Evidence for neuroendocrine function of a unique splicing form of TCF7L2 in human brain, islets and gut

AIMS/HYPOTHESIS

Variants in the TCF7L2 gene remain the strongest genetic associations with increased risk of type 2 diabetes. Recently, we identified a unique splicing form of TCF7L2 expressed in pancreatic islets, pancreas and colon and detected by assay 'ex13-13b'. The expression of ex13-13b strongly correlated with proinsulin in glucose-stimulated pancreatic islets, suggesting a potential role for this form in the development of type 2 diabetes. The goal of this study was to further characterise this unique TCF7L2 splicing form in human tissues.

METHODS

We used a panel of 34 human tissues and 80 human cell lines to measure the expression of assay ex13-13b with use of quantitative RT-PCR.

RESULTS

The highest expression of assay ex13-13b was detected in several areas of the brain (hypothalamus/thalamus, occipital lobe) and in neuronal cell line SHS5Y5. Low expression was confirmed in pancreatic islets, small intestine, pancreas and colon, while no expression was detected in other human tissues and cell lines. The expression of assay ex13-13b correlated with the gene for cocaine- and amphetamine-regulated transcript (CART, also known as CARTPT) in a panel of human tissues (n = 12, r = 0.85, p = 0.00046), pancreatic islets (n = 23, r = 0.62, p = 0.0016) and colon (n = 98, r = 0.54, p < 0.0001).

CONCLUSIONS/INTERPRETATION

The significant correlation between expression of a unique splicing form of TCF7L2, named here TCF7L2-NE, and CART, the gene for an anorexigenic neurohormone expressed in the central and peripheral nervous system, suggests that these transcripts may share neuroendocrine functions important for brain, gut and pancreatic islets.

The T-allele of TCF7L2 rs7903146 associates with a reduced compensation of insulin secretion for insulin resistance induced by 9 days of bed rest

OBJECTIVE

The aim of this study was to determine whether the type 2 diabetes-associated T-allele of transcription factor 7-like 2 (TCF7L2) rs7903146 associates with impaired insulin secretion to compensate for insulin resistance induced by bed rest.

RESEARCH DESIGN AND METHODS

A total of 38 healthy young Caucasian men were studied before and after bed rest using the hyperinsulinemic-euglycemic clamp technique combined with indirect calorimetry preceded by an intravenous glucose tolerance test. The TCF7L2 rs7903146 was genotyped using allelic discrimination performed with an ABI 7900 system. The genetic analyses were done assuming a dominant model of inheritance.

RESULTS

The first-phase insulin response (FPIR) was significantly lower in carriers of the T-allele compared with carriers of the CC genotype before bed rest, with and without correction for insulin resistance. The incremental rise of FPIR in response to insulin resistance induced by bed rest was lower in carriers of the T-allele (P < 0.001). Fasting plasma glucagon levels were significantly lower in carriers of the T-allele before and after bed rest. While carriers of the CC genotype developed increased hepatic insulin resistance, the TCF7L2 rs7903146 did not influence peripheral insulin action or the rate of lipolysis before or after bed rest.

CONCLUSIONS

Healthy carriers of the T-allele of TCF7L2 rs7903146 exhibit a diminished increase of insulin secretion in response to intravenous glucose to compensate for insulin resistance as induced by bed rest. Reduced paracrine glucagon stimulation may contribute to the impairment of beta-cell function in the carriers TCF7L2 rs7903146 T-allele associated with increased risk of type 2 diabetes.

Dehydroepiandrosterone administration or G{alpha}q overexpression induces {beta}-catenin/T-Cell factor signaling and growth via increasing association of estrogen receptor-{beta}/Dishevelled2 in androgen-independent prostate cancer cells

beta-Catenin/T-cell factor signaling (beta-CTS) plays multiple critical roles in carcinogenesis and is blocked by androgens in androgen receptor (AR)-responsive prostate cancer (PrCa) cells, primarily via AR sequestration of beta-catenin from T-cell factor. Dehydroepiandrosterone (DHEA), often used as an over-the-counter nutritional supplement, is metabolized to androgens and estrogens in humans. The efficacy and safety of unregulated use of DHEA are unclear. We now report that DHEA induces beta-CTS via increasing association of estrogen receptor (ER)-beta with Dishevelled2 (Dvl2) in AR nonresponsive human PrCa DU145 cells, a line of androgen-independent PrCa (AiPC) cells. The induction is temporal, as assessed by measuring kinetics of the association of ERbeta/Dvl2, protein expression of the beta-CTS targeted genes, c-Myc and cyclin D1, and cell growth. However, in PC-3 cells, another human AiPC cell line, DHEA exerts no detectible effects, partly due to their lower expression of Galpha-subunits and DHEA down-regulation of ERbeta/Dvl2 association. When Galphaq is overexpressed in PC-3 cells, beta-CTS is constitutively induced, including increasing c-Myc and cyclin D1 protein expression. This effect involved increasing associations of Galphaq/Dvl2 and ERbeta/Dvl2 and promoted cell growth. These activities require ERbeta in DU-145 and PC-3 cells because they are blocked by ICI 182-780 treatment inactivating ERbeta, small interfering RNA administration depleting ERbeta, or AR overexpression arresting ERbeta. These data suggest that novel pathways activating beta-CTS play roles in the progression of AiPC. Although DHEA may enhance PrCa cell growth via androgenic or estrogenic pathways, the effects of DHEA administration on clinical prostate function remain to be determined.

