Activating transcription factor 6 polymorphisms and haplotypes are associated with impaired glucose homeostasis and type 2 diabetes in dutch Caucasians

Context: Activating transcription factor 6 (ATF6) is critical for initiation and full activation of the unfolded protein response. An association between genetic variation in ATF6 and type 2 diabetes (DM2) was recently reported in Pima Indians. Objectives: To investigate the broader significance of this association for DM2, replication studies in distinct ethic populations are required. We investigated ATF6 for its association with DM2 in Dutch Caucasians. Design/Setting: A genetic association study was conducted at an academic research laboratory. Study Participants: Two independent Dutch cohorts were studied. Cohort 1 (n = 154) was used to evaluate genetic variation in the ATF6 gene in relation to glucose homeostasis in the general population. Cohort 2 (n = 798) consisted of patients with DM2, impaired glucose tolerance, impaired fasting glucose, and normoglycemic control subjects, and was used to investigate ATF6 polymorphisms for their contribution to disturbed glucose homeostasis and DM2. Main Outcome Measures: There were 16 tag single nucleotide polymorphisms genotyped in all subjects of both cohorts. Those single nucleotide polymorphisms included three nonsynonymous coding variants and captured all common allelic variation of ATF6. Results: Our data show that common ATF6 variants are associated with elevated glucose levels in the general population (cohort 1, P = 0.005-0.05). Furthermore, the majority of these variants, and haplotypes thereof, were significantly associated with impaired fasting glucose, impaired glucose tolerance, and DM2 ( cohort 2, P = 0.006-0.05). Associated variants differ from those identified in Pima Indians. Conclusions: Our results strengthen the evidence that one or more variants in ATF6 are associated with disturbed glucose homeostasis and DM2

Electrical stimulation of primary neonatal rat ventricular cardiomyocytes using pacemakers

The study of gene regulation in cardiac myocytes requires a reliable in vitro model. However, monolayer cultures used for this purpose are typically not exposed to electrical stimulation, though this has been shown to strongly affect cardiomyocyte gene expression. Based on pacemakers for clinical use, we developed an easy-to-use portable system that allows the user to perform electro-stimulation of cardiomyocyte cultures in standard tissue incubators without the need for bulky equipment. In addition, we present a refined protocol for culturing high-purity cardiomyocyte cultures with excellent contractile properties for a wide variety of applications

Upstream Stimulatory Factor (USF) and CCAAT/Enhancer Binding Protein δ (C/EBPδ) Compete for overlapping Sites in the Negative Regulatory Region of the HIV-1 LTR

Human immunodeficiency virus type 1 (HIV-1) is a human retrovirus and the causative agent of the acquired immunodeficiency syndrome. Genetic analysis has revealed that the HIV-1 LTR contains a potential negative regulatory element (NRE) with an E box, the recognition sequence for the helix-loop-helix (HLH) family of transcription factors. Furthermore, the upstream stimulatory factor (USF) has been implicated as a negative regulator of HIV-1 expression. Here, we report that the NRE is a composite element and that both C/EBPδ and USF can specifically bind to the NRE. The recognition sequence for C/EBPδ overlaps with the E box in the NRE of HIV-1. Competition experiments showed that either USF or C/EBPδ binds to this NRE but not both together

Functional annotation of heart enriched mitochondrial genes GBAS and CHCHD10 through guilt by association

Despite the mitochondria ubiquitous nature many of their components display divergences in their expression profile across different tissues. Using the bioinformatics-approach of guilt by association (GBA) we exploited these variations to predict the function of two so far poorly annotated genes: Coiled-coil-helix-coiled-coil-helix domain containing 10 (CHCHD10) and glioblastoma amplified sequence (GBAS). We predicted both genes to be involved in oxidative phosphorylation. Through in vitro experiments using gene-knockdown we could indeed confirm this and furthermore we asserted CHCHD 10 to play a role in complex IV activity

Electrical signals affect the cardiomyocyte transcriptome independently of contraction

Martherus RS, Vanherle SJ, Timmer ED, Zeijlemaker VA, Broers JL, Smeets HJ, Geraedts JP, Ayoubi TA. Electrical signals affect the cardiomyocyte transcriptome independently of contraction. Physiol Genomics 42A: 283-289, 2010. First published September 21, 2010; doi:10.1152/physiolgenomics.00182.2009.-Cardiomyocytes in vivo are continuously subjected to electrical signals that evoke contractions and instigate drastic changes in the cells' morphology and function. Studies on how electrical stimulation affects the cardiac transcriptome have remained limited to a small number of heart-specific genes. Furthermore, these studies have ignored the interplay between the electrical excitation and the subsequent contractions. We carried out a genomewide assessment of the effects of electrical signaling on gene expression, while distinguishing between the effects deriving from the electrical pulses themselves and the effects instigated by the evoked contractions. Changes in gene expression in primary cultures of neonatal ventricular cardiomyocytes from Lewis Rattus norvegicus were investigated with microarrays and RT-quantitative PCR (QPCR). A series of experiments was included in which the culture medium was supplemented with the contraction inhibitor blebbistatin to allow for electrical stimulation in the absence of contraction. Electrical stimulation was shown to directly enhance calcium handling and induce cardiomyocyte differentiation by arresting cell division and activating key cardiac transcription factors as well as additional differentiation mechanisms such as wnt signaling. Several genes involved in metabolism were also directly activated by electrical stimulation. Furthermore, our data suggest that contraction exerts negative feedback on the transcription of various genes. Together, these observations indicate that intercellular electric currents between adjacent cardiomyocytes have an important role in cardiomyocyte development. They act at least partially through a pulse-specific gene expression program that is activated independently from the evoked contractions

The ATF6-Met[67]Val Substitution Is Associated With Increased Plasma Cholesterol Levels

Objective-Activating transcription factor 6 (ATF6) is a sensor of the endoplasmic reticulum stress response and regulates expression of several key lipogenic genes. We used a 2-stage design to investigate whether ATF6 polymorphisms are associated with lipids in subjects at increased risk for cardiovascular disease (CVD). Methods and Results-In stage 1, 13 tag-SNPs were tested for association in Dutch samples ascertained for familial combined hyperlipidemia (FCHL) or increased risk for CVD (CVR). In stage 2, we further investigated the SNP with the strongest association from stage 1, a Methionine/Valine substitution at amino-acid 67, in Finnish FCHL families and in subjects with CVR from METSIM, a Finnish population-based cohort. The combined analysis of both stages reached region-wide significance (P=9x10(-4)), but this association was not seen in the entire METSIM cohort. Our functional analysis demonstrated that Valine at position 67 augments ATF6 protein and its targets Grp78 and Grp94 as well as increases luciferase expression through Grp78 promoter. Conclusions-A common nonsynonymous variant in ATF6 increases ATF6 protein levels and is associated with cholesterol levels in subjects at increased risk for CVD, but this association was not seen in a population-based cohort. Further replication is needed to confirm the role of this variant in lipids. (Arterioscler Thromb Vasc Biol. 2009;29:1322-1327.