Genetic variation near the hepatocyte nuclear factor-4 alpha gene predicts susceptibility to type 2 diabetes

The Finland-United States Investigation Of NIDDM Genetics (FUSION) study aims to identify genetic variants that predispose to type 2 diabetes by studying affected sibling pair families from Finland. Chromosome 20 showed our strongest initial evidence for linkage. It currently has a maximum logarithm of odds (LOD) score of 2.48 at 70 cM in a set of 495 families. In this study, we searched for diabetes susceptibility variant(s) at 20q13 by genotyping single nucleotide polymorphism (SNP) markers in case and control DNA pools. Of 291 SNPs successfully typed in a 7.5-Mb interval, the strongest association confirmed by individual genotyping was with SNP rs2144908, located 1.3 kb downstream of the primary beta-cell promoter P2 of hepatocyte nuclear factor-4 alpha (HNF4A). This SNP showed association with diabetes disease status (odds ratio [OR] 1.33, 95% CI 1.06-1.65, P = 0.011) and with several diabetes-related traits. Most of the evidence for linkage at 20q13 could be attributed to the families carrying the risk allele. We subsequently found nine additional associated SNPs spanning a 64-kb region, including the P2 and P1 promoters and exons 1-3. Our results and the independent observation of association of SNPs near the P2 promoter with diabetes in a separate study population of Ashkenazi Jewish origin suggests that variant(s) located near or within HNF4A increases susceptibility to type 2 diabetes.     

Hepatocyte nuclear factor-1alpha modulates pancreatic beta-cell growth by regulating the expression of insulin-like growth factor-1 in INS-1 cells

Maturity-onset diabetes of the young type 3 (MODY3) is characterized by impaired insulin secretion. Heterozygous mutations in the gene encoding hepatocyte nuclear factor (HNF)-1alpha are the cause of MODY3. Transgenic mice overexpressing dominant-negative HNF-1alpha mutant in pancreatic beta-cells and HNF-1alpha knockout mice are animal models of MODY3. These mice exhibit defective glucose-stimulated insulin secretion and have reduced beta-cell mass and beta-cell proliferation rate. Here we examined the effect of HNF-1alpha on beta-cell proliferation by overexpressing a human naturally occurring dominant- negative mutation P291fsinsC in INS-1 cells under the control of doxycycline-induction system. INS-1 cells overexpressing P291fsinsC showed apparent growth impairment. The proliferation rate estimated by [(3)H]thymidine incorporation was significantly reduced in P291fsinsC-expressing INS-1 cells compared with noninduced or wild-type HNF-1alpha-overexpressing INS-1 cells. Growth inhibition occurred at the transition from G1 to S cell cycle phase, with reduced expression of cyclin E and upregulation of p27. cDNA array analysis revealed that the expression levels of IGF-1, a major growth factor for beta-cells, and macrophage migration inhibitory factor (MIF), a cytokine expressed in pancreatic beta-cells, were reduced in P291fsinsC-HNF-1alpha-expressing INS-1 cells. Although MIF seemed to have proliferative function, blockade of MIF action by anti-MIF antibody stimulated INS-1 cell proliferation, excluding its direct role in the growth impairment. However, addition of IGF-1 to P291fsinsC-expressing INS-1 cells rescued the growth inhibition. Our data suggest that HNF-1alpha is critical for modulating pancreatic beta-cell growth by regulating IGF-1 expression. IGF-1 might be a potential therapeutic target for the treatment of MODY3.     

AMP-activated protein kinase (AMPK) is activated in muscle of subjects with type 2 diabetes during exercise

Insulin-stimulated GLUT4 translocation is impaired in people with type 2 diabetes. In contrast, exercise results in a normal increase in GLUT4 translocation and glucose uptake in these patients. Several groups have recently hypothesized that exercise increases glucose uptake via an insulin-independent mechanism mediated by the activation of AMP-activated protein kinase (AMPK). If this hypothesis is correct, people with type 2 diabetes should have normal AMPK activation in response to exercise. Seven subjects with type 2 diabetes and eight matched control subjects exercised on a cycle ergometer for 45 min at 70% of maximum workload. Biopsies of vastus lateralis muscle were taken before exercise, after 20 and 45 min of exercise, and at 30 min postexercise. Blood glucose concentrations decreased from 7.6 to 4.77 mmol/l with 45 min of exercise in the diabetic group and did not change in the control group. Exercise significantly increased AMPK alpha2 activity 2.7-fold over basal at 20 min in both groups and remained elevated throughout the protocol, but there was no effect of exercise on AMPK alpha1 activity. Subjects with type 2 diabetes had similar protein expression of AMPK alpha1, alpha2, and beta1 in muscle compared with control subjects. AMPK alpha2 was shown to represent approximately two-thirds of the total alpha mRNA in the muscle from both groups. In conclusion, people with type 2 diabetes have normal exercise-induced AMPK alpha2 activity and normal expression of the alpha1, alpha2 and beta1 isoforms. Pharmacological activation of AMPK may be an attractive target for the treatment of type 2 diabetes.     

