Project description:Circulating cell-free unmethylated DNA fragments arising from the human INS gene have been proposed as biomarkers of β-cell death for the presymptomatic detection of diabetes. However, given the variability of CpG methylation in the INS gene in different cell types, this gene alone may not yield sufficiently specific information to unambiguously report β-cell damage. We employed an unbiased approach using data from a human DNA methylation gene array to identify the CHTOP gene as a candidate biomarker whose CpGs show a greater frequency of unmethylation in human islets. When tested across an array of non-islet human tissues by digital PCR, both INS and CHTOP contain unmethylated CpG sites in several of these tissues, but in a non-overlapping pattern: INS showed a slightly higher frequency of unmethylation in adipose tissue, whereas CHTOP appeared to be unmethylated in pancreas, brain, and skeletal muscle. Notably, INS and CHTOP genes are both unmethylated in human β and α cells, suggesting that each species at best would represent markers of islet cell death in general, and together might distinguish death arising from islets vs. other tissues. To validate unmethylated CHTOP as a biomarker for islet cell damage, we used digital PCR to measure cell-free circulating DNA in human populations. Compared to healthy controls, we observed that levels of differentially methylated CHTOP and INS were higher in youth with new onset type 1 diabetes and in healthy youth who have first-degree relatives with T1D. When tested in youth across a spectrum of metabolic dysfunction, increased levels of unmethylated INS and CHTOP were observed in obese individuals compared to lean controls. Together, these data suggest that simultaneous measurement of both circulating differentially methylated INS and CHTOP is likely to detect islet death in T1D, and raise new questions about β-cell health in populations at risk for both T1D and T2D. Importantly, our data support the use of multiple parameters to increase the accuracy of biomarkers of β-cell health in youth with diabetes.

Project description:Intrauterine growth restriction (IUGR) increases susceptibility to age-related diseases including type 2 diabetes (T2DM), and is associated with permanent and progressive changes in gene expression and epigenetic regulation. We studied cytosine methylation throughout the genome in pancreatic islets from a rat model of uteroplacental insufficiency, providing a novel and detailed assessment of the genomic distribution and locus-specific patterns of DNA methylation in normal islets as well as the changes that occur as a consequence of IUGR. Utilizing a high throughput approach to study DNA methylation at almost 1 million unique sites throughout the genome, we found ~1,400 changes in methylation (IUGR compared to control) with an estimated false discovery rate of 4.2%. These epigenetic differences were observed in IUGR male rats at 7 weeks of age, preceding the development of diabetes in this model. Therefore, these epigenetic differences represent candidates for mediating the pathogenesis of metabolic disease that occurs later in life in these animals. Moreover, many of the changes we identify are located near genes that regulate processes known to be abnormal in IUGR islets, such as vascularization, Î²-cell proliferation, insulin secretion, and cell death. Consistent changes in mRNA expression were identified at some of the epigenetically-dysregulated genes including Fgfr1, Gch1, Pcsk5, and Vgf. Globally, epigenetic dysregulation occurred preferentially at conserved intergenic sequences, which are candidate cis-regulatory elements driving differential expression of nearby genes. These results provide insights into the complex developmental consequences of IUGR, and suggest that changes in DNA methylation could mediate a constellation of changes in both gene expression and pancreatic islet development and function, with relevance to T2DM. Direct comparison of DNA methylation in 8 samples consisting of isolated, pooled pancreatic islets from 7-week-old male offspring belonging to 4 IUGR and 4 control litters (Sprague-Dawley rats). Each microarray consists of a two-color comparison of a methylation-sensitive representation of the genome (HpaII) with an internal methylation-insensitive control/reference (MspI).

Dataset Information

Human pancreatic islets methylation array

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