Abstract 493: The Regulation of Thrombospondin-1 Release through SIRPa-CD47 Mediated-Signaling in Platelets
Introduction Decreasing the inflammatory response to medical devices remains an unmet clinical need. Our group has recent evidence that CD47, a ubiquitous transmembrane protein that serves as a self-marker via interactions with its receptor, Signal Regulatory Protein alpha (SIRP-α), confers significant anti-inflammatory properties on synthetic surfaces. Also, our group was the first to find the presence of SIRP-α on platelets. Interestingly, platelets are the primary source of Thrombospondin-1 (TSP-1), a CD47 ligand involved in pro-inflammatory processes. These experiments test the hypothesis that SIRPα-CD47 mediated signaling in platelets, in part, regulates TSP-1 release.
Methods and Results As our group previously published, clinical-grade PVC tubing was modified via a photo-activated polymer with recombinant human CD47. Citrated whole blood or platelet-rich plasma (PRP), (30 cc), was obtained from healthy volunteers and added to the unmodified and CD47-modified tubing. The blood or PRP was perfused, via a Chandler Loop apparatus, over the PVC surfaces for 3 hours. All samples were then processed for platelet poor plasma, and TSP-1 expression was analyzed via western blot and ELISA. Confirmed with western blot and densitometry, when whole blood was exposed to CD47-coated PVC, TSP-1 concentration (as compared to the percent of the time-zero control) was consistently reduced compared to that of unmodified PVC (CD47: 78.42% ± 5.62, PVC: 189.87% ± 28.95). In contrast, when PRP was exposed under analogous conditions, there was no significant difference in TSP-1 concentration (CD47: 2.55% ± 1.02, PVC: 2.72% ± 0.81). To ensure that changes in TSP-1 concentration were not the result of TSP-1 adsorption to the CD47-modified surface, proteins were eluted from the luminal tube surface, and western blot analysis confirmed a 30% decrease in relative intensity from the CD47-coated PVC compared to that of unmodified PVC.
Conclusion CD47-modified PVC tubing significantly decreases TSP-1 levels in isolated plasma from whole blood, suggesting that CD47 decreases platelet activation. However, work so far with PRP suggests that platelet TSP-1 release is mediated indirectly through monocytes. Further work on this cascade includes SEM analysis of PVC tubing.
- © 2013 by American Heart Association, Inc.