rs7903146 TCF7L2 gene showed significantly higher 4hrTg (p<0.01), TgAUC (p<0.01), peakTg (p<0.01) as well as higher postprandial plasma glucose (p=.006) levels and HOMA-IR (p=0.03) and significantly lower adiponectin levels (p=0.02) as compared to CC genotype. The expression of TCF7L2 gene in VAT was 11-fold higher in prediabetes group as compared to NGT (P<0.01) and 5.7-fold higher in T2DM group as compared to NGT group(P=0.003) and was significantly associated with PPTg and glucose levels.

CONCLUSION

There is significant PPTg dysmetabolism associated with the risk allele of rs7903146 polymorphism as well as adipocyte expression of TCF7L2 gene. Significant upregulation of TCF7L2 gene expression in VAT that correlates with PPTg and glycaemia is also seen in Asian Indians with glucose intolerance. Modulation of PPTg metabolism by TCF7L2 gene and the resultant PPHTg may be a novel mechanism that contributes to its diabetes risk in them.

Genetics of Familial Combined Hyperlipidemia (FCHL) Disorder: An Update

Familial combined hyperlipidemia (FCHL) is one of the most common familial lipoprotein disorders of the lipoproteins, with a prevalence of 0.5% to 2% in different populations. About 10% of these patients suffer from cardiovascular disease and this number is increased by up to 11.3% in the young survivors of myocardial infarction and by 40% among all the survivors of myocardial infarction. Although initially thought to be that FCHL has an inheritance pattern of monogenic, the disease's etiology is still not fully understood and it appears that FCHL has a complex pattern related to genetic variants, environmental factors, and lifestyles. Two strategies have been used to identify its complex genetic background: candidate gene and the linkage approach, which have yielded an extensive list of genes associated with FCHL with a variable degree of scientific evidence. Until now, more than 30 different genetic variants have been identified related to FCHL. In this study, we aimed to review the individual genes that have been described in FCHL and how these genes and variants can be related to the current concept of metabolic pathways resulting in familial combined hyperlipidemia.

The role of transcription factor 7-like 2 in metabolic disorders

Transcription factor 7-like 2 (TCF7L2), a member of the T cell factor/lymphoid enhancer factor family, generally forms a complex with β-catenin to regulate the downstream target genes as an effector of the canonical Wnt signalling pathway. TCF7L2 plays a vital role in various biological processes and functions in many organs and tissues, including the liver, islet and adipose tissues. Further, TCF7L2 down-regulates hepatic gluconeogenesis and promotes lipid accumulation. In islets, TCF7L2 not only affects the insulin secretion of the β-cells but also has an impact on other cells. In addition, TCF7L2 influences adipogenesis in adipose tissues. Thus, an out-of-control TCF7L2 expression can result in metabolic disorders. The TCF7L2 gene is composed of 17 exons, generating 13 different transcripts, and has many single-nucleotide polymorphisms (SNPs). The discovery that these SNPs have an impact on the risk of type 2 diabetes (T2D) has attracted thorough investigations in the study of TCF7L2. Apart from T2D, TCF7L2 SNPs are also associated with type 1, posttransplant and other types of diabetes. Furthermore, TCF7L2 variants affect the progression of other disorders, such as obesity, cancers, metabolic syndrome and heart diseases. Finally, the interaction between TCF7L2 variants and diet also needs to be investigated.

No detectable effect of a type 2 diabetes-associated TCF7L2 genotype on the incretin effect