Genotype and tissue-specific effects on alternative splicing of the transcription factor 7-like 2 gene in humans

CONTEXT

Noncoding single-nucleotide polymorphisms (SNPs) within the TCF7L2 gene are confirmed risk factors for type 2 diabetes, but the mechanism by which they increase risk is unknown.

OBJECTIVE

We hypothesized that associated SNPs alter TCF7L2 splicing and that splice forms have altered biological roles.

DESIGN

Splice forms and 5' and 3' untranslated regions were characterized in sc adipose, muscle, liver, HepG2 cells, pancreas, and islet. Isoform-specific transcript levels were quantified in sc adipose. Alternative splice forms were characterized in HepG2 liver cells under glucose and insulin conditions and in SGBS cells with differentiation. Major isoforms were characterized by transfection.

SETTING

The study was conducted at an ambulatory general clinical research center.

PATIENTS

PATIENTS included 78 healthy, nondiabetic study subjects characterized for insulin sensitivity and secretion.

RESULTS

We identified 32 alternatively spliced transcripts and multiple-length 3' untranslated region transcripts in adipose, muscle, islet, and pancreas. Alternative exons 3a, 12, 13, and 13a were observed in all tissues, whereas exon 13b was islet specific. Transcripts retaining exons 13 and 13a but not total TCF7L2 transcripts were significantly correlated with both obesity measures (P < 0.01) and rs7903146 genotype (P < 0.026) in sc adipose. Insulin (5-10 nm) suppressed all TCF7L2 isoforms in SGBS cells but suppressed exon 13a-containing isoforms most significantly (P < 0.001). The isoform distribution differed throughout SGBS cell differentiation. Isoforms with predicted early stop codons yielded stable proteins of the predicted size, bound beta-catenin, and targeted correctly to the nucleus.

CONCLUSIONS

Intronic TCF7L2 variants may regulate alternative transcript isoforms, which in turn may have distinct physiologic roles.

Gene variants of TCF7L2 influence weight loss and body composition during lifestyle intervention in a population at risk for type 2 diabetes

OBJECTIVE

The impact of the diabetes risk gene transcription factor 7-like 2 (TCF7L2) on body weight is unclear. As TCF7L2 is expressed in adipose tissue and involved in Wnt-dependent regulation of adipogenesis, we studied the impact of TCF7L2 variants on body composition and weight loss during lifestyle intervention.

RESEARCH DESIGN AND METHODS

We genotyped 309 German subjects at increased risk for type 2 diabetes for single nucleotide polymorphisms (SNPs) rs7903146, rs12255372, rs11196205, and rs7895340 in TCF7L2 and performed oral glucose tolerance tests before and after a 9-month lifestyle intervention. Fat distribution was quantified using whole-body magnetic resonance imaging/spectroscopy in a subgroup of 210 subjects.

RESULTS

After adjustment for confounding variables, we observed a negative impact of the type 2 diabetes allele of SNP rs7903146 on change in BMI (P = 0.0034) and on changes in nonvisceral (P = 0.0032) and visceral fat (P = 0.0165) during lifestyle intervention. An association of rs7903146 with lifestyle intervention-induced changes in insulin secretion, glucose concentrations, liver fat, or insulin sensitivity were not detected (all P > 0.2). Essentially the same results were obtained with SNP rs1255372. In contrast, we found no effects of SNPs rs11196205 and rs7895340 on change in BMI (all P > or = 0.5).

CONCLUSIONS

Our data reveal that diabetes-associated alleles of TCF7L2 are associated with less weight loss in response to lifestyle intervention. Thus, diabetes-associated TCF7L2 gene variation predicts the success of lifestyle intervention in terms of weight loss and determines individual susceptibility toward environmental factors.

