Epigenetic malprogramming of the insulin receptor promoter due to developmental overfeeding.

Aim: Prenatal and neonatal overfeeding programs a permanent obesity and diabetes disposition, e.g., due to induction of hypothalamic insulin resistance. We investigated acquired alterations of the DNA methylation pattern of the hypothalamic insulin receptor promoter (IRP) which might be an underlying molecular mechanism.

Methods: Neonatal overfeeding was induced by rearing Wistar rats in small litters (SL). Methylation of CpG-dinucleotides of the hypothalamic IRP was mapped using bisulfite sequencing.

Results: Neonatal overfeeding led to rapid early weight gain, resulting in a metabolic syndrome phenotype, i.e., obesity, hyperleptinemia, hyperglycemia, hyperinsulinemia, and increased insulin/glucose-ratio. The proportion of animals carrying any methylated CpG residue in the 322 bp CpG island of the IRP was increased in neonatally overfed SL rats (n=8), as compared to controls (n=8; P=0.04). Moreover, the mean percentage of methylated CpG positions was also higher in SL rats (P=0.01). Over both groups, neonatal blood glucose levels were positively correlated to the extent of promoter methylation (r=0.52; P=0.04).

Conclusions: This study characterizes for the first time the IRP epigenomically in any species and tissue. Our data reveal that the IRP is vulnerable to hypermethylation due to overnutrition, probably especially glucose-dependent in a dose-response manner. This paradigmatically indicates the impact of nutrient-dependent epigenetic malprogramming, leading to a "diabesity" disposition which may become pathogenic throughout life.