Figure 6.

Endogenous TSP-1 from vascular endothelial cells induces increased VCAM-1 expression via CD36. Primary vascular endothelial cell cultures were treated overnight with 10 nM or 10 mM of CD47-binding 4N1K or control peptide 4NGG (n = 4 per group). (a) Peptide-treated WT cells were immunostained for VCAM-1, imaged at 200×, and fluorescence intensities (AUF) were analyzed using ImageJ, and their RNA was analyzed in real-time PCR to detect VCAM-1 message level relative to housekeeping gene GAPDH (n = 3 reactions per group); (b–d) Fluorescence intensity of VCAM-1 immunostaining in endothelial cells (EC) derived from TSP-1- or CD36-deficient mice treated with indicated peptides (b); in untreated or TNF-α-treated TSP-1-deficient endothelial cells (c) and in WT endothelial cells treated with CD36-binding peptide CSV or control peptide ANK (d). Data are presented as the mean values ± SEM. * p < 0.05. Together, these results suggest that VCAM-1 expression on vascular endothelial cells is differentially regulated by two receptors of TSP-1. While increased endogenous TSP-1 expression favors CD36-mediated signaling causing increased VCAM-1 expression, reduced endogenous TSP-1 expression allows for CD47-mediated downregulation of VCAM-1. These results not only explain the dichotomy in our results from those reported previously but also shed light on the opposite roles of TSP-1 in acute vs. chronic inflammation with predominant roles for TNF-α vs. IL-17, respectively.