Transcription factor 7-like 2-gene polymorphism is related to fasting C peptide in latent autoimmune diabetes in adults (LADA)

Common polymorphisms in the transcription factor 7-like 2 gene (TCF7L2) have been associated with type 2 diabetes in different populations and recently with LADA, but not with type 1 diabetes. The aim of our study was to investigate association between the rs7903146 polymorphism in the TCF7L2 gene and LADA in Polish patients. Link between the "high risk for type 2 diabetes genotype" with clinical features was analyzed. 68 newly diagnosed patients with LADA and 195 healthy controls were genotyped for the rs7903146 polymorphism in the TCF7L2 gene using the PCR-based RFLP method. Fasting C peptide level was measured by ELISA. We observed increased frequencies of the TT genotype of the rs7903146 polymorphism in the TCF7L2 gene in LADA patients compared to controls (15 vs. 6%, P = 0.03). Fasting C peptide serum concentration was significantly lower in group of patients with LADA carrying the TT genotype (P < 0.01). In conclusion, the data from this study confirmed previous results showing genetic similarities between patients with LADA and type 2 diabetes. Non-autoimmune mechanism may be related to beta cell dysfunction in patients with LADA.

Protein phosphatase 2A (PP2A) is increased in old murine B cells and mediates p38 MAPK/tristetraprolin dephosphorylation and E47 mRNA instability

The transcription factor E47, which regulates immunoglobulin class switch in murine splenic B cells, is down-regulated in aged B cells due to reduced mRNA stability. Part of the decreased stability of E47 mRNA is mediated by tristetraprolin (TTP), a physiological regulator of mRNA stability. We have previously shown that TTP mRNA and protein expression are higher in old B cells, and the protein is less phosphorylated in old B cells, both of which lead to more binding of TTP to the 3'-UTR of E47 mRNA, thereby decreasing its stability. PP2A is a protein phosphatase that plays an important role in the regulation of a number of major signaling pathways. Herein we show that not only the amount but also the activity of PP2A is increased in old B cells. As a consequence of this higher phosphatase activity in old B cells, p38 MAPK and TTP (either directly or indirectly by PP2A) are less phosphorylated as compared with young B cells. PP2A dephosphorylation of p38 MAPK and/or TTP likely generates more binding of the hypophosphorylated TTP to the E47 mRNA, inducing its degradation. This mechanism may be at least in part responsible for the age-related decrease in class switch.

Investigation of type 2 diabetes risk alleles support CDKN2A/B, CDKAL1, and TCF7L2 as susceptibility genes in a Han Chinese cohort

Background

Recent genome-wide association studies (GWASs) have reported several genetic variants to be reproducibly associated with type 2 diabetes. Additional variants have also been detected from a metaanalysis of three GWASs, performed in populations of European ancestry. In the present study, we evaluated the influence of 17 genetic variants from 15 candidate loci, identified in type 2 diabetes GWASs and the metaanalysis, in a Han Chinese cohort.

Methodology/Principal Findings

Selected type 2 diabetes–associated genetic variants were genotyped in 1,165 type 2 diabetic patients and 1,136 normoglycemic control individuals of Southern Han Chinese ancestry. The OR for risk of developing type 2 diabetes was calculated using a logistic regression model adjusted for age, sex, and BMI. Genotype-phenotype associations were tested using a multivariate linear regression model. Genetic variants in CDKN2A/B, CDKAL1, TCF7L2, TCF2, MC4R, and PPARG showed a nominal association with type 2 diabetes (P≤0.05), of whom the three first would stand correction for multiple testing: CDKN2A/B rs10811661, OR: 1.26 (1.12–1.43) P = 1.8*10⁻⁴; CDKAL1 rs10946398, OR: 1.23 (1.09–1.39); P = 7.1*10⁻⁴, and TCF7L2 rs7903146, OR: 1.61 (1.19–2.18) P = 2.3 * 10⁻³. Only nominal phenotype associations were observed, notably for rs8050136 in FTO and fasting plasma glucose (P = 0.002), postprandial plasma glucose (P = 0.002), and fasting C-peptide levels (P = 0.006) in the diabetic patients, and with BMI in controls (P = 0.033).

Conclusions/Significance

We have identified significant association between variants in CDKN2A/B, CDKAL1 and TCF7L2, and type 2 diabetes in a Han Chinese cohort, indicating these genes as strong candidates conferring susceptibility to type 2 diabetes across different ethnicities.

TCF7L2 variant rs7903146 affects the risk of type 2 diabetes by modulating incretin action

OBJECTIVE

Common variants in the gene TCF7L2 confer the largest effect on the risk of type 2 diabetes. The present study was undertaken to increase our understanding of the mechanisms by which this gene affects type 2 diabetes risk.

