Tyrosine Sulfation of Native Mouse Psgl-1 Is Required for Optimal Leukocyte Rolling on P-Selectin In Vivo

Background: We recently demonstrated that tyrosine sulfation is an important contributor to monocyte recruitment and retention in a mouse model of atherosclerosis. P-selectin glycoprotein ligand-1 (Psgl-1) is tyrosine-sulfated in mouse monocyte/macrophages and its interaction with P-selectin is important in monocyte recruitment in atherosclerosis. However, whether tyrosine sulfation is required for the P-selectin binding function of mouse Psgl-1 is unknown. Here we test the function of native Psgl-1 expressed in leukocytes lacking endogenous tyrosylprotein sulfotransferase (TPST) activity. Methodology/Principal Findings: Psgl-1 function was assessed by examining P-selectin dependent leukocyte rolling in post-capillary venules of C57BL6 mice transplanted with hematopoietic progenitors from wild type (WTRB6) or Tpst1;Tpst2 double knockout mice (Tpst DKORB6) which lack TPST activity. We observed that rolling flux fractions were lower and leukocyte rolling velocities were higher in Tpst DKORB6 venules compared to WTRB6 venules. Similar results were observed on immobilized P-selectin in vitro. Finally, Tpst DKO leukocytes bound less P-selectin than wild type leukocytes despite equivalent surface expression of Psgl-1. Conclusions/Significance: These findings provide direct and convincing evidence that tyrosine sulfation is required for optimal function of mouse Psgl-1 in vivo and suggests that tyrosine sulfation of Psgl-1 contributes to the development o