title: Liver X receptor-dependent repression of matrix metalloproteinase-9 expression in macrophages.
abstract: Matrix metalloproteinases (MMPs) are zinc endopeptidases that degrade extracellular matrix (ECM) components during normal and pathogenic tissue remodeling. Inappropriate expression of these enzymes contributes to the development of vascular pathology, including atherosclerosis. MMP-9 is expressed in its active form in atherosclerotic lesions and is believed to play an important role in vascular remodeling, smooth muscle cell migration, and plaque instability. We demonstrate here that the liver X receptors (LXRs) LXRalpha and LXRbeta inhibit basal and cytokine-inducible expression of MMP-9. Treatment of murine peritoneal macrophages with the synthetic LXR agonists GW3965 or T1317 reduces MMP-9 mRNA expression and blunts its induction by pro-inflammatory stimuli including lipopolysaccharide, interleukin-1beta, and tumor necrosis factor alpha. In contrast, macrophage expression of MMP-12 and MMP-13 is not altered by LXR ligands. We further show that the ability of LXR ligands to regulate MMP-9 expression is strictly receptor-dependent and is not observed in macrophages obtained from LXRalphabeta null mice. Analysis of the 5'-flanking region of the MMP-9 gene indicates that LXR/RXR heterodimers do not bind directly to the MMP-9 promoter. Rather, activation of LXRs represses MMP-9 expression, at least in part through antagonism of the NFkappaB signaling pathway. These observations identify the regulation of macrophage MMP-9 expression as a mechanism whereby activation of LXRs may impact macrophage inflammatory responses.
authors.affiliation: Howard Hughes Medical Institute, University of California, Los Angeles 90095, USA.
authors.forename: Antonio
authors.initials: A
authors.lastname: Castrillo
authors.forename: Sean B
authors.initials: SB
authors.lastname: Joseph
authors.forename: Chaitra
authors.initials: C
authors.lastname: Marathe
authors.forename: David J
authors.initials: DJ
authors.lastname: Mangelsdorf
authors.forename: Peter
authors.initials: P
authors.lastname: Tontonoz
mesh_terms: D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D004268:DNA-Binding Proteins; D015971:Gene Expression Regulation, Enzymologic; D000071518:Liver X Receptors; D008264:Macrophages / Q000201:enzymology*; D020780:Matrix Metalloproteinase 9 / Q000235:genetics*; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism; D057093:Orphan Nuclear Receptors; D011401:Promoter Regions, Genetic; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D018168:Receptors, Retinoic Acid / Q000502:physiology; D012097:Repressor Proteins / Q000502:physiology*; D047488:Retinoid X Receptors; D014157:Transcription Factors / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D004268:DNA-Binding Proteins; D000071518:Liver X Receptors; D016328:NF-kappa B; C000605214:Nr1h3 protein, mouse; D057093:Orphan Nuclear Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D012097:Repressor Proteins; D047488:Retinoid X Receptors; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D020780:Matrix Metalloproteinase 9