RESEARCH DESIGN AND METHODS

Eight subjects with risk-conferring TCF7L2 genotypes (TT or TC at rs7903146) and 10 matched subjects with wild-type genotype (CC) underwent 5-h oral glucose tolerance test (OGTT), isoglycemic intravenous glucose infusion, and graded glucose infusion (GGI). Mathematical modeling was used to quantify insulin-secretory profiles during OGTT and glucose infusion protocols. The incretin effect was assessed from ratios of the insulin secretory rates (ISR) during oral and isoglycemic glucose infusions. Dose-response curves relating insulin secretion to glucose concentrations were derived from the GGI.

RESULTS

beta-cell responsivity to oral glucose was 50% lower (47 +/- 4 vs. 95 +/- 15 x 10(9) min(-1); P = 0.01) in the group of subjects with risk-conferring TCF7L2 genotypes compared with control subjects. The incretin effect was also reduced by 30% (32 +/- 4 vs. 46 +/- 4%; P = 0.02) in the at-risk group. The lower incretin effect occurred despite similar glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) responses to oral glucose. The ISR response to intravenous glucose over a physiologic glucose concentration range (5-9 mmol/l) was similar between groups.

CONCLUSIONS

The TCF7L2 variant rs7903146 appears to affect risk of type 2 diabetes, at least in part, by modifying the effect of incretins on insulin secretion. This is not due to reduced secretion of GLP-1 and GIP but rather due to the effect of TCF7L2 on the sensitivity of the beta-cell to incretins. Treatments that increase incretin sensitivity may decrease the risk of type 2 diabetes.

Interactions between genetic factors that predict diabetes and dietary factors that ultimately impact on risk of diabetes

PURPOSE OF REVIEW

The purpose of the present review is to summarize recent advances in investigations of interactions between established genetic and dietary risk factors for type 2 diabetes (T2D).

RECENT FINDINGS

Several studies reported that dietary factors related to carbohydrate quality and quantity, such as whole grains and glycemic load, might interact with transcription factor 7-like 2 variants in relation to T2D risk. The genetic predisposition defined by the combination of 10 established T2D risk alleles was found to modulate the association between Western dietary pattern (high intakes of red meat, processed meat, and low fiber) and T2D; a stronger association was observed in those with a high-risk genetic profile. Variants in genes HHEX, CDKN2A/2B, JAZF1, and IGF2BP2 were found to interact with prenatal nutrition in relation to T2D risk and glucose levels in later life.

SUMMARY

The available data provide preliminary support for the gene-diet interactions in determining T2D. However, most findings have yet to be validated. Future studies will need agreed standards of study design and statistical power, dietary measurement, analytical methods, and replication strategies.

Neonatal growth and regeneration of beta-cells are regulated by the Wnt/beta-catenin signaling in normal and diabetic rats

Wnt/beta-catenin signaling is critical for a variety of fundamental cellular processes. Here, we investigated the implication of the Wnt/beta-catenin signaling in the in vivo regulation of beta-cell growth and regeneration in normal and diabetic rats. To this aim, TCF7L2, the distal effector of the canonical Wnt pathway, was knocked down in groups of normal and diabetic rats by the use of specific antisense morpholino-oligonucleotides. In other groups of diabetic rats, the Wnt/beta-catenin pathway was activated by the inhibition of its negative regulator GSK-3beta. GSK-3beta was inactivated by either LiCl or anti-GSK-3beta oligonucleotides. The beta-cell mass was evaluated by morphometry. beta-cell proliferation was assessed in vivo and in vitro by BrdU incorporation method. In vivo beta-cell neogenesis was estimated by the evaluation of PDX1-positive ductal cells and GLUT2-positive ductal cells and the number of beta cells budding from the ducts. We showed that the in vivo disruption of the canonical Wnt pathway resulted in the alteration of normal and compensatory growth of beta-cells mainly through the inhibition of beta-cell proliferation. Conversely, activation of the Wnt pathway through the inhibition of GSK-3beta had a significant stimulatory effect on beta-cell regeneration in diabetic rats. In vitro, GSK-3beta inactivation resulted in the stimulation of beta-cell proliferation. This was mediated by the stabilization of beta-catenin and the induction of cyclin D. Taken together, our results demonstrate the involvement of the canonical Wnt signaling in the neonatal regulation of normal and regenerative growth of pancreatic beta-cells. Moreover, we provide evidence that activation of this pathway by pharmacological maneuvers can efficiently improve beta-cell regeneration in diabetic rats. These findings might have potential clinical applications in the regenerative therapy of diabetes.

