Inflammatory environment and oxidized LDL convert circulating human proangiogenic cells (PACs) into functional antigen presenting cells (APCs)

The function of human circulating proangiogenic cells (PACs) has been described extensively. However, little focus has been placed on understanding how these cells differ in their functions in the presence of microenvironments mimicking vascular inflammation. We hypothesized that exposure to proinflammatory cytokines or the oxLDL, an autoantigen abundant in advanced atherosclerotic plaques, converts PACs into immune-modulating/proinflammatory cells. Hence, we examined the effect of oxLDL and inflammatory stimuli on their phenotype by use of a functional genomics model based on secretome and whole genome transcriptome profiling. PACs obtained from culturing a PBMC fraction in angiogenic medium were primed with DC differentiation cytokines for 3 days and then exposed to proinflammatory cytokines or oxLDL for 2 days. Under these conditions, PACs converted into APCs (APCcy and APCox, respectively), expressed maturation markers CD80 and CD83, and showed an up-regulation of CD86. APCcy and APCox induced a robust T cell BrdU incorporation. Despite a similar ability to induce lymphocyte proliferation, APCcy and APCox differed for the secretory pathway and mRNA expression. Analysis of the differentially expressed genes identified 4 gene "clusters", showing reciprocal modulation in APCcy vs. APCox justifying, according to functional genomics analyses, a different putative function of the cells in antigen processing. Together, these data show that treatment with inflammatory cytokines or oxLDL converts human PAC phenotype and function into that of APCs with similar lymphocyte-activating ability but distinct maturation degree and paracrine functions. PBMC-derived PACs were committed with GM-CSF and IL-4 to a dendritic phenotype, and then exposed to proinflammatory cytokines (IL-1β and TNF-α) or to the oxidized form of LDL (oxLDL). Functional assays and whole genome gene expression profiling were performed both on PACs (n=6) and or resulting cytokine- (APCcy, n=6) and oxLDL-induced APCs (APCox, n=6). RNA was reverse transcribed, labeled, and linearly amplified, and then hybridized to HumanHT-12 v.4 Expression BeadChip microarrays. To estimate technical variability, ≈20% of the samples (n=4) were hybridized in duplicate.