Platelet-rich fibrin induces an inflammatory phenotype of U937 macrophages

Platelet-rich fibrin (PRF) is widely used to support local healing, a process that requires the transient polarization of macrophages towards an inflammatory phenotype. PRF and blood clot components, in general, can potentially incite this macrophage response. To test this hypothesis, we performed a screening assay to identify the overall response of macrophages to PRF. To this aim, U937, a histiocytic lymphoma cell line, and THP1, a leukemia cell line, both commonly used bioassays to study macrophage responses, were exposed to PRF lysates. Transcriptomic changes were identified by bulk RNA sequencing. Analysis was based on significantly regulated genes with an adjusted p-value of p<0.05. In U937 macrophages, consistent with our hypothesis, the clustering of increased genes revealed chemokine activity (CCL2, CCL3, CCL4, CCL5, CCL7, CCL8, CCL20, CCL23, CCL26, CXCL5, CXCL6, CXCL8, CXCL16, and PPBP), RAGE receptor binding (FPR1, S100A8, S100A9, and S100A12), IgG binding (FCGR1A, FCGR2A, FCGR2B, FCGR3A), prostaglandin biosynthetic process (CBR1, CD74, EDN1, FABP5, IL1B, MIF, PTGES, PTGS1) and collagen catabolic process (CTSL, FAP, MMP3, MMP7, MMP9, MMP12, MMP14, MMP19 and MRC2). In THP1 cells, clustering highlighted only steroid biosynthesis. These findings emphasize U937 as an appropriate bioassay to study inflammatory macrophage polarization upon PRF exposure, being consistent with clinical macrophage signatures during early wound healing and holding the potential to recover inflammatory macrophages in chronic wounds. Overall design: We proposed using THP-1 and U937, as THP-1 is a leukemia cell line, and U937 originates from the pleural effusion of a patient with histiocytic lymphoma, both widely established monocytic cell lines, exposed to PRF lysates, to identify the overall response of macrophages to PRF. Transcriptomic changes were determined by bulk RNA sequencing. In the indicated experiments, RT-PCR was conducted to verify some gene expression changes relevant to the RNA-seq.