Study of platelet production from megakaryocyte by using induced pluripotent stem cell

Abstract

Thrombopoiesis is the process of platelet production from hematopoietic stem cells (HSCs). Glycoproteins (GP) Ib-IX-V that is expressed on the surface of megakaryocytes and platelets binds von Willebrand factor (VWF) plays roles in platelet production. Either the GPIb deficiency or hyper-function can cause macrothrombocytopenia, the molecular mechanisms remain unclear. In this study, the pathogenesis investigations were performed in the human induced pluripotent stem cell (hiPSC) model. CRISPR-Cas9 was used to generate the hiPSCs carrying a gain-of-function GP1BA p.M255V mutation which was described in platelet-type von Willebrand disease (PT-VWD). The GPIb deficiency hiPSCs were previously derived from a Bernard Soulier syndrome (BSS) patient. After megakaryocyte differentiation, both hiPSC mutations showed large proplatelet tips and yielded fewer but larger platelets compared with normal hiPSCs. The Capillary Western analyses revealed the lower ERK1/2 activation and higher MLC2 (Myosin light chain 2) phosphorylation in megakaryocytes with mutated GPIb. Adding a mitogen-activated protein kinase (MAPK) pathway inhibitor to normal hiPSCs recapitulated the phenotypes of GPIb mutations and increased MLC2 phosphorylation. Notably, a ROCK inhibitor which could inhibit MLC2 phosphorylation rescued the macrothrombocytopenia phenotypes of both GPIb alterations and normal hiPSCs with a MAPK inhibitor. In conclusion, the genetically-modified hiPSCs can be used to model disorders of proplatelet formation. Both loss- and gain-of-function GPIb reduced MAPK/ERK activation but enhanced ROCK/MLC2 phosphorylation resulting in dysregulated platelet generation.