Karl-Fredrik Eriksson

PGC-1alpha-responsive genes involved in oxidative phosphorylation are coordinately downregulated in human diabetes.

DNA microarrays can be used to identify gene expression changes characteristic of human disease. This is challenging, however, when relevant differences are subtle at the level of individual genes. We introduce an analytical strategy, Gene Set Enrichment Analysis, designed to detect modest but coordinate changes in the expression of groups of functionally related genes. Using this approach, we identify a set of genes involved in oxidative phosphorylation whose expression is coordinately decreased in human diabetic muscle. Expression of these genes is high at sites of insulin-mediated glucose disposal, activated by PGC-1α and correlated with total-body aerobic capacity. Our results associate this gene set with clinically important variation in human metabolism and illustrate the value of pathway relationships in the analysis of genomic profiling experiments.

Prevention of type 2 (non-insulin dependent) diabetes mellitus by diet and physical exercise : the 6-year Malmo feasibility study

SummaryFrom a previously reported 5-year screening programme of 6,956 47–49-year-old Malmö males, a series of 41 subjects with early-stage Type 2 (non-insulin-dependent) diabetes mellitus and 181 subjects with impaired glucose tolerance were selected for prospective study and to test the feasibility aspect of long-term intervention with an emphasis on life-style changes. A 5-year protocol, including an initial 6-months (randomised) pilot study, consisting of dietary treatment and/or increase of physical activity or training with annual check-ups, was completed by 90% of subjects. Body weight was reduced by 2.3–3.7% among participants, whereas values increased by 0.5–1.7% in non-intervened subjects with impaired glucose tolerance and in normal control subjects (p<0.0001); maximal oxygen uptake (ml · min−1 · kg−1) was increased by 10–14% vs decreased by 5–9%, respectively (p<0.0001). Glucose tolerance was normalized in > 50% of subjects with impaired glucose tolerance, the accumulated incidence of diabetes was 10.6%, and more than 50% of the diabetic patients were in remission after a mean follow-up of 6 years. Blood pressure, lipids, and hyperinsulinaemia were reduced and early insulin responsiveness to glucose loading preserved. Improvement in glucose tolerance was correlated to weight reduction (r=0.19, p<0.02) and increased fitness (r=0.22, p<0.02). Treatment was safe, and mortality was low (in fact 33% lower than in the remainder of the cohort). We conclude that long-term intervention in the form of diet and physical exercise is feasible even on a large scale, and that substantial metabolic improvement can be achieved which may contribute to prevent or postpone manifest diabetes.

Mechanisms by which common variants in the TCF7L2 gene increase risk of type 2 diabetes

Genetic variants in the gene encoding for transcription factor-7-like 2 (TCF7L2) have been associated with type 2 diabetes (T2D) and impaired beta cell function, but the mechanisms have remained unknown. We therefore studied prospectively the ability of common variants in TCF7L2 to predict future T2D and explored the mechanisms by which they would do this. Scandinavian subjects followed for up to 22 years were genotyped for 3 SNPs (rs7903146, rs12255372, and rs10885406) in TCF7L2, and a subset of them underwent extensive metabolic studies. Expression of TCF7L2 was related to genotype and metabolic parameters in human islets. The CT/TT genotypes of SNP rs7903146 strongly predicted future T2D in 2 independent cohorts (Swedish and Finnish). The risk T allele was associated with impaired insulin secretion, incretin effects, and enhanced rate of hepatic glucose production. TCF7L2 expression in human islets was increased 5-fold in T2D, particularly in carriers of the TT genotype. Overexpression of TCF7L2 in human islets reduced glucose-stimulated insulin secretion. In conclusion, the increased risk of T2D conferred by variants in TCF7L2 involves the enteroinsular axis, enhanced expression of the gene in islets, and impaired insulin secretion.

A six months exercise intervention influences the genome-wide DNA methylation pattern in human adipose tissue.

