QTL analysis and localization of genes involved in the variation of cholesterol levels in the rat

Abstract

Epidemiological studies in man and experimental studies in animals have shown that serum and liver cholesterol levels are influenced by both environmental and genetic factors. Research that aims to dissect which genetic factors are involved in the differences of blood and hepatic cholesterol levels requires standardization of both environmental circumstances and the genetic background. Therefore, genetically defined laboratory animals are indispensable for these studies. In this thesis the four rat inbred strains, BC/CpbU (BC), BN.lx/Cub (BN), LEW/OlaHsd (LEW) and SHR/OlaIpcv (SHR), selected for their response to a cholesterol-rich diet, have been used. BN and LEW are hyperresponders whereas BC and SHR are hyporesponders with respect to serum cholesterol levels. The strains differ also for liver cholesterol accumulation. The BN, SHR and the recombinant inbred (RI) strains, derived from the progenitors BN and SHR, have been used. The genetic linkage map that is based on these RI strains has been extended by using amplified fragment length polymorphism (AFLP) markers. DNA from the BN and SHR have been used to amplify the Fabp6 gene. As no polymorphism could be detected between the BN and the SHR, the location of Fabp6 has been determined by screening a radiation hybrid (RH) panel with rat specific primers. The chromosomal location was, as expected, on rat chromosome 10, in the vicinity of a QTL for liver cholesterol concentration. The F2 progeny of a cross between BC and LEW has been used for the construction of a genetic linkage map, consisting of 258 polymorphic DNA markers. This F2 progeny has been used for QTL analysis for the parameters basal serum cholesterol levels (before a cholesterol-rich diet), and for the post-dietary (i.e. after a cholesterol-rich diet) levels of serum cholesterol, liver cholesterol, serum phospholipids and circulating steroid hormones. For basal serum cholesterol levels, QTLs has been found on chromosome 1 and 7. For post-dietary serum cholesterol levels, two significant QTLs have been found, on chromosome 2 and 16. For liver cholesterol concentrations, two suggestive associations have been found on chromosome 6 and 10. For serum phospholipids level, a QTL has been found on chromosome 11. For postdietary aldosterone levels, two significant QTLs have been found on chromosome 1 and 18. Chapters 6 and 7 deal with the chromosomal localization of genes that are involved in the biosynthesis, metabolism and transport of cholesterol by using the RH panel. In conclusion, this thesis describes the work that has been performed for increasing the marker density of the genetic map of the rat and for the localization of QTLs and genes involved in the cholesterol metabolism in this species. This contributes to the value of the rat as an animal model in studies towards the role of cholesterol in the pathogenesis of atherosclerosis an other cholesterol related disease