Current understanding of human megakaryocytic-erythroid progenitors and their fate determinants

PI3K/HSCB axis facilitates FOG1 nuclear translocation to promote erythropoiesis and megakaryopoiesis

Erythropoiesis and megakaryopoiesis are stringently regulated by signaling pathways. However, the precise molecular mechanisms through which signaling pathways regulate key transcription factors controlling erythropoiesis and megakaryopoiesis remain partially understood. Herein, we identified heat shock cognate B (HSCB), which is well known for its iron-sulfur cluster delivery function, as an indispensable protein for friend of GATA 1 (FOG1) nuclear translocation during erythropoiesis of K562 human erythroleukemia cells and cord-blood-derived human CD34+CD90+hematopoietic stem cells (HSCs), as well as during megakaryopoiesis of the CD34+CD90+HSCs. Mechanistically, HSCB could be phosphorylated by phosphoinositol-3-kinase (PI3K) to bind with and mediate the proteasomal degradation of transforming acidic coiled-coil containing protein 3 (TACC3), which otherwise detained FOG1 in the cytoplasm, thereby facilitating FOG1 nuclear translocation. Given that PI3K is activated during both erythropoiesis and megakaryopoiesis, and that FOG1 is a key transcription factor for these processes, our findings elucidate an important, previously unrecognized iron-sulfur cluster delivery independent function of HSCB in erythropoiesis and megakaryopoiesis.

Thrombopoietin treats erythropoietin resistance by correcting EPO-induced progenitorcell depletion

Recombinant human erythropoietin (rHuEPO) is a prevalent treatment for anemia in patients with chronic kidney disease. However, up to 10% of these patients exhibit EPO resistance or hyporesponsiveness, which may be caused by the depletion of erythroid progenitor cells. Thrombopoietin (TPO) has the potential to promote the growth of early progenitor cells and correct the depletion. In this study, we investigate the efficacy and the underlying mechanism of the combination therapy of TPO and EPO to EPO resistance. First, the in vivo studies suggested that intensive EPO treatment induced progenitor cell depletion in the bone marrow, where the depletion was corrected by TPO. Then, colony assays showed that EPO and TPO synergistically enhanced the burst-forming unit-erythroid (BFU-E) production but antagonistically boosted the colony-forming units of megakaryocytes (CFU-MK) production. Also, we found TPO promoted hematopoietic stem and progenitor cells (HSPCs) production, while EPO drove HSPCs toward the erythroid lineage. Additionally, EPO induced more megakaryocytic-erythroid progenitors (MEPs) toward the erythroid output. Model-based simulations indicate the efficacy of this combination therapy for treating EPO-resistant anemia in rats. In conclusion, our study demonstrated the efficacy of combination therapy in addressing EPO-resistant anemia by correcting EPO-induced erythroid progenitor depletion.

Phenotypic and proteomic characterization of the human erythroid progenitor continuum reveal dynamic changes in cell cycle and in metabolic pathways

Human erythropoiesis is a complex process leading to the production of 2.5 million red blood cells per second. Following commitment of hematopoietic stem cells to the erythroid lineage, this process can be divided into three distinct stages: erythroid progenitor differentiation, terminal erythropoiesis, and reticulocyte maturation. We recently resolved the heterogeneity of erythroid progenitors into four different subpopulations termed EP1-EP4. Here, we characterized the growth factor(s) responsiveness of these four progenitor populations in terms of proliferation and differentiation. Using mass spectrometry-based proteomics on sorted erythroid progenitors, we quantified the absolute expression of ~5500 proteins from EP1 to EP4. Further functional analyses highlighted dynamic changes in cell cycle in these populations with an acceleration of the cell cycle during erythroid progenitor differentiation. The finding that E2F4 expression was increased from EP1 to EP4 is consistent with the noted changes in cell cycle. Finally, our proteomic data suggest that the protein machinery necessary for both oxidative phosphorylation and glycolysis is present in these progenitor cells. Together, our data provide comprehensive insights into growth factor-dependence of erythroid progenitor proliferation and the proteome of four distinct populations of human erythroid progenitors which will be a useful framework for the study of erythroid disorders.