Epigenetic mechanisms are implicated in gene regulation and the development of different diseases. The epigenome differs between cell types and has until now only been characterized for a few human tissues. Environmental factors potentially alter the epigenome. Here we describe the genome-wide pattern of DNA methylation in human adipose tissue from 23 healthy men, with a previous low level of physical activity, before and after a six months exercise intervention. We also investigate the differences in adipose tissue DNA methylation between 31 individuals with or without a family history of type 2 diabetes. DNA methylation was analyzed using Infinium HumanMethylation450 BeadChip, an array containing 485,577 probes covering 99% RefSeq genes. Global DNA methylation changed and 17,975 individual CpG sites in 7,663 unique genes showed altered levels of DNA methylation after the exercise intervention (q<0.05). Differential mRNA expression was present in 1/3 of gene regions with altered DNA methylation, including RALBP1, HDAC4 and NCOR2 (q<0.05). Using a luciferase assay, we could show that increased DNA methylation in vitro of the RALBP1 promoter suppressed the transcriptional activity (p = 0.03). Moreover, 18 obesity and 21 type 2 diabetes candidate genes had CpG sites with differences in adipose tissue DNA methylation in response to exercise (q<0.05), including TCF7L2 (6 CpG sites) and KCNQ1 (10 CpG sites). A simultaneous change in mRNA expression was seen for 6 of those genes. To understand if genes that exhibit differential DNA methylation and mRNA expression in human adipose tissue in vivo affect adipocyte metabolism, we silenced Hdac4 and Ncor2 respectively in 3T3-L1 adipocytes, which resulted in increased lipogenesis both in the basal and insulin stimulated state. In conclusion, exercise induces genome-wide changes in DNA methylation in human adipose tissue, potentially affecting adipocyte metabolism.

Common Missense Variant in the Glucokinase Regulatory Protein Gene Is Associated With Increased Plasma Triglyceride and C-Reactive Protein but Lower Fasting Glucose Concentrations

OBJECTIVE—Using the genome-wide association approach, we recently identified the glucokinase regulatory protein gene (GCKR, rs780094) region as a novel quantitative trait locus for plasma triglyceride concentration in Europeans. Here, we sought to study the association of GCKR variants with metabolic phenotypes, including measures of glucose homeostasis, to evaluate the GCKR locus in samples of non-European ancestry and to fine- map across the associated genomic interval. RESEARCH DESIGN AND METHODS—We performed association studies in 12 independent cohorts comprising >45,000 individuals representing several ancestral groups (whites from Northern and Southern Europe, whites from the U.S., African Americans from the U.S., Hispanics of Caribbean origin, and Chinese, Malays, and Asian Indians from Singapore). We conducted genetic fine-mapping across the ∼417-kb region of linkage disequilibrium spanning GCKR and 16 other genes on chromosome 2p23 by imputing untyped HapMap single nucleotide polymorphisms (SNPs) and genotyping 104 SNPs across the associated genomic interval. RESULTS—We provide comprehensive evidence that GCKR rs780094 is associated with opposite effects on fasting plasma triglyceride (Pmeta = 3 × 10−56) and glucose (Pmeta = 1 × 10−13) concentrations. In addition, we confirmed recent reports that the same SNP is associated with C-reactive protein (CRP) level (P = 5 × 10−5). Both fine-mapping approaches revealed a common missense GCKR variant (rs1260326, Pro446Leu, 34% frequency, r2 = 0.93 with rs780094) as the strongest association signal in the region. CONCLUSIONS—These findings point to a molecular mechanism in humans by which higher triglycerides and CRP can be coupled with lower plasma glucose concentrations and position GCKR in central pathways regulating both hepatic triglyceride and glucose metabolism.

Long-term outcome of the Malmö preventive project: mortality and cardiovascular morbidity.

Abstract. Berglund G, Nilsson P, Eriksson K‐F, Nilsson J‐Å, Hedblad B, Kristenson H, Lindgärde F (University Hospital, Malmö, Sweden). Long‐term outcome of the Malmö Preventive Project: mortality and cardiovascular morbidity. J Intern Med 2000; 247: 19–29.

Cardiovascular risk groups and mortality in an urban Swedish male population: the Malmö Preventive Project

Objectives. To describe the size, overlap and mortality of four cardiovascular risk groups, in order to give a scientific background for the prevention of cardiovascular disease in a representative urban population.

Poor physical fitness, and impaired early insulin response but late hyperinsulinaemia, as predictors of NIDDM in middle-aged Swedish men.

