No / Platelet microparticle (PMP)-induced angiogenesis plays a key role in tumour metastasis and has been proposed to contribute towards cardiovascular disease by enhancing atherosclerotic plaque vulnerability. However, the mechanisms underlying PMP induced angiogenesis are ill defined. Recent reports demonstrate that PMPs deliver micro-RNAs (miRNAs) to recipient cells, controlling gene expression. We therefore evaluated whether miRNA transfer was a key regulator of PMP-induced angiogenesis. Co-culturing PMPs with human umbilical vein endothelial cells (HUVEC) on extracellular matrix gel induced robust capillary like structure formation. PMP treatment altered the release of angiogenesis modulators from HUVEC, including significantly reducing production of anti-angiogenic thrombospondin-1 (THBS-1). Both functional responses were abrogated by treating PMPs with RNase, suggesting the transfer of PMP-derived RNA was a critical event. PMPs were an abundant source of miRNA Let-7a, which was transferred to HUVEC following co-incubation. Using luciferase reporter assays we have shown that Let-7a directly targets the 3’UTR of the THBS-1 mRNA. HUVEC transfection with a Let-7a anti-sense oligonucleotide reduced the ability of PMPs to inhibit THBS-1 release, and significantly decreased PMP induced in vitro angiogenesis. Antibody neutralisation of THBS-1 reversed the anti-angiogenic effect of let-7a inhibition in PMP treated HUVEC, highlighting Let-7a dependent translational repression of THBS-1 drives angiogenesis. Importantly, plasmid overexpression of Let-7a in HUVEC alone induced robust tubule formation on extracellular matrix gel. These data reveal a new role for Let-7a in promoting angiogenesis and show for the first time PMPs induced angiogenic responses occur through miRNA regulation of HUVEC.

Cardiovascular disease is a major cause of morbidity and mortality around the globe, which is linked to athero-thrombosis. The risk factors for atherothrombosis, thus cardiovascular disease is impaired anti-thrombotic and antiinflammatory functions of the endothelium. Thrombosis is a hallmark of cardiovascular disease/complications characterised by increased platelet activation and increased secretion of platelet micro-particles that induce angiogenesis. This study determined the role of platelet micro-particles derived microRNA in the regulation of angiogenesis and migration, with a focus on the regulation of thrombospondin-1 release by platelet micro-particles delivered Let- 7a. The role of thrombospondin-1 receptors (integrin beta-1 and integrin associated protein) and downstream caspase-3 activation were explored by Let-7a inhibition prior to PMP treatment. MicroRNA dependent modulation of proangiogenic proteins including monocyte chemoattractant protein-1 and placental growth factor, and recruitment of activating transcription factor-4 protein to their promoter regions were explored. Main findings are: 1. Platelet micro-particles induce angiogenesis, migration, and release of novel cytokine subsets specific to platelet micro-particle’s RNA content. 2. The targeting of thrombospondin-1 mRNA by platelet micro-particles’ transferred Let-7a chiefly modulate the angiogenic effect on endothelial cells. 3. The inhibition of thrombospondin-1 translation enable platelet micro-particles to increase angiogenesis and migration in the presence of functional integrin beta-1 and integrin associated protein, and reduced cleaving of caspase-3. 4. Platelet micro-particle modulate the transcription of monocyte chemoattractant protein-1 and placental growth factor in a Let-7a dependent manner. 5. Let-7a induce angiogenesis ii independent of other platelet micro-particle’s microRNAs. Platelet micro-particle derived Let-7a is a master regulator of endothelial cell function in this model, which presents an opportunity for the development of new biomarkers and therapeutic approaches in the management of cardiovascular disease. Future studies should aim to confirm these findings in-vivo.

Cardiovascular disease is a major cause of morbidity and mortality around the globe, which is linked to athero-thrombosis. The risk factors for atherothrombosis, thus cardiovascular disease is impaired anti-thrombotic and antiinflammatory functions of the endothelium. Thrombosis is a hallmark of cardiovascular disease/complications characterised by increased platelet activation and increased secretion of platelet micro-particles that induce angiogenesis. This study determined the role of platelet micro-particles derived microRNA in the regulation of angiogenesis and migration, with a focus on the regulation of thrombospondin-1 release by platelet micro-particles delivered Let- 7a. The role of thrombospondin-1 receptors (integrin beta-1 and integrin associated protein) and downstream caspase-3 activation were explored by Let-7a inhibition prior to PMP treatment. MicroRNA dependent modulation of proangiogenic proteins including monocyte chemoattractant protein-1 and placental growth factor, and recruitment of activating transcription factor-4 protein to their promoter regions were explored. Main findings are: 1. Platelet micro-particles induce angiogenesis, migration, and release of novel cytokine subsets specific to platelet micro-particle’s RNA content. 2. The targeting of thrombospondin-1 mRNA by platelet micro-particles’ transferred Let-7a chiefly modulate the angiogenic effect on endothelial cells. 3. The inhibition of thrombospondin-1 translation enable platelet micro-particles to increase angiogenesis and migration in the presence of functional integrin beta-1 and integrin associated protein, and reduced cleaving of caspase-3. 4. Platelet micro-particle modulate the transcription of monocyte chemoattractant protein-1 and placental growth factor in a Let-7a dependent manner. 5. Let-7a induce angiogenesis ii independent of other platelet micro-particle’s microRNAs. Platelet micro-particle derived Let-7a is a master regulator of endothelial cell function in this model, which presents an opportunity for the development of new biomarkers and therapeutic approaches in the management of cardiovascular disease. Future studies should aim to confirm these findings in-vivo.