Abstract 556: Soluble TREM-Like Transcript-1 Differentially Responds to PAR1 and PAR4 Signaling: A Possible New Role for sTLT-1 in Angiogenesis?
Platelets have been shown to play important roles in angiogenesis due in part to the differential release of proteins from their α-granules. For example PAR-1 receptor activation in platelets releases α-granules containing pro-angiogenic molecules, while PAR-4 receptor activation promotes the release of anti-angiogenic molecules. Studies from our laboratory reported the identification of the Triggering Receptor Expressed in Myeloid cells (TREM)-Like 1 transcript (TLT)-1, a protein preferentially expressed in platelets and megakaryocytes. TLT-1 is stored in platelet α-granules with p-selectin and has a soluble extracellular fragment that is released upon platelet activation. Comparative immunofluorescence (IF) to p-selectin shows that only ~50% of the TLT-1 colocalized with p-selectin suggesting that TLT-1 may be differentially stored and dispersed from α-granules. To address this possibility we compared colocalization of TLT-1 to VEGF and endostatin, two proteins that are stored segregated into granules differentially. IF staining demonstrated greater colocalization with pro-angiogenic VEGF than anti-angiogenic endostatin. We then hypothesized that pro- or anti-angiogenic PAR-1 & PAR-4 signaling would differentially affect TLT-1 dispersion in platelets. To test this, purified human platelets were stimulated with a PAR-1 or a PAR-4 agonist and TLT-1 was monitored by IF. Results showed that PAR-1 activation caused a greater TLT-1 dissemination throughout the platelet than PAR-4. Supernatants of platelets activated by PAR-1 showed an increased amount of sTLT-1 compared to those activated by PAR-4 agonist. Our results suggest that TLT-1 is associated to platelet release of pro-angiogenic α-granules. We next addressed the question if sTLT-1 has an effect on endothelial cells. Soluble TLT-1 was added to primary endothelial cells 30 minutes and cells were evaluated for changes in size and actin polymerization. Studies by IF showed an increase in the size and actin polymerization of cells, suggesting it promotes a pro-angiogenic morphology. Ongoing experiments are addressing if sTLT-1 affects tube formation and migration of endothelial cells. These results could shed light into TLT-1 properties and its possible new role in angiogenesis.
Author Disclosures: Y. Ferrer-Acosta: None. K.M. Lugo-Cintron: None. J. Morales: None. A.V. Washington: None.
- © 2014 by American Heart Association, Inc.