Maternal Under- and Over-Nutrition during Gestation Causes Islet Hypertrophy and Sex-Specific Changes to Pancreas DNA Methylation in Fetal Sheep

SIMPLE SUMMARY: The development of the fetal pancreas tissue can be affected during gestation by alterations to the intrauterine environment, often referred to as fetal programming. However, the mechanisms by which fetal programming predisposes offspring to reduced β-cell function later in life are poorly understood. The aims of this study were to (1) determine how under or over-nutrition during gestation can affect the growth and development of the pancreas tissue during gestation and (2) determine how the DNA methylation patterns of the pancreas tissue could be affected. We were able to determine that maternal under- and over-nutrition during gestation altered offspring pancreas structure causing reductions in islet size and number. Additionally, the changes in DNA methylation patterns were determined to be in a diet-specific and sex-dependent manner. These data are being used to better understand the mechanisms by which the development of the pancreas is affected by fetal programming with the ultimate goals of developing appropriate intervention strategies for these offspring. ABSTRACT: The mechanisms by which fetal programming predisposes offspring to reduced β-cell function later in life are poorly understood. We hypothesized that maternal under- and over-nutrition during gestation would negatively affect offspring pancreas development and alter DNA methylation patterns. Pregnant ewes (n = 78) were fed 100, 60, or 140% of NRC requirements beginning at d 30.2 ± 0.2 of gestation. The fetuses are referred to as CON, RES, and OVER, respectively. Fetal pancreas tissue was collected at d 90 or 135 of gestation or within 24 h of birth. Tissue was preserved for histological (n = 8 to 9 offspring per treatment per time point) and DNA methylation analyses (n = 3 to 4 fetuses per treatment per sex). At d 135, OVER exhibited an increased islet size, reduced islet number, and greater insulin positive area compared with CON (p ≤ 0.03). An increased islet size was also observed at d 135 in RES (p ≤ 0.03) compared with CON. Cellular proliferation was reduced at birth in OVER vs. CON (p = 0.01). In the RES vs. CON females, 62% of the differentially methylated regions (DMRs) were hypomethylated (p ≤ 0.001). In the RES vs. CON males, 93% of the DMRs were hypermethylated (p ≤ 0.001). In OVER, 66 and 80% of the DMRs were hypermethylated in the female and male offspring compared with CON (p ≤ 0.001). In conclusion, changes to maternal diet during pregnancy affects the islet hypertrophy and cellular proliferation of the offspring at early post-natal time points. Additionally, changes in DNA methylation patterns appear to be in a diet-specific and sex-dependent manner.