Metformin increases AMP-activated protein kinase activity in skeletal muscle of subjects with type 2 diabetes

Metformin is an effective hypoglycemic drug that lowers blood glucose concentrations by decreasing hepatic glucose production and increasing glucose disposal in skeletal muscle; however, the molecular site of metformin action is not well understood. AMP-activated protein kinase (AMPK) activity increases in response to depletion of cellular energy stores, and this enzyme has been implicated in the stimulation of glucose uptake into skeletal muscle and the inhibition of liver gluconeogenesis. We recently reported that AMPK is activated by metformin in cultured rat hepatocytes, mediating the inhibitory effects of the drug on hepatic glucose production. In the present study, we evaluated whether therapeutic doses of metformin increase AMPK activity in vivo in subjects with type 2 diabetes. Metformin treatment for 10 weeks significantly increased AMPK alpha2 activity in the skeletal muscle, and this was associated with increased phosphorylation of AMPK on Thr172 and decreased acetyl-CoA carboxylase-2 activity. The increase in AMPK alpha2 activity was likely due to a change in muscle energy status because ATP and phosphocreatine concentrations were lower after metformin treatment. Metformin-induced increases in AMPK activity were associated with higher rates of glucose disposal and muscle glycogen concentrations. These findings suggest that the metabolic effects of metformin in subjects with type 2 diabetes may be mediated by the activation of AMPK alpha2.     

Decreased glibenclamide uptake in hepatocytes of hepatocyte nuclear factor-1alpha-deficient mice: a mechanism for hypersensitivity to sulfonylurea therapy in patients with maturity-onset diabetes of the young,type 3 (MODY3)

Diabetes in subjects with hepatocyte nuclear factor (HNF)-1alpha gene mutations (maturity-onset diabetes of the young [MODY]-3) is characterized by impaired insulin secretion. Surprisingly, MODY3 patients exhibit hypersensitivity to the hypoglycemic actions of sulfonylurea therapy. To study the pharmacogenetic mechanism(s), we have investigated glibenclamide-induced insulin secretion, glibenclamide clearance from the blood, and glibenclamide metabolism in wild-type and Hnf-1alpha-deficient mice. We show that despite a profound defect in glucose-stimulated insulin secretion, diabetic Hnf-1alpha(-/-) mice have a robust glibenclamide-induced insulin secretory response. We demonstrate that the half-life (t(1/2)) of glibenclamide in the blood is increased in Hnf-1alpha(-/-) mice compared with wild-type littermates (3.9 +/- 1.3 vs. 1.5 +/- 1.8 min, P 相似文献   

Common variants in maturity-onset diabetes of the young genes contribute to risk of type 2 diabetes in Finns

Prior reports have suggested that variants in the genes for maturity-onset diabetes of the young (MODY) may confer susceptibility to type 2 diabetes, but results have been conflicting and coverage of the MODY genes has been incomplete. To complement our previous studies of HNF4A, we examined the other five known MODY genes for association with type 2 diabetes in Finnish individuals. For each of the five genes, we selected 1) nonredundant single nucleotide polymorphisms (SNPs) (r(2)< 0.8 with other SNPs) from the HapMap database or another linkage disequilibrium map, 2) SNPs with previously reported type 2 diabetes association, and 3) nonsynonymous coding SNPs. We tested 128 SNPs for association with type 2 diabetes in 786 index cases from type 2 diabetic families and 619 normal glucose-tolerant control subjects. We followed up 35 of the most significant SNPs by genotyping them on another 384 case subjects and 366 control subjects from Finland. We also supplemented our previous HNF4A results by genotyping 12 SNPs on additional Finnish samples. After correcting for testing multiple correlated SNPs within a gene, we find evidence of type 2 diabetes association with SNPs in five of the six known MODY genes: GCK, HNF1A, HNF1B, NEUROD1, and HNF4A. Our data suggest that common variants in several MODY genes play a modest role in type 2 diabetes susceptibility.     

Insulin gene analysis in a family with maturity-onset diabetes of the young

The insulin gene locus has been studied in a large kindred with maturity-onset diabetes of the young (MODY) characterized by hypoinsulinemia. DNA was isolated from peripheral leukocytes of 42 family members and 5 spouses. A highly polymorphic region in the 5'-flanking portion of the human insulin gene provided an opportunity for linkage analysis. The presence of three different length polymorphisms of + 1600 base pairs (bp), - 50 bp, and - 150 bp different from the common size allele allowed haplotype assignment of insulin alleles. The hypothesis of linkage was tested by calculating the log of the ratio of the likelihood of the hypothesis of linkage to that of the hypothesis of nonlinkage (LOD score) at a given recombination distance between the insulin polymorphism and the diabetes locus. At a recombination frequency of 0.0, the LOD score was - 14.50 and, therefore, the hypothesis of tight linkage can be strongly rejected. This report is the third study of the relationship between the insulin locus and MODY; however, it is the first report in which a formal linkage analysis indicates with a high degree of probability no linkage between the insulin locus and hypoinsulinemia in a family. Because MODY is a heterogeneous disorder, it may be that different genotypes result in a composite phenotype. The lack of linkage between an insulin allele and MODY in a total of four families studied, however, suggests that the insulin locus is probably not a marker for the MODY phenotype. These results do not exclude the possibility that the insulin locus may be involved in the etiology of other forms of NIDDM.