Associations of Haplotypes Upstream of IRS1 with Insulin Resistance, Type 2 Diabetes, Dyslipidemia, Preclinical Atherosclerosis, and Skeletal Muscle LOC646736 mRNA Levels

Hindawi Publishing Corporation Journal of Diabetes Research Volume 2015, Article ID 405371, 11 pages http://dx.doi.org/10.1155/2015/405371 Research Article Associations of Haplotypes Upstream of IRS1 with Insulin Resistance, Type 2 Diabetes, Dyslipidemia, Preclinical Atherosclerosis, and Skeletal Muscle LOC646736 mRNA Levels Selma M. Soyal,1 Thomas Felder,2 Simon Auer,2 Hannes Oberkofler,2 Bernhard Iglseder,3 Bernhard Paulweber,4 Silvia Dossena,1 Charity Nofziger,1 Markus Paulmichl,1 Harald Esterbauer,5 Franz Krempler,6 and Wolfgang Patsch1 1 Institute of Pharmacology and Toxicology, Paracelsus Medical University, 5020 Salzburg, Austria Department of Laboratory Medicine, Paracelsus Medical University, 5020 Salzburg, Austria 3 Department of Geriatric Medicine, Paracelsus Medical University, 5020 Salzburg, Austria 4 Department of Internal Medicine I, Paracelsus Medical University, 5020 Salzburg, Austria 5 Department of Laboratory Medicine, Medical University of Vienna, 1090 Vienna, Austria 6 Department of Internal Medicine, Krankenhaus Hallein, 5400 Hallein, Austria 2 Correspondence should be addressed to Wolfgang Patsch; Received 9 December 2014; Revised 22 March 2015; Accepted 30 April 2015 Academic Editor: Mitsuhiko Noda Copyright © 2015 Selma M. Soyal et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The genomic region ∼500 kb upstream of IRS1 has been implicated in insulin resistance, type 2 diabetes, adverse lipid profile, and cardiovascular risk. To gain further insight into this chromosomal region, we typed four SNPs in a cross-sectional cohort and subjects with type 2 diabetes recruited from the same geographic region. From 16 possible haplotypes, 6 haplotypes with frequencies >0.01 were observed. We identified one haplotype that was protective against insulin resistance (determined by HOMAIR and fasting plasma insulin levels), type 2 diabetes, an adverse lipid profile, increased C-reactive protein, and asymptomatic atherosclerotic disease (assessed by intima media thickness of the common carotid arteries). BMI and total adipose tissue mass as well as visceral and subcutaneous adipose tissue mass did not differ between the reference and protective haplotypes. In 92 subjects, we observed an association of the protective haplotype with higher skeletal muscle mRNA levels of LOC646736, which is located in the same haplotype block as the informative SNPs and is mainly expressed in skeletal muscle, but only at very low levels in liver or adipose tissues. These data suggest a role for LOC646736 in human insulin resistance and warrant further studies on the functional effects of this locus. 1. Introduction Insulin resistance (IR) and impaired upregulation of insulin secretion are hallmarks of type 2 diabetes. IR is thought to be central to the metabolic syndrome [1] and, even in the absence of type 2 diabetes, it enhances the risk of cardiovascular disease [2]. While IR is strongly associated with obesity, it also occurs in lean individuals [1]. Genome-wide associations studies (GWAS) implicated several loci in IR pathways [3, 4]. rs2943641, located ∼500 kb upstream of IRS1, was the first type 2 diabetes risk locus identified in a GWAS that was linked to IR and hyperinsulinemia [5]. In addition, rs2943641 or SNPs in strong linkage disequilibrium (LD) with it displayed associations with coronary artery disease [6] and HDL cholesterol and/or triglycerides (TG) in other populations [7, 8], but not with BMI. To gain further insight into the role of this chromosomal region in IR and related phenotypes, we typed three additional SNPs in the LD block harboring rs2943641 in a cross-sectional cohort and in subjects with type 2 diabetes, all recruited from the same geographical region. We describe here a common protective haplotype against type 2 diabetes that is associated with reduced levels of surrogate IR markers and average intima media thickness (IMT) of the common carotid arteries, but not obesity or 2 indices of fat mass or distribution. As IRS1 is located >500 kb downstream of the genomic region harboring the informative SNPs and the size of associations is typically less than 200 kb [9], we performed an initial characterization of LOC646736, which is located within the same LD block as the informative SNPs. 2. Materials and Methods 2.1. Study Populations. The two study populations comprised white Europeans, living in the same geographic region. SNPs and haplotype frequencies were analyzed in 1028 male, 40 to 65 years old, and 622 female, 45 to 70 years old, participants of the Salzburg Atherosclerosis Prevention Program in Subjects of High Individual Risk (SAPHIR). Study design and recruitment procedures have been described [10] and clinical data were obtained between 1999 and 2003. Associations of SNPs and haplotypes with anthropometric and metabolic parameters were ascertained in 983 male and 599 female SAPHIR participants without type 2 diabetes. Diabetes was diagnosed by fasting plasma glucose concentrations of ≥126 mg/dL and/or use of hypoglycemic medications. Associations with type 2 diabetes were determined in 600 patients with type 2 diabetes and 1350 SAPHIR participants who were not using hypoglycemic medications and had fasting glucose levels <100 mg/dL and 2 h OGTT values <140 mg/dL. Type 2 diabetes cases included 68 SAPHIR participants and 532 unrelated patients, recruited from the outpatient clinics of the University Hospital Salzburg and the Krankenhaus Hallein between 1999 and 2002. Clinical data of the populations used for these comparisons are shown in Supplementary Tables 1–3 (in Supplementary Material available online at http://dx.doi.org/10.1155/2015/405371). Biopsies from the rectus abdominis muscle, visceral and subcutaneous adipose tissues (VAT and SAT, resp.), and liver of obese subjects were obtained during bariatric surgery between 1998 and 2005. Such tissue samples were also obtained from lean control subjects undergoing an elective surgical procedure such as repair of hernias and cholecystectomy during the same time period [11–13]. Tissue samples were placed immediately in RNA-later (Qiagen) and stored at −80∘ C. The study protocols were approved by the local ethics committee. Informed consent was obtained from all patients included in the study. Fat and lean body mass were determined in SAPHIR participants by bioelectric impedance analysis using the phase-sensitive, fully digital multifrequency analyzer BIA2000M (Data Input, Hofheim, Germany). Abdominal adipose tissue areas were assessed by computed tomography using MX TWIN Picker CT scanner (Marconi Medical Systems, Cleveland, OH) in 897 men and 540 women without type 2 diabetes as described in [14]. An abdominal scan was obtained between the fourth and fifth lumbar vertebrae (L4L5), and the adipose tissue area (...truncated)