SummaryIn a prospective population-based study of middle-aged Caucasian men, performed in Malmö, Sweden, specifically designed to evaluate physical fitness, early and late insulin response as predictors of non-insulin-dependent diabetes mellitus (NIDDM), 4,637 non-diabetic men underwent oral glucose tolerance tests at the ages of 48 and 54 years. At the baseline examination, physical fitness was measured in terms of lung vital capacity and oxygen uptake during ergometry; early insulin response in terms of the 40-min insulin increment during an oral glucose tolerance test (a correlate of acute insulin response to an intravenous glucose tolerance test), and late insulin response were measured in terms of the 2-h insulin value during the oral glucose tolerance test (a correlate of glucose disposal during euglycaemic clamp testing). Of the subjects studied 116 developed NIDDM (0.4% annually), and when compared with non-diabetic men at baseline, they were found to have an 11% higher mean body mass index (p<0.001), a higher frequency of family history of diabetes (31 vs 18%, p<0.001), 16% lower mean physical activity index (p<0.05), 16% lower mean estimated maximal oxygen uptake (p<0.001), 10% lower mean vital capacity (p<0.001), 26% lower 40-min to total insulin response ratio (p<0.001), and a 2.7 times higher mean 2-h insulin value during an oral glucose tolerance test (p<0.001). Regression analysis (using Coxs proportional hazards model) showed both low vital capacity, and impaired early insulin response but late hyperinsulinaemia to be independent predictors of NIDDM, in addition to body mass index and fasting blood glucose level (p=0.05−0.0001). Among subjects with impaired glucose tolerance at baseline (44 of 278 developed NIDDM), fasting glucose level alone predicted diabetes in this model. The findings suggest that in this age group in a Caucasian population, not only does insulin resistance precede glucose intolerance and NIDDM, but also loss of early insulin response indicating impaired beta-cell function to be an early feature of the process culminating in diabetes. As both physical fitness [which correlates inversely with late insulin response (r=−0.42, p<0.0001)], and the level of physical activity were shown to correlate with diabetes development in this large series, measures to correct these adverse features should be included in future strategies for preventing NIDDM.

Impact of age, BMI and HbA1c levels on the genome-wide DNA methylation and mRNA expression patterns in human adipose tissue and identification of epigenetic biomarkers in blood

Increased age, BMI and HbA1c levels are risk factors for several non-communicable diseases. However, the impact of these factors on the genome-wide DNA methylation pattern in human adipose tissue remains unknown. We analyzed the DNA methylation of ∼480 000 sites in human adipose tissue from 96 males and 94 females and related methylation to age, BMI and HbA1c. We also compared epigenetic signatures in adipose tissue and blood. Age was significantly associated with both altered DNA methylation and expression of 1050 genes (e.g. FHL2, NOX4 and PLG). Interestingly, many reported epigenetic biomarkers of aging in blood, including ELOVL2, FHL2, KLF14 and GLRA1, also showed significant correlations between adipose tissue DNA methylation and age in our study. The most significant association between age and adipose tissue DNA methylation was found upstream of ELOVL2. We identified 2825 genes (e.g. FTO, ITIH5, CCL18, MTCH2, IRS1 and SPP1) where both DNA methylation and expression correlated with BMI. Methylation at previously reported HIF3A sites correlated significantly with BMI in females only. HbA1c (range 28-46 mmol/mol) correlated significantly with the methylation of 711 sites, annotated to, for example, RAB37, TICAM1 and HLA-DPB1. Pathway analyses demonstrated that methylation levels associated with age and BMI are overrepresented among genes involved in cancer, type 2 diabetes and cardiovascular disease. Our results highlight the impact of age, BMI and HbA1c on epigenetic variation of candidate genes for obesity, type 2 diabetes and cancer in human adipose tissue. Importantly, we demonstrate that epigenetic biomarkers in blood can mirror age-related epigenetic signatures in target tissues for metabolic diseases such as adipose tissue.

Impaired glucose tolerance in a middle-aged male urban population: a new approach for identifying high-risk cases.

SummaryFrom an urban population (n=9,033) of 47–49-year-old males, 6,956 participated in a multiphase screening programme, of whom 1.5% were already registered as diabetic patients, 1.7% were then found to be diabetic; of 6,325 subjects given oral glucose tolerance tests, 6.6% were found to have impaired glucose tolerance (WHO criteria, 1985). In 889 asymptomatic cases with initial capillary whole blood glucose values ≥ 6.6 mmol/l fasting and/or 2 h postload, fluctuation in oral glucose tolerance was studied at repeat tests within one month; the mean differences in glucose values between the first and second test were <−1% (fasting) and −15% (2 h post-load); there were no differences in body weight, and 62% of those with initially impaired glucose tolerance had normalised by the repeat test. Only in 109 cases (1.7%) were 2 h post-load values in the 7.8–11.0 mmol/l range both at the first and the repeat test; these cases were comparable vis-à-vis body mass index, triceps skin fold, blood pressure and initial glucose and insulin values, but had significantly lower oxygen uptake (2.34±0.54 l/min vs 2.63±0.681/min; p<0.003), as compared with subjects with initially impaired glucose tolerance but normal repeat test outcome. However, subjects with high normal first test results (2 h value in the 7.0–7.7 mmol/l range) and second test results in the 7.0–11.0 mmol/l range, resembled those with persistent impairment of glucose tolerance in all respects (including oxygen uptake). The repeat test procedure (including ergometry), is therefore to be recommended in selecting true risk cases.