Fibrocytes mediate intimal hyperplasia post-vascular injury and are regulated by two tissue factor-dependent mechanisms

Abstract

Background: CD34+ α-smooth muscle actin (SMA)+ cells mediate intimal hyperplasia (IH) after mechanical endoluminal injury. We previously found that IH is tissue factor (TF) dependent. The precise phenotype of the CD34+ cells mediating IH is unknown and the mechanisms of TF are also unknown. Objective: To define the phenotype of cells mediating IH and compare the effects of inhibiting TF on different subsets of CD34+ cells. Methods: Endoluminal injury was induced in C57BL/6 and two strains of mice expressing a human tissue factor pathway inhibitor (hTFPI) fusion protein on different subsets of CD34+ cells. Confocal microscopy, immunocytofluorescence and real-time PCR were used to determine phenotype. Results: Neointimal cells in C57BL/6 mice were defined as a subset of fibrocytes (CD34+CD45+collagen-1+) expressing SMA, CD31, TIE-2, CXCR4 and CXCL12. Similar cells circulated post-injury and were also found in mice expressing hTFPI on CD34+CD31+ cells, though in these mice, hTFPI inhibited CD31+ fibrocyte hyperplasia, so no IH developed. Mice with hTFPI on all CD34+ α-SMA+ cells repaired arteries back to a pre-injured state. No CD31+ fibrocytes were found in these mice unless an anti-hTFPI antibody was administered. Similar findings in protease activated receptor (PAR)-1-deficient mice suggested hTFPI prevented thrombin signaling through PAR-1. In vitro, thrombin increased the number of CD31+ fibrocytes. Conclusions: Inhibition of TF on CD31+ fibrocytes inhibits IH whereas inhibition on all CD34+ α-SMA+ cells (or PAR-1 deficiency) inhibits the appearance of CD31+ fibrocytes and promotes repair. These data enhance our understanding of IH and suggest novel ways to promote regenerative repair. © 2013 International Society on Thrombosis and Haemostasis.