Platelet soluble mediators induce a monocyte gene expression profile that is anti-inflammatory, antithrombotic and pro-angiogenic

Abstract

Platelets interact with monocytes in the circulation, and within a growing thrombus, forming aggregates via platelet P-selectin and monocyte PSGL-1. Further influence of platelets on the monocyte also occurs via soluble mediators released upon activation. To compare the effect of these two mechanisms on monocyte gene expression isolated mononuclear cells were incubated for 4 h at 37 oC in autologous plasma containing the releasate from platelets maximally activated by CRP-XL, or with P-selectin-Fc chimera to stimulate through PSGL-1. Monocytes were isolated by positive selection, total RNA extracted and cRNA was hybridised to Illumina-WG6v2 expression arrays. Similarities in the pattern of gene expression was seen with both stimuli but the soluble mediators affected larger numbers of genes (> 5 · more), at higher fold change. The platelet releasate induced a pro-apoptotic profile, with upregulation of anti- (eg BCL2A, ANGPLT4), and downregulation of pro-apoptotic genes (eg CASP2, PYCARD & CARD9). Similarly, upregulation of genes that promote angiogenesis (eg FGFR1), was paralleled by downregulation of angiogenesis inhibitors (eg SERPINEF1). In addition, there was increased expression of anti-inflammatory cytokines and chemokines (eg IL10 & CXCL3), and antithrombotic genes (eg TFPI). Expression of genes that facilitate interaction with Extracellular Matrix (ECM) (eg LAMB3) was increased, whereas genes for proteins that interact with selectins were downregulated (eg FUT7). PSGL-1 stimulation resulted in a similar, albeit weaker, pro-angiogenic and anti-apoptotic profile but also induced genes involved in cell-cell adhesion (eg ICAM1). Activation of monocytes via PSGL-1 generates a pro- angiogenic expression profile; platelet soluble mediators significantly enhance this profile, additionally inducing anti-inflammatory, and anti-atherothrombotic genes, and enabling monocytes to interact with ECM components involved in the wound healing environment of the thrombus.