Estudio del perfil transcripcional de los receptores nucleares lxr en un modelo celular de macrófago murino inmortalizado

Abstract

The LXR proteins, LXRα and LXRβ, are transcription factors that belong to the nuclearreceptor superfamily. They are activated by modified forms of cholesterol (oxysterols) andcontrol the transcription of genes that play a crucial role in the regulation of lipid metabolism.They also mediate several aspects of macrophage biology like the inflammatory response, cellsurvival in response to infection and phagocytosis of cell debris. These proteins share a highsequence homology and even some functions are known to be performed equally by LXRα andLXRβ, but the individual biological role of each LXR nuclear receptor has not been characterizedto date.One of the objectives that we have pursued in the present thesis project has been toidentify both the common and differential biological functions in which the LXR nuclearreceptors take part in mouse macrophages. We have developed a cellular model of expression toisolate transcriptional activities of LXRα and LXRβ, in addition to a control model that does notexpress LXR proteins. We performed a gene expression analysis of LXRα and LXRβ, in thepresence of a synthetic agonist and antagonist, using microarray technology. Additionally, wemade use of this technique to carry out a comparative analysis of gene expression among thedifferent macrophage cell lines. Using bioinformatics tools we analysed the number andidentities of the gene transcripts that were expressed significantly higher and the biologicalpathways in which they were involved. These bioinformatics tools have also been useful inclarifying possible mechanisms underlying LXR transcriptional gene control, like expressioninduction or repression.Here we show that ligand‐dependent transcriptional activity is similar for both LXRα andLXRβ nuclear receptors and that, despite their high sequence homology, they share the controlof a proportionally reduced fraction of genes. Stable expression of LXRβ in macrophages is linkedto preferential transcription of a relevant group of genes for their implication in different aspectsof inflammatory response. On the other hand, LXRα displays a dual transcriptional activity: it isresponsible for both transcriptional expression and repression of large group of genes involvedin several different biological activities...