Role of Thrombopoietin in Stimulating Megakaryopoiesis of ITP Patients Via Rescuing Vascular Niche

Background: Previous studies have shown that the vascular niche was damaged in patients with immune thrombocytopenia (ITP). It is mainly manifested that the migration and tube-formation ability of bone marrow endothelial progenitor cells (BM-EPCs) were significantly reduced. Endothelial cells as an important part of the vascular niche play an important role in regulation of megakaryocytes and platelet hematopoiesis. Our previous studies suggested that thrombopoietin (TPO) has a protective effect on human endothelial cells. This study aim to investigate whether TPO has a protective effect in EPCs of ITP patients and to explore its mechanism. Methods: BM-EPCs were isolated from ITP patients, and divided into two groups: TPO-treated group and TPO-free (control group). CCK8 was used to explore whether TPO has proliferative effect on BM-EPCs. BM-EPCs was identified by flow cytometry with co-expression of mouse anti-humanCD133, mouse anti-human CD34 and mouse anti-human vascular endothelial growth factor receptor (CD309) monoclonal antibodies. Moreover, the number of EPCs was evaluated with DiL-Ac-LDL uptake and FITC-UEA -I binding assay. Furthermore, the function of BM-EPCs was studied by using tube-formation and migration experiments. Results: The ITP patient-derived EPCs in TPO-treated group exhibited longer fusiform and elliptical shape after 5 days and cobblestone-like morphology after 7-10 days. The result of CCK-8 showed TPO could promote the proliferation of EPCs and the optional drug concentration is 100 ng/ml. Much higher expression of CD34/CD133/CD309 in TPO-treated group was detected by flow cytometry. The number of cells with immunofluorescence double staining in TPO group was significantly higher than of control group (n=4, p Conclusion: Our studies indicates that TPO may exert megakaryopoiesis effect in ITP patients via protection of BM-EPCs. This may provide a supplemental explanation of how recombinant TPO and TPO receptor antagonist acts on ITP treatment. Keywords: thrombopoietin; vascular niche; endothelial progenitor cell, megakaryopoiesis; endothelial cell Disclosures No relevant conflicts of interest to declare.