Project description:To identify the gene which is regulated by Let-7a-5p, we performed global gene expression analysis of immortalized megakaryocyte cell lines.
Project description:The role of the bone marrow microenvironment for regulating megakaryocyte and platelet function remains incompletely understood. We examined the mechanism by which MSCs can lower platelet activation through communication with megakaryocytes.
Project description:Immune thrombocytopenia (ITP) is a common platelet disorder in pediatric patients. Pediatric and adult ITP have been associated with sialic acid alterations, but the pathophysiology of ITP remains elusive, and ITP is often a diagnosis of exclusion. Our analysis of pediatric ITP plasma samples showed increased anti-Thomsen-Friedenreich antigen (TF-antigen) antibody representation, suggesting increased exposure of the typically sialylated and cryptic TF-antigen in these patients. The O-glycan sialyltransferase St3gal1 add sialic acid specifically on the TF-antigen. To understand if TF-antigen exposure associates with thrombocytopenia, we generated a mouse model with targeted deletion of St3gal1 in megakaryocytes (MK) (St3gal1MK-/-). TF-antigen exposure was restricted to MKs and resulted in thrombocytopenia. Deletion of Jak3 in St3gal1MK-/- mice normalized platelet counts implicating involvement of immune cells. Interferon-producing Siglec H-positive bone marrow (BM) immune cells engaged with O-glycan sialic acid moieties to regulate type I interferon (IFN-I) secretion and platelet release (thrombopoiesis), as evidenced by partially normalized platelet count following and inhibition of interferon and Siglec H receptors. Single cell RNAseq determined that TF-antigen exposure by MKs primed St3gal1MK-/- BM immune cells to release IFN-I. Single cell RNAseq further revealed a new population of immune cells with a plasmacytoid dendritic cell (pDC)-like signature and concomitant upregulation of immunoglobulin re-arrangement gene transcripts Igkc and Ighm, suggesting additional immune regulatory mechanisms. Thus, aberrant TF-antigen moieties, often found in pathological conditions, regulate immune cells and thrombopoiesis in the BM, leading to reduced platelet count.
Project description:ChIP-seq assay was performed with anti-p45 antibody using in vitro cultured primary megakaryocytes to identify direct p45 target genes in megakaryocytes. This analysis revealed genes that regulate platelet function, which were not known previously to be p45-regulated. ChIP was performed using a day-3 primary culture of megakaryocytes from E13.5 fetal livers of wild-type mice with an anti-p45 antibody.
Project description:ChIP-seq assay was performed with anti-p45 antibody using in vitro cultured primary megakaryocytes to identify direct p45 target genes in megakaryocytes. This analysis revealed genes that regulate platelet function, which were not known previously to be p45-regulated.
Project description:We developed a novel differentiation system that directionally induces hESCs into megakaryocytes and functional platelet in vitro by highly mimicking the in vivo developmental process of megakaryocytes and platelets. We then performed gene expression profiling analysis using data obtained by RNA-seq at different stages of differentiation during the differentiation of hESCs into megakaryocyte lineages.
Project description:Megakaryocytes are bone marrow (BM) resident cells that derive from hematopoietic stem cells. A pivotal function of megakaryocytes is the generation of platelets through the release of long protrusions called proplatelets into sinusoidal vessels. single-cell RNA-sequencing on murine BM megakaryocytes has previously revealed transcriptional heterogeneity with segmentation into four distinct categories. These studies postulated functions beyond platelet production with evidence for immunoregulatory and stem cell niche supporting subtypes, as well as a cycling population. The spatial context and transcriptional heterogeneity of megakaryocytes is of great interest as localization of for instance the vasculature is a necessity for platelet production. For single-cell RNA sequencing this spatial orientation is however lost due to the dissociation of tissues. Recent technological advances have enabled the interrogation of gene expression profiles of tissues in situ. This enables the integration of morphological, situational and transcriptional information to classify cells in the context of their microenvironment. In the following we present, for the first time, the application of this technology to BM megakaryocytes at a single cell level.
Project description:Background: While potassium ion (K+) is known to be vital to platelet functions, we have limited knowledge about K+ channels involved in thrombopoiesis from imMKCLs, the iPSC-derived megakaryocyte progenitor cell lines that we have established for ex vivo manufacturing of platelet products for clinical use. Objective: We aimed to elucidate how K+ channels contribute to platelet biogenesis and focused on the role of Ca2+-activated K+ channel KCNN4 (also known as KCa3.1). Methods: Using imMKCLs and human cord blood hematopoietic stem cell-derived megakaryocytes (CB-megakaryocytes), we examined the dynamic changes of intracellular cations during platelet biogenesis. Along with RNA-seq profiling of K+ channels, we investigated the role of KCNN4 by using inhibitors or by direct gene knockdown in proplatelet formation or platelet production. We further examined its relationship with tubulin reorganization, mitochondrial functions, and reactive oxygen species (ROS) levels. Results: Continuous reduction of intracellular K+ levels ([K+]i) was observed during the 6-day of maturing imMKCLs. KCNN4 was expressed at the initiation of platelet generation in megakaryocytes and KCNN4 inhibition resulted in impaired proplatelet formation and reduced platelet productivity in imMKCLs and CB-megakaryocytes, accompanied by decreased [K+]i, diminished mitochondrial membrane potential and an elevated level of ROS. Conclusions: Our findings suggest that the decline of [K+]i via KCNN4 is a key mechanism linking tubulin regulation, ROS, and mitochondrial functions to proplatelet formation and intact thrombopoiesis. This study sheds new light on thrombopoiesis mechanism that contributes to improved ex vivo platelet manufacturing.
Project description:Dominant-negative mutations in transcription factor Growth Factor Independence-1B (GFI1B) cause a bleeding disorder characterized by a plethora of megakaryocyte and platelet abnormalities. The deregulated molecular mechanisms and pathways are unknown. Here we show that normal and mutant GFI1B interacted most strongly with the LSD1-RCOR-HDAC corepressor complex in megakaryoblasts. Sequestration of this complex by mutant GFI1B and chemical separation of GFI1B from LSD1 induced abnormalities in normal megakaryocytes comparable to those seen in patients. Megakaryocytes derived from GFI1B-mutant induced pluripotent stem cells (iPSC) also phenocopied abnormalities seen in patients. Proteome studies on normal and mutant iPSC-derived megakaryocytes identified a multitude of deregulated pathways downstream of mutant GFI1B. Proteome studies on primary normal and GFI1B-mutant platelets showed reduced expression of proteins implicated in platelet function, and sustained expression of proteins normally downregulated during megakaryocyte differentiation. Thus, GFI1B regulates a broad developmental program during megakaryopoiesis. Mutant GFI1B deregulates this program through LSD1-RCOR-HDAC sequestering.