Tao-Hong-Si-Wu Decoction promotes angiogenesis after cerebral ischaemia in rats via platelet microparticles

Body fluids contain surprising numbers of cell-derived vesicles which are now thought to contribute to both physiology and pathology. Tools to improve the detection of vesicles are being developed and clinical applications using vesicles for diagnosis, prognosis, and therapy are under investigation. The increased understanding why cells release vesicles, how vesicles play a role in intercellular communication, and how vesicles may concurrently contribute to cellular homeostasis and host defense, reveals a very complex and sophisticated contribution of vesicles to health and disease. Copyright © 2012 Elsevier Ltd. All rights reserved.

Platelet activation leads to secretion of granule contents and to the formation of microvesicles by shedding of membranes from the cell surface. Recently, we have described small internal vesicles in multivesicular bodies (MVBs) and alpha-granules, and suggested that these vesicles are secreted during platelet activation, analogous to the secretion of vesicles termed exosomes by other cell types. In the present study we report that two different types of membrane vesicles are released after stimulation of platelets with thrombin receptor agonist peptide SFLLRN (TRAP) or alpha-thrombin: microvesicles of 100 nm to 1 microm, and exosomes measuring 40 to 100 nm in diameter, similar in size as the internal vesicles in MVBs and alpha-granules. Microvesicles could be detected by flow cytometry but not the exosomes, probably because of the small size of the latter. Western blot analysis showed that isolated exosomes were selectively enriched in the tetraspan protein CD63. Whole-mount immuno-electron microscopy (IEM) confirmed this observation. Membrane proteins such as the integrin chains alpha(IIb)-beta(3) and beta(1), GPIbalpha, and P-selectin were predominantly present on the microvesicles. IEM of platelet aggregates showed CD63(+) internal vesicles in fusion profiles of MVBs, and in the extracellular space between platelet extensions. Annexin-V binding was mainly restricted to the microvesicles and to a low extent to exosomes. Binding of factor X and prothrombin was observed to the microvesicles but not to exosomes. These observations and the selective presence of CD63 suggest that released platelet exosomes may have an extracellular function other than the procoagulant activity, attributed to platelet microvesicles.

Insufficient vessel growth associated with ischemia remains an unresolved issue in vascular medicine. Mesenchymal stem cells (MSCs) have been shown to promote angiogenesis via a mechanism that is potentiated by hypoxia. Overexpression of hypoxia inducible factor (HIF)-1α in MSCs improves their therapeutic potential by inducing angiogenesis in transplanted tissues. Here, we studied the contribution of exosomes released by HIF-1α-overexpressing donor MSCs (HIF-MSC) to angiogenesis by endothelial cells. Exosome secretion was enhanced in HIF-MSC. Omics analysis of miRNAs and proteins incorporated into exosomes pointed to the Notch pathway as a candidate mediator of exosome communication. Interestingly, we found that Jagged1 was the sole Notch ligand packaged into MSC exosomes and was more abundant in HIF-MSC than in MSC controls. The addition of Jagged1-containing exosomes from MSC and HIF-MSC cultures to endothelial cells triggered transcriptional changes in Notch target genes and induced angiogenesis in an in vitro model of capillary-like tube formation, and both processes were stimulated by HIF-1α. Finally, subcutaneous injection of Jagged 1-containing exosomes from MSC and HIF-MSC cultures in the Matrigel plug assay induced angiogenesis in vivo, which was more robust when they were derived from HIF-MSC cultures. All Jagged1-mediated effects could be blocked by prior incubation of exosomes with an anti-Jagged 1 antibody. All together, the results indicate that exosomes derived from MSCs stably overexpressing HIF-1α have an increased angiogenic capacity in part via an increase in the packaging of Jagged1, which could have potential applications for the treatment of ischemia-related disease. Stem Cells 2017;35:1747-1759.