The Steroltalk microarray: a systemic approach to studies of cholesterol homeostasis and drug metabolism T. Režen1, P. Juvan1, J. Acimovic1, A. Belic2, J.A. Contreras1, U.A Meyer3, K. Monostory4, H. Delacroix5, J.M. Pascussi6, I. Bjorkhem7, D. Rozman1 1 Center for Functional Genomics and Bio-Chips, Institute of Biochemistry, Faculty of Medicine, 2Faculty of Electrical Engineering, University of Ljubljana, Slovenia, 3Biozentrum, University of Basel, Switzerland, 4Chemical Research Center, Hungarian Academy of Sciences, Budapest, Hungary, 5CNRS, Gif-sur-Ivette, France, 6INSERM UMR-U632, University of Montpellier, France; 6Karolinska University Hospital at Huddinge, Stockholm, Sweden. Cholesterol homeostasis and xenobiotic metabolism are complex biological processes which are difficult to study with traditional methods. Deciphering complex regulation and response of these two processes to different factors is crucial for understanding of the disease development (Rezen T. et al., Drug Metab Rev. 39:389, 2007). We have developed a series of low density Steroltalk cDNA microarrays as original tools for systemic studies of the crosstalk between cholesterol homeostasis and xenobiotic metabolism. The arrays include genes involved in cholesterol synthesis and metabolism, drug metabolism, nuclear receptors, transporters, regulators and circadian regulators. In the mouse liver, we observed down-regulation of cholesterol biosynthesis by high-cholesterol diet. Drug metabolism was up-regulated by phenobarbital treatment and high-cholesterol diet. The performance of the Sterolgene v0 was compared to the two commercial high density microarray platforms: the Agilent cDNA (G4104A) and the Affymetrix MOE430A GeneChip. We show that the Sterolgene performance is comparable in terms of cholesterol homeostasis and drug metabolism (Rezen T. et al., BMC Genomics 9:76, 2008). The human primary hepatocytes have been treated by rifampicin, rosuvastatin and atorvastatin and changes in expression have been monitored after 12, 24 and 48h. For rifampicin, transcriptome analyses shows that the primary response to the drug happened before 12h while later the secondary effects have been observed. Some genes from cholesterol biosynthesis were up-regulated at 12h, but not at 24 h. At 48h the induction of drug metabolism genes was still increasing. The response time of the hepatocytes was different for the two statins. Gene expression peaked at 24h for rosuvastatin and at 48h for atorvastatin. Most genes regulated via SREBFs as and genes involved in the degradation drugs (Cytochromes P450) were up-regulated by the two statins To study the system, a mathematical model of cholesterol biosynthesis has been constructed and its properties studied through simulation. Bayesian inference has been employed to identify gene-to-gene interactions from both microarray measurements and the simulated data. Simulations showed that a large number of perturbations of the system are critical for identification of genetic interactions, and that differences in gene expression between human individuals pose a serious problem. Bayesian networks show that expression of cholesterogenic genes can be predicted from expression of 4 key genes, one of them being SREBF2 (Juvan et al., ACSi, in press). Acknowledgements: This abstract and work it concerns was generated in the context of the STEROLTALK project, funded by the European Community as contract No. LSHG-CT-2005-512096.