Altered intragenic DNA methylation of <i>HOOK2</i> gene in adipose tissue from individuals with obesity and type 2 diabetes

<div><p>Aims/Hypothesis</p><p>Failure in glucose response to insulin is a common pathology associated with obesity. In this study, we analyzed the genome wide DNA methylation profile of visceral adipose tissue (VAT) samples in a population of individuals with obesity and assessed whether differential methylation profiles are associated with the presence of type 2 diabetes (T2D).</p><p>Methods</p><p>More than 485,000 CpG genome sites from VAT samples from women with obesity undergoing gastric bypass (n = 18), and classified as suffering from type 2 diabetes (T2D) or not (no type 2 diabetes, NT2D), were analyzed using DNA methylation arrays.</p><p>Results</p><p>We found significant differential methylation between T2D and NT2D samples in 24 CpGs that map with sixteen genes, one of which, <i>HOOK2</i>, demonstrated a significant correlation between differentially hypermethylated regions on the gene body and the presence of type 2 diabetes. This was validated by pyrosequencing in a population of 91 samples from both males and females with obesity. Furthermore, when these results were analyzed by gender, female T2D samples were found hypermethylated at the cg04657146-region and the cg 11738485-region of HOOK2 gene, whilst, interestingly, male samples were found hypomethylated in this latter region.</p><p>Conclusion</p><p>The differential methylation profile of the <i>HOOK2</i> gene in individuals with T2D and obesity might be related to the attendant T2D, but further studies are required to identify the potential role of <i>HOOK2</i> gene in T2D disease. The finding of gender differences in T2D methylation of <i>HOOK2</i> also warrants further investigation.</p></div

The anthropometric and clinical characteristics of the discovery cohort and the validation cohort.

<p>The anthropometric and clinical characteristics of the discovery cohort and the validation cohort.</p

Altered intragenic DNA methylation of <i>HOOK2</i> gene in adipose tissue from individuals with obesity and type 2 diabetes - Fig 1

<p>A. Hierarchical clustering heatmap. Showing differentially methylated CpGs of autosomal probes from women with obesity and discordant for type 2 diabetes (8 T2D and 10 NT2D). The heat map scale shows the range of methylation values, from 0 (blue) to 1 (yellow). Whether the CpG site analyzed is associated with a CpG island (CGI) or not can clearly be distinguished. Red asterisks mark the differentially methylated probes validated by pyrosequencing on <i>HOOK2</i> gene. B. Strip charts showing β values of three differentially methylated CpGs (dmCpGs) located on <i>HOOK2</i> gene in individual samples of the discovery cohort. The bold dotted line with the rhombus indicates the median value of each group of samples. C. Distribution of differentially methylated CpGs (dmCpGs) relative to CGIs, and relative distribution of dmCpGs across different genomic regions. <i>Abbreviations</i>: <i>T2D (Type 2 Diabetes); NT2D (No Type 2 Diabetes)</i>.</p

Differentially methylated CpG sites in T2D compared with NT2D samples.

<p>Differentially methylated CpG sites in T2D compared with NT2D samples.</p

Box plots illustrate the methylation values of differentially methylated CpG regions between T2D and NT2D samples validated by pyrosequencing in <i>HOOK2</i> gene.

<p>Schematic representation of the target regions studied and the methylation values from T2D and NT2D samples in the discovery cohort and the validation cohort are shown. Vertical lines represent the location of each CpG site. The analyzed region (blue line) and the CpG sites in the array (red box) are highlighted. The <i>p</i>-values for the comparison of the groups are also indicated (**adjusted <i>p</i>-value <0.05; ***adjusted <i>p</i>-value <0.0001). <i>Abbreviations</i>: <i>T2D (Type 2 Diabetes); NT2D (No Type 2 Diabetes)</i>.</p