Type 2 Diabetes risk alleles in Peptidyl-glycine Alpha-amidating Monooxygenase influence GLP-1 levels and response to GLP-1 Receptor Agonists.

Patients with type 2 diabetes vary in their response to currently available therapeutic agents (including GLP-1 receptor agonists) leading to suboptimal glycemic control and increased risk of complications. We show that human carriers of hypomorphic T2D-risk alleles in the gene encoding peptidyl-glycine alpha-amidating monooxygenase (PAM), as well as Pam-knockout mice, display increased resistance to GLP-1 in vivo. Pam inactivation in mice leads to reduced gastric GLP-1R expression and faster gastric emptying: this persists during GLP-1R agonist treatment and is rescued when GLP-1R activity is antagonized, indicating resistance to GLP-1's gastric slowing properties. Meta-analysis of human data from studies examining GLP-1R agonist response (including RCTs) reveals a relative loss of 44% and 20% of glucose lowering (measured by glycated hemoglobin) in individuals with hypomorphic PAM alleles p.S539W and p.D536G treated with GLP-1R agonist. Genetic variation in PAM has effects on incretin signaling that alters response to medication used commonly for treatment of T2D.

TCF7L2 plays a complex role in human adipose progenitor biology, which might contribute to genetic susceptibility to type 2 diabetes.

INTRODUCTION: Non-coding genetic variation at TCF7L2 is the strongest genetic determinant of type 2 diabetes (T2D) risk in humans. TCF7L2 encodes a transcription factor mediating the nuclear effects of WNT signaling in adipose tissue (AT). In vivo studies in transgenic mice have highlighted important roles for TCF7L2 in adipose tissue biology and systemic metabolism. OBJECTIVE: To map the expression of TCF7L2 in human AT, examine its role in human adipose cell biology in vitro, and investigate the effects of the fine-mapped T2D-risk allele at rs7903146 on AT morphology and TCF7L2 expression. METHODS: Ex vivo gene expression studies of TCF7L2 in whole and fractionated human AT. In vitro TCF7L2 gain- and/or loss-of-function studies in primary and immortalized human adipose progenitor cells (APCs) and mature adipocytes (mADs). AT phenotyping of rs7903146 T2D-risk variant carriers and matched controls. RESULTS: Adipose progenitors (APs) exhibited the highest TCF7L2 mRNA abundance compared to mature adipocytes and adipose-derived endothelial cells. Obesity was associated with reduced TCF7L2 transcript levels in whole subcutaneous abdominal AT but paradoxically increased expression in APs. In functional studies, TCF7L2 knockdown (KD) in abdominal APs led to dose-dependent activation of WNT/ß-catenin signaling, impaired proliferation and dose-dependent effects on adipogenesis. Whilst partial KD enhanced adipocyte differentiation, near-total KD impaired lipid accumulation and adipogenic gene expression. Over-expression of TCF7L2 accelerated adipogenesis. In contrast, TCF7L2-KD in gluteal APs dose-dependently enhanced lipid accumulation. Transcriptome-wide profiling revealed that TCF7L2 might modulate multiple aspects of AP biology including extracellular matrix secretion, immune signaling and apoptosis. The T2D-risk allele at rs7903146 was associated with reduced AP TCF7L2 expression and enhanced AT insulin sensitivity. CONCLUSIONS: TCF7L2 plays a complex role in AP biology and has both dose- and depot-dependent effects on adipogenesis. In addition to regulating pancreatic insulin secretion, genetic variation at TCF7L2 might also influence T2D risk by modulating AP function.

Elevated risk of invasive group A streptococcal disease and host genetic variation in the human leucocyte antigen locus.

Invasive group A streptococcal (GAS) disease is uncommon but carries a high case-fatality rate relative to other infectious diseases. Given the ubiquity of mild GAS infections, it remains unclear why healthy individuals will occasionally develop life-threatening infections, raising the possibility of host genetic predisposition. Here, we present the results of a case-control study including 43 invasive GAS cases and 1540 controls. Using HLA imputation and linear mixed models, we find each copy of the HLA-DQA1*01:03 allele associates with a twofold increased risk of disease (odds ratio 2.3, 95% confidence interval 1.3-4.4, P = 0.009), an association which persists with classical HLA typing of a subset of cases and analysis with an alternative large control dataset with validated HLA data. Moreover, we propose the association is driven by the allele itself rather than the background haplotype. Overall this finding provides impetus for further investigation of the immunogenetic basis of this devastating bacterial disease.

The proposed systemic thermogenic metabolites succinate and 12,13-diHOME are inversely associated with adiposity and related metabolic traits: evidence from a large human cross-sectional study.

