Platelet glycoprotein IIIa gene expression in normal and malignant megakaryopoiesis

Bone marrow niche-mimetics modulate HSPC function via integrin signaling

The bone marrow (BM) microenvironment provides critical physical cues for hematopoietic stem and progenitor cell (HSPC) maintenance and fate decision mediated by cell-matrix interactions. However, the mechanisms underlying matrix communication and signal transduction are less well understood. Contrary, stem cell culture is mainly facilitated in suspension cultures. Here, we used bone marrow-mimetic decellularized extracellular matrix (ECM) scaffolds derived from mesenchymal stromal cells (MSCs) to study HSPC-ECM interaction. Seeding freshly isolated HSPCs adherent (AT) and non-adherent (SN) cells were found. We detected enhanced expansion and active migration of AT-cells mediated by ECM incorporated stromal derived factor one. Probing cell mechanics, AT-cells displayed naïve cell deformation compared to SN-cells indicating physical recognition of ECM material properties by focal adhesion. Integrin αIIb (CD41), αV (CD51) and β3 (CD61) were found to be induced. Signaling focal contacts via ITGβ3 were identified to facilitate cell adhesion, migration and mediate ECM-physical cues to modulate HSPC function.

Targeted correction of RUNX1 mutation in FPD patient-specific induced pluripotent stem cells rescues megakaryopoietic defects

Familial platelet disorder with predisposition to acute myeloid leukemia (FPD/AML) is an autosomal dominant disease of the hematopoietic system that is caused by heterozygous mutations in RUNX1. FPD/AML patients have a bleeding disorder characterized by thrombocytopenia with reduced platelet numbers and functions, and a tendency to develop AML. No suitable animal models exist for FPD/AML, as Runx11/2 mice and zebra fish do not develop bleeding disorders or leukemia. Here we derived induced pluripotent stem cells (iPSCs) from 2 patients in a family with FPD/AML, and found that the FPD iPSCs display defects in megakaryocytic differentiation in vitro. We corrected the RUNX1 mutation in 1 FPD iPSC line through gene targeting, which led to normalization of megakaryopoiesis of the iPSCs in culture. Our results demonstrate successful in vitro modeling of FPD with patient-specific iPSCs and confirm that RUNX1 mutations are responsible for megakaryopoietic defects in FPD patients.

Crucial role for endoplasmic reticulum stress during megakaryocyte maturation

OBJECTIVE

Apoptotic-like phase is an essential step for the platelet formation from megakaryocytes. How controlled is this signaling pathway remained poorly understood. The aim of this study was to determine whether endoplasmic reticulum (ER) stress-induced apoptosis occurs during thrombopoiesis.

APPROACH AND RESULTS

Investigation of ER stress and maturation markers in different models of human thrombopoiesis (CHRF, DAMI, MEG-01 cell lines, and hematopoietic stem cells: CD34(+)) as well as in immature pathological platelets clearly indicated that ER stress occurs transiently during thrombopoiesis. Direct ER stress induction by tunicamycin, an inhibitor of N-glycosylation, or by sarco/endoplasmic reticulum Ca(2+) ATPase type 3b overexpression, which interferes with reticular calcium, leads to some degree of maturation in megakaryocytic cell lines. On the contrary, exposure to salubrinal, a phosphatase inhibitor that prevents eukaryotic translation initiation factor 2α-P dephosphorylation and inhibits ER stress-induced apoptosis, decreased both expression of maturation markers in MEG-01 and CD34(+) cells as well as numbers of mature megakaryocytes and proplatelet formation in cultured CD34(+) cells.

CONCLUSIONS

Taken as a whole, our research suggests that transient ER stress activation triggers the apoptotic-like phase of the thrombopoiesis process.