Alterations of the Juvenile Primate Epigenome and Peripheral Circadian Regulation Due to In Utero and Postnatal High Fat Diet Exposure.

Abstract

The molecular mechanisms controlling cyclic expression of circadian genes over a 24-hour period have been well characterized. However, the physiologic entrainment of the peripheral circadian system due to high fat diet consumption is just beginning to be elucidated. We have previously reported that in utero exposure to a maternal high fat (HF) diet alters the fetal hepatic histone code, increasing levels of acetylation of lysine 14 of histone H3 (H3K14ac) in a nonhuman primate model of maternal obesity. We have also reported that expression of the peripheral circadian transcription factor, Npas2, is epigenetically regulated in fetal life and is altered with maternal HF diet exposure. Specifically, increased expression of Npas2 in HF diet exposed animals is associated with increased levels of H3K14ac occupancy in a regulatory region (the RORE) of the Npas2 promoter. We postulated that these alterations in fetal life would persist postnatally, and would be sensitive to postnatal diet exposure. Pregnant macaques were fed either a control (CTR) or caloric dense, high fat diet and offspring were delivered naturally. To evaluate the effects of both in utero and postweaning diet exposure, juvenile animals were grouped to yield four offspring exposure models (in utero diet/postweaning diet: i.e., CTR/CTR, n = 5; CTR/HF, n = 4; HF/CTR, n = 4; HF/HF, n = 5). We utilized western blotting with antibodies to specific histone modifications (H3K14ac, H3K4me3, H3K9me3, and H3K27me3) to determine if diet exposure altered the juvenile histone code. Contrary to the fetal histone code where we observed increased levels of fetal H3K14ac but unchanged H3K4me3 with HF diet exposure, in juveniles H3K4me3 levels were reduced in both the CTR/HF and HF/CTR groups (P < 0.05). Of interest, regardless of in utero diet exposure, persistent upregulation of Npas2 was observed among juvenile offspring exposed to a high fat postweaning diet (CTR/HF, 2.7-fold, P = 0.044; HF/HF, 2.3-fold, P = 0.028). In contrast, Npas2 expression in offspring exposed to a maternal high fat diet in utero and subsequently weaned to a control diet (HF/CTR) did not significantly differ from the CTR/CTR group (1.5-fold, P = 0.182). Analysis of the RORE region within the Npas2 promoter revealed that the association with H3K14ac seen in fetal life does not persist postnatally. However, H3K4me3 is enriched in the RORE HF/HF group (P = 0.017) compared with CTR/CTR. These findings are consistent with two primary observations, namely (1) the fetal and postnatal histone code is modified in a site and modification specific manner, and (2) genes that are epigenetically reprogrammed in fetal life can be modified ex utero by virtue of the postweaning diet. We speculate that in utero followed by chronic exposure to a HF diet disrupts histone-code mediated hepatic circadian gene expression, and may contribute to the adult onset of metabolic syndrome. (poster)