Polymorphisms of TCF7L2 and HHEX genes in Chinese women with polycystic ovary syndrome

PURPOSE

This study was to evaluate whether polymorphisms of TCF7L2 (rs7903146) and HHEX (rs1111875) genes responsible for insulin secretion are associated with the polycystic ovary syndrome (PCOS) in Chinese people.

METHODS

326 PCOS patients and 290 healthy individuals as controls were studied. Blood samples were obtained for DNA analyses and hormone measurements. Genotyping of the TCF7L2 (rs7903146) and HHEX (rs1111875) genes was carried out by the polymerase chain reaction-restriction fragment length polymorphism method.

RESULTS

We did not find statistically significant differences in the distribution of the TCF7L2 rs7903146 and HHEX rs1111875 polymorphisms between the Chinese women with PCOS and the controls. Levels of hormones such as insulin, FSH, LH, LH/FSH, P, T and E2 were also similar between the different genotypes of the genes TCF7L2 and HHEX, respectively, which was confirmed within either the PCOS subjects or controls.

CONCLUSIONS

There was no association of either of the two variants, rs7903146 of TCF7L2 and rs1111875 of HHEX, with the occurrence of PCOS in the Chinese population.

Interactions between TCF7L2 genotype and growth hormone-induced changes in glucose homeostasis in small for gestational age children

CONTEXT

The Transcription factor 7-like 2 (TCF7L2) rs7903146 gene polymorphism has been associated with risk of developing type 2 diabetes mellitus (DM), possibly by decreasing insulin secretion. Small for gestational age (SGA) birth has been associated with type 2 DM in later life. Growth hormone (GH) treatment reduces insulin sensitivity and increases insulin secretion. Therefore, GH-treated SGA children are an ideal group to investigate whether the TCF7L2 rs7903146 genotype is associated with changes in glucose homeostasis.

OBJECTIVE

To determine the impact of the TCF7L2 rs7903146 polymorphism on changes in insulin secretion and insulin sensitivity during 4 years of GH treatment in children born SGA.

SUBJECTS

A total of 246 Caucasian short children born SGA, with a median age of 7.8 years.

OUTCOME MEASURES

Insulin sensitivity and insulin secretion were measured by the frequently sampled intravenous glucose tolerance test (FSIGT) (n = 68) and homeostasis model assessment (HOMA) calculations (all).

RESULTS

There was no association between rs7903146 genotype and insulin sensitivity or insulin secretion at baseline but after adjustment for possible confounders, insulin secretion was higher in the CT/TT group than in the CC group. During GH treatment, carriers of the rs7903146 T allele had an increase in insulin secretion similar to that of carriers of the CC genotype. The decrease in insulin sensitivity was only significant in the CT/TT group, but the difference in decrease between genotype groups did not reach significance (P = 0.06). The disposition index (insulin secretion x insulin sensitivity), which is an estimate of beta cell function, was not associated with genotype and did not change during GH treatment.

CONCLUSION

The TCF7L2 rs7903146 polymorphism is not associated with the change in insulin secretion during GH treatment in short SGA children.

Regulation of wingless-type MMTV integration site family (WNT) signalling in pancreatic islets from wild-type and obese mice

AIMS/HYPOTHESIS

TCF7L2 is a type 2 diabetes susceptibility gene and downstream effector of canonical wingless-type MMTV integration site family (WNT) signalling. However, it is unknown whether this pathway is active in adult pancreatic islets in vivo, and whether it is regulated in obesity.

METHODS

We analysed activation of endogenous WNT signalling in the endocrine pancreas from wild-type and obese mice (ob/ob) using a reporter transgene (Topgal). Regulation of WNT signalling was compared using gene chip experiments from isolated pancreatic islets. Activation of canonical WNT signalling in pancreatic islets and the mouse beta cell line MIN6 was measured using immunoblotting for cytosolic beta-catenin.

RESULTS

Endogenous canonical WNT signalling was absent in the adult endocrine pancreas in both wild-type and obese mice. We identified WNT4 as an abundant WNT signalling molecule in adult pancreatic islets that is induced in two different insulin-resistant mouse models. Increased expression of WNT4 inhibited canonical WNT signalling in pancreatic islets and MIN6 cells.

CONCLUSIONS/INTERPRETATION

Canonical WNT signalling is not active in adult beta cells in vivo. WNT4 provides a potential mechanism for suppression of canonical WNT signalling in obese mice.

