Study On The Role And Mechanism Of UPAR Promoting Monocyte Differentiation And Uptake Of Ox - LDL

Background:Urokinase plasminogen activator receptor (uPAR), a cell surface receptor involved in multiple physiologic and pathologic processes, is mainly expressed on invasive cells including monocytes, fibroblasts and tumor cells. Pro-inflammatory Ml and anti-inflammatory M2 macrophage sub-populations are present in human atherosclerotic plaques. uPAR has been reported to be co-localized with CD36 in foam cells. Cerivastatin suppresses the expression of uPAR and reduces the uptake of oxidised LDL (ox-LDL) in macrophages. uPAR expression in cancer cells promotes co-cultured macrophage differentiating into M2 macrophage phenotype.Objects:This experiment was designed to investigate the correlation between plasma LDL-C concentrations and uPAR expression levels. This study also aimed to identify uPAR roles in macrophage polarization as well as the effects of uPAR in macrophage phagocytosis.Methods:Hyperlipidemic mice models were established by using high fat diet in ApoE (-/-) mice. uPAR expression levels in peripheral monocytes were tested by flowcytometry. uPAR overexpression and low-expression cell lines were constructed with transgenic methods in THP-1 cells. Inflammatory properties of macrophage under dil-ox-LDL stimulation were observed and CD36、IL-1β、TNF-α、CD206、arginase-1 and IL-10 were evaluated by RT-PCR. Lipid uptake was evaluated via Laser Scanning Confocal Microscope.Results:1、In hyperlipidemic mice, uPAR expression levels in peripheral monocytes were positively correlated to plasma LDL-C concentrations (r=0.5527, p<0.0001). Monocytic uPAR expression were significantly reduced in mice with atorvastatin administration.2、Transgenic uPAR overexpression THP-1 cells (UOT) exhibited M2 phenotype, characterizing by higher levels of anti-inflammatory factors (CD26、arginase-1 and IL-10, p<0.05) and lower levels of inflammatory factors (IL-1β and TNF-α, p<0.05).3、Under stimulation of ox-LDL, UOT cells converted to Ml macrophages with decreased anti-inflammatory factors (CD206、arginase-1 and IL-10, p<0.05) and increased pro-inflammatory factors (IL-1β and TNF-α, p<0.05).4、Ox-LDL stimulation increased both pro-and anti-inflammatory factors in WTT cells remarkably. The increase of the pro-inflammatory cytokines in UOT cells were significantly higher than that of WTT cells.5、UOT cells displayed enhanced dil-ox-LDL uptake. First, UOT cells started dil-ox-LDL uptake much earlier than WTT cells. In addition, a greater portion of UOT cells engulfed dil-ox-LDL than that of WTT cells. Linear regression analysis revealed a significant correlation between intracellular dil-ox-LDL and GFP-uPAR fluorescence intensity in UOT cells (r=0.591, p<0.0001).6、Dil-ox-LDL loading in uPAR low expression THP-1 cells (ULT) was less than WTT cells at the same observation time point.7、Expression levels of CD36 in UOT cells were lower than in WTT cells. Upon ox-LDL stimulation, CD36 expression levels in UOT cells were significantly higher than that in WTT cells.Conclusion:Plama LDL-C upregualted uPAR expression levels on circulating monocytes. uPAR may promote the differentiation of macrophages into M2 subset. uPAR-mediated LDL-C uptake in macrophages was probably via CD36 upregulation.