Genome-wide census of ATF4 binding sites and functional profiling of trait-associated genetic variants overlapping ATF4 binding motifs

Activating Transcription Factor 4 (ATF4) is an important regulator of gene expression in stress responses and developmental processes in many cell types. Here, we catalogued ATF4 binding sites in the human genome and identified overlaps with trait-associated genetic variants. We probed these genetic variants for allelic regulatory activity using a massively parallel reporter assay (MPRA) in HepG2 hepatoma cells exposed to tunicamycin to induce endoplasmic reticulum stress and ATF4 upregulation. The results revealed that in the majority of cases, the MPRA allelic activity of these SNPs was in agreement with the nucleotide preference seen in the ATF4 binding motif from ChIP-Seq. Luciferase and electrophoretic mobility shift assays in additional cellular models further confirmed ATF4-dependent regulatory effects for the SNPs rs532446 (GADD45A intronic; linked to hematological parameters), rs7011846 (LPL upstream; myocardial infarction), rs2718215 (diastolic blood pressure), rs281758 (psychiatric disorders) and rs6491544 (educational attainment). CRISPR-Cas9 disruption and/or deletion of the regulatory elements harboring rs532446 and rs7011846 led to the downregulation of GADD45A and LPL, respectively. Thus, these SNPs could represent examples of GWAS genetic variants that affect gene expression by altering ATF4-mediated transcriptional activation.

Chemotherapy-induced tumor immunogenicity is mediated in part by megakaryocyte-erythroid progenitors

Chemotherapy remains one of the main treatment modalities for cancer. While chemotherapy is mainly known for its ability to kill tumor cells directly, accumulating evidence indicates that it also acts indirectly by enhancing T cell-mediated anti-tumor immunity sometimes through immunogenic cell death. However, the role of immature immune cells in chemotherapy-induced immunomodulation has not been studied. Here, we utilized a mouse pancreatic cancer model to characterize the effects of gemcitabine chemotherapy on immature bone marrow cells in the context of tumor immunogenicity. Single cell RNA sequencing of hematopoietic stem and progenitor cells revealed a 3-fold increase in megakaryocyte-erythroid progenitors (MEPs) in the bone marrow of gemcitabine-treated mice in comparison to untreated control mice. Notably, adoptive transfer of MEPs to pancreatic tumor-bearing mice significantly reduced tumor growth and increased the levels of anti-tumor immune cells in tumors and peripheral blood. Furthermore, MEPs increased the tumor cell killing activity of CD8 + T cells and NK cells, an effect that was dependent on MEP-secreted CCL5 and CXCL16. Collectively, our findings demonstrate that chemotherapy-induced enrichment of MEPs in the bone marrow compartment contributes to anti-tumor immunity.

The Application of Ethnomedicine in Modulating Megakaryocyte Differentiation and Platelet Counts

Megakaryocytes (MKs), a kind of functional hematopoietic stem cell, form platelets to maintain platelet balance through cell differentiation and maturation. In recent years, the incidence of blood diseases such as thrombocytopenia has increased, but these diseases cannot be fundamentally solved. The platelets produced by MKs can treat thrombocytopenia-associated diseases in the body, and myeloid differentiation induced by MKs has the potential to improve myelosuppression and erythroleukemia. Currently, ethnomedicine is extensively used in the clinical treatment of blood diseases, and the recent literature has reported that many phytomedicines can improve the disease status through MK differentiation. This paper reviewed the effects of botanical drugs on megakaryocytic differentiation covering the period 1994-2022, and information was obtained from PubMed, Web of Science and Google Scholar. In conclusions, we summarized the role and molecular mechanism of many typical botanical drugs in promoting megakaryocyte differentiation in vivo, providing evidence as much as possible for botanical drugs treating thrombocytopenia and other related diseases in the future.