TCF7L2 polymorphism associates with new-onset diabetes after transplantation

New-onset diabetes after transplantation (NODAT) is a serious and frequent complication in transplant recipients. Whether NODAT shares the same susceptibility genes as type 2 diabetes is unknown. In this multicenter study, we genotyped 1076 white patients without diabetes at transplantation for 11 polymorphisms that associate with type 2 diabetes. We defined NODAT as a fasting plasma glucose > or =126 mg/dl on at least two occasions or de novo hypoglycemic therapy. We compared clinical and genetic factors between patients who developed NODAT within 6 mo of transplantation (n = 118; incidence 11%) and patients without diabetes (n = 958). In multivariate analysis, NODAT significantly associated with the following characteristics: TCF7L2 polymorphism (odds ratio [OR] 1.60 per each T allele; P = 0.002), age (OR 1.03 per year; P < 0.001), body mass index at transplantation (OR 1.09 per unit; P < 0.001), tacrolimus use (OR 2.26; P < 0.001), and the occurrence of a corticoid-treated acute rejection episode (OR 2.78; P < 0.001). In summary, our data show that the TCF7L2 rs7903146 polymorphism, a known risk factor for type 2 diabetes in the general population, also associates with NODAT.

Preliminary report: No association between TCF7L2 rs7903146 and euglycemic-clamp-derived insulin sensitivity in a mixed-age cohort

There are conflicting reports about the significance of TCF7L2 single nucleotide polymorphism rs7903146, a single nucleotide polymorphism found to be associated with type 2 diabetes mellitus in several genomewide association studies, and insulin sensitivity. The association of rs7903146 and euglycemic-clamp-derived insulin sensitivity was tested in a cohort of children and their parents. Four hundred seventy whites (from 226 families) and 89 African Americans (from 48 families) were included in the analysis. No significant associations were seen between rs7903146 and insulin sensitivity. Adjusted genotype means were consistent across races and generational subgroups.

Alternative splicing of TCF7L2 gene in omental and subcutaneous adipose tissue and risk of type 2 diabetes

BACKGROUND

Single nucleotide polymorphisms (SNPs) rs7903146 and rs12255372 located within TCF7L2 gene have been identified as the strongest common genetic risk factors for development of type 2 diabetes (T2D). We hypothesized that these genetic variants might increase the risk of T2D through regulation of alternative splicing or expression level of TCF7L2 in human adipose tissue.

METHODOLOGY/PRINCIPAL FINDINGS

Expression of 13 assays detecting alternatively spliced forms of TCF7L2 was measured by quantitative reverse-transcriptase PCR (qRT-PCR) in paired biopsies of omental and subcutaneous adipose tissue from 159 obese individuals (BMI 54.6+/-12.2 kg/m(2)). TCF7L2 expression in both types of adipose tissue was not associated with SNPs rs7903146 and rs12255372, T2D status and blood levels of glucose or glycosylated hemoglobin (HbA1c). Expression of assays "ex12-13", "ex12-14" and "ex13-13a" detecting C-terminal alternative exons of TCF7L2 was higher in subcutaneous compared to omental adipose tissue by 1.46 fold (p = 6.5x10(-15)), 1.41 fold (p = 1.4x10(-9)) and 1.26 fold (p = 4.7x10(-6)) in the control group and by 1.86 fold (p = 1.7x10(-4)), 1.77 fold (p = 7.3x10(-4)) and 1.58 fold (p = 6.1x10(-4)) in the T2D group. A pathway enrichment analysis on transcripts significantly co-expressed with TCF7L2 in a microarray set combined with individual expression assays, suggested tissue-specific roles of TCF7L2 splicing forms in regulation of transcription, signal transduction and cell adhesion.

CONCLUSIONS

Expression of TCF7L2 alternatively spliced forms may have different functional roles in omental and subcutaneous adipose tissue but is not associated with SNPs rs7903146 and rs12255372 or T2D status.

A susceptibility gene for type 2 diabetes confers substantial risk for diabetes complicating cystic fibrosis

AIMS/HYPOTHESIS

Insulin-requiring diabetes affects 25-50% of young adults with cystic fibrosis (CF). Although the cause of diabetes in CF is unknown, recent heritability studies in CF twins and siblings indicate that genetic modifiers play a substantial role. We sought to assess whether genes conferring risk for diabetes in the general population may play a risk modifying role in CF.

METHODS

We tested whether a family history of type 2 diabetes affected diabetes risk in CF patients in 539 families in the CF Twin and Sibling family-based study. A type 2 diabetes susceptibility gene (transcription factor 7-like 2, or TCF7L2) was evaluated for association with diabetes in CF using 998 patients from the family-based study and 802 unrelated CF patients in an independent case-control study.

