Dietary fatty acids, cell signals, and sucrose intake

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The contribution of a high fat diet (HFD) to cardiovascular and metabolic pathology including risk for diabetes and obesity is well-documented. What has not been recognized is the influence of HFD on preference and intake of fructose-containing sugars, creating a behavioral component to the development of cardiometabolic pathology. Clinical and public health studies document the contribution of sucrose-containing foods and drinks to the onset of cardiometabolic disease, which are independent of obesity. We have focused upon the effect on HFD on motivation for sucrose, using a classic operant self-administration paradigm, and reported that a semi- chronic, moderate (31%) mixed-fat diet in rats increases motivation for sucrose intake relative to low fat- (LF) fed controls, an effect independent of increased adiposity. Now we have determined that the specific dietary fatty acids, stearate (STEAR) or palmitate (PALM) (but not oleic acid [OL]), increase sucrose motivation. We have begun to investigate the downstream consequences of dietary STEAR or PALM in the medial hypothalamus (HYP) and striatum (STR), key CNS sites for the sucrose motivation task. Because there is some commonality in neural substrates for different types of rewarding stimuli, we focused on gen-regulatory signals that have been functionally linked to drug-reward/motivation behaviors and found two significant changes. First, phosphorylation of the cell signal GSK3B is decreased in HYP and STR. Since phosphorylation inactivates GSK3B, the implication would be that GSK3B activity is increased, consistent with findings in the drug abuse field. Second, the epigenetic modification of Histone 3 (H3), H3K4me3 (tri-methylation at lysine-4), is decreased in the HYP. This modification (“mark”) is functionally linked with motivational behaviors for drugs of abuse. Because K3K4me3 is transcription-activating, the prediction would be that transcription of proteins which suppress motivation for food is decreased. The proposed studies follow on from these newly-published observations, to extend them, and to address the hypothesis that altered GSK3B and H3K4me3 contribute to or underlie the increased sucrose motivation caused by PALM diet. This will be tested in four Aims, with rats eating PALM, LF, or OL (a dietary fat control) diets. The first two Aims utilize identified pharmacologics which should decrease active GSK3B, or increase H3K4me3. Additionally, we will screen diet influences on an additional group of cell signals, and a set of histone 4 (H4) marks, all of which also have been linked to reward/motivation. In the third Aim we will focus on identifying cell-level targets for these signal changes, and will obtain gene expression data for the histone marks that are modified by the diets. We will use dual-immunocytochemistry to identify neurons, astrocytes, or glia co-expressing any of the altered cell signals or histone marks. We will use ChIP-Seq methodology to identify gene expression for genes that are linked to a specific histone mark, followed by quantitation and gene identification-path analysis. Finally, in a fourth Aim, we will determine diet effects on self- administration behavior and metabolic parameters in age-matched female rats. Collectively these studies will substantially add to our understanding of the cellular and behavioral effects of dietary fatty acids, in the context of a behavior that confers metabolic risk. Recent studies shed light on veterans’ obesity and the contribution of eating habits and attitudes, including a strong preference for sweets and overeating of palatable foods. Our new data should move this field towards the goal of identifying pathways for interventions, including dietary recommendations and psychological or pharmacotherapeutic treatment approaches.