title: Mechanistic insights into Lp(a)-induced IL-8 expression: a role for oxidized phospholipid modification of apo(a).
abstract: Elevated lipoprotein (a) [Lp(a)] levels are a causal risk factor for coronary heart disease. Accumulating evidence suggests that Lp(a) can stimulate cellular inflammatory responses through the kringle-containing apolipoprotein (a) [apo(a)] component. Here, we report that recombinant apo(a) containing 17 kringle (17K) IV domains elicits a dose-dependent increase in interleukin (IL)-8 mRNA and protein expression in THP-1 and U937 macrophages. This effect was blunted by mutation of the lysine binding site in apo(a) kringle IV type 10, which resulted in the loss of oxidized phospholipid (oxPL) on apo(a). Trypsin-digested 17K had the same stimulatory effect on IL-8 expression as intact apo(a), while enzymatic removal of oxPL from apo(a) significantly blunted this effect. Using siRNA to assess candidate receptors, we found that CD36 and TLR2 may play roles in apo(a)-mediated IL-8 stimulation. Downstream of these receptors, inhibitors of MAPKs, Jun N-terminal kinase and ERK1/2, abolished the effect of apo(a) on IL-8 gene expression. To assess the roles of downstream transcription factors, luciferase reporter gene experiments were conducted using an IL-8 promoter fragment. The apo(a)-induced expression of this reporter construct was eliminated by mutation of IL-8 promoter binding sites for either NF-κB or AP-1. Our results provide a mechanistic link between oxPL modification of apo(a) and stimulation of proinflammatory intracellular signaling pathways.
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON, Canada.
authors.forename: Corey A
authors.initials: CA
authors.lastname: Scipione
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON, Canada.
authors.forename: Sera E
authors.initials: SE
authors.lastname: Sayegh
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON, Canada.
authors.forename: Rocco
authors.initials: R
authors.lastname: Romagnuolo
authors.affiliation: Vascular Medicine Program, University of California San Diego, La Jolla, CA.
authors.forename: Sotirios
authors.initials: S
authors.lastname: Tsimikas
authors.affiliation: Department of Medicine, Northwest Lipid Research Laboratories, University of Washington, Seattle, WA.
authors.forename: Santica M
authors.initials: SM
authors.lastname: Marcovina
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON, Canada.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Boffa
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON, Canada mlk@robarts.ca.
authors.forename: Marlys L
authors.initials: ML
authors.lastname: Koschinsky
mesh_terms: D001053:Apolipoproteins / Q000235:genetics / Q000378:metabolism*; D001054:Apolipoproteins A / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002460:Cell Line; D006801:Humans; D016209:Interleukin-8 / Q000235:genetics / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D034741:RNA, Small Interfering; D018808:Transcription Factor AP-1 / Q000378:metabolism
chemical_list: D001053:Apolipoproteins; D001054:Apolipoproteins A; C508606:CXCL8 protein, human; D016209:Interleukin-8; D016328:NF-kappa B; D010743:Phospholipids; D034741:RNA, Small Interfering; D018808:Transcription Factor AP-1
keywords: apolipoprotein (a); atherosclerosis; inflammation; interleukin-8; lipoprotein (a)