Multiple effects of circadian dysfunction induced by photoperiod shifts: alterations in context memory and food metabolism in the same subjects.

Humans exposed to shiftwork conditions have been reported to have increased susceptibility to various health problems including various forms of dementia, cancer, heart disease, and metabolic disorders related to obesity. The present experiments assessed the effects of circadian disruption on learning and memory function and various food related processes including diet consumption rates, food metabolism, and changes in body weight. These experiments utilized a novel variant of the conditioned place preference task (CPP) that is normally used to assess Pavlovian associative learning and memory processes produced via repeated context-reward pairings. For the present experiments, the standard CPP paradigm was modified in that both contexts were paired with food, but the dietary constituents of the food were different. In particular, we were interested in whether rats could differentiate between two types of carbohydrates, simple (dextrose) and complex (starch). Consumption rates for each type of carbohydrate were measured throughout training. A test of context preference without the food present was also conducted. At the end of behavioral testing, a fasting glucose test and a glucose challenge test were administered. Chronic photoperiod shifting resulted in impaired context learning and memory processes thought to be mediated by a neural circuit centered on the hippocampus. The results also showed that preferences for the different carbohydrate diets were altered in rats experiencing photoperiod shifting in that they maintained an initial preference for the simple carbohydrate throughout training. Lastly, photoperiod shifting resulted in changes in fasting blood glucose levels and elicited weight gain. These results show that chronic photoperiod shifting, which likely resulted in circadian dysfunction, impairs multiple functions of the brain and/or body in the same individual.

Epigenetic control of a VDR-governed feed-forward loop that regulates p21(waf1/cip1) expression and function in non-malignant prostate cells.

In non-malignant RWPE-1 prostate epithelial cells signaling by the nuclear receptor Vitamin D Receptor (VDR, NR1I1) induces cell cycle arrest through targets including CDKN1A (encodes p21((waf1/cip1))). VDR dynamically induced individual histone modification patterns at three VDR binding sites (R1, 2, 3) on the CDKN1A promoter. The magnitude of these modifications was specific to each phase of the cell cycle. For example, H3K9ac enrichment occurred rapidly only at R2, whereas parallel accumulation of H3K27me3 occurred at R1; these events were significantly enriched in G(1) and S phase cells, respectively. The epigenetic events appeared to allow VDR actions to combine with p53 to enhance p21((waf1/cip1)) activation further. In parallel, VDR binding to the MCM7 gene induced H3K9ac enrichment associated with rapid mRNA up-regulation to generate miR-106b and consequently regulate p21((waf1/cip1)) expression. We conclude that VDR binding site- and promoter-specific patterns of histone modifications combine with miRNA co-regulation to form a VDR-regulated feed-forward loop to control p21((waf1/cip1)) expression and cell cycle arrest. Dissection of this feed-forward loop in a non-malignant prostate cell system illuminates mechanisms of sensitivity and therefore possible resistance in prostate and other VDR responsive cancers.