RESULTS

Family history of type 2 diabetes increased the risk of diabetes in CF (OR 3.1; p = 0.0009). A variant in TCF7L2 associated with type 2 diabetes (the T allele at rs7903146) was associated with diabetes in CF in the family study (p = 0.004) and in the case-control study (p = 0.02; combined p = 0.0002). In the family-based study, variation in TCF7L2 increased the risk of diabetes about three-fold (HR 1.75 per allele, 95% CI 1.3-2.4; p = 0.0006), and decreased the mean age at diabetes diagnosis by 7 years. In CF patients not treated with systemic glucocorticoids, the effect of TCF7L2 was even greater (HR 2.9 per allele, 95% CI 1.7-4.9, p = 0.00011).

CONCLUSIONS/INTERPRETATION

A genetic variant conferring risk for type 2 diabetes in the general population is a modifier of risk for diabetes in CF.

Genetic variants of TCF7L2 are associated with insulin resistance and related metabolic phenotypes in Taiwanese adolescents and Caucasian young adults

OBJECTIVES

The effect of TCF7L2 rs7903146 on glucose homeostasis is considered primarily due to impaired insulin secretion in European populations. Because we previously demonstrated that TCF7L2 rs290487 near the 3' end of TCF7L2 was significantly associated with type 2 diabetes (T2D) in Taiwanese subjects, we aimed to investigate potential mechanisms underlying the associations of rs290487 with T2D.

METHODS

Eighteen single nucleotide polymorphisms (SNPs) were tested for association with glucose/insulin homeostasis as well as other quantitative metabolic phenotypes using the quantitative transmission disequilibrium test in 525 Taiwanese adolescent twin-pairs and siblings. The results were further replicated in 116 nondiabetic normotensive Caucasian young adults.

RESULTS

Among the 18 SNPs, rs290487 C allele was significantly associated with higher 60-, 90-, and 120-min glucose concentrations (P = 0.001, 0.01, and 0.02, respectively); higher 60- and 90-min insulin concentrations (P = 0.01 and 0.01, respectively); and a lower insulin sensitivity index (P = 0.04). No association was found for rs290487 with measures of insulin secretion. The rs290487 C allele was also associated with HOMA-IR (P = 0.005) and insulin sensitivity index (P = 0.01) in Caucasian young adults. Another SNP, rs10749127 C allele located in intron 4, was also associated with features of the metabolic syndrome, including elevated systolic (P = 0.02) and diastolic (P = 2.0 x 10(-4)) blood pressure, triglycerides (P = 7.0 x 10(-4)), and uric acid (P = 0.03). In a meta-analysis, the rs290487 C allele was confirmed to be associated with an increased risk of T2D (odds ratio, 1.11; 95% confidence interval, 1.03-1.19; P = 0.005) across East Asian populations.

CONCLUSIONS

These findings support an important role for T2D risk-conferring gene TCF7L2 in insulin resistance in both Taiwanese and Caucasian youth and underscore the emerging role of Wnt signaling in insulin resistance.

Genetic variation of FTO and TCF7L2 in premature adrenarche

Premature adrenarche (PA) has been associated with increased body mass index. Our aim was to determine whether the obesity-associated variant at fat mass and obesity gene (FTO) is more frequent in PA subjects. Furthermore, we hypothesized that altered Wnt signaling due to genetic variants at transcription factor 7-like 2 (TCF7L2) could play a role in the polygenic pathogenesis of PA. We genotyped polymorphisms at FTO rs9939609 and at TCF7L2 rs7903146 and rs12255372 in 73 Finnish white prepubertal children with PA and in 97 age- and sex-matched healthy controls. In addition, we investigated the associations of these genetic variations with weight, height, circulating adrenocortical hormone levels, glucose metabolism, lipid profile, and blood pressure. The differences in the minor allele frequencies (MAFs) of rs9939609, rs7903146, and rs12255372 were not statistically significant between the PA and control groups (difference in MAFs [95% confidence interval]: -0.06 [-0.18, 0.05], 0.04 [-0.05, 0.12], and 0.01 [-0.07, 0.10]; P = .3, .4, and .8, respectively). However, the risk allele at TCF7L2 rs7903146 was more frequent in PA subjects than in controls when we restricted the analysis to the subjects with lower weight-for-height than the median of the PA subjects (weight-for-height <108%, corresponding body mass index SD score <0.79; difference in MAFs [95% confidence interval]: 0.12 [-0.001, 0.23]; P = .038). Risk variant at FTO rs9939609 associated with higher weight-for-height in the healthy children (P = .001). In conclusion, the minor variant at FTO rs9939609 seems to play no major role in the increased weight-for-height of PA subjects; but the risk allele at TCF7L2 rs7903146 may have a role in the pathogenesis of PA in lean subjects.