AIMS/HYPOTHESIS: Circulating succinate and 12,13-dihydroxy-9Z-octadecenoic acid (12,13-diHOME) were recently shown to promote brown adipocyte thermogenesis and protect against metabolic disorders in rodents. This study aimed to evaluate the associations between plasma levels of these metabolites and adiposity and metabolic profile in humans. METHODS: Fasting plasma succinate and 12,13-diHOME levels were quantified using ultra HPLC-tandem MS in 2248 individuals (50% female, mean age 41.3 ± 5.9 years, mean BMI 26.1 ± 4.6 kg/m2) in addition to fasting plasma biochemistry. Total and regional adiposity were assessed with dual-energy x-ray absorptiometry. An age- and sex-adjusted linear regression model was used to determine the associations between succinate and 12,13-diHOME levels and body composition and metabolic profile. Two-sample Mendelian randomisation was used to assess the associations between genetically determined BMI and metabolic traits with circulating plasma succinate and 12,13-diHOME. RESULTS: A one-SD higher plasma succinate and 12,13-diHOME concentration was associated with a 0.15 SD (95% CI 0.28, 0.03) and 0.08 SD (0.15, 0.01) lower total fat mass respectively. Additionally, a one-SD higher plasma 12,13-diHOME level was associated with a 0.09 SD (0.16, 0.02) lower fasting plasma insulin and 0.10 SD (0.17, 0.04) lower plasma triacylglycerol. In Mendelian randomisation analyses, genetically determined higher BMI, fasting hyperinsulinaemia and elevated lipid levels were not associated with changes in either plasma succinate or plasma 12,13-diHOME concentrations. No indications of bias due to directional pleiotropy were detected in the Mendelian randomisation analyses. CONCLUSIONS/INTERPRETATION: Our findings tentatively suggest that plasma succinate and 12,13-diHOME may play a role in the regulation of energy metabolism and brown adipose tissue activation in humans. Further studies encompassing direct assessment of brown adipose tissue activity and dietary supplementation are necessary to investigate the potential beneficial effects of these metabolites on systemic metabolism.

Assessing association between protein truncating variants and quantitative traits.

MOTIVATION: In sequencing studies of common diseases and quantitative traits, power to test rare and low frequency variants individually is weak. To improve power, a common approach is to combine statistical evidence from several genetic variants in a region. Major challenges are how to do the combining and which statistical framework to use. General approaches for testing association between rare variants and quantitative traits include aggregating genotypes and trait values, referred to as 'collapsing', or using a score-based variance component test. However, little attention has been paid to alternative models tailored for protein truncating variants. Recent studies have highlighted the important role that protein truncating variants, commonly referred to as 'loss of function' variants, may have on disease susceptibility and quantitative levels of biomarkers. We propose a Bayesian modelling framework for the analysis of protein truncating variants and quantitative traits. RESULTS: Our simulation results show that our models have an advantage over the commonly used methods. We apply our models to sequence and exome-array data and discover strong evidence of association between low plasma triglyceride levels and protein truncating variants at APOC3 (Apolipoprotein C3). AVAILABILITY: Software is available from http://www.well.ox.ac.uk/~rivas/mamba

Associations of variants in FTO and near MC4R with obesity traits in South Asian Indians.

Recent genome-wide association studies show that loci in FTO and melanocortin 4 receptor (MC4R) associate with obesity-related traits. Outside Western populations the associations between these variants have not always been consistent and in Indians it has been suggested that FTO relates to diabetes without an obvious intermediary obesity phenotype. We investigated the association between genetic variants in FTO (rs9939609) and near MC4R (rs17782313) with obesity- and type 2 diabetes (T2DM)-related traits in a longitudinal birth cohort of 2,151 healthy individuals from the Vellore birth cohort in South India. The FTO locus displayed significant associations with several conventional obesity-related anthropometric traits. The per allele increase is about 1% for BMI, waist circumference (WC), hip circumference (HC), and waist-hip ratio. Consistent associations were observed for adipose tissue-specific measurements such as skinfold thickness reinforcing the association with obesity-related traits. Obesity associations for the MC4R locus were weak or nonsignificant but a signal for height (P < 0.001) was observed. The effect on obesity-related traits for FTO was seen in adulthood, but not at younger ages. The loci also showed nominal associations with increased blood glucose but these associations were lost on BMI adjustment. The effect of FTO on obesity-related traits was driven by an urban environmental influence. We conclude that rs9939609 variant in the FTO locus is associated with measures of adiposity and metabolic consequences in South Indians with an enhanced effect associated with urban living. The detection of these associations in Indians is challenging because conventional anthropometric obesity measures work poorly in the Indian "thin-fat" phenotype.

Downregulation of adipose tissue fatty acid trafficking in obesity: a driver for ectopic fat deposition?