The T allele of TCF7L2 rs7903146 is a common genetic variant associated with type 2 diabetes (T2D), possibly by modulation of incretin action. In this study, we evaluated the effect of the TCF7L2 rs7903146 T allele on the incretin effect and other glucometabolic parameters in normal glucose tolerant individuals (NGT) and participants with T2D. The rs7903146 variant was genotyped in cohorts of 61 NGT individuals (23 were heterozygous (CT) or homozygous (TT) T allele carriers) and 43 participants with T2D (20 with CT/TT). Participants were previously examined by an oral glucose tolerance test (OGTT) and a subsequent isoglycemic intravenous glucose infusion (IIGI). The incretin effect was assessed by quantification of the difference in integrated beta cell secretory responses during the OGTT and IIGI. Glucose and hormonal levels were measured during experimental days, and from these, indices of beta cell function and insulin sensitivity were calculated. No genotype-specific differences in the incretin effect were observed in the NGT group (P = 0.70) or the T2D group (P = 0.68). NGT T allele carriers displayed diminished glucose-dependent insulinotropic polypeptide response during OGTT (P = 0.01) while T allele carriers with T2D were characterized by lower C-peptide AUC after OGTT (P = 0.04) and elevated glucose AUC after OGTT (P = 0.04). In conclusion, our findings do not exclude that this specific TCF7L2 variant increases the risk of developing T2D via diminished incretin effect, but genotype-related defects were not detectable in these cohorts.

Quantile-dependent expressivity of postprandial lipemia

Purpose

“Quantile-dependent expressivity” describes an effect of the genotype that depends upon the level of the phenotype (e.g., whether a subject’s triglycerides are high or low relative to its population distribution). Prior analyses suggest that the effect of a genetic risk score (GRS) on fasting plasma triglyceride levels increases with the percentile of the triglyceride distribution. Postprandial lipemia is well suited for testing quantile-dependent expressivity because it exposes each individual’s genotype to substantial increases in their plasma triglyceride concentrations. Ninety-seven published papers were identified that plotted mean triglyceride response vs. time and genotype, which were converted into quantitative data. Separately, for each published graph, standard least-squares regression analysis was used to compare the genotype differences at time t (dependent variable) to average triglyceride concentrations at time t (independent variable) to assess whether the genetic effect size increased in association with higher triglyceride concentrations and whether the phenomenon could explain purported genetic interactions with sex, diet, disease, BMI, and drugs.

Results

Consistent with the phenomenon, genetic effect sizes increased (P≤0.05) with increasing triglyceride concentrations for polymorphisms associated with ABCA1, ANGPTL4, APOA1, APOA2, APOA4, APOA5, APOB, APOC3, APOE, CETP, FABP2, FATP6, GALNT2, GCKR, HL, IL1b, LEPR, LOX-1, LPL, MC4R, MTTP, NPY, SORT1, SULF2, TNFA, TCF7L2, and TM6SF2. The effect size for these polymorphisms showed a progressively increasing dose-response, with intermediate effect sizes at intermediate triglyceride concentrations. Quantile-dependent expressivity provided an alternative interpretation to their interactions with sex, drugs, disease, diet, and age, which have been traditionally ascribed to gene-environment interactions and genetic predictors of drug efficacy (i.e., personalized medicine).

Conclusion

Quantile-dependent expressivity applies to the majority of genetic variants affecting postprandial triglycerides, which may arise because the impaired functionalities of these variants increase at higher triglyceride concentrations. Purported gene-drug interactions may be the manifestations of quantile-dependent expressivity, rather than genetic predictors of drug efficacy.

Targeted deletion of Tcf7l2 in adipocytes promotes adipocyte hypertrophy and impaired glucose metabolism

OBJECTIVE

Activation of the Wnt-signaling pathway is known to inhibit differentiation in adipocytes. However, there is a gap in our understanding of the transcriptional network regulated by components of the Wnt-signaling pathway during adipogenesis and in adipocytes during postnatal life. The key intracellular effectors of the Wnt-signaling pathway occur through TCF transcription factors such as TCF7L2 (transcription factor-7-like 2). Several genetic variants in proximity to TCF7L2 have been linked to type 2 diabetes through genome-wide association studies in various human populations. Our work aims to functionally characterize the adipocyte specific gene program regulated by TCF7L2 and understand how this program regulates metabolism.

METHODS

We generated Tcf7l2^F/F mice and assessed TCF7L2 function in isolated adipocytes and adipose specific knockout mice. ChIP-sequencing and RNA-sequencing was performed on the isolated adipocytes with control and TCF7L2 knockout cells. Adipose specific TCF7L2 knockout mice were challenged with high fat diet and assessed for body weight, glucose tolerance, and lipolysis.