Fate determination role of erythropoietin and romiplostim in the lineage commitment of hematopoietic progenitors

Erythropoietin (EPO) and thrombopoietin (TPO) have long been known to promote erythropoiesis and megakaryopoiesis, respectively. However, the fate changing role of EPO and TPO on megakaryocyte-erythroid progenitors (MEPs) to develop along the erythroid versus megakaryocyte (MK) lineage remains unclear. We have previously shown that EPO may have fate changing role because EPO treatment could induce progenitor cells depletion and resulted in EPO resistance. Therefore, we hypothesize that a combination of romiplostim, a TPO receptor agonist that could stimulate the expansion of progenitors, with EPO can treat EPO resistance. Using rats with anemia due to chronic kidney disease, we demonstrated that romiplostim synergized with EPO to promote red blood cells production while EPO inhibited platelet production in a dose-dependent manner to reduce the risk of thrombosis. Corroborating findings from in vivo, in vitro experiments demonstrated that romiplostim expanded hematopoietic stem cells and stimulated megakaryopoiesis, while EPO drove the progenitors toward an erythroid fate. We further developed a novel pharmacokinetic-pharmacodynamic model to quantify the effects of EPO and romiplostim on megakaryopoiesis and erythropoiesis simultaneously. The modeling results demonstrated that EPO increased the differentiation rate of MEPs into burst-forming unit-erythroid up to 22-fold, indicating that the slight increase of MEPs induced by romiplostim could be further amplified and recruited by EPO to promote erythropoiesis. The data herein support that romiplostim in combination with EPO can treat EPO resistance. Significance Statement This study clarified that erythropoietin (EPO) drives the fate of megakaryocyte-erythroid progenitors (MEP) toward the erythroid lineage, thus reducing their megakaryocyte (MK) lineage commitment, whereas romiplostim, a thrombopoietin (TPO) receptor agonist (RA), stimulates megakaryopoiesis through the MK-committed progenitor and MEP bifurcation pathways simultaneously. These findings support an innovative combination of romiplostim and EPO to treat EPO-resistant anemia, because the combination therapy further promotes erythropoiesis compared to EPO monotherapy and inhibit platelet production compared to romiplostim monotherapy.

Vaccination Accelerates Liver-Intrinsic Expression of Megakaryocyte-Related Genes in Response to Blood-Stage Malaria

Erythropoiesis and megakaryo-/thrombopoiesis occur in the bone marrow proceeding from common, even bipotent, progenitor cells. Recently, we have shown that protective vaccination accelerates extramedullary hepatic erythroblastosis in response to blood-stage malaria of Plasmodium chabaudi. Here, we investigated whether protective vaccination also accelerates extramedullary hepatic megakaryo-/thrombopoiesis. Female Balb/c mice were twice vaccinated with a non-infectious vaccine before infecting with 106 P. chabaudi-parasitized erythrocytes. Using gene expression microarrays and quantitative real-time PCR, transcripts of genes known to be expressed in the bone marrow by cells of the megakaryo-/thrombocytic lineage were compared in livers of vaccination-protected and unprotected mice on days 0, 1, 4, 8, and 11 p.i. Livers of vaccination-protected mice responded with expression of megakaryo-/thrombocytic genes faster to P. chabaudi than those of unvaccinated mice, evidenced at early patency on day 4 p.i., when livers exhibited significantly higher levels of malaria-induced transcripts of the genes Selp and Pdgfb (p-values < 0.0001), Gp5 (p-value < 0.001), and Fli1, Runx1, Myb, Mpl, Gp1ba, Gp1bb, Gp6, Gp9, Pf4, and Clec1b (p-values < 0.01). Together with additionally analyzed genes known to be related to megakaryopoiesis, our data suggest that protective vaccination accelerates liver-intrinsic megakaryo-/thrombopoiesis in response to blood-stage malaria that presumably contributes to vaccination-induced survival of otherwise lethal blood-stage malaria.