OBJECTIVE: Lipotoxicity and ectopic fat deposition reduce insulin signaling. It is not clear whether excess fat deposition in nonadipose tissue arises from excessive fatty acid delivery from adipose tissue or from impaired adipose tissue storage of ingested fat. RESEARCH DESIGN AND METHODS: To investigate this we used a whole-body integrative physiological approach with multiple and simultaneous stable-isotope fatty acid tracers to assess delivery and transport of endogenous and exogenous fatty acid in adipose tissue over a diurnal cycle in lean (n = 9) and abdominally obese men (n = 10). RESULTS: Abdominally obese men had substantially (2.5-fold) greater adipose tissue mass than lean control subjects, but the rates of delivery of nonesterified fatty acids (NEFA) were downregulated, resulting in normal systemic NEFA concentrations over a 24-h period. However, adipose tissue fat storage after meals was substantially depressed in the obese men. This was especially so for chylomicron-derived fatty acids, representing the direct storage pathway for dietary fat. Adipose tissue from the obese men showed a transcriptional signature consistent with this impaired fat storage function. CONCLUSIONS: Enlargement of adipose tissue mass leads to an appropriate downregulation of systemic NEFA delivery with maintained plasma NEFA concentrations. However the implicit reduction in adipose tissue fatty acid uptake goes beyond this and shows a maladaptive response with a severely impaired pathway for direct dietary fat storage. This adipose tissue response to obesity may provide the pathophysiological basis for ectopic fat deposition and lipotoxicity.

Transcriptional control of human adipose tissue blood flow.

Adipose tissue is highly vascularized and expresses several genes involved in vasodilatory and vasoconstrictive regulation. We took a transcriptional approach to study the relationships between adipose tissue blood flow (ATBF) and genes involved in vasoactive processes. As ATBF is impaired in obesity, we tested whether body weight interfered with the transcriptional regulation of ATBF. The mRNA content (real-time PCR) of 26 genes was quantified in subcutaneous adipose tissue biopsies from 28 healthy men with a wide range of BMI. ATBF was measured by 133Xe washout. None of the transcripts was related to fasting ATBF (ATBFF). However, the expression levels of two transcripts involved in vasodilation (natriuretic peptide receptor A/guanylate cyclase A (NPRA) and endothelial nitric oxide synthase (eNOS)) were positively associated with postprandial ATBF (r = 0.53 and r = 0.55, P < 0.01, respectively). Although BMI was negatively related to the mRNA content of NPRA and eNOS (r = -0.78 and r = -0.63, P < 0.01, respectively), the strong associations found between postprandial ATBF and the two transcripts were not affected by obesity. Several genes were subject to coordinated regulation of expression. This study demonstrates for the first time that ATBF responsiveness to nutrient intake is related to the transcription of two genes expressed in adipose tissue and directly involved in vasodilatory actions (eNOS and NPRA), suggesting that part of the regulation of ATBF is at a transcriptional level. Interestingly, these associations were not secondary to changes in BMI. We also found that certain genes involved in the regulation of ATBF are subject to coordinate regulation of expression suggesting physiological autoregulation.

Common variation in the FTO gene alters diabetes-related metabolic traits to the extent expected given its effect on BMI.

OBJECTIVE: Common variation in the FTO gene is associated with BMI and type 2 diabetes. Increased BMI is associated with diabetes risk factors, including raised insulin, glucose, and triglycerides. We aimed to test whether FTO genotype is associated with variation in these metabolic traits. RESEARCH DESIGN AND METHODS: We tested the association between FTO genotype and 10 metabolic traits using data from 17,037 white European individuals. We compared the observed effect of FTO genotype on each trait to that expected given the FTO-BMI and BMI-trait associations. RESULTS: Each copy of the FTO rs9939609 A allele was associated with higher fasting insulin (0.039 SD [95% CI 0.013-0.064]; P = 0.003), glucose (0.024 [0.001-0.048]; P = 0.044), and triglycerides (0.028 [0.003-0.052]; P = 0.025) and lower HDL cholesterol (0.032 [0.008-0.057]; P = 0.009). There was no evidence of these associations when adjusting for BMI. Associations with fasting alanine aminotransferase, gamma-glutamyl-transferase, LDL cholesterol, A1C, and systolic and diastolic blood pressure were in the expected direction but did not reach P < 0.05. For all metabolic traits, effect sizes were consistent with those expected for the per allele change in BMI. FTO genotype was associated with a higher odds of metabolic syndrome (odds ratio 1.17 [95% CI 1.10-1.25]; P = 3 x 10(-6)). CONCLUSIONS: FTO genotype is associated with metabolic traits to an extent entirely consistent with its effect on BMI. Sample sizes of >12,000 individuals were needed to detect associations at P < 0.05. Our findings highlight the importance of using appropriately powered studies to assess the effects of a known diabetes or obesity variant on secondary traits correlated with these conditions.