RESULTS

Here we report that TCF7L2 regulates adipocyte size, endocrine function, and glucose metabolism. Tcf7l2 is highly expressed in white adipose tissue, and its expression is suppressed in genetic and diet-induced models of obesity. Genome-wide distribution of TCF7L2 binding and gene expression analysis in adipocytes suggests that TCF7L2 directly regulates genes implicated in cellular metabolism and cell cycle control. When challenged with a high-fat diet, conditional deletion of TCF7L2 in adipocytes led to impaired glucose tolerance, impaired insulin sensitivity, promoted weight gain, and increased adipose tissue mass. This was accompanied by reduced expression of triglyceride hydrolase, reduced fasting-induced free fatty acid release, and adipocyte hypertrophy in subcutaneous adipose tissue.

CONCLUSIONS

Together our studies support that TCF7L2 is a central transcriptional regulator of the adipocyte metabolic program by directly regulating the expression of genes involved in lipid and glucose metabolism.

Metabolites related to purine catabolism and risk of type 2 diabetes incidence; modifying effects of the TCF7L2-rs7903146 polymorphism

Studies examining associations between purine metabolites and type 2 diabetes (T2D) are limited. We prospectively examined associations between plasma levels of purine metabolites with T2D risk and the modifying effects of transcription factor-7-like-2 (TCF7L2) rs7903146 polymorphism on these associations. This is a case-cohort design study within the PREDIMED study, with 251 incident T2D cases and a random sample of 694 participants (641 non-cases and 53 overlapping cases) without T2D at baseline (median follow-up: 3.8 years). Metabolites were semi-quantitatively profiled with LC-MS/MS. Cox regression analysis revealed that high plasma allantoin levels, including allantoin-to-uric acid ratio and high xanthine-to-hypoxanthine ratio were inversely and positively associated with T2D risk, respectively, independently of classical risk factors. Elevated plasma xanthine and inosine levels were associated with a higher T2D risk in homozygous carriers of the TCF7L2-rs7903146 T-allele. The potential mechanisms linking the aforementioned purine metabolites and T2D risk must be also further investigated.

Transcription factor 7-like 2 single nucleotide polymorphisms are associated with lipid profile in the Balinese

Transcription factor 7-like 2 (TCF7L2) protein plays an important role in glucose and lipid metabolisms. Single nucleotide polymorphisms (SNPs) in the TCF7L2 gene contribute to increased fasting plasma glucose (FPG) and body mass index (BMI), and altered lipid concentrations in various population. We investigated whether the TCF7L2 SNPs were associated with obesity, high FPG and altered lipid profile in the Balinese. A total of 608 Balinese from rural and urban Bali, Indonesia, were recruited. Triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), total cholesterol (TC) and FPG were measured, and BMI was calculated. Ratios of TG/HDL-C, LDL-C/HDL-C, and TC/HDL-C were determined. Genotyping of SNPs rs7903146, rs10885406, and rs12255372 were done in all samples. Genetic association analyses under a dominant model showed that the rs7903146 (OR 5.50, 95% CI 2.34-12.91, p = 8.5 × 10^-5), rs12255372 (OR 4.15, 95% CI 1.66-10.33, p = 0.003) and rs10885406 (OR 2.43, 95% CI 1.39-4.25, p = 0.003) were significantly associated with high TC/HDL-C ratio. The rs10885406 also presented a significant association with high TG (OR 2.21, 95% CI 1.29-3.81, p = 0.004) and low HDL-C (OR 3.02, 95% CI 1.58-5.80, p = 0.001) concentrations, as well as high TG/HDL-C ratio (OR 1.95, 95% CI 1.16-3.27, p = 0.013). None of the SNPs exhibited significant association with obesity or high FPG. SNPs in the TCF7L2 gene are associated with altered lipid profile in the Balinese.