Abstract 809: Pleiotrophin Is Expressed In Highly Vascularized Regions Of Human Atherosclerotic Plaques: Interferon-gamma Regulates Pleiotrophin Expression In Macrophages Through The Jak/stat Pathway
Background: Pleiotrophin (PTN) is an angiogenic factor that is strongly expressed in ischemic tissues by macrophages. We have previously shown that PTN affects the phenotype of macrophages, by coaxing them to acquire endothelial cell characteristics. Currently, nothing is known about the role of PTN in atherosclerosis. We hypothesize that PTN may be involved in the neovascularization of atherosclerotic plaques.
Results: Immunocytochemical analysis of human plaques (n =6) has shown that PTN expression is associated with microvessels and, in addition to endothelial cells, it co-localized with macrophages. To understand the mechanism of PTN expression in atherosclerotic plaques, we treated macrophages with inflammatory factors known to be important in plaque development. Quantitative PCR analysis revealed that the basal expression levels of PTN were consistently low without stimulation; however, IFN-γtreatment significantly induced PTN mRNA expression by 6 –10 fold in a time and dose dependent manner. IFN-γwas found to regulate PTN expression at both the transcriptional and posttranscriptional level. Actinomycin D (Act D) directly blocked PTN induction, and furthermore real-time PCR analysis of cells pre-treated with IFN-γshowed that 80% of the induced PTN mRNA remained 5 hrs. following the addition of Act D, suggesting that IFN-γhad stabilized the mRNA. Analysis of the signal transduction pathway activated by IFN-γshowed that signal transducer and activator 1 (STAT1) protein was phosphorylated in 5 mins. on Tyr-701 in IFN-γ stimulated macrophages, and the JAK/STAT pathway inhibitors (AG490, WHI-P154 and ATA) abolished IFN-γ induced phosphorylation. Furthermore, IFN-γ up-regulation of PTN expression was found to correlate with the extent of STAT1 phosphorylation.
Conclusion: Our findings established for the first time that PTN is expressed in human atherosclerotic plaques. In addition, we show that IFN-γ regulates PTN expression in macrophages through the JAK/STAT1 signaling pathway. Thus, we propose that the expression of PTN in atherosclerotic plaques may be regulated by a coordinated interaction between macrophages and T cells leading to neovascularization of atherosclerotic plaques.