Abstract
Gestational exposure to a high-fat diet (HFD) stimulates the differentiation of orexigenic peptide-expressing neurons in the hypothalamus of offspring. To examine possible mechanisms that mediate this phenomenon, this study investigated the transcriptional factor, transcription enhancer factor-1 (TEF), and co-activator, Yes-associated protein (YAP), which when inactivated stimulate neuronal differentiation. In rat embryos and postnatal offspring prenatally exposed to a HFD compared to chow, changes in hypothalamic TEF and YAP and their relationship to the orexigenic peptide, enkephalin (ENK), were measured. The HFD offspring at postnatal day 15 (P15) exhibited in the hypothalamic paraventricular nucleus a significant reduction in YAP mRNA and protein, and increased levels of inactive and total TEF protein, with no change in mRNA. Similarly, HFD-exposed embryos at embryonic day 19 (E19) showed in whole hypothalamus significantly decreased levels of YAP mRNA and protein and TEF mRNA, and increased levels of inactive TEF protein, suggesting that HFD inactivates TEF and YAP. This was accompanied by increased density and fluorescence intensity of ENK neurons. A close relationship between TEF and ENK was suggested by the finding that TEF co-localizes with this peptide in hypothalamic neurons and HFD reduced the density of TEF/ENK co-labeled neurons, even while the number and fluorescence intensity of single-labeled TEF neurons were increased. Increased YAP inactivity by HFD was further evidenced by a decrease in number and fluorescence intensity of YAP-containing neurons, although the density of YAP/ENK co-labeled neurons was unaltered. Genetic knockdown of TEF or YAP stimulated ENK expression in hypothalamic neurons, supporting a close relationship between these transcription factors and neuropeptide. These findings suggest that prenatal HFD exposure inactivates both hypothalamic TEF and YAP, by either decreasing their levels or increasing their inactive form, and that this contributes to the stimulatory effect of HFD on ENK expression and possibly the differentiation of ENK-expressing neurons.
Highlights
Obesity is a growing epidemic, with the latest National Health and Nutrition Survey finding that 36% of adults and 17% of adolescents and children are obese [1]
To determine whether prenatal high-fat diet (HFD) exposure has an effect on the expression of transcription enhancer factor-1 (TEF) and Yes-associated protein (YAP), mRNA from the paraventricular nucleus (PVN) of postnatal day 15 (P15) offspring prenatally exposed to a HFD or chow was extracted, and qRT-PCR was performed
Prenatal HFD effects on hypothalamic TEF and YAP protein levels. To determine whether these changes in mRNA were accompanied by changes in protein levels of TEF and YAP and whether these proteins were in their active or inactive forms, western blotting was performed on purified protein extracted from the PVN of P15 offspring, and both the nonphosphorylated and phosphorylated forms of TEF and YAP were probed
Summary
Obesity is a growing epidemic, with the latest National Health and Nutrition Survey finding that 36% of adults and 17% of adolescents and children are obese [1]. Clinical and animal studies have attributed this rise, in part, to fetal programming produced by maternal obesity and overconsumption of a fatrich diet, which in the offspring increases preference for a highfat diet (HFD) and risk for higher weight gain and metabolic disorders [2,3,4,5,6]. The hypothalamus, which is an important part of the brain that controls energy homeostasis by regulating food intake and energy expenditure, has been shown to be markedly affected by prenatal exposure to a HFD. Maternal ingestion of a HFD stimulates neurogenesis in early embryonic hypothalamus and increases the number of neurons that express neuropeptides known to stimulate ingestive behavior [4,7]. Prenatal HFD exposure increases the peptideexpressing neuroprogenitor cell population in embryos, which later differentiate into functional peptide neurons [8,9]. The cellular factors involved in this stimulatory effect on the differentiation and expression of peptide neurons are unknown but are likely to involve transcriptional regulators of neuronal differentiation, many of which, with the exception of c-Fos and CREB [10,11,12], have never been studied in relation to the orexigenic peptides in the hypothalamus
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