A Tcf4-GFP reporter mouse model for monitoring effects of Apc mutations during intestinal tumorigenesis

Apc mutations cause intestinal tumorigenesis through Tcf4 activation. However, direct techniques for studying Tcf4 activation in vivo are limited. Here, we describe the development of a Tcf4-GFP reporter mouse model for directly studying Tcf4 activation. We first developed a GFP reporter construct (Tcf4-GFP) and transfected it into SW480 cells that have constitutively activated Tcf4. Reporter activity increased 47-fold. Next, we created transgenic (Tg) mice by transducing the construct into C57BL/6J mice. Fluorescence microscopy did not detect GFP in intestinal sections, but flow cytometry showed 5% of crypt cells to be GFP(+). We then established cross-bred mice (Tg x Apc(Min/+)), which have a germline Apc mutation and sustained Tcf4 activation. Here, fluorescence microscopy showed GFP(+) cells at or near the base of normal-appearing crypts. In adenomas, in which Apc is inactivated, GFP(+) signal was even greater. Immunostaining for the Tcf4 target genes survivin (BIRC5) and cyclin D1 (CCND1) showed that their expression also paralleled GFP positivity. We conclude that GFP directly reports Tcf4 activation in vivo and tracks the predicted increases in Tcf4 activation that result from Apc inactivation, and that Apc mutation contributes to survivin and cyclin D1 overexpression through Tcf4 activation. Our Tcf4 mouse should be useful in studying the effects of chemopreventive agents on Wnt signaling and changes in proliferative crypt cell populations-including stem cells-during intestinal tumorigenesis.

Meta-analysis of the association between SNPs in TCF7L2 and type 2 diabetes in East Asian population

AIMS

To evaluate the effect of TCF7L2 on genetic susceptibility of type 2 diabetes (T2DM) in East Asian population by using the meta-analysis.

METHODS

Search all the publications about the association between TCF7L2 and T2DM in East Asian population from PubMed, CNKI and abstracts of major diabetes conferences. Perform the meta-analysis of all the validated studies and evaluate the association between rs7903146 T allele, rs12255372 T allele, rs11196205 C allele, rs290487 C allele and rs11196218 G allele of TCF7L2 and the risk of T2DM.

RESULTS

Eleven studies from nine eligible papers and one unpublished study of ours were included in the meta-analysis. Ten eligible studies were analyzed for rs7903146, five were analyzed for rs12255372 and rs11196205, and three were analyzed for rs290487 and rs11196218. We found that four SNPs (rs7903146, rs12255372, rs11196205, rs290487) in TCF7L2 were significantly associated with T2DM in East Asian populations. The rs11196218 also showed a marginal association. The estimated population-attributable risk (PAR) associated with analyzed SNPs ranged from 2% to 7%.

CONCLUSIONS

SNPs in TCF7L2 were strongly associated with the risk of T2DM in East Asian population. But the contribution of its genetic variants to the epidemic of type 2 diabetes in East Asian was relatively low.

The T allele of rs7903146 TCF7L2 is associated with impaired insulinotropic action of incretin hormones, reduced 24 h profiles of plasma insulin and glucagon, and increased hepatic glucose production in young healthy men

AIMS/HYPOTHESIS

We studied the physiological, metabolic and hormonal mechanisms underlying the elevated risk of type 2 diabetes in carriers of TCF7L2 gene.

METHODS

We undertook genotyping of 81 healthy young Danish men for rs7903146 of TCF7L2 and carried out various beta cell tests including: 24 h glucose, insulin and glucagon profiles; OGTT; mixed meal test; IVGTT; hyperglycaemic clamp with co-infusion of glucagon-like peptide (GLP)-1 or glucose-dependent insulinotropic polypeptide (GIP); and a euglycaemic-hyperinsulinaemic clamp combined with glucose tracer infusion to study hepatic and peripheral insulin action.

RESULTS

Carriers of the T allele were characterised by reduced 24 h insulin concentrations (p < 0.05) and reduced insulin secretion relative to glucose during a mixed meal test (beta index: p < 0.003), but not during an IVGTT. This was further supported by reduced late-phase insulinotropic action of GLP-1 (p = 0.03) and GIP (p = 0.07) during a 7 mmol/l hyperglycaemic clamp. Secretion of GLP-1 and GIP during the mixed meal test was normal. Despite elevated hepatic glucose production, carriers of the T allele had significantly reduced 24 h glucagon concentrations (p < 0.02) suggesting altered alpha cell function.

CONCLUSIONS/INTERPRETATION

Elevated hepatic glucose production and reduced insulinotropic effect of incretin hormones contribute to an increased risk of type 2 diabetes in carriers of the rs7903146 risk T allele of TCF7L2.