Cafestol, a diterpene present in unfiltered coffee brews such as Scandinavian boiled, Turkish and Cafetière coffee, is the most potent cholesterol-elevating compound known in the human diet. Several genes involved in cholesterol homeostasis have previously been shown to be targets of cafestol, including CYP7A1, the rate-limiting enzyme in bile acid biosynthesis. We have examined the mechanism by which cafestol elevates serum lipid levels. Changes in several lipid parameters were observed in cafestol-treated APOE3Leiden mice, including a significant increase in serum triglyceride levels. Microarray analysis of these mice identified alterations in hepatic expression of genes involved in lipid metabolism and detoxification, many of which are regulated by the nuclear hormone receptors FXR and PXR. Further studies demonstrate that cafestol is an agonist ligand for FXR and PXR, and that cafestol down-regulates expression of the bile acid homeostatic genes CYP7A1, CYP8B1 and NTCP in the liver of wild type but not FXR null mice. Cafestol did not affect genes known to be up-regulated by FXR in the liver of wild type mice, but did increase expression of the positive FXR-target genes IBABP and FGF15 in the intestine. Since FGF15 has recently been shown to function in an enterohepatic regulatory pathway to repress liver expression of bile acid homeostatic genes, its direct induction in the gut may account for indirect effects of cafestol on liver gene expression. PXR-dependent gene regulation of CYP3A11, and other targets by cafestol was also only seen in the intestine. Using a double FXR/PXR knockout mouse model, we found that both receptors contribute to the cafestol-dependent induction of intestinal FGF15 gene expression. In conclusion, cafestol acts as an agonist ligand for both FXR and PXR and this may contribute to its impact on cholesterol homeostasis.

The mechanisms of diet induced hyperlipidemia and atherosclerosis have been widely studied by delineating the role of candidate genes in transgenic and gene targeted mouse models. However, diet induced hyperlipidemia represents a complex process determined by many lipid genes that is only partly understood. This study is aimed at delineating the events induced by dietary intervention in different mouse models at the level of gene expression using microarray analysis. The focus is on the liver as the organ primarily responding to diet, and crucial in determining plasma lipid levels. Firstly, the effect of the genotype was studied. Expression profiles of liver genes were compared between APOE3Leiden (E3L), APOE knockout (E-/-) and C57BL/6JIco (B6) mice using the Incyte GEM 2.03 array carrying 9552 genes. Several hundred differentially expressed genes were identified indicating that the genotype alone effects gene expression. Secondly, the response of E3L mice to high-fat feeding was investigated using a mild and severe high-fat diet (diet W and N, respectively). Diet W caused differential regulation of 200 genes, while diet N affected the expression of 788 genes in B6 and 1010 genes in E3L mice. Annotation of these genes using the Gene Ontology (GO) database showed that two major processes were strongly affected by genotype and diet, namely lipid metabolism and inflammation, the latter as determined by "immune/defense response and detoxification" processes. Many nuclear receptor target genes were differentially regulated, with the largest effects modulated by the severe high-fat diet N, leading to the suppression of genes involved in bile acid, sterol, steroid, fatty acid, and detoxification metabolism. Strikingly, a substantial part of these nuclear receptor target genes were commonly regulated during the different experimental conditions. The common regulation of many nuclear receptor target genes underlying lipid and detoxification processes as found in this study, suggest a defense mechanism involving many nuclear receptors to protect against the accumulation of toxic endogenous lipids and bile acids. These results further strengthen the close link between hyperlipidemia and inflammatory processes.

Global gene-expression analysis is carried out using different technologies that are either array- or sequence-tag-based. To compare experiments that are performed on these different platforms, array probes and sequence tags need to be linked. An additional challenge is cross-referencing between species, to compare human profiles with those obtained in a mouse model, for example. We have developed the web-based search engine GeneHopper to link different expression resources based on UniGene clusters and HomoloGene orthologs databases of the National Center for Biotechnology Information (NCBI).

Although genes determining lipoprotein homeostasis and atherosclerosis are the subject of intensive investigation, only a subset of these genes is known at present. Hence, we do not have sufficient knowledge to explain the genetic basis of hyperlipidemia in the majority of subjects. Our aim was to identify novel genes and pathways underlying lipoprotein homeostasis by using serial analysis of gene expression. The liver expression profile of mild hyperlipidemic apolipoprotein E3-Leiden (E3L) transgenic mice was compared with that of the wild-type C57BL/6JIco (B6) mice. Over 18 000 liver transcripts of B6 as well as E3L mice were analyzed, representing >9400 unique genes. One hundred seventy-five genes showed altered expression between the strains (P<0.05). Although several of these genes belonged to known metabolic pathways, such as lipoprotein metabolism, detoxification processes, glycolysis, and the acute-phase response, most were novel. Differential gene expression of 8 of 10 genes tested could be confirmed by Northern blot analysis. This inventory of differentially expressed genes will provide a unique basis for detailed studies to gain more insight into their role in lipoprotein homeostasis and atherosclerosis.