LXR-activating oxysterols induce the expression of inflammatory markers in endothelial cells through LXR-independent mechanisms.
OBJECTIVE
Liver X receptors alpha and beta (LXRalpha, LXRbeta) are key regulators of cholesterol homeostasis. The effects of LXR ligands on endothelial cells are largely unknown. While oxysterol LXR agonists can increase the endothelial-leukocyte interaction, synthetic LXR agonists are anti-atherogenic and anti-inflammatory. Mechanistic differences may underlie such findings.


RESULTS
LXRalpha and LXRbeta were found to be expressed in human endothelial cells. While synthetic LXR agonists could blunt the LPS-induced up-regulation of adhesion molecules (ICAM-1, VCAM-1, E-Selectin), 22-hydroxycholesterol and 24,25-epoxycholesterol enhanced such response. Microarray profiling further showed that the endothelial gene expression fingerprints of 22-hydroxycholesterol and T0901317 largely differed and unexpectedly shared only a restricted number of genes. Indeed, 22-hydroxycholesterol down-regulated eNOS and up-regulated a vast cohort of inflammatory mediators such as adhesion molecules, cytokines, enzymes and transcription factors. Other LXR-activating oxysterols such as 24,25-epoxycholesterol, 25-hydroxycholesterol and 27-hydroxycholesterol could also stimulate the endothelial expression of inflammatory markers, although significant differences were observed. These effects persisted in LXR-silenced cells, confirming the mechanistic dissociation of oxysterol and LXR pathways. Furthermore, the oxysterol-induced expression of inflammatory markers was not secondary to cell apoptosis and may relate to oxidative stress.


CONCLUSIONS
LXR-activating oxysterols comprehensively activate the expression of endothelial inflammation markers independently from LXRs. At proper dosage, synthetic LXR agonists are safe on endothelial cells and may even transrepress inflammatory reactions.
SCU Medicina d'Urgenza, San Giovanni Battista Hospital and Molecular Biotechnology Center, Torino, Italy. fulvio.morello@unito.it
Fulvio
F
Morello
Elisa
E
Saglio
Alessio
A
Noghero
Domenica
D
Schiavone
Tracy Ann
TA
Williams
Andrea
A
Verhovez
Federico
F
Bussolino
Franco
F
Veglio
Paolo
P
Mulatero
D000924:Anticholesteremic Agents / Q000494:pharmacology; D001565:Benzoates / Q000494:pharmacology; D001596:Benzylamines / Q000494:pharmacology; D002478:Cells, Cultured; D018925:Chemokines / Q000235:genetics; D002784:Cholesterol / Q000031:analogs & derivatives / Q000378:metabolism*; D019040:E-Selectin / Q000235:genetics; D042783:Endothelial Cells / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006801:Humans; D006845:Hydrocarbons, Fluorinated / Q000494:pharmacology; D006888:Hydroxycholesterols / Q000378:metabolism; D018836:Inflammation Mediators / Q000378:metabolism*; D018799:Intercellular Adhesion Molecule-1 / Q000235:genetics; D008070:Lipopolysaccharides / Q000494:pharmacology; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D013449:Sulfonamides / Q000494:pharmacology; D014157:Transcription Factors / Q000235:genetics; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D019010:Vascular Cell Adhesion Molecule-1 / Q000235:genetics; D005466:Fluorocarbons; D000096926:Benzenesulfonamides
D000924:Anticholesteremic Agents; D001565:Benzoates; D001596:Benzylamines; D018925:Chemokines; D002784:Cholesterol; D019040:E-Selectin; D006845:Hydrocarbons, Fluorinated; D006888:Hydroxycholesterols; D018836:Inflammation Mediators; D018799:Intercellular Adhesion Molecule-1; D008070:Lipopolysaccharides; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors; D012333:RNA, Messenger; D013449:Sulfonamides; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D019010:Vascular Cell Adhesion Molecule-1; C473027:GW 3965; C000605213:NR1H3 protein, human; C423915:T0901317; D005466:Fluorocarbons; D000096926:Benzenesulfonamides; C003585:22-hydroxycholesterol; C028358:24,25-epoxycholesterol; C076996:27-hydroxycholesterol