Abnormal proplatelet formation and emperipolesis in cultured human megakaryocytes from gray platelet syndrome patients

none10siThe Gray Platelet Syndrome (GPS) is a rare inherited bleeding disorder characterized by deficiency of platelet α-granules, macrothrombocytopenia and marrow fibrosis. The autosomal recessive form of GPS is linked to loss of function mutations in NBEAL2, which is predicted to regulate granule trafficking in megakaryocytes, the platelet progenitors. We report the first analysis of cultured megakaryocytes from GPS patients with NBEAL2 mutations. Megakaryocytes cultured from peripheral blood or bone marrow hematopoietic progenitor cells from four patients were used to investigate megakaryopoiesis, megakaryocyte morphology and platelet formation. In vitro differentiation of megakaryocytes was normal, whereas we observed deficiency of megakaryocyte α-granule proteins and emperipolesis. Importantly, we first demonstrated that platelet formation by GPS megakaryocytes was severely affected, a defect which might be the major cause of thrombocytopenia in patients. These results demonstrate that cultured megakaryocytes from GPS patients provide a valuable model to understand the pathogenesis of GPS in humans.openDi Buduo, Christian A.; Alberelli, Maria Adele; Glembostky, Ana C.; Podda, Gianmarco; Lev, Paola R.; Cattaneo, Marco; Landolfi, Raffaele; Heller, Paula G.; Balduini, Alessandra; De Candia, EricaDI BUDUO, CHRISTIAN ANDREA; Alberelli, Maria Adele; Glembostky, Ana C.; Podda, Gianmarco; Lev, Paola R.; Cattaneo, Marco; Landolfi, Raffaele; Heller, Paula G.; Balduini, Alessandra; De Candia, Eric

Pathophysiological Significance of Store-Operated Calcium Entry in Megakaryocyte Function: Opening New Paths for Understanding the Role of Calcium in Thrombopoiesis

Store-Operated Calcium Entry (SOCE) is a universal calcium (Ca2+) influx mechanism expressed by several different cell types. It is now known that Stromal Interaction Molecule (STIM), the Ca2+ sensor of the intracellular compartments, together with Orai and Transient Receptor Potential Canonical (TRPC), the subunits of Ca2+ permeable channels on the plasma membrane, cooperate in regulating multiple cellular functions as diverse as proliferation, differentiation, migration, gene expression, and many others, depending on the cell type. In particular, a growing body of evidences suggests that a tight control of SOCE expression and function is achieved by megakaryocytes along their route from hematopoietic stem cells to platelet production. This review attempts to provide an overview about the SOCE dynamics in megakaryocyte development, with a focus on most recent findings related to its involvement in physiological and pathological thrombopoiesis

Mechanisms of platelet release: in vivo studies and in vitro modeling

Mechanisms related to platelet release in the context of the bone marrow niche are not completely known. In this review we discuss what has been discovered about four critical aspects of this process: 1) the bone marrow niche organization, 2) the role of the extracellular matrix components, 3) the mechanisms by which megakaryocytes release platelets and 4) the novel approaches to mimic the bone marrow environment and produce platelets ex vivo

Hyaluronan based hydrogels provide an improved model to study megakaryocyte-matrix interactions

Hyaluronan (HA) is a glycosamminoglican involved in cell biology as well as a relevant polymer for tissue engineering and regenerative medicine. Megakaryocytes (Mks) are immersed in a mesh of extracellular matrix (ECM) components that regulate their maturation in the bone marrow (BM) and the release of platelets into the bloodstream. While fibrous ECMs such as collagens and fibronectin have been demonstrated to differently regulate Mk function and platelet release, the role of HA, that fills the majority of the BM extracellular interstitial space, has not been investigated so far. Here we demonstrated that, although human Mks express HA receptors, they are not affected by HA in terms of in vitro differentiation, maturation and platelet formation. Importantly, chemical properties of HA were exploited to generate hydrogels with entrapped ECMs that represent a useful model to more closely mimic the tridimensional characteristics of the BM environment for studying Mk function. In conclusion, in this work we demonstrated that HA is an ideal candidate for a 3D ex vivo model